JP2010138301A - Method for producing hydrophilic polymeric particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing hydrophilic polymeric particles with slight residual hydrophobic solvent. <P>SOLUTION: The method for producing hydrophilic polymeric particles includes the following solvent substitution step in which: a substitution solvent is added to a suspension wherein crude polymeric particles containing a hydrophilic polymer and a hydrophobic solvent and having 10 μm or less in volume-average size and 60% or less in the coefficient of variation of the particle size are dispersed in the hydrophobic solvent, and the hydrophobic solvent is distilled off. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing hydrophilic polymer particles.

  In the reverse phase suspension polymerization method or the dispersion polymerization method, a suspension (slurry) in which particles containing a polymer are dispersed in a hydrophobic solvent is obtained. Then, the hydrophobic solvent is substituted with a substitution solvent as necessary.

In Patent Document 1, a hydrophobic solvent is distilled off after adding a substitution solvent to a suspension in which water-containing hydrophilic polymer particles having a water content of 1.5 to 10.0% by weight based on the polymer weight are dispersed in a hydrophobic solvent. Is disclosed.
JP 2008-138106 A

  However, in some cases, the hydrophobic solvent cannot be distilled off efficiently only by controlling the amount of water as in the method of Patent Document 1.

  An object of the present invention is to provide a method capable of efficiently distilling off a hydrophobic solvent and producing hydrophilic polymer particles with little remaining hydrophobic solvent.

  The method for producing hydrophilic polymer particles of the present invention comprises a hydrophobic solvent containing a hydrophilic polymer and the hydrophobic solvent in a hydrophobic solvent, having a volume average particle size of 10 μm or less and a coefficient of variation in particle size of 60% or less. A solvent replacement step of adding a substitution solvent to the suspension in which the polymer particles are dispersed and distilling off the hydrophobic solvent is provided.

  According to the present invention, since the volume average particle size of the hydrophobic solvent-containing polymer particles before substitution of the hydrophobic solvent with the substitution solvent is 10 μm or less and the variation coefficient of the particle size is 60% or less, It is possible to produce hydrophilic polymer particles with a small amount of hydrophilic solvent.

  The manufacturing method of the hydrophilic polymer particle which concerns on embodiment is demonstrated in detail. In the present application, the particles in the production process are distinguished as “crude polymer particles”, and the finally obtained particles are distinguished as “hydrophilic polymer particles”.

  The method for producing polymer particles according to this embodiment includes a polymerization step, a dehydration step, and a solvent replacement step. Hereinafter, each step will be described in detail.

(Polymerization process)
In the method for producing hydrophilic polymer particles according to this embodiment, first, a hydrophilic polymer is obtained by a reverse phase polymerization reaction using a hydrophobic solvent (for example, suspension polymerization method, dispersion polymerization method, emulsion polymerization method, etc.). By synthesizing, a suspension in which crude polymer particles are dispersed in a hydrophobic solvent is obtained.

  Specifically, a hydrophobic solvent is charged into a reaction tank, a monomer, a polymerization initiator, and water that are uniformly mixed in advance are charged, and the mixture is emulsified and dispersed by a mixing device. At this time, it is preferable to add a dispersant as well. Note that a monomer, a polymerization initiator, water, and a hydrophobic solvent may be charged into a reaction vessel at a time and emulsified and dispersed with a stirrer. Then, a polymerization reaction is performed in the reaction tank to obtain a suspension (slurry) in which the coarse polymer particles are dispersed in the hydrophobic solvent.

  The monomer is a polymer for a hydrophilic polymer. For example, a vinyl monomer containing a cationic group such as an amino group, an ammonium group, a pyridyl group, an imino group, or a betaine structure and a salt thereof (hereinafter referred to as “cationic monomer”). .); Hydrophilic nonionic group-containing vinyl monomers such as hydroxy groups, amide groups, ester groups, ether groups (hereinafter referred to as “nonionic monomers”); carboxy groups, sulfonic acid groups, phosphoric acid groups, etc. Anionic group-containing vinyl monomers and salts thereof (hereinafter referred to as “anionic monomers”). Examples of the monomer include a crosslinkable vinyl monomer having at least two reactive unsaturated groups in the molecule (hereinafter referred to as “crosslinkable monomer”). A single type of monomer may be used, or a plurality of types may be used, but it is preferable to use one or more types of cationic monomers and one or more types of nonionic monomers in combination.

