JP2004061908A - Transfer device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device free from the occurrence of toner scattering to a transfer entrance guide plate, and free from staining on the edge and rear faces of a wide paper even after continuously forming an image on a narrow paper. <P>SOLUTION: As for the transfer device comprising a primary transfer process of transferring a toner image charged with a desired polarity from an image carrier to an intermediate transfer member and a secondary transfer process of transferring the toner image from the intermediate transfer member to a recording medium, the transfer device is provided with voltage applying means (7f and 31) for applying a voltage whose polarity is opposite to that of the toner image on this side of the secondary transfer process and behind the intermediate transfer member 6. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transfer device used for an image forming apparatus such as a color electrophotographic apparatus.
[0002]
[Prior art]
As an apparatus of this type, the present applicant has previously proposed Japanese Patent Application No. 2002-132665 as an image forming apparatus. This is a device that performs secondary transfer from the intermediate transfer belt to transfer paper as a recording medium at a roller portion around which an intermediate transfer belt as an intermediate transfer member is wound. A pre-transfer (transfer dust) is prevented by providing a contact means for bringing the transfer paper into close contact.
[0003]
[Problems to be solved by the invention]
In the above-described apparatus, since the transfer entrance guide plate and the intermediate transfer belt at the position of the fixed sliding member are close to each other, a part of the toner on the intermediate transfer belt scatters on the transfer entrance guide plate. The amount of scattered toner is small, and is not an amount that causes a problem in an image forming operation for one sheet. However, scattered toner accumulates on the transfer entrance guide plate in an area where the narrow paper does not pass while the narrow paper is repeatedly imaged. Then, when the next wide paper is passed, the paper passes through the area where the scattered toner is accumulated, and there is a problem that the edge surface and the back surface of the paper corresponding to this area are stained.
[0004]
Therefore, the present invention solves the above-mentioned problems of the related art, and there is no toner scattering on the transfer entrance guide plate, and even after the image is continuously formed on a narrow paper, the edge of the wide paper is covered. It is an object of the present invention to provide a transfer device free from surface and back surface contamination.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a primary transfer step of transferring a toner image charged to a desired polarity from an image carrier to an intermediate transfer body, and a method of transferring the toner image from the intermediate transfer body to a recording medium. In a transfer apparatus having a secondary transfer step for transferring a toner image, a voltage applying means for applying a voltage having a polarity opposite to that of the toner image is provided on the back surface of the intermediate transfer member before the secondary transfer step.
[0006]
According to a second aspect of the present invention, in the first aspect, the voltage applying means is a contact member provided in contact with the back surface of the intermediate transfer member, and a power supply for applying a voltage having a polarity opposite to that of the toner image to the contact member. And According to a third aspect of the present invention, in the second aspect, the close contact member is a fixed sliding member that is one of the tension members of the intermediate transfer member. According to a fourth aspect of the present invention, in the second aspect, the close contact roller is one of the tension members of the intermediate transfer member. It is desirable that the close contact roller rotates together with the intermediate transfer member.
[0007]
According to a fifth aspect of the present invention, in the third or fourth aspect, a secondary transfer step is performed by the intermediate transfer member and the secondary transfer roller, and a voltage having a polarity opposite to that of the toner image is applied to the secondary transfer roller. .
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings. In this embodiment, most of the features including the configuration around the secondary transfer portion of the transfer apparatus are the same as those described in the above-mentioned Japanese Patent Application No. 2002-132665. The configuration will be mainly described.
[0009]
FIG. 1 is a schematic configuration diagram of the vicinity of a secondary transfer portion of a transfer device installed in an image forming apparatus. A secondary transfer roller 11 that can be separated and moved by an unillustrated contact and separation mechanism contacts an intermediate transfer belt 6. Shows the state when it is running. The transfer device transfers a toner image charged to a desired polarity from a photosensitive drum as a first image carrier (not shown) to the intermediate transfer belt 6, and an endless belt-shaped second image. There is a secondary transfer step of transferring a toner image from the intermediate transfer belt 6 as a carrier to transfer paper. The intermediate transfer belt 6 is stretched around a plurality of stretching members including the illustrated secondary transfer facing roller 7d and the fixed sliding member 7f, and is movably disposed as indicated by arrows.
[0010]
Both the secondary transfer opposing roller 7d and the fixed sliding member 7f are disposed in contact with the back surface of the intermediate transfer belt 6. The secondary transfer roller 11 forms a secondary transfer nip in a state in which the secondary transfer roller 11 is in contact with the intermediate transfer belt 6, and performs a secondary transfer process at the nip portion. In the secondary transfer step, the fixed sliding member 7f is positioned between the intermediate transfer belt 6 and the secondary transfer roller at a position before the secondary transfer step, that is, at a position upstream of the secondary transfer nip along the moving direction of the intermediate transfer belt 6. It functions as a member (close contact member) that makes 11 closely contact.
