JPH08160756A - Color image forming device - Google Patents

Abstract

PURPOSE: To provide a color image forming device which is free from the occurrence of color slippage in the hue of a color image. CONSTITUTION: Separate toner images of different colors are formed on an image formation carrier and the toner images are transferred to an intermediate transfer medium 11 in order, thereby forming color toner images to the medium 11, and the color toner images are transferred all at once to a recording medium 12 by the use of a secondary transfer means, and thus the color image is formed on the recording medium 12. The secondary transfer means is a transfer roller 27 and its resistance value is 10<8> Ω or higher. This eliminates the need to control minutely a secondary transfer voltage or a secondary transfer current, and therefore makes it possible to obtain the same batch transfer efficiently in its monochromatic part and intermediate-color part at the same time irrespective of the resistance value of the intermediate transfer medium 11 and the thickness of each toner layer. As a result, color slippage is prevented from occurring in the hue of the color image.

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.

[0002]

2. Description of the Related Art Conventionally, various types of color image forming apparatuses have been provided. Among them, toner images of respective colors are sequentially transferred onto an intermediate transfer medium to form color toner images, and thereafter, color image forming apparatuses are formed. In a color image forming apparatus that transfers a toner image onto a recording medium, an endless belt, a cylindrical drum, or the like is used as an intermediate transfer medium.

To form a color image, yellow, magenta, and cyan toners are used, and the toner images of the respective colors are superposed in a multiple transfer process. For example, in a color image forming apparatus using an intermediate transfer medium, when a primary transfer voltage is applied to the intermediate transfer medium, an electric field is generated between the intermediate transfer medium and the image forming carrier by the primary transfer voltage. The toner image is transferred from the image forming carrier to the intermediate transfer medium. Therefore, a color toner image can be formed by sequentially transferring each color toner image to the intermediate transfer medium.

Subsequently, in a batch transfer step, the recording medium is sandwiched between the intermediate transfer medium and the secondary transfer means, and the secondary transfer voltage is applied to the secondary transfer means. Then, the color toner image formed on the intermediate transfer medium is transferred to the recording medium by the same operation as the multiple transfer step.
After that, the color toner image transferred to the recording medium is
It is fixed by a fixing device to form a color image (see Japanese Patent Application Laid-Open No. 5-142955).

[0005]

However, in the conventional color image forming apparatus, since the thickness of the toner layer is different in the entire area of the color toner image, the hue of the color image is deviated. This is because the color toner images are formed by superposing different color toner images. For example, in order to form a blue toner image, a magenta toner image and a cyan toner image are superposed. As described above, since most color toner images are formed by the toner images of the respective colors, there are monochromatic portions, intermediate color portions, etc., and it is rare that the thickness of the toner layer becomes uniform over the entire area of the color toner image. (Rare).

FIG. 2 is a diagram showing the relationship between the secondary transfer voltage and the batch transfer efficiency in the conventional color image forming apparatus.
The horizontal axis represents the secondary transfer voltage and the vertical axis represents the batch transfer efficiency η. As described above, the color toner image is formed on the intermediate transfer medium in the multiple transfer step, and the color toner image is transferred to the recording medium in the subsequent batch transfer step.

By the way, if the thickness of the toner layer transferred to the recording medium in the batch transfer process is different, the batch transfer efficiency η is different even when the secondary transfer voltage of the same value is applied, as shown in FIG. The hue of the color image formed on the medium is different from the desired hue, and color shift occurs.
For example, after forming a single color portion of a yellow toner image on the intermediate transfer medium and forming a red portion as an intermediate color portion by sequentially superposing each of the yellow and magenta toner images, the single color portion and the red portion are formed. When the portions are transferred to the recording medium at the same time, the toner layer thickness differs between the monochromatic portion and the red portion, so that the batch transfer efficiency η also differs, and generally, the thicker the toner layer, the lower the batch transfer efficiency η.

The batch transfer efficiency η is the ratio of the toner on the intermediate transfer medium adhered to the recording medium.
That is, the amount of toner on the intermediate transfer medium before transfer is set to W
1 and the amount of toner attached to the recording medium in the batch transfer process is W2, the batch transfer efficiency η is expressed by the equation (1). η = (W2 / W1) × 100 [%] (1) As described above, the batch transfer efficiency η of the single color portion becomes high, and the density of the yellow toner can be sufficiently obtained, while that of the red portion can be obtained. The batch transfer efficiency η becomes low, the yellow toner partially remains on the intermediate transfer medium, and the density of the yellow toner decreases. As a result, when the red portion is transferred to the recording medium, color shift occurs from the red side to the magenta side, and it becomes impossible to obtain the desired hue.

When the hue of the color image is deviated, the color reproducibility is remarkably reduced and the reproduction range is narrowed. SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the conventional color image forming apparatus described above and to provide a color image forming apparatus in which the hue of a color image does not shift.

[0010]

Therefore, in the color image forming apparatus of the present invention, toner images of respective colors are formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium. A color toner image is formed on an intermediate transfer medium, and the color toner image is collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

The secondary transfer means is a transfer roller.
Yes, the resistance value of the transfer roller is 10 ⁸[Ω] or more
It In another color image forming apparatus of the present invention, each color
Of the toner image on the image forming carrier,
Intermediate transfer by sequentially transferring the image to the intermediate transfer medium
A color toner image is formed on the medium, and the toner of the color is formed.
-The image is collectively transferred to a recording medium by the secondary transfer means and recorded.
A color image is formed on the recording medium.

