GB1522854A - Transparent paper - Google Patents

Abstract

1522854 Transparent paper KANZAKI PAPER MFG CO Ltd and TORAY TNDUSTRIES INC 9 Sept 1975 [9 Sept 1974] 37151/75 Heading D2B A transparent paper has a fibrous matrix which consists, per 100 parts by wt. on a dry basis, of (a) from 94 to 40 parts by wt. of natural pulp and (b) from 6 to 60 parts by wt. of a synthetic pulp having a freeness of from 50 to 600 cc formed of a blended polymer system comprising (i) from 5 to 40% by wt. of a polyvinyl alcohol-acrylonitrile copolymer, the polyvinyl alcohol content of which is from 20 to 80% by wt. and (ii) from 60 to 95% by wt. of an acrylonitrilestyrene copolymer the acrylonitrile content of which is from 5 to 45% by wt. The natural pulp may be wood pulp, bast fibre pulp, or animal fibre pulp. The blended polymer system of the synthetic pulp may include unreacted polyvinyl alcohol and/or an acrylonitrile polymer. The polyvinyl alcohol-acrylonitrile copolymer may be a block or graft copolymer, and monomers in addition to acrylonitrile e.g. vinyl acetate, methyl acrylate, styrene, and vinyl chloride may be used in its preparation. The transparent paper may be made by moistening the fibrous matrix to a moisture content of 5 to 40% and pressing the moistened sheet at a temperature of at least 130‹C. Conventional papermaking additives e.g. a starch e.g. oxidised starch, polyvinyl alcohol, carboxymethyl cellulose, sodium alginate, solutions or emulsions of synthetic resins, transparentising agents, release agents e.g. wax, plasticisers e.g. glycerine, antistatic agents e.g. salt, fillers e.g. talc, and dyestuffs may be added in the manufacture of the paper. The pressing may be carried out using a supercalender, machine calender, rolls, or a hot press.