Mirable-type silicone rubber composition

Abstract

To provide a millable silicone rubber composition that becomes a silicone rubber (cured material) excellent in heat resistance and fire retardancy.SOLUTION: A millable silicone rubber composition comprising: (A) organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule with an average degree of polymerization of 100 or more: 100 pts.mass; (B) reinforcing silica having a specific surface area of 50 m2 / g or more by a BET method: 5-100 pts.mass; (C) platinum-based compounds: 0.5-1,000 ppm to a total mass of the (A) component; (D) one or more types selected from cerium oxide and cerium hydroxide: 0.01-10 pts.mass, (E) fumed titanium oxide having a specific surface area of 5-200 m2 / g or more by the BET method: 1.0-20 pts.mass, (F) magnesium ferrite having an oil absorption amount of 20-40 g / 100 g: 0.5-30 pts.mass; and (G) organic peroxide: 0.1-10 pts.mass.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a millable-type silicone rubber composition. [Background technology]

[0002] Silicone rubber has a main skeleton made of siloxane bonds and has a lower proportion of organic components (hydrocarbon components) compared to ordinary organic rubber, making it flame-retardant. However, under harsh conditions such as direct contact with flames, silicone rubber can ignite and burn. To solve the above problem, it is known that a platinum compound or a reaction product of a platinum compound with an alkynyl group and an alcoholic hydroxyl group, and a triazole compound are incorporated into the silicone rubber composition as a flame retardant (Patent Document 1).

[0003] Furthermore, a method has been proposed (Patent Document 2) in which titanium dioxide with an average particle size of 0.10 to 0.50 μm is added to the silicone rubber composition, but in either case, the heat resistance of the resulting cured silicone rubber product is reduced.

[0004] It is known that additives such as cerium oxide, cerium hydroxide, iron oxide, and carbon black are incorporated into silicone rubber compositions to improve their heat resistance. However, the heat resistance of silicone rubber under high-temperature conditions of 250°C or higher is not sufficient.

[0005] Patent Document 3 describes how the heat resistance of silicone rubber can be improved by adding 0.1% or more by mass of titanium dioxide and iron oxide (particularly diiron trioxide) to a silicone rubber composition, but the flame retardancy is reduced due to the effect of iron oxide.

[0006] Patent Document 4 describes that adding hydrated cerium oxide and / or hydrated zirconium oxide to a silicone rubber composition improves the heat resistance of the silicone rubber, and measures the physical properties after being placed in a 225°C dryer for 72 hours. However, the heat resistance at higher temperatures is not sufficient.

[0007] Patent documents 5 and 6 describe titanium oxide doped with metal ions (metal salts) such as transition metals. However, while adding titanium oxide doped with metal ions (metal salts) to a silicone rubber composition improves high-temperature heat resistance, it reduces flame retardancy.

[0008] Patent Document 7 describes an addition-curing type organopolysiloxane composition containing yellow iron oxide fine powder, preferably yellow iron oxide in which aluminic acid or aluminate is solid-solved. The composition is described as curing by an addition reaction to provide a cured product with excellent heat resistance in a high-temperature range of 280°C or higher. However, the addition of yellow iron oxide significantly reduces flame retardancy.

[0009] Currently, the demand for silicone rubber is increasing, and there is a growing need for the development of silicone rubber that possesses excellent heat resistance and superior flame retardancy. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 11-140325 [Patent Document 2] Japanese Patent Application Publication No. 9-194730 [Patent Document 3] Special Publication No. 2016-518461 [Patent Document 4] Japanese Patent Publication No. 2014-031408 [Patent Document 5] Japanese Patent Publication No. 2006-021991 [Patent Document 6] International Publication No. 2010 / 140499 [Patent Document 7] Japanese Patent Application Publication No. 7-292256 [Overview of the project] [Problems that the invention aims to solve]

[0011] Therefore, an object of the present invention is to provide a millable silicone rubber composition that becomes a silicone rubber (cured product) having excellent heat resistance at a high temperature of 200°C or higher, particularly 300°C, and excellent flame retardancy.

Means for Solving the Problems

[0012] As a result of intensive studies to achieve the above object, the present inventors have found that by blending a platinum-based compound, titanium oxide, cerium oxide, and magnesium ferrite into a silicone rubber composition, the cured product of this silicone rubber composition is excellent in flame retardancy and heat resistance at high temperatures, and thus have arrived at the present invention. That is, the present invention provides a millable silicone rubber composition as follows.

