JPH10316859A - Silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicone rubber composition capable of providing a hardened product excellent in flame retardance and electric insulation. SOLUTION: This silicone rubber composition comprises (A) 100 pts.wt. organosiloxane of the formula Ra SiO(4-a)/2 [R is a same or a different monovalent hydrocarbon; (a) is a positive number of 1.90-2.05], (B) 10-100 pts.wt. reinforcing silica having a >=50 m<2> /g specific surface area, (C) a amount a hardening agent required for hardening, (D) 0.001-0.01 pt.wt. platinum-based compound (in terms of platinum) and (E) 0.1-15 pts.wt. MT carbon having >=200 nm average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a silicone rubber composition which gives a cured product having improved flame retardancy and can be suitably used in the fields of electric / electronic parts, automobile parts and the like.

[0002]

2. Description of the Related Art Silicone rubber has advantages such as heat resistance, weather resistance, durability, mold release properties, and electrical characteristics, and has been conventionally processed into various shapes. It is used in various fields such as electric / electronic related parts, automobile parts, OA equipment parts, and building materials.

[0003] In addition, various additives have been added to silicone rubber to impart flame retardancy. As a method for imparting flame retardancy to a silicone rubber composition, a method using a platinum catalyst as a flame retardant is generally used.

However, the use of a platinum catalyst alone does not provide sufficient flame retardancy, and various assistants have been considered. For example, U.S. Pat. No. 3,635,874
Japanese Patent Publication No. 51-24302 proposes a method of adding titanium oxide, and Japanese Patent Publication No. 51-24302 discloses a method of adding iron oxide (FeO) _x (Fe ₂ O ₃ ) _y .

US Pat. No. 3,652,488 discloses carbon black, and describes that acetylene black is particularly effective. In addition to acetylene black, carbon black includes furnace black made by the furnace method, thermal black made by the thermal method, channel black, etc., but these do not only contribute to flame retardancy, but also worsen, Acetylene black was often used.

[0006] However, acetylene black has the disadvantage that the electrical properties of the rubber are drastically changed by the addition thereof, and it is generally used in combination with other titanium oxides or iron oxides to provide more effective flame retardancy. The development of the technology to do it was desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silicone rubber composition which provides a cured product having excellent flame retardancy and good electrical insulation.

[0008]

Means for Solving the Problems and Embodiments of the Invention The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that an organopolysiloxane represented by the following average composition formula (1), a specific surface area (BET) Mod.) Is at least 50 m ² /
g of a silicone rubber composition containing reinforcing silica, a curing agent, a platinum compound as a flame retardant, and MT carbon (medium thermal (medium thermal decomposition method) carbon) having an average particle diameter of 200 nm or more. It has been found that a cured product having excellent insulation properties is provided.

That is, as described above, carbon black is generally classified into a furnace black produced by a furnace method and a thermal black produced by a thermal method according to its production method. When MT carbon with average particle size of 200 nm or more in thermal black is added as a flame retardant aid to a silicone rubber composition containing a platinum-based compound as a flame retardant, electrical properties change unexpectedly. It has been found that a cured product having flame retardancy higher than that of acetylene black can be obtained without causing the present invention, and the present invention has been accomplished.

Accordingly, the present invention relates to (A) the following average composition formula (1): R _a SiO _{(4-a) / 2} (1) (wherein R is the same or different monovalent hydrocarbon group; , A is a positive number from 1.90 to 2.05.) 100 parts by weight of an organopolysiloxane (B) 10 to 100 parts by weight of a reinforcing silica having a specific surface area of at least 50 m ² / g (C ) Curing agent Curing required amount (D) Platinum compound 0.001 to 0.01 parts by weight in terms of platinum (E) 0.1 to 15 parts by weight of MT carbon having an average particle diameter of 200 nm or more The present invention provides a silicone rubber composition characterized by the following.

Hereinafter, the present invention will be described in more detail. The organopolysiloxane of the component (A) of the silicone rubber composition of the present invention is represented by the following average composition formula (1), and is mainly composed of a linear compound. It is a diorganopolysiloxane. R _a SiO _{(4-a) / 2} (1)

Here, R is the same or different monovalent hydrocarbon group, preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl and the like. Alkyl group, vinyl group, allyl group,
Alkenyl groups such as butenyl group and hexenyl group, aryl groups such as phenyl group and tolyl group, and unsubstituted hydrocarbon groups such as alkyl group, alkenyl group and aryl group are partially or entirely hydrogen atoms halogen atoms and cyano groups. Examples thereof include a 3,3,3-trifluoropropyl group and a 2-cyanoethyl group substituted with, for example, and a monovalent group selected from a methyl group, a vinyl group, and a phenyl group is particularly preferable.

Further, both ends of the molecular chain are preferably blocked with, for example, a hydroxy group, a trimethylsilyl group, a dimethylvinylsilyl group, a methyldiphenylsilyl group, a methylphenylvinylsilyl group, but are not particularly limited. In addition, in said Formula (1), a is 1.90-.
It is a positive number of 2.05.

