JP5862512B2 - Method for improving flame retardancy of cured silicone rubber - Google Patents

Description

  The present invention relates to a method for stably improving the flame retardancy of a silicone rubber obtained by heating and curing a liquid addition-curable silicone rubber composition.

Flame retardant silicone rubber is used in electrical and electronic parts, automobile parts, building material parts and the like. In order to impart flame retardancy to silicone rubber, it is indispensable to blend platinum or a platinum compound (Japanese Patent Publication No. 44-2591: Patent Document 1), but it cannot be said that platinum or a platinum compound alone is sufficient. Combinations of platinum or platinum compounds with carbon black, fumed titanium dioxide, iron oxide or manganese oxide, or some mixture thereof have been proposed (for example, Japanese Patent Publication Nos. 47-16546 and 47-21826). Gazette, Japanese Patent Publication No. 51-35501, Japanese Patent Publication No. 51-23979, Japanese Patent Publication No. 53-16019: Patent Documents 2-6).
However, in the liquid addition-curable silicone rubber composition forming the flame-retardant silicone rubber, there is a problem that the flame retardancy becomes unstable when platinum, a platinum compound, or iron oxide is used in combination.

Japanese Examined Patent Publication No. 44-2591 Japanese Patent Publication No. 47-16546 Japanese Examined Patent Publication No. 47-21826 Japanese Patent Publication No. 51-35501 Japanese Patent Publication No. 51-23979 Japanese Examined Patent Publication No. 53-16019

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for stably expressing flame retardancy in a silicone rubber obtained by heat curing a liquid addition-curable silicone rubber composition. To do.

  As a result of intensive studies to achieve the above object, the present inventors have conducted a hydrosilylation addition reaction with an alkenyl group in a base polymer (main agent) in a liquid addition-curable silicone rubber composition, thereby producing a crosslinking agent ( The present inventors have found that flame retardancy is stably exhibited by controlling the heating loss of the organohydrogenpolysiloxane acting as a curing agent to a specific mass% or less, and completed the present invention.

Accordingly, the present invention provides the following method for improving the flame retardancy of a cured silicone rubber.
[1]. (A) Organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule: 100 parts by mass;
(B) R ₃ SiO _1/2 units (wherein R is independently an unsubstituted or substituted monovalent hydrocarbon group) and SiO ₂ units, and R ₃ SiO _1/2 units and SiO ₂ A three-dimensional structure in which the molar ratio [R ₃ SiO _1/2 / SiO ₂ ] to the unit is 0.5 to 1.5 and the alkenyl group content is 1 × 10 ^{−4 to} 5 × 10 ⁻³ mol / g. Organopolysiloxane resin having a network structure: 3 to 50 parts by mass,
(C) One or more organohydrogenpolysiloxanes containing hydrogen atoms bonded to at least two silicon atoms in one molecule: 0.5 to 20 parts by mass,
(D) Inorganic filler: 5-300 parts by mass,
(E) Iron oxide fine powder: 0.1 to 30 parts by mass,
(F) Addition reaction catalyst: In the liquid addition-curable silicone rubber composition containing a catalytic amount, for each of the organohydrogenpolysiloxane components constituting the component (C), and for each organohydrogenpolysiloxane component, The total flame retardancy of the silicone rubber obtained by curing the composition is characterized by controlling the weight loss after heating for 3 hours at 105 ° C. to 2.0% by mass or less for the total component (C). How to improve.
[2]. (A) component is the following average composition formula (I)
R ¹ _a SiO _{(4-a) / 2} (I)
(In the formula, R ¹ is independently an unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and a is a positive number in the range of 1.9 to 2.4.)
And an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule, wherein the component (C) contains hydrogen atoms bonded to at least two silicon atoms in one molecule. The silicone rubber according to [1], wherein the group contained and bonded to a silicon atom other than a silicon-bonded hydrogen atom is an organohydrogenpolysiloxane which is an unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms. A method to improve flame retardancy.

