Polymer particles and method for producing polymer

Abstract

The present invention provides polymer particles having excellent gel strength while having sufficient water absorption capacity, and provides a suitable method for producing a polymer having excellent gel strength while having sufficient water absorption capacity. The present invention pertains to polymer particles comprising, as a main component, crosslinked polymer particles having structural units derived from ammonium (meth)acrylate, the polymer particles characterized in that: (1) the water absorption ratio (30-minute value) using deionized water is 35-90 g / g; (2) a gel swollen with deionized water has a gel strength of 10 mm or less under a 1 kg displacement, as measured with a texture analyzer; (3) the average particle diameter (D50) is 1-50 μm; and (4) the aspect ratio is 1.15-10.

Description

Polymer particles and method for producing polymers

[0001] The present invention relates to polymer particles and a method for producing a polymer, and more particularly to polymer particles useful for absorbent articles and the like, and a method for producing a polymer.

[0002] Water-absorbent resins such as poly(meth)acrylic acid (salt) polymers have excellent water-absorbing capabilities and are therefore widely used in a variety of applications, such as water-absorbent articles, etc. Various research and development efforts have been made on such water-absorbent resins (for example, Patent Documents 1 to 10).

[0003] Japanese Patent Publication No. 2012-012482 Japanese Patent No. 3357093 Japanese Patent No. 3259143 Japanese Patent No. 5091477 Japanese Patent Publication No. 2024-052478 Japanese Patent No. 4540094 Japanese Patent No. 6003827 Japanese Patent No. 5273311 Japanese Patent No. 5660136 Japanese Patent No. 5660135

[0004] As described above, various polymers have been disclosed, but the conventional polymers still have room for improvement in terms of achieving excellent gel strength while maintaining sufficient water absorption capacity. For example, there has been a demand for a water retention modifier that can be used not only for short periods in disposable diapers, etc., but also for long periods under high loads in soil, cement, etc., and that has excellent miscibility with inorganic materials such as soil and cement.

[0005] The present invention has been made in view of the above-mentioned current situation, and aims to provide polymer particles having sufficient water absorption capacity yet excellent gel strength, and a suitable method for producing a polymer having sufficient water absorption capacity yet excellent gel strength.

[0006] The present inventors have conducted extensive research into polymers and have found that a method for producing a crosslinked polymer having structural units derived from ammonium (meth)acrylate, comprising the steps of: (1) polymerizing, with a radical polymerization initiator, monomers in a monomer-containing composition containing at least ammonium (meth)acrylate as a monomer, the monomer comprising 0.8 to 2 mol % of a crosslinking agent relative to 100 mol % of all monomers, the monomer concentration being 35 to 60 mass %, and the proportion of neutralized acidic functional groups in 100 mol % of all acidic functional groups in the monomers being 40 to 100 mol %, (2) pulverizing the hydrogel during or after polymerization; and (3) drying the finely pulverized gel with hot air at 0.01 to 10 m / sec and 110°C to 220°C for 10 minutes or more, can easily produce a polymer having sufficient water absorption capacity and very excellent gel strength. The present inventors have also found that this production method can produce polymer particles with a specific water absorption capacity, specific gel strength, and specific particle size and shape. Furthermore, the present inventors have conducted extensive research on polymer particles and found that by producing polymer particles with a specific water absorption capacity, specific gel strength, and specific particle size and shape, they can be used for a long period of time and segregation can be reduced when mixed with inorganic materials such as soil or cement. Furthermore, the present inventors have found that by converting the polymer particles into an ammonium salt, they can be used as a fertilizer and are suitable for soil. Furthermore, the present inventors have found that they have a low chlorine content and are suitable for composite use with cement. As described above, the present inventors have conceived a brilliant solution to the above problems and have arrived at the present invention.

[0007] The present invention includes the following methods for producing polymers: [1] Polymer particles comprising, as a main component, crosslinked polymer particles having structural units derived from ammonium (meth)acrylate, the polymer particles having (1) a water absorption capacity (30-minute value) using deionized water of 35 to 90 g / g, (2) a gel strength of 10 mm or less at 1 kg displacement measured with a texture analyzer for a gel swollen with deionized water, (3) an average particle diameter (D50) of 1 to 50 μm, and (4) an aspect ratio of 1.15 to 10. [2] The polymer particles according to [1] above, further comprising: (5) a span value of the number % aspect value of the particles, represented by the following formula (i), of 1.5 or less: (i) Span value of number % of aspect values ​​of particles = (aspect value at 10% by number of particles - aspect value at 90% by number of particles) / (aspect value at 50% by number of particles). (3) The polymer particles according to the above item (1) or (2), further comprising (6) a water absorption capacity (1 minute value) using deionized water of 10 g / g or more. (4) The polymer particles according to any one of the above items (1) to (3), wherein (1) a water absorption capacity (30 minutes value) using deionized water of more than 60 g / g and 90 g / g or less. (5) The polymer particles according to any one of the above items (1) to (4), wherein (1) [water absorption capacity (30 minutes value) using deionized water] > (2) [gel strength × 6.5 (× 1 / mm)]. (6) The polymer particles according to any one of the above items (1) to (5), wherein the chlorine content is 100 ppm or less. [7] The polymer particles according to any one of [1] to [6], further comprising a modifier. [8] The polymer particles according to [7], wherein the mass ratio of the modifier is 1 mass % or more and 20 mass % or less, relative to 100 mass % of the crosslinked polymer particles. [9] The polymer particles according to [7] or [8], wherein the modifier is polyacrylic acid sodium salt.

[10] A method for producing a crosslinked polymer having structural units derived from ammonium (meth)acrylate according to any one of [1] to [9] above, comprising: (1) polymerizing, with a radical polymerization initiator, monomers in a monomer-containing composition containing at least ammonium (meth)acrylate as a monomer, the composition comprising 0.8 to 2 mol % of a crosslinker relative to 100 mol % of all monomers, a monomer concentration of 35 to 60 mass %, and a ratio of neutralized acidic functional groups of 40 to 100 mol % of all acidic functional groups in the monomers (100 mol %), (2) pulverizing the hydrogel during or after polymerization, and (3) drying the pulverized gel with hot air at 0.01 to 10 m / sec and 110 to 220°C for 10 minutes or more.

[11] A method for producing the polymer according to

[10] above, further comprising: (4) cooling the dried polymer to 60°C or below.

[12] The method for producing a polymer according to

[11] above, further comprising the step of (5) pulverizing the cooled polymer in two or more stages.

[0008] Incidentally, Production Example 12 of Patent Document 7 and Production Example 1 of Patent Document 8 disclose a technique relating to crosslinked water-absorbent resin microparticles produced by reversed-phase suspension polymerization using a macromonomer composition UM-1 as a dispersion stabilizer. The crosslinked water-absorbent resin microparticles obtained by carrying out a polymerization reaction by reversed-phase suspension polymerization are nearly spherical (with an aspect ratio of nearly 1.0). Such microparticles tend to generate lumps or have a reduced water absorption rate when absorbing water.

[0009] On the other hand, the polymer particles of the present invention are specified to have an aspect ratio of 1.15 to 10. Furthermore, the method for producing a polymer of the present invention can suitably produce the polymer particles of the present invention.

[0010] The polymer particles of the present invention have the above-mentioned constitution and have sufficient water absorption capacity and excellent gel strength. Furthermore, the method for producing a polymer of the present invention has the above-mentioned constitution and can obtain a polymer that has sufficient water absorption capacity and excellent gel strength.

[0011] Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description and can be appropriately modified and applied within the scope of the present invention. Note that a combination of two or more of the individual preferred embodiments of the present invention described below also falls within the scope of the present invention.

[0012] In the following, first, the method for producing the polymer of the present invention will be explained, and then the polymer particles of the present invention will be explained.

[0013] <Method for Producing Polymer> (1) Polymerization Step The method for producing a polymer of the present invention includes a step of polymerizing, with a radical polymerization initiator, a monomer in a monomer-containing composition containing 0.8 to 2 mol % of a crosslinker relative to 100 mol % of all monomers, a monomer concentration of 35 to 60 mass %, a proportion of neutralized acidic functional groups of 40 to 100 mol % of all 100 mol % of the monomers, and at least ammonium (meth)acrylate as a monomer. The monomer-containing composition is preferably a monomer-containing aqueous solution. The monomer-containing composition can be suitably obtained, for example, by the step of preparing a monomer-containing composition described below. Furthermore, the polymerization step is preferably an aqueous solution polymerization step. For example, in reversed-phase suspension polymerization, residual surfactants may cause a decrease in water absorption rate and initial liquid compatibility, a decrease in the surface tension of the absorbed liquid, and other problems. Furthermore, there is also the issue of odor from the remaining hydrophobic organic solvent, which may be undesirable for solving the present problem.

