JP4202738B2 - 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 such as a copying machine and a laser printer that can improve the quality of a printed image in a double-sided image forming mode.
[0002]
[Prior art]
Conventionally, as a color image forming apparatus, a transfer material (paper or the like) is conveyed by a transfer belt in a four-tandem configuration, and a bias applying member is disposed at a position facing the photosensitive drum via the transfer belt. A structure in which toner images on a photosensitive drum are sequentially transferred onto a transfer material by applying a bias to an application member is well known. In this quadruple tandem type image forming apparatus, since the transfer material is adsorbed to the transfer belt and conveyed, the surface speed of the transfer material is the same as or almost the same as the surface speed of the transfer belt.
[0003]
By the way, regarding the surface speed of the transfer belt and the surface speed of the photosensitive drum, if they are the same, the transfer is performed only by an electrostatic force. In addition to the mechanical force, mechanical stripping force is added, so that it is possible to prevent image quality deterioration due to poor transfer. More specifically, when a surface speed difference is provided between the transfer belt and the photosensitive drum, particularly good transferability can be obtained when two or more colors are superimposed. Further, when there is no color overlap such as a single color, the toner image is easily held on the surface of the transfer material, and a transfer property of a certain level or more can be easily secured. However, when two or more colors are superimposed on the transfer material, the transfer property of the new toner layer is lowered because the transfer material portion already has the transferred toner layer. In order to eliminate this problem, it is effective to provide a surface speed difference between the transfer belt and the photosensitive drum.
[0004]
In the electrophotographic color image forming apparatus, the following (1) and (2) are inventions that can stably form a high-quality image.
(1) The present invention (see Patent Document 1 below) relates to a transfer apparatus for an electrophotographic copying machine or the like that can prevent image distortion during transfer, and more specifically, when a plurality of photoconductors are used. However, the present invention relates to a transfer device for an image output device that can obtain a color image with good registration (highly consistent printing in multi-color printing) in which the positions of each color match each other accurately without increasing the dimensional accuracy of parts. Is.
[0005]
In the configuration of the present invention, the plurality of photoconductors are opposed to the transfer body that conveys the paper, and the respective color toner images of the plurality of photoconductors are transferred to the paper within one rotation of the transfer body. In the transfer device of the tandem type image output apparatus that performs the formation, the surface speed of the transfer body is made 0.1% to 1% faster than the surface speed of each of the plurality of photoconductors, and on the peripheral surface of the transfer body The transfer device of the image output apparatus is characterized in that a flexible member that is elastically pressed against each of the plurality of photosensitive members is attached.
[0006]
However, the invention of (1) above shows a method in which the paper speed can be kept constant regardless of the expansion or misalignment of the image during writing due to the diameter difference or eccentricity of the photosensitive drum. It ’s just that. In the present invention, there is no description that the surface speed ratio between the photosensitive drum and the transfer belt is different between the front surface printing and the back surface printing in the duplex printing mode. A method for improving transferability by providing a surface speed difference between a transfer belt having a transfer material conveying function and a photosensitive member has been already frequently performed in a monochrome copying machine.
[0007]
(2) The object of the present invention (see Patent Document 2 below) is to make the transfer material good for the transfer belt regardless of the use environment or the print mode (regardless of the single-sided printing mode or the double-sided printing mode). An object of the present invention is to provide a color image forming apparatus that is attracted and that does not cause image defects due to poor suction even with a transfer belt having a vertical track.
[0008]
In the configuration of the present invention, a plurality of image forming stations each including a photosensitive drum, a transfer roller, and the like are arranged along the running direction of the transfer belt, and the sheet is formed on each drum while conveying the paper with the transfer belt. In a color image forming apparatus that sequentially superimposes toner images on a sheet, the toner image is applied to a suction roller that constitutes a paper suction unit according to the environmental conditions in which the main body of the image forming apparatus is used and the single-sided / double-sided printing mode. The sheet suction bias or the transfer bias applied to the transfer roller can be changed and controlled.
