JP2016023259A - Curable silicone rubber composition and silicone rubber member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a curable silicone rubber composition which provides a silicone rubber hardened product excellent in dynamic fatigue durability when hardened.SOLUTION: A curable silicone rubber composition is based on (A) an organopolysiloxane of an average composition formula (I) RSiOhaving a polymerization degree of 100 or greater, (B) reinforcement silica of a specific surface area of 50 m/g or greater, measured by the BET adsorption method, (C) a silazane compound of formula (II) and (D) a hardener. In the formula (I), Rand Rare independently identical or different substituted/unsubstituted monovalent hydrocarbon groups and/or alkenyl groups free of an aliphatic unsaturated bond; and at least one of Rand Ris an alkenyl group.SELECTED DRAWING: None

Description

  The present invention relates to a curable silicone rubber composition that provides a cured silicone rubber having excellent durability against dynamic fatigue that repeatedly undergoes deformation such as stretching and bending after molding, and silicone rubber for a keypad formed by curing the composition. It relates to members.

  Silicone rubber (an elastomeric elastic body obtained by curing a silicone rubber composition) has excellent weather resistance, electrical characteristics, low compression set, heat resistance, cold resistance, and the like. Widely used in various fields, including architecture, medicine and food. For example, rubber contacts used as rubber contacts for remote controllers, computer terminals, musical instruments, etc., architectural gaskets, rolls for copying machines, developing rolls, transfer rolls, charging rolls, feeding rolls, and other rolls, audio devices, etc. Applications include anti-vibration rubber, packing for compact discs, mobile phones, and keyboards for personal computers.

  Among them, materials used for keypad materials, joint boots for automobiles, etc. are repeatedly subjected to deformation such as stretching and bending, and silicone rubber used in this application has high dynamic fatigue durability. It has been demanded. For example, the keypad characteristics are required to have a small load change when the key is pressed. Normally, when the keystroke of a molding key is repeated, the load on the key decreases as the number of keystrokes increases. As the peak load decreases less, the key characteristics are better, and a material exhibiting such load characteristics is excellent as a keypad material.

  As a material excellent in such dynamic fatigue characteristics, a material made of silicone rubber is widely used. JP-A-6-145523 (Patent Document 1), JP-A-9-132712 (Patent Document 2), JP-A 2000-309710 (Patent Document 3), JP-A 2001-164111 (Patent Document 4) ), Japanese Patent Application Laid-Open No. 2013-2221090 (Patent Document 5), Japanese Patent No. 3184231 (Patent Document 6) and the like have proposed silicone rubber compositions having excellent dynamic fatigue durability.

  However, with recent downsizing of devices used, the number of materials that are subject to large strains is increasing. For this reason, the dynamic fatigue durability is not fully satisfied with the recent severe requirements.

  On the other hand, as patents relating to a silicone rubber composition containing a silazane compound having an alkenyl group, JP-A-54-146850 (Patent Document 7) and JP-A-5-65417 (Patent Document 8) can be mentioned. Is only described as an increase in strength or a silica treating agent, and there is no description of improvement in fatigue durability.

JP-A-6-145523 JP-A-9-132712 JP 2000-309710 A JP 2001-164111 A JP 2013-2221090 A Japanese Patent No. 3184231 JP 54-146850 A JP-A-5-65417

  The present invention has been made in view of the above circumstances, and a curable silicone rubber composition that cures to give a cured silicone rubber excellent in dynamic fatigue durability and a keypad obtained by curing the composition. An object of the present invention is to provide a silicone rubber member.

  As a result of intensive studies to achieve the above object, the present inventor has found that an organopolysiloxane having a degree of polymerization of 100 or more (particularly 1,000 or more), reinforcing silica, a silazane compound having a specific alkenyl group, It has been found that a cured silicone rubber (elastomer-like elastic body) excellent in dynamic fatigue characteristics can be obtained by curing a curable silicone rubber composition blended with the present invention, and has led to the present invention.

