JP2003162107A - Multicolor image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use photoreceptors and toners for corresponding colors only for the same period of time when forming a color image using the colors and to achieve a cost reduction. <P>SOLUTION: Among image forming stations Pa-d, the photoreceptor (photoreceptor drum 222a) in the image forming station Pa corresponding to black uses a cleaning system which makes it difficult for the photoreceptor to wear in comparison with the photoreceptors (photoreceptor drums 222b-222d) in the other image forming stations Pb-d. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus, and more particularly to a so-called tandem type color printer in which a plurality of photoconductors are charged and a developing device for accommodating multicolor toners is arranged. The present invention relates to a multicolor image forming apparatus.

[0002]

2. Description of the Related Art In recent years, in a color electrophotographic process, a so-called tandem type multicolor image forming apparatus for obtaining a color image by arranging a plurality of photosensitive drums corresponding to toner colors is provided in order to increase a printing speed. It is being used.

As a typical conventional multicolor image forming apparatus,
A digital color copying machine will be described as an example. Figure 3
It is a longitudinal sectional view showing a schematic configuration of a conventional digital color copying machine. As shown in FIG. 3, the conventional digital color copying machine is provided with an original table 111 on the upper surface of the copying machine main body 1, and the image reading section 11 is provided inside the copying machine main body 1.
0 and the image forming unit 210 are provided. A two-sided automatic document feeder (RADF; Reversing Aut) is supported on the upper surface of the document table 111 in a state of being openable and closable with respect to the document table 111.
Omatic Document Feeder) 11
2 is installed.

The double-sided automatic document feeder 112 first conveys the document so that one surface of the document faces the image reading section 110 at a predetermined position of the document table 111,
After the image reading on this one side is completed,
The document is inverted and conveyed so that the other surface faces the image reading unit 110 at a predetermined position of the document table 111. Then, the double-sided automatic document feeder 112
After discharging the image on both sides of one document, this document is discharged and the two-sided conveyance operation for the next document is executed. The above-described operation of conveying the document and inverting the front and back is controlled in relation to the operation of the entire copying machine.

The image reading unit 110 is arranged below the document table 111 in order to read an image of a document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image reading unit 110 includes the document table 11
It has an original scanning member that reciprocates in parallel along the lower surface of the optical disc 1, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.

This original scanning body is composed of a first scanning unit 1
13 and the second scanning unit 114. The first scanning unit 113 has an exposure lamp for exposing the surface of the original image and a first mirror for deflecting a reflected light image from the original in a predetermined direction. It reciprocates in parallel at a predetermined scanning speed while maintaining a constant distance from the lower surface.

The second scanning unit 114 further comprises second and third scanning units for deflecting the reflected light image from the document deflected by the first mirror of the first scanning unit 113 toward a predetermined direction. It has a mirror and reciprocates in parallel with the first scanning unit 113 while maintaining a constant speed relationship.

The optical lens 115 reduces the reflected light image from the document deflected by the third mirror of the second scanning unit, and the reduced light image is CCD line sensor 116.
The image is formed at a predetermined position above.

The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electric signal. The CCD line sensor 116 reads a black-and-white image or a color image, R (red), G (green),
It is composed of a three-line color CCD capable of outputting line data obtained by color-separating each color component of B (blue). The document image information converted into an electric signal by the CCD line sensor 116 is further transferred to an image processing section and subjected to predetermined image data processing.

Next, the structure of the image forming unit 210 and the structure of each unit related to the image forming unit 210 will be described. Below the image forming unit 210, a sheet feeding mechanism 2 for separating the sheets (recording media) P stacked and accommodated in the sheet tray one by one and supplying the sheets P toward the image forming unit 210.
11 is provided. Then, the sheets P, which are separated and supplied one by one, are conveyed to the image forming unit 210 at a timing controlled by a pair of registration rollers 212 arranged in front of the image forming unit 210.

