JP2005316104A - Transfer apparatus and image forming apparatus equipped with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer apparatus capable of satisfactorily transferring an image, irrespective of the thickness and kind of a recording medium, and also, which is excellent in long durability, and to provide an image forming apparatus equipped with the transfer apparatus capable of always forming an image of good quality in a stable state. <P>SOLUTION: Regarding the transfer apparatus 90 provided with an image carrier 20, a transfer belt 100 for transporting the recording medium P while holding the medium P together with the image carrier 20, and a transfer roll 30 arranged opposite to the image carrier 20 so as to freely rotatably stretch the transfer belt 100, and for transferring the toner image on the image carrier 20 to the recording medium P, the transfer roll 30 is provided with a supporting shaft 30a, an elastic base material layer 30b arranged on the circumference of the supporting shaft 30a, and at least one or more surface layers 30c having hardness higher than that of the layer 30b, and arranged on the surface of the layer 30b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transfer device that electrostatically transfers a toner image on an image carrier to a recording medium, and more particularly to a transfer device including a transfer belt. The present invention also relates to an image forming apparatus such as a color printer, a copying machine, a facsimile, or the like provided with this transfer device.

Japanese Patent Laid-Open No. 8-234581 JP 2002-189353 A

  Conventionally, an image forming apparatus using an electrophotographic method has been widely used. This image forming apparatus forms a static electrostatic image by uniformly charging a photosensitive member and irradiating light based on image information, and developing the electrostatic static image to form a toner on the photosensitive member. The image is transferred directly or indirectly to the recording medium via an intermediate transfer member, and the toner image transferred onto the recording medium is fixed to form an image on the recording medium.

  Patent Documents 1, 2 and the like disclose a transfer device using a transfer belt as transfer means used in an image forming apparatus using an electrophotographic system. The transfer device using the transfer belt has an advantage that both transfer efficiency and separation effect can be transferred satisfactorily even when a relatively thin recording paper is used in a high humidity environment. Further, in the transfer device disclosed in Patent Document 2, the belt width of the belt layer having the smallest elongation rate of the belt composed of a plurality of layers is set to the roller width of the stretching roller having the shortest roller width among the plurality of stretching rollers. By setting the belt width as follows, both end portions of the belt layer having the smallest elongation rate are less likely to protrude outward from the stretching roller, and cracks at both end portions of the belt layer are prevented. .

  However, in the transfer device having a transfer belt disclosed in Patent Document 1 or 2, when a thick recording paper is continuously used, the surface of the transfer belt 95 at the end portion of the recording paper (P) is used. Concentration of shear stress (E) is unavoidable, and cracks (K) in the conveying direction (C) occur on the surface of the transfer belt 95 (FIG. 6). For this purpose, for example, after a large number of toner images are transferred onto a narrow recording sheet, such as supplying the longitudinal direction of a B5 size or A4 size recording sheet along the transport direction, for example, the A4 size or B4 size If the toner image is transferred to a wide recording paper, such as supplying the longitudinal direction of the recording paper substantially orthogonal to the transport direction, the image may deteriorate due to circumferential cracks on the surface of the transfer belt. is there.

  Therefore, the present invention has been made in view of the above-mentioned problems of the prior art, and the problem to be solved by the present invention is that it can be transferred well regardless of the thickness and type of the recording medium and is excellent in long-term durability. Another object of the present invention is to provide an image forming apparatus including the transfer apparatus, and an image forming apparatus that can always provide good and stable image formation.

  The transfer device of the present invention includes an image carrier, a transfer belt that conveys a recording medium between the image carrier, and a transfer belt that is disposed to face the image carrier and is rotatably stretched. And a transfer device that transfers a toner image on the image carrier to a recording medium. The transfer roller includes a support shaft, an elastic base layer outside the support shaft, and the elastic base. It has at least one surface layer having a hardness higher than that of the elastic base material layer on the surface of the material layer.

