Millable silicone rubber composition and its cured product

Abstract

To provide a millable type silicone rubber composition that becomes a silicone rubber cured product having small compression permanent strain only by primary vulcanization without deteriorating curability.SOLUTION: Provided is a millable type silicone rubber composition, which is one that contains (A) a raw rubber-like organopolysiloxane having an alkenyl group bonded to two or more silicon atoms in one molecule and having a weight average polymerization degree of 1,000 to 100,000; 100 pts.mass, (B) a reinforcing silica having a specific surface area of 50 m2 / g or more by BET method; 10 to 100 pts.mass, (C) a saturated aliphatic carboxylic acid; 0.1 to 5 pts.mass for 100 pts.mass of (A) component; and (D) a curing agent; an effective amount.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a millable silicone rubber composition and a cured product thereof. [Background technology]

[0002] Silicone rubber has excellent properties such as weather resistance, electrical properties, low compression set, heat resistance, and cold resistance.

[0003] Silicone rubber compositions can be molded and cured by conventional methods, and the molding method can be selected from injection molding, transfer molding, injection molding, compression molding, etc., depending on the purpose. Heat treatment (primary vulcanization) at 40 to 230°C for 3 seconds to 160 minutes can be used as the curing method. Furthermore, to reduce compression set, secondary vulcanization (post-cure) is performed at 40 to 230°C for 10 minutes to 24 hours.

[0004] In recent years, there has been a demand for reducing electricity consumption in order to achieve carbon neutrality. However, there is a problem that without post-vulcanization, it is not possible to obtain a product with a sufficiently small compression set.

[0005] Patent Document 1 describes that the inclusion of hydrous cerium oxide and hydrous zirconium oxide improves the heat resistance and compression set of silicone rubber. However, there is no specific description that good compression set properties can be obtained by primary vulcanization alone, and the above-mentioned problem remains unresolved.

[0006] Patent Document 2 describes that the use of sulfur-containing compounds allows for the production of silicone rubber cured products with excellent compression set properties through primary vulcanization alone. However, the use of sulfur-containing compounds can inhibit addition curing and deteriorate vulcanization properties.

[0007] Patent Document 3 describes that silicone rubber cured products containing reinforcing fillers that have been surface-treated with benzotriazole derivatives have low compression set, and also describes that the deterioration of vulcanization properties can be suppressed, but neither of these results has reached a level that is practical for use. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-031408 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-196591 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-165931 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to provide a millable type silicone rubber composition that will yield a silicone rubber cured product with small compression set after only primary vulcanization without impairing curability. [Means for solving the problem]

[0010] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that by adding a specific carboxylic acid, it is possible to obtain a millable silicone rubber composition that can reduce the compression set of the cured product. That is, the present invention provides the following millable silicone rubber composition and cured product thereof.

[0011] [1] (A) 100 parts by mass of a raw rubber-like organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each 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 of reinforcing silica; 10 to 100 parts by mass, (C) saturated aliphatic carboxylic acid; 0.1 to 5 parts by mass per 100 parts by mass of component (A); and (D) a curing agent; an effective amount A millable type silicone rubber composition comprising: [2] The millable silicone rubber composition according to [1], wherein component (D) is an addition reaction curing agent that combines an organohydrogenpolysiloxane and a hydrosilylation catalyst. [3] The millable silicone rubber composition according to [1], wherein component (D) is an organic peroxide curing agent. [4] A cured product of the millable silicone rubber composition according to any one of [1] to [3]. [Effects of the Invention]

[0012] The present invention provides a millable silicone rubber composition that can be cured into a silicone rubber product with small compression set after only primary vulcanization without compromising curability. Therefore, the cured product of the millable silicone rubber composition of the present invention is useful for applications such as gaskets, O-rings, and packings. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but the present invention is not limited thereto.

[0014] In this specification, the mixture of the (A), (B), and (C) components described below before the addition of the (D) component will be referred to as a (Millable type) silicone rubber compound, and the mixture of this silicone rubber compound with the (D) component will be referred to as a (Millable type) silicone rubber composition.

