Addition-curable silicone rubber composition

Abstract

The present invention provides an addition-curable silicone rubber composition which is characterized by containing (A) a linear organopolysiloxane that has an average polymerization degree of 480 or more, while containing at least two alkenyl groups, each of which is bonded to a silicon atom, in each molecule, (B) an alkenyl group-containing silicone resin represented by formula (1), (C) a linear organohydrogen polysiloxane represented by formula (2), and (D) an addition reaction catalyst that is from 0.1 to 10 ppm (in terms of mass) of a platinum group metal relative to the total mass of the composition, said addition-curable silicone rubber composition being also characterized in that the mass ratio of the component (A) to the component (B), namely (A) / (B) is from 40 / 60 to 60 / 40. Consequently, the present invention provides an addition-curable silicone rubber composition which enables the achievement of a cured product that exhibits excellent releasability from a mold, while having high transparency.　(1): (R1 3SiO1 / 2)a(R1 2SiO2 / 2)b(R1SiO3 / 2)c(SiO4 / 2)d　

Description

[Technical Field]

[0001] The present invention relates to an addition-curable silicone rubber composition. [Background technology]

[0002] Silicone resins with high hardness and transparency have attracted attention in order to improve the weather resistance and optical waveguides of LED lights and various LCD monitor screens, and among these, addition-curing silicone rubber cured products have come to be adopted because they contain no silica, are highly transparent, do not lose elasticity even at low temperatures, and are relatively easy to mold by thermosetting (Patent Documents 1 to 6).

[0003] Generally, silicone rubber used as optical waveguides in LED lights and other devices is required to have a high hardness (JIS K 6253, durometer type A) of 65 or higher. The molding method for such silicone rubber involves first performing primary vulcanization using a mold, followed by secondary vulcanization using a high-temperature dryer (oven) to stabilize the physical properties and remove volatile components from the cured product. However, with high-hardness silicone rubber that does not contain reinforcing silica, there is a problem in that the cured product can be scratched or torn when removed from the mold after primary molding due to its hardness and low extensibility. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-335857 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-101056 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-174233 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-174234 [Patent Document 5] WO2016 / 098883 issue [Patent Document 6] WO2016 / 098884 issue Summary of the Invention [Problems to be Solved by the Invention]

[0005] The present invention has been made to improve the above circumstances, and an object thereof is to provide an addition-curable silicone rubber composition that is excellent in mold release properties and can give a cured product having high transparency. [Means for Solving the Problems]

[0006] In order to solve the above problems, the present invention provides an addition-curable silicone rubber composition comprising: (A) a linear organopolysiloxane having an average degree of polymerization of 480 or more and containing an alkenyl group bonded to at least two silicon atoms in one molecule; (B) an alkenyl group-containing silicone resin represented by the following formula (1) (R , 3 / 2 , , b , , 3 , 1 , 1 , , 1 / 2 , 4 / 2 , c , , 1 , 2 / 2 , a , , 2 , d , 3SiO 1 / 2 ) a (R 1 2SiO 2 / 2 ) b (R 1 SiO 3 / 2 ) c (SiO 4 / 2 ) d (1) (In formula (1), R 1 is independently a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms and an alkenyl group having 2 to 10 carbon atoms, has an average of 2.5 or more alkenyl groups in one molecule, 0 < a ≤ 0.7, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.2, 0 < d ≤ 0.7, provided that 0.8 ≤ a + d ≤ 1, and a + b + c + d = 1); (C) a linear organohydrogenpolysiloxane represented by the following formula (2) [Chemical Formula] (In formula (2), R 2 is independently an alkyl group having 1 to 10 carbon atoms, and R 3are independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, e is an integer of 8 or greater, f is an integer of 0 to 100, e / (e+f) is 40 mol % or greater, and the number of silicon-bonded hydrogen groups per molecule is 10 or greater), (D) Addition reaction catalyst: 0.1 to 10 ppm as platinum group metal (by mass) based on the total mass of the composition The present invention provides an addition-curable silicone rubber composition comprising the above components, wherein the mass ratio of component (A) to component (B) is (A) / (B) = 40 / 60 to 60 / 40, the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups in the composition (Si-H groups / total alkenyl groups) is 1.0 to 1.5, and in a vulcanization test using a torsional vibration cone die vulcanization tester (B-2 method) described in JIS K 6300-2:2001, the T90-T10 value is 160 seconds or longer, where T10 is the 10% cure time and T90 is the 90% cure time when measured at 150°C for 5 minutes.

