JP2024165522A - Method for producing composite particles - Google Patents

Abstract

To provide a method for producing composite particles in which multiple core particles are not contained in each composite particle, the shapes and particle diameters of the core particles are mostly maintained without strong aggregation or fixation of the particles, and substantially all of the added silicone rubber adheres to the surfaces of substantially all of the core particles.SOLUTION: A method for producing composite particles in each of which a silicone rubber adheres to the surface of a core particle comprises: a step in which a curable liquid silicone composition is emulsified to make an oil-in-water emulsion, and is subsequently cured to produce an aqueous dispersion of spherical silicone rubber particles; a step in which core particles, the aqueous dispersion, a cationic surfactant and water are mixed to have the silicone rubber particles adsorbed to the surfaces of the core particles; and a step in which water is volatilized and removed from the mixed liquid, thereby fixing the silicone rubber particles to the surfaces of the core particles. In the mixed liquid, the content of the core particles is 1-100 pts.mass per 100 pts.mass of water, and the content of the spherical silicone rubber particles is 0.1-25 pts.mass per 100 pts.mass of the core particles.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing composite particles.

Various powder treatments are used to obtain the functions required for makeup cosmetics such as foundations and makeup bases. Powders coated with silicone rubber have been proposed, which are said to have light diffusing properties that improve the natural finish, excellent adhesion to the skin, and a soft, moist feel. In powder cosmetics, they are also said to have excellent drop stability.

Several methods have been proposed for producing particles in which silicone rubber is attached and coated onto the surface of core particles.

Patent Document 1 proposes a method of grinding and mixing silica and silicone rubber, but because the silica particles that serve as core particles are ground, it is not possible to obtain particles that maintain their original shape and particle size. In other words, it is not possible to obtain particles with a specific shape such as a sphere, plate, or rod, and it is also difficult to control the particle size.

Patent Documents 2 and 3 propose a method of mixing core particles with a curable silicone that becomes silicone rubber, and then curing the silicone; however, all or some of the particles have a structure in which multiple core particles exist within the particle, which results in a large particle size, making it difficult to maintain the shape of the core particles and control the particle size. Furthermore, if the proportion of silicone is low, it is difficult to coat all of the core particles.

Patent Document 4 proposes a method in which an aqueous dispersion of silica particles and a curable silicone that will become silicone rubber are emulsified and dispersed in water, and then the silicone is cured. However, the particles obtained in powder form have a structure that contains multiple silica particles that will become core particles, and the content of silicone rubber is high, making it difficult for the properties of the core particles to be expressed.

Patent Document 5 proposes a method of spray-drying a mixture of inorganic particles and an emulsion of a curable silicone that becomes silicone rubber, while curing the silicone at the same time; however, this method can result in particles that contain multiple inorganic particles that become core particles, or particles that consist only of uncoated silicone rubber.

Patent Document 6 proposes a method in which core particles are mixed with silicone rubber particles dispersed in a dispersion medium, and then the dispersion medium is distilled off. However, since the particles aggregate when the dispersion medium is distilled off, it becomes difficult to maintain the shape of the core particles and control the particle size.

Patent Document 7 proposes a method in which a crosslinking agent is added to a mixture of core particles and an emulsion of slightly crosslinked silicone, then the mixture is centrifuged to form a cake-like material, which is then dried and cured into rubber at the same time. However, the core particles harden together during curing, and it is difficult to completely loosen them, making it difficult to maintain the shape of the core particles and control their particle size.

Japanese Patent Application Publication No. 8-3451 Japanese Patent Application Publication No. 3-294357 JP 2017-214565 A Japanese Patent Application Publication No. 3-281536 Japanese Patent Application Publication No. 5-32914 JP 2010-163375 A International Publication No. WO2018/084176

In view of the above circumstances, the present invention aims to provide a method for producing composite particles in which silicone rubber is attached to the surface of a core particle, in which the composite particles do not contain multiple core particles, the particles do not strongly aggregate or adhere to each other, the shape and particle size of the core particles are largely maintained, and substantially all of the blended silicone rubber is attached to the surface of substantially all of the core particles.

In order to solve the above problems, the present invention provides
A method for producing composite particles comprising adhering silicone rubber to the surface of core particles having a volume average particle size of 1 to 50 μm, comprising the steps of:
(i) emulsifying a curable liquid silicone composition with a surfactant to prepare an oil-in-water emulsion, and then curing the curable liquid silicone composition to prepare an aqueous dispersion of silicone rubber spherical particles having a volume average particle size of 50 to 1,000 nm;
(ii) mixing the core particles, the aqueous dispersion of the silicone rubber spherical particles prepared in step (i), a cationic surfactant, and water to adsorb the silicone rubber particles onto the surfaces of the core particles, thereby preparing a mixture containing the core particles having the silicone rubber particles adsorbed thereon; and
(iii) removing by volatilization water contained in the mixed liquid containing the core particles having the silicone rubber particles adsorbed thereon, prepared in step (ii), and fixing the silicone rubber particles adsorbed on the surfaces of the core particles, wherein the amount of the core particles per 100 parts by mass of water contained in the mixed liquid prepared in step (ii) is in the range of 1 to 100 parts by mass, the amount of the silicone rubber spherical particles per 100 parts by mass of the core particles is in the range of 0.1 to 25 parts by mass, and the amount of the cationic surfactant per 100 parts by mass of the water is in the range of 0.02 to 0.9 parts by mass.

This method of manufacturing composite particles makes it possible to produce composite particles in which the composite particles do not contain multiple core particles, the particles do not strongly aggregate or adhere to each other, the shape and particle size of the core particles are largely maintained, and almost all of the compounded silicone rubber adheres to the surface of almost all of the core particles.

The core particles may be made of at least one of inorganic particles and organic particles.

In this way, the method for producing composite particles of the present invention can be applied to either inorganic particles or organic particles as core particles, or they may be inorganic-organic composite particles, and one type can be used alone or two or more types can be used in appropriate combination.

The silicone rubber spherical particles preferably have a rubber hardness in the range of 5 to 95, as measured using a Type A durometer as specified in JIS K6253.

If the rubber hardness is 5 or more, it will have low and good cohesion, and when used in cosmetics, it will not cause a decrease in the slipperiness or spread of the cosmetics, or cause twisting. Also, if the rubber hardness is 95 or less, it will be possible to impart good adhesion to the skin, a soft and moist feel, and drop stability to the cosmetics when used in cosmetics.

The present invention makes it possible to produce composite particles in which the core particles do not contain multiple core particles, the particles do not strongly aggregate or adhere to each other, the shape and particle size of the core particles are largely maintained, and substantially all of the silicone rubber is attached to the surface of substantially all of the core particles. Furthermore, when the composite particles produced by the production method of the present invention are incorporated into cosmetics, they can improve the natural finish due to their light diffusion properties, have excellent adhesion to the skin, provide a soft and moist feel, and, in the case of powder cosmetics, can have excellent drop stability.

1 is an electron microscope photograph of the composite particles obtained in Example 6. 1 is an electron microscope photograph of the composite particles obtained in Example 7. 1 is an electron microscope photograph of the composite particles obtained in Example 8. 1 is an electron microscope photograph of the composite particles obtained in Example 9. 1 is an electron microscope photograph of the composite particles obtained in Example 10. 1 is an electron microscope photograph of the composite particles obtained in Example 11. 1 is an electron microscope photograph of the composite particles obtained in Example 12. 1 is an electron microscope photograph of cellulose particles used in Examples and Comparative Examples. 1 is an electron microscope photograph of the composite particles obtained in Example 13. 1 is an electron microscope photograph of the composite particles obtained in Example 18. 1 is an electron microscope photograph of silica particles used in Examples and Comparative Examples.

As a result of extensive research into the above-mentioned problems, the inventors discovered that the above-mentioned objectives could be achieved by adsorbing silicone rubber particles onto the surface of core particles in an aqueous solution of a cationic surfactant and then removing the water, thus completing the present invention.

The present invention will be described in detail below.
[Composite particles]
The composite particles produced by the method for producing composite particles of the present invention are composite particles having silicone rubber attached to the surface of a core particle.

Most composite particles have a structure in which there is only one core particle. That they have this structure can be confirmed by comparative observation of the raw core particle and the manufactured composite particle under an electron microscope. If the shape and size of the composite particle are roughly the same as the core particle, it is determined to have the above structure.

