GB419306A - Improvements in or relating to methods for the production of sheet material from artificial plastic masses - Google Patents

Abstract

Plano-parallel sheets of artificial masses containing urea and formaldehyde are made by casting the liquid mass into closed moulds of non-metallic material, particularly acid igneous rock, glass and plywood. The condensation may be carried out entirely in a non-acid medium, acid being added to the final mass only for the purpose of more rapid gel formation and for controlling the colloidal chemical properties. Condensation products consisting of polyhydric alcohols and aliphatic polybasic carboxylic acids or their derivatives may be added. Softeners such as ethyl acetanilide, glyceryl triacetate, or benzyl acetate may be added to the condensation products. The pH value of the solution is less than 7. Examples with numerical data are given. The p Specification includes a disclaimer of the process and product thereof, claimed in Specification 408,460.ALSO:Sheets &c. of artificial masses containing urea and formaldehyde and suitable for use as a substitute for sheets of glass are made by casting the liquid mass into closed moulds, consisting of a non - metallic material, particularly acid igneous rock, glass and plywood, the cast sheets then being uniformly dried by an agent which is initially moist but of which the moisture content is gradually diminished. The mould surfaces may, if desired, be furnished with a thin coating of a metal which is not readily attacked by the condensation mass, e.g. a limestone mould may be protected by a coating of aluminium which is renewed after the mould has been used several times. The uniform drying of the cast sheets may be effected by automatically turning them about during drying and the edges and margins of the sheets may be covered with a quick-drying lacquer or varnish &c. The castings may be encased in porous clay, porous rubber, felt &c. during drying. A permanently located rubber band resiliently mounted on wooden strips &c. may also be used to cover the edges of the cast sheets. The cast sheets may be pressed before they are completely dry, and they may be immersed in water at a temperature of 50-80 DEG C. for a short time before carrying out the pressing operation. The pressure is effected between sheets of polished metal or of plate glass at a temperature of about 115-130 DEG C. the pressure being increased gradually (up to 250-300 atmospheres in 30-50 minutes), and maintained for 15-30 minutes. The condensation may be carried out entirely in a non-acid medium, acid being added to the final mass only for the purpose of more rapid gel formation and for controlling the colloidal chemical properties. Condensation products consisting of polyvalent alcohols and polybasic carboxylic acids or their derivatives may be used. The sheets may be coated at certain points with a thin foil of glass. Various examples, with numerical data, of the manner of carrying out the invention are given in the Specification. The Specification includes a disclaimer of the process and product thereof claimed in Specification 408,460.