JP2006201444A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus with which a good-quality image can be obtained and transfer of high durability is made possible by improving the transfer efficiency of a primary transfer and a secondary transfer even if a linear speed of an intermediate transfer body due to a higher speed of image formation is increased. <P>SOLUTION: The image forming apparatus transfers the toner images formed on photoreceptors 1, 1Y, 1M, 1C, 1K of an image forming section to an intermediate transfer body 7 by primary transfer means 5Y, 5M, 5C, 5K and transfers the toner images to a transfer material P, in which the primary transfer electrodes 5YA, 5MA, 5CA, 5KA of the primary transfer means are formed by a conductive foamable member 52 coming into surface-to-surface contact with the inner side of the intermediate transfer body 7 in the primary transfer position where the photoreceptors 1Y, 1M, 1C, 1KA and the intermediate transfer body 7 oppose. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a copying machine, a printer, a facsimile, and an image forming apparatus using an electrophotographic system having these functions, and in particular, has an intermediate transfer member, and a plurality of color toner images are formed on the intermediate transfer member. The present invention relates to a superposed color image forming apparatus.

  In an electrophotographic color image forming apparatus using an intermediate transfer member, a toner image formed on an image carrier as a photosensitive member is transferred onto the intermediate transfer member, and the toner image on the intermediate transfer member is transferred to a transfer material ( Those which are transferred onto recording paper (also referred to as recording paper or paper) are known. In such a color image forming apparatus, a toner image sequentially formed on an image bearing member and charged with a predetermined polarity is transferred onto an intermediate transfer member using electrostatic force, and then the toner on the intermediate transfer member is transferred. The image is collectively transferred onto the transfer material using electrostatic force.

  Since the image forming apparatus using the intermediate transfer member can superimpose the toner image formed on the image carrier on the intermediate transfer member, it can be widely applied to a color image forming apparatus for forming a color image on a transfer material. Has been. In this color image forming apparatus, each color toner image formed on an image carrier is transferred onto an intermediate transfer member, and then transferred to a transfer material using electrostatic force.

  Since the charge amount per toner particle is substantially uniform, the toner layer potential on the intermediate transfer member is determined by the toner adhesion amount within a predetermined area. In the color image forming apparatus, a plurality of toner images on the intermediate transfer member are included. The charging potential of the portion where the color toners are superimposed is higher than the charging potential of the portion where only one color toner is attached. For example, when the toner image on the intermediate transfer member has a solid portion and a halftone portion, the charging potential of the solid portion is larger than that of the halftone portion.

  In addition, variations in the charged potential in the toner image after passing through the primary transfer portion that transfers the toner image from the image carrier to the intermediate transfer member may also occur depending on the environment.

  Thus, when the variation in the potential of the toner image on the intermediate transfer member is large, portions having different transfer characteristics exist in the same toner image. If all the parts having different transfer characteristics are transferred to the transfer material under the same transfer conditions, various image defects are likely to occur during the secondary transfer from the intermediate transfer member to the transfer material.

  In recent years, colorization has progressed in image forming apparatuses such as copiers, printers, facsimiles, and multifunction devices having these functions, and there has been a demand for higher image quality in the transfer process by using polymerized toner and small-diameter toner. Is getting bigger. The speed of the image forming apparatus is also increasing. In order to obtain a good image, it is necessary to improve the secondary transfer performance by correcting the toner potential on the intermediate transfer body, which changes depending on the number of times of primary transfer and the environment, to be substantially uniform. There is.

In order to solve the above-described problem, in Patent Document 1, the secondary transfer means includes a first member and a second member made of conductive foamed urethane rubber having different volume resistivity. At normal temperature, the first member is in pressure contact with the intermediate transfer member, and when it becomes hot and humid, the second member is in pressure contact with the intermediate transfer member.
JP-A-11-52763

  In order to meet the demand for higher printing speed, it is necessary to increase the contact area between the transfer roller and the intermediate transfer member in order not to lower the transfer rate. For this purpose, conventionally, there has been a response by increasing the pressing force of the transfer roller, lowering the elasticity of the sponge of the transfer roller, and increasing the diameter of the transfer roller.

