JPH0417907B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-based glass fiber binder that is useful in producing glass fiber nonwoven fabrics, papers, or glass fiber bundles, and has excellent adhesion to glass, water resistance, acid resistance, discoloration resistance, durability, etc. It is something. Conventionally, as binders for glass fibers, water-soluble resins such as gelatin, starch, and CMC; copolymer emulsions such as vinyl acetate and acrylic esters; epoxy resins; and phenolic resins have been used. Among these, water-soluble resins have poor water resistance and acid resistance, so when used as a binder for glass mat or glass paper used in lead-acid battery separators, for example, the binder easily dissolves into the sulfuric acid solution and loses its adhesive strength. It also causes contamination of the sulfuric acid solution. Vinyl acetate emulsions have poor color fastness, so when used as a sizing agent for chopped strands used in glass fiber reinforced thermoplastics (FRTP), for example, vinyl acetate emulsions are used as a sizing agent for chopped strands used in glass fiber reinforced thermoplastics (FRTP). There is a drawback that the chopped strands change color due to heat during kneading, and they also have poor water resistance. Acrylic acid ester emulsions do not have sufficient adhesion to glass, and when used as a sizing agent for chopped strands, for example, they have a strong tendency to break due to their weak sizing power. As a binder for paper and glass mats, it also has the drawbacks of insufficient adhesive strength and low hardness and strength. or,
Epoxy resins and phenolic resins also have the disadvantage that the resin itself is colored and easily discolored by heat or light. The present inventors found that the adhesive strength to glass is strong;
As a result of repeated research aimed at developing a binder with excellent water resistance and acid resistance, and less coloring and discoloration,
A copolymer obtained by emulsion polymerization containing an alkyl ester of (meth)acrylic acid as a main component, and having an organosilicon group and a carboxyl group with a specific structure in the copolymer, and It has been discovered that a blend of the copolymer and aqueous colloidal silica and/or a silane compound having a specific structure exhibits excellent properties as a binder for glass fibers,
This has led to the present invention. That is, the present invention uses 0.1 to 40% by weight of a silane compound (A) having a hydrolyzable group directly bonded to a silicon atom and having no polymerizable unsaturated group, and 1 to 30% by weight of a polymerizable unsaturated carboxylic acid (B). %, polymerizable monomer (C) having a functional group other than carboxyl group 0-30% by weight, (meth)acrylic acid alkyl ester (D) having an alkyl group having 1-18 carbon atoms 50-98.9% by weight and other polymerizable monomers (E) 0 to 40% by weight (however, (A),
The sum of components (B), (C), (D) and (E) is 100% by weight. 100 parts by weight (in terms of non-volatile content) of an aqueous polymer dispersion obtained by emulsion polymerizing a monomer mixture consisting of ) in an aqueous medium with or without addition of a basic substance, aqueous colloidal silica () 0
Provided is a binder for aqueous glass fiber characterized by comprising ~200 parts by weight (calculated as SiO ₂ content) and 0 to 40 parts by weight of a silane compound () having a hydrolyzable group directly bonded to a silicon atom. . The silane compound (A) used in the present invention is a silane compound that has a silicon atom to which at least one hydrolyzable group is directly bonded in the molecule and does not have a polymerizable unsaturated group. In the subsequent process, some or all of the hydrolyzable groups directly bonded to the silicon atom undergo hydrolysis to generate silanol groups, which have a strong affinity with glass, resulting in a strong adhesive force to glass. It is something that can be demonstrated. Examples of the silane compound (A) include aminomethyltriethoxysilane, N-β-aminoethylaminomethyltrimethoxysilane, γ-aminopropyltrimethoxysilane, N-(trimethoxysilylpropyl)-ethylenediamine, N-(dimethoxymethyl Aminoalkylalkoxysilanes such as silylpropyl-ethylenediamine:
-glycidoxypropyltrimethoxysilane, γ
- Epoxyalkylalkoxysilanes such as glycidoxypropylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, etc.: γ-mercaptopropyl Mercaptoalkylalkoxysilanes such as trimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, etc.: Tetraaloxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraptoxysilane, etc.: methyltrimethoxysilane, methyltriethoxysilane, methyl Alkyltrialkoxysilanes such as trimethoxyethoxysilane, ethyltrimethoxysilane, etc. Dialkylnadialkoxysilanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, etc.: γ-chloropropyltrimethoxysilane, 3,3,3-trichloropropyltrisilane, etc. Examples include halogenated alkyl alkoxysilanes such as methoxysilane; alkyl acyloxysilanes such as methyltriacetoxysilane and dimethyldiacetoxysilane; hydrosilane compounds such as trimethoxysilane and triethoxysilane; One type or a mixture of two or more types can be used. In the present invention, the silane compound (A) is contained in a monomer mixture in a proportion of 0.1 to 40% by weight,
More preferably, it is used in a proportion of 0.1 to 20% by weight.
