WO1998044608A1

WO1998044608A1 - Corona electrode arrangement

Info

Publication number: WO1998044608A1
Application number: PCT/EP1998/001791
Authority: WO
Inventors: Manfred Steffl; Werner Bamberger
Original assignee: Brückner Maschinenbau GmbH
Priority date: 1997-03-27
Filing date: 1998-03-26
Publication date: 1998-10-08
Also published as: JP2000511694A; EP0920718A1; KR20000011122A; DE19713127C1

Abstract

The invention relates to a corona electrode arrangement for electrical treatment of plastic films which are guided in a partial angle area in a cylindrical electrode (1) acting as a counter electrode. The inventive arrangement has a corona electrode (7) moving over the treatment area of the plastic film (3). Said electrode also includes a discharge section (11). The inventive device is improved by using perforated sheet metal in the discharge section (11).

Description

Corona electrode arrangement

The invention relates to a corona electrode arrangement for the electrical treatment of plastic films according to the preamble of claim 1.

In order to be able to better print plastic films with water-soluble inks, for example, they first have to be treated accordingly. For this it is necessary that the surface tension of the plastic films is influenced accordingly, for which purpose corona treatment stations are used. During the production process, the plastic film is exposed to a corona discharge, which is generated by a high-voltage electrode at a distance of a few millimeters from the film over the entire working width. The film itself is passed over an earthed roller during the treatment. The film is influenced in a targeted manner by the corona discharge occurring and by the ozone formed. Corona pretreatment is often carried out especially on foils that are later printed, metallized or laminated to other surfaces.

So that the toxic ozone cannot flow out in an uncontrolled manner, the entire electrode arrangement is usually accommodated in a housing. The resulting ozone can be continuously extracted from the housing and bound or broken down accordingly.

The corona electrode and the surrounding housing reach as close as possible to the grounded roller.

A corresponding corona electrode has become known, for example, from US 3,973,132. It comprises a roller electrode over which the film is guided and which serves as a grounding electrode. The corona electrode consists of a roller body with a plurality of ribs running in its longitudinal direction and offset in the circumferential direction.

A corona electrode, which is also suitable for plastic surface treatment, has become known from EP 0 095 051. It comprises a knife electrode arrangement which consists of at least three knife edges aligned parallel to one another and whose discharge edges are at a constant distance from the surface of the roller electrode. The knife edges are aligned perpendicular to the direction of movement of the film. The discharge edges of the measuring electrodes are rounded or semicircular mig trained. The interior of the electrode is again connected to a vacuum source for the removal of the ozone that is produced.

The object of the present invention is to create an improved corona electrode arrangement based on the last-mentioned prior art, with which an improved corona discharge and thus an improved plastic film treatment can be achieved.

The object is achieved according to the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims.

It has now surprisingly been found that a completely new design of the corona electrodes according to the invention enables a significantly improved corona discharge. It also proves to be advantageous that the corona electrodes according to the invention are even easier and cheaper to produce than conventional corona electrodes.

Surprisingly, it has been shown that a significantly improved discharge can be achieved with the corona electrode according to the invention with a perforated structure, preferably using a perforated plate. The improved corona discharge may be due to a large number of holes or the discharge line resulting therefrom in the corona electrode structure. Especially then If the corona electrode consists of a sheet metal part in which the holes are punched, the sharp edges of the holes prove to be favorable for the improved corona discharge.

A corona electrode arrangement is also known from WO 94/28568, in which a plastic film to be treated is passed between two electrodes aligned parallel to one another, an earthed perforated plate being provided between the two electrode surfaces aligned parallel to one another. However, this perforated plate does not represent a corona electrode, but, according to this prior publication, merely serves as a support plate, via which the plastic film to be treated is passed through the plane-parallel electrode arrangement. In addition to the purely mechanical support function for the plastic film, this previously known perforated plate also has the function of damping the electrical field built up between the plane-parallel electrodes, for which purpose the perforated plate is grounded.

In a preferred embodiment of the invention, the electrodes furthermore have features which ensure, even under thermal stress, that the electrodes are not subjected to warping. For this purpose, it is preferably provided that the electrodes are provided with lateral holding webs which point away from their concave electrode treatment surface and which are preferably provided with a plurality of slots which are offset from one another in the longitudinal direction of the electrode arrangement. These slots run in a preferred embodiment of the invention starting from the free web end over the entire web height. The height of the web here means the height of the inner wall of the corona electronics.

