WO1994022059A1

WO1994022059A1 - Heated wire charging device

Info

Publication number: WO1994022059A1
Application number: PCT/NL1993/000067
Authority: WO
Inventors: Dorron Levy
Original assignee: Indigo BV
Current assignee: HP Indigo BV
Priority date: 1993-03-23
Filing date: 1993-03-23
Publication date: 1994-09-29
Anticipated expiration: 1995-09-23

Abstract

Apparatus for reducing contamination of a corona emitter (30) during an imaging operation of imaging apparatus including a source of high voltage (32) operative to energize the corona emitter (30) during the imaging operation and a heater power supply (34) operative to heat the corona emitter (30) to a temperature above that of its surroundings during the imaging operation.

Description

HEATED WIRE CHARGING DEVICE FIELD OF THE INVENTION The present invention relates to charging devices using corona wire in general, and especially to such charging devices used in electrostatographic printers and copiers. BACKGROUND OF THE INVENTION Charging devices are often used in electrostatographic imaging apparatus to charge a photoreceptor. Initially, a photoreceptor surface is charged to a uniform high potential by a charging device. The charge potential can be positive or negative, depending on the type of photoreceptor used. The Corotron and the Scorotron are two common types of photoreceptor chargers that employ an electrified corona wire to deposit charged particles on the surface of the photoreceptor in order to charge it. In the Corotron, a wire charged to a high voltage is placed close to the photoreceptor. The Scorotron includes an electrically biased grid between the charged corona wire and the photoreceptor surface, whereby the bias level controls the charge level on the photoreceptor. Research Disclosure 20321 describes a method of cleaning contaminants of airborne particles built up on corona wire in a powder toner system. When the imaging system is not in operation, the wire is directly heated by passing an alternating current through it to a temperature of 350 degrees Fahrenheit (about 177 degrees Celsius), thereby oxidizing deposited powder toner contaminants and reducing them to ash. Additionally, vibrations, caused by the electric fields of the alternating current, aid in shaking the contaminants off the wire. Japanese Patent Publication No. 59058453 discloses a method stabilizing the temperature surrounding a corona wire in an imaging system to a temperature range between 10 and 35 degrees Celsius in order to obtain a stable electrified state on the photosensitive drum surface and a uniform image irrespective of an environmental change in temperature. In one embodiment, heated air is blown at the wire. German Patent Publication No. 3132047 teaches an electrostatic dust filter including a corona wire which charges dust particles which are deposited on oppositely charged filter electrodes. The corona wire is heated by continuously passing an electric current through it during the operation of the filter to limit the production of ozone. SUMMARY OF THE INVENTION It is an object of the present invention to reduce or eliminate contamination of the corona wire by means of an improved charging apparatus . The present inventor has found that when liquid toner is used , corona wire contamination occurs . Thi s contamination is different from that in powder toner systems ( and is unexpected ) since in liquid toner systems there is no deposition of solid toner material on the wire . The source of contamination in liquid toner systems appears to be carrier l iquid which evaporates during the imaging process and re-deposits on the corona wire. This deposited carrier liquid in the presence of corona forms a coating on the wire which appears to include at least parti al ly polymerized carrier liquid . This contamination causes increased probability of sparking and changes the emission properties of the wire . To avoid these undes irable qualities , periodic replacement of the corona wire i s required. The apparatus of the present invention preferably includes a high voltage power supply attached to a floating heater power supply which is connected to the corona wire. When the high voltage power supply is activated the heater power supply heats the corona wire by means of resistive (Joule) heating. Although the corona wire is raised preferably to a temperature of 100 to 300 degrees Celsius, more preferably to 200 degrees Celsius, a temperature above 50 degrees Celsius is helpful in carrying out the invention. At these temperatures the technique successfully reduces contaminant accumulation by minimizing the adsorption of organic materials to the surface of the corona wire. Furthermore, polymerization is unlikely under these conditions. By heating the corona wire from room temperature to 100 degrees Celsius it is also observed that the production of ozone is reduced substantially. Even greater reductions are possible when the wire is heated to higher temperatures. Ozone emissions can also be reduced by heating the corona housing and/or the grid ( in a Scorotron ) , however, these methods appear to be less efficient than heating of the wire. The Scorotron is a preferred over the Corotron in this invention. When a DC current is passed through a Corotron wire the voltage varies between the ends of the corona wire thereby varying the amount of charge emitted. However, if the resistance of the wire is low, this effect is not of primary importance. In a Scorotron the amount of charge emitted is substantially uniform as it depends to first order only on the voltage of the grid. The advantages of some aspects of the present invention over prior art include minimizing downtime of