[0009]
However, the present invention does not change the surface speed ratio between the photosensitive drum and the transfer belt in accordance with the printing mode. Further, according to the present invention, when the paper type is different or when the temperature and humidity of the atmosphere are greatly changed, when a slight speed fluctuation occurs on the paper due to the effect of the surface speed difference between the photosensitive drum and the transfer belt, It is difficult to reliably reduce the deviation. Furthermore, in the present invention, the transfer current condition and the transfer material adsorption current condition are made variable so as to achieve stable conveyance of the transfer material. In order to obtain a good image, the photosensitive drum and the transfer belt are used. However, the apparatus having a difference in surface velocity has a problem that the color shift in the sub-scanning direction on the transfer material cannot be sufficiently suppressed.
[0010]
[Patent Document 1]
Japanese Patent No. 2743359
[Patent Document 2]
JP 2001-109325 A
[0011]
As described above, by providing a difference in surface speed between the photosensitive member and the transfer belt, it is possible to prevent a white spot (worm-eaten image) from being printed on the printed character or to ensure transferability of two colors. . However, when the above surface speed difference is provided, the transfer material attracting force with respect to the transfer belt is reduced. As a result, the transfer material transport speed is not equal to the transfer belt transport speed, and the transport speed becomes unstable. Color misregistration is likely to occur. More specifically, since the electrostatic attraction force of the transfer material to the transfer belt differs depending on the type of transfer material and humidity control conditions (atmosphere humidity), a surface speed difference is provided between the photosensitive drum and the transfer belt. In such a case, it is necessary to prevent the above color shift by setting and maintaining the optimum transfer conditions in consideration of the environmental humidity, the type of transfer material to be used, and the front / back of the transfer material.
[0012]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to perform a double-sided image formation mode, that is, a double-sided printing mode (printing on the front side, subsequently reversing the transfer material, In printing mode (printing mode), high image quality is stabilized by ensuring both high toner image transfer rate on the back side of the paper and suppressing increase in color misregistration in the sub-scanning direction (on the transfer material). Another object of the present invention is to provide an electrophotographic color image forming apparatus that can be formed as described above.
[0013]
[Means for Solving the Problems]
The invention according to claim 1 includes an image forming unit including a photosensitive drum, a transfer roller, and the like, and a toner image on the photosensitive drum is transferred by the transfer roller to a transfer material sucked and conveyed by a circulating transfer belt. In the electrophotographic color image forming apparatus that can be set to the double-sided image forming mode, the surface speed of the photosensitive drum is Vd, the surface speed of the transfer belt is Vb, and the ratio of Vb to Vd is “Vb / Vd”. Value ”, in the double-sided image formation mode, Vb when transferring the toner image to the back side of the transfer material is the same as Vb when transferring the toner image to the front side of the transfer material, and Vd when transferring the toner image to the back side of the transfer material Vd when transferring a toner image on the surface side of The distance between the Vb / Vd value and 1 when the toner image is transferred to the back surface side of the transfer material is made larger than the distance between the Vb / Vd value and 1 when the toner image is transferred to the surface side of the transfer material. This is a color image forming apparatus.
[0014]
That is, according to the first aspect of the present invention, in the double-sided image forming mode, the difference between the Vb / Vd value and 1 when printing on the back surface side of the transfer material: | Vb / Vd value-1 | Difference between Vb / Vd value and 1 when printing: greater than | Vb / Vd value-1 |.
[0015]
According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, a plurality of image forming units corresponding to the respective color toner images are arranged along the running direction of the transfer belt.
[0016]
According to a third aspect of the present invention, a plurality of image forming portions each including a photosensitive drum, a transfer roller, and the like are disposed along the traveling direction of the intermediate transfer belt that circulates in correspondence with each color toner image. An electrophotographic color image forming apparatus that transfers a toner image on each photosensitive drum with the transfer roller, and transfers the transferred toner image on the intermediate transfer belt onto a transfer material that is fed on a run at a secondary transfer portion. When the surface speed of the intermediate transfer belt is Vi, the surface speed of the transfer material is Vp, and the ratio of Vp to Vi is “Vp / Vi value”, the double-sided image forming mode can be set. Then Vp when transferring the toner image to the back side of the transfer material is the same as Vp when transferring the toner image to the front side of the transfer material, and Vi when transferring the toner image to the back side of the transfer material By changing from Vi when the toner image is transferred to the surface side of The distance between the Vp / Vi value and 1 when the toner image is transferred to the back surface side of the transfer material is made larger than the distance between the Vp / Vi value and 1 when the toner image is transferred to the surface side of the transfer material. This is a color image forming apparatus.