  Examples of the cationic monomer include (meth) acrylic acid ester having a dialkylamino group having 2 to 44 carbon atoms, (meth) acrylamide having a dialkylamino group having 2 to 44 carbon atoms, and 2 to 44 carbon atoms. Acid-neutralized products of monomers having amino groups such as styrene, vinylpyridine, N-vinyl heterocyclic compounds, vinyl ethers having a dialkylamino group; alkyl halides (C1-22), halogens of these monomers Quaternized with benzylated alkyl, alkyl (C1-18), aryl (C6-24) sulfonic acid, dialkyl sulfate (total C2-8), etc .; diallyl-type quaternary ammonium salt, betaine structure And vinyl monomers having Of these cationic monomers, amino group-containing monomers and ammonium group-containing monomers are preferably used, and quaternary ammonium salt monomers are more preferably used.

  Nonionic monomers include, for example, vinyl alcohol, (meth) acrylic acid ester having a hydroxyalkyl (C1-8) group, (meth) acrylamide having a hydroxyalkyl (C1-8) group, polyvalent Alcohol (meth) acrylic acid ester, (meth) acrylamide, alkyl (1-8 carbon atoms) (meth) acrylamide, dialkyl (2-8 total carbon atoms) (meth) acrylamide, diacetone (meth) acrylamide, N-vinyl Examples include cyclic amides, (meth) acrylic acid esters having an alkyl (C 1-8) group, and (meth) acrylamides having a cyclic amide group. Among these, it is preferable to use a (meth) acrylamide monomer, a (meth) acrylic acid ester having a hydroxyalkyl (C1-C8) group, or a (meth) acrylic acid ester of a polyhydric alcohol.

  Examples of the anionic monomer include a carboxylic acid monomer having a polymerizable unsaturated group, an acid anhydride thereof (when two or more carboxyl groups are contained in one monomer), and a sulfonic acid monomer having a polymerizable unsaturated group. And phosphoric acid monomers having a polymerizable unsaturated group. Among these, a carboxylic acid monomer having a polymerizable unsaturated group, an acid anhydride thereof (when two or more carboxyl groups are contained in one monomer), a sulfonic acid monomer having a polymerizable unsaturated group, It is preferable to use it.

  The anionic group may be neutralized with a basic substance to an arbitrary degree of neutralization. In that case, some or all of the anionic groups in the resulting hydrophilic polymer form a salt. Examples of the cation in the salt include ammonium ions, trialkylammonium ions having 3 to 54 carbon atoms (for example, trimethylammonium ions and triethylammonium ions), hydroxyalkylammonium ions having 2 to 4 carbon atoms, and 4 to 8 carbon atoms in total. Examples include dihydroxyalkylammonium ions, trihydroxyalkylammonium ions having 6 to 12 carbon atoms, alkali metal ions, and alkaline earth metal ions. Neutralization may be performed with a monomer or after a hydrophilic polymer is formed.

  Examples of the crosslinkable monomer include (meth) acrylic acid esters of polyhydric alcohols, acrylamides, divinyl compounds, polyallyl compounds, and (meth) acrylic acid esters of unsaturated alcohols. Among these, it is preferable to use ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, divinylbenzene, pentaerythritol triallyl ether, and pentaerythritol tetraallyl ether.

  Examples of other monomers include (meth) acrylic acid derivatives.

  It is preferable to use at least one monomer as a constituent component among a cationic monomer, a nonionic monomer, and an anionic monomer. These amounts are preferably 70 to 100% by mass and more preferably 85 to 100% by mass with respect to the total monomer amount. Moreover, it is preferable that a monomer uses a crosslinkable monomer as a structural component, and it is preferable that the quantity shall be 0.005-5 mass% with respect to the total monomer quantity, 0.01-1.0 mass% More preferably. A particularly preferable monomer structure includes a cationic monomer, a nonionic monomer, and a crosslinkable monomer.

  As the polymerization initiator, a radical polymerization initiator is preferably used. For example, a peroxide, an organic peroxide and a salt thereof, an inorganic peroxide and a salt thereof, and an azobis-based compound that are uniformly dissolved in the monomer component. The redox type | system | group by independent and the combination of it and a reducing agent is mentioned. A single type of polymerization initiator may be used, or a plurality of types may be used. The addition amount of the polymerization initiator increases the degree of polymerization of the main chain and decreases the proportion of the polymer chain that is not crosslinked, makes it difficult to dissolve in a hydrophobic solvent or water, and increases the reaction rate of the polymerization reaction. From the viewpoint of reducing the residual monomer amount, it is preferably 0.01 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, more preferably 0.1 to 1 part with respect to 100 parts by mass of all monomers. It is more preferable to set it as a mass part.

