JP6830879B2 - Silicone rubber composition and silicone rubber - Google Patents

Description

The present invention relates to a silicone rubber composed of a silicone rubber composition and a cured product thereof.

Silicone rubber has excellent weather resistance, electrical properties, low compression permanent strain resistance, heat resistance, cold resistance, etc., so it is used in various fields such as electrical equipment, automobiles, construction, medical care, and food. Widely used in. For example, keypads used as rubber contacts for remote controllers, typewriters, word processors, computer terminals, musical instruments, etc .; architectural gaskets; anti-vibration rubber for audio equipment, etc .; for automobile parts such as connector seals, spark plug boots, and computers. Examples include packing for compact discs used, molds for breads and cakes, and the like. At present, the demand for silicone rubber is increasing more and more, and the development of silicone rubber having excellent properties is desired.

In order to further improve the heat resistance of silicone rubber, it is known to add additives such as cerium oxide, cerium hydroxide, iron oxide, and carbon black. Patent Document 1 describes that the heat resistance is improved by adding 0.1% by mass or more of titanium oxide and iron oxide. However, when heated at 300 ° C. for 1 hour, formaldehyde and octamethylcyclo Only the amount of tetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane generated is measured, and there is no description of changes in physical properties. Further, iron oxide is also well known as a colorant for silicone rubber, and even a small amount of iron oxide colors the silicone rubber red, so that it is difficult to color the silicone rubber even if a color other than red is desired.

Patent Document 2 describes that the heat resistance is improved by adding cerium-containing hydroxide and / or zirconium-containing hydroxide, and measures the physical properties after putting the particles in a dryer at 225 ° C. for 72 hours. However, there is no description about transparency, and since the particle size of the cerium-containing hydroxide and / or zirconium-containing hydroxide used is on the order of microns, transparency cannot be expected.

Japanese Patent Application Laid-Open No. 2016-518461 Japanese Unexamined Patent Publication No. 2014-031408

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silicone rubber composition and a silicone rubber which are silicone rubbers (cured products) having excellent transparency and heat resistance performance.

In order to solve the above problems, the present invention
(A) Organopolysiloxane represented by the following average composition formula (1) and having at least two alkenyl groups in one molecule: 100 parts by mass R ¹ _n SiO _{(4-n) / 2} (1)
(In the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, and n is a positive number of 1.95 to 2.05.),
(B) Reinforcing silica with a specific surface area of 50 m ² / g or more: 5 to 100 parts by mass,
(C) Silica that supports cerium oxide, has a surface hydrophobicized with a silicon atom-containing hydrophobizing agent, and has a primary particle size in the range of 5 to 50 nm: 0.01 to 50 parts by mass,
(D) Hardener: 0.01 to 10 parts by mass,
To provide a silicone rubber composition containing.

Such a silicone rubber composition is a silicone rubber composition that can provide a silicone rubber having excellent transparency and heat resistance.

Further, in the component (C), the content of the cerium oxide is preferably 0.1 to 30% by mass with respect to the total mass of the silica supporting the cerium oxide.

When the content of cerium oxide is within the above range, a sufficient heat resistance improving effect can be obtained, and the dispersibility of silica becomes good.

Further, it is preferable that the component (D) is an addition reaction curing agent composed of a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst.

Further, the component (D) may be an organic peroxide curing agent.

Such a component (D) can be suitably used for the silicone rubber composition of the present invention.

Further, the present invention provides a silicone rubber made of a cured product of the above silicone rubber composition.

Such a silicone rubber is excellent in transparency and heat resistance.

As described above, the silicone rubber composition of the present invention can provide a silicone rubber (cured product) having excellent transparency and heat resistance.

As described above, there has been a demand for the development of a silicone rubber composition which is a silicone rubber having excellent transparency and heat resistance.

As a result of diligent studies on the above-mentioned problems, the present inventors made silicone, which carries cerium oxide, has a surface hydrophobized by a silicon atom-containing hydrophobizing agent, and has a primary particle size in the range of 5 to 50 nm. The present invention has been completed by finding that a silicone rubber having excellent transparency and heat resistance can be obtained by adding it to a rubber composition.

That is, the present invention
(A) Organopolysiloxane represented by the following average composition formula (1) and having at least two alkenyl groups in one molecule: 100 parts by mass R ¹ _n SiO _{(4-n) / 2} (1)
(In the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, and n is a positive number of 1.95 to 2.05.),
(B) Reinforcing silica with a specific surface area of 50 m ² / g or more: 5 to 100 parts by mass,
(C) Silica that supports cerium oxide, has a surface hydrophobicized with a silicon atom-containing hydrophobizing agent, and has a primary particle size in the range of 5 to 50 nm: 0.01 to 50 parts by mass,
(D) Hardener: 0.01 to 10 parts by mass,
It is a silicone rubber composition containing.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

<Silicone rubber composition>
The silicone rubber composition of the present invention contains the above components (A) to (D). The silicone rubber composition includes an organopolysiloxane (A) having at least two alkenyl groups in one molecule as a base polymer, an addition reaction curing agent (D-1) and / or an organic as a curing agent (D). Those using a peroxide curing agent (D-2) are preferable. The shape of the silicone rubber composition may be a mirrorable type or a liquid type. The liquid silicone rubber composition has self-fluidity at room temperature (usually 25 ° C. ± 10 ° C.), whereas the miraculous silicone rubber composition has high viscosity and self-fluidity at room temperature. It means a non-liquid (solid or highly viscous paste), raw rubber-like composition that can be uniformly mixed under high shear stress by a kneading means such as a roll mill.

Hereinafter, each component of the silicone rubber composition of the present invention will be described in detail.