[0011]
The fixed sliding member 7f is conductive or semiconductive and is insulated from the housing ground, so that a voltage having a polarity opposite to that of the toner image is applied from the power supply 31. The fixed sliding member 7f and the power supply 31 constitute voltage applying means. As the fixed sliding member 7f, stainless steel whose surface rubbing with the intermediate transfer belt 6 is mirror-finished is used. The reason why stainless steel is used is that it is conductive, does not rust, and that aluminum wears itself and abrasion powder damages the back surface of the intermediate transfer belt 6, but does not occur with stainless steel. However, since the back surface of the intermediate transfer belt 6 wears out during long-term use, a resin brush having good slidability such as nylon or Teflon (registered trademark) containing a conductive filler is adhered to the sheet metal. It is desirable that the brush be in contact with the intermediate transfer belt 6. The secondary transfer roller 11 is configured to apply a voltage having a polarity opposite to that of the toner image from another power source 32 similarly to the fixed sliding member 7f. The secondary transfer opposing roller 7d is grounded.
[0012]
In FIG. 1, 10 is a transfer paper, 12 is a paper discharging charger, and 17 is a transfer paper transport belt. Further, 21 is an upper guide plate, 22 is a lower guide plate, and 23 is an entrance guide mylar, and these constitute a transfer entrance guide plate.
[0013]
When a voltage having a polarity opposite to that of the toner image is applied from the power supply 31 to the fixed sliding member 7f, an electric field is generated on the intermediate transfer belt 6 to attract the toner image to the intermediate transfer belt 6 just before the transfer nip. Elimination of toner scattering. Therefore, even if an image is formed on a wide transfer paper after the image formation is continued on a narrow transfer paper, the edge surface and the back surface are not stained. When the voltage is applied to the fixed sliding member 7f, it is preferable to apply a voltage having a polarity opposite to that of the toner image to the secondary transfer roller 11 from another power source 32.
[0014]
FIG. 2 shows another embodiment. In this embodiment, in order to withstand long-term use, the fixed sliding member 7f, which is a close contact member, is of a roller type, and the close contact roller 7r rotates along with the intermediate transfer belt 6 so as to avoid rubbing. ing. Other configurations are the same as those of the above embodiment.
[0015]
In the above-mentioned close contact roller 7r type, if the diameter is excessively small, the roller is bent due to insufficient strength, the roller central portion escapes, and the center of the transfer paper 10 bends. The adhesion between the paper 10 and the intermediate transfer belt 6 may be deteriorated, or the bent transfer paper 10 may enter the transfer nip and cause wrinkles. On the other hand, if the diameter becomes large, even if the secondary transfer opposing roller 7d and the close contact roller 7r are brought close to each other, the wrapped portion of the intermediate transfer belt 6 is further away by the radius of both rollers, so that the close contact roller 7r cannot approach the transfer nip. . Then, the distance in which the transfer paper 10 comes into close contact with the intermediate transfer belt 6 becomes long, and the transfer paper once in contact with the intermediate transfer belt 6 cannot maintain the contact state up to the nip, and there is a problem that a contact failure occurs halfway.
[0016]
However, when a voltage having a polarity opposite to that of the toner image is applied from the power supply 31 to the contact roller 7r, an electric field is generated on the intermediate transfer belt 6 to attract the toner image to the intermediate transfer belt 6 just before the transfer nip. Elimination of toner scattering. Therefore, even if an image is formed on a wide transfer paper after the image formation is continued on a narrow transfer paper, the edge surface and the back surface are not stained. Therefore, if the contact roller diameter is strong, the life of the intermediate transfer belt 6 is reduced due to the scraping of the back surface, the transfer paper is bent due to the roller bending, and wrinkles are generated due to entering the transfer nip. The occurrence of transfer dust due to poor adhesion between the belt and the intermediate transfer belt 6 can also be prevented. Upon application to the contact roller 7r, it is preferable to apply a voltage having a polarity opposite to that of the toner image to the secondary transfer roller 11 from another power source 32 as described above.
[0017]
Although the contact roller 7r of this embodiment is made of stainless steel of φ16, for the intermediate transfer belt 6 which is resistant to high voltage and discharge, the contact roller 7r is made of a resin having a medium resistance around the cored bar. Rubber may be used.
[0018]
The voltage applied to the contact member (fixed sliding member 7f, contact roller 7r) and the amount of toner scattered on the transfer entrance guide plate will be described below. Measured by Mitsubishi Chemical Hiresta AP, applied voltage 100 V, measurement duration 10 seconds, volume resistivity 10 ⁹ Ωcm, surface resistivity of back surface 10 ⁸ Ω / □, surface resistivity of front surface 10 ⁹ Ω / □, The intermediate transfer belt 6 having a thickness of 100 μm hardly scatters regardless of the voltage of the close contact roller 7r. However, discharge is likely to occur with respect to the transfer voltage in the belt having a low resistance, and therefore, a small white image which is considered to be a discharge mark, and transfer dust which is considered to be caused by a decrease in the toner charge amount due to the discharge are generated. is there.
