US3692519A

US3692519A - Electrophotographic color process

Info

Publication number: US3692519A
Application number: US841256A
Authority: US
Inventors: Toru Takahashi
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1968-07-23
Filing date: 1969-07-14
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19
Also published as: JPS4834770B1; DE1937488A1; GB1282018A; DE1937488B2; DE1937488C3

Abstract

AN ELECTROPHOTOGRAPHIC PROCESS FOR PREPARING A MULTICOLORED COPY FROM A MULTI-COLORED ORIGINAL COMPRISES APPLYING A PRIMARY CHARGE ON A PHOTOSENSITIVE MEMBER, IRRADIATING AN OPTICAL IMAGE OF A COLOR WHICH IT IS DESIRED TO REPRODUCE, APPLYING A SECONDARY DISCHARGE CONTEMPORANIOUSLY WITH IRRADIATING AN OPTICAL IMAGE OF COLORS OTHER THAN SAID DESIRED COLOR, EXPOSING THE WHOLE SURFACE OF THE PHOTOSENSITIVE MEMBER IF NECESSARY, DEVELOPING THE FORMED

LATENT IMAGE AND TRANSFERRING THE IMAGE CORRESPONDING TO THE IMAGE OF THE DESIRED COLOR ONTO A TRANSFER MEDIUM, AND REPEATING THESE STEPS FOR EACH COLOR OF THE MULTI-COLORED ORIGINAL.

Description

sept. 19, 1972 Filed July 14 1969 TORU TAKAHASHI 3,692,519

ELECTROPHOTOGRAPHIC COLOR PROCESS 3 Sheets-Sheet l FIG. HA) FlG. HB)

3 Sheets-Sheet 2 Filed July 14 1969 @WWW-#SW obo FIG. 5

FIG. 3K2) Sept- 19, 1972 ToRu TAKAHASHI 3,692,519

I ELECTROPHOTOGRAPHIC COLOR PROCESS Filed July 14. 1969 3 Sheets-Sheet 3 F|G.4(A) L Will.

MH Il abaco' FIG. 4(8) l) 2 9j IO u b o C o United States Patent 3,692,519 ELECTROPHOTOGRAPHC COLOR PROCESS Torn Takahashi, Tokyo, Japan, assigner to Canon Kahushiki Kaislia, Tokyo, Japan Filed July 14, 1969, Ser. No. 841,256 Claims priority, application Japan, July 23, 1968, :t3/52,077 int. Cl. G03g 13/00 U.S. Cl. gti-1.2 20 Claims ABSTRACT 0F THE DISCLOSURE This invention relates to an electrophotographic process capable of copying multi-colored originals. More particularly, it pertains to a novel electrophotographic process capable of reproducing only those portions of the multicolored original having a specified color and of obtaining a multi-colored reproduction true to the multi-colored original by repeating said copying process with respect to each color.

The general technique hitherto employed in electrophotography for reproducing multi-colored originals, for example, of the kind having black letters surrounded by red frames, is to uniformly charge a photosensitive body having a photoconductive layer, then form a latent image corresponding to the black letters by projecting an optical image through a red lter, then develop said latent image with black toner, and then transfer the developed image to paper, etc. Next, the photosenstive plate is cleaned and recharged, and a latent image corresponding to both the red frames and black letters is formed by projecting an irradiating optical image through a cyan lilter which blocks red. The latent image thus formed is developed with red toner and the developed image is superimposed on said paper, etc. As a result, the black letters are liable to be illegible and dirty if there is lack of color registration caused by inaccurate superposition of the red toner image on the black toner image. Complete avoidance of such displacement is hard to obtain because it depends upon position matching at time of transfer and requires high mechanical precision. Moreover, since red toner is placed on black letters, color reproduction lacks delity.