[0014] The polymerization step is preferably carried out using a kneader. Polymerization reactions using a kneader can suitably produce polymer particles with an aspect ratio greater than 1.0. Therefore, when absorbing water, lumps are less likely to occur, and the water absorption rate is improved. When the aspect ratio is greater than 1.0, gaps are formed between the particles, and such effects can be expected. Examples of the kneader include single-arm kneaders and double-arm kneaders, with double-arm kneaders being preferred. Furthermore, in the polymerization step, it is preferable to use a kneader as a stirring device and stir while breaking down the particles using the shear force of the kneader. The main vessel and / or stirrer of the kneader can be made of commonly used materials, but are preferably made of stainless steel, for example. Polymerization (preferably aqueous polymerization) using a kneader can produce a crosslinked polymer with a high aspect ratio. The polymerization step can be carried out either batchwise or continuously.

[0015] As described above, the polymerization step is preferably an aqueous solution polymerization step. The aqueous solution polymerization step may be carried out in the presence of an organic solvent together with water. When an organic solvent is used in the aqueous solution polymerization step, examples of the organic solvent include one or more selected from alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and diethylene glycol. From the viewpoint of the safety of the resulting composition, it is preferable to use water as the solvent. In this case, a solvent substitution step or the like can be omitted, thereby improving productivity. It is preferable not to use an organic solvent in the aqueous solution polymerization step. Note that, by performing aqueous solution polymerization, uneven crosslinking in the crosslinked polymer can be suppressed.

[0016] The polymerization step is carried out in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and hydrogen peroxide; and azo compounds such as 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, and 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}. These radical polymerization initiators may be used alone or in combination of two or more.

[0017] The amount of the radical polymerization initiator used is preferably, for example, 0.001 to 1 mol % relative to 100 mol % of the total monomers in the monomer-containing aqueous solution.

[0018] The radical polymerization initiator is preferably used as a redox polymerization initiator, for example, in combination with a reducing agent such as sodium sulfite, sodium bisulfite, ferrous sulfate, or ascorbic acid. Polymerization reactions using a redox polymerization initiator can be carried out at relatively low temperatures. For example, polymerization of the monomer and crosslinking agent can be initiated by adding a redox polymerization initiator to an aqueous solution containing the monomer and crosslinking agent. The redox polymerization initiator is not particularly limited as long as it generates radicals by combining an oxidizing agent and a reducing agent. Examples of the redox polymerization initiator include a combination of ascorbic acid and a peroxide such as hydrogen peroxide or t-butyl hydroperoxide, or a persulfate such as sodium persulfate, potassium persulfate, or ammonium persulfate; a combination of sodium sulfoxylate and t-butyl hydroperoxide; and a combination of a persulfate and a metal salt. A combination of ascorbic acid and a persulfate is preferred. When a redox polymerization initiator is used, the polymerization initiation temperature can be relatively low. Furthermore, compared with water-soluble azo initiators such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride, the chlorine content of the polymer can be reduced.

[0019] The amount of oxidizing agent used in the redox polymerization initiator is preferably 0.001 to 1 mol% relative to 100 mol% of the total monomers in the monomer-containing aqueous solution. By using an amount of oxidizing agent in the redox polymerization initiator of 0.001 mol% or more, the proportion of unreacted monomers contained in the resulting crosslinked polymer can be sufficiently reduced. Furthermore, by using an amount of oxidizing agent in the redox polymerization initiator of 1 mol% or less, the proportion of impurities contained in the resulting crosslinked polymer can be sufficiently reduced. Furthermore, by using an amount of oxidizing agent in the redox polymerization initiator in such a proportion, coloration of the resulting crosslinked polymer can be suppressed. The amount of oxidizing agent used in the redox polymerization initiator is more preferably 0.005 to 0.5 mol%, and even more preferably 0.01 to 0.3 mol%. Furthermore, the molar ratio of oxidizing agent / reducing agent in the redox polymerization initiator is preferably 1000 to 10 (molar ratio), and more preferably 1000 to 100 (molar ratio).

[0020] The redox polymerization initiator may be added before the start of polymerization of the monomer components and the crosslinking agent, or may be added after the completion of polymerization, for example, after the aging step described below.

[0021] The monomer concentration (preferably, the (meth)acrylic acid (salt) concentration) of 35 to 60% by mass contributes to providing the resulting polymer with sufficient water absorption capacity and very excellent gel strength. From the viewpoint of providing the polymer with even better water absorption capacity, the monomer concentration (preferably, the (meth)acrylic acid (salt) concentration) is preferably 55% by mass or less, more preferably 50% by mass or less, even more preferably 48% by mass or less, and particularly preferably 45% by mass or less.

[0022] In this specification, (meth)acrylic acid (salt) refers to methacrylic acid (salt) and / or acrylic acid (salt). Methacrylic acid (salt) refers to methacrylic acid and / or a methacrylate salt, and acrylic acid (salt) refers to acrylic acid and / or an acrylate salt.

[0023] When the proportion of neutralized acidic functional groups (preferably acidic functional groups in the form of ammonium salts) in the total acidic functional groups of the monomer (100 mol %) is 40 to 100 mol %, the water absorption capacity can be improved. The proportion of neutralized acidic functional groups is preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 65 mol % or more. The proportion of neutralized acidic functional groups is preferably 90 mol % or less, and more preferably 80 mol % or less.

[0024] In this specification, the term "acidic functional group" includes not only a carboxylic acid group but also acidic functional groups other than a carboxylic acid group, such as a sulfonic acid group. The acidic functional group also includes an acidic functional group that has become an acid anhydride group and a neutralized acidic functional group. The acidic functional group is preferably a carboxylic acid group, a carboxylic acid group that has become an acid anhydride group, or a neutralized carboxylic acid group. Examples of the neutralized acidic functional group (preferably a neutralized carboxylic acid group) include ammonium salts, metal salts such as alkali metal salts (e.g., sodium salts, potassium salts), alkaline earth metal salts (e.g., magnesium salts, calcium salts), and organic amine salts (e.g., monoethanolamine salts), and the like. One or more of these may be used.

[0025] The monomer-containing aqueous solution contains at least ammonium (meth)acrylate as a monomer. Here, ammonium (meth)acrylate refers to ammonium acrylate and / or ammonium methacrylate.

[0026] The monomer-containing aqueous solution may contain, as a monomer, a (meth)acrylate salt other than ammonium (meth)acrylate, such as sodium (meth)acrylate.

[0027] The monomer-containing aqueous solution may contain other monomers as monomers other than (meth)acrylic acid salts. Examples of other monomers include unsaturated monocarboxylic acids other than (meth)acrylic acid, such as crotonic acid and itaconic acid, and salts thereof; unsaturated dicarboxylic acids, such as fumaric acid, maleic acid, methylene glutaric acid, and itaconic acid, and salts thereof (which may be monosalts or disalts); unsaturated sulfonic acids, such as 3-allyloxy-2-hydroxypropanesulfonic acid, (meth)allylsulfonic acid, and isoprenesulfonic acid, and salts thereof; unsaturated alcohols, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 3-(meth)allyloxy-1,2-dihydroxypropane, (meth)allyl alcohol, and isoprenol, and alkylene oxide adducts in which alkylene oxides are added to the hydroxyl groups of these unsaturated alcohols; and unsaturated alcohols, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and cyclohexyl (meth)acrylate. vinyl aryl monomers such as styrene, indene, and vinylaniline; alkenes such as ethylene, propylene, butadiene, isobutylene, and octene; vinyl carboxylates such as vinyl acetate and vinyl propionate; unsaturated amines such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylamide, (meth)acrylamide, vinylpyridine, vinylimidazole, and salts thereof or quaternized products thereof; vinyl amides such as vinyl formamide, vinyl acetamide, and vinyl oxazolidone; unsaturated anhydrides such as maleic anhydride and itaconic anhydride; vinyl ethylene carbonate and derivatives thereof; (meth)acrylic acid-2-ethyl sulfonate and derivatives thereof; and vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether.

[0028] The content of other monomers in the monomer-containing aqueous solution is preferably 10% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the monomers. It is particularly preferable that the monomer-containing aqueous solution does not contain other monomers.

[0029] Furthermore, by including 0.8 to 2 mol % of a crosslinking agent in the monomer-containing aqueous solution relative to 100 mol % of the total monomers, a highly crosslinked crosslinked polymer with excellent gel strength can be produced. The proportion of the crosslinking agent is preferably 1.5 mol % or less. In this specification, the term "monomer" includes (meth)acrylic acid (salt), such as the above-mentioned ammonium (meth)acrylate, and the other monomers described above, but does not include the crosslinking agent.

