JP5183897B2 - Method for producing water absorbent resin and water absorbent resin - Google Patents

Description

  The present invention relates to a method for producing a water-absorbing resin, which can prevent adhesion of a water-containing gel-like polymer and can be smoothly dried, and a water-absorbing resin and use thereof.

  It is well known that a water-containing gel-like polymer can be obtained as a water-absorbing polymer by aqueous polymerization of a water-soluble ethylenically unsaturated monomer (for example, Patent Document 1). This hydrogel polymer is obtained as a semi-solid and highly elastic gel, and is cut and dried to be used as a water absorbent resin, that is, a water absorbent.

  When cutting the hydrogel, if it is not cut and no action is taken, the cut hydrogel polymers will adhere to each other. For example, when mechanically cut, cut continuously. Work efficiency is reduced. Therefore, a surfactant, a polymer polyhydric alcohol, or the like is usually used to prevent the adhesion (for example, Patent Documents 2 and 3).

  On the other hand, the unreacted monomer (hereinafter referred to as “residual monomer”) in the water-containing gel is an impurity in the polymer and may cause odor and sanitary problems. Conventionally, as a technique for reducing the residual monomer, a method of increasing the amount of radical polymerization initiator added, a method of adding radical polymerization initiator in a divided manner, etc. are known (Patent Documents 4 to 10).

  Patent Document 11 describes that the water absorption rate of the water-absorbing material can be improved by spraying a polyvalent metal salt aqueous solution onto dry powdery hydrophilic polymer particles having a water content of 20% by mass or less. Has been.

  However, the above-described conventional technique has a problem that adhesion between the water-containing gel polymers cannot be sufficiently prevented.

  In addition, in the case of Patent Documents 6 and 7, although the detailed cause is unclear, there is a strange odor that is considered to be derived from the component in which the added reducing substance and the impurities derived from the raw material are combined by the heat treatment in the subsequent process. There is a problem that occurs. Further, even in the case of the above-mentioned Patent Document 8, the residual monomer amount is surely reduced, but there is a large variation in the residual monomer amount of the absorbent, and the residual monomer amount is not reduced to a desired level. There is a problem that goods can be seen.

  Furthermore, when the amount of residual monomers is reduced using the techniques of Patent Documents 4 and 5, the resulting water-absorbent resin may be colored, resulting in a problem that the commercial value is lowered. In addition, since various harsh reaction conditions are required to reduce the amount of residual monomer, physical properties may deteriorate due to deterioration of the polymer. Reduction to the desired residual monomer level, absorption capacity under no pressure and under pressure There is also a problem that it is difficult to achieve both maintenance and improvement of absorption characteristics such as absorption magnification.

  That is, Patent Document 4 mentions polyethylene glycol and surfactant as adhesion preventing agents, but there is no specific description on how to treat the hydrogel polymer using these. . Further, in the technique described in Patent Document 5, a surfactant, a polymer polyhydric alcohol, or the like is used to prevent adhesion between the water-containing gel polymers, but the particle size distribution of the water-containing gel polymer is wide. Since the shape of the hydrogel polymer is not homogeneous, the particles are likely to aggregate.

In addition, as described in Patent Document 11, a method of spraying a polyvalent metal salt aqueous solution onto dry powdery polymer particles is already known, but this technique prevents adhesion of hydrogel polymers. However, there is no knowledge yet about a technique for sufficiently preventing adhesion of hydrogel polymers by coating with a polyvalent metal salt aqueous solution or the like.
JP-A-8-92307 (published on April 9, 1996) JP 61-110510 A (published May 28, 1986) Japanese Patent Laid-Open No. 11-349687 (published on December 21, 1999) US Pat. No. 4,973,632 US Pat. No. 5,998,553 Japanese Examined Patent Publication No. 63-7203 (announced February 16, 1988) US Patent 2004-0068057 Japanese Examined Patent Publication No. 7-98847 (announced on October 25, 1995) Japanese Patent Laid-Open No. 4-106108 (published on April 8, 1992) US Pat. No. 5,229,488 Japanese Patent Publication No. 5-40780 (announced on June 21, 1993)

  The present invention has been made in view of the above problems. Its purpose is to provide a water-absorbing resin production method and a water-absorbing resin that can prevent the adhesion of the water-containing gel-like polymer and can be smoothly dried, and use thereof. The present invention relates to a method for producing a water-absorbing resin having a reduced monomer content, a water-absorbing resin having a reduced content of residual monomer, and use thereof.

  As a result of intensive studies in view of the above problems, the present inventors have determined that at least a part of the surface of the hydrogel polymer having a polyhedral shape having a square shape and a smooth surface is formed from a polyvalent metal. Coating with a specific method using an anti-adhesive agent containing at least one of the compounds classified as salts, polyhydric alcohols or surfactants improves the workability during cutting. It has been found that even when dried, it is in a non-aggregated state and can be dried well. Further, the present inventors have found that residual monomers can be reduced by drying a hydrogel polymer having a specific mass average particle diameter, thereby completing the present invention.

That is, the method for producing a water absorbent resin according to the present invention includes:
(1) An ethylenically unsaturated monomer containing acrylic acid and / or acrylate in an amount of 30 mol% or more and 100 mol% or less (excluding a crosslinking agent) is statically polymerized in the form of a sheet, and the water content is 40 mass%. A polymerization step for obtaining a hydrogel polymer that is 70% by mass or less;
(2) The above-mentioned hydrogel polymer has a mass average particle diameter of 3 mm or more and 10 mm or less, and particles having a shape of tetrahedron or more and dodecahedron or less are 50% by mass or more and 100% by mass with respect to the mass of the hydrogel polymer. A cutting step for cutting to be not more than%, or after drying the hydrated gel polymer so that the moisture content is not less than 5% by mass and not more than 60% by mass, the mass average particle diameter is not less than 2 mm and not more than 10 mm. A cutting step of cutting so that particles having a shape of a tetrahedron or more and a dodecahedron or less are 50% by mass or more and 100% by mass or less with respect to the mass of the hydrogel polymer,
(3) Adhesion containing at least one of the compounds classified as polyvalent metal salts, polyhydric alcohols or surfactants before, simultaneously with and / or after cutting the hydrogel polymer. A coating step of coating at least a part of the surface of the water-containing gel-like polymer with an anti-oxidant;
(4) A drying step of drying the coated hydrogel polymer is characterized.

  According to the above configuration, the hydrated gel polymer containing particles having a shape of a tetrahedron or more and a dodecahedron or less having a square shape and a smooth surface is contained in an amount of 50% by mass to 100% by mass. The adhesion preventive agent functions as a release agent between the hydrogel polymers. Therefore, adhesion of the hydrogel polymer at the time of cutting and / or after cutting can be prevented, and drying can be performed smoothly.

  Further, since the water content of the hydrogel polymer is 40% by mass or more and 70% by mass or less and the mass average particle size is 3 mm or more and 10 mm or less, the residual monomer is sufficiently reacted in the drying step. be able to. Therefore, it is possible to obtain a water-absorbent resin that has a low residual monomer content and does not affect the sanitation and odor problems.

  In the method for producing a water absorbent resin according to the present invention, it is preferable to include a sorting step of sorting the obtained water absorbent resin after the drying step.

  The display effect of the water-absorbent resin can be further improved by removing the small-sized and large-sized objects by the sorting step.

  In the method for producing a water-absorbent resin according to the present invention, the selection step is a step for removing small and large irregularities, and is a production method for obtaining a water-absorbent resin having a mass average particle diameter of 2 mm to 10 mm. Is preferred.

  The mass average particle diameter of the water-absorbent resin is in the above range, and the display effect of the water-absorbent resin can be further improved by removing the small variant and the large variant by the sorting step.

  The method for producing a water-absorbent resin according to the present invention is a method for producing a water-absorbent resin in which the cutting step uses a cutting machine, the vertical cutting blade, scraper, transverse cutting blade, casing provided in the cutting machine. It is preferable that at least one of these is covered with at least one of a non-adhesive paint, a lubricating paint, and a metal material.

  Thereby, it can suppress that the malfunction by a water-containing gel-like polymer clogging arises in a cutting process.

  In the method for producing a water-absorbent resin according to the present invention, the cutting step includes a hydrogel polymer, and hexahedral particles having a square shape and a smooth surface are formed as the hydrogel polymer. It is preferable to cut so as to be 50% by mass or more and 100% by mass or less with respect to the mass of the polymer.

  The hexahedron-shaped particles can be easily produced by cutting the hydrated gel polymer vertically and across. Therefore, the cutting process can be made efficient and the size of the hydrogel polymer can be easily adjusted.

  In the method for producing a water-absorbent resin according to the present invention, the coating step includes a step of spraying and / or spraying the adhesion preventing agent on the vertical cutting blade, the transverse rotary blade, the fixed blade and / or the hydrogel polymer. It is preferable that it is included.

  According to the above configuration, at least the adhesion preventive agent directly adheres to the hydrogel polymer, or indirectly adheres from the vertical cutting blade and / or the transverse rotary blade, the fixed blade, and the hydrogel polymer. Can be coated. Therefore, adhesion between the hydrated gel polymers can be effectively prevented, and reattachment of the hydrated gel after cutting can be prevented. In addition, the cutting force of the vertical cutting blade, fixed blade, and rotary blade can be maintained because the release of the vertical cutting blade, fixed blade, and rotary blade from the hydrogel polymer is promoted.

  In the method for producing a water absorbent resin according to the present invention, the adhesion preventive agent is added to the vertical cutting blade, the transverse rotary blade, the fixed blade and / or the hydrogel polymer with respect to the solid content of the water absorbent resin. It is preferable to spray and / or spray so as to be not less than .0015 mass% and not more than 35 mass%.

  According to the said structure, at least one part of the surface of a hydrogel polymer can be coat | covered. Therefore, adhesion between the hydrated gel polymers can be effectively prevented, the drying can be performed smoothly, and the content of the residual monomer of the water absorbent resin can be reduced.

  The method for producing a water-absorbent resin according to the present invention further comprises an ethylenically unsaturated monomer containing acrylic acid and / or acrylate in an amount of 30 mol% to 100 mol% (excluding a crosslinking agent) in the polymerization step. It is preferable to include a step of incorporating a surfactant and / or a polyhydric alcohol into the aqueous solution of the body and / or the hydrogel polymer.

  According to the above configuration, since the surfactant or polyhydric alcohol has an effect of preventing adhesion between the water-containing gel polymers, the effect of preventing adhesion between the water-containing gel polymers by the surface coating can be further enhanced. Further, the content of the residual monomer in the water absorbent resin can be further reduced.

  Further, by introducing a mixing step in addition to the cutting step as the coating step, it is possible to mix while spraying and / or spraying the adhesion inhibitor.

  The method for producing a water-absorbent resin according to the present invention preferably further includes a step of containing a chelating agent and / or an ultraviolet absorber on the surface of the hydrated gel polymer and / or the surface including the cut surface.

  According to the above configuration, the metal ions that cause one of the causes of deterioration of the water absorbent resin are trapped by the chelating agent and / or the ultraviolet rays that are one of the causes of deterioration of the water absorbent resin are absorbed by the ultraviolet absorber. It is possible to produce a water-absorbent resin having high durability against light and the like.

  In the method for producing a water absorbent resin according to the present invention, the water-containing gel-like polymer after the coating step is dried at 80 ° C. or higher and 150 ° C. or lower, so that the water content of the water absorbent resin is 5 mass% or more and 30 mass%. The residual monomer content of the water-absorbent resin is preferably 0 ppm by mass or more and 300 ppm by mass or less. According to the said structure, a water-containing gel-like polymer can be dried favorably without foaming, and content of a residual monomer can be decreased. Therefore, it is possible to obtain a water-absorbing resin that does not affect hygienic and odor problems, and it is possible to obtain a water-absorbing resin that is non-aggregated and excellent in display effect.

  In the method for producing a water-absorbent resin according to the present invention, it is preferable to pass a step of drying the hydrogel polymer after the coating step at 10 ° C. or more and less than 120 ° C.

  Thereby, since it passes through the process which dries the said water absorbing resin at the temperature of 10 degreeC or more and less than 120 degreeC, the amount of generated dust can be reduced preferably.

  In the method for producing a water absorbent resin according to the present invention, the stationary polymerization is performed with a sheet thickness of 3 mm or more and 10 mm or less, and the mass average particle diameter of the water absorbent resin that has undergone the cutting step, the coating step, and the drying step is 2 mm or more and 10 mm or less. The logarithmic standard deviation value of the particle size distribution is preferably 0 or more and 0.25 or less.

  The water-absorbent resin having a mass average particle size and logarithmic standard deviation of the particle size distribution in the above range is obtained by drying a hydrogel polymer having a uniform particle size. That is, it is obtained by drying a hydrogel polymer in a state where the reaction between the residual monomer and the polymerization initiator remaining in the hydrogel polymer is likely to occur. Therefore, it is possible to obtain a water-absorbent resin with a small content of residual monomer.

  As described above, the method for producing a water-absorbent resin according to the present invention is such that at least a part of the surface of a hydrogel polymer having a polyhedral shape is coated with an adhesion inhibitor and dried. It is possible to obtain a water-absorbing resin that has been dried smoothly, and preferably has a reduced residual monomer content.

  Therefore, the present invention can be suitably used as a method for producing a water-absorbing resin with little deterioration in physical properties, and the water-absorbing resin can be used for applications such as water-retaining agents for plant growth and artificial ice for displays. it can.

  Further, the cutting machine according to the present invention is a cutting machine for cutting a sheet-like hydrogel polymer, and includes at least one vertical cutting blade for longitudinally cutting the hydrogel polymer, At least one or more transverse rotary blades and fixed blades traversing the hydrogel polymer, and spraying and / or adhering an anti-adhesive agent to the vertical cutting blades, transverse rotary blades, fixed blades and / or hydrogel polymers. One or more spraying and / or spraying means for spraying.

  According to the said structure, an adhesion preventing agent can be efficiently sprayed and / or spread | dispersed to the hydrogel polymer which became polyhedron shape by vertical cutting or crossing. Therefore, adhesion between the water-containing gel polymers can be reduced. Therefore, it can be suitably used for the production of a non-aggregated water-absorbing resin having a uniform particle shape, and can be suitably used for the production of a water-absorbing resin with a low residual monomer content.

  In the cutting machine according to the present invention, at least one of the vertical cutting blade, the scraper, the transverse rotary blade, and the casing provided in the cutting machine is at least one of a non-adhesive paint, a lubricating paint, and a metal-based material. Preferably it is covered by type.

  Thereby, it can suppress that the malfunction by a water-containing gel-like polymer clogging arises inside a cutting machine.

  Further, the water-absorbent resin according to the present invention is a polymer of an ethylenically unsaturated monomer containing 30 mol% or more and 100 mol% or less of acrylic acid and / or acrylate, and has a tetrahedron or more and a dodecahedron or less. A water-absorbent resin obtained by drying a hydrogel polymer cut so that the shaped particles are 50% by mass or more and 100% by mass or less with respect to the mass of the hydrogel polymer, the mass average The particle diameter is 2 mm or more and 10 mm or less, and the logarithmic standard deviation value of the particle size distribution is 0 or more and 0.25 or less.

  The water absorbent resin is obtained by drying a hydrogel polymer having a uniform particle size. Therefore, adhesion of the water-containing gel polymers is sufficiently prevented in the production process, and a sufficiently dried water-absorbing resin can be obtained.

  The water-absorbent resin according to the present invention preferably has a mass average particle size of 2 mm or more and 10 mm or less after the sorting step and a logarithmic standard deviation value of the particle size distribution of 0 or more and 0.25 or less.

  A water-absorbing resin having an excellent display effect can be obtained by passing the water-absorbing resin through a sorting step.

  In the water absorbent resin according to the present invention, the content of the residual monomer is preferably 0 mass ppm or more and 300 mass ppm or less.

  The water-absorbent resin is obtained by drying a hydrogel polymer in a state in which a reaction between the residual monomer in the hydrogel polymer and the polymerization initiator is likely to occur. Therefore, it is possible to obtain a water-absorbing resin with a small content of residual monomer in the above range.

  In the water absorbent resin according to the present invention, the water content of the obtained water absorbent resin is preferably 5% by mass or more and 30% by mass or less.

  The water-absorbing resin is obtained by drying a water-containing gel-like polymer having a water content suitable for the reaction between the residual monomer and the polymerization initiator. As a result, the water content is reduced to the mass of the water-absorbing resin. On the other hand, it is 5 mass% or more and 30 mass% or less. Therefore, it becomes a water-absorbent resin with a low content of residual monomer.

  The water absorbent resin according to the present invention is a water absorbent resin obtained by drying a hydrogel polymer having a polyhedral shape, wherein at least a part of the surface of the water absorbent resin is a polyvalent metal salt, It is characterized by being coated with an anti-adhesive agent containing at least one of compounds classified as a monohydric alcohol or a surfactant.

  According to the above configuration, the adhesion inhibitor acts as a release agent on at least a part of the surface of the water-absorbent resin having a polyhedral shape. Therefore, it becomes difficult for water-containing gel-like polymers to aggregate, and the adhesiveness of water-containing gel-like polymers can be reduced significantly. Moreover, even if an aggregate is formed, it can be easily dissociated into primary particles only by applying a weak external force to the aggregate. Therefore, drying can be performed smoothly and the content of the residual monomer in the water absorbent resin can be reduced.

  In the water absorbent resin according to the present invention, the content of the adhesion inhibitor is preferably 0.0015% by mass or more and 35% by mass or less with respect to the solid content of the water absorbent resin. According to the said structure, content of the said adhesive prevention agent becomes a suitable range in order to prevent aggregation of a hydrogel polymer. Therefore, it is possible to obtain a water-absorbent resin having a uniform particle shape, and further, it is possible to smoothly dry, and to reduce the content of residual monomer in the water-absorbent resin.

  The water-absorbent resin according to the present invention has a rectangular shape and a hexahedral particle whose surface is a smooth surface is 50% by mass or more and 100% by mass or less based on the mass of the hydrogel polymer. It is preferably included. The hexahedron-shaped particles can be easily produced by cutting the hydrated gel polymer vertically and across. Therefore, if hexahedral particles are the main component, a water-absorbing resin with a small content of residual monomer can be obtained inexpensively and easily.

  The water-absorbing resin according to the present invention preferably further contains a chelating agent and / or an ultraviolet absorber. According to the above configuration, the metal ions that cause one of the causes of deterioration of the water absorbent resin are trapped by the chelating agent and / or the ultraviolet rays that are one of the causes of deterioration of the water absorbent resin are absorbed by the ultraviolet absorber. For example, durability of a water-absorbing resin used outdoors can be enhanced.

  Moreover, the sorter according to the present invention is a sorter that sorts the water-absorbent resin after drying, and includes a gas injection mechanism.

  Since this sorter can remove the large-sized and small-sized water-absorbing resin after drying, a water-absorbing resin having a desired mass average particle diameter can be obtained. Thereby, since the mass average particle diameter of the obtained water absorbent resin is equal, the display effect of the water absorbent resin can be improved.

  In addition, the water-retaining agent for plant cultivation according to the present invention is characterized by containing the water-absorbent resin produced by the method according to the present invention and / or the water-absorbent resin according to the present invention. Since the water-absorbing resin according to the present invention has few residual monomers that deteriorate the physical properties of the water-absorbing resin, it does not affect hygiene and odor problems. The water-retaining agent for plant growth according to the present invention can take in a sufficient amount of water, and once absorbed, can save the trouble of giving water to the plant for a long time and has an excellent appearance in display effect. Have.

  Moreover, the artificial ice for a display according to the present invention is characterized in that it contains the water absorbent resin produced by the method according to the present invention and / or the water absorbent resin according to the present invention. Since the water-absorbing resin according to the present invention has few residual monomers that deteriorate the physical properties of the water-absorbing resin, it does not affect hygiene and odor problems. The artificial ice for a display according to the present invention can take in a sufficient amount of water, and once absorbed, can maintain an appearance similar to real ice for a long period of time and keep the display effect long. Can do.

