Mouldable silicone gel composition

A moldable silicone gel composition that forms a low compression set silicone gel that exhibits an excellent mold releasability. The composition comprises the following components: A, 100 parts by weight of an organopolysiloxane having at least two alkenyl groups in each molecule, B, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in each molecule, in an amount such that the molar ratio of silicon bonded hydrogen atoms in component B to alkenyl groups in component A is from 0.5:1 to 10:1, C 100 to 500 parts by weight of organopolysiloxane whose molecule contains which is free of both alkenyl groups and silicon bonded hydrogen, and D a platinum group catalyst, in an amount sufficient to effect the cure of the composition.

EXAMPLES The mouldable silicone gel composition in accordance with the present invention will be exemplified in the following examples, in which all values of viscosity were measured at 25° C. 
 Example 1 The following were blended: 100 parts by weight of trimethylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxane copolymer having a viscosity of 10,000 mpa·s, 40 parts by weight of fumed silica with a BET specific surface area of 200 m 2 /g, 5 parts by weight of hexamethyldisilazane as treatment agent for the silica, and 2 parts by weight of water. The resulting blend was subsequently mixed and heated under reduced pressure to produce a fluid silicone gel base. A mouldable silicone gel composition was then prepared by mixing the following: 140 parts by weight of the fluid silicone gel base described above, 230 parts by weight of trimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 3,000 mpa·s, trimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 10 mPa·s, in an amount such that there was 1.6 moles of silicon-bonded hydrogen per mole of vinyl groups in the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, a platinum-1,3-divinyltetramethyldisiloxane complex in an amount such that there was present 35 parts by weight of platinum metal per 1,000,000 parts by weight of the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, and 0.12 parts by weight of 3,5-dimethyl-1-hexyn-3-ol. The mould releasability, Asker C hardness, and compression set of the resulting cured product were measured using the test methods described hereafter and the results thereof are reported in Table 1. Mould Releasability The silicone gel composition was cast into a steel mould provided with a square cavity (depth&equals;5 mm, length of 1 side&equals;100 mm) and was press-cured for 10 minutes at 150° C. The ease with which the resulting silicone gel could be removed from the mould was then evaluated. Asker C Hardness The hardness of the silicone gel after press-curing (primary vulcanisation) was measured using an Asker C hardness meter. The hardness of the silicone gel was also measured by the same method after a secondary vulcanisation consisting of heating for 4 hours at 200° C. Compression Set The silicone gel composition was cured for 10 minutes at 150° C. in order to fabricate a test piece for measurement of the compression set in accordance with the method described in JIS K 6249. The test piece was then subjected to secondary vulcanisation for 4 hours at 200° C. This was followed by measurement of the compression set (compression for 70 hours at 150° C.) in accordance with the method specified in JIS K 6249. 
 Comparative Example 1 A mouldable silicone gel composition was prepared by mixing the following: 140 parts by weight of fluid silicone gel base prepared as described in Example 1, 100 parts by weight of dimethylvinylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 40,000 mpa·s, trimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 10 mPa·s in an amount such that there was 0.5 moles of silicon-bonded hydrogen per mole of vinyl groups in the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, a platinum-1,3-divinyltetramethyldisiloxane complex in an amount such that there was present 10 parts by weight of platinum metal per 1,000,000 parts by weight of the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, and 0.1 parts by weight 3,5-dimethyl-1-hexyn-3-ol. The mould releasability, Asker C hardness, and compression set were measured as in Example 1 on silicone gels produced by the cure of this silicone gel composition. The results are reported in Table 1. 
