Addition-curing liquid silicone rubber composition and flame-retardant silicone rubber

Abstract

Provided is a silicone rubber composition that yields a cured product having excellent colorability and flame retardancy. [Solution] (A) 100 parts by mass of an organopolysiloxane having a polymerization degree of 50 to 2,000 and containing two or more silicon atom-bonded alkenyl groups per molecule, (B) an organohydrogenpolysiloxane containing two or more SiH groups per molecule: an amount such that the SiH groups in the composition are 1 to 10 mol per 1 mol of the total of silicon atom-bonded alkenyl groups in the composition, (C) a specific surface area of 50 m 2 fine silica powder of / g or more: 10 to 50 parts by mass, (D) a catalyst: 1 to 500 ppm in terms of the mass of the catalytic metal element relative to the total mass of (A), (B) and (C), (E) 1,2,3-benzotriazole or a derivative thereof: an amount of 2 to 500 mol per 1 mol of the catalytic metal atom in (D), and (F) (RSiO 3 / 2 ) n silicone resin powder: 20 to 150 parts by mass, An addition-curable silicone rubber composition comprising the components above.

Description

Technical Field

[0001] The present invention relates to an addition-curable liquid silicone rubber composition and a flame-retardant silicone rubber that is a cured product thereof.

Background Art

[0002] Silicone rubbers are used in various fields because they have properties such as excellent heat resistance, weather resistance, and electrical properties. However, silicone rubbers are combustible, and although they do not burn easily when exposed to a flame, they have the property of continuing to burn once ignited. For this reason, various developments have been attempted to improve the flame retardancy of silicone rubbers.

[0003] For example, Patent Document 1 discloses a composition in which quartz powder or aluminum oxide is combined with nano zinc oxide in an addition-curable or condensation-curable silicone composition. It is described that this composition can provide a cured silicone rubber product with high flame retardancy. Patent Document 2 discloses a composition in which talc powder and a benzotriazole derivative are combined in an addition-curable silicone composition. It is described that this composition can provide a cured silicone rubber product that has high flame retardancy and high storage stability. Patent Document 3 discloses a composition in which a hollow ceramic filler and quartz powder are blended into an addition-curable liquid silicone rubber composition. It is described that this composition can provide a cured silicone rubber product that is excellent in flame retardancy and has a low fume emission amount. Patent Document 4 discloses a silicone rubber composition containing carbon black and aluminum hydroxide as flame retardancy-improving materials. It is described that this composition is excellent in fluidity, moldability and curability, and can provide a silicone rubber having flame retardancy.

[0004] In addition, Patent Document 5 discloses an addition-curable silicone rubber composition in which a triazole compound and a phosphate ester compound are combined. This composition is described as providing a cured silicone rubber product with high flame retardancy without impairing the properties of the silicone rubber. Further, Patent Document 6 discloses an addition-curable silicone rubber composition formulated with a crosslinking agent having a defined hydrosilyl group content in side chains. This composition is described as yielding a cured silicone rubber product that has high flame retardancy and excellent rubber strength. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2023-509568 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2019-031601 [Patent Document 3] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-515898 [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2004-161944 [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2016-094514 [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2023-130798 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, the compositions described in Patent Documents 1 to 4 contain a large amount of inorganic compounds that have a flame retardancy improving effect, and the resulting cured silicone rubber product is colored by the inorganic filler. This poses a problem that it is difficult to color the silicone rubber to a desired color using a pigment. In addition, since the density of the silicone rubber composition becomes high, there is another problem that the weight increases when it is used for parts of automobiles and the like.

[0007] Furthermore, in recent years, the level of flame retardancy required for silicone rubber used in automobiles, railways, home appliances, and other components has increased in order to improve performance and extend lifespan, and the compositions described in Patent Documents 5 and 6 do not meet these requirements.

[0008] Therefore, there is a need for the development of a silicone rubber composition that is easy to color and can provide a cured silicone rubber product with excellent flame retardancy and rubber properties.

[0009] The present invention has been made to solve the above problems, and aims to provide an addition-curing type liquid silicone rubber composition that can provide a silicone rubber cured product with excellent colorability due to its high total light transmittance and excellent flame retardancy. [Means for solving the problem]

[0010] The present inventors conducted diligent studies to achieve the above objective and found that an addition-curing liquid silicone rubber composition contains (RSiO 3 / 2 ) n We have discovered that by incorporating a silicone resin powder represented by [the specified formula], it is possible to obtain a cured silicone rubber product that has high total light transmittance and excellent flame retardancy.

[0011] In other words, the present invention is an addition-curing type liquid silicone rubber composition, (A) Organopolysiloxane having a weight-average degree of polymerization of 50 to 2,000, containing two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass, (B) Organohydrogenpolysiloxane containing two or more hydrosilyl groups (SiH groups) in one molecule: The amount of hydrosilyl groups contained in the addition-curing liquid silicone rubber composition is such that it is 1 to 10 moles per mole of the total number of alkenyl groups bonded to silicon atoms in the addition-curing liquid silicone rubber composition. (C) Specific surface area of ​​50m² using the BET method 2 Silica fine powder with a content of 10-50 parts by mass of 1g or more, (D) Catalyst for hydrosilylation reaction: 1 to 500 ppm in mass of the catalyst metal element relative to the total mass of component (A), component (B), and component (C), (E) 1,2,3-benzotriazole or its derivative: in an amount of 2 to 500 moles per mole of catalyst metal atoms of component (D), and (F) (RSiO 3 / 2 ) n Silicone resin powder represented by (wherein R is a monovalent hydrocarbon group having 1 to 10 carbon atoms): 20 to 150 parts by mass, The present invention provides an addition-curing liquid silicone rubber composition containing [a specific substance].

