Patent GB-573779-A (GB)
Title: Improvements in the production of ornamental and other effects on organic ester of cellulose materials
IPC: B44C1/22
Filed: 1943-12-06
Abstract: Ornamental or other effects are produced on non-fibrous plastic materials made of or containing an organic ester of cellulose by etching a design therein by the action of a sulphuric acid solution of a concentration not exceeding 75 per cent by volume, i.e. 80.5 per cent by weight.  A resist may be applied in the form of a design to the material and the latter may then be etched by immersion in a bath of aqueous sulphuric acid.  The plastic material or the acid etching solution may contain a water-soluble softening agent, plasticizer, or solvent for the cellulose ester, e.g. diacetin, diethyl tartrate, methyl ether of ethylene glycol acetate, triethylene glycol, dioxane, acetone, or alcohol.  The sulphuric acid may be brought down to the desired concentration by dilution with water or phosphoric acid.  The cellulose ester material may be of cellulose acetate, propionate, butyrate, or aceto-butyrate.  In an example, a sheet composed of cellulose acetate, diethyl phthalate, and triphenyl phosphate, is printed in a design with a resist, e.g. a linseed oil base containing carbon black, pitch, or asphaltum.  The resist is dried at ordinary temperature or by use of an infra-red lamp.  The sheet is then etched in a hot aqueous solution of sulphuric acid.  The etched part may be painted to produce a colour contrast with the unetched part.  The process may be used for making printing plates or ornamental articles.  The etching may be applied to rods, tubes, or other forms of plastic material as well as flat pieces. Resists containing paraffin or acid-resistant plastic compositions may be used.  Plastic materials to be treated may be made with heterogeneous or multi-coloured plastic laminae or inlays, vertically or horizontally disposed, some of which are resistant and some non-resistant to the etching liquid. Polystyrene, ethyl cellulose, polyvinyl chloride, or polyvinylidene chloride, may be used as acid resistant plastic material to be used in association with the non-resistant cellulose ester material.  A thin white sheet of cellulose acetate plastic may be laminated to a black sheet of ethyl cellulose or polystyrene.  The top cellulose acetate sheet is resist-inked with a design or lettering and then etched to expose the black background layer. Metal foil interlayers or pearl, fluorescent, or phosphorescent laminated plastics, may also be used to produce decorative effects. Signs may be made with a signature or design which luminesces in the dark.  The plastic article after etching may be dipped in acetone to produce an overall polished effect. Depending on the solvent used and the character of the plastic interlayers or inlays, contrasting polished and matt effects may be produced.  The etched article containing plastic layers of different kinds may be subjected to differential dyeing so as to produce colour-contrasts.  A lace or filigree design may be printed on the plastic material and the etching may be carried out to such an extent that the acid eats through the unprinted portion to produce a fine lace-like product suitable for table mats.