JP2001042582A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a smooth image where roughness is kept down in an image forming device where a stable image quality is obtained by adapting a binary process. SOLUTION: In this device, such a constitution is adapted that each condition within the device is set so that the diameter of a toner image of 1 pixel on a photoreceptor 1a is 20 μm to 50 μm, and a transfer means provided with an intermediate transfer belt 51 as a primary transfer material so that toner is easily scattered on an image transferred on transfer paper 100, an intermediate transfer device 5 as a primary transfer means transferring the toner image on the photoreceptor 1a to the intermediate transfer belt 51 and a transfer roll 81 as a secondary transfer means transferring the toner image on the intermediate transfer belt 51 to the transfer paper 100, is provided.

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, and a printer.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image is formed by irradiating a light beam generated by an LD, LED, or the like onto a uniformly charged photosensitive member surface as an image bearing member, and developing, transferring, and developing the latent image. 2. Related Art An image forming apparatus that forms a toner image on a recording member such as transfer paper by fixing is known. In such an image forming apparatus, for a high-density image portion, ON / OF of a light beam having an intensity capable of sufficiently attenuating the potential of the photosensitive member.
F (hereinafter referred to as "saturated writing") to form an electrostatic latent image, and in a halftone portion or a highlight portion, modulate the intensity, irradiation time, etc. of the light beam to form an intermediate electrostatic latent image. A method of expressing the entire gradation is known. In an image forming apparatus employing such a gradation expression method, generally, in order to sufficiently reproduce the gradation and reproduce a highlight portion,
A method of forming an electrostatic latent image of an intermediate potential by making the steps of the light beam intensity, irradiation time, and the like for one dot, which is a pixel serving as a basic unit constituting an image, sufficiently small (hereinafter, 1).
Dot multi-value process).

However, in the electrophotographic recording method, since static electricity plays a central role, a large change in the characteristics of the photosensitive member and the developer over time due to environmental conditions and aging is inevitable. A problem is the change in image quality centered on the tonal portion. For this reason, there has been proposed a method of stabilizing the image quality by increasing the pixel density in the highlight area and reproducing with a larger dot, but as long as an electrostatic latent image having an intermediate potential is used, Instability is inevitable.

On the other hand, among the pixels which form an electrostatic latent image by the above-described saturation writing for the high density portion, the halftone portion, and the highlight portion, and which are the basic units of the image, the toner-attached pixels to which toner is to be attached There is known a gradation expression method for expressing a gradation by the density per area (hereinafter, referred to as a binary process). FIG. 4 shows an example of the relationship between the writing energy and the photoconductor surface potential. Note that the characteristic line a1 shows the distribution of the writing energy of the light beam, and the characteristic line a1
2 shows the distribution of the surface potential of the dot portion on the photoreceptor irradiated with the light beam. In FIG. 4, the surface of the photoconductor is charged in advance to have a potential of a charging potential Vd. As shown in the figure, the light beam whose energy is maximum at the center, that is, the photoconductor surface potential is reduced to almost 0V. By irradiating the light beam with the intensity that can be attenuated, the photoconductor surface potential at the center of the dot is attenuated to almost 0V. Note that the dot diameter after development is substantially equal to the diameter D of the surface portion of the photoconductor in which the absolute value of the surface potential has been attenuated to a potential lower than the absolute value of the development start potential.

In the binary process, irrespective of the high density portion, the halftone portion, and the highlight portion, while forming a toner-attached pixel by saturated writing using writing energy as shown by a characteristic line a1 in FIG. A gradation is expressed by adjusting the density per area of the toner attached pixel. More specifically, the higher the density, the more visually it is visually recognized after development to express the gradation.

If such a binary process of expressing the gradation by the density per area of the toner-attached pixel is employed, the change in image quality due to development conditions and the like is reduced since basically no intermediate potential portion is used. .

[0007]

However, when the above-described binary process is employed, in an image formed on a transfer material such as transfer paper, a toner-attached pixel in a halftone portion or a highlight portion causes toner to adhere. There is a problem that the image becomes conspicuous surrounded by unexposed pixels, and the image tends to be rough. In fact, in an electrophotographic apparatus using a binary process which has been put to practical use, an insufficient image quality with noticeable roughness has been obtained as compared with the one-dot multi-value process.

The present invention has been made in view of the above background, and an object of the present invention is to form a smooth image in which the above-mentioned roughness is not conspicuous, and to further improve development conditions and the like as compared with the case where a multi-value process is used. An object of the present invention is to provide an image forming apparatus capable of suppressing a change in image quality due to image formation.

[0009]

In order to achieve the above object, the invention according to claim 1 is directed to an image bearing member and a density per area of a toner-adhered pixel for adhering toner among pixels constituting an image. Image processing means for processing image data of an image to be formed so as to express a gradation; and electrostatically controlling an image comprising the pixels on the image carrier based on the image data processed by the image processing means. A latent image forming unit that forms a latent image, a developing unit that visualizes the electrostatic latent image of the image to form a toner image, and a transfer unit that transfers the toner image on the image carrier to a transfer material In the image forming apparatus,
The diameter of a pre-transfer pixel image, which is a toner image of one pixel on the image carrier, is 20 μm or more and 50 μm or less, and the transfer image of the pre-transfer pixel image on the transfer material is used as the transfer unit. The post-transfer pixel image is formed by a transfer so that the post-transfer pixel image is composed of a nucleus portion formed with the same diameter as the pre-transfer pixel image and a scattered portion around which toner adheres as if scattered. The present invention is characterized in that a material that generates a scattered portion is used.

