Silicone rubber composition for keypad production and keypad

Abstract

To provide a silicone rubber composition suitable for keypad materials, the composition allowing formation of a cured product exhibiting excellent dynamic fatigue durability through primary vulcanization alone.SOLUTION: A millable-type silicone rubber composition comprising: (A) a linear organopolysiloxane having a weight-average polymerization degree of 1,000 to 100,000 and containing two or more alkenyl groups bonded to silicon atoms in one molecule; (B) a precipitated silica having a specific surface area of 50 m2 / g or more as measured by the BET method; (C) an organosiloxane represented by formula (1) (where each R1 independently represents an alkyl group having 1 to 6 carbon atoms, and n represents an integer of 1 to 50); (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule; and (E) a catalyst for hydrosilylation reaction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicone rubber composition for use in producing keypads, and to keypads. More specifically, the present invention relates to a silicone rubber composition that gives a cured product with excellent dynamic fatigue resistance and is therefore suitable as a keypad material, and to a keypad obtained by curing and molding the composition. [Background technology]

[0002] Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance, and other properties, and is therefore widely used in a variety of fields, including electrical equipment, automobiles, construction, medicine, and food. Examples of applications include keypads used as rubber contacts in remote controllers, typewriters, word processors, computer terminals, musical instruments, etc., construction gaskets, vibration-isolating rubber for audio equipment, connector seals, spark plug boots, and other automotive parts, packing for compact discs used in computers, and molds for bread and cakes. Currently, demand for silicone rubber is increasing, and the development of silicone rubber with excellent properties is desired.

[0003] Among these, keypad materials are widely used in keyboards for mobile phones, personal computers, etc., and a required characteristic of these keypad materials is that the change in load when the key is pressed is small. Normally, when a molded key is pressed repeatedly, the key load decreases as the number of key presses increases. The smaller the decrease in this peak load, the better the key characteristics are, and materials that exhibit such load characteristics are excellent as keypad materials.

[0004] Silicone rubber is widely used as a material for such keypads, and Patent Document 1 proposes a silicone rubber composition for keypads.

[0005] However, in recent years, as the shapes of the keys have become more complex, the strain on the keys themselves has become greater, and furthermore, as the devices used in recent years have become smaller, the shapes of the keys that are subject to greater strain on the material have increased. As a result, dynamic fatigue durability does not fully meet the strict requirements of recent years.

[0006] In response to this, Patent Document 2 proposes a silicone rubber composition suitable for keypads, which uses a phosphate ester of an alkyl group partially substituted with chlorine to give a cured product with excellent dynamic fatigue resistance (keystroke durability). However, this is not preferred because the keystroke durability is still insufficient and the manufacturing equipment corrodes. To solve this problem, Patent Document 3 proposes a silicone rubber composition suitable for keypads, which uses an organodisilazane having an alkenyl group in the molecule and a fatty acid ester and / or an ester of an aliphatic alcohol to obtain a cured product with excellent dynamic fatigue durability. Patent Document 4 proposes a silicone rubber composition suitable for keypads, which uses a vinyl-group-containing alkoxysilane instead of an organodisilazane having an alkenyl group in the molecule, which is cheaper and suppresses catalyst poisoning during addition vulcanization and yellowing of the cured product, to obtain a cured product with excellent dynamic fatigue durability. However, both products undergo a secondary vulcanization at 200°C for four hours, and primary vulcanization alone may result in reduced durability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-164111 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-275158 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-105782 [Patent Document 4] Japanese Patent Application Publication No. 2017-218487 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and aims to provide a silicone rubber composition suitable as a keypad material, since a cured product with excellent dynamic fatigue durability (keystroke durability) can be obtained even by primary vulcanization alone, and a keypad obtained by curing and molding said composition. [Means for solving the problem]

[0009] As a result of extensive research to solve the above problems, the inventors discovered that by adding a specific organosiloxane to a millable silicone rubber composition containing precipitated silica, a millable silicone rubber composition can be obtained that exhibits good dynamic fatigue durability in the cured product even after only primary vulcanization, which led to the creation of the present invention.