When particles are observed overlapping under an electron microscope, it is difficult to distinguish whether they are separate particles or have stuck together to form a single particle. In other words, it is difficult to distinguish whether the number of core particles in a composite particle is one structure, or whether multiple structural particles are stuck together to form multiple core particles within a particle. In such cases, this can be confirmed by measuring the particle size. If the shape of a particle size distribution diagram with particle size on the horizontal axis and frequency on the vertical axis is roughly the same as that of the core particle, it is determined that the number of core particles in the composite particle is one structure.

The core particles may be inorganic particles, organic particles, or inorganic-organic composite particles, and may be used alone or in appropriate combination of two or more types. Particles that are substantially usable in cosmetics and particles of any particle size range may be used. In addition, as long as the geometric form is one that is normally used in cosmetics, it may be any shape such as spherical, polyhedral, spindle-shaped, needle-shaped, or plate-shaped, and may be either non-porous or porous.

The volume average particle size of the core particles is in the range of 1 to 50 μm, and preferably 2 to 30 μm. If the particle size is 1 μm or more, it provides a silky feel when used and smoothness, as well as extensibility, while if it is 50 μm or less, it does not feel rough. The volume average particle size is measured by the Coulter counter method (electrical resistance method).

Inorganic particles include particles of titanium oxide, titanium mica, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, calcium sulfate, magnesium sulfate, calcium carbonate, magnesium carbonate, talc, cleaved talc, mica, kaolin, sericite, muscovite, synthetic mica, phlogopite, lepidolite, biotite, lithia mica, silicic acid, silica (silicon dioxide), hydrated silicon dioxide, aluminum silicate, magnesium silicate, aluminum magnesium silicate, calcium silicate, barium silicate, strontium silicate, metal tungstate, hydroxyapatite, vermiculite, higilite, bentonite, montmorillonite, hectorite, zeolite, ceramics, secondary calcium phosphate, alumina, aluminum hydroxide, boron nitride, boron nitride, and glass.

Further examples include inorganic pigments, specific examples of which include inorganic red pigments such as iron oxide, iron hydroxide, and iron titanate; inorganic brown pigments such as γ-iron oxide; inorganic yellow pigments such as yellow iron oxide and ochre; inorganic black pigments such as black iron oxide and carbon black; inorganic purple pigments such as manganese violet and cobalt violet; inorganic green pigments such as chromium hydroxide, chromium oxide, cobalt oxide, and cobalt titanate; inorganic blue pigments such as iron blue and ultramarine; colored pigments such as lakes made from tar-based pigments and lakes made from natural pigments; pearl pigments such as titanium oxide-coated mica, titanium oxide-coated mica, bismuth oxychloride, titanium oxide-coated bismuth oxychloride, titanium oxide-coated talc, fish scale foil, and titanium oxide-coated colored mica; and metal powder pigments such as aluminum powder, copper powder, and stainless steel powder.

Organic resin particles include particles of polyethylene; polypropylene; polystyrene; divinylbenzene resin; polyvinyl chloride; methacrylic resin; polytetrafluoroethylene; methacrylic-styrene copolymer; polyamide; polycarbonate; polyesters such as polyethylene terephthalate, polybutylene succinate, polyhydroxybutyric acid, and polycaprolactone; cellulose; cellulose derivatives; phenolic resin; melamine resin; benzoguanamine resin; epoxy resin; and polyurethane.

Specific examples of organic dyes include tar dyes such as Red No. 3, Red No. 104, Red No. 106, Red No. 201, Red No. 202, Red No. 204, Red No. 205, Red No. 220, Red No. 226, Red No. 227, Red No. 228, Red No. 230, Red No. 401, Red No. 505, Yellow No. 4, Yellow No. 5, Yellow No. 202, Yellow No. 203, Yellow No. 204, Yellow No. 401, Blue No. 1, Blue No. 2, Blue No. 201, Blue No. 404, Green No. 3, Green No. 201, Green No. 204, Green No. 205, Orange No. 201, Orange No. 203, Orange No. 204, Orange No. 206, and Orange No. 207; and natural dyes such as carminic acid, laccaic acid, carthamine, brazilian, and crocin.

The inorganic/organic composite particles may be composite particles in which the surfaces of inorganic particles commonly used in cosmetics are coated with organic particles by a publicly known method.

The particles may be surface-treated with metal soap, silane, silicone, silicone resin, fluorine compound, amino acid, iron oxide, titanium oxide, iron oxide titanium oxide, or aluminum hydroxide.

There are no particular limitations on the shape of the silicone rubber attached to the surface of the core particles, but as described below, in the manufacturing method of the present invention, the silicone rubber becomes spherical, resembles fused spherical particles, has a lump-like shape, or is membrane-like.

There is no particular limit to the density of the rubber attached to the surface of the core particle. In other words, the rubber may be sparsely attached to the surface of the core particle, or it may cover the surface of the core particle without any gaps. The shape and density of the attached rubber can be confirmed using an electron microscope.

The amount of silicone rubber attached to the core particles is in the range of 0.1 to 25 parts by mass, preferably 0.2 to 20 parts by mass, and more preferably 0.5 to 15 parts by mass or more, per 100 parts by mass of the core particles. If the amount attached is 0.1 parts by mass or more, it is possible to impart to the cosmetic a natural finish due to light diffusion, good adhesion to the skin, a soft and moist feel, and drop stability. If the amount attached is 25 parts by mass or less, cohesion is low, and there is no decrease in the slipperiness and spreadability of the cosmetic, or wrinkling.

The rubber constituting the silicone rubber is preferably non-sticky, and its rubber hardness, measured by a type A durometer as specified in JIS K6253, is preferably in the range of 5 to 95, more preferably 10 to 80. If the rubber hardness is 5 or more, the cohesiveness is low, and the cosmetic does not lose its slipperiness or spreadability, or become twisted. If the rubber hardness is 95 or less, the cosmetic can be given good adhesion to the skin, a soft and moist feel, and drop stability. The rubber hardness is the value measured by preparing a test piece of the rubber composition with the shape and dimensions as specified in JIS K6253.

The silicone rubber preferably comprises a cured product having linear organosiloxane blocks of the formula -(R ₂ SiO _2/2 ) _a -, where R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms, and a is a positive integer from 5 to 5,000.

The above R has 1 to 30 carbon atoms, preferably 1 to 22, and more preferably 1 to 18. Examples of R 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, furan, and the like. Examples of such groups include aralkyl groups such as phenyl groups; alkenyl groups such as vinyl groups and allyl groups; cycloalkyl groups such as cyclopentyl groups, cyclohexyl groups and cycloheptyl groups; and hydrocarbon groups in which some or all of the hydrogen atoms bonded to the 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, epoxy groups, glycidoxy groups and carboxyl groups. Preferred are alkyl groups or phenyl groups having 1 to 18 carbon atoms, and it is preferable that 50 mol % or more of all R groups are methyl groups.

Silicone rubber is obtained from a curable liquid silicone composition, and its curing can be exemplified by addition reactions, condensation reactions, radical reactions, etc. A curable liquid silicone composition contains a component having a reactive group for the above curing reaction (one having both reactive groups, or one component having one reactive group and the other reactive group), a curing catalyst, and a radical generator.

When silicone rubber is produced by curing through an addition reaction, the curable liquid silicone composition may contain (A) an organopolysiloxane having alkenyl groups, (B) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms, and an addition reaction catalyst.

The component (A) has the following average composition formula (1):
R ¹ _b R ² _c SiO _(4-b-c)/2 (1)
and is an organopolysiloxane having at least two alkenyl groups in one molecule. In the formula, R ¹ 's are each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms which does not contain an alkenyl group. R ² 's are each independently an alkenyl group having 2 to 6 carbon atoms. b and c are positive numbers which satisfy 0<b<3, 0<c≦3 and 0.1≦b+c≦3.

One type of organopolysiloxane represented by the average composition formula (1) may be used alone, or two or more types may be used in combination.