[0015] [Component (A)] In the present invention, component (A) is a crude rubber-like organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each 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.

[0016] The organopolysiloxane used as component (A) has two or more alkenyl groups per molecule, preferably 2 to 50, and especially 2 to 20. The alkenyl groups may be bonded to silicon atoms at the molecular chain terminals, or to silicon atoms in the middle of the molecular chain (non-terminal), or both, but are preferably bonded to silicon atoms at the molecular chain terminals.

[0017] The alkenyl group bonded to the silicon atom in component (A) typically has 2 to 8 carbon atoms, and preferably 2 to 4. Examples include alkenyl groups such as vinyl, allyl, propenyl, butenyl, and hexenyl; and cycloalkenyl groups such as cyclohexenyl; with vinyl and allyl groups being preferred, and vinyl being particularly preferred. Examples of groups other than alkenyl groups include alkyl groups having 1 to 10 carbon atoms, cycloalkyl groups having 5 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, and aralkyl groups having 7 to 10 carbon atoms. Specific examples 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 particularly preferred.

[0018] The molecular structure of the organopolysiloxane of component (A) is preferably linear or linear with a partially branched structure. Specifically, the diorganosiloxane units (R 1 2SiO 2 / 2 , R 1is the same as above, the same applies hereinafter) is preferably one in which the repeating structure is composed of only repeating dimethylsiloxane units, or one in which a diorganosiloxane unit having a phenyl group, vinyl group, or the like as a substituent, such as a diphenylsiloxane unit, methylphenylsiloxane unit, or methylvinylsiloxane unit, has been introduced as part of the dimethylpolysiloxane structure composed of repeating dimethylsiloxane units that constitute the main chain.

[0019] Both molecular chain terminals are preferably 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 degree of polymerization of the organopolysiloxane is 1,000 to 100,000, preferably 2,000 to 100,000, more preferably 2,000 to 50,000, and particularly preferably 3,000 to 20,000. It is characterized by a lack of self-flowability at room temperature (25°C), being a so-called raw rubber (non-liquid) state. If the degree of polymerization is less than 1,000, problems such as roll adhesion can occur when the silicone rubber compound is made, resulting in poor roll workability. The degree of polymerization is determined as the weight-average degree of polymerization from the weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC) analysis under the following conditions: [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)

[0022] The component (A) may be a single type, or a mixture of two or more types with different molecular weights (degrees of polymerization) or molecular structures.

[0023] In addition to the component (A), the millable silicone rubber composition of the present invention may contain an organopolysiloxane that is liquid at 25°C and contains two or more alkenyl groups per molecule, for the purpose of adjusting the viscosity of the composition and the physical properties of the rubber. The degree of polymerization of the liquid organopolysiloxane is preferably 100 or more and less than 1,000, and more preferably 100-800. Examples of the alkenyl groups and groups other than alkenyl groups in the liquid organopolysiloxane include the same groups as those exemplified for component (A). The organopolysiloxane preferably has a viscosity at 25°C of 10 to 120,000 mPa·s, and more preferably 100 to 100,000 mPa·s. In the present invention, the viscosity is a value measured by a rotational viscometer at 25° C. as described in JIS K7117-1:1999 (the same applies hereinafter). The amount of the liquid organopolysiloxane blended is preferably 0 to 20 parts by mass per 100 parts by mass of component (A).

[0024] [(B) Reinforcing Silica] The reinforcing silica of component (B) acts as a component that imparts excellent mechanical properties to the resulting silicone rubber composition. The reinforcing silica may be precipitated silica (wet silica) or fumed silica (dry silica), and has numerous silanol groups (SiOH) on its surface. In the present invention, the specific surface area of ​​the reinforcing 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.

