JPH06100866B2 - 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. 9 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. 10 shows a schematic configuration diagram of an apparatus adopting a sequential transfer method other than 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. 11 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. 12 shows a schematic configuration diagram of an apparatus which employs a similar overdevelopment method but adopts a color recording method for forming a latent image by another 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 reduce 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. Further, the electrostatic latent image formed in the first exposure unit 10 is developed at the fringe portion (near the boundary between the high potential portion and the low potential portion of the latent image) after passing through the second developing device, and the image quality is improved. There is also a phenomenon that is significantly deteriorated.

The present invention has been made in view of the above points, and provides a color recording method that enables small-sized and high-speed copying by using the overdeveloping method and further prevents image quality deterioration due to development of a fringe portion. That is the purpose.

"Means for Solving Problems" In the color recording method of the present invention, a photosensitive member formed by laminating a photoconductive layer on a transparent conductive substrate is subjected to a first charging treatment, and then positive exposure is performed thereon. To form a first electrostatic latent image by
The electrostatic latent image is developed to form a first toner image, and thereafter, exposure is performed with uniform light from the back side of the toner image forming surface of the photoconductor through the transparent conductive substrate, and then the second charging process is performed. Then, a second electrostatic latent image is formed by negative exposure, and the electrostatic latent image is developed using a toner of a color different from that of the first toner.

[Operation] In the above method, a photoconductor having a photoconductive layer laminated on a transparent conductive substrate is used. Next, the back surface of the photoreceptor on which the toner image is formed is exposed with uniform light through the transparent conductive substrate. As a result, the potential of the fringe portion of the first electrostatic latent image is uniformly raised. After that, the second charging process is performed.

After that, a second electrostatic latent image is formed by negative exposure. When transferring these toner images to recording paper,
The first toner image and the second toner image can have the same polarity.

"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 device, 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 are provided on the outer periphery of a belt-shaped photoreceptor 1. A container 6, a pre-transfer corotron 14 and a transfer device 8 are arranged. Further, between the first charging device 4 and the first developing device 5,
A first exposure unit 10 is provided, and a second exposure unit 20 is provided between the second charger 15 and the second developing device 6. The recording paper 12 is sent from the paper feed tray 16 and transferred to the transfer device 8.
And the photoconductor 1 and then discharged through 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.

Further, the photosensitive member 1 has, for example, as shown in FIG. 3, a transparent electrode 1b, a photoconductive layer 1c, and a transparent electrode 1d on a transparent conductive substrate 1a.
Was used in this order.

In such a photoreceptor 1, as shown in FIG. 2, the exposure lamp 17 is arranged on the back surface of the photoconductor 1 to expose the photoconductive layer 1c from the back surface, and the charge can be removed.

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 potential of each part of the photoconductor when the prior art is applied to the device as 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 positively 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 the color recording method of the present invention, after the first development, the exposure lamp 17 shown in FIG. 2 is used to uniformly expose the photoreceptor 1 from the back surface thereof. As a result, the charge is uniformly discharged regardless of whether the toner is attached to the surface of the photoconductor 1 (a4 in FIG. 1). Usually, the larger the potential difference from the background potential 23, the greater the static elimination effect.
As indicated by a4, the black portions BH and BL are discharged until the potential distribution becomes a relatively high potential with a relatively high potential.

After that, the second charger 15 further uniformly charges the photoconductor 1. In this case, a scorotron is used as the second charger 15. The grid potential of the scorotron is set to a potential substantially equal to the potential 22 of the portion of the black toner image having the lowest development density, that is, the portion of the black portion BL.

FIG. 5 shows a schematic configuration 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, according to the embodiment shown in FIG. 1, the photosensitive member 1 positively charged by the charger 4 is exposed and developed, and a predetermined potential is applied to the grid 33 so that a high DC voltage is applied to the corotron wire 32 of this scorotron. Is applied, the positive ions are irradiated only to a portion of the photoconductor 1 having a potential equal to or lower than the grid 33 thereof. As a result, the surface potential of the photoconductor 1 becomes equal to or higher than the grid 33. 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.

In the case of this embodiment, the photoreceptor surface is recharged almost uniformly in any case (FIG. 1, a5).

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 a6). This is developed by the second developing device 6 using negatively 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, 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. Moreover, the red toner does not adhere to the fringe portion.

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 the apparatus shown in FIG. 12, the photoconductor 1 is uniformly charged by the first charger 4 (b1 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 photosensitive member 1
The charges are removed to potentials 21 and 22 having a level according to the densities of the black portions BH and BL. For the red area R, a potential 24 close to the background potential 23
Is discharged (Fig. 1, b2). 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 to enhance the effect of uniform exposure by the exposure lamp.

Next, the 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 performs development using positively 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 high enough to obtain sufficient contrast at the next second exposure, for example, the potential of the black portion BH. twenty one
And a potential near the middle of the potential 22 of BL.

