JPH05181340A - Polychrome image forming method and device - Google Patents

Abstract

PURPOSE:To provide a high quality output image by forming a latent image so that a latent potential of the image part on which no toner image is formed, and a toner layer potential of the image part before development, on which a toner image is formed, satisfy a specific relationship, thereby equalizing developing potentials on the toner adhered part and the bare part on a photoreceptor. CONSTITUTION:A polychrome image forming device consists of a photoreceptor drum 11, an electrification charger 12, developing machines 13-16, a transfer charger 18, a separation charger 19, etc. A reference power of a laser beam from a writing device is set by an exposure value setting means so that a latent potential of the bare part on the photoreceptor drum 11, on which no toner layer is formed, is at least above a toner layer potential. When exposure is performed on the photoreceptor drum 11 from above the toner layer by means of the writing device, the power of the laser beam from the writing device is raised above the reference power by the exposure value setting means, and a surface potential of the bare part on the photoreceptor drum 11 and a latent potential of the image part exposed through the toner layer become almost constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming method and a multicolor image forming apparatus.

[0002]

2. Description of the Related Art The one-drum color-overlap-one-rotation method is known as one of the color electrophotographic multicolor image forming methods used in color hard copy apparatuses such as color copying machines and color printers. This 1-drum color-overlap 1-rotation system
Uniform charging by corona charging of the photosensitive drum,
An image forming process of forming a latent image by exposure to a laser beam and developing the latent image with color toners is repeated for images of a plurality of colors, for example, yellow, magenta, cyan, and black images, and is repeated. This is a method in which a multicolor visible image is formed on a drum and then this multicolor visible image is transferred onto a recording sheet once.

In this one-drum color-overlap-one-rotation system, a transfer drum and the like are not required, so that the size is small and the cost is low, there is a paper-free property due to the linear conveyance of the recording paper, and the color shift at the time of transfer is small. However, there is a process of corona charging from the toner layer formed on the photoconductor to charge the photoconductor drum, performing image exposure from the toner layer, and superimposing toner images of different colors again. Therefore, due to the shielding of the laser beam by the toner layer, the toner layer holding charge, and the like, the amount of toner adhering to the superposed toner image decreases, and the color balance of the superposed toner image cannot be obtained. Further, the latent image potential due to exposure to a portion of the photosensitive drum where the toner image is not formed is different from the latent image potential due to overlapping exposure from the toner layer, and similar image reproducibility cannot be obtained. ..

To solve these problems, basically, even when image exposure is carried out from the toner layer on the photoconductor drum, the part where the toner layer is not formed on the photoconductor drum (here The image forming conditions may be controlled so that the same development potential can be obtained even when the image exposure is performed on the bare portion). As a multicolor image forming method or a multicolor image forming apparatus based on such an idea, the following techniques are conventionally known.

First, in Japanese Laid-Open Patent Publication No. 63-172284, a toner image is formed on a photoconductor at 1.6 times or more and 10 times or less the amount of light required to reduce the initial surface potential of a bare photoconductor by 500V. From US Pat. Japanese Patent Application Laid-Open No. 63-172286 discloses a color electrophotographic apparatus in which the relationship between the surface potential Vst of the photosensitive member with toner, the developing bias Vb, and the surface potential Vs of the bare photosensitive member is Vst>Vb> Vs. Has been done.

In Japanese Patent Laid-Open No. 3-72380, the developing bias is kept constant, the first exposure potential and the re-exposure potential are the same, and the laser power applied in the first image exposure is the laser power applied in the re-exposure. A color image forming method of 50% or less is described. JP-A-3-723
No. 86 discloses that the average particle diameter of the toner is 2 to 7 μm,
The amount of toner adhered during development is 0.25 to 0.5 mg / cm ²
And the relationship between the toner layer surface potential Vlt and the developing potential Vp after recharging / image exposure is 15% <Vlt / Vp / 3.
A toner image forming method of 0% is described.

In Japanese Patent Laid-Open No. 60-238864, 1
A developing device is described which switches the developing bias for the second color and the developing bias for the second color to different values. Tokuhei 2
JP-A-63224 discloses an image forming method in which the potential difference between latent images in each image forming step is set so that the subsequent image forming step is larger than the previous image forming step.

Japanese Unexamined Patent Publication No. 63-97967 discloses an image forming method in which the difference between the surface potential of the image carrier and the developing bias potential at the developing position by each developing device is made substantially constant. ..

In addition, as a related technique, the relationship between the dry toner forming the toner image already formed on the photosensitive member at the time of repeated image exposure and the image exposure of the exposure means is such that the dry toner is different from the image exposure by the exposure means. Spectral reflectance of 40
A multicolor image forming method in which the image exposure is performed in such a manner that the image exposure is performed as a spot distribution exposure and the spot positions of the previous image exposure and the spot positions of the subsequent image exposure are overlapped is described. Image recording method is Japanese Patent Laid-Open No. 3-7
It is described in Japanese Patent Publication No. 946. Further, Japanese Patent Application Laid-Open No. 3-61967 discloses a laser drive device that selectively changes the on-duty of the laser and the laser drive current value according to the change cycle of the laser power.

Further, there are the followings, which are already known in general copying machines and printers, and which improve the image stability by the one-drum color superposing one rotation system. Japanese Unexamined Patent Publication No. 63-95471 describes a multicolor image forming method in which a reference toner image of one color is formed, the reflection density of the reference toner image is read, and image forming conditions are set according to the result. Japanese Patent Publication No. 3-6500, Japanese Patent Publication No. 3-65
No. 01 publication, an image forming method for forming reference toner images of a plurality of colors for controlling toner image forming conditions, and forming the image toner images of the plurality of colors based on information obtained from the reference toner images. Is listed.

Next, an image forming process of uniformly charging the photosensitive member, forming a latent image by exposure, and developing the latent image with color toners is repeated for a plurality of color images. A multi-color image forming method of a color superposition method for forming a multi-color visible image will be described in detail from an electrostatic aspect. Figure 2
Shows schematically an electrostatic model of an image forming process in a color superposition multicolor image forming method. As shown in FIG. 2 (a), the photoconductor 1 is uniformly charged by a charger 2 such as a scorotron, and then the photoconductor 1 is written by a writing device based on the image signal of the first color as shown in FIG. 2 (b). An electrostatic latent image is formed by scanning and exposing with a laser beam for writing, and as shown in FIG. 2C, a developing device 3 develops with a toner of a first color, for example, yellow toner to develop a photoconductor. A toner image is formed by forming the toner layer 4 on the surface 1.

This toner image is not transferred to a recording sheet, and is not cleaned, and preferably, after the charge is removed by a charge eliminator such as an AC corona charger, the photoreceptor 1 is re-applied to the toner as shown in FIG. 2 (d). The layer 4 is uniformly charged by the charger 2, and the photoconductor 1 is scanned from above the toner layer 4 by the writing device with the writing laser beam based on the image signal of the second color by the writing device as shown in FIG. And then exposed to form an electrostatic latent image.

