Addition-curable silicone composition and flame-retardant cured silicone rubber

Abstract

[Problem] The purpose of the present invention is to provide an addition-curable silicone composition that can be used to provide a cured silicone rubber having excellent flame retardancy and rubber characteristics with a small blending amount of flame retardant. [Solution] An addition-curable silicone composition containing: (A) 100 parts by mass of a linear organopolysiloxane that include two or more alkenyl groups bonded to a silicon atom per molecule and has a weight-average degree of polymerization of 50-2,000; (B) an organohydrogenpolysiloxane that includes two or more hydrogen atoms (hydrosilyl groups) bonded to a silicon atom per molecule, the ratio of the number of moles of hydrosilyl groups contained in the component (B) to the number of moles of silicon atom-bonded alkenyl groups contained in the component (A) being 1-10; (C) 1-50 parts by mass of silica fine powder that has a specific surface area of 50 m2 / g or greater according to the BET method; (D) a hydrosilylation reaction catalyst in a catalytic amount; and 1-50 parts by mass of metal-doped zinc oxide.

Description

Addition-curing silicone composition and flame-retardant silicone rubber cured product

[0001] The present invention relates to an addition-curing silicone composition and a flame-retardant silicone rubber cured product obtained by curing the composition.

[0002] Silicone rubber is used in various fields due to its excellent heat resistance, weather resistance, and electrical properties. However, silicone rubber is flammable; although it does not easily burn when exposed to flame, once ignited, it will continue to burn. Therefore, various developments have been attempted to improve the flame retardancy of silicone rubber.

[0003] For example, Patent Document 1 discloses an addition-curing type silicone rubber composition combining a triazole compound and a phosphate ester compound. Patent Document 1 states that this composition provides a silicone rubber cured product with high flame retardancy without impairing the properties of silicone rubber. Patent Document 2 also discloses an addition-curing type silicone rubber composition using a crosslinking agent with low heat loss. Patent Document 2 states that this composition provides a silicone rubber cured product with high flame retardancy. However, such silicone rubber compositions have not been able to meet the flame retardancy requirements for automotive and railway materials in recent years.

[0004] Patent Document 3 discloses a composition obtained by combining an addition-curing or condensation-curing silicone composition with quartz powder or aluminum oxide and nano-zinc oxide. Patent Document 3 states that this composition provides a cured silicone rubber product with high flame retardancy. Patent Document 4 discloses a composition obtained by combining an addition-curing silicone rubber composition with a hollow ceramic filler and quartz powder. Patent Document 4 states that this composition provides a cured silicone rubber product with excellent flame retardancy and low smoke emission. Patent Document 5 discloses a composition containing carbon black and aluminum hydroxide as flame retardancy enhancers in a silicone rubber composition. Patent Document 5 states that this composition provides a silicone rubber product with excellent fluidity, moldability, and curability, as well as flame retardancy.

[0005] Japanese Patent Publication No. 2016-094514, Japanese Patent Publication No. 2014-040522, Japanese Patent Publication No. 2023-509568, Japanese Patent Publication No. 2006-515898, Japanese Patent Publication No. 2004-161944

[0006] However, the above-mentioned compositions contain large amounts of inorganic compounds that improve flame retardancy in order to achieve high flame retardancy, which leads to the problem of high density in the resulting cured silicone rubber product. Furthermore, there are concerns that the mechanical strength and heat resistance of the resulting cured product may deteriorate when large amounts of inorganic compounds are included in the composition. In recent years, for the sake of energy saving, lower weight is preferred for automotive parts, and the level of rubber properties and heat resistance required for silicone rubber parts has increased in order to improve the performance and lifespan of automobiles.

[0007] Therefore, there is a need for the development of a silicone composition that can provide a silicone rubber cured product with lower density than conventional compositions and excellent flame retardancy and rubber properties. The present invention has been made in view of these circumstances and aims to provide an addition-curing type silicone composition that can provide a silicone rubber cured product with excellent flame retardancy and rubber properties with a small amount of flame retardant added.

[0008] As a result of diligent research to achieve the above objective, the inventors have found that by incorporating a small amount of metal-doped zinc oxide into an addition-curing silicone composition, a silicone rubber cured product with excellent flame retardancy can be obtained.

[0009] In other words, the present invention comprises: (1) (A) a linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule and having a weight-average degree of polymerization of 50 to 2,000: 100 parts by mass; (B) an organohydrogenpolysiloxane having at least two hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in one molecule: in an amount such that the ratio of the number of moles of hydrosilyl groups contained in component (B) to the number of moles of silicon atom-bonded alkenyl groups contained in component (A) is 1 to 10; (C) a specific surface area of ​​50 m² by the BET method. ２The present invention provides an addition-curing silicone composition containing: (D) silica fine powder having a concentration of 1 to 50 parts by mass, (E) a hydrosilylation reaction catalyst in a catalytic amount, and (D) metal-doped zinc oxide in 1 to 50 parts by mass.