the imaging system by use of the heating apparatus that works concurrently with the power supply during operation of the imaging apparatus. Furthermore such operation, with liquid toner, avoids contamination buildup and ash production. There are no vibrations resulting from the preferred use of direct current as exist when using alternating current. In addition, ozone production is substantially reduced by heating the corona wire to a sufficient temperature. In the broadest aspect of the invention, the corona wire is heated to a temperature higher than the temperature of its surroundings during operation of the imaging machine. Depending on the temperature, the advantages of the invention are achieved to differing degrees. Charging devices of the present invention are suitable for use in other charging operations such as the charging of paper to effect the transfer of toner thereto, and are also suitable for use in powder toner systems both for photoreceptor charging and image transfer. BRIEF DESCRIPTION OF THE DRAWINGS The present invention wi l l be understood and appreciated more fully from the following description taken in conjunction with the drawings in which: Fig . 1 is a schematic cross-sectional drawing of an imaging system; and Fig . 2 shows a schematic drawing of the heated wire charging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig . 1 shows a general plan of an imaging system in accordance with a preferred embodiment of the present invention . A drum 10 having a photoreceptor surface 12 is rotated by any suitable means ( not shown ) about an axle 14 in a direction indicated by arrow 16. Photoreceptor 12 first passes a charger 18 , which may be a Corotron or, preferably, a Scorotron, which is adapted to charge the photoreceptor to a relatively high voltage, typically 1000 volts . Both the Corotron and the Scorotron employ a corona wire to charge photoreceptor 12 by depositing charged particles at its surface . Other charging methods which use corona wire are also suitable for use with the present invention. While the present invention i s described in accordance with a pre ferred embodiment where it i s used to charge a photoreceptor of an imaging apparatus, it is also useful for charging electrostatic masters or for charging substrates for image transfer thereto. Photoreceptor 12 next passes an exposure device 20. Any method known in the art for producing a latent electrostatic image on a photoreceptor can be used , including exposure by a scanning laser system or by an array of LED devices or to a reflection from a copy sheet. Other methods are also suitable . If an electrostatic master is used, the exposure device is omitted . The latent image on photoreceptor 12 is developed by a developer 22. Developer 22 can be of any convenient type known in the art, preferably using liquid toners, although the invention is also useful in powder toner systems . The developed image produced by developer 22 is transferred to a final substrate at a transfer station 24. Transfer station 24 may be of any suitable type known in the art and may operate by direct transfer to the final substrate or by transfer via an intermediate transfer member. If transfer to the substrate includes charging the substrate with a Corotron or Scorotron, a Corotron or Scorotron according to the invention is preferred. After transfer of the developed image from the photoreceptor, some toner may remain on the photoreceptor. At cleaning station 26, which is next on the route of photoreceptor 12, the remains of the developed image are removed. Any suitable cleaning station known in the art can be used in the practice of the present invention. A discharge system 28 completes the cycle. Generally discharge system 28 comprises a lamp or a series of lamps, which illuminate the photoreceptor and remove any remaining charge on the photoreceptor. Other systems for removing charge as are known in the art are also suitable for use in the invention. Ideally, the photoreceptor, after passing discharge system 28 is completely discharged and is ready for the next cycle. All of the steps and apparatus thus far described (except for charger 18 and transfer station 24) are purely conventional and perform the same functions which they perform in conventional systems. Fig. 2 shows a simplified schematic of a corona wire 30 which is electrified to a high voltage power supply 32. A heater power supply 34, which is preferably electrically floating is preferably activated when the high voltage power supply 32 is activated. The corona wire 30 is thus heated, preferably between 100 and 300 degrees Celsius, more preferably to 200 degrees Celsius, although in general, heating the wire to temperatures above room temperature or above the surroundings of the wire are useful. In accordance with one aspect of the invention, heating the corona wire prevents carrier liquid in the liquid toner from adhering to the corona wire 30. Heating the corona wire also reduces ozone accumulation. In a preferred embodiment of the invention, control of the power supply 34 can be achieved by means of opto- couplers as used in many high voltage instruments. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been described hereinabove . Rather the scope of the present invention is defined only by the following claims :

Claims

CLAIMS 1. Apparatus for reducing contamination of a corona emitter during an imaging operation of imaging apparatus comprising: a source of high voltage operative to energize the corona emitter during the imaging operation; and a heater power supply operative to heat the corona emitter to a temperature above that of its surroundings during the imaging operation.

