JPH05265295A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain a fine color image by making toner adhesion quantity always uniform everywhere in an image forming method of lapping toner over a photoconductor so as to uniform color reproduction. CONSTITUTION:Using a KNC(Konica color) process, a static elimination process of photoconductor surface potential immediately before image exposure or a static elimination process of only a non-image part further using a page memory is interposed in a normal image forming proces of electro static charge exposure developing so as to smoothen electrostatic latent image potential after the following image exposure. A color image of desirable color reproducibility is obtained by repeating this cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method, and more particularly to an improvement in a color image forming method by electrophotography, and more particularly to a method for uniformizing the surface potential of a photoreceptor surface immediately before image exposure.

[0002]

2. Description of the Related Art As a color image forming method by electrophotography, a photosensitive member surface uniformly charged with a color-separated optical signal is used.
An electrostatic latent image formation process that converts an optical signal into an electric signal by repeatedly exposing the image in the number of separated colors (usually adding black) and electrostatically or rheology is used to electrostatically charge the charged fine particles. It consists of a visible image forming process of adhering to a latent image and then fixing it onto paper or the like. Of these, those particularly related to the present invention are charging, exposure and development.

Conventionally, selenium or a selenium alloy has been used most frequently as an electrophotographic photosensitive member as a photosensitive layer. However, in recent years, organic photoconductors (OPC) for electrophotography have begun to be used as a substitute for metals that realize higher conductivity. However, most of the photoconductors have a negative charging operation, and up to the present, few examples of the positive charging operation have been put to practical use. N for negative charging operation
For charging the PC, a scorotron charger having excellent uniformity of charging potential is used.

Halogen lamps and LEDs for image exposure and charge removal
An array, an LD (semiconductor laser), or the like is used, and the developing method is generally reverse development. The reversal development method is to form an electric field on the surface of a uniformly charged photoconductor with the help of a developing electrode by exposing the surface of a uniformly charged photoconductor in the separated color of reflected light corresponding to the density of the original image. This is a developing method in which toner charged to the same polarity as that of uniform charging is attached by this electric field.

[0005]

As described above, in the color image forming apparatus, uniform charging, image exposure and reversal development are performed by one rotation of the photoconductor, and this is repeated a plurality of times. The density of the toner image is closely related to the amount of decrease in the surface potential of the photoconductor due to exposure. Therefore, it is desirable that the surface potential of the photoconductor surface immediately before the image exposure is made uniform. On the other hand, for a photoconductor on which a toner image has been once subjected to uniform charging, image exposure, and reversal development, the surface potential after recharging is uneven and the potential difference after recharging between the toner image portion and the non-toner image portion is large. However, the latent image potential after the next image exposure is not smooth, and there is a difference in developability, resulting in poor color reproducibility. There is not much conventional technology to deal with this, and it is slightly disclosed in JP-A-60-7.
As can be seen in 6766, in JP-A-60-76766, the electric potential after reversal development on the surface of the photoconductor is excessively discharged (about 0 V), and the polarity of the toner is changed, so the transferability is deteriorated. .. Also, if the charge amount of the toner on the surface of the photoconductor becomes too small, the adhesive force between the toner and the surface of the photoconductor becomes small, causing toner scattering, color mixing to other developing devices, and disturbance of the toner image. was there.

[0006]

An image forming method in which toner is superposed on the surface of a photoconductor, particularly, the surface potential of the photoconductor just before image exposure is made uniform, and thereby, the same developability can be output anywhere on the photoconductor surface. The problem is solved by obtaining a beautiful color image for a long period of time by always making the toner adhesion amount uniform and making the color reproduction uniform.

[0007]

【Example】

Example 1 Hereinafter, the present invention will be described in detail with reference to the illustrated examples.

FIG. 1 is a schematic configuration diagram showing an example of a recording apparatus for carrying out the method of the present invention, FIG. 2 is a schematic configuration diagram of a laser beam scanner for image exposure, and FIG. 3 is a partial sectional view showing an example of a developing device. FIG. 4, FIG. 4 and FIG. 5 are flow charts for implementing the method of the present invention.

