JP3661563B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus, and more particularly to a color image forming apparatus that forms a color image by forming a plurality of color toner images on a photoreceptor and then superimposing them on an intermediate transfer material.
[0002]
[Prior art]
In a conventional image forming apparatus such as an electrophotographic apparatus, a blade formed of urethane rubber or the like is brought into contact with a photosensitive drum to remove residual toner on the photosensitive drum after transfer, and this is used as a waste toner container. Collected. When the waste toner container is filled with the waste toner, the user discards the waste toner outside the apparatus.
[0003]
Further, for example, in Japanese Patent Application Laid-Open No. 10-198117, four color image forming units are arranged along the transport surface of the transport belt, and toner images of the respective colors formed on the transfer paper are transported by the transport belt. A tandem type color image forming apparatus is disclosed in which a multi-color image is formed by sequentially transferring the color toners and superimposing each color toner. In such a tandem type color image forming apparatus, color misregistration is likely to occur due to the difference between the peripheral speed of the photosensitive drum and the transport speed of the transport belt in each image forming unit. It is an important issue how to prevent the difference from the transport speed.
[0004]
Therefore, in order to solve this problem, a tandem of a driven drive system in which the conveyance belt is driven in a state where the photosensitive drum and the conveyance belt are in contact with each other, and the photosensitive drum is driven by the conveyance belt to form an image. A type of color image forming apparatus has been proposed. In such a color image forming apparatus, the conveyance belt, which is an endless belt stretched between two rollers, is pressed against the photosensitive drum by a pressing plate and one of the rollers is driven, thereby driving the conveyance belt. The rotational force is transmitted to the photoconductive drum, thereby preventing the occurrence of color misregistration by matching the conveying speed of the conveying belt with the peripheral speed of all the photosensitive drums.
[0005]
In monochrome printers and copiers, the urethane rubber blades are eliminated by scattering residual toner after transfer with a brush, etc. to weaken the adhesion to the photosensitive drum and recover it to the developing means. An apparatus that reduces the driving load of the photosensitive drum and eliminates the waste toner container has been proposed.
[0006]
[Problems to be solved by the invention]
However, in the technique of driving the photosensitive drum with the conveyance belt, if a blade formed of urethane rubber or the like as a residual toner removing unit on the photosensitive drum is brought into contact with the photosensitive drum, the driving load of the photosensitive drum is large. Therefore, it is necessary to drive the photosensitive drum with a motor or the like. As a result, the rotation of the four photosensitive drums must be controlled in a complicated manner, so that the drive device becomes large, and slippage occurs between the photosensitive drum and the conveyor belt, resulting in color misregistration. It was.
[0007]
In addition, when the transfer paper on the conveyor belt enters the pressure contact portion with the photosensitive drum, it is indirectly affected by the impact due to the thickness of the transfer paper or the direct contact state between the conveyor belt and the photosensitive drum. Due to the change in the frictional force caused by the change to a proper contact state, a speed difference occurs between the conveying belt and the transfer paper and the photosensitive drum, resulting in a color shift.
[0008]
Further, since the removed toner is finally discarded outside the apparatus, there is a problem that the toner that is fine powder contaminates the environment, and the waste toner is collected and processed with great expense.
[0009]
In the case of using a blade cleaner which is a toner removing unit of the urethane rubber blade, the toner after transfer is not reduced to the developing unit, so that a storing unit is required, which causes a problem that the apparatus becomes large.
[0010]
In order to solve such a problem, there is a cleanerless type image forming apparatus in which the residual toner on the photosensitive drum is disturbed and collected by the developing means and reused. Many image forming apparatuses have been proposed for monochrome printers and copiers. However, in a high-speed tandem color image forming apparatus, a plurality of image forming stations that return toner to a developing unit are arranged in a color image. If an attempt is made to form a reverse transfer phenomenon, an upstream image slightly adheres to the photosensitive drum. Therefore, in the long term or even in a short period depending on the image forming pattern, the toner of the color formed upstream is mixed into the color developing means for performing the image forming process later, thereby causing an image defect that changes the color of the image. There was a problem.
