| 摘要 |
1,138,316. Films. FIBER INDUSTRIES Inc. 15 June, 1966 [29 June, 1965], No. 26688/66. Heading B5B. [Also in Division C3 and H1] A thermoplastic film suitable for use as the substrate for a magnetic recording medium, contains particles of an inert inorganic substance insoluble in aqueous or organic liquids and melts, the particles having diameters within the range of 5 to 200 millimicrons and being so uniformly dispersed throughout the film that the surface protrusions they cause are no higher than approximately 100 millimicrons. The preferred film-forming material is polyethylene terephthalate, but the film forming material may be a linear polyester in general, a polyamide, e.g. nylon 66 or nylon 6, a polyolefin, e.g. polypropylene, or a vinyl polymer. The particles preferably consist of silica, but aluminosilicates, e.g. kaolin or diatomaceous earth, may also be used as may carbon black. Preferably, the film contains from 0À01 to 0À5% of its weight of the particles, which preferably have diameters of from 5 to 50 millimicrons. In preferred methods of making the film, (a) the particles are dispersed with the aid of ultrasonic vibrations in the melt from which the film is to be made; (b) the particles are dispersed with the aid of ultrasonic vibrations in a liquid monomer from which the film-forming material is to be made. An example of method (b) is given illustrating the production of polyethylene terephthalate containing silica particles. In the example, the polymer so made is cast into ribbon which is cut into irregular strips and dried to reduce the moisture content below 0À02%. The dried polymer is melted and extruded in a thickness of 0À015 inch on a polished revolving drum, and the film obtained is then subjected successively to a forward stretching of 3À2 times its original length and then to a lateral stretching 2À8 times its original length. The resulting film, 0À0015 inch in thickness, is heat set at 225‹C. for approximately 30 seconds, cooled below 100‹ C. and wound on a mandrel. The finished film has a coefficient of friction of from 0À5 to 0À7, and the protrusions on its surface all project between 2 and 10 millimicrons above the film surface. The film is transparent and may be used in the production of magnetic tape by coating with a suitable composition containing magnetic ferric oxide. The coefficient of friction of such tape is low enough to avoid serious interfacial tension, i.e. blocking, and hence the tendency of superimposed layers of the film to adhere tenaciously as a result of the generation of electrostatic charges is minimized. |