  Examples of water include distilled water and ion exchange water. The amount of water is preferably 1 to 50% by volume and more preferably 5 to 40% by volume with respect to the total amount of the hydrophobic solvent.

  In the present application, the “hydrophobic solvent” refers to a solvent having a solubility in 100 g of water at 25 ° C. of 1% by mass or less. Examples of the hydrophobic solvent include hydrocarbon solvents such as hexane, cyclohexane, heptane, octane, benzene, toluene, xylene, and ethylbenzene, halogenated hydrocarbon solvents such as carbon tetrachloride and dichloroethane, and mineral oil such as Isobar. Is mentioned. Of these, hydrocarbon solvents are preferably used, and hexane and cyclohexane are more preferably used. As the hydrophobic solvent, a single species may be used, or a plurality of species may be mixed and used. The addition amount of the hydrophobic solvent is preferably 1 to 20 times by mass, more preferably 1 to 10 times by weight based on the total monomer amount.

  Examples of the dispersant include sorbitan monostearate, sorbitan monopalmitate, polyvinyl alcohol, methyl cellulose, ethyl cellulose, hydroxy cellulose, carboxymethyl cellulose, carboxyethyl cellulose, sugar ester (trade name, manufactured by Mitsubishi Chemical Foods), polyoxyethylene alkyl Examples include ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, alkyl sulfate, and polyoxyethylene alkyl ether sulfate. Of these, sorbitan monostearate and sugar ester are preferably used from the viewpoint of dispersion stability. A single type of dispersant may be used, or a plurality of types may be mixed and used. The addition amount of the dispersant is preferably 0.3 to 20 parts by mass, and more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of all monomers.

  Examples of the mixing apparatus used for emulsification dispersion include a high-pressure homogenizer, a line mixer, and a static mixer.

  As a static mixer, from the viewpoint of excellent mixing properties, for example, a contraction / split type static mixer (trade name: Disperse-kun, manufactured by Fujikin Co., Ltd.) can be used. This static mixer can be configured by providing a plurality of units each having the same flow path hole configuration so that the flow path holes communicate with each other.

  The inner diameter of the flow path constriction portion of the flow path hole is preferably 0.2 to 20 mm, more preferably 0.5 to 10 mm, and further preferably 0.5 to 5 mm.

  The polymerization reaction is started by raising the temperature under an inert gas such as nitrogen. In this polymerization operation, although it varies depending on the monomer type, the polymerization start temperature is set to 40 to 90 ° C., and the reaction time is set to 1 to 24 hours, for example.

  The obtained suspension preferably has a content of coarse polymer particles (mass of coarse polymer particles / (mass of coarse polymer particles + mass of hydrophobic solvent) × 100) of 10 to 70% by mass. More preferably, it is 50 mass%. The content of the coarse polymer particles can be controlled by the amount of the hydrophobic solvent added.

(Dehydration process)
Water in the crude polymer particles contained in the suspension obtained in the polymerization step is dehydrated.

  Specifically, the temperature inside the reaction vessel is raised to vaporize the solvent, and after condensing it with a condenser, it is left and separated into water and a hydrophobic solvent, while the separated hydrophobic solvent is refluxed to the reaction vessel, Only water is distilled off. In this dehydration operation, the temperature in the tank is set to 60 to 100 ° C., the dehydration time is set to 0.5 to 20 hours, for example, and the pressure in the tank is reduced to 10 to 100 kPa as necessary.

  In the suspension after dehydration, the content of the crude polymer particles is preferably 5 to 70% by mass, and more preferably 10 to 60% by mass.

  The volume average particle diameter of the crude polymer particles after dehydration is 10 μm or less, and preferably 0.1 to 7 μm. The volume average particle diameter of the coarse polymer particles can be controlled by the pruning force at the time of emulsification dispersion, the treatment time, the type and amount of the dispersing agent. The coefficient of variation (hereinafter referred to as “CV value”) of the coarse polymer particles after dehydration is 60% or less, preferably 50% or less. The volume average particle diameter and the CV value can be determined using a laser diffraction / scattering particle size distribution analyzer.

  From the viewpoint of reducing the CV value of the coarse polymer particles after dehydration, for example, in the case of a static mixer, the pressure loss in the static mixer during circulation is preferably 0.01 to 0.15 MPa.