  According to the method of the present invention, it is possible to stably improve the flame retardancy of silicone rubber obtained by heat curing a liquid addition curable silicone rubber composition.

Hereinafter, the present invention will be described in more detail.
In the method for improving the flame retardancy of silicone rubber obtained by curing the liquid addition curable silicone rubber composition of the present invention, the liquid addition curable silicone rubber composition is:
(A) an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) R ₃ SiO _1/2 units (wherein R is independently an unsubstituted or substituted monovalent hydrocarbon group) and SiO ₂ units, and R ₃ SiO _1/2 units and SiO ₂ A three-dimensional structure in which the molar ratio [R ₃ SiO _1/2 / SiO ₂ ] to the unit is 0.5 to 1.5 and the alkenyl group content is 1 × 10 ^{−4 to} 5 × 10 ⁻³ mol / g. Network-structured organopolysiloxane resin,
(C) an organohydrogenpolysiloxane containing hydrogen atoms bonded to at least two silicon atoms in one molecule;
(D) inorganic filler,
(E) Iron oxide fine powder,
(F) An addition reaction catalyst is contained.

-(A) Alkenyl group-containing organopolysiloxane-
The organopolysiloxane containing at least two silicon atom-bonded alkenyl groups in one molecule of the component (A) is generally a known organo used as a base polymer (main agent) of a liquid addition-curable silicone rubber composition. It is a polysiloxane, and is a liquid organopolysiloxane having a viscosity of about 1 to 100 Pa · s, preferably 5 to 100 Pa · s, more preferably about 10 to 100 Pa · s at 23 ° C., and self-flowing at room temperature.
In the present invention, the viscosity can usually be measured with a rotational viscometer (for example, BL type, BH type, BS type, cone plate type, etc.).

As the alkenyl group-containing organopolysiloxane, usually, those represented by the following average composition formula (I) are preferably used.
R ¹ _a SiO _{(4-a) / 2} (I)
(In the formula, R ¹ is independently an unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number in the range of 1.9 to 2.4.)

Here, R ¹ is independently an unsubstituted or substituted monovalent hydrocarbon group, preferably having 1 to 10 carbon atoms, particularly 1 to 8 carbon atoms. Specific examples of the monovalent hydrocarbon group represented by R ¹ include Specifically, alkyl group such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, hexyl group, cyclohexyl group, vinyl group, allyl group, propenyl group, isopropenyl group, Unsubstituted monovalent hydrocarbon groups such as alkenyl groups such as butenyl groups, aryl groups such as phenyl groups, tolyl groups and xylyl groups, and aralkyl groups such as benzyl groups; 3,3,3-trifluoropropyl groups, cyanomethyl groups A substituted monovalent hydrocarbon group such as a substituted alkyl group in which at least a part of the hydrogen atoms of the above monovalent hydrocarbon group is substituted with a halogen atom, a cyano group or the like. The plurality of substituents may be different or the same, but it is necessary that the molecule contains 2 or more, preferably 2 to 50, more preferably 2 to 20 alkenyl groups. . a is a number in the range of 1.9 to 2.4, preferably 1.95 to 2.05, more preferably 1.98 to 2.01.

Further, this organopolysiloxane may be linear, and it contains a small amount of branching units such as R ¹ SiO _3/2 units (R ¹ is the same as described above) or SiO _4/2 units. Although it may be branched, the main chain is usually composed of repeating diorganosiloxane units (R ¹ ₂ SiO _2/2 ), and both ends of the molecular chain are triorganosiloxy groups (R ¹ ₃ SiO _1/2). It is preferable that it is a linear diorganopolysiloxane blocked with
The substituent bonded to the silicon atom may be basically any of the above, but the alkenyl group is preferably a vinyl group, and other substituents (other than the alkenyl group bonded to the silicon atom). The monovalent hydrocarbon group is preferably a methyl group or a phenyl group.

