JPS63168664A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain specified charge potential so that an image having stable color tones and density is obtd. by controlling the 2nd and ensuing charge currents to the value smaller than at least the value of the 1st charge current. CONSTITUTION:The voltage and/or current insulation values of the 2nd and ensuing charge electrode are controlled to the values smaller than at least the value of the 1st charge electrode in an image forming method in which an image carrier 1 contg. metallic phthalocyanine and/or nonmetallic phthalocyanine is used and a stage including electrostatic charge, formation of an electrostatic charge image and development is repeated plural times with the image carrier 1. For example, the charge currents of the 2nd and ensuing times are preferably controlled to the insulation values smaller by >=4% than the value of the 1st time. The charge potential of the metallic or nonmetallic phthalocyanine having the sufficient sensitivity to a semiconductor laser is thereby stabilized and the image having the stable color tones and sufficient density without having fogging is obtd.

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, recording devices have become larger and
Similarly, this method has the problems of high cost, difficulty in synchronizing the exposure control of each exposure means, and easy 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 electrostatic images on an image carrier using the same device, the recording device can be made smaller and less costly, and non-contact development using a two-component developer is proposed. This method prevents fogging, mixing and adhesion of different colored toners.

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, in JP-A-60-76766 and JP-A-60-95456, it is described that a scorotron charger is used to provide stable charging; It was found that it is not easy to provide a constant charging potential multiple times using only a scorotron charger, and that the charging potential tends to fluctuate. In particular, when charging, electrostatic image formation, and development are repeated for each color in one color image forming process, the charging potential of the first color and the second color are
The charged potentials of different colors often differ. In addition, in such cases, in order to simplify the process, if the static elimination step between development and the next charging process is omitted,
The charging potential becomes even more likely to become 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.

Incidentally, in recent years, semiconductor lasers have been developed that are small, low cost, capable of direct modulation, and expected to be highly reliable. The oscillation wavelength of such a semiconductor laser is 7
50 nm or more, and is sensitive to light in such a long wavelength range, for example, Japanese Patent Application Laid-Open No. 58-100
No. 134 contains a photoreceptor containing ε-type copper phthalocyanine,
Further, JP-A-58-182639 describes a photoreceptor containing a τ-type metal-free phthalocyanine. Although photoreceptors using these metals or achromatic phthalocyanine are sensitive to the oscillation wavelength of semiconductor lasers,
When used as an image carrier in a color image recording method such as No. 0-76766 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 is improved.

C.6 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.

29 Structure of the Invention That is, the present invention uses an image bearing member containing metal phthalocyanine and/or metal-free phthalocyanine, and performs a step including charging, electrostatic image formation, and development on the image bearing member. An image forming method that is repeated multiple times, characterized by making the absolute value of the voltage and/or current of the charging electrode in the second and subsequent times smaller than that in the first time (setting the charging conditions so as to make it smaller) The invention relates to an image forming method.

In the present invention, the above-mentioned "voltage and/or current of the charging electrode" applies not only to the original electrode of the charging electrode, but also to the grid electrode if a grid electrode exists, and therefore applies to the original charging electrode. This means the charging electrode voltage, high-voltage power supply current flowing into the charging electrode, or grid voltage.

This "voltage and/or current of the charging electrode" may be referred to as "charging current of the image carrier" below.

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

First, the image forming apparatus used in this example is shown in Figures 1 to 3.
This will be explained with a diagram.

In the apparatus shown in FIG. 1, 1 is a metal phthalocyanine and/or
or a drum-shaped image carrier having a photoreceptor surface layer of metal-free phthalocyanine and rotating in the direction of the arrow, 2 is the image carrier 1;
4 is an image exposure for each color of a color image; 5 to 8 are each developer in which toner of a different color such as yellow, magenta, cyan, and black is used as a developer. It is a vessel. 9 and 10 are image carriers I
A pre-transfer charger and a pre-transfer exposure lamp are provided as necessary to facilitate the transfer of a color image formed by combining a plurality of color toner images onto a recording medium P; 1;
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.

(The laser beam scanner shown in FIG. 2 is used for the tJ light 4. In this, 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 image is formed. Image exposure 4 is formed by scanning the surface of the image carrier 1 at a constant speed through the f-theta lens 24.

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. 2 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. 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. A layer thickness regulating blade 34 regulates the thickness of the developer layer formed on the developing sleeve 31, and a scraper blade 34 removes the developed developer layer from 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, the second and subsequent development steps are
It is preferable to carry out this process 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 this example will be explained.

This developer is a two-component system and consists of the following resin-coated carrier and toner, which are prepared as follows.