^R1 has 1 to 30 carbon atoms, preferably 1 to 22, and more preferably 1 to 18. Among the above-mentioned R, R1 may be a monovalent hydrocarbon group excluding an alkenyl group, and it is preferable that 50 mol % or more of ^R1 is a methyl group. ^R2 may be a vinyl group, an allyl group, a propenyl group, a butenyl group, a pentenyl group, or a hexenyl group, and is preferably ^a vinyl group. b and c are positive numbers that preferably satisfy 0<b≦2.295, 0.005≦c≦2.3, or 0.5≦b+c≦2.3.

The kinetic viscosity of component (A) at 25°C is preferably 100,000 ^mm2 /s or less, more preferably 10,000 ^mm2 /s or less. If the kinetic viscosity is 100,000 ^mm2 /s or less, it is particularly easy to obtain silicone microparticles with a narrow particle size distribution in the preparation of an aqueous dispersion of silicone rubber particles described below. There is no particular lower limit to the kinetic viscosity, but it may be 0.7 ^mm2 /s or more, particularly 2 ^mm2 /s or more. In the present invention, the value of the kinetic viscosity may be a value measured using a capillary viscometer at 25°C.

The structure of component (A) may be linear, cyclic, or branched, but is preferably linear or branched with fewer branch units. There are no particular restrictions on the bonding site of the alkenyl group, and it may be bonded to either a silicon atom on the side chain or at the end of the molecule, but it is particularly preferred that it is bonded to silicon atoms at both ends of the linear organopolysiloxane.

An example of a linear structure is the one represented by the following general formula (2):

（式中、Ｒ^１、Ｒ^２は前記と同じであり、ｄは正数、ｅは０又は正数、ｆは０、１、２又は３、ただしｅおよびｆはｅ＋２×ｆ≧２を満たす数である。）

(In the formula, R ¹ and R ² are the same as above, d is a positive number, e is 0 or a positive number, and f is 0, 1, 2, or 3, provided that e and f are numbers satisfying e+2×f≧2.)

An example of the branched structure is one represented by the following general formula (3) which is branched by R ¹ SiO _3/2 units.

（式中、Ｒ^１、Ｒ^２は前記と同じであり、ｇは正数、ｈは０又は正数、ｉは正数、ｊは０、１、２又は３、ただしｈおよびｊはｈ＋ｊ≧１を満たす数である。）

(In the formula, R ¹ and R ² are the same as above, g is a positive number, h is 0 or a positive number, i is a positive number, and j is 0, 1, 2, or 3, with the proviso that h and j are numbers satisfying h+j≧1.)

An example of the structure branched by SiO _4/2 units is one represented by the following general formula (4).

（式中、Ｒ^１、Ｒ^２は前記と同じであり、ｋは正数、ｌは０又は正数、ｍは正数、ｎは０、１、２又は３、ただしｌおよびｎはｌ＋ｎ≧１を満たす数である。）

(In the formula, R ¹ and R ² are the same as above, k is a positive number, l is 0 or a positive number, m is a positive number, and n is 0, 1, 2, or 3, provided that l and n are numbers satisfying l+n≧1.)

Another example is one represented by the following unit formula (5) that has two or more alkenyl groups per molecule.

[R ¹ ₃ SiO _1/2 ] _o [R ² (R ¹ ) ₂ SiO _1/2 ] _p [SiO _4/2 ] _q
[(OR ³ )SiO _3/2 ] _r (5)
(In the formula, R ¹ and R ² are the same as defined above, R ³ is a hydrogen atom or an unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, o is 0 or a positive number, and p is a positive number.) q is a positive number, and r is 0 or a positive number.

The component (B) has the following average composition formula (6):
R ⁴ _s H _t SiO _(4-s-t)/2 (6)
and is an organohydrogenpolysiloxane having at least two hydrogen atoms (referred to as SiH groups) bonded to silicon atoms in each molecule. In the formula, ^R4 is each independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms that does not contain an alkenyl group. s and t are numbers that satisfy 0<s<3, 0<t≦3, and 0.1≦s+t≦3.

One type of organopolysiloxane represented by the average composition formula (6) may be used alone, or two or more types may be used in combination.

^R4 has 1 to 30 carbon atoms, preferably 1 to 22, and more preferably 1 to 18. ^R4 may be the same monovalent hydrocarbon group as ^R1 , and preferably 80 mol % or more of R4 is a methyl group, and more preferably 95 mol % or more of R4 is a methyl group. s and t are preferably positive numbers satisfying 0<s≦2.295, 0.005≦t≦2.3, and 0.5≦s+t≦2.3.

The kinetic viscosity of component (B) at 25°C is preferably 100,000 ^mm2 /s or less, and more preferably 10,000 ^mm2 /s or less. If the kinetic viscosity is 100,000 ^mm2 /s or less, it is particularly easy to obtain silicone microparticles with a narrow particle size distribution in the preparation of an aqueous dispersion of silicone rubber particles described below. The lower limit of the kinetic viscosity is not particularly limited, but is preferably 0.4
It is sufficient that the speed is at least mm ² /s, and in particular at least 2 mm ² /s.

The structure of component (B) may be linear, cyclic, or branched, with linear or branched being particularly preferred. There are no particular limitations on the bonding site of the hydrogen atom bonded to the silicon atom, and the hydrogen atom may be bonded to either the side chain or the terminal silicon atom of the molecule.

An example of a linear structure is represented by the following general formula (7):

（式中、Ｒ^４は前記と同じであり、ｕは正数、ｖは０又は正数、ｗは０、１、２又は３、ただしｖおよびｗはｖ＋２×ｗ≧２を満たす数である。）

(In the formula, ^R4 is the same as above, u is a positive number, v is 0 or a positive number, and w is 0, 1, 2, or 3, provided that v and w are numbers that satisfy v+2×w≧2.)

An example of the branched structure is one represented by the following general formula (8) which is branched by R ⁴ SiO _3/2 units.

（式中、Ｒ^４は前記と同じであり、ｘは正数、ｙは０又は正数、ｚは正数、ａ１は０、１、２又は３、ただしｙおよびａ１はｙ＋ａ１≧１を満たす数である。）

(In the formula, ^R4 is the same as above, x is a positive number, y is 0 or a positive number, z is a positive number, and a1 is 0, 1, 2, or 3, provided that y and a1 are numbers that satisfy y+a1≧1.)

An example of a structure branched by SiO _4/2 units is one represented by the following general formula (9).

（式中、Ｒ^４は前記と同じであり、ｂ１は正数、ｃ１は０又は正数、ｄ１は正数、ｅ１は０、１、２又は３、ただしｃ１およびｅ１はｃ１＋ｅ１≧１を満たす数である。）

(In the formula, ^R4 is the same as above, b1 is a positive number, c1 is 0 or a positive number, d1 is a positive number, and e1 is 0, 1, 2, or 3, provided that c1 and e1 are numbers that satisfy c1+e1≧1.)

Further, examples include those represented by the following formula (10) having two or more hydrogen atoms bonded to silicon atoms per molecule.
[R ⁴ ₃ SiO _1/2 ] _f1 [H(R ⁴ ) ₂ SiO _1/3 ] _g1 [SiO _4/2 ] _h1
[(OR ⁵ )SiO _3/2 ] _i1 (10)
In the formula, R ⁴ is the same as defined above, R ⁵ is a hydrogen atom or an unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, f1 is 0 or a positive number, g1 is a positive number, h1 is a positive number, and i1 is 0 or a positive number.

As mentioned above, component (A) is an organopolysiloxane having two or more alkenyl groups in one molecule, and component (B) is an organohydrogenpolysiloxane having two or more hydrogen atoms bonded to silicon atoms in one molecule. However, the combination of an organopolysiloxane (A) having only two alkenyl groups and an organohydrogenpolysiloxane (B) having only two SiH groups is excluded. This is because the combination of an organopolysiloxane having two alkenyl groups as component (A) and an organohydrogensiloxane having two SiH groups as component (B) results in a sticky cured product, making it impossible to obtain silicone rubber. That is, when component (A) has two alkenyl groups, at least one of components (B) is an organohydrogensiloxane having three or more SiH groups, and when component (B) has two SiH groups, at least one of components (A) is an organosiloxane having three or more alkenyl groups.

The amount of component (B) relative to component (A) is preferably an amount that results in a ratio of the number of SiH groups in component (B) to the number of monovalent alkenyl groups in component (A) of 0.5 to 2, and more ... that is within the above range. When component (B) is blended in an amount that results in a ratio of the number of SiH groups within the above range, the resulting silicone rubber cured product is not sticky and has appropriate reactivity.

