JP2008239637A - Method for producing polymer particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain polymer particles having desired particle diameters and uniform sizes. <P>SOLUTION: The method for producing polymer particles comprises heating seed particles having absorbed an ethylenic monomer and a polymerization initiator and an aqueous medium containing a dispersant and polymerizing the ethylenic monomer absorbed in the seed particles. The dispersant is an acidic silica sol containing colloidal silica particles having an average particle diameter of 20-200 nm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing polymer particles. More specifically, the present invention relates to a method for producing polymer particles using acidic silica sol particles as a dispersant.

  Polymer particles having a particle size in the range of 1 to 100 μm and having a uniform size are required in the fields of spacers, slipping agents, copying machine toners, paint matting agents, functional carriers and the like. Yes. Furthermore, in recent years, in the liquid crystal field, the polymer particles are also required for applications such as light diffusion plates, light diffusion films, and antiglare films. The following methods are known as methods for producing polymer particles to meet such demands.

First, an emulsion polymerization method is known as a method for producing fine polymer particles. However, particles produced by the emulsion polymerization method have a particle size usually smaller than 1 μm, and it is difficult to produce particles larger than that.
A suspension polymerization method is known as a method for producing polymer particles having a particle diameter larger than 1 μm. According to the suspension polymerization method, polymer particles having a particle diameter ranging from 5 to several hundred μm can be produced. However, the suspension polymerization method yields particles having irregular sizes and having a particle size distributed over a wide range.

Therefore, it is desired to provide a method capable of producing polymer particles having a particle size in the range of 1 to 100 μm and having a uniform size.
A seed polymerization method is known as a production method that meets the above-mentioned demand. The seed polymerization method uses polymer particles as seed particles, absorbs the monomer in the seed particles, and polymerizes the absorbed monomer in the seed particles, thereby making the polymer larger than the seed particles. It is a method of obtaining particles. In this method, it is possible to obtain particles of uniform size by using seed particles of uniform size and by allowing each seed particle to uniformly absorb the monomer. Seed particles having a uniform size as a raw material can be produced by a soap-free emulsion polymerization method, a dispersion polymerization method, or the like.

As a seed polymerization method, for example, a method described in JP-A-9-241310 (Patent Document 1) is known. This publication describes a method of obtaining particles by seed polymerization in the presence of seed particles obtained by dispersion polymerization using a dispersion medium having a solubility parameter of 10.5 to 12 at 25 ° C. Further, the obtained particles are said to be excellent in solvent resistance and excellent in monodispersibility. In this publication, a water-soluble polymer such as polyvinyl alcohol is actually used as a dispersant.
JP-A-9-241310

  When a water-soluble polymer such as polyvinyl alcohol used as a dispersing agent in the above publication is used, a part of the water-soluble polymer remains attached to the particles even when the obtained polymer particles are washed. When the adhesion amount of the dispersant is large, the obtained particles may adhere. Furthermore, when the particles are exposed to a high temperature, the particles may be discolored due to the alteration of the dispersant. For example, when a product comprising particles and a transparent resin containing the particles is produced by an extrusion method, the particles may turn yellow by heating when the particles are kneaded into the transparent resin and extruded.

  In order to solve the above adhesion and discoloration, there is a method of washing particles with a large amount of water or warm water or an organic solvent. However, such a cleaning method has a low cleaning effect, and the dispersant remaining between the particles or the dispersant adhering to the particles cannot be sufficiently removed. In addition, this method is uneconomical because it uses large amounts of water. In addition, in the method of washing with an organic solvent, equipment for waste liquid treatment or recovery of the organic solvent is required, resulting in high equipment costs.

