JPS63149661A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain an image with excellent balance by setting up the electrostatically charged capacity/mass of each developer in each developing device in proportional to the difference between the surface potential of an image carrier and the potential of a developing bias in each developing position at the time of forming an image of the image carrier. CONSTITUTION:A photoconductive layer of a photosensitive body to be an image carrier is constituted of a layer especially including epsilon-type copper phthalocyanine or gamma-type non-metallic phthalocyanine and developing devices 5-8 are arranged with prescribed intervals on the downstream side of the photoconductive layer so as to be opposed to the layer. When it is defined that the charged capacity of the developer in each developing device is Q (unit C) and its mass is M (unit g), the difference between the surface potential of each developing position and the developing bias voltage is made almost proportional and absolute values (Q/M)5>(Q/M)6>(Q/M)7>(Q/M)8 is defined. Even if dark attenuation is increased and a potential difference is reduced in accordance with a distance from a charging position, the Q/M is reduced in accordance with said changes so that toner adhesion can be sufficiently held.

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.

Prior Art Conventionally, as a color image recording method, Japanese Patent Application Laid-Open No. 56-144
The methods described in Japanese Patent Application Laid-open No. 452, Japanese Patent Application Laid-Open No. 58-116553 and Japanese Patent Application Laid-open No. 58-116554 are known.

The method described in JP-A-56-144452 is
After the surface of the photoreceptor as an image carrier is charged by a charger, an electrostatic image is formed on the charged surface by a first exposure means, and developed by a first developer, and then an electrostatic image is formed on the charged surface by a first developing device. An electrostatic image is formed by a second exposure means, which is developed by a second developing device, an electrostatic image is further formed by a third exposure means on the same charged surface, and the electrostatic image is developed by a third exposure means. This is a method of forming a colored toner composite image on an image carrier by developing with a developing device. JP-A-58-116553 and JP-A-58-116553
The method described in JP-A-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 device becomes larger and more expensive, and it is difficult to synchronize the exposure control of each exposure means.
Similarly, it has the problem of easily causing color shift.

In order to solve these problems, Japanese Patent Application Laid-Open No. 60-767
No. 66 and JP-A 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 lower in cost. By using a developing method, fogging, mixing and adhesion of different color toners are prevented.

That is, for example, in the apparatus shown in FIG. 1, 1 is a drum-shaped image carrier having a photoconductive surface made of Se or the like and rotating in the direction of the arrow; 4 is an image exposure device for each color of a color image; 5 to B are:
Each developing device uses toner of a different color, such as yellow, magenta, cyan, and black, as a developer. Reference numerals 9 and 10 denote a pre-transfer charger and a pre-transfer charger, respectively, which are provided as necessary to facilitate the transfer of a color image formed by superimposing a plurality of color toner images on the image carrier 1 onto the recording medium P. An exposure lamp, 11 a transfer device, and 12 a fixing device for fixing 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 far ply that separate from the surface of the image carrier 1 by the time the surface on which the first development has been performed reaches. However, when such a method is adopted, the surface potential of the photoreceptor undergoes dark decay, so that the surface potential of the photoreceptor differs at each development position.

In other words, between the developing device near the charging position and the developing device far from the charging position,
If the developing bias, charging current, and scorotron grid voltage are kept constant, the image density will differ when an image is formed.On the other hand, the method described in JP-A-53-60230 uses multiple developing devices. The developing bias of each latent image is controlled, but by forming one latent image, one
Since the latent image is only written once, it is only possible to perform multi-coloring on a line-by-line basis, and it cannot be applied when a plurality of colors are irregularly mixed in a line.

In addition, U.S. Patent No. 3357989,
The focused N/metal phthalocyanine described in No. 2639 is a GaAJA which is currently widely used as a semiconductor laser.
It has high enough sensitivity to the oscillation wavelength of 790 ns, which is the oscillation wavelength of s-based light-emitting particles, and has a long enough lifetime for practical use.

By using a photoreceptor using such a photosensitive material, good images and durability can be obtained in the image forming method described in JP-A-60-95456. However, in terms of density balance, the image is not fully satisfactory because the development potential at each development position is different.

OBJECTS OF THE INVENTION An object of the present invention is to provide an image forming method in which the density of images developed by each developing device can be obtained in a well-balanced manner without fogging or insufficient density.

Another object of the present invention is to easily control the adhesion of toner to an electrostatic image, not only in the case of a regular development method in which toner charged with opposite polarity is attached to an electrostatic image, but also in the case of a reversal development method. Another object of the present invention is to provide an image forming method that can obtain sufficient development density under non-contact jumping development conditions and can also prevent fogging and mixed adhesion of toners of different colors.