Further, the paper P having an image formed on one side thereof
Are re-supplied and conveyed to the image forming unit 210 at the same timing as the image formation of the image forming unit 210. A transfer / conveying belt mechanism 213 is arranged below the image forming unit 210. The transfer / conveying belt mechanism 213 is configured to electrostatically adsorb the paper P to the transfer / conveying belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend in parallel and to convey the paper P. A pattern image detection unit is provided near the lower side of the transfer / transport belt 216.

Further, on the downstream side of the transfer / transport belt mechanism 213 in the paper transport path, a fixing device 217 for fixing the toner image transferred and formed on the paper P onto the paper P.
Are arranged. In the fixing device 217, the sheet P that has passed through the nip between the pair of fixing rollers passes through the conveyance direction switching gate 218, and is discharged by the discharge roller 219 to the discharge tray 2 attached to the outer wall of the copying machine body 1.
20 is discharged.

The transport direction switching gate 218 selectively transports the sheet P after fixing between a route for discharging the sheet P to the copying machine main body 1 and a route for re-feeding it toward the image forming section 210. It is to switch. The sheet P whose conveyance direction has been switched again toward the image forming unit 210 by the conveyance direction switching gate 218 is turned upside down via the switchback conveyance path 221, and then supplied again to the image forming unit 210.

Further, above the transfer / transport belt 216 in the image forming section 210, close to the transfer / transport belt 216, the first image forming station Pa, the second image forming station Pb, and the third image forming station. P
c and the fourth image forming station Pd are arranged in parallel in order from the upstream side of the paper transport path.

The transfer / conveying belt 216 includes a driving roller 21.
1 carries the paper P that is frictionally driven in the direction indicated by arrow Z in FIG. 1 and is fed through the paper feeding mechanism 211 as described above, and the paper P is transferred to the image forming station Pa.
To Pd sequentially. Each image forming station Pa
Pd has substantially the same structure. Each of the image forming stations Pa to Pd includes a photosensitive drum 222a to 222d that is rotationally driven in the direction of arrow F shown in FIG.

Each photosensitive drum 222a, 222b, 22
2c and 222d, the photosensitive drums 222a-2
Charging unit 223 for uniformly charging 22d
a, 223b, 223c, 223d and the photosensitive drum 2
Developing devices 224a, 224b, 224c for developing the electrostatic latent images formed on 22a to 222d, respectively.
224d and the developed photosensitive drums 222a to 222
transfer dischargers 225a, 225b, 225c, 225d for transferring the toner image on the sheet P to the sheet P, and cleaning devices 226a, 226b, 226c, 22 for removing the toner remaining on the photoconductor drums 222a to 222d.
6d are sequentially arranged along the rotation direction of the photoconductor drums 222a to 222d.

Further, each of the photosensitive drums 222a to 222d.
Above the above, laser beam scanner unit 227
a, 227b, 227c and 227d are provided respectively. The laser beam scanner unit 227a
Denoted at 227d are semiconductor laser elements (not shown) that emit dot light modulated according to image data, and polygon mirrors (deflecting devices) for deflecting the laser beam from the semiconductor laser elements in the main scanning direction. 240a, 2
40b, 240c, 240d and the polygon mirror 24
Fθ lenses 241a, 241b, 241c, 241d, and mirrors 242a, 242b, 242c, 242d and mirrors 243a, 243b, 243c, 243c, 243c, 242a, 242c, 242d, and 243a, 243b, 243c, 242d for focusing the laser beams deflected by the laser beams 0a to 240d on the surfaces of the photoconductor drums 222a to 222d. 243d and the like.

The laser beam scanner unit 22
The pixel signal corresponding to the black component image of the color original image is input to 7a, and the laser beam scanner unit 227 is input.
The pixel signal corresponding to the cyan color component image of the color original image is input to b, and the laser beam scanner unit 22
Pixel signals corresponding to the magenta color component image of the color original image are input to 7c, and pixel signals corresponding to the yellow color component image of the color original image are input to the laser beam scanner unit 227d.

