JPH1067805A - Manufacture of crosslinked polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a crosslinked polymer with high absorption ration and little soluble matter, with a simple and compact process and with high productivity, and to provide a water absorbing resin which, when incorporated into a paper diaper, etc., exhibits an excellent prop erty, and its manufacturing method. SOLUTION: This manufacturing method of a crosslinked polymer is as follows. At the polymerization of an aq. solution of a polymerizing monomer contg. a water-soluble ethylenic unsaturated monomer and the 1st crosslinking agent, the polymerization is carried out essentially in a stand still condition, from the beginning of the polymerization until the polymerizing system is gelled, and then, sufficient shearing stress is applied to the polymerization system to make the water-contg. gelled polymer into particles until the polymerizing system reaches the max. temp. by the heat of polymerization, and, moreover, polymerization is continued.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a crosslinked polymer. More specifically, the present invention relates to a method for producing a crosslinked polymer for obtaining a water absorbent resin. Further, the present invention relates to a water-absorbent resin having a large absorption capacity under normal pressure and under load and having a small amount of degradable soluble components and exhibiting excellent performance when used as a sanitary material and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a water-absorbing resin has been developed as a polymer that absorbs a large amount of water and gels, and is used as an absorbent for sanitary materials such as sanitary napkins and disposable diapers, or in agricultural and horticultural fields.
In the field of civil engineering, it is applied to a wide range of uses as a water retention agent, a dehydration agent, and the like.

Examples of the crosslinked polymer for obtaining a water-absorbent resin include a crosslinked product of partially neutralized polyacrylic acid, a crosslinked polyvinyl alcohol modified product, a crosslinked isobutylene-maleic anhydride copolymer, a crosslinked product of polyethylene oxide, and acrylic acid. Saponified ester-vinyl acetate copolymers, hydrolyzed starch-acrylonitrile graft polymers, starch-acrylic acid graft polymers, and the like are known.

As a method for producing these crosslinked polymers, a reverse phase suspension polymerization method is described, for example, in JP-A-56-161408 and JP-A-57-9.
Nos. 4,011, 57-158,209 and 57-198,714 are known, and as aqueous solution polymerization methods, for example, Japanese Patent Publication No. 2-19,122, Japanese Patent Publication No. 48-42,466,
-49,714, JP-B-59-37,003, U.S. Patent No. 4,286,08
No. 2 and U.S. Pat. No. 4,625,001 are known.

[0005] Since the reversed-phase suspension polymerization method uses an organic solvent, not only the working environment is deteriorated, but also there is a danger of a flash explosion. The cost is high together with the removal cost. Also, since a small amount of this organic solvent remains in the product,
Eliminating this completely would be even more costly. Furthermore, since the crosslinked polymer obtained by the reversed-phase suspension polymerization method is spherical and has a small particle size, when used in, for example, a disposable diaper, the crosslinked polymer tends to fall off without being retained by a fibrous absorbent core component such as pulp. Moreover, handling is inconvenient.

On the other hand, the aqueous solution polymerization method has no such problems as described above, and is disclosed in Japanese Patent Publication No. 2-19,122 and US Pat. No. 4,625,00.
The method disclosed in No. 1 or the like is known. The method described in the above-mentioned patent publication is a method in which an aqueous solution of a monomer and a polymerization initiator which form a crosslinked structure during aqueous solution polymerization and become a hydrogel polymer are polymerized in a radical aqueous solution in a vessel equipped with a rotary stirring shaft. In this process, the hydrogel polymer produced as the polymerization proceeds is subjected to radical aqueous polymerization while being subdivided by shearing force generated by rotation of a rotating arm or a stirring blade provided on the stirring shaft. It is a manufacturing method of united. According to these production methods, not only the workability is extremely good, but also there is an advantage that a finely divided hydrogel polymer having a crosslinked structure in the molecule can be produced with high productivity. However, in such a method, satisfactory conditions for producing a crosslinked polymer having a relatively large absorption capacity and a sufficiently low soluble content have not been known. In an attempt to obtain a crosslinked polymer having a sufficiently low soluble content, the productivity was remarkably reduced, and the amount of residual monomers increased.

It is well known to those skilled in the art that the absorption capacity is improved by lowering the crosslink density, but at the same time, the soluble matter is also increased. The soluble component is leached out of the crosslinked polymer when it comes into contact with the liquid to be absorbed, such as water, urine, or body fluid, to form a hydrogel. As described above, the soluble matter extracted by the liquid to be absorbed not only lowers the absorption capacity of the crosslinked polymer but also promotes the deterioration of the crosslinked polymer. In addition, such an unfavorable situation is created such as giving an unpleasant sensation or contaminating the liquid to be absorbed.

Accordingly, there has been a demand for a method for producing a crosslinked polymer having a high water absorption capacity and a low soluble content.

US Pat. No. 4,654,039 and JP-A-1-144,40
No. 4 proposes a method for producing a crosslinked polymer having a high absorption capacity and a low soluble content by polymerizing a free acid type or a monomer having a specific neutralization ratio in an aqueous solution. However, these production methods have low productivity due to an increase in residual monomers, a need for a post-neutralization step, and complicated operations.

In JP-A-56-91,837 and JP-A-4-175,319, the absorption capacity is high by controlling the temperature during the polymerization without stirring the aqueous monomer solution, thereby increasing the absorption capacity, A method for producing a crosslinked polymer having a low residual monomer is disclosed. However, performing the polymerization step without agitation limits the number of polymerization machines when performing this on an industrial scale, and in order to perform polymerization while controlling the temperature during polymerization to a predetermined range, it is necessary to carry out production. However, there were problems such as a decrease in performance and a remarkably large polymerization machine.

As described above, a method for producing a crosslinked polymer with a simple and compact process, high productivity, high absorption capacity and low soluble content has not been established.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a production method capable of producing a crosslinked polymer having a high absorption capacity and a low soluble content with high productivity. .

The desired properties of these cross-linked polymers as a water-absorbing resin include a high absorption capacity under a load, in addition to a high absorption capacity and a small amount of soluble components in the liquid to be absorbed. However, when the water-absorbent resin swells with pure water or physiological saline, it maintains its properties stably for a long time, but when it swells with urine, it deteriorates with time and the soluble component increases, There were problems when used in sanitary materials such as disposable diapers, for example, the absorption capacity under normal pressure and under load was reduced, and the nullification caused significant discomfort.

Accordingly, another object of the present invention is to provide a water-absorbent resin in which a product such as a disposable diaper incorporating the water-absorbent resin can exhibit excellent performance in actual use conditions.

[0015]

These objects are achieved by the following (1) to (9).

(1) When polymerizing an aqueous solution of a polymerizable monomer containing a water-soluble ethylenically unsaturated monomer which becomes a hydrogel polymer by polymerization and a first crosslinking agent, polymerization is started. From the point in time to the point in time when the entire polymerization system gels, polymerization is carried out in a substantially stationary state, and thereafter, a sufficient shearing force is applied to the polymerization system until the polymerization system reaches the maximum temperature due to the heat of polymerization. In addition, a method for producing a crosslinked polymer, which comprises converting the hydrogel polymer into particles and continuing the polymerization.

(2) When the aqueous solution of a polymerizable monomer containing a water-soluble ethylenically unsaturated monomer and a first cross-linking agent, which is converted into a hydrogel polymer by polymerization, is polymerized. From the point in time to the point in time when the entire polymerization system gels, the heat removal polymerization is carried out in a substantially stationary state, and thereafter, sufficient shearing force is applied to the polymerization system until the polymerization system reaches the maximum temperature due to the heat of polymerization. , The hydrogel polymer is made into particles, and the heat removal polymerization is continued, wherein the crosslinked polymer is produced as described in (1) above.

(3) When polymerizing an aqueous solution of a polymerizable monomer containing a water-soluble ethylenically unsaturated monomer and a first crosslinking agent to form a hydrogel polymer by polymerization, the rotating arm Alternatively, in a reaction vessel having a stirring blade, from the start of polymerization to the point at which the entire polymerization system gels, the heat removal polymerization is performed in a substantially stationary state, and then the polymerization system reaches the maximum temperature due to the heat of polymerization. By the time, the rotating arm or the stirring blade rotates to apply a sufficient shearing force to the polymerization system to form the hydrogel polymer into particles, and to continue the heat removal polymerization. Or the method for producing a crosslinked polymer according to (2).

