JP2008145849A - Image forming apparatus - Google Patents

Abstract

An object of the present invention is to reduce the number of parts, reduce costs, save space, reduce the size of an image forming apparatus, and facilitate control, and make the amount of film reduction of each image carrier arranged in tandem substantially the same.
Of the charging brushes 3Yd, 3Md, 3Cd, and 3Kd for each color, the charging brushes 3Yd, 3Md, and 3Cd for three colors of yellow (Y), magenta (M), and cyan (C) except black (K) are used. Are provided with a common DC power supply 11 and a common switch 12 common to the respective colors. The black (K) charging brush 3 </ b> Kd is provided with a black (K) dedicated DC power supply 13 and a dedicated switch 14. By controlling the common switch 12 on / off, the charging rollers 3Ya, 3Ma, 3Ca of the three colors simultaneously negatively charge the image carriers 2Y, 2M, 2C, respectively, and the dedicated switch 14 is controlled on / off. As a result, the black (K) charging roller 3Ka negatively charges the image carrier 2K.
[Selection] Figure 1

Description

  The present invention is an image forming apparatus such as an electrophotographic, electrostatic copying machine, printer, facsimile, etc., and in a tandem type full-color image forming apparatus, the process unit of each color performs contact double charging (W charging). The present invention relates to a technical field of an image forming apparatus including the apparatus.

  In a conventional image forming apparatus composed of an electrophotographic apparatus such as an electrostatic copying machine, a printer, a facsimile, etc., the surface of the photoconductor as an image carrier is uniformly charged by the contact charging device, and then the photoconductor by the exposure device. An electrostatic latent image is formed on the surface. The electrostatic latent image is developed into a toner image by a developing device, and is transferred to a transfer material such as paper via an intermediate transfer member or directly. Finally, an image is formed by fixing the toner image on the transfer material by a fixing device.

  As a conventional image forming apparatus, there is an image forming apparatus provided with a charging device that performs charging by bringing two contact charging members into contact with the photosensitive member in order to uniformly and satisfactorily charge the surface of the rotating photosensitive member. It is known (see, for example, Patent Document 1). In the charging device of this image forming apparatus, the charging unevenness when the surface of the photosensitive member is charged by the first charging member upstream of the photosensitive member rotation direction is removed by the second charging member downstream of the photosensitive member rotation direction, The photoreceptor is uniformly charged.

Conventionally, as an electrophotographic multi-color or full-color image forming apparatus, a photoconductor is arranged in tandem for each color, and a toner image of each color formed on each photoconductor is transferred to an intermediate transfer medium or transfer material. A so-called tandem type image forming apparatus has been proposed in which a color image is formed by superimposing the images on top of each other (see, for example, Patent Document 2).
JP 2005-215321 A JP 2001-324850 A.

  By the way, it is conceivable to apply the W charging of the image carrier disclosed in Patent Document 1 to the charging of the multi-color or full-color image forming apparatus disclosed in Patent Document 2. However, in the image forming apparatus disclosed in Patent Document 2, since the power sources are arranged independently for each color, the number of parts is increased, the cost is increased, the image forming apparatus is enlarged, and the control is complicated. Has various problems.

  In contact charging, since a relatively high voltage in absolute value is applied to the contact of the charging member and the first charging member, film loss of the photosensitive layer of the image carrier occurs due to long-term use of the image forming apparatus. At this time, in the full-color image forming apparatus, the film thickness of the photosensitive layer of the image carrier for each color is different. For this reason, it is difficult to charge each color image carrier stably for a long time.

  The present invention has been made in view of such circumstances, and its purpose is to reduce the number of parts, reduce costs, save space in the image forming apparatus, downsize, and facilitate control. An object of the present invention is to provide an image forming apparatus capable of making the amount of film reduction of each image carrier arranged in tandem substantially the same.

  In order to solve the above-described problems, in the image forming apparatus according to the first aspect of the present invention, the photosensitive layers of the plurality of color image carriers are subjected to double contact charging by the first charging member and the second charging member. A common power source is provided to apply two or more charging devices among the charging devices of a plurality of colors. As a result, the number of parts (for example, two transformers and their wirings) can be reduced, and charging control is facilitated. Therefore, the cost of the image forming apparatus can be reduced, and the space saving, size reduction, and control of the image forming apparatus can be facilitated.

  In addition, by providing one power source in common to the first charging members of two or more charging devices, the same DC voltage can always be applied to the first charging members at the same time. Accordingly, since two or more image carriers are always charged at the same time, the film thickness reduction of the photosensitive layer of each image carrier can be made substantially the same. Thereby, the voltage characteristics of the photosensitive layers of the respective image carriers can be made the same over a long period of time, so that stable charging can be performed stably over the long term. As a result, a high-quality image can be stably obtained for a long time.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention.

