WO2008001919A1

WO2008001919A1 - Silicone rubber composition

Info

Publication number: WO2008001919A1
Application number: PCT/JP2007/063183
Authority: WO
Inventors: Tomoko Tasaki; Osamu Takuman
Original assignee: Dow Corning Toray Co., Ltd.
Priority date: 2006-06-27
Filing date: 2007-06-22
Publication date: 2008-01-03

Abstract

A silicone rubber composition comprising at least the following components: a diorganopolysiloxane (A) having in one molecule at least two alkenyl groups; an organopolysiloxane (B) having in one molecule at least three silicon-bonded hydrogen atoms and at least one silicon-bonded silylalkyl group, an organopolysiloxane (C) having in one molecule on average at least 2 silicon-bonded hydrogen atoms; a powdered calcium carbonate (D); and a hydrosilylation catalyst (E).

Description

DESCRIPTION

SILICONE RUBBER COMPOSITION

Technical Field

[0001] The present invention relates to a hydrosilylation-curable silicone rubber composition that contains a calcium carbonate powder.

Background Art [0002] Known in the art is a silicone rubber composition that contains calcium carbonate and is suitable for curing by means of hydrosilylation (see Japanese Unexamined Patent Application Publication (hereinafter referred to as "Kokai") Hl 0-60281). This composition comprises a diorganopolysiloxane that contains in one molecule at least two alkenyl groups; an organopolysiloxane having in one molecule at least two silicon-bonded hydrogen atoms; a platinum-type catalyst; and a calcium carbonate powder surface treated with a product of partial hydrolysis and condensation of a tetraalkoxysilane. Other known silicone rubber compositions comprise a diorganopolysiloxane having in one molecule at least two alkenyl groups; a calcium carbonate powder; an organopolysiloxane having in one molecule at least two silicon-bonded hydrogen atoms; and a platinum catalyst (see Kokai 2002-38016 (equivalent to US6613440), Kokai 2002-285130 (equivalent to US6811650), and Kokai 2005-82661). These compositions are known to have adhesive properties with respect to silicone rubber.

[0003] Since the aforementioned silicone rubber compositions contain a calcium carbonate powder, curing of such compositions at relatively low temperatures, such as below 100⁰C, requires a very long period of time before a practically acceptable force of adhesion to silicone rubber is developed. Furthermore, in order to adjust the adhesion force to a practically acceptable range, it is necessary to use a large amount of a costly platinum catalyst, which makes the use of such compositions economically unjustifiable. Moreover, the known silicone rubber compositions that contain calcium carbonate powder cannot develop a sufficient force of adhesion to silicone rubber.

[0004] Kokai Hl 0-324805 describes a curable organopolysiloxane composition that contains a copolymer of a silalkylene and a branched siloxane having silicon-bonded hydrogen atoms. However, the above publication does not contain information on the content of calcium carbonate or adhesion to silicone rubber.

Disclosure of Invention [0005] It is an object of the present invention to provide a silicone rubber composition that is capable of quickly developing of adhesion force and has strong adhesion to silicone rubber. [0006] The silicone rubber composition comprises at least the following components:

100 parts by weight of a diorganopolysiloxane (A) having in one molecule at least two alkenyl groups; an organopolysiloxane (B) having in one molecule at least three silicon-bonded hydrogen atoms and at least one silicon-bonded [group] X¹, which is a silylalkyl group represented by the following formula (1), when i = 1 :

X¹ (1)

(where R¹ is an aryl group or an alkyl group with 1 to 10 carbon atoms; R² is an alkylene group having 2 to 10 carbon atoms; R³ is an alkyl group having 1 to 10 carbon atoms; "i" shows the hierarchical level of the silylalkyl group; if hierarchical number is designated by "c", this number may be an integer from 1 to "c"; the hierarchical number "c" is an integer from 1 to 10; when "i" is 1, then "b¹" is an integer from 0 to 2; when "i" is 2 or greater than 2, then "b¹" is a number which is less than 3; when "i" is less than "c", then X¹⁺¹ is the aforementioned silylalkyl group, and when i=c, then X¹⁺¹ is a hydrogen atom) {the mole ratio of silicon-bonded hydrogen atoms in this component to alkenyl groups in the composition from 0.01 to 20}; an organopolysiloxane (C) having in one molecule on average at least 2 silicon-bonded hydrogen atoms {except for component (B) } {the mole ratio of silicon-bonded hydrogen atoms in this component to alkenyl groups in the composition ranges from 0.01 to 20}; 1 to 200 parts by mass of powdered calcium carbonate (D); and a hydrosilylation catalyst (E) (in the amount required to accelerate curing of the composition ). [0007] It is recommended that in the aforementioned composition component (B) be a carbopolysiloxane represented by the following formula:

or the following formula:

{where "d" is 3 or 4; R¹ is aryl group or an alkyl group with 1 to 10 carbon atoms; when i = 1 , then Y¹ is a silylalkyl group of the formula given below:

(where R¹ is the same as defined above; R² is an alkylene group with 2 to 10 carbon atoms;

"i" shows the hierarchical level of the silylalkyl group designated by Y¹; the hierarchical number "c" is 1 or 2; when the hierarchical number "c" is 1, then Y¹⁺¹ is a hydrogen atom; when the hierarchical number "c" is 2, then Y¹⁺¹ is the aforementioned silylalkyl group when "i" = 1, or a hydrogen atom when "i" = 2)} . The ratio of the mole number of silicon-bonded hydrogen atoms contained in component (B) to the mole number of silicon-bonded hydrogen atoms contained in component (C) ranges from

(1:1 to 1:10). The mole ratio of all silicon-bonded hydrogen atoms contained in components

(B) and (C) to alkenyl groups contained in the composition ranges from 0.1 to 10. Component (D) is a light (or precipitated) calcium carbonate powder.

[0008] The silicone rubber composition of the invention may further contain a silica powder (F) in an amount of 1 to 100 parts by mass per hundred parts by mass of component

(A). When component (F) is present, it can be preliminarily mixed with component (A) while heating. [0008] The composition of the invention can be used as an adhesive agent for silicone rubber, as an adhesive agent for a silicone rubber-coated fabric, or as a sealer for a silicone rubber-coated fabric. [0009] The silicone rubber composition of the invention is characterized by quick development of adhesion force and by strong adhesion to silicone rubber. An economic advantage of the silicone rubber composition of the invention is that the length of time required for development of adhesion force can be achieved with a smaller amount of platinum catalyst than needed for a conventional composition. Moreover, the composition of the invention allows development of a stronger force of adhesion to silicone rubber than a conventional composition.

Best Mode for Carrying Out the Invention [0010] The silicone rubber composition of the invention will now be described in more detail.

Component (A) is one of the main components of the silicone rubber composition of the invention. This component comprises a diorganopolysiloxane that contains in one molecule on average at least two alkenyl groups. These alkenyl groups of component (A) are exemplified by vinyl, allyl, butenyl, pentenyl, hexenyl, or heptenyl. Most preferable are vinyl groups. In addition to alkenyl groups, component (A) can contain other silicon-bonded organic groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, or similar alkyl groups; phenyl, tolyl, xylyl, or similar aryl groups; 3-chloropropyl, 3, 3, 3-trifluoropropyl, or similar halogenated alkyl groups; most preferable are methyl and phenyl groups. Component (A) may have a substantially linear molecular structure, but if it is not contradictory to the objects of the invention, the linear molecular structure may be slightly branched. There are no special restrictions with regard to the viscosity of component (A) at 25°C; however, it is recommended that viscosity range from 100 to 1,000,000 mPa-s, preferably 100 to 500,000. [0011] Specific examples of the diorganopolysiloxane of component (A) are the following: a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups; a copolymer of methylvinylsiloxane and dimethylsiloxane capped at both molecular terminals with dimethylvinylsiloxy groups; a copolymer of methylvinylsiloxane and dimethylsiloxane capped at both molecular terminals with trimethylsiloxy groups; the aforementioned diorganopolysiloxanes having a part or all of their methyl groups substituted with ethyl, propyl, or similar alkyl groups; phenyl groups, tolyl groups, or similar aryl groups; or halogenated alkyl groups such as 3,3,3- trifluoropropyl groups; the aforementioned diorganopolysiloxanes having a part or all of their vinyl groups substituted with allyl groups, propenyl groups, or similar alkenyl groups; or a mixture of two or more of the aforementioned diorganopolysiloxanes. [0013] Component (B) is another component of the silicone rubber composition of the invention, which is intended to improve adhesion to silicone rubber and to shorten the time required to develop the force of adhesion of the composition to silicone rubber. Component (B) is an organopolysiloxane that contains in one molecule on average of three or more silicon-bonded hydrogen atoms. Component (B) is represented by the following formula (1), which is a silylalkyl group when i = 1 :

[0012] In the above formula, R¹ is a methyl, ethyl, propyl, butyl, pentyl, isopropyl, hexyl, octyl, or a similar alkyl group with 1 to 10 carbon atoms; or a phenyl, tolyl, xylyl, or a similar aryl group. Use of the alkyl group with 1 to 10 carbon atoms, especially a methyl group, is preferable. In the above formula, R² is an alkylene group having 2 to 10 carbon atoms, such as ethylene, propylene, butylene, hexylene, or a similar linear alkylene; methylmethylene, methylethylene, 1-methylpentylene, 1, 4-dimethylbutylene, or a similar branched alkylene group. Preferable among these groups are ethylene, methylmethylene, hexylene, 1- methylpentylene, or 1, 4-dimethylbutylene. hi the above formula, R³ is an alkyl group having 1 to 10 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, isopropyl, hexyl, or an octyl group; most preferable among these groups are methyl and ethyl groups. [0015] In the above formula (1), "i" shows a hierarchical level of the silylalkyl group designated by X¹. When the hierarchical number, i.e., the number of repetitions of aforementioned silylalkyl groups, is designated by "c", then "i" is an integer from 1 to "c". The hierarchical number "c" is an integer from 1 to 10. When "i" is less than "c", X¹⁺¹ is the aforementioned silylalkyl group. When i=c, then X¹⁺¹ is a hydrogen atom. When i=l, then b¹ is an integer from 0 to 2; when "i" is equal to or greater than 2, then b¹ is less than 3, preferably less than 1, and most preferably 0. This is because when numerous amounts of alkoxy groups are present in one molecule of component (B), the above condition will impair flowability and curing characteristics of the composition of the invention. [0016] When the hierarchical number "c" is 1 , the silylalkyl group of formula (1) is represented by the following formula:

When the hierarchical number "c" is 2, the silylalkyl group of formula (1) is represented by the following formula:

When the hierarchical number "c" is 3, the silylalkyl group of formula (1) is represented by the following formula:

When several silylalkyl groups are present in formula (1) of component (B), all silylalkyl groups of formula (1) may be identical or different, but it is preferable that silylalkyl groups of formula (1) have the same hierarchical number "c".

[0017] Component (B) may be exemplified by an organopolysiloxane that contains siloxane units selected from X¹R^SiOy₂, X¹R¹SiO_2Z2, and X^!Siθ_3/2. In addition to the aforementioned siloxane units, component (B) may also include monofunctional siloxane units

(D units), three- functional siloxane units R¹SiO₃^ (T units), or four-functional siloxane units SiO_4/2 (Q units), where R¹ and X¹ are the same as defined above.

[0018] Component (B) can be exemplified by organopolysiloxanes of the following formulae:

R¹

R^J 4-a — Si-fo-Si— X¹

(X¹R¹ _ZSiOy₂)_P (R¹SiO_3Z2)^

(X¹SiO_3/^, and

In the above formulae, X and R¹ are the same as defined above; "a" is an integer from 1 to 4;

"z" is an integer from 3 to 20; "m", "n", "x", "y""p", "q", "r", "s", and "t" are integers equal to or greater than 1; (p+q) is 5 or greater than 5; and (s+t) is 6 or greater than 6.

[0019] Among the above compounds most preferable from the viewpoint of ease of manufacture are organopolycarbosiloxanes with alternatively arranged siloxane bonds and alkylene bonds which are represented by the following formulae:

or

In these formulae, "d" is 3 or 4; R¹ is he same as defined above; and, when i=l, Y¹ is a silylalkyl group of the formula given below:

In this formula, R² is the same as defined above; "i" shows the hierarchical level of the silylalkyl group designated by Y¹; the hierarchical number, i.e., the number of repetitions of aforementioned silylalkyl groups, is 1 or 2; when the hierarchical number is 1, then Y¹⁺¹ is a hydrogen atom, and when the hierarchical number is 2, then Y¹⁺¹ is the aforementioned silylalkyl group when i=l, or a hydrogen atom when i=2.

[0020] Component (B) may comprise a single compound or a mixture of aforementioned compounds, but it is recommended to provide a dispersion index of molecular weight referenced to polystyrene, i.e., a ratio of a weight-average molecular weight to a number- average molecular weight (Mw/Mn) equal to or lower than 2.

[0021] Specific examples of component (B) are polymers represented by the following average molecular formulae:

[0022] Component (B) is added to the composition in such an amount that the mole ratio of silicon-bonded hydrogen atoms contained in this component to alkenyl groups contained in the silicone rubber composition of the invention is in the range of 0.01 to 20, preferably 0.1 to 10, and most preferably, 0.1 to 5. If the content of component (B) is below the recommended lower limit, the silicone rubber composition will not be cured to a sufficient degree, the development of the adhesion force will be delayed, and the adhesion force value will be low. If, on the other hand, the content of component (B) exceeds the recommended upper limit, this will impair mechanical characteristics of the obtained silicone rubber. [0023] Component (B) can be manufactured by a method known in the art, e.g., by a method disclosed in Kokai H10-298288 or Kokai 2000-212283. A specific example is a method that consists of forming silylalkyl group of formula (1) with hierarchical number "c" by using an organopolysiloxane with silicon-bonded hydrogen atoms as a starting material and alternately repeating "c" times step (X) and step (Y) described below. Step (X): Obtaining a copolymer of a silalkylene and a siloxane that contains silicon- bonded alkoxy groups by subjecting an organopolysiloxane that contains silicon-bonded hydrogen atoms and an alkenyltrialkoxysilane to an addition reaction in the presence of a hydrosilylation catalyst; and