[0011]
Accordingly, the present invention provides an image forming apparatus capable of preventing the occurrence of color misregistration while reducing other color toner mixed in each color developing unit to a level that does not cause image deterioration while reducing fluctuations in the rotational load of the photosensitive member. The purpose is to provide.
[0012]
[Means for Solving the Problems]
  In order to solve this problem, a color image forming apparatus according to the present invention includes a plurality of photoconductors provided corresponding to development colors.,PreviousA developing means for forming a toner image on the photosensitive member and a circumferential rotation while being pressed against the plurality of photosensitive members, and the toner images formed on these photosensitive members are sequentially superimposed and transferred to form a composite image. An intermediate transfer belt, and the residual toner on the photoconductor after the toner image is transferred to the intermediate transfer belt within the range of the color difference in which a change in color cannot be recognized at a human visual level. The toner is mixed into the developing means located downstream of the transfer belt in the rotation direction.When the residual toner mixing amount exceeds the color difference range, the developing means mixed with the residual toner rotates the intermediate transfer belt until the stored toner falls within the color difference range. Mixed in the developing means located downstream in the directionIt is made to let you.
[0013]
As a result, it is possible to prevent the occurrence of color misregistration while suppressing fluctuations in the rotational load of the photoreceptor and suppressing other color toners mixed in the developing means for each color to a level that does not cause image degradation.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
  According to a first aspect of the present invention, there are provided a plurality of photoconductors provided corresponding to a development color.,PreviousA developing means for forming a toner image on the photosensitive member and a circumferential rotation while being pressed against the plurality of photosensitive members, and the toner images formed on these photosensitive members are sequentially superimposed and transferred to form a composite image. An intermediate transfer belt, and the residual toner on the photoconductor after the toner image is transferred to the intermediate transfer belt within the range of the color difference in which a change in color cannot be recognized at a human visual level. The toner is mixed into the developing means located downstream of the transfer belt in the rotation direction.When the residual toner mixing amount exceeds the color difference range, the developing means mixed with the residual toner rotates the intermediate transfer belt until the stored toner falls within the color difference range. A color image forming apparatus characterized in that it is mixed in the developing means located on the downstream side in the direction.In other words, it is possible to prevent the occurrence of color misregistration while suppressing fluctuations in the rotational load of the photoconductor and suppressing other color toners mixed in the developing means for each color to a level that does not cause image degradation. Have
[0016]
  Of the present inventionClaim 2The invention described in,PreviousThe mixing ratio of the residual toner of other colors in the developing means is defined by different values for each color.Claim 1The color image forming apparatus describedTherefore, the color mixture is allowed up to the allowable limit with respect to the color change, and it is possible to prevent wasteful discharge of the toner.
[0017]
  Of the present inventionClaim 3The invention described in,PreviousThe mixing ratio of the residual toner of other colors in the developing unit is set to be the smallest for the yellow developing unit and the largest for the black developing unit.Claim 2The color image forming apparatus describedThus, the operation of mixing the residual toner can be performed smoothly.
[0018]
  Of the present inventionClaim 4The invention described in,PreviousThe yellow developing means is disposed on the most upstream side and the black developing means is disposed on the most downstream side with respect to the rotational direction of the intermediate transfer belt.Claim 3The color image forming apparatus describedThus, the operation of mixing the residual toner can be performed smoothly.
[0019]
  Of the present inventionClaim 5The invention described in,PreviousA voltage in a direction opposite to the charging direction of the toner is applied to the intermediate transfer belt to move the residual toner from the photoreceptor to the intermediate transfer belt, and then the voltage in the same direction as the charging direction of the toner is applied to the intermediate transfer belt. And the residual toner is moved to the downstream photoconductor to be mixed into the developing means.Claims 1-4A color image forming apparatus according to any one of the aboveThus, there is an effect that the residual toner can be mixed into the downstream developing means without providing a special transfer means.
[0020]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.