（式中、Ｒ¹及びＲ²はそれぞれ独立に同一又は異種の脂肪族不飽和結合を有さない非置換又は置換一価炭化水素基又はアルケニル基であり、Ｒ¹及びＲ²のうち少なくとも１個はアルケニル基である。ｎはそれぞれ独立に１〜１０の整数である。）
で示されるシラザン化合物 ０．０１〜１０質量部、
（Ｄ）硬化剤 有効量
を主成分としてなる硬化性シリコーンゴム組成物。
〔２〕
（Ｃ）成分の一般式（ＩＩ）において、Ｒ¹が脂肪族不飽和結合を有さない非置換又は置換一価炭化水素基であり、Ｒ²の少なくとも１個がアルケニル基である〔１〕記載の硬化性シリコーンゴム組成物。
〔３〕
（Ｃ）成分のシラザン化合物が、下記一般式（ＩＩＩ）で示されるものである〔１〕又は〔２〕記載の硬化性シリコーンゴム組成物。

〔４〕
更に、（Ｅ）成分として、下記一般式（ＩＶ）

（式中、Ｒ³は同一又は異種のアルキル基もしくは水素原子であり、Ｒ⁴は同一又は異種の非置換もしくは置換一価炭化水素基であり、ｍは０〜５０の整数である。）
で表されるオルガノシラン又はオルガノシロキサンを（Ａ）成分と（Ｂ）成分の合計１００質量部当たり０．１〜５０質量部含む〔１〕〜〔３〕のいずれかに記載のシリコーンゴム組成物。
〔５〕
硬化して１００％伸長疲労試験が２００万回以上となるシリコーンゴム硬化物を与えるものである〔１〕〜〔４〕のいずれかに記載のシリコーンゴム組成物。
〔６〕
〔１〕〜〔５〕のいずれかに記載の硬化性シリコーンゴム組成物を硬化させてなるキーパッド用シリコーンゴム部材。 Accordingly, the present invention provides the following curable silicone rubber composition and a silicone rubber member obtained by curing the composition.
[1]
(A) The following average composition formula (I)
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.05.)
100 parts by mass of an organopolysiloxane having a degree of polymerization represented by
(B) Reinforcing silica having a specific surface area of 50 m ² / g or more by BET adsorption method
5-70 parts by weight,
(C) The following general formula (II)

Wherein R ¹ and R ² are each independently an unsubstituted or substituted monovalent hydrocarbon group or alkenyl group having no identical or different aliphatic unsaturated bond, and at least one of R ¹ and R ² Each is an alkenyl group, each n is independently an integer of 1 to 10.)
0.01 to 10 parts by mass of a silazane compound represented by
(D) Curing agent A curable silicone rubber composition comprising an effective amount as a main component.
[2]
In the general formula (II) of the component (C), R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having no aliphatic unsaturated bond, and at least one of R ² is an alkenyl group [1] The curable silicone rubber composition described.
[3]
The curable silicone rubber composition according to [1] or [2], wherein the silazane compound of component (C) is represented by the following general formula (III).

[4]
Further, as the component (E), the following general formula (IV)

(In the formula, R ³ is the same or different alkyl group or hydrogen atom, R ⁴ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and m is an integer of 0 to 50.)
The silicone rubber composition according to any one of [1] to [3], comprising 0.1 to 50 parts by mass of the organosilane or organosiloxane represented by the formula (A) and the component (B) per 100 parts by mass in total. .
[5]
The silicone rubber composition according to any one of [1] to [4], which is cured to give a cured silicone rubber having a 100% elongation fatigue test of 2 million times or more.
[6]
[1] A silicone rubber member for a keypad obtained by curing the curable silicone rubber composition according to any one of [5].

  ADVANTAGE OF THE INVENTION According to this invention, the curable silicone rubber composition which gives the silicone rubber hardened | cured material excellent in dynamic fatigue durability can be obtained.

Hereinafter, the present invention will be described in more detail.
-Component (A)-
In the present invention, the component (A) is an organopolysiloxane having a degree of polymerization represented by the following average composition formula (I) of 100 or more (particularly 1,000 or more). ).
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.05.)

