JP6957960B2 - Transparent silicone rubber composition and its cured product - Google Patents

Description

The present invention, electric equipment, automobiles, construction, medical, relates preferably silicone rubber composition is used and a cured product thereof in various fields such as food, more detail, excellent transparency and excellent heat resistance The present invention relates to a silicone rubber composition and a cured product thereof, which gives a cured product to have.

Silicone rubber, which is a cured product of the silicone rubber composition, has excellent weather resistance, electrical properties, low compression permanent strain resistance, heat resistance, cold resistance, etc., and therefore has properties such as electrical equipment, automobiles, construction, and medical care. , Widely used in various fields including food. 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.

It is known to add additives such as cerium oxide, cerium hydroxide, iron oxide, and carbon black in order to further improve the heat resistance of silicone rubber. Patent Document 1 (Japanese Patent Laid-Open No. 2016-518461) describes that the heat resistance is improved by adding 0.1% by mass or more of titanium oxide and iron oxide, but the heat resistance is improved at 300 ° C. for 1 hour. Only the amount of formaldehyde, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane generated when heated 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 (Japanese Unexamined Patent Publication No. 2014-031408) describes that the heat resistance is improved by adding cerium-containing hydroxide and / or zirconium-containing hydroxide, and the mixture is placed in a dryer at 225 ° C. for 72 hours. After that, the physical properties are measured, but the physical properties deteriorate under higher temperature conditions. In addition, 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 cured product which are silicone rubbers (cured products) having excellent transparency and heat resistance performance.

As a result of diligent studies to achieve the above object, the present inventor has applied dynamic light to a silicone rubber composition containing an organopolysiloxane having at least two alkenyl groups in one molecule and reinforcing silica. By blending a mixed solution of cerium oxide sol, alkoxysilane, and water having a 50% cumulative distribution diameter of 1 to 200 nm in the volume-based particle size distribution by the scattering method, the cured product of this silicone rubber composition becomes transparent. It has been found that it is excellent and has excellent heat resistance, and has led to the present invention.

Therefore, the present invention provides the following silicone rubber composition and a cured product thereof.
[1]
(A) The following average composition formula (1)
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.)
Organopolysiloxane represented by and having at least two alkenyl groups in one molecule
100 parts by mass,
(B) Reinforcing silica with a specific surface area of 50 m ² / g or more 5 to 100 parts by mass,
(C) The following general formula (2)
R ² _m Si (OR ³ ) _(4-m) (2)
(In the formula, R ² is an independently hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, R ³ is an same or different unsubstituted or substituted alkyl group, and m is 0, 1, 2 or 3 Is.)
Alkoxysilane (C-1) represented by, cerium oxide sol (C-2) and water (C-3) having a 50% cumulative distribution diameter of 1 to 200 nm in the volume-based particle size distribution by the dynamic light scattering method. [However, the amount of the component (C-1) added is 2 to 1,000 times the mass of the cerium oxide in the component (C-2), and the content of the cerium oxide in the above mixed solution. Is 0.1 to 10% by volume. ] 0.01 to 50 parts by mass,
(D) A transparent silicone rubber composition containing an effective amount of a curing agent.
[2]
The amount of water contained in the mixed solution of the alkoxysilane of the component (C), the cerium oxide sol and water is 0.3 to 5 times the molar number of the alkoxy groups in the alkoxysilane of the (C-1) component []. 1] The silicone rubber composition according to the above.
[3]
The pH of the mixed solution of the component (C) is 1.0 to 5.0 or 9.0 to 11.0, and the content of cerium oxide in the cerium oxide sol of the component (C-2) is 1 to 50. The silicone rubber composition according to [1] or [2], which is by mass%.
[4]
The silicone rubber composition according to any one of [1] to [3], wherein the curing agent (D) is an organic peroxide.
[5]
The silicone rubber composition according to any one of [1] to [3], wherein the curing agent (D) is an addition reaction curing type composed of a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst.
[6]
The silicone rubber composition according to any one of [1] to [5], wherein the cured product of the silicone rubber composition is formed into a sheet having a thickness of 2 mm and the total light transmittance is 80% or more.
[7]
A silicone rubber cured product comprising a cured product of the silicone rubber composition according to any one of [1] to [6].

