JPS6144312B2 - - 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. Known electrophotographic methods include the electrofax method, the Xerox method, the PIP method, and the NP method (for example, Japanese Patent Publication No. 42-23910, etc.). 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 photosensitive plate is uniformly charged by corona discharge, and then an original image is irradiated to attenuate the charge in the light-irradiated area.
An electrostatic image that follows the light and dark pattern of the original image is developed with charged colored particles to make it visible, and then fixed or transferred onto a support such as another paper and then fixed to obtain an electrophotographic image. In addition, the PIP method uses the physical properties of fluorescent substances, such as persistent internal polarization and photoconductivity, to form a latent image.
The NP method uses the capacitance difference and photoconductivity between the photoconductor layer and the insulating layer used above to form an electrostatic image, and then goes through the same development, transfer, and fixing steps to create an electrophotographic image. It's something you get. 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. If you try to achieve such a positive/positive and negative/positive device with one machine, you will have to change the charging polarity between positive/positive and negative/positive, or 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 these 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 according to the present invention, in which 1 is a conductive support, and 2 is a photosensitive plate that is coated on the conductive support 1 by, for example, spraying or using a coater, a faller, etc. If necessary, a small amount of a binder, mainly a resin, may be added to the photoconductive layer coated with the photoconductive layer to improve bonding with other layers. Reference numeral 3 denotes an insulating layer that is uniformly formed in close contact with the photoconductive layer 2 . In this way, the photosensitive plate A basically consists of a conductive support 1, a photoconductive layer 2 and an insulating layer 3.
A control layer that restricts the movement of charges is formed between the conductive support and the photoconductive layer, and a control layer is formed between the conductive support and the photoconductive layer, and the layer is formed on or near the surface of the photoconductive layer. A layer or the like for trapping charges may be added to the layer. Further, 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 a convenient thing to use. Material of photoconductive layer is CdS, CdSe, crystalline
Se, ZnS, ZnO, TiO ₂ , SeTe, PbO, or a mixture thereof can be used. Some 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 when charged in the dark. In the embodiment, if having such a property causes an unfavorable effect on the charge distribution due to the first light image irradiation performed almost simultaneously with the primary charging, such a dark place as the primary charging polarity may be used. It shall be charged with a polarity that does not cause charge injection. 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 either polarity. The material constituting the insulating layer 3 may be any material that satisfies the following three requirements: high abrasion resistance, high resistance and ability to retain static charge, and transparency, and may include fluororesin, polycarbonate resin, polyethylene resin, Films such as cellulose acetate resin and polyester resin can be used, and fluororesin in particular has the property of being easy to clean, so after development and transfer, the photosensitive plate is repeatedly coated through a cleaning process by sliding contact with an elastic body, etc., as described below. It is a preferred material for use in embodiments of the invention. FIGS. 2 to 4 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. Although the following figures up to Figure 12, including these Figures 2 through 4, are not embodiments of the present invention, they are explained to help understand the embodiments of the present invention that will be described later. In FIG. 2, first, the surface of the insulating layer 3 of the photosensitive plate A is charged, for example, negatively (-) by the initial charging corona discharger 4, and at the same time, a first light image is irradiated. At this time, since the photoconductive layer 2 has high resistance in a dark place, the interface with the photoconductive layer 2 of the conductive support 1 or the portion of the photoconductive layer 2 close to the conductive support 1 has a positive (+ ) is induced. In addition, in the bright area, the photoconductive layer 2 becomes conductive due to light stimulation, so positive (+) charges are injected from the conductive support 1 and are attracted to the (-) charges on the surface of the insulating layer, causing the photoconductive layer 2 to become conductive. It stops at the interface of the insulating layer 3. (FIG. 2) Through this process, the surface potential of the insulating layer 3 increases negatively (-) with the charging time, and exhibits the characteristics shown in FIG. 5 Vp. Next, a corona discharge having a polarity opposite to the charging polarity, that is, positive (+), is applied to the surface of the insulating layer 3 by a corona discharger 8 almost simultaneously with the second light image irradiation. Since the corona discharger 4 for primary charging and the corona discharger 8 for reverse polarity irradiation are carried out almost simultaneously with the light image irradiation, it is preferable that their upper parts are transparent or have an optically open structure without a shield plate. Negative (-) charge 31 that was charged on the surface of the insulating layer 3 in the dark area during the first light image irradiation
