Electric heating – Metal heating – By arc
Reexamination Certificate
2000-04-20
2001-07-24
Walberg, Teresa (Department: 3742)
Electric heating
Metal heating
By arc
C219S121390, C219S121520
Reexamination Certificate
active
06265690
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for plasma treatment of surfaces. More particularly, the invention relates to a pretreatment enabling the coating of surfaces of synthetic resin materials with adhesives, printing inks and the like. Such a pretreatment is necessary because the surfaces of synthetic resins can normally not be wetted with liquids and do therefore not accept the printing ink or the adhesive. The pretreatment changes the surface structure of the synthetic resin so that it becomes wettable with liquids having a comparatively large surface tension. The surface tension of the liquids with which the surface can still be wetted is an indictor for the quality of the pretreatment.
A well established method for the pretreatment of synthetic resin surfaces is based on the principle of corona discharge. In this method the resin to be treated is typically passed through between two electrodes which are coated with a ceramic material and to which a high voltage with high frequency is applied so that a corona discharge occurs through the synthetic resin material. However, this method is suitable only for relatively thin workpieces having a flat surface, such as plastic foils.
DE 195 32 112 A discloses an apparatus for pretreatment of surfaces by means of a plasma jet. Thanks to a specific construction of the plasma nozzle a relatively cool but nevertheless highly reactive plasma jet is achieved which has a shape and dimensions similar to those of a flame of a candle and, as a consequence, permits also the pretreatment of profiles having relatively deep recesses. Due to the high reactivity of the plasma jet a short pretreatment time is sufficient, so that the workpiece can be passed along the plasma jet with a relatively high velocity. Thus, as a result of the comparatively low temperature of the plasma jet, a pretreatment of heat-sensitive plastic materials is also possible. Since no counter electrode is necessary on the back side of the workpiece, it is also possible to pretreat the surfaces of arbitrarily thick block-like workpieces, hollow bodies, and the like. For a uniform pretreatment of larger surfaces, the cited publication discloses an array of a plurality of staggered plasma nozzles. In this case, however, relatively high expenses are necessary for the equipment.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus for plasma surface treatment which permits a rapid and efficient pretreatment of larger surfaces at low equipment expenses. This object is achieved by an apparatus which comprises a rotating head which has at least one excentrically disposed plasma nozzle for generating a plasma jet directed in parallel with the axis of rotation.
When the workpiece is moved relative to the rotating head which rotates with a high speed of revolution, the plasma jet sweeps a stripe-shaped surface zone of the workpiece, and the width of this zone corresponds to the diameter of the circle described by the revolving plasma nozzle. Thus, a comparatively large surface can be pretreated in a rational way.
In this context, it is tolerable that the intensity of the pretreatment in the stripe being swept is not completely uniform. The parameters of the pretreatment, especially the speed of revolution of the rotating head and the translational speed of the workpiece relative to the rotating head can, within broad ranges, always be selected such that a sufficient wettability of the workpiece is achieved everywhere in the pretreated stripe and, on the other hand, the material is not thermally damaged in the zones which have been treated most intensively.
Thanks to the long range of the plasma jet, the pretreated surface of the workpiece can also be curved or profiled. Thus, the apparatus is also suitable for example for the pretreatment of frame profiles for windows or doors made of plastics, plastic bottles or buckets, and the like.
It has been found to be particularly useful in the apparatus according to the invention that the rotation of the head and the corresponding rotation of the plasma jet creates an extended vortex and, as a result, a low pressure is formed in the center of the vortex. This low pressure counteracts a radial escape of the plasma jet and has the effect that the plasma jet is “sucked” to the surface of the workpiece, so that it comes into intimate contact with the surface of the workpiece.
Preferably, two or more plasma jets are mounted to the rotating head with uniform angular spacings, so that at least two plasma jets are operating and the treatment time is shortened correspondingly. This arrangement has also the advantage that the rotating head is substantially balanced due to the symmetric arrangement of the plasma nozzles.
Thanks to the high speed of revolution of the rotating head, which may amount to, for example, 1000 min
−1
or more, Coriolis forces and the like lead to a swirl in the plasma jets exiting from the individual plasma nozzles. In addition, each plasma nozzle preferably has its own swirl arrangement which assures a stabilisation and focusing of the plasma jet. The sense of rotation of the rotating head should in this case be adapted to the sense of the swirling movement in the individual plasma nozzles.
REFERENCES:
patent: 4896016 (1990-01-01), Broberg et al.
patent: 4912296 (1990-03-01), Schlienger
patent: 4969432 (1990-11-01), Scharnweber et al.
patent: 5043554 (1991-08-01), Kohsaka et al.
patent: 5208442 (1993-05-01), Ahola et al.
patent: 5317126 (1994-05-01), Couch, Jr. et al.
patent: 5539176 (1996-07-01), Ikegaya et al.
patent: 5548611 (1996-08-01), Cusick et al.
patent: 5837958 (1998-11-01), Förnsel
patent: 298 05 999 U (1998-08-01), None
patent: WO93/13905 (1993-07-01), None
Buske Christian
Fornsel Peter
Burns Doane , Swecker, Mathis LLP
Cottin Development Ltd.
Van Quang
Walberg Teresa
LandOfFree
Plasma processing device for surfaces does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plasma processing device for surfaces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plasma processing device for surfaces will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2471913