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

Hereinafter, the present invention will be described in detail.
The silicone rubber composition of the present invention contains the following components (A), (B), (C-1) to (C-3) and (D).
(A) The following average composition formula (1)
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.)
Organopolysiloxane represented by and having at least two alkenyl groups in one molecule
100 parts by mass,
(B) Reinforcing silica with a specific surface area of 50 m ² / g or more 5 to 100 parts by mass,
(C) The following general formula (2)
R ² _m Si (OR ³ ) _(4-m) (2)
(In the formula, R ² is an independently hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, R ³ is an same or different unsubstituted or substituted alkyl group, and m is 0, 1, 2 or 3 Is.)
Alkoxysilane (C-1) represented by, cerium oxide sol (C-2) and water (C-3) having a 50% cumulative distribution diameter of 1 to 200 nm in the volume-based particle size distribution by the dynamic light scattering method. 0.01 to 50 parts by mass of the mixed solution of
(D) An effective amount of a curing agent is contained as an essential component.

<(A) Organopolysiloxane>
In the present invention, the component (A) is an organopolysiloxane represented by the following average composition formula (1).
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.)

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

In particular, the organopolysiloxane as the component (A) has two or more, usually 2 to 50, particularly 2 to 20 alkenyl groups, cycloalkenyl groups and other aliphatic unsaturated groups in one molecule. Those having a vinyl group are preferable, and those having a vinyl group are particularly 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.

Further, in the above formula (1), all 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, it is desirable that it is a methyl group.

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

The molecular structure of the organopolysiloxane as the component (A) is preferably linear or linear with a partially branched structure. ^{Specifically, the repeating structure of the diorganosiloxane units (R 1} ₂ SiO _2/2 , R ¹ is the same as above, the same applies hereinafter) constituting the main chain of the organopolysiloxane is based on the repetition of only the dimethylsiloxane unit. Diphenylsiloxane having a phenyl group, a vinyl group, a 3,3,3-trifluoropropyl group or the like as a substituent as a part of a dimethylpolysiloxane structure composed of repeating dimethylsiloxane units constituting the main chain. It is preferable to introduce a diorganosiloxane unit such as a unit, a methylphenylsiloxane unit, a methylvinylsiloxane unit, or a methyl-3,3,3-trifluoropropylsiloxane unit.

Further, the organopolysiloxane of the component (A) has a triorganosyloxy group having both ends of its molecular chain, for example, a trimethylsiloxy group, a dimethylphenylsiloxy group, a vinyldimethylsiloxy group, a divinylmethylsiloxy group, a trivinylsiloxy group and the like. It is preferably sealed with a hydroxydiorganosyloxy group (R ¹ ₂ (HO) SiO _1/2 ) such as (R ¹ ₃ SiO _{1/2) or a hydroxydimethylsiloxy group.}

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), preferably 150 to 100,000. This degree of polymerization can be measured as a polystyrene-equivalent weight average degree of polymerization by gel permeation chromatography (GPC) analysis.

The component (A) may be used alone or as a mixture of two or three or more having different molecular weights (degrees of polymerization) and molecular structures.
<(B) Reinforcing silica>
Reinforcing silica, which is a component (B), is a filler added to obtain a silicone rubber composition having excellent mechanical strength, and for this purpose, the specific surface area by the BET adsorption method is 50 m ² / g. The above is necessary, ^{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 fuming silica (humped silica), precipitated silica (wet silica), and the like, and the surfaces thereof are an organosilane compound such as methylchlorosilane, hexamethyldisilazane, and the like. A product which has been hydrophobized with a silazane compound or the like is also preferably used. Of these, aerosol silica, which has excellent dynamic fatigue characteristics, is preferable. In addition, 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 more preferably 20 to 60 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). It is a department. If the amount of the component (B) is too small, the reinforcing effect cannot be obtained, and if it is too large, the workability is deteriorated, the mechanical strength is lowered, and the dynamic fatigue durability is also deteriorated. It ends up.