Examples of the catalyst for the addition reaction include platinum group metal catalysts used in hydrosilylation reactions. For example, platinum group metals such as platinum (including platinum black), rhodium, and palladium; H ₂ PtCl _{4.XH 2} O, H ₂ PtCl _{6.XH 2} O, NaHPtCl _6.XH 2 _O , KHPtCl 6.XH ₂ O, Na ₂ PtCl _{6.XH 2 O} , K ₂ PtCl 4.XH _{2 O ,} PtCl 4.XH ₂ O, PtCl ₂ , Na ₂ HPtCl _{4.XH 2 O} ; O (wherein, X is an integer of 0 to 6, preferably 0 or 6), chloroplatinic acid, and chloroplatinate salts; alcohol-modified chloroplatinic acid; platinum chloride, a complex of chloroplatinic acid with an olefin, a complex of chloroplatinic acid with a vinyl group-containing siloxane, a complex of platinum with a vinyl group-containing siloxane; platinum black, a platinum group metal such as palladium supported on a carrier such as alumina, silica, or carbon; rhodium-olefin complex; chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst), and the like. One type may be used alone, or two or more types may be used in combination.

The amount of platinum group metal catalyst used may be an effective amount as a hydrosilylation reaction catalyst, and the amount of platinum group metal in the platinum group metal catalyst relative to the total amount of components (A) and (B) is usually about 0.1 to 500 ppm, preferably about 0.5 to 200 ppm, and more preferably about 1 to 100 ppm, by mass.

The silicone rubber may contain silicone oil, organosilane, inorganic powder, organic powder, antioxidant, etc.

[Method of manufacturing composite particles]
The present invention relates to a composite particle comprising:
(i) emulsifying a curable liquid silicone composition with a surfactant to prepare an oil-in-water emulsion, and then curing the curable liquid silicone composition to prepare an aqueous dispersion of silicone rubber spherical particles having a volume average particle size of 50 to 1,000 nm;
(ii) mixing the core particles, the aqueous dispersion of the silicone rubber spherical particles prepared in step (i), a cationic surfactant, and water to adsorb the silicone rubber particles onto the surfaces of the core particles, thereby preparing a mixture containing the core particles having the silicone rubber particles adsorbed thereon; and
(iii) The silicone rubber particles are produced by a method including a step of volatilizing and removing water contained in the mixture containing the core particles having the silicone rubber particles adsorbed thereon, prepared in step (ii), and fixing the silicone rubber particles adsorbed on the surfaces of the core particles.

In addition, in the method for producing composite particles of the present invention, the amount of the core particles per 100 parts by mass of water contained in the mixed liquid prepared in step (ii) is in the range of 1 to 100 parts by mass, and the amount of the silicone rubber spherical particles per 100 parts by mass of the core particles is in the range of 0.1 to 25 parts by mass.

The aqueous dispersion of silicone rubber spherical particles in step (i) can be produced by a known method. The above-mentioned curable liquid silicone composition is emulsified using a surfactant to produce an oil-in-water emulsion, and then the curable liquid silicone is cured by carrying out an addition reaction, a condensation reaction, a radical reaction, or the like. To incorporate silicone oil, organosilane, inorganic powder, organic powder, antioxidant, and the like into the silicone rubber particles, these may be blended into the curable liquid silicone composition. If the method involves emulsifying this curable liquid silicone composition and then carrying out a curing reaction, the shape of the resulting silicone rubber particles will be spherical.

When making an aqueous dispersion of silicone rubber spherical particles by curing through an addition reaction, a method can be used in which a surfactant and water are added to the curable liquid silicone composition consisting of (A) an organopolysiloxane having alkenyl groups and (B) an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms, which is emulsified to form an oil-in-water emulsion, and then a platinum group metal catalyst is added to carry out the addition reaction. A method in which a platinum group metal catalyst is blended in advance with the curable liquid silicone composition is also acceptable, but in that case, it is necessary to prevent the reaction from proceeding before the emulsification is completed by adjusting the temperature, adjusting the amount of catalyst, blending a control agent, etc.

The surfactant used for emulsification is not particularly limited, and may be a nonionic surfactant, an anionic surfactant, a cationic surfactant, or an amphoteric surfactant. A nonionic surfactant is preferable. These surfactants may be used alone or in appropriate combination of two or more.

Nonionic surfactants 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 sorbitol 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, polyoxyethylene polyoxypropylene modified organopolysiloxanes, etc.

Examples of anionic surfactants include alkyl sulfate salts such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfate salts, polyoxyethylene alkyl phenyl ether sulfate salts, sulfate salts of fatty acid alkylol amides, alkyl benzene sulfonates, polyoxyethylene alkyl phenyl ether sulfonates, α-olefin sulfonates, α-sulfofatty acid ester salts, alkyl naphthalene sulfonates, alkyl diphenyl ether disulfonates, alkanesulfonates, N-acyltaurate salts, dialkyl sulfosuccinate salts, monoalkyl sulfosuccinate salts, polyoxyethylene alkyl ether sulfosuccinate salts, fatty acid salts, polyoxyethylene alkyl ether carboxylate salts, N-acyl amino acid salts, monoalkyl phosphate salts, dialkyl phosphate salts, polyoxyethylene alkyl ether phosphate salts, etc.

Examples of cationic surfactants include alkyltrimethylammonium salts, dialkyldimethylammonium salts, trialkylmethylammonium salts, polyoxyethylenealkyldimethylammonium salts, dipolyoxyethylenealkylmethylammonium salts, tripolyoxyethylenealkylammonium salts, alkylbenzyldimethylammonium salts, alkylpyridinium salts, monoalkylamine salts, and monoalkylamidoamine salts.

Examples of amphoteric surfactants include alkyl dimethylamine oxide, alkyl dimethyl carboxybetaine, alkyl amidopropyl dimethyl carboxybetaine, alkyl hydroxysulfobetaine, alkyl carboxymethyl hydroxyethyl imidazolinium betaine, etc.

To emulsify, a general emulsifying and dispersing machine may be used, including a high-speed rotating centrifugal radiation type agitator such as a Homo Disper, a high-speed rotating shear type agitator such as a Homo Mixer, a high-pressure jet type emulsifying and dispersing machine such as a homogenizer, a colloid mill, an ultrasonic emulsifying machine, etc. There are no particular limitations on the stirring speed, time, etc., as long as the mixture can be emulsified and the desired particle size can be obtained.

The volume average particle size of the rubber particles in the aqueous dispersion of silicone rubber spherical particles is preferably smaller than that of the core particles. If it is smaller than the core particles, it can impart a natural finish due to light diffusion, good adhesion to the skin, a soft and moist feel, and drop stability to the cosmetic. The volume average particle size is in the range of 50 to 1,000 nm, and preferably 100 to 500 nm. If it is 1,000 nm or less, it can adhere to the core particles. The volume average particle size is measured by a laser diffraction/scattering method.

The core particles used in step (ii) can be the inorganic particles, organic particles, or inorganic-organic composite particles described above, and can be used alone or in appropriate combination of two or more types. An aqueous dispersion prepared in advance or an aqueous dispersion synthesized in water can be used as is.

In step (ii), the amount of core particles is in the range of 1 to 100 parts by mass, preferably 5 to 50 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of water contained in the mixed liquid. When the amount of core particles is 1 part by mass or more, production efficiency is high. Also, when the amount of core particles is 100 parts by mass or less, the kinetic viscosity of the mixed liquid does not become too high, making it easier to adhere the silicone rubber particles.

In step (ii), the amount of the aqueous dispersion of silicone rubber spherical particles should be the amount of silicone rubber to be attached to the surface of the core particles. The amount of silicone rubber spherical particles in the aqueous dispersion of silicone rubber spherical particles is in the same range as the amount of silicone rubber relative to the core particles in the composite particles described above, and is in the range of 0.1 to 25 parts by mass, preferably 0.2 to 20 parts by mass, and more preferably 0.5 to 15 parts by mass or more, relative to 100 parts by mass of the core particles.

