JPH08227222A - Multicolor image forming device - Google Patents

Abstract

PURPOSE: To provide a multicolor image forming device capable of making a selection range of color wide, adjusting the hue of the selected color as well and suppressing the increase of the number of developing units, a device scale and the cost, etc. CONSTITUTION: At least three developing units of a black developing unit 4, a yellow developing unit 7 and a magenta developing unit 73 are provided and they can be controlled independently of each other. The first developing unit 4 is used for developing a first latent image formed on a photoreceptor belt 1, the second and third developing units 7 and 73 are used for developing a second latent image and two-color toner can be superimposed on the picture element of the second latent image. Red is expressed by superimposing two colors of yellow and magenta, so that the selection range of the color is made wide besides black, yellow and magenta and the hue of the selected red can be adjusted as well.

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 an electrophotographic apparatus, and more particularly to a multicolor image forming apparatus for performing multicolor printing.

[0002]

2. Description of the Related Art Conventionally, a two-color electrophotographic apparatus has been known as a multicolor image forming apparatus. According to this multicolor image forming apparatus, as understood from FIG. 11, the first charger 2
To uniformly charge the surface of the photosensitive belt 1 to, for example, -600V, and irradiate the photosensitive belt 1 with the first image light 3a by the first exposure means 3 to set the surface potential of the exposed portion on the photosensitive belt 1 to, for example, A first latent image of −100V is formed. This first latent image is converted into the first latent image having black toner, for example.
By the developing device 4 of, for example, 2000Hz, 1500V
The first latent image is visualized as a black toner image by reversal development under application of a developing bias in which a direct current of -500 V is superimposed on an alternating current of pp.

Next, the photosensitive belt 1 is charged by the second charger 5.
Are recharged to increase the dark part potential to −700V and the potential of the first toner image to −520V, for example. Then, the second exposure means 6 irradiates the second exposure 6a to form a second latent image on the surface of the photosensitive belt 1 with an exposed portion potential of, for example, -80V. In this way, when the second latent image is formed and the second developing device 7 having color toner is used to perform reverse development while applying a developing bias in which a direct current of −420 V is superimposed on an alternating current of 1600 Hz and 1600 Vpp, for example, Without developing the toner image portion of the first
It is possible to develop only a portion of the latent image of 1) as a color toner image.

After the two-color image of the black toner image and the color toner image is formed on the photosensitive belt 1 as described above, the toner is charged by the charger 12 to optimize the charge amount of those toners, and then the registration roller. By the operation of the transfer charger 8, the image is collectively transferred onto the transfer material 9 supplied in synchronization with the image formation by 34. Then, the fixing device 10 is fixed by the conveyor belt 36.
Then, the toner images of two colors are fixed on the transfer material 9 and then discharged as a two-color print to the outside of the image forming apparatus. On the other hand, the photosensitive belt 1 is subjected to the next image forming process after the residual toner is removed by the cleaning device 11.

However, in the conventional two-color image forming apparatus, it is difficult to place different color toners such as black and magenta on the same pixel, and thus on the same position on the photosensitive belt. The reason is that the second latent image is not sufficiently formed because it is difficult for the second exposure to pass through the first toner image.

[0006]

[Patent Document 1] Japanese Patent Laid-Open No. 2-2
As disclosed in 19074, a method has been considered in which an image carrier having a photosensitive member formed on a transparent substrate is used and the photosensitive member is subjected to second exposure from the back surface. This makes it possible to place toners of different colors on the same pixel.
Therefore, a full-color original can be reproduced in a pseudo-color space of two colors by using a copying machine having gradation and capable of color-separating the original. This is accomplished by developing two color toners on the same pixel. This method has faster copying speed and lower cost than a full-color copying machine.
The image expressiveness of the two-color copying machine will become richer than before.

However, when reproducing a full-color original with two colors, for example, black and other colors, it is usually the case that an arbitrary color other than the set one color is selected and used. Was not possible, and the tint of that one color could not be adjusted. Although it is possible to give a wide range of color selection, there are drawbacks that the number of developing devices increases, the apparatus becomes large, and the cost also increases.

The object of the present invention is to increase the range of color selection, adjust the tint of the selected color, and suppress the increase in the number of developing devices, the size of the apparatus, and the cost increase. A multicolor image forming apparatus is provided.