(4) The temperature of the polymerization system is at least 40 ° C.
The method for producing a crosslinked polymer according to the above (1) or (2), wherein the polymerization is carried out in a substantially stationary state until the temperature reaches the value of (1).

(5) Any one of the above (1) to (4), wherein the formed hydrogel polymer is temporarily broken during the period from the start of the polymerization to the point at which the entire polymerization system gels. The method for producing a crosslinked polymer according to the above.

(6) Between the time when the polymerization is started and the time when the entire polymerization system gels, the formed hydrogel polymer is temporarily broken by the rotation of the rotating arm or the stirring blade. A method for producing the crosslinked polymer according to the above.

(7) The aqueous solution of a polymerizable monomer is composed of acrylic acid and / or an alkali metal salt, an ammonium salt, or an amine salt thereof, and a first polymer having at least two polymerizable unsaturated double bonds per molecule. The method for producing a crosslinked polymer according to any one of the above (1) to (6), which comprises a crosslinking agent as a main component.

(8) Crosslinked polymer particles obtained by drying and pulverizing the crosslinked polymer obtained by the production method according to any one of (1) to (6), and the crosslinked polymer particles A method for producing a water-absorbent resin, comprising mixing a second crosslinking agent that reacts with at least two functional groups in the vicinity of the surface with a second crosslinking agent and subjecting the mixture to heat treatment.

(9) The absorption capacity of physiological saline at normal pressure is at least 30 g / g, the absorption capacity of physiological saline under load is at least 25 g / g, and the degradable soluble content is 15% by weight or less. A water-absorbent resin having an irregular shape.

In the present invention, the heat-removal polymerization refers to polymerization in which the temperature of the polymerization system is controlled to an optimum temperature by external cooling, specifically, by circulating cooling water through a jacket. This is a polymerization method in which better physical properties can be obtained as compared with adiabatic polymerization without the concept of actively removing heat. For example, the temperature of the jacket cooling water is controlled to be equal to or lower than the temperature of the polymerization system from the start of the polymerization until the polymerization system reaches the maximum temperature. More preferably, the temperature of the cooling water is kept equal to or lower than the polymerization initiation temperature.
Further, the polymerization vessel preferably has a large conduction area for cooling with a jacket.

In the present invention, the polymerization system refers to an aqueous solution of a polymerizable monomer and / or a hydrogel polymer. The point of initiation of the polymerization can be known from an increase in the viscosity of the polymerization system, cloudiness of the polymerization system, or an increase in the temperature of the polymerization system.
The point in time when the entire polymerization system gels is, for example, a point in time when the polymerization system does not flow even when the reaction vessel is tilted, or a point in time when the polymerization system can maintain a predetermined shape.

In the present invention, performing the polymerization in a substantially stationary state means not only performing the polymerization while keeping the rotating arm or the stirring blade in a stopped state, but also the following method, for example. It shall be included in the meaning of polymerization in a substantially stationary state.

(A) A method in which polymerization is carried out at a low speed of about 5 rpm, preferably at 0 rpm.

(B) No rotation at all, 5r
A method in which polymerization is carried out using a low-speed rotation of about pm, preferably 0 rpm.

(C) The method of (a), wherein the polymerization is carried out by temporarily rotating the film so that a sufficient shearing force for breaking the gel can be applied.

(D) The method according to (b), wherein the polymerization is carried out by temporarily rotating the film so that a sufficient shearing force can be applied to break the gel.

(E) A method in which the polymerization is carried out temporarily without rotating at all, but temporarily rotating to such an extent that a shearing force sufficient to break the gel can be applied.

However, the present invention is not limited to these methods (a) to (e).

The absorption capacity under normal pressure in the present invention is the absorption capacity of physiological saline measured under conditions where no pressure is applied to the water absorbent resin. The method for measuring the absorption capacity under normal pressure will be described in detail in Examples below.

On the other hand, the absorption capacity under load in the present invention is the absorption capacity of physiological saline measured under the condition that a predetermined load is applied to the water-absorbent resin. The method of measuring the absorption capacity under load will be described in detail in Examples below.

The term “degradable soluble matter” in the present invention refers to a water-containing gel obtained by allowing a predetermined amount of artificial urine to be absorbed by a water-absorbent resin and swelling to a predetermined magnification under a predetermined condition for a predetermined time. It is the amount of soluble matter. After absorbing artificial urine, the water-absorbent resin deteriorates with time, and at the same time, the soluble matter increases.If the amount of the increased soluble matter is large, the absorption capacity of the water-absorbent resin under normal pressure and under load may decrease. It is particularly unfavorable as a water-absorbing agent for sanitary materials, for example, because of its nullness, which gives a significant discomfort.
Therefore, the smaller the amount of the degradable soluble components, the higher the gel stability in urine and the superior performance is maintained for a long time, and it is optimal as a water-absorbing resin used for disposable diapers and the like. In addition, artificial urine is urea, sodium chloride, magnesium sulfate, calcium chloride, and L-ascorbic acid,
It is an aqueous solution dissolved so that the content is almost equal to that of actual urine. The method for measuring the amount of the degradable soluble component will be described in detail in the examples below.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

[0038] The water-soluble ethylenically unsaturated monomer used in the present invention is not particularly limited as long as it is a water-soluble ethylenically unsaturated monomer. A hydrophobic monomer may be used in combination without departing from the purpose of the invention. Examples of the water-soluble ethylenically unsaturated monomers include (meth) acrylic acid, (anhydride) maleic acid, fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloylethanesulfonic acid, and 2- (meth) Anionic monomers such as acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid and styrenesulfonic acid, and salts thereof; (meth) acrylamide, N-substituted (meth) acrylamide , 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate,
Nonionic hydrophilic group-containing monomers such as polyethylene glycol (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl ( Specific examples include amino group-containing unsaturated monomers such as (meth) acrylamide and quaternized compounds thereof, and one or more selected from these groups can be used. In addition, in an amount that does not extremely impair the hydrophilicity of the obtained polymer, for example, acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, vinyl acetate, and propionic acid A hydrophobic monomer such as vinyl may be used.

From the viewpoint of the performance and cost of the obtained crosslinked polymer, preferred monomers are anionic monomers, which are neutralized with acrylic acid and / or its alkali metal salt, ammonium salt or amine salt. It is particularly preferable to use a salt of acrylic acid as a main component because the obtained crosslinked polymer has excellent absorption characteristics. At this time, the content of acrylic acid and / or a salt of acrylic acid neutralized with an alkali metal salt, an ammonium salt, or an amine salt thereof is 50% by weight or more in the water-soluble ethylenically unsaturated monomer. It is more preferable that the content be 75% by weight or more. When an acid group-containing monomer such as (meth) acrylic acid is used as a main component and the neutralization ratio of the acid group is less than 50 mol%, during or after polymerization (for example, when the polymerization system is After reaching the maximum temperature), an alkali substance such as a hydroxide, an alkali metal salt, an ammonium salt, or an amine salt is added to the polymerization system, mixed, and the neutralization rate of the acid group is reduced to 5%.
The content is preferably 0 to 90 mol%, more preferably 55 to 80 mol%.

The first cross-linking agent used in the present invention is for forming a cross-linked structure at the time of polymerization, and as such, it has two or more polymerizable unsaturated double bonds in the molecule. Compounds, compounds having two or more groups in the molecule that react with functional groups such as acid groups, hydroxyl groups, and amino groups of the water-soluble ethylenically unsaturated monomer, unsaturated bonds and monomers in the molecule Each group that reacts with a functional group
Compound, a compound having two or more points in the molecule that react with the functional group of the monomer, or a hydrophilic polymer capable of forming a cross-linked structure by graft bonding or the like when the monomer component is polymerized. Can be given.

