JPH09185268A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate transfer paper without image disturbance by means of a simple structure by providing a transfer-paper separation roller on the side of the inner surface of an intermediate transfer belt and downstream from the transfer position of the intermediate transfer belt in the direction of the rotation of the belt. SOLUTION: The transfer-paper separation roller 30 is arranged on the side of the inner surface of the intermediate transfer belt positioned downstream from the transfer position of the intermediate transfer belt in the direction of the rotation of the belt. By means of an elastic material 30a such as a coil spring, an elastic force is exerted to the separation roller 30 toward the inner surface of the belt, thereby making the belt project toward its periphery, and the curvature of the belt in this energizing position is given along the curvature of the periphery of the separation roller 30 into the shape of R. This transfer-paper separation roller 30 is formed from a roller member which is smaller than a backup roller 57A in radius, and obtains a nip in a transfer position. Further, it is preferable that the center of the rotation of the transfer roller 19 be in an area between a straight line L1 connecting the center of the rotation of the intermediate transfer belt and the center of the backup roller 57A and a straight line L2 connecting the center of the rotation of the intermediate transfer belt and the center of the separation roller 30.

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 for sequentially transferring a toner image of each color formed on a surface of a photosensitive drum onto an intermediate transfer belt and then transferring the toner image onto a transfer paper to obtain a color image. The present invention relates to an improvement in an image forming apparatus using a transfer paper separating device that separates a transfer paper from an intermediate transfer belt.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic system for forming a color image by superimposing toner images of respective colors such as cyan, magenta, and yellow, the toner image is not directly superposed on a transfer paper, but a cylindrical intermediate transfer belt is used. There is an intermediate transfer system in which toner images of respective colors are superposed on a belt-shaped endless transfer sheet, and then the superposed color image is transferred again to a recording medium.

As such an intermediate transfer system, for example, as shown in Japanese Patent Application Laid-Open No. 5-265331, toner images of respective colors formed on a photosensitive member are temporarily transferred to a cylindrical intermediate transfer belt which is internally held by a backup roller. After performing various color overlapping, the transfer paper is conveyed to a nip portion formed by the intermediate transfer belt and the transfer roller, and transferred onto the transfer paper surface to form a color image.

[0004]

The above-mentioned technique is used in the nip portion formed by the intermediate transfer belt and the transfer roller.
It is common that the intermediate transfer belt has a large curvature and the transfer roller has a small curvature, and the transfer paper that passes through the nip portion of both when transferring the toner image to the paper has a large curvature. It will be pulled around the belt and wrapped around. For this reason, only a special thick paper having strong elasticity can be used, or a jam of the transfer paper or the like occurs, so that the separating claw is used for peeling. However,
Such a configuration not only increases the cost, but also when forming a color image due to color superposition, there is a possibility that image distortion may occur due to vibration or the like. Further, when the separating claw is used, the separating claw comes into contact with the unfixed toner image, and vertical stripes are likely to occur.

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide an image forming apparatus having a simple structure and capable of peeling a transfer sheet without image distortion.

[0006]

In order to solve the above-mentioned problems, the present invention does not separate the transfer paper by using the nip of the transfer roller as in the prior art, but separates the toner from the transfer means. The transfer means and the separating means are effectively combined to further enhance the separation effect of the transfer paper. That is, the invention according to claim 1 is in contact with an intermediate transfer belt having a backup roller in contact with the inner peripheral side thereof, in contact with the surface of the intermediate transfer belt, and in opposition to the backup roller via the intermediate transfer belt. A transfer roller arranged so that the toner can be carried on the surface of the intermediate transfer belt, and the transfer paper is conveyed to a nip portion formed by the intermediate transfer belt and the transfer roller to transfer the toner to the transfer paper. In an image forming apparatus configured to be transferable to the surface, a transfer paper separating roller is arranged on the inner peripheral surface side of the intermediate transfer belt located downstream of the transfer position of the intermediate transfer belt in the belt rotation direction. Of the transfer paper is urged toward the inner peripheral surface of the belt so that the belt curvature at the urged position is formed along the curvature of the peripheral surface of the separating roller. And performing separation.

According to this invention, even if the curvature of the intermediate transfer belt is large, the curvature of the intermediate transfer belt at the portion where the transfer paper is separated can be made small. Since the transfer paper is separated from the surface and is discharged in the direction away from the intermediate transfer belt, it does not wind around the intermediate transfer belt. Further, since the belt curvature for separating the transfer paper can be set independently of the nip of the transfer roller, while ensuring a sufficient nip amount necessary for transfer, the curvature of the separating belt is arbitrarily set by the separating roller. Therefore, more specifically, the most preferable separation curvature can be set by setting the transfer paper separating roller as a roller having a radius smaller than that of the backup roller.

