JP2002174942A - Tandem system color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device of a tandem system using an intermediate transfer belt by which sufficient transfer efficiency is obtained without causing defective transfer, the collapse of a void character and toner scattering or the like. SOLUTION: This image forming device 10 of the tandem system is provided with the primary transfer parts 20-50 of plural colors successively arranged at the intermediate transfer belt 13 and a secondary transfer part 60 to transfer a toner layer primarily transferred to the intermediate transfer belt to a transfer body P, and the circumferential speed of each image carrier is set mutually same, and the circumferential speed V1 of the image carrier, that V2 of the intermediate transfer belt and that V3 of the transfer body are set mutually different, and the respective kinds of the press-contact force F1y, F1m, F1c and F1k of the intermediate transfer belt to the image carrier at the primary transfer parts and that F2 of the intermediate transfer belt to the transfer body are set mutually different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tandem type color image forming apparatus using an intermediate transfer belt.

[0002]

2. Description of the Related Art Conventionally, such a tandem type color image forming apparatus is configured as shown in FIG. 6, for example. In FIG. 6, a tandem type color image forming apparatus 100 includes an intermediate transfer belt 10 that is disposed obliquely and stretched between a driving roller 101 and a tension roller 102.
3 and four color developing units 104 sequentially arranged on the upper side of the intermediate transfer belt 103, ie, yellow, magenta, cyan, and black developing units 104y,
104m, 104c, 104k and each developing unit 10
Developer roller 1 in 4y, 104m, 104c, 104k
05, (105y, 105m, 105c, 105k)
And a roller-shaped image carrier 106 (106y, 106m, 1) arranged so as to be in contact with the intermediate transfer belt 103.
06c, 106k) and these image carriers 106y, 1
06m, 106c, and 106k, the intermediate transfer belt 103 and the developing rollers 105y,
The charging rollers 107, (107y, 107m, 107c, 10
7k) and LEDs 108, (108y, 108m, 10
8c, 108k) and the image carrier 10 inside the intermediate transfer belt 103 with the intermediate transfer belt 103 interposed therebetween.
6y, 106m, 106c, 106k, and the primary transfer roller 109 (109y, 109m, 109c, 10
9k), the stabilizing roller 1 around which the intermediate transfer belt 103 is wound at a lower portion of the intermediate transfer belt 103.
10, the belt cleaning blade 111 facing the stabilizing roller 110, the secondary transfer roller 112 facing the lower side of the drive roller 101, and the space between the drive roller 101 and the secondary transfer roller 112. A fixing device 113 through which the paper P passes. Here, each of the developing units 104 includes a supply roller 104a and a thin layer forming member 104b that come into contact with the developing roller 105, respectively.

According to the tandem-type color image forming apparatus 100 having such a configuration, when print data is input from the outside, the intermediate transfer belt 103 starts driving and rotating at a predetermined speed in the direction of the arrow, and accordingly, Primary transfer roller 109
Also start driven rotation, and the charging roller 107
Is applied with a charging voltage. At the same time, the secondary transfer roller 112 also starts to rotate. The image carrier 106, the charging roller 107, and the developing roller 10 of each color are used.
5 and supply roller 104 of each developing unit 104
a starts rotating at a predetermined speed in the direction of the arrow, after which a predetermined developing voltage is applied to the developing roller 105, and a predetermined supply voltage is applied to the supply roller 104a and the thin layer forming member 104b, respectively.

As a result, each image carrier 106 is charged by the charging roller 107 with its rotation, is exposed by the LED 108 based on the input print data, and an electrostatic latent image is formed on its surface. You. Thereafter, each image carrier 106 comes into contact with the developing roller 105, and the image carrier 106 and the developing roller 1 are transported by the negatively charged toner T of each color conveyed by the developing roller 105.
Developed by an electric field between 05 Then, the primary transfer roller 109 is applied with a primary transfer voltage having a polarity opposite to the toner charging polarity, and is pressed against each image carrier 106 with the intermediate transfer belt 103 interposed therebetween, thereby developing on each image carrier 106. The formed image is transferred to the intermediate
Transcribed above. At that time, the toner of each color is sequentially transferred onto the intermediate transfer belt 103 in a superimposed manner.