The cationic surfactant used in step (ii) has the effect of adsorbing the silicone rubber particles to the core particles. The cationic surfactant is adsorbed to the surface of the silicone rubber particles, increasing the zeta potential (a value that indicates the charged state of a solid surface) of the rubber particle surface, which in turn increases the difference in zeta potential with the core particles, and it is presumed that this causes the silicone rubber particles to adhere to the core particles through electrostatic interaction.

The cationic surfactant used in step (ii) may be any of those mentioned above. It may be in the form of an aqueous solution, a solution in a water-soluble organic solvent such as an alcohol, or an aqueous solution containing a water-soluble organic solvent.

The amount of cationic surfactant used in step (ii) is in the range of 0.02 to 0.9 parts by mass, more preferably 0.03 to 0.7 parts by mass, per 100 parts by mass of water contained in the mixed liquid. If the amount is 0.02 to 0.9 parts by mass, the silicone rubber particles can be adsorbed to the surface of the core particles.

When the aqueous dispersion of silicone rubber spherical particles prepared in step (i) contains a cationic surfactant, and the amount of cationic surfactant in step (ii) is the desired amount, the cationic surfactant is already mixed, so there is no need to add additional cationic surfactant. The mixing of the aqueous dispersion of silicone rubber spherical particles prepared in step (i), the cationic surfactant, and water in step (ii) of the present invention also includes such cases.

In step (ii), surfactants other than cationic surfactants and water-soluble polymers may be included. The surfactants used for emulsifying the silicone rubber spherical particles produced in step (i) in the aqueous dispersion are included. When the core particles are mixed in the form of an aqueous dispersion, surfactants other than cationic surfactants and water-soluble polymers may be included as dispersants. Also, surfactants other than cationic surfactants and water-soluble polymers may be mixed in step (ii).

Surfactants other than cationic surfactants are not particularly limited and include nonionic surfactants, anionic surfactants, and amphoteric surfactants, as mentioned above, with nonionic surfactants or amphoteric surfactants being preferred.

Examples of water-soluble polymers include nonionic water-soluble polymers and anionic water-soluble polymers, with nonionic water-soluble polymers being preferred. It is preferable not to use cationic water-soluble polymers, as they may inhibit the adsorption of silicone rubber particles to the surface of the core particles.

Nonionic water-soluble polymers include polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, polyethylene oxide, polymethyl vinyl ether, polyisopropylacrylamide, methylcellulose, hydroxypropylmethylcellulose, starch, guar gum, xanthan gum, etc.

Examples of anionic water-soluble polymers include sodium polyacrylate, carboxyvinyl polymer, polysodium styrene sulfonate, sodium naphthalene sulfonate condensate, sodium cellulose sulfate, sodium carboxymethylcellulose, carboxymethyl starch, sodium alginate, gum arabic, carrageenan, and derivatives thereof obtained by copolymerizing monomers having nonionic or anionic groups.

In step (ii), the core particles, the aqueous dispersion of silicone rubber spherical particles, the cationic surfactant, and the water can be mixed using stirring blades such as paddle blades, propeller blades, swept-back blades, and anchor-shaped blades.

The core particles, the aqueous dispersion of silicone rubber spherical particles, the cationic surfactant, and the water are preferably mixed by stirring the core particles, the cationic surfactant, and the water, and then the aqueous dispersion of silicone rubber spherical particles is added while stirring. The core particles, the cationic surfactant, and the water may be added in any order. Alternatively, the core particles and the water are preferably mixed by stirring, and then the aqueous dispersion of silicone rubber spherical particles is added, and then the cationic surfactant is added while stirring.

When the core particles are used in the form of an aqueous dispersion, the order may be to mix the aqueous dispersion of silicone rubber spherical particles, the cationic surfactant, and water with stirring, and then add the aqueous dispersion of core particles with stirring. The aqueous dispersion of silicone rubber spherical particles, the cationic surfactant, and water may be added in any order. Alternatively, the aqueous dispersion of core particles, the aqueous dispersion of silicone rubber spherical particles, and water may be mixed with stirring, and then add the cationic surfactant with stirring. The aqueous dispersion of core particles, the aqueous dispersion of silicone rubber spherical particles, and water may be added in any order.

In step (ii), an acid or alkali may be added to lower or raise the pH of the water. If the change in pH increases the zeta potential difference between the core particles and the silicone rubber spherical particles, this may facilitate the adsorption of the silicone rubber spherical particles to the core particles.

In step (ii), a water-soluble organic solvent such as alcohol may be added to the mixture to facilitate the adsorption of the silicone rubber spherical particles to the core particles.

The temperature for step (ii) is not particularly limited and may be in the range of 0 to 100°C.

After mixing the core particles, the aqueous dispersion of silicone rubber spherical particles, the cationic surfactant, and water, it is preferable to continue stirring for a while until the silicone rubber spherical particles are adsorbed onto the core particles.

In step (iii), the removal of water (moisture contained in the mixed liquid) by volatilization from the mixed liquid containing the core particles adsorbed with the silicone rubber particles produced in step (ii) can be carried out, for example, by heating under normal pressure or reduced pressure. Specific examples of the method include a method in which the mixed liquid is left to stand under heating to remove moisture, a method in which the mixed liquid is stirred and fluidized under heating to remove moisture, a method in which the mixed liquid is sprayed and dispersed in a hot air current as in a spray dryer, and a method using a fluidized heat medium. As a pretreatment for this operation, the mixed liquid may be concentrated by a method such as heating and dehydration, filtration separation such as pressure filtration, centrifugation, decantation, etc.

If an acid or alkali is added in step (ii), the mixture may be neutralized by adding an acid or alkali before the water is removed by evaporation. If necessary, the mixture may be washed with water, alcohol, etc.

The adhesion of the silicone rubber particles to the core particle surface in step (iii) is presumably achieved through the following process. When the amount of moisture decreases due to the evaporation of water, a capillary force is generated between the core particle and the silicone rubber spherical particles adsorbed to its surface. The silicone rubber particles are attracted to the core particle surface by the capillary force, and deform so as to spread over the core particle surface, increasing the adhesion area with the core particle. This increases the adhesive force, and the particles remain adhered even after the water is removed and the capillary force disappears.

The shape of the silicone rubber that adheres to the surface of the core particles as the water evaporates away varies depending on the hardness of the rubber. If the rubber hardness is high, it is spherical; if the rubber hardness is lowered, it takes on a shape similar to fused spherical particles; if the rubber hardness is lowered even further, it takes on a lump-like or film-like shape.

The silicone rubber spherical particles are deformed by adhering to the surface of the core particle, which is presumably due to the action of capillary forces between the core particle and the silicone rubber spherical particles that arise in step (iii) as described above. It is also presumed that capillary forces also arise between the silicone rubber spherical particles themselves, which also have an effect.

As described above, in the method for producing composite particles of the present invention, the produced composite particles have low cohesion, but may be weakly cohesive. In such cases, when the particles obtained by removing water from the mixture are cohesive, it is advisable to disintegrate them using a grinding machine such as a jet mill, ball mill, or hammer mill.

The composite particles of the present invention can have their particle surfaces treated with silylation agents, silicone oils, waxes, paraffins, organic fluorine compounds, surfactants, etc. to impart or improve water repellency or improve dispersibility in oils.

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

[Example 1]
(Step (i): Preparation of an aqueous dispersion of silicone rubber spherical particles)
313 g of vinyl-containing dimethylpolysiloxane (A1) with a kinetic viscosity of 10 mm ² /s, as shown in the following formula (11), 87 g of methylhydrogenpolysiloxane (B1) with a kinetic viscosity of 117 mm ² /s, as shown in the following formula (12) (amount blended such that there are 1.15 hydrosilyl groups per vinyl group), and 0.1 g of dl-α-tocopherol (antioxidant) were charged into a 1-liter glass beaker and mixed and dissolved using a homomixer. 45 g of polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) and 150 g of water were added and stirred using a homomixer, and an increase in viscosity was observed, and stirring was continued for another 15 minutes. Next, 402 g of water was added to dilute the mixture, and the mixture was passed through a homogenizer at a pressure of 100 MPa to obtain a uniform white emulsion. 498.5 g of this emulsion was transferred to a 1 liter glass flask fitted with a stirrer using an anchor-shaped impeller, 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 g of polyoxyethylene lauryl ether (product name: Emulgen 109P, manufactured by Kao Corporation) was added with stirring at the same temperature for 24 hours, yielding an aqueous dispersion of silicone rubber spherical particles.