Further, in this case, by forming the intermediate transfer belt from a PEEK material whose surface charge is rapidly attenuated,
The charges generated by the transfer are attenuated by the time they reach the separation position, which enables more efficient separation.

Further, the separation of the transfer paper is not necessarily separated only by the curvature, but may be combined with the electrostatic separation.
For such electrostatic separation, the intermediate transfer belt is formed by a resistor belt having a volume resistivity in the medium resistance region of 10 ¹⁰ to 10 ¹⁴ Ω · cm, and a bias is applied to the transfer paper separating roller. Alternatively, it is preferable to provide a transfer paper separation electrode on the outer peripheral surface side of the intermediate transfer belt from the transfer position outlet side to the biasing position of the transfer paper separation roller.

Further, in the transfer roller of the present invention, the center of rotation of the transfer roller is a first straight line connecting the center of rotation of the intermediate transfer belt and the center of the backup roller, and the second center of rotation is the center of rotation of the intermediate transfer belt and the center of the separation roller. It is preferable to place it in a region sandwiched by straight lines.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an image forming apparatus to which the present invention is applied, and FIG. 2 is an explanatory diagram for explaining the vicinity of a transfer portion, which is a characteristic portion of the present invention.

In the image forming apparatus according to the embodiment of the present invention, as shown in FIG. 1, a light beam from a light source (not shown) is mirrored by an optical scanning system 1 including a polygon mirror 2, a lens system 3 and the like. , 6 and 7, 8 through the photosensitive drum 9
Irradiate A and 9B to form an electrostatic latent image. Note that 87
A and 87B are photosensitive members 9A prior to the formation of the electrostatic latent image.
And 9B are chargers for uniformly charging the surface. Then, on the photosensitive drum 9A, the black toner developing device 10
A and a developing device 10B for magenta toner are attached,
The photoconductor drum 9B has a developing device 10 for cyan toner.
A developing device 10D for C and yellow toner is attached.

The surfaces of the photosensitive drums 9A and 9B are in contact with an intermediate transfer belt 11 which is an endless belt formed in a cylindrical shape. The intermediate transfer belt 11 has a volume resistivity of 10 ¹⁰ to ¹⁰ 10.
It is a resistor in the medium resistance region of ¹⁴ Ω · cm and has a thickness of 15
It is about 0 μm and is flexible and hardly stretchable. For example, polycarbonate, polyimide, polyether (PEE).
K) or the like. Although not shown, flanges are arranged at both ends of the intermediate transfer belt 11 formed in a cylindrical shape. Both ends of the intermediate transfer belt 11 are adhered to the flanges, and the flanges are connected to a driving source so that the intermediate transfer belt 11 can be formed.
Is configured to be rotatable.

The latent images on the surfaces of the photosensitive drums 9A and 9B are sequentially developed by the developing devices 10A to 10D one by one for each rotation of the drum, and are primary-transferred onto the intermediate transfer belt 11 by electrostatic force. After the transfer of one color is completed, the photosensitive drums 9A and 9B are cleaned by the cleaner mechanisms 88A and 88B to remove the residual toner, and then charged again to the chargers 87A and 87B.
And another color is developed on the photosensitive drums 9A and 9B through latent image formation by the optical scanning system 1. Specifically, black is transferred from the photosensitive drum 9A to the intermediate transfer belt 11,
Thereafter, the intermediate transfer belt 11 rotated to the position of the photoconductor drum 9B transfers the cyan color from the photoconductor drum 9B.

On the other hand, the photoconductor drum 9A removes the residual toner after transferring the black color to the intermediate transfer belt 11 by a cleaner mechanism 88.
A is removed, the magenta color is developed, and the magenta color is transferred to the intermediate transfer belt 11. Similarly, on the photosensitive drum 9B, after the cyan color is transferred, the residual toner is removed by the cleaner mechanism 88B and the yellow color is developed, and then the transfer is performed.

