JPH06100867B2 - Color recording method - Google Patents

Description

The present invention relates to a color recording method for recording a color image on a recording sheet using an electrophotographic recording method.

“Prior Art” In the conventionally well-known electrophotographic recording method, a photoconductor is uniformly charged, a light image is formed on the photoconductor, and exposure is performed to form an electrostatic latent image. After that, the electrostatic latent image is developed to form a toner image corresponding to the electrostatic latent image, and the toner image is transferred to a recording sheet.

Various methods for recording a color image using such an electrophotographic recording method have been developed as follows, but each has its own problems.

"Problems to be Solved by the Invention" First, FIG. 6 shows a schematic configuration diagram of a so-called overlap transfer method.

This method is a method in which charging, exposure, development and transfer of the photoconductor are repeated a plurality of times. For example, the first time is a black image, the second time is a red image, and the third time is a blue image. An electrostatic latent image corresponding to a color image is formed, and development and transfer are repeated using toner of a color corresponding to the electrostatic latent image (JP-A-61-48871).

This device includes a preclean corotron 2, a cleaning device 3, a charging device 4, a first developing device 5, a second developing device 6, a third developing device 7, and a transfer device 8 on the outer periphery of the photoconductor 1. Is arranged. An exposure unit 10 is provided between the charging device 4 and the first developing device 5. Further, the photoconductor 1
, A hollow transfer drum 9 is arranged so as to be circumscribed at the transfer portion 11. The recording paper 12 is wound around the transfer drum 9 and repeatedly passes through the transfer unit 11 by the rotation of the transfer drum 9.

In this apparatus, first, when a black image is exposed, the electrostatic latent image is developed by the developing device 5 containing black toner. The toner image is transferred to the recording paper 12 by the transfer unit 11. Next, the red image is exposed, and the electrostatic latent image is developed by the developing device 6 containing the red toner. The toner image is transferred by the transfer unit 11 onto the recording paper 12 which is wound around the transfer drum 9 and made one round. Similarly, when the blue toner image is transferred onto this recording paper 12, the recording paper 12
Is released from the transfer drum 9 toward the fixing device 13. In this way, a total of three color images can be recorded.

However, in the apparatus having such a configuration, the space for providing the transfer drum 9 is relatively large, which leads to an increase in the size of the apparatus. Further, since the steps from exposure to transfer are repeated for the number of colors used, the copying speed is increased. It has the drawback of being late.

FIG. 7 shows a schematic configuration diagram of an apparatus adopting a sequential transfer method different from this.

In this method, a separate photoconductor is prepared for each color, and charging, exposure, development, and transfer of the photoconductor are performed in different steps. For example, a black image is used in the first step and a red image is used in the second step. Is sequentially transferred to the recording sheet 12 (Japanese Patent Laid-Open No. 61-
No. 36767).

In this apparatus, a preclean corotron 2, a cleaning device 3, a charging device 4, and a black toner developing device 5 or a red toner developing device 6 are arranged around the outer periphery of each photoconductor 1. Further, exposure units 10 and 20 are provided between the charging device 4 and the developing device 5 or the developing device 6, respectively.
Further, a transfer unit 8 is arranged below each photoconductor 1.

The recording paper 12 passes through the two transfer portions 11a and 11b in the direction of the arrow in the drawing toward the fixing device 13. In this way, a total of two color images can be recorded.

The apparatus having such a structure does not have a drawback that the copying speed becomes slow, but since a plurality of colors corresponding to the number of colors of the photoconductor 1 and the like are provided, there is a problem that the apparatus becomes large.

Further, in both of the above-mentioned two methods, since toner images of different colors are superposed on the recording paper, color misregistration occurs unless the transfer positions are accurately aligned at the time of the second and subsequent transfers. There is also a drawback that registration is required.

Now, FIG. 8 shows a schematic configuration diagram of an apparatus which employs a so-called overlap development method (Japanese Patent Laid-Open No. 59-124354).

