JP2691987B2 - Multicolor electrophotographic equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor electrophotographic apparatus that obtains a multicolor recorded image by using a laser beam printer or the like by utilizing an electrophotographic process, and particularly charging, exposure and development. After repeating each step of multiple times to form a visible image of a plurality of colors on the latent image carrier,
The present invention relates to a multicolor electrophotographic device capable of multicolor printing by transferring onto a recording material. 2. Description of the Related Art Printers using the electrophotographic method have been widely used as output devices for computers, facsimiles, CAD, etc. so far. These devices form image information as a latent image on an electrostatic latent image carrier by laser, LED, LCD, etc., visualize it by a developing device, and then transfer the visible image onto a recording material, A recorded image is obtained by the fixing step, but in the conventional printer, the recorded image was only one color, for example, black. However, recently, for example, because the recorded image becomes clearer and the information is easier to understand, for example, the color of the format is different from the color of the calculated value or the value of the data, or it is output by CAD. It is desired to obtain a recorded image by distinguishing between two or more colors, such as outputting a part of the drawn drawings in many colors. As an example of the electrophotographic apparatus capable of such multicolor recording, an image forming process by an image forming apparatus as shown in FIG. 2 is known (Japanese Patent Laid-Open No. 52-106743).
Reference). In this image forming process, for example, the surface of the photosensitive drum 1, which is a latent image carrier, is uniformly charged by the first charger 2 and is irradiated with the laser light 3 modulated according to the first image information. As a result, an electrostatic latent image is formed, and thereafter, the electrostatic latent image is developed by the first developing device 4 with the toner of the first color and visualized. Then
The recharging device 5 sets the first image portion potential and the non-image portion potential to level. Up, that is, hold it,
After that, the laser beam 6 modulated according to the second image information is irradiated, and a second-color electrostatic latent image to be developed is formed. This electrostatic latent image is visualized by developing the electrostatic latent image with the second color toner by the second developing device 7. The two color toner images formed on the photoconductor drum 1 as described above are transferred onto the recording material P supplied by the transfer charger 8. The recording material P is separated from the photosensitive drum 1 by the separation charge eliminator 9 and conveyed to a fixing device (not shown).
The toner image is fixed. The residual toner on the photosensitive drum 1 is scraped off by the cleaner 10, and the same image forming process is repeated again. FIG. 3 shows the transition of the surface potential on the photosensitive drum 1 in the above-mentioned image forming process, and FIG. 3 shows the transition of the surface potential on the photosensitive drum 1 in this image forming process. First, first
A first dark portion potential Vd1 and a first exposed portion potential Vl1 are formed by the charger 2 and the image exposure laser light 3 (FIG. 3 (a)). Then, the first developing unit 4 causes the first exposed portion potential.
The toner image of the first color is developed on Vl1. At this time, due to the charge of the toner layer, the potential of the developing portion, that is, the image portion rises to some extent and becomes the first image portion potential Vl1t (FIG. 3 (b)).
Next, the photoconductor drum 1 that has been recharged by the recharger 5
The upper potentials are Vd1 and Vl1, Vl1 and Vl2.
t increases to Vd2l and Vd2lt, respectively (Fig. 3 (c)).
Thereafter, the second image exposure laser 6 is irradiated to form the second exposure portion potential V12 (FIG. 3 (d)), and the toner image of the second color is developed on the exposure portion. . As a result, the first toner image potential Vd2lt can be made sufficiently higher than the second exposure portion potential Vl2,
The developing bias Vdc2 of the second developing device can be set lower than Vd2lt, and the color mixing phenomenon in which the second color toner adheres to the first toner image can be prevented. However, as in the conventional example described above, if the recharging device is simply provided, the dark area potential Vd2 and the first portion after the recharging are reduced.
Since the difference in the toner image potential Vd2lt cannot be sufficiently reduced, the following problems occur. That is, (1) it is necessary to set the developing bias Vdc2 of the second developing device in order to prevent the toner of the second color from adhering to the portion of the first toner image potential Vd2lt. Since the contrast with the dark part potential Vd2 is large, inversion fog is likely to occur. (2) For the same reason as (1), the fog toner of the first color is more likely to be mixed into the second developing device (the toner of the first color on Vd2). In order to prevent such a phenomenon, it has been proposed to eliminate the difference between the potential of the first toner image and the potential of the dark portion after recharging so that the potential is substantially the same. For example, JP-A-58-116553 suggests to use a scorotron with a grid, and JP-A-60-17464 and U.S. Pat. No. 4,647,181 show recharging. It has been proposed to use AC corona charging. However, according to a study by the present inventor, it is disclosed in Japanese Patent Laid-Open No. 58-116553.