In the recording apparatus of FIG. 1, 1 is an organic photosensitive member OPC (hereinafter abbreviated as photosensitive member) which rotates in the direction of the arrow, 2
Is a charging device scorotron for uniformly charging the surface of the photoconductor 1,
4 is exposure light, 5 to 8 are developing devices in which toners of different colors such as yellow, magenta, cyan, and black are used as developers, and 9 and 10 are multicolor toner images on the photoconductor 1. A pre-transfer charger and a pre-transfer exposure lamp, which are provided as necessary to facilitate transfer of the color images formed by superposition to the recording medium P, 11 is a transfer device,
12 is a fixing device for fixing the toner image transferred to the recording medium P, 13 is a scorotron charge eliminator, and 14 is a surface of the photoconductor 1 after the color image is transferred to contact the surface thereof to remove the residual toner on the surface. The cleaning device has a cleaning blade and a fur brush that are separated from the surface of the photoconductor 1 by the time the surface on which development has been performed once arrives.

Here, the charging device 2 is a scorotron corona discharge device capable of giving stable charging with little influence of the previous charging, particularly for a charging device which is superposed on the surface of the already charged photosensitive member 1. It is preferable to use an electric appliance. Also,
In this recording apparatus, the exposure means is preferably a laser beam scanner as shown in FIG.
An exposure means such as D, CRT, or liquid crystal that performs image exposure with image information input by electric signals is used.

The laser beam scanner of FIG. 2 has a wavelength of 780 nm.
The laser beam emitted from the semiconductor laser 21 is ON / OFF-modulated by the pulse width modulation method, and is deflected by the mirror scanner 23 composed of a rotary polygon mirror, and the f-θ lens 24 for imaging is formed.
The exposure light 4 for scanning the surface of the photoconductor 1 at a low speed is formed therethrough. Numerals 25 and 26 are mirrors, and 27 is an image forming f-θ lens 24 in order to reduce the diameter of the beam on the photoconductor 1.
It is a lens for enlarging the diameter of the beam incident on. A laser beam scanner as shown in FIG. 2 is used as the exposure means, and in each image forming step, exposure is performed with light of the same wavelength by a single semiconductor laser. However, such color image recording is not limited to dot exposure with a laser beam, and it is also possible to use, for example, an LED, a CRT, or a liquid crystal device.

The developing devices 5 to 8 preferably have a structure as shown in FIG. 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 having a plurality of magnetic poles in the circumferential direction, 33 is a layer thickness regulating blade for regulating the thickness of the developer layer formed on the developing sleeve 31, and 34 is the developing sleeve 31. A scraper blade for removing the developer layer after development from above, 35 is a stirring rotator for stirring the developer in the developer reservoir 36, 37 is a toner hopper, 38 is a toner hopper having a recess for the toner to enter on the surface, and a toner hopper 37 From the developer pool
Toner replenishing roller to replenish toner to 36, 39 to protect resistance
A power supply for applying a bias voltage containing an oscillating voltage component to the developing sleeve 31 via 40 to form an electric field for controlling the movement of the toner between the developing sleeve 31 and the photoconductor 1. Is the developing sleeve 31 and the magnet body 32.
Indicate that the developing sleeve 31 is fixed, the magnet body 32 is fixed, or the developing sleeve 31 and the magnet body 32 are in the same direction. It may be something that rotates. Magnet body 32
In order to fix the magnetic flux density, in order to make the magnetic flux density of the magnetic pole facing the photoconductor 1 larger than the magnetic flux density of other magnetic poles,
The magnetization is strengthened or two magnetic poles having the same or different polarities are provided close to each other.