[0025] The reinforcing silica of component (B) may be used in an untreated state, or may be surface-treated with an organosilicon compound such as a silanol-containing organopolysiloxane, organopolysilazane, chlorosilane, or alkoxysilane, as necessary. To reduce the amount of low-molecular-weight siloxane generated from the silicone rubber during or after curing, it is preferable to use an organosilicon compound such as an organopolysilazane, chlorosilane, or alkoxysilane. These reinforcing silicas may be used alone or in combination of two or more.

[0026] The amount of reinforcing silica (B) added 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 (A). If the amount added is outside this range, not only will the processability of the silicone rubber composition decrease, but the mechanical properties of the cured silicone rubber will also be insufficient.

[0027] [(C) component] Component (C) is a saturated aliphatic carboxylic acid, which can reduce the compression set of the cured product after primary vulcanization.

[0028] The saturated aliphatic carboxylic acid of component (C) preferably has 1 to 20 carbon atoms, and more preferably has 1 to 10 carbon atoms. Specific examples include formic acid, acetic acid, propionic acid, butyric acid, caproic acid, 2-ethylhexanoic acid, lauric acid, and myristic acid. Of these, acetic acid and 2-ethylhexanoic acid are preferred. These saturated aliphatic carboxylic acids may be used alone or in combination of two or more.

[0029] The amount of saturated aliphatic carboxylic acid (C) blended is 0.1 to 5 parts by mass, and preferably 0.3 to 3 parts by mass, per 100 parts by mass of organopolysiloxane (A).

[0030] [(D) component] The curing agent is not particularly limited as long as it can cure the silicone rubber compound, but examples thereof include the following (D-1) addition reaction curing agents and (D-2) organic peroxide curing agents.

[0031] (D-1) Addition reaction curing agent As the addition reaction curing agent (D-1), an organohydrogenpolysiloxane and a hydrosilylation catalyst are used in combination.

[0032] The organohydrogenpolysiloxane may have a linear, cyclic, branched, or three-dimensional network structure, as long as it contains two or more, preferably three or more, more preferably 3 to 200, and even more preferably about 4 to 100 hydrogen atoms bonded to silicon atoms per molecule (i.e., hydrosilyl groups). Organohydrogenpolysiloxanes known as crosslinkers for addition reaction curable silicone rubber compositions can be used, and for example, organohydrogenpolysiloxanes represented by the following average composition formula (1) can be used. R 1 a H b SiO (4-a-b) / 2 (1)

[0033] In the above average composition formula (1), R 1Independently, it is a monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and preferably having no aliphatic unsaturated bond. Specifically, alkyl groups such as methyl group, ethyl group, propyl group; cycloalkyl groups such as cyclohexyl group; aryl groups such as phenyl group, tolyl group; aralkyl groups such as benzyl group, 2-phenyl ethyl group, 2-phenylpropyl 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 can be mentioned.

[0034] In addition, a satisfies 0 < a < 3, preferably 0.5 ≤ a ≤ 2.2, more preferably 1.0 ≤ a ≤ 2.0. Also, b satisfies 0 < b ≤ 3, preferably 0.002 ≤ b ≤ 1.1, more preferably 0.005 ≤ b ≤ 1. Furthermore, it is a positive number satisfying 0 < a + b ≤ 3, preferably 1 ≤ a + b ≤ 3, more preferably 1.002 ≤ a + b ≤ 2.7.

[0035] The organohydrogenpolysiloxane has two or more, preferably three or more hydrosilyl groups in one molecule, and these may be at the molecular chain ends, in the middle of the molecular chain, or both. Also, as this organohydrogenpolysiloxane, the viscosity at 25°C is preferably 0.5 to 10,000 mPa·s, particularly 1 to 300 mPa·s.

[0036] 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.

[0037] The amount of the organohydrogenpolysiloxane blended is preferably 0.1 to 40 parts by mass per 100 parts by mass of the silicone rubber compound (total amount of components (A), (B), and (C)). Furthermore, the ratio of silicon-bonded hydrogen atoms (hydrosilyl groups) per aliphatic unsaturated bond (such as an alkenyl group or a diene group) in component (A) is preferably in the range of 0.5 to 10, and more preferably 0.7 to 5. A ratio of 0.5 or more ensures sufficient crosslinking and mechanical strength, while a ratio of 10 or less ensures that post-cure physical properties are not impaired, particularly without adverse effects such as poor heat resistance or large compression set.