  In the above average composition formula (I), R represents the same or different unsubstituted or substituted monovalent hydrocarbon group, usually having 1 to 12 carbon atoms, particularly preferably having 1 to 8 carbon atoms, specifically, Alkyl group such as methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group, cycloalkyl group such as cyclopentyl group, cyclohexyl group, alkenyl group such as vinyl group, allyl group, propenyl group, cycloalkenyl group Aryl groups such as phenyl group and tolyl group, aralkyl groups such as benzyl group and 2-phenylethyl group, or groups in which part or all of hydrogen atoms of these groups are substituted with halogen atoms or cyano groups, etc. 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 2 or more, usually 2 to 50, particularly about 2 to 20 alkenyl groups, cycloalkenyl groups and other aliphatic unsaturated groups in one molecule. Those having a vinyl group are particularly preferable. In this case, 0.01 to 20 mol%, particularly 0.02 to 10 mol% of all R is preferably an aliphatic unsaturated group such as an alkenyl group. The aliphatic unsaturated group may be bonded to the silicon atom at the molecular chain end, or may be bonded to the silicon atom in the middle of the molecular chain (molecular chain non-terminal), or both. Is preferably bonded to at least a silicon atom at the end of the molecular chain.
Further, it is desirable that 90% by mole or more, preferably 95% by mole or more, and more preferably, all Rs excluding aliphatic unsaturated groups are all alkyl groups, particularly methyl groups.

  Moreover, a is a positive number of 1.95 to 2.05, preferably 1.98 to 2.02, more preferably 1.99 to 2.01.

Specifically, the repeating structure of the diorganosiloxane unit (R ₂ SiO _2/2 , R is the same as above, the same shall apply hereinafter) constituting the main chain of the organopolysiloxane consists of repeating dimethylsiloxane units only, Or a diphenylsiloxane unit 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, methyl What introduced diorganosiloxane units, such as a phenylsiloxane unit, a methylvinylsiloxane unit, and a methyl-3,3,3-trifluoropropylsiloxane unit, is suitable.
The molecular chain both ends are, for example, triorganosiloxy groups (R ₃ SiO _1/2 ) such as trimethylsiloxy group, dimethylphenylsiloxy group, vinyldimethylsiloxy group, divinylmethylsiloxy group, trivinylsiloxy group, and hydroxydimethyl. It is preferably blocked with a hydroxydiorganosiloxy group (R ₂ (HO) SiO _1/2 ) such as a siloxy group.

As the organopolysiloxane of component (A), the end of the molecular chain is a triorganosiloxy group such as trimethylsiloxy group, dimethylphenylsiloxy group, dimethylvinylsiloxy group, methyldivinylsiloxy group, trivinylsiloxy group (R ₃ SiO _{1 / 2} ) or is blocked with a hydroxydiorganosiloxy group (R ₂ (HO) SiO _1/2 ) such as a dimethylhydroxysiloxy group, and the main chain is composed of repeating diorganosiloxane units (R ₂ SiO _2/2 ). A linear thing can be mentioned preferably. Particularly preferred are the types of substituents in the molecule (that is, unsubstituted or substituted monovalent hydrocarbon groups bonded to silicon atoms) as methyl vinyl polysiloxane, methyl phenyl vinyl polysiloxane, methyl trifluoropropyl vinyl poly Examples thereof include siloxane.

  Such an organopolysiloxane can be obtained by, for example, hydrolyzing and condensing one or more types of organohalogenosilanes, or by making cyclic polysiloxanes (siloxane trimers, tetramers, etc.) alkaline or It can be obtained by ring-opening polymerization using an acidic catalyst. These are basically linear diorganopolysiloxanes, but the component (A) may be a mixture of two or more different molecular weights (degree of polymerization) and molecular structures.