  The method for producing a water-absorbent resin of the present invention comprises (1) an ethylenically unsaturated monomer containing acrylic acid and / or acrylate in an amount of 30 mol% to 100 mol% (excluding a crosslinking agent) in a sheet form. A polymerization step of static polymerization to obtain a hydrogel polymer having a water content of 40% by mass or more and 70% by mass or less; and (2) a mass average particle diameter of 3 to 10 mm for the hydrogel polymer. A cutting step in which particles having a shape of a tetrahedron or more and a dodecahedron or less are 50% by mass or more and 100% by mass or less with respect to the mass of the hydrogel polymer, or the above hydrogel polymer, After drying so that the water content is 5% by mass or more and 60% by mass or less, particles having a shape of a tetrahedron or more and a dodecahedron having a mass average particle diameter of 2 mm or more and 10 mm or less are included in the mass of the hydrogel polymer. 50 against A cutting step of cutting to a concentration of not less than 100% and not more than 100% by weight; (3) before cutting, simultaneously with and / or after cutting the hydrogel polymer, a polyvalent metal salt, a polyhydric alcohol Or a coating step of covering at least a part of the surface of the hydrogel polymer with an adhesion inhibitor containing at least one of the compounds classified as surfactants; and (4) the coated hydrogel polymer coated above. And a drying step of drying.

  According to the above configuration, the hydrated gel polymer containing particles having a shape of a tetrahedron or more and a dodecahedron or less having a square shape and a smooth surface is contained in an amount of 50% by mass to 100% by mass. The adhesion preventive agent functions as a release agent between the hydrogel polymers. Therefore, it is possible to prevent adhesion of the water-containing gel-like polymer at the time of cutting and / or after the cutting, and it is possible to smoothly perform the drying.

  An embodiment of the present invention will be described as follows, but the present invention is not limited to this. Hereinafter, the manufacturing method of the water absorbing resin which concerns on this invention is explained in full detail.

(1. Manufacturing method of water-absorbing resin)
In one embodiment, a method for producing a water absorbent resin according to the present invention includes:
(1) An ethylenically unsaturated monomer containing acrylic acid and / or acrylate in an amount of 30 mol% or more and 100 mol% or less (excluding a crosslinking agent) is statically polymerized in the form of a sheet, and the water content is 40 mass%. A polymerization step for obtaining a hydrogel polymer that is 70% by mass or less;
(2) The above-mentioned hydrogel polymer has a mass average particle diameter of 3 mm or more and 10 mm or less, and particles having a shape of tetrahedron or more and dodecahedron or less are 50% by mass or more and 100% by mass with respect to the mass of the hydrogel polymer. A cutting step for cutting to be not more than%, or after drying the hydrated gel polymer so that the moisture content is not less than 5% by mass and not more than 60% by mass, the mass average particle diameter is not less than 2 mm and not more than 10 mm. A cutting step of cutting so that particles having a shape of a tetrahedron or more and a dodecahedron or less are 50% by mass or more and 100% by mass or less with respect to the mass of the hydrogel polymer,
(3) Adhesion containing at least one of the compounds classified as polyvalent metal salts, polyhydric alcohols or surfactants before, simultaneously with and / or after cutting the hydrogel polymer. A coating step of coating at least a part of the surface of the water-containing gel-like polymer with an anti-oxidant;
(4) A drying step of drying the coated hydrogel polymer.

  The hydrated gel polymer is prepared by polymerizing an ethylenically unsaturated monomer, preferably in the presence of a small amount of a crosslinking agent, before cutting the polymer, simultaneously with the cutting, and / or after cutting. It is obtained by coating at least a part of the surface with an anti-oxidant. In this specification, the term “hydrogel polymer” includes a hydrogel polymer in which the hydrogel polymer is not crosslinked and a hydrogel polymer in which the hydrogel polymer is crosslinked. Both cross-linked polymers are included. Further, in this specification, “mass” and “mass%” are treated as synonyms for “weight” and “wt%”, respectively.

  The ethylenically unsaturated monomer used as a raw material for the water-containing gel polymer is a monomer having water solubility, specifically, for example, (meth) acrylic acid, β-acryloyloxypropionic acid, Maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, cinnamic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methyl Acid group-containing monomers such as propanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, vinylphosphonic acid, 2- (meth) acryloyloxyethyl phosphoric acid, (meth) acryloxyalkanesulfonic acid, and the like Alkali metal salts, alkaline earth metal salts, ammonium salts, alkylamine salts; N, N-dimethyl Dialkylaminoalkyl (meth) acrylates such as aminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and the quaternized compounds thereof (for example, alkyl hydrides) Reaction products with dialkyl sulfate, dialkylaminohydroxyalkyl (meth) acrylates and quaternized products thereof; N-alkylvinylpyridinium halides; hydroxymethyl (meth) acrylate, 2-hydroxyethyl methacrylate, Hydroxyalkyl (meth) acrylates such as 2-hydroxypropyl (meth) acrylate; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylate Rilamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide; alkoxy polyethylene glycol (meth) acrylate such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate; vinylpyridine, N- Vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine; N-vinylacetamide; and the like. Only one kind of these ethylenically unsaturated monomers may be used, or two or more kinds may be appropriately mixed.

  Among the ethylenically unsaturated monomers exemplified above, acrylic acid and / or acrylate is 30 mol% or more and 100 mol% or less, preferably 50 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less. It is preferable to contain less than mol%. If it is less than 30 mol%, the water-absorbing performance and safety of the resulting hydrogel may be further lowered, and the polymerization reactivity may be lowered. Furthermore, versatility may be reduced and economic efficiency may be reduced. Here, the acrylate refers to an alkali metal salt, an alkaline earth metal salt, an ammonium salt, a hydroxyammonium salt, an amine salt, and an alkylamine salt of acrylic acid.

  Of the water-soluble salts exemplified above, sodium salts and potassium salts are particularly preferred. These acrylate monomers may be used alone or in combination of two or more. In addition, the average molecular weight (degree of polymerization) of the water absorbent resin is not particularly limited.

  The above water-containing gel-like polymer can be obtained by polymerizing a monomer composition containing the ethylenically unsaturated monomer as a main component, preferably in the presence of a small amount of a crosslinking agent. Furthermore, the monomer composition may contain other monomers (copolymerizable monomers) copolymerizable with the ethylenically unsaturated monomer to such an extent that the hydrophilicity of the resulting hydrogel polymer is not impaired. May be included.

  Specific examples of the copolymerizable monomer include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate; vinyl acetate, vinyl propionate, and the like. And a hydrophobic monomer. These copolymerizable monomers may be used alone or in combination of two or more.

  Examples of the crosslinking agent used in polymerizing the monomer component include a compound having a plurality of vinyl groups in the molecule; a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule. And the like. These crosslinking agents may be used alone or in combination of two or more.

  Specific examples of the compound containing a plurality of vinyl groups in the molecule include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol di (meta). ) Acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerol tri (meth) acrylate, glycerol acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) Acrylate, dipentaerythritol hexa (meth) acrylate, N, N-diallylacrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, tria Triethanolamine, diallyloxyacetic acid, bis (N- vinylcarboxamides), such as tetraallyloxyethane, and the like.

  As a compound having a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule, (poly) ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, Dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, (poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, Polyhydric alcohol compounds such as intererythritol and sorbitol; Epoxy compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, diglycerol polyglycidyl ether, (poly) propylene glycol diglycidyl ether, glycidol; ethylenediamine , Diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamidepolyamine, polyethyleneimine and other polyvalent amine compounds, and condensates of these polyvalent amines with haloepoxy compounds; 2,4-tolylene diisocyanate, Polyvalent isocyanate compounds such as hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline Silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4 , 5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl- 1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, Alkylene carbonate compounds such as 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin; zinc, calcium, magnesium, aluminum, iron, di Koniumu like hydroxides or chlorides, such as.

  The amount of the crosslinking agent used is not particularly limited, but is preferably in the range of 0.0001 mol% or more and 10 mol% or less with respect to the monomer component. More preferably, it is in the range of mol% or more and 1 mol% or less. In the present invention, a method for polymerizing the above monomer components includes aqueous solution polymerization, and specific methods include static polymerization on a bat or belt, or polymerization in a kneader. Among these, the method of standing polymerization on a movable endless belt is preferable because the next cutting step can be continuously performed.

  The static polymerization is not limited in the thickness of the polymer gel sheet, but is preferably performed at a sheet thickness of 3 mm to 10 mm. That is, it is preferable that the thickness of the sheet-like hydrogel polymer produced by the polymerization step is 3 mm or more and 10 mm or less. By performing the stationary polymerization with the above sheet thickness, the residual monomer can be effectively reduced in the drying step.

  That is, when a sheet-like hydrogel polymer is cut vertically and transversely, a hexahedral gel having a rectangular shape and a smooth surface is produced, but the thickness is 3 mm or more and 10 mm. By cutting the following sheet-like hydrogel polymer vertically and transversely, the mass average particle diameter is 3 mm or more and 10 mm or less, and the shape is mainly hexagonal and the surface is a smooth surface. A gel is created. As will be described later, the hydrogel polymer having a mass average particle diameter of 3 mm or more and 10 mm or less is effective in reducing the residual monomer content in the water absorbent resin after drying. Therefore, it is preferable that the stationary polymerization is performed with a sheet thickness of 3 mm or more and 10 mm or less.

  In addition, when the above ethylenically unsaturated monomer is polymerized in an aqueous solution, any one of continuous polymerization or batch polymerization may be employed, and any of normal pressure, reduced pressure, and pressurized pressure may be employed. You may implement under pressure. The polymerization reaction may be performed in an air atmosphere, but is preferably performed in a stream of an inert gas such as nitrogen, helium, argon, or carbon dioxide.

  At the start of polymerization in the polymerization reaction, for example, a polymerization initiator or activation energy rays such as radiation, electron beam, ultraviolet ray, electromagnetic ray, or the like can be used.

  Although it does not specifically limit as said polymerization initiator, A thermal decomposition type initiator and a photolysis type initiator are used, The usage-amount is 0.001-5 mol%, Preferably 0.01- 0.5 mol%. Thermal decomposition initiators include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide and methyl ethyl ketone peroxide; azonitrile compounds, azoamidine compounds, cyclic Azoamidine compounds, azoamide compounds, alkylazo compounds, azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride Is mentioned.

  Examples of the photolytic initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, and the like. These polymerization initiators may be used alone or in appropriate combination. Considering the residual monomer reducing ability, it is preferable to use a thermal decomposition initiator and a photodecomposition initiator in combination. Moreover, when using a peroxide as a polymerization initiator, you may perform oxidation-reduction (redox) polymerization using reducing agents, such as a sulfite, a bisulfite, and L-ascorbic acid, for example.

  In order to start the polymerization reaction stably, it is preferable to keep the amount of dissolved oxygen in the aqueous solution of the ethylenically unsaturated monomer constant, and in order to start the polymerization more smoothly, the aqueous solution It is preferable to reduce the amount of dissolved oxygen therein. The preferable range of dissolved oxygen is 8 mg / l or less, more preferably 6 mg / l or less, and particularly preferably 2 mg / l or less.

  When the polymerization reaction is started in a state where bubbles remain in the aqueous solution by the deaeration operation, bubbles remain in the sheet, and as a result, the display effect of the water absorbent resin is impaired, which is not preferable. In order to maintain the display effect of the water-absorbent resin in the above case, it is necessary to perform defoaming simultaneously with deaeration.

  Examples of a method for removing residual oxygen in an aqueous solution in an ethylenically unsaturated monomer include an inert gas blowing method, a vacuum degassing method, a membrane degassing method, and a reducing agent addition method. These methods will be described below.

(A. Inert gas blowing)
(I) A method of blowing an inert gas into a pipe of an aqueous solution of an ethylenically unsaturated monomer that leads to a polymerization apparatus, or (II) a method of introducing an inert gas into a liquid tank containing an ethylenically unsaturated monomer. There is a method of bubbling with an active gas. In any method, it is necessary to start the polymerization after removing the blown inert gas and bubbles of precipitated oxygen.

  As a method for removing bubbles, (I) When an inert gas is blown into a pipe of an aqueous solution of an ethylenically unsaturated monomer that leads to a polymerization apparatus, for example, a swirl flow is used to separate the bubbles and the liquid. And a method in which an aqueous solution of an ethylenically unsaturated monomer is once put into a deaeration tank and allowed to stand until bubbles are removed. As a method of using the swirling flow, for example, a quicktron manufactured by Nippon Petrochemical Co., Ltd. can be used.

  A defoaming machine represented by the Quicktron will be described below with reference to FIG. The defoamer 400 has a cylindrical shape and includes a conical cyclone chamber 30 inside. A bubble removing tube 31 is further provided at the center of the cyclone chamber 30. In addition, an inlet hole 28 into which a liquid containing bubbles is introduced and a preliminary swirl flow chamber 29 are provided. Further, an outlet hole 32 is provided in the upper part of the defoaming machine 400.

  First, the fluid introduced in the direction of arrow F is introduced into the cyclone chamber 30 from the inlet hole 28. Thereafter, the fluid from which bubbles have been removed in the cyclone chamber 30 passes through a large number of small holes and is discharged from the outlet holes 32 in the direction of arrow H.

  On the other hand, bubbles with a small amount of fluid are collected in the center of the cyclone chamber 30 and discharged through the bubble removal pipe 31 in the direction G.

  Further, (II) when bubbling an inert gas in a liquid tank containing an aqueous solution of an ethylenically unsaturated monomer, it is allowed to stand until bubbles are removed.

(B. Vacuum degassing method)
This is a method of reducing dissolved oxygen in the aqueous solution of the ethylenically unsaturated monomer by reducing the pressure of the aqueous solution of the ethylenically unsaturated monomer. In addition to the method of reducing the pressure of the ethylenically unsaturated monomer aqueous solution, a method using a deaeration pump can be used. As a method of using the deaeration pump, for example, deaeration pumps ASP-0310 and ASP-0510 manufactured by Yokota Corporation can be used.

(C. Membrane degassing method)
One method of the vacuum degassing method is that when an aqueous solution of an ethylenically unsaturated monomer passes through the inside of the degassing membrane module, the outside of the degassing membrane module is depressurized to thereby reduce the ethylenically unsaturated monomer. In this method, dissolved oxygen in the aqueous solution of the monomer is discharged outside the degassing membrane module.

  As the deaeration membrane, a porous membrane or a separation membrane can be used. M80-B, non-porous membrane manufactured by Mitsubishi Rayon Engineering Co., Ltd., polyethylene degassing membrane modules MHF0504MBFT, MHF1704, MHF3504, MHF304EED, MGF304KMD, MHF0498P, etc. can be used.

  FIG. 2 shows an outline of the deaeration membrane module. The deaeration membrane module 500 is provided with a plurality of deaeration membranes 35 inside the cover 36. A vacuum pump is provided from the side of the degassing membrane 35 via a pipe 34, and the pressure can be reduced in the direction of the arrow K. First, a fluid containing dissolved gas such as dissolved oxygen is introduced into the degassing membrane module 500 in the direction of arrow I. Thereafter, the dissolved gas in the fluid permeates through the degassing membrane 35 in the direction of the arrow K, and the fluid degassed from the direction of the arrow J is discharged.

(D. Reducing agent addition method)
In this method, hydrazine, sodium sulfite or sodium bisulfite is added to an aqueous solution of an ethylenically unsaturated monomer and chemically deaerated.

  In addition to the above methods, or alone, deaeration and defoaming by ultrasonic waves may be performed.

  During the polymerization reaction, if bubbles are mixed into the gel sheet, the display effect of the water-absorbent resin is impaired, which is not preferable. For this reason, for example, (I) performing degassing and defoaming of an aqueous solution of an ethylenically unsaturated monomer, (II) suppressing heat generation during polymerization, In order to avoid bumping of the aqueous solution, the polymerization is preferably carried out at a temperature of the aqueous solution of the ethylenically unsaturated monomer of 30 ° C. or lower, preferably 25 ° C. or lower, more preferably 20 ° C. or lower. (III) It is preferable to start the polymerization by a polymerization reaction using ultraviolet rays using a photolysis initiator.

  In addition, the highest ultimate temperature of the hydrogel polymer during polymerization is 60 ° C. or higher and 100 ° C. or lower, preferably 70 ° C. or higher and 90 ° C. or lower, and more preferably 80 ° C. or higher and 90 ° C. or lower. If the temperature exceeds 100 ° C., bumping of the aqueous solution of the ethylenically unsaturated monomer occurs, which is not preferable. If the temperature is less than 80 ° C., the polymerization time becomes long and the productivity is lowered, which is not preferable.

As the integrated light quantity of ultraviolet light required for the polymerization reaction, preferably 500 mJ / cm ² or more 5000 mJ / cm ² or less, further preferably 600 mJ / cm ² or more 4000 mJ / cm ² or less. When the integrated light quantity is less than 500 mJ / cm ² , more photolysis initiator is required, which is not preferable. When the integrated light quantity exceeds 5000 mJ / cm ² , the polymerization reaction occurs rapidly, and the aqueous solution of the ethylenically unsaturated monomer may suddenly boil due to heat generated at that time. Furthermore, the gel sheet is irradiated with more energy than necessary, which is not preferable because the hydrogel polymer is deteriorated or decomposed.

  Examples of the UV lamp for generating ultraviolet rays include a black light mercury lamp, a metal halide lamp, a high-pressure mercury lamp, and the like. Any of these lamps may be used, or these lamps may be used in combination. In particular, it is preferable to use a metal halide lamp and a black light mercury lamp together to adjust the integrated light quantity.

  When the monomer component is polymerized in the presence of a crosslinking agent, it is preferable to use water as a solvent. That is, it is preferable to make the monomer component and the crosslinking agent into an aqueous solution. This is for improving the water absorption performance of the obtained water absorbent resin.

  The concentration of the monomer component in the aqueous solution (hereinafter referred to as a monomer aqueous solution) is more preferably in the range of 30% by mass to 60% by mass. When the concentration of the monomer component is less than 30% by mass, the amount of the water-soluble component of the resulting water absorbent resin may increase. On the other hand, when the concentration of the monomer component exceeds 60% by mass, it may be difficult to control the reaction temperature. In this way, a hydrogel polymer having a water content of 40% by mass to 70% by mass can be obtained.

  Moreover, water and the organic solvent soluble in water can also be used together as a solvent of monomer aqueous solution. Specific examples of the organic solvent include methyl alcohol, ethyl alcohol, acetone, dimethyl sulfoxide, ethylene glycol monomethyl ether, glycerin, (poly) ethylene glycol, (poly) propylene glycol, and alkylene carbonate. These organic solvents may be used alone or in combination of two or more.

  In the cutting step, the above hydrogel polymer shaped into a sheet is cut vertically and transversely to form a tetrahedron or more and a dodecahedron or less having a square shape and a smooth surface. The hexagonal shape is cut so that the particles of the hydrogel polymer are 50% by mass or more and 100% by mass or less with respect to the mass of the hydrated gel polymer, and preferably have a square shape and a smooth surface. Of the water-containing gel polymer is 50% by mass or more and 100% by mass or less, preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass. It cut | disconnects so that it may become mass% or more and 100 mass% or less.

  Among the obtained hydrogel polymers, hexahedral particles having a square shape and a smooth surface are 50% by mass or less based on the mass of the hydrogel polymer. In such a case, since the shapes are not uniform, the display performance when the water-absorbent resin obtained after drying the hydrogel polymer is swollen with an aqueous liquid may be unfavorable.

  When the hydrated gel-like polymer formed into a sheet is cut longitudinally and transversely, a gel whose main component is hexahedral particles having a square shape and a smooth surface is obtained. However, since cutting may occur, not only hexahedral particles, but also a mixture of polyhedral particles, and particles having a tetrahedral shape or more and a dodecahedron shape with respect to the mass of the hydrogel polymer are included. A hydrogel polymer having a content of 50% by mass to 100% by mass is obtained.

  A hydrogel polymer having a polyhedral shape less than a tetrahedron and / or a polyhedron shape exceeding a dodecahedron is not preferable because the display performance when a water-absorbing resin obtained after drying the polymer is swollen with an aqueous liquid is poor.

  For the cutting, for example, various cutting means such as a roller cutter, a guillotine cutter, a slicer, a roll cutter, a shredder, a scissor, or a combination thereof can be used, and the cutting is not particularly limited.

  Next, the adhesion preventing agent will be described. The anti-adhesive agent includes at least one of compounds classified as a polyvalent metal salt, a polyhydric alcohol or a surfactant, covers at least a part of the surface of the hydrogel polymer, and contains the hydrogel polymer. Prevents adhesion of particles.

