JP2013100543A - Method for producing water-absorbing resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a water-absorbing resin particle, which has excellent water-absorbing performance, an appropriate particle size, and narrow particle size distribution and is suitably used for an absorbent article etc.SOLUTION: In the method for producing a water-absorbing resin particle, the water-absorbing resin particle is produced by performing reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon solvent by using a water-soluble radical polymerization initiator in the presence of a dispersion stabilizer, wherein a trehalose fatty acid ester is used as the dispersion stabilizer. According to the production method, the method for producing a water-absorbing resin particle, which has excellent water-absorbing performance, an appropriate particle size, and narrow particle size distribution and is suitably used for an absorbent article etc., such as a sanitary napkin, an incontinence pad, and a disposable diaper, is provided.

Description

  The present invention relates to a method for producing water absorbent resin particles. More specifically, the present invention relates to a method for producing water-absorbing resin particles that have excellent water absorption performance and have an appropriate particle size and a narrow particle size distribution, and are suitably used for absorbent articles and the like.

  Water-absorbent resin particles are mainly used in disposable diapers, sanitary napkins, incontinence pads, pet sheets, water retention agents for soil, water-stopping agents for power cables, anti-condensation agents, and the like. For example, absorbent articles such as disposable diapers generally have an absorbent body composed of water-absorbent resin particles and hydrophilic fibers, and a liquid-permeable sheet disposed on the side in contact with the body and a liquid impermeable sheet disposed on the opposite side. It is formed by being sandwiched between permeable sheets. The absorbent body is produced, for example, by laminating a mixture of water-absorbing resin particles and crushed hydrophilic fibers on a wire mesh by an air flow, and then compressing with a press.

  Examples of the water-absorbent resin particles include starch-acrylonitrile graft copolymer hydrolyzate, starch-acrylic acid graft copolymer neutralized product, vinyl acetate-acrylic ester copolymer saponified product, and polyacrylic acid. Partially neutralized products are known.

  The water-absorbent resin particles used in the absorber are required to have an appropriate particle size and a narrow particle size distribution, in addition to being excellent in water absorption capability, water retention capability, and the like. When there are many particles having a large particle diameter, the absorber tends to harden when compressed. Moreover, when there are many particles with a small particle diameter, since it loses | misses and loses from a metal mesh at the time of manufacture of an absorber, it is unpreferable. Therefore, it is desirable that the water-absorbent resin particles used in the absorbent body have a narrow particle size distribution while having a median particle diameter suitable for designing the intended absorbent body and absorbent article.

  As a method for producing the water-absorbent resin particles, a method of polymerizing a water-soluble ethylenically unsaturated monomer is mainly used from the viewpoint of the high performance of the water-absorbent resin particles obtained and the simplicity of the production method. As the polymerization method, for example, an aqueous solution of a water-soluble ethylenically unsaturated monomer is obtained by polymerizing an aqueous solution of a water-soluble ethylenically unsaturated monomer to obtain a hydrous gel, and then pulverizing and drying; The aqueous solution is dispersed in a hydrophobic organic solvent such as a petroleum hydrocarbon solvent in the presence of a dispersion stabilizer and subjected to suspension polymerization to obtain a hydrous gel, followed by dehydration and drying. Legal etc. are mentioned.

  In the aqueous solution polymerization method, the water-containing gel after polymerization is a viscous lump, which not only complicates the pulverization process and drying process, but also facilitates the generation of fine particles by the pulverization process. In addition, it is difficult to obtain water-absorbing resin particles having a narrow particle size distribution. On the other hand, in the reverse phase suspension polymerization method, the particle size can be controlled by the size of water-soluble ethylenically unsaturated monomer droplets dispersed in a petroleum hydrocarbon solvent. Therefore, various particle diameter control techniques have been proposed, centering on the reverse phase suspension polymerization method.

  As a technique for obtaining a narrow particle size distribution, for example, a method using a sorbitan fatty acid ester as a dispersant (see Patent Document 1), a method using a sorbitan fatty acid ester of HLB 8-12 as a dispersant (see Patent Document 2), polyglycerin. A method using a fatty acid ester as a dispersant (see Patent Document 3) has been proposed. However, even with these conventional technologies, water-absorbing resin particles having satisfactory performance have not been obtained from the viewpoints of excellent water absorption performance, moderate particle size and narrow particle size distribution.

JP-A-56-26909 JP 56-131608 A JP-A-62-172006

  An object of the present invention is to provide a method for producing water-absorbent resin particles that have excellent water absorption performance, an appropriate particle size and a narrow particle size distribution, and are suitably used for absorbent articles and the like.