As a result, the electrostatic latent images corresponding to the color-converted original image information are converted into the photosensitive drums 222a to 222a.
It is formed on 2d. The developing device 224a contains black toner, the developing device 224b contains cyan toner, the developing device 224c contains magenta toner, and the developing device 224d contains yellow toner. It is housed. Then, the photosensitive drum 222
The electrostatic latent images on a to 222d are developed with the toners of the respective colors. As a result, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.

A sheet suction charger 228 is provided between the first image forming station Pa and the sheet feeding mechanism 211. The sheet suction charger 228 charges the surface of the transfer / conveyance belt 216, and the sheet P supplied from the sheet feeding mechanism 211 is securely adsorbed on the transfer / conveyance belt 216 in the first image forming station. The sheet is conveyed from Pa to the fourth image forming station Pd without being displaced.

On the other hand, a static eliminator 229 is provided between the fourth image forming station Pd and the fixing device 217 and just above the drive roller 214. An alternating current is applied to the static eliminator 229 to separate the paper P electrostatically attracted to the transfer / transport belt 216 from the transfer / transport belt 216.

In the digital color copying machine having the above-mentioned structure, cut sheet-shaped paper is used as the paper P. When the paper P is sent out from the paper feed cassette and fed into the guide of the paper feed transport path of the paper feed mechanism 211, the tip portion of the paper P is detected by a sensor (not shown). Based on the detection signal output from the pair of registration rollers 212, the registration rollers 212 temporarily stop.

Then, the paper P is sent onto the transfer / conveying belt 216 rotating in the direction of arrow Z in FIG. 3 at a timing with the image forming stations Pa to Pd. At this time, since the transfer / conveying belt 216 is charged to a predetermined level by the sheet suction charger 228 as described above, the sheet P is stable while passing through the image forming stations Pa to Pd. Transported and supplied.

In each of the image forming stations Pa to Pd, a toner image of each color is formed and superposed on the supporting surface of the paper P that is electrostatically attracted by the transfer and transport belt 216 and is transported. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially peeled off from the transfer conveying belt 216 by the discharging discharging device and guided to the fixing device 217.

Finally, the paper P on which the toner image is fixed
Is discharged onto the discharge tray 220 from a paper discharge port (not shown). In the above description, the laser beam scanner units 227a to 227d are used to perform optical writing on the photoconductor drums 222a to 222d by scanning and exposing the laser beam. However, instead of the laser beam scanner units 227a to 227d, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used.

The LED head is smaller in size than the laser beam scanner units 227a to 227d,
There are no moving parts and there is no sound. Therefore, it can be preferably used in an image forming apparatus such as a tandem type digital color copying machine which requires a plurality of optical writing units.

In such a multicolor image forming apparatus, not only actual color printing but also monochrome (black) printing is frequently performed. Next, the operation control executed according to the user's mode designation will be described with reference to the flowchart shown in FIG.

In the operation control of the multicolor image forming apparatus,
As shown in FIG. 4, first, it is determined whether or not the color image output mode is designated (S1), and when the color image output mode is designated, each of the photosensitive drums 222a to 222a.
2d is returned to the normal position in contact with the transfer / conveying belt 216 (S2), and the photosensitive drums 222a to 222d are rotatably driven (S3) to correspond to the photosensitive drums 222a to 222d according to the electrophotographic process. The charging / developing operation is executed (S4). In this way, a color image is formed on the transfer paper.

On the other hand, when the monochrome image output mode is designated, the contact / separation mechanism is driven to drive each of the photosensitive drums 222b for cyan (C), magenta (M), and yellow (Y).
222d is separated from the transfer / transport belt 216 (S
5). Then, the rotational drive of each of the photosensitive drums 222b to 222d is turned off and brought into a stopped state (S6).
The charging / developing operations for the photosensitive drums 222b to 222d are also turned off (S7). In this state, the black photosensitive drum 222a is rotationally driven (S8), and the black photosensitive drum 22a is subjected to the electrophotographic process.
The charging / developing operation or the like is performed on 2a (S9).
Thus, a black and white image is formed on the transfer paper.