[0021]
FIG. 1 is an explanatory diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a generation pattern of a composite image by the image forming apparatus of FIG. 1, and FIG. 3 is an image forming apparatus of FIG. FIG. 4 is a graph showing the relationship between the temperature and humidity and the reverse transfer amount, FIG. 5 is a flowchart showing the operation of the image forming apparatus of FIG. 1, and FIG. It is a flowchart following FIG.
[0022]
As shown in FIG. 1, the color image forming apparatus includes four image forming stations 1a, 1b, 1c, and 1d, and each of the image forming stations 1a, 1b, 1c, and 1d is a photosensitive member as an electrostatic latent image carrier. Each of the photosensitive drums 2a, 2b, 2c and 2d has charging drums 3a, 3b, 3c, which uniformly charge the surfaces of the photosensitive drums 2a, 2b, 2c and 2d. 3d, developing means 4a, 4b, 4c, 4d for visualizing the electrostatic latent image, and the toner remaining on the photosensitive drums 2a, 2b, 2c, 2d after the toner image transfer is disturbed to weaken the adhesive force. Image information sent from brushes 5a, 5b, 5c, 5d, a personal computer or the like is an exposure optical system which is a scanning optical system in which image processing means 13 irradiates each photosensitive drum 2a, 2b, 2c, 2d with light according to data. Means 6a, 6b 6c, 6d, transfer device 8a for transferring the toner image to the intermediate transfer belt (image bearing member) 12 constituting the transfer means 7, 8b, 8c, 8d are disposed respectively.
[0023]
Here, a black image, a magenta image, a cyan image, and a yellow image are formed at the image forming stations 1a, 1b, 1c, and 1d, respectively, and the black image, the magenta image, and the cyan image are formed from the exposure units 6a, 6b, 6c, and 6d. Then, exposure light 9a, 9b, 9c, 9d, which is scanning light corresponding to the yellow image, is output.
[0024]
An endless belt-like intermediate transfer belt 12 supported by rollers 10 and 11 is disposed below the photosensitive drums 2a, 2b, 2c and 2d in such a manner as to pass through the image forming stations 1a, 1b, 1c and 1d. And rotate in the direction of arrow A.
[0025]
The intermediate transfer belt 12 is provided with an intermediate transfer belt cleaning unit 24 for cleaning the surface of the intermediate transfer belt.
[0026]
The sheet material 17 stored in the sheet feeding cassette 16 is fed by a sheet feeding roller 18 and is discharged to a sheet discharge tray (not shown) through a sheet material transfer roller 19 and a fixing unit 20.
[0027]
In the color image forming apparatus configured as described above, first, in the image forming station 1d, a yellow component color as image data is formed on the photosensitive drum 2d by a known electrophotographic process means using the charging means 3d and the exposure means 6d. Latent image is formed. Thereafter, the developing unit 4d visualizes the yellow toner image with a developer having yellow toner, and the transfer device 8d transfers the yellow toner image to the intermediate transfer belt 12.
[0028]
On the other hand, while the yellow toner image is transferred to the intermediate transfer belt 12, a cyan component color latent image is formed at the image forming station 1c, and the cyan toner image is formed into a visible image by the developing means 4c. This is transferred by the transfer unit 8c and superimposed on the yellow toner image previously transferred onto the intermediate transfer belt 12.
[0029]
Thereafter, image formation is performed in the same manner for the magenta toner image and the black toner image, and when the four color toner images are superimposed on the intermediate transfer belt 12, the paper is fed from the paper cassette 16 by the paper feed roller 18. The four color toner images are collectively transferred and conveyed by the sheet material transfer roller 19 onto the sheet material 17 such as paper, and heated and fixed by the fixing means 20, and a full color image is obtained on the sheet material 17.
[0030]
Note that toner remains on the photosensitive drums 2a, 2b, 2c, and 2d after the transfer, but the toner is disturbed by the brushes when passing through the brushes 5a, 5b, 5c, and 5d. The adhesion is weakened and the printing operation is completed in preparation for the next image formation.