  In producing water-absorbing resin particles by the reverse-phase suspension polymerization method, the present inventors have used trehalose fatty acid ester as a dispersion stabilizer to provide excellent water absorption performance, as well as moderate particle size and narrow particle size distribution. It has been found that water-absorbent resin particles suitable for absorbent articles and the like can be obtained, and the present invention has been completed.

  That is, the present invention relates to water absorption by subjecting a water-soluble ethylenically unsaturated monomer to reverse phase suspension polymerization in a petroleum hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a dispersion stabilizer. The present invention relates to a method for producing water-absorbent resin particles, characterized in that trehalose fatty acid ester is used as a dispersion stabilizer in the method for producing water-soluble resin particles.

  According to the present invention, by using trehalose fatty acid ester as a dispersion stabilizer, water-absorbent resin particles having excellent water absorption performance, moderate particle size and narrow particle size distribution, and suitably used for absorbent articles and the like Can be manufactured.

  The method for producing water-absorbent resin particles of the present invention comprises a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon solvent, using a water-soluble radical polymerization initiator in the presence of a dispersion stabilizer, In the method for producing water-absorbent resin particles by suspension polymerization, a trehalose fatty acid ester is used as a dispersion stabilizer.

  In the reversed-phase suspension polymerization method, a water-soluble ethylenically unsaturated monomer is further added to the water-absorbent resin particle precursor obtained by reversed-phase suspension polymerization, and polymerization is performed in two or more stages. Can also be done. In multi-stage polymerization of two or more stages, the water-absorbent resin particles obtained in the first-stage reversed-phase suspension polymerization can be aggregated to increase the particle diameter of the water-absorbent resin particles. It becomes easier to obtain an appropriate particle size suitable for the absorbent article.

  Examples of the water-soluble ethylenically unsaturated monomer include (meth) acrylic acid (in this specification, “acryl” and “methacryl” are collectively referred to as “(meth) acryl”. The same), 2- (meth) acrylamide-2-methylpropanesulfonic acid and their alkali metal salts; (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N- Nonionic monomers such as methylol (meth) acrylamide and polyethylene glycol mono (meth) acrylate; N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, and diethylaminopropyl (meta ) Amino group-containing unsaturated monomers such as acrylamide Quaternized product like thereof in rabbi. These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

  Among the water-soluble ethylenically unsaturated monomers, (meth) acrylic acid and alkali metal salts thereof, (meth) acrylamide, and N, N-dimethyl (meth) acrylamide are industrially easily available. Preferably used. Furthermore, (meth) acrylic acid and its alkali metal salt are used more suitably from a viewpoint that the water-absorbing performance of the water-absorbing resin particles obtained is high.

  In addition, when performing polymerization in two or more stages, the water-soluble ethylenically unsaturated monomer component used in the second and subsequent stages is the same type as the water-soluble ethylenically unsaturated monomer component used in the first stage. Or it may be different.

  The water-soluble ethylenically unsaturated monomer is preferably used as an aqueous solution. The concentration of the water-soluble ethylenically unsaturated monomer in the aqueous solution of the water-soluble ethylenically unsaturated monomer is preferably in the range of 20% by mass to the saturated concentration.

  When the water-soluble ethylenically unsaturated monomer has an acid group such as (meth) acrylic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, etc., the acid group is converted to an alkali metal salt or the like. It may be neutralized with an alkaline neutralizer. The degree of neutralization of all acid groups by the alkaline neutralizing agent is problematic in terms of safety, etc. due to the viewpoint of increasing the absorption capacity by increasing the osmotic pressure of the resulting water-absorbent resin particles, and the presence of excess alkaline neutralizing agent. Is preferably in the range of 10 to 100 mol%, more preferably in the range of 30 to 80 mol%.

  Examples of the alkaline neutralizing agent include sodium hydroxide, potassium hydroxide, and ammonium hydroxide. These alkaline neutralizers may be used alone or in combination of two or more.

  Examples of the water-soluble radical polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl kumi Peroxides such as ruperoxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, and hydrogen peroxide; 2,2′-azobis [2- (N- Phenylamidino) propane] dihydrochloride, 2,2′-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2 -Imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis {2-methyl-N- [1,1-bis (H Roxymethyl) -2-hydroxyethyl] propionamide}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], and 4,4′-azobis (4-cyanovaleric acid) And azo compounds. These water-soluble radical polymerization initiators may be used alone or in combination of two or more.

  It is preferable that the usage-amount of a water-soluble radical polymerization initiator is 0.005-1 mol% with respect to the usage-amount of the water-soluble ethylenically unsaturated monomer in each superposition | polymerization stage, respectively. If the amount used is less than 0.005 mol%, the polymerization reaction may take a long time. When the amount used exceeds 1 mol%, a rapid polymerization reaction may occur.

  The radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid.

