JPH0697361B2 - 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. 7 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. 8 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 (JP-A-61-367).
67 publication).

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. 9 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. 10 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 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. As described above, in the image forming method using the overlapping development method, how to carry out the development in the subsequent stage without disturbing the toner image in the previous stage is a very important issue.

As a method of developing the toner image on the photoconductor without disturbing it, it is conceivable to carry out the subsequent developing step by one-component non-contact development, but it is difficult to accelerate the one-component non-contact development. It is preferable to use a two-component developer composed of a carrier and a toner. Further, by using toners of opposite polarities for the first development and the second development, it is possible to prevent toner from mixing in principle, and such a technique has been disclosed (JP-A-57-2047). Issue). But,
Actually, it has not yet been possible to completely prevent contamination.

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 the photoconductor is exposed to form a first electrostatic latent image. The image is developed to form a first toner image, and then a second electrostatic latent image is formed by negative exposure if the first electrostatic latent image is formed by positive exposure, and then the first electrostatic latent image is formed. When the electrostatic latent image of is formed by negative exposure, a second electrostatic latent image is formed by positive exposure, and the electrostatic latent image is developed using a toner of a color different from that of the first toner. , The first toner and the second toner to the second developing carrier,
It is characterized in that they are on opposite sides of each other on the triboelectric series.

[Operation] In the above method, when the toner image formed on the photoconductor by the first development enters the magnetic brush during the second development, the toner image comes into contact with the carrier. Since the first toner and the second toner are on the opposite sides of this carrier in the triboelectric charging train, assuming that the second toner is negatively charged by contact with the carrier, the first toner is positively charged. To do. When the first toner image is positively charged and adheres to the photoconductor, the polarity of the first toner image does not reverse even if it comes into contact with the carrier.
Therefore, the attraction force to the photoconductor is further increased and the toner is not scraped off.

"Embodiment" FIG. 1 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 color controller 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.

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

Further, the toner of the first developing device 5 and the toner of the second developing device 6 have the triboelectrification polarity opposite to that of the carrier of the second developing device 6, respectively.

Now, an embodiment of the color recording method of the present invention will be described with reference to FIG.

In this figure, a to e in the figure show changes in the surface potential of the photoconductor by the method of the present invention. The recorded image has a black portion (B) and a red portion (R) on a white background (W) as shown in the upper part of the drawing.

First, the photoconductor 1 is uniformly charged to the positive polarity by the first charger 4 (FIG. 2a).

Next, in the first exposure unit 10, the photoreceptor 1 is negatively exposed. As a result, in the photoconductor 1, the red portion R is discharged to the potential 21. On the other hand, the black portion B is held at the potential 23 close to the background potential 22 (FIG. 2B).

Next, a developing bias 24 is set between the electrostatic latent image potential 21 of the red portion R and the background potential 22, and the first developing device 5 performs development using negatively charged red toner (first Figure 2c).

Next, after the completion of the first development, the second charger 15 does not operate, and the second exposure unit 20 performs positive exposure to form a second electrostatic latent image corresponding to the black portion B (second). Figure d). This is developed by the second developing device 6 using negatively charged black toner (second
Figure e). At this time, the developing bias potential 25 is set to the middle of the electrostatic latent image potential 21 of the red portion and the electrostatic latent image potential 26 of the black portion. In this case, the polarity of the red toner does not reverse from the positive polarity to the negative polarity, and the toner is not mixed. This development will be described later. 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.

FIG. 3 shows another embodiment of the color recording method of the present invention. This time, black toner is used in the first development and red toner is used in the second development.

First, the photoconductor 1 is uniformly charged to the positive polarity by the first charger 4 (FIG. 3a). Next, in the first exposure unit 10, the photoconductor 1 is positively exposed by the imaging optical system via the red filter. As a result, the photosensitive member 1 has the black portion B at a high
The charge is removed with 21. For red area R, the background potential
The charge is removed to a potential 23 close to 22 (Fig. 3b).