Step (Y): Carrying out a reaction between the copolymer of a silalkylene and a siloxane that contains silicon-bonded alkoxy groups obtained in Step (X) and 1, 1, 3, 3- teramethyldisiloxane, or a similar tetraorganodisiloxane, in the presence of an acidic aqueous solution, thus substituting alkoxy groups with diorganosiloxy groups. [0024] In Step (Y), after the reaction between the copolymer of a silalkylene and a siloxane that contains silicon-bonded alkoxy groups and the tetraorganodisiloxane in the presence of an alcohol-containing acidic aqueous solution, it is recommended to treat the product with carboxylic acid and sulfonic acid catalysts. The reason for this is that residual alkoxy groups are efficiently converted into diorganosiloxy groups. [0025] The organopolysiloxane of component (C) is a curing agent of the aforementioned silicone rubber composition. There are no special restrictions with regard to the molecular structure of component (C)₅ it can be exemplified a linear, branched, cyclic, or a three-dimensional net-like resinous molecular structure, however, except for component (B). Silicon-bonded organic groups of component (C) can be exemplified by methyl, ethyl, propyl, butyl, pentyl, hexyl, or similar alkyl groups; phenyl, tolyl, xylyl, or similar aryl groups; benzyl, phenyl, or similar aralkyl groups; 3-chloropropyl, 3, 3, 3-trifluoropropyl, or similar halogenated alkyl groups. The methyl groups are preferable. There are no special restrictions with regard to the viscosity of component (C) at 25⁰C; however, it is recommended that viscosity range from 1 to 1,000, 000 mPa-s.

[0026] Specific examples of component (C) are the following: a methylhydrogenpolysiloxane capped at both molecular terminals with trimethylsiloxy groups; a copolymer of methylhydrogensiloxane and dimethylsiloxane capped at both molecular terminals with trimethylsiloxy groups; a methylhydrogenpolysiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups; a copolymer of methylhydrogensiloxane and dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups; a cyclic methylhydrogenpolysiloxane; an organopolysiloxane composed of siloxane units represented by formula: (CHs)₂HSiO₁Z₂ and siloxane units represented by formula: SiO₄Q; the aforementioned organosiloxanes where a part of or all methyl groups are substituted with ethyl, propyl, or similar alkyl groups; phenyl, tolyl or similar aryl groups; 3, 3, 3-trifiuoropropyl, or similar halogenated alkyl groups; or a mixture of two or more of the aforementioned organopolysiloxanes. Most preferable from the viewpoint of mechanical properties and adhesion to silicone rubber, are organohydrogenpolysiloxanes or copolymers of a diorganopolysiloxane and an organohydrogensiloxane, especially the organohydrogenpolysiloxane capped at both molecular terminal with triorganosiloxy groups or the copolymer of an organohydrogenpolysiloxane and a diorganosiloxane capped at both molecular terminals with triorganosiloxy groups. [0027] Component (C) is added to the silicone rubber composition of the invention in an amount such that the mole ratio of silicon-bonded hydrogen atoms in this component to alkenyl groups in the silicone rubber composition of the invention ranges from 0.01 to 20, preferably 0.1 to 10, and most preferably, 0.1 to 5. If the component (C) is below the recommended lower limit, the obtained silicone rubber composition will be insufficiently cured. If, on the other hand, the content of component (C) exceeds the recommended upper limit, this will impair mechanical properties of the obtained silicone rubber composition. In the composition of the invention, both components (B) and (C) are used as curing agents and both should be used in the amounts prescribed above. It is recommended, however, to maintain a ratio of the mole number of silicon-bonded hydrogen atoms contained in component (B) to the mole number of silicon-bonded hydrogen atoms contained in component (C) in the range of (1:1) to (1:10). If the ratio of the mole number of silicon- bonded hydrogen atoms contained in component (B) to the mole number of silicon-bonded hydrogen atoms contained in component (C) is below the recommended lower limit, this will either delay development of the force of adhesion to silicone rubber, or will reduce the force of adhesion to silicone rubber. On the other hand, if the ratio of the mole number of silicon- bonded hydrogen atoms contained in component (B) to the mole number of silicon-bonded hydrogen atoms contained in component (C) exceeds the recommended upper limit, this will impair mechanical properties, e.g., elongation characteristics of the silicone rubber obtained by curing the silicone rubber composition of the invention. Furthermore, it is recommended that the mole ratio of the sum of silicon-bonded hydrogen atoms contained in components (B) and (C) to alkenyl groups contained in the silicone rubber composition of the invention be in the range of 0.1 to 10, preferably 0.1 to 5, and further preferable 0.5 to 2.0. [0028] Component (D) is a calcium carbonate powder which is added to the silicone rubber composition of the invention for improving adhesion thereof to silicone rubber. There are no special limitations with regard to BET specific area of component (D), but in general it should be in the range of 5 to 50 m²/g, preferably 10 to 50 m²/g. The calcium carbonate powder of component (D) can be exemplified by heavy (or dry-process-grinded) calcium carbonate powder, light (or precipitated) calcium carbonate powder, or the aforementioned powders surface-treated with fatty acids, resin acids, or similar organic acids. Most preferable is the light (or precipitated) calcium powder, especially one surface-treated with fatty acids, resin acids, or similar organic acids. [0029] Component (D) is added to the composition of the invention in an amount of 1 to 200 parts by mass, preferably 5 to 200 parts by mass, and most preferably, 10 to 100 parts by mass per 100 parts by mass of component (A). If component (D) is added in an amount of less than the recommended lower limit, this may impair adhesion of the silicone rubber composition of the invention to silicone rubber. If, on the other hand, the added amount exceeds the recommended upper limit, it may be difficult to prepare the composition in a uniform state.