Examples of these first crosslinking agents include, for example, polyvalent (meth) acrylamide compounds such as N, N'-methylenebis (meth) acrylamide; (poly) ethylene glycol di (meth) acrylate; Pyrene glycol di (meth) acrylate, glycerin di (meth) acrylate, glycerin acrylate methacrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane acrylate methacrylate, pentaerythritol di (meth) acrylate, glycerin tri (meth) acrylate, tri Polyvalent (meth) acrylate compounds such as methylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and pentaerythritol tetra (meth) acrylate; Polyvalent allyl compounds such as amine, (poly) allyloxyalkane, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate; (poly) ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin Polyvalent glycidyl compound such as triglycidyl ether; polyvalent isocyanate compound such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate; polyoxazoline compound; containing reactive groups such as N-methylol (meth) acrylamide and glycidyl (meth) acrylate (Meth) acrylamide or (meth) acrylate; aluminum chloride, magnesium chloride, calcium chloride, aluminum sulfate, magnesium sulfate, calcium sulfate And the like, and among them, one or more kinds can be used in consideration of reactivity.

From the viewpoint of the performance of the obtained crosslinked polymer as a water-absorbing resin, preferred first crosslinking agents are compounds having two or more polymerizable unsaturated double bonds in the molecule, more preferably A polyvalent (meth) acrylamide compound and a polyvalent (meth) acrylate compound. The amount of the first crosslinking agent used is not particularly limited, but is preferably 0.001 to 20% by weight, and more preferably 0.001 to 20% by weight, based on the type of the first crosslinking agent used. Is 0.005
Used in the range of 5% by weight. 0.001% by weight used
If it is less than 3, the crosslinked density of the obtained hydrogel polymer becomes small, the uncrosslinked portion becomes remarkably large, and the soluble component increases. When the amount exceeds 20% by weight, the absorption capacity of the obtained crosslinked polymer becomes small.

In addition to the first crosslinking agent, starch,
A method in which a graft bond or a complex is formed simultaneously with the polymerization by polymerizing the above monomer component in the presence of a hydrophilic polymer such as cellulose, polyvinyl alcohol, and poly (meth) acrylic acid may be used. These hydrophilic polymers are preferably used, for example, in the range of 0.5 to 50% by weight based on the water-soluble ethylenically unsaturated monomer. If necessary, a thickener may be used in the aqueous solution of the polymerizable monomer. Examples of such a thickener include polyvinylpyrrolidone, polyacrylamide, methylcellulose, hydroxyethylcellulose and the like.

In the present invention, the concentration of the aqueous solution of the polymerizable monomer is from 10 to 80% by weight, preferably from 10 to 45% by weight, more preferably from 10 to 80% by weight, based on the weight of the aqueous solution. It is contained in the range of 10 to 35% by weight. If the concentration is less than 10% by weight, not only does the productivity in the polymerization step deteriorate, but also a large amount of energy is required in the drying step for obtaining a dried product, which is not preferable from the viewpoint of industrial productivity. On the other hand, if it exceeds 80% by weight, it is difficult to control the polymerization reaction, the maximum temperature of the polymerization system due to the polymerization heat becomes too high, and the absorption performance may decrease such as increasing the soluble component.

As a method for polymerizing the aqueous polymerizable monomer solution in the present invention, a usual polymerization method can be used. For example, a method using a radical polymerization initiator, a polymerization method using active energy rays, and the like can be mentioned, and a method using a water-soluble radical polymerization initiator is preferable. Known water-soluble radical polymerization initiators can be used,
For example, persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl hydroperoxide and cumene hydroperoxide; 2,2′-azobis (2-methyl- N-phenylpropionamidine) dihydrochloride,
2,2'-azobis [N- (4-chlorophenyl) -2
-Methylpropionamidine] dihydrochloride,
2,2'-azobis [N- (4-hydroxyphenyl)
-2-methylpropionamidine] dihydrochloride, 2,2'-azobis [2-methyl-N- (2-propenyl) propionamidine] dihydrochloride,
2,2′-azobis [2-methyl-N- (phenylmethyl) propionamidine] dihydrochloride,
2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-hydroxyethyl) -2-methylpropionamidine] dihydrochloride, 2,2′-azobis [2- (5-
Methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- ( 4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (3,4,5,6-tetrahydropyrimidine −
2-yl) propane] dihydrochloride, 2,2 '
-Azobis [2- (5-hydroxy-3,4,5,6-
Tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2′-azobis {2- [1-
(2-Hydroxyethyl) -2-imidazolin-2-yl] propane dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane]
And other azo compounds; ceric salts, permanganates and the like.

Among them, one or more selected from the group consisting of persulfates, peroxides and azo compounds are preferred from the viewpoint of the performance of the obtained crosslinked polymer and the safety of the compound. When the radical polymerization initiator is an oxidizing radical polymerization initiator, sulfites; hydrogen sulfites; thiosulfates; dithionites; metal salts such as cuprous sulfate and ferrous sulfate;
It may be used as a redox initiator in combination with an organic reducing agent such as ascorbic acid; a reducing agent such as amines such as aniline and monoethanolamine. The amount of these polymerization initiators is not particularly limited, but is usually 0.001 to 10% by weight, preferably 0.002 to 10% by weight, based on the monomer components.
5% by weight. If the amount used is less than 0.001% by weight, the polymerization time and the induction period are prolonged, and the residual monomer tends to increase, which is not preferable. If the amount exceeds 10% by weight, it is difficult to control the polymerization reaction, and the performance of the obtained crosslinked polymer tends to decrease, which is not preferable.

In carrying out the production method of the present invention, a particularly preferred polymerization initiator is a combination of a thermally decomposable initiator, at least two kinds of oxidative radical polymerization initiators having different decomposition temperatures, and a reducing agent. is there. Preferred azo compounds include the above-mentioned azo compounds. The present invention uses a redox initiator capable of initiating polymerization from a low temperature, and an azo compound and a persulfate which are effective for reducing the amount of residual monomers in the formed hydrogel polymer. It is preferable to achieve the purpose of. The redox initiator capable of initiating polymerization from the low temperature is 0 to
At 40 ° C., preferably 0-30 ° C., the induction period is zero.
It is a redox initiator whose polymerization is started within 1 hour, preferably within 0 to 30 minutes, more preferably within 0 to 10 minutes.

In the present invention, the polymerization initiation temperature is not particularly limited, but is appropriately selected depending on the decomposition temperature of the polymerization initiator used, and is usually in the range of 0 to 45 ° C, preferably 0 to 40 ° C. If the polymerization initiation temperature is too low, the induction period will be long and the productivity may decrease. On the other hand, if the polymerization initiation temperature is too high, the polymerization reaction, that is, it is difficult to control the heat generated by the heat of polymerization, the maximum temperature of the polymerization system is too high,
It causes deterioration of physical properties such as increase in solubles.

The method for producing a crosslinked polymer of the present invention comprises a step of carrying out polymerization in a substantially stationary state from the time of initiation of polymerization to the time of polymerization of the entire polymerization system (hereinafter referred to as a retention period); A step of applying sufficient shearing force to the polymerization system after the holding period to form a hydrogel polymer into particles (hereinafter, referred to as a gel crushing step), and further continued until the polymerization system reaches the maximum temperature due to heat of polymerization. (Hereinafter referred to as a continuous polymerization step).

As the polymerization reaction vessel used in the above-mentioned holding period and continuous polymerization step, a conventionally known polymerization reaction vessel can be used. These may be the same or different. The polymerization reaction vessel used in the continuous polymerization step is preferably provided with an appropriate jacket, a rotating arm or a stirring blade, since the polymerization system can be controlled to an optimum maximum temperature. Further, each of the above steps may be performed continuously in the same polymerization reaction vessel, may be performed in a different place for each step, or may be performed in any suitable combination.

As a means for converting the hydrogel polymer into particles in the gel disintegrating step, a conventionally known gel disintegrating and / or pulverizing apparatus can be used. For example,
Examples thereof include a screw type extruder having a perforated plate such as a meat chopper, an extruder, a shredder, an edge runner, a cutter mill, and a screw type crusher (for example, manufactured by Nippon Spindle Co., Ltd., Alpha etc.). Further, in a polymerization reaction vessel having a rotating arm or stirring, the hydrogel polymer may be formed into particles by shearing force generated by rotation of the rotating arm or stirring blade. A reaction vessel having a large stirring force for the hydrogel polymer is preferred. For example, a batch type such as a kneader, a (mechanical) pressure kneader, an internal mixer, a Banbury mixer, or a continuous type such as a continuous kneader can be used.