When the four color toners are transferred onto the intermediate transfer belt 11, the transfer paper 2 stored in the paper cassette 14 is transferred.
6 is conveyed to the nip portion 30 formed by the intermediate transfer belt 11 and the transfer roller 19, which is a feature of the present invention, through the reversing passage 16 and the passage 17 by the roller 15, the registration roller 18, and the transfer paper 26. The toner for forming each image is transferred onto the transfer sheet 26, and the transferred transfer sheet 26 is separated from the transfer sheet 26 by utilizing the curvature of the intermediate transfer belt located downstream of the transfer position of the intermediate transfer belt in the belt rotation direction. To do. Then, after the transfer paper 26 is separated by the above-described action and is discharged from the conveying device 20, the fixing portion 2 is fixed by the conveying belt 21.
2 is transferred. In the fixing unit 22, the fixing roller 2
3 is fixed by the pressure roller 24 and the pressure roller 24, and is discharged to the outside by the feed roller 25.

A cleaning device 13 cleans untransferred toner on the surface of the intermediate transfer belt 11.
Reference numeral 12a is a blade that directly contacts the intermediate transfer belt 11, and 12b is a rubbing roller. The untransferred toner is scraped off by the blade 12a and the rubbing roller 12b, sent in the axial direction by the toner carrying device 12c, and collected in a collecting container (not shown).

Further, backup rollers 57A to 57D made of sponge rubber or soft rubber rollers are provided inside the intermediate transfer belt 11, and backup auxiliary rollers 58A, 58 made of rubber rollers having high hardness.
B is provided with transfer backup rollers 59A and 59B composed of a conductive rubber roller having higher hardness and capable of applying a transfer bias, and these are biased to the intermediate transfer belt 11 by a predetermined pressing force to perform intermediate transfer. The belt 11 is configured to be rotatable around the shaft 53.

Next, the construction around the transfer sheet position, which is the main construction of the present invention, is constructed based on FIG. Intermediate transfer belt 1
As for the curvature at the transfer position of 1, the transfer paper separating roller 30 is arranged on the belt inner peripheral surface side, and the separating roller 30 is directed toward the belt inner peripheral surface side by using a coil spring, rubber or other elastic material 30a. An elastic force is applied, in other words, the peripheral surface of the separating roller 30 is utilized to urge the belt so as to project toward the outer peripheral side, whereby the belt curvature at the energized position is determined by the peripheral surface of the separating roller 30. It is curved in an R shape along the surface curvature. At this time, the radius of curvature of the intermediate transfer belt 11 is 60 m.
In the case of m, it is sufficient that the protruding amount is about 1 to 2 mm.

Further, the transfer paper separating roller 30 is formed of a roller member having a radius smaller than that of the backup roller 57A to secure a nip at the transfer position. The intermediate transfer belt 11 has a volume resistivity of 10 ¹⁰ to 10 ¹⁴ Ω · c.
Resistor belt in the medium resistance region of m, specifically PEE
It is preferable to use K material. Alternatively, a PC material and a PET material may be used. In this case, a transfer paper separation bias may be applied to the transfer paper separation roller 30 in order to promote the electrostatic separation effect.

The bias is applied to the transfer paper separating electrode 27 on the outer peripheral surface side of the intermediate transfer belt 11 from the transfer position outlet side to the biasing position of the transfer paper separating roller 30 and is applied to the electrode. May be. The backup roller 57A is formed of a rubber roller made of sponge rubber or soft rubber, while the transfer roller 19 is harder than the backup roller 57A, specifically, the peripheral surface of the transfer roller 19 can be concavely curved on the peripheral surface of the backup roller 57A. Of a hard conductive roller, the transfer roller 19 is bitten into the peripheral surface of the backup roller 57A to secure a sufficient nip amount, and a DC transfer bias having a polarity opposite to that of the charged toner is applied to the transfer roller 19. ing.

Further, the rotation center of the transfer roller is the rotation center of the intermediate transfer belt 11 and the backup roller 57A.
A first straight line L ₁ connecting the centers, and a second straight line L ₂ connecting the center of rotation of the intermediate transfer belt 11 and the center of the separation roller 30.
It is better to place them in the area sandwiched by.

[0023]