If the silane compound (A) is less than 0.1% by weight, the adhesion to glass will be weak, and water resistance and acid resistance will be insufficient. This is not preferable because the adhesion strength is not improved compared to the case where the binder is used, and disadvantages such as destabilization of emulsion polymerization and increase in binder price occur. The polymerizable unsaturated carboxylic acid (B) used in the present invention has one or more carboxyl groups in its molecule, and is a copolymer obtained by a polymerization reaction of components (B) to (E). In addition to acting as a bonding point between the silane compound (A) and the silane compound (A), it also improves the adhesive strength to glass, and contributes to improving the freeze stability, mechanical stability, and chemical stability of the aqueous binder for glass fibers. , has the effect of making it possible to adjust the viscosity of the aqueous glass fiber binder to a desired range by adding an appropriate amount of a basic substance. Examples of the polymerizable unsaturated carboxylic acid (B) include unsaturated monobasic acids such as acrylic acid, methacrylic acid, and crotonic acid; unsaturated dibasic acids such as maleic acid, fumaric acid, and itaconic acid; and carbonic acid. Monoester compound of number 1 to 17 alkyl alcohol and unsaturated dibasic acid: monoester compound of dihydric alcohol such as ethylene glycol, diethylene glycol, propylene glycol and lower monohydric alcohol such as methyl alcohol, ethyl alcohol, butyl alcohol Examples include monoester compounds of ether and unsaturated dibasic acids, and one type or a mixture of two or more types selected from these groups can be used. In the present invention, the polymerizable unsaturated carboxylic acid (B) is 1 to 30% by weight in the monomer mixture.
Use at a ratio of If the proportion of polymerizable unsaturated carboxylic acid (B) is less than 1% by weight, the adhesion will decrease and the effect of improving various stability of the aqueous glass fiber binder will not be sufficient, and if it exceeds 30% by weight, If used, the water resistance and acid resistance of the binder will become poor. In the present invention, a polymerizable monomer (C) having a functional group other than a carboxyl group may be used in a proportion of 30% by weight or less in the monomer mixture, if necessary.
The polymerizable monomer (C) has at least one functional group other than a carboxyl group in addition to a polymerizable unsaturated group in its molecule, and examples of the functional group include a hydroxyl group, an epoxy group, and an alkoxy group. Mention may be made of silyl, methylol, amino and vinyl groups. These functional groups function as bonding points between the silane compound (A) and the copolymer obtained by the polymerization reaction of components (B) to (E). silane compound
If (A) has high reactivity with carboxyl groups, there is no need to use a polymerizable monomer (C), but the silane compound (A) has only low reactivity with carboxyl groups. If not, it is necessary to select and use a polymerizable monomer (C) having a functional group that exhibits higher reactivity than the silane compound (A). Examples of the polymerizable monomer (C) include unsaturated alcohols such as allyl alcohol and croton alcohol; polyamides such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-butylene glycol, neopentyl glycol, glycerin, and pentaerythritol; Vinyl etherified product of alcohol: Monoester compound of polyhydric alcohol and (meth)acrylic acid or crotonic acid:
Unsaturated glycidyl esters such as glycidyl (meth)acrylate: Unsaturated glycidyl ethers such as (meth)allyl glycidyl ether: vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, allyltriethoxysilane , γ−
Silane compounds containing unsaturated groups such as (meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, etc.: ethylene glycol di(meth)acrylate , polyethylene glycol di(meth)
Acrylate, 1,6-hexane glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, allyl acrylate,
Polyunsaturated compounds such as butadiene, isoprene, chloroprene, dicyclopentadiene, divinylbenzene, diallyl phthalate, etc.: Acrylamide derivatives such as methylolated (meth)acrylamide, methylolated diacetone acrylamide, etc.: aminoethyl (meth)acrylate, dimethyl Examples include unsaturated amine compounds such as aminoethyl (meth)acrylamide, etc., and one type or a mixture of two or more types selected from these groups can be used. Polymerizable monomer (C)