[0013] [1] (A) Organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule and having an average degree of polymerization of 100 or more: 100 parts by mass, (B) Reinforcing silica having a specific surface area by the BET method of 50 m / g or more: 5 to 100 parts by mass, (C) Platinum-based compound: 0.5 to 1,000 ppm based on the total mass of component (A), (D) One or more selected from cerium oxide and cerium hydroxide: 0.01 to 10 parts by mass, (E) Fumed titanium oxide having a specific surface area by the BET method of 5 to 200 m 2 / g: 1.0 to 20 parts by mass, (F) Magnesium ferrite having an oil absorption of 20 to 40 g / 100 g: 0.5 to 30 parts by mass, and, (G) Organic peroxide: 0.1 to​​​​​​​​​​​(A) component has an average degree of polymerization of 1,000 to 100,000, the mirabilite-type silicone rubber composition according to [1] or [2]. [4] (G) component is benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide or o-methylbenzoyl peroxide, the mirabilite-type silicone rubber composition according to any one of [1] to [3]. [5] Furthermore, the mirabilite-type silicone rubber composition according to any one of [1] to [4], containing 0.1 to 50 parts by mass of a dispersant for (H) filler with respect to 100 parts by mass of the (A) component. [6] The cured product of the mirabilite-type silicone rubber composition according to any one of [1] to [5]. [Effect of the Invention]

[0014] The mirabilite-type silicone rubber composition of the present invention can provide a silicone rubber excellent in flame retardancy and heat resistance. That is, the cured product (silicone rubber) of the mirabilite-type silicone rubber composition of the present invention exhibits excellent heat resistance at a high temperature of 200 °C or higher, particularly 300 °C. Further, the cured product exhibits good flame retardancy comparable to V-0 in the combustion test by the UL-94 test method. [Embodiments for Carrying out the Invention]

[0015] In the present specification, the specific surface area is a value measured by the BET method. Note that the mirabilite-type composition is a high-viscosity and non-liquid composition having no self-fluidity at room temperature (25 °C), and means a composition that can be uniformly kneaded under shear stress by a kneader such as a roll mill (for example, a two-roll or three-roll mill).

[0016] [(A) Organopolysiloxane] Component (A) is an organopolysiloxane, which is the main component (base polymer) of this composition, and has two or more alkenyl groups bonded to silicon atoms in one molecule, preferably 2 to 50 alkenyl groups bonded to silicon atoms. It is preferable that there is one or more alkenyl groups at each end of the molecular chain, and it is even more preferable that there are alkenyl groups in the side chains of the molecular chain.

[0017] Component (A) has an average degree of polymerization of 100 or more, preferably in the range of 1,000 to 100,000, more preferably in the range of 3,000 to 50,000, and particularly preferably in the range of 4,000 to 20,000. If the average degree of polymerization is less than 100, the millable silicone rubber composition of the present invention will not satisfy the properties of millable rubber, and the roll kneadability and other properties will deteriorate significantly, which is undesirable. This average degree of polymerization is determined from the weight-average molecular weight in polystyrene terms in GPC (gel permeation chromatography) analysis measured under the following conditions.

[0018] [Measurement conditions] • Developing solvent: Toluene ·Flow rate: 1mL / min • Detector: Differential refractive index detector (RI) • Columns: KF-805L x 2 (Shodex) • Column temperature: 25℃ • Sample injection volume: 30 μL (0.2% by mass toluene solution)

[0019] In the present invention, component (A) is preferably a non-liquid organopolysiloxane raw rubber with a high degree of polymerization (high viscosity) and no self-flowing properties at room temperature (25°C).

[0020] The component (A) may be any alkenyl group-containing organopolysiloxane that satisfies the above average degree of polymerization.

[0021] Examples of the above-mentioned alkenyl groups include vinyl groups, allyl groups, butenyl groups, and hexenyl groups. Preferably, it is an alkenyl group having 2 to 8 carbon atoms, more preferably a vinyl group or an allyl group, and even more preferably a vinyl group.

[0022] Substituents bonded to silicon atoms other than the alkenyl group are monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8, and more preferably 1 to 6 carbon atoms. Examples of such monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, and butyl groups, cycloalkyl groups such as cyclohexyl groups, aryl groups such as phenyl and tolyl groups, and aralkyl groups such as β-phenylpropyl groups. Some or all of the hydrogen atoms bonded to the carbon atoms of these groups may be substituted with halogen atoms, for example, 3,3,3-trifluoropropyl groups. Among these, methyl, phenyl, and trifluoropropyl groups are preferred, and methyl groups are more preferred. Preferably, 50% or more of the total substituents in the alkenyl group-containing organopolysiloxane are methyl groups, more preferably 80% or more are methyl groups, and even more preferably all substituents other than the alkenyl group are methyl groups.

