JP3554173B2 - Color image forming equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic color image forming apparatus, and more particularly to a technique for improving transfer efficiency when an intermediate transfer member is used.
[0002]
[Prior art]
2. Description of the Related Art Japanese Patent Application Laid-Open No. 4-287070 discloses an example in which a conductive sponge, which is an elastic body, is lined with a cylindrical metal drum as an intermediate transfer member used in a color image forming apparatus.
According to this technology, the eccentricity of the intermediate transfer drum, the photosensitive drum, the transfer roller, or the like, or the vibration in contact can be prevented and the color can be absorbed on the intermediate transfer body which is the center of the process in order to eliminate the color shift and the like. It is disclosed that a good output image can be obtained by using a configuration that does not affect image transfer.
[0003]
[Problems to be solved by the invention]
Although the above-described prior art can certainly absorb the eccentricity and contact vibration of the roller in the intermediate transfer member, the intermediate transfer member is in rotational contact with the eccentric state of each of the intermediate transfer drum, the photosensitive drum, and the transfer roller. In some cases, the upper surface layer was displaced, which caused the color to be easily displaced.
In order to suppress the displacement of the surface layer, a method of increasing the hardness of the elastic body can be considered. Loose force tends to increase and transfer efficiency tends to decrease.
[0004]
In addition, in order to lower the volume resistivity of the adhesive when bonding the conductive elastic body to the metal drum, a conductive adhesive containing a large amount of carbon in the material is often used. Since the conductive adhesive contains a large amount of carbon, the conductivity is increased, but the adhesive strength is accordingly reduced, peeling is liable to occur, and color shift is liable to occur.
[0005]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a color image forming apparatus capable of forming a good color image without color shift, deterioration of a transfer member, and peeling of a conductive elastic body. Aim.
[0006]
According to the present invention, there is provided an image forming apparatus for forming a toner image by providing charging, exposing and developing means around an image carrier for forming an electrostatic latent image. Means, and an intermediate transfer member for temporarily transferring and holding the toner image, wherein a plurality of the image forming means are arranged around the intermediate transfer member, and a plurality of toner images are superimposed on the surface of the intermediate transfer member for color transfer. In the color image forming apparatus for forming an image, the intermediate transfer body is formed by sequentially laminating an elastic body and a high-resistance film on a conductive cylindrical substrate, and the hardness of the elastic body is out of the range of the image formation. In that it has a high hardness.
[0007]
Further, the present invention is characterized in that the thickness of the elastic body is configured to be thicker than the range of the image formation.
Further, in the intermediate transfer body, an elastic body is formed on a conductive cylindrical substrate via an adhesive, and a high-resistance film is laminated on the elastic body, and the resistivity of the adhesive is adjusted to the range of the image formation. Another feature is that the resistivity of the adhesive bonding outside the range is higher than that of the inside. At this time, an adhesive within the range of image formation may not be used, and the resistivity may be defined by volume resistivity or surface resistivity.
[0008]
According to the above configuration, since the hardness, pressure, and adhesive strength of the adhesive are increased outside the image forming range and the high-resistance film or the elastic body is supported at both ends, displacement of the film or the like is prevented. Color shift can be suppressed. On the other hand, in the image forming range, good low hardness and moderate pressure for transfer were obtained, and the transfer efficiency was set to an appropriate range in terms of transfer efficiency. Can be provided.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of the present invention. A is a first image forming unit. Reference numeral 1 denotes a photosensitive drum which is configured to form an electrostatic latent image. Reference numeral 2 denotes a charger, which uniformly charges the surface of the photosensitive drum 1. An exposure unit 3 forms an electrostatic latent image by this exposure. Reference numeral 4 denotes a developing device having a toner, which is configured to attach the toner to the electrostatic latent image. The toner image on the photoreceptor 1 thus formed is temporarily held on the surface of the intermediate transfer member 5 and is superimposed on the toner image of another color formed by the other image forming means B to form a color image. Is formed.
[0010]
Next, the principle of the present embodiment will be described in detail with reference to FIGS.