As a result of extensive studies by the present inventors, when the size of the pixel image after transfer on the transfer material derived from the toner-adhered pixels on the image carrier becomes about 50 μm or less, the clear visual distance, specifically, Found that the human visual acuity at 25 to 30 cm sharply decreased. On the other hand, it has been empirically known that in order to stably develop a toner-attached pixel on an image carrier, the diameter of the pixel must be about four times or more the toner particle diameter. If the diameter of the toner-adhered pixel is smaller than four times the toner particle diameter, a pixel image after development may or may not be obtained due to a change in environment or development characteristics even when saturation writing is performed. Therefore, considering that the limit of reducing the particle size of the toner is about 5 μm, the diameter of the toner-attached pixel that can be stably reproduced is about 20 μm or more. Further, as a result of further studies by the inventors, even if the diameter of the pre-transfer pixel image developed on the image carrier is the same, the roughness is not conspicuous on the transfer material in the following cases. It was found that a smooth image was formed. That is, on the transfer material, when toner scatters around the nucleus portion of the post-transfer pixel image obtained by the transfer of the pre-transfer pixel image, a smoother image than that which does not occur is obtained. It turned out to be observed. Here, the toner scattering refers to a state in which the toner is sparsely dispersed as the distance from the center increases in the pixel image. It has been found that, in the pixel image in which such scattering occurs, the boundary between the edge portion and the background portion is blurred, so that the pixel image becomes less noticeable even when surrounded by the background portion. In this image forming apparatus, as a method of expressing the gradation, a method of expressing the gradation by the density per area of the toner attached pixel, that is, a binary process is used. Therefore, it is possible to perform saturation writing or writing with an intensity close to the saturation writing even in a halftone portion or a highlight portion on the image carrier, and suppress a change in image quality due to development conditions and the like as compared with the case where a multi-value process is used. Image quality can be stably maintained. Further, a pixel image before transfer on the image carrier is formed with a diameter of 20 μm or more and 50 μm or less, and then transferred onto a transfer material to form a post-transfer pixel image. The post-transfer pixel image is composed of a nucleus portion having substantially the same diameter as the pre-transfer pixel image on the image carrier, and a scattered portion formed around the nucleus portion. Of these, the core has a diameter of 20 μm or more and 50 μm or less,
It is less noticeable at a clear viewing distance of 0 cm. In addition, the scattered portion has sparsely scattered toners almost independently present, and for a person who cannot visually recognize each toner, only the whole is almost inconspicuous as a low-density cloud. Do not recognize. In addition, by blurring the boundary between the entire edge portion of the post-transfer pixel image and the surrounding background portion, the core portion is made less noticeable. As a result, in the image formed on the transfer material, the post-transfer pixel image is not conspicuous not only at the clear viewing distance but also at a shorter distance.

According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the diameter of the post-transfer pixel image is 1.5 times or more the diameter of the nucleus portion. It is characterized by causing scattering of toner.

In this image forming apparatus, toner is scattered around the core so that the diameter of the post-transfer pixel image on the transfer material is at least 1.5 times the diameter of the core. Thus, a smooth image with less graininess can be formed.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the toner image is formed around the core portion so that the diameter of the pixel image after transfer is three times or less the diameter of the core portion. It is characterized by causing scattering.

In this image forming apparatus, toner is scattered around the core so that the diameter of the pixel image after transfer on the transfer material is three times or less the diameter of the core. Deterioration of sharpness of a line image or a character image due to scattering of toner can be suppressed.

[0015] The invention of claim 4 is the invention of claim 1, 2, or
In the image forming apparatus of Item 3, a photoreceptor having an electric charge generated by light near the surface opposite to the surface on which the electrostatic latent image is formed and having a thickness of 15 μm or less is used as the image carrier. It is characterized by the following.

In this image forming apparatus, charge is generated by light in the vicinity of the surface of the photosensitive member used as the image carrier opposite to the surface on which the electrostatic latent image is formed.
Then, of the generated charges, charges having a polarity opposite to a predetermined polarity move the photoconductor in the thickness direction toward the surface, whereby an electrostatic latent image is formed. Here, when the electric charge moves in the thickness direction of the photoconductor, the electric charge diffuses in a direction perpendicular to the thickness direction to some extent due to a repulsive force (repulsive force) between the electric charges. The degree of the diffusion increases as the thickness of the photoconductor increases. Therefore,
If an attempt is made to increase the thickness of the photoreceptor and form a toner-attached pixel of the same size, a light beam with a smaller diameter is used,
It is necessary to reduce the beam light amount and use a toner-attached pixel having an intermediate potential. The former raises costs and the latter raises a problem of unstable development. We have found that 50 μm
A dot-shaped toner-adhered pixel having a write beam diameter of about 50 μm was formed, and the film thickness of the photoconductor and the variation in the diameter of the formed pre-transfer pixel image were measured. It was confirmed that if it exceeded, the variation in the diameter of the pixel image before transfer sharply increased. Further, when the thickness of the photoconductor is 1
If it exceeds 5 μm, even if the beam diameter is reduced to 30 μm, the variation of the diameter of the pixel image before transfer can be reduced, but the diameter remains about 50 μm. It has been found that thinning is effective. From this, it is expected that the magnitude of the charge diffusion is at the same level as the thickness of the photoconductor.
Therefore, in this image forming apparatus, a photoconductor having a thickness of 15 μm or less is used. In such a configuration, even if the charges diffuse in the direction perpendicular to the film thickness direction due to the repulsive force of each other during movement, the spread is unlikely to increase. Therefore, it is possible to easily form a small toner-adhered pixel which becomes a small pre-transfer pixel image that cannot be visually recognized even if developed by toner.

The invention of claim 5 is the invention of claim 1, 2 or
The image forming apparatus according to the third aspect is characterized in that a photoreceptor that generates charges by light near the surface on which the electrostatic latent image is formed is used as the image carrier.

In this image forming apparatus, electric charges are generated by light in the vicinity of the surface of the photosensitive member serving as the image carrier on which the electrostatic latent image is formed. Then, of the generated charges, charges of a predetermined polarity move in the photoconductor from near the surface to the surface opposite to the surface. On the other hand, the charge having the polarity opposite to the predetermined polarity stays near the surface to form the electrostatic latent image. Even in the case where the electrostatic latent image is formed in this way, diffusion of the charge due to repulsion is suppressed. Therefore, it is possible to easily form a small electrostatic latent image, which becomes a small pre-transfer pixel image that cannot be visually recognized even if developed by toner.

According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, an amorphous silicon photosensitive member is used as the image carrier.

In this image forming apparatus, since the amorphous silicon photosensitive member having excellent mechanical strength is used as the image carrier, the life of the image carrier is extended, and the safety is enhanced.

According to a seventh aspect of the present invention, the image data of the image to be formed is expressed so that the gradation is expressed by the density per area of the image carrier and the toner-adhered pixel to which the toner is adhered among the pixels constituting the image. Image processing means for processing, based on the image data processed by the image processing means,
Latent image forming means for forming an electrostatic latent image of an image comprising the pixels on the image carrier, developing means for developing the electrostatic latent image of the image into a toner image, And a transfer unit for transferring the toner image to a transfer material, wherein a post-transfer pixel image, which is a one-pixel toner image after being transferred onto the transfer material, is formed by the aggregated toner. And a scatter portion around which toner is scattered, and the core portion is formed such that the diameter of the post-transfer pixel image is 1.5 times or more the diameter of the nucleus portion. Is characterized in that toner is scattered around the image.