[0023] The above alkenyl group-containing organopolysiloxane is preferably linear or branched, and more preferably linear. In particular, it is preferable that the main chain consists of repeating diorganosiloxane units and both ends of the molecular chain are sealed with triorganosiloxy groups. With such a structure, the resulting cured product exhibits sufficient rubber elasticity. It is preferable that both ends of the molecular chain are sealed with trimethylsiloxy groups, dimethylvinylsiloxy groups, dimethylhydroxysiloxy groups, methyldivinylsiloxy groups, trivinylsiloxy groups, etc., and in particular, it is preferable that they are sealed with triorganosiloxy groups having one or more vinyl groups. These organopolysiloxanes may be used individually, or two or more with different degrees of polymerization and molecular structures may be used in combination.

[0024] In the millable-type silicone rubber composition of the present invention, the content of component (A) is preferably 43 to 96% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass.

[0025] [(B) Reinforced silica] (B) Reinforcing silica is a filler that imparts excellent mechanical properties to the resulting silicone rubber. The reinforcing silica may be precipitated silica (wet silica) or fumed silica (dry silica), and has a large number of silanol (hydroxysilyl) groups on its surface. In the present invention, (B) reinforcing silica has a specific surface area of ​​50 m² determined by the BET method. 2 It is necessary to have a value of at least / g. There is no particular upper limit on the specific surface area, but 400m² is required. 2 It is sufficient if it is less than or equal to / g, preferably 100 to 400m 2 It is / g. The specific surface area is 50m². 2 If the amount is less than / g, the reinforcing effect of the silicone rubber provided by component (B) may be insufficient.

[0026] (B) The reinforcing silica may be used in its untreated state, or, if necessary, may be reinforcing surface-treated silica that has been surface-treated with organosilicon compounds (surface treatment agents) such as organopolysiloxane, organopolysilazane, chlorosilane, or alkoxysilane. Furthermore, the reinforcing surface-treated silica may be treated with one type of surface treatment agent, or with two or more types of surface treatment agents. Note that this organosilicon compound (surface treatment agent) differs from the dispersant for fillers (H) described later in that it does not have a silanol group in one molecule. The reinforcing silica of component (B) may be used alone, or in combination of two or more types.

[0027] (B) The amount of reinforcing silica added is 5 to 100 parts by mass per 100 parts by mass of organopolysiloxane of component (A), preferably 10 to 80 parts by mass, and more preferably 20 to 70 parts by mass. If the amount of component (B) added is less than 5 parts by mass or more than 100 parts by mass per 100 parts by mass of component (A), not only will the processability of the resulting millable silicone rubber composition decrease, but the mechanical properties such as tensile strength and tear strength of the cured silicone rubber product obtained by curing the silicone rubber composition may also be insufficient.

[0028] [(C) Platinum compound] Examples of platinum-based compounds in component (C) include platinum black, platinum-dic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, and platinum bisacetate.

[0029] The amount of platinum-based compound used is 0.5 to 1,000 ppm, and especially 1 to 500 ppm, relative to the amount of component (A), in terms of platinum (by mass). If the amount is less than 0.5 ppm, the flame retardancy will be insufficient, and if it is more than 1,000 ppm, it will not be economical and may reduce the flame retardancy.

[0030] [(D) Cerium oxide and / or cerium hydroxide] Component (D) is one or more cerium compounds selected from cerium oxide and cerium hydroxide. When used in combination with magnesium ferrite (F), described later, the heat resistance of the silicone rubber is significantly improved.

[0031] Commercially available cerium oxide products include Showa Denko FL-2 (manufactured by Showa Denko Corporation), SN-2 (manufactured by Nikki Co., Ltd.), and Cerium Oxide S (manufactured by Anan Kasei Co., Ltd.). Commercially available cerium hydroxide products include Cerium Hydroxide (manufactured by Nikki Co., Ltd.) and Cerhydrate 90 (manufactured by Tribach Industries, Ltd.).