  However, the increase in the pressing force of the transfer roller and the lower elasticity of the sponge of the transfer roller have a problem that the replacement frequency increases due to a decrease in durability. Further, when the diameter of the transfer roller is increased, there are problems that the apparatus becomes larger and the manufacturing cost increases.

  In the method described in Patent Document 1, the transfer is performed by bringing the secondary transfer means including the first member and the second member made of conductive foamed urethane rubber into direct contact with the transfer material. There is a problem that paper dust generated by contact with or sliding on the surface adheres to the surface of the secondary transfer means and the initial performance cannot be maintained.

  The present invention improves the transfer efficiency of the primary transfer and the secondary transfer to obtain a high-quality image and enables a highly durable transfer even if the linear transfer speed of the intermediate transfer member increases due to the high-speed image formation. An object is to provide an image forming apparatus.

  The above object is achieved by the following configuration.

  The image forming apparatus according to claim 1, wherein the toner image formed on the image carrier of the image forming unit is transferred to an intermediate transfer member by a primary transfer unit, and the toner image is transferred to a transfer material by a secondary transfer unit. In the image forming apparatus, the primary transfer pole of the primary transfer unit is made of a conductive foam member that is in surface contact with the inside of the intermediate transfer body at a primary transfer position where the image carrier and the intermediate transfer body face each other. It is characterized by.

  According to a second aspect of the present invention, in the first aspect, the conductive foam member is connected to a voltage applying unit and further grounded.

  The image forming apparatus according to claim 3, wherein the toner image formed on the image carrier of the image forming unit is transferred to an intermediate transfer member by a primary transfer unit, and the toner image is transferred to a transfer material by a secondary transfer unit. In the image forming apparatus, the secondary transfer pole of the secondary transfer unit is a conductive foam member that is in surface contact with the inner side of the intermediate transfer body at a secondary transfer position where the image carrier and the intermediate transfer body face each other. It is characterized by comprising.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to the third aspect, wherein the conductive foam member is grounded.

  An image forming apparatus according to a fifth aspect is the image forming apparatus according to the first or third aspect, wherein a metal film is formed on a surface of the conductive foam member in pressure contact with the intermediate transfer member.

  7. The image forming apparatus according to claim 6, further comprising a transfer unit that transfers a toner image formed on the image carrier of the image forming unit to a transfer material, wherein the transfer pole of the transfer unit includes the transfer electrode. It consists of a conductive foam member in surface contact with the inside of the material.

  An image forming apparatus according to a seventh aspect is the image forming apparatus according to the sixth aspect, wherein a metal film is formed on a surface of the conductive foam member.

The image forming apparatus according to claim 8 is characterized in that, in any one of claims 1 to 7, a volume resistivity of the conductive foam member is 1 × 10 ¹¹ Ω · cm or less. It is.

  According to the first aspect of the present invention, the primary transfer pole of the primary transfer unit is composed of the conductive foam member that is in surface contact with the inside of the intermediate transfer body at the primary transfer position where the image carrier and the intermediate transfer body face each other. As a result, the contact area with the intermediate transfer member is increased and the transfer efficiency is improved as compared with the conventional driven rotation transfer roller, and even if the linear speed of the intermediate transfer member is increased due to the high-speed image formation, it is good in quality. Images can be obtained.

  According to the second aspect of the present invention, since the conductive foam member fixedly arranged is connected to the voltage applying means and grounded, there is no rotation mechanism and connection is easy and power distribution is stable.

  According to the third aspect of the present invention, the secondary transfer pole of the secondary transfer means is a conductive foam that is in surface contact with the inside of the intermediate transfer body at the secondary transfer position where the image carrier and the intermediate transfer body face each other. Due to the material, the contact area with the intermediate transfer member is increased and the transfer efficiency is improved, and the linear speed of the intermediate transfer member is increased by speeding up image formation, compared to the conventional driven rotation transfer roller. Even a good image can be obtained.

  According to the fourth aspect of the present invention, since the conductive foam member is grounded, there is no rotation mechanism, connection is easy, and power distribution is stable.

  According to the invention described in claim 5, the durability of the conductive foam member is improved by forming the metal film on the surface of the conductive foam member in pressure contact with the intermediate transfer member.