  The degree of polymerization of the organopolysiloxane (or the number of silicon atoms in the molecule) is 100 or more (usually 100 to 100,000), preferably 1,000 to 100,000, more preferably 2,000 to 50,000. 000, particularly preferably 3,000 to 20,000, and is preferably a so-called raw rubber (non-liquid) that does not have self-fluidity at room temperature (25 ° C). When the degree of polymerization is too small, when it is compounded, it is a so-called millable type (that is, it can be uniformly mixed under shear stress using a kneader such as a roll mill, and is non-liquid without self-fluidity at room temperature) It becomes difficult to obtain a silicone rubber compound, problems such as roll adhesion occur, and roll workability deteriorates. The degree of polymerization (or molecular weight) can be measured, for example, as a weight average degree of polymerization (or weight average molecular weight) in terms of polystyrene by gel permeation chromatography (GPC) analysis using toluene or the like as a developing solvent.

-(B) component-
Component (B), reinforcing silica, is a reinforcing filler added to obtain a silicone rubber composition having excellent mechanical strength. For this purpose, the specific surface area (BET adsorption method) is 50 m ^2. / G or more, preferably 100 to 450 m ² / g, more preferably 100 to 300 m ² / g. When the specific surface area is less than 50 m ² / g, the mechanical strength of the cured product is lowered.

  Examples of such reinforcing silica include fumed silica (fumed silica), precipitated silica and the like, and those whose surfaces are hydrophobized with chlorosilane, hexamethyldisilazane, or the like are also preferably used. . Among these, fumed silica excellent in dynamic fatigue characteristics is preferable. (B) A component may use together 1 type (s) or 2 or more types.

  (B) The compounding quantity of the reinforcing silica of a component is 5-70 mass parts with respect to 100 mass parts of (A) component organopolysiloxane, and it is preferable that it is 10-50 mass parts. When the blending amount of the component (B) is too small, the reinforcing effect cannot be obtained, and when it is too large, the workability is deteriorated, the mechanical strength is lowered, and the dynamic fatigue durability is also deteriorated. End up.

（式中、Ｒ¹及びＲ²はそれぞれ独立に同一又は異種の脂肪族不飽和結合を有さない非置換又は置換一価炭化水素基又はアルケニル基であり、Ｒ¹及びＲ²のうち少なくとも１個はアルケニル基である。ｎはそれぞれ独立に１〜１０の整数である。）
で示されるシラザン化合物である。 -(C) component-
Component (C) has the following general formula (II)

Wherein R ¹ and R ² are each independently an unsubstituted or substituted monovalent hydrocarbon group or alkenyl group having no identical or different aliphatic unsaturated bond, and at least one of R ¹ and R ² Each is an alkenyl group, each n is independently an integer of 1 to 10.)
It is a silazane compound represented by

In the above formula (II), n, which represents the number of repeating difunctional diorganosiloxane units ((R ² ) ₂ SiO _2/2 ), is preferably about 1 to 10 and particularly about 3 to 7 It is preferable that

R ¹ and R ² are each independently an unsubstituted or substituted monovalent hydrocarbon group or alkenyl group that does not have the same or different aliphatic unsaturated bond, and at least one of R ¹ and R ² Is an alkenyl group. Examples of the unsubstituted or substituted monovalent hydrocarbon group having no aliphatic unsaturated bond include the same groups as those other than the alkenyl group among the examples of R in the component (A), and particularly methyl. An alkyl group having about 1 to 6 carbon atoms such as a group or an ethyl group is preferred. Examples of the alkenyl group include those having 2 to 10 carbon atoms, particularly about 2 to 4 carbon atoms such as vinyl group, allyl group, and propenyl group, with vinyl group being particularly preferable.

In addition, the silazane compound of component (C) has one or more, preferably two or more alkenyl groups in the molecule, particularly three or more and twenty or less, especially four or more and twelve or less. Preferably there is. This alkenyl group is more bifunctional than it exists as R ¹ bonded to the silicon atom in the terminal triorganosiloxy group ((R ¹ ) ₃ SiO _1/2 ) (ie, as a terminal alkenyl group). The presence of R ² bonded to a silicon atom in the diorganosiloxane unit ((R ² ) ₂ SiO _2/2 ) (that is, as a side chain alkenyl group) improves dynamic fatigue durability. This is more preferable.

  Specific examples of the component (C) include vinyl group-containing silazane compounds represented by the following general formulas (III), (V), (VI), and (VII). Particularly preferred are vinyl group-containing silazane compounds.