If necessary, (B) a dispersant (wetter) for reinforcing silica can be blended as an optional component. 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 (low polymer polymers having 2 to 30 silicon atoms, particularly 3 to 20 silicon atoms) 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)). ..

<(C) mixed solution>
The component (C) is an alkoxysilane (C-1) represented by the following general formula (2) and a cerium oxide sol having a 50% cumulative distribution diameter of 1 to 200 nm in a volume-based particle size distribution by a dynamic light scattering method. It is a mixed solution of C-2) and water (C-3).
R ² _m Si (OR ³ ) _(4-m) (2)
(In the formula, R ² is an independently hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, R ³ is an same or different unsubstituted or substituted alkyl group, and m is 0, 1, 2 or 3 Is.)

The alkoxysilane of the component (C-1) is not particularly limited, and for example, an organoalkoxysilane such as an organotrialkoxysilane, a diorganodialkoxysilane, or a triorganoalkoxysilane, or ^{a trie in which R 2} is a hydrogen atom. Examples thereof include alkoxysilane and tetraalkoxysilane with m = 0.

^{Here, R 2} in the above formula (2) is a hydrogen atom or the same or different unsubstituted or substituted monovalent hydrocarbon group, and the unsubstituted or substituted monovalent hydrocarbon group is the above (A). ^{Examples of the components are the same as those of R 1} in the formula (1), but those having 1 to 8 carbon atoms, particularly preferably 1 to 4 carbon atoms are preferable, and specifically, methyl group, ethyl group, and propyl group. Alkyl groups such as groups, butyl groups, hexyl groups and octyl groups, cycloalkyl groups such as cyclopentyl groups and cyclohexyl groups, alkenyl groups such as vinyl groups, allyl groups and propenyl groups, cycloalkenyl groups such as cyclohexenyl groups and phenyl groups. , An aryl group such as a trill group, an aralkyl group such as a benzyl group or a 2-phenylethyl group, or a part or all of the hydrogen atom of these groups is replaced with a halogen atom such as fluorine, chlorine or bromine or a cyano group. Examples thereof include a chloromethyl group, a 3,3,3-trifluoropropyl group, a 2-cyanoethyl group, and the like, preferably a methyl group, a vinyl group, a phenyl group, a trifluoropropyl group, and particularly a methyl group, a vinyl group, and a phenyl group. preferable.

^{Examples of the unsubstituted or substituted alkyl group of R 3 in} the above formula (2) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group and the like, which are usually carbon. Examples thereof include an alkyl group having a number of about 1 to 4 and an alkoxy group-substituted alkyl group such as a methoxymethyl group, a methoxyethyl group and an ethoxymethyl group, and a methyl group and an ethyl group are preferable. M in the above formula (2) is 0, 1, 2 or 3, preferably 1 or 2.

Examples of such alkoxysilanes include dimethoxydimethylsilane, diethoxydimethylsilane, dimethoxydiethylsilane, diethoxydiethylsilane, dimethoxymethylvinylsilane, dimethoxydiphenylsilane, dimethoxymethylphenylsilane, trimethoxymethylsilane, and triethoxymethylsilane. , Trimethoxyvinylsilane, trimethoxyphenylsilane, trimethoxysilane, triethoxysilane, tetramethoxysilane, tetraethoxysilane and the like, but diorganodialkoxysilane such as dialkyldialkoxysilane with m = 2 is preferable.

The above alkoxysilanes can be used alone or in combination of two or more. The amount of the component (C-1) added is preferably 2 to 1,000 times the mass of cerium oxide in the component (C-2). If the amount of alkoxysilane added is too small, the dispersibility of cerium oxide deteriorates, and the transparency of the molded product deteriorates.