[0012] Such an addition-curing liquid silicone rubber composition provides a cured silicone rubber product that has excellent colorability due to its high total light transmittance and excellent flame retardancy.

[0013] In this case, the addition-curing liquid silicone rubber composition can be made in which the component (E), 1,2,3-benzotriazole or its derivative, is represented by the following formula (1) (wherein Me is a methyl group). [ka]

[0014] This results in an addition-curing type liquid silicone rubber composition that provides a cured product with superior flame retardancy.

[0015] At this time, the (F) component is RSiO 3 / 2 An addition-curing liquid silicone rubber composition can be obtained in which the average particle size of the silicone resin powder, consisting of units, is 0.1 to 10 μm.

[0016] This results in an addition-curing type liquid silicone rubber composition that provides a cured product with superior flame retardancy.

[0017] At this time, the (F) component is RSiO 3 / 2In a silicone resin powder consisting of units, R is a methyl group, which can be used to create an addition-curing type liquid silicone rubber composition.

[0018] Such (F) components are readily available and economical.

[0019] At this time, a flame-retardant silicone rubber, which is the cured product of the above-mentioned addition-curing liquid silicone rubber composition, can be provided.

[0020] Such flame-retardant silicone rubber is a cured product that exhibits excellent flame retardancy and total light transmittance. [Effects of the Invention]

[0021] As described above, the addition-curing liquid silicone rubber composition of the present invention provides a cured silicone rubber product that has excellent colorability due to its high total light transmittance and excellent flame retardancy. The addition-curing liquid silicone rubber composition of the present invention corresponds to V-0 in the UL94 standard, and provides a cured silicone rubber product that has excellent flame retardancy and excellent colorability due to its higher total light transmittance than conventional compositions. [Modes for carrying out the invention]

[0022] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0023] As described above, there has been a need for an addition-curing type liquid silicone rubber composition that can provide a cured silicone rubber product with excellent colorability due to its high total light transmittance and excellent flame retardancy.

[0024] As a result of diligent research into the above-mentioned problems, the present inventors have developed an addition-curing type liquid silicone rubber composition, (A) Organopolysiloxane having a weight-average degree of polymerization of 50 to 2,000, containing two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass, (B) Organohydrogenpolysiloxane containing 2 or more hydrosilyl groups (SiH groups) in one molecule: an amount such that the hydrosilyl groups contained in the addition-curable liquid silicone rubber composition are 1 to 10 moles per 1 mole in total of alkenyl groups bonded to silicon atoms contained in the addition-curable liquid silicone rubber composition, (C) Silica fine powder having a specific surface area by the BET method of 50 m 2 / g or more: 10 to 50 parts by mass, (D) Hydrosilylation reaction catalyst: 1 to 500 ppm in terms of the mass of the catalytic metal element relative to the total mass of the aforementioned component (A), the aforementioned component (B) and the aforementioned component (C), (E) 1,2,3-benzotriazole or a derivative thereof: an amount of 2 to 500 moles per 1 mole of the catalytic metal atom of the aforementioned component (D), and (F) Silicone resin powder represented by (RSiO 3 / 2 ) n (wherein R is a monovalent hydrocarbon group having 1 to 10 carbon atoms): 20 to 150 parts by mass, The present inventors have found that an addition-curable liquid silicone rubber composition containing the above components can provide a cured product that is excellent in flame retardancy and has a higher total light transmittance than conventional ones, thus being excellent in colorability, and have completed the present invention.

[0025] In the present specification, unless otherwise specified, the viscosity is a value measured at 25°C by a rotational viscometer according to the method described in JIS K 7117-1:1999. In addition, the weight average degree of polymerization is a value determined as the weight average molecular weight (weight average degree of polymerization) in terms of polystyrene by GPC (gel permeation chromatography) analysis using tetrahydrofuran (THF) as a developing solvent measured under the following conditions. [Measurement Conditions] Developing solvent: Tetrahydrofuran Flow rate: 0.35 mL / min Detector: Differential refractive index detector (RI) Column: TSK Guardcolumn SuperH-L TSKgel SuperH4000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH3000(6.0mmI.D.×15cm×1) TSKgel SuperH2000(6.0mmI.D.×15cm×2) (All manufactured by Tosoh Corporation) Column temperature: 40℃ Sample injection volume: 10 μL (0.5 wt% tetrahydrofuran solution)

[0026] [(A) component] In the present invention, component (A), the organopolysiloxane, is an organopolysiloxane containing two or more alkenyl groups bonded to silicon atoms in one molecule and having a degree of polymerization of 50 to 2,000, and is the base polymer (main component) of the addition-curing liquid silicone rubber composition according to the present invention.

[0027] Furthermore, the molecular structure of component (A) is preferably linear. In particular, a diorganopolysiloxane is preferred, in which the main chain basically consists of repeating diorganosiloxane units and both ends of the molecular chain are sealed with triorganosiloxy groups. In addition, the position of the silicon atom to which the alkenyl group is attached in the molecule of the linear organopolysiloxane of component (A) may be either at the end of the molecular chain (i.e., the triorganosiloxy group) or in the middle of the molecular chain (i.e., a bifunctional diorganosiloxane unit located at the non-terminus of the molecular chain), or both. Particularly preferred as component (A) is a linear diorganopolysiloxane containing alkenyl groups attached to at least the silicon atoms at both ends of the molecular chain.

[0028] (A) The alkenyl group bonded to the silicon atom in component (A) is typically one having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms. Specific examples include vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, cyclohexenyl, and heptenyl groups, with vinyl being particularly preferred.

[0029] (A) The number of alkenyl groups bonded to silicon atoms in component (A) is two or more per molecule, preferably 2 to 100, and more preferably 2 to 50.

