JPH06149000A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the lowering of the reproducibility of the color tone of a color image based on the difference of sticking condition between a 1st color and a 2nd color by modulating light quantity between the quantity of exposing light at an image part to which only one color of toner is stuck and the quantity of exposing light in the case another color of toner is stuck on the image part and develops it concerning the exposure of a specified color. CONSTITUTION:B, G and R signals are converted in terms of complementary colors to yellow, magenta and cyan and become (y), (m) and (c) signals, and a black component is extracted from the respective data (y), (m) and (c) and the digital signal (k) of the black component is generated. A re-exposure signal generation circuit 58 in which the (y), the (m) and the (c) signals are inputted from a masking circuit 57 and the (k) signal is inputted from a black component extraction circuit 56 generates a reexposure signal for performing re-exposure to the image part except the image part of the black component which is the final image exposure as necessary, and inputs it in an image signal storage circuit 59 with the (y), the (m), the (c) and the (k) signals. Then, each image signal is read out according to the order of the image exposure and transmitted to a laser write device 13 after the pulse width or intensity is modulated by a modulation circuit 61.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer using an electrophotographic system, and more particularly, an image for obtaining a multicolor image by superposing a toner image on an image carrier and then transferring it onto a transfer material. The present invention relates to a forming device.

[0002]

2. Description of the Related Art Many methods and apparatuses have been proposed for obtaining a color image using electrophotography. For example, JP-A-61
As disclosed in Japanese Patent Laid-Open No. -100770, a latent image is formed and developed on a photoconductor drum, which is an image forming body, according to the number of separated colors of an original image, and the latent image is transferred to a transfer drum each time the image is developed. There is a method in which a multicolor image is formed on the surface and then transferred onto a recording paper to obtain a color copy. The device by this method is
In addition to the photoconductor drum, it is necessary to provide a transfer drum having a size capable of transferring an image for one sheet on the peripheral surface thereof, and it is inevitable that the apparatus has a large size and a complicated structure.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-149972, latent images are formed and developed on the photosensitive drum in accordance with the number of separated colors of the original image, and the latent image is formed on the transfer material each time the development is performed. There is a method of transferring to obtain a multicolor color copy. With this method, it is difficult to accurately superimpose multicolor images, and it is not possible to obtain high-quality color images.

Further, latent image formation according to the number of separated colors of the original image on the photosensitive drum and development with color toner are repeated,
There is a method of obtaining a color image by superimposing color toner images on a photosensitive drum and then transferring them. The basic process for forming this multicolor image is disclosed in Japanese Patent Application Laid-Open Nos. 60-75850 and 60-767 by the present applicant.
No. 66, No. 60-95456, No. 60-95458, No. 60-158475.

In an image forming apparatus which obtains a color image by superposing such toner images, the image forming steps of charging, exposing and developing are repeated for each component color,
A method has been proposed and practiced in which toner images of respective colors are superposed on an image carrier and then transferred onto a transfer material.

The principle of this image forming method will be described with reference to the flowchart of FIG. FIG. 5 shows changes in the surface potential of the photoconductor, which is an image carrier, and shows an example in which the charging polarity is negative.

The photoconductor is uniformly charged by a scorotron charger or the like to give a constant negative surface potential VH. The surface potential VH is lowered to VL close to zero potential by the first image exposure by an exposure source such as a laser, a cathode ray tube, a liquid crystal shutter, and an LED.

Here, the DC component is the surface potential V of the unexposed portion.
By developing with the developing means to which a negative bias approximately equal to H is applied, the negatively charged toner T in the developing means adheres to the exposed portion having a relatively low electric potential in a larger amount as the electric potential becomes lower, A visible image of the first color is formed.

In the area where this visible image is formed, the potential rises because the negatively charged toner T adheres, and the potential is further raised by the second charging by the charger. Thus, the initial surface potential VH can be obtained similarly to the unexposed portion.

Next, a second image exposure is performed on the surface of the photosensitive member having a uniform surface potential VH on the surface to form an electrostatic latent image, and the second development is conducted through the same developing operation. The image is obtained.

By repeating the above process, a multicolor toner image can be obtained on the photoreceptor. The photosensitive member carrying the multi-color toner image has a lower pressure resistance of the transfer material under high humidity, so that a good transfer can be performed without causing transfer defects such as cissing at the time of transfer. Re-exposure is performed only on. After that, the above-mentioned multicolor toner image is transferred onto a transfer material by a transfer means, and the multicolor image is obtained by fixing it by heating or pressurizing it.