The secondary transfer means is a transfer roller, and the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more. In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner on the intermediate transfer medium. An image is formed, and the color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

The secondary transfer means is a transfer roller, and the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more. Also, the process speed is v
_{When P} [m / s] is set and the width of the transfer roller is set to L [m], the transfer portion between the transfer roller and the intermediate transfer medium is 87
A secondary transfer current of 3 · v _P · L to 1782 · v _P · L [μA] is supplied.

In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to thereby form an image on the intermediate transfer medium. Form a color toner image,
The color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

Then, the resistance value of the intermediate transfer medium is set to 10
⁸ [Ω] or more. In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner on the intermediate transfer medium. An image is formed, and the color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

Then, the volume resistivity of the intermediate transfer medium is set to 2.2 × 10 ⁹ [Ω · cm] or more.

[0017]

According to the present invention, as described above, in the color image forming apparatus, the toner image of each color is formed on the image forming carrier, and the toner images are sequentially transferred to the intermediate transfer medium, thereby performing the intermediate transfer. A color toner image is formed on a medium, and the color toner image is collectively transferred to a recording medium by a secondary transfer means to form a color image on the recording medium.

The secondary transfer means is a transfer roller.
Yes, the resistance value of the transfer roller is 10 ⁸[Ω] or more
It In this case, the resistance value of the transfer roller is 10⁸[Ω] Not yet
If it is full, depending on the resistance value of the intermediate transfer medium, the monochromatic area
The same batch transfer efficiency can be obtained simultaneously for the
Cannot be achieved, and if the batch transfer efficiency of the single color part is increased,
The batch transfer efficiency of the intermediate color area is low, and conversely, the intermediate color area is
If you increase the batch transfer efficiency of
Will be low.

However, the resistance value of the transfer roller is set to 10
^{When it is 8} [Ω] or more, the same batch transfer efficiency can be obtained simultaneously in the single color portion and the intermediate color portion regardless of the resistance value of the intermediate transfer medium or the thickness of the toner layer. In another color image forming apparatus of the present invention, a color toner image is formed on an intermediate transfer medium by forming toner images of respective colors on an image forming carrier and sequentially transferring the toner images to the intermediate transfer medium. Is formed, and the color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

The secondary transfer means is a transfer roller, and the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more. In this case, if the combined resistance value of the intermediate transfer medium and the transfer roller is less than 10 ⁸ [Ω], equal batch transfer efficiencies cannot be obtained at the same time for the single color portion and the intermediate color portion, and the batch transfer efficiency of the single color portion cannot be obtained. When is high, the batch transfer efficiency of the intermediate color area is low, and conversely,
If the batch transfer efficiency of the intermediate color portion is increased, the batch transfer efficiency of the single color portion becomes low.

However, when the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more, the secondary transfer voltage and the secondary transfer current are kept at the same value, and the single color portion and the intermediate color portion are separated. The same batch transfer efficiency can be obtained at the same time. In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier,
A color toner image is formed on the intermediate transfer medium by sequentially transferring the toner images onto the intermediate transfer medium, and the color toner images are collectively transferred onto the recording medium by the secondary transfer means, and then transferred onto the recording medium. It is designed to form a color image.

The secondary transfer means is a transfer roller, and the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more. Also, the process speed is v
_{When P} [m / s] is set and the width of the transfer roller is set to L [m], the transfer portion between the transfer roller and the intermediate transfer medium is 87
A secondary transfer current of 3 · v _P · L to 1782 · v _P · L [μA] is supplied.

In this case, if the combined resistance value of the intermediate transfer medium and the transfer roller is less than 10 ⁸ [Ω], equal batch transfer efficiencies cannot be obtained at the same time for the single color portion and the intermediate color portion, and the single color portion cannot be obtained at the same time. If the batch transfer efficiency is high, the batch transfer efficiency of the intermediate color portion is low, and conversely, if the batch transfer efficiency of the intermediate color portion is high, the batch transfer efficiency of the single color portion is low.

However, when the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more, the secondary transfer voltage and the secondary transfer current are kept at the same value, and the single color portion and the intermediate color portion are separated. The same batch transfer efficiency can be obtained at the same time. Further, the transfer portion between the transfer roller and the intermediate transfer _{medium, 873 · v P · L~1782 ·} v P · L [μ
When the secondary transfer current A] is supplied, the same batch transfer efficiency can be obtained at the same time for the single color portion and the intermediate color portion.

In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to thereby form an image on the intermediate transfer medium. Form a color toner image,
The color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

Then, the resistance value of the intermediate transfer medium is set to 10
⁸ [Ω] or more. In this case, if the resistance value of the intermediate transfer medium is less than 10 ⁸ [Ω], equal batch transfer efficiencies cannot be obtained at the same time for the single color portion and the intermediate color portion, and if the batch transfer efficiency for the single color portion is increased, If the batch transfer efficiency of the intermediate color portion becomes low, and conversely, if the batch transfer efficiency of the intermediate color portion becomes high, the batch transfer efficiency of the single color portion becomes low.

