US3887809A

US3887809A - Corona discharge device

Info

Publication number: US3887809A
Application number: US523751A
Authority: US
Inventors: Gerhard Marx; Hermann Frank
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1972-06-22
Filing date: 1974-11-14
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03

Abstract

A corona discharge device for use in the electrophotographic field having an element which is in the form of a tape, has at least one conductive layer at its discharge edges, is so movable in the direction of its discharge edges that the corona discharge element can be moved at least by the length of the discharge zone and in that at least one cleaning device is provided for the corona discharge element, preferably outside the discharge zone. The tape is an endless belt having at least one edge which can discharge with that edge exhibiting various profiles. The belt also may be shaped with a depression or carry a guiding element to prevent lateral movement of the tape.

Description

United States Patent 1191 Marx et a1.

[ CORONA DISCHARGE DEVICE [75] Inventors: Gerhard Marx, Hahn/Taunus;

Hermann Frank, Sulzbach, both of Germany [73] Assignee: Hoechst Aktiengesellschatt,

Wiesbaden-Biebrich, Germany 22 Filed: Nov. 14, 1974 211 Appl. No.: 523,751

Related US. Application Data [63] Continuation of Ser. No. 372,305, June 21,1973,

abandoned.

[30] Foreign Application Priority Data June 22, 1972 Germany 2230483 [52] US. Cl. 250/324; 250/325; 317/262 A [51] Int. Cl G03g 15/00 [58] Field of Search 250/324, 325, 326; 317/262 A [56] References Cited UNITED STATES PATENTS 2,856,533 10/1958 Rosenthal 250/325 3,169,886 2/1965 Simm 250/325 3,499,143 3/1970 Martin.. 250/324 3,546,545 12/1970 Sato 250/324 June 3,1975

OTHER PUBLICATIONS Corona Unit Cleaning Device, Voit, IBM Technical Disclosure Bulletin, Vol. 11, No. 8, January 1969, pp, 1025 and 250-324.

Primary Examiner-Craig E. Church Attorney, Agent, or FirmStevens, Davis, Miller & Mosher 5 7] ABSTRACT A corona discharge device for use in the electrophotographic field having an element which is in the form of a tape, has at least one conductive layer at its discharge edges, is so movable in the direction of its discharge edges that the corona discharge element can 25 Claims, 33 Drawing Figures SHEET PATENTEDJUH3 |9rs sum PATENTEIJJUH 3 I975 F i g 3 F ig.3b 1 31a FATENTEI] JUH 3 ms SHEET Fig.5

SUB-1200M 10B HIUUV SUB-1500M vv no no on 21 1 on on 5 1 CORONA DISCHARGE DEVICE This is a continuation, of application Ser. No. 372,305, filed June 21, 1973 now abandoned.

The present invention relates to a corona discharge device having at least one corona discharge element.

Corona discharge devices are required particularly in the electrophotographic field. With these corona discharge devices, insulating surfaces are charged or their charge is reversed. In an often employed process the insulating surfaces are photoconductive layers which are charged and, after each uniform charge, imagewise exposed to light and the remaining charge image is made visible by means of a toner.

Particularly in those cases in which a negative charge of the photoconductive material is necessary, there rises the problem that the known corona discharge devices lead to an undesirable non-uniform charge. Particularly serious are those non-uniformities when the electrophotographic copying device permits development of continuous tones, i.e., when not only the presence of a charge difference plays a part but also the extent of the charge difference leads to differing blackening in the copy. In reverse processes, in which discharged areas correspond to black areas of the copy, charge faults lead to particularly undesirable tinted lines or spots whereas such faults in the normal pro cesses lead to image blanks.

Numerous attempts have been made to solve those problems. According to one attempt, a known wire corona is used and the wire in the corona is circulated or rotated about its own longitudinal axis. Such devices are described in US. Pat. No. 2,856,533, for example. Another solution is described in this publication, in which the discharge wire is caused to execute an oscillating movement. Another device is described in German Auslegeschrift No. 1,128,293. It consists of an endless belt support on which individually arranged discharge pins are positioned perpendicularly to the belt surface. These discharge pins are movable together with the belt support transversely to the direction of movement of the surface to be charged.