  According to the sixth aspect of the present invention, in the image forming apparatus having the transfer unit that transfers the toner image formed on the image carrier of the image forming unit to the transfer material, the transfer pole of the transfer unit is formed of the transfer material. Due to the conductive foam member in surface contact with the inner surface, the contact area with the intermediate transfer member is increased and the transfer efficiency is improved as compared with the conventional driven rotating transfer roller. Even if the linear velocity of the transfer body increases, a good image can be obtained.

  According to the seventh aspect of the present invention, the durability of the conductive foam member is improved by forming the metal film on the surface of the conductive foam member in pressure contact with the intermediate transfer member.

According to the eighth aspect of the invention, the volume resistivity of the conductive foam member is 1 × 10 ¹¹ Ω · cm or less, so that the transfer efficiency is improved.

  The present invention will be described below with reference to embodiments, but the present invention is not limited to the embodiments described below.

[Color image forming apparatus]
FIG. 1 is a cross-sectional view showing the overall configuration of a color image forming apparatus A according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the main part of the color image forming apparatus A.

  The color image forming apparatus A is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 7, primary transfer units 5Y, 5M, An intermediate transfer unit including 5C and 5K and secondary transfer means 5A, a paper feeding device 20, and a fixing device 8 are provided.

  Above the color image forming apparatus A, an image reading apparatus B is installed. The document placed on the document table is scanned and exposed by the optical system of the document image scanning exposure apparatus of the image reading apparatus B, and read by the line image sensor. The analog signal photoelectrically converted by the line image sensor is subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the image processing unit, and then input to the exposure means 3Y, 3M, 3C, 3K. .

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 6Y disposed around a photoreceptor 1Y as an image carrier.

  The image forming unit 10M that forms a magenta (M) color image includes a photoreceptor 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 6M.

  The image forming unit 10C that forms a cyan (C) image includes a photoreceptor 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 6C.

  The image forming unit 10K that forms a black (K) image includes a photoconductor 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 6K.

  The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  As the photoconductors 1Y, 1M, 1C, and 1K, known ones such as an OPC photoconductor and an aSi photoconductor are used. An OPC photoconductor is preferable, and a negatively chargeable OPC photoconductor is particularly preferable. Then, negatively chargeable OPC is used.

  As the charging means 2Y, 2M, 2C, 2K, a corona discharge means such as a scorotron or a corotron is used, and a scorotron discharge means is preferably used.

  As the exposure means 3Y, 3M, 3C, and 3K, light emitting elements that emit light according to image data, such as lasers and LED arrays, are used.

  The belt-like intermediate transfer member 7 is semiconductive, and is wound around a plurality of rollers 71a, 71b, 71c, 71d, etc., and is supported so as to be able to circulate. In the present embodiment, the intermediate transfer member 7 is supported between the roller 71c and the roller 71d in a planar shape. That is, the roller 71c and the roller 71d function as support members.

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) and synthesized on the rotating intermediate transfer body 7 by the primary transfer means 5Y, 5M, 5C, and 5K. A color image is formed.

  The transfer material P stored in the paper storage unit (paper feed cassette) 21 of the paper supply device 20 is fed by a paper feed unit (first paper feed unit) 22, and is fed with paper feed rollers 23, 24, 25, registration. A roller (second paper feed unit) 26 and the like are conveyed to the secondary transfer unit 5A, and a color image is transferred onto the transfer material P (secondary transfer).

  The transfer material P to which the color image has been transferred is subjected to heat and pressure by the fixing device 8, and the color toner image (or toner image) on the transfer material P is fixed and fixed on the transfer material P, and then discharged. The paper is discharged from the roller 27 and placed on a paper discharge tray 28 outside the apparatus.

  On the other hand, after transferring the color image to the transfer material P by the secondary transfer means 5A, the residual toner is removed by the intermediate transfer body cleaning means 6A from the intermediate transfer body 7 from which the transfer material P is separated by curvature.

  In the case of reversely discharging the transfer material P after the fixing process, the transfer material P passes through the conveyance path on the right side of the branch plate 29 arranged at the branch point between the fixing device 8 and the paper discharge roller 27, and below. Then, the sheet is conveyed in the reverse direction, passes through the conveyance path r2 on the left side of the branch plate 29 in the drawing, and is discharged out of the apparatus by the paper discharge roller 27.

