GB511996A - Process for the manufacture of reinforced glass - Google Patents

Abstract

511,996. Polyvinyl acetal resins. SOC. DES USINES CHIMIQUES RHONE-POULENC. April 20, 1938, No. 11869. Convention date, May 4, 1937. [Class 2 (iii)] [Also in Group VIII] A process for the manufacture of reinforced glass, the reinforcement of which is constituted by a polyvinyl resin of the acetal or partial ester type, consists in softening a sheet of the resin by immersion in a plastifying bath, none of the constituents of which has a boiling point below 175‹ C:, placing this sheet between two sheets of glass below the surface of the bath, pressing the assemblage gently and then heating under pressure. The acetal resin is the combination of polyvinyl alcohol and aldehyde, and the partial ester type resin is a polyvinyl ester saponified until it can swell in water while still being completely soluble in organic solvents such as the lower alcohols and ketones. Examples of liquids which can be used as the plastifying bath, alone or in mixture, are benzyl alcohol, the monoacetate of ethylene glycol, the formal of glycerine, and the lactones of y-hydroxyacids such as y-hydroxybutyric acid or gamma-hydroxy-n-valeric acid. To improve the adhesion of the resin to the glass, silicic or boric esters may be added to the plastifying bath, as is shown in the case of intermediate layers containing a cellulose derivative in Specification 428,548. In examples (1) 18 parts of a polyvinyl acetal obtained by the reaction of 1 mol. of formaldehyde and 2 mols. of polyvinyl alcohol of average viscosity, is dissolved in 100 parts of a mixture of 80 parts of methylene chloride and 20 parts of absolute alcohol. The solution is cast to give a film of .5mm. thickness after evaporation of the solvent. A piece of the film is immersed in a bath of benzyl alcohol at 18‹ C. for 20 secs. and assembled between two sheets of polished glass of 3 mm. thickness, and the assemblage is passed between pressing rollers covered with rubber, and heated at 115‹ C. in an autoclave under a pressure of 3 kgs. per sq. cm. for 35 minutes. Cooling also is effected under pressure. (2) 50 parts of a polyvinyl acetate of low viscosity are dissolved in 100 parts methyl alcohol. Saponification is effected by heating in the presence of small quantities of sulphuric acid until a product is obtained which can be swollen by water but is still soluble in methyl alcohol. The acid is neutralized and the solution is cast to obtain a film .8 mm. thick. The film is softened and assembled between two thin sheets of glass under a bath composed of 20 parts of glycol, 75 parts of glycerine formal and 5 parts of methyl silicate. The assemblage is pressed between rollers, heated in an autoclave at 135‹ C. under 3 kgs. pressure and cooled under pressure. Other examples are given. Specifications 316,955, [Class 20 (iii)], and 389,106, [Group VIII], also are referred to.