Another not published solution has been suggested, in which a rotating roller of small diameter is used. In this case, the electrode consists of a roughened cylindrical body. With this device, the problem encountered with the first described corona discharge device, viz. of burning-off and of the undesirable non-uniformity of discharge, has been solved in that the rotating cylindrical electrode is cleaned on the back side, i.e., on the side away from the surface to be charged.

The last described corona discharge device has led to satisfactory results in the case of small widths of surfaces to be charged but, for charging wider surfaces, particularly the trueness of rotation of such a thin roller could not be achieved with reasonable technical means.

The object of the present invention thus is to provide a corona discharge device with which simultaneously two problems are solved in a satisfactory manner, i.e., to provide an apparatus with which 1. surfaces of large widths can be charged in an extremely homogeneous manner, and

2. the difficulties connected with contamination of the discharge element by dust, cutting residues, burning-off or ZnO particles are overcome; particularly in the case of negative charges and in the reverse process.

The present invention provides a corona discharge of the initially defined kind, which is characterized in that the corona discharge element is in the form of a tape, has at least one conductive layer at its discharge edges, is so movable in the direction of its discharge edges that the corona discharge element can be moved at least by the length of the discharge zone and in that at least one cleaning device is provided for the corona discharge element, preferably outside the discharge zone.

The use of tape-shaped material as the discharge element of such a corona has the double advantage that cleaning of the tape from burning-off residues is possible in a simple manner and that simultaneously wide surfaces can be charged. The latter results from the fact that such tape material may be secured against any kind of distortion and vibration by tightening faster, by shaping or by supports or bearings.

In accordance with the present invention, it is preferable to use an endless belt as the tape-shaped corona discharge element and to circulate it about two rotatably mounted rolls'or corresponding guides. But it is also possible to work with a larger tape supply and to move the same to and fro between two coils. The switching mechanism in an automatically operating apparatus may be similar to that known with typewriter ribbons.

it is is preferable to shape the tape at least in the discharge area in the longitudinal direction. This may be performed in that a shape is impressed into the tape. But is also possible, before or after or even along the actual discharge path, to draw the tape through appropriate profile guides which give the tape the corresponding shape.

The tape-shaped discharge element also may be an only partially elastic tape or a tape provided with links.

To the tape there may be applied special discharge layers. Furthermore, there may be applied conductive layers which are insulated from the discharge layers and serve for discharge control, for example.

When the tape-shaped discharge element is a tape capable of discharging at both edges it is possible and preferable in accordance with the invention to move the tape between the two longitudinal edges, e.g., in the center between guides over the entire discharge area on the back side and possibly also on the front side. When the tape is provided with a longitudinal corrugation', for example, which is held by corresponding shaped parts of the guides every movement of the discharge element is impossible except that in the longitudinal direction of the tape.-

The tape-shaped discharge element may be tightened and guided particularly easily when it is a very thin tape which, for the purpose of providing mechanical strength, has a wire or sheet-metal strip between the edges and firmly connected with the tape. When the thicker tape material is used, the discharging tape edges are sharp-edged or pointed.

In order to achieve increased flexibility of the tape, the wire or sheet-metal strip may be disconnected at certain distances. The dischargeable tape material then consists of preferably 0.2 to 15 mm long elements abutting on one another. The joints between the elements may be similar to locks to be able to transfer longitudinal tensions at least in the stretched state.

In accordance with the present invention, a corona discharge device is preferred in which an auxiliary electrode is coordinated to the circulating tape-shaped discharge element. This auxiliary electrode may consist of a row of needles, the needle points having a constant distance from the tape edge. The movable tape-shaped discharge element may be such that it discharges on two sides. In this case, it is a double corona with one discharge element. This increases the uniformity of charge. If desired, the tape may be toothed or corrugated on the edges.