  Moreover, in order to control the water absorption performance of the water absorbent resin particles, a chain transfer agent may be added. Examples of such chain transfer agents include hypophosphites, thiols, thiolic acids, secondary alcohols, amines, and the like.

  You may superpose | polymerize by adding a crosslinking agent to the aqueous solution of the said water-soluble ethylenically unsaturated monomer as needed. As the crosslinking agent (internal crosslinking agent) added to the water-soluble ethylenically unsaturated monomer aqueous solution before the polymerization reaction, a compound having two or more polymerizable unsaturated groups is used. As a specific example of the internal cross-linking agent, for example, (poly) ethylene glycol (in this specification, “polyethylene glycol” and “ethylene glycol” are collectively referred to as “(poly) ethylene glycol”. ), (Poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and di- or tri (meth) acrylates of polyols such as (poly) glycerin, the aforementioned polyols and maleic acid And unsaturated polyesters obtained by reacting unsaturated acids such as fumaric acid; obtained by reacting bisacrylamides such as N, N′-methylenebis (meth) acrylamide, polyepoxides and (meth) acrylic acid Di or tri (meta) access Luric acid esters; di (meth) acrylic acid carbamyl esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylate; allylated starch, allylated cellulose, Examples include diallyl phthalate and N, N ′, N ″ -triallyl isocyanurate.

  In addition to the compound having two or more polymerizable unsaturated groups, a compound having two or more other reactive functional groups can be used. Specific examples of compounds having two or more other reactive functional groups include glycidyl group-containing compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether. Etc.

  These internal crosslinking agents may be used alone or in combination of two or more.

  The addition amount of the internal crosslinking agent is 1 mol% or less with respect to the amount of the water-soluble ethylenically unsaturated monomer used in each polymerization stage, from the viewpoint of sufficiently enhancing the water absorption performance of the water-absorbing resin particles obtained. It is preferable that it is 0.5 mol% or less. The addition of the internal cross-linking agent is optional in the vicinity of the surface of the water-absorbent resin particles by adding a cross-linking agent in any step from the polymerization of the water-soluble ethylenically unsaturated monomer to the drying. This is because the water-absorbing performance of the water-absorbent resin particles can also be controlled by post-crosslinking to.

  For the purpose of adjusting the particle diameter of the resulting water-absorbent resin particles, a thickener may be added to the aqueous solution of the water-soluble ethylenically unsaturated monomer. Examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid neutralized product or partially neutralized product, and polyethylene glycol. Usually, if the stirring rotation speed at the time of polymerization is the same, the higher the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution, the larger the particle diameter of the water-absorbent resin particles obtained.

  Examples of the petroleum hydrocarbon solvent used as the dispersion medium include aliphatic hydrocarbons having 6 to 8 carbon atoms such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, and n-octane; cyclohexane And alicyclic hydrocarbons having 6 to 8 carbon atoms such as methylcyclopentane and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene. Of these, aliphatic hydrocarbons having 6 to 8 carbon atoms and alicyclic hydrocarbons having 6 to 8 carbon atoms are suitably used from the viewpoint of industrial availability and stable quality. Specifically, n-heptane, cyclohexane, and isomer mixtures thereof are preferably used. These petroleum hydrocarbon solvents may be used alone or in combination of two or more.

  The amount of the petroleum hydrocarbon solvent used is from the viewpoint of easy removal of heat of polymerization and control of the polymerization temperature, with respect to 100 parts by mass of the total amount of water-soluble ethylenically unsaturated monomer aqueous solution used for the polymerization. 50 to 600 parts by mass, and more preferably 100 to 550 parts by mass.

  In the present invention, a water-soluble ethylenically unsaturated monomer is subjected to reverse phase suspension polymerization in a petroleum hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a dispersion stabilizer to absorb water. In the method for producing resin particles, the greatest feature is that trehalose fatty acid ester is used as a dispersion stabilizer.

  The hydrophilic / lipophilic balance (HLB) of the trehalose fatty acid ester is 2 to 2 from the viewpoint that the trehalose fatty acid ester is dissolved in the petroleum hydrocarbon solvent and the dispersion stability of the water-soluble ethylenically unsaturated monomer aqueous solution is increased. It is preferably 17, more preferably 2 to 10, and most preferably 3 to 7.

  The trehalose fatty acid ester is not particularly limited. It is done. Among these, trehalose palmitate, trehalose stearate, and trehalose behenate are preferably used from the viewpoint of dispersion stability of the water-soluble ethylenically unsaturated monomer aqueous solution in the petroleum hydrocarbon solvent. These trehalose fatty acid esters may be used alone or in combination of two or more.