[0030] Component (A) includes monovalent substituted or unsubstituted hydrocarbon groups bonded to silicon atoms other than alkenyl groups, such as monovalent hydrocarbon groups typically having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms. Specific examples of monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, and heptyl groups; aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups; aralkyl groups such as benzyl and phenethyl groups; and halogen-substituted alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl groups. Methyl or phenyl groups are particularly preferred.

[0031] The weight-average degree of polymerization of component (A) is 50 to 2,000, preferably 100 to 1,500, and more preferably 200 to 1,000. If the weight-average degree of polymerization is lower than 50, the mechanical properties of the cured product of the resulting addition-curing liquid silicone rubber composition may deteriorate. If the weight-average degree of polymerization is greater than 2,000, the viscosity of the resulting addition-curing liquid silicone rubber composition may increase, resulting in poor handling.

[0032] The viscosity of component (A) is preferably 50 to 200,000 mPa·s, more preferably 400 to 150,000 mPa·s, and even more preferably 1,000 to 100,000 mPa·s at 25°C. If the viscosity of component (A) is 50 mPa·s or higher, the mechanical properties of the cured product of the resulting addition-curing liquid silicone rubber composition will be good. If the viscosity is 200,000 mPa·s or lower, the viscosity of the resulting addition-curing liquid silicone rubber composition will not be high, and the handling workability will also be good.

[0033] Specific examples of organopolysiloxanes of component (A) include: dimethylsiloxane-methylvinylsiloxane copolymer with trimethylsiloxy groups sealed at both ends of the molecular chain, methylvinylpolysiloxane with trimethylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer with trimethylsiloxy groups sealed at both ends of the molecular chain, dimethylpolysiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, and dimethylsiloxane-methylvinylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends of the molecular chain. Examples include nylsiloxane copolymers, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylpolysiloxane with divinylmethylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymers with divinylmethylsiloxy groups sealed at both ends of the molecular chain, dimethylpolysiloxane with trivinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymers with trivinylsiloxy groups sealed at both ends of the molecular chain, and mixtures of two or more organopolysiloxanes thereof.

[0034] (A) The organopolysiloxane may be used alone or in combination of two or more types.

[0035] [(B) Component] Component (B) is an organohydrogenpolysiloxane containing two or more hydrosilyl groups (SiH groups) in one molecule, and acts as a crosslinking agent for the composition according to the present invention.

[0036] The molecular structure of component (B), the organohydrogenpolysiloxane, may be linear, cyclic, branched, or three-dimensional network structure. In this case, the number of silicon atoms (or weight-average degree of polymerization) in one molecule is 2 or more, for example, 2 to 300, and particularly 4 to 200, and a liquid at 25°C is preferably used. The number of hydrosilyl groups contained in one molecule is 2 to 200, preferably 2 to 150, and more preferably 2 to 100. Note that the hydrosilyl groups may be at the end of the molecular chain, in the side chain (middle of the molecular chain), or both.

[0037] (B) The substituent bonded to the silicon atom is typically a monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms. Specific examples of monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, and heptyl groups; aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups; aralkyl groups such as benzyl and phenethyl groups; and halogen-substituted alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl groups. A methyl or phenyl group is particularly preferred.

[0038] Examples of such organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, methylhydrogenpolysiloxane with trimethylsiloxy groups sealed at both ends, dimethylsiloxane-methylhydrogensiloxane copolymer with trimethylsiloxy groups sealed at both ends, and dimethylhydrogen methylpolysiloxane with methylhydrogensiloxane at both ends, methylsiloxane-methylhydrogensiloxane copolymer, methylhydrogensiloxane-diphenylsiloxane copolymer with trimethylsiloxane at both ends, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer with trimethylsiloxane at both ends, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane-dimethylsiloxane copolymer, cyclic methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer, (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 A copolymer consisting of units, (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 Units and (C6H5)SiO 3 / 2 Examples include copolymers consisting of units, and in each of the above example compounds, some or all of the methyl groups are substituted with other alkyl groups such as ethyl groups and propyl groups, or aryl groups such as phenyl groups. Specifically, examples of such organohydrogenpolysiloxanes include compounds with the following structural formulas.

[0039] [ka] (In the formula, b is an integer between 2 and 200, and a, c, and d are integers between 0 and 200.)

[0040] The organohydrogen polysiloxane is preferably one with a viscosity of 0.5 to 10,000 mPa·s, and particularly preferably 1 to 300 mPa·s, at 25°C.

[0041] (B) The amount of component (B) is such that, for every 1 mole (or individual) of alkenyl groups bonded to silicon atoms in the addition-curable liquid silicone rubber composition, the amount of hydrosilyl groups contained in the addition-curable liquid silicone rubber composition is 1 to 10 moles (or individual), preferably 1.2 to 5 moles (or individual), and more preferably 1.5 to 3 moles (or individual). If the amount of hydrosilyl groups contained in the addition-curable liquid silicone rubber composition is less than 1 mole for every 1 mole of alkenyl groups bonded to silicon atoms in the addition-curable liquid silicone rubber composition, the addition-curable liquid silicone rubber composition will not cure sufficiently. Furthermore, if the amount of hydrosilyl groups contained in the addition-curable liquid silicone rubber composition exceeds 10 moles for every 1 mole of alkenyl groups bonded to silicon atoms in the addition-curable liquid silicone rubber composition, the heat resistance of the cured product obtained from the addition-curable liquid silicone rubber composition may be extremely poor.

[0042] (B) The organohydrogenpolysiloxane may be used alone or in combination of two or more types.