[0010] Therefore, the present invention provides 1. (A) 100 parts by mass of a linear organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule and a weight-average degree of polymerization of 1,000 to 100,000; (B) The specific surface area by BET method is 50m 2 / g or more precipitated silica: 10 to 100 parts by mass, (C) The following formula (1) [ka] (In the formula, R 1 are each independently an alkyl group having 1 to 6 carbon atoms, and n is a positive number of 1 to 50. 5 to 50 parts by mass of an organosiloxane represented by the formula: (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the molar ratio of hydrosilyl groups in component (D) to the combined amount of alkenyl groups in components (A) and (C) is 0.5 to 10; and (E) Hydrosilylation reaction catalyst: catalytic amount a millable type silicone rubber composition containing 2. As the (F) component, the following formula (3) R 2 Si(OR 3 )3(3) (In the formula, R 2 is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 4 carbon atoms. 2. The millable silicone rubber composition according to 1, which contains 0 to 10 parts by mass of a partial hydrolyzate of an organoalkoxysilane represented by the formula: 3. A cured product of the millable silicone rubber composition according to 1 or 2. 4. A keypad made of the cured product described in 3. to provide. [Effects of the Invention]

[0011] The present invention provides a millable silicone rubber composition that can be cured to provide excellent dynamic fatigue resistance even after primary vulcanization alone. Therefore, the cured product of the millable silicone rubber composition of the present invention is useful for applications such as keypads. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments. [1] Silicone rubber composition The millable silicone rubber composition of the present invention contains the following components (A) to (E): (A) A linear organopolysiloxane containing silicon-bonded alkenyl groups and having a weight-average degree of polymerization of 1,000 to 100,000. (B) The specific surface area by BET method is 50m 2 / g or more precipitated silica (C) Organosiloxane represented by formula (1) (D) Organohydrogenpolysiloxane (E) Hydrosilylation reaction catalyst

[0013] In the present invention, a mixture containing components (A), (B), and (C) described below, prior to the addition of components (D) and (E), is referred to as a (millable type) silicone rubber compound. A mixture of this silicone rubber compound with components (D) and (E) is referred to as a (millable type) silicone rubber composition.

[0014] [Component (A)] In the present invention, component (A) is a linear organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule and a weight-average degree of polymerization of 1,000 to 100,000, and is the base polymer (main component) of the composition of the present invention.

[0015] The organopolysiloxane used as component (A) has two or more silicon-bonded alkenyl groups per molecule, preferably 2 to 50, and especially 2 to 20, silicon-bonded alkenyl groups per molecule. These alkenyl groups may be bonded to silicon atoms at the molecular chain terminals, or to silicon atoms in the molecular chain (non-terminal), or both, but are preferably bonded to silicon atoms at both the molecular chain terminals (both terminals or one terminal) and in the molecular chain.

[0016] Examples of alkenyl groups bonded to silicon atoms in component (A) include those having 2 to 8 carbon atoms, preferably 2 to 4. Specific examples of such alkenyl groups include vinyl, allyl, propenyl, butenyl, and hexenyl groups, with vinyl and allyl groups being preferred, and vinyl groups being more preferred.

[0017] Furthermore, groups other than alkenyl groups bonded to silicon atoms are not particularly limited, and examples thereof include alkyl groups having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms; cycloalkyl groups having 5 to 10 carbon atoms, preferably 5 to 8 carbon atoms; aryl groups having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms; and aralkyl groups having 7 to 10 carbon atoms. Specific examples of these include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl and 2-phenylethyl. Of the above, methyl and phenyl groups are preferred, with methyl being more preferred.

[0018] The molecular structure of the organopolysiloxane of component (A) is linear, but may also be linear with a partially branched structure. Specifically, the repeating structure of the diorganosiloxane units constituting the main chain of the organopolysiloxane is preferably one consisting solely of repeating dimethylsiloxane units, or one in which a diorganosiloxane unit having a phenyl group, vinyl group, or other substituent, such as a diphenylsiloxane unit, methylphenylsiloxane unit, or methylvinylsiloxane unit, has been introduced as part of the dimethylpolysiloxane structure consisting of repeating dimethylsiloxane units constituting the main chain.

[0019] In addition, it is preferable that both molecular chain terminals of the organopolysiloxane (A) be blocked with triorganosiloxy groups such as trimethylsiloxy groups, dimethylphenylsiloxy groups, vinyldimethylsiloxy groups, divinylmethylsiloxy groups, and trivinylsiloxy groups.

[0020] Such organopolysiloxanes can be obtained, for example, by (co)hydrolyzing and condensing one or more organohalogenosilanes, or by ring-opening polymerization of cyclic polysiloxanes (such as siloxane trimers and tetramers) using an alkaline or acidic catalyst.