As shown in FIG. 1, the image forming apparatus 1 of this example is formed as a full-color tandem type image forming apparatus composed of yellow (Y), magenta (M), cyan (C), and black (K). Yes. The image forming apparatus 1 includes, for example, image carriers 2Y, 2M, 2C, and 2K formed of a photosensitive drum, and these image carriers 2Y and 2M, on which electrostatic latent images and toner images are formed for the respective colors. , 2C, 2K, charging devices 3Y for charging the image carriers 2Y, 2M, 2C, 2K, which are sequentially arranged from the upstream side of the rotation direction α of the image carriers 2Y, 2M, 2C, 2K, respectively. , 3M, 3C, 3K, image writing devices 4Y, 4M, 4C, 4K for writing an electrostatic latent image on each image carrier 2Y, 2M, 2C, 2K, on each image carrier 2Y, 2M, 2C, 2K The toner images on the developing devices 5Y, 5M, 5C, and 5K and the image carriers 2Y, 2M, 2C, and 2K that develop the electrostatic latent image with the toner that is the developer of each color to form the toner image are primarily transferred. Cleaning for cleaning the primary transfer devices 6Y, 6M, 6C, 6K and the image carriers 2Y, 2M, 2C, 2K Location 7Y, is equipped with 7M, 7C, and 7K.
The arrangement order of yellow (Y), magenta (M), cyan (C), and black (K) is not limited to the example shown in FIG. 1, and is arbitrary. In the following description, the arrangement order of each color is the arrangement order of the example shown in FIG.

  Each image carrier 2Y, 2M, 2C, 2K, each charging device 3Y, 3M, 3C, 3K, each image writing device 4Y, 4M, 4C, 4K, each developing device 5Y, 5M, 5C, 5K, primary transfer device The configurations of 6Y, 6M, 6C, and 6K and the cleaning devices 7Y, 7M, 7C, and 7K are the same for the colors Y, M, C, and K, respectively.

FIG. 2 is a diagram for explaining each device configured in the same manner for each color. In FIG. 2, the description will be made by taking the Y, M, C, and K symbols of each color.
As shown in FIG. 2, the surface layer of the image carrier 2 is formed on a photosensitive layer 2a having a predetermined thickness. As will be described later, an electrostatic latent image is written by the image writing device 4 on the surface of the photosensitive layer 2 a charged by the charging device 3.

  Further, the charging device 3 charges the photosensitive layer 2a of the image carrier 2, and a charging roller (CR) 3a as a second charging member, and the image carrier on the upstream side in the rotation direction α from the charging roller 3a. And a charging brush (CB) 3d which is a first charging member for charging the second photosensitive layer 2a. The charging roller 3a is in contact with the surface of the photosensitive layer 2a of the image carrier 2 and is rotated in the direction β opposite to the rotation direction α of the image carrier 2 (counterclockwise in FIG. 1).

  As the charging roller 3a, a known charging roller that has been conventionally used can be used. That is, the charging roller 3a can be manufactured by a manufacturing method described in, for example, JP-A-10-48916. That is, the charging roller 3a is configured by providing, for example, a cylindrical conductive elastomer layer 3c made of, for example, conductive rubber or the like having a surface inclined resistance layer on a metal shaft 3b made of stainless steel. ing. The conductive elastomer layer 3c is set to have a constant outer diameter and a substantially constant electric resistance along the axial direction.

  As an example of the charging roller 3a having the conductive elastomer layer 3c, 0.3 parts by weight of sodium trifluoroacetate as a conductive material, zinc oxide (ZnO) with respect to 100 parts by weight of epichlorohydrin rubber (Epichromer CG-102; manufactured by Daiso Corporation) ) 5 parts by weight and 2 parts by weight of 2-mercaptoimidazoline (Axel-22) as a vulcanizing agent are kneaded with a roll mixer, press-molded on the surface of a metal shaft having a diameter of 6 mm, and polished to a diameter of 12 mm. A roller having a conductive rubber elastic member formed on the surface can be obtained.

  The charging brush 3d is a deck brush, has a large number of brush hairs, and is supported by a brush support member (not shown). The tips of a large number of brush bristles are in contact with the outer peripheral surface of the image carrier 2. As the charging brush 3d, a known charging brush that has been conventionally used can be used. An example of the charging brush 3d is shown in Table 1.

