GB410717A - Improvements in or relating to moulding of plastic material - Google Patents

Abstract

Articles such as artificial fruits or toys, moulded from plastic material, are hardened with formaldehyde liberated from a surface in contact with the material, such surface being in shape the obverse of the article to be moulded. A mould negative may be formed from gypsum which has been stirred in a 5-8 per cent solution of formaldehyde and the material then cast in this mould. The material may comprise one thousand parts of glue or size, one thousand parts of oil varnish or lacquer, five parts of wood tar and two hundred parts of asphalte or mineral substances for colouring or filling. It may be poured into the mould hot and when the layer in contact with the mould has hardened under the action of formaldehyde evaporated or otherwise liberated from the mould, the still-liquid material inside this layer may be poured off. Successive layers are built up in this way to give a desired thickness. The article may then be filled with a sealing filling such as paraffin to prevent contraction during drying. After drying the filling may be removed, or it may be a permanent filling such as of marble cement. Before filling, a protective layer of bonedust, sand or other nonhygroscopic material may be applied to the interior of the moulded article. The plastic material may alternatively be cast in an ordinary mould and, after removal therefrom as a rubber-like mass, coated with gypsum p impregnated with formaldehyde and left until hardened. The article is then heated up to the melting point of the plastic material and unset material poured off from the interior.