JPH087476B2 - Color image forming apparatus and method of using the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color printer or a color copying machine and a method of using the same, and particularly, in one cycle in which a latent image carrier is rotated once. The present invention relates to an improved color image recording apparatus for transferring a plurality of color images to a recording sheet at once and a method of using the same.

[Conventional technology]

Taking a printer as an example of a conventional color image forming apparatus, a toner image of a corresponding system is formed on each photosensitive drum in each rotation cycle of a plurality of rotating photosensitive drums, and a transfer drum that rolls in contact with the photosensitive drum is formed. A so-called transfer drum system in which toner images of various systems on a photosensitive drum are superposed and transferred on a wound recording sheet in each rotation cycle, or, for example, a plurality of image forming units (photosensitive drum, latent image forming unit, developing unit) A tandem system in which the image forming units are arranged in a predetermined direction and the toner images formed by the image forming units are sequentially transferred to a recording sheet conveyed by the sheet conveying device along the predetermined direction. The term has already been proposed.

However, in the former type, in order to form one color image, the photosensitive drum must be rotated a plurality of times, which causes a problem that it takes a long time to form a color image, and the transfer position accuracy of each toner image is high. In order to raise the speed, it is necessary to accurately control the rotation of the photosensitive drum and the transfer drum, which causes a problem that the apparatus control becomes complicated.

Further, in the latter type, it is possible to shorten the color image forming time as compared with the former type,
Not only the apparatus itself becomes large, but also the rotation control of the photosensitive drum of each image forming unit and the conveyance control of the recording sheet have to be accurately performed, which causes a problem that the apparatus control becomes complicated (Japanese Patent Laid-Open No. 61-61). -174564 gazette).

In order to solve such a problem, there has already been provided one in which a plurality of systems of toner images are formed on a photosensitive drum and then these toner images are collectively transferred to a recording sheet (Japanese Patent Laid-Open No. 58-58160). -57139 and 60-247650).

For example, as shown in FIG.
Around the periphery of, a charging device 101 for precharging the photosensitive drum 100, a first laser 102 for forming a first latent image, a developing bias type first developing device 103 for developing the first latent image, a photosensitive drum A first recharging device 104 for recharging 100, a second laser 105 for forming a second latent image, a second developing device 106 of a developing bias system for developing the second latent image, and a photosensitive drum 100 for recharging. A second recharger 107 for charging, a third laser 108 for forming a third latent image, a third developing device 109 of a developing bias system for developing the third latent image, each toner image on the photosensitive drum 100. , A transfer device 111 for collectively transferring each toner image on the photosensitive drum 100 to the recording sheet 112, and a cleaner 113 for removing the residual toner on the photosensitive drum 100. .

Then, in the image forming process in this type, for example, as shown in FIG.
After being uniformly positively charged at 01 (step a), the first laser 102 forms a first negative latent image Zn whose image portion potential is lower than the background portion potential (step b). Developing device 10
In the state where a predetermined developing bias V _B1 is applied to 3, the negative latent image Zn is reversely developed with the first toner T ₁ (step c),
Thereafter, the photosensitive drum 100 is recharged by the first recharging device 104 (step d), and then the second laser 105 forms a second negative latent image Zn in which the image portion potential is lower than the background portion potential. (Step e), a predetermined developing bias V is applied to the second developing device 106.
While applying the _B2 at the second toner T ₂ to reversal development only the second negative latent image Zn (step f), further re-charge the photosensitive drum 100 by the second re-charger 107 ( After step g), a third negative latent image Zn whose image portion potential is lower than the background portion potential is formed by the third laser 108 (step h), and a predetermined developing bias V _{B3 is applied} to the third developing device 109. In the applied state, the third negative latent image Zn is reversely developed with the third toner T ₃ (step i), and the potentials of the toner images of the respective systems described above are adjusted to be substantially equal by the charger 100 (step After j),
The transfer device 112 transfers all the toner images to the recording sheet 111 side at a time.

