JPS6134677B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic apparatus capable of selecting a mode in which the yin and yang of an image can be reversed and a mode in which it is not. As electrophotographic methods, electrofax method, Xerox method, PIP method, NP method (for example, Japanese Patent Publication No. 42-23910, etc.) are known. The electrofax method and Xerox method form electrostatic images using the so-called Carlson process, in which a photoconductor layer of zinc oxide (Electrofax), amorphous selenium (Xerox), etc. is placed on a support. The photoconductor surface of the photosensitive plate formed on the plate is uniformly charged by corona discharge,
Next, the original image is irradiated to attenuate the electric charge in the light-irradiated area, and an electrostatic image that follows the light and dark pattern of the original image is developed and visualized with charged colored particles, and then fixed or temporarily transferred to a support such as another paper. The PIP method uses the physical properties of fluorescent substances, such as persistent internal polarization and photoconductivity, to form a latent image. In the NP method, an electrostatic image is formed using the capacitance difference and photoconductivity between the photoconductor layer and the insulating layer used above it, and then the electronic image is transferred through the same development, transfer, and fixing steps. It is used to obtain photographic images. To date, copying devices utilizing these electrophotographic methods have been developed. Copying machines generally operate on a positive-positive basis, that is, a positive copy is obtained from a positive original. However, part of the demand is for a positive-positive machine to produce a negative-positive image, that is, a positive image rather than a negative original. For example, it is a microfilm enlargement printing device. In order to achieve such a positive/positive and negative/positive device with one function, it is necessary to change the charging polarity between positive/positive and negative/positive, or to change the polarity of the developing toner. I had to. Therefore, the apparatus becomes complicated, large, and expensive, and the image itself becomes unstable. The present invention aims to eliminate such conventional drawbacks, and one of its objects is to provide a device that can be used for both positive and negative and negative and positive, and can select one of them by a selective switching operation. It is in. This makes it possible to achieve multiple functions in one device by combining an electrophotographic copying device with a laser beam printer, which has been actively developed in recent years, or by combining an electrophotographic copying device with a microfilm enlargement printing device. It is what it is. Next, embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram of the structure of a photosensitive plate for forming an electrostatic image, in which 1 is a conductive support; 2 is a conductive support 1;
a photoconductive layer applied thereon, e.g. by spraying or using a coater, faller, etc.;
If necessary, a small amount of binder, mainly a resin, may be added to improve binding with other layers. 3
is an insulating layer uniformly and closely formed on the photoconductive layer 2. In this way, the photosensitive plate A is basically formed of three layers: the conductive support 1, the photoconductive layer 2, and the insulating layer 3. A layer for trapping charges may be formed between the support and the photoconductive layer, and may also or solely be added to the surface or near the surface of the photoconductive layer. In addition, it is preferable that the photoconductive property has as high a resistance as possible in a dark place. The conductive support 1 is made of a metal conductor such as tin, copper, or aluminum, or hygroscopic paper, but a support made of paper with aluminum foil attached is inexpensive and can be wrapped around a drum or the like. It is convenient when used. Material of photoconductive layer is CdS, CdSe, crystalline
Se, ZnO, ZnS, Se, TiO ₂ , SeTe, PbO, or a mixture thereof can be used. Some of such photoconductive layers have a charge injection property in which charges of a specific polarity are injected from the conductive support into the photoconductive layer during charging in a dark area. In this aspect, if having such properties has an unfavorable effect on the charge distribution due to the first light image irradiation performed after primary charging, charge injection in such a dark place as the primary charging polarity is It shall be charged with a polarity that does not cause In the case of a photoconductive material that does not substantially have a charge injection property, or even if it does have it, it does not substantially affect the charge distribution due to the above-mentioned photoimage irradiation, it can be charged to any polarity. The material constituting the insulating layer 3 has high abrasion resistance;
Any material can be used as long as it satisfies the three requirements of high resistance, ability to hold static charge, and transparency, and coatings such as fluororesin, polycarbonate resin, polyethylene resin, cellulose acetate resin, and polyester resin can be used. In particular, since fluororesin has the property of being easy to clean, it is a preferable material in the embodiment of the present invention because the photosensitive plate is repeatedly used after undergoing a cleaning process after development and transfer, as will be described later. FIGS. 2 to 5 illustrate the process of forming a composite latent image on the photosensitive plate constructed as described above and the charging pattern of the photosensitive plate. The following figures up to and including FIG. 13, including these FIGS. 2 to 5, are not embodiments of the present invention, but are explained to help understand the embodiments of the present invention to be described later. First, the surface of the insulating layer 3 of the photosensitive plate A is charged, for example, negatively (-) by a corona discharger 4 in a dark place.