In such a developing device, the magnetic poles of the magnet body 32 fixedly arranged inside the developing sleeve are magnetized to have a magnetic flux density of usually 500 to 1500 gauss, and the magnetic force causes the developer to collect on the surface of the developing sleeve 31. Adsorbs 36 developers. The thickness of the adsorbed developer is regulated by the layer thickness regulating blade 33 as the developing sleeve 31 rotates to form a developer layer, and the developer layer is in the same direction as the rotational direction of the photoconductor 1 or in the opposite direction. In the developing area in which the surface of the developing sleeve 31 faces the surface of the photoconductor 1, the electrostatic image on the photoconductor 1 is developed. After that, the scraper blade 34 removes it from the surface of the developing sleeve 31 and returns it to the developer reservoir 36. Then, the development is repeated for overlapping the color toner images so that the toner adhered to the photoconductor 1 in the previous development will not be displaced in the subsequent development, at least for the second and subsequent developments. The non-contact jumping development condition is preferable. FIG. 3 shows a state of developing under non-contact jumping developing conditions.

Further, for the developing devices 5 to 8, it is preferable to use a so-called two-component developer comprising a mixture of a non-magnetic toner and a magnetic carrier which can easily control the charging of the toner. In particular, magnetic carriers include resins such as styrene-based resins, vinyl-based resins, ethylene-based resins, rosin-modified resins, acrylic resins, polyamide resins, epoxy resins, and polyester resins, and iron tetroxide, γ-ferric oxide, and dioxide. From those in which fine particles of ferromagnetic material or paramagnetic material such as chromium, manganese oxide, ferrite, manganese-copper alloy, etc. are dispersedly contained, or the surface of the particles of these magnetic materials is coated with the resin as described above. And has a resistivity of 10 ⁸ Ωcm or more, preferably 1
It is preferable that the carrier is an insulating carrier of ¹³ Ωcm or more.

If the average particle size of the carrier is less than 5 μm, the magnetization becomes too weak, and if it exceeds 80 μm, the image tends to be easily damaged. Further, in the case of a carrier having a relatively low resistivity (10 ⁸ Ωcm to 10 ¹² Ωcm), breakdown or discharge is likely to occur, and a high voltage tends not to be applied, so that the average particle size is 5
It is preferably from 80 μm to 80 μm and more preferably from 20 μm
50 μm is more preferable. If necessary, a fluidizing agent such as hydrophobic silica is appropriately added as an additive.

The toner preferably has an average particle size of 1 to 20 μm, which is obtained by adding various pigments and a charge control agent to the resin, and when the average particle size is less than 1 μm, it becomes difficult to separate from the carrier and exceeds 20 μm. And the resolution of the image will be reduced. Further, 4 μm to 8 μm is more preferable because it is less affected by process problems of development and cleaning.

When the developer composed of the mixture of the insulating carrier and the toner as described above is used, the developing sleeve 31 shown in FIG.
It is possible to easily set the bias voltage to be applied to the toner so that the toner is sufficiently attached to the electrostatic latent image and the fog does not occur, without causing a leak. It should be noted that, in order to more effectively control the development movement of the toner by applying such a bias voltage, the toner may contain a magnetic material that is used as a magnetic carrier within a range that does not impair the sharpness of color. Is also good.

In this embodiment, a negatively charged organic photoconductor (O
PC) 1 in the charger 2 in the scorotron system (DC
By negative corona discharge), it is charged with scorotron 7.0KV and grid potential -820V. The discharge wire has a diameter of 0.06 m
It consists of two tungsten oxide films of m, and the grid wire uses 14 stainless steel wires with a diameter of 0.1 mm.
For image exposure, a semiconductor laser having a wavelength of 780 nm is used, and the laser used as the light source for the image signal is pulse-width modulated to multi-value one dot to 256 gradations / pixel.