  The compounding amount of the alkenyl group-containing organosilazane compound of component (C) is 0.01 to 10 parts by mass and 0.1 to 3 parts by mass with respect to 100 parts by mass of component (A) organopolysiloxane. Is preferred. When the blending amount of the component (C) is too small, the effect of improving the dynamic fatigue durability cannot be obtained, and when it is too large, the hardness of the resulting rubber becomes too high, which is not economically preferable. .

-(D) component-
The curing agent for component (D) is not particularly limited as long as it can cure the component (A), but (i) addition reaction (hydrosilylation reaction) generally known as a rubber curing agent. ) Type curing agent, that is, a combination of an organohydrogenpolysiloxane (crosslinking agent) and a hydrosilylation catalyst, or (ii) an organic peroxide.

  The organohydrogenpolysiloxane as a crosslinking agent in the above (i) addition reaction (hydrosilylation reaction) contains hydrogen atoms (SiH groups) bonded to at least two silicon atoms in one molecule. A conventionally known organohydrogenpolysiloxane represented by the composition formula (VIII) is applicable.

R ⁵ _b H _c SiO _{(4-bc) / 2} (VIII)
(Here, R ⁵ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and preferably has no aliphatic unsaturated bond. Specific examples include a methyl group, an ethyl group, Propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, alkyl group such as pentyl group, hexyl group, cycloalkyl group such as cyclohexyl group, aryl group such as phenyl group, aralkyl group such as benzyl group, etc. Substituted alkyl groups in which at least part of the hydrogen atoms of the monovalent hydrocarbon group such as unsubstituted monovalent hydrocarbon group, 3,3,3-trifluoropropyl group, cyanomethyl group, etc. are substituted with halogen atoms or cyano groups, etc. And b is from 0.7 to 2.1, c is from 0.01 to 1.0, and b + c is from 0.8 to 3.0, preferably b is from 0.8 to 2. 0.0, c is 0.10 to 1 0, more preferably from 0.18 to 1.0, more preferably 0.2 to 1.0, and b + c is a positive number that satisfies the 1.0 to 2.5.)

  Further, the molecular structure of the organohydrogenpolysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is preferably 2 to 300, particularly about 4 to 200 at room temperature. The hydrogen atom (SiH group) bonded to the silicon atom may be at the end of the molecular chain, at the side chain (in the middle of the molecular chain), or both, and at least two (usually normal) 2 to 300), preferably 3 or more (for example, 3 to 200), more preferably about 4 to 150.

Examples of the organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane and dimethyl. Siloxane cyclic copolymer, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, trimethylsiloxy group-blocked methylhydrogenpolysiloxane at both ends, trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane at both ends Copolymers, dimethylpolysiloxane blocked with dimethylhydrogensiloxy groups at both ends, dimethylsiloxane / methylhydrogenblocked with dimethylhydrogensiloxy groups at both ends Siloxane copolymer, trimethylsiloxy group-capped methylhydrogensiloxane / diphenylsiloxane copolymer, trimethylsiloxy group-capped methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane, Cyclic methylhydrogensiloxane / dimethylsiloxane copolymer, cyclic methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units and SiO _4/2 units, In a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 unit, SiO _4/2 unit and (C ₆ H ₅ ) SiO _3/2 unit, etc., and each of the above exemplified compounds, a part or all of the methyl group is Other alkyl groups such as ethyl and propyl groups and phenyl And those substituted with an aryl group such as a group. Moreover, as such organohydrogenpolysiloxane, the compound of the following structural formula can be illustrated specifically.

（式中、ｋは２〜１０の整数、ｓ及びｔは０〜１０の整数である。）

(In the formula, k is an integer of 2 to 10, and s and t are integers of 0 to 10.)

  The organohydrogenpolysiloxane preferably has a viscosity at 25 ° C. of 0.5 to 10,000 mPa · s, particularly 1 to 300 mPa · s. The viscosity can be measured with a rotational viscometer.