  The residual content of water in the crude polymer particles after dehydration is preferably 1.5 to 10% by mass, and more preferably 2 to 8% by mass.

(Solvent replacement step)
A substitution solvent is added to the suspension dehydrated in the dehydration step, and the hydrophobic solvent is distilled off.

  Specifically, after the substitution solvent is added to the suspension dehydrated in the dehydration step, the temperature in the reaction vessel is raised and the hydrophobic solvent is vaporized and distilled off.

  Examples of the substitution solvent include polyhydric alcohols, surfactants, oils and fats. As the substitution solvent, a single species may be used, or a plurality of species may be mixed and used.

  Examples of the polyhydric alcohol include dihydric alcohols such as tetraethylene glycol, polyethylene glycol, and propylene glycol, trihydric alcohols such as trimethylolpropane, and tetravalent or more such as diglycerin, triglycerin, polyglycerin, pentaerythritol, and sorbitol. Of alcohol. Of these, polyethylene glycol is particularly preferred.

  Examples of the surfactant include anionic surfactants such as polyoxyethylene alkyl ether sulfates and nonionic surfactants such as polyoxyethylene alkyl ethers and glycerin fatty acid esters.

  Examples of the fats and oils include fatty oils, fats and waxes represented by fatty acid glycerin esters.

  The melting point of the substitution solvent is preferably 30 ° C. or higher from the viewpoint of favorably distilling off the hydrophobic solvent from the coarse polymer particles and combining the three components of the coarse polymer particles / hydrophobic solvent / substitution solvent. More preferably, the temperature is higher than or equal to ° C. Further, the boiling point of the substitution solvent is preferably 101 ° C. or more, and the boiling point at normal pressure is 101 ° C. or more, from the viewpoint that the larger the difference in boiling point from the hydrophobic solvent is, the easier removal of the hydrophobic solvent is. It is more preferable that

  From the viewpoint of improving the fluidity of the suspension after solvent substitution, the amount of substitution solvent added is the content of substitution solvent in the suspension finally obtained by solvent substitution (mass of hydrophilic polymer particles / (Mass of hydrophilic polymer particles + mass of substitution solvent) × 100) is preferably 10 to 70% by mass, and more preferably 20 to 50% by mass.

  The amount of the substitution solvent added to the total monomer weight used for the polymerization of the hydrophilic polymer particles is 0.3 to 10 kg-solvent / kg-total monomer from the viewpoint of improving the fluidity of the suspension after solvent substitution. 0.5-8 kg-solvent / kg-total monomer is more preferable, and 0.8-5 kg-solvent / kg-total monomer is particularly preferable.

  In the operation of distilling off the hydrophobic solvent, the temperature in the tank is, for example, 60 to 100 ° C., the distillation time is, for example, 0.5 to 20 hours, and the pressure in the tank is reduced to, for example, 10 to 100 kPa as necessary.

  This operation of distilling off the hydrophobic solvent is not performed only once, but when almost no distillation of the hydrophobic solvent ceases, a predetermined amount of substitution solvent and / or water is added, and the second and third times. The hydrophobic solvent may be distilled off.

  After distilling off the hydrophobic solvent, a suspension in which the solvent is substituted and the hydrophilic polymer particles are dispersed in the substitution solvent is obtained. According to such a method for producing hydrophilic polymer particles, the volume average particle size of the crude polymer particles before substitution of the hydrophobic solvent with the substitution solvent is 10 μm or less, and the CV value of the particle size is 60% or less. Thus, hydrophilic polymer particles with little remaining hydrophobic solvent can be produced. Specifically, in the hydrophilic polymer particles, the content of the hydrophobic solvent is reduced to, for example, less than 2000 ppm, preferably less than 1000 ppm.

  The obtained suspension preferably has a hydrophilic polymer particle content of 10 to 90% by mass, and more preferably 20 to 80% by mass. The content of the coarse polymer particles can be controlled by the addition amount of the substitution solvent.

The volume average particle diameter of the hydrophilic polymer particles and the CV value of the particle diameter are almost the same as those of the coarse polymer particles after the dehydration step.
In the present embodiment, the solvent replacement is performed on the suspension dehydrated in the dehydration step. However, the present invention is not particularly limited thereto, and the dehydration step is performed when the aggregation of the coarse polymer particles does not occur. Is not essential, and in such a case, solvent substitution may be performed directly on the suspension obtained in the polymerization step.
In this embodiment, the hydrophobic solvent is distilled off after the addition of the substitution solvent, but the present invention is not particularly limited thereto, and the substitution solvent may be added after the hydrophobic solvent is distilled off. Moreover, you may perform these partially or entirely simultaneously.

