| 摘要 |
1,173,688. Stretching vinylidene fluoride polymer films. KUREHA KAGAKU KOGYO K.K. 14 July, 1967 [14 July, 1966; 10 May, 1967], No. 32631/67. Heading B5B. [Also in Division HI] The electrical properties of unorientated films of homopolymers or copolymers of vinylidene fiuoride containing at least 80% by weight of vinylidene fluoride are improved by stretching such a film in the longitudinal and/or transverse direction at a stretch ratio of at least 2-5 and at room temperature or at a higher temperature, whereby the film is either monoaxially or biaxially orientated. The film after having been stretched may be heat treated at a temperature within the range 125‹ to 175‹ C. while being maintained under such a tension that it does not elongate or contract by more than 10% in any direction in which it has been orientated. The film may be rapidly cooled immediately after having been heat treated. The polyvinylidene fluoride used for producing the film is preferably prepared by polymerizing the monomer at a low temperature initially below the critical temperature. In an example, polyvinylidene fluoride having an intrinsic viscosity of 1-00 and prepared by emulsion polymerization at 25‹ C. is formed into a film by melt extrusion at 230‹ to 240‹ C. and the molten film rapidly cooled by contacting it with metal rolls maintained at 80‹ C. The unorientated film thus obtained is stretched at 150‹ C. in its longitudinal direction at a stretch ratio of 3.5 and thereby orientated in this direction. In another example, an orientated PVDF film produced in a similar manner is heat set in an oven at 140‹ C. while under such tension as to restrict its shrinkage to 5% in the direction in which it was stretched. Data are furnished showing that the dielectric constants of PVDF films produced according to the invention are higher and their dielectric loss tangents lower than those of PVDF films which have not been stretched in accordance with the invention. |
