Addition-curable silicone composition and flame-retardant silicone rubber

Abstract

To provide a liquid addition-curable silicone composition that yields a cured silicone rubber product with exceptional flame retardancy and rubber strength.SOLUTION: An addition-curable silicone composition includes (A) 100 pts.mass of organopolysiloxane with two or more alkenyl groups bound to a silicon atom in one molecule, (B) 3-50 pts.mass of resin including R13SiO1 / 2 unit and SiO4 / 2 unit, with [R13SiO1 / 2 / SiO4 / 2] of 0.5-1.5 and an alkenyl group content of 1×10-4-5×10-3 mol / g, (C) organohydrogenpolysiloxane of formula (1) in such an amount that the ratio of the number of silicon atom-bound hydrogen atoms in (C) to the total number of silicon atom-bound alkenyl groups in (A) and (B) is 1.5-1.7, (D) addition reaction catalyst in a catalyst amount, (E) 10-50 pts.mass of fumed silica with a specific surface area of 100 m2 / g or more, and (F) 0.001-0.5 pt.mass of triazole compound.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a liquid addition-curable silicone composition and a flame-retardant silicone rubber obtained by curing said composition. [Background technology]

[0002] Flame-retardant silicone rubber is used in electric and electronic parts, automobile parts, building material parts, etc. In order to impart flame retardancy to silicone rubber, it is essential to add platinum or a platinum compound, but platinum or a platinum compound alone is not sufficient. Patent Document 1 describes that a silicone rubber molded product with excellent flame retardancy can be obtained by adding aluminum hydroxide powder and zinc carbonate powder to a liquid silicone rubber composition. Patent Document 2 describes that a liquid silicone rubber composition containing carbon black and aluminum hydroxide can provide a silicone rubber with flame retardancy. However, when a basic inorganic filler such as aluminum hydroxide or zinc carbonate is added to a liquid silicone rubber composition, there is a problem that the density of the material increases and the rubber properties decrease.

[0003] Patent Document 3 describes a method of improving flame retardancy by blending iron oxide fine powder into a liquid addition curing silicone rubber composition and controlling the heat loss of organohydrogenpolysiloxane. However, iron oxide fine powder has a high specific gravity, so there is a problem of settling over time. Patent Document 4 and Patent Document 5 describe blending a triazole compound and a phosphorous ester into a silicone rubber composition to obtain a silicone rubber with high flame retardancy. However, these silicone rubber compositions have not yet achieved sufficient flame retardancy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-316335 [Patent Document 2] JP 2004-161944 A [Patent Document 3] JP 2014-040522 A [Patent Document 4] JP 2016-094514 A [Patent Document 5] JP 2017-031364 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above problems, and has as its object to provide a liquid addition-curable silicone composition that gives a cured silicone rubber having excellent flame retardancy and rubber strength. [Means for solving the problem]

[0006] In order to achieve the above object, the present inventors have specified the structure of the organohydrogenpolysiloxane, which is the crosslinking agent (curing agent) in a liquid addition-curable silicone composition. Furthermore, they have limited the ratio of the number of moles of hydrosilyl groups to the total number of moles of silicon-bonded alkenyl groups in the composition to a certain limited range. By doing so, they have found that the resulting silicone rubber can stably have excellent flame retardancy and good rubber strength, and have completed the present invention.

[0007] That is, the present invention provides a composition comprising: (A) 100 parts by mass of an organopolysiloxane which has two or more alkenyl groups bonded to silicon atoms in each molecule and is liquid at 23° C.; (B)R 1 3SiO 1 / 2 Units (wherein R 1 are each independently a monovalent hydrocarbon radical) and SiO 4 / 2 Contains the unit SiO 4 / 2 R for units 1 3SiO 1 / 2 Unit of mole ratio [R 1 3SiO 1 / 2 / SiO 4 / 2 ] is 0.5 to 1.5, and the alkenyl group content is 1×10 -4 ~5×10-3 mol / g three-dimensional network structure organopolysiloxane resin: 3 to 50 parts by mass (C) A linear organohydrogenpolysiloxane represented by the following formula (1): [ka] (In formula (1), y is an integer of 4 to 98, z is an integer of 2 to 50, and y+z is an integer of 6 to 110, and the ratio of y / z is 2.5 4, and R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups), and R 3 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups) or a hydrogen atom. : composition Total silicon-bonded alkenyl groups in Mole For the number do Silicon-bonded hydrogen atoms Number of moles The ratio is 1.5 to 1.7. (D) Addition reaction catalyst: catalytic amount (E) Specific surface area by BET method 100m 2 Fumed silica of 10 to 50 parts by mass / g or more, (F) Triazole compound: 0.001 to 0.5 parts by mass The present invention provides an addition-curable silicone composition comprising: Effect of the Invention

[0008] The silicone composition of the present invention can provide a flame-retardant silicone rubber that has excellent flame retardancy and rubber strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will now be described in further detail.

