JPH0528738B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a curable liquid silicone rubber composition, which is particularly useful for potting, coating, and insulating sealing of electrical and electronic circuit parts, television flyback transformers, and various HICs. The present invention relates to a curable liquid silicone rubber composition having a low viscosity and a low coefficient of thermal expansion. (Prior technology) For insulating potting and coating of general home appliances such as audio, television, and video tapes, HICs used in automobiles, flyback transformers of televisions, and various electric and electronic circuits. Liquid rubber filled with silica is used, but this liquid rubber does not undergo thermal expansion or
Due to large thermal contraction, the surface of many products swells due to stress during curing, testing, and use, resulting in distortion of the case, cracking of the ceramic substrate, and
Inconveniences such as breakage of lead wires often occur. For this reason, attempts have been made to fill this liquid rubber with silica particles that have a low coefficient of thermal expansion, but this is not practical because the viscosity of the composition increases with high filling and the fluidity deteriorates. The disadvantage is that it cannot be used. (Structure of the Invention) The present invention relates to an effective liquid silicone rubber composition that solves the above-mentioned disadvantages.
average formula

[Formula] (where R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and a is 1.9 to 8 carbon atoms.
2.07), contains at least one aliphatic unsaturated group in one molecule, and has a viscosity of 50 at 25°C.
100 parts by weight of an organopolysiloxane with ~10000 cS, (2) 0.1 to 50 parts by weight of an organohydrodiene polysiloxane having at least two hydrogen atoms bonded to silicon atoms (≡Si-H bonds) in one molecule, ( 3)(a) Densely fused silica powder with an average particle size of 60μm or less
30 to 100% by weight; and (b) 70 to 0% by weight of crystalline silica powder with an average particle size of 60 μm or less.
100 to 1000 parts by weight, (4) a catalytic amount of platinum or a platinum-based compound, and (5) an organosilicon with a molecular weight of 2300 or less, containing at least one hydrosilylation functional group and/or SiOH group in one molecule. compound 0.5
~30 parts by weight. That is, the present inventors have conducted various studies on the development of a liquid silicone rubber composition with low viscosity, good fluidity, and a small thermal expansion coefficient that overcomes the conventional disadvantages. They identified the average particle diameter and type of silica powder as a filler used in products, and found that it was sufficient to add an appropriate organopolysiloxane diluent to the silica powder. We confirmed that the objective could be achieved by selecting fused silica with a diameter of 60 μm or less and adding a low-viscosity organosilicon compound containing a hydroxylated functional group or SiOH group in one molecule, and developed the present invention. Completed. The organopolysiloxane as the first component constituting the composition of the present invention has an average formula of

[Formula], R is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a cycloalkyl group such as a cyclohexyl group, an alkenyl group such as a vinyl group or an allyl group, a phenyl group, a tolyl group, etc. Some or all of the hydrogen atoms bonded to the aryl group or the carbon atoms of these groups are replaced by halogen atoms,
Unsubstituted or substituted 1 having 1 to 8 carbon atoms selected from chloromethyl group substituted with cyano group, trifluoropropyl group, cyanoethyl group, etc.
It is a linear or branched hydrocarbon with a value of 1.9 to 2.07, but it has a vinyl group in one molecule for addition reaction with the organohydrodiene polysiloxane as the second component described later. It contains at least one aliphatic unsaturated group such as, for example, the following. (b to f are positive integers). Such organopolysiloxanes can serve as terminal groups, e.g.

[Formula] and

【Formula】Ya

[Formula] or

[Formula] In the presence of an alkaline catalyst such as caustic potash, cesium hydroxide, or sulfuric acid, heat equilibration reaction is carried out at an appropriate temperature of -10 to 200℃, and then the catalyst is neutralized. However, if the degree of polymerization is too low, the cured product obtained from this composition will be hard and brittle, and if it is too high, the viscosity of the composition will increase too much. The viscosity at 25° C. is preferably in the range of 50 to 10,000 cS, with a preferred range of 100 to 1,000 cS. Next, since the organohydrodiene polysiloxane as the second component in this composition is subjected to an addition reaction with the above-mentioned vinyl group-containing organopolysiloxane as the first component, it is necessary to add the organohydrodiene polysiloxane as the second component to the vinyl group-containing organopolysiloxane in one molecule. Hydrogen atom (≡
It is necessary to contain at least two (SiH bonds), and the following are exemplified, but it is preferable that this be compatible with the vinyl group-containing organopolysiloxane as the first component. . This type of organohydrodiene polysiloxane is composed of [(CH ₃ ) ₃ Si] ₂ O or [H(CH ₃ ) ₂ Si] ₂ O.