[0038] The hydrosilylation catalyst is a catalyst that induces a hydrosilylation addition reaction between the alkenyl groups of component (A) and the silicon-bonded hydrogen atoms (hydrosilyl groups) of the organohydrogenpolysiloxane. Examples of hydrosilylation catalysts include platinum group metal catalysts, including platinum group metals and their compounds. These include catalysts that have been used in addition reaction-curing silicone rubber compositions. Examples include particulate platinum metal adsorbed on a carrier such as silica, alumina, or silica gel; platinum catalysts such as platinic chloride, chloroplatinic acid, and alcohol solutions of chloroplatinic acid hexahydrate; palladium catalysts; and rhodium catalysts. Platinum or platinum compounds (platinum catalysts) are preferred.

[0039] The catalyst may be added in any amount sufficient to promote the addition reaction, and is usually used in a range of 1 ppm by mass to 1% by mass, calculated as the amount of platinum group metal relative to the silicone rubber compound, with a range of 10 to 500 ppm by mass being preferred. If the amount added is 1 ppm by mass or more, the addition reaction is sufficiently promoted and sufficient curing is achieved, while if the amount added is 1% by mass or less, sufficient reactivity is maintained and it is not uneconomical.

[0040] In addition to the above catalysts, an addition reaction inhibitor may be used depending on the purpose of the present invention to adjust the curing rate. Specific examples include acetylene alcohol inhibitors such as ethynylcyclohexanol, and tetracyclomethylvinylpolysiloxane. The addition reaction inhibitors may be used alone or in combination of two or more.

[0041] (D-2) Organic peroxide curing agent (D-2) Examples of organic peroxide curing agents include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butyl peroxide, t-butyl perbenzoate, and 1,6-hexanediol-bis-t-butylperoxycarbonate.

[0042] The amount of organic peroxide curing agent added is preferably 0.1 to 10 parts by mass, and particularly preferably 0.2 to 5 parts by mass, per 100 parts by mass of the silicone rubber compound (total amount of components (A), (B), and (C)). If the amount is 0.1 part by mass or more, curing will not be insufficient, and if it is 10 parts by mass or less, the cured silicone rubber will not yellow due to decomposition residues of the organic peroxide curing agent.

[0043] In addition, component (A) can also be combined with components (D-1) and (D-2) within the above-mentioned blending amounts to form a co-vulcanization millable silicone rubber composition that combines addition reaction curing and organic peroxide curing.

[0044] [Other ingredients] In addition to the above components, 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, etc., 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 group-containing alkoxysilanes and their hydrolysates, diphenylsilanediol, carbon functional silane, and other fillers and additives known in thermosetting silicone rubber compositions.

[0045] [Method of producing the composition] The millable silicone rubber composition of the present invention can be obtained by mixing the components constituting the composition using a known mixer such as a kneader, Banbury mixer, or twin-roll mill. When a composition containing the aforementioned components (A) to (D) is used as the millable silicone rubber composition, it is preferable to first mix components (A) and (B) to obtain a mixture, then mix component (C) with the mixture, and then add the curing agent for component (D). When the composition containing components (A) to (D) further contains other components, it is preferable to mix components (A), (B), and (C) with the other components to obtain a mixture, and then add the curing agent for component (D) to the mixture. The millable silicone rubber composition of the present invention may be mixed under heating during preparation.

[0046] [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]

[0047] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these.

[0048] For the cured products of the silicone rubber compositions prepared in the following examples and comparative examples, hardness (Durometer A), tensile strength, and elongation at break were measured according to JIS K 6249:2003, and compression set (150°C / 22 hours, 25% compression) according to JIS K 6262. The viscosity was measured using a rotational viscometer at 25°C as described in JIS K7117-1:1999.