Only using a scorotron with a grid as shown in Japanese Patent Publication is not sufficient to reduce the difference between the first toner image potential Vd2lt and the dark portion potential Vd2 after recharging. In the method of using AC corona charging for recharging as shown in JP-A-60-17464 and US Pat. No. 4,647,181, the difference between the first toner image potential Vd2lt and the dark portion potential Vd2 after recharging is calculated. Although it is effective to shrink, the cost of the high voltage transformer becomes high because of using AC corona,
Further, since the amount of corona products is large, there is a disadvantage that the photosensitive drum is easily deteriorated. Further, since the recharging device performs corona charging with the toner image of the first color on the photosensitive drum, the recharging device is contaminated with the toner of the first color, and the first color of the recharging device is corona-discharged. There is also a problem that the toner image is disturbed. Even with respect to these problems, a sufficient solution cannot be obtained by the technical disclosure disclosed in the above-mentioned publication and US patent, and further improvement is required. The present invention has been made in view of the above viewpoints. Therefore, an object of the present invention is to reduce the difference between the non-image area potential and the first toner image area potential after recharging when forming a multicolored recording image. , A multicolor electrophotography capable of preventing reversal fog of the second color toner, preventing the first color toner from mixing into the second developing device, and preventing deterioration of the photosensitive drum due to corona products with a simple structure. It is to provide a device. Another object of the present invention is to form a multicolor recorded image,
The difference between the potential of the non-image portion and the potential of the first toner image portion after recharging can be reduced, the contamination phenomenon due to the toner of the first color of the recharging device can be prevented, and the corona discharge from the recharging device can prevent An object of the present invention is to provide a multicolor electrophotographic apparatus capable of preventing the image disturbance phenomenon of the first color toner. Means for Solving the Problems The above object is achieved by the multicolor electrophotographic apparatus according to the present invention. In summary, the present invention is a multicolor electrophotographic method in which a visible image of a plurality of colors is formed on a latent image bearing member by repeating the steps of charging, exposing and developing a plurality of times, and then the developed image is transferred onto a recording material. In the apparatus, at least after the second charging, a corona charging method having a grid to which a self-bias is applied is used, and the corona discharge opening width L of the corona charger is L / V> with respect to the image forming speed V. It is a multicolor electrophotographic apparatus characterized by satisfying a relationship of 0.1. Furthermore, preferably in the multicolor electrophotographic apparatus of the present invention,
The distance between the grid and the latent image carrier is 0.8 mm or more. Further, in the multicolor electrophotographic apparatus of the present invention, the distance between the grid and the latent image carrier is larger in the upstream side in the rotation direction of the latent image carrier than in the central portion of the charger. Is more desirable. This makes it possible to reduce the difference between the potential of the non-image portion and the potential of the first toner image portion after the recharging, and the reversal fog of the second color toner to the second developing device can be achieved with a simple configuration. It is possible to prevent deterioration of the photosensitive drum due to the mixing of the first color toner and the corona product. Furthermore, it is possible to prevent the phenomenon that the recharging device is contaminated by the first color toner and that the image of the first color toner is disturbed due to corona discharge from the recharging device. EXAMPLES Hereinafter, the present invention will be described based on the examples with reference to the accompanying drawings. FIG. 1 shows an embodiment of a multicolor electrophotographic apparatus according to the present invention. Referring to FIG. 1, a multicolor image is formed around a photosensitive drum 11 serving as a latent image carrier. Predetermined various devices necessary for carrying out, for example, first charger 12, first laser light source 13, first developing device 14, recharging device 15, second laser light source 16, second developing device 17, transfer A charger 18, a separation charge eliminator 19 and a cleaner 20 are arranged respectively, and a predetermined process, that is, the first charger 12 uniformly charges the surface of the drum 11 of the photoconductor, according to the first image information. Irradiation with the modulated laser beam 13a forms an electrostatic latent image, and then the first developing device 14 develops the electrostatic latent image with the toner of the first color. The image part potential and the non-image part potential of No. 1 are lifted respectively, and then according to the second image information. Is irradiated with the modulated laser beam 16a to form an electrostatic latent image of the second color, and the electrostatic latent image is developed with the toner of the second color by the second developing device 17, and is thus exposed. The two-color toner images formed on the body drum 11 are transferred onto the recording material P by the transfer charger 18, and the recording material P is separated from the photosensitive drum 11 by the separation charge eliminator 19 and fixed ( (Not shown),
The toner image is fixed. The residual toner on the photosensitive drum 11 is scraped off by the cleaner 20, and the same image forming process is repeated again. Here, regarding the process of recharging the photosensitive drum 11 by the recharging device 15 according to the present invention, referring to FIG.