However, the resistance value of the intermediate transfer medium is set to 10 ⁸
[Ω] or more, it is possible to obtain the same batch transfer efficiency at the same time for the single color portion and the intermediate color portion regardless of the resistance value of the secondary transfer means or the thickness of the toner layer. In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner on the intermediate transfer medium. An image is formed, and the color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

Then, the volume resistivity of the intermediate transfer medium is set to 2.2 × 10 ⁹ [Ω · cm] or more. In this case, the volume resistivity of the intermediate transfer medium is 2.2 × 10 ⁹ [Ω · c
If it is less than m], the same batch transfer efficiency cannot be obtained at the same time for the single color portion and the intermediate color portion, and if the batch transfer efficiency for the single color portion is increased, the batch transfer efficiency for the intermediate color portion becomes low, and conversely If the batch transfer efficiency of the portion is increased, the batch transfer efficiency of the single color portion is lowered.

However, when the volume resistivity of the intermediate transfer medium is set to 2.2 × 10 ⁹ [Ω · cm] or more, the solid color portion and the intermediate color portion are irrespective of the resistance value of the secondary transfer means and the thickness of the toner layer. It is possible to obtain the same batch transfer efficiency at the same time for the parts.

[0030]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a color image forming apparatus according to an embodiment of the present invention. In the figure, 11
Is an intermediate transfer medium that can be rotated in the direction of arrow A. As the intermediate transfer medium 11, a medium in which carbon is dispersed in order to avoid charging is used. In this embodiment, a cylindrical drum made of aluminum is used, a silicone rubber in which carbon is dispersed is molded on the cylindrical drum, and the surface of the silicone rubber is coated with a fluororesin such as PFA or FEP. I used what I did.

A photosensitive drum 21 is arranged in contact with the intermediate transfer medium 11. The photosensitive drum 21 is rotated in the direction of arrow B, and the charging device 22, the exposure device 23, and the developing device 24 are provided around the photosensitive drum 21.
Y, 24M, 24C and 24K are arranged. Further, toners 25Y, 25M, 25C and 25K of yellow, magenta, cyan and black are stored in the toner storage tanks of the developing devices 24Y, 24M, 24C and 24K, respectively. The toners 25Y, 25M, 25C and 25K are
Toner carrier 26Y, 26M, 26C, 26K, respectively
It is attached to the photoconductor drum 21 via.

The photoconductor drum 21 is formed by laminating a photoconductive layer on a conductive support, and any of a selenium photoconductor, an organic photoconductor, a zinc oxide photoconductor, an amorphous silicon photoconductor, etc. is used. can do. The charging device 22 is arranged so as to face the photoconductor drum 21. In this embodiment, as shown in the figure, a contact type charging roller was used. The charging roller is formed by laminating a conductive rubber on a metal shaft, for example. In addition, a conductive charging blade, a non-contact type corona charger, or the like may be used.

Then, the exposure device 23 converts the image signal into light and irradiates the photoconductor drum 21 with the light to perform exposure. As the exposure device 23, a combination of a light source such as a laser and an LED array and an image forming optical system can be used. In this embodiment, the light source is an LED
An array was used, and a rod lens array was used as an image forming optical system.

The developing devices 24Y, 24M, 2
In 4C and 24K, each toner carrier 26Y and 26
Toners 25Y and 25 attracted to M, 26C, and 26K
M, 25C, and 25K are conveyed in the direction of arrow C, adhere to the photosensitive drum 21, and develop the electrostatic latent image formed on the photosensitive drum 21. Each of the developing devices 24Y, 24M,
As 24C and 24K, a two-component magnetic brush developing device, a one-component magnetic brush developing device, a one-component non-magnetic developing device or the like can be used.

A transfer roller 27, which serves as a secondary transfer means, is arranged on the downstream side of the photosensitive drum 21 in the rotation direction of the intermediate transfer medium 11 so as to be movable back and forth with respect to the intermediate transfer medium 11. Any secondary transfer means may be used as long as it can electrostatically attach toner, and a contact-type conductive material can be used. In this example, a conductive roller was used as shown in the figure. The conductive roller is formed by laminating a resistance material having elasticity such as rubber or sponge on a metal support. If necessary, the surface of the resistance material may be coated with a protective material or the like. In the batch transfer process, a secondary transfer voltage having a polarity opposite to that of the toners 25Y, 25M, 25C and 25K is applied to the metal support of the transfer roller 27.

A heating / pressurizing means 28 as a fixing device is disposed downstream of the intermediate transfer medium 11 in the transport direction of the recording medium 12. The heating / pressurizing means 28
Is composed of a heating roller 29 and a pressure roller 30 which are arranged in a pair so as to face each other with the recording medium 12 interposed therebetween. The heating roller 29 is disposed so as to face the front side of the recording medium 12 onto which the toner image has been transferred, and is pressed against the recording medium 12 with a constant pressure. The heating roller 29 is formed by disposing a halogen lamp in a hollow member made of metal. Further, it is also possible to use one in which a heating resistance layer made of Ni-P or the like is laminated on a base material such as glass or ceramic, and a protective layer such as Ta ₂ O ₅ or fluororesin is further laminated thereon. .