[0010] -(A) Alkenyl group-containing organopolysiloxane- The component (A) of the present invention is an organopolysiloxane that has two or more silicon-bonded alkenyl groups per molecule and is liquid at 23° C. The viscosity of the component (A) is preferably in the range of 1 to 100 Pa s at 23° C. as measured with a rotational viscometer described in JIS K7117-1:1999, more preferably 5 to 100 Pa s, and even more preferably 10 to 100 Pa s.

[0011] As the alkenyl-containing organopolysiloxane, one having the following average composition formula (2) is usually preferably used. R a SiO (4-a) / 2 (2) (In the formula, R is independently a monovalent hydrocarbon group, and a is a positive number ranging from 1.9 to 2.4.)

[0012] In the above formula (2), R is each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 8 carbon atoms. Examples of the R include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, and cyclohexyl groups, alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, and butenyl groups, aryl groups such as phenyl, tolyl, and xylyl groups, and aralkyl groups such as benzyl groups. In addition, the above monovalent hydrocarbon groups may be used in which a part of the hydrogen atoms is substituted with a halogen atom. Examples of the R include a 3,3,3-trifluoropropyl group and a 3,3,4,4,5,5,6,6,6-nonafluorohexyl group. Two or more of the Rs must be alkenyl groups, and preferably 2 to 50, more preferably 2 to 20 Rs are alkenyl groups. The letter a is a number ranging from 1.9 to 2.4, preferably from 1.95 to 2.05, and more preferably from 1.98 to 2.01.

[0013] The organopolysiloxane may be linear or may contain a small amount of R 1 SiO 3 / 2 Units (R 1 (As stated above, the same applies below) or SiO 4 / 2In particular, the main chain may be a branched chain containing a diorganosiloxane unit (R 1 2SiO 2 / 2 ) repeating units, and both ends of the molecular chain are triorganosiloxy groups (R 1 3SiO 1 / 2 The alkenyl group is preferably a vinyl group, and the monovalent hydrocarbon group other than the alkenyl group is preferably a methyl group or a phenyl group.

[0014] (A) Organopolysiloxane is preferably 1.0×10 -5 ~2.0×10 -4 mol / g of alkenyl groups. -5 ~1.3×10 -4 It is preferable that the alkenyl group content is 100 moles / g. If the alkenyl group content is too low, the crosslink density will be low and the practical rubber strength may decrease, while if the alkenyl group content is too high, the crosslink density will be high and the elongation at break of the cured rubber may decrease. The amount of alkenyl groups is 1 This was measured by H-NMR spectroscopy.

[0015] The average degree of polymerization (or the number of silicon atoms in the molecule) of the organopolysiloxane (A) is preferably from 100 to 1,500, and particularly preferably from 150 to 1,000. This average degree of polymerization (or average molecular weight) can be determined as the number average degree of polymerization (or number average molecular weight) in terms of polystyrene in a GPC (gel permeation chromatography) analysis using toluene as the developing solvent.

[0016] -(B) Alkenyl group-containing three-dimensional network structure organopolysiloxane resin- The alkenyl-containing organopolysiloxane resin (resin copolymer) of component (B) is R 1 3SiO 1 / 2 Units and SiO 4 / 2It is an organopolysiloxane resin having a three-dimensional network structure containing units as a main component. It is preferable that the component (B) is a solid at 25°C.

[0017] R 1 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl groups, aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups, aralkyl groups such as benzyl, phenylethyl, and phenylpropyl groups, and alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl groups.

[0018] The alkenyl-containing three-dimensional network-structured organopolysiloxane resin (resin copolymer) of component (B) is 1 3SiO 1 / 2 Units and SiO 4 / 2 It may be composed of units, and optionally R 1 2SiO 2 / 2 Units and R 1 SiO 3 / 2 Units (R 1 may include the above.

[0019] R 1 3SiO 1 / 2 Units and SiO 4 / 2 Units and molar ratios [R 1 3SiO 1 / 2 / SiO 4 / 2 is 0.5 to 1.5, and preferably 0.5 to 1.3. If this molar ratio is less than 0.5, the tackiness of the rubber increases, and if it is more than 1.5, the compatibility decreases, making compounding difficult.

[0020] R 1 2SiO 2 / 2 Units and R 1 SiO3 / 2 The total amount of these units may be in the range of 50% by mass or less (0 to 50% by mass), preferably 40% by mass or less (0 to 40% by mass), and more preferably 30% by mass or less (0 to 30% by mass) based on the entire copolymer.