As described above, when the black-and-white image output mode is designated, the photosensitive drums 222b to 222d other than the black photosensitive drum 222a are brought into the non-operating state such as the rotation operation thereof being stopped, and the transfer / conveying belt 216 is performed. Is separated from. As a result, the photosensitive drums 222b to 222d which are unnecessary when the monochrome image output mode is designated are subjected to film scraping by a cleaning blade or the like, and the photosensitive drums 222b by the transfer paper and the transfer / transport belt 216.
It is possible to prevent the surface of ~ 222d from being scraped as much as possible.

However, the monochrome printing may be used more frequently than the color printing, and the black photosensitive drum 222a may be used for other colors.
There was a defect that the wear was relatively quicker than that of b to 222d.

Further, in the usual case, four photosensitive drums 222a to 222 are prepared for each of black, C, M and Y toners.
Since the abrasion characteristics of d are different, the deterioration of the photosensitive drums 222a to 222d may be different due to the difference in toner color. In this way, the photosensitive drums 222a to 222 are
When d is unevenly worn and deteriorated for each toner, there is a problem in that color unevenness in color image quality occurs as the number of copies increases.

Further, the abrasion deterioration rate of the photosensitive drums 222a to 222d differs depending on the type of the color-specific developer, and when only one photosensitive drum (for example, 222a) deteriorates, the replaced photosensitive drum (for example, 222a), which has not been replaced with a photosensitive drum (for example, 222b to 222d)
Since the color balance between the photosensitive drums 222 and is not good and a good image cannot be obtained, all the photosensitive drums 222a to 222a.
I had to replace 222d.

That is, the photosensitive drums 222a to 222
The interval until the replacement of d is 4 photosensitive drums 2
There is a problem that the photosensitive drum (black photosensitive drum 222a for black) corresponding to the most severely deteriorated color of 22a to 222d is rate-controlled and waste is increased.

As countermeasures against the above problems, Japanese Patent Laid-Open Nos. 10-333393 and 11-2
As disclosed in Japanese Patent Laid-Open No. 4358 and Japanese Patent Application Laid-Open No. 11-52599, only the black photoconductor has an α-Si or α-SiC photoconductor to prolong the life of the photoconductor and for other colors except black. A technique using an OPC (organic photoconductor) for the photoconductor is proposed. However, α-Si or α
-SiC photoconductor has a problem of low chargeability.

Therefore, as countermeasures against the above problems, Japanese Patent Laid-Open Nos. 10-333393 and 11-2
There are proposed methods such as those disclosed in Japanese Patent No. 4358 and Japanese Patent Laid-Open No. 11-52599. That is, in Japanese Patent Laid-Open No. 10-333393, the thickness of the photoconductor is set to 30.
A technique has been proposed in which the thickness is set to at least μm and the charging difference from the organic photoconductor is set to 200 V or less. Japanese Patent Application Laid-Open No. 11-24358 proposes a technique for increasing the applied voltage to the α-Si photoconductor by 1.05 to 2.50 times that of the organic photoconductor. Japanese Unexamined Patent Application Publication No. 11-52599 proposes a technique of increasing the chargeability by providing a surface layer of α-SiC.

However, in order to use the black photoconductor for a long time and to compensate for the low chargeability of the α-Si or α-SiC photoconductor, only the black photoconductor is complicatedly charged. Therefore, there is a problem in that a large amount of cost is required because the control is required. In addition, α-Si or α
-SiC photoconductors and organic photoconductors are different in how they are affected by photosensitivity and temperature / humidity. Therefore, the exposure amount is different for α-Si for black or α-SiC photoconductors and organic photoconductors used for other than black. The transfer conditions are also different, and different control methods must be adopted for the black photoconductor and the non-black photoconductor, so that a large cost is required in addition to the charging control described above. The problem arises that

Further, Japanese Patent Laid-Open No. 10-333393,
JP-A-11-24358 and JP-A-11-5259.
No. 9 discloses a method using an α-Si or α-SiC photoconductor, the α-Si or α-SiC photoconductor according to the above-mentioned publication has a lower production cost than a conventional organic photoconductor. The cost is obviously high, and there is a problem that the black toner is also consumed in a large amount.