[0021] The weight-average degree of polymerization of the organopolysiloxane of component (A) is 1,000 to 100,000, preferably 2,000 to 100,000, more preferably 2,000 to 50,000, and even more preferably 3,000 to 20,000. It is characterized by a lack of self-flowability at room temperature (25°C), a so-called raw rubber-like (non-liquid) state. If the weight-average degree of polymerization is less than 1,000, problems such as roll adhesion can occur when the silicone rubber compound is formed, resulting in poor roll workability. If the weight-average degree of polymerization exceeds 100,000, it becomes difficult to incorporate precipitated silica. The weight-average degree of polymerization in this invention is a value calculated from the weight-average molecular weight in terms of polystyrene by gel permeation chromatography (GPC) analysis measured under the following conditions:

[0022] [Measurement conditions] Developing solvent: toluene Flow rate: 0.35mL / min Detector: Refractive index detector (RI) Column: TSK Guardcolumn SuperH-L TSKgel SuperH4000(6.0mmI.D.×15cm×1) TSKgel SuperH3000(6.0mmI.D.×15cm×1) TSKgel SuperH2000(6.0mmI.D.×15cm×2) (All manufactured by Tosoh Corporation) Column temperature: 40℃ Sample injection volume: 10 μL (0.5% by mass toluene solution)

[0023] Specific examples of component (A) include dimethylpolysiloxane terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-diphenylsiloxane copolymer terminally capped with dimethylvinylsiloxy groups, methylvinylpolysiloxane terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymer terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer terminally capped with trimethylsiloxy groups, methylvinylpolysiloxane terminally capped with trimethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer terminally capped with trimethylsiloxy groups, and dimethylpolysiloxane terminally capped with trivinylsiloxy groups. Among these, a dimethylsiloxane-methylvinylsiloxane copolymer in which both molecular chain terminals are blocked with dimethylvinylsiloxy groups is preferred.

[0024] The component (A) may be one type alone, or a mixture of two or more types with different molecular weights (degrees of polymerization) or molecular structures.

[0025] [(B) Component] (B) component has a specific surface area of ​​50m by the BET method. 2 / g or more. Component (B), precipitated silica, is also called wet silica, and is essential for imparting sufficient strength to silicone rubber. In the present invention, the specific surface area of ​​the precipitated silica of component (B) measured by the BET method is 50 m 2 / g or more, and preferably 100 to 400m 2 / g. This specific surface area is 50m 2 If it is less than 1 / g, the reinforcing effect of component (B) will be insufficient.

[0026] The precipitated silica of component (B) is preferably surface-treated with an organosilicon compound such as a silanol-containing organopolysiloxane, organopolysilazane, chlorosilane, or alkoxysilane. These precipitated silicas surface-treated with organosilicon compounds may be used alone or in combination of two or more.

[0027] As the component (B), commercially available products can be used, such as Nipsil LP and Nipsil KQ (both manufactured by Tosoh Silica Corporation).

[0028] The amount of precipitated silica (component (B)) blended is 10 to 100 parts by mass, preferably 15 to 80 parts by mass, and more preferably 20 to 70 parts by mass per 100 parts by mass of organopolysiloxane (component (A)). If the amount of component (B) blended is less than 10 parts by mass or exceeds 100 parts by mass, not only will the processability of the silicone rubber composition decrease, but the mechanical properties of the cured silicone rubber will also be insufficient.

[0029] [(C) component] Component (C) is an organosiloxane represented by the following formula (1), and is a component that improves the dynamic fatigue durability of the cured product even after primary vulcanization alone. [ka] (In the formula, R 1 are each independently an alkyl group having 1 to 6 carbon atoms, and n is a positive number of 1 to 50.

[0030] In the above formula (1), R 1 R each independently represents an alkyl group having 1 to 6 carbon atoms. 1 The alkyl group in R may be either linear or branched, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, and a hexyl group. 1 is preferably a methyl group or an ethyl group, more preferably a methyl group. Furthermore, n is a positive number of 1 to 50, and preferably a positive number of 5 to 40. If n is less than 1, dynamic fatigue durability is poor, and if it exceeds 50, the amount added increases, which is not economical.

[0031] Examples of component (C) include dimethylpolysiloxanes that have a dimethylvinylsiloxy group at one end of the molecular chain and a trimethoxysiloxy group at the other, and dimethylsiloxane-methylphenylsiloxane copolymers that have a dimethylvinylsiloxy group at one end of the molecular chain and a trimethoxysiloxy group at the other. The component (C) may use one type alone, or two or more types in combination.