Next, as shown in FIG. 2 (f), a toner image is formed by forming a toner layer 5 on the photosensitive member 1 by developing with a second color toner, for example, magenta toner by the developing device 3. .. At this time, when the toner layer 5 is formed on the photoconductor 1, when the corona charging is applied from above the toner layer 4, some of the ions adhere to the toner layer 4 (the toner layer 4 is charged). It is considered that a part of the toner passes through the toner layer 4 and directly adheres to the surface of the photoconductor 1 (the photoconductor 1 is charged). When the photoconductor 1 is exposed from above the toner layer 4, the potential of the exposed image portion on the photoconductor 1 (exposure potential) is the potential of the toner layer and the surface below the toner layer 4 on the photoconductor 1. If the toner has a high resistance, the potential of the toner layer 4 is the sum of the potential and the charge held in the toner itself during development without being lowered by exposure and the charge attached to the toner layer 4 due to corona charging. It is a potential that is generated, and it is the same as when charged.

The surface potential below the toner layer 4 on the photoreceptor 1 reaches the surface of the photoreceptor 1 after being absorbed and scattered by the toner layer 4 when the writing laser beam passes through the toner layer 4. This is the potential attenuated by. This potential is different from the potential of the bare portion of the photoconductor 1 on which the toner layer 4 is not formed, which is attenuated by exposure with a laser beam having the same intensity distribution as the writing laser beam after passing through the toner layer 4, and 1 is influenced by the holding charge of the toner layer 4 adhered on the toner layer 1 (the sum of the charge at the time of development and the charge by corona charging), and conceptually, the charge by the surface charge of the photoconductor 1 and the holding charge of the toner layer 4. Can be considered to be the sum of the electric potential induced in the photoconductor 1 and.

Although not shown, the toner layer 5 formed on the photoconductor 1 is charged, exposed again on the basis of the image signal of the third color (for example, cyan), and developed with the toner of the third color, as described above. By performing the following, a multicolor visible image is formed on the photoconductor 1, and the multicolor visible image is formed on the recording paper.
After the transfer, the residual image on the photoconductor 1 is cleaned to return the photoconductor 1 to the initial state.

[0016]

In the multicolor image forming method of the color superposition method, one of the fundamental problems is that the electric charge of the toner layer is not attenuated even when the toner layer is irradiated with light. .. Due to this problem, in the above-described color electrophotographic apparatus, when the toner adhesion amount is large or the toner charge amount is large, the bare portion of the photoconductor and the toner-adhered portion will not be affected even if the light exposure is performed. In some cases, the same development potential cannot be obtained and a high-quality output image cannot be obtained.

Due to the same problem, in the above-mentioned color electrophotographic apparatus, the developing potentials of the bare portion and the toner-attached portion on the photosensitive member cannot be made the same during the work of the same color, and the above-mentioned color image forming method is used. In some cases, the same developing potential cannot be obtained in the bare portion of the photoconductor and the toner-adhered portion, so that a high-quality output image cannot be obtained. In the toner image forming method, the average particle diameter of the toner is set to 2 to 7
μm, and the toner adhesion amount during development is 0.25 to 0.5 m
g / cm ² , and the relationship between the toner layer surface potential Vlt and the developing potential Vp after recharging and image exposure is 15% <Vl.
Since t <30%, it is possible to suppress the toner adhesion amount on the photoconductor and reduce the influence of the toner layer, but there are many other technical problems in order to realize high-density image formation with a small amount of toner. Exists.

In the developing device, the image forming method, and the image forming method, due to the same problem, it is possible to make the developing potentials of the bare portion and the toner adhering portion on the photosensitive member the same during the work of the same color. Can not.

The present invention solves the above-mentioned drawbacks and makes it possible to make the developing potential of the toner-adhered portion and the bare portion on the photosensitive member the same and obtain a high-quality output image. And a device can be provided.

[0020]

In order to achieve the above object, the invention according to claim 1 forms a latent image by exposing a photoreceptor to charging and exposing the latent image to a color toner. In a multicolor image forming method of forming a multicolor visible image by repeatedly performing an image forming process of developing with a plurality of color images, a multicolor image forming method for forming an image portion on which a toner image is not formed on the photoconductor is performed. The latent image is formed such that the latent image potential V1 and the toner layer potential Vt of the image portion on the photoconductor on which the toner image is formed before development satisfy the relationship of | V1 | ≧ | Vt |. According to a second aspect of the present invention, in the multicolor image forming method according to the first aspect, the exposure is performed by optical scanning of a laser beam on the photoconductor, and the latent image potential V1 is adjusted by the intensity or emission pulse of the laser beam. Set the width, According to a third aspect of the present invention, in the multicolor image forming method according to the first aspect, the developing bias voltage Vb and the toner layer potential Vt are set in the image forming process for the second and subsequent colors during the same multicolor visible image formation. | Vb-Vt | ≧ 300
The developing bias voltage Vb is set so as to satisfy the relationship of V, and the invention according to claim 4 is the multicolor image forming method according to claim 1 or 3, wherein the toner layer potential Vt is set to the toner on the photoconductor. The toner adhesion amount of the photosensitive member is controlled so that | Vst−Vt | ≧ 300 V with respect to the charging potential Vst of the adhered image portion, and the invention according to claim 5 charges the photosensitive member. A multicolor image forming method for forming a multicolor visible image by repeatedly performing an image forming process of forming a latent image by performing exposure and developing the latent image with color toners for images of a plurality of colors. In a data table for storing a light attenuation characteristic table of the photoconductor, a standard pattern toner image is formed on the photoconductor,
An electric potential sensor for reading the latent image electric potential Vlt0 obtained by exposing the toner image on the standard pattern toner image is collated with the electric potential Vlt0 data read by the electric potential sensor and the data in the data table. Exposure latent image potential V of the image portion where the toner image on the body is not formed
An exposure amount setting means for setting the intensity or emission pulse width of the laser beam such that 1 is V1 = Vlt0 to the reference intensity or reference emission pulse width of the laser beam at the time of image output. According to a sixth aspect of the invention, in the multicolor image forming apparatus according to the fifth aspect, the standard pattern is a pattern including all toner images exposed from the toner layer in each image forming step, or a plurality of predetermined patterns. And the latent image potential Vlt obtained by the exposure amount setting means exposing from the standard pattern toner image of each color.
The absolute value of 0 is set to the maximum value Vlt0 (max) and the data in the data table are collated, and the result is V1 = Vlt0 (ma
x), the intensity of the laser beam or the emission pulse width is set, and the invention according to claim 7,
The latent image is formed by charging the photoconductor and exposing it with a laser beam, and the latent image is developed with color toners. In a multi-color image forming apparatus for forming a color visible image, a laser light source for irradiating a laser beam on the photoconductor, and driving the laser light source according to image data of each color to write the image data on the photoconductor A laser light source drive circuit, a write image data storage unit for storing image data of each color written on the photoconductor, and a laser light source drive unit according to input image data and stored contents of the write image data storage unit. When a circuit is controlled to form an image on a photoconductor having at least a toner image, the latent image potential of an image portion where the toner image of the photoconductor is not formed l and the toner layer potential Vt of the image portion where the toner image on the photoconductor is formed are set to satisfy the relation of | Vl | ≧ | Vt | to the reference intensity or reference emission pulse width of the laser beam. On the other hand, the latent image potential Vlt and the potential Vl of the image portion where the toner image on the photoconductor is formed.
And a data conversion means for determining the intensity or the emission pulse width of the laser beam so as to satisfy the relationship of Vlt = Vl. The invention according to claim 8 is the multicolor image according to claim 7. In the forming apparatus, the image data is multi-valued data representing gradation and the data conversion means
When forming an image of the same density, the intensity of the laser beam or the emission pulse width is modulated so that the exposure potential of the toner image forming portion and the toner image non-forming portion on the photoconductor are substantially the same. It is a thing.

