JPS63139374A - Color electrophotographing method - Google Patents

Abstract

PURPOSE:To distinctly reproduce an image in which black and other color contact closely with each other, by forming the vicinity of the edge end part of a close contact part of toner images of different colors which are repeated and formed, to a composite color of black to which plural kinds of toners are superposed. CONSTITUTION:After an electrification by a corona electrifier, a black toner 6 is scattered to areas E, F, when the areas E, F in the vicinity of the edge end part of a black toner developing area A and an adjacent point of the area E are exposed. Subsequently, when a development is executed by a yellow toner 8, a toner 8 is superposed onto the toner 6 of the areas E, F. By the same repetition, a magenta toner 10 and the toner 6 are superposed successively to the areas E, F, the vicinity of the end edge part of the black area brought into contact closely with a yellow toner area and a magenta toner area becomes a composite black color to which each color toner is superposed, and an image in which black and other color contact closely with each other can be reproduced distinctly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color electrophotographic method that can be used in a color hard copy device such as a color copying machine or a color printer. Specifically, the present invention relates to a one-time transfer type color electrophotographic method in which a plurality of toner images of different colors are formed on a photoreceptor by repeating the steps of charging, exposing, and developing a plurality of times.

BACKGROUND ART Conventionally, as a one-time transfer type color electrophotographic method, for example, Japanese Patent Application Laid-Open No. 58-57139 and Japanese Patent Application Laid-open No. 60-7676 are known.
Techniques disclosed in Japanese Patent Application Publication No. 8 and Japanese Patent Application Laid-Open No. 60-95456 are known. However, until now, it has been completely unclear what kind of technical issues exist when reproducing images in which different colors are placed close to each other, and how to reproduce such images clearly. there were.

Problems to be Solved by the Invention A common problem with single-transfer color electrophotographic methods that has been proposed in the past is that when images of different colors are formed in close proximity, the images formed in the previous process may appear in the vicinity of the close contact areas. We have discovered that images are blurred and lines become thinner, and colors from the previous process are mixed into images formed in the later process. An analysis of the cause revealed the following. A case in which image formation is negative/positive reversal will be described below.

(1) After recharging the photoreceptor carrying the first toner image by corona discharge, in order to form a second toner image, the photoreceptor is placed in close contact with the first toner image and its surroundings are imagewise exposed; The toner at the edge of the toner image scatters into the exposed area. As a result, the image formed in the previous process becomes blurred and the lines become thinner. Therefore, when the image exposure area is developed with a second toner, the second toner is superimposed on the first toner scattered in the image exposure area. is mixed in.

(2) The scattering width of the first toner due to the exposure explained in the previous section varies depending on the surface potential of the first toner image area, the amount of exposure, or the amount of charge of the toner, but is approximately 0.02 mm to
The range is 0.5 mm.

By the way, documents used in general offices overwhelmingly contain black images such as text. Therefore, even when recording in color, it is especially important to clearly reproduce black images. In color recording, the traditional number of methods for reproducing black is 2.
The street method was common. The first method is to use a monochromatic black toner, and the second method is to synthesize by subtractive color mixing of two or more types of toner. However, although the former provides an ideal hue, it has the aforementioned problem of toner scattering, while the latter alleviates the problem of toner scattering, but has the disadvantage that the hue is worse than that of monochromatic black.

As explained above, with the prior art, it has not been possible to reproduce a clear black image in close contact with other colors. To solve this problem, it is necessary to devise a method of forming an electrostatic latent image or an order in which toner images are stacked, taking into full consideration the above-mentioned toner scattering phenomenon.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to overcome these conventional problems and provide a color electrophotographic method that can clearly reproduce images in which black and other colors are closely related.

Means for Solving the Problems The present invention provides a color electrophotographic method in which a plurality of toner images of different colors are formed on a photoreceptor by repeating the steps of charging, exposing, and developing a plurality of times. When forming a close image, the vicinity of the edge of the black image in the close contact area with other colors is reproduced with a black composite color made by overlapping two or more types of toner, and the area other than the 1 m edge is reproduced with a monochromatic black. By reproducing with toner, images in which black and other colors are closely reproduced are clearly reproduced.