In the cerium oxide sol of the component (C-2), the particle size of cerium oxide in the sol is 1 to 200 nm, preferably 1 to 100 nm in the 50% cumulative distribution diameter in the volume-based particle size distribution by the dynamic light scattering method. Use a cerium oxide sol such as. 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 an acidity of pH 7 or less is preferable. Commercially available cerium oxide sol can be used. Examples of commercially available cerium oxide sol include CESL-30N (manufactured by Daiichi Rare Element Chemical Industries, Ltd.), Needral P10 (manufactured by Taki Chemical Co., Ltd.), and Nanouse CE. -T20B (manufactured by Nissan Chemical Industries, Ltd.) and the like.

The content of cerium oxide contained in the sol in the component (C-2) is as described above, but the content of cerium oxide in the total amount of the mixed solution of the component (C) is 0.1 to 10% by mass. Is preferable.

The water of the component (C-3) is used to hydrolyze the alkoxysilane of the component (C-1). This hydrolysis reaction is preferably carried out using an acidic aqueous solution having a pH of 1.0 to 5.0, preferably 2.0 to 4.0. If this pH is too low, hydrolysis will occur rapidly, and the generated silanol groups will undergo a condensation reaction to form a high molecular weight siloxane, which will be formed by the cerium oxide in the component (C-2) and the reinforcing silica in the component (B). It may not work effectively as a treatment agent.

Here, examples of the acid used for adjusting the pH include inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as formic acid and acetic acid, but hydrochloric acid is the most preferable.

As the pH at the time of the hydrolysis reaction, a basic aqueous solution adjusted to the range of 9.0 to 11.0 can also be preferably used. In this case as well, if the pH is close to the neutral region, the catalytic activity required for hydrolysis may not be obtained, and if the pH is too high, the produced silanol groups will be condensed to form a high molecular weight siloxane. It may not act effectively as a treatment agent for cerium oxide in the component (C-2) or reinforcing silica for the component (B). Here, examples of the base used for adjusting the pH include sodium hydroxide, potassium hydroxide, aqueous ammonia and the like.

The amount of water added in the present invention is not particularly limited, but is 0.3 to 5 times mol, particularly 0.5 to 2 times mol, with respect to the alkoxy group of the alkoxysilane of the above (C-1) component. Is preferable. Further, it is desirable to determine the addition amount in consideration of the pH of the cerium oxide sol to be used. If this amount is less than the above range, there arises a problem that the alkoxy group is not completely hydrolyzed and only a few hydroxyl groups are generated. Even if a large amount is added, it is necessary to remove excess water.

In the present invention, the reaction conditions for mixing and hydrolyzing the above components (C-1) to (C-3) are preferably 0 to 100 ° C, more preferably 10 to 70 ° C. Is preferably hydrolyzed under the conditions of temperature and time for 1 second to 2 hours, more preferably 10 seconds to 10 minutes.

That is, in the present invention, a mixed solution of alkoxysilane (C-1), cerium oxide sol (C-2) and water (C-3) is used as the component (C), and in the presence of cerium oxide sol. In the above, a mixed solution obtained by (partially) hydrolyzing the alkoxysilane is used, whereby a mixed solution in which cerium oxide acts on the (partially) hydrolyzed product of alkoxysilane is used. Even if the above alkoxysilane and water are mixed and (partially) hydrolyzed and cerium oxide sol is mixed, the cerium oxide particles cannot be uniformly dispersed, and the effect of the present invention cannot be obtained. ..

<(D) Hardener>
The component (D) is a curing agent, and the curing agent is not particularly limited as long as it can cure the component (A). As the curing agent, the following (D-1) organic peroxide curing agent and / or (D-2) addition reaction curing agent can be used.

(D-1) Organic Peroxide Hardener (D-1) Examples of the organic peroxide curing agent include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, and 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 blending amount of the organic peroxide is 0.01 to 10 parts by mass, preferably 1 to 10 parts by mass, and particularly preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the component (A). If the blending amount is too small, the curing may be insufficient, and if the blending amount is too large, the cured silicone rubber may turn yellow due to the decomposition residue of the organic peroxide.