[0030] The crosslinking agent is not particularly limited as long as it can form a crosslinked structure in the crosslinked polymer, and examples thereof include a compound having at least two polymerizable ethylenically unsaturated hydrocarbon groups; a compound having a plurality of functional groups that react with the carboxylic acid (salt) group in the (meth)acrylic acid (salt), such as the above-mentioned ammonium (meth)acrylate; etc. The carboxylic acid (salt) group is a carboxylic acid group and / or a carboxylate salt group.

[0031] Examples of the compound having at least two polymerizable ethylenically unsaturated hydrocarbon groups include N,N'-alkylenebis(meth)acrylamides having an alkylene group having 1 to 4 carbon atoms, such as N,N'-methylenebis(meth)acrylamide; (poly)alkylene glycol di(meth)acrylates such as (poly)ethylene glycol di(meth)acrylate and (poly)propylene glycol di(meth)acrylate; trimethylolpropane (di, tri)(meth)acrylates which may be modified with an alkylene oxide having an alkylene group having 1 to 4 carbon atoms, such as trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, and ethylene oxide-modified trimethylolpropane tri(meth)acrylate; glycerin (di, tri)(meth)acrylates such as glycerin tri(meth)acrylate and glycerin acrylate methacrylate; pentaerythritol tetra( pentaerythritol (di, tri, tetra) (meth)acrylates such as dipentaerythritol hexa(meth)acrylate; pentaerythritol (di, tri, tetra) (meth)allyl ethers such as pentaerythritol tri(meth)allyl ether; triallyl cyanurate (triallyl cyanurate), triallyl isocyanurate, tri(meth)allyl isocyanurate, Examples include triallyl compounds having 9 to 20 carbon atoms, such as triallyl phosphate and triallylamine; diallyl compounds having 6 to 20 carbon atoms, such as diallyl carbonate and 1,3-bis(allyloxy)-2-propanol; (di, tri)vinyl compounds having 4 to 20 carbon atoms, such as divinyl ether, divinyl ketone and trivinylbenzene; diisocyanates having 2 to 20 carbon atoms, such as tolylene diisocyanate and hexamethylene diisocyanate; and poly(meth)allyloxyalkanes.

[0032] Examples of the compound having a plurality of functional groups reactive with the carboxylic acid (salt) group include ethylenediamine, hexamethylenediamine, phenylenediamine, oxazoline group-containing polymer (Epocross manufactured by Nippon Shokubai Co., Ltd.), (di-, tri-)ethanolamine, butanediol, tolylene diisocyanate, and hexamethylene diisocyanate.

[0033] The crosslinking agent is preferably a compound having at least two polymerizable ethylenically unsaturated hydrocarbon groups, more preferably a compound having two polymerizable ethylenically unsaturated hydrocarbon groups, even more preferably a (poly)alkylene glycol di(meth)acrylate, and particularly preferably a (poly)alkylene glycol di(meth)acrylate having an alkylene group having 1 to 4 carbon atoms. In the (poly)alkylene glycol di(meth)acrylate, the number of moles of alkylene oxide added in the (poly)alkylene glycol is preferably 1 or more, more preferably 3 or more, and even more preferably 6 or more, from the viewpoint of further increasing gel strength. The number of moles of alkylene oxide added is preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less, from the viewpoint of further increasing water absorption capacity.

[0034] The (poly)alkylene glycol di(meth)acrylate is more preferably (poly)ethylene glycol di(meth)acrylate, and even more preferably (poly)ethylene glycol diacrylate. From the viewpoint of further increasing gel strength, the number of moles of ethylene oxide added in the (poly)ethylene glycol is preferably 1 or more, more preferably 3 or more, and even more preferably 6 or more. From the viewpoint of further increasing water absorption capacity, the number of moles of ethylene oxide added is preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less.

[0035] In the polymerization step, the atmosphere during polymerization is not particularly limited, but it is preferable to carry out the polymerization under an inert gas (nitrogen, argon, etc.) atmosphere. By carrying out the polymerization under an inert gas atmosphere, it is possible to further increase the gel strength of the obtained crosslinked polymer, improve the crushing efficiency of the obtained crosslinked polymer, and further reduce the proportion of unreacted monomers and the amount of water-soluble components contained in the obtained crosslinked polymer.

[0036] In the polymerization step, the polymerization initiation temperature is not particularly limited, but is preferably in the range of 20°C to 100°C because this improves the polymerization rate, and is even more preferably in the range of 20°C to 40°C because this increases the molecular weight of the crosslinked polymer. The polymerization temperature may be maintained at a constant temperature or may be changed over time. The reaction time may be appropriately set depending on the reaction temperature, the types (properties), combinations, and amounts used of the monomer components, polymerization initiator, and solvent, etc., so that the polymerization reaction is completed.

[0037] The material of the reactor for carrying out the polymerization step is not particularly limited as long as it can carry out the polymerization step, but it is preferable to use a reactor made of a material such as stainless steel. By carrying out the polymerization reaction using a reactor made of such a material that easily transfers heat, the polymerization reaction can be sufficiently progressed and the content of unreacted monomer in the obtained crosslinked polymer can be reduced.

[0038] In the above production method, an aging step may be performed after the addition of the monomers is completed, for the purpose of increasing the polymerization rate of the monomers. The aging step begins after the polymerization reaction has progressed and the temperature of the heat generated by polymerization has reached its peak. The aging time is usually 1 to 240 minutes, preferably 1 to 180 minutes, and more preferably 1 to 120 minutes.

[0039] The temperature of the polymer solution in the aging step is preferably in the range of 20° C. to 100° C., more preferably in the range of 50° C. to 100° C. The temperature here may also be maintained at a constant temperature, or may be changed over time during aging.

[0040] In the above production method, a polymerization initiator may be added after the aging step, as described above, which makes it possible to more sufficiently reduce the amount of residual monomer.

[0041] (2) Pulverizing Step The production method of the present invention further includes a step of pulverizing the hydrogel during or after polymerization. The "gel pulverization" means adjusting the hydrogel to a predetermined size using a gel pulverizer such as a kneader, a meat chopper, or a cutter mill.

[0042] With regard to the gel crushing method, operation conditions, etc., the contents described in Japanese Patent No. 5989913 or Japanese Patent No. 6067126 also apply to the present invention. When the polymerization mode is kneader polymerization, the polymerization step and the gel crushing step are carried out simultaneously.

[0043] The particle size of the particulate hydrogel pulverized by the gel crushing step is preferably 0.05 mm or more and 10 mm or less. If the particle size of the particulate hydrogel is too small, the physical properties of the resulting polymer may be poor. On the other hand, if the particle size of the particulate hydrogel is too large, drying may be insufficient.

[0044] The particulate hydrogel pulverized by the gel crushing step has a mass average particle diameter D50 of preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 140 μm or more. The mass average particle diameter D50 is preferably 2000 μm or less, more preferably 1500 μm or less, and even more preferably 1000 μm or less.

[0045] (3) Drying Step: The manufacturing method of the present invention includes a step of drying the pulverized gel for 10 minutes or more with hot air at 0.01 to 10 m / sec and 110 to 220°C. Including a drying step at a high temperature reduces the amount of residual monomer in the crosslinked polymer. In the present invention, "drying" refers to an operation to increase the solids content. Typically, the ratio of solids to the total weight of the crosslinked polymer is increased compared to before drying. However, the solids content is preferably increased to 85% by mass or more, more preferably 90% by mass or more, based on 100% by mass of the total weight of the crosslinked polymer. Due to concerns about the by-production of acrylamide, the upper limit of the solids content is preferably approximately 98% by mass. Drying may be performed simultaneously with polymerization, or both drying during polymerization and drying after polymerization may be performed. However, a drying step using a drying device after polymerization is more preferred. Increasing the solids content to the above range is preferable because it increases the amount of active ingredient. Furthermore, since the amount of residual monomer can be reduced, it is also preferable because it is suitable for composite applications with soil or cement, in terms of safety and compatibility. The solid content of the crosslinked polymer herein refers to a value measured by the following method. Approximately 1 g of crosslinked polymer particles (after pulverization) is weighed (mass W2 (g)) into a weighing can (mass W1 (g)) with a bottom diameter of approximately 5 cm, and the can is left to stand in a constant temperature dryer at 130°C for 1 hour to dry. The mass (W3 (g)) of the weighing can + crosslinked polymer particles after drying is measured, and the solid content is calculated using the following formula: Solid content (mass %) = ((W3 (g) - W1 (g)) / W2 (g)) × 100

[0046] The drying step is preferably carried out for at least 50% of the total drying time, more preferably in the range of 80°C to 250°C throughout substantially the entire drying step. Keeping the temperature within this range tends to further improve the physical properties of the crosslinked polymer. The drying temperature is determined by the heat medium temperature, but in cases where it cannot be determined by the heat medium temperature, such as microwaves, it is determined by the material temperature. The drying method is not particularly limited as long as the drying temperature is within the above range, and hot air drying, windless drying, reduced-pressure drying, infrared drying, microwave drying, etc. can be suitably used. When hot air drying is used, the drying air volume is preferably in the range of 0.01 to 10 m / sec, more preferably 0.1 to 5 m / sec. The drying temperature range is preferably 110°C to 220°C, and even more preferably 120°C to 200°C. Drying may be performed at a constant temperature or by varying the temperature, but it is preferable that substantially all drying steps be performed within the above temperature range.