Next, the reversal development method of the white part potential V _H = −800 V and the black part potential _VL = −50 V is used. The two-component developer used is a ferrite core resin-coated with a weight average particle diameter of 35 μm + A polar carrier and a negative polarity toner having a weight average particle size of 6 μm. During this non-contact development, a bias component V _PP = 1.8 KV and a frequency F = from a power source (not shown) to a DC component with a bias potential V _DC = −600 V.
4KH developing bias obtained by superposing an AC component of _Z is applied to the developing sleeve 31, as a result, the developer on the developing sleeve 31 in the developing abutment, the electrostatic toner alone is selectively transition Adhere to the surface of the latent image.

4 and 5 are flow charts showing the embodiments of the present invention, and these embodiments can be carried out by using the recording apparatus described above. 4 and 5 all show up to the stage where the second development is performed.

FIG. 4 shows a case where yellow, magenta, and cyan toner images of the electrostatic latent image are formed at different positions on the photosensitive member 1. In the initial stage (static elimination), the static eliminator 13 in FIG. By the cleaning by the cleaning device 14, there is no toner on the photoconductor 1 and the surface potential thereof is zero. The surface of the photoconductor 1 in the initial state is uniformly charged by the charger 2 in the first rotation, and the charged surface is subjected to dot exposure by the laser beam scanner of FIG. The first dot exposure of 0 is performed, and the obtained electrostatic latent image is first developed with the yellow toner of the developing device 5. After this development, normally the second uniform charging is performed.
In the present invention, the second color toner adhesion amount does not differ depending on the presence or absence of the yellow toner image of the first development.
Before the second recharging (after the first development), the surface potential of the photoconductor 1 is uniformly smoothed, and the surface potential of the photoconductor 1 is reduced by neutralization so as to be approximately equal to the surface potential of the yellow toner image layer. This static elimination may be AC corona static elimination, or DC superimposition on this, or DC static elimination. In this embodiment, after the first development, static electricity is removed at a potential V _S (1) = − 120 V to reduce the surface potential of the photoconductor 1 to V _T (one color).
= -100V (± 30V). Next, even after the second uniform charging, the surface potential of the photoconductor 1 is naturally substantially uniform. In this state, if the development with magenta toner is carried out after the second image exposure, the electrostatic latent image potential of the same developing property is uniformly smoothed, so that the color reproducibility is excellent. At this time, since the magenta electrostatic latent image does not overlap the yellow toner image, the charge elimination potential of the second time and the surface potential of the photoconductor 1 after the charge elimination are exactly the same as those of the first time. Similarly, the fourth color is transferred to the transfer step without charge removal (the charge may be removed).

FIG. 5 shows a case where two colors overlap, for example, a yellow toner image and a magenta toner image. The first charge after the initial state, the first exposure, and the first charge removal after the first development were performed at V _S (1) = − 120 V, and the surface potential of the photoconductor 1 was set to approximately the yellow toner image layer. Surface potential V _T (1 color) =-100
Align to V (± 30V). V _S (2) during the second charge removal
= Remove electricity at -230V. Yellow toner after the second development,
The surface potential of the superimposed image of magenta toner is V _T (two-color overlapping)
= -220V (± 40V).

Generally, 3 is a two-color superposition in which no two toner images of yellow, magenta and cyan overlap.
In each case of color superimposition, the surface potential of the toner image after charge elimination is V _T (1 color) = − 100 V (± 30 V), V _T
(2 color overlay) = -220V (± 40V), V _T (3 color overlay) =
It is −350V (± 50V). The static elimination potential after development is the first color,
At the time of static elimination after the second and third colors, respectively, V _S (1) = − 1
_{20V, V S (2) =} - 230V, V S (3) = - for discharge potential of 350 V. The switching of the static elimination potential is adjusted by making the grid potential of the static elimination scorotron variable.

