Improvements in electrical insulating varnish based on an oil modified alkyd resin in admixture with a phenolic resin

摘要

1,144,432. Phenoplast/alkyd compositions. WESTINGHOUSE ELECTRIC CORP. 21 Feb., 1966 [17 March, 1965], No. 7469/66. Heading C3R. [Also in Division B2] An electrical insulating varnish comprises a mixture of 20 to 35 wt. per cent of a defined alkyd resin (A) and 80 to 65% of a defined phenolic resin (B). Resin (A) is defined as that derived by heating to 200‹ to 240‹ C. a mixture of (1) a drying oil, (2) an aliphatic polyol, (3) a catalyst and (4) a monobasic acid for a time to ensure substantially complete reaction and thereafter reacting the product at 200‹ to 240‹ C. with (5) iso- and/or terephthalic acid, the oil (1) constituting 40 to 50 wt. per cent of the alkyd and the acid number of the alkyd being 15. Resin (B) is defined as the condensation product derived by heating to 70‹ C. to reflux a mixture of (a) 0À9 to 0À8 moles of an eutectic mixture of p-tertiary butyl phenol and p-sec.-butyl phenol, (b) 0À1 to 0À2 moles of a substituted phenol having at least three reactive positions, and (c) 1À5 to moles of aqueous formaldehyde or a polymer of formaldehyde in the presence of 0À2 to 5% by weight of the phenols of an alkali metal hydroxide, acidifying the product to a pH of 4 to 7, and removing water therefrom by decantation and heating under vacuum at up to 125‹ C. The substituted phenol (b) may be bisphenol A or cresylic acid. In the Examples, A is derived from (1) linseed oil, (2) glycerol, (3) litharge, (4) and 85/15 mixture of benzoic and phthalic acids and (5) isophthalic acid, and a 30/70 mixture of (A) and (B) in xylene is used to coat coils of 18 gauge copper wire by dipping.' Each coil was dipped, cured 50 minutes at 135‹ C. and 10 minutes at 170‹ C. and then reversed and dipped and cured a second time.