The transfer device of the present invention, the hardness of the elastic substrate layer (H _1), the relationship between the hardness (H ₂₎ of the surface layer can be expressed by the following formula 2 or formula 3.
Formula 2: H ₁ <H ₂
Formula 3: H ₁ / H ₂ <1

  An image forming apparatus according to the present invention includes the transfer device according to the present invention as a transfer unit. The image forming apparatus of the present invention is an image forming apparatus comprising an image forming unit, the transfer device of the present invention, and a fixing unit, wherein the image carrier is an intermediate transfer unit, and the image forming unit is The toner image formed on the photosensitive member is primarily transferred onto the intermediate transfer member, and the toner image on the intermediate transfer member is secondarily transferred onto a recording medium using the transfer device. It is possible to employ a configuration in which the toner image transferred onto the toner image is fixed using the fixing unit.

  The image forming apparatus of the present invention is an image forming apparatus comprising an image forming unit, the transfer device of the present invention, and a fixing unit, wherein the image carrier is a photoconductor, and the image forming unit. The toner image formed on the photoreceptor using the transfer device is transferred to a recording medium using the transfer device, and the toner image transferred onto the recording medium is fixed using the fixing unit. You can also

  According to the transfer apparatus of the present invention, even when a relatively thick recording medium is used, the surface of the elastic base layer of the transfer roll has at least one surface layer having a hardness higher than that of the elastic base layer. Therefore, it is possible to bear the strain load due to the compression pressure at the transfer nip on the transfer roll side, and it is possible to reduce the concentration of shear stress at the end position of the recording medium on the transfer belt surface, Generation of cracks on the surface of the transfer belt can be suppressed, and toner image transfer can be stably realized.

  In addition, according to the image forming apparatus of the present invention, it is possible to prevent image formation defects due to cracks on the surface of the transfer belt, and it is possible to realize good and stable image formation without being affected by environmental fluctuations. .

In the transfer device of the present invention, the hardness (H ₁ ) of the elastic base material layer measured by the type C hardness test of JIS K7312 and the hardness of the surface layer (H ₂ ) measured by the type C hardness test. )
Formula _{1: (H 2/33)} × (91-H 2) <H 1 <H 2
It is preferable that the relationship is By having this relationship, the occurrence of cracks on the surface of the transfer belt can be suppressed even if there are variations in diameter and base layer thickness between the plurality of rolls on which the transfer roll is stretched.

  In the transfer device of the present invention, the hardness of the side surface of the transfer roll, measured in the hardness test, is preferably 35 degrees or less, and more preferably 30 degrees or less. Thereby, a transfer nip having a favorable size can be easily secured, and transfer can be performed more satisfactorily.

  In the transfer device of the present invention, it is preferable that the transfer roll has a cylindrical shape or a drum shape. By making the shape of the transfer roll in this way, it is possible to prevent the transfer roll from being displaced due to misalignment of a plurality of rolls that stretch the transfer belt, and to suppress the occurrence of cracks on the surface of the transfer belt. .

  Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited thereby.

In the following examples, each hardness evaluation was performed by a type C hardness test according to JIS K7312 using an Asker C type rubber / plastic hardness meter. However, the hardness of the secondary transfer roller 30 of the elastic substrate layer 30b (H ₁₎ and hardness of the surface layer 30c (H ₂₎ is obtained by measurement by forming a material for forming the respective layers of 5mm thick is there. Further, the hardness of the side surface of the secondary transfer roll 30 is obtained by directly measuring the hardness of the side surface portion of the secondary transfer roll 30 in the type C hardness test.

  FIG. 1 is a schematic configuration diagram showing a transfer device 90 according to the first embodiment of the present invention. The transfer device 90 conveys the recording sheet P between the intermediate transfer belt 20 and the intermediate transfer belt 20, which is a toner image carrier and circulates and moves in the direction of the arrow B, in the direction of the arrow D. In this way, an endless belt-shaped secondary transfer belt 100 that is stretched around the secondary transfer roll 30 and the support roll 101 on the outer surface side of the intermediate transfer belt 20 and circulates in the direction of the arrow C, and the intermediate transfer The belt 20 is provided with a secondary transfer belt 100 and a backup roll 23 disposed so as to face the secondary transfer roll 30 on the inner surface side of the belt 20, and the toner image on the outer surface of the intermediate transfer belt 20 is, for example, a recording sheet or an OHP sheet The recording sheet P is electrostatically transferred.

