|Publication number||US3918971 A|
|Publication date||Nov 11, 1975|
|Filing date||Apr 19, 1971|
|Priority date||Apr 19, 1971|
|Publication number||US 3918971 A, US 3918971A, US-A-3918971, US3918971 A, US3918971A|
|Original Assignee||Pitney Bowes Inc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (20), Classifications (11)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 1191 Zweig METHOD FOR CREATING MULTIPLE ELECTROSTATIC COPIES BY PERSISTENT CONDUCTIVITY  Inventor: Gilbert Zweig, Stamford, Conn.  Assignee: Pitney-Bowes, lnc.. Stamford, Conn.  Filed: Apr. 19. 197] 1211 Appl. No.: 135,179
[521 US. Cl 96/].4; 96/1 R; 96/18; 355/3 R; 355/3 DD [511 int. Cl.'-' G03G 13/14; G036 13/22  Field of Search 96/1 R. 1.4. 1.8; 101/426. 101/DIG. 13;355/3. 17; 118/637; 117/175 OTHER PUBLICATIONS Cassiers. Memory Effects in Electrophotography."
1 1 Nov. 11, 1975 Jour. Photo. Science. Vol. 10. 1963. pp. 57-64. Schaffert. Electrophotography.- Focal Press. 1965. pp. 70-77.
Schaffert. Multiple Copy Printing Process." lBM Tech. Discl. Bulletin. Vol. 1. No. 4. Dec. 1958. p. 4.
Primary F..\'muinerRoland E. Martin. Jr. Attorney. Agent. or Firm-Wi1liam D. Solton'. Jr.; Albert W. Scribner: Martin D. Wittstein  ABSTRACT A photoconductive insulating layer coated onto a substrate is rendered uniformly non-conductive to make multiple copies by negatively charging the surface. The layer is next sensitized by positively charging the surface after which it is imaged and conventionally developed \vith electrostatically attractable material. The electrostatically attractable material is then conventionally transferred in offset fashion onto a copy sheet. Surface charge is lost and the latent image is thereby degraded during the process of toning the imaged photoconductive surface and transferring the toner to the copy sheet. Repetitive copies can then he made from the latent image by passing a uniform positive charge over the layer to rejuvenate the latent image and repeating the developing and transferring steps each time.
2 Claims. 11 Drawing Figures US. Patent Nov. 11, 1975 NEGATIVE D.C.VOLTAGE FIG I 6 Ell] IIIt 2 POSITIVE D.C.VOLTAGE IB .1? WM 1 1/ POSITIVE D.C.VOLTAGE Sheet 1 of2 1=1e.2
l FIG. 6:
FIGJO INVENTOR GILBERT ZWEJG BY J a. jwa- ATTORNEY U.S. Patent Nov. 11,1975 shw 2 of2 3,918,971
' INVENTOR GILBERT ZWEIG ATTORNEY METHOD FOR CREATING MULTIPLE ELECTROSTATIC COPIES BY PERSISTENT CONDUCTIVITY BACKGROUND OF THE INVENTION The present invention relates generally to a method for creating repeatable electrostatic copies in an electrostatic photocopier.
In presently available electrostatic photocopiers, it is the usual practice to create an electrostatic latent image of the indicia to be reproduced on the photoconductive insulating member. This electrostatic latent image is then developed using electroscopic developer or toner particles. The developed image is then either fixed on the photoconductive member surface, typically zinc oxide coated paper, as in the direct imaging process, or the toner in image formation is transferred or offset printed onto plain paper and fixed, as in the indirect imaging process. In either the direct or indirect imaging processes, the latent image carried by the photoconductive member surface must be totally renewed each time after it is visibly developed, as it is lost as a master for making any additional copies in the process of making the single copy. This is quite obvious in the direct imaging process where the optical image is fixed directly on the photoconductive surface itself which is then used as the copy. Although not obvious, the result is the same in the indirect imaging process since much of the surface charge is lost in the process of toning the imaged photoconductive surface. Even a second copy made from the imaged photoconductive surface is not commercially acceptable since the surface potential of the latent image is decrease to about one-tenth of its former level and canrqt be increased again without reimaging. Likewise, each succeeding copy continues to be less acceptable than the copy made before it.
It is thus necessary in present electrostatic photocopiers to reimage and process the photoconductive member for every copy desired. This is time consuming, requires additional use of the illumination system and usually involves more repairs and additional maintenance.
Further, during duplicate copying the operator is hampered from removing the original until the last reimaging of the photoconductive member has been finished. This delay is unavoidable because the original must be used to continually reimage the photoconductive member and therefore the next original cannot be positioned on or in the machine in readiness for photocopiers to be made.