[0032] The amount of organosiloxane (C) blended is 5 to 50 parts by mass, and preferably 5 to 30 parts by mass, per 100 parts by mass of organopolysiloxane (A). If the amount of component (C) blended is less than 5 parts by mass, good dynamic fatigue durability cannot be obtained, while if it exceeds 50 parts by mass, the plasticity of the resulting silicone rubber composition will be too low and it is also economically undesirable.

[0033] [(D) component] Component (D) is an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule. The organohydrogenpolysiloxane may have a linear, cyclic, branched, or three-dimensional network structure, so long as it has two or more, preferably three or more, more preferably 3 to 200, and even more preferably 4 to 100 hydrosilyl groups per molecule. Organohydrogenpolysiloxanes known as crosslinkers for addition reaction curable silicone rubber compositions can be used, such as organohydrogenpolysiloxanes represented by the following formula (2): R 4 a H b SiO (4-a-b) / 2 (2)

[0034] In the above formula (2), R 4Each is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and preferably having no aliphatic unsaturated bond. Specific examples thereof include alkyl groups such as methyl group, ethyl group, and propyl group; cycloalkyl groups such as cyclohexyl group; aryl groups such as phenyl group and tolyl group; aralkyl groups such as benzyl group, 2-phenyl ethyl group, and 2-phenyl propyl group; 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-trifluoropropyl group and the like. Among these, an alkyl group having 1 to 3 carbon atoms and a phenyl group are preferable, and a methyl group, an ethyl group, and a phenyl group are more preferable.

[0035] In the above formula (2), a is a positive number satisfying 0 < a < 3, preferably 0.5 ≤ a ≤ 2.2, and more preferably 1.0 ≤ a ≤ 2.0. Also, in the above formula (2), b is a number satisfying 0 < b ≤ 3, preferably 0.002 ≤ b ≤ 1.1, and more preferably 0.005 ≤ b ≤ 1. Further, a + b is a positive number satisfying 0 < a + b ≤ 3, preferably 0.5 ≤ a + b ≤ 3, and more preferably 1.002 ≤ a + b ≤ 2.7.

[0036] The organohydrogenpolysiloxane of component (D) has two or more, preferably three or more hydrosilyl groups in one molecule, and these may be at the molecular chain ends (one end or both ends), in the middle of the molecular chain, or both.

[0037] The weight average degree of polymerization of the organohydrogenpolysiloxane of component (D) is preferably 1 to 200, more preferably 1 to 100, and still more preferably 1 to 50. Further, as this organohydrogenpolysiloxane, the viscosity at 25°C is preferably 0.5 to 10,000 mPa·s, particularly 1 to 300 mPa·s. In the present invention, the viscosity refers to the measured value by the rotational viscometer described in JIS K7117-1:1999.

[0038] Specific examples of such organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(hydrogendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, dimethylpolysiloxane capped at both ends with dimethylhydrogensiloxy groups, dimethylsiloxane capped at both ends with dimethylhydrogensiloxy groups, methylhydrogen ... Methylsiloxane-methylhydrogensiloxane copolymer, methylhydrogensiloxane-diphenylsiloxane copolymer endblocked with trimethylsiloxy groups at both ends, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer endblocked with trimethylsiloxy groups at both ends, methylhydrogensiloxane-methylphenylsiloxane-dimethylsiloxane copolymer endblocked with trimethylsiloxy groups at both ends, methylhydrogensiloxane-dimethylsiloxane-diphenylsiloxane copolymer endblocked with dimethylhydrogensiloxy groups at both ends, methylhydrogensiloxane-dimethylsiloxane-methylphenylsiloxane copolymer endblocked with dimethylhydrogensiloxy groups at both ends, (CH3)2HSiO 1 / 2 Units and (CH3)3SiO 1 / 2 Units and SiO 4 / 2 A copolymer consisting of (CH3)2HSiO units 1 / 2 Units and SiO 4 / 2 A copolymer consisting of (CH3)2HSiO units 1 / 2 Units and SiO 4 / 2 Units and (C6H5)3SiO 1 / 2 and copolymers consisting of the above-exemplified compounds in which some or all of the methyl groups have been substituted with other alkyl groups, phenyl groups, or the like.

[0039] The organohydrogenpolysiloxane of component (D) may use either a single compound, or a combination of two or more different compounds.

[0040] The amount of organohydrogenpolysiloxane blended is such that the molar ratio of the total number of hydrosilyl groups in component (D) to the total number of alkenyl groups in components (A) and (C) is in the range of 0.5 to 10, preferably 0.7 to 5. If the molar ratio of hydrosilyl groups in component (D) to the total number of alkenyl groups in components (A) and (C) is less than 0.5, crosslinking will be insufficient, resulting in insufficient mechanical strength. If this molar ratio exceeds 10, the physical properties after curing will be impaired, particularly heat resistance and compression set.

