Millable type silicone rubber composition and cured product of the same

Abstract

To provide a millable type silicone rubber composition which becomes a silicone rubber cured product having slight compression set even only by primary vulcanization.SOLUTION: A millable type silicone rubber composition contains: (A) linear organopolysiloxane having an alkenyl group bonded to two or more silicon atoms in one molecule and a weight average degree of polymerization of 1,000-100,000; (B) precipitated silica having a specific surface area of 50 m2 / g or more by BED method; (C) trialkoxysilane having an alkenyl group represented by the following composition formula (1): (R1O)3Si-(CH2)n-CH=CH2 (1) (where R1 independently represents a 1-6C alkyl group, and n represents an integral number of 1-12); (D) organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule of an amount in which a mole ratio of the hydrosilyl groups in the (D) component to the total amount of the alkenyl groups in the (A) component and the (C) component is 0.5-10; and (E) a hydrosilylation reaction catalyst of a catalyst 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] The silicone rubber composition may be cured under heat treatment (primary vulcanization) conditions of 40 to 230° C. for 3 seconds to 160 minutes or so. Furthermore, in order to reduce compression set, secondary vulcanization (post cure) is performed at 40 to 230° C. for 10 minutes to 24 hours or so.

[0003] In recent years, there has been a demand for reducing electricity consumption in order to achieve carbon neutrality. However, there is a problem in that the compression set cannot be sufficiently reduced unless post-vulcanization is performed. In addition, the secondary vulcanization has the effect of removing low molecular weight siloxanes, which can cause contact failures, from the cured product.

[0004] Patent Document 1 describes that silicone rubber cured products containing reinforcing fillers that have been surface-treated with benzotriazole derivatives have low compression set, and that the deterioration of vulcanization properties can also be suppressed, but none of these results have reached a level that can withstand practical use.

[0005] Patent Document 2 describes that the use of a sulfur-containing compound makes it possible to obtain a silicone rubber cured product with excellent compression set properties even with only primary vulcanization. However, the use of a sulfur-containing compound can cause addition cure inhibition, which can deteriorate the vulcanization properties. The above patent document also states that wet silica is preferred as a reinforcing filler from the viewpoint of compression set characteristics.

[0006] Patent Document 3 describes the blending of a linear organopolysiloxane having silanol groups or alkoxy groups at both ends as a treatment agent for wet silica. However, because linear organopolysiloxane contains a large amount of low molecular weight siloxane components, problems such as contact failure may occur if secondary vulcanization is not performed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-165931 A [Patent Document 2] JP 2016-196591 A [Patent Document 3] JP 2005-146029 A Summary of the Invention [Problem to be solved by the invention]

[0008] Thus, there has been a demand for the development of a millable type silicone rubber composition that will give a silicone rubber cured product with small compression set even after only primary vulcanization.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a millable type silicone rubber composition which, even when subjected to only primary vulcanization, produces a cured silicone rubber product with small compression set. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides The following components (A) to (E): (A) 100 parts by mass of a linear 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 the BET method is 50 m 2 / g or more precipitated silica; 10 to 100 parts by mass, (C) The following composition formula (1): (R 1 O)3Si-(CH2) n -CH=CH2(1) (In the formula, R 1 are independently an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 12. 0.1 to 10 parts by mass of a trialkoxysilane having an alkenyl group 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) a hydrosilylation catalyst; a catalytic amount; The present invention provides a millable type silicone rubber composition comprising:

[0011] Such a millable type silicone rubber composition of the present invention can reduce the compression set of the cured product even when subjected to only primary vulcanization.

[0012] Furthermore, in order to solve the above problems, the present invention provides a cured product of the above millable type silicone rubber composition.

