JP2006337640A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses the occurrence of striped abnormal images to form images of high quality regardless of the change in environment for use or the change with time. <P>SOLUTION: The image forming apparatus includes a primary transfer means 5 which applies a bias having a polarity opposite to that of toner from a rear side of an intermediate transfer belt 41 being an intermediate transfer member, in the vicinity of a contact position between a photoreceptor belt 11 being an image carrier and the intermediate transfer belt 41, to transfer a toner image on the photoreceptor drum 11 to the intermediate transfer belt 41. In the image forming apparatus, the primary transfer means 45 is provided with an elastic roller, and the elastic roller has the resistance value set to ≤1/100 of the resistance value of the intermediate transfer belt 41 and is made of conductive foamed rubber softer than the rear side of the intermediate transfer belt 41. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an image forming apparatus using an electrophotographic process such as a copying machine, a printer, and a facsimile, and more particularly to a color image forming apparatus provided with an intermediate transfer member.

As a conventional image forming apparatus, for example, an outer peripheral surface of an intermediate transfer belt as a transfer member is brought into contact with the image carrier and formed on the image carrier by a transfer electric field formed by a transfer bias applying unit as a charge applying unit. A primary transfer means for primarily transferring the toner image to the outer peripheral surface of the intermediate transfer belt, and a toner image primarily transferred to the outer peripheral surface of the intermediate transfer belt is carried along the outer peripheral surface of the intermediate transfer belt. A device that forms an image by a secondary transfer unit that transfers onto a transfer material to be transferred is known. In such an image forming apparatus, for example, an intermediate transfer belt having a medium resistivity of 10 ⁸ to 10 ¹¹ Ωcm is often used. Such an intermediate resistance intermediate transfer belt normally does not require belt neutralizing means for neutralizing the charge remaining on the intermediate transfer belt, so that the cost can be reduced.

As a conventional technique related to such an intermediate transfer body or an image forming apparatus including the intermediate transfer body, for example, Patent Document 1 discloses that a high-quality image without a horizontal band on the halftone is formed by surely removing the charge from the intermediate transfer belt. For this purpose, a secondary transfer bias roller that is arranged so as to be able to contact with and separate from the intermediate transfer belt and also serves as a charge eliminating member for neutralizing the intermediate transfer belt, and the secondary transfer bias roller is used as the intermediate transfer belt. An image forming apparatus comprising: a contact / separation mechanism for contacting / separating the belt; and a high voltage source for applying a neutralizing bias to the secondary transfer bias roller for removing the charged charge of the intermediate transfer belt charged during the image forming operation. Is disclosed.
Further, in Patent Document 2, for the purpose of providing an image forming apparatus capable of cleaning even when a toner having a reverse polarity remains on the intermediate transfer member, the cleaning unit has an interval in the rotation direction of the intermediate transfer member. An image forming apparatus having a first cleaning roller located upstream and a second cleaning roller located downstream is disclosed.

Further, in Patent Document 3, charges remaining on the transfer belt can be efficiently removed, and even when a plurality of biases are applied to the inner peripheral surface of the transfer belt, interference between the biases is prevented. In order to provide an image forming apparatus capable of performing appropriate bias control, a grounding means is brought into contact with the belt inner peripheral surface of the intermediate transfer belt between the belt neutralizing roller and the primary transfer bias roller. An arranged image forming apparatus is disclosed.
Furthermore, Patent Document 4 evaluates whether or not the belt is suitable as an intermediate transfer belt through which a current flows through a path having direction components in a surface direction and a thickness direction from a transfer bias roller for forming a transfer electric field. For the purpose of providing an evaluation method, in a method for measuring the electrical resistance of a transport member used in an image forming apparatus, the measurement electrode is in contact with the surface of the transport member opposite to the contact surface of the voltage application electrode. A method for measuring the electrical resistance of a conveying member that measures the electrical resistance by contacting the portion is disclosed.