  In addition, other dispersion stabilizers can be used in combination as long as the dispersion stability by the trehalose fatty acid ester is not inhibited. Examples of the dispersion stabilizer used in combination include sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester and the like.

  Further, as the dispersion stabilizer, a polymer dispersion stabilizer may be used in combination with the trehalose fatty acid ester. Examples of the polymer dispersion stabilizer used include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, and maleic anhydride-modified ethylene-propylene copolymer. These polymer dispersion stabilizers may be used alone or in combination of two or more.

  The amount of the dispersion stabilizer used is the first step from the viewpoint of maintaining a good dispersion state of the water-soluble ethylenically unsaturated monomer aqueous solution in the petroleum hydrocarbon solvent and obtaining a dispersion effect commensurate with the amount used. The amount is preferably 0.1 to 5 parts by mass and more preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the aqueous solution of the water-soluble ethylenically unsaturated monomer used for the polymerization. The first-stage polymerization means a single-stage polymerization process and a first-stage polymerization process in two or more stages.

  Although the reaction temperature of a polymerization reaction changes with water-soluble radical polymerization initiators to be used, it is preferable that it is 20-110 degreeC, and it is more preferable that it is 40-90 degreeC. When the reaction temperature is lower than 20 ° C., the polymerization rate is slow and the polymerization time becomes long, which is not economically preferable. When the reaction temperature is higher than 110 ° C., it is difficult to remove the heat of polymerization, and thus it may be difficult to carry out the reaction smoothly. The reaction time is preferably 10 minutes to 4 hours.

  In the present invention, it is preferable to carry out post-crosslinking by adding a cross-linking agent to the precursor of the obtained water-absorbent resin particles after completion of the reverse phase suspension polymerization. By carrying out post-crosslinking by adding a cross-linking agent after polymerization, water absorption performance such as water absorption capacity under load can be enhanced, and for example, it is suitably used as an absorbent article such as a paper diaper.

  Examples of the crosslinking agent (post-crosslinking agent) used for the post-crosslinking include compounds having two or more reactive functional groups. Specific examples of the compound having two or more reactive functional groups include polyhydric alcohols such as (poly) propylene glycol, (poly) ethylene glycol, and (poly) glycerin; ethylenediamine, triethylenetetramine, tetraethylenepentamine, etc. A polyvalent amine compound such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; a polyvalent oxazoline compound such as 1,2-ethylenebisoxazoline; (poly) ethylene glycol diglycidyl ether, (poly) Polyvalent glycidyl compounds such as glycerol (poly) glycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether; carbodihydrazide, malonic dihydrazide, adipic acid dihydride Multivalent hydrazide compounds such disilazide and dodecanedioic acid dihydrazide, and the like. These post-crosslinking agents may be used alone or in combination of two or more.

  The addition amount of the post-crosslinking agent does not decrease the water-holding ability (absorption capacity) of the water-absorbent resin particles obtained, and also increases the water-absorbing performance such as water-absorbing capacity under load by increasing the cross-linking density near the surface. From 0.005 to 1 mol%, more preferably from 0.01 to 0.5 mol%, based on the total amount of water-soluble ethylenically unsaturated monomers used in the polymerization preferable.

  The addition time of the post-crosslinking agent is not particularly limited as long as it is any step from the polymerization of the water-soluble ethylenically unsaturated monomer to the end of drying. The post-crosslinking agent is preferably added in the presence of 1 to 400 parts by mass of water and added in the presence of 5 to 200 parts by mass of water with respect to 100 parts by mass of the solid content of the water-absorbent resin particles. More preferably, it is most preferably added in the presence of 10 to 100 parts by mass of water. Thus, by controlling the amount of water at the time of post-crosslinking agent addition, appropriate cross-linking can be performed in the vicinity of the surface of the water-absorbent resin particles, and excellent water absorption ability under load can be achieved. .

  Moreover, when adding a post-crosslinking agent, you may use a hydrophilic organic solvent as needed. Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane, and tetrahydrofuran; N And amides such as N-dimethylformamide; sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents may be used alone or in combination of two or more.

  The addition form of the post-crosslinking agent is not particularly limited. For example, a method of adding the post-crosslinking agent solution to the water-containing gel-like product of water-absorbing resin particles dispersed in the petroleum hydrocarbon solvent; Examples include a method of spraying the post-crosslinking agent solution by spraying or the like while stirring the powdery water-absorbent resin particles after the distillation.

  The temperature after the addition of the post-crosslinking agent allows the post-crosslinking agent and the water-absorbent resin particles to sufficiently react to increase the cross-linking density in the vicinity of the surface, thereby effectively enhancing the water absorption performance such as water absorption capability under load. Therefore, the temperature is preferably 70 to 250 ° C, more preferably 80 to 200 ° C, and most preferably 90 to 180 ° C.

