Plastic and nonmetallic article shaping or treating: processes – Disparate treatment of article subsequent to working,... – Effecting temperature change
Patent
1984-04-18
1986-09-09
Lowe, James
Plastic and nonmetallic article shaping or treating: processes
Disparate treatment of article subsequent to working,...
Effecting temperature change
2642902, B29C 5514
Patent
active
046108335
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to a process for preparing biaxially stretched polyester films. More particularly, this invention relates to a process for preparing biaxially stretched polyester films which are flatter and more slippery and that less breakable and more uniform in thickness.
TECHNICAL BACKGROUND
Biaxially stretched polyester films are excellent in mechanical, thermal and electrical properties as well as chemical resistance and therefore are widely used in various fields. They are matched by no other polymer films especially for application as the base film for magnetic recording tapes. The quality of base films for magnetic tapes greatly influences the quality of the finished magnetic tapes and, therefore, quality standards required of base films for magnetic tapes are becoming higher and higher with progress in magnetic tape technology.
For instance, characteristics of a magnetic tape for video recording output, various S/N ratios, dropout, generation of envelop, etc. are related to flatness of the base film, whereas appearance of the wound-up tape, sliding property and wear resistance of a magnetic tape are closely related to the slipperiness of the base film. Thus, furnishing polyester films provided with both flatness and slipperiness is essential for production of magnetic tapes, especially those for video. Flatness and slipperiness are keenly desired characteristics of base films especially when a thinner magnetic layer or evaporated metal coating is employed in order to increase recording density.
The enhancement of the slipperiness of polyester films has hitherto been achieved by roughening the surface of the polyester film by externally incorporating or internally depositing minute particles. However, there is a limit in the effect of such methods in enhancement of flatness and they are not suitable for production of base films for high quality magnetic tapes for video recording in so far as the polyester films are produced under the conventional conditions. It has been considered that flatness and slipperiness are incompatible characteristics and that it is difficult to obtain a film satisfactory in the two characteristics in combination.
With respect to the polyester film represented by polyethylene terephthalate film, it has been known that biaxially stretched films excellent in slipperiness, which cannot be obtained by film-making at the ordinary stretching temperature, can be obtained by longitudinally stretching at a higher temperature. However, it is difficult to obtain a longitudinally stretched film with a uniform thickness by stretching an amorphous polyester film as prepared in single stage stretching at a higher temperature, since such a method generally increases irregularity in thickness, which eventually results in unevenness in thickness in the resulting biaxially stretched film. Multiple stage longitudinal stretching methods, which inhibit increase in thickness irregularity in the high temperature stretching are disclosed in Japanese Laying-Open Patent Publication No. 43772/73 and No. 122573/75. According to these high temperature longitudinal stretching processes, however, it is, at the highest, only up to the stretching temperature of 100.degree. C. that generation of thickness uniformity is inhibited. The increase in thickness irregularity is unavoidable in stretching at higher temperatures. That is to say, although it is expected that a biaxially stretched film with excellent flatness and slipperiness may possibly be obtained by longitudinally stretching the film at a higher temperature, it is difficult to stretch a film at such a high temperature in the conventional stretching because are thickness unevenness increases. In the case of magnetic tape, especially video magnetic tape, the requirement in the thickness uniformity is very high. The commercial value of a magnetic tape is reduced if the tape is unsatisfactory in the thickness uniformity no matter how excellent it is in its other properties.
We proposed a new process by which
REFERENCES:
patent: 4234532 (1980-11-01), Motegi
patent: 4238443 (1980-12-01), Levy
patent: 4370291 (1983-01-01), Kazama et al.
patent: 4497865 (1985-02-01), Minami
Kanesaki Tateo
Tomitaka Kichinojyo
Utsumi Shigeo
Diafoil Company Limited
Lowe James
LandOfFree
Process for preparing biaxially stretched polyester films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparing biaxially stretched polyester films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing biaxially stretched polyester films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1014636