The inventor of the present invention uses an acidic silica sol containing colloidal silica particles having a specific average particle size as a dispersant in a seed polymerization method, thereby having a polymer having a desired particle size and a uniform size. Surprisingly, it was found that particles were obtained, and the present invention was achieved.
Thus, according to the present invention, the aqueous medium containing the seed particles and the dispersant in which the ethylene monomer and the polymerization initiator are absorbed is heated to polymerize the ethylene monomer absorbed in the seed particles. A method for obtaining polymer particles, comprising:
There is provided a method for producing polymer particles, wherein the dispersant is an acidic silica sol containing colloidal silica particles having an average particle diameter of 20 to 200 nm.

  According to the present invention, polymer particles having a desired particle size and uniform size can be obtained. In addition, when the obtained polymer particles are not washed, colloidal silica is present on the surface of the polymer particles. Therefore, polymer particles having excellent heat resistance can be obtained.

One feature of the present invention is that an acidic silica sol containing colloidal silica particles having an average particle diameter of 20 to 200 nm is used as a powder in the seed polymerization method.
The colloidal silica particles have an average particle size of 20 to 200 nm. When the average particle size is smaller than 20 nm, the colloidal silica particles aggregate and lose fluidity, which is not preferable. When the average particle size is larger than 200 nm, the fluidity of the colloidal silica particles is maintained, but the resulting polymer particles are aggregated, which is not preferable. A preferable average particle diameter is 20 to 150 nm, and a more preferable average particle diameter is 20 to 50 nm. The average particle diameter usually means a primary particle diameter, but may be the particle diameter of an aggregate of colloidal silica particles as long as it is within the above range.

Moreover, acidic silica sol means the sol which shows the acidity whose pH of a dispersion liquid is about 2-4 when colloidal silica particle is disperse | distributed to water. When silica sol that does not show acidity is used, particles aggregate during polymerization or the particle size distribution becomes wide.
Examples of the colloidal silica particles include colloidal silica particles such as precipitated silica powder and gas phase method silica powder, and aqueous colloidal silica particles dispersed in an aqueous medium. The latter aqueous colloidal silica particles are preferred.

Aqueous colloidal silica particles are usually used as a suspension. The aqueous medium constituting the suspension mainly consists of water. The aqueous colloidal silica particles can be present in the suspension at a concentration of, for example, 5 to 50% by weight. You may add another water-soluble organic solvent to this aqueous medium in the range which does not inhibit the effect of this invention. Examples of such an organic solvent include lower alcohols such as methanol and ethanol.
As a colloidal silica particle, a well-known thing can be used, for example, the Nissan Chemical Corporation snow tech series is mentioned.

The amount of colloidal silica particles used is preferably 1 to 150 parts by weight and more preferably 3 to 150 parts by weight with respect to 100 parts by weight of the ethylene monomer. When the amount is less than 1 part by weight, it is difficult to stably disperse the ethylene monomer droplets, and thus it is difficult to obtain polymer particles having a uniform size. When the amount is more than 150 parts by weight, an effect commensurate with the addition cannot be obtained, and the production cost is high, which is not preferable. The polymer particles include seed particles and a dispersing agent in which an ethylene monomer and a polymerization initiator are absorbed. It is obtained by polymerizing an ethylene monomer absorbed in the seed particles by heating an aqueous medium containing.
The absorption of the ethylene monomer and the polymerization initiator into the seed particles may be performed before the addition to the aqueous medium or may be performed at the time of the addition. The dispersant may be added to the aqueous medium at the time of adding the seed particles, or may be added to the aqueous medium in advance before adding the seed particles.

  The ethylene monomer is not particularly limited, and any known monomer can be used. For example, styrene monomers such as styrene and p-methylstyrene; acrylic acid ester monomers such as ethyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, dimethylaminoethyl acrylate, and diethylaminoethyl acrylate; methyl methacrylate, ethyl methacrylate , Methacrylate monomers such as lauryl methacrylate and dimethylaminoethyl methacrylate, polyethylene glycol mono (meth) acrylate; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl ester monomers such as vinyl acetate and vinyl butyrate; N-methyl N-alkyl substituted (meth) acrylamides such as acrylamide and N-ethylacrylamide; Nitto such as acrylonitrile and methacrylonitrile Le monomer; divinylbenzene, ethylene glycol diacrylate, ethylene glycol di (meth) acrylate, polyfunctional monomers such as polyethylene glycol mono (meth) acrylate. These ethylene monomers can be used alone or in combination of two or more. In addition, (meth) acrylate means an acrylate or a methacrylate.