Since the photoconductive layer 2 has a high resistance in the dark, positive (+) charges 32 are induced at the interface between the conductive support 1 and the photoconductive layer 2 or at the portion of the photoconductive layer 2 close to the conductive support 1. Ru. (FIG. 2) Through this process, the surface potential of the insulating layer 3 increases negatively (-) with charging time, and exhibits the characteristics shown in FIG. 6 Vp. Of course, the charging may be carried out at the electrodes instead of by corona discharge. Next, a first optical image is irradiated onto the insulating layer surface 3.
At this time, in the bright area of the photosensitive plate A, since the photoconductive layer 2 becomes conductive due to optical stimulation, the interface between the conductive support 1 and the photoconductive layer 2 or the photoconductive layer 2 is caused by pre-charging.
Positive (+) induced in the part near the conductive support 1
The charge 32 is a negative (-) charge on the surface of the insulating layer 3.
It moves to the interface between the photoconductive layer 2 and the insulating layer 3, attracted by the electric charge, and stops there. On the other hand, in the dark area, since the resistance value of the photoconductive layer 3 is high, the charge state is maintained almost as it is (FIG. 3). Through this process, the surface potential of the insulating layer 3 is changed to V _L (potential on the surface of the insulating layer in the bright part) and V _D (potential on the surface of the insulating layer in the dark part) in FIG.
It exhibits the characteristics shown in . Next, the surface of the insulating layer 3 is recharged with a polarity opposite to the charging polarity, ie, positive (+), by a corona discharger 8 almost simultaneously with the second light image irradiation. Since the recharging corona discharger 8 performs optical image irradiation almost simultaneously, it is preferable that its upper part be transparent or have an optically open structure without a shield plate. The negative (-) electrode 31 charged on the surface 4 of the insulating layer 3 in the dark part in the first optical image is neutralized by the recharged positive (+) charge, and further The surface of the insulating layer 3 is charged with recharge polarity (+). Also, in the areas that are bright in the first light image irradiation and are also bright in the second light image irradiation, the negative (-) charge that had been charged on the insulating coating surface 3 due to primary charging is due to recharging. It is neutralized by positive (+) charges and is further charged to recharge polarity (+). In this case, the resistance of the photoconductive coating 2 decreases due to light irradiation and becomes conductive, and the positive (-) of the charged layer formed at the interface between the photoconductive coating surface 2 and the insulating coating surface 3 due to primary charging. The charges become free and disappear, and further, the positive (+) charges on the insulating coating surface 3 induce negative (-) charges. The amount of these charges depends on the time and intensity of recharging. On the other hand, in the part that was a bright part when the first light image was irradiated and a dark part when the second light image was irradiated, the negative (-) charge formed on the insulating coating surface 3 due to primary charging has a reverse polarity due to recharging. Even if it is partially or completely neutralized by positive (+) charges, the extent to which it becomes polarized by recharging is small. This means that
After primary charging, the positive (+) charge of the charged layer formed at the interface between the conductive film 2 and the insulating film 3 due to the first light image irradiation causes the blocking layer on the surface of the photoconductive film to Because the presence and the resistance of the photosensitive film are high, it exists without being released even when recharging is performed, so it is thought that the degree to which the insulating coating surface 3 is charged to the recharging polarity due to this field of charge is reduced. It can be done. (FIG. 4) Next, the entire surface of the insulating film on which the electrostatic image as described above is formed is uniformly exposed. Since there is not much change in the state of the chargeable member A in the dark part of the first light image or the bright part of the second light image, the positive (+) charge on the insulating coating surface is transferred to the back surface. It maintains a stable state with a negative (-) charge, does not attenuate much, and its surface potential remains almost constant. However, in the bright part of the first light image and the dark part of the second light image, the photoconductive film showed high resistance because it was not irradiated with light in the above process, but because it was exposed in this process, The resistance value decreases rapidly and becomes conductive. Therefore, in the process, the positive (+) charges that were stuck at the interface between the photoconductive film 2 and the insulating film 3 disappear, and as a result, the surface potential of the insulating film surface decreases rapidly. In addition, if the negative (-) charges caused by primary charging are not completely neutralized by the positive (+) charges caused by recharging, the surface potential not only decreases, but conversely, the surface potential due to the negative (-) charges remaining on the surface A potential appears.