[0021] Furthermore, the alkenyl-containing three-dimensional network-structure organopolysiloxane resin of component (B) has an alkenyl group content of 1×10 -4 ~5×10 -3 mol / g, preferably 2×10 -4 ~3×10 -3 moles / g, more preferably 3×10 -4 ~2×10 -3 mol / g vinyl group. Alkenyl group content is 5×10 -3 More than 1×10 moles / g makes the rubber hard and brittle. -4 Less than mol / g will make the rubber softer and weaker.

[0022] The resin copolymer is usually prepared by a suitable method (i.e., hydrolysis and condensation to obtain R 1 3SiO 1 / 2 Units and SiO 4 / 2 The copolymers can be prepared by co-hydrolytic condensation of mono- and tetra-functional chlorosilanes and alkoxysilanes (which form the copolymer units) by methods well known in the art.

[0023] The amount of these alkenyl group-containing three-dimensional network organopolysiloxane resins blended per 100 parts by mass of component (A) is 3 to 50 parts by mass, and preferably 4 to 40 parts by mass. If it is less than 3 parts by mass, there is no effect of reinforcing the rubber, and if it exceeds 50 parts by mass, the rubber becomes hard and brittle.

[0024] -(C) Organohydrogenpolysiloxane- The organohydrogenpolysiloxane of component (C) acts as a crosslinking agent (curing agent). A crosslinked structure is formed by a hydrosilylation addition reaction between the alkenyl groups in component (A) and the alkenyl groups in component (B) and the silicon-bonded hydrogen atoms (hydrosilyl groups) in component (C). The organohydrogenpolysiloxane is characterized by being a linear organohydrogenpolysiloxane represented by the following formula (1). [ka] In formula (1), y is an integer of 4 to 98, z is an integer of 2 to 50, and y+z is an integer of 6 to 110, the ratio of y / z is 2 to 4, and R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups), and R 3 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups) or a hydrogen atom.

[0025] In order for the resulting silicone rubber to stably have good flame retardancy, y is preferably 4 to 98, and more preferably 4 to 80, z is 2 to 50, and more preferably 2 to 45, and y+z is preferably 6 to 110, and more preferably 6 to 100. The ratio of y / z is preferably 2 to 4, and more preferably 2.5 to 3.5.

[0026] Above R 2 Examples of the monovalent hydrocarbon group having 1 to 10 carbon atoms represented by the formula include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; and aralkyl groups such as benzyl, phenylethyl, and phenylpropyl. In addition, some or all of the hydrogen atoms of these groups may be substituted with halogen atoms such as fluorine, bromine, and chlorine. Examples of the group include a chloromethyl group, a chloropropyl group, a bromoethyl group, and a trifluoropropyl group. In addition, R 2does not contain an alkenyl group. 2 90 mol % or more of R 2 is preferably a methyl group. 3 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups) or a hydrogen atom. The monovalent hydrocarbon group having 1 to 10 carbon atoms is 2 The groups exemplified for the definition of R are given below. 3 90 mol % or more of R 3 is preferably a methyl group.

[0027] Examples of linear organohydrogenpolysiloxanes include methylhydrogenpolysiloxanes blocked at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers blocked at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers blocked at both ends with dimethylhydrogensiloxy groups, etc. Component (C) may be used alone or in combination of two or more types.

[0028] The compounding ratio of the organohydrogenpolysiloxane of component (C) is , composition The ratio of the number of hydrosilyl groups in the (C) component to the total number of alkenyl groups contained therein (hydrosilyl group / alkenyl group) is 1.5 to 1.7. It is preferably 1.5 to 1.6. If it is within the above range, it is preferable because the obtained silicone rubber can be stably imparted with flame retardancy. The amount of the (C) component to be blended is 0.5 to 25 parts by mass, preferably 0.5 to 20 parts by mass, and more preferably 1 to 15 parts by mass, based on 100 parts by mass of the (A) component, depending on the structure of the organohydrogenpolysiloxane represented by the formula (1) and the amount of hydrosilyl groups. If the amount of the (C) component is too small, the crosslink density becomes too low, which adversely affects the physical properties of the rubber molded product. If the amount is too large, a problem of foaming due to dehydrogenation occurs, and similarly adversely affects the physical properties.

[0029] -(D) Addition reaction catalyst- Examples of the (D) addition reaction catalyst include platinum black, platinic chloride, chloroplatinic acid, a reaction product of chloroplatinic acid with a monohydric alcohol, a complex of chloroplatinic acid with an olefin, platinum-based catalysts such as platinum bisacetoacetate, palladium-based catalysts, rhodium-based catalysts, etc. The amount of the addition reaction catalyst may be any catalytic amount, and is usually about 0.5 to 1,000 ppm, particularly about 1 to 200 ppm, calculated as the mass of the platinum group metal relative to the mass of component (A).