Although the technique of creating latent images on the photoconductive surface as fixed static charges, i.e. electrical surface charges or internally bound charges, is the usual method for photocopying, another method is known which forms an image by persistent conductivity on a photoconductor member. This type of photocopying is described in Schafferts reference book entitled "Electrophotography (1965), Chapter IV. Other disclosures of particular methods involving photocopying with a photoconductive member which forms an image by undergoing a persistent change in electrical conductivity upon illumination are found in US. Pat. No. 2,845,348 granted to Kallman and US. Pat. No. 3,010,883 granted to Johnson et al.
Image formation on a photosensitive medium exhibiting persitent conductivity involves coating a layer of photoconductive insulating material onto a conductive base and exposing the photoconductive member to an optical image. The exposed background area becomes more or less conductive, depending upon the amount of light impinging upon the photoconductive surface during exposure. This conductivity persists in the dark after the exposure while the image or dark areas remain relatively non-conductive.
Kallman proposed making copies on photoconductive mediums exhibiting persistent conductivity by applying an electrical surface charge to the photoconductive surface wherein the surface charge is dissipated in the conductive areas but remains as a latent electrostatic image on the non-conductive areas (i.e. the areas not exposed to light because of the presence of indicia on the original). However, the photoconductive medium is also the copy paper and the imaging step must be repeated on a separate photoconductive medium for each print with this process.
Johnson el al. also suggest making a copy directly on the photoconductive medium exhibiting persistent conductivity by using the plate with the latent image thereon as the cathode in an electroplating solution and including developer material as the anode in the system. The toner particles are electroplated out of the solution onto the conductive areas to form a visible image. However, the photosensitive medium is used up in the process and thus cannot be rejuvenated for reuse.
.l. P. Ebert in his US. Pat. No. 3,081,165 also describes a photoconductive layer exhibiting persistent conductivity which yields a photographically positive or negative electrophotographic or xerographic print. The layer may be developed to yield a photographically positive print which can be processed for direct positive photographic duplication. However in so yielding the photographically positive print, the layer is used up and is thus unavailable for resensitization.
BRIEF SUMMARY OF THE INVENTION The present invention obviates the foregoing disadvantages of prior art photocopying systems especially where a multiplecopy process is involved by providing a relatively simple yet reliable process and apparatus for using the process wherein many copies may be duplicated from the same original document without the necessity of imaging the photoconductive member after the first time.
In accordance therewith, the present invention provides in combination with a method of making multiple copies from a photoconductive insulating layer coated onto a conductive substrate and exhibiting persistent conductivity for uniformly conditioning the layer to bring the layer to a condition of substantially equal non-conductivity throughout. The present invention also provides for uniformly sensitizing the surface of the layer to a d-c potential, whereby the layer is receptive to becoming conductive in those areas exposed to light, and exposing the surface of the layer to an optically dark image on a lighted background to create a corresponding non-conductive latent image on the surface thereof wherein the latent image remains relatively non -conductive and the background is made conductive, thereby draining any charge developed thereon to the substrate. The improvement in the present invention provides for a method which comprises attractably depositing finelydivided particles of electrostatically attractable material in conformity with the latent image on the layer, transferring the attractable material in the latent image configuration to a support base, uniformly passing a charge over the surface of the layer in the dark at a potential which is at least near the acceptance potential, whereby the latent image on the layer remaining relatively non-conductive is rejuvenated with surface charges without imaging, and repeating the steps of attractably depositing and transferring, whereby the attractable material is transferred in the latent image configuration to a next support base.
It is thus an object of the present invention to provide a method for duplicating an image from a persistently conductive member onto a copypaper a plurality of times without reimaging the member after the first copy.
It is a further object of the present invention to pro vide a method for resensitizing a member exhibiting persistent conductivity for use in making a number of copies therefrom of each latent image formed on the sensitized member.
It is a still further object of the present invention to provide a method for reconditioning a member exhibiting persistent conductivity.
These and other objects, features and improvements of the present invention will be described in greater detail in the description below.
BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the various FIGS. and in which:
FIGS. 1, 3, 5, 7, 8 and 9 are diagrammatic illustrations of the steps performed in making multiple copies from a photosensitive member exhibiting persistent conductivity;
FIGS. 2, 4, 6 and I are graphs showing electrical characteristics of the potential on the surface of the member plotted along the vertical axis and distance across the member plotted along the horizontal axis; and
FIG. 11 is a schematic illustration of apparatus for practicing the successive method steps illustrated in the FIGS.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In reference to FIGS. 1 to which illustrate steps in the invention and demonstrate the effect of the steps, a photoconductive insulating layer 2 exhibiting substantial persistent conductivity is coated onto a conductive substrate such as an aluminum plate 4. A photoconductive insulating layer which exhibits persistent conductivity is a layer of a photoconductive material which, after illumination, exhibits a lag in returning to its original state of dark conductivity. The layer 2 can be made from any material which exhibits persistent photoconductivity such as zinc oxide ground up and blended in an acrylic-polyester binder, the zinc oxide being present in the proportion from about to 95 of the total composition.
Other examples of photoconductive insulating materials exhibiting persistent conductivity include phosphor powders such as zinc-cadmium sulphide and zinccadmium selenide dispersed in a bland cement binder. photoconductive powders dispersed in resin binders,
zinc sulphide phosphor in a binder and Ieuco malachite green in a binder.
Initially, the layer 2 is charged to an overall uniform negative d-c potential in order to unifonnly condition the layer so that it is uniformly non-conductive throughout. While there are known numerous ways in which to charge the surface of an insulating layer, the most practical method is to employ a corona charging unit such as is generally indicated at 6 in FIG. I. The corona charging unit 6 is passed over the layer 2 or the layer 2 is moved under the corona charging unit 6 in order to uniformly deposit electrostatic surface charges. The polarity of these charges is indicated as being negative in FIG. 1, however, it will be understood that the surface of a photoconductive layer may be charged to a positive potential. The polarity of the electrostatic charges is determined by the type of photoconductor material used in member 2.
To illustrate the effect of the step carried out in FIG. 1, FIG. 2 graphically depicts the voltage level measured across the layer 2. As can be seen from line l0, the voltage across the entire layer is uniformly negative. The voltage would be at an operable level of between about 300 and 900 volts for zinc oxide in a binder.
FIG. 3 illustrates the next step wherein the layer 2 is uniformly sensitized to a d-c potential by moving the layer 2 relative to a sensitizing corona charging unit generally indicated at 12. For zinc oxide the sensitizing unit 12 charges the surface of the layer 2 to an operative positive d-c potential between about and 500 volts, preferably 500 volts. The uniform potential level of 500 volts is shown in FIG. 4 by line 14 as the potential uniformly developed on the surface of the layer 2.
After the layer 2 has been sensitized, it is then imaged (see illustrative FIG. 5 and the graph shown in FIG. 6) with an indicia, in this instance a bar graph illustrated by the bars I6, on an original document 18. This is accomplished by exposing the layer 2 to the optical image to be reproduced as shown in FIG. 5. The optical image (the illustrated bar graph) borne by the document 18, is projected by a lens system, schematically indicated at 20, onto the layer 2.
As is well understood in the electrophotography art, the areas of the layer 2 struck by light lose their insulative properties and become conductive. The surface charges overlying these light struck areas 22 are conducted through the body of the semi-conductive layer 2 to the substrate or electrode plate 4, which is illustrated as being electrically connected to ground in FIG. 5. Those areas 24 of the layer 2 which are not illuminated by the optical image retain their insulative properties, thus preserving the surface charges overlying these dark areas. In FIG. 5, the non-illuminated areas (i.e. the indicia) of the layer 2, indicated at 24, receive little or no reflected light from the bars 16 which are dark image areas. and the light struck area indicated at 22 receives reflected light from the light background area of document 18. Thus, the surface charges overlying area 22 of the layer 2 are conducted away and the surface charges overlying the areas 24 remain. There is thus created on the surface of the layer 2, an electrostatic latent image corresponding to the optical image projected by the lens system 20 as is illustrated by the graph shown in FIG. 6 wherein the voltage across the surface of the layer 2 has been conventionally measured and the results plotted with distance across the member as the abscissa and potential as the ordinate.
Those areas 24 which correspond to the bars 16 on the document 18 are indicated at 26 on the graph and due to the surface charges being maintained in place by the insulative underlying area measure a potential level of, for example, 200 volts. However, those areas 22, which correspond to the light background on the document 18 are non-conductive and are represented at line 28 on the graph. As shown, line 28 is at a uniform potential level of volts, and illustrates an exemplary conventional surface potential measurement.
Turning to FIG. 7, the electrostatic latent image is visibly developed, as schematically indicated at 30, using any conventional development technique. Basically the development technique involves attractably depositing finely-divided particles on the latent image on the upper surface of the layer 2. The electric charges making up the latent electrostatic image effectively attract and hold the electroscopic particles or pigmented toner particles and thereby render the electrostatic image visible. Of course, those areas of the electrostatic latent image which are uncharged do not attract and hold the toner particles.
