| 摘要 |
A permeable multi-ply paper or like fibrous sheet material that is sealable by the application of heat and/or pressure, at least one of the outer layers thereof consisting of natural cellulose fibres that have been coated on the surface with a thermoplast before forming the fibres into a layer, and the other layer or layers is or are substantially free from thermoplast. The multi-ply paper is preferably made by the process and apparatus shown in Specification No. 1006567. The coating of the fibres is preferably effected by precipitating particles of the thermoplast from an aqueous suspension thereof onto the fibres whilst the latter are in suspension in an aqueous medium or by applying dry particles of the thermoplast to the fibres whilst the latter are maintained in suspension in a gas stream and in an electric field. Specified thermoplasts are polymers and copolymers of vinyl chloride, vinylidene chloride, vinyl acetate, acrylic acid, methacrylic acid and acrylonitrile; polymers and copolymers of butadiene, styrene and isoprene; polymers and copolymers of mono - 2 - olefins e.g. ethylene and propylene and polyamides and polyesters. |