[Problems to be Solved by the Invention]

However, in such an image forming process,
In either case when forming the toner image of each system, the negative latent image is developed by reversal development with the toner of the same polarity. Mixed color development that is mixed with each other is likely to occur, and when a part of the toner of the developed toner image on the photosensitive drum 100 is separated and enters the developing device of the next stage, the mixed toner remains in the developing device. The accumulated toner will change the triboelectrification characteristics of the toner in the developing device, which will accelerate the deterioration of the toner in the developing device and also cause the toner tones in the developing device to be different, and the color of the reproduced image It also causes a loss of quality.

Also, when reproducing a two-color image using this type of device, for example, two lasers 102 and 105 and two developing devices 1
A two-color image will be reproduced using 03 and 106, but the reproduced image color will be limited to the color of the toner of the developing device used, and the color image desired by the customer (custom) will be reproduced. Was difficult unless the toner in the developing device was replaced.

The present invention has been made in view of the above problems, and effectively suppresses the color mixing and mixing phenomenon of reproduced images while satisfying the demands for speeding up the color image forming speed and downsizing of the apparatus. A color image forming apparatus capable of maintaining good color image quality of a system and efficiently reproducing a two-color image including a color image desired by a customer, and a method of using the same.

[Means for solving the problem]

That is, in the color image forming apparatus according to the present invention, as shown in FIG. 1A, the latent image carrier 1 carrying an electrostatic latent image and the image portion potential on the latent image carrier 1 are A first latent image forming unit 2 that forms a negative latent image Zn whose absolute value is lower than the background potential, and the negative latent image Zn formed by this first latent image forming unit 2 is inverted by a first toner T1. A positive latent image Zp, which is arranged in the latter stage of the first developing means 3 for developing and the first latent image forming means 2 and has an image portion potential higher in absolute value than a background portion potential on the latent image carrier 1. A second latent image forming means 4 for forming, a second developing means 5 for normally developing the positive latent image Zp formed by the second latent image forming means 4 with the second toner T2, and a color image of three systems. It operates when the formation mode is selected, and reverses the polarity of the second toner T2 while preventing the polarity reversal of the first toner T1 from reversing the polarity of the first toner image and the second toner image. On the recharging means 6 for adjusting the toner image potentials substantially equal to each other, and on the latent image carrier 1 recharged by the recharging means 6, a positive latent image Zp in which the image portion potential is higher in absolute value than the background portion potential is formed. Third latent image forming means 7 for forming,
On the latent image carrier 1, the third developing means 8 for normally developing the positive latent image Zp formed by the second latent image forming means 4 or the third latent image forming means 7 with the third toner T3. It is characterized in that it is provided with a transfer pretreatment means 9 for making the polarities of the toner images uniform and a transfer means 10 for collectively transferring the toner images of the same polarity on the recording sheet 11.

In such an apparatus invention, as the latent image carrier 1, a photoreceptor is used when an electrostatic latent image is formed by light, and a dielectric is used when an electrostatic latent image is formed by ions. The design may be changed appropriately according to the type of forming means. Also, regarding the configuration of the latent image carrier 1, a drum shape,
It does not matter whether it is in the form of a belt, and the charging type may be positive or negative.

Further, the first latent image forming means 2 and the second latent image forming means 4 described above.
As the third latent image forming means 7, a latent image writing means for forming an electrostatic latent image on the latent image carrier 1 is provided, and the surface of the latent image carrier 1 is used for writing the electrostatic latent image. When it is necessary to precharge the battery, it is necessary to provide a charging means.

In this case, as the latent image writing means, an exposure lamp, an optical imaging system, a laser, an LED, a liquid crystal shutter, or the like can be appropriately selected as a type using a light beam, and an ion type is also used. The discharge head and the like can be appropriately selected.