In this apparatus, a pre-clean corotron 2, a cleaning device 3, a charging device 4, a first developing device 5, a second developing device 6, a pre-transfer corotron 14 and a transfer device 8 are provided on the outer periphery of the photoconductor 1. It is arranged. A first exposure unit 10 is provided between the charger 4 and the first developing unit 5, and a second exposure unit 20 is provided between the first developing unit 5 and the second developing unit 6. It is provided.

In this apparatus, after uniformly charging the photoconductor 1, an electrostatic latent image is formed in a positive polarity in the first exposure unit 10 and a negative polarity in the second exposure unit 20 with the charging potential as a reference. An electrostatic latent image is formed and developed with different color toners having different polarities.
In this way, two color toner images are formed on the photoconductor 1,
These toner images are transferred onto the recording paper 12 at once.

Since this method develops a two-color image by forming a so-called three-value latent image, it does not reduce the copying speed and does not require highly accurate registration.

However, there is an upper limit to the charging potential of the photoconductor, and when the potential is divided into two and charged in the positive and negative opposite polarities, the potential contrast of both the first electrostatic latent image and the second electrostatic latent image is increased. However, there was a difficulty that it would be half of the usual one. further,
In order to perform such exposure, there is a drawback that a special photoconductor is used, and light energy modulation is also required.

On the other hand, FIG. 9 shows a schematic configuration diagram of an apparatus which adopts a color recording method in which a latent image is formed by another method, which is the same superposition developing method.

In this apparatus, a preclean corotron 2, a cleaning device 3, a first charging device 4, a first developing device 5, a second charging device 15, and a second developing device 6 are provided on the outer periphery of the photoreceptor 1. A pre-transfer corotron 14 and a transfer device 8 are arranged. Also, the first
The first exposure unit 10 is provided between the charging device 4 and the first developing device 5 of
And a second exposure unit 20 is provided between the second charger 15 and the second developing device 6.

In this apparatus, after the photoconductor 1 is uniformly charged by the first charger 4, an electrostatic latent image is formed by the first exposure unit 10.
Development is performed by the first developing device 5 using, for example, black toner. Next, after the photosensitive member 1 is uniformly charged again by the second charger 15, an electrostatic latent image is formed by the second exposure unit 20, and the second developing unit 6 develops it by using, for example, red toner. To do. In this way, two color toner images are formed on the photoconductor 1, and these toner images are transferred to the recording paper 12 at once.

This method also does not lower the copying speed and does not require highly accurate registration.

However, in the second developing device 6, the toner image already formed on the photoconductor 1 is disturbed, the developing density is lowered, or the toner is mixed in the second developing device 6, There is a drawback that it causes a problem such as a shortened life of the developer. In particular, in the electrostatic latent image formed by the first exposure unit 10, one having a latent image potential close to the background portion potential has a weak toner adsorption force to the photoconductor 1 and the toner in the second developing device 6 is weak. Is easily scraped off by the developing brush. Therefore, there is a drawback that image information is lost.

The present invention has been made by paying attention to the above points, and provides a color recording method that enables small-sized and high-speed copying by using the overdeveloping method, and further secures sufficient image contrast and is stable. It is intended to be provided.

"Means for Solving Problems" In the color recording method of the present invention, a first charging process is performed on a photoconductor, a first electrostatic latent image is formed on the photoconductor by positive exposure, and the electrostatic latent image is formed. Develop the latent image to form a first toner image,
The second charging process is performed on the photoconductor at the same polarity as that of the first charging process and at a potential equal to or more than the charging potential of the first charging process, and then the reverse of the first charging process is performed on the photoconductor. Polar third
Second charging step while the toner of the first toner image is made to have the same polarity as the third charging polarity and the charging polarity of the photoconductor is maintained at the charging polarity of the second charging processing. The photosensitive member is charged so that the electric potential required to obtain a predetermined electric potential contrast is maintained, and the second photosensitive member is negatively exposed on the photosensitive member charged to the predetermined electric potential in the third charging process.
Is formed, and the electrostatic latent image is developed using a toner having a color different from the first toner.

Here, it is preferable to use a scorotron for both the second charging process and the third charging process.

