JP2002365873A - Method and apparatus for image forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method by which the deterioration of an image quality due to the color mixture of recovered toner at the time of reusing the recovered toner recovered from an image carrier as recycle toner can be suppressed and an image forming device using the method thereof. SOLUTION: Residual toner on a photoreceptor 21 after a toner image is transferred is recovered, and the recovered toner is reused by returning it as the recycle toner to a developing unit 20. The rate of the recycle toner in color mixture toner in a state that the hue change of an image formed with the color mixture toner in which the toner of other color is mixed reaches an allowable limit level is set as a limit color mixture ratio, the color mixture ratio of the recycle toner to specific color toner at the inside of the developing unit 20 is controlled so as to be equal to or lower than the limit color mixture ratio. Thereby, the deterioration of the image quality due to the color mixture of the recovered toner can be suppressed when the recovered toner is reused as the recycle toner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus for a copying machine, a printer, a facsimile, and the like, and more particularly, to a method for forming an image on an image carrier by an image forming process such as an electrostatic recording system or an electrophotographic system. An image forming method and apparatus for obtaining a multicolor image by multiplex-transferring a plurality of toner images formed on an intermediate transfer body or a transfer material as a transfer body onto which the toner images are transferred, wherein the toner images are transferred. The untransferred toner of each color remaining on the image carrier after the cleaning is recovered by a cleaning unit, the recovered toner recovered by the cleaning unit is returned to the developing device, and the recovered toner is reused as recycled toner. The present invention relates to a method and an apparatus.

[0002]

2. Description of the Related Art In recent years, a large number of color documents have been handled in offices, and it has been desired to provide a small and high-speed image forming apparatus such as a full-color printer and a full-color copying machine. 2. Description of the Related Art In recent years, a color laser printer, which has become widespread, generally has a plurality of developing units arranged so as to be able to contact one photoconductor, and creates a toner image of each color for each rotation of the photoconductor, and then prints the toner image on paper or paper. A so-called one-drum configuration in which a color toner image is formed by transferring the image onto a transfer material such as an OHP sheet is mainly used.

In this one-drum type image forming apparatus, toner images of respective colors on a photoreceptor are primarily transferred onto an intermediate transfer member and superimposed, and then collectively secondarily transferred onto a transfer material. There are an intermediate transfer type and a direct transfer type in which a toner image of each color on a photoreceptor is sequentially transferred to transfer paper held on a transfer drum or the like to create a color toner image.

The direct transfer type image forming apparatus has the advantages that the structure is simple and the cost is low, and that the image forming speed can be increased. However, in this direct transfer type image forming apparatus, stable transfer is difficult because the resistance and moisture content of the transfer paper change in the process of sequentially transferring the toner images of each color and the transfer conditions are different. On the other hand, in the intermediate transfer type image forming apparatus, since the transfer of the toner image to the transfer material only needs to be performed once, stable transfer can be performed. Further, in an image forming apparatus of a direct transfer system in which a transfer material is wound around a transfer drum, the thickness and type of the transfer material are limited. On the other hand, the intermediate transfer type image forming apparatus has an advantage that the versatility of the transfer material is high without any limitation on the thickness and type of the transfer material.

However, in the above-described one-drum image forming apparatus, in any method, when obtaining a full-color image in which four-color toner images are superimposed, for example, the photosensitive member is rotated at least four times to obtain the toner of each color. It is necessary to form an image, and it takes time to form a color image, so that there is a problem that productivity is not improved.

Therefore, conventionally, in order to cope with high-speed color image formation, a plurality of photoconductors (usually three or four) are juxtaposed along a transfer material conveying path, and each photoconductor is individually provided. After the formed latent images of each color are individually formed into toner images by a plurality of developing devices mounted on each photoconductor, the toner images of each color are transferred onto the conveyed transfer material while being sequentially superimposed on each other. A so-called tandem type or in-line type image forming apparatus configured to obtain a color image has been proposed. For example, Japanese Patent Application Laid-Open No. Sho 53-74037 (U.S. Pat. No. 4,162,843) discloses that in order to speed up the color image output, a plurality of photoconductors are stacked and the transfer material is belt-shaped. There has been proposed an image forming apparatus for sequentially transferring a toner image in a multiplex manner while being conveyed by a conveying means.

In the tandem type or in-line type image forming apparatus, if the peripheral speed of the photosensitive member is the same, it is possible to form an image at four times or more the speed of the one-drum type image forming apparatus. is there. However, since a normal tandem type or in-line type image forming apparatus is configured to directly transfer a toner image on a photosensitive member onto a transfer material, as described above, transfer of a toner image to a transfer material is performed. There are many problems such as unstable image quality and difficulty in positioning the transfer material when transferring the toner image. In order to solve such a problem, an image forming apparatus of a so-called tandem intermediate transfer system using a tandem system and an intermediate transfer member has been proposed (Japanese Utility Model Application Laid-Open No. 59-59).
192159).

In this type of image forming apparatus, each color toner image formed on a photoreceptor as an image carrier by a plurality of developing devices containing toners of each color is transferred to an intermediate transfer member or a transfer material. After the superposition and transfer, the untransferred toner of each color remaining on the surface of the photoconductor is removed and collected by a cleaning device, and the next image is formed on the surface of the photoconductor. Therefore, when the cleaning device has a configuration for removing and collecting the untransferred toner of each color so as not to mix colors, the collected toner of each color removed and collected from the photoreceptor by the cleaning device is the same. By returning the collected toner to the developing device in which the color toners are stored, the collected toner can be reused as recycled toner.

In particular, in the tandem type color image forming apparatus, a plurality (usually three) of image forming units including a photoreceptor, a developing device, a cleaning device, etc., corresponding to the number of toners of each color required for full color image formation. Or 4
And each of the image forming units is configured to individually form a toner image of each color. Therefore, in the tandem-type image forming apparatus, the untransferred toner remaining on each photoconductor can be collected by the cleaning device corresponding to each photoconductor without color mixing. The collected toner can be returned to each developing device, and the collected toner can be easily reused as recycled toner.

[0010] Such recycling of the recovered toner is particularly important in an image forming apparatus for forming a color image as described above. That is, in this type of image forming apparatus, an image having a large image area ratio and a large number of colors, such as a photographic document, is often output as compared with black and white, so that the toner consumption of each color is relatively large. However, as the size and weight have been reduced, it has become difficult to secure a large storage space capable of sufficiently accommodating the toners of the respective colors. Therefore, the viewpoints of resource saving, space saving, running cost reduction, etc. Therefore, it is important to make the collected toner recyclable.

[0011]

However, the conventional image forming apparatus has the following problems when the collected toners of a plurality of colors are used as recycled toners. That is, in an image forming apparatus that forms an image using a toner of a plurality of colors of this type, different colors of toner are mixed in the collected toner of each color removed and collected from the photoreceptor by the cleaning device. When the recovered toner is reused as recycled toner, image quality may be degraded due to the effect of the color mixture.

Such color mixing of the collected toner occurs in any type of image forming apparatus. Particularly, in the image forming apparatus having the one-drum configuration, generally, the
Since a toner image of each color is sequentially formed on one photoreceptor and the residual toner of each color remaining on the photoreceptor is collected by one cleaning device, it is possible to avoid color mixing of the collected toner. Can not. However, if the residual toner of each color is collected by a plurality of cleaning devices corresponding to the respective colors, extreme color mixing of the collected toner can be avoided as in the case of the tandem-type image forming apparatus. become. However, even with such a configuration, it is unavoidable to mix colors of the collected toner.

