JPH11231663A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an image quality by correcting a defective contact of an image carrier with an intermediate transfer body. SOLUTION: A transfer nipping part is provided with a means 40 to press the back side of an intermediate transfer belt 32 as an intermediate transfer body onto a photoreceptor drum 8. The means 40 is constituted of a holding member 66 fixed on the device main body and of a conductive brush body 64 struck to the holding member 66, and both end parts in the axial direction of the holding member 66 are projecting in the direction of the image carrier further than the middle part, and the brush body 64 has a higher pressure on the image carrier at the both end parts in the axial direction than in the middle part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color copying machine or a color printer utilizing an electrostatic transfer process.

[0002]

2. Description of the Related Art In this type of image forming apparatus, an electrostatic latent image is formed on an image carrier, developed and visualized, and the visualized toner image is transferred to an intermediate transfer belt or the like. The toner image is transferred electrostatically to the body, and the toner image transferred to the intermediate transfer member is further electrostatically transferred to a transfer material. That is, the electrostatic transfer of the toner image is performed twice from the image carrier to the intermediate transfer member and from the intermediate transfer member to the transfer material. As an image forming apparatus using an intermediate transfer member,
For example, Japanese Patent Application Laid-Open No. 64-92771 and Japanese Patent Application Laid-Open
The thing described in 273080 is known. As shown in FIGS. 6 and 7, a device using an intermediate transfer belt is known which is provided with a belt detent for preventing the belt from shifting. In FIG.
Reference numeral 0 denotes a photosensitive member, 102 denotes an intermediate transfer belt, 104 denotes a bias application roller, 106 denotes an earth roller also serving as a tension roller, and 108 denotes a belt stopper. Belt stoppers 108 are attached to both ends of the intermediate transfer belt 102 over the entire belt. As shown in FIG. 7, the belt stoppers 108 are engaged with the end side surfaces of the respective rollers, thereby displacing the belt in the width direction. Is prevented.

[0003]

In an image forming apparatus using an intermediate transfer member, the state of close contact between the image carrier and the intermediate transfer member greatly affects the transfer accuracy of the toner image. If the adhesion between the image carrier and the intermediate transfer belt is poor, that is, if a certain portion cannot be contacted, the toner image on the image carrier is not transferred to the intermediate transfer member, and that portion is eventually A so-called “white spot” often occurs on the transfer paper. Further, since a minute gap is generated between the image carrier and the intermediate transfer member, abnormal discharge occurs, and various abnormal images are often generated particularly in a portion where the toner density is low. When a relatively low-resistance material is used as the intermediate transfer member, poor electrical contact is unlikely to occur because of the strong electrical adhesion between the image carrier and the intermediate transfer member, but when a high-resistance material is used. In this case, the electrical adhesion is weakened, and the above problem is likely to occur.

However, when a low-resistance material is used, scattering of a toner image is likely to occur at a transfer portion. Therefore, it is desirable to use a high-resistance material in order to achieve high image quality. Therefore, in order to obtain high image quality, measures are required to use a high-resistance material as the intermediate transfer member and to ensure a close contact between the image carrier and the intermediate transfer member. Conventionally, measures to secure the close contact state include increasing the contact area between the image carrier and the intermediate transfer body and increasing the tension of the intermediate transfer body. The initial state could not be maintained due to aging, scratches, shrinkage, curling, and the like of the transfer member or the intermediate transfer member. In particular, there was a situation where the above-mentioned white spots were likely to occur at the end of the image carrier in the axial direction.

[0005] In particular, in the case of using the intermediate transfer belt 102 having the belt deviation stopper 108 shown in FIGS. 6 and 7, white spots are particularly likely to occur at the ends. The state shape of the intermediate transfer belt 102 shown in FIG. 7 is an ideal shape. In actuality, the portion to which the belt stopper 108 is adhered is restrained by the adhesion and follows the shape of the belt stopper 108, so that the amount of shrinkage is Is less, but the belt stop 108
Since the part without the mark has a large amount of shrinkage, the earth roller 10
When it is located at position 6, the shape as shown in FIG. When the belt enters the transfer nip portion between the photoconductor 100 and the intermediate transfer belt 102 in a belt-shaped state as shown in FIG. 8, a minute gap 110 is generated between the photoconductor 100 at both ends. Become. In the above description, it is assumed that the intermediate transfer belt 102 is formed of a material that contracts due to heat or the like over time, but it has been confirmed that a similar problem occurs when the intermediate transfer belt 102 is formed of a material that expands.