[0009]

The above object can be achieved by a multicolor image forming apparatus according to the present invention. In summary, the present invention provides a first charging means for uniformly charging an image carrier, a first exposing means for forming a first latent image on the image carrier, and a development of the first latent image. First developing means, subsequently second charging means for uniformly charging the image carrier, second exposing means for forming a second latent image on the image carrier, and second latent image. A multi-color image forming apparatus including at least a second developing means for developing the toner, and a transfer means for collectively transferring the toner images of a plurality of colors formed on the image carrier onto a transfer material. At least after the first or second developing means, a third developing means for further developing the toner image obtained by the developing means is provided, and at least three different toners are provided in the same pixel. It is possible to mount it, and the number of developing means can be reduced according to the color adjustment signal. Is a multi-color image forming apparatus, characterized in that it is possible to change the one developing conditions.

According to the present invention, the developing condition changed according to the tint adjusting signal can be a developing bias condition or a developer carrying force condition. The tint adjustment signal can select any one of a high-density portion, a halftone portion, and a low-density portion, and the developing condition to be changed can be different depending on the selected state. Further, the developing bias condition is Vpp of AC voltage, frequency or DC voltage to be superimposed, and the developer carrying force condition is
It may be the rotation speed of the magnet arranged in the developing sleeve or the rotation speed of the developing sleeve.

[0011]

1 is a sectional view showing a multicolor image forming apparatus according to an embodiment of the present invention. In the multicolor image forming apparatus of this embodiment, the second image exposing unit 6 between the second charging device 5 and the second developing device 7 is exposed in the rotational direction of the photosensitive belt (belt photosensitive member) 1. It is provided on the back side of the belt 1, and further on the downstream side of the second developing device 7, a third developing device 73 is provided.
The main feature is that The first developing device 4 is 2
The component developing devices, the second and third developing devices 7 and 73, are single-component developing devices. Further, the photosensitive belt 1 can transmit light from the back surface. Other configurations of this embodiment are basically the same as those of the conventional multicolor image forming apparatus shown in FIG. 11, and the same reference numerals as those in FIG. 11 denote the same members.

The image forming process in this embodiment will be described with reference to the potential diagram shown in FIG. First, the photosensitive belt 1 is uniformly charged to, for example, −600 V (dark portion potential) by the first charger 2 (FIG. 2A), and the image exposure 3 a by the first image exposing means 3 is performed.

The first image exposure 3a is a laser beam modulated by the first image signal using the semiconductor laser 15 of the image exposure means 3 as a light source. The laser beam is polarized by a multifaceted surface 13 rotating at a constant rotation speed by a motor 14, reflected by a folding mirror 16 via an imaging lens, and then raster-scanned on the photosensitive belt 1 to image the surface potential of the exposed portion as an image. Attenuating according to the signal level, a first latent image is formed.

The output image has a portion A of only the first color and a first portion
The first image exposure 3a consists of a portion B for mixing the color and the second color and a portion C for the second color only. As a result, the first latent image is formed not only in the portion A of only the first color but also in the portion B of mixed colors. Due to the formation of the first latent image, the portion (maximum density portion) A of only the first color has, for example, -1.
It is attenuated to a potential of 00V (FIG. 2 (b)).

The first latent image is developed by a first developing device 4 using a two-component developer consisting of negatively charged black toner and magnetic particles such as ferrite. To the developing device 4, for example, a developing bias in which a DC voltage (Vdc1) of −500V is superimposed on an AC voltage of 2000 Hz and 1500 Vpp is applied, and the first latent image is reversely developed to obtain a first toner image ( FIG. 2C). At this time, the electric potential of the first toner image (black toner image) is lowered by about −50 V at the maximum density portion A to about −150 V due to the toner charge.

After the first latent image is developed by the first developing device 4, the photosensitive belt 1 is entirely exposed from the back side by the exposure device 17 having an EL or LED element to remove the charge.
The potential difference between the maximum density portion of the first toner image (the toner layer potential of the maximum density portion) and the dark portion potential of the photosensitive belt 1 is set to be small, for example, −100 V and −200 V (FIG. 2). (D)).

Then, the photosensitive belt 1 is charged by the second charger 5.
Is recharged, and the potential of the maximum density portion A of the first toner image is set to −6.
70V and the dark part potential are set to -700V (FIG.2 (e)).
That is, the dark portion potential is set to be slightly lower than the toner layer potential of the maximum density portion, and the toner layer potential of the maximum density portion is set to such an extent that the contrast of the second latent image can be obtained.

Then, image exposure 6a is performed by the second image exposure means 6 to form a second electrostatic latent image on the photosensitive belt 1. The second image exposure 6a is the first image exposure 3a.
Similarly to the above, the semiconductor laser 25 of the image exposure means 6 is a laser beam modulated by a second image signal using the semiconductor laser 25 as a light source, and the second laser beam is rotated by a motor 24.
And the folding mirror 26 that is polarized by 3 and passes through the imaging lens.
After the reflection, the photoconductor is raster-scanned from the back surface of the photosensitive belt 1 to form a second latent image on the photosensitive belt 1.

