JP2000047499A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device capable of providing a satisfactory transfer image without causing transfer failure/separation failure in an intermediate transfer body. SOLUTION: This color image forming device is provided with a photoreceptor 1 developing means 4a-4d for developing a plurality of colors of toners, and an intermediate transfer body 8 for once transferring the developed toner to form a multiple transferred toner image. The intermediate transfer body 8 is formed by winding a non-stretchable film 8c on the surface of a conductive support 8a through a conductive elastic body 8b, and a conductive layer is formed on the side opposed to the conductive elastic body 8b on the reverse side of the non-stretchable film 8c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to an improvement in a color image forming apparatus using an intermediate transfer member.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 7-50358 (prior art 1) discloses an example in which a conductive layer is provided on the back surface of an intermediate transfer in a color image forming apparatus using an intermediate transfer body as a prior art. According to this patent, a back-facing electrode is provided on the side opposite to the secondary transfer roller of the intermediate transfer body, and a surface in contact with the back-facing electrode is formed as a conductive layer. Even if a partial floating occurs, the charge passes through the conductive layer of the intermediate transfer member and escapes from the portion where the conductive layer and the back electrode are in contact with each other. However, stable transferability from the intermediate transfer member to the transfer paper can be obtained.

On the other hand, as another prior art, an example in which an intermediate transfer body is formed into a cylindrical shape and an intermediate transfer film (non-stretchable film) is wound thereon is disclosed in Japanese Patent Application Laid-Open No. 5-35125 (prior art 2). According to this patent, since the intermediate transfer body is composed of a conductive elastic body and a detachable transfer film and has a fixing means for the film, maintenance and replacement are possible while taking into account the application of film tension. There is a feature. In addition, the conductive layer on the back surface of the film is not worn away, and has a feature of good durability.

[0004]

SUMMARY OF THE INVENTION
No. 2 had the following problems. That is, in the prior art 1, when the intermediate transfer member having the back surface as the conductive layer is moved while the back electrode is fixed to the facing portion of the secondary transfer roller, the conductive layer is worn due to friction between the two. Eventually, there is a problem that the conduction path of the electric charge is cut off.

On the other hand, in the prior art 2, the transfer film receives a tangential frictional force due to the contact with the photosensitive member and the secondary transfer roller while the intermediate transfer member is driven to rotate, although there is a film fixing means. And the conductive path is cut off at the time of secondary transfer or separation of the transfer paper by the separation electrode, resulting in transfer failure and paper separation failure. There was a problem. When the conductive elastic body is formed of a foam, the adhesion of the conductive elastic body to the film is reduced due to the cells in the elastic body. If you increase the cell diameter to increase the power,
Such a phenomenon is remarkable.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has a problem in that a defective transfer in an intermediate transfer member is not performed.
An object of the present invention is to provide a color image forming apparatus capable of obtaining a good transfer image without causing separation failure. Another object of the present invention is to provide a color image forming apparatus capable of obtaining a good transfer image and having durability even when the conductive elastic body and the non-stretchable film partially shift. It is in.

[0007]

In order to solve the above-mentioned problems, a color image forming apparatus according to the present invention comprises an image carrier for forming an electrostatic latent image, and toners of a plurality of colors.
A color image forming apparatus comprising: a developing unit that sequentially develops the toner into the electrostatic latent image; and an intermediate transfer body that temporarily transfers the developed toner to form a multi-transferred toner image. The intermediate transfer member is formed by winding a non-stretchable film on the surface of a conductive support via a conductive elastic body, and a conductive layer is formed on the back surface of the non-stretchable film facing the conductive elastic body. Is formed.