2. Apparatus according to claim 1 wherein the temperature of the corona emitter is above room temperature.

3. Apparatus according to claim 1 or claim 2 wherein the temperature of the corona emitter is above 50 degrees Celsius.

4. Apparatus according to claim 3 wherein the temperature of the corona emitter is above 100 degrees Celsius.

5. Apparatus according to claim 3 wherein the temperature of the corona emitter is above 200 degrees Celsius.

6. Apparatus according to any of the preceding claims wherein the corona emitter is directly heated by the passage of current through the emitter.

7. Apparatus according to claim 6 wherein the current is D.C. current.

8. Apparatus according to any of the preceding claims wherein the corona emitter is a wire.

9. Apparatus according to claim 1 further comprising opto- couplers to control the heater power supply.

10. Imaging apparatus comprising: an imaging surface; 1 a charger operative to charge the imaging surface

2 during an imaging operation of the imaging apparatus, the

3 charger comprising:

4 a corona emitter; and

5 apparatus according to any of claims 1-9. 6

7 11. Apparatus according to claim 10 and further comprising:

8 means for forming an image on the imaging surface using

9 toner;

10 means for transferring the image to a substrate from

11 the imaging surface, the means for transferring comprising:

12 a charger operative to charge the substrate , the

13 charger comprising:

14 a corona emitter; and

15 apparatus according to any of claims 1-9. 16

17 12. Imaging apparatus comprising:

18 means for forming an image on an imaging surface using

19 toner;

20 means for transferring the image to a substrate from

21 the imaging surface, the means for transferring comprising:

22 a charger operative to charge the substrate, the

23 charger comprising:

24 a corona emitter; and

25 apparatus according to any of claims 1-9. 26

27 13. Apparatus according to any of claims 10-12 wherein the

28 imaging surface is a photoreceptor. 29

30 14. Apparatus according to any of claims 10-13 wherein the

31 charger comprises a Scorotron including a biased grid

32 between the corona emitter and the surface to be charged

33 whereby the bias level controls the level of charge on the

34 surface to be charged. 35

36 15. Apparatus according to any of the preceding claims

37 wherein the imaging apparatus utilizes liquid toner. 38 1 16. A method for reducing contamination of a corona emitter

2 during an imaging operation of imaging apparatus comprising

3 the steps of:

4 electrifying the corona emitter to a high voltage

5 during the imaging operation; and

6 heating the corona emitter to a temperature above that

7 of its surroundings during the imaging operation. 8

9 17. A method according to claim 1 wherein the step of

10 heating includes the step of heating the corona emitter to a

11 temperature higher than room temperature. 12

13 18. A method according to claim 16 or claim 17 wherein the

14 step of heating includes heating the corona emitter to a

15 temperature above 50 degrees Celsius. 16

17 19. A method according to claim 18 wherein the step of

18 heating includes heating the corona emitter to a temperature

19 above 100 degrees Celsius. 20

21 20. A method according to claim 18 wherein the step of

22 heating includes heating the corona emitter to a temperature

23 above 200 degrees Celsius. 24

25 21. A method according to any of claims 16-20 wherein the

26 step of heating includes the step of passing a current

27 through the emitter. 28

29 22. A method according to claim 21 wherein the current is

30 D.C. current. 31

32 23. A method according to any of claims 16-22 wherein the

33 corona emitter is a wire. 34

35 24. An imaging method comprising:

36 charging an imaging surface during an imaging operation

37 of an imaging apparatus with a corona emitter, the step of

38 charging comprising the step of: PBZ Se)Z - 10 -

1 reducing contamination of the corona emitter

2 according to the method of any of claims 15-23. 3

4 25. A method according to claim 24 and further comprising

5 the steps of :

6 forming an image on the imaging surface using toner;

7 transferring the image to a substrate from the imaging

8 surface, utilizing a corona emitter, the step of

9 transferring comprising the step of:

10 reducing contamination of the corona emitter

11 according to the method of any of claims 15-23. 12

13 26. An imaging method comprising:

14 forming an image on an imaging surface using toner;

15 transferring the image to a substrate from the imaging

16 surface, utilizing a corona emitter, the step of

17 transferring comprising the step of:

18 reducing contamination of the corona emitter

19 according to the method of any of claims 15-23. 20

21 27. A method according to any of claims 24-26 wherein the

22 imaging surface is a photoreceptor. 23

24 28. A method according to any of claims 24-27 and further

25 comprising the step of biasing a grid located between the

26 corona emitter and the surface to be charged whereby the

27 bias level controls the level of charge on the surface to be

28 charged. 29

30 29. A method according to any of claims 16-28 wherein the

31 imaging method utilizes liquid toner. 32

33 34 35 36 37 38