JPH1010876A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of forming an image with an excellent picture being free from the occurrence of irregularity on the image by preventing wilds and the color irregularity of the image on a high light part on an intermediate transfer body derived from the transfer of the unfixed toner image on a latent image carrier such as a photoreceptor being performed out of a nip area of a primary transfer. SOLUTION: This device, provided with an intermediate transfer belt 2 extended around while supported from inside by two or more shafts of supporting rolls 18 including at least a driving roll 17 on one side and held in touch with the latent image carrier 1 with a specified nipping width at least on a primary transferring position, and primary transferring means 9 disposed on the primary transferring position P opposite to the latent image carrier 1 across the intermediate transfer belt 2, makes nip angles of the latent image carrier 1 corresponding to the intermediate transfer belt 2 different namely, the angle α on the upstream side of the primary transfer position P and the angle β on the downstream side different. In the case the primary transferring means 9 is composed of corotron, a range of two nip angles of the intermediate transfer belt 2 corresponding to the latent image carrier 1 is severally made the range of angle (9 deg. to 11 deg.) for the larger angle αon the upstream side of the primary transferring means 9, the range of angle (4 deg. to 6 deg.) for the smaller angle on the downstream side.

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 an electrophotographic copying machine or a laser printer, and more particularly to an unfixed image formed on a latent image carrier such as a photosensitive drum via an intermediate transfer member. The present invention relates to an image forming apparatus that transfers a toner image to a recording medium such as a sheet.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus for transferring an unfixed toner image on a latent image carrier to a recording medium via an intermediate transfer member is disclosed in JP-A-5-323800 and JP-A-4-204.
780, JP-A-3-44681, and the like. An outline of an image forming apparatus using an intermediate will be described with reference to FIG. The image forming apparatus converts the unfixed toner image T formed on the latent image carrier 100 such as the photoconductor drum, by using the electrostatic force of the transfer electric field formed in the primary transfer unit by the discharge of the primary transfer device 107. Belt-shaped intermediate transfer body 10
First transfer to 1 After that, the unfixed toner image T on the intermediate transfer body 101 is secondarily transferred to the recording medium 102 to form a desired image on the recording medium 102.

In particular, as shown in the drawing, a color image forming apparatus for forming a full-color image is provided with developing devices 103 to 106 corresponding to black (Bk), yellow (Y), magenta (M) and cyan (C). In the above, based on the position signal of the intermediate transfer member detected by the position detection device 109 provided at an appropriate position with respect to the intermediate transfer member, the exposure timing by the image exposure means 200 performed on the latent image carrier 100 Control. Then, the electrostatic latent image formed on the latent image carrier 100 is developed by the developing units 103 to 106, and the final fixed toner image of each color is sequentially primary-transferred onto the intermediate transfer body 101 in order, and the unfixed toner image of each color is formed. A composite image is formed by overlapping the toner images. The composite image on the intermediate transfer body 101 after the primary transfer is transferred to the recording medium 102 at a time. Here, the residual toner on the latent image carrier 100 after the primary transfer is cleaned by the latent image carrier cleaning device 111 before the next cycle.

In a conventional color image forming apparatus which does not use an intermediate body, a recording medium such as paper conveyed by conveying means such as a conveying belt is formed in advance on a latent image carrier such as a photosensitive drum. Since the composite image of the final fixed toner image of each color is directly transferred by multiple transfer, it may be formed on the recording medium due to factors such as the thickness and surface characteristics of the recording medium or the transport characteristics of the recording medium with respect to the latent image carrier. The quality of the color image is affected. However, in the color image forming apparatus using the intermediate transfer body, since the composite image multi-transferred onto the intermediate transfer body has already been transferred to the recording medium, an unstable factor in image formation is eliminated. This has the advantage that image disturbance and color unevenness during multiple transfer can be effectively prevented.

[0005] In the conventional image forming apparatus configured as described above, the intermediate transfer member 1 is moved from the latent image carrier 100 to the intermediate transfer member 1.
01 or from the intermediate transfer member 101 to the recording medium 102
The transfer of the unfixed toner image T to the toner image is performed by an electrostatic transfer method. That is, by applying a voltage having a polarity opposite to that of the toner to the corona discharger 107 or the bias roll 108 disposed on the back side of the transfer target body at each transfer position, the unfixed toner image T is transferred to the latent image carrier 100. From the intermediate transfer member 101 to the recording medium 102 at the secondary transfer position.