For example, using four developing units in which four color toners of yellow, magenta, cyan, and black are individually stored, four colors are formed on one to four photosensitive members as an image carrier. Toner images of yellow, magenta, cyan,
The toner images of each color formed on the photoreceptor are sequentially superimposed on an intermediate transfer body as a transfer receiving body and primary-transferred, and then the toner image on the intermediate transfer body is transferred. Secondary transfer is collectively performed on the material, and the residual toner of each color remaining on the photoreceptor after the primary transfer is collected separately for each color toner by four cleaning devices corresponding to the residual toner of each color. Think about it. Here, it is assumed that no toner remains on the intermediate transfer body after the secondary transfer.

In such a case, the remaining toner on the photoreceptor after the first transfer of the first color yellow toner image to the intermediate transfer member is not mixed with another color toner.
Therefore, the image quality of the residual toner of the first color does not deteriorate even if the collected toner is reused as recycled toner. However, the remaining toner on the photoconductor after the magenta, cyan, and black toner images of the second and subsequent colors are sequentially primary-transferred onto the intermediate transfer body may be mixed with another color toner. That is, in this type of image forming apparatus, when the magenta toner image of the second color is primarily transferred to the intermediate transfer body, the yellow toner already primary-transferred on the intermediate transfer body is applied to the surface of the photoconductor. The reversely transferred first color yellow toner may mix with the reversely transferred second color magenta toner remaining on the photoreceptor. Similarly, the first color yellow toner and the second color magenta toner reverse-transferred to the photoreceptor are mixed with the residual toner composed of the third color cyan toner on the photoreceptor, and the fourth color black toner on the photoreceptor. The residual toner composed of
Yellow toner of the second color, magenta toner of the second color and 3
Colors may be mixed. For this reason, with respect to the remaining toner of each color of magenta, cyan, and black of the second and subsequent colors, if the collected toner is reused as recycled toner as it is, there is a high possibility that the image quality is deteriorated.

Several measures have been proposed to prevent such mixed color of the collected toner. For example, JP-A-2000-
In the "color image forming apparatus" disclosed in Japanese Patent Application Laid-Open No. 242152, a part of the toner previously transferred onto the intermediate transfer member is normally charged due to discharge when the toner image is transferred from the image bearing member to the intermediate transfer member. It is considered that the charged toner has the opposite polarity to the polarity, and the toner having the opposite charged polarity is reversely transferred to the image bearing member when transferring the toner of the next color. By providing a recovery means utilizing the opposite, color mixing on the image bearing member is prevented.

However, in such a color image forming apparatus, it is necessary to newly provide a reversely-charged toner removing means for removing the reversely-charged toner, which is unnecessary in the related art, near the photoreceptor. In addition, it is disadvantageous in that the cost increases due to an increase in parts. Further, the toner charged with the opposite polarity has a stable normal charging polarity from the beginning, and the charging amount of the toner having the opposite polarity is not stable. Furthermore,
In many cases, the toner reversely transferred to the photoconductor has a charge close to “0”. Therefore, the above-described reverse-charged toner removing unit cannot completely collect the mixed color toner. Therefore, such a method cannot reliably prevent the mixed color of the collected toner.

The "image forming apparatus" disclosed in Japanese Patent Application Laid-Open No. 10-293432 is not a tandem type apparatus. However, in order to prevent reverse charging of toner, which causes reverse transfer of toner to a photosensitive member, A method of removing the background potential before transfer is employed. Here, it is assumed that the toner image before transfer is not scattered by adjusting the degree of static elimination. However, in actuality, the potential in the static elimination by light irradiation sharply decreases, so that the toner in the image area moves to the periphery and the image is removed. It blurs.
Also, if the static electricity removal of the background potential before transfer is small, the toner image is transferred from the image bearing member to the intermediate transfer member as in the case of the “color image forming apparatus” of JP-A-2000-242152 described above. Then, the reversely charged toner is reverse-transferred to the photoconductor by the discharge, so that it is not possible to prevent the mixed color of the collected toner due to the reverse transfer of the reverse-charged toner to the photoconductor. Thus, with this image forming apparatus, it is very difficult to completely prevent color mixing of the collected toner.

Further, in the "image forming apparatus" disclosed in JP-A-8-63067 and JP-A-2000-267366, problems of the toner collected by cleaning include aggregation of the toner and deterioration of charging characteristics. It proposes to determine the supply ratio of recycled toner and optimize the process conditions. However, in this image forming apparatus, focusing on the color mixing state of the collected toner as described above,
Since it is not possible to detect or predict the color mixture state of the collected toner, it is not possible to suppress the deterioration in image quality due to the mixed color of the collected toner when the collected toner is reused as the recycled toner.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for mixing color of recovered toner collected from an image carrier when the recovered toner is reused as recycled toner. An object of the present invention is to provide an image forming method capable of suppressing a decrease in image quality, and an image forming apparatus using the method.

[0020]

In order to achieve the above object, according to the present invention, a plurality of latent images corresponding to respective colors of an image composed of at least two colors are formed on an image bearing member. Each latent image is visualized by a plurality of developing units that supply a specific color toner corresponding to the image color, and the toner images of each color on the image carrier that are visualized by the unique color toner in each developing unit are covered. An image forming method for forming a multi-color image by sequentially superimposing and transferring on a transfer body, wherein untransferred toner of each color remaining on the image carrier after transferring the toner image is collected. In the image forming method in which the collected toner is returned to the developing device and the collected toner is reused as a recycled toner, the image forming method is performed using the mixed color toner in a state where each of the recycled toner is mixed with the unique color toner in each of the developing devices. Of the image When the phase change reaches an acceptable limit level, the ratio of the recycled toner in the mixed color toner is defined as the limit color mixture ratio, and the color mixture ratio of the recycled toner with respect to each unique color toner in each developing device is defined as the limit color mixture ratio. The ratio is controlled so as to be equal to or less than the rate.

In this image forming method, the color mixture ratio of the recycled toner with respect to each intrinsic color toner in each developing unit is controlled so as to be equal to or less than the above-mentioned limit color mixture ratio. As described above, by controlling the color mixture ratio to be equal to or less than the limit color mixture ratio, the hue change of an image formed by the mixed color toner in a state where the recycled toner is mixed with the intrinsic color toner is reduced.
It is possible to keep the state below an acceptable limit level. Therefore, in this image forming method, it is possible to suppress a decrease in image quality due to color mixing of the collected toner when the collected toner collected from the image carrier is reused as a recycled toner. Here, as a method of controlling the color mixture ratio of the recycled toner with respect to each intrinsic color toner in each of the developing devices to be equal to or less than the limit color mixture ratio, each developing device is so controlled that the color mixture ratio is equal to or less than the limit color mixture ratio. A method of controlling the amount of new toner supplied to the developing device, a method of controlling the amount of recycled toner returned to each developing device, and the like can be given.

According to a second aspect of the present invention, in the image forming method of the first aspect, the amount of each recycled toner returned to each of the developing units is controlled so that the color mixing ratio of the recycled toner with respect to the intrinsic color toner of each developing unit is adjusted. The color mixing ratio is maintained at or below the limit color mixing ratio.

As described above, as one method of controlling the color mixture ratio of the recycled toner to each intrinsic color toner in each of the developing devices to be equal to or less than the limit color mixture ratio, the color mixture ratio is set to be equal to or less than the limit color mixture ratio. There is a method for controlling the amount of new toner supplied to each developing device. But,
In this method, when each developing device uses a two-component developer, new toner is supplied into each developing device in order to maintain the color mixture ratio below the limit color mixture ratio. There is a possibility that the toner density of the two-component developer becomes higher than an appropriate density, and an image having a target density cannot be formed. When each developing device uses a one-component developer containing only toner, the toner concentration does not increase due to such replenishment of new toner, but in this case, replenishment of new toner causes There is a possibility that the amount of the developer in the developing device becomes larger than an appropriate amount and the replenished new toner cannot be sufficiently charged. Further, in this method, the developer may overflow from each developing device. Therefore, in this image forming method, the amount of each recycled toner returned to each of the developing devices is controlled so that the color mixing ratio of the recycled toner with respect to the intrinsic color toner of each developing device is maintained at or below the limit color mixing ratio. I do. As a result, it is possible to solve the above-described problems such as an increase in the toner concentration of the developer in each developing device, insufficient charging of the toner, and overflow of the developer from each developing device. In other words, most of the recycled toner returned to each developing device is originally supplied from each developing device. Therefore, when this recycled toner is returned to each developing device, There is no increase in the toner concentration of the developer, insufficient charging of the toner, or overflow of the developer from each developing device.