[0043] [(C) component] The specific surface area of ​​component (C) calculated by the BET method is 50 m². 2 Silica fine powder with a specific surface area of ​​50 m² or more acts as a reinforcing filler. That is, it imparts strength to the silicone rubber cured product obtained from the addition-curing liquid silicone rubber composition according to the present invention. By using silica fine powder as a reinforcing filler, it is possible to form a cured product that satisfies the required strength. Such silica fine powder has a specific surface area of ​​50 m² by the BET method. 2 The amount is 1 / g or more, preferably 50-400m 2 / g, comfortable 100~300m 2 It is / g. The specific surface area is 50m². 2If the amount is less than / g, it may not be possible to impart sufficient mechanical strength properties to the cured product of the addition-curing liquid silicone rubber composition according to the present invention. The method for measuring the specific surface area by the BET method can be the method described in JIS Z 8830:2013.

[0044] Such silica fine powders may be known ones that have been conventionally used as reinforcing fillers for cured silicone rubber, provided that their specific surface area is within the above range. Examples include fumed silica and precipitated silica.

[0045] The silica fine powder used may be silica fine powder whose surface has been hydrophobized with a surface treatment agent such as a (usually hydrolyzable) organosilicon compound such as chlorosilane, alkoxysilane, or organosilazane. In this case, the silica fine powder may be used that has been directly surface-hydrophobized with a surface treatment agent in its powder form beforehand. Alternatively, the silica fine powder may be used that has been surface-hydrophobized by adding a surface treatment agent during kneading with silicone oil (for example, an organopolysiloxane containing the alkenyl group of component (A) above).

[0046] (C) The surface treatment method for component (C) can be performed by known techniques. For example, the untreated silica fine powder and the surface treatment agent can be placed in a sealed mechanical kneading apparatus or fluidized bed at atmospheric pressure and mixed at room temperature (25°C) or under heat treatment (heating) in the presence of an inert gas as needed. In some cases, water or a catalyst (such as a hydrolysis accelerator) may be used to accelerate the surface treatment. After kneading, the surface-treated silica fine powder can be produced by drying. The amount of surface treatment agent to be added should be equal to or greater than the amount calculated from the coverage area of ​​the surface treatment agent.

[0047] Specific examples of surface treatment agents include silazanes such as hexamethyldisilazane, silane coupling agents such as methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltris(methoxyethoxy)silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane, and chloropropyltrimethoxysilane, as well as polymethylsiloxane and organohydrogenpolysiloxane. Surface treatment with these surface treatment agents can be used to produce hydrophobic silica fine powder. Silazanes are particularly preferred as surface treatment agents.

[0048] Furthermore, when using silica fine powder of component (C) that has been directly surface-hydrophobized in advance in powder form with a surface treatment agent containing alkenyl groups, it is preferable that the amount of hydrosilyl groups contained in the addition-curable liquid silicone rubber composition be 1 to 10 moles (or groups), preferably 1.2 to 5 moles (or groups), more preferably 1.5 to 3 moles (or groups), for every 1 mole (or group) of alkenyl groups bonded to silicon atoms contained in the addition-curable liquid silicone rubber composition.

[0049] This is because if there is 1 mole or more hydrosilyl groups per mole of alkenyl groups bonded to silicon atoms in the addition-curing liquid silicone rubber composition, the curing of the addition-curing liquid silicone rubber composition is stable. On the other hand, if there are 10 moles or less of hydrosilyl groups, the heat resistance of the cured product obtained from the addition-curing liquid silicone rubber composition is also stable.

[0050] The amount of component (C) is 10 to 50 parts by mass, preferably 15 to 45 parts by mass, and more preferably 20 to 40 parts by mass, per 100 parts by mass of organopolysiloxane (A). If the amount is less than 10 parts by mass, a cured product with sufficient strength cannot be obtained, and if the amount exceeds 50 parts by mass, the viscosity of the resulting addition-curing liquid silicone rubber composition may increase, resulting in poor handling.

[0051] (C) The silica fine powder of component (C) may be used alone or in combination of two or more types.

[0052] [(D) component] The catalyst for the hydrosilylation reaction of component (D) mainly promotes the addition reaction between the alkenyl group bonded to the silicon atom in component (A) and the hydrosilyl group in component (B). This catalyst for the hydrosilylation reaction is not particularly limited and includes, for example, platinum group metals such as platinum, palladium, and rhodium; chloroplatinic acid; alcohol-modified chloroplatinic acid; coordination compounds of chloroplatinic acid with olefins, vinylsiloxanes, or acetylene compounds; and platinum group metal compounds such as tetrakis(triphenylphosphine)palladium and chlorotris(triphenylphosphine)rhodium, with platinum group metal compounds being preferred.

[0053] The amount of component (D) is 1 to 500 ppm, preferably 5 to 100 ppm, relative to the total mass of components (A), (B), and (C), in terms of the mass of the catalyst metal element. If the amount is less than 1 ppm, the addition reaction will be significantly slowed or the addition-curing liquid silicone rubber composition will not cure, which is undesirable. If the amount exceeds 500 ppm, the heat resistance of the cured silicone rubber product may decrease.

[0054] The catalyst for the hydrosilylation reaction of component (D) may be used alone or in combination of two or more types.

[0055] [(E) component] Component (E) is 1,2,3-benzotriazole or a derivative thereof, and acts as a flame retardancy enhancer. While 1,2,3-benzotriazole or its derivative alone cannot provide sufficient flame retardancy when incorporated into an addition-curing silicone composition, combining it with component (F) below makes it possible to provide a silicone rubber with high total light transmittance and excellent flame retardancy (i.e., flame retardancy of V-0 according to the UL94 standard). In this invention, a benzotriazole derivative is a compound in which a hydrogen atom bonded to a carbon or nitrogen atom in benzotriazole is replaced by a monovalent organic group. Examples include a compound in which at least one carbon atom of benzotriazole is bonded to a substituted or unsubstituted monovalent hydrocarbon group, or an organosiloxysilylalkyl group, which is bonded to the nitrogen atom of benzotriazole via a carbonyl group, amide bond, or ester bond.

