JP2010059254A - Method for producing water-absorbing resin particle, absorbent, and absorbing article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-absorbing resin particle that is not broken to pieces by mutual collision of the absorbing resin particles and does not make worse working environment. <P>SOLUTION: The method for producing the water-absorbing resin particle (D) comprises the first process of obtaining a reaction mixture (A) containing a moist water-absorbing resin particle (a) by performing reversed phase suspension polymerization of an aqueous solution of a water soluble ethylenic unsaturated monomer containing a crosslinking agent in a hydrophobic organic solvent in the presence of a dispersant, the second process of obtaining a reaction mixture (B) containing a moist water-absorbing resin particle (b) by further addition of an aqueous solution of a water soluble ethylenic unsaturated monomer containing a crosslinking agent to the (A), then performing reversed phase suspension polymerization, the third process of obtaining a water-absorbing resin cake (C) by dehydrating and desolvating the (B), and the fourth process of drying the water-absorbing resin cake, wherein bulk density of the moist water-absorbing resin particle (b) is 0.25-0.35 g/ml, and bulk density of the water-absorbing resin particle (D) after drying is 0.45-0.55 g/ml. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing water-absorbent resin particles, an absorbent body using the water-absorbent resin particles obtained thereby, and an absorbent article.

A method for producing porous water-absorbing polymer particles having a bulk density of 0.30 to 0.50 g / mL is known. (Patent Documents 1 and 2)
JP 2006-342306 A JP 2001-2935 A

However, conventional water-absorbent resin particles of low bulk density products have a high absorption rate. However, when used in absorbent articles such as diapers, napkins, urine pads, and pet sheets, the absorbent resin particles are dispersed during the preparation of the absorbent body. In doing so, there is a problem that the absorbent resin particles are broken due to collisions between the absorbent resin particles and the working environment is deteriorated.
That is, the object of the present invention is water-absorbing resin particles having a high absorption rate, and when used in absorbent articles such as diapers, napkins, urine-absorbing pads, and pet sheets, the absorbent resin particles are dispersed during the production of the absorbent body. It is an object of the present invention to provide a method for producing water-absorbent resin particles that does not cause breakage of the absorbent resin particles due to collisions between the absorbent resin particles and does not deteriorate the working environment.

  That is, the present invention relates to a reaction mixture containing water-absorbing water-absorbing resin particles (a) by subjecting a water-soluble ethylenically unsaturated monomer aqueous solution containing a crosslinking agent to reverse phase suspension polymerization in a hydrophobic organic solvent in the presence of a dispersant ( A first step of obtaining A); a reaction mixture containing water-absorbing water-absorbent resin particles (b) by adding a water-soluble ethylenically unsaturated monomer aqueous solution further containing a crosslinking agent to reverse-phase suspension polymerization to (A) ( A second step of obtaining B); a third step of dehydrating and desolvating the (B) to obtain a water absorbent resin cake (C); and a fourth step of drying the water absorbent resin cake; It is a manufacturing method of (D), Comprising: The bulk density of the water-containing water absorbent resin particle (b) is 0.25 to 0.35 g / ml, and the bulk density of the water absorbent resin particle (D) after drying is 0.00. The gist is 45 to 0.55 g / ml.

  The water-absorbent resin particles obtained by the production method of the present invention have a high absorption rate, and when the absorbent resin particles are dispersed during the production of the absorbent body, the absorbent resin particles are broken due to collisions between the absorbent resin particles. There is no worsening of the work environment.

First, the water-absorbent resin particles (D) will be described. The water-soluble ethylenically unsaturated monomer is not particularly limited as long as it has a property of dissolving at least 100 g in 100 g of water at 25 ° C. Water-soluble radically polymerizable monomers described in JP-0775982 (C3-C30 vinyl group-containing carboxylic acid (salt) {unsaturated monocarboxylic acid (salt) ((meth) acrylic acid, crotonic acid, cinnamic acid And unsaturated dicarboxylic acids (salts) (maleic acid, fumaric acid, citraconic acid, itaconic acid and salts thereof); and monoalkyl (carbon number 1 to 8) esters of the unsaturated dicarboxylic acids (Maleic acid monobutyl ester, fumaric acid monobutyl ester, maleic acid ethyl carbitol monoester, fumaric acid ethyl carbitol monoester Tellurium, citraconic acid monobutyl ester and itaconic acid glycol monoester, etc.}, unsaturated monocarboxylic acid (salt), acrylic acid (salt)), among these, absorption performance (high absorption rate, water-absorbing resin particles) The most preferred is acrylic acid (salt) from the viewpoints of the fragility of the resin, industrial ease of availability, and safety.
In addition, (meth) acrylic acid means methacrylic acid and / or acrylic acid, and an acid (salt) means an acid and / or a salt thereof, and the same applies to the following description.