  When copying on both surfaces of the transfer material P, after fixing the image formed on the first surface of the transfer material P, the transfer material P is branched from the paper discharge conveyance path by the branch plate 29, and the lower conveyance path r1. Further, after being introduced into the transport path r3, the sheet is transported in the reverse direction, transported to the transport path r4, and then detoured upward and transported by the registration rollers 26. As for the transfer material P, images of the respective colors are formed on both sides in the image forming units 10Y, 10M, 10C, and 10K, heated and fixed by the fixing device 8, and discharged to the outside by the paper discharge roller 27.

[Developing means, developer]
As the developing means 4Y, 4M, 4C, 4K, a developing means using a two-component developer containing a carrier and a toner as main components, or a developing means using a one-component developer containing no carrier but containing a carrier as a main component. However, a two-component developer is preferable. In addition, a developer that performs development by regular development or a developer that performs reversal development can be used as a developing means, but a developing bias having the same polarity as the charging of the photoreceptors 1Y, 1M, 1C, and 1K is applied to the developer carrying member. However, reversal development in which development is performed with toner charged to the same polarity as that of the photosensitive member is preferable. In this embodiment, development is performed by reversal development using negatively charged toner.

  From the viewpoint of maintaining high image quality and preventing the occurrence of fogging, the toner preferably has a volume average particle diameter of 3 to 6 μm.

  The volume average particle diameter is a volume-based average particle diameter, and is a value measured by “Coulter Counter TA-II” or “Coulter Multisizer” (both manufactured by Coulter Co., Ltd.) equipped with a wet disperser.

  With such a toner, a high-quality image having high resolution can be formed.

  In the present invention, spherical toner is desirable, and the degree of spheroidization is 0.94 or more and 0.98 or less that does not receive strong stress in the developing means, hardly causes fogging or toner scattering, and can maintain high cleaning performance. Is preferred.

  The degree of spheroidization is obtained by the following formula.

Degree of spheroidization = (perimeter of a circle with the same area as the particle projection image) / (perimeter of the particle projection image)
The degree of spheroidization is obtained by taking a photograph of resin particles enlarged 500 times with a scanning electron microscope or laser microscope for 500 resin particles, and using an image analysis apparatus “SCANNING IMAGE ANALYSER” (manufactured by JEOL Ltd.) Then, the photographic image is analyzed, the circularity is measured, and the arithmetic average value can be obtained. Moreover, as a simple measuring method, it can measure with "FPIA-1000" (made by Toa Medical Electronics Co., Ltd.).

  For the toner having a small particle diameter and a high sphericity as described above, it is desirable to use a polymerized toner.

  The polymerized toner means a toner obtained by forming a binder resin for toner and forming the toner shape by polymerization of a raw material monomer or prepolymer of the binder resin and subsequent chemical treatment. More specifically, it means a toner obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and, if necessary, a step of fusing particles between them. In a polymerized toner, a raw material monomer or prepolymer is uniformly dispersed in an aqueous system and then polymerized to produce a toner, so that a toner having a uniform toner particle size distribution and shape can be obtained.

  Specifically, a polymer is produced by emulsion polymerization of a monomer in a liquid of an aqueous medium to which an emulsion is added or a suspension polymerization method, and then an organic solvent, agglomeration is produced. It can manufacture by the method of adding an agent etc. and making it associate. A method of preparing by mixing with a dispersion liquid of a release agent or a colorant necessary for the constitution of the toner at the time of association, or a toner component such as a release agent or a colorant dispersed in a monomer Examples thereof include emulsion polymerization. Here, the association means that a plurality of resin particles and colorant particles are fused.

[Primary transfer means]
The primary transfer means 5Y for transferring a yellow image is composed of a primary transfer pole 5YA and a power source 5YE for applying a voltage to the primary transfer pole 5YA. The primary transfer pole 5YA is opposed to the photoreceptor 1Y with the intermediate transfer member 7 interposed therebetween, and is in sliding contact with the inner surface of the intermediate transfer member 7. The power source 5YE is grounded.

