Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1988-09-15
1989-10-03
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264154, 2642107, 2642888, 2642902, 521 97, C08J 932, C08J 936, B29C 5512
Patent
active
048717843
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a polyester film fabricated so as to contain numerous minute cells in the surface and inner parts thereof. More particularly, this invention relates to a stretched polyester film which has a lowered apparent specific gravity owing to formation therein of minute closed cells and is excellent in whiteness and in mechanical strength, and especially in opacifying properties.
BACKGROUND ART
Heretofore, polyester films have been found extensive utility in various industrial fields owing to their excellence in mechanical properties, electrical properties, resistance to chemicals, weathering properties, and resistance to heat. Particularly the biaxially stretched polyethylene terephthalate film excels other films in planarity, dimensional stability and modulus of elasticity, and, therefore, it constitutes itself an indispensable materials for printing plates and for substrates in data devices.
The information industries have been remarkably advance in recent years and a number of new devices and articles of various kinds have been developed. Among such devices, there mentioned the electronic white board which have completely changed the concept of the conventional black board. The electronic white board is free from dust of chalk, therefore, is helpful for air cleaning for offices and meeting rooms. Further, an electronic white board provided with a copying device is accepted as an epoch-making article which contributes to the efficiency of meeting. In addition, the advent of the cashless age has brought about increased spread of magnetic cards such as cash card, telephone card, etc.
Biaxially stretched polyethylene terephthalate films provided with white color and high opacifying properties by the addition of a white pigment such as titanium oxide powder are conventionally used as one of the important materials for the above articles.
These films under mentioned are used in the important part of the final product, i.e. used as the copy board part of the electronic white board and as the substrate for magnetic cards due to their excellent planatory and dimentional stability. In these electronic white board and magnetic cards, the films are fully manifesting their outstanding properties mentioned above.
Indeed these films has highly desirable properties. They nevertheless suffer from various drawbacks because they require to contain a white pigment in a very large amount for the purpose of acquiring an enhanced opacifying properties. Since these films contain inorganic particles such as titanium oxide particles having a lagre specific gravity in a ratio exceeding 10% by weight, they have an apparent specific gravity exceeding 1.7 g/cm.sup.3, occasionally exceeding 2.0 g/cm.sup.3, and a weight per unit volume becomes 20 to 50% larger than that of their regular counter-types containing no pigment. This causes heavy labor during the work of slitting, transporting or packing in the course of the production of film products.
In the case of the white board mentioned above, the phenomenon of sagging of the board surface with aging is caused during long-term use, thereby seriously impairing the commercial value of the white board.
Moreover, the large amount of inorganic particles added to the polyester film contribute to increase the rigidity of the film and cause a problem that the film edges are liable to inflict lacerations on operative's hands in the flim slitting process and the cutting process of a product such as magnetic card. Thus, polyester films containing a large amount of such inorganic particles have difficulties in terms of handling properties. The present inventors started a study on a process for producing cellular film from the view point that it is most important for solving the above problems to find out a method for reducing the apparent specific gravity of the film. That is, the reduction of the apparent specific gravity was attempted by providing a film with cellular structure by employing a method in which a cellular product which is used as heat insulat
REFERENCES:
patent: 3903234 (1975-09-01), Ikeda et al.
patent: 4814124 (1989-03-01), Aoyama et al.
Kotani Tomoyuki
Masuda Narihiro
Otonari Satoshi
Sato Yoshinori
Buckley Linda M.
Conlin David G.
Diafoil Company Limited
Foelak Morton
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