According to a third aspect of the present invention, in the image forming method according to the first aspect, the limit color mixing ratio of each unique color toner in each developing unit is determined by the color of each unique color toner in each developing unit and each developing unit. It is characterized in that it is determined in advance for each combination with the color of the specific color toner of another developing device returned to the developing device.

In this type of image forming apparatus, the limit color mixing ratio of each of the intrinsic color toners, that is, the allowable limit level of the hue change of the image formed by the mixed color toner when the yellow toner is mixed with the magenta toner, and the cyan The allowable limit level of the hue change of the image formed by the mixed color toner when the yellow toner and the magenta toner are mixed with the toner, and the mixed color toner when the yellow toner, the magenta toner, and the cyan toner are mixed with the black toner. It has been found that the permissible limit levels of the hue change of the image differ from each other (details will be described later). Therefore, in this image forming method, the limit color mixing ratio of each unique color toner in each developing device in the image forming method according to claim 1 is returned to the color of each unique color toner in each developing device and to each developing device. It is determined in advance according to the combination with the color of the specific color toner of another developing device to be used. As a result, the amount of change in hue on an image formed by the mixed-color toner in each developing device, that is, the degree of image quality deterioration of the image can be suppressed within a range equal to or less than the allowable limit level.

According to a fourth aspect of the present invention, in the image forming method of the third aspect, a toner image of each color on an image carrier formed by each unique toner in each of the developing units is transferred onto the transfer-receiving member. The transfer order is such that the total of the critical color mixing ratios of each unique color toner and other unique color toners in each developing unit is ascending.

As described above, the toner mixed with each unique color toner in each developing unit is a toner of a different color from each unique color toner. Therefore, the limit color mixture ratio of the mixed color toner in which the toners of the other colors are mixed with the respective color toners in the respective developing units is different due to different colors of the mixed toner. That is, the limit color mixing ratio when a toner of another color is mixed with a developing device in which magenta toner is a unique color toner, and a toner in another color with a developing device in which cyan toner is a unique color toner. Are different from each other when the color mixture is mixed with the developing device in which the black toner is the intrinsic color toner and when the other color toner is mixed. For example, even if a small amount of yellow toner is mixed in a developing device containing black toner, the hue of an image formed by the mixed color toner does not change so much. On the other hand, when the black toner is mixed, the hue of the image formed by the mixed color toner is largely changed even if the mixed amount is small. As described above, each developing device in this type of image forming apparatus has a unique limit color mixing ratio corresponding to the color of the stored unique color toner. For this reason, for example, if the first color toner image is formed by a developing device having a high marginal color mixture such as a developing device containing a black toner, each developing device forming the second and subsequent color toner images is formed. In the meantime, the black toner of the first color toner image is mixed, and the limit color mixing ratio of each developing device that forms the second and subsequent color toner images is significantly reduced. Such a decrease in the limit color mixing ratio of the developing device means that the color hue of the image changes due to the color mixing of a small amount of toner, and the image quality deteriorates. As described above, in this type of image forming apparatus, there is a large difference in the hue of the formed image depending on the order in which the toner images of each color are formed. Therefore, in this image forming method, the transfer order of the toner images of each color on the image carrier formed by the respective toners in the respective developing devices onto the transfer-receiving member is determined by each of the specific toners in the respective developing devices. The order of the total of the limit color mixing ratios of the color toner and the other unique color toner is ascending. As a result, the limit color mixture ratio of each developing device can be set to the maximum, and a larger amount of recycled toner can be reused.

According to a fifth aspect of the present invention, in the image forming method of the third aspect, a limit color mixing ratio of the yellow toner as the other unique color toner to the magenta toner as the unique color toner is 6%. It is characterized by the following.

As described above, the limit color mixing ratio of each of the developing units has a different value depending on the difference in the color of the toner mixed into each unique color toner. Therefore, the present inventor conducted an experiment in which an image was formed using various kinds of mixed-color toners in which toners of the respective colors were combined, and a limit color mixing ratio of the various kinds of mixed-color toners was determined from a change in hue on the image. See below). From this experiment, it was found that the allowable limit level of the image when the yellow toner was mixed in the developing device using the magenta toner as the intrinsic color toner was when the color mixing ratio of the yellow toner to the magenta toner was 6%. I found it. Therefore, in this image forming method, the limit color mixing ratio of the yellow toner to the magenta toner is set to 6%. Thereby, the hue change on the image of the toner image formed by the developing device using the magenta toner as the intrinsic color toner can be kept within an allowable level.

According to a sixth aspect of the present invention, in the image forming method of the third aspect, the limit color mixing ratio of the magenta toner as the color of the other unique color toner to the cyan toner as the unique color toner is 7%. It is characterized by having done.

According to the experiment described in claim 5, when the magenta toner is mixed in the developing device using the cyan toner as the intrinsic color toner, the permissible limit level of the image is such that the color mixing ratio of the magenta toner to the cyan toner is 7%. I found that it was the case. Therefore, in this image forming method, the limit color mixing ratio of the magenta toner to the cyan toner is set to 6%. Thus, the hue change on the image of the toner image formed by the developing device using the cyan toner as the intrinsic color toner can be kept within an allowable level.

According to a seventh aspect of the present invention, in the image forming method of the second aspect, each of the recycled toners calculated on the basis of a value indicating the image area of the toner image in which the order in which the toner images are transferred to the transfer object comes first. And the color mixture ratio of the intrinsic color toner and the recycled toner of each developing device before the recycled toner is returned to the respective developing devices when the recycled toner is returned to each developing device. Calculate the color mixing ratio of the recycled toner with respect to the specific color toner, and supply the amount of each recycled toner returned to each developing device so that the color mixing ratio of the recycled toner with respect to the specific color toner of each developing device is equal to or less than the limit color mixing ratio. Is determined.

In this image forming method, the color mixing ratio of the different color toner to each recycled toner is calculated based on the value indicating the image area of the toner image in which the order in which the toner image is transferred to the transfer object comes first. You. When the recycled toner is returned to each developing device, the color mixing ratio of the different color toner to each recycled toner and the color mixing ratio of the intrinsic color toner and the recycled toner of each developing device before the recycled toner is returned. The color mixing ratio of the recycled toner to the intrinsic color toner in each developing device is calculated. Then, based on the calculation result, the supply amount of each recycled toner to be returned to each developing device is determined so that the color mixing ratio of the recycled toner with respect to the intrinsic color toner of each developing device is equal to or less than the limit color mixing ratio. As a result, the color mixture ratio of the recycled toner with respect to the intrinsic color toner in each developing device is always maintained at or below the limit color mixture ratio, and good image formation is performed (details will be described later).

According to a further aspect of the present invention, there is provided an image bearing member on which a plurality of latent images corresponding to at least two or more colors of an image are formed, and a specific color toner corresponding to each image color is supplied. A plurality of developing devices for visualizing each latent image formed on the carrier, and a toner image of each color on the image carrier visualized by a toner of a unique color in each developing device is transferred onto a transfer-receiving member. Transfer means for sequentially superimposing and transferring the toner images, cleaning means for collecting untransferred toner of each color remaining on the image carrier after transferring the toner image, and developing device for collecting the collected toner collected by the cleaning means. 7. An image forming apparatus comprising: a toner conveying means for returning the toner to a toner image;
Alternatively, the image forming method according to the seventh aspect is characterized in that an image is formed by controlling the color mixture ratio of the intrinsic color toner and the recycled toner in each of the developing units.