[0017]
That is, according to the third aspect of the present invention, in the double-sided image forming mode, the difference between the Vp / Vi value and 1 when printing on the back side of the transfer material: | Vp / Vi value-1 | Difference between Vp / Vi value and 1 when printing: greater than | Vp / Vi value-1 |.
[0018]
In the first aspect of the invention, in the double-sided image forming mode, the Vb / Vd value when the image is transferred to the back surface side of the transfer material is compared with the Vb / Vd value when the image is transferred to the front surface side of the transfer material. By setting the distance away from 1 more appropriately, the transfer rate of the printed image on the back side becomes almost equal to the transfer rate of the printed image on the front side (see the graph of FIG. 3 described later). In addition, an increase in the amount of color misregistration in the sub-scanning direction is suppressed to a low level (see the graph of FIG. 4 to be described later), and as a result, a high-quality transfer image can be stably formed. Also, a color image forming apparatus having a plurality of photosensitive drums is usually more likely to cause color misregistration than a color image forming apparatus having only one photosensitive drum. In contrast, in the second aspect of the invention, since the image forming conditions are set as in the first aspect, a transfer image having a quality equivalent to that of a color image forming apparatus provided with only one photosensitive drum is obtained. , Can be formed stably.
[0019]
In the invention according to claim 3, the Vp / Vi value when the image is transferred to the back surface side of the transfer material is further away from 1 than the Vp / Vi value when the image is transferred to the front surface side of the transfer material. In addition, the transfer rate of the printed image on the back surface side is almost equal to the transfer rate of the printed image on the front surface side, as in the case of the invention of claim 1 by setting the degree of separation to an appropriate value. In addition, an increase in the amount of color misregistration in the sub-scanning direction is suppressed to a low level, and as a result, a high-quality transfer image can be stably formed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments and examples of the present invention will be described with reference to the drawings.
First embodiment
As shown in FIG. 1, the color image forming apparatus according to the present embodiment forms a plurality of image forming portions by using photoconductor drums 11 to 14 and transfer rollers 21 to 24 and adsorbs them by a transfer belt 50 that circulates. An electrophotographic color image forming apparatus that transfers a toner image on a photosensitive drum onto a conveyed paper P by a transfer roller, where the surface speed of the photosensitive drum is Vd and the surface speed of the transfer belt is Vb. In the double-sided image forming mode, the drum speed control unit 31 controls the rotational speed of the photosensitive drum, and the toner image is transferred to the back side of the transfer material by maintaining the running speed of the transfer belt at a constant value. The distance between the Vb / Vd value and 1 is larger than the distance between the Vb / Vd value and 1 when the toner image is transferred to the front surface side of the transfer material (Vb during printing on the back side of the paper). The Vd values from 1 compared to Vb / Vd value during the paper surface printing is to control more away) as.
[0021]
First, the configuration of this color image forming apparatus will be described. FIG. 1 is an explanatory diagram showing a main configuration of a direct transfer type quadruple tandem color image forming apparatus. In this image forming apparatus, a photosensitive drum 11 for forming a magenta toner image, a photosensitive drum 12 for forming a cyan toner image, a photosensitive drum 13 for forming a yellow toner image, and a photosensitive drum for forming a black toner image. The body drum 14 is arranged in this order in the traveling direction of a sheet (transfer sheet) P as a transfer material. Each photosensitive drum is rotatable by an M drum drive motor 21, a C drum drive motor 22, an M drum drive motor 23, and a BK drum drive motor 24, respectively. These drive motors are communicated to the drum speed change control unit 31 so that the rotational speeds of the respective photosensitive drums can be controlled independently, or these drums can be collectively controlled to the same rotational speed. That is, the drum speed change control unit 31 is for changing and setting the Vb / Vd value. The transfer rollers 41 to 44 are arranged immediately below the respective photosensitive drums, and a transfer bias can be applied to these transfer rollers.