[0041] [(E) component] Component (E) is a hydrosilylation catalyst. Component (E) is a catalyst that causes a hydrosilylation addition reaction between the alkenyl groups in components (A) and (C) and the hydrosilyl groups of the organohydrogenpolysiloxane in component (D). Examples of hydrosilylation catalysts include platinum group metal catalysts, such as simple platinum group metals and their compounds. These catalysts can be any of the conventional catalysts known for use in addition reaction-curing silicone rubber compositions. Specific examples include particulate platinum metal adsorbed on a carrier such as silica, alumina, or silica gel; platinic chloride, chloroplatinic acid, or a reaction product of chloroplatinic acid with a monohydric alcohol; a complex of chloroplatinic acid with an olefin; a complex of chloroplatinic acid with a vinyl group-containing (poly)siloxane; a complex of chloroplatinic acid with a phosphite ester; a palladium catalyst; and a rhodium catalyst. Of these, a complex of chloroplatinic acid with a vinyl group-containing (poly)siloxane is preferred.

[0042] The hydrosilylation reaction catalyst of component (E) may use either a single compound, or a combination of two or more different compounds.

[0043] The catalyst of component (E) may be added in any amount sufficient to promote the hydrosilylation reaction, and is typically used in an amount of 1 ppm by mass to 1% by mass, calculated as the platinum group metal amount relative to component (A), with 10 to 1,000 ppm by mass being preferred. Addition of 1 ppm by mass or more sufficiently promotes the addition reaction, resulting in sufficient curing. On the other hand, addition of 1% by mass or less provides sufficient reactivity and is not uneconomical.

[0044] [Component (F)] The composition of the present invention may contain, as component (F), a partial hydrolyzate of an organoalkoxysilane represented by the following formula (3): By using this component (F), it is possible to suppress the decrease in hardness of the silicone rubber composition over time. R 2 Si(OR 3 )3(3)

[0045] In the formula, R 2 is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 4 carbon atoms. R 2 The monovalent hydrocarbon group may be linear, branched, or cyclic and has 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and more preferably 1 to 6 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; alkenyl groups such as vinyl, allyl, propenyl, butenyl, and hexenyl; cycloalkenyl groups such as cyclohexenyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl, 2-phenylethyl, and β-phenylpropyl. R 3 The alkyl group may be either straight-chain or branched, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and an isobutyl group.

[0046] Specific examples of the organoalkoxysilane include trimethoxy(methyl)silane, trimethoxy(ethyl)silane, trimethoxy(propyl)silane, trimethoxy(butyl)silane, trimethoxy(hexyl)silane, triethoxy(methyl)silane, tripropoxy(methyl)silane, and tributoxy(methyl)silane. Of these, trimethoxy(methyl)silane, trimethoxy(ethyl)silane, and triethoxy(methyl)silane are preferred. Partial hydrolysates of these organoalkoxysilanes are used as component (F). Note that, since component (F) is a partial hydrolysate, the above R 2 Monovalent hydrocarbon groups derived from the above R 3 In addition to the alkoxy groups derived from the alkyl groups, some hydroxy groups (hydroxysilyl groups) are also present.

[0047] The kinematic viscosity of component (F) is not particularly limited, but is preferably 1 to 100 mm 2 / s is preferable, 1 to 50 mm 2 / s is more preferable, 1 to 30 mm 2 The kinematic viscosity is a value measured at 25°C using a Cannon-Fiske viscometer according to the method described in JIS Z 8803:2011.

[0048] The amount of the organoalkoxysilane partial hydrolyzate (F) added is preferably in the range of 0 to 20 parts by mass per 100 parts by mass of the above-mentioned (A), and when using component (F), it is more preferably 0.1 to 10 parts by mass, and even more preferably 1 to 10 parts by mass. By adding component (F), it is possible to suppress the decrease in hardness of the silicone rubber composition over time, but if the amount added exceeds 20 parts by mass, the processability of the resulting silicone rubber composition may deteriorate.

[0049] [Other ingredients] In addition to the above components (A) to (E) and the optional component (F), the millable silicone rubber composition of the present invention may optionally contain, as needed, fillers such as crushed quartz, crystalline silica, diatomaceous earth, calcium carbonate, and fumed silica, colorants, tear strength improvers, acid acceptors, thermal conductivity improvers such as alumina and boron nitride, mold release agents, various alkoxysilanes as dispersants for fillers, particularly phenyl-containing alkoxysilanes and their hydrolysates, diphenylsilanediol, carbon functional silane, and other fillers and additives known in thermosetting silicone rubber compositions, such as carbon functional silanes, within the scope of the invention.

