JPH03212661A - Color image forming device and its using method - Google Patents

Abstract

PURPOSE:To effectively restrain the color mixture and the contamination phenomenon of a reproduced image and to excellently secure the image quality of the color of three systems by using toner having a different polarity in forming an image. CONSTITUTION:A 1st positive latent image Zp where the potential of an image part is higher than that of a background part is formed on a latent image carrier 1 by a 1st latent image forming means 2. The latent image Zp is normally developed with the 1st toner T1 (negative polarity) by a 1st developing means 3. Next, a 2nd negative latent image Zn where the potential of the image part is lower than that of the background part is formed by a 2nd latent image forming means 4. The latent image Zn is reversely developed with the 2nd toner T2 (positive polarity) by a 2nd developing means 5. Then, a recharging means 6 prevents the inversion of the polarity of the toner T1 and adjusts the potentials of the 1st and the 2nd toner images nearly equal. The negative image Zn where the potential of the image part is lower than that of the background part is formed by a 3rd latent image forming means 7. The latent image Zn is reversely developed with the 3rd toner T3 (positive polarity) by a 3rd developing means 8. After the polarities of the respective toner images are arranged by a pre-transfer processing means 9, the respective toner images are transferred on a recording sheet 11 en bloc by a transfer means 10.

Description

[Detailed Description of the Invention] [Industrial Application Field] 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 relates to a color image forming apparatus such as a color printer or a color copying machine, and a method of using the same. , relates to an improvement in a color image forming apparatus that transfers a plurality of color images onto a recording sheet at once, and a method for using the same.

[Conventional technology]

Taking a printer as an example of a conventional color image forming apparatus, in each rotation cycle of a photosensitive drum that rotates multiple times, a corresponding system of toner images is formed on the photosensitive drum, and the toner images are wound around a transfer drum that comes into contact with the photosensitive drum. For example, there is a so-called transfer drum method in which toner images of each system on a photosensitive drum are superimposed and transferred onto a recording sheet in each rotation cycle, and a method in which a plurality of image forming units (photosensitive drums, latent image forming units, This is a so-called tandem system in which the toner images formed by each image forming unit are sequentially transferred onto a recording sheet that is conveyed along the predetermined direction by a sheet conveying device. Something called this has already been proposed.

However, in the former type, the photosensitive drum must be rotated multiple times to form one color image, which poses problems such as the time it takes to form a color image, and the accuracy of the transfer position of each toner image. In order to increase the speed, the rotation of the photosensitive drum and the transfer drum must be controlled with high accuracy, which poses a problem in that device control becomes complicated.

In addition, in the latter type, it is possible to shorten the color image forming time compared to the former type, but not only does the device itself become larger, but it is also difficult to control the rotation of the photosensitive drum of each image forming unit. In addition, conveyance control of the recording sheet must be performed with high precision, and there is a problem that device control becomes complicated (see Japanese Patent Laid-Open No. 174564/1983).

In order to solve this problem, a device has already been proposed in which multiple systems of toner images are formed on a photosensitive drum and then these toner images are transferred all at once to a recording sheet (Japanese Patent Laid-Open No. 58 -57139, 60-2476
(See Publication No. 50).

For example, as shown in FIG.
A charger 1 for pre-charging the photosensitive drum 100 is placed around the photosensitive drum 100.
01, a first laser 102 for forming a first latent image;
A first developing device 1 of a developing bias type that develops a first latent image
03. First recharger 10 that recharges the photosensitive drum 100
4. A second laser 105 for forming a second latent image, and a second developing device 10 of a developing bias type for developing the second latent image.
6. Second recharger 107 that recharges the photosensitive drum 100
, a third laser 108 for forming a third latent image, and a third developer 109 of a developing bias type for developing the third latent image.
, a charger 110 that adjusts the potential level of each toner image on the photosensitive drum 100, a transfer device 111 that transfers all the toner images on the photosensitive drum 100 onto a recording sheet 112, and a cleaner that removes residual toner on the photosensitive drum 100. - 113 are respectively arranged.