-(A) component-
In the present invention, the component (A) is an organopolysiloxane represented by the following average composition formula (1) and having at least two alkenyl groups in one molecule.
R ¹ _n SiO _{(4-n) / 2} (1)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, and n is a positive number of 1.95 to 2.05.)

In the above average composition formula (1), R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably one having 1 to 8 carbon atoms. Specifically, alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group and octyl group, cycloalkyl groups such as cyclopentyl group and cyclohexyl group, alkenyl groups such as vinyl group, allyl group and propenyl group. , Cycloalkenyl group, phenyl group, aryl group such as tolyl group, aralkyl group such as benzyl group, 2-phenylethyl group, or halogen atom such as fluorine, chlorine or cyano as part or all of hydrogen atom of these group. Examples thereof include a chloromethyl group, a trifluoropropyl group, a cyanoethyl group and the like substituted with a group, and a methyl group, a vinyl group, a phenyl group and a trifluoropropyl group are preferable, and a methyl group and a vinyl group are particularly preferable.

The organopolysiloxane of the component (A) has at least 2 alkenyl groups in one molecule, preferably 2 to 50, and particularly preferably 2 to 20 alkenyl groups. Specific examples thereof include an alkenyl group such as a vinyl group, an allyl group and a propenyl group, and a cycloalkenyl group such as a 2- (3-cyclohexene-1-yl) ethyl group, and in particular, those having a vinyl group. preferable. In this case, it is preferable that 0.01 to 20 mol%, particularly 0.02 to 10 mol% of the total R ¹ is an aliphatic unsaturated group. The aliphatic unsaturated group may be bonded to a silicon atom at the end of the molecular chain, to a silicon atom in the middle of the molecular chain (non-terminal of the molecular chain), or both. However, it is preferable that it is bonded to at least a silicon atom at the end of the molecular chain.

The total R ¹ in 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, more preferably all of R ¹ is an alkyl group other than an aliphatic unsaturated group, especially a methyl group Is desirable.

In the average composition formula (1), n is 1.95 to 2.05, preferably 1.98 to 2.02, and more preferably 1.99 to 2.01.

The molecular structure of the organopolysiloxane as the component (A) is preferably a linear structure or a linear structure having a partially branched structure. Specifically, diorganosiloxane units constituting the main chain of the organopolysiloxane ^{_{(R 1 2 SiO 2/2, R}} 1 is as defined above, hereinafter the same) is repeated structures, repeating only dimethylsiloxane units Diphenylsiloxane having a phenyl group, a vinyl group, a 3,3,3-trifluoropropyl group or the like as a substituent as a part of the dimethylpolysiloxane structure composed of repeating dimethylsiloxane units constituting the main chain. A unit introduced with a diorganosiloxane unit such as a unit, a methylphenylsiloxane unit, a methylvinylsiloxane unit, or a methyl-3,3,3-trifluoropropylsiloxane unit is preferable.

Further, the both ends of the molecular chain, for example, trimethylsiloxy groups, dimethylphenylsiloxy groups, vinyldimethylsiloxy group, divinyl trimethylsiloxy groups, triorganosiloxy groups such as tri-siloxy group (R 1 ³ _{SiO 1/2),} etc. It is preferably blocked.

As described above, in the organopolysiloxane of the component (A), both ends of the molecular chain are sealed with a triorganosyloxy group (R ¹ ₃ SiO _1/2 ), and the main chain is a diorganosiloxane unit (R ¹ ₂ SiO _{2). A} linear one consisting of the repetition of _{/ 2} ) can be preferably mentioned. Particularly preferred are methylvinylpolysiloxane, methylphenylvinylpolysiloxane, and methyltrifluoropropylvinyl as the type of substituent in the molecule (ie, an unsubstituted or substituted monovalent hydrocarbon group attached to a silicon atom). Examples thereof include polysiloxane and dimethylpolysiloxane.

Such an organopolysiloxane can be obtained, for example, by (co) hydrolyzing and condensing one or more of organohalogenosilanes, or by making cyclic polysiloxanes (trimers of siloxanes, tetramers, etc.) alkaline or It can be obtained by ring-opening polymerization using an acidic catalyst.

The degree of polymerization of the organopolysiloxane is preferably 100 or more (usually 100 to 100,000), particularly preferably 150 to 100,000. The degree of polymerization referred to in the present invention refers to a degree of polymerization measured as a polystyrene-equivalent weight average degree of polymerization by gel permeation chromatography (GPC) analysis measured under the following conditions.

[Measurement condition]
・ Developing solvent: Toluene ・ Flow rate: 1 mL / min
-Detector: Differential refractive index detector (RI)
-Column: KF-805L x 2 (manufactured by Shodex)
-Column temperature: 25 ° C
-Sample injection amount: 30 μL (toluene solution with a concentration of 0.2% by mass)

The component (A) may be used alone or as a mixture of two or more kinds having different molecular weights (degrees of polymerization) and molecular structures.

-(B) component-
The reinforcing silica of the component (B) is a filler added to obtain silicone rubber having excellent mechanical strength, and for this purpose, the specific surface area (BET adsorption method) is 50 m ² / g or more. It is necessary to have, preferably 100 to 450 m ² / g, and more preferably 100 to 300 m ² / g. If the specific surface area is less than 50 m ² / g, the mechanical strength of the cured product will be low.

Examples of such reinforcing silica include fumes silica (fumed silica) and precipitated silica (wet silica). Further, those whose surfaces are hydrophobized with an organosilane compound such as methylchlorosilane or a silazane compound such as hexamethyldisilazane are also preferably used, but silica as a component (C) described later is excluded. Of these, aerosol silica, which has excellent transparency of the cured product, is preferable.

