JPH1078705A - Multicolor image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multicolor image forming device of a multiple image collectively transfer system capable of obtaining a plural-color image having excellent quality by separating transfer material without causing retransfer or faulty separation across the image of all image ratio and total image amount. SOLUTION: The image amounts classified by red and black of a two-color image are integrated according to a video signal and the image ratio and the image total amount of every color are calculated in a control circuit. A control function showing relation between the total image amount and a separation difference current, that means, difference current values (a), (b) and (c) at which the separation efficiency of the transfer material at the time of the red single color, the black single color (image total amount 100%) and at the time of solid white (0%) becomes maximum are plotted with reference to the total image amount, and the separation difference current values Ia' and Ib' at the time of the calculated total image amount (e%) on two characteristic lines GA and GB linking (a), (b) with (c) at the time of the red single color and the black single color are obtained. The obtained values are proportionally distributed by the image ratio α/β of the red/black toner image, and the obtained difference current value Ic' is decided as an optimum separation difference current value in the case of collectively transferring the two-color image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam printer and an electrostatic recording apparatus, and more particularly to a multicolor image forming apparatus capable of forming a multicolor image.

[0002]

2. Description of the Related Art In recent years, many images having different colors or different information are formed on a single sheet of paper with different colors, and a multi-color image forming apparatus for reproducing the same has a plurality of colors. Is provided on the market.

[0003] Among such multicolor image forming apparatuses, those of the type in which development is performed by two or more developing units while the image carrier rotates once, and the obtained multicolor image is collectively transferred to paper. There are many proposals. For example,
Some of the two developing units perform development while keeping the electric field constant with a DC bias (US Pat. Nos. 4,572,651 and 4,416,533). These methods mainly focus on a method of forming a latent image, and do not suggest a problem at the time of development or at the time of collective transfer of a plurality of color toner images on an image carrier onto a transfer material.

On the other hand, US Pat. No. 4,349,268 and Japanese Patent Application Laid-Open No. 56-14445 published earlier in Japan.
No. 2 discloses a method of applying a non-contact AC bias to the development of the second color by using a developing method.
No. 50 discloses a technique for preventing the second color developer from rubbing and disturbing the first color toner image by using a developing method in which a DC bias is applied in a non-contact manner to the second color development. I have.

As described above, in the formation of a multicolor image by multiple development, a technique for developing the next toner image so as not to disturb the previously formed toner image is known. U.S. Pat. No. 4,660,961 discloses a technique for realizing this by increasing the potential (latent image potential) of a previously developed toner image. After the development of the first color, the same polarity as the developer is applied to the entire surface of the image carrier, so that the potential of the toner image of the first color becomes substantially the same as that of the non-development portion. Was significantly prevented. This is a one-pass multicolor image forming apparatus, and has been actively studied in recent years, particularly by a method called a negative-negative recharging method.

As another important technique in forming a multicolor image, there is a transfer process of collectively transferring a plurality of color toner images formed on an image carrier under different conditions onto a transfer material. In this technique, a pre-transfer charger is installed immediately before the transfer charger to make the potentials of the toner images of multiple colors on the image carrier the same, and the same polarity as the charge polarity of the image carrier is used. (Japanese Patent Application Laid-Open No. 63-204273).

Further, in order to reduce the amount of charge of the recharged toner image on the image carrier in order to equalize the potentials of the toner images of a plurality of colors on the image carrier, a pre-transfer charger is provided. A method of applying an alternating voltage biased to the opposite polarity to the transfer voltage has been proposed (Japanese Patent Laid-Open No. 59-121348).
issue).