In this type of image forming process, for example, as shown in FIG. 12, after the photosensitive drum 100 is uniformly positively charged with the charger 101 (step a), the image area is In order to form a first negative latent image Zn whose potential is lower than the background potential, in step b), the first toner T is used to form the negative latent image with a predetermined developing bias VB+ applied to the first developing device 103. After the image Zn is reversely developed (step c), the photosensitive drum 100 is recharged by the first recharger 104 (step d), and the potential of the image area is lower than the potential of the background area by the second laser 105. To form a second negative latent image Zn, step e), with a predetermined developing bias VBI applied to the second developing device 106, only the second negative latent image Zn is reversely developed using the second toner T2. In step f), furthermore, the second recharger 10
After recharging the photosensitive drum 100 in step 7 (step g), a third laser 108 is used to form a third negative latent image Zn in which the potential of the image area is lower than the potential of the background area (step h), and the third development described above. With a predetermined developing bias VBI applied to the device 109, the third negative latent image Zn is formed using the third toner T.
In step i), the charger 100 adjusts the potentials of the toner images of each system to be approximately equal (step j), and then the transfer device 112 transfers each toner image at once to the recording sheet Ill side. This is how it was done.

[Problem to be solved by the invention]

However, in such an image forming process, when forming toner images of each system, the negative latent image is developed in reverse using toner of the same polarity. In the second and third development steps, a color mixing phenomenon in which each toner mixes with each other on the image tends to occur, and
When some of the toner from the developer toner image on the photosensitive drum 100 peels off and enters the next developing device, the mixed toner will accumulate in the developing device, and the triboelectric charging characteristics of the toner in the developing device will deteriorate. This not only accelerates the deterioration of the toner inside the developing device, but also changes the color tone of the toner inside the developing device, which causes a corresponding loss in the color quality of the reproduced image.

In addition, when reproducing a two-color image using this type of device, for example, two lasers 102, 105 and two developing devices 103, 106 are used to reproduce the two-color image. The image color is limited to the color of the toner in the developing device being used, and it is difficult to reproduce a customer's (custom) desired color image unless the toner in the developing device is replaced.

The present invention has been made in view of the above-mentioned problems, and satisfies the demands of increasing the color image forming speed and making the device more compact, while effectively suppressing color mixing and mixing phenomena in reproduced images. To provide a color image forming device that can maintain good three-system color image quality and efficiently reproduce two-color images including a customer's favorite color image, and a method for using the same. .

[Means to solve the problem]

That is, the color image forming apparatus according to the present invention has a first
As shown in Figure (a), there is a latent image carrier 1 carrying an electrostatic latent image, and a positive latent image zp on which the image area potential is higher in absolute value than the background area potential. a first latent image forming means 2 for forming a first latent image; a first developing means 3 for regularly developing a positive latent image zp formed by the first latent image forming means 2 with a first toner TI; Arranged after the forming means 2,
A second latent image forming means 4 for forming a negative latent image Zn on the latent image carrier l, the potential of the image area being lower in absolute value than the potential of the background area.
and a negative latent image Z formed by this second latent image forming means 4.
a second developing means 5 that reversely develops the toner T2 with the second toner T2; and a recharging means 6 that adjusts the potentials of the first toner image and the second toner image to be substantially equal while preventing polarity reversal of the first toner Tl. and a third latent image forming means 7 for forming a negative latent image Zn in which the image area potential is lower in absolute value than the background area potential on the latent image carrier l recharged by the recharging means 6; a third developing means 8 for reversing and developing the negative latent image Zn formed by the second latent image forming means 4 or the third latent image forming means 7 with a third toner T3; This apparatus is characterized by comprising a transfer pre-processing means 9 for aligning the polarities of the toner images, and a transfer means 10 for collectively transferring the toner images of the same polarity onto the recording sheet 11.

In such an apparatus invention, the latent image carrier 1 includes:
The design may be changed as appropriate depending on the type of latent image forming means, such as using a photoreceptor when forming an electrostatic latent image using light and using a dielectric when forming an electrostatic latent image using ions.

Further, the structure of the latent image carrier 1 may be drum-shaped or belt-shaped, and the charging type may be positive or negative.

Further, the first latent image forming means 2, the second latent image forming means 4, and the third latent image forming means 7 include latent image writing means for forming an electrostatic latent image on the latent image carrier 1. If it is necessary to charge the surface of the latent image carrier 1 in advance for writing an electrostatic latent image, it is necessary to configure the charging means to include a charging means.

In this case, the latent image writing means can be appropriately selected from an exposure lamp, an optical imaging system, a laser, an LED, a liquid crystal shutter, etc. in the case of a type using a light beam, or an appropriate one for a type using ions. The discharge head and the like can be selected as appropriate.

Furthermore, the developing method and type of developer for the first developing means 2, second developing means 5, and third developing means 7 may be selected as appropriate, but in consideration of developing efficiency, it is preferable to use a two-component developer. A magnetic brush development type is preferred. In this case, from the viewpoint of preventing disturbance of the developer toner image in the second developing step and the third developing step,
For example, when adopting a magnetic brush development method using a two-component developer, a low-density developer carrier is used, a repulsive magnetic pole is provided at the development area of the developer carrier, and the developer Decrease the relative speed ratio between the carrier and the latent image carrier l (Japanese Patent Laid-Open Nos. 142363-1983 and 1999), etc.
-287581, Patent Application No. 168696/1983)
Therefore, it is preferable to use a soft magnetic brush using the developer, or it is preferable to use a non-contact developing method.