The component (B) may be used alone or in combination of two or more.

The blending amount of the reinforcing silica of the component (B) is 5 to 100 parts by mass, preferably 10 to 100 parts by mass, and 20 to 60 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). Is more preferable. If the amount of the component (B) is less than 5 parts by mass, the reinforcing effect cannot be obtained, and if it is more than 100 parts by mass, the workability is deteriorated and the mechanical strength is lowered. Fatigue durability also deteriorates.

-(C) component-
The component (C) is silica (cerium oxide-supported silica) that supports cerium oxide, has a surface hydrophobicized with a silicon atom-containing hydrophobizing agent, and has a primary particle size in the range of 5 to 50 nm.

When supporting the above cerium oxide, it is preferable to use a dispersion liquid (sol) of cerium oxide fine particles. The average particle size of cerium oxide in the sol is preferably 1 to 100 nm, and particularly preferably 1 to 50 nm, because transparency in the visible region is important. When the average particle size of the fine particles is 100 nm or less, the particle size is smaller than the light wavelength in the visible region, and scattering is not remarkable. Further, if it is 1 nm or more, aggregation is unlikely to occur.

In the present invention, the average particle size of cerium oxide refers to the 50% cumulative distribution diameter in the volume-based particle size distribution by the dynamic light scattering method.

The sol concentration of the cerium oxide sol is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, and further preferably 10 to 30% by mass. The dispersion medium of this cerium oxide sol is usually water, but it may be a buffer system such as an aqueous phosphoric acid solution. The pH of the above-mentioned cerium oxide sol is not particularly limited, but acidity of pH 7 or less is preferable. A commercially available cerium oxide sol can be used, and examples of the commercially available cerium oxide sol include CESL-30N (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.), Needral P10 (manufactured by Taki Chemical Co., Ltd.), and Nanouse CE. -T20B (manufactured by Nissan Chemical Industry Co., Ltd.) and the like.

As the silica that supports cerium oxide in the component (C), for example, fumed silica can be used. The silica component (C) has a primary particle size of 5 to 50 nm, preferably 5 to 10 nm. That is, in the component (C) of the present invention, cerium oxide is supported on silica having a primary particle diameter of 5 to 50 nm. If the primary particle size is less than 5 nm, it becomes difficult to disperse in the silicone polymer. If it exceeds 50 nm, the transparency of the silicone polymer containing cerium oxide-supported silica may deteriorate.

In the present invention, the primary particle diameter of silica refers to the diameter of particles measured by a transmission electron microscope.

As a method for supporting cerium oxide on the silica, batch equipment such as a Henschel mixer, an Erich mixer, and a high-speed mixer, and continuous equipment such as a horizontal axis rotary blade can be used. In these facilities, it is possible to spray cerium oxide sol to the place where silica powder is stirred and mixed at high speed to uniformly disperse it. As a result, silica carrying cerium oxide is obtained.

The silica component (C) may be granulated with a solvent such as water or alcohol. Granulation improves the handleability of silica.

Another feature of the present invention is that the cerium oxide-supported silica is hydrophobized with a silicon atom-containing hydrophobizing agent when or after the cerium oxide is supported on the silica.
The degree of hydrophobization of the cerium oxide-supported silica is preferably 40 or more. When the degree of hydrophobization is within such a range, aggregation of silica can be prevented, and the transparency of the obtained silicone rubber becomes good. The method for measuring the degree of hydrophobicity will be described in the following examples.

As the silicon atom-containing hydrophobizing agent, one represented by the following general formula (2) can be used.
R ² Si (Y) ₃ (2)
(In the formula, R ² may be the same or different, and may be substituted with a (meth) acrylic group, an oxylanyl group, an amino group, a mercapto group, an isocyanate group or a fluorine atom. The number of carbon atoms is 1 or more and 20 or less. Substituent or hydrogen atom selected from the group consisting of an alkyl group of 2 or more and 20 or less, an aryl group having 6 or more and 20 or less carbon atoms, and a (poly) dimethylsiloxy group having 50 or less silicon atoms. Y is a substituent selected from the group consisting of an alkoxy group, an acetoxy group, an enol group, and a chlorine atom.)

In this case, the alkyl group preferably includes an alkyl group having 1 to 6 carbon atoms, particularly a methyl group and an ethyl group, and the aryl group includes an aryl group having 6 to 10 carbon atoms, particularly a phenyl group. Further, the number of silicon of the (poly) dimethylsiloxy group is preferably 1 to 50, particularly preferably 1 to 30.

Specific examples of the silicon atom-containing hydrophobizing agent represented by the general formula (2) include hydrogen trimethoxysilane, hydrogen triethoxysilane, methyl trimethoxysilane, methyl triethoxysilane, methyl triisopropoxysilane, and ethyl trimethoxysilane. , Ethyltriethoxysilane, ethyltriisopropoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltriisopropoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacry Loxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-Chloropropyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, perfluorooctylethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-Aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (2-aminoethyl) aminopropyltrimethoxysilane, γ-isocyanuppropyltrimethoxysilane, γ-isocyanoxidetriethoxysilane, phenyltrimethoxysilane , Phenyltriethoxysilane, tris (3-trimethoxysilylpropyl) isocyanurate with isocyanate groups bonded to each other, tris (3-triethoxysilylpropyl) isocyanurate, partial hydrolysis condensate of methyltrimethoxysilane (trade name " "KC-89S", "X-40-9220" manufactured by Shin-Etsu Chemical Industry Co., Ltd.), Partial hydrolysis condensate of methyltrimethoxysilane and γ-glycidoxypropyltrimethoxysilane (trade name "X-41-" 1056 ”alkoxysilanes such as Shin-Etsu Chemical Industry Co., Ltd .; allylsilanes such as triallylmethylsilane, triallylethylsilane, and triallylisopropylsilane; triacetoxymethylsilane, triacetoxyethylsilane, triacetoxypropylsilane , Acetoxysilanes such as triacetoxyphenylsilane; trichloromethylsilane, trichloroethylsilane, trichloropropylsilane, trichlorophenylsila Chlorosilanes such as chlorosilanes; enolsilanes such as triisopropenyloxymethylsilane, ethyltriisopropenyloxysilane, triisopropenyloxypropylsilane, phenyltriisopropenyloxysilane and the like can be mentioned.