In the production method of the present invention, the above three steps can be continuously performed in the same container, the stirring power for the hydrogel polymer is large, the heat transfer area is large, and the control of the maximum temperature is easy. For some reasons, it is particularly preferable to use a polymerization reaction vessel having the above-mentioned rotating arm or stirring blade. In particular, a double-arm kneader is preferably used. A pressure kneader as described in JP-A-5-112654 and JP-A-5-247225 is also preferably used.

Conventionally, a method is known in which a hydrogel polymer produced as polymerization proceeds in a reaction vessel having a rotating arm or stirring blade is polymerized while being fragmented by shearing force generated by rotation of the rotating arm or stirring blade. Although it was known, since the attention was paid only to the fragmentation of the hydrogel polymer in order to remove the heat of polymerization or homogenize the polymerization system, an attempt to provide a retention period as in the present invention was made. Has never been done before. When the holding period is not provided, the absorption capacity of the obtained crosslinked polymer tends to decrease. By providing a holding period, Trommms in the early stage of polymerization
Although the molecular weight can be increased under conditions where the dorff effect cannot be expected, or because a uniform crosslinked network is formed without mechanical stirring, the effect of the present invention may be obtained. The invention is not limited by such a concept.

In the present invention, it is preferable to carry out the polymerization in a substantially stationary state until the temperature of the polymerization system reaches at least 40 ° C. Further, the temperature of the polymerization system is at least 50.
More preferably, the polymerization is carried out in a substantially stationary state until the temperature reaches ° C.

When the holding period is completed when the temperature of the polymerization system is lower than 40 ° C. and a shearing force is applied to the polymerization system, the crosslinked polymer intended for the present invention may not be obtained. That is, the soluble component may increase or the absorption capacity may decrease. Although it depends on the concentration of the aqueous polymerizable monomer solution and the polymerization initiation temperature, it is more preferable to carry out the polymerization in a substantially stationary state until the temperature of the polymerization system reaches 60 ° C.

On the other hand, even if the temperature of the polymerization system exceeds 70 ° C., unless a shearing force is applied to the polymerization system, the hydrogel polymer cannot be finely divided, and the maximum temperature of the polymerization system becomes too high. In some cases, physical properties such as an increase in soluble matter may be reduced.

The holding period is preferably at least 60 seconds. If the time is less than 60 seconds, it is difficult to obtain the effects of the present invention. More preferably, at least one
A retention time of 20 seconds, most preferably at least 180 seconds.

In a preferred embodiment of the method for producing a crosslinked polymer of the present invention, the total amount of mechanical energy per unit weight applied to the polymerization system during the holding period is set to about 800 joules / kg or less. is there. The mechanical energy applied to the polymerization system can be determined from the input power to the motor that stirs the polymerization system. By significantly reducing the mechanical energy applied to the polymerization system during the holding period, a crosslinked polymer having a high absorption capacity and a low soluble content, which is the object of the present invention, can be obtained. During the holding period, the total amount of mechanical energy applied to the polymerization system is preferably about 800
Joules / kg or less, more preferably about 500 joules / kg or less, and even more preferably about 0 joules / kg.

In the method for producing a crosslinked polymer of the present invention,
After the holding period, it is necessary to apply sufficient shearing force to the polymerization system to pulverize the hydrogel polymer into particles. The hydrogel polymer is increased in surface area by being pulverized into particles, so that cooling by evaporation of water or cooling by the jacket of the reaction vessel becomes more effective and control of the polymerization temperature becomes easy.

When the polymerization system reaches the maximum temperature, 1
It is preferable that there is no hydrogel polymer having a size of 50 mm or more. If the size of the hydrogel polymer at the time of reaching the maximum temperature exceeds 150 mm, it becomes difficult to control the temperature of the polymerization system, and not only the soluble content of the obtained crosslinked polymer increases. In addition, the temperature distribution in the polymerization system is widened, and a polymer having uniform physical properties cannot be obtained.
The size of the hydrogel polymer is representative of its shortest length. It is preferable that there is no hydrogel polymer having a size of 100 mm or more, and it is more preferable that there is no hydrogel polymer having a size of 50 mm or more. Most preferably, it is not.

In the method for producing a crosslinked polymer of the present invention,
The maximum temperature of the polymerization system is preferably controlled in the range of 65 to 85 ° C. If the maximum temperature is too low, the polymerization rate of the polymerizable monomer decreases, and the amount of the residual monomer in the obtained crosslinked polymer increases. On the other hand, if the maximum temperature is too high, the physical properties tend to decrease, such as an increase in the soluble component. In the present invention, the maximum temperature of the polymerization system can be easily controlled because the hydrogel polymer is pulverized into particles. That is, the surface area of the hydrogel polymer increases, and when the polymerization system is slightly exothermic, the latent heat of evaporation due to water evaporation increases, and cooling can be efficiently performed by conduction heat transfer from the reaction vessel or a jacket attached thereto.

In the production method of the present invention, the produced hydrogel polymer may be temporarily broken during the holding period. By performing this operation, it may be easy to make the hydrogel polymer into a particulate form after the holding period.
The method of temporary breakage varies depending on the polymerization reaction vessel used during the holding period, but it is particularly preferable to use a rotation of a rotating arm or a stirring blade provided in the polymerization vessel. The rupture timing is after the time when the polymerization system gels to the extent that it can be ruptured by shearing force. The degree of breaking may be such that the hydrogel polymer is broken into large blocks.
The breaking time may be usually within 30 seconds.

In the production method of the present invention, after the polymerization system reaches the maximum temperature, it is preferable that the polymerization system be kept at 50 to 85 ° C. for at least 5 minutes, preferably for at least 10 minutes, in order to reduce the residual monomer. It is preferable in that a crosslinked polymer is obtained. During this time, the rotating gel or the stirring blade may be rotated as necessary to further subdivide the hydrogel. It is more preferable to keep in an inert gas atmosphere.

Further, in the production method of the present invention, an oxygen-containing sulfur-based reducing agent may be added and mixed after the polymerization system reaches the maximum temperature in order to reduce residual monomers.
It is preferable to add and mix to the hydrogel polymer at least at 45 ° C. The oxygen-containing sulfur-based reducing agent used in the present invention is not particularly limited as long as it is an oxygen-containing sulfur-based compound having a reducing action. For example, sulfites such as sulfurous acid, sodium sulfite, and potassium sulfite; sodium bisulfite, hydrogen sulfite Bisulfites such as potassium; thiosulfates such as sodium thiosulfate and potassium thiosulfate; Among them, sodium hydrogen sulfite is preferable. The amount of the oxygen-containing sulfur-based reducing agent to be used is not particularly limited, but is preferably 0.1 to 10% by weight of the water-soluble ethylenically unsaturated monomer.
It is 001 to 5% by weight, preferably 0.01 to 2% by weight. As a method of adding to the hydrogel polymer, a conventionally known addition and mixing method is used. For example, a powdered oxygen-containing sulfur-based reducing agent may be added as it is, or the reducing agent may be dissolved or dispersed in water or an organic solvent and added.

The particulate hydrogel polymer obtained in the method for producing a crosslinked polymer of the present invention is subjected to gel crushing and / or
Alternatively, the particles may be further refined by a pulverizer. If necessary, it is preferable to heat the particulate hydrogel to a temperature of 45 to 90 ° C. to form fine particles. A conventionally known gel disintegrating and / or pulverizing machine can be used as a method for pulverizing. In particular, it is preferable to extrude from a perforated plate to make fine particles by the method described in JP-A-5-70,597, JP-A-6-41,319 and the like. If necessary, coarse particles are disclosed in JP-A-6-107,
After classification by a gel classifier as described in No. 800, only the coarse particles may be refined.

