JP4178487B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using electrophotographic technology, for example, a printing machine, a copying machine, a printer, a fax machine, and the like.
[0002]
[Prior art]
There are various printing methods for color image forming apparatuses based on electrophotography. For example, a method of forming a color image on a photosensitive member by repeating exposure and development on the photosensitive member, and then transferring the image onto a sheet at a time. A toner image is transferred to form a color image, and finally the paper is peeled off from the transfer drum. An intermediate transfer member is used to transfer the toner image from the photoconductor to the intermediate transfer member one color at a time. There is a system in which a color image is formed on a transfer body, and finally the color image is collectively transferred onto a sheet. Among these, the intermediate transfer body method described last has an advantage that a high-quality image can be obtained and images can be formed on a wide variety of sheets. Examples of the image forming apparatus using the intermediate transfer member include an image forming apparatus described in Japanese Patent Application Laid-Open No. 1-198773, an image forming apparatus described in Japanese Patent Application No. 6-68295, and the like. . By the way, in the intermediate transfer body method, since the color toners of the respective colors are electrostatically superimposed on the intermediate transfer body, the electrical characteristics of the intermediate transfer body are very important. As an example of the configuration of the intermediate transfer member, the above-described image forming apparatus is exemplified. In the image forming apparatus described in Japanese Patent Application Laid-Open No. 1-198773, the surface of the intermediate transfer member is electrically conductive by applying a voltage for transfer. In the image forming apparatus disclosed in Japanese Patent Laid-Open No. 7-281577, the surface of the intermediate transfer member grounded to zero potential is covered with a semiconductive layer. ing.
[0003]
[Problems to be solved by the invention]
However, in the configuration as in the above-described known example, the following problem occurs. In the image forming apparatus described in JP-A-1-198773 in which the surface of the intermediate transfer member is covered with an insulator, the charge is transferred from the surface of the photosensitive member to the surface of the intermediate transfer member when the toner is transferred from the photosensitive member. This remains and raises the surface potential of the intermediate transfer member, so that the toner is not transferred. This is because the charge transferred to the surface remains because the intermediate transfer member exhibits insulating properties. For this reason, it is necessary to provide a neutralizing means for neutralizing the surface of the intermediate transfer member, and there is a problem that the apparatus becomes large and complicated. Further, in the image forming apparatus described in JP-A-7-281577 in which the surface of the intermediate transfer member is covered with a semiconductive layer, the semiconductive layer is made of a medium resistance plastic material or rubber material. Since the resistance value changes by about 1 to 3 digits in response to a change in the environmental condition of humidity, there is a problem that when the environmental condition changes, the toner transfer performance changes and the image quality is not stable.
[0004]
The present invention has been devised in order to solve the above-described problems, and provides an image forming apparatus capable of forming stable image quality without complicating the apparatus.
[0005]
[Means for Solving the Problems]
The present invention has a photosensitive member and an intermediate transfer member disposed in contact with the photosensitive member, and transfers a toner image formed on the photosensitive member to the intermediate transfer member to be formed on the intermediate transfer member. In the image forming apparatus for transferring the toner image to a recording medium and outputting the final image, the intermediate transfer member is composed of a base material, a conductive member, and a surface treatment layer, and the volume resistance of the surface treatment layer is reduced. 10 4 Ωcm or less , connected to an electrode set at a predetermined potential, the photoconductor has a current-carrying portion whose surface is a conductive layer at the end of the photoconductor, An insulating material is provided outside the image area in contact with the energization portion .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Details of the invention will be described with reference to FIGS.