Next, the developing bias 24 is set between the electrostatic latent image potential 21 of the black portion B and the background potential 22, and the first developing device 5 performs development using negatively charged black toner (third embodiment). Figure c).

This time, the photoconductor 1 is uniformly charged again by the second charger 15 (FIG. 3d). In this case, if a scorotron is used for the second charger 15, the grid potential of this scorotron is set to be substantially the same as the potential 21 of the black portion B.

After that, an electrostatic latent image corresponding to the red portion R is formed by negative exposure in the second exposure unit 20 (FIG. 3e).

Further, the second developing device 6 performs development using, for example, positively charged red toner (FIG. 3f). At this time, the developing bias potential 25 is set in the middle of the background potential 21 and the electrostatic latent image potential 26 of the red portion. Also at this time, the polarity of the black toner does not reverse from the negative charge to the positive charge, so that the toner is not mixed.

Now, the actual effect of the embodiment shown in FIG. 1 will be described. The specific configuration of each part of the recording device and the set potential thereof were selected as follows.

<Example> (However, the first exposure is positive and the second exposure is a negative case) * Photoreceptor-Se (selenium) -based photoreceptor-Drum diameter 200mm * Process speed 150mm / sec * No. Both 1st and 2nd development are two-component magnetic brush development ☆ Development parameters (1st and 2nd developer) TG (trimming gap) 0.9mm DRS (drum roll space) 1.0mm MSA (Inclination of magnetic pole) + 5 ° Vd (Rotation speed of developing roll) 450mm / sec Main pole of magnetic pole 650G Rotation of developing roll WITH (forward direction with photoreceptor) ☆ 1st developer ・ Carrier 100μm Ferrite carrier ・ Toner (red) Styrene-n-butyl methacrylate (copolymerization ratio 70: 3
0) 92 parts and 8 parts of red pigment resorce cult (manufactured by BASF) were melt-kneaded and then pulverized to 12 μm.

・ Toner charge amount -13μc / g ☆ Second developer ・ Carrier Styrene-n-butyl methacrylate copolymer (copolymerization ratio 65:35) 30 parts and magnetite 70 parts were melt-kneaded and then pulverized into a magnetic powder dispersion type Career. Its average particle size is 30 μm and its density is 2.4 g / cm ³ .

・ Toner 35 parts polyester, styrene-butyl methacrylate-
57 parts of acrylonitrile copolymer (copolymerization ratio 70: 25: 5),
8 parts of carbon black melt-kneaded and then pulverized to 12 μm.

・ Toner charge amount +10 μc / g <Comparative example> ☆ Sensor process speed etc. are the same as in the example ☆ Both first and second development are two-component magnetic brush development ☆ Development parameters are the same as the example ☆ 1 developer-Carrier 100 μm Ferrite carrier-Toner Styrene-n-butylmethacrylate copolymer (copolymerization ratio 60:40) 92 parts, red pigment resole scult (manufactured by BASF) 8 parts after melt-kneading to 12 μm Crushed.

・ Toner charge amount -12 μc / g ☆ Second developer ・ Carrier Styrene-n-butylmethacrylate copolymer (copolymerization ratio 65:35) 30 parts and magnetite 70 parts were melt-kneaded and then pulverized to disperse magnetic powder. Mold carrier. The average particle size is 30 μm and the density is 2.4 g / cm ³ .

・ Toner 35 parts polyester, styrene-butyl methacrylate-
57 parts of acrylonitrile copolymer (copolymerization ratio 70: 25: 5),
8 parts of carbon black melt-kneaded and then pulverized to 12 μm.

Toner charge amount +8 μc / g The toner charge amount was measured by the blow-off tribo value.

