JPH0731439B2 - Color-Electrophotographic method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic method applicable to a color hard copy apparatus such as a color copying machine or a color printer.

2. Description of the Related Art Conventionally, a plurality of toner images of different colors are formed on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) by repeating charging / exposure and development a plurality of times, and then the toner images are collectively transferred onto paper. Various color electrophotographic methods for obtaining a color image have been proposed (for example, JP-A-60-95456).

In this type of color electrophotographic method, when reproducing images in which different colors are adjacent to each other, a first toner image is formed on the photoconductor and then the photoconductor is recharged to form a second optical image. At the time of exposure, it is common to expose the first toner image in close contact with it.

Problems to be Solved by the Invention Conventional problems will be described with reference to FIG. In FIG. 4A, after the photoconductor 2 carrying the first toner image 1 on the area B is recharged, the area A is formed adjacent to the toner image 1.
The image-exposed state is shown in FIG. First toner image 1 as shown
It was found that the first toner 1 is scattered in the area A because the electric field strength at the boundary between the area A and the area B is increased when the image exposure is performed in close contact with the area A.

Therefore, when the area A is developed with the second toner 3 as shown in FIG. 4B, there is a problem that the scattered first toner 1 reduces the color purity of the area A near the boundary. Further, since the first toner 1 near the boundary portion does not scatter, there is a problem that the image line becomes thin.

Therefore, an object of the present invention is to provide a color electrophotographic method which overcomes the above-mentioned conventional problems, clearly reproduces images in which different colors are adjacent to each other, and in which the image lines of the toner image previously formed are not thin. To provide.

Means for Solving the Problems The present invention is a color electrophotographic method comprising the steps of repeatedly charging, exposing and developing toners of different colors to form toner images of a plurality of colors on a photoconductor. First on the body
When the image exposure for forming the second toner image is performed adjacent to the first toner image after the first toner image is formed, the width of the boundary between the first toner image and the first toner image is 0.02 mm to 0.2 mm. By providing the non-image area of (1) and performing image exposure, scattering of the first toner in the vicinity of the boundary portion is prevented, and a clear color image having high color purity and resolution is obtained.

Action As in the present invention, when the second image exposure is performed by providing the non-image area at the boundary with the first toner image and performing the exposure, compared to the case where the first toner image is exposed closely. The electric field strength at the edge of the toner image is reduced, and the toner can be prevented from scattering. Therefore, an image in which different colors are adjacent to each other can be clearly reproduced, and a color image in which the image line of the toner image previously formed is not thin can be obtained.

Examples Examples of the present invention will be described below.

As the photoconductor that can be used in the present invention, any electrophotographic photoconductor such as selenium, phthalocyanine, amorphous silicon, and organic photoconductor can be used.

As the light source, any of a normal lamp, a semiconductor laser, a gas laser such as He-Ne, a combination of a liquid crystal switching element and a lamp, or a light emitting diode can be used.

As the developer, any toner that is used in ordinary electrophotography, such as non-magnetic and magnetic one-component toner or toner for two-component developer, can be applied. In particular,
For full-color use, a non-magnetic toner that is transparent and has excellent color purity and has a specific resistance of 10 ¹⁰ Ωcm or more is preferable.

As a developing method, a well-known method can be applied and is not particularly limited. Among them, an electric field flying developing method of causing toner to fly to a photosensitive member by the action of an electric field to develop it, and a gas discharge generated A non-contact developing method such as a method of developing toner by bringing the toner into close proximity to the photoconductor by the propelling force of an air flow or a toner cloud developing method is preferable. In particular, an electric field flying type non-contact developing method in which toner is flying in one direction toward a photoconductor by the action of a DC electric field is suitable.

Further, the developing device is preferably one that can control the on / off of the development. For example, in a non-contact developing method utilizing electric field flight of toner by a DC electric field, a method of separating a developing device from a photoconductor is effective.