Further, the developing system of the first developing means 2, the second developing means 5 and the third developing means 7, the kind of the developer, etc. may be appropriately selected, but in consideration of the developing efficiency, the two-component developer is used. The magnetic brush developing type is also preferable. In this case, from the viewpoint of preventing the disturbance of the developed toner image in the second developing step and the third developing step, for example, when the magnetic brush developing method using a two-component developer is adopted, A low density carrier for the developer is used, a repulsive magnetic pole is provided at the developing portion of the developer carrier, the relative speed ratio between the developer carrier and the latent image carrier 1 is reduced, etc. 63-142363, JP-A-1-28
No. 7581 and Japanese Patent Application No. 63-168696), it is preferable to use a soft magnetic brush with a developer, or it is preferable to employ a non-contact developing method.

Furthermore, the recharging means 6 recharges the second toner T2 with the polarity reversed, without reversing the polarity of the first toner T1 when forming three-system toner images. Is used.

Further, the transfer pretreatment means 9 may be appropriately changed in design as long as it can make the polarities of the toner images on the latent image carrier 1 uniform, but in consideration of the transfer efficiency of each toner image, for example, When the latent image carrier 1 is a photoconductor, the potential of the latent image carrier 1 of each toner image portion is lowered by performing an exposure process at the same time as or after the charging process. Means are preferably provided.

As for the transfer means 10, if the toner image on the latent image carrier 1 is transferred to the recording sheet 11 side, each toner image on the latent image carrier 1 is electrostatically transferred to the recording sheet 11 side. The transfer sheet is not limited to the one that is transferred, but includes one that is transferred to the recording sheet 11 side by another method such as thermal transfer.

Furthermore, in consideration of the life of the developer, when a two-component developer having an insulating carrier is used as the developer of the first developing means 3, the toner image forming area in the second developing step is accurately measured. From the viewpoint of definition, a recharging means 12 is provided in front of the second latent image forming means 4 as shown by a virtual line in FIG. It is preferable to design so as to reduce the absolute value.

Further, as shown in FIG. 1 (b), the image forming process in the case of obtaining color images of three systems using the color image forming apparatus is carried out by the first latent image forming means 2 by the latent image carrier 1. In the first system toner image forming step A1 in which a negative latent image Zn is formed on the negative latent image Zn and the negative latent image Zn is reversely developed by the first toner T1 of the first developing means 3, and in the second latent image forming means 4. A second system toner image forming step A2 of forming a positive latent image Zp on the latent image carrier 1 and normally developing the positive latent image Zp with the second toner T2 of the second developing means 5, and a recharging means 6. While the polarity reversal of the first toner T1 is prevented by adjusting the potentials of the first system toner image and the second system toner image to be substantially equal to each other, the third latent image forming means 7 forms a latent image on the latent image carrier 1. Third system toner image forming step A3 in which a positive latent image Zp is formed and the positive latent image Zp is normally developed by the third toner T3 of the third developing means 8. Pre-transfer treatment means 9
And a toner image transfer step A4 for collectively transferring the respective toner images to the recording sheet 11 by the transfer means 10 after aligning the polarities of the first to third system toner images. Is.

Further, as shown in FIG. 1 (c), the image forming process for obtaining a two-system color image by using the above-mentioned color image forming apparatus is carried out on the latent image carrier 1 by the first latent image forming means 2. A first system toner image forming step B1 of forming a negative latent image Zn and reversal developing the negative latent image Zn with the first toner T1 of the first developing means 3, and carrying a latent image with the second latent image forming means 4. A positive latent image Zp is formed on the body 1, and the positive latent image Zp is normally developed with the second toner T2 other than black of the second developing means 5, and then the third developing means 8 is used.
Second system toner image forming step B2 in which the third toner T3 other than black is further overlaid for regular development, and the transfer preprocessing means 9 aligns the polarities of the first and second system toner images, and the transfer means 10
And a toner image transfer step B3 for collectively transferring each toner image to the recording sheet 11.

Then, in the image forming process shown in FIG. 1 (c), the toners of the second developing means 5 and the third developing means 8 can be adjusted so as to be overlaid on the same positive latent image Zp. If the second and third developing means 5 and 8 are of a developing bias system, for example, the developing degrees of the second toner T2 and the third toner T3 are set in a state where different developing biases are applied. It should be adjusted.

