JPH1039654A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can prevent generation of transfer dust without loosing sharpness of an image by restraining influence of edge efficiency in a profile part of a toner image on an intermediate transfer member. SOLUTION: An edge part of image data read by a color scanner 1 is detected and lapped based on a result from comparison of density with an image data inside part adjacent the edge part in an image processing part. Potential of the edge part of a latent image optically written by an optical unit 8 is adjusted by this image processing and a toner image in which toner bonded amount ratio a/b with the profile part and the profile part inside part of the toner image is 1.0<=a/b<1.3 is formed on an intermediate transfer belt 19.

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 copying machine, a facsimile, a printer, a printing machine and the like, and more particularly, to a toner image forming means for forming a toner image on an image carrier, and an intermediate transfer member. And a transfer unit for transferring a toner image on the image carrier.

[0002]

2. Description of the Related Art In recent years, an electrophotographic image forming apparatus capable of copying and printing a full-color image has been put to practical use. As a method of transferring a full-color image onto a transfer material in this type of image forming apparatus, (A) Transfer drum method:
Yellow (Y), magenta (M), cyan (C), black (B) formed for each color on an image carrier such as a photoconductor.
(B) an intermediate transfer method: Y, M formed for each color on an image carrier such as a photoconductor, wherein each image of (K) is sequentially superimposed and transferred onto a transfer material fixed on a transfer drum. , C, B
Each image of K is sequentially superimposed and transferred on an intermediate transfer body, and a full-color toner image on the intermediate transfer body is collectively transferred and transferred to a transfer material. The intermediate transfer method (b) is advantageous in that it has a paper-free property that it can be transferred, and that it is possible to copy the entire surface without being unable to form an image on the clamp / holding portion at the tip unlike the transfer drum method. is there.

Conventionally, in the above-described intermediate transfer type image forming apparatus, a phenomenon of toner dust (hereinafter referred to as transfer dust) sometimes occurs when a toner image is transferred from an image carrier to an intermediate transfer member. Are known. Here, the transfer dust refers to the toner image (visible image) formed on the image carrier when the toner image is transferred from the image carrier to the intermediate transfer member (primary transfer). This is a phenomenon in which the image is not transferred to the position, but is diffused and transferred to the periphery thereof, and as a result, the image is blurred. In particular, the sharpness of the image in a thin line portion is impaired.

As a technique for preventing the transfer dust, for example, the charge of the toner image transferred onto the intermediate transfer member is removed by a charge remover arranged opposite to the intermediate transfer member, so that the next toner image can be removed. There has been known an image forming apparatus which prevents electrostatic repulsion between a toner image on an intermediate transfer member and a toner image on an image carrier during transfer (Japanese Patent Application Laid-Open No. 1-28-28).
No. 4883). According to this, it is possible to prevent transfer dust and obtain a good image.

[0005]

However, the present inventor has studied and found that the cause of the above-mentioned transfer dust is the influence of the edge effect. FIG. 8 shows the intermediate transfer member 19.
FIG. 7 is an explanatory diagram of a process of forming a toner layer by superimposing toner images sequentially. Generally, a large amount of toner tends to adhere to an edge portion of a latent image formed on a photoconductor as an image carrier due to an edge effect. Therefore, the toner layer formed on the intermediate transfer member 19 is relatively thicker at the outline than at the center, and the ratio of the thickness of the toner layer between the outline and the center becomes larger as the color is superimposed. Become.
On the other hand, in a region where the transfer bias does not act on the intermediate transfer member, the toner is held by the image force of the intermediate transfer member caused by electrostatic induction or the like, and the holding force is limited. Therefore, it is difficult to hold the toner by the intermediate transfer member particularly at the contour portion where the toner layer is relatively thicker than the central portion of the toner image due to the edge effect. As a result, the toner in the upper layer of the toner image is diffused out of the image range due to the electrostatic repulsion between the toners, causing transfer dust.
Therefore, even if the electrostatic repulsion between toner images is suppressed by the above-described technology for preventing transfer dust, if the amount of toner adhering to the contour of the toner layer formed on the intermediate transfer member is large due to the effect of the edge effect. In addition, transfer dust may occur.

Although only an electrophotographic image forming apparatus capable of copying and printing a full-color image has been described herein, an electrophotographic image forming apparatus capable of copying and printing a single-color image is also described. Similarly, transfer dust may occur due to the edge effect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of suppressing the influence of an edge effect and preventing the occurrence of transfer dust without impairing the sharpness of an image. To provide.