  In addition, you may add additives, such as a lubricant, a deodorant, and an antibacterial agent, to the water absorbing resin particle of this invention further according to the objective.

  The water-absorbing resin particles obtained in this way have excellent water absorption performance, an appropriate particle size and a narrow particle size distribution, and therefore are suitably used for absorbent bodies and water-absorbing articles using the same.

  In addition, the water retention ability (absorption capacity), the median particle diameter, and the uniformity of the particle diameter distribution of the water-absorbent resin particles are values measured by a measurement method described later.

  The water retention capacity of the water-absorbent resin particles obtained by the production method of the present invention is preferably 20 g / g or more, and preferably 25 g / g or more from the viewpoint of increasing the absorption capacity of the absorbent body used in the absorbent article. Is more preferable, and it is most preferable that it is 30 g / g or more.

  Since the median particle diameter of the water-absorbent resin particles obtained by the production method of the present invention varies depending on the intended application, it cannot be generally limited. For example, when used for a thin sheet-like material such as a waterproofing agent for power cables. The medium particle size is selected as small as about 20 to 200 μm. On the other hand, when an absorbent body is prepared by mixing water-absorbent resin particles and fibers and used for absorbent articles such as paper diapers, a relatively large medium particle diameter of about 200 to 600 μm is selected.

  The particle diameter distribution of the water absorbent resin particles is preferably narrow. Small particles are inferior to the fluidity of the powder and have problems such as dust generation. Moreover, there exists a possibility that the particle | grains larger than necessary may deteriorate the quality of the applied product using a water-absorbent resin particle. For example, when explaining a paper diaper, small particles have problems such as difficulty in transferring the water-absorbent resin particles during the production of the absorbent body, and the water-absorbent resin particles are missing from the wire mesh. On the other hand, large particles may become hard or gritty and uncomfortable when the absorber is compressed. Accordingly, the uniformity indicating the narrowness of the particle size distribution of the water-absorbent resin particles is preferably 3.0 or less, more preferably 2.6 or less, and most preferably 2.4 or less. . The uniformity can be determined to be narrower as the particle size distribution is closer to the lower limit of 1.0.

  Hereinafter, the present invention will be described in more detail based on examples and comparative examples. However, the present invention is not limited to such examples.

  The performance of the water-absorbent resin particles obtained in each Example and Comparative Example was evaluated by the following method.

(1) Water retention capacity of physiological saline Mamako generates 2.0 g of water-absorbent resin particles while weighing 500 g of 0.9 mass% saline (physiological saline) in a 500 mL beaker and stirring at 600 rpm. Not to be dispersed. The mixture was allowed to stand for 30 minutes with stirring to sufficiently swell the water-absorbent resin particles. Then, it was poured into a cotton bag (Membroad No. 60, width 100 mm x length 200 mm), the upper part of the cotton bag was tied with a rubber band, and a centrifugal force was set to 167 G (manufactured by Kokusan Centrifuge Co., Ltd., product number: The cotton bag was dehydrated using H-122) for 1 minute, and the mass Wa (g) of the cotton bag containing the swollen gel after dehydration was measured. The same operation was performed without adding the water-absorbent resin particles, the empty mass Wb (g) when the cotton bag was wet was measured, and the water retention capacity was calculated from the following equation.
Saline retention capacity (g / g) = [Wa-Wb] (g) / mass of water-absorbent resin particles (g)

(2) Median particle diameter of water-absorbent resin particles About 50 g of water-absorbent resin particles are passed using a JIS standard sieve sieve having a mesh size of 250 μm. When 50% by mass or more of the sieve combination remained on the sieve, the median particle diameter was measured using the sieve combination (B).

    (A) From above, a sieve with an opening of 500 μm, a sieve with an opening of 250 μm, a sieve with an opening of 180 μm, a sieve with an opening of 150 μm, a sieve with an opening of 106 μm, a sieve with an opening of 75 μm, an opening of 45 μm Combined in order of sieve and saucer.

    (B) JIS standard sieve from above, sieve with an opening of 850 μm, sieve with an opening of 600 μm, sieve with an opening of 500 μm, sieve with an opening of 425 μm, sieve with an opening of 300 μm, sieve with an opening of 250 μm, sieve with an opening of 150 μm Combined in order of sieve and saucer.

  About 50 g of the water-absorbent resin particles were put on the combined uppermost sieve, and classified by shaking for 10 minutes using a low-tap shaker.

  After classification, the mass of the water-absorbent resin particles remaining on each sieve was calculated as a mass percentage with respect to the total amount of the water-absorbent resin particles, and accumulated in order from the largest particle diameter. Thereafter, the relationship between the opening of the sieve and the integrated value of the mass percentage of the water-absorbent resin particles remaining on the sieve was plotted on a logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to an integrated mass percentage of 50 mass% was defined as the median particle diameter.

