| 摘要 |
1,084,722. Seaming non-metallic sheet material. O. B. RASMUSSEN. May 25, 1965 [March 31, 1964], No. 13300/64. Heading B5K. Thermoplastic organic film material is welded by applying, as a .welding aid to selected areas of at least one of the films to be welded, a thin layer of a low-molecular weight substance which is capable of dissolving the film material at the welding temperature and which is liquid at a temperature below that necessary to effect a substantial dissolution of the material, the low molecular weight substance being applied in liquid form and rapidly cooled to a congealed state, subsequently arranging the layers of film material in the desired position for welding and heating the arranged-layers sufficiently to make the welding aid at least swell the film material at the places to be welded but insufficiently to make the surfaces stick together without the welding aid. Preferably, the welding aid is applied to the film or films by printing, e.g. by an engraved roller, and is applied in a layer the thickness of which is 1-25% of the thickness of the films to be welded, the higher percentages being used for thinner films. Fine particles of the same polymer as the film material or a closely related polymer of preferably the same or similar molecular weight may be mixed with the welding aid. Specified films are high density polyethylene and isotactic polypropylene which are welded at a temperature in the range 95-120‹ C. Oriented film material may be used and the films to be welded may each be a laminate in which the directions of orientation of the single layers cross one another. The welding aid is preferably an aromatic hydrocarbon or a chlorinated hydrocarbon, e.g. one melting within the range 40-100‹ C., such as naphthalene or paradichlorobenzene. Polyethylene terephthalate may be welded by means of nitrobenzene in a cooled room. The welding aid may be applied to both sides of a narrow band of polymeric material which is interposed between the films to be welded together. The invention is applicable to welding block bottom bags. The films may be continuous or partly fiberized, e.g. an oriented polyolefine which has been mechanically treated to produce a multitude of splits or cracks close to one another. |