The organopolysiloxane has an alkenyl group of 1.0 × 10 ^{−5 to} 2.0 × 10 ⁻⁴ mol / g, particularly 1.3 × 10 ^{−5 to} 1.3 × 10 ⁻⁴ mol / g. It is preferable to contain. If the alkenyl group content is too low, the crosslinking density may be lowered, and the practical rubber strength may be reduced. If the content is too high, the crosslinking density may be increased, and the elongation at the time of cutting the cured rubber product may be reduced. .

  Further, the average degree of polymerization (or the number of silicon atoms in the molecule) of the organopolysiloxane is preferably 100 to 1,500, particularly 150 to 1,000. This average degree of polymerization (or average molecular weight) can be determined as a polystyrene-equivalent weight average degree of polymerization (or weight average molecular weight) in GPC (gel permeation chromatography) analysis using toluene as a developing solvent.

-(B) Alkenyl group-containing three-dimensional network organopolysiloxane resin-
The (B) component alkenyl group-containing organopolysiloxane resin (resin-like copolymer) is an organopolysiloxane resin having a three-dimensional network structure containing R ₃ SiO _1/2 units and SiO ₂ units as main components.

  Here, R is independently an unsubstituted or substituted monovalent hydrocarbon group, preferably having 1 to 10 carbon atoms, particularly 1 to 8 carbon atoms, and specifically as the monovalent hydrocarbon group represented by R, Are alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, decyl, Aryl group such as phenyl group, tolyl group, xylyl group, naphthyl group, aralkyl group such as benzyl group, phenylethyl group, phenylpropyl group, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl group, Alkenyl groups such as cyclohexenyl and octenyl groups, and some or all of the hydrogen atoms of these groups are substituted with halogens such as fluorine, bromine and chlorine. Children, those substituted with a cyano group or the like, such as chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, cyanoethyl group and the like.

The (B) component alkenyl group-containing three-dimensional network organopolysiloxane resin (resin-like copolymer) may be composed only of the R ₃ SiO _1/2 unit and the SiO ₂ unit. Accordingly, R ₂ SiO _2/2 units and RSiO _3/2 units (R is as described above) as a total amount thereof are 50% by mass or less (0 to 50% by mass) with respect to the entire copolymer, preferably May be included in the range of 40% by mass or less (0 to 40% by mass), more preferably 30% by mass or less (0 to 30% by mass), but the molar ratio of R ₃ SiO _1/2 unit to SiO ₂ unit. [R ₃ SiO _1/2 / SiO ₂ ] needs to be 0.5 to 1.5, particularly 0.5 to 1.3. If this molar ratio is less than 0.5, the tack force of the rubber is increased, and if it is greater than 1.5, the compatibility is lowered and blending becomes difficult.

Furthermore, the (B) component alkenyl group-containing three-dimensional network organopolysiloxane resin is 1 × 10 ^{−4 to} 5 × 10 ⁻³ mol / g, preferably 2 × 10 ^{−4 to} 3 × 10 ⁻³ mol / g. More preferably, it is necessary to contain 3 × 10 ⁻⁴ to 2 × 10 ⁻³ mol / g of vinyl groups. When the vinyl group content is more than 5 × 10 ⁻³ mol / g, the rubber is hard and brittle, and when it is less than 1 × 10 ⁻⁴ mol / g, the rubber becomes soft and weak.

In addition, the above-mentioned resin copolymer is usually a suitable monofunctional or tetrafunctional chlorosilane or alkoxysilane (that is, hydrolyzed and condensed to produce R ₃ SiO _1/2 units or SiO ₂ units). Can be produced by cohydrolytic condensation using a known method.

  The blending amount of the alkenyl group-containing three-dimensional network organopolysiloxane resin is preferably 3 to 50 parts by weight, particularly 5 to 40 parts by weight with respect to 100 parts by weight of component (A). If it is less than 3 parts by mass, there is no effect of rubber reinforcement, and if it exceeds 50 parts by mass, the rubber is hard and brittle.