Accordingly, the present invention can maintain a good contact state between the image carrier and the intermediate transfer member for a long period of time regardless of having a transfer belt having a belt detent, thereby achieving high image quality. An object of the present invention is to provide an image forming apparatus.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an image bearing member and an intermediate transfer member by correcting an inevitable change of the intermediate transfer member with time while correcting the change. To prevent the deterioration of the close contact state. Specifically, in the invention according to claim 1, an image forming apparatus that transfers a toner image formed on an image carrier to an intermediate transfer member, and further transfers the toner image transferred to the intermediate transfer member to a transfer material. And a pressing means for pressing the intermediate transfer body from the back surface thereof toward the image carrier at a transfer nip portion between the image carrier and the intermediate transfer body.

According to a second aspect of the present invention, in the first aspect, the pressing force of the pressing means is larger at both ends in the axial direction of the image carrier than at the center. .

According to a third aspect of the present invention, in the configuration of the first aspect, the pressing means has a brush body.
The configuration is adopted.

According to a fourth aspect of the present invention, in the configuration according to the third aspect, both end portions of the brush body in the axial direction of the image carrier protrude from the central portion toward the image carrier. The configuration is such that the pressing force at both ends is greater than that at the center.

According to a fifth aspect of the present invention, in the configuration of the third aspect, the brush body is provided on a holding member that is long along the axial direction of the image carrier with its tips aligned. That is, both ends in the axial direction of the holding member protrude more toward the image carrier than the center, and the pressing force of both ends of the brush body in the axial direction of the image carrier is larger than the center. It has a configuration.

According to a sixth aspect of the present invention, in the configuration of the third, fourth or fifth aspect, the density of both ends of the brush body in the axial direction of the image carrier is larger than that of the central part, Is larger than the central part.

According to the invention described in claim 7, according to claim 3,
The structure described in 4, 5, or 6, wherein the brush body is formed of a conductive material.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, an outline of a color printer 2 as an image forming apparatus according to the present embodiment will be described with reference to FIG. The writing optical unit 4 of the color printer 2 converts the color image data from the color scanner 6 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 8. The writing optical unit 4 includes a laser light emitting unit 10 and its light emission drive control unit (not shown), a polygon mirror 12 and its rotation motor 14, an f / θ lens 1
6 and a reflection mirror 18. The photoreceptor drum 8 rotates counterclockwise as shown by the arrow, and around the photoreceptor cleaning unit 20, the static elimination lamp 2
2, a charger 24, a potential sensor 26, a revolver developing device 28, a development density pattern detector 30, an intermediate transfer belt 32 as an intermediate transfer member, and the like are arranged.

The revolver developing device 28 includes a Bk (black) developing device 28K, a C (cyan) developing device 28C, an M (magenta) developing device 28M, and a Y (ero) developing device 28Y.
A revolver rotation drive (not shown) for rotating each of these developing units in a counterclockwise direction as shown by an arrow is provided. Each developing device is provided with a developing sleeve 28 that rotates by bringing an ear of developer into contact with the surface of the photosensitive drum 8 to develop an electrostatic latent image.
KS, 28CS, 28MS, and 28YS, and a developing paddle that rotates to pump and agitate the developer. In the standby state, the revolver developing device 28 is set at a position where the black developing device 28K faces the photosensitive drum 8, and when the copying operation is started, the reading of the Bk image data is started from the color scanner 6 at a predetermined timing. Then, optical writing / latent image formation by laser light is started based on the image data (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk latent image. The same applies to C, M, and Y). In order to enable development from the front end of the Bk latent image, before the front end of the latent image reaches the development position of the Bk developing device 28K, the rotation of the developing sleeve 28KS is started to develop the Bk latent image with Bk toner. I do. And after that, B
The developing operation of the k latent image area is continued, but when the rear end portion of the latent image passes the position of the Bk developing device 28K, the revolver developing device 28 is quickly moved from the position of the Bk developing device 28K to the position of the next color developing device. Rotate. This is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, first, the photosensitive drum 8 is rotated counterclockwise as shown by an arrow, and the intermediate transfer belt 32 is rotated clockwise by a drive motor (not shown). As the intermediate transfer belt 32 rotates, Bk toner image formation, C image formation, M image formation, and Y image formation are performed, and finally a toner image is formed on the intermediate transfer belt 32 in the order of BkCMY. First, the formation of a Bk image is performed as follows. The charger 24 uniformly charges the photosensitive drum 8 with a negative charge to about -700 V by corona discharge. Subsequently, the laser emitting unit 10 performs raster exposure based on the Bk signal. When the raster exposure is performed in this manner, in the exposed portion of the photosensitive drum 8 that is initially uniformly charged, the charge proportional to the exposure light amount disappears, and an electrostatic latent image is formed.
The toner in the revolver developing device 28 is negatively charged by stirring with the ferrite carrier, and the developing sleeve 28KS of the revolver developing device 28
The negative direct current potential and the alternating current are biased by a power source (not shown) to the metal base layer. As a result, the toner does not adhere to the portion of the photosensitive drum 8 where the charge remains, and the Bk toner is adsorbed to the portion having no charge, that is, the exposed portion.
A k-visible image will be formed.

