JP2006098964A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the recovery rate of waste developer adhering to a developer carrying member without increasing the size of the apparatus and increasing the cost, and to prevent the adverse effect on image formation by the waste developer.
SOLUTION: The toner recovery capability of the fourth developing unit 51BK is set higher than that of the other developing units 51Y to 51C, and the waste toner for the developing roller 52BK of the fourth developing unit 51BK having the largest reverse transfer amount. Is improved over the other developing units 51Y to 51C. In addition, the stirring ability of the toner in the fourth developing unit 51BK is set higher than those of the other developing units 51Y to 51C, and the stirring ability of the fourth developing unit 51BK having the largest reverse transfer amount is set by the agitator 56BK. The development units 51Y to 51C are improved.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus for transferring a developer image sequentially formed on an image carrier by a plurality of developing units onto a transfer material to form a multicolor image.

  Conventionally, a developer image is sequentially formed on each surface of a plurality of image carriers on which electrostatic latent images are formed (one image carrier in the case of a so-called four-cycle system) by a plurality of developing units. There is known an image forming apparatus that forms a multicolor image by sequentially transferring an agent image on a transfer material such as a sheet or an intermediate transfer member.

  In such an image forming apparatus, when the developer image formed on the image carrier is transferred to the transfer material, a part of the developer forming the developer image is not transferred. It remains on the image carrier. The developer (waste developer) adhering to the image carrier after the developer image is transferred is transferred to a place other than the original image after one rotation of the image carrier. ", Which adversely affects image formation. In order to prevent such a waste developer from adversely affecting image formation, an image forming apparatus is known in which a cleaner for scraping off the waste developer is provided at a position facing the image carrier.

  Assuming that the apparatus is miniaturized and the cost is reduced without using this cleaner, the developing unit develops the electrostatic latent image on the surface of the image carrier, and at the same time, the electrostatic latent image is applied to a place other than the electrostatic latent image. 2. Description of the Related Art An image forming apparatus that employs a simultaneous development cleaning system that recovers attached waste developer from an image carrier is known (see, for example, Patent Document 1).

This simultaneous development cleaning method develops waste developer other than the electrostatic latent image by utilizing the fact that the potential on the surface of the image carrier other than the electrostatic latent image is higher than that of the developing unit. It is a method of adsorbing and collecting by a unit.
Japanese Patent No. 3154757

  By the way, when a multicolor image is formed by the image forming apparatus, the image carrier having the second or subsequent order in which the developer image is transferred to the transfer material is developed as a waste developer due to the transfer residue. In addition to the agent (transfer residual toner), it has been newly found that there is a developer (reverse transfer toner) attached by reverse transfer.

  This reverse transfer is a developer (reversely charged developer) charged to a part of the developer image transferred from the image carrier to the transfer material with a polarity opposite to the polarity charged by the developing unit. Therefore, when the developer image is transferred to the transfer material on the second or subsequent image carrier in which the developer image is formed, the reversely charged developer is reverse to the normal transfer. Transfer from the transfer material in the direction to the image carrier.

Further, in such reverse transfer, the reverse transfer tends to occur more easily as the amount of the developer (toner amount) transferred to the transfer material increases. For example, in the case of the tandem system, the reverse transfer is likely to occur downstream. In general, the amount of developer reversely transferred increases as the image carrier is arranged on the side.
However, conventionally, an image forming apparatus using a so-called simultaneous development cleaning method (also referred to as a cleaner-less method) does not have a dedicated cleaning device for collecting waste developer. The developer moves to the development carrier at the nip point between the image carrier and the developer carrier and is accumulated on the surface of the developer carrier. For this reason, when the accumulated highly charged waste developer (reverse transfer toner) is mixed with the developer supplied by the developer, color mixing occurs. In particular, when there is a difference in charging ability between the reversely transferred waste developer (reverse transfer toner) and the developer supplied by the reverse developer (reverse transfer toner has a higher absolute value of the charge amount), reverse transfer is performed. Since the waste developer is more actively involved in the developing operation, the above-mentioned color mixing problem is likely to occur.

Moreover, due to frictional charging with the reversely transferred highly charged waste developer, some of the developer supplied by itself changes to the opposite polarity to the original charging polarity due to the difference in charging ability (difference in charging amount). There is also a problem that the developer having the reversed polarity adheres to the outside of the electrostatic latent image area of the image carrier, and so-called background fog occurs.
Conversely, when the reversely transferred waste developer (reverse transfer toner) is deteriorated (has poor charging ability), the waste developer has the opposite polarity due to frictional charging with the developer supplied by itself. In this case, there is a possibility that the waste developer (reverse transfer toner) becomes a background fog and deteriorates the image quality.

  In order to remedy this problem, a dedicated cleaning device is provided to collect waste developer (transfer residual toner and reverse transfer toner) adhering to the image carrier after transfer, and the waste developer is carried by the developer. It may be possible not to adhere to the body. However, there is a problem that adding a dedicated cleaning device leads to an increase in the size and cost of the device, and even if there is a dedicated cleaning device, if the cleaning effect is not sufficiently exhibited, As in the case of the cleaning method, there is a possibility that problems such as color mixing and background fogging may occur.

  The present invention has been made in view of such problems, and in the image forming apparatus as described above, the waste developer adhered to the developer carrying member by reverse transfer without increasing the size of the apparatus or increasing the cost. An object of the present invention is to prevent adverse effects on image formation due to the above.