Furthermore, as for the recharging means 6, as long as the polarity reversal of the first toner is suppressed, the recharging means 6 may be configured to recharge the first toner and the second toner without changing their polarities, or the recharging means 6 may be configured to recharge the first toner and the second toner without changing their polarities. Instead of reversing the polarity of the first toner, recharging may be performed with the polarity of the second toner reversed. In this case, from the viewpoint of effectively suppressing color mixing and mixing phenomena in the third developing step, it is preferable that the polarity of the second toner be reversed by the recharging means 6.

Further, the design of the transfer pretreatment means 9 may be changed as appropriate as long as it at least aligns the polarity of each toner image on the latent image carrier 1, but considering the transfer efficiency of each toner image, For example, when the latent image carrier 1 is a photoreceptor, an exposure process is performed simultaneously with the charging process or after the charging process, etc.
It is preferable to take measures to lower the potential of .

Further, regarding the transfer means IO, if the toner image on the latent image carrier l 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. It is not limited to those that are transferred to the side, but also includes those that are transferred to the recording sheet 11 side by a method such as thermal transfer.

Furthermore, in consideration of the lifespan 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 must be accurately set. From the perspective of defining, Figure 1 (
As shown by the imaginary line in a), it is preferable to arrange a recharging means 12 in front of the second latent image forming means 4 so as to reduce the electric potential of the first toner image in absolute value. Note that when a two-component developer having a conductive carrier is used as the developer in the first developing means 3, the potential of the first toner image naturally decreases in absolute value in the first developing step. , there is no need to provide the recharging means 12 as described above.

Further, the image forming process when obtaining three systems of color images using the above color image forming apparatus is shown in FIG. 1(b).
As shown, a positive latent image Zp is formed on the latent image carrier L by the first latent image forming means 2, and this positive latent image Zp is regularly developed with the first toner Tl of the first developing means 3. In the first system toner image forming step At, a negative latent image Zn is formed on the latent image carrier 1 by the second latent image forming means 4, and this negative latent image Zn is transferred to the second toner T2 of the second developing means 5. A second system toner image forming step A2 in which reversal development is performed at a recharging means 6, and the potentials of the first system toner image and the second system toner image are adjusted to be approximately equal while preventing polarity reversal of the first toner Tl. After that, a negative latent image Zn is formed on the latent image carrier 1 by the third latent image forming means 7, and this negative latent image Zn is reversely developed by the third toner T3 of the third developing means 8. Systemic toner image forming step A3
and a toner image transfer step A4 in which the polarities of the first to third system toner images are aligned by the transfer pretreatment means 9, and the toner images are transferred all at once to the recording sheet 11 by the transfer means 10. This is a characteristic feature.

Furthermore, in the image forming process of obtaining two color images using the above-mentioned color image forming apparatus, as shown in FIG. A positive latent image Zp is formed, and this positive latent image Zp is transferred to the first developing means 3.
A first system toner image forming step B1 in which regular development is performed with the first toner TI of After reversal development with the second toner T2 other than black in the second developing means 5,
A second system toner image forming step B2 in which the third toner other than black toner T3 of the third developing means 8 is further superimposed and regularly developed, and each toner image of the first and second systems is This method is characterized by comprising a toner image transfer step B3 in which each toner image is transferred at once to a recording sheet 11 by a transfer means 10 while aligning the polarities.

In such a method of using a color image forming apparatus, when a recharging means 12 is added to the front side of the second latent image forming means 4, as shown by the imaginary lines in FIG. 1(b) and (c), In addition, in the second system toner image forming steps A2 and B2, the first system toner image potential may be lowered in absolute value before forming the second negative latent image Zn.

Furthermore, in the image forming process shown in FIG. 1(C), it is necessary to make adjustments so that the same negative latent image Zn can be developed with each toner in the second developing means 5 and the third developing means 8 in an overlapping manner. If the second and third developing means 5 and 8 are of a developing bias type, for example, the second toner T2. The degree of development of the third toner T3 may be adjusted.