The intermediate transfer belt 32 is stretched around a bias roller 34 also serving as a driving roller, a transfer opposing roller 36, a cleaning opposing roller 38 serving as an earth roller, and a driven roller group, and is driven and controlled by a driving motor (not shown). . From the photosensitive drum 8 to the intermediate transfer belt 32
In the transfer nip portion where the toner image is transferred to the photosensitive drum 8, a pressing unit 40 is provided for pressing the back surface of the intermediate transfer belt 32 toward the photosensitive drum 8.

The Bk toner image formed on the photosensitive drum 8 is applied to the surface of the intermediate transfer belt 32 moving at a constant speed in contact with the photosensitive drum 8 by applying a bias of opposite polarity to the toner to the bias roller 34. It is transferred by applying. Hereinafter, the transfer of the toner image from the photosensitive drum 8 to the intermediate transfer belt 32 is referred to as belt transfer. Photoconductor drum 8
The slightly untransferred residual toner on the upper side is cleaned by the photoconductor cleaning unit 20 in preparation for reuse of the photoconductor drum 8. The collected toner is stored in a waste toner tank (not shown) via a collection pipe (not shown).
The Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 8 are sequentially aligned on the same surface on the intermediate transfer belt 32 to form a four-color superimposed belt transfer image. Batch transfer is performed on transfer paper as a material by a bias roller 34.

On the photosensitive drum 8 side, the process proceeds to the process C after the process Bk. At a predetermined timing, the reading of the C image data by the color scanner 6 is started. Perform formation. With respect to the developing position of the C developing device 28C, the rotating operation of the revolver developing device 28 is performed after the trailing end of the previous Bk latent image has passed and before the leading end of the C latent image has arrived. The C latent image is developed with C toner. Thereafter, development of the C latent image area is continued, but when the rear end of the latent image has passed, the B
As in the case of the k developing device 28K, the revolver developing device 28
Is performed. This is also completed before the leading end of the next M latent image arrives. Note that the operations of reading and latent image formation and development of the respective image data are the same as those of the above-described steps Bk and C in the steps M and Y, and a description thereof is omitted.

A belt cleaning device 42 is provided at a position facing the cleaning facing roller 38. The belt cleaning device 42 includes an inlet seal (not shown),
It is composed of a rubber blade, a discharge coil, an inlet seal, a rubber blade contacting / separating mechanism, and the like. The second, third, and fourth colors after the belt transfer of the first color Bk image are transferred to the inlet while the belt is transferred. The seal and the rubber blade are separated from the belt surface by the contact / separation mechanism. A paper feed bank is formed below the color printer 2, and transfer paper cassettes 44A, 44B and 44C storing transfer papers of different sizes.
Is provided. From the transfer paper cassette in which the transfer paper of the designated size is stored, the corresponding paper feed rollers 46A,
The paper is fed and conveyed in the direction of the registration rollers by 6B and 46C. Reference numeral 48 denotes a manual paper feed tray for OHP paper or thick paper.

