| 摘要 |
1,217,498. Treating a tape of a synthetic organic thermoplastic material. DUNLOP CO. Ltd. 5 April, 1968 [20 April, 1967], No. 18129/67. Heading B5B. A tape of a synthetic organic polymeric thermoplastic material which has been "fully drawn" in the longitudinal direction is heat-set (at a temperature above that at which it was fully drawn) under controlled conditions of relaxation. The term "fully drawn" is defined as meaning that the tape has been stretched to such an extent that if it were stretched further it would either contract back to its fully drawn length when the stretching force is removed, or, if stretched beyond the extent to which it is elastic, it would break. It is preferred to use a tape which has been fully drawn at a temperature near the softening point of the polymer of which the tape consists e.g. 120-140‹ C. for polypropylene. The heat-setting temperature is preferably as high as possible without causing degradation or melting of the polymer. The fully drawn tape is preferably further stretched, e.g. up to 5% of its fully drawn length, prior to being allowed to relax under controlled conditions during the heat-setting operation. A fully drawn tape of polypropylene may have been drawn from 8 to 11 times its original length. The tape may be heated in a fluidized bed of solid particles during the heatsetting operation, whereby the tape becomes fibrillated. The tape is preferably twisted during heat-setting and/or while it is being drawn and/ or as a separate operation. The twisting process may be used to fibrillate the tape or the tape may be fibrillated prior to being twisted, e.g. by passage through a fluidized bed of solid particles. The tape may be crimped prior to being heat-set. The tape material is preferably polypropylene, especially isotactic popropylene. It may be polyethylene, polystyrene, a polyepisulphide, polyacrylonitrile, a polyamide, polyvinyl chloride, a polyurea, a polyurethane or a polyester, e.g. polyethylene terephthalate. The heat-setting temperaure may be within 50‹ C. of the normal melting point of the tape material. A cold solvent may be applied to the fully drawn tape prior to the heat-setting step and the solvent evaporated from the tape during the heat-setting step. In an example, a fully drawn 3200 denier polypropylene fibrillatable tape having 2¢ turns per inch is heat-set by the continuous process using driven godets and festoon rollers in association with a fluidized bed of Ballotinic at a temperature of 140‹ C. The tape had previously been drawn at 130‹ C. and a draw ratio of 9 to 1. The speeds of rotation of the rollers was such that the tape was stretched between the input godets and the festoon rollers by about 4% and was allowed to relax between the festoon rollers and the output godets by about 5%. |