In the image forming apparatus for obtaining a multicolor image by the above method, since a plurality of developing devices are provided at the peripheral portion of the photosensitive drum for superimposing toner images on the photosensitive member, the drum diameter becomes large and the separation performance deteriorates. Sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method. Therefore, a more reliable separating means is required, and in the method of superposing toner images, a large transfer charge amount is required because the toner adhesion amount is large. A transfer belt device is used.

In the above multicolor image forming method,
A reversal developing method is used as a method for developing an electrostatic latent image. In this reversal development method, only the toner image forming portion of the photoconductor needs to be exposed, and it is not necessary to expose the background portion without gaps as in the case of regular development, so that fatigue of the photoconductor is reduced and the life is extended. Further, there is an advantage that the color mixture does not occur because the potential of the visualized image formed before that becomes VH by the second and subsequent charging and the development is not performed unless writing is performed again thereafter.

[0014]

When a toner image is superposed on the above-mentioned photosensitive member to obtain a color image,
There were the following problems. FIG. 6 is a flow chart showing this. For example, the peripheral portion of the photosensitive drum contains a developer composed of toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier. When trying to reproduce a red (R) image portion in an image forming apparatus which is provided with a developing device for obtaining a color image, first, as shown in FIG. 6A, on a photoreceptor charged with VH. Is exposed to L and the potential becomes VL. Then, development with yellow (Y) is performed, and charging is performed again.
The state of (b) is obtained. When the yellow (Y) toner adheres to the surface and is exposed to L, a toner having a property of transmitting infrared light is used as the toner, and infrared light is used for image exposure. Is transmitted to the photoreceptor surface,
As shown in (C), the potential becomes VM (| VM | ≤ | VH |).

Here, the image is developed by magenta (M), and the state shown in FIG. 6 (d) is obtained. The magenta (M) toner adheres to the adhered portion of the yellow (Y) toner, so that the red (R) image portion should be reproduced, but in reality, the hue differs from the desired red color. . This is because the adhesion amount of the second color magenta (M) toner is smaller than the adhesion amount of the first color yellow (Y) toner.

According to the present invention, when the development is carried out under the same conditions,
An object of the present invention is to provide an image forming apparatus capable of eliminating the deterioration in the reproducibility of the color tone of a color image due to the difference in toner adhesion condition between the second color and the second color.

[0017]

The above object is to repeat the steps of charging, image exposure and development to form a multicolor toner image by superposing toner images on an image bearing member, and transfer the multicolor toner image to a transfer material. In the image forming apparatus that transfers and fixes the image onto the image forming apparatus, the exposure light amount is the exposure light amount for the image portion where only one color of toner is attached for the exposure of the specific color, and the exposure when the toner of the other color is developed and attached. An image forming apparatus (first invention) characterized by performing light quantity modulation with respect to light quantity, and a multicolor toner image is formed by superposing toner images on an image carrier by repeating the steps of charging, image exposure and development. In an image forming apparatus that transfers / fixes the multicolor toner image onto a transfer material, the toner to be developed on the image portion on which toner has already been attached has a higher number of pigment parts than the toner on which the first color is developed. What you did Is achieved by an image forming apparatus, wherein (a second invention).

[0018]

1 is a sectional view showing the construction of an embodiment of an image forming apparatus of the present invention, and FIG. 2 is a block diagram showing an example of an image signal processing section of the image forming apparatus of FIG. The configuration and operation of this embodiment will be described with reference to FIGS. 1, 2 and 5.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is an image bearing member, for example, an OPC photosensitive member coated on the drum, which is grounded and driven and rotated clockwise. 12 on this photoconductor drum 10 is a scorotron charger,
A uniform charge of VH (-600 to -800V) is applied to the 10 circumferential surface VG
It is given by corona discharge with a grid and corona discharge wire whose potential is held at (-550 to -850V). Prior to the charging by the scorotron charger 12, the peripheral surface of the photoconductor is neutralized by exposure by the PCL 11 using a light emitting diode or the like in order to remove the history of the photoconductor until the previous printing.

After uniformly charging the photosensitive member, a laser writing device 13, which is an image exposing means, performs image exposure based on an image signal. In this image exposure, an image signal input from a computer to a laser writing device or an image reading device is processed by an image signal processing unit shown in FIG. 2 and then input to the laser writing device to form a latent image on an image carrier. Is done.

