| 摘要 |
1,185,006. Compressing foamed articles. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 31 Dec., 1968 [2 Jan., 1968], No. 61898/68. Heading B5A. Articles of thermoplastic material are formed by pressing a blank of foamed thermoplastic material in a die mould at a temperature between the glass transition temperature and the melting temperature of the polymer with a pressure sufficiently high to greatly reduce or eliminate the cellular space in the material and to form it to the shape of the die. Preferably the final article has a density of at least 85% of that of the unfoamed polymer and the blank has a density of at least 60% of that of the unfoamed polymer. The polymer may be polystyrene, polyethylene or polypropylene, the polypropylene blank having a density of 0À68-0À70 gcm.<SP>-3</SP> and the formed article 0À85-0À89 gcm.<SP>-3</SP> compared with 0À90 gcm.<SP>-3</SP> for the unfoamed material. In the example a pump rotor is formed from a foamed polypropylene blank at a temperature of 150‹ C. and a pressure of 560 kg. cm.<SP>-2</SP> |