The second latent image is formed not only on the portion C of only the second color but also on the mixed color portion B, and due to the formation of the second latent image, the portion of only the second color (maximum density portion). The voltage is attenuated to a potential of, for example, −80 V at C, and −400 V at the portion B where color mixing is performed (FIG. 2 (f)).

For the second latent image thus formed, one or both of the second developing device 7 and the third developing device 73 are selected in accordance with the designation of the color (for example, designated by the operating section). , The second latent image is developed.

For example, when the second developing device 7 is a yellow developing device, the third developing device 73 is a magenta developing device, and the color designation is red, the second developing device 7 has, for example, 1600H.
When a bias in which a direct current of -570 V is superposed on an alternating current of z, 1600 Vpp is applied and developed, the yellow toner is formed into a portion of the first toner image, that is, a portion A of only the first color.
Portion B and the second portion which are not adhered to the black toner image of
The toner adheres only to the color-only portion C and is developed as a yellow toner image. Further, subsequently, in the third magenta developing unit 73, for example, 1600 Hz, 1600 Vp
When a bias in which a direct current of -570 V is superimposed on an alternating current of p is applied and development is performed, similarly, the magenta toner does not adhere to the black toner image of the portion A of only the first color, and the portion B is mixed.
And a portion C of only the second color adheres to the yellow toner image and is developed as a magenta toner image (FIG. 2).
(F)).

Therefore, the yellow toner and the magenta toner are placed on the portion C of only the second color, and these two colors are expressed in red to form a red image in the output two-color image. Black, yellow, and magenta toners are placed on the portion B where the colors are mixed, and as a result, black and red are represented as overlapping colors. That is, the color tint of the two-color image is expressed by the color mixture of black and red. Black toner is placed on the portion A of only the first color, whereby the black image in the two-color image is expressed.

After that, the charger 1 for adjusting the toner charge amount
The bias of superimposing an AC voltage on the DC voltage is applied to 2, and the black of the toner image on the photosensitive belt 1 is charged by the charger 12
After the charge amounts of the yellow and magenta toners are optimized, the transfer charging device 8 transfers the transfer material 9 onto the transfer material 9 supplied to the photosensitive belt 1 by the registration roller 34. Then, the transfer material 9 is separated from the photosensitive belt 1 by the curvature of the separation charging device 30 and the photosensitive belt 1, and sent to the fixing device 10 to fix the two-color image on the transfer material 9, and then as an image forming apparatus as a two-color color print. To the outside of the machine. On the other hand, the photosensitive belt 1
After the residual toner is removed by the cleaning device 11, it is subjected to the next image forming process.

The present invention will be described in more detail. FIG. 3 shows an example of a display on the operation unit of the image forming apparatus. The image forming apparatus uses magenta, yellow, and
You can set two colors of cyan,
The display of the operation unit 200 shown in FIG. 3 indicates that magenta and yellow developing devices are set and red is selected as one color other than black. A liquid crystal panel or the like is used for the operation unit 200, and a shaded portion in the drawing indicates that a cyan developing device is set instead of the magenta developing device and a cyan developing device is set instead of the yellow developing device. Indicates that the selectable expression colors are displayed in light characters. For example, as a default, the intensity of magenta and yellow, that is, the density is Max.
It is (dark), and it is possible to reduce the color strength independently.

The relationship between the surface potential of the photosensitive belt and the density during yellow development is shown in FIG. 4 for the case of different peak-to-peak voltages of the developing bias AC voltage. The DC voltage of the developing bias applied to the yellow developing device is Vdc.
= -570V. In FIG. 4, when the developing bias AC voltage Vpp is 1600 V, the solid line indicates Vp.
The dashed line indicates when p = 1100V. From FIG. 4, Vpp
It can be seen that the smaller the value, the lower the density of the obtained yellow toner image. Further, it can be seen that the change in the density becomes larger in the high density portion.

FIG. 5 shows the relationship between the surface potential of the photosensitive belt and the density at the time of yellow development, in the case of direct current voltages having different developing biases. DC voltage of developing bias is Vd
The solid line shows when c = -570V, and the broken line shows when Vdc = -470V. From this, it can be seen that the density of the obtained yellow toner image is lowered by increasing Vdc (negative and decreasing the absolute value). The change in concentration moves parallel to the horizontal axis.