(FIG. 5) Changes in the surface potential of the insulating layer 3 due to these processes exhibit characteristics as shown in FIG. Next, the electrostatic image formed by the above method is developed using a developer mainly composed of charged colored particles by a known developing method such as a magnetic brush developing method or a cascade developing method. FIG. 7 shows a case where development is performed with toner having a polarity opposite to that of the primary charge, that is, a positive polarity, and the toner adheres to bright areas in the first light image and dark areas in the second light image. Figure 7 shows reversal development, that is, the first
This indicates development with toner having the same negative polarity as the next charge, and development is performed in the opposite direction to that of positive development, and toner adheres to the . Figures 9 to 12 show examples of such composite image formation, in which a is the original of the first optical image, b is the original of the second optical image, and c is the toner with positive polarity. A composite microscopic image of a and b when developed is shown, and d shows a composite microscopic image of a and b when developed with toner having negative polarity. As can be seen from these composite images, different composite images can be obtained according to the light and dark patterns of the first and second light images and their yin and yang, and can be selected depending on the purpose. Next, the visible image formed on the surface of the insulating layer is transferred onto a transfer material 11 such as paper by applying a corona discharge, an external voltage such as a bias voltage, or an internal electric field, as shown in FIG. Finally, the transferred image is fixed by a fixing means such as infrared rays, a hot plate, or pressure fixing to obtain an electrophotographic image. On the other hand, since the photosensitive plate is used repeatedly, after the transfer is performed, the surface of the insulating layer is cleaned by a known cleaning method to remove charged particles remaining on the surface. At this time, the cleaning effect will be increased if the cleaning is performed after the electrostatic image formation charges that have been accumulated on the surface of the insulating layer in the bright areas of the original image are removed mainly by recharging. To do this, before cleaning, the surface of the insulating coating may be exposed to an alternating current corona discharge to remove the electrostatic image formation charges, and then cleaned with an elastic blade, fur brush, or the like. In this case, the cleaning effect can be enhanced by providing the cleaning means with a potential of opposite polarity to that of the charged colored particles. This cleaning effect also depends on the tackiness and the properties of the material of the insulating coating, so all of the above-mentioned resins are suitable as the electrostatic image forming material according to the present invention, but among them, the fluororesin coating is particularly suitable. is the most effective in that it has excellent non-adhesive properties, assists in the removal of charged colored particles during cleaning, and has a remarkable cleaning effect. Preferable electrostatic images for development include (1) a sufficient surface potential difference between the V _LD and V _DD V _DL V _LL ; and (2) no large surface potential difference between the V _DD V _DL V _LL . It is. In order to satisfy this requirement, (1) the photoconductive material 2, (2) the first and second exposure doses, (3) the polarity and intensity of the initial charge, (4) the intensity of the alternating current corona discharge, etc. are appropriately set. things are necessary. Next, a quantitative explanation of an example of the electrophotographic method for forming the composite image is as follows. 100g of cadmium sulfide activated by copper
Add 10 g of vinyl chloride and a small amount of thinner and mix. The photosensitive material obtained is coated on an aluminum cylinder with a polished surface to a thickness of about 50 μm. Next, an insulating layer with a thickness of 35 μm is laminated on the surface of this photoconductive film to obtain a photosensitive plate. Next, a +7KV corona discharge is applied to the surface of the insulating layer of the photosensitive plate to uniformly charge it with a positive (+) charge. Next, a first light image (bright part is approximately 12 lux/0.3 seconds light intensity) is irradiated, and then, at the same time as recharging to -6KV, a second light image with the same light intensity as the first light image is irradiated. . Further, the entire surface is uniformly exposed to light at about 12 lux for about 0.8 seconds to form a high contrast electrostatic image on the surface of the insulating layer. When the surface potential during this electrostatic image formation process is measured with a surface potentiometer, the part corresponding to V _D in Figure 6 is +1700V, the part corresponding to V _L is -1400V, the part corresponding to V _LD and the parts corresponding to V _LL and V _DL . A surface potential difference of approximately 350V was obtained. The present _invention relates to the _formation of a composite image as described _above , but in terms of _FIG . This was done by focusing on the fact that the latter order of potentials is opposite to the order of potentials. FIG. 14 shows an example of a copying machine that can freely make positive-positive and negative-positive copies using an embodiment of the process according to the present invention. Of course, the polarity of each charger and toner is fixed mechanically, and the polarity does not change even if the mode is switched between