[0050] Fumed silica has a specific surface area of ​​50 to 400 m2 by the BET method. 2 / g is preferred. As such fumed silica, commercially available products can be used, such as the Aerosil series (manufactured by Nippon Aerosil Co., Ltd.) including Aerosil 130, Aerosil 200, Aerosil 300, Aerosil R-812, Aerosil R-972, and Aerosil R-974, and Cabosil MS-5 and MS-7 (manufactured by Cabot Corporation), Reolosil QS-102, 103, MT-10, Reolosil DM-20S, and Reolosil DM-30S (manufactured by Tokuyama Corporation), and other surface-untreated or surface-hydrophobically treated (i.e., hydrophilic or hydrophobic) fumed silica. These may be used alone or in combination of two or more. When fumed silica is added, the amount added is preferably 1 to 20 parts by mass per 100 parts by mass of component (A).

[0051] In addition, the millable silicone rubber composition of the present invention may contain an organopolysiloxane that has two or more alkenyl groups per molecule, is liquid at 25°C, and has a weight-average degree of polymerization of less than 1,000, for the purpose of adjusting the viscosity of the composition and rubber properties.

[0052] Specific examples of the alkenyl group and non-alkenyl group in the liquid organopolysiloxane include the same groups as those exemplified for component (A).

[0053] The weight average degree of polymerization of the liquid organopolysiloxane is preferably 100 or more and less than 1,000, and more preferably 100-800. The liquid organopolysiloxane preferably has a viscosity at 25°C of 10 to 120,000 mPa·s, more preferably 100 to 100,000 mPa·s.

[0054] The amount of the liquid organopolysiloxane blended is preferably 0 to 20 parts by mass, and when blended, more preferably 1 to 20 parts by mass, per 100 parts by mass of component (A). These liquid organopolysiloxanes can be used alone or in combination of two or more.

[0055] In addition to the catalyst of component (E), an addition reaction inhibitor may be used in the present invention to adjust the curing rate depending on the purpose of the present invention. Specific examples include acetylene alcohol-based inhibitors such as 1-ethynyl-1-cyclohexanol and 2-methyl-3-butyn-2-ol, and vinyl siloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The addition reaction inhibitors may be used alone or in combination of two or more.

[0056] [Method of producing the composition] The method for producing the millable silicone rubber composition of the present invention is not particularly limited, but it can be obtained by mixing the components that make up the composition in a known mixer such as a kneader, Banbury mixer, twin-roll mill, etc. In this case, it is preferable to mix components (A), (B), (C), and optionally component (F) to obtain a mixture, and then add components (D) and (E) to the mixture.

[0057] When the composition containing the above components (A) to (F) further contains other components, it is preferable to first mix the components (A), (B), and (C) with the other components to obtain a mixture, and then add the components (D) and (E) to the mixture.

[0058] [2] Cured product and keypad The millable silicone rubber composition of the present invention is used for keypads. In the present invention, the silicone rubber composition is molded simultaneously with heat curing to obtain a molded keypad body made of a rubber-like elastic body (cured silicone rubber). [Curing conditions] The millable silicone rubber composition of the present invention can be cured by a known curing method under known curing conditions. Specifically, the composition can be cured by heating at a temperature of typically 25 to 200°C, preferably 80 to 160°C. The heating time may be about 0.5 minutes to 5 hours, and particularly about 1 minute to 3 hours. The millable silicone rubber composition of the present invention may be cured under pressure. [Example]

[0059] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, the viscosity is a value measured at 25° C. using a rotational viscometer according to JIS K 7117-1:1999. The kinematic viscosity is a value measured at 25°C using a Cannon-Fiske viscometer according to the method described in JIS Z 8803:2011. The weight-average degree of polymerization was determined from the weight-average molecular weight in terms of polystyrene by gel permeation chromatography (GPC) analysis measured under the following conditions. [Measurement conditions] Measuring device: Tosoh Corporation HLC-8420GPC Developing solvent: toluene Flow rate: 0.35mL / min Detector: Refractive index detector (RI) Column: TSK Guardcolumn SuperH-L TSKgel SuperH4000(6.0mmI.D.×15cm×1) TSKgel SuperH3000(6.0mmI.D.×15cm×1) TSKgel SuperH2000(6.0mmI.D.×15cm×2) (All manufactured by Tosoh Corporation) Column temperature: 40℃ Sample injection volume: 10 μL (0.5% by mass toluene solution)

[0060] The physical property measurement method and dynamic fatigue test method are shown below. (1) Physical property measurement methods (hardness, tensile strength, elongation at break) The silicone rubber composition was cured, and the hardness (durometer A), tensile strength, and elongation at break were measured in accordance with JIS K6249:2003.

