| 摘要 |
1,240,852. Pencils. FARBENFABRIKEN BAYER A.G. 24 Sept., 1968 [4 Oct., 1967], No. 45223/68. Heading B6P. A pencil has a sheath comprising a foamed thermoplastic moulding composition, the foam having a density of from 0À3 to 0À7 g./c.c. The pencil may be formed by passing a lead through the inner nozzle of a reversal-type extruder whilst the outer nozzle is used to guide and form the surrounding, expandible thermoplastic composition. The lead may contain a thermoplastic composition as binder and may be formed in an extruder which directly applies the sheath as above. The foamed thermoplastic moulding composition may comprise polystyrene; copolymers of styrene with other vinyl or vinylidene monomers (e.g. acrylonitrile or methyl methacrylate); polymethyl methacrylate; polyvinyl chloride; polyvinyl chloride modified with monomeric or polymeric plasticizers; cellulose esters modified with plasticizers; rubber-modified polystyrenes with a styrene content of at least 50% by weight. In a preferred embodiment the moulding compositions comprise copolymer mixtures of polymers of acrylonitrile, butadiene and styrene (ABS-polymers). According to examples, the moulding composition may comprise (A) an elastomeric butadiene polymer with optionally copolymerized styrene, isoprene, acrylonitrile or a lower alkyl ester of acrylic acid or methacrylic acid, together with (B) polymerized styrene and acrylonitrile, the two monomer components being replaceable either wholly or in part by their alkyl derivatives or by methyl methacrylate. The binder for the lead may comprise (C) a graft polymer of ethylene/vinyl acetate copolymer and possibly also a grafted-on vinyl chloride together with (D) a polymer mixture as in (A) and (B) above. The foaming agents may be azodicarbonamide and sulphohydrazide-based agents. The lead may contain graphite. The moulding composition used for the sheath may contain anti-static agents and the finished sheath may be polished by immersion in a solvent, e.g. methyl ethyl ketone. |