The image signal will be described with reference to FIG. 2 assuming that it is input from an image reading device (not shown).

The image color signal B of the original is read from the image reading device 40.
Analog signals of (blue), G (green), and R (red) are input to the image signal processing unit 50. After this signal is A / D converted by the A / D conversion circuit 51, distortion due to the optical system or the like is removed by the shading correction circuit 52, and then temporarily input to the buffer memory 53 so that each of B, G, and R is the same image. Corresponds to the position. Next, B, G, from the buffer memory 53
The R signal is supplied to the complementary color conversion circuit 54 with Y (yellow), M
(Magenta), C (cyan) are converted into complementary colors y, m, c
Signal. This signal is subjected to gradation correction in the gradation correction circuit 55a, and then y,
The black component is extracted from each data of m and c to generate the digital signal k of the black component. Of these signals, the y, m, and c signals are color-corrected in the masking circuit 57, and are gradation-corrected again in the gradation correction circuit 55b together with the k signal, and the reproduced image is yellow (Y) magenta (M) cyan (C) black ( K) Red (R) [Yellow (Y) + Magenta (M)] Green (G) [Yellow (Y) + Cyan (C)] Blue (B) [Magenta (M) + Cyan (C)] 7 colors Is corrected so that it is configured with. on the other hand,
Y, m, c signal from masking circuit 57, black component extraction circuit
The re-exposure signal generation circuit 58, to which the k signal is input from 56, re-exposes the image (toner image) portion excluding the image portion of the black component, which is the final image exposure, if necessary. r is generated and input to the image signal storage circuit 59 together with the y, m, c and k signals. Each image signal is read from the image signal storage circuit 59 by a read circuit 60 according to the image exposure order (in this embodiment, the order of y, m, c, k) and the modulation circuit 61.
At, pulse width modulation or intensity modulation is performed and the data is sent to the laser writing device 13.

The laser writing device 13 uses a laser diode (not shown) as a light source to rotate a rotary polygon mirror 131, fθ.
An optical path is bent by a plurality of reflecting mirrors 133 through a lens 132 and the like to perform scanning, and a latent image is formed by rotation (sub-scanning) of the photosensitive drum 10. In this embodiment, the image portion is exposed (y) based on the image signal, and as shown in FIG. 5, the image portion has a lower potential VL (-100 V to 0).
To form a reverse latent image.

Yellow (Y) on the periphery of the photosensitive drum 10,
Developers each containing a developer composed of a toner T such as magenta (M), cyan (C), and black (K) and a carrier.
14 (Y), 14 (M), 14 (C), 14 (K) are provided, and the developing device for the first color (Y) is a developing device 14 for rotating a magnetic body built-in and holding a developer. (Y) developing sleeve 141
Done by The developer is composed of a carrier in which ferrite is used as a core and an insulating resin is coated around the core, and a toner T in which a pigment as a main material, a charge control agent, silica, titanium oxide and the like are added, The developer is regulated by the layer forming rod on the developing sleeve 141 to have a layer thickness of 300 to 800 μm and is conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.4 to more than the layer thickness (developer).
When the distance is 1.0 mm, AC bias of VAC (1.5 to 3.0 KV _PP ) and VDC are applied between the developing sleeve 141 and the photosensitive drum 10.
A DC bias of (-500 to -700V) is superimposed and applied. Since the charges of VDC and VH and the toner T are all of the same polarity, the toner T (Y), which has been given the opportunity to be separated from the carrier by VAC, does not adhere to the portion of VH having a higher potential than VDC, and is larger than VDC. A toner amount corresponding to the potential difference adheres to the VL portion having a low potential, and visualization (reversal development) is performed.

After the visualization of the first color is completed, the process for forming the second color image is started, the uniform charging is performed again by the scorotron charger 12, and the latent image based on the image data (m) of the second color is formed on the image exposing means. Formed by 13. At this time, the charge elimination by the PCL 11 performed in the image forming process for the first color is not performed because the toner T (Y) attached to the image portion for the first color scatters due to the sudden decrease in the potential around the toner.