[0007] The addition-curable silicone rubber composition of the present invention can provide a cured product that is easy to remove from a mold and has high transparency.

[0008] Furthermore, it is preferable that the amount of alkenyl groups in the component (A) is 0.00006 mol / g or less.

[0009] Such an addition-curable silicone rubber composition provides desirable elongation of the rubber after primary vulcanization.

[0010] The amount of alkenyl groups in the component (B) is preferably 0.0006 to 0.001 mol / g.

[0011] Such an addition-curable silicone rubber composition will provide a cured product with favorable hardness and elongation at break after primary vulcanization. [Effects of the Invention]

[0012] According to the present invention, an addition-curable silicone rubber composition can be obtained which has a low hardness (Durometer Type A) of 55 or less after primary vulcanization, an elongation at break of 300% or more, and a hardness of 65 or more after secondary vulcanization, which is easy to remove from a mold, and which gives a highly transparent cured product. DETAILED DESCRIPTION OF THE INVENTION

[0013] As mentioned above, there has been a need for the development of an addition-curable silicone rubber composition that can provide a cured product with excellent mold removability and high transparency.

[0014] As a result of extensive research conducted by the present inventors to achieve the above-mentioned object, they discovered that by using a relatively long-chain alkenyl-containing linear organopolysiloxane, a specific alkenyl group-containing silicone resin, and an organohydrogensiloxane having a specific structure in appropriate ratios to prepare a composition adjusted so that the difference between the 10% cure time and the 90% cure time in a vulcanization test is large, it is possible to obtain a silicone rubber composition that gives a cured product with a hardness of 55 or less and an elongation at break of 300% or more after primary vulcanization, and that can further increase the hardness to the desired hardness (for example, 65 or more) by secondary vulcanization, and that gives a highly transparent cured product. This discovery led to the completion of the present invention.

[0015] The above findings were obtained from an investigation of various materials and the finding that when the hardness (Durometer Type A) of the cured product after primary vulcanization is 55 or less and the elongation at break is 300% or more, it is easy to remove from the mold.

[0016] That is, the present invention provides an addition-curable silicone rubber composition, (A) a linear organopolysiloxane having an average degree of polymerization of 480 or more and containing at least two alkenyl groups bonded to silicon atoms in each molecule; (B) an alkenyl group-containing silicone resin represented by the following formula (1): (R 1 3SiO 1 / 2 ) a (R 12SiO 2 / 2 ) b (R 1 SiO 3 / 2 ) c (SiO 4 / 2 ) d (1) (In formula (1), R 1 is independently a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms and an alkenyl group having 2 to 10 carbon atoms, has an average of 2.5 or more alkenyl groups in one molecule, 0 < a ≤ 0.7, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.2, 0 < d ≤ 0.7, provided that 0.8 ≤ a + d ≤ 1, and a + b + c + d = 1.) (C) Linear organohydrogenpolysiloxane represented by the following formula (2)

Chemical formula

[0017] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.)

[0018] <Addition-curable silicone rubber composition> The addition-curable silicone rubber composition of the present invention is characterized by containing the following components (A) to (D): The addition-curable silicone rubber composition is preferably in a liquid state.