  Each of the water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

  In the present invention, a crosslinking agent is used in the first and second steps.

  As the crosslinking agent, known ones (Patent No. 3648553, JP-A No. 2003-165883, JP-A No. 2005-75982, JP-A No. 2005-95759, etc.) can be used, and water-soluble ethylenically unsaturated monomers can be used. A cross-linking agent having at least two functional groups capable of reacting with the water-soluble substituent is preferable, more preferably polyvalent glycidyl, particularly preferably ethylene glycol diglycidyl ether and glycerin diglycidyl ether, most preferably ethylene glycol diglycidyl. Ether.

The content (mol%) of the crosslinking agent is 0.01 to 1 based on the number of moles of the water-soluble ethylenically unsaturated monomer from the viewpoint of absorption performance (high absorption rate, breakability of water-absorbent resin particles) and the like. Is more preferable, 0.02 to 0.7 is more preferable, and 0.03 to 0.6 is particularly preferable.
In addition, about content of the crosslinking agent used at a 1st process, and content of the crosslinking agent used at a 2nd process, it is the same as that of the above, and its preferable range is also the same.

The water absorbent resin particles (D) may further be copolymerized with other copolymerizable vinyl monomers, but it is preferable not to copolymerize other vinyl monomers.
The other vinyl monomer is not particularly limited as long as it is a monomer that can be copolymerized with a water-soluble ethylenically unsaturated monomer, and examples thereof include a vinyl monomer described in JP-A-2003-225565.
When copolymerizing other vinyl monomers, the content (mol%) of the other vinyl monomers is determined from the viewpoint of absorption performance (high absorption rate, breakage of water-absorbent resin particles), etc. And, based on the total number of moles of other vinyl monomers, 0.01 to 30 is preferable, 0.05 to 20 is more preferable, and 0.1 to 15 is particularly preferable.

As the dispersant, those known as reverse phase suspension polymerization dispersants can be used. For example, anionic dispersants (polyoxyethylene alkyl ether sulfate (described in JP-A-6-93008), monoalkyl phosphates ( JP-A-61-209201), nonionic dispersants (sucrose fatty acid ester, sorbitol fatty acid ester, aliphatic alcohol alkylene oxide adduct, alkylphenol alkylene oxide adduct, etc.) and the like.
The use amount (% by weight) of the dispersant is preferably 0.001 to 10, more preferably 0.005, based on the weight of the hydrophobic organic solvent, from the viewpoint of high absorption rate and breakability of the water-absorbent resin particles. -8, particularly preferably 0.01-5.
In addition, it is preferable to introduce | transduce the whole quantity used by the 1st process from viewpoints of absorption performance (high absorption speed, the breakability of a water absorbing resin particle) etc. as the dispersing agent to be used.

As the hydrophobic organic solvent used in the present invention, known ones (Patent No. 3363000, JP-A No. 2003-147005) can be used, which is basically hardly soluble in water and inert to polymerization. Can also be used. For example, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, aromatic carbons such as benzene, toluene and xylene Hydrogen etc. are mentioned. From the viewpoints of absorption performance (high absorption rate, breakability of water-absorbing resin particles), industrially easy availability, and safety, preferably n-hexane, n-heptane and cyclohexane, most preferably Cyclohexane.
The amount of the hydrophobic organic solvent used is preferably 100 to 1,000% by weight, more preferably, based on the weight of the aqueous monomer solution, from the viewpoint of absorption performance (high absorption rate, breakability of water-absorbing resin particles) and the like. 110 to 500% by weight, most preferably 120 to 300% by weight.
In addition, as for the hydrophobic organic solvent to be used, it is preferable to introduce | transduce the whole quantity used at a 1st process from viewpoints of absorption performance (high absorption speed, breakability of a water absorbing resin particle), etc.

  In the present invention, when polymerizing the water-soluble ethylenically unsaturated monomer aqueous solution, a polymerization initiator can be used. The polymerization initiator to be used is not particularly limited, and conventionally known polymerization initiators can be used. For example, azo initiators, peroxide initiators, redox initiators, organic halogen compound initiators, and the like can be used. Examples of the azo initiator include azobisisobutyronitrile, azobiscyanovaleric acid and salts thereof, 2,2′-azobis (2-amidinopropane) hydrochloride, and 2,2′-azobis (2-methyl-N—). (2-hydroxyethyl) propionamide is mentioned.