  The primary transfer means 5M for transferring a magenta color image includes a primary transfer pole 5MA and a power source 5ME for applying a voltage to the primary transfer pole 5MA. The primary transfer pole 5MA faces the photoconductor 1M via the intermediate transfer member 7 and is in sliding contact with the inner surface of the intermediate transfer member 7. The power source 5ME is grounded.

  The primary transfer means 5C for transferring a cyan image is composed of a primary transfer pole 5CA and a power source 5CE for applying a voltage to the primary transfer pole 5CA. The primary transfer pole 5CA faces the photoconductor 1C through the intermediate transfer member 7 and is in sliding contact with the inner surface of the intermediate transfer member 7. The power supply 5CE is grounded.

  The primary transfer means 5K for transferring a black image is composed of a primary transfer pole 5KA and a power source 5KE for applying a voltage to the primary transfer pole 5KA. The primary transfer pole 5KA is opposed to the photoreceptor 1K with the intermediate transfer member 7 interposed therebetween, and is in sliding contact with the inner surface of the intermediate transfer member 7. The power supply 5KE is grounded.

  A current value of 40 μA and a voltage value of +1.5 kV are applied to the power supplies 5YE, 5ME, 5CE, and 5KE of the primary transfer units 5Y, 5M, 5C, and 5K.

  Further, the primary transfer units 5Y, 5M, 5C, and 5K are moved by a driving unit (not shown) and retracted away from the inner surface of the intermediate transfer body 7 except during the primary transfer.

  FIG. 3 is a sectional view of the primary transfer means.

  Since the primary transfer poles 5YA, 5MA, 5CA, and 5KA of the primary transfer means 5Y, 5M, 5C, and 5K have substantially the same configuration, the primary transfer pole 5YA will be described below as a representative.

  The primary transfer electrode 5YA supports a wear-resistant conductive member 51 that is in sliding contact with the inner surface of the intermediate transfer member 7, a conductive foam member 52 joined to the wear-resistant conductive member 51, and a conductive foam member 52. The supporting member 53 is laminated and integrated. The support member 53 is biased by a spring 54 and is held movably by a fixed support member 55.

  The conductive foam member 52 is obtained by mixing conductive carbon black into a foam member such as sponge. As a manufacturing method of the conductive foam member 52, carbon black is mixed by a method of core-processing a polymer material in a liquid in which carbon black is dispersed, a method of kneading into a resin in a blending stage, or the like. Electricity flows in the polymer material by the foamed member mixed with carbon black.

  Other than using carbon black, compounds such as polyacetylene, polyphenylacetylene, poly-p-phenylene, metal phthalocyanine polymer, etc., which are composed of conjugated double bonds in the main chain, may be iodine or arsenic pentafluoride. There is also a method of promoting ionization by delocalization of charges by mixing (doping) or the like.

[Secondary transfer means]
As shown in FIG. 2, the secondary transfer means 5A is composed of a conductive foam member 5AA, a transfer roller 5AR, and a power source 5AE. The conductive foam member 5AA is opposed to the transfer roller 5AR through the intermediate transfer body 7, and is in sliding contact with the inner surface of the intermediate transfer body 7. The conductive foam member 5AA is grounded. A power supply 5AE for applying a voltage to the transfer roller 5AR is grounded.

  6A is an intermediate transfer member cleaning means for cleaning the intermediate transfer member 7, and 8 is a fixing device for fixing the toner image to the transfer material P.

The intermediate transfer member 7 is a single layer or multilayer belt made of polyamide, polyimide, or the like, and has a volume resistivity of 10 ⁷ to 10 ¹² Ωcm.

  After the secondary transfer to the transfer material P by the secondary transfer means 5A, the intermediate transfer body 7 passes through the intermediate transfer body cleaning means 6A and is cleaned.

  A current value of 50 μA and a voltage value of +3 kV are applied to the power supply 5AE of the secondary transfer unit 5A. The conductive foam member 5AA of the secondary transfer means 5A has substantially the same configuration as the primary transfer poles 5YA, 5MA, 5CA, 5KA, the wear-resistant conductive member that is in sliding contact with the inner surface of the intermediate transfer body 7, and the conductive material. The conductive foam member joined to the conductive member and the support member that supports the conductive foam member are laminated and integrated. The supporting member urges and presses the conductive foam member 5AA against the inner surface of the intermediate transfer body 7 by a spring.