[0061] (2) Dynamic fatigue durability test method The dynamic fatigue durability was measured by the following method. [100% extension fatigue test] Using the test sheets obtained in the Examples and Comparative Examples, test specimens were punched out with a No. 3 dumbbell, and marks were made so that the distance between the marks was 20 mm. The test specimens were set in a De Mattia tester so that the distance between the marks was 20 mm to 40 mm (0 to 100% elongation), and were repeatedly stretched at a rate of 300 times per minute. The number of times until the test specimen broke was measured.

[0062] [Ingredients] The following components were used as component (A): (A): A crude rubber-like dimethylsiloxane-methylvinylsiloxane copolymer with a weight-average degree of polymerization of 8,000, end-blocked with dimethylvinylsiloxy groups and containing 10 methylvinylsiloxane units.

[0063] The following components were used as component (B): (B): Specific surface area by BET method is 210m2 / g precipitated silica (trade name: Nipsil LP, manufactured by Tosoh Silica Corporation)

[0064] The following components were used as component (C): [ka] (C-1): R in the above formula (1) 1 : Methyl group, n: 30 organosiloxane (C-2): R in the above formula (1) 1 : methyl group, n: 9 organosiloxane (C-3): R in the above formula (1) 1 : methyl group, n: 6 organosiloxane (Comparative to C-4): Vinyltrimethoxysilane (for comparison) (C-5 ratio): 7-octenyltrimethoxysilane (for comparison) (C-6 ratio): Organosiloxane represented by the following formula (4) (for comparative examples) [ka]

[0065] The following components were used as component (D): (D): Methylhydrogen-dimethylpolysiloxane having hydrosilyl groups in the side chains (both molecular chain terminals are blocked with trimethylsiloxy groups, weight average degree of polymerization is 38, in the formula (2) representing the (D) component, a = 1.55, b = 0.5, R 4 =CH3, number of hydrosilyl groups: 20, viscosity: 17 mPa s)

[0066] The following components were used as component (E): (E): Platinum catalyst (a dimethylpolysiloxane solution containing 1% by mass of chloroplatinic acid / 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex as platinum atom content)

[0067] The following components were used as component (F): Partial hydrolysis product of trimethoxy(methyl)silane (trade name: KC-89S, manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity (25°C): 5 mm 2 / s)

[0068] The following components were used as optional components other than the components (A) to (F). Addition reaction inhibitor: 1-ethynyl-1-cyclohexanol (ethynylcyclohexanol) Vinyl-containing liquid organopolysiloxane: A liquid dimethylsiloxane-methylvinylsiloxane copolymer with a weight-average degree of polymerization of 500, containing four methylvinylsiloxane units and terminated at both ends with trimethylsiloxy groups. Filler: BET specific surface area of ​​200m 2 / g of fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.)

[0069] [Example 1] 100 parts by mass of component (A), 45 parts by mass of component (B), and 25.2 parts by mass of component (C-1) were added and mixed in a kneader at 170°C for 2 hours to prepare base compound (1). The base compound (1) was mixed with 2.00 parts by mass of component (D) (1.25 moles of hydrosilyl groups per mole of alkenyl groups in base compound (1)), 0.07 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.08 parts by mass of component (E) using a twin roll mill to obtain a silicone rubber composition. The obtained silicone rubber composition was subjected to a pressure of 120°C and 70 kgf / cm 2 The test sheets were then measured for hardness (Durometer A), tensile strength, elongation at break, and 100% elongation fatigue. The results are shown in Table 1.

[0070] [Comparative Examples 1 and 2] A silicone rubber composition was prepared in the same manner as in Example 1, except for the formulation shown in Table 1. Test sheets were made from the resulting silicone rubber composition, and various physical properties were evaluated. The results are shown in Table 1.

[0071] [Examples 2 to 6, Comparative Examples 3 and 4] A silicone rubber composition was prepared in the same manner as in Example 1, except for the formulation shown in Table 2. Test sheets were made from the resulting silicone rubber composition, and various physical properties were evaluated. The results are shown in Table 2.

