|Publication number||US3884572 A|
|Publication date||May 20, 1975|
|Filing date||Dec 26, 1972|
|Priority date||Dec 26, 1972|
|Also published as||CA1033405A, CA1033405A1, DE2362097A1|
|Publication number||US 3884572 A, US 3884572A, US-A-3884572, US3884572 A, US3884572A|
|Inventors||Bacon James L, Simpson Henry W|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (22), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent [1 1 Bacon et al.
[ CLEANING APPARATUS  Inventors: James L. Bacon; Henry W. Simpson,
both of Lexington, Ky.
22 Filed: Dec. 26, 1972 211 Appl: No.: 317,974
 Int. Cl B08b 1/02  Field of Search 15/15; 96/1 A, 1.4;
 References Cited UNITED STATES PATENTS 2,752,271 6/1956 Walkup et al. l5/l.5 X 3,438,706 4/1969 Tanaka et al, 1 1 355/15 3,580,673 5/1971 Yang 355/15 3,634,077 l/l972 Sullivan 355/15 X 3,655,373 4/1972 Fisher et al. 15/].5 X 3,728,016 4/1973 Harbour et al. 15/1.5 X 3,781,105 12/1973 Meagher 96/].4
Primary Examiner-Edward L. Roberts Attorney, Agent, or Firm.lohn W. Girvin, Jr.
[ 1 May 20,1975
 ABSTRACT A cleaning apparatus for cleaning the residual toner image from an electrostatic plate of an electrostatic reproduction apparatus incorporates a continuous wiper member having an outer layer of a compliant material which has a resistivity of less than 10*" ohm.- centimeters and an outer skin thereon. The wiper member is connected to ground. As the wiper member wipingly engages the toner particles, the toner partricles are mechanically dislodged from the surface of the electrostatic plate. Additionally, an image charge is produced on the outer skin surface of the conductive wiper member equal to but opposite in sign from the charge on the toner particles in proximity therewith. This image charge causes the toner particles to adhere to the skin surface as the wiper member moves away from the electrostatic plate regardless of the sign of the toner charge. A further cleaning member is utilized to remove the toner particles from the skin surface of the wiper member which travels in a closed loop past the electrostatic plate and the further cleaning member.
5 Claims, 4 Drawing Figures HAYZOIQYB FIG. 1
CLEANING APPARATUS CROSS-REFERENCES TO RELATED APPLICATIONS The following applications are assigned to the same assignee as the present application:
BRIEF BACKGROUND OF INVENTION 1. Field This invention relates to the cleaning of toned electrostatic images on a plate and, more particularly, to an improved compliant wiper cleaning apparatus.
2. Description of 'the'Prior Art In well-known electrostatic printing processes, an electrostatic plate bearing a latent electrostatic image is developed by applying a developer material including charged electroscopic toner particles to the plate. The charged toner is selectively attracted to the image areas on the plate and is electrostatically maintained thereon. The toned image is thereafter transferred to a support surface such as paper and thereafter permanently affixed to the support surface. Transfer of the toner particles from the image area on the plate to the support surface is often effected by a corona generating device which imparts an electrostatic charge to attract the toner particles from the plate to the support surface. Other transfer techniques such as pressure transfer and heat transfer are also utilized. In any event, a residual toner image usually remains on the plate after transfer which must be cleaned therefrom before the plate may be reused for subsequent imaging.
Well-known brush and web-type cleaning apparatus have often been employed to remove the residual toned image from the electrostatic plate in prior electrostatic printing apparatus. The brush-type cleaning devices usually comprise one or more rotating brushes which brush the toner powder from the plate into a stream of air which is exhausted through a filtering system. Often, a knockoff bar or similar apparatus is utilized in conjunction with the rotating brush to free' the toner particles from the brush thus maintaining the brush operable over a number of cycles. It has further been suggested to utilize a belt form of brush which passes over mandrels having an electrical field applied thereto which tends to attract toner from the plate as the brush engages the plate and to repel toner from the brush as While the brush and web cleaning apparatus of the prior devices satisfactorily clean the electrostatic plate for a limited number of operations, they are generally complex and occupy a great deal of space in the electrostatic printing apparatus, thereby preventing such machines from being compact. Both the brush-type cleaner and the web-type cleaner must be frequently replaced due to wear and accumulation of toner particles on the individual brush and web fibers. In addition, an elaborate and noisy vacuum and filtering system is necessary to collect the residual toner particles removed from the electrostatic plate.