-(C) Organohydrogenpolysiloxane-
The organohydrogenpolysiloxane of component (C) is an alkenyl group in the alkenyl group-containing organopolysiloxane of component (A) and an alkenyl group in the alkenyl group-containing three-dimensional network organopolysiloxane resin of component (B); The component (C) is a component that acts as a crosslinking agent (curing agent) by hydrosilylation addition reaction with a silicon atom-bonded hydrogen atom (SiH group) in the component (C). The organohydrogenpolysiloxane is not particularly limited in molecular structure, and various types such as linear (linear), cyclic, branched, and three-dimensional network structures that have been conventionally produced can be used. Although there are at least two hydrogen atoms bonded to silicon atoms (that is, hydrosilyl groups represented by SiH) in one molecule (usually 2 to 300), preferably 3 or more (for example, about 3 to 200). ), More preferably about 4 to 100. The organohydrogenpolysiloxane is preferably 0.001 to 0.020 mol / g, more preferably 0.002 to 0.018 mol / g, still more preferably 0.003 to 0.017 mol / g. It is desirable to contain SiH groups. The silicon-bonded hydrogen atom may be bonded to the silicon atom at the end of the molecular chain or may be bonded to the silicon atom in the middle of the molecular chain (non-terminal of the molecular chain), and bonded to both of these. It may be what you did.

The group bonded to the silicon atom other than the silicon atom-bonded hydrogen atom of the component (C) is the same as the above-described unsubstituted or substituted, preferably carbon number, as R ¹ in the average composition formula (I) of the component (A). 1 to 10 monovalent hydrocarbon groups can be exemplified, but those not containing an aliphatic unsaturated bond such as an alkenyl group are preferred. Specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, An unsubstituted monovalent hydrocarbon group such as an alkyl group such as an isobutyl group, a tert-butyl group, a hexyl group and a cyclohexyl group, an aryl group such as a phenyl group, a tolyl group and a xylyl group, and an aralkyl group such as a benzyl group; A substituted alkyl group in which at least a part of hydrogen atoms of the monovalent hydrocarbon group such as 3,3-trifluoropropyl group and cyanomethyl group is substituted with a halogen atom, a cyano group or the like; And a substituted monovalent hydrocarbon group, particularly a methyl group and phenyl group are preferred.

  In addition, the number of silicon atoms (or the degree of polymerization) in one molecule of the organohydrogenpolysiloxane of component (C) is usually 2 to 300, preferably 3 to 200, more preferably about 4 to 100. Those are preferably used. In the present invention, the degree of polymerization (or molecular weight) can usually be determined as a weight average degree of polymerization (or weight average molecular weight) in terms of polystyrene in gel permeation chromatography (GPC) analysis using toluene as a developing solvent.

Examples of the (C) component organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, 1,3. , 5,7-tetramethyltetracyclosiloxane, 1,3,5,7,8-pentamethylpentacyclosiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, both ends of the molecular chain Trimethylsiloxy group-blocked methylhydrogenpolysiloxane, molecular chain both ends trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, molecular chain both ends silanol-blocked methylhydrogenpolysiloxane, Silanol group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both chain ends dimethylhydrogensiloxy group-blocked dimethylpolysiloxane, Molecular chain both ends dimethylhydrogensiloxy group-blocked methylhydrogenpolysiloxane, both molecular chains Terminal dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, consisting of R ² ₂ (H) SiO _1/2 units and SiO _4/2 units, optionally R ² ₃ SiO _1/2 units, R ² ₂ SiO _2/2 unit, R ² (H) SiO _2/2 unit, (H) SiO _3/2 unit or R ² SiO _3/2 unit [wherein R ² excludes an aliphatic unsaturated bond An unsubstituted or substituted monovalent hydrocarbon group, the same as those exemplified as the group bonded to a silicon atom other than the above-mentioned silicon-bonded hydrogen atom. It can be exemplified by the. In these compounds, those in which some or all of the methyl groups are substituted with other alkyl groups or phenyl groups can be exemplified.