"Operation" In the above method, the first charging process is performed on the photoconductor, and the first electrostatic latent image is formed on the photoconductor by positive exposure.
The electrostatic latent image is developed to form a first toner image. Next, the second charging is performed on the photoconductor to a potential that has the same polarity as that of the first charging process and is equal to or higher than the charging potential of the first charging process. This reverses the polarity of the first toner image. Further, this time, a third charging process having a polarity opposite to that of the first charging process is performed on the photoconductor. As a result, the polarity of the first toner image is reversed and aligned. This makes it possible to create a state in which the polarity of the toner image is high and the polarity of the toner image is the same as that during the first development.

After that, a second electrostatic latent image is formed by negative exposure on the photoconductor charged to a predetermined potential by the third charging process. At this time, by appropriately selecting the developing bias of the second developing device and developing with the toner having the opposite polarity to the first toner image, the disturbance of the first toner image can be surely prevented.

If scorotron is used for the second charger and the third charger, appropriate second and third charging processes can be performed.

"Embodiment" FIG. 2 shows a schematic configuration diagram of an apparatus suitable for carrying out the color recording method of the present invention.

In this apparatus, a preclean corotron 2, a cleaning device 3, a first charging device 4, a first developing device 5, a second charging device 15, a third charging device 16 are provided around the outer periphery of the photoconductor 1. A second developing device 6, a pre-transfer corotron 14 and a transfer device 8 are arranged. Further, a first exposure unit 10 is provided between the first charger 4 and the first developing device 5, and the third charger 16 and the second charger 10 are provided.
A second exposure section 20 is provided between the developing devices 6 of FIG. The recording paper 12 is sent out from the paper feed tray 17, passes between the transfer device 8 and the photoconductor 1, and is discharged via the fixing device 13.

A so-called imaging optical system using a mirror and a lens system is used for the first exposure unit 10 of this apparatus, and a laser diode array, a light emitting diode array, a liquid crystal shutter is used for the second exposure unit 20. A so-called optical writing device such as an array or a fluorescent display element array is used.

In this embodiment, the image forming optical system (first exposure unit 10) is exposed with the photoconductor 1 at an analog level linearly corresponding to the density of the recorded image. On the other hand, the optical writing device (second exposure unit 20) exposes the photoconductor 1 at a digital level, that is, a binary level.

Now, the first embodiment of the color recording method of the present invention will be described.
It will be described with reference to the drawings.

In this figure, a1 to a7 in the figure show changes in the potential of each part of the photosensitive member according to the method of the present invention, and b1 in the figure to b6 in the figure.
The above shows comparative examples showing changes in the electric potential of each part of the photoconductor when the prior art is applied to the apparatus shown in FIG. Further, as shown in the upper part of the figure, the recorded image has a high density portion (H) of black (B), a low density portion (L) of black (B), and a red portion (R) on a white background (W). ) And.

First, the photoconductor 1 is uniformly charged by the first charger 4 (a1 in FIG. 1).

Next, in the first exposure unit 10, the photoconductor 1 is exposed by the imaging optical system through the red filter. As a result, the photoconductor 1 is discharged to the potentials 21 and 22 having a level corresponding to the density of the black portion BH or the black portion BL. For red area R, the background potential
The charge is removed to a potential 24 close to 23 (Fig. 1, a2).

Next, a developing bias 25 is set between the electrostatic latent image potential 22 of the black portion BL and the background potential 23, and the first developing device 5 develops using negatively charged black toner. By this development, a large amount of toner adheres to a portion having a high electrostatic latent image potential (a portion corresponding to the black portion BH), and a small amount of toner adheres to a portion having a low electrostatic latent image potential (a portion corresponding to the black portion BL). Then, development is performed in proportion to the density of the recorded image (a3 in FIG. 1).

The relationship between the relative exposure amount of the photoconductor and the surface potential is generally as shown in the graph of FIG. This relative exposure amount indicates the ratio of the actual exposure amount to the case where the brightest image in the background portion is exposed.