is neutralized by the positive (+) charge that has been recharged with the reverse polarity, and the surface of the insulating layer 3 at that portion is further charged with the 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 becomes positive due to recharging. It is neutralized by the (+) charge and is further charged to the recharge polarity (+). In this case, the resistance of the photoconductive coating 2 decreases due to light irradiation and becomes conductive, and the positive (+) charge 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 the positive (+) charge, the degree of polarity charging due to recharging is small. This means that the positive (+) charge of the charged layer formed at the interface between the photoconductive coating 2 and the insulating coating 3 due to the first light image irradiation after primary charging is transferred to the surface of the photoconductive coating. Due to the presence of the blocking layer and the high resistance of the photosensitive coating, it remains unreleased even when recharging is performed, so the extent to which the insulating coating surface 3 is charged to the recharging polarity due to this field of charges is limited. It seems that it will become smaller. (FIG. 3) Next, the photosensitive plate on which the electrostatic image as described above is formed is uniformly exposed to light from the insulating coating surface. 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. Charged negative (-)
It maintains a stable state with a charge of , does not decay 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 there was no light irradiation in the step, but the photoconductive film showed high resistance because it was exposed to light in this step. The value drops rapidly and becomes conductive. Therefore, in the step described above, the positive (+) charges remaining 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. 4) Changes in the surface potential of the insulating layer 3 due to these steps 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. 6 shows the case where development is performed with a toner having a polarity opposite to the primary charge polarity, that is, a positive polarity, and the toner adheres to the bright areas when the first light image is irradiated and the dark areas when the second light image is irradiated. do. Figure 7 shows reversal development, that is, development with a toner having the same negative polarity as the above-mentioned primary charging polarity. do. In this case, it is well known that better development can be achieved if a developing electrode is used. 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 10, 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 subjected to an alternating current corona discharge to eliminate the charge caused by the electrostatic image formation, and then cleaning may be performed 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. The effectiveness of this cleaning also depends on the properties and tackiness of the material of the insulating coating, so all of the resins mentioned above are suitable as electrostatic image forming materials, but fluororesin coatings are particularly suitable for use as electrostatic image forming materials. It is the most effective in that it has excellent adhesiveness, assists in the detachment 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 surface potential difference between the V _DD V _DL V _LL . be. In order to satisfy these requirements, (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., must be appropriately set. is necessary. Next, a quantitative explanation of an example of the synthetic image forming method 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 +6.5 kV corona discharge is applied to the surface of the insulating layer of the photosensitive plate, and a first light image (bright area is about 12 lux, light intensity for 0.3 seconds) is irradiated almost simultaneously. Thereafter, a second light image having the same amount of light as the first light image is irradiated almost simultaneously with recharging by -6 kV corona discharge. Furthermore, the entire surface is coated with approximately 12 Lux.
Form an electrostatic image by uniformly exposing for 0.8 seconds. When the surface potential during this electrostatic image formation process was measured using a surface potentiometer, the portion corresponding to Vp in Figure 5 was -1400V, V _LD
The surface potential difference between the corresponding part and the V _LL and V _DL equivalent parts is approximately
350V was obtained. The above explanation relates to _the formation of a composite image, but in terms of _the present _invention in _FIG . This was done by focusing on the fact that the order in which the potentials rise and fall and the latter order in which the potentials rise and fall are reversed. FIG. 13 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 drawings), and the recharging corona discharger 8 is a positive (+) polarity high voltage power source (not shown in the drawings). (not connected). 33 is a developer which is a mixture of a carrier (for example, iron powder) and charged colored particles (toner), or a one-component developer, and the toner is set to have a positive (+) polar charge. First, a case will be described in which this apparatus is used to obtain a positive copy from a positive original using the positive-positive method. 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, passes through the imaging lens 13, and reaches 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 positive/negative switching mirror 2
Tungsten lamp 31 that turns on (in the case of A) and turns off (in the case of B) in conjunction with the positions A and B of 9.
works. 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. Prior to this, the photosensitive plate A was exposed to the tungsten lamp 3.