[0007]
FIG. 1 is a schematic cross-sectional view of a color image forming apparatus using an electrophotographic system which is an embodiment of the present invention. The configuration of the apparatus will be described with reference to the drawings. On the back side of the printer main body, there is a controller (not shown) that controls the printer. The controller incorporates an image signal processor and a print command controller. A photosensitive belt 1 stretched by a plurality of shafts is provided at the center of the main body. The photosensitive belt 1 has a three-layer structure of a photosensitive layer (for example, OPC) on the surface, a conductive layer (for example, aluminum) below the surface, and a base material for giving the belt mechanical strength, as indicated by arrows in the figure. It has become. The photosensitive belt 1 runs in the X direction. In the vicinity of the photoreceptor belt 1, a charger 2, an exposure device 3, a developing device 4a,
4b, 4c, 4d, an intermediate transfer drum 5, an erase lamp 6, and a photoreceptor cleaner 7 are provided. A drum cleaner 8 is provided above the intermediate transfer drum 5. A paper cassette 9, a pick roller 10, a transfer roller 11, a peeling device 12, and a fixing device 13 are arranged on the paper conveyance path. The charger 2 is a scorotron charger that uses corona wire discharge, or a roller charger in which a conductive roller to which a voltage is applied is brought into contact with the photosensitive member, and charges the surface of the photosensitive member to a specified potential. The exposure device 3 uses a laser diode and a lens system or an LED array, and exposes the photosensitive belt 1 to form an electrostatic latent image. The four developing devices 4a, 4b, 4c, and 4d are for charging the toner to a predetermined charge amount and developing the electrostatic latent image on the photosensitive belt 1, and in this embodiment, there are four developing devices. Different colors of toner, for example, yellow (Y), magenta (M), cyan (C), and black (K) are stored in the developing unit. The intermediate transfer drum 5 has a drum shape with a diameter of 80 to 200 mm. The present invention is characterized by the surface of the intermediate transfer drum 5, and details will be described later. The intermediate transfer drum 5 is in contact with the photosensitive belt 1 with a nip width of 5 to 20 mm, and the toner formed on the photosensitive belt 1 is transferred onto the intermediate transfer drum 5 by a voltage applied to the conductive layer of the photosensitive belt 1. Is transcribed. The erase lamp 6 removes the residual potential on the photosensitive belt 1 by light irradiation. The photoreceptor cleaner 7 removes residual toner remaining on the photoreceptor belt 1. The drum cleaner 8 removes the toner remaining on the intermediate transfer drum 5 after the sheet is transferred, and retracts upward while the toner image is present on the intermediate transfer drum 5. . Below the photoreceptor belt 1, there is a paper cassette 9, from which paper is pulled out by a pick roller 10 and then sent to a transfer section. The transfer roller 11 is for transferring a toner image formed on the intermediate transfer drum 5 onto a sheet, and is composed of a metal shaft and an elastic layer (1 k to 10 GΩ) having an appropriate resistance value. A DC voltage having a polarity opposite to that of the toner is applied to the metal shaft, and the toner is electrostatically transferred to the paper by an electric field generated by the voltage. The transfer roller 11 is retracted so as not to contact the intermediate transfer drum 5 while the toner image is formed on the intermediate transfer drum 5. The peeling device 12 is provided to neutralize the transfer charge on the back surface of the paper and peel the paper. The fixing device 13 heats and melts the toner on the paper and fixes it.
[0008]
The operation of the image forming apparatus of this embodiment will be described. First, when a computer print command is input to the controller, the charger 2 charges the photosensitive belt 1 and the exposure device 3 exposes to form a latent image. This latent image is first developed by the developing device 4a (for example, developed with yellow toner). The toner image developed on the surface of the photoreceptor belt 1 is transferred onto the intermediate transfer drum 5 when passing through the nip between the photoreceptor belt 1 and the intermediate transfer drum 5. Next, the photosensitive belt 1 is charged and exposed again, and then development is performed by the developing device 4b (for example, development is performed with magenta toner). The developed toner image is transferred onto the intermediate transfer drum 5 so as to overlap the previous toner image (yellow toner image). Thereafter, this process is repeated with the developing devices 4c and 4d to form toner images of a plurality of colors on the intermediate transfer drum 5. The toner images of a plurality of colors formed on the intermediate transfer drum 5 are transferred onto the paper at once by the transfer roller 11. Thereafter, the paper is peeled off by the peeling device 12 and is discharged after fixing by the fixing device 13. Thereafter, the residual toner remaining after the transfer on the photosensitive belt 1 and the intermediate transfer drum 5 is mechanically scraped off by the photosensitive cleaner 7 so that the residual toner on the intermediate transfer drum 5 remains. The toner is cleaned by the drum cleaner 8.
