JPH06100865B2 - 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. 5 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. 6 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. This is a method of sequentially transferring to the recording paper 12 (Japanese Patent Laid-Open No. 61-36).
No. 767).

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. 7 shows a schematic configuration diagram of an apparatus which employs a so-called over-developing method (JP-A-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. 8 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 overlapping development 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 is uniformly charged by the first charger 4, an electrostatic latent image is formed by the first exposure unit 10 and, for example, black toner is used by the first developing unit 5. develop.
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. Thus
Two-color toner images are formed on the photoconductor 1, and these toner images are transferred onto 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 in view of the above points, and enables small-sized and high-speed copying by using the overdeveloping method, and further prevents image loss and density decrease to improve image quality. It is intended to provide a color recording method.

"Means for Solving Problems" In the color recording method of the present invention, a first charging process is performed on a photoconductor, and positive exposure is performed thereon to apply a plurality of levels of potential in an image portion according to image density. A first electrostatic latent image is formed so that the non-image portion holds it at a predetermined potential, and the electrostatic latent image is developed to form a first toner image. The toner image has the lowest development density. The second charging process is performed with the same polarity as the charging polarity in the first charging process, using a potential that is closer to the background potential than the potential of the portion of No. 2 as the reference potential, and the photosensitive member charged to about the reference potential by the second charging process. A second electrostatic latent image is formed on the body by negative exposure, and the electrostatic latent image is developed using a toner having a color different from that of the first toner.

Here, it is preferable to use a scorotron in which the reference potential is applied to the grid for the second charging process.

[Operation] In the above method, the first charging process is performed on the photoconductor, and positive exposure is performed on the photoconductor to hold a plurality of levels of potential in the image area according to the image density, and a predetermined potential is applied to the non-image area. A first electrostatic latent image is formed so as to be held, and the electrostatic latent image is developed to first form a first toner image. Then, the second charging process is performed with the same polarity as the charging polarity in the first charging process, with a potential closer to the background potential than the potential of the lowest development density portion of the toner image. As a result, in this charging process, the polarity of the toner image developed by the first developing device does not reverse with the same polarity.

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

If a scorotron having the above-mentioned reference potential applied to the grid is used as the second charger, an appropriate second charging process 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, 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. The recording paper 12 is
It is configured so that it is sent out from the paper feed tray 16, 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 imaging optical system (first exposure unit 10)
Exposes the photoconductor 1 at an analog level that linearly corresponds 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, an embodiment of the color recording method of the present invention will be described with reference to FIG.

In this figure, a1 to a6 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 to b6 in the figure
The above shows comparative examples showing changes in the potential of each part of the photoconductor when the prior art is applied to the same device as that shown in FIG. In addition, as shown in the upper part of the figure, the recorded image has a low density portion (L) of black (B), a high density portion (H) 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 BL or the black portion BH. 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 21 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 photosensitive member 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 FIG. 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 drops by several tens to hundreds of volts due to the charge of the toner. The larger the relative exposure amount, the smaller the reduction amount. This is because the toner adhesion amount is small (low density).

Now, after the completion of the first development, the second charger 15 charges the photoreceptor 1 again uniformly. 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 the potential 21 of the portion of the black toner image having the lowest development density, that is, the portion of the black portion BL.

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 a high voltage is applied to the grid 33 and a high DC 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 a DC superposed AC high voltage to the corotron wire 32. In this case, the photoconductor surface is uniformly recharged equal to the grid potential.

Then, the second exposure unit 20 forms a second electrostatic latent image corresponding to the red portion R. This electrostatic latent image, as explained earlier,
Written at a binary level. Therefore, there are only two potentials of the second electrostatic latent image, the background potential 23 and the red part potential 26 (first
Figure a5). This is developed by the second developing device 6 using positively charged red toner, for example (a6 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, toner images of two colors are formed on the photoconductor 1, and these toner images are recorded at once on the recording paper 12.
Is transcribed to. 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.