[Action]

When a color image of three systems is formed by using the color image forming apparatus, a negative latent image Zn corresponding to the first image on the latent image carrier 1 is formed in the first system toner image forming step A1. Reversal development with one toner T1 and a positive latent image corresponding to the second image on the latent image carrier 1 in the second system toner image forming step A2
Zp is normally developed with the second toner T2, and the positive latent image Zp corresponding to the third image on the latent image carrier 1 is normally developed with the third toner T3 in the third system toner image forming step A3. In the toner image transfer step A4, the toner images of the respective systems are collectively transferred to the recording sheet 11.

In such an image forming process, even if the first system toner image by the first toner T1 comes into contact with the second toner T2 and the third toner T3 in the second developing step and the third developing step, the first toner T1 Since the second and third toners T2 and T3 have different polarities, the second and third toners T2 and T3 do not mix with the first system toner image.

Further, even if the first toner T1 of the first system toner image comes off and enters the housings of the second developing means 5 and the third developing means 8, the first toner T1 is the second toner in the second developing means 5. Since the toner is repelled by T2 or the third toner T3 in the third developing means 8, the first toner T1 is easily discharged from each housing and is not accumulated in the housing.

When two color images are formed using the color image forming apparatus, a negative latent image corresponding to the first image on the latent image carrier 1 in the first system toner image forming step B1.
Zn is reversely developed with the first toner T1, and the positive latent image Zp corresponding to the second image on the latent image carrier 1 is normally developed with the second toner T2 in the second system toner image forming step B2. At the same time, the third toner T3 is further overlaid and subjected to regular development, and the toner images of the respective systems are collectively transferred onto the recording sheet 11 in the toner image transfer step B3.

In such an image forming process, the first toner image is transferred to the second toner T by the same operation as described above.
2. The third toner T3 does not mix, and the first toner T1 does not mix in the housings of the second developing means 5 and the third developing means 8.

Further, in this image forming process, the second system toner image is a combination of the second toner T2 and the third toner T3, so that the color of the second system toner image is the second toner T2 or the second toner T2. Three toner T3 has been adjusted to something different.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

(Basic Structure) FIG. 2 shows an embodiment in which the present invention is applied to a color printer.

In the figure, reference numeral 20 is a negatively charged OPC (Organic Pho
to Conductor) type photosensitive drum, 21 is a charging scorotron for pre-charging the photosensitive drum 20, 22 is a first laser for forming a first negative latent image corresponding to the first image on the photosensitive drum 20, and 23 is a first A two-component magnetic brush developing type first developing device for reversing and developing the negative latent image of the above with the first toner T1 (negative polarity),
24 is a second laser that forms a second positive latent image corresponding to the second image on the photosensitive drum 20, and 25 is a two-component that normally develops the second positive latent image with the second toner (positive polarity) T2. A magnetic brush developing type second developing device, 26 is a recharging scorotron that reverses the polarity of the second toner T2 while reversing the polarity of the first toner T1 and recharges the surface of the photosensitive drum 20, and 27 is a photosensitive drum. A third laser that forms a third positive latent image corresponding to the third image on the drum 20, 28 is a two-component that normally develops the third or second positive latent image with, for example, third toner (positive polarity). A magnetic brush developing type third developing device, 29 is a pre-transfer corotron for aligning the polarity of each toner image formed on the photosensitive drum 20 to, for example, a negative polarity, 30 is a recording sheet 31 charged, and each of the toner on the photosensitive drum 20 is charged. The transfer corotron 32 that electrostatically transfers the toner image to the recording sheet 31 side at once is A Ditac corotron that removes electricity from the recording sheet 31 on which the toner images are transferred on the optical drum 20 and separates the recording sheet 31 from the photosensitive drum 20, 33 is a cleaner that removes residual toner on the photosensitive drum 20, and 34 Is a discharge lamp for removing the residual charge on the photosensitive drum 20.

In this embodiment, in the charging scorotron 21 and the recharging scorotron 26, as shown in FIG. 3, a discharge wire 42 is provided in a shield 41 having a U-shaped cross section, and a control grid is provided in an opening portion of the shield 41. 43 is provided, and a high negative voltage of a predetermined level is applied to the discharge wire 42 and the control grid 43 from high voltage power supplies 44 and 45, respectively.

