| 摘要 |
Polar melamine-formaldehyde resins are prepared by the transesterification of a highly etherified melamine formaldehyde condensate by means of a hydroxy carboxylic acid which does not contain an ether linkage. The initial condensate may be a polymethoxymethyl melamine, in which the degree of substitution is not less than five and in which at least 80% of the methylol groups are etherified. The hydroxy acid may be aliphatic or cycloaliphatic and contain one, two or three carboxyl groups and one or two primary or secondary hydroxyl groups. Aromatic acids may be used but are less reactive. Acids used in the examples include dimethylol propionic acid, 12-hydroxy stearic acid, lactic acid, 2-hydroxybutyric acid and m-hydroxy benzoic acid. The proportions of condensate and hydroxy acid may correspond to one melamine nucleus per hydroxyl group of the hydroxy acid. The trans-etherified product may be partially or completely neutralized by a volatile base (e.g. triethylamine) and diluted with water. The resins are suitable for use in electrodeposition processes and may be readily mixed with other resins, e.g. alkyds and other polyesters, to form coating compositions. |