As a means for achieving the above object, an image forming apparatus according to the invention of claim 1 is provided corresponding to an image carrier on which an electrostatic latent image is formed on a surface and corresponding to each of different colors. A plurality of developer carriers that carry a developer corresponding to the color of the image, and the developer carrier is used to develop the electrostatic latent image on the surface of the image carrier with the developer of the color. A development unit, and developing each of the development units to form a developer image on the image carrier in sequence, and transferring the developer image onto a transfer material. In each of the developing units, the developer attached to the developer carrier is collected by contact with the developer carrier after the development on the image carrier. Collecting means for collecting, and the collecting ability of each collecting means The development unit with the last developer image formation order is higher than at least the development unit with the first developer image formation order, and each of the development units has a developer image formation order one before the self. It is characterized in that it exceeds the recovery capacity of the development unit.
The “image forming apparatus” is not limited to a printing apparatus such as a printer (laser printer), but may be a facsimile machine or a multifunction machine having a printer function and a scanner function. Further, the development unit is not limited to a tandem system provided with an image carrier for each development unit, and a four-cycle system in which each development unit performs development formation on a common image carrier may be used.
The “transfer material” may be not only a recording medium such as paper or an OHP sheet, but also an intermediate transfer member such as an intermediate transfer belt or an intermediate transfer drum.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the collecting ability of each of the collecting means is that the developer image forming order is second or higher than the developing unit having the first developer image forming order. It is characterized in that the developing unit is higher.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the collecting ability of each of the collecting means is such that the developing unit having the last developer image formation order has a developing unit other than the last developing unit. It is characterized by being higher than.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the collecting ability of each of the collecting means is such that the developing unit with the third developer image forming rank is higher than the developing unit with the second or earlier developing image. It is also characterized by high.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, each of the collecting units rotates while contacting the respective developer carrying members to thereby carry the developer carrying It has a rotator that collects the developer adhering to the body, and the peripheral speed of the rotator is higher for the developing unit whose recovery capability should be increased.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the rotating body rotates while being in contact with the developer carrying body, and the developer in the developer containing chamber of the developing unit is developed. It is a supply roller for supplying to the agent carrier.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, each of the collecting means moves relative to each of the developer carrying members by moving relative thereto. A contact body for collecting the developer adhering to the agent carrier, wherein the hardness of the contact body is higher for a developing unit whose recovery capability is to be increased.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, each of the collecting means moves relative to each of the developer carrying members to move the developing unit. A contact body for recovering the developer adhering to the developer carrier, and a contact width in a moving direction of the contact body between the contact body and the developer carrier increases the recovery capability. It is characterized in that the developing unit to be widened becomes wider.
The “contact body” here is not limited to a rotating body such as a supply roller, but may be a flat plate such as a blade pressed against the developer carrier. In this case, the contact width can be changed by changing the pressing pressure of the blade.
Further, in the case where the contact body is a “rotating contact body that rotates while being in contact with the developer carrying body”, examples of the configuration that makes the “contact width” different include the following.
(A) A configuration in which the diameters of the rotating contact bodies of the developing units are the same, and the distance between the rotation center axis of the rotating contact bodies and the surface of the developer carrier is different.
(B) A configuration in which the distance between the rotation center axis of the rotating contact body of each developing unit and the surface of the developer carrier is the same, and the diameter of the rotating contact body is different.
(C) A configuration in which the ratio between the “distance between the rotation center axis of the rotating contact member and the developer carrying member” and the “diameter of the rotating contact member” is different.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh or eighth aspect, the contact member rotates while being in contact with the developer carrying member, and development in the developer accommodating chamber of the developing unit is performed. It is a supply roller for supplying the developer to the developer carrying member.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the collecting units rotate while contacting the developer carrying members, and the developing unit develops. A supply roller for collecting the developer adhering to the developer carrier while supplying the developer in the developer storage chamber to the developer carrier, and developing bias voltage to each developer carrier A developing bias applying means for applying a supply bias, and a supply bias applying means for applying a supply bias voltage to each supply roller, and the recovery capability of each developing unit is determined based on the supply bias voltage with respect to the developing bias voltage. Features.

  According to an eleventh aspect of the present invention, there is provided an image forming apparatus according to an eleventh aspect, wherein the image bearing member on which the electrostatic latent image is formed is provided corresponding to each color different from each other and carries a developer of a color corresponding to itself. A plurality of development units configured to develop the electrostatic latent image on the surface of the image carrier with the developer of the color. In the image forming apparatus capable of sequentially forming a developer image on the image carrier by developing an electrostatic latent image by a unit, and transferring the developer image to a transfer material to form a multicolor image. The developing unit is provided with stirring means for stirring the developer in a developer storage chamber for storing the developer, and the stirring ability of each of the stirring means is at least higher than that of the developing unit having the first developer image formation order. Is the last developer image formation order Towards developing unit is high and, each developing unit is characterized in that the developer image formed rank than the self has become more stirring ability of the previous development unit.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the stirring ability of each of the agitating units is such that the developer image formation order is second or higher than the development unit having the first developer image formation order. It is characterized in that the developing unit is higher.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the stirrability of each of the stirrers is such that the developing unit having the last developer image formation order has a developing unit other than the last developing unit. It is characterized by being higher than.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the stirring capacity of each of the stirring means is such that the developing unit with the third developer image forming order is the developing unit with the third or subsequent developing unit. It is also characterized by high.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to fourteenth aspects, each of the agitation units includes a rotation agitation member that rotates in the developer accommodating chamber, and the rotation is performed. The rotating speed of the stirring member is characterized in that the developing unit whose speed of stirring should be increased is faster.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to fifteenth aspects, each of the agitation units includes a rotation agitation member that rotates in the developer accommodating chamber, and the rotation is performed. The size of the stirring member is larger as the developing unit should have higher stirring ability.

  According to a seventeenth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed on a surface; and a development which is provided corresponding to each different color and carries a developer of a color corresponding to itself. A plurality of development units configured to develop the electrostatic latent image on the surface of the image carrier with the developer of the color. An image forming apparatus capable of sequentially forming a developer image on the image carrier by developing an electrostatic latent image by a unit and transferring the developer image to a transfer material to form a multicolor image. A recovery means according to any one of claims 1 to 10 and a stirring means according to any one of claims 11 to 16 are provided.

  According to an eighteenth aspect of the present invention, in the image forming apparatus according to any one of the first to seventeenth aspects, the developing unit having the last developer image formation order is such that the developer carrying member carries a black developer. The electrostatic latent image is developed with a black developer.

  According to a nineteenth aspect of the present invention, in the image forming apparatus according to any one of the eleventh to seventeenth aspects, the developing unit having the last developer image formation order has the developer carrying member carrying a black developer. The electrostatic latent image is developed with a black developer, and the capacity of the developer storage chamber of the last developing unit is larger than that of the other developing units.