(3) Uniformity of particle size distribution (2) In the measurement of the median particle size, the particle size (X1) corresponding to an integrated mass percentage of 15.9% by mass and the particle size corresponding to 84.1% by mass ( X2) was determined, and the uniformity was determined by the following formula. Note that the closer the uniformity is to 1.0, the narrower the particle size distribution.
Uniformity = X1 / X2

[Example 1]
Prepared a 2 L round bottom cylindrical separable flask with an inner diameter of 100 mm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, a stirrer, and a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. did. Into this flask, 321 g (472 ml) of n-heptane was taken, and 0.92 g of trehalose stearate ester of HLB5 [saponification value: 107, acid value: 0.2, hydroxyl value: 367] as a dispersion stabilizer, high polymer dispersion stability 0.92 g of maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, High Wax 1105A) was added as an agent, and the dispersion stabilizer was dissolved by heating to 80 ° C. while stirring, and then 65 ° C. Until cooled.

  On the other hand, 92 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution and 51.2 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask and cooled from the outside, and 30% sodium hydroxide aqueous solution 102. 9g was dripped and 75 mol% neutralization was performed. Thereafter, 0.27 g of hydroxyethyl cellulose (AW-15F, manufactured by Sumitomo Seika Co., Ltd.) as a thickener, 0.11 g (0.41 mmol) of potassium persulfate as a polymerization initiator, and ethylene glycol diglycidyl ether as an internal crosslinking agent 9.2 mg (0.05 mmol) was added and dissolved to prepare an aqueous monomer solution.

  The monomer aqueous solution was added to the separable flask at a rotation speed of 700 rpm with a stirrer, and the system was maintained at 45 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and polymerization was carried out for 60 minutes.

  After the polymerization, the rotation speed of the stirrer is changed to 1000 rpm, the temperature is raised using an oil bath at 125 ° C., and n-heptane is refluxed by azeotropic distillation of water and n-heptane. 7 g of water was extracted out of the system. Thereafter, 3.68 g of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added as a post-crosslinking agent, followed by removal of water and n-heptane by distillation and drying to obtain 97.9 g of spherical water-absorbing resin particles. Obtained. The physical properties of the water-absorbent resin particles were evaluated by the above methods, and the results are shown in Table 1.

[Example 2]
Prepared a 2 L round bottom cylindrical separable flask with an inner diameter of 100 mm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, a stirrer, and a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. did. Into this flask, 321 g (472 ml) of n-heptane was taken, and 0.92 g of trehalose stearate ester of HLB5 [saponification value: 107, acid value: 0.2, hydroxyl value: 367] as a dispersion stabilizer, high polymer dispersion stability 0.92 g of maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, High Wax 1105A) was added as an agent, and the dispersion stabilizer was dissolved by heating to 80 ° C. while stirring, and then 65 ° C. Until cooled.

  On the other hand, 92 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution and 51.2 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask and cooled from the outside, and the 30% by mass sodium hydroxide aqueous solution 102 was taken. .9 g was dropped to neutralize 75 mol%. Thereafter, 0.27 g of hydroxyethyl cellulose (AW-15F, manufactured by Sumitomo Seika Co., Ltd.) as a thickener, 0.11 g (0.41 mmol) of potassium persulfate as a polymerization initiator, and ethylene glycol diglycidyl ether as an internal crosslinking agent 9.2 mg (0.05 mmol) was added and dissolved to prepare a first-stage monomer aqueous solution.

  The first-stage monomer aqueous solution was added to the separable flask at a rotation speed of 700 rpm with the stirrer, and the system was maintained at 45 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and the first stage polymerization was carried out for 60 minutes to obtain a post-polymerization slurry.

  On the other hand, 128.2 g (1.43 mol) of an 80.5% by mass acrylic acid aqueous solution and 30.5 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask, and 30% by mass sodium hydroxide was cooled from the outside. The aqueous solution 143.3g was dripped and 75 mol% neutralization was performed. Thereafter, 0.15 g (0.56 mmol) of potassium persulfate as a polymerization initiator and 12.8 mg (0.07 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added and dissolved. An aqueous body solution was prepared.

  After changing the rotation speed of the stirrer to 1000 rpm, the second-stage monomer aqueous solution was added to the separable flask and maintained at 20 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and the second polymerization was carried out for 30 minutes.

  After the second stage polymerization, the temperature was raised using an oil bath at 125 ° C., and 258.5 g of water was extracted out of the system by refluxing n-heptane by azeotropic distillation of water and n-heptane. It was. Thereafter, 3.96 g of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added as a post-crosslinking agent, followed by removal of water and n-heptane by distillation and drying to form a water-absorbent resin in the form of aggregated spherical particles 242.6 g of particles were obtained. The physical properties of the water-absorbent resin particles were evaluated by the above methods, and the results are shown in Table 1.

