JPS62227903A - Production of solvent-resistant porous fine particle of uniform particle diameter - Google Patents

Abstract

PURPOSE:To produce the titled fine particles excelling in solvent resistance and having a uniform particle diameter, by extracting solvent-soluble matter from a specified precursor of porous fine crosslinked polymer particles. CONSTITUTION:A monomer mixture comprising 99-99.95wt% noncrosslinking monomer and 1-0.05wt% crosslinking monomer is copolymerized in an aqueous medium in the presence of an emulsifier and a water-soluble polymerization initiator to obtain a low crosslinking density crosslinked polymer. The diameter of the polymer particles is increased by repeating seed polymerization at least thrice by using the polymer particles as initial seed particles to obtain a low-crosslinking degree fine polymer particles having a particle diameter of 0.5-10mum and a standard deviation of a particle size distribution <=0.1mum. 100-3,000pts.wt. monomer mixture comprising 50-90wt% noncrosslinking monomer and 50-10wt% crosslinking monomer and 100-6,000pts.wt. pore modifier are absorbed by 100pts.wt. above produced fine particles and copolymerized in an aqueous medium to obtain a precursor of crosslinked porous fine polymer particles. Solvent-soluble matter is extracted from this precursor to obtain solvent-resistant porous fine particles having a uniform diameter, a particle diameter of 2-30mum and a standard deviation of a particle size distribution <=1mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Application The present invention provides a solution to a solvent-soluble precursor of porous cross-linked polymer fine particles comprising a cross-linked polymer with a low cross-link density, a pore control agent, and a cross-linked polymer with a high cross-link density. characterized by the removal of substances,
The present invention relates to a method for producing uniformly sized fine particles having a particle size of 2 to 30 μm and a standard deviation of particle size distribution of lum or less, which is solvent resistant and porous.

BACKGROUND OF THE INVENTION Polymer fine particles used as opacifying agents, matting agents, organic pigments or fillers, thickness and gap adjusting agents, carriers for chromatography, etc. are strongly required to have uniform particle diameters. Furthermore, when used in a dispersed state in various solvents, such as when used as a thickness gap adjustment material or a carrier for chromatography, it is required that the material does not dissolve or swell in the solvent. Furthermore, in applications where a large surface tank is advantageous, such as when used as a carrier for chromatography or a carrier for various substances, porous properties are also desired.

Conventionally, methods for producing solvent-resistant, uniformly sized fine particles include:
There has been known a method of polymerizing polymer particles in a crosslinked state by using them as seed particles and absorbing a non-crosslinkable monomer or a crosslinkable monomer mixture (Japanese Unexamined Patent Application Publication No. 1983-1992).
18705, British Patent No. 728508, British Patent No. 1116800).

On the other hand, as a method for producing porous particles of uniform particle size, hydrophilic vinyl monomers and acrylic acid, etc. are mixed in the presence of an organic solvent that dissolves the monomers used but does not dissolve the reaction product. A method has been known in which a phenyl group-containing hydrophobic monomer and a hydrophilic monomer are polymerized in aqueous suspension and then the organic solvent is removed (Japanese Patent Application Laid-open No. 88657/1983,
(Japanese Unexamined Patent Publication No. 58-83260).

Problems to be Solved by the Invention However, in any of the above-mentioned methods for simply obtaining solvent-resistant particles, there is a problem in that the resulting fine particles have poor uniformity in particle size.

Furthermore, even in the aqueous suspension polymerization method for obtaining porous materials, there is a problem in that the resulting particles have a wide particle size distribution ((several microns to several tens of microns)) and are poor in uniformity.

As described above, it has been difficult to obtain fine particles with excellent uniformity in particle size using conventional methods. Therefore, the current practice is to perform a classification process after polymerization to make the particle size uniform. However, classification processing has not yet been carried out so that the standard deviation of the particle size distribution is 1 μm or less in the particle size range of 2 to 30 μm. .

Therefore, there has been no known method for producing solvent-resistant, porous, uniformly sized fine particles having a particle size of 2 to 30 μm and a standard deviation of particle size distribution of 1 ttm or less.

