JP3160060B2 - Multicolor image forming method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming a multicolor image used in a multicolor image forming apparatus such as an electrophotographic copying machine, a facsimile, a printer and the like. The present invention relates to a method and an apparatus for forming a multicolor image in which images are formed in a superimposed manner and the superimposed toner image is collectively transferred to a transfer material.

[0002]

2. Description of the Related Art Conventionally, in a multicolor image forming method in which a multicolor toner image is formed on a photoreceptor by repeating charging, optical writing, and development, and is collectively transferred to a transfer material, for example,
When a yellow toner image is formed on a photoconductor on which a black toner image is formed, it is known that a phenomenon that black toner is scattered around a yellow toner image portion around the black toner image (hereinafter referred to as toner scatter) occurs. (See, for example,
133073). This phenomenon is illustrated in FIG.
Description will be made based on (b). As shown in FIG.
In the image forming process of the yellow image, when corona charging is performed in a state where the black toner is adhered on the photoreceptor, the charged potential of the portion without toner is, for example, -900 V, and the portion with toner is -100 V, for example. The lower photoconductor is-
Charge to 800V. Here, when the peripheral portion of the black toner image is exposed to an image signal of a yellow image, the photoconductor potential drops to -100 V as shown in FIG. 7B, but the photoconductor potential under the black toner becomes-. It remains at about 800V. Therefore, at the boundary, the negatively charged black toner scatters around. This is toner scattering.

In order to prevent this, in the above publication,
In order to reduce the potential difference at the boundary between the black toner image and its peripheral portion, it has been proposed to lower the charging potential at the time of forming a yellow image.

[0004]

However, if the charging potential is lowered and the developing bias voltage is fixed, the background becomes dirty. Further, if the charging potential is lowered and the developing bias is also lowered in order to prevent this background contamination, there arises a problem that the developing potential becomes small and a sufficient density cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a multicolor image forming apparatus for forming a superimposed toner image of a plurality of colors on a photoreceptor. Without inviting, it is an object to prevent toner scattering due to image light writing on an adjacent portion of a previously developed toner image.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, an image forming step including charging, image light writing, and developing steps is repeated for each color.
In a multicolor image forming method in which a multi-colored toner image is formed on a photoreceptor and the multi-colored toner image is collectively transferred to a transfer material, in the image forming process for the second and subsequent colors, the image light writing process is completed. And an edge in a toner image portion of another color formed in the preceding image forming process, which is present in a photoreceptor portion corresponding to a non-image portion of an image in the image forming process.
The optical writing is performed to reduce the potential of the photoreceptor to a potential at which the toner does not adhere by development.

[0007]

According to a second aspect of the present invention, an image forming step including charging, image light writing, and developing steps is repeated for each color to form a superimposed toner image of a plurality of colors on a photoreceptor. In the multi-color image forming method of collectively transferring the superimposed toner image onto the transfer material, in the image forming process for the second and subsequent colors,
When performing image light writing adjacent to a toner image portion of another color formed in the preceding image forming process, which is formed on the photosensitive member portion corresponding to the non-image portion of the image related to the image forming process, By the time the writing step is completed, optical writing is performed on an edge of the toner image portion where the image light writing is performed adjacently, so that the potential of the photoconductor is reduced to a level at which toner does not adhere by development. It is assumed that.

Here, in the first or second aspect of the present invention, the potential of the photosensitive member to which the toner does not adhere is determined by the magnitude of the developing bias used for the development and the like. If the development potential, which is the potential difference, is a potential that is smaller than 200 V,
It is possible to prevent toner adhesion. The optical writing may be performed only when the other color is black.