The compounding amount of the organohydrogenpolysiloxane is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 10 parts by mass, and still more preferably 100 parts by mass of the organopolysiloxane (A). Is 0.3 to 10 parts by mass.
Further, this organohydrogenpolysiloxane has a hydrogen atom bonded to a silicon atom in the organohydrogenpolysiloxane with respect to an aliphatic unsaturated group such as an alkenyl group bonded to the silicon atom in the component (A) (that is, SiH group). ) In a quantity of 0.5 to 10 mol / mol, preferably 0.8 to 6 mol / mol, more preferably 1 to 5 mol / mol. If it is less than 0.5 mol / mol, crosslinking may not be sufficient, and sufficient mechanical strength may not be obtained. If it exceeds 10 mol / mol, physical properties after curing will be deteriorated, particularly heat resistance and compression. Permanent distortion may be significantly degraded.

  The hydrosilylation catalyst used for the crosslinking reaction in the above (i) addition reaction (hydrosilylation reaction) is an aliphatic unsaturated group (such as an alkenyl group) in the component (A) and the organohydrogen as a crosslinking agent. It is a catalyst for the addition reaction of silicon-bonded hydrogen atoms (SiH groups) in polysiloxane. Examples of the hydrosilylation catalyst include a platinum group metal catalyst, which includes a platinum group metal and a compound thereof, and conventionally known catalysts for addition reaction curable silicone rubber compositions can be used. For example, particulate platinum metal adsorbed on a carrier such as silica, alumina or silica gel, platinum chloride, chloroplatinic acid, chloroplatinic acid hexahydrate alcohol solution, palladium catalyst, rhodium catalyst, etc. Platinum or platinum compounds are preferred.

  The addition amount of the hydrosilylation catalyst may be a so-called catalyst amount that can promote the addition reaction, and is usually used in the range of 1 ppm to 1% by mass in terms of the platinum group metal mass relative to the component (A). However, the range of 10-500 ppm is preferable. If the addition amount is less than 1 ppm, the addition reaction may not be sufficiently promoted and curing may be insufficient. On the other hand, if it exceeds 1% by mass, there is little influence on the reactivity even if it is added more than this. It may be an economy.

  In addition to the above catalyst, an addition crosslinking controller may be used for the purpose of adjusting the curing rate. Specific examples include ethynylcyclohexanol and tetramethyltetravinylcyclotetrasiloxane.

  On the other hand, (ii) as the organic peroxide, for example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, di-t-butylperoxide, t-butylperbenzoate, 1,6-hexanediol-bis-t-butylperoxycarbonate, etc. Is mentioned.

  The addition amount of the organic peroxide is preferably 0.1 to 15 parts by mass, particularly preferably 0.2 to 10 parts by mass with respect to 100 parts by mass of the component (A). If the amount added is too small, the crosslinking reaction does not proceed sufficiently, which may result in deterioration of physical properties such as hardness reduction, insufficient rubber strength, increased compression set, and if too large, it is not only economically undesirable, but also a curing agent. In some cases, a large amount of decomposition products of the above may occur, resulting in deterioration of physical properties such as an increase in compression set and discoloration of the obtained sheet.

  In the silicone rubber composition of the present invention, in addition to the above components, if necessary, as an optional component, (E) component, both ends of the molecular chain represented by the following general formula (IV) are silanol groups (silicon atoms). May be contained as a dispersant for the reinforcing silica filler. By adding this, the dispersibility of the silica filler in the rubber can be increased, and the processability can also be improved.

（式中、Ｒ³は同一又は異種のアルキル基もしくは水素原子であり、Ｒ⁴は同一又は異種の非置換もしくは置換一価炭化水素基であり、ｍは０〜５０の整数である。）

(In the formula, R ³ is the same or different alkyl group or hydrogen atom, R ⁴ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and m is an integer of 0 to 50.)