  Although the usage-amount of an adhesion inhibitor is not specifically limited, 0.0015 mass% or more and 35 mass% or less with respect to solid content of a water absorbing resin, Preferably it is 0.002 mass% or more and 30 mass% or less, More preferably, it is 0.002 mass% or more and 25 mass% or less. When the amount used is less than 0.0015% by mass, the release effect of the particulate hydrous gel obtained by cutting is small, and reaggregation tends to occur. On the other hand, when the amount used is more than 35% by mass, not only an effect commensurate with the addition cannot be obtained, but also the physical properties of the water absorbent resin of the final product may be lowered.

  Examples of the polyvalent metal salt include aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum nitrate, potassium bissulfate aluminum, sodium bissulfate, potassium alum, ammonium alum, sodium aluminate, calcium chloride, calcium nitrate, and chloride. Magnesium, magnesium sulfate, magnesium nitrate, zinc chloride, zinc nitrate, iron (III) chloride, cerium (III) chloride, ruthenium (III) chloride, yttrium chloride (III), chromium chloride (III), zirconium sulfate, hexafluoride Zirconium potassium, zirconium hexafluoride sodium, ammonium zirconium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, zirconium acetate, zirconium propionate Etc. can be used.

  Especially, since the solubility with aqueous liquids, such as water, is favorable, it is preferable to use the salt which has these crystal waters. Particularly preferred are aluminum compounds, among which aluminum chloride, polyaluminum chloride, aluminum nitrate, potassium aluminum bissulfate, sodium aluminum bissulfate, potassium alum, ammonium alum, sodium alum, and sodium aluminate are preferred. Aluminum is particularly preferred. As aluminum sulfate, powders of hydrous crystals such as aluminum sulfate 18 hydrate and aluminum sulfate 14-18 hydrate can be most preferably used. These may be used alone or in combination of two or more.

  The polyvalent metal salt is preferably used as an aqueous solution. The concentration of the aqueous polyvalent metal salt solution is not particularly limited, but is preferably 1% by mass to 50% by mass, more preferably 3% by mass to 40% by mass, and still more preferably 5% by mass to 30%. It is 10 mass% or less, Most preferably, it is 10 mass% or more and 20 mass% or less.

  When the concentration of the polyvalent metal salt aqueous solution is less than 1% by mass, a large amount of the polyvalent metal salt aqueous solution is required to provide mold release performance. Absent. On the other hand, when the concentration of the polyvalent metal salt aqueous solution exceeds 50% by mass, the mold release performance is improved, but the water solubility is lowered and it is difficult to spray uniformly on the surface of the hydrogel polymer. Therefore, it is not preferable. In addition, the amount used is too uneconomical.

  Examples of the polyhydric alcohol include ethylene glycol, polyethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene glycol, polypropylene glycol, and 2,2,4-trimethyl-1,3. -Pentanediol, glycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedi Methanol, 1,2-cyclohexanol, trimethylolpropane, 2,3,4-trimethyl-1,3-pentanediol and the like can be used. Among them, propylene glycol is particularly preferable because of its high versatility. These polyhydric alcohols may be used alone or in combination of two or more.

  As the surfactant, for example, an anionic surfactant, a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant can be used. Among the above surfactants, the anionic surfactants specifically include fatty acid salts such as mixed fatty acid sodium soap, semi-cured tallow fatty acid sodium soap, sodium stearate soap, potassium oleate soap, castor oil potassium soap, etc. Alkyl sulfonates such as sodium lauryl sulfate, higher alcohol sodium sulfate and triethanolamine; alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate; alkyl naphthalene sulfonates such as sodium alkyl naphthalene sulfonate; dialkyl sulfosuccinic acid Alkyl sulfosuccinates such as sodium; alkyl diphenyl ether disulfonates such as sodium alkyl diphenyl ether disulfonate; Polyoxyethylene alkyl (or alkyl) such as sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl ether sulfate triethanolamine, polyoxyethylene alkyl phenyl ether sodium sulfate Allyl) sulfate ester salt; special reaction type anionic surfactant; special carboxylic acid type surfactant; sodium salt of β-naphthalenesulfonic acid formalin condensate, naphthalenesulfonic acid such as sodium salt of special aromatic sulfonic acid formalin condensate Formalin condensate; special polycarboxylic acid type polymer surfactant; polyoxyethylene alkyl phosphate ester; and the like.

  Specific examples of nonionic surfactants include polyolefin oxides such as polyethylene glycol, polypropylene glycol, and polyethylene glycol-polypropylene glycol block copolymers; polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene Stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene alkyl ether such as polyoxyethylene higher alcohol ether, polyoxyethylene alkyl aryl ether such as polyoxyethylene nonylphenyl ether; polyoxyethylene derivative; sorbitan monolaurate, sorbitan mono Palmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monoolee Sorbitan fatty acid esters such as sorbitan trioleate, sorbitan sesquioleate, sorbitan distearate; polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tri Polyoxyethylene sorbitan fatty acid esters such as stearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate; polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitol tetraoleate; glycerol monostearate, glycerol monoole Glycerol, fatty acid esters such as self-emulsifying glycerol monostearate; Polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate; polyoxyethylene alkylamines; polyoxyethylene hydrogenated castor oil; alkyl alkanolamides; Can be mentioned.

  Furthermore, specific examples of the cationic surfactant and amphoteric surfactant include alkylamine salts such as coconut amine acetate and stearylamine acetate; lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, Quaternary ammonium salts such as stearyldimethylammonium chloride and alkylbenzyldimethylammonium chloride; alkylbetaines such as laurylbetaine, stearylbetaine, laurylcarboxymethylhydroxyethylimidazolinium betaine; amine oxides such as lauryldimethylamine oxide; It is done. In addition to the above surfactants, it is also possible to use a fluorine-based surfactant or a siloxane-based surfactant.

  Among the above surfactants, polypropylene glycol or polyethylene glycol-polypropylene glycol block copolymer is particularly preferable. These surfactants need only be added in a small amount when added to the hydrogel. Further, these surfactants do not hinder the physical properties (for example, water absorption capacity under pressure) of the hydrogel even when the surface of the hydrogel is subjected to surface treatment after addition. Furthermore, these surfactants are preferable because of high safety in use.

  The adhesion preventing agent only needs to contain at least one kind of compound classified as a polyvalent metal salt, a polyhydric alcohol, or a surfactant. When two or more types of adhesion inhibitors are used in combination, they may be used in a mixed state with compounds classified as polyvalent metal salts, polyhydric alcohols, or surfactants, or used separately. May be. When using a combination of a polyvalent metal salt, a polyhydric alcohol, and a surfactant, the amount of each used is not particularly limited, but is preferably a combination of a polyvalent metal salt and a polyhydric alcohol, In the case of this combination, the mass of the polyvalent metal salt is preferably 20% by mass or less based on the total mass of the anti-adhesive agent.

  The water-containing gel-like polymer only needs to have at least a part of its surface coated with the above-mentioned adhesion preventive agent, but if the entire surface is coated, the release effect of the adhesion preventive agent is sufficient. Since it is obtained, it is preferable. In addition, the above “coating” means that the anti-adhesive agent does not necessarily have penetrated to the inside of the water-containing gel polymer. However, unless the function of the water-containing gel polymer is impaired, May penetrate.

  The moisture content of the hydrated gel polymer is not particularly limited, but is preferably 40% by mass or more and 70% by mass or less, more preferably 45% by mass or more and 65% by mass or less, It is particularly preferable that the content is not less than mass% and not more than 60 mass%.

  When the water content is less than 40% by mass, heat generation during the polymerization reaction is increased, and many foams may be generated in the water-containing gel polymer. On the other hand, when the water content exceeds 70% by mass, the polymerization reaction may not be performed smoothly, which is not preferable. In addition, although the residual monomer can be sufficiently reacted, moisture remaining after drying becomes too much, and a lot of energy is required for drying, which is not preferable.

  Further, the mass average particle diameter of the hydrated gel polymer is preferably 3 mm or more and 10 mm or less, more preferably 3 mm or more and 8 mm or less, and the particle size distribution of the hydrated gel polymer is 0 or more and 0.00 in logarithmic standard deviation value. It is preferable that it is 25 or less.

  In general, the larger the particle size of the hydrated gel, the more the residual monomer tends to decrease when dried under the same conditions. That is, when the hydrogel is dried, drying (moisture evaporation due to temperature rise) starts from the surface and gradually proceeds to the inside. However, in the case of a hydrogel having a small particle size, the moisture evaporates to the inside relatively quickly. The reaction between the residual monomer and the polymerization initiator remaining in the hydrogel polymer is unlikely to occur, and as a result, the residual monomer is difficult to decrease. When the weight average particle size of the hydrated gel polymer is less than 3 mm, the particle size is small, which makes it difficult to reduce the residual monomer, which is not preferable.

  On the other hand, in the case of a hydrogel having a large particle size, moisture evaporation inside the gel is delayed even though the temperature inside the gel is increased by drying, so that the residual monomer reacts with the polymerization initiator and the residual monomer It tends to decrease. When the weight average particle diameter of the hydrated gel polymer exceeds 10 mm, the residual monomer tends to decrease for the same reason as described above. However, in order to dry the gel to the inside, a lot of drying time (energy) is required. This is not preferable because it requires work efficiency.

  When the weight average particle diameter of the hydrated gel polymer is 3 mm or more and 10 mm or less, and the particle size distribution of the hydrated gel polymer is 0 or more and 0.25 or less in logarithmic standard deviation value, Since the particle size of the coalescence is relatively large and the particle size distribution is uniform, the remaining monomer can easily react with the polymerization initiator in the drying step.

  Here, “mass average particle diameter” refers to the average particle diameter defined by the standard sieve classified particles. The logarithmic standard deviation value is a value representing the distribution of the average particle diameter. In addition, the calculation method of an average particle diameter and a logarithmic standard deviation value is demonstrated in an Example.

  The spraying and / or spraying of the anti-adhesive agent should be performed using a conventionally known spraying means such as an atomizer, an air mixing type spraying device such as a 1 fluid nozzle, a 2 fluid nozzle, a liquid injection pump, a brush, and a roller. There is no particular limitation. Further, the number of spraying and / or spraying means is not particularly limited.

  The method for spraying and / or spraying the adhesion preventing agent is not particularly limited as long as the adhesion preventing effect of the water-containing gel polymer by the adhesion preventing agent can be obtained, but the vertical cutting blade, the horizontal cutting blade, the fixed blade It is preferable to include a step of spraying and / or spraying the adhesion preventive agent on the hydrogel polymer. In other words, as long as the anti-adhesion effect is obtained, the anti-adhesive agent may be sprayed and / or sprayed directly on the water-containing gel polymer, or may be applied to the vertical cutting blade, the transverse rotary blade and / or the fixed blade. Spraying and / or spraying may be applied to the hydrogel polymer from the vertical cutting blade, horizontal cutting blade and / or fixed blade.

  Further, by introducing a mixing step in addition to the cutting step as the coating step, it is possible to mix while spraying and / or spraying the adhesion inhibitor. The mixing device is not particularly limited as long as it is a mixing device that is usually used for mixing a liquid with a solid material, but a mixing device such as a Roedige mixer or a Nauter mixer is preferable.

  The amount of spraying and / or spraying amount of the anti-adhesive agent to the vertical cutting blade, horizontal cutting blade, fixed blade and / or hydrogel polymer is not particularly limited, but the solid content of the water-absorbing resin It is preferable to spray and / or spray so that it may be 0.0015 mass% or more and 35 mass% or less. More preferably, it is 0.0015 mass% or more and 25 mass% or less, Most preferably, it is 0.0015 mass% or more and 20 mass% or less, Most preferably, it is 0.0015 mass% or more and 18 mass% or less.

  When the spraying amount and / or the spraying amount is less than 0.0015% by mass, the water-containing gel-like polymer cannot be sufficiently coated, so that a sufficient adhesion preventing effect cannot be obtained. On the other hand, when the spraying amount and / or the spraying amount exceeds 35% by mass, not only the energy required for drying increases, but also the dust amount increases. In addition, when a polyvalent metal salt is used, the gel surface cross-linking reaction proceeds, resulting in a problem that the water absorption ratio is reduced, and a problem that the corrosivity to a cutting machine is improved depending on the type of the polyvalent metal salt.

  As a method of containing a chelating agent and / or an ultraviolet absorber, it is possible to mix while spraying and / or spraying. The mixing apparatus is not limited as long as it is a mixer that is usually used for mixing liquids, but a mixing apparatus such as a Laedige mixer and a Nauter mixer is preferable.

  Further, among the above adhesion preventing agents, a surfactant or a polyhydric alcohol may be contained in the aqueous solution of ethylenically unsaturated monomer and / or the hydrogel polymer in the polymerization step. The method for containing the hydrated gel polymer is not particularly limited. For example, an ethylenically unsaturated monomer containing 30 mol% or more and 100 mol% or less of acrylic acid and / or acrylate is used. A method in which a surfactant and / or a polyhydric alcohol is introduced into an aqueous solution of, and uniformly mixed and then polymerized.

  By containing at least one of the compounds classified as surfactants or polyhydric alcohols in the water-containing gel polymer, the surface of the water-containing gel polymer and / or adhesion between cut surfaces when cut Can be reduced.

  The amount of the surfactant and / or polyhydric alcohol used in the hydrogel polymer is not particularly limited, but is 0.001% by mass to 10% by mass with respect to the solid content of the water-absorbent resin. Preferably, it is 0.01 mass% or more and 8 mass% or less, More preferably, it is 0.03 mass% or more and 5 mass% or less. When the amount used is less than 0.001% by mass, the effect of reducing the adhesion between the cut surfaces of the hydrogel is small and reaggregation is likely. On the other hand, if the amount used is more than 10% by mass, the transparency of the water-absorbent resin is impaired, and for example, whitening occurs, which may reduce the display effect.

  Furthermore, a chelating agent and / or an ultraviolet absorber may be contained in the inside of the hydrated gel polymer and / or the surface including the cut surface. The method of containing the chelating agent and / or the ultraviolet absorber is not particularly limited. For example, as with the anti-adhesive agent, an air mixing type spraying device such as an atomizer, one fluid nozzle, and two fluid nozzles and Examples thereof include a method of spraying and / or spraying the hydrogel polymer using a conventionally known means such as a liquid injection pump.

  In addition, as with the anti-adhesive agent, the hydrogel polymer is sprayed and / or sprayed on a fixed blade and / or a rotary blade for longitudinally or transversely crossing, and the hydrogel form from the fixed blade and / or the rotary blade. You may make it adhere to a polymer and may make it contain in the surface containing the inside of the said water-containing gel-like polymer as a result, or a cut surface.

  As the chelating agent, any conventionally known compound having a sequestering ability can be used without particular limitation. For example, (1) aminocarboxylic acid and salts thereof, (2) citric acid monoalkylamide and citric acid monoalkenylamide and salts thereof, (3) malonic acid monoalkylamide and malonic acid monoalkenylamide and salts thereof, (4) monoalkyl phosphate esters and monoalkenyl phosphate esters and salts thereof, (5) N-acylated glutamic acid and N-acylated aspartic acid and salts thereof, (6) β-diketone derivatives, (7) And tropolone derivatives. These chelating agents may be used alone or in combination of two or more.

  (1) As aminocarboxylic acids and salts thereof, aminocarboxylic acids having 3 or more carboxyl groups and salts thereof are preferred in terms of sequestering ability. Specifically, nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl ether diamine tetraacetic acid, ethylenediamine Examples include tetrapropionic acid, N-alkyl-N′-carboxymethylaspartic acid, N-alkenyl-N′-carboxymethylaspartic acid, and alkali metal salts, alkaline earth metal salts, ammonium salts, or amine salts thereof.

  (2) Citric acid monoalkylamides and citric acid monoalkenylamides and salts thereof are obtained, for example, by dehydration condensation of alcohol and citric acid.

  (3) Malonic acid monoalkylamides and malonic acid monoalkenylamides and salts thereof are obtained, for example, by adding an α-olefin to methyl malonate and then hydrolyzing it.

  (4) Examples of monoalkyl phosphate esters and monoalkenyl phosphate esters and salts thereof include lauryl phosphate and stearyl phosphate.

  (5) Examples of N-acylated glutamic acid, N-acylated aspartic acid and salts thereof include Amisoft HS-11 and GS-11 commercially available from Ajinomoto Co., Inc.

  (6) Examples of β-diketone derivatives include acetylacetone and benzoylacetone.

  (7) Examples of tropolone derivatives include tropolone, β-tyaprisin, and γ-tyaprisin.

  Among these chelating agents, aminocarboxylic acids having 3 or more carboxyl groups and salts thereof are preferred. Among them, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, cyclohexane-1,2-diaminotetraacetic acid, N-hydroxyethylethylenediaminetrimethyl. Acetic acid and its salt are most preferable in terms of light resistance.

The type of the UV absorber is not particularly limited, and any UV absorber may be used as long as it can efficiently absorb light having a wavelength region of 300 nm to 400 nm. Among them, as benzophenone type,
(I) 2-hydroxybenzophenone-4-diglyceryl ether, (b) 2,2′-dihydroxybenzophenone-4-diglyceryl ether, (c) 2-hydroxybenzophenone-4, 4′-diglyceryl ether, ( D) 2,2′-dihydroxybenzophenone-4, 4′-bisglyceryl ether, (e) 2-hydroxy-4-methoxy-5-sulfobenzophenone sodium salt, (f) 2,2′-dihydroxy-4, 4'-dimethoxy-5-sulfobenzophenone sodium salt, (to) 2,2'-dihydroxy-4-methoxybenzophenone-5-sulfonic acid, (thi) 2- (2'-hydroxy-4'-methoxy-5 ' -Sulfophenyl) benzotriazole sodium salt, (ri) 2- (2'-hydroxy-4'-butoxy-5'-sulfophenyl) benzoto Riazole sodium salt, and the like.

  Of these, benzophenone and nonionic ones, that is, (i) to (d) are particularly preferable.

  The amount of the chelating agent and / or ultraviolet absorber used is usually 0.001 to 10% by mass, preferably 0.01 to 5% by mass, based on the solid content of the water-absorbent resin. When the amount used exceeds 10% by mass, not only an effect commensurate with the use cannot be obtained, but also the problem arises that the amount of absorption or the required amount of group 8 transition metal ions becomes large. . Moreover, when the said usage-amount is less than 0.001 mass%, the durable improvement effect of a water absorbing resin is not acquired.

  Next, the drying process will be described. A drying process is a process of drying the said hydrogel polymer. The drying method at this time is not particularly limited. For example, conventional drying methods such as aeration band dryers, rotary aeration dryers, agitation dryers, fluidized bed dryers, and vibration fluidized dryers are used. A drying method can be suitably used.

  Moreover, it is preferable to perform high-humidity drying using these dryers. High-humidity drying is drying using the above-mentioned dryer while bringing at least water vapor and a gas having a dew point of 50 to 100 ° C. into contact with an object.

  The temperature at which the hydrogel polymer is dried can be applied as the ambient temperature or the temperature of the hydrogel polymer (material temperature), and is preferably applied as the material temperature of the hydrogel polymer.

  Here, the atmospheric temperature refers to the hot air temperature, and the material temperature refers to the temperature measured by inserting a temperature sensor near the center in the thickness direction in a state where the water-containing gel polymer is stacked by 40 mm or more and dried. Point to.

  The temperature for drying the hydrogel polymer is preferably 80 ° C. or higher and 150 ° C. or lower, more preferably 100 ° C. or higher and 145 ° C. or lower, and particularly preferably 120 ° C. or higher and 140 ° C. or lower. preferable. When the drying temperature is less than 80 ° C., it is not preferable because much time is required for reducing the residual monomer and drying. Further, if the drying temperature exceeds 150 ° C., the water present in the water-containing gel polymer suddenly boils, and the shape of the water-absorbent resin after drying becomes indefinite, which may impair the display effect. Absent.

  Moreover, when drying the water-containing gel polymer, the material temperature is rapidly increased, so that the adhesion preventive agent is dried at the cut gel surface layer portion by the rapid drying at the cut gel surface layer portion of the adhesion preventive agent. Since it progresses all at once, dust components are likely to be generated, and dust may increase in the resulting water-absorbent resin, there is a need for a drying method that avoids sudden rises in material temperature. There are a technique of using a multi-stage temperature rise and a technique of using a rotary aeration dryer such as a funnel through manufactured by Okawara Manufacturing Co., Ltd.