[0006]

However, in a conventional image forming apparatus using an intermediate transfer member, a final fixed toner image formed on a latent image carrier such as a photoreceptor is transferred onto the intermediate transfer member by a primary transfer device. However, the following problems occur when the image is transferred to the image. At the primary transfer position, the primary transfer device 107
Is wider than the nip width formed at the contact position between the latent image carrier 100 and the intermediate transfer body 101, the transfer electric field extends to outside the nip width, and particularly outside the nip width, particularly upstream. On the side, a transfer electric field acts on the final fixed toner image T formed on the latent image carrier 100. As a result, the final fixed toner image T on the latent image carrier 100 is gap-transferred onto the intermediate transfer member 101 at a small upstream gap that enters the nip region between the intermediate transfer member 101 and the latent image carrier 100. As a result, an image quality defect such as a disturbance of an image, particularly, a rough image of a highlight portion occurs.

Particularly, in a color image forming apparatus which forms a full-color image by superimposing each color on the intermediate transfer member 101, if gap transfer occurs upstream of the nip area for each color, the composite color However, there is a problem that the graininess of the highlight portion deteriorates, and the image of the highlight portion becomes fatal inferior image quality such as not only image roughness but also color unevenness. Also, in an image forming apparatus that conveys paper or the like with a conveyance belt or a transfer film and directly transfers the final fixed toner image on the latent image carrier to a recording medium, the rigidity of the conveyance belt and the transfer film in the pulling direction is low. In addition, because of high elasticity, the adhesion to the latent image carrier in the primary transfer portion is high,
Many nip areas could be formed between the latent image carrier and the recording medium in the primary transfer section. Then, the transfer electric field falls within the nip width formed by the primary transfer portion,
Gap transfer occurring on the upstream side of the primary transfer portion could be prevented.

On the other hand, the intermediate transfer member needs to have a high rigidity in the pulling direction due to the problem of color misregistration of the image and the like. The degree of adhesion of the intermediate transfer member to the image carrier is lower than that of an image forming apparatus using a transfer belt, a transfer film, or the like, which uses a method of directly transferring the image onto a recording medium such as paper.

Means for preventing roughening of an image in a highlight portion caused by a transfer electric field generated in a primary transfer portion in an image forming apparatus using a transport belt being outside a nip width formed in the primary transfer portion Japanese Patent Application Laid-Open No. Hei 5-3238
No. 00, JP-A-4-204780 and the like. The disclosed image forming apparatus will be described (see FIG. 6). At the primary transfer position, a pressing roll 123 is disposed on the back side of the transport belt 121 on the upstream side of the primary transfer device 107 where a transfer electric field is formed.
The pressing roll 123 presses from the rear surface side of the transport belt 121 in a direction in which the nip width between the transport belt 121 and the latent image carrier 100 is more secured, thereby increasing the nip width between the latent image carrier 100 and the transfer electric field. A method has been proposed to prevent gap transfer occurring on the upstream side of the nip area by keeping the width in the transfer nip area.

However, when the conveying belt 121 is pressed by the pressing roll 123 toward the latent image carrier 100 to increase the nip width and prevent the transfer electric field from reaching outside the nip width, paper or the like is used. The gap between the pressing roll 123 and the latent image carrier 100 changes depending on the thickness and surface characteristics of the recording medium 102 and the thickness of the toner layer on the latent image carrier 100. As a result, a speed difference is generated between the recording medium 102 and the surface of the latent image carrier 100, and image displacement or color unevenness occurs if necessary. Further, when this means is applied to an image forming apparatus using the intermediate transfer member 101, the pressing roll 123 vibrates due to a change in the thickness of the toner layer on the intermediate transfer member 101 or the driving speed of the intermediate transfer member 101. Problems such as image displacement and color unevenness due to vibration were confirmed.