[0049] The following components were used as component (A): (A-1): A dimethylsiloxane-methylvinylpolysiloxane copolymer with a weight-average degree of polymerization of approximately 8,000, having 10 methylvinylsiloxane units and both ends capped with dimethylvinylsiloxane units.

[0050] The following components were used as component (B): (B-1): Specific surface area is 110m 2 / g of fumed silica (trade name: Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.) (B-2): Specific surface area is 200m 2 / g of fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.)

[0051] The following components were used as component (C): (C-1): 2-ethylhexanoic acid (C-2): Acetic acid (C-3): Ethyl acetate (for comparison)

[0052] The following components were used as component (D): (D-1-1): 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 above formula (1), a = 1.55, b = 0.5, R 1 =CH3, number of hydrosilyl groups: 20) (D-1-2): Platinum catalyst (a dimethylpolysiloxane solution containing 1% by mass of chloroplatinic acid / 1,3-divinyltetramethyldisiloxane complex as platinum atom content) (D-2): 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane

[0053] The following components were used as addition reaction inhibitors: Ethynylcyclohexanol

[0054] [Example 1] 100 parts by mass of component (A-1) as component (A) and 35 parts by mass of component (B-1) as component (B) were mixed in a kneader, and then 0.3 parts by mass of component (C-1) as component (C) was added and further mixed in the kneader. After this, the mixture was heat-treated at 170°C for 2 hours to prepare base compound (1).

[0055] A silicone rubber composition was obtained by mixing 100 parts by mass of the base compound (1) with 0.9 parts by mass of component (D-1-1) as a curing agent, 0.04 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.05 parts by mass of component (D-1-2) using a twin roll mill. The resulting composition was subjected to a temperature test at 120°C and a viscosity of 6.86 MN / m 2 The test sheet (1) (dimensions: 150 × 170 mm, thickness: 2.0 ± 0.2 mm) was prepared by press curing for 10 minutes under the above conditions, and its hardness (Durometer A), tensile strength, and elongation at break were measured. The results are shown in Table 1. The resulting composition was subjected to a test at 120°C and 6.86 MN / m 2 The test piece was press-cured for 15 minutes under the above conditions to prepare a cured product (1) for measuring compression set (dimensions: diameter 29.0±0.5 mm, thickness: 12.5±0.5 mm), and the compression set was measured. The results are shown in Table 1.

[0056] [Examples 2 and 3, Comparative Examples 1 and 2] A silicone rubber composition was prepared using the formulation shown in Table 1 in the same manner as in Example 1. Test sheets and cured products were prepared from the resulting compositions, and various physical properties were evaluated. The results are shown in Table 1.

[0057] [Example 4] 100 parts by mass of component (A-1) as component (A) and 40 parts by mass of component (B-1) as component (B) were mixed in a kneader, and then 0.3 parts by mass of component (C-2) as component (C) was added and further mixed in the kneader. After this, the mixture was heat-treated at 170°C for 2 hours to prepare base compound (6).

[0058] A silicone rubber composition was obtained by mixing 100 parts by mass of the base compound (6) with 0.4 parts by mass of the component (D-2) as the component (D). The resulting composition was subjected to a test at 165°C and 6.86 MN / m 2 The test sheet (6) (dimensions: 150 × 170 mm, thickness: 2.0 ± 0.2 mm) was prepared by press curing for 10 minutes under the above conditions, and its hardness (Durometer A), tensile strength, and elongation at break were measured. The results are shown in Table 2. The resulting composition was subjected to a test at 165°C and 6.86 MN / m 2 The test piece was press-cured for 15 minutes under the above conditions to prepare a cured product (6) for compression set measurement (dimensions: diameter 29.0±0.5 mm, thickness: 12.5±0.5 mm), and the compression set was measured. The results are shown in Table 2.