Means for Solving the Problems The present inventors have overcome the above problems, and have
The standard deviation of the particle size distribution is 1 μm or less at p to,
As a result of intensive research to develop a manufacturing method that can produce solvent-resistant, porous, and uniformly sized fine particles without the need for classification, we have developed a method with a low crosslinking density in which the particle size is grown using a seed polymerization method. A monomer mixture containing a high concentration of crosslinkable monomers and a pore control agent are infiltrated into polymer fine particles, and this is copolymerized, and the precursor of the obtained porous crosslinked polymer fine particles is made solvent-free. It was discovered that the objective could be achieved by extracting and removing the dissolved substance, and the present invention was completed.

That is, in the present invention, (A) an aqueous dispersion of seed particles contains water, a monomer mixture consisting of 99 to 99.95% by weight of a non-crosslinkable monomer and 1 to 0.05% by weight of a crosslinkable monomer. The non-crosslinkable monomer 99-9
A crosslinked polymer with a low crosslinking density obtained by treating a monomer mixture consisting of 9.95% by weight and 1 to 0.05% by weight of a crosslinkable monomer in an aqueous medium was used as initial seed particles three times or more. 50 to 90% by weight of non-crosslinkable monomers and crosslinkable monomers are contained in the repeatedly obtained low crosslinked polymer fine particles with a particle size of 0.5 to 10 μm and a standard deviation of particle size distribution of 0.1 μm or less. (B) obtaining a precursor of porous crosslinked polymer fine particles by absorbing a monomer mixture consisting of 50 to IO weight % and a pore adjusting agent and copolymerizing the same in an aqueous medium; The process consists of extracting a solvent-soluble substance from the precursor of the obtained porous crosslinked polymer fine particles.The particle size is 2 to 30 μm and the standard deviation of the particle size distribution is lum.
The following provides a method for producing solvent-resistant, porous, uniformly sized fine particles.

In the method of the present invention, first, a monomer mixture containing a high concentration of crosslinkable monomers and a pore adjusting agent are absorbed into low crosslinked polymer fine particles obtained by a seed polymerization method, and this is copolymerized to form a pore-forming agent. A precursor of crosslinked polymer fine particles is obtained (Step A).

At that time, the non-crosslinked monomer 9 is used as the low crosslinked polymer fine particles.
A crosslinked polymer made of a monomer mixture consisting of 9 to 99.95% by weight and 1 to 0.05% by weight of a crosslinkable monomer, and obtained by repeating seed polymerization three or more times, and has a particle size of 0. 5-1
A particle having a standard deviation of particle size distribution of 0.1 μm or less, preferably 0.05 μm or less is used.

That is, water is added to the aqueous dispersion of seed particles, a monomer mixture consisting of 99 to 99.95% by weight of a non-crosslinkable monomer and 1 to 0.05% by weight of a crosslinkable monomer, and further, as necessary. The amount of emulsifier required to stabilize the reaction (surface tension 55 dynes/
It is preferable to set it to 0 m or more. ) and a polymerization initiator, preferably a water-soluble polymerization initiator, are polymerized, and the obtained particles are used as the next seed particles to further grow the diameter, which is repeated three or more times to reach a predetermined size. things are used. Initial seed particles were prepared by treating a monomer mixture consisting of 99 to 99.95% by weight of non-crosslinking monomers and 1 to 0.05% by weight of crosslinking monomers in an aqueous medium. Crosslinking polymerization of crosslinking density is used.

That is, for example, a crosslinked polymer having a low crosslinking density in an emulsion obtained by processing the monomer mixture by a conventional emulsion polymerization method or the like is used. By using low-crosslinked polymer fine particles that satisfy these conditions, the standard deviation of particle size and particle size distribution in the final target product can be achieved, and the final target product can generally have excellent sphericity. . Further, it can be made into a material that can be swollen with a monomer mixture containing a high crosslinkable monomer or its constituent monomers to be used later. The swelling degree (the volume ratio of the particles before and after swelling) of the low crosslinked polymer fine particles obtained using the monomer mixture having the above-mentioned mixing ratio is usually 8 to 100. A material with a swelling degree of this level is preferred in the present invention. Therefore, if the content of the crosslinkable monomer in the monomer mixture used in the above treatment is too low, a product with an excessive degree of swelling will be obtained, and the solvent resistance of the final target product, uniform particle size fine particles, will be reduced. On the other hand, if the content of the crosslinkable monomer is too high, a product with an insufficient degree of swelling (excessive crosslinking density) may be obtained.
A monomer mixture containing a high concentration of crosslinkable monomers used later cannot be sufficiently diffused into the particles, resulting in insufficient polymerization in the particles, and new particles are formed that cause variation in particle size. (This makes it difficult to fully achieve the purpose of the present invention.)