（式中、Ｍｅはメチル基であり、ｒは０〜４９の整数である） In the silicon atom-containing hydrophobizing agent represented by the general formula (2), as a specific example when R ² is (poly) dimethylsiloxane, a compound represented by the following general formula (3) can be mentioned.

(In the formula, Me is a methyl group and r is an integer from 0 to 49)

In the general formula (3), r is an integer of 0 or more and 49 or less, preferably an integer of 5 or more and 40 or less, and more preferably an integer of 10 or more and 30 or less. When r is 49 or less, the properties as a silicone oil are appropriate, and the solubility of the surface-treated organosol in various resins is not limited. In the general formula (3), the compound having an average structure of r = 30 can be obtained under the trade name “X-24-9822” (manufactured by Shin-Etsu Chemical Co., Ltd.).

The amount of the silicon atom-containing hydrophobizing agent added is preferably 0.01 times or more and 50 times or less, more preferably 1 time or more and 25 times or less, based on the mass of silica as the component (C). More preferably, it is 2 times or more and 10 times or less. When the amount added is 50 times or less the mass of silica, it does not form a slurry, the cohesive force of silica after drying becomes small, and the transparency when dispersed in a silicone polymer becomes good. When it is 0.01 times or more, the treatment of silanol groups on the silica surface is sufficient, the cohesive force of silica after drying is small, and the transparency when dispersed in the silicone polymer is good.

In the silica of the component (C), the content of cerium oxide is preferably 0.1 to 30% by mass, more preferably 1 to 10% by mass, based on the total mass of the silica carrying cerium oxide. .. If the content of cerium oxide is 0.1 % by mass or more, there is no risk that the heat resistance improving effect will not be exhibited, and if it is 30% by mass or less, the dispersibility of silica will be good.

The blending amount of the cerium oxide-supported silica of the component (C) is 0.01 to 50 parts by mass with respect to 100 parts by mass of the component (A).

-(D) component-
The component (D) is a curing agent. Examples of this curing agent include (D-1) addition reaction curing agent and (D-2) organic peroxide curing agent as described above.

The blending amount of the curing agent for the component (D) is 0.01 to 10 parts by mass with respect to 100 parts by mass for the component (A).

(D-1) Addition reaction curing agent (D-1) As the addition reaction curing agent, an organohydrogenpolysiloxane and a hydrosilylation catalyst are used in combination.
As the organohydrogenpolysiloxane, hydrogen atoms bonded to 2 or more, preferably 3 or more, more preferably 3 to 200, and further preferably about 4 to 100 silicon atoms in one molecule (that is, SiH). As long as it contains a group), it may have a linear, cyclic, branched, or three-dimensional network structure. As an example of the organohydrogenpolysiloxane, a known organohydrogenpolysiloxane as a cross-linking agent for the addition reaction curable silicone rubber composition can be used, and more specifically, it is represented by the following average composition formula (4). Organohydrogenpolysiloxane is used.
R ³ _p H _q SiO _{(4-p-q) / 2} (4)
(In the formula, R ³ may be the same or different and represents an unsubstituted or substituted monovalent hydrocarbon group, where p and q are 0 <p <3, 0 <q ≦ 3, 0 <p + q ≦. It is a positive number that satisfies 3.)

In the average composition formula (4), R ³ may be the same or different, and preferably shows an unsubstituted or substituted monovalent hydrocarbon group and excludes an aliphatic unsaturated bond. The monovalent hydrocarbon group of R ³ is usually preferably one having 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms, and specifically, an alkyl group such as a methyl group, an ethyl group or a propyl group, or a cyclo such as a cyclohexyl group. Aryl groups such as alkyl groups, phenyl groups and trill groups, aralkyl groups such as benzyl groups, 2-phenylethyl groups and 2-phenylpropyl groups, and some or all of the hydrogen atoms of these groups are replaced with halogen atoms or the like. Examples thereof include 3,3,3-trifluoropropyl groups and the like.

In the average composition formula (4), p and q are 0 <p <3, preferably 0.5 ≦ p ≦ 2.2, more preferably 1.0 ≦ p ≦ 2.0, 0 <q ≦ 3, Preferably 0.002 ≦ q ≦ 1.1, more preferably 0.005 ≦ q ≦ 1, 0 <p + q ≦ 3, preferably 1 ≦ p + q ≦ 3, more preferably 1.002 ≦ p + q ≦ 2.7. It is a positive number that satisfies.

The organohydrogenpolysiloxane has two or more, preferably three or more SiH groups in one molecule, both at the end of the molecular chain and in the middle of the molecular chain. You may. Further, as this organohydrogenpolysiloxane, the viscosity at 25 ° C. measured by the method described in JIS K 7117-1: 1999 at 25 ° C. is 0.5 to 10,000 mPa · s, particularly 1 to 300 mPa · s. Is preferable.