Regarding the separation of the transfer material, it has been proposed to appropriately adjust the separation current applied to the separation charger by the total amount of the image. As an extreme example, in the case of a solid white image (image amount is 0), there is no toner particle interposed between the image carrier and the transfer material, and therefore, the electrostatic attraction force of the transfer material to the image carrier is very small. As a result, the separation becomes slightly defective, so that a strong charge eliminating effect is required, and a large separation current is required. In the case of a solid black image (maximum image amount), if the transfer material is excessively neutralized, the toner once transferred onto the transfer material is reversely transferred onto the image carrier (so-called retransfer phenomenon). The separation current must be set to a value that is not too large. Therefore, it is beneficial to adjust the separation current based on the total image amount.

[0009]

However, the optimal conditions for separating the transfer material are not only the total amount of the image but also the image amount (toner amount) of each color and the image forming process of single color or plural colors. Conventionally, the optimal setting of the separation condition in consideration of such an image amount for each color and a difference in an image forming process between a single color and a plurality of colors has not been performed. For this reason, problems such as retransfer of the toner, poor separation of the transfer material, occurrence of a jam, and the like may occur frequently.

Taking a two-color image as an example, an image portion using only the first color toner, an image portion using only the second color toner,
The optimal separation conditions in the image portion where the color toners are superimposed should differ depending on the respective image ratios and the total amount of images. However, in the batch transfer method, in order to separate them under one condition, the toner of one color must be separated. Often causes retransfer or poor separation of the transfer material, resulting in an image defect or a transfer material jam.

An object of the present invention is to separate the transfer material from the image carrier while simultaneously transferring the toner images of a plurality of colors formed on the image carrier onto the transfer material, and to obtain an image having all image ratios and the total amount of images. An object of the present invention is to provide a multicolor image forming apparatus capable of separating a transfer material without causing retransfer or separation failure and obtaining a multicolor image of good quality.

[0012]

The above object is achieved by a multicolor image forming apparatus according to the present invention. In summary, the present invention is directed to a method of forming a multi-color toner image on an image carrier by repeating charging, exposing and developing the image carrier, and transferring the multi-color toner image to the image carrier. In a multicolor image forming apparatus in which a transfer material onto which a plurality of color toner images are transferred collectively on a material and separated from an image carrier by a separation charging unit, a current applied to the separation charging unit is changed to a multicolor toner image. The multi-color image forming apparatus is characterized in that it is adjusted to an optimum value in accordance with the image ratio for each color and the total image amount.
According to the present invention, the current applied to the separation charging means is obtained by superimposing a DC voltage and an AC voltage, and the DC voltage of the current is
The value is adjusted to an optimum value according to the image ratio of each color of the plurality of color toner images and the total image amount.

According to one aspect of the present invention, the first charging means, the exposing means and the developing means, the second charging means, the exposing means and the developing means are arranged along the rotating direction of the image carrier, Subsequently, a pre-transfer charging unit, a transfer charging unit and a separation charging unit are arranged, charged by the first charging unit, exposed by the first exposing unit, developed by the first developing unit, and developed by the first developing unit. After the first color toner image is formed thereon, the first color toner is charged by the second charging means to the same polarity as the first charging means, exposed by the second exposure means, developed by the second developing means, and A second color toner image is formed on the image carrier having the toner image formed thereon, and the two color toner images are further charged by a pre-transfer charging unit, and then transferred collectively onto a transfer material by a transfer charging unit. Then, the transfer material is separated by the separation charging means.

According to the present invention, the image reading means, the integrating means disposed between the image reading means and the first and second exposure means for integrating the image amount for each color, and the image reading means based on the image amount for each color Calculating means for calculating the image ratio for each color and the total image amount. Further, the image formation is performed by (1) (a)
A first charging unit, a first exposing unit and a first developing unit, (b) a first charging unit, a first or a second exposing unit and a second developing unit, or (c) a second developing unit. A monochrome mode using any one of the charging unit, the second exposing unit and the second developing unit, the pre-transfer charging unit, the transfer charging unit and the separation charging unit; and (2) the first charging unit and the first charging unit. And a first developing unit, a second charging unit, a second exposing unit and a second developing unit, and a multicolor method using a pre-transfer charging unit, a transfer charging unit, and a separation charging unit. And the current applied to the separation charging means can be adjusted to an optimum value according to each mode.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a multicolor image forming apparatus according to the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic diagram showing an embodiment of a multicolor image forming apparatus according to the present invention. This embodiment shows a two-color electrophotographic apparatus.