Therefore, as a solution to these problems, Japanese Patent Laid-Open No.
000-242056, JP 2000-2420 A.
57, JP 2001-51467 A, JP 2
A method disclosed in Japanese Patent Application Laid-Open No. 000-330303 has been proposed. That is, Japanese Patent Laid-Open No. 2000-24205
No. 6, JP-A-2000-242057 propose a technique of increasing the drum diameter or increasing the film thickness only for the black photoconductor. In addition, JP-A-2001-51
Japanese Patent No. 467 proposes a technique in which a non-contact charging unit is used only for a black photoconductor, a thick film is used, and a resin having a large viscosity average molecular weight is used. In addition, JP-A-2000-
In JP 330303, there is proposed a technique using a copolycarbonate resin as a resin for a tandem photoreceptor. Furthermore, a method of providing a protective layer only on the black photoconductor is also under study.

[0040]

However, according to the above-mentioned conventional method, as shown below, (1) it is troublesome in management to use the other photoconductor only for the black photoconductor. There is a problem that (2) When a resin having a large viscosity average molecular weight is used, there is a problem that it is difficult to apply. (3) When the coating film thickness is increased, there is a problem that the charge amount of the photoconductor is reduced and the resolution is reduced. (4) If the drum diameter of the photoconductor is increased, the size of the device becomes large. Various problems occur.

Further, most of the photoconductors currently used do not have a protective layer. This means that no effective protective layer has been developed yet. further,
The cause of abrasion of the photoconductor is due to abrasion of a transfer paper, a cleaning blade, charging, a developing portion, etc., and it is considered that the main cause thereof is abrasion with a cleaning blade. Therefore, even if the non-contact charging means for only the black photoconductor is used as the charging means which is not the main factor, the effect can be slightly improved, but it is not the main solution.

On the other hand, Japanese Patent Application Laid-Open Nos. 5-53414 and 11-249452 propose a technique in which a so-called cleanerless system is adopted in a tandem image forming apparatus without using a dedicated cleaner for removing toner. But,
These are carried out only for the purpose of making the machine compact, and the idea of extending the life of the photoconductor is not incorporated at all.

The present invention has been made in view of the above problems of the prior art, and when forming a color image using a plurality of colors, it is possible to use the photoconductor and the toner for the same period for each color. Another object of the present invention is to provide a multi-color image forming apparatus with low cost.

[0044]

SUMMARY OF THE INVENTION The present invention relates to a multicolor image forming apparatus, in which a plurality of image forming stations each having a photoconductor having a different corresponding color are arranged along the sheet conveying direction and each image forming station is formed. In a multicolor image forming apparatus that sequentially superimposes color images formed by the stations to form an image, the image forming station includes a cleaning mechanism that removes toner from a photoconductor. The photoconductor of the image forming station corresponding to the black color among the stations is characterized by being applied with a cleaning method which is less likely to wear than the photoconductors of the other image forming stations.

Further, it is preferable that the photoconductor in the image forming station corresponding to the black color is not equipped with a cleaner. Further, it is preferable that the image forming station corresponding to the black color is arranged on the most upstream side in the sheet conveying direction. Further, in the single copy mode, it is preferable to stop the operation of the photoconductors in the image forming stations other than the image forming station corresponding to black.

[0046]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of an image forming unit of a multicolor image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a detailed configuration of a black image forming station. The multicolor image forming apparatus according to the embodiment of the present invention has a schematic configuration that is substantially the same as the conventional multicolor image forming apparatus shown in FIG. Therefore, the description of the overall configuration of the multicolor image device will be omitted, and the detailed description of the configurations having the same reference numerals as those in the drawing of FIG. 3 will be omitted.