That is, as the relative exposure amount increases, the surface potential of the photoconductor decreases as shown by the solid line in the figure. On the other hand, the surface potential when developing this photoreceptor is shown by the one-dot chain line. In this way, after development, the surface potential of the photoconductor is several tens to about 10 due to the charge of the toner.
It drops about 100 volts. The larger the relative exposure amount, the smaller the reduction amount. This is because the toner adhesion amount is small (low density). In this graph, the part surrounded by the broken line circle is the part where the surface potential changes greatly with the change of the relative exposure amount, and if the charging potential is near this, the stability of the image quality is poor, and the potential should be charged as high as possible. Is desirable.

Therefore, in the present invention, after the completion of the first development, the second charger 15 charges the photosensitive member 1 again to the same potential as that of the first charger 4 with the same polarity. In this case, a scorotron is used as the second charger 15. The grid potential of this scorotron is set to a potential almost equal to that during the first charging process.

FIG. 4 shows a schematic block diagram of a conventionally known scorotron.

This device has a diameter of 50 to 150 μm in the shield case 31.
A grid with a diameter of 50 to 150 μm and an arrangement pitch of 1 to 3 mm on the side facing the photoconductor 1
33 is arranged. This shield case 31
When the DC voltage is applied to the grid 33 and the DC high voltage (7 to 9 kV) is applied to the corotron wire 32, the ions generated from the corotron wire 32 are higher in the photoconductor 1 than the grid 33. The photoconductor 1 is irradiated only when the potential is applied.
That is, in the embodiment shown in FIG. 1, the photosensitive member 1 positively charged by the charger 4 is exposed and developed, and a potential lower than the potential of the portion where the toner image is formed is applied to the grid 33.
When a DC high voltage is applied to the corotron wire 32 of this scorotron, positive ions are irradiated only to a portion of the photoconductor 1 having a potential equal to or lower than the grid 33. As a result, the surface potentials of the photoconductor 1 are all equal to or higher than the grid 33 (a4 in FIG. 1). There is also a method of applying an AC high voltage to the corotron wire 32. In this case, the photoconductor surface is uniformly recharged equal to the grid potential.

Now, in FIG. 1 a3, when the charging process of the same potential and the same polarity as the first charging process is performed, the photoconductor 1 and the entire surface of the toner image are irradiated with positive ions, so that the polarity of the toner image becomes positive. It reverses and is charged to a constant potential (Fig. 1, a4).

Next, a third charging process having a polarity opposite to that of the first charging process is performed. That is, the photoconductor and the toner image are irradiated with negative ions. This potential is selected so as not to significantly reduce the second charging potential. As a result, the potential of the photoconductor is slightly lowered, and the polarity of the toner image is reversed to the negative polarity again (a5 in FIG. 1). In this case, since the polarities of the toner images are made uniform by the second charging and the potential of the photoconductor is almost flat, it is easy to make all the polarities of the toners forming the toner image to be negative as shown in the figure. Is. On the other hand, in the second charging process, if there is a portion where the potential of the toner image is slightly higher than the charging potential, the polarity may not be reversed, and a small part of the toner may remain with the polarity as it was during development. However, at the time of the third charging, this does not become an obstacle at all, and all the toners can be aligned in the same polarity.

In this way, the polarities of the toner are made uniform, and the toner is recharged at a sufficiently high potential, and then the second exposed portion 20 forms a second electrostatic latent image corresponding to the red portion R. This electrostatic latent image is written at the binary level as described above. Therefore, there are only two potentials of the second electrostatic latent image, that is, the background potential 23 and the red portion potential 26 (a6 in FIG. 1). This is developed by the second developing device 6 using positively charged red toner, for example (a7 in FIG. 1). At this time, the developing bias potential 27 is set to the middle of the background potential 23 and the electrostatic latent image potential 26 of the red part. In this way, two color toner images are formed on the photoconductor 1, and these toner images are transferred to the recording paper 12 at once. Before this transfer, both the black toner and the red toner are charged to the same polarity by the pre-transfer corotron 14.

It goes without saying that this method does not reduce the copying speed and does not require highly accurate registration. Further, since the charging potential is high, the contrast of the second exposure can be sufficiently taken, and the image quality is stable. Therefore, even if the image forming optical system is used for the second exposure section, it is possible to perform recording with sufficiently high image quality.