Further, according to the invention of claim 3, the photosensitive member,
Device, optical writing optical device, developing device, and image information of each color.
Generating a drive signal for the optical writing optical device based on the
And a drive signal generating means for each color.
Repeat image forming process including optical writing and developing processes
To form a multi-color superimposed toner image on the photoreceptor,
Multi-color image forming device that collectively transfers toner image to transfer material
The image information of each color toner image formed on the photoreceptor.
An image information storage unit for storing the driving signal;
To the image formed by the preceding image forming process.
The second color based on the storage contents of the image information storage unit.
When writing an image in the subsequent image forming process,
In the photoreceptor portion corresponding to the non-image portion of the image related to the forming process.
Toners of other colors formed in the preceding image forming process
-When writing image light adjacent to the image area,
The edge of the image portion where the image light writing is performed adjacently
It is configured to generate a drive signal for performing optical writing.
It is characterized by having. According to a fourth aspect of the present invention, there is provided a photoconductor, a charger, an optical writing optical device, a developing device, and a drive signal generating means for generating a driving signal of the optical writing optical device based on image information of each color. The image forming process including the steps of charging, image light writing, and developing is repeated for each color to form a superimposed toner image of a plurality of colors on a photoconductor, and the superimposed toner image is collectively transferred onto a transfer material. In the multi-color image forming apparatus for transferring, an image information storage unit for storing image information of each color toner image formed on the photoreceptor is provided, and the driving signal generation unit is provided for the image formed by the preceding image forming step. based on the stored contents of the image information storage unit, the optical specification with respect to the edge portion of the 2 time of image writing in of the subsequent colors of the image forming process, the preceding image forming toner images of other colors are formed by the steps It is characterized in that it has configured to generate a drive signal for causing a write.

The invention of claim 5 is the invention of claim 3 or 4
In the multicolor image forming apparatus of (1), the optical writing optical device is configured so that the light source for writing image light is also used for writing light to the toner image portion, and the drive signal generation unit is configured to output the image light. A drive signal for switching the light emission amount of the light source for writing and for optical writing is generated.

[0012]

According to the present invention, in the image forming process for the second and subsequent colors, by the time the image light writing process is completed, the image forming process preceding the photosensitive member portion corresponding to the non-image portion of the image in the image forming process is performed. Optical writing is performed on the formed toner image portion of another color to lower the photoreceptor potential of the toner image portion, whereby image light is written on the adjacent portion of the toner image portion and the image light is written on the adjacent portion. Even when the photoconductor potential of the portion is lowered, the potential difference between the toner image portion and the adjacent portion is set to a potential at which the toner constituting the toner image does not scatter. Here, the optical writing to the toner image portion is performed so that the potential of the photoconductor is reduced to a level at which the toner does not adhere by development. So that toner due to development does not adhere to the part.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine having a full color mode as an image forming apparatus (hereinafter referred to as a copying machine) will be described below. FIG. 1 (a)
1 is a schematic configuration diagram of a copying machine according to an embodiment. First, an outline of the image forming operation in the full-color mode will be described. In the full-color mode, a yellow (hereinafter, referred to as Y) image is written by the laser beam L onto the photoreceptor 2 uniformly charged to −900 V by the scorotron charger 1, thereby forming an image on which toner is to be attached. The electrostatic latent image of a negative Y image (hereinafter referred to as Y
A latent image is formed. Here, the potential of the image portion is −
It has dropped to 100. This Y latent image is a negatively charged Y
The image is reversely developed by a Y developing device 3 provided with a toner to form a Y toner image. The developer employs one non-magnetic component. The transfer unit 7 and the cleaning unit 8 are retracted from the surface of the photoreceptor 1 during the superposition development, and the transfer and cleaning are not performed, and the second color image is formed (image forming process).
Enter.

Photoconductor 3 with Y toner image formed
Is charged uniformly to -900 V again by the scorotron charger 1, and then the laser exposure L
, A magenta (hereinafter, referred to as M) image is written, and a negative M electrostatic latent image (hereinafter, referred to as M latent image) is formed. This M latent image is reversal-developed by the M developing device 4 having the negatively charged M toner without disturbing the image of the first color due to non-contact, and becomes an M toner image.

Thereafter, similarly, a cyan (hereinafter, referred to as C) toner image and, if necessary, a black (hereinafter, referred to as K) toner image are formed by using the C developing device 5 and the K developing device 6.