In FIG. 1, a photosensitive drum 1 as an image carrier is rotatably supported in a direction indicated by an arrow R1 in the figure. Around the photosensitive drum 1, in the order of its rotation, a first primary charger 2, a first exposure device, a first developing device 4, a second primary charger (recharger) 5, a second exposure device, 2 developing device 7, pre-transfer charger 8, transfer charger 9, separation charger 10,
A cleaner 11 and a pre-exposure lamp 12 are provided, and a fixing device 13 is provided on an outer extension of the separation charger 10. An image scanner unit 18 is provided above the photosensitive drum 1.

The image scanner section 18 includes a photoelectric conversion element (CCD) 19 as an image reading device. An original 15 placed on an original glass table 14 is illuminated by an illumination lamp 16.
And the reflected light from the original 15 is reflected by the mirror 17
The light is guided to a, 17b, and 17c, and is imaged by a lens 17d on a photoelectric conversion element 19 including a red (red), green (green), and blue (blue) filter.

The photoelectric conversion element 19 reads the red, green and blue components of the image information of the original 15 and outputs them as analog electric signals. The electric signals are converted into digital image signals by the A / D converter 20. After that, the image processing device 2
Sent to 1. The image processing device 21 includes the semiconductor laser 2
Red and black (black) image signals (video signals) for driving the pixels 3 and 24 are generated.

The semiconductor lasers 23 and 24 constitute first and second exposure devices. The red image signal (first image signal) and the black image signal (second image signal) are sent to a laser driver (not shown). By driving by the laser driver, the lasers 23 and 24 emit light in accordance with the red and black image signals, respectively, and the laser beam modulated in accordance with the red signal outputs a polygon mirror 25 as first image information. A cylindrical lens 26,
The first exposure 3 is performed by being guided to the charged photosensitive drum 1 via the mirror 17 e, and a first electrostatic latent image is written on the photosensitive drum 1. The laser beam modulated according to the black signal passes through a polygon mirror 25, a cylindrical lens 26, and mirrors 17f and 17g as second image information.
The photosensitive drum 1 is recharged and guided to the second exposure 6 to write a second electrostatic latent image on the photosensitive drum 1.

The image processing apparatus 21 and the semiconductor lasers 23 and 2
4, a video counter 22 is provided, and the video counter 22 is interface-connected to a control circuit (CPU) 40. The video counter 22 accumulates the image amount of each of the red and black colors based on the video signal from the image processing device 21, and the control circuit 40 determines whether the image is a single color or two colors based on the image amount for each color. The image type, the image ratio of the two-color image, and the like are calculated.

The pre-transfer charger 8 has a high-voltage power supply 30 in which an AC power supply and a DC power supply are connected in series.
It has a sine wave output with a pp of 9 kV and a frequency of 500 Hz. The DC power supply has a bias amount of an AC component, that is, a bias amount of an AC oscillation center (hereinafter, referred to as a difference current) of -100 to -100.
It consists of a constant current source that can be varied up to +300 μA. The output of the power supply 30 is appropriately adjusted by a control circuit (CPU) 40.

The transfer charger 9 has a DC current of -100 to-
High voltage power supply 3 consisting of a constant current source that can be varied up to 500 μA
1, and the output of the power supply 31 is similarly adjusted appropriately by the control circuit 40. The high-voltage power supply 3 of the separation charger 10
Reference numeral 2 denotes an AC power supply and a DC power supply connected in series, and the AC power supply has a sine wave output having a Vpp of 14 kV and a frequency of 500 Hz. DC power supply has a differential current of -100 to +
It is a constant current source that can be varied up to 300 μA. Similarly, the power supply 32 is subjected to output control by the control circuit 40.