The crosslinked polymer obtained by the production method of the present invention may be dried by a conventionally known method. For example, a method using azeotropic dehydration in an organic solvent, a forced air oven, a reduced-pressure drier, a microwave drier, an infrared drier, a drying method using a belt or a drum drier heated to a predetermined temperature, and the like can be given. Using these drying methods, the hydrogel polymer after polymerization can be dried at 50 ° C to 230 ° C, more preferably at 50 ° C to 180 ° C. 50 ℃
If it is less than this, drying takes a long time, which is not preferable in terms of productivity. If the temperature exceeds 230 ° C., the crosslinked polymer may be degraded, so caution is required. Usually, it is preferable that the solid content is dried to 60% by weight or more, and more preferably 90% by weight or more by these methods.

The crosslinked polymer dried as described above may be ground and / or classified by a conventionally known method, if necessary. For example, a high-speed rotary pulverizer (pin mill, hammer mill, etc.), a screw mill (coffee mill), a roll mill and the like can be mentioned. When a powdery crosslinked polymer is intended, the average particle size is 10 to 2000 μm, more preferably 100 to 1000 μm, and most preferably 300 to 60 μm.
It is preferable that the particle size is adjusted to about 0 μm and the particle size distribution is narrow.

The crosslinked polymer obtained by the production method of the present invention has a larger water absorption capacity, a smaller amount of soluble components, and exhibits excellent water absorption properties as compared with conventional crosslinked polymers.

Further, the present invention provides a crosslinked polymer particle obtained by drying and pulverizing the crosslinked polymer obtained by any of the above-mentioned production methods, and at least two functional groups near the surface of the crosslinked polymer particle. A method for producing a water-absorbent resin, which comprises mixing a second crosslinking agent that reacts with the mixture and heat-treating the mixture.

As the second crosslinking agent used in the present invention, for example, when the crosslinked polymer has a carboxyl group, any compound which can react with at least two carboxyl groups can be used without any particular limitation. For example, ethylene glycol, propylene glycol, glycerin, pentaerythritol, sorbitol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 1,4-butanediol, 1, Polyhydric alcohol compounds such as 5-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2,5-hexanediol, and trimethylolpropane; ethylene glycol diglycidyl ether, polyethylene glycol Polyhydric epoxy compounds such as rudiglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether; diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, triethylene Polyvalent amines such as ethylenetetramine; 2,4
Polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate; ethylene carbonate (1,3-dioxolan-2-one) and propylene carbonate (4-methyl-1,3-dioxolan-2)
-One), 4,5-dimethyl-1,3-dioxolane-
Examples include 2-one, epichlorohydrin, epibromohydrin and the like, but are not limited to these compounds. These may be used alone or as a mixture of two or more.

The amount of the second crosslinking agent used depends on the compound to be used and the combination thereof, but is preferably 0.001 to 10% by weight, more preferably 100 to 10% by weight, based on 100% by weight of the solid content of the crosslinked polymer. Is 0.01 to 5% by weight. If the amount of the second cross-linking agent exceeds 10% by weight, not only is it uneconomical, but also the amount of the cross-linking agent used becomes excessive in forming an optimum cross-linked structure in the obtained water-absorbent resin. Not preferred. The amount of the second crosslinking agent used is 0.001.
If the amount is less than% by weight, it is difficult to obtain the effect of improving the absorption capacity under load and the degradable soluble component of the obtained water-absorbent resin, and it is difficult to obtain the improvement effect.

When mixing the crosslinked polymer and the second crosslinking agent, it is preferable to use water as a solvent. The amount of water used depends on the type and particle size of the crosslinked polymer, but is preferably more than 0 and 20% by weight or less, preferably 0.5 to 10% by weight, based on 100% by weight of the solid content of the crosslinked polymer. % Is more preferable. When mixing the crosslinked polymer with the second crosslinking agent, a hydrophilic organic solvent may be used as a solvent, if necessary. As the hydrophilic organic solvent, for example,
Lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol and t-butyl alcohol; ketones such as acetone; ethers such as dioxane and tetrahydrofuran; Examples include amides such as dimethylformamide; sulfoxides such as dimethyl sulfoxide.

The amount of the hydrophilic organic solvent used depends on the type and particle size of the crosslinked polymer, but is preferably 20% by weight or less based on 100% by weight of the solid content of the crosslinked polymer. 1
More preferably, it is in the range of 0% by weight. When mixing the crosslinked polymer and the second crosslinking agent, the mixing method is not particularly limited. Among various mixing methods, a method in which the second crosslinking agent dissolved in water and / or a hydrophilic organic solvent is directly sprayed or dropped on the crosslinked polymer as necessary is preferable. In the case of mixing using water, fine powder insoluble in water, a surfactant or the like may be allowed to coexist. The mixing device used for mixing the crosslinked polymer and the second crosslinking agent preferably has a large mixing force in order to uniformly and surely mix the two. Examples of the above mixing device include a cylindrical mixer, a double-walled conical mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a fluidized-type rotary desk mixer, a gas-flow mixer. A machine, a double-arm kneader, an internal mixer, a pulverizing kneader, a rotary mixer, a screw extruder and the like are suitable.

After the crosslinked polymer and the second crosslinker are mixed, a heat treatment is performed to crosslink the vicinity of the surface of the crosslinked polymer with the second crosslinker. The treatment temperature of the above heat treatment is preferably from 50 ° C. to 250 ° C., although it depends on the crosslinking agent used. When the treatment temperature is lower than 50 ° C., a uniform crosslinked structure is not formed, and therefore, a water-absorbent resin excellent in performance such as absorption capacity under load cannot be obtained. If the treatment temperature exceeds 250 ° C., the resulting water-absorbent resin is deteriorated, and its performance is undesirably reduced. The above heat treatment can be performed using a usual dryer or heating furnace. As the above dryer, for example, a groove-type mixing dryer, a rotary dryer,
Desk dryers, fluidized bed dryers, air-flow dryers, infrared dryers and the like can be mentioned.

The crosslinked polymer obtained with high productivity according to the present invention has excellent water absorption capacity and a small amount of soluble components as compared with conventional crosslinked polymers, and has excellent characteristics. Further, the water-absorbent resin having an irregular shape obtained from the crosslinked polymer has an absorption capacity under normal pressure of at least 30 g / g, preferably at least 35 g / g, and an absorption capacity under load of at least 25 g.
/ G, preferably at least 28 g / g, both high,
In addition, it has an unprecedented characteristic in that the content of the degradable soluble component is as low as 15% by weight or less, preferably 10% by weight or less.

(1) Since the absorption capacity under no load and under load is high, when used in a disposable diaper or the like, a large amount of urine or the like can be absorbed and held while withstanding the load such as weight from a baby to an adult.

(2) Since the amount of soluble components to be eluted is small, it does not give any discomfort such as nulling when the disposable diaper is worn.

(3) Since the amount of degradable soluble components is small, the excellent performances of the above (1) and (2) can be maintained for a long time.

(4) Since it has an irregular shape, it is less likely to fall off the absorbent core when the disposable diaper is worn, and the safety to the wearer's skin is high.

Because of the above effects, the crosslinked polymer and water-absorbent resin obtained in the present invention can be used for sanitary materials such as paper diapers for children and adults, sanitary napkins, incontinence pads, breast milk pads, and pet sheets. Can be used especially optimally.

The crosslinked polymer and the water-absorbing resin obtained by the present invention include a water retention material such as a freshness retention material, a cold insulation material, a drip absorption material, a dew condensation preventing agent, a waterproof material and a packing material for civil engineering, It is also useful for various applications utilizing water-absorbing resins, such as waterproofing materials for electric wires and optical fibers.

[0082]

Hereinafter, the present invention will be described with reference to Examples.
The scope of the present invention is not limited to these examples. In the present invention, the absorption capacity and soluble content of the crosslinked polymer, the absorption capacity under normal pressure of the water-absorbent resin, the absorption capacity under load,
And the amount of degradable soluble matter was measured by the following method.

