JPH0563793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an image forming method, and particularly to a color image forming method.

B. Prior art Conventionally, as a color image recording method, Japanese Patent Laid-Open Publication No. 1986-
Publication No. 144452 and Japanese Unexamined Patent Publication No. 116553/1983
A method described in Japanese Patent No. 116554 is known.

The method described in JP-A-56-14452 is
After charging the surface of a photoreceptor as an image carrier with a charger, forming an electrostatic image on the charged surface with a first exposure means and developing it with a first developer, Next, an electrostatic image is formed on the same charged surface by a second exposure means, developed by a second developing device, and further an electrostatic image is formed on the same charged surface by a third exposure means. This is a method in which a color toner composite image is formed on an image carrier by developing it in a third developing device. JP-A-58-116553 and JP-A-58-116553
The method described in JP-A No. 116554 is substantially the same as that in JP-A-56-144452 in that the electrostatic image formation and development are performed using different devices each time. Therefore, the recording apparatus becomes larger and more expensive, and it is difficult to control the exposure synchronization of each exposure means, which similarly causes color misregistration.

In order to solve these problems, Japanese Patent Application Laid-Open No. 1986-
No. 76766 and Japanese Patent Application Laid-open No. 60-95456, by repeatedly forming an electrostatic image on an image carrier using the same device, the recording device can be made smaller and less costly, and a two-component developer can be used to reduce the cost. By using a contact development method, fogging, mixing and adhesion of different colored toners are prevented.

However, in such a color image forming process, in order to obtain an image with stable density and tone, it is necessary to keep the charging potential of the image carrier constant. However, JP-A-60-76766 and JP-A-Sho
No. 60-95456 describes the use of a scorotron charger to provide stable charging. It was found that it is not easy to apply a constant charging potential with only a single charge, and that the charging potential tends to fluctuate. In particular, when charging, electrostatic image formation, and development are repeated for each color in a single color image forming process, the charging potential of the first color and the charging potential of the second color often differ. Further, in such a case, in order to simplify the process, if the neutralization step between development and the next charging process is omitted, the charging potential is likely to become even more unstable. For this reason, there is a drawback that the density of each color changes, and the color tone, which is important in color images in particular, becomes unstable.

By the way, in recent years, in addition to being small and low cost,
Semiconductor lasers that can be directly modulated and are expected to be highly reliable have been developed. The oscillation wavelength of such a semiconductor laser is about 750 nm or more, and examples of photoreceptors sensitive to light in such a long wavelength range include a photoreceptor containing ε-type copper phthalocyanine disclosed in JP-A-58-100134. However, JP-A-1988-
No. 182639 describes a photoreceptor containing a τ-type metal-free phthalocyanine. Photoreceptors using these metal or metal-free phthalocyanines are sensitive to the oscillation wavelength of semiconductor lasers, but
When used as an image carrier in a color image recording method such as No. 60-76766 or JP-A No. 60-95456, the charging potential of the first color is particularly low, and the charging potential of the second and subsequent colors is relatively low. It was found that the potential difference between the first color and the second and subsequent colors tends to increase. The reason for this is not clear, but phthalocyanine has many levels that act as traps for carriers, so when the second color and subsequent colors are charged, the traps are filled with carriers and the photosensitive layer becomes highly resistive. It is presumed that the charging ability will be improved.

C. Purpose of the Invention The purpose of the present invention is to provide a method capable of obtaining images with stable color tone, no fog, stable sufficient density, and sufficient resolution.

D. Constitution of the Invention That is, the present invention uses an image bearing member containing a τ-type metal-free phthalocyanine, and performs a process on the image bearing member including charging, formation of an electrostatic image, and development using a colored toner. On the other hand, in a color image forming method in which a color image in which toner images are superimposed on the image carrier is formed by repeating the process multiple times for each color of the toner, the process is repeated multiple times for each color of the toner to form a color image. The present invention relates to a color image forming method characterized in that the absolute value of the developing bias potential for the second color and subsequent colors in the step of forming a plurality of times of repetition is made higher than that in the step of at least the first color. Here, the above-mentioned "development bias potential" particularly means the development potential applied to the development sleeve.

Example Examples of the present invention will be described in detail below.

First, the image forming apparatus used in this example is
This will be explained with reference to FIGS.