[0013] The millable silicone rubber composition of the present invention provides a cured silicone rubber with low compression set. Effect of the Invention

[0014] As described above, the present invention can provide a millable silicone rubber composition that uses precipitated silica and that can be cured into a silicone rubber with small compression set even with only primary vulcanization. Therefore, the cured product of the millable silicone rubber composition of the present invention is useful for gaskets such as O-rings and packings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Thus, there has been a demand for millable silicone rubber compositions that, even when subjected to only primary vulcanization, will produce cured silicone rubber products with small compression set.

[0016] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that by adding a specific alkenyl group-containing silane when using precipitated silica, a millable type silicone rubber composition can be obtained that can reduce the compression set of the cured product even when only the primary vulcanization is performed.

[0017] That is, the present invention provides the following components (A) to (E); (A) 100 parts by mass of a linear 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 the BET method is 50 m 2 / g or more precipitated silica; 10 to 100 parts by mass, (C) The following composition formula (1): (R 1 O)3Si-(CH2) n -CH=CH2(1) (In the formula, R 1 are independently an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 12. 0.1 to 10 parts by mass of a trialkoxysilane having an alkenyl group 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) a hydrosilylation catalyst; a catalytic amount; The millable type silicone rubber composition is characterized by comprising:

[0018] The present invention will be described in detail below, but the present invention is not limited thereto.

[0019] In the present invention, components (A), (B), and (C) described below are blended, and then components (D) and (E) are blended, but the mixture before components (D) and (E) are blended is called the (millable type) silicone rubber compound.The mixture obtained by blending components (D) and (E) with this silicone rubber compound is called the (millable type) silicone rubber composition.

[0020] [Component (A)] In the present invention, component (A) is an organopolysiloxane having a weight average degree of polymerization of 1,000 to 100,000 and containing two or more alkenyl groups bonded to silicon atoms in each molecule, and is the base polymer (main component) of the composition according to the present invention.

[0021] The organopolysiloxane as component (A) has two or more alkenyl groups bonded to silicon atoms per molecule, and preferably has 2 to 50, and particularly 2 to 20, alkenyl groups bonded to silicon atoms per molecule. 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 molecular chain), or both, but are preferably bonded to silicon atoms at the molecular chain terminals.

[0022] The alkenyl group bonded to the silicon atom in component (A) typically has, for example, 2 to 8 carbon atoms, and preferably 2 to 4. Examples of the alkenyl group include alkenyl groups such as a vinyl group, an allyl group, a propenyl group, a butenyl group, and a hexenyl group; and cycloalkenyl groups such as a cyclohexenyl group, with the vinyl group and the allyl group being preferred, and the vinyl group being particularly preferred.

[0023] Examples of groups other than the alkenyl group include an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms. Specific examples include alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, and an octyl group; cycloalkyl groups such as a cyclopentyl group and a cyclohexyl group; aryl groups such as a phenyl group and a tolyl group; and aralkyl groups such as a benzyl group and a 2-phenylethyl group. Of the above, a methyl group and a phenyl group are preferred, and a methyl group is particularly preferred.

[0024] The molecular structure of the organopolysiloxane of component (A) is preferably linear or partially branched. Specifically, the repeating structure of the diorganosiloxane unit constituting the main chain of the organopolysiloxane is preferably composed of only repeating dimethylsiloxane units, or the like in which diorganosiloxane units having phenyl groups, vinyl groups, or the like as substituents, such as diphenylsiloxane units, methylphenylsiloxane units, or methylvinylsiloxane units, are introduced as part of the dimethylpolysiloxane structure composed of repeating dimethylsiloxane units constituting the main chain.

[0025] In addition, it is preferable that both molecular chain terminals of the organopolysiloxane of component (A) are blocked with triorganosiloxy groups such as trimethylsiloxy groups, dimethylphenylsiloxy groups, vinyldimethylsiloxy groups, divinylmethylsiloxy groups, and trivinylsiloxy groups.

[0026] Such organopolysiloxanes can be obtained, for example, by (co)hydrolyzing and condensing one or more organohalogenosilanes, or by ring-opening polymerization of a cyclic polysiloxane (e.g., a siloxane trimer or tetramer) using an alkaline or acidic catalyst.