[0010] Preferably, the present invention provides an addition-curing type liquid silicone composition comprising the above components (A) to (E). The addition-curing type silicone composition of the present invention yields a cured product with excellent flame retardancy and rubber properties.

[0011] Furthermore, the present invention provides the following addition-curing silicone compositions, silicone rubber cured products, and laminates. [2] The addition-curing silicone composition according to [1], wherein the metal in component (E) is aluminum or gallium. [3] The addition-curing silicone composition according to [1] or [2], wherein component (E) has a volume average particle size of 1 to 50 μm. [4] Silicone rubber which is a cured product of the addition-curing silicone composition according to any one of [1] to [3]. [5] A laminate having a base material and a cured product layer made of silicone rubber according to any one of [1] to [4], characterized in that the cured product layer is on one or both sides of the base material. [6] A laminate for electric wire or electrode protection material having a base material and a cured product layer made of silicone rubber according to any one of [1] to [4], characterized in that the cured product layer is on one or both sides of the base material. [7] The laminate according to [5] or [6], wherein the base material is glass cloth.

[0012] In this invention, preferably, component (E) is zinc oxide doped with aluminum or gallium. The addition-curing silicone composition provides a cured product with superior flame retardancy. More preferably, component (E) has a volume-average particle size of 1 to 50 μm. The addition-curing silicone composition provides a cured product with superior flame retardancy and rubber properties.

[0013] The present invention preferably provides a laminate of silicone rubber and a substrate, wherein the laminate has a cured layer of the above-mentioned addition-curing silicone composition on one or both sides of the substrate. The laminate has excellent flame retardancy. The substrate is preferably glass cloth. The laminate is a flexible laminate with excellent flame retardancy and can be suitably used as a protective material for electrical cables, electrodes, etc.

[0014] The silicone composition of the present invention corresponds to V-0 in the UL94 standard, exhibits excellent flame retardancy, and can provide a cured silicone rubber product with lower density and superior rubber properties compared to conventional products.

[0015] The present invention will be described in detail below.

[0016] In this specification, unless otherwise specified, viscosity is measured at 23°C using a rotational viscometer according to the method described in JIS K 7117-1:1999. The weight-average degree of polymerization is the weight-average molecular weight (weight-average degree of polymerization) on a polystyrene basis, obtained by GPC (gel permeation chromatography) analysis using tetrahydrofuran (THF) as the 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 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH2000 (6.0 mm I.D. × 15 cm × 2) (All manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 10 μL (0.5 wt% tetrahydrofuran solution)

[0017] [Component (A)] Component (A) 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. Component (A) is the base polymer (main component) of the addition-curing silicone composition according to the present invention.

[0018] The molecular structure of component (A) is characterized by being 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. Furthermore, in the molecule of the linear organopolysiloxane, the position of the silicon atom to which the alkenyl group is attached 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.

[0019] Examples of alkenyl groups bonded to the silicon atom include alkenyl groups having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms. Examples include vinyl groups, allyl groups, propenyl groups, butenyl groups, pentenyl groups, hexenyl groups, cyclohexenyl groups, and heptenyl groups. Vinyl groups are particularly preferred.

[0020] (A) In component (A), the number of alkenyl groups bonded to the silicon atom is two or more per molecule, preferably 2 to 100, and more preferably 2 to 50.

[0021] In component (A), monovalent substituted or unsubstituted hydrocarbon groups bonded to silicon atoms other than alkenyl groups include, for example, monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms. 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.

[0022] The weight-average degree of polymerization of component (A) is 50 to 2,000, preferably 100 to 1,500, and more preferably 120 to 1,000. If the weight-average degree of polymerization is lower than the above lower limit value, the mechanical properties of the cured product of the resulting addition-curable silicone composition may deteriorate. If the weight-average degree of polymerization is greater than the above upper limit value, the viscosity of the resulting addition-curable silicone composition may increase, and the handling workability may deteriorate.

[0023] The viscosity of component (A) at 23°C is preferably 50 to 200,000 mPa·s, more preferably 100 to 150,000 mPa·s, and even more preferably 400 to 100,000 mPa·s. If the viscosity of component (A) is at least the above lower limit value, the mechanical properties of the cured product of the resulting addition-curable silicone composition will be good. If the viscosity of component (A) is at most the above upper limit value, the viscosity of the resulting addition-curable silicone composition will not increase, and the handling workability will also be suitable.