[0056] The component (E), 1,2,3-benzotriazole or its derivative, is preferably represented by the following formula (2). [ka]

[0057] In equation (2), R 1 These are, independently of each other, hydrogen atoms, or substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms. Examples of such monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, and cyclohexyl groups, or groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine, bromine, or chlorine, or cyano groups, for example, chloromethyl, chloropropyl, bromoethyl, trifluoropropyl, and cyanoethyl groups. 1 It is preferably a hydrogen atom, and particularly preferably R 1 All of them are hydrogen atoms.

[0058] R 2 This is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 14 carbon atoms, more preferably 1 to 10 carbon atoms, which may have a hydrogen atom or a heteroatom, and may have an alkoxysilyl group or organosiloxysilyl group at the terminal end. Examples of monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, and cyclohexyl groups, or groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine, bromine, chlorine, or cyano groups, such as chloromethyl, chloropropyl, bromoethyl, trifluoropropyl, and cyanoethyl groups. Examples of groups having heteroatoms include groups having an ether bond or a carbonyl group, such as monovalent hydrocarbon groups having a keto group, amide group, or carboxyl group. For example, a compound in which the monovalent hydrocarbon group is bonded to the nitrogen atom of benzotriazole via a keto group, amide group, or carboxyl group is an example. A compound having an alkoxysilyl group or organosiloxysilyl group at the terminal is a compound in which an alkoxysilyl alkyl group or organosiloxysilyl alkyl group is bonded to the nitrogen atom of benzotriazole via a keto group, amide group, or carboxyl group.

[0059] Examples of groups having a keto group, an amide group, or a carboxyl group include the groups represented by the following formulas (3) to (5). [ka] [ka] [ka] In formulas (3) to (5), R 3 and R 3’ These are, independently of each other, a hydrogen atom, or a monovalent hydrocarbon group such as an alkyl group having 1 to 10 carbon atoms, or -(CH2) p -Si(OR 4)3. R 4 is an alkyl group having 1 to 4 carbon atoms or SiR 5 There are 3 units, R 5 R is an alkyl group having 1 to 3 carbon atoms. 4 The group is preferably a methyl group or an ethyl group. p is an integer from 1 to 6, preferably an integer from 1 to 3. The monovalent hydrocarbon group is one of the groups listed above.

[0060] Benzotriazole derivatives having the group represented by formula (3), (4), or (5) above can be represented, for example, by the following formulas (3') to (5'). [ka] [ka] [ka] In each of the above formulas, R 1 , R 3 , and R 3’ The above applies. More preferably, all R 1 This is a hydrogen atom. Also, R 3 is, -(CH2) p -Si(OR 4 )3 is preferred. 3’ It is preferable that R is a hydrogen atom. 4 And p are as described above, preferably R 4 is a methyl group or an ethyl group, and p is an integer from 1 to 3.

[0061] Component (E) is particularly preferably R in formula (2) above. 1 and R 2 The compound is either 1,2,3-benzotriazole, in which all of the atoms are hydrogen atoms, or a benzotriazole derivative represented by any of the above formulas (3') to (5'). More preferably, the benzotriazole derivative is a compound represented by the following formula (6). [ka] (In the formula, R4 And p are as described above, preferably R 4 (where p is a methyl group or an ethyl group, and p is an integer from 1 to 3, particularly preferably p is 3)

[0062] As for the specific (E) component, the one represented by the following formula (1) (wherein Me is a methyl group) is particularly preferred. [ka]

[0063] The amount of component (E) is 2 to 500 moles per mole of catalyst metal atoms in component (D), preferably 2.5 to 300 moles, more preferably 3 to 200 moles, and most preferably 4 to 100 moles. If the amount of component (E) is less than the lower limit (2 moles), a sufficient flame retardancy improvement effect cannot be obtained, and if it exceeds the upper limit (500 moles), the silicone rubber may not harden.

[0064] [(F) component] (F) component is RSiO 3 / 2 The silicone resin powder (wherein R is a monovalent hydrocarbon group having 1 to 10 carbon atoms) is expressed in units (hereinafter sometimes referred to as T units), is in powder form at 25°C, and acts as a flame retardancy enhancer. The average particle size of component (F) is preferably 0.1 to 10 μm, more preferably 0.3 to 8 μm, and particularly preferably 0.5 to 5 μm. If the average particle size is 0.1 μm or more, the viscosity of the resulting silicone rubber composition is stably kept low, resulting in stable handling and workability. If the average particle size is 10 μm or less, the dispersibility in the silicone rubber composition can be stably maintained, so a stable and sufficient flame retardancy enhancement effect can be obtained. The average particle size can be measured by dispersing the sample in a suitable solvent and using laser diffraction / scattering (static light scattering) or dynamic light scattering.

[0065] Component (F), R, is a monovalent hydrocarbon group having 1 to 10 carbon atoms. Specific examples of R include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, and heptyl groups, aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups, and aralkyl groups such as benzyl and phenethyl groups. However, a methyl group is particularly preferred. Silicone resin powder in which R is a methyl group is readily available and economical.

[0066] There are no particular restrictions on the method for preparing component (F), but for example, it can be obtained by dropping RSi(OCH3)3 into an alkaline aqueous solution and hydrolyzing it. Furthermore, it is preferable to grind the obtained silicone resin using a bead mill, roll mill, wet jet mill, ball mill, hammer mill, etc., until the average particle size is 10 μm or less.

[0067] The amount of component (F) is 20 to 150 parts by mass, preferably 25 to 130 parts by mass, and more preferably 30 to 100 parts by mass, per 100 parts by mass of component (A). If the amount of component (F) is less than 20 parts by mass, a sufficient improvement in flame retardancy cannot be obtained, and if it exceeds 150 parts by mass, the viscosity of the resulting composition may increase, worsening the handling workability.