(A) Absorption capacity of crosslinked polymer Particulate hydrogel crosslinked polymer W having a solid content of A% by weight
₁ g (about 0.2 g as a solid content of 100% by weight) is uniformly placed in a nonwoven bag (60 mm × 60 mm).
It was immersed in a 9% by weight aqueous solution of sodium chloride (physiological saline). Twenty-four hours later, the bag is pulled up, drained with a centrifuge at 250 G for 3 minutes, and then weighed W
₂ (g) was measured. The same operation was performed without using the hydrogel crosslinked polymer, and the weight W ₀ (g) at that time was measured. The absorption capacity (g / g) was calculated from the weights W ₁ , W ₂ and W ₀ according to the following equation.

Absorbency (g / g) = [(W ₂ (g) −W ₀ )
(G))] / W ₁ (g) × (100 / A) -1 (B) Amount of Soluble Content of Crosslinked Polymer Particulate Aqueous Gel Crosslinked Polymer W having a solid content of A% by weight
₃ (g) (about 0.5 g as 100% by weight solids)
Dispersed in 000 g of deionized water, stirred for 16 hours, and filtered with filter paper. Next, 50 g of the obtained filtrate was added to 10
In a 0 ml beaker, 1 ml of a 0.1 N aqueous solution of sodium hydroxide, 10 ml of an aqueous solution of N / 200-methylglycol chitosan, and 4 drops of a 0.1% aqueous solution of toluidine blue were added to the filtrate. Next, the solution in the above beaker was subjected to colloid titration using an aqueous solution of N / 400-potassium polyvinyl sulfate, and the titration end point was determined as the end point of the titration when the color of the solution changed from blue to magenta.
The same operation was performed using 50 g of deionized water instead of 50 g of the filtrate, and the titer C (ml) was obtained as a blank. From these titration amounts B and C and the molecular weight D of the repeating unit of the hydrogel crosslinked polymer, the amount of soluble matter (% by weight) was calculated according to the following equation.

Soluble content (% by weight) = [(CB) × 0.00
5 × D / W ₃ ] × (100 / A) (C) Absorption capacity of water-absorbent resin under normal pressure 0.2 g of water-absorbent resin is wrapped in a nonwoven bag (60 mm × 60 m
m), and immersed in a 0.9% by weight aqueous solution of sodium chloride (physiological saline). Thirty minutes later, the bag was lifted, and after draining with a centrifuge at 250 G for 3 minutes, the weight W ₄ (g) of the bag was measured. The same operation was performed without using a water-absorbing resin, and the weight W
₀ (g) was measured. And these weights W ₄ and W
_The absorption capacity under normal pressure (g / g) was calculated from ₀ according to the following equation.

Absorption capacity under normal pressure (g / g) = (W ₄ (g) −
W ₀ (g)) / water-absorbent resin (g) -1 (D) Absorption capacity under load of water-absorbent resin First, a measuring apparatus used for measuring the absorption capacity under load will be briefly described with reference to FIG. Will be described.

As shown in FIG. 1, the measuring device is a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have. The container 2 has an opening 2a at the top and an opening 2b at the side surface thereof.
The outside air suction pipe 3 is fitted into the opening a, and the conduit 4 is attached to the opening 2b. The container 2 contains a predetermined amount of physiological saline 12. The lower end of the outside air suction pipe 3 is submerged in the physiological saline 12. The outside air suction pipe 3 is provided to keep the pressure in the container 2 at substantially the atmospheric pressure. The above glass filter 6 has a diameter of 70 m.
m. The container 2 and the glass filter 6 communicate with each other by a conduit 4 made of a silicone resin. The position and height of the glass filter 6 with respect to the container 2 are fixed. The measuring unit 5 includes a filter paper 7, a support cylinder 9 having an inner diameter of 60 mm, a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11.
And Then, the measuring section 5 places the filter paper 7 and the support cylinder 9 (that is, the wire mesh 10) on the glass filter 6 in this order, and also, inside the support cylinder 9, that is, the wire mesh 1.
The weight 11 is placed on the zero. Wire mesh 10
Made of stainless steel, 400 mesh (eye size 3
8 μm). In addition, the height of the upper surface of the wire mesh 10, that is, the contact surface between the wire mesh 10 and the water absorbent resin 15 is
The height is set to be equal to the height of the lower end surface 3 a of the outside air suction pipe 3. Then, a predetermined amount of the water-absorbing resin is evenly spread on the wire mesh 10. Weight 1
The weight of 1 is 1390 g, so that a load can be uniformly applied to the wire net 10, that is, the water absorbent resin 15.

The absorption capacity under load was measured using the measuring apparatus having the above-mentioned configuration. The measuring method will be described below.

First, a predetermined amount of physiological saline 12 is put into the container 2. A predetermined preparation operation such as fitting the outside air suction pipe 3 into the container 2 was performed. Next, the filter paper 7 was placed on the glass filter 6. In parallel with this placing operation, 0.9 g of the water-absorbent resin is placed inside the support cylinder 9, that is, on the wire mesh 10.
And the weight 11 was placed on the water-absorbent resin 15. Next, on the filter paper 7, the supporting cylinder 9 on which the wire mesh 10, that is, the water absorbent resin 15 and the weight 11 are placed
Was placed such that the center part thereof coincided with the center part of the glass filter 6. Then, the support cylinder 9 is placed on the filter paper 7.
The weight W of the physiological saline solution 12 absorbed by the water-absorbent resin 15 over a period of 60 minutes after the
₅ (g) was obtained from the measured value of the balance 1. In addition, the same operation was performed without using the water absorbent resin 15, and the blank weight,
That is, the weight of the physiological saline solution 12 absorbed by the filter paper 7 and the like other than the water-absorbent resin was determined from the measured value of the balance 1, and was set as a blank value W ₆ (g). And, to the weight W ₅ (g),
After correcting the blank value W ₆ (g), 6
After 0 minute, the weight W ₇ (g) = W ₅ (g) −W ₆ (g) of the physiological saline actually absorbed by the water-absorbent resin was determined. From the weight W ₇ (g) and the weight of the water-absorbent resin (0.9 g),
The absorption capacity under load (g / g) was calculated according to the following equation.

Absorption capacity under load (g / g) = weight W ₇ (g)
/ Water-absorbent resin (g) (E) Degradable soluble content of water-absorbent resin Artificial urine (artificial urine composition: urea 95 g, sodium chloride 40)
g, magnesium sulfate 5 g, calcium chloride 5 g, L-
Using 0.25 g of ascorbic acid and 4855 g of deionized water), 1 g of a prepared water-absorbent resin which has been classified and prepared to 300 to 600 μm in advance in a 100 ml plastic container with a lid is swelled 25-fold, and heated at a temperature of 37 ° C. for 16 hours. I left it. After 16 hours, the swollen gel was dispersed in 975 g of deionized water, stirred for 1 hour, and then filtered for 1 minute with filter paper. Next, 50 g of the obtained filtrate was placed in a 100 ml beaker, and the filtrate was added with 1 m of a 0.1 N aqueous sodium hydroxide solution.
1, N / 200-methyl glycol chitosan aqueous solution 10
ml and 4 drops of 0.1% toluidine blue aqueous solution. Next, the solution of the beaker was added to N / 400-
Colloid titration was performed using an aqueous solution of polyvinyl potassium sulfate, and the titration end point B (ml) was determined as the end point of the titration when the color of the solution changed from blue to magenta. The same operation was performed without using the water-absorbing resin, and the titer C (ml) was obtained as a blank. Then, from these titration amounts B and C and the molecular weight D of the repeating unit of the water absorbent resin, the amount of degradable soluble matter (% by weight) was calculated according to the following equation.