The photosensitive drum 1 has a photoconductive layer provided on a cylindrical conductive substrate. In this embodiment, an a-Si photoreceptor having an amorphous silicon layer formed thereon is used as the photoconductive layer.

The formation of a two-color image according to this embodiment will be described with reference to the model diagram of FIG.

In forming an image, the photosensitive drum 1 is rotated, and first, the surface of the photosensitive drum 1 is
Then, as shown in FIG. 2A, after being uniformly charged to about +400 V, the first image exposure 3 is performed by the first exposure device using a laser beam based on the first image signal (red image signal).
To write and form a first electrostatic latent image having a potential of about +50 V on the photosensitive drum 1 (FIG. 2B). The first latent image is developed by a first developing device 4 using a two-component developer containing a positively charged red toner and a ferrite carrier, and a first toner image (red toner image) is formed on the photosensitive drum 1. Form. The surface potential of the first toner image is a potential slightly higher than +50 V due to the positive charge of the toner (FIG. 2).
(C)).

Next, the photosensitive drum 1 on which the first toner image has been formed is again charged positively by the recharger 5, whereby the potential on the surface of the photosensitive drum 1 is increased to about +550 V, and the potential of the first toner image is increased. Rises from more than +50 V to about +400 V (FIG. 2D)). The second photosensitive drum 1
The exposure device performs a second image exposure 6 using a laser beam based on a second image signal (black image signal) to write and form a second electrostatic latent image on the photosensitive drum 1 at a potential of about +50 V (FIG. 2 (e)).

The second latent image is formed by a second developing device 7 using a positively charged black magnetic toner (one-component magnetic developer). A reverse bias development is performed by a jumping development method by applying a developing bias on which a voltage is superimposed, and a second toner image (black toner image) is superposed on the photosensitive drum 1 from above the first toner image.
To form The surface potential of the second toner image is a potential slightly higher than +50 V due to the positive charge of the toner (FIG. 2).
(F)).

In this manner, the first,
When a two-color toner image on which the second toner image is superimposed is formed, the photosensitive drum 1 is charged by the pre-transfer charger 8.

In the charging by the pre-transfer charger 8,
On the positive side where the difference current of the AC component is the same as the polarity of the photosensitive drum 1, as shown in FIG. 3A, the potential of the white background portion of the photosensitive drum 1 decreases due to the charge removal effect of the AC current (potential +
500V). Conversely, a positive charge is applied to the second toner image by the charge applying effect (potential exceeds +75 V), and the potential difference from the white background is reduced. At this time, a positive charge is also applied to the first toner image, and the charge amount increases (potential +450 V).

On the other hand, on the negative side where the difference current is opposite to the polarity of the photosensitive drum 1, as shown in FIG.
, The potential of the white toner and the potential of the first toner image both decrease (the potential of the white toner +300 V, the potential of the first toner image +250).
V). At this time, a negative charge is applied to the second toner image at the same time, and the charge amount is reduced (more than the potential +75 V).

As described above, by performing the pre-transfer charging, the potential on the photosensitive drum 1 is adjusted so that an optimal transfer current can be appropriately given to the batch transfer of the first and second toner images. And the charge amount of the toner image thereon, in particular, the charge amount of the first toner image.

If the charge amount is controlled in this way,
The first and second toner images on the photosensitive drum 1 are
Is collectively electrostatically transferred by the transfer charger 9 onto the transfer material P sent to the printer. The transfer current uses a negative polarity having a polarity opposite to that of the toner.

Thereafter, the transfer material P is electrostatically separated from the photosensitive drum 1 by the separation charger 10, and the separated transfer material P is sent to the fixing device 13 to be fixed. Finally, a fixed image of a two-color image is obtained. . The difference current of the separation current applied to the separation charger 10 has a polarity that removes the charge on the back surface of the transfer material P that has contributed to holding the transfer material P on the photosensitive drum 1 in the transfer process, that is, a positive polarity in this embodiment. Use biased.