[0008]

In order to achieve the above object, according to the present invention, there is provided a toner image forming means for forming a toner image on an image carrier, and an image forming apparatus comprising: In the image forming apparatus provided with a transfer unit for transferring a toner image, a is a maximum amount of toner attached to a contour portion of the toner image on the intermediate transfer body, and a toner attached amount is an inner portion of the toner image close to the contour portion. Where b is 1.0 ≦ a / b
It is characterized by satisfying the condition represented by <1.3.

In the image forming apparatus according to the first aspect of the present invention, by satisfying the above condition, the amount of toner adhered to the contour portion of the toner image on the intermediate transfer member can be made smaller than the toner image inner portion adjacent to the contour portion. So that it does not become too large. The amount of toner attached to the contour of the toner image affects the occurrence of transfer dust due to the edge effect. If the amount of toner attached to the contour is suppressed, the toner in the upper layer of the toner image will It is held on the intermediate transfer member without being diffused out of the image range due to electrostatic repulsion. On the other hand, if the amount of toner adhered to the outline of the toner image is excessively suppressed, the sharpness of the image may be impaired. Therefore, it is desirable to set a lower limit value for the degree of suppression. According to the study by the present inventor, when the ratio a / b of the toner adhesion amount between the contour portion of the toner image and the inner portion of the toner image satisfies 1.0 ≦ a / b <1.3, It was confirmed that the edge effect was suppressed, and a sharp image with less transfer dust was obtained.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the above condition is satisfied by image processing.

In the image forming apparatus of the present invention, the distribution of the amount of toner adhered to the toner image on the intermediate transfer member is formed by image processing so as to satisfy the above condition. For example, the image processing unit detects an edge portion of the image data read by the image reading unit, compares the density of the detected edge portion with the inner portion of the image data adjacent to the edge portion, and compares the density with the edge portion. Weight based on the result. By this image processing, in the image forming apparatus using the negative / positive developing method, the latent image potential at the edge portion is formed to be higher than the image data inside portion. Further, in an image forming apparatus employing the positive / positive developing method, the latent image potential at the edge portion is formed to be lower than the image data inner portion. Depending on how the latent image potential is formed, the magnitude of the edge effect of the image contour changes.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the above condition is satisfied by controlling a developing gap.

According to the third aspect of the present invention, the distribution of the amount of toner adhered to the toner image on the intermediate transfer member is formed so as to satisfy the above condition by controlling the developing gap. The control of the developing gap is to control the gap between the image carrier and the developing device, and the size of the gap changes the magnitude of the edge effect of the image contour.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, there is provided a transfer unit for sequentially transferring the toner images on the image carrier to the intermediate transfer body by superimposing them.
The above condition is satisfied, where a is the maximum amount of toner attached to the contour of the toner image superimposed on the intermediate transfer member, and b is the amount of toner attached to the inner portion of the toner image close to the contour. It is assumed that.

In the image forming apparatus according to the present invention, by satisfying the above condition, the toner adhesion amount of the toner image superimposed on the intermediate transfer member can be made smaller than that of the toner image inner part close to the contour portion. So that it does not become too large.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a full-color copying apparatus (hereinafter, referred to as a color copying apparatus) as an image forming apparatus will be described. The intermediate transfer member may be configured as an intermediate transfer drum in addition to the intermediate transfer belt. However, in the following description, an example in which the intermediate transfer belt is configured as an intermediate transfer belt will be described.

FIG. 1 is an enlarged view around a photoreceptor and an intermediate transfer belt of a color copying apparatus according to this embodiment, and FIG. 2 is a schematic configuration diagram of the entire color copying apparatus. A color image reading device (hereinafter, referred to as a color scanner) 1 irradiates an image of a document 3 with an illumination lamp 4 and reflects the reflected light on a mirror 5.
An image is formed on a color sensor 7 via a mirror group such as a, 5b, and 5c and a lens 6. The color image information of the document 3 formed on the color sensor 7 is, for example, blue (hereinafter, referred to as “B”), green (hereinafter, referred to as “G”), and red (Red, hereinafter referred to as “R”). ) Is read for each color separation light and converted into an electrical image signal. In this embodiment, the color sensor 7 is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD.
Performs color simultaneous reading.