By providing a conductive layer on the back surface of the non-stretchable film of the intermediate transfer member, a conductive path in transfer can be ensured in any state due to partial displacement or the like, and there is no transfer failure and good. Transfer can be secured. In addition, since the transfer is performed by an intermediate transfer member, a constant transfer efficiency can be always secured even if the durability is partially shifted, and a color having a durability with no transfer failure / separation failure even when rotated for a long time. An image forming apparatus is provided. In the invention, the surface resistivity of the conductive layer on the back surface of the non-stretchable film is 1 × 1.
0 ⁸ Ω / □ may be used the following:.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a color image forming apparatus according to the present invention, which includes a photosensitive member 1, a charging unit 2 such as a scorotron charger, an exposure unit 3 such as a laser optical system, and four developing units 4a to 4 for each color. 4d, pre-transfer static elimination lamp 5, cleaning means 6, main static elimination lamp 7, intermediate transfer body 8, transfer means 9
Consisting of

The first color is developed by any one of the charging means 2, the exposing means 3, and the developing means 4a to 4d, and is primarily transferred onto the intermediate transfer member 8. For the second color, the residual toner of the first color is cleaned by the cleaning unit 6, and after the charge is removed by the main discharge lamp 7, the toner is developed again by any one of the charging unit 2, the exposure unit 3, and the developing units 4a to 4d. The charge is removed by the pre-transfer charge removing lamp 5, and primary transfer is performed on the intermediate transfer member 8.

The third and fourth colors are also transferred onto the intermediate transfer member 8 in the same manner as the second color, and then secondary-transferred to a transfer material by transfer means 9, and the transfer material is separated and fixed to form a full-color image. can get.

The photosensitive member 1 preferably uses a cylindrical a-Si drum. This is because when the photoconductor is OPC, the film thickness of the photoconductor decreases with the number of prints, or the dielectric thickness and resistivity in charging and transfer change due to electrical deterioration, so that long-term stable quality is maintained. This is because complicated control is required to perform the control. 30 ~
What is necessary is just 80 mm.

The photoconductor 1 has a surface heating element in contact with the inner surface of the support. The surface temperature of the photoconductor 1 is detected by a thermistor in contact with the surface of the photoconductor.
４５45 ° C.). Since the a-Si photoreceptor has little change in film thickness and exhibits stable electrostatic characteristics over a long period of time only by controlling the temperature at a constant level, complicated control as in the case of the OPC photoreceptor is necessary. Absent. Note that such a heating unit and a temperature control unit may be located at any position as long as it is inside or around the photoconductor 1. By controlling the temperature to be constant in this way, it is possible to prevent image deletion and to stabilize electrostatic characteristics.

The intermediate transfer member 8 includes a cylinder base 8a (conductive support) formed in a cylindrical shape and having conductivity, and a conductive elastic body 8b provided concentrically laminated outside the cylinder base 8a. And a non-stretchable film 8c (non-stretchable film) wound concentrically around the outside of the conductive elastic body 8b as a surface layer. In this embodiment, the non-stretchable film 8c has no seam, that is, a so-called seamless film. However, the present invention is not limited to this, and a method of applying a tension with a seam may be used.

The use of the cylindrical intermediate transfer member 8 has the following advantages. When the intermediate transfer body 8 is cylindrical, the film 8c is wound on a large circular cylinder base 8a, so that the transfer nip width is wider than a simple transfer roller and stable transfer characteristics can be obtained. is there. Since the conductive elastic body 8b can be provided between the firm cylinder base 8a and the film 8c, the conductive elastic body 8b is hardly damaged by external force from the surface and has excellent durability. For example, when the intermediate transfer member 8 is formed in a belt shape, although there is an advantage that the color image forming apparatus can be made compact, color misalignment is likely to occur due to the meandering of the belt or misalignment in the running direction, and complicated control is required. Cracks tend to be formed at the end of the belt, but this is not the case and durability is improved. Further, when the intermediate transfer member 8 is formed in a belt shape, the bias application area is transferred at the nip portion of the roller that normally rotates the belt, so that the surface resistivity of the transfer belt has to be lowered, so the transfer efficiency is reduced. If the surface resistivity changes due to surface deposits or the like, the image density may partially change, or the low surface resistivity may cause scattering or bleeding, resulting in an image with low resolution. However, since the transfer efficiency of the cylindrical intermediate transfer member depends only on the volume resistivity, the surface resistivity can be set to be high.

The conductive elastic body 8b is made of a foam as shown in FIG. 2, and has cells 8bh. In the configuration of the present invention, the average cell ratio is high at 600 μm (maximum 1 m).
m) or more are used. If it is more than this, a gap is formed between the non-stretchable film and the conductive elastic body so that a conduction path of electricity cannot be formed, but by adopting the configuration of the present invention, it is possible to use even such a high average cell ratio. It is possible. This reduces costs.