In the multicolor image forming apparatus 1 according to the embodiment of the present invention, as shown in FIGS. 1 and 3, the transfer / transport belt 2 is provided above the transfer / transport belt 216 in the image forming section 210.
Close to 16, the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and the fourth image forming station Pd.
Are arranged side by side from the upstream side of the paper transport path.

The transfer / conveying belt 216 is frictionally driven by a driving roller 214 in the direction of arrow Z shown in the drawing.
The paper P that is fed through a paper feed mechanism (not shown) is carried, and the paper P is sequentially conveyed to the image forming stations Pa to Pd. The image forming station Pa is for forming a black (B) image, and is an image forming station Pb.
Is for forming a cyan (C) image, the image forming station Pc is for forming a magenta (M) image, and the image forming station Pd is for forming a yellow (Y) image. It is for doing. Also,
The image forming stations Pa to Pd are indicated by arrows F in the figure.
Photoconductor drums 222a to 222d that are rotationally driven in the direction
Contains each.

Around the photosensitive drums 222a to 222d, chargers 223a to 223d for uniformly charging the photosensitive drums 222a to 222d, respectively, and static electricity formed on the photosensitive drums 222a to 222d. Developing devices 224a to 224d for developing the latent images, respectively
And a transfer discharger 225a for transferring the developed toner images on the photosensitive drums 222a to 222d to the paper P.
To 225d and a cleaning device 226 for removing the toner remaining on the photosensitive drums 222a to 222d.
a to 226d are sequentially arranged along the rotation direction of the photoconductor drums 222a to 222d. Further, a fixing device 217 for fixing the toner image transferred and formed on the paper P on the paper P is disposed on the downstream side of the paper conveyance path.

In each of the image forming stations Pa to Pd, the cleaning mechanism used in the cyan (C), magenta (M), and yellow (Y) image forming stations Pb to Pd is a conventional multicolor cleaning mechanism shown in FIG. Similar to the image forming apparatus, it has a blade cleaning system. On the other hand, the black (B) image forming station Pa arranged on the most upstream side employs a cleaning mechanism that causes little wear on the photosensitive drum 222a.

Next, the cleaning mechanism in the black (B) image forming station Pa will be described in detail with reference to FIG. In the black (B) image forming station Pa, as shown in FIG. 2, as the cleaning device 226a, a transfer residual toner depatterning means 2 is provided instead of the cleaning blade.

This transfer residual toner depatterning means 2 is set to 1
It has a brush 2a made of a fiber (trade name: trading card, Kynol, etc.) having an electric resistance of 0 ³ to 10 ⁹ Ωcm. The brush 2a is arranged so as to be in sliding contact with the photosensitive drum 222a, and a voltage of +200 to 1200v is applied. In addition, the charger 223
a is a scotron charger, and is a photosensitive drum 222.
The surface of a is negatively charged substantially uniformly at -450 to -800V.

The conductive brush 2a of the transfer residual toner non-patterning means 2 is brought into sliding contact with the photosensitive drum 222a as the photosensitive drum 222a rotates, and 200 to 1500V is applied.
Is applied to temporarily attract the transfer residual toner on the black photoconductor drum 222a. Since most of the transfer residual toner has a negative polarity, it is adsorbed to the transfer residual toner non-patterning means 2. However, some of the transfer residual toner of the fog toner is positively charged, and these transfer residual toners are Passes without being adsorbed. However, since there is a small amount of transfer residual toner that is not adsorbed and passes through, there is no problem.

Transfer residual toner non-patterning means 2 temporarily
The transfer residual toner trapped in the toner is injected with a positive charge in a time corresponding to the conditions such as the applied bias, the resistance of the brush 2a, the toner particle size, and the resistance, and is formed by the brush 2a and the photosensitive drum 222a. The generated electric field causes the electric field to be returned to the photosensitive drum 222a.