[0019] (A) Alkenyl-containing linear organopolysiloxane The organopolysiloxane of component (A) is an alkenyl-containing linear organopolysiloxane having at least two silicon-bonded alkenyl groups per molecule and an average degree of polymerization of 480 or greater.

[0020] As this component (A), a compound represented by the following general formula (3) can be preferably used. [ka] (In the formula, R 4 are the same or different monovalent hydrocarbon groups selected from alkyl groups having 1 to 10 carbon atoms and alkenyl groups having 2 to 10 carbon atoms, and g is an integer of 500 or more, usually 500 to 10,000, and preferably 500 to 8,000.

[0021] R 4 Examples of the monovalent hydrocarbon group represented by R include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and cyclohexyl; and alkenyl groups such as vinyl, allyl, butenyl, pentenyl, hexenyl, and cyclohexenyl. 4 The alkyl group is preferably a methyl group, but the molecule must contain two or more alkenyl groups, and the alkenyl group is preferably a vinyl group.

[0022] Examples of the alkenyl group-containing linear organopolysiloxane include dimethylpolysiloxanes both ends of which are capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers both ends of which are capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers both ends of which are capped with trimethylsiloxy groups, dimethylpolysiloxanes both ends of which are capped with trivinylsiloxy groups, and dimethylsiloxane-methylvinylsiloxane copolymers both ends of which are capped with trivinylsiloxy groups. These may be used alone or in combination of two or more.

[0023] The average degree of polymerization of this organopolysiloxane must be at least 480, and is usually 480 to 10,000, and preferably 500 to 8,000. If it is less than 480, the elongation of the rubber after primary vulcanization will be low. The average degree of polymerization referred to in the present invention refers to the number-average degree of polymerization, which is the average degree of polymerization measured by gel permeation chromatography (GPC) under the following conditions using polystyrene as a standard substance. [Measurement conditions] Developing solvent: toluene Flow rate: 1mL / min Detector: Refractive index detector (RI) Column: KF-805L x 2 (Shodex) Column temperature: 25℃ Sample injection volume: 30 μL (0.2% by mass toluene solution)

[0024] Furthermore, the amount of alkenyl groups bonded to silicon atoms in this organopolysiloxane (alkenyl group amount) must be 0.00006 mol / g or less, and is usually 0.00006 to 0.000003 mol / g, preferably 0.00006 to 0.000006 mol / g, and more preferably 0.00006 to 0.00001 mol / g. If it is 0.00006 mol / g or less, the elongation of the rubber after primary vulcanization will not be reduced.

[0025] As component (A), as long as it is a linear organopolysiloxane containing alkenyl groups, one or more types of organopolysiloxanes differing in molecular structure (for example, the type and ratio of triorganosiloxy groups at the molecular chain terminals or the substituents on the diorganosiloxane units in the main chain) or degree of polymerization can be used in combination.

[0026] (B) Alkenyl group-containing silicone resin (B) component is R 1 3SiO 1 / 2 Unit (M unit), R 1 2SiO 2 / 2 Unit (D unit), R 1 SiO 3 / 2 Units (T units) and SiO 4 / 2 The silicone resin is composed of structural units selected from units (Q units), and the silicone resin is represented by the following formula (1). (R 1 3SiO 1 / 2 ) a (R 1 2SiO 2 / 2 ) b (R 1 SiO 3 / 2 ) c (SiO 4 / 2 ) d (1)

[0027] In formula (1), R 1 are independently monovalent hydrocarbon groups selected from alkyl groups having 1 to 10 carbon atoms and alkenyl groups having 2 to 10 carbon atoms. 4 and at least an average of 2.5, preferably 2.5 to 5 R 1 is an alkenyl group. If the average number of alkenyl groups per molecule is less than 2.5, the cured product will be sticky and difficult to handle. Furthermore, from the viewpoint of compatibility with other components, the alkenyl group of component (B) is preferably a vinyl group, and R 1It is preferable that 80 mol% or more thereof is a methyl group. If the compatibility of each component deteriorates, the transparency of the cured product of the addition-curable silicone rubber composition may decrease. Also, a satisfies 0 < a ≤ 0.7, preferably 0.3 < a < 0.7; b satisfies 0 ≤ b ≤ 0.2, preferably 0 ≤ b ≤ 0.1; c satisfies 0 ≤ c ≤ 0.2, preferably 0 ≤ c ≤ 0.1; d satisfies 0 < d ≤ 0.7, preferably 0.3 < d < 0.7, and a + b + c + d = 1.

