JPH0752308B2 - Color image recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording a color image using an electrostatic latent image, and more particularly to a visible image (toner) already formed on a latent image carrier. The present invention relates to a color image recording method for developing a color toner image without disturbing the image.

2. Description of the Related Art Conventionally, various color recording methods utilizing electrophotography have been proposed. As such a color recording method, for example, n color monochromatic units including a latent image forming unit, a photoconductor, a developing unit, and a transfer unit are prepared, and the paper is moved through each unit so that the monochromatic units are sequentially formed. There is known a so-called sequential transfer method in which a color image is transferred and finally obtained. Although this method can make the copying speed equal to that of monochromatic copying, it has a drawback that the apparatus becomes extremely large. On the other hand, from the viewpoint of downsizing of the apparatus, a latent image is formed by using one photoconductor and a transfer drum in pressure contact with the photoconductor.
The so-called layer transfer method (transfer drum method), in which development and transfer are repeated for n colors, is known, but the size of the device can be reduced to a certain extent, but the copying speed becomes 1 / n and slows down. Have The over-developing method forms a binary or ternary electrostatic latent image on one photoconductor, and the first latent image of the photoconductor having these binary or ternary latent images is formed by a first developing machine. After development, the second latent image on the photoconductor is subsequently developed by a second developing machine, and the finally formed toner image is transferred at one time to obtain a color image. The method is effective because the copying speed is extremely fast with the downsizing of the apparatus.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in such an overdeveloping method, after the second developing step, the photosensitive member carrying the toner image is already rubbed with the developer again by the first developing step. Therefore, the toner image formed by the first developing process is significantly disturbed by the developing process of the second stage. As a result, the final color image has the drawback of becoming a significantly distorted color image. Therefore, 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 an extremely 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.

However, when the magnetic brush developing method is used, a two-component developer is carried on a non-magnetic sleeve having a magnet roll inside, and a latent image is rubbed with a magnetic brush to perform development. In the method, the toner image formed in the former developing process is disturbed by the tip of the magnetic brush rubbing the toner image in the latter developing process.

As a means for solving such a problem, Japanese Patent Laid-Open No. 60-12666
Japanese Patent Laid-Open No. 5 (1994) proposes a color developing device using a two-component developer in which a magnetic carrier having a particle diameter of 50 μm or less is mixed with toner particles. However, although the image turbulence development is improved by making the particles of the carrier smaller, the smaller the particle size, the more the so-called carry-over phenomenon in which the carrier is transferred from the developing device to the surface of the photoreceptor.
In order to avoid the carryover phenomenon, it is necessary to increase the magnetic force, and for that purpose, it is necessary to increase the particle size of the carrier particles to some extent. Therefore, sufficient results cannot be obtained only by defining the particle size of the carrier.

The present invention has been made in view of the above problems. Therefore, an object of the present invention is to provide a color recording method capable of developing without disturbing an already existing toner image even when a two-component developer is used.

Means for Solving the Problems The inventors of the present invention have conducted intensive studies using a magnetic brush developing machine using a two-component developer, and as a result, found that the density of the carrier used for the two-component developer is The inventors have found that it is an important factor for disturbance and completed the present invention.

That is, according to the present invention, a latent image forming step of forming an electrostatic latent image on a latent image carrier by a latent image forming means and a formed electrostatic latent image is visualized with two or more different toners. A color image recording method comprising a developing step and a transferring step, wherein the latent image forming step and the developing step are alternately repeated a plurality of times and then the visualized color toner images are collectively transferred to a transfer material. , Multiple development steps are performed using toners of different colors and different polarities, and at least the second and subsequent development steps have a density of 1.7 to 3.0 g / cm ³ and a particle size of 25 to 50 μm. Then, a two-component developer obtained by mixing a magnetic carrier in which magnetic powder is dispersed in a binder resin is used.

The carrier used in the present invention has a density of 1.7 to 3.0 g /
The carrier has a cm ³ particle diameter of 25 to 50 μm and magnetic powder dispersed in a binder resin. The density of this carrier can be easily controlled by the content of the magnetic powder. From the results of the experiment, it was found that the image turbulence development and the carryover phenomenon were in the permissible range if the density was in the range of 1.7 to 3.0 g / cm ³ . It is speculated that this is because the ears formed are soft because the density of each carrier is low.

The particle size of such low-density carrier particles in the present invention is arbitrary, but from the result of the experiment, the average particle size is 25 to 50 μm.
The range of m is required to be, and the one having an average particle size of about 30 μm is most suitable. This is because if the average particle diameter is out of the above range, it becomes difficult to achieve both carry-over phenomenon and prevention of image distortion phenomenon.