[0027] 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. The organopolysiloxane is characterized by being in a raw rubber state (non-liquid state) without self-flowability at room temperature (25°C). If the degree of polymerization is less than 1,000, problems such as roll adhesion will occur when the organopolysiloxane is made into a silicone rubber compound, and roll workability will deteriorate. If the degree of polymerization is more than 100,000, it will be difficult to incorporate precipitated silica. The degree of polymerization in the present invention is determined as the weight-average degree of polymerization from the weight-average molecular weight in terms of polystyrene by gel permeation chromatography (GPC) analysis measured 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 (toluene solution with a concentration of 0.5% by mass)

[0028] The component (A) may be a single type, or a mixture of two or more types differing in molecular weight (degree of polymerization) or molecular structure.

[0029] [(B) Component] The precipitated silica of component (B), also known as precipitated silica or wet silica, is essential for imparting sufficient strength to silicone rubber. It is particularly effective in improving compression set properties. In the present invention, the precipitated silica of component (B) has a specific surface area of ​​50 m2 or less as measured by the BET method. 2 / g or more, and preferably 100 to 400m2 / g. This specific surface area is 50m 2 If it is less than 1 / g, the reinforcing effect of component (B) will be insufficient.

[0030] The precipitated silica of component (B) is preferably surface-treated with an organosilicon compound such as silanol-containing organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, etc. The precipitated silica surface-treated with these organosilicon compounds may be used alone or in combination of two or more.

[0031] 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 the organopolysiloxane, component (A). If the amount of component (A) 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.

[0032] [(C) component] Component (C) is an alkenyl-containing silane represented by the following formula (1), which is a component for reducing compression set of the cured product even after only primary vulcanization. (R 1 O)3Si-(CH2) n -CH=CH2(1) In the above formula (1), R 1 independently represents an alkyl group having 1 to 6 carbon atoms. Specific examples include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, and cyclohexyl groups. Among these, methyl and ethyl groups are preferred, and methyl is more preferred. n is an integer of 1 to 12, and preferably an integer of 1 to 8. When n is 0, there is no compression set reducing effect, and when n is 13 or more, the amount of addition increases, which is not economical.

[0033] The component (C) may use either a single type alone, or a combination of two or more types.

[0034] Examples of the alkenyl-containing silane of the component (C) include allyltrimethoxysilane, 3-butenyltrimethoxysilane, 5-hexenyltrimethoxysilane, 7-octenyltrimethoxysilane, and 10-undecenyltrimethoxysilane.

[0035] The amount of the alkenyl-containing silane (C) is 0.1 to 10 parts by mass, and preferably 0.3 to 5 parts by mass, per 100 parts by mass of the organopolysiloxane (A). If the amount of component (C) is less than 0.1 part by mass, the effect of reducing compression set cannot be obtained, whereas if it exceeds 10 parts by mass, the plasticity of the obtained silicone rubber composition may become too low, which is also economically undesirable.

[0036] [(D) component] The (D) component is an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule. The organohydrogenpolysiloxane may have a linear, cyclic, branched, or three-dimensional network structure, as 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 in one molecule. Any organohydrogenpolysiloxane known as a crosslinking agent for addition reaction curing silicone rubber compositions can be used, and for example, an organohydrogenpolysiloxane represented by the following formula (2) can be used. R 2 a H b SiO (4-a-b) / 2 (2)

[0037] In the above formula (2), R 2Independently, 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-phenylethyl 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.

[0038] In the above formula (2), a satisfies 0 < a < 3, preferably 0.5 ≤ a ≤ 2.2, more preferably 1.0 ≤ a ≤ 2.0. Also, in the above formula (2), b satisfies 0 < b ≤ 3, preferably 0.002 ≤ b ≤ 1.1, more preferably 0.005 ≤ b ≤ 1. Further, it is a positive number satisfying 0 < a + b ≤ 3, preferably 1 ≤ a + b ≤ 3, more preferably 1.002 ≤ a + b ≤ 2.7.