Effect, 4 shots'''1'''-1-11, exposure 1911 color, scattering 51-pool, in order to reproduce that part with a composite color of black and reproduce the rest with a single color and one color of black, You can get a clear black image with no blurring, where black and other colors are perfectly in close contact with each other.

Example Examples of the present invention will be described below.

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

The light source is a combination of a normal lamp and lens.

Any of 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 developer used in normal electrophotography, such as a non-magnetic or magnetic one-component developer or two-component developer, can be used.

The color combination of the toner used is a combination of a monochromatic black toner and two or more types of color toners that become black when mixed. In particular, color toner is transparent and has a specific resistance of 1012
Non-magnetic toners with a resistance of Ω・Cl11 or more are preferred. Examples of combinations of color toners that become black when mixed include the three primary colors of yellow, magenta, and cyan for full color, red and cyan, red and green, and red and green for multicolor. Use combinations of brown and green, blue-purple and yellow, green and magenta, etc.

As the developing means, commonly known methods can be applied. However, for color toner, there are two methods: one in which the toner is ejected onto the photoconductor using the action of an electric field, an electric field development method in which the toner is developed by bringing the toner close to the photoconductor using the propulsive force of an air flow generated by a gas discharge, and another method in which the toner is developed using air. Non-contact development methods such as toner cloud development, in which toner is placed in a stream and developed in close proximity to the photoreceptor, are preferred, especially electric field flying type, in which the toner is flown in one direction toward the photoreceptor by the action of a DC electric field. The non-contact developing method remains.

Regarding the order of forming toner images on the photoreceptor, it is preferable to form a monochromatic black toner image first, because contact type developing means can be applied only to the first toner image formed. Therefore, if a black toner image is formed first, there is an advantage that a reliable black contact type developing means, which has a proven track record in black and white copying machines, can be used.

Next, the basic principle of the present invention will be explained based on FIG. Here, photoconductors for positive charging and black, yellow,
A case will be described in which four types of toner, magenta and cyan, are used to form an image in which yellow and magenta are close to each other in black with negative/positive inversion.

A photoreceptor consisting of a conductive support (1) and a photosensitive layer (2)
3) is charged to (+) using a charger (4) (FIG. 1a), and the area A is exposed to a first optical image (5) (FIG. 1b).

Here, area A is the area to be developed with black toner, area B is the area that will eventually be reproduced as black, area C is the area that will be reproduced as yellow, area D is the area that will be reproduced as magenta, and areas E and F are reproduced with the composite color of black. This is the part to do. The width of @areas E and F should be larger than the toner scattering width generated during exposure and as narrow as possible, preferably 0.5 mm or less, preferably 0.0 mm.
The range of 2mm to 0.2mm is good, after image exposure, area A
is reversely developed with black toner (6) (FIG. 1C).

Next, the photoreceptor (3) is again charged to (+) using the charger (4) (Fig. 1d).
The light image (7) of is exposed. At this time, part of the black toner near the boundary between areas E and F is scattered to areas E and F (FIG. 1e). Subsequently, reversal development is performed using yellow toner (8). Area C has only yellow toner, and areas E and F have yellow toner (6) on top of black toner (6).
8) is obtained (Fig. 1 f).

Next, the photoreceptor (3) is charged (+) again with the charger (4) (Fig. 1g), and a third optical image (9) is formed in the areas E and F.
). Then, a part of the yellow toner (8) near the boundary of area E scatters to area E (Fig. 1h)
, followed by region E and F with magenta toner (10
) for reversal development (Figure 1 1).

Next, the photoreceptor (3) is charged (+) again by the charger (4) (FIG. 1j), and areas E and F are exposed to the fourth optical image (11). A part of the magenta toner near area F is
It scatters to area F (Fig. 1k).