Degradable soluble content (% by weight) = (CB) × 0.005 × D Example 1 First cross-linking was conducted with 6570 g of a 30% by weight aqueous solution of a partially neutralized sodium acrylate having a neutralization ratio of 75 mol%. Polyethylene glycol diacrylate (PEGDA) 1 as an agent
0.6 g (0.1 mol% based on the monomer) was dissolved, and this was covered with a jacketed stainless steel double-armed kneader (manufactured by Koike Iron Works Co., Ltd.) having an internal volume of 10 liters and having two sigma-type blades. The atmosphere in the reactor was replaced with nitrogen while maintaining the liquid temperature at 30 ° C. by a jacket in which water at 30 ° C. was circulated. Next, 15.6 g of a 20% by weight aqueous sodium persulfate solution and 14.9 g of a 0.1% by weight aqueous L-ascorbic acid solution were added as polymerization initiators while stirring the kneader blade at 40 rpm to initiate polymerization. When the start of polymerization was confirmed by cloudiness, the blade was stopped, and the temperature was kept as it was while removing heat with a jacket until the internal temperature reached 60 ° C. (holding period). When the internal temperature exceeds 60 ° C. (at this point, the polymerization system lost its fluidity and was in a gel state), the blade was rotated to break the gel into particles, and the maximum internal temperature was reached. Was further polymerized so as to be 75 ° C. Subsequently, the jacket temperature was raised to 60 ° C. and 2
While the gel is crushed for 0 minute, the polymerization system is maintained at 65 ° C. or higher to complete the polymerization, and the particulate hydrogel crosslinked polymer (1)
I got The absorption capacity and the soluble content of the obtained crosslinked polymer (1) were measured, and the results are shown in Table 1.

Example 2 The same procedure as in Example 1 was repeated except that the amount of PEGDA used was changed to 6.39 g (based on 0.06 mol% of monomer), whereby a particulate hydrogel crosslinked polymer ( 2) was obtained. At this time, the maximum internal temperature reached 76 ° C. The absorption capacity and the soluble content of the obtained crosslinked polymer (2) were measured, and the results are shown in Table 1.

Example 3 The same operation as in Example 1 was carried out except that the hydrogel polymer produced at 40 rpm for 30 seconds was temporarily broken at an internal temperature of 40 ° C. during the holding period. By repeating the process, a particulate hydrogel crosslinked polymer (3) was obtained. At this time, the maximum internal temperature reached 72 ° C. The absorption capacity and soluble content of the obtained crosslinked polymer (3) were measured, and the results are shown in Table 1.

Example 4 To a gel polymer at about 65 ° C. obtained by polymerization in the same manner as in Example 1, 39.4 g of a 10% aqueous sodium hydrogen sulfite solution was added, and the mixture was thoroughly mixed. Subsequently, the hydrogel polymer was extruded from a screw type extruder (manufactured by Hiraga Kosakusho, chopper: perforated plate thickness: 10 mm, hole diameter: 12.5 mm, opening ratio: 39%) to obtain a particulate hydrogel crosslinked polymer. (4) was obtained. Absorption capacity of the obtained crosslinked polymer (4),
And soluble components were measured, and the results are shown in Table 1.

Example 5 In a polymerization vessel similar to that of Example 1, a 30% by weight aqueous solution of a partially neutralized sodium acrylate having a neutralization ratio of 65 mol% was prepared.
00g, 3.59 g of PEGDA as the first crosslinking agent
(0.06 mol% with respect to the monomer) was dissolved and replaced with nitrogen while keeping the liquid temperature at 25 ° C. by a jacket in which water at 25 ° C. was circulated. Next, the kneader blade is set to 40r.
While stirring at pm, 10% by weight of a polymerization initiator
-Azobis (2-amidinopropane) dihydrochloride aqueous solution 1
2.5 g, 10% by weight aqueous sodium persulfate solution 6.3
g, 8.8 g of a 0.1% by weight aqueous L-ascorbic acid solution and 5.4 g of a 0.35% by weight aqueous hydrogen peroxide solution were added to initiate polymerization. After confirming the initiation of polymerization by cloudiness,
When the internal temperature reached 30 ° C., the blade was stopped, and the internal temperature was maintained until the internal temperature reached 60 ° C. (retention period) while removing heat with a jacket. When the internal temperature exceeds 60 ° C. (at this point, the polymerization system lost its fluidity and was in a gel state), the blade was rotated to break the gel into particles, and the maximum internal temperature was reached. Was further polymerized so as to be 77 ° C. Hereinafter, by performing the same operation as in Example 1,
A particulate hydrogel crosslinked polymer (5) was obtained. The absorption capacity and the soluble content of the obtained crosslinked polymer (5) were measured, and the results are shown in Table 1.

Example 6 In a polymerization vessel similar to that of Example 1, 550 of a 30% by weight aqueous solution of a partially neutralized sodium acrylate having a neutralization ratio of 75 mol% was used.
In 0 g, 8.90 g (0.1 mol% based on monomer) of PEGDA was dissolved as a first cross-linking agent, and the atmosphere was replaced with nitrogen while maintaining the liquid temperature at 30 ° C. by a jacket in which water at 30 ° C. was circulated. Next, while stirring the kneader blade at 40 rpm, 13.0 g of a 20% by weight aqueous sodium persulfate solution and 12.5 g of a 0.1% by weight aqueous L-ascorbic acid solution were added as polymerization initiators to initiate polymerization. When the initiation of polymerization was confirmed by raising the temperature in the system, the blade was stopped, and the temperature was kept as it was until the internal temperature reached 60 ° C. (retention period) while removing heat with the jacket. At the time when the internal temperature exceeds 60 ° C. (at this point, the polymerization system lost its fluidity and was in a gel state), a sufficient shearing force was applied instead of using a separately prepared pressure lid. Rotate the blade in the state,
The polymerization was continued while the gel was crushed into particles. At this time, the maximum internal temperature reached 72 ° C. Subsequently, for 20 minutes, the pressure lid is returned to the normal lid again, and the jacket temperature is raised to 60 ° C. without shearing excessively, and the gel is crushed and the temperature is kept at 65 ° C. or higher to complete the polymerization. Thus, a particulate hydrogel crosslinked polymer (6) was obtained. The absorption capacity and the soluble content of the obtained crosslinked polymer (6) were measured, and the results are shown in Table 1.

Example 7 In a reaction vessel equipped with a jacketed stainless steel double-armed kneader (manufactured by Koike Tekko Co., Ltd.) having two sigma-type blades having an internal volume of 2.5 liters, acrylic acid was 20% by weight. PEGD as the first crosslinking agent
A6 (0.1 mol% based on monomer) was dissolved,
The liquid temperature is set to 20 ° C by a jacket circulating 20 ° C water.
While maintaining the pressure. Then, while stirring the kneader blade at 40 rpm, 9.6 g of a 5% by weight aqueous solution of 2,2'-azobis (2-amidinopropane) dihydrochloride as a polymerization initiator and 4.0 g of a 1% by weight aqueous solution of L-ascorbic acid were used. And a 3.5% by weight aqueous solution of hydrogen peroxide 4.57
g was added to initiate polymerization. When the start of polymerization was confirmed by raising the temperature in the system, the blade was stopped, and the temperature was kept as it was until the internal temperature reached 50 ° C. while removing heat by the jacket (holding period). At the time when the internal temperature exceeded 50 ° C. (at this point, the polymerization system lost its fluidity and was in a gel state), the blade was rotated to continue the polymerization while pulverizing the gel into particles. At this time, the maximum internal temperature reached 60 ° C. Subsequently, the temperature of the jacket was raised to 60 ° C. for 60 minutes, and the temperature was kept at 60 ° C. or higher while the gel was crushed to complete the polymerization. Further, 76.6 g of sodium carbonate powder was added to the obtained hydrogel crosslinked polymer while rotating the blade.
Was added and mixed, and the mixture was maintained for 1 hour while maintaining the gel temperature at 60 ° C., and sufficiently neutralized to obtain a particulate hydrogel crosslinked polymer (7). Absorption capacity of the obtained crosslinked polymer (7),
And soluble components were measured, and the results are shown in Table 1.

Example 8 In Example 6, the concentration of the aqueous solution of acrylic acid was changed to 25% by weight.
The amount of the polymerization initiator used was 2.4 g of a 5% by weight aqueous solution of 2,2′-azobis (2-amidinopropane) dihydrochloride,
2. 1.0 g of a weight% L-ascorbic acid aqueous solution, and
The same operation was repeated, except that the aqueous solution was changed to 1.14 g of a 5% by weight aqueous hydrogen peroxide solution, to obtain a hydrogel crosslinked polymer. The highest temperature reached at this time was 65 ° C. Further, 95.7 g of sodium carbonate powder was added to the obtained hydrogel crosslinked polymer while rotating the blade, and the mixture was mixed. The hydrated gel-like crosslinked polymer (8)
I got The absorption capacity and soluble content of the obtained crosslinked polymer (8) were measured, and the results are shown in Table 1.

