| 摘要 |
<p>A coating composition comprises 100 parts by weight of a 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, and 0,5 to 20 parts 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 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, pentaerythritol, or hexanetriol. The melamine resin may be obtained by reacting a melamine with an aldehyde, optionally in the presence of an alcohol, or subsequently with an alcohol, or by aftertreating a melamine-aldehyde-alcohol re-action product with an aryl sulphonamide. The organic solvent may be trichloroethylene, ethylene dichloride, a hydrocarbon, or a mixed solvent comprising an alcohol, ester, and a hydrocarbon. The compositions may be used for electrical insulation purposes, e.g. for coating wires. The compositions are "cured" by heat-treatment at an elevated temperature, e.g. about 150 DEG C.</p> |