Also in this image forming apparatus, by expressing gradation by a binary process, it is possible to suppress a change in image quality due to development conditions and the like and to maintain a stable image quality as compared with the case of using a multi-value process. it can. Further, in this image forming apparatus, the toner scatters around the core so that the diameter of the post-transfer pixel image transferred onto the transfer material is 1.5 times or more the diameter of the core. Is caused, the boundary between the edge portion and the background portion of the post-transfer pixel image is blurred. Then, by blurring the boundary in this manner, the toner-attached pixels are less noticeable in the image formed on the transfer material. The present inventor has conducted intensive studies to cause scattering of toner around the core portion so that the diameter of the post-transfer pixel image is 1.5 times or more the diameter of the core portion.
Even if the post-transfer pixel image has a diameter larger than 50 μm,
It has been found that the boundary can be blurred to make it less noticeable in the image on the transfer paper. Further, they have found that a smooth image with less graininess can be formed on transfer paper.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the toner image is formed around the core portion so that the diameter of the pixel image after transfer is three times or less the diameter of the core portion. It is characterized by scattering.

In this image forming apparatus, the toner may be scattered around the core portion so that the diameter of the pixel image after transfer on the transfer material is three times or less the diameter of the core portion. Thus, it is possible to suppress the deterioration of sharpness of a line image or a character image due to scattering of toner.

The ninth aspect of the present invention is the first aspect of the present invention.
The image forming apparatus of any one of 4, 5, 6, 7 and 8, wherein the transfer means transfers the toner image to an intermediate transfer member and then transfers the toner image to the transfer material. .

In this image forming apparatus, the toner image on the image carrier is transferred onto the transfer material via the intermediate transfer member. In such a transfer, unlike the method in which a toner image is directly transferred from an image carrier to the transfer material, at least two transfer steps are performed on the toner image, and sufficient transfer is performed in each transfer step. In order to obtain efficiency, it is necessary to create a state in which toner transfer is very likely to occur. When such a state is created, the toner is easily scattered and the scattered portion is easily formed around the core portion, as compared with a method in which the toner image is directly transferred from the image carrier to the transfer material. be able to.

As a method of adjusting the density per area of the toner-adhered pixels, a method of adjusting the size of an adhering pixel group composed of an aggregate of the toner-adhered pixels and a method of adjusting the distance between the toner-adhered pixels are used. There are methods. Among these, the former method represented by the dot concentration type of the dither method, etc., increases the size of the attached pixel group formed of the aggregate of the toner attached pixels as the image density is increased. Even if the attached pixels are formed to have a diameter of 50 μm or less, there is a possibility that the attached pixel group is conspicuous and the image becomes rough.

Therefore, the invention of claim 10 is based on claim 1,
2. The image forming apparatus according to 2, 3, 4, 5, 6, 7, 8, or 9, wherein the image processing means determines a density of the toner-attached pixels per unit area by a distance between the toner-attached pixels. It is characterized by adjustment.

In this image forming apparatus, a dot dispersion type dither method, an error diffusion method, and the like are used.
A method of adjusting the density of the toner-attached pixels per area according to the distance between the respective toner-attached pixels is used. In such a configuration, unlike the case where the density of the toner attached pixels per area is adjusted according to the size of the attached pixel group, it becomes difficult for the toner attached pixels to aggregate. Therefore, the roughness of the image due to the increase in the image density can be suppressed as compared with the case where the density of the toner attached pixels per area is adjusted by the size of the attached pixel group.

However, if the dither method is used as a method for adjusting the distance between the toner-attached pixels, the sharpness of the image is easily reduced by blurring the edges of the character image or interrupting the line image. It is known.
Also, yellow individually formed on the image carrier,
To form a color image by superimposing and transferring magenta, cyan, and black toner images on an intermediate transfer member,
It is also known that interference fringes called moiré fringes tend to occur in this color image. The moiré fringes are caused by interference between a light and shade pattern of a toner image of each color and a predetermined interval pattern of toner-attached pixels.

Therefore, the invention of claim 11 is based on claim 10
Wherein the error diffusion method is used as a method for adjusting the density of the toner-attached pixels per unit area according to the distance between the toner-attached pixels.

In this image forming apparatus, by using the error diffusion method, a character image or a line image having better resolution and sharpness can be formed than in the case of using the dither method. In addition, while forming a character image and a line image with excellent resolution in this way, it is possible to form an image with excellent gradation on a picture portion. Further, in the error diffusion method, the toner-attached pixels are not formed in a predetermined interval pattern, but the interval pattern of the toner-adhered pixels is changed according to the light and shade pattern of the image. However, generation of moiré fringes can be suppressed.

The twelfth aspect of the present invention is the first aspect of the present invention.
The image forming apparatus according to any one of 4, 5, 6, 7, 8, 9, 10, and 11, wherein a superimposed toner image in which a plurality of the toner images are superimposed is formed on the transfer material.

In this image forming apparatus, the toner-adhered pixels are less noticeable in a superimposed toner image in which a plurality of the toner images are superimposed.

[0035]

[Embodiment 1] Hereinafter, the present invention will be described.
An embodiment applied to an image forming apparatus that forms an image by employing a digital electrophotographic recording method will be described. FIG.
1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment.
First, a basic configuration and operation of the image forming apparatus will be described. Around a photoreceptor drum 1 having a photoreceptor 1a as a latent image carrier and a photoreceptor support 1b for supporting the same, development is performed using a charging device 2, an optical writing device 3, and a dry developer. A developing device 4, an intermediate transfer device 5 having an intermediate transfer belt 51 as an intermediate transfer body, a static eliminator 6,
A cleaning device 7 having a cleaning blade is provided.

In the intermediate transfer device 5, the intermediate transfer belt 51 is suspended by a plurality of suspension rollers 52, and is configured to run endlessly in a direction indicated by an arrow by driving means such as a motor (not shown). One of the suspension rollers 52 also serves as a transfer bias roller for supplying a transfer bias to the intermediate transfer belt 51, and a predetermined transfer bias voltage is applied from a power source (not shown). At a position facing the intermediate transfer belt 51, a transfer roller 81 for transferring a developed image to transfer paper 100 as a final transfer material is provided.
1 is supplied with a transfer bias by a power supply device (not shown). A fixing device 9 is provided downstream of the transfer roller 81 in the transfer paper transport direction.

In the image forming apparatus shown in FIG. 1, the photosensitive drum 1 is charged uniformly to a predetermined polarity by the charging device 2 while rotating in the direction of the arrow, in the example shown in FIG. The optical system forms an electrostatic latent image for an image to be formed on the surface of the photoconductor 1a of the photoconductor drum 1. In the example shown in the figure, the potential is attenuated in the portion where the optical writing is performed, and the charged potential is held in the portion where the optical writing is not performed. The electrostatic latent image is developed by supplying a predetermined polarity, that is, a negative toner 10 in the illustrated example, by the developing device 4 to form a toner image as a visible image. The toner image developed by the developing device 4 is transferred onto the surface of the intermediate transfer belt 51 at a contact portion (primary transfer area) between the photosensitive drum 1 and the intermediate transfer belt 51 moving at a constant speed (primary transfer). Transcription). In the case of performing transfer in which three or four colors are superimposed, this process is repeated for each color to form a color image as a superimposed toner image on the intermediate transfer belt 51. Then, the toner image on the intermediate transfer belt 51 is transferred to the surface of the transfer paper 100 (secondary transfer). The toner image on the transfer paper 100 is fixed by the fixing device 9, whereby an image is formed.