Based on the intensity levels of the B, G, and R color separation image signals obtained by the color scanner 1 in this manner, a color conversion process is performed by an image processing unit (not shown), and black (Black, Black, Hereinafter, referred to as “Bk”), cyan (C
yan, hereinafter referred to as "C". ), Magenta (Magenta, hereinafter referred to as “M”), yellow (Yellow, hereinafter “Y”)
That. ) Is obtained.

These color image data are visualized in a color image recording device (hereinafter referred to as a color printer) 2 in each of Bk, C, M, and Y colors, and the visualized toner The images are superimposed to obtain a four-color full-color image.

A writing optical unit 8 of the color printer 2 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and a drum-shaped photosensitive member 9 as an image carrier. To form an electrostatic latent image.

The writing optical unit 8 is composed of a laser light source 8a, a light emission driving device (not shown), a polygon mirror 8b and a rotation driving motor 8c, an f-θ lens 8d, a reflection mirror 8e, and the like. .

The photoreceptor 9 rotates counterclockwise as indicated by an arrow A, and around the photoreceptor cleaning unit (including a pre-cleaning static eliminator) 10, a static elimination lamp 11, a charger 12, a potential sensor 13, A Bk developing unit 14, a C developing unit 15, an M developing unit 16, a Y developing unit 17, an optical sensor 18 for detecting a development density pattern, an intermediate transfer belt 19 as an intermediate transfer body, and the like are arranged. The toner image forming means for forming a toner image on the photoreceptor 9 includes the optical unit 8,
It is composed of a charging unit 12, developing units 14 to 17, and the like.

Each of the developing units rotates developing sleeves 14a and 15a which rotate by contacting the surface of a photoreceptor 9 with an ear of a developer containing a toner and a carrier charged to a predetermined polarity in order to develop an electrostatic latent image. , 16a, 17a, and developing paddles 14b, 15b rotating to pump and agitate the developer.
16b, 17b and developer toner concentration sensor 14
c, 15c, 16c, 17c and the like. In this embodiment, a negatively charged toner is used.

In the standby state of the color copying apparatus, the developing sleeves 14a to 17a are provided for all of the four developing units.
The upper developer is in a cutting state (development is not activated).

Hereinafter, the outline of the copying operation will be described with an example in which the order of the developing operation (color image forming order) is Bk, C, M, and Y. However, the image forming order is not limited to this. When the copy operation is started, reading of Bk image data is started by the color scanner 1 at a predetermined timing. At the same time, the photoconductor 9 is driven to rotate counterclockwise by a photoconductor driving mechanism (not shown), and the photoconductor 9 is uniformly charged to a negative polarity by the charger 12.

Then, based on the Bk image data read by the color scanner 1, optical writing is performed by the laser light from the optical unit 8, and the uniformly charged photoconductor 9 is formed.
Is partially lowered in accordance with the Bk image data, whereby an electrostatic latent image is formed on the photoconductor 9. Hereinafter, the electrostatic latent image based on the Bk image data is referred to as a Bk latent image. Each of the electrostatic latent images formed based on the respective image data of C, M, and Y is also a C latent image, M
The latent image is referred to as a Y latent image.

Before the front end of the latent image reaches the developing position of the Bk developing device 14 so that development can be performed from the front end of the Bk latent image, the developing sleeve 14a is started to rotate and the developer is spiked. The Bk latent image is developed with a negatively charged Bk toner. Thereafter, the developing operation of the Bk latent image area is continued, but when the trailing edge of the latent image passes the Bk developing position, the B
The developer on the k-development sleeve 14a is cut off to set the development inoperative state. This is completed at least before the leading end of the C latent image based on the next C image data arrives. The ear cutting is performed by switching the rotation direction of the developing sleeve 14a to a direction opposite to that during the developing operation.

The Bk toner image formed on the photoconductor 9 is transferred to the surface of an intermediate transfer belt 19 driven at a constant speed with the photoconductor (hereinafter, transfer of the toner image from the photoconductor to the intermediate transfer belt is referred to as belt transfer). ). This belt transfer is performed by applying a predetermined bias voltage to a transfer bias roller 20a, which will be described later, in a contact state between the photoconductor 9 and the intermediate transfer belt 19.

Bk, C, M, and Y toner images are sequentially formed on the photosensitive member 9, and the intermediate transfer belt 1 is formed in the order in which the toner images are formed.
A belt transfer image of four-color superposition is formed by sequentially aligning the same with the same transfer surface of No. 9. After the full-color toner image is thus formed, the full-color toner image is collectively transferred to transfer paper 24 as a transfer material. The transfer from the intermediate transfer belt 19 to the transfer paper 24 is called paper transfer.