[0022]
An endless transfer belt 50 that circulates at a constant speed by a driving roller 51 is provided. In this case, the transfer belt 50 travels from the M drum 11 toward the BK drum 14, that is, the nip portion between the driving roller 51 and the paper suction roller 52, the photosensitive drums 11 to 14, and the transfer rollers 41 to 44. And the guide rollers (idle rollers) 53 and 54, the nip portion between the static eliminating roller 61 and the counter roller 62, and the guide roller (idle roller) 55 in this order.
[0023]
A sheet adsorbing portion A is configured by the nip portion between the driving roller 51 and the sheet adsorbing roller 52. Further, a cleaning portion B is constituted by the nip portion between the charge eliminating roller 61 and the counter roller 62 and the cleaning blade 63. The static eliminating roller 61 is for removing static electricity remaining on the transfer belt 50. In the cleaning unit B, a cleaning blade 63 is disposed in contact with the opposing roller 62 so that the toner remaining on the transfer belt 50 can be removed and collected by the cleaning blade 63 via the opposing roller 62. Further, a resist portion C including a pair of opposed rollers is provided on the upstream side of the paper suction portion A. The registration portion C is for introducing the paper P into the paper suction portion A. Further, the temperature / humidity detection unit E is connected to the drum speed change control unit 31. The temperature / humidity detection unit E detects the temperature / humidity in the image forming apparatus and outputs the result to the drum speed change control unit 31 to set the rotation speed of the photosensitive drum to a value suitable for the detected temperature / humidity. Is to do.
[0024]
In the color image forming apparatus, the sheet P is adsorbed to the transfer belt 50 by the sheet adsorbing portion A, and is transported by the transfer belt 50 while traveling from the M drum 11 toward the BK drum 14 integrally with the transfer belt. When the toner images of the respective colors are transferred and pass through the nip portion between the BK drum 14 and the transfer roller 44, the transfer of the color toner image onto the paper P is completed. The toner image on the paper P is heat-fixed in a fixing unit (not shown).
[0025]
Here, a method for measuring the Vb / Vd value will be described.
When the electrostatic adsorption of the paper P to the transfer belt 50 is accurately performed, the surface speed of the transfer belt 50 and the surface speed of the paper P can be regarded as the same speed. Therefore, when measuring the surface speed of the transfer belt, detection marks at regular intervals are written at appropriate positions on the surface of the transfer belt, the marks are read by a sensor, and the surface speed is obtained from the mark interval and the sensor detection time interval. The same applies to the surface speed of the photoconductor, and measurement is performed by writing detection marks at regular intervals on the photoconductor. However, although the above method is possible experimentally, it is not always easy to apply this method to an actual machine.
[0026]
Therefore, the present inventor has devised a simple method for obtaining the surface speed ratio (Vb / Vd value) between the transfer belt and the photosensitive drum. That is, by forming a lattice pattern with a constant lattice spacing on the photosensitive drum, and measuring the lattice spacing in the sub-scanning direction on the drum and the lattice spacing in the sub-scanning direction transferred to the transfer belt,
[0027]
Transfer belt surface speed / photosensitive drum surface speed
= Lattice spacing on transfer belt / lattice spacing on photoreceptor drum
[0028]
Using the relationship, it was decided to measure the Vb / Vd value in the actual machine. In the above measurement method, the lattice spacing on the photosensitive member becomes longer as the surface speed of the photosensitive member becomes faster, and the lattice spacing on the photosensitive member becomes shorter when the surface speed becomes slower.
[0029]
Second embodiment
First, the configuration of the color image forming apparatus according to the present embodiment will be described. FIG. 2 is an explanatory diagram showing a main configuration of a four-tandem color image forming apparatus using an intermediate transfer method. In this image forming apparatus, a photosensitive drum 14 for forming a black toner image, a photosensitive drum 13 for forming a yellow toner image, a photosensitive drum 12 for forming a cyan toner image, and a photosensitive drum for forming a magenta toner image. The body drums 11 are arranged in this order from the upstream side to the downstream side of the intermediate transfer belt 100 that is an endless belt. Each photosensitive drum is configured to be driven by a BK drum driving motor 24, a Y drum driving motor 23, a C drum driving motor 22, and an M drum driving motor 21, respectively. These drive motors are communicated to the drum speed change control unit 31 so that the rotational speeds of the respective photosensitive drums can be controlled independently, or these drums can be collectively controlled to the same rotational speed. The transfer rollers 41 to 44 are arranged immediately below the respective photosensitive drums, and a transfer bias can be applied to these transfer rollers.