Further, the image forming apparatus according to the present embodiment
It has a control unit (not shown) for controlling each unit in the apparatus. The control unit performs image processing as image processing means for processing image data of an image to be formed so as to express a gradation by a density per area of a toner-attached pixel to which toner is applied among pixels constituting the image. Part. Specifically, the image processing unit performs data processing for adjusting the area ratio of the toner-attached pixel per area to express a gradation.

The control unit controls the optical writing device 3 based on the image data processed by the image processing unit.
Drive control. In the image forming apparatus according to the present embodiment, an electrostatic latent image is formed by the above-described saturation writing for the high density portion, the halftone portion, and the highlight portion, and toner is attached to the pixels which are the basic units of the image. A binary process, which is a method of expressing a gradation by the density per area of a pixel to which toner should be attached, is adopted. By employing this binary process, it is possible to maintain stable image quality as compared with the case where a one-dot multi-value process is employed.

When this binary process is employed, as described above, in the image formed on the transfer paper 100, the post-transfer pixel image on the transfer paper 100 originating from the toner-adhered pixels becomes conspicuous and becomes an image in which roughness is felt. In some cases.

In order to solve the above problems, the inventors of the present invention have conducted intensive studies and as a result, have formed on the transfer material 100.
It has been found that when the size of the post-transfer pixel image is about 50 μm or less, the human visual recognition ability at a clear visual distance, specifically, 25 to 30 cm, rapidly decreases. In addition, it was found that the lower the size and shape of the post-transfer pixel image were, the more remarkable the reduction in the visibility was. Therefore, transfer paper 1
If the above-mentioned binary process is adopted such that the size of the pixel image after transfer becomes uniform at 50 μm or less, it is expected that a stable electrophotographic process with high image quality will be achieved.

On the other hand, in order to stably develop a dot-shaped toner-attached pixel in the electrophotographic method by dry development employed in the image forming apparatus of the present embodiment, the dot diameter is about the toner particle diameter. It is empirically known that it is required to be four times or more. Considering that the limit of reducing the particle diameter of the toner is about 5 μm, the diameter of the dot-like toner-attached pixel that can be stably reproduced is about 20 μm or more.

From the above, in the electrophotographic binary process using dry development, 20 μm on the transfer paper 100
The toner-attached pixel having a diameter of not less than m and not more than 50 μm and having a stable shape after transfer is obtained by the photoconductor 1a.
If it can be formed on the top, it is considered that a stable image can be obtained without roughness.

However, under the conditions of the conventional general electrophotographic system, a stable dot-shaped post-transfer pixel image having a diameter of 20 μm or more and 50 μm or less is formed on the transfer paper 100 using the above-described binary process. It was difficult to do. In order to achieve this, an optical writing device having a beam diameter much smaller than the conventional one, an electrostatic pixel latent image (electrostatic latent image of one pixel) due to diffusion of charges even when writing is performed with a small beam diameter A photoreceptor that is unlikely to spread, a development method that faithfully converts a small dot-shaped electrostatic pixel latent image into a toner image, and transferred onto transfer paper without crushing the pre-transfer pixel image developed on the photoreceptor Transfer method,
It is necessary that all the fixing methods for fixing the post-transfer pixel image transferred onto the transfer paper with minimum thickness are used. Moreover, the parameters of each of these units are interrelated. For example, the specifications of the beam diameter of the writing optical system differ depending on the characteristics of the photoconductor and the performance of each unit of development, transfer, and fixing. If one of the units exceeds the limit, recovery by another unit becomes impossible.

Since strict specifications are required for all units as described above, the transfer paper 10
Even if it is possible to stably obtain a post-transfer pixel image having a diameter of 20 μm or more and 50 μm or less on 0, there is a possibility that a significant increase in cost may occur.

However, as a result of further intensive studies, the present inventors have found that a pixel image after transfer is composed of a nucleus portion composed of an aggregate of toner and a scattered portion where toner scattered around the core portion is adhered. In this case, it has been found that even if the diameter is the same, the image becomes less noticeable than a post-transfer pixel image having no scattering portion. Here, the toner scatter refers to a state in which a toner image sparsely scatters as the distance from the center increases in a pixel image composed of a plurality of toners. FIGS. 2A to 2F show dot-shaped pixel images formed under conditions where toner scattering is unlikely to occur.
FIG. 4 is an explanatory diagram showing a dot-shaped pixel image formed under a condition in which toner scattering is likely to occur. Specifically, FIG.
(A), (b), and (c) respectively show a dot-shaped pre-transfer pixel image formed on the photoreceptor 1a, a post-transfer pixel image formed on the transfer paper 100, and the transfer paper 100 formed on the photoreceptor 1a under the condition that toner scattering hardly occurs. The above shows a post-transfer pixel image after fixing. Also,
FIGS. 2D, 2E, and 2F respectively show a dot-shaped pre-transfer pixel image, a post-transfer pixel image on the transfer paper 100, and a fixation on the transfer paper 100, which are formed under conditions that easily cause toner scattering. 7 shows a post-transfer pixel image.

When the pre-transfer pixel images on the photoreceptor 1a shown in FIGS. 2A and 2D are transferred under conditions in which toner scattering is less likely to occur and toner scattering is more likely to occur, respectively, A pixel image after transfer is formed on the transfer paper 100 after transfer. In other words, when the image is transferred under the condition that the toner is hardly scattered, the edge portion 10
a is crushed and spread by the contact pressure between the intermediate transfer belt 51 and the photosensitive drum 1 or the like. On the other hand, when the image is transferred under the condition that toner scattering is likely to occur, a state in which a scattering portion 10c due to the toner scattering occurs around a core portion 10b having a diameter substantially equal to the diameter of the pre-transfer pixel image on the photoconductor 1a. Become. Each of the post-transfer pixel images is fixed by the fixing device 9 and becomes a final pixel image.