Finally, it is also possible to have the auxiliary electrode in the form of a tape and to circulate it. In this case it is advantageous when the auxiliary electrode or electrodes can be circulated in a direction opposite to the direction of rotation of the discharge element. But it is also possible to circulate these at least two electrodes at different speeds.

For cleaning the discharge element a doctor blade is preferred. It may be of metal or also of a softer material, such as velvet leather or bristle-like material. It may also be a floating knife.

With the corona discharge device of the present invention it is easily possible to suck off any undesirable ozone.

Further details of the present invention can be seen from the following description of exemplary embodiments by way of the figures of the drawings in which:

FIG. 1 is a diagrammatic sectional view of a corona according to the present invention;

FIG. 2 is a sectional view on the line II-II through the apparatus shown in FIG. 1;

FIGS. 3a-3m show several different shapes of the tape-shaped discharge element;

FIG. 4 is a sectional view of another embodiment of a corona according to the present invention;

FIG. 5 shows a specific embodiment of a corona with deflecting electrodes;

FIGS. 6a-6k show plan views of examples of discharge elements;

FIGS. 7a-7dshow side elevations of examples of articulated discharge elements;

FIG. 8 is a perspective partial view of another corona discharge device; and

FIG. 9 is a sectional view of another embodiment of a corona discharge device according to the present invention.

FIGS. 1 and 2 are two sectional views of a corona discharge'device in which the corona discharge element 1 is an endless circulating belt. The corona discharge element 1 consists of a metal tape of a thickness of a few ,um and a width of some mm. A flexible plastics tape provided with an electroconductive layer, e.g., vapor-deposited tungsten, also may be used.

The metal tape is provided with a corrugation 3 the depth of which corresponds at least to the tape thickness. The tape 1 is passed around two

drivable rolls

4 and 5 andruns on the back side of the actual discharge path through cleaning material 6. As indicated in FIGS.

10 of the circulating tape 1 are each faced by a row of densely arranged needles II and 12, respectively.

The plastics block 13 is the actual carrying element of the corona discharge device. The two needle rows 1] and 12 are secured to this plastics block by means of two angle sheets 14 and 15. The guide rolls 4 and 5 are also positioned in the block 13. On its reverse side, the plastics block is provided with a recess 16 in which is arranged the cleaning material 6 and in which runs the discharge element 1. This cleaning channel 16 of the block 13 is closed with a lid 17.

On its front side, the block 13 has two

channels

18 and 19 between which is a bridge 20. This bridge 20 is narrower than the width of the discharge element 1. Furthermore, the bridge 20 has a longitudinal recess the form and depth of which substantially correspond to the corrugation 3. The tape 1 is on this bridge 20 and is secured by the corresponding recess against lateral displacement. A plastics plate 21 which, if desired, may additionally have a rib engaging the corrugation 3 is connected on both ends with the plastics block 13. This plate 21 serves to secure the tape against displacement transverse to the direction of movement also in those cases in which the corona is operated when the material to be charged or discharged is beneath the corona.

For removing possibly disturbing ozone, one or more longitudinal channels 23 may be provided in the plastics block 13, which, via several bores 24, are in connection with the

recesses

18 and 19. Through the bores 24 and the channels 23, the ozone may then be removed by means of a suction device.

By the operation of such a corona discharge device it has been found that it is possible to solve the burningoff problems by the cleaning of the tape-shaped material as well as to overcome those difficulties which occur when a corona for larger widths of the material to be charged shall be designed. The tape-shaped discharge element offers the considerable advantage that it may be considerably tightened and also positioned between the discharge edges.

Some examples of possible cross-sections of the tapeshaped discharge element are illustrated in FIG. 3. The direction of movement of the tape-shaped discharge element is normally perpendicular to the drawing plane.