[0009]
Next, details of the present invention will be described. FIG. 2A shows the detailed structure of the intermediate transfer drum 5 in the image forming apparatus of this embodiment. The intermediate transfer drum 5 has a structure in which the raw tube is supported by three ribs from the central axis. Of course, the structure which inserted the bracket in the cylindrical drum both ends and passed the axis | shaft in the center, or the structure which penetrated the axis | shaft to the cylinder may be sufficient. The material of the members constituting these drums is a metal such as aluminum, iron, or copper, and conductive rubber, conductive resin, or the like whose volume resistance value is adjusted to 10 4 Ωcm or less. Further, the central axis is grounded through the intermediate transfer drum ground terminal 14 so that the entire intermediate transfer drum 5 is always at zero potential. In this embodiment, the potential of the intermediate transfer drum 5 is zero, but it is not particularly necessary to be zero, and is determined in relation to the process around the intermediate transfer member.
[0010]
A feature of the present invention is that the surface portion of the intermediate transfer member (including the entire intermediate transfer member) is made of a conductive material and set to a predetermined potential. For this reason, since there is no charge accumulation on the surface of the intermediate transfer member that occurs when the surface of the intermediate transfer member is covered with an insulating member, it is not necessary to provide a means for eliminating the charge on the intermediate transfer member. In addition, the instability of toner transfer with respect to environmental conditions that occurs when the intermediate transfer member is covered with a semiconductive member is also a metal conductor or a photoreceptor or toner that has a very stable resistance value with respect to environmental conditions as in this embodiment. The transfer is not unstable because the intermediate transfer member is made of conductive rubber or conductive resin having a resistance of 10 4 Ωcm or less that does not contribute to the transfer and is extremely small compared to paper.
[0011]
By the way, the structure which can anticipate the effect of this invention is not restricted only to said structure. Since the effect of the present invention is sufficiently exhibited if the surface of the intermediate transfer member is a conductor and set to a predetermined potential, for example, the configuration of FIG. FIG. 2B is an enlarged view of only the surface portion of the intermediate transfer drum 5. The surface of the drum base material 15 is covered with a conductive layer 16 having a thickness of 1 μm to 10 mm, and this conductive layer 16 is covered. The configuration is set to a specified potential. In this case, since the material of the drum base material 15 is only required to function as a drum structural material, it may be a non-conductive material such as plastic or, of course, a metal such as aluminum, iron, or copper. The conductive layer 16 is made of the above-described metal, conductive rubber having a volume resistance of 10 4 Ωcm or less, and conductive plastic. A predetermined potential is applied to the conductive layer 16.
[0012]
Further, the surface of the intermediate transfer drum 5 is often subjected to surface treatment for various purposes. In the color image forming apparatus of this embodiment, the surface of the intermediate transfer drum 5 is made of metal, conductive rubber or conductive plastic with a volume resistance of 10 4 Ωcm or less, and the surface is roughened by sandblasting and polishing. It is used after being processed to a shape of Ra 10 μm or less, preferably Ra 1 μm or less. In addition, as shown in FIG. 2C, a release treatment layer may be formed on the surface for the purpose of improving the releasability with the toner, or a protective treatment layer may be provided for the purpose of preventing mechanical wear. . At this time, when these surface treatment layers 17 are formed on the surface of the intermediate transfer drum 5 with a thickness of 1 μm or more, in order to exert the effects of the present invention, these surface treatments are mixed with carbon or metal particles. The volume resistance value of the layer 17 needs to be 10 4 Ωcm or less.