Here, the secondary transfer belt 100 is a surface layer in which conductive carbon black is dispersed in various rubbers such as chloroprene and EPDM (ethylene propylene diene) and the surface thereof is coated with PTFE-dispersed urethane emulsion or the like. The volume resistivity is 10 ⁶ to 10 ¹² Ωcm and the thickness is 0.45 mm.

The secondary transfer roll 30 has a substantially cylindrical shape and is a grounded conductive roll having a width of 350 mm. The surface potential of the secondary transfer roll 30 is always kept equal to the ground position. As shown in FIG. 2, the secondary transfer roll 30 has a support shaft 30a, an elastic base material layer 30b outside the support shaft 30a, and a surface layer 30c on the surface of the elastic base material layer 30b. The support shaft 30a is made of aluminum. The elastic base material layer 30b is made of polyurethane foam rubber imparted with conductivity by carbon black, and has a hardness (H ₁ ) of 10 degrees according to a type C hardness test. The surface layer 30c is made of polyethylene propylene diene foamed rubber imparted with conductivity by carbon black, and has the same hardness (H ₂ ) of 90 degrees. The thickness of the surface layer 30c is 0.5 mm. At this time, the hardness of the side surface of the secondary transfer roll 30 was 20 degrees.

The transfer device of this embodiment, the secondary transfer roll 30, and the hardness of the elastic substrate layer 30b (H _1), since the relationship between the hardness (H ₂₎ of the surface layer 30c is in a predetermined range, for example, Even when a relatively thick recording medium of about 300 g / m ² is used, generation of cracks on the surface of the secondary transfer belt can be suppressed. Further, since the hardness of the side surface of the secondary transfer roll 30 is relatively soft and rich in elasticity, a transfer nip having a good size can be easily secured, and even when a relatively thick recording medium is used, the image can be obtained. The transfer of the toner image on the carrier to the recording medium can be realized satisfactorily and stably.

  In the transfer device of the present invention, the material constituting the surface layer 30c of the secondary transfer roll 30 may be appropriately selected as long as it has predetermined conductivity and hardness. In addition to the above, polyimide, polycarbonate, Resins such as polyester, polypropylene, polyethylene terephthalate, acrylic, vinyl chloride, or various rubbers containing a suitable amount of conductive carbon black can be used.

  Next, the color image forming apparatus 1 provided with the transfer device 90 of Example 1 will be described. FIG. 4 is a schematic configuration diagram showing the color image forming apparatus 1. The color image forming apparatus 1 can be used not only as a color printer, but also as an image forming unit and an output unit of a copier, a facsimile machine, or a multifunction machine that combines various functions.

  The color image forming apparatus 1 is provided with a photosensitive drum 10 having an organic photosensitive layer formed on the outer peripheral surface thereof and driven to rotate in the direction of arrow A. A charging device (for example, a roll-type charging device) is provided around the photosensitive drum 10. 11. Latent image writing device (for example, laser beam scanner) 12, yellow (Y), magenta (M), cyan (C) and black (B) developing devices 14Y, 14M, each containing toner of one color. The photosensitive drum cleaning device 15 cleans the surface of the rotary developing device 14, the intermediate transfer belt 20, and the photosensitive drum 10 after the primary transfer. Etc. are arranged in this order.

The intermediate transfer belt 20 is made of a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate, acrylic, vinyl chloride, or various rubbers containing carbon black as an antistatic agent and has a width of 364.8 mm. The volume resistivity is 10 ⁶ to 10 ¹⁴ Ωcm, and the thickness is 0.1 mm. It is stretched around a plurality of support rolls 21 to 24 (for example, a drive roll 21, a driven roll 22, a secondary transfer backup roll 23, and a tension roll 24) in a state where the photosensitive drum 10 is in contact with the surface to be the primary transfer position. , And is arranged to be driven to rotate in the direction of arrow B. Here, the surface moving speed of the photosensitive drum 10 is 220 mm / sec, and the intermediate transfer belt 20 moves with a speed difference of + 0.25% with respect to this speed.