[0024] Examples of the organopolysiloxane of component (A) include dimethylsiloxane-methylvinylsiloxane copolymer blocked with trimethylsiloxy groups at both ends of the molecular chain, methylvinylpolysiloxane blocked with trimethylsiloxy groups at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer blocked with trimethylsiloxy groups at both ends of the molecular chain, dimethylpolysiloxane blocked with dimethylvinylsiloxy groups at both ends of the molecular chain, methylvinylpolysiloxane blocked with dimethylvinylsiloxy groups at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer blocked with dimethylvinylsiloxy groups at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer blocked with dimethylvinylsiloxy groups at both ends of the molecular chain, dimethylpolysiloxane blocked with divinylmethylsiloxy groups at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer blocked with divinylmethylsiloxy groups at both ends of the molecular chain, dimethylpolysiloxane blocked with trivinylsiloxy groups at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer blocked with trivinylsiloxy groups at both ends of the molecular chain, and mixtures composed of two or more of these organopolysiloxanes.

[0025] The linear organopolysiloxane of component (A) may be used alone or in combination of two or more.

[0026] [Component (B)] Component (B) is an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule and acts as a crosslinking agent for this composition.

[0027] The molecular structure of the organohydrogenpolysiloxane of component (B) may be any of linear, cyclic, branched, and three-dimensional network structures. Preferably, the number of silicon atoms (or degree of polymerization) in one molecule is 2 to 300, particularly preferably about 4 to 200, and a siloxane liquid at 23 °C is preferably used. Also, the number of hydrosilyl groups contained in one molecule is 2 to 200, preferably 2 to 150, more preferably 2 to 100. The hydrosilyl group may be at the molecular chain end, in the side chain (in the middle of the molecular chain), or both.

[0028] Examples of the substituent bonded to the silicon atom of component (B) include monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms. Examples of the monovalent hydrocarbon group include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, cyclohexyl group, and heptyl group; aryl groups such as phenyl group, tolyl group, xylyl group, and naphthyl group; aralkyl groups such as benzyl group and phenethyl group; and halogen-substituted alkyl groups such as chloromethyl group, 3-chloropropyl group, and 3,3,3-trifluoropropyl group. Particularly, a methyl group or a phenyl group is preferable.

[0029] Examples of the organohydrogenpolysiloxane include, for example, 1,1,3,3 - tetramethyldisiloxane, 1,3,5,7 - tetramethylcyclotetrasiloxane, methylhydrogen - cyclopolysiloxane, methylhydrogen - siloxane / dimethylsiloxane cyclic copolymer, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, both - ends - trimethylsiloxy - group - blocked methylhydrogenpolysiloxane, both - ends - trimethylsiloxy - group - blocked dimethylsiloxane / methylhydrogen - siloxane copolymer, both - ends - dimethylhydrogensiloxy - group - blocked dimethylpolysiloxane, both - ends - dimethylhydrogensiloxy - group - blocked dimethylsiloxane / methylhydrogen - siloxane copolymer, both - ends - trimethylsiloxy - group - blocked methylhydrogen - siloxane / diphenylsiloxane copolymer, both - ends - trimethylsiloxy - group - blocked methylhydrogen - siloxane / diphenylsiloxane / dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogen - siloxane / dimethylsiloxane copolymer, cyclic methylhydrogen - siloxane / diphenylsiloxane / dimethylsiloxane copolymer, a copolymer composed of (CH ３ ), ２ HSiO １／２ units and SiO ４／２ units, a copolymer composed of (CH ３ ), ２ HSiO １／２ units, SiO ４／２ units, and (C ６ H ５ )SiO ３／２ units, etc. Also, among the above - exemplified compounds, those in which part 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 can be mentioned.

[0030] Examples of the organohydrogenpolysiloxane include, for example, compounds having the following structural formula. (In the formula, e is an integer from 2 to 200, and f, g, and h are each an integer from 0 to 200)

[0031] The above organohydrogenpolysiloxane preferably has a viscosity of 0.5 to 10,000 mPa·s at 23°C, and more preferably has a viscosity of 1 to 300 mPa·s.

[0032] In this composition, the amount of component (B) is such that, for every 1 mole (or individual) of alkenyl groups bonded to silicon atoms in component (A) contained in this composition, there are 1 to 10 moles (or individual) of hydrosilyl groups in component (B), preferably 1.2 to 5 moles (or individual), and more preferably 1.5 to 3 moles (or individual). If the molar ratio of hydrosilyl groups in component (B) to the total 1 mole of silicon atom-bonded alkenyl groups in component (A) contained in the composition is less than 1 mole, the resulting addition-curable silicone composition will not cure sufficiently. Furthermore, if the number of moles of hydrosilyl groups in component (B) exceeds 10 moles, the heat resistance of the cured product obtained from the addition-curable silicone composition may be extremely poor.

[0033] (B) Organohydrogenpolysiloxanes may be used individually or in combination of two or more types.