Color control is dependent upon extremely complex factors when the known process is applied to natural color photographs. For example, since a thick red toner image is superimposed on a thick black image in reproducing a dark red image, only a red or black image is obtained if the toner placed on top is opaque. This is especially true in cases of business documents composed largely of black letters. When a document composed mainly of black letters contains a natural color photograph, the user must bear the inconvenience of color shift in the black letters caused by the presence of the natural color photograph. Moreover, this method has the defect of being unable to reproduce just a given color from a multi-colored original.

This invention olers a novel electrophotographic proc- ICC ess capable of eliminating the above-mentioned inconveniences, and it is characterized by converting the difference between the light intensity of a desired color to be copied and the light intensities of the remaining colors into difference in copying density by using filters, etc., and by converting the difference between the intensity of a spectral wavelength region A of an image of the original and the intensity of a spectral wavelength region B into the difference in image density.

Accordingly, an object of this invention is to obtain a reproduction of a portion of a multi-colored original having a specified or discrete color in a simple manner as compared with conventional techniques.

Another object of this invention is to obtain a multicolored reproduction, not olf-color and with fidelity to the original, from a multi-colored original by repeating said single color copying process a desired number of times.

A still further object of this invention is to provide means for practicing the invention.

The present invention will be more apparent from the following description referring to the illustrative embodiments shown in the attached drawings, in which:

FIGS. 1(A), (B), and (C) are explanatory diagrams of the electrophotographic process as practiced according to the invention;

FIG. 2 is a diagram showing steps in the production of a copy according to said process;

FIGS. 3 and 4, (A), (B), (C), are explanatory diagrams for other embodiments of the invented electrophotographic process as practiced; and

FIGS. 5 through 7 are side views of three embodiments of the discharger used in practicing this invention.

An embodiment of the electrostatic image forming process according to the invention now will be described hereafter referring to the attached drawings. Referring to FIG. l, 1 is a multi-colored original; 2 is a colored image on the multi-colored original 1, having a color, for example, red, to be copied; 3 is another image having a color other than red, for example, black; 4 is a lter that passes the color of image 2, in this example a red filter, placed between the multi-colored original 1 Iand a photosensitive member p; 5 is also a lter which blocks the color of image 2 but passes other colors; 6 is a corona dischargei for primary charging; 7 is a discharger which performs either AC discharge or secondary charging opposite in polarity to the primary charging; p is the photosensitive member comprising a transparent insulating (insulative) layer 8, photoconductive layer 9, and base plate 10 Assume that the surface of the insulating layer 8 of photosensitive member p is primary charged positively by the discharger 6 which is optically transparent either with the upper part of shield 6, optically open or composed of transparent material as shown schematically in FIG. 1(A). Contemporaneously with or after the primary charging an optical image is projected on the same surface. The actual means employed for projeting the optial image an be either a reflex or direct arrangement or other known means the details of which are omitted from the drawing. At the regions a of the photosensitive member p, only the red component of light from the original 1 passes through the filter 4, all other components of light being blocked, and reaches the photosensitive member p. Due to the light irradiation, the resistance of the photoconductive layer 9 is decreased, and negative charge (i.e opposite in polarity to the primary charge) is induced on the back surface of the insulating layer 8. At the same time, in the region b, the reflected light from the image 2, which in this example is red, also reaches the photosensitive member p after passing through the filter 4, and a negative charge is induced on the back surface of the insulating layer 8 similar to that in the regions a. In the region c, however, no light reaches the photosensitive member p since the image 3 is black (absence of color) and no light is reflected. Therefore, at this location the resistance of the photoconductive layer 9 is not decreased and negative charge is not induced on the back surface of the insulating layer 8. The same thing happens even when the image 3 has a distinct color containing no red, for example blue, since the reviiected light from such an image Would be interrupted by the filter 4. In this way, negative charge, i.e. opposite in polarity to the primary charge, is induced on the back surface of the insulating layer 8 of the photosensitive member p in the regions a and b but not the region c.

Alternatively, projection of the optical image can be accomplished by using light of a single wave-length having the color desired for reproduction instead of using a iilter.

