JP4589167B2 - Transfer device and image forming apparatus - Google Patents

Description

The present invention relates to a transfer device such as a copying machine or a printer, and an image forming apparatus having the transfer device.

In the image forming apparatus comprising a secondary transfer device, comprising: an intermediate transfer belt; a bias roller that supports or drives the intermediate transfer belt; and a backup roller that contacts the bias roller via the intermediate transfer belt. There is a problem that the transfer electric field fluctuates due to a change in voltage accompanying a change in transfer current flowing from the roller to the bias roller or from the bias roller to the backup roller. Further, if it is attempted to eliminate such a variation in the transfer electric field, the variation in resistance in the axial direction of the backup roller increases, and there arises a problem that the toner image cannot be secondarily transferred stably.

Therefore, in order to solve such a problem, an attempt has been made to minimize the fluctuation of the secondary transfer current flowing from the bias roller to the backup roller or vice versa.
As a conventional technique relating to such a secondary transfer apparatus, Patent Document 1 discloses a backup roller of a secondary transfer apparatus using a cured film of a conductive paint in which a conductive agent having a small resistance variation in the usable resistance region is dispersed. An image forming apparatus having a surface layer formed thereon is disclosed. This image forming apparatus includes an image carrier on which an electrostatic latent image corresponding to image information is formed, a developing device that visualizes the electrostatic latent image formed on the image carrier as a toner image with toner, and an image carrier. An intermediate transfer belt on which a toner image carried on the toner image is primarily transferred, a bias roller for secondary transfer of an unfixed toner image on the intermediate transfer belt to a recording medium, and an intermediate transfer belt facing the bias roller. A backup roller supported from the back surface, the backup roller comprising a rubber roller coated with a cured film of a conductive paint in which two or more kinds of conductive agents having different characteristics are dispersed, and the two kinds of conductive agents having different polarities For example, granular carbon black having different shapes and conductive whiskers are used.
According to such an image forming apparatus, the surface resistivity of the backup roller is, for example, 10 ⁷ to 10 ¹⁰ Ω / □, the change in the resistance of the backup roller due to voltage application is small, and an electrode member is provided on the backup roller. Even when pressed, there is no possibility of permanent deformation or wrinkles at the end of the roller surface, so that a high-quality image can be obtained.

Next, in Patent Document 2, a recording medium is sandwiched between an image carrier and an image carrier so as to provide a transfer roller that can prevent toner scattering and a transfer memory even when the allowable range of the resistance value is wide. The transport direction in which the developed image is transferred to the recording medium by applying a voltage having a polarity opposite to the polarity of the developed image formed on the image carrier to the recording medium. A transfer roller that rotates about a conductive axis extending in a direction perpendicular to the elastic member; and an elastic member that surrounds an outer peripheral surface of the conductive shaft and has a uniform volume resistivity when pressed against the image carrier. A transfer roller is provided.

Further, Patent Document 3 discloses a transfer roller that maintains stable transferability against environmental, endurance fluctuations, or applied voltage fluctuations, and prevents the recording material from being stained, and image formation using the transfer roller. For the purpose of providing an apparatus, an image carrier having a toner image corresponding to image information and a transfer roller for transferring the toner image formed on the image carrier to a recording material are provided. The roller is composed of two or more layers. At least the outermost layer is an electronic conductive layer containing an electronic conductive agent and is an elastic layer formed of a foam. Further, at least one layer other than the outermost layer is a volume resistivity of the outermost layer. An ionic conductive layer containing an ionic conductive agent whose resistance is adjusted to a smaller value, and is an elastic layer formed of a foam, and transfers the toner image formed on the image carrier to the recording material. To make the above transfer law A transfer voltage applying means for applying a predetermined transfer voltage to the transfer roller, and a toner having a polarity opposite to the transfer voltage with respect to the transfer roller in order to transfer the toner adhering to the surface of the transfer roller to the surface of the image carrier. An image forming apparatus provided with a cleaning application unit that alternately applies a voltage having the same polarity as the transfer voltage at a predetermined timing is disclosed.