[0021]

According to the present invention, the light attenuation characteristic table of the photoconductor is stored in the data table, the standard pattern toner image is formed on the photoconductor, and the latent image obtained by exposing from the standard pattern toner image is obtained. The image potential Vlt0 is read by the potential sensor. Then, the exposure amount setting means compares the data of the potential Vlt0 read by the potential sensor with the data of the data table, and as a result, the exposure latent image potential V1 of the image portion where the toner image on the photoconductor is not formed is obtained. V1
The intensity or emission pulse width of the laser beam such that = Vlt0 is set to the reference intensity or reference emission pulse width of the laser beam during image output.

In a sixth aspect of the present invention, the standard pattern is a pattern including all toner images exposed from the toner layer in each image forming step or a plurality of predetermined patterns, and the exposure amount setting means is for each color. The maximum value Vlt0 (max) of the latent image potential Vlt0 obtained by exposure from the standard pattern toner image is compared with the data in the data table, and the result is V1 = Vlt0 (max). Set the laser beam intensity or emission pulse width.

According to the seventh aspect of the invention, the laser light source irradiates the photosensitive member with a laser beam, and the laser light source drive circuit drives the laser light source according to the image data of each color to write the image data on the photosensitive member. In addition, the image data of each color written on the photoconductor is stored in the written image data storage unit. Then, the data conversion unit controls the laser light source drive circuit according to the input image data and the stored contents of the write image data storage unit, and when performing image formation on a photoconductor having at least a toner image, The latent image potential Vl of the image portion where the toner image of the body is not formed and the toner layer potential Vt of the image portion where the toner image on the photoconductor is formed are |
The latent image potential Vlt and the potential Vl of the image portion on which the toner image is formed on the photoconductor is set with respect to the reference intensity of the laser beam or the reference emission pulse width set so as to satisfy the relationship of Vl | ≧ | Vt | The intensity of the laser beam or the emission pulse width is determined so as to satisfy the relationship of Vlt = Vl.

According to the eighth aspect of the invention, the image data is multi-valued data representing gradation, and the data converting means forms a toner image forming portion on the photoconductor and the toner when forming an image of the same density. The intensity of the laser beam or the emission pulse width is modulated so that the exposure potential is substantially the same as that of the non-image forming portion.

[0025]

EXAMPLES First, examples of the present invention will be described.
As described above, one of the fundamental problems in the color superposition type multicolor image forming method is that the electric charge held in the toner layer is hardly attenuated even when the laser beam is irradiated onto the photoconductor from above the toner layer. The holding current of the toner layer always raises the development potential.

The specific holding current (potential) of the toner layer which causes this problem will be described. FIG. 3 shows measured data and a theoretical curve of the relationship between the toner adhesion amount M / A after development on the photoconductor and the toner layer potential Vt in the color superposition multicolor image forming method: Vt = 5.3 × (Q /
M: toner charge amount) × (M / A), and FIG. 4 shows the relationship between the toner adhesion amount M / A after corona charging and the toner layer potential Vtc on the photoconductor in the color superposition multicolor image forming method. Measurement data and theoretical curve: Vtc = 5.3 × (Q / M) ×
(M / A) ² is shown.

Here, the measured toner layer potential means that the surface potential of the toner layer on the photoconductor is sufficiently exposed by room light from the top of the toner layer on the photoconductor after development and after corona charging. Made by Trek (model 334) after being attenuated to
It is the electric potential measured by the surface electrometer. In this case, the toner has physical properties such as a volume average diameter of 10.27 [μm], a volume resistance (logarithmic value) of 11.40Ω, and a relative dielectric constant of 2.70. As is apparent from FIGS. 3 and 4, the toner layer potentials Vt and Vtc increase as the toner adhesion amount M / A increases.

The toner layer potential can be expressed by the Poisson equation as follows, assuming that the charges are uniformly distributed in the toner layer. Ut: toner layer potential, ρt: toner layer volume charge density, d
t: toner layer thickness ε ₀ : vacuum permittivity, ε t: apparent relative permittivity of toner layer If the toner layer thickness is defined as the average height of the toner layer, the toner layer thickness dt is the toner adhesion amount as shown in FIG. A linear relationship for M / A: dt = 12.611 × (Q / M).

Therefore, the toner layer potential dt is Q / M and M / A.
Using C: Toner layer thickness / toner adhesion amount conversion constant Q / M: Toner charge amount per unit mass M / A: Toner adhesion amount per unit mass can be approximated.

In this measurement, εt = 1.34,
After development and after corona charging, the measured data and the theoretical curve were in very good agreement as shown in FIGS. The toner layer potential described in the examples of the present invention is thus experimentally,
It means a theoretically specified potential.

The first embodiment of the present invention will be described below. FIG. 1 shows a first embodiment of the present invention. In this first embodiment, a plurality of colors of 2
This is an example of a binary printer that prints a multicolor image with value image data, and uses the toner having the physical properties described above. After the photosensitive drum 11 is rotationally driven by the driving unit and uniformly charged by the charger 12 including a scorotron,
An electrostatic latent image is formed by being scanned and exposed by a writing laser beam by the writing device based on the first color yellow image signal, and is developed by the developing device 13 with the first color yellow toner to be exposed. An image forming process for the first color in which a toner image is formed on the body drum 11 is performed.

In this case, the other developing devices 14, 15 and 16 do not perform the developing operation, and the transfer charger 18, the separating charger 19, the pre-transfer charge eliminator 20, and the cleaning device 2 are used.
1 is also in the inoperative state. Therefore, the photosensitive drum 1
1 pass through the toner image developing devices 14, 15, 16 on the sheet 1, pass through the transfer charger 18 and the separating charger 19, are not transferred to the recording sheet 17, and pass through the pre-transfer static eliminator 20 and the cleaning device 21. And not cleaned.