FIG. 6 shows the relationship between the surface potential of the photosensitive belt and the density at the time of yellow development, in the case of different frequencies of the developing bias AC voltage. When the frequency of the AC voltage of the developing bias is 1600 Hz, the solid line indicates 200 Hz
Is indicated by a broken line. From this, it can be seen that the higher the frequency, the lower the density of the obtained yellow toner image.
Also, it can be seen that the density change is larger in the low density portion.

Therefore, in the case of strongly adjusting the red tint to the magenta side, for example, a signal for lowering the yellow density for strongly adjusting the red tint to the magenta side by operating the operating unit 200. (Yellow adjustment signal as a tint adjustment signal) is output from the operation unit 200, and the yellow developing device (second developing device) 7 is supplied to the CPU 100 installed in the image forming apparatus of FIG. 1 according to the yellow adjustment signal.
In the output of the bias power source 500, at least Vpp is decreased, Vdc is increased (development contrast is decreased), or frequency is increased.

FIG. 7 shows an example of changes in the peak-to-peak voltage of the developing bias with respect to the yellow adjustment signal. As a result, the tint on the yellow side of red is suppressed, and a red color in which the tint on the magenta side is emphasized is obtained.

When strongly adjusting the above red tint to the magenta side, the developing bias is given by giving a selectivity to which of the high density side, the halftone and the low density side is adjusted. It is also possible to change Vpp, Vdc, or the frequency.

In order to strongly emphasize the red tint to the yellow side, similarly, a magenta adjustment signal from the operation unit 200 (a signal for lowering the magenta density to strongly adjust the red tint to the yellow side). Via the CPU 100 via
Bias power source 6 of magenta developing device (third developing device) 73
Of the output of 00, at least reduce Vpp, or
Increase Vdc (decrease development contrast)
Alternatively, control may be performed to increase the frequency.

In FIG. 1, reference numeral 400 indicates a bias power source for the first developing device 4, and 500 indicates a bias power source for the second developing device 7.

In the above embodiments, the case where red is selected as one color other than black has been described. However, if the selected color is blue, cyan and magenta are selected, and if green is selected, cyan and yellow are selected in the same manner. Good.

In this embodiment, the case where the photosensitive belt is used as the image bearing member has been described. However, the same can be done by using the photosensitive drum, and the color sequence of the first development and the second development and the development are the same. There is no particular limitation on the method.

Another embodiment of the present invention will be described. In the embodiment of FIG. 1, a two-component developing device is used for the first black developing device 4, but a one-component developing device is used for the second and third yellow developing devices 7 and magenta developing device 73. Using. In the first embodiment, the second and third developing units 7 and 73 also have two
A component developing device was used. FIG. 8 shows a cross-sectional view of a two-component developing device suitable for use as the second and third yellow developing devices and the magenta developing device in this embodiment.

In FIG. 8, the two-component developing device 40 is shown arranged below the photosensitive belt 1 moving in the direction of arrow a, as in the developing device arrangement shown in FIG. There is. The developing device 40 has a developing sleeve 41 that rotates in the direction of arrow b in a developing container 44 that contains a two-component developer 43, and a part of the developing sleeve 41 is a developing container 44.
Exposed from the opening facing the photosensitive belt 1, and faces the photosensitive belt 1.

A roller-shaped magnet 42 is rotatably arranged in the developing sleeve 41, and is carried on the developing sleeve 41 by rotating the magnet 42 in the opposite direction to the developing sleeve 41 rotating in the b direction. Developer 4
3 is conveyed in the b direction. The magnet 42 is driven by a driving means (not shown), such as a DC motor.

FIG. 9 shows the relationship between the surface potential and the density of the photosensitive belt at the time of yellow development, in the case where the rotation speed of the magnet of the developing device is different. The solid line represents the case where the rotation speed of the magnet 42 is 2000 rpm, and the rotation speed is 1500.
The case of rpm is shown by a broken line. From now on, the magnet 42
It can be seen that when the rotation speed of is decreased, the concentration is decreased. This is because the rotation speed of the magnet 42 decreases.
This is because the carrying force of the developer 43 by the developing sleeve 42 is reduced.

Therefore, in the present embodiment, when the red tint is strongly adjusted to the magenta side, the yellow adjustment signal output from the operation unit 200 of FIG. 3 (in order to strongly adjust the red tint to the magenta side) The CPU 100 of the image forming apparatus of FIG. 1 causes the rotation speed of the DC motor of the magnet 42 of the developing unit 40 of FIG. Take control.

FIG. 10 shows an example of changes in the rotation speed of the magnet with respect to the yellow adjustment signal. As a result, the amount of yellow developer conveyed by the developing sleeve 41 is reduced, and the amount of yellow toner in the two-color image is reduced. As a result, the tint of red on the yellow side is suppressed, and the tint on the magenta side is reduced. An enhanced red color is obtained.