A further prior art approach has suggested the utilization of a cleaning roller made of a resilient or elastic material such as natural or synthetic rubber or sponge which is mechanically biased in compressed rolling contact against the electrostatic plate. The rubber roller is continuously cleaned by a brush which dislodges toner particles therefrom at a postion that is not adjacent the plate. While such a roller provides excellent cleaning characteristics over a relatively few number of reproduction cycles while operating at relatively low processing speeds, it soon becomes clogged with toner particles and is no longer effective in removing toner from the plate. Further, the device relies upon the mechanical scrubbing action to effect the cleaning operation. This action is often not great enough to dislodge highly charged toner particles from the electrostatic plate and to carry the toner particles away therefrom to a point whereat the toner particles may be readily removed from the roller.
SUMMARY In order to overcome the above-noted shortcomings of the prior art and to provide a compact cleaning apparatus which consistently cleans large quantities of residual toner from an electrostatic plate over numerous reproduction cycles without becoming appreciably worn or clogged with toner, a continuous wiper cleaning member having an outer layer of compliant material which has a resistivity of less than l0 ohm centimeters and an outer skin thereon is utilized to wipingly engage the electrostatic plate in compressed rolling contact therewith to remove toner therefrom. The conductive material is connected to a current source such as ground, thereby allowing an image charge to be produced on the outer skin surface of the wiper member which is opposite in sign but equal in magnitude to the charge on the toner particles in proximity therewith. Since the image charge is produced regardless of the sign of the toner charge, toner particles of either polarity of charge may be simultaneously cleaned from the plate. The image charge causes the toner particles to adhere to the wiper surface as it moves away from the electrostatic plate. The toner particles may thereafter be readily cleaned from the outer skin surface of the wiper member since the toner particles are not deeply entrained therein. Therefore, the wiper member remains relatively free of trapped toner particles and can be readily reused over numerous cycles of operation. The low resistivity of the outer skin enables high processing speeds since the requisite image charge is rapidly produced.
A further benefit that is obtained by utilizing a conductive cleaning roller is that the photoconductive surface is completely discharged thereby. Such uniform 3 discharge of the photoconductor eliminates the need for a post clean erase lamp in the system.
Accordingly, it is the principle object of the invention to provide and improved reusable electrostatic plate cleaning system.
It is a further object of this invention to provide a compact cleaning system for use in an electrostatic reproduction machine.
A still further object of this invention is to provide a cleaning member for cleaning toner from an electrostatic plate which itself can be readily purged of toner thereon.
The foregoing objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawmg.
IN THE DRAWING FIG. 1 is a schematic illustration of a conventional electrostatic reproduction apparatus incorporating the cleaning apparatus of the present invention.
FIG. 2 is a three-dimensional schematic illustration of the wiper member of the cleaning apparatus of the present invention.
FIG. 3 is a schematic illustration depicting the physical parameters of the cleaning apparatus of the present invention.
FIG. 4 is a schematic illustration of an alternate wiper member for use with the cleaning apparatus of the present invention.
DESCRIPTION Referring now to the drawings, and more particularly to FIG. 1 thereof, a schematic illustration of a conventional electrostatic reproduction apparatus incorporating the cleaning apparatus of the present invention is depicted.
The reproduction apparatus comprises a plurality of processing stations located about a cylindrically shaped electrostatic photosensitive plate 11. The cylindrical plate comprises a layer of photoconductive material superimposed over a conductive non-magnetic backing layer. A suitable photoconductive material is disclosed in U.S. Pat No. 3,484,237, issued Dec. 16, 1969. The backing layer can comprise a substrate made of an insulating material sprayed with aluminum, the aluminum providing a requisite conduction path to ground.