In this image forming apparatus,
Image formation is performed by 2, 3, 4, 5, 6, or 7 image forming methods. As a result, the deterioration of image quality due to the mixture of a plurality of toners is suppressed, and an image forming apparatus that can effectively reuse the collected toner as recycled toner can be provided.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A color printer (hereinafter simply referred to as a "printer") as an image forming apparatus according to the present invention will be described below.
An embodiment applied to the present invention will be described. FIG. 1 shows an overall schematic configuration of a copier equipped with a printer 10 according to the present embodiment. The printer 10 includes an image writing unit 12, an image forming unit 13, a paper feeding unit 14, and the like for forming a color image by an electrophotographic method. FIG.
FIG. 1 is a schematic configuration diagram illustrating a configuration of only the image forming unit 13 of the printer 10.

First, the schematic configuration and operation of the printer 10 will be described. In FIGS. 1 and 2, an image writing unit 12 of a printer 10 stores an image signal, which has been subjected to image processing in the image processing unit 1 of the copying machine based on the image signal, in magenta (M) and yellow for image formation. (Y), cyan (C),
The signals are converted into black (BK) color signals and transmitted. The image writing unit 12 includes, for example, a laser light source, a deflector such as a rotating polygon mirror, a scanning imaging optical system, a laser scanning optical system including a mirror group, and a large number of one-dimensional or two-dimensional mirrors. It is composed of an LED array in which LEDs are arranged, and an LED writing system composed of an imaging optical system, and has four writing optical paths 12BK, 12Y, 12Y corresponding to the respective color signals.
M, 12C. This image writing unit 12 is configured as shown in FIG.
As shown in FIG. 4, four colors for each color provided in the image forming unit 13 are provided.
Photoreceptors 21Y, 21M, 21 of each image forming unit
C, 21BK, each writing optical path 12Y, 12M, 12C,
An image corresponding to each color signal is written through 12BK.

Each of the image forming units provided in the image forming unit 13 includes a yellow (Y), a magenta (M),
Photoconductors 21Y and 21 for cyan (C) and black (BK)
As M, 21C, and 21BK, an OPC photoconductor is usually used. Further, each photoconductor 21Y, 21M, 21C, 2
As shown in FIGS. 2 and 3, the charging devices 16Y, 16M, 16C, and 16BK, the image writing unit 12
Developing units 20Y, 20M, 20C, 20B for each color of black, magenta, yellow, and cyan
K, primary transfer bias roller 23 as primary transfer means
Y, 23M, 23C, 23BK, cleaning device 30
Y, 30M, 30C, 30BK, and static eliminators 24Y, 24M, 24C, 24B for eliminating charges on the surface of the photoconductor
K, etc. are provided.

Here, the developing units 20Y, 20M, 20
As C and 20BK, a two-component magnetic brush developing type developing device is used. Further, each photoconductor 21Y, 21M, 2
1C, 21BK, and each primary transfer bias roller 23Y,
An intermediate transfer belt 22 is stretched so as to be interposed between the intermediate transfer belts 23M, 23C, and 23BK. On the intermediate transfer belt 22, toner images of respective colors formed on respective photoconductors are sequentially superimposed. Transcribed.

On the other hand, after the transfer paper P is fed from the paper feed section 14 of the printer 10 or the paper feed bank (see FIG. 1) of the copying machine, the registration roller 17 shown in FIG.
Is carried on the transfer / conveying belt 50 via the And
When the intermediate transfer belt 22 and the transfer conveyance belt 50 come into contact with each other, the toner image transferred onto the intermediate transfer belt 22 is transferred to a secondary transfer bias roller 60 as a secondary transfer unit.
Is subjected to secondary transfer (collective transfer). Thereby, a color image is formed on the transfer paper P. The transfer paper P on which the color image is formed in this manner is transported to the fixing device 15 by the transfer transport belt 50. And the transfer paper P is
After the image transferred thereto is fixed by the fixing device 15, the image is discharged outside the printer main body.

The toner remaining on the intermediate transfer belt 22 without being transferred onto the transfer paper P during the secondary transfer is removed from the intermediate transfer belt 22 by the belt cleaning device 25. A lubricant application device 26 is provided downstream of the belt cleaning device 25. The lubricant applying device 26 includes a solid lubricant 26a and a conductive brush 26b that rubs the intermediate transfer belt 22 to apply the solid lubricant 26a. The conductive brush 26b
Is in constant contact with the intermediate transfer belt 22 to apply the solid lubricant 26a to the intermediate transfer belt 22. The solid lubricant 26a has a function of improving the cleaning property of the intermediate transfer belt 22, preventing occurrence of filming, and improving durability.

Each of the photoconductors 21Y, 21M, 21C, 2
Before the image writing is performed, each charging surface 16BK, 16M, 1B provided at an upstream portion of each of the writing optical paths 12Y, 12M, 12C, 12BK is formed on each surface of the 1BK.
It is charged to about -700 V by 6Y and 16C.
The charging device 16Y, 1 of the printer 10 according to the present embodiment.
As 6M, 16C and 16BK, conductive rubber rollers are used. The charging devices 16Y, 16M, 16
Each rubber roller serving as C, 16BK
Y, 21M, 21C, and 21BK are installed at a distance of about 50 μm so as to perform non-contact charging. An AC voltage of about 1 kHz and a peak-to-peak voltage of 2 kV is applied to each rubber roller, and the center value thereof is set to be about -800 V. As a result, the surfaces of the photoconductors 21Y, 21M, 21C, and 21BK are uniformly charged to about -700V.

Each of the photoconductors 21Y, 21M, 21C,
The charging means for charging the surface of the 21BK is not limited to the above-described non-contact charging means. For example, a conductive rubber roller may be connected to each of the photoconductors, 21M, 21Y, 21C,
Contact charging, which is installed so as to be in contact with 21BK, AC + DC charging, DC bias roller charging, which charges each photoreceptor by applying only a DC bias of about -1400 V without applying an AC bias, and is conventionally used. Charging means such as corona charging or brush charging using a corotron or scorotron can be used.

As described above, each photoconductor 21Y, 21
After the surfaces of M, 21C and 21BK are charged, an image is written from the image writing unit 12 onto the surfaces of the photoconductors 21BK, 21M, 21Y and 21C. This allows
On the surface of each photoconductor 21Y, 21M, 21C, 21BK,
An electrostatic latent image corresponding to each color image of black, magenta, yellow, and cyan is formed. These electrostatic latent images are developed by black, magenta, yellow, and cyan developing units 20Y and 20Y.
M, 20C, and 20BK.

Each of the developing units 20Y, 20M, 20C, 2
OBK is a developing roller 201, a doctor blade 202, two screws 203 and 204, as shown in FIG.
It comprises a toner density sensor 205, a developing case 206 and the like. Here, the developing roller 201 and the screw 2
The positional relationship between the screws 203 and 204 is such that the screws 203 and 204 are positioned diagonally below the developing roller 201. Also, two screws 203, 204
Are arranged in parallel in the horizontal direction. Further, two screws 203,
A partition plate 206a is provided to partition between the developing case 204 and the developing case 206.
Is divided into two rooms. Further, the rear side and the front side of the partition plate 206a are cut out so that the developer in each chamber of the developing case 206 is circulated and conveyed by two screws 203 and 204.