(D-2) Addition Reaction Curing Agent (D-2) As the addition reaction curing agent, an organohydrogenpolysiloxane and a hydrosilylation catalyst can be used in combination. As the organohydrogenpolysiloxane, hydrogen atoms bonded to 2 or more, preferably 3 or more, more preferably 3 to 200, still more preferably 4 to 100 hydrogen 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, and a known organohydrogenpolysiloxane is used as a cross-linking agent for the addition reaction curable silicone rubber composition. For example, an organohydrogenpolysiloxane represented by the following average composition formula (3) can be used.
R ⁴ _p H _q SiO _{(4-pq) / 2} (3)

In the above formula (3), R ⁴ represents an unsubstituted or substituted monovalent hydrocarbon group, which may be the same or different, and preferably does not have an aliphatic unsaturated bond. Usually, those having 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms are preferable, and specific examples thereof include an alkyl group such as a methyl group, an ethyl group and a propyl group, a cycloalkyl group such as a cyclohexyl group, a phenyl group and a trill group. Aralkyl groups such as aryl groups, benzyl groups, 2-phenylethyl groups and 2-phenylpropyl groups, and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms or the like, for example, 3,3,3- Examples thereof include a trifluoropropyl group.

In the above formula (3), 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, the organohydrogenpolysiloxane preferably has a viscosity at 25 ° C. of 0.5 to 10,000 mPa · s, particularly preferably 1 to 300 mPa · s. This viscosity can be measured with a rotational viscometer.

Specific examples of such organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, and tris (hydrogendimethylsiloxy). ) Methylsilane, Tris (hydrogendimethylsiloxy) phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, both-terminal trimethylsiloxy group blockage methylhydrogenpolysiloxane, both-terminal trimethylsiloxy group blockade Dimethylsiloxane / methylhydrogensiloxane copolymer, both-terminal dimethylhydrogensiloxy group-blocking dimethylpolysiloxane, both-terminal dimethylhydrogensiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer, both-terminal trimethylsiloxy group-blocking methylhydro Gensiloxane / diphenylsiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane / methylphenylsiloxane / dimethylsiloxane copolymer, Both-terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / diphenylsiloxane copolymer, both-terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / methylphenylsiloxane copolymer, (CH ₃ ) ₂ HSiO _1/2 unit and (CH ₃ ) ₃ Siloxane _1/2 unit and SiO _4/2 unit, (CH ₃ ) ₂ HSiO _1/2 unit and SiO _4/2 unit Combined, _{such as a copolymer consisting of (CH 3} ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) ₃ SiO _1/2 units, and some of the methyl groups in the above exemplified compounds. Alternatively, those in which all of them are replaced with other alkyl groups, phenyl groups, or the like can be mentioned.

The blending amount of the organohydrogenpolysiloxane is preferably 0.01 to 40 parts by mass, particularly 0.1 to 10 parts by mass with respect to 100 parts by mass of the component (A). Further, it is appropriate that the ratio of hydrogen atoms (≡SiH groups) bonded to silicon atoms to one aliphatic unsaturated bond (alkenyl group, diene group, etc.) of component (A) is in the range of 0.5 to 10. The range is preferably 0.7 to 5 pieces. If the number is less than 0.5, the cross-linking may not be sufficient and sufficient mechanical strength may not be obtained, and if the number exceeds 10, the physical characteristics after curing are deteriorated, and the heat resistance is particularly deteriorated. The compression set may increase.

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 this hydrosilylation catalyst include platinum group metal-based catalysts, which include a single platinum group metal and a compound thereof, and conventionally, known catalysts for addition reaction curing type silicone rubber compositions are used. Can be done. For example, a platinum catalyst such as a particulate platinum metal adsorbed on a carrier such as silica, alumina or silica gel, a second platinum chloride, a platinum chloride acid, an alcohol solution of a hexahydrate of platinum chloride acid, a palladium catalyst, a rhodium catalyst and the like can be used. Although it can be mentioned, it is preferable to use platinum or a platinum compound (platinum catalyst).