Further, Patent Document 5 aims to provide an image forming apparatus capable of transferring an image without causing expansion and contraction of the intermediate transfer belt and in a state where the transfer paper is in close contact with the intermediate transfer belt. An image forming apparatus for forming an image by transferring a toner image formed on a carrier onto a sheet-like transfer material via an intermediate transfer member, and forming an endless belt member across a plurality of holding rollers A first transfer for transferring the toner image on the image carrier to the intermediate transfer member by bringing the image carrier into contact with the intermediate transfer member and a stretched portion between the intermediate transfer member and the holding roller. And an electrically conductive bias roller disposed in contact with the intermediate transfer member, and is applied to the intermediate transfer member at a position where an applied electric field does not affect the toner image of the intermediate transfer member. Seats introduced after contact The transfer material, the bias roller position, the intermediate transfer body an image forming apparatus and a second transfer means for transferring the toner image has been disclosed.

JP 2001-201954 A JP 2001-337542 A JP 2002-278313 A JP 05-216353 A Japanese Patent Application Laid-Open No. 09-026709

However, in each of the above prior arts, the intermediate transfer belt is caused by an increase in the resistance value of the transfer roller that supports the intermediate transfer member due to a change in usage environment or a change over time, or by a roller that supports the intermediate transfer member. Nothing is described regarding the occurrence of transfer defects due to damage to the surface.
In an intermediate transfer belt as an intermediate transfer body suspended by a plurality of rollers, if the surface of the suspended roller is hard, such as metal, the back surface of the intermediate transfer body is scratched by the rotation operation. As the image proceeds, streaks, particularly concave streaks, may appear on the surface, which may cause a problem that streaks appear in the halftone image or solid image.

In order to prevent such problems, even if an elastic roller is used, when the elastic roller is used with a bias applied as a primary transfer means (hereinafter referred to as a primary transfer bias roller), the resistance value of the primary transfer bias roller The resistance of the primary transfer bias roller is the same as the resistance value of the intermediate transfer member or about an order of magnitude lower, due to changes in the resistance due to the environment and the increase in roller resistance as a result of bias application over a long period of time. The value may exceed the resistance value of the intermediate transfer member.
In such a case, there is a problem that a sufficient current for transferring the toner image on the image bearing member to the intermediate transfer member does not flow, and a transfer failure occurs. In particular, the resistance of the roller increases. Transfer defects tend to occur frequently in a low temperature and low humidity environment.

The present invention has been made in view of such problems, and the problem is to obtain a high-quality image by preventing transfer failure during image transfer even if the usage environment changes and changes over time occur. An object of the present invention is to provide an image forming apparatus capable of performing the above.

In order to solve the above problems, the image forming apparatus of the present invention applies a bias having a polarity opposite to that of the toner from the back side of the intermediate transfer member in the vicinity of the contact position between the image carrier and the intermediate transfer member. In the image forming apparatus including a primary transfer unit that transfers the toner image carried on the intermediate transfer member, the primary transfer unit includes a roller having elasticity, and the resistance value of the roller is determined by the intermediate transfer member. The resistance value is 1/100 or less.
In this case, the elastic roller can be a conductive foam rubber roller that is softer than the back surface hardness of the intermediate transfer member. Further, it is preferable that the surfaces of all the rollers that support the intermediate transfer member are formed of a material that is softer than the hardness of the back surface of the intermediate transfer member.

According to the image forming apparatus of the present invention, the primary transfer unit has the elastic roller, and the electrical resistance value of the elastic roller is set to 1/100 or less of the resistance value of the intermediate transfer member. Even if the resistance value of the elastic roller rises due to fluctuation over time, the resistance value of the primary transfer roller does not exceed the resistance value of the intermediate transfer member, so that a high-quality image is formed by good image transfer. can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus (hereinafter also simply referred to as a printer) according to an embodiment of the present invention. In FIG. 1, the printer 1 includes a support roller 16 provided at an approximately upper position in the drawing, a support roller 14 provided at a lower position facing the support roller 16, and support rollers 16 and 14. And a support roller 15 provided at a position approximately moved to the center of the straight line in the height direction and on the right side in the figure by a predetermined interval. The support rollers 14 to 16 are exposed to a photosensitive member as a latent image carrier. A body belt 11 is stretched over.