The superimposed toner image on the photoreceptor 2 is transferred to the transfer roller 7 of the transfer unit 7 returned to the normal operation position.
A positive DC bias is applied to “a”, and the image is transferred onto the transfer paper sent from the registration roller 9. Further, the fixing device 1
0 and is discharged by the discharge roller 11. On the other hand, the transfer residual toner on the photoreceptor is subjected to pre-cleaning charge removal by DC superimposed AC charging by the pre-cleaning charge remover 12, and then the conductive fur brush 8 of the cleaning unit 8 is returned to the normal operation position.
Cleaning is performed by a.

In the above example, the order of forming the toner images is Y, M, C and, if necessary, K. However, the present invention is not limited to this, and the toner images may be formed in any predetermined order. The formation may be performed.

Next, prevention of toner scattering due to image exposure will be described. As described above, in the image formation for the second and subsequent colors, when the adjacent portion of the already developed toner image corresponds to the image portion of the image related to the image formation, the image signal exposure is performed on the adjacent portion. The potential of the adjacent portion is reduced to -100 V by this image signal exposure, whereas if the photosensitive member potential of the toner image portion remains at -800 V, the potential difference between the two portions in the toner image portion near the boundary between the two portions. There is a possibility that the toner constituting the toner image is scattered in the image area.

Therefore, in this embodiment, FIG.
As shown in the image portion of the image according to the image formation of the second color after B
Is also adjacent to the toner image portion A already formed on the photoconductor, when the image signal exposure related to this image formation is completed,
As shown in FIG. 1C, the potential difference between the image portion B and the toner image portion A is a potential difference that does not cause toner scattering, and the photoconductor potential of the toner image portion is such that toner does not adhere by development. Optical writing for preventing toner scattering is performed on the toner image portion A so that the potential becomes.

Here, the development potential, which is the potential difference between the photoconductor potential and the development bias used for development, is usually 20.
When the voltage is lower than 0 V, toner adhesion due to development does not occur, and when the potential difference between the photosensitive member potential of the toner image portion and the image portion B is 500 V or less, toner scattering does not occur. Optical writing for preventing toner scattering is performed so that the potential becomes about -600 V, for example.

It is desirable that the exposure amount of the optical writing for preventing toner scattering be different depending on whether the already formed toner image is color (Y, M, C) or K. This is because the transmittance of laser light differs between the color toner and the K toner, and the amount of exposure necessary to obtain a photoconductor potential of a target toner image portion differs. For example, FIG. 2 shows the exposure amount of the laser beam on the horizontal axis, the photoconductor potential on the vertical axis, a when no toner is attached, b when color toner is attached b, and K toner is attached 13 is a graph showing the relationship between the exposure amount and the photoconductor potential for each of cases c. As can be seen from this graph, since the transmittance of the K toner is smaller than that of the color toner, the potential of the photoreceptor is reduced to a target of, for example, -600 V.
Exposure amount P ₁ required for photoconductor color toner is K
Towards exposure amount P ₂ required in the case of the toner increases.

In order to perform the above-described optical writing for preventing toner scattering, in this embodiment, a laser light source LD for exposing an image signal is used. FIG. 3 is a block diagram of the electrical unit for driving the laser light source. The electrical unit is configured so that image data from an image signal processing unit (not shown) is input to the data conversion circuit 21. This image data is converted by the data conversion circuit 21 into a light emission intensity signal. This emission intensity signal is sent to the LD drive circuit 22 that drives the laser light source LD. In the present embodiment, in order to perform the optical writing for preventing the toner scattering, a write image information storage unit 23 which is an image information storage unit for storing image data relating to an executed image formation is provided. . At the time of image signal exposure in image formation for the second and subsequent colors, the data from the image information storage unit 23 is used as position information of the toner image portion already formed on the photoconductor 2 as
The data is input to the data conversion circuit 21 in synchronization with the image data from the image processing unit. The data conversion circuit 21 generates a light intensity signal for normal image signal writing based on the image data from the image processing unit, sends the light intensity signal to the LD drive circuit 22, and based on the data from the written image information storage unit 23. A light intensity signal for toner scattering prevention exposure is generated and sent to the LD drive circuit 22. Here, the data conversion circuit 21 according to the present embodiment determines the light intensity signal for writing the image signal for the portion included in the image portion related to the image signal exposure among the toner image portions already formed on the photoconductor 2. Is configured to generate

