JPS6336340Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a transfer assisting device used in an electrophotographic device.

(Prior art) In order to transfer the serographic image developed on the photoreceptor onto a recording medium such as paper using electrostatic attraction, it is necessary to overcome the potential of the latent image area that electrostatically attracts the toner. It is necessary to move this onto the recording medium. Therefore, this can be achieved by weakening the bond between the toner and the latent image area, by further strengthening the bond between the charged recording medium and the toner, or by performing these processes simultaneously.The former is particularly important. Many proposals have been made so far regarding the pre-transfer process.

One method is to reduce the latent image potential (surface potential of the photoconductor) in the dark area (toner adhering area) by applying a DC corona with a polarity opposite to that of the photoconductor on the upper side of the transfer area. In addition, the toner attached here is further charged (U.S. Patent No.
2959153), the surface potential of the photoreceptor changes as shown in FIG. 1 by eliminating the charge before transfer. In other words, if the static elimination effect is weak, the potential in the dark area remains without dropping sufficiently (see figure 2).
The transfer efficiency does not improve much, and when the static elimination effect is strong, the potential in the dark area drops to nearly 0, while the potential in the bright area greatly swings to the opposite polarity, resulting in significant background staining as described below.

On the other hand, the static elimination method disclosed in Japanese Patent Publication No. 45-26480 is for separating transfer paper, and an AC corona with an eccentric DC voltage is applied to a photoreceptor in front of a transfer corona. This method eliminates the edge effect between the dark and bright areas and weakens the attraction between the photoreceptor and the transfer paper. Although the potential difference can be made considerably smaller, there is a risk that the charge on the toner will also be reduced at the same time.

In addition, another method that has been put into practical use is the method of removing latent image charges in dark areas by irradiating light.
As shown in the figure, although there is a slight difference depending on the strength of the irradiated light, it has the advantage of almost eliminating the potential difference between dark and bright areas, but on the other hand, it has no effect of increasing the charge on the toner. I don't have it.

(Problem to be solved by the invention) The invention was created in view of the above problem, and its purpose is to eliminate the potential difference between bright and dark areas and to lower these potentials to almost zero. Another object of the present invention is to provide a new transfer auxiliary device that can sufficiently increase the charge of toner and greatly improve transfer efficiency.

(Means for Solving the Problems) That is, the present invention provides a device for achieving the above-mentioned problems, which includes a charging means having a discharge characteristic of the same polarity as the toner, on the upper side of the transfer unit in the direction of movement of the photoreceptor; This device is equipped with a charging exposure device consisting of an exposure device that simultaneously irradiates the areas charged by this charging device.This makes the photoconductive layer conductive and reduces the potential of the bright and dark areas to near zero. On the other hand, by performing corona discharge under this condition, erasing the charge on the photoreceptor becomes unnecessary and the charge is efficiently applied to the toner, thereby greatly improving transfer efficiency without causing background stains. It was made so that it could be done.

(Example) Therefore, an example of the present invention will be described below.

Figure 4 shows an embodiment of the present invention.
2 is a conductive substrate, 2 is a photoconductive layer with positive charging polarity, 3 is a transfer charger that charges the transfer paper p to positive polarity, 4 is a separation claw, 5 is a conveyor belt, and other The illustration of the image forming process unit is omitted.

Therefore, the transfer auxiliary device that forms the main part of the present invention is the charging exposure device 6 disposed in front of the transfer charger 3.
This embodiment consists of a corona wire 6a connected to a negative polarity DC power source (not shown) and a light source 6b, and is configured to simultaneously charge and expose the same portion of the photoconductive layer 2.

Next, the operation of this embodiment will be explained. On the surface of the photoconductive layer 2, which is uniformly positively charged by a charger (not shown), a latent image corresponding to the optical image pattern is formed by exposure. The toner is developed with negatively charged toner in a developing device and is then acted upon by a charging exposure device 6 disposed on the upper side of the transfer unit.

FIG. 5 shows how the surface potential a of the photoreceptor before processing decreases depending on the intensity of the irradiated light from the charging exposure device 6 and the corona voltage.

b is a case where the irradiation light intensity is low and the corona voltage is low; because the light is weak, the potential difference between the dark and bright areas is small, as in the case where static electricity is removed only by corona discharge, but the potential in the dark areas drops sufficiently. There will be nothing left.

c is a case where the irradiation light intensity is high and the corona voltage is low; the light is strong and enough carriers are generated to make the photoconductive layer 2 conductive, so all surface charges escape and the potentials of the dark and bright areas are reduced. becomes almost 0.

d is a case where both the irradiation light intensity and the corona voltage are strong, and the potential in the dark and bright areas becomes almost 0, but at the same time a strong corona voltage is applied there, so the surface potential of the photoconductive layer moves to the opposite polarity side. shift.

e is a case where the irradiation light intensity is low and the corona voltage is high; in this case, in the dark area, the static elimination effect by light is not sufficiently performed because it is blocked by the toner covering the surface of the photoconductive layer; When a strong corona voltage with the same polarity as the charging characteristics of the toner is applied, the newly added charge is removed because the bright areas become conductive, but the dark areas are not sufficiently conductive. Therefore, the charge remains without being completely removed, and as a result, the potential in the dark area moves to the opposite polarity side, resulting in an inverted state.