In this embodiment, the second developing device 25, 28
As shown in FIGS. 4 and 5, the developing roller 62 is disposed in the housing 61. As the developing roller 62, there are 7 poles (N1 to N4, S1 to S) in the rotating sleeve 63.
3) A magnet roll 64 having an asymmetrical magnetization structure is fixedly provided, and the magnetic flux density of the main pole (repulsion magnetic pole composed of N2 and N3) 65 is 120.
About 0 gauss, the difference between the peak and the valley is set to about 50 to 200 gauss, and the magnetic flux density of the other magnetic pole 66 is set to about 800 gauss.

Furthermore, as the developer for the second developing device 25 and the third developing device 28, a carrier in which magnetic powder is dispersed in a resin binder and the density is 4 g / cm ³ or less is used.

Operation of Apparatus Next, the operation of the color printer according to this embodiment in each image forming mode will be described.

The process speed of the photosensitive drum 20 in this embodiment is 150 mm / sec.

(1) Three-color image mode (see FIG. 6) In this mode, it is difficult to use non-transparent black toner as the toner of the first and second developing units 23 and 25, and A transparent yellow toner is used as the first toner T1 of the device 23, a transparent magenta toner is used as the second toner T2 of the second developing device 25, and a black toner is used as the third toner of the third developing device 28. There is.

Uniform charging step (step a) The surface of the photosensitive drum 20 is uniformly charged to -600V.

First exposure step (step b) A first negative latent image Zn whose image portion potential is lower than the background portion potential is formed by the first laser 22 (a pattern generator is used for the image signal, the same applies to the following lasers). To do. In this embodiment, the image portion potential is set to -100V and the background portion potential is set to -600V.

First developing step (step c) The developing bias V _B1 of the first developing device 23 is set to −450 V, and the negative latent image Zn is reversely developed with the first black toner T1 (negative polarity).

Second exposure step (step d) The second laser 24 forms a second positive latent image Zp in which the image portion potential is higher than the background portion potential. At this time, the first system toner image potential V _T1 is set to be smaller than the background portion potential in absolute value. In this embodiment, the background potential is −250 V, the image potential is −580 V, and the first system toner image potential is
Set V _T1 to about –130V.

Second developing step (step e) The developing bias V _B2 of the second developing device 25 is set to −400 V, and the positive latent image Zp is normally developed with the second yellow toner T2 (positive polarity).

In this case, since the first system toner image is held and held by the well type potential pattern, the first system toner image is hardly destroyed, and the second toner T2 is contained in the first system toner image. There is almost no mixing, and the separation toner T1 of the first-system toner image does not mix into the second developing device 25.

Recharging Step (Step f) By appropriately adjusting the voltage of the control grid 43 of the recharging scorotron 26 and the applied voltage of the discharge wire 42, the polarity of the second toner T2 can be maintained without reversing the polarity of the first toner T1. Is reversed, and the surface potential of the photosensitive drum 20 is recharged to the initial charging level (about -600V).

Third exposure step (step g) The third laser 27 forms a third positive latent image Zp in which the image portion potential is higher than the background portion potential. At this time, since each toner of the first system toner image and the second system toner image is a transparent toner, the potential of the photosensitive drum 20 corresponding to each toner image can be sufficiently reduced in absolute value in this exposure process. It is possible, and the first system toner image potential V _T1 and the second system toner image potential V _T2 are set to be slightly lower in absolute value than the background portion potential by appropriately adjusting the exposure amount. In this example,
The background potential is set to −150 V, the image potential is set to −580 V, and the first and second system toner image potentials V _T1 and V _T2 are set to about −100 V.

A developing bias V _B3 of the third developing step (step h) a third developing device 28 and -350 V, for normal development of the positive latent image Zp at the third black toner T3 (positive polarity).