[0039] The organohydrogenpolysiloxane of component (D) has 2 or more, preferably 3 or more hydrosilyl groups in one molecule, and these may be at the molecular chain end, 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. In the present invention, the viscosity refers to the measured value by the rotational viscometer described in JIS K7117-1:1999.

[0040] 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 with trimethylsiloxy groups at both ends, dimethylsiloxane-methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends, dimethylpolysiloxane capped with dimethylhydrogensiloxy groups at both ends, dimethylsiloxane-methylhydrogensiloxane copolymer ... Methylsiloxane-methylhydrogensiloxane copolymer, methylhydrogensiloxane-diphenylsiloxane copolymer with trimethylsiloxy groups at both ends, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer with trimethylsiloxy groups at both ends, methylhydrogensiloxane-methylphenylsiloxane-dimethylsiloxane copolymer with trimethylsiloxy groups at both ends, methylhydrogensiloxane-dimethylsiloxane-diphenylsiloxane copolymer with dimethylhydrogensiloxy groups at both ends, methylhydrogensiloxane-dimethylsiloxane-methylphenylsiloxane copolymer 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 these units, and compounds in which part or all of the methyl groups in the above exemplary compounds have been substituted with other alkyl groups, phenyl groups, or the like.

[0041] The organohydrogenpolysiloxane of the component (D) may use either a single compound, or a combination of two or more different compounds.

[0042] The amount of the organohydrogenpolysiloxane is such that the molar ratio of the hydrosilyl groups in the (D) component to the total amount of the alkenyl groups in the (A) component and the (C) component is in the range of 0.5 to 10, preferably 0.7 to 5. If the molar ratio of the hydrosilyl groups in the (D) component to the total amount of the alkenyl groups in the (A) component and the (C) component is less than 0.5, the crosslinking is insufficient and sufficient mechanical strength cannot be obtained. If the molar ratio exceeds 10, the physical properties after curing are deteriorated, particularly the heat resistance is deteriorated and the compression set is large.

[0043] [(E) component] The hydrosilylation catalyst of component (E) is a catalyst that causes a hydrosilylation addition reaction between the alkenyl group of component (A) and the hydrosilyl group of the organohydrogenpolysiloxane of component (D). Examples of the hydrosilylation catalyst include platinum group metal catalysts, including simple platinum group metals and their compounds, and those that have been known as catalysts for addition reaction curing silicone rubber compositions can be used. For example, 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 and a monohydric alcohol; a complex of chloroplatinic acid and an olefin; a complex of chloroplatinic acid and a vinyl group-containing (poly)siloxane; a complex of chloroplatinic acid and a phosphorous ester; a palladium catalyst; and a rhodium catalyst, among which a complex of chloroplatinic acid and a vinyl group-containing (poly)siloxane is preferred.

[0044] The hydrosilylation reaction catalyst of the component (E) may use either a single compound, or a combination of two or more different compounds.

[0045] The catalyst of component (E) may be added in any amount sufficient to promote the hydrosilylation reaction, and is usually used in an amount of 1 ppm by mass to 1% by mass calculated as the platinum group metal relative to component (A), preferably 10 to 1,000 ppm by mass. If the amount is 1 ppm by mass or more, the addition reaction is sufficiently promoted and curing is sufficient. On the other hand, if the amount is 1% by mass or less, sufficient reactivity is obtained and it is not uneconomical.

[0046] In addition to the above catalysts, an addition reaction inhibitor may be used according to the purpose of the present invention to adjust the curing rate. Specific examples include acetylene alcohol 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.

[0047] The addition reaction inhibitor may be used alone or in combination of two or more kinds.

[0048] [Other ingredients] In addition to the above components (A) to (E), the millable silicone rubber composition of the present invention may optionally contain, as necessary, 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, 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.