[0047] The time for the drying step is, for example, preferably 10 minutes to 10 hours, more preferably 20 minutes to 8 hours, even more preferably 30 minutes to 6 hours, and particularly preferably 1 hour to 4 hours. By performing drying within the above temperature range and time, the amount of residual monomer in the crosslinked polymer can be reduced.

[0048] (4) Other Steps The method for producing polymer particles of the present invention may include other steps described below in addition to the steps described above. For example, the production method of the present invention preferably further includes a step of cooling the dried polymer to 60°C or less. Since the glass transition temperature of the crosslinked polymer is higher than 60°C and not higher than 80°C, it is difficult to pulverize it at a temperature higher than that. The cooling step may be performed by forced cooling using a machine or by natural cooling.

[0049] The production method of the present invention preferably further comprises a step of pulverizing the dried product obtained in the drying step to obtain a powder (crosslinked polymer particles) having an average particle size (D50) of 1 to 50 μm. The dried product obtained in the drying step is preferably further subjected to the cooling step.

[0050] The average particle size (D50) is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. The average particle size (D50) is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. The average particle size (D50) is measured by the method described in the Examples.

[0051] In the step of obtaining the powder, the dried product is preferably pulverized using a pulverizer. The pulverizer is not particularly limited, but examples thereof include roll pulverizers such as roll mills, hammer pulverizers such as hammer mills, impact pulverizers, cutter mills, turbo grinders, ball mills, pin mills, flash mills, and jet mills such as fluidized bed jet mills and target jet mills. To pulverize the material to a smaller average particle size range, it is more preferable to use a target jet mill. Furthermore, it is also preferable to use a roll mill, hammer pulverizer, impact pulverizer, pin mill, or jet mill to control the particle size distribution. To control the particle size distribution, it is more preferable to perform pulverization in two or more consecutive stages, and even more preferable to perform two-stage pulverization. Furthermore, when performing pulverization in two or more stages, the respective pulverizers may be the same or different. It is also possible to use a combination of different types of pulverizers. For example, when performing two-stage pulverization, it is preferable to use a roll pulverizer such as the roll mill, a hammer pulverizer such as a hammer mill, an impact pulverizer, a cutter mill, turbo grinder, ball mill, pin mill, or flash mill as the first stage. It is also preferable to use a jet mill such as a fluidized bed jet mill or a target jet mill as the second stage. By adjusting the pulverization conditions, the average particle size and particle size distribution of the obtained powder can be appropriately adjusted.

[0052] The pulverization method is not particularly limited, and pulverization may be performed at room temperature or by freeze-pulverization. However, since the glass transition temperature of the crosslinked polymer is above 60°C and not more than 80°C as described above, pulverization is preferably performed at a temperature not more than the glass transition temperature of the crosslinked polymer, and more preferably at a temperature not more than 60°C. Pulverization at temperatures below the above-mentioned temperature is preferred because it is easier to achieve a more uniform aspect ratio (described below) and a lower span value (described below). Use of the target-type jet mill allows for finer pulverization even at room temperature, thereby reducing production costs compared to freeze-pulverization. Furthermore, use of the target-type jet mill also makes it possible to omit the classification step (described below), thereby further improving productivity.

[0053] For example, in order to adjust the average particle size of the polymer particles of the present invention to a more suitable range and / or to control the particle size distribution to a specific range, the process for obtaining the powder may include a classification process or a granulation process. A sieve with a specific mesh size may be used for the classification. The classifier used for classification with a sieve is not particularly limited, and examples thereof include a vibrating sieve (unbalanced weight-driven type, resonance type, vibration motor type, electromagnetic type, circular vibration type, etc.), an in-plane motion sieve (horizontal motion type, horizontal circular-linear motion type, three-dimensional circular motion type, etc.), a movable mesh sieve, a forced stirring sieve, a mesh surface vibration sieve, a wind sieve, and an ultrasonic sieve. A vibrating sieve or an in-plane motion sieve is preferably used.

[0054] The manufacturing method of the present invention preferably further comprises a step of mixing the powder (crosslinked polymer particles) obtained in the step of obtaining the powder with a modifier, which is also a polymer particle. The modifier is a polymer particle other than the powder (crosslinked polymer particles) obtained in the step of obtaining the powder, and is not particularly limited as long as it can achieve the purpose of modification. However, it is preferable to mix a modifier for increasing gel strength and / or water absorption capacity and / or water absorption rate, and it is more preferable to mix a fibrous material such as cellulose nanofiber or a highly absorbent fiber (such as a crosslinked polyacrylic acid (salt)-based material), or a water-absorbent resin (particulate) such as a crosslinked polyacrylic acid (salt)-based material.

[0055] The modifier preferably satisfies at least one of the following (1) to (4): (1) Particle size: The average particle size (D50) is 1 to 50 μm. This minimizes segregation during mixing. (2) Water absorption capacity: The water absorption capacity (30-minute value) using deionized water is 1 to 800 g / g. A high water absorption capacity allows the water absorption capacity of the composition to be high. (3) Gel strength: The modifier is a fibrous substance. Fibrous substances tend to have high gel strength. (4) Structure of the modifier: The modifier contains a polymer. More preferably, the modifier contains polyacrylic acid sodium salt.

[0056] The mass ratio of the modifier mixed in the mixing step is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, relative to 100% by mass of the powder (crosslinked polymer particles) obtained in the powder obtaining step. Furthermore, the mass ratio of the modifier mixed in the mixing step is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and particularly preferably 6% by mass or less. When the modifier is used to enhance water absorption capacity, by setting the mass ratio of the modifier within the above range, the gel strength of the resulting polymer particles can be sufficiently excellent, while the water absorption capacity can be further improved. Specifically, the water absorption capacity of the polymer particles using deionized water can be made to be greater than 60 g / g.

[0057] The method for producing polymer particles of the present invention may further include a step of preparing a monomer-containing aqueous solution before the polymerization step (1). Also, it may include a post-crosslinking step or the like.

[0058] (Step of Preparing Monomer-Containing Composition) The production of the polymer of the present invention may include a step of preparing a monomer-containing composition containing 0.8 to 2 mol % of a crosslinking agent relative to 100 mol % of all monomers, having a monomer concentration of 35 to 60 mass %, and containing at least ammonium (meth)acrylate as a monomer, with the proportion of neutralized acidic functional groups being 40 to 100 mol % of 100 mol % of all acidic functional groups in the monomers. The monomer-containing composition is preferably a monomer-containing aqueous solution.

[0059] The preparation step is not particularly limited as long as it prepares the monomer-containing composition. For example, it may include a step of obtaining (meth)acrylic acid, a step of neutralizing (meth)acrylic acid to obtain ammonium (meth)acrylate, or a step of adjusting the monomer concentration in a monomer-containing aqueous solution. The preparation step may consist of only one of these steps, or a combination of two or more of them. The step of obtaining (meth)acrylic acid and the step of neutralizing (meth)acrylic acid to obtain ammonium acrylate can be carried out under conventionally known conditions. For example, ammonia can be used as a neutralizing agent for neutralization. The temperature, pressure, and atmosphere of the preparation step are not particularly limited.

[0060] <Polymer Particles> The polymer particles of the present invention are polymer particles mainly composed of crosslinked polymer particles having structural units derived from ammonium (meth)acrylate, and have: (1) a water absorption capacity (30-minute value) using deionized water of 35 to 90 g / g; (2) a gel strength of 10 mm or less as measured by a texture analyzer for a 1 kg displacement of a gel swollen with deionized water; (3) an average particle size (D50) of 1 to 50 μm; and (4) an aspect ratio of 1.15 to 10.

[0061] The term "mainly composed of the crosslinked polymer particles" means that the mass proportion of the crosslinked polymer particles in the polymer particles of the present invention is 50% by mass or more. The mass proportion of the crosslinked polymer particles in the polymer particles of the present invention is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Furthermore, the mass proportion of the crosslinked polymer particles in the polymer particles of the present invention may be 100% by mass, but is preferably 99% by mass or less.

[0062] The polymer particles of the present invention have excellent gel strength because they at least partially contain crosslinked polymer particles having structural units derived from ammonium (meth)acrylate, and by using the above-mentioned production method of the present invention, the proportion of neutralized acidic functional groups in the total acidic functional groups of the monomer and the proportion of crosslinking agent to the monomer are set within a predetermined range, and they are produced in the presence of a radical polymerization initiator (preferably a redox-based polymerization initiator), etc., the balance between water absorption capacity and gel strength is favorable, and both water absorption capacity and gel strength can be achieved.In addition, because the polymer particles have excellent gel strength, they can maintain their gel shape even when absorbing water under pressure, and for example, when the polymer particles are used as a water absorbent for inorganic materials such as soil and cement, the gel is less likely to collapse.