Next, the basic principle of the present invention will be described with reference to FIG. The photoreceptor 6 having the photosensitive layer 5 provided on the conductive support 4 is positively charged by the corona charger 7 (FIG. 1 (a)), and the first optical image 8 is exposed (FIG. 1 (b)). ). Next, the first toner 9
After negative / positive reversal development in (1), the corona charger 7 charges the photoreceptor 6 positively again (1). Here, although not shown in the drawings, after developing with the first toner 9, the electrostatic latent image on the photoconductor 6 may be neutralized with, for example, an AC corona neutralizer, and then the photoconductor 6 may be recharged.

Next, when the second optical image 10 is exposed in close contact with the first toner 9 image, a minute gap is opened from the edge portion of the first toner 9 image in the region C for exposure. That is, regions B and D
The second light image 10 so that it is not exposed to the areas A and E.
(Fig. 1 (e)). The gap between the areas B and D is set so that the electric field strength at the edge portion of the toner image is sufficiently small so that the first toner does not scatter. Moreover, it is desirable that this gap be as small as possible. Generally, the desired gap depends on the surface potential of the photoreceptor,
The range of 0.02 mm to 0.2 mm is appropriate if the surface potential of a normal photoconductor is 1,500 V or less.

By exposing the second optical image with an appropriate gap as described above, it is possible to reduce the electric field strength at the edge portion of the first toner 9 image and prevent the toner from scattering. Therefore, when the areas A and E are negatively and positively reversed-developed with the second toner 11, a toner image having no color mixture at the boundary between the first toner 9 image and the second toner 11 image is obtained (first (F)).

Embodiment 1 FIG. 2 is a schematic view of a cutter printer using the color electrophotographic method according to the present invention. In the following description, the arrangement of the developing devices and the order of development are for convenience of description and are not conclusive.

12 is a photoconductor in which coelenteru is vapor-deposited on an aluminum drum, 13 is a corona charger, 14 is a light source combining a light emitting diode array with a main emission wavelength of 660 nm and a pixel density of 16 dots / mm, and a focusing rod lens array, 15, 16, 17 and 18 are electric field flying type developing devices containing yellow (Y), magenta (M), cyan (C) and black (B1) toners respectively, 19 is an AC corona neutralizer, and 20 is a cleaning brush. ,twenty one
Is a corona transfer device, 22 is a corona peeling device, and 23 is a transfer paper.

The developing devices 15, 16, 17 and 18 have the same basic configuration,
It has developing rollers 24, 25, 26 and 27 each carrying a thin layer of toner. The structure of the developing device is shown in FIG. 28
Is a toner container, 29 is toner, 30 is a developing roller made of cylindrical aluminum, 31 is a conductive fur brush in which rayon fibers containing carbon having a specific resistance of about 10 ⁵ Ωcm are planted on an aluminum drum, and 32 is on the developing roller. It is a rubber blade for uniformly thinning the toner. Also 33
Is a power source for adjusting the amount of toner supplied to the developing roller.

Each developing device adjusts the pressure of the rubber blade 32 and the voltage applied between the developing roller 30 and the conductive fur brush 31 so that the toner layer thickness on the developing roller 30 is 20 to 20.
It was adjusted to be 50 μm.

In addition, each developing device is equipped with a separating / contacting mechanism, and the gap between the developing roller and the photosensitive member is 0.1 to 0.2 mm when developing.
And when it does not contribute to development, it was set to 0.7 mm or more.

As the Y, M, C and B1 toners, non-magnetic toners containing resin and pigment as main components were used. The average particle size of each toner is 10μ
m, the amount of charge is 2-5 μC / g, and the specific resistance is about 10 ¹³ Ωcm.

Next, a method of forming a color image using this apparatus will be described.

While rotating the photoconductor 12 in the direction of the arrow,
The surface of the photoconductor 12 was charged to +800 V with 13 (corona voltage: +7 KV). Then, the black image signal was scanned and exposed by the light source 14 to form a negative electrostatic latent image. At this time, the surface potential of the non-image area (non-exposed area) was + 800V, and that of the image area (exposed area) was + 50V.

After exposure, the developing rollers 24, 25, and
When 26 is grounded and a voltage of +750 V is applied only to the developing roller 27 of the developing device 18, the photoconductor 12 is passed through,
A black toner image was obtained on the photoconductor 12. After development, the black electrostatic latent image was erased with an AC corona discharger 19 (charge removal voltage: ± 7 KV).