By the way, in the photoreceptor 9, the process proceeds to the process C after the process Bk. At a predetermined timing, the reading of the C image data by the color scanner 1 starts, and the formation of the C latent image is performed by writing the laser light with the image data. Do.

The C developing device 15 starts rotating the developing sleeve 15a with respect to the developing position after the rear end of the preceding Bk latent image has passed and before the leading end of the C latent image has arrived. The latent image is developed with C toner.

Thereafter, the development of the C latent image area is continued, but when the trailing end of the latent image has passed, the developer on the C developing sleeve 15a is cut off in the same manner as in the case of the Bk developing unit described above. Make the development inoperative state. This is also completed before the leading end of the next M latent image arrives. In each of the steps M and Y, the operations of reading the image data, forming the latent image, and developing are the same as those in the steps Bk and C described above.
Description is omitted.

In FIG. 1, the intermediate transfer belt 19 is wound around a drive roller 21, a transfer bias roller 20a, an entrance roller 20b, and a group of driven rollers. Also,
The intermediate transfer belt 19 is pressed against the photosensitive member 9 between the transfer bias roller 20a and the entrance roller 20b, and the two rollers 20a and 20b are arranged so that an appropriate nip pressure is applied at the pressure contact portion. . Drive roller 2
1 is connected to a drive motor (not shown).
The rotational drive of the intermediate transfer belt 19 is controlled via this drive motor.

Further, an intermediate transfer is performed by a transfer bias power source (not shown) for applying a predetermined transfer bias voltage (a positive voltage in this embodiment) to the transfer bias roller 20a, the entrance roller 20b, and the transfer bias roller 20a. Intermediate transfer means for sequentially transferring the toner images on the photoconductor 9 to the belt 19 in a superimposed manner is configured.

The belt cleaning unit 22 includes a brush roller 22a, a rubber blade 22b, a mechanism 22c for contacting and separating from the belt, and the like.
After the image is transferred to the belt, the second, third and fourth colors are separated from the belt surface by the contact / separation mechanism 22c during the belt transfer.

A paper transfer unit 23 as a transfer material transfer means for transferring the superimposed toner image on the intermediate transfer belt 19 to the transfer paper 24 includes a paper transfer bias roller 23a, a roller cleaning blade 23b, and a mechanism 2 for contacting and separating from the belt.
3c and the like. Paper transfer bias roller 23
a is normally separated from the transfer surface of the intermediate transfer belt 19, but when the four-color superimposed images formed on the transfer surface are collectively transferred to the transfer paper 24, the contact / separation mechanism 23c is timed. , And a predetermined bias voltage is applied to the roller 23a to perform transfer to the transfer paper 24.

As shown in FIG. 2, transfer paper 24 is fed by paper feed roller 25 and registration roller 26 at the timing when the leading end of the four-color superimposed image on intermediate transfer belt 19 reaches the paper transfer position. Paper is fed between the driving roller 21 and the paper transfer bias roller 23a, and the paper is transferred. The transfer paper 24 after the transfer is conveyed by a conveyance belt 27 and sent to a fixing device 28, where the toner image is fixed, and then discharged onto a tray 29.

Here, the drive control of the intermediate transfer belt 19 will be described. As a method of driving the intermediate transfer belt 19, the following three methods can be considered as an operation method after the belt transfer of the Bk toner image of the first color is completed to the end, and one of these methods or one of the copy speeds is considered. The intermediate transfer belt 19 is driven by efficiently combining a plurality of these methods according to the copy size from the surface. (Hereinafter, margin)

(1) Constant-speed forward movement method Even after the belt transfer of the Bk toner image, the forward movement is continued at a constant speed. Then, when the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position of the contact portion with the photoconductor 9 again, the front end portion of the next C toner image on the photoconductor 9 side is exactly at that position. The images are formed at appropriate timing. As a result, the C image is belt-transferred on the intermediate transfer belt 19 while being accurately aligned with the Bk image. Thereafter, the process proceeds to the M and Y image processes by the same operation, and a belt transfer image of four-color superposition is obtained. Following the belt transfer process for the fourth color Y toner image,
While moving forward, the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred to the transfer paper 24 as described above.