At the time when the image formation is started, the transfer paper is fed from one of the above-mentioned transfer paper cassettes and is waiting at the nip portion of the registration roller pair 50. Transfer facing roller 3
6, a paper transfer device 52 for transferring the image onto the transfer paper from the intermediate transfer belt 32 is provided. When the leading end of the toner image on the intermediate transfer belt 32 approaches the paper transfer unit 52, the registration roller pair 50 is driven so that the leading end of the transfer paper coincides with the leading end of the image, and registration of the transfer paper and the image is performed. Will be In this way, the transfer paper passes over the paper transfer unit 52 which is superimposed on the image on the intermediate transfer belt 32 and connected to a positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper is passed by an unillustrated AC + DC corona separating static eliminator disposed on the left side of the paper transfer unit 52, the transfer paper is discharged, separated from the intermediate transfer belt 32 and moved to the transport belt 54. The transfer paper on which the four-color superimposed toner image is collectively transferred from the intermediate transfer belt 32 is conveyed to a fixing device 56 by a conveyance belt 54, and a fixing roller 58 controlled to a predetermined temperature and a pressure roller 6
The toner image is melted and fixed in the nip portion of 0, and sent out of the apparatus main body by the discharge roll pair 62. Thereafter, the sheets are stacked face up on a tray (not shown) to obtain a full-color copy.

The surface of the photosensitive drum 8 after the belt transfer is cleaned by a photosensitive member cleaning unit 20 composed of a brush roller, a rubber blade, or the like, and is uniformly discharged by a discharge lamp 22. Further, the intermediate transfer belt 32 after the transfer of the toner image onto the transfer paper is transferred to the belt cleaning device 42 whose blade is pressed by the contact / separation mechanism.
To clean the surface. At the time of the repeat copy, the operation of the color scanner 6 and the image formation on the photosensitive drum 8 proceed to the second color image process at a predetermined timing after the first color image process. In the intermediate transfer belt 32, following the batch transfer step of the first four-color superimposed image onto the transfer paper, the surface of the second transfer belt 32 is cleaned by the belt cleaning device 42.
The k toner image is transferred to the belt. Then 1
The operation is the same as that of the first sheet. The above is a description of the mode for obtaining a four-color full-color copy.
In the case of the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. In the case of the single-color copy mode, only the developing device of the predetermined color of the revolver developing device 28 is in the developing operation state until the predetermined number of sheets is completed, and the blade of the belt cleaning device 42 is pressed against the belt. The copy operation is performed continuously.

FIG. 2 is an enlarged view of a main part of the transfer nip portion. As shown in FIG. 3, the pressing means 40 includes a brush body 64 that contacts the back surface of the intermediate transfer belt 32, and a holding member 66 that holds the brush body 64. The holding member 66 is a photosensitive drum. 8 has a long shape along the axial direction. The holding member 66 is attached to the apparatus main body member (not shown) so as to be able to adjust the proximity to the photosensitive drum 8 side. When the pressing force is reduced due to wear of the brush body 64, the holding member 66 is loosened and moved. The reduction in the pressing action can be repaired. As shown in FIG. 3, also in this embodiment, belt stoppers 68 are attached to both ends of the intermediate transfer belt 32. Brush body 6
The length of the photosensitive drum 8 is uniform throughout the axial direction of the photosensitive drum 8, but its number density is larger at both ends than at the center. The brush body 6 is provided at both ends 64a and 64b.
Because of the high density of 4, the rigidity or stiffness at both ends is increased, and the pressing force is greater than at the center. Therefore, even if a minute gap is generated due to factors such as shrinkage of the intermediate transfer belt 32, the intermediate transfer belt 32 is brought into close contact with the photosensitive drum 8 by the pressing force of the brush body 64. Further, the pressing force of the brush body 64 damages the intermediate transfer belt 32,
Even when shrinkage, curl, or the like occurs, poor adhesion due to unevenness due to this is corrected.

In this embodiment, as the material of the intermediate transfer belt 32, a material having a high volume resistivity of about 10 11 Ωcm or more is used. In the case of a high-resistance material, the adhesion force between the photosensitive drum 8 and the intermediate transfer belt 32 is small, so that poor adhesion due to the irregularities easily occurs. However, a favorable adhesion state is always obtained by the pressing force of the brush body 64. . Accordingly, high image quality can be obtained in combination with the use of a high-resistance material for the intermediate transfer belt 32. Further, the brush body 64 in this embodiment is formed of a conductive material and is grounded. When the brush body 64 is an insulator,
This is because there is a problem that charges are accumulated in the brush body 64 and abnormal discharge is likely to occur during transfer. The volume resistance of the brush body 64 is desirably 10 ⁹ Ωcm or less.

