JP2006243514A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus which is less expensive than the conventional image forming apparatus having electric supply sources for respective colors corresponding to transfer bias applying parts in a tandem system, and in which measures against toner spattering liable to occur at the most downstream color can be taken. <P>SOLUTION: The color image forming apparatus is equipped with two electric supply source systems for respective primary transfer bias applying members, wherein one of the systems is an electric supply source system (42) for a primary transfer bias applying member (14) corresponding to the most downstream color (1BK) of four image carriers, and the other is an electric supply source system (41) common to primary transfer bias applying members corresponding to the upstream three colors (1Y, 1M, 1C). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus.

  As a typical method for forming a color image, there is an intermediate transfer method in which toner images of different colors formed on a plurality of photosensitive members are transferred while being superimposed on an intermediate transfer member, and then transferred onto a transfer sheet in a lump. Since a plurality of photoconductors are arranged side by side facing a transfer paper or intermediate transfer body, this is called a tandem method, and yellow (Y), magenta (M), cyan (C), and black (K) for each photoconductor. For each color, an electrophotographic process such as formation and development of an electrostatic latent image is performed, and the image is transferred onto a running transfer sheet in the direct transfer method, or onto a running intermediate transfer member in the intermediate transfer method. The tandem method has an advantage that color copying can be performed at a higher speed than the one-drum method.

  In general, a tandem system is more expensive than a one-drum system. One of the causes is that the tandem method requires a power supply to the primary transfer bias applying member for each color.

  In order to solve this problem, there is a technique in which a single power supply is supplied to a primary transfer bias applying member in a tandem system, that is, four transfer devices corresponding to each color (for example, see Patent Document 1). By doing so, it is possible to make the unit cheaper than the configuration in which the power supply is used for each of the four conventional transfer devices, while ensuring a faster speed than the one-drum method, The cost was close to the one-drum system.

  Further, there is a technique in which two voltage adjustment circuits are provided in total, one for two transfer rollers (two colors) out of four transfer rollers corresponding to each color in spite of being a tandem method (for example, Patent Document 2). reference).

  On the other hand, in the tandem system, there is a problem peculiar to the most downstream color that dust is likely to be generated in the most downstream color toner in the traveling direction of the transfer belt. This is because the charge amount increases when the upstream toner passes through the downstream transfer nip, and the adhesion between the transfer belt and the toner can be secured, whereas the most downstream color is only the charge amount at the time of transfer. This is probably because a sufficient charge amount cannot be obtained.

  It is also known that the higher the transfer belt potential just before the final color transfer nip, the more likely it is that dust (image disturbance) occurs in the final color transfer nip. The transfer bias of the three colors upstream from the final color transfer nip is made as low as possible, the transfer belt potential just before the final color transfer nip is lowered, and the final color transfer bias is made as high as possible to obtain the final color transfer nip. It is most effective to increase the toner charge amount immediately after. In the case of a configuration in which current and voltage can be set for each color, the optimum value can be set for each color. However, since four power supplies are used, the unit becomes expensive.

  There is also a method of using one power supply as in Patent Document 1, but in this case, the same voltage is simultaneously applied to four colors, and the transfer bias is applied only to the most downstream color in which a specific problem occurs as described above. This is not an example of a high setting.

  In Patent Document 2, two transfer rollers for two downstream colors are set with a single power supply (transfer voltage control circuit), and this is not an example of setting a transfer voltage setting value for only the most downstream color transfer roller. To prevent abnormal discharge in the most downstream color, suppress the charge amount (potential) on the transfer belt immediately before the most downstream color transfer nip as much as possible and increase the toner charge amount on the transfer belt immediately after the most downstream color transfer nip. However, if the two downstream colors have the same power supply, if the bias is set high, the potential of the transfer belt immediately before the most downstream transfer nip increases, and if the bias is set low, the toner immediately after the most downstream transfer nip. The charge amount cannot be set high.

JP-A-6-289686 JP 11-119562 A

  The present invention is a tandem method, and is cheaper than a conventional image forming apparatus having a separate power supply for each color for a transfer bias applying unit, and can take countermeasures for toner dust generated in the most downstream color. It is an object to provide a color image forming apparatus.