As shown in Table 1, the brush hair of the brush 1 as an example has a material of 6 nylon, a fineness of 220T / 96F, a density of 240 kf / inch ² , a yarn resistance of 7.1 LogΩ, and a pile length of 5 mm. The overall shape of the brush 1 is 300 mm in length (along the axial direction of the image carrier 2), 5 mm in width, and 5 mm in height. This brush 1 is a brush made by Toei Sangyo Co., Ltd.

In the image forming apparatus 1 of this example, the image carrier 2 is first uniformly charged by the charging brush 3d (primary charging) and then uniformly charged by the charging roller 3a (secondary charging).
That is, for example, when the image carrier 2 is negatively charged by a DC voltage, first, as shown in FIG. 3, the absolute value of the discharge start voltage −Vth ₁ (V) between the charging brush 3d and the image carrier 1 is _{first obtained.} A negative voltage −Va ₁ (V) having a higher absolute value is applied to the charging brush 3d. Thereby, the photosensitive layer 2a of the image carrier 2 is negatively charged to the primary charging potential (eg, −800 V) (primary charging) by the charging brush 3d. On the other hand, the negative voltage −Va ₂ (V) or the positive voltage + Va ₂ (V) whose absolute value is lower than the absolute value of the discharge start voltage −Vth ₂ (V) between the charging roller 3 a and the image carrier 1. The voltage Va ₂ (V) is applied to the charging roller 3a. As a result, the primary charging potential of the photosensitive layer 2a is leveled by the charging roller 3a, and the photosensitive layer 2a of the image carrier 2 is uniformly charged (secondary charging). Thus, in the image forming apparatus 1 of this example, double contact charging (W charging) of the image carrier 2 is performed by the charging brush 3d and the charging roller 3a. As a result, the surface of the photosensitive layer 2a of the image carrier 2 is uniformly charged to an image writing potential (for example, −600 V) set in advance for image writing.

  By the way, in the image forming apparatus 1 of this example, a direct current (DC) voltage is applied as a charging voltage to the charging rollers 3Ya, 3Ma, 3Ca, 3Ka of each color and the charging brushes 3Yd, 3Md, 3Cd, 3Kd of each color as described above. It has come to be. In that case, as shown in FIG. 1, the charging rollers 3Ya, 3Ma, 3Ca, 3Ka of the respective colors have independent individual DC power supplies 9Y, 9M, 9C, 9K and independent switches 10Y, 10, 10, 10K. Is provided. In the example shown in FIG. 1, each of the charging rollers 3Ya, 3Ma, 3Ca, 3Ka is respectively controlled by turning on / off the individual switches 10Y, 10, 10, 10K independently. , 2C, 2K are negatively charged.

  Among the charging brushes 3Yd, 3Md, 3Cd, and 3Kd for each color, the charging brushes 3Yd, 3Md, and 3Cd for three colors of yellow (Y), magenta (M), and cyan (C) excluding black (K) One common DC power source 11 common to each color and one common switch 12 common to each color are provided. Further, the black (K) charging brush 3Kd is provided with one black (K) dedicated DC power supply 13 and one black (K) dedicated switch. In the example shown in FIG. 1, the common switch 12 is turned on / off so that the three color charging rollers 3Ya, 3Ma, 3Ca simultaneously negatively charge the corresponding image carriers 2Y, 2M, 2C, respectively. Further, by controlling on / off of the dedicated switch 14, the black (K) charging roller 3Ka negatively charges the image carrier 2K.

  The image writing device 4 writes an electrostatic latent image on the image carrier 2 charged by the charging device 3 with, for example, a laser beam. The developing device 5 includes a developing roller 5a, a toner supply roller 5b, and a toner layer thickness regulating member 5c. At both ends of the developing roller 5a, developing rollers 5d (only one developing roller 5a is shown in FIG. 2) are provided. These developing rollers 5d constitute a developing roller / image carrier axis distance regulating member. In other words, the distance between the axial center of the developing roller 5 a and the axial center of the image carrier 2 is regulated by the development rollers 5 d coming into contact with the outer peripheral surface of the image carrier 2. Thus, a predetermined development gap is set between the outer peripheral surface of the developing roller 5a and the outer peripheral surface of the image carrier 2.

  Then, toner (not shown) as a developer is supplied onto the developing roller 5a by the toner supply roller 5b, and the toner on the developing roller 5a is regulated in its thickness by the toner layer thickness regulating member 5c and the image is carried. The electrostatic latent image on the image carrier 2 is developed in a non-contact jumping manner with the conveyed toner, and a toner image is formed on the image carrier 2.