To form a copy, a support base or plain paper sheet 32 is then conventionally pressed against the surface of the layer 2 to pick up the electroscopic particles in an image transfer of the visible electrostatic image onto the sheet 32. The sheet 32 is then separated from the surface of the layer 2 as shown in FIG. 8 and by this step the attractable material is transferred in image configuration onto the sheet 32. The particles on the sheet 32 are fixed to the sheet 32 is a conventionally acceptable manner.
To make additional copies from the imaged layer 2, the following steps only are necessary and no reimaging is required.
The first step in the process of making additional copies from the layer 2 is illustrated in FIG. 9. It involves uniformly passing a charge over the surface of the layer 2 in the dark at a potential which is at least near the acceptance potential of the material of the layer 2. This is accomplished with the corona charging unit 12 being passed relatively over the surface of the layer 2. For zinc oxide in a combination acrylicpolyester binder as disclosed herein the potential charge passed over the surface of the layer 2 is between about 100 volts and 500 volts, and preferably 500 volts. This step is carried out so that an electrophotographic latent image is developed on the non-conductive latent image surface indicated at 24 in FIGS. and 9 and the charge is dissipated on the conductive background indicated at 22, to the substrate or plate 4.
FIG. 10 illustrates the effect of the charging step shown in FIG. 9 and as in FIGS. 2, 4 and 6, the potential value has been measured by conventional means and plotted along the ordinate with the distance across the surface of the layer 2 plotted along the abscissa. As can be readily seen in FIG. 10, lines 26 which correspond to the areas 24 which overlie the non-conductive latent image surface have accepted a charge from the corona charging unit 12 and measure a potential value of 500 volts. Lines 28 which correspond to the areas 22 which overlie the conductive portion of the layer 2 have conducted the charges from the corona charging unit 12 through the body of the layer 2 to the plate 4. Thus the line 28 is at a potential of 0 volts.
The steps of attractably depositing the finely-divided particles onto the surface of the layer 2, and transferring the particles onto the support base are then repeated and a second copy is made on a sheet 32.
For each additional copy to be made from the layer 2 onto a plurality of sheets 32, it is only necessary to repeat in sequence, the same steps in making the second copy.
Thus a plurality of copies can be made without reimaging the layer 2 by the present method since the image persists on the layer 2 after a single exposure to an optically dark image on a lighted background. Of course a negative image can be produced if there is an optically light image on a dark background.
To recondition the member 2, after it is no longer desirable to reproduce any more copies from the latent image on the layer 2, the surface of the member 2 is conditioned by uniformly charging the surface in darkness, to a voltage which is opposite the acceptance potential of the material in the member 2, as described in accordance with the first step illustrated in FIG. 1, where the charge was negative. By this step the layer is made uniformly non-conductive and any nonconductive latent image is erased thereby.
An illustrative apparatus for carrying out the method steps shown in FIGS. 1 through 10 and disclosed herein appears in FIG. 11. It should be understood that the embodiment of FIG. 11 is not the only apparatus for practicing the present invention and is merely illustrative and the method of the present invention can be used in any conventional copier capable of producing the steps indicated herein. The layer 2 consists of a coating 40 of photoconductive insulating material ex hibiting substantially persistent conductivity on a conductive substrate or drum 42 formed of electrically conductive material. The drum 42 is mounted for rotation in the clockwise direction as indicated by the arrow 42a. The surface of the coating 40 on drum 42 is conveniently charged to a first d-c potential which is negative in the manner described in connection with FIG. 1, at the 7:00 oclock position of the drum 42 as shown in FIG. 11, by the corona charging unit 6.
The coating 40 is sensitized to a second d-c potential which is positive or opposite to the first d-c potential anad imaged next as shown in FIG. II, and in conformity with FIGS. 3 and 5, as the drum 42 continues its clockwise rotation. The sensitizing unit 12 is positioned at approximately 9 oclock and the light 44 and lens system 20 are positioned to image the layer 40 as it passes station 48 located at 12 o'clock in FIG. 11.
The light 44 is operated to illuminate the face of the document 18 as it is moved past a reading station 46 and the illumination is reflected therefrom and imaged through the lens system 20 onto the surface of the layer 40 at 48, thus exposing the layer 40 to an optically dark image on a light background. This creates a corresponding latent image on the surface of the layer 40 wherein the background remains relatively conductive and the latent image remains non-conductive and retains a d-c potential of the same sign as the second d-c potential (i.e. positive for zinc-oxide in a binder).
