JP7784965B2 - Aqueous dispersion of silica-containing silicone rubber particles, silica-containing silicone rubber particles, and methods for producing the same - Google Patents

Description

The present invention relates to high-strength silicone rubber particles. More specifically, it relates to an aqueous dispersion of silica-containing silicone rubber particles, silica-containing silicone rubber particles, and methods for producing the same.

Silicone rubber particles are used in applications such as stress relief agents for resins, light diffusing agents for resins, texture improvers for cosmetics, matting agents for paints and coatings, texture improvers, and slip improvers. When used in paints and coatings, silicone rubber that does not contain fillers such as silica has low strength, so when the paint film is subjected to friction, the silicone rubber particles contained in it may break.

Patent Document 1 proposes high-strength silicone rubber particles containing silica. They are produced by mixing silica into a curable liquid silicone composition, dispersing (emulsifying) the mixture in water containing a surfactant, and then subjecting the mixture to a curing reaction. The silica used here is wet silica that has been hydrophobized with a liquid organopolysiloxane. As noted in Patent Document 1, if silica that has not been hydrophobized is used, during the emulsification process of the curable liquid silicone composition containing silica, the silica migrates from the silicone composition to the aqueous phase, which serves as the dispersion medium, and silica-containing silicone rubber particles cannot be obtained.
In the case of hydrophobic treatment using organopolysiloxane, the siloxane does not chemically modify the silica surface, but rather physically adsorbs to it, and during the process of emulsifying a curable liquid silicone composition containing silica, some of the incorporated silica may migrate into the aqueous phase.

Japanese Unexamined Patent Publication No. 4-168117

When wet silica is hydrophobized with silane or silazane, the silyl groups are chemically modified to produce sufficiently hydrophobic silica. However, curable liquid silicone compositions containing silica hydrophobized with silane or silazane cannot be emulsified with surfactants typically used to emulsify curable liquid silicones.

The present invention has been developed in light of the above circumstances, and aims to provide high-strength silicone rubber particles and their aqueous dispersions.

As a result of extensive research to achieve the above objective, the inventors discovered that by using a low HLB nonionic surfactant in a method for producing silicone rubber particles containing silica that has been hydrophobized with silane or silazane, it is possible to effectively emulsify a curable liquid silicone composition containing silica, thereby providing silicone rubber particles containing silica within the silicone rubber particles, leading to the completion of the present invention. Because the silicone rubber particles contain silica within the silicone rubber particles, they are able to possess high strength.

That is, the present invention provides the following aqueous dispersion of silica-containing silicone rubber particles and silica-containing silicone rubber particles.
The silicone rubber particles comprise 1 to 50 parts by mass of (A-2) hydrophobized silica per 100 parts by mass of (A-1) silicone rubber, the silicone rubber particles having a volume average particle size of 0.5 to 100 μm and being spherical, and the (A-2) hydrophobized silica has been hydrophobized with at least one group selected from the group consisting of a triorganosilyl group, a diorganosilyl group, a monoorganosilyl group, and a polydiorganosiloxy group.

The present invention further provides the above-mentioned silicone rubber particles, wherein the (A-1) silicone rubber is a cured product obtained by an addition reaction between (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms.
The present invention further provides the above-mentioned silicone rubber particles, wherein the (A-1) silicone rubber is a cured product obtained by a condensation reaction between (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom and (d) a silane having a hydrolyzable group bonded to a silicon atom.
The present invention further provides the above-mentioned silicone rubber particles, wherein the silicone rubber (A-1) is a radical reaction cured product of (e) an organopolysiloxane having a radical polymerization reactive group.

The present invention further provides a method for producing silicone rubber particles containing hydrophobically treated silica, the method comprising the steps of:
(i) mixing 100 parts by mass of at least one curable organosilicon compound selected from organopolysiloxanes and silanes with 1 to 50 parts by mass of (A-2) hydrophobized silica;
(ii) adding 0.1 to 20 parts by mass of (B) a nonionic surfactant having an HLB of 1.0 to 12.0, 5 to 2,000 parts by mass of (C) water, and optionally 0.05 to 5 parts by mass of (D) a water-soluble polymer to the mixture obtained in (i) and emulsifying the mixture to obtain an oil-in-water emulsion;
(iii) curing the curable organosilicon compound in the oil-in-water emulsion to obtain an aqueous dispersion of silicone rubber particles; and (iv) removing water from the aqueous dispersion obtained in step (iii) to obtain silicone rubber particles.
The present invention provides a method for producing silicone rubber particles, characterized in that the silicone rubber particles have a volume average particle size of 0.5 to 100 μm and are spherical, and the hydrophobized silica is hydrophobized with at least one group selected from a triorganosilyl group, a diorganosilyl group, a monoorganosilyl group, and a polydiorganosiloxy group.

The present invention further provides a method for producing an aqueous dispersion of silicone rubber particles containing hydrophobized silica, the method comprising the steps of:
(i) mixing 100 parts by mass of at least one curable organosilicon compound selected from organopolysiloxanes and silanes with 1 to 50 parts by mass of (A-2) hydrophobized silica;
(ii) adding 0.1 to 20 parts by weight of (B) a nonionic surfactant having an HLB of 1.0 to 12.0, 5 to 2,000 parts by weight of (C) water, and optionally 0.05 to 5 parts by weight of (D) a water-soluble polymer to the mixture obtained in (i) and emulsifying the mixture to obtain an oil-in-water emulsion; and (iii) curing the curable organosilicon compound in the oil-in-water emulsion to obtain an aqueous dispersion of silicone rubber particles,
The silicone rubber particles have a volume average particle size of 0.5 to 100 μm and are spherical, and the hydrophobized silica is hydrophobized with at least one group selected from a triorganosilyl group, a diorganosilyl group, a monoorganosilyl group, and a polydiorganosiloxy group.
A method for producing the aqueous dispersion is provided.

The silicone rubber particles of the present invention have high mechanical strength because they contain silica. Therefore, aqueous dispersions of these silicone rubber particles are useful for paints and coatings that are subject to friction.

The present invention is described in detail below.

(A) Silica-Containing Silicone Rubber Particles Component (A) is a particle containing (A-2) hydrophobized silica in (A-1) silicone rubber. The amount of hydrophobized silica (A-2) in the particle is in the range of 1 to 50 parts by mass, preferably 3 to 35 parts by mass, and more preferably 5 to 30 parts by mass, per 100 parts by mass of (A-1) silicone rubber. If the amount of hydrophobized silica is less than the above lower limit, the improvement in mechanical strength will be low. If the amount of hydrophobized silica is more than the above upper limit, the mixture of the curable liquid silicone and hydrophobized silica, described below, will lack fluidity, making it difficult to emulsify.

The particle shape is spherical. In this specification, "spherical" means that the particle shape is not only a perfect sphere, but also a deformed sphere in which the average ratio of the longest axis length to the shortest axis length (aspect ratio) is typically in the range of 1.0 to 4.0, preferably 1.0 to 2.0, more preferably 1.0 to 1.6, and even more preferably 1.0 to 1.4. The particle shape can be confirmed by observing the particles with an optical microscope, an electron microscope, or the like. It can also be measured using a particle shape analyzer using dynamic image analysis.
The volume average particle size of the particles is 0.5 to 100 μm, preferably 1 to 40 μm, and more preferably 2 to 20 μm. The volume average particle size is measured by the Coulter counter method (electrical resistance method).

The silicone rubber particles are preferably non-sticky, and their rubber hardness, measured using a Type A durometer as specified in JIS K6253, is preferably in the range of 5 to 95, and more preferably 20 to 85. Note that the rubber hardness is measured by preparing test specimens with the particle composition and the shape and dimensions specified in JIS K6253.

The mechanical strength of silicone rubber is preferably a tensile strength at break of 0.5 to 10 MPa, more preferably 0.8 to 5 MPa, measured using the method specified in JIS K 6251. The elongation at break is preferably in the range of 5 to 1000%, more preferably 10 to 500%. The tensile strength at break and elongation at break are values measured using a 1 mm thick sheet prepared with the particle composition and the shape and dimensions of a dumbbell-shaped No. 3 test specimen specified in JIS K 6251.

The silicone rubber particles may contain non-functional silicone oil, inorganic powders (excluding silica), organic powders, antioxidants, etc.

The silicone rubber (A-1) preferably comprises a cured product having linear organosiloxane blocks represented by the formula -(R ¹ ₂ SiO _2/2 ) _f -, where R ¹ in the formula is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, and more preferably 1 to 18 carbon atoms. f is a positive integer of 5 to 5,000, preferably 10 to 2,000, and more preferably 20 to 1,000.

Examples of R ¹ include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, and triacontyl; aryl groups such as phenyl, tolyl, and naphthyl; benzyl, phenethyl, and the like. alkenyl groups such as vinyl and allyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; and hydrocarbon groups in which some or all of the hydrogen atoms bonded to carbon atoms of these groups have been substituted with atoms such as halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms) and/or substituents such as acryloyloxy groups, methacryloyloxy groups, amino groups, epoxy groups, glycidoxy groups, and carboxyl groups, and it is preferred that 50 mol % or more of all R ^1s are methyl groups.

The silicone rubber is preferably a cured product of a curable liquid silicone composition. Examples of curable liquid silicone compositions include addition reaction, condensation reaction, and radical reaction curing types. The curable liquid silicone composition contains at least one curable organosilicon compound selected from organopolysiloxanes and silanes having reactive groups for the above curing reactions, and preferably a curing catalyst. The curable organosilicon compound may be an organosilicon compound having both reactive groups in one molecule, or a combination of an organosilicon compound having one reactive group and another organosilicon compound having a reactive group that reacts with the reactive group.