The light intensity signal for toner scattering prevention exposure is, as described above, an exposure amount P ₁ for a color toner image.
And a signal corresponding to the exposure amount P ₂ for the K toner image can be selectively generated, an arithmetic circuit for selecting a light intensity signal for toner scattering prevention exposure is provided by:
It is added to the write image information storage unit 23 or the data conversion circuit 21.

In the above configuration, for example, FIG.
As shown in the figure, the English character "A" is used as the first color K toner image.
When a rectangular image (an image portion in the Y image) located around the upper half of the English character “A” is formed as the second color Y toner image in a state where “Y” and “B” are formed, the main scanning shown in FIG. The exposure amount for each position on the line 1 is as shown in FIG. That is, a range of points l _{1 to} l _2, a range of points l _{3 to} l ₄ , and a range of points l _{5 to} l ₆ , which are rectangular image portions to be developed with the Y toner, are used for normal image signal exposure. Laser light source L driven based on the light intensity signal of
D is exposed by a laser at an exposure amount P ₀ , and is a K toner image area in the range of points l _{2 to} l ₃ and points l _{4 to} l ₅
Is the exposure amount P by the laser from the laser light source LD driven based on the light intensity signal for preventing toner scattering.
Exposure at ₂ . These two types of exposure are performed during one main scan on the main scan line l.

As described above, according to this embodiment, in the image formation for the second and subsequent colors, optical writing for preventing toner scattering is performed on the toner image portion already formed on the photosensitive member 2, so that toner scattering is prevented. can do. Further, as long as it is included in the non-image portion of the image related to the second or subsequent image formation, the toner is scattered to all of the toner image portions already formed on the photoreceptor 2 irrespective of whether they are adjacent to the image portion. Since the optical writing for prevention is performed, it is possible to minimize the improvement of the electrical unit for optical writing for preventing toner scattering.

In the above embodiment, optical writing for preventing toner scattering is performed not only at the edge portion of the toner image but also at the center portion. However, toner scattering is almost caused by toner from the edge portion. Therefore, for example, as shown in FIG. 5B, optical writing for preventing toner scattering may be performed only on the edge portion of the toner image. FIG. 5A shows the potential of the toner image portion adjacent to the image portion when optical writing for preventing toner scattering is not performed, for comparison. In order to perform the optical writing for preventing toner scattering to only the edge portion, for example, a determination circuit for determining the edge portion of the toner image on the photoconductor 2 using the data from the written image information storage unit 23 is provided. And the edge part data generated by this is input to the data conversion circuit 21.

In the above-described embodiment, as long as the non-image portion of the image relating to the second or subsequent image formation is included in the non-image portion, the image is already formed on the photosensitive member 2 regardless of whether it is adjacent to the image portion. In this case, optical writing for preventing toner scattering is performed on all the toner image portions.
As shown in FIG. 3A, a hatched area indicates an optical writing area for preventing toner scattering, and only a portion adjacent to the image section of the toner image section included in the non-image section has light for preventing toner scattering. Writing may be performed. FIG. 6B shows an exposure amount for each position on the main scanning line 1 in FIG. 6A. In this case, FIG.
Since the image portion of the English character "B" is not adjacent to the image portion of the Y image, no optical writing for preventing toner scattering is performed on the K toner image portion of the English character "B". In order to perform such optical writing for preventing toner scattering, for example, the above-described data conversion circuit 21 is used based on the image data from the image signal processing unit and the data from the written image information storage unit 23 as described above. A function for determining the position of the toner image portion adjacent to the image portion may be provided, or data from a circuit for performing such determination may be sent to the data conversion circuit 21 instead of the data from the written image information storage portion 23. You may input it.