  Peroxide initiators include inorganic peroxides [eg, hydrogen peroxide, ammonium persulfate, potassium persulfate and sodium persulfate], organic peroxides [eg, benzoyl peroxide, di-t-butyl peroxide, Cumene hydroperoxide, succinic acid peroxide, and di (2-ethoxyethyl) peroxydicarbonate]. Examples of the redox initiator include reducing agents such as alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, ferric chloride, ferric sulfate and ascorbic acid, and alkali metal persulfates, Examples thereof include a combination of an oxidizing agent such as ammonium persulfate, hydrogen peroxide and organic peroxide.

  Examples of the organic halogen compound initiator include halogenated alkyls, halogenated alkylphenyl ketones, halogenated alkylcarboxylic acids and halogenated alkylcarboxylic acid alkyl esters selected from the group consisting of 1 to 10 or more halogen atoms and 1 to 1 carbon atoms. 15 or more organic halogen compounds are used, for example, tetrachloromethane, trichlorobromomethane, trichloroiodomethane, dichloromethylphenylketone, 1-bromo-1-methylethylcarboxylic acid, and alkyl groups having 1 to 1 carbon atoms. 8 1-bromo-1-methylethylcarboxylic acid alkyl esters (for example, methyl 1-bromo-1-methylethylcarboxylate, ethyl 1-bromo-1-methylethylcarboxylate, 1-bromo-1-methylethylcarboxylic acid) Octyl and 1-bromo 1-methyl carboxylate lauryl), and the like.

  These initiators may be used alone or in combination of two or more. Of these, an azo initiator, a redox initiator, and a combination thereof are preferable from the viewpoint of absorption performance (high absorption rate, breakability of water-absorbing resin particles) and the like. The amount of the polymerization initiator used is preferably 0.001 to 5% by weight, more preferably 0.01 to 1% by weight from the viewpoint of high absorption rate and fragility of the water-absorbent resin particles with respect to the ethylenically unsaturated monomer. %.

  Reverse phase suspension polymerization is carried out in the same manner as known methods {for example, reverse phase suspension polymerization methods disclosed in JP-A Nos. 13-2935, 2003-147005, and 2003-165883}. However, in order to obtain the water-absorbent resin particles of the present invention, it is necessary to carry out in at least two stages.

In the present invention, in the first step, water-soluble water-absorbent resin particles (a) are obtained by subjecting a water-soluble ethylenically unsaturated monomer aqueous solution containing a crosslinking agent to reverse phase suspension polymerization in a hydrophobic organic solvent in the presence of a dispersant. A reaction mixture (A) containing is obtained.
In the reverse phase suspension polymerization in the first step, for example, a part of the monomer aqueous solution is supplied into a hydrophobic organic solvent containing a dispersant to cause suspension polymerization. During the reverse phase suspension polymerization in the first step, it is preferable to control the supply rate and stirring strength of the aqueous monomer solution so that the aqueous monomer solution is dispersed as fine droplets (diameter of about 1 to 9 μm). The ratio (% by weight) of the monomer aqueous solution to be subjected to the reverse phase suspension polymerization in the first step is 0.1 to 40 based on the weight of the total monomer aqueous solution from the viewpoint of the absorption rate and the breakability of the water absorbent resin particles. Is more preferable, and more preferably 1-25.

In the present invention, in the second step, a reaction mixture containing water-absorbing water-absorbing resin particles (b) by adding a water-soluble ethylenically unsaturated monomer aqueous solution further containing a crosslinking agent to reverse-phase suspension polymerization to (A). (B) is obtained.
The reverse-phase suspension polymerization in the second step is performed after the polymerization rate of the monomer subjected to the reverse-phase suspension polymerization in the first step reaches at least 10% by weight from the viewpoint of absorption speed and breakability of the water-absorbent resin particles. Preferably it is done. For that purpose, preferably after 3 minutes or more, more preferably 5 minutes or more after the supply of the monomer aqueous solution in the reverse phase suspension polymerization of the first step is completed, the reverse phase suspension polymerization of the second step is performed. It is preferred to initiate reverse phase suspension polymerization. In addition, since productivity will fall easily when this time is long, it is within 60 minutes, More preferably, it is within 30 minutes. The polymerization rate here is a ratio (% by weight) of the produced polymer to the monomer used. That is, {(monomer weight used) − (residual monomer weight)} × 100 / (monomer weight used).

  In the reverse phase suspension polymerization in the second step, the remaining monomer aqueous solution is supplied into the reaction mixture (A) containing the water-containing water-absorbing resin particles (a) produced in the reverse phase suspension polymerization in the first step. Do. The supply of the monomer aqueous solution in the reverse phase suspension polymerization of the second step should be performed over a period of at least 10% (preferably 40% or more, particularly preferably 60% or more) of the total polymerization time of the second step. Is preferred. The total polymerization time in the second step is 98% by weight, preferably 98.5% by weight, based on the total amount of monomer supplied in the second step from the start of polymerization in the second step (start of supply of the monomer aqueous solution). Means time to reach%. The total polymerization time in the second step varies depending on the type of initiator and the like, but is preferably 2 to 8 hours from the viewpoint of absorption rate and breakability of the water-absorbent resin particles.