In the simplest case as illustrated in FIG. 3 in the first line, right column, the tape-shaped discharge element 1c has a rectangular cross-section the width considerably exceeding the thickness. The thickness of the tapeshaped discharge element may be 0.02 mm, for example, whereas the width is 4 mm. In order to further increase the tensile strength of the discharge element and to guarantee the uniformity of running of the discharge element, the latter may be provided with reinforcing elements. The first line of the profiles of FIG. 3, i.e., FIGS. 3a and 3b, shows two examples of a discharge element 1a and 1b reinforced with a

wire

31 and 31a, respectively. In the first case, the wire 31 is on the side facing the material to be charged of the discharge element 1a, whereas in the second case 31a is fastened on the side of the discharge element away from the material to be charged. This applies similarly to the second and third embodiments of the cross-sections shown in column 1 of FIG. 3, i.e., FIGS. 3d and 3g. A reinforcing metal sheet strip 32 and 320 are used instead of a

wire

31 and 31a. The other variations shown in line 3 of FIG. 3, i.e., FIGS. 312 and 3j, show discharge elements II: and 1 provided with

corrugations

3a and 3. Finally, in the fourth embodiment of column 1 of the variations shown in FIG. 3, i.e., FIG. 3k, the tape-shaped discharge element lk is provided with a reinforcing element 33 having a narrow base 34 and a head 35 of a semi-circular cross-section. A corresponding guiding element 33a has the discharge element lu illustrated in FIG. 3 1. In this case the discharge element In has the form of a blade.

In these variations the guiding and holding

element

31 or 31a or 32 or 32a or 33 or 33a as well as the corru gations 3 and 3a serve to guarantee the uniformity of circulation of the discharge element 1a, lb, 1d, lg. 1k, Ill, 1 or 1/2, transversely to the direction of movement. In the ready corona discharge devices, the corresponding elements are engaging complementary profile guides. The guiding

elements

31 or 31a or 32 or 32a or 33 or 33a increase the tensile strength of the dicharge element and generally take up a large portion of the tension.

The second and third examples in the second line of the profile variations of the discharge element 1e and If, i.e., FIGS. 3e and 3f show curved tape crosssections. In one case, the tape 1e is concave and in the second case convex with respect to the surface to be charged. The curve of the discharge element can be achieved by internal tensions in that the tape is passed through correspondingly shaped guide slits at both ends of the discharge length. By this curvature of the tape, a very stable position without too high a tension is achieved with respect to the distance of the discharge element from the surface to be charged as well as in the direction transverse to the tape movement. Between the slits for the curved profile and the guide rolls, there is provided a sufficient distance so that the tape is not exposed to exceedingly high stresses during conversion from the plane into the curved state and vice versa.

The last tape cross-section variation shown in FIG. 3m is a composite discharge element. The actual discharge element 1c which is connected with the voltage source 8 has

insulations

25 and 26 on both sides. On these insulations, there are

conductor surfaces

27 and 28 connected to

auxiliary voltage sources

29 and 30. By means of these conductor surfaces 27 and 28, it is possible to influence the discharge deriving from the discharge element 10. With these electrodes it is possible to spread the discharge streams apart or to concentrate them.

FIG. 4 shows the cross-section of another corona discharge device. The figure corresponds to FIG. 2. In this case, not only the discharge element 1 is in the form of a circulating tape but also the

auxiliary electrodes

11a and 12a are in the form of such circulating tapes. All three tapes are provided with

corrugations

3 or 1 l and 120, respectively, which cooperate with complementary recesses or profiles and exclude lateral running inaccuracies. The tapes Ila and 12a run in the direction opposite to the direction of rotation of the discharge element 1 or in the same direction at different speeds.

Cleaning devices

61 and 62 also are provided for the counter electrode tapes Ila and 12a on the reverse side of the plastics block 13a, which devices substantially correspond to the cleaning device 6 for the discharge element 1 with respect to design and mode of action. The discharge edges have the

numerals

9, 10, in FIG. and 71 and 72 in FIG. 4.