Next, after the photosensitive drum 11 is uniformly charged from above the toner layer by the charger 12, the writing device emits a laser beam for writing from above the toner layer based on the image signal of magenta of the second color. By scanning and exposing, an electrostatic latent image is formed so as to overlap with the image formation of the first color, and this electrostatic latent image passes through the developing device 13 and the developing device 14
Thus, a second color image forming step is performed in which the toner image is developed with magenta toner to form a toner image on the photosensitive drum 11.

In this case, the other developing devices 13, 15, 16,
The transfer charger 18, the separation charger 19, the pre-transfer charge eliminator 20, and the cleaning device 21 are inoperative. Therefore, the toner image on the photoconductor drum 11 passes through the developing devices 14 and 15, does not pass through the transfer charger 18 and the separating charger 19 and is not transferred to the recording paper sheet 17, and the pre-transfer charge eliminator 20 and the cleaning device. 21 and not cleaned.

Next, after the photosensitive drum 11 is uniformly charged from above the toner layer by the charger 12, a writing laser beam is applied from above the toner layer to the writing device based on the cyan image signal of the third color. By scanning and exposing, an electrostatic latent image is formed so as to overlap with the image formation of the second color, and the electrostatic latent image passes through the developing devices 13 and 14 and is developed by the developing device 15 with cyan toner. As a result, a toner image is formed on the photoconductor drum 11, and a third color image forming process is performed.

In this case, the developing device 16, the transfer charger 18, the separation charger 19, the pre-transfer static eliminator 20, and the cleaning device 21 are inoperative. Therefore,
The toner image on the photosensitive drum 11 passes through the developing device 16,
The pre-transfer charge eliminator 20 is not transferred to the recording paper 17 through the transfer charger 18 and the separation charger 19.
And, it does not pass through the cleaning device 21 and is not cleaned.

Next, after the photoconductor drum 11 is uniformly charged from above the toner layer by the charger 12, a writing laser beam is applied from above the toner layer by the writing device based on the black image signal of the fourth color. By scanning and exposing, an electrostatic latent image is formed overlapping with the image formation of the third color, and this electrostatic latent image passes through the developing devices 13, 14, 15 and is developed by the developing device 16 by the black toner. A fourth-color image forming step is performed in which the toner image is formed on the photosensitive drum 11 by being developed, and a multicolor visible image is obtained.

The multicolor visible image on the photoconductor drum 11 is transferred to the recording sheet 17 by the transfer charger 18 at one time, and the recording sheet 17 is separated from the photoconductor drum 11 by the separating charger 19. A multicolor visible image 17 is fixed by a fixing device and is discharged to the outside as a hard copy having an output image. Further, the photoconductor drum 11 is destaticized by the pre-cleaning static eliminator 20, the residual image is cleaned by the cleaning device 21, and the initial state is restored.

In this embodiment, when, for example, 1 mg / cm ^{2 of} yellow toner is attached on the photosensitive drum 11, the potential of the toner layer is about −12 as shown in FIG.
It becomes 0 V, and the toner layer potential is not attenuated even when exposed to light as described above. Conversely, the latent image potential of the image portion exposed through the toner layer on the photosensitive drum 11 is increased by increasing the power of the laser beam from the writing device.
It can be attenuated up to 120V.

Therefore, the writing device is arranged so that the latent image potential of the bare portion (image portion) where the toner layer on the photosensitive drum 11 is not formed (the potential of the exposed image portion) is at least the toner layer potential or more. The reference power of the laser beam from the photoconductor drum 11 is set by the exposure amount setting means.
When the writing device is exposed from above the toner layer on the top, the power of the laser beam from the writing device is raised above the reference power by the exposure amount setting means, and the photosensitive drum 1 is exposed.
The surface potential of the bare area on 1 and the latent image potential of the image area exposed through the toner layer are substantially constant.

FIG. 6 shows the relationship between the power of the laser beam and the surface potential of the image portion on the photosensitive drum 11. When the power of the laser beam from the writing device to the bare portion on the photosensitive drum 11 is set to 0.45 mW so that the latent image potential of the bare portion on the photosensitive drum 11 is about -160 V, the When the yellow toner layer is exposed by the writing device, the latent image potential of the bare portion on the photoconductor drum 11 and the image portion having the toner layer are exposed by the laser beam having a power of 0.8 mW from the writing device. And the latent image potential of are almost constant.

When the writing device exposes the magenta toner layer on the photoconductor drum 11, it is exposed by a laser beam having a power of 0.8 mW from the writing device to expose the bare portion on the photoconductor drum 11. The latent image potential and the latent image potential of the image portion having the toner layer become substantially constant, and when the writing device exposes the cyan toner layer on the photoconductor drum 11, the power of 0.85 mW from the writing device. The latent image potential of the bare portion on the photosensitive drum 11 and the latent image potential of the image portion having the toner layer become substantially constant by being exposed by the laser beam.

FIG. 7 shows the developing characteristics of the developing devices 13-16. As is apparent from this, at least the developing potential should be 300 V or more in order to obtain a good toner adhesion amount on the photoconductor drum 11 in the developing devices 13 to 16, generally 0.5 mg / cm ² or more. Is preferred. That is, considering that the toner layer potential is not attenuated by exposure, the developing bias voltage applied to each of the developing units 13 to 16 from each developing bias power source is preferably -420V or more in this example. Therefore, the developing device 1
The developing bias voltage applied to each of Nos. 3 to 16 from each developing bias power source was set to -500 V or more, and a good output image was obtained. In this case, the charging potential by the charger 12 on the photoconductor drum 11 (the surface potential of the unexposed portion) is -900V, and the optimum developing bias voltage applied to each of the developing devices 13 to 16 from each developing bias power source is It was -750V.

Further, in order to set the developing potential to 300 V or more, the difference between the charging potential of the photosensitive drum 11 and the toner layer potential needs to be at least 300 V or more. The toner layer potential is approximately proportional to Q / M and (M / A) ² as described above. Therefore, it is necessary to control M / A so that the toner layer potential does not become too high with respect to the charging potential of the photosensitive drum 11. In this example, M / A is 1 mg / cm
By setting the value to ² , the toner layer potential was suppressed to -120 V (charging potential was -900 V), and a good output image that was not significantly affected by the toner layer potential could be obtained.

Q / M is determined by the triboelectric charge held by the toner layer at the time of development and the charge attached to the toner layer by the charger 12, which is M / A, toner, photoconductor drum 11, charger. 12 depends on the corona charging conditions and the like. Under the corona charging conditions of the toner, the photosensitive drum 11, and the charger 12 used in this example, Q / M has a relationship with M / A as shown in FIG. 8, and the M / A of 1.0 mg / cm ² is obtained. Then, Q / M is about -22 μc / g.

Next, a second embodiment of the present invention will be described. In the second embodiment, in the first embodiment, the potential sensor 22 (see FIG. 10) is provided on the downstream side of the writing position of the photosensitive drum 11 in the rotational direction and on the upstream side of the developing position of the developing devices 13 to 16. , The position sensor 22 has little distance dependency, for example, manufactured by Trek (model 33
The same operating principle as in 4) is used.

