| 摘要 |
An expanded synthetic resin is made by polymerizing a phenol-formaldehyde casting resin with a foaming agent constituted by a diazonium salt as specified below, the water liberated in the curing of the resin reacting with the salt to form nitrogen which causes foaming of the resin, phenol which reacts with excess of formaldehyde, and an acid which aids the curing of the resin. The diazonium salts specified are benzene diazonium sulphate and phosphate, salts of the formula <FORM:0766066/IV(a)/1> where X represents any acidic radical and R1 and R2 represent, e.g., hydrogen, alkyl, aryl, hydroxy, alkoxy, acyloxy, nitro, amino, halogen, carboxylic acid or ester, or sulphonic acid grouping, and more highly substituted diazonium salts, preferably having at least one free ortho- or para-position; these salts must be comparatively pure and must be soluble in the casting resin. The casting resin used preferably has a viscosity from 40,000 to 70,000 cp. A finely-divided filler, e.g. wood flour, cork flour, diatomaceous silica and mica, may be mixed with the resin, and also a wetting-agent in amount, e.g., of 0.05 mil. per 100 grams of resin. Curing agents specified, other than the diazonium salts, are benzene sulphonic, sulphuric, acetic, oxalic, and p-toluene sulphonic acids and metal chlorides. Examples are given.
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