[0030]
The intermediate transfer belt 100 can be circulated by a driving roller 71. In this case, the belt 100 travels from the BK drum 14 toward the M drum 11 by the driving roller 71, that is, the driving roller 71, the nip portion between each photosensitive drum and each transfer roller, and the secondary transfer roller 72. And the secondary transfer portion D composed of the counter roller 73 and the guide rollers 74 and 75 in this order. The rotation speed of the drive roller 71 can be controlled by the drive roller speed change control unit 70. The drive roller speed change control unit 70 is for changing and setting the Vp / Vi value. Further, a resist portion C is provided so that the paper P from the resist portion can be conveyed toward the secondary transfer portion D. In addition, a cleaning blade 76 is disposed in contact with a portion of the intermediate transfer belt 100 that is stretched over the guide roller 75 so that toner remaining on the intermediate transfer belt 100 can be removed and collected.
[0031]
In the color image forming apparatus, the toner images of the respective colors are transferred onto the intermediate transfer belt 100 that circulates, and the color toner images formed on the intermediate transfer belt 100 are transferred from the registration unit C in the secondary transfer unit D. It is transferred to the paper P. The toner remaining on the intermediate transfer belt 100 is removed by the cleaning blade 76 and travels toward the BK drum 14. The toner image on the paper P is heat-fixed in a fixing unit (not shown).
[0032]
【Example】
Next, examples of the present invention will be described.
Example 1 (first embodiment)
In FIG. 1, the transfer belt 50 is brought into contact with the four photosensitive drums 11 to 14. Charge is applied to the paper P by the paper suction roller 52, and the paper is sucked onto the transfer belt 50. Then, the sheet P is conveyed while being attracted to the transfer belt 50, and the toner images of the respective colors are superimposed while passing the photosensitive drums 11 to 14 in this order. In this case, the sheet P is strongly attracted to the transfer belt 50 toward the downstream side by the transfer current of each color.
[0033]
3 and 4 relate to the results of the embodiment when the image forming apparatus of FIG. 1 is set to the double-sided image forming mode, and FIG. 3 shows the relationship between the Vb / Vd value and the toner image transfer rate to the paper. FIG. 4 is a graph showing the relationship between the Vb / Vd value and the amount of color misregistration in the sub-scanning direction. As apparent from FIG. 3, when the Vb / Vd values are the same, the transfer rate of the toner image is lower on the back side than on the front side. Further, as the Vb / Vd value is further away from 1, the toner image transfer rate becomes higher on both the front side and the back side. Further, as apparent from FIG. 4, when the Vb / Vd value is the same, the color shift amount in the sub-scanning direction is lower on the back side than on the front side, and the further away the Vb / Vd value is from 1, the more the surface The amount of color misregistration in the sub-scanning direction increases on both the side and the back side.
[0034]
As described above, in the double-sided image formation mode, the toner image transfer rate and the color misregistration amount with respect to the Vb / Vd value are in a trade-off relationship, and the image quality is different between the front side and the back side at the same Vb / Vd value. Different. Therefore, in the present invention, by setting the Vb / Vd value at the time of printing on the back surface side to an appropriate value further away from 1 than the Vb / Vd value at the time of printing on the front surface side, The toner image transfer rate is improved, and an increase in the amount of color misregistration in the sub-scanning direction on the back side is suppressed. In this case, the drum speed change control unit 31 controls the drive motors 21 to 24 of the respective photosensitive drums to set the respective rotational speeds to predetermined values, while maintaining the circulating running speed of the transfer belt at a constant value. To do.
[0035]
As shown in FIG. 4, in the double-sided image forming mode, the amount of color misregistration is lower on the back side than on the front side. This is because the paper once passes through the heat fixing unit and the moisture content is reduced. This is because, since the resistance is high, the electrostatic attracting force to the transfer belt is increased in the back side printing compared to the front side printing. In the double-sided image formation mode, even if the surface speed of the transfer belt is maintained at a constant value, the electrostatic adsorption force to the transfer belt is increased in the back side printing compared to the front side printing. The reverse side printing is higher than the front side printing.