On the other hand, the pressure roller 30 is used for the recording medium 1
The toner image of No. 2 is disposed so as to face the back side on which the toner image is not transferred. Further, the pressure roller 30 is biased toward the heating roller 29 side, and sandwiches the recording medium 12 with the heating roller 29 by a constant pressing force. The pressure roller 30 is made of an elastic roller and is formed by laminating rubber on a metal pipe. In this example, silicone rubber was used as the rubber.

Further, a paper feed roller 31 is provided for inserting the recording medium 12 between the intermediate transfer medium 11 and the transfer roller 27. Next, the operation of the color image forming apparatus having the above configuration will be described. As shown in the figure, the intermediate transfer medium 11 and the photoconductor drum 21 are rotated by a driving unit (not shown) at a constant peripheral speed in the directions of arrow A and arrow B, and at the same peripheral speed.

Then, based on the recording start signal,
The photoconductor drum 21 is uniformly and uniformly charged by the charging device 22. Next, the exposure device 23 emits light corresponding to the yellow image signal of the first color to the photosensitive drum 2
1 to form an electrostatic latent image. Here, since the light is irradiated only to the portion corresponding to the image, the charge in the image portion is erased, and the charge in the non-image portion is left as it is.

A developing device 24Y is disposed in contact with or close to the photosensitive drum 21, and the electrostatic latent image is visualized by the developing device 24Y to become a toner image. In the present embodiment, reversal development is used and the toner carrier 26Y is used.
A bias voltage is applied to. As a result, the charged toner 25Y on the toner carrier 26Y is attracted and adhered to the photoconductor drum 21 by the electrostatic force.

The yellow toner image formed on the photoconductor drum 21 is transferred to the intermediate transfer medium 11 arranged opposite to the photoconductor drum 21 by static electricity due to the primary transfer voltage. Therefore, the intermediate transfer medium 1
A primary transfer voltage having a polarity opposite to that of the toner 25Y is applied to No. 1 by a voltage applying unit (not shown). When the head of the image portion on the intermediate transfer medium 11 reaches the head of the yellow toner image formed on the photosensitive drum 21,
The yellow toner 25Y is sequentially attached to the intermediate transfer medium 11 from above the photoconductor drum 21 according to the movement of the intermediate transfer medium 11, and the yellow toner image is transferred.

Next, when the last part of the yellow toner image is developed on the photoconductor drum 21, the photoconductor drum 21 is made to coincide with the beginning of the image portion on the intermediate transfer medium 11.
Then, the second-color magenta toner image starts to be developed. Then, when the head of the image portion on the intermediate transfer medium 11 reaches the head of the magenta toner image, a primary transfer voltage is applied to the intermediate transfer medium 11, and the magenta toner image is transferred to the intermediate transfer medium 11. Overlaid with a yellow toner image. Similarly, the cyan and black toner images are sequentially transferred to the intermediate transfer medium 11, and when the toner images of all colors are transferred to the intermediate transfer medium 11, the intermediate transfer medium 11 is transferred.
A color toner image is formed on the surface.

In this way, all the toner images of each color are transferred onto the intermediate transfer medium 11, and when the head of the image portion approaches the transfer roller 27, the transfer roller 27 is moved by an unillustrated movable means. 11, the recording medium 12 is fed by the feeding roller 31,
It is conveyed to a transfer section between the intermediate transfer medium 11 and the transfer roller 27.

On the transfer roller 27, the intermediate transfer medium 11
A secondary transfer voltage having a polarity opposite to that of the color toner image formed on the above is applied by a voltage applying unit (not shown). Therefore, the color toner images formed on the intermediate transfer medium 11 are collectively transferred to the recording medium 12. Next, the recording medium 12 to which the color toner images have been transferred is heated and pressed by the heating / pressurizing means 28. That is, when the recording medium 12 is inserted between the heating roller 29 and the pressure roller 30, the toners 25Y, 25M, 25C and 25K of the color toner images transferred onto the recording medium 12 are
Heat is transferred from the heating roller 29 and heated and melted. Then, the recording medium 1 that has passed through the heating / pressurizing means 28
The toners 25Y, 25M, 25C, and 25K on the 2 are naturally cooled and returned to the solid state again. In this way, the color toner image is fixed on the recording medium 12.

Then, the recording medium 12 is discharged to a stacker (not shown) arranged outside the color image forming apparatus. By the way, in order to prevent the color shift of the hue of the color image, it is necessary to always obtain a constant batch transfer efficiency η even if the thickness of the toner layer changes.

In the batch transfer process, color toner images having partially different toner layer thicknesses are simultaneously recorded on the recording medium 1.
Must be transferred to 2. However, when the thickness of the toner layer changes, the resistance value of the toner layer also changes in proportion to it. Therefore, when a constant secondary transfer voltage is applied to the transfer roller 27 from a power source (not shown), according to Ohm's law, the toner is supplied from the power source each time a portion having a different toner layer thickness reaches the transfer portion. The next transfer current is different.

Even if a constant secondary transfer current is supplied from the power source, the amount of current flowing due to a change in the resistance value of the toner layer each time a portion having a different toner layer thickness reaches the transfer portion. Will also change. That is, most of the secondary transfer current supplied from the power source flows to the thin monochrome portion of the toner layer and the non-image portion where the toner layer is not formed, and one of the secondary transfer current supplied from the power source is supplied. Part flows to the thicker neutral part of the toner layer.