  The polymerization initiator is not particularly limited. For example, persulfate such as potassium persulfate and ammonium persulfate, benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexa Organic peroxides such as noyl peroxide, t-butylperoxy-2-ethylhexanoate, di-t-butyl peroxide; azobisisobutyronitrile, azobiscyclohexacarbonitrile, azobis (2,4 -Azo compounds such as (dimethylvaleronitrile). These polymerization initiators can be used alone or in combination of two or more.

The polymerization initiator may be added when the seed particles are added to the ethylene monomer, or may be added in advance to the ethylene monomer. Of these, the polymerization initiator is preferably added to the ethylene monomer in advance.
The seed particles are preferably particles that are as uniform in size as possible. The seed particles must have an average particle size smaller than the polymer particles to be obtained (for example, 85% or less of the average particle size of the polymer particles). Such seed particles can be obtained by a known soap-free emulsion polymerization method or dispersion polymerization method. In addition, the seed particle can use the particle | grains originating in the monomer illustrated as an ethylene-type monomer.

Improvement in the absorption amount of the ethylene monomer can be realized by lowering the molecular weight of the polymer constituting the seed particles. The molecular weight can be reduced by using a chain transfer agent during the polymerization for producing the seed particles. Examples of the chain transfer agent include normal octyl mercaptan.
Examples of the aqueous medium include water or a mixed medium of water and a water-soluble organic solvent (for example, a lower alcohol such as ethanol).

In order to increase the dispersion stability of the polymer particles and / or the seed particles that have absorbed the ethylene monomer at the time of polymerization, a water-soluble organic dispersant or auxiliary stabilizer may be added to the aqueous medium. Examples of the water-soluble organic dispersant include polyvinyl alcohol, carboxymethyl cellulose, gelatin and the like. Examples of auxiliary stabilizers include anionic surfactants, nonionic surfactants, and long-chain alcohols.
Furthermore, a water-soluble polymerization inhibitor may be used during the polymerization in order to suppress the generation of new particles other than the intended polymer particles. Examples of such a polymerization inhibitor include sodium nitrite, ferric chloride, hydroquinone and the like.

Hereinafter, an example of the manufacturing method of the polymer particle of this invention is explained in full detail.
First, an ethylene monomer and a polymerization initiator are added to an aqueous medium, and the resulting system is finely dispersed by a fine emulsifier such as a homogenizer, an ultrasonic processor, a nanomizer, a mount gallin type, etc. An emulsion in which a monomer and a polymerization initiator are finely dispersed can be obtained. The polymerization initiator may be finely dispersed in an aqueous medium separately from the ethylene monomer, and then added to the emulsion in which the ethylene monomer is finely dispersed. Further, the polymerizable monomer and the polymerization initiator may be finely dispersed after previously mixing. The particle size of the finely dispersed ethylene monomer droplets is preferably smaller than the seed particles from the viewpoint of absorbability to the seed particles.

Mix seed particles into the emulsion. Thereafter, when the resulting mixture is stirred for a while at room temperature, the ethylene monomer is absorbed by the seed particles. This absorption can be easily confirmed by observing the mixture with an optical microscope, for example.
Absorption is preferably performed at a temperature at which the ethylene monomer does not substantially polymerize. If polymerization proceeds before sufficient absorption, polymer powder derived from an ethylene monomer may be produced, which is not preferable. A higher temperature at which the ethylene-based monomer is not substantially polymerized is advantageous for increasing the absorption rate. The absorption time is suitably from 30 minutes to 3 hours.