[0049] In addition, the millable silicone rubber composition of the present invention may contain an organopolysiloxane that is liquid at 25°C and has a degree of polymerization of less than 1,000, and has two or more alkenyl groups per molecule, for the purpose of adjusting the viscosity of the composition and the rubber properties.

[0050] The degree of polymerization of the liquid organopolysiloxane is preferably 100 or more and less than 1,000, and more preferably 100-800.

[0051] Examples of the alkenyl group and non-alkenyl group in the liquid organopolysiloxane include the same groups as those exemplified for component (A).

[0052] The liquid organopolysiloxane preferably has a viscosity at 25°C of 10 to 120,000 mPa·s, and more preferably 100 to 100,000 mPa·s.

[0053] The amount of the liquid organopolysiloxane added is preferably 0 to 20 parts by mass per 100 parts by mass of the component (A).

[0054] [Method of producing the composition] The millable silicone rubber composition of the present invention can be obtained by mixing the components constituting the composition with a known mixer such as a kneader, a Banbury mixer, a two-roll mill, etc. It is preferable to mix components (A), (B), and (C) to obtain a mixture, and then add components (E) and (D) to the mixture.

[0055] When the composition containing the above components (A) to (E) 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 (E) and (D) to the mixture.

[0056] [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 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. EXAMPLES

[0057] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0058] The hardness (Durometer A), tensile strength, and elongation at break of the cured products of the silicone rubber compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were measured according to JIS K 6249:2003. In addition, the compression set (150°C / 22 hours, 25% compression) was measured using a large test piece (disk-shaped with a diameter of 29.0±0.5 mm and a thickness of 12.5±0.5 mm) according to JIS K 6262:2013. The viscosity was measured using a rotational viscometer at 25°C as described in JIS K 7117-1:1999.

[0059] The following components were used as component (A): (A): A crude rubber-like dimethylsiloxane-methylvinylpolysiloxane copolymer with 10 methylvinylsiloxane units and a weight-average degree of polymerization of 8,000, both ends of which are capped with dimethylvinylsiloxy groups.

[0060] The following components were used as component (B): (B): Specific surface area by BET method is 210m 2 / g precipitated silica (trade name: Nipsil LP, manufactured by Tosoh Silica Corporation)

[0061] The following components were used as component (C): (C-1): Allyltrimethoxysilane (C-2): 7-octenyltrimethoxysilane (C-3): Vinyltrimethoxysilane (for comparison)

[0062] The following components were used as component (D): (D-1): Methylhydrogen-dimethylpolysiloxane having hydrosilyl groups in the side chains (both ends of the molecular chain are blocked with trimethylsiloxy groups, weight average degree of polymerization is 38, in the formula (2) showing the (D) component, a = 1.55, b = 0.5, R 2 =CH3, Number of hydrosilyl groups: 20, Viscosity: 17 mPa s) (D-2): 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane (for comparison)

[0063] The following components were used as component (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)

[0064] As an optional addition reaction inhibitor other than the components (A) to (E), the following components were used. 1-Ethynyl-1-cyclohexanol (Ethynylcyclohexanol)

[0065] [Example 1] 100 parts by mass of component (A), 35 parts by mass of component (B), and 0.33 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 0.68 parts by mass of the (D-1) component (the amount of hydrosilyl groups per mole of alkenyl groups in the base compound (1) being 1.17 moles), 0.06 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.07 parts by mass of the (E) component using a twin roll to obtain a silicone rubber composition. The obtained silicone rubber composition was subjected to a compressive stress test at 120°C and 70 kgf / cm 2 The test sheets were then subjected to measurements of hardness (Durometer A), tensile strength and elongation at break. The results are shown in Table 1. The obtained silicone rubber composition was subjected to a test at 120°C and 70 kgf / cm 2The test pieces were press cured for 15 minutes under the above conditions to prepare cured products for measuring compression set, and the compression set was measured. The results are shown in Table 1.

