GB1496345A - Resinous coating composition forming a hygroscopic non-fogging coating film with a high surface hardness and method of forming such coating films - Google Patents

Abstract

1496345 Non-fogging coatings and articles NIPPON HYDRON CO Ltd 25 Nov 1974 [29 Nov 1973 30 Nov 1973 21 Dec 1973] 50961/74 Heading C3P [Also in Division B2] Hygroscopic non-fogging coatings and articles having high surface hardness are formed from compositions comprising a hygroscopic resin which is a polymer or copolymer of a hydroxy- C 1-4 alkyl acrylate or methacrylate or a hydroxy- C 1-4 alkoxy-C 1-4 alkyl acrylate or methacrylate admixed with (a) 5-60 wt. per cent, based on the resin, of a surface active agent which is of anionic or polyoxyethylene non-ionic type, and (b) 5-70 equivalent per cent, based on the resin, of a cross-linking agent in which at least 80% of the functional groups are of the same kind and which has a single- or condensed-ring carbo- or hetero-cyclic skeleton, each ring being 4 to 8 membered, and the linkage between said skeleton and the point of reaction with the resin being at most 4 atoms long inclusive of the atom of the reaction point. A cross-linking catalyst may also be included, and the compositions may be first formed in a solvent, e.g. ethylene glycol monomethyl ether. A coating film formed from such a composition preferably has a cross-linking density gradient decreasing from its surface towards its point of contact with a substrate. This gradient is achieved by forming the film from a composition from which at least one component is absent, and then incorporating the absent component in a concentration gradient by contacting the film with a solution or vapour containing it. The absent component may be the cross-linking agent or the catalyst. On curing the resulting film, a cross-linking density gradient forms by virtue of the concentration gradient of one or other component. Further improvement in the film properties may also be attained by contacting it with water or steam before, during or after curing. In examples, which also illustrate the preferred features described above, the following components are used: resin: 2-hydroxyethyl methacrylate homopolymer or copolymer with methyl methacrylate; surfactant: alkyl methyl tauride, a dialkyl sulphosuccinate, poly(oxyethylene)nonylphenyl ether or a polyoxyethylene glycol ester of a fatty acid; crosslinking agent: trimellitic acid, pyromellitic anhydride, or hexamethoxymethylolmelamine; catalyst: p-toluene sulphonic acid, trifluoroacetic acid or HCl. Many other alternatives are listed. The substrates on which these coatings are formed are sheets or panels of glass, polycarbonate or poly(methyl methacrylate).