[0068] Component (F) may be used alone or in combination of two or more types.

[0069] [Reaction control agent] The reaction control agent is not particularly limited as long as it is a compound that has a hardening inhibitory effect on the catalyst for the hydrosilylation reaction of component (D), and known compounds can be used. Specific examples include phosphorus-containing compounds such as triphenylphosphine; nitrogen-containing compounds such as tributylamine, tetramethylethylenediamine, and benzotriazole; sulfur-containing compounds; acetylene-based compounds such as acetylene alcohols; compounds containing two or more alkenyl groups; hydroperoxy compounds; and maleic acid derivatives.

[0070] The degree of curing inhibition by reaction control agents varies depending on the chemical structure of the reaction control agent. Therefore, it is preferable to adjust the amount of reaction control agent added to the optimal amount for each reaction control agent used. By adding the optimal amount of reaction control agent, the addition-curing liquid silicone rubber composition will have excellent long-term storage stability and curing properties at room temperature.

[0071] [Non-reinforcement filler] (C) Component silica fine powder and (F) Component RSiO 3 / 2 Other fillers besides silicone resin powder consisting of units include, for example, crystalline silica (for example, with a specific surface area of ​​50 m² by the BET method). 2 Fillers such as quartz powder (less than 1g / g), hollow organic resin fillers, fumed titanium dioxide, magnesium oxide, iron oxide, aluminum hydroxide, magnesium carbonate, calcium carbonate, zinc carbonate, carbon black, diatomaceous earth, talc, kaolinite, and glass fibers; fillers obtained by surface hydrophobizing these fillers with organosilicon compounds such as organoalkoxysilane compounds, organochlorosilane compounds, organosilazane compounds, and low molecular weight siloxane compounds. These inorganic fillers can be blended to the extent that the total light transmittance of the resulting cured silicone rubber does not decrease.

[0072] [Three-dimensional reticular organopolysiloxane resin] The addition-curing liquid silicone rubber composition according to the present invention uses a tetrafunctional SiO as a reinforcing agent. 4 / 2 It may also contain a powdery, three-dimensional network organopolysiloxane resin containing units (hereinafter sometimes referred to as Q units) (however, the organopolysiloxane resin does not contain hydrosilyl groups). If necessary, monofunctional R 6 3SiO 1 / 2 The unit (hereinafter sometimes referred to as the M unit), and / or the bifunctional R 6 2SiO 2 / 2 Units (hereinafter sometimes referred to as D units), and / or trifunctional R 6 SiO 3 / 2The product may contain any number of units (hereinafter sometimes referred to as T units). However, this organopolysiloxane resin does not contain hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in its molecule, and is therefore clearly distinguishable from component (B). Furthermore, this organopolysiloxane resin has a three-dimensional network (resin-like) structure and is in powder form at 25°C, and is therefore clearly distinguishable from component (A) which has a linear structure. In addition, because it contains Q units, it is clearly distinguishable from component (F) which consists only of T units.

[0073] The above R 6 These are independently monovalent substituted or unsubstituted hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and include the same alkenyl groups and monovalent hydrocarbon groups exemplified in component (A) above. Specifically, examples include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, and heptyl groups; alkenyl groups such as vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, cyclohexenyl, and heptenyl groups; aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups; aralkyl groups such as benzyl and phenethyl groups; and halogen-substituted alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl groups. Methyl and vinyl groups are particularly preferred.

[0074] The content of alkenyl groups bonded to silicon atoms in the three-dimensional network organopolysiloxane resin is preferably 0 to 10 mol%, and particularly preferably 2 to 8 mol%, relative to the total amount of substituents bonded to silicon atoms.

[0075] Three-dimensional network organopolysiloxane resins are formed by SiO 4 / 2 While units are present, their content is preferably 20 to 75 mol%, particularly 30 to 65 mol%. Within this range, sufficient strength can be imparted to the cured product obtained from the addition-curing liquid silicone rubber composition of the present invention.

[0076] Here, the three-dimensional reticular organopolysiloxane resin contains, as described above, R 6 3SiO 1 / 2 Units, and / or, R 6 2SiO 2 / 2 Units, and / or, R 6 SiO 3 / 2 The unit may be included at will. The total content is preferably 0 to 70 mol%, and particularly preferably 0 to 50 mol%, in the organopolysiloxane resin of component (B).

[0077] Furthermore, in GPC (gel permeation chromatography) analysis of three-dimensional network organopolysiloxane resins using tetrahydrofuran (THF) as the developing solvent, the weight-average molecular weight in polystyrene terms is preferably in the range of 2,000 to 50,000, and particularly preferably in the range of 4,000 to 20,000. A weight-average molecular weight within the range of 2,000 to 50,000 provides an even more sufficient reinforcing effect.

[0078] [Other ingredients] In addition, for example, organopolysiloxanes containing one hydrogen atom bonded to a silicon atom per molecule and no other functional groups, organopolysiloxanes containing one alkenyl group bonded to a silicon atom per molecule and no other functional groups, non-functional organopolysiloxanes (so-called dimethyl silicone oil) that do not contain a hydrogen atom bonded to a silicon atom, an alkenyl group bonded to a silicon atom, or any other functional groups, organic solvents, creep hardening inhibitors, plasticizers, thixotropic agents, pigments, dyes, antifungal agents, etc., can be blended in an amount that does not reduce the total light transmittance.