The time from the transfer residual toner being trapped in the transfer residual toner non-patterning means 2 to receiving the electric charge and returning it to the photosensitive drum 222a again is, as described above, the particle size of the toner, the resistance, etc. Therefore, the distribution will have a certain width. Therefore, the transfer residual toner is not patterned. Further, the mechanical cleaning effect of the brush 2a also contributes to the non-patterning of the transfer residual toner.

The toner returned to the photosensitive drum 222a has a positive polarity which is the opposite polarity to the regular polarity.
When the photoconductor drum 222a is charged by the charger 223a, the toner is exposed to the negative corona and has the negative polarity, and is cleaned by the developing device 224a.

In the cleaning mechanism according to this embodiment,
The rubbing force on the photoconductor drum 222a is weaker than that of the blade system used conventionally, and the photoconductor drum 222a
Has the advantage of being less likely to wear.

The cleanerless method is described in detail in Japanese Patent Nos. 27404047 and 2739984.
The description is omitted because it is described in Japanese Patent Publication No. 2667562 and Japanese Patent Publication No. 2667562.

A fur brush method can be used as a method in which the photosensitive drum 222a is less likely to wear. In the case of the fur brush method, it is necessary to collect the cleaned developer. As other methods, a blade cleaning method similar to the cleaning methods of other colors, and a method of setting the contact pressure of the cleaning blade to be smaller than that of the other colors may be considered.

On the other hand, in the tandem system, a reverse transfer phenomenon occurs in which the unfixed toner once transferred onto the transfer material at the image forming station located upstream is taken away at the image forming stage immediately downstream. , A good color image may not be obtained.

The reverse transfer phenomenon will be described below. In the tandem type multicolor image forming apparatus, the first color toner image formed in the developing process of the most upstream image forming station is transferred onto the transfer material, but is formed in the developing process of the next image forming station. When the second color toner image is transferred to the transfer material in an overlapping manner, a phenomenon occurs in which a part of the first color toner image transferred first is reversely transferred to the photoreceptor side.

The same thing occurs when the toner images of the third and fourth colors are transferred onto the transfer material. For this reason, after the transfer of the fourth color toner image is completed at the most downstream image forming station, the toner adhesion amount of the first color toner image on the transfer paper is several tens% of the initial adhesion amount.
Will be reduced to. Then, a similar phenomenon occurs in the second color toner image and the third color toner image.

This is because when the toner adheres to the photoconductor from the developing roller in accordance with the image potential of the photoconductor (drum or belt) in the image forming process, the toner is always charged with a uniform negative charge. However, there is a mixture of one having a weak negative polarity and one having a positive polarity charge on the contrary, and a discharge having a positive polarity after the discharge is generated in the peeling process from the photoconductor. It is said that these phenomena are caused by the fact that each time a transfer charge having a positive polarity is received in the subsequent transfer process, the charge gradually returns to the photoconductor.

In this embodiment, since the black image forming station is arranged at the most upstream side in the paper conveying direction, even if the cleaning-less system is adopted for black, the other color developer is mixed with the black developer. Can be prevented.

If the cleaning-less system is adopted in the downstream image forming station, there is a possibility that other developers may be mixed in. Therefore, the image forming stations for the other color developing agents are used in the blades that have been conventionally used. By adopting a cleaning method, it is possible to prevent other color developers from entering.

With the above-described structure, the multicolor image forming apparatus according to this embodiment has the cyan (C), magenta (M), and yellow (Y) image forming stations Pb.
The cleaning method of ~ Pd is a blade cleaning method, and the black (B) image forming station Pa is provided with a transfer residual toner non-patterning means 2 instead of the cleaning blade, and a cleaning mechanism with a small abrasion to the photosensitive drum 222a is provided. Since it is configured, it is possible to use the photoconductor and the toner for the same period for each color.

When a monochrome image other than the color image is formed, the method shown in FIG. 4 is adopted. By performing such control, it is possible to prevent unnecessary wear of the photoconductor for forming a color image when forming a monochrome image.