  In both the first and second steps of reversed-phase suspension polymerization, the monomer aqueous solution can be supplied from a batch polymerization method in which the monomer aqueous solution is charged all at once from the beginning, or a dropping method in which the monomer aqueous solution is dropped into a hydrophobic solvent. . The monomer aqueous solution is preferably supplied continuously at a constant rate from the viewpoint of the absorption rate and the breakability of the water-absorbing resin particles, but the supply rate may be changed. In addition, the supply of the monomer aqueous solution can be temporarily interrupted. In the reversed-phase suspension polymerization in the second step, the supplied monomer aqueous solution is absorbed by the polymer already present in the hydrophobic organic solvent and grows, or the polymer formed from the supplied monomer aqueous solution. It is thought that the particles grow by combining with the already existing polymer. Therefore, it is preferable to carry out the supply rate and stirring strength of the monomer aqueous solution so that the monomer aqueous solution is sufficiently dispersed.

  Although superposition | polymerization temperature is based also on a polymerization initiator etc., it is preferable that it is 40-150 degreeC. When the temperature is too high, the self-crosslinking becomes active and the absorption rate of the polymer produced tends to decrease. On the other hand, if the temperature is too low, not only does the polymerization take a long time, but there is a risk of causing sudden polymerization and generating a lump. A more preferable polymerization temperature is 60 to 90 ° C., and it is particularly preferable to carry out the reaction under reflux conditions of a hydrophobic organic solvent.

The monomer concentration (% by weight) of the monomer aqueous solution, that is, the ratio of the total monomer weight to the weight of the monomer aqueous solution (total monomer weight × 100 / monomer aqueous solution weight:% by weight) is preferably 10 to 45, more preferably 12 -40, particularly preferably 15-35. Within this range, in addition to being efficient when removing water later, side reaction such as self-crosslinking does not occur and the molecular weight distribution of the main chain is narrowed, resulting in the absorption rate of the water-absorbent resin particles finally obtained Is even better.
The monomer aqueous solution used in the first step and the monomer aqueous solution used in the second step are the same as described above, and the preferred ranges are also the same.

Although 2nd process can also be performed in multiple times (2-5 times), from a viewpoint of an absorption rate and the destructibility of a water absorbing resin particle, 1 time is preferable.
When performing the second step a plurality of times, the description of the water-absorbing water-absorbing resin particles (a) {that is, the water-absorbing water-absorbing resin particles obtained in the first step} in the second step is as appropriate. It shall refer to the water-containing water-absorbent resin particles obtained in the immediately preceding second step.

  The water-soluble ethylenically unsaturated monomer aqueous solution in the second step may be the same as or different from the water-soluble ethylenically unsaturated monomer aqueous solution in the first step. Further, the water-soluble ethylenically unsaturated monomer in the first step and the second step may be the same type of water-soluble ethylenically unsaturated monomer or different blending conditions. For example, an aqueous solution of water-soluble ethylenically unsaturated monomer is acrylic. In the case of an aqueous solution of acid soda, the aqueous solution used in the first step and the second step may be performed at a different neutralization degree of acrylic acid or a water-soluble ethylenically unsaturated monomer concentration in different aqueous solutions.

  In addition, the water-soluble radical polymerization initiator is not necessarily required in the water-soluble ethylenically unsaturated monomer aqueous solution in the second step, and is appropriately determined according to the required product quality. The water-soluble radical initiator is not newly added to the water-soluble ethylenically unsaturated monomer in the second step, but the reaction mixture (A) containing the water-containing water-absorbing resin particles (a) obtained in the first step (in the slurry state) In many cases, the water-soluble ethylenically unsaturated monomer in the second step is easily added to (A) and brought to a predetermined temperature to be polymerized easily.

In the present invention, in the third step, the water-absorbent resin cake (C) is obtained by dehydrating and desolvating the reaction mixture (B) containing the water-containing resin particles (b).
As a method for dehydration and desolvation, the obtained reaction mixture (B) is preferably stirred from the viewpoint of the breakability of the water-absorbent resin particles and a high absorption rate while stirring in a dehydration and desolvation tank equipped with a stirrer. Is preferably 60 to 90 ° C., more preferably 70 to 80 ° C., and preferably 20 to 40 minutes, more preferably 25 to 35 minutes, from the viewpoint of the breakability of the water-absorbent resin particles and the high absorption rate. The method of dehydrating by boiling is mentioned.
When the stirring is stopped after completion, the water-absorbent resin cake (C) settles to the bottom of the tank. The water-absorbent resin cake is separated by decantation, centrifuge (preferred conditions are 150 G for 5 minutes), etc. (C) is obtained.

