GB741521A - Nitrocellulose lacquers - Google Patents

Abstract

A lacquer composition consists essentially of (1) 25-90 per cent by weight of cellulose nitrate, and (2) 10-75 per cent of a silicoalkyd resin which is a reaction product of (a) 25-90 per cent by weight of one or more organo-silicon compounds of an average general formula RnSiX4-n or a partial condensate thereof, R being a monovalent hydrocarbon radical, n having a value of 1 to 2 inclusive, and X being a hydrolysable radical or hydroxyl radical, (b) 2.5-49 per cent by weight of glycerol, (c) 5.2-62 per cent of a dicarboxylic acid or anhydride, alkyl ester or acid chloride derivative thereof, and optionally (d) up to 60 per cent of a fatty acid containing 8-20 carbon atoms in the molecule; there being in the final product from 2 to 30 per cent by weight, calculated on the total weight of (1) and (2), of the reaction residue of the organosilicon component (a), the weight of this residue being calculated on the basis of the formula RnSiO (4-n)/2 . The lacquer compositions have high stability on exposure to atmospheric conditions, this being shown by high gloss retention and freedom from crazing and cracking. The lacquers may be applied as coatings to metal surfaces such as motor bodies. Silanes in which R is cyclohexyl, methyl, allyl, stearyl, phenyl or xylyl, and in which X is an alkoxy, acyloxy, halogen (e.g. chlorine or bromine), amino or hydroxyl group, may be used for preparing the silico-alkyd resin. A partially condensed alkoxy silane may also be used for making the silico-alkyd resin. An alkoxy silane may be hydrolysed with less than the theoretical amount of water required for complete hydrolysis. The dicarboxylic acid may be phthalic, terephthalic, isophthalic, malonic or maleic acid. The fatty acid containing 8-20 carbon atoms may be stearic acid or 2-ethyl hexoic acid or it may be a mixture of tung oil acids, castor oil acids, linseed oil acids or oiticica oil acids. The reactants for forming the silico-alkyd resins may be brought together in any desired order. Solvent mixtures of toluene, xylene, alcohols and ketones may be used to produce lacquer solutions of the cellulose nitrate and the resin. Driers such as cobalt naphthenate and pigments may be incorporated in the lacquers. In an example, a mixture of phenyl methyl dimethoxy silane and phenyl trimethoxy silane is partially hydrolysed and condensed. The condensate is heated and stirred with a liquid linseed oil acid mixture at 200 DEG C. Methanol is distilled off and the mixture is then cooled to 150 DEG C. Glycerol is added and the mixture is again heated to 200 DEG C. and methanol is distilled off. The mixture is cooled to 150 DEG C., phthalic anhydride is added and the mixture is heated to 200 DEG C. to remove volatile constituents, xylene being added during the distillation so as to remove residual water as an azeotrope. The mixture is then diluted with a mixture of xylene and a high boiling aromatic petroleum solvent. In other examples, silico-alkyd resins are produced in a similar manner except that coconut oil acids or dehydrated castor oil acids are used instead of linseed oil acids. Other examples describe the production of lacquers containing cellulose nitrate, a silico-alkyd resin and a solvent mixture. The silico-alkyd resin may be prepared by condensing 7.2 gm. mols. of phenyl methyl diethoxy silane and 0.8 gm. mols. of phenyl triethoxy silane with 8.35 gm. mols. of glycerol and 4.57 gm. mols. of phthalic anhydride. Specifications 583,754, 650,247 and 722,484 are referred to.