  Thereby, the dust amount whose particle diameter is 10 micrometers or less with respect to the water-absorbing resin obtained can be reduced. For example, the drying temperature in the first stage may be 10 ° C. or higher and lower than 120 ° C., preferably 30 ° C. or higher and lower than 115 ° C., and more preferably 50 ° C. or higher and lower than 110 ° C. The drying time for the first stage is preferably 10 minutes to 5 hours (preferably 10 minutes to 2 hours, more preferably 10 minutes to 1.5 hours).

  The drying temperature in the second stage can be 120 ° C. or higher and lower than 180 ° C., preferably 130 ° C. or higher and lower than 175 ° C., and more preferably 140 ° C. or higher and lower than 175 ° C. The drying time of the second stage is preferably 10 minutes or more and 5 hours or less, preferably 10 minutes or more and 2 hours or less.

  By setting the drying temperature in the first stage in this way, the hydrogel polymer is dried in advance at a temperature of less than 120 ° C. Therefore, when drying at the drying temperature in the second stage, the hydrogel form It is possible to suppress bumping of water existing inside the polymer. Further, when the temperature is raised to the drying temperature in the second stage, bumping can be suppressed as described above, so that drying is performed at a high temperature of 120 ° C. or more and less than 180 ° C. without being accompanied by deformation of the obtained water absorbent resin. Can be performed. Thereby, the shape of the water-absorbing resin obtained is stable, and a water-absorbing resin excellent in display effect can be obtained.

  In addition, when the drying temperature of the 1st step is 120 degreeC or more, there exists a possibility that the dust amount of the obtained water absorbing resin may increase. Further, when the drying temperature in the second stage is less than 120 ° C., it is necessary to spend a lot of time for drying. When the drying temperature in the second stage is 180 ° C. or more, the above hydrous gel The water present in the inside of the polymer is bumped, and the resulting water-absorbent resin becomes indefinite, which may be unfavorable, and the display effect may be impaired.

When using a rotary ventilation dryer (for example, a funnel through Okawara Seisakusho Co., Ltd.), the drum rotation speed is 5 min ^-1 or more and 20 min ^-1 or less, depending on the amount of hydrogel polymer to be dried. The wind speed is preferably from 0.5 m / s to 20 m / s, and the hot air temperature is preferably from 150 ° C. to 200 ° C. By using the funnel through, it is possible to continuously dry the material temperature, so that it is possible to reduce the amount of dust after drying the hydrogel polymer.

  By such a drying method, it is possible to effectively reduce the dust amount of the obtained water absorbent resin.

  The water content of the water-absorbent resin after drying is preferably 5% by mass to 30% by mass, more preferably 10% by mass to 25% by mass, and particularly preferably 15% by mass to 25% by mass. In order to make the water content less than 5% by mass, a relatively long drying time is required, which is not preferable. On the other hand, when the water content exceeds 30% by mass, the water-absorbing resins are easily reattached when the water-absorbing resins are stored for a long period of time, and the water content of the water-absorbing resin itself is increased so that the water can be absorbed. It is not preferable because the amount of

  The content of the residual monomer in the water absorbent resin is 0 mass ppm or more and 300 mass ppm or less, more preferably 0 mass ppm or more and 200 mass ppm or less, and particularly preferably 0 mass ppm or more and 100 mass ppm or less. When the content exceeds 300 ppm by mass, it is not preferable because it may affect the hygienic and odor problems of the water absorbent resin. The method for measuring the residual monomer will be described in Examples.

  The mass average particle diameter of the water absorbent resin according to the present invention is preferably 2 mm or more and 10 mm or less, more preferably 2.5 mm or more and 9.0 mm or less, and 3.0 mm or more and 8.0 mm or less. Further preferred. If the mass average particle diameter is less than 2 mm, it is not preferable because a large amount of residual monomer may be contained, and if it exceeds 10 mm, the moisture content becomes high and it tends to reattach when stored for a long period of time, and This is not preferable because a relatively long drying time is required.

  The logarithmic standard deviation value of the particle size distribution of the water absorbent resin according to the present invention is preferably 0 to 0.25 or less, more preferably 0 to 0.23 or less, and 0 to 0.20. More preferably, it is as follows. If the logarithmic standard deviation value is within this range, the particle size distribution of the particulate hydrous gel is very sharp, indicating that uniform particles are obtained as a whole.

  In the present invention, the vicinity of the surface of the particulate water-absorbing resin may be subjected to a crosslinking treatment, whereby a water-absorbing resin having a large absorption capacity under load can be obtained. For the surface cross-linking treatment, a cross-linking agent capable of reacting with a functional group of the water-absorbent resin, for example, an acidic group, may be used, and a known cross-linking agent usually used for the application is exemplified.

  Examples of the surface crosslinking agent include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3- Pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentadiol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, Multivalents such as 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol Polyol compounds; ethylene glycol diglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol and other polyvalent epoxy compounds; ethylenediamine, diethylenetriamine, triethylenetetramine, tetra Polyvalent amine compounds such as ethylenepentamine, pentaethylenehexamine, and polyethyleneimine, and inorganic or organic salts thereof (for example, aditinium salts); polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 1 Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one, 4 Methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1, 3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6 -Alkylene carbonate compounds such as dimethyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopan-2-one; epichlorohydrin, epi Haloepoxy compounds such as bromhydrin and α-methylepichlorohydrin, and polyvalent amine adducts thereof (for example, Kaymen (registered trademark) manufactured by Hercules); zinc, calcium, magnesium , Aluminum, iron, polyvalent metal compound hydroxide or chlorides such as zirconium and the like.

  Among these, polyhydric alcohol compounds, polyhydric epoxy compounds, polyhydric amine compounds and their salts, and alkylene carbonate compounds are preferred. These surface crosslinking agents may be used alone or in combination of two or more.

  The amount of the surface crosslinking agent is preferably 0.001% by mass to 10% by mass and more preferably 0.01% by mass to 5% by mass with respect to 100% by mass of the water absorbent resin.

  A normal dryer or a heating furnace can be used for the heat treatment. For example, a thin stirring dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, a flash dryer, an infrared dryer, a vibrating fluid dryer, and the like can be given. In that case, the heat treatment temperature is preferably 40 ° C. or higher and 250 ° C. or lower, more preferably 90 ° C. or higher and 230 ° C. or lower, and further preferably 120 ° C. or higher and 220 ° C. or lower. The heat treatment time is usually preferably from 1 minute to 120 minutes and more preferably from 10 minutes to 60 minutes.

  A tetrahedron having a mass average particle diameter of 2 mm or more and 10 mm or less obtained by drying a particulate hydrogel polymer having a shape of tetrahedron or more and dodecahedron or less having a mass average particle diameter of 3 mm or more and 10 mm or less according to the present invention. The water-absorbing resin particles having a shape of a dodecahedron or less may be pulverized, classified and granulated, and used as an irregularly crushed water-absorbing resin.

  The water-absorbent resin obtained by the production method of the present invention is composed of inorganic fine particles such as titanium oxide, silicon oxide and activated carbon; organic fine particles such as polymethyl methacrylate; hydrophilic fibers such as pulp; and synthetic fibers such as polyethylene fibers and polypropylene fibers. Fiber: Surfactant such as polyethylene glycol and polyoxyethylene sorbitan monostearate may be added during or after the production process.

  The novel water-absorbing resin of the present invention can be obtained, for example, by taking the above-mentioned production method as an example, and the production method of the present invention can produce the water-absorbing resin most efficiently. A resin may be obtained.

(Manufacturing method 2)
After cutting the hydrous gel or dried product thereof, the case where the mass average particle size of the hydrous gel deviates from 3 mm or more and 10 mm or less, the case where the mass average particle size of the dry product deviates from 2 mm or more and 10 mm or less, The manufacturing method which selects only this-application water-absorbing resin, when the ratio of the particle | grains of the shape of the above-mentioned dodecahedron or less is 50 mass% or more and 100 mass% or less.

  As a manufacturing method which sorts out only the above-mentioned water-absorbing resin of the present application, for example, a method of sorting by using a sorter described later can be mentioned. Moreover, it can also sort using the rotary sorter mentioned later.

(Manufacturing method 3)
A polymerized container obtained by polymerizing the above monomer and having a mass average particle diameter of 3 mm or more and 10 mm or less and having a shape of tetrahedron or more and dodecahedron or less without undergoing a cutting step. To obtain a hydrogel polymer having a mass average particle diameter of 3 mm or more and 10 mm or less and a tetrahedron or more and a dodecahedron or less.

(2. Cutting machine)
The cutting machine which concerns on this invention is a cutting machine for cut | disconnecting a sheet-like hydrogel polymer (gel sheet), Comprising: At least 1 or more vertical machine which cuts the said hydrogel polymer vertically (width cut) A cutting blade, at least one transverse rotary blade and fixed blade that crosses (length-cuts) the hydrated gel polymer, and an adhesive agent for the vertical cutting blade, horizontal cutting blade, fixed blade, and / or One or more spraying and / or spraying means for spraying and / or spraying the hydrogel polymer. Therefore, when the cutting process is performed using this cutting machine, at least a part of the surface is mainly composed of hexahedral particles having a square shape and a smooth surface. A hydrogel polymer coated with an inhibitor can be obtained.

  Hereinafter, the cutting machine will be described with reference to FIGS. FIG. 3 is a longitudinal sectional view showing the configuration of the cutting machine according to the present embodiment. As shown in FIG. 3, the cutting machine 100 includes vertical cutting blades (roll cutters) 1, 2, scrapers 3 and 4, transverse cutting blades 200, fixed blades 8, spraying and / or spraying device (spraying and / or spraying means). ) 9, 10, 11, 12, a gel sheet inlet 13, and a casing 14. If necessary, spraying and / or spraying devices 9 ', 10' may be provided. The cross-cutting rotary blade 200 includes a rotary shaft 5 for cross-cutting (length cutting), a blade 6, and a cross-cutting rotary body 7. Further, the transverse cutting blade 200 and the fixed blade 8 constitute a pinching device.

  The spraying and / or spraying device (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′ includes an adhesion preventing agent as a fixed blade 8, a blade 6, a vertical cutting blade (roll cutter) 1, 2 and / or for spraying and / or spraying a hydrogel polymer (not shown). Since the cutting machine 100 is provided with a spraying and / or spraying device (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′, the water-containing gel polymer is efficiently treated with an adhesion preventive agent. It can coat | cover well and can prevent the adhesion | attachment of the water-containing gel-like polymers after a cutting process effectively.

  That is, the adhesion preventing agent sprayed and / or sprayed from the spraying and / or spraying device (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′ is applied to the fixed blade 8, the blade 6, By attaching to the vertical cutting blade (roll cutter) 1, 2 and / or the hydrogel polymer, the fixed blade 8, the blade 6, the vertical cutting blade (roll cutter) 1, 2 and / or the hydrogel polymer Since at least a part of the surface is coated, it is possible to effectively prevent adhesion of the hydrogel polymers after the cutting step.

  The method for supplying the adhesion preventing agent to the spraying and / or spraying device (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′ is not particularly limited, and a conventionally known pump Etc. (not shown). Further, the number of spraying and / or spraying devices (spraying and / or spraying means) in FIG. 3 is the number of spraying and / or spraying devices (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′. However, the present invention is not limited to this, and can be appropriately increased or decreased according to the efficiency of spraying and / or spraying.

  Further, the position of the spraying and / or spraying device (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′ is not particularly limited. In order to improve the coating efficiency of the coalescence, it is preferably a position where spraying and / or spraying to the hydrogel polymer, the blade 6, the fixed blade 8, and the vertical cutting blades (roll cutters) 1 and 2 is possible.

  In FIG. 3, the anti-adhesive agent sprayed and / or sprayed from the spraying and / or spraying devices (spraying and / or spraying means) 9 and 10 adheres mainly to the vertical cutting blades (roll cutters) 1 and 2. , Before the hydrogel polymer supplied from the gel sheet inlet 13 is cut by passing between the longitudinal cutting blades (roll cutters) 1 and 2, simultaneously with the cutting and / or after being cut, The vertical cutting blades (roll cutters) 1 and 2 are transferred to the hydrogel polymer, and the hydrogel polymer is coated.

  Further, the adhesive agent sprayed and / or sprayed from the spraying and / or spraying device (spraying and / or spraying means) 9 and 10 is a water-containing gel cut mainly by vertical cutting blades (roll cutters) 1 and 2. It adheres directly to the polymer and coats the hydrogel polymer.

  Further, the anti-adhesive agent sprayed and / or sprayed from the spraying and / or spraying devices (spraying and / or spraying means) 11 and 12 adheres mainly to the blade 6, the fixed blade 8, and the transverse rotating body 7, and contains water. Before the gel polymer is cut by the blade 6 and the fixed blade 8, simultaneously with the cutting and / or after being cut, the gel polymer is mainly transferred from the blade 6 and the fixed blade 8 to the water-containing gel polymer. Cover the gel polymer.

  Further, spraying and / or spraying from spraying and / or spraying devices (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′, vertical cutting blades (roll cutters) 1, 2, blade 6 The adhesion preventive agent attached to the members of the cutting machine 100 such as the transverse rotating body 7 prevents the hydrated gel polymer from adhering to these members and retains the functions such as the cutting force of these members. Also plays a role.

  In addition, as said spraying and / or spraying device (spraying and / or spraying means) 9, 10, 11, 12, 9 ′, 10 ′, an air mixing type spraying device such as an atomizer, 1 fluid nozzle, 2 fluid nozzle, etc. And it can carry out using conventionally well-known spraying and / or spraying means, such as a liquid injection pump, and is not specifically limited.

  The crossing (length cutting) rotary shaft 5 is for rotating the crossing rotary body 7. The power for rotating the rotary shaft 5 for transverse cutting (length cutting) is not particularly limited, and a known motor or the like may be used, or it may be rotated manually. Further, in FIG. 3, the rotation direction of the rotary shaft 5 for transverse cutting (length cutting) is clockwise, but is not limited to this.

  The transverse rotator 7 is provided with a blade 6 on the outer peripheral portion, and operates along with the rotation of the rotary shaft 5 for transverse (length-cut). That is, in FIG. 3, there are two types, a transverse cutting blade 200 composed of a rotating shaft 5 for cutting (length cutting), a blade 6, and a transverse rotating body 7, and vertical cutting blades (roll cutters) 1 and 2. The rotary blade is provided.

  The ratio between the circumferential speed of the longitudinal cutting blades (roll cutters) 1 and 2 and the circumferential speed of the transverse cutting blade 200 is determined by the length of the hydrogel polymer to be cut. The peripheral speed is determined in consideration of the influence of the rigidity, temperature, etc. of the hydrogel polymer formed into a strand-like strip by longitudinal cutting. In general, when the peripheral speed is too slow, cutting tends to be difficult and the smoothness of the cut surface tends to decrease, and when the peripheral speed is too high, the cut gel becomes a certain size. It is hard to become, and there exists a tendency for the dimension of a cut piece to become unsteady.

  The blade 6 is used for horizontally cutting (length cutting) the hydrogel polymer cut by the vertical cutting blades (roll cutters) 1 and 2 between the fixed blade 8. The arrangement and the number of blades 6 are not particularly limited, but are preferably about 1 to 10 at a uniform position, and the number is selected mainly in consideration of the cutting speed and the cutting length. In consideration of balance, the number is often an even number, but may be an odd number.

  The fixed blade 8 is used to cross the water-containing gel polymer cut by the vertical cutting blades (roll cutters) 1 and 2 while being sandwiched between the blades 6. The clearance between the fixed blade 8 and the blade 6 is not particularly limited, but is preferably 0.005 mm or more and 0.05 mm or less, more preferably 0.01 mm or more and 0.04 mm or less. It is particularly preferable that the distance is from 01 mm to 0.03 mm.

  If the clearance is less than 0.005 mm, the clearance is too narrow, and the cutting edges hit against each other due to changes in temperature and the like, resulting in wear and damage. If the clearance exceeds 0.05 mm, the clearance is too wide, so that it is difficult to cut the hydrogel polymer, which is not preferable.

  The vertical cutting blades (roll cutters) 1 and 2 are used for vertical cutting (width cutting) of the hydrogel polymer supplied from the gel sheet inlet 13. The longitudinal cutting blades (roll cutters) 1 and 2 have a tendency that the diameter of the blade is determined depending on the sheet width to be longitudinally cut. When the sheet width increases, the accuracy of the cutting width is maintained and the deflection of the blade is reduced. Therefore, the diameter of the blade is increased.

  FIG. 5 is an explanatory view showing the configuration of the vertical cutting blades (roll cutters) 1 and 2 as viewed from above. FIG. 6 is an explanatory diagram regarding the vertical cutting blade (roll cutter) 1 and the meshing portion, and FIG. 7 is an enlarged explanatory diagram of the meshing portion shown in FIG. On the surfaces of the vertical cutting blades (roll cutters) 1 and 2, as shown in FIG. 5 and more specifically in FIGS. 6 and 7, the cutter blades are formed in a concavo-convex shape so as to engage each other. . The rotary shafts 15 and 16 are for transmitting rotational force to the vertical cutting blades (roll cutters) 1 and 2.

  The vertical cutting blades (roll cutters) 1 and 2 that mesh with each other have, for example, the same dimensions and rotate in the meshing direction at the same rotational speed. The width, depth, and height of the irregularities of the blades formed so as to engage with each other may be determined depending on the size desired for the hydrogel polymer. For example, the width (X1) in FIG. 7 is 2 mm or more and 10 mm or less. Even when the depth of the concave portion (X4) is about 10 mm to 15 mm and the height of the convex portion (X5) is about 10 mm to 15 mm, and the concave portion and the convex portion are engaged most deeply, the hydrated gel is cut. It is usually formed so that the gap ((X3) in FIG. 7) necessary for the passage of the polymer is about 10 mm or more and 25 mm or less.

  The vertical cutting blades (roll cutter) 1 and 2 are formed in such a shape, and two vertical cutting blades are used by using the rotary shafts 15 and 16 of the vertical cutting blades 1 and 2 shown in FIG. (Roll cutter) 1 and 2 are rotated, the hydrogel polymer supplied from the gel sheet inlet 13 is bitten and cut, and the hydrogel polymer is easily cut vertically by feeding it downward. For example, it can be shortened in a strand shape.

  In order to supply the hydrogel polymer to the vertical cutting blades (roll cutters) 1 and 2, the hydrogel polymer is continuously taken out from the movable support, for example, the other end of the endless belt. (Roll cutter) When continuously carried out using a method of biting into 1 and 2, the entire process can be continued and the production efficiency can be improved.

  Next, a method of traversing a strand that has been shortened will be described. The strands of the hydrogel polymer cut into, for example, a short shape by the vertical cutting blades (roll cutters) 1 and 2 that rotate in the direction of meshing with each other, are the vertical cutting blades (roll cutters) at the upper edges of the scrapers 3 and 4. ) It peels from the outer peripheral part of the inner blades 1 and 2 (A shown in FIG. 6), descends between the scraper 3 and the scraper 4, and reaches the position of the fixed blade 8 provided at the lower end of the scraper 4. Normally, the strands of the hydrogel polymer do not adhere to the outer cutters (B shown in FIG. 6) of the vertical cutters (roll cutters) 1 and 2.

  The scrapers 3 and 4 are preferably made of a material that does not cause clogging due to adhesion of strands of a hydrogel polymer that has been cut into short shapes, or is preferably coated. It is particularly preferable to perform coating from the viewpoint of cost. Specifically, in the vertical cutting blades (roll cutters) 1 and 2, the transverse rotary blade 200, the casing 14, and the scraper 3 and 4 shown in FIG. 4, the scraper 3 'and 4 that are in contact with the strands of the hydrogel polymer. It is preferable to coat '.

  Examples of the coating method include plating using a metal-based material, thermal spraying, vapor deposition, and the like, and a heat-treating method using a resin-based material, but are not particularly limited.

  Examples of coating materials include non-adhesive paints and lubricating paints as resin-based materials. Specifically, PTFE (polytetrafluoroethylene) paint system, FEP (tetrafluoroethylene / hexafluoropropylene copolymer) Fluorine paints such as paint), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) paint system, fluororesin-modified paint system (one coat enamel), ETFE (ethylene / tetrafluoroethylene), and silicone There are paints, polyvinyl chloride paints, polyamide paints and the like.