Next, the photoconductor 12 carrying the black toner image was charged again by the corona charger B (corona voltage: +7 KV), and the yellow image signal was scanned and exposed by the light source 14. After exposure, photoreceptor 12
Was passed through a group of developing devices set in the following state, and developed with yellow toner. + Only to the developing roller 24 of the developing device 15
A voltage of 750 V was applied and the developing rollers of the other developing devices 16, 17, and 18 were separated from the photoconductor 12 by 0.7 mm or more so that they did not contribute to the development. Next, AC corona neutralizer 19 (static neutralization voltage: ±
(7KV) erased the yellow electrostatic latent image.

Next, the photoconductor 12 carrying the black and yellow toner images was charged again by the corona charger B (corona voltage: 7 KV), and the light source 14 was used to scan and expose the magenta image signal. After the exposure, the photoconductor 12 was passed through a developing device group set in the following state, and the image was developed with magenta toner. + 750V voltage is applied only to the developing roller 25 of the developing device 16, and other developing device 1
The developing rollers 6, 17, and 18 are separated from the photoconductor 12 by 0.7 mm or more so that they do not contribute to the development. After development, the magenta electrostatic latent image was erased with an AC corona charge eliminator 19 (charge erasing voltage: ± 7 KV).

Next, the photoreceptor 12 is again charged with the corona charger B (corona voltage: 7K
V) was charged, and the cyan image signal was scanned and exposed using the light source 14. After exposure, the photoconductor 12 was passed through a group of developing devices set to the following state, and developed with cyan toner. A voltage of + 750V is applied only to the developing roller 26 of the developing device 18, and the developing rollers of the other developing devices 15, 16 and 18 are connected to the photoconductor 12
It was separated by 0.7 mm or more from the above so as not to contribute to the development.
After development, AC static eliminator 19 with + 200V bias voltage applied
The electrostatic latent image of cyan was erased at (zero peak 7 KV), and the toner on the photoconductor 12 was positively charged.

Next, after the toner image is electrostatically transferred onto the transfer paper 23 by the corona transfer device 21 to which −5.5 KV is applied, the transfer paper 23 is discharged by the corona peeling device 21 (peeling voltage: ± 7 KV) and peeled off from the photoconductor 12. did. The transfer paper 23 carrying the toner image was heat-fixed to obtain a color print. After the transfer, the toner remaining on the photoconductor 12 was removed by the cleaning brush 20 and again used for the next image formation.

In order to form a different toner image adjacent to the previously formed toner image by using the above-mentioned apparatus, one line of the light source, that is, about 0.06 mm, is separated from the edge portion of the previously formed toner image, When a light image was exposed to light, a clear color image with no color mixture at the boundary was obtained. Moreover,
The undeveloped non-image area at the boundary (the area that is originally a white area) becomes slightly thick due to corona transfer and heat fixing of the toner image in the print image, and the white area is almost invisible to the naked eye. Met.

The image quality of the color print was clear with no total color fog at an overall resolution of 14 dots / mm and background fog density of 0.01.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to prevent a decrease in color purity at the boundary between different images adjacent to each other and reproduce an image clearly. Further, there is no thinning of the image lines in the adjacent portions of different colors at the boundary between the respective images, and there is an effect that a color image with high resolution can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of the color electrophotographic method according to the present invention. 2 is a schematic view of a color printer using the color electrophotographic method of the present invention, FIG. 3 is a schematic view of a developing device used in the color printer of FIG. 2, and FIG. 4 is a conventional color printer. It is a figure for demonstrating the problem of an electrophotographic method. 6 ... photoreceptor, 7 ... corona charger, 9 ... first toner, 11 ... second toner.

Claims (2)

[Claims] 1. A color electrophotographic method comprising the steps of repeatedly charging, exposing, and developing toners of different colors to form toner images of a plurality of colors on a photoconductor, the first toner on the photoconductor. When performing image exposure for forming a second toner image adjacent to the first toner image after forming the image,
A color electrophotographic method, wherein a non-image area having a width of 0.02 mm to 0.2 mm is provided at a boundary with the first toner image and image exposure is performed. 2. The color electrophotographic method according to claim 1, wherein the development is a negative / positive reversal phenomenon.