One aspect of the present invention is a curable liquid silicone composition that provides a silicone rubber, wherein the curable organosilicon compounds are (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms.
Another embodiment is a curable liquid silicone composition that provides a silicone rubber, wherein the curable organosilicon compound is (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom, and (d) a silane having a hydrolyzable group bonded to a silicon atom.
In another embodiment, in a curable liquid silicone composition that provides a silicone rubber, the curable organosilicon compound is (e) an organopolysiloxane having a radical polymerization reactive group.

One embodiment of the silicone rubber (A-1) of the present invention is preferably an addition reaction cured product of (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms. The curable liquid silicone composition that gives this addition reaction cured product contains (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms, and preferably further contains an addition reaction catalyst. This is explained in detail below.

(a) The organopolysiloxane having alkenyl groups is preferably represented by the following average composition formula (2) and has at least two alkenyl groups in one molecule.
R ² _g R ³ _h SiO _(4-gh)/2 (2)
In the formula, R2 ^'s are each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms that does not contain an alkenyl group, ^R3 's are each independently an alkenyl group having 2 to 6 carbon atoms, and g and h are positive numbers that satisfy the conditions 0<g<3, 0<h≦3, and 0.1≦g+h≦3.

^R2 is a monovalent hydrocarbon group having 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, and more preferably 1 to 18 carbon atoms. Of the monovalent hydrocarbon groups exemplified for ^R1 , ^R2 may be a monovalent hydrocarbon group excluding alkenyl groups, and preferably 50 mol % or more of R2 is methyl groups.

Examples of ^R3 include a vinyl group, an allyl group, a propenyl group, a butenyl group, a pentenyl group, and a hexenyl group, and a vinyl group is preferred.

g and h are preferably positive numbers that satisfy the following conditions: 0<g≦2.295, 0.005≦h≦2.3, 0.5≦g+h≦2.3.

The alkenyl group-containing organopolysiloxane preferably has 2 to 500 alkenyl groups per molecule. The amount of alkenyl groups is preferably 5.4 × 10 ^-4 to 1.1 mol/100 g. The degree of polymerization of the organopolysiloxane is preferably 2 to 5,000, more preferably 10 to 2,000, and even more preferably 20 to 1,000.

Component (a) preferably has a viscosity at 25°C of 0.7 to 100,000 mm ² /s, more preferably 2 to 10,000 mm ² /s, even more preferably 5 to 1,000 mm ² /s, and even more preferably 10 to 500 mm ² /s. The structure of component (a) may be linear, cyclic, or branched, with linear or branched being preferred. There are no particular restrictions on the bonding site of the alkenyl group, and it may be bonded to either a silicon atom in the side chain or at the terminal of the molecule.

An example of the linear organopolysiloxane is one represented by the following general formula (3).
In the formula, ^R2 and ^R3 are as defined above, i is a positive number, j is 0 or a positive number, and k is 0, 1, 2, or 3, provided that j and k are numbers that satisfy j+2×k≧2.

Examples of branched organopolysiloxanes include those branched with R ² SiO _3/2 units and represented by the following general formula (4):

In the formula, ^R2 and ^R3 are as defined above, l is a positive number, m is 0 or a positive number, n is a positive number, and o is 0, 1, 2, or 3, provided that m and o are numbers that satisfy m+o≧1.

Examples of organopolysiloxanes having a structure branched by SiO _4/2 units include those represented by the following general formula (5).

In the formula, ^R2 and ^R3 are as defined above, p is a positive number, q is 0 or a positive number, r is a positive number, and s is 0, 1, 2, or 3, provided that q and s are numbers that satisfy q+s≧1.

Further examples include organopolysiloxanes represented by the following formula (6) and having two or more alkenyl groups per molecule.
[R ² ₃ SiO _1/2 ] _t [R ³ (R ² ) ₂ SiO _1/2 ] _u [SiO _4/2 ] _v
[(OR ⁴ )SiO _3/2 ] _W (6)
In the formula, ^R2 and ^R3 are as defined above, ^R4 is a hydrogen atom or an unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, t is 0 or a positive number, u is a positive number, v is a positive number, and w is 0 or a positive number.

(b) The organohydrogenpolysiloxane having silicon-bonded hydrogen atoms is preferably represented by the following average composition formula (7), and has at least two silicon-bonded hydrogen atoms (referred to as SiH groups) per molecule.
R ⁵ _x H _y O _(4-x-y)/2 (7)
In the formula, ^R5s are each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms that does not contain an alkenyl group, and x and y are positive numbers that satisfy the conditions 0<x<3, 0<y≦3, and 0.1≦x+y≦3.

^R5 is a monovalent hydrocarbon group having 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, and more preferably 1 to 18 carbon atoms. Examples of ^R5 include monovalent hydrocarbon groups excluding alkenyl groups from the monovalent hydrocarbon groups exemplified for ^R1 , and it is preferable that 50 mol % or more of these groups are methyl groups.

x and y are preferably positive numbers satisfying the conditions 0<x≦2.295, 0.005≦y≦2.3, and 0.5≦x+y≦2.3.

The number of SiH groups in one molecule is preferably 2 to 500. The amount of SiH groups is preferably 5.3×10 ⁻⁴ to 1.7 mol/100 g. The degree of polymerization is preferably 2 to 5,000, more preferably 10 to 2,000, and even more preferably 20 to 1,000.

The viscosity of component (b) at 25°C is preferably 0.4 to 100,000 mm ² /s, more preferably 2 to 10,000 mm ² /s, even more preferably 5 to 1,000 mm ² /s, and even more preferably 10 to 500 mm ² /s. The structure of component (b) may be linear, cyclic, or branched, with linear or branched being preferred. There are no particular restrictions on the bonding site of the hydrogen atom bonded to the silicon atom, and the hydrogen atom may be bonded to either a side chain or terminal silicon atom of the molecule.

An example of the organopolysiloxane having a linear structure is one represented by the following general formula (8).

In the formula, ^R5 is as defined above, z is a positive number, _a1 is 0 or a positive number, and _b1 is 0, 1, 2, or 3, provided that _a1 and _b1 are numbers that satisfy _a1 +2× _b1 ≧2.

Examples of organopolysiloxanes having a branched structure include those branched by R ⁵ SiO _3/2 units and represented by the following general formula (9).
In the formula, ^R5 is as defined above, _c1 is a positive number, _d1 is 0 or a positive number, _e1 is a positive number, and _f1 is 0, 1, 2, or 3, provided that _d1 and _f1 are numbers that satisfy _d1 + _f1 ≧1.

An example of the organopolysiloxane branched by SiO _4/2 units is one represented by the following general formula (10).

In the formula, ^R5 is the same as above, _g1 is a positive number, _h1 is 0 or a positive number, _i1 is a positive number, and _j1 is 0, 1, 2, or 3, provided that _h1 and _j1 are numbers that satisfy _h1 + _j1 ≧1.

Further examples include organopolysiloxanes represented by the following formula (11) and having two or more SiH groups per molecule.
[R ⁵ ₃ SiO _1/2 ] _k1 [H(R ⁵ ) ₂ SiO _1/2 ] _l1 [SiO _4/2 ] _m1
[(OR ⁶ )SiO _3/2 ] _n1
(11)
In the formula, ^R5 is as defined above, ^R6 is a hydrogen atom or an unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, _k1 is 0 or a positive number, _l1 is a positive number, _m1 is a positive number, and _n1 is 0 or a positive number.

As described above, component (a) is an organopolysiloxane having at least two alkenyl groups per molecule, and component (b) is an organohydrogenpolysiloxane having at least two SiH groups per molecule. However, it is preferable that the composition excludes the combination of (a) having only two alkenyl groups and (b) having only two SiH groups. That is, more preferably, when component (a) has two alkenyl groups, at least one component (b) has three or more SiH groups, and when component (b) has two SiH groups, at least one component (a) has three or more alkenyl groups.

The amount of component (b) relative to component (a) is such that the ratio of the number of SiH groups in component (b) to one alkenyl group in component (a) is 0.5 to 2, preferably 0.7 to 1.5, and more preferably 0.8 to 1.3.

Examples of the catalyst for the addition reaction include platinum group metal catalysts used in hydrosilylation reactions, such as platinum group metals such as platinum (including platinum black), rhodium, and palladium;
_{H2PtCl4.XH2O , H2PtCl6.XH2O , NaHPtCl6.XH2O , ​ ​}
KHPtCl _{6.XH 2} O, Na ₂ PtCl _{6.XH 2} O, K ₂ PtCl _{4.XH 2} O,
Examples of suitable _{platinum chlorides} include _PtCl4.XH2O , _PtCl2 , _{and Na2HPtCl4.XH2O} (wherein X is an integer of 0 to 6, preferably 0 or 6), as well as chloroplatinic acid and chloroplatinic salts; alcohol-modified chloroplatinic acid; platinum chloride, complexes of chloroplatinic acid with olefins, complexes of chloroplatinic acid with vinyl group-containing siloxanes, and complexes of platinum with vinyl group-containing siloxanes; platinum black, platinum group metals such as palladium supported on carriers such as alumina, silica, and carbon; rhodium-olefin complexes; and chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst).

The amount of platinum group metal catalyst to be added may be an amount effective as a hydrosilylation reaction catalyst. For example, the amount of platinum group metal in the platinum group metal catalyst component relative to the total amount of components (a) and (b), converted to mass, is preferably 0.1 to 500 ppm, and more preferably 1 to 100 ppm.