FIG. 4 shows a modification of the pressing means 40. The pressing means 70 according to the present embodiment includes a conductive brush body 72 and a holding member 66 for holding the conductive brush body 72. The holding member 66 has a long shape along the axial direction of the photosensitive drum 8. ing. In the brush body 72, both end portions 72 a and 72 b in the axial direction of the photoconductor drum 8 protrude toward the photoconductor drum 8 from the center portion, so that the brush body 72 is intermediate between the both end portions 72 a and 72 b. The contact deformation with respect to the transfer belt 32 is large, and the pressing force becomes larger than that of the central portion due to the magnitude of the elastic force. The adhesion improving action based on this is the same as in the above embodiment.
In the present embodiment, the brush density of both end portions 72a and 72b may be higher than that of the central portion.

FIG. 5 shows another modification of the pressing means 40. The pressing means 74 in this embodiment includes a conductive brush body 76 and a holding member 78 for holding the conductive brush body. The holding member 78 has a long shape along the axial direction of the photosensitive drum 8. ing. The holding member 78 is formed such that both end portions 78a and 78b protrude from the central portion toward the photosensitive drum 8, and the tip of the brush body 76 is aligned over the entire axial direction of the photosensitive drum 8. I have. Since the length of the brush is short at both ends of the holding member 78, rigidity or stiffness is obtained, and the pressing force is larger than that at the center. The adhesion improving action based on this is the same as in the above embodiment. In the present embodiment,
The brush density of the brush body 76 at both ends 78a and 78b may be higher than that at the center.

In the present invention, the brush bodies 64, 72,
Since the alignment accuracy of the tip position of the key 76 is an important factor of the pressing force, a method of obtaining the accuracy of the tip position is, for example, to attach the brush body 64 to the holding member 66 and then apply the brush body 6
The method of cutting the tip of 4 is good. In this case, in the case of the shape shown in FIG.
After sticking the brush body 64 having a low density at the center, the tip must be cut, which increases the number of processing steps and increases the cost. In the shape shown in FIG. 4, the length of the brush body 72 is different between the end portion and the center portion, so that the brush bodies 72 having different lengths must be attached, which is troublesome. On the other hand, in the example shown in FIG. 5, since the shape of the holding member 78 is changed, the brush body 76 having the same density may be attached to the holding member 78, and then the tip of the brush may be cut off. A shape in which the pressing force of the end portion is larger than that of the portion can be easily obtained with high precision.

In the above-described embodiment, a brush body is exemplified as a specific example of the pressing means, but a roller body may be used. In this case, if the end of the roller is formed to have a slightly raised shape, even when a minute gap is generated at both ends, such as in the case of an intermediate transfer belt having a belt detent, this can be corrected. In this case, the roller body may be formed of an elastic material such as sponge or rubber, and the diameter of the roller is fixed, and the elastic force or hardness of only the end is increased to increase the pressing force at the end. It is good also as a structure which performs. Further, the pressing means may be configured to have a blade having a width extending in the axial direction of the image carrier. Also in this case, if the both ends are slightly raised, even if a minute gap is generated at both ends as in the case of an intermediate transfer belt having a belt detent, this can be corrected. Further, in the above-described embodiment, the intermediate transfer belt is exemplified as the intermediate transfer body. However, even when a cylindrical intermediate transfer roller is used, similar to the above-described embodiment, a good contact state can be obtained by the pressing unit, Higher image quality can be achieved.

[0030]

According to the first aspect of the present invention, since the pressing means for pressing the intermediate transfer body toward the image carrier is provided, the image carrier or the intermediate transfer body can be settled with time. Even if scratches, shrinkage, curl, and the like occur, poor adhesion between the image carrier and the intermediate transfer member can be improved, thereby preventing occurrence of abnormal images such as white spots. In addition, since a high-resistance material can be used for the intermediate transfer member, high image quality can be achieved.

According to the second aspect of the present invention, the pressing force of the pressing means is set to be greater at both ends in the axial direction of the image carrier than at the center thereof. A minute gap at both ends which occurs in the case of the intermediate transfer belt having the deviation prevention can also be corrected, and occurrence of an abnormal image can be prevented.