[0032] The amount of component (D) added is 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, per 100 parts by mass of organopolysiloxane (A). If the amount is less than 0.01 parts by mass per 100 parts by mass of component (A), the heat resistance of the silicone rubber will not improve, and if more than 10 parts by mass is added, the mechanical properties of the silicone rubber may be significantly reduced. Cerium oxide and cerium hydroxide may be used individually or in combination of two or more. Among these, the use of cerium oxide alone is preferred. When cerium oxide and cerium hydroxide are used in combination, the total amount should satisfy the above range.

[0033] [(E) Fumed Titanium Oxide] (E) Fumed titanium oxide is titanium oxide produced by the dry process, with a specific surface area of ​​5 to 200 m² as determined by the BET method. 2 The value is / g, preferably 20-100m 2 The concentration is / g. Furthermore, the crystal structure may be either rutile or anatase, and these two types may be present in a mixture. The amount of component (E) added is 1.0 to 20 parts by mass, preferably 3.0 to 10 parts by mass, per 100 parts by mass of organopolysiloxane component (A). (A) If the amount is less than 1.0 part by mass per 100 parts by mass of component (A), the flame retardancy of the silicone rubber will not improve, and if more than 20 parts by mass is added, the mechanical properties of the silicone rubber may deteriorate significantly.

[0034] [(F) Magnesium ferrite] (F) The magnesium ferrite has an oil absorption capacity of 20-40 g / 100 g obtained by the mixing method. The amount of component (F) added is 0.5-30 parts by mass, preferably 1.0-20 parts by mass, per 100 parts by mass of organopolysiloxane (A). If the amount is less than 0.5 parts by mass per 100 parts by mass of component (A), the heat resistance of the silicone rubber will not improve, and if more than 30 parts by mass is added, the mechanical properties of the silicone rubber (e.g., elongation at break (%)) may be significantly reduced. Note that diferric oxide and yellow iron oxide are undesirable because they worsen the flame retardancy. Commercially available magnesium ferrite products include TAROX T-20 and those manufactured by Titanium Industries Co., Ltd.

[0035] [(G)Organic peroxide] (G) Organic peroxides are curing agents capable of curing the millable-type silicone rubber composition of the present invention.

[0036] Examples of organic peroxides 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-butyl peroxycarbonate. The amount of organic peroxide added is 0.1 to 10 parts by mass per 100 parts by mass of component (A), with 0.2 to 5 parts by mass being preferred. If the amount added is less than 0.1 parts by mass per 100 parts by mass of component (A), curing may be insufficient, and if more than 10 parts by mass is added, the cured silicone rubber may discolor due to the decomposition residue of the organic peroxide.

[0037] [(H) Dispersant for fillers] The millable-type silicone rubber composition of the present invention may further contain, in addition to components (A) to (G) above, a dispersant for fillers, particularly an inorganic filler or silica dispersant, and preferably a silica dispersant. By further including the dispersant, the reinforcing silica described above can be well dispersed in the composition. The dispersant is characterized by having one or more silanol groups in one molecule, and examples include low molecular weight organosilicon compounds having silanol groups and alkoxy groups, and their hydrolysates. More specifically, examples include various alkoxysilanes, particularly hydrolysates of phenyl group-containing alkoxysilanes, diphenylsilanediol, silanol group-containing carbon functional silanes, and silanol group-containing low molecular weight siloxanes (e.g., organopolysiloxanes with silanol groups sealed at both ends). Among these, the use of diphenylsilanediol is preferred because it further improves the heat resistance of the silicone rubber. Furthermore, the use of diphenylsilanediol in combination with alkylalkoxysilane or its hydrolysates is even more preferred because it further improves the dispersibility of the reinforcing silica. As mentioned above, component (H) differs from the organosilicon compound used for surface treatment of the reinforcing silica (B) in that it has one or more silanol groups in one molecule.

[0038] The amount of component (H) is preferably 0.1 to 50 parts by mass, and particularly preferably 1 to 20 parts by mass, per 100 parts by mass of component (A). If the amount of component (H) is too small, the effect of the addition will not be observed, and if it is too large, the plasticity of the composition will become too low, which may cause roll adhesion in kneading means such as roll mills and worsen the roll workability.

[0039] [Other ingredients] The millable silicone rubber composition used in the present invention may, in addition to the above components, optionally contain other known fillers and additives used in thermosetting silicone rubber compositions, as long as they do not impair the effects of the present invention. Examples include fillers other than components (B) and (H) (e.g., crushed quartz, diatomaceous earth, calcium carbonate), colorants (pigments), tear strength enhancers, flame retardancy enhancers, acid acceptors, thermal conductivity enhancers (e.g., alumina, boron nitride), and mold release agents. Other components may be used individually or in combination of two or more. The amounts of these components may be adjusted as appropriate, as long as they do not impair the effects of the present invention.