Here, R ³ is the same or different alkyl group or hydrogen atom, and the organosilane or organosiloxane represented by the general formula (IV) has an alkoxy group or a hydroxyl group at both ends of the molecular chain. Examples of R ³ include a hydrogen atom or an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. A hydrogen atom is preferred.
R ⁴ usually has 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms, and specifically includes methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group and the like. Cycloalkyl groups such as alkyl groups and cyclohexyl groups, vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, isobutenyl groups, alkenyl groups such as hexenyl groups and cyclohexenyl groups, and aryl groups such as phenyl groups and tolyl groups Aralkyl groups such as β-phenylpropyl group, or a part or all of hydrogen atoms bonded to carbon atoms of these groups are substituted with halogen atoms, cyano groups or the like, for example, chloromethyl group, trifluoropropyl group, cyanoethyl group Methyl group, vinyl group, phenyl group, trifluoropropyl group are preferable, and methyl group is particularly preferable. A vinyl group is preferred. Further, from the viewpoint of compatibility with the organopolysiloxane of component (A), it is preferably the same as the monovalent hydrocarbon group of component (A) (that is, R in formula (1)).

  m is an integer of 0 to 50, and preferably an integer of 1 to 30. When m exceeds 50, the effect may be reduced as a treating agent for treating the reinforcing silica of the component (B).

  The component (E) is an optional component that may be added as necessary, but when the component (E) is blended, the blending amount of the component (E) is (A) and (B). 0.1 to 50 parts by mass, particularly 0.5 to 30 parts by mass, and particularly 0.5 to 20 parts by mass are preferred per 100 parts by mass of the total amount of components. If the amount is less than 0.1 parts by mass, kneading may become difficult and the plastic return may increase, and if it exceeds 50 parts by mass, the resulting silicone rubber composition may be tacky.

  In addition to the above components, the silicone rubber composition of the present invention includes a conductivity imparting agent such as carbon black, a flame retardant imparting agent such as iron oxide and a halogen compound, and a softening agent, as long as the object of the present invention is not impaired. Anti-aging agents, ultraviolet absorbers, colorants and the like can be added.

  The silicone rubber composition of the present invention can be obtained by kneading predetermined amounts of the above-described components with a two-roll, kneader, Banbury mixer or the like.

The silicone rubber composition of the present invention is mainly used for a keypad. In order to form such a keypad, it is necessary to cure the silicone rubber composition, but the curing conditions are not particularly limited. Generally, a keypad can be obtained by heating and curing at 80 to 300 ° C., particularly 100 to 250 ° C., for 5 seconds to 1 hour, particularly 30 seconds to 30 minutes. Moreover, you may post-cure about 10 minutes-10 hours at 100-200 degreeC.
Although it does not specifically limit as a shaping | molding method, Press molding is preferable.

  The silicone rubber composition of the present invention is particularly 100% elongation of a cured silicone rubber obtained by curing under conditions of press cure (primary curing) 165 ° C./10 minutes and post cure (secondary curing) 200 ° C./4 hours. The fatigue test is preferably 2 million times or more, particularly 3 million times or more, particularly 3.5 million times or more. If the 100% elongation fatigue test is less than 2 million times, the dynamic fatigue durability may be poor when molded into a keypad. In addition, in order to obtain a cured silicone rubber having a 100% elongation fatigue test of 2 million times or more, at least the above-described components (A) to (D) are uniformly kneaded at the above-described predetermined blending ratio. A silicone rubber composition prepared by mixing may be used.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In addition, the part in the following example shows a mass part. The physical property measurement method and dynamic fatigue property evaluation method are shown below.

Physical Properties Measurement Method Using the test sheets obtained in Examples and Comparative Examples, hardness (durometer type A), tensile strength, and elongation at break were measured according to JIS K6249. The results are shown in Table 1.

Dynamic fatigue characteristic test method The dynamic fatigue durability was measured by the following method.
[100% stretch fatigue test]
Using the test sheets obtained in the examples and comparative examples, test pieces were punched with a No. 3 dumbbell, and marked lines were inserted so that the distance between marked lines was 20 mm. It was set in a dematcher tester so that the distance between the marked lines was 20 mm to 40 mm (0 to 100% extension), and the extension was repeated at a speed of 300 times per minute. The number of times until the dumbbell broke was measured. The results are shown in Table 1.