In the apparatus shown in FIG. 1, numeral 1 is a drum-shaped image carrier which has a photoreceptor surface layer of τ-type metal-free phthalocyanine and rotates in the direction of the arrow, and numeral 2 uniformly charges the surface of the image carrier 1. Charger, 4, image exposure for each color of color image, 5 to 8, yellow, magenta,
Each developing device uses toner of a different color, such as cyan and black, as a developer. 9
and 10 are a pre-transfer charging device and a pre-transfer charging device provided as necessary to facilitate the transfer of a color image formed by superimposing a plurality of color toner images onto the recording medium P on the image carrier 1, respectively. exposure lamp, 11
1 is a transfer device, and 12 is a fixing device that fixes the toner image transferred to the recording medium P. 13 is a static eliminator consisting of one or a combination of a static eliminator lamp and a corona discharger for static elimination; 14 is a static eliminator that comes into contact with the surface of the image carrier 1 after the color image has been transferred to remove residual toner on the surface; This cleaning device has a cleaning blade and a fur brush that separate from the surface of the image carrier 1 by the time the surface on which the first development has been performed reaches.

For image exposure 4, a laser beam scanner shown in FIG. 2 is used. In this process, a laser beam 20 emitted from a laser 21 such as a semiconductor laser is deflected by a mirror scanner 23 consisting of an octahedral rotating polygon mirror, and scans the surface of the image carrier 1 at a constant speed through an imaging f-theta lens 24. The image is formed on the image exposure 4. Note that 25 and 26 are mirrors, and 27 is a lens for enlarging the diameter of the beam incident on the imaging f-theta lens 24 in order to reduce the diameter of the beam on the image carrier 1. 2nd for forming image exposure 4
If you use a laser beam scanner like the one shown in the figure,
Electrostatic images for different colors can be easily formed with shifts, and therefore clear color images can be recorded. However, the image exposure 4 is not limited to slit exposure or dot exposure using a laser beam, and may be obtained using, for example, an LED, a CRT, a liquid crystal, or an optical fiber transmission body.
In a recording apparatus in which the image carrier can take a flat state such as a belt, the image exposure may be a flash exposure.

As the developing units 5 to 8, those having a structure as shown in FIG. 3 are preferably used. In FIG. 3, 31 is a developing sleeve made of a non-magnetic material such as aluminum or stainless steel, 32 is a magnet body provided inside the developing sleeve 31 and has a plurality of magnetic poles in the circumferential direction, and 33 is a developing sleeve 31 A layer thickness regulating blade 34 that regulates the thickness of the developer layer formed on the developing sleeve 31 is a scraper blade that removes the developed developer layer from the developing sleeve 31 . 35 is a stirring rotating body that stirs the developer in the developer reservoir 36; 37 is a toner hopper; 38 is a toner replenishment roller that has a recess on its surface into which the toner enters and replenishes toner from the toner hopper 37 to the developer reservoir 36; 39 applies a bias voltage including an oscillating voltage component in some cases to the developing sleeve 31 via the protective resistor 40;
This is a power source for forming an electric field to control the movement of toner between the image carrier 1 and the image carrier 1.

In addition, in the above, the development of the second and subsequent colors in the process of repeating multiple times to form a color image for each toner color is performed without the developer layer formed in the developing device coming into contact with the surface of the image carrier. It is best to do it on Further, after the color image in which the toner images are superimposed on the image carrier is transferred, the image carrier is preferably cleaned by a cleaning device.

Further, in the present invention, in addition to transferring an image to a transfer body P such as a recording paper as described above, an intermediate transfer body used for a known adhesive transfer can also be employed as a transfer body.

Next, the composition of the developer used in this example will be explained. This developer is a two-component system consisting of a resin-coated carrier and a toner, which are prepared as follows.

Preparation of resin-coated carrier) Styrene-methyl methacrylate copolymer with a monomer composition ratio of styrene and methyl methacrylate of 30:70 (82000, :25000, Tg: 110°C)
was dissolved in 300 ml of methyl ethyl ketone to prepare a coating solution. Ferrite was coated with this coating solution using a spira coater (manufactured by Okada Seiko Co., Ltd.), and the film thickness was
Carrier A was produced with a coating layer of 1.0 μm.
The average particle size of this carrier A is 30μ, and the magnetization is
25emu/g, specific resistance 10 ¹⁴ Ω-cm or more, specific gravity
It was 5.2g/ ^cm2 .

In addition, carrier B was prepared in the same manner as carrier A except that vinylidene fluoride-tetrafluoroethylene copolymer "VT-100" (manufactured by Daikin Industries, Ltd.) was dissolved in 300 ml of acetone-methyl ethyl ketone (1:1). I got it. The average particle size of this carrier B is
30 μm, magnetization 25 emu/g, specific resistance 10 ¹⁴ Ω−
cm or more, with a specific gravity of 5.2 g/cm ² .

(Preparation of toner) 100 parts by weight of polyester resin, polypropylene
3 parts by weight of 660p (manufactured by Sanyo Chemical Industries, Ltd.) and 10 parts by weight of Carbon Black: Mogul L (manufactured by Cabot Corporation) were mixed in a Henschel mixer. After that,
After thoroughly kneading with three rolls at a temperature of 140℃,
After cooling and coarsely pulverizing, the mixture was pulverized in a jet mill and classified to obtain a "black toner" with an average particle size of 10 μm.