At the primary transfer position where the intermediate transfer belt 20 comes into contact with the photosensitive drum 10, the intermediate transfer belt 20 is brought into contact with the photosensitive drum 10 from the inner surface side of the intermediate transfer belt 20 to form a primary transfer contact portion N1. A primary transfer device (for example, a primary transfer roll 25) that realizes electrostatic transfer is provided. The primary transfer roll 25 is made of urethane foam rubber having a width of 312 mm and a volume resistivity of 10 ⁶ to 10 ⁸ Ωcm, and a primary transfer bias voltage having a polarity opposite to the charging polarity of the toner is applied from a bias power source (not shown). It has come to be. Further, around the intermediate transfer belt 20, an intermediate transfer belt cleaning device 50 for cleaning the outer surface of the intermediate transfer belt 20 after the secondary transfer, and a reference position mark formed or pasted on the surface of the intermediate transfer belt 20 are provided. A belt position detection sensor 28 for detection is provided.

  At the secondary transfer position stretched around the backup roll 23 of the intermediate transfer belt 20, a secondary transfer roll 30 is disposed on the outer surface side of the intermediate transfer belt 20. The stretched secondary transfer belt 100 and the intermediate transfer belt 20 come into contact with each other to form a secondary transfer contact portion N2. The backup roll 23 has a width of 344 mm and is formed by covering an insulating roll with a semiconductive thin film, which is formed to a thickness of 10 μm to 200 μm. In addition, at this secondary transfer position, a power supply roll 31 that contacts the peripheral surface of the backup roll 23 is disposed. As a result, at the secondary transfer position, a secondary bias voltage having the same polarity as the toner charging polarity is applied to the backup roll 23 via the power supply roll 31 from a bias power source (not shown).

  The secondary transfer belt cleaning device 106 is disposed on the surface of the secondary transfer belt 100 in the vicinity of the transfer contact portion N and upstream of the transfer contact portion N.

  Further, around the intermediate transfer belt 20, an intermediate transfer belt cleaning device 50 including a cleaning brush is provided between the backup roll 23 and the tension roll 24, on the downstream side of the backup roll 23 and on the tension roll 24. It is arranged at a position close to it.

  The secondary transfer roll 30 and the cleaning device 50 are disposed so as to be in contact with and away from the intermediate transfer belt 20 by a predetermined displacement mechanism. In this embodiment, when a color image is formed, the secondary transfer is performed from the time before the primary transfer of the first color toner image constituting the color image to the time when the final color toner image is primarily transferred to the intermediate transfer belt 20. The belt 100 and the cleaning device 50 are set to be separated from the intermediate transfer belt 20.

  The color image forming apparatus 1 includes a sheet storage tray 35 that stores a recording sheet P as a recording medium, a feeding mechanism 36 that feeds the recording sheet P from the sheet storage tray 35, and a pair of transport rollers 37 that transport the recording sheet P. Then, after the recording sheet P is temporarily stopped, a registration roll pair 38 fed to the transfer contact portion N2 between the intermediate transfer belt 20 and the secondary transfer roll 30 at the secondary transfer position in accordance with the secondary transfer timing. Prepare. In FIG. 4, the conveyance path of the recording sheet P is indicated by a dotted line.

  The fixing device 40 for fixing the toner image secondarily transferred to the recording sheet P includes a heating roll 41 and a pressure roll 42 that rotate while being pressed against each other. The pressure roll 42 may also have a heating function. The discharge roll pair 43 discharges the recording sheet P after fixing out of the apparatus.