上記コンパウンド１００部に対し、架橋剤として２，５−ジメチル−２，５−ビス（ｔ−ブチルパーオキシ）ヘキサン０．４部を添加し、均一に混合した後、１６５℃、７０ｋｇｆ／ｃｍ²の条件で１０分間プレスキュアーを行い、厚さ２ｍｍの試験用シートを作製した。その後、２００℃で４時間のポストキュアーを行った。 [Example 1]
The average degree of polymerization containing 99.850 mol% of dimethylsiloxane units and 0.125 mol% of methylvinylsiloxane units as diorganosiloxane units constituting the main chain and 0.025 mol% of dimethylvinylsiloxy groups as molecular chain end groups is 100 parts of linear organopolysiloxane (raw rubber) of about 6,000, 30 parts of fumed silica (trade name Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) with a BET specific surface area of 200 m ² / g, both ends as a dispersant 3 parts of dimethylpolysiloxane having a silanol group and an average degree of polymerization of 5 and 1.19 parts of a silazane compound represented by the following general formula (III) are kneaded with a kneader and heat-treated at 170 ° C. for 2 hours. A compound was prepared.

To 100 parts of the above compound, 0.4 part of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane is added as a crosslinking agent and mixed uniformly, then at 165 ° C. and 70 kgf / cm ^2. Under the above conditions, press curing was performed for 10 minutes to prepare a test sheet having a thickness of 2 mm. Thereafter, post-curing was performed at 200 ° C. for 4 hours.

[Example 2]
Production was conducted in the same manner as in Example 1 except that 1.11 parts of the silazane compound represented by the following general formula (V) was added instead of the silazane compound represented by the general formula (III).

[Example 3]
Production was conducted in the same manner as in Example 1 except that 1.11 parts of the silazane compound represented by the following general formula (VI) was added instead of the silazane compound represented by the general formula (III).

[Example 4]
Production was conducted in the same manner as in Example 1 except that 1.50 parts of the silazane compound represented by the following general formula (VII) was added instead of the silazane compound represented by the general formula (III).

[Comparative Example 1]
Production was conducted in the same manner as in Example 1 except that 1.07 part of the silazane compound represented by the following general formula (IX) was added instead of the silazane compound represented by the general formula (III).

[Comparative Example 2]
Production was conducted in the same manner as in Example 1 except that 0.28 part of the silazane compound represented by the following general formula (X) was added instead of the silazane compound represented by the general formula (III).

[Comparative Example 3]
Production was conducted in the same manner as in Example 1 except that 0.33 part of the silazane compound represented by the following general formula (XI) was added instead of the silazane compound represented by the general formula (III).

Claims (6)

(A) The following average composition formula (I)
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.05.)
100 parts by mass of an organopolysiloxane having a degree of polymerization represented by
(B) Reinforcing silica having a specific surface area of 50 m ² / g or more by BET adsorption method
5-70 parts by weight,
(C) The following general formula (II)

Wherein R ¹ and R ² are each independently an unsubstituted or substituted monovalent hydrocarbon group or alkenyl group having no identical or different aliphatic unsaturated bond, and at least one of R ¹ and R ² Each is an alkenyl group, each n is independently an integer of 1 to 10.)
0.01 to 10 parts by mass of a silazane compound represented by
(D) Curing agent A curable silicone rubber composition comprising an effective amount as a main component. In the general formula (II) of the component (C), R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having no aliphatic unsaturated bond, and at least one of R ² is an alkenyl group. The curable silicone rubber composition described. The curable silicone rubber composition according to claim 1 or 2, wherein the silazane compound of component (C) is represented by the following general formula (III).

Further, as the component (E), the following general formula (IV)

(In the formula, R ³ is the same or different alkyl group or hydrogen atom, R ⁴ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and m is an integer of 0 to 50.)
The silicone rubber composition according to any one of claims 1 to 3, comprising 0.1 to 50 parts by mass of the organosilane or organosiloxane represented by the formula (A) and the component (B) per 100 parts by mass in total.   The silicone rubber composition according to any one of claims 1 to 4, which is cured to give a cured silicone rubber having a 100% elongation fatigue test of 2 million times or more.   The silicone rubber member for keypads which hardens the curable silicone rubber composition of any one of Claims 1-5.