In other words, the negatively charged toner is further charged by this pre-transfer charging exposure, and the surface potential of the photoconductive layer is greatly reduced, but when the irradiation light intensity is low and the corona voltage is low as shown in Figure 5b, for,
Since the potential of the dark area that attracts the toner does not become zero and remains, the transfer efficiency does not improve much, and if the corona voltages are both strong as shown in d and e of the same figure, the photoconductive layer 2 Since the surface potential shifts to the opposite polarity side, that is, to the same polarity as the charged polarity of the toner, it works to actively move the toner toward the transfer paper during transfer, improving transfer efficiency. Since the potential tends to shift to the opposite polarity side, toner tends to move easily in this area, causing background stains.

Therefore, taking the above points into consideration, if the irradiation light intensity is strong and the corona voltage is kept low, as in the case of Figure 5c, the potential difference between the bright and dark areas will disappear, and the surface potential of the photoreceptor will also decrease. Since it can be made almost 0, it is possible to make the photoconductive layer 2 conductive and efficiently charge the toner, without causing background stains, and to sufficiently increase the transfer efficiency.

[Example] 15
Light from a tungsten lamp with strong lux is irradiated through an aperture with a width of 20 mm, and under this condition, the corona discharge voltage of the same polarity as the toner is sequentially changed from 5 KV to 7 KV, and the conditions shown in Figure 5 c are obtained. In other words, when we conducted an experiment under the conditions of "higher irradiation light intensity and lower corona voltage," the amount of charge on the toner increased as the corona discharge voltage increased (Figure 6).
Along with this, it was found that the higher the corona discharge voltage, the better the transfer rate (FIG. 7).

It was also found that when the corona discharge voltage was further increased to exceed the range shown in Figure 5c, the surface potential of the photoreceptor shifted to the same polarity as the toner, and the background stain suddenly became severe. Ta.

Note that the above example uses DC discharge as the power source for the charging exposure device, but the
The above-mentioned method also uses charging means as seen in Publication No. 26480, in which alternating current is superimposed on direct current having the same polarity as the toner, or in other words, alternating current biased toward the same polarity as the toner. The same effects as in the embodiment can be achieved.

[Comparative Example] As described above, the present invention is capable of reducing charging before transfer,
It is characterized by the fact that the exposure process is performed at the same time, and the advantage of this is that the process before transfer is performed in the order of "charging and exposure" and the process in which it is performed in the order of "exposure and charging". This becomes clear by comparing the two.

In other words, in the former method, which is performed in the order of charging and exposure, it is possible to reduce the potential of both bright and dark areas to near zero, but on the other hand, the corona discharge before exposure mostly erases the charge on the photoreceptor. Since the toner is used up, the charge efficiency to the toner is low, and the transfer efficiency cannot be improved much.In addition, in the latter method, which is performed in the "exposure and charging order", the surface potential is reduced to zero by exposure.
Since the photoconductive layer is charged with the same polarity as the toner, the surface of the photoconductive layer is uniformly charged with the same polarity as the toner.As a result, the transfer efficiency is high, but at the same time, the background stain is extremely large. Become. On the other hand, in the present invention, which employs a "simultaneous charging and exposure" method, the photoconductive layer is brought into a conductive state and the potentials in the bright and dark areas are lowered to near zero, while corona discharge occurs under this condition. Therefore, there is no erasure due to the charge on the photoconductor, and the charge is applied to the toner more efficiently.
It becomes possible to greatly improve transfer efficiency without causing background stains.

(Effects) As described above, according to the present invention, a charging exposure device that performs charging and exposure at the same time is provided on the upper side of the transfer section of a transfer type electrophotographic device, so bright and dark areas can be differentiated by exposure light irradiation. At the same time as lowering the surface potential to nearly 0, this potential difference is eliminated to uniformly eliminate the electrostatic toner adsorption force, and the photoconductive layer is made conductive to reduce the charge on the toner attached thereto. By making the application more efficient, transfer efficiency can be greatly improved without causing background stains.

[Brief explanation of drawings]

1 to 3 are diagrams showing changes in the surface potential of a photoreceptor due to the conventional transfer pretreatment method, FIG. 4 is a schematic diagram of the configuration of an apparatus showing an embodiment of the present invention, and FIG. 5 6 is a diagram showing the change in the photoreceptor surface potential due to pre-transfer treatment using the same device as above, and FIG. 6 is a diagram showing the relationship between the pre-transfer charging voltage and the toner charge amount.
FIG. 7 is a diagram showing the pre-transfer charging voltage and the transfer rate. DESCRIPTION OF SYMBOLS 1... Conductive substrate, 2... Photoconductive layer, 3... Transfer charger, 6... Charging exposure device, 6a... Corona wire, 6
b...Light source.

Claims (1)

[Scope of utility model registration request] In an electrophotographic apparatus equipped with image forming process units for charging, exposure, development, and transfer, a charging means having a discharge characteristic of the same polarity as the toner polarity is provided on the upper side of the transfer unit in the direction of movement of the photoreceptor; 1. A transfer auxiliary device for electrophotography, comprising a charging exposure device comprising an exposure device that simultaneously irradiates a portion charged by the device.