Another embodiment of the silicone rubber (A-1) of the present invention is preferably a condensation reaction cured product of (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom and (d) a silane having a hydrolyzable group bonded to a silicon atom. The curable liquid silicone composition that gives this condensation reaction cured product contains (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom and (d) a silane having a hydrolyzable group bonded to a silicon atom, and preferably further contains a condensation reaction catalyst. This is explained in detail below.

(c) The organopolysiloxane having hydroxyl groups or hydrolyzable groups bonded to silicon atoms is preferably represented by the following average composition formula (12), and has at least two hydroxyl groups or hydrolyzable groups bonded to silicon atoms per molecule.
R ⁷ _o1 R ⁸ _p1 SiO _(4-o1-p1)/2 (12)
In the formula, R ^7s are each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms, R ^8s are each independently a hydroxyl group or a hydrolyzable group bonded to a silicon atom, and o ₁ and p ₁ are positive numbers satisfying 0<o ₁ <3, 0<p ₁ ≦3, and 0.1≦o ₁ +p ₁ ≦3.

^R7 is a monovalent hydrocarbon group having 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, and more preferably 1 to 18 carbon atoms. ^R7 may be any of the monovalent hydrocarbon groups exemplified for ^R1 above, and preferably 50 mol % or more of these groups are methyl groups.

^R8 are each independently a hydroxyl group or a hydrolyzable group bonded to a silicon atom. Examples of the hydrolyzable group include alkoxy groups such as methoxy, ethoxy, and propoxy; oxime groups such as methyl ethyl ketoxime and dimethyl ketoxime; acetoxy groups, and aminoxy groups, with alkoxy groups being preferred. ^R8 is preferably a hydroxyl group bonded to a silicon atom.

o ₁ and p ₁ are preferably positive numbers satisfying 0<o ₁ ≦2.295, 0.005≦p ₁ ≦2.3, and 0.5≦o ₁ +p ₁ ≦2.3.

The viscosity of component (c) at 25°C is preferably 1 to 100,000 ^{mm 2} /s, more preferably 2 to 10,000 mm ² /s, and even more preferably 10 to 1,000 mm ² /s. The structure of component (c) may be linear, cyclic, or branched, with linear or branched structures with few branching units being preferred. There are no particular restrictions on the bonding site of the hydroxyl group or hydrolyzable group bonded to the silicon atom, and they may be bonded to either a side chain or terminal silicon atom of the molecule.

Examples of organopolysiloxanes in which R ⁸ is a hydroxyl group and which have a linear structure include compounds represented by the following general formula (13).

In the formula, R ⁷ is as defined above, q ₁ is a positive number, r ₁ is 0 or a positive number, and s ₁ is 0, 1, 2, or 3, provided that r ₁ and s ₁ are numbers that satisfy r ₁ +2×s ₁ ≧2.

Examples of organopolysiloxanes in which R ⁸ is a hydroxyl group and which have a branched structure include compounds branched with R ⁷ SiO _3/2 units and represented by the following general formula (14):
In the formula, R ⁷ is as defined above, t ₁ is a positive number, u ₁ is 0 or a positive number, v ₁ is a positive number, and w ₁ is 0, 1, 2, or 3, provided that u ₁ and w ₁ are numbers that satisfy u ₁ +w ₁ ≧1.

An example of the organopolysiloxane branched by SiO _4/2 units is a compound represented by the following general formula (15).

In the formula, R ⁷ is as defined above, x ₁ is a positive number, y ₁ is 0 or a positive number, z ₁ is a positive number, and a ₂ is 0, 1, 2, or 3, provided that y ₁ and a ₂ are numbers that satisfy y ₁ +a ₂ ≧1.

Component (d) is a silane having at least three silicon-bonded hydrolyzable groups per molecule. Examples of silicon-bonded hydrolyzable groups include alkoxy groups such as methoxy, ethoxy, and propoxy; oxime groups such as methyl ethyl ketoxime and dimethyl ketoxime; and acetoxy groups, with alkoxy groups being preferred.

Silanes in which the hydrolyzable group is alkoxy are represented by the following formulas (16) and (17), and may also be partial hydrolysis condensates thereof.
R ⁹ Si (OR ¹⁰ ) ₃ (16)
Si(OR ¹¹ ) ₄ (17)
In the formula, R ⁹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and R ¹⁰ and R ¹¹ are unsubstituted monovalent hydrocarbon groups having 1 to 6 carbon atoms.

Examples of ^R9 include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and icosyl groups; aryl groups such as phenyl, tolyl, and naphthyl groups; aralkyl groups such as benzyl and phenethyl groups; alkenyl groups such as vinyl and allyl groups; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; and hydrocarbon groups in which some or all of the hydrogen atoms bonded to carbon atoms of these groups have been substituted with atoms such as halogen atoms (fluorine, chlorine, bromine, and iodine atoms) and/or substituents such as acryloyloxy, methacryloyloxy, epoxy, glycidoxy, and carboxyl groups.

R ¹⁰ and R ¹¹ may be a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, or a hexyl group, and are preferably a methyl group or an ethyl group.

The amount of component (d) relative to component (c) is an amount such that the ratio of the number of hydrolyzable groups bonded to silicon atoms in component (d) to one hydroxyl group or hydrolyzable group bonded to silicon atoms in component (c) is 0.8 or more, and preferably 1.0 or more.
Component (d) is a crosslinking agent for component (c). However, components (d) can undergo a condensation reaction with each other. Therefore, the ratio of the number of hydrolyzable groups bonded to silicon atoms in component (d) to one hydroxyl group or hydrolyzable group bonded to a silicon atom in component (c) may be in large excess.
The upper limit of the amount of component (d) is preferably 50 parts by mass or less, and more preferably 30 parts by mass or less, of component (d) per 100 parts by mass of component (c).

Examples of condensation reaction catalysts include organic tin compounds such as dibutyltin dilaurate, dioctyltin diversatate, dioctyltin dilaurate, tin octenoate, and tin laurate; organic titanium compounds such as titanium acetylacetonate, titanium tetraacetylacetonate, and titanium octanedioleate; acidic compounds such as hydrochloric acid, sulfuric acid, and dodecylbenzenesulfonic acid; and alkaline compounds such as ammonia and sodium hydroxide.
The amount of the condensation reaction catalyst to be added may be an effective amount as a condensation reaction catalyst, preferably 0.001 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the total amount of components (d) and (c).

Another embodiment of the silicone rubber (A-1) of the present invention is preferably a radical reaction cured product of (e) an organopolysiloxane having a radical polymerization reactive group. The curable liquid silicone composition that provides this radical reaction cured product contains (e) an organopolysiloxane having a radical polymerization reactive group, and preferably contains a radical generator.

(e) The organopolysiloxane having a radical polymerization reactive group is preferably represented by the following average composition formula (18) and has at least one radical polymerization reactive group in each molecule.
R ¹² _b2 R ¹³ _c2 SiO _(4-b2-c2)/2 (18)
In the formula, R ¹² are each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms and not having a radical polymerization reactive group, R ¹³ are each independently a hydrocarbon group having 2 to 10 carbon atoms and having a radical polymerization reactive group, and b2 and c2 are positive numbers satisfying 0<b ₂ <3, 0<c ₂ ≦3, and 0.1≦b ₂ +c ₂ ≦3.

^R12 is a monovalent hydrocarbon group having 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, and more preferably 1 to 18 carbon atoms. Of the monovalent hydrocarbon groups exemplified for ^R1 above, ^R12 may be a monovalent hydrocarbon group excluding alkenyl groups and hydrocarbon groups substituted with an acryloyloxy group or methacryloyloxy group. It is preferable that 50 mol % or more of ^R12 are methyl groups.

Examples of the radical polymerization reactive group of R ¹³ include an acryloyl group, a methacryloyl group, an acrylamide group, a vinyl group, an allyl group, an isoprenyl group, and a styryl group, and preferred are an acryloyl group and a methacryloyl group.

_b2 and _c2 are preferably positive numbers that satisfy 0< _b2 ≦2.295, 0.005≦ _c2 ≦2.3, and 0.5≦ _b2 + _c2 ≦2.3.

The viscosity of component (e) at 25°C is preferably 1 to 100,000 mm ² /s, more preferably 2 to 10,000 mm ² /s. It is even more preferably 5 to 1,000 mm ² /s, and even more preferably 10 to 500 mm ² /s. The structure of component (e) may be linear, cyclic, or branched, with linear or branched structures with few branching units being preferred. There are no particular restrictions on the bonding site of the radical polymerization reactive group, and it may be bonded to any silicon atom in the side chain or at the terminal of the molecule.

Examples of organopolysiloxanes having a linear structure and a methacryloyl group as a radical polymerization reactive group include those represented by the following general formula (19).
In the formula, R ¹² is the same as above, and R ¹⁴ is represented by the following formula (20).
_d2 is a positive number, _e2 is 0 or a positive number, _f2 is 0, 1, 2 or 3, and _g2 is 0, 1, 2 or 3, provided that any one of _e2 , _f2 and _g2 is 1 or more.

Examples of compounds in which the radical polymerization reactive group in R ¹³ is a methacryloyl group and which have a branched structure include compounds branched by R ¹² SiO _3/2 units and represented by the following general formula (21):
In the formula, R ¹² is as defined above, R ¹⁴ is represented by the above formula (20), h ₂ is a positive number, i ₂ is 0 or a positive number, j ₂ is a positive number, and k ₂ is 0, 1, 2, or 3, provided that either i ₂ or k ₂ is 1 or greater.