If the proportion exceeds 30% by weight, it may lead to poor water resistance and an increase in binder price. As the (meth)acrylic acid alkyl ester (D), one or more types of acrylic acid alkyl ester and methacrylic acid alkyl ester having an alkyl group having 1 to 18 carbon atoms are used; When used together with the above ingredients, it has the effect of preventing the binder from coloring due to heat or light and improving long-term durability. (Meth)acrylic acid alkyl ester (D) is an ester compound of a linear or branched aliphatic alkyl alcohol or alicyclic alkyl alcohol having 1 to 18 carbon atoms and acrylic acid or methacrylic acid, Examples include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, octyl, 2-ethylhexyl, lauryl, stearyl, or cyclohexyl esters of acrylic acid or methacrylic acid, and one or two selected from these groups. Mixtures of the above can be used. In the present invention, the (meth)acrylic acid alkyl ester (D) is used in a proportion of 50 to 98.9% by weight in the monomer mixture. If the proportion of the (meth)acrylic acid alkyl ester (D) is less than 50% by weight, the color fastness, durability, water resistance, and acid resistance of the binder will be poor. In the present invention, the polymerizable monomer (E) may be used in a proportion of 40% by weight or less in the monomer mixture, if necessary. Examples of the polymerizable monomer (E) include aromatic vinyl compounds such as styrene and vinyltoluene; vinyl halides such as vinyl fluoride and vinyl chloride; vinylidene halides such as vinylidene chloride; (meth)acrylonitrile; , unsaturated cyanide compounds such as crotonitrile; olefinic hydrocarbons such as ethylene and propylene; vinyl ester compounds of monovalent carboxylic acids such as acetic acid and propionic acid; unsaturated amide compounds such as (meth)acrylamide, etc. : etc., and one type or a mixture of two or more types selected from these groups can be used. If the proportion of polymerizable monomer (E) exceeds 40% by weight, the color fastness, durability, water resistance, and acid resistance of the binder may be poor depending on the type of monomer (E). It may happen. In the present invention, a silane compound (A), a polymerizable unsaturated carboxylic acid (B), a (meth)acrylic acid alkyl ester (D), and, if necessary, a polymerizable monomer (C) and/or a polymerizable monomer. The body (E) is emulsion polymerized in an aqueous medium. Although it is not always necessary to use an aqueous medium as a binder for glass fibers, it is preferable to use an aqueous medium rather than an organic solvent medium from the viewpoint of fire prevention, improvement of the working environment, etc. Therefore, as a method for obtaining the aqueous copolymer dispersion () in the present invention, there is also a method of carrying out a polymerization reaction in the presence or absence of an organic solvent to obtain a polymer, and then dispersing it in water. However, as mentioned above, emulsion polymerization in an aqueous medium is optimal from the viewpoint of fire prevention and improvement of the working environment, simplification of the manufacturing process, shortening of required time, and stability of the aqueous copolymer dispersion. This is the method. For the emulsion polymerization, known methods such as a monomer dropping method, a pre-emulsion method, or a combination of these methods can be used. Furthermore, a multi-step polymerization method may be used in which the monomer mixture is divided into two or more sets, in which case the composition of the monomer mixture in each divided set may be the same or different. According to such a multi-step polymerization method, the features of the present invention may be better exhibited. That is, for example, in a two-step polymerization method, by making the silane compound (A) and the polymerizable unsaturated carboxylic acid (B) exist only in the second-stage monomer mixture, the compound (A) and the unsaturated Carboxylic acid (B) is an aqueous copolymer dispersion ()
It is possible to obtain an aqueous glass fiber binder that is distributed near the surface of the dispersed particles without being incorporated into the dispersed particles, and has improved adhesive strength to glass. In emulsion polymerization, the emulsifiers used are:
Conventionally known anionic, cationic, or nonionic emulsifiers or polymeric emulsifiers may be used, such as sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium dodecyl polyglycol ether sulfate, alkali metal salts of sulfonated paraffin, Ammonium salt of sulfonated paraffin, sodium dodecylbenzene sulfonate, sodium laurate, high alkylnaphthalene sulfonate, dialkyl sulfosuccinate, polyoxyethylene alkyl sulfate, polyoxyethylene alkylaryl sulfate, polyoxyethylene alkyl ether, poly Oxyethylene alkylaryl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxypropylene polymer, lauryltrimethylammonium chloride, alkylbenzyldimethylammonium chloride, polyvinyl alcohol, sodium poly(meth)acrylate, poly(meth)acrylic Examples include ammonium acid, polyhydroxyethyl (meth)acrylate, polyhydroxypropyl (meth)acrylate, and one kind or a mixture of two or more kinds selected from these groups can be used. There is no particular restriction on the amount of emulsifier used, but if too much is used, the water resistance of the binder tends to deteriorate, so it is preferable to use an amount of 10% by weight or less based on the amount of the monomer mixture. Preferably, an amount of 5% by weight or less is used. As the polymerization catalyst, those commonly used in emulsion polymerization, such as ammonium persulfate,
Potassium persulfate, sodium persulfate, ammonium perborate, hydrogen peroxide, benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, peracetic acid, 2,2'-azobisisobutyronitrile, 4, A radical-forming polymerization initiator such as 4'-azobis(4-cyanopentanoic) acid or an alkali metal salt thereof can be used, and the amount used is 0.01 to 3% by weight based on the monomer mixture.
It may be within the range of . And if it is necessary to increase the polymerization rate or lower the reaction temperature when using peroxides, peroxides and ascorbic acid, soluble sulfites, hydrosulfites, thiosulfates, sulfone oxalates, sulfuric acid It can be used as a redox system in combination with ferrous iron or the like. The polymerization temperature is preferably in the range of 30 to 90°C, and additives customary in emulsion polymerization technology, such as chelating agents, buffers, salts of mineral or organic acids, pH regulating aids, etc., may be used. is also free. After performing emulsion polymerization in this way, it can be used as is as an aqueous copolymer dispersion () as a component of a binder for aqueous glass fibers, but by adding a chlorinated substance to increase the pH, the aqueous copolymer dispersion can be used as is. Freeze stability of polymer dispersion (),
Since mechanical stability and chemical stability can be improved, and adhesion to glass may also be improved, it is usually preferable to add a basic substance so that the pH is 5 or more. Examples of basic substances include ammonia, ethylamine, diethylamine, triethylamine, ethanolamine,
Triethanolamine, diethylethanolamine, caustic soda, caustic potash, etc. can be used. The thus obtained aqueous copolymer dispersion () can be used alone as an excellent binder for aqueous glass fibers, but by adding aqueous colloidal silica () and/or silane compound (), Furthermore, the performance as a binder for glass fibers can be improved. In the present invention, the aqueous colloidal silica () used as necessary is added to the aqueous copolymer dispersion () or the dispersion () during the manufacturing process of the aqueous glass fiber binder and/or the subsequent process. and the silane compound (), and have the effect of further improving adhesive strength and water resistance. The aqueous colloidal silica () is preferably a condensate of silicic acid with a particle size of 5 to 100 millimicrons, particularly 7 to 50 millimicrons, and is usually supplied in the form of an aqueous dispersion. You can use what is provided as is. Examples of such aqueous colloidal silica include commercially available products such as "Snowtex O", "Snowtex N", "Snowtex NCS", and "Snowtex
20” “Snowtex C” (manufactured by Nissan Chemical Co., Ltd.),
"Cataloid SN" and "Cataloid Si-500" (manufactured by Catalysts Kasei Kogyo Co., Ltd.), and surface-treated colloidal silica such as "Cataloid SA" (manufactured by Catalysts Kasei Kogyo Co., Ltd.) treated with aluminic acid are listed. one or two selected from these groups.