The photoconductive material is sensitized by a charge corona 13 as the plate rotates therepast in the direction of arrow 15. A light image of the copy 17 to be reproduced is projected onto the sensitized surface of the electrostatic photosensitive plate 11 rotating thereunder to form an electrostatic latent image thereon. The rotating plate thereafter passes a magnetic brush developing station 19 whereat multiple component developer material including electrostatically charged toner is applied to the surface of the electrostatic photosensitive plate 11 containing the electrostatic latent image thereon. The charged toner particles are preferentially attracted to the latent image on the the surface of the plate and then past a pre-clean lamp 26 which discharges the photoconducitve surface.
. Thereafter, the plate rotates past the cleaning station plate 11 and are subsequently transferred to a support The plate 11 continues to rotate past a pre-clean co- 7 rona 25 which charges the residual'toner particles on 27 which removes the residual toner from the surface of the plate prior to the arrival of the plate at the charge corona 13.
When utilizing the photoconductive material described in the aforereferenced U.S. Pat. No. 3,484,237, and when producing positive images thereon, the
charge corona 13 applies a uniform negative charge to i the plate 11. When thusly making a positive image, light emanating from the ligher areas of the copy 17 discharges the photoconductor so that a negative charge pattern corresponding to the dark areas on the copy 17 remains on the plate 11 as it rotates toward the magnetic brush developing station 19.
The detailed operation of the magnetic brush developing station is described in the aforereferenced copending application of Allison H. Caudill, et al. The magnetic brush developing station 19 is continuously operable and contains a multi-component developer material which is applied to the plate 11 as it rotates therepast. The principle components of the developer material are electroscopic toner and aferromagnetic carrier material. Suitable materials for use as toners are well known in the art and generally comprise finely divided resinous materials capable of being attracted and held by electrical charges. Examples of toners which can be employed are commercially marketed by the International Business Machines Corporation as IBM part no. 1162057 and IBM part no. 1162051. The IBM part no. 1162057 toner comprises a copolymer of styrene/n-butylmethacrylate resin, maleic anahydride modified polyester, polyvinyl stearate plasticizer, and carbon black pigment. The IBM part no. 1 162051 toner comprises a copolymer of nbutymethacrylate/methymethacrylate resin, maleic anahydride modified polyester, polyvinyl butyral plasticizer, carbon black pigment, and a fumed silica physically mixed in the toner after compounding.
Many well-known suitable ferromagnetic carrier materials can be utilized, the carrier particles generally being between 50 and 1,000 microns in size. Often, the carrier particles are manufactured by coating a ferromagnetic core or bead with a material which triboelectrically interacts with the selected toner to produce a desired charge on the toner in order to provide good imaging quality. An example of such a carrier and the method by which it can be made to obtain a desired triboelectric characteristic for any selected toner is dis- 7 closed in the aforereferenced copending application of William J. Kukla, et al.
As has been described, the toned image leaving the magnetic brush developing station 19 is transferred to a support surface 21. The transfer corona creates an electrostatic charge on the support surface causing the toner to be preferentially attracted thereto from the surface of the electrostatic photosensitive plate v11. Since the toner is triboelectrically charged positive, the
transfer corona 23 applies a negative charge to the support surface 21 causing the toner to be attracted thereto.
While the major portion of the toned image is transferred to the support surface 21, a residual toned image remains which must be cleaned from the electrostatic photosensitive plate 11 prior to a subsequent imaging cycle. Accordingly, the residual toner image is rotated past a pre-clean corona 25 which places a charge on the toner to facilitate electrostatic removal of the toner from the plate 11. As will be described hereinafter, the cleaning apparatus removes toner which has been charged to either sign (e.g., positively and negatively charged toner). Accordingly, the pre-clean corona 25 can be an AC corona thereby charging the toner to both polarities, a positive corona which tends to enhance the positive triboelectric charge on the toner or a negative corona which, in conjunction with the transfer corona 23, tends to cause the majority of the toner particles to be charged negatively. It has been found that the most satisfactory results occur with a negative pre-clean corona. The pre-clean lamp 26 illuminates the plate 11 thereby discharging electrostatic charges existing on the plate 11 which might otherwise tend to attract toner thereto.