Still another object of the present invention is to form an image in which the same device is used for repeatedly forming electrostatic images, the recording device can be made compact and low-cost, and the synchronization control of image exposure can be easily and accurately controlled. The purpose is to provide a method.

21 Structure of the Invention That is, the present invention provides an image forming method in which steps including charging, electrostatic image formation, and development are repeated multiple times on an image bearing member, in which each development is performed by each developing device used for said development. Q/M of the developer in each developing device is approximately proportional to the difference between the surface potential of the image carrier (unexposed area and/or exposed area) and the developing bias potential at the position (where Q is Charge amount (unit: μc)
), M is mass (unit: g), respectively.

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

First, an image forming apparatus used in this embodiment will be explained with reference to FIG.

As mentioned above, in this device, the photoconductive layer of the photoreceptor, which is the image carrier 1, is formed of a layer containing a metal or a focused phthalocyanine, such as an ε-type copper phthalocyanine or a τ-type metal-free phthalocyanine. Descriptions of parts that are different from, but are common to, the apparatus are omitted.

It should be noted that in FIG. 1, according to the present invention, the Q/M of the developer in each developing device 5.6.7.8 is sequentially expressed as (Q/M)s, (Q/M)
a, (Q/M)? , (Q/M)e, the absolute value is (Q/M)s>(Q/M)e>(Q
/M)? > (Q/M)s.

Here, although the developing bias may be changed, it is assumed to be constant here. In this case, since the developing order of the developing device 5.6.7.8 is arbitrary, the order is set so that there is less mixing of toner and a clear image is obtained.

In this way, if Q/M is set respectively, the dark decay will increase according to the distance from the charging position, and even if the difference between the photoreceptor surface potential and the developing bias potential becomes small, the Q/M will be adjusted accordingly.
Since the amount of toner adhering to the surface of the photoreceptor can be maintained sufficiently, the amount of toner adhering to the surface of the photoreceptor can be maintained sufficiently.

Here, the methods for controlling Q/M include (1) components of carrier coating resin (for example, methyl methacrylate/styrene mixture ratio), (2) mixture ratio of external additives (for example, silica), and (3) toner concentration. (4) Type of toner resin (5) Changing the intensity and time of the toner/carrier mixing process.

FIG. 2 shows a color image forming process using a reversal development method, and FIG. 3 shows a color image forming process using a regular development method.

For image exposure 4, a laser beam scanner shown in FIG. 4 is used. In this system, 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 an r-θ lens 2 for imaging is used.
4 to form an image exposure 4 that scans the surface of the image carrier 1 at a constant speed.

Note that 25 and 26 are mirrors, and 27 is an imaging f-θ lens 24 to reduce the diameter of the beam on the image carrier 1.
This lens is used to expand the diameter of the beam that enters the beam. If a laser beam scanner as shown in FIG. 4 is used to form the image exposure 4, electrostatic images of 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 like a belt, the image exposure can also be flash exposure.

As the developing units 5 to 8, those having a structure as shown in FIG. 5 are preferably used. In FIG. 5, 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 scratches in the circumferential direction, and 33 is a developing sleeve. A layer thickness regulating blade 34 that regulates the thickness of the developer layer formed on the sleeve 31 is a scraper blade that removes the developer layer after development from on the developing sleeve 31. 3
5 is a stirring rotating body that stirs the developer in the developer reservoir 36;
37 is a toner hopper; 38 has a recess on the surface into which the toner enters; and a developer reservoir 36 from the toner hopper 37
A toner supply roller 39 supplies toner to the developing sleeve 31 by applying a bias voltage including an oscillating voltage component in some cases to the developing sleeve 31 via a protective resistor 40.
This is a power source for forming an electric field that controls the movement of toner between the image bearing member 1 and the image bearing member 1 .

In addition, in the above, after the second repetition
□Development is preferably performed without bringing the developer layer formed in the developing device into contact with the surface of the image carrier. 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 the examples of the present invention will be explained. This developer is a two-component system, and a different developer is used for each developer, but it usually consists of the following resin-coated carrier and toner, and these are prepared as follows.