SUMMARY OF THE INVENTION The present invention solves these problems in the prior art. An intermediate transfer which occurs when a final fixed toner image on a latent image carrier such as a photoreceptor is transferred outside a nip area of a primary transfer. Provided is an image forming apparatus that forms a high-quality image in which a highlight portion on a body is prevented from being roughened and uneven in color, and is free from image displacement. Furthermore, by increasing the nip width between the intermediate transfer member and the latent image carrier, high transfer efficiency is maintained, the amount of toner scattered inside the device is reduced, the amount of contamination inside the device is reduced, and maintenance is easy. An object of the present invention is to provide an image forming apparatus with high reliability.

[0012]

An image forming apparatus according to the present invention comprises a latent image carrier on which a toner image corresponding to image information is formed, and a support roll having two or more axes having a driving roll on at least one side. An intermediate transfer belt that is longer and in contact with the latent image carrier at a predetermined nip width at least in the primary transfer position, and a primary transfer that is disposed on the opposing surface of the latent image carrier at the primary transfer position via the intermediate transfer belt Means,
A configuration in which the nip angle of the intermediate transfer belt to the latent image carrier is different between the upstream side and the downstream side of the primary transfer position, for example, when the primary transfer unit is configured by a corotron,
The nip angle of the intermediate transfer belt to the latent image carrier is such that the upstream angle of the primary transfer means is smaller than the downstream angle (4 ° to 4 °).
In the case where the primary transfer means has a transfer roll having a range of 6 °, the nip angle of the intermediate transfer belt to the latent image carrier is such that the upstream angle of the primary transfer means is larger than the downstream angle (9). ° to 11 °).

The nip width between the intermediate transfer belt and the latent image carrier formed at the primary transfer position has at least a width of the transfer electric field exerted by the transfer means, or is upstream of the primary transfer position supporting the intermediate transfer belt. Side support row
The roller and the downstream supporting roll are configured so as to be disposed in a non-contact manner with the image carrier between a tangent line drawn to the latent image carrier and the image carrier at the primary transfer position.

According to these technical means, the transfer electric field formed by the primary transfer means at the primary transfer position extends beyond the nip width formed at the contact position between the latent image carrier such as a photosensitive member and the intermediate transfer body. Therefore, the electrostatic force due to the transfer electric field does not act on the final fixing toner image T formed on the latent image carrier at the upstream side of the transfer nip portion, and the gap is transferred due to the gap transfer outside the primary transfer nip area. It is possible to output a high-quality image without image roughness of the light section. Further, since the primary transfer area is large, the transfer efficiency is high, and the scattering of toner into the apparatus is suppressed to a minimum, so that an image forming apparatus with good maintainability and high reliability and productivity can be provided.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image forming apparatus of the present invention will be described below in detail with reference to the drawings. Embodiment 1 In the case of an image forming apparatus using a corona discharger as a primary transfer device FIG. 1 shows a schematic configuration of a color electrophotographic copying machine using a corotron as a primary transfer device. The color electrophotographic copying machine includes a latent image carrier (photosensitive drum) 1, developing devices 5, 6, 7, 8 for developing toners of respective colors, and a corona discharger disposed at the primary transfer position so as to face the photosensitive drum 1. 9. Belt-shaped intermediate transfer body 2 and photosensitive drum cleaning device 16
Equipped with

The belt-shaped intermediate transfer member 2 is disposed so as to be in contact with a point P on the photosensitive drum (latent image carrier) 1 at a primary transfer position. The intermediate transfer body 2 uses an endless belt, is stretched from a back side to a plurality of support rolls 17 to 20, and rotates in the direction of arrow B. At least one of the support rolls of the intermediate transfer body 2 is provided as a drive roll for rotating the intermediate transfer body 2 in the direction of arrow B. In the color electrophotographic copying machine shown in this embodiment, the bias roll 1 provided at the secondary transfer position is used.
The drive roll 17 is a support roll disposed downstream of the opposing electrode roll 20 disposed opposite to 0. The belt-shaped intermediate transfer member 2 is composed of four support rolls provided downstream of the drive roll 17 as a first support roll 18 and a support roll disposed downstream of the first support roll 18 as a second support roll 19. It is supported and stretched by two support rolls.

The belt-like intermediate transfer body 2 forms a nip between the photosensitive drum 1 and the contact points a and b between the drive roll 17 and the first support roll 18, which are two support rolls. I have. In this embodiment, the photosensitive drum 1 is located directly above the corona discharger 9 and at a primary transfer position where the final fixed toner image T formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer body 2. If the upper point is point P,
The nip distance from the point P on the upstream side of the primary transfer position to the point a is shorter than the nip distance from the point P on the downstream side to the point b.