Further, Patent Document 4 discloses that an image on an image carrier is sequentially superposed on an intermediate transfer member for primary transfer, and the primary transfer image on the intermediate transfer member is collectively transferred to a transfer material for secondary transfer. In an intermediate transfer type image forming apparatus, a plurality of color developed images sequentially formed on an image carrier are endless in order to solve a transferability defect due to environmental fluctuation of a transfer roller used for secondary transfer. In the intermediate transfer type image forming apparatus that performs primary transfer by sequentially superimposing on an intermediate transfer member running on the intermediate transfer, and secondary transfer the primary transfer image on the intermediate transfer member collectively to a transfer material. The transfer roller used for transfer is composed of a cored bar and two or more layers formed on the cored bar, and the two or more layers are a base layer on the cored bar, A surface layer formed on the outside, and the base layer and the surface layer In the resistance per unit length of the free layer ^{1.57 × 10 6 ~1.57 × 10 9} Ω, and the volume resistivity of the surface layer is in the range of ^{1 × 10 6 ~1 × 10 9} Ω · cm An intermediate transfer type image forming apparatus is disclosed.

JP 10-254262 A JP 2002-268409 A JP 2003-241541 A JP 2000-137391 A

However, in each of the above prior arts, a spot-like discharge occurs in the secondary transfer nip, and a so-called solid portion or halftone portion falls out in a white spot shape within a range of, for example, 0.1 to 0.3 mm. There is a problem in that no attempt has been made to suppress the occurrence of the above.
The present invention has been made in view of such a problem, and the problem is to improve the image quality of a toner image transferred onto a recording medium and to suppress the occurrence of white spots in the toner image. Another object of the present invention is to provide a transfer device that can be used and an image forming apparatus equipped with the transfer device.

In order to solve the above problems, the transfer device of the present invention forms an electrostatic latent image corresponding to image information on the surface of the image carrier, a charging unit for charging the surface of the image carrier, and the charged image carrier. In the transfer device for transferring the toner image formed on the surface of the image carrier of the image forming apparatus having an exposing unit for developing and a developing unit for visualizing the electrostatic latent image to form a toner image, on the recording medium, An intermediate transfer member to which a toner image is temporarily transferred, a primary transfer roller for transferring the toner image on the image carrier to the intermediate transfer member, and the toner image transferred to the intermediate transfer member to the recording medium a secondary transfer b over La to be transferred to, and a counter roller opposing the secondary transfer roller, said counter roller is biased portion, the secondary transfer roller is grounded to the earth, the secondary the transfer roller is a metal cored bar Has a two-layer structure of the surface layer and the inner layer, the inner layer is coated on the core metal, the volume resistivity of the inner layer may be greater than the volume resistivity of the surface layer.

In this case, the volume resistivity of the inner layer is preferably 1 × 10 ⁹ to 1 × 10 ¹² Ω · cm. The volume resistivity of the surface layer is preferably 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm. Further, the thickness of the inner layer can be 1 0 to 200 [mu] m. Furthermore, the surface layer may be made of a foam. Furthermore, the hardness of the surface layer can be set to Asker C60 or less.
Also, the pre Symbol counter roller may be a drive roller. Further, the volume resistivity of the facing roller can be set to 1 × 10 ⁶ Ω · cm or less. Furthermore, the intermediate transfer member is a transfer belt, and the volume resistivity of the intermediate transfer belt may be 1 × 10 ^7.5 to 1 × 10 ¹⁰ Ω · cm.

The image forming apparatus of the present invention includes an image carrier, a charging unit that charges the surface of the image carrier, and an exposure unit that forms an electrostatic latent image according to image information on the surface of the charged image carrier. An image forming apparatus comprising: a developing unit that visualizes the electrostatic latent image to form a toner image; and a transfer device that transfers the toner image to a recording medium. The transfer device is one of the transfer devices described above It is characterized by being.

  According to the present invention, the secondary transfer roller is provided with an inner layer and a surface layer covering the inner layer, and the volume resistivity of the inner layer is made larger than the volume resistivity of the surface layer, thereby effectively suppressing the occurrence of white spots. High-quality images can be formed.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an explanatory diagram showing a transfer device portion of an image forming apparatus according to an embodiment of the present invention. This transfer apparatus is of a tandem intermediate transfer system using an intermediate transfer belt, and can also be applied to a drum intermediate transfer system.
In FIG. 1, an intermediate transfer belt 1 as an intermediate transfer member is supported by a secondary transfer counter roller 2, an entrance roller 3, a backup roller 4, a tension roller (cleaning counter roller) 5, and the like. A secondary transfer roller 6 is disposed so as to be in contact with the secondary transfer counter roller 2 via the intermediate transfer belt 1, and this secondary transfer roller 6 is opposed to a secondary transfer counter roller (hereinafter simply referred to as a counter roller). The toner image on the intermediate transfer belt 1 is secondarily transferred to a recording medium (not shown). A plurality of photoconductors 7 for color images are arranged at predetermined intervals so as to contact the outer peripheral surface of the intermediate transfer belt 1.

