| 摘要 |
1432219 Containers E I DU PONT DE NEMOURS & CO 9 Nov 1973 [10 Nov 1972] 52049/73 Heading B8C A container C having a tray, or bottom part, 10 with a side wall, or walls 15, and a lid or top part 11, the two parts being adapted to be secured with an adhesive 13, is characterized in that an adhesive is applied only at the upper surface 16 of the side wall or walls the tray, or bottom 10 and the lid, or top part, is of polyethylene terephthalate polymer or copolymer or a blend of at least about 70% thereof by weight with a compatible polymer or copolymer, the adhesive being free from flow at cooking temperatures up to about 205‹ C. and having a bond strength at such cooking temperatures. Sufficient to prevent leakage and the lid is peelable from the tray, or bottom, part without tearing at such cooking temperatures. As shown, the container C, formed of polyethylene terephthalate comprises a tray 10 with a bottom part 14, side walls 15 with a peripheral flange 16 having an adhesive 13 on its upper surface, and a lid 11 which may have, one, or more, pull-tabs, not shown. After the contents have been placed in the tray 10 the lid 11 is sealed to the flange 16 by the adhesive 13 using heat and pressure. The tray 10 may be thermoformed in one piece particularly by apparatus having a heated mould and ram to enhance crystallization of the structure, the unorientated amorphous polyethylene film being preheated preferably within the range of 100-110‹C. for not more than 30 seconds and the tray 10 being orientated and crystallized in the forming process. The flange 16 is crystallized but receives little, if any, orientation in the forming process but is free from embrittlement. In an apparatus, Fig. 6, for applying adhesive to the flange 16 of the tray, a conveyer 20 carries trays, either singly or in groups, beneath a roll 23 which may be heated and which receives adhesive from a hopper 25, the coating thickness being controlled by a doctor blade 26. If a solvent is used in the adhesive a heated drying tunnel is employed. A suitable sealing compound can be formed from a composition consisting essentially of from 60-70 per cent by weight of ethylene copolymer, e.g. a terpolymer, with from 40-30 per cent of petroleum wax. Minor amounts of other materials such as pigments, dyes, anti-oxidents &c., may also be present. The terpolymer component provides the effective bonding agent, the wax controlling the peel strength.
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