[0013]
By the way, when printing is performed with the image forming apparatus of the present invention, if the potential difference between the photosensitive belt 1 and the intermediate transfer drum 5 is increased, the image may be uneven. This is caused by discharge generated between the surface of the photosensitive belt 1 and the toner surface when the toner transferred onto the intermediate transfer drum 5 passes through the contact portion between the photosensitive belt 1 and the intermediate transfer drum 5 again. I found out. This discharge causes unevenness in the chargeability of the toner, resulting in a partial difference in transfer efficiency to the subsequent paper and unevenness in the image. Such image unevenness can be solved by providing a potential adjusting means 18 for adjusting the potential of the surface of the photoreceptor belt 1 and a potential adjusting means 19 as shown in FIGS. The potential adjusting means 18 and 19 adjust the potential difference between the surface of the photoreceptor belt 1 and the surface of the toner on the intermediate transfer drum 5 to 500 V or less, and an LED array or lamp that lowers the photoreceptor surface potential by light irradiation. The light source (18) for irradiating the photosensitive belt 1 with light, the DC corona charger, the AC corona charger, etc. (19) for irradiating the surface of the photosensitive belt 1 with a charge having a polarity opposite to the surface charge of the photosensitive member 1 are used. Is done. By using these potential adjusting means, in order to further increase the transfer efficiency of toner from the photosensitive belt 1 to the intermediate transfer drum 5, even if the voltage difference applied to both is increased, the surface of the photosensitive belt 1 and the intermediate transfer are transferred. The potential difference on the surface of the toner on the drum 5 can be reduced. As a result, no discharge occurs between the surfaces of the two toners, so that the toner is not unevenly charged, and a high-quality image without image unevenness can be provided.
The uneven charging of the toner generated at the nip between the photosensitive belt 1 and the intermediate transfer drum 5 can be eliminated by the following method. FIG. 4 shows an example in which the toner charge amount adjusting means 20 for adjusting the charge amount of the toner is arranged upstream of the contact portion between the intermediate transfer drum 5 and the transfer roller 11 in the intermediate transfer member moving direction. The toner charge amount adjusting means 20 uses a corona charger, an AC corona charger, or the like that irradiates charges having the same polarity as the toner. The toner charge amount adjusting means 20 imparts charges to the toner on the surface of the intermediate transfer drum 5 to make the toner charge amount uniform. To do. By using this, even if toner charging unevenness occurs at the nip between the photosensitive belt 1 and the intermediate transfer drum 5, image unevenness does not occur in order to make the charging uniform before transfer to the recording medium. An image forming apparatus capable of outputting a quality image is obtained.
[0014]
By the way, in the image forming apparatus of this embodiment, in order to supply a voltage to the conductive layer of the photoreceptor belt 1, there is a portion where there is no photosensitive layer at the end of the belt and the conductive layer is exposed. FIG. 5 is a diagram illustrating a contact portion between the photosensitive belt 1 and the intermediate transfer drum 5. When the energizing portion 21 with the conductive layer of the photosensitive belt 1 exposed directly contacts the intermediate transfer drum 5, an excessive current flows and the power supply is short-circuited. For this reason, in this embodiment, an insulating material 22 is provided on the surface of the intermediate transfer drum 5 at a portion where the energizing portion 21 of the photosensitive belt 1 is in contact with the intermediate transfer drum 5. As shown in the drawing, a groove having a depth of 10 μm to 10 mm is formed on a portion of the intermediate transfer drum 5 where the current-carrying portion 21 contacts, and a high-resistance urethane rubber is fitted in the groove. Of course, since the portion where the insulating material 22 is provided is out of the image area, the effect of the present invention is not invalidated. The insulating material 22 can use electrically semiconductive or insulating plastic or rubber in addition to the high-resistance rubber material described above, and prevents an excessive current from flowing therethrough. Such an insulating material 22 may be provided in any region on the intermediate transfer drum excluding the image region to which the toner image adheres, for example, a portion where the photosensitive layer is easily peeled off or a joint portion of the belt. The present invention may be applied to a portion where current leakage or short-circuit occurs in processes other than the photoreceptor belt 1.