An example of the organopolysiloxane branched by SiO _4/2 units is one represented by the following general formula (22).
In the formula, R ¹² is as defined above, R ¹⁴ is represented by the above formula (20), l ₂ is a positive number, m ₂ is 0 or a positive number, n ₂ is a positive number, and o ₂ is 0, 1, 2, or 3, provided that either m ₂ or o ₂ is 1 or greater.

Examples of radical generators include organic peroxides, inorganic peroxides, azo initiators, redox initiators that combine an oxidizing agent and a reducing agent, and photopolymerization initiators. Of these, redox initiators and photopolymerization initiators are preferred.

As redox initiators, particularly preferred are redox initiators that combine ferrous sulfate, sodium pyrophosphate, glucose, and hydroperoxide, and redox initiators that combine ferrous sulfate, ethylenediaminetetraacetic acid disodium salt, Rongalite, and hydroperoxide.

Examples of photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one, phenylglyoxylic acid methyl ester, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

(A-2) Examples of silica in hydrophobically treated silica include wet silica such as precipitated silica, and dry silica such as silica xerogel and fumed silica. All of these silicas are hydrophilic silicas. Hydrophobically treated silica is a type of silica that has been hydrophobically treated.

Hydrophobization of silica is preferably achieved by modifying the hydrophilic groups of hydrophilic silica with triorganosilyl groups, diorganosilyl groups, monoorganosilyl groups, or polydiorganosiloxy groups. More preferred modifying groups are trimethylsilyl groups, dimethylsilyl groups, and monomethylsilyl groups. These hydrophobization treatments can be achieved by conventional methods, i.e., by treating with organosilicon compounds such as organochlorosilanes, organoalkoxysilanes, organodisilazanes, partial hydrolyzed condensates of organochlorosilanes, partial hydrolyzed condensates of organoalkoxysilanes, organopolysiloxanes, and organohydrogenpolysiloxanes. The organosilicon compound is preferably a silane or silazane containing a methyl group. More specifically, these include trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane, hexamethyldisilazane, and 1,3-divinyl-1,1,3,3-tetramethyldisilazane.

Hydrophobization is preferably performed to the point where the silica does not disperse in water under agitation. In other words, the hydrophobicity degree is preferably greater than 0, more preferably 5 or greater, and even more preferably 40 or greater. If the hydrophobicity degree is low, during the emulsification process of the curable liquid silicone composition containing silica described below, the silica will migrate from the silicone composition to the aqueous phase (dispersion medium), making it impossible to obtain silicone rubber particles containing silica. There is no particular upper limit to the hydrophobicity degree, but it is preferably 80 or less, more preferably 70 or less. The hydrophobicity degree, also known as methanol wettability, is the methanol concentration (volume %) at which the powder disperses completely in an aqueous methanol solution under agitation. A higher value indicates higher hydrophobicity.

(A-2) Hydrophobized silica is a fine powder, and preferably has a specific surface area measured by the BET method of 100 m ² /g or more, more preferably 100 to 500 ^{m 2} /g, and even more preferably 150 to 400 m ² /g.

The present invention further provides an aqueous dispersion of silicone rubber particles, comprising 100 parts by mass of the above-mentioned (A) silicone rubber particles, 0.1 to 20 parts by mass of (B) a nonionic surfactant having an HLB of 1.0 to 12.0, and 5 to 2,000 parts by mass of (C) water.

(B) Nonionic Surfactant The (B) nonionic surfactant functions as a dispersant for the (A) silicone rubber particles and also functions as an emulsifier for the mixture of organopolysiloxane, silane, and hydrophobized silica in the production of an aqueous dispersion of the (A) silicone rubber particles, which will be described later.

Component (B) has an HLB of 1.0 to 12.0, preferably 3.0 to 11.5, more preferably 6.0 to 11.0, and even more preferably 6.5 to 10.5. If the HLB is greater than 12.0, the dispersion stability of the (A) silicone rubber particles decreases. Furthermore, emulsification may not be possible during the emulsification process of the mixture of organopolysiloxane, silane, and hydrophobized silica, or the silicone rubber particles obtained by curing the organopolysiloxane and silane may aggregate. When two or more nonionic surfactants are used in combination, the average HLB should be in the range of 1.0 to 12.0, preferably 3.0 to 11.5, more preferably 6.0 to 11.0, and even more preferably 6.5 to 10.5. A nonionic surfactant with an HLB greater than 12.0 may also be included. In this case, the HLB should be 15.0 or less, preferably 13.0 or less, and even more preferably 12.5 or less.
The HLB value in the present invention is calculated by the following formula: HLB=[molecular weight of polyoxyethylene moiety and alcohol moiety/molecular weight of surfactant]×20
When two or more nonionic surfactants with different HLB values are used in combination, the HLB value is a weighted average value.

Nonionic surfactants having the above HLB include polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyethylene glycol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbit fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, propylene glycol fatty acid esters, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, polyoxyethylene hydrogenated castor oil fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, polyoxyethylene-modified organopolysiloxanes, and polyoxyethylene polyoxypropylene-modified organopolysiloxanes. These may be used alone or in appropriate combinations of two or more.

The amount of (B) nonionic surfactant is 0.1 to 20 parts by mass, preferably 1 to 18 parts by mass, and more preferably 3 to 15 parts by mass, per 100 parts by mass of (A) silicone rubber particles. If the amount of nonionic surfactant is less than the above lower limit, the dispersion stability of the (A) silicone rubber particles will decrease. Furthermore, when emulsifying the curable liquid silicone composition containing silica, emulsification may fail or the resulting silicone rubber particles may aggregate. Furthermore, if the amount is greater than the above upper limit, the water dispersion performance of the (A) silicone rubber particles will not be improved, and in applications such as paints and coatings, the physical properties of the paint film may be reduced.

The aqueous dispersion of the present invention may further contain a water-soluble polymer (D). The water-soluble polymer (D) functions as an aid to the dispersibility and emulsification of component (B), and also increases the viscosity of the aqueous dispersion, thereby inhibiting settling of the silicone rubber particles (A).

Component (D) includes natural water-soluble polymers such as gum arabic, tragacanth gum, galactan, guar gum, carob gum, karaya gum, carrageenan, pectin, agar, quince seed, algae colloid (cassow extract), starch (rice, corn, potato, wheat), plant-based polymers such as glycyrrhizic acid, microbial polymers such as xanthan gum, dextran, succinoglucan, pullulan, animal-based polymers such as collagen, casein, albumin, gelatin; starch-based polymers such as carboxymethyl starch and methylhydroxypropyl starch; methylcellulose, nitrocellulose, ethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, sodium cellulose sulfate, hydroxypropylcellulose, Examples include semi-synthetic water-soluble polymers such as cellulose-based polymers such as cellulose, sodium carboxymethylcellulose (CMC), crystalline cellulose, and cellulose powder; alginate-based polymers such as sodium alginate and propylene glycol alginate; vinyl-based polymers such as polyvinyl alcohol, polyvinyl methyl ether, polyvinylpyrrolidone, carboxyvinyl polymer, and alkyl-modified carboxyvinyl polymer; polyoxyethylene-based polymers such as polyethylene glycol 1500, 4000, and 6000; polyoxyethylene-polyoxypropylene copolymer-based polymers; acrylic polymers such as sodium polyacrylate, polyethyl acrylate, and polyacrylamide; polyethyleneimine; and synthetic water-soluble polymers such as cationic polymers.

The amount of (D) water-soluble polymer is 0 to 5 parts by mass, preferably 0.05 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.1 to 1.5 parts by mass, per 100 parts by mass of component (A). If it is more than the upper limit, the viscosity of the dispersion will be too high, making it difficult to handle.

(C) Water: Water is a dispersion medium for the silicone rubber particles. The amount of water in the aqueous dispersion is 5 to 2,000 parts by mass, and preferably 10 to 100 parts by mass, per 100 parts by mass of the (A) silicone rubber particles.

In addition to the above components (A) to (D), various additives can be blended into the aqueous dispersion of silica-containing silicone rubber particles of the present invention, as needed. Examples include preservatives, pH adjusters, antioxidants, and colorants. It is preferable not to blend anionic surfactants, cationic surfactants, or amphoteric surfactants, as they may not be able to be emulsified in the manufacturing method described below, may form aggregates during the curing reaction, or may destroy the emulsion.

[Method for producing an aqueous dispersion of silica-containing silicone rubber particles]
The aqueous dispersion of silica-containing silicone rubber particles of the present invention is produced by a method comprising the following steps (i) to (iii).
(i) mixing 100 parts by mass of at least one curable organosilicon compound selected from organopolysiloxanes and silanes with 1 to 50 parts by mass of (A-2) hydrophobized silica;
(ii) adding 0.1 to 20 parts by weight of (B) a nonionic surfactant having an HLB of 1.0 to 12.0, 5 to 2,000 parts by weight of (C) water, and optionally 0.05 to 5 parts by weight of (D) a water-soluble polymer to the mixture obtained in (i) and emulsifying the mixture to obtain an oil-in-water emulsion; and (iii) curing the curable organosilicon compound in the oil-in-water emulsion to obtain an aqueous dispersion of silicone rubber particles.

To mix the organopolysiloxane and silane with the hydrophobic treated silica, a kneading machine such as a gate mixer, kneader, pressure kneader, twin-screw mixer, or intensive mixer, or an agitator such as a homodisper or homomixer, can be used.