[Effect]

When forming three systems of color images using the color image forming apparatus described above, in the first system toner image forming step AI, the positive latent image Zp corresponding to the first image on the latent image carrier l is The negative latent image Zn corresponding to the second image on the latent image carrier 1 is developed normally with the first toner T1, and the negative latent image Zn corresponding to the second image on the latent image carrier 1 is developed with the second toner bottom 2 in the second system toner image forming step A2, and the third In the system toner image forming step A3, the negative latent image Zn corresponding to the third image on the latent image carrier 1 is reversely developed with the third toner T3, and in the toner image transfer step A4, the toner images of each system are developed. The images are transferred to the recording sheet 11 all at once.

In such an image forming process, even if the first system toner image formed by the first toner TI comes into contact with the second toner bottom 2 and the third toner T3 in the second and third development steps, the first toner Tl and second and third toners T2. T3
Since the polarity is different from that of the second and third toners T2. T3 is never mixed into the first system toner image.

Further, the first toner TI of the first system toner image is peeled off, and the second developing means 5. Even if the first toner T1 enters into the housing of the third developing means 8, the first toner T1 is transferred to the second toner under 2 in the second developing means 5 or the third toner T3 in the third developing means 8.
The first toner Tl is easily discharged from each housing and is not accumulated in the housing.

Further, when forming two systems of color images using the color image forming apparatus, a positive latent image Zp corresponding to the first image on the latent image carrier 1 is formed in the first system toner image forming step Bl. is normally developed with the first toner T1, and in the second system toner image forming step B2, a negative latent image Zn corresponding to the second image on the latent image carrier 1 is reversely developed with the second toner bottom 2. At the same time, it is further reversely developed with the third toner T3,
In the toner image transfer step B3, the toner images of each system are collectively transferred to the recording channel Il.

In such an image forming process, the second toner under the second toner is added to the first system toner image by the same effect as described above.
, the third toner T3 will not be mixed, and the first toner T1 will not be mixed into the housings of the second developing means 5 and the third developing means 8.

Furthermore, in this image forming process, since the second system toner image is a superposition of the second toner bottom 2 and the third toner T3, the color of the second system toner image is different from that of the second toner bottom 2. Alternatively, the toner is adjusted to be different from the third toner T3.

〔Example〕

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

◎Basic configuration Figure 2 shows an embodiment in which the present invention is applied to a color printer.

In the figure, reference numeral 20 denotes a positively charged Se-based photosensitive drum, 21 a charging scorotron for pre-charging the photosensitive drum 20, and 22 a first positive latent image corresponding to the first image on the photosensitive drum 20. A first laser 23 for forming a first positive latent image is a first developing device 24 of a two-component magnetic brush developing system that regularly develops a first positive latent image with, for example, a first black toner TI (positive polarity).
25 is a first recharging scorotron that recharges the first toner T1 while preventing polarity reversal and lowers the potential of the first toner image; 25 is a second negative scorotron that corresponds to a second image on the photosensitive drum 20; A second laser beam 26 generates a second negative latent image using, for example, a second cyan toner (negative polarity) T2.
27 is a second recharging scorotron that re-charges the surface of the photosensitive drum 20 while preventing polarity reversal of the first toner Tl; 28 is a photosensitive scorotron; A third laser 29 forms a third negative latent image corresponding to the third image on the drum 20, and 29 regularly develops the third or second negative latent image with, for example, a third magenta toner (negative polarity). 30 is a pre-transfer corotron that aligns the polarity of each toner image formed on the photosensitive drum 20; 31 charges the recording sheet 32, and 31 charges the recording sheet 32 so that each toner image on the photosensitive drum 20 A transfer corotron 33 electrostatically transfers images to the recording sheet 32 side at once, and a transfer corotron 33 is a transfer corotron that removes static electricity from the recording sheet 32 on which each toner image on the photosensitive drum 20 has been transferred, and peels off this recording sheet 32 from the photosensitive drum 20. A tack corotron, 34, a cleaner for removing residual toner on the photosensitive drum 20;
Reference numeral 5 denotes a static elimination lamp that removes residual charges on the photosensitive drum 20.

In this embodiment, the charging scorotron 21 has a discharge wire 42 disposed inside a shield 41 having a U-shaped cross section, and a control grid 43 disposed in an opening of the shield 41, as shown in FIG. A positive voltage is applied to the discharge wire 42 and the control grid 43.

In addition, the recharging scorotron 24.27 is particularly suitable for the third
As shown in the figure, a high voltage power source 45 applies a negative high voltage to the discharge wire 42 disposed inside the shield 41 having a U-shaped cross section, and a high voltage is applied to the control grid 43 disposed in the opening of the shield 41. A power source 46 applies a positive high voltage.