The amount of the hydrosilylation catalyst added can be appropriately selected as long as it can promote the addition reaction, and is usually 1% by mass to mass ppm with respect to the organopolysiloxane of the component (A) in terms of the amount of platinum group metal. It is used in the range of 1% by mass, but is particularly preferably in the range of 10 to 500% by mass. If the amount added is less than 1% by mass, the addition reaction may not be sufficiently promoted and curing may be insufficient, while if it exceeds 1% by mass, even if a larger amount is added, the effect on the reactivity is affected. It may be uneconomical.

In the (D) curing agent of the present invention, the above-mentioned (D-1) component and (D-2) component can be used alone, but with the (D-1) organic peroxide curing agent. (D-2) It can also be used as a co-vulcanization type curing agent in combination with an addition reaction curing agent. In this case, the components (D-1) and (D-2) may be combined with the component (A) within the range of the above-mentioned blending amounts and used.

[Other ingredients]
The silicone rubber composition of the present invention contains a filler such as pulverized quartz, crystalline silica, diatomaceous earth, calcium carbonate, etc. as other components, if necessary, in addition to the above components as long as the object of the present invention is not impaired. Various alkoxysilanes, especially phenyl group-containing alkoxysilanes and their hydrolysates, as colorants, tear strength improvers, acid receivers, thermal conductivity improvers such as alumina and boron nitride, mold release agents, and dispersants for fillers. Known fillers and additives in the heat-curable silicone rubber composition, such as diphenylsilanediol, carbon functional silane, and silanol group-containing low-molecular-weight siloxane, may be optionally added. Other components may be used alone or in combination of two or more.

The method for preparing the silicone rubber composition of the present invention can be obtained by mixing each of the above components with a known kneader such as a kneader, a Banbury mixer, or a double roll, but usually, the organodone of the component (A) is used. It is preferable to add the curing agent of the component (D) after mixing a mixed solution of polysiloxane, reinforcing silica of the component (B), an aqueous sol composed of alkoxysilane of the component (C) and cerium oxide, and water. Is.

The shape of the silicone rubber composition of the present invention 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 is non-liquid (usually 25 ° C. ± 10 ° C.) and has no self-fluidity at room temperature. It is a solid or highly viscous paste), and means a raw rubber-like composition that can be uniformly mixed under high shear stress by a kneading means such as a roll mill.

The silicone rubber composition of the present invention thus obtained is cured by heating to become a cured silicone rubber having excellent transparency and heat resistance. As this molding method, a known molding method may be selected according to the shape and size of the target molded product. For example, methods such as injection molding, compression molding, injection molding, calender molding, extrusion molding, coating, and screen printing are exemplified. The curing conditions may be those known in the molding method, and are generally 60 to 450 ° C., particularly 80 to 400 ° C., and further 120 to 200 ° C. for several seconds to one day. Further, for the purpose of reducing the compressive permanent strain property of the cured silicone rubber product, reducing the low molecular weight siloxane component remaining in the cured product, or removing the decomposed product of the organic peroxide. Post-curing (secondary vulcanization) may be carried out in an oven at 150 to 250 ° C., preferably 200 to 240 ° C. for 1 hour or longer, preferably 1 to 70 hours, more preferably 1 to 10 hours. good.

The cured silicone rubber obtained in this manner is highly transparent, and the cured product (silicone rubber) having a thickness of 2 mm preferably has a total light transmittance of 85% or more (85 to 100%), more preferably. It is 89% or more (89 to 100%). Further, the cured silicone rubber product thus obtained has excellent heat resistance and 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. The degree of polymerization of siloxane is the polystyrene-equivalent weight average degree of polymerization obtained by gel permeation chromatography analysis using toluene as a developing solvent. The particle size refers to a 50% cumulative distribution diameter in a volume-based particle size distribution by a dynamic light scattering method.

[Various physical property measurement methods]
With respect to the silicone rubber compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 4 below, various physical characteristics [hardness (durometer A)] were used using a cured product sheet for testing prepared in accordance with JIS K 6249: 2003. ), Tensile strength, elongation at the time of cutting] was measured. The results are shown in Table 1.