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, the photoconductor 1 is uniformly charged by the first charger 4 (FIG. 1, b1). 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 the levels corresponding to the densities of the black portions BL and BH. The red area R is discharged to a potential 24 close to the background potential 23 (Fig. 1b).
2). At this time, comparing the conventional technique with the present invention, the background potential 23 after the static elimination is set to be slightly higher in the present invention. This is because the potential of the black portion BL after the first development is set to be somewhat high, and the polarity reversal of the toner during the second charging is prevented, and the second charging with sufficient contrast is performed.

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). 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). 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 the same as that of the black part BL, which is high enough to obtain sufficient contrast during the next second exposure. Set to a potential near the middle of BH.

However, at the time of this second charging, the polarity of the toner is reversed in the black portion BL where the electrostatic latent image potential is low (see FIG. 1).
b4). Then, the second exposure unit 20 forms an electrostatic latent image corresponding to the red portion R. This electrostatic latent image is 2 in comparison with the present invention.
It shall be written at the value level (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. However, here, a part of the toner whose polarity was previously inverted during the second charging is drawn into the second developing device 6 to cause so-called mixing. On the other hand, in the case of the present invention, since the polarity of the toner is not reversed, there is no possibility of mixing.

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 embodiment> ☆ Photoreceptor ・ Se (selenium) -based photoreceptor ・ Drum diameter 200 mm ☆ First developer ・ Two-component system (negatively charged black toner) ・ Carrier Ferrite carrier with average particle size 100 μm ・ Black toner After 92 parts of styrene-n-butyl methacrylate copolymer and 8 parts of carbon black # 4000 (manufactured by Mitsubishi Kasei) and 2 parts of a charge control agent (Bontron S-34, manufactured by Orient Chemical Co., Ltd.) were mixed and melt-kneaded. , Finely pulverized to an average particle size of 12 μm. The carrier is negatively charged.

☆ Second developer ・ Two-component system (positively charged red toner) ・ Carrier 35 parts of styrene-n-butyl methacrylate copolymer and 65 parts of magnetite are mixed, melt-kneaded, and then finely pulverized magnetic powder dispersion type . 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 lysol skarts (BASF), and 2 parts of quaternary ammonium charge control agent were mixed, melt-kneaded, and then had an average particle size of 12
Finely pulverized to μm. The carrier is positively charged.

☆ Process speed 150mm / 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) 450mm / Sec 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 (of magnetic pole Tilt) 0 ° Vd (Development roll rotation speed) 200mm / 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 directly 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 after the first development.

☆ Recorded image density measurement results ☆ Evaluation There is little decrease in density even with the second development.

<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 ☆ Evaluation A large decrease in the density of black areas due to the second development.

"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, the developing system of each developing device may be freely selected.

[Advantages of the Invention] According to the color recording method of the present invention described above, since the polarity of the toner is not reversed in the second charging process, the toner is mixed in the second developing device and a part of the recorded image is lost. Etc. does not occur.

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. 4 is a schematic configuration diagram of a scorotron used for this, and FIGS. 5 to 8 are schematic diagrams of an apparatus adopting a conventional color recording method. It is a block diagram. 1 ... Photoconductor, 21, 22 ... Toner image potential, 23 ... Background potential.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Adachi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Works (72) Inventor Toshiro Yamamoto 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.Ebina Business (72) Inventor Nobumasa Furuya 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd. Ebina Works (56) References JP 61-219964 (JP, A) JP 53-149033 (JP, A) JP-A-55-32035 (JP, A) JP-A-60-158467 (JP, A)

Claims (2)

[Claims] 1. A first charging process is performed on a photoconductor, and positive exposure is performed on the photoconductor so that a plurality of levels of potentials are held in an image area according to image density and a predetermined potential is held in a non-image area. 1 electrostatic latent image is formed, the electrostatic latent image is developed to form a first toner image, and a potential closer to the background potential than the potential of the lowest development density portion of the toner image is formed. The first as the reference potential
The second charging process is performed with the same polarity as the charging polarity of the second charging process, and a second electrostatic latent image is formed by negative exposure on the photoconductor charged to about the reference potential by the second charging process. A color recording method, wherein 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 in which the reference potential is applied to a grid is used in the second charging process.