In order to achieve the above object, an invention according to claim 1 is an image forming apparatus having a transfer belt, four image carriers, and a primary transfer bias applying member disposed opposite to each image carrier via the transfer belt. There are two power supply systems for each primary transfer bias application member, one power supply system for the primary transfer bias application members corresponding to the most downstream colors of the four image carriers, and three upstream colors. One power supply system common to the primary transfer bias applying member is provided.
Here, the two supply power sources for the primary transfer bias application unit can both be controlled at a constant voltage (Claim 2), or the supply power source for the primary transfer bias application member corresponding to the most downstream color is a constant current. The power supply to the primary transfer bias applying member on the upstream side of the control can be a constant voltage control.
In the color image forming apparatus, the most downstream color of the four image carriers can be black (Claim 4), and the transfer belt can be an intermediate transfer belt having a four-tandem configuration. 5).
Further, the color image forming apparatus has a color mode and a black and white mode, and the power supply for transfer can be constituted by a black power supply system and a common power supply system for three colors. Item 6). An image formed by the toner formed on the image carrier is transferred to the transfer belt. The toner is a polymerized toner manufactured by a polymerization method (Claim 7), and the toner has a shape. The coefficient SF-1 is in the range of 100 to 180, and the shape factor SF-2 is in the range of 100 to 180 (claim 8).

  In this invention, the power supply is reduced to a total of two, including one for the bias application member corresponding to the most downstream color, and the abnormal application image corresponds to the most downstream color bias application member. This can be avoided by the power supply provided.

Embodiments of the present invention will be described below.
FIG. 1 is a color image forming apparatus showing an embodiment of the present invention using an intermediate transfer belt as an intermediate transfer member. Reference numerals 1Y, 1C, 1M, and 1BK denote cylindrical photosensitive drums as image carriers, which are rotated in the arrow direction at a peripheral speed of 150 mm / sec. The surface of the photosensitive drums 1Y, 1C, 1M, and 1BK is pressed against a roller-shaped charger 4 as charging means, and is driven to rotate by the rotation of the photosensitive drums 1Y, 1C, 1M, and 1BK, not shown. A surface potential of −500 V is uniformly charged by applying an AC and DC bias from a high voltage power source.

  The photosensitive drums 1Y, 1C, 1M, and 1BK are exposed to image information by an exposure unit 5 that is a latent image forming unit, and an electrostatic latent image is formed. This exposure process is performed by a laser beam scanner or LED using a laser diode. The photoreceptor cleaning unit 3 cleans the transfer residual toner on the surface of the photoreceptor drum 1. Reference numeral 2 denotes a blade of the photoconductor cleaning unit 3.

  In the present embodiment, the developing means is nonmagnetic contact development using a two-component developer, and the latent image on the photosensitive drum 1Y is developed with the yellow developer 6 for developing the latent image on the photosensitive drum 1Y with yellow toner. Four developments: a cyan developing unit 7 for developing with cyan toner, a magenta developing unit 8 for developing the latent image on the photosensitive drum 1M with magenta toner, and a black developing unit 9 for developing the latent image on the photosensitive drum 1BK with black toner The electrostatic latent image on the photosensitive drum is visualized as a toner image by a predetermined developing bias supplied from a high voltage power source (not shown). The toner used in this embodiment is a polymerized toner produced by a polymerization method. The toner shape will be described later.

  The photosensitive drums 1Y, 1C, 1M, and 1BK are arranged side by side along the traveling direction of the intermediate transfer belt 10, and when a full-color image is formed, a visible image is formed in the order of yellow, cyan, magenta, and black. The visible images of the respective colors are sequentially transferred onto the intermediate transfer belt 10 to form a full color image.

  The intermediate transfer belt 10 is stretched by a driving roller 21, primary transfer bias rollers 11 to 14 as one embodiment of a primary transfer bias applying member, a secondary transfer counter roller 19, and a belt cleaning counter roller 20. The motor is driven to rotate in the direction of the arrow in the figure. The primary transfer bias roller 14 is held by a primary transfer bias roller holding member 15 and pressed by the contact / separation cam 16 in the direction of the photosensitive drum 1BK.