1, the surface of the insulating layer 3 is exposed to light, and at the same time, the primary charging corona discharger 4 charges the insulating layer 3 negatively (-). Next, the photosensitive plate is irradiated with the above-described original reflected light from the surface of the insulating layer 3 through the recharging corona discharger 8, and at the same time, a corona discharge of positive (+) polarity is applied by the recharging corona discharger 8, and then a tungsten lamp is used. 23, the entire surface of the insulating layer 3 is uniformly exposed to light to form an electrostatic image on the surface of the insulating layer 3 in accordance with the light and dark 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. 14A is an explanatory diagram showing the charge pattern at each step until a visible image is formed when the positive-positive process is selected in this way, and the change in surface potential at each step is the 14th 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. The charged colored particles do not adhere to the portion L corresponding to the bright area because the surface potential V _L thereof is negative, and therefore a positive visible powder image can be formed from the positive original. Next, this visible powder image is transferred to the feed roller 16
Transfer material 11 that comes into contact with the visible powder image due to
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 is performed, the photosensitive plate A is charged with residual electrostatic image forming charges remaining on the insulating layer surface 3 by an AC corona discharger 20, 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 this apparatus is used to obtain a negative-positive copy, that is, a positive copy 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 system signal is outputted by a positive/negative changeover switch (not shown in the drawing), the following occurs. 1 The positive/screw switching mirror 29 is set at the position B, and the reflected light from the original 25 does not go to the reverse polarity charging corona discharger 8 (reverse polarity charging corona discharge is performed in the dark). Corona discharger 4 for primary charging reflected by 30
guided to the department. 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 you can see from this figure, the location L corresponds to the part with the original reflected light, that is, the white part.
becomes positive (+) due to the electric field due to its surface potential V _L
The charged color particles adhere to the dark area D, but do not adhere to the dark area D because its surface potential V _D is negative, and a positive visible powder image is finally formed from the negative original. The above example uses charged colored particles that are positively (+) charged, but in the same device, negatively (-)
(In this case, it is generally called reversal development.) In the case of using charged colored particles charged to Since the negatively charged colored particles are attached to the surface, the positive/positive mode in the above example can be changed to negative/positive, and the negative/positive mode can be changed to positive/positive, and both modes can be selected with one device. It is possible to switch the Further, in the above embodiment, one example was explained as a copying machine, but the document table 25, document 24 and illumination system 2 shown in FIG.
If the part 6 is an illumination system that uses a microfilm as an original, a microfilm enlarger that can freely switch between positive and negative and positive and negative can be obtained. Furthermore, a laser beam is used instead of the above-mentioned optical image irradiation light, and the intensity of the laser beam is modulated according to the information to perform spot exposure on the photosensitive plate.
The present invention is also applicable to beam printer devices. Although the embodiments have been described in detail above, the present invention has the effect of enabling a simple, compact, and low-cost image forming apparatus such as a Yin/Yang switching copying machine, a microfilm enlarger, and a laser beam printer.

[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 4 show the photosensitive plate shown in FIG. 1 irradiated with first and second light images, and their synthesis An explanatory diagram showing the process of forming a latent image, Figure 5 is the second
Figures 6 and 7 are diagrams showing the development process of the latent image, and Figure 8 is a graph schematically showing changes in the surface potential of the photosensitive plate during the processes shown in Figures 4 to 4. Diagrams showing the transfer process of a visual image, Figures 9a, b,
c, d to FIGS. 12a, b, c, and d are explanatory diagrams showing the original patterns of the first and second images and a composite microscopic image. FIG. 13 is an embodiment of the electrophotographic apparatus according to the present invention. 14A and 15A are explanatory diagrams showing the process of forming positive-positive images and negative-positive images by the embodiment apparatus, and FIGS. 14B and 15B are schematic diagrams of FIGS.
is a graph schematically showing changes in the surface potential of the photosensitive plate during these processes. 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; a surface of the insulating layer of the movable photosensitive plate is electrically charged; charge imparting means for inducing charges of opposite polarity to the charges on the surface of the insulating layer at or near the interface between the conductive support and the photoconductive layer; a charging means for applying a charge with a polarity opposite to that of the charge applying means; in a first mode, the photosensitive plate is irradiated with image light at the operating position of the charge applying means; in a second mode, the photosensitive plate is at the operating position of the charging means; image light irradiation means that switches the image light irradiation position according to the selected mode so as to irradiate the image light on the image light; a first exposure means that uniformly exposes the entire surface of the photosensitive plate at a position; and a second exposure means that uniformly exposes the entire surface of the photosensitive plate after being acted on by the charging means in either the first mode or the second mode. An electrophotographic apparatus comprising: a developing means for developing the electrostatic image formed on the photosensitive plate using toner charged to the same polarity in both the first mode and the second mode.