FIG. 5 is a sectional view of another embodiment of a corona discharge device which substantially differs from that illustrated in FIG. 2 by guide or control electrodes 40-44. The electrodes 40 and 41 are each arranged on the side of the discharge path away from the surface to be charged. The

further control electrodes

42, 43 and 44 are so arranged along the discharge path that the charging current can pass between them. It is also possible to use a control grid instead of the control electrodes 42-44.

The voltages indicated in FIG. 5 are so selected regarding height and sign that optimum charge with respect to current yield and uniformity is achieved. The voltage is supplied preferably through several electronically controlled supply parts.

FIG. 6 shows ten examples of discharge elements 1m to It, 50 and 50a in which one or both edges have sawtoothed profiles. It is also possible to work with tapeshaped discharge elements the edges of which, viewed in the direction of rotation, are slightly corrugated (not shown).

The discharge electrodes shown in FIGS. 7a 7d differ from those hitherto described in that they consist of rigid individual elements. These individual elements 50b may consist of thicker sheet metal material and have discharge edges 51. In the example shown in FIG. 7a, the rigid individual elements 50b are mounted by means of fastenings 53 (rivets or spot welds) on a flexible tape 52 passed around the guide roll 4b.

In FIG. 7b, the round guide roll is replaced by a hexagon roll 4c the edge length of which corresponds to the length of the individual element 50b. In this case, the individual element 50b may be connected at several places or over its entire area with the guiding tape 52. The individual elements may be

needles

50, 50a or 50c (round or edged) provided with flat or pointed ends and mounted densely beside one another on the guiding tape 52 (see FIGS. 60 and 611 as well as FIG. 7d).

Instead of a guiding tape 52, there may also be elastic or mechanical joints 54 between the elements passing around a guide roller 4d. This is shown in FIG. 7c. The joints may be similar to locks. When they are spring locks a special tightening device for the tape is no longer necessary.

The above described corona discharge device provides the possibility to charge surfaces of very large widths considerably uniformly as well as to solve the problems involved by burning-off in a very satisfactory manner. This possibility is provided by the tape-shaped material, cleaning as well as uniform vibration-free movement being possible due to the tape structure.

FIG. 8 shows a corona discharge device in which the circulating endless corona discharge element In is arranged perpendicularly to the web 59 to be charged. The tape In is passed around two rolls 4e and 5e (the latter is not shown in FIG. 8) and driven by one of the

rolls

4e and 52. The tape In is connected to a voltage source 8. A tape-shaped endless auxiliary electrode 11b is likewise arranged perpendicularly to the surface of the paper 59 and includes the corona discharge element In. The auxiliary electrode 11b is driven by means of

rolls

57 and 58. In the discharge zone, both

tapes

1n and 11b are parallel to one another and are passed through a cleaning station 6a arranged in a housing 130. The auxiliary electrode 11b is connected to a voltage source 29.

In the discharge device shown in section in FIG. 9, the corona discharge element In corresponds in arrangement and design to that shown in FIG. 8. The

auxiliary electrodes

11 and 12, however, are stationary rows of needles. Furthermore, another auxiliary electrode 11 may be provided within the loop of the corona discharge element 1n. This auxiliary electrode 11' is a row of needles in the example shown in FIG. 9.

What is claimed is: I

1. A corona discharge device comprising an endless movable belt as at least one corona discharge element, said belt having at least one conductive layer at two discharge edges of the belt, a row of supported electrodes facing each discharge edge a uniform distance therefrom for a portion of said belt which with said portion form a discharge zone and a cleaning device through which said belt moves positioned outside of the discharge zone and extending along said belt.

2. The corona discharge device as claimed in claim 1, including a block in which the corona discharge device is arranged, two angle sheets securing said rows of electrodes to this block, guide rolls for driving said belt positioned in said block, which is arranged in a manner such that the corona discharging element is parallel to the web to be charged.