positive and positive and negative and positive. Reference numeral 12 denotes a rotating drum which rotates in the direction of the arrow and supports a photosensitive plate A having a conductive support 1, a photoconductive layer 2 and an insulating layer 3 successively laminated in close contact with each other on its circumferential surface. The primary charging corona discharger 4 is a negative (-) polarity high voltage power source (not shown in the drawing), and the reverse polarity corona discharger 8 is a positive (+) polarity high voltage power source (not shown in the drawing). (not connected). Reference numeral 33 denotes a developer, which is a mixture or one-component developer of a carrier (for example, iron powder) and charged colored particles (toner), and the toner is set to have a positive (+) polar charge. A case will be described in which the present apparatus is not used and a positive copy is obtained from a positive original. The document table 25 on which the original 24 is placed is moved in synchronization with the rotation of the photosensitive plate A in response to a copy instruction signal according to a known method. The original reflected light illuminated by the original illumination lamp 26 is reflected by mirrors 27 and 28 and is reflected by the imaging lens 1.
3 to reach the positive/negative switching mirror 29. The positive/negative switching mirror 29 is set in advance to the position ○A by a signal from a positive/negative switching switch (not shown in the drawing) or the like. Also, with this set, the tungsten lamp 31 is activated which turns on (in the case of ○A) and turns off (in the case of ○B) in conjunction with the positions ○A and ○B of the positive/negative switching mirror 29. The reflected light from the original 24 that enters the positive/negative switching mirror 29 located at the position ◯A is reflected by the mirror 32, reaches the recharging corona discharger 8, and exposes the photosensitive plate. First, the surface of the insulating layer 3 of the photosensitive plate A is negatively charged (-) by the initial corona discharger 4. Then, the surface of the insulating layer 3 is uniformly exposed by a tungsten lamp 31. Next, the photosensitive plate is irradiated with the original reflection described above from the surface of the insulating layer 3 through the recharging corona discharger 8, and at the same time, corona discharge of positive (+) polarity is applied by the recharging corona discharger 8. Next, the entire surface of the insulating layer 3 is uniformly exposed to light using a tungsten lamp 23 to form an electrostatic image on the surface of the insulating layer 3 in accordance with the bright pattern of the original reflected light. When the electrostatic image passes through a developing device 14, it is developed by a magnetic brush 15 mainly composed of charged colored particles to form a visible image. FIG. 16A is an explanatory diagram showing the charge pattern at each step up to forming a visible image when the positive-positive process is selected in this way, and the change in surface potential at each step is the 16th Shown in Figure B. As can be seen from these figures, the part D of the latent image corresponding to the part where there is no reflected light of the original, that is, the black part, is positively charged (+) by the electric field caused by the surface potential V _D. Charged colored particles do not adhere to portions L corresponding to bright areas because their surface potential V _L is positive, and therefore a positive visible powder image can be formed from a positive original. Next, this visible powder image is transferred to the feed roller 1.
6, the transfer material 11 comes into contact with the visible powder image and transfers thereto.
Then, a corona discharge having a polarity opposite to that of the charged particles is applied by a transfer accelerating corona discharger 10 to perform transfer. Next, the transfer material 11 moves along the circumferential surface of a heat drum 18 of a fixing device having an infrared lamp 17 therein to fix the transferred image, and finally an electrophotographic copy image is obtained on a tray 19. On the other hand, after the transfer has been performed, the photosensitive plate A is charged with an AC corona discharger 20 to remove the electrostatic image forming charges remaining on the insulating layer surface 3, and then a cleaning device 2
In step 1, the powder image remaining on the insulating coating surface 3 is cleaned by rubbing with a rotating brush 22 having soft bristles such as a fur brush on the periphery, and the insulating coating surface 3 is used for the first process of repeated use. will be prepared. Next, a case will be described in which the present apparatus is used in a negative/positive method, that is, a case in which a positive copy is obtained from a negative original. In this case, the operation of the device is exactly the same as the positive-positive method described above, except for the following. That is, when a negative/positive type signal is outputted by a positive/negative changeover switch (not shown in the drawing), the following occurs. 1 The positive/negative switching mirror 29 is set at the ○ and ○ positions, and the reflected light from the original 25 does not go to the recharging corona discharger 8 (positive (+) polarity corona discharge is performed in the dark). .) Insulating layer 3 reflected by mirror 30 and located between primary charging corona discharger 4 and recharging corona discharger 8
guided to the surface of 2 The tungsten lamp 31 is turned off. The above points are different from the described positive-positive method. The principle diagram of this negative/positive method is shown in Figure 15A.