In this case, the first system toner image and the second system toner image are held and held by the well type potential pattern,
The first system toner image and the second system toner image are hardly destroyed, and the third toner T3 and the first toner T1,
Since the polarity is different from that of the second toner T2, the third toner T3 hardly mixes in the first system toner image and the second system toner image, and the first system toner image and the second system toner image are separated. The toner is not mixed in the third developing device 29.

Pre-Transfer Processing Step (Step i) A predetermined DC component voltage in which an AC component is superimposed is applied to the discharge wire of the pre-transfer corotron 29, and the toner polarities of the toner images of the respective systems are made positive.

Transfer process When a predetermined DC component voltage in which AC component is superimposed is applied to the discharge wire of the transfer corotron 31, the toner images of each system on the photosensitive drum 20 are collectively transferred to the recording sheet 32 side, and yellow, magenta, and black are transferred. Color images of three lines were obtained.

(2) Two-color stipulated color image mode (see FIG. 7) In this mode and the two-color custom color image mode described next, for example, the first toner T1 of the first developing device 23 is, for example, a black toner, the second developing device. For example, yellow toner is used as the second toner T2 of 25, and cyan toner is used as the third toner T3 of the third developing device 28.

The uniform charging process (step a) and the first exposure process (step b) are performed in the same manner as in the three-color image mode.

First developing step (step c) The developing bias V _B1 of the first developing device 23 is set to −450 V, and the negative latent image Zn is reversely developed with the first black toner T1 (negative polarity).

Second exposure step (step d) The second laser 24 forms a second positive latent image Zp in which the image portion potential is higher than the background portion potential. At this time, the first system toner image potential V _T1 is set to be smaller than the background portion potential in absolute value. In this embodiment, the background potential is −250 V, the image potential is −580 V, and the first system toner image potential is
Set V _T1 to about −140V.

Second developing step (step e) The developing bias V _B2 of the second developing device 25 is set to −350 V, and the positive latent image Zp is normally developed with the second yellow toner T2 (positive polarity).

In this case, the first system toner image is held and held by the well-type potential pattern, so that the first system toner image is hardly destroyed, and the yellow toner
Almost no T2 is mixed in the first system toner image,
Moreover, the peeling toner of the first system toner image is the second developing device 25.
It is not mixed in.

Pre-Transfer Processing Step (Step f) A predetermined DC component voltage in which an AC component is superposed is applied to the discharge wire of the pre-transfer corotron 29, and the toner polarity of the toner image of each system is made positive.

Transfer process When a predetermined DC component voltage in which AC component is superimposed is applied to the discharge wire of the transfer corotron 30, the toner images of each system on the photosensitive drum 20 are collectively transferred to the recording sheet 31 side,
Two color images, black and yellow, were obtained.

Incidentally, instead of forming the second system toner image by the second laser 24 and the second developing device 25, the latent image formed by the second laser 45 or the third laser 27 is transferred to the cyan color of the third developing device 28. There is no problem even if the second system toner image is formed by developing with the toner T3.

(3) Two-color custom color image mode (see FIG. 8) This image forming mode forms a two-color image including a color (custom color) that is different from the toner color used and can be arbitrarily selected by the customer. This is possible, and image formation is performed through the following steps.

The uniform charging process (step a), the first exposure process (step b), the first development process (step c), and the second exposure process (step d) are performed in the same manner as in the two-color specified color image mode.

Second developing step (step e) The developing bias V _B2 of the second developing device 25 is set to −450 V, and the positive latent image Zp is normally developed with the second yellow toner T2 (positive polarity).

In this case, due to the same operation as described above, the first-system toner image is hardly destroyed, and the yellow toner T2 is rarely mixed in the first-system toner image. The peeling toner of the system toner image does not enter the second developing device 25.

Third developing step (step f) The developing bias V _B3 of the third developing device 28 is set to −350 V which is different from the developing bias V _B2 of the second developing device 25, and the positive latent image Zp is set to the third cyan toner T3 (positive electrode). Regular development.
Then, development is performed in a state where the third toner T3 is superposed on the second toner T2, and a second system toner image composed of the second toner T2 and the third toner T3 is formed.