The characteristics of this rechargeable scorotron 24.27 are:
A voltage was applied to the conductive plate 50 (corresponding to the photosensitive drum 20) from the power source 51, and the current ip flowing into the conductive plate 50 and the voltage Vp of the conductive plate 50 were measured with an ammeter 52 and a voltmeter 53. However, the trend is as shown in FIG. Note that the intersection point X with the voltage axis substantially coincides with the control grid voltage.

Further, in this embodiment, the second developing device 26, 29
As shown in FIGS. 5 and 6, a developing roll 62 is disposed within a housing 61, and the developing roll 62 has seven poles (NL to N4.
St to S3) A magnet roll 64 with an asymmetrical magnetization configuration is fixedly provided, and the magnetic flux density of the main pole (repulsion magnetic pole made of N2 and N3) 65 is about 1200 Gauss, and the difference between its peak and valley is 50 to 200 Gauss. Furthermore, the magnetic flux density of the other magnetic pole 66 is set to about 800 Gauss.

Furthermore, as the developer in the second developing device 26 and the third developing device 29, a carrier having a density of 4 g/cnf or less, which is made by dispersing magnetic powder in a resin binder, is used.

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

Note that the process speed of the photosensitive drum 20 in this example is 160 mm/sec.

(1) Three-color image mode (see FIG. 7) - Uniform charging process (step a) The surface of the photosensitive drum 20 is uniformly charged to 1200V.

(1) First exposure process (step b) The first laser 22 forms a first positive latent image zp in which the potential of the image portion is higher than the potential of the background portion. In this case, in order to make the potential difference between the image part potential and the background part potential about 1/3 of the initial charging potential, the image part potential is 12OOV and the background part potential is 800V.
Set to V.

■First developing step (Step C) The developing bias V B+ of the first developing device 23 is set to 900 V, and the positive latent image Zp is transferred to the first black toner TI (negative polarity).
Regularly develop the image.

■First recharging process (step d) By setting the voltage of the control grid 43 of the first recharging scorotron 24 near the background potential of the first exposure process, and adjusting the voltage applied to the discharge wire 42 as appropriate, the first recharging process is performed. The first system toner image potential V 1 , T I is set to be slightly higher than the background potential without reversing the polarity of the toner Tl.

In this embodiment, the control grid voltage is set to 750V and the discharge wire voltage is set to -4.5KV, thereby setting the first system toner image potential V□1 to 800V and the background potential to 750V.

(2) Second exposure step (step e) A second negative latent image Zn is formed by the second laser 25, the potential of the image area being lower than the potential of the background area. In this example, the background potential is set to 750V, and the image potential is set to 400V.

. ■Second developing process (step f) The developing bias VB□ of the second developing device 26 is set to 650V,
The negative latent image Zn is reversely developed using a second cyan toner T2 (positive polarity).

In this case, since the first system toner image is held by the well-shaped potential pattern, the first system toner image is almost never destroyed (and the cyan toner T
2 is hardly mixed in the first system toner image,
Moreover, the peeled toner of the first system toner image is transferred to the second developing device 2.
It will not be mixed into 6.

Further, as schematically shown in FIG. 8(a), the fringe electric field Sf of the first system toner image before the recharging step is extremely large, and when the second developing step is performed in this state, the fringe electric field Sf is extremely large. There is a risk that Sf may become lower than the developing bias VB2, and a fogging phenomenon may occur in which the second toner layer 2 adheres to the periphery of the first system toner image. In the recharging step, the first system toner image potential V7. As a result, as schematically shown in FIG. 8(b), the fringe electric field Sf of the first system toner image becomes small, and the fringe electric field Sf
The potential is sufficiently higher than the developing bias VB2, and there is no possibility that a fogging phenomenon in which the second toner layer 2 will adhere to the peripheral edge of the first system toner image will occur.

■Second recharging process (step g) By setting the voltage of the control grid 43 of the second recharging scorotron 27 near the image area potential of the second system toner image, and adjusting the voltage applied to the discharge wire 42 as appropriate, Without reversing the polarity of the first toner T1 and the second toner lower 2, the first system toner image potential VTI is slightly higher than the recharging potential level, and the second system toner image potential VT□ is slightly higher than the recharging potential level. Also set it so that it is slightly lower.

In this example, the control grid voltage is 450V and the discharge wire voltage is -4.5KV, so that the first system toner image potential VTI is 500V and the second system toner image potential V
Set T2 to 410V and background potential to 450V.

(3) Third exposure process (step h) A third negative latent image Zn is formed using the third laser 28, the potential of the image area being lower than the potential of the background area. In this example, the background potential is set to 450V, and the image potential is set to 100V.