[0005] Thereafter, the intermediate transfer belt 103 is pressed against the secondary transfer roller 112 with the sheet P interposed therebetween, and a secondary transfer voltage having a polarity opposite to the toner charging polarity is applied to the sheet P. The image transferred above is secondarily transferred onto the sheet P. Then, when the sheet P passes through the fixing device 113, each toner is fixed on the sheet P, and a full-color print is obtained.

[0006]

However, in the color image forming apparatus 100 having such a configuration, the speeds of the image carrier 106, the intermediate transfer belt 103 and the paper P are the same, and the primary transfer rollers 109 of each color are used. And the pressing force of the secondary transfer roller 112 were the same. For this reason, sufficient transfer efficiency could not be obtained.

On the other hand, for example, Japanese Patent Application Laid-Open No. 63-583
No. 87 discloses a method of making the speeds of the image carrier and the intermediate transfer belt different, but even if this method is adopted,
As shown by the symbol X in FIG. 7, since the intermediate transfer belt 103 does not contact the toner layer, the intermediate transfer belt 103 is not transferred onto the intermediate transfer belt 103, and a transfer failure may occur.

When the speed of the image carrier 106 is higher than that of the intermediate transfer belt 103,
The thickness of the image to be primarily transferred thereon becomes thick, and in some cases, toner scattering or crushing of outline characters may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an intermediate transfer belt capable of obtaining sufficient transfer efficiency without causing poor transfer, crushed outline characters, toner scattering, and the like. It is an object of the present invention to provide a tandem type color image forming apparatus using the image forming apparatus.

[0010]

In order to achieve this object, a tandem type color image forming apparatus according to claim 1 of the present invention is arranged sequentially with respect to an intermediate transfer belt,
A primary transfer section for transferring the toner layer of the image carrier developed on the electrostatic latent image to the intermediate transfer belt; and a secondary transfer section for transferring the toner layer primarily transferred to the intermediate transfer belt to the transfer body. A tandem-type color image forming apparatus provided with a next transfer section, wherein the peripheral speeds of the respective image carriers are the same, the peripheral speed of the image carrier, the peripheral speed of the intermediate transfer belt, and the speed of the transfer body. Are different from each other, and the state in which the intermediate transfer belt is pressed against the image carrier and the state in which the intermediate transfer belt is pressed against the transfer body in each primary transfer unit are different from each other.

When the tandem type color image forming apparatus is configured as described above, since the peripheral speed of the image carrier and the peripheral speed of the intermediate transfer belt are different from each other in each primary transfer section, the image is developed on the image carrier. The toner layer receives a shearing force and a rolling force. Therefore, the adhesive force of the toner layer to the image carrier is reduced, and even if the toner layer sequentially transferred onto the intermediate transfer belt is thickened by being superimposed, the intermediate transfer belt adheres to the image carrier. Since the pressure contact states are different from each other, the intermediate transfer belt surely comes into contact with the toner layer on the image carrier, so that sufficient transfer efficiency can be obtained.

Similarly, in the secondary transfer section, since the peripheral speed of the intermediate transfer belt and the speed of the transfer member are different from each other, each toner layer primary-transferred to the intermediate transfer belt receives a shearing force and a rolling force. Will be. Therefore,
The adhesion of the toner layer to the image carrier is reduced, and the pressing force of each intermediate transfer belt against the image carrier and the state of pressing the intermediate transfer belt against the transfer member are different from each other. Because it contacts the toner layer on the intermediate transfer belt,
Sufficient transfer efficiency can be obtained.

According to a second aspect of the present invention, in the tandem type color image forming apparatus, the peripheral speed of the image carrier is lower than the peripheral speed of the intermediate transfer belt. With such a configuration of the tandem type color image forming apparatus, in the primary transfer section, the toner layer on the image carrier receives a shearing force and a rolling force, and the toner layer primary-transferred on the intermediate transfer belt becomes thick. It does not become too much. Therefore, sufficient transfer efficiency can be obtained, and scattering of the toner layer on the intermediate transfer belt does not occur.

According to a third aspect of the present invention, in the tandem type color image forming apparatus, the peripheral speed of the intermediate transfer belt is lower than the speed of the transfer member. With such a configuration of the tandem type color image forming apparatus, the toner layer on the intermediate transfer belt receives a shearing force and a rolling force in the secondary transfer unit, and the toner layer secondary-transferred on the transfer body is removed. It doesn't get too thick. Therefore, sufficient transfer efficiency can be obtained, and no collapse of white characters occurs.

