| 摘要 |
A wire enamel comprises a solution in an organic solvent of (a) 100 parts of a "neu-tralized" polyvinyl acetal resin (i.e. a polyvinyl acetal not acting as an acidic material); (b) 5-100 parts of a soluble phenol-aldehyde resin obtained by reacting 1 mol. of a phenol with 0.7-2.0 mol. of a lower aldehyde under alkaline conditions; and (c) a minor amount of an acidic substance consisting of sulphuric acid, phosphoric acid, benzene phosphonic acid, hypophosphorous acid, phosphorous acid or an ammonium salt or alkyl ester of one of said phosphorus acids. The polyvinyl acetal may contain 1-30% ester groups and 3-25% alcohol groups and may be acetalized with formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde or mixtures thereof and in the examples it is made by reacting polyvinyl acetate dissolved in glacial acetic acid with the aldehyde in the presence of sulphuric or hydrochloric acid. After acetalization, the acid catalyst is neutralized (e.g. with ammonia, KOH or triethanolamine) and water added to precipitate the resin followed, if desired, by steeping the precipitated resin in a base (e.g. an alkali hydroxide, a tertiary amine, hexamethylene tetramine, methacrylol urea or di-o-toluylguanidine). In the manufacture of phenolaldehyde resin, the phenol may be phenol, cresols, xylenols, ethylphenol or p-t-butylphenol; the aldehyde may be formaldehyde, acetaldehyde or butyraldehyde; and the catalyst may be triethanolamine. The resin solvent may be cresol, furfural, coal tar naphtha, toluol or xylol. |