(2) Skip Forward System When the belt transfer of the Bk toner image is completed, the photosensitive member 9
The intermediate transfer belt 19 is separated from the surface, skipped at a high speed in the forward movement direction, and moved by a predetermined amount, and then returned to the original forward movement speed. Thereafter, the intermediate transfer belt 19 is brought into contact with the photoconductor 9 again. When the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position again, the photosensitive member 9 forms an image at a timing such that the front end of the next C toner image is exactly at that position. Have been. As a result, the C image is transferred to the Bk image while being accurately aligned with and superimposed on the Bk image. Thereafter, the process proceeds to the M and Y image processes by the same operation, and a belt transfer image of four-color superposition is obtained. Subsequent to the fourth color Y toner image belt transfer step, the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred onto the transfer paper 24 at the same forward movement speed.

(3) Reciprocating (Quick Return) Method When the belt transfer of the Bk toner image is completed, the photosensitive member 9
The intermediate transfer belt 19 is separated from the surface, and the forward movement is stopped. By this return operation, the front end position of the Bk image on the surface of the intermediate transfer belt 19 passes through a position corresponding to the belt transfer in the reverse direction, and after moving a predetermined distance, stops and enters a standby state. Next, when the leading end of the C toner image on the photoconductor 9 reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is started again in the forward movement direction. Further, the intermediate transfer belt 19 is brought into contact with the surface of the photoconductor 9 again. Also in this case, the C image is transferred to the intermediate transfer belt 19 under the condition that the C image accurately overlaps the Bk image on the intermediate transfer belt 19. Thereafter, the process proceeds to the M and Y image processes by the same operation, and a belt transfer image of four-color superposition is obtained. Following the belt transfer process for the fourth color Y toner image,
The toner image moves forward at the same speed without returning, and the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred to the transfer paper 24.

The transfer paper 24 on which the four-color superimposed toner image is collectively transferred from the surface of the intermediate transfer belt 19 by any one of the above methods is transferred to the fixing device 2 by the transport belt 27 of the paper transport unit.
The toner image is melted and fixed by a fixing roller 28a and a pressure roller 28b controlled to a predetermined temperature, and is conveyed to a copy tray 29 to obtain a full-color copy.

On the other hand, the photoreceptor 9 after the belt transfer is a photoreceptor cleaning unit 1 comprising a pre-cleaning neutralizer 10a, a brush roller 10b, a rubber blade 10c and the like.
At 0, the surface is cleaned, and the charge is uniformly removed by the charge removing lamp 11.

The surface of the intermediate transfer belt 19 after the transfer of the toner image onto the transfer paper 24 is cleaned. This cleaning is performed by pressing the cleaning unit 22 again by the contact / separation mechanism 22c.

In the case of the repeat copy, the operation of the color scanner 1 and the image formation on the photosensitive member 9 are performed on the first sheet Y (4
Subsequent to the (color) image process, the process proceeds to a second Bk (first color) image process at a predetermined timing.

In the intermediate transfer belt 19, following the batch transfer process of the first four-color superimposed image onto the transfer paper 24, the surface of the intermediate transfer belt 19 is cleaned by the cleaning unit 22 so that the second Bk The toner image is transferred to the belt. After that, the operation is the same as that of the first sheet.

In FIG. 2, transfer paper cassettes 30, 3
Transfer rollers 1, 32, and 33 store transfer papers of various sizes, and the registration rollers 2 are set at appropriate timing from a storage cassette of the size paper specified on an operation panel (not shown).
Paper is fed and transported in six directions. Reference numeral 34 denotes a paper feed tray for manually feeding OHP paper for an overhead projector or transfer paper such as thick paper.

The copy mode for obtaining four full colors has been described above. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Will be.

In the case of the single-color copying mode, only the developing unit of the color is set in the developing operation (springing) until the predetermined number of sheets is completed, and the intermediate transfer belt 19 is set.
Is driven at a constant speed in the forward direction while being in contact with the surface of the photoreceptor 9, and the copying operation is performed with the belt cleaner 22 still in contact with the belt 19.

Next, means for suppressing the edge effect as a cause of the occurrence of the transfer dust will be described. As described above, in order to prevent the occurrence of transfer dust, the amount of toner adhering at the contour of the toner image superimposed on the intermediate transfer belt 19 is determined by measuring the amount of toner adhering to the inner part of the toner image (hereinafter referred to as the contour). (Referred to as an inner part).