■Third developing process (step i) The developing bias VB2 of the third developing device 29 is set to 350V,
The above negative latent image Zn is transferred to the third magenta color toner T3 (
Reverse development with positive polarity). In this example, since the second system toner image potential VT2 is 410V,
There is no possibility that the third toner T3 will be developed in the second system toner image.

In this case, since the first system toner image and the second system toner image are held together by the well-shaped potential pattern, the first system toner image and the second system toner image are almost never destroyed. The magenta toner T3 is hardly mixed into the first system toner image, and furthermore, the peeled toner of the first system toner image is not mixed into the third developing device 29. In addition, since the magenta color toner T3 and the second toner bottom 2 have the same polarity, there is a possibility that the magenta color toner T3 may be mixed in the second system toner image or the second toner bottom 2 may be mixed in the third developing device 29. Therefore, the third development is preferably a non-contact development method.

[Phase] Transfer pretreatment process (step j) 400Hz, vp is applied to the discharge wire of the corotron 30 before transfer.
-p DC component with superimposed AC component of 10 KV -1
, 5KV is applied to adjust the toner polarity of the toner image of each system to negative polarity.

■Transfer process When 5.5 KV was applied to the discharge wire of the transfer corotron 31, the toner images of each system on the photosensitive drum 20 were transferred at once to the recording sheet 32 side, creating three color images of black, cyan, and magenta. Obtained.

(2) Two-color standard color image mode (see FIG. 9) - Uniform charging process (step a) The surface of the photosensitive drum 20 is uniformly charged to 800V.

(1) First exposure process (step b) The first laser 22 forms a first positive latent image Zp in which the potential of the image portion is higher than the potential of the background portion. In this case, in order to make the potential difference between the image part potential and the background part potential about 1/2 of the initial charging potential, the image part potential is 800V, and the background part potential is 400V.
Set to .

■First developing step (Step C) The developing bias VBI of the first developing device 23 is set to 500V,
The positive latent image zp is regularly developed with a first black toner T1 (negative polarity).

■Recharging process (step d) By setting the voltage of the control grid 43 of the first recharging scorotron 24 near the foreground potential of the first exposure process and adjusting the voltage applied to the discharge wire 42 as appropriate, the first toner The first system toner image potential VTj is set to be slightly higher than the background potential without reversing the polarity of TI.

In this embodiment, the control grid voltage is 380V and the discharge wire voltage is -4.3KV, thereby setting the first system toner image potential VTI to 400V and the background potential to 350V.

(2) Second exposure step (step e) A second negative latent image Zn is formed by the second laser 25, the potential of the image area being lower than the potential of the background area. In this example, the background potential is set to 350V, and the image potential is set to 80V.

■Second developing process (step f) The developing bias VB2 of the second developing device 26 is set to 280v,
The negative latent image Zn is reversely developed using a second cyan toner T2 (positive polarity).

In this case, since the first system toner image is held by the well-shaped potential pattern, the first system toner image is hardly destroyed, and the cyan toner T
2 is hardly mixed in the first system toner image,
Moreover, the peeled toner of the first system toner image is transferred to the second developing device 2.
It will not be mixed into 6.

In addition, since the first system toner image potential V71 decreases during the recharging process, the fogging phenomenon in which the second toner T2 adheres to the periphery of the first system toner image potential V71 occurs as described above. There is no possibility that this will occur.

■Pre-transfer treatment process (step g) 400H2, Vp on the discharge wire of the corotron 30 before transfer
-p 10 KV AC component and superimposed DC component -1
, 5KV is applied to adjust the toner polarity of the toner image of each system to negative polarity.

■Transfer process When 5.5 KV was applied to the discharge wire of the transfer corotron 31, the toner images of each system on the photosensitive drum 20 were transferred at once to the recording sheet 32 side, and two color images of black and cyan were obtained. Ta.

Incidentally, instead of forming the second system toner image with the second laser 25 and the second developing device 26, the latent image formed with the second laser 25 or the third laser 28 is transferred to the magenta color of the third developing device 29. A second system toner image may be formed by developing with toner T3.

(3) Two-color custom color image mode (see Figure 10) This image forming mode forms a two-color image that includes a color that is different from the color of the toner being used and that can be selected arbitrarily by the customer to some extent (custom color). Image formation is performed through the following steps.

--like charging process (step a), ■first exposure process (step b), ■first development process (step C), ■recharging process (step d), and ■second exposure process (step e) are as described above. This is done in the same way as the two-color standard color image mode.

■Second developing process (step f) The developing bias ■8□ of the second developing device 26 is set to 180■,
The negative latent image Zn is reversely developed using a second cyan toner T2 (positive polarity).