[0063] The structural unit refers to a structure in which the ethylenically unsaturated hydrocarbon group (carbon-carbon double bond) of ammonium (meth)acrylate becomes a single bond. When the crosslinking agent has a plurality of polymerizable ethylenically unsaturated hydrocarbon groups and forms a crosslink via the unsaturated hydrocarbon groups, the crosslinked polymer particles have a structure in which the unsaturated hydrocarbon groups of the crosslinking agent become a single bond. Furthermore, the crosslinked polymer particles have a structure in which the crosslinking agent has a plurality of functional groups that react with carboxylic acid (salt) groups in a monomer such as ammonium (meth)acrylate, and these functional groups react to form a crosslink, resulting in the functional groups of the crosslinking agent reacting.

[0064] In the crosslinked polymer particles, the proportion of structural units derived from the crosslinking agent is 2 mol% or less relative to 100 mol% of structural units derived from all monomers. This can enhance the water absorption capacity of the crosslinked polymer particles. Furthermore, the proportion of structural units derived from the crosslinking agent is preferably 0.8 mol% or more. This can further enhance the gel strength of the crosslinked polymer particles. Furthermore, by increasing the gel strength, the gel becomes less likely to collapse when used as a water absorbent for inorganic materials such as soil and cement, and also facilitates powderization when obtaining crosslinked polymer particles. The proportion of structural units derived from the crosslinking agent is preferably 1.5 mol% or less.

[0065] A preferred embodiment of the present invention is one in which the crosslinked polymer particles have structural units derived from (poly)alkylene glycol di(meth)acrylate, more preferably a structural unit derived from (poly)ethylene glycol di(meth)acrylate, and even more preferably a structural unit derived from polyethylene glycol diacrylate.

[0066] The proportion of neutralized acidic functional groups in 100 mol % of all acidic functional groups in the crosslinked polymer particles is preferably 40 to 100 mol %, which can increase the gel strength of the polymer particles of the present invention.

[0067] The crosslinked polymer particles may have structural units derived from other monomers other than (meth)acrylic acid (salt) and the crosslinking agent.

[0068] The polymer particles of the present invention preferably contain the above-mentioned modifier together with the crosslinked polymer particles. The mass ratio of the modifier is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, relative to 100% by mass of the crosslinked polymer particles. The mass ratio of the modifier is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and particularly preferably 6% by mass or less. It is more preferable that the above-mentioned preferred modifier has the above-mentioned preferred mass ratio.

[0069] The polymer particles of the present invention may contain surfactants, reducing agents, chelating agents, etc. as other components other than polymer particles. Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants, and one or more of these may be used. Examples of reducing agents include sodium sulfite, sodium bisulfite, ferrous sulfate, ascorbic acid, etc., and one or more of these may be used. Examples of chelating agents include aminocarboxylic acid chelating agents, phosphonic acid chelating agents, phosphoric acid chelating agents, and ether carboxylate chelating agents, and one or more of these may be used. The content of the above other components in the polymer particles of the present invention is preferably 10% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less.

[0070] The polymer particles of the present invention preferably have a water absorption capacity (30-minute value) using deionized water of 40 g / g or more, more preferably 45 g / g or more, even more preferably 50 g / g or more, and particularly preferably more than 60 g / g. By setting the water absorption capacity within the above range, moderate water absorption is possible. For example, when used as a water retention modifier for inorganic materials such as soil and cement, an optimal water absorption amount is achieved. Furthermore, the polymer particles of the present invention preferably have a water absorption capacity (30-minute value) using deionized water of 90 g / g or less, more preferably 80 g / g or less, and even more preferably 70 g / g or less. Setting the water absorption capacity within the above range can increase the gel strength described below. For example, when used as a water retention modifier for inorganic materials such as soil and cement, a gel strength greater than or equal to the gel strength required can be achieved. The water absorption capacity (30-minute value) using deionized water is measured by the method described in the Examples.

[0071] The polymer particles of the present invention preferably have a water absorption capacity (1-minute value) using deionized water of 10 g / g or more. Furthermore, the polymer particles of the present invention usually have a water absorption capacity (1-minute value) using deionized water of 20 g / g or less. The water absorption capacity (1-minute value) using deionized water is measured by the method described in the Examples.

[0072] The polymer particles of the present invention have a gel strength of 10 mm or less as measured by a 1 kg displacement of a gel swollen with deionized water using a texture analyzer. From the viewpoint of gel strength, the 1 kg displacement of the gel swollen with deionized water using a texture analyzer is preferably 9.5 mm or less, more preferably 5 mm or less, and even more preferably 3 mm or less. By setting the displacement within the above range, the gel strength can be increased to a level required for use as a water retention modifier for inorganic materials such as soil and cement. The 1 kg displacement of the gel swollen with deionized water using a texture analyzer is measured by the method described in the Examples. It is also preferable that [water absorption capacity (30-minute value) using deionized water] > [gel strength × 6.5 (× 1 / mm)]. By satisfying the above formula, the polymer particles of the present invention can absorb water more appropriately and have high gel strength, thereby making the effects of the present invention more pronounced. For example, when used as a water retention modifier for inorganic materials such as soil and cement, the optimal water absorption amount and gel strength can be achieved. It should be noted that "water absorption capacity" is a dimensionless quantity that is essentially unitless, and "gel strength" has a unit of "mm." Therefore, in order to match the units on both sides of the above equation, "(×1 / mm)" is introduced on the right side to cancel out the unit of "gel strength."

[0073] The aspect ratio of the polymer particles of the present invention is 1.15 to 10. This makes it less likely for the polymer particles to become lumpy, even when they are microparticulated, and increases the absorption rate. The aspect ratio is preferably 1.2 to 2.5, and more preferably 1.25 to 1.5.

[0074] From the viewpoint of mixing with inorganic materials and preventing segregation, the aspect ratio is preferably in the range of 1.15 to 10. Spherical particles with an aspect ratio of less than 1.15, for example 1.0, are undesirable because the spherical polymer particles may move or segregate after mixing due to the difference in aspect ratio with inorganic materials that generally have irregular shapes (e.g., sand, soil, cement, etc.).

[0075] Furthermore, the aspect ratio distribution (span) of the polymer particles of the present invention preferably has a number percent span value of 1.5 or less. Here, the span value = (aspect value at 10 number percent of particles - aspect value at 90 number percent) / (aspect value at 50 number percent). If the SPAN value is greater than 1.15, i.e., if there is a difference in the aspect ratio distribution, the aspect ratio of the polymer particles may be poorly mixed uniformly with inorganic materials (e.g., sand, soil, cement, etc.). The aspect ratio of the polymer particles can be measured by the method described in the Examples. Note that, for example, by performing the step of obtaining the powder, the aspect ratio of the polymer particles, along with the average particle size of the dried product, can be adjusted to a more suitable range.

[0076] The polymer particles of the present invention preferably have a water-soluble content of 35% by mass or less, based on 100% by mass of the total crosslinked polymer. It is more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less. By achieving the above water-soluble content, the amount of the active ingredient as a water-absorbing agent in the crosslinked polymer increases. The water-soluble content is measured as follows. <Measurement of Water-Soluble Content> Approximately 0.3 g (mass W7 (g)) of crosslinked polymer (powder) and approximately 100 g (mass W8 (g)) of deionized water are accurately weighed into a 110 ml glass screw tube, a rotor is inserted, and the tube is sealed. The mixture is then stirred at room temperature for 16 hours or more (rotation speed 600 rpm) using a magnetic stirrer, and then filtered through qualitative filter paper (Advantec Co., Ltd., Model: No. 2) to obtain a soluble component extract. Next, approximately 10 g of the above extract (mass W10 (g)) is weighed into an aluminum cup (mass W9 (g)) with a bottom diameter of approximately 5 cm, and the cup is left to stand in a constant temperature dryer at 120°C for 2 hours to dry. After drying, the mass of the aluminum cup + soluble components (W11 (g)) is measured, and the soluble content is calculated using the following formula: Soluble content (mass %) = ((W11 (g) - W9 (g)) / (W10 (g) × W7 (g) / W8 (g))) × 100