[0034] [Component (C)] Component (C) has a specific surface area of ​​50 m² as determined by the BET method. ２ This is a silica fine powder having a concentration of 1 / g or more, and acts as a reinforcing filler. Component (C) imparts strength to the silicone rubber cured product obtained from the addition-curing silicone composition of the present invention. By incorporating this silica fine powder as a reinforcing filler into the addition-curing silicone composition, it is possible to provide a cured product that satisfies the strength required by the present invention. The silica fine powder has a specific surface area of ​​50 m² by the BET method. ２ It has a concentration of 1 / g or more, preferably 50 to 400 m ２ It has a concentration of / g, and more preferably 100 to 300 m ２ It is preferable that the specific surface area is less than the above lower limit. If the specific surface area is less than the above lower limit, sufficient mechanical strength properties cannot be imparted to the cured product of the addition-curing silicone composition according to the present invention.

[0035] The above-mentioned silica fine powder may be any silica having a specific surface area within the above range, and may be any known silica that has been conventionally used as a reinforcing filler for cured silicone rubber. Examples include fumed silica and precipitated silica.

[0036] The above-mentioned silica fine powder may be silica fine powder whose surface has been hydrophobized with a surface treatment agent such as chlorosilane, alkoxysilane, and organosilazane (usually hydrolyzable) organosilicon compounds. The silica fine powder may also be directly surface-hydrophobized with a surface treatment agent in its powder form beforehand. Alternatively, the surface treatment agent may be added during the kneading of the silica fine powder and silicone oil (for example, an organopolysiloxane containing the alkenyl group of component (A) above) to perform surface hydrophobization of the silica fine powder.

[0037] (C) The surface hydrophobic treatment method for silica fine powder can follow 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 (23°C) or under heat treatment (heating) in the presence of an inert gas as needed. Depending on the case, 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 used is not particularly limited, but it should be greater than or equal to the amount calculated from the coating area of ​​the surface treatment agent used.

[0038] 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, polymethylsiloxane, organohydrogenpolysiloxane, etc. Surface treatment with these agents can be used to produce hydrophobic silica fine powder. Silazanes are particularly preferred as surface treatment agents.

[0039] When the above-mentioned silica fine powder is used in a powder state and has been directly surface-hydrophobized with a surface treatment agent containing alkenyl groups, it is preferable to blend the composition in such a ratio that the hydrosilyl groups contained in component (B) are 1 to 10 moles (or groups), preferably 1.2 to 5 moles (or groups), and 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 entire composition (for example, alkenyl groups in the surface treatment agents of component (A) and component (C)).

[0040] If the molar ratio of hydrosilyl groups to silicon-bonded alkenyl groups in an addition-curable silicone composition is less than 1 mole, the addition-curable silicone composition may not cure sufficiently. On the other hand, if the molar ratio of hydrosilyl groups to silicon-bonded alkenyl groups in an addition-curable silicone composition exceeds 10 moles, the heat resistance of the cured product obtained from the addition-curable silicone composition may deteriorate drastically.

[0041] In this composition, the amount of component (C) is 1 to 50 parts by mass, preferably 10 to 45 parts by mass, and more preferably 15 to 40 parts by mass, per 100 parts by mass of component (A). If the amount of component (C) is less than the lower limit, a cured product with sufficient strength cannot be obtained. If the amount of component (C) exceeds the upper limit, the viscosity of the resulting addition-curing silicone composition will increase, which may worsen the handling properties.

[0042] The above silica fine powder (C) may be used alone or in combination of two or more types.

[0043] [Component (D)] Component (D) is a hydrosilylation catalyst that primarily promotes the addition reaction between the alkenyl group bonded to the silicon atom in component (A) and the hydrosilyl group in component (B). The hydrosilylation catalyst is not particularly limited and may be any known platinum group metal catalyst. More specifically, examples include 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. Platinum group metal compounds are preferred. The above hydrosilylation catalysts may be used individually or in combination of two or more.

[0044] In the present invention, the amount of (D) hydrosilylation reaction catalyst blended is sufficient to allow the addition curing reaction to proceed. Preferably, it is 1 to 500 ppm, and more preferably 5 to 100 ppm, in terms of the mass of the catalyst metal element relative to the blended mass of component (A). If the amount of component (D) blended is less than the above lower limit, the addition reaction may be significantly delayed, or the addition-curable silicone composition may not cure. If the amount of component (D) blended exceeds the above upper limit, the heat resistance of the cured silicone rubber may decrease.

[0045] [Component (E)] Component (E) is metal-doped zinc oxide and acts as a flame retardant enhancer. In this invention, "doped" means that a small amount of a metal other than zinc is added to zinc oxide. Therefore, in this invention, component (E) is a composite fine particle mainly composed of zinc oxide and containing a small amount of a metal other than zinc.

