| 摘要 |
<p>A normally non-transparent coating material comprises a spreadable homogenous dispersion of discrete non-transparent particles of a polyvalent metal soap of a fatty acid having from 6-24 carbon atoms, the dispersion vehicle including a cellulose derivative binder dissolved in a volatile water-miscible organic solvent to which water is added and in which solvent mixture the soap particles are insoluble, the dispersion when dried on a backing support forming a non-transparent coating the light transmission of which is increased in selected areas in response to heat or pressure, the dispersion vehicle being substantially inert with respect to said soap and also with respect to the backing support on which the dispersion is dried and the dispersion being homogenous and being dried at a temperature at which no change in the physical characteristics of the coating occurs. Advantageously, the soap fatty acid has 6-18 carbon atoms, e.g. palmitic, stearic, hydroxy stearic, lauric, oleic, sebacic, capric and caprylic acids. Specified soaps include calcium stearate, zinc stearate, magnesium stearate, and zinc sebacate. Specified cellulose derivatives include cellulose nitrate, acetate, butyrate and acetate-butyrate, ethyl cellulose, benzyl cellulose and ethyl cellulose acetate. A modifying resin may be added, e.g. an aryl sulphonamide-formaldehyde resin. Specified solvents include acetone, methyl alcohol, ethyl alcohol, dioxane, methyl ethyl ketone, ethyl ether and mixtures of these. Wetting agents, pigments and dyes may also be added. Preferably the soap particles comprise 15-80% by weight of the solid constituents of the dispersion, and the binder comprises a cellulose ester or cellulose ether to constitute a clear homogeneous cellulose derivative solvent mixture. The dispersion may be prepared by mixing about 30 parts of the cellulose derivative with the solvent therefor, adding water in an amount slightly less than that required to precipitate the cellulose derivative from solution, about 10-80 parts of the soap in finely powdered form and milling in a colloid, ball or roll mill until the composition is homogeneous, when it is spread on the support and dried at a temperature at which no change in the physical characteristics of the coating occurs. The proportions of the ingredients in the dispersion may be such as to render the coating when dried unitarily strippable from the backing support. For the application of the invention to the production of recording blanks see Group VIII.</p> |