Example 9 The particulate hydrogel crosslinked polymer obtained in Example 1 (1)
Was dried with hot air at 160 ° C. for 65 minutes, and the dried product was further ground using a vibration mill and classified to a particle size of 75 to 850 μm to obtain crosslinked polymer particles. Based on 100 parts of the crosslinked polymer particles, 0.05 part of ethylene glycol diglycidyl ether, 0.5 part of glycerin, 3 parts of water and 0.7 part of isopropyl alcohol were used as a second crosslinking agent.
An aqueous liquid consisting of 5 parts was added and mixed, and the resulting mixture was added to 2 parts.
Heat treatment was performed at 00 ° C. for 50 minutes to obtain a water absorbent resin (9). With respect to the water absorbent resin (9), the absorption capacity under normal pressure and under load and the amount of degradable soluble matter were measured, and the results are shown in Table 2.

Comparative Example 1 A comparative hydrogel crosslinked polymer (10) was obtained in the same manner as in Example 1, except that the holding time for stopping the blade from the start of polymerization was not provided. The absorption capacity and soluble content of the obtained comparative crosslinked polymer (10) were measured, and the results are shown in Table 1.

Comparative Example 2 A comparative hydrogel crosslinked polymer (11) was obtained in the same manner as in Example 2 except that the holding time for stopping the blade was not provided from the start of the polymerization. The absorption capacity and soluble content of the obtained comparative crosslinked polymer (11) were measured, and the results are shown in Table 1.

Comparative Example 3 In Example 1, except that the holding time for stopping the blade from the start of polymerization was set to the maximum temperature at which the internal temperature was reached,
By carrying out exactly the same, a hydrogel crosslinked polymer (12) for comparison was obtained. At this time, the maximum temperature exceeded 100 ° C., and the hydrogel polymer violently bumped. The absorption capacity and the soluble content of the obtained comparative crosslinked polymer (12) were measured, and the results are shown in Table 1.

Comparative Example 4 In the same container as in Example 1, an aqueous solution of the same polymerizable monomer as in Example 1 was kept at 30 ° C. by means of a jacket in which water at 30 ° C. was circulated. It was replaced with nitrogen. Then
14. While stirring the kneader blade at 40 rpm, a 20% by weight aqueous solution of sodium persulfate as a polymerization initiator.
6 g and a 0.1 wt% aqueous solution of L-ascorbic acid 14.9
Was added to initiate polymerization. When the initiation of polymerization was confirmed by cloudiness, the blade was stopped, and the jacket was kept in an adiabatic state while heating. The gel formed at the time when the internal temperature exceeds 60 ° C. is taken out of the polymerization vessel,
Screw type extruder (Hiraga Manufacturing Co., chopper:
(3 mm pore size) to obtain a comparative particulate hydrogel crosslinked polymer (13). Immediately after this, the temperature of the particulate crosslinked polymer was cooled to 55 ° C. The absorption capacity and soluble content of the obtained comparative crosslinked polymer (13) were measured, and the results are shown in Table 1.

Comparative Example 5 The procedure of Example 9 was repeated, except that the hydrogel cross-linked polymer (1) was changed to the hydrogel cross-linked polymer (11) for comparison. Water absorbent resin (1
4) was obtained. About this comparative water absorbent resin (14),
The absorption capacity under normal pressure and under load and the amount of degradable soluble matter were measured, and the results are shown in Table 2.

[0105]

[Table 1]

[0106]

[Table 2]

[0107]

The crosslinked polymer obtained according to the present invention has excellent water absorption and a small amount of soluble components as compared with conventional crosslinked polymers, and has excellent characteristics. Further, the crosslinked polymer particles obtained by drying and pulverizing the crosslinked polymer and a second crosslinking agent that reacts with at least two functional groups near the surface of the crosslinked polymer particles are mixed and heat-treated. The water-absorbent resin having an irregular shape obtained as described above has an absorption capacity under normal pressure of physiological saline of at least 30 g / g, an absorption capacity of physiological saline under load of at least 25 g / g, and a degradable soluble content of 15% by weight. The following is shown, and it has an unprecedented feature. Therefore, the water absorbent resin of the present invention can be optimally used for sanitary materials such as disposable diapers and sanitary napkins.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a measuring device used for measuring an absorption capacity under load used in the present invention.

[Explanation of symbols]

 1 balance, 2 containers, 3 outside air suction pipe, 4 conduit, 5 measuring section, 6 glass filter, 7 filter paper, 9 support cylinder, 10 wire mesh, 11 weight, 12 saline, 15 water absorbing resin.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) The inventor Kazuki Kimura 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo

Claims (9)

[Claims] 1. The method according to claim 1, wherein when the polymerization of the aqueous solution of the polymerizable monomer containing the water-soluble ethylenically unsaturated monomer and the first crosslinking agent, which results in a hydrogel polymer by polymerization, From the time until the point when the entire polymerization system gels, the polymerization is carried out in a substantially stationary state, and then a sufficient shearing force is applied to the polymerization system until the polymerization system reaches the maximum temperature due to the heat of polymerization. A method for producing a crosslinked polymer, which comprises converting the hydrogel polymer into particles and continuing the polymerization. 2. The method according to claim 1, wherein when the aqueous solution of the polymerizable monomer containing the water-soluble ethylenically unsaturated monomer and the first cross-linking agent, which is converted into a hydrogel polymer by polymerization, is polymerized. From the time until the point at which the entire polymerization system gels, the heat-removal polymerization is performed in a substantially stationary state, and thereafter, a sufficient shearing force is applied to the polymerization system until the polymerization system reaches the maximum temperature due to the heat of polymerization. 2. The method for producing a crosslinked polymer according to claim 1, wherein the hydrogel polymer is formed into particles, and the heat removal polymerization is continued. 3. The method according to claim 1, wherein when the aqueous solution of the polymerizable monomer containing the water-soluble ethylenically unsaturated monomer and the first crosslinking agent, which is converted into a hydrogel polymer by polymerization, is polymerized, a rotating arm or In a reaction vessel having stirring blades, the heat removal polymerization is performed in a substantially stationary state from the start of the polymerization to the point at which the entire polymerization system gels, and then the polymerization system reaches the maximum temperature due to the heat of polymerization. By the time, sufficient shearing force is applied to the polymerization system by rotation of the rotary arm or the stirring blade, the hydrogel polymer is formed into particles, and the heat removal polymerization is continued. The method for producing a crosslinked polymer according to the above. 4. The method for producing a crosslinked polymer according to claim 1, wherein the polymerization is carried out in a substantially stationary state until the temperature of the polymerization system reaches at least 40 ° C. 5. The crosslink according to claim 1, wherein the formed hydrogel polymer is temporarily broken during the period from the start of the polymerization to the point in time when the entire polymerization system gels. A method for producing a polymer. 6. The hydrogel polymer according to claim 5, wherein the produced hydrogel polymer is temporarily broken by the rotation of the rotating arm or the stirring blade from the time when the polymerization is started until the time when the entire polymerization system gels. A method for producing a crosslinked polymer. 7. An aqueous solution of a polymerizable monomer comprising acrylic acid and / or an alkali metal salt, an ammonium salt, or an amine salt thereof, and a first polymer having at least two polymerizable unsaturated double bonds per molecule. The method for producing a crosslinked polymer according to any one of claims 1 to 6, comprising a crosslinking agent as a main component. 8. A crosslinked polymer particle obtained by drying and pulverizing the crosslinked polymer obtained by the production method according to any one of claims 1 to 6, and a portion near the surface of the crosslinked polymer particle. A method for producing a water-absorbent resin, comprising mixing at least two functional groups with a second crosslinking agent that reacts with the mixture, followed by heat treatment. 9. The absorption capacity of physiological saline at normal pressure is at least 30 g / g, the absorption capacity of physiological saline under load is at least 25 g / g, and the degradable soluble component is 15% by weight or less. A water-absorbent resin having an irregular shape.