  (C) The compounding quantity of the organohydrogenpolysiloxane of a component is 0.5-20 mass parts with respect to 100 mass parts of (A) component, Preferably it is 0.5-15 mass parts, More preferably, it is 1-13 masses. If the blending amount is too small, the crosslinking density becomes too low, which adversely affects the heat resistance of the rubber molded product. On the other hand, when the amount is too large, the problem of foaming due to the dehydrogenation reaction occurs, and the heat resistance is similarly adversely affected. In addition, the compounding quantity of (C) component is the molar ratio of the SiH group in (C) component with respect to the sum total of the alkenyl group contained in (A) component and (B) component for the same reason as the above ( (SiH group / alkenyl group) may be added in an amount of 0.4 to 5.0 (mol / mol), particularly 0.8 to 3.0 (mol / mol).

Component (C) may be used alone or in combination of two or more. In the present invention, the flame retardancy of silicone rubber obtained by curing a liquid addition-curable silicone rubber composition is stabilized. Therefore, the organohydrogenpolysiloxane of the component (C) (that is, each of the organohydrogenpolysiloxane components constituting the component (C) and the respective organohydrogenpolysiloxane components were summed up. With regard to (C) the whole component), the loss on heating of component (C) after heating at 105 ° C. for 3 hours is 2.0 mass% or less (0 to 2.0 mass%), preferably 1.5 It is essential to control in advance to less than or equal to mass% (0 to 1.5 mass%). When this heating loss (that is, at least one of the heating loss of the individual organohydrogenpolysiloxane components constituting the component (C) and the heating loss of the entire component (C)) exceeds 2.0% by mass, it is the target. The flame retardancy of the cured silicone rubber does not appear stably.
That is, even if the heating loss as a whole of the component (C) is 2.0% by mass or less, at least one component among the individual organohydrogenpolysiloxane components constituting the component (C) has the above heating loss. When it exceeds 2.0 mass%, the flame retardance of the target silicone rubber hardened | cured material is not expressed stably.

-(D) Inorganic filler-
The inorganic filler (D) imparts physical strength such as predetermined hardness and tensile strength to the liquid addition-curable silicone rubber composition. As this inorganic filler, those conventionally used in conventional silicone rubber compositions can be used, for example, silica-based materials such as fumed silica, crystalline silica (quartz powder), precipitated silica, and hydrophobized silica. A filler is mentioned, These may be single 1 type or may combine 2 or more types. The inorganic filler of component (D) does not include iron oxide fine powder described later.

  As such a silica-based filler, specifically, Aerosil 130, 200, 300 (manufactured by Nippon Aerosil Co., Ltd., manufactured by Degussa), Cabosil MS-5, MS-7 (manufactured by Cabot) as hydrophilic silica. Fumed silica such as Rheorosil QS-102, 103 (manufactured by Tokuyama), precipitated silica such as Toxeal US-F (manufactured by Tokuyama), Nipsil LP (manufactured by Nippon Silica), etc. Precipitation of fumed silica such as Aerosil R-812, R-812S, R-972, R-974 (Degussa), Rheorosil MT-10 (made by Tokuyama), Nipsil SS series (made by Nippon Silica) Silica and the like are crystalline silica, such as crystallite, Minsil, misil, and the like. These silica-based fillers may be used as they are, but those previously surface-treated with a silylating agent are used, or when kneading with silicone oil (for example, (A) component alkenyl group-containing organopolysiloxane). It is preferable to use a surface treated by adding a silylating agent. These silylating agents may be any known ones such as alkylalkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate treatment agents, fatty acid esters, etc. You may use simultaneously or at a different timing. Further, the above silylating agent is added again to the surface-treated silica by adding a silylating agent during kneading with silicone oil (for example, the alkenyl group-containing organopolysiloxane of component (A)), and the surface treatment is performed. Also good.