In the present invention, in the fourth step, the water absorbent resin cake (C) obtained in the third step is dried.
Examples of the method of drying (C) include a method of drying using a dryer such as a disk dryer, a turbo dryer, or a drum dryer. The drying temperature is preferably 60 to 230 ° C, more preferably 100 to 200 ° C. If the drying temperature is 60 ° C. or higher, it does not require a long time for drying and is economical in terms of energy consumption. On the other hand, if it is 230 ° C. or lower, side reactions and resin decomposition do not occur. This is preferable because the absorption performance does not decrease. The drying atmosphere may be normal pressure or reduced pressure (for example, 500 mmHg or less). The drying time is preferably 0.5 to 3 hours from the viewpoint of the high absorption rate and the breakability of the water absorbent resin particles. If it is 0.5 hours or longer, an undried portion is hardly formed, and if it is 3 hours or less, the bulk density is difficult to exceed 0.56 g / ml, which is preferable.

The water-absorbing water-absorbing resin particles (b) obtained in the second step have a bulk density of 0.25 to 0.35 g / ml, and preferably 0 from the viewpoint of the breakability of the water-absorbing resin particles and the high absorption rate. .27 to 0.30 g / ml, more preferably 0.28 to 0.29. In addition, the bulk density of (b) is measured by the following method.
When the bulk density of (b) is less than 0.25, the breakability of the water-absorbent resin particles is deteriorated, and when it exceeds 0.35, the absorption rate is deteriorated.

<Method for measuring bulk density of water-containing water-absorbent resin particles (b)>
First, a bulk density measurement sample is prepared by the following method.
In a 450 cc sample bottle, 150 g of cyclohexane is weighed, amino-modified silicone (KF-880 manufactured by Shin-Etsu Chemical Co., Ltd.) is placed, and a stirrer chip is placed. 40 g of water-containing water-absorbing resin particles (b) are added and stirred with a stirrer for 5 minutes to obtain a water-containing water-absorbing resin particle dispersion. The stirrer tip to be used is 30 mm × 8 mmφ (for example, Teflon (registered trademark) rotor SA-5 manufactured by Mutual Riken Glass Manufacturing Co., Ltd.), and the stirrer is, for example, AS-2T manufactured by Toyo Manufacturing Co., Ltd. . The temperature during stirring is 25 ± 2 ° C.
After stirring for 5 minutes, 400 g of acetone is put into a 900 cc sample bottle and stirred with a stirrer (stirring conditions, apparatus, and temperature during stirring are the same as above), and from there, the water-containing water-absorbing resin particle dispersion, Cut the water-absorbing water-absorbent resin particles as much as possible, and add a small amount (about 1 to 2 teaspoons) at a time (filling time is about 3 minutes). The water-containing water-absorbent resin particles are dispersed into particles immediately after being put into acetone.
The mixture is stirred for 10 minutes after completion of the addition, and then filtered under reduced pressure {filter used: FILTER PAPER2 100CIRCLES 125 mm (manufactured by Toyo Roshi Kaisha, Ltd.), reduced pressure condition: 150 mmHg}. The water-absorbing water-absorbent resin particles filtered in the above are transferred onto a SUS tray so that the thickness is 5 mm or less, and left at 25 ° C. for 10 minutes.
Next, the apparent density is measured in accordance with the measurement method described in JIS K6872-1995 5.4 except that the receiver (balance bottle) is changed from the one with the internal volume of 100 ml to the one with the internal volume of 15 ml. The bulk density of the particles (b) is taken.

  The bulk density of (b) obtained in the second step can be adjusted by changing the time from the completion of the supply of the monomer aqueous solution in the first step to the start of the supply of the monomer aqueous solution in the second step. is there. That is, if the time is shortened, the bulk density of (b) tends to increase, and if the time is increased, it tends to decrease.

The bulk density of the water-absorbent resin particles (D) after drying is 0.45 to 0.55 g / ml, and from the viewpoint of high absorption rate and breakability of the water-absorbent resin particles, preferably 0.48 to 0.00. 51 g / ml, more preferably 0.49 to 0.50. The bulk density of the water absorbent resin particles (D) after drying can be adjusted by changing the drying time. When the drying time is shortened, the bulk density decreases, and when the drying time is lengthened, it tends to increase. The drying time is preferably 0.5 hours to 3 hours. If the drying time is less than 0.5 hours, an undried portion is likely to be generated, and if it is 3 hours or more, the bulk density tends to exceed 0.56 g / ml.
The bulk density of the water-absorbent resin particles (D) after drying is measured in accordance with JIS-K6892 5.4.