Specific examples of such an organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris (hydrogendimethylsiloxy) methylsilane, and the like. Tris (hydrogendimethylsiloxy) phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogenpolysiloxane, both-terminal trimethylsiloxy group-blocked dimethylsiloxane Methylhydrogensiloxane copolymer, both-terminal dimethylhydrogensiloxy group-blocked dimethylpolysiloxane, both-terminal dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane Diphenylsiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane / methylphenylsiloxane / dimethylsiloxane copolymer, both-terminal dimethyl Hydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / diphenylsiloxane copolymer, both-terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / methylphenylsiloxane copolymer, (CH ₃ ) ₂ HSiO _{1 / A} copolymer consisting of ₂ units and (CH ₃ ) ₃ SiO _1/2 unit and SiO _4/2 unit, (CH ₃ ) ₂ HSiO _1/2 unit and SiO _4/2 unit, (CH ₃ ) CH ₃ ) ₂ HSiO _1/2 unit, SiO _4/2 unit and (C ₆ H ₅ ) ₃ SiO _1/2 unit, etc., and some or all of the methyl groups in the above exemplified compounds. Examples thereof include those substituted with other alkyl groups and phenyl groups.

The blending amount of the organohydrogenpolysiloxane is preferably 0.1 to 40 parts by mass with respect to 100 parts by mass of the component (A). Further, the ratio of hydrogen atoms (= SiH groups) bonded to silicon atoms in the organohydrogenpolysiloxane is appropriately in the range of 0.5 to 10 with respect to one alkenyl group of the component (A). A range of 0.7 to 5 is suitable. When the above ratio is 0.5 or more, the cross-linking is sufficient and sufficient mechanical strength can be obtained. Further, when the above ratio is 10 or less, the physical characteristics after curing are not deteriorated, and there is no possibility that the heat resistance is particularly deteriorated or the compression set is increased.

The hydrosilylation catalyst is a catalyst in which the alkenyl group of the component (A) and the silicon atom-bonded hydrogen atom (SiH group) of the organohydrogenpolysiloxane are hydrosilylated and added. Examples of the hydrosilylation catalyst include platinum group metal-based catalysts, and examples thereof include simple substances of platinum group metals and their compounds. For this, conventionally known catalysts for addition reaction curable silicone rubber compositions can be used. For example, a platinum catalyst such as an alcohol solution of particulate platinum metal adsorbed on a carrier such as silica gel, alumina, or silica gel, secondary platinum chloride, platinum chloride acid, or hexahydrate of platinum chloride acid, a palladium catalyst, a rhodium catalyst, or the like. However, platinum or a platinum compound (platinum catalyst) is preferable.

The amount of the catalyst added may be such that the addition reaction can be promoted, and is usually used in the range of 1 mass ppm to 1 mass% with respect to the organopolysiloxane of the component (A) in terms of the amount of platinum group metal. The range of 10 to 500 mass ppm is preferable. When the addition amount is 1 mass ppm or more, the addition reaction is sufficiently promoted and the curing becomes sufficient. On the other hand, if the addition amount exceeds 1% by mass, even if a larger amount is added, the effect on the reactivity is small, so that the addition amount is economically 1% by mass or less.

(D-2) Organic peroxide curing agent (D-2) Organic peroxide curing agent includes, for example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methyl. Benzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, di-t-butyl peroxide, t-butylperbenzoate, 1,6 -Hexanediol-bis-t-butylperoxycarbonate and the like can be mentioned. The amount of the organic peroxide curing agent added is preferably 0.1 to 10 parts by mass, particularly 0.2 to 5 parts by mass, based on 100 parts by mass of the component (A). If the blending amount is 0.1 parts by mass or more, curing is sufficient, and if it is 10 parts by mass or less, there is no possibility that the cured silicone rubber product will turn yellow due to the decomposition residue of the organic peroxide. In addition, addition reaction curing and organic peroxide curing, in which the component (D-1) and the component (D-2) were combined and blended in the above-mentioned blending amount, were used in combination with the component (A). It can also be a co-vulcanized silicone rubber composition.

-Other ingredients-
In the present invention, if necessary, a dispersant (wetter) can be blended for the purpose of uniformly dispersing the reinforcing silica of the component (B) in the organopolysiloxane of the component (A). Examples of this wetter include a silanol group (that is, a silicon atom-bonded hydroxyl group) -containing silane compound such as diphenylsilanediol, and a linear dimethylsiloxane oligomer having a silanol group block at both ends of the molecular chain (for example, the degree of polymerization or in the molecule). One or more selected from silanol group-containing organosiloxane oligomers such as (low polymerization degree polymers having 2 to 30 silicon atoms, particularly 3 to 20 silicon atoms), silazan, and the like are used.

The blending amount of the wetter is preferably 0 to 25 parts by mass, more preferably 3 to 20 parts by mass with respect to 100 parts by mass of the base polymer (component (A)). ..

Further, in the silicone rubber composition of the present invention, in addition to the above components, if necessary, a filler such as pulverized quartz, crystalline silica, diatomaceous earth, calcium carbonate, a colorant, an acid receiving agent, alumina, boron nitride, etc. Various alkoxysilanes such as phenyl group-containing alkoxysilanes and their hydrolysates, diphenylsilanediols, carbon functional silanes, and silanol group-containing low-molecular-weight siloxanes as heat conductivity improvers, mold release agents, and dispersants for fillers. It is optional to add known fillers and additives in the thermocurable silicone rubber composition.

<Silicone rubber>
Further, the present invention provides a silicone rubber made of a cured product of the above silicone rubber composition.