[0068]

Since the multicolor image forming apparatus according to the present invention has the above-mentioned structure, the following effects can be obtained. That is, in the multicolor image forming apparatus according to the present invention, the cleaning method used for the black photoconductor is made less likely to wear than the cleaning method used for the photoconductors of other colors. Therefore, the life of the black photoconductor is extended, and the wear and deterioration rates of the photoconductors can be equalized. Therefore, in order to prevent the color balance between the exchanged photoconductor and the photoconductor that was not exchanged from being disturbed as in the conventional technique, and a good image quality cannot be obtained, only one photoconductor is used. Even if deterioration occurs, it is possible to eliminate the inconvenience of having to replace all the photoconductors. That is, the intervals until the replacement of the photoconductors are the same for all the photoconductors, and it is possible to prevent wasteful replacement of the photoconductors.

Further, by making the photoconductor in the image forming station corresponding to black color cleaner-less, the transfer residual toner which is conventionally collected in the cleaning box and discarded is collected in the developing section and used again. Is possible. For this reason, the copy cost can be reduced, and the toner collecting space is not required, so that the apparatus can be made compact.

Further, by arranging the image forming station corresponding to the black color at the most upstream side in the paper conveying direction, it is possible to prevent the mixing of the other color developer due to the retransfer to the black developer adopting the cleanerless system. can do. Further, in the single copy mode, by stopping the operation of the photoconductors in the image forming stations other than the image forming station corresponding to black, it is possible to prevent unnecessary wear of the photoconductor for forming the color image.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an image forming unit of a multicolor image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a detailed configuration of the black image forming station shown in FIG.

FIG. 3 is a vertical cross-sectional view showing a schematic configuration of a conventional digital color copying machine.

FIG. 4 is a flowchart showing a procedure of operation control in a conventional multicolor image forming apparatus.

[Explanation of symbols]

1 Copier body 2 Transfer residual toner non-patterning means 2a brush 110 Image reading unit 111 Platen 112 Double-sided automatic document feeder 113,114 scanning unit 115 Optical lens 116 CCD line sensor 210 Image forming unit 211 Paper feed mechanism 212 Registration roller 213 Transfer Conveyor Belt Mechanism 214 drive roller 215 Driven roller 216 Transfer conveyor belt 217 Fixing device 218 Transport direction switching gate 219 discharge roller 220 output tray 221 Switchback transport route 222a-222d photoconductor drum 223a to 223d charger 224a to 224d Developing device 225a-225d Transfer Discharger 226a to 226d cleaning device 227a to 227d Laser beam scanner unit 228 Paper suction charger 229 Static eliminator 240a-d polygon mirror 241a-d fθ lens 242a-d and 243a-d mirrors P paper Pa-Pd image forming station

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 507 G03G 21/00 21/00 314 21/10 15/08 507B F term (reference) 2H030 AA00 AA06 AB02 AD03 AD07 AD16 BB63 BB71 2H077 AC16 BA10 GA00 GA13 2H134 GA01 GB02 HB00 JA05 JA11 KH10 KH15 KJ02 MA03 MA07 MA11

Claims (4)

[Claims] 1. A plurality of image forming stations having photoconductors having different corresponding colors are arranged along a sheet conveying direction, and color images formed by the image forming stations are sequentially superposed to form an image. In the multi-color image forming apparatus for forming, the image forming station is provided with a cleaning mechanism for removing toner of the photoconductor, and the photoconductor of the image forming station corresponding to black of the image forming stations, A multicolor image forming apparatus to which a cleaning method that is less likely to wear than a photoconductor in an image forming station other than that is applied. 2. The multicolor image forming apparatus according to claim 1, wherein the photoconductor in the image forming station corresponding to the black color is not provided with a cleaner. 3. The multicolor image forming apparatus according to claim 1, wherein the image forming station corresponding to the black color is arranged on the most upstream side in the sheet conveying direction. 4. The operation of the photoconductor in an image forming station other than the image forming station corresponding to the black color is stopped in the single copy mode. The multicolor image forming apparatus described in 1.