[Measurement of total light transmittance]
The silicone rubber compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 4 below are post-cured at 200 ° C. for 4 hours using a haze meter (manufactured by Suga Test Instruments Co., Ltd., model: HGM-2). The light transmittance of the later 2 mm thick silicone rubber cured product sheet was measured. The results are shown in Table 1.

A mixed solution of alkoxysilane, cerium oxide sol and water (acidic aqueous solution) was prepared as follows.

[Preparation Example 1]
(Preparation of mixed solution 1)
190 g of dimethyldimethoxysilane, 2 g of cerium oxide sol (particle size: 10 nm, trade name: CESL-30N, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.), and 50 g of hydrochloric acid water having a pH of 3.5 were mixed to prepare a mixed solution 1. ..

[Preparation Example 2]
(Preparation of mixed solution 2)
The mixed solution 2 was prepared in the same manner as in Preparation Example 1 except that the amount of cerium oxide sol was 1 g instead of 2 g.

[Preparation Example 3]
The mixed solution 3 was prepared in the same manner as in Preparation Example 1 except that methyltrimethoxysilane was used instead of dimethyldimethoxysilane.

[Preparation Example 4]
The mixed solution 4 was prepared in the same manner as in Preparation Example 1 except that the cerium oxide sol was not added.

[Example 1]
100 parts by mass of organopolysiloxane raw rubber having an average degree of polymerization of about 6,000, consisting of 99.850 mol% of dimethylsiloxane unit, 0.125 mol% of methylvinylsiloxane unit, and 0.025 mol% of dimethylvinylsiloxy unit, BET To 40 parts by mass of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, 24.2 parts by mass of the mixed solution 1 prepared in Preparation Example 1 was added and mixed with a kneader. The mixture was kneaded and heat-treated at 170 ° C. for 2 hours to prepare a composition (base compound 1).

To 100 parts by mass of this composition (base compound 1), 0.4 parts by mass of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane as a curing agent was added by two rolls. After uniformly mixing to produce a raw rubber-like silicone rubber composition, the composition was ^{press-cured at 165 ° C. and 70 kgf / cm 2} for 10 minutes to prepare a sheet having a thickness of 2 mm. Post-cure was then performed in an oven at 200 ° C. for 4 hours. These silicone rubber sheets were returned to room temperature (25 ° C.), and the rubber physical characteristics and light transmittance were measured. The results are shown in Table 1. Further, the physical characteristics (heat resistance) of the rubber after being placed in a dryer at 300 ° C. for 3 days and 7 days were measured. The results are shown in Table 1.

[Example 2]
Various physical properties and light transmittance were measured in the same manner as in Example 1 except that 24.1 parts by mass of the mixture 2 was added instead of the mixture 1. The results are shown in Table 1.

[Example 3]
Various physical properties and light transmittance were measured in the same manner as in Example 1 except that the mixture was not the mixture 1 but the mixture 3. The results are shown in Table 1.

[Example 4]
As a curing agent, methylhydrogenpolysiloxane having a SiH group in the side chain (polymerization degree 38, SiH group 0.0074 mol%, both-terminal trimethylsiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer) 0.25 mass , 0.05 part by mass of ethynylcyclohexanol as a reaction control agent and 0.1 part by mass of platinum catalyst (Pt concentration 1% by mass) were added with two rolls and mixed uniformly to form a raw rubber-like silicone rubber composition. Was produced, the composition was press-cured at 120 ° C. and 70 kgf / cm ² for 10 minutes to prepare a 2 mm-thick sheet, and various physical properties and light transmittance were obtained in the same manner as in Example 1. Was measured. The results are shown in Table 1.

[Comparative Example 1]
Various physical properties and light transmittance were measured in the same manner as in Example 1 except that 24.0 parts by mass of the mixture 4 was added instead of the mixture 1. The results are shown in Table 1.