According to the third aspect of the present invention, since the pressing means has a brush body, in addition to the effect of the first aspect, the intermediate transfer body is pressed against the image carrier with a simple configuration. be able to.

According to the fourth aspect of the present invention, both end portions of the brush body project toward the image carrier from the center portion, and
Since the pressing force at both ends is larger than that at the center,
In addition to the effect of the third aspect, a minute gap at both ends which occurs in the case of an intermediate transfer belt having a belt deviation stopper can be corrected, and occurrence of an abnormal image can be prevented.

According to the fifth aspect of the present invention, both ends in the axial direction of the holding member protrude more toward the image carrier than the central portion, and thereby the pressing force at both ends of the brush body is more than that of the central portion. Since the configuration is made large, in addition to the effect of the third aspect, a minute gap at both ends which occurs in the case of the intermediate transfer belt having the belt deviation stopper can be corrected, and occurrence of an abnormal image can be prevented. Further, the pressing force at both ends can be increased with a simpler and cheaper configuration.

According to the sixth aspect of the present invention, the brush body has a configuration in which the density of both ends in the axial direction of the image carrier is higher than that of the central portion, and the pressing force of both ends is higher than that of the central portion. In addition to the effects of the third aspect, it is possible to correct a minute gap at both ends which occurs in the case of an intermediate transfer belt having a belt deviation stopper, thereby preventing occurrence of an abnormal image. Further, in addition to the effects of the fourth and fifth aspects, the pressing force at both ends of the brush body can be easily increased.

According to the seventh aspect of the present invention, since the brush body is formed of a conductive material, in addition to the effects of the third, fourth, fifth, or sixth aspect, electric charges accumulate in the brush body. Can prevent occurrence of an abnormal image.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged side view of a main part of a transfer nip portion.

FIG. 3 is a cross-sectional view illustrating a pressed state of a transfer nip portion by a pressing unit.

FIG. 4 is a front view of a pressing unit according to another embodiment.

FIG. 5 is a front view of a pressing unit in another embodiment.

FIG. 6 is an enlarged side view of a main part of a transfer nip portion in a conventional example.

FIG. 7 is a sectional view of an ideal shape of an intermediate transfer belt in a conventional example.

FIG. 8 is a cross-sectional view of a main part when a contraction occurs in an intermediate transfer belt in a conventional example.

FIG. 9 is a cross-sectional view illustrating a relationship between the intermediate transfer belt and the image carrier when the intermediate transfer belt shrinks in the conventional example.

[Explanation of symbols]

 8 Photoconductor drum 32 as image carrier 32 Intermediate transfer belt 40, 70, 74 Pressing means 64, 72, 76 Brush body 66, 78 Holding member

Claims (7)

[Claims] An image forming apparatus for transferring a toner image formed on an image carrier to an intermediate transfer member and further transferring the toner image transferred to the intermediate transfer member to a transfer material. An image forming apparatus, further comprising a pressing unit that presses the intermediate transfer member from the back surface thereof toward the image carrier in a transfer nip portion between the transfer member and the transfer member. 2. The image forming apparatus according to claim 1, wherein the pressing force of the pressing means is larger at both ends in the axial direction of the image carrier than at the center. 3. An image forming apparatus according to claim 1, wherein said pressing means has a brush. 4. The image forming apparatus according to claim 3, wherein both ends of the brush body in the axial direction of the image carrier protrude from the center toward the image carrier, and the pressing force of the both ends is reduced. An image forming apparatus characterized by being larger than a central part. 5. The image forming apparatus according to claim 3, wherein the brush is provided on a holding member that is long along the axial direction of the image carrier, with its tips aligned.
Both ends in the axial direction of the holding member protrude more toward the image carrier than the central portion, and the pressing force of both ends of the brush body in the axial direction of the image carrier is larger than the central portion. Image forming apparatus. 6. The image forming apparatus according to claim 3, wherein the density of both ends of the brush body in the axial direction of the image carrier is larger than that of the central part, and the pressing force of both ends is central part. An image forming apparatus characterized by being larger than the above. 7. An image forming apparatus according to claim 3, wherein said brush body is formed of a conductive material.