The density of the carrier of the present invention is defined by the density obtained by the true specific gravity measured by the following measuring method.

The pycnometer method (true specific gravity bin method) is used to calculate the true specific gravity by completely replacing the voids of the powder with liquid and applying the relationship between the weight and volume to the following formula. : Auto True Denser MAT-
Using 5000 (manufactured by Seishin Enterprise Co., Ltd.), obtain the true specific gravity from the following formula.

(In the formula, Pd: true specific gravity, Ld: specific gravity of liquid, Wa: cell tare (empty cell) (g), Wb: cell tare + powder (g), Wc: cell tare + powder + liquid (liquid level (After determination) (g), Wd: cell tare + liquid (after determination of liquid level) (g)) In the developing step (second time or later) according to the present invention, any two-component developing device can be used. It is preferable to use the most common magnetic brush developing device.

The magnetic brush developing device carries a two-component developer on a developing roll composed of a magnet roll having a plurality of magnetic poles and a non-magnetic cylindrical sleeve provided on the peripheral surface thereof, and the ears are restrained by an optional shaving restraining member or the like. By adjusting the vertical length to form a magnetic brush and moving the magnetic brush by relative movement of the magnet roll and the sleeve, the latent image is rubbed by rubbing the surface of the photoconductor opposite to the magnetic brush. Toner is attached to the surface of the toner to develop it. On this occasion,
From the perspective of preventing image distortion, fix the magnet roll,
A method of rotating the sleeve is preferable. At this time, it is preferable that the sleeve rotates in the same direction as the photosensitive member in the developing section. Further, the magnet roll fixedly arranged inside is at least at the developing nip position,
Most preferably, it is arranged to form a repulsive magnetic field.

Examples Hereinafter, the color image recording method of the present invention will be described with reference to the drawings.

FIG. 1 is an example of a color image recording apparatus used for carrying out the present invention, and shows a case where a color image is formed by forming a binary latent image. FIG. 2 is a diagram for explaining the surface potential of the photoconductor and the state of development when the color image recording apparatus of FIG. 1 is operated. In FIG. 1, 1a is a first charging device, 2a is a first exposing device, 3a is a first developing device, 1b is a second charging device, 2b is a second exposing device, and 3b is a second exposing device.
Developing means, 4 is a transfer corotron, 5 is a charge eliminating corotron,
6 is a cleaner, 7 is an optical static eliminator, 8 is a recording sheet, 9 is a pre-transfer corotron, 10 is a photosensitive drum, and 10a is a photosensitive layer.

The photoconductor drum 10 rotates in the direction of the arrow. First,
By the first charger 1a, the photosensitive layer 10 on the surface of the photosensitive drum 10
a is uniformly charged (Fig. 2 (a)).

Next, the first exposure unit 2a irradiates light according to the image information corresponding to the first color to form an electrostatic latent image corresponding to the first color on the photoconductor. Any exposure means can be selected. Then, toner corresponding to the first color is supplied to the photosensitive layer 10a having the first electrostatic latent image formed by the first exposure means by the first developing means 3a to visualize it. Fig. 2 (b)). The color of the toner may be different from the first color. Any means can be used as the first developing means. At this time, the developing bias is selected depending on whether regular development or reverse development is performed.

Next, the photosensitive layer 10a is uniformly charged again by the second charger 1b (FIG. 2C).
Can be omitted depending on the imaging process.
For example, negative writing is performed in the first exposure unit and second writing is performed.
This can be omitted when positive writing is performed in the exposure section. Then, the second exposure unit 2b performs light irradiation according to the image information corresponding to the second color, and the photosensitive layer 10a
An electrostatic latent image corresponding to the second color is formed on the upper surface. The exposure means and the writing method are arbitrary. Then, a second layer is formed on the photosensitive layer 10a having the second electrostatic latent image formed by the second exposure means.
The developing means 3b supplies toner corresponding to the second color to visualize the toner (FIG. 2 (d)). Also in this case, the color of the toner may be different from the second color. At this time, the developing bias can also be arbitrarily selected.

The pre-transfer corotron 9 is used to align the polarities of the first toner and the second toner carried on the photosensitive member before transfer, but this can also be omitted in the specific process. The first toner image and the second toner image are transferred onto the recording paper 8 by the transfer corotron 4, but they may be transferred using a means other than electrostatic transfer. The recording paper is then fixed by a fixing unit (not shown). Also, the photoconductor that has passed through the transfer section
Cleaning is performed by the static elimination corotron 5, the cleaner 6 and the optical static eliminator 7 for reuse.