An opening 206b is formed in a portion of the developing case 206 facing the photoconductor, and a part of the developing roller 201 is exposed from the opening 206b. Further, the developing roller 201 and the screw 2
3, the doctor blade 201 is arranged so that the space above the screw 204 of the developing case 206 is slightly larger, as shown in FIG. Each developing unit 2
The developing cases 206 of 0Y, 20M, 20C, and 20BK contain developers of black, magenta, yellow, and cyan for developing the electrostatic latent images corresponding to the respective color images. Here, a two-component developer in which a non-magnetic toner and a magnetic carrier are dispersed and mixed is used as the developer.

Each developing unit 20Y, 20M, 20C, 20B
The K developer is stirred by the two screws 203 and 204 rotating in opposite directions so as to constantly circulate in each chamber of the developing case 206 through the notch on the back side and the front side of the partition plate 206a. It is conveyed while.
Then, the developer is supplied to the developing roller 201 by a screw 205 which stirs and transports the developer while circulating. The developing roller 201 includes a magnet roller 201a serving as a magnetic field generating unit and a magnet roller 2a.
And a non-magnetic developing sleeve 201b rotatably mounted so as to cover the outer periphery of the developing sleeve 201a.

The developer supplied to the developing roller 201 as described above is applied to the developing sleeve 20 by the magnetic force of the magnet roller 201a and the rotation of the developing sleeve 201b.
It is pumped to the surface of 1b and held in the shape of a magnetic brush. The developer held in a magnetic brush shape on the surface of the developing sleeve 201b is conveyed toward the opening 206b of the developing case 206 while rotating along with the rotation of the developing sleeve 201b. The developer is cut by a doctor blade 202 in front of the opening 206b and measured so as to have an appropriate amount, and then the surface of the developing roller 201 exposed from the opening 206b and the photosensitive member It is sent to the development area between the surface.

The developer, which has been cut off by the doctor blade 202 and thus prevented from proceeding to the above-described developing area, is moved along the outer periphery of the magnetic brush-like developer held on the surface of the developing sleeve 201b. , Screw 2
05, and returns to the circulating conveyance path of the developing case 206 by its own weight. The developer returned to the circulating conveyance path is again stirred and conveyed by the two screws 203 and 204, and then supplied to the developing roller 201 again by the screw 205.

On the other hand, the developer sent to the developing area
The toner is transferred to the electrostatic latent image formed on the photoreceptor to visualize the electrostatic latent image, thereby forming a toner image on the photoreceptor. That is, a developing bias composed of an AC voltage of 2.25 kHz and a peak-to-peak voltage of about 1 kV is applied to the developing sleeve 201b with a center value of -500V. Due to this developing bias, a potential difference from an exposed area (charge potential of about -150 V) on the photoreceptor causes
The toner in the developer held on the developing sleeve 201b shifts to an electrostatic latent image formed on the photoconductor.

The surplus developer consisting of the toner and the carrier not consumed when the electrostatic latent image is visualized is transferred into the developing case 206 while being held on the developing sleeve 201b. Will be returned. Then, the portion of the surface of the developing sleeve 201b where the magnetic force of the magnet roller 201a is not acting is separated from the developing sleeve 201b,
It falls on the screw 205 by its own weight. As a result, the surplus developer is recovered in the circulating transport path of the developing case 206, is again agitated and transported by the two screws 203 and 204, and is again supplied to the developing roller 201 by the screw 205.

As described above, the developer is stirred and conveyed by the two screws 203 and 204, whereby
While circulating in the developing case 206, the developing sleeve 20
Supply and recovery for 1b are repeated. Here, when the developing process for visualizing the electrostatic latent image on the photoreceptor is repeatedly executed and toner consumption in the developer proceeds,
The toner concentration of the developer contained in the developing case 206 gradually decreases. Therefore, each developing unit 20
In Y, 20M, 20C, and 20BK, the toner concentration of the developer contained in the developing case 206 is detected by the toner concentration sensor 205. Then, based on the detection result of the toner concentration sensor 205, the developing case 2 is supplied by a toner replenishing device (not shown) so that the toner concentration of the developer in the developing case 206 always becomes constant.
A new toner for replenishment is supplied in a timely manner.

In this manner, each of the photoconductors 21Y, 21M,
The toner images of the respective colors formed on the photoconductors 21C and 21BK are brought into contact with the surfaces of the photoconductors by the primary transfer bias rollers 23Y, 23M, 23C and 23BK arranged corresponding to the photoconductors. Rotating intermediate transfer belt 22
Are sequentially superimposed on each other and are primarily transferred. That is, the primary transfer bias rollers 23Y and 23Y provided opposite to the respective photoconductors so as to sandwich the intermediate transfer belt 22 therebetween.
The toner image on the photoconductor is electrostatically transferred onto the intermediate transfer belt 22 by the transfer electric field generated in the primary transfer area between each photoconductor and the intermediate transfer belt 22 by 3M, 23C, and 23BK. You. In the present embodiment, a primary transfer bias roller made of conductive foamed EPDM rubber (rubber hardness JIS-A 30 degrees, volume resistance 108 Ωcm) is used.
A transfer electric field is generated by applying a voltage of about 1.5 kV.

The intermediate transfer belt 22 can be made of various materials.
Polyurethane rubber layer is formed on polyimide belt with excellent durability and high Young's modulus, Pvdf belt with excellent surface smoothness, or polyurethane resin layer,
Further, it is preferable to use a multilayer belt or the like in which a coating layer containing a fluorine component is formed on the polyurethane rubber layer and an elastic layer is provided on the surface. In particular, a multilayer belt having an elastic coat layer provided on a polyurethane rubber layer has an elastic surface, so that it has good adhesion to a photoreceptor surface and a transfer material surface, and has excellent primary transferability and secondary transferability. ing.
Further, as the intermediate transfer belt 22, 10 ¹⁰ to 10
^{A material} having a volume resistance of about ¹² Ωcm and a surface resistance of a portion on which the toner is applied and having a characteristic value of 10 ¹² / □ or more and having excellent transferability is preferable.

As described above, each photoconductor 21Y, 21
The toner images of the respective colors formed on M, 21C, and 21BK are sequentially superimposed on the surface of the intermediate transfer belt 22 so as to form one image.
By the next transfer, 4
A full-color toner image composed of color toners is formed.
Then, the full-color toner image formed on the intermediate transfer belt 22 is fed by the registration roller 16 and transferred onto the transfer paper P carried on the transfer conveyance belt 50 by the secondary transfer bias roller 60. Next transfer (collective transfer) is performed. The transfer paper P on which the full-color image is secondarily transferred in this manner is conveyed to the fixing device 15 by the transfer conveyance belt 50, and after the secondary transfer image is fixed by the fixing device 15, is discharged outside the printer main body. . The residual toner remaining on the intermediate transfer belt 22 during the secondary transfer is
Intermediate transfer belt 2 by belt cleaning device 25
2 removed. After that, the next image is formed by the image forming units of each color of the image forming unit 13.

Next, cleaning devices 30Y and 30Y for removing the toner remaining on the photoreceptor after the primary transfer.
0M, 30C, and 30BK will be described. As shown in FIG. 3, the cleaning device of the present embodiment includes a cleaning blade 30 made of an elastic polyurethane rubber.
1 and a fur brush 302 having conductivity are used. An electric field roller 303 made of metal is arranged in contact with the fur brush 302. A scraper 304 is disposed in contact with the electric field roller 303.