3. The corona discharge device as claimed in claim 2, in which said block defines two recesses between which is a bridge on which the endless belt is supported, each edge of the belt facing a row of electrodes resting on the side walls of the recesses and protruding from the side walls in the direction of the belt edges.

4. The corona discharge device as claimed in claim 3, in which said block defines one or more longitudinal channels in connection with said recesses via several bores to remove ozone produced by the discharge process.

5. The corona discharge device as claimed in claim 2, in which the block defines a recess on its reverse side to the discharging zone, said recess housing said cleaning device and closed with a lid.

6. The corona discharge device as claimed in claim 5, in which said cleaning device consists of brushes distributed over the entire distance between the guide rolls in the recess on the reverse side of the block.

7. The corona discharge device as claimed in claim 1, in which the belt has at least one endless corrugation in its length direction.

8. The corona discharge device as claimed in claim 7, in which the bridge defines a longitudinal recess in form and depth corresponding to the corrugation of the belt, said longitudinal recess and corrugation being in engagement to secure said belt against lateral displacement.

9. The corona discharge device as claimed in claim 7, including a plate connected at both ends of the block, said plate having a rib engaging the corrugation of the belt to secure said belt against displacement l 1, including a block in which the corona discharge device is arranged and defining recesses for a cleaning device for each electrode belt on the side of the block opposite to the discharging zone.

13. The corona discharge device as claimed in claim 11, including a block in which the corona discharge device is arranged, said block defining two recesses between which is a bridge and outer side walls having horizontal ends, said electrode belts having corrugations which are in engagement with corresponding nips at the inner faces of the horizontal ends of the outer side walls of the block to prevent lateral displacement of the electrode belts.

14. The corona discharge device as claimed in claim 13, including means for driving said electrode belts in a direction opposite to the direction of rotation of the discharge element.

15. The corona discharge device as claimed in claim 13, including means for driving said electrode belts in the same direction as the discharge element at different speeds.

16. The corona discharge device as claimed in claim 1, in which the corona discharge element consists of several rigid individual elements connected with one another by joints.

17. The corona discharge device as claimed in claim 1, in which the corona discharge element consists of several rigid individual elements mounted on a flexible tape.

18. The corona discharge device as claimed in claim 1, in which the corona discharge element has at least one further electroconductive layer separated from the discharge edges of the corona discharge element by an insulating layer and connectable to a controlled voltage source with a variable output voltage.

19. The corona discharge device as claimed in claim 1, in which the corona discharge element and the electrodes are toothed.

20. The corona discharge device as claimed in claim 1, in which the endless belt is arranged parallel to the rows of electrodes in the form of an endless belt.

21. The corona discharge device as claimed in claim 20, including a housing containing cleaning devices for both belts, said housing partly including one of the guide rolls about which the belts are turned.

22. The corona discharge device as claimed in claim 1, including a block in which the corona discharge device is arranged, said block defining two recesses between which is a bridge and side walls and control electrodes arranged on both sides of each row of electrodes and in the bridge of the block.

23. The corona discharge device as claimed in claim 22, in which a control electrode is provided in the bridge of the block above the corona discharge element and is arranged in the same plane with the control electrodes on one side of the rows of electrodes.

24. The corona discharge device as claimed in claim 22, in which each recess of the block has a control electrode arranged on the bottom of the recess.

25. The corona discharge device as claimed in claim 22, in which the electrodes of the corona discharging device are connected to several voltage supply parts with different output voltages.

Claims

9. The corona discharge device as claimed in claim 7, including a plate connected at both ends of the block, said plate having a rib engaging the corrugation of the belt to secure said belt against displacement transverse to the direction of its movement.

10. The corona discharge device as claimed in claim 1, in which the two rows of electrodes consist of densely arranged needles.

11. The corona discharge device as claimed in claim 1, in which the two rows of electrodes consist of endless circulating belts.

12. The corona discharge device as claimed in claim 11, including a block in which the corona discharge device is arranged and defining recesses for a cleaning device for each electrode belt on the side of the block opposite to the discharging zone.