Example 2 In Example 1, after the charging, the image exposure, and the development, AC corona discharge of the non-toner image area (non-image area) was performed. Example 2 takes different measures for the same purpose. That is, instead of the AC corona discharge operation of the first embodiment, an exposure means is used which performs weak exposure (compared to image exposure) only on the non-toner-attached portion, that is, the non-image portion which is the non-light-receiving portion. In a digital color copying machine, a color printer, etc., yellow Y, magenta M, and cyan C information are temporarily stored in a page memory, and image exposure is performed on the photoconductor 1 based on this information, and at least Y, M, C, (black When performing color recording with BK) toner, after the development with each color toner, the output of the same color information stored in each page memory is reversed by an appropriate signal processing circuit, so that only the non-image portion has the same color information. The exposure is weaker than the image exposure intensity in which the color information is written. This block diagram is shown in FIG. However, B, which is the final color of the four-color seven-rotation process shown in FIG.
If re-exposure is not performed after K toner development, the LD power for image exposure and charge removal is 1.5 mW during image exposure in the 4-color 8-rotation process.
By setting the LD power in the non-image area at the time of static elimination to 0.8 mW, the potential of the exposed portion of the photoconductor can be made approximately the toner layer potential. Further, when toners of three colors and four colors overlap, it is preferable to control the LD powers respectively. In the four-color four-rotation process shown in FIG. 8, a semiconductor laser beam scanner different from that used for image exposure is used for image exposure at a position downstream of the developing device group. Further, an LED array or a liquid crystal device device may be used for exposing the non-image area.

[0025]

EFFECT OF THE INVENTION By equalizing the potential after recharging in both the portion with the toner layer and the portion without the toner layer, the potential drop due to the next image exposure can be made uniform. Therefore, the same amount of toner adheres in the next development at both places, and the color reproduction can be improved. The potential can be made uniform without making the corona current during recharging extremely large. Compared to JP-A-60-76766, since proper charge removal is performed, transferability is good and color reproducibility after transfer is also good.

Further, since the charge is removed to approximately the potential of the toner image,
It is possible to prevent toner scattering and color mixing without significantly reducing the adhesive force between the toner and the photoconductor. Therefore, a color image with high image quality and high color reproducibility can be reproduced over a long period of time.

[Brief description of drawings]

FIG. 1 Schematic diagram of the configuration around a photoconductor

FIG. 2 is a schematic configuration diagram of a laser beam scanner as an exposure unit that performs dot exposure.

FIG. 3 is a partial cross-sectional view showing an example of a developing device.

FIG. 4 is a flowchart for explaining the implementation of the method of the present invention.

FIG. 5 is a flowchart for explaining the implementation of the method of the present invention.

FIG. 6 is a block diagram illustrating an implementation of the method of the present invention.

FIG. 7 is an explanatory diagram of Example 2.

FIG. 8 is an explanatory diagram of the second embodiment.

[Explanation of symbols]

 1 Photoreceptor 2 Charging Device 4 Exposure Light 5 Developer 6 Developer 7 Developer 8 Developer 10 Pre-Transfer Exposure Lamp 11 Transferor 12 Fixer 13 Static eliminator 14 Cleaning Device P Recorder 21 Laser 22 Acousto-optic Modulator 23 Mirror Scanner 25 Mirror 26 Mirror 27 Lens 31 Development sleeve 32 Magnet body 33 Layer thickness regulating blade 34 Scraper blade 35 Agitation rotor 36 Developer pool 37 Toner hopper 38 Toner supply roller 39 Power supply 40 Protection resistance

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G03G 21/00 307

Claims (4)

[Claims] 1. An image forming method for forming a composite toner image by repeating uniform charging, image exposure, and reversal development on a photoreceptor a plurality of times, after the reversal development other than final reversal development,
An image forming method comprising the step of equalizing the surface potential on the photoconductor. 2. The image forming method according to claim 1, wherein the target potential for making the surface potential uniform is substantially the potential of the toner layer. 3. An image forming method for forming a composite toner image by repeating uniform charging, image exposure, and reversal development on a photosensitive member a plurality of times. In the image forming method, after the image exposure and reversal development, the image exposure is not performed. An image forming method, which comprises at least one step of exposing only a non-image portion that was a light receiving portion. 4. The image forming method according to claim 3, wherein the illuminance during exposure of the non-image portion is smaller than the illuminance during image exposure.