In this case, due to the same effect as described above, the first system toner image is hardly destroyed, and the cyan toner T2 is almost never mixed into the first system toner image. Peeled toner of the systematic toner image does not get mixed into the second developing device 26. Furthermore, there is no possibility that a fogging phenomenon in which the second toner T2 adheres to the periphery of the first system toner image potential VT1 will occur.

■Third developing process (step g) The developing bias Va+ of the third developing device 29 is changed to the second developing device 26.
The developing bias is set to 280 V, which is different from the developing bias VB□, and the negative latent image Zn is reversely developed with the third magenta color toner T3 (positive polarity). Then, development is performed with the third toner T3 superimposed on the second toner bottom 2, and the second toner bottom 2
A second system toner image consisting of the third toner T3 and the third toner T3 is formed.

In this case, due to the same effect as described above, the first system toner image is almost never destroyed, and the magenta color toner T3 is almost never mixed into the first system toner image. Peeled toner of the systematic toner image does not get mixed into the third developing device 29. Furthermore, there is no possibility that a fogging phenomenon in which the third toner T3 adheres to the periphery of the first system toner image potential VT1 will occur.

■Pre-transfer treatment process (step h),■Transfer process is the above 2
It is carried out in the same way as the color specification color image mode, and the photosensitive drum 2
After each toner image on 0 was aligned to have negative polarity, it was transferred all at once to a recording sheet 32, and a two-system color image consisting of blue by overlapping black, cyan, and magenta was obtained on the recording sheet 32.

〔Effect of the invention〕

As described above, according to the color image forming apparatus according to any one of claims 1 to 4, three or two color images are printed on a recording sheet at once in one rotation cycle of the latent image carrier. Since a transfer method can be adopted, the basic requirements of making the device more compact, increasing speed, and simplifying positioning control can be satisfied compared to the so-called transfer drum method or tandem method. 3,5
．． Since a three-system or two-system color image can be formed by the usage method described in 6.7, a color image with good image quality can be reliably obtained.

That is, according to the method of use described in claims 2.3 and 5.6.7, mixing of the second and third toners in the first system toner image in the second and third development steps is avoided, Since it is possible to avoid mixing of the first toner into the second developing means and the third developing means, it is possible to prevent the color quality of the first system toner image from being deteriorated due to color mixture. It is possible to effectively prevent early deterioration of the second and third toners due to the mixing of the first toner in the third developing means, and also prevent color images from changing due to color changes of the second and third toners due to toner mixing. This can prevent the risk of damage.

Further, according to the method of using the color image forming apparatus according to any one of claims 3.6.7, since the second system toner image is formed by overlapping the plurality of toners used, It is possible to easily obtain two types of color images including colors that can be arbitrarily selected to a certain extent that are different from the colors themselves.

In particular, according to the method of using a color image forming apparatus according to claim 7, in a developing bias type apparatus, two toners can be reliably superimposed on the image area of a latent image when forming a custom color image. , can maintain good custom color image quality.

Furthermore, according to the color image forming apparatus and the method of using the same according to any one of claims 4, 5 and 6, in the type in which the first system toner image potential is maintained high in the first developing step, the first system toner image potential is maintained high. Since the first-system toner image potential is reduced in absolute value in the recharging process, the fringe electric field at the periphery of the first-system toner image can be suppressed to a small level.
In the second and third development steps, it is possible to avoid the fogging phenomenon in which the second and third toners adhere to the periphery of the first system toner image, thereby maintaining good color image quality for multiple systems. be able to.

[Brief explanation of drawings]

FIG. 1(a) is an explanatory diagram showing an outline of a color image forming apparatus according to the present invention, FIGS. 1(b) and 1(c) are explanatory diagrams showing how to use the color image forming apparatus according to the present invention, and FIG. FIG. 3 is an explanatory diagram showing an embodiment in which the present invention is applied to a color printer, FIG. 3 is an explanatory diagram showing the configuration of a recharging scorotron, and FIG. 4 is a graph diagram showing the characteristics of the recharging scorotron.
Fig. 5 is an explanatory diagram of the main parts showing the configuration of the second developing device and the third developing device, Fig. 6 is an explanatory diagram showing the magnetic pole characteristics thereof, and Fig. 7 is an explanatory diagram showing the image forming process of the three-color image mode. 8(a) is an explanatory diagram showing the surface potential of the photosensitive drum and its electric field state when the second developing step is performed without passing through the first recharging step, and FIG. 8(b) is an explanatory diagram showing the surface potential of the photosensitive drum and its electric field state. FIG. 9 is an explanatory diagram showing the surface potential of the photosensitive drum and its electric field state when the second developing process is performed after the first recharging process. FIG. 10 is an explanatory diagram showing an image forming process in a two-color custom color image mode, FIG. 11 is an explanatory diagram showing an example of a conventional color printer, and FIG. 12 is an explanatory diagram showing the image forming process. [Explanation of symbols] ■...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...Third developing means...Transfer pretreatment means 0...Transfer means 1...Recording sheet