More than one species can be used. To obtain a blend of an aqueous copolymer dispersion () and an aqueous colloidal silica (), an aqueous copolymer dispersion () prepared by emulsion polymerization using the method described above is prepared.
and aqueous colloidal silica () may be mixed, or the mixture may be obtained all at once by emulsion polymerization in the presence of aqueous colloidal silica (). Even in the latter case where emulsion polymerization is carried out in the presence of aqueous colloidal silica (2), the same various methods as in the case where aqueous colloidal silica (2) is not present can be used as the emulsion polymerization method. For example, (a) a method of polymerizing by dropping a monomer mixture into an aqueous medium containing aqueous colloidal silica (), and (b) a method of polymerizing by dropping a premix of aqueous colloidal silica (a) and a monomer mixture. (c) A method in which the aqueous colloidal silica () and the monomer mixture are separately dropped and polymerized, etc. can be employed. Furthermore, the various additives mentioned above may be used freely during or after the emulsion polymerization. Furthermore, the pH can also be adjusted by adding the above-mentioned basic substance after emulsion polymerization. A method for obtaining a blend of an aqueous copolymer dispersion () and an aqueous colloidal silica () at once by emulsion polymerization in the presence of an aqueous colloidal silica () is as follows:
Since the emulsion polymerization of the aqueous copolymer dispersion () and the mixing of the aqueous copolymer dispersion () and the aqueous colloidal silica () can be performed simultaneously, there is an advantage that the process can be simplified. Furthermore, the adhesion to glass may be improved compared to simply mixing the aqueous copolymer dispersion () and the aqueous colloidal silica (). Aqueous colloidal silica () is 100 parts by weight of aqueous copolymer dispersion () (in terms of non-volatile content)
It is used in a proportion of 200 parts by weight or less (based on SiO ₂ content), preferably 100 parts by weight or less.
If the proportion of the aqueous colloidal silica () exceeds 200 parts by weight, the fusion of the dispersed particles contained in the aqueous copolymer dispersion () will be insufficient, and the adhesion to glass will become poor. In the present invention, a silane compound () is further used as necessary. Both the aqueous copolymer dispersion () alone or a blend of the dispersion () and aqueous colloidal silica () exhibit sufficiently excellent performance as a binder for glass fibers when used relatively early after production. However, if it is stored for a long time after production, its performance as a binder, especially its adhesion and water resistance, may deteriorate. By adding the silane compound () to the aqueous copolymer dispersion () whose performance has deteriorated in this way or the blend of the dispersion () and the aqueous colloidal silica (), the performance shown immediately after production can be improved. It is possible to recover the excellent performance as a binder equivalent to that of a binder. The silane compound () used in the present invention is a compound having a hydrolyzable group directly bonded to a silicon atom. As the silane compound (), for example, the above-mentioned silane compound (A)
In addition to the compounds used as Propyltriethoxysilane, γ-(meth)
Examples include unsaturated group-containing silane compounds such as acryloxypropylmethyldimethoxycin, and one type or a mixture of two or more types selected from these groups can be used. The proportion of the silane compound () is 40 parts by weight or less per 100 parts by weight (in terms of non-volatile content) of the aqueous copolymer dispersion (),
It is preferably used in a proportion of 20 parts by weight or less. Even if the proportion of the silane compound () exceeds 40 parts by weight, no improvement in performance commensurate with the amount used will result in an increase in binder price. The silane compound () may be diluted with water or other solvents if necessary prior to formulation. The aqueous copolymer dispersion () or a blend of the dispersion () and the aqueous colloidal silica () and/or silane compound () can be used as it is as a binder for glass fibers, but other than that, it can be used as a binder for glass fibers. Conditioners, coupling agents, lubricants, water repellents, crosslinking agents, antistatic agents, etc. can be added. The aqueous glass fiber binder of the present invention comprises a silane compound (A), a polymerizable unsaturated carboxylic acid (B), a polymerizable monomer (C), and a (meth)acrylic acid alkyl ester.