(Preparation of resin-coated carrier) A styrene-methyl methacrylate copolymer having a desired monomer composition ratio of styrene and methyl methacrylate, for example 30:70 (for example, "VrTt: 82,0
00, Mn: 25,000, 'r'g: 110°C
) was dissolved in 300 mff1 of methyl ethyl ketone to prepare a coating solution. Ferrite was coated with this coating solution using a Subira coater (manufactured by Kaida Seiko Co., Ltd.), and the film thickness was 1.0 μm.
A carrier with m coating layers was produced. For example, this carrier has an average particle size of 30μ and a magnetization of 25e+++u.
/ g, specific resistance is 10 Ω-1 or more, specific gravity 5.2 g
/cd.

(Preparation of Toner) For example, 100 parts by weight of polyester resin, 3 parts by weight of polypropylene 660p (manufactured by Kochu Kasei Kogyo Co., Ltd.), and 10 parts by weight of carbon black: Monigal L (manufactured by Cabot Corporation) were mixed in a Henschel mixer. Thereafter, the mixture was sufficiently kneaded with three rolls at a temperature of 140° C., allowed to cool, coarsely pulverized, then pulverized with a jet mill and classified to obtain a “black toner” having 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 in the same manner as the black toner. ”
I got it.

(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, an image was formed 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 area becomes an electrostatic image with a lower potential than the background area, and the development process uses toner that charges the electrostatic image to the same polarity as the background area potential. This method (reversal development) is carried out by the adhesion of .

At the first time, charging is carried out by the charging electrode 2, and the image exposure 4 for each color is projected by the laser beam scanner shown in FIG. The image exposure shown in the figure was carried out. The obtained electrostatic image is first developed by one of the developing devices 5 to 8 that uses a developer of a color toner corresponding to image exposure 4, and then the image carrier (or image forming The surface of the body) 1 is uniformly charged again by the charging electrode 2, and the charged surface is subjected to a second image exposure, and then a second development is performed, and the third and fourth electrostatic images are then formed in the same manner. Formation and development were repeated.

In this way, 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. The AC bias was 2kllzS 1kV.

For example, using copper phthalocyanine as a photoreceptor, the following four methods (
In the processes a to d), the Q/M of the developer of each developer is set according to the difference between the surface potential (this can be measured with a surface potential needle) and the bias potential at the development position of each developer. did. However, in the following, × indicates poor, △ indicates slightly poor, ◯ indicates good, and ◎ indicates very good. Further, MMA is methyl methacrylate, and St is styrene.

Reverse development (reversal development) Linear velocity of photoreceptor = 58+n/sec Scorotron grid voltage = -800V Carrier generating substance of photoreceptor: metal-free phthalocyanine The results are shown in Table 1 below.

(The following is a margin, continued on the next page.) From this result, as in Examples a and b, based on the present invention, the Q/M4 of each developing device is approximately proportional to the difference between the developing bias potential and the surface potential. If each adjustment is made, the color tone will be good or very good. However, in examples c and d in which such Q/M adjustment is not made, the results are poor.

Dish I (regular development) Linear speed of photoreceptor = 58 W/sec Scorotron grid voltage - 800 V Carrier generating substance of photoreceptor: w4 phthalocyanine The results are shown in Table 2 below.

(The following is a margin, continued on the next page.) From this result, as in Examples e and f, based on the present invention, the Q/M of each developing device is determined approximately in proportion to the difference between the developing bias potential and the surface potential. Adjustment results in good or very good color tone. However, example g in which such Q/M adjustment is not made
, h gives a poor result.

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, the nine types of phthalocyanine used, their content, etc. may be varied based on known techniques, and the type of toner, arrangement of developing devices, operating order, etc. may also be varied.

Effects of the Invention As described above, the present invention sets the developer Q/M approximately in proportion to the difference between the surface potential of the image carrier and the development bias potential at each development position by each development device. Therefore, the density of the image developed by each developing device can be obtained in a well-balanced manner without guffling or insufficient density.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, in which Fig. 1 is a schematic diagram of the main parts of an image forming apparatus, Figs. 2 and 3 are flowcharts of processes by each developing method, and Fig. 4 is a laser beam scanner. FIG. 5 is a sectional view of the developing device. In addition, in the symbols shown in the drawings, 1... Image carrier 2... Charger 4... Image exposure 5.6.7 .8...Developer 12...
...Fuser 14...Cleaning device PH...
...Exposed area DA...Non-exposed area T, T...Toner.

Claims (1)

[Scope of Claims] 1. An image forming method in which a step including charging, electrostatic image formation, and development is repeated multiple times on an image bearing member, in which each developing device used for the development is used at each developing position. Q/M of the developer in each developing device is approximately proportional to the difference between the surface potential of the image carrier and the developing bias potential. is g). ] is set respectively.