Then, the second exposure unit 20 forms a second 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, negatively 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, part of the red toner is
The image quality is deteriorated by being attached to the fringe parts on both sides of the black part BH.

This development will be described in detail with reference to the potential explanatory diagrams of FIGS. 6 to 8.

First, FIG. 6 is an enlarged view of the potential distribution diagram shown in FIG. 1 b6.

Here, red toner (toner with a minus sign in the figure) is attached to both sides of the black portion BH, that is, the high density portion. The developing bias at this time was set to a potential V _B 27 which is slightly lower than the background potential 23 in the figure.

The red toner adheres to the fringe portion in this way
As shown by the arrow in the figure, it is considered that the lines of electric force are concentrated on the boundary portion where the potential difference is remarkable and the electric field in the vicinity thereof is disturbed.

As a result, as shown in FIG. 7, when the accurate electric field intensity distribution is observed, it is largely fluctuated vertically on both sides of the black portion BH.

For this reason, the relationship with the developing bias V _B is reversed in the fringe portion, and the fringe portion is developed with the red toner in the same manner as the electrostatic latent image in the red portion.

On the other hand, in the method of the present invention, by applying the back exposure as shown in FIG. 8, the potential difference between the potential 21 of the black portion BH and the potential 23 of the background portion is sufficiently changed from the solid line state to the dashed line state. I will lower it. By recharging after that, the fringe electric field does not exceed the developing bias, and the adhesion of the red toner can be prevented.

Further, in the case of the present invention, as can be seen from FIGS. 1, a4 to a7 and b4 to b6, the polarity of a part of the toner is not reversed during recharging. Therefore, no trouble such as mixing of the polarity-reversed toner with the second developing device occurs.

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

<Examples> ☆ Photoreceptor A charge generating layer made of a polyvinyl butyral resin and dibromoanthanthrone, a charge transporting layer made of a triarylamine charge transporting agent and a polyester resin were sequentially laminated on an aluminum substrate. , An organic photosensitizer (organic font contactor) was used.

☆ 1st developer ・ 2-component system (positively charged black toner) ・ Carrier Ferrite carrier with an average particle size of 100 μm ・ Black toner styrene-n-butyl methacrylate copolymer 92 parts and carbon black # 4000 (manufactured by Mitsubishi Kasei) ) 8 parts and 2 parts of a charge control agent (Bontron P-51, manufactured by Orient Chemical Co., Ltd.) are mixed, melt-kneaded, and then finely pulverized to an average particle size of 12 μm. The carrier is positively charged.

☆ Second developer ・ Carrier A magnetic powder dispersion type in which 35 parts of styrene-n-butylmethacrylate copolymer and 65 parts of magnetite are mixed, melt-kneaded, and then 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 negatively 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.

☆ Evaluation No red toner adhered around the black area BH even after the second development.

<In the case of Comparative Example> * Photoreceptor is a Se (selenium) type photoreceptor * Other parts of the device are the same as those of the example * Potential of each part of the photoconductor The potential measurement position is as shown in FIG. 12, and the measurement conditions are the same as in the example.

☆ Evaluation Red toner adhered around the black part BH by the second development.

[Modification] In the above embodiments, the photoconductor is negatively charged by each charger, but the same effect can be obtained by positively 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, the fringe electric field is weakened by the uniform exposure on the back surface of the photoconductor regardless of the presence or absence of toner. Is not likely to deteriorate.

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

[Brief description of drawings]

FIG. 1 is an explanatory view of the potential of each part of the photoreceptor 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. 4 is a partial cross-sectional view of the photoconductor used in FIG. 4, FIG. 4 is a graph showing the relationship between the relative exposure amount of the photoconductor and the surface potential, FIG. 5 is a schematic configuration diagram of the scorotron used for this, and FIGS.
The drawings are explanatory views of the principle of the method of the present invention, and FIGS. 9 to 12 are schematic configuration diagrams of an apparatus adopting a conventional color recording method. 1 ... Photoconductor, 21, 22 ... Toner image potential, 23 ... Background potential.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Maruyama 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 In-house (72) Inventor Nobumasa Furuya 2274 Hongo, Ebina-shi, Kanagawa Fuji-Xerox Co., Ltd. Ebina Works (56) References JP 54-112634 (JP, A) JP 61-219964 (JP, A) JP-A-50-144447 (JP, A) JP-A-62-39882 (JP, A)

Claims (1)

[Claims] 1. A first charging process is performed on a photoconductor formed by laminating a photoconductive layer on a transparent conductive substrate, and a first electrostatic latent image is formed thereon by positive exposure. The electrostatic latent image is developed to form a first toner image, and thereafter, exposure is performed with uniform light through the transparent conductive substrate from the back surface of the toner image forming surface of the photoconductor, and the second charging process is performed. And then forming a second electrostatic latent image by negative exposure, and developing the electrostatic latent image with a toner of a color different from that of the first toner. .