Next, upon the photosensitive member p that has been through the above-mentioned process, an optical image of the above-mentioned original 1 is projected as shown in iFIG. l(B) through the filter 5, which blocks red light, simultaneously with further charging, i.e., either secondary charging opposite in polarity to the primary charge or AC disharge using, respetively, for the discharge 7 either a -DC discharger or an AC discharger. In either case the shield 71 should be open optically similar to discharger 6. The drawing shows the case in which an AC discharger is used.

During this step in the regions a, those rays of light reected from the original 1 except red will pass through the filter and reach the photosensitive member p. Upon receipt of this light, the resistance of the photoconductive layer 9 is decreased and the negative charge which was previously induced on the back surface of the insulating layer 8 is eliminated along with the removal of the positive (-1-) charge from the front surface.

In the region b, the reflected light from the image 2 is blocked by the filter 5 and does not reach the photosensitive member p. Therefore, the resistance of the photoconductive layer 9 at this location does not decrease. As a result, the negative charge previously induced on the back of the insulating layer 8 does not disappear even though the discharge from the discharger 7 is applied. Instead the negative charge attracts the positive charge and greatly reduces the effect of the discharging action. Thus the positive (-1-) charge developed during the primary charging remains on the surface of the insulating layer.

In the region c, since no light is reflected by the image 3 (it is black in this example), no light reaches the photosensitive member p, and the resistance of the photoconductive layer 9 does not decrease. However, since no negative charge was induced on the back surface of the insulating layer 8 during the primary charging, the discharging action of discharger 7 is not inhibited and the positive charge on the insulating layer in ths location is removed.

After completion of the above-mentioned process, the surface of the photosensitive member p is subjected to unpatterned or blanket radiation to Which the photoconductive layer 9 is sensitive (whole surface exposure) as shown in FIG. l(C) to release the induced charge in the photoconductive layer which is not bound by the charge on the insulating layer 8 and to increase the electrostatic contrast. Next, the latent image on the photosensitive member p is developed as shown in FIG. 2(1) by using colored toner or o-set master toner having the same color as the picture image and is transferred onto the transfer paper 11. Thus a specified color 2 can be selectively reproduced from the multi-colored original 1.

An embodiment of the above-mentioned photosensitive member p was made as follows: Onto an aluminum base plate 10, selenium was evaporated to a thickness of about 30p. at a temperature of about `60" C. t0 which a polyester film, 25u in thickness, was adhered.

Another photosensitive member was prepared by melting at about 500 C. for about three hours, a mixture of Se Te 10% and a small amount of Ge (0.004- 0.5 then heating it at about 250-350 C. in a vacuum (below 10-4l mm. Hg) and evaporating it on an aluminum base plate held at 58 C. to a thickness of about 50p., to which a polyester film, 25a in thickness was secured by an epoxy adhesive. The surface of the aluminum base plate was oxidized before the evaporation step. In either case, excellent results were obtained.

This three-layer photosensitive member p has properties intermediate N-type and =Ptype, having a specific resistance of 1013 Sl cm., and capable of being charged to over 500 v., either positive or negative.

As another embodiment of this invention it is also possible to use a photosensitive member comprising the abovementioned three layers but with the base plate 10 consisting of an insulating layer. When this photosensitive member is used, it is sufficient to place the photosensitive member on an electrically conductive holding plate or to apply voltages, opposite in polarity, to both surfaces of the photosensitive body during charging or discharging according to the above-mentioned process.

A four-layer photosensitive member p having a base plate 10 comprising an insulating layer 101 and an electrically conductive layer 102 as shown in FIG. 3 can be used in place of the photosensitive member p. The addition of the insulating layer 101 enables highly sensitive photoconductive materials, hitherto incapable of use as the photoconductive layer 9 because of their low resistance, to be used while at the same time avoiding damage due to insulation breakdown of the photosensitive body.