In the above-described embodiment, in the image formation for the second and subsequent colors, optical writing for preventing toner scattering is performed for toner images of all colors already formed on the photosensitive member 2. Since the toner scattering of the K toner is most noticeable and the toner scattering of the color toner is not so noticeable, only when the K toner image has already been formed on the photoreceptor 2 in the image formation for the second and subsequent colors. ,
Optical writing for preventing toner scattering may be performed on the K toner image. In this case, only the image data relating to the K image is stored in the write image information storage unit 23.

Further, in the above embodiment, the light source for image signal exposure is also used as the light source for optical writing for preventing toner scattering, but another optical writing light source for preventing toner scattering is provided instead. Is also good. Also in this case, since toner scattering occurs due to image signal exposure, optical writing for preventing toner scattering is performed until the image signal exposure is completed.

[0030]

According to the first to fifth aspects of the present invention, in the image forming process for the second and subsequent colors, by the time the image light writing process is completed, the photosensitive material corresponding to the non-image portion of the image related to the image forming process is obtained. Optical writing is performed on a toner image portion of another color formed in the image forming process preceding the body portion to lower the photoconductor potential of the toner image portion, thereby reducing the potential of the toner image portion adjacent to the toner image portion. Even when the image light writing is performed and the photosensitive member potential of the adjacent portion is lowered, the potential difference between the toner image portion and the adjacent portion is set to a potential that does not disperse the toner constituting the toner image. It is possible to prevent toner scattering due to image light writing to a portion adjacent to a previously developed toner image without causing a decrease in the density of the image portion. Optical writing to the toner image portion is performed such that the potential of the photoconductor is reduced to such a level that the toner does not adhere to the toner by development. The toner is prevented from adhering to the image, so that the image is not stained.

In particular, according to the first aspect of the invention, optical writing for preventing toner scattering is performed on the edge of the toner image except for the center of the toner image where there is almost no possibility of toner scattering. Thus, optical writing for preventing toner scattering can be performed efficiently, and fatigue of the photoconductor can be relatively reduced.

According to the second aspect of the present invention, when the image light writing is performed adjacent to the toner image portion where the toner may be scattered, the image light writing is performed adjacent to the toner image portion. Since optical writing for preventing toner scattering is performed on the edge, optical writing for preventing toner scattering can be performed more efficiently, and fatigue of the photoconductor can be relatively reduced.

According to the third or fourth aspect of the present invention, the area in which the optical writing for preventing toner scattering is performed is stored in the image information storage section for storing image information of each color toner image formed on the photosensitive member. Therefore, optical writing for preventing toner scattering can be performed with high accuracy.

According to the fifth aspect of the present invention, since the light source for writing image light is also used as the light source for writing light for preventing toner scattering, the cost is not increased and the exposure control is easy. is there.

[Brief description of the drawings]

FIG. 1A is a front view illustrating a schematic configuration of a copying machine according to an embodiment, and FIGS. 1B and 1C are explanatory diagrams of a change in photoconductor potential due to writing of toner scattering prevention light.

FIG. 2 is a graph showing a relationship between an exposure amount and a photoconductor potential.

FIG. 3 is a block diagram of an electrical unit for driving the laser light source of the copying machine.

4A is an explanatory diagram of an example of an image, and FIG. 4B is a graph showing an exposure amount for each position on a certain main scanning line in the image.

FIG. 5A is a potential distribution diagram of a toner image portion, and FIG. 5B is a potential distribution diagram when optical writing for preventing toner scattering according to a modification is performed.

6A is a graph showing an exposure amount at each position on a certain main scanning line in the same image when performing optical writing for preventing toner scattering according to a modified example, and FIG. 6B is a graph showing the same. FIG. 4 is an explanatory diagram of an optical writing unit for preventing toner scattering in the same image when performing optical writing for the image.