Claims (1)

[Claims] 1) A latent image carrier (1) on which an electrostatic latent image is carried, and a positive latent image carrier (1) on which the image area potential is higher in absolute value than the background area potential. a first latent image forming means (2) that forms an image (Zp); and a positive latent image (2) formed by this first latent image forming means (2).
A first developing means (3) for regularly developing Zp) with a first toner (T1), and a first developing means (3) disposed after the first latent image forming means (2), and disposed on the latent image carrier (1). a second latent image forming means (4) forming a negative latent image (Zn) whose image part potential is lower in absolute value than the background part potential; and a negative latent image formed by the second latent image forming means (4). image(
a second developing means (5) for reversing and developing Zn) with a second toner (T2); A recharging means (6) for equal adjustment, and a latent image carrier (1) recharged by the recharging means (6).
), the second latent image forming means (4) or the third latent image forming means (7) forming a negative latent image (Zn) on which the image part potential is lower in absolute value than the background part potential. The negative latent image (Zn) formed by the image forming means (7) is transferred to the third toner (
a third developing means (8) that performs reversal development at T3); a transfer pretreatment means (9) that aligns the polarity of each toner image on the latent image carrier (1); A color image forming apparatus characterized by comprising a transfer means (10) for transferring data all at once onto a recording sheet (11). 2) When forming three systems of color images using the color image forming apparatus according to claim 1, a positive latent image (Zp) is formed on the latent image carrier (1) by the first latent image forming means (2). ), and this positive latent image (Zp) is regularly developed with the first toner (T1) of the first developing means (3), a first system toner image forming step (A1), and a second latent image forming means In (4), a negative latent image (Zn) is formed on the latent image carrier (1), and this negative latent image (Zn) is reversely developed with the second toner (T2) of the second developing means (5). A second system toner image forming step (A2) of forming a first system toner image and a second system toner image potential while preventing polarity reversal of the first toner (T1) using a recharging means (6). After equal adjustment, the third latent image forming means (7
) to form a negative latent image (Zn) on the latent image carrier (1), and this negative latent image (Zn) is reversely developed with the third toner (T3) of the third developing means (8). The three-system toner image forming step (A3) and the transfer pretreatment means (9) align the polarities of the first to third system toner images, and the transfer means (10) transfers each toner image onto a recording sheet (11). Toner image transfer process (toner image transfer process)
A4) A method of using a color image forming apparatus characterized by comprising: 3) When forming two systems of color images using the color image forming apparatus according to claim 1, a positive latent image (Zp) is formed on the latent image carrier (1) by the first latent image forming means (2). ), and this positive latent image (Zp) is regularly developed with the first toner (T1) of the first developing means (3), a first system toner image forming step (B1), and a second latent image forming means In step (4), a negative latent image (Zn) is formed on the latent image carrier (1), and this negative latent image (Zn) is transferred to a second toner other than black (T2) in the second developing means (5). After reversal development, the third toner (other than black) in the third developing means (8) is
A second system toner image forming step (B2) in which the toner images of the first and second systems are further overlapped and regularly developed in T3), and the polarity of each toner image of the first and second systems is aligned in a transfer pretreatment means (9), and then the toner images are formed in a transfer means ( 11) A method for using a color image forming apparatus, comprising a toner image transfer step (B3) for collectively transferring each toner image onto a recording sheet (10). 4) The apparatus according to claim 1, further comprising a recharging means (12) for reducing the first system toner image potential in absolute value between the first developing means (3) and the second latent image forming means (4). ) is added. 5) When forming three systems of color images using the color image forming apparatus according to claim 4, the second system toner image forming step (A2) among the steps (A1 to A4) according to claim 2. At the beginning of the recharging means (1
2) A method for using a color image forming apparatus, characterized in that the first system toner image potential is lowered in absolute value. 6) When forming two systems of color images using the color image forming apparatus according to claim 4, the second system toner image forming step (B2) among the steps (old to B3) according to claim 3. At the beginning of the recharging means (12
), the first system toner image potential is lowered in absolute value. 7) The method of use according to claim 3 or 6, wherein the second developing means (5) and the third developing means (8) are of a developing bias type, and when different developing biases are applied. Second toner (T2), third toner (T3)
1. A method for using a color image forming apparatus, characterized in that the degree of development is adjusted.