[0077] The polymer particles of the present invention preferably have a residual monomer content of 1000 ppm or less relative to 100% by mass of the total crosslinked polymer. More preferably, it is 800 ppm or less, even more preferably 500 ppm or less, and particularly preferably 300 ppm or less. By achieving the above residual monomer content, the amount of the active ingredient as a water absorbent in the crosslinked polymer increases, resulting in excellent safety as a water absorbent. The residual monomer content is measured as follows. <Measurement of the amount of residual ammonium (meth)acrylate> Approximately 0.3 g (mass W9 (g)) of particulate crosslinked polymer and approximately 100 g (mass W10 (g)) of deionized water are accurately weighed into a 110 ml screw tube, a rotor is inserted, and the tube is sealed. The tube is then stirred (600 rpm) at room temperature using a magnetic stirrer for at least 16 hours. By the above procedure, the residual ammonium (meth)acrylate in the particulate crosslinked polymer is extracted. The amount of residual ammonium (meth)acrylate in this extract is quantitatively analyzed by liquid chromatography under the following conditions. Apparatus: Alliance HPLC system manufactured by Waters Column: Shodex RS pak DE-413L, Shodex RS pak DE-G manufactured by Showa Denko K.K., 40°C Eluent: 0.1% aqueous phosphoric acid solution Flow rate: 1 mL / min Amount of remaining ammonium (meth)acrylate (ppm) = Measured value (ppm) × (W9 (g) + W10 (g)) / W9 (g)

[0078] The polymer particles of the present invention preferably have a chlorine content of 100 ppm or less.In the above-mentioned method for producing a polymer of the present invention, the chlorine content can be sufficiently reduced by neutralizing with chlorine-free ammonia instead of sodium hydroxide containing sodium chloride, using a chlorine-free redox polymerization initiator instead of a chlorine-containing polymerization initiator as the polymerization initiator, and using a chlorine-free crosslinking agent such as polyethylene glycol diacrylate (PEGDA) instead of a chlorine-containing crosslinking agent as the crosslinking agent.The chlorine content can be measured by the method described in the Examples.

[0079] <Uses of Polymer Particles> The polymer particles of the present invention have a water absorption capacity within a suitable range and excellent gel strength, and therefore can be suitably used as a cement admixture, a water retention material for inorganic composite materials such as a heat island suppression water retention material, a water retention material for greening, a water retention material for agricultural and horticultural use, a surgical waste liquid solidification material, a moisture absorbing and releasing material, water swelling rubber, a water stop material, a fragrance / deodorizer, a drip absorption sheet, cat litter, a heat removal sheet, artificial snow, etc. One preferred embodiment of the present invention is that the polymer particles of the present invention are, for example, a water retention modifier for inorganic materials.

[0080] <Method of Using Polymer Particles> The present invention relates to polymer particles primarily composed of crosslinked polymer particles having structural units derived from ammonium (meth)acrylate, the polymer particles having (1) a water absorption capacity (30-minute value) using deionized water of 35 to 90 g / g, (2) a gel strength of 10 mm or less at 1 kg displacement when the gel is swollen with deionized water, as measured using a texture analyzer, (3) an average particle diameter (D50) of 1 to 50 μm, and (4) an aspect ratio of 1.15 to 10, and also to a method of using the polymer particles as a cement admixture, a water-retaining material for inorganic composites such as a heat island suppression water-retaining material or a greening water-retaining material, an agricultural and horticultural water-retaining material, a surgical waste liquid solidification material, a moisture absorbing and desorbing material, a water-swelling rubber, a water-stop material, a fragrance / deodorizer, a drip-absorbing sheet, cat litter, a heat-removing sheet, or artificial snow. The polymer particles are the same as the polymer particles of the present invention described above, and the same explanations apply mutatis mutandis.

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "% by mass."

[0082] <Evaluation of water absorption capacity (30-minute value)> A tray (SUS square, D20 cm × L20 cm × H10 mm) was placed on a panel heater set at 25°C, a glass filter (diameter 120 mm, pore size JIS standard No. 0, height 5 mm) was placed in the center of the tray, and deionized water (25°C) was added up to the height of the upper surface of the glass filter. Filter paper (manufactured by ADVANTEC, No. 2, 110 mm) was placed on the glass filter, and then a cylinder (manufactured by Machintek, C-207431-D-2 with screen (400 mesh)) was placed on top. A water-absorbent resin (0.15 g, evenly spread on the filter paper) sandwiched between two sheets of filter paper (Advantec No. 2 55 mm) was placed in the cylinder, and a PP lid with a diameter of 60 mm, a height of 14 mm, and a weight of 6.8 g was gently placed on top of it, and the total mass of the cylinder (W1 (g)) was measured. The cylinder was placed in the center of the filter paper for the device and immersed for 30 minutes, and then the cylinder was gently pulled out and the total mass of the cylinder (W2 (g)) was measured. As a blank measurement, the total mass of the cylinder before immersion in deionized water (W3 (g)) and the total mass of the cylinder after immersion in deionized water (W4 (g)) were measured when no water-absorbent resin was placed in the cylinder were measured. Using the above measurement results, the water absorption capacity (g / g) of the water-absorbent resin was calculated using the following formula: Water absorption capacity = (W2 - W1 - (W4 - W3)) / 0.15

[0083] <Evaluation of Water Absorption Capacity (1 Minute Value)> The same procedure as in <Evaluation of Water Absorption Capacity (30 Minute Value)> was repeated except that the immersion time was changed to 1 minute.

[0084] <Evaluation of Gel Strength> Measurements were made using a texture analyzer (Stable Micro Systems, XTPL / 5). A sample was prepared by placing 100 g of gel swollen 20 times with deionized water (25°C) in a 250 ml container (Teraoka Pack Ace P-250, material: polypropylene, size (mm): (top diameter) 69 × (bottom diameter) 63 × (height) 97). (The crosslinked polymer (powder) was placed in Pack Ace, followed by deionized water and allowed to stand until equilibrium was reached.) Using a 35 mm diameter probe (P / 35), the probe was lowered to the center of the gel in Pack Ace at a constant speed of 2 mm / sec, and the displacement (mm) until a 1 kg load was applied was measured. Samples may also be prepared by polymerization in 250 ml of Pack Ace. In this case, the polymer was polymerized to form a 100 g unified gel. When evaluating a solid gel polymerized in Pack Ace, a probe (P / 10) with a diameter of 10 mm was used and lowered to the center of the gel in Pack Ace at a constant speed of 2 mm / sec, and the displacement (mm) until a load of 1 kg was applied was measured.

[0085] <Measurement of average particle size> The crosslinked polymer (powder) was measured using a dry particle size distribution measuring device (Mastersizer 3000 dry type, manufactured by Spectris Co., Ltd., Malvern Division), and the cumulative 50% value was taken as the average particle size. The measurement conditions are as follows: <Measurement conditions> Dry laser diffraction scattering method Dispersion pressure: 2 bar Particle refractive index: 1.52 Particle absorption rate: 0.01 Particle shape: Aspherical Solvent name: Air (AIR) Measurement range: 0.1 to 3500 μm

[0086] <Measurement of Aspect Ratio> The major and minor axes of the crosslinked polymer (powder) were measured using an optical microscope, and the value obtained by dividing the major axis by the minor axis was used as the aspect ratio. The aspect ratio was calculated using a particle image analyzer, Morphologi G3 (manufactured by the Malvern Division of Spectris Co., Ltd.). One hundred or more randomly selected particles were measured, and the average aspect ratio, as well as the aspect ratios of particles corresponding to 10%, 50%, and 90% of the total number when the particles were sorted in ascending order of aspect ratio, were calculated. The SPAN value was calculated as follows: (aspect value at 10% by number of particles - aspect value at 90% by number of particles) / (aspect value at 50% by number of particles). In addition to the above-mentioned devices, the aspect ratio can also be measured using image analysis particle size analysis software, Mac-viewver.4 (manufactured by Mountec Co., Ltd.), based on image data of the sample obtained by optical and / or electron microscopy.

[0087] <Evaluation of Chlorine Content> Approximately 0.3 g (mass W9 (g)) of particulate crosslinked polymer and approximately 100 g (mass W10 (g)) of deionized water were accurately weighed into a 110 ml screw tube, a rotor was placed inside, and the tube was sealed. The tube was then stirred (600 rpm) at room temperature for 16 hours or more using a magnetic stirrer. By the above procedure, chlorine in the particulate crosslinked polymer was extracted. The chlorine content of this extract was quantitatively analyzed by X-ray fluorescence analysis (XRF).