In the batch transfer process, an electric field is applied to the toner layer, and the electrostatic force generated by the electric field is used to perform the transfer. Also,
The electrostatic force is proportional to the strength of the electric field, and the strength of the electric field is proportional to the value of the secondary transfer current. Therefore, in order to increase the batch transfer efficiency η, it is necessary to flow an appropriate secondary transfer current to the toner layer.

Therefore, it is conceivable to increase the batch transfer efficiency η by controlling the secondary transfer current flowing in the toner layer, but the secondary transfer current that can be detected when actual printing is performed is Only the secondary transfer current supplied from the power supply. Normally, the image area where the toner layer is formed and the non-image area where the toner layer is not formed reach the batch transfer process at the same time, so it is not only difficult to measure the secondary transfer current flowing only to the image area. It is also difficult to control the secondary transfer current. Even if the secondary transfer current can be measured and controlled, measuring and controlling the secondary transfer current on a dot-by-dot basis increases the cost.

By the way, the members involved in the batch transfer process are mainly the intermediate transfer medium 11, the toner layer, and the recording medium 12.
And a transfer roller 27. Among them, it is known that the resistance value of the recording medium 12 changes depending on the temperature and humidity conditions. However, the change in the resistance value of the recording medium 12 is extremely small as compared with the change in the resistance value of the toner layer due to the change in the thickness, and can be ignored. Therefore, the parameters of the batch transfer efficiency η in the batch transfer step are the resistance values of the intermediate transfer medium 11, the toner layer, and the transfer roller 27.

Therefore, three kinds of the intermediate transfer medium 11 and the transfer roller 27 having different resistance values are prepared, and the value of the secondary transfer current supplied from the power source (hereinafter referred to as "power source current value") is changed. On the other hand, the batch transfer efficiencies η of the single-color portion, the two-color overlapping portion, the intermediate-color portion such as the three-color overlapping portion in the color image were simultaneously measured. And
It was examined whether or not there is a range of power supply current values such that the batch transfer efficiency η of each part becomes equal. Table 1 shows the results. In Table 1, ∘ indicates that there is a range of power supply current values where the batch transfer efficiency η is the same, and x indicates that there is no range of power supply current values where the batch transfer efficiency η is the same.

[0052]

[Table 1]

As can be seen from Table 1, when the resistance value of the transfer roller 27 is less than 10 ⁸ [Ω], the intermediate transfer medium 11
Depending on the resistance value of, the same batch transfer efficiency η cannot be obtained at the same time for the single color portion and the intermediate color portion, and if the batch transfer efficiency η for the single color portion is increased, the batch transfer efficiency η for the intermediate color portion will decrease, and conversely. If the batch transfer efficiency η of the intermediate color portion is increased, the batch transfer efficiency η of the single color portion is lowered.

However, the resistance value of the transfer roller 27 is set to 10
^{When it is 8} [Ω] or more, the same batch transfer efficiency η can be simultaneously obtained in the single color portion and the intermediate color portion regardless of the resistance value of the intermediate transfer medium 11 and the thickness of the toner layer. As a result, it is possible to prevent a color shift in the hue of the color image. In this case, in order to measure the resistance value of the transfer roller 27, in the actual printing state, the transfer roller 27
The transfer roller 27 is pressed against the stainless steel plate with the same force as that for pressing the intermediate transfer medium 11, and 200 [V] is applied between the shaft of the transfer roller 27 and the stainless steel plate. Then, at this time, the current flowing through the transfer roller 27 is measured, and the resistance value of the transfer roller 27 is calculated using Ohm's law.

When the resistance value of the transfer roller 27 is set as described above, the resistance value of the intermediate transfer medium 11 becomes irrelevant to the batch transfer efficiency η. Therefore, when the intermediate transfer medium 11 is manufactured, there is a margin in accuracy and variation of resistance value, and the manufacturing cost of the intermediate transfer medium 11 can be reduced. In this embodiment, the contact type transfer roller 27 was used as the secondary transfer means. The basic principle of the secondary transfer is to apply an electric charge having a polarity opposite to that of the toner image to the back surface of the recording medium 12, and use the electrostatic force due to the electric charge for each toner 25Y,
25M, 25C and 25K are attached to the recording medium 12. Therefore, even if a contact-type blade-type transfer device using a plate material as the secondary transfer means is used, the same effect as when the transfer roller 27 is used can be expected within the range of the resistance value described above. .

Next, a second embodiment of the present invention will be described.

In this case, three kinds of the intermediate transfer medium 11 and the transfer roller 27 having different combined resistance values are prepared, and the monochromatic portion of the color image and 2 are changed while changing the power supply current value.
The batch transfer efficiencies η of the intermediate color portions such as the color overlapping portion and the three color overlapping portion were simultaneously measured. Then, it was examined whether or not there is a range of power supply current value such that the batch transfer efficiency η of each part becomes equal. The results are shown in Table 2. In Table 2, ∘ indicates that there is a range of power supply current values where the batch transfer efficiency η is equal, and × indicates that there is no range of power supply current values where the batch transfer efficiency η is equal.