Mixing can be carried out at room temperature (e.g., 1 to 30°C), but can also be carried out under heating at temperatures below 200°C. The aforementioned organosilicon compound for hydrophobizing the silica or an alkaline catalyst for hydrophobizing the silica can also be added. If an alkaline catalyst is added, a neutralizing agent can be added after mixing, if necessary, to carry out a neutralization reaction.

(A-2) Colloidal silica, in which silica is dispersed in water, cannot be used in place of hydrophobized silica. Because the dispersant is water, this type of colloidal silica does not mix with organopolysiloxane and silane. Furthermore, even if the above colloidal silica is added during the process of emulsifying organopolysiloxane and silane, the silica is hydrophilic and therefore does not enter the organopolysiloxane and silane.

The nonionic surfactant (B) used for emulsification has an HLB of 1.0 to 12.0, preferably 3.0 to 11.5, more preferably 6.0 to 11.0, and even more preferably 6.5 to 10.5. It is preferable not to use anionic surfactants, cationic surfactants, or amphoteric surfactants during emulsification. Emulsification can be carried out using a general emulsifying disperser. Examples include a high-speed rotation centrifugal radial mixer such as a Homodisper; a high-speed rotation shear mixer such as a Homomixer; a high-pressure jet emulsifying disperser such as a homogenizer; a colloid mill; and an ultrasonic emulsifier.

The curing catalyst and radical generator may be mixed with the organopolysiloxane and silane in advance in the above step (i), or may be added after the oil-in-water emulsion is obtained in the above step (ii).
When the silicone rubber particles contain other components such as non-functional silicone oil, inorganic powder (excluding silica), organic powder, and antioxidants, they are preferably mixed with the organopolysiloxane and silane in step (i). The amounts of these components may be adjusted as appropriate within a range that does not impair the properties of the silicone rubber particles of the present invention.

In the method of blending a curing catalyst or radical generator after preparing an emulsion (step (ii) above), if the curing catalyst or radical generator has poor water dispersibility, it is preferable to add it to the emulsion in a state dissolved in a surfactant or to emulsify it with a surfactant. The surfactant used here is preferably nonionic and, more preferably, has a high HLB. The HLB and amount of the nonionic surfactant used in emulsifying the mixture of organopolysiloxane, silane, and hydrophobized silica must be set so that the average HLB is in the range of 1.0 to 12.0. The average HLB is preferably in the range of 3.0 to 11.5, more preferably 6.0 to 11.0, and even more preferably 6.5 to 10.5. If the average HLB is greater than 12.0, the silicone may aggregate or the emulsion may break down during the curing reaction. When using a nonionic surfactant with an HLB greater than 12.0, its HLB should be 15.0 or less, preferably 13.0 or less, and even more preferably 12.5 or less.

In the above step (iii), if curing is performed by an addition reaction or condensation reaction, the reaction may be carried out at room temperature (1 to 30°C), but if the reaction does not go to completion, it may be carried out under heating at less than 100°C.

In the above step (iii), when curing by radical reaction, if a redox initiator is used, heating at less than 100°C is sufficient, and if a photopolymerization initiator is used, irradiation with light such as ultraviolet light is sufficient.

[Method of producing silica-containing silicone rubber particles]
The silica-containing silicone rubber particles of the present invention can be obtained by removing water from the aqueous dispersion of silica-containing silicone rubber particles obtained in the above step (step (iv)).

Water can be removed, for example, by heating the aqueous dispersion under normal or reduced pressure to volatilize it. More specific examples include a method in which the dispersion is left to stand under heating to remove the water, a method in which the dispersion is stirred and fluidized under heating to remove the water, a method in which the dispersion is sprayed and dispersed in a hot air stream as in a spray dryer, and a method using a fluidized heat medium. As a pretreatment for this operation, the particles may be agglomerated by adding an inorganic salt or the like, and then concentrated by filtration separation such as pressure filtration, centrifugation, decantation, or other methods. If necessary, the concentrate may be washed with water, alcohol, or the like.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.
In the examples, the kinematic viscosity is a value measured at 25° C. using a capillary viscometer, and the "%" representing the concentration and content is "% by mass".

[Example 1]
186 g (a-1) of a vinyl group-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s, represented by the following average formula (23): 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s, represented by the following average formula (24):
24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method: 300 m ² /g, hydrophobicity degree: 60) prepared by treating dry silica with hexamethyldisilazane was placed in a 1-liter glass beaker and mixed with stirring at 2,000 rpm using a homomixer.
Next, to the mixture was added 20 g of Sannonik SS-30 (B-1, trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxyethylene alkyl (C ₁₂ H ₂₅ -C ₁₄ H ₂₉ ) ether, HLB = 8.0) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) (amount equivalent to 1.3 parts by weight per 100 parts by weight of the resulting silicone rubber particles) and 300 g of water. The mixture was stirred at 6,000 rpm using a homomixer, resulting in an oil-in-water emulsion and increased viscosity. Stirring was continued for an additional 15 minutes. Next, while stirring at 2,000 rpm, 436 g of water (amount equivalent to 307 parts by weight of water in total per 100 parts by weight of the resulting silicone rubber particles) was added, resulting in a uniform white oil-in-water emulsion.
This emulsion was transferred to a 1-liter glass flask fitted with an anchor-type stirring blade stirrer, and the temperature was adjusted to 20-25°C. After that, a mixed solution of 0.5 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 1.0 g of Finesurf TD-70 (B-2, trade name, manufactured by Aoki Oil & Fat Industries Co., Ltd., polyoxyethylene tridecyl ether, HLB = 12.0) was added with stirring, and the mixture was stirred at the same temperature for 5 hours, yielding an aqueous dispersion of silica-containing silicone rubber particles.
The average HLB of the nonionic surfactant (B) in the aqueous dispersion is 8.2. The amount of the nonionic surfactant is 8.8 parts by mass per 100 parts by mass of the silicone rubber particles.

When the aqueous dispersion was filtered through a 100-mesh screen, the amount of silica-containing silicone rubber particles retained (i.e., the amount of agglomerates) was less than 1.0% of the total amount filtered.

When the silica-containing silicone rubber particles in the aqueous dispersion were observed under an optical microscope, they were found to be spherical, and when the volume average particle size was measured using a particle size distribution analyzer "Multisizer 3" (product name, manufactured by Beckman Coulter, Inc.), it was found to be 6 μm.

The hardness of the silica-containing silicone rubber constituting the silica-containing silicone rubber particles was measured as follows.
The same vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), hydrophobic treated silica (A-2-1), and an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content: 0.5%) as above were mixed in the above-described blending ratio, and the mixture was poured into an aluminum petri dish to a thickness of 10 mm.
After leaving the mixture at 25°C for 24 hours, it was heated in a thermostatic chamber at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber. The hardness of this silicone rubber was measured using a Type A durometer specified in JIS K6253 and found to be 62.

The tensile strength at break and elongation at break of the silica-containing silicone rubber that constitutes the silica-containing silicone rubber particles were measured as follows.
The same vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), hydrophobic treated silica (A-2-1), and an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content: 0.5%) as above were mixed in the blending ratio described above, and the mixture was poured into a polypropylene tray to a thickness of approximately 1 mm.
After leaving the sheet at 25°C for 24 hours, it was heated in a constant temperature bath at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber sheet. This silicone rubber sheet was cut to the shape and dimensions of a dumbbell-shaped No. 3 test piece specified in JIS K6251, and the tensile strength at break and elongation at break were measured according to the methods specified in JIS K6251, finding values of 1.4 MPa and 52%, respectively.

[Examples 2 to 8]
An aqueous dispersion of silica-containing silicone rubber particles was obtained by repeating the steps of Example 1, except that the nonionic surfactant (Sanonic SS-30) used in emulsifying the mixture of vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), and hydrophobic treated silica (A-2-1) was replaced with the nonionic surfactant shown in Table 1.

The resulting aqueous dispersion of silicone rubber particles was evaluated in the same manner as in Example 1.
The average HLB of the nonionic surfactant (B) in the aqueous dispersion is shown in Table 1, and the amount of silica-containing silicone rubber particles retained when the aqueous dispersion was filtered through a 100-mesh screen (i.e., the amount of aggregates) is shown in Table 4.
Table 4 also shows the results of observing the shape of the silica-containing silicone rubber particles in the aqueous dispersion and the results of measuring the volume average particle size.

[Examples 9 to 10]
An aqueous dispersion of silica-containing silicone rubber particles was obtained by repeating the steps of Example 1, except that the 30 g of water-soluble polymer (Cellogen WS-C) used in emulsifying the mixture of vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), and hydrophobic treated silica (A-2-1) in Example 1 was replaced with the water-soluble polymer and amount shown in Table 1.
In the table, D-2 is hydroxypropyl methylcellulose (Metolose 60SH-10000, manufactured by Shin-Etsu Chemical Co., Ltd.).

The resulting aqueous dispersion of silicone rubber particles was evaluated in the same manner as in Example 1.
The average HLB of the nonionic surfactant (B) in the aqueous dispersion is shown in Table 1, and the amount of silica-containing silicone rubber particles retained when the dispersion was filtered through a 100-mesh screen is shown in Table 4. Table 4 also shows the results of observing the shape of the silica-containing silicone rubber particles and the results of measuring the volume average particle size.