  As a fluororesin modified paint system (one coat enamel), for example, DuPont's trade name 420-105 ONE COAT GRAY can be used. The components and content of this paint are: fluororesin 10-15 wt%, organic binder resin 10-15 wt%, methyl isobutyl ketone 15-25 wt%, diacetone alcohol 1-5 wt%, N-methylpyrrolidone 50-55 wt%, oxidation Titanium is 5 to 10 wt%.

  In addition, the metal material is not limited as long as it is a material to which the hydrogel polymer does not adhere. However, for example, Kanigen plating obtained by electroless chemical treatment of nickel and phosphorus, fluorine-based in the Kanigen plating film Cananiflon plating in which resin fine particles are uniformly dispersed and co-deposited, ceramic Kanigen plating in which fine particles such as metal oxide and carbide are uniformly co-deposited in the Kanigen plating film, titanium, and the like can be used. Titanium can be coated with TiN, TiCN, TiAlN, CrN or the like by, for example, vacuum deposition, sputtering, or ion plating.

  It is preferable to use a durable titanium coating for the vertical cutting blades (roll cutters) 1, 2, blade 6, and fixed blade 8, where wear is a problem, and a portion of the scrapers 3, 4. In addition, it is preferable to use a fluorine-based paint for a portion where wear such as a boulder or casing of a rotary blade is less likely to be a problem.

  The short strand that has reached the position of the fixed blade 8 and has come out below the position is cut by the cutting force acting between the blade 6 and the fixed blade 8 and has a square shape and a smooth surface. The main component is a hexahedron having a flat surface, and preferably a strip having a mass average particle diameter of 3 mm to 10 mm and a logarithmic standard deviation value of particle size distribution of 0.25 or less.

  The cross-sectional shape in the width direction of the short-shaped object is the machine dimension after assembly of the vertical cutting blades (roll cutters) 1 and 2, that is, the uneven width (X1) of the blade, the depth of the recess (X4), and the height of the protrusion It is determined by the height (X5), the depth of engagement (X2), and the rotational speed of the vertical cutting blades (roll cutters) 1 and 2. Then, the rotational speed of the vertical cutting blades (roll cutters) 1, 2, the rotational speed of the transverse rotary body 7 that rotates at a speed corresponding to the cutting length, and the number of blades 6 provided on the transverse rotary body 7. By adjusting, the mass average particle diameter of the hydrogel polymer can be determined.

  As described above, the scrapers 3 and 4 are for peeling the hydrogel polymer from the outer peripheral portion of the inner cutter (A shown in FIG. 6) of the vertical cutters (roll cutters) 1 and 2. The gel sheet inlet 13 is for supplying a hydrogel polymer that has been statically polymerized in a sheet form to the longitudinal cutting blades (roll cutters) 1 and 2. The casing 14 is for preventing scattering of the cut hydrogel polymer, and the shape thereof is not particularly limited.

  In the above description, the fixed blade 8 is provided at the lower end of the scraper 4 and performs cross-cutting. However, the number and installation positions of the fixed blade 8 are not necessarily limited to this, and are not particularly limited. Further, the fixed blade 8 may be used not only for cross cutting but also for vertical cutting.

  In the cutting machine 100, it is preferable to lower the temperature of the hydrogel polymer at the time of cutting and / or control the tension of the gel sheet in order to increase the cutting efficiency and cut into a uniform shape. The preferred temperature of the hydrogel polymer during cutting is 70 ° C. or less, more preferably 60 ° C. or less, more preferably 50 ° C. or less, still more preferably 40 ° C. or less, particularly preferably 30 ° C. or less, and most preferably 20 ° C. It is as follows.

  Since the gel sheet is pulled by the vertical cutting blades (roll cutters) 1 and 2 when entering the cutting machine 100, tension is applied and the width thereof is usually narrowed. Therefore, the tension of the gel sheet can be indirectly controlled by the width of the gel sheet. The width of the gel sheet varies depending on the cutting speed and the transfer means until cutting, but the width of the gel sheet immediately before entering the cutting machine is preferably maintained at 90% or more of the width of the gel sheet in a state where no tension is applied. When the tension is excessively applied, the gel sheet before cutting is greatly deformed, and therefore, the width of the gel sheet after cutting is not uniform, which is not preferable.

  Examples of the method for lowering the temperature of the hydrogel polymer include a method of sufficiently cooling in the polymerization step, a method of forcibly cooling with cold air before the cutting step, and / or a method of using a cooling belt. . As the cooling belt, for example, there is a method of applying cold water from the lower surface (inner side) of the belt while transferring the gel sheet to the upper part of the SUS endless belt placed horizontally.

  In addition, when the cutting process is performed through dry air or cold air, preferably dry air or cold air at 25 ° C. or less, the water-containing polymer is sticky due to frictional heat at the time of cutting, or the water-containing gel is cut. The adhesion of the polymer can be further reduced. Specific examples of the cutting machine include a corner cutting pelletizer PM-300 manufactured by Tanaka Co., Ltd.

(3. Mixer)
In addition, in order to make the coating of the anti-adhesive agent on the cut hydrogel polymer uniform and / or improve the anti-adhesion property of the hydrogel polymer by adding an anti-adhesive agent It is preferable that the later hydrogel polymer is further mixed by a mixing device. Alternatively, a mixing device can be used for mixing the chelating agent and / or the ultraviolet absorber.

  The apparatus used in this case may be an ordinary apparatus, such as a Ladige mixer, a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a nauter mixer, a V mixer, and a ribbon type. Examples include a mixer, a double-arm kneader, a fluid mixer, an airflow mixer, a rotating disk mixer, a roll mixer, a rolling mixer, and the like, either a continuous mixing system or a batch mixing system may be used. . In order to stabilize the adhesion preventing property, the batch time is preferable in order to make the residence time in the apparatus and the spray amount of the adhesion preventing agent constant, and the use of a Laedige mixer is preferable as the apparatus.

  Examples of the mixing method when a batch-type Ladige mixer is used include the following methods. That is, after a predetermined amount of the hydrogel polymer cut by the cutting machine 100 is put into a Laedige mixer, it is mixed while spraying the anti-adhesive agent.

  It is also possible to perform mixing for a predetermined time before spraying the anti-adhesion agent (preliminary mixing) and / or to continue mixing after the spraying is completed (post-process). In the premixing, the water-containing gel can be crushed to coat the water-containing gel more uniformly with the anti-adhesive agent.

Upon mixing, the rotation speed of the blades 100 min ^-1 or 200 min ^-1 or less, the rotational speed of the side chopper is preferably less 1000min ^-1 or 4000 min ^-1. The mixing time varies depending on the capacity of the Ladige mixer and the filling rate of the material, but the pre-mixing is 0 second to less than 2 minutes, the main mixing is 10 seconds to less than 3 minutes, and the post-mixing is 0 seconds to less than 5 minutes. Preferably there is.

  Moreover, it is preferable to use or coat a material that prevents adhesion of the hydrogel polymer to the inside of the apparatus. It is particularly preferable to perform coating from the viewpoint of cost.

  Examples of the coating method include plating using a metal-based material, thermal spraying, vapor deposition, and the like, and a heat-treating method using a resin-based material, but are not particularly limited.

  Examples of coating materials include non-adhesive paints and lubricating paints as resin-based materials. Specifically, PTFE (polytetrafluoroethylene) paint system, FEP (tetrafluoroethylene / hexafluoropropylene copolymer) Fluorine paints such as paint), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) paint system, fluororesin-modified paint system (one coat enamel), ETFE (ethylene / tetrafluoroethylene), and silicone There are paints, polyvinyl chloride paints, polyamide paints and the like.

  As a fluororesin modified paint system (one coat enamel), for example, DuPont's trade name 420-105 ONE COAT GRAY can be used. The components and content of this paint are: fluororesin 10-15 wt%, organic binder resin 10-15 wt%, methyl isobutyl ketone 15-25 wt%, diacetone alcohol 1-5 wt%, N-methylpyrrolidone 50-55 wt%, oxidation Titanium is 5 to 10 wt%.

  In addition, the metal material is not limited as long as it is a material to which the hydrogel polymer does not adhere. However, for example, Kanigen plating obtained by electroless chemical treatment of nickel and phosphorus, fluorine-based in the Kanigen plating film Cananiflon plating in which resin fine particles are uniformly dispersed and co-deposited, ceramic Kanigen plating in which fine particles such as metal oxide and carbide are uniformly co-deposited in the Kanigen plating film, titanium, and the like can be used. Titanium can be coated with TiN, TiCN, TiAlN, CrN or the like by, for example, vacuum deposition, sputtering, or ion plating.

  In addition, these mixers can be used also for mixing of the surface cross-linking agent in the surface cross-linking of the water-absorbent resin. Further, the anti-adhesive agent is added by spraying and / or spraying, but conventionally known sprays such as an atomizer, an air mixing type spraying device such as a one-fluid nozzle, a two-fluid nozzle, a liquid injection pump, a brush, and a roller are used. It can be performed using a spraying means and / or is not particularly limited.

(4. Water-absorbing resin)
In one embodiment, the water-absorbent resin according to the present invention polymerizes an ethylenically unsaturated monomer containing 30 mol% or more and 100 mol% or less of acrylic acid and / or acrylate, and is tetrahedral or more and 12 or more. A water-absorbent resin obtained by drying a hydrogel polymer that is cut so that particles having a shape of a plane or less are 50% by mass or more with respect to the mass of the hydrogel polymer, and is a mass-average particle The diameter is 2 mm or more and 10 mm or less, and the logarithmic standard deviation value of the particle size distribution is 0 or more and 0.25 or less.

  Moreover, it is preferable that content of the residual monomer is 0 mass ppm or more and 300 mass ppm or less.

  The above-mentioned acrylic acid and / or acrylate refers to acrylic acid-based monomers described above and refers to acrylic acid and / or water-soluble salts of acrylic acid. Of the ethylenically unsaturated monomers, use of a monomer containing an acrylate monomer as a main component is preferable because the water absorption performance and safety of the resulting hydrogel are further improved.

  Acrylates are alkali metal salts, alkaline earth metal salts of acrylic acid having a neutralization rate in the range of 30 mol% to 100 mol%, preferably in the range of 50 mol% to 99 mol%, Ammonium salt, hydroxyammonium salt, amine salt, alkylamine salt are shown. Of the water-soluble salts exemplified above, sodium salts and potassium salts are particularly preferred.

  When the neutralization rate is 70 mol% or more and 100 mol% or less, the polymerization reaction proceeds particularly smoothly and the yield of the water-absorbent resin is increased, which is preferable. These acrylate monomers may be used alone or in combination of two or more.

  As described above, when the hydrated gel polymer formed into a sheet is vertically cut and crossed, particles having a shape of tetrahedron or more and dodecahedron or less are 50% by mass with respect to the mass of the hydrated gel polymer. A hydrogel polymer having a content of 100% by mass or less is obtained. Among the water-absorbent resins obtained by drying this, the water-absorbent resin having a mass average particle diameter of 2 mm to 10 mm and a logarithmic standard deviation value of the particle size distribution of 0.25 or less is Since this is a dried hydrogel polymer which is homogeneous as a whole, it has a good dry state.

  Moreover, if content of a residual monomer is 0 mass ppm or more and 300 mass ppm or less, high-quality water-absorbing resin with very little content of a residual monomer and few odor and hygiene problems can be obtained.

  The water-absorbing resin having a water content of 5% by mass to 30% by mass with respect to the mass of the water-absorbing resin is obtained by drying a water-containing gel-like polymer having a water content suitable for the reaction between the residual monomer and the polymerization initiator. Therefore, the water-absorbing resin having a residual monomer content of 0 ppm by mass to 300 ppm by mass can be obtained more reliably.

  In one embodiment, the water absorbent resin according to the present invention is a water absorbent resin obtained by drying a hydrogel polymer having a polyhedral shape, and is classified as a polyvalent metal salt, a polyhydric alcohol, or a surfactant. The water-absorbent resin is characterized in that at least a part of the surface thereof is coated with an anti-adhesive agent containing at least one of the compounds formed.

  Such a water absorbent resin can be obtained by the method for producing a water absorbent resin according to the present invention described above. The spray amount and / or the spray amount of the adhesion inhibitor is preferably 0.0015% by mass to 35% by mass with respect to the solid content of the water absorbent resin.

  When the spray amount and / or the spray amount is less than 0.0015% by mass, the water-containing gel polymer cannot be sufficiently covered, and the water-containing gel polymers are likely to adhere to each other. Accordingly, even if the hydrogel polymer is dried, it tends to be agglomerated and is not preferable because drying is not performed smoothly. When the spray amount exceeds 35% by mass, it is difficult to handle due to stickiness and / or scattering during drying is not preferable. Moreover, since there is too much usage-amount and it is uneconomical, it is not preferable.

  In one embodiment, in the water-absorbent resin according to the present invention, hexahedral particles having a square shape and a smooth surface are 50% by mass or more based on the solid content of the water-absorbent resin. included. The other particles are not particularly limited as long as the shape is a polygonal shape having a square shape and a smooth surface, and are preferably particles having a shape of tetrahedron or more and dodecahedron or less. . Furthermore, in order to improve durability, the water-absorbent resin according to the present invention preferably contains a chelating agent and / or an ultraviolet absorber.

(5. Sorter)
The sorter according to the present embodiment sorts the obtained water-absorbent resin according to a desired mass average particle diameter after the drying step. As an example, FIG. 8 shows a schematic configuration from the side of a sorter 300 that is a rotary sorter.

  The sorter 300 includes a water absorbent resin inlet 21 for introducing the water absorbent resin, a first sorting unit 19 for removing the small-sized water-absorbing resin, and a large-sized water-absorbing resin for removing the water-absorbing resin. A second sorting unit 17.

  The water-absorbing resin of the small atypical material is a water-absorbing resin that is smaller than the mass particle diameter of the water-absorbing resin after drying and that can pass through a mesh or punching of 0.1 mm or more and 9 mm or less. For example, dry hydrated gel polymer cut twice, scraped, dust, etc. are applicable. Further, the large variant is a water absorbent resin that is larger than the mass average particle diameter of the water absorbent resin after drying and cannot pass through a mesh or punching of 2.0 mm or more and 10 mm or less, For example, those in which two or more water-absorbing resins are aggregated, incompletely cut, and the like are applicable.

  By passing through the sorting process using the sorter 300, the mass average particle diameter is 2 mm or more and 10 mm or less, and the logarithmic average standard deviation can be 0 or more and 0.25 or less.

  In order to change the diameter of the water-absorbing resin of the small-sized product to be removed and the water-absorbing resin of the large-sized material, the diameter of the punching 18 provided in the second sorting unit 17 and the mesh opening of the first sorting unit 19 are described. Can be done by changing.

  The first sorting unit 19 and the second sorting unit 17 are cylindrical, and a weir 22 having an inner diameter smaller than that of the first sorting unit 19 and the second sorting unit 17 is preferably provided between them. Further, the second sorting unit 17 is provided with a punching 18 that is an opening, and has one gas injection nozzle 20 that is a gas injection mechanism for injecting gas to the water absorbent resin in the first selection unit 19. More than that. Of course, the installation location and the number of the gas injection nozzles 20 may be set as appropriate and are not particularly limited. By spraying gas from the gas injection nozzle 20 from, for example, at least one of the upper surface, the side surface, the lower surface, and the material input port 21 of the first selection unit 19, it is possible to further remove small anomalies.

  The material insertion port 21 is an opening through which a water absorbent resin is introduced. The material inlet 21 and the first sorting unit 19 are adjacent to each other, and the water absorbent resin moves to the first sorting unit 19 as it is fed. The 1st selection part 19 is for removing the water absorbent resin of the small particle size in the particle size distribution of water absorbent resin, and is comprised by the cylindrical net | network.

  The filling rate of the material of the first sorting unit 19 is 5% by volume or more and 40% by volume or less, preferably 10% by volume or more and 30% by volume or less, more preferably 10% by volume of the water-absorbing resin with respect to the volume of the first sorting unit 19. % Or more and 20% by volume or less. When the filling rate is less than 5% by volume, the residence time of the water-absorbent resin in the first sorting unit 19 is short, so that the effect of removing small irregularities becomes insufficient. On the other hand, when the filling rate exceeds 40% by volume, the volume of the water-absorbent resin in the first sorting unit 19 is too large, so that the effect of removing small irregularities is reduced.

  The diameter of the mesh of the first selection unit 19 is not particularly limited, but when obtaining a spider-like water-absorbing resin having a mass average particle diameter of 4.0 mm, it may be 2.0 mm or more and 3.0 mm or less. preferable.

  FIG. 9 shows a cross-sectional view of the first selection unit 19. As shown in FIG. 9, the first sorting unit 19 has a structure that rotates in the direction of the arrow D. In addition, a gas injection nozzle 20 is provided around the first selection unit 19 so that gas is injected in the direction of arrow C. The gas to be injected is not particularly limited, but air is preferably used from the viewpoint of cost. It is preferable to use dry air having a dew point of −10 ° C. or less, particularly preferably dry air having a dew point of −20 ° C. or less. Thus, by rotating the 1st classification | selection part 19, gas can be efficiently injected to the water absorbing resin 24 inside.

  The rotation speed (residence time) of the first sorting unit 19 is 5 rpm to 50 rpm, preferably 10 rpm to 40 rpm, and more preferably 10 rpm to 20 rpm. If it is less than 10 rpm, the material feeding speed is slow, and the filling rate of the water-absorbent resin in the first sorting section 19 is too high, which is not preferable. On the other hand, if it exceeds 30 rpm, the material feeding speed is high, and the filling rate of the water-absorbent resin in the first sorting section 19 is too low.

  Although it does not specifically limit as the gas injection nozzle 20, For example, well-known gas injection mechanisms, such as an atomizer, a 1 fluid nozzle, a wonder gun, can be used. Gas injection may be performed continuously or discontinuously (intermittently).

  Further, hammers 23, 23 a, 23 b may be provided inside the first sorting unit 19 and / or the second sorting unit 17. When the first sorting unit 19 and / or the second sorting unit 17 rotates, the hammers 23, 23a, 23b vibrate in the direction of arrow E, so that the hammers 23, 23a, 23b vibrate and the first sorting unit 19 is vibrated. And / or the second sorting unit 17 vibrates. Due to this vibration, the abnormal material clogged in the mesh of the first sorting unit 19 and / or the second sorting unit 17 is removed from the first sorting unit 19 and / or the second sorting unit 17, so the first sorting unit 19 and / or Alternatively, clogging of the second sorting unit 17 can be prevented. In order to prevent clogging, the first sorting unit 19 and / or the second sorting unit 17 are preferably provided with at least one hammer 23, 23a, 23b.

  It is preferable that a weir 22 is provided between the first sorting unit 19 and the second sorting unit 17. Since the weir 22 has an inner diameter smaller than that of the first sorting unit 19, when the water absorbing resin 24 in the first sorting unit 19 is small, the weir 22 is prevented from moving to the second sorting unit 17. . Therefore, the residence time in the 1st selection part 19 of the water absorbing resin 24 increases, and a small variant can be cut. By cutting the small variant in this way, it becomes difficult for the small variant to be mixed into the resulting water-absorbent resin, so that a water-absorbent resin excellent in display effect can be obtained.

  The second sorting unit 17 has a plurality of punching 18. Since the diameter of the punching 18 is larger than the desired mass-average particle diameter of the water-absorbing resin, and the water-absorbing resin having a diameter larger than the diameter of the punching 18 remains in the second sorting section 17, a large irregular shape is removed. Can do.

  The second sorting unit 17 may have a layered structure of one punching cylinder as shown in FIG. 10, but has a layered structure of a plurality of punching cylinders as shown in FIG. May be. In the sorter 300 shown in FIG. 8 which is an example of the sorter according to the present invention, the cylindrical second sorter 17 further includes the second sorter 17 inside thereof and has a double structure. Further, the second sorting units 17 are opposed to each other. On the other hand, the punching 18 provided in the two layers of the second sorting section 17 is provided so as not to face each other. “The punching 18 does not face each other” means that part of the punching 18 does not face each other.