[0030] Component (E) is a hydrosilylation catalyst that is added to the silicone rubber composition of the invention in order to accelerate curing of the composition. This component may comprise a platinum-type catalyst, such as a fine platinum powder, platinum black, chloroplatinic acid, platinum tetrachloride, an alcohol solution of chloroplatinic acid, an olefin complex of platinum, an alkenylsiloxane complex of platinum, or a carbonyl complex of platinum; a rhodium-type catalyst such as rhodium chloride, di(n-butyl)sulfide complex of rhodium chloride, or chloro-tris (triphenylphosphine) rhodium; a palladium-type catalyst such as a carbon supported palladium, or palladium chloride; or a fine-powder form , thermoplastic organic resins such as methylmethacrylate resin, polycarbonate resin, polystyrene resin, silicone resin, etc which contain the aforementioned hydrosilylation catalysts. [0031] There are no special limitations with regard to amounts in which component (E) can be added to the silicone rubber composition of the invention, provided that the added amount accelerates curing. It may be recommended, however, to add component (E) in an amount of 0.01 to 500 parts by mass, preferably 0.1 to 100 parts by mass, and most preferably, 5 to 70 parts by mass per 1x10⁶ parts of the silicone rubber composition of the invention.

[0032] In order to improve mechanical strength of a cured body obtained from the silicone rubber composition of the invention, the composition may be further combined with silica powder (F). Such component (F) may comprise fumed silica, precipitated silica, fused silica, crushed quartz, or the aforementioned powdered materials surface treated with organoalkoxysilane, organohalosilane, organosilazane, or a similar organic silicon compound. In particular, for improving mechanical strength in the obtained cured body of the adhesive agent, it is recommended to use a silica powder having BET specific surface area no less than 50 m²/g. [0033] Component (F) can be used in the silicone rubber composition of the invention in an arbitrary amount, but in order to improve mechanical strength in the obtained silicone rubber, it is recommended to add component (F) in an amount of 1 to 100 parts by mass, preferably 1 to 50 parts by mass per 100 parts by mass of component (A). [0034] The silicone rubber composition of the invention may be further combined with arbitrary components such as fumed titanium oxide, carbon black, diatomaceous earth, iron oxide, aluminum oxide, aluminosilicate, zinc oxide, aluminum hydroxide, silver, nickel, or a similar inorganic filler, as well as the aforementioned fillers surface treated with organic silicon compounds.

[0035] Furthermore, in order to improve adhesive properties, the silicone rubber composition of the invention may incorporate adhesion improving agents such as methyl trimethoxysilane, vinyl trimethoxysilane, allyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-aminopropyl trimethoxysilane, N -(2-aminoethyl)-3 -aminopropyl trimethoxysilane, bis(trimethoxysilyl) propane, bis(trimethoxysilyl) hexane, or a similar silane coupling agent; tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetra(2-ethylhexyl) titanate, titanium ethylacetonate, titanium acetylacetonate, or a similar titanium compound; ethylacetoacetate aluminum diisopropylate, aluminum tris(ethylacetoacetate), alkylacetoacetate aluminum diisopropylate, aluminum tris(acetylacetonate), aluminum monoacetylacetonate bis(ethylacetoacetate), or a similar aluminum compound; zirconium acetylacetonate, zirconium butoxyacetylacetonate, zirconium bisacetylacetonate, zirconium ethylacetoacetate, or a similar zirconium compound; alkoxysilyl-substituted triallylisocyanyrate with alkoxysilyl groups such as trimethyloxysilyl group added to 1 to 3 allyl groups, siloxane derivative obtained by partial hydrolysis and condensation of the aforementioned triallylisocyanyrate, or a similar triallylisocyanurate-type compound. The aforementioned adhesion-imparting agents can be used in an amount of 0.01 to 10 parts by mass per 100 parts by mass of component (A). [0036] If necessary, the silicone rubber composition of the invention may further incorporate a curing inhibitor to improve storage stability or handling propertiesof the silicone rubber composition of the invention such as 2-methyl-3-butyn-2-ol, 3,5-dimethyl- l-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, 1-ethynylcyclohexan-l-ol, or a similar acetylene-type compound; 3-methyl-3-penten-l-yne, 3,5-dimethyl-3-hexen-l-yne, or a similar enyne compound; l,3,5,7-tetramethyl-l,3,5,7-tetravinyl cyclotetrasiloxane, 1,3,5,7-tetramethyl- 1,3,5,7-tetrahexenyl cyclotetrasiloxane, methylvinylsiloxane capped at both molecular terminals with silanol groups, a copolymer of dimethylsiloxane and methylvinylsiloxane capped at both molecular terminals with silanol groups, or a similar organosiloxane compound having in one molecule more than 5 wt.% of vinyl group; benzotriazole, or similar triazols, phosphines, mercaptanes, hydrazines. Although there are no special restrictions with regard to the amount in which the aforementioned curing inhibitors can be added to the composition, it is recommended to add them in an amount of 0.001 to 5 parts by mass per 100 parts by mass of component (A). [0037] There are no restrictions with regard to a method for the preparation of the silicone rubber composition of the invention, and the composition is prepared by merely mixing components (A) to (E), if necessary, with the addition of component (F), or other arbitrary components. When component (F) is added to the composition, it can be first premixed with component (A) while heating, and then the mixture can be combined with components (B) to (E). When components (A) and (F) are mixed while heating and then combined with the aforementioned organic silicon compound, the surface of component (F) can be treated with the aforementioned organic silicon compound in-situ. The silicone rubber composition of the invention can be mixed by conventional means such as a 2-roll mill, kneader-mixer, Ross mixer, etc. [0038] From the viewpoint of improved storage stability, it is recommended to prepare the silicone rubber composition of the invention as a two-part silicone rubber composition consisting of a composition (I) that contains components (A), (D) and (E) without components (B) and (C), and a composition (I!) that consists of components (A), (B), and (C) without component (E). Composition (II) may be prepared without component (D), but, in order to reduce difference in flowability with respect to composition (I), addition of component (D) is recommended. If component (F) is included, it can be preheated and premixed with component (A) as composition (I) and/or as composition (II).