In comparison with the method of the present invention described above, a comparative example to which the prior art is applied will be briefly described, and the features of the present invention will be described.

First, in FIG. 9, the photoconductor 1 is uniformly charged by the first charger 4 (FIG. 1, b1). Next, the first exposure unit
At 10, the photoreceptor 1 is exposed by the imaging optics through the red filter. As a result, the photoconductor 1 is discharged to the potentials 21 and 22 at the levels corresponding to the densities of the black portions BH and BL.
The red part R is discharged to a potential 24 close to the background potential 23 (FIG. 1, b2). At this time, comparing the prior art and the present invention, the background potential 23 after the static elimination is set to about ½ of the first charging potential which is slightly higher than that of the present invention. . This is because the contrast at the time of the second exposure is sufficiently obtained.

Next, a developing bias 25 is set between the electrostatic latent image potential 21 of the black portion BL and the background potential 23, and the first developing device 5 develops using negatively charged black toner (first (Figure b3). As a result of this development, a large amount of toner adheres to the portion where the electrostatic latent image potential is high (the portion corresponding to the black portion BH), and a small amount of toner adheres to the portion where the electrostatic latent image potential is low (the portion corresponding to the black BL). To do.
This is similar to the case of the present invention.

At this time, the photoconductor 1 is again uniformly charged by the second charger 15 (FIG. 1, b4). In this case, if a scorotron is used for the second charger 15, the grid potential of this scorotron is set to a potential almost equal to the background potential 23.

Then, the second exposure unit 20 forms an electrostatic latent image corresponding to the red portion R. This electrostatic latent image is written at a binary level for comparison with the present invention (FIG. 1, b5).

Further, the second developing device 6 performs development using, for example, positively charged red toner (FIG. 1, b6). At this time, the developing bias potential 27 is set to the middle of the background potential 23 and the electrostatic latent image potential 26 of the red part. Here, when comparing this comparative example with the example of the present invention, the contrast of the electrostatic latent image of the red image is greatly different. When the contrast is small as in the comparative example, as described with reference to FIG. 3, the potential fluctuation with respect to the relative exposure amount is severe and the recording density is unstable.

Further, in the present invention, since the polarities of the toner images are re-inverted again by the second charging process and the third charging process, the polarities of the toner images are uniform, and toner is mixed during the second development. hard. Moreover, according to such a method, since the attraction force of the toner image to the photoconductor is increased, the toner image is hard to be scraped off when passing through the second developing device.

In the above examples, the specific configuration of each part, the set potential, and the like were selected as follows.

<In the case of the example> ☆ Photoreceptor-Se (selenium) -based photoreceptor-Drum diameter 200 mm ☆ First developer-Two-component system (negatively charged black toner) -Carrier Styrene-n-butylmethacrylate copolymer 35 Part and 65 parts of magnetite are mixed, melt-kneaded, and then finely pulverized into a magnetic powder dispersion type. The average powder diameter is 30 μm and the density is 2.2 g / cm ³ .

Black toner 92 parts of styrene-n-butyl methacrylate copolymer, 8 parts of carbon black # 4000 (manufactured by Mitsubishi Kasei) and 2 parts of charge control agent (Bontron S-34, manufactured by Orient Chemical Co., Ltd.) were mixed and melted. After kneading, finely pulverized to an average particle size of 12 μm. The carrier is negatively charged.

☆ Second developer ・ Two-component system (color-charged red toner) Carrier A magnetic powder dispersion type in which 35 parts of styrene-n-butyl methacrylate copolymer and 65 parts of magnetite are mixed, melt-kneaded, and finely pulverized. The average particle size is 30 μm and the density is 2.2 g / cm ³ .

-Red toner: 92 parts of styrene-n-butyl methacrylate copolymer, 8 parts of red pigment resource cult (BASF), charge control agent (E
-84, manufactured by Orient Chemical Co., Ltd.), melt-kneaded, and then pulverized to an average particle size of 12 μm. The carrier is positively charged.