Shown in B. As can be seen from this figure, charged colored particles, which are positively charged (+) due to the electric field caused by the surface potential V _L , are attached to L in the area corresponding to the original reflected light, that is, the white background area, and on the other hand, the dark area Since D has a positive surface potential V _D , there is virtually no adhesion and a positive visible powder image is formed from the negative original. The above explanation was based on an example in which positively (+) charged colored particles are used, but when negatively (-) charged colored particles are used in the same device (in this case, reversal development is generally used). ) In FIGS. 15A and 16A, negatively (-) charged colored particles adhere to areas where positively (+) charged colored particles did not adhere, resulting in the positive coloring of the previous example.
By simply changing the positive mode to negative/positive and the negative/positive mode to positive/positive, it is possible to selectively switch between both modes with one device. Further, in the above embodiment, one example was explained as a copying machine, but if the parts of the document table 25, document 24 and illumination system 26 in FIG. It can be a flexible microfilm enlarger. Furthermore, the present invention is also applicable to a laser beam printer device that uses a laser beam instead of the above-mentioned optical image irradiation light and modulates the intensity of the laser beam according to information to perform spot exposure on a photosensitive plate. It is possible. Although the embodiments have been described above, according to the present invention, the yin and yang of the latent image can be selectively switched depending on the desired original, and a single device can satisfy multiple purposes.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the structure of a photosensitive plate that can be applied to the present invention, and FIGS. 2 to 5 show the composition of the photosensitive plate shown in FIG. An explanatory diagram showing the process of forming a latent image, Figure 6 is the second
Figures 7 and 8 are graphs schematically showing changes in the surface potential of the photosensitive plate during the processes shown in Figures 5 to 5, Figures 7 and 8 are diagrams showing the development process of the latent image, and Figure 9 is a diagram showing the process of developing the latent image. Diagrams showing the transfer process of a visual image, Figures 10a, b,
c, d to FIGS. 13a, b, c, and d are explanatory diagrams showing the original patterns of the first and second light images and a composite microscopic image. FIG. 14 is an embodiment of the electrophotographic apparatus according to the present invention. 15A and 16A are explanatory diagrams showing the process of forming negative/positive images and positive/positive images by the embodiment apparatus, and FIGS. 15B and 16B are diagrams showing the process of forming negative/positive images and positive/positive images. FIG. 2 is a graph schematically showing changes in surface potential of a photosensitive plate. 1... Conductive support, 2... Photoconductive layer, 3...
Insulating layer, A... Photosensitive plate, 4... Charge imparting means, 8
...Reverse polarity charging means, 23...Full surface exposure means, 2
9... Means for switching light image irradiation, 31... Uniform light irradiation means.

Claims (1)

[Scope of Claims] 1. A movable photosensitive plate whose basic constituents are a conductive support, a photoconductive layer, and an insulating layer; the surface of the insulating layer of this movable photosensitive plate is charged, and thereby the conductive support charge applying means for inducing a charge having a polarity opposite to that on the surface of the insulating layer at or near the interface between the photoconductive layer and the photoconductive layer; is a charging means that charges to opposite polarity; in a first mode, the photosensitive plate is irradiated with image light at a position between the operating position of the charge applying means and the operating position of the charging means; and in a second mode, the charging means image light irradiation means that switches the image light irradiation position in accordance with the selected mode so as to irradiate the photosensitive plate with the image light at the action position; a first exposing means for uniformly exposing the entire surface of the photosensitive plate at a position between the operating position of the charge applying means and the operating position of the charging means; a second exposure means that uniformly exposes the entire surface of the photosensitive plate after the photosensitive plate is exposed; and a second exposure means that uniformly exposes the entire surface of the photosensitive plate; An electrophotographic apparatus comprising: a developing means for developing;