| 摘要 |
Weldable oriented polypropylene film is produced by (1) coating an unstretched polypropylene film on one or both sides with a plastics material which can be welded after it has been stretched and can be stretched at least to the same extent as the polypropylene film and softens below about 150 DEG C, and then stretching the coated film at least uniaxially by at least 300%; (2) stretching a polypropylene film in its longitudinal direction, coating the film on one or both of its surfaces with a plastics material which can be welded after it has been stretched and can be stretched at least to the same extent as the polypropylene film and softens below about 150 DEG C, and then stretching the coated film in the transverse direction by at least 300%; or (3) providing two longitudinally stretched polypropylene films on one surface with a weldable coating, bonding the uncoated sides of the two films together e.g. with polyisobutylene, and transversely stretching the compound film carrying weldable coating on both outer surfaces. The thickness of the plastics coating is so selected that after the coated material has been stretched the plastics coating is at least 1 micron thick. The plastics coating may be produced from a solution, dispersion or melt, or is in the form of a film laminated with the unstretched or the longitudinally stretched polypropylene film. The two sides of the unstretched film may be coated with two different plastics materials prior to stretching in process (1). The two sides of the longitudinally stretched film may be coated with two different plastics materials in process (2). The weldable film may be laminated to the polypropylene film by passage between two rubber rollers, one of which may be heated, and then through a hot zone to unite the films by softening or melting of the weldable material with the polypropylene film, or the polypropylene film may first be coated with adhesive and then laminated with the weldable film at an elevated temperature. The weldable plastics material may be high pressure polyethylene and copolymers of vinylidene chloride e.g. with acrylonitrile, or methyl methacrylate and itaconic acid. A second coating of a welded plastic may be applied to produce a relatively thick weldable layer. |