The organopolysiloxane of the above formula (1) may be linear or branched, but is preferably a linear one, and has an average degree of polymerization of 3,000 in order to obtain sufficient mechanical strength. As described above, it is particularly preferable that the number is from 3,000 to 10,000, and especially from 5,000 to 10,000.
It is preferably 0.

As the reinforcing silica of the component (B), a silicone rubber having a BET specific surface area of 50 m ² / g or more is used in order to improve mechanical strength such as moderate hardness and tensile strength of silicone rubber. In particular, it is preferable to use one having a thickness of 100 to 400 m ² / g. Specifically, fumed silica, calcined silica, precipitated silica, and the like are used alone or in combination of two or more as the fine powder silica.

These reinforcing silicas can be used after being surface-treated with a chain organopolysiloxane, a cyclic organopolysiloxane, hexamethyldisilazane, dichlorodimethylsilane or the like.

The compounding amount of the reinforcing silica of the component (B) is 10 to 100 parts, preferably 15 to 50 parts with respect to 100 parts (parts by weight, hereinafter the same) of the organopolysiloxane of the component (A). . 1 even if the amount is more than 100 parts
If the amount is less than 0 part, the processability of the silicone rubber composition containing the compound becomes poor, or sufficient mechanical strength cannot be obtained.

Next, the curing agent of the component (C) is used to cure the composition of the present invention into a silicone rubber, and generally an organic peroxide is used. When the organopolysiloxane raw rubber of the component (A) contains an alkenyl group, an organohydrogenpolysiloxane can also be used, and these curing agents are used in an amount sufficient to cure the composition of the present invention. Mix.

Here, specific examples of the organic peroxide include dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di (t-butyl peroxide). Butylperoxy) hexane,
2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) -3,3,5-trimethylcyclohexane, benzoyl peroxide, Examples thereof include 2,4-dichlorobenzoyl peroxide and 4-chlorobenzoyl peroxide. The amount of these organic peroxides is preferably in the range of 0.1 to 10 parts based on 100 parts of the component (A).

The organohydrogenpolysiloxane has at least two, and preferably three or more, SiH groups in one molecule, and specifically includes methylhydrogenpolysiloxane having trimethylsiloxy groups at both ends. Examples thereof include a dimethylsiloxane / methylhydrogensiloxane copolymer having a terminal-trimethylsiloxy group and a dimethylsiloxane / methylhydrogensiloxane copolymer having both ends of a methylhydrogensiloxy group. The mixing amount of the organohydrogenpolysiloxane is generally such that the ratio of the number of moles of silicon-bonded hydrogen atoms contained in the organohydrogenpolysiloxane to the number of moles of alkenyl groups in the component (A) is 0.
The amount is 5: 1 to 20: 1.

Usually, when an organohydrogenpolysiloxane is used as a curing agent, a platinum compound is required as a catalyst, but the component (D) also has this catalytic action.

The platinum compound as the component (D) is compounded as a flame retardant in the present invention, and specific examples thereof include chloroplatinic acid and an alcohol solution of chloroplatinic acid.
The amount of the platinum-based compound added is (A) component 1 in terms of platinum.
0.001 to 0.01 parts for 00 parts.

In the silicone rubber composition of the present invention, MT carbon as the component (E) is added as a flame retardant aid.

In general, carbon black is classified into furnace black produced by the furnace method, thermal black produced by the thermal method, and the like according to the production method.
In the present invention, among thermal blacks, the average particle
MT carbon of 0 nm or more provides flame retardancy over acetylene black without significantly changing electrical properties.

The average particle size of the MT carbon is 200 to 5
00 nm, especially 250 to 400 nm, is preferred. Those having an average particle size of less than 200 nm may have little effect on flame retardancy, and those having an average particle size of more than 500 nm are not commercially available.

The amount of MT carbon added depends on the amount of component (A) 10
0.1 to 15 parts, more preferably 1 to 10 parts per 0 parts
Department. If the amount is less than 0.1 part, the effect of improving the flame retardancy cannot be expected. If the amount exceeds 15 parts, the flame retardancy is adversely affected.

When the MT carbon is blended with the silicone rubber composition, a kneading machine such as a kneader, a Banbury mixer, or an open roll can be used.

The silicone rubber composition of the present invention may contain, in addition to the above-mentioned components (A) to (E), various known rubber compounding agents which are appropriately compounded with the silicone rubber in an amount which does not impair the object of the present invention. For example, diphenylsilanediol, silicone oil having a low degree of polymerization at the molecular chain terminal hydroxyl group, dispersant such as hexamethylsilazane, alkoxysilane, ground silica, diatomaceous earth, iron oxide, zinc oxide, titanium oxide, carbon black other than MT carbon, oxidation Barium, calcium carbonate, magnesium carbonate, zinc carbonate, asbestos, glass wool, fine mica, fused silica powder and the like may be added and blended. Further, if necessary, a pigment, a dye, an antioxidant, an antioxidant, an antistatic agent, and a thermal conductivity improver such as boron nitride and aluminum nitride may be blended.