A circuit for setting the latent image potential of the bare portion as shown in FIG. 9 is used, and the exposure amount setting means is composed of the light attenuation characteristic data table 24 and the data conversion circuit 25. When the image is not output, for example, when the machine is started up, the toner image of the standard pattern is formed by the image forming operation of charging the photosensitive drum 11, writing the standard pattern by the exposure of the writing device, and developing as described above. .. This standard pattern preferably includes at least all toner images that can be exposed from above the toner layer during the formation of the first and second colors.

Specifically, in the case of a binary printer which performs the image forming operation in the order of yellow Y, magenta M, cyan C, and black B as described above, the standard pattern is, for example, a bare portion as shown in FIG. Pattern 23S, yellow Y pattern 23Y, magenta M pattern 23M and red R
The pattern 23R of (yellow Y + magenta M) is included.
The light attenuation characteristic data table 24 is for the bare photoconductor drum 11.
Is a table that stores data indicating the light attenuation characteristics of the photosensitive drum 11 of FIG.
The light attenuation characteristics of the photoconductor drum 11 as shown in FIG.

The data conversion circuit 25 is the maximum value detection circuit 25.
a and a comparison circuit 25b, the maximum value detection circuit 25a detects the maximum value of the measurement signal from the potential sensor 22 for each standard pattern 23s, 23Y, 23M, 23R. Then, the data conversion circuit 25 compares the output signal of the maximum value detection circuit 25a with the contents of the light attenuation characteristic data table 24 by the comparison circuit 26b, and based on the result, the bare portion exposure potential Vl on the photosensitive drum 11 and the toner. The exposure power of the writing device is set so as to be the same as the exposure potential through the layer, and it is output to the laser light source (LD) drive circuit 26 as the laser beam reference power of the laser light source in the writing device. The standard pattern is formed as a toner image on the photosensitive drum 11 by the above-described image forming operation, and the potential sensor 22 measures the potential of the image portion having the toner layer after the exposure after the toner image is formed. The output signal of the potential sensor 22 is input to the data conversion circuit 25.

When the standard pattern includes a plurality of patterns 23S, 23Y, 23M and 23R as shown in FIG. 10, the data conversion circuit 25 uses the plurality of patterns 23S and 23R.
Maximum value detection circuit 25 for Y, 23M and 23R latent images
The potential Vlt (max) with the highest absolute value among the output signals of a
The output signal of the maximum value detection circuit 25a is selected and compared with the contents of the light attenuation characteristic data table 24, and as a result, the bare surface potential Vl on the photosensitive drum 11 and the potential Vlt ( The exposure power of the writing device is set so as to be equal to (max) and is output to the LD drive circuit 26 as the laser beam reference power of the laser light source 27 in the writing device.

For example, if the potential Vlt (max) read from the standard pattern by the potential sensor 22 is -200V,
Based on the light attenuation characteristics of the photoconductor drum 11 as shown in FIG. 6, about 0.4 mW is set to the laser beam reference power of the laser light source 27 in the writing device and output to the LD drive circuit 26. The LD driving circuit 26 intensity-modulates the laser light source 27 according to the image data of each color and turns it on / off to expose the image portion where the toner layer is not formed on the photoconductor drum 11 with the above laser beam reference power. The light is emitted and the laser beam from the laser light source 27 is applied to the photosensitive drum 11.

The LD drive circuit 26 is used for the photosensitive drum 1.
When the image portion on which the toner layer is formed is exposed to output an image, the laser light source 27 is driven by the image data of each color so that the laser light source emits light with a power higher than the reference power of the laser beam. The laser beam from 27 causes the bare portion exposure potential Vl on the photosensitive drum 11.
And the electric potential on the image portion where the toner layer is present are set to be the same as shown in FIG.

In this example, the time when the image is not output means not only the time when the multicolor image is not output (the time when the hard copy is not made) but also the time when the multicolor image is output ( When making a hard copy) (including exposing the non-image area).

Next, a third embodiment of the present invention will be described. The third embodiment is an example in which the latent image potential of the bare portion and the latent image potential of the image portion exposed from above the toner layer on the photosensitive drum are made equal even in the image forming process of the same color. In the first embodiment, the circuit as shown in FIG. 11 is used and the exposure amount setting means is composed of the writing image information storage section 28 and the data conversion circuit 29. The image data is input to the writing image information storage unit 28 and the data conversion circuit 29, and the image forming process is performed in the order of yellow, magenta, cyan, and black as described above to create a hard copy of a multicolor image. .. Yellow, magenta, cyan,
The black image data is sequentially input to the writing image information storage unit 28 and the data conversion circuit 29 during each image forming process.

First, in the first image forming process, yellow image data is input to the writing image information storage section 28 and the data conversion circuit 29, but at this time, no toner image exists on the photosensitive drum 11. Therefore, the data conversion circuit 29 sets the laser beam power of the laser light source in the writing device to a reference power, for example, 0.45 mW, and outputs the yellow image data to the LD drive circuit 30, and the laser light source uses the yellow image data as the reference. Make it emit light with power. The LD drive circuit 30 turns on / off the laser light source of the writing device according to the yellow image data from the data conversion circuit 29 to cause the laser light source of the writing device to emit light with the above-mentioned reference power, and the laser beam from the laser light source irradiates the photosensitive drum 11. To be done. Further, the yellow image data is stored in the written image information storage unit 28.

After that, in the second image forming step, the magenta image data is input to the write image information storage section 28 and the data conversion circuit 29 and stored in the write image information storage section 28 together with the yellow image data. A yellow toner image exists on the photosensitive drum 11. At this time, the data conversion circuit 29 receives the yellow image data from the writing image information storage unit 28.
Then, the data conversion circuit 29 compares the magenta image data and the yellow image data for each pixel, and an image portion having no yellow image data, that is, a magenta image having no yellow toner image on the photosensitive drum 11 is formed. In the writing portion, the laser beam power of the laser light source in the writing device is set to the reference power to output the magenta image data to the LD drive circuit 30, and the image portion having the yellow image data, that is, on the photosensitive drum 11. In the image section for writing a magenta image with a yellow toner image in the background, the laser beam power of the laser light source in the writing device is equal to or higher than the reference power, for example, 0.8 mW.
To output the magenta image data to the LD drive circuit 30.

The LD drive circuit 30 intensity-modulates the laser light source of the writing device according to the yellow image data from the data conversion circuit 29 and turns it on / off to turn on / off the image portion where the yellow toner image is not present on the photosensitive drum 11. Then, the light is emitted at the reference power and 0.8 mW is emitted in the image portion where the yellow toner image is present on the photosensitive drum 11, and the laser beam from the laser light source is emitted.
1 is irradiated. As a result, as described with reference to FIG. 6, the bare portion exposure potential Vl on the photosensitive drum 11 becomes equal to the potential (exposure potential from the toner layer) Vlt of the image portion where the yellow toner layer is present. ..