This will be described in more detail. FIG. 1a is a partially enlarged sectional view of the recharging device and the photosensitive drum according to the present invention. As shown in FIG. 1a, it is arranged around the photosensitive drum 11. The recharging device 15 is provided with a grid 15a which is slightly separated from the surface of the photosensitive drum. This grid 15a is a resistor 15
b, grounded via constant voltage element 15c, etc., recharger
When the corona discharge is performed from 15, the self-bias is applied. At this time, a bias voltage Vg may be applied to the grid 15a by a DC power supply. In order to reduce the difference between the dark portion potential Vd2 (non-image portion potential) after the recharging and the first toner image potential Vd2lt in such a configuration, the inventors of the present invention have earnestly studied, and as a result, In order to reduce the above-mentioned difference between the dark portion potential Vd2 and the first toner image potential Vd2lt, the corona discharge opening width L of the recharger is set.
And that the relationship between the image formation speed V and
Various experiments were conducted. The effect will be described below based on the experimental results. Experiment 1 An image forming speed of 200 mm / sec, an organic photoconductor (hereinafter referred to as OPC) was used as the photoconductor drum 11, the dark potential Vd1 by the first charging by the first charger 12 was −600 V, and the laser beam 13a.
The light potential Vl1 due to the image exposure of was set to -100V. Next, as the recharger 15, with the opening width L as a parameter, the grid 15a is provided with a tungsten wire having a wire diameter of 100 μm at intervals of 2 mm, and the distance at which the grid 15a is separated from the surface of the photosensitive drum is 1.0 mm. Also, the dark area potential V after recharging
The bias value of the grid 15a was adjusted so that d2 was −700 V, and the value of ΔV = | Vd2-Vd2l | was obtained as ΔV to confirm the potential convergence of the recharger 15a. At this time, the value of the corona current flowing through the recharging device 15 was -300 μA so that the amount of corona products did not become too large. As a result, the following Table 1 was obtained. According to experiments and studies conducted by the present inventors, if the difference ΔV between the first exposed portion potential Vd2l and the dark portion potential Vd2 after recharging is 50 V or less, the toner layer is actually present in that portion. There is almost no difference between the first exposure portion potential Vd2l and the dark portion potential Vd2, reversal fog of the second developing device and mixing of the first toner into the second developing device do not occur, and it is possible to always obtain a good image. Become. Therefore, it can be seen from Table 1 of the above experimental results that the opening width L of the recharger 15 should be 20.0 mm or more. Experiment 2 The image forming speed was 200 mm / sec, OPC was used as the photoconductor drum 11, dark area potential Vd1 was set to −600 V, and light area potential Vl1 was set to −100 V as in Experiment 1, and the grid 15a had a wire diameter of 1 mm. A 100 μm tungsten wire was attached and the other conditions were the same as in Experiment 1, and the experiment was conducted. As a result, the following Table 2 was obtained. As can be seen from the above experimental results, the potential convergence of the recharging device 15 is slightly improved by narrowing the gap between the grids 15a, but it is clear that the opening width L is also required to be 20.0 mm or more. Experiment 3 Image forming speed was 320 mm / sec, and other conditions were Experiment 1
An experiment was conducted in exactly the same manner as above, and as a result, the following Table 3 was obtained. As can be seen from the above experimental results, the opening width L of the recharger 15 must be 34.4 mm or more. Experiment 4 The experiment was conducted under the same conditions as Experiment 3 except that the distance between the grid 15a and the surface of the photosensitive drum was 1.5 mm, and as a result, the following Table 4 was obtained. As can be seen from the above experimental results, the potential convergence of the recharging device 15 is slightly deteriorated by increasing the distance between the grid 15a and the surface of the photoconductor drum, but the opening width L of the recharging device 15 is 34.0 mm. It is understood that the above is enough. From the results of Experiments 1 to 4 described above, the potential convergence of the recharger 15 is slightly dependent on the distance l between the grids 15a and the distance between the grid 15a and the surface of the photoconductor drum. It can be seen that the ratio between the opening width L and the image forming speed V can be obtained. Specifically, L / V> 20 from experiments 1 and 2.