According to a fourth aspect of the present invention, in the tandem type color image forming apparatus, the pressing force of the intermediate transfer belt against the image carrier in each of the primary transfer portions is sequentially increased. With such a configuration of the tandem type color image forming apparatus, the intermediate transfer belt can be reliably formed in each primary transfer section even if the toner layer primary-transferred onto the intermediate transfer belt becomes thicker as the colors are superimposed. Since it comes into contact with the toner layer on the image carrier, sufficient transfer efficiency can be obtained.

According to a fifth aspect of the present invention, in the tandem type color image forming apparatus, the pressing force of the intermediate transfer belt against the image carrier at the last primary transfer portion is smaller than the pressing force of the intermediate transfer belt against the transfer member. is there. In the tandem type color image forming apparatus according to the sixth aspect, the pressing force of the intermediate transfer belt against the image carrier at the last primary transfer portion is the same as the pressing force of the intermediate transfer belt against the transfer member. .

With such a configuration of the tandem type color image forming apparatus, even if the toner layer primary-transferred onto the intermediate transfer belt in each primary transfer section becomes thicker as the colors are superimposed, the secondary transfer Since the transfer body surely contacts the toner layers of the respective colors on the intermediate transfer belt in the section, a sufficient transfer efficiency can be obtained.

According to a seventh aspect of the present invention, in the tandem type color image forming apparatus, the hardness of the roller portion of the primary transfer roller for pressing the intermediate transfer belt against the image carrier in each of the primary transfer portions is sequentially reduced. There is a configuration. With such a configuration of the tandem type color image forming apparatus, the intermediate transfer belt can be reliably formed in each primary transfer section even if the toner layer primary-transferred onto the intermediate transfer belt becomes thicker as the colors are superimposed. Since it comes into contact with the toner layer on the image carrier, sufficient transfer efficiency can be obtained.

According to a tandem type color image forming apparatus of the present invention, the hardness of the roller portion of the primary transfer roller for pressing the intermediate transfer belt against the image carrier in the last primary transfer portion is determined. The configuration is higher than the hardness of the roller portion of the secondary transfer roller for pressing against the transfer member. In the tandem type color image forming apparatus according to the ninth aspect, the hardness of the roller portion of the primary transfer roller for pressing the intermediate transfer belt against the image carrier in the last primary transfer portion may be adjusted to the transfer member of the intermediate transfer belt. The hardness is the same as the hardness of the roller portion of the secondary transfer roller for pressing.
According to a tenth aspect of the present invention, the tandem-type color forming apparatus is arranged sequentially with respect to the intermediate transfer belt, and transfers the toner image of the image carrier developed with respect to the electrostatic latent image to the intermediate transfer belt. A tandem-type color image forming apparatus, comprising: a primary transfer unit for a plurality of colors; and a secondary transfer unit for transferring a toner layer primarily transferred to an intermediate transfer belt to a transfer body. The pressing force of the intermediate transfer belt against the image bearing member at each of the sections sequentially increases.

With such a configuration of the tandem type color image forming apparatus, in each primary transfer section, even if the toner layer primarily transferred on the intermediate transfer belt becomes thicker each time the color is superimposed, the secondary transfer Since the transfer member surely contacts the toner layers of the respective colors on the intermediate transfer belt in the portion, sufficient transfer efficiency can be obtained.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. First, an embodiment of a tandem type color image forming apparatus of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 1 is a schematic side view showing the configuration of an embodiment of a tandem type color image forming apparatus according to the present invention.

In FIG. 1, a tandem-type color image forming apparatus 10 includes an intermediate transfer belt 13 stretched between a driving roller 11 and a tension roller 12, and an upper left side of the intermediate transfer belt 13 above the intermediate transfer belt 13. , And four-color primary transfer units 20, 30, 40, and 50, and a secondary transfer unit 60 disposed at the lower right end of the intermediate transfer belt 13.
And a fixing device 70.

The driving roller 11 is driven at a predetermined rotational speed by a driving means (not shown). The tension roller 12 applies a predetermined tension to the intermediate transfer belt 13 and is rotatably supported.