  In the normal state, the contact / separation cam 16 presses the primary transfer bias roller 14 toward the photosensitive drum 1, and the contact / separation cam 16 rotates only when the photosensitive drum 1 or the intermediate transfer belt 10 is attached / detached, and the fulcrum 15 a is moved. The primary transfer bias roller holding member 15 swings in the center so that the primary transfer bias roller 14 is separated. Although not shown, the same applies to the other photosensitive drums 1Y, 1C, and 1M. The primary transfer bias roller 14 will be described later.

  The belt cleaning unit 24 performs cleaning by scraping off the transfer residual toner on the intermediate transfer belt 10 with the blade 23. Each roller that stretches the intermediate transfer belt 10 is supported from both sides of the intermediate transfer belt 10 by an intermediate transfer belt unit side plate (not shown).

  As a material used for the intermediate transfer belt 10, a conductive material such as carbon black is dispersed in PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), and the like. A resin film-like endless belt can be used.

  The intermediate transfer belt 10 used in this embodiment has a single-layer structure in which carbon black is added to PI (polyimide) and the thickness thereof is adjusted to 100 μm. By the way, as a method for measuring the resistance of the intermediate transfer belt 10, a probe (inner electrode diameter 50 mm, ring electrode inner diameter 60 mm: JIS-K6911 compliant) is connected to a digital ultrahigh resistance microammeter (manufactured by Advantest: R8340A). A voltage of 1000 V (surface resistivity is 500 V) was applied to the front and back of the intermediate transfer belt 10 and measurement was performed at discharge 5 sec and charge 10 sec. The measurement environment was fixed at 22 ° C. and 55% RH. .

Here, the volume resistivity and the surface resistivity of the intermediate transfer belt 10 are preferably in the range of 10 ⁸ to 10 ¹² Ωcm and the surface resistivity of 10 ⁹ to 10 ¹² Ω / □. . When the volume resistivity and the surface resistivity of the intermediate transfer belt 10 exceed the above-described ranges, the transfer belt is charged. Therefore, it is necessary to take a measure such as setting the set voltage value higher as it goes downstream in the image forming order. This makes it difficult to use a single power supply for the primary transfer portion (primary transfer bias roller). This is because the charge generated on the surface of the intermediate transfer belt 10 becomes high due to the discharge generated in the transfer process, the transfer material peeling process, and the like, and self-discharge becomes difficult. Need arises. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays quickly, which is advantageous for static elimination by self-discharge, but toner scatter occurs because the current during transfer flows in the surface direction. End up. Therefore, the volume resistivity and surface resistivity of the intermediate transfer belt 10 in the present invention must be within the above ranges.

The secondary transfer bias roller 22 provided at the lower portion of the intermediate transfer belt 22 is urethane having a resistance adjusted to 10 ⁶ to 10 ¹⁰ Ω by a conductive material on a metal core such as SUS. It is comprised by coating | covering elastic bodies, such as. Here, if the resistance value of the secondary transfer bias roller 22 exceeds the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain the required transfer property, which increases the power supply cost. Invite. In addition, since it is necessary to apply a high voltage, discharge occurs in the gap before and after the nip of the transfer portion, and white spots are lost on the halftone image due to the discharge. This is remarkable in a low temperature and low humidity environment (for example, 10 ° C., 15% RH). On the contrary, if the resistance value of the secondary transfer bias roller 22 is below the above range, the transferability between the multi-color image portion (for example, three-color superimposed image) and the single-color image portion existing on the same image cannot be achieved. This is because the resistance value of the secondary transfer bias roller 22 is low, so that a sufficient current flows to transfer the monochrome image portion at a relatively low voltage. However, it is optimal for the monochrome image portion to transfer the multiple color image portion. This is because a voltage value higher than the required voltage is required, and if the voltage is set to a voltage capable of transferring a plurality of color image portions, the transfer current becomes excessive in a single color image, resulting in a reduction in transfer efficiency.