FIGS. 7A and 7B are explanatory diagrams of toner scattering. FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 scorotron charger 2 photoreceptor 3 Y developing device 4 M developing device 5 C developing device 6 K developing device 7 transfer unit 8 cleaning unit 9 registration roller 10 fixing device 21 data conversion circuit 22 LD drive circuit 23 write image information storage section LD Laser light source L Laser light

Continued on the front page (72) Inventor Kenji Okada 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Yoshio Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company In Ricoh (56) References JP-A-63-68865 (JP, A) JP-A-63-292157 (JP, A) JP-A-63-172284 (JP, A) JP-A-2-156261 (JP, A) JP-A-4-50964 (JP, A) JP-A-1-287581 (JP, A) JP-A-3-72380 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/01 G03G 15/01-15/01 117

Claims (5)

(57) [Claims] An image forming process including charging, image light writing, and developing is repeated for each color to form a multi-colored toner image on a photoreceptor, and the superposed toner image is formed on a transfer material. In the multi-color image forming method of collectively transferring, in the image forming process for the second and subsequent colors, before the image light writing process is completed, the image present in the photoconductor portion corresponding to the non-image portion of the image related to the image forming process Optical writing is performed on the edge portion of the toner image portion of another color formed in the formed image forming step so as to reduce the photoconductor potential to a potential at which toner does not adhere by development. Multicolor image forming method. 2. Charging, image light writing, and development for each color.
By repeating the image forming process including each process of
A toner image is formed on the photoreceptor, and the superimposed toner image is transferred.
In the multi-color image forming method of collectively transferring to a material, in the image forming process for the second and subsequent colors ,
The tip that exists on the photoconductor portion corresponding to the non-image portion of the image
And the other color toner image formed in the image forming process.
When image light writing is performed adjacently, image light writing
By the time the process is completed, the image light writing of the toner image portion
The photoconductor potential to the edge where
Writing to reduce the potential to a level where toner does not adhere
A multicolor image forming method. 3. A photoconductor, a charger, and an optical writing optical device.
, A developing unit, and the optical writing based on the image information of each color.
Driving signal generation means for generating a driving signal for the optical device.
Charge, image light writing, and development steps for each color
Repeat the image forming process including
An image is formed on a photoconductor, and the superimposed toner image is collectively transferred to a transfer material.
In a multicolor image forming apparatus for transferring , image information of each color toner image formed on a photoconductor is stored.
An image information storage unit is provided, and the drive signal generation unit is operated by a preceding image forming process.
Stored contents of the image information storage unit about the formed image
Based on the image writing for the image forming process for the second and subsequent colors
At the time of embedding, it corresponds to the non-image portion of the image related to the image forming process
Formed in the preceding image forming process existing in the photoconductor
Image light writing adjacent to the other color toner image area
When performing, the image light writing of the toner image portion is adjacent to the image light writing.
Drive signal to perform optical writing on the edge
A multi-color image forming apparatus characterized in that
Place. 4. A photoconductor, a charger, an optical writing optical device, a developing device, and drive signal generating means for generating a driving signal of the optical writing optical device based on image information of each color, An image forming process including charging, image light writing, and developing steps is repeated for each color to form a multi-color superimposed toner image on a photoreceptor, and collectively transfer the superimposed toner image to a transfer material. In the image forming apparatus, an image information storage unit for storing image information of each color toner image formed on the photoreceptor is provided, and the drive signal generation unit is configured to store the image information of the image formed by the preceding image forming process. based on the stored contents of the parts, 2 during image writing in of the subsequent colors of the image forming step, the line optical writing with respect to an edge portion of the preceding image forming toner images of other colors are formed by the steps Multi-color image forming apparatus characterized by being configured to generate a drive signal for. 5. The optical writing optical device according to claim 1, wherein the light source for writing the image light is also used for writing the light to the toner image portion. 5. The multicolor image forming apparatus according to claim 3 , wherein a drive signal for switching a light emission amount of the light source is generated for the optical writing.