The method for producing the silicone rubber composition of the present invention is not particularly limited, but the components (A) and (B) are charged into a kneading device such as a kneader and blended at room temperature. A method of heat-treating for 30 minutes to 5 hours, and then kneading the components (D) and (E) with a roller mill, a Banbury mixer, or the like can be employed. Thereafter, the component (C) may be added, and the composition may be heated and cured by a known method. The curing conditions vary depending on the type of the curing agent, the curing method, the molded product, and the like, but are usually preferably at 80 to 400 ° C. for several seconds to several days.

[0030]

The silicone rubber composition of the present invention provides a cured silicone rubber having good flame retardancy and heat resistance. The cured product is suitable for roll materials, electric wires, and other electric parts. You can use it.

[0031]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In addition, in the following examples, a part shows a weight part. Example 1 99.85 mol% of (CH ₃ ) ₂ SiO units as an organopolysiloxane (A), (CH ₃ )
(CH ₂ ＣＨCH) SiO units consisting of 0.15 mol%,
A methylvinylpolysiloxane raw rubber having a degree of polymerization of about 7,000 and having a molecular chain terminal blocked with (CH ₂ ＣＨCH) (CH ₃ ) ₂ SiO units was used. 100 parts of the above methylvinylpolysiloxane raw rubber, fumed silica 25 having a specific surface area of 200 m ² / g as a reinforcing silica of the component (B).
Parts of dimethylpolysiloxane containing hydroxyl groups at the molecular chain terminals (degree of polymerization 10) as a dispersant and methylvinylpolysiloxane containing hydroxyl groups at both molecular chain terminals (degree of polymerization 15, vinyl group content based on all organic groups) 5 mol%) 3
The parts were uniformly mixed in a kneader and heat-treated at 150 ° C. for 2 hours. Next, as a component (D), a platinum catalyst was added so as to be 0.005% by weight of chloroplatinic acid to obtain a silicone rubber base. Further, as a component (E), 3 parts of MT carbon (average particle size: 350 nm) was added to the base by a two-roll mill to obtain a silicone rubber composition.

The obtained silicone rubber composition was added with (C)
After adding 0.5 part of 2,5-bis (t-butylperoxy) -2,5-dimethylhexane as a component curing agent,
Press cure at 170 ° C x 10 minutes, then 200 ° C x 2
After-curing was performed for 40 minutes to obtain a sheet-like molded product.
The volume resistivity of the molded product and the flame retardant seconds of the 0.8 mm thick sheet were measured by the method specified in UL94.

Example 2 A silicone rubber molded product was prepared in the same manner as in Example 1 except that the amount of MT carbon (average particle diameter: 350 nm) was changed to 8 parts. The flame retardant seconds were measured.

Comparative Example 1 A silicone rubber molded product was prepared by adding 3 parts of acetylene black (average particle size of 50 nm) instead of 3 parts of MT carbon (average particle size of 350 nm) of Example 1, and producing a volume resistivity. , Flame retardant seconds were measured.

Comparative Example 2 The volume resistivity and flame retardant seconds of the silicone rubber molded product prepared in Example 1 without adding the component (E) were measured. Table 1 shows the results of the above Examples and Comparative Examples.
Shown in

[0036]

[Table 1]

[Example 3] Silicone rubber molding was performed in the same manner as in Example 1 except that 5 parts of MT carbon (average particle diameter 250 nm) was added instead of 3 parts of MT carbon (average particle diameter 350 nm) of Example 1. An article was prepared, and its volume resistivity and flame retardant seconds were measured.

Comparative Example 3 In the same manner as in Example 1 except that 5 parts of FT carbon (average particle diameter: 80 nm) of thermal black was added instead of 3 parts of MT carbon (average particle diameter: 350 nm) of Example 1. A silicone rubber molded product was prepared, and its volume resistivity and flame retardant seconds were measured. Table 2 shows the results of Example 3 and Comparative Example 3.

[0039]

[Table 2]

Example 4 Silicone rubber molding was carried out in the same manner as in Example 1 except that 6 parts of MT carbon (average particle diameter 350 nm) was added instead of 3 parts of MT carbon (average particle diameter 350 nm) of Example 1. An article was prepared, and its volume resistivity and flame retardant seconds were measured.

Comparative Example 4 A silicone rubber molded product was produced in the same manner as in Example 1 except that the addition amount of MT carbon (average particle diameter: 350 nm) was changed to 0.05 part. The rate and flame retardant seconds were measured.

Comparative Example 5 A silicone rubber molded article was prepared in the same manner as in Example 1 except that the amount of MT carbon (average particle diameter: 350 nm) was changed to 20 parts. The flame retardant seconds were measured. Table 3 shows the results of Example 4 and Comparative Examples 4 and 5.

[0043]

[Table 3]

Claims (1)

[Claims] (A) The following average composition formula (1) R _a SiO _{(4-a) / 2} (1) (wherein R is the same or different monovalent hydrocarbon group, and a is 1 (B) a reinforcing silica having a specific surface area of at least 50 m ² / g, (C) a curing agent, and a curing agent. Required amount (D) Platinum compound 0.001 to 0.01 parts by weight in terms of platinum (E) 0.1 to 15 parts by weight of MT carbon having an average particle diameter of 200 nm or more Silicone rubber composition.