<Invention of Claims 1-4>
In an image forming apparatus that forms a multicolor image, the developer carrying member with the first developer image formation order is only attached with a developer due to a residual transfer as a waste developer. In addition to the developer adhering due to the transfer residue, the reversely charged developer generated in a part of the developer image transferred to the transfer material is reversed on the developer carrier having the second image formation order. It is copied and attached. For this reason, the second and subsequent developer carriers have more waste developer attached than the first developer carrier. Moreover, in reverse transfer, the reverse transfer tends to occur as the amount of developer (toner amount) transferred to the material to be transferred increases. The amount of waste developer (reverse transfer toner) adhering to the developer carrying member is increased accordingly.
Therefore, according to this configuration, the developing unit with the last developer image formation order has a higher recovery ability (so-called scraping ability) of the recovery means than the development unit with the first developer image formation order, and Each developing unit has a developer image formation rank higher than that of the developing unit of the previous one (recovery ability equivalent to or exceeding the collecting ability of the previous developing unit). Therefore, with respect to the developer carrier having the second developer image formation order, the waste developer can be collected by a developing unit having a high waste developer collection capability, and color mixing and fogging can be suppressed.
A configuration that improves the recovery capability for all the developing units is also conceivable. However, in such a configuration, the driving load of the recovery mechanism for all the developing units becomes large, and accordingly, a large driving source is required, which may increase the cost and increase the size of the apparatus. For this reason, in Claim 1, it is set as the structure which improves collection | recovery capability about some developing units.

According to the second aspect of the present invention, the collecting ability of each collecting means is higher in the developing units having the second developer image forming order than the developing unit having the first developer image forming order.
According to the third aspect of the present invention, the recovery capability of the last development unit that is most affected by reverse transfer is set higher than the recovery capability of the development units other than the last development unit.
In addition, the effect of reverse transfer is noticeable in the third and subsequent development units. Accordingly, in the configuration of claim 4, the collecting ability of the developing units with the third developer image formation order is higher than that of the second and earlier developing units.

<Inventions of Claims 5 and 6>
In the configuration in which the developer (waste developer) attached is collected using a rotating body (“supply roller” in claim 6) that rotates while being in sliding contact with the developer carrier, the peripheral speed (unit time) of the rotating body is recovered. The faster the outer peripheral surface movement speed), the higher the recovery capability. Therefore, in this configuration, by adjusting the peripheral speed of the contact body in each developing unit, that is, by rotating the rotating body at a peripheral speed corresponding to a desired recovery capability for each developing unit. The configuration of Item 4 is realized. In addition, if the rotating bodies have the same diameter, the peripheral speed, that is, the recovery ability can be made different by changing each rotation speed (the number of rotations per unit time). Further, if the rotating bodies have different diameters, even if the rotational speed is the same, the peripheral speed, that is, the recovery ability can be made different.

<Invention of Claim 7>
A developer (waste) attached using a contact member that slides on the developer carrier (a rotating contact member that rotates while being in contact with the developer carrier). In the configuration for collecting (developer), the higher the hardness of the contact portion of this contact body, the stronger the developer carrying body and the contact body rub against each other, and the higher the recovery capability. Therefore, in this configuration, by adjusting the hardness of the contact body in each developing unit, that is, by making the contact body have a hardness corresponding to a desired recovery capability for each developing unit, The configuration is realized.

<Inventions of Claims 8 and 9>
A developer (waste) attached using a contact member that slides on the developer carrier (a rotating contact member that rotates while being in contact with the developer carrier). In the configuration in which the developer is collected, the larger the contact width (nip width) in the moving direction of the contact body between the contact body and the developer carrier, the greater the difference between the developer carrier and the contact body. Because it rubs strongly, the recovery ability is increased. Therefore, in this configuration, by adjusting the contact width in each developing unit, that is, by setting the contact width for each developing unit to a width corresponding to a desired recovery capability, the configurations according to claims 1 to 4 described above. Is realized.

<Invention of Claim 10>
For example, when the developer has a positive polarity, the developer collecting ability of the supply roller can be suppressed by setting the supply bias voltage higher than the development bias voltage. On the other hand, when the developer has a negative polarity, the collection capability of the supply roller can be suppressed by making the supply bias voltage lower than the development bias voltage.
Therefore, in this configuration, the configurations of the first to fourth aspects are realized by adjusting the relative amount of the supply bias voltage with respect to the development bias voltage in each development unit.

<Invention of Claims 11-14>
In an image forming apparatus that forms a multicolor image, the developer carrying member with the first developer image formation order is only attached with a developer due to a residual transfer as a waste developer. In addition to the developer adhering due to the transfer residue, the reversely charged developer generated in a part of the developer image transferred to the transfer material is reversed on the developer carrier having the second image formation order. It is copied and attached. For this reason, the second and subsequent developer carriers have more waste developer attached than the first developer carrier. And there is a possibility that this waste developer is mixed with its own developer to cause color mixing.
In addition, when there is a difference in charging ability between the reversely transferred waste developer (reverse transfer toner) and the developer supplied by the developer (reverse transfer toner has a higher absolute charge amount), reverse transfer is performed. As a result of frictional charging with the highly charged waste developer, a part of the developer supplied by itself changes from the difference in charging ability (difference in charging amount) to the opposite polarity to the original charging polarity. There is also a problem that the reversed developer adheres to the outside of the electrostatic latent image area of the image carrier and so-called background fog occurs.
When the amount of developer that changes to a polarity opposite to the original charged polarity is very small, even if “fogging” occurs, there is little possibility of adversely affecting the image quality. If the amount of (reverse transfer toner) is large, the amount of developer charged to a reverse polarity increases accordingly, and “fogging” becomes conspicuous.
Therefore, according to this configuration, the developing unit with the last developer image formation order has higher stirring ability of the stirring means than the development unit with the first developer image formation order, and each developing unit Also, the developer image formation order is set to be equal to or higher than the stirring ability of the previous developing unit (stirring ability equal to or exceeding the stirring ability of the previous developing unit). Therefore, by effectively dispersing the developer reversely transferred in the developer accommodating chamber by the developing unit having a high stirring ability with respect to the developer carrying member having the second developer image formation order, fog and color mixing can be achieved. Can be suppressed.
In addition, the structure which improves the stirring ability about all the developing units is also considered. However, in such a configuration, the driving load of the agitating mechanism for all the developing units increases, and accordingly, a large driving source is required, which may increase the cost and increase the size of the apparatus. For this reason, in Claim 11, it is set as the structure which improves the stirring ability about some developing units.

According to the twelfth aspect of the present invention, the stirring ability of each stirring means is higher in the developing units with the second developer image forming order than the developing units with the first developer image forming order.
Further, in the structure of the thirteenth aspect, the stirring ability of the last developing unit having the greatest influence by reverse transfer is made higher than the stirring ability of the developing units other than the last developing unit.
In addition, the effect of reverse transfer is noticeable in the third and subsequent development units. Therefore, in the structure of the fourteenth aspect, the agitating ability of the developing units with the third developer image formation order is higher than that of the second and earlier developing units.