Prior to describing transfer material separation control according to the present invention, conventional control will be described.

FIG. 11 shows a relationship between the difference current (separation difference current) I of the separation current and the transfer efficiency η when the black toner is used alone.
At this time, the difference current condition of the pre-transfer charger 8 is +200 μm.
A, the difference current condition of the separation charger 10 is +300 μA.

The definition of the separation efficiency η is defined as follows, without causing the separation failure of the transfer material and the retransfer of the toner to the photosensitive drum.
This refers to the rate at which the transfer material passes through the transfer and separation steps, and a good image is obtained on the separated transfer material. Quantitatively, 10
0 images were formed and separation failure or retransfer was 1
If it occurs on 0 sheets, the separation efficiency is 90%, and if it occurs on 20 sheets, the separation efficiency is 80%.

As shown in FIG. 11, the separation efficiency η tends to be deteriorated if the separation difference current is too small or too large. If the transfer material P is too small, the transfer material P cannot be completely separated from the photosensitive drum 1 and separation failure occurs. If the transfer material P is too large, the toner is retransferred to the photosensitive drum 1.

Conventionally, for a solid white image (total image amount 0%), which is difficult to separate, the separation difference current I is set to I = Ic (about 40% in the example in the figure) within a range where the separation efficiency is not reduced to 100%.
0 μA) as much as possible (this Ic is a separation difference current value at which separation failure does not occur most), and for a solid black image that can cause retransfer, a separation efficiency of 100% is not reduced. And the separation difference current I = Ib
(Ib is about 170 μA) (Ib is a separation difference current value at which retransfer of a solid black image does not occur most).

Actually, as shown in FIG. 12, the difference current value Ic between the solid white and the solid black is used as a separation difference current control function for obtaining the separation difference current I for obtaining the separation efficiency of 100% with respect to an arbitrary image total amount. , And Ib by a straight line (control line), and based on this, the separation difference current in the separation of the transfer material in the two-color image of red and black as well as the black alone is determined by the total amount of the black image. For optimal control.

FIG. 4 is a graph showing the relationship between the separation difference current I and the transfer efficiency η in the case of the present invention, in which the case of the red toner alone is added to FIG. In FIG. 4, a curve A represents the separation efficiency η of the transfer material P to which the red toner image of the first image has been transferred, and a first electrostatic latent image is formed on the photosensitive drum 1 and developed by the first developing device 4. The red toner image obtained by the
Is transferred to the transfer material P after being recharged. Curve B is the same as the curve in FIG. 11, and is the separation efficiency η of the transfer material P on which the black toner image of the second image has been transferred.
A black toner image obtained by forming an electrostatic latent image and developing by the second developing device 7 is directly transferred to the transfer material P.

In FIG. 4, the separation difference current Ia of the curve A is shown.
(Approximately 280 μA in the example in the figure) is a set value set as small as possible within a range that does not lower the separation efficiency of 100% with respect to the red toner image, and is a separation difference current value at which retransfer of the first image (red) does not occur most. is there. The meanings of Ic in curve B (common to curve A) and separation difference current Ib are as described above.

As shown in FIG. 4, the separation efficiency curve A of the transfer material for the red toner image has the upper side shifted to the right while the lower left end of the separation efficiency curve B for the black toner image is fixed. It is almost in shape. It is generally described that this difference in the separation characteristics is due to the difference in the charge amount of the toner on the photosensitive drum 1. In particular, in the multiplex image forming process as in the present invention, the charge amount is increased by the charge applying effect in the red toner image of the first image that is recharged, so that the difference is large.

In the conventional transfer material separation control, as described above, the separation difference current I for obtaining the transfer material separation efficiency of 100% is determined by the image total amount-separation difference current characteristic shown in FIG. It was adjusted to the optimal value based only on. In the present embodiment, the separation difference current is adjusted to an optimum value in consideration of the image ratio of the first image and the second image, based on the image total amount-separation difference current characteristic of FIG.