[0046] In the present invention, the metal doped (added) to zinc oxide is preferably aluminum or gallium. Zinc oxide doped with aluminum or gallium provides better flame retardancy to the resulting addition-curing silicone composition. Component (E) may be one type of metal-doped zinc oxide or two or more types in combination. The amount of metal added to the zinc oxide doped is preferably 0.1 to 5% by mass ratio to the mass of zinc oxide, and preferably 0.2 to 3%. The method for producing the metal-doped zinc oxide is not particularly limited and can be any conventionally known method. In the present invention, the metal-doped zinc oxide may be a commercially available product, for example, 23-K (aluminum-doped zinc oxide), Pazet CK (aluminum-doped zinc oxide), and Pazet GK (gallium-doped zinc oxide) manufactured by Hakusui Tech Co., Ltd. can be used.

[0047] Component (E) preferably has a volume-average diameter of 1 to 50 μm, more preferably 1 to 40 μm, even more preferably 1 to 30 μm, even more preferably 2 to 20 μm, and even more preferably 2 to 10 μm. If the volume-average diameter is less than 1 μm, the viscosity of the resulting silicone composition will be high, which may worsen the handling properties. If the volume-average diameter exceeds the above upper limit, the dispersibility in the silicone composition will deteriorate, and a sufficient flame retardancy improvement effect may not be obtained. The volume-average diameter of component (E) is measured using an MT3300 manufactured by Microtrac-Bell Co., Ltd.

[0048] Metal-doped zinc oxide may be treated with surface treatment agents such as organosilicon compounds. Surface-treated zinc oxide powder has improved affinity with silicone resin, resulting in lower viscosity of the composition and improved handling.

[0049] The method for surface-treating metal-doped zinc oxide with organosilicon compounds or the like is not particularly limited. For example, the untreated zinc oxide 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 (23°C) or under heat treatment (heating) in the presence of an inert gas as needed. Alternatively, water or a catalyst (such as a hydrolysis accelerator) can be used to accelerate the surface treatment. After kneading, the surface-treated zinc oxide powder can be produced by drying.

[0050] The amount of surface treatment agent to be added should be equal to or greater than the amount calculated from the coating area of ​​the surface treatment agent used. For example, 0.1 to 20 parts by mass, preferably 0.1 to 15 parts by mass, and more preferably 0.1 to 10 parts by mass of surface treatment agent may be added to 100 parts by mass of untreated zinc oxide powder.

[0051] Examples of organosilicon compounds include silazanes such as hexamethyldisilazane and 1,1,3,3,5,5-hexamethylcyclotrisilazane; alkoxysilanes such as methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltris(methoxyethoxy)silane, and chloropropyltrimethoxysilane; chlorosilanes such as trimethylchlorosilane and dimethyldichlorosilane; silane coupling agents such as trimethylsilanol and hydroxypentamethyldisiloxane; or polymethylsiloxane, organohydrogenpolysiloxane, etc. However, it is preferable that the organosilicon compound is different from the components (A) and (B) described above.

[0052] The amount of component (E) is 1 to 50 parts by mass, preferably 1 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of component (A). If the amount of component (E) is less than the lower limit, a sufficient flame retardancy improvement effect cannot be obtained. If the amount of component (E) exceeds the upper limit, the mechanical strength of the resulting cured product may deteriorate.

[0053] • Reaction Control Agent The composition of the present invention may contain a 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 (D) hydrosilylation reaction catalyst, and any known compound will suffice. 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 1-ethynylcyclohexanol and acetylene alcohols; compounds containing two or more alkenyl groups; hydroperoxide compounds; and maleic acid derivatives.

[0054] The degree of curing inhibition effect obtained by the reaction control agent varies depending on the chemical structure of the reaction control agent. The amount of reaction control agent to be added should be adjusted to the optimal amount according to the structure of the reaction control agent used. Adding the optimal amount of reaction control agent is preferable because it results in an addition-curing silicone composition with excellent long-term storage stability and curing properties at room temperature.

[0055] - Non-reinforcing fillers (C) may include non-reinforcing fillers other than silica powder and (E) metal-doped zinc oxide. Examples of fillers include crystalline silica (for example, with a specific surface area of ​​50 m² by the BET method). ２Examples include fillers such as quartz powder (less than 1g / g), hollow organic resin fillers, polymethylsilsesquioxane fine particles (so-called silicone resin powder), 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; silicone rubber powder; and silicone resin powder.