The residual toned image thereafter passes cleaning station 27. The cleaning station 27 comprises a wiper roller 31 for removing toner particles from the plate 11. The wiper roller 31 is mounted for rotation in the direction of arrow 33 at a surface velocity between 6 and inches per second when the plate 1 1 rotates at a surface speed of 9.3 inches a second. The wiper roller 31 is approximately 3 inches in diameter and is biased into the plate 11 for wiping engagement therewith.
The wiper roller 31 is shown in detail in FIG. 2 and comprises an outer layer 35 of a conductive compliant elastomer material. An example of a suitable elastomer material is a silicone rubber produced by the Ames Rubber Company having formulation number ARX5424 which is a silicone rubber having conductive carbon particles embedded therein, the carbon particles comprising 26 to 41 percent by weight of the material. Other elastomer materials such as conductive neophrene, conductive urathane, or conductive ethylene propylene terpolymer have also been successively utilized. The outer skin of the conductive silicone rubber material has a compliance as measured on a Shore A2 scale of 60 or softer, a resistivity of 10* ohm.- centimeters and a surface smoothness having an average height asperity of 200 micro inches.
The wiper roller 31 further comprises a conductive metallic core 37 made of materials such as aluminum or hardened steel. A non-conductive plastic roller could also be utilized. A compliant material layer 39 comprising a foam material such as conductive neophrene or urathane foam is mounted on the core 37 and provides additional cushioning to compensate for mechanical tolerance variations between the wiper roller 31 and the plate 11 and insures an adequate sized cleaning footprint 40.
Referring again to FIG. 1 of the drawings, the wiper roller 31 is engaged by a scavenge roller 41 which removes toner particles from the wiper roller 31. The scavenge roller 41 is in turn scraped by a knife blade 43 which removes the toner particles to the lower portion of the cleaning station 27 whereat they are removed by the continuously rotating auger 45. The scavenge roller 41 may be a conductive smooth roller as depicted in FIG. 1 or a roller which is made of an insulator material such as nylon which triboelectrically interacts with the toner particles on the wiper roller 31 to effect removal there-0f. As depicted, the scavenge roller 41 is a conductive steel roller which is grounded at current source 47. The current source 47 is thereby connected through the scavenge roller 41 to the outer skin of the wiper roller 31.
Referring now to FIG. 3 of the drawings, a schematic illustration depicting the physical parameters of the cleaning apparatus of the present invention is depicted. As previously indicated, toner particles 51, 52 having a charge of either polarity are located on the surface of the plate 11 as it rotates in the direction of arrow 15 toward the wiper roller 31. The toner particles are retained on the surface of the plate 11 by adhesion forces and, to a lesser extent, by electrostatic forces. The adhesion forces are greater than the electrostatic forces since these forces prevented the toner from transferring at the transfer station.
As the toner particles 51, 52 are wipingly engaged by the wiper roller 31, the adhesion forces causing the toner particles to remain on the plate 11 are mechanically overcome thereby causing the toner particles to become dislodged from the plate 11. As the thusly dislodged charged toner particles come in proximity to the conductive outer skin of the outer layer 35, an image charge is produced at the surface of the outer layer 35 equal in magnitude but opposite in sign to the charge on the toner particles. The image charge is produced by the current which flows from the current source 47 through the scavenge roller 41 and through the conductive outer layer 35 to that area of the surface adjacent the charged toner particle.
Since it is easier for the dislodged toner particles to progress out of the nip formed by the rollers 31 and 41 rather than further into the nip, the toner particles tend to move with wiper roller 31 in the direction of arrow 33. Further, since the adhesion forces are mechanically broken, the image charge on the outer surface of the wiper roller 31 acts on the toner particles thereby causing the toner particles to adhere to the outer skin of the outer layer.35 as it rotates away from contact with the plate 1 1.
Continued rotation of the wiper roller 31 in the direction of arrow 33 brings the wiper roller into contact with scavenge roller 41 rotating in the direction of arrow 61. The toner particles 57, 58 are held to the surface of the wiper roller 31 by an image charge as has been explained heretofore. As these particles enter the nip between rollers 41 and 31, they are again mechanically dislodged. Since it is easier for the toner particles to progress out of the nip than further into the nip, they tend to remain on the scavenge roller 41. An image charge is produced on the surface of the scavenge roller in a manner analogous to the production of the image charge on the wiper roller 31 as previously described which causes the toner particles to remain on the surface thereof until they are mechanically dislodged by the knife blade 43 as the scavenge roller 41 rotates therepast in the direction of arrow 61.