  The resistance value of the secondary transfer bias roller 22 is measured by installing the secondary transfer bias roller 22 on a conductive metal plate and applying a load of 4.9N on one side (total of 9.8N on both sides) to both ends of the core metal. In this state, it was calculated from the value of the current flowing when a voltage of 1000 V was applied between the metal core and the metal plate. The measurement of the resistance of the secondary transfer bias roller 22 was performed with the environment fixed at 22 ° C. and 55% RH. In this embodiment, the resistance of the secondary transfer bias roller 22 is adjusted to be 7.8 LogΩ when measured by the method described above.

  Here, the primary transfer bias rollers 11 to 14 have the same configuration as the secondary transfer bias roller described above. This is because the intermediate transfer belt 10 is in contact with the photosensitive drum 1 and, therefore, a primary transfer nip cannot be secured unless the primary transfer bias roller has an appropriate elastic layer. However, the resistance range is not as severe as the secondary transfer bias roller of the intermediate transfer belt layer, but in this embodiment, when the resistance of the primary transfer bias roller is measured by the above-described method, it becomes 7.0 LogΩ. Adjusted.

  A transfer material 29 made of a sheet-like medium is fed by a pickup roller 28, a paper feeding / conveying roller 27, and a registration roller 26 at the timing when the leading edge of the toner image on the surface of the intermediate transfer belt 10 reaches the secondary transfer position. The toner image on the intermediate transfer belt 10 is transferred to the transfer material 29 by applying a predetermined transfer bias from the high voltage power source 100.

  The transfer material 29 is separated from the intermediate transfer belt 10 by the curvature of the secondary transfer counter roller 19 and a predetermined separation bias applied by the separation means 30, and the toner image transferred to the transfer material 29 is fixed by the fixing means 25. Then it is ejected.

  In this embodiment, a single color mode for forming an image of one of yellow, magenta, cyan, and black, a two-color mode for forming an image of two colors of yellow, magenta, cyan, and black, yellow , Magenta, cyan, and black, a three-color mode that forms an image with three colors superimposed, and a full-color mode that forms a four-color superimposed image as described above. These modes can be specified on the operation unit. is there. Of the single color mode, a mode with one black color is called a black and white mode, and other modes are color modes.

  In this embodiment, the process speed at the time of fixing is changed depending on the type of the transfer material 29. Specifically, when a transfer material with a continuous weight of 110 kg or more is used, the process speed is set to half speed, and the transfer material takes twice the normal process speed over the fixing nip formed by the fixing roller pair. The toner image can be secured.

  Here, the reaming amount described above will be described. A ream is a unit that collectively represents 1000 sheets of paper that have been finished to the same specified dimensions. In the case of 4/6 size paper, the 4/6 size is defined as the specified size, and the weight of the 1000 sheets is set to “continuous”. It is called “quantity” and the unit is expressed in <kg>.

  On the other hand, since the secondary transfer process of transferring the toner image on the intermediate transfer belt 10 to the transfer material 29 at this time is also performed at half speed, the bias value applied to the secondary transfer bias roller 22 is “thick paper”. Mode ”is applied. In this embodiment, the type of the transfer material 29 can be specified by an operation unit (not shown), and each of the “plain paper mode” (normal process speed), “thick paper mode” (half speed), and “OHP mode” ( Half speed).

  It is preferable that the shape factor SF-1 of the toner used in this embodiment is in the range of 100 to 180, and the shape factor SF-2 is in the range of 100 to 180. 2 and 3 are diagrams schematically showing the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.

SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

  The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.

SF-2 = {(PERI) ² / AREA} × (100 / 4π) (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated.

  When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

  FIG. 4 shows the power supply system of the primary transfer unit in the four-photoreceptor drum system configuration as described above. FIG. 4 shows an essential part of the configuration of the color image forming apparatus shown in FIG.

  In the present embodiment, the primary transfer bias applying members, that is, the primary transfer bias rollers 11 to 13 positioned on the upstream side in the moving direction indicated by the arrow of the intermediate transfer belt 10 are commonly transferred from the supply power supply 41. A bias voltage is applied, and the transfer bias voltage from the supply power source 42 is applied to the primary transfer bias roller 14 corresponding to the most downstream color black.