In FIG. 3, the toner remaining on the photoconductor is first scraped off from the photoconductor by a fur brush 302 rotating in a direction opposite to the rotation direction of the photoconductor (counter direction). At this time, the fur brush 30
2 adheres to the electric field roller 303 rotating in the counter direction with respect to the fur brush 302 and is removed. Further, the toner attached to the electric field roller 303 is scraped off by the scraper 304 and collected in the cleaning case 305. Here, a cleaning bias is applied to the electric field roller 303, and the residual toner on the photoreceptor moves from the fur brush 302 to the electric field roller 303 by the electrostatic force by the cleaning bias, and is scraped from the electric field roller 303 by the scraper 304. It is scraped off.

In this manner, the cleaning case 305 is provided.
The collected toner is sent by a collection screw 306 to a waste toner bottle (not shown) or a developing device of an image forming unit in which the cleaning device is mounted. In the printer of the present embodiment, the toner collected from the inside of the cleaning case 305 by the collecting screw 306 is returned to the corresponding developing device and reused.

Further, in the cleaning device of each of the image forming units, the arrangement portion of the collection screw 306 is
The developing case 20 above the screw 203 of the developing unit of the image forming unit adjacent to the downstream side of the cleaning device
6 are arranged so as to overlap with each other. Thus, the image forming units can be arranged close to each other, and the size of the printer body can be reduced.

Further, in this printer, in addition to the full-color mode in which a full-color image is formed by using all the four color toners, for example, a single-color mode in which a single-color image is formed by using only yellow and cyan toners, Image forming modes such as a green image combining yellow and cyan, a red image combining yellow and magenta, and a two-color mode in which a two-color image is formed using two-color toner with black characters on cyan or yellow. And an image forming mode such as a three-color mode.

As described above, the toner images formed on the photoconductors 21Y, 21M, 21C, and 21BK are transferred onto the intermediate transfer belt 22, but some of the toner is not transferred. Remain on the respective photoconductors 21Y, 21M, 21C, 21BK. The remaining toner is applied to each of the photoconductors 21Y, 21M, 21C, 21BK.
Cleaning devices 30Y, 30M, 30
C, 30BK to collect individually.

As described above, the printer 10 has four photoconductors 21 corresponding to four color toners used for image formation.
Y, 21M, 21C, and 21BK, and removes the toner of each color remaining on each photoconductor 21Y, 21M, 21C, and 21BK with each cleaning device 30Y, 30M, 30C,
30BK enables individual cleaning and collection. Accordingly, in the printer 10, the toner of each color collected by each of the cleaning devices 30Y, 30M, 30C, and 30BK is applied to each of the developing units 20Y, 20Y of that color.
M, 20C, and 20BK are returned, and the collected toner can be easily reused as recycled toner.

In such a tandem type printer 10, since the image forming units for forming the toner images of the respective colors are independent, color mixing of the toner should theoretically not occur. Color mixture of toner has occurred. Such color mixture of the toner is caused by the respective photoconductors 21Y and 21Y.
It occurs at the time of transfer from M, 21C, 21BK to the intermediate transfer belt 22. That is, in the printer 10, for example, when the second color toner image is transferred to the intermediate transfer belt 22, the first color toner image has already been transferred onto the intermediate transfer belt 22. Therefore, a part of the toner of the first color toner image may be reversely transferred from the intermediate transfer belt 22 to the photoconductor at the time of transferring the second color toner image.
Then, the toner reversely transferred to the photoconductor is cleaned by a photoconductor cleaning device on which a second color toner image is formed.
Collected together with the residual toner of the second color. Thus, the first color toner is mixed into the collected toner collected by the second color cleaning device.

Since such a mixed color toner causes deterioration in image quality, it has been conventionally mixed with a black toner developing device having a high limit of the mixed color ratio, and reused or discarded as waste toner. Was. However, when the mixed-color toner is mixed and used in the developing device, it is necessary to balance the consumption of the toner contained in the developing device with the supply amount of the mixed-color toner to the developing device. difficult. That is, although it depends on the type of image to be formed, in a printer for forming a color image as described above, a document having little black such as a photographic image is often used as a document. Therefore, if the mixed-color toner described above is returned to the developing device and reused as recycled toner, the supply amount of the recycled toner to the developing device may be larger than the consumed toner amount. In addition, if all of the mixed toners are returned to the developing units for the respective colors as they are, there is a problem that the hue of the toner in the developing units is greatly different from the state where there is no color mixture.

Accordingly, the present inventor has studied the involvement of the color mixing ratio of the mixed color toner in the hue of the final image formed by the mixed color toner. As a result, it has been found that the hue change of the final image is at an acceptable level if the color mixing ratio of the different color toner to the toner of the specific color contained in the developing device is equal to or less than a certain color mixing ratio. And
When the hue change of the final image reaches the allowable limit level, the value of the color mixture ratio of the different color toner with respect to the intrinsic color toner is set as the limit color mixture ratio, and the toner color mixture ratio in each developing device is set to be equal to or less than the limit color mixture ratio. To form an image. As a result, it was found that if the toner color mixture ratio in each developing device was equal to or less than the above-mentioned limit color mixture ratio, an image in a range in which the hue change due to the color mixture toner could be tolerated could be obtained.

Example 1 The following experiment was performed using the magenta toner developing device 20M of the printer 10 shown in FIG. An image is formed using a mixed color toner of a known color mixing ratio in which a yellow toner is mixed in a predetermined amount of a two-component developer composed of a magenta toner and a carrier housed in the developing device 20M, and formed with a toner of 100% magenta toner. The hue difference between the image formed and the image formed with the mixed color toner was measured. Table 1 shows the evaluation results of the mixing ratio of the magenta toner and the yellow toner of the developer used in this experiment and the hue of the formed image. In this experiment,
Using the photograph of the fruit as a document image, the image was printed out with the developer, and the hue of the printed image was visually evaluated by the change in the color of the fruit.

[Table 1]

As a result of the above experiment, as shown in Table 1,
When images were formed using 1, 2, 3, and 4 developers, it was found that the hue of the output final image was at an acceptable level. The visual evaluation of an image in which the hue was at or above an acceptable level was rated as “○”. In addition, in Table 1, Agent No.
It was found that when images were formed using the developers 5 and 6, the hue of the output final image was lower than an acceptable level. The visual evaluation of an image in which the hue was lower than an acceptable level was evaluated as “x”. The above agent No. The color mixing ratio of the yellow toner to the magenta toners of 1, 2, 3, and 4 is 1
% To 6%. Therefore, the limit color mixing ratio of the yellow toner in the magenta toner is set to 6%.

The inventor of the present invention also mixed toners of different colors with a specific color toner of another color so as to have a preset color mixing ratio, and similarly used a developer in which the toners of the respective colors were combined. Various experiments were performed to measure the hue difference of the image at each color mixing ratio. FIG. 4 shows a graph in which the horizontal axis represents the color mixing ratio of the toner and the vertical axis represents the measured hue difference. This graph is a graph showing a hue difference when four color toners of yellow, magenta, cyan, and black are mixed. Assuming that the allowable value of the color difference is A, it is sufficient to form an image under the color mixing conditions that fall within the range of A. Therefore, the limit color mixing ratio of each color is represented by the X coordinate of the intersection of A and each line.

In the graph of FIG. 4, group C is a mixture of black toner and each color toner, group D is a mixture of yellow toner and black toner, and group E is a mixture of black toner and cyan toner and magenta. The group B is a combination of toners of other colors.

Then, the limit color mixture ratio of the toner of each color is determined from the above graph, and the yellow toner having the smallest total of the limit color mixture ratios when the other three colors are mixed with these toners is the first color and the largest black toner. Was output as the fourth color. Here, the second color is magenta toner, 3
The color was cyan toner. As a result, a full color image is printed with the limit color mixture ratio of the yellow toner to the magenta toner being 6%, the limit color mixture ratio of the magenta toner to the cyan toner being 7%, and the limit color mixture ratio of the cyan toner to the black toner being 40%. As a result, a good image was obtained.