[0058]

[Table 2]

Incidentally, the combined resistance value means the toner 25.
The transfer roller 27 is pressed against the intermediate transfer medium 11 with the same force as in the actual printing state without passing through Y, 25M, 25C, 25K and the recording medium 12, and the transfer roller 27 is pressed between the shaft of the transfer roller 27 and the intermediate transfer medium 11 by 200. A resistance value calculated from the secondary transfer current flowing through the transfer roller 27 and the intermediate transfer medium 11 at that time by applying the secondary transfer voltage of [V] using Ohm's law.

As can be seen from Table 2, when the combined resistance value of the transfer roller 27 and the intermediate transfer medium 11 is less than 10 ⁸ Ω, the same batch transfer efficiency η can be obtained at the same time for the single color portion and the intermediate color portion. However, if the batch transfer efficiency η of the single color portion is increased, the batch transfer efficiency η of the intermediate color portion is decreased, and conversely, if the batch transfer efficiency η of the intermediate color portion is increased,
The batch transfer efficiency η of the single color portion becomes low.

However, when the combined resistance value of the transfer roller 27 and the intermediate transfer medium 11 is set to 10 ⁸ [Ω] or more, the secondary transfer voltage and the secondary transfer current are set to the same value regardless of the thickness of the toner layer. As it is, it is possible to simultaneously obtain the same batch transfer efficiency η for the single color portion and the intermediate color portion. As a result, it is possible to prevent a color shift in the hue of the color image.

Next, a third embodiment of the present invention will be described. In this case, three types of intermediate transfer medium 11 and transfer roller 27 having different resistance values and combined resistance values are prepared respectively, and the monochromatic part, the two-color overlapping part and the three-color overlapping part in the color image are changed while changing the power supply current value. The batch transfer efficiencies η of the intermediate color areas such as the above were simultaneously measured. And
It was examined whether or not there is a range of power supply current values such that the batch transfer efficiency η of each part becomes equal. Table 3 shows the results. In Table 3, ∘ indicates that there is a range of power supply current values where the batch transfer efficiency η is the same, and x indicates that there is no range of power supply current values where the batch transfer efficiency η is the same.

[0063]

[Table 3]

As can be seen from Table 3, the resistance value of the transfer roller 27 and the resistance value of the intermediate transfer medium 11 are both 10
^If it is less than ⁸ [Ω], the same batch transfer efficiency η cannot be obtained at the same time for the single color part and the intermediate color part. If the batch transfer efficiency η for the single color part is increased, the batch transfer efficiency η for the intermediate color part becomes low. , Conversely, the batch transfer efficiency η of the intermediate color part
If the value is high, the batch transfer efficiency η of the single color portion will be low.

However, at least one of the resistance value of the transfer roller 27 and the resistance value of the intermediate transfer medium 11 is set to 10
^{When 8} [Ω] or more, the same batch transfer efficiency η can be simultaneously obtained for the single color portion and the intermediate color portion while keeping the secondary transfer voltage and the secondary transfer current at the same value regardless of the toner layer thickness. it can. If the combined resistance value of the transfer roller 27 and the intermediate transfer medium 11 is less than 10 ⁸ [Ω], equal batch transfer efficiency η cannot be obtained at the same time for the single color portion and the intermediate color portion, and the single color portion is collectively transferred. If the efficiency η is high, the batch transfer efficiency η of the intermediate color portion is low, and conversely, if the batch transfer efficiency η of the intermediate color portion is high, the batch transfer efficiency η of the single color portion is low.

However, when the combined resistance value of the transfer roller 27 and the intermediate transfer medium 11 is set to 10 ⁸ [Ω] or more, the secondary transfer voltage and the secondary transfer current are kept at the same value, and the single color portion and the intermediate color portion are separated. The same batch transfer efficiency η can be obtained at the same time. As a result, it is possible to prevent a color shift in the hue of the color image. By the way, the secondary transfer current supplied from the power source is used to apply a charge having a polarity opposite to that of the toners 25Y, 25M, 25C and 25K to the back surface of the recording medium 12, and the charge is provided when the power supply current value is large. Becomes faster, and the charge is delayed when the power supply current value is small. When the process speed v _P is high and the width L of the transfer roller 27 is wide, a sufficient amount of electric charges cannot be applied to the back surface of the recording medium 12 within a fixed time. On the other hand, when the process speed v _P is low and the width L of the transfer roller 27 is narrow, a sufficient amount of electric charges can be applied to the back surface of the recording medium 12 within a fixed time.

As described above, when the process speed v _P and the width L of the transfer roller 27 are different, the range of the power supply current value where the batch transfer efficiency η is the same is also different. Therefore, the width L is 0.22
Using the transfer roller 27 of [m], the process speed v _P was changed, and the power supply current value at which the same batch transfer efficiency η can be simultaneously obtained in the single color portion and the intermediate color portion was measured. The results are shown in Table 4.