  FIG. 12 is a schematic perspective view showing a structure in which the second selection unit 17 has a two-layer structure. As shown in FIG. 12, the punching 18 (shown by a solid line) provided in the second sorting unit 17 is the same as the punching 18 (shown by a broken line) provided in the other second sorting unit 17. The structure is not opposite. Further, the interval between the two second sorting portions 17 is preferably 1 to 2 times the mass average particle diameter of the water-absorbent resin, more preferably 1 to 1.8 times. By setting the interval between the second sorting parts 17 in this way, the water absorbent resin having a desired mass average particle diameter can pass through the punching 18. On the other hand, since the long water-absorbing resin remains in the second sorting portion 17, a water-absorbing resin having a uniform mass average particle diameter can be obtained, and a water-absorbing resin excellent in display effect can be obtained.

  The diameter of the punching 18 is not particularly limited, but is preferably 6.0 mm or more and 8.0 mm or less when obtaining a ridged water-absorbing resin having a mass average particle diameter of 4.0 mm.

  For example, in the sorter 300, in order to obtain a spider-like water-absorbing resin having a mass average particle diameter of 4 mm, the mesh diameter of the first sorting unit 19 is set to 2.8 mm as a specific example, and the second layer of the second layer. The diameter of each punching 18 in the sorting unit 17 may be set such that the inner punching diameter is 7 mm, the outer punching diameter is 9 mm, and the clearance between the inner punching and the outer punching is 7 mm.

  Specific examples of the rotary sorter include SPSR-2000, SPSR-1500, SPSR-1000, SPSR-500, SPSR-250, and stock, in which the second sorter 17 manufactured by Seiwa Iron Works Co., Ltd. has a one-layer structure. SPSR-2000W, SPSR-1500W, SPSR-1000W, SPSR-500W, SPSR-250W, etc., in which the second sorting unit 17 manufactured by Seiwa Iron Works Co., Ltd. has a two-layer structure can be used.

By using the sorting machine and the sorting method described above, it is possible to effectively reduce dust having a particle diameter of 10 μm or less from the water-absorbent resin obtained through the drying step. The amount of dust is preferably 0 mg / m ³ or more and 500 mg / m ³ or less, more preferably 0 mg / m ³ or more and 350 mg / m ³ or less. If the amount of dust exceeds 500 mg / m ³ , dust may fly when handling the water-absorbent resin, which is not preferable.

  Although the sorter 300 is a rotary sorter, the sorter that can be used in the present embodiment is not limited to this, and a vibration plane sorter may be used. FIG. 13 shows the structure of the vibration plane type sorter 600. In the vibration plane type sorter 600, the first sorting unit 19 and the second sorting unit 17 'have a planar structure, and the second sorting unit 17' has at least a two-layer structure. Further, at least two layers of the second sorting units 17 'are provided to face each other, and a first sorting unit 19 is provided below the plurality of second sorting units 17'. The diameter of the net of the first sorting unit 19 and the diameter of the punching 18 ′ provided in the second sorting unit 17 ′ are the same as those of the sorter 300. Further, as shown in FIG. 14, the same applies to the punching 18 ′ indicated by the solid line and the broken line provided in the two-layer second sorting unit 17 ′, which are not opposed to each other.

  The second sorting section 17 ′ of the vibration plane type sorter 600 is provided with a product inlet 37 into which the water-absorbing resin is introduced and a large variant outlet 38 from which a large variant is taken out. An inclination is provided from 37 to the large variant object outlet 38 so that the large variant object outlet 38 side is lowered. Although not shown, the vibration plane type sorter 600 is provided with a vibration motor, and as the vibration is applied, the water-absorbing resin introduced from the product introduction port 37 moves to the second selection unit 17 ′ and the second selection unit 17 ′. After passing through the punching provided in the portion 17 ′, the small variant is removed by the first sorting portion 19 and taken out from the small variant outlet 39. Thereafter, the water absorbent resin sorted on the first sorting unit 19 is obtained at the product outlet 40. A large water-absorbing resin that does not pass punching is discharged from the large-sized object outlet 38.

  As specific examples of the vibration plane type sorter, PS-280, PSL-300, PSL-400, PSLL-400, etc., which are pellet sorters manufactured by Tanaka Co., Ltd. can be used.

  Foreign matter (size, shape is the same as that of the water-absorbent resin during the production of the water-absorbent resin, but water-absorbent resin, colored water-absorbent resin, etc. to which metal pieces, dust, and / or small foreign matter with different color tone are attached In addition to impairing the display effect of the water-absorbent resin, if the foreign material is a metal, it is not preferable because it promotes the deterioration of the water-absorbent resin or reduces the storage stability of the water-absorbent resin. . Therefore, it is preferable to remove foreign matters.

  As a method for removing the foreign matter, for example, there are a method of removing it after visually confirming, a method of using a foreign matter sorter, a method of using an iron remover, and the like.

  As the iron remover, any of an electromagnet and a permanent magnet can be used, but those having 2000 to 12000 gauss are preferable, more preferably 5000 to 12000 gauss, and particularly preferably 8000 to 12000. Less than Gauss.

(6. Water retention agent for plant growth)
The water-retaining agent for plant cultivation according to the present invention contains the water-absorbent resin according to the present invention. That is, the water-absorbing resin manufactured by the method for manufacturing a water-absorbing resin according to the present invention is included. Since the water-absorbing resin according to the present invention has few residual monomers that deteriorate the physical properties of the water-absorbing resin, it does not affect the problems of hygiene, odor, and plant growth inhibition. The water-retaining agent for plant cultivation according to the present invention does not affect the problem of sanitation and odor, and can take in a sufficient amount of water. Can be omitted.

  Hereinafter, the water retention agent for plant growth will be described. The water-retaining agent for plant growth is not particularly limited as long as it contains the water-absorbing resin according to the present invention, and for example, a polyvalent metal compound can be suitably used.

  The polyvalent metal compound is a salt or hydroxide of a polyvalent metal, a divalent metal such as calcium, magnesium, barium, alkaline earth metal, and a trivalent metal such as aluminum, zinc, iron, manganese, Inorganic transition salts such as halides, nitrates, sulfates, carbonates and the like, transition salts such as copper and molybdenum, organic salts such as lactic acid and fatty acids, and hydroxides and oxides.

  Among them, calcium, aluminum, magnesium sulfate, sulfates, carbonates, nitrates, chlorides, water to give a good environment for physiological effects on plants such as stability of gel state after water absorption and germination and growth of plants. Although an oxide and an oxide are preferable, a divalent metal compound is more preferable, and a calcium compound is more preferable.

  Examples of calcium compounds include calcium sulfate, calcium carbonate, calcium hydroxide, calcium oxide, calcium nitrate, calcium chloride, tricalcium phosphate, calcium borate, calcium lactate, calcium citrate, calcium stearate, and other organic acid calcium. Although not particularly limited, calcium sulfate, calcium carbonate, calcium hydroxide, and calcium oxide are particularly preferable.

  The polyvalent metal compound is water-soluble or slightly soluble in water, but the solubility in 100 g of ion-exchanged water at 20 ° C. is 10.0 g or less, preferably 1.0 g or less, more preferably Is 0.5 g or less, particularly preferably more than 0 and 0.3 g or less.

  In the water retention material for plants in the present invention, when the solubility of the polyvalent metal salt is higher than the above, especially in the case of a water absorbent resin having a carboxyl group, the penetration of the polyvalent metal ions into the water absorbent resin particles is fast. In addition, salt exchange with a monovalent counter ion (such as sodium) inside the water-absorbent resin causes internal metal cross-linking, which greatly reduces the water-absorbing characteristics of the water-retaining material such as the water-absorption rate and the water-absorption factor. In addition, a polyvalent metal compound that is insoluble in water is not preferable because the polyvalent metal compound cannot adhere to or bind to the surface of the water-absorbent resin or cannot penetrate into the vicinity of the surface layer.

  The polyvalent metal compound is usually in the form of a powder containing water of crystallization having a water content of 10% by mass or less, and the particle size is not particularly limited, but is usually from the mass average particle size of the water-absorbent resin. Smaller ones are used. In addition, the addition method and addition amount of this polyvalent metal compound are mentioned later.

  Although the method to manufacture the water retention material for plants which concerns on this invention is not specifically limited, For example, the following methods can be mentioned.

  (1) A production method in which a polyvalent metal compound slurry having a concentration of 50% by mass or more is added and mixed in a state where the water content of the water absorbent resin is 50% by mass or less.

  (2) A production method in which a powder of a polyvalent metal compound is added and mixed in a powder state where the water content of the water-absorbent resin is 20% by mass or less, preferably 10% by mass or less, and then an aqueous liquid or water vapor is added and mixed. .

  (3) The manufacturing method which mixes a polyvalent metal compound with a powder in the state whose water content of a water absorbing resin is 20 mass% or more and 50 mass% or less.

  As a production method other than the above methods (1) to (3), for example, a dry blend method in which a polyvalent metal compound is added to and mixed with a water absorbent resin (A) having a water content of 20% by mass or less. However, since it is desirable that the polyvalent metal compound is supported, adhered or coated on the surface of the water absorbent resin (A), the production methods (1) to (3) are preferable. .

  Further, when the polyvalent metal compound is mixed in a solution or a slurry state so that the water content of the water absorbent resin (A) exceeds 50% by mass, the polyvalent metal compound penetrates into the resin of the water absorbent resin, Since the water-absorbent resin is salt-crosslinked with a polyvalent metal compound and the water-absorbing property as a water retention material for plants is greatly deteriorated, it is not preferable. In addition, when a polyvalent metal compound is added to the monomer in the polymerization step, the inside of the water-absorbent resin is not preferable because it is salt-crosslinked by the polyvalent metal compound.

  When the water retention material for plants according to the present invention is produced by the method of (1) above, the water content of the water absorbent resin is preferably low, preferably in order to prevent permeation of the polyvalent metal compound into the water absorbent resin. The moisture content is 0% by mass or more and 50% by mass or less, next preferably 0% by mass or more and 40% by mass or less, more preferably 0% by mass or more and 35% by mass or less, and further preferably 0% by mass or more and 30% by mass or less. Particularly preferably, it is 0 to 20% by mass, and most preferably 0 to 10% by mass.

  Further, the polyvalent metal compound is added in a solution or slurry, but many polyvalent metal compounds have low solubility in water, and therefore are mixed with a solvent such as an aqueous liquid and mixed with the water absorbent resin in a slurry state.

  The concentration of the polyvalent metal compound in the slurry is preferably 50% by mass or more, more preferably 50% by mass to 90% by mass, and particularly preferably 50% by mass to 80% by mass. When the concentration is 90% by mass or more, the slurry loses fluidity and becomes a wet powder state, which is not preferable because uniform addition is difficult.

  The amount of the slurry added is not particularly limited depending on the type of the polyvalent metal compound and the like. However, when an aqueous liquid is used as the solvent in the slurry, the water content of the water-absorbent resin increases when the amount added is large. The addition amount of the slurry is preferably 0% by mass or more and 50% by mass or less, more preferably 0% by mass or more and 40% by mass or less, still more preferably 0% by mass or more and 30% by mass or less, and particularly preferably 0% by mass or more and 30% by mass or less. Preferably they are 0 mass% or more and 20 mass% or less, Most preferably, they are 0 mass% or more and 10 mass% or less, Most especially preferably they are 0 mass% or more and 5 mass% or less.

  Further, the solvent used in the slurry containing the polyvalent metal compound is not particularly limited as long as the polyvalent metal compound can be uniformly dispersed, but the polyvalent metal compound is formed on the surface of the water absorbent resin. In order to carry or adhere the water, a polar solvent is preferable, and water is particularly preferable. In order to adjust the fluidity of the slurry, an organic or inorganic dispersant may be added.

  In the present invention, among various mixing methods, a method of spraying or dropping and mixing the slurry onto the water absorbent resin is preferable. Further, depending on the type of each polyvalent metal compound, the slurry may be heated or cooled as appropriate in consideration of the temperature and solubility of the polyvalent metal compound in water, and the slurry concentration and slurry fluidity with respect to the temperature. Usually, it is heating to the boiling point beyond the freezing point, but 20 ° C. or higher and 80 ° C. or lower is preferable.

  When the plant water-retaining material used in the present invention is produced by the method (2) above, the water content of the water-absorbent resin is 0% by mass or more and 20% by mass or less, preferably 0% by mass or more and 10% by mass or less. Then, after adding and mixing the powder of the polyvalent metal compound, an aqueous liquid or water vapor is added and mixed. When the aqueous liquid is added, the aqueous liquid described in the above (1) is used as the aqueous liquid to be added, and the amount used is preferably 0% by mass to 30% by mass, more preferably 0% by mass to 20% by mass. Hereinafter, it is more preferably 0% by mass to 15% by mass, particularly preferably 0% by mass to 10% by mass, and most preferably 0% by mass to 5% by mass.

(7. Artificial ice for display)
The artificial ice for a display according to the present invention includes the water-absorbing resin according to the present invention. Although it does not specifically limit as components other than the said water absorbing resin, For example, the coloring agent etc. may be included. The water-absorbent resin according to the present invention has a polyhedral shape mainly composed of hexahedral particles, and the particle size thereof is larger than that of a normal water-absorbent resin (mass average particle size of about 400 μm). mm order. In addition, a sufficient amount of water can be taken up. Therefore, an appearance similar to real ice can be maintained, and for example, it can be suitably used for a product sample of a restaurant.

  Note that the present invention is not limited to the configurations described above, and various modifications are possible within the scope of the claims, and technical means disclosed in different embodiments are appropriately combined. Embodiments obtained in this manner are also included in the technical scope of the present invention.

  The present invention will be described more specifically based on examples, but the present invention is not limited to this. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. The evaluation method was as follows.

(1) Absorption capacity Absorption capacity means the absorption capacity 48 hours after under no pressure with respect to 0.90 mass% salt solution, and can be measured by the following methods.

  That is, after 0.200 g of the water-absorbing resin was uniformly put into a non-woven fabric (Nangoku Pulp & Co., Ltd., trade name: Heatron paper, model: GSP-22) bag (85 mm × 60 mm) and heat sealed, It was immersed in 0.90 mass% sodium chloride aqueous solution (physiological saline) of large excess (usually about 500 g) at room temperature.

  After 48 hours, the bag was pulled up and drained for 3 minutes with a centrifugal force (250 G) described in edana ABSORBENCY II 441, 1-99 using a centrifuge (manufactured by Kokusan Co., Ltd., centrifuge: model H-122). After performing, the mass W2 (g) of the bag was measured. Further, the same operation was performed without using the water absorbent resin or the water absorbent resin composition, and the mass W1 (g) at that time was measured. And from these masses W1 and W2, the absorption capacity (g / g) was calculated according to the following formula.

Absorption capacity (g / g) = (mass W2 (g) −mass W1 (g)) / (mass of water absorbent resin (g)) − 1 (1)
(2) Residual monomer The content of the residual monomer in the water-absorbent resin can be measured by a conventionally known method. For example, 1.0 g of a water-absorbing resin is added to 184.3 g of 0.90% by mass sodium chloride aqueous solution (saline), and the mixture is extracted with stirring for 2 hours. A method of separating by filtration and analyzing the amount of residual monomer in the filtrate by liquid chromatography can be mentioned. In this case, a calibration curve obtained by analyzing a monomer standard solution having a known concentration in the same manner can be used as an external standard, and the amount of residual monomer in the water-absorbent resin can be determined in consideration of the dilution rate of the filtrate.

(3) Measurement of mass average particle diameter and logarithmic standard deviation value of hydrogel polymer 30 g of hydrogel polymer sample was put into 1000 g of a 20% by mass NaCl aqueous solution, and the stirrer chip was rotated at 300 rpm for 120 minutes. Stir. After the completion of the stirring, 5 to 8 types of sieves (THE with the logarithmic standard deviation (R = 15.9%, 50.0%, 84.9% in the following formula (2)) described below can be measured from the following sieves. IIDA TESTING SIEVE: Diameter 20 cm, sieve opening 16.0 mm, 13.2 mm, 11.2 mm, 9.5 mm, 8.0 mm, 6.70 mm, 5.6 mm, 4.75 mm, 4.0 mm, 3.35 mm 2.8 mm, 2.36 mm, 2.0 mm, and 1.0 mm JIS standard sieve Z8801-1 (1998)) is selected, 100 g of sample is added, and 6000 g of 20% by mass NaCl aqueous solution is added, followed by classification. did. The sample on the classified sieve was thoroughly drained and weighed.

  Based on the following formula (2), the particle size distribution of the particulate hydrous gel is defined as follows: w is the mass of the particulate hydrogel after classification and draining, w is the sieve opening, and r is the sample mass w0 = 30 g. Plotted on log probability paper. The particle diameter corresponding to 50% by mass on the integrated sieve on the plot was taken as the average particle diameter of the particulate hydrous gel. Formula (2) is shown below.

R (α) = (w0 / w) ^1/3 × r (2)
The logarithmic standard deviation value σζ is calculated by calculating the particle size (assumed as X1) and the particle size (assumed as X2) when R = 84.1% and R = 15.9% in the above plot. It calculated from X1 and X2 by the following formula (3).

σζ = (1/2) ln (X2 / X1) (3)
(4) Measurement of mass average particle diameter and logarithmic standard deviation value of water-absorbent resin Logarithmic standard deviation of the water-absorbent resin from the sieve described later (R = 15.9% in the above formula (2), 50.0) %, 84.9%) can be measured 5 to 8 types of sieves ((THE IIDA TESTING SIEVE; diameter 20 cm, sieve opening 16.0 mm, 13.2 mm, 11.2 mm, 9.5 mm, 8.0 mm, 6.70mm, 5.6mm, 4.75mm, 4.0mm, 3.35mm, 2.8mm, 2.36mm, 2.0mm, 1.0mm JIS standard sieve Z8801-1 (1998)) 100 g of the sample was added and classified for 5 minutes by a vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65 type, SER No. 0501). The above sample was weighed, the weight of the water-absorbing resin after the classification was set to w, the opening of the sieve was set to r, and the mass of the sample was w0 = 30 g. The diameter distribution was plotted on logarithmic probability paper, and the particle diameter corresponding to 50% by mass on the cumulative sieve of the plot was taken as the average particle diameter of the water-absorbent resin.

  The logarithmic standard deviation value σζ is calculated by calculating the particle size (assumed as X1) and the particle size (assumed as X2) when R = 84.1% and R = 15.9% in the above plot. Calculation was performed from X1 and X2 by the above equation (3).

(5) Light resistance test 30 g of gel that completely absorbed 25 times the ion-exchange water with respect to the solid content of the water-absorbent resin was placed in a 225 cc mayonnaise bottle, sealed with a lid, and then left outdoors for 1 week. The later state was observed visually.

(6) Measurement of hydrous gel shape (hedron) 30 g of hydrogel polymer sample after completion of cutting is taken, and each shape (hedron) is visually checked to obtain a tetrahedron or more and a dodecahedron shape. Alternatively, the mass percentage of the hexahedral hydrated gel polymer was calculated.

Concentration (mass%) of tetrahedral to 12-hedral or 6-sided hydrogel polymer = mass (of tetrahedral to 12-sided or hexahedral hydrogel polymer) (G) / 30 (g) × 100
(7) Moisture content measurement of hydrated gel polymer (solid content)
A small portion of the hydrated gel polymer taken out from the polymerization machine was cut off and quickly cooled, and 4 g of the hydrated gel polymer quickly divided into pieces with scissors was placed in a petri dish having an inner diameter of 50 mm, and was placed in a stationary dryer at 180 ° C. for 16 Calculated by drying for hours.

Water content of hydrogel polymer (mass%) = 100− (mass of hydrogel polymer after drying (g) / mass of hydrogel polymer before drying (g) × 100)
The solid content can be calculated backward from the water content.

Solid content (mass%) = 100-water content (mass%)
(8) Measurement of water content of water-absorbent resin (solid content)
It calculated by taking 2 g of water-absorbing resin in a petri dish having an inner diameter of 50 mm and drying it in a 180 ° C. static dryer for 16 hours.

Water content of water-absorbing resin (mass%) = 100− (mass of water-absorbing resin after drying (g) / mass of water-absorbing resin before drying (g) × 100)
The solid content can be calculated backward from the water content.

Solid content (mass%) = 100-water content (mass%)
(9) Measurement of dust amount The vibration feeder 25 (CF-2 manufactured by Shinko Electric Co., Ltd.), the digital dust meter 26 (P-5L manufactured by Shibata Chemical Instruments Co., Ltd.), and the receiving cup 27 are arranged at intervals as shown in FIG. Arrange.