As described above, the pixel image formed under the condition that the toner is hardly scattered is transferred from the photosensitive member 1a to the transfer paper 10a.
When the pre-transfer pixel image is transferred to 0, the edge portion of the pre-transfer pixel image is widened and becomes a pixel image having a larger diameter on the transfer paper 100 than the pre-transfer pixel image. In particular, when a plurality of toners are overlapped to form an overlapped toner image on the transfer paper 100 as in the case of forming a color image, the toner layer developed into a plurality of layers is subjected to pressure applied in the transfer and fixing steps. It tends to be easily crushed and spread by such means. On the other hand, the pixel image formed under the condition in which the scattering easily occurs is the photosensitive member 1a.
A core portion 10b having a diameter substantially the same as the diameter of the pixel image before transfer above,
A scattered portion 10c made of toner sparsely scattered around the periphery is a pixel image. The toner scattered portion 10c is recognized only as a low density cloud which is hardly noticeable. In addition, the edge of the core portion 10b is blurred to make the entire pre-transfer pixel image inconspicuous. Therefore, compared to a post-transfer pixel image without the scattered portion 10c, it becomes difficult for a human to visually recognize the image.

Therefore, in the image forming apparatus according to the present embodiment, on the photoreceptor 1a, 20 μm or more and 50 μm
A configuration in which image forming conditions, for example, transfer conditions are set so that a pre-transfer pixel image having a diameter of m or less and a scattered portion 10c easily occurs.

Hereinafter, this configuration will be described in detail. First,
The diameter of the pre-transfer pixel image on the photoconductor 1a is 20 μm or more,
A configuration that is 50 μm or less will be described in detail. In order to keep the diameter of the pre-transfer pixel image on the photoconductor 1a in such a range, the conditions of each part in the apparatus, such as the optical writing apparatus, must be such that a pre-transfer pixel image having such a diameter can be formed. The beam diameter, the characteristics of the photoconductor, the development conditions of the developing device, and the like are set.

In the present image forming apparatus, the photosensitive member 1
As a, an element having a characteristic that is advantageous for forming a small-diameter pre-transfer pixel image of 20 μm or more and 50 μm or less, that is, a characteristic capable of forming an electrostatic pixel latent image faithful to a small-diameter writing beam is used. For example, as the photoconductor 1a,
A commonly used photoconductor, a two-layer organic photoconductor having a charge transport layer provided on a charge generation layer (hereinafter referred to as OPC)
Is adopted). However, even when OPC was employed, the following was found as a result of measuring the diameter of the pre-transfer pixel image developed on the surface of the photoconductor 1a under various writing beam diameters and developing conditions. That is, the photoconductor thickness 15
Above μm, it was found that even if the writing beam diameter was reduced to 50 μm or less, a dot-shaped pre-transfer pixel image of 50 μm or less could not be stably reproduced under the condition of saturated writing. The main reason for this is that the charge generated in the charge generation layer by optical writing moves when moving toward the surface of the photoreceptor 1a in the charge transport layer in order to neutralize the charge on the surface of the photoreceptor 1a. It is conceivable that the electric charges are diffused by the mutual repulsion according to the thickness of the photoconductor.
For this reason, in the image forming apparatus according to the present embodiment, the photosensitive member 1a is exposed to light near the surface opposite to the surface on which the electrostatic pixel latent image is formed (hereinafter, referred to as a latent image forming surface). It is preferable to use a photoreceptor that generates charges and has a thickness of 15 μm or less. When such a photoconductor 1a is used, the predetermined polarity of the charge generated by light near the surface opposite to the surface on which the latent image is formed, that is, near the surface on the photoconductor support 1b, An opposite polarity, for example, a positive charge in the illustrated apparatus, moves through the photoconductor film toward the latent image forming surface. Such movement neutralizes the charge on the surface of the photoreceptor 1a irradiated with light, and forms the electrostatic pixel latent image. At this time, since the film thickness of the photoreceptor 1a is 15 μm or less, even if the electric charges are diffused by the repulsive force during the movement, the spread does not easily increase. Therefore, it is possible to easily form a small electrostatic pixel latent image that becomes a small pre-transfer pixel image that cannot be visually recognized by a human after development, which is effective in realizing the binary process.

Further, as the photoreceptor 1a, a photoreceptor whose charge is generated by light in the vicinity of the latent image forming surface may be used. When such a photoreceptor 1a is used, a charge of a predetermined polarity, for example, a negative charge in the apparatus shown in FIG. In the photoreceptor toward the surface on the opposite side, that is, the surface on the photoreceptor support 1b side. At the time of this movement, a charge having a polarity opposite to the predetermined polarity, for example, a positive charge in the illustrated apparatus stays near the latent image forming surface to neutralize the charge on the surface of the photoreceptor 1a, thereby forming an electrostatic pixel. A latent image is formed. Even when an electrostatic pixel latent image is formed in this way, the diffusion of the charge due to the repulsive force is suppressed. Therefore, it is possible to easily form a small electrostatic pixel latent image that becomes a small pre-transfer pixel image that is invisible to humans after development, which is advantageous in realizing a binary process. As a typical example of such a photoconductor 1a,
Inorganic photoreceptors such as a selenium photoreceptor and an amorphous silicon photoreceptor can be mentioned, but an amorphous silicon photoreceptor is most suitable in view of the stability of the surface layer. These photoconductors 1a
Of course, it is of course possible to make improvements such as adding a surface layer as long as the characteristics are not impaired.

Further, even when the photoreceptor 1a is a photoreceptor that generates charges by light in the vicinity of the latent image forming surface, the photoreceptor 1a preferably has a thickness of 20 μm or less. This is for the following reasons. That is, if the charge of the predetermined polarity remains on the surface of the photoreceptor 1a, a charge of the same polarity and opposite in polarity to the charge (hereinafter referred to as a counter charge) is induced on the photoreceptor support 1b. Becomes The spread of the counter charge is wider than the spread of the charge of a predetermined polarity on the surface of the photoconductor 1a. At the time of development, the photosensitive member 1a and the developing device 4
A developing electric field is generated between the developing electrode and the electric charge on the surface of the photoconductor in a developing region between the developing electrode and the developer carrier (not shown). When a dot-shaped toner-attached pixel is developed under the influence of the developing electric field, the lines of electric force are spatially spread at the edge of the toner-attached pixel.
As a result, when the dot-shaped toner-adhered pixels are developed with the toner, the diameter of the pre-transfer pixel image obtained by the development is increased. Therefore, it is desirable to minimize the spread of the counter charge. This spread depends on the thickness and dielectric constant of the photoconductor 1a,
It is determined by various conditions such as the thickness of the developer and the dielectric constant of the developer. However, under normal development conditions, for example, development gap 2
Under the conditions of not less than 00 μm, the dielectric constant of the toner is 3 to 10, the thickness of the photoconductor 1a is about 40 μm, and the dielectric constant of the photoconductor 1a is 3 to 5, it is almost determined by the thickness of the photoconductor 1a. Become. Therefore, in order to form the above-mentioned small-diameter toner-attached pixel, it is desirable to set the thickness of the photoreceptor small, specifically, to 20 μm or less.