The intermediate transfer belt 13 is formed of an endless semiconductive belt (for example, a carbon-added resin belt) having a width wider than a width of a coating portion of the image carriers 21 to 51 described later. The surface is coated with silicon, and is arranged obliquely to the upper left in FIG. 1 and is rotationally driven in the direction of the arrow at a speed V2 (for example, 122.81 mm / s) higher than the speed of the image carriers 21 to 51. You. Further, the intermediate transfer belt 13 is provided at both ends of the inner surface thereof.
A bead 13a (see FIGS. 2 and 3) is attached so that the intermediate transfer belt 13 does not come off from the drive roller 11 and the tension roller 12 during rotation.

Further, the intermediate transfer belt 13 is provided with a belt cleaning blade 15 which is wound around the stabilizing roller 14 at a lower intermediate position, and is arranged to face the stabilizing roller 14. Here, the belt cleaning blade 15 is formed of a plate-like urethane rubber member having the same width as the width of the intermediate transfer belt 13, and is constantly in contact with the intermediate transfer belt 13 at a leading edge, so that the intermediate transfer belt 1
Then, the toner layer T remaining on the sheet 3 without being subjected to the secondary transfer is removed.

Each of the primary transfer units 20 to 50 has the same configuration, and is in charge of each color of yellow, magenta, cyan, and black. Each of the primary transfer units 20 to 50 includes a roller-shaped image carrier 21 that contacts the intermediate transfer belt 13,
31, 41, 51, and the charging rollers 2 sequentially arranged counterclockwise in FIG. 1 with respect to the image carriers 21 to 51.
2, 32, 42, 52 and LED2 as an exposure means
3, 33, 43, 53 and developing units 24, 34, 4
, 54, and primary transfer rollers 25, 35, 4 facing the image carriers 21-51 with the intermediate transfer belt 13 interposed therebetween.
5, 55.

Each of the image carriers 21 to 51 is subjected to an alumite treatment on the surface of the aluminum tube, and is further provided with a CG layer and a CT.
It is composed of a cylindrical member coated with a layer, and both ends are rotatably supported by a support (not shown). During a printing operation, a speed V1 (for example, 121.59 mm /
It is rotationally driven in s). The image carriers 21 to 51 of each color are used.
Are set to the same speed V1.

The charging rollers 22 to 52 are connected to the image carrier 2
It is composed of a cylindrical member provided with a roller portion composed of a semiconductive brush narrower than the width of the coating portions 1 to 51, and has shaft portions at both ends. The shaft portion is made of a metal member, and is rotatable by a charging roller support (not shown).
51 is rotatably supported so as to come into contact with the surface. Further, during the printing operation, the charging rollers 22 to 52 apply a charging voltage (for example, −150) from the end of the shaft portion.
0V) is applied and the surfaces of the image carriers 21 to 51 are charged by being rotationally driven in the direction of the arrow.

Further, adjacent to the charging rollers 22 to 52, image carrier cleaning blades 22a, 32a, 4
2a and 52a are arranged. The image carrier cleaning blades 22a to 52a are made of a plate-like urethane rubber member having the same width as the width of the coated portion of the image carriers 21 to 51, and are always in contact with the image carriers 21 to 51 at a leading edge. As a result, the toner layer T remaining without being primarily transferred onto the image carriers 21 to 51 is removed.

The LEDs 23 to 53 are connected to the image carriers 21 to
An image which is configured to extend over the entire coating portion in the longitudinal direction of 51 and is driven and controlled by a drive control circuit (not shown) based on print data input from the outside, and charged by the charging rollers 22 to 52. Carriers 21-5
By exposing the surface of No. 1 to an electrostatic latent image is formed. Note that the LEDs 23 to 53 may be exposure units having other arbitrary configurations.

Each of the developing units 24 to 54 has a well-known structure, and is composed of a toner tank for storing toner of each color. When,
It has supply rollers 24b, 34b, 44b, 54b, and thin layer forming members 24c, 34c, 44c, 54c.