[0031]
Thereafter, in the printing operation which is again charged and subsequently performed in the order of exposure and development, a part of the residual toner whose adhesion is weakened is partially passed through the developing means 4a, 4b, 4c and 4d. It is returned to the developing means 4a, 4b, 4c, 4d and is used for development.
[0032]
A color image is obtained as described above. In this embodiment, a two-component developing unit is used as the developing units 4a, 4b, 4c, and 4d.
[0033]
Next, the principle and amount of mixing of toners of other colors into the developing means 4a, 4b, 4c, 4d of the image forming stations 1a, 1b, 1c, 1d having four colors of yellow, cyan, magenta and black are calculated. Then, a process of recognizing the color mixture ratio of other colors by the developing units 4a, 4b, 4c, and 4d at a moment will be described in consideration of consumption conditions and the like.
[0034]
In order to simplify the explanation, a case where yellow toner is mixed with the cyan developing means 4c that occurs when the next cyan image is superimposed on the image formed at the yellow image forming station 1d will be described. In the case of magenta and black, color mixing occurs on the same principle. As shown in FIG. 2, the print pattern will be described in a state where a pattern including a green portion in which a yellow pattern A and a cyan pattern B are combined is printed.
[0035]
The image forming process in the present embodiment is performed by a general color laser printer using negatively charged toner.
[0036]
First, the apparatus receives an image forming signal, and the yellow image forming station 1d starts an image forming operation. Then, the photosensitive drum is charged to about −600 V by the charging unit 3d, and the exposure unit 9d irradiates the exposure light 9d to obtain an electrostatic latent image of about −80V.
[0037]
Next, in the developing unit 4d, the yellow toner is charged to about −15 μC / g in the negative direction by friction and conveyed to the latent image portion by a developing roll (not shown). At this time, a bias voltage of about −300 V is applied to the developing roll, and the non-image portion of the photosensitive drum 2d is charged to −600 V, so that the potential difference from the developing roll is −400 V in the negative direction. Thus, the negatively charged toner does not adhere due to the repulsive force. Further, in the image portion, yellow toner that is negatively charged due to a potential difference of +220 V with respect to the above-described latent image of −80 V adheres to the electrostatic latent image, and a yellow toner image corresponding to the latent image is obtained on the photosensitive drum 2 d. .
[0038]
Further, the yellow toner image formed on the photosensitive drum 2d joins the intermediate transfer belt 12 as the photosensitive drum 2d rotates. A positive electric field of about +800 V is applied to the transfer device 8d facing the intermediate transfer belt 12, and the yellow toner image is transferred onto the intermediate transfer belt 12 according to the force of the electric field.
[0039]
Here, not all of the toner on the photosensitive drum 2d is transferred to the intermediate transfer belt 12, but about 7% of the entire toner image remains on the photosensitive drum 2d.
[0040]
Since the remaining toner is only disturbed by the brush 5d, the toner passes through the brush 5d and is conveyed to the developing means 4d, and a part of the toner returns to the developing means 4d and is used for development. At this time, since the yellow image forming station 1d is the first station for image formation, there is no other color toner image on the intermediate transfer belt 12, and no color mixing occurs.
[0041]
The yellow toner image transferred to the intermediate transfer belt 12 is conveyed and passes under the photosensitive drum 2c of the cyan image forming station 1c downstream. On the photosensitive drum 2c, a cyan image pattern B is formed in the same manner as when a yellow image is formed, and the toner image of this yellow pattern passes when it is about to be transferred to the intermediate transfer belt 12. Become.
[0042]
Here, as shown in FIG. 3, since the cyan toner overlaps the yellow toner image at the overlapping portion of the pattern, the yellow toner is blocked by the cyan toner and does not adhere to the photosensitive drum 2c.
[0043]
However, the yellow monochrome portion of the image pattern is in direct contact with the photosensitive drum 2c having a surface potential of −650V. At this time, as a transfer voltage, +800 V is generally applied, although it varies somewhat depending on environmental conditions. Accordingly, since the potential difference between the photosensitive drum 2c and the intermediate transfer belt 12 reaches 1350V, a slight spark discharge occurs, and a part of the toner (in this case, yellow toner) adhering to the intermediate transfer belt 12, The phenomenon that the charging is reversed occurs, and reverse transfer toner attracted to the photosensitive drum 2c is generated. For other reasons, the toner adheres to the photosensitive drum 2c due to the adhesive force or intermolecular force of the toner to the photosensitive drum 1c.