[0068]

[Table 4]

Here, the minimum value of the power supply current value range is I_min
And the maximum value of the power supply current value range is I _maxAnd when
Process speed v_PThe standard value of 0.025 [m / s]
And I_min≒ 4.8 x (v_P/0.025) (2) I_max≈ 9.6 × (v_P/0.025) ... (3)

Next, the process speed v _P is 0.025 [m
/ S], the width L of the transfer roller 27 was changed, and the power supply current value capable of simultaneously obtaining the same batch transfer efficiency η in the single color portion and the intermediate color portion was measured. The results are shown in Table 5.
Shown in

[0071]

[Table 5]

Thus, when the process speed v _P is constant and the reference value of the width L of the transfer roller 27 is set to 0.22 [m], I _min ≈4.9 × (L / 0.22) ... (4) I _max ≈10.0 × (L / 0.22) (5)

Then, by summarizing the above equations (2) to (5), the following equations (6) and (7) can be obtained. I _min ≈4.8 × (v _P /0.025)×(L/0.22) ≈873 · v _P · L [μA] (6) I _max ≈9.8 × (v _P / 0 .025) × (L / 0.22) ≈1782 · v _P · L [μA] (7) Therefore, the combined resistance value of the transfer roller 27 and the intermediate transfer medium 11 is set to 10 ⁸ [Ω] or more, and from the power supply, the power supply current value is _{873 · v P · L~1782 · v} P · L [μ
When the secondary transfer current [A] is supplied to the transfer portion, the same batch transfer efficiency η can be simultaneously obtained in the single color portion and the intermediate color portion regardless of the thickness of the toner layer. As a result, it is possible to prevent a color shift in the hue of the color image.

Next, a fourth embodiment of the present invention will be described. In this case, three types of the intermediate transfer medium 11 and the transfer roller 27 having different resistance values are prepared, and while changing the power supply current value supplied from the power supply, a single-color portion and a two-color overlapping portion in the color image, and three. Each batch transfer efficiency η of the intermediate color portion such as the color overlapping portion was simultaneously measured. Then, it was examined whether or not there is a range of power supply current value such that the batch transfer efficiency η of each part becomes equal. Table 6 shows the results. In Table 6, a circle indicates that there is a range of power supply current values where the batch transfer efficiency η is equal, and a cross indicates that there is no range of power source current values where the batch transfer efficiency η is equal.

[0075]

[Table 6]

As can be seen from Table 6, the intermediate transfer medium 11
When the resistance value of is less than 10 ⁸ [Ω], the transfer roller 27
Depending on the resistance value of, the same batch transfer efficiency η cannot be obtained at the same time for the single color portion and the intermediate color portion, and if the batch transfer efficiency η for the single color portion is increased, the batch transfer efficiency η for the intermediate color portion will decrease, and conversely. If the batch transfer efficiency η of the intermediate color portion is increased, the batch transfer efficiency η of the single color portion is lowered.

However, the resistance value of the intermediate transfer medium 11 is set to 1
When 0 ⁸ [Ω] or more, regardless of the thickness and the like of the resistance value and the toner layer of the transfer roller 27, it is possible to obtain single color portion and an intermediate color portion equal collective transfer efficiency η simultaneously with. As a result, it is possible to prevent a color shift in the hue of the color image. In this case, in order to measure the resistance value of the intermediate transfer medium 11, the transfer roller 2 is used in the actual printing state.
The intermediate transfer medium 11 is pressed against the stainless steel plate with the same force as pressing the intermediate transfer medium 7 onto the intermediate transfer medium 1.
200 between the conductive drum 1 and the stainless steel plate.
[V] is applied. Then, the current flowing through the intermediate transfer medium 11 at this time is measured, and the resistance value of the intermediate transfer medium 11 is calculated by utilizing Ohm's law.

In the present embodiment, the intermediate transfer medium 11 used is a cylindrical drum made of aluminum, on which a silicone rubber in which carbon is dispersed is molded to have a thickness d of 0.3 [cm]. did. Then, the contact width (nip width) w between the intermediate transfer medium 11 and the transfer roller 27 is set to 0.3 [cm], and the width L of the transfer roller 27 is set to 22 [c].
m]. When the resistance value of the intermediate transfer medium 11 is converted into the volume resistivity by using the following formula (8) based on these numerical values, R _V = R · w · L / d = 2.2 × 10 ⁹ [Ω・ Cm] …… (8) However, in this case, the volume resistivity is R _v and the resistance value of the intermediate transfer medium 11 is R.

Therefore, when the volume resistivity of the intermediate transfer medium 11 is set to 2.2 × 10 ⁹ [Ω · cm] or more, the solid color portion and the intermediate color portion are irrespective of the resistance value of the transfer roller 27 and the toner layer thickness. The same batch transfer efficiency η can be obtained at the same time for the portions. As a result, it is possible to prevent a color shift in the hue of the color image. In addition, when the transfer roller 27 is manufactured, the transfer roller 27 is not limited in accuracy and variation in resistance value, and a metal transfer roller without a resistance layer such as rubber or a coating layer can be used. The manufacturing cost of 27 can be reduced.

In this embodiment, the contact type transfer roller 27 is used as the secondary transfer means, but a non-contact type corona discharger may be used. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0081]

As described in detail above, according to the present invention, in the color image forming apparatus, the toner image of each color is formed on the image forming carrier, and the toner image is sequentially transferred onto the intermediate transfer medium. By transferring, a color toner image is formed on the intermediate transfer medium, and the color toner image is collectively transferred to the recording medium by the secondary transfer means to form a color image on the recording medium. There is.

The secondary transfer means is a transfer roller.
Yes, the resistance value of the transfer roller is 10 ⁸[Ω] or more
It Therefore, the secondary transfer voltage and secondary transfer current are
The resistance value of the intermediate transfer medium and toner
Regardless of layer thickness, etc.
The batch transfer efficiency can be obtained at the same time. as a result,
It is possible to prevent color shifts in the hue of color images.
it can.