The low-crosslinked polymer fine particles described above are used as a reaction base for a monomer mixture containing a high concentration of crosslinkable monomers. That is, the monomer mixture and the pore-adjusting agent are absorbed into the low-crosslinked polymer fine particles and subjected to a copolymerization treatment in the presence of a polymerization initiator. As a result, a crosslinked polymer with a high crosslinking density based on a monomer mixture with a high concentration of crosslinking monomers and a pore control agent are contained at least inside the low crosslinked polymer fine particles made of a crosslinked polymer with a low crosslinking density. However, a precursor of porous cross-dodecpolymer fine particles with an expanded particle size can be obtained, and a final target product with a large specific surface area can be obtained.

The process of absorbing the monomer mixture and the pore adjuster into the low crosslinked polymer fine particles involves adding the monomer mixture and the pore adjuster to a dispersion of the low crosslinked polymer fine particles, especially an aqueous dispersion as an emulsion polymerization liquid. A common method is to add and stir. According to this method,
This method has the advantage that a series of copolymerization treatments can be performed using a preparation solution of low crosslinked polymer fine particles. However, the present invention is not limited to this, and any method may be used as long as the absorption state is formed as a result.

The monomer mixture and the pore regulator may be added as a mixture, or may be added separately (or may be added in combination. Therefore, the monomer mixture and the pore regulator may be added separately (or may be added in combination). may or may not be present in a mixed and integrated state in the low crosslinked polymer fine particles.Furthermore, during the absorption treatment, heating may be performed to increase the absorption rate,
A water-soluble solvent such as acetone or ethanol may also be added.

Furthermore, the monomer mixture and the pore regulator may be emulsified in advance and added. This method of adding as an emulsion is particularly preferable because of its good absorbability. In addition, in a method using a solvent, it is preferable to remove the solvent before starting the polymerization.

The appropriate amount of the monomer mixture used in the treatment for obtaining the precursor of the porous crosslinked polymer fine particles described above is 100 to 3000 parts by weight per 100 parts by weight of the low crosslinked polymer fine particles. If the amount used is less than 100 parts by weight, the resulting fine particles of uniform particle size will have insufficient solvent resistance.
If the amount exceeds 1 part by weight, polymerization outside the low-crosslinked polymer particles tends to proceed, which is undesirable.

The mixing ratio of the non-crosslinkable monomer and the crosslinkable monomer in the monomer mixture is 50 to 90% by weight of the non-crosslinkable monomer;
50 to IO weight percent of crosslinking monomer is suitable. If the mixing ratio of the crosslinkable monomer exceeds 50% by weight, the crosslinking density of the crosslinked polymer will be too high, and if it is less than 10% by weight, the crosslinking density will be too low, making it difficult to achieve the object of the present invention.

In the present invention, monomers in the monomer mixture for obtaining precursors of low crosslinked polymer fine particles or porous crosslinked polymer fine particles include those which themselves or their polymers are poorly soluble or insoluble in water. is preferably used. If it is easily dissolved in water, polymerization will progress in water, making it difficult for the particle size of seed particles to grow, creating new particles (or forming them), or making them difficult to absorb into low-crosslinked polymer fine particles. This is not desirable.

Examples of non-crosslinkable monomers that can be preferably used include styrene monomers such as styrene, methylstyrene, and ethylstyrene, butyl acrylate, butyl methacrylate,
Examples include acrylic acid and methacrylic acid ester monomers having an alkyl group having 4 or more carbon atoms, such as 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate.

Examples of crosslinkable monomers that can be preferably used include monomers having two or more ethylenic double bonds, such as trimedylolpropane trimethacrylate, diethylene glycol dimethacrylate, and divinylbenzene.

The number of non-crosslinkable monomers and crosslinkable monomers may be one, or two or more.

Determined according to the intended use of the object. For example, when used as a thickness gap adjustment material or a carrier for chromatography, pressure resistance is required. It is preferable to use divinylbenzene, which has low solubility, as the crosslinking monomer. The styrene monomer also has the advantage that the copolymerization process can proceed stably without agglomeration.