[0044]
Thus, the reversely transferred yellow toner is conveyed to the photosensitive drum 2c and mixed into the cyan developing means 4d.
[0045]
The above is the physical explanation of the toner in the upstream image forming station being mixed into the developing means in the downstream image forming station by reverse transfer. The reverse transfer amount is proportional to the amount of other color toner present in the portion where the toner image is not present in the mixed image forming station. In other words, in the case of the image pattern shown in FIG. 2, it is considered that this occurs only in a portion obtained by subtracting the portion where the cyan pattern overlaps (the green portion of the composite image) from the yellow pattern A. Furthermore, since the toner amount itself present in the toner image varies depending on the environment and the reverse transfer phenomenon is an event due to static electricity, the amount of mixing varies depending on the environment.
[0046]
According to experiments, it is known that the mixing rate is approximately 0.5 to 3% and varies depending on the temperature and humidity. That is, as shown in FIG. 4, when the absolute moisture content in the air increases, the peripheral electrical resistance of the toner on the intermediate transfer belt 12 decreases and the discharge phenomenon hardly occurs, and the reverse transfer amount decreases. The reverse is also true in a low humidity environment.
[0047]
Next, the principle of recognizing the other color toner amount of the developer present in the developing means at a certain moment will be described.
[0048]
The toner is mixed in the developing unit as described above, but it is not unilaterally mixed, and it is necessary to calculate in consideration that the color mixing ratio is reduced by toner consumption.
[0049]
The two-component developing unit is operated while replenishing a toner equivalent to the consumed toner so that the carrier and the toner are always constant. Therefore, when the developer is mixed in color, by consuming the toner for printing or the like, other color toners in an amount corresponding to the mixing ratio of the total amount of toner contained in the mixed developer at that time can also be obtained. Consumed and consumed toner is replenished with the correct color toner, so the total mixing ratio is reduced (this is called purification of the developer by consumption). Assuming that the current color mixture rate is 3%, when the pattern of this example is printed, the toner mixed and discharged in one printing are calculated as follows. The adhesion amount existing only in the yellow portion excluding the green portion of the pattern is 327.4 mg.
[0050]
As shown in FIG. 4, the reverse transfer amount is 1.75%, for example, when the operating environment at that time is 23 ° C. and 50% RH, and 5.73 mg adheres to the photosensitive drum 2c from the intermediate transfer belt 12. In this printing example, the discharge amount is 75.6 mg of cyan toner used for development.
[0051]
The relationship between the data amount of the print pattern used in the description and the toner adhesion amount is previously determined by experiment as an image forming condition of the apparatus such as the developing bias and the intensity of the electrostatic latent image, and is stored in the program.
[0052]
If the color mixture rate of the cyan developer at this time is 3%, for example, 2.27 mg of yellow toner, which is 3% of 75.6 mg consumed in development, is discharged by this printing. Since the mixing amount is 5.73 mg, 3.46 mg of yellow toner is added to the cyan developing unit, and as a result, the color mixture rate increases to 3.024%. As described above, since the toner is mixed or purified in a very small amount in each sheet, and the printing pattern is different every time, the calculation values for the purification by mixing and discharging are different each time.
[0053]
By using the calculation method of the present embodiment, the amount of toner entering and exiting can be accurately calculated according to all patterns.
[0054]
Up to this point, the means for accurately grasping the color mixing ratio of the developing means has been described. However, with this alone, it is only possible to recognize the color mixing ratio, and the image quality is not immediately maintained.
[0055]
Therefore, in the present embodiment, a purification effect by toner consumption is used so as not to exceed a predetermined color mixture rate.