[0056] - Three-dimensional network organopolysiloxane resin The composition of the present invention may contain a powdered three-dimensional network organopolysiloxane resin (provided that the organopolysiloxane resin does not contain hydrosilyl groups) as a reinforcing agent. Preferably, a trifunctional R １ SiO ３／２ Unit and tetrafunctional SiO ４／２ It is basically composed of one or more branched siloxane units selected from the units. Monofunctional R １ ３ SiO １／２ Unit and / or bifunctional R １ ２ SiO ２／２ The organopolysiloxane resin may contain any number of units. However, the organopolysiloxane resin does not contain hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in its molecule. Furthermore, the organopolysiloxane resin has a three-dimensional network (resin-like) structure and is in powder form at 23°C, so it is clearly distinguishable from component (A) which has a linear structure.

[0057] In each of the above siloxane units, R １These are independently substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms. Examples include the alkenyl groups and monovalent hydrocarbon groups exemplified in component (A) above. 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; halogen-substituted alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl groups, and in particular, methyl or vinyl groups are preferred.

[0058] In the above-described three-dimensional network organopolysiloxane resin, the content of alkenyl groups bonded to silicon atoms is preferably 0 to 10 mol%, and particularly preferably 2 to 8 mol%, relative to the total amount of substituents bonded to silicon atoms.

[0059] Three-dimensional reticular organopolysiloxane resins form a three-dimensional reticular structure, R １ SiO ３／２ Units and SiO ４／２ The composition may contain one or more siloxane units selected from the available units. The total amount of siloxane units is preferably 20 to 75 mol%, particularly 30 to 65 mol%, in the three-dimensional network organopolysiloxane resin. Being within this range allows for sufficient strength to be imparted to the cured product obtained from the addition-curing silicone composition of the present invention.

[0060] As described above, the three-dimensional network organopolysiloxane resin is R １ ３ SiO １／２ Units and / or R １ ２ SiO ２／２ The unit may be included as desired. The total content is preferably 0 to 70 mol%, and more preferably 0 to 50 mol%, in the three-dimensional network organopolysiloxane resin.

[0061] The weight-average molecular weight of the above three-dimensional network organopolysiloxane resin is preferably in the range of 2,000 to 50,000, and particularly preferably in the range of 4,000 to 20,000. A sufficient reinforcing effect can be obtained when the weight-average molecular weight is in the range of 2,000 to 50,000. This weight-average molecular weight is the weight-average molecular weight on a polystyrene basis in GPC (gel permeation chromatography) analysis using tetrahydrofuran (THF) as the developing solvent.

[0062] Other Components: In addition to the above components, the composition of the present invention may also contain, for example, an organopolysiloxane having one hydrogen atom bonded to a silicon atom per molecule and not containing any other functional groups, an organopolysiloxane having one alkenyl group bonded to a silicon atom per molecule and not containing any other functional groups, a non-functional organopolysiloxane (so-called dimethyl silicone oil) that does not contain a hydrogen atom bonded to a silicon atom, an alkenyl group bonded to a silicon atom, or any other functional groups, an organic solvent, a creep hardening inhibitor, a plasticizer, a thixotropic agent, a pigment, a dye, and an antifungal agent.

[0063] <Preparation of Addition-Curing Silicone Composition> The addition-curing silicone composition of the present invention can be prepared by uniformly mixing components (A) to (E) above and any other optional components. The viscosity of the resulting addition-curing silicone composition at 23°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 23°C, the handling workability is good. The addition-curing silicone composition of the present invention is preferably liquid at 23°C.

[0064] The molding and curing methods for the addition-curable 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, and compression molding to find the most suitable method for the purpose. As for the curing conditions, the 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, a secondary vulcanization (post-cure) 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 0.5 to 10 mm, and particularly preferably 1 to 6 mm.

[0065] The cured silicone rubber obtained by curing the silicone composition of the present invention has excellent flame retardancy, and in particular, cured products having the thickness described above have particularly excellent flame retardancy. In particular, cured silicone rubber having a thickness of 0.5 mm or more, preferably 1 mm or more, can achieve 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, for example, to use a strip-shaped cured silicone rubber with a thickness of 1 mm as a test piece, to apply a burner flame to the lower end of the test piece which is supported vertically and burn it, and to determine the flame retardancy performance by the rate at which the combustion progresses (vertical combustion test). V-0 means that after two flame applications, 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 flame 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.

[0066] The cured silicone rubber product obtained by curing the silicone composition of the present invention can have low density while possessing the excellent flame retardancy described above. Preferably, the density is 1.00 to 1.50 g / cm³ as measured according to JIS K 6249:2003.３ More preferably 1.05 to 1.30 g / cm³ ３ It can have.

[0067] The silicone composition of the present invention can provide a cured silicone rubber product that maintains low density while exhibiting excellent flame retardancy and good rubber properties. Therefore, the silicone composition is useful for electrical appliances, cable terminal components, automotive materials, railway materials, housing materials, and the like, where flame retardancy is required.