Thus, a dispersant is added to the emulsion in order to stabilize the dispersion state of the seed particles that have absorbed the ethylene monomer. After the addition, the emulsion is heated for several hours while stirring is continued to polymerize the ethylene monomer absorbed in the seed particles. By the above process, polymer particles are obtained.
The polymerization of the ethylene monomer is preferably performed at 40 to 80 ° C. When the polymerization temperature is higher than 80 ° C., the reaction may occur abruptly, which is not preferable. When the polymerization temperature is lower than 40 ° C., the polymerization may take time, which is not preferable. In addition, it is preferable to raise the temperature to the polymerization temperature by gradually or gradually increasing the temperature (the rate of temperature increase at this time is, for example, 0.1 to 2 ° C./min).

The resulting polymer particles are isolated from the aqueous medium as required. The polymer particles after isolation may be washed with water to remove the dispersant adhering to the surface. Further, when the dispersant is not removed, the colloidal silica particles are present on the surface, so that the heat resistance of the polymer particles can be increased.
According to the production method of the present invention, polymer particles having an average particle diameter in the range of 1 to 100 μm can be obtained. In addition, polymer particles having a uniform CV value in the range of 3 to 15% can be obtained. Further, when the polymer particles are not washed, the colloidal silica particles can remain on the surface. Such polymer particles of the present invention have good light scattering characteristics and light reflection characteristics with respect to visible light, and also have good water resistance, solvent resistance, and heat resistance.

  The polymer particles obtained by the present invention include paints, inks, various abrasives, various analytical reagents, diagnostic reagents, printing materials, toners and external additives for toners, matting agents, resin fillers, and resin film slipping agents. , Chromatographic fillers, antiwear agents, spacers for display devices (PDPs, liquid crystal display panels), light diffusing agents for light diffusion sheets, pigments for electrophoretic display devices such as digital paper, hard coat agents for touch panels, optical materials It is useful as a magnetic material, a conductive material, a flame retardant, a papermaking material, a fiber treatment material and the like.

Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to this. In addition, the measuring method of the various values in an Example and a comparative example is described below.
<Measurement method of average particle diameter>
-Average particle diameter of colloidal silica particles and seed particles The average particle diameters of colloidal silica particles and seed particles are measured with an LS230 type manufactured by Beckman Coulter. Specifically, 0.1 g of particles and 10 ml of a 0.1% nonionic surfactant solution are added and mixed for 2 seconds with a touch mixer TOUCHMIXER MT-31 manufactured by Yamato Kagaku. Thereafter, the test tube is dispersed for 10 minutes using a commercially available ultrasonic cleaner, ULTRASONIC CLEANER VS-150, manufactured by Velvo Crea. The dispersed material is measured while irradiating ultrasonic waves with a model LS230 manufactured by Beckman Coulter. The optical model at that time was adjusted to the refractive index of the produced particles.
-Average particle diameter of polymer particles The average particle diameter of the polymer particles was measured with a Coulter counter manufactured by Beckman Coulter. The measurement is performed by performing calibration using a 50 μm aperture according to REFERENCE MANUAL FOR THE COULTER MULTISIZER (1987) published by Coulter Electronics Limited.

<PH>
The pH is measured with a glass electrode type hydrogen ion concentration meter HM-11P manufactured by Toa Denpa Kogyo. Before the measurement, calibration is performed with a standard solution of pH 6.86 and a standard solution of pH 4.01, and after washing the electrode with washing water, the electrode is placed in silica sol and the pH is measured.

<CV value>
The coefficient of variation (CV value) is calculated by substituting the standard deviation (σ) and average particle diameter (x) of the particle diameter into the following equation.
CV value (%) = (σ / x) × 100

<Color difference b value>
The slurry containing the polymer particles is dehydrated by a suction filtration device and sufficiently dried in a constant temperature bath at 60 ° C. The dried polymer particles are crushed in a mortar, placed in an aluminum container, and heated at 200 ° C. for 1 hour in a thermostatic bath. Next, the polymer particles are further crushed in a mortar, and the color difference b value of the obtained crushed material is measured with a color difference meter (CR-300; manufactured by Minolta).