FIG. 3 is an explanatory diagram of the photosensitive member p' for the same conditions as the embodiment shown in FIG. 1. As shown in FIG. 3(A), an optical image is projected onto the photosensitive member p' either contemporaneously with or after the primary charging. Only light that can pass through the lilter 4 reaches the photosensitive member p and the portions of the photoconductive layer 9 corresponding to the light pattern is charged as shown in FIG. 3 (A).

Next, as shown in FIG. 3(B), either secondary charging or AC discharging is performed While projecting an optical image through the filter 5. The charged state at this time is as shown in FIG. 3(B). After the preceding steps, radiant energy to which the photoconductive layer 9 is sensitive, is applied all over the surface of the photoconductive layer to the extent necessary to increase the electrostatic contrast as shown in FIG. 3(C).

An embodiment of the above-mentioned 4-layer photosensitive member p' may be constructed as follows: On an electrically conductive aluminum base plate a polyester film, 6p. in thickness, is fastened with an epoxy resin adhesive. A coating of copper-activated cadmium sulfide consisting of particles of about 10p in diameter, is applied thereon to a thickness of about 50p, using cellulose acetate as the bonding agent. Thereupon, a polyester film, 20u in thickness, is fastened thereto using an epoxy resin adhesive.

The insulating layers in the photosensitive member used in this invention are composed of insulating substances having charge holding properties, and can be selected from among organic and inorganic insulating materials. As for the electrically conductive layer, metallic materials, paper and other electrostatically conductive materials can be employed.

FIG. 4 is an explanatory diagram of the process of an embodiment of this invention when DC corona discharge reverse in polarity to the primary charge polarity is used as the secondary discharge. FIGS. 4(A), (B), and (C) correspond to (AB), (B), and (C) of FIG. l, respectively. However, differences exist in the charged states of the photosensitive member, and the electrostatic image formed here is higher in potential in areas corresponding to the light area (background) of the original than in areas corresponding to the dark area.

The region b of FIG. 4(B) which is different in charged state from that of FIG. 1 will 'be explained. Upon application of the negative secondary discharge, charging is influenced by the negative charge trapped in the interface between the photoconductive layer 9 and the insulating layer 8, and only positive charge due to the primary charge is eliminated with the surface of the insulating layer 8 developing either zero charge or a slightly negative charge.

It is, therefore, sufficient for obtaining a multi-colored reproduction from a multi-colored original 1, to use filters that correspond to each color and to repeat the process described above for each of the colors to be reproduced. To describe a complete example, an optical image that has passed through a cyan (red blocking) filter is projected onto the above-described three-layer photosensitive member contemporaneously with charging by a primary charger. Next, the photosensitive member is simultaneously exposed to the optical image that has passed a red filter and subjected to AC corona discharge by an AC discharger. Then whole surface exposure is accomplished. The electrostatic latent image thus formed is developed with cyan toner according to conventional developing methods. The developed image is transferred to a transfer medium by appropriate means. The photosensitive member is cleaned and then discharged with whole surface exposure.

Next, the optical image of the above-mentioned original is impressed on the photosensitive member through a magenta (green blocking) yfilter along with primary charging, and then while projecting the same optical image through a green filter, an AC corona discharge is applied with the AC discharger. Then whole surface exposure is again performed and the latent image is developed with magenta toner. The image is then transferred onto the above-mentioned transfer medium after matching positions. The foregoing operation is repeated again but now with a yellow (blue blocking) filter and a blue filter being used in that order. Yellow toner is used for development. The image formed by the yellow toner is also transferred and superimposed on the image already present on the above-mentioned transfer medium.

Finally, the cleaned photosensitive body is charged by the primary charger with whole surface exposure, followed by lAC corona discharge by means of the AC discharger while the optical image is being projected without a filter. After another whole surface exposure, the electrostatic image is developed with black toner and transferred onto the above-mentioned transfer medium in similar manner to the above.

Then the composite toner image formed on the transfer medium is Ifixed to the above-mentioned transmedium by any suitable method, for example, by heatfixing. In this way a color copy is produced from four superimposed colored images.