It should be noted that a good image could be obtained in the same manner even when the image forming colors of the respective color toners were different, but in this case, the consumption of the recycled toner in the developing unit for the yellow toner was small. became. This is because the yellow toner has the lowest color mixing ratio, and if the image forming order of the yellow toner is lower, the amount of recycled toner that can be returned to the developing device for the yellow toner becomes extremely small.

As described above, when the collected toner collected by cleaning is reused as recycled toner, the color mixing ratio of the toner in each of the developing units is
It is preferable to control the supply amount of the recycled toner supplied to each developing device so as to be equal to or less than the limit color mixing ratio. That is, the amount of toner in each developing unit of the printer gradually decreases as it adheres to the electrostatic latent image formed on the photoconductor and is consumed. Therefore, as a system, the amount of new toner corresponding to the toner reduced due to this consumption is sequentially replenished in each developing device,
The toner is continuously adhered to the electrostatic latent image formed on the photoconductor.

When the collected toner is reused as recycled toner, the recycled toner and the new toner are supplied to each developing device. Therefore,
In this printer, the total amount of recycled toner and new toner to be supplied to each developing unit is adjusted so as to be the same as the amount of toner consumed in each developing unit, and the total amount of toner in each developing unit is kept constant. I have. At this time, the different color toner mixed in each developing device is included only in the recycled toner, and is not included in the new toner. Therefore,
By appropriately controlling the supply amount of the recycled toner, it becomes possible to control the color mixing ratio of the toner of another color with respect to the toner in each developing device.

Further, as shown in the graph of FIG. 4, each of the developing devices accommodates a specific color toner contained in each of the developing devices and a mixed color toner mixed in the specific color toner. The relationship between the color mixing ratio of the toner and the amount of change in the hue of the final image has been clarified by the above experiment. Therefore, in the present printer, the above-described limit color mixing ratio is determined by a combination of the color of the toner contained in each developing device and the image forming order considered to be mixed with the toner and the color of the previous toner. I do.

That is, the effect on the final image when the toner in each developing device and the other color toner are mixed differs depending on the combination of the colors of the toners. The strength of this effect can be obtained by quantifying the color difference when the color mixture ratio of the toner of another color with respect to the toner in each developing device is changed. Therefore, the limit color mixture ratio of each developing device is determined by mixing the color of the toner contained in each developing device with the color of the toner contained in the immediately preceding developing device on the upstream side in the moving direction of the intermediate transfer belt. Set from the hue difference at the time. As a result, the amount of change in hue on an image formed by the mixed-color toner in each developing device, that is, the degree of image quality deterioration of the image can be suppressed within a range equal to or less than the allowable limit level.

As described above, when the recovered toner is used as a recycled toner, a good image cannot be obtained unless the ratio of the mixed color toner in each developing device is equal to or less than the above-mentioned limit color mixing ratio. Therefore, the order of image forming colors by the respective color toners of the system and the above-mentioned limit color mixing ratio will be considered. Here, the color mixture rates of the recycled toners of the first to fourth colors are Pa, Pb, Pc, and Pd, and the limit color mixture rates of the respective developing devices are Ra, Rb, Rc, and Rd. Assuming that the total amount of the toner of each color is T (g), it is necessary to supply the total amount of the mixed color toner in the recycled toner supplied to each developing device so as not to exceed T × R.

That is, assuming that the color mixture ratio of the recycled toner is constant in all the developing units, all the developing devices containing the toner of the color having a small limit color mixture ratio require a small amount of reuse of the recycled toner. Is limited to Also,
Assuming that there is no residual toner on the intermediate transfer belt 22, in the developing device containing the first color toner, color mixing due to reverse transfer of the toner does not occur.
Is zero, and for the first color recycled toner,
The entire amount can be recycled. Therefore,
In the above-described printer, when forming an image of four colors, a developing device containing a toner of a color having the smallest critical color mixing ratio for the other three colors is used as a developing device for forming a toner image of the first color. By arranging, it is possible to maximize the usable amount of recycled toner of each developing device in the entire system.

In this printer, the limit color mixing ratio of yellow toner to magenta toner is 6%. Similarly, the limit color mixing ratio of the magenta toner to the cyan toner is 7%. As a result, as is clear from the experiment of the first embodiment, a good image can be obtained.

Further, in the present printer, the supply amount of the recycled toner of each color is calculated by using the value indicating the image area of the immediately preceding upstream color toner image and the value indicating the image area of the toner image of the toner image. It is determined based on the color mixing ratio. As described above, each developing device containing the toner of each color is newly supplied with the toner consumed by the development. The toner supplied to each developing device is a new toner and a recycled toner collected by cleaning. Therefore, when determining the distribution of the replenishment amounts of these two toners, the color mixing ratio of the upstream color toner in the recycled toner returned to each developing unit is estimated from the information of the image to be formed. The color mixing ratio of the toner of another color with respect to the toner in the container can be suppressed below the limit color mixing ratio.

(Embodiment 2) Using the copying machine shown in FIG. 1, replenishment of the above-mentioned recycled toner and new toner to each developing unit for forming a toner image of the second and subsequent colors in accordance with the flowchart shown in FIG. The image was formed while performing the above. Although the flowchart shown in FIG. 5 is a process applicable to all the developing devices, the process in each developing device is the same, and therefore, the description will be given focusing on only the developing device of the second color. The full-color image output by the copying machine is formed by combining four color toners.

Therefore, first, as shown in step S1 of FIG. 5, the consumption amount t of the second color toner is estimated from the second color image data. Next, the relationship between the color mixture ratio Pv in the developing device and the color mixture ratio Pc in the recycled toner is Pv> Pc.
Is determined (step S2). Here, when the relationship of Pv> Pc is satisfied, that is, the color mixture ratio Pc in the recycled toner is larger than the color mixture ratio Pv in the developing device.
Is smaller, the same amount of recycled toner as the toner amount t consumed in the developing device is supplied into the developing device. On the other hand, when the color mixture ratio Pc in the recycled toner is larger than the color mixture ratio Pv in the developing device, the color mixture ratio of the toner in the developer after supplying the recycled toner exceeds the limit color mixture ratio. The amount tm of the mixed color toner which can be added to the developing device and which can be suppressed to the range not calculated is calculated (step S3).

The mixed color toner amount tm is calculated by (total toner amount in developing unit × (limit color mixing ratio−color mixing ratio in developing unit)) + consumed toner amount t × Pv. Further, the amount of the toner reversely transferred to the photosensitive member of the second color in the transfer portion of the toner image of the second color is G, the reverse transfer ratio of the toner of the first color is G, the image area of the first color is Sa, and the image area of the second color is Assuming that Sb and the transfer rate are R, it is Sa × R × G, and this toner amount is collected as a mixed color toner at the cleaning section of the photoconductor of the second color.

Further, of the toner image of the second color, the amount of toner collected by the cleaning unit without being transferred to the intermediate transfer belt is Sb × (1-R). The color mixture ratio of the recycled toner at this time is Sa × R × G /
((Sb × (1-R)) + Sa × R × G). Therefore, after n times of image formation with time, Sa × R × G is a value obtained by adding n times each, whereby the color mixing ratio after n times can be estimated. Using this estimation, the calculation in the flowchart shown in FIG. 5 was performed. Then, step S4 in FIG.
In, it is determined that tm / Pc> t, and in the case of Yes, as shown in step S5, all the consumed toner amounts t
Is supplied from the recycled toner, and in the case of No, tm / Pc is supplied from the recycled toner as shown in step S6, and the remainder is supplied from new toner as shown in step S7.