In this case, due to the same operation as described above, the first system toner image is hardly destroyed, and the cyan toner T3 is hardly mixed in the first system toner image. The peeling toner of the system toner image does not enter the third developing device 28.

The transfer pretreatment process (step h) and the transfer process are the same as those in the above 2
Color regulation Same as color image mode
After the above toner images are aligned in the positive polarity, the recording sheet 31
Then, two color images of black, yellow, and green by superimposing cyan and cyan were obtained on the recording sheet 31.

〔The invention's effect〕

As described above, according to the color image forming apparatus of the first aspect, the method of collectively transferring the three or two color images to the recording sheet in one cycle in which the latent image carrier makes one rotation is adopted. Therefore, as compared with the so-called transfer drum system or tandem system, it is possible to satisfy the basic requirements of downsizing of the device, speeding up, and simplification of alignment control. Since a three-system or two-system color image can be formed depending on the method of use, a color image of good image quality can be reliably obtained.

That is, according to the method of use according to claims 2, 3, and 4, the second developing unit is prevented from being mixed with the second and third toners in the first system toner image in the second developing process and the third developing process. Since it is possible to avoid mixing the first toner into the third developing device, it is possible to prevent the color quality of the first system toner image from being deteriorated due to color mixture, and the second and third developing devices can be prevented. It is possible to effectively prevent early deterioration of the second and third toners due to the mixing of the first toner, and there is a risk that the color image is damaged due to the color change of the second toner and the third toner due to the mixing of the toner. Can be prevented.

Further, the applicant of the present invention, as an image forming process having the same effect as the image forming process of the present invention, first forms a first positive latent image and performs regular development, and then forms a second negative latent image. Then, a color image forming method (hereinafter abbreviated as positive, negative, negative method) of performing reverse development and then forming a third negative latent image and performing reverse development is provided. Compared to the system, the present invention can set the initial charging potential of the latent image carrier to a low level even when forming a three-color image, so that the occurrence of damage such as pinholes can be prevented and the intermediate potential (non-potential) can be set. In addition to the advantages such as the ability to control the potential of the image area), in the positive, negative and negative systems, if the fringe electric field around the first system toner image is considerably large, the recharging means is used to To reduce the fringe electric field, There is a possibility that toner fogging occurs to the peripheral edge of the image, but in the present invention, minute there is no need to provide the re-charging means, it is possible to simplify the apparatus configuration.

Further, according to the method of using the color image forming apparatus of claims 3 and 4, since a plurality of toners to be used are overlapped to form the second system toner image, the color of the toner itself to be used is the same. It is possible to easily obtain a two-system color image including colors that can be arbitrarily selected by different customs.

In particular, according to the method of using the color image forming apparatus of the fourth aspect, in the developing bias method, the two toners can be reliably overlapped with the image portion of the latent image when forming the custom color image. , Custom color image quality can be kept good.

[Brief description of drawings]

FIG. 1 (a) is an explanatory view showing an outline of a color image forming apparatus according to the present invention, and FIGS. 1 (b) and (c) are explanatory views showing a method of using the color image forming apparatus according to the present invention. FIG. 4 is an explanatory view showing an embodiment in which the present invention is applied to a color printer, FIG. 3 is an explanatory view showing the constitution of a charging scorotron and a recharging scorotron, and FIG. 4 is a second developing device and a third developing device. FIG. 5 is an explanatory view showing the main part of the structure, FIG. 5 is an explanatory view showing its magnetic pole characteristics, FIG. 6 is an explanatory view showing an image forming process in a three-color image mode, and FIG. 7 is an image in a two-color specified color image mode. FIG. 8 is an explanatory diagram showing a forming process, FIG. 8 is an explanatory diagram showing an image forming process in a two-color custom color image mode, FIG. 9 is an explanatory diagram showing an example of a conventional color printer, and FIG. 10 is the image forming process. It is an explanatory view shown. [Description of Reference Signs] 1 ... Latent image carrier 2 ... First latent image forming means 3 ... First developing means 4 ... Second latent image forming means 5 ... Second developing means 6 ... Recharging means 7 ... Third latent image forming means 8 ... Third developing means 9 ... Transfer pretreatment means 10 ... Transfer means 11 ... Recording sheet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobumasa Furuya 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd. Ebina Business Office (56) References JP-A-58-57139 (JP, A) JP-A-57- 2047 (JP, A) JP 63-142363 (JP, A) JP 62-293261 (JP, A)