In FIG. 5, a straight line GB is a control straight line for the separation difference current when black alone is used, and is the same as the straight line in FIG. The straight line GA is a control line for the separation difference current when red alone, and is obtained from the separation efficiency curve A for red alone in the same manner as when the straight line GB is obtained from the separation efficiency curve B for black alone in FIG. .
However, the total image amount in FIG. 5 is represented as the sum α + β of the image amounts α and β of the first image (red) and the second image (black).

First, based on the output value of the video counter 22, the control circuit 40 sets the image ratio α / of the first and second images.
β and the total image amount α + β are integrated (this is set to e%).
Next, the straight lines GB and GA of the separation difference current I in FIG.
The optimum value of the separation difference current for each of the red image and the black image when the integrated image total amount is e% is obtained. This is called Ia ', Ib'
And Then, the optimal values Ia 'and Ib' are proportionally distributed (proportionally proportional) with the red / black image ratio α / β, and I ′ = (Ia′−Ib ′) × {β / (α + β)} + Ib ′ After the calculation, this proportional distribution value I 'is determined as the optimum value of the separation difference current, and the separation control of the transfer material of the two-color image is performed.

The separation difference current shown in FIG. 5 is set so that the transfer material separation efficiency is maximized in images having various image ratios. When α / β is 0%, that is, when black alone,
Alternatively, when α / β is 100%, that is, when red alone, the separation current Ia or Ib and further Ic are set so that the respective separation efficiencies are maximized.

FIG. 6 is a diagram showing a separable range of the transfer material according to the present embodiment together with a comparative example. In this embodiment,
In a triangular region formed by the horizontal axis of the total image amount of the black image from 0 to 100% and the vertical axis of the total image amount of the red image from 0 to 100%, that is, at all image ratios and the total image amount, retransfer and separation are performed. The transfer material could be separated without causing defects. On the other hand, in the conventional example, especially when a red image is included, the separable range is narrowed, and retransfer and poor separation occur.

Embodiment 2 In this embodiment, the equipment to be used, that is, the image forming process is changed depending on the type of image, that is, single color or two colors, and single color is red or black.

That is, as shown in Table 1, in forming a monochromatic image of red alone, the first charging, the first exposure, and the first development are performed to obtain a red toner image, and then the second charging is performed without performing the second charging. The transfer material is charged and transferred, and then the transfer material is separated. In black-only single-color image formation, a first charging, a second exposure, and a second development are performed to obtain a black toner image, and then the pre-transfer charging is performed without performing the second charging, and the transfer material is then transferred. To separate. In the formation of a two-color image of red and black, the first charging, the first exposure, and the first developing are performed to obtain a red toner image of the first image, and then the second charging (recharging), as described in the first embodiment. The second exposure and the second development are performed to form a black toner image of the second image on the red toner image, and then charged and transferred before transfer, and thereafter, the transfer material is separated.

[0051]

[Table 1]

As described above, the reason why the image forming process is changed depending on the type of the image of red alone, black alone, and two-color image is as follows.
This is to minimize the use of the second charger 5 in FIG. At the time of forming a two-color image, the second charger 5 performs a charging operation from the toner image on the photosensitive drum 1, so that the contamination by the toner becomes a problem. In addition, since it is located between the first developing device 4 and the second developing device 7 in terms of arrangement, contamination due to toner scattering from these developing devices also poses a problem.
I want to use as little as possible.