The inorganic filler has a specific surface area by the BET method is preferably of a 50 to 400 m ² / g, in particular 100 to 350 m ² / g. If the specific surface area is too small, the reinforcing effect is not sufficiently exhibited, and the physical strength of the rubber cured product may be lowered. If it is too large, it may be difficult to produce.

  The compounding quantity of an inorganic filler is 5-300 mass parts with respect to 100 mass parts of (A) component, Preferably it is 20-200 mass parts. If the blending amount is less than 5 parts by mass, sufficient rubber strength cannot be obtained, and if it exceeds 300 parts by mass, blending becomes difficult.

-(E) Iron oxide fine powder-
The iron oxide fine powder of component (E) is used to impart effects such as flame retardancy and heat resistance, and black bengara (Fe ₃ O ₄ ) and red bengara (Fe ₂ O ₃ ) Preferably used.
The average particle diameter of the iron oxide fine powder is preferably 0.08 to 0.6 μm, particularly preferably 0.1 to 0.3 μm. If the average particle size is too small, the primary particles may aggregate and the flame retardancy of the cured product may vary. If the average particle size is too large, the particles aggregate over time, and further settle, resulting in flame retardancy. The effect may not appear. The average particle diameter is a value as a weight average value D ₅₀ in the particle size distribution measurement by laser diffraction method.
The usage-amount of iron oxide fine powder is 0.1-30 mass parts with respect to 100 mass parts of (A) component, Preferably it is 0.2-20 mass parts, More preferably, it is 2-20 mass parts. is there. If it is less than 0.1 parts by mass, the flame retardancy is not effective, and if it exceeds 30 parts by mass, the fluidity of the material is impaired.

-(F) Addition reaction catalyst-
Examples of the addition reaction catalyst for component (F) include platinum black, platinous chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and an olefin, platinum bisacetoacetate, etc. Platinum-based catalysts, palladium-based catalysts, rhodium-based catalysts, and the like. In addition, the compounding quantity of this addition reaction catalyst can be made into a catalyst quantity, and is about 0.5-1,000 ppm, especially about 1-200 ppm by mass conversion with respect to (A) component as a platinum group metal normally. .

  In the liquid addition-curable silicone rubber composition of the present invention, as other components, as necessary, a conductive agent such as carbon black, conductive zinc white, metal powder, nitrogen-containing compound, acetylene compound, phosphorus compound, nitrile compound , Carboxylate, tin compounds, mercury compounds, sulfur compounds and other hydrosilylation addition reaction control agents, titanium oxide, heat-resistant agents such as cerium oxide, internal mold release agents such as dimethyl silicone oil, adhesion-imparting agents, thixotropic properties Mixing an agent or the like is optional as long as the appearance of the rubber molded product is not impaired.

  The liquid addition-curable silicone rubber composition of the present invention can be prepared by uniformly mixing the above components using a normal mixing stirrer such as a kneader or a planetary mixer, a kneader or the like.

  The curing conditions for the liquid addition curable silicone rubber composition of the present invention may be the same as those for known addition reaction curable silicone rubber compositions. For example, the liquid addition curable silicone rubber composition is sufficiently cured at room temperature, but may be heated if necessary. Well, in this case, it can be cured by heating at 80 to 220 ° C., particularly 120 to 200 ° C. for 3 seconds to 10 minutes, particularly 5 seconds to 3 minutes.

  The liquid addition curable silicone rubber composition of the present invention is characterized in that, as component (C), the weight loss after heating at 105 ° C. for 3 hours is controlled to 2.0% by mass or less. Since the silicone rubber molded product obtained by molding the composition is superior in flame retardancy compared to conventional products, it is suitable for electrical / electronic parts, automobile parts, building material parts, etc. Can be used.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, these do not limit this invention at all. The degree of polymerization (or average degree of polymerization) means the weight average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) analysis using toluene as a developing solvent.