[0028] In the silicone resin (formula (1)) of the component (B), among the above four types of structural units, the M unit and the Q unit are essential. In order to improve the hardness of the cured product of the addition-curable silicone rubber composition, it is necessary that the proportion of these two types of structural units in all the structural units is 80 mol% or more (0.8 ≤ a + d ≤ 1.0), preferably 90 mol% or more (0.9 ≤ a + d ≤ 1.0), more preferably 100 mol% (a + d = 1.0). Note that the D unit and the T unit may or may not be included. If the molar ratio (a / d) of the M unit to the Q unit is 0.5 or more, the compatibility between the component (B) and other components will not deteriorate, and if it is 1.5 or less, there is no risk that the hardness of the cured product of the addition-curable silicone rubber composition will decrease. Therefore, the molar ratio (a / d) of the M unit to the Q unit is preferably in the range of 0.5 to 1.5, more preferably in the range of 0.7 to 1.2.

[0029] The alkenyl group content (amount of alkenyl group) of the component (B) is preferably 0.0006 to 0.001 mol / g, more preferably 0.0007 to 0.001 mol / g. If the alkenyl group content is 0.0006 mol / g or more, the cured product will not be too soft in hardness, and if it is 0.001 mol / g or less, the elongation at break after the primary vulcanization will not be low.

[0030] Specific examples of the silicone resin of component (B) include a copolymer of a vinyldimethylsiloxy group and a Q unit, a copolymer of a vinyldimethylsiloxy group, a trimethylsiloxy group and a Q unit, a copolymer of a vinyldimethylsiloxy group, a dimethylsiloxane and a Q unit, a copolymer of a trimethylsiloxy group, a vinylmethylsiloxane and a Q unit, etc. These may be used alone or in combination of two or more.

[0031] (C) Organohydrogenpolysiloxane Component (C) is a linear organohydrogenpolysiloxane containing silicon-bonded hydrogen atoms (Si-H groups), and the Si-H groups in the molecule crosslink with silicon-bonded alkenyl groups in components (A) and (B) via a hydrosilylation addition reaction, thereby acting as a curing agent to cure the composition.

[0032] The component (C) is represented by the following general formula (2). [ka] (In formula (2), R 2 are independently alkyl groups having 1 to 10 carbon atoms, and R 3 are independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, e is an integer of 8 or greater, f is an integer of 0 to 100, e / (e+f) is 40 mol % or greater, and the number of silicon-bonded hydrogen groups per molecule is 10 or greater.

[0033] where R 2 Examples of the alkyl group having 1 to 10 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a cyclohexyl group, an octyl group, a nonyl group, a decyl group, and the like, as well as groups in which some or all of the hydrogen atoms have been substituted with a halogen atom such as fluorine, bromine or chlorine, a cyano group, or the like, such as a chloromethyl group, a chloropropyl group, a bromoethyl group, a trifluoropropyl group, a cyanoethyl group, and the like. 290 mol % or more of R 2 Preferably, the R group is a methyl group. 3 is R 2 In addition to those represented by the formula: hydrogen atom is also included.