[0036]
In the double-sided image forming mode according to Example 1, the Vb / Vd value was set as follows. That is, at the time of surface printing, the surface speed of the transfer belt was 125 mm / sec, the surface speed of the photosensitive drum was 127 mm / sec, and Vb / Vd value = 0.984 was set. At the time of printing on the back surface, the surface speed of the transfer belt was kept at 125 mm / sec, the surface speed of the photosensitive drum was increased to 129 mm / sec, and Vb / Vd value = 0.969 was set. That is, the Vb / Vd value at the time of printing on the back surface was controlled to be further away from 1 compared with the Vb / Vd value at the time of printing on the front surface. As a result, good quality images could be stably formed on both the front and back surfaces.
[0037]
As in this embodiment, when only the surface speed of the photosensitive drum is changed, the running speed of the transfer belt does not change, so that the paper feeding of the registration portion C, the paper suction portion A, the fixing portion (not shown), etc. There are advantages that there is no need to change the speed and that the number of prints per unit time does not increase or decrease. In this embodiment, as shown in FIG. 1, the apparatus is configured to change the surface speed of the photosensitive drum. However, instead of this, a transfer belt running speed change control unit (not shown) is provided to transfer the image. It can also be configured to change only the surface speed of the belt. Furthermore, it is possible to change the surface speed of both the photosensitive drum and the transfer belt.
[0038]
Example 2 (second embodiment)
The relationship between the Vp / Vi value and the toner image transfer rate and the color in the sub-scanning direction when the double-sided image forming mode is set in the color image forming apparatus according to the second embodiment of the present invention It has been confirmed through experiments that the relationship with the amount of deviation is the same as in FIGS.
(1) When the Vp / Vi value is the same, the toner image transfer rate is lower on the back side than on the front side, and the toner image transfer rate is higher on both the front side and the back side as the Vp / Vi value is far from 1. Become. Also,
(2) When the Vp / Vi values are the same, the amount of color misregistration in the sub-scanning direction is lower on the back side than on the front side, and the farther the Vp / Vi value is from 1, the more the front side and the back side are both in the sub-scanning direction. The amount of color misalignment increases.
[0039]
As described above, in the double-sided image forming mode, the toner image transfer rate and the color misregistration amount with respect to the Vp / Vi value are in a trade-off relationship, and the image quality is different between the front side and the back side with the same Vp / Vi value. Different. Therefore, in the present invention, the Vp / Vi value at the time of printing on the back surface side is set to an appropriate value that is further away from 1 than the Vp / Vi value at the time of printing on the front surface side. The toner image transfer rate is improved, and an increase in the amount of color misregistration in the sub-scanning direction on the back side is suppressed.
[0040]
In the double-sided image forming mode according to Example 2, the Vp / Vi value was set as follows. That is, at the time of surface printing, the surface speed of the paper was 125 mm / sec, the surface speed of the intermediate transfer belt was 123 mm / sec, and Vp / Vi value = 1.016 was set. Further, at the time of back side printing, the surface speed of the paper was kept at 125 mm / sec, the surface speed of the intermediate transfer belt was lowered to 121 mm / sec, and Vp / Vi value = 1.033. That is, the Vp / Vi value at the time of printing on the back surface was controlled to be further away from 1 than the Vp / Vi value at the time of printing on the front surface. As a result, good quality images could be stably formed on both the front and back surfaces. In the present embodiment, only the surface speed Vi of the intermediate transfer belt is changed by the drive roller speed change control unit 70, but instead, only the sheet conveyance speed Vp of the registration unit C can be changed. In addition, the surface speeds of both the intermediate transfer belt and the paper can be changed. In any case, the Vp / Vi value at the time of front side printing and back side printing may be controlled as described above.
[0041]
【The invention's effect】
As is apparent from the above description, according to the present invention, the following effects can be obtained.
According to the first aspect of the present invention, the Vb / Vd value when the image is transferred to the back surface side of the transfer material is 1 to more than the Vb / Vd value when the image is transferred to the front surface side of the transfer material. By setting the distance away from the screen, the transfer rate of the print image on the back side is almost equal to the transfer rate of the print image on the front side, and the amount of color misregistration in the sub-scanning direction. The increase is suppressed low, and as a result, a high-quality transfer image can be stably formed. Further, in the color image forming apparatus according to claim 2, wherein a plurality of photosensitive drums are provided, a transfer image having an excellent quality equivalent to that of a color image forming apparatus provided with only one photosensitive drum can be stably provided. Can be formed.