[Example 1]
100 parts by mass of dimethylpolysiloxane (vinyl group content = 0.00010 mol / g) having an average degree of polymerization of 210 blocked at both ends with dimethylvinylsiloxy groups, and a BET specific surface area surface-treated with hexamethyldisilazane After mixing 15 parts by weight of fumed silica of 190 m ² / g, 30 parts by weight of Toxeal USF (wet silica, manufactured by Tokuyama Corporation), 2 parts by weight of hexamethyldisilazane, and 1.0 part by weight of water at room temperature for 30 minutes, 150 The temperature was raised to 0 ° C. and stirring was continued for 3 hours, followed by cooling to obtain a silicone rubber base.
70 parts by mass of this silicone rubber base, 12.5 parts by mass of dimethylpolysiloxane having an average degree of polymerization of 450 blocked at both ends with dimethylvinylsiloxy groups, (CH ₃ ) ₃ SiO _1/2 units, CH ₂ = Resin-like copolymer comprising CH (CH ₃ ) ₂ SiO _1/2 units and SiO ₂ units [[(CH ₃ ) ₃ SiO _1/2 units + CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 units] / SiO ₂ unit = 0.85, vinyl group content = 0.0080 mol / g] 7.5 parts by mass, 5 parts by mass of iron oxide (Fe ₃ O ₄ ) having an average particle size of 0.27 μm were added, and stirred for 30 minutes. Then, it was passed once through three rolls. Furthermore, as a cross-linking agent, a molecular chain both ends trimethylsiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer having a SiH group in the side chain having a heating loss of 0.4% by mass at 105 ° C. for 3 hours (polymerization degree 46 Methyl hydrogen polysiloxane having a SiH group at both ends (SiH group amount 0.0050 mol / g) is 3.0 parts by mass and the heat loss at 105 ° C. for 3 hours is 1.8% by mass. , SiH group amount 0.0014 mol / g) 4.6 parts by mass [two types of crosslinking agents SiH groups / 3 types of alkenyl groups = 1.9 (mol / mol)], and ethynylcyclohexanol as a reaction control agent 0.1 part by mass and 0.25 part by mass of a platinum catalyst (Pt concentration 1% by mass) were added and mixed with stirring for 15 minutes to obtain a silicone rubber composition. In addition, the heating loss (105 degreeC, 3 hours) of the whole (C) component was 1.25 mass%.
This silicone rubber composition was subjected to press curing at 120 ° C./10 minutes to prepare a cured sheet having a thickness of 1 mm, and flame retardancy was measured by the method described below. The measurement results are shown in Table 1.

[Flame resistance measurement]
The flame retardancy measurement was performed using five silicone rubber sheets according to the method specified in the UL94 20 mm vertical combustion test, and after-flame times T1 and T2 and the sum of the after-flame times of each set by all treatments (5 The total of T1 + T2 of one silicone rubber sheet) was measured, and the flame retardant classification of the material was performed based on the result. T1 represents the afterflame time after the first flame contact, and T2 represents the afterflame time after the second flame contact.
Burning means that the sample has burned up to the holding clamp.
94V-1 represents the flame retardant classification of UL94 material, and the criteria are shown in Table 3.

[Example 2]
In Example 1, as a cross-linking agent, a molecular chain both ends trimethylsiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer having SiH groups in the side chain having a heat loss of 0.4 mass% at 105 ° C. for 3 hours. The blending amount of (polymerization degree 46, SiH group amount 0.0050 mol / g) is 3.0 parts by mass, and the heat loss for 3 hours at 105 ° C. is 1.8% by mass. 2.9 parts by mass of a dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer (polymerization degree 20, SiH group amount 0.0053 mol / g) having both ends of the molecular chain having a [total SiH group / A silicone rubber composition was produced in the same manner as in Example 1 except that the total alkenyl group = 2.6 (mol / mol). In addition, the heating loss (105 degreeC, 3 hours) of the whole (C) component was 1.09 mass%. This silicone rubber composition was subjected to a press cure at 120 ° C./10 minutes to prepare a cured sheet having a thickness of 1 mm, and flame retardancy was measured. The measurement results are shown in Table 1.