[0059] [Example 5, Comparative Examples 3 and 4] A silicone rubber composition was prepared using the formulation shown in Table 2 in the same manner as in Example 4. Test sheets and cured products were prepared from the resulting compositions, and various physical properties were evaluated. The results are shown in Table 2.

[0060] [Example 6] 100 parts by mass of component (A-1) as component (A), 40 parts by mass of component (B-2) as component (B), and 4 parts by mass of dimethylpolysiloxane as a surface treatment agent for component (B) having silanol groups at both ends, a weight-average degree of polymerization of 4, and a viscosity at 25°C of 15 mPa s were mixed in a kneader, followed by addition of 0.3 parts by mass of component (C-1) and mixing in the kneader. The mixture was then heat-treated at 170°C for 2 hours to prepare base compound (10).

[0061] A silicone rubber composition was obtained by mixing 100 parts by mass of the base compound (10), 0.9 parts by mass of the (D-1-1) component as the (D) component, 0.04 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.05 parts by mass of the (D-1-2) component with a twin roll. The resulting composition was subjected to a temperature test at 120°C and a viscosity of 6.86 MN / m 2 The test sheet (10) (dimensions: 150 × 170 mm, thickness: 2.0 ± 0.2 mm) was prepared by press curing for 10 minutes under the above conditions, and its hardness (Durometer A), tensile strength, and elongation at break were measured. The results are shown in Table 3. The resulting composition was subjected to a test at 120°C and 6.86 MN / m 2 The test piece was press-cured for 15 minutes under the above conditions to prepare a cured product (10) for compression set measurement (dimensions: diameter 29.0±0.5 mm, thickness: 12.5±0.5 mm), and the compression set was measured. The results are shown in Table 3.

[0062] Comparative Example 5 A test sheet (11) and a cured product (11) for measuring compression set were prepared in the same manner as in Example 6, except that component (C) was not added, and various physical properties were measured. The results are shown in Table 3.

[0063] Comparative Example 6 10 parts by mass of the benzotriazole derivative represented by the following chemical formula (1) and 100 parts by mass of component (B-2) were mixed at room temperature in a closed mechanical mixer under atmospheric pressure. After mixing, the mixture was dried to obtain a reinforcing filler surface-treated with the benzotriazole derivative. [ka]

[0064] A base compound was prepared in the same manner as in Example 1, except that 1.1 parts by mass of the reinforcing filler prepared above (benzotriazole derivative / platinum atom = 88 mol / mol) was added instead of component (C). Then, a test sheet (12) and a cured product (12) for measuring compression set were prepared, and various physical properties were measured. The results are shown in Table 4.

[0065] The curability of the silicone rubber compositions prepared in Example 1, Comparative Example 1, and Comparative Example 6 at 120°C was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). The values ​​in the table indicate the time (seconds) required for a 10% torque value of the maximum torque value obtained 6 minutes after the start of measurement at 120°C, where T10 is the value of the torque obtained 6 minutes after the start of measurement at 120°C. The T90 value indicates the time (seconds) required for a 90% torque value of the maximum torque value obtained 6 minutes after the start of measurement at 120°C. The smaller the T10 value, the shorter the time until curing begins. The smaller the T90-T10 value, the shorter the time from the start of curing to complete curing, indicating better curability of the composition. The results are shown in Table 4.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] [Table 4]

Claims

1. (A) 100 parts by mass of a crude rubber-like organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in each 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 of reinforcing silica; 10 to 100 parts by mass, (C) a saturated aliphatic carboxylic acid having 1 to 10 carbon atoms; 0.1 to 5 parts by mass per 100 parts by mass of the component (A); and (D) a curing agent; an effective amount A millable type silicone rubber composition comprising:

2. 2. The millable silicone rubber composition according to claim 1, wherein component (D) is an addition reaction curing agent that combines an organohydrogenpolysiloxane with a hydrosilylation catalyst.

3. 2. The millable silicone rubber composition according to claim 1, wherein component (D) is an organic peroxide curing agent.

4. A cured product of the millable silicone rubber composition according to any one of claims 1 to 3.

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