The volume resistivity of the conductive elastic body 8b is 3
× 10 ⁹ Ωcm or less, more preferably 1 × 1
0 ² to 1 × 10 ⁷ Ωcm is good. If this volume resistivity is too high, there is a risk of causing transfer failure / paper separation failure,
Even if it is low, there is a problem that the cost of the conductive material for lowering the resistance increases, the layer of the conductive elastic body 8 generated due to an excessive amount of the additive of the conductive material is broken, and the conductive material peels off. .

The material of the film 8c is fluororesin (ET)
FE, PVDF, etc.), polyether tether ketone,
Polycarbonate or the like may be used. However, it is necessary to select a conductive agent for the fluororesin in order to moderate the electric field dependence. The film 8c has a thickness of 20 to 200 μm, preferably 50 to 80 μm. If the film thickness is too large, the pressure applied to the toner image in the transfer nip portion becomes high, and the hollow image occurs. On the other hand, if it is too thin, the stiffness of the film is too weak, so that bundling to the film 8c becomes difficult during production and winding around the intermediate transfer member 8.

As shown in FIG. 2, a conductive layer 8d is formed on the back surface of the film 8c. The material of the conductive layer 8d is a rubber, an elastomer, a resin, or the like in which conductive inorganic particles, carbon black, an ionic conductive agent, a conductive resin, a conductive particle-dispersed resin, and the like are dispersed, and is extruded simultaneously with the film 8c. It is formed by a method such as adhesion or coating. The surface resistivity on the back surface of the film 8c on which the conductive layer 8d is formed is preferably 1 × 10 ⁸ Ω / □ or less, preferably 1 × 10 ² to 1 × 10 ⁷ Ω / □, more preferably. Is 1 × 10 ³ to 1 × 10 ⁶ Ω / □.

If the surface efficiency is too high, poor transfer or poor sheet separation will occur. On the other hand, if the surface resistivity is too low, the cost of the conductive layer 8d increases, and the addition of the conductive agent increases, so that problems such as cracking and peeling of the conductive layer 8d occur.

The thickness of the conductive layer 8d is 0.1 to 50.
μm, preferably 1 to 10 μm. If the film thickness is too large, the bending stiffness of the film 8c increases, and the toner image may drop out or the transfer efficiency may decrease. If the film thickness is too small, the conductive layer 8d may be worn due to friction with the conductive elastic body 8b, or a predetermined amount. Cannot be obtained.

An advantage of the provision of the conductive layer 8d is that the transfer belt of the prior art 1 does not directly contact the photosensitive member and the primary transfer roller in order to reduce the pressure of the transfer nip, so that the transfer belt is located on the downstream side in the rotation direction of the transfer belt. The transfer is performed with the earth roller arranged on the upstream side, so that the transfer current flows in the direction of the surface resistance of the transfer film and must be reduced to a predetermined value in order to be applied. But,
In the intermediate transfer member 8 of the present invention, the charge and discharge of the surface charge are determined only by the volume resistivity of the conductive elastic member 8b, and therefore, the surface resistance of the film 8c is not considered much.

Reference numeral 9 denotes a transfer roller for transferring the multiple toner transferred to the intermediate transfer member 8 to a sheet. Reference numeral 10 denotes a separation charger that separates the sheet from the intermediate transfer member 8.

[0024]

EXAMPLES (Experimental Example 1) An experimental machine having the same contents as in FIG. 1 was prepared under the following conditions. 1. 1. Intermediate transfer body Diameter of conductive substrate: φ110 Thickness of conductive elastic body: 5 mm Thickness of transfer film: 80 μm Thickness of conductive layer 5 μm Preparation of Intermediate Transfer Member An intermediate transfer member was formed by winding a seamless film on a cylinder substrate as shown in FIG. 1 via a conductive elastic body. Although not shown, the seamless film was fixed by bearings at both ends of the cylinder base. Using this experimental machine, Table 1
An experiment was performed with the film of No. However, the surface resistivity in the table indicates the surface resistivity on the side facing the conductive elastic body of the conductive layer formed on the back side of the film.