  Basic image formation by the color image forming apparatus 1 is performed as follows. First, upon receiving an instruction to start the image forming process, the photosensitive drum 10 starts to rotate, and the surface of the photosensitive drum 10 is charged to a predetermined dark potential by the charger 11 and then emitted from the latent image writing device 12 in accordance with the image signal. The light beam Bm is exposed to form an electrostatic latent image. Subsequently, the developing device 14 rotates the rotary support 13 by a predetermined angle to expose the developing devices (14Y, 14M, 14C, 14K) containing toner corresponding to the color of the electrostatic latent image. The developer is moved to a developing position facing the drum 10, and in this state, a developing bias voltage is applied to generate a developing electric field, and the toner is attached to the electrostatic latent image for development.

  By this development, a toner image T having a predetermined color component is formed on the photosensitive drum 10. Next, the toner image T formed on the photosensitive drum 10 is conveyed to the primary transfer contact portion N1 where the photosensitive drum 10 and the intermediate transfer belt 20 are in contact with the rotation of the photosensitive drum 10, and at this timing. In addition, a primary transfer bias voltage is applied to the primary transfer roll 25. As a result, the toner image T is primarily transferred from the photosensitive drum 10 onto the outer surface of the intermediate transfer belt 20 by receiving an electrostatic action due to a transfer electric field formed between the photosensitive drum 10 and the primary transfer roll 25. The surface of the photosensitive drum 10 after the primary transfer is cleaned by removing residual toner and the like by the cleaning device 15.

  Here, when forming a single color image, the single color toner image T primarily transferred onto the intermediate transfer belt 20 is immediately secondarily transferred to the recording sheet P at the secondary transfer portion. In the case of forming a color image in which the toner images are superimposed, the process of forming each toner image on the photosensitive drum 10 and the primary transfer process of each toner image are repeated by the number of colors. For example, when a full color image is formed by superimposing four color toner images, yellow, magenta, cyan, and black toner images are formed in this order on the photosensitive drum 10, and the intermediate transfer belt 20 is successively formed in that order. And the primary transfer.

  Subsequently, the toner image T primarily transferred to the intermediate transfer belt 20 is conveyed to the secondary transfer contact portion N2 where the intermediate transfer belt 20 and the secondary transfer belt 100 are in contact with the rotation of the intermediate transfer belt 20. In addition, the secondary transfer belt 100 and the cleaning device 50 that are stretched around the secondary transfer roll 30 in accordance with this timing are in contact with the intermediate transfer belt 20, and the backup roll 23 is connected to the secondary roll via the power supply roll 31. A transfer bias voltage is applied. Further, in accordance with this timing, the recording sheet P is transported from the sheet storage tray 36 by the transport force of each roll pair 36 to 38, and the secondary transfer contact between the intermediate transfer belt 20 and the secondary transfer belt 100 is performed. Sent to part N2. As a result, the toner image T is subjected to secondary transfer from the intermediate transfer belt 20 to the recording sheet P in a lump by receiving an electrostatic action due to a transfer electric field formed between the backup roll 23 and the secondary transfer roll 30. Is done. Further, the outer surface of the intermediate transfer belt 20 after the secondary transfer is cleaned by removing residual toner and the like by the cleaning device 50.

  Finally, the recording sheet P onto which the toner image T is secondarily transferred is sent to the fixing device 40 and passes through a fixing nip portion that is a pressure contact portion between the heating roll 41 and the pressure roll 42 to fix the toner image. Is done. Thereafter, it is discharged out of the apparatus by the discharge roll 43 or the like. In this way, basic image formation is completed. When all the image forming operations are completed, the secondary transfer belt 100 and the cleaning device 50 are separated from the intermediate transfer belt 20 again.

(Evaluation experiment)
In the transfer device 90 of Example 1, two types of secondary transfer rolls in which the thickness of the surface layer 30c was changed to 0.1 mm and 2.5 mm were used, and the hardness (H ₁ ) of the elastic base material layer 30b and the surface layer The presence or absence of cracks on the surface of the secondary transfer belt 100 when the hardness (H ₂ ) of 30c was varied was evaluated. As the material of the surface layer 30c of the secondary transfer roll 30, EPDM (ethylene propylene diene) foamed rubber is used for a hardness of 10 to 90 degrees, and PI (polyimide resin) is used for a hardness of 100 degrees. In an appropriate amount. The hardness of the surface layer 30c is adjusted by the foaming rate and the amount of carbon black contained.