[0034] Furthermore, e in formula (2) is an integer of 8 or more, preferably 10 to 200, and more preferably 12 to 100. If e is less than 8, the hardness may be lower than the target (e.g., 65 or more) even after secondary vulcanization. f is an integer of 0 to 100, preferably 5 to 80. Furthermore, the molar ratio (ratio) of e units to the total of e units and f units, e / (e+f), is 40 mol% (0.4) or more, preferably 45 mol% (0.45) or more. The upper limit is not particularly limited, but can be, for example, 90 mol% (0.9) or less. If e / (e+f) is less than 40 mol%, the elongation at break after primary vulcanization is low, resulting in poor mold removal. Furthermore, the number of silicon-bonded hydrogen groups (Si—H groups) per molecule is 10 or more, preferably 12 or more.

[0035] Specific examples of the linear organohydrogenpolysiloxane of component (C) include methylhydrogenpolysiloxanes both end-blocked with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers both end-blocked with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers both end-blocked with dimethylhydrogensiloxy groups, etc. These may be used alone or in combination of two or more.

[0036] (D) Addition reaction catalyst The addition reaction catalyst for component (D) is not particularly limited as long as it is suitable for hydrosilylation addition reactions, and examples include platinum-based catalysts such as platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, platinum bisacetoacetate, etc., palladium-based catalysts, and rhodium-based catalysts.

[0037] Other ingredients The addition-curable silicone rubber composition of the present invention can optionally contain other components, such as hydrosilylation reaction inhibitors such as nitrogen-containing compounds, acetylene compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, and sulfur compounds; internal release agents such as dimethylsilicone oil; and adhesion promoters (particularly organosilicon compounds such as alkoxysilanes that contain at least one functional group selected from alkenyl groups, epoxy groups, amino groups, (meth)acryloxy groups, mercapto groups, and the like in the molecule, but that do not contain Si-H groups in the molecule).

[0038] Amount of ingredients (A) to (D) The amounts of components (A) and (B) in the addition-curable silicone rubber composition are such that the mass ratio of components (A) to (B) is (A) / (B) = 40 / 60 to 60 / 40, and preferably 45 / 55 to 55 / 45. If the proportion of component (B) is greater than 60, the hardness of the cured product after primary vulcanization will be too high, while if it is less than 40, the elongation at break of the cured product after primary vulcanization will be low, and the hardness will be low even after secondary vulcanization.

[0039] Furthermore, the amount of component (C) in the addition-curable silicone rubber composition is such that the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups in the composition (Si-H groups / total alkenyl groups) is 1.0 to 1.5, with 1.0 to 1.4 being particularly preferred. If the ratio is lower than 1.0, the cured product will be very sticky and will have low hardness even after secondary vulcanization. On the other hand, if the ratio is higher than 1.5, the cured product will be too hard after primary vulcanization, making it difficult to remove from the mold.

[0040] Furthermore, the blending amount of component (C) is preferably 7.4 parts by mass or less per 100 parts by mass of the combined total of components (A) and (B). This blending amount provides the cured product after primary vulcanization with more desirable hardness and elongation at break, making it easier to remove from the mold.

[0041] The amount of component (D), an addition reaction catalyst, can be a catalytic amount, and is 0.1 to 10 ppm, and preferably 0.5 to 10 ppm, of platinum group metal (by mass) relative to the total mass of the composition. If the amount of component (D) is less than 0.1 ppm, curing will be slow to proceed, and if it is more than 10 ppm, the cured product may become discolored.

[0042] <Preparation of Addition-Curable Silicone Rubber Composition> An addition-curable silicone rubber composition can be prepared by uniformly mixing the above components (A) to (D), and optionally other optional components, and this mixing can be performed using a mixer typically used in compounding silicone rubber, such as a kneader, gate mixer, Shinagawa mixer, pressure mixer, three-roll mill, or two-roll mill.