[0025]

[Table 1]

Using this film, printing was performed by A4 longitudinal feed, and the results of an evaluation of density unevenness in an experiment of transferability at the initial stage (after printing 10 sheets) are shown in Table 2. For the measurement of density, see Macbeth densitometer (Macbeth reflection densitometer R
D914) is used, and the measurement points are evaluated by measuring the image density at a total of 9 points of 3 points in the horizontal direction (center and both sides) and 3 points in the vertical direction (center and both sides) of A4. Was done. However, in the experimental environment shown in the table,
The term “gap” refers to the use of an intermediate transfer member produced by visually observing the state in which the conductive elastic body and the seamless film are completely in contact with each other, and the “void” between the conductive elastic body and the seamless film. A gap is formed at least at a measurement point with a spacer interposed between the two. The evaluation is as follows. ：: The maximum and minimum values of the image density are 0 to 0.1 Δ: The maximum and minimum values of the image density are 0.1 to 0.2 ×: The maximum and minimum values of the image density Is 0.2 or more

[0027]

[Table 2]

According to this experiment, when a conductive layer is formed on the back surface of the film, even if there is a gap, a conduction path in transfer can be sufficiently secured, and good transfer can be performed without transfer failure.

(Example 2) Next, the separability from which the sheet was separated from the intermediate transfer member was examined. "Contact" and "void" are the same as in Example 1,
Table 2 shows the results of an experiment conducted on the separation property by applying a fixed charge to the separation charger and changing the type of paper by using the above-described apparatus. Here, α, β, and γ are paper weighing (g / cm
² ) are different, and have a relationship of α <β <γ.
Also, in the table, Y is the horizontal line for vertical feed, T is the vertical line,
F indicates the front of the sheet, and B indicates the back of the sheet. Regarding the sheet separability, the order of sheets that are difficult to separate and wrap around the intermediate transfer member is αYB, αYF, αTB, αTF, βTF, β
TB, γTF, and γTB, with γTB having the highest stiffness and excellent separability. The evaluation is shown below. ：: Separation is sufficiently performed even when 50 sheets are continuously printed. Δ: Winding around the intermediate transfer body occurs with a probability of less than 20% when printing 50 sheets continuously. ×: Intermediate with a probability of 20% or more when printing 50 sheets continuously. Winding around the transfer body occurs

[0030]

[Table 3]

According to this experiment, by providing a conductive layer on the back surface of the film, the intermediate transfer member of the present invention has good separation properties for any kind of paper that has good separation properties from paper that originally has poor separation properties. As a result, good separation of paper is possible.

[0032]

As is apparent from the above description, according to the present invention, the transfer / separation property can be improved while minimizing the abrasion of the intermediate transfer film. For example, the cell diameter and volume of the conductive elastic body can be improved. Even when the resistivity is uneven or the resistance is increased due to energization, the effect that the allowable range of transfer / separation can be set wide can be expected.

Further, according to the present invention, the allowable range of the floating between the film and the conductive elastic body generated during the repetition of the image forming process is widened, so that a good image can be obtained for a long period of time. A remarkable effect is produced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of the present invention.

FIG. 2 is a partial cross-sectional view of the intermediate transfer member of the present invention.

[Explanation of symbols]

 1: photoreceptor (image carrier) 2: charging means 3: exposure means 4a to 4d: developing means 5: pre-transfer charge removing lamp 6: cleaning means 7: main charge removing lamp 8: intermediate transfer member 8a: cylinder base (conductive) 8b: conductive elastic body 8bh: cell 8c: non-stretchable film 8d: conductive layer 9: transfer roller 10: separation charger

Claims (2)

[Claims] An image bearing member for forming an electrostatic latent image; a developing means for storing a plurality of color toners; and a developing unit for sequentially developing the toner into the electrostatic latent image; And an intermediate transfer member for forming a multi-transfer toner image by transferring the image, wherein the intermediate transfer member is formed by winding a non-stretchable film on a conductive support surface via a conductive elastic material. A color image forming apparatus, wherein the conductive layer is formed on the back surface of the non-stretchable film and on the side facing the conductive elastic body. 2. The color image forming apparatus according to claim 1, wherein the surface resistivity of the back surface of the non-stretchable film on which the conductive layer is formed is 1 × 10 ⁸ Ω / □ or less.