Seed particle production example 1

After adding 108 g of methyl methacrylate (MMA) and 1.1 g of octyl mercaptan in 630 g of pure water, nitrogen purge was performed and the temperature was further raised to 55 ° C. Thereafter, potassium persulfate dissolved in 0.54 g of pure water 100 g was added, and then nitrogen purge was performed again. Thereafter, polymerization was carried out at 55 ° C. for 12 hours, and seed particles having an average particle diameter of 0.75 μm were obtained in a slurry state (containing 14% by weight of seed particles).
Table 1 summarizes the constituent monomers and average particle size of the seed particles.

Example 1
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution of 112 g of methyl methacrylate and 48 g of ethylene glycol dimethacrylate as an ethylene monomer, and the polymerizable monomer Ingredients.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The seed particles were swollen by stirring at 120 rpm for 4 hours.

  0.13 g of sodium nitrite is added to 480 g of a colloidal silica particle-containing dispersion (Snowtex OL: Nissan Chemical Co., Ltd., average particle size 40-50 nm, pH 2-4, particle concentration 20%), and then the slurry after swelling And polymerizing at 70 ° C. for 12 hours to obtain polymer particles having an average particle diameter of 2 μm and a CV value of 10.5. An electron micrograph (magnification 2300 times) of the obtained polymer particles is shown in FIG.

Example 2
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution of 112 g of methyl methacrylate and 48 g of ethylene glycol dimethacrylate as an ethylene monomer, and the polymerizable monomer Ingredients.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The seed particles were swollen by stirring at 120 rpm for 4 hours.

  0.13 g of sodium nitrite was added to 480 g of a colloidal silica particle-containing dispersion (Snowtex O-40, manufactured by Nissan Chemical Co., Ltd., average particle size 20-30 nm, pH 2-4, particle concentration 40%), and then the swelling was completed Then, polymerization was carried out at 70 ° C. for 12 hours to obtain polymer particles having an average particle diameter of 2 μm and a CV value of 10.1. An electron micrograph (magnification 2200 times) of the polymer particles obtained is shown in FIG.

Comparative Example 1
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution consisting of 112 g of methyl methacrylate as an ethylene monomer and 48 g of ethylene glycol dimethacrylate to obtain a polymerizable monomer. A body component.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The resulting system was stirred at 120 rpm for 4 hours to swell the seed particles.

  0.13 g of sodium nitrite was added to 480 g of a 5% aqueous polyvinyl alcohol solution (GOHSENOL GM-14: manufactured by Nippon Synthetic Chemical Co., Ltd.), then the slurry after swelling was added, and polymerization was further performed at 70 ° C. for 12 hours. Polymer particles having a particle diameter of 2 μm and a CV value of 10.0 were obtained.

Comparative Example 2
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution of 112 g of methyl methacrylate and 48 g of ethylene glycol dimethacrylate as an ethylene monomer, and the polymerizable monomer Ingredients.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The seed particles were swollen by stirring at 120 rpm for 4 hours.

  0.13 g of sodium nitrite is added to 480 g of a colloidal silica particle-containing dispersion (Snowtex ZL: manufactured by Nissan Chemical Co., Ltd., average particle size 70-100 nm, pH 9-10, particle concentration 40%), and then the slurry after completion of swelling And polymerizing at 70 ° C. for 12 hours to obtain polymer particles having an average particle diameter of 2 μm and a CV value of 16.0%. An electron micrograph (magnification 3300 times) of the polymer particles obtained is shown in FIG.

Comparative Example 3
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution of 112 g of methyl methacrylate and 48 g of ethylene glycol dimethacrylate as an ethylene monomer, and the polymerizable monomer Ingredients.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The seed particles were swollen by stirring at 120 rpm for 4 hours.