It should be noted that the coefficient of friction of the outer surfaces of the plate 11, the wiper roller 31, and the scavenge roller 41 are chosen so that there is a greater coefficient of friction between the toner particles and the wiper roller 31 than between the toner particles and the surface of the plate 11. Further, there is a greater coefficient of friction between the surface of may be sized by controlling the smoothness of the respective rollers.
As has been described heretofore, a non-conductive scavenge roller 41 can be' utilized in lieu of a conductive roller, the requisite current source connection to the wiper roller 31 being made directly from the current source 47 to the roller 31. When insulator materials such as nylon are utilized for the scavenge roller 41, the nylon material triboelectrically charges the toner particles located on the surface of the wiper roll 31 as these toner particles progress into the nip between the rolls 41 and 31. The triboelectric charge created at the surface of nylon roll provides a slightly stronger force than the image charge discussed with respect to a conductive roll thereby facilitating removal of the toner particles from the wiper roll 31.
Referring now to FIG. 4 of the drawings,-a schematic illustration of an alternate wiper member for use with the cleaning apparatus of thepresent invention is depicted. In this embodiment, the cleaning station 27 comprises two mandrels, 71, 73, over which a belt 75 of wiper material is mounted. The belt 75 can comprise a single layer of conductive'elastomer material such as silicone rubber. The'be'lt 75 is mounted for movement in the direction of arrow 77 and wipirigly engages toner particles located on the surface of the plate 11 as it moves into contact therewith. The wiping engagement of the compliant layer mechanically dislodges the toner particles. The mandrel 71 is connected to ground thereby providing a current to the outer skin of the belt 75 to create an image charge equal to but opposite in sign from the charge of the toner particles in proximity thereto. The image charge causes the toner particles to be retained on the outer skin of the belt 75 as it rotates away from the plate 11 toward the knife blade 43. The knife blade 43 wipes directly against the belt 75 scraping toner therefrom into the continuously moving auger 45.
Referring once again to FIG. 1 of the drawings, it has been found that best of cleaning results are obtained when the outer skin of the wiper roller 31 is relatively smooth. Thus, a surface having an average surface height asparity in a range between and 400 micro inches, depending upon the material selected, provides the best cleaning results. However, a porous or irregular outer skin also produces satisfactory cleaning re-' sults although care must be taken to select a proper mechanism such as a biased rotary brush to dislodge toner which may accumulate in the pores of such a wiper member.
. As noted heretofore, the resistivity of the outer layer 35 of the wiper roller 31 that is required to achieve satisfactory cleaning results is dependant upon the processing speed of the apparatus. This is because the re sistivity of the outer layer must be sufficiently low to enable a current to flow rapidly therethrough to create the requisite image charge on that portion of the surface thereof in proximity with a charged toner particle before that portion of the surface rotates away from the plate 11. An increase in processing speed produces a corresponding decrease in the time that a given portion of the outer layer 35 contacts the plate 11. Thus, increased processing speeds require a corresponding decrease in resistivity.
Other factors which determine the requisite resistivity of the outer layer 35 include the thickness of the outer layer, the length of the footprint 40 (contact distance)'and the capacity of the toner particles. When utilizing the afore referenced IBM part number toners,
the radius of an average toner particle is 5 microns, and
its relative dielectric constant is 6,6,, E (3)(8.85 X 10 Thus its capacity is r/e e,,= 1.8 X 10 The requisite resistivity of the outer layer 35 may therefore be calculated by the following equation:
where l is the length of the footprint V is the relative velocity of the plate 11 and roller t is the thickness of the outer layer 35 (cm) p is the resistivity of the outer layer (ohm cm) When utilizing minimum material thicknesses (e.g., 10 mils) it has been found that for processing speeds ranging from 3 to 20 inches per second, elastomer materials having a resistivity greater than 10 ohm centimeters fail to adequately-remove charged toner from the plate 11 since the time constant of such materials I is too great to enable an image charge to be produced rapidly enough to be effective. It is to be noted that slower systems employing extremely thin outer layers and large footprints could utilize materials having resistivities in the range of 10 to 10 ohm centimeters. However, compliant materials in this range of resistivity exhibit large scale resistivity variations with temperature thereby causing the cleaning system to be marginal. Further, minute changes in doping levels of such materials effect large resistivity changes thereby greatly adding to the manufacturing costs thereof.