[0040] Method for manufacturing the composition The millable silicone rubber composition of the present invention can be obtained by mixing the above-mentioned components in a known kneader such as a kneader, Banbury mixer, or double-roll mixer. For example, when preparing a composition containing the above components (A) to (G), it is preferable to mix (A) organopolysiloxane, (B) reinforcing silica, (C) platinum-based compound, (D) cerium oxide or cerium hydroxide, (E) titanium oxide, and (F) magnesium ferrite, and then add (G) organic peroxide to the resulting mixture. If other components are included, it is preferable to mix components (A), (B), (C), (D), (E), and (F) with the other components, and then add (G) organic peroxide to the resulting mixture. Furthermore, if component (H) is included, it is preferable to prepare a mixture of component (A), component (B), and component (H), mix this mixture with component (C), component (D), component (E), component (F), and other components as needed, and then add component (G) to the resulting mixture.

[0041] The Mirable-type silicone rubber composition can be molded by known molding methods according to the desired shape and size of the molded product. Examples of molding methods include injection molding, compression molding, injection molding, calendering, and extrusion molding.

[0042] cured product The curing conditions for the Mirable-type silicone rubber composition can be any known conditions for the molding method used, and the Mirable-type silicone rubber composition is generally heated at a temperature of 60 to 450°C for several seconds to about one day. Furthermore, a post-cure (secondary cure) may be performed in an oven at 200°C or higher, preferably 200 to 250°C, for at least one hour, preferably 1 to 70 hours, more preferably 1 to 10 hours, for purposes such as reducing the compression set of the resulting cured product, reducing the amount of low molecular weight siloxane components remaining in the resulting silicone rubber, and removing decomposition products of organic peroxides in the silicone rubber. [Examples]

[0043] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0044] In the examples and comparative examples, heat resistance tests and flame retardancy tests were conducted according to the following procedures. [Heat resistance] Using test sheets prepared by curing a millable-type silicone rubber composition, the initial values ​​of hardness (durometer A) and elongation at break (%) were measured in accordance with JIS K 6249:2003. After placing the test sheets in a 300°C dryer for 3 days, the hardness and elongation at break were measured again. The results are shown in Table 1. [Flame retardant] Using test sheets prepared by curing a millable-type silicone rubber composition, five 1 mm thick silicone rubber sheets were used to measure the afterflame periods T1 and T2, as well as the total afterflame time for each set of treatments (sum of T1 + T2 for the five silicone rubber sheets), according to the method specified in the UL94 20 mm vertical combustion test. T1 represents the afterflame time after the first flame application, and T2 represents the afterflame time after the second flame application. The results are shown in Table 1.