  The absorption rate of the water-absorbent resin particles (D) obtained by the present invention is preferably 8 to 15 seconds, and most preferably 9 to 13 seconds, from the viewpoint of the high absorption rate and the breakability of the water-absorbent resin particles. The absorption rate is measured by the following measurement method.

<Absorption rate measurement method>
After sufficiently shaking the container containing the water-absorbing resin particles so as to eliminate the uneven distribution of the particle size distribution, the water-absorbing resin particles are weighed with an accuracy of 2.00 ± 0.001 g.
Next, 50 g of 0.900 ± 0.001 wt% physiological saline adjusted to 25 ± 1 ° C. and a stirrer chip are placed in a 100 ml beaker, the beaker is placed on a magnetic stirrer, and the vortex becomes the center of the beaker. Stir at a rotation speed of 600 ± 60 rpm. At this time, it is performed in an atmosphere of room temperature 23 ± 2 ° C. and relative humidity 50 ± 5%. Next, 2.00 g of the weighed water-absorbing resin particles are collectively put into the center of the vortex formed in the beaker, and at the same time, measurement is started with a stopwatch. Along with the absorption of saline by the water-absorbent resin particles, the end point is the point where the vortex starts to disappear and the liquid level becomes horizontal, and the time (unit: seconds) required until the end point is measured.
The time (unit: second) measured above is taken as the absorption rate.

  The absorption rate of the water-absorbing resin particles is adjusted to the above range by adjusting the bulk density of the water-containing water-absorbing resin particles (b) and the bulk density of the water-absorbing resin particles (D) after drying to the range of the present invention. Can be adjusted.

  The weight average particle diameter (μm) of the water-absorbent resin particles (D) is preferably from 100 to 800, more preferably from 200 to 500, particularly preferably from 250 to 500, from the viewpoint of high absorption rate and breakability of the water-absorbent resin particles. 400.

  The weight average particle size is measured using a conventional method, for example, a low-tap test sieve shaker and a standard sieve (JIS Z8801-1: 2000), Perry's Chemical Engineers Handbook, 6th edition (Mac Glow Hill Book) -It is measured by the method described in Kanbany, 1984, page 21). That is, the JIS standard sieves are 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm and 150 μm from the top, and the order of the saucer, or 500 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and the saucer from the top. Combine in order. About 50 g of the measured particles are put in the uppermost screen and shaken for 5 minutes with a low-tap test sieve shaker. Weigh the measured particles on each sieve and pan, and calculate the weight fraction of the particles on each sieve with the total as 100% by weight. This value is the logarithmic probability paper (the horizontal axis is the sieve aperture (particle size ), The vertical axis is plotted in the weight fraction}, a line connecting the points is drawn, and the particle diameter corresponding to the weight fraction of 50% by weight is obtained, and this is defined as the weight average particle diameter.

In addition, the content of the fine particles is preferably 0 to 10% by weight or less, more preferably 1 to 6% by weight, from the viewpoint of high absorption rate and breakability of the water-absorbent resin particles. % By weight or less.
The content of the fine particles can be determined using a plot created when determining the above weight average particle diameter.

  The water-absorbent resin particles (D) may be surface-crosslinked with a surface cross-linking agent as necessary. Examples of the surface cross-linking agent include polyvalent glycidyl described in JP-A No. 59-189103, JP-A No. 58- Polyhydric alcohols, polyhydric amines, polyhydric aziridines and polyhydric isocyanates described in JP-A No. 180233 or JP-A No. 61-16903, JP-A No. 61-212305 or JP-A No. 61-252212, etc. And polyvalent metals described in JP-A No. 51-136588 or JP-A No. 61-257235, and the like. Of these surface cross-linking agents, from the viewpoint of high absorption rate and breakability of the water-absorbent resin particles, polyvalent glycidyl, polyvalent amine and silane coupling agent are preferred, more preferably polyvalent glycidyl and silane coupling agent, Particularly preferred is polyvalent glycidyl. Among polyvalent glycidyl, ethylene glycol diglycidyl ether and glycerin diglycidyl ether are preferable, and ethylene glycol diglycidyl ether is particularly preferable.

  The content (% by weight) of the surface cross-linking agent is 0.01 to 0 based on the weight of the water-absorbent resin particles (D) from the viewpoint of absorption performance (high absorption rate, breakability of the water-absorbent resin particles) and the like. .10 is preferable, 0.03 to 0.8 is more preferable, and 0.05 to 0.06 is particularly preferable.

  When performing surface crosslinking, the surface crosslinking method may be a known method {for example, the method disclosed in JP-A No. 13-2935, JP-A No. 2003-147005, or JP-A No. 2003-165883}. Can do.