In the image forming apparatus shown in FIG. 1, an OPC having a thickness of 15 μm is used as the photoreceptor 1a. As the optical writing device 3, a laser optical system having a beam diameter of 50 μm for writing at a density of 600 dpi is used. Thereby, the pixel image before transfer on the photoreceptor 1a is formed in a dot shape having a small diameter of 20 μm or more and 50 μm or less.

Next, a configuration for easily causing the toner scattering portion 10c will be described. In the image forming apparatus according to the present embodiment, an intermediate transfer belt 51 as an intermediate transfer member, and an intermediate transfer device 5 for transferring the toner image on the photosensitive member 1a onto the intermediate transfer belt 51
The transfer of the toner image onto the transfer paper 100 is performed using a transfer unit having a transfer roller 81 for transferring the toner image on the intermediate transfer belt 51 onto the transfer paper 100. In this transfer means, it is necessary to create a state in which toner transfer is very likely to occur in order to obtain sufficient transfer efficiency in two transfer steps, and it is easy for toner to scatter around the dot-shaped pixel image before transfer. Become. Therefore, the photoconductor 1
a core portion 10b having substantially the same diameter as the pre-transfer pixel image and the scattered portion formed around the core portion 10b, as compared with a case where a transfer means for directly transferring the toner image from above to the transfer paper 100 is employed. 10c, the post-transfer pixel image composed of
It can be easily formed on the transfer paper 100.

In the image forming apparatus according to the present embodiment, at least 20 μm and 50 μm formed on the photoreceptor 1 a
When the pre-transfer pixel image having a diameter of μm or less is transferred to the transfer paper 100 through the primary transfer and secondary transfer steps by the above-described transfer means, the edge portion and the background portion of the post-transfer pixel image on the transfer paper 100 Is blurred, and becomes less noticeable on the transfer paper 100. Further, the post-transfer pixel image formed on the transfer paper 100 has a nucleus portion 10 having substantially the same diameter as the pre-transfer pixel image.
b and the splattered portion 10c formed therearound.
It is composed of As described above, the diameter of the pre-transfer pixel image on the photoreceptor 1a is not less than 20 μm and not more than 50 μm, so that the size of the core portion 10b can be kept in a range that cannot be visually recognized by humans. Can be stably maintained. In addition to the above, the scattered portion 10c around the core portion 10b does not allow individual toners to exist almost independently and is visible to humans, but the whole is made as a cloudy haze. It is only slightly visible. Therefore, the transfer paper 1
The core portion 10 in the post-transfer pixel image formed at 00
Both b and the scattered portion 10c are difficult for a human to visually recognize. As described above, the core portion 10b is formed to have a diameter that is difficult for humans to visually recognize, and the entire post-transfer pixel image is blurred by the scattered portion 10c that is slightly visible to humans, so that the transfer paper 100 In the image formed as described above, the individual post-transfer pixel images can be made extremely inconspicuous. Therefore, an image with less noticeable roughness can be stably obtained. In particular, it is possible to obtain an image excellent in stability of reproduction of halftone and highlight, which is a problem in the electrophotographic system.

The present inventors have confirmed this effect as follows. That is, in the apparatus of FIG. 1, a pre-transfer pixel image was formed on the photoreceptor 1a with a diameter of approximately 50 μm, and was transferred under transfer conditions in which toner scatter was likely to occur. Then
When the scattering portion 10c is included, a pixel image after transfer having a diameter of 50 μm or more is formed on the transfer paper 100, but the whole image is observed as a smooth image having no problem at all. In addition, since the binary process is used in the steps up to the development, there is no influence from changes in environment and development characteristics.

On the other hand, under normal transfer conditions, the same 50 μm
Even if a pre-transfer pixel image having a diameter of 50 μm is formed on the photoconductor 1a, 50 μm
m, which was a clear pixel image after transfer. Although the overall diameter of the image was slightly smaller than that of the former, the whole image was rough.

FIGS. 3A and 3B are explanatory views showing unfixed post-transfer pixel images on the transfer paper 100. FIG. FIGS. 3A and 3B show the same post-transfer pixel image. As described above, this post-transfer pixel image is
The core portion 10b and the scattered portion 10c around the core portion 10b
It is composed of In the present invention, the toner in point contact with the core portion 10b is considered to belong to the scattering portion 10c. Here, the toner scattering level is defined as follows. That is, FIG.
As shown in (a), the minimum width Amin and the maximum width Amax of the core portion 10b which does not include the toner belonging to the scattering portion 10c are measured. Then, the sum of these is halved to obtain the average diameter A. Further, as shown in FIG. 3B, the minimum width Bmin and the maximum width Bmax of the entire post-transfer pixel image including the toner belonging to the scattered portion 10c are measured. Next, similarly, the sum of them is halved to obtain the average diameter B, and the ratio B / A between the two average diameters is set as the scattering level. Specifically, an isolated post-transfer pixel image is formed on the transfer paper 100 under various transfer conditions, and a photograph is taken without fixing. And
The photographed image is enlarged and printed 200 times and the scattering level is calculated. Further, a toner image composed of a plurality of post-transfer pixel images was formed on the transfer paper 100 under the same transfer conditions, and the image quality after fixing was compared. When the scattering level became 1.5 or more, a granular feeling was observed. Less,
It was found that the image was observed as a smooth image. For this reason, it is desirable to set the image forming conditions so that the scattering level is 1.5 or more. Specifically, transfer conditions such as a transfer bias voltage / current, a resistance value of the intermediate transfer belt 51, a diameter of the transfer roller 81, and the like,
It is desirable to set the fluidity of the toner. In order to adjust the fluidity of the toner, the shape of the toner, specifically, the sphericity, the amount and type of the external additive, and the mixing conditions may be adjusted. Considering the deterioration of the sharpness of lines and character images, it is desirable that the scattering level is 3.0 or less.

Next, image processing for gradation expression in the image forming apparatus according to the present embodiment will be described. As a general image processing method for tone expression generally used in an electrophotographic method, a dither method can be cited. In this method, a matrix composed of a plurality of basic pixels is set, and a density threshold set for each basic pixel is compared with density information of each pixel represented by a multi-value. The gradation is expressed in a matrix unit by such a method that it is regarded as below, and if it is less than that, it is regarded as the background. As a method of setting the threshold value of the density, a dot concentration type matching the developing characteristic peculiar to the electrophotographic method is often used. In this method, since the matrices are regularly arranged, it has a characteristic that the eyes are relatively hard to feel grainy. However, in this method, as the density increases, the size of the toner-attached portion composed of the toner-attached pixels in the matrix increases, so that if the matrix size is too large, the roughness becomes noticeable. For this reason, it is necessary to suppress the matrix size to about 120 × 120 μm,
In order to obtain a necessary number of gradations, it is necessary to make the size of the basic pixel extremely small. As a result, in this method, it is necessary to use the above-described one-dot multi-value process, and instability occurs in a halftone area or a highlight area.