[0068] <Laminate of Silicone Rubber and Substrate> The present invention provides a laminate having a substrate and a cured layer made of the above-mentioned silicone rubber, characterized in that the cured layer is present on one or both sides of the substrate. The laminate of silicone rubber and substrate can be manufactured by coating one or both sides of the substrate with the above-mentioned silicone composition and curing it by heat. Conventional methods can be used for coating, and examples include knife coating, pipe coating, gravure coating, roll coating, kiss coating, dipping coating, dip squeeze coating, comma direct coating, and comma reverse coating.

[0069] If the viscosity of the addition-curing silicone composition obtained in the present invention is high, a method can be adopted to reduce the viscosity of the composition by diluting it with an organic solvent such as toluene, xylene, and hydrocarbons, or a low-viscosity silicone oil, in order to facilitate coating by the method described above, and then coating the composition.

[0070] The above-mentioned base material is not particularly limited, but glass cloth is preferred. When the base material is glass cloth, the resulting laminate of silicone rubber and glass cloth has excellent flame retardancy and strength, as well as flexibility, making it ideal as a protective material for cables, electrodes, and the like.

[0071] 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.

[0072] The following components were used as component (A): (A-1): A linear dimethylpolysiloxane with both ends of the molecular chain sealed with vinyldimethylsiloxy groups, a weight-average degree of polymerization of 700, and a viscosity of 30,000 mPa·s at 23°C. (A-2): A linear dimethylpolysiloxane with both ends of the molecular chain sealed with vinyldimethylsiloxy groups, a weight-average degree of polymerization of 200, and a viscosity of 1,000 mPa·s at 23°C.

[0073] (B) The following component was used as component (B): A linear dimethylsiloxane-methylhydrogensiloxane copolymer (hydrosilyl group content 0.0073 mol / g) in which both ends of the molecular chain are sealed with trimethylsiloxy groups, has a weight-average degree of polymerization of 35, and has a viscosity of 18 mPa·s at 23°C.

[0074] (C) The following component was used as component (C): Specific surface area of ​​300 m² by the BET method. ２ Silica fine powder containing / g (product name: Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.)

[0075] (D) The following component was used as component: Dimethylpolysiloxane solution containing 1% by mass of chloroplatinic acid / 1,3-divinyltetramethyldisiloxane complex as the platinum atom content.

[0076] The following components were used as component (E): (E-1): 23-K (manufactured by Hakusui Tech Co., Ltd., volume average diameter 6 μm, aluminum-doped zinc oxide) (E-2): Pazet CK (manufactured by Hakusui Tech Co., Ltd., volume average diameter 6 μm, aluminum-doped zinc oxide)

[0077] In addition, the following zinc oxides were used for comparative examples: (E'-3): JIS standard type 2 zinc oxide (manufactured by Hakusui Tech Co., Ltd., average volume diameter 3 μm, zinc oxide) (E'-4): Calcined zinc oxide (manufactured by Hakusui Tech Co., Ltd., average volume diameter 13 μm, zinc oxide) (E'-5): Zinc oxide (manufactured by Fujifilm Wako Pure Chemical Industries Ltd., average volume diameter 5 μm, nano zinc oxide)

[0078] The volume-average diameter of component (E) was measured using an MT3300 manufactured by Microtrac-Bell Corporation. Water was used as the solvent.

[0079] [Preparation Example 1] 60 parts by mass of base oil (A-1), 8 parts by mass of hexamethyldisilazane (surface treatment agent for component (C)), 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 that, 30 parts by mass of base oil (A-1) were added and mixed until homogeneous to obtain a base compound.

[0080] [Examples 1-9, Comparative Examples 1-13] The base compound obtained in Preparation Example 1 above and (A-1) or (A-2) above, and each component listed in Tables 1-3 as a further base oil were mixed in a mixer at room temperature for 30 minutes in the proportions shown in the table to prepare an addition-curing silicone composition.

[0081] [Viscosity Measurement Method] The viscosity of the addition-curing silicone composition was measured using a HAKKE MARS40 manufactured by Thermo Fisher Scientific Co., Ltd. at 23°C with a shear rate of 0.9 s. －１ The measurements were taken using [specified method]. The results are shown in Tables 1-3.

[0082] [Flame Retardancy Test Method] Each of the addition-curing silicone compositions prepared above was press-cured at 120°C for 10 minutes to produce a 130 mm x 170 mm x 1.0 mm thick cured silicone rubber sheet. This rubber sheet was cut to a length of 127 mm and a width of 12.7 mm to prepare flame retardancy test specimens. A flame retardancy test was performed on these specimens in accordance with the UL-94 standard. If the flame reached the clamp that fixed the specimen to the apparatus, it was evaluated as total burning. Total burning indicates poor flame retardancy. The test results are shown in Tables 1 to 3.