Here, the arrangement of the drive roll 17 and the first support roll 18 of the belt-shaped intermediate transfer member 2 will be described. The tangent drawn to the photosensitive drum 2 through the point P on the photosensitive drum 1 at the primary transfer position is defined as a reference tangent c. further,
The tangent drawn to the belt support surface of the drive roll 17 which supports the street intermediate transfer member 2 to the point P to the first tangent line m _1. A tangent drawn through the point P on the photosensitive drum 1 to the belt supporting surface of the support roll 18 of the intermediate transfer body 2 is a second tangent n
_Set to ₁ . The angle formed at the upstream side of the primary transfer position when the reference tangent c and the first tangent m ₁ intersect at the point P is defined as an angle α. The angle formed downstream of the primary transfer position when the reference tangent c and the second tangent n ₁ intersect at point P is angle β. At this time, the positions of the supporting (driving) roll 17 and the first supporting roll 18 of the intermediate transfer body 2 are defined so that the relationship between the angle α and the angle β satisfies the relationship α <angle β. In this case, the drive roll 17 and the first support roll 18 are positioned so as not to contact the photosensitive drum 1.

The support rolls 17 and 18 thus arranged
When the belt-like intermediate transfer body 2 is stretched between the photosensitive drums 1
The intermediate transfer member 2 is in a nip state with respect to the photosensitive drum 1 between the point a and the point b, and the nip width on the angle α side where the arrangement angle is large is formed larger than the nip width on the angle β side where the angle is small. The nip width thus formed is such that the width of the transfer electric field exerted by the transfer means (corona discharger) 9 is within the nip area.

The formation of an image by the image forming apparatus constituting the primary transfer section will be described below. Around the intermediate transfer body 2, a position detection device 21 for the intermediate transfer body that detects a position detection mark disposed on the intermediate transfer body 2, and between the secondary transfer position and the primary transfer position, that is, the support roll 20. A cleaning device 15 for the intermediate transfer body 2 as a means for removing the residual toner on the intermediate transfer body 2 after the secondary transfer is disposed between the drive roll 17 and the drive roll 17.

In this color electrophotographic copying machine, as the photosensitive drum 1 rotates in the direction of the arrow A, the position of the intermediate transfer member output from the intermediate transfer member position detecting device 21 using an optical detection method. Based on the detection signal, the control section of the image forming apparatus controls the exposure timing of the image exposing means in accordance with the image information performed on the latent image carrier 1 to form an electrostatic latent image. Further, developing units 5 to 8 corresponding to black (Bk), yellow (Y), magenta (M), and cyan (C) are arranged around the photosensitive drum 1, respectively. The toner image T is formed by developing the electrostatic latent image formed in No. 1 with any one of the developing devices. Therefore, if the electrostatic latent image written on the photosensitive drum 1 corresponds to the yellow image information, this electrostatic latent image is developed by the developing device 6 containing yellow (Y) toner, and A yellow toner image is formed on the body drum 1.

The unfixed toner image T formed on the photosensitive drum 1 is transferred from the photosensitive drum 1 to the surface of the intermediate transfer member 2 at a primary transfer position where the photosensitive drum 1 contacts the intermediate transfer member 2. An unfixed toner image T on the photosensitive drum 1 is applied to the corona discharger 9 on the back surface side of the intermediate transfer body 2 at the primary transfer position by applying a voltage having a polarity opposite to that of the toner. Is electrostatically attracted. Here, the residual toner on the latent image carrier after the primary transfer is cleaned by the latent image carrier cleaning means 16 before the next cycle.

When a single-color image is formed, the unfixed toner image T primarily transferred to the intermediate transfer member 2 is secondarily transferred to the recording medium 3 immediately. When forming a color image in which toner images of a plurality of colors are superimposed, the formation of the toner image on the photosensitive drum 1 and the primary transfer process of the toner image are repeated by the number of colors. For example, when a full-color image is formed by superimposing four color toner images, an unfixed toner image T of black, yellow, magenta, and cyan is formed on the photosensitive drum 1 for each rotation, and these unfixed toner images are formed. Statue T
Are sequentially primary-transferred to the intermediate transfer body 2. On the other hand, the intermediate transfer body 2 rotates at the same cycle as the photosensitive drum 1 while holding the black unfixed toner image T that has been primarily transferred first, and
An unfixed yellow, magenta, and cyan toner image T is transferred onto the intermediate transfer body 2 for each rotation so as to overlap the black unfixed toner image T.

