GB1271188A - Improvements in or relating to the production of polyvinyl butyral films - Google Patents

Abstract

1,271,188. Treating polyvinylbutyral films. DYNAMIT NOBEL AG. 17 April, 1970 [18 April, 1969; 24 Feb., 1970], No. 18578/70. Heading B5B. A process for treating a film of plasticized polyvinylbutyral to remove tackiness, comprises immersing the tacky film in a bath containing a non-solvent for polyvinylbutyral and imparting a matted appearance to both surfaces by calendering the surfaces either simultaneously or successively while the film is immersed in the bath; calendering being carried out at a film surface temperature lying in the range from 5‹ C. above the lowest temperature at which "stamping" can occur to 140‹ C. This temperature is defined as the minimum temperature at which roughening of the film will occur when it is guided between them. The preferred temperature range is from 85‹ to 100‹ C. The fluid in the bath may be water, which can have compounds dissolved in it to raise its boiling point, e.g. water-soluble polyhydric alcohols NaCl, KC1, CaCl 2 and Na 2 SO 4 , or it may consist of water-soluble polyhydric alcohols such as ethylene or propylene glycol or glycerine. In Fig. 1, there is shown an arrangement whereby the surfaces of a film may be roughened in succession. The matting rollers 1 and 2 are heated but the pressure rollers 3 and 4 are not. The surface X is treated first and the surface Y thereafter. The surface X is protected against the thermal recovery that would otherwise occur when surface Y is heated, by the cooling effect of the fluid in the bath. In Fig. 2, both sides of the film are roughened simultaneously between rollers 6 and 7. The rollers 6 and 7 are not directly heated, the temperature being maintained by heating the fluid in the bath. The guide roller 8 may be omitted. The roller speeds may be adjusted so that the film is held under tension or stretched during the roughening process to a draw ratio of from 1.2 to 3.0, preferably to 1.8 to 2.0. Subsequently the film may be allowed to shrink back to its original dimensions, the film thus aquiring a rough base structure on both surfaces, in addition to the matt finish.