[0056]
First, there is an allowable value for the color mixing ratio of the developing means. Since the color changes when other color toner is mixed in the developing means, the change can be measured as a color difference (ΔE). According to the experiment, with the cyan developer, the amount of change in the color mixture ratio X and the color difference (ΔE) is ΔE = 0.505 ײIt was found to be obtained at -1.24.
[0057]
In general, when the color difference (ΔE) is within 5, it is difficult to feel that the color has changed at the human visual level.
[0058]
Therefore, in the present embodiment, the condition that the color difference (ΔE) of each color developing unit is 5 or less is stored in advance in the apparatus as the color mixture rate allowable value. For example, in the case of cyan, it is 3.96%, but the same experiment is performed for magenta and black, and 4.23% and 15.34% are stored, respectively.
[0059]
However, with regard to yellow, it was found that even when a slight color difference (ΔE) is about 3, it can be detected that the color has changed in the human eye. It is desirable to arrange.
[0060]
Next, in addition to recognizing the mixing amount in this way, the discharge amount (consumption) is calculated and recognized, and the instantaneous other color toner mixing ratio of the developing means can be recognized from the mixing amount and the discharge amount. As described above, for example, the allowable limit of the cyan developing means 4c is given to be 3.96%. If this limit is exceeded, toner is consumed (discharged) by forming and developing an image in a non-printing area. To do. The discharged toner is transferred to the intermediate transfer belt 12 and sent one downstream (in this case, magenta) to the position of the image forming station, and a voltage (for example, −300 V) having a reverse polarity to the normal is applied to the magenta photosensitive drum 2b. To capture. When the allowable limit is reached also in the magenta image forming station 1b, the toner is discharged and absorbed in the same manner to the black image forming station 1a further downstream.
[0061]
When black exceeds the allowable limit of 15.34%, the toner is discharged, but there is no image forming station that absorbs downstream of this, so it is transferred to the paper and fixed, and then discharged outside the machine. To do.
[0062]
Since the final waste toner is small in quantity, the intermediate transfer belt 12 may be removed by providing a cleaner, and stored in the storage tank, and then collected by the user.
[0063]
Actually, the color mixture allowable rate of the black developing means 4a is very large as 15.34% as described above, and in the usage situation of the user, it is consumed about 2 to 4 times as much as the color toner in the text document. Therefore, the above-described purification by consumption is frequently performed. Accordingly, it is rare that the black developing unit 4a discharges the toner beyond the allowable range, and the black developing unit 4a functions as a dam for the toner discharged from the cyan and magenta developing units 4b and 4c.
[0064]
By performing such discharge and capture operations, it is possible to maintain the degree of color change of an image for all colors below an allowable value.
[0065]
The above series of operations is shown in the flowcharts of FIGS.
[0066]
As described above, in the present embodiment, the blade cleaner is not necessary, and the rotational torque of the photosensitive drums 2a, 2b, 2c, and 2d is not reduced. Therefore, the photosensitive drums 2a, 2b, and 2c and 2d can be driven, and a driving device for the photosensitive drum is not mounted.
[0067]
That is, between the intermediate transfer belt 12 and the photosensitive drums 2a, 2b, 2c, and 2d, there is an electrostatic attraction force, a friction coefficient of each member, a friction force due to the belt tension and the transfer roller pressing. The photosensitive drums 2a, 2b, 2c, and 2d are rotated by the intermediate transfer belt 12 by this force. Accordingly, the rotation amount of each of the photosensitive drums 2a, 2b, 2c, and 2d is governed by the movement amount of the intermediate transfer belt 12, and it is necessary to drive the photosensitive drums 2a, 2b, 2c, and 2d in synchronization with each other. Disappear.
[0068]
Therefore, according to the present embodiment, it is possible to prevent the occurrence of color misregistration while suppressing other color toners mixed in the developing means 4a, 4b, 4c, and 4d for each color to a level that does not cause image degradation. Become.
[0069]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the occurrence of color misregistration while suppressing other color toners mixed in the developing means for each color to a level that does not cause image degradation while reducing fluctuations in the rotational load of the photosensitive member. The effective effect that it becomes possible to obtain is obtained.