In the measurement of the blow-off tribo value, as shown in FIG. 4, first, a first electrostatic latent image is formed on a predetermined section of the photoconductor 1 and the toner 35 is attached thereto. Then, the toner 35 is peeled off from the photoconductor and the weight thereof is measured. On the other hand,
Toner is attached to the photoconductor under the same conditions, and the amount of charge on the photoconductor is measured. This is obtained by grounding the photoconductor 1 via the charge measuring device 36 and measuring the charge flowing in the circuit when the toner 35 is blown off. Then, the charge amount per unit weight of the toner can be obtained by dividing this charge amount by the toner weight previously obtained.

☆ Electrical potential of each part of the photoconductor (Example, Comparative example) This shows the actual potential of the potential explanatory diagrams shown in FIGS.

Note that these potentials were 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. As shown in FIG. 3, when recharging is performed after the first development, the charging potential is measured at the position.

☆ Recorded image density measurement results It should be noted that the variation of the developing toner weight is obtained by subtracting the first developing weight after passing through the second developing device from the first developing weight, and subtracting this from the first developing weight.
Divide by the development weight of and multiply by 100 to obtain. Units%
(Percent).

The density fluctuation is the amount of change in the recorded image density (original density 0.7) after the first development when the second development is not performed.

From the above results, as in the comparative example, if the toners having opposite polarities are simply used for the first developer and the second developer, color mixing and density decrease occur.

In other words, the triboelectrification polarities of the two toners with respect to the carrier of the second developer are opposite polarities in the embodiment, and are the same polarity in the comparatively low case.

This value is the charge amount after 3.5% of the total weight of the first carrier was mixed with the second carrier and mixing was performed for 5 minutes. This measurement was also performed by the blow-off tribo method.

Therefore, in the case of the comparative example, as shown in FIGS. 5A and 5B, during the second development, both the positive exposure and the negative exposure, a part of the first toner becomes a carrier of the second developer. Contact,
It can be seen that the polarity is reversed by triboelectric charging, and it is mixed in the second developer.

FIG. 6 shows triboelectrification characteristics. In the case of this embodiment,
On this triboelectric charge train, for the carrier of the second developer,
The first toner is on the negative side and the second toner is on the positive side.

Therefore, when the carrier and the toner are rubbed under the same conditions, the first toner is negatively positively charged and the second toner is positively charged.

On the other hand, in the case of the comparative example, both the first toner and the second toner are charged to the same positive polarity due to friction with the carrier.

Due to this difference, the method of the present invention can prevent toner color mixture.

[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 polarity reversal of the first toner does not occur during the second development.
The toner is not mixed into the developing device and the density of the recorded image is not lowered.

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

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a recording apparatus suitable for carrying out the color recording method of the present invention, and FIGS. 2 and 3 are explanatory views of potentials of respective portions of a photoconductor showing an embodiment of the color recording method of the present invention. Fourth
FIG. 5 is an explanatory diagram of a toner charge amount measuring method, FIG. 5 is an explanatory diagram showing a toner state of a comparative example, FIG. 6 is an explanatory diagram of a triboelectric charging column, and FIGS. It is a schematic block diagram of the apparatus which employs the recording method. 1 ... Photosensitive member, 5 ... First developing device, 6 ... Second developing device

Front page continuation (72) Inventor Koji Adachi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor Toshiro Yamamoto 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.Ebina Business Office (72 ) Inventor Nobumasa Furuya 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd. Ebina Works (56) Reference JP 62-141582 (JP, A) JP 61-219964 (JP, A) JP Sho 58-72158 (JP, A)

Claims (1)

[Claims] 1. A first charging process is performed on a photoconductor, which is exposed to form a first electrostatic latent image, and the electrostatic latent image is developed to form a first toner image. After that, when the first electrostatic latent image is formed by positive exposure, the second electrostatic latent image is formed by negative exposure, and when the first electrostatic latent image is formed by negative exposure Form a second electrostatic latent image by positive exposure, develop the electrostatic latent image with a toner of a color different from that of the first toner, and generate the first toner and the second toner. Are on the opposite sides of the second developing carrier on the triboelectric charging train.