As a molding and curing method of the silicone rubber composition of the present invention, a conventional method can be adopted, but as a molding method, an optimum means suitable for the purpose is selected from injection molding, transfer molding, injection molding, compression molding and the like. It is possible. As the curing conditions, heat treatment (primary vulcanization) conditions of about 3 seconds to 160 minutes at 40 to 230 ° C. can be adopted. Further, if necessary, secondary vulcanization (post-cure) may be performed at 40 to 230 ° C. for about 10 minutes to 24 hours.

The silicone rubber thus obtained has high transparency, and the total light transmittance of the 2 mm thick silicone rubber (cured product) measured by the method described in JIS K 7361-1: 1997 is 85% or more (85 to 5). It is preferably 100%), more preferably 89% or more (89 to 100%). Further, the silicone rubber thus obtained is excellent in heat resistance performance and excellent transparency.

Hereinafter, the present invention will be specifically described with reference to Preparation Examples, Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following example, the degree of polymerization of siloxane is the polystyrene-equivalent weight average degree of polymerization by gel permeation chromatography analysis using toluene as a developing solvent. The particle size of cerium oxide refers to the 50% cumulative distribution diameter in the volume-based particle size distribution by the dynamic light scattering method. The particle size of silica refers to the diameter of the particles measured by a transmission electron microscope.

(Preparation Example 1: Preparation of silica (1) carrying cerium oxide)
200 g of fumed silica (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g and a primary particle diameter of 12 nm by the BET method was charged into a high-speed mixer (volume 10 L) and operated at a rotation speed of 1500 rpm. When the rotation was stable, 70 g of dimethylpolysiloxane having an average degree of polymerization of 4, 25 ° C. and a viscosity of 15 mPa · s was sprayed as a silicon atom-containing hydrophobizing agent in 20 seconds, and then cerium oxide sol (average particle diameter 10 nm, trade name). CESL-30N, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd., and 200 g of pure water were sprayed in 60 seconds. This was heated at 250 ° C. for 2.5 hours after removing water with a dryer. The obtained silica (1) carrying cerium oxide had a loose bulk density of 180 g / L measured by the following method and a degree of hydrophobization by the methanol titration method of 53.

<Measurement method of loose bulk density>
A multi-tester MT-1000 manufactured by Seishin Enterprise is used. Place the funnel, fluid (opening 150 μm), and fluid spacer in this order on the upper part of the feeder unit, and fix them with stoppers. A 100 ml cell is placed on a sample table, the sample is put into the sample unit, the feeder is vibrated, the cell is filled with the sifted sample, and the cell is scraped off with a fray plate. The loose bulk density ρ (g / l) is obtained by the following equation.
ρ = ((W1-W0) / 100) × 1000
W0: Weight of cell container (g)
W1: Cell container + sample weight (g)

<Measurement method of hydrophobicity>
Put 50 ml of pure water in a 200 ml beaker, add 0.2 g of a sample, and stir with a magnetic stirrer. When the tip of a burette containing methanol is put into a liquid, methanol is added dropwise with stirring, and the amount of methanol added until the sample is completely dispersed in water is Z ml, the following formula is obtained.
Degree of hydrophobization = (Z / (50 + Z)) x 100

(Preparation Example 2: Preparation of silica (2) carrying cerium oxide)
Cerium oxide sol (particle diameter 10 nm, trade name CESL-30N, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.) and not 200 g of pure water, but cerium oxide sol (particle diameter 10 nm, trade name CESL-30N, first rare element) It was prepared in the same manner as in Preparation Example 1 except that 300 g (manufactured by Chemical Industry Co., Ltd.) was used. The obtained silica (2) carrying cerium oxide had a loose bulk density of 190 g / L and a degree of hydrophobization by the methanol titration method of 48.

(Preparation Example 3: Preparation of silica (3) carrying cerium oxide)
It was prepared in the same manner as in Preparation Example 1 except that 50 g of dimethyldimethoxysilane was used as the silicon atom-containing hydrophobizing agent instead of dimethylpolysiloxane having a viscosity of 15 mPa · s at an average degree of polymerization of 4 and 25 ° C. The obtained silica (3) carrying cerium oxide had a loose bulk density of 180 g / L and a degree of hydrophobization by the methanol titration method of 64.

(Preparation Example 4: Preparation of silica (4) carrying cerium oxide)
It was prepared in the same manner as in Preparation Example 1 except that dimethylpolysiloxane having a viscosity of 15 mPa · s at an average degree of polymerization of 4 and 25 ° C. was not added as a silicon atom-containing hydrophobizing agent. The obtained silica (4) carrying cerium oxide had a loose bulk density of 175 g / L. The silica (4) carrying cerium oxide was dissolved in water (hydrophobicity 0).

(Preparation Example 5: Preparation of silica paste (1) carrying cerium oxide)
After mixing 100 parts by mass of dimethylpolysiloxane having an average degree of polymerization of 180 with both ends of the molecular chain sealed with a dimethylvinylsiloxy group and 30 parts by mass of silica (1) carrying cerium oxide, three rolls were passed through three times. , A silica paste (1) carrying cerium oxide was prepared.

(Preparation Example 6: Preparation of silica paste (2) carrying cerium oxide)
A cerium oxide-supported silica paste (2) was prepared in the same manner as in Preparation Example 5, except that the cerium oxide-supported silica (4) was used instead of the cerium oxide-supported silica (1).

(Preparation Example 7: Preparation of cerium oxide paste (1))
Cerium oxide paste in the same manner as in Preparation Example 5, except that cerium oxide (average particle size: 1 μm, trade name: SN-2, manufactured by Nikki Co., Ltd.) was used instead of silica (1) carrying cerium oxide. (1) was prepared.