FIG. 2 shows the layer structure of the intermediate transfer member 5. A cylinder 50 is a metal cylinder. A conductive elastic body 52 is adhered to the surface of the cylinder 50 via a conductive adhesive 51, and a high-resistance film 53 is wound on the surface. The cylinder is preferably made of metal and has a diameter of 75 to 135 mm. The type of the conductive adhesive includes a conductive double-sided tape and a conductive paste. Examples of the type of the conductive elastic body include polyurethane and EPDM. Further, the high resistance film 53 is made of polycarbonate, fluorine resin, or polyimide resin, has a thickness of 50 to 200 μm, a volume resistivity of 10 ¹⁰ Ω · cm to 10 ¹² Ω · cm, and a surface resistivity of 10 ⁸ Ω / cm. □ to 10 ¹³ Ω / □ are used.
[0011]
Next, the relationship between the color shift and the hardness of the elastic body 52 is shown in FIG. Here, the measurement point is obtained by dividing the measurement point in the longitudinal direction of A4 into 16 and changing the Asker F value to 50 to 90 to measure the color shift amount (μm). In this case, it can be understood that the color shift decreases as the hardness increases. In other words, when the hardness of the elastic body 52 is low, the pressure at the nip portion of the transfer is low, and the high-resistance film 53 on the surface is easily shifted, which is likely to cause color shift. However, increasing the hardness suppresses color shift. be able to.
[0012]
However, when the hardness of the elastic body 52 is increased, a dropout phenomenon of the toner image occurs. FIG. 4 shows the relationship between the hardness of the elastic body 52 and the void. Here, it can be seen that, when the hardness (Young's modulus) increases, the transfer pressure increases, so that a dropout, a decrease in image density, and the like are likely to occur.
[0013]
Accordingly, as a first embodiment of the present invention, as shown in FIG. 5, the hardness of the elastic body 52 laminated on the cylinder 50 is set to a high hardness at L1 outside the image forming area and L2 within the image forming area. Then, the hardness is made low. By increasing the hardness outside the image forming range in this way, the adhesion between the elastic body 52 and the high-resistance film 53 at both ends of the intermediate transfer drum 5 is good, and the pressure between the elastic body 52 and the film 53 also increases at both ends. In addition, the high-resistance film 53 is less likely to shift at both ends, and as a result, the entire film 53 is prevented from shifting. Further, in the image forming range L2, the hardness is set to be low in order to prevent the "missing" of the toner image. Thereby, it is possible to solve both the color misregistration and the “missing” of the transfer. The range in which the hardness of the elastic body 52 is set to the high hardness or the low hardness is a range in which “color shift” and “hollowout” do not occur. Specifically, the amount of color misregistration is preferably 120 μm or less on average of a plurality of points measured in the axial direction.
[0014]
As for the hardness of the elastic body 52, Asker F is preferably 50 to 70 °, more preferably 50 to 60 ° within the image forming range. Outside the image forming range, Asker F is preferably 90 ° or more.
[0015]
When the transfer voltage is constant, particularly when the resistivity of the elastic body 52 and the resistivity at the interface with the cylinder (adhesive layer) are low, the current at the end of the photoconductor (the portion of the conductive substrate) is reduced. The volume resistivity of the conductive elastic body may be set low inside the image forming range and high outside the image forming range, since excessively easy flow may cause deterioration of the transfer member.
[0016]
Next, as a second embodiment, the transfer pressure is increased at both ends by reducing the thickness of the elastic body 52 in the image forming range and increasing the thickness L1 outside the range. Similarly, it is configured to prevent the high-resistance film 53 from being rubbed. In this case, the axial length L3 of the photoconductor 1 is configured to be longer than the sum of L1 × 2 places outside the image forming range and L2 inside the image forming range. Here, the range in which the thickness of the elastic body 52 outside the image forming range and the thickness within the image forming range are set to “thick” and “thin” depends on the pressure when the elastic layer is covered with the film. It is conditioned on being equivalent to the embodiment. Specifically, the thickness of the elastic body 52 is preferably 5 to 10 mm in the image forming range, and is preferably 1.2 times the thickness in the image forming range outside the image forming range.