As for the characteristics of the photoconductive layer of the photosensitive member in the present electrophotographic process, it is desirable to have a dark resistance of more than 10o1 S2 cm., preferably more than 1011 Q cm., in the presence of both positive corona charging and negative corona charging. Those photoconductive layers hitherto used which are greatly dependent on the polarity of charging will not always yield good results. It is, therefore, advisable in order to realize the aforementioned characteristics to install an insulating layer or a barrier layer which impedes the flow of charge between the photoconductive layer and the electrically conductive base plate. This property can be also obtained by the use of true semiconductors. Substances that show internal polarization can also be used. Those that have a wide range of spectral sensitivity are desirable. Particularly, CdS, CdSe, ZnO, ZnS, PbO, anthracene etc. should be used.

The

corona dischargers

6 and 7 are preferably constructed with tungsten wire 12 of .05 to .10 mm. diameter. However, this does not bar the use of such discharge electrodes as needles, etc. Whether the

corona dischargers

6 and 7 are constructed separately as shown in FIG. 5, with

filters

4 and 5 attached, respectively thereto, or the

corona dischargers

6 and 7 are combined into one assembly as shown in FIG. 6 with the

filters

4 and 5 attached in tandem, they are more conveniently handled than when the

corona dischargers

6 and 7 and the

filters

4 and 5 are installed separately.

When primary charging and optical image irradiation is not performed simultaneously, it is advisable to arrange the lter 4 between the

corona dischargers

6 and 7 as shown in FIG. 7. It is also convenient to mount two filters having complementary colors in a single frame, preparing such frames for individual colors, and to insert a required one into the upper part of the discharger either manually or automatically.

When combining the

corona dischargers

6 and 7 and the

filters

4 and 5 into one unit, the upper surface of the corona discharger must be made translucent. It is advisable to provide a translucent electrically conductive layer linked with the shield plate 13 of the

corona dischargers

6 and 7, inside the

filters

4 and 5. It is possible to direct the AC corona discharge very effectively upon the photosensitive member by installing insulating layers of 50a t0 200g in thickness, for instance a polyester film and a translucent insulating layer, inside the above-mentioned shield plate 13 and the above-mentioned translucent electrically conductive layer, respectively.

The

filters

4 and 5 can be inserted into the path of the light for illuminating the original instead of inserting them into the path of the reflected optical image.

Since this invention is constructed as mentioned above,

it is possible to obtain a specified colored reproduction from a multi-colored original, selectively and very easily.

It is also possible to obtain a multi-colored reproduction, which is faithful in color production to the original and has no color mismatching, from a multi-colored original by repeating this copying process the required number of times.

Furthermore, when, for instance, it is desired to reproduce a dark red image, the corresponding dark red color can be reproduced by superimposing a thin red toner image upon a thin black toner image without using a semi-transparent toner.

It is of course possible to use electrode charging or other conventional methods besides the use of corona discharge when performing the primary charging and secondary discharging steps.

I claim:

1. An electrophotographic process in which an electrostatic latent image of a desired color of a multi-colored original image pattern is formed on a photosensitive member including a photoconductive layer and an insulative layer overlying said photoconductive layer which comprises the steps of applying to said insulative layer a charge of one polarity and exposing said photoconductive layer to a first optical image derived from said original image pattern and of said desired color, and then subjecting said insulative layer to further charging with either a D.C. discharge of opposite polarity to said one polarity or with an A.C. discharge while exposing said photoconductive layer to a second optical image derived from said original image pattern and of the colors in said original except said desired color.

2. An electrophotographic process according to claim 1, wherein said first optical image is derived from said original by exposing said photoconductive layer to an image of said original image pattern through a ffirst filter that transmits said desired color, and wherein said second optical image is derived from said original by exposing said photoconductive layer to an image of said original through a second iilter that transmits the colors in said original image pattern except said desired color.

3. An electrophotographic process according to claim 1, wherein said formed latent image is developed with a colored developing agent having the color of said desired color and wherein said developed image is transferred to a transfer medium.