The operation of the above three stations, specifically, the corona charging unit 6, the sensitizing unit 12 and the imaging station at 48, are all conventionally connected to their source of power so that they are actuated at the start of the first cycle of copying to prepare the layer 40 with a clear latent image of the document 18 to be copied.
The next station in FIG. H is located at :00 oclock and it conventionally prepares the surface of the coating 40 with toner and thereby electrophotographically duplicates the latent image onto a copypaper 50 similar to the illustration of FIG. 7. The toner is suspended in a fluid contained in a tank 52 through which the coating 40 passes. With the toner adhering to the latent image. the surface of the coating 40 is pressed against a sheet of copypaper 50 by roller 54. The copypaper 50 is pulled from a roll of copypaper 56 by a pair of rollers 58 and directed out of the photocopier by rollers 59 through exit 60. The length of the copypaper 50 is conventionally measured against the length of the document l8 and a knife 61 is activated to cut the roll of copypaper 54 when the copypaper is long enough to reproduce all of the indicia on the surface of the document 18 onto a single sheet of copypaper 50. A tray 62 is conventionally arranged at the exit 60 to receive the single sheets leaving the photocopier.
To make additional copies of the document 18, the
steps of uniformly recharging the coating 40 and using the coating 40 to electrophotographically duplicate the latent image onto the copypaper 50 are repeated for each additional duplication. This is accomplished as can be seen in FIG. 11 by the drum 42 being rotated a complete cycle for each copy. However. only the sensitizing unit 12 is actuated each cycle as the coating 40 passes thereby and is recharged positively.
As the coating 40 is recharged. the background maintains its substantially uncharged condition and the latent image portion increases the d-c potential existing thereon to a value substantially equal to the recharging potential but not greater than the acceptance potential of the coating 40. The recharged coating 40 then passes through the tank 52 where toner particles adhere to the latent image and the toner particles are transferred in image configuration onto the sheet of copypaper 50 by roller 54. As for the first sheet of copypaper 50, each next sheet of copypaper 50 is cut to the length of the document 18 by the knife 61 and passed out of the exit 60 onto the tray 62.
To reproduce a next desired indicia from a next document 18, the coating 40 is uniformly charged to the first d-c potential by the corona charging unit 6 which charge is negative and which erases the latent conductive image from the coating 40. The above steps are then repeated for each new document 18.
The method of the present invention is not limited to a specific persistent photoconductive material for use as the member or layer but rather any persistent photoconductive material will suffice. Further the method and material for toning the layer is conventional and therefore any known method or toner can be used herewith.
Having described my invention. what I claim as new and desire to secure by Letters Patent is:
1. An electrophotographic process for making multiple copies from a single, repetitively rejuvenated electrostatic latent image residing on the surface of an electrophotographic plate comprising a photoconductive insulating layer coated on a conductive substrate. wherein said layer exhibits persistent conductivity said process comprising the steps of:
A. uniformly electrostatically charging the exposed surface of said layer in the absence of activating radiation to a voltage of a first polarity to condition said layer by rendering said layer unifonnly nonconductive. thereby converting any pre-existing condition of persistent conductivity in non-image areas to a condition of non-conductivity and also converting any pre'existing image pattern from its given polarity to a condition of being indistinguishable from said pre-existing non-image areas;
B. uniformly electrostatically charging the exposed surface of said layer to a voltage of a second but opposite polarity to sensitize said layer, said opposite polarity voltage being greater than zero and approaching the charge acceptance potential of said layer;
C. subjecting said exposed layer surface to an activating radiation in imagewise configuration corresponding an image to be reproduced to create a varying presistent conductivity non-image area in contrast to said imagewise configuration in said layer. said persistent conductivity non-image area operating to selectively discharge said exposed layer surface and thereby result in electrostatic latent image;
D. developing said electrostatic latent image with electroscopic marking material;
E. transferring said marking material in image formation to a first copy sheet;
F. rejuvenating said electrostatic latent image on said exposed layer surface by depositing thereon electrostatic charges of said second sensitizing polarity;
G. developing said rejuvenated electrostatic latent image with electroscopic marking material;
H. transferring said marking material in image formation to a second copy sheet; and
l. repeating said rejuvenating, developing and transferring steps in sequence to produce further multiple copies from said electrostatic latent image.
2. The process defined in claim 1, wherein said layer is composed of zinc oxide in an acrylicpolyester binder, said first polarity is negative and said second but opposite polarity is positive.
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|U.S. Classification||430/26, 430/54, 430/51, 399/168, 430/55, 430/87, 101/DIG.370|
|Cooperative Classification||Y10S101/37, G03G13/22|