[0030] In addition, a reaction inhibitor for the above-mentioned addition reaction catalyst may be added for the purpose of improving storage stability. Examples of reaction inhibitors include acetylene compounds, alkenyl group-containing low molecular weight siloxanes, nitrogen-containing compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, and sulfur compounds. Among them, acetylene compounds such as ethynylcyclohexanol, 2-methyl-3-propyne-1-ol, and 3-methyl-1-tridecyne-3-ol, and alkenyl group-containing low molecular weight siloxanes such as 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane are preferred. These reaction inhibitors may be used alone or in combination of two or more.

[0031] The amount of the reaction inhibitor can be set arbitrarily depending on the desired storage stability and the molecular weight of the reaction inhibitor, but is preferably 0.01 to 1 part by mass per 100 parts by mass of the component (A).

[0032] -(E) Specific surface area by BET method 100m 2 / g or more fumed silica The reinforcing fine silica powder of component (E) may be any powder that is normally used as a reinforcing agent for rubber. The reinforcing fine silica powder may be any powder that is used in conventional silicone rubber compositions, but it should have a specific surface area of ​​100 m2 as determined by the BET method. 2 The reinforcing silica fine powder should have a specific surface area of ​​100 to 400 m2 / g or more. 2 / g, especially 100-350m 2 / g precipitated silica (wet silica), fumed silica (dry silica), calcined silica, etc. are preferably used, and fumed silica is preferred because it improves rubber strength. The reinforcing silica fine powder may be a 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 one whose surface has been hydrophobized directly with a surface treatment agent in a powder state in advance, or one whose surface has been hydrophobized by adding a surface treatment agent when kneading with silicone oil (for example, the alkenyl-containing organopolysiloxane of the above component (A)).

[0033] The surface treatment method is not particularly limited and may be carried out by a known technique. For example, the untreated silica fine powder and the treatment agent are placed in a mechanical kneader or fluidized bed sealed at normal pressure, and mixed at room temperature or by heat treatment (heating) in the presence of an inert gas as necessary. In some cases, a catalyst (such as a hydrolysis promoter) may be used to promote the treatment. After kneading, the mixture is dried to produce a treated silica fine powder. The amount of the treatment agent to be added may be equal to or greater than the amount calculated from the area covered by the treatment agent.

[0034] Examples of surface treatment agents include silazane such as hexamethyldisilazane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltris(methoxyethoxy)silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane and chloropropyltrimethoxysilane, and other silane coupling agents, polymethylsiloxane, organohydrogenpolysiloxane, and other organic silicon compounds, and these are used for surface treatment as hydrophobic silica fine powder.As treatment agents, silane coupling agents or silazane are particularly preferred.

[0035] The blending amount of component (E) is 10 to 50 parts by mass, preferably 10 to 45 parts by mass, and more preferably 10 to 40 parts by mass, per 100 parts by mass of component (A). Less than 10 parts by mass will not provide a sufficient reinforcing effect, whereas more than 50 parts by mass will cause the viscosity of the silicone rubber composition to become too high, resulting in poor workability and processability. In addition to the above component (E), if necessary, fillers such as precipitated silica, quartz powder, diatomaceous earth, calcium carbonate, etc. The amount of these fillers to be added may be any amount within a range that does not impair the effects of the present invention, but it is preferable that the amount is 50 parts by mass or less per 100 parts by mass of component (A).

[0036] -(F) Triazole compound- Component (F) is a triazole compound. The amount of component (F) is 0.001 to 0.5 parts by mass, and preferably 0.005 to 0.1 parts by mass, per 100 parts by mass of component (A). Component (F) is a flame retardant imparting agent for imparting flame retardancy to the silicone rubber cured product without impairing the physical properties (rubber physical properties) such as mechanical strength and elongation at break.

[0037] Examples of triazole compounds include 1,2,3-triazole, 1,2,4-triazole, and derivatives thereof. For example, derivatives of 1,2,3-triazole include benzotriazole, 4-hydroxy-1,2,3-triazole, 1,2,3-triazole-4-aldehyde, and 4-cyano-1,2,3-triazole. Derivatives of 1,2,4-triazole include 5-amino-3-methyl-1,2,4-triazole, and 3-mercapto-1,2,4-triazole. Among these, the most suitable are benzotriazole, 1,2,3-triazole, and 1,2,4-triazole. These may be used alone or in combination of two or more.