[0019]
Measured by Mitsubishi Chemical Hiresta AP, applied voltage 500 V, measurement duration 10 seconds, volume resistivity 10 ¹³ Ωcm, back surface surface resistivity 10 ⁹ Ω / □, front surface surface resistivity 10 ¹⁴ Ω / □ ( The abnormal image due to the low resistance does not occur in the intermediate transfer belt 6 having a thickness near the limit of the measurable width and a thickness of 150 μm. However, toner was scattered from the fixed sliding member 7f and the close contact roller 7r to the transfer entrance guide plate. FIG. 3 shows the voltage applied to the contact roller 7r on the horizontal axis and the transfer entrance guide plate stain when the image formation is continued on a narrow sheet of paper in a fixed pattern on a vertical axis. The toner has a negative polarity. It was found that as the voltage applied to the close contact roller 7r becomes larger to the opposite polarity to that of the toner, the amount of scattering of the toner decreases, and the voltage does not scatter at a voltage higher than about 1.2 kV.
[0020]
From this, the following can be considered. In an intermediate transfer belt having a low resistance, the toner on the intermediate transfer belt is attracted to the intermediate transfer belt by the mirror image force of the intermediate transfer belt and does not scatter. In an intermediate transfer belt having a high resistance, the mirror image force is small and toner is easily scattered. By applying a voltage of the opposite polarity to the back surface of the intermediate transfer belt, an electric field that attracts the toner to the front surface of the intermediate transfer belt is generated, and the toner does not scatter.
[0021]
The fixed sliding member 7f and the close contact roller 7r as the close contact members described in each of the above embodiments are merely preferred examples, and do not exclude other close contact members having other shapes. In addition, it goes without saying that various design changes and modifications can be made within the scope of the technical matters described in the claims, including the specific configuration of the voltage applying means.
[0022]
【The invention's effect】
According to the first to third aspects of the present invention, since a voltage having a polarity opposite to that of the toner image is applied to the back surface of the intermediate transfer belt by the voltage application means before the secondary transfer process, An electric field that attracts the toner to the intermediate transfer member is generated, so that the toner does not scatter to the transfer entrance guide plate, and the edge of the wide paper and the back surface of the wide paper are not stained even after the image is formed on the narrow paper.
[0023]
According to the fourth aspect of the present invention, an electric field for attracting the toner to the intermediate transfer body is generated before the transfer nip. Conventionally, the distance that the recording medium adheres to the intermediate transfer body increases, and the recording medium that once contacts the intermediate transfer body cannot maintain the contact state up to the nip, resulting in poor contact in the middle, leaving no room for transfer dust. The transfer dust was reduced even with the roller. Further, since the back surface of the intermediate transfer member is not stained with the contact roller, it is possible to achieve both a longer life of the intermediate transfer member and a reduction in transfer dust, which have been difficult to achieve in the past. According to the fifth aspect of the present invention, since a voltage having a polarity opposite to that of the toner image is also applied from the secondary transfer roller, scattering of the toner on the transfer entrance guide plate and transfer dust can be more effectively reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram around a secondary transfer unit according to an embodiment of the present invention, showing a state when a secondary transfer roller is in contact with an intermediate transfer belt.
FIG. 2 is a schematic configuration diagram corresponding to FIG. 1 in another embodiment.
FIG. 3 is a graph illustrating a voltage applied to a contact member and an amount of toner scattered on a transfer entrance guide plate.
[Explanation of symbols]
6 Intermediate transfer belt (intermediate transfer body)
7d Secondary transfer opposed roller 7f Fixed sliding member (close contact member)
7r contact roller (contact member)
10 Transfer paper (recording medium)
11 Secondary Transfer Roller 12 Paper Charger 17 Transfer Paper Conveying Belt 21 Upper Guide Plate 22 Lower Guide Plates 31, 32 Power Supply

Claims (5)

In a transfer apparatus having a primary transfer step of transferring a toner image charged to a desired polarity from an image carrier to an intermediate transfer body and a secondary transfer step of transferring a toner image from the intermediate transfer body to a recording medium, A transfer device comprising a voltage applying means for applying a voltage having a polarity opposite to that of the toner image to the back surface of the intermediate transfer member before the next transfer step. 2. The transfer device according to claim 1, wherein the voltage applying means includes a contact member provided in contact with the back surface of the intermediate transfer member, and a power supply for applying a voltage having a polarity opposite to that of the toner image to the contact member. 3. The transfer device according to claim 2, wherein the contact member is a fixed sliding member that is one of the tension members of the intermediate transfer member. The transfer device according to claim 2, wherein the contact member is a contact roller that is one of tension members of the intermediate transfer body. 5. The transfer device according to claim 3, wherein a secondary transfer step is performed by the intermediate transfer member and the secondary transfer roller, and a voltage having a polarity opposite to that of the toner image is applied to the secondary transfer roller.

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