[Example 11]
165 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 27 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (a blending amount so that there are 1.15 SiH groups per vinyl group), and 48 g (25.0 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method 300 m ² /g, hydrophobicity degree 60) prepared by treating dry silica with hexamethyldisilazane were charged into a gate mixer and mixed until uniform.
The resulting mixture was mixed with 20 g of Sannonik SS-30 (B-1, trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxyethylene alkyl (C ₁₂ H ₂₅ -C ₁₄ H ₂₉ ) ether, HLB = 8.0) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) (amount equivalent to 1.3 parts by weight per 100 parts by weight of the resulting silicone rubber particles), and 600 g of water. The mixture was placed in a 1-liter glass beaker and stirred at 6,000 rpm using a homomixer. The mixture became oil-in-water and thickened. Stirring was continued for another 15 minutes. Next, while stirring at 2,000 rpm, 136 g of water (amount equivalent to 307 parts by weight of water per 100 parts by weight of the resulting silicone rubber particles) was added, resulting in a uniform white oil-in-water emulsion.
This emulsion was transferred to a 1-liter glass flask equipped with an anchor-type stirring blade stirrer, and the temperature was adjusted to 20-25°C. After that, a mixed solution of 0.5 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 1.0 g of Finesurf TD-70 (B-2, trade name, manufactured by Aoki Oil & Fat Industries Co., Ltd., polyoxyethylene tridecyl ether, HLB = 12.0) was added with stirring, and the mixture was stirred at the same temperature for 5 hours to obtain an aqueous dispersion of silica-containing silicone rubber particles. The average HLB of the nonionic surfactant (B) in the aqueous dispersion was 8.2. The amount of nonionic surfactant was 8.8 parts by mass per 100 parts by mass of silicone rubber particles.

When the aqueous dispersion was filtered through a 100 mesh screen, the amount of silica-containing silicone rubber particles retained (ie, the amount of agglomerates) was less than 1.0 wt % of the total amount filtered.
The shape of the silica-containing silicone rubber particles in the aqueous dispersion was observed under an optical microscope and was found to be spherical, and the volume average particle size was measured using a particle size distribution analyzer "Multisizer 3" (trade name, manufactured by Beckman Coulter, Inc.) and was found to be 3 μm.

The hardness of the silica-containing silicone rubber constituting the silica-containing silicone rubber particles was measured as follows.
The same vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), hydrophobic treated silica (A-2-1), and an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content: 0.5%) as above were mixed in the above-described blending ratio, and the mixture was poured into an aluminum petri dish to a thickness of 10 mm.
After leaving the mixture at 25°C for 24 hours, it was heated in a thermostatic chamber at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber. The hardness of this silicone rubber was measured using a Type A durometer specified in JIS K6253 and found to be 71.

The tensile strength at break and elongation at break of the silica-containing silicone rubber that constitutes the silica-containing silicone rubber particles were measured as follows.
The same vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), hydrophobic treated silica (A-2-1), and an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content: 0.5%) as above were mixed in the blending ratio described above, and the mixture was poured into a polypropylene tray to a thickness of approximately 1 mm.
After leaving the sheet at 25°C for 24 hours, it was heated in a constant temperature bath at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber sheet. This silicone rubber sheet was cut to the shape and dimensions of a dumbbell-shaped No. 3 test piece specified in JIS K6251, and the tensile strength at break and elongation at break were measured according to the methods specified in JIS K6251, finding values of 1.9 MPa and 54%, respectively.

[Example 12]
196 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 32 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (amount to give 1.15 SiH groups per vinyl group), and 12 g (5.3 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-2, specific surface area by BET method 300 m ² /g, hydrophobicity degree 55) prepared by treating dry silica with 1,3-divinyl-1,1,3,3-tetramethyldisilazane were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer.
Next, a mixture of 20 g of Sannonik SS-30 (B-1, trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxyethylene alkyl (C ₁₂ H ₂₅ -C ₁₄ H ₂₉ ) ether, HLB = 8.0) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) (amount equivalent to 1.3 parts by weight per 100 parts by weight of the resulting silicone rubber particles) and 300 g of water was added, and the mixture was stirred at 6,000 rpm using a homomixer. The mixture became oil-in-water and thickening was observed. Stirring was continued for a further 15 minutes. Next, while stirring at 2,000 rpm, 436 g of water (amount equivalent to 307 parts by weight of water in total per 100 parts by weight of the resulting silicone rubber particles) was added, resulting in a uniform white oil-in-water emulsion.
This emulsion was transferred to a 1-liter glass flask equipped with an anchor-type stirring blade stirrer, and the temperature was adjusted to 20-25°C. After this, a mixed solution of 0.5 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 1.0 g of Finesurf TD-70 (B-2, trade name, manufactured by Aoki Oil & Fat Industries Co., Ltd., polyoxyethylene tridecyl ether, HLB = 12.0) was added with stirring, and the mixture was stirred at the same temperature for 5 hours to obtain an aqueous dispersion of silica-containing silicone rubber particles. The average HLB of the nonionic surfactant in the aqueous dispersion was 8.2. The amount of nonionic surfactant was 8.8 parts by mass per 100 parts by mass of silicone rubber particles.

When the aqueous dispersion was filtered through a 100 mesh screen, the amount of silica-containing silicone rubber particles retained (ie, the amount of agglomerates) was less than 1.0 wt % of the total amount filtered.
The shape of the silica-containing silicone rubber particles in the aqueous dispersion was observed under an optical microscope and was found to be spherical, and the volume average particle size was measured using a particle size distribution analyzer "Multisizer 3" (trade name, manufactured by Beckman Coulter, Inc.) and was found to be 7 μm.

The hardness of the silica-containing silicone rubber constituting the silica-containing silicone rubber particles was measured as follows.
The same vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), hydrophobic treated silica (A-2-2), and an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) as above were mixed in the above-described blending ratio, and the mixture was poured into an aluminum petri dish to a thickness of 10 mm.
After leaving the mixture at 25°C for 24 hours, it was heated in a thermostatic chamber at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber. The hardness of this silicone rubber was measured using a Type A durometer specified in JIS K6253 and found to be 57.

The tensile strength at break and elongation at break of the silica-containing silicone rubber that constitutes the silica-containing silicone rubber particles were measured as follows.
The same vinyl group-containing dimethylpolysiloxane (a-1), methylhydrogenpolysiloxane (b-1), hydrophobic treated silica (A-2-2), and an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content: 0.5%) as above were mixed in the blending ratio described above, and the mixture was poured into a polypropylene tray to a thickness of approximately 1 mm.
After leaving the sheet at 25°C for 24 hours, it was heated in a constant temperature bath at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber sheet. This silicone rubber sheet was cut to the shape and dimensions of a dumbbell-shaped No. 3 test piece specified in JIS K6251, and the tensile strength at break and elongation at break were measured according to the methods specified in JIS K6251, finding values of 1.2 MPa and 48%, respectively.

[Example 13]
205 g (c-1) of a hydroxyl-containing dimethylpolysiloxane having a kinematic viscosity of 690 mm ² /s, represented by the following average formula (25):
11 g of phenyltriethoxysilane (d-1, a blending amount giving 6.7 ethoxy groups per hydroxyl group) and 24 g of hydrophobized silica (A-2-1, specific surface area by BET method: 300 m ² /g, hydrophobicity degree: 60) prepared by treating dry silica with hexamethyldisilazane (amount giving 11.4 parts by mass per 100 parts by mass of the resulting silicone rubber) were charged into a gate mixer and mixed until uniform.
The resulting mixture was mixed with 20 g of Sannonik SS-30 (B-1, trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxyethylene alkyl (C ₁₂ H ₂₅ -C ₁₄ H ₂₉ ) ether, HLB = 8.0) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) (amount equivalent to 1.4 parts by weight per 100 parts by weight of the resulting silicone rubber particles), and 600 g of water. A 1-liter glass beaker was charged with the mixture and stirred at 6,000 rpm using a homomixer. The mixture became oil-in-water and thickened. Stirring was continued for 15 minutes. Next, while stirring at 2,000 rpm, 135 g of water (amount equivalent to 312 parts by weight of the total amount of water per 100 parts by weight of the resulting silicone rubber particles) was added, resulting in a uniform white oil-in-water emulsion.
This emulsion was transferred to a 1-liter glass flask equipped with an anchor-type stirring blade stirrer, and after adjusting the temperature to 20-25°C, a mixed solution of 1.0 g of dioctyltin dilaurate and 1.0 g of Finesurf TD-70 (D-2, trade name, manufactured by Aoki Oil & Fat Industries Co., Ltd., polyoxyethylene tridecyl ether, HLB = 12.0) was added, and the mixture was stirred at the same temperature for 24 hours to obtain an aqueous dispersion of silica-containing silicone rubber particles. The average HLB of the nonionic surfactant in the aqueous dispersion was 8.2. The amount of nonionic surfactant was 10.0 parts by mass per 100 parts by mass of silicone rubber particles.

When the aqueous dispersion was filtered through a 100 mesh screen, the amount of silica-containing silicone rubber particles retained (ie, the amount of agglomerates) was less than 1.0 wt % of the total amount filtered.
The shape of the silica-containing silicone rubber particles in the aqueous dispersion was observed under an optical microscope and was found to be spherical, and the volume average particle size was measured using a particle size distribution analyzer "Multisizer 3" (trade name, manufactured by Beckman Coulter, Inc.) and was found to be 4 μm.

The hardness of the silica-containing silicone rubber that makes up the silica-containing silicone rubber particles was measured as follows. The same hydroxyl-containing dimethylpolysiloxane (c-1), phenyltriethoxysilane (d-1), hydrophobized silica (A-2-1), and dioctyltin dilaurate as above were mixed in the ratios described above and poured into an aluminum petri dish to a thickness of 10 mm. After leaving at 25°C for 48 hours, it was heated in a thermostatic chamber at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber. The hardness of this silicone rubber was measured using a Type A durometer specified in JIS K6253, and was found to be 40.

