Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-11-09
2003-01-28
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C264S288400, C264S290200, C526S242000, C526S348100
Reexamination Certificate
active
06512064
ABSTRACT:
The present invention relates to a fluororesin film having mechanical strength such as tensile break strength or tensile modulus remarkably improved as compared with conventional films.
A fluororesin film has excellent physical properties which are not observed with other films, in that it has physical and chemical properties such as heat resistance, weather resistance, chemical resistance and non-tackiness basically in good balance. By virtue of such properties, it is used in a wide range of fields including, for example, a film material for laminates, a film material for adhesive tapes, an agricultural covering material for tunnel houses or pipe houses, a film for electrical insulation, a film for packaging, a release film for printed circuit boards, a film for capacitors, a film for surface protection, a protective film for kitchens or kitchen equipments, a gas sampling bag, a protective film for road sound insulating walls, a laminated film as a building material, an inner film for solar collectors, a cover film for fireman's or work clothings, and a surface film for copying boards. However, a fluororesin film is usually not so good with respect to the mechanical properties such as tensile break strength or tensile modulus, as compared with other resin films for industrial use.
If it is possible to substantially improve the mechanical strength such as tensile break strength of a fluororesin film while maintaining the excellent various properties such as heat resistance, the above-mentioned applications, such as an agricultural covering material for tunnel houses or pipe houses, a film for packaging, a film material for laminates, a film material for adhesive tapes, a film for electrical insulation, etc. can be realized by a film substantially thinner than the film presently available, and such is very desirable also from the viewpoint of the weight reduction or resource saving. Further, it is expected that the application of such a fluororesin film will be expanded also to an industrial field where higher strength of a film is required together with the above-mentioned excellent various properties.
A stretching method may be mentioned as one of conventional methods for improving mechanical strength, etc. of a resin film. This is a method to increase the strength or crystallinity of a film by monoaxially or biaxially stretching the film to have molecular chains or crystallites oriented, and such a method is commonly employed in the field of various industrial films. However, in the field of fluororesin films, it is commonly believed that the effect of stretching for improvement of the physical properties is rather low. Further, the stretchability is not good. Accordingly, as a stretched film of a fluororesin, only a polyvinylidene fluoride is practically industrially used at present.
As a result of a detailed study from such a viewpoint by the present inventors, it has been found that a raw fabric of a fluororesin film is certainly basically poor in stretchability, and if it is stretched as it is (hereinafter referred to as simple substance stretching), even if it can be stretched, it can hardly be uniformly stretched, and it is impossible to accomplish improvement of mechanical strength in good balance as the entire film. Further, it has been found very difficult to carry out stretching so that the mechanical strength is balanced in the longitudinal direction and in the transverse direction.
The present inventors have found that if, instead of stretching a fluororesin film alone, such a fluororesin film is sandwiched between readily stretchable films to obtain a laminated film, and such a laminated film is stretched mainly with the readily stretchable films constituting the outer layers, the objective fluororesin film constituting the core layer, will be forcibly stretched as pulled by the readily stretchable films of the outer layers, and consequently, it will be uniformly stretched.
It is an object of the present invention to provide a novel fluororesin film of high strength, which has mechanical strength such as tensile break strength or tensile modulus of the fluororesin film substantially improved, while maintaining various excellent properties such as heat resistance, and which can be prepared by the above-mentioned new stretching principle.
The present invention has been made to solve the above-mentioned problems, and it provides a novel fluororesin film of high strength, which has a dielectric constant of at most 5, and which has a tensile break strength of at least 40 MPa in each of MD direction (longitudinal direction) and TD direction (transverse direction).
Further, the present invention provides a fluororesin film of high strength which is a biaxially stretched film of a fluororesin having a dielectric constant of at most 5, wherein the ratio of the tensile break strength in each of MD and TD directions after stretching to the tensile break strength in each of MD and TD directions before stretching, is at least 1.5.
Still further, the present invention provides a fluororesin film having a high tensile modulus, which has a dielectric constant of at most 5, and which has a tensile modulus of at least 3,000 MPa in each of MD and TD directions.
In the accompanying drawing,
FIG. 1
shows a schematic flow chart illustrating the stretching process in the present invention.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The fluororesin film of the present invention is not particularly limited so long as it is a fluororesin film having a dielectric constant of at most 5. For example, the following may be mentioned as preferred materials. Namely, a tetrafluoroethylene type fluororesin such as a tetrafluoroethylene/perfluoro(alkyl vinyl ether) type copolymer (PFA) (wherein the carbon number of the perfluoroalkyl group is preferably from about 1 to 18) or a tetrafluoroethylene/hexafluoropropylene type copolymer (FEP); or a ethylene/tetrafluoroethylene type copolymer (ETFE); or a chlorofluoroethylene type fluororesin such as a polychlorotrifluoroethylene (PCTFE) or an ethylene/chlorotrifluoroethylene type copolymer (ECTFE), may, for example, be mentioned. Further, a blend material of these resins or further copolymers of such monomer components may also be used.
The definition of “a dielectric constant of at most 5” is meant for excluding a fluororesin film of vinylidene fluoride type such as polyvinylidene fluoride (PVDF) (dielectric constant: 10 to 13) or of a vinyl fluoride type such as polyvinyl fluoride (PVF) (dielectric constant: 8 to 9). Namely, PVDF or the like is different in the electrical nature from other fluororesins covered by the present invention, and such a resin can be relatively easily stretched by single substance stretching, whereby a film having a sufficiently high mechanical property such as tensile strength is already available, and there is no substantial practical merit in applying the present invention.
The fluororesin film of the present invention can be obtained by firstly forming a raw fabric film from the above fluororesin and then stretching it under certain specific conditions.
Now, this stretching process will be described with reference to the accompanying drawing.
FIG. 1
is a schematic flow chart illustrating this stretching process which essentially comprises a step I of forming a laminate of a raw fabric film and an assist film, a step II of stretching the laminate, and a step III of peeling the assist film after stretching. Here, the reference numerals have the following meanings.
10
: a raw fabric film;
20
,
20
′: an assist film;
30
: a raw fabric film laminate;
41
: a preheating step;
43
: a stretching step;
45
: a heat treatment step;
47
: a step of peeling an assist film;
50
: a fluororesin film after stretching;
60
,
60
′: an assist film after stretching.
Firstly, the step I will be described.
The step I is a step of laminating an assist film
20
or
20
′ to assist stretching, on at least one side, preferably on each side, of a raw fabric
Higuchi Yoshiaki
Jitsugiri Yukio
Asahi Glass Company Limited
Zitomer Fred
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