It is further noted that while elastomer materials having lower resistivity than 10 ohm centimeters adequately supply an image charge, care must be taken in controlling the amount of conductive particles embedded in the elastomer since the amount of conductive particles controls the compliance of the material as well as its resistivity.
The importance of controlling the resistivity and surface smoothness of the outer layer 35 of the wiper roller 31 of FIG. 1 is demonstrated by the following example.
A robot having a cleaning station like that depicted in FIG. 1 and having a processing speed of 20 inches per second and a wiper roller surface velocity of 6 to 8 inches per second and a footprint 40 about 0.125 inches long'was constructed. The outer layer 35 of the wiper roller 31 consisted of a porous neophrene layer of material approximately 0.062 inches thick having a resistivity of 10 to 10 ohm. centimeters. Failure of the wiper roller to remove toner from the rotating plate 11 without smearing occurred within 1,000 cycles of operation. Thereafter, the wiper roller 31 was replaced with a wiper roller 31 having an outer layer 35 consisting of a porous neophrene layer approximately 0.062
inches thick and having a resistivity of 10 ohm. centimeters. Failure occurred after approximately 20,000 cycles of operation. The wiper roller 31 was then replaced with a wiper roller 31 having an outer layer 35 consisting of a smooth neophrene layer approximately 0.062 inches thick and having a resistivity of 10 ohm.- centimeters. Failure occurred after 100,000 cycles of operation.
As noted heretofore, a ground potential current source 47 may be connected to the wiper roller 31 in order to cleanthe plate 11 of toner which is charged to either polarity. A current source 47 having a relatively low DC. potential (e.g., 10 to 50 volts) may be utilized when it is desirous to clean toner which is substantially charged to a polarity opposite the polarity of the supply.
An added benefit obtained by utilizing a conductive cleaning member is the complete discharge of the photoconductive plate 11 effected thereby. Previous cleaning devices which mechanically dislodged toner particles from the plate left the plate with an electrostatic charge thereon at the location whereat the toner particle was attached thereto. This charge often had to be eliminated with a post-clean erase lamp Such plate charges are eliminated by providing a conductive path to the photoconductor with the conductive cleaning roller after the toner particle has been removed therefrom. Thus continued motion of the plate 11 past the cleaning roller causes electrostatic charges on the plate to become neutralized.
While the foregoing invention has been particularly shown and described with reference to a preferred embodiment thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.
What is claimed is:
1. Cleaning apparatus for removing electrostatically charged toner particles from the surface of an electrostatic plate comprising: 7
a continuous wiper means mounted for movement in a closed loop in wiping engagement with the surface of the electrostatic plate containing toner particles attracted thereto for removing said toner particles from said electrostatic plate, said wiper means comprising at least an outer layer of a compliant material having a resistivity of less than l0 ohm. centimeters and having an outer skin thereon;
cleaning means engagingly connected to said wiper means for removing toner therefrom;
drive means for moving said wiper in said closed loop past said electrostatic plate and past said cleaning means;
a current source connected to said wiper means for supplying current to the outer skin of said, wiper means proportional to the image charge of the toner in contact therewith.
2. The cleaning apparatus set forth in claim 1 wherein said outer skin has a smooth outer surface thereon.
3. The cleaning apparatus set forth in claim 1 wherein said electrostatic plate is mounted for motion in a first direction and said wiper means engages said plate when moving in a direction opposite said first direction.
4. The cleaning apparatus set forth in claim 1 wherein said current source comprises a grounded connection.
5. The cleaning apparatus set forth in claim 4 further comprising a preclean corona unit for electrostatically charging said toner on said plate prior to said toner being engaged by said wiper means toward a polarity opposite its polarity established when applied to the plate.
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|U.S. Classification||399/129, 15/1.51, 399/357|
|International Classification||G03G21/10, B08B1/04, G03G21/00|