In order to ensure a stable electrode construction, it is also preferably provided that the lateral holding or mounting webs of the corona electrode are provided with angled portions that point towards one another. A square profile can preferably be used here, which is made of stainless steel, for example, and which serves to stiffen the corona electrode.

In a particularly simple embodiment, the explained corona electrode can thus consist of a sheet metal part, which the plurality of holes are punched in, and which, according to one embodiment of the invention, can be provided with lateral retaining webs.

Finally, a plurality of such corona electrodes can be arranged offset in circumferential direction from a grounding roller which interacts with these corona electrodes and via which the plastic film to be treated is guided over a partial circumferential surface of the grounding roller.

Furthermore, the corona electrode according to the invention can also be used to conduct treatment gas, for example an inert gas, in particular nitrogen, in the direction of the roller. This measure prevents the formation of toxic ozone, since the atmospheric oxygen is reduced by the treatment gas. is pushing. In addition, the gas simultaneously cools the electrode and thus, among other things, reduces the problem of thermal distortion. It has also been shown that the treatment result can be influenced positively when using nitrogen.

In particular when using such a treatment gas, it can prove to be advantageous if the corona electrode is not provided with slits on its opposite sides, but with a large number of material weakenings which run transversely to the longitudinal direction of the web and are spaced from one another, so that the corona electrode then only on the the surface opposite the roller is perforated and only there can the gas flow in a targeted manner onto the plastic film to be treated. Due to the fact that the slits otherwise provided in the side webs are replaced by material weakening, which for example have a wall thickness that only corresponds to a fraction of the other wall thickness of the mounting webs, the side surfaces are made gas-tight on the one hand, but on the other hand have the necessary elasticity for thermal Extension to.

The invention is explained in more detail below using an exemplary embodiment with reference to two drawings. The individual shows:

Figure 1: A schematic perspective arrangement of three corona electrodes according to the invention, which are parallel to the axial direction a grounding roller running and offset in the withdrawal direction of a plastic film to be treated;

Figure 2 is a schematic perspective bottom view of the corona electrode shown in Figure 1;

3 shows a schematic end view of the embodiment according to FIG. 1 with a cover covering all three corona electrodes, in which the front end cover is omitted for better clarity;

Figure 4 is a perspective view of the figure

3 arrangement shown with the cover housing omitted;

FIG. 5: shows a schematic central longitudinal section through the exemplary embodiment shown in FIG. 3 with the roller omitted; and

Figure 6: a representation corresponding to Figure 2 with respect to a modified corona electrode with dense side walls.

A roller electrode 1 is shown in FIG. 1 in a schematic perspective illustration, which is usually is grounded. A plastic film 3 to be treated, which is only indicated by dashed lines, is guided around the roller electrode 1 in a partial angle range according to the arrow representation 5 during its surface treatment and conveyed further in the withdrawal direction 5.

In the exemplary embodiment according to FIG. 1, three corona electrodes 7 are provided, which run parallel to the axis of the roller electrode 1, with a length corresponding to the treatment width. The corona electrodes 7 thus usually have a length which corresponds at least to the width of the plastic film web to be treated and thus usually approximately to the axial length of the roller electrode 1.

The corona electrodes 7 are arranged offset in the circumferential direction of the roller electrodes 1 at a close distance in the take-off direction 5. Each corona electrode 7 is usually accommodated individually, or a plurality or all or all of the corona electrodes 7 are accommodated in a common housing, which is not shown in more detail in FIG. 1 for the sake of simplicity. This corona electrode housing surrounds the respective corona electrode 7 as completely as possible and extends as close as possible to the surface of the roller electrode 1 in order to continuously suck off the ozone formed by applying a vacuum so that it cannot get into the environment.

1 and the partial bottom view of a single corona electrode according to FIG 2 it can be seen that the corona electrode has a discharge section 11 which is of concave design and whose surface curvature in cross-sectional representation is adapted transversely to the roll axis of the roll electrode 1 to the radius of curvature of the roll electrode 1. The radius of curvature of the discharge section 11 is chosen so that a constant distance between the surface of the discharge section 11 and the surface of the roller electrode 1 is maintained.

The discharge section 11 has a cylinder jacket cutout in which a plurality of holes 13 are made in a plurality of longitudinal and transverse rows.