<Invention of Claim 15>
In the configuration in which the developer in the developer accommodating chamber is stirred by the rotation of the rotating stirring member, the faster the rotating speed (the number of rotations per unit time) of the rotating stirring member, the higher the stirring ability. Therefore, in this configuration, the rotational stirring member is adjusted at the rotational speed in each developing unit, that is, the rotational stirring member is rotated at a rotational speed corresponding to a desired stirring ability for each developing unit. The structure of Claim 14 is implement | achieved.

<Invention of Claim 16>
In the configuration in which the developer in the developer accommodating chamber is stirred by the rotation of the rotating stirring member, the larger the rotating stirring member (the wider the stirring area), the higher the stirring ability. Therefore, in this configuration, the size of the rotating agitating member in each developing unit (the width in the rotation axis direction and the length in the radial direction of the rotating agitating member) is adjusted, that is, the rotating agitating member is desired for each developing unit. The structure according to the above-mentioned claims 11 to 14 is realized by making the size according to the stirring ability. By combining with the configuration of the fifteenth aspect, it is possible to further increase the difference in stirring ability between the developing units.

<Invention of Claim 17>
According to this configuration, it is possible to reliably prevent fogging and color mixing by efficiently stirring the developer in the developer storage chamber while reliably collecting the waste developer.

<Invention of Claim 18>
In the developing unit that performs black development, since the influence of color mixing with other color developers is small, it is desirable that the developing unit with the last developer image formation order be the one for black development. In addition, “fogging” with colors other than black is less conspicuous than black, so that the influence on image quality can be minimized.

<Invention of Claim 19>
Since the black developer is also used when a monochrome image is formed, it is required more than other developers. Therefore, in this configuration, the developer storage chamber of the last development unit of black development is made larger than the other development units so that a large amount of black developer can be accommodated. In this case, sufficient stirring ability is required to stir this large amount of black developer. Therefore, the structure of claim 13 is particularly desirable.

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS.
1. Configuration of Color Laser Printer FIG. 1 is a side sectional view showing a schematic configuration of a color laser printer 1 as an image forming apparatus to which the present invention is applied. As shown in FIG. 1, the color laser printer 1 (image forming apparatus) of this embodiment includes a visible image forming unit 4, a paper transport belt 6, a fixing unit 8, a paper feeding unit 9, and a stacker 12. The control unit 10 and the bias supply unit 11 are provided, and toner images (developer images) of four colors corresponding to image data input from the outside are sequentially formed on the paper P (transfer material, recording medium). By doing so, a multicolor image is formed.

(1) Visible image forming section The visible image forming section 4 is provided corresponding to four developing units 51 (51Y, 51M, 51C, 51BK) and these developing units 51Y, 51M, 51C, 51BK, respectively. And four photosensitive drums 3 (3Y, 3M, 3C, 3BK, image carrier), four chargers 31, 32, 33, 34, and four exposure devices 41, 42, 43, 44. Has been. Each of the developing units 51Y, 51M, 51C, and 51BK contains yellow (Y), magenta (M), cyan (C), and black (BK) toner (developer). That is, the alphabetical characters in the reference numerals indicating the developing units in FIG. 1 indicate the colors of the toners stored in the developing units, and are yellow (Y), magenta (M), cyan (C), black (BK). ) Development is performed on the paper P in the order.

Hereinafter, the configuration of each component will be described in detail.
(A) Photosensitive drums The four photosensitive drums 3Y, 3M, 3C, and 3BK that constitute the visible image forming unit 4 are all formed by substantially cylindrical members, and these four are arranged in the horizontal direction at substantially equal intervals ( In the horizontal direction of FIG. As the substantially cylindrical member of each of the photosensitive drums 3Y, 3M, 3C, and 3BK, for example, a member in which a positively chargeable photosensitive layer is formed on an aluminum base material is used. The aluminum substrate is grounded to the ground line of the color laser printer 1.

(B) Charger The four chargers 31 to 34 are so-called scorotron chargers. Among these, the detailed configuration of the charger 31 for charging the photosensitive drum 3Y on which the yellow toner image is formed is as shown in FIG. 2, and is opposed to the photosensitive drum 3Y in the width direction (the depth of the drawing in the drawing). And a shield case 37 in which the charging wire 36 is accommodated and the photosensitive drum 3Y side is opened. By applying a high voltage to the charging wire 36, the photosensitive member is formed. The surface of the drum 3Y is charged to a positive polarity (for example, + 700V). The shield case 37 has a structure in which a grid 38 is provided in an open portion on the photosensitive drum 3Y side. By applying a constant voltage to the grid 38, the surface of the photosensitive drum 3Y is charged with the voltage of the grid 38. The potential is almost the same. The chargers 32 to 34 provided to face the other photosensitive drums 3M, 3C, and 3BK have the same configuration as the charger 31 shown in FIG.

(C) Exposure Device As for the four exposure devices 41 to 44, the exposure device 41 that exposes the photosensitive drum 3Y on which yellow toner is formed will be described as a representative with reference to FIG. As shown in the figure, the exposure device 41 is arranged on the downstream side of the charger 31 with respect to the rotation direction of the photosensitive drum 3Y (clockwise in the figure), and corresponds to one color of image data input from the outside. A laser beam corresponding to (here, yellow) is emitted from the light source, and the laser beam is scanned by a mirror surface of a polygon mirror (not shown) that is rotationally driven by a polygon motor (not shown). Irradiate the surface. Note that most of the exposure devices 41 to 44 shown in FIGS. 1 and 2 are omitted, and only the portion from which laser light is finally emitted is shown.

  By irradiating the surface of the photosensitive drum 3Y with the laser light from the exposure device 41, the surface potential of the irradiated portion is reduced (for example, reduced to + 150V), and electrostatic latent potential is applied to the surface of the photosensitive drum 3Y. An image is formed. Each of the exposure units 42 to 44 disposed opposite to the other photosensitive drums 3M, 3C, and 3BK has the same configuration as the above-described exposure unit 41, and image data input from the outside. Based on the above, laser light corresponding to the corresponding color is emitted.

(D) Developing Unit As for the four developing units 51Y, 51M, 51C, and 51BK, a developing unit 51Y that develops an electrostatic latent image with yellow toner will be described as a representative with reference to FIG.