[Comparative Example 1]
In Example 1, as a cross-linking agent, a molecular chain both ends trimethylsiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer having SiH groups in the side chain having a heat loss of 0.4 mass% at 105 ° C. for 3 hours. The blending amount of (polymerization degree 46, SiH group amount 0.0050 mol / g) is 3.0 parts by mass, and the heat loss for 3 hours at 105 ° C. is 2.1% by mass. 2.7 parts by mass of a dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer (polymerization degree 12, SiH group amount 0.0057 mol / g) having both ends of the molecular chain having a [total SiH group / A silicone rubber composition was produced in the same manner as in Example 1 except that the total alkenyl group = 2.6 (mol / mol). In addition, the heating loss (105 degreeC, 3 hours) of the whole (C) component was 1.21 mass%. This silicone rubber composition was subjected to a press cure at 120 ° C./10 minutes to prepare a cured sheet having a thickness of 1 mm, and flame retardancy was measured. The measurement results are shown in Table 2.

[Comparative Example 2]
In Example 1, as a cross-linking agent, a molecular chain both ends trimethylsiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer having SiH groups in the side chain having a heat loss of 0.4 mass% at 105 ° C. for 3 hours. Molecules having SiH groups in the side chain in which the blending amount (polymerization degree 46, SiH group amount 0.0050 mol / g) is 3.0 parts by mass and the heating loss for 3 hours at 105 ° C. is 2.8% by mass. 4.0 parts by mass of trimethylsiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane copolymer (polymerization degree 25, SiH group amount 0.0039 mol / g) were used [total SiH groups / total alkenyl groups = 2. .6 (mol / mol)], a silicone rubber composition was prepared in the same manner as in Example 1. In addition, the heating loss (105 degreeC, 3 hours) of the whole (C) component was 1.77 mass%. This silicone rubber composition was subjected to a press cure at 120 ° C./10 minutes to prepare a cured sheet having a thickness of 1 mm, and flame retardancy was measured. The measurement results are shown in Table 2.

Claims (2)

(A) Organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule: 100 parts by mass
(B) R ₃ SiO _1/2 units (wherein R is independently an unsubstituted or substituted monovalent hydrocarbon group) and SiO ₂ units, and R ₃ SiO _1/2 units and SiO ₂ A three-dimensional structure in which the molar ratio [R ₃ SiO _1/2 / SiO ₂ ] to the unit is 0.5 to 1.5 and the alkenyl group content is 1 × 10 ^{−4 to} 5 × 10 ⁻³ mol / g. Organopolysiloxane resin having a network structure: 3 to 50 parts by mass,
(C) One or more organohydrogenpolysiloxanes containing hydrogen atoms bonded to at least two silicon atoms in one molecule: 0.5 to 20 parts by mass,
(D) Inorganic filler: 5-300 parts by mass,
(E) Iron oxide fine powder: 0.1 to 30 parts by mass,
(F) Addition reaction catalyst: In the liquid addition-curable silicone rubber composition containing a catalytic amount, for each of the organohydrogenpolysiloxane components constituting the component (C), and for each organohydrogenpolysiloxane component, The total flame retardancy of the silicone rubber obtained by curing the composition is characterized by controlling the weight loss after heating for 3 hours at 105 ° C. to 2.0% by mass or less for the total component (C). How to improve. (A) component is the following average composition formula (I)
R ¹ _a SiO _{(4-a) / 2}                     (I)
(Wherein R ¹ Is independently an unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and a is a positive number in the range of 1.9 to 2.4. )
And an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule, wherein the component (C) contains hydrogen atoms bonded to at least two silicon atoms in one molecule. 2. The silicone rubber according to claim 1, wherein the group contained and bonded to a silicon atom other than a silicon atom-bonded hydrogen atom is an organohydrogenpolysiloxane which is an unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms. A method to improve flame retardancy.