[0043] In a vulcanization test using a torsional vibration cone die vulcanization tester (B-2 method) described in JIS K 6300-2:2001, the addition-curable silicone rubber composition obtained above must have a T90-T10 value of 160 seconds or longer, preferably 160 to 260 seconds, and particularly preferably 170 to 240 seconds, where T10 (seconds) is the 10% cure time and T90 (seconds) is the 90% cure time when measured at 150°C for 5 minutes. If the T90-T10 value is shorter than 160 seconds, the hardness of the cured product after primary vulcanization will be high and the elongation at break will be low.

[0044] Thus, the addition-curable silicone rubber composition of the present invention is characterized by a sufficiently long time from 10% cure to 90% cure (i.e., the cure proceeds slowly during this time), with a T90 of less than 300 seconds (5 minutes).

[0045] <Molding of addition-curable silicone rubber composition> The molding and curing methods for the addition-curable silicone rubber composition are not particularly limited and can be conventional, although compression molding and injection molding are preferred. Furthermore, a highly flat liner may be used during molding to reduce the surface roughness of the cured product and increase transparency. For example, primary vulcanization is performed in a mold at 100 to 180°C for 5 seconds to 30 minutes, preferably at 110 to 180°C for 10 seconds to 20 minutes, and particularly at 120 to 160°C for 30 seconds to 10 minutes. After removing the cured product from the mold, secondary vulcanization is performed in an oven or the like at 80 to 200°C, particularly at 100 to 200°C, for 10 minutes to 24 hours, particularly 30 minutes to 10 hours, to obtain a molded product of the desired hardness.

[0046] <Silicone rubber molded body> The addition-curable silicone rubber composition of the present invention can provide a silicone rubber molding (elastomer) that, after a 10-minute press cure (primary vulcanization) at 120°C, has a hardness (Durometer Type A) according to JIS K 6253-3:2012 of 55 or less and an elongation at break of 300% or more in a tensile test according to JIS K 6251:2017. Furthermore, after a 1-hour post cure (secondary vulcanization) at 150°C, the resulting silicone rubber molding (elastomer) has a hardness (Durometer Type A) of 65 or more. After the post cure, a 2-mm-thick molding exhibits a total light transmittance of 90% or more, particularly 92% or more, for D65 light according to JIS K 7361-1:1997. The post cure 2-mm-thick molding exhibits a haze value of 2% or less in a haze test using D65 light according to JIS K 7136:2000. This silicone rubber molding is capable of providing a high-hardness, high-transparency silicone rubber. If the hardness (durometer type A) of the cured product after primary vulcanization is 55 or less and the elongation at break is 300% or more, it will be easy to remove from the mold.

[0047] As described above, the addition-curable silicone rubber composition of the present invention has excellent mold removability and, after secondary vulcanization, gives a silicone rubber that is both highly hard and highly transparent, making it suitable for optical applications such as LEDs. [Example]

[0048] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, parts refer to parts by mass. The average degree of polymerization refers to the number-average degree of polymerization.

[0049] [Example 1] 50 parts of dimethylpolysiloxane (A-1, alkenyl group content: 0.000038 mol / g) whose both ends are blocked with dimethylvinylsiloxy groups and whose average degree of polymerization is 720; 50 parts of silicone resin (B-1, alkenyl group content: 0.00089 mol / g, molar ratio of constituent units: M:D:T:Q=46:0:0:54, M / Q=0.85) which is a copolymer of vinyldimethylsiloxy groups, trimethylsiloxy groups, and Q units and has an average of 3.6 vinyl groups per molecule and a number average molecular weight of 4000; and a crosslinking agent represented by the following formula (4): [ka] 6.2 parts of hydrogenpolysiloxane (C-1, hydromethylsiloxane unit / (hydromethylsiloxane unit+dimethylsiloxane unit)=51 mol%) and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 50 / 50, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.1.