4. An electrophotographic process according to claim 3, wherein the steps of the process are repeated for superimposing in registration on said transfer medium successive developed images for at least two of the colors in said original image pattern.

5. An electrophotographic process according to claim 1, wherein said photoconductive layer is exposed to said first optical image while said charge of one polarity is being applied to said insulative layer.

6. An electrophotographic process according to claim 1, wherein said photoconductive layer is exposed to said irst optical image following the application of said charge of one polarity to said insulative layer.

7. An electrophotographic process according to claim 1, wherein said member further includes a base plate underlying said photoconductive layer.

8. An electrophotographic process according to claim 7, wherein said base plate is comprised of electrically conductive material.

9. An electrophotographic process according to claim 7, wherein said base plate is comprised of insulative niaterial.

10. An electrophotographic process according to claim 7, wherein said base plate comprises an insnlative member and an electrically conductive member underlying said insulative member.

11. An electrophotographic process according to claim 1, wherein said step of applying said charge of one polarity and said step of further charging are practiced by applying corona discharge to said insulative layer.

12. An electrophotographic process according to claim 11, wherein said step of further charging is practiced by applying to said insulative layer a D.C. corona discharge of polarity opposite to said one polarity.

13. An electrophotographic process according to claim 11, wherein said step of further charging is practiced by applying to said insulative layer an A C. corona discharge.

14. An electrophotographic process according to claim 1, wherein said first optical image is derived from said original image pattern by illuminating the original image pattern with light of a single Wave-length having said desired color.

CII

15. An electrophotographic process according to claim 2, wherein said step of applying said charge of one polarity and said step of further charging are practiced with first and second corona discharging means, and said iirst and second tilters are mounted on said first and second discharging means, respectively, for applying said first and second optical images therethrough.

16. An electrophotographic process according to claim 1S, wherein said first and second discharging means are integrated in a unitary structure side-by-side.

17. An electrophotographic process according to claim 2, wherein said step of applying said charge of one polarity and said step of further charging are practiced with first and second discharging means supported side-by-side with a gap therebetween, and said tirst ilter is mounted between said discharging means bridging said gap and said second filter is mounted on said second discharging means whereby said ffirst optical image is transmitted between said discharging means and said second optical image is transmitted through said second discharging means.

1S. An electrophotographic process according to claim 1, wherein said photocondnctive layer is exposed to unpatterned light after said step of further charging, and the formed latent image is thereafter utilized to provide a developed image.

19. An electrophotographic process according to claim 3, wherein, preceding the step of developing but after the step of further charging, said photoconductive layer is exposed to unpatterned light.

20. An electrophotographic process according to claim 19, wherein the steps of the process are repeated for superimposing in registration on said transfer medium successive developed images for at least two of the colors in said original.

References Cited UNITED STATES PATENTS 2,986,466 5/1961 Kaprelian 96l.2 X 3,043,686 7/1962 Bickmore 96-1.2 X 3,438,706 4/1969 Tanaka et al 96-1 X GEORGE F. LESMES, Primary Examiner J. R. MILLER, Assistant Examiner U.s. C1. X.R. 96-1.3, 1.4, 1.5

UNITED STATES TTTNT @TTTQE @TFEE @TF @R'QTN Patent No. 3,692,519 Dated September' 19, 1972 nventor (E) TOru Takahashi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 57, "projeting" should read --projecting;

line 58,- "optial" should read --optical--g same line, "an" should read "can".

Column 3, line 24, "disharge" should read --discharge; same line, "respetively" should read --respectively; same line, "discharge" should read "discharger".

Column 5, line 54, "transli should read transfer; line 59, after "member" insert -used; line 6l, "1001" should read --l l v Signed and sealed this 29th da)7 of May 1973A.l

(SEAL) Attest:

EDWARD MFLETCHERJR. l ROBERT GOTTSCHALK Attesting Gffcsr Commissioner of Patents