(Hydrophilic polymer particles)
Hydrophilic polymer particles were produced in the following Examples 1-2 and Comparative Examples 1-2. The contents of each are also shown in Table 1.

<Example 1>
Into a glass beaker with a capacity of 5 L, 55.7 g of diethylsulfate quaternized dimethylaminoethyl methacrylate (90% effective content), 143.6 g of N, N-dimethylacrylamide, and polyethylene glycol dimethacrylate (14 mol of EO) were added as monomers. Product) 0.041 g, 0.95 g of 2,2-azobis (2-amidinopropane) dihydrochloride as a polymerization initiator, 277.8 g of water, 1697 g of cyclohexane as a hydrophobic solvent, and sugar ester 1 as a dispersant .93 g was added and emulsified and dispersed using a homomixer at a rotation speed of 9000 r / min and a treatment time of 4 minutes. Then, the obtained emulsified dispersion was transferred to a 5 L SUS reaction vessel with a jacket for temperature control, and the temperature inside the reaction vessel was raised to 55 ° C. under nitrogen gas to cause a polymerization reaction for 40 minutes.

  After completion of the reaction, the temperature in the tank was set to 80 ° C., and cyclohexane and water were distilled from the reaction tank to perform a dehydration operation. The fraction was condensed in a condenser and then allowed to stand and separate into water and cyclohexane. The separated cyclohexane was continuously refluxed to the reaction tank during the dehydration operation, while only water was distilled off from the reaction tank. A total of 269 g of water was distilled off.

  After cooling the obtained suspension, the volume average particle diameter of the coarse polymer particles and the CV value of the particle diameter were measured. The volume average particle diameter of the coarse polymer particles was 4.0 μm, and the CV value of the particle diameter was 34.9%. In addition, the volume average particle diameter and the CV value of the particle diameter were determined using a laser diffraction scattering method particle size distribution measuring apparatus (model number: LS-230, manufactured by Coulter).

  Then, 246 g of polyoxyethylene alkyl ether (trade name: Emulgen 116, manufactured by Kao Corporation) is added to the obtained suspension, the jacket temperature is set to 80 ° C., and the pressure in the tank is reduced to 60 kPa to reduce cyclohexane. Distilled off. When distillate of cyclohexane can no longer be confirmed visually, a mixed solution of 49.1 g of polyoxyethylene alkyl ether and 5.5 g of water is added, the jacket temperature is set again to 80 ° C., and the pressure in the tank is changed. The hydrophilic polymer particles of Example 1 were produced by reducing the pressure to 60 kPa and performing a second distillation of cyclohexane.

<Example 2>
In a 300 L SUS reaction vessel, as monomers, dimethylaminoethyl methacrylate, diethyl sulfate quaternized product 3.1 kg (effective content 90%), N, N-dimethylacrylamide 8.0 kg, and polyethylene glycol dimethacrylate (EO 14 mol) Adduct) 0.0023 kg, 2,2-azobis (2-amidinopropane) dihydrochloride 0.053 kg as a polymerization initiator, water 15.4 kg, cyclohexane 94.0 kg as a hydrophobic solvent, and dispersant 0.11 kg of sugar ester was added, and an external circulation line installed with a static mixer (trade name: Dispersion, flow path hole diameter 3.5 mm, 4 units, manufactured by Fujikin Co., Ltd.) The resulting mixture was emulsified and dispersed with a pressure loss of 0.09 MPa and a treatment time of 2 hours. The obtained emulsified dispersion was transferred to a reaction vessel, and the temperature in the reaction vessel was raised to 55 ° C. under nitrogen gas to cause a polymerization reaction for 40 minutes.

  After completion of the reaction, the temperature in the tank was set to 80 ° C., and cyclohexane and water were distilled from the reaction tank to perform a dehydration operation. The fraction was condensed in a condenser and then allowed to stand and separate into water and cyclohexane. The separated cyclohexane was continuously refluxed to the reaction tank during the dehydration operation, while only water was distilled off from the reaction tank. The total distilled water was 14.9 kg.

  After cooling the obtained suspension, the volume average particle diameter of the coarse polymer particles and the CV value of the particle diameter were measured. The volume average particle diameter of the coarse polymer particles was 5.1 μm, and the CV value of the particle diameter was 28.5%.