[0045] The components used in the examples and comparative examples of the present invention are as follows. (A) Alkenyl group-containing organopolysiloxane (A-1) Organopolysiloxane raw rubber consisting of 99.85 mol% of dimethylsiloxane units, 0.125 mol% of methylvinylsiloxane units, and 0.025 mol% of dimethylvinylsiloxy units (number of vinyl groups in one molecule: 10), with an average degree of polymerization of 6,000 (B) Reinforcing silica (B-1) Fumed silica with a specific surface area measured by the BET method of 200 m 2 / g (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) (B-2) Reinforcing surface-treated silica The reinforcing surface-treated silica was produced by the following method. 200 g of fumed silica with a specific surface area measured by the BET method of 200 m 2 / g (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) was charged into a high-speed mixer (capacity 1*0 L) and operated at a rotation speed of 1,500 rpm. When the rotation became stable, a mixture of 20 g of dimethylpolysiloxane having silanol groups at both ends, with an average degree of polymerization of 4 and a viscosity of <15> mPa·s at 25°C, and 1.2 g of vinyltrimethoxysilane as a surface treatment agent (hydrophobic agent) was sprayed in 20 seconds to obtain wet silica. 100 g of this wet silica was charged into a 2 L flask and heated at 250°C for 2.5 hours to produce reinforcing surface-treated silica with a specific surface area measured by the BET method of 200 m 2 / g. (C) Platinum-based compound (C-1) 2-ethylhexanol solution of chloroplatinic acid hexahydrate (platinum concentration in mass conversion: 2 mass%, manufactured by Shin-Etsu Chemical Co., Ltd.) (D) Cerium oxide and cerium hydroxide (D-1) Cerium oxide (trade name: SN-2, manufactured by Nikki Co., Ltd.) (D-2) Cerium hydroxide (trade name: Cerhydrate90, manufactured by Tribach Industrie AG) (E) Fumed titanium oxide (E-1) Titanium dioxide (product name: AEROXIDE TiO2P25, manufactured by Nippon Aerosil Co., Ltd.) (Specific surface area: 50m² by BET method) 2 / g) (F) Magnesium ferrite (F-1) Magnesium ferrite (Product name: TAROX T-20, manufactured by Titanium Industry Co., Ltd.) (Oil absorption capacity: 30g / 100g) (F'-1) Red iron oxide (product name: BAYFERROX 130M, manufactured by Lanxess Co., Ltd.) [for comparative example] (F'-2) Yellow iron oxide (product name: TAROX-LL-XLO, manufactured by Titanium Industry Co., Ltd.) [for comparative example] Titanium oxide doped with (F'-3)3% by mass of iron oxide (product name: AEROXIDE TiO2 PF2, manufactured by Nippon Aerosil Co., Ltd.) [for comparative example] (F'-4) Titanium dioxide (product name: Typeque R-820, manufactured by Ishihara Sangyo Co., Ltd.) [for comparative example] (G)Organic peroxide (G-1) p-methylbenzoyl peroxide (H) Dispersant for fillers (H-1)diphenylsilanediol (H-2) Dimethylpolysiloxane containing silanol groups at both ends (average degree of polymerization: 4, viscosity (25℃): 15 mPa·s)

[0046] [Example 1] (A-1) 100 parts by mass, (B-1) 40 parts by mass, (H-1) 5 parts by mass, and (H-2) 2 parts by mass were added, and the mixture was heated at 170°C for 2 hours in a kneader to prepare base compound (1).

[0047] Compound (A) was prepared by adding (C-1) 0.1 parts by mass, (D-1) 1.5 parts by mass, (E-1) 5.0 parts by mass, and (F-1) 0.5 parts by mass to the base compound (1) using a double roll mill.

[0048] 0.7 parts by mass of (G-1) was added to compound (A) and uniformly mixed using a double roll to obtain a millable-type silicone rubber composition. The silicone rubber composition was heated at 120°C and 70 kgf / cm². 2 Press curing was performed for 10 minutes under the specified conditions to prepare 2 mm thick test sheets for heat resistance testing and 1 mm thick test sheets for flame retardancy testing. These test sheets were then post-cured in a 150°C oven for 1 hour. The resulting cured materials were subjected to the heat resistance and flame retardancy tests described above. The results are shown in Table 1.

[0049] [Examples 2-7, Comparative Examples 1-8] A silicone rubber composition was prepared using the formulations listed in Table 1, in the same manner as in Example 1. The resulting cured product was subjected to heat resistance and flame retardancy tests in the same manner as in Example 1. The results are shown in Table 1.

[0050] [Table 1]

Claims

1. (A) Organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, with an average degree of polymerization of 100 or more: 100 parts by mass, (B) Specific surface area of ​​50 m² by the BET method 2 Reinforcing silica with a concentration of 5 to 100 parts by mass, (C) Platinum-based compound: 0.5 to 1,000 ppm relative to the total mass of component (A) (D) One or more selected from cerium oxide and cerium hydroxide: 0.01 to 10 parts by mass, (E) Specific surface area of ​​5 to 200 m² by the BET method 2 Fumed titanium oxide per g: 1.0 to 20 parts by mass, (F) Magnesium ferrite with an oil absorption capacity of 20 to 40 g / 100 g: 0.5 to 30 parts by mass, (G) Organic peroxide: 0.1 to 10 parts by mass A Mirable-type silicone rubber composition containing the following:

2. The millable-type silicone rubber composition according to claim 1, wherein component (A) is a linear organopolysiloxane.

3. The millable-type silicone rubber composition according to claim 1, wherein component (A) has an average degree of polymerization of 1,000 to 100,000.

4. The millable silicone rubber composition according to claim 1, wherein component (G) is benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, or o-methylbenzoyl peroxide.

5. The millable-type silicone rubber composition according to claim 1, further comprising 0.1 to 50 parts by mass of (H) a dispersant for fillers per 100 parts by mass of component (A).

6. A cured product of the millable-type silicone rubber composition according to any one of claims 1 to 5.

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