The developing rollers 24a to 54a are cylindrical members narrower than the width of the charging rollers 22 to 52. The roller portion is made of semiconductive urethane rubber, and the shaft portion is made of a metal member. In addition, the above-mentioned developer roller 24
a to 54a are rotatably supported by developing roller supports (not shown) at both ends, and the roller portion is always fixed to the image carrier 21.
~ 51. Further, during the printing operation, the developing rollers 24a to 54a are applied with a developing voltage (e.g., -430 V) from the end of the shaft portion.
By being driven to rotate in the direction of the arrow, the image carriers 21 to 21 are driven.
Develop the 51 electrostatic latent image.

Each of the supply rollers 24b to 54b is a cylindrical member having a width smaller than that of each of the development rollers 24a to 54a. The roller portion is made of semiconductive urethane foam, and the shaft portion is made of a metal member. The supply rollers 24b to 54b are rotatably supported by supply roller supports (not shown) at both ends, so that the roller portions always contact the development rollers 24a to 54a. Further, the supply rollers 24b to 54b
During the printing operation, a supply voltage (for example, −560 V) is applied from the end of the shaft portion, and the charged toner T is driven to rotate in the direction of the arrow, thereby charging the charged toner T with the developing roller 2.
4a to 54a.

The thin layer forming members 24c to 54c are formed by bending the tip of a plate-like metal into an L shape, and have the same width as the developing rollers 24a to 54a.
Then, the thin-layer forming members 24c to 54c are always in contact with the developing rollers 24a to 54a at their leading edges at the leading ends of the L-shape, and the supply rollers 24b to 54b
Thus, the toner T supplied to the surfaces of the developing rollers 24a to 54a is thinned. Further, the thin layer forming member 24c
To 54c, the supply voltage of the supply rollers 24b to 54b is applied, and the toner T is charged at the same time as the toner T is thinned.

The primary transfer rollers 25 to 55 are cylindrical members having a smaller width than the developing rollers 24a to 54a.
The roller portion is made of semiconductive urethane foam, and the shaft portion is made of a metal member. The primary transfer rollers 25 to 55 are primary transfer roller supports 25a, 3 at both ends.
5a, 45a, and 55a are rotatably supported at positions facing the image carriers 21 to 51 of the respective colors, and the roller portion is always supported by the image carrier 21 via the intermediate transfer belt 13.
To 51, the primary compression springs 25b,
It is urged by 35b, 45b, 55b.

Here, these primary compression springs 25
b to 55b, the pressing forces F1y, F1m, F1c, F of the primary transfer rollers 25 to 55 against the image carriers 21 to 51
1k is, for example, F1y = 1kgf, F1m = 2k such that F1y <F1m <F1c <F1k.
gf, F1c = 3 kgf, and F1k = 4 kgf. Further, during the printing operation, the primary transfer rollers 25 to 55 are applied with a primary transfer voltage (for example, about +2000 V) from the end of the shaft portion, and are driven to rotate by the frictional force with the intermediate transfer belt 13 in the direction of the arrow. Thus, the toner layer T on the image carriers 21 to 55 is transferred onto the intermediate transfer belt 13.

The secondary transfer section 60 is composed of a secondary transfer roller 61 that contacts the drive roller 11 from below with the intermediate transfer belt 13 interposed therebetween. The secondary transfer roller 61 is a cylindrical member having a width smaller than that of the intermediate transfer belt 13. The roller portion is made of semiconductive urethane foam, and the shaft portion is made of a metal member. Also,
The secondary transfer roller 61 includes the secondary transfer roller supports 6 at both ends.
2 is supported at a position facing the drive roller 11 so as to be rotatable with respect to the intermediate transfer belt 1.
The secondary compression spring 63 urges the driving roller 11 through the third roller 3.

Here, the pressing force F2 of the secondary transfer roller 61 against the drive roller 11 by the secondary compression spring 63 is set to, for example, F2 = 4 kgf so that F1k ≦ F2. Further, during the printing operation, the secondary transfer roller 61 applies a secondary transfer voltage (for example, about +4) from the end of the shaft portion.
000 V) is applied, and the toner layer T on the intermediate transfer belt 13 is rotated on the paper P as a transfer member inserted between the secondary transfer roller 61 and the drive roller 11 by being driven to rotate in the direction of the arrow. Transfer to Here, the paper P is supplied at a speed V3, and the speed V3 is set to, for example, V3 ≒ 124 mm / s so that V2 <V3.

The fixing device 70 has a known structure.
By heating the passing paper P, the toner secondary-transferred onto the paper P is melted and fixed.