Then, after such toner supply processing,
As shown in step S8, the change amount of the mixed color toner in the developing device is estimated, and as shown in step S9, the value of the mixed color ratio Pv in the developing device is updated. As a result of outputting 100 images and measuring the hue difference for every 10 images using such processing, the hue differences of all the images are within the allowable range (this experiment assumes that the hue difference within the allowable range is 5). , The critical color mixing ratio was set), and a good image was obtained. Here, the above-described processing may be performed each time one image is output, but may be performed each time a predetermined number of prints are output, or each time a necessity is detected by a sensor. You may do so. In this case, the same processing can be performed by integrating and using the image areas.

Here, the case where the present invention is applied to a printer using the intermediate transfer belt 22 has been exemplified.
The present invention may be applied to an intermediate transfer drum type image forming apparatus in consideration of the layout of the apparatus main body, required accuracy, size, and the like. In addition, the present invention may be applied to an image forming apparatus of a direct transfer system in which a transfer sheet is transported by a belt or a drum and is directly transferred from each photoconductor.

[0086]

According to the first to seventh aspects of the present invention, the color mixing ratio of the toner in each developing device is equal to or less than the limit color mixing ratio.
There is an excellent effect that it becomes possible to change the hue of the formed image within the allowable range.

In particular, according to the second aspect of the present invention, the color mixing ratio of the toner in each developing device is set to be equal to or less than the limit color mixing ratio.
Since the recycled toner is supplied to the developing device, there is an excellent effect that it is possible to prevent the toner color mixing ratio in the developing device from exceeding the limit color mixing ratio due to the excessive supply of the recycled toner.

According to the third aspect of the present invention, since the limit color mixing ratio is determined by the combination of the color of the developing device and the mixed color, the hue change amount on the image can be set within an allowable value. Has an excellent effect.

According to the fourth aspect of the present invention, since the image formation is performed in the order of the lowest total color mixing ratio for the other three color toners, a larger amount of recycled toner can be reused. Has an excellent effect.

According to the fifth aspect of the present invention, since the limit color mixing ratio of the yellow toner to the magenta toner is 6%, there is an excellent effect that the hue change on the image can be within an allowable value.

According to the sixth aspect of the present invention, since the limit color mixing ratio of magenta toner to cyan toner is 7%, there is an excellent effect that a hue change on an image can be within an allowable value.

According to the seventh aspect of the present invention, the supply amount of the recycled toner of each color is determined by the value indicating the image area of the upstream color and the recycled toner color mixing ratio calculated from the value indicating the image area of the color. Since it is determined, there is an excellent effect that the color mixing ratio of the toner in the developing device can be made equal to or less than the limit color mixing ratio.

According to the eighth aspect of the invention, it is possible to provide an image forming apparatus capable of suppressing a deterioration in image quality due to a mixture of a plurality of toners and effectively reusing the collected toner as recycled toner. Has an excellent effect.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an overall schematic configuration of a copier equipped with a printer according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram illustrating a configuration of only an image forming unit of the printer.

FIG. 3 is a schematic configuration diagram illustrating a configuration of an image forming unit provided in the image forming unit.

FIG. 4 is a graph showing a hue difference when four color toners of yellow, magenta, cyan, and black are mixed.

FIG. 5 is a flowchart showing replenishment processing of recycled toner and new toner in the printer.

[Explanation of symbols]

Reference Signs List 10 printer 12 image writing unit 13 image forming unit 14 paper feeding unit 15 fixing device 16BK, 16M, 16Y, 16C charging device 17 registration roller 20BK, 20M, 20Y, 20C developing device 21BK, 21M, 21Y, 21C photoconductor 22 intermediate Transfer belt 23BK, 23M, 23Y, 23C Primary transfer bias roller 24BK, 24M, 24Y, 24C Static eliminator 25 Belt cleaning device 26 Lubricant application device 27 Exposure member 28 Static elimination member 30BK, 30M, 30Y, 30C Cleaning device 50 Transfer conveyance Belt 60 Secondary transfer bias roller 201 Developing roller 201a Magnet roller 201b Developing sleeve 202 Doctor blade 206 Developing case

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AA04 AB02 AD03 AD16 BB36 BB38 BB63 DD14 2H134 GA01 GA06 GB02 HB03 HB12 HB16 HD00 JA02 JA11 JA14 KA40 KB11 KH01 KH11 KJ02 LA01

Claims (8)

[Claims] A plurality of latent images corresponding to each color of an image composed of at least two colors are formed on an image bearing member, and each latent image is formed by a plurality of developing units that supply a unique color toner corresponding to each image color. To form a multicolor image by sequentially superimposing the toner images of each color on the image carrier, which are visualized by the toners of the unique colors in the respective developing units, onto the transfer receiving body, and transferring the toner images. Forming a non-transferred toner of each color remaining on the image carrier after transferring the toner image, returning the collected toner to the developing device, and using the collected toner as recycled toner. In the image forming method for reuse, the hue change of an image formed by the mixed color toner in a state in which each of the recycled toners is mixed with the unique color toner in each of the developing devices reaches an allowable limit level. Mixed Tona An image forming method wherein the ratio of the recycled toner in the developing device is defined as a limit color mixture ratio, and the color mixture ratio of the recycled toner with respect to each intrinsic color toner in each developing device is controlled to be equal to or less than the limit color mixture ratio. 2. The image forming method according to claim 1, wherein the amount of each recycled toner returned to each of said developing devices is controlled so that the color mixing ratio of the recycled toner with respect to the intrinsic color toner of each developing device is equal to or less than said limit color mixing ratio. An image forming method, characterized in that: 3. The image forming method according to claim 1, wherein the limit color mixing ratio of each unique color toner in each developing device is set to the color of each unique color toner in each developing device and returned to each developing device. An image forming method which is determined in advance for each combination with the color of the specific color toner of the developing device. 4. An image forming method according to claim 3, wherein the transfer order of the toner images of each color on the image carrier formed by the respective toners in the respective developing units onto the transfer receiving member is defined by: An image forming method, wherein the total of the limit color mixing ratios of each unique color toner and another unique color toner in a developing device is set in ascending order. 5. The image forming method according to claim 3, wherein a limit color mixing ratio of the yellow toner as the other unique color toner to the magenta toner as the unique color toner is 6%. Forming method. 6. The image forming method according to claim 3, wherein a limit color mixing ratio of magenta toner as a color of the other unique color toner to cyan toner as the unique color toner is 7%. Image forming method. 7. The image forming method according to claim 2, wherein the order of transfer of the different color toner to each recycled toner calculated based on the value indicating the image area of the toner image in which the order in which the toner image is transferred to the transfer target is earlier. Based on the color mixture ratio and the color mixture ratio of the specific color toner of each developing device and the recycled toner before the recycled toner is returned, the recycling of the specific color toner of each developing device when the recycled toner is returned to each developing device. The color mixing ratio of the toner is calculated, and based on the calculation result,
An image forming method comprising: determining a supply amount of each recycled toner to be returned to each developing device such that a color mixing ratio of the recycled toner with respect to the intrinsic color toner in each developing device is equal to or less than the above-mentioned limit color mixing ratio. 8. An image bearing member on which a plurality of latent images corresponding to respective colors of at least two or more colors are formed, and a specific color toner corresponding to each image color is supplied to form the image bearing member on the image bearing member. A plurality of developing devices for visualizing each of the latent images thus formed, and toner images of each color on the image carrier visualized by the toner of a unique color in each developing device are sequentially superimposed on the transfer receiving body. Transfer means for transferring, cleaning means for collecting untransferred toner of each color remaining on the image carrier after transferring the toner image, and toner transport means for returning the collected toner collected by the cleaning means to the developing device The image forming apparatus according to claim 1, wherein the image forming method according to claim 1, 2, 3, 4, 5, 6, or 7 controls the color mixing ratio of the intrinsic color toner and the recycled toner of each of the developing devices to form an image. And an image forming apparatus.