Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Patent
1999-08-09
2000-12-12
Parker, Fred J.
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
427458, 427471, 427482, 427444, 118620, 118638, B05D 104, G03G 1502
Patent
active
061595551
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method as well as a device for electrostatic charging of the two outer sides of at least one material web with charges of opposite polarity, prior to the further processing of the at least one material web wherein the web is guided through the nip of a pair of rollers that are parallel to one another and have a small distance between them.
2. Description of the Prior Art
A method of this kind and a device for electrostatic charging is known (DE 31 17 419 A1). In this document, a plurality of material webs are brought together to form a hank and only the two outer sides are charged by means of a device designed as a corona-charging electrode for electrostatic charging downstream from the first pair of rollers by means of a high voltage source of 30 kV.
The disadvantage of this known device is a charging of the two outer sides of the material webs that is not highly directed in space. Thus, a large number of charged particles migrate throughout the area where charging is taking place. This results in poor charging efficiency. In addition, there is the danger that under unfavorable environmental conditions, the corona charging electrodes will become contaminated and consequently fall to operate. The cleaning expense can be very high.
SUMMARY OF THE INVENTION
The invention is a method providing a more closely directed charging with improved efficiency.
The invention uses the unequal electrostatic charging of the two outer sides of the at least one material web, performed in the nip by each roller of the pair.
The rollers can be charged through the surface, namely by means of a so-called contact roller (DE 38 23 739 A1), or by wiper brushes known of themselves, or by a wiper contact.
In an advantageous improvement according to the invention, charging is performed from the inside by the device composed of the pair of rollers, with each roller having a covering with limited electrical conductivity (so-called semiconducting) on top of a steel jacket, with the steel jacket of each roller being connected to a positive or negative high voltage source for electrical charging of the coating with limited conductivity. In the device according to the invention, because the voltage is applied from the inside, retrofitting in existing systems for processing material webs, preferably made of plastic or paper, using a high voltage source of 3 to 7 kV is possible. Therefore, much lower voltages are used relative to the prior art. In addition, charging takes place precisely at the charged point, namely at the outside of the at least one material web, so that efficiency is achieved that is considerably better by comparison with the prior art. Finally, due to the elimination of corona charging electrodes, their cleaning cost is eliminated completely so that lower downtime expenses are achieved as well as when the system is in operation.
Advantageously, in the invention the axis or shaft of the roller is connected in an electrically conducting fashion with the steel jacket and is insulated electrically from the machine frame supporting the roller. For electrical charging of the coating with limited conductivity, the high electrical voltage is applied to the axis or shaft which has a terminal for this purpose. This could be either a fixed terminal on the axis or a pressure bearing located at the end of the shaft.
In an advantageous improvement on the invention, it is also possible to mount a primary coil permanently relative to the machine frame and concentrically with respect to the axis or shaft of the roller at one end, concentrically with respect to the axis or shaft of the roller and next to the roller, and to provide a secondary coil that turns with the roller, with its one terminal on the axis or shaft and its other terminal connected to the steel jacket through a rectifier circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
Three embodiments of the invention will be described in greater detail below with reference to the drawing.
FIG. 1 is a firs
REFERENCES:
patent: 3876917 (1975-04-01), Gaynor et al.
patent: 4056314 (1977-11-01), Silverberg
patent: 4978118 (1990-12-01), Kashahara
patent: 5138971 (1992-08-01), Nakajima et al.
"Static Electricity in Folding Apparatus and in Further Processing" appearing in Der Polygraph 11, 1986, pp. 1258, 1260.
Hahne Ernst August
Knopf Franz
Kunzig Hermann
Eltex-Elektrostatik GmbH
Parker Fred J.
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