The volume average particle size of the silicone rubber spherical particles was measured using a laser diffraction/scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) and found to be 320 nm.

Separately from the preparation of the aqueous dispersion of silicone rubber spherical particles, vinyl group-containing dimethylpolysiloxane (A1) shown in formula (11) below, methylhydrogenpolysiloxane (B1) shown in formula (12) below, and an isododecane solution of platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) were mixed in the above-mentioned ratio, poured into an aluminum petri dish to a thickness of 10 mm, and left at 25°C for 6 hours, and then heated in a thermostatic chamber at 50°C for 1 hour. The resulting cured product was a non-sticky rubber elastic body, and its hardness was measured with a durometer A hardness tester to be 73.

(A1): Vinyl group-containing dimethylpolysiloxane

(B1): Methylhydrogenpolysiloxane

[Example 2]
(Step (i): Preparation of an aqueous dispersion of silicone rubber spherical particles)
343 g of vinyl-containing dimethylpolysiloxane (A2) with a kinetic viscosity of 61 mm ² /s, as shown in the following formula (13), 57 g of methylhydrogenpolysiloxane (B2) with a kinetic viscosity of 30 mm ² /s, as shown in the following formula (14) (amount blended such that there are 1.15 hydrosilyl groups per vinyl group), and 0.1 g of dl-α-tocopherol (antioxidant) were charged into a 1-liter glass beaker and mixed and dissolved using a homomixer. When 30 g of polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) and 40 g of water were added and stirred using a homomixer, the mixture thickened to the point where it could not be stirred. The thickened mixture was kneaded for 15 minutes using a homodisper. Next, 527 g of water was added and mixed using a homomixer, resulting in a uniform white emulsion. This emulsion was transferred to a 1 liter glass flask fitted with a stirrer using an anchor-shaped impeller, and the temperature was adjusted to 20-25°C. After that, a mixed solution of 1 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 2 g of polyoxyethylene lauryl ether (product name: Emulgen 109P, manufactured by Kao Corporation) was added with stirring at the same temperature for 24 hours, yielding an aqueous dispersion of silicone rubber spherical particles.

The volume average particle size of the silicone rubber spherical particles was measured using a laser diffraction/scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) and found to be 330 nm.

Separately from the preparation of the aqueous dispersion of silicone rubber spherical particles, vinyl group-containing dimethylpolysiloxane (A2) shown in formula (13) below, methylhydrogenpolysiloxane (B2) shown in formula (14) below, and an isododecane solution of platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) were mixed in the above-mentioned ratio, poured into an aluminum petri dish to a thickness of 10 mm, and left at 25°C for 6 hours, and then heated in a thermostatic chamber at 50°C for 1 hour. The resulting cured product was a non-sticky rubber elastic body, and its hardness was measured with a durometer A hardness tester to be 50.

(A2): Vinyl group-containing dimethylpolysiloxane

(B2): Methylhydrogenpolysiloxane

[Example 3]
(Step (i): Preparation of an aqueous dispersion of silicone rubber spherical particles)
365 g of vinyl-containing dimethylpolysiloxane (A3) with a kinetic viscosity of 125 mm ² /s, as shown in the following formula (15), 35 g of methylhydrogenpolysiloxane (B2) with a kinetic viscosity of 30 mm ² /s, as shown in the above formula (14) (amount blended such that there are 1.17 hydrosilyl groups per vinyl group), and 0.1 g of dl-α-tocopherol (antioxidant) were charged into a 1-liter glass beaker and mixed and dissolved using a homomixer. 30 g of polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) and 35 g of water were added and stirred using a homomixer, resulting in viscosity increase to a state where stirring was not possible. The thickened material was kneaded for 15 minutes using a homodisper. Next, 532 g of water was added and mixed using a homomixer, resulting in a uniform white emulsion. This emulsion was transferred to a 1 liter glass flask fitted with a stirrer using an anchor-shaped impeller, and the temperature was adjusted to 20-25°C. After that, a mixed solution of 1 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 2 g of polyoxyethylene lauryl ether (product name: Emulgen 109P, manufactured by Kao Corporation) was added with stirring at the same temperature for 24 hours, yielding an aqueous dispersion of silicone rubber spherical particles.

The volume average particle size of the silicone rubber spherical particles was measured using a laser diffraction/scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) and found to be 310 nm.

Separately from the preparation of the aqueous dispersion of silicone rubber spherical particles, vinyl group-containing dimethylpolysiloxane (A3) shown in formula (15) below, methylhydrogenpolysiloxane (B2) shown in formula (14) above, and an isododecane solution of platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) were mixed in the above-mentioned ratio, poured into an aluminum petri dish to a thickness of 10 mm, and left at 25°C for 6 hours, and then heated in a thermostatic chamber at 50°C for 1 hour. The resulting cured product was a non-sticky rubber elastic body, and its hardness was measured with a durometer A hardness tester to be 43.

(A3): Vinyl group-containing dimethylpolysiloxane

[Example 4]
(Step (i): Preparation of an aqueous dispersion of silicone rubber spherical particles)
384 g of vinyl-containing dimethylpolysiloxane (A4) with a kinetic viscosity of 600 mm ² /s, as shown in the following formula (16), 16 g of methylhydrogenpolysiloxane (B2) with a kinetic viscosity of 30 mm ² /s, as shown in the above formula (14) (amount blended such that there are 1.18 hydrosilyl groups per vinyl group), and 0.1 g of dl-α-tocopherol (antioxidant) were charged into a 1-liter glass beaker and mixed and dissolved using a homomixer. 32 g of polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) and 36 g of water were added and stirred using a homomixer, resulting in viscosity increase to a state where stirring was not possible. The thickened material was kneaded for 15 minutes using a homodisper. Next, 530 g of water was added and mixed using a homomixer, resulting in a uniform white emulsion. This emulsion was transferred to a 1 liter glass flask fitted with a stirrer using an anchor-shaped impeller, and the temperature was adjusted to 20-25°C. After that, a mixed solution of 0.6 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 1 g of polyoxyethylene lauryl ether (product name: Emulgen 109P, manufactured by Kao Corporation) was added with stirring at the same temperature for 24 hours, yielding an aqueous dispersion of silicone rubber spherical particles.

The volume average particle size of the silicone rubber spherical particles was measured using a laser diffraction/scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) and found to be 320 nm.

Separately from the preparation of the aqueous dispersion of silicone rubber spherical particles, vinyl group-containing dimethylpolysiloxane (A4) represented by the following formula (16), methylhydrogenpolysiloxane (B2) represented by the above formula (14), and an isododecane solution of platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) were mixed in the above-mentioned ratio, poured into an aluminum petri dish to a thickness of 10 mm, and left at 25°C for 6 hours, and then heated in a thermostatic chamber at 50°C for 1 hour. The resulting cured product was a non-sticky rubber elastic body, and its hardness was measured using a durometer A hardness tester to be 27.

(A4): Vinyl group-containing dimethylpolysiloxane

[Example 5]
(Step (i): Preparation of an aqueous dispersion of silicone rubber spherical particles)
393 g of vinyl-containing dimethylpolysiloxane (A5) with a kinetic viscosity of 5,060 mm ² /s and represented by the following formula (17), 7 g of methylhydrogenpolysiloxane (B2) with a kinetic viscosity of 30 mm ² /s and represented by the above formula (14) (amount blended such that there are 1.19 hydrosilyl groups per vinyl group), and 0.1 g of dl-α-tocopherol (antioxidant) were charged into a 1-liter glass beaker and mixed and dissolved using a homomixer. Polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation)
When 42 g of the mixture and 35 g of water were added and stirred using a homomixer, the mixture thickened to a state where it could not be stirred. The thickened mixture was kneaded for 15 minutes using a homodisper. Next, 521 g of water was added and mixed using a homomixer, resulting in a uniform white emulsion. This emulsion was transferred to a 1-liter glass flask equipped with a stirrer using an anchor-shaped stirring blade, and the temperature was adjusted to 20 to 25°C. After that, a mixed solution of 0.6 g of an isododecane solution of a platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) and 1 g of polyoxyethylene lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) was added under stirring, and the mixture was stirred at the same temperature for 24 hours to obtain an aqueous dispersion of silicone rubber spherical particles.