The primary transfer device 6 includes a primary transfer roller 6a, and the toner image on the image carrier 2 is transferred to an intermediate transfer medium 8 formed of, for example, an intermediate transfer belt by the primary transfer roller 6a.
The cleaning device 7 has a cleaning blade 7a made of an elastic material such as rubber. The cleaning blade 7a is attached to the apparatus main body via a blade support member (not shown). The cleaning blade 7 a is always in pressure contact with the outer peripheral surface of the image carrier 2. The image carrier 2 is cleaned by the cleaning blade 7a, and the transfer residual toner on the image carrier 2 is removed and collected by a toner collection unit (not shown).

  Further, the image forming apparatus 1 in this example is not shown in the figure, but is secondarily transferred to a known secondary transfer device that transfers the toner image transferred to the intermediate transfer medium 8 to a transfer material such as paper, and to a transfer material. At least a known fixing device that heats and presses and fixes the toner image.

  Next, an image forming operation of the image forming apparatus 1 of this example will be described with reference to FIG. In this case, the constituent members provided for the respective colors will be described with reference numerals of the corresponding colors Y, M, C, and K attached to the constituent members.

  In FIG. 1, when the common switch 11 is turned on, the photosensitive layers of the yellow (Y), magenta (M), and cyan (C) image carriers 2Y, 2M, and 2C are primary by the charging brushes 3Yd, 3Md, and 3Cd. Charged. Next, the yellow (Y) switch 10Y is turned on, the image carrier 2Y is secondarily charged by the charging roller 3Ya, and the photosensitive layer of the image carrier 2Y is set to the image writing potential. Next, after an electrostatic latent image is written on the image carrier 2Y by the image writing device 4Y, the electrostatic latent image is developed with yellow toner conveyed by the developing roller 5Ya in the developing device 5Y. Thus, a yellow (Y) toner image is formed on the image carrier 2Y.

  Similarly, for the other colors M, C, and K, the switches 10M and 10C for each color are turned on with a predetermined time delay, and the respective image carriers 2M and 2C are secondarily charged by the respective charging rollers 3Ma and 3Ca. Thus, the photosensitive layers of the image carriers 2M and 2C are set to the image writing potential. Further, after the black (K) dedicated switch 14 is turned on and the photosensitive layer of the image carrier 2K is primarily charged by the charging brush 3Kd, the black (K) switch 10K is turned on and the image carrier 2K is charged by the charging roller. Secondary charging is performed at 3 Ka, and the photosensitive layer of the image carrier 2M is set to an image writing potential. Similarly to the case of yellow (Y), electrostatic latent images are written on the image carriers 2M, 2C, and 2K by the image writing devices 4M, 4C, and 4K, respectively. Thereafter, these electrostatic latent images are developed with the respective color toners conveyed by the developing rollers 5Ma, 5Ca, and 5Ka in the developing devices 5M, 5C, and 5K, respectively. In this way, toner images of corresponding colors are sequentially formed on the image carriers 2M, 2C, and 2K.

  The yellow (Y) toner image on the image carrier 2Y is primarily transferred onto the intermediate transfer medium 8 by the primary transfer device 6Y, and the yellow (Y) toner image on the intermediate transfer medium 8 is magenta (M ) To the primary transfer device 6M. Then, the magenta (M) toner image on the image carrier 2M is primary-transferred to the predetermined position on the intermediate transfer medium 8 with the yellow (Y) toner image by the primary transfer device 6M. Further, the toner image on the intermediate transfer medium 8 in which the colors of yellow (Y) and magenta (M) are superimposed is conveyed toward the primary transfer device 6C of cyan (C). Then, the cyan (C) toner image on the image carrier 2C is primary-transferred at the predetermined position on the intermediate transfer medium 8 with the yellow (Y) and magenta (M) toner images by the primary transfer device 6C. Is done. Further, the toner image on the intermediate transfer medium 8 on which the colors of yellow (Y), magenta (M), and cyan (C) are superimposed is conveyed toward the primary transfer device 6K of black (K). Then, the black (K) toner image on the image carrier 2K is transferred to the yellow (Y), magenta (M), and cyan (C) toner images and colors at predetermined positions on the intermediate transfer medium 8 by the primary transfer device 6C. Overlaid and primary transferred. Thus, a full-color toner image is formed on the intermediate transfer medium 8.

  Further, the full-color toner image on the intermediate transfer medium 8 is secondarily transferred onto a transfer material such as paper by a secondary transfer device in the same manner as a conventionally known tandem type image forming apparatus, and the full-color toner image on the transfer material is also transferred. The toner image is heated and pressurized and fixed by a fixing device. Thus, a full color image is formed on the transfer material.