Examples [0039] The invention will be described in more detail with reference to application and comparative examples. All values of viscosity given in examples were measured at 25⁰C. Characteristics of the silicone rubber were measured by methods described below. [0040] [Physical Properties of Silicone Rubber]

The silicone rubber was produced by retaining the silicone rubber composition intact for 24 hours at 25⁰C. Hardness of the obtained silicone rubber was measured by means of type A durometer in accordance with JIS K 6253-1997. Dumbbell specimens No. 7 with broadened holding portions in accordance with JIS K 6251-1993 "Procedure for Testing Tensile Strength of Vulcanized Rubber" were prepared from the specimens being prepared by holding the aforementioned silicone rubber composition intact for 2 hours or for 24 hours at 25⁰C. The prepared dumbbell specimens were used for testing tensile strength and elongation of the silicone rubber as specified by JIS K 6251-1993. [0041] [Force of Adhesion to Silicone Rubber]

The force of adhesion to silicone rubber was measured by the following method in accordance with JIS K6854. More specifically, the silicone rubber composition was applied onto 50 mm- wide Nylon tapes coated with silicone rubber, the tapes were pasted together to bring the composition thickness to 1.0 mm, and then the applied composition was cured by holding the composition intact for 2 hours or for 24 hours at 25°C. Following this, the force of adhesion of the composition to silicone rubber was measured by subjecting the Nylon tape coated with silicone rubber composition to a T-shaped peeling test at a stretching rate of 200 rnm/min. [0042] [Reference Example 1] A 300 ml-capacity four-neck flask equipped with a stirrer, thermometer, reflux condenser, and a dropping funnel was loaded with 107.9 g of vinyltrimethoxysilane and 0.02 g of 3% isopropanol solution of chloroplatinic acid. The components were stirred and heated to 100⁰C. The mixture was then combined with 80.O g of a tetrakis (dimethylsiloxy) silane which was added slowly dropwise through the dropping funnel while maintaining the reaction temperature at 100 to 110⁰C. Upon completion of the dropwise addition, the reaction solution was heated for 1 hour at 12O⁰C and then cooled. After cooling, the contents were transferred to a flask of the type used for forming reaction solutions, and after the product was subjected to condensation under reduced pressure in a rotary evaporator, 166.9 g of a slightly brown liquid were obtained. Analysis of the obtained liquid showed that this liquid comprised a copolymer of silalkylene and siloxane that contained silicon-bonded methoxy groups and was represented by the following formula:

CH,

Si-j-O— Si— C₂H-Si-(OCH₃) , CH₃ [0043] A 1000 ml-capacity four-neck flask equipped with a stirrer, thermometer, reflux condenser, and a dropping funnel was loaded with 235.4 g of 1,1,3,3-tetramethyldisiloxane, 74 ml of concentrated hydrochloric acid, 148 ml of water, and 148 ml of isopropanol. The obtained product was then combined with 222.6 g of the aforementioned copolymer of silalkylene and siloxane that contained silicon-bonded methoxy groups and was represented by the following formula:

CH₃

Si- -O— St-C₂H₄- Si-f OCH₈) _j CH₃ which was added in a dropwise manner through the dropping funnel during 1 hour. Upon completion of the dropwise addition, the reaction solution was stirred for 1 hour and then transferred to a liquid separation funnel where the lower layer was separated. The remaining upper layer was three times washed with 200 ml of water and then dried with calcium chloride. The obtained solids were separated by filtering, the product was combined with 210 g of acetic acid and 0.86 mg of trifluoromethane-sulfonic acid, and the mixture was heated to 50⁰C to cause a reaction. Upon completion of the reaction, the reaction solution was transferred to a dropping-type separation funnel, the lower layer was separated, the remaining product was washed three times with 200 ml of water, once with 200 ml of an aqueous solution of a saturated sodium carbonate, and then dried with calcium chloride. The obtained solids were separated by filtering, and the obtained reaction solution was condensed at vacuum to produce 342.4 g of a colorless transparent liquid. Checking of the obtained liquid by means of a ²⁹Si NMR analysis showed that the product comprised a copolymer of sylalkylene and siloxane that contained in one molecule 12 silicon-bonded hydrogen atoms and that was represented by the following average molecular formula:

(hereinafter referred to as "a polycarbosiloxane having silicon-bonded hydrogen atoms"). A gel-permeation chromatography analysis showed that the obtained polycarbosiloxane having silicon-bonded hydrogen atoms had an average molecular weight referred to polystyrene equal to 1866 and a dispersity index equal to 1.19. [0044] [Application Example 1]

A uniform mixture was prepared from the following components: 100 parts by mass of a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups having a viscosity of 40,000 mPa-s; 15 parts by mass of fumed silica having BET specific surface area of 200 m²/g; 1.5 parts by mass of hexamethyldisiloxane as a surface coating agent for silica; and 1 part by mass of water. The prepared mixture was heated and further mixed for 2 hours at 17O⁰C₅ whereby a mixture of fumed silica and dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups was obtained. [0045] 40.7 parts by mass of the obtained mixture were further combined with the following components: 40 parts by mass of a precipitated calcium carbonate powder having BET specific surface area of 18 m²/g (Hakuenka CCR from Shiraishi Kogyo Co., Ltd.); 70.3 parts by mass of dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups and having viscosity of 40,000 mPa-s; 0.15 parts by mass of the carbopolysiloxane obtained in Reference Example 1, having silicon-bonded hydrogen atoms, and represented by the following average structural formula:

(the mole ratio of silicon-bonded hydrogen atoms contained in this component to vinyl groups contained in the silicone rubber composition was 0.27); 2.11 parts by mass of dimethylpolysiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups and having viscosity of 9.5 mPa-s (the mole ratio of silicon-bonded hydrogen atoms contained in this component to vinyl groups contained in the silicone rubber composition was 0.63); and 1,3-divinyltetramethyldisiloxane solution of a 1,3-divinyltetramethyldisiloxane complex of platinum (with 45 parts by mass of metallic platinum of this catalyst per 1 x 10⁶ parts by mass of the silicone rubber composition). The silicone rubber produced by curing the obtained silicone rubber composition was tested with regard to mechanical properties and adhesion force. Results of measurements are shown in Table 1. [0046] [Application Example 2]

The silicone rubber composition was prepared in the same manner as in Application Example 1, except that the mixture consisted of the following components: 0.13 parts by mass of the carbopolysiloxane with silicon-bonded hydrogen atoms obtained in Reference Example 1 (the mole ratio of silicon-bonded hydrogen atoms contained in this component to vinyl groups contained in this silicone rubber composition was 0.27); 1.74 parts by mass of dimethylpolysiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups and having viscosity of 9.5 mPa-s (the mole ratio of silicon-bonded hydrogen atoms contained in the component to vinyl groups contained in this silicone rubber composition was 0.63); and 1,3-divrnyltetramethyldisiloxane solution of a 1,3-divinyltetramethyldisiloxane complex of platinum (with 22 parts by mass of metallic platinum of this catalyst per 1 x 10⁶ parts by mass of the silicone rubber composition). The silicone rubber produced by curing the obtained silicone rubber composition was tested with regard to mechanical properties and , adhesion force. Results of measurements are shown in Table 1. [0047] [Comparative Example]

A silicone rubber composition was prepared in the same manner as in Application Example 1, except that 0.7 part by mass of a copolymer of methylhydrogensiloxane and dimethylsiloxane having both molecular terminals capped with trimethylsiloxy groups and having viscosity of 13 mPa-s (with on average three silicon-bonded hydrogen atoms in one molecule and with the mole ratio of silicon-bonded hydrogen atoms contained in this component to vinyl groups contained in this silicone rubber composition equal to 0.27) was used instead of the carbopolysiloxane having silicon-bonded hydrogen atoms obtained in Reference Example 1.The silicone rubber produced by curing the obtained silicone rubber composition was tested with regard to mechanical properties and adhesion force. Results of measurements are shown in Table 1. [0048] [Comparative Example 2]

A silicone rubber composition was prepared in the same manner as in Application Example 2, except that 0.7 part by mass of a copolymer of methylhydrogensiloxane and dimethylsiloxane having both molecular terminals capped with trimethylsiloxy groups and having viscosity of 13 mPa-s (with on average three silicon-bonded hydrogen atoms in one molecule and with the mole ratio of silicon-bonded hydrogen atoms contained in this component to vinyl groups contained in this silicone rubber composition equal to 0.27) was used instead of the carbopolysiloxane having silicon-bonded hydrogen atoms and obtained in Reference Example l.The silicone rubber produced by curing the obtained silicone rubber composition was tested with regard to mechanical properties and adhesion force. Results of measurements are shown in Table 1.