Such a defect is caused not only when the dither method using a dot concentration type threshold matrix is adopted as the above-mentioned gradation expression method, but also when a pixel group consisting of a plurality of toner pixels This can occur if a method of expressing gradation by the size of a pixel itself is adopted.

Therefore, as a gradation expression method in the image forming apparatus according to the present embodiment, it is desirable to use a method of adjusting the density of toner-attached pixels per area according to the distance between each toner-attached pixel. More preferably, an error diffusion method is used as such a method. In the error diffusion method, when binarizing the density information of a certain pixel represented by multi-values, the difference between the binarized value and the multi-valued density value is distributed to neighboring pixels, and It is a method of expressing tones. If such a method is adopted, the interval between the toner-attached pixels is large in the low-density portion, and small in the high-density portion. Therefore, the toner-attached pixels are less likely to be aggregated than in the method in which the density of the toner-attached pixels per area is adjusted by the size of the attached pixel group or the toner-attached pixels themselves. This makes it difficult to form a large point image that can be visually recognized by humans. Further, a character image or a line image having excellent resolution and sharpness can be formed. Further, while forming a character image or a line image having excellent resolution, an image having excellent gradation can be formed in a picture portion. As a result, it is possible to obtain a good image which does not cause roughness as compared with the case where the dot concentration type of the dither method is used. In particular, in the image forming apparatus according to the present embodiment, scattering is caused to make the post-transfer pixel images less noticeable, so that a smooth image such as a silver halide photograph can be obtained.

In recent years, there has been proposed a method of expressing the gradation by adjusting the distance between the toner-adhered pixels by the error diffusion method while adjusting the diameter of the toner-adhered pixels themselves. You may. However, when this method is used, the diameter of the pre-transfer pixel image on the photoconductor 1a is set to 20 μm.
It is necessary to adjust in the range of m to 50 μm.

The image forming apparatus according to this embodiment differs from the image forming apparatus shown in FIG. 1 in that a plurality of toners are superimposed on the transfer paper 10 as in the case of forming a color image.
When a configuration in which a superimposed toner image is formed on zero is adopted, each post-transfer pixel image is less noticeable in the superimposed toner image, and a smooth high-quality superimposed toner image can be obtained. In addition, when the error diffusion method is used, the toner-attached pixels are not formed in a predetermined interval pattern, and the interval pattern of the toner-adhered pixels is changed according to a light and shade pattern of the image. Even when it is formed, the occurrence of moiré fringes can be suppressed.

[Second Embodiment] Next, an image forming apparatus according to another embodiment will be described. The basic configuration of the present image forming apparatus is the same as that of the image forming apparatus of the first embodiment, and a description thereof will not be repeated. The present inventors have intensively studied and found that when toner scattering was caused such that the toner scattering level became 1.5 times or more, the diameter of the photosensitive member 1a exceeded 50 μm. It was found that even after forming the pre-transfer pixel images, the post-transfer pixel images are less noticeable in the entire image on the transfer paper 100. Therefore, the image forming apparatus according to the present embodiment employs a configuration that can form each post-transfer pixel image such that the scattering level is 1.5 or more. Specifically, the image forming conditions are set so that the scattering level is 1.5 or more. More specifically, transfer conditions for transferring the pre-transfer pixel image on the photoreceptor 1a to the transfer paper 100, such as a transfer bias voltage / current, the resistance value of the transfer belt when the belt transfer method is adopted, and transfer. The shape of the entrance and exit of the unit and the fluidity of the toner are set. As described above, to adjust the fluidity of the toner, the shape of the toner, specifically, the sphericity, the amount and type of the external additive, and the mixing conditions may be adjusted.

In order to facilitate the occurrence of the scattering, a transfer means for transferring the pre-transfer pixel image on the photoreceptor 1a via an intermediate transfer member rather than a transfer means for directly transferring the pre-transfer pixel image to the transfer paper 100 is adopted. It is more advantageous to employ. However, if the scattering level can be set to 1.5 or more, the pre-transfer pixel image on the photoreceptor 1a is transferred to the transfer paper 1
Alternatively, a transfer unit that directly transfers the image data to C.00 may be used. For example, by adjusting the transfer bias voltage / current, the transfer bias application position in the transfer nip portion, and the resistance value of the transfer belt when the belt transfer method is adopted, the scattering level can be adjusted to 1.5 or more. Good.

With such a configuration, in the entire image formed on the transfer paper 100, each post-transfer pixel image is less noticeable, and a smooth image with reduced roughness can be stably obtained.

Also, in the image forming apparatus according to the present embodiment, it is desirable that the level of the scattering is 3.0 or less in consideration of the deterioration of the sharpness of the line and character images.

Also in the image forming apparatus according to the present embodiment, it is desirable to use an error diffusion method or the like for adjusting the density of the toner-attached pixels per area according to the distance between the toner-adhered pixels as the gradation expression method. . If such a method is adopted, the interval between the toner-attached pixels is large in the low-density portion, and small in the high-density portion. Therefore, the toner-attached pixels are less likely to aggregate than in the method of adjusting the density according to the size of the attached pixel group or the toner-attached pixels themselves. This makes it difficult to form a large point image that can be visually recognized by humans. Further, a character image or a line image having excellent resolution and sharpness can be formed. Further, while forming a character image or a line image having excellent resolution, an image having excellent gradation can be formed in a picture portion. As a result, it is possible to obtain a good image which does not cause roughness as compared with the case where the dot concentration type of the dither method is used. In particular, also in the image forming apparatus according to the present embodiment, scattering is caused to make the post-transfer pixel images less noticeable, so that a smooth image such as a silver halide photograph can be obtained.

In the case where the image forming apparatus according to the present embodiment employs a configuration in which a plurality of toners are overlapped to form an overlapped toner image on the transfer paper 100 as in the case of forming a color image, The toner pixels are less noticeable in the superimposed toner image, and a smooth high-quality superimposed toner image can be obtained. In addition, when the error diffusion method is used, the toner-attached pixels are not formed in a predetermined interval pattern, and the interval pattern of the toner-adhered pixels is changed according to a light and shade pattern of the image. Even when it is formed, the occurrence of moiré fringes can be suppressed.