[Examples 1 to 5, Comparative Examples 1 to 6: Preparation of silicone rubber composition]
(Example 1)
Fumed silica (Japan) having 60 parts by mass of dimethylpolysiloxane (component (A)) having an average degree of polymerization of 750 and having a specific surface area of 300 m ² / g by the BET method, with both ends of the molecular chain sealed with dimethylvinylsiloxy groups. Aerosil 300) (component (B)) manufactured by Aerosil Co., Ltd., 40 parts by mass, silica (1) (component (C)) carrying cerium oxide obtained in Preparation Example 1, 1.5 parts by mass, hexamethyldisilazane 8 A parts by mass and 2.0 parts by mass of water were mixed at room temperature for 30 minutes, then heated to 150 ° C., stirred for 3 hours, and cooled to obtain a silicone rubber base (1).
In 100 parts by mass of this silicone rubber base (1), 6 parts by mass of dimethylpolysiloxane (component (A)) having an average degree of polymerization of 750 in which both ends of the molecular chain are sealed with a dimethylvinylsiloxy group and both ends of the molecular chain are 5 parts by mass of dimethylpolysiloxane (component (A)), which is sealed with a trimethylsiloxy group and contains 10 mol% of vinylmethylsiloxane units in the diorganosiloxane units of the main chain and has an average degree of polymerization of 150, and a platinum catalyst (Pt). Concentration 1% by mass) 0.1 part by mass, methylhydrogenpolysiloxane having SiH group in the side chain as a cross-linking agent (polymerization degree 38, SiH group 0.0074 mol%, both terminal trimethylsiloxy group-blocking dimethylsiloxane-methyl Add 3 parts by mass of (hydrogensiloxane copolymer) (total amount of SiH group / vinyl group = 1.81 mol / mol) (component (D)) and 0.05 part by mass of ethynylcyclohexanol as a reaction control agent, and add 15 parts. Minute stirring was continued to obtain the silicone rubber composition (1).
The silicone rubber composition (1) was pre-cured (primary vulcanization) at 120 ° C. for 10 minutes and then post-cured (secondary vulcanization) at 150 ° C. for 1 hour in a dryer to obtain a cured product. With respect to the obtained cured product, various rubber physical characteristics and light transmittance were measured by the methods shown below. Further, the physical characteristics (heat resistance) of the rubber after being placed in a dryer at 225 ° C. for 5 days were measured. The results are shown in Table 1.

(Example 2)
Silicone rubber composition (2) in the same manner as in Example 1 except that 0.7 parts by mass of silica (2) carrying cerium oxide of Preparation Example 2 was used instead of silica (1) carrying cerium oxide. Got Various physical properties and light transmittance of the obtained composition were measured. The results are shown in Table 1.

(Example 3)
A silicone rubber composition (3) was obtained in the same manner as in Example 1 except that the cerium oxide-supported silica (3) of Preparation Example 3 was used instead of the cerium oxide-supported silica (1). Various physical properties and light transmittance of the obtained composition were measured. The results are shown in Table 1.

(Example 4)
Fumed silica (Japan) having 60 parts by mass of dimethylpolysiloxane (component (A)) having an average degree of polymerization of 750 and having a specific surface area of 300 m ² / g by the BET method, with both ends of the molecular chain sealed with dimethylvinylsiloxy groups. Aerosil 300) (component (B)) manufactured by Aerosil, 40 parts by mass, 8 parts by mass of hexamethyldisilazane, and 2.0 parts by mass of water are mixed at room temperature for 30 minutes, then heated to 150 ° C. and stirred for 3 hours. Was continued and cooled to obtain a silicone rubber base (2).
In 100 parts by mass of this silicone rubber base (2), 6 parts by mass of dimethylpolysiloxane (component (A)) having an average degree of polymerization of 750, in which both ends of the molecular chain are sealed with a dimethylvinylsiloxy group, and both ends of the molecular chain are 5 parts by mass of dimethylpolysiloxane (component (A)), which is sealed with a trimethylsiloxy group and contains 10 mol% of vinylmethylsiloxane unit in the diorganosiloxane unit of the main chain and has an average degree of polymerization of 150, in Preparation Example 5. Silica paste carrying cerium oxide (1) (component (C)) 4 parts by mass, platinum catalyst (Pt concentration 1% by mass) 0.1 parts by mass, methylhydrogenpoly having a SiH group in the side chain as a cross-linking agent 3 parts by mass of siloxane (dimethylsiloxane / methylhydrogensiloxane copolymer with a degree of polymerization of 38 and 0.0074 mol% of SiH groups) (total amount of SiH groups / vinyl groups = 1.75 mol / mol) (Component (D)) and 0.05 parts by mass of ethynylcyclohexanol as a reaction control agent were added, and stirring was continued for 15 minutes to obtain a silicone rubber composition (4).
The silicone rubber composition (4) was press-cured (primary vulcanization) at 120 ° C. for 10 minutes and then post-cured (secondary vulcanization) at 150 ° C. for 1 hour in a dryer to obtain a cured product. Various rubber physical characteristics and light transmittance were measured for the obtained cured product. Further, the physical characteristics (heat resistance) of the rubber after being placed in a dryer at 225 ° C. for 5 days were measured. The results are shown in Table 1.