  In an ordinary quadruple tandem color image forming apparatus, four power supplies to the primary transfer bias applying member corresponding to the image carrier are used in order to individually set the bias of each color. However, this increases the cost. Further, as a further low-cost configuration, there is a method in which a single power supply is supplied to the primary transfer bias applying member corresponding to the image carrier. However, since an individual bias cannot be set for each subtle color, an abnormal image is avoided. Means are limited.

  Therefore, paying attention to the fact that the abnormal images are caused to concentrate on the most downstream color in the quadruple tandem machine, in this embodiment, as described above, the total number of power supplies is two and provided individually. The cost is reduced by reducing the number by half to 4 in the case, and the transfer bias voltage is applied only to the primary transfer bias roller 14 of the most downstream color by the supply power source 42. In particular, the system solves the problem inherent to the most downstream color, in which dust is likely to be generated in the most downstream color toner in the traveling direction of the transfer belt. The toner dust increases when the upstream toner passes through the downstream transfer nip, so that the adhesion between the transfer belt and the toner can be secured, while the most downstream color has only the charge amount when transferred. Therefore, it is considered that a sufficient amount of charge cannot be obtained. Therefore, the primary transfer bias roller 14 corresponding to the most downstream color black is supplied only from the power supply 42 so that the voltage can be individually set. A transfer bias voltage is applied.

  As in Patent Document 1, in the method of increasing the discharge amount on the downstream side by decreasing the resistance value of each transfer unit toward the downstream side in the belt running direction, the resistance values of all color transfer units are changed. Strict transfer roller resistance value management is required, and the transfer roller unit price may increase. In the present embodiment, there is no such risk. Further, against the adverse effects caused by the extreme belt charge-up described in Patent Document 1, the charge-up can be suppressed by using a transfer belt having a surface resistivity of 1E + 12Ω / □ or less.

  In this embodiment, the most downstream color is black. However, the present invention is not limited to this. However, when black is used as the final color, there are many opportunities for black to be used in the monochrome monochrome mode, so it is possible to have a single power supply (primary transfer power supply) with only black, so the efficiency of the power supply Use is possible.

  Here, the two supply power sources 41 and 42 are both controlled at a constant voltage. By adopting the constant voltage control method, the cost can be further reduced as compared with the case of using a power supply requiring constant current control. As a modification, the power supply 14 to the primary transfer bias applying member (primary transfer bias roller 14) corresponding to the most downstream color is constant current control, the upstream primary transfer bias applying member (primary transfer bias rollers 11 to 13). The power supply to) is controlled at a constant voltage. This is to apply a high electric field as much as possible in order to avoid an abnormal image of the final color. However, if a high electric field is applied when the toner layer is small, an excessive electric field is generated, and an abnormal image is produced. Therefore, by controlling constant current only for the final color, the applied bias can be set high when the toner layer is large (transfer portion resistance is large), and the applied bias can be set low when the toner layer is small (transfer portion resistance is small). It is possible to obtain an optimum electric field according to the image pattern.

  In this embodiment, the color image forming apparatus has a four-tandem tandem configuration in which four transfer units are arranged along the transfer belt, and has an intermediate transfer belt. Therefore, the primary transfer unit is used as the intermediate transfer belt. Since it can be controlled with 10 resistors, the transfer belt surface resistivity is 1E + 12Ω / □ compared to a color image forming apparatus that directly transfers the transfer image onto the transfer material while transporting the transfer material without intermediate transfer. By setting the following, charging on the intermediate transfer belt can be suppressed as much as possible, and the step-up setting in the next image forming process becomes unnecessary. Therefore, the optimum condition setting range is expanded by using the three upstream colors under a constant voltage condition using one power source.

  In FIG. 4, in the full color mode, the four photosensitive drums are in contact with the intermediate transfer belt 10, and the primary transfer bias rollers 11 to 14 are also in contact with the intermediate transfer belt 10. In this color image forming apparatus, a fixed backup roller 43 is provided at a position between the photosensitive drum 1M and the photosensitive drum 1BK, inside the upper stretched portion of the intermediate transfer belt 10. Further, the belt cleaning counter roller 20 can be displaced up and down, and the belt cleaning counter roller 20 is displaced upward so that the state in the full color mode (four photosensitive drums are in contact with the intermediate transfer belt 10). State).