In place of the carbon black used in this black toner, yellow pigment, magenta pigment, and cyan pigment were used, but in the same manner as the black toner, "yellow toner", "magenta toner", and "cyan toner" with an average particle size of 12 μm were used. ” was obtained.

(Preparation of developer) A developer was prepared using the carrier and toner so that the toner concentration was 12% by weight.

Using the developer thus obtained, image formation was performed using the apparatus shown in FIG. As for the development method, an electrostatic image is formed by an electrostatic image forming method in which the exposed part of the image becomes an electrostatic image with a lower potential than the background part, and the development charges the electrostatic image with the same polarity as the potential of the background part. This method (reversal development) is carried out by the adhesion of toner.

At the first time, charging is performed by the charging electrode 2, and the image exposure 4 for each color is projected by the laser beam scanner in FIG.
The image exposure shown in FIG. 1 was carried out so that the following was obtained. The obtained electrostatic image was developed into a first color by one of the developing devices 5 to 8 using a developer of a color toner corresponding to image exposure 4. Next, the surface of the image carrier (or image carrier) 1 is uniformly charged again by the charging electrode 2 as it is (that is, without being transferred), and the charged surface is exposed to a second color image. Then, the second color was developed, and the electrostatic image formation and development of the third and fourth colors were repeated in the same manner.

In this manner, the color image formed on the image carrier was transferred to the recording medium P by the transfer device 11. With such a method, a color image can be easily obtained without color shift.

A semiconductor laser was used for image exposure, and the AC bias was 2kHz and 1kV. Examples based on the present invention will be described below together with comparative examples, and FIG. 4 shows them together.

Example 1 and Comparative Examples 1 and 2 When ODC (organic photoconductive material) containing τ-type metal-free phthalocyanine (manufactured by Toyo Ink Co., Ltd.) is used, as in Comparative Examples 1 and 2, the first color and the second color are If the development potentials after the first color are made the same, fog will appear on the first color. On the other hand, if the development potential (DC development bias) for the second and subsequent colors is set higher than that for the first color as in Examples 1 and 2, each dye,
Images with sufficient density and no fog can be obtained.

Comparative Examples 3 and 4 With Se/Te photoreceptors and a-SiGe photoreceptors, even if the development potential of the second and subsequent colors is the same as that of the first color, the charging potentials of each color are almost equal, so
There is no problem in this respect.

However, Se/Te has insufficient sensitivity to semiconductor lasers, and sufficient image density cannot be obtained. Furthermore, a-SiGe has insufficient charging ability and cannot obtain sufficient image density.

As described above, according to the present invention, in a color image recording device, the charged potential of τ-type metal-free phthalocyanine having sufficient sensitivity to semiconductor lasers can be stabilized, and the τ-type metal-free phthalocyanine can have stable color tone and sufficient density. , it is possible to obtain images without fog.

Although the present invention has been illustrated above, the embodiments described above can be further modified based on the technical idea of the present invention.

For example, regarding the development bias potential mentioned above,
It is preferable that the values for the second and subsequent colors be at least 30 V higher in absolute value than those for the first color. Further, the content of the τ-type metal-free phthalocyanine to be used may be variously changed based on known techniques, and
The type of toner, the arrangement of developing devices, the order of operations, etc. can also be changed.

F. Effects of the Invention As described above, the present invention uses an image bearing member containing a τ-type metal-free phthalocyanine, and performs a step including charging, forming an electrostatic image, and developing with a colored toner on the image bearing member. In a color image forming method, the process is repeated multiple times for each color of the toner to form a color image in which toner images are superimposed on the image carrier. Since the absolute value of the developing bias potential for the second and subsequent colors in the multiple image forming steps is made larger than that for the first color, changes in the surface potential of the image carrier are canceled out and the potential is kept almost constant. Development conditions can be obtained, and images with stable color tone and density can be obtained.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which FIG. 1 is a schematic diagram of main parts of an image forming apparatus, FIG. 2 is a schematic diagram of a laser beam scanner, FIG. 3 is a sectional view of a developing device, and FIG. Figure 4 is a table that compares and shows the data of each example. In addition, in the symbols shown in the drawings, 1... image carrier, 2... charger, 4... image exposure, 5, 6, 7,
8...developing device, 12...fixing device, 14...cleaning device.

Claims (1)

[Claims] 1 Using an image carrier containing a τ-type metal-free phthalocyanine, a plurality of steps including charging, electrostatic image formation, and development using colored toner are applied to the image carrier for each color of the toner. In a color image forming method in which a color image in which toner images are superimposed on the image carrier is formed by repeating the process several times, the process is repeated multiple times for each color of the toner to form a color image. A color image forming method characterized in that the absolute value of the developing bias potential for the second and subsequent colors is made higher than that in the process for at least the first color.