Again over the entire surface of the photosensitive drum 10, V
A latent image similar to that of the first color (Y) is formed and developed on a portion of the photoconductor having the H potential but without the first color (Y) image, but the first color image is present. In the portion where the exposure and development are performed again on the portion, the toner T attached to the first color
VT due to the light shielded by (Y) and the electric charge of the toner itself
Latent image is formed, and development is performed according to the potential difference between VDC and VT. In the red (R) image portion formed by overlapping the first color (Y) image and the second color (M) image, if the development of the first color is performed by forming a latent image of VL, the first color (Y) image is formed. Since the amount of the second color (M) toner is smaller than the amount of toner and the balance is lost and red (R) color is not reproduced, the exposure amount of the first color for the portion where the two colors overlap is determined in the first invention. Image exposure is performed so that the intermediate potential becomes VH> VM (-100 to -300V)> VL by reducing the amount. In the image forming apparatus of the present embodiment, image exposure by laser light as shown in the following table is performed. It is a thing.

[0028]

[Table 1]

Here, both f (m) and f (c) are constants smaller than 1, and in the gradation correction circuit 55b shown in FIG. 2, laser exposure light L (y), L (m), For L (c), it is judged whether color reproduction is performed only by monochromatic light, or whether the second color image exposure is performed on the second color by another color and the second color image exposure is performed. For the image-exposed portions that are overlapped, the light amount modulation is performed in a form in which f (m) or f (c) is integrated.

The light quantity modulation of the laser output from the laser writing device 13 may be pulse width modulation for changing the duty ratio of the laser or intensity modulation for changing the laser output. By setting the constants f (m) and f (c) to appropriate values through experiments, clear red (R) and green colors can be obtained by superimposing the toner adhesion amount of the first color and the toner adhesion amount of the second color as equal amounts. It is possible to obtain reproduction color tones of (G) and blue (B). FIG. 3 is a flowchart of the above description.

For the third and fourth colors, the same image forming process as that for the second color is performed, and toner images of seven colors are formed on the peripheral surface of the photosensitive drum 10. The photoconductor drum 10 holding the toner image in this manner further rotates and is not recharged. Other than the image (toner image) finally formed by laser scanning based on the r signal of the laser writing device 13, Re-exposure is performed only on the image portion. The re-exposure of the image portion with a laser is performed so that the electric charge of each image portion is removed by the exposure, transfer repellency is prevented, and good transfer is performed in the next transfer step.

On the other hand, the recording paper P, which is the transfer material fed from the paper feed cassette 21 by the paper feed mechanism 22 and the timing roller 24 in synchronization with the toner image, is a transfer means in which the transfer belt 31 is stretched. The multi-color toner images on the peripheral surface of the photoconductor drum 10 are collectively transferred onto the recording paper P by being fed to the transfer area by the transfer belt device 30.

The transfer belt 31 is an endless rubber belt having a resistance of 10 ⁸ to 10 ¹⁴ Ω · cm and a thickness of 0.4 to 1.0 mm and an FLC layer formed on the outside of a urethane rubber base, and prevents deviation during rotation. Therefore, a rib may be provided at the end. It should be noted that a film such as PET or a high resistance belt such as a film coated with these may be provided if a charge removing mechanism is provided.

Holding roller 3 for stretching the transfer belt 31
A voltage of VPC is applied to the shaft 32a of the upstream side holding rollers 32 of Nos. 2 and 33, and at a position in contact with the shaft 32a via the transfer belt 31, the recording paper P is electrically conductive as a charging unit. Brushes 34 are installed in a grounded state. The fed recording paper P enters between the brush 34 and the transfer belt 31, and the brush 34 injects an electric charge into the recording paper P, so that an attraction force is exerted between the recording paper P and the transfer belt 31. Occurs. After that, the recording paper P enters the nip portion (transfer area) 35 formed by the photosensitive drum 10 and the transfer belt 31, and the transfer electric field is generated from the back surface of the transfer belt 31 by the corona discharger 36 or a bias roller instead. The multicolor toner image is transferred and transferred onto the recording paper P.

The recording paper P holding the transferred multicolor toner image is subjected to static neutralization by AC corona discharge using the shaft 33a of the holding roller 33 on the downstream side, which stretches the transfer belt 31, as an opposing electrode, or AC. Separating from the transfer belt 31 while receiving corona discharge. A cleaning blade 37 removes the toner adhering to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photosensitive drum 10 about a shaft 33a of a holding roller 33 on the downstream side as a rotation center during formation of a multicolor toner image and re-exposure.

The recording paper P, which holds the multicolor toner image separated from the transfer belt device 30, is transferred to the fixing device 23 which is composed of two pressure-bonding rollers having a heater at a close position inside or outside one of the rollers. The adhered toner is conveyed and is applied with heat and pressure between the pressure bonding rollers to be melted, fixed on the recording paper P, and then discharged to the outside of the apparatus.