Similarly, in the case of strongly emphasizing the red tint to the yellow side, a magenta adjustment signal from the operation unit 200 (a signal for lowering the magenta density in order to strongly adjust the red tint to the yellow side). Via the CPU 100 via
Magnet 4 of developing unit 40 as magenta developing unit 73
Control for reducing the rotation speed of the second DC motor may be performed.

In the above, the rotation speed of the DC motor of the magnet 42, that is, the rotation speed of the magnet 42 is changed to change the developer carrying force by the developing sleeve 41. However, the rotating speed of the developing sleeve 41 is changed. The developer carrying force may be changed by the above, and the same effect can be obtained.

[0043]

As described above, the multicolor image forming apparatus of the present invention includes at least three developing devices of different colors, and each developing device can be independently controlled. Then, with respect to either one of the first latent image and the second latent image formed on the image bearing member, two consecutive developing devices of the latent images are simultaneously activated to generate the first or second latent image. Two
The toner of two colors can be superposed on the pixels of the latent image of. Therefore, it is possible to obtain a color in which two colors are superposed in addition to the number of colors of the developing devices, the selection range of colors is increased, and the tint of the selected color can be adjusted. Further, since two different colors are obtained by superimposing two colors, it is possible to suppress an increase in the number of developing devices, and it is possible to avoid an increase in size of the apparatus and a high cost.

[Brief description of drawings]

FIG. 1 is a sectional view showing a multicolor image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a potential diagram illustrating an image forming process in the image forming apparatus of FIG.

FIG. 3 is an explanatory diagram illustrating an operation unit of the image forming apparatus in FIG.

FIG. 4 is a diagram showing the relationship between the surface potential and the density of a photosensitive belt in the case of peak-to-peak voltages with different developing biases.

FIG. 5 is a diagram showing the relationship between the surface potential and the density of the photosensitive belt in the case of DC voltages having different developing biases.

FIG. 6 is a diagram showing the relationship between the surface potential of the photosensitive belt and the density in the case where the AC voltages of the developing biases have different frequencies.

7 is a diagram showing an example of changes in the peak-to-peak voltage of the developing bias with respect to the tint adjustment signal used for tint adjustment in the embodiment of FIG.

FIG. 8 is a sectional view showing a two-component developing device suitable for use in another embodiment of the present invention.

9 is a diagram showing the relationship between the surface potential and the density of the photosensitive belt for different rotation speeds of the magnet of the developing device of FIG.

10 is a diagram showing an example of changes in the rotation speed of the magnet with respect to a tint adjustment signal used for tint adjustment in the embodiment of FIG.

FIG. 11 is a cross-sectional view showing a conventional multicolor image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive belt 2 1st charging device 3 1st image exposure means 4 1st developing device 5 2nd charging device (recharging device) 6 2nd image exposing means 7 2nd developing device 17 Back exposure device 40 two-component developing device 73 third developing device 100 CPU 200 operation unit

Claims (7)

[Claims] 1. A first charging unit for uniformly charging an image carrier, a first exposure unit for forming a first latent image on the image carrier, and a first unit for developing the first latent image. Developing means, subsequently, second charging means for uniformly charging the image carrier, second exposing means for forming a second latent image on the image carrier, and developing the second latent image. At least a second developing unit for transferring the toner images of a plurality of colors formed on the image carrier onto the transfer material at one time. A third developing unit for further developing the toner image obtained by the developing by the developing unit is provided after the first or second developing unit, and at least three different toners are placed on the same pixel. Is possible, and at least one of the developing means is responsive to the tint adjustment signal. A multicolor image forming apparatus characterized in that development conditions can be changed. 2. The multicolor image forming apparatus according to claim 1, wherein the developing condition changed in accordance with the tint adjustment signal is a developing bias condition. 3. The multicolor image forming apparatus according to claim 1, wherein the developing condition changed in accordance with the tint adjustment signal is a developer conveying force condition. 4. The color tone adjustment signal can select one of a high-density portion, a halftone portion, and a low-density portion, and the developing condition to be changed is different depending on the selected state. 1. Multicolor image forming apparatus. 5. The developing bias condition is V of AC voltage.
3. The pp, frequency or superimposed DC voltage.
Multi-color image forming apparatus. 6. The developer carrying force condition is a rotational speed of a magnet disposed in a developing sleeve.
Multi-color image forming apparatus. 7. The multicolor image forming apparatus according to claim 3, wherein the condition of the developer carrying force is the rotation speed of the developing sleeve.