Polyimidosiloxane resin and composition thereof and method of applying same

A polyimidosiloxane resin composition comprising:

• (I) a polyimidosiloxane resin comprising a polymerization-imidization product of:
• (A) an aromatic tetracarboxylic acid component comprising:
• (a) 80 to 100 molar % of a principal acid ingredient consisting of at least one member selected from the group consisting of 2,3,3',4'-biphenyltetracarboxylic acid and dianhydrides and esters thereof;
• and
• (b) 0 to 20 molar % of an additional acid ingredient consisting of at least one member selected from the group consisting of aromatic tetracarboxylic acids different from 2,3,3',4'-biphenyltetracarboxylic acid and dianhydrides and esters thereof;
• and
• (B) a diamine component comprising:
• (c) 45 to 90 molar % of a principal diamine ingredient consisting of at least one diaminopolysiloxane compound of the formula (I):
• ##STR5## wherein R.sub.1 represents a divalent hydrocarbon residue, R.sub.2 represents a member selected from alkyl groups having 1 to 3 carbon atoms and a phenyl group, and n represents an integer of from 3 to 30;
• and
• (d) 10 to 55 molar % of an additional diamine ingredient comprising 55 to 99.5 molar % of at least one aromatic diamine compound having a plurality of benzene ring structures and different from the diaminopolysiloxane compound of formula (I), and 0.5 to 45 molar % of at least one diaminobenzoic acid, based on the total molar amount of the additional diamine ingredient (d);
• and
• (II) an epoxy resin having an epoxy equivalent of 100 to 1000 and a molecular weight of 400 to 5000, in an amount of 1 to 50 parts by weight per 100 parts by weight of the polyimidosiloxane resin, the polyimidosiloxane resin and the epoxy resin being dissolved or dispersed in an organic solvent having a boiling point of from 100.degree. C. to 300.degree. C.