  The surface crosslinking may be performed by repeating the above surface crosslinking twice or more. That is, the water-absorbent resin particles obtained by surface cross-linking with a surface cross-linking agent can be subjected to additional surface cross-linking with the same or different surface cross-linking agents. The content of the additional surface crosslinking agent, the treatment method, the treatment temperature, the treatment time, etc. are the same as in the above case.

If necessary, an additive can be added to the water-absorbent resin particles at any stage {polymerization step, drying step, surface cross-linking step and / or before and after these steps}.
Examples of additives include known additives (for example, Japanese Patent Application Laid-Open No. 2003-225565) {preservatives, fungicides, antioxidants, ultraviolet absorbers, colorants, deodorants, organic fibrous materials, etc.} These can be used, and one or more of these may be used in combination.

Absorbent articles can be produced by applying the water-absorbent resin particles obtained by the present invention to various absorbers. The absorber and the absorbent article are manufactured by a known method (for example, Japanese Patent Application Laid-Open No. 2005-186016).
Absorbent articles include sanitary products {paper diapers (children's disposable diapers and adult disposable diapers, etc.), napkins (sanitary napkins, etc.), vomit absorption etiquette bags, paper towels, pads (incontinence pads and surgical underpads) Etc.) and pet sheets (pet sheets and heat insulation sheets etc.)}, and various household and industrial absorbent sheets {freshness retention sheets, drip absorbent sheets, etc.}.

  Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Hereinafter, unless otherwise specified, parts are parts by weight.

<Example 1>
145.4 parts of acrylic acid was diluted with 9.4 parts of water and neutralized by adding 242.3 parts of a 25 wt% aqueous sodium hydroxide solution while cooling to 30-20 ° C. To this solution, 0.0727 parts of ethylene glycol diglycidyl ether (manufactured by Nagase Chemical Industries, Denacol EX-810), 0.0146 parts of sodium hypophosphite monohydrate and 0.0727 parts of potassium persulfate were added. And dissolved in an aqueous monomer solution. Into a four-necked round bottom flask equipped with a stirrer, reflux condenser, thermometer and nitrogen gas introduction tube, 624 parts of cyclohexane was added, and polyoxyethylene octylphenyl ether phosphate (Daiichi Kogyo Seiyaku Co., Ltd. (Blysurf A210G) 1.56 parts was added and dispersed by stirring at 470 rpm. After the flask was purged with nitrogen, the temperature was raised to 75 ° C. to reflux cyclohexane. The monomer aqueous solution prepared above was added dropwise thereto at a rate of 6.6 parts / minute for 6 minutes as the first step, and maintained at 75 ° C. for 15 minutes after the completion of the dropwise addition.
Next, as a 2nd process, it was dripped over 54 minutes at 6.6 parts / min.
Next, as the third step, after completion of the dropping of the second step, the mixture is held at 75 ° C. for 30 minutes to reduce the water content of the reaction mixture to 10% (weight basis). Since it settled to the bottom of this, it was separated by decantation.
Next, as a fourth step, the separated water-absorbent resin cake is dried for 60 minutes at a drying temperature of 150 ° C. with a CD dryer (biaxial indirect heat dryer) (manufactured by Kurimoto Steel Works), and water-absorbent resin particles (1 )

<Example 2>
In Example 1, after completion | finish of dripping at a 1st process, it carries out similarly to Example 1 except hold | maintaining at 75 degreeC for 30 minutes, and hold | maintaining at 75 degreeC for 60 minutes at a 3rd process, and a water absorbing resin particle (2). Got.

<Example 3>
In Example 1, after the completion of dropping in the first step, it was carried out in the same manner as in Example 1 except that it was kept at 75 ° C. for 3.0 minutes, and in the third step was kept at 75 ° C. for 60 minutes. 3) was obtained.

<Example 4>
In Example 1, after completion | finish of dripping at a 1st process, it hold | maintains for 15 minutes at 75 degreeC, and it hold | maintains at 75 degreeC for 30 minutes by a 3rd process, it carries out similarly to Example 1, and water-absorbent resin particle (4) Got.

<Example 5>
In Example 1, after completion | finish of dripping at a 1st process, it carries out similarly to Example 1 except hold | maintaining at 75 degreeC for 15 minutes, and hold | maintaining at 75 degreeC for 180 minutes at a 3rd process, and a water absorbing resin particle (5). Got.

<Comparative Example 1>
In Example 1, water-absorbent resin particles (6) were prepared in the same manner as in Example 1 except that the first step was held at 75 ° C. for 70 minutes after completion of dropping, and the third step was held at 75 ° C. for 60 minutes. Got.