[Comparative Example 2]
Same as Example 1 except that 24.0 parts by mass of the mixture 4 and 0.2 parts by mass of cerium oxide sol (CESL-30N, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.) were added instead of the mixture 1. Then, various physical properties and light transmittance were measured. The results are shown in Table 1.

[Comparative Example 3]
100 parts by mass of organopolysiloxane raw rubber having an average degree of polymerization of about 6,000, consisting of 99.850 mol% of dimethylsiloxane unit, 0.125 mol% of methylvinylsiloxane unit, and 0.025 mol% of dimethylvinylsiloxy unit, BET To 40 parts by mass of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, 24.0 parts by mass of the mixed solution 4 prepared in Preparation Example 4 was added and mixed with a kneader. The mixture was kneaded and heat-treated at 170 ° C. for 2 hours to prepare a composition (base compound 1).

1 part by mass of cerium oxide (particle size: 1 μm, trade name: SN-2, manufactured by Nikki Co., Ltd.) with respect to 100 parts by mass of this composition (base compound 1), 2,5-dimethyl-2 as a curing agent, 0.4 parts by mass of 5-bis (t-butylperoxy) hexane was added in two rolls and mixed uniformly to produce a raw rubber-like silicone rubber composition, and then the composition was added at 165 ° C. and 70 kgf. Precure was performed for 10 minutes under the condition of / cm ² , and a sheet having a thickness of 2 mm was prepared. Post-cure was then performed in an oven at 200 ° C. for 4 hours. These silicone rubber sheets were returned to room temperature (25 ° C.), and the rubber physical characteristics and light transmittance were measured. The results are shown in Table 1. Further, the physical characteristics (heat resistance) of the rubber after being placed in a dryer at 300 ° C. for 3 days and 7 days were measured. The results are shown in Table 1.

[Comparative Example 4]
Various physical properties and light transmittance were measured in the same manner as in Example 4 except that 24.0 parts by mass of the mixture 4 was added instead of the mixture 1. The results are shown in Table 1.

Claims (7)

(A) The following average composition formula (1)
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.)
Organopolysiloxane represented by and having at least two alkenyl groups in one molecule
100 parts by mass,
(B) Reinforcing silica with a specific surface area of 50 m ² / g or more 5 to 100 parts by mass,
(C) The following general formula (2)
R ² _m Si (OR ³ ) _(4-m) (2)
(In the formula, R ² is an independently hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group, R ³ is an same or different unsubstituted or substituted alkyl group, and m is 0, 1, 2 or 3 Is.)
Alkoxysilane (C-1) represented by, cerium oxide sol (C-2) and water (C-3) having a 50% cumulative distribution diameter of 1 to 200 nm in the volume-based particle size distribution by the dynamic light scattering method. [However, the amount of the component (C-1) added is 2 to 1,000 times the mass of the cerium oxide in the component (C-2), and the content of the cerium oxide in the above mixed solution. Is 0.1 to 10% by volume. ] 0.01 to 50 parts by mass,
(D) A transparent silicone rubber composition containing an effective amount of a curing agent. Claimed that the amount of water contained in the mixed solution of the alkoxysilane of the component (C), the cerium oxide sol and water is 0.3 to 5 times the molar number of the alkoxy groups in the alkoxysilane of the (C-1) component. Item 2. The silicone rubber composition according to Item 1. The pH of the mixed solution of the component (C) is 1.0 to 5.0 or 9.0 to 11.0, and the content of cerium oxide in the cerium oxide sol of the component (C-2) is 1 to 50. The silicone rubber composition according to claim 1 or 2, which is by mass%. The silicone rubber composition according to any one of claims 1 to 3, wherein the curing agent (D) is an organic peroxide. The silicone rubber composition according to any one of claims 1 to 3, wherein the curing agent (D) is an addition reaction curing type comprising a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst. The silicone rubber composition according to any one of claims 1 to 5, wherein the total light transmittance when the cured product of the silicone rubber composition is formed into a sheet having a thickness of 2 mm is 80% or more. A silicone rubber cured product comprising a cured product of the silicone rubber composition according to any one of claims 1 to 6.