| 摘要 |
988,816. Laminates; films. O. B. RASMUSSEN. Feb. 28, 1964 [March 2, 1963], No. 8429/63. Headings B5B and B5N. A laminated sheet has at least two plies of uni-axially oriented film of organic thermoplastic material bonded together so that the directions of orientation of adjacent plies cross, at least one of the plies containing a multitude of interior microcavities which do not penetrate through the ply from one surface to the other. Preferably, the thermoplastic material is an 1-olefins such as high density polyethylene and ethylene co-polymers or highly crystalline polypropylene. Preferably the cavities are produced by forming a film containing a major amount of the orientable 1-olefine and a minor amount of a foreign polymer capable of swelling when exposed to a volatile solvent which does not significantly swell the 1-olefins polymer, applying such a solvent and thereafter evaporating it by heating. Suitable foreign polymers indude esters of polyacrylic acid, polyvinyl esters, polyvinyl ethers, polystyrene, polyvinyl chloride, cellulosic polymers, polycarbonates, polyvinyl butyral &c. Several examples of suitable volatile solvents are given. The volatile or gas forming agent may be incorporated before or after orientation of the film, but is not removed until after orientation. Preferably, three plies are used, each containing a multitude of interior microcavities, and they are associated so that the directions of orientation of adjacent plies form 45-60 degrees with each other, the orientation of the centre ply being preferably parallel to the longitudinal direction of the sheet. The plies may be bonded together by welding with solvents or heat, or preferably with a pressure-sensitive adhesive, e.g. polyisobutylene, polyvinyl-isobutyl ether, a normally tacky fatty-polyamide used alone or with 20-30% of micro crystalline wax. The oriented films may be produced by bias-cutting stretched tubular extruded film. Specifications 816,607 and 865,707 are referred to. |