[0015]
As described above, in the color image forming apparatus of the above embodiment, the surface of the intermediate transfer member is covered with the conductor set to a predetermined potential, so that a high-quality image can be stably obtained with respect to environmental conditions with a simple configuration. Could be provided. In the present embodiment, the drum-shaped intermediate transfer drum is described in detail as the intermediate transfer member. However, the present invention is not limited to the drum-shaped configuration, and may be applied to a belt-shaped intermediate transfer member. There is no problem.
[0016]
【The invention's effect】
According to the present invention, it is not necessary to provide a neutralizing unit for neutralizing the surface of the intermediate transfer member, and a small and low-cost image forming apparatus can be provided. In addition, since it is made of a material with a power of 10 4 Ωcm or less, which has extremely low resistance compared to photoreceptors, toner, paper, etc. and does not contribute electrically to toner transfer, toner transfer can be performed against changes in temperature and humidity. Since the performance is stable, an image forming apparatus capable of outputting a high-quality image can be provided.
In addition, toner charging unevenness generated at the contact portion between the photosensitive member and the intermediate transfer member can be eliminated or affected, so that an image forming apparatus capable of forming a high-quality image can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a color image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing a detailed structure of an intermediate transfer drum 5 of a color image forming apparatus that is an embodiment of the present invention.
FIG. 3 is a diagram illustrating a potential adjusting unit of a color image forming apparatus according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating a toner charge amount adjusting unit of a color image forming apparatus according to an embodiment of the present invention.
FIG. 5 is a diagram showing a detailed structure of an intermediate transfer drum 5 of a color image forming apparatus that is an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoconductor belt, 2 ... Charger, 3 ... Exposure device, 4a, 4b, 4c, 4d ... Developing device, 5 ... Intermediate transfer drum, 6 ... Erase lamp, 7 ... Photoconductor cleaner, 8 ... Drum cleaner, 9 Paper cassette, 10 ... Pick roller, 11 ... Transfer roller, 12 ... Peeling device, 13 ... Fixer, 14 ... Intermediate transfer drum ground terminal, 15 ... Drum base, 16 ... Conductive layer (intermediate transfer drum), 17 ... Surface treatment layer, 18 ... potential adjusting means (light source), 19 ... potential adjusting means (corona charger), 20 ... toner charge amount adjusting means (corona charger), 21 ... energizing section, 22 ... insulating material.

Claims (3)

A photosensitive member and an intermediate transfer member disposed in contact with the photosensitive member; and a toner image formed on the photosensitive member is transferred to the intermediate transfer member, and a toner image formed on the intermediate transfer member is transferred to the intermediate transfer member. In an image forming apparatus for transferring to a recording medium and outputting a final image, the intermediate transfer member includes a base material, a conductive member, and a surface treatment layer, and the volume resistance of the surface treatment layer is set to 10 4. and Ωcm or less, is connected to the set electrode at a predetermined potential, the photosensitive member, the surface on the end portion of the photosensitive member has a conductive portion is a conductive layer, wherein the intermediate transfer member, and the conductive portion the image forming apparatus you characterized in that a dielectric material outside the image region contacting.   The image forming apparatus according to claim 1, further comprising a potential adjusting unit that adjusts a potential of the surface of the photoconductor disposed upstream of the contact portion between the photoconductor and the intermediate transfer member in the photoconductor moving direction.   3. The image forming apparatus according to claim 1, wherein the toner charge amount adjusting unit adjusts the charge amount of the toner on the surface of the intermediate transfer member disposed upstream of the contact portion between the intermediate transfer member and the recording medium in the intermediate transfer member moving direction. An image forming apparatus.

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