[0083] [Measurement of Rubber Properties] Each of the compositions prepared above was press-cured at 120°C for 10 minutes to produce a sheet with dimensions of 130 mm × 170 mm × 2.0 mm thick, in accordance with JIS K 6249:2003. The density, hardness, elongation at break, and tensile strength of the sheet were measured according to JIS K 6249:2003, and the results are shown in Tables 1 to 3.

[0084] <Method for preparing a laminate of silicone rubber and glass cloth> Glass cloth (manufactured by Unitika Ltd., 19 warp threads / 25 mm, 18 weft threads / 25 mm, thickness 0.20 mmt) is coated with 200 g / m of each of the addition-curing silicone compositions prepared according to the compositions described in Tables 1 and 2. ２ The material was coated using a knife coater to achieve the desired result. Then, the silicone rubber coating composition was cured in a 200°C dryer for 1 minute. A flame retardancy test was performed on the resulting laminate, consisting of the cured silicone rubber and glass cloth, in accordance with the UL-94 standard. The results are shown in Table 3.

[0085]

[0086]

[0087]

[0088] As shown in Table 1, the addition-curing silicone composition of the present invention, by incorporating a predetermined amount of metal-doped zinc oxide, can provide a cured silicone rubber product that has V-0 flame retardancy according to the UL94 standard and excellent rubber properties (Examples 1 to 6). On the other hand, as shown in Table 2, compositions with too little metal-doped zinc oxide and compositions without a flame retardancy enhancer cannot obtain a silicone rubber with sufficient flame retardancy (Comparative Examples 1 and 2).

[0089] Furthermore, as shown in Table 2, compositions containing undoped zinc oxide, calcined zinc oxide, or nano-zinc oxide in an amount equivalent to that of the (E) flammability enhancer of the present invention could not obtain sufficient flame retardancy (Comparative Examples 3-7). While compositions containing a large excess of these zinc oxides improved flame retardancy, the resulting cured silicone rubber had a higher density, resulting in decreased strength and elongation at break (Comparative Example 8).

[0090] Furthermore, as shown in Table 3, even when the addition-curing silicone composition of the present invention is coated onto glass cloth and cured, it exhibits flame retardancy of V-0 according to the UL94 standard (Examples 7-9). On the other hand, even when a composition without a flame retardancy enhancer, or a silicone composition containing metal-doped zinc oxide, calcined zinc oxide, or nano-zinc oxide in the same amount as in the present invention is coated onto glass cloth and cured, sufficient flame retardancy could not be obtained.

[0091] As described above, the addition-curing silicone composition of the present invention, by incorporating metal-doped zinc oxide, can impart exceptionally superior flame retardancy to the cured silicone rubber compared to compositions containing ordinary zinc oxide. Furthermore, in the addition-curing silicone composition of the present invention, a good flame retardant effect can be achieved even with a smaller amount of metal-doped zinc oxide than with conventional flame retardants, resulting in a lower density in the resulting cured silicone rubber and less degradation of rubber properties. Therefore, it can be effectively used as a protective material for electrical cables and electrodes that require flame retardancy.

[0092] The addition-type silicone composition of the present invention provides a silicone rubber with excellent flame retardancy and heat resistance. This silicone composition is useful for electrical appliances, cable protection components, automotive materials, railway materials, and housing materials where flame retardancy is required.

[0093] 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. (A) A linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule and having a weight-average degree of polymerization of 50 to 2,000: 100 parts by mass; (B) An organohydrogenpolysiloxane having at least two hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in one molecule: in an amount such that the ratio of the number of moles of hydrosilyl groups contained in component (B) to the number of moles of silicon atom-bonded alkenyl groups contained in component (A) is 1 to 10; (C) Specific surface area of ​​50 m² by BET method ２ An addition-curing silicone composition containing: (D) silica fine powder having a concentration of 1 to 50 parts by mass, (E) a catalytic amount of hydrosilylation reaction catalyst, and (D) metal-doped zinc oxide.

2. The addition-curing silicone composition according to claim 1, wherein the metal in component (E) is aluminum or gallium.

3. The addition-curing silicone composition according to claim 1, wherein the (E) component has a volume-average particle size of 1 to 50 μm.

4. A silicone rubber that is a cured product of an addition-curing silicone composition according to any one of claims 1 to 3.

5. A laminate comprising a base material and a cured product layer made of the silicone rubber described in claim 4, characterized in that the cured product layer is present on one or both sides of the base material.

6. A laminate for protecting electric wires or electrodes, comprising a base material and a cured layer made of the silicone rubber described in claim 4, characterized in that the cured layer is present on one or both sides of the base material.

7. The laminate according to claim 5, wherein the substrate is glass cloth.

8. The laminate for protecting electric wires or electrodes according to claim 6, wherein the base material is glass cloth.

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