Specifically, the same stress as that when the intermediate transfer belt 20 in FIG. 1 is removed and 1,000,000 sheets of 300 g / m ² A4 size paper are continuously flowed is always applied to the surface of the secondary transfer belt 100. The paper was wound around the backup roll 23, and the backup roll 23 and the secondary transfer belt 100 were idled. Here, the total distance that the paper wound around the backup roll 23 passes through the transfer nip from the rotation speed of the backup roll 23 was converted into A4 size paper. Since the thickness of the surface layer 30c did not significantly affect the occurrence of cracks on the surface of the secondary transfer belt 100, Table 1 shows the evaluation results when the thickness of the surface layer 30c is 2.5 mm. .

Further, paying attention from the viewpoint of adhesion to the elastic substrate layer 30b of the surface layer 30c in the dimensionless quantity H ₁ / H ₂ in a ratio of both hardness and dimensionless quantity H ₁ / H ₂ in the vertical axis, the surface When the hardness (H ₂ ) of the layer 30c is taken as the horizontal axis, the results of Table 1 are again represented as a graph as shown in FIG. That is, in FIG. 3, cracks on the surface of the secondary transfer belt 100 did not occur in a region where the dimensionless amount H ₁ / H ₂ was larger than the black circle point of the experimental data. When the experimental data is linearly approximated, this relationship is expressed by the following equation 4.

Formula 4: (1/33) × (91−H ₂ ) <H ₁ / H ₂ <1

That is, if the hardness (H ₁ ) of the elastic base material layer 30b of the secondary transfer roll 30 is between the following formula 1, even if a relatively thick A4 size paper of 300 g / m ² is continuously run on 1,000,000 sheets. Even if transferred, no cracks have occurred on the surface of the secondary transfer belt 100.

Formula _{1: (H 2/33)} × (91-H 2) <H 1 <H 2

  The recording sheet P having a small thickness passes through the transfer nip without damaging the surface of the secondary transfer belt 100 and is conveyed by being electrostatically attracted to the secondary transfer belt 100. Therefore, it was confirmed that when the transfer device 90 of the present invention satisfying the relationship of Formula 1 was used, the surface of the secondary transfer belt 100 was not damaged regardless of the thickness of the recording medium.

  Moreover, if the hardness of the side surface of the secondary transfer roll 30 is 35 degrees or less, a transfer nip having a favorable size can be secured, and transfer can be performed more satisfactorily. Therefore, in the transfer device 90, if Expression 1 is satisfied and the hardness of the side surface of the transfer roll 30 is 35 degrees or less, the transfer is favorably performed regardless of the thickness of the surface layer 30c of the secondary transfer roll 30. In addition, it can be expected that transfer performance excellent in long-term durability can be obtained. In the range where surface cracks are not generated, the range where the hardness of the side surface of the secondary transfer roll 30 is 35 degrees or less corresponds to the range indicated by ◎ in Table 1.

FIG. 5 is a schematic configuration diagram showing a color image forming apparatus 1 according to the second embodiment of the present invention. In this color image forming apparatus 1, the transfer device 90 of the present invention is applied to an image forming apparatus having a tandem configuration. 5, components having the same reference numerals as those in FIG. 4 are the same as the components shown in FIG. Also in the transfer device 90 applied to the color image forming apparatus 1 in FIG. 5, the hardness (H ₁ ) of the elastic base material layer 30b of the secondary transfer roll 30 and the surface layer 30c are the same as in the transfer device of the first embodiment. Since the relationship with the hardness (H ₂ ) is within a predetermined range, the occurrence of cracks on the surface of the transfer belt can be suppressed even when a relatively thick recording medium of about 300 g / m ² is used. Further, since the hardness of the side surface of the transfer roll 30 is relatively soft and rich in elasticity, a transfer nip having a good size can be easily secured, and even when a relatively thick recording medium is used, the image carrier The transfer of the upper toner image to the recording medium can be realized satisfactorily and stably.