  As described above, according to the image forming apparatus 1 of this example, the DC power source 11 of the charging brushes 3Yd, 3Md, and 3Cd in the charging devices 3Y, 3M, and 3C of three colors of Y, M, and C is set to 1 The DC power supplies 9Y, 9M, 9C of the charging rollers 3Ya, 3Ma, 3Ca are provided independently for the charging rollers 3Ya, 3Ma, 3Ca. Thereby, the number of parts can be reduced and charging control can be facilitated. Accordingly, the cost of the image forming apparatus 1 can be reduced, and the space saving, size reduction, and control of the image forming apparatus can be facilitated.

In addition, the same charging voltage −Va ₁ (V) can be applied to the charging brushes 3Yd, 3Md, and 3Cd simultaneously for the three colors (Y, M, and C). Therefore, since the three color image carriers 2Y, 2M, and 2C are always charged simultaneously by the respective charging brushes 3Yd, 3Md, and 3Cd, the film thickness reduction of the photosensitive layers of the image carriers 2Y, 2M, and 2C is substantially the same. Can be. As a result, the voltage characteristics of the photosensitive layers of the image carriers 2Y, 2M, and 2C (for example, the surface potential characteristics of the photosensitive layer of the image carrier with respect to the applied voltage) can be made the same over a long period of time. Can be charged easily. As a result, a high-quality image can be stably obtained for a long time.

  In the image forming apparatus 1 of the above example, the present invention is applied to an image forming apparatus in which the image carrier 2 is negatively charged by the charging device 3 during image formation. However, the present invention is not limited to this, and can also be applied to an image forming apparatus in which the image carrier 2 is positively charged by the charging device 3 during image formation. The above-described effects of the present invention can be obtained even when the image carrier 2 is positively charged.

  In the image forming apparatus 1 of the above-described example, the charging brush 3d is used as the first charging member, and the charging roller 3a is used as the second charging member. However, in the present invention, the charging roller 3a '(metal shaft 3b', conductive elastomer layer 3c ') can also be used for the first charging member as shown in FIG. 4A. In this case, the charging roller 3a is used as the second charging member. As shown in FIG. 4B, a charging roller brush 3a '(metal shaft 3b', charging brush 3d ') can be used as the first charging member. In this case, the charging roller 3a is used as the second charging member.

Further, in the image forming apparatus 1 of each of the examples described above, the present invention includes an intermediate transfer belt 8 on which a toner image is primarily transferred from the image carrier 2 and the transferred toner image is secondarily transferred to a transfer material such as paper. This is applied to the used image forming apparatus. However, the image forming apparatus of the present invention is not limited to this, and can also be applied to an image forming apparatus that directly transfers the toner image of the image carrier 2 onto a transfer material such as paper.
Furthermore, the image forming apparatus of the present invention is not limited to the full-color image forming apparatus of four colors, and can be applied to an image forming apparatus of a plurality of colors such as three colors or two colors.

1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention. It is a figure explaining each apparatus comprised by the same color of the image forming apparatus shown in FIG. It is a figure explaining the voltage application to the 1st and 2nd charging member. (A) And (b) is a figure which shows the other example of embodiment of the charging device concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image carrier, 3 ... Charging device, 3a ... Charging roller (second charging member), 3d ... Charging brush (first charging member), 11 ... Common DC power supply, 13 ... Dedicated DC power supply

Claims (2)

A plurality of image carriers arranged in tandem and forming an electrostatic latent image according to each of a plurality of colors, and a plurality of image carriers provided for each of the plurality of image carriers to charge each of the plurality of image carriers. A charging device, a writing device that is provided for each of the plurality of image carriers and writes an electrostatic latent image on each of the image carriers, and a plurality of image carriers that are provided for each of the plurality of image carriers. A plurality of developing devices that respectively develop the electrostatic latent images on the image carrier to form developer images on the image carrier, and a developer provided on each of the plurality of image carriers. A plurality of transfer devices each for transferring an image,
Each of the plurality of charging devices is in contact with the surface of the corresponding image carrier and charges the surface, and the first charging member is downstream of the first charging member in the rotation direction of the corresponding image carrier. A second charging member that contacts and charges the surface of the corresponding image carrier,
An image forming apparatus, wherein a power source for applying a voltage to each of the first charging members of at least two charging devices among the plurality of charging devices is a common power source. The image forming apparatus according to claim 1, wherein each of the first charging members of the plurality of charging devices includes any one of a deck brush, a charging roller, and a charging brush roller.

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