  First, 1 kg of the water-absorbent resin 24 is placed on the vibration feeder 25, and the setting of the vibration feeder 25 is adjusted so that the dropping is finished in about one minute after the drop starts from the vibration feeder 25. Thereafter, 1 kg of the water absorbent resin 24 is placed on the vibration feeder 25, and the digital dust meter is operated for 1 minute at the same time as the water absorbent resin 24 falls from the feeder. Then, after 1 minute, check the display on the digital dust meter.

[Example 1]
37mass% sodium acrylate aqueous solution 254.50 g, acrylic acid 29.50 g, 10 mass% polyethylene glycol diacrylate (n = 9) aqueous solution 0.747 g, ion-exchanged water 20.26 g, 10 mass% polyethylene glycol (trade name: A monomer aqueous solution containing 6.25 g of an aqueous solution of polyethylene glycol 6,000 (manufactured by Kanto Chemical Co., Inc.) was prepared. That is, an ethylenically unsaturated monomer containing 100 mol% of acrylic acid and sodium acrylate (excluding the crosslinking agent) was prepared. Nitrogen was blown into the aqueous monomer solution to adjust the dissolved oxygen concentration in the aqueous solution to 0.1 ppm or less.

  Subsequently, 1.41 g of a 1.0% by mass acrylic acid solution of hydroxycyclohexyl phenyl ketone (trade name Irgacure 184; manufactured by Ciba Specialty Chemicals Co., Ltd.) and 1.41 g of a 3.0% by mass aqueous sodium persulfate solution were sequentially added. The monomer solution was poured into a 30 cm × 30 cm PFA vat and polymerized at a high pressure mercury lamp 450 W (trade name Toscure 401; manufactured by Harrison Toshiba Lighting Co., Ltd.) with an irradiation distance of 60 cm.

  The polymerization initiation temperature was 22 ° C., and reached 80 ° C. after 2 minutes and 30 seconds. After irradiating the high-pressure mercury lamp for 5 minutes, the high-pressure mercury lamp was turned off to complete the polymerization. The water content of the water-containing gel at this time was 55% by mass.

The polymerization sheet thickness was about 5 mm. The water-containing gel sheet after polymerization was cut into 5 mm squares with scissors cut to prepare a hexahedral water-containing gel (1) having a square shape and a smooth surface. That is, the hexahedral hydrous gel was 98.5% by mass. Moreover, the mass average particle diameter of the hydrogel was 5.0 mm, and the logarithmic standard deviation value of the particle size distribution was 0.20. 300 g of this hydrogel (1) was put into a 5 liter Laedige mixer (manufactured by Matsubo), and 0.75 g (0.05 mass%) of 10 mass% aqueous aluminum sulfate solution and 10 mass% Diethylene Triamine were added by syringe. An aqueous solution of Pentaacetic Acid (trade name Kyrest PC45, manufactured by Kyrest Co., Ltd.) was mixed for 1 minute at a rotation speed of 200 min ⁻¹ while 0.03 g (0.02% by mass) was added dropwise. The hydrogel after addition was in a non-aggregated state.

  When this hydrogel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 130 ° C. for 30 minutes, a water absorbent resin (1) having a water content of 20% by mass was obtained. The obtained water absorbent resin had an average particle diameter of 3.8 mm and a logarithmic standard deviation value σζ of 0.19. The absorption capacity (hereinafter referred to as “CRC”) was 41.0 g / g, and the residual monomer content was 100 ppm. In the light resistance test, no discoloration or deformation of the gel was observed.

  In order to measure the average particle diameter and logarithmic standard deviation of the hydrogel polymer and the water-absorbent resin, the openings are 8.0 mm, 6.70 mm, 5.6 mm, 4.75 mm, 4.0 mm, and 2. 8 mm and 2.0 mm sieves were used.

[Example 2]
377.2 mass% sodium acrylate aqueous solution 407.2 g, acrylic acid 47.2 g, 10 mass% polyethylene glycol diacrylate (n = 9) aqueous solution 1.195 g, ion-exchanged water 40.35 g, 10 mass% polyethylene glycol (trade name: A monomer aqueous solution containing 10.00 g of an aqueous solution of polyethylene glycol 6,000 (manufactured by Kanto Chemical Co., Inc.) was prepared. That is, an ethylenically unsaturated monomer containing 100 mol% of acrylic acid and sodium acrylate (excluding the crosslinking agent) was prepared. Nitrogen was blown into the aqueous monomer solution to adjust the dissolved oxygen concentration in the aqueous solution to 0.1 ppm or less.

  Then, 2.256 g of 1.0 mass% acrylic acid solution of hydroxycyclohexyl phenyl ketone (trade name: Irgacure 184; manufactured by Ciba Specialty Chemicals Co., Ltd.) and 2.256 g of 3.0 mass% sodium persulfate aqueous solution were sequentially added. The monomer solution was poured into a 30 cm × 30 cm PFA vat and polymerized at a high pressure mercury lamp 450 W (trade name: Toscure 401; manufactured by Harrison Toshiba Lighting Co., Ltd.) with an irradiation distance of 60 cm. The polymerization initiation temperature was 22 ° C., and reached 88 ° C. after 4 minutes. The polymerization sheet thickness was about 8 mm.

The water-containing gel sheet after polymerization was cut into 8 mm squares with scissors cut to prepare a hexahedral water-containing gel (2) having a square shape and a smooth surface. That is, the hexahedral hydrous gel was 97.0% by mass. Moreover, the mass average particle diameter of the hydrogel was 8.0 mm, and the logarithmic standard deviation value of the particle size distribution was 0.18. 300 g of this hydrous gel (2) was put into a 5 liter Laedige mixer (manufactured by Matsubo), and 0.75 g (0.05 mass%) of 10 mass% aqueous aluminum sulfate solution and 2-hydroxybenzophenone- While adding 0.105 g (0.05% by mass) of 4-diglyceryl ether dropwise, the mixture was mixed for 1 minute at a rotational speed of 200 min ⁻¹ . The hydrogel after addition was in a non-aggregated state.

  When this hydrogel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 130 ° C. for 30 minutes, a water absorbent resin (2) having a moisture content of 19% by mass was obtained. The obtained water-absorbent resin (2) had an average particle size of 6.8 mm and a logarithmic standard deviation value σζ of 0.17. The CRC was 41.0 g / g and the residual monomer content was 80 ppm. In the light resistance test, no discoloration or deformation of the gel was observed.

  For the measurement of the average particle diameter and logarithmic standard deviation of the hydrogel polymer and the water-absorbent resin, the openings are 11.2 mm, 9.5 mm, 8.0 mm, 6.70 mm, 5.6 mm, 4. A 75 mm, 4.0 mm and 2.8 mm sieve was used.

Example 3
An aqueous liquid was prepared by sufficiently mixing 43.7 kg of acrylic acid and 286 kg of a 37 mass% sodium acrylate aqueous solution, 337 g of polyethylene glycol diacrylate (n = 9), and 86.3 g of ion-exchanged water. That is, an ethylenically unsaturated monomer containing 100 mol% of acrylic acid and sodium acrylate (excluding the crosslinking agent) was prepared.

  Fluorine-based adhesive tape with glass fiber (trade name: TGF Glass Cloth, manufactured by Yodogawa Hutec Co., Ltd.) is pasted on an endless steel belt, and a weir with a height of 3.0 cm is attached at intervals of 30 cm in width to 1.0 m The aqueous liquid was supplied at a rate of 1.2 kg / min to a belt polymerization machine operating at a speed of / min. The aqueous liquid was filled to a height of 5 mm. The aqueous liquid was heated on the supply line so that the temperature of the aqueous liquid was 22 ° C. at the supply port of the belt polymerization machine. Moreover, nitrogen gas was continuously blown on the supply line, so that the dissolved oxygen was reduced to 0.5 ppm or less.

  To an aqueous liquid with a reduced dissolved oxygen level, hydroxycyclohexyl phenyl ketone (trade name Irgacure 184; manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.01 g / monomer mole, sodium persulfate 0.03 g / unit An acrylic acid solution and an aqueous solution of these polymerization initiators were injected and mixed well so as to obtain a monomer mole (monomer concentration: 40.0% by mass).

  UV light was irradiated for 4 minutes with a high-pressure mercury lamp (Toshiba MERCURYLUMP H400BL) placed at a height of 20 cm from the surface of the aqueous liquid at an equal interval of 6/3 m, and the aqueous liquid supplied to the belt polymerizer was 3 minutes 30 seconds later. A polymerization peak temperature of 90 ° C. was exhibited. Nitrogen gas was supplied from the same position as the aqueous liquid supply port at 5 L / min and from the center of the belt at 5 L / min.

  The obtained water-containing gel had a water content of 55.4% by mass and a thickness of 4 mm. The water-containing gel coming out of the polymerization machine is fed to the cutting machine 100 shown in FIG. 3 at a speed of 1.0 m / min, and cut so that the cutting width is about 4 mm and the cutting length is about 4 mm. A hexahedral water-containing gel (3) having a rectangular shape and a smooth surface was obtained. The content of the hexahedral hydrated gel was 85% by mass. Further, the mass average particle size of the hydrogel was 4.0 mm, and the logarithmic standard deviation value of the particle size distribution was 0.20.

  At that time, propylene glycol was sprayed from the two-fluid nozzle (BIMV11002, manufactured by Ikeuchi Co., Ltd.) under the conditions of propylene glycol 8 g / min and air pressure 0.1 MPa from the spray devices 9, 10, and 11, using a gear pump from the spray device 12. Was sprayed at 10 g / min. The propylene glycol used was 7.08 wt% based on the water-absorbent resin solid content.

While putting 5000 g of hydrous gel (3) into a 20 liter Leedige mixer (Matsubo, type; M20), 22.3 g (0.10 mass%) of 10 mass% aqueous aluminum sulfate solution was added dropwise with a syringe. Mixing was performed for 1 minute at a rotation speed of 200 min ⁻¹ . At that time, the rotation speed of the side chopper of the Roedige mixer was set to 4000 rpm. The hydrogel was in a non-aggregated state.

  When this hydrogel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 130 ° C. for 30 minutes, a water absorbent resin (3) having a water content of 20 mass% was obtained. The water absorbent resin (3) obtained had an average particle diameter of 3.5 mm and a logarithmic standard deviation value σζ of 0.18. Moreover, CRC was 42.0 g / g and residual monomer content was 120 ppm.

  In order to measure the average particle diameter and logarithmic standard deviation of the hydrogel polymer and the water-absorbent resin, the openings are 8.0 mm, 6.70 mm, 5.6 mm, 4.75 mm, 4.0 mm, and 2. 8 mm and 2.0 mm sieves were used.

Example 4
In Example 3, it carried out by the same method except having changed the adhesive prevention agent used with the cutting machine 100 to 50 mass% propylene glycol aqueous solution.

  The hydrogel after cutting was in a non-aggregated state, and the hexahedral hydrogel was 80% by mass. The mass average particle size of the hydrogel was 4.2 mm, and the logarithmic standard deviation value of the particle size distribution was 0.18.

  When this hydrogel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 130 ° C. for 30 minutes, a water absorbent resin (4) having a water content of 19% by mass was obtained. The water absorbent resin (4) obtained had an average particle diameter of 3.7 mm and a logarithmic standard deviation value of 0.17. Moreover, CRC was 42.0 g / g and residual monomer content was 120 ppm.

Example 5
2 kg of the sheet-like hydrogel obtained by the same polymerization method as in Example 3 was dried at 120 ° C. for 30 minutes as it was. The moisture content of the dried sheet gel was 39.3%.

  The dried sheet gel was cut in the same manner as in Example 3. The hydrogel after cutting was in a non-aggregated state, and the content of the hexahedral hydrogel was 95% by mass. Moreover, the mass average particle diameter of the hydrogel was 5.0 mm, and the logarithmic standard deviation value of the particle size distribution was 0.18.

  When this water-containing gel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 120 ° C. for 30 minutes, a water absorbent resin (5) having a water content of 20% by mass was obtained. The water absorbent resin (5) obtained had an average particle diameter of 4.5 mm and a logarithmic standard deviation value of 0.18. Moreover, CRC was 43.0 g / g and residual monomer content was 115 ppm.

  The average particle size and logarithmic standard deviation of the water-containing gel polymer and the water-absorbent resin were measured at 8.0 mm, 6.70 mm, 5.6 mm, 4.75 mm, 4.0 mm, 2.8 mm. A 2.0 mm sieve was used.

Example 6
300 g of the water-absorbent resin (3) obtained by the same method as in Example 3 was put into a 5 L Ladige mixer (Matsubo, type: M5R), and while adding 60 g of a 50 mass% slurry of calcium sulfate, 330 rpm And stirred for 15 seconds. After mixing, it was dried with hot air at 120 ° C. for 10 minutes to obtain a water-retaining material for plant growth (1).

  150 ml of ion-exchanged water is put into a polypropylene container having an inner diameter of 80 mm and a height of 250 mm, and then 1.5 g of the water-retaining material for plant growth (1) is weighed and put into the container, and left for 1 hour after the addition. Thus, a gel medium (gel medium having a water absorption ratio of 100 times) made of a water-retaining material for plant growth was prepared. Subsequently, 30 seeds of radish seeds were sown, covered with a non-woven cloth on the container, and cultured for 1 week in a culture room (25 ° C., 500 Lux, 12 hours long) to germinate.

  One week later, the sprouted Japanese radish was taken out, and the stem length from the germinated solid base (branch point of root and stem) to the tip of the leaf (length above ground) was 610 mm, and the length of the underground part was germinated. The root length (base length) from the solid base to the tip of the main root was 560 mm. Furthermore, root hair was confirmed.

Example 7
Artificial ice for display was prepared by swelling the water-absorbent resin (3) obtained by the same method as in Example 3 100 times with ion-exchanged water.

Example 8
Monomer of acrylic acid 15.9 kg and 37 mass% sodium acrylate aqueous solution 173.4 kg, polyethylene glycol diacrylate (n = 9), 104.6 g, and ion-exchanged water 7.9 kg, 15 mass% polyethylene glycol (product) Name: Polyethylene glycol 6000 (Nippon Yushi Co., Ltd.) 2.7 kg of an aqueous solution was sufficiently mixed to prepare an aqueous monomer solution. After adjusting the temperature of this aqueous solution to 20 ° C., nitrogen gas was blown to make the dissolved oxygen 1 ppm. Thereafter, it was confirmed by visual observation that bubbles were removed.

  Next, hydroxycyclohexyl phenyl ketone (trade name Irgacure 184; manufactured by Ciba Specialty Chemicals Co., Ltd.) was dissolved in acrylic acid / water = 1/1 (mass ratio) to prepare a 3% by mass acrylic acid aqueous mixed solvent solution. Next, a 3% by mass aqueous sodium persulfate solution was prepared.

  A glass fiber-containing fluorine-based adhesive tape (trade name CHEMLAM6R, manufactured by Saint-Gobain Co., Ltd.) was pasted on the endless steel belt. A weir with a height of 1.0 cm is attached to the belt with a spacing of 22 cm on top of it, and the above monomer aqueous solution is mixed with 1.4 kg / min of acrylic acid water of hydroxycyclohexyl phenyl ketone in a belt polymerization machine moving at 1.0 m / min. The solvent solution was supplied at 10 g / min, and the sodium persulfate aqueous solution was supplied at 10 g / min.

The ultraviolet light was irradiated for 4.3 minutes with a black light mercury lamp (Toshiba MERCURYLUMP H400BL-L), and the integrated light quantity at that time was 820 mJ / cm ² . Polymerization was performed while supplying nitrogen gas at 50 L / min.

  The obtained water-containing gel had a water content of 45.0% by mass and a thickness of 4.5 mm. The maximum temperature reached during polymerization was 90 ° C. No bubbles of 200 μm or more were visually confirmed in the hydrous gel sheet. The hydrated gel sheet from the belt polymerization machine is sent to the cutting machine 100 shown in FIG. 3 at a speed of 1.0 m / min via a horizontal conveyor, and the cutting width is about 4 mm and the cutting length is about 4 mm. Was cut to obtain a hexahedral hydrated gel (4) mainly having a square shape and a smooth surface. As shown in FIG. 4, the scraper 3, 4 of the cutting machine 100 has a fluororesin enamel paint (trade name 420-105 on the surface through which the hydrogel sheet cut in the width direction by slitter rolls 1, 2, which are vertical cutting blades, passes. ONE COAT GRAY manufactured by DuPont Co., Ltd.), and clogging inside the cutting machine 100 was not observed.

  In addition, the surface temperature of the water-containing gel sheet immediately before entering the cutting machine 100 was about 50 ° C. by applying cold air of 25 ° C. to the water-containing gel sheet from the upper part of the roller conveyor. The content of the hexahedral hydrogel was 99% by mass. Moreover, the mass average particle diameter of the hydrogel was 4.4 mm, and the logarithmic standard deviation value of the particle size distribution was 0.19.

  When cutting the hydrous gel, propylene glycol 30 g / min is sprayed from the spraying devices 9, 10, and 11 using a spray nozzle, and propylene glycol is introduced at a rate of 30 g / min from the spraying device 12 using a gear pump. did. The propylene glycol used was 19.05% by mass with respect to the water-absorbent resin solid content.

40 kg of hydrous gel (4) is put into a batch-type Ladige mixer (manufactured by Matsubo Co., Ltd.) having a capacity of 130 liters, the blade rotation speed is 140 min ⁻¹ , and the side chopper rotation speed is 3000 min ⁻¹ and 10 mass%. Mixing was performed while spraying 600 g of an aqueous aluminum sulfate solution using a spray nozzle. The hydrogel was in a non-aggregated state.

  When this hydrogel was spread on a 50 mesh (mesh opening 300 μm) wire mesh of a batch type hot air dryer and hot air was applied for 30 minutes at 105 ° C. and an air flow of 1 m / s, the temperature of the hydrogel (4) was 30 minutes later. When hot air was applied for 50 minutes at 150 ° C. and air flow of 1 m / s, the water-containing gel (4) became 149 ° C. after 50 minutes to obtain a water-absorbing resin (6) having a water content of 12% by mass. It was.

  This water absorbent resin (6) was sent to the sorter 300 at 1.5 kg / min to obtain a water absorbent resin (7). The first sorting unit 19 of the sorting machine 300 was provided with a mesh having an opening of 2.8 mm, and dry air was blown from one place at a rate of 200 L / min from the lower side of the first sorting unit 19. The second sorting unit 17 has a double structure, the inner second sorting unit 17 is provided with a punching with a diameter of 7 mm, and the outer second sorting unit 17 is provided with a punching with a diameter of 9 mm. It was a structure. The clearance between the punchings was 7 mm.

The water absorbent resin (7) obtained had a mass average particle diameter of 4.0 mm and a logarithmic standard deviation value σζ of 0.18. The CRC was 37.0 g / g, the residual monomer content was 280 ppm, and the dust amount was 220 mg / m ³ . In the water absorbent resin (7), the ratio of the hexahedral water absorbent resin was 99% by mass.

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 9
In Example 8, it dried by the same method except implementing with a band dryer. The rooms divided into five at equal intervals were passed through the hydrogel (4) at intervals of 120 minutes, the first to third rooms were 105 ° C, the fourth to fifth rooms were 150 ° C, and each room was 1.0 m / s. It dried with the wind speed and obtained the water absorbing resin (8).

  The temperature of the hydrogel (4) when it passed through the three chambers was 105 ° C., and the temperature of the hydrogel (4) when it passed through the five chambers was 148 ° C. The hydrated gel (4) was dried at a height of 4 cm.

The water absorbent resin (9) obtained after the treatment with the sorter 300 had a water content of 13% by mass, a mass average particle diameter of 4.0 mm, and a logarithmic standard deviation value σζ of 0.19. The CRC is 38.0 g / g, the residual monomer content is 290 ppm, the dust amount is 250 mg / m ³ , and the ratio of the hexahedral water absorbent resin in the water absorbent resin (9) is: It was 98 mass%. In addition, no bubbles were visually confirmed inside the water absorbent resin (9).

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 10
The drying was performed in the same manner as in Example 8, except that the drying was performed with a rotary aeration dryer (trade name: Roth Through SRTA-2 manufactured by Okawara Seisakusho Co., Ltd.).