  The transfer roller 5AR is moved by a driving unit (not shown) and retracted away from the surface of the intermediate transfer member 7 except during the secondary transfer.

  FIG. 4 is a configuration diagram of the image forming unit 10 of the image forming apparatus that forms a monochrome image.

  Around the photoreceptor 1, a charging unit 2, an exposure unit 3, a developing unit 4, a transfer unit 5, a cleaning unit 6, and a transport belt 7A are arranged.

  The transfer means 5 is composed of a conductive foam member and a wear-resistant conductive member, and presses and contacts the photoreceptor 1 via a conveying belt 7A that rotates during image transfer. When the image is not transferred, the transfer unit 5 is moved by a driving unit (not shown) and is moved away from the transport belt 7A.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In this embodiment, an image is formed by the color image forming apparatus A provided with the primary transfer units 5Y, 5M, 5C, and 5K and the secondary transfer unit 5A shown in FIGS.

[Primary transfer means]
Photoconductors 1Y, 1M, 1C, 1K: outer diameter φ60 mm
Primary transfer electrode 5YA, 5MA, 5CA, 5KA: transfer current 40 μA, transfer voltage +1.5 kV applied Intermediate transfer body 7: polyimide belt (volume resistivity 10 ⁹ Ωcm), linear velocity 220 mm / second Toner: volume average particle diameter Polymerized toner of 4.5 μm and sphericity of 0.96 Charging means 2Y, 2M, 2C, 2K: Charging voltage V0 is −700 V (variable: left is standard value)
Exposure means 3Y, 3M, 3C, 3K: semiconductor laser (wavelength 780 nm), image forming body surface potential Vi during exposure is -50V
Developing means 4Y, 4M, 4C, 4K: Development sleeve potential Vdc is -500 V (variable: standard value on the left), development bias voltage AC component Vac is 1 kVp-p rectangular wave (frequency 5 kHz)
The examples of the present invention were compared with conventional comparative examples under the following transfer conditions.

(Examples of primary transfer poles 5YA, 5MA, 5CA, 5KA)
Material: Conductive urethane foam Shape: rectangular parallelepiped Volume resistivity: 1 × 10 ⁷ Ω · cm
Pressing force: 0.2kgf
Sub-scanning direction nip width: 5 mm
(Comparison example of primary transfer electrode)
Material: Nitrile butadiene rubber (NBR)
Shape: Roller (outer diameter φ20mm, cored bar diameter φ9mm)
Volume resistivity: 1 × 10 ⁷ Ω · cm
Pressing force: 0.6kgf
Sub-scanning direction nip width: 3 mm
Under these conditions, in the general environment of normal temperature and normal humidity, the transfer state was almost the same in the example and the comparative example, but when a solid image such as a photograph was formed in a low temperature and low humidity environment, the conductive foamed urethane rubber Although no problem occurred in the embodiment consisting of the above, image defects such as voids occurred in the rubber roller of the comparative example.

[Secondary transfer means]
In this example, an image was formed by the color image forming apparatus A provided with the secondary transfer means 5A shown in FIGS.

  When an outer diameter of the photoconductors 1Y, 1M, 1C, and 1K is 60 mm, a transfer current of 50 μA and a transfer voltage of +3.0 kV are applied to the transfer roller 5AR, the embodiment of the present invention is compared with the conventional comparative example under the following transfer conditions. Were compared.

(Example of conductive foam member 5AA)
Material: Conductive urethane foam Shape: rectangular parallelepiped Volume resistivity: 1 × 10 ⁷ Ω · cm
Pressing force: 0.2kgf
Sub-scanning direction nip width: 10 mm
(Comparative example of secondary transfer electrode)
Material: Nitrile butadiene rubber (NBR)
Shape: Roller (outer diameter φ30mm, cored bar diameter φ15mm)
Volume resistivity: 1 × 10 ⁷ Ω · cm
Pressing force: 5kgf
Sub-scanning direction nip width: 3 mm
Under these conditions, in the general environment of normal temperature and normal humidity, the transfer state was almost the same in the example and the comparative example, but when a solid image such as a photograph was formed in a low temperature and low humidity environment, Although no problem occurred in the embodiment made of the conductive foamed urethane rubber that was in contact with the rubber roller of the comparative example, image defects such as hollowing out occurred.