An organic photosensitive layer is formed on the surface of the photosensitive belt 11, and the photosensitive belt 11 is driven to rotate clockwise as indicated by an arrow A in the drawing. Around the photosensitive belt 11, a charger 13, an optical writing unit 20, four sets of developing devices 31K, 31C, 31M, and 31Y, an intermediate transfer belt 41 as an intermediate transfer member, a photosensitive member cleaning device 12, and the like are disposed. ing. A sheet feeding unit 80 is provided below the intermediate transfer belt 41. The sheet feeding unit 80 conveys a sheet feeding cassette 81 for storing recording sheets and a recording sheet taken out from the sheet feeding cassette 81. It comprises rollers 82, 83 and the like. A paper transfer roller 50 is provided so as to face the secondary transfer counter roller 46, and the recording paper is conveyed between the paper transfer roller 50 and the secondary transfer counter roller 46. The carried toner image is transferred to the recording paper.
The recording sheet on which the toner image has been transferred is conveyed to the downstream fixing device 60. The fixing device 60 mainly includes, for example, a fixing belt 61 and a pressure roller 62.

The printer 1 is always in contact with the photosensitive belt 11 and is held at a position separated from the surface of the intermediate transfer belt 41 during the image forming operation, and the photosensitive member cleaning device 12 for cleaning the residual toner on the photosensitive belt 11. Then, after the formed image is transferred onto the transfer paper, an intermediate transfer member cleaning device 42 is provided that contacts the surface of the intermediate transfer belt 41 and cleans residual toner on the intermediate transfer belt 41.

Next, characteristic portions of the present embodiment will be described in detail.
FIG. 2 is a cross-sectional view showing a schematic configuration of the intermediate transfer unit 40 in the present embodiment. The intermediate transfer belt 41 as an intermediate transfer member is suspended from five rollers, that is, a driving roller 44, a cleaning counter roller 47, a primary transfer bias roller 45, a secondary transfer counter roller 46, and a tension roller 48. Rotate in the direction of arrow B. The intermediate transfer belt 41 is made of, for example, a fluorine-based resin material having a plurality of layers, and the five rollers are configured as follows, for example.

That is, the drive roller 44 is made of a material having an outer diameter of 30φ and a relatively high friction coefficient such as EP rubber. The cleaning facing roller 47, the secondary transfer facing roller 46, and the tension roller 48 are each formed by forming a thin coating layer made of a resin-based material on the surface of a cored bar made of an aluminum material. 24φ and 20φ. The primary transfer bias roller 45 is made of, for example, foamed EPDM having an outer diameter of 12φ and imparted conductivity by carbon dispersion.

Since the photosensitive belt 11 is in tension and is in contact with the intermediate transfer belt 41 at the upstream position immediately before the primary transfer bias roller 45, the surface hardness and surface roughness of the primary transfer bias roller 45 are the intermediate transfer belt 41. In the present embodiment, the primary transfer bias roller 45 is composed of a foamed EPDM (conductive foam rubber roller) that is softer than the hardness of the back surface of the intermediate transfer belt 41. Will not hurt. Further, the primary transfer bias roller 45 applies a bias by a high-voltage power source controlled by constant current to transfer the toner image on the photosensitive belt 11 to the intermediate transfer belt 41. The resistance of the primary transfer bias roller 45 is, for example, 10 ⁵ Ω, and is, for example, 1/100 or less of 10 ⁸ Ω, which is the resistance of the intermediate transfer belt 41. As described above, if the resistance value is different by two digits, the resistance value of the primary transfer bias roller 45 does not exceed the resistance value of the intermediate transfer belt 41 even if there is a change with time. Accordingly, a current sufficient to transfer the toner is secured by this, and a high-quality image can be formed with good transferability.

Hereinafter, the operation of the printer according to the present embodiment having such a configuration will be described. First, a high voltage is applied to the charger 13 to uniformly charge the surface of the photoreceptor belt 11 (see FIG. 1). An image signal processing unit (not shown) converts, for example, a color image signal sent from an external computer into an optical writing signal as color image information, and sends the optical writing signal to the optical writing unit 20. The optical writing unit 20 controls the laser light as the light source based on the transmitted optical writing signal, and passes through the polygon mirror, the f / θ lens, and the reflection mirror, Black (K), Cyan (C), Optical writing corresponding to the image signals of Magenta (M) and Yellow (Y) is performed, and an electrostatic latent image is formed on the photosensitive belt 11.