[0071]

According to the present invention, claims 1, 2, 3, 4, 5, 6, 7,
According to the invention of 8, 9, 10, 11 or 12, there is an excellent effect that a change in image quality due to development conditions and the like can be suppressed and the image quality can be stably maintained as compared with the case where a multi-value process is used. . Further, there is an excellent effect that a smooth image with less noticeable roughness can be formed.

In particular, according to the first, second, third, fourth, fifth and sixth aspects of the present invention, not only the clear viewing distance but also a distance shorter than this makes the post-transfer pixel image less noticeable. There is an excellent effect that an inconspicuous smooth image can be formed.

In particular, according to the second, third, seventh or eighth aspect of the present invention, there is an excellent effect that a smooth image with less graininess can be obtained.

In particular, according to the third or eighth aspect of the present invention, there is an excellent effect that a sharp image of a line image or a character image caused by scattering of toner can be suppressed and a good image can be obtained. .

In particular, according to the invention of claim 4, 5 or 6, a small electrostatic latent image can be easily formed, so that a smooth image with less noticeable roughness can be easily obtained. Has an effect.

In particular, according to the invention of claim 6, there is an excellent effect that the life of the image carrier is prolonged and the safety is enhanced.

According to the ninth aspect of the present invention, the scattered portion can be easily formed around the nucleus portion as compared with the method of directly transferring a toner image from an image carrier to a transfer material. There is an excellent effect that it can be done.

In particular, according to the tenth aspect of the invention, the roughness of the image due to the increase in the image density is suppressed as compared with the case where the density of the toner attached pixels per area is adjusted by the size of the attached pixel group. There is an excellent effect that you can.

In particular, according to the eleventh aspect of the present invention, there is an excellent effect that a character image or a line image having better resolution and sharpness can be formed than when the dither method is used. Further, there is an excellent effect that an image having excellent gradation can be formed in a picture portion while forming a character image or a line image having excellent resolution. Further, even when a color image is formed by superimposing toner images of the respective colors, there is an excellent effect that generation of moire fringes can be suppressed.

In particular, according to the twelfth aspect of the invention, there is an excellent effect that a smooth superimposed toner image with less noticeable roughness can be obtained.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a schematic configuration of an image forming apparatus according to an embodiment.

FIGS. 2A to 2F are explanatory diagrams showing a dot-shaped pixel image formed under conditions in which toner scattering is unlikely to occur and a dot-shaped pixel image formed under conditions in which toner scattering is likely to occur. .

FIGS. 3A and 3B are explanatory views showing an unfixed post-transfer pixel image on transfer paper 100. FIGS.

FIG. 4 is an explanatory diagram illustrating an example of a relationship between writing energy and a photoconductor surface potential.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 1a Photoconductor 1b Photoconductor support 2 Charging device 3 Optical writing device 4 Developing device 5 Intermediate transfer device 51 Intermediate transfer belt 6 Static eliminator 7 Cleaning device 81 Transfer roller 9 Fixing device 10 Toner 100 Transfer paper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference)

Claims (12)

[Claims] An image processing apparatus for processing image data of an image to be formed such that a gradation is expressed by a density per area of an image carrier and a toner-adhered pixel to which a toner is adhered among pixels constituting the image. Means, a latent image forming means for forming an electrostatic latent image of an image comprising the pixels on the image carrier based on the image data processed by the image processing means, and an electrostatic latent image of the image. In an image forming apparatus having developing means for developing a toner image into a toner image and transfer means for transferring the toner image on the image carrier to a transfer material, transfer of a toner image of one pixel on the image carrier is performed. The diameter of the previous pixel image is 2
0 μm or more and 50 μm or less, and as the transfer means, a post-transfer pixel image which is a transfer image of the pre-transfer pixel image on the transfer material is formed with a diameter similar to that of the pre-transfer pixel image. An image forming apparatus which uses a nucleus portion to be formed and a splattered portion around which toner is scattered so as to form the splattered portion by transfer. 2. The image forming apparatus according to claim 1, wherein toner is scattered around the core so that the diameter of the post-transfer pixel image is 1.5 times or more the diameter of the core. An image forming apparatus comprising: 3. The image forming apparatus according to claim 2, wherein toner is scattered around the core portion so that the diameter of the post-transfer pixel image is three times or less the diameter of the core portion. An image forming apparatus comprising: 4. The image forming apparatus according to claim 1, wherein light is generated by light as an image carrier near a surface opposite to a surface on which the electrostatic latent image is formed, And an image forming apparatus using a photoreceptor having a thickness of 15 μm or less. 5. An image forming apparatus according to claim 1, wherein the image carrier is a photoconductor which generates electric charges by light near a surface on which the electrostatic latent image is formed. An image forming apparatus comprising: 6. The image forming apparatus according to claim 5, wherein an amorphous silicon photosensitive member is used as the image carrier. 7. Image processing for processing image data of an image to be formed so as to express a gradation by an image carrier and a density per pixel of a toner-adhered pixel to which toner is applied among pixels constituting the image. Means, a latent image forming means for forming an electrostatic latent image of an image comprising the pixels on the image carrier based on the image data processed by the image processing means, and an electrostatic latent image of the image. In an image forming apparatus having developing means for developing a toner image into a toner image and transfer means for transferring the toner image on the image carrier to a transfer material, one pixel of toner after being transferred onto the transfer material The post-transfer pixel image, which is an image, is composed of a nucleus portion formed of the aggregated toner and a scattered portion around which toner adheres as if scattered, and the diameter of the post-transfer pixel image is the nucleus. 1.5 times the diameter of the part As described above, the image forming apparatus characterized by causing scattering of the toner around the nucleic portion. 8. The image forming apparatus according to claim 7, wherein the toner is scattered around the core portion so that the diameter of the post-transfer pixel image is three times or less the diameter of the core portion. An image forming apparatus comprising: 9. The method of claim 1, 2, 3, 4, 5, 6, 7 or 8.
The image forming apparatus according to any one of claims 1 to 3, wherein the transfer unit transfers the toner image to an intermediate transfer member and then transfers the toner image to the transfer material. 10. The method of claim 1, 2, 3, 4, 5, 6, 7,
8. The image forming apparatus according to 8 or 9, wherein the image processing means adjusts the density of the toner attached pixels per unit area according to the distance between the toner attached pixels. 11. An image forming apparatus according to claim 10, wherein an error diffusion method is used as a method for adjusting the density of said toner-attached pixels per unit area according to the distance between each toner-attached pixel. Image forming device. 12. The method of claim 1, 2, 3, 4, 5, 6, 7,
8. The image forming apparatus according to any one of 8, 9, 10, or 11, wherein the toner image is formed by superimposing a plurality of the toner images on the transfer material.