[0038] -Other ingredients- In the addition-curable silicone composition of the present invention, other components that may be blended as necessary include conductivity imparting agents such as conductive zinc oxide and metal powder, heat resistance imparting agents such as iron oxide and cerium oxide, colorants such as carbon black and titanium oxide, internal release agents such as dimethylsilicone oil, adhesion imparting agents (particularly organosilicon compounds such as alkoxysilanes that contain in their molecule at least one functional group selected from alkenyl groups, epoxy groups, amino groups, (meth)acryloxy groups, mercapto groups, and the like, but do not contain hydrosilyl groups in their molecule), thixotropy imparting agents, and the like. The amount of these may be any amount within a range that does not impair the appearance of the rubber molded product or reduce the flame retardancy, which is an effect of the present invention. For example, the amount of the electrical conductivity imparting agent is preferably 0.1 to 20 parts by mass per 100 parts by mass of the (A) component, and the amount of the heat resistance imparting agent is preferably 0.01 to 20 parts by mass per 100 parts by mass of the (A) component. The amount of the coloring agent is preferably 0.01 to 10 parts by mass per 100 parts by mass of the (A) component.

[0039] The addition-curable silicone composition of the present invention can be produced by uniformly mixing the above-mentioned components using a conventional mixer, stirrer, kneader, or other such device, such as a kneader or planetary mixer.

[0040] The addition-curable silicone composition of the present invention is liquid at 23° C. The viscosity at 23° C., measured using a viscosity / viscoelasticity measuring device (HAKKEMARS40, manufactured by Thermo Fisher Scientific Co., Ltd.), is preferably 1,000 mPa·s to 5,000,000 mPa·s. Furthermore, when component (F) is contained, the preferred range of viscosity at 23° C. is 10,000 mPa·s to 10,000,000 mPa·s, and preferably 10,000 mPa·s to 5,000,000 mPa·s.

[0041] The molding and curing method of the addition curable silicone composition of the present invention is not particularly limited, and may be any conventionally known method. The molding method may be selected from injection molding, transfer molding, injection molding, compression molding, and the like, and the most suitable means may be selected according to the purpose. As for the curing conditions, the composition can be primarily cured by heating at, for example, 80 to 230°C, preferably 100 to 180°C. The heating time is about 30 seconds to 3 hours, and particularly about 1 minute to 1 hour. As for the curing conditions, secondary vulcanization (post cure) may be performed as necessary. The secondary vulcanization is performed, for example, at 150 to 200°C for about 60 minutes to 24 hours. The advantage of being able to cure only by primary vulcanization is that the time required for secondary vulcanization is not required, and thus productivity is greatly improved. In addition, since the thermal energy during production can be reduced, molding that reduces the environmental load is possible.

[0042] There are no particular limitations on the thickness of the cured silicone rubber, but it is preferably 0.5 to 10 mm, and more preferably 1 to 6 mm.

[0043] The silicone rubber cured product obtained by curing the silicone composition of the present invention has particularly excellent flame retardancy at the above thickness. In particular, a silicone rubber cured product having a thickness of 0.5 mm or more, preferably 1 mm or more, can have a flame retardancy of V-1 in a flame retardancy test based on the UL94 standard. In the present invention, the flame retardancy test was performed according to the following method based on the vertical flame test method of the UL94 standard. [Measurement method] 1. A rectangular test piece with a width of 13.0 mm, a length of 125 mm, and a practical minimum thickness is hung vertically by a fixing clamp. 2. Apply the centre of a 20mm high gas burner flame to the bottom edge of the test piece for 10 seconds. 3. Remove the flame and measure the burning time. If the burning stops within 30 seconds, reapply the flame for a further 10 seconds. 4. Five test pieces were used, and the evaluation results were n=5. [Evaluation Criteria] 1. There is no sample to burn up to the position of the fixing clamp. 2. The test piece is exposed to flame twice, and the after-flame time (T1) after the first exposure to flame and the after-flame time (T2) after the second exposure to flame for each test piece must be 30 seconds or less. 3. The residual flame time (T2) and afterglow time (T3) after the second exposure to flame must be 60 seconds or less. 4. The total afterflame time (T1+T2) of the five test specimens is 250 seconds or less. 5. The absorbent cotton placed underneath the test specimen is ignited, and no test specimen causes the burning particles to fall. Products that satisfied all five of the above criteria were judged to have flame retardancy of V-1.

[0044] The addition-curable silicone composition of the present invention is capable of providing silicone rubber with excellent flame retardancy, and because it has excellent storage stability, it is useful in applications where flame retardancy is required, such as electrical appliances, cable terminal parts, polymer insulators, and automotive materials. EXAMPLES

[0045] 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. The average degree of polymerization means the number-average degree of polymerization in terms of polystyrene measured by gel permeation chromatography (GPC) analysis using toluene as a developing solvent.