The volume resistivity of the intermediate transfer belt 1 is set in a range of 1 × 10 ^7.5 to 1 × 10 ¹⁰ Ω · cm. If the volume resistivity of the intermediate transfer belt 1 is greater than 1 × 10 ¹⁰ Ω · cm, electric charges accumulate, and a residual potential may remain during the next transfer, resulting in an abnormal image, and 10 ^7.5 Ω.・ If it is smaller than cm, the pressure resistance is insufficient, and a leak may occur, resulting in a hole.

FIG. 2 is an explanatory view showing a secondary transfer roller. In FIG. 2, the core bar 61 of the secondary transfer roller 6 is made of metal such as iron, SUS, or Al, and the volume resistivity of the metal core bar 61 is 1 × 10 ⁹ to 1 × 10 ^12. The inner layer 62 of Ω · cm is coated by, for example, coating. The thickness of the inner layer 62 is, for example, 10 μm to 200 μm. By doing so, an inexpensive and stable inner layer film can be obtained. Although the material of an inner layer is not specifically limited, A fluororesin, a urethane resin, etc. are used suitably. Since these volume resistivity satisfy | fills the above-mentioned range, the effect which suppresses generation | occurrence | production of a white spot is exhibited.
The inner layer 62 is covered with a surface layer 63. The volume resistivity of the surface layer 63 is 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm. An optimum electric field is obtained within this range, and an optimum transfer property is obtained. The surface layer 63 is made of, for example, a foamed body, and the material thereof is made of, for example, urethane foam, NBR or the like, and cleaning is performed with a bias. The hardness of the surface layer is set to Asker C60 or less, thereby following the unevenness from the back of the transfer paper, the solid filling is improved, and the nip formation can be stabilized.
FIG. 3 is an explanatory diagram of the opposing roller. In FIG. 3, the counter roller 2 has a surface of a metal roller 21 made of iron, SUS, Al or the like covered with, for example, rubber 22. The volume resistivity of the facing roller 2 is set to 1 × 10 ⁶ Ω · cm or less, which is substantially conductive, so that the balance with the resistance of the secondary transfer roller is not reversed. The opposing roller 2 also functions as a driving roller. The reason why the opposing roller is the driving roller is to reduce the shock when the transfer paper as the recording medium enters and to reduce the cost by using the rollers of each function. In the present embodiment, the opposing roller is a bias applying unit, and it is possible to prevent the current from escaping through the back surface of the transfer paper as compared with the conventional technique in which a bias is applied from the secondary transfer roller side. Will improve.

The operation of the intermediate transfer device having such a configuration and the image forming apparatus having the transfer device will be described below.
The toner image developed on the photoconductor 7 as an image carrier by a developing device (not shown) comes into contact with the intermediate transfer belt 1 that rotates in synchronization with the photoconductor 7 in the primary transfer portion, and is given a predetermined bias potential. Transferred to the intermediate transfer belt 1. Each toner image developed to each color of yellow, magenta, cyan, and black is transferred from each photoconductor 7 to the intermediate transfer belt 1 and superimposed on the intermediate transfer belt 1 as a color toner image.
The color toner image superimposed on the intermediate transfer belt 1 reaches between the secondary transfer roller 6 and the opposing roller 2 by the rotation of the intermediate transfer belt 1. On the other hand, a recording sheet (not shown) as a transfer material is conveyed between the secondary transfer roller 6 and the opposing roller 2 in synchronization with the intermediate transfer belt 1, and between the intermediate transfer belt 1 and the secondary transfer roller 6. pass. At this time, a bias voltage having a polarity opposite to the charging polarity of the toner image is applied to the opposing roller 2, and the toner image is secondarily transferred to the recording paper. Thereafter, the recording paper is given a predetermined charge by the static eliminator to remove the charge, and peels off from the intermediate transfer belt 1.
The recording sheet peeled off from the intermediate transfer belt 1 moves to a fixing step (not shown), and after the color toner image is fixed, it is discharged out of the apparatus. The toner remaining on the intermediate transfer belt 1 is removed by a cleaning device and initialized.