0/200 = 0.1, L / V> 34.0 / 320 = 0.106 was obtained from Experiments 3 and 4. Therefore, if L / V> 0.1 is satisfied, the potential convergence of the recharger 15 is I know enough. Next, as a result of intensive studies by the present inventors, in order to eliminate the contamination of the recharging device 15 due to the first color toner and the disturbance of the first color toner image on the photoconductor drum 11, the recharging is performed. The contamination of the container 15 is mainly caused by the inversion component in the first color toner (toner that has become opposite in polarity to the originally expected charging polarity), and the amount of this toner adhering to the recharging device 15 is It was found that it depends on the distance between the grid 15a of the charger 15 and the photosensitive drum and the bias voltage applied to the grid. Further, the present inventors have found that the image disturbance due to the corona discharge from the recharger 15 also depends on the distance between the grid 15a and the surface of the photosensitive drum and the bias voltage applied to the grid 15a. The effects will be described below based on the results of experiments based on the above findings. Experiment 5 500 characters images under the condition that the image forming speed is 200 mm / sec, the printing rate is 35 sheets / A4, and the printing rate of the first color toner is 5%.
After printing one sheet, the stain state of the recharger 15 and the disordered state of the print image of the first color toner at that time were observed. At this time, the conditions for setting the potential of the photosensitive drum 11 were adjusted so that Vd1 = −600V, Vl1 = −100V, Vd2 = −700V as in Experiment 1. As the toner of the first color, red toner developed by two-component magnetic brush was used. At this time,
The parameters are the distance d between the grid 15a and the surface of the photosensitive drum, and the bias voltage Vg applied to the grid 15a.
It was used. In that case, since the dark portion potential Vd2 after recharging is changed by applying the bias voltage Vg applied to the grid 15a, the current supplied to the recharging device 15 was changed in order to keep the dark portion potential Vd2 constant. The experimental results at this time are shown in Table 5 below. In Table 5, the mark ○ indicates a good condition, and △
The mark shows the state that it can be used at a practical level, and the X mark shows
This indicates a state where dirt and image distortion are conspicuous. Further, in the table, the left side shows stains and the right side shows image disturbance. As a result of the above, if the distance between the grid 15a and the surface of the photoconductor drum is 1.5 mm or more, even if the value of the grid bias Vg is considerably large, the recharging device 15 is contaminated by the first-color toner and the photoconductor drum is stained. It can be seen that the image disturbance of the first color toner image can be sufficiently prevented. Also, in practice, the grid bias Vg is -750V, and the recharger 15 has -300μ.
If the current of A is passed, the dark part potential Vd2 after recharging is sufficient -700
Since it becomes V, it can be said that the distance d between the grid 15a and the surface of the photosensitive drum is 0.8 mm or more. Next, another embodiment of the multicolor electrophotographic apparatus according to the present invention will be described. In this embodiment also, since the schematic structure of the multicolor electrophotographic apparatus shown in FIG. 1 of the above-mentioned embodiment is the same,
The description thereof is omitted, and the parts of the recharging device and the photosensitive drum shown in FIG. 1a which are different from the above-described embodiment will be described below with reference to FIG. 1b. Further, the same parts as those in FIG. 1A will be described with the same reference numerals. 1b is a partially enlarged sectional view of the recharging device 15 and the photosensitive drum 11 according to the present invention, as shown in FIG. 1a. As shown in FIG. 1b, Photoconductor drum
The recharger 15 arranged around 11 is provided with a grid 15a at a distance from the surface of the photosensitive drum. In the case of this embodiment, unlike the one shown in FIG. 1A, the distance between the grid 15a of the recharger 15 and the surface of the photosensitive drum is smaller than the distance d1 at the center of the recharger 15. That is, the distance d2 on the upstream side in the rotation direction of the photoconductor drum 11 is wider. By using such a configuration, it becomes easy to prevent the recharger 15 from being contaminated by the toner of the first color. Specifically, when evaluated by the same method as in Experiment 5, if the distance between the grid 15a and the surface of the photosensitive drum is 0.7 mm or more, the recharging device 15 was not contaminated in practice. Further, there was no difference in the potential convergence of the recharging device 15 from the above-mentioned embodiment. This is because the toner of the first color is recharged when the distance between the grid 15a and the surface of the photoconductor drum on the upstream side of the recharger 15 is large, and the charge polarity of the toner on the photoconductor drum 11 is normal. It is considered that it is difficult to fly toward the recharging device 15 because the charging amount increases further. Further, with such a configuration, the corona product generated in the recharger 15 can be removed relatively easily. This is the grid 15a of the recharger 15 and the photosensitive drum 11
The distance to the surface of the recharger 15 is the distance at the center of the recharger 15.