[0046] The component (A) used in the following examples and comparative examples is a linear dimethylpolysiloxane represented by the following average composition formula: R a SiO (4-a) / 2 (2) (a≒2)

[0047] The component (B) used in the following examples and comparative examples is the following compound. Solid (CH3)3SiO at 25°C 1 / 2 Unit: CH2=CH(CH3)2SiO 1 / 2 Units and SiO 4 / 2 Organopolysiloxane resin consisting of units (b1) [(CH3)3SiO 1 / 2Units and CH2=CH(CH3)2SiO 1 / 2 [total moles in units] / SiO 4 / 2 Molar unit = 0.85, vinyl group content = 0.00086 mol / g

[0048] The component (C) used in the following examples and comparative examples is the following compound. Crosslinking agent (c1): Methylhydrogenpolysiloxane having hydrosilyl groups at both ends of the following formula (3) (amount of hydrosilyl groups: 0.00424 mol / g) [ka] Crosslinking agent (c2): Methylhydrogenpolysiloxane (hydrosilyl group amount: 0.00379 mol / g) represented by the following formula (4) [ka] Comparative crosslinking agent (c3): A dimethylsiloxane-methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends (hydrosilyl group amount: 0.00739 mol / g), represented by the following formula (5). [ka] Comparative crosslinking agent (c4): Dimethylsiloxane-methylhydrogensiloxane copolymer capped with trimethylsiloxy groups at both ends (hydrosilyl group amount 0.00228 mol / g), represented by the following formula (6) [ka]

[0049] The component (E) used in the following examples and comparative examples is as follows. (E): BET specific surface area is 200m 2 / g of fumed silica (e1) (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) The specific surface area according to the BET method is 300m 2 / g of fumed silica (e2) (Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) The specific surface area according to the BET method is 200m 2 / g fumed silica (e3) (Tokuyama Corporation, Leoloseal (registered trademark) DM-20S)

[0050] [Example 1] Both ends are blocked with dimethylvinylsiloxy groups. The average degree of polymerization is 510. The viscosity at 23°C is 40 parts by mass of linear dimethylpolysiloxane (a1) having a viscosity of 10 Pa·s, 5.0 parts by mass of the organopolysiloxane resin (b1), 5.0 parts by mass of linear dimethylpolysiloxane (a2) having an average degree of polymerization of 450 and both ends blocked with dimethylvinylsiloxy groups, 27 parts by mass of the fumed silica (e1), 5.0 parts by mass of hexamethyldisilazane, 0.1 parts by mass of bis(N,N-trimethylsilylamino)methylvinylsilane, and 2.5 parts by mass of water were mixed at room temperature for 120 minutes. Then, 10 parts by mass of the linear dimethylpolysiloxane (a1) was further added, and the mixture was mixed at 25°C for 60 minutes, and the mixture was heated to 150°C and stirred for 150 minutes. Next, the mixture is cooled, and 40 parts by mass of the linear dimethylpolysiloxane (a1) is further added to the mixture, 200 D Vi 10 and the vinyl value is 6.5 x 10 -4 5 parts by mass of linear dimethylpolysiloxane (a3) ​​having an average degree of polymerization of 200 and a molecular weight of 1.0 moles / g, and 5 parts by mass of non-functional linear dimethylpolysiloxane having trimethylsiloxy groups at both molecular chain terminals and an average degree of polymerization of 42 were added, and after mixing for 30 minutes, a silicone base was obtained.

[0051] To 140 parts by mass of this silicone base, 5 parts by mass of linear dimethylpolysiloxane (a4) whose molecular chain is terminated at both ends with dimethylvinylsiloxy groups and has an average degree of polymerization of 750, 5.70 parts by mass of the above crosslinking agent (c1) [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components=1.6 (mol / mol)], 0.2 parts by mass of 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane as a reaction inhibitor, 0.08 parts by mass of ethynylcyclohexanol, 0.30 parts by mass of a platinum catalyst (Pt concentration: 1% by mass), and 0.2 parts by mass of a 10% by mass solution of 1,2,3-benzotriazole in ethanol were added, and the mixture was stirred and mixed for 15 minutes to obtain a liquid silicone composition.

[0052] [Viscosity measurement] The viscosity of the silicone composition was measured at 23° C. at a shear rate of 2.0 s using a HAAKE MARS40 manufactured by Thermo Fisher Scientific Co., Ltd. -1 The results are shown in Table 1.

[0053] [Measurement of physical properties of cured product] The physical properties of the cured product of the above silicone composition were measured. The composition was press cured at 150° C. for 10 minutes, and the hardness, tensile strength, elongation at break, and tear strength (angle type) of the resulting cured product were measured in accordance with JIS K6249:2003. The results are shown in Table 1.

[0054] [Flame retardancy measurement] The above silicone composition was press cured at 150° C. for 10 minutes to produce a cured sheet having a thickness of 1 mm, and the flame retardancy was measured by the method described below. Flame retardancy was measured according to the method prescribed in the vertical flame test based on the UL94 standard, the details of which are as described above.

