Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Electro-static or inductive field
Patent
1996-10-04
1998-03-31
Nguyen, Khanh P.
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Electro-static or inductive field
425363, 425373, 425370, 264484, B29C 4714, B29D 701
Patent
active
057335842
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns an apparatus for the manufacture of films, in particular thin or very thin films, with a rotating roller with which a plastically deformable film preferably supplied by a slot extruder is conveyed and stretched, wherein between the roller and a metal belt arranged parallel and at a short distance from the roller is applied a voltage by which the film supplied is applied to the roller.
2. Description of the Related Art
For the manufacture of films, in particular thin or very thin films, an apparatus is known in which the film supplied to the apparatus is applied to a roller and contacts the roller surface over a certain angle of wrap. Due to adhesion of the film to the roller surface, the moment produced by the roller is transmitted to the film, so that the film is stretched in the region located in front of the roller. By stretching, the film which is usually supplied by a slot extruder is reduced to a lower thickness. This thickness in the case of thin or very thin films is between 30 m.mu. and <1 m.mu.. Use of a slot extruder in the apparatus is preferred, as the heat supplied to the film in the slot extruder is utilised in plastic deformation of the film. Between the roller and a metal belt arranged at a distance of about 3-6 mm parallel to the roller, a relatively high d.c. voltage of 5 and 7 kV is applied, the belt being connected to the positive terminal and the roller to the negative terminal. The film is fed to the roller through the gap formed between-the metal belt and the roller, the film being applied to the roller on account of the electric field formed between the metal belt and the roller. This is intended to prevent the occurrence of trapped air between the film and the roller, which leads to reduced productivity and reduced film quality.
It is known that metal belts of rectangular cross-section made of special steel can be arranged parallel to the roller by clamping. The known metal belts are cut from a film about 0.02 mm thick to the necessary width of 10 mm. These belts have the drawback that the edges produced by the cutting process are irregular, so that the electric field between the metal belt and the roller is distorted. These distortions lead on the one hand to electric arcing, by which the film is damaged, and on the other hand to a decrease in efficiency of the voltage, so that the effect of applying the film to the roller, which is produced by the voltage, is reduced, and breakdowns in production as well as trapped air between film and roller occur. Furthermore the metal belt cut from special steel film has the drawback that strong enough clamping forces to clamp the belt with the necessary precision at a uniform distance from the roller cannot be applied. This irregular distance also results in distortion of the electric field between the steel belt and the roller. Distortions of the electric field lead in general to reduced productivity and reduced film quality in the manufacture of films, in particular thin or very thin films, with this apparatus known from the state of the art.
SUMMARY OF THE INVENTION
It is the object of the invention to develop an apparatus of the kind described hereinbefore in such a way that manufacture of films, in particular thin and very thin films, is possible with increased productivity and film quality.
To achieve this object it is proposed that the metal belt comprises a sharp longitudinal edge which is arranged closest to the roller and directed onto it.
As the longitudinal edge of the metal belt is arranged closest to the roller and directed onto it, the shortest distance between the metal belt and the roller arises between the longitudinal edge and the roller, so that an electric field of high field strength spreads out, starting from this longitudinal edge. As the metal belt comprises only one longitudinal edge, the steel belt itself may have a thickness which allows application of the necessary clamping forces, so that the metal belt can be clamped with suffic
REFERENCES:
patent: 3223757 (1965-12-01), Owens et al.
patent: 3823061 (1974-07-01), Frayer et al.
patent: 4309368 (1982-01-01), Groves
patent: 4608212 (1986-08-01), Isner
Almer Charles W.
Nguyen Khanh P.
Warner-Lambert Co.
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