In the third image forming step, cyan image data is input to the write image information storage section 28 and the data conversion circuit 29 and stored in the write image information storage section 28, but on the photosensitive drum 11. Has a toner image. At this time, the data conversion circuit 29 receives the yellow image data and the magenta image data from the writing image information storage unit 28. Then, the data conversion circuit 29
Compares the cyan image data with the yellow and magenta image data for each pixel, and writes in the image portion without the yellow image data and the magenta image data, that is, the image portion with no toner image on the photosensitive drum 11. The laser beam power of the laser light source in the apparatus is set to the reference power, and magenta image data is output to the LD drive circuit 30. Further, the data conversion circuit 29 determines that the image portion having the yellow image data and / or the magenta image data, that is, the image portion having the toner image on the photosensitive drum 11,
The power of the laser beam of the laser light source in the writing device is equal to or higher than the reference power, that is, the photoconductor drum 11
The LD drive circuit 30 sets the cyan image data to the power by setting the power so that the upper bare portion exposure potential Vl is equal to the potential of the image portion where the toner layer is present (exposure potential from the toner layer).
Output to.

The LD drive circuit 30 intensity-modulates the laser light source of the writing device by the cyan image data from the data conversion circuit 29 to turn it on / off, and in the image portion where there is no toner image on the photosensitive drum 11 when it is on. The bare portion exposure potential V on the photoconductor drum 11 is emitted in the image portion where the toner image is present on the photoconductor drum 11 by emitting light with the reference power.
Light is emitted with a power such that l and the exposure potential of the image portion having the toner layer are equal.

In the fourth image forming process, black image data is input to the writing image information storage unit 28 and the data conversion circuit 29, but yellow, magenta, and cyan toner images are formed on the photosensitive drum 11. Exists. At this time, the data conversion circuit 29 causes the write image information storage unit 28 to
To input yellow image data, magenta image data, and cyan image data. Then, the data conversion circuit 29
Compares the black image data with the yellow, magenta, and cyan image data for each pixel, and finds no toner image on the image portion where there is no yellow image data, magenta image data, or cyan image data, that is, on the photosensitive drum 11. In the non-existing image area, the laser beam power of the laser light source in the writing device is set to the reference power and the black image data is LDed.
Output to the drive circuit 30. Further, the data conversion circuit 29 uses the laser beam power of the laser light source in the writing device as a reference in an image portion having yellow image data, magenta image data, and cyan image data, that is, an image portion having a toner image on the photosensitive drum 11. The LD drive circuit 30 sets the black image data to a power equal to or higher than the power, that is, a power such that the bare portion exposure potential Vl on the photosensitive drum 11 and the exposure potential of the image portion where the toner layer is present are equal.
Output to.

The LD drive circuit 30 intensity-modulates the laser light source of the writing device with the black image data from the data conversion circuit 29 to turn it on / off, thereby turning on / off the image portion where there is no toner image on the photosensitive drum 11 at the time of turning on. The light is emitted at the reference power, and in the image portion where the toner image is present on the photoconductor drum 11, power is emitted so that the bare portion exposure potential Vl on the photoconductor drum 11 becomes equal to the potential of the image portion where the toner layer is present.

In the above embodiment, the photosensitive drum 11
The laser beam power of the laser light source is set to the reference power in the image portion where there is no toner image on the top, and the laser beam power of the laser light source is raised to the reference power or more in the image portion where the toner image is present on the photosensitive drum 11. However, conversely, in the image portion where the toner image is not present on the photoconductor drum 11, the laser beam power of the laser light source is set to be lower than the reference power, and when the toner image is present on the photoconductor drum 11, the laser light source of the laser light source is set. By setting the beam power to the reference power, the bare portion exposure potential on the photosensitive drum 11 and the exposure potential of the image portion having the toner layer may be made equal.

FIG. 12 shows a part of the fourth embodiment of the present invention. The fourth embodiment is a case where the image data is multi-valued data having gradation, and it is determined according to the presence / absence of a writing pixel, the presence / absence of a toner image in a pixel writing area, and the data regarding the gradation of the writing pixel. Thus, the emission intensity and emission pulse width of the laser light source in the writing device are determined. In the fourth embodiment, the circuit shown in FIG. 12 is used in the first embodiment, and the exposure amount setting means is composed of a writing image information storage unit 31, a data conversion circuit 32 and a pulse width conversion circuit 33. ..

Multivalued image data having gradation is input to the writing image information storage unit 31 and the data conversion circuit 32, and the image forming process is performed in the order of yellow, magenta, cyan and black as described above. To make a hard copy of the multicolor image. Image data of yellow, magenta, cyan, and black are sequentially written in each image forming process, and the image information storage unit 3
1 and the data conversion circuit 32.

First, in the first image forming step, the yellow image data is input to the write image information storage unit 31 and the data conversion circuit 32 to write image information storage unit 3.
However, there is no toner image on the photosensitive drum 11 at this time. The data conversion circuit 32 determines the emission intensity and emission pulse width data of the laser light source in the writing device based on the yellow image data, outputs the emission intensity data to the LD drive circuit 34, and outputs the emission pulse width data to the pulse width modulation circuit 33. Output to. In this case, the data conversion circuit 32 determines the emission intensity of the laser light source in the writing device based on the reference intensity and the yellow image data.

The pulse width modulation circuit 33 is the data conversion circuit 3
The light emission pulse width data from 2 is used to determine the light emission pulse width of the laser light source in the writing device, and the light emission pulse width signal is output to the LD drive circuit 34. The LD drive circuit 34 is driven by the intensity corresponding to the emission intensity data from the laser light source conversion circuit 32 of the writing device, that is, the reference power, and is ON / OFF modulated by the emission pulse width signal from the pulse width modulation circuit 33. .. The laser beam from the laser light source is applied to the photosensitive drum 11,
An electrostatic latent image is formed on it.

Thereafter, in the second image forming step, the magenta image data is input to the writing image information storage unit 31 and the data conversion circuit 32 and stored in the writing image information storage unit 31. A toner image exists on the drum 11, and yellow image data is input from the writing image information storage unit 31 to the data conversion circuit 32. The data conversion circuit 32 determines the emission intensity and emission pulse width data of the laser light source in the writing device based on the magenta image data and the yellow image data from the writing image information storage unit 31, and outputs the emission intensity data to the LD drive circuit 34. At the same time, the light emission pulse width data is output to the pulse width modulation circuit 33. In this case, the data conversion circuit 32
Compares the image data of magenta with the image data of yellow for each pixel, and in the image portion having no yellow image data, that is, the image portion having no yellow toner image on the photoconductor drum 11, the laser light source of the writing device emits light. The intensity is set to the reference intensity, and in the image portion having the yellow image data, that is, the image portion having the yellow toner image on the photosensitive drum 11, the emission intensity of the laser light source in the writing device is set to the photosensitive drum 11. Exposure potential of solid bare area and exposure potential Vl of solid image area with yellow toner layer
It is set by magenta image data and yellow image data with an intensity higher than the reference intensity as a reference so that t becomes equal.