(D) and the aqueous copolymer dispersion () derived from the polymerizable monomer (E) as essential components, it has excellent adhesion to glass, water resistance, acid resistance, and discoloration resistance. Since it is an aqueous dispersion, it has excellent features such as no worries about fire or environmental pollution, and by adding water-based colloidal silica (), it can further improve adhesion and water resistance. By adding the compound (), it is possible to exhibit excellent performance equivalent to that immediately after production even after long-term storage, and it can be used extremely effectively in the production of various glass fiber products. For example, a glass mat can be manufactured by attaching it to the developed glass fiber web by spray coating, shower coating, dipping, etc., and then drying it, and the obtained glass mat has good hardness, strength, and acid resistance. For example, when used as a separator for lead-acid batteries, it exhibits excellent performance. The water-based binder for glass fibers of the present invention can also be used to manufacture glass paper by passing through a papermaking process from a glass fiber dispersion containing the binder, and the obtained glass paper has good strength, water resistance, and acid resistance. Because of its excellent properties of hardness, color fastness, and durability, it is effectively used in lead-acid battery separators, air filters, printed wiring boards, etc. Furthermore, the aqueous glass fiber binder of the present invention is
It can be used as a sizing agent in the production of chopped strands, roping, yarn, etc. For example, when used as a sizing agent for chopped strands, there are fewer cracks in the glass fiber bundles, there is no coloration of the glass fibers when kneading them into molten thermoplastic resin, and the resin reinforced with glass fibers is not colored. It has features such as improved durability and water resistance. The aqueous glass fiber binder of the present invention can be effectively used as a binder for various glass fiber nonwoven fabrics and woven fabrics other than those mentioned above. Hereinafter, the present invention will be explained in detail with reference to Examples, but the scope of the present invention is not limited to these Examples. In addition, unless otherwise specified in the examples, % means weight %, and parts mean % by weight. Each part shall be indicated by weight. Example 1 220 parts of water was placed in a flask equipped with a dropping funnel, a stirrer, an inert gas inlet tube, a thermometer, and a reflux condenser.
Add 1.5 parts of sodium dodecylbenzenesulfonate as an emulsifier and 0.5 parts of potassium persulfate as a polymerization catalyst, heat to 75°C while slowly blowing nitrogen gas, and stir to form a homogeneous aqueous solution, which is then added in advance through a dropping funnel. 5 parts of γ-glycidoxypropyltrimethoxysilane, 10 parts of methacrylic acid, methyl methacrylate
A monomer mixture consisting of 60 parts and 25 parts of butyl acrylate was added dropwise over 2 hours. Then the temperature
The temperature was maintained at 75°C and stirred for an additional 1 hour for emulsion polymerization, then cooled to 30°C, 2.8% ammonia water was added to adjust the pH to 5.7, and the non-volatile content was 30.0%.
An aqueous copolymer dispersion () was obtained. Let this be binder(). Examples 2 to 5 The same operations as in Example 1 were repeated to prepare an aqueous copolymer, except that the monomer mixture composition, emulsifier, polymerization catalyst, polymerization temperature, water, and basic substance were as shown in Table 1. A combined dispersion was obtained. Binder 2
~5.

【table】

Claims (1)

[Claims] 1 Silane compound (A) having a hydrolyzable group directly connected to a silicon atom and having no polymerizable unsaturated group (A) 0.1 to
40% by weight, polymerizable unsaturated carboxylic acid (B) 1-30% by weight, polymerizable monomer (C) having a functional group other than carboxyl group 0-30% by weight, alkyl group having 1-18 carbon atoms (meth)acrylic acid alkyl ester (D) 50 to 98.9% by weight and other polymerizable monomers
(E) 0 to 40% by weight (however, (A), (B), (C), (D) and (E)
The sum of the ingredients is 100% by weight. 100 parts by weight (in terms of non-volatile content) of an aqueous copolymer dispersion obtained by emulsion polymerizing a monomer mixture consisting of ) in an aqueous medium with or without addition of a basic substance, aqueous colloidal silica ( ) 0 to 200 parts by weight (in terms of SiO ₂ content) and 0 to 40 parts by weight of a silane compound ( ) having a hydrolyzable group directly bonded to a silicon atom.