According to the present embodiment, since the inner layer 62 made of a high resistance layer is provided on the inner surface of the secondary transfer roller 6, it is the cheapest and well-balanced and can effectively prevent the occurrence of a white spot phenomenon and produce a high quality image. Obtainable. The white spot phenomenon hardly occurs when the volume resistivity of the transfer belt is increased in the secondary transfer portion, and is less likely to occur when a high resistance layer is provided on the surface layer of the secondary transfer roller. Further, it is difficult to generate unless a high electric field is applied to the transfer member. Accordingly, it is important not to generate a high electric field on the transfer member anywhere in the secondary transfer. In this embodiment, the secondary transfer roller has a two-layer structure of a surface layer and an inner layer. The volume resistivity of the inner layer is made larger than the volume resistivity of the surface layer to prevent the occurrence of the white spot phenomenon.
In the present embodiment, the intermediate transfer belt 1 can have a high resistance, but the necessary cost increases. Further, if the opposing roller 2 as a driving roller has a high resistance, slip occurs on the surface of the opposing roller. On the other hand, if the inner surface of the opposing roller is a high resistance layer, the opposing roller is a place where a bias is applied, so that the pressure resistance is insufficient and the effect is small. Further, if the surface of the secondary transfer roller is a high resistance layer, the surface of the secondary transfer roller is a sponge roller, so the film is not stable and expensive. Therefore, in this embodiment, the inner layer 2 of the secondary transfer roller 6 is a high resistance layer.

In this embodiment, the case where the intermediate transfer belt is used as the intermediate transfer member has been described. However, the intermediate transfer member in the present invention is not limited to the intermediate transfer belt, and may be an intermediate transfer drum or other intermediate transfer member. May be.

1 is a diagram illustrating a transfer device portion of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the secondary transfer roller of FIG. It is a figure which shows the opposing roller of FIG.

Explanation of symbols

1: Intermediate transfer belt 2: Secondary transfer counter roller (counter roller)
3: Entrance roller 4: Backup roller 5: Tension roller 6: Secondary transfer roller 7: Photoconductor 21: Roller 22: Surface layer (rubber)
61: Metal core 62: Inner layer 63: Surface layer

Claims (10)

An image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for forming an electrostatic latent image according to image information on the surface of the charged image carrier, and visualizing the electrostatic latent image. In a transfer device for transferring a toner image formed on the surface of the image carrier of an image forming apparatus having a developing unit for forming a toner image to a recording medium,
The intermediate transfer member to which the toner image is temporarily transferred, a primary transfer roller for transferring the toner image on the image carrier to the intermediate transfer member, and the toner image transferred to the intermediate transfer member to the recording a secondary transfer b over La to transfer to the medium, and a counter roller opposing the secondary transfer roller,
The opposing roller is a bias applying unit, and the secondary transfer roller is grounded to the ground,
The secondary transfer roller has a metal core, a two-layer structure of a surface layer and an inner layer, and the inner layer is coated on the core.
The volume resistivity of the inner layer is larger than the volume resistivity of the surface layer. 2. The transfer device according to claim 1, wherein a volume resistivity of the inner layer is 1 × 10 ⁹ to 1 × 10 ¹² Ω · cm. The volume resistivity of the surface layer is 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm. The transfer device according to claim 1, wherein the surface resistivity is 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm. The thickness of the inner layer, transfer device according to any one of claims 1 to 3, characterized in that a 1 0 to 200 [mu] m. The transfer device according to any one of claims 1 to 4, wherein the surface layer is made of a foam. The transfer device according to claim 1, wherein the hardness of the surface layer is Asker C60 or less. The transfer device according to claim 1 , wherein the facing roller is a driving roller . The transfer device according to claim 1, wherein the counter roller has a volume resistivity of 1 × 10 ⁶ Ω · cm or less . The intermediate transfer member is a transfer belt, the volume resistivity of the intermediate transfer ^{belt, 1 × 10 7.5 ~1 × 10} 10 Ω · claims 1 to be cm 8 any one of the transfer device according to. An image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for forming an electrostatic latent image according to image information on the surface of the charged image carrier, and a toner by visualizing the electrostatic latent image 10. The image forming apparatus having a developing unit that forms an image and a transfer device that transfers the toner image onto a recording medium, wherein the transfer device is the transfer device according to any one of claims 1 to 9.
An image forming apparatus.

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