[0079] <Preparation of addition-curing liquid silicone rubber composition> In addition to the components (A) to (F) above, an addition-curing liquid silicone rubber composition can be prepared by uniformly mixing other components as needed. The viscosity of the thus obtained addition-curing liquid silicone rubber composition at 25°C is preferably 10 to 5,000 Pa·s, more preferably 15 to 4,000 Pa·s, and even more preferably 20 to 3,000 Pa·s. If the viscosity is within the above range at 25°C, the handling workability is good.

[0080] The molding and curing methods for the addition-curing liquid silicone composition are not particularly limited and can be carried out according to conventionally known methods. For example, the molding method can be selected from injection molding, transfer molding, injection molding, compression molding, knife coating, roll coating, dipping, etc., to suit the purpose. As for the curing conditions, the above composition can be cured by heating at, for example, 80 to 230°C, preferably 100 to 200°C. The heating time is preferably about 30 seconds to 1 hour, and particularly preferably about 30 seconds to 10 minutes. Furthermore, if necessary, secondary vulcanization (post-curing) may be performed at 40 to 230°C for about 10 minutes to 24 hours. The thickness of the cured silicone rubber is not particularly limited, but is preferably 0.1 to 10 mm, and particularly preferably 0.5 to 6 mm.

[0081] The cured silicone rubber obtained by curing the addition-curing liquid silicone composition of the present invention has particularly excellent flame retardancy at the above thickness. In particular, a cured silicone rubber having a thickness of 0.5 mm or more, preferably 1 mm or more, can be made to have a flame retardancy of V-0 in the flame retardancy test based on the UL94 standard. The flame retardancy test based on the UL94 standard is performed by using, for example, a strip-shaped cured silicone rubber having a thickness of 1 mm as a test piece, applying a burner flame to the lower end of the test piece which is supported vertically, and burning it, and determining the flame retardancy performance by the rate at which the burning progresses (vertical combustion test). V-0 means that, after applying the flame twice, the duration of flaming combustion after the end of the flame application is 10 seconds or less for both the first and second applications, the sum of the duration of flaming combustion and flameless combustion after the end of the second application is 30 seconds or less, and the sum of the flaming combustion times of the five test pieces is 50 seconds or less. V-1 means that the flame contact is performed twice, and the duration of flaming after the end of the flame contact is 30 seconds or less for both the first and second contacts, the sum of the duration of flaming and flameless burning after the end of the second contact is 60 seconds or less, and the sum of the flaming burning times of the five test specimens is 250 seconds or less.

[0082] The addition-curing liquid silicone rubber composition of the present invention can provide a cured silicone rubber product with higher total light transmittance and superior flame retardancy and rubber properties than conventional products, making it useful for electrical appliances, cable terminal components, automotive materials, railway materials, housing materials, and the like where flame retardancy is required. [Examples]

[0083] The present invention will be specifically described below using examples of adjustments, embodiments, and comparative examples, but the present invention is not limited to these.

[0084] (A) The following components were used as components. (A): A linear dimethylpolysiloxane in which both ends of the molecular chain are sealed with vinyldimethylsiloxy groups, with a weight-average degree of polymerization of 750 and a viscosity of 30,000 mPa·s.

[0085] (B) The following components were used as components. (B): A linear dimethylsiloxane-methylhydrogensiloxane copolymer in which both ends of the molecular chain are sealed with trimethylsiloxy groups, with a weight-average degree of polymerization of 35 and a viscosity of 18 mPa·s (hydrosilyl group content: 0.0073 mol / g).

[0086] The following components were used as component (C): (C): Specific surface area is 300m² using the BET method. 2 Silica fine powder (product name: Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) in a quantity of / g.

[0087] The following components were used as component (D): (D): A dimethylpolysiloxane solution containing 1% by mass of chlorplatinic acid / 1,3-divinyltetramethyldisiloxane complex as a platinum atom content.

[0088] As component (E), the component represented by the following formula (1) was used. [ka]

[0089] The following components were used as component (F): (F-1):(CH3)SiO 3 / 2 A silicone resin powder consisting of units (average particle size 2 μm). This is component (F) according to the present invention. (F-2):(CH3)SiO 3 / 2 A silicone resin powder consisting of units (average particle size 5 μm). This is component (F) according to the present invention. (F-3): Carbon black (product name: Denka Black, manufactured by Denka Co., Ltd., average particle size 35nm). (F-4): Talc fine powder (product name: P-3, manufactured by Nippon Talc Co., Ltd., average particle size 5 μm). (F-5):(CH3)3SiO 1 / 2 Units and SiO 4 / 2 Silicone resin powder consisting of units (average particle size 0.1 μm). The average particle size of component (F) was measured using the MT3300 laser diffraction / scattering method manufactured by Microtrac Bell Co., Ltd. The instrument was sonicated before measurement, and water was used as the solvent.

[0090] The following components were used as curing control agents. (Curing control agent): 1-ethynylcyclohexanol.

[0091] [Example of base compound preparation] 60 parts by mass of base oil (A), 8 parts by mass of hexamethyldisilazane, 0.2 parts by mass of 1,3-divinyltetramethyldisiloxane, 2 parts by mass of water, and 40 parts by mass of silica fine powder (C) were placed in a kneader and mixed at room temperature for 1 hour. Then the temperature was raised to 150°C and mixing continued for 2 hours. After this, 30 parts by mass of base oil (A) were added and mixed until homogeneous to obtain a base compound.

[0092] [Examples 1-4, Comparative Examples 1-5] The components were mixed in the proportions shown in Tables 1 and 2 in a mixer at room temperature for 30 minutes to prepare an addition-curing liquid silicone rubber composition.

[0093] [Viscosity measurement method] Using a HAKKE MARS40 manufactured by Thermo Fisher Scientific, at 23°C and a shear rate of 10s, -1 The measurements were taken using [specified method]. The results are shown in Tables 1 and 2.