FIG. 3 is a schematic diagram of a cross section of the toner image on the intermediate transfer belt 19 on which the four colors have been sequentially transferred and superimposed. Here, the maximum toner adhesion amount at the outline portion of the toner image is a, and the toner adhesion amount at the outline inner portion c is b.
And

FIG. 4 is a block diagram showing the configuration of the color copying machine. Here, the image processing unit 40 in the present embodiment
Will be described. Image data read by the color scanner 1 is input to the color printer 2 via a gamma correction circuit 41, an edge detection circuit 42, a level correction circuit 43, and an LD modulation circuit 44.

The edge detection circuit 42 is for detecting the edge of the image data that has passed through the gamma correction circuit 41. For each pixel of the image, the edge detection circuit 42 detects whether or not the pixel belongs to the edge. The result is used as the level correction circuit 4
Output to 3. The level correction circuit 43 compares the density of the pixel of the edge part detected by the edge detection circuit 42 with the density of the pixel of the inner part close to the edge part,
Based on a relationship between a preset ratio of these densities and a transfer chile rank described later, the weight of the pixel of the edge portion is adjusted so as to correspond to the transfer chile rank input to the setting input section 45. . With this weighting, in the present embodiment adopting the negative-positive developing method, as shown in FIG. 5, in the writing optical unit 8, the latent image potential of the pixel at the edge portion is changed to the value at the inner portion close to the edge portion. Optical writing is performed so as to be higher than the pixel. As a result, it is possible to prevent the toner attachment amount on the contour portion of the toner image transferred onto the intermediate transfer belt 19 from becoming too large due to the influence of the edge effect.

FIG. 6 is a graph showing the relationship between the ratio a / b of the amount of toner adhering to the contour portion of the toner image and the portion inside the contour portion, and the evaluation of the transfer dust. Here, as for the ratio a / b of the toner adhesion amount shown on the horizontal axis, the larger the numerical value is, the larger the toner adhesion amount is on the contour portion of the toner image, and the more the distance from the origin is, the better the evaluation of the transfer dust rank shown on the vertical axis is .
The ratio a / b of the toner adhesion amount is determined by the image processing unit 40.
Can be changed by changing the degree of weighting of the pixel of the edge portion in the edge detection circuit 42 and the level correction circuit 43. In addition, the amount of toner attached to the contour portion and the inner portion of the contour portion of the toner image is measured using a laser displacement method. Further, the numerical value of the transfer dust rank is obtained from a correspondence table (Table 1) showing the relationship between the number of dust particles per predetermined observation area (500 μm × 500 μm) and the transfer dust rank. FIGS. 7A to 7E
Shows an enlarged view of an evaluation reference image (line image in the sub-scanning direction with a line width of 100 μm and a line interval of 100 μm) for each numerical value of the transfer chile rank. A predetermined observation area (500
The number of dust particles per μm × 500 μm) is counted, and an average value of count values for successive transfer dust ranks (for example, rank 1 and rank 2) is defined as a boundary value between the transfer dust ranks, and each transfer in the correspondence table in Table 1 is performed. The range of the number of dust toners in the dust rank is set. 7A to 7E are toner particles, and the line width and line interval of the image of FIG. 7A corresponding to the transfer dust rank 5 are 100 μm. The images having the transfer dust rank of 4 or more (FIGS. 7A and 7B) were good images with little transfer dust as a result of observation with the naked eye. Therefore, the transfer dust rank 4 is set as the allowable level m. In order to satisfy the permissible level m, the ratio a / b of the toner adhesion amount between the contour portion of the toner image and the inner portion of the contour portion is as follows:

## EQU1 ## It is necessary to form a distribution of the amount of toner adhered so as to satisfy the condition represented by 1.0 ≦ <a / b <1.3. If the amount of toner adhered to the contour of the toner image is excessively suppressed, the sharpness of the image may be impaired. Therefore, the above lower limit 1.0 is provided for the degree of the suppression.

[0055]

[Table 1]

In the above color copying machine, image formation was performed by image processing such that the ratio a / b of the toner adhesion amount was 1.2 or more and 1.3 or less. It was confirmed that an image satisfying the allowable level m of 4.5 was obtained.

As described above, in the present embodiment, the image processing satisfies Equation 1 above, that is, the amount of toner adhering to the contour portion of the toner image superimposed on the intermediate transfer belt 19 is reduced by the inner portion of the contour portion. By preventing the amount from becoming too large as compared with the above, the effect of the edge effect can be suppressed, and the generation of transfer dust can be prevented without impairing the sharpness of the image.