  As shown in the drawing, the developing unit 51Y includes a toner hopper 54 (developer storage chamber) as a toner storage portion, a supply roller 55Y as a toner supply unit and a recovery unit in a development unit case 53 that stores yellow toner. And a developing roller 52Y as a developer carrier.

  Among these, the toner hopper 54 is formed as an internal space of the developing unit case 53. The toner hopper 54 is provided with an agitator 56Y as a stirring means on the side close to the developing roller 52Y, and contains yellow toner. Here, the toner accommodated in the toner hopper 54 is a positively charged non-magnetic one-component developer, which is manufactured by suspension polymerization or emulsion polymerization, has a substantially spherical shape, and has extremely good fluidity. .

  The supply roller 55Y is disposed below the toner hopper 54, and a metal roller shaft is covered with a roller portion made of a conductive sponge member. The supply roller 55Y is rotatably supported so as to rotate in a direction opposite to the developing roller 52Y (counterclockwise in FIG. 2) at a nip portion facing and contacting the developing roller 52Y.

  The developing roller 52Y is rotatably disposed at a position opposite to and in contact with the supply roller 55Y on the side of the supply roller 55Y. The developing roller 52Y is formed in a cylindrical shape using conductive silicone rubber or the like as a base material, and a coating layer of a resin containing fluorine or a rubber material is formed on the surface thereof.

The developing roller 52Y is disposed on the downstream side of the exposure device 41 with respect to the rotation direction of the photosensitive drum 3Y so as to contact the photosensitive drum 3M. The developing unit 51Y charges the toner to “+” (positive polarity) and supplies the toner to the developing roller 52Y as a uniform thin layer. Then, at the contact portion between the developing roller 52Y and the photosensitive drum 3Y, the “+” (positive polarity) electrostatic latent image formed on the photosensitive drum 3Y is charged to “+” (positive polarity). The toner is developed by a reversal development method to form a toner image.
Each of the other developing units 51M, 51C, and 51BK has the same configuration as the developing unit 51Y shown in FIG. 2 except that the color of the toner to be stored is different, and stores magenta, cyan, and black toners, respectively. Yes.

(2) Paper Feed Unit The paper feed unit 9 is provided at the lowermost part of the color laser printer 1 and includes a storage tray 91 that stores the paper P and a pickup roller 92 that feeds the paper P. Then, the paper P stored in the storage tray 91 is picked up one by one from the paper feeding unit 9 by the pickup roller 92 and is sent to the paper transport belt 6 through the transport roller 99 and the like.

(3) Paper Conveying Belt Further, the paper conveying belt 6 is narrower than the width of each photosensitive drum 3, and is configured in an endless state so as to travel integrally with the paper P held on the upper surface side. And over the driven roller 63. Four transfer rollers 66, 67, 68, and 69 are provided so as to face the respective photosensitive drums 3 and sandwich the paper transport belt 6.

  The surface of the sheet conveying belt 6 facing the respective photosensitive drums 3 (hereinafter simply referred to as “the surface of the sheet conveying belt 6”) is rotated in the right direction in the drawing as shown in FIG. Move to the left in the figure. Then, the paper P sent via the transport rollers 99 and the like is sequentially transported between the photosensitive drums 3 and the surface of the paper transport belt 6 and sent to the fixing unit 8.

  The four transfer rollers 66, 67, 68, 69 are applied with voltages of a polarity (positive polarity in this example) and a reverse polarity (that is, negative polarity) in which the chargers 31 to 34 charge the photosensitive drums 3 respectively. Thus, an appropriate transfer bias is applied between the transfer rollers 66 to 69 and the photosensitive drums 3 by so-called constant current control (for example, −10 to −15 μA). With this transfer bias, the toner images formed on the respective photosensitive drums 3 are sequentially electrostatically transferred onto the paper P transported by the paper transport belt 6.

  For example, in the case of a toner image with yellow toner, a transfer bias is applied by applying a negative high voltage to the transfer roller 66 as shown in FIG. Thus, the toner image on the photosensitive drum 3Y is transferred to the paper P at a position where the photosensitive drum 3Y and the transfer roller 66 face each other, that is, at a transfer nip portion TP where the paper P and the photosensitive drum 3Y are in contact with each other. The

  That is, by applying a transfer bias, an electric field is generated from the photosensitive drum 3Y to the transfer roller 66, and the positive toner image on the photosensitive drum 3Y is electrostatically transferred onto the paper P by this electric field. It is. The same applies to the transfer of the toner images on the other photosensitive drums 3M, 3C, and 3BK. By applying a transfer bias to the respective transfer rollers 67 to 69, the corresponding color toner images are transferred onto the paper P. Are sequentially transferred. In this way, a desired multicolor image is formed by transferring the four color toner images onto the paper P in the order of yellow, magenta, cyan, and black. Note that the constant current control of the transfer bias is merely an example, and the control method may be determined as appropriate, for example, constant voltage control.

  A cleaning brush 105 is provided on the surface of the paper transport belt 6 that is turned back by the driving roller 62. The cleaning brush 105 has a configuration in which a brush is provided around a substantially cylindrical member extending in the width direction of the paper conveyance belt 6, and the electrode roller 104 provided at a position facing the paper conveyance belt 6. A bias voltage for generating a predetermined potential is applied to the sheet conveying belt 6 so as to rotate while being in contact with the sheet conveying belt 6. Further, in the vicinity of the cleaning brush 105, a collection roller 106 that removes toner adhering to the cleaning brush 105 from the cleaning brush 105, and a storage box that stores toner removed from the cleaning brush 105 by the collection roller 106. 107 is provided.

(4) Fixing Unit The fixing unit 8 includes a heating roller 81 and a pressure roller 82, and the sheet P carrying a multicolor image composed of four color toner images is transferred to the heating roller 81 and the pressure roller 82. The multicolor image is fixed on the paper P by heating and pressurizing while nipping and conveying.

(5) Stacker A stacker 12 is formed on the upper surface of the color laser printer 1. The stacker 12 is provided on the paper discharge side of the fixing unit 8 and accommodates the paper P discharged from the fixing unit 8.

(6) Control Unit The control unit 10 is configured by a control device using a known CPU, and controls the overall operation of the color laser printer 1. Then, by controlling the bias supply unit 11, a development bias (for example, 400V) to each developing roller 52 (52Y, 52M, 52C, 52BK) and a supply bias to the supply roller 55 (55Y, 55M, 55C, 55BK) (For example, 400 V), a transfer bias to the transfer rollers 66 to 69, a cleaning bias applied between the electrode roller 104 and the cleaning brush 105, and an applied voltage to the chargers 31 to 34 are controlled. . The bias supply unit 11 supplies the biases and the like to a predetermined supply target according to the control signal from the control unit 10 as described above.