Claims (4)

[Claims] 1. A latent image carrier (1) carrying an electrostatic latent image.
A first latent image forming means (2) for forming a negative latent image (Zn) on the latent image carrier (1) in which the image portion potential is lower in absolute value than the background portion potential, and the first latent image A first developing means (3) for reversing and developing the negative latent image (Zn) formed by the forming means (2) with the first toner (T1), and a latter stage of the first latent image forming means (2). Second latent image forming means (4) which is provided and forms a positive latent image (Zp) on the latent image carrier (1) in which the image portion potential is higher in absolute value than the background portion potential. Second developing means (5) for normally developing the positive latent image (Zp) formed by the latent image forming means (4) with the second toner (T2), and operating when the three-system color image forming mode is selected, While preventing the polarity reversal of the first toner (T1),
2) reversing the polarity to adjust the potentials of the first toner image and the second toner image to be substantially equal, and the latent image carrier (1) recharged by the recharging means (6). ) A third latent image forming means (7) for forming a positive latent image (Zp) in which the image portion potential is higher in absolute value than the background portion potential, and the second latent image forming means (4) or the third latent image forming means. The positive latent image (Zp) formed by the image forming means (7) is transferred to the third toner (T
The third developing means (8) for regular development in 3), the transfer pretreatment means (9) for making the polarities of the toner images on the latent image carrier (1) uniform, and the toner images having uniform polarities A color image forming apparatus comprising: a transfer unit (10) for transferring a batch onto a recording sheet (11). 2. A negative latent image is formed on a latent image carrier (1) by a first latent image forming means (2) when a three-system color image is formed by using the color image forming apparatus according to claim 1. A first system toner image forming step (A1) in which an image (Zn) is formed and the negative latent image (Zn) is reversely developed with the first toner (T1) of the first developing means (3); A positive latent image (Zp) is formed on the latent image carrier (1) by the image forming means (4), and this positive latent image (Zp) is applied to the second toner (T2) of the second developing means (5). The second system toner image forming step (A2) for normal development and the first system toner image and the second system toner image while preventing the polarity reversal of the first toner (T1) by the recharging means (6). After adjusting the potentials to be substantially equal, the third latent image forming means (7)
To form a positive latent image (Zp) on the latent image carrier (1), and to develop this positive latent image (Zp) normally with the third toner (T3) of the third developing means (8). System toner image forming process (A
3) and the toner for collectively transferring the toner images to the recording sheet (11) by the transfer means (10) after aligning the polarities of the first to third system toner images by the transfer pretreatment means (9). A method of using a color image forming apparatus, comprising: an image transfer step (A4). 3. A negative latent image is formed on the latent image carrier (1) by the first latent image forming means (2) when forming a two-system color image by using the color image forming apparatus according to claim 1. A first system toner image forming step (B1) of forming an image (Zn) and reversal developing the negative latent image (Zn) with the first toner (T1) of the first developing means (3); A ghost latent image (Zp) is formed on the latent image carrier (1) by the image forming means (4), and this positive latent image (Zp) is used as a second toner (T2) other than black by the second developing means (5). ), A second system toner image forming step (B2) of performing regular development by further developing with third toner (T3) other than black of the third developing means (8), and transfer pretreatment means ( Toner image transfer step (B3) in which the polarities of the first and second system toner images are made uniform in 9), and each toner image is collectively transferred to the recording sheet (11) by the transfer means (10). Using a color image forming apparatus characterized by comprising a. 4. The method according to claim 3, wherein when the second developing means (5) and the third developing means (8) are of a developing bias system, different developing biases are applied. A method of using a color image forming apparatus, characterized in that the developing degree of a toner (T2) and a third toner (T3) is adjusted.