| 摘要 |
A composition comprises 100 parts by weight of polyvinyl acetal, 20 to 200 parts by weight of an adduct of a polyisocyanate and an organic compound containing reactive hydrogen, i.e. a polyurethane, 1 to 30 parts by weight of a phenol-aldehyde resin and 0,5 to 20 parts by weight of a melamine resin. The composition may be a solution in an anhydrous organic solvent. The polyvinyl acetal is obtained by reacting a polyvinyl alcohol or partially hydrolysed polyvinyl acetate with an aldehyde such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, or benzaldehyde. The polyisocyanate may be phenylene, diphenylene, tolylene, naphthylene, diphenylmethane, cyclohexane, ethylene, tetramethylene, or hexamethylene diisocyanate, or a polyaryl polyisocyanate, a trimer of a polyisocyanate, or a reaction product of a diisocyanate or triisocyanate with polyhydric alcohols, or trimers and isomers thereof. The reactive hydrogen compound may be a phenol, cresol, xylenol, secondary aromatic amine, a mono or polyhydric alcohol, amide lactam, mercaptan or enol. The preferred polyurethanes are those obtained by reacting a monohydric phenol with the reaction product of an arylene diisocyanate and a polyhydric alcohol such as ethylene glycol, propylene glycol, glycerol, trimethylol propane, pentaarythritol, or hexanetriol. The malemine resin may be obtained by reacting a melamine with an aldehyde, optionally in the presence of an alcohol, or by aftertreating a melamine-aldehyde-alcohol-reaction product with an aryl sulphonamide. The phenol-aldehyde resin may be any of the conventional types. The preferred composition of the phenol aldehyde resin is that obtained by reacting one mol. of meta-para-cresol or para-tertiary butyl phenol with 0,1 to 2,0 mols. of formaldehyde. The compositions may be used for electrical insulation, e.g. for coating wires. The compositions are "cured" by heat-treatment at about 150 DEG C. The solvent for the composition may be trichloroethylene, ethylene dichloride, a hydrocarbon, or a mixed solvent comprising an alcohol, ester, and a hydrocarbon. |