(Example 5)
Organopolysiloxane raw rubber ((A) component) consisting of 99.825 mol% of dimethylsiloxane unit, 0.15 mol% of methylvinylsiloxane unit, 0.025 mol% of dimethylvinylsiloxy unit, and an average degree of polymerization of about 6,000. ) 100 parts by mass, BET method specific surface area of 200 m ² / g of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) (component (B)) 40 parts by mass, silica carrying cerium oxide of Preparation Example 1 ( 1) (Component (C)) 1.4 parts by mass, 6 parts by mass of dimethylpolysiloxane having silanol groups at both ends and a viscosity of 15 mPa · s at an average degree of polymerization of 4, 25 ° C. was added, and at 170 ° C. After heating under mixing with a kneader for 2 hours, the base compound (1) was prepared.
For 100 parts by mass of this base compound (1), 0.4 parts by mass of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane (component (D)) as a curing agent was added to two rolls. And mixed uniformly to obtain a raw rubber-like silicone rubber composition (5).
The silicone rubber composition (5) was press-cured (primary vulcanization) at 165 ° C. for 10 minutes and then post-cured (secondary vulcanization) at 200 ° C. for 4 hours in a dryer to obtain a cured product. Various rubber physical characteristics and light transmittance were measured for the obtained cured product. Further, the physical characteristics (heat resistance) of the rubber after being placed in a dryer at 225 ° C. for 5 days were measured. The results are shown in Table 1.

(Comparative Example 1)
A comparative silicone rubber composition (1) containing no component (C) was obtained in the same manner as in Example 1 except that silica (1) carrying cerium oxide was not added. Various physical properties of the obtained composition were measured. The results are shown in Table 1.

(Comparative Example 2)
Comparison in which the component (C) is not hydrophobized in the same manner as in Example 1 except that the silica (4) carrying cerium oxide of Preparation Example 4 was used instead of the silica (1) carrying cerium oxide. A silicone rubber composition (2) was obtained. Various physical properties of the obtained composition were measured. The results are shown in Table 1.

(Comparative Example 3)
The component (C) was made hydrophobic in the same manner as in Example 4 except that the silica paste (2) supporting cerium oxide of Preparation Example 6 was used instead of the silica paste (1) supporting cerium oxide. A comparative silicone rubber composition (3) which was not used was obtained. Various physical properties of the obtained composition were measured. The results are shown in Table 1.

(Comparative Example 4)
Silica is contained in the component (C) in the same manner as in Example 4 except that 1 part by mass of the cerium oxide paste (1) of Preparation Example 7 was used instead of the silica paste (1) carrying cerium oxide. A comparative silicone rubber composition (4) was obtained. Various physical properties of the obtained composition were measured. The results are shown in Table 1.

(Comparative Example 5)
Example 1 except that 0.2 parts by mass of cerium oxide sol (particle size 10 nm, trade name CESL-30N, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.) was used instead of silica (1) carrying cerium oxide. In the same manner as above, a comparative silicone rubber composition (5) containing no silica in the component (C) was obtained. Various physical properties of the obtained composition were measured. The results are shown in Table 1.

(Comparative Example 6)
A comparative silicone rubber composition (6) containing no component (C) was obtained in the same manner as in Example 5 except that silica (1) carrying cerium oxide was not added. Various physical properties of the obtained composition were measured. The results are shown in Table 1.

[Various physical property measurement methods]
With respect to the silicone rubber compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 6, various physical characteristics [hardness (durometer A), using a cured product sheet for testing prepared in accordance with JIS K 6249: 2003, Tensile strength, elongation at cutting] was measured. In addition, a heat resistance test was conducted using the cured product sheet at 225 ° C. for 5 days, and various physical properties were measured after the test.

[Measurement of total light transmittance]
For the silicone rubber compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 6, a haze meter (manufactured by Suga Test Instruments Co., Ltd., model: HGM-2) was used to obtain a C light source with a 2 degree field and a luminous flux of φ13 mm. Under the conditions, the total light transmittance of the 2 mm thick silicone rubber cured product sheet was measured.

As shown in Table 1, the silicone rubbers (Examples 1 to 5) made of a cured product of the silicone rubber composition of the present invention are all excellent in physical characteristics, transparency, and heat resistance of each rubber. .. In particular, in Example 5 in which the organic peroxide curing agent was used as the component (D), the fluctuation in elongation at the time of cutting after the heat resistance test was small, and the heat resistance performance was excellent.

On the other hand, in Comparative Examples 1 and 6 in which the cerium oxide-supported silica of the component (C) was not contained, the heat resistance performance was inferior. Further, in Comparative Examples 2 and 3 in which the cerium oxide-supported silica was not hydrophobized, and Comparative Examples 4 and 5 in which silica was not contained in the component (C) and only cerium oxide was added, the heat resistance performance and transparency were improved. It got worse.

From the above, it has been clarified that the present invention can provide a silicone rubber composition which is a silicone rubber having excellent transparency and heat resistance.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

Claims (4)

(A) Organopolysiloxane represented by the following average composition formula (1) and having at least two alkenyl groups in one molecule: 100 parts by mass R ¹ _n SiO _{(4-n) / 2} (1)
(In the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, and n is a positive number of 1.95 to 2.05.),
(B) Reinforcing silica with a specific surface area of 50 m ² / g or more: 5 to 100 parts by mass,
(C) Silica that supports cerium oxide, has a surface hydrophobicized with a silicon atom-containing hydrophobizing agent, and has a primary particle size in the range of 5 to 50 nm: 0.01 to 50 parts by mass,
(D) Hardener: 0.01 to 10 parts by mass,
In der is, the component (C) which contains a content of the cerium oxide, with respect to the total mass of the silica carrying the cerium oxide, characterized in that from 0.1 to 30 wt% Silicone rubber composition. The silicone rubber composition according to claim 1, wherein the component (D) is an addition reaction curing agent comprising a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst. The silicone rubber composition according to claim 1, wherein the component (D) is an organic peroxide curing agent. A silicone rubber comprising a cured product of the silicone rubber composition according to any one of claims 1 to 3 .