The pulse width modulation circuit 33 is the data conversion circuit 3
The light emission pulse width data from 2 is used to determine the light emission pulse width of the laser light source in the writing device, and the light emission pulse width signal is output to the LD drive circuit 34. The LD drive circuit 34 drives the laser light source of the writing device at an intensity according to the emission intensity data from the data conversion circuit 32, and performs on / off modulation by the emission pulse width signal from the pulse width modulation circuit 33.

In the third image forming process, cyan image data is input to the writing image information storage unit 31 and the data conversion circuit 32 and stored in the writing image information storage unit 31. At this time, the photosensitive drum 11 is used. A toner image is present on the upper side, and yellow image data and magenta image data are input from the write image information storage unit 31 to the data conversion circuit 32. The data conversion circuit 32 determines the emission intensity and emission pulse width data of the laser light source in the writing device based on the cyan image data, the yellow image data from the writing image information storage unit 31, and the magenta image data, and outputs the emission intensity data to the LD drive circuit 34. And the emission pulse width data to the pulse width modulation circuit 33.
In this case, the data conversion circuit 32 uses the cyan image data,
The yellow image data and the magenta image data are compared for each pixel, and in the image portion where the yellow image data and the magenta image data are not present, that is, the image portion where the toner image is not present on the photosensitive drum 11, the laser in the writing device is used. The light emission intensity of the light source is set to the reference intensity, and in the image portion having the image data, that is, the image portion having the toner image on the photoconductor drum 11, the light emission intensity of the laser light source in the writing device is set on the photoconductor drum 11. The intensity is set higher than the reference intensity so that the exposure potential of the solid bare area and the exposure potential of the solid image area where the toner layer is the same are set by the cyan image data, the yellow image data, and the magenta image data.

The pulse width modulation circuit 33 is the data conversion circuit 3
The light emission pulse width data from 2 is used to determine the light emission pulse width of the laser light source in the writing device, and the light emission pulse width signal is output to the LD drive circuit 34. The LD drive circuit 34 drives the laser light source of the writing device at an intensity according to the emission intensity data from the data conversion circuit 32, and performs on / off modulation by the emission pulse width signal from the pulse width modulation circuit 33.

In the fourth image forming process, black image data is input to the written image information storage unit 31 and the data conversion circuit 32 and stored in the written image information storage unit 31. At this time, the photosensitive drum 11 is used. There is a toner image on the upper side, and the writing image information storage unit 31 transfers the yellow image data, the magenta image data, to the data modulation circuit 32.
Cyan image data is input. The data conversion circuit 32 determines the emission intensity and emission pulse width data of the laser light source in the writing device based on the black image data and the yellow image data, the magenta image data, and the cyan image data from the write image information storage unit 31, and outputs the emission intensity data. L
The pulse width data is output to the D drive circuit 34 and the emission pulse width data is output to the pulse width modulation circuit 33. In this case, the data conversion circuit 32 compares the black image data with the yellow, magenta, and cyan image data for each pixel, and the image portion without the yellow, magenta, and cyan image data, that is,
In the image portion where the toner image is not present on the photosensitive drum 11, the emission intensity of the laser light source in the writing device is set to the reference intensity, and the image portion where the image data is present, that is, the toner image is present on the photosensitive drum 11. In the image section, the emission intensity of the laser light source in the writing device is set to the photosensitive drum 11
It is set by the black image data and each of the yellow, magenta, and cyan image data with reference to an intensity higher than the reference intensity so that the exposure potential of the solid area of the solid image and the exposure potential of the solid image area of the toner layer are equal.

The pulse width modulation circuit 33 is the data conversion circuit 3
The light emission pulse width data from 2 is used to determine the light emission pulse width of the laser light source in the writing device, and the light emission pulse width signal is output to the LD drive circuit 34. The LD drive circuit 34 drives the laser light source of the writing device at an intensity according to the emission intensity data from the data conversion circuit 32, and performs on / off modulation by the emission pulse width signal from the pulse width modulation circuit 33.

Further, in the fifth embodiment of the present invention, the fourth
In the embodiment, the data conversion circuit 32 simply sets the emission intensity of the laser light source in the writing device based on the black image data, the yellow image data, the magenta image data, and the cyan image data. In the image portion where there is no toner image on the top, the emission pulse width of the laser light source in the writing device is determined by the emission pulse width data from the data modulation circuit 32 with reference to a predetermined reference emission pulse width, and the photosensitive drum 11
In the image portion having the toner image on the upper side, the emission pulse width of the laser light source in the writing device is adjusted so that the exposure potential of the bare portion on the photosensitive drum 11 and the exposure potential of the image portion having the toner layer are equal to each other. It is determined based on the pulse width wider than the width, based on the image data from the writing image storage unit 31, the light emission pulse width data and the gradation data from the data conversion circuit 32.

[0074]

As described above, according to the first to fourth aspects of the invention, the latent image potential Vl of the image portion where the toner image on the photoconductor is not formed and the toner image on the photoconductor is formed. The toner layer potential Vt before color development of the image area is | V1 | ≧ | V
Since the latent image is formed so as to satisfy the relationship of t |, it is possible to make the developing potential of the image portion on the photoconductor on which the toner image is not formed and the image portion on which the toner image is formed the same. Therefore, the influence of the toner layer can be reduced, and a high-quality output image can be obtained.

According to the fifth and sixth aspects of the invention,
A data table that stores a light attenuation characteristic table of the photoconductor, and a latent image potential V obtained by forming a standard pattern toner image on the photoconductor and exposing from the standard pattern toner image.
The potential sensor for reading lt0 and the data of the potential Vlt0 read by the potential sensor are collated with the data of the data table, and as a result, the latent image of the image portion on which the toner image on the photoconductor is not formed is formed. The potential V1 is V1 = V
Since a laser beam intensity or a light emission pulse width such as lt0 is set to the reference intensity or the reference light emission pulse width of the laser beam at the time of image output, a toner image is formed on the photoconductor. The developing portion can have the same developing potential in the image portion not formed and the image portion in which the toner image is formed, the influence of the toner layer can be reduced, and a high-quality output image can be obtained. Moreover, the power of the laser beam can be set at any time by the standard pattern, and an output image with stable image quality that does not depend much on time and environment can be obtained.