[0050] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0051] [Example 2] 50 parts of dimethylpolysiloxane (A-2, alkenyl group content: 0.000054 mol / g) having an average degree of polymerization of 500 and both ends blocked with dimethylvinylsiloxy groups, 50 parts of the silicone resin (B-1) described in Example 1, and a compound represented by the following formula (5) as a crosslinking agent, [ka] 4.6 parts of hydrogenpolysiloxane (C-2, hydromethylsiloxane unit / (hydromethylsiloxane unit+dimethylsiloxane unit)=73 mol%) and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 50 / 50, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.1.

[0052] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0053] [Example 3] 55 parts of the dimethylpolysiloxane (A-1) described in Example 1, 45 parts of the silicone resin (B-1) described in Example 1, 5.3 parts of the hydrogenpolysiloxane (C-2) described in Example 2 as a crosslinking agent, and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 55 / 45, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.4.

[0054] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0055] [Example 4] 47.5 parts of the dimethylpolysiloxane (A-1) described in Example 1, 5 parts of a dimethylpolysiloxane (A-3, alkenyl group content: 0.000020 mol / g) capped at both ends with dimethylvinylsiloxy groups, having an average of 10 vinyl groups in the side chains, and having an average degree of polymerization of 8000, 47.5 parts of the silicone resin (B-1) described in Example 1, and a compound represented by the following formula (6) as a crosslinking agent: [ka] 7.3 parts of hydrogenpolysiloxane (C-3, hydromethylsiloxane unit / (hydromethylsiloxane unit+dimethylsiloxane unit)=50 mol%) and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 52.5 / 47.5, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.2.

[0056] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0057] [Comparative Example 1] 50 parts of dimethylpolysiloxane (A-4, alkenyl group content: 0.000060 mol / g) with an average degree of polymerization of 450 and both ends blocked with dimethylvinylsiloxy groups, 50 parts of the silicone resin (B-1) described in Example 1, 4.7 parts of the hydrogenpolysiloxane (C-2) described in Example 2 as a crosslinking agent, and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 50 / 50, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.1.

[0058] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0059] Comparative Example 2 61 parts of the dimethylpolysiloxane (A-1) described in Example 1, 39 parts of the silicone resin (B-1) described in Example 1, 4.7 parts of the hydrogenpolysiloxane (C-2) described in Example 2 as a crosslinking agent, and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 61 / 39, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.4.

[0060] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0061] Comparative Example 3 55 parts of the dimethylpolysiloxane (A-1) described in Example 1, 45 parts of the silicone resin (B-1) described in Example 1, 9.8 parts of the hydrogenpolysiloxane (C-3) described in Example 4 as a crosslinking agent, and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 55 / 45, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.6.

[0062] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0063] Comparative Example 4 50 parts of the dimethylpolysiloxane (A-1) described in Example 1, 50 parts of the silicone resin (B-1) described in Example 1, and a compound represented by the following formula (7) as a crosslinking agent: [ka] 10.8 parts of hydrogenpolysiloxane (C-4, hydromethylsiloxane unit / (hydromethylsiloxane unit+dimethylsiloxane unit)=36 mol%) and 0.025 parts of ethynylcyclohexanol as a reaction inhibitor were added, and stirring was continued for 15 minutes to obtain a silicone rubber mixture. In this mixture, the mass ratio of component (A) to component (B) was (A) / (B) = 50 / 50, and the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups (Si-H groups / total alkenyl groups) was 1.2.

[0064] 0.05 parts of a platinum catalyst (Pt concentration 1% by mass) was mixed into this silicone rubber mixture to form a silicone rubber composition. The curability (10% cure time T10 and 90% cure time T90) of this composition measured at 150°C for 5 minutes in accordance with JIS K 6300-2:2001 was measured using a rheometer MDR2000 (manufactured by Alpha Technologies). Furthermore, the hardness of a 2mm-thick cured product obtained after 120°C / 10 minutes of press curing (primary vulcanization) was measured using a durometer type A in accordance with JIS K 6253-3:2012, and the elongation at break in accordance with JIS K 6251:2017. The results are shown in Table 2. In addition, after press curing, a 2 mm thick cured product was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour. The hardness using a durometer type A was measured in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017.The total light transmittance under D65 light as specified in JIS K 7361-1:1997 and the haze using D65 light as specified in JIS K 7136:2000 were also measured.The results are shown in Table 3.