[0088] Example 1 172.0 parts of acrylic acid (80% aqueous solution, hereinafter also referred to as AA) and 25% aqueous ammonia solution (hereinafter referred to as 25% NH ３97.6 parts of AA (also referred to as an aqueous solution) were mixed while cooling, and the acrylic acid was partially neutralized with ammonia. The partially ammonia-neutralized acrylic acid, 13.5 parts of polyethylene glycol diacrylate (EO addition moles: 9 moles, hereinafter also referred to as PEGDA) as a crosslinker (0.8 mol% relative to the partially ammonia-neutralized AA), and 204.4 parts of deionized water were charged into a kneader (manufactured by Chuorika Co., Ltd., PNV-1H type) with a stainless steel (SUS304) main tank. Next, nitrogen substitution was performed at 200 ml / min for 30 minutes. Next, nitrogen introduction was increased to 30 ml / min, and stirring was initiated by rotating the kneader blades. After stabilizing the liquid temperature at 25°C, 3.5 parts (0.11 mol% relative to the partially ammonia-neutralized AA) of 25% aqueous sodium persulfate solution (hereinafter also referred to as NaPS) and 4.3 parts of 2% aqueous L-ascorbic acid solution (hereinafter also referred to as L-As) were added as polymerization initiators to initiate polymerization. After the polymerization reaction progressed and a gel was formed, the mixture was aged at 60°C for 60 minutes, and the resulting gel was dried at 130°C for 2 hours to obtain a dried crosslinked polymer. The resulting crosslinked polymer was then pulverized in a pulverizer and further pulverized in a target jet mill to obtain a crosslinked polymer (powder). The physical properties of the resulting crosslinked polymer (powder) were evaluated using the methods described above. The evaluation results are shown in Table 1.

[0089] Example 2: 201.2 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that the aqueous solution was 95.9 parts, PEGDA was used as a crosslinking agent (1.0 mol % relative to the AA partially neutralized with ammonia), deionized water was 180.4 parts, 25% NaPS was used as a polymerization initiator (0.05 mol % relative to the AA partially neutralized with ammonia), and 2% L-As was used (2.1 parts). Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0090] Example 3: 201.1 parts of 80% AA aqueous solution, 25% NH ３A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that the aqueous solution was 152.1 parts, PEGDA was used as a crosslinking agent (1.3 mol % relative to the AA partially neutralized with ammonia), deionized water was 136.1 parts, 25% NaPS was used as a polymerization initiator (0.01 mol % relative to the AA partially neutralized with ammonia), and 2% L-As was used (0.5 parts). Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0091] Example 4: 278.5 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that the aqueous solution was 105.3 parts, PEGDA was used as a crosslinking agent (0.8 mol % relative to the AA partially neutralized with ammonia), deionized water was 84.5 parts, 25% NaPS was used as a polymerization initiator (0.01 mol % relative to the AA partially neutralized with ammonia), and 2% L-As was used (0.3 parts). Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0092] Example 5: 192.8 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that the aqueous solution was 109.4 parts, PEGDA was used as a crosslinking agent (0.8 mol % relative to the AA partially neutralized with ammonia), deionized water was 169.7 parts, 25% NaPS was used as a polymerization initiator (0.11 mol % relative to the AA partially neutralized with ammonia), and 2% L-As was used (4.8 parts). Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0093] Example 6: 173.5 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 98.4 parts of the aqueous solution, 13.6 parts of PEGDA as a crosslinking agent (0.8 mol% relative to the AA partially neutralized with ammonia), 206.2 parts of deionized water, 3.6 parts of 25% NaPS as a polymerization initiator (0.11 mol% relative to the AA partially neutralized with ammonia), and 4.3 parts of 2% L-As were used. Next, 1.8 parts of cellulose nanofiber (hereinafter also referred to as CNF) as a modifier (1 wt% relative to the crosslinked polymer) were added and mixed. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0094] Example 7: 197.6 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 112.1 parts of the aqueous solution, 19.4 parts of PEGDA as a crosslinker (1.0 mol% relative to the AA partially neutralized with ammonia), 172.1 parts of deionized water, 1.9 parts of 25% NaPS as a polymerization initiator (0.05 mol% relative to the AA partially neutralized with ammonia), and 2.3 parts of 2% L-As were used. Next, 6.2 parts (3 wt% relative to the crosslinked polymer) of a superabsorbent resin (AQUALIC CA manufactured by Nippon Shokubai, hereinafter also referred to as SAP) was added as a modifier and mixed. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0095] Example 8 The procedure was the same as in Example 7 until a crosslinked polymer (powder) was obtained. Next, 10.4 parts (5 wt % based on the crosslinked polymer) of sodium polyacrylate-based superabsorbent fiber (hereinafter also referred to as SAF) was added as a modifier and mixed. Evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0096] Comparative Example 1: 293.3 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 190.0 parts of the aqueous solution, 46.2 parts of PEGDA as a crosslinking agent (1.5 mol % relative to the AA partially neutralized with ammonia), no deionized water was added (monomer concentration 62% by mass), 3.0 parts of 25% NaPS (0.05 mol % relative to the AA partially neutralized with ammonia) and 3.6 parts of 2% L-As were used as polymerization initiators. Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0097] Comparative Example 2: 159.0 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 67.9 parts of the aqueous solution, 10.5 parts of PEGDA as a crosslinking agent (0.8 mol % relative to the AA partially neutralized with ammonia), 252.0 parts of deionized water (monomer concentration 32% by mass), 1.3 parts of 25% NaPS as a polymerization initiator (0.05 mol % relative to the AA partially neutralized with ammonia), and 1.6 parts of 2% L-As were used. Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0098] Comparative Example 3: 224.9 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that the aqueous solution was 34.0 parts, PEGDA was used as a crosslinking agent (1.3 mol % relative to the AA partially neutralized with ammonia), deionized water was 226.4 parts, 25% NaPS was used as a polymerization initiator (0.06 mol % relative to the AA partially neutralized with ammonia), and 2.0 parts of 2% L-As were used. Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0099] Comparative Example 4: 176.7 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that the aqueous solution was 78.8 parts, PEGDA was used as a crosslinking agent (0.6 mol % relative to the AA partially neutralized with ammonia), deionized water was 219.1 parts, 25% NaPS was used as a polymerization initiator (0.02 mol % relative to the AA partially neutralized with ammonia), and 2% L-As was used (0.5 parts). Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0100] Comparative Example 5: 172.2 parts of an 80% aqueous solution of AA and 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 123.6 parts of the aqueous solution, 41.3 parts of PEGDA as a crosslinking agent (2.2 mol % relative to the AA partially neutralized with ammonia), 224.1 parts of deionized water, 2.0 parts of 25% NaPS as a polymerization initiator (0.05 mol % relative to the AA partially neutralized with ammonia), and 2.4 parts of 2% L-As were used. Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0101] Comparative Example 6: 27.3 parts of n-hexane and 0.17 parts of sorbitan monooleate were placed in a 50 mL glass vessel equipped with a cross-shaped stirrer and a thermometer. The vessel was set in an EYELA personal organic synthesis apparatus PPS-2511. 6.9 parts of an 80% aqueous solution of AA and 0.17 parts of 25% NH ３3.9 parts of aqueous solution, 0.5 parts of PEGDA (0.8 mol% relative to the partially ammonia-neutralized AA) as a crosslinker, and 2.7 parts of deionized water were mixed while cooling. The mixed monomer solution was then added to a 50 mL glass container containing n-hexane while stirring at 800 rpm. Nitrogen substitution was then performed at 200 mL / min for 30 minutes. Nitrogen introduction was then increased to 30 mL / min, and the reactor was heated to an internal temperature of 30°C while stirring at 800 rpm. After stabilizing the liquid temperature at 30°C, 0.03 parts of 25% aqueous NaPS solution (0.02 mol% relative to the partially ammonia-neutralized AA) and 0.03 parts of 2% L-As were added as initiators to initiate polymerization. The reaction was continued for 5 hours from the start of polymerization, yielding a fine particle dispersion. The fine particle dispersion was then subjected to solid-liquid separation by natural sedimentation. The resulting cake was dried with hot air at 50°C for 10 hours to obtain a crosslinked polymer (powder). Evaluation was also carried out in the same manner as in Example 1. The results are shown in Table 1. The primary particles of the obtained powder particles had a sharp particle size distribution and were spherical particles with an aspect ratio of 1.0. It was difficult to achieve a particle diameter of 10 μm or more using this method.

[0102] Comparative Example 7 A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 161.6 parts of an 80% aqueous AA solution, 107.2 parts of a 48% aqueous sodium hydroxide solution, 6.4 parts of PEGDA as a crosslinking agent (0.6 mol % relative to the AA partially neutralized with sodium), 197.0 parts of deionized water, 0.4 parts of 25% NaPS as a polymerization initiator (0.02 mol % relative to the AA partially neutralized with sodium), and 0.5 parts of 2% L-As were used. Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0103] Example 9: 192.8 parts of 80% AA aqueous solution, 25% NH ３A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 109.4 parts of the aqueous solution, 15.8 parts (0.8 mol % relative to the partially ammonia-neutralized AA) of polyethylene glycol diglycidyl ether (Denacol EX-832 manufactured by Nagase ChemteX, EO addition mole number 9, hereinafter also referred to as Denacol) as a crosslinking agent, 175.5 parts of deionized water, 4.0 parts (0.11 mol % relative to the partially ammonia-neutralized AA) of 25% NaPS as a polymerization initiator, and 4.8 parts of 2% L-As were used. Evaluation was also performed in the same manner as in Example 1. The results are shown in Table 1.