  In the black and white mode, the belt cleaning counter roller 20 is slightly lowered. Accordingly, the primary transfer bias rollers 11 to 13 are also lowered with the fixed backup roller 43 as a rotation fulcrum, and from the photosensitive drums 1Y, 1C, and 1M. The primary transfer bias roller 14 is in contact with the photosensitive drum 1Bk through the intermediate transfer belt 10 only apart. Thus, in the black and white mode, only the black image has to be transferred, so that only the power supply 42 can be operated to transfer the image, and the power supply can be used efficiently.

  The present invention does not use an intermediate transfer belt as in the embodiment, but instead uses a transfer material conveyance belt, and transfers the transfer material directly to the transfer material from the photosensitive drum while conveying the transfer material by the transfer material conveyance belt. The present invention can also be applied to a method for transferring an image.

  FIG. 6 shows the relationship between the charging potential on the intermediate transfer belt immediately before the final color transfer nip and the final color abnormal image. It can be seen from this figure that abnormal images are likely to occur in the final color when the belt potential before the final color transfer nip is high. To avoid this, the transfer bias setting values for the upstream three colors are set. It is necessary to set it as low as possible. The present invention can meet such requirements.

  FIG. 7 shows the relationship between the toner charge amount on the intermediate transfer belt immediately after the final color transfer nip and the abnormal image of the final color. As can be seen from this figure, in order to avoid an abnormal image with the final color, it is necessary to increase the toner charge amount on the intermediate transfer belt after the transfer nip of the final color as much as possible. The present invention can meet such requirements. However, such a setting can be set to an infinitely high value because it is a setting condition while avoiding an abnormal image in the transfer nip portion.

1 is a schematic configuration diagram of an image forming apparatus according to the present invention. FIG. 3 is a diagram schematically illustrating the shape of a toner for explaining a shape factor. FIG. 3 is a diagram schematically illustrating the shape of a toner for explaining a shape factor. 1 is a diagram illustrating a configuration of a main part of an image forming apparatus according to the present invention. 1 is a diagram illustrating a configuration of a main part of an image forming apparatus according to the present invention. FIG. 6 is a diagram illustrating a relationship between a charging potential on an intermediate transfer belt immediately before a final color transfer nip and an abnormal image of a final color. FIG. 6 is a diagram illustrating a relationship between a toner charge amount on an intermediate transfer belt immediately after a final color transfer nip and an abnormal image of a final color.

Explanation of symbols

11-14 Primary transfer bias rollers 41, 42 Power supply

Claims (8)

In an image forming apparatus having a transfer belt, four image carriers, and a primary transfer bias applying member disposed opposite to each image carrier via the transfer belt,
There are two power supply systems for each primary transfer bias applying member, one power supply system for the primary transfer bias applying members corresponding to the most downstream colors of the four image carriers, and the primary corresponding to the upstream three colors. A color image forming apparatus comprising a common supply power system for a transfer bias applying member. The image forming apparatus according to claim 1.
A color image forming apparatus, wherein two power supplies for the primary transfer bias applying unit are controlled at a constant voltage. The image forming apparatus according to claim 1.
2. A color image forming apparatus according to claim 1, wherein the supply power to the primary transfer bias application member corresponding to the most downstream color is constant current control, and the supply power to the upstream primary transfer bias application member is constant voltage control. The color image forming apparatus according to any one of claims 1 to 3,
A color image forming apparatus, wherein the most downstream color of the four image carriers is black. The color image forming apparatus according to any one of claims 1 to 4,
A color image forming apparatus, wherein the transfer belt is an intermediate transfer belt having a quadruple tandem configuration. The color image forming apparatus according to any one of claims 1 to 5,
A color image forming apparatus having a color mode and a black and white mode, wherein a power supply for transfer is composed of a black power supply system and a common power supply system for three colors. The color image forming apparatus according to any one of claims 1 to 6,
An image formed by the toner formed on the image carrier is transferred to the transfer belt, and the toner is a polymerized toner manufactured by a polymerization method. The color image forming apparatus according to claim 7.
9. The color image forming apparatus according to claim 1, wherein the toner has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180.

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