【formula】 [Thermal expansion coefficient]

A 5 x 5 x 6 mm sample was prepared from the composition and measured using a thermal daylight meter DL-1500 (trade name, manufactured by Shinku Riko Co., Ltd.). [Burning time] 5 test pieces according to UL94V measurement method
It is expressed as the total combustion time when ignited 10 times. Examples 1 to 4, Comparative Examples 1 to 3 Dimethylpolysiloxane with a viscosity of 600 cS, in which both ends of the molecular chain are blocked with dimethylvinylsilyl groups.
Add 70 parts of the silica powder shown in Table 1 to 24.5 parts by approximately 10 mm.
After mixing under reduced pressure for 60 minutes under Hg and leaving it at room temperature for 20 hours, the viscosity was measured using a Burckfield viscometer, and then the formula Methylhydrodiene polysiloxane represented by
0.52 parts, the above dimethylpolysiloxane solution of platinum-vinylsiloxane complex salt (platinum content: 1% by weight)
0.05 parts, 0.005 parts of ethynylcyclohexanol as curing rate regulator and 1 part of carbon black.
0.6 parts of carbon black paste obtained by roll-kneading 5 parts of dimethylpolysiloxane described above was added, kneaded uniformly, and press-cured at 120°C for 10 minutes. The results shown in Figure 1 are obtained, and from these results, the viscosity of the fused silica is lower, and the coefficient of thermal expansion is lower.For this silica, the coarse particles are better than the fine particles after post-curing at 200℃ for 4 hours. It was confirmed that the change in combustion time was also small.

【table】

【table】

[Table] Example 5, Comparative Example 4 The dimethylpolysiloxane and methylhydrodienepolysiloxane whose molecular chain ends were blocked with dimethylvinylsilyl groups used in Examples 1 to 4 above, and the melting conditions shown in Table 1. Silica (spherical silica) S-C5, 2-ethylhexanol modified solution of chloroplatinic acid (platinum concentration 2% by weight), formula A benzotriazole paste obtained by roll kneading the organosilicon compound represented by ethynylcyclohexanol, the carbon black paste used in Examples 1 to 4, and 1 part of benzotriazole with 99 parts of the above dimethylsiloxane was used as the third Two types of compositions were made by blending in the amounts shown in the table, and these were treated in the same manner as in Examples 1 to 4 to examine their physical properties, and the results shown in Table 4 were obtained. . In addition, when these compositions were observed after being stored at room temperature for 2 months without methylhydrodiene polysiloxane, Example 5 was found.
The composition of Comparative Example 4 could be easily remixed and showed good fluidity, but the composition of Comparative Example 4 suffered from creep hardening and required more than twice as much mixing to achieve fluidity upon remixing. I needed time.

【table】

【table】

【table】

【table】

Claims (1)

[Claims] 1 (1) Average formula [Formula] (where R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms,
100 parts by weight of an organopolysiloxane with a viscosity of 50 to 10,000 cS at 25°C, containing at least one aliphatic unsaturated group in one molecule, where a is 1.9 to 2.07), (2) Organohydrodiene polysiloxane having at least two hydrogen atoms bonded to silicon atoms (≡Si-H bonds)
0.1 to 50 parts by weight, (3) (a) Fused silica powder with an average particle size of 60 μm or less30
silica powder consisting of ~100% by weight and (b) 70% to 0% by weight of crystalline silica powder with an average particle size of 60 μm or less
100 to 1000 parts by weight, (4) Catalytic amount of platinum or platinum-based compound (5) Organosilicon compound containing at least one hydrosilylation functional group and/or SiOH group in one molecule and having a molecular weight of 2300 or less
0.5 to 30 parts by weight of a curable liquid silicone rubber composition.