After the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then reaches a cleaning device 16 which is a cleaning means to contact the photoconductor. It is scraped off into the cleaning device 16 by the cleaning blade 16a made of the rubber material and discharged or stored by a screw or the like.

The photoconductor drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed by the PCL 11 and then uniformly charged by the scorotron charger 12 to start the next image forming cycle. During the formation of the multicolor toner image and the re-exposure, the cleaning blade 16a is separated from the surface of the photoconductor, and the AC neutralization by the static eliminator 15 is disabled.

In the embodiment described above, the exposure light amount when the toner of another color develops and adheres to the exposure light amount of the image portion to which the toner of only one color is attached for the exposure of the specific color. It is an embodiment of the first invention for performing light quantity modulation so as to reduce

In the second invention described below, the exposure light amount does not perform the light amount modulation particularly for the first color, but the toner to be developed (in the image forming apparatus shown in FIG. M) toner and (C) toner have a higher number of pigment parts than the toner ((Y) toner) on which the first color is developed, and the toner adhesion amount of the second color is smaller than the toner adhesion amount of the first color. This is intended to correct a color balance imbalance.
FIG. 4 is a graph showing the relationship between the toner adhesion amount on the photoconductor and the reflection density for toners having different numbers of pigment parts. The reflection color density is (a) in the case where the amount of toner adhering to the second color pigment is 2 parts. If the toner of the second color is also 2 parts of the pigment, the reflection color density in the case of the amount of the second color toner deposited on the photoconductor is (b),
When the color density of (a) overlaps with the color density of (a), it is not possible to obtain a clear and well-balanced overlapping color tone of red (R), green (G), and the like. If, for example, the toner of 4 parts of pigment is used for the toner of the second color, the reflection color density is (c) even if the toner adhesion amount on the photoconductor is
However, when the color density of (c) overlaps the color density of (a), it is possible to obtain a balanced overlay color tone that is almost satisfactory.

Regarding the (M) toner in the examples, the (M) toner may be used as both the first color toner and the second color toner. In this case, it is appropriate to use 4 parts of pigment. Thus, the reflection color density of only one color is close to that of (a) ((a ′) in FIG. 4), and in the case of the second color, it is (c), and a good color tone is obtained. Further, in the above description, an example in which the number of pigments is increased to 4 parts of pigment has been described, but the present invention is not limited to this.

[0042]

According to the present invention, not only the color image portion of only one color but also red (R), green (G) and blue obtained by superimposing the second color toner on the first color toner are obtained. With regard to the color tone of the combined image portion of (B), a well-balanced and clear color image can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention.

FIG. 2 is a block diagram showing an example of an image signal processing unit of the image forming apparatus of the present invention.

FIG. 3 is a flowchart showing toner image formation according to the present invention.

FIG. 4 is a graph showing a relationship between a toner adhesion amount and a reflection color density.

FIG. 5 is a flowchart showing the principle of a multicolor image forming method.

FIG. 6 is an explanatory diagram showing a state in which toners of two colors are superposed on a photoconductor.

[Explanation of symbols]

 10 Photoconductor drum (image bearing member) 11 PCL 12 Scorotron charger 13 Laser writing device 14 Developing device 15 Static eliminator 16 Cleaning device 16a Cleaning blade 30 Transfer belt device 50 Image signal processing unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G03G 15/04 116 H04N 1/23 103 C 9186-5C

Claims (4)

[Claims] 1. An image forming apparatus for repeating a process of charging, image exposure and development to form a multicolor toner image by superposing toner images on an image carrier and transferring and fixing the multicolor toner image on a transfer material. In regard to the exposure light amount, the exposure light amount for the image portion where the toner of only one color is adhered for the exposure of the specific color and the exposure light amount when the toner of the other color is developed and adhered are modulated. An image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, wherein the light amount modulation is performed by pulse width modulation of a laser. 3. The image forming apparatus according to claim 1, wherein the light quantity modulation is based on a laser intensity modulation. 4. An image forming apparatus that repeats the steps of charging, image exposure and development to form a multicolor toner image by superimposing toner images on an image carrier, and transfers and fixes the multicolor toner image on a transfer material. The image forming apparatus is characterized in that the toner to be developed on the image portion on which toner has already been attached has a higher number of pigment portions than the toner on which the first color is developed.