[0094] [Method for preparing cured silicone rubber products] Each of the compositions prepared above was press-cured at 120°C for 10 minutes, followed by post-curing in a 200°C dryer for 4 hours to produce a 130mm x 170mm x 1.0mm thick cured silicone rubber sheet.

[0095] [Method for measuring density] The rubber sheet prepared above was cut to a length of 40 mm and a width of 20 mm, and measured using the water displacement method described in JIS K 6249:2003. A DSG-1 automatic hydrometer manufactured by Toyo Seiki Co., Ltd. was used as the measuring device. The results are shown in Tables 1 and 2.

[0096] [Method for measuring total light transmittance] The total light transmittance of the rubber sheet prepared as described above was measured using a HZ-V3 haze meter manufactured by Suga Test Instruments Co., Ltd. The results are shown in Tables 1 and 2.

[0097] [Flame retardancy test method] The rubber sheet prepared above was cut to a length of 127 mm and a width of 12.7 mm to create flame-retardant test specimens. These specimens were subjected to flame-retardant testing in accordance with the UL-94 standard. If the flame reached the clamp securing the specimen to the apparatus, it was considered a complete burn. Complete burn indicates poor flame-retardant performance. The test results are shown in Tables 1 and 2.

[0098] [Table 1]

[0099] [Table 2]

[0100] As shown in Table 1, by incorporating a predetermined amount of silicone resin consisting of T units, it is possible to provide a cured silicone rubber product with excellent flame retardancy (V-0) according to the UL94 standard and high total light transmittance. On the other hand, as shown in Table 2, when the amount of silicone resin consisting of T units was small or not incorporated, sufficient flame retardancy (V-1) could not be obtained. Furthermore, when carbon black or talc powder was incorporated, the total light transmittance was low. In addition, when silicone resin consisting of M units and Q units was incorporated, the combustion performance was poor and the total light transmittance was low.

[0101] This specification includes the following embodiments: [1]: Addition-curing liquid silicone rubber composition, (A) Organopolysiloxane having a weight-average degree of polymerization of 50 to 2,000, containing two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass, (B) Organohydrogenpolysiloxane containing two or more hydrosilyl groups (SiH groups) in one molecule: The amount of hydrosilyl groups contained in the addition-curing liquid silicone rubber composition is such that it is 1 to 10 moles per mole of the total number of alkenyl groups bonded to silicon atoms in the addition-curing liquid silicone rubber composition. (C) Specific surface area of ​​50m² using the BET method 2 Silica fine powder with a content of 10-50 parts by mass of 1g or more, (D) Catalyst for hydrosilylation reaction: 1 to 500 ppm in mass of the catalyst metal element relative to the total mass of component (A), component (B), and component (C), (E) 1,2,3-benzotriazole or its derivative: in an amount of 2 to 500 moles per mole of catalyst metal atoms of component (D), and (F) (RSiO 3 / 2 ) n Silicone resin powder represented by (wherein R is a monovalent hydrocarbon group having 1 to 10 carbon atoms): 20 to 150 parts by mass, An addition-curing liquid silicone rubber composition containing [a specific substance]. [2]: The addition-curing liquid silicone rubber composition of [1] above, wherein the (E) component, 1,2,3-benzotriazole or a derivative thereof, is represented by the following formula (1) (wherein Me is a methyl group). [ka] [3]: The above (F) component is RSiO 3 / 2 An addition-curing liquid silicone rubber composition according to [1] or [2] above, wherein the average particle size of the silicone resin powder consisting of units is 0.1 to 10 μm. [4]: The above (F) component RSiO 3 / 2An addition-curing liquid silicone rubber composition according to [1], [2], or [3] above, wherein R in the silicone resin powder consisting of units is a methyl group. [5]: Flame-retardant silicone rubber which is a cured product of the addition-curing liquid silicone rubber composition of [1], [2], [3], or [4] above.

[0102] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. An addition-curing liquid silicone rubber composition, (A) Organopolysiloxane having a weight-average degree of polymerization of 50 to 2,000, containing two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass, (B) Organohydrogenpolysiloxane containing two or more hydrosilyl groups (SiH groups) in one molecule: The amount of hydrosilyl groups contained in the addition-curing liquid silicone rubber composition is 1 to 10 moles per mole of the total number of alkenyl groups bonded to silicon atoms contained in the addition-curing liquid silicone rubber composition. (C) Specific surface area of ​​50 m² by the BET method ２ Silica fine powder of 10 to 50 parts by mass, with a content of 1g or more. (D) Catalyst for hydrosilylation reaction: 1 to 500 ppm in mass of the catalyst metal element relative to the total mass of component (A), component (B), and component (C), (E) 1,2,3-benzotriazole or its derivative: in an amount of 2 to 500 moles per mole of catalyst metal atoms of component (D), and (F) (RSiO ３／２ ) ｎ Silicone resin powder represented by (wherein R is a monovalent hydrocarbon group having 1 to 10 carbon atoms): 20 to 150 parts by mass, An addition-curing liquid silicone rubber composition characterized by containing [a specific substance].

2. The addition-curing liquid silicone rubber composition according to claim 1, characterized in that the (E) component, 1,2,3-benzotriazole or a derivative thereof, is represented by the following formula (1) (wherein Me is a methyl group). 【Chemistry 1】

3. The aforementioned (F) component is RSiO ３／２ The addition-curing liquid silicone rubber composition according to claim 1, characterized in that the average particle size of the silicone resin powder consisting of units is 0.1 to 10 μm.

4. The aforementioned (F) component is RSiO ３／２ The addition-curing liquid silicone rubber composition according to claim 1, characterized in that R in the silicone resin powder consisting of units is a methyl group.

5. A flame-retardant silicone rubber that is a cured product of an addition-curing liquid silicone rubber composition according to any one of claims 1 to 4.

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