FIG. 7 shows the relationship between the separation difference current I and the separation efficiency η in this embodiment. At this time, the current condition of the pre-transfer charging was +300 μA, and the current condition of the transfer charging was +300 μA.
It is. In FIG. 7, a curve D represents the separation characteristics of the red-only image shown in Table 1, and shows the case where the transfer material is separated after the formation of the red toner image, before the transfer, without being recharged.
The separation difference current Id on the curve D is a separation difference current value at which retransfer of the red toner image does not occur most without recharging.
Curve B indicates the separation characteristics for the black-only image in Table 1, which is the same as that shown in FIG. Curve A is also the same as that shown in FIG. 5, which is the case where after the formation of the red toner image, recharging is performed, and then charging before transfer is performed. As shown in FIG. 7, the separation characteristics of a red image that is not recharged approach those of a black image. That is,
For the same red image, the appropriate conditions for separation differ depending on the presence or absence of the most charge, and the control function needs to be changed depending on the presence or absence of the most charge.

The control function of the separation difference current in the present embodiment,
That is, the characteristic of the total image amount-separation difference current is shown in FIG. The control straight line GD of the separation difference current I corresponds to the curve D in FIG.
The control straight lines GA and GB correspond to the curves A and B in FIG.
Is the same as shown in FIG. FIG. 9 shows a control flow of the separation difference current in this embodiment.

As shown in FIG. 9, the video counter 22
When the control circuit 40 integrates the image ratio α / β based on the output value of α and α / β = 0, as shown in FIG. The line (straight line) GD is set based on the total amount of the red image, and the transfer material on which the red toner image has been transferred is separated. When .alpha ./. beta. = 100, it is determined that a black-only image is to be formed, and the separation difference current is set on the line GB in FIG. 8 based on the total amount of the black image to separate the transfer material on which the black toner image has been transferred. 2 when α / β ≠ 0,100
It is determined that a color image has been formed, and the separation difference current is indicated by line G in FIG.
The transfer material is separated by setting the total image amounts of the two colors in A and GB and the proportional distribution of the ratio α / β.

According to this embodiment, the transfer material could be separated at all image ratios and total image amounts without causing retransfer or poor separation.

Embodiment 3 In Embodiments 1 and 2, two color toner images of red and black are formed during one rotation of the photosensitive drum, and the two color images are obtained by collectively transferring them to a transfer material. The embodiment is applied to a case where four color toner images of yellow, magenta, cyan, and black are formed during one rotation of the photosensitive drum, and are collectively transferred to a transfer material to obtain a full-color image.

FIG. 10 shows a main part of the image forming apparatus in this embodiment.
Shown in The image forming apparatus includes a first charger 2a, an exposure device (exposure 3a), a developing device (yellow) 4a, a second charger 2b, and an exposure device (exposure 3) around the photosensitive drum 1.
b), developing device (magenta) 4b, third charging device 2c, exposure device (exposure 3c), developing device (cyan) 4c, fourth charging device 2d, exposure device (exposure 3d), developing device (black)
4d. Other configurations of the present image forming apparatus are basically the same except that there are semiconductor lasers for four colors.

Also in this embodiment, when forming an image of each color alone, the transfer material can be separated with the maximum separation efficiency by setting the separation difference current of each color by the total amount of the image on the control line of each color. Was. In addition, when forming a full-color image of four colors, by using the control straight line of each color and by setting the separation difference current by proportional distribution of the total amount and the image ratio of the four colors (weighted average by the image ratio of the four colors),
The transfer material could be separated without lowering the separation efficiency.

[0060]

As described above, according to the present invention,
A separation difference current applied to a separation charger when a transfer material is separated from an image carrier while a multi-color toner image is formed on an image carrier by superimposing the toner images and the multi-color toner images are collectively transferred onto the transfer material. That is, the DC current of the separation current obtained by superimposing AC and DC is controlled by the image ratio of the toner images of a plurality of colors and the total amount of the entire image so that the maximum separation efficiency is obtained. A transfer material can be separated from the total amount of images without causing retransfer or separation failure, and a multi-color image of good quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a multicolor image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram showing a transition of a photosensitive drum surface potential in a two-color image forming process in the embodiment of FIG.

FIG. 3 is an explanatory diagram showing a surface potential of a photosensitive drum subjected to pre-transfer charging.