The appropriate amount of the pore regulator used is 100 to 6,000 parts by weight per 100 parts by weight of the low crosslinked polymer fine particles. If the amount used is less than 100 parts by weight, the pores formed will be too small and the obtained uniform particle size fine particles will have poor porosity properties.If the amount used exceeds 6000 parts by weight, the low crosslinking As the pore adjusting agent, which is undesirable because it tends to generate new particles in addition to molecular fine particles, there is used one that can be removed as a solvent-soluble substance in the subsequent extraction process. Generally, the solubility in water is 1% by weight at room temperature.
(water-insoluble) and soluble in the non-crosslinkable 4L-mer and/or crosslinkable monomer used. If the solubility exceeds 1% by weight, it may not be absorbed into the low-crosslinked polymer fine particles and may remain in the water medium, not contributing to the formation of porosity, or inhibiting the stability of the reaction system. be.

Specific examples of pore control agents include saturated hydrocarbons such as hexane, heptane, and isooctane, aromatic hydrocarbons such as toluene, xylene, and ethylbenzene, and n-hexyl alcohol, n-octyl alcohol, and 2-ethylhexyl alcohol. Examples include linear polymers such as alcohols, polystyrene, and liquid paraffin. Only one type of pore adjusting agent may be used, or two or more types may be used in combination.

In addition, in the present invention, when a good solvent for the polymer of the non-crosslinkable monomer used is used as a pore control agent, the pore size in the obtained uniform particle size fine particles is small, and when a poor solvent is used as a pore control agent, the pore size becomes small. tends to be large. Therefore,
The porosity characteristics can also be controlled by the type of pore control agent.

The copolymerization treatment for obtaining a precursor of porous crosslinked polymer fine particles can be carried out using an appropriate medium under usual polymerization treatment conditions. When using an aqueous medium, a common oil-soluble radical initiator is preferably used as the polymerization initiator.

If it is water-soluble, new particles may be generated, which may cause problems. Note that it is preferable to use the oil-soluble polymerization initiator dissolved in the monomer mixture at a concentration of 0.1 to 5% in order to smoothly carry out the polymerization in the low-crosslinked polymer fine particles.

Incidentally, during the copolymerization treatment, it is desirable to stabilize the particles using an emulsifier or a polymerization stabilizer.

It is appropriate that the amount used is such that no new particles are generated other than the precursor of the porous crosslinked polymer fine particles.

By carrying out the copolymerization treatment as described above, the particle size of 2 to 30 μm 1, preferably 2 μm, of a structure having a pore control agent and a crosslinked polymer with a high crosslink density inside the low crosslinked polymer fine particles is obtained.
~20 μm, the standard deviation of the particle size distribution is 1 am or less, preferably 0.5 μm or less, and a precursor of porous crosslinked polymer fine particles having generally excellent sphericity can be obtained. In addition,
The crosslinked polymer having a high crosslinking density in the precursor of porous crosslinked polymer fine particles may be chemically bonded to the precursor, or may be in a solid state. It is also possible to have a crosslinked polymer with a high crosslinking density on the surface of the body.

In the method of the present invention, the precursor of the porous crosslinked polymer fine particles obtained in the above step is then subjected to a step of extracting a solvent-soluble substance (step B). As a result, uniform particle size particles can be obtained, which are made of crosslinked polymer particles imparted with porosity. These uniformly sized fine particles generally have poor mechanical strength.

Extraction of solvent-soluble substances can be performed, for example, by the following method.

That is, the water as a dispersion medium in the aqueous dispersion containing the precursor of porous crosslinked polymer fine particles obtained in the above step is gradually replaced with a less polar medium, and the pore control agent used is Finally, the medium is replaced with a medium having a similar SP value (solubility parameter), and washing is repeated with this medium to extract the solvent-soluble substances in the precursor of the porous crosslinked polymer fine particles.

As the substitution medium, it is generally desired to use a low boiling point solvent with a volatility of 11 because it is ultimately desired to remove it from the fine particles. Typical examples include alcohols such as methanol and ethanol, ketones such as acetone, acetonitrile, chloroform, tetrahydrofuran, benzene, toluene, xylene, and ethylbenzene. The displacement medium may be a hot medium with water or a hot medium using two or more types of solvents.

In some cases, it is efficient to carry out the extraction process by dispersing the precursor of the porous crosslinked polymer particles in a replacement medium. In that case, it is also possible to apply a dispersion method using ultrasonic waves, for example.

The present inventors believe that the main component removed by the extraction process is the pore control agent.