In another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color image on the intermediate transfer medium. Toner image is formed, and the color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

The secondary transfer means is a transfer roller, and the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more. Therefore, it is not necessary to finely control the secondary transfer voltage and the secondary transfer current, and the same batch transfer efficiency can be simultaneously obtained in the single color portion and the intermediate color portion regardless of the thickness of the toner layer. As a result, it is possible to prevent a color shift in the hue of the color image.

In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to thereby form an image on the intermediate transfer medium. Form a color toner image,
The color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

The secondary transfer means is a transfer roller, and the combined resistance value of the intermediate transfer medium and the transfer roller is set to 10 ⁸ [Ω] or more. Also, the process speed is v
_{When P} [m / s] and the width of the transfer roller are L [m],
In the transfer section between the transfer roller and the intermediate transfer medium, 873.
v supplying secondary transfer current of _P · _L~1782 · v _P · L [μA].

Therefore, it is not necessary to finely control the secondary transfer voltage and the secondary transfer current, and the same batch transfer efficiency can be obtained simultaneously for the single color portion and the intermediate color portion regardless of the thickness of the toner layer. As a result, it is possible to prevent a color shift in the hue of the color image. Further, even if the process speed v _P and the width L of the transfer roller are changed, the secondary transfer current is changed correspondingly to them,
Regardless of the thickness of the toner layer, the same batch transfer efficiency can be obtained at the same time for the single color portion and the intermediate color portion. As a result, it is possible to prevent a color shift in the hue of the color image.

In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred onto an intermediate transfer medium to thereby form an image on the intermediate transfer medium. Form a color toner image,
The color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

Then, the resistance value of the intermediate transfer medium is set to 10
⁸ [Ω] or more. Therefore, it is not necessary to finely control the secondary transfer voltage and the secondary transfer current, and uniform batch transfer efficiency can be obtained in the single color portion and the intermediate color portion regardless of the resistance value of the secondary transfer means and the thickness of the toner layer. You can get it at the same time. As a result, it is possible to prevent a color shift in the hue of the color image.

In still another color image forming apparatus of the present invention, a toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to thereby form an image on the intermediate transfer medium. Form a color toner image,
The color toner images are collectively transferred onto a recording medium by a secondary transfer means to form a color image on the recording medium.

Then, the volume resistivity of the intermediate transfer medium is set to 2.2 × 10 ⁹ [Ω · cm] or more. Therefore,
There is no need to finely control the secondary transfer voltage and the secondary transfer current, and the same batch transfer efficiency can be obtained simultaneously in the single color portion and the intermediate color portion regardless of the resistance value of the secondary transfer means and the thickness of the toner layer. be able to. As a result, it is possible to prevent a color shift in the hue of the color image.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a secondary transfer voltage and a batch transfer efficiency in a conventional color image forming apparatus.

[Explanation of symbols]

11 Intermediate Transfer Medium 12 Recording Medium 21 Photosensitive Drum 27 Transfer Roller v _P Process Speed L Width

Claims (5)

[Claims] 1. A color toner image is formed on an intermediate transfer medium by forming a toner image of each color on an image forming carrier and sequentially transferring the toner image to the intermediate transfer medium. In a color image forming apparatus for collectively transferring a toner image onto a recording medium by a secondary transfer unit to form a color image on the recording medium, (a) the secondary transfer unit is a transfer roller, and (b) the transfer. Roller resistance value is 1
A color image forming apparatus characterized by having a value of 0 ⁸ [Ω] or more. 2. A toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner image on the intermediate transfer medium. In a color image forming apparatus for collectively transferring a toner image onto a recording medium by a secondary transfer unit to form a color image on the recording medium, (a) the secondary transfer unit is a transfer roller, and (b) the intermediate A color image forming apparatus characterized in that a combined resistance value of a transfer medium and a transfer roller is set to 10 ⁸ [Ω] or more. 3. A toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner image on the intermediate transfer medium. In a color image forming apparatus for collectively transferring a toner image onto a recording medium by a secondary transfer unit to form a color image on the recording medium, (a) the secondary transfer unit is a transfer roller, and (b) the intermediate When the combined resistance value of the transfer medium and the transfer roller is 10 ⁸ [Ω] or more, and (c) the process speed is v _P [m / s] and the width of the transfer roller is L [m], the transfer roller is 873 · v _P · L ~ 1782 · in the transfer section between the intermediate transfer medium and
v color image forming apparatus and supplying the secondary transfer current of _P · L [μA]. 4. A toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner image on the intermediate transfer medium. In a color image forming apparatus for collectively transferring a toner image onto a recording medium by a secondary transfer means to form a color image on the recording medium, the resistance value of the intermediate transfer medium is set to 10 ⁸ [Ω] or more. And a color image forming apparatus. 5. A toner image of each color is formed on an image forming carrier, and the toner images are sequentially transferred to an intermediate transfer medium to form a color toner image on the intermediate transfer medium. In a color image forming apparatus in which toner images are collectively transferred onto a recording medium by a secondary transfer unit to form a color image on the recording medium, the volume resistivity of the intermediate transfer medium is 2.2 × 10 ⁹ [Ω · cm]. ] A color image forming apparatus characterized by the above.