The tensile strength at break and elongation at break of the silica-containing silicone rubber that constitutes the silica-containing silicone rubber particles were measured as follows.
The same hydroxyl group-containing dimethylpolysiloxane (c-1), phenyltriethoxysilane (d-1), hydrophobic treated silica (A-2-1), and dioctyltin dilaurate as above were mixed in the above-described mixing ratio, and the mixture was poured into a polypropylene tray to a thickness of approximately 1 mm.
After leaving the sheet at 25°C for 48 hours, it was heated in a constant temperature bath at 50°C for 1 hour to obtain a non-sticky silica-containing silicone rubber sheet. This silicone rubber sheet was cut to the shape and dimensions of a dumbbell-shaped No. 3 test piece specified in JIS K6251, and the tensile strength at break and elongation at break were measured according to the methods specified in JIS K6251, finding values of 1.2 MPa and 190%, respectively.

[Example 14]
216 g (e-1) of a methacryloyl group-containing dimethylpolysiloxane having a kinematic viscosity of 180 mm ² /s, represented by the following average formula (26):
24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-3, specific surface area by BET method: 200 m ² /g, hydrophobicity degree: 48) prepared by treating dry silica with dimethyldichlorosilane, and 2 g of 2-hydroxy-2-methyl-1-phenyl-propan-1-one were charged into a gate mixer and mixed until uniform.
The resulting mixture was mixed with 20 g of Sannonik SS-30 (B-1, trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxyethylene alkyl (C ₁₂ H ₂₅ -C ₁₄ H ₂₉ ) ether, HLB = 8.0) (amount equivalent to 8.3 parts by mass per 100 parts by mass of the resulting silicone rubber particles) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) (amount equivalent to 1.3 parts by mass per 100 parts by mass of the resulting silicone rubber particles), and 600 g of water (C) were added to a 1-liter glass beaker and stirred at 6,000 rpm using a homomixer. The mixture became oil-in-water and thickened. Stirring was continued for another 15 minutes. Next, 135 g of water (amount such that the total amount of water was 306 parts by mass per 100 parts by mass of the resulting silicone rubber particles) was added while stirring at 2,000 rpm, resulting in a uniform white oil-in-water emulsion.
This emulsion was transferred to a 1-liter glass flask equipped with an anchor-type stirring blade stirrer, and after adjusting the temperature to 20-25°C, the probe of an LED light source for photochemical reactions (356 nm wavelength, 507 mW) was inserted into the emulsion and irradiation began. Irradiation was continued with stirring at the same temperature for 4 hours, yielding an aqueous dispersion of silica-containing silicone rubber particles.

When the aqueous dispersion was filtered through a 100 mesh screen, the amount of silica-containing silicone rubber particles retained (ie, the amount of agglomerates) was less than 1.0 wt % of the total amount filtered.
The shape of the silica-containing silicone rubber particles in the aqueous dispersion was observed under an optical microscope and was found to be spherical, and the volume average particle size was measured using a particle size distribution analyzer "Multisizer 3" (trade name, manufactured by Beckman Coulter, Inc.) and was found to be 4 μm.

The hardness of the silica-containing silicone rubber constituting the silica-containing silicone rubber particles was measured as follows.
The same methacryloyl group-containing dimethylpolysiloxane (e-1), hydrophobized silica (A-2-3), and 2-hydroxy-2-methyl-1-phenyl-propan-1-one as above were mixed in the above-described compounding ratio and poured into an aluminum petri dish to a thickness of 10 mm. Irradiation was performed for 5 minutes using a UV-LED irradiator (wavelength 365 nm, 154 mW) under a nitrogen atmosphere to obtain a non-sticky silica-containing silicone rubber. The hardness of this silicone rubber was measured using a Type A durometer specified in JIS K6253 and found to be 48.

The tensile strength at break and elongation at break of the silica-containing silicone rubber that constitutes the silica-containing silicone rubber particles were measured as follows.
The same methacryloyl group-containing dimethylpolysiloxane (e-1), hydrophobized silica (A-2-3), and 2-hydroxy-2-methyl-1-phenyl-propan-1-one as above were mixed in the ratios described above and poured into a polypropylene tray to a thickness of approximately 1 mm. Irradiation was performed for 5 minutes using a UV-LED irradiator (wavelength 365 nm, 154 mW) under a nitrogen atmosphere to obtain a non-sticky silica-containing silicone rubber sheet. This silicone rubber sheet was cut to the shape and dimensions of a dumbbell-shaped No. 3 test piece specified in JIS K6251, and the tensile strength at break and elongation at break were measured according to the methods specified in JIS K6251, finding values of 1.5 MPa and 190%, respectively.

[Comparative Example 1]
186 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above, in an amount such that there were 1.14 SiH groups per vinyl group, and 24 g (A-2-1) of hydrophobized silica (A-2-1, specific surface area measured by the BET method: 300 m ² /g, hydrophobicity degree: 60) prepared by treating dry silica with hexamethyldisilazane (an amount equivalent to 11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer.
Next, to this mixture was added a mixture of 20 g of Sannonic SS-70 (B-10, trade name, manufactured by Sanyo Chemical Industries, Ltd., polyoxyethylene alkyl (C ₁₂ H ₂₅ -C ₁₄ H ₂₉ ) ether, HLB = 12.1) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) and 300 g of water (C), and the mixture was stirred at 6,000 rpm using a homomixer, resulting in an oil-in-water emulsion and an increase in viscosity. Stirring was continued for an additional 15 minutes. Next, 436 g of water was added while stirring at 2,000 rpm, and a uniform white oil-in-water emulsion was obtained.
This emulsion was transferred to a 1-liter glass flask equipped with an anchor-type stirring blade stirrer, and the temperature was adjusted to 20-25°C. Then, with stirring, a mixed solution of 0.5 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 1.0 g of Finesurf TD-70 (B-2, trade name, manufactured by Aoki Oil & Fat Industries Co., Ltd., polyoxyethylene tridecyl ether, HLB = 12.0) was added. Stirring was continued at the same temperature, and after a while, the emulsion particles all began to aggregate and the emulsion was destroyed.

[Comparative Example 2]
186 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (a blending amount so that there are 1.14 SiH groups per vinyl group), and 24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method 300 m ² /g, hydrophobicity degree 60) prepared by treating dry silica with hexamethyldisilazane were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer.
Next, to this mixture was added a mixture of 22 g of Tergitol TMN-6 <90% aqueous solution> (B-11, trade name, manufactured by Dow Chemical Japan, Ltd., 90% aqueous solution of polyoxyethylene trimethyl nonyl ether, HLB = 13.1) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethyl cellulose), and 298 g of water, and the mixture was stirred at 6,000 rpm using a homomixer, but the mixture of polysiloxane and hydrophobic treated silica did not disperse at all in the water and could not be emulsified.

[Comparative Example 3]
186 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (a blending amount so that there are 1.14 SiH groups per vinyl group), and 24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method 300 m ² /g, hydrophobicity degree 60) prepared by treating dry silica with hexamethyldisilazane were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer.
Next, to this mixture was added a mixture of 20 g of Emulgen 123P (B-12, trade name, manufactured by Kao Corporation, polyoxyethylene lauryl ether, HLB = 16.9) and 3 g of Cellogen WS-C (D-1, trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium carboxymethylcellulose) and 300 g of water, and the mixture was stirred at 6,000 rpm using a homomixer. However, the mixture of polysiloxane and hydrophobic treated silica did not disperse in the water at all and could not be emulsified.

[Comparative Example 4]
186 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (a blending amount so that there are 1.14 SiH groups per vinyl group), and 24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method 300 m ² /g, hydrophobicity degree 60) prepared by treating dry silica with hexamethyldisilazane were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer.
Next, 20 g of Nikkol SLS (B-13, trade name, manufactured by Nikko Chemicals Co., Ltd., anionic surfactant, sodium lauryl sulfate) and 300 g of water (C) were added, and the mixture was stirred at 6,000 rpm using a homomixer. However, the mixture of polysiloxane and hydrophobic treated silica did not disperse in the water at all, and emulsification was not possible.

[Comparative Example 5]
186 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (a blending amount so that there are 1.14 SiH groups per vinyl group), and 24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method 300 m ² /g, hydrophobicity degree 60) prepared by treating dry silica with hexamethyldisilazane were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer.
Next, 67 g of Nissan Cation BB (B-14, trade name, manufactured by NOF Corporation, cationic surfactant, 30% aqueous solution of dodecyltrimethylammonium chloride) and 253 g of water were added, and the mixture was stirred at 6,000 rpm using a homomixer. However, the mixture of polysiloxane and hydrophobic treated silica did not disperse in the water at all, and emulsification was not possible.

[Comparative Example 6]
186 g (a-1) of a vinyl-containing dimethylpolysiloxane having a kinematic viscosity of 55 mm ² /s and represented by the average formula (23) above, 30 g (b-1) of a methylhydrogenpolysiloxane having a kinematic viscosity of 30 mm ² /s and represented by the average formula (24) above (a blending amount so that there are 1.14 SiH groups per vinyl group), and 24 g (11.1 parts by mass per 100 parts by mass of the resulting silicone rubber) of hydrophobized silica (A-2-1, specific surface area by BET method 300 m ² /g, hydrophobicity degree 60) prepared by treating dry silica with hexamethyldisilazane were charged into a 1-liter glass beaker and mixed by stirring at 2,000 rpm using a homomixer. Next, 65 g of Amphitol 20BS (B-15, trade name, manufactured by Kao Corporation, amphoteric surfactant, 31% aqueous solution of lauryldimethylaminoacetate betaine) and 255 g of water (C) were added, and the mixture was stirred at 6,000 rpm using a homomixer. However, the mixture of polysiloxane and hydrophobic treated silica did not disperse in the water at all, and emulsification was not possible.