  The color laser printer 1 according to the present embodiment uses the developing roller 52 and the residual toner remaining on the surface of the photosensitive drum 3 without being transferred after the transfer of the toner image from each photosensitive drum 3 onto the paper P. This is configured as a so-called simultaneous development cleaning method in which the toner is collected in the toner hopper 54 via the supply roller 55.

2. Operation of this embodiment (1) Reverse transfer Although the exact mechanism of reverse transfer has not yet been clarified, the results of repeated verification of the cause of reverse transfer, more specifically, the cause of reverse charging of toner, I got one reasoning. First, reverse charging is caused by discharge in the toner layer transferred onto the paper P. The discharge in the toner layer is caused by a strong electric field between the surface potential (eg, 700 V) of the photosensitive drums 3Y, 3M, 3C, and 3BK and the potential of the transfer rollers 66 to 69 (transfer bias; eg, −1 kV). It is. As the toner of each color is sequentially transferred, the toner on the paper P is also multilayered, so that the charge amount (positive potential) of the entire toner layer increases. When this enters a strong electric field, a discharge occurs inside the toner layer, and the upper layer portion is reversely charged to a negative polarity.

  More specifically, as illustrated in FIG. 3A, a positive toner image 70 transferred onto a sheet (not shown) conveyed in the left direction in the figure by the sheet conveying belt 6 includes: The toner image (positive polarity) 71 on the photosensitive drum 3 is transferred at the transfer nip portion TP where the photosensitive drum 3 and the transfer roller 66 (67, 68, 69) face each other. As a result, a layered toner image 72 is formed as illustrated in FIG. When the toner image 72 moves away from the transfer nip portion TP, a discharge (peeling discharge) occurs inside the toner image 72 due to the influence of a strong electric field between the surface of the photosensitive drum 3 and the transfer roller 66. As shown in FIG. 3A, a reversely charged toner image 73 in which the upper layer portion is reversely charged to a polarity (negative polarity) opposite to the normal charging polarity is generated. Even if reverse charging does not occur after passing the transfer nip portion TP, reverse charging may occur at the time of entering the transfer position during the transfer of the next color. It has also been clarified through experiments that reverse charging tends to occur more easily as the charge amount (potential) of the toner image on the transfer material increases.

  Furthermore, in the case where the development is sequentially performed by the four development units 51Y, 51M, 51C, and 51BK corresponding to the four colors as in this embodiment, the development unit having the third developer image formation order as shown in FIG. The magenta toner by the second developing unit 51M, which is superimposed on the yellow toner by the first developing unit 51Y on the paper P, is reversely transferred to 51C. Further, the magenta toner and cyan toner by the second and third developing units 51M and 51C, which are superimposed on the yellow toner by the first developing unit 51Y, and the second developing unit with respect to the fourth developing unit 51BK. The cyan toner from the third developing unit 51C superimposed on the 51M magenta toner is reversely transferred. It has been found that the amount of the second, third magenta toner, and cyan toner superimposed on the first yellow toner is reversely transferred to the fourth developing unit 51BK. Note that, as in this embodiment, when using a non-magnetic one-component toner in which charge transfer occurs when the toners rub against each other, the toner with inferior charging performance is charged to a reverse polarity due to the charge transfer, which is particularly affected. large.

(2) Regarding Toner Collection Capability As described above, a bias voltage (400 V) of substantially the same level is applied to each developing roller 52 and each supply roller 55. Accordingly, each supply roller 55 supplies the toner in the toner hopper 54 to the developing roller 52 at the nip portion, while scraping the toner (waste developer) adhering to the surface of the developing roller 52 at the nip portion. It functions as a collecting means for taking and collecting it in the toner hopper 54.

  In this embodiment, each of the supply rollers 55 is a cylindrical body having the same diameter, and the rotation speed (the number of rotations per unit time) of the supply roller 55BK of the fourth developing unit 51BK is the first to third. It is faster than the rotation speed of the supply rollers 55Y to 55C of the developing units 51Y to 51C. That is, the toner collection capability of the fourth development unit 51BK is set higher than that of the other development units 51Y to 51C.

(3) Toner Stirring Ability In this embodiment, the agitators 56Y, 56M, 56C, and 56BK that rotate in the toner hopper 54 and stir the toner in the toner hopper 54 all have the same shape and size. The rotational speed (the number of revolutions per unit time) of the agitator 56BK of the fourth developing unit 51BK is higher than the rotational speed of the agitators 56Y to 56C of the first to third developing units 51Y to 51C. That is, the toner stirring ability in the fourth developing unit 51BK is set higher than those of the other developing units 51Y to 51C.

3. Effects of the present embodiment (1) According to the present embodiment, the toner recovery capability of the fourth developing unit 51BK is set higher than those of the other developing units 51Y to 51C. As a result, the waste toner collecting ability of the fourth developing unit 51BK having the largest reverse transfer amount with respect to the developing roller 52BK can be improved as compared with the other developing units 51Y to 51C, and color mixing and fogging can be suppressed.

  (2) Further, the toner stirring ability in the fourth developing unit 51BK is set higher than those of the other developing units 51Y to 51C. As a result, the agitator 56BK of the fourth developing unit 51BK having the largest reverse transfer amount is improved in the agitator 56BK as compared with the other developing units 51Y to 51C, so that the reversely transferred toner is efficiently contained in the toner hopper 53. It can be dispersed well to effectively suppress fogging.

  (3) Further, in a developing unit that performs black toner development, the influence of color mixture with other color toners is small. Therefore, in the present embodiment, the fourth developing unit 51BK is for black toner development. As a result, it is possible to more effectively suppress a decrease in image quality.

<Embodiment 2>
FIG. 5 shows Embodiment 2 (corresponding to the invention of claim 8). The difference from the first embodiment lies in the method of changing the recovery capability, and the other points are the same as in the first embodiment. Therefore, the same reference numerals as those in the first embodiment are given and the redundant description is omitted, and only different points will be described next.
In the present embodiment, the collection capacity is changed by changing the nip width N (the contact width in the rotation direction of the supply roller 55) where the developing roller 52 and the supply roller 55 come into contact with each other. Specifically, as shown in FIG. 5, the fourth developing unit 51BK is changed to the first to third developing units 51Y to 51C with respect to the inter-axis distance d between the rotating shaft of the developing roller 52 and the rotating shaft of the supply roller 55. Is shorter. Thereby, the nip width N in the fourth developing unit 51BK is made wider than those of the other developing units 51Y to 51C.