In order to ensure as uniform a surface treatment of the film as possible, the rows of holes with the holes 13 shown in the drawings are preferably not arranged in the discharge section 11 parallel to the film running direction. In the exemplary embodiment shown, a hole pattern is shown in which the holes 13 are arranged in rows 12a of holes which run obliquely to the pull-off direction of the film. In the longitudinal direction of the corona electrode, the holes 13 can certainly be arranged in rows 12b of holes parallel to the longitudinal direction of the corona, since these rows of holes lie transversely to the direction in which the film web is drawn off.

The corona electrode 7 thus formed preferably consists of a conductive perforated plate in which the holes 13 can be made by stamping. In particular by one of Like punching process, sharp-edged holes 13 are generated, whereby the corona discharge is positively influenced.

Each of the corona electrodes 7 is provided on its parallel to the axis of the roller electrode 1 and thus transversely to the withdrawal direction 5 of the plastic film web 3, each with a lateral mounting web 15, which can be produced by using a corona electrode 7 from punched sheet metal by edges.

The assembly webs 15 mentioned are aligned parallel to one another in the exemplary embodiment shown. However, an arrangement is also possible in which the mounting webs 15 run from the discharge section 11 towards one another or away from one component.

In order to avoid that during the operation of the corona electrodes explained, the heat occurring during the corona treatment causes the corona electrodes to warp, with the result that the distance between the discharge distance 11 and the surface of the roller electrode 1 and thus the one above it may also be Film is disadvantageously changed, a plurality of slots 17 are made in the mounting webs 15. In the exemplary embodiment shown, the slots 17 are introduced into the lateral mounting webs 15 parallel and at a distance from the longitudinal direction of the corona electrode 7, namely from their free end only at a partial height of the mounting webs 15. The slots 17 each end in Hole recesses 19.

These lateral recesses in the form of slots 17 thus allow a certain thermal expansion of the electrode material without it leading to noticeable changes in the shape of the corona electrode.

In addition, the slots 17 and the holes 13 'also provided in the mounting webs 15 allow the electrode temperature to be kept low during the operation of the corona electrode, since fresh air flowing in through the constant ozone extraction takes place through the electrode and thus results in optimal cooling .

In order to design and stiffen the simplest constructed corona electrode as dimensionally stable as possible, a support profile 23 is also provided in the embodiment shown, in the embodiment shown in the form of a hollow profile 23 ', which can be made of metal or stainless steel, for example. This support profile 23, which is rectangular in cross section, runs between the two opposite mounting webs 15 in the region of their free ends, for which purpose the mounting webs 15 are also provided at their free ends with angled portions 27 which are also provided with the slots 17. These bends 27 overlap the support profile 23 at least to a small extent and can be connected to the support profile 23 there, for example by welding. In the exemplary embodiment shown, the perforated plate forming the corona is fastened to the support profile 23 in such a way that a longitudinal expansion is made possible between the support profile 23 forming the support element and the perforated plate forming the actual corona, so that the electrode cannot be distorted. This can be implemented, for example, by attaching guide elements 31 to the corona electrode 11 on the side opposite the discharge section 11 to the support profile 23 on the opposite longitudinal sides, each of which forms an opposite groove-shaped receiving slot 33 facing outward. In this embodiment, the above-mentioned bends 27 engage in the groove-shaped receiving slots 33 thus formed. The guide elements 31 are fixedly attached to the support profile 23, the corona electrode preferably being firmly connected to the profile of the guide element 31 and / or the support profile 23 only at one point, ie preferably in the middle of the corona electrode. As a result, the corona electrode, which is preferably formed in the manner of an electrode sheet, can slide in the longitudinal direction relative to the support profile.

The corona electrodes 7 are accommodated in three individual, separate cover housings or, as in the exemplary embodiment shown in FIG. 3 or 5, in a common cover housing 41.

