Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Reexamination Certificate
2000-06-16
2001-11-06
Lam, Cathy (Department: 1775)
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
C427S569000, C428S409000
Reexamination Certificate
active
06312566
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plastic film formed from polypropylene or the like that has a good running characteristic and to a production method for the same.
Due to their excellent properties, plastic films are widely used for industrial purposes, for example, capacitors. As greater quantities of plastic films are being demanded, speedups in all plastic film-processing steps are lately being pursued.
However, as the processing speed is increased, meandering, deviation, wrinkling and the like during film wind-up and the like have become more likely to occur, and have become factors that impede increases in productivity.
Therefore, a high-speed processing characteristic is required in the plastic film itself. Winding-up characteristic, running characteristic and the like are now important quality requirements.
Conventionally, various proposals have been made to prevent deviation and wrinkling of a plastic film during the slitting, the winding-up and the like of the film. For example, Japanese Patent Application Laid-Open No. SHO 58-16415 discloses that the wetting tension of a non-vapor-deposited surface is specified. Japanese Patent Application Laid-Open No. SHO 60-183449 discloses that the coefficient of static friction of a vapor-deposited film is specified.
Furthermore, Japanese Patent Application Laid-Open No. SHO 62-20137, as for example, proposes a method in which, in a film vapor deposition step, a film is uniformly electrified immediately after the film is unwound, and the film is diselectrified immediately before it is wound up.
However, in the case of polypropylene films, which are relatively apt to have winding deviation, wrinkling or blocking among the plastic films, the aforementioned conventional arts are still insufficient, for example, with regard to the running characteristic or the winding-up characteristic under a high-speed condition of at least 400 m/min.
For example, in the art described in Japanese Patent Application Laid-Open No. SHO 58-16415, both surfaces of a film are subjected to a corona treating process, so that a drawback exists; for example, wrinkling is likely to occur and, therefore, films may block each other. Furthermore, merely specifying the coefficient of static friction of a vapor-deposited film as described in Japanese Patent Application Laid-Open No. SHO 60-183449 is not adequate for the running characteristic in the atmosphere. In either proposal, the drawback is particularly remarkable in, for example, a case where a film has a small thickness of 10 &mgr;m or less, a case where the rigidity of a film is low in comparison with the wind-up tension due to the material of the film, etc.
Furthermore, a method of uniformly electrifying a film immediately after unwinding the film, and diselectrifying the film immediately before winding it up, as described in Japanese Patent Application Laid-Open No. SHO 62-20137, can prevent slippage between a cylindrical can and a guide roller or the like during the film-running and can achieve an improvement with regard to meandering during the running. However, due to the diselectrification immediately before the wind-up, the method is insufficient as a measure for preventing a winding deviation.
SUMMARY OF THE INVENTION
In view of the aforementioned problems, it is an object of the invention to provide a plastic film that does not cause any one of winding deviation, wrinkling and blocking even under a high-speed running condition of, for example, at least 400 m/min in the case of a polypropylene film, as a result of intensive research.
To achieve the aforementioned object, a plastic film according to the invention is a plastic film wherein many fine electrified patterns of the positive and negative polarities on a surface of the film. A characteristic of the electrified patterns is that at least 1,000 positive electrified patterns having areas of at most 10 mm
2
and arbitrary shapes, and at least 1,000 negatively electrified patterns having areas of at most 10 mm
2
and arbitrary shapes are distributed per 100 cm
2
of the film.
In a preferred mode of the invention, an average area of the electrified patterns is within a range of 0.2 mm
2
to 1.0 mm
2
, and at least one positively electrified pattern and at least one negatively electrified pattern exist in an arbitrary circle having a diameter of 1 cm on a surface of the plastic film.
In a polypropylene film, in particular, it is an effective characteristic that at least 2,000 positive electrified patterns having areas of at most 10 mm
2
and arbitrary shapes, and at least 2,000 negatively electrified patterns having areas of at most 10 mm
2
and arbitrary shapes are distributed per 100 cm
2
of the film. It is a more effective characteristic that at least 3,000 positive electrified patterns having areas of at most 10 mm
2
and arbitrary shapes, and that an average area of the positively electrified patterns is at most 0.5 mm
2
.
Furthermore, a polypropylene according to the invention is characterized in that a static friction coefficient &mgr;
s
between one surface of the film and another surface of the film is at least 0.2, and a dynamic friction coefficient &mgr;
d
therebetween is at least 0.08.
It is preferable that the plastic film of the invention be obtained by subjecting a surface of the film to a corona treating process.
The production method for a plastic film of the invention is a plastic film production method wherein at least one film surface is subjected to a corona treating process at least once, and a discharge degree of a last-performed corona treating process is at most 4 W/cm
2
.
Furthermore, it is preferred that the corona treating process be performed only on one surface of the film.
REFERENCES:
patent: 4297187 (1981-10-01), Deguchi et al.
patent: 5401446 (1995-03-01), Tsai et al.
patent: 0346242 A (1989-12-01), None
patent: 5816415 A (1983-01-01), None
patent: WO9605045 A (1996-02-01), None
Iwaisaki Yoko
Moriguchi Isamu
Onishi Keitaro
Sato Makoto
Birch & Stewart Kolasch & Birch, LLP
Lam Cathy
Toray Industries Inc.
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