[0017]
Furthermore, as a third embodiment of the present invention, regarding the adhesive for bonding the cylinder 50 and the elastic body 52, the resistivity of the conductive adhesive 51 outside the image forming range L1 is increased or the insulating property is increased to increase the adhesive force. Even if the image forming range is configured to contain a large amount of carbon in the adhesive and lower the resistivity in the image forming range, the adhesive force between the elastic body 52 and the cylinder 50 becomes strong at both ends, and the peeling of the elastic body 52 is prevented. It is possible to prevent the image from being displaced or deteriorated due to peeling. The thickness of the conductive adhesive 51 is preferably 1 to 100 μm, and the volume resistivity of the adhesive 51 that adheres within the image forming range is preferably 10 ⁸ Ω · cm or less. The surface resistivity is preferably 10 ⁸ Ω / □ or less, more preferably 10 ⁶ Ω / □ or less. In addition, the problem of peeling can be solved by using an insulating adhesive having a high adhesive strength outside the image forming range for bonding the elastic body.
[0018]
【The invention's effect】
As described above, according to the present invention, the color is misaligned because it is increased outside the image forming range, the hardness of the conductive elastic body is reduced within the image forming range, and the transfer pressure is further reduced. Image transfer omission can be prevented while preventing transfer film displacement.
[0019]
The same effect can be obtained even if the thickness of the elastic body is small in the image forming range and is large outside the image forming range. In addition, since the volume (or surface) resistivity of the adhesive layer is set low in the image forming range and high outside the image forming range, it is possible to prevent current concentration at the end of the photoreceptor and to solve the problem of peeling of the elastic body. As a result, image displacement and the like can be prevented.
[Brief description of the drawings]
FIG. 1 is an external view of a color image forming apparatus of the present invention. FIG. 2 is a view for explaining a layer configuration of an intermediate transfer member. FIG. 3 is a view showing a relationship between hardness of an elastic body and an amount of color misregistration. FIG. 5 is a diagram showing the relationship between the hardness (Young's modulus) of the body and the void in the transfer. FIG. 5 is an explanatory view of the present invention.
1: photosensitive drum 2: charging device 3: exposure device 4: developing device 5: intermediate transfer body 50: cylinder 51: conductive adhesive 52: conductive elastic body 53: high resistance film L1: outside the image forming area L2: Within the range of the image forming area L3: Length of the photosensitive drum in the axial direction

Claims (3)

Image forming means for forming a toner image by providing charging, exposing and developing means around an image carrier for forming an electrostatic latent image; and an intermediate transfer member for temporarily transferring and holding the toner image. In a color image forming apparatus that arranges a plurality of the image forming units around an intermediate transfer body and forms a color image by overlapping a plurality of toner images on the surface of the intermediate transfer body,
The intermediate transfer body is formed by sequentially laminating an elastic body and a high-resistance film on a conductive cylindrical substrate, and setting the hardness of the elastic body to be higher than the range of the image formation and the hardness outside the range. Characteristic color image forming apparatus. Image forming means for forming a toner image by providing charging, exposing and developing means around an image carrier for forming an electrostatic latent image; and an intermediate transfer member for temporarily transferring and holding the toner image. In a color image forming apparatus that arranges a plurality of the image forming units around an intermediate transfer body and forms a color image by overlapping a plurality of toner images on the surface of the intermediate transfer body,
The intermediate transfer member is formed by sequentially laminating an elastic body and a high-resistance film on a conductive cylindrical substrate, and the thickness of the elastic body is set to be larger than the thickness of the image forming area. Color image forming apparatus. Image forming means for forming a toner image by providing charging, exposing and developing means around an image carrier for forming an electrostatic latent image; and an intermediate transfer member for temporarily transferring and holding the toner image. In a color image forming apparatus that arranges a plurality of the image forming units around an intermediate transfer body and forms a color image by overlapping a plurality of toner images on the surface of the intermediate transfer body,
The intermediate transfer body has an elastic body formed on a conductive cylindrical substrate via an adhesive, a high-resistance film is laminated on the elastic body, and the resistivity of the adhesive is set within the range of the image formation. A color image forming apparatus characterized in that the resistivity of an adhesive that adheres outside the range is increased.

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