A treatment gas, for example an inert gas such as nitrogen in particular, can also be passed through the corona electrodes in the direction of the roller. For this purpose, the cover housing 41 is constructed such that the end walls 43 of the cover housing 41 overlap the end opening areas 45 of the corona electrodes 7 at a distance. Normally, the outer cover housing 41 is at earth potential for reasons of occupational safety. In contrast, the electrical voltage that is present at the corona electrode is, for example, in the order of magnitude of 7,000 V. Therefore, the corona electrodes and the cover housing 41 are not in direct electrical contact. Nevertheless, the end faces of the corona electrodes (as they are mainly visible in FIG. 4) can be covered or closed in a suitable manner. An inert gas, for example nitrogen, can then be introduced into the interior of the corona electrodes 47 through supply lines 47. In the exemplary embodiment shown, two feed lines 47 are shown per corona electrode, which open into the hollow or support profile 23, as shown in FIG. 3 in a schematic end view (with the end cover wall of the cover housing 41 not shown) and in the schematic perspective view according to FIG. 4 can be seen. This profile 23 thus simultaneously serves as a distribution channel for the gas. In the case of high demands on the uniformity of the gas distribution, the outflow cross sections from the carrier profile into the interior of the electrode could also be optimized accordingly, for example by the inert gas being able to flow out through a series of small holes via the hollow profile 23 into the interior of the corona electrode and being distributed therein. This nitrogen can then through the holes 13 in each Discharge section 11 are passed directly onto the roller surface, ie onto the plastic film which is guided along the roller surface and is to be treated. This measure counteracts the formation of toxic ozone, since the atmospheric oxygen is displaced by the inert treatment gas, in particular the nitrogen mentioned. The inert gas can then be sucked out of the cover housing interior 53 via corresponding suction or discharge lines 51. With this arrangement, not only is the formation of toxic ozone avoided, but the gas flowing around also simultaneously cools the electrode, thereby reducing the problem of thermal distortion. As mentioned, the use of nitrogen is particularly favorable.

It is also possible for the gas drawn off via the suction or discharge line 51 to be returned to the process. Since the nitrogen consumption at the corona stations can be relatively high, which would certainly increase the operating costs of such a system, it can make sense for the extracted gas either to be reprocessed or, since it is mixed with pure nitrogen, to be fed back into the process.

In order to improve the treatment with a treatment gas accordingly, it can also be provided that the corona electrodes on their opposite mounting webs 15 are not provided with a plurality of slots 17 introduced there, but instead of the slots 17 material tapers 17 'are provided, as shown in FIG Figure 6 is indicated. The material tapers 17 'can have a material thickness which at this point only corresponds to a fraction of the otherwise remaining material thickness, that is to say for example less than 50%, in particular less than 40%, 30%, 20% or for example only 10% and less of that other material thickness. This ensures that the electrode is gas-tight on the side areas, so that the flowing inert gas, which is used in the cooling to avoid toxic ozone, is then specifically supplied only via the holes 13 provided in the discharge section 11 of the plastic film to be treated. The opposite end faces of the corona electrodes can be covered by separate caps already mentioned.

In particular, if an inert gas is supplied to the individual corona electrodes, the tightness of the slots 17 shown in FIGS. 1 and 2 can be achieved not only by using a corona electrode according to FIG. 6, but also in that the tightness of the side walls or assembly webs 15 the corona electrode is achieved by gluing a foil, in particular metal foil, to the side surface. This also means that the electrode remains relatively flexible and allows thermal expansion movements. The metal foil can follow these thermal processes without impairing the tightness of the side walls or assembly webs 15 of the corona electrode.

Claims

117 P 110 claims;

1. Corona electrode arrangement for the electrical treatment of plastic films, which are guided in a partial angular range around a roller electrode (1), which serves as a counter electrode, with a corona electrode (7) which extends over the treatment width of the plastic film (3), the Corona electrode has a discharge section (11), characterized in that the discharge section (11) consists of a perforated plate.

2. Corona electrode arrangement according to claim 1, characterized in that the discharge section (11) of the corona electrode (7) consists of a concave cylinder jacket cutout, in which the plurality of holes (13) is made.

3. Corona electrode arrangement according to claim 1 or 2, characterized in that the plurality of holes (13) in the discharge section (11) is arranged in a plurality of rows of holes (12a, 12b) running in the longitudinal and transverse directions.

4. Corona electrode arrangement according to claim 3, characterized in that the holes (13) are arranged in a plurality of rows of holes (12a), the rows of holes (12a) forming an acute angle to the withdrawal direction of the plastic film and thus to the circumferential rotational movement of the roller electrode (1) .

5. Corona electrode arrangement according to claim 4, characterized in that the obliquely arranged rows of holes

(12a), viewed in the pull-off direction of the plastic film and thus in the circumferential rotational movement of the roller electrode (1), at least touch, preferably overlap.

6. Corona electrode arrangement according to one of claims 3 to 5, characterized in that the holes (13) are arranged in parallel to the longitudinal direction of the corona electrode (11) rows of holes (12b).

7. Corona electrode arrangement according to one of claims 1 to 6, characterized in that the distance of the discharge section (11) to the surface of the roller electrode (1) or to the plastic film (3) extending above it is constant.