 Comparative Example 2 A mouldable silicone gel composition was prepared by mixing the following: 140 parts by weight of fluid silicone gel base prepared as described in Example 1, 70 parts by weight of trimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 3,000 mPa·s, trimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 10 mPa·s in an amount such that there was 0.9 moles of silicon-bonded hydrogen per mole of vinyl group in the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, a platinum-1,3-divinyltetramethyldisiloxane complex in an amount such that there was present 10 parts by weight of platinum metal per 1,000,000 parts by weight of the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, and 0.1 parts by weight 3,5-dimethyl-1-hexyn-3-ol. The mould releasability, Asker C hardness, and compression set were measured as in Example 1 on silicone gels produced by the cure of this silicone gel composition. The results are reported in Table 1. 1 TABLE 1 Example 1 Comp. Ex. 1 Comp. Ex. 2 Asker C hardness after primary 5 5 5 vulcanisation after secondary 6 7 7 vulcanisation Mould no sticking to strong sticking to strong sticking to releasability the mould, the mould, the the mould, the could be easily silicone gel was silicone gel was peeled out torn torn compression set 18% 60% 55% 
 Example 2 The following were blended: 100 parts by weight of dimethylvinylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 10,000 mPa·s and 20 parts by weight of fumed silica with a BET specific surface area of 200 m 2 /g whose surface had already been treated with dimethyldichlorosilane. Blending was followed by mixing and heating under reduced pressure to produce a fluid silicone gel base. A mouldable silicone gel composition was then prepared by mixing the following: 120 parts by weight of the fluid silicone gel base described above, 140 parts by weight of trimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 100 mPa·s, a trimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 5 mPa·s in an amount such that there was 1.4 moles of silicon-bonded hydrogen per mole of vinyl groups in the dimethylvinylsiloxy-endblocked dimethylpolysiloxane present in the silicone gel base, a platinum-1,3-divinyltetramethyldisiloxane complex in an amount such that there was present 35 parts by weight of platinum metal per 1,000,000 parts by weight of the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, and 0.12 parts by weight of 3,5-dimethyl-1-hexyn-3-ol, and 1 part by weight of finely divided copper phthalocyanine. The mould releasability, Asker C hardness, and compression set were measured as described below on silicone gels produced by the cure of the aforementioned silicone gel composition. The results are reported in Table 2. Mould Releasability The silicone gel composition was cast into a chromium-plated steel mould provided with a cylindrical cavity (diameter&equals;2 mm, length&equals;100 mm) and was press-cured for 10 minutes at 120° C. The ease with which the resulting silicone gel could be removed from the mould was then evaluated. Asker C Hardness The hardness of the silicone gel after press-curing (primary vulcanisation) was measured using an Asker C hardness meter. Compression Set The silicone gel composition was cured for 10 minutes at 120° C. in order to fabricate a test piece for measurement of the compression set in accordance with the method described in JIS K 6249. The compression set (compression for 70 hours at 150° C.) was then measured on this test piece in accordance with the method specified in JIS K 6249. 
 Comparative Example 3 A mouldable silicone gel composition was prepared by mixing the following: 120 parts by weight of fluid silicone gel base prepared as described in Example 2, 100 parts by weight of dimethylvinylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 10,000 mPa·s, trimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 5 mPa·s in an amount such that there was 0.6 moles of silicon-bonded hydrogen per mole of vinyl groups in the dimethylvinylsiloxy-endblocked dimethylpolysiloxane present in the silicone gel base, a platinum-1,3-divinyltetramethyldisiloxane complex in an amount such that there was present 10 parts by weight of platinum metal per 1,000,000 parts by weight of the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel base, parts by weight of 3,5-dimethyl-1-hexyn-3-ol, and 1 part by weight of finely divided copper phthalocyanine. The mould releasability, Asker C hardness, and compression set were measured as in Example 2 on silicone gels produced by the cure of this silicone gel composition. The results are reported in Table 2. 
 Comparative Example 4 A mouldable silicone gel composition was prepared by mixing the following: 120 parts by weight of fluid silicone gel base prepared as described in Example 2, 50 parts by weight of trimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 100 mPa·s, trimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 5 mPa·s in an amount such that there was 0.9 moles of silicon-bonded hydrogen per mole of vinyl groups in the dimethylvinylsiloxy-endblocked dimethylpolysiloxane present in the silicone gel base, a platinum-1,3-divinyltetramethyldisiloxane complex in an amount such that there was present 10 parts by weight of platinum metal per 1,000,000 parts by weight of the dimethylsiloxane-methylvinylsiloxane copolymer present in the silicone gel, 0.1 parts by weight of 3,5-dimethyl-1-hexyn-3-ol, and 1 part by weight of finely divided copper phthalocyanine. The mould releasability, Asker C hardness, and compression set were measured as in Example 2 on silicone gels produced by the cure of this silicone gel composition. The results are reported in Table 2. 2 TABLE 2 Example 2 Comp. Ex. 3 Comp. Ex. 4 Asker C hardness 11 11 11 Mould no sticking to strong sticking to strong sticking to releasability the mould, the mould, the the mould, the could be easily silicone gel was silicone gel was peeled out torn torn compression set 22% 83% 71% The mouldable silicone gel composition in accordance with the present invention is distinguished by its capacity for moulding into a low compression set silicone gel that exhibits an excellent mould releasability.