  With such a configuration, in the fourth developing unit 51BK, the developing roller 52BK and the supply roller 52BK rub against each other more strongly than those of the other developing units 51Y to 51C, so that the collecting ability can be improved. Further, with the configuration of the present embodiment, the collecting ability can be easily changed by changing the inter-axis distance d between the developing roller 52 and the supply roller 55 without changing the material and rotation speed of the roller portion of the supply roller 55. There is an advantage that you can.

<Embodiment 3>
FIG. 6 shows Embodiment 3 (corresponding to the invention of claim 10). The difference from the first embodiment lies in the method of changing the recovery capability, and the other points are the same as in the first embodiment. Therefore, the same reference numerals as those in the first embodiment are given and the redundant description is omitted, and only different points will be described next.
When the toner has a positive polarity as in the present embodiment, the supply bias voltage V1 applied from the bias supply unit 11 to the supply roller 55 is set higher than the development bias voltage V2 applied to the developing roller 52. The toner collecting ability by the roller 55 can be suppressed.

Therefore, as shown in FIG. 6, for the fourth development unit BK, the supply bias voltage V2 is set to, for example, +400 V, which is substantially the same as the development bias voltage V2, so that the supply roller 55BK supplies toner to the development roller 52BK. The waste toner is collected. On the other hand, for the first to third developing units 51Y to 51C, the supply bias voltage V2 is set to, for example, +500 V higher than the development bias voltage V2, so that the toner is supplied by the supply rollers 55Y, 55M, and 55C. The waste toner is not collected.
Even if it is such a structure, the effect similar to the said Embodiment 1 can be acquired.

<Embodiment 4>
FIG. 7 shows a fourth embodiment (corresponding to the inventions of claims 16 and 19). The difference from the first embodiment is the configuration of the toner hopper portion of the fourth developing unit 51BK, and the other points are the same as in the first embodiment. Therefore, the same reference numerals as those in the first embodiment are given and the redundant description is omitted, and only different points will be described next.
In this embodiment, as shown in FIG. 7, the toner popper 53 ′ of the fourth developing unit 51BK has a larger toner storage volume than the other developing units 51Y to 51C, and can accommodate a large amount of black toner. Yes. Further, the agitator 56BK ′ provided rotatably in the toner hopper 53 ′ can agitate a larger amount of toner longer than the other developing units 51Y to 51C.

  Here, since black toner is used also when forming a monochrome image, it is required more than other toners. Therefore, in the present embodiment, the toner hopper 53 'of the fourth developing unit 51BK for black development is made larger than the other developing units 51Y to 51C to accommodate a large amount of black toner. Then, the agitator 56BK of the fourth developing unit 51BK having the largest reverse transfer amount is improved in agitating ability over the other developing units 51Y to 51C, so that the reversely transferred toner is efficiently dispersed in the toner hopper 53. To prevent fogging and color mixing.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
(1) In the first to fourth embodiments, the recovery capability of the fourth developing unit 51BK is set higher than that of the other developing units 51Y to 51C. However, the present invention is not limited to this. For example, it may be configured such that the slower the developer image formation order, the higher the recovery capability. Further, the collection capacity of the second to fourth development units 51M to 51BK is set higher than that of the first development unit 51Y, or the collection capacity of the third and fourth development units 51C and 51BK is the first and second. It may be configured higher than the developing units 51Y and 51M.

  (2) In the first to fourth embodiments, the stirring ability of the fourth developing unit 51BK is set higher than that of the other developing units 51Y to 51C, but the present invention is not limited to this. For example, the slower the developer image formation order, the higher the stirring ability may be. In addition, the stirring capacity of the second to fourth developing units 51M to 51BK is higher than that of the first developing unit 51Y, or the stirring capacity of the third and fourth developing units 51C and 51BK is the first and second. It may be configured higher than the developing units 51Y and 51M.

  (3) In the configuration of the first embodiment, the collection capability is changed by making the rotation speed of the supply roller 55BK faster than the other supply rollers 55Y to 55C. However, the present invention is not limited to this, and the roller portion of the supply roller 55 The recovery capability may be changed by adjusting the hardness. For example, a material harder than the other supply rollers 55Y to 55C is used for the roller portion of the supply roller 55BK. More specifically, urethane foam having a hardness of 70 ± 5 ° (measurement method is ASKAER F) is used for the supply rollers 55Y to 55C, and a sponge material or a resin coating harder than the urethane foam is used for the supply roller 55BK. Apply.

  (4) Compared with the first to fourth embodiments, the developer image order of the developing units 51 of yellow, magenta, cyan, and black, that is, the arrangement order in the transport direction of the paper P may be changed. However, considering the influence of the mixed color fogging, it is desirable to set the fourth developing unit to black development as described above.

  (5) In the above first to fourth embodiments, four color development of yellow, magenta, cyan, and black is given as an example. However, the present invention is not limited to this, and seven-color development that adds three colors of red, green, and blue is used. May be. Furthermore, the present invention can be applied to, for example, two-color development with red toner and black toner and six-color development.

  (6) In the above embodiment, the supply roller 55 that also serves to supply the toner to the developing roller 52 is used as the collecting means. However, the invention is not limited to this, and other rotating members or moving members that contact the developing roller 52 may be used. Also good.

  (7) In the first to fourth embodiments, the simultaneous development cleaning method is used. However, the present invention is not limited to this, and a cleaning mechanism that separately collects waste toner may be provided around the photosensitive drum 3. In such a case, the present invention is useful when the waste toner cannot be sufficiently collected due to, for example, deterioration of the operation of the cleaning mechanism.

1 is a side sectional view showing a schematic configuration of a color laser printer according to Embodiment 1 of the present invention. Schematic diagram showing the configuration near the photosensitive drum Explanatory diagram for explaining the cause of reverse charging Explanatory diagram for explaining developer image formation order and ease of reverse transfer Schematic diagram for explaining the nip width in the second embodiment Schematic diagram for explaining application of a bias voltage in the third embodiment Side sectional view showing a schematic configuration of a color laser printer according to a fourth embodiment.