FIG. 1 is a schematic perspective view illustrating a transfer device 90 according to the first embodiment. FIG. 2 is a schematic cross-sectional view illustrating the secondary transfer roll 30 of the transfer device 90 according to the first embodiment. FIG. 3 is a graph showing a region where cracks on the surface of the secondary transfer belt 100 are not generated in relation to the dimensionless amount H1 / H2 and the hardness (H ₂ ) of the surface layer 30c. FIG. 4 is a schematic configuration diagram of a color electrophotographic copying machine using the transfer device 90 of the present invention. FIG. 5 is a schematic configuration diagram of a color electrophotographic copying machine showing an embodiment in which the transfer device 90 of the present invention is applied to an image forming apparatus having a tandem configuration. FIG. 6 is a schematic perspective view showing a conventional transfer device, and shows the occurrence of cracks on the surface of the transfer belt.

Explanation of symbols

  1: color image forming device, 9: image carrier, 10: photosensitive drum, 11: charging device, 12: latent image writing device, 14: rotary developing device, 15: cleaning device, 20: intermediate transfer belt (image carrier) Body), 21: drive roll, 22: driven roll, 23: backup roll, 24: tension roll, 25: primary transfer roll, 28: belt position detection sensor, 29: transfer roll, 30: secondary transfer roll, 30a: Support shaft, 30b: elastic base layer, 30c: surface layer, 31: power supply roll, 36: sheet storage tray, 36 to 38: roll pair, 40: fixing device, 41: heating roll, 42: pressure roll, 43 : Discharge roll, 50: intermediate transfer belt cleaning device, 90: transfer device, 95: transfer belt, 100: secondary transfer belt, 101: support roll, 1 6: the second transfer belt cleaning device, C: conveying direction of the transfer belt, E: shear stress, K: cracks, P: recording sheet (recording paper, recording medium), T: the toner image

Claims (6)

An image carrier, a transfer belt that conveys a recording medium between the image carrier, and a transfer roll that is disposed to face the image carrier and rotatably stretches the transfer belt. In the transfer device for transferring the toner image on the image carrier to a recording medium,
The transfer roll has a support shaft, an elastic substrate layer outside the support shaft, and at least one surface layer having a hardness higher than that of the elastic substrate layer on the surface of the elastic substrate layer. A transfer device characterized by. 2. The transfer device according to claim 1, wherein the hardness (H ₁ ) of the elastic base material layer measured by the type C hardness test of JIS K7312 and the hardness of the surface layer measured by the type C hardness test (2). H ₂ )
Formula _{1: (H 2/33)} × (91-H 2) <H 1 <H 2
A transfer device characterized by the following relationship:   3. The image forming apparatus according to claim 1, wherein the hardness of the side surface of the transfer roll measured in the hardness test is 35 degrees or less. 4.   4. The transfer device according to claim 1, wherein the transfer roll has a cylindrical shape or a drum shape. 5.   An image forming apparatus comprising an image forming unit, the transfer device according to any one of claims 1 to 4, and a fixing unit, wherein the image carrier is an intermediate transfer member, and the image forming unit The toner image formed on the photosensitive member is primarily transferred onto the intermediate transfer member using the means, the toner image on the intermediate transfer member is secondarily transferred onto a recording medium using the transfer device, and the recording is performed. An image forming apparatus for fixing a toner image transferred onto a medium using the fixing unit. An image forming apparatus comprising an image forming unit, the transfer device according to claim 1, and a fixing unit, wherein the image carrier is a photoconductor, and the image forming unit An image forming apparatus for transferring a toner image formed on the photoreceptor using a transfer device to a recording medium using the transfer device, and fixing the toner image transferred on the recording medium using the fixing unit .

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