Next, the operation of the tandem type color image forming apparatus 10 according to the present embodiment will be described. When print data is input from outside, the intermediate transfer belt 13
The drive roller 11 starts driving and rotating at a speed V2 in the direction of the arrow, and accordingly, the primary transfer rollers 25 to 55 also start driven rotation by the intermediate transfer belt 13, and a charging voltage is applied to the charging rollers 22 to 52, respectively. Is done. At the same time, the secondary transfer roller 61 also starts to rotate in the direction of the arrow.

Then, the image carriers 21 to 51, the charging rollers 22 to 52, the developing rollers 24a to 54a, and the supply rollers 24b to 54b of the respective colors start rotating at predetermined speeds in the directions indicated by arrows, respectively. Of the developing roller (−430 V)
A predetermined supply voltage (−560 V) is applied to each of 4b to 54b and thin layer forming members 24c to 54c.

As a result, the respective image carriers 21 to 51 are charged to about -750 V by the charging rollers 22 to 52 with their rotation, and are exposed by the LEDs 23 to 53 based on the input print data. Then, an electrostatic latent image is formed on the surface. The exposed portions on the surfaces of the image carriers 21 to 51 have a voltage of about -150V. At this time,
Each of the LEDs 23 to 53 has the exposure timing shown in FIG.
Also, considering that the image carrier peripheral speed <the intermediate transfer belt peripheral speed <the paper speed, the image elongation occurs because the image carrier peripheral speed <the intermediate transfer belt peripheral speed <the paper speed. The latent image on the image carrier is shrunk so as not to cause the image carrier.) The generated image carriers 21 to 51 are exposed. That is,
When the intermediate transfer belt 13 moves at a speed V2 with respect to a distance L between two adjacent primary transfer portions, for example, 20 and 30, the required time becomes L / V2, and each of the LEDs 23 to
Each of the light-emitting elements 53 emits light at a time L / V2 shifted from each other, so that the same position on the intermediate transfer belt 13 can be exposed.

Thereafter, each of the image carriers 21 to 51 comes into contact with the developing rollers 24a to 54a, and
The image carriers 21 to 51 and the developing roller 2 are transported by the negatively charged toner T of each color transported by the toner carrier 4a.
4a to 54a (that is, the image carriers 21 to 51).
(The potential difference between the exposed portion potential of −150 V and the developer roller potential of −430 V). Each of the primary transfer rollers 25 to 55 is applied with a primary transfer voltage (approximately +2000 V) having a polarity opposite to the toner charging polarity, and is brought into predetermined contact with each of the image carriers 21 to 51 with the intermediate transfer belt 13 interposed therebetween. The images developed on the image carriers 21 to 51 are transferred onto the intermediate transfer belt 13 by being pressed by the forces F1y, F1m, F1c, and F1k. that time,
The toner of each color is sequentially transferred onto the intermediate transfer belt 103 in a superimposed manner.

Here, the speed V1 of the image carriers 21-51
Is that the toner layer on the image carriers 21 to 51 receives a shearing or rolling force because the speed is lower than the speed V2 of the intermediate transfer belt 13, and the toner layer primarily transferred on the intermediate transfer belt 13 becomes too thick. There is no. Therefore, sufficient transfer efficiency can be obtained, and scattering of the toner layer on the intermediate transfer belt 13 does not occur. Further, for example, in the primary transfer of the toner layer of the last color (black in the illustrated case), the intermediate transfer belt 13 is pressed against the image carrier 51 with a pressure contact force F1k = 4 kgf, as indicated by reference numeral X1 in FIG. This ensures that the intermediate transfer belt 13 contacts the black toner layer T on the image carrier 51 even if the toner layers of other colors are transferred in an overlapping manner. Therefore, a sufficient transfer efficiency of the black toner layer T to the intermediate transfer belt 13 can be obtained.

Thereafter, the intermediate transfer belt 13 is pressed against the secondary transfer roller 61 with the supplied paper P interposed therebetween.
When a secondary transfer voltage (approximately +4000 V) having a polarity opposite to the toner charging polarity is applied to the sheet P, the toner layer transferred onto the intermediate transfer belt 13 is secondarily transferred onto the sheet P. Then, when the paper P passes through the fixing device 70, each toner layer is fixed on the paper P, and a full-color print is obtained. Here, since the speed V2 of the intermediate transfer belt 13 is lower than the supply speed V3 of the sheet P, the toner layer on the intermediate transfer belt 13 receives a shearing force and a rolling force, and the toner transferred secondarily onto the sheet P. The layers do not become too thick. Therefore, a sufficient transfer efficiency can be obtained, and no white characters are crushed after fixing by the fixing device 70.