The first and second exposure means include a light illuminating means, a document scanning means and an image forming optical system as used in a normal copying machine, but an optical writing device capable of performing light modulation according to image information. , A liquid crystal light valve consisting of a laser writing device, a uniform light source and a liquid crystal micro shutter,
Anything such as LED array, optical fiber, etc. can be used according to the purpose.

In the present invention, when the color image recording apparatus shown in FIG. 1 is used, two types of developers having different hues using toners having polarities different from each other are used as the developers. Of the two developing means, at least in the second developing means, the toner has a density of 1.7 to 3.0 g / cm.
^3. It is necessary to use a two-component developer having a particle size of 25 to 50 μm and mixing a magnetic carrier in which magnetic powder is dispersed in a binder resin.

The two-component developer used in the present invention was manufactured as follows.

Carrier Styrene-n-butyl methacrylate copolymer (density 1 /
1 g / cm ³ ) and cubic magnetite (density 4.8 g / cm ³ ) were mixed in the following ratios, melt-kneaded and then finely pulverized to obtain the following carriers.

Toner: 92 parts by weight of a resin obtained by graft-polymerizing a low molecular weight polyolefin into a styrene-butyl methacrylate copolymer and 8 parts by weight of a red pigment: Resorskart (trade name, BASF) are melt-kneaded and finely pulverized. A toner having an average particle size of 9.8 μm was obtained.

Two-component developer 90 parts by weight of the above carrier and 10 parts by weight of toner were mixed to obtain a developer.

A test was conducted using the color image recording apparatus shown in FIG. A Se-based material was used as the photoconductor. However,
The first exposure is regular exposure (non-image area exposure), and the second exposure is
It was reverse exposure (image area exposure). Also, the surface potential of the photoconductor due to the first charging is 900V, and the exposed portion due to the first exposure is 200V.
Met. The first development was carried out by the first developing means by a two-component magnetic brush method with a developing bias of 300 V and black toner. Further, the surface potential of the photoconductor by the second charging was 900V, and the exposed portion by the second exposure was 200V.
The second development was carried out by the second developing means by a two-component magnetic brush method with a developing bias of 800 V and using red toner.

For comparison, the following was used as a carrier of the two-component developer used in the second developing means, and the same test was conducted.

FIG. 3 shows the relationship between the carrier density and image disturbance and carryover development in these tests. In addition,
In FIG. 3, ◯ means that there was no image disturbance or carryover phenomenon, and × means that image disturbance or carryover phenomenon occurred.

EFFECTS OF THE INVENTION According to the color image recording method of the present invention in which the above-mentioned two-component developer is used to perform overdevelopment by the magnetic brush method, the toner image in the preceding stage in the overdevelopment is not disturbed, and a carryover phenomenon occurs. There is nothing to do. Therefore,
The color image obtained by the present invention has excellent image quality without image distortion.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a color image recording apparatus used for carrying out the present invention, and FIG. 2 is a surface potential of a photoconductor and development when the color image recording apparatus of FIG. 1 is operated. FIG. 3 is an explanatory diagram for explaining the above state, and FIG. 3 is an explanatory diagram for explaining the relationship between carrier density and image distortion and carryover. 1a ... first charger, 1b ... second charger, 2a ... first exposure means, 2b ... second exposure means, 3a ... first developing means, 3b ...
... second developing means, 4 ... transfer corotron, 8 ... recording paper, 10 ... photosensitive drum.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Noami 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Works (72) Inventor Toshiro Yamamoto 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.Ebina Co., Ltd. In-house (72) Inventor Koji Adachi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.In Ebina Office (72) Inventor Toru Okamoto 2274 Hongo, Ebina-shi, Kanagawa Fuji-Xerox Co., Ltd.Ebina Office (72) Invention Ken Kenjigawa 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. Ebina Works (56) Reference JP 57-147655 (JP, A) JP 54-14238 (JP, A) JP 60 -147749 (JP, A) JP-A-60-126665 (JP, A)

Claims (1)

[Claims] 1. A latent image forming step of forming an electrostatic latent image on a latent image carrier by a latent image forming means, and a developing process for developing the formed electrostatic latent image with toners of two or more colors. Process,
In the color image recording method, which comprises a transfer process, the latent image forming process and the developing process are alternately repeated a plurality of times, and then the visualized color toner images are collectively transferred to a transfer material. The developing process is performed using toners of different colors having different polarities. At least in the second and subsequent developing processes, the toner has a density of 1.7 to 3.0 g / cm ³ and a particle size of 2
A color image recording method, wherein a two-component developer having a particle size of 5 to 50 μm and containing a magnetic carrier in which magnetic powder is dispersed in a binder resin is used.