[Comparative Example 1]
Prepared a 2 L round bottom cylindrical separable flask with an inner diameter of 100 mm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, a stirrer, and a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. did. Into this flask, 321 g (472 ml) of n-heptane was taken, 0.92 g of tetraglycerin stearate ester of HLB4 (manufactured by Mitsubishi Chemical Foods Co., Ltd., Ryoto Polygly TS-4) as a dispersion stabilizer, and as a polymer dispersion stabilizer. Add 0.92 g of maleic anhydride modified ethylene-propylene copolymer (Mitsui Chemicals, High Wax 1105A), raise the temperature to 80 ° C. with stirring and dissolve the dispersion stabilizer, then cool to 55 ° C. did.

  On the other hand, 92 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution and 51.2 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask and cooled from the outside, and 30% sodium hydroxide aqueous solution 102. 9g was dripped and 75 mol% neutralization was performed. Thereafter, 0.27 g of hydroxyethyl cellulose (AW-15F, manufactured by Sumitomo Seika Co., Ltd.) as a thickener, 0.11 g (0.41 mmol) of potassium persulfate as a polymerization initiator, and ethylene glycol diglycidyl ether as an internal crosslinking agent 9.2 mg (0.05 mmol) was added and dissolved to prepare an aqueous monomer solution.

  The monomer aqueous solution was added to the separable flask at a rotation speed of 700 rpm with a stirrer, and the system was maintained at 35 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and polymerization was carried out for 60 minutes.

  After the polymerization, the rotation speed of the stirrer is changed to 1000 rpm, the temperature is raised using an oil bath at 125 ° C., and n-heptane is refluxed by azeotropic distillation of water and n-heptane. 7 g of water was extracted out of the system. Thereafter, 3.68 g of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added as a post-crosslinking agent, followed by removal of water and n-heptane by distillation and drying to obtain 97.0 g of spherical water-absorbing resin particles. Obtained. The physical properties of the water-absorbent resin particles were evaluated by the above methods, and the results are shown in Table 1.

[Comparative Example 2]
Prepared a 2 L round bottom cylindrical separable flask with an inner diameter of 100 mm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, a stirrer, and a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. did. Into this flask, 321 g (472 ml) of n-heptane was taken, 0.92 g of tetraglycerin stearate ester of HLB4 (manufactured by Mitsubishi Chemical Foods Co., Ltd., Ryoto Polygly TS-4) as a dispersion stabilizer, and as a polymer dispersion stabilizer. Add 0.92 g of maleic anhydride modified ethylene-propylene copolymer (Mitsui Chemicals, High Wax 1105A), raise the temperature to 80 ° C. with stirring and dissolve the dispersion stabilizer, then cool to 55 ° C. did.

  On the other hand, 92 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution and 51.2 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask and cooled from the outside, and the 30% by mass sodium hydroxide aqueous solution 102 was taken. .9 g was dropped to neutralize 75 mol%. Thereafter, 0.27 g of hydroxyethyl cellulose (AW-15F, manufactured by Sumitomo Seika Co., Ltd.) as a thickener, 0.11 g (0.41 mmol) of potassium persulfate as a polymerization initiator, and ethylene glycol diglycidyl ether as an internal crosslinking agent 9.2 mg (0.05 mmol) was added and dissolved to prepare a first-stage monomer aqueous solution.

  The first-stage monomer aqueous solution was added to the separable flask at a rotation speed of a stirrer of 450 rpm, and the system was maintained at 35 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and the first stage polymerization was carried out for 60 minutes to obtain a post-polymerization slurry.

  On the other hand, 128.2 g (1.43 mol) of an 80.5% by mass acrylic acid aqueous solution and 30.5 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask, and 30% by mass sodium hydroxide was cooled from the outside. The aqueous solution 143.3g was dripped and 75 mol% neutralization was performed. Thereafter, 0.15 g (0.56 mmol) of potassium persulfate as a polymerization initiator and 12.8 mg (0.07 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added and dissolved. An aqueous body solution was prepared.

  After changing the rotation speed of the stirrer to 1000 rpm, the second-stage monomer aqueous solution was added to the separable flask and maintained at 25 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and the second polymerization was carried out for 30 minutes.

  After the second stage polymerization, the temperature was raised using an oil bath at 125 ° C., and 267.8 g of water was extracted out of the system by refluxing n-heptane by azeotropic distillation of water and n-heptane. It was. Thereafter, 3.96 g of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added as a post-crosslinking agent, followed by removal of water and n-heptane by distillation and drying to form a water-absorbent resin in the form of aggregated spherical particles 242.5 g of particles were obtained. The physical properties of the water-absorbent resin particles were evaluated by the above methods, and the results are shown in Table 1.