Further, according to the present invention, the laser light source for irradiating the photosensitive member with the laser beam and the laser light source are driven in accordance with the image data of each color so that the image data is transferred to the photosensitive member. A laser light source drive circuit for writing, a write image data storage unit for storing image data of each color written on the photoconductor, and a laser light source drive circuit according to the input image data and the stored contents of the write image data storage unit. Control is performed to form an image on the photoconductor having at least a toner image, the latent image potential Vl of the image portion of the photoconductor on which the toner image is not formed and the image on which the toner image on the photoconductor is formed. The toner layer potential Vt of the part is | Vl | ≧
With respect to the reference intensity or reference emission pulse width of the laser beam set so as to satisfy the relationship | Vt |
And data conversion means for determining the intensity of the laser beam or the emission pulse width so as to satisfy the relationship of Vlt = Vl, the toner image is formed on the image portion on which the toner image is not formed on the photoconductor. The developing potential can be made to be the same as that of the image area, and the influence of the toner layer can be reduced, so that a high-quality output image can be obtained. Further, not only the binary image data but also the multi-valued image data includes an image portion on which a toner image is not formed on the photoconductor and an image portion on which a toner image is formed during formation of the same multicolor visible image. The development potential can be made the same, and a higher quality multicolor image can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing an electrostatic model of an image forming process in a color overlapping multicolor image forming method.

FIG. 3 is a characteristic diagram showing measured data and a theoretical curve of a relationship between a toner adhesion amount after development on a photosensitive member and a toner layer potential in a color superposition multicolor image forming method.

FIG. 4 is a characteristic diagram showing measured data and a theoretical curve of a relationship between a toner adhesion amount after corona charging on a photosensitive member and a toner layer potential in a color superposition multicolor image forming method.

FIG. 5 is a characteristic diagram showing a relationship between a toner adhesion amount and an average toner layer thickness.

FIG. 6 is a characteristic diagram showing characteristics of the first embodiment.

FIG. 7 is a characteristic diagram showing the relationship between the developing potential and the toner adhesion amount in the first embodiment.

FIG. 8 is a characteristic diagram showing the relationship between the toner adhesion amount and the toner charge amount after corona charging in the first embodiment.

FIG. 9 is a block diagram showing a part of a second embodiment of the present invention.

FIG. 10 is a development view showing a development of the photosensitive drum of the second embodiment.

FIG. 11 is a block diagram showing a part of a third embodiment of the present invention.

FIG. 12 is a block diagram showing a part of a fourth embodiment of the present invention.

FIG. 13 is a waveform diagram showing each potential on the photoconductor in the above embodiment.

[Explanation of symbols]

 11 Photoreceptor Drum 12 Charging Charger 13, 14, 15, 16 Developer 22 Potential Sensor 24 Optical Attenuation Characteristic Data Table 25, 29, 32 Data Conversion Circuit 26, 34 LD Drive Circuit 28, 31 Write Image Information Storage 33 Pulse Width modulation circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G03B 27/72 A 8507-2K G03G 15/00 303 15/01 111 A 7818-2H 112 A 7818- 2H 113 A 7818-2H H04N 1/29 E 9186-5C G 9186-5C

Claims (8)

[Claims] 1. An image forming process of forming a latent image by charging a photosensitive member and exposing the latent image and developing the latent image with color toners is repeated for a plurality of color images. In the multicolor image forming method for forming a multicolor visible image by means of: a latent image potential V1 of an image portion on which the toner image is not formed on the photoconductor, A multicolor image forming method, wherein a latent image is formed so that the toner layer potential Vt before development satisfies the relationship of | V1 | ≧ | Vt |. 2. The multicolor image forming method according to claim 1, wherein the exposure is performed by optical scanning of a laser beam on the photoconductor, and the latent image potential V1 is adjusted by the intensity of the laser beam or the emission pulse width. A multicolor image forming method, characterized in that 3. The multicolor image forming method according to claim 1, wherein the developing bias voltage Vb and the toner layer potential Vt are | Vb in the image forming process for the second and subsequent colors during formation of the same multicolor visible image.
A multicolor image forming method characterized in that the developing bias voltage Vb is set so as to satisfy the relationship of −Vt | ≧ 300V. 4. The multicolor image forming method according to claim 1, wherein the toner layer potential Vt is | Vst−Vt | ≧ 300 with respect to a charging potential Vst of an image portion on the photosensitive member to which toner adheres.
A multicolor image forming method, wherein the toner adhesion amount of the photoconductor is controlled so as to be V. 5. An image forming process of forming a latent image by charging a photosensitive member and exposing the latent image and developing the latent image with color toners is repeated for a plurality of color images. A multicolor image forming method for forming a multicolor visible image by a data table storing a light attenuation characteristic table of the photoconductor, a standard pattern toner image is formed on the photoconductor, and the standard pattern toner image is formed on the standard pattern toner image. Latent image potential V obtained by exposure from
A potential sensor that reads lt0 and the data of the potential Vlt0 read by the potential sensor and the data of the data table are collated, and as a result, the latent image of the image portion where the toner image on the photoconductor is not formed is formed. Exposure amount setting means for setting the intensity or emission pulse width of the laser beam such that the potential V1 becomes V1 = Vlt0 to the reference intensity or reference emission pulse width of the laser beam at the time of image output. Multicolor image forming apparatus. 6. The multicolor image forming apparatus according to claim 5, wherein the standard pattern is a pattern including all toner images exposed from a toner layer in each image forming process, or a plurality of predetermined patterns. The maximum amount Vlt0 (max) of the latent image potential Vlt0 obtained by exposing the standard pattern toner image of each color by the exposure amount setting means is compared with the maximum value Vlt0 (max), and the result is V1. A multicolor image forming apparatus characterized in that the intensity of the laser beam or the emission pulse width is set so that Vlt0 (max). 7. An image forming process of forming a latent image by charging a photoreceptor and exposing it with a laser beam and developing the latent image with color toners is repeated for a plurality of color images. In the multicolor image forming apparatus for forming a multicolor visible image by performing the above, a laser light source for irradiating the photoconductor with a laser beam, and driving the laser light source according to image data of each color to the photoconductor. A laser light source drive circuit for writing image data, a write image data storage unit for storing image data of each color written on the photoconductor, an input image data and a storage content of the write image data storage unit. When the laser light source drive circuit is controlled to form an image on a photoconductor having at least a toner image, the image on which the toner image of the photoconductor is not formed is formed. The reference intensity of the laser beam set so that the latent image potential Vl of the image portion and the toner layer potential Vt of the image portion on which the toner image on the photoconductor is formed satisfy the relationship of | Vl | ≧ | Vt | Alternatively, the intensity or the emission pulse width of the laser beam is set so that the latent image potential Vlt of the image portion on which the toner image is formed on the photoconductor and the potential Vl satisfy the relationship of Vlt = Vl with respect to the reference emission pulse width. A multicolor image forming apparatus, comprising: 8. The multi-color image forming apparatus according to claim 7, wherein the image data is multi-valued data representing gradation, and the data converting means forms the photosensitive material when forming an image of the same density. A multicolor image forming apparatus characterized in that the intensity of the laser beam or the emission pulse width is modulated so that the exposure potential is substantially the same between the toner image forming portion and the toner image non-forming portion on the body.