(Preparation of resin-coated carrier) The monomer composition ratio of styrene and methyl methacrylate is 3.
0:70 styrene-methyl methacrylate copolymer (Mw: 82,000.Mn: 25,
000, Tg: 110℃) to methyl ethyl ketone 300
mjl! A coating solution was prepared by dissolving it in Ferrite was coated with this coating liquid using a Subira coater (manufactured by Kaida Seiko Co., Ltd.), and carrier A had a coating layer with a thickness of 1.0 μm.
was manufactured. This carrier A has an average particle size of 30 μ, magnetization of 25 emu/g, specific resistance of 10 Ω or more, and specific gravity of 5.2 g/co! Met.

In addition, vinylidene fluoride-tetrafluoroethylene copolymer r
VT-100J (manufactured by Daikin Industries, Ltd.) in acetone
Carrier B was prepared in the same manner as carrier A except that methyl ethyl ketone (1:1) was dissolved in 300 mβ.
I got it. The average particle size of this carrier B is 30 μm, the magnetization is 25 emu/g, the specific resistance is 1014 Ω-1 or more,
The ratio M was 5.2 g/crA.

(Preparation of toner) 100 parts by weight of polyester resin, polypropylene 660
p (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, the mixture was thoroughly kneaded with three rolls at a temperature of 140°C, allowed to cool, coarsely ground, then ground with a jet mill, classified, and the average particle size was 1O.
A "black toner" of .mu.m was obtained.

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 performed by the charging electrode 2, and the image exposure 4 of each color is projected by the laser beam scanner shown in FIG. Image exposure was performed. The obtained electrostatic image was first developed by one of the developing devices 5 to 8 using a developer of a color toner corresponding to image exposure 4. Next, the image bearing member (or image forming member) 1 as it is (that is, without being transferred)
The surface of the image 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 image formation and development are performed in the same manner. 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 2 kHz and 1 kV. Examples based on the present invention will be described below together with comparative examples, and FIG. 4 shows them together.

−11, 2, 3, 4, 5, 6 and 1.2.3τ−
Type-free metal phthalocyanine (manufactured by Toyo Ink Co., Ltd.) and ε-type copper phthalocyanine (Glue Onor Blue, manufactured by Toyo Ink Co., Ltd.)
When using OPC (organic photoconductive substance) containing OPC, if the charging conditions for the first color and the second color and subsequent colors are the same as in Comparative Example 1.2.3, the charging potential of the first color is low; 1st
A fog appears in the color. . Moreover, the charging potential of the second and subsequent colors increases significantly, which is unsatisfactory. In contrast, Example 1
．． As shown in 2.3.4.5.6, set the outflow current value of the high voltage power supply, the voltage of the high voltage power supply, or the grid voltage of the scorotron so that the inflow current of the photoreceptor for the second color and subsequent colors is sufficiently smaller than that of the first color. If the charging current of the photoconductor is set to be small for the second and subsequent colors, the charging potential of the first to fourth colors will be almost the same, and each color will have sufficient density and no fog. An image with good color tone was obtained.

For this 124 discharge 1/J-3e/'l'6 photoconductor and a-3tGe photoconductor, charging conditions are set so that the current flowing into the photoconductor after the second color is smaller than that for the first color. Even without it, the charged potentials of each color will be almost equal.

However, Se/Te has insufficient sensitivity to semiconductor lasers, and sufficient image density cannot be obtained. Also,
a-3iGe 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 a metal or a metal-free phthalocyanine having sufficient sensitivity to a semiconductor laser can be stabilized, and a stable color tone and sufficient density can be obtained. , it is possible to obtain images without gabbing.

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, it is preferable that the charging current of the photoreceptor described above is lower by 4% or more in absolute value than that of the first color for the second and subsequent colors. Further, even after the second color, the value of the charging current may be changed each time, or it may be changed only partially and kept constant in other times. Further, when adjusting the grid voltage, it is preferable that the grid voltage for the second and subsequent colors is lowered by at least 30 V in absolute value than that for the first color. Further, the type and content of the phthalocyanine used may be variously changed based on known techniques, and the type of toner, the arrangement of the developing device, the order of operation, etc. can also be changed.

Effects of the Invention As described above, the present invention provides the following advantages:
By changing the charging conditions after the first and second charging,
Since the charging current after the first charging is made to be at least smaller than that at the first charging, the inherent property of metal or metal-free phthalocyanine that the charging potential at the first charging is lower than that after the second is canceled. As a result, a constant charging potential can be obtained, and an image with stable color tone and density can be obtained.

[Brief explanation of the drawing]

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. The figure is a table showing a comparison of data on each side. In addition, in the symbols shown in the drawings, 1... Image carrier 2... Charger 4... Image exposure 5.6.7 .8...Developer 12...
. . . Fixing device 14 . . . Cleaning device.

Claims (1)

[Claims] 1. In an image forming method using an image carrier containing metal phthalocyanine and/or metal-free phthalocyanine, steps including charging, electrostatic image formation, and development are repeated multiple times on the image carrier. An image forming method characterized in that the absolute value of the voltage and/or current of the charging electrode in the second and subsequent times is at least smaller than that in the first time.