The volume average particle size of the silicone rubber spherical particles was measured using a laser diffraction/scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.) and found to be 300 nm.

Separately from the preparation of the aqueous dispersion of silicone rubber spherical particles, vinyl group-containing dimethylpolysiloxane (A5) shown in formula (17) below, methylhydrogenpolysiloxane (B2) shown in formula (14) above, and an isododecane solution of platinum-vinyl group-containing disiloxane complex (platinum content 0.5%) were mixed in the above-mentioned ratio, poured into an aluminum petri dish to a thickness of 10 mm, and left at 25°C for 6 hours, and then heated in a thermostatic chamber at 50°C for 1 hour. The resulting cured product was a non-sticky rubber elastic body, and its hardness was measured with a durometer A hardness tester to be 20.

(A5): Vinyl group-containing dimethylpolysiloxane

[Example 6]
(Steps (ii) and (iii): Adsorption and adhesion of silicone rubber particles to the surface of cellulose particles (core particles))
In a 1-liter glass flask equipped with an anchor-shaped stirring blade, 75 g (amount of cellulose particles of 17.9 parts by mass per 100 parts by mass of water) of core particles (product name: CELLULOBEADS D5, manufactured by Daito Kasei Kogyo Co., Ltd., shape = spherical, volume average particle size = 12 μm, electron microscope photograph: FIG. 8), 2.8 g (amount of lauryl trimethyl ammonium chloride of 0.2 parts by mass per 100 parts by mass of water) of 30% aqueous solution of lauryl trimethyl ammonium chloride (product name: CATION BB, manufactured by NOF Corp.), and 412.2 g of water were charged. The pH of the liquid at this time was 6.6. Under impeller stirring, 10 g of the aqueous dispersion of silicone rubber spherical particles obtained in Example 1 was added (amount of silicone rubber particles of 5.3 parts by mass per 100 parts by mass of cellulose particles), and stirring was performed for 2 hours. The liquid temperature at this time was 25°C.

The resulting mixture was filtered using a pressure filter with a filter paper with a particle retention diameter of 4 μm (product name: Quantitative Filter Paper No. 5B, manufactured by Toyo Roshi Kaisha, Ltd.) to separate the particles. The filtrate was colorless and transparent, and it was determined that the silicone rubber particles had not passed through the filter paper, suggesting that the silicone rubber particles were possibly adsorbed onto the surfaces of the cellulose particles. The resulting hydrous particles were placed in a stainless steel tray, and the water was removed by volatilization at a temperature of 105°C in a hot air flow dryer. The dried material was crushed using a jet mill to obtain particles.

When the obtained particles were observed under an electron microscope, it was confirmed that the particles had the same shape and diameter as the cellulose particles, with spherical particles about 300 nm in size attached to the entire surface, forming composite particles with silicone rubber attached to the surface of the cellulose particles. An electron microscope photograph is shown in Figure 1. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and diameter of the cellulose particles were maintained.

The volume average particle size of the resulting composite particles was measured using an electrical resistance particle size distribution measuring device (Multisizer 3, manufactured by Beckman Coulter, Inc.) and found to be 12 μm. The particle size distribution was approximately the same as that of the cellulose particles, and it was determined that the shape and particle size of the cellulose particles were maintained.

[Examples 7 to 12]
(Steps (ii) and (iii): Adsorption and adhesion of silicone rubber particles to the surface of cellulose particles (core particles))
Particles were obtained in the same manner as in Example 6, except that the type of cationic surfactant, the type and amount of the aqueous dispersion of silicone rubber particles, and the amount of water were as shown in Table 1.

Table 1 shows the results of observing the appearance of the filtrate from filtering the mixture through a filter paper, observing the silicone rubber adhesion to the surface of the cellulose particles (core particles) using an electron microscope, and measuring the volume average particle size.

When the particles obtained in Example 7 were observed under an electron microscope, it was confirmed that the particles had the same shape and diameter as the cellulose particles, and that spherical particles about 300 nm in size and particles that looked like spherical particles fused together were attached to the entire surface of the particles, forming composite particles in which silicone rubber was attached to the surface of the cellulose particles. An electron microscope photograph is shown in Figure 2. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and diameter of the cellulose particles were maintained.

When the particles obtained in Example 8 were observed under an electron microscope, it was confirmed that the particles had the same shape and diameter as the cellulose particles, and that spherical particles about 300 nm in size and particles that looked like spherical particles fused together were attached to the entire surface of the particles, forming composite particles in which silicone rubber was attached to the surface of the cellulose particles. An electron microscope photograph is shown in Figure 3. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and diameter of the cellulose particles were maintained.

When the particles obtained in Example 9 were observed under an electron microscope, it was confirmed that the particles had a nodular coating attached to the entire surface of the particles, which had the same shape and particle size as the cellulose particles, and that they were composite particles in which silicone rubber was attached to the surface of the cellulose particles. An electron microscope photograph is shown in Figure 4. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and particle size of the cellulose particles were maintained.

When the particles obtained in Example 10 were observed under an electron microscope, it was confirmed that the particles had a nodular coating attached to the entire surface of the particles, which had the same shape and particle size as the cellulose particles, and that they were composite particles in which silicone rubber was attached to the surface of the cellulose particles. An electron microscope photograph is shown in Figure 5. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and particle size of the cellulose particles were maintained.

When the particles obtained in Example 11 were observed under an electron microscope, it was confirmed that the particles had the same shape and diameter as the cellulose particles, with spherical particles about 300 nm in size sparsely attached to their surfaces, forming composite particles in which silicone rubber was attached to the surfaces of the cellulose particles. An electron microscope photograph is shown in Figure 6. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and diameter of the cellulose particles were maintained.

When the particles obtained in Example 12 were observed under an electron microscope, it was found that the particles had the same shape and particle size as the cellulose particles, and had scattered nodules on their surfaces, confirming that they were composite particles in which silicone rubber was attached to the surface of the cellulose particles. An electron microscope photograph is shown in Figure 7. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and particle size of the cellulose particles were maintained.

[Comparative Example 1]
(Steps (ii) and (iii): Adsorption and adhesion of silicone rubber particles to the surface of cellulose particles (core particles))
A 1-liter glass flask equipped with an anchor-shaped impeller stirrer was charged with 75 g of the above-mentioned cellulose particles as core particles (an amount equivalent to 17.8 parts by mass of cellulose particles per 100 parts by mass of water) and 415.0 g of water. The pH of the liquid at this time was 6.4. No cationic surfactant was added. With impeller stirring, 10 g of the silicone rubber spherical particle aqueous dispersion obtained in Example 1 was added (an amount equivalent to 5.3 parts by mass of silicone rubber particles per 100 parts by mass of cellulose particles), and the mixture was stirred for 2 hours. The liquid temperature at this time was 25°C.

The resulting mixture was filtered using a pressure filter with filter paper (product name: Quantitative Filter Paper No. 5B, manufactured by Toyo Roshi Kaisha, Ltd.) with a particle retention diameter of 4 μm to separate the particles. The filtrate was cloudy, indicating that the silicone rubber particles had passed through the filter paper, which means that at least the silicone rubber particles that had permeated the filter paper were not adsorbed onto the surface of the cellulose particles.

The resulting hydrous particles were placed in a stainless steel tray and the water was removed by evaporation in a hot air flow dryer at 105°C. The dried material was crushed in a jet mill to obtain particles.

When the resulting particles were observed under an electron microscope, no silicone rubber was found to be attached to the surface of the cellulose particles.