Note that the substitution medium remaining in the porous crosslinked polymer fine particles after the extraction treatment can be easily removed by, for example, a vacuum drying method, a spray dryer, or the like.

As described above, the particle size is 2 to 30 μm, preferably 2
~20 νm, the standard deviation of particle size distribution is 1 μm or less, preferably 0.5 μm or less, and excellent solvent resistance and porous uniform particle size can be obtained. These uniform particle size particles generally consist of crosslinked polymer particles having a structure containing a crosslinked polymer with a high crosslinking density inside a crosslinked polymer with a low crosslinking density, and have a specific surface area of 30n? /g or more, good mass 50-100
011r/g1 better than 100~500nf/
g, and has excellent sphericity and mechanical strength.

In addition, it is also possible to use an ion exchange resin or the like as the uniform particle size fine particles having a functional group such as an ion exchange group.

Effects of the Invention According to the present invention, a porous crosslinked polymer is produced by treating low crosslinked polymer fine particles with excellent particle size uniformity with a monomer mixture containing a high concentration of crosslinkable monomer and a pore control agent. Since the method uses a precursor of fine particles and then removes solvent-soluble substances from this precursor, the fine particles with a uniform particle size, which is excellent in particle size uniformity 11, can be used for practical purposes without classification, and can be In addition to being able to obtain a high yield, the obtained uniformly sized fine particles have excellent solvent resistance and a large specific surface area due to their porosity.

Examples Reference Examples Sodium lauryl sulfate 0.6 part (M part, same below)
After dispersing 30 parts of styrene containing 0.25% (wt%) of divinylbenzene in 70 parts of ion-exchanged water, the mixture was stirred and heated at 70°C under a nitrogen stream.
Then, 5 parts of ion-exchanged water in which 0.03 part of potassium persulfate was dissolved was added, and the mixture was kept at 70°C for 8 hours to form an aqueous dispersion of a crosslinked polymer with a low crosslink density as initial seed particles. I got it. The particle size of this crosslinked polymer with low crosslinking density is 0
．． The standard deviation of the particle size distribution was 0.01 part m or less.

Next, 10 parts of the aqueous dispersion of the obtained initial seed particles and 65 parts of ion-exchanged water were mixed and heated to 70°C, and then 30 parts of styrene containing 0.25% divinylbenzene was added.
Stir for an hour, then add 5 parts of ion-exchanged water in which 0.03 part of potassium persulfate is dissolved and maintain at 70°C for 8 hours.
Particle size is 0.149uIlx Standard deviation of particle size distribution is 0.0
An aqueous dispersion of secondary seed particles of 12 uI11 was obtained. Further, according to the above procedure, tertiary seed particles were prepared from secondary seed particles, quaternary seed particles were prepared from tertiary seed particles, and 5th seed particles were prepared from quaternary seed particles in the compositions shown in the table.゛The swelling degree of the fifth-order seed particles against styrene was measured to be 15.

Example 1 The quaternary seed particles obtained in Reference Example were used as low-crosslinked polymer fine particles, and 120 parts of ion-exchanged water and 10% by weight of polyvinyl alcohol with a saponification degree of 88% were added to 10 parts of an aqueous dispersion as a preparation liquid. After adding 18 parts of water solution and stirring uniformly,
Dissolve 0.5 part of benzoyl peroxide in a mixture of 48 parts of a monomer mixture of 65% styrene and 35% divinylbenzene and 30 parts of 11-hexyl alcohol, add 200 parts of ion-exchanged water, and 0.018 parts of sodium lauryl sulfate. The mixture was mixed with an emulsified liquid under ultrasonic treatment, and stirred at 60°C under a nitrogen stream for 2 hours, then heated to 80°C and copolymerized for 6 hours to form a porous crosslinked polymer. An aqueous dispersion containing a precursor of fine particles was obtained. The particle size of this precursor is 3.07
The standard deviation of the particle size distribution was 0.18 parts m.

Next, the dispersion medium in this aqueous dispersion was changed from water to methanol, ethanol, acetone, acetone/toluene (1/l
) and toluene to prepare a toluene dispersion, which was then heated at its boiling point temperature for 40 hours. Thereafter, fine particles were separated from the toluene dispersion and further washed with toluene, and then the dispersion medium was replaced in the reverse order to prepare an aqueous dispersion.

Porous crosslinked polymer fine particles after the extraction treatment were separated from the obtained aqueous dispersion, and dried with a spray dryer.

