GB565210A - Improvements in or relating to coating compositions - Google Patents

Abstract

A coating composition for use in determining the relative distribution of elastic strains in a rigid article comprises a solution of a brittle resin in a low boiling solvent, the resin being plasticized barely sufficient to prevent crazing upon drying. The amount of plasticizer with a given resin is such as to confer on the resulting film a strain sensitivity of from 0.0005 to 0.0010 inches per inch and varies with the prevailing temperature and humidity conditions. The test is effected by coating the article with a uniformly brittle film and subjecting the article to increasing predetermined loads initially incapable of effecting crack formation in the film over the areas to be tested, and continuing said loading until the film has cracked over said areas. Certain thermoplastic phenol formaldehyde condensation products may be used, and also natural resins, such as gum rosin, wood rosin, dammar and copals such as manila, kauri, congo, &c. The natural resins may be hardened by fusion or in the presence of water or solvents, or by treatment by calcium, magnesium or zinc oxide in the presence of a catalyst such as acetic acid or calcium acetate; by oxidation with hot air &c. Dibutyl phthalate and normal butyl stearate may serve as plasticizers. Carbon disulphide, methylene dichloride, and 1, 2 (cis) dichlor ethylene are suitable solvents. The compositions may be pigmented or a light-reflecting film, for instance, a solution of nitro-cellulose in ethyl acetate containing bright aluminium power, may be interposed between the surface of the article and the transparent brittle film. A standardized member and the article to be tested may be coated at the same time under the same conditions, and the crack patterns compared to give the magnitude of the strains.