<Comparative example 2>
In Example 1, after the completion of dropping in the first step, the same procedure as in Example 1 was performed except that the mixture was held at 75 ° C. for 2.5 minutes and the third step was held at 75 ° C. for 60 minutes. 7) was obtained.

<Comparative Example 3>
In Example 1, water-absorbent resin particles (8) were prepared in the same manner as in Example 1 except that the first step was held at 75 ° C. for 70 minutes after the completion of dropping, and the third step was dried at 75 ° C. for 20 minutes. Got.

<Comparative example 4>
In Example 1, water-absorbent resin particles (9) were prepared in the same manner as in Example 1 except that the first step was held at 75 ° C. for 70 minutes after completion of dropping, and the third step was dried at 75 ° C. for 200 minutes. Got.

  In Examples 1 to 5 and Comparative Examples 1 to 4, the bulk density of the water-containing water-absorbent resin particles (b) obtained in the second step, the bulk density after drying of the water-absorbent resin particles, and the water absorption rate were measured. It was shown to. Moreover, the breakability test was implemented by the following method and it summarized in Table 1.

<Fracture test>
A 3 L round bottom flask (manufactured by AS ONE) was charged with 30 g of water-absorbing resin particles, and a nylon net (JIS Z8801-1: 2000) having an aperture of 63 μm with a 6 mm hole in the center was formed at the top of the round bottom flask. Lay down and set a four-mouth separable cover (AS ONE main pipe TS29 / 42, side pipe TS24 / 40, 24/40, 15/35) on it. Next, a stainless steel tube (outer diameter 6 mm, inner diameter 4 mm) is passed through the nylon net to the main pipe TS 29/42 of the four-neck separable cover so that the tip is positioned 45 mm from the bottom of the round bottom flask. The other end of the stainless steel pipe is equipped with a urethane tube (length 1500 mm, inner diameter 8.5 mm) and connected to an air line that can achieve a pressure of 0.3 MPa or more. Next, the air line was opened, the pressure was set to 0.2 MPa, and after 3 minutes, the water-absorbing resin particles were taken out, the content (%) of fine particles of 150 μm or less was obtained, and the numerical value obtained to the first decimal place by the following formula Is fragile.

Breakability = Content of fine particles of 150 μm or less after the breakability test (%) / Content of fine particles of 150 μm or less before the breakability test (%)

  From the results of Table 1, the water-absorbent resin particles of Examples 1 to 5 are extremely less fragile in spite of the same water absorption rate as compared to the water-absorbent resin particles of Comparative Examples 1 to 4. I understand.

The water-absorbent resin particles obtained by the production method of the present invention are water-absorbent resin particles having a high absorption rate and can be absorbed immediately when used in absorbent articles such as diapers, napkins, urine pads, and pet sheets. It can be made into an absorbent article. In addition, when the absorbent resin particles are dispersed during the production of the absorbent body, the absorbent resin particles are not broken due to collision between the absorbent resin particles, and the water-absorbent resin particles that do not deteriorate the working environment are produced. Is suitable.
The water-absorbent resin particles of the present invention are not only sanitary products, but also pet urine absorbents, urine gelling agents for portable toilets, freshness preservation agents such as fruits and vegetables, drip absorbents for meat and seafood, cold insulation agents, disposable warmers It is also useful for various applications such as battery gelling agents, water retention agents such as plants and soil, anti-condensation agents, water-stopping materials and packing materials, and artificial snow.

Claims (4)

  A water-soluble ethylenically unsaturated monomer aqueous solution containing a crosslinking agent is subjected to reverse phase suspension polymerization in a hydrophobic organic solvent in the presence of a dispersant to obtain a reaction mixture (A) containing water-containing water-absorbing resin particles (a). 1 step; a water-soluble ethylenically unsaturated monomer aqueous solution further containing a crosslinking agent is added to (A) and subjected to reverse phase suspension polymerization to obtain a reaction mixture (B) containing water-containing water-absorbing resin particles (b). Production of water-absorbent resin particles (D) comprising two steps; a third step of dehydrating and removing the solvent (B) to obtain a water-absorbent resin cake (C); and a fourth step of drying the water-absorbent resin cake The water-containing water-absorbent resin particles (b) have a bulk density of 0.25 to 0.35 g / ml, and the dried water-absorbent resin particles (D) have a bulk density of 0.45 to 0.55 g. / Ml of water-absorbing resin particles.   The production method according to claim 1, wherein the absorption rate of the water-absorbent resin particles (D) is 8 to 15 seconds.   The absorber formed by containing the water absorbing resin particle (D) obtained by the manufacturing method of Claim 1 or 2, and a fiber.   An absorbent article comprising the absorbent body according to claim 3.