[0055] [ Reference example 2] 60 parts by mass of linear dimethylpolysiloxane (a5) with an average degree of polymerization of 750 and a viscosity of 30 Pa.s at 23°C, both ends of which are blocked with dimethylvinylsiloxy groups, 40 parts by mass of the fumed silica (e2), 8.0 parts by mass of hexamethyldisilazane, 0.2 parts by mass of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and 2.0 parts by mass of water were mixed at room temperature for 120 minutes. The mixture was then heated to 150°C and stirred for 150 minutes, cooled, and 30 parts by mass of the linear dimethylpolysiloxane (a5) was further added, and after mixing for 30 minutes, a silicone base was obtained. To 140 parts by mass of this silicone base, 13.75 parts by mass of the linear dimethylpolysiloxane (a5), 5 parts by mass of the organopolysiloxane resin (b1), 0.6 parts by mass of a linear dimethylpolysiloxane (a7) whose molecular chain is terminated at both ends with dimethylvinylsiloxy groups and has an average degree of polymerization of 180, 2.5 parts by mass of titanium oxide (Super Titania F-4A, manufactured by Showa Denko K.K.) and 1.25 parts by mass of titanium oxide (Typec CR-60, manufactured by Ishihara Sangyo Kaisha Ltd.) as white colorants, 0.10 parts by mass of carbon (Denka Black granular, manufactured by Denki Kagaku Co., Ltd.) as a black colorant, and 3.25 parts by mass of the crosslinking agent (c1) [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components= 1.1 (mol / mol)], 0.2 parts by mass of 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane as a reaction inhibitor, 0.08 parts by mass of ethynylcyclohexanol, 0.30 parts by mass of a platinum catalyst (Pt concentration: 1% by mass), and 0.2 parts by mass of a 10% solution of 1,2,3-benzotriazole in ethanol were added, and the mixture was stirred for 15 minutes to obtain a liquid silicone composition. The viscosity of the resulting silicone composition and the physical properties and flame retardancy of the cured product were measured in the same manner as in Example 1. The results are shown in Table 1.

[0056] [Example 3] Both ends are blocked with dimethylvinylsiloxy groups. The average degree of polymerization is 215 and the viscosity at 23°C is 40 parts by mass of linear dimethylpolysiloxane (a8) having a viscosity of 1 Pa.s, 5.0 parts by mass of the organopolysiloxane resin (b1), 5.0 parts by mass of linear dimethylpolysiloxane (a9) having an average degree of polymerization of 450 and both ends blocked with dimethylvinylsiloxy groups, 27 parts by mass of the fumed silica (e3), 2.0 parts by mass of hexamethyldisilazane, 0.1 parts by mass of bis(N,N-trimethylsilylamino)methylvinylsilane, and 2.5 parts by mass of water were mixed at room temperature for 120 minutes. Then, 10 parts by mass of the linear dimethylpolysiloxane (a8) were further added, and the mixture was mixed at 25°C for 60 minutes, and the mixture was heated to 150°C and stirred for 150 minutes. Next, after cooling, 40 parts by mass of the linear dimethylpolysiloxane (a8), 5 parts by mass of linear dimethylpolysiloxane (a10) whose both molecular chain terminals are blocked with trimethylsiloxy groups and which has 5.0 mol% vinyl groups on its side chains and has an average degree of polymerization of 200, and 5 parts by mass of nonfunctional linear dimethylpolysiloxane having trimethylsiloxy groups at both molecular chain terminals and an average degree of polymerization of 42, were added, and after mixing for 30 minutes, a silicone base was obtained. To 140 parts by mass of this silicone base, 5 parts by mass of the linear dimethylpolysiloxane (a8), 5 parts by mass of a nonfunctional linear dimethylpolysiloxane having trimethylsiloxy groups at both molecular chain terminals and having an average degree of polymerization of 86, 9.80 parts by mass of the crosslinking agent (c2) [hydrosilyl groups of the crosslinking agent in the blended components / alkenyl groups in the blended components=1.5 (mol / mol)], 2.5 parts by mass of a linear dimethylpolysiloxane (a11) whose molecular chain terminals are blocked with dimethylvinylsiloxy groups and whose average degree of polymerization is 1,080, To the mixture were added 1.7 parts by mass of linear dimethylpolysiloxane (a12), 2.5 parts by mass of titanium oxide (Typaque CR-60, manufactured by Ishihara Sangyo Kaisha) as a white colorant, 0.30 parts by mass of carbon (Denka Black granular, manufactured by Denki Kagaku Kabushiki Kaisha) as a black colorant, 0.2 parts by mass of 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane as a reaction inhibitor, 0.08 parts by mass of ethynylcyclohexanol, 1.00 part by mass of a platinum catalyst (Pt concentration: 1% by mass), and 0.2 parts by mass of a 10% by mass solution of 1,2,3-benzotriazole in ethanol, and the mixture was stirred and mixed for 15 minutes to obtain a liquid silicone composition. The viscosity of the resulting silicone composition and the physical properties and flame retardancy of the cured product were measured in the same manner as in Example 1. The results are shown in Table 1.