（注１）カチオン性界面活性剤
Ｄ－１：３０％ラウリルトリメチルアンモニウムクロライド水溶液（商品名：カチオンＢＢ、日油（株）製）
Ｄ－２：３０％セチルトリメチルアンモニウムクロライド水溶液（商品名：コータミン６０Ｗ、花王（株）製）
Ｄ－３：２５％ステアリルトリメチルアンモニウムクロライド水溶液（商品名：カチオンＡＢ－２５０ＡＱ、日油（株）製）
（注２）ノニオン性界面活性剤：シリコーンゴム球状粒子の水分散液中に含まれるポリオキシエチレンラウリルエーテル

(Note 1) Cationic surfactant D-1: 30% aqueous solution of lauryltrimethylammonium chloride (product name: Cation BB, manufactured by NOF Corporation)
D-2: 30% cetyltrimethylammonium chloride aqueous solution (product name: QUARTAMINE 60W, manufactured by Kao Corporation)
D-3: 25% stearyltrimethylammonium chloride aqueous solution (product name: CATION AB-250AQ, manufactured by NOF Corporation)
(Note 2) Nonionic surfactant: Polyoxyethylene lauryl ether contained in the aqueous dispersion of silicone rubber spherical particles

[Example 13]
(Steps (ii) and (iii): Adsorption and adhesion of silicone rubber particles to the surface of silica (core particles))
Into a 1-liter glass flask equipped with a stirrer using an anchor-shaped stirring blade, 75 g (amount of silica of 17.8 parts by mass per 100 parts by mass of water) of silica (product name: SILICA MICRO BEAD P-1500, manufactured by JGC COSAIKA SEIKAISHA, LTD., shape = spherical, volume average particle size = 16 μm, electron microscope photograph: FIG. 11), 2.8 g (amount of lauryl trimethyl ammonium chloride of 0.2 parts by mass per 100 parts by mass of water) of 30% aqueous solution of lauryl trimethyl ammonium chloride (product name: CATION BB, manufactured by NOF CORPORATION), and 412.2 g of water were charged. The pH of the liquid at this time was 6.8. With stirring using the blade, 10 g of the aqueous dispersion of silicone rubber particles obtained in Example 2 was added (amount of silicone rubber particles of 5.3 parts by mass per 100 parts by mass of silica), and stirring was continued for 2 hours. The liquid temperature at this time was 25°C.

The resulting suspension was filtered using a pressure filter with filter paper (product name: Quantitative Filter Paper No. 5B, manufactured by Toyo Roshi Kaisha, Ltd.) with a particle retention diameter of 4 μm to separate the particles. The filtrate was colorless and transparent, and it was determined that the silicone rubber particles had not passed through the filter paper, suggesting that the silicone rubber particles were possibly adsorbed onto the silica surface.

The resulting hydrous particles were placed in a stainless steel tray and the water was removed by evaporation in a hot air flow dryer at 105°C. The dried material was crushed in a jet mill to obtain particles.

When the obtained particles were observed under an electron microscope, it was confirmed that spherical particles with a size of about 300 nm were attached to the entire surface of particles with the same shape and diameter as silica, and that they were composite particles with silicone rubber attached to the silica surface. An electron microscope photograph is shown in Figure 9. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and diameter of the silica were maintained.

The volume average particle size of the resulting composite particles was measured using an electrical resistance particle size distribution measuring device (Multisizer 3, manufactured by Beckman Coulter, Inc.) and found to be 16 μm.
The particle size distribution was approximately the same as that of silica, and it was determined that the shape and particle size of the silica was maintained.

[Examples 14 to 20, Comparative Examples 2 to 4]
(Steps (ii) and (iii): Adsorption and adhesion of silicone rubber particles to the surface of silica (core particles))
Particles were obtained in the same manner as in Example 13, except that the type of cationic surfactant, the type and amount of the aqueous dispersion of silicone rubber particles, and the amount of water were as shown in Tables 2 and 3.

The results of observing the appearance of the filtrate from filtering the mixture through a filter paper, observing the silicone rubber adhesion to the surface of the silica particles (core particles) using an electron microscope, and measuring the volume average particle size are shown in Tables 2 and 3.

When the particles obtained in Example 18 were observed under an electron microscope, nodules were observed all over the surface of the particles, which had the same shape and particle size as silica, and it was confirmed that they were composite particles with silicone rubber attached to the silica surface. An electron microscope photograph is shown in Figure 10. Furthermore, no adhesion between the composite particles was observed, and it was determined that the shape and particle size of the silica were maintained.

The particles obtained in Examples 14 to 17, 19, and 20 also had the properties shown in Tables 2 and 3, and were determined to maintain the same silica shape and particle size as the particles obtained in Example 18.

When the particles obtained in Comparative Examples 2 to 4 were observed under an electron microscope, no silicone rubber was found to adhere to the surface of the silica particles.

（注３）カチオン性界面活性剤
Ｄ－１：３０％ラウリルトリメチルアンモニウムクロライド水溶液（商品名：カチオンＢＢ、日油（株）製）
Ｄ－４：７５％ジアルキル（Ｃ１２～Ｃ１８）ジメチルアンモニウムクロライドのイソプロピルアルコール溶液（商品名：コータミンＤ－２３４５Ｐ、花王（株）製、）
Ｄ－５：８０％トリオクチルメチルアンモニウムクロライド水溶液（商品名：ＴＯＭＡＣ８０％水溶液、日本特殊化学工業（株）製）
Ｄ－６：２０％トリ（ポリオキシエチレン）ステアリルアンモニウムクロライド水溶液（カチナールＳＰＣ－２０Ｖ－Ｓ、東邦化学工業（株）製）
Ｄ－７：５０％ベンザルコニウムクロライド水溶液（ニッコールＣＡ－１０１、日光ケミカルズ（株）製）

(Note 3) Cationic surfactant D-1: 30% aqueous solution of lauryltrimethylammonium chloride (product name: Cation BB, manufactured by NOF Corporation)
D-4: 75% dialkyl (C12-C18) dimethylammonium chloride in isopropyl alcohol (product name: CORTAMIN D-2345P, manufactured by Kao Corporation)
D-5: 80% trioctylmethylammonium chloride aqueous solution (product name: TOMAC 80% aqueous solution, manufactured by Nippon Specialty Chemical Industry Co., Ltd.)
D-6: 20% aqueous solution of tri(polyoxyethylene)stearyl ammonium chloride (Catinal SPC-20V-S, manufactured by Toho Chemical Industry Co., Ltd.)
D-7: 50% benzalkonium chloride aqueous solution (Nikkol CA-101, manufactured by Nikko Chemicals Co., Ltd.)

In Examples 6 to 22, composite particles were produced in which the core particles did not contain multiple core particles, the particles did not strongly aggregate or adhere to each other, the shape and particle size of the core particles were largely maintained, and almost all of the silicone rubber blended was attached to the surface of almost all of the core particles. On the other hand, in Comparative Examples 1 and 2, no cationic surfactant was blended in step (ii), so no silicone rubber adhered to the core particle surface, and the desired composite particles could not be produced. In Comparative Example 3, the amount of cationic surfactant in step (ii) was insufficient, and in Comparative Example 4, the amount of cationic surfactant in (ii) was excessive, so no silicone rubber adhered to the core particle surface, and the desired composite particles could not be produced.

The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and provides similar effects is included within the technical scope of the present invention.

Claims (3)

A method for producing composite particles comprising adhering silicone rubber to the surface of core particles having a volume average particle size of 1 to 50 μm, comprising the steps of:
(i) emulsifying a curable liquid silicone composition with a surfactant to prepare an oil-in-water emulsion, and then curing the curable liquid silicone composition to prepare an aqueous dispersion of silicone rubber spherical particles having a volume average particle size of 50 to 1,000 nm;
(ii) mixing the core particles, the aqueous dispersion of the silicone rubber spherical particles prepared in step (i), a cationic surfactant, and water to adsorb the silicone rubber particles onto the surfaces of the core particles, thereby preparing a mixture containing the core particles having the silicone rubber particles adsorbed thereon; and
(iii) removing by volatilization water contained in the mixed liquid containing the core particles having the silicone rubber particles adsorbed thereon, prepared in step (ii), and fixing the silicone rubber particles adsorbed on the surfaces of the core particles, wherein the amount of the core particles per 100 parts by mass of water contained in the mixed liquid prepared in step (ii) is in the range of 1 to 100 parts by mass, the amount of the silicone rubber spherical particles per 100 parts by mass of the core particles is in the range of 0.1 to 25 parts by mass, and the amount of the cationic surfactant per 100 parts by mass of the water is in the range of 0.02 to 0.9 parts by mass. The method for producing composite particles according to claim 1, characterized in that the core particles are made of at least one of inorganic particles and organic particles. The method for producing composite particles according to claim 1 or 2, characterized in that the rubber hardness of the silicone rubber spherical particles is in the range of 5 to 95, as measured by a type A durometer specified in JIS K6253.