The electrostatic latent image on the photosensitive belt 11 is developed for each color by the developing devices 31K, 31C, 31M, and 31Y each having color toner. Thereby, a toner image is formed for each color on the photosensitive belt 11. At the contact portion between the photosensitive belt 11 and the intermediate transfer belt 41, a charge having a polarity opposite to that of the toner is applied to the primary transfer bias roller 45, and the toner image on the photosensitive belt 11 is transferred onto the intermediate transfer belt 41 ( (See FIG. 2).

This toner image formation and transfer operation is repeated four times for each toner color, whereby a four-color color toner image is formed on the intermediate transfer belt 41. The color toner image on the intermediate transfer belt 41 is transferred by a paper transfer roller 50 as a secondary transfer member onto a transfer paper as a recording material sent from a paper feed cassette 81 by a pair of conveying rollers 82b, 82c, and 83. Is done. The transfer sheet on which the color toner image has been transferred is carried into a downstream fixing device 60, and the toner image is melted and fixed on the recording sheet between a fixing belt 61 having a heater and a pressure roller 62.

According to the present embodiment, the primary transfer bias roller 45 as the primary transfer means has an elastic roller, and its resistance value is set to 1/100 or less of the resistance value of the intermediate transfer belt 41, so that the use environment is improved. Since the resistance value of the primary transfer bias roller 45 does not exceed the resistance value of the intermediate transfer belt 41 even if there is a change or variation over time, a high-quality image can be formed by good image transfer.
In addition, since the primary transfer bias roller 45 is a conductive foam rubber roller that is softer than the hardness of the back surface of the intermediate transfer belt, the back surface of the intermediate transfer belt 41 may be damaged even if the primary transfer bias roller rotates. Absent. Therefore, it is possible to form a high-quality image while suppressing the occurrence of streaky abnormal images when forming a halftone image or a solid image.
In the present embodiment, it is preferable that the surfaces of the driving roller 44, the secondary transfer counter roller 46, the cleaning counter roller 47, and the tension roller 48 are made of a material softer than the inner surface that is the back surface of the intermediate transfer belt 41. Accordingly, it is possible to more reliably avoid damage to the inner side surface of the intermediate transfer belt 41 and to ensure good transferability and a high quality image.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. FIG. 2 is a schematic configuration diagram of an intermediate transfer body unit.

Explanation of symbols

1: Printer 11: Photoconductor belt 12: Photoconductor cleaning device 13: Charger 14: Support roller 15: Support roller 16: Support roller 20: Optical writing unit 31: Developing device 40: Intermediate transfer unit 41: Intermediate transfer belt 42 : Intermediate transfer member cleaning device 44: Drive roller 45: Primary transfer bias roller 46: Secondary transfer counter roller 47: Cleaning counter roller 48: Tension roller 50: Paper transfer roller 60: Fixing device 61: Fixing belt 62: Pressure roller 80: paper feed unit 81: paper feed cassettes 82b, 82c: transport roller pair 83: transport roller pair

Claims (3)

In the vicinity of the contact position between the image carrier and the intermediate transfer member, a bias having a polarity opposite to that of the toner is applied from the back side of the intermediate transfer member to transfer the toner image carried on the image carrier to the intermediate transfer member. In the image forming apparatus including the primary transfer unit, the primary transfer unit includes an elastic roller, and the resistance value of the roller is 1/100 or less of the resistance value of the intermediate transfer member. A color image forming apparatus. The color image forming apparatus according to claim 1, wherein the roller having elasticity is a conductive foam rubber roller that is softer than a hardness of a back surface of the intermediate transfer member. The color image forming apparatus according to claim 2, wherein the surfaces of all the rollers that support the intermediate transfer member are formed of a material that is softer than the hardness of the back surface of the intermediate transfer member.

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