[0104] Example 10: 192.8 parts of 80% AA aqueous solution and 25% NH ３ The resulting solution was mixed with 109.4 parts of the aqueous solution while cooling, and the acrylic acid was partially neutralized with ammonia. The partially neutralized acrylic acid, 15.1 parts of PEGDA as a crosslinker (0.8 mol% relative to the partially neutralized ammonia AA), and 174.5 parts of deionized water were charged into a kneader (PNV-1H model, manufactured by Chuorika Co., Ltd.) with a stainless steel (SUS304) main vessel. Nitrogen substitution was then performed at 200 ml / min for 30 minutes. Nitrogen introduction was then increased to 30 ml / min, and stirring was initiated by rotating the kneader blades. The jacket temperature was increased to stabilize the liquid temperature at 45°C, and then 1.0 part (0.02 mol% relative to the partially neutralized ammonia AA) of a 20% aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., hereinafter also referred to as V-50) was added as a polymerization initiator to initiate polymerization. After the polymerization reaction progressed and a gel was formed, the mixture was aged at 60°C for 60 minutes, and the resulting gel was dried at 130°C for 2 hours to obtain a dried crosslinked polymer. The resulting crosslinked polymer was then pulverized in a pulverizer and further finely pulverized in a target jet mill to obtain a crosslinked polymer (powder). The physical properties of the resulting crosslinked polymer (powder) were evaluated using the methods described above. The evaluation results are shown in Table 1.

[0105] Comparative Example 8 332.0 parts of acrylamide (40% aqueous solution, hereinafter also referred to as AAm), 83.8 parts of a 37% aqueous sodium acrylate solution, 1.19 parts of N,N-methylenebisacrylamide (hereinafter also referred to as MBAAm) as a crosslinkable monomer (0.35 mol% relative to AAm + AA), and 83.0 parts of deionized water were charged into a kneader (manufactured by Chuo Rika Co., Ltd., PNV-1H type) with a main vessel made of stainless steel (SUS304). Next, nitrogen substitution was carried out at 200 ml / min for 30 minutes. Next, nitrogen introduction was increased to 30 ml / min, the temperature was raised to 48 ° C, and stirring was initiated by rotating the kneader blades. After the liquid temperature was stabilized at 25 ° C, 3.2 parts of a 21% aqueous NaPS solution (0.13 mol% relative to a portion of the AAm + AA salt) and 3.2 parts of a 2% aqueous L-As solution were added as a polymerization initiator, and polymerization was initiated. After the polymerization reaction progressed and a gel was formed, the mixture was aged at 60°C for 60 minutes to terminate the polymerization. The resulting gel was evaluated by the method described above. The resulting gel was then dried at 130°C for 2 hours to obtain a dried crosslinked polymer. The resulting crosslinked polymer was then pulverized in a pulverizer and further finely pulverized in a target jet mill to obtain a crosslinked polymer (powder). The physical properties of the resulting crosslinked polymer (powder) were evaluated by the method described above. The evaluation results are shown in Table 1.

[0106]

[0107] The polymer particles of the present invention can achieve both water absorption capacity and gel strength. Furthermore, it has been found that the method for producing polymer particles of the present invention can suitably produce polymer particles that can achieve both water absorption capacity and gel strength.

[0108] Example 11: 175.0 parts of 80% AA aqueous solution, 25% NH ３A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 75.5 parts of the aqueous solution, 13.8 parts of polyethylene glycol diacrylate (EO addition moles: 4) as a crosslinking agent (1.5 mol % relative to the AA partially neutralized with ammonia), 228.7 parts of deionized water, 6.0 parts of 25% NaPS as a polymerization initiator (0.2 mol % relative to the AA partially neutralized with ammonia), and 7.2 parts of 2% L-As were used. The water absorption capacity and gel strength were also evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0109] Example 12: 161.9 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 69.8 parts of the aqueous solution, 21.3 parts of polyethylene glycol diacrylate (EO addition moles: 9) as a crosslinking agent (1.5 mol% relative to the AA partially neutralized with ammonia), 227.9 parts of deionized water, 5.5 parts of 25% NaPS as a polymerization initiator (0.2 mol% relative to the AA partially neutralized with ammonia), and 6.7 parts of 2% L-As were used. The water absorption capacity and gel strength were also evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0110] Example 13: 154.2 parts of 80% AA aqueous solution, 25% NH ３ A crosslinked polymer (powder) was obtained in the same manner as in Example 1, except that 66.5 parts of the aqueous solution, 30.0 parts of polyethylene glycol diacrylate (EO addition mole number: 14 moles) as a crosslinking agent (1.5 mol% relative to the AA partially neutralized with ammonia), 234.9 parts of deionized water, 5.3 parts of 25% NaPS as a polymerization initiator (0.2 mol% relative to the AA partially neutralized with ammonia), and 6.4 parts of 2% L-As were used. The water absorption capacity and gel strength were also evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0111]

[0112] It was found that there is a trade-off between the gel strength and the water absorption capacity and the number of moles of alkylene oxide added in the (poly)alkylene glycol crosslinking agent, and that from the viewpoint of increasing both the gel strength and the water absorption capacity, a number of moles added of about 9 is preferable.

[0113] Example 14 Evaluation of Water Retention Agent for Plant Cultivation Culture Soil (manufactured by Takii Seed Co., Ltd., product name "Takii Culture Soil") containing the particulate water-absorbing agent (a) obtained in Example 1 at a ratio of 0.05% by weight was poured into a vinyl resin flowerpot (length 30 cm, width 30 cm, height 50 cm) with a 38 μm wire mesh opening in the bottom hole, up to a height of 20 cm from the bottom, and then seedlings and the culture soil were poured in. The surface height from the bottom was 40 cm. Tap water (Suita City) was applied as irrigation water once every 10 days until the water came out of the bottom hole of the flowerpot. This procedure was repeated, and the height of the seedlings was measured after 2 months to be 50 cm, meaning that they had grown by 20 cm.

Claims

1. Polymer particles whose main component is a crosslinked polymer particle having structural units derived from ammonium (meth)acrylate, characterized in that: (1) the water absorption capacity (30-minute value) using deionized water is 35 to 90 g / g; (2) the gel strength, measured using a texture analyzer, of a gel swollen with deionized water, is such that the 1 kg displacement is 10 mm or less; (3) the average particle size (D50) is 1 to 50 μm; and (4) the aspect ratio is 1.15 to 10.

2. The polymer particles according to claim 1, further comprising: (5) a number % span value of the particle aspect value, represented by the following formula (i), of 1.5 or less: number % span value of the particle aspect value = (aspect value at 10% by number of particles - aspect value at 90% by number of particles) / (aspect value at 50% by number of particles) (i) 3. The polymer particles according to claim 1 or 2, further comprising (6) a water absorption capacity (1 minute value) using deionized water of 10 g / g or more.

4. The polymer particles according to any one of claims 1 to 3, wherein the water absorption capacity (30-minute value) using deionized water (1) is more than 60 g / g and not more than 90 g / g.

5. Polymer particles according to any one of claims 1 to 4, wherein (1) [water absorption capacity using deionized water (30-minute value)] > (2) [gel strength × 6.5 (× 1 / mm)].

6. The polymer particles according to any one of claims 1 to 5, having a chlorine content of 100 ppm or less.

7. The polymer particles according to any one of claims 1 to 6, further comprising a modifier.

8. The polymer particles according to claim 7, wherein the mass ratio of the modifier is 1 mass % or more and 20 mass % or less relative to 100 mass % of the crosslinked polymer particles.

9. The polymer particles according to claim 7 or 8, wherein the modifier is a sodium salt of polyacrylic acid.

10. A method for producing a crosslinked polymer having structural units derived from ammonium (meth)acrylate according to any one of claims 1 to 9, comprising: (1) a step of polymerizing, with a radical polymerization initiator, monomers in a monomer-containing composition containing at least ammonium (meth)acrylate as a monomer, the composition comprising 0.8 to 2 mol % of a crosslinking agent relative to 100 mol % of all monomers, the monomer concentration being 35 to 60 mass %, and the proportion of neutralized acidic functional groups in 100 mol % of all acidic functional groups in the monomers being 40 to 100 mol %, (2) a step of pulverizing the hydrogel during or after polymerization, and (3) a step of drying the finely pulverized gel with hot air at 0.01 to 10 m / sec and 110 to 220°C for 10 minutes or longer.

11. The method for producing a polymer according to claim 10, further comprising the step (4) of cooling the dried polymer to 60°C or less.

12. The method for producing a polymer according to claim 11, further comprising the step of (5) pulverizing the cooled polymer in two or more stages.

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