EXAMPLE Next, in the above-described embodiment, the separation state of the transfer sheet 26 is confirmed based on the transfer sheet separating roller 30, the arrangement angle of the transfer roller, and the presence or absence of the separation electrode 27. First,
PE with a film thickness of 150 μm and volume resistivity of 1.3 × 10 ¹⁴ .
Using the intermediate transfer belt 11 made of EK material, the rotation radius of the intermediate transfer belt 11 is 67.5 mm, the backup roller 57A has a radius of 20 mm, and the transfer roller 19 has a radius of 20 m.
m, the radius of the transfer paper separating roller 30 is 12 mm, and the direct current transfer bias applied to the transfer roller 19 is 2.5 kv and the printing density is 5%.
5 g, 90 g, and 128 g) and OHP paper are used to dispose the transfer roller and the separation roller 30 at the position shown in FIG. (Locus position) When protruding by 1.5 mm (Example 1)
When the separation efficiency of the transfer paper was confirmed for each of 10 sheets with the case of not projecting (Comparative Example 1), it was possible to separate with a probability of 100% in the case of Example 1 for both plain paper and OHP paper. In Comparative Example 1, none of them could be separated except 128 g of plain paper. In each of Example 1 and Comparative Example 1, the center of rotation of the transfer roller 19 is the first straight line L ₁ connecting the center of rotation of the intermediate transfer belt 11 and the center of the backup roller 57A, and the center of rotation of the intermediate transfer belt 11. And a second straight line L ₂ connecting the center of the separation roller 30 with each other, specifically, a second straight line about 1 mm from the intersection (nip center position) connecting the first straight line L ₁ and the intermediate transfer belt 11. It is displaced (dx: +1 mm) toward the L ₂ side.

Next, the transfer roller is reversed from the first embodiment,
The transfer roller 1 is more than the first straight line L ₁ connecting the rotation centers of the intermediate transfer belt 11 and the backup roller 57A.
The center of rotation of the transfer roller 19 is located on the upstream side of the transfer paper conveyance direction.
Specifically, the first straight line L is positioned so that the rotation center of
Intersection point between ₁ and intermediate transfer belt 11 (nip center position)
About 1 mm (dx: -1 mm), the sheets were arranged on the upstream side with a shift, and the other conditions were exactly the same as those in Example 1 (Example 2). As a result, plain paper could be separated with 100% probability. However, OHP paper could not be separated by about (6/10).

Next, in the second embodiment, a transfer paper separating electrode 27 is provided on the outer peripheral surface side of the intermediate transfer belt 11 substantially corresponding to the urging position of the transfer paper separating roller 30, and the separating electrode 27 is about 2.5 Kv. Where a separation voltage is applied, plain paper,
Separation was possible with 100% probability in any case of OHP paper.

[0026]

According to the present invention, even if the curvature of the intermediate transfer belt is large, the radius of curvature of the intermediate transfer belt that separates the transfer paper is small. The transfer paper is separated, and the transfer paper is ejected in the direction away from the intermediate transfer belt so that it does not wind around the intermediate transfer belt. With a simple configuration, it is possible to peel the transfer paper without image distortion. .

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a structure near a transfer-separation roller position, which is a main part structure of the present invention.

[Explanation of symbols]

 11 Intermediate Transfer Belt 19 Transfer Roller 26 Transfer Paper 27 Separation Electrode 57A Backup Roller 30 Separation Roller 30a Elastic Material

Claims (6)

[Claims] 1. An intermediate transfer belt having a backup roller abutting on an inner peripheral side thereof, and a transfer roller abutting on a surface of the intermediate transfer belt and being opposed to the backup roller via the intermediate transfer belt. And the toner can be carried on the surface of the intermediate transfer belt, and the toner can be transferred to the surface of the transfer paper by conveying the transfer paper to a nip portion formed by the intermediate transfer belt and the transfer roller. In the image forming apparatus configured as described above, the transfer paper separating roller is arranged on the inner peripheral surface side of the intermediate transfer belt located downstream of the transfer position of the intermediate transfer belt in the belt rotation direction, and the peripheral surface of the separating roller is By urging the inner peripheral surface of the belt, the curvature of the belt at the urging position is formed along the peripheral curvature of the separating roller, and the transfer paper is separated by using the belt curvature. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the transfer paper separating roller is a roller having a radius smaller than a backup roller. 3. The intermediate transfer belt has a volume resistivity of 10
The image forming apparatus according to claim 1, wherein the image forming apparatus is formed by a resistor belt in a medium resistance region of ¹⁰ to 10 ¹⁴ Ω · cm, and a bias is applied to the transfer paper separating roller. 4. The intermediate transfer belt has a volume resistivity of 10
^A transfer belt separating electrode is formed on the outer peripheral surface side of the intermediate transfer belt from the transfer position outlet side to the biasing position of the transfer paper separating roller, while being formed by a resistor belt in the medium resistance region of ¹⁰ to 10 ¹⁴ Ω · cm. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided. 5. The image forming apparatus according to claim 1, wherein the intermediate transfer belt is formed of a PEEK material. 6. The center of rotation of the transfer roller is sandwiched by a first straight line connecting the center of rotation of the intermediate transfer belt and the center of the backup roller and a second straight line connecting the center of rotation of the intermediate transfer belt and the center of the separation roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged in a region.