Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-11-29
2001-09-04
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069140, C219S068000, C219S384000
Reexamination Certificate
active
06284994
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the perforation of synthetic plastic films, and more particularly to an apparatus and method for perforating synthetic plastic films.
BACKGROUND OF THE INVENTION
In U.S. Pat. 4,777,338, the inventor in common to the subject invention describes a device for producing spark perforation of synthetic plastic films. The perforation is performed by applying electrodes to opposite sides of the film as the film is passed through a water bath. The apparatus disclosed in this patent has certain limitations when operated as a perforation machine on a commercial scale.
The limitations of the perforation device disclosed in U.S. Pat. No. 4,777,338 arise from the behaviour of the water bath. While the water bath makes it possible to produce closely spaced perforations in a synthetic plastic film, it has been found difficult to maintain uniform small hole diameters. This problem arises because the water bath can vary in electrical conductivity and the charge lost from the electrodes due to conductive leakage will also vary. Furthermore, charge leakage through the large amount of water surrounding the electrodes makes the perforation process inefficient, because rather large amounts of electrical pulse energy are needed to overcome the charge leakage. The high electrical pulse energy, in turn, causes the electrode rollers to wear rapidly as they are small and have a small contact area with the film. The wear on the rollers results in a wide contact band and erratic perforation of the film. Contamination in the water bath is also difficult to control because the water bath has no controlled flow pattern and as a result contaminants can accumulate in the region of the electrodes. Another shortcoming in the prior art apparatus is the marking of the film as it is pulled through bath pressed between the roller electrodes and the ground electrode (i.e. the bottom surface of the bath).
In view of the foregoing, there remains a need for a new perforation apparatus suitable for commercial use which overcomes the shortcomings of the prior device.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a novel apparatus and method for perforating synthetic plastic films suitable for commercial application.
In one aspect, the present invention provides an apparatus for perforating a film, the apparatus comprises, one or more electrodes, said electrodes being mounted in an electrode holder and said electrodes being positioned to lightly contact the film to be perforated; a return electrode, the return electrode provides a support surface for the film; a water jet sprayer mounted in the electrode holder, and providing a jet of water in the location the electrodes contact the film; the electrodes including an electrical coupler for coupling to a high voltage supply for energizing the electrodes to produce a discharge between the electrodes and the return electrodes to perforate the film.
In another aspect, the present invention provides a method for perforating a synthetic film, said method comprising the steps of, moving the film to be perforated through a gap defined by one or more rod electrodes and a roller electrode, the rod electrodes being in light contact with the film and the film being supported by the roller electrode; applying high voltage pulses to the rod electrodes to cause a discharge between the rod electrodes and the roller electrode sufficient to perforate the film in an area where each of the rod electrodes contacts the film; simultaneously applying a jet spray of water to the region of contact between each of the rod electrodes and the film.
REFERENCES:
patent: 2141869 (1938-12-01), Konig
patent: 2495534 (1950-01-01), Meaker
patent: 2763759 (1956-09-01), Mito et al.
patent: 3502845 (1970-03-01), Schirmer
patent: 3862396 (1975-01-01), Machinda et al.
patent: 4278871 (1981-07-01), Schmidt-Kufeke et al.
patent: 4314142 (1982-02-01), Brown et al.
patent: 4777338 (1988-10-01), Cross
patent: 5356497 (1994-10-01), Lee
patent: 5415538 (1995-05-01), Kagawa
Cooke Colleen P.
Dunn Tom
Ridout & Maybee
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