[0042]
According to the invention of claim 3, the Vp / Vi value when transferring an image to the back side of the transfer material is 1 to more than the Vp / Vi value when transferring the image to the front side of the transfer material. By making the distance away and setting the distance to an appropriate value, the transfer rate of the printed image on the back side is almost the same as the transfer rate of the printed image on the front side, as in the case of the invention of claim 1. In addition, the increase in the amount of color misregistration in the sub-scanning direction is kept low, and as a result, a high-quality transfer image can be stably formed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a main configuration of a color image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a main configuration of a color image forming apparatus according to a second embodiment of the present invention.
FIG. 3 is a graph relating to the result of Example 1 of the present invention, and shows the relationship between the Vb / Vd value and the toner image transfer rate to the paper.
FIG. 4 is a graph related to the result of Example 1 of the present invention, and shows the relationship between the Vb / Vd value and the amount of color misregistration in the sub-scanning direction on the paper.
[Explanation of symbols]
11: Photosensitive drum (M drum)
12: Photosensitive drum (C drum)
13: Photosensitive drum (M drum)
14: Photosensitive drum (BK drum)
21: M drum drive motor
22: C drum drive motor
23: M drum drive motor
24: BK drum drive motor
31: Drum speed change control unit
41: Transfer roller
42: Transfer roller
43: Transfer roller
44: Transfer roller
50: Endless transfer belt
51: Driving roller
52: Paper adsorption roller
53: Guide roller
54: Guide roller
55: Guide roller
61: Static elimination roller
62: Opposing roller
63: Cleaning blade
70: Drive roller speed change control unit
71: Drive roller
72: Secondary transfer roller
73: Opposing roller
74: Guide roller
75: Guide roller
76: Cleaning blade
100: Intermediate transfer belt
A: Paper adsorption part
B: Cleaning section
C: Resist part
D: Secondary transfer part
E: Temperature / humidity detector
P: Paper (transfer material)

Claims (3)

An electrophotographic color image forming device comprising an image forming unit comprising a photosensitive drum, a transfer roller, etc., and transferring a toner image on the photosensitive drum by the transfer roller onto a transfer material sucked and conveyed by a circulating transfer belt. In the apparatus that can be set to the double-sided image forming mode,
When the surface speed of the photosensitive drum is Vd, the surface speed of the transfer belt is Vb, and the ratio of Vb to Vd is “Vb / Vd value”.
In the double-sided image formation mode, Vb when transferring the toner image to the back side of the transfer material is the same as Vb when transferring the toner image to the front side of the transfer material, and the toner image is transferred to the back side of the transfer material. The Vb / Vd value when transferring the toner image to the back surface side of the transfer material is changed from the Vd when transferring the toner image to the front surface side of the transfer material. A color image forming apparatus, wherein the distance between the Vb / Vd value and 1 at the time of transferring a toner image to the front side is larger.   The color image forming apparatus according to claim 1, wherein a plurality of image forming units corresponding to the respective color toner images are arranged along a traveling direction of the transfer belt. A plurality of image forming units including photosensitive drums, transfer rollers, and the like are arranged along the running direction of the intermediate transfer belt that circulates in correspondence with the toner images of each color, and the toner images on the photosensitive drums are arranged on the intermediate transfer belt. Is an electrophotographic color image forming apparatus that transfers a transfer toner image on the intermediate transfer belt to a transfer material that is fed by running at a secondary transfer portion in a batch manner. In what can be set,
When the surface speed of the intermediate transfer belt is Vi, the surface speed of the transfer material is Vp, and the ratio of Vp to Vi is “Vp / Vi value”,
In the double-sided image forming mode, Vp when transferring the toner image to the back side of the transfer material is the same as Vp when transferring the toner image to the front side of the transfer material, and the toner image is transferred to the back side of the transfer material. When the toner image is transferred to the back side of the transfer material, the difference between the Vp / Vi value and 1 when the toner image is transferred to the back surface side of the transfer material is changed. A color image forming apparatus, wherein a distance between a Vp / Vi value and 1 when a toner image is transferred to the front side is larger.

Images