[0049] [Table 1]

Industrial Applicability

[0050] Since the silicone rubber composition of the invention quickly develops a force of adhesion to silicone rubber and provides excellent strength of adhesion to silicone rubber, when the composition is used as an adhesive agent for bonding to silicone rubber, bonding occurs in a short time and with a strong bonding force. For example, the composition can be used as an adhesive or a sealer for manufacturing air bags formed by silicone rubber- impregnated or -coated fabric which are then laminated onto each other and bonded or sewed together at their peripheral edges. Alternatively, the composition can be used as an adhesive agent for shock-absorbing or vibration absorbing elements formed by laminating silicone gel or silicone rubber elements. The silicone rubber composition of the invention may also be used for reinforcing or protecting surfaces, or for keeping the shape of silicone gel.

Claims

1. A silicone rubber composition comprising the following components:

100 parts by weight of a diorganopolysiloxane (A) having in one molecule at least two alkenyl groups; an organopolysiloxane (B) having in one molecule at least three silicon- bonded hydrogen atoms and at least one silicon-bonded group X¹, which is a silylalkyl group represented by the following formula (1), when i = 1 :

(where R is an aryl group or an alkyl group with 1 to 10 carbon atoms; R is an alkylene group having 2 to 10 carbon atoms; R³ is an alkyl group having 1 to 10 carbon atoms; "i" shows the hierarchical level of the silylalkyl group; if the hierarchical number is designated by "c", "i" may be an integer from 1 to "c"; the hierarchical number "c" is an integer from 1 to 10; when "i" is 1, then "b¹" is an integer from 0 to 2; when "i" is 2 or greater than 2, then "b¹" is a number which is less than 3; when "i" is less than "c", then X¹⁺¹ is the aforementioned silylalkyl group, and when i=c, then X¹⁺¹ is a hydrogen atom) {the mole ratio of silicon-bonded hydrogen atoms in this component to alkenyl groups in the composition ranges from 0.01 to 20}; an organopolysiloxane (C) having in one molecule on average at least 2 silicon-bonded hydrogen atoms {except for component (B)} {the mole ratio of silicon-bonded hydrogen atoms in this component to alkenyl groups in the composition ranges from 0.01 to 20}; 1 to 200 parts by mass of powdered calcium carbonate (D); and a hydrosilylation catalyst (E) (in the amount required to accelerate curing of the composition).

2. The silicone rubber composition of Claim 1 , wherein component (B) is a polycarbosiloxane represented by the following formula:

or by the following formula:

{where "d" is 3 or 4; R¹ is aryl group or an alkyl group with 1 to 10 carbon atoms; Y¹ is a silylalkyl group of the formula given below, when i = 1 :

(where R¹ is the same as defined above; R² is an alkylene group with 2 to 10 carbon atoms; "i" shows the hierarchical level of the silylalkyl group designated by Y¹; the hierarchical number "c" is 1 or 2; when the hierarchical number "c" is 1, then Y¹⁺¹ is a hydrogen atom; when the hierarchical number "c" is 2, then Y¹⁺¹ is the aforementioned silylalkyl group when "i" = 1, or a hydrogen atom when "i" = 2)} .

3. The silicone rubber composition according to Claim 1 or Claim 2, wherein the mole number of silicon-bonded hydrogen atoms contained in component (B) to the mole number of silicon-bonded hydrogen atoms contained in component (C) ranges from (1:1 to 1:10) and wherein the mole ratio of all silicon-bonded hydrogen atoms contained in components (B) and (C) to alkenyl groups contained in the composition ranges from 0.1 to 10.

4. The silicone rubber composition according to Claim 1 or Claim 2, wherein component (D) is a light (or precipitated) calcium carbonate powder.

5. The silicone rubber composition according to Claim 1 or Claim 2, further comprising a silica powder (F) {in an amount of 1 to 100 parts by mass per 100 parts by mass of component (A)}.

6. The silicone rubber composition according to Claim 4, wherein components (A) and (F) are preliminarily mixed while heating.

7. The silicone rubber composition according to any of Claims from 1 to 6, which is an adhesive agent for silicone rubber.

8. The silicone rubber composition according to any of Claims from 1 to 6, which is an adhesive agent for a silicone rubber-coated fabric.

9. The silicone rubber composition according to any of Claims from 1 to 6, which is a sealer for a silicone rubber-coated fabric.