  Then, 7.3 kg of polyoxyethylene alkyl ether (trade name: Emulgen 116, manufactured by Kao Corporation) is added to the obtained suspension, the jacket temperature is set to 80 ° C., and the pressure inside the tank is reduced to 60 kPa. Cyclohexane was distilled off. When distillate of cyclohexane can no longer be confirmed visually (residual cyclohexane amount of about 1.6% by mass), a mixed solution of 4.5 kg of polyoxyethylene alkyl ether and 0.5 g of water is added, and the jacket temperature is again measured. Was set to 80 ° C., and the pressure in the tank was reduced to 60 kPa, and cyclohexane was distilled off a second time to produce hydrophilic polymer particles of Example 2.

<Comparative Example 1>
Comparative Example 1 was a hydrophilic polymer particle produced in the same manner as in Example 1 except that the rotation speed of the homomixer during emulsification dispersion was 4500 r / min and the treatment time was 6 minutes. The volume average particle diameter of the coarse polymer particles contained in the suspension before solvent substitution was 11.1 μm, and the CV value of the particle diameter was 34.4%.

<Comparative example 2>
The hydrophilic polymer particle manufactured by the same operation as Example 2 was set as the comparative example 2 except that the pressure loss of the mixer part at the time of emulsification dispersion was 0.2 MPa, and processing time was 2.5 hours. The volume average particle diameter of the coarse polymer particles contained in the suspension before solvent substitution was 4.3 μm, and the CV value of the particle diameter was 86.7%.

(Test evaluation method)
For each of Examples 1 and 2 and Comparative Examples 1 and 2, the amount of residual cyclohexane relative to the amount of polymer particle suspension (polymer particles and solvent) from the start of the second distillation of cyclohexane was measured. In addition, the amount of residual cyclohexane was measured by gas chromatography (internal standard method) after extracting cyclohexane with methyl acetate.

(Test evaluation results)
The test results are shown in Table 1.

  In Example 1, the amount of residual cyclohexane at the start of the second cyclohexane distillation (after 0 hours) was 19,420 mg / kg-suspension. The amount of cyclohexane remaining 12 hours after the start of the second distillation of cyclohexane was 555 mg / kg-suspension.

  In Example 2, the amount of residual cyclohexane at the start of the second distillation of cyclohexane was 9,708 mg / kg-suspension. The amount of residual cyclohexane 12 hours after the start of the second distillation of cyclohexane was 1,308 mg / kg-suspension.

  In Comparative Example 1, the amount of residual cyclohexane at the start of the second distillation of cyclohexane was 7,228 mg / kg-suspension. The amount of cyclohexane remaining 12 hours after the start of the second distillation of cyclohexane was 3,460 mg / kg-suspension.

  In Comparative Example 2, the amount of residual cyclohexane at the start of the second distillation of cyclohexane was 11,245 mg / kg-suspension. The amount of residual cyclohexane 13 hours after the start of the second distillation of cyclohexane was 2,144 mg / kg-suspension.

  The present invention is useful for a method for producing hydrophilic polymer particles.

Claims (6)

  A substitution solvent is added to a suspension in which hydrophobic solvent-containing polymer particles having a volume average particle size of 10 μm or less and a coefficient of variation in particle size of 60% or less are dispersed in a hydrophobic solvent, and the hydrophobic solvent is distilled off. The manufacturing method of the hydrophilic polymer particle provided with the solvent substitution process to do.   The method according to claim 1, further comprising a polymer polymerization step of obtaining the suspension by synthesizing the hydrophobic solvent-containing polymer particles by a reverse-phase polymerization reaction using the hydrophobic solvent before the solvent substitution step. Process for producing the described hydrophilic polymer particles.   The hydrophilic property according to claim 2, further comprising a dehydration step of distilling off water in the hydrophobic solvent-containing polymer particles contained in the suspension after the polymer polymerization step and before the solvent substitution step. A method for producing polymer particles.   The method for producing hydrophilic polymer particles according to any one of claims 1 to 3, wherein the hydrophobic solvent is a hydrocarbon solvent.   The method for producing hydrophilic polymer particles according to any one of claims 1 to 4, wherein the substitution solvent contains at least one of a polyhydric alcohol, a surfactant, and an oil and fat.   Copolymerization of a cationic group-containing vinyl monomer and / or a salt thereof, a hydrophilic nonionic group-containing vinyl monomer, and a crosslinkable vinyl monomer having at least two reactive unsaturated groups in the molecule. The method for producing hydrophilic polymer particles according to any one of claims 1 to 5, which is a coalescence.