[0065] The amounts of each component used in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] As shown in Tables 2 and 3, the addition-curable silicone rubber compositions of Examples 1 to 4 had a low hardness (Durometer Type A) of 55 or less after primary vulcanization, an elongation at break of 300% or more, and a hardness of 65 or more after secondary vulcanization, resulting in highly transparent addition-curable silicone rubber compositions.

[0070] On the other hand, in Comparative Example 1, which used a linear organopolysiloxane with an average degree of polymerization of less than 480, the rubber had low elongation after primary vulcanization, and in Comparative Example 2, in which the mass ratio of component (A) to component (B) was outside the range of (A) / (B) = 40 / 60 to 60 / 40, the hardness was low even after secondary vulcanization.

[0071] Furthermore, in Comparative Example 3, where the ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups in the composition (Si-H groups / total alkenyl groups) was outside the range of 1.0 to 1.5, the hardness of the cured product after primary vulcanization was high and the elongation at break was low. In Comparative Example 4, where the ratio of hydromethylsiloxane units to (hydromethylsiloxane units + dimethylsiloxane units) was not 40 mol % or more, the hardness of the cured product after primary vulcanization was high and the elongation at break was low.

[0072] As described above, the addition-curable silicone rubber composition of the present invention is an addition-curable silicone rubber composition that is easy to remove from a mold and can give a cured product with high transparency.

[0073] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. An addition-curable silicone rubber composition comprising: (A) a linear organopolysiloxane having an average degree of polymerization of 480 or more and containing at least two silicon-bonded alkenyl groups per molecule; (B) an alkenyl group-containing silicone resin represented by the following formula (1): (R １ ３ SiO １／２ ) ａ (R １ ２ SiO ２／２ ) ｂ (R １ SiO ３／２ ) ｃ (SiO ４／２ ) ｄ (1) (In formula (1), R １ are independently monovalent hydrocarbon groups selected from alkyl groups having 1 to 10 carbon atoms and alkenyl groups having 2 to 10 carbon atoms, containing an average of 2.5 or more alkenyl groups per molecule, and satisfying the conditions 0<a≦0.7, 0≦b≦0.2, 0≦c≦0.2, and 0<d≦0.7, with the proviso that 0.8≦a+d≦1 and a+b+c+d=1; (C) A linear organohydrogenpolysiloxane represented by the following formula (2): 【Chemistry 1】 (In formula (2), R ２ are independently alkyl groups having 1 to 10 carbon atoms; R ３ are independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, e is an integer of 8 or greater, f is an integer of 5 to 100 (excluding 10), e / (e+f) is 40 mol % or greater, and the number of silicon-bonded hydrogen groups per molecule is 10 or greater). (D) Addition reaction catalyst: 0.1 to 10 ppm as platinum group metal (by mass) based on the total mass of the composition an addition-curable silicone rubber composition comprising: a mass ratio of component (A) to component (B) of (A) / (B) = 40 / 60 to 60 / 40; a ratio of the number of moles of all Si-H groups to the number of moles of all alkenyl groups in the composition (Si-H groups / total alkenyl groups) of 1.0 to 1.5; in a vulcanization test using a torsional vibration cone die vulcanization tester (B-2 method) described in JIS K 6300-2:2001, where T10 is the 10% cure time and T90 is the 90% cure time when measured at 150°C for 5 minutes, T90 - T10 is 160 seconds or longer; and the amount of alkenyl groups in component (B) is 0.0006 to 0.001 mol / g.

2. 2. The addition-curable silicone rubber composition according to claim 1, wherein the amount of alkenyl groups in component (A) is 0.00006 mol / g or less.

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