Since the distance d2 on the upstream side in the rotation direction of the photosensitive drum 11 is larger than that of d1, the recharger is
This is because it is easy to form an air flow for removing the corona product generated in the recharger 15 from the upstream side of 15. In the multicolor electrophotographic apparatus, the number of corona chargers is large, so that the deterioration of the photoreceptor due to corona products is likely to occur.However, by adopting the configuration of this example, it is easy to remove the corona products. , It is possible to extend the life of the photoconductor. Further, although the present invention has been described by taking the two-color printer as an example, it is needless to say that the present invention can be similarly applied to a multi-color printer having three or more colors. As described above, according to the multicolor electrophotographic apparatus of the present invention, at least the charger after the second charging is a charger having a grid to which a self-bias is applied, and the corona of the charger is used. By setting the relationship between the discharge opening width L and the image forming speed V so that L / V> 0.1, it is possible to obtain a sufficient potential convergence of the charger, and the reversal during the second development. Fogging, mixing of the first color toner into the second developing device,
Deterioration of the latent image carrier due to corona products can be prevented, and preferably the distance between the grid of the charger and the latent image carrier is set to 0.8 mm or more so that the first color toner It is possible to prevent dirt on the charger and image disturbance of the first color toner on the latent image carrier. Further, preferably, with respect to the distance between the grid of the charger and the surface of the latent image carrier, at least the distance on the upstream side with respect to the rotation direction of the latent image carrier is made wider than the distance in the central portion of the charger. The above effect is further increased. In this way, it is possible to maintain a good image that is stable over a long period of time in both the first and second colors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing a schematic configuration of an embodiment of a multicolor electrophotographic apparatus according to the present invention. FIG. 1a is a partially enlarged sectional view of a recharger and a photosensitive drum according to the present invention. FIG. 1b is a partially enlarged sectional view of another embodiment of the recharging device and the photoconductor drum according to the present invention, as shown in FIG. 1a. FIG. 2 is a schematic sectional view of a conventional two-color electrophotographic apparatus. FIG. 3 is a diagram showing the transition of the potential level on the photosensitive drum in the conventional two-color electrophotographic apparatus shown in FIG. 11: Photosensitive drum 12: First charger 13: First laser light sources 13a and 16a: Laser light 14: First developing device 15: Recharging device 15a: Grid 17: Second developing device 18: Transfer charging device 19 : Separating static eliminator 20: Cleaner P: Recording material L: Recharger opening width V: Image forming speed d, d1, d2: Distance between the grid and the surface of the photosensitive drum

Claims (1)

(57) [Claims] In a multicolor electrophotographic apparatus in which each step of charging, exposing and developing is repeated a plurality of times to form a visible image of a plurality of colors on the latent image carrier, and then the visible image is transferred onto a recording material, at least the second After charging, a corona charging method having a grid to which a self-bias is applied is used, and the corona discharge opening width L of the corona charger satisfies the relationship of L / V> 0.1 with respect to the image forming speed V. Characteristic multicolor electrophotographic device. 2. Claim 1 wherein the distance between the grid and the latent image carrier is 0.8 mm or more.
The multicolor electrophotographic apparatus according to the item 1. 3. 2. The distance between the grid and the latent image carrier is larger on the upstream side in the rotation direction of the latent image carrier than on the center of the charger. The multicolor electrophotographic apparatus according to 1.