[Comparative Example 3]
Prepared a 2 L round bottom cylindrical separable flask with an inner diameter of 100 mm, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, a stirrer, and a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. did. 378 g (472 ml) of cyclohexane was taken into this flask, 0.92 g of sorbitan monostearate of HLB4.7 (manufactured by Kao Corporation, Rhedol SP-10V) as a dispersion stabilizer, and maleic anhydride-modified ethylene as a polymer dispersion stabilizer. -0.92 g of a propylene copolymer (manufactured by Mitsui Chemicals, high wax 1105A) was added, the temperature was raised to 80 ° C while stirring to dissolve the dispersion stabilizer, and then cooled to 55 ° C.

  On the other hand, 92 g (1.03 mol) of an 80.5% by mass acrylic acid aqueous solution and 51.2 g of ion-exchanged water were placed in a 500 mL Erlenmeyer flask and cooled from the outside, and 30% sodium hydroxide aqueous solution 102. 9g was dripped and 75 mol% neutralization was performed. Thereafter, 0.11 g (0.41 mmol) of potassium persulfate as a polymerization initiator and 2.3 mg (0.01 mmol) of N, N′-methylenebisacrylamide as an internal cross-linking agent were added and dissolved to prepare an aqueous monomer solution. Was prepared.

  The monomer aqueous solution was added to the separable flask at a rotation speed of a stirrer of 250 rpm, and the system was maintained at 35 ° C. for 30 minutes while replacing the system with nitrogen. Thereafter, the flask was immersed in a 70 ° C. water bath to raise the temperature, and polymerization was carried out for 60 minutes.

  After the polymerization, the rotation speed of the stirrer was changed to 1000 rpm, the temperature was raised using an oil bath at 125 ° C., and 125.7 g of water was added while refluxing cyclohexane by azeotropic distillation of water and cyclohexane. I pulled out of the system. Thereafter, 3.68 g of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added as a post-crosslinking agent, followed by removal of water and cyclohexane by distillation, followed by drying to form a water-absorbent resin in which spherical particles were partially agglomerated. 70.3 g of particles were obtained. The physical properties of the water-absorbent resin particles were evaluated by the above methods, and the results are shown in Table 1.

  From the results shown in Table 1, the water-absorbent resin particles obtained in each example have an appropriate water retention capacity (absorption capacity), and have an appropriate particle size and a narrow particle size distribution. I understand.

In addition, the following are mentioned as an aspect of this invention.
[1] Water-absorbent resin particles obtained by subjecting a water-soluble ethylenically unsaturated monomer to reverse phase suspension polymerization in a petroleum hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a dispersion stabilizer. In the method for producing water-absorbent resin particles, a trehalose fatty acid ester is used as a dispersion stabilizer.
[2] At least the trehalose fatty acid ester is selected from the group consisting of trehalose capric acid ester, trehalose lauric acid ester, trehalose myristic acid ester, trehalose palmitic acid ester, trehalose stearic acid ester, trehalose behenic acid ester and trehalose oleic acid ester The method for producing water-absorbent resin particles according to [1], which is one type.
[3] The water-absorbent resin particle according to [1] or [2], wherein the amount of the dispersion stabilizer used is 0.1 to 5 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. Manufacturing method.
[4] The method for producing water-absorbent resin particles according to any one of [1] to [3], wherein after the reverse phase suspension polymerization, a cross-linking agent is added to perform post-crosslinking.

  According to the production method of the present invention, the water-absorbent resin having excellent water absorption performance, moderate particle size and narrow particle size distribution, and suitably used for absorbent articles such as sanitary napkins, incontinence pads, and disposable diapers. A method for producing particles can be provided.

Claims (4)

  Water-absorbent resin particles are produced by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a petroleum hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a dispersion stabilizer. In the method, a method for producing water-absorbent resin particles, wherein trehalose fatty acid ester is used as a dispersion stabilizer.   The trehalose fatty acid ester is at least one selected from the group consisting of trehalose caprate, trehalose laurate, trehalose myristate, trehalose palmitate, trehalose stearate, trehalose behenate and trehalose oleate A method for producing the water-absorbent resin particles according to claim 1.   The method for producing water-absorbent resin particles according to claim 1 or 2, wherein the amount of the dispersion stabilizer used is 0.1 to 5 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. The method for producing water-absorbent resin particles according to any one of claims 1 to 3, wherein after crosslinking by reverse phase suspension polymerization, post-crosslinking is performed by adding a crosslinking agent.