  What effect can be obtained by reducing the pressing force shown in this embodiment.

  In the primary transfer, the toners are condensed due to the pressure, and the condensed toner is prevented from remaining on the photosensitive drum 1, thereby eliminating the occurrence of image defects such as voids. Further, when a carrier is present on the photosensitive drum 1, the primary transfer means of the present invention made of conductive foamed urethane rubber works effectively because the photosensitive drum 1 is damaged if the pressing force is high.

  In the secondary transfer, a highly smooth paper such as coated paper has a low adhesion force between the toner and the paper, and if the pressing force is high, the toner B may adhere to the intermediate transfer body 7. This phenomenon was also eliminated by the secondary transfer means comprising the conductive foam member of the present invention. Further, when an aluminum foil having a thickness of 10 μm is attached to the surface of the conductive foam member, the same effect is obtained, the wear resistance is improved, and the replacement cycle of the conductive foam member can be lengthened.

  In this embodiment, an example in which an intermediate transfer belt is used as the intermediate transfer member 7 has been described. However, the present invention can also be applied to one using an intermediate transfer member of another shape. In addition, the electrical characteristics, thickness, layer configuration, material, and the like of the intermediate transfer member 7 can be selected and used according to image forming conditions.

  The conductive foamed member thus formed can be applied to a charging member or a charge eliminating member of an electrophotographic copying machine or printer.

1 is a cross-sectional view illustrating an overall configuration of a color image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a main part of the color image forming apparatus. Sectional drawing of a primary transfer means. 1 is a configuration diagram of an image forming unit of an image forming apparatus that forms a monochrome image.

Explanation of symbols

1,1Y, 1M, 1C, 1K photoconductor (image carrier)
5 Transfer means 5A Secondary transfer means 5AA Conductive foam member (secondary transfer electrode)
5AR transfer roller 5Y, 5M, 5C, 5K Primary transfer means 5YA, 5MA, 5CA, 5KA Primary transfer pole 7 Intermediate transfer body 7A Conveying belt 10, 10Y, 10M, 10C, 10K Image forming part 51 Wear-resistant conductive member 52 conductive foam member 53 support member 54 spring 55 fixed support member A color image forming apparatus P transfer material

Claims (8)

In an image forming apparatus in which a toner image formed on an image carrier of an image forming unit is transferred to an intermediate transfer member by a primary transfer unit, and the toner image is transferred to a transfer material by a secondary transfer unit.
The primary transfer pole of the primary transfer means is formed of a conductive foam member that is in surface contact with the inside of the intermediate transfer body at a primary transfer position where the image carrier and the intermediate transfer body face each other. apparatus. The image forming apparatus according to claim 1, wherein the conductive foam member is connected to a voltage applying unit and further grounded. In an image forming apparatus in which a toner image formed on an image carrier of an image forming unit is transferred to an intermediate transfer member by a primary transfer unit, and the toner image is transferred to a transfer material by a secondary transfer unit.
The secondary transfer pole of the secondary transfer means is composed of a conductive foam member that is in surface contact with the inside of the intermediate transfer body at a secondary transfer position where the image carrier and the intermediate transfer body face each other. Image forming apparatus. The image forming apparatus according to claim 3, wherein the conductive foam member is grounded. The image forming apparatus according to claim 1, wherein a metal film is formed on a surface of the conductive foam member in pressure contact with the intermediate transfer member. In an image forming apparatus having transfer means for transferring a toner image formed on an image carrier of an image forming unit to a transfer material,
The image forming apparatus according to claim 1, wherein the transfer pole of the transfer means is made of a conductive foam member in surface contact with the inside of the transfer material. The image forming apparatus according to claim 6, wherein a metal film is formed on a surface of the conductive foam member. The image forming apparatus according to claim 1, wherein a volume resistivity of the conductive foam member is 1 × 10 ¹¹ Ω · cm or less.

Images