*In Comparative Examples 2 to 6, the mixture of organopolysiloxane and hydrophobic treated silica did not disperse in water and did not emulsify.

[Example 15]
The water dispersion of silica-containing silicone rubber particles obtained in Example 1 was volatilized using a spray dryer at an inlet temperature of 150°C and an outlet temperature of 80°C to remove water, yielding silica-containing silicone rubber particles.
The silica-containing silicone rubber particles obtained were not sticky, and when observed under an electron microscope, they were found to be spherical. No silica was observed, which suggests that silica is present within the silicone rubber particles.

[Example 16]
The water dispersion of silica-containing silicone rubber particles obtained in Example 13 was subjected to evaporation and removal of water using a spray dryer at an inlet temperature of 150°C and an outlet temperature of 80°C, yielding silica-containing silicone rubber particles.
The silica-containing silicone rubber particles obtained were not sticky, and when observed under an electron microscope, they were found to be spherical. No silica was observed, which suggests that silica is present within the silicone rubber particles.

[Example 17]
The water from the aqueous dispersion of silica-containing silicone rubber particles obtained in Example 14 was volatilized using a spray dryer at an inlet temperature of 150°C and an outlet temperature of 80°C to obtain silica-containing silicone rubber particles.
The silica-containing silicone rubber particles obtained were not sticky, and when observed under an electron microscope, they were found to be spherical. No silica was observed, which suggests that silica is present within the silicone rubber particles.

As described above, the present invention uses a low-HLB nonionic surfactant in the method for producing silicone rubber particles containing hydrophobically treated silica, which enables a mixture of organopolysiloxane and hydrophobically treated silica to be successfully emulsified in water. Because the silicone rubber particles of the present invention contain silica within the particles, they can have high strength.

The silicone rubber particles of the present invention have high mechanical strength, and aqueous dispersions of these silicone rubber particles are useful for paints and coatings that are subject to friction.

Claims (18)

(A-1) silicone rubber particles containing 1 to 50 parts by mass of hydrophobized silica (A-2) per 100 parts by mass of silicone rubber, the silicone rubber particles having a volume average particle size of 0.5 to 100 μm and being spherical;
The silicone rubber particles (A-2) are characterized in that the hydrophobized silica is hydrophobized with at least one group selected from a triorganosilyl group, a diorganosilyl group, and a monoorganosilyl group, or a partial hydrolysis condensate of an organochlorosilane, a partial hydrolysis condensate of an organoalkoxysilane, an organopolysiloxane, and an organohydrogenpolysiloxane , and has a degree of hydrophobicity of 40 or more as indicated by methanol wettability , the degree of hydrophobicity being expressed as the methanol concentration (volume %) at which the powder is completely dispersed in an aqueous methanol solution under stirring . The silicone rubber particles according to claim 1, wherein the (A-1) silicone rubber is an addition reaction cured product of (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms. The silicone rubber particles according to claim 1, wherein the (A-1) silicone rubber is a cured product obtained by a condensation reaction between (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom and (d) a silane having a hydrolyzable group bonded to a silicon atom. The silicone rubber particles according to claim 1, wherein the (A-1) silicone rubber is a radical reaction cured product of (e) an organopolysiloxane having a radical polymerization reactive group. The silicone rubber particles according to any one of claims 1 to 4, wherein the hydrophobized silica is hydrophilic silica that has been hydrophobized with at least one silane or silazane selected from trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane, hexamethyldisilazane, and 1,3-divinyl-1,1,3,3-tetramethyldisilazane. The silicone rubber particles according to any one of claims 1 to 4, wherein the silicone rubber particles have a tensile strength at break of 0.5 to 10 MPa measured using the method specified in JIS K6251. (A) (A-1) 100 parts by mass of silicone rubber particles (A-2) containing 1 to 50 parts by mass of hydrophobic treated silica per 100 parts by mass of silicone rubber;
An aqueous dispersion of silicone rubber particles, comprising: (B) 0.1 to 20 parts by mass of a nonionic surfactant having an HLB of 1.0 to 12.0; and (C) 5 to 2,000 parts by mass of water,
the silicone rubber particles have a volume average particle size of 0.5 to 100 μm and are spherical; the hydrophobized silica is hydrophobized with at least one group selected from a triorganosilyl group, a diorganosilyl group, and a monoorganosilyl group, or a partial hydrolysis condensate of an organochlorosilane, a partial hydrolysis condensate of an organoalkoxysilane, an organopolysiloxane, and an organohydrogenpolysiloxane; and has a hydrophobicity degree of 40 or more as indicated by methanol wettability , the hydrophobicity degree being represented by the methanol concentration (volume %) at which the powder is completely dispersed in an aqueous methanol solution under stirring ;
The aqueous dispersion. The aqueous dispersion according to claim 7, wherein the silicone rubber is an addition reaction cured product of (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms. The aqueous dispersion according to claim 7, wherein the silicone rubber is a cured product obtained by a condensation reaction between (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom and (d) a silane having a hydrolyzable group bonded to a silicon atom. The aqueous dispersion according to claim 7, wherein the silicone rubber is a radical reaction-cured product of (e) an organopolysiloxane having a radical polymerization reactive group. The aqueous dispersion according to any one of claims 7 to 10, further comprising (D) a water-soluble polymer in an amount of 0.05 to 5 parts by mass per 100 parts by mass of the silicone rubber particles. The aqueous dispersion according to any one of claims 7 to 10, wherein the hydrophobized silica is hydrophilic silica that has been hydrophobized with at least one silane or silazane selected from trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane, hexamethyldisilazane, and 1,3-divinyl-1,1,3,3-tetramethyldisilazane. A method for producing silicone rubber particles containing hydrophobized silica, comprising the steps of:
(i) mixing 100 parts by mass of at least one curable organosilicon compound selected from organopolysiloxanes and silanes with 1 to 50 parts by mass of (A-2) hydrophobized silica;
(ii) adding 0.1 to 20 parts by mass of (B) a nonionic surfactant having an HLB of 1.0 to 12.0, 5 to 2,000 parts by mass of (C) water, and optionally 0.05 to 5 parts by mass of (D) a water-soluble polymer to the mixture obtained in (i) and emulsifying the mixture to obtain an oil-in-water emulsion;
(iii) curing the curable organosilicon compound in the oil-in-water emulsion to obtain an aqueous dispersion of silicone rubber particles; and (iv) removing water from the aqueous dispersion obtained in step (iii) to obtain silicone rubber particles.
the silicone rubber particles have a volume average particle size of 0.5 to 100 μm and are spherical; the hydrophobized silica is hydrophobized with at least one group selected from a triorganosilyl group, a diorganosilyl group, and a monoorganosilyl group, or a partial hydrolysis condensate of an organochlorosilane, a partial hydrolysis condensate of an organoalkoxysilane, an organopolysiloxane, and an organohydrogenpolysiloxane; and has a hydrophobicity degree of 40 or more as indicated by methanol wettability , the hydrophobicity degree being represented by the methanol concentration (volume %) at which the powder is completely dispersed in an aqueous methanol solution under stirring ;
The manufacturing method. A method for producing an aqueous dispersion of silicone rubber particles containing hydrophobized silica, comprising the steps of:
(i) mixing 100 parts by mass of at least one curable organosilicon compound selected from organopolysiloxanes and silanes with 1 to 50 parts by mass of (A-2) hydrophobized silica;
(ii) adding 0.1 to 20 parts by weight of (B) a nonionic surfactant having an HLB of 1.0 to 12.0, 5 to 2,000 parts by weight of (C) water, and optionally 0.05 to 5 parts by weight of (D) a water-soluble polymer to the mixture obtained in (i) and emulsifying the mixture to obtain an oil-in-water emulsion; and (iii) curing the curable organosilicon compound in the oil-in-water emulsion to obtain an aqueous dispersion of silicone rubber particles,
the silicone rubber particles have a volume average particle size of 0.5 to 100 μm and are spherical; the hydrophobized silica is hydrophobized with at least one group selected from a triorganosilyl group, a diorganosilyl group, and a monoorganosilyl group, or a partial hydrolysis condensate of an organochlorosilane, a partial hydrolysis condensate of an organoalkoxysilane, an organopolysiloxane, and an organohydrogenpolysiloxane; and has a hydrophobicity degree of 40 or more as indicated by methanol wettability , the hydrophobicity degree being represented by the methanol concentration (volume %) at which the powder is completely dispersed in an aqueous methanol solution under stirring ;
The manufacturing method. The manufacturing method according to claim 13 or 14, wherein the hydrophobized silica is obtained by hydrophobizing hydrophilic silica with at least one silane or silazane selected from trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane, hexamethyldisilazane, and 1,3-divinyl-1,1,3,3-tetramethyldisilazane. The manufacturing method according to claim 13 or 14, wherein the curable organosilicon compound is (a) an organopolysiloxane having alkenyl groups and (b) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms. The manufacturing method according to claim 13 or 14, wherein the curable organosilicon compound is (c) an organopolysiloxane having a hydroxyl group or a hydrolyzable group bonded to a silicon atom, and (d) a silane having a hydrolyzable group bonded to a silicon atom. The manufacturing method according to claim 13 or 14, wherein the curable organosilicon compound is (e) an organopolysiloxane having a radical polymerization reactive group.