GB661639A - Improvements relating to cellulosic lacquers, films, filaments and the like - Google Patents

Abstract

A composition suitable for use as a "gellacquer" or for making filaments or self-supporting films comprises cellulose propionate in a medium comprising toluene or a xylene and an acetate of propyl, isopropyl, a butyl or an amyl alcohol, in such proportions that the composition is a gel at atmospheric temperatures which is capable of a reversible change to a liquid by heating, and of irreversible change to a coherent film of the film-forming substance by evaporation of the medium. The cellulose propionate may be completely esterified, containing 67 per cent of combined propionic acid, but preferably contains 63-65 per cent of combined propionic acid. The composition may contain 15-40 parts of cellulose propionate for each 100 parts of the liquid medium (all the parts and percentages are by weight) and the medium is preferably a mixture of a butyl acetate with a xylene. The mixture may contain 10-50 per cent and preferably 30-50 per cent of the acetate. In addition, the composition may contain up to about 6 parts, e.g. 2.5-6 parts of a plasticizer such as dibutyl sebacate, butoxyethyl stearate, dibutyl phthalate, dioctyl phthalate and tricresyl phosphate for each 100 parts of the liquid medium. Dyes, pigments, nacreous substances or similar effect materials may also be included. The article to be coated may be provided with an undercoat having a basis of cellulose nitrate obtained by the application of a conventional lacquer before applying the gel lacquer. In an example, to 100 parts of a liquid medium consisting of 40 per cent of butyl acetate and 60 per cent of xylene there is added a mixture of 22 parts of cellulose propionate containing about 64 per cent of combined propionic acid, 3 parts of dibutyl sebacate, and 1 part of butoxyethyl stearate, and the mixture is heated with stirring to about 70 DEG C., producing a clear, relatively viscous solution which sets to a gel at about 28 DEG C. A metal article is dipped into the lacquer in the liquid condition and the lacquer adhering to the article upon its withdrawal sets to a gel within a few seconds. Thereafter the liquid medium is evaporated from the gel layer by passing a stream of air over the coated article, producing a smooth lacquer about 0.015 inch thick. Coatings are said to be obtainable, by a single dip as above, 10-15 times as thick as could be obtained using a conventional lacquer in a similar manner. The compositions may also be used for the production of self-supporting films and foils by conventional methods of casting. Thus, the hot composition may be flowed on to a film-casting surface, cooled to gel the composition and the medium evaporated, preferably after stripping the film from the support. The compositions may also be used for the production of filaments, for example by extruding the composition, in a liquid condition, into filament-form, gelling the filaments by cooling, evaporating the medium and collecting the filaments.