FIG. 4 is a graph showing the relationship between the separation difference current and the transfer efficiency in the embodiment of FIG.

FIG. 5 is a diagram showing a total image amount-separation difference current characteristic used for the separation difference current control performed in the embodiment of FIG. 1;

FIG. 6 is a diagram illustrating a separable range of a transfer material according to the embodiment of FIG. 1 together with a comparative example.

FIG. 7 is a graph showing the relationship between the separation difference current and the transfer efficiency in another embodiment of the present invention.

FIG. 8 is a diagram showing a total image amount-separation difference current characteristic used for the separation difference current control performed in the embodiment of FIG. 7;

FIG. 9 is a flowchart showing the separation / difference current control performed in the embodiment of FIG. 7;

FIG. 10 is a schematic view showing a main part of a multicolor image forming apparatus according to still another embodiment of the present invention.

FIG. 11 is a graph showing a relationship between a separation difference current I and a transfer efficiency in a conventional multicolor image forming apparatus.

FIG. 12 is a diagram illustrating a total image amount-separation difference current characteristic used for the separation difference current control performed in the conventional multicolor image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 first primary charger 4 first developing device 5 second primary charger (recharger) 7 second developing device 8 pre-transfer charger 9 transfer charger 10 separation charger 21 image processing device 22 video counter 23, 24 Semiconductor laser 30-32 High voltage power supply 40 Control circuit

Claims (5)

[Claims] 1. An image bearing member is repeatedly charged, exposed and developed to form a toner image of a plurality of colors on the image bearing member.
In a multicolor image forming apparatus, a plurality of color toner images are collectively transferred onto a transfer material supplied to an image carrier, and the transfer material onto which the plurality of color toner images are transferred is separated from the image carrier by a separation charging unit. A multicolor image forming apparatus, wherein a current applied to a separation charging unit is adjusted to an optimum value according to an image ratio for each color of a plurality of color toner images and an entire image amount. 2. The method according to claim 1, wherein the current applied to the separation charging means is obtained by superimposing a DC voltage and an AC voltage, and the DC current is adjusted to an optimum value according to an image ratio of each color of a plurality of color toner images and an entire image amount. 2. The multi-color image forming apparatus according to claim 1, wherein the adjustment is performed in the following manner. 3. A first charging unit, an exposing unit and a developing unit, a second charging unit, an exposing unit and a developing unit are arranged along a rotating direction of the image carrier, and subsequently, a pre-transfer charging unit is provided. Means, a transfer charging means and a separation charging means, which are charged by the first charging means, exposed by the first exposing means, developed by the first developing means, and formed into a first color toner image on the image carrier. Was formed, the second charging means charged the same polarity as the first charging means, the second exposure means exposed, and the second developing means developed to form a first color toner image. A second color toner image is formed on the image carrier, and then the two color toner images are further charged by a pre-transfer charging unit, then transferred collectively onto a transfer material by a transfer charging unit, and transferred to a transfer material by a separation charging unit. Claim 1 which separates
Or 2) a multicolor image forming apparatus. 4. Image reading means, and first and second image reading means.
4. An accumulating means for accumulating an image amount for each color arranged between the exposure means and an arithmetic means for calculating an image ratio for each color and an entire image amount based on the image amount for each color.
Multicolor image forming apparatus. 5. An image forming apparatus comprising: (1) (a) a first charging unit, a first exposing unit, and a first developing unit; and (b) a first developing unit.
(C) any one of the second charging means, the second exposing means and the second developing means, and the pre-transfer charging means, A monochromatic mode performed by using a transfer charging unit and a separation charging unit; (2) a first charging unit, a first exposing unit, a first developing unit, a second charging unit, and a second charging unit.
Exposure means and second developing means, and pre-transfer charging means,
5. The multicolor image forming apparatus according to claim 3, further comprising: a multicolor image formed by using a transfer charging unit and a separation charging unit, wherein the current applied to the separation charging unit is adjusted to an optimum value according to each mode. apparatus.