  16 kg of the hydrogel (4) was put into SRTA-2 and dried at a hot air temperature of 190 ° C. and a wind speed of 1.0 m / s while rotating at 8 rpm. The drum punching had a diameter of 1.0 mm. The hydrogel (4) reached 110 ° C. for 40 minutes after being put into the dryer, and further reached 149 ° C. after 80 minutes. After 80 minutes, drying was completed to obtain a water absorbent resin (10).

After the treatment with the sorter 300, the water-absorbing resin (11) obtained had a water content of 13.8% by mass, a mass average particle diameter of 3.9 mm, and a logarithmic standard deviation value σζ of 0.17. It was. The CRC was 42.1 g / g, the residual monomer content was 270 ppm, and the dust amount was 190 mg / m ³ . In the water absorbent resin (11), the ratio of the hexahedral water absorbent resin was 98% by mass.

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 11
Five metal pieces were added to the water absorbent resin (7) to prepare the water absorbent resin (12). When the water-absorbing resin (12) was fed to the iron remover at 1.5 kg / min and then examined again visually, the metal piece was completely removed.

  The iron removal machine passed three 10000 gauss permanent magnets 10 cm in length and placed in parallel at intervals of 2 cm.

Example 12
The first light of the black light mercury lamp (Toshiba MERCURYLUMP H400BL-L) in Example 8 was replaced with UV-152 / 1MNSC3-AA06 manufactured by USHIO INC., To which a metal halide lamp (emission length 125 mm) was attached, and the shutter was replaced at 1.0 kW. Used open. The integrated light quantity at this time was 1300 mJ / cm ² . The monomer aqueous solution prepared in Example 8 was 2.1 kg / min, the hydroxycyclohexyl phenyl ketone aqueous acrylic acid mixed solvent solution was 10 g / min, and the sodium persulfate aqueous solution was 15 g / min. supplied in min.

  The obtained water-containing gel had a water content of 45.1% by mass and a thickness of 4.5 mm. The maximum temperature reached during polymerization was 94 ° C. No bubbles of 200 μm or more were visually confirmed in the hydrous gel sheet. The hydrated gel sheet fed from the belt polymerization machine was fed into the cutting machine 100 shown in FIG. 3 at a speed of 1.5 m / min via a horizontally set cooling belt. A cutting machine 100 is used to cut the cut width to about 4 mm and the cut length to about 4 mm, and the hexahedral water-containing gel (mainly a square shape with a smooth surface) 7) was obtained.

  As shown in FIG. 4, the scraper 3, 4 of the cutting machine 100 has a fluororesin enamel paint (trade name: 420-105 ONE COAT) on the surface through which the water-containing gel sheet cut in the horizontal direction by the vertical cutting blades 1, 2 passes. Since the coating was carried out by GRAY DuPont Co., Ltd., no clogging or the like inside the cutting machine was observed.

  The surface temperature of the hydrated gel sheet immediately before entering the cutting machine 100 was about 40 ° C. by applying cold water of 13 ° C. from the lower part of the cooling belt. The hexahedral hydrous gel content was 99 mass%, the mass average particle diameter of the hydrogel sheet was 4.3 mm, and the logarithmic standard deviation of the particle size distribution was 0.19.

  At the time of cutting the hydrogel, propylene glycol was sprayed from the spray nozzles 9 ', 10', 11 to the hydrogel under conditions of 65 g / min of propylene glycol, and further, 65 g of propylene glycol was sprayed from the spraying device 12 using a gear pump. It sprayed on the conditions of / min. The propylene glycol used was 27.45% by mass with respect to the water-absorbent resin solid content.

  60 kg of hydrous gel (7) is put into a batch-type Ladige mixer (manufactured by Matsubo Co., Ltd.) having a capacity of 130 liters, the blade rotation speed is 140 min-1, the side chopper rotation speed is 3000 min-1, and 10 masses. Mixing was performed while spraying 900 g of a 100% aqueous solution of aluminum sulfate. The hydrogel was in a non-aggregated state.

  While this hydrogel was passed through a room that was 4cm high and divided into five equally spaced parts over 120 minutes, rooms 1 to 3 were 105 ° C, rooms 4 to 5 were 150 ° C, and rooms 1 and 3 were upblown. The second, fourth, and fifth chambers were dried by downblowing at a wind speed of 1.0 m / s. The temperature of the hydrogel (7) when passing through the three chambers was 105 ° C., and the temperature of the water absorbent resin when leaving the five chambers was 148 ° C. Then, the water absorbing resin (13) was obtained by the same screening method as described in Example (8).

The water-absorbing resin (13) thus obtained has a water content of 12.5% by mass, a mass average particle size of 4.4 mm, a logarithmic standard deviation value σζ of 0.19, and a CRC of 51.0 g / g. The residual monomer content was 260 ppm and the dust amount was 250 g / m ³ . In the water absorbent resin (13), the ratio of the hexahedral water absorbent resin was 99% by mass.

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 13
A monomer aqueous solution was prepared by sufficiently mixing 15.9 kg of acrylic acid and 173.4 kg of 37 mass% aqueous sodium acrylate monomer, 104.6 g of polyethylene glycol diacrylate (n = 9), and 7.9 kg of ion-exchanged water. did. After adjusting the temperature of this aqueous liquid to 20 ° C., nitrogen gas was continuously blown at 200 ml / min when liquid was fed through the supply line at 1.75 kg / min, and then the defoamer 400 shown in FIG. Defoaming machine having the same structure (trade name: Quicktron 01 type, manufactured by Nippon Oil Co., Ltd. was used for defoaming. Degassed monomer aqueous liquid of 1.4 kg / min from the outlet hole of Quicktron 15 wt% polyethylene glycol (trade name: polyethylene glycol 6000 manufactured by Nippon Oil & Fats Co., Ltd.) aqueous solution 18.9 g / min, hydroxycyclohexyl phenyl ketone aqueous solution described in Example 8 is 10 g / min, and Example 8 is described. Of sodium persulfate aqueous solution was supplied at 10 g / min.

  The dissolved oxygen in the monomer aqueous liquid was 5 ppm, and no bubbles were observed in the monomer aqueous liquid. On the other hand, the monomer aqueous liquid containing bubbles was discharged from the bubble discharge hole at 0.35 kg / min. This was again charged into the monomer preparation layer before degassing.

  About this monomer aqueous solution, the process after superposition | polymerization was performed like Example 8. FIG. Thereby, the water content of the obtained water-containing gel was 45.3 mass%, the thickness was 4.5 mm, and the logarithmic standard deviation value of the particle size distribution was 0.19.

Furthermore, the water-absorbent resin (14) obtained after treating the hydrated gel with the sorter 300 has a mass average particle diameter of 4.0 mm, a logarithmic standard deviation value σζ of 0.19, and a CRC of 42 The residual monomer content was 280 ppm and the dust amount was 220 mg / m ³ .

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 14
As a method for removing dissolved oxygen in the monomer aqueous solution adjusted to 20 ° C. prepared in Example 8, a deaeration module having the same configuration as the deaeration membrane module 500 shown in FIG. 2 (trade name: MHF0504MBFT Mitsubishi Rayon Engineering Co., Ltd.) The method was the same except that (made by company) was used. When deaeration was performed with a vacuum pump at a degree of vacuum of 7 kPa, dissolved oxygen was 1 ppm, and no bubbles were observed in the monomer aqueous solution. For this monomer aqueous solution, the steps after polymerization were carried out in the same manner as in Example 8.

  The obtained water-containing gel had a water content of 45.0% by mass and a thickness of 4.5 mm. Moreover, the mass average particle diameter of the hydrogel was 4.5 mm, and the logarithmic standard deviation value of the particle size distribution was 0.19.

After the treatment with the sorter 300, the water-absorbent resin (15) obtained had a mass average particle diameter of 3.9 mm and a logarithmic standard deviation value σζ of 0.19. The CRC was 42.0 g / g, the residual monomer content was 275 ppm, and the dust amount was 260 mg / m ³ .

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 15
In Example 8, the drying was performed in the same manner except that drying was performed at 150 ° C. and an air volume of 1 m / s for 60 minutes. The temperature of the hydrogel (4) was 120 ° C. 10 minutes after the start of drying, and 150 ° C. 20 minutes after the start of drying.

In the water-absorbent resin (16) obtained after the treatment with the sorter 300, many bubbles that seemed to boil were observed. The water-absorbent resin (16) had a mass average particle diameter of 4.0 mm, a logarithmic standard deviation value σζ of 0.18, a residual monomer content of 280 ppm, and a dust amount of 2520 mg / m ³ .

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 16
In Example 8, when water-containing gel was cut, propylene glycol was sprayed from the two-fluid nozzle (BIMV11002, manufactured by Ikeuchi Co., Ltd.) from the spray devices 9, 10, and 11 under the conditions of propylene glycol 60 g / min and air pressure 0.1 MPa. This was carried out in the same manner except that propylene glycol was introduced under the condition of 60 g / min using a gear pump from the spraying device 12. In addition, the used propylene glycol was 38.10 wt% with respect to water-absorbent resin solid content.

The mass average particle diameter of the water absorbent resin (17) obtained after the treatment with the sorter 300 was 4.1 mm, the residual monomer content was 225 ppm, and the dust amount was 3020 mg / m ³ .

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

Example 17
In Example 13, the monomer aqueous liquid adjusted to 20 ° C. was supplied at 1.4 kg / min from the liquid inlet of the two-fluid nozzle, and nitrogen gas was blown from the gas inlet side at 200 ml / min. TRON 01 type (Nippon Petrochemical Co., Ltd.) was not used. About this monomer aqueous liquid, the process after a superposition | polymerization process was performed similarly to Example 13. FIG.

  The obtained water-containing gel had a water content of 45.3 mass% and a thickness of 4.5 mm. It was confirmed that many bubbles were mixed in this hydrogel. In addition, the content of the hexahedral hydrogel after cutting was 90% by mass, the mass average particle size of the hydrogel was 4.6 mm, and the logarithmic standard deviation value of the particle size distribution was 0.24.

The water-absorbent resin (18) obtained after the treatment with the sorter 300 has a mass average particle diameter of 4.2 mm, a logarithmic standard deviation value σζ of 0.23, and a CRC of 42.4 g / g. The residual monomer content was 230 ppm and the dust amount was 200 mg / m ³ . In addition, a large number of bubbles were visually confirmed inside the water absorbent resin (18).

  In addition, the measurement of the mass average particle diameter and logarithmic standard deviation value of the water-containing gel-like polymer and the water-absorbent resin was performed with a mesh size of 8.0 mm, 6.70 mm, 5.60 mm, 4.75 mm, 4.0 mm, 3 mm .35 mm, 2.8 mm, and 2.0 mm sieves were used.

[Comparative Example 1]
A water-containing gel sheet was prepared in the same manner as in Example 1, and the water-containing gel sheet was cut into 1 mm squares by scissors cutting to prepare a hexahedral water-containing gel (5). The hydrous gel (5) had reagglomerated. The content of the hexahedral hydrated gel was 100% by mass. Moreover, the mass average particle diameter of the hydrogel was 1.0 mm, and the logarithmic standard deviation value of the particle size distribution was 0.20.

  When this hydrous gel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 130 ° C. for 30 minutes, the gel was fused to form one lump. The water content of the obtained water-absorbent resin was 16.5% by mass, and the CRC was 41.0 g / g. The residual monomer content was 450 ppm. In the light resistance test, yellowing of the gel was observed.

[Comparative Example 2]
A water-containing gel sheet was prepared with a composition obtained by removing polyethylene glycol from the composition of Example 1, and the water-containing gel sheet was cut into 4 mm squares with scissors to prepare a hexahedral water-containing gel (6). The content of the hexahedral hydrated gel was 100% by mass. Further, the mass average particle size of the hydrogel was 4.0 mm, and the logarithmic standard deviation value of the particle size distribution was 0.20. The hydrous gel (6) was re-aggregated.

  When this hydrogel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried at 130 ° C. for 30 minutes, gel fusion occurred and formed one lump. The water content of the obtained water-absorbent resin was 24.0% by mass, and the CRC was 41.0 g / g. The residual monomer content was 550 ppm.

  The above embodiments or examples are merely to clarify the technical contents of the present invention, and should not be construed in a narrow sense by limiting only to such specific examples. Various modifications can be made within the scope of the claims described below.

  As described above, the method for producing a water-absorbent resin according to the present invention is such that at least a part of the surface of a hydrogel polymer having a polyhedral shape is coated with an adhesion inhibitor and dried. A water-absorbing resin that is in a non-aggregated state and is smoothly dried can be obtained.

  Therefore, the present invention can be suitably used as a method for producing a water-absorbing resin with little deterioration in physical properties, and the water-absorbing resin can be used for applications such as water-retaining agents for plant growth and artificial ice for displays. it can.

It is a longitudinal cross-sectional view which shows the structure of a defoamer. It is a longitudinal cross-sectional view which shows the structure of a deaeration membrane module. It is a longitudinal section showing the composition of the cutting machine concerning this embodiment. It is a longitudinal cross-sectional view which shows the coated scraper. It is explanatory drawing which shows the structure which looked at the vertical cutting blade (roll cutter) 1 and 2 from the top. It is explanatory drawing regarding the meshing part of the vertical cutting blade (roll cutter) 1,2. FIG. 7 is an enlarged explanatory view of a meshing portion shown in FIG. 6. It is a side view which shows the structure of the rotary sorter | selector which concerns on this Embodiment. It is sectional drawing which shows the structure of the 1st selection part shown in FIG. It is sectional drawing which shows the structure whose 2nd selection part shown in FIG. 8 is one layer. It is sectional drawing which shows the structure where the 2nd selection part shown in FIG. 8 is two layers. It is a typical perspective view which shows the structure of the 2nd selection part shown in FIG. It is sectional drawing which shows the structure of the vibration plane type | mold sorter which concerns on this Embodiment. It is a typical perspective view which shows the structure of the 2nd selection part shown in FIG. It is the schematic of the apparatus which measures the dust amount of a water absorbing resin.

Explanation of symbols

1, 2, Vertical cutting blade 3, 3 ', 4, 4' Scraper 8 Fixed blade 9 Spraying and / or spraying device (spraying and / or spraying means)
9 'Spraying and / or spraying device (spraying and / or spraying means)
10 Spraying and / or spraying device (spraying and / or spraying means)
10 'spraying and / or spraying device (spraying and / or spraying means)
11 Spraying and / or spraying device (spraying and / or spraying means)
12 Spraying and / or spraying device (spraying and / or spraying means)
14 Casing 17 Second sorter 17 'Second sorter 18 Punching (opening)
18 'punching (opening)
19 1st selection part 20 Gas injection nozzle (gas injection fog mechanism)
24 Water-absorbing resin 100 Cutting machine 200 Cross-cutting rotary blade 300 Sorting machine

Claims (14)

(1) An ethylenically unsaturated monomer containing acrylic acid and / or acrylate in an amount of 30 mol% or more and 100 mol% or less (excluding a crosslinking agent) is statically polymerized in the form of a sheet, and the water content is 40 mass%. A polymerization step for obtaining a hydrogel polymer having a sheet thickness of 3 mm or more and 10 mm or less, which is 70% by mass or less,
(2) The above-mentioned hydrogel polymer has a mass average particle diameter of 3 mm or more and 10 mm or less, and particles having a shape of tetrahedron or more and dodecahedron or less are 50% by mass or more and 100% by mass with respect to the mass of the hydrogel polymer. The cutting step of cutting to be not more than%, or after drying the hydrated gel polymer so that the moisture content is not less than 5% by mass and not more than 60% by mass, the mass average particle diameter is not less than 2 mm and not more than 10 mm. A cutting step of cutting so that particles having a shape of a tetrahedron or more and a dodecahedron or less are 50% by mass or more and 100% by mass or less with respect to the mass of the hydrogel polymer,
(3) Adhesion containing at least one of the compounds classified as polyvalent metal salts, polyhydric alcohols or surfactants before, simultaneously with and / or after cutting the hydrogel polymer. A coating step of coating at least a part of the surface of the water-containing gel-like polymer with an anti-oxidant;
(4) drying the coated hydrogel polymer at 80 ° C. or higher and 150 ° C. or lower;
Including
The water content of the water-absorbent resin obtained through the cutting step, the coating step and the drying step is 5% by mass to 30% by mass, the mass average particle size is 2 mm to 10 mm, and the logarithmic standard deviation value of the particle size distribution is 0. A method for producing a water-absorbent resin, characterized in that the content of the residual monomer is 0 mass ppm or more and 300 mass ppm or less.   The method for producing a water absorbent resin according to claim 1, further comprising a sorting step of sorting the obtained water absorbent resin after the drying step. The sorting step is a step of removing small variants and large variants,
The method for producing a water absorbent resin according to claim 2, wherein a water absorbent resin having a mass average particle diameter of 2 mm or more and 10 mm or less is obtained. The cutting step is a method for producing a water absorbent resin using a cutting machine,
That at least one of the vertical cutting blade, scraper, transverse rotary blade, and casing provided in the cutting machine is covered with at least one of a non-adhesive paint, a lubricating paint, and a metal-based material. The method for producing a water-absorbent resin according to any one of claims 1 to 3.   In the cutting step, the hydrogel polymer is formed into a hexagonal particle having a rectangular shape and a smooth surface. The mass of the hydrogel polymer is 50% by mass or more to 100% by mass. It cut | disconnects so that it may become below mass%, The manufacturing method of the water absorbing resin of any one of Claims 1-4 characterized by the above-mentioned.   6. The covering step includes a step of spraying and / or spraying the adhesion preventive agent on a vertical cutting blade, a transverse rotary blade, a fixed blade and / or a hydrogel polymer. The manufacturing method of the water absorbing resin of any one of these.   The adhesion preventive agent is added to the vertical cutting blade, the horizontal cutting blade, the fixed blade and / or the hydrogel polymer in an amount of 0.0015% by mass to 35% by mass with respect to the solid content of the water absorbent resin. The method for producing a water absorbent resin according to claim 6, wherein the water absorbent resin is sprayed and / or sprayed on the surface.   Further, in the polymerization step, an aqueous solution of ethylenically unsaturated monomer and / or a hydrogel polymer containing 30 mol% to 100 mol% (excluding a crosslinking agent) of acrylic acid and / or acrylate is contained. The method for producing a water absorbent resin according to claim 1, further comprising a step of containing a surfactant and / or a polyhydric alcohol.   Furthermore, the process which contains a chelating agent and / or a ultraviolet absorber in the inside and / or the surface containing a cut surface of the said hydrogel polymer is included in any one of Claims 1-8 characterized by the above-mentioned. A method for producing the water-absorbent resin as described. An ethylenically unsaturated monomer containing acrylic acid and / or acrylate in an amount of 30 mol% to 100 mol% is allowed to stand and polymerize in a sheet thickness of 3 mm to 10 mm, and has a shape of a tetrahedron to a dodecahedron. A water-absorbent resin obtained by drying a hydrogel polymer cut so that particles are 50% by mass to 100% by mass with respect to the mass of the hydrogel polymer at 80 ° C or higher and 150 ° C or lower. There,
At least a part of the surface of the water-absorbent resin is coated with an adhesion preventive agent containing at least one of a compound classified as a polyvalent metal salt, a polyhydric alcohol or a surfactant,
The mass average particle diameter is 2 mm or more and 10 mm or less, and the logarithmic standard deviation value of the particle size distribution is 0 or more and 0.25 or less,
A water-absorbent resin, wherein the residual monomer content is from 0 to 300 ppm by weight, and the water content is from 5 to 30% by weight.   The water-absorbing resin obtained by drying the hydrated gel polymer is selected, and the mass average particle size after the selection step for removing small and large irregularities is 2 mm or more and 10 mm or less, and the particle size distribution The water-absorbent resin according to claim 10, wherein a logarithmic standard deviation value of is from 0 to 0.25. The water-absorbent resin according to claim 10 or 11 , wherein the content of the adhesion inhibitor is 0.0015% by mass or more and 35% by mass or less based on the solid content of the water-absorbent resin. The hexagonal particles having a square shape and a smooth surface are contained in an amount of 50% by mass to 100% by mass with respect to the mass of the hydrogel polymer. The water absorbent resin according to any one of claims 10 to 12 . Furthermore, a chelating agent and / or a ultraviolet absorber are contained, The water absorbing resin of any one of Claims 10-13 characterized by the above-mentioned.

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