The unfixed toner image T primarily transferred to the intermediate transfer body 2 in this manner is conveyed to a secondary transfer position facing the conveyance path of the recording medium 3 with the rotation of the intermediate transfer body 2. You. In the secondary transfer position, a semiconductive bias roll 10
Are in contact with the intermediate transfer body 2, and the recording medium 3 carried out of the tray 12 by the feed roller 11 at a predetermined timing is sandwiched between the bias roll 10 and the intermediate transfer body 2. Further, a counter electrode of the bias roll 10 is formed on the back side of the intermediate transfer member at the secondary transfer position,
Further, a backup roll 20 as a support roll for the intermediate transfer member 2 is provided. When a voltage having a polarity opposite to the charging polarity of the toner is applied to the bias roll 10, the unfixed toner image T carried on the intermediate transfer body 2 is electrostatically transferred to the recording medium 3 at the secondary transfer position.

Then, the recording medium 3 to which the unfixed toner image has been transferred is peeled off from the intermediate transfer body 2 by the peeling claw 13 and sent to a fixing device (not shown) by the conveyor belt 14 to perform a fixing process of the unfixed toner image. You. On the other hand, the intermediate transfer member 2 on which the secondary transfer of the unfixed toner image has been completed has the residual toner removed by the intermediate transfer member cleaning unit 15.

The bias roll 10 is formed by winding a semiconductive elastic body around a conductive metal roll. For example, the volume resistivity is adjusted to 105 Ω · cm. A voltage is applied to the bias roll 10 from a power supply (not shown). The peeling claw 13 and the cleaner 15 are disposed so as to be able to freely contact and separate from the intermediate transfer member 2. When a color image is formed, the unfixed toner image of the final color is primarily transferred to the intermediate transfer member 2. These members are separated from the intermediate transfer member 2.

The intermediate transfer member 2 contains a suitable amount of an antistatic agent such as carbon black in a resin such as acrylic, vinyl chloride, polyester, or polycarbonate, or various rubbers. 1014Ω · c
m. On the other hand, a backup roll 20, which is a support roll of the intermediate transfer body 2 and serves as an opposite electrode of the bias roll 10, is grounded, and its surface is covered with a semiconductive or insulating thin film.・ Adjusted to cm or more. In the color copying machine configured as described above, a stable transfer electric field is always formed between the bias roll 10 and the backup roll 20, so that the toner image can be satisfactorily transferred from the intermediate transfer body 2 to the recording medium 3. it can.

Next, in this image forming apparatus, the upstream side (Pre side) and the downstream side (Post side) of the primary transfer position P.
The experiment was conducted by changing the nip angle of the intermediate transfer member 2 in the above-mentioned Example 1 and the nip angle and dot reproducibility. The results are shown in FIG.
According to the results, the reproducibility is good when the nip angle α on the upstream side of the primary transfer position P is in the range of 4 ° to 6 °. The nip angle β on the downstream side of the primary transfer position P is 9
Good reproducibility was obtained in the range of ° to 12 °, and better reproducibility was obtained by setting the nip angle β to 9 ° to 11 °.

This is because the corona discharger 9 is provided with a transfer baffle 95 on the upstream side to converge the transfer electric field of the corotron to the primary transfer position P, and cut off the influence of the transfer electric field on the upstream side of the primary transfer position P. doing. Further, the primary transfer position P
The nip angle of the intermediate transfer body 2 on the upstream side is made larger than the normal angle to increase the nip width, thereby preventing the transfer of the electric field from being exerted outside the nip area to prevent gap transfer. On the downstream side of the primary transfer position P, the nip angle is increased and the nip width between the photosensitive drum 1 and the intermediate transfer body 2 is increased to increase transfer efficiency and reduce the amount of toner scattered in the apparatus. Thus, contamination in the apparatus is eliminated and maintenance efficiency is improved.

