GB1306373A - - Google Patents

Abstract

1306373 Foamed polyolefin films IMPERIAL CHEMICAL INDUSTRIES Ltd 30 Dec 1970 [30 Jan 1970] 4647/70 Heading B5B [Also in Division C3] A process for improving the bonding properties of at least one surface of a film of a foamed blend containing 60 to 90% by weight of an ethylene homopolymer of less than 0À934 gm./c c. and correspondingly 40 to 10% by weight of a crystalline polyolefin said percentages being based on the combined weight of the ethylene homopolymer and the crystalline polyolefin comprises subjecting the film to a surface treatment. The film may be a foamed blend containing 60 to 90% by weight of a low density polyethylene (i.e. homopolymers and copolymers of ethylene having a density less than 0À934 g./c.c.) and corresponding between 40 and 10% by weight of a crystalline polyolefin said percentages being based on the combined weight of the low density polyethylene and the crystalline polyolefin, the film having an open cell structure of between 40 and 90% by volume of open cells, at least one surface of the film having been subjected to surface treatment to improve the bonding properties. Preferably the films, which may be used as wall and ceiling covering materials, include 5 to 20% by weight of titanium dioxide and 0À05 to 1À0% by weight of metallic aluminium particles of medium size at least 20 Ám as opacifying agent. If some greyness can be tolerated up to 100 parts per million of carbon black may be included to improve opacity. The surface treatment of the film may be a physical or chemical treatment or the film may be coated with a layer of a more polar material, e.g. the surface of the film may be subjected to chemical oxidation by a mixture of chromic and sulphuric acid, or physically treated by subjecting the surface of the foamed film to corona discharge treatment or by coating with a layer of a polar polymer such as chlorinated polythene which may be applied as a solution and the solvent evaporated off. The blends containing a blow agent may be extruded from an annular or a slot die but preferably by extruding through an annular die and to inflate the tube so produced. The blend of the polyolefines and the blowing agent system may be mixed maybe in a pressure vessel. The first blowing agent which is completely miscible with the blended polyolefines to be foamed must have a b.pt. below the temperature at which the homogeneous mixture is extruded. The most suitable first blowing agents are liquids whose b.pts. at atmos. pres. are greater than 20‹ C. and are at least 10‹ C. below the extrusion temp. of the mixture. Examples of liquids used as first blowing agent include saturated and unsaturated hydrocarbons, petroleum ethers and halogenated hydrocarbons and preferably pentane, 1,1,2 - trichloro - 1,2,2- trichloroethane, hexane, petroleum ether (B.P. 40‹ to 60‹ C. or 60‹ to 80‹ C.) or methylene chloride. The concentration of the first blowing agent should not exceed 10% by wt. The second blowing agent is normally a gas or a low boiling liquid and preferably carbon dioxide or nitrogen in a concentration of not exceeding 0À05% by weight.