8. Corona electrode arrangement according to one of claims 1 to 7, characterized in that on the two opposite longitudinal sides of the corona electrode (7) there is in each case a rear mounting web (15) running away from the discharge section (11).

9. corona electrode arrangement according to claim 8, characterized in that in the mounting web (15) also a plurality of holes (13 ') is introduced.

10. Corona electrode arrangement according to claim 8 or 9, characterized in that in the two lateral mounting webs (15) a plurality of in the longitudinal direction of the corona electrode (7) offset slots (17) is provided.

11. Corona electrode arrangement according to claim 10, characterized in that the slots (17) from the free end of the mounting webs (15), starting at a partial height of the mounting webs (15), are preferably introduced over the entire web height in this.

12. Corona electrode arrangement according to claim 10 or 11, characterized in that the slots (17) are aligned parallel to each other.

13. Corona electrode arrangement according to one of claims 10 to 12, characterized in that the slots (17) end in hole recesses (19), preferably with a concave shape.

14. Corona electrode arrangement according to one of claims 8 to 13, characterized in that the holes (13 ') or slots (17) provided in the side walls or mounting webs (15) are sealed by means of a cover, in particular a foil or metal foil cover are.

15. Corona electrode arrangement according to claim 8, characterized in that in the two lateral mounting webs (15) a plurality of in the longitudinal direction of the corona electrode (7) offset material weakenings (17 ') are provided.

16. Corona electrode arrangement according to claim 15, characterized in that the material weakenings (17 ') from the free end of the mounting webs (15) starting at a partial height of the mounting webs (15), are preferably introduced over the entire web height in this.

17. Corona electrode arrangement according to claim 15 or 16, characterized in that the material weakenings (17 ') run in the manner of grooves or material recesses aligned parallel to one another with a smaller thickness compared to the adjacent material thickness.

18. Corona electrode arrangement according to one of claims 1 to 17, characterized in that between the two lateral mounting webs (15) of the corona electrode (7) to the discharge section (11) lying offset to the outside a support profile (23) runs and is connected to the mounting webs (15).

19. Corona electrode arrangement according to claim 18, characterized in that the support profile (23) consists of a hollow profile (23 ').

20. Corona electrode arrangement according to claim 18 or 19, characterized in that the support profile (23), in particular the hollow profile (23 ') consists of a metal part, in particular stainless steel.

21. Corona electrode arrangement according to one of claims 8 to 20, characterized in that at the free end of the mounting webs (15) mutually facing bends (27) are provided.

22. Corona electrode arrangement according to claim 21, characterized in that the bends (27) with the support profile (23) are fixedly connected.

23. Corona electrode arrangement according to one of claims 1 to 22, characterized in that the corona electrode

(7) is only permanently connected to the support profile (23) in part over its length, preferably only in a punctiform section.

24. Corona electrode arrangement according to claim 23, characterized in that the material of the corona electrode (7) opposite the discharge section (11) to the support profile (23) along a guide device, whereby at least a section relative movement of the material of the corona electrode (7) relative to the support profile (23) and / or the guide device is possible.

25. Corona electrode arrangement according to claim 23 or 24, characterized in that on the support plate (23) preferably on its opposite longitudinal sides each have a guide element (31) with the formation of a receiving slot (33) on the support profile (23) or The respective mounting web (15), in particular a bend (27) formed there, engages in the receiving slot (33) and the corona electrode (11) is kept slightly movable over it at least in part.

26. Corona electrode arrangement according to one of claims 1 to 25, characterized in that the end faces of the

Corona electrode (7) are completed.

27. Corona electrode arrangement according to one of claims 1 to 26, characterized in that the lateral mounting webs (15) are sealed.

28. Corona electrode arrangement according to one of claims 1 to 27, characterized in that the plurality of holes (13) provided in the discharge section (11) a treatment gas, in particular nitrogen, flows through.

29. Corona electrode according to one of claims 1 to 28, characterized in that the corona electrode (7) is housed alone or with one or more corona electrodes (7) in a cover housing (41), via which a treatment gas in at least one feed line (47) the respective interior of the corona electrode (7) can be fed, and wherein the treatment gas flowing through the holes (13) in the discharge section (11) and accumulating in the cover housing interior (53) via a discharge or suction line (51) from the Cover housing interior (53) is removable.

30. Corona electrode according to one of claims 18 to 29, characterized in that the at least one corona electrode (7) associated supply line (47) opens into the interior of a corona electrode (7), preferably in the space delimited by the support profile (23).