Explanation of symbols

1. Color laser printer (image forming device)
3 (3Y, 3M, 3C, 3BK) ... photosensitive drum (image carrier)
11. Bias supply unit (development bias application means, supply bias application means)
51 (51Y, 51M, 51C, 51BK) ... developing unit 52 (52Y, 52M, 52C, 52BK) ... developing roller (developer carrier)
53, 53 '... Toner hopper (developer storage chamber)
55 (55Y, 55M, 55C, 55BK) ... supply roller (collecting means, rotating body, contact body)
56 (56Y, 56M, 56C, 56BK), 56BK '... (stirring means, rotary stirring member)
N: Nip width (contact width)
P ... paper (transfer material)

Claims (19)

An image carrier on which an electrostatic latent image is formed;
A developer carrying member that is provided corresponding to each of the different colors and carries a developer of a color corresponding to the self; and the electrostatic latent image on the surface of the image carrier is transferred by the developer carrying member; A plurality of development units configured to develop with a color developer,
In the image forming apparatus capable of sequentially forming a developer image on the image carrier by developing an electrostatic latent image by each developing unit and transferring the developer image to a transfer material to form a multicolor image. ,
Each of the development units includes a recovery unit that recovers the developer adhering to each developer carrier by contact with the developer carrier after development on the image carrier.
The collecting ability of each of the collecting means is higher at least in the developing unit with the last developer image forming order than the developing unit with the first developer image forming order, and each developing unit is more than the developer. An image forming apparatus, wherein the image forming order is equal to or higher than the recovery capability of the preceding developing unit. 2. The collecting ability of each of the collecting means is higher in a developing unit having a developer image forming order second and higher than that of a developing unit having a developer image forming order first. The image forming apparatus described. 2. The image according to claim 1, wherein the collection capacity of each of the collection units is higher in a development unit having the last developer image formation order than development units other than the last development unit. Forming equipment. 2. The image forming apparatus according to claim 1, wherein the collecting ability of each of the collecting means is higher in a developing unit having a developer image formation order of the third and subsequent ranks than in a developing unit having the second or earlier position. apparatus. Each of the recovery means has a rotating body that recovers the developer adhering to the developer carrier by rotating while being in contact with the developer carrier, and the peripheral speed of the rotor is 5. The image forming apparatus according to claim 1, wherein a developing unit whose recovery capability is to be increased is faster. The rotating body is a supply roller for rotating while being in contact with the developer carrier and supplying the developer in a developer storage chamber of the development unit to the developer carrier. Item 6. The image forming apparatus according to Item 5. Each of the recovery means is a contact body that recovers the developer adhering to the developer carrier by moving relatively while contacting the developer carrier, and the hardness of the contact body 5. The image forming apparatus according to claim 1, wherein a developing unit whose recovery capability should be increased is higher. Each of the recovery means is a contact body that recovers the developer attached on the developer carrier by moving relatively while contacting the developer carrier, and the contact body and the 5. The contact width in the moving direction of the contact body with the developer carrying member is wider for a developing unit whose recovery capability should be increased. The image forming apparatus described. The contact body is a supply roller for rotating while being in contact with the developer carrying body and for supplying the developer in the developer containing chamber of the developing unit to the developer carrying body. The image forming apparatus according to claim 7 or 8. Each of the recovery means rotates while contacting the developer carrier, and supplies the developer in the developer storage chamber of the development unit to the developer carrier, while on the developer carrier. A supply roller for collecting the adhered developer,
Developing bias applying means for applying a developing bias voltage to each developer carrier;
Supply bias applying means for applying a supply bias voltage to each supply roller is provided,
The image forming apparatus according to claim 1, wherein a recovery capability of each developing unit is determined based on the supply bias voltage with respect to the developing bias voltage. An image carrier on which an electrostatic latent image is formed;
A developer carrying member that is provided corresponding to each of the different colors and carries a developer of a color corresponding to the self; and the electrostatic latent image on the surface of the image carrier is transferred by the developer carrying member; A plurality of development units configured to develop with a color developer,
In the image forming apparatus capable of sequentially forming a developer image on the image carrier by developing an electrostatic latent image by each developing unit and transferring the developer image to a transfer material to form a multicolor image. ,
Each developing unit is provided with a stirring means for stirring the developer in a developer storage chamber for storing the developer.
The agitating ability of each of the agitating means is higher at least in the developing unit with the last developer image forming order than the developing unit with the first developer image forming order, and each developing unit is more developer than self. An image forming apparatus, wherein the image forming order is equal to or higher than the stirring ability of the preceding developing unit. 12. The agitating ability of each of the agitating means is higher in a developing unit having a second developer image formation order than in a developing unit having a first developer image forming order. The image forming apparatus described. 12. The image according to claim 11, wherein the stirring ability of each of the stirring means is higher in the developing unit having the last developer image formation order than the developing units other than the last developing unit. Forming equipment. 12. The image forming apparatus according to claim 11, wherein the agitating ability of each of the agitating units is higher in a developing unit having a developer image forming order of the third and subsequent ranks than in a developing unit having the second and earlier. apparatus. Each of the stirring means includes a rotating stirring member that rotates in the developer accommodating chamber,
The image forming apparatus according to claim 11, wherein the rotation speed of the rotary stirring member is higher for a developing unit whose stirring ability is to be increased. Each of the stirring means includes a rotating stirring member that rotates in the developer accommodating chamber,
The image forming apparatus according to claim 11, wherein a size of the rotating stirring member is larger as a developing unit whose stirring ability is to be increased. An image carrier on which an electrostatic latent image is formed;
A developer carrying member that is provided corresponding to each of the different colors and carries a developer of a color corresponding to the self; and the electrostatic latent image on the surface of the image carrier is transferred by the developer carrying member; A plurality of development units configured to develop with a color developer,
In the image forming apparatus capable of sequentially forming a developer image on the image carrier by developing an electrostatic latent image by each developing unit and transferring the developer image to a transfer material to form a multicolor image. ,
The recovery means according to any one of claims 1 to 10,
An image forming apparatus comprising: the stirring unit according to any one of claims 11 to 16. The developing unit having the last developer image formation order is configured such that the developer carrying member carries a black developer and develops an electrostatic latent image with the black developer. The image forming apparatus according to claim 1. The development unit having the last developer image formation order is configured such that the developer carrier carries a black developer, and the electrostatic latent image is developed with the black developer,
The image forming apparatus according to claim 11, wherein the capacity of the developer storage chamber of the last developing unit is larger than that of the other developing units.

Images