[0070]
If the residual toner mixing amount exceeds the color difference range, the stored toner may be mixed into the developing means located on the downstream side in the rotation direction of the intermediate transfer belt until it falls within the color difference range. In addition, it is possible to prevent the occurrence of color misregistration while reducing the fluctuation of the rotational load of the photoconductor and suppressing the other color toner mixed in the developing unit of each color to a level that does not cause image deterioration. Is obtained.
[0071]
If the mixing ratio of residual toner of other colors in the developing means is defined by different values for each color, color mixture is allowed up to the allowable limit with respect to color change, and wasteful discharge of toner can be prevented. The effective effect of becoming is obtained.
[0072]
If the mixing ratio of the residual toner of the other color in the developing means is set to be the smallest for the yellow developing means and the largest for the black developing means, it is possible to smoothly perform the residual toner mixing operation. Is obtained.
[0073]
If the yellow developing unit is disposed on the most upstream side and the black developing unit is disposed on the most downstream side with respect to the rotation direction of the intermediate transfer belt, the residual toner can be mixed smoothly. Is obtained.
[0074]
A voltage in the direction opposite to the toner charging direction is applied to the intermediate transfer belt to move the residual toner from the photoreceptor to the intermediate transfer belt, and then a voltage in the same direction as the toner charging direction is applied to the intermediate transfer belt to apply the residual toner. If the toner is moved to the downstream photoconductor to be mixed into the developing means, an effective effect is obtained that the residual toner can be mixed into the downstream developing means without providing a special transfer means. can get.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a composite image generation pattern by the image forming apparatus of FIG.
3 is an explanatory diagram showing a generation mechanism of reverse transfer toner and residual toner in the image forming apparatus of FIG. 1. FIG.
FIG. 4 is a graph showing the relationship between temperature and humidity and reverse transfer amount.
FIG. 5 is a flowchart showing the operation of the image forming apparatus of FIG.
FIG. 6 is a flowchart following FIG.
[Explanation of symbols]
2a, 2b, 2c, 2d Photosensitive drum (photosensitive member)
3a, 3b, 3c, 3d Charging means
4a, 4b, 4c, 4d Developing means
6a, 6b, 6c, 6d Exposure means
12 Intermediate transfer belt

Claims (5)

A plurality of photoconductors provided corresponding to development colors ;
A developing unit for forming a toner image on the front Symbol photoreceptor,
An intermediate transfer belt on which a plurality of the photoconductors are pressed against and rotated, and the toner images formed on the photoconductors are sequentially superimposed and transferred to form a composite image;
Residual toner on the photoconductor after the toner image is transferred to the intermediate transfer belt is moved downstream in the rotational direction of the intermediate transfer belt within a color difference range in which a change in color cannot be recognized at human visual level. Mixed in the developing means located ,
When the amount of residual toner mixed exceeds the color difference range, the developing means mixed with the residual toner rotates the intermediate transfer belt until the stored toner falls within the color difference range. A color image forming apparatus, wherein the color image forming apparatus is mixed in the developing unit located on the downstream side. 2. The color image forming apparatus according to claim 1 , wherein a mixing ratio of the residual toner of other colors in the developing unit is defined by a different numerical value for each color. 3. The color image forming apparatus according to claim 2 , wherein the mixing ratio of the residual toner of other colors in the developing unit is set to be the smallest for the yellow developing unit and the largest for the black developing unit. . 4. A color image forming apparatus according to claim 3 , wherein said yellow developing means is arranged on the most upstream side and said black developing means is arranged on the most downstream side with respect to the rotational direction of said intermediate transfer belt. apparatus. A voltage in a direction opposite to the charging direction of the toner is applied to the intermediate transfer belt to move the residual toner from the photosensitive member to the intermediate transfer belt, and then the voltage in the same direction as the charging direction of the toner is applied to the intermediate transfer belt. 5. The color image forming apparatus according to claim 1 , wherein the residual toner is moved to the downstream photoconductor to be mixed into the developing unit.

Images