At this time, the yellow toner near the area E hardly scatters because the toner that is easy to scatter has been scattered in the previous process. After image exposure, areas E and F are coated with cyan toner (1
2) to perform reversal development (Fig. 1 1).

When the toner image obtained on the photoconductor is transferred to an image receptor by conventional means and fixed, an image in which black, yellow, and magenta are closely combined is obtained on the image receptor (not shown). Since the image is composed of black, which is composed of four types of toner, at the boundary with other colors, the image is sharp and closely blends with the other colors. Moreover, since the width of the composite black is narrow, 0.5 mm or less, the resulting black is so clear that it is almost indistinguishable from monochromatic black.

Embodiment 1 FIG. 2 is a schematic diagram of a color printer using the color electrophotographic method according to the present invention.

(13) is a photoreceptor with selenium deposited on an aluminum drum, (14) is a corona charger, and (15) is a main emission wavelength: 660 nm + pixel density: 16 dots/mm
A light source that combines a light emitting diode array and a focusing rod lens array, (16), (17), (18)
and (19) are yellow (Y) and magenta (M), respectively.
), an electric field type developer containing cyan (C) and black (Bl) toner, (20) a cleaning brush, (21) a corona transfer device, (22) a corona peeler,
(23) is transfer paper.

Developing units (16), (17), (18) and (19)
) have the same basic configuration, each consisting of developing rollers (24), (25), and (25) for supporting a thin layer of toner.
(2B) and (27). The specific 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)
(32) is a conductive fur brush made by flocking carbon-containing rayon fibers with a specific resistance of 105 Ω・cm onto an aluminum drum, and (32) is a rubber blade for uniformly thinning the toner on the developing roller (30). . Also, (33
) is a power source for adjusting the amount of toner supplied to the developing roller (30).

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) to increase the thickness of the toner on the developing roller (30). The thickness was adjusted to 20 to 50 μm.

Furthermore, a separation mechanism is attached to each developing device, so that the gap between the developing roller and the photoreceptor is 0.1 to 0.2 mm when used for development, and 0.7 mm or more when not contributing to development. I did it like that.

For the Y, M, C, and Bl toners, nonmagnetic insulating toners containing resin and pigment as main components were used. The average particle size of each toner is 10 μm, the amount of charge is 2-5 μC/g, and the specific resistance is approximately 1
013Ω·cm.

Next, a specific method for forming the three-color image described in FIG. 1 using this apparatus will be described.

While rotating the photoreceptor (13) in the direction of the arrow, charge the photoreceptor (13) with the corona charger (14) (corona voltage: +7kV).
The surface of 13) was charged to +800v. And the light source (
15), black image signal (width of areas E and F: 0.1 m
m) was scanned and exposed to area A to form a negative electrostatic latent image. At this time, the surface potential of the non-image area (unexposed area) was +800V, and the surface potential of the image area (exposed area) was +50V.

After exposure, the developing rollers (24), (25), (2) of the developing devices (16), (17), (18), respectively
B) is grounded and a voltage of +750V is applied only to the developing roller (27) of the developing device (19).
3), a black toner image was obtained on the photoreceptor (13).

Next, the photoreceptor (13) carrying the black toner image is charged again with a corona charger (14) (corona voltage: +7 kV) for 100 mA.
It was charged to oov, and areas C, E, and F were scanned and exposed to a yellow image signal using a light source (15). After exposure, the photoreceptor (13) was passed through a group of developing devices set as shown below, and developed with yellow toner. A voltage of +750V is applied only to the developing roller (24) of the developing device (16), and the developing rollers of the other developing devices (17), (18), and (19) are separated from the photoreceptor (13) by 0.7 aha or more. They were separated so that they did not contribute to development.