  0.13 g of sodium nitrite is added to 480 g of a colloidal silica particle-containing dispersion (Snowtex MP-4540M, manufactured by Nissan Chemical Co., Ltd., average particle size 450 nm, pH 8 to 10, particle concentration 40%), and then the slurry after swelling Was further added and polymerization was carried out at 70 ° C. for 12 hours. The obtained polymer was a large lump that did not maintain the shape of the particles. An electron micrograph (magnification of 750 times) of the obtained polymer is shown in FIG.

Comparative Example 4
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution of 112 g of methyl methacrylate and 48 g of ethylene glycol dimethacrylate as an ethylene monomer, and the polymerizable monomer Ingredients.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The seed particles were swollen by stirring at 120 rpm for 4 hours.

  0.13 g of sodium nitrite is added to 480 g of a colloidal silica particle-containing dispersion (Snowtex MP-2040, manufactured by Nissan Chemical Co., Ltd., average particle size 200 nm, pH 8 to 10, particle concentration 40%), and then the slurry after swelling Was further added and polymerization was carried out at 70 ° C. for 12 hours. The obtained polymer was a large lump that did not maintain the shape of the particles. An electron micrograph (magnification 2300 times) of the obtained polymer is shown in FIG.

Comparative Example 5
0.96 g of 2,2-azobis- (2,4-dimethylvaleronitrile) is dissolved in a mixed solution of 112 g of methyl methacrylate and 48 g of ethylene glycol dimethacrylate as an ethylene monomer, and the polymerizable monomer Ingredients.
Separately, 0.8 g of sodium dodecylbenzenesulfonate was dissolved in 160 g of pure water, the above polymerizable monomer component was mixed in this aqueous solution, and the mixture was stirred at 8000 rpm for 10 minutes using a TK homomixer. . This emulsion was put into a reaction vessel having a capacity of 1 L equipped with a stirrer and a thermometer, and 57 g of the slurry of seed particle production example 1 was added. The seed particles were swollen by stirring at 120 rpm for 4 hours.

0.13 g of sodium nitrite is added to 480 g of a colloidal silica particle-containing dispersion (Snowtex 30: manufactured by Nissan Chemical Co., Ltd., average particle size 10 nm, pH 9.5-10, particle concentration 30%), and then the slurry after swelling Was further added and polymerization was carried out at 70 ° C. for 12 hours. The obtained polymer was a large lump that did not maintain the shape of the particles.
Table 2 shows the ethylene monomer used in Examples 1 and 2 and Comparative Examples 1-5, seed particles and dispersant types, average particle size of the dispersant, pH, and average particle size of the resulting polymer particles. , CV value and color difference b value are shown together.

According to Examples 1 and 2, by using colloidal silica particles having an average particle size of 20 to 50 nm as a dispersant, polymer particles having a desired particle size and uniform size can be obtained. I understand that. Moreover, it turns out that there is little discoloration by heating.
It can be seen that the polymer particles of Comparative Example 1 are discolored due to the alteration of polyvinyl alcohol.
In addition, according to Comparative Examples 2 to 5, when silica sol that does not show acidity is used as a dispersant, polymer particles having a high CV value and a non-uniform size are obtained, or the polymer maintains the shape of the particles. It can be seen that the polymer particles cannot be obtained.

2 is an electron micrograph of polymer particles of Example 1. FIG. 2 is an electron micrograph of polymer particles of Example 2. FIG. 4 is an electron micrograph of polymer particles of Comparative Example 2. 4 is an electron micrograph of polymer particles of Comparative Example 3. 4 is an electron micrograph of polymer particles of Comparative Example 4.

Claims (2)

An aqueous medium containing seed particles and a dispersing agent in which an ethylene monomer and a polymerization initiator are absorbed is heated to polymerize the ethylene monomer absorbed in the seed particles to obtain polymer particles. A method,
The method for producing polymer particles, wherein the dispersant is an acidic silica sol containing colloidal silica particles having an average particle diameter of 20 to 200 nm.   The method for producing polymer particles according to claim 1, wherein the acidic silica sol has a pH of 2 to 4.