The obtained porous crosslinked polymer fine particles having a uniform particle size had a particle size of 3.07 μm and a standard deviation of the particle size distribution of 0.18 μm, which was the same as that of the precursor described above. In addition, the weight loss of the fine particles after the extraction treatment, that is, the weight loss of the uniform-sized fine particles as the porous crosslinked polymer fine particles obtained by the extraction treatment with respect to the precursor of the porous crosslinked polymer fine particles is 37 %Met.

Furthermore, B, E.

The specific surface area determined by the T method (nitrogen gas adsorption) is 200
．． It was 5 J/g. Furthermore, as a result of observation using a scanning electron microscope, it was found that in addition to being porous, it also had excellent sphericity.

Example 2 The 5th seed particles obtained in Reference Example were used as low-crosslinked polymer fine particles, and 120 parts of ion-exchanged water and the above polyvinyl alcohol aqueous solution 5 were added to 10 parts of an aqueous dispersion as a preparation liquid.
75% by weight of styrene,
60 parts of a monomer mixture containing 25% by weight of divinylbenzene and n
- Adding 0.6 part of benzoyl peroxide dissolved in a mixture of 20 parts of hexyl alcohol and 20 parts of toluene,
4 hours at 60°C under a nitrogen stream with stirring, followed by 80°C.
The mixture was copolymerized for 5 hours at an elevated temperature to obtain an aqueous dispersion containing a precursor of porous crosslinked polymer fine particles. The particle size of this precursor was 7.519 ml, and the standard deviation of the particle size distribution was 0.25 μm.

Next, extraction treatment and drying treatment were carried out in the same manner as in Example 1 to obtain porous crosslinked polymer fine particles.

The uniform particle size fine particles as porous crosslinked polymer fine particles obtained have a particle size of 7.51 parts ms and a standard deviation of particle size distribution of 0.25 μmn, which is almost different from the case of the precursor described above. There wasn't. Furthermore, the weight reduction of the fine particles after the extraction treatment was 38%.

Furthermore, the specific surface area determined by the B, E, T method (nitrogen gas adsorption) is 150.511? /g. Furthermore, as a result of observation using a scanning electron microscope, it was found that in addition to being porous, it also had excellent sphericity.

Claims (1)

[Scope of Claims] 1. (A) Water in the aqueous dispersion of seed particles, monomers consisting of 99 to 99.95% by weight of non-crosslinking monomers and 1 to 0.05% by weight of crosslinking monomers. A mixture of 99 to 99.95% by weight of non-crosslinkable monomers and 1 to 1 to 100% of crosslinkable monomers is added to polymerize the particles, and the obtained particles are used as the next seed particles to further grow the diameter. A crosslinked polymer with a low crosslinking density obtained by treating a monomer mixture consisting of 0.05% by weight in an aqueous medium was used as an initial seed particle three times or more, and the particle size was 0.
．． 5 to 90% of non-crosslinked monomers are contained in low crosslinked polymer fine particles of 5 to 10 μm and a standard deviation of particle size distribution of 0.1 μm or less.
A step of absorbing a monomer mixture consisting of 50 to 10% by weight of a crosslinkable monomer and a pore control agent, and copolymerizing the same in an aqueous medium to obtain a precursor of porous crosslinked polymer fine particles. (B) consists of a step of extracting a solvent-soluble substance from the precursor of porous crosslinked polymer fine particles obtained in the above step.The particle size is 2 to 30 μm and the standard deviation of the particle size distribution is 1.
A method for producing fine particles having a uniform particle size of .mu.m or less, solvent resistance, and porosity. 2. The method according to claim 1, which uses an emulsifier. 3. The method according to claim 1, wherein the pore regulating agent is insoluble in water and soluble in the monomer mixture or its constituent monomers. 4. 100 to 30% of a monomer mixture containing 50 to 10% by weight of a crosslinkable monomer per 100 parts by weight of low crosslinked polymer fine particles
2. The method according to claim 1, wherein the pore-adjusting agent is used in an amount of 100 to 6,000 parts by weight. 5. The method according to claim 1, wherein the monomer mixture containing 50 to 10% by weight of the crosslinkable monomer contains a polymerization initiator. 6. The method according to claim 1, wherein a monomer mixture containing 50 to 10% by weight of a crosslinkable monomer and a pore regulator are added in an emulsified state to an aqueous dispersion of low crosslinked polymer fine particles.