GB1310430A - Process for producing a synthetic resin sheet - Google Patents

Abstract

1310430 Heat-stretched polyolefin sheets SEKISUI KAGAKU KOGYO KK 29 Dec 1970 [26 Dec 1969 (2) 29 Dec 1969 12 Jan 1970 (3) 16 Jan 1970 (2)] 61634/70 Headings B5A and B5B [Also in Division C3] Porous or void-containing synthetic resin sheets suitable for use as synthetic paper are prepared by a process which comprises uniaxially or biaxially stretching an unstretched sheet of an olefinic resin at a temperature below its melting point, the temperature of both surface layers of the sheet being at least 10‹ C. higher than that of the inner layer. The olefinic resin, which is preferably a C 2 -C 4 α-olefin polymer or copolymer having a melt index of from 0À01 to 5, may be blended with up to 50 wt. per cent of a resin having poor compatibility with the olefin polymer or copolymer, e.g. a styrene polymer, polyamide, polyacetal, polyacrylate, vinyl chloride, vinyl acetate, phenoxy or high molecular weight elastomer resin and the blend may also contain up to 75% (based on the weight of the composition) of a powdered inorganic filler material, e.g. talc, mica, zeolite, asbestos, lithopone, clay, kaolin, diatomaceous earth, silica, alumina, CaCO 3 , MgCO 3 , CaSO 4 , BaSO 4 , ZnS, TiO 2 or ZnO. To further improve the weight and surface characteristics of the sheets they may be uni- or bi-axially after-stretched at a temperature which is below the melting temperature of the resin and may be either below or above the temperature of the surface layers of the sheet during the primary stretching process. In examples olefinic resins comprising low pressure polyethylene (Examples 1 and 7); high density polyethylene (6); and low pressure polyethylene blended with inorganic filler materials and polystyrene and an ethylene/vinylacetate copolymer (2); high pressure polyethylene, styrene/vinyl acetate copolymer and a phenoxy resin (3); ethylene/vinyl acetate copolymer, polystyrene, and a styrene/butadiene copolymer (4); and styrene/vinyl acetate copolymer, polybutadiene, and polystyrene (5) are kneaded with a roller at 150-160‹ C., converted into sheets by hot pressing or calendering, cooled to 80‹ C. and passed between rollers maintained at 100-124‹ C. and stretched biaxially to 2À5 x their original length and width. The sheets so produced were white and opaque, had densities in the range 0À580-0À665 g./cm.<SP>3</SP>, both the surface and inner layers of the sheets having a porous structure with the void size of the surface layers being smaller than those of the inner layers and the void size distribution being symmetrical with respect to the centre line of a section of the sheets. In further examples the sheets obtained above are further biaxially stretched at 120‹ C., the sheets of Examples 1, 6 and 7 also being heated to 120‹ C. and allowed to shrink 5% (Example 8) and supercalendered in three stages at a pressure of 50 kg./cm.<SP>3</SP> (Example 9).