☆ Process speed 250mm / sec ☆ Development parameter (1st developer) TG (Trimming gap) 0.9mm DRS (Drum roll space) 1.0mm MSA (Inclination of magnetic pole) + 5 ° Vd (Development roll rotation speed) 750mm / Second main pole of magnetic pole 650G Rotation of developing roll WITH (forward direction with photoconductor) ☆ Development parameter (second developing device) TG (trimming gap) 0.9mm DRS (drum roll space) 1.0mm MSA (inclination of magnetic pole) ) 0 ° Vd (Development roll rotation speed) 300mm / sec Main pole of magnetic pole 1300G Repulsion type Development roll rotation WITH (forward direction with photoconductor) ☆ Potential of each part of photoconductor Note that these potentials are measured at the positions from in FIG. Further, the white area is a value obtained by measuring the potential on the surface of the photoconductor, and the black area is a value obtained by measuring the potential on the surface of the toner image.

☆ Recorded image density measurement results ☆ Evaluation concentration changes little over time.

<In the case of comparative example> ☆ Each part of the device is the same as the example ☆ Electric potential of each part of the photoreceptor The potential measurement position and the measurement conditions are the same as in the embodiment.

☆ Recorded image density measurement results ☆ Toner fogging occurred due to a large change in evaluation density over time.

"Modification" In the above embodiments, the photoconductor is positively charged by each charger, but the same effect can be obtained by negatively charging the photoconductor.

Further, as shown in FIG. 5, the second charger 15 and the third charger 16 are integrated, and the shield case 31 is grounded together, and the corotron wire 32 and the grid 33 are individually connected to the direct current. The power supplies 34 to 37 may be connected. This way
It is possible to reduce the size of the charger.

Further, the developing system of each developing unit may be freely selected and each exposing unit may use any one of an image forming optical system, an optical writing device and the like.

"Effects of the Invention" According to the color recording method of the present invention described above, the second,
In the third charging process, since the polarities of the toners are aligned and charged to a high potential, the recording density is stable, and the toner is not mixed into the second developing device and a part of the recorded image is not lost.

Therefore, high-speed and high-quality color recording can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory view of the potentials of various parts of the photoconductor showing an embodiment of the color recording method of the present invention, FIG. 2 is a schematic configuration diagram of a recording apparatus suitable for carrying out the color recording method of the present invention, and FIG. A graph showing the relationship between the relative exposure amount of the body and the surface potential,
FIG. 5 is a schematic configuration diagram of a scorotron used for this, FIG. 5 is a schematic configuration diagram showing an embodiment in which a second charger and a third charger are integrated, and FIGS. 6 to 9 are conventional. It is a schematic block diagram of an apparatus which employs a color recording method. 1 ... Photoconductor, 21, 22 ... Toner image potential, 23 ... Background potential.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiro Yamamoto 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor Koji Adachi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business (72) Inventor Nobumasa Furuya 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd. Ebina Works (56) References JP-A-50-144447 (JP, A) JP-A-61-219964 (JP, A) JP-A-60-143364 (JP, A) JP-A-60-182450 (JP, A)

Claims (2)

[Claims] 1. A first charging process is performed on a photoconductor, a first electrostatic latent image is formed on the photoconductor by positive exposure, and the electrostatic latent image is developed to form a first toner image. Then, the second charging process is performed on the photoconductor to a potential that has the same polarity as the first charging process and is at least about the same as the charging potential of the first charging process, and then the first charging process is performed on the photoconductor. A third charging process having a polarity opposite to that of the charging process is performed to make the toner of the first toner image have the same polarity as the third charging polarity, and the photoconductor has a second charging
In the second exposure process, the photoconductor is charged so that the potential required to obtain a predetermined potential contrast is maintained while maintaining the charge polarity of the third charging process, and is charged to the predetermined potential in the third charging process. A second electrostatic latent image is formed on the photosensitive member by negative exposure, and the electrostatic latent image is developed using a toner having a color different from that of the first toner. 2. The color recording method according to claim 1, wherein a scorotron is used in the second charging process and the third charging process.