Embodiment 2 In the case of an image forming apparatus using a transfer roll as the primary transfer apparatus The operation of this image forming apparatus is the same as the mechanical configuration and the operation shown in Embodiment 1 and the image processing is performed. The description of the creation is omitted. Therefore, the relationship between the nip angle formed on the upstream side of the primary transfer portion and the nip angle formed on the downstream side of the primary transfer portion when the intermediate transfer member and the latent image carrier contact each other at the primary transfer position will be described.

FIG. 4 is an enlarged view of a main part of a color electrophotographic copying machine according to a second embodiment to which the present invention is applied. The belt-shaped intermediate transfer body 2 arranged so as to be in contact with the surface of the photosensitive drum 1 at the primary transfer position P is stretched from a back side to a plurality of support rolls including support rolls 170 and 180. It turns in the direction of arrow B. Here, the support roll 170 also serves as a drive roll for rotating the intermediate transfer body 2 in the direction of arrow B. In addition, a transfer roll 90 is provided at a position facing the primary transfer position P. The belt-shaped intermediate transfer body 2 has two support rolls, a drive roll 1
A nip portion is formed between the photoconductor drum 1 and the contact points e and f between the photoconductor drum 1 and the first support roll 180. In this embodiment, immediately above the position where the transfer roll 90 is provided, and upstream from the primary transfer position point P where the final fixing toner image T formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer body 2. The distance to the point e on the side is formed longer than the distance from the point P to the point f on the downstream side.

Here, the arrangement of the drive roll 170 and the first support roll 180 of the belt-shaped intermediate transfer member 2 will be described. The tangent drawn to the photosensitive drum 2 through the point P on the photosensitive drum 1 at the primary transfer position is defined as a reference tangent c. Further, a driving roll 17 that supports the intermediate transfer body 2 through the point P
A tangent drawn to the belt support surface of 0 is a first tangent m ₂ . Further, the intermediate transfer body 2 passes through a point P on the photosensitive drum 1.
The tangent drawn to the belt support surface of the support roll 180 of the second
Tangent line n ₂ . Then, the reference tangent c and the first tangent m ₂
The angle formed at the upstream side of the primary transfer position P when. The angle formed downstream of the primary transfer position P when the reference tangent c and the second tangent n ₂ intersect at the point P is defined as an angle β. At this time, the positions of the supporting (driving) roll 170 and the first supporting roll 180 of the intermediate transfer body 2 are defined so that the relationship between the angle α and the angle β satisfies the relationship of angle α> angle β. In this case, the driving roll 170 and the first support roll 18
0 is disposed at a position that does not contact the photosensitive drum 1.

The support rolls 170, 1 thus arranged
When the belt-shaped intermediate transfer member 2 is stretched between the intermediate transfer members 80, the intermediate transfer member 2 is in a nip state with respect to the photosensitive drum 1 between the point e and the point f of the photosensitive drum 1, and the nip on the angle α side where the arrangement angle is large. The width is formed larger than the nip width on the angle β side where the angle is small. The formed nip width is such that the width of the transfer electric field exerted by the transfer means (transfer roll) 90 is in the nip area. The formation of an image by the image forming apparatus constituting the primary transfer unit as described above will be described below. Then, the unfixed toner image T formed on the photosensitive drum 1
Is transferred from the photosensitive drum 1 to the surface of the intermediate transfer body 2 at a primary transfer position P where the photosensitive drum 1 and the intermediate transfer body 2 are in contact with each other. At this primary transfer position P, an unfixed toner image T on the photosensitive drum 1 is applied to the transfer roll 90 disposed on the back surface side of the intermediate transfer body 2 by applying a voltage having a polarity opposite to that of the toner. It is electrostatically attracted to the transfer body 2. Here, the residual toner on the photosensitive drum 1 after the primary transfer is cleaned by the photosensitive drum cleaning unit before the next cycle.

The transfer electric field applied by the transfer roll 90 having this structure also affects the upstream side of the primary transfer position P, but the nip width of the photosensitive drum 1 and the intermediate transfer body 2 on the upstream side is widened. Therefore, the width of the transfer electric field is within the nip area, and the transfer roll 9 extends to the upstream of the nip point e.
The effect of an electric field of 0 has no effect. Therefore, gap transfer on the upstream side of the nip region, which has been generated by the conventional image forming apparatus, can be prevented. Although the downstream side of the primary transfer position P is narrower than the nip width on the upstream side, the nip width is larger than the nip width of a normal apparatus, so that the transfer efficiency is high and the amount of toner scattered in the apparatus is high. Is reduced, thereby eliminating contamination in the apparatus and improving maintenance efficiency.

