PURPOSE: To form a composition of high softening point, excellent heat resistance and large solvent resistance by heating and cross-linking a mixture consisting of a high-polymer cyanoethylate having a hydroxyl radical and not less than 35% of a cyanoethyl radical in content, and also of a compound having not less than two isocyanic acid radicals in its molecule.
CONSTITUTION: Cyanoethyl radical content is required to have not less than 35%, and any cyanoethylate having its cyanoethyl radical of less than 35% in content may be low in dielectric constant not to be suited for practical use. Meanwhile, a compound having not less than two isocyanic acid radicals in its molecule is very suited for practical use because it has the ability to cause a sure cross-link reaction with a hydroxyl radical in a cyanoethylate at not less than a specified temperature. For the compounding ratio of the cyanoethylate having its hydroxyl radical and its cyanoethyl radical to the compound having not less than two isocyanic acid radicals, the increase of the latter by not less than 50% causes a decrease in the dielectric constant of the resultant product, whereas any decrease thereof by less than 0.5% causes the degree of cross-link to be decreased, thereby refusing to obtain sufficient heat resistance and sufficient solvent resistance. In this cross-linking process the heat treatment for that is made at a temperature ranging from 100 to 180 degrees Centigrade. Thus, a composition can be obtained with excellence in heat resistance and in solvent resistance besides the high dielectric constant of the cyanoethylate in itself.
KANEKO TATSUSHI
CHIBA TORU
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