[0057] [Comparative Example 1] A liquid silicone composition was obtained by repeating Example 1, except that the amount of the crosslinking agent (c1) was 6.50 parts by mass [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components=1.8 (mol / mol)]. The viscosity, physical properties of the cured product, and flame retardancy of the resulting silicone composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0058] [Comparative Example 2] A liquid silicone composition was obtained by repeating Example 1, except that the amount of the crosslinking agent (c1) was 5.00 parts by mass [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components=1.4 (mol / mol)]. The viscosity, physical properties of the cured product, and flame retardancy of the resulting silicone composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0059] [Comparative Example 3] A liquid silicone composition was obtained by repeating Example 1, except that the crosslinking agent (c1) was changed to 3.27 parts by mass of the comparative crosslinking agent (c3) [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components=1.6 (mol / mol)]. The viscosity, physical properties of the cured product, and flame retardancy of the resulting silicone composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0060] [Comparative Example 4] A liquid silicone composition was obtained by repeating Example 1, except that the crosslinking agent (c1) was changed to 10.60 parts by mass of the comparative crosslinking agent (c4) [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components=1.6 (mol / mol)]. The viscosity, physical properties of the cured product, and flame retardancy of the resulting silicone composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0061] [Comparative Example 5] A liquid silicone composition was obtained by repeating Example 2, except that the crosslinking agent (c1) was replaced with 5.90 parts by mass of the comparative crosslinking agent (c4) [hydrosilyl groups of crosslinking agent in blended components / alkenyl groups in blended components=1.6 (mol / mol)]. The viscosity, physical properties of the cured product, and flame retardancy of the resulting silicone composition were measured in the same manner as in Example 1. The results are shown in Table 1.

[0062] [Table 1]

Claims

1. (A) an organopolysiloxane that is liquid at 23° C. and has two or more alkenyl groups bonded to silicon atoms in each molecule: 100 parts by mass, (B) R １ ３ SiO １／２ Units (wherein R １ are each independently a monovalent hydrocarbon group) and SiO ４／２ Contains units, SiO ４／２ R for units １ ３ SiO １／２ Molar ratio of units [R １ ３ SiO １／２ / SiO ４／２ ] is 0.5 to 1.5, and the alkenyl group content is 1×10 －４ ~5×10 －３ mol / g three-dimensional network structure organopolysiloxane resin: 3 to 50 parts by mass (C) A linear organohydrogenpolysiloxane represented by the following formula (1): 【Chemistry 1】 (In formula (1), y is an integer from 4 to 98, z is an integer from 2 to 50, and y+z is 6 to 110, the ratio of y / z is 2.5 to 4, and R ２ are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups); R ３ are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms (excluding alkenyl groups) or a hydrogen atom. : an amount such that the ratio of the number of moles of silicon-bonded hydrogen atoms to the total number of moles of silicon-bonded alkenyl groups in the composition is 1.5 to 1.7 (D) Addition reaction catalyst: catalytic amount (E) Specific surface area by BET method 100 m ２ / g or more fumed silica: 10 to 50 parts by mass, and (F) Triazole compound: 0.001 to 0.5 parts by mass An addition-curable silicone composition comprising:

2. In the formula (1), all R ２ 2. The addition-curable silicone composition according to claim 1, wherein at least 90 mol % of the groups are methyl groups.

3. 3. The addition-curable silicone composition according to claim 1, wherein the component (A) has an average degree of polymerization of 100 to 1,500.

4. The addition-curable silicone composition according to any one of claims 1 to 3, which has a viscosity at 23°C of 10,000 mPa·s to 10,000,000 mPa·s.

5. The addition-curable silicone composition according to any one of claims 1 to 4, wherein the component (F) is benzotriazole.

6. The addition-curable silicone composition according to claim 1, wherein the fumed silica (E) is a silica fine powder that has been surface-hydrophobized with an organosilicon compound.

7. The addition-curable silicone composition according to any one of claims 1 to 6, further comprising at least one reaction inhibitor selected from acetylene compounds, alkenyl group-containing low molecular weight siloxanes, nitrogen-containing compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, and sulfur compounds in an amount of 0.01 to 1 part by mass per 100 parts by mass of component (A).

8. A silicone rubber obtained by curing the addition-curable silicone composition according to any one of claims 1 to 7.

9. 9. The method for producing silicone rubber according to claim 8, further comprising a step of curing the addition-curable silicone composition after molding to obtain a silicone rubber molded product, wherein the curing method is only primary vulcanization.

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