[0035]

As described above, in the image forming apparatus of the present invention, the transfer electric field formed by the discharge of the primary transfer device at the primary transfer position causes the nip position between the latent image carrier such as the photosensitive member and the intermediate transfer member. Does not extend beyond the nip width formed by In particular, no electrostatic force due to the transfer electric field acts on the final fixed toner image T formed on the latent image carrier on the upstream side of the transfer nip portion, and the gap transfer outside the primary transfer nip region is eliminated. As a result, this image forming apparatus can output a high-quality image with no image roughness in the highlight portion. Further, since the nip width of the primary transfer is wide, the transfer efficiency is high, toner scattering into the apparatus can be suppressed to a minimum, and an image forming apparatus with high maintainability, high reliability and high productivity can be provided. it can.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a color electrophotographic copying machine using a corona discharger of the present invention.

FIG. 2 is a schematic explanatory view showing a main part of a primary transfer unit.

FIG. 3 is a graph showing nip angles and image reproducibility.

FIG. 4 is a schematic view showing an embodiment of a color electrophotographic copying machine using the transfer roll of the present invention.

FIG. 5 is a schematic diagram of an image forming apparatus using a conventional corona discharger.

FIG. 6 is a schematic view of an image forming apparatus using a conventional transfer roll.

[Explanation of symbols]

1 photosensitive drum (latent image carrier), 2 intermediate transfer body,
Reference Signs List 3 recording medium, 5 to 8 developing device, 9 corona discharger, 10 bias roll, 11 feed roller, 12 tray, 13 peeling claw, 14 transport belt, 15 intermediate transfer body cleaning device, 16 photosensitive drum cleaning device, 17 to 17 20 intermediate transfer member support roll (20 also serves as a counter electrode of bias roll 10), 21 intermediate transfer member position detecting device, 22
Transfer roll, 90 transfer roll, 95 transfer baffle, T unfixed toner image.

Claims (6)

[Claims] 1. A latent image carrier on which a toner image corresponding to image information is formed and a support roller having two or more axes having a drive roll on at least one side, and are extended from the inside by a latent image carrier at least at a primary transfer position. An intermediate transfer belt that contacts the carrier,
A primary transfer means disposed on the opposite surface of the latent image carrier at the primary transfer position via an intermediate transfer belt, and the unfixed toner image on the latent image carrier is primarily transferred to the intermediate transfer belt by the primary transfer means. In an image forming apparatus which is transferred and transferred from an intermediate transfer belt to a transfer material by a secondary transfer unit at a secondary transfer position, the intermediate transfer belt forms a nip of a predetermined width with the latent image carrier at the primary transfer position And an image forming apparatus in which the nip angle of the intermediate transfer belt to the latent image carrier is different between the upstream side and the downstream side of the primary transfer position. 2. When the primary transfer means is a corotron, the nip angle of the intermediate transfer belt to the latent image carrier is configured so that the downstream angle of the primary transfer means is larger than the upstream angle. The image forming apparatus according to claim 1. 3. When the primary transfer means is constituted by a transfer roll, the nip angle of the intermediate transfer belt to the latent image carrier is configured so that the upstream angle of the primary transfer means is larger than the downstream angle. The image forming apparatus according to claim 1, wherein: 4. The image forming apparatus according to claim 1, wherein a nip width between the intermediate transfer belt and the latent image carrier formed at the primary transfer position has at least a width of a transfer electric field exerted by the transfer unit. 5. A support roll upstream and downstream of a primary transfer position for supporting an intermediate transfer belt disposed so as to form a nip having a predetermined width with a latent image bearing member has a primary roll. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed between the tangent drawn to the latent image carrier at the transfer position and the image carrier without contacting the image carrier. 6. A nip angle of the intermediate transfer belt to the latent image carrier, wherein a large angle is in a range of 9 ° to 11 °, and an angle corresponding to the large angle is in a range of 4 ° to 6 °. Or the image forming apparatus according to 3.