[0072] [Example 7] Component (A): 100 parts by mass, component (B): 32 parts by mass, specific surface area by BET method: 200 m 2 8 parts by mass of fumed silica (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a molecular weight of 1 / g, 10.0 parts by mass of component (C-1), and 10 parts by mass of a liquid dimethylsiloxane-methylvinylsiloxane copolymer having four methylvinylsiloxane units and a weight-average degree of polymerization of 500, both molecular chain terminals of which are blocked with trimethylsiloxy groups, were added, and the mixture was mixed in a kneader at 170°C for 2 hours to prepare base compound (11). The base compound (11) was mixed with 1.68 parts by mass of component (D) (amount of hydrosilyl groups per mole of alkenyl groups in base compound (11): 1.80 moles), 0.06 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.08 parts by mass of component (E) using a twin roll mill to obtain a silicone rubber composition. The obtained silicone rubber composition was subjected to a pressure of 120°C and 70 kgf / cm 2 The test sheets were then measured for hardness (Durometer A), tensile strength, elongation at break, and 100% elongation fatigue. The results are shown in Table 3.

[0073] Separately, the obtained base compound (11) was left to stand at 23°C for 2 months, and then 1.68 parts by mass of component (D), 0.06 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.08 parts by mass of component (E) were mixed using a twin roll mill to obtain a silicone rubber composition. The obtained silicone rubber composition was subjected to a pressure of 120°C and 70 kgf / cm 2The test sheets were then measured for hardness (Durometer A), tensile strength, elongation at break, and 100% elongation fatigue. The results are shown in Table 3.

[0074] [Examples 8 and 9] A silicone rubber composition was prepared in the same manner as in Example 7, except for the formulation shown in Table 3. Test sheets were made from the resulting silicone rubber composition and various physical properties were evaluated. The results are shown in Table 3.

[0075] Comparative Example 5 A silicone rubber composition was prepared in the same manner as in Example 7, except for the formulation shown in Table 3. Test sheets were made from the resulting silicone rubber composition and various physical properties were evaluated. The results are shown in Table 3.

[0076] [Table 1]

[0077] [Table 2]

[0078] [Table 3]

[0079] Table 1 shows the results of the physical property evaluation of Example 1 and Comparative Examples 1 and 2. The cured product obtained in Example 1 exhibited good elongation fatigue. Unlike Example 1, no cured product was obtained in Comparative Example 1, which contained the comparative component (C-4), and Comparative Example 2, which contained the comparative component (C-5), exhibited poor elongation fatigue.

[0080] Table 2 shows the results of physical property evaluation for Examples 2 to 6 and Comparative Examples 3 and 4. Examples 2 to 4, which contained the component (C-1), showed good elongation fatigue. Examples 5 and 6, which contained the component (C-2) or the component (C-3), showed good elongation fatigue. On the other hand, Comparative Examples 3 and 4, which contained the comparative component (C-6), showed low hardness and poor elongation fatigue.

[0081] Table 3 shows the results of evaluating the physical properties of Examples 7 to 9 and Comparative Example 5. Example 7 showed good extension fatigue, but after two months, the hardness decreased by 3 points. Examples 8 and 9, which contained the (F) component, showed good extension fatigue and inhibited the decrease in hardness after two months. On the other hand, Comparative Example 5, which contained the (C-4) component, did not produce a cured product.

Claims

1. (A) 100 parts by mass of a linear organopolysiloxane having two or more silicon-bonded alkenyl groups per molecule and a weight-average degree of polymerization of 1,000 to 100,000; (B) A specific surface area measured by the BET method is 50 m 2 / g or more precipitated silica: 10 to 100 parts by mass, (C) Formula (1) below 【Chemistry 1】 (In the formula, R 1 are each independently an alkyl group having 1 to 6 carbon atoms, and n is a positive number from 1 to 50. Organosiloxane represented by the formula: 5 to 50 parts by mass, (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: in an amount such that the molar ratio of hydrosilyl groups in component (D) to the combined amount of alkenyl groups in components (A) and (C) is 0.5 to 10; and (E) Hydrosilylation reaction catalyst: catalytic amount A millable type silicone rubber composition comprising:

2. The component (F) is a compound represented by the following formula (3): R 2 Si(OR 3 ) 3 (3) (In the formula, R 2 is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 3 are each independently an alkyl group having 1 to 4 carbon atoms.

2. The millable silicone rubber composition according to claim 1, which contains 0 to 10 parts by mass of a partial hydrolyzate of an organoalkoxysilane represented by the formula:

3. A cured product of the millable silicone rubber composition of claim 1 or 2.

4. A keypad comprising the cured product according to claim 3.

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