[0066] [Examples 2 to 4] A silicone rubber composition was prepared in the same manner as in Example 1 using the formulation shown in Table 1. Test sheets and cured products were made from the resulting silicone rubber composition, and various physical properties were evaluated. The results are shown in Table 1.

[0067] [Comparative Examples 1 to 4] A silicone rubber composition was prepared in the same manner as in Example 1 using the formulation shown in Table 2. Test sheets and cured products were made from the resulting silicone rubber composition, and various physical properties were evaluated. The results are shown in Table 2.

[0068] [Comparative Example 5] 100 parts by mass of component (A), 35 parts by mass of component (B-1), and 3.28 parts by mass of component (C-1) were added and mixed in a kneader at 170° C. for 2 hours to prepare base compound (2). The base compound (2) was mixed with 0.55 parts by mass of component (D-2) using a twin roll mill to obtain a silicone rubber composition. The obtained silicone rubber composition was subjected to a pressure test at 165°C and 70 kgf / cm 2 The test sheets were then subjected to measurements of hardness (Durometer A), tensile strength and elongation at break. The results are shown in Table 3. The obtained silicone rubber composition was subjected to a test at 165°C and 70 kgf / cm 2 The test pieces were press cured for 15 minutes under the above conditions to prepare cured products for measuring compression set, and the compression set was measured. The results are shown in Table 3.

[0069] [Table 1] In the table, "Si-H / alkenyl group" indicates the molar ratio of hydrosilyl groups in component (D-1) to the combined amount of alkenyl groups in components (A) and (C).

[0070] [Table 2] In the table, "Si-H / alkenyl group" indicates the molar ratio of hydrosilyl groups in component (D-1) to the combined amount of alkenyl groups in components (A) and (C).

[0071] [Table 3]

[0072] Table 1 shows the results of various physical property evaluations of Examples 1 to 4. All of the cured products obtained in Examples 1 to 4 exhibited low compression set rates. In particular, the higher the blend amount of component C (Example 2 (component (C-1)) and Example 4 (component (C-2))) and component D (Example 2 and Example 4 (component (D-1)))), the lower the compression set rate.

[0073] Table 2 shows the results of evaluation of various physical properties of Comparative Examples 1 to 4. In all of the examples, the (C) component (C-3) (vinyltrimethoxysilane) was blended, unlike in Examples 1 to 4, and as a result, no cured product was obtained (Comparative Example 3), and the compression set rate was higher than in the Examples (Comparative Examples 1, 2, and 4). In particular, the higher the blending amount of the (C-3) component, the less cured the product was obtained (Comparative Example 3), or the compression set rate increased (Comparative Example 4).

[0074] Table 3 is a table comparing the evaluation of various physical properties of Example 2 and Comparative Example 5. Comparative Example 5, in which component (C-1) was blended as component (C), component (D-2) (peroxide) was blended as component (D), and no hydrosilylation reaction catalyst (E) was added, showed a compression set rate similar to that of Example 2, but the tensile strength and elongation at break were lower than those of Example 2. This result shows that if addition curing does not occur, compression set is reduced, but other physical properties such as tensile strength and elongation at break are deteriorated.

[0075] In this way, the present invention can provide a millable silicone rubber composition that, by adding a specific alkenyl group-containing silane when using precipitated silica, can reduce the compression set of the cured product even when only the primary vulcanization is performed.

[0076] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. The following components (A) to (E): (A) 100 parts by mass of a linear 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 material with a specific surface area of ​​50 m2 measured by the BET method ２ / g or more precipitated silica; 10 to 100 parts by weight, (C) The following composition formula (1): (R １ O) ３ H. ２ ) ｎ -CH=CH ２ (1) (In the formula, R １ are independently an alkyl group having 1 to 6 carbon atoms, and n is an integer from 1 to 12. 0.1 to 10 parts by mass of a trialkoxysilane having an alkenyl group represented by the formula: (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) a hydrosilylation catalyst; a catalytic amount; A millable type silicone rubber composition comprising:

2. A cured product of the millable type silicone rubber composition according to claim 1.

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