In the above-described embodiment, the pressing force F1k of the primary transfer roller 55 against the image carrier 51 is set to be the same as the pressing force F2 of the secondary transfer roller 61 against the drive roller 11, but F2 is set to F1k. It may be larger.

In the above-described embodiment, the press-contact forces F1y, F1m, F1c, F1k, and F2 are adjusted by the primary compression springs 25b to 55b and the secondary compression spring 63, and are appropriately set. But not limited to this, each primary compression spring 25b
To 55b and the secondary compression spring 63 are all the same, and the hardness of the roller portions of the primary transfer rollers 25 to 55 and the secondary transfer roller 61 acting on the image carrier 51 and the drive roller 11 is made different. That is, the hardness H1y, H1m, H1c, H1k, and H2 of the roller portions of the primary transfer rollers 25 to 55 and the secondary transfer roller 61 may be set so that H1y>H1m>H1c> H1k ≧ H2.

As a result, the above-described pressing forces F1y, F1
As in the case where m, F1c, F1k and F2 are set to be different from each other, the intermediate transfer belt 13 for the image carriers 21 to 51 of the roller portions of the primary transfer rollers 25 to 55 and the secondary transfer roller 61 and the drive roller 11 is used. Are different from each other. Therefore, for example, in the primary transfer of the toner layer of the last color (black in the case of the drawing), the intermediate transfer belt 13 is sufficiently pressed against the image carrier 51 as shown in FIG. Even when the toner layers of the black toner layer T are superimposed on each other, the intermediate transfer belt 13 surely comes into contact with the black toner layer T on the image carrier 51 to transfer the black toner layer T to the intermediate transfer belt 13. , Sufficient transfer efficiency can be obtained.

Further, in the above-described embodiment, the primary transfer units 20 to 50 are provided for the yellow, magenta, cyan,
Although arranged in the order of black, the present invention is not limited to this, and may be arranged in a different order, or may be only three colors of yellow, magenta, and cyan, or may be a combination of other colors.

[0050]

As described above, according to the present invention, since the peripheral speed of the image carrier and the peripheral speed of the intermediate transfer belt are different from each other in each primary transfer section, the toner developed on the image carrier is The layers will be subjected to shear and rolling forces. Therefore, the adhesive force of the toner layer to the image carrier is reduced, and even if the toner layer sequentially transferred onto the intermediate transfer belt is thickened by being superimposed, the intermediate transfer belt adheres to the image carrier. Since the pressure contact states are different from each other, the intermediate transfer belt surely comes into contact with the toner layer on the image carrier, so that sufficient transfer efficiency can be obtained.

Similarly, in the secondary transfer section, since the peripheral speed of the intermediate transfer belt and the speed of the transfer member are different from each other, each toner layer primary-transferred to the intermediate transfer belt receives a shearing force or a rolling force. Will be. Therefore,
Since the adhesion of the toner layer to the image carrier is reduced and the state of pressure contact of each intermediate transfer belt to the image carrier and the state of pressure contact of the intermediate transfer belt to the transfer body are different from each other, Since it contacts the toner layer on the intermediate transfer belt, sufficient transfer efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a structural diagram showing a configuration of an embodiment of a tandem type color image forming apparatus of the present invention.

FIG. 2 is a detailed view of a primary transfer unit in the tandem type color image forming apparatus of FIG.

FIG. 3 is a detailed view of a secondary transfer unit in the tandem type color image forming apparatus of FIG.

FIG. 4 is a diagram showing exposure timings of LEDs in the tandem type color image forming apparatus of FIG. 1;

FIG. 5 is an enlarged cross-sectional view showing a transfer state in a final primary transfer section in the tandem type color image forming apparatus of FIG.

FIG. 6 is a structural diagram showing a configuration of an example of a conventional tandem type color image forming apparatus.

