process for the preparation of manufat you points printed

摘要

Process is carried out using injection moulding into a long mould, with a piston, hollowed at the end to the shape of the point of the moulded article, which exerts a counter-pressure on the material during injection. The material is allowed to harden under pressure. The moulding composition contains =1 olefinic polymer, =1 ethylene/vinylacetate copolymer, and =1 high-boiling-point ester, each being 5-15% of the total and in approx. equal proportions. The copolymer pref. contains 10-50% pref. 10-35% of vinylacetate. The olefinic polymers are high-pressure polyethylene consisting of 25-40% or 15% of the total. The mixt. pref. contains =1 petroleum waxes and/or metal salts of fatty acids, and also an epoxide resin 10%. Pigments are added for colouring. The chalks and crayons produced are suitable for writing on matt surfaces e.g., blackboards and slates, and do not soil the hands.