Next, a photoreceptor (13) carrying black and yellow toner images
Then turn on the corona charger (14) again (corona voltage: +7kV
) was charged to +800V, a magenta image signal was applied to the area using a light source (15), and scanning exposure was performed to E and F. After exposure, the photoreceptor (13) was passed through a group of developing devices set as shown below, and developed with magenta toner. A voltage of +750V is applied only to the developing roller (25) of the developing device (17), and the other developing devices (16), (18), (
19) at a distance of 0.7 m from the photoreceptor (13).
They were separated by a distance of m or more so that they did not contribute to development.

Again, the photoreceptor (13) was charged with a corona charger (14) (corona voltage: +7 kV) (corona voltage: +800 Vk), and a cyan image signal was scanned and exposed to areas E and F using the light source (15) e. After exposure, the photoreceptor (13) was passed through a group of developing devices set as shown below to receive and develop cyan toner. The developing roller (
26), and the developing rollers of the other developing devices (16), (17), and (19) are separated by 0.7 mm or more from the photoreceptor (13) so that they do not contribute to development. I made it.

Next, the toner image is electrostatically transferred onto the transfer paper (23) using the corona transfer device (21) to which −5.5 kV is applied, and then the toner image is electrostatically transferred onto the transfer paper (23) using the corona peeler (22) (peel voltage: +7 kV).
23) was removed from the photoreceptor (13). The transfer paper (23) carrying the toner image was heat-fixed to obtain a color print. After the transfer, the toner remaining on the photoreceptor (13) was removed with a cleaning brush (20), and the photoreceptor (13) was used again for the next image formation.

As a result, the density of area A: 1.5. Concentration of regions E and F: 1.4. Yellow color density: 1.2. Magenta color density: 1.5. Background fog density: 0.01 or less,
A clear color print with yellow and magenta in close contact with black with a total resolution of 8 crabs/mm was obtained. Visually, the difference in density between areas E and F and area A was hardly perceivable.

Comparative Example Using the apparatus of Example 1, a color image was formed by placing yellow and magenta toner images in close contact with a black toner image. An image with scattered particles was obtained. Furthermore, the resolution of the black image decreased to 3 lines/mm, resulting in a blurred and unclear image.

Example 2 In place of the black developer (19) described in Example 1, a contact type magnetic two-component developer used in the black and white copying machine FP-1300 manufactured by Matsushita Electric Industrial Co., Ltd. was used. When an image was formed in the same manner as in Example 1, a clear color image similar to that in Example 1 was obtained.

As described in detail, the present invention has the effect that images in which black and other colors are closely reproduced can be clearly reproduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the color electrophotographic method according to the present invention, FIG. 2 is a diagram schematically showing a color printer using the color electrophotographic method according to the present invention, and FIG. 3 is a diagram showing the color printer of FIG. FIG. 3 is a schematic cross-sectional view of the developing device used. 3...Photoreceptor, 4...Corona charger,
6...Black toner, 8...Yellow toner, 10...Magenta toner Name of agent Patent attorney Toshio Nakao 1 person Figure 1 1m Electrical support BookFigure 1Figure 1Figure 1Figure 2Figure 3

Claims (6)

[Claims] (1) In a color electrophotographic method in which the steps of charging, exposure, and development are repeated multiple times to form multiple toner images of different colors on a photoreceptor, when forming an image in which black and other colors are closely aligned, The vicinity of the edge of the black image in the close contact area with the color of is reproduced with a composite black color made by overlapping two or more types of toner,
A color electrophotographic method characterized in that an area other than the vicinity of the edge portion is reproduced with monochromatic black toner. (2) The color electrophotographic method according to claim 1, wherein image formation is negative/positive reversal. (3) A color electrophotographic method according to claim 1 or 2, wherein when exposing a black image signal, an undeveloped area is provided at the edge of the image. (4) The color electrophotographic method according to claim 3, wherein the width of the undeveloped area is 0.5 mm or less. (5) The color electrophotographic method according to claim 3, wherein the width of the undeveloped area is in the range of 0.02 to 0.2 mm. (6) Color electrophotography according to claim 1, or 2, or 3, or 4, or 5, which forms a monochromatic black toner image prior to other colors. Method.