FIG. 7 is an enlarged cross-sectional view showing a transfer state in a final primary transfer section in the tandem type color image forming apparatus of FIG.

[Explanation of symbols]

 Reference Signs List 10 tandem type color image forming apparatus 11 drive roller 12 tension roller 13 intermediate transfer belt 14 stabilizing roller 15 belt cleaning blade 20, 30, 40, 50 primary transfer unit 21, 31, 41, 51 image carrier 22, 32, 42, 52 Charging roller 23, 33, 43, 53 LED (exposure means) 24, 34, 44, 54 Developing unit 24a, 34a, 44a, 54a Develo roller 24b, 34b, 44b, 54b Supply roller 24c, 34c, 44c, 54c Thin layer forming member 25, 35, 45, 55 Primary transfer roller 60 Secondary transfer section 61 Secondary transfer roller 70 Fixing device T Toner P Paper

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshinobu Takeda 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Yasuhiro Funayama 5-7-1 Shiba, Minato-ku, Tokyo Japan F-term in the Electric Company (reference) 2H027 DA16 DE09 EB04 EC06 ED24 EE02 EE03 2H030 AB02 AD17 BB42 BB46 BB53 BB56 BB63 2H032 AA05 AA14 AA15 BA09 BA23 BA30 CA13

Claims (10)

[Claims] A first transfer unit configured to sequentially transfer a toner image of an image carrier developed on an electrostatic latent image on an intermediate transfer belt to the intermediate transfer belt; A secondary transfer section for transferring a primary-transferred toner layer to a transfer body, comprising: a tandem-type color image forming apparatus; The peripheral speed of the intermediate transfer belt, the peripheral speed of the intermediate transfer belt, and the speed of the transfer member are different from each other, and the pressure contact state of the intermediate transfer belt with the image carrier and the pressure contact state of the intermediate transfer belt with the transfer member in each primary transfer section are mutually different. A tandem-type color image forming apparatus characterized by being different. 2. The tandem type color image forming apparatus according to claim 1, wherein the peripheral speed of the image carrier is lower than the peripheral speed of the intermediate transfer belt. 3. The tandem type color image forming apparatus according to claim 1, wherein the peripheral speed of the intermediate transfer belt is lower than the speed of the transfer member. 4. The tandem-type color image forming apparatus according to claim 1, wherein the pressing force of the intermediate transfer belt against the image carrier in each of the primary transfer sections increases in order. apparatus. 5. The image forming apparatus according to claim 1, wherein the pressing force of the intermediate transfer belt against the image carrier at the last primary transfer portion is smaller than the pressing force of the intermediate transfer belt against the transfer member. A tandem-type color image forming apparatus as described in the above. 6. The image forming apparatus according to claim 1, wherein the pressing force of the intermediate transfer belt against the image carrier at the last primary transfer portion is the same as the pressing force of the intermediate transfer belt against the transfer member.
A tandem-type color image forming apparatus according to any one of the above. 7. The method according to claim 1, wherein the hardness of the roller portion of the primary transfer roller for pressing the intermediate transfer belt against the image carrier in each of the primary transfer portions is sequentially reduced.
4. A tandem-type color image forming apparatus according to any one of items 1 to 3. 8. The secondary transfer roller for pressing the intermediate transfer belt against the transfer member, wherein the hardness of the roller portion of the primary transfer roller for pressing the intermediate transfer belt against the image carrier at the last primary transfer portion is determined. 8. The tandem-type color image forming apparatus according to claim 1, wherein the hardness of said roller portion is higher than that of said roller portion. 9. The secondary transfer roller for pressing the intermediate transfer belt against the transfer member, wherein the hardness of the roller portion of the primary transfer roller for pressing the intermediate transfer belt against the image carrier at the last primary transfer portion is determined. 8. The tandem type color image forming apparatus according to claim 1, wherein the hardness of the roller portion is the same as that of the roller portion. 10. A plurality of primary transfer portions, which are sequentially arranged on an intermediate transfer belt and transfer a toner image of an image carrier developed on an electrostatic latent image to the intermediate transfer belt, A tandem-type color image forming apparatus provided with a secondary transfer section for transferring a primary-transferred toner layer to a transfer body, wherein each of the primary transfer sections presses an intermediate transfer belt against an image carrier. A tandem-type color image forming apparatus characterized in that the force increases sequentially.