Further, in the present embodiment, the image forming apparatus using the negative-positive developing method using the negatively charged toner has been described, but the present invention is applied to the image forming apparatus adopting the positive-positive developing method. , The same effect can be obtained. However, in this case, it is necessary to form the latent image potential at the edge portion so as to be lower than the pixels in the image inner portion adjacent to the edge portion.

The present embodiment satisfies the above expression 1 by image processing. However, instead of this, the developing gap, that is, the intermediate transfer belt 19 and the developing sleeves 14a, 15a, 16a, 17a are replaced. May be controlled. The ratio a / b of the toner adhesion amount increases as the gap increases, and decreases as the gap decreases.

As a carrier for the developer, the average particle diameter is 80 μm.
m, a developing gap of 0.8 mm using an iron powder carrier having a resistivity of 10 ⁸ to 10 ⁹ Ωcm / 50 V, and a photosensitive drum 9 of
Has a charging potential of -650 V and a developing bias voltage of -500.
When developed at V, the transfer dust rank was 4
It was confirmed that an image satisfying the allowable level m of 4.5 to 4.5 was obtained. Similar results were obtained even when the developing gap was changed within the range of 0.6 mm or more and 0.8 mm or less.

In this embodiment, only the copy mode for obtaining four full colors has been described.
A similar effect can be obtained by applying the present invention to a three-color copy mode, a two-color copy mode, or a single-color copy mode.

[0062]

According to the first to fourth aspects of the present invention, the amount of toner adhering to the contour portion of the toner image on the intermediate transfer member is increased as compared with the inner portion of the toner image close to the contour portion. By making it so small, there is an excellent effect that the influence of the edge effect can be suppressed and the generation of transfer dust can be prevented without impairing the sharpness of the image.

In particular, according to the second aspect of the present invention, the image processing can easily suppress the influence of the edge effect on the contour of the toner image on the intermediate transfer member without using a new apparatus. effective.

In particular, according to the third aspect of the invention, by controlling the developing gap, the influence of the edge effect on the contour of the toner image on the intermediate transfer member can be easily suppressed without using a new device. There is an excellent effect.

In particular, according to the fourth aspect of the present invention, in a full-color image forming apparatus for sequentially transferring a toner image on an image carrier onto an intermediate transfer member and transferring the same, the method is adapted as means for suppressing the influence of the edge effect. There is an excellent effect that it can be done.

[Brief description of the drawings]

FIG. 1 is an enlarged view around a photoconductor and an intermediate transfer belt of a color copying apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the entire color copying apparatus.

FIG. 3 is a schematic diagram of a cross section of a toner image.

FIG. 4 is a configuration block diagram of the color copying machine.

FIG. 5 is an explanatory diagram of latent image potential formation in a writing optical unit.

FIG. 6 is a graph showing a relationship between a ratio a / b of a toner adhesion amount and a transfer dust rank.

7A to 7E are enlarged views of an evaluation reference image corresponding to each numerical value of a transfer chile rank.

FIG. 8 is an explanatory diagram of a toner layer forming process.

[Explanation of symbols]

 Reference Signs List 9 photoconductor 12 charging device 14 Bk developing device 15 C developing device 16 M developing device 17 Y developing device 19 intermediate transfer belt 20 a transfer bias roller 20 b entrance roller (counter electrode) 23 a paper transfer bias roller 24 transfer paper 40 image processing section

Claims (4)

[Claims] An image forming apparatus comprising: a toner image forming means for forming a toner image on an image carrier; and a transfer means for transferring a toner image on the image carrier to an intermediate transfer body. Assuming that the maximum amount of toner attached to the contour of the toner image on the body is a and the amount of toner attached to the inner side of the toner image adjacent to the contour is b, 1.0 ≦ a / b <1.3. An image forming apparatus that satisfies the following conditions. 2. An image forming apparatus according to claim 1, wherein said condition is satisfied by image processing. 3. An image forming apparatus according to claim 1, wherein said condition is satisfied by controlling a developing gap. 4. The image forming apparatus according to claim 1, further comprising: transfer means for sequentially superimposing and transferring the toner image on the image carrier onto the intermediate transfer body, wherein the toner image is superimposed on the intermediate transfer body. A, the maximum amount of toner adhering to the contour of
An image forming apparatus, wherein the above condition is satisfied, where b is the amount of toner adhering to the inside of the toner image near the contour.