JP2000131928A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent degradation image characteristic due to an edge effect, etc., and to obtain a sharp image of high resolution by forming an electrostatic latent image on a single-layer, positively-electrifiable organic photoreceptor and then developing it by a pressure-contact development method. SOLUTION: When toner 8 on a developing roller 9 is carried to a pressure contact part, the toner 8 charged according to the potential contrast of a latent- image carrier 1 and a development electric field by a development bias application means 14 sticks to a photoreceptive layer 3, so that an electrostatic latent image is developed. Further, an image of toner is transferred onto recording paper 16 by means of a transfer unit 15 such as corona transfer unit or a transfer roller, the transfer toner is fixed onto the recording paper by the application of heat and pressure, and thus a required image can be formed on the recording paper. In the use of a single-layer, positively charged organic photoreceptor in particular, such a surface-potential distribution that surface potential greatly changes in a boundary between a line image and a non-line image is exhibited, therefore a sharp development electric field can be obtained by the closest contact of a development electrode through pressure-contact development.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method using an electrophotographic process, and more particularly, to an image forming method having an excellent resolution mainly using a one-component toner.

[0002]

2. Description of the Related Art As a developing device used in a conventional image forming method by an electrophotographic process, for example, US Pat.
As disclosed in Japanese Patent No. 121931, a magnetic brush made of a one-component magnetic toner is formed on a sleeve using a developing roller having a magnet roller inside a non-magnetic cylindrical sleeve to transfer the one-component magnetic toner and Development is performed, and is known as a one-component magnetic brush development method.

A developing method for improving the one-component magnetic brush developing method described above is disclosed in US Pat. No. 4,564,428.
5, a so-called FEED developing method in which a developing electrode is provided with a floating electrode to improve the image quality of a line image and a solid image, or a magnet roller as disclosed in US Pat. No. 4,851,874. There has been proposed a developing method in which the toner thinned on the surface of the toner image is conveyed and developed on a belt-like latent image carrier.

Further, focusing on a photosensitive member for forming a latent image, as disclosed in Japanese Patent Application Laid-Open No. 1-169454, a photosensitive member for inputting digital light has conventionally been used.
One having a so-called high γ characteristic has been proposed.

[0005]

The conventional image forming methods each have a feature in that development can be performed while maintaining a constant image quality. However, in terms of further improving image characteristics such as resolution, the conventional image forming methods have characteristics. It is not always satisfactory. For example, in the conventional one-component magnetic brush developing method and the FEED developing method, the developing roller is constituted by a developing sleeve and a magnet roller, which complicates the structure, and causes uneven density and image edge due to the magnetic field fluctuation of the magnet roller. There is a problem that there are relatively many image quality deterioration factors such as tailing of a portion (edge effect). Furthermore, the same problem as described above also occurs in a developing method in which the toner thinned on the surface of the magnet roller is transported and developed.

The present invention has been made in view of the above-mentioned prior art, and in particular, an image for obtaining a sharp and high-resolution image by effectively preventing deterioration of image characteristics due to an edge effect or the like. It is intended to provide a forming method.

[0007]

SUMMARY OF THE INVENTION The present invention has been made based on the finding that the resolution of a formed image can be improved by combining a specific organic photoreceptor with a pressure contact developing method.

The present invention has been made based on the above-mentioned findings, and more specifically, an electrophotographic process for forming an image by forming an electrostatic latent image on a photosensitive member and developing the electrostatic latent image. Forming an electrostatic latent image on a single-layer positively charged organic photoreceptor, and developing the electrostatic latent image by a pressure-contact development method to form an image with excellent resolution. And an image forming method.

Further, in a preferred embodiment of the present invention,
In performing the development by the press-contact development method, the speed ratio A of the peripheral speed of the photosensitive member to the peripheral speed of the developing roller (the peripheral speed of the developing roller / the peripheral speed of the photosensitive member) is 1 ≦ A ≦ 5.
Can be controlled within the range.

Hereinafter, the present invention will be described more specifically with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus including a developing device used in the method of the present invention. In the present embodiment, the latent image carrier 1 is formed by forming a photoconductive photosensitive layer 3 on a conductive support portion 2, and the photosensitive layer 3 is charged by a charger 4 such as a corona charger or a charging roller. And then selectively irradiating the photosensitive layer 3 with light from a light source 5 such as a laser or an LED through the imaging optical system 6 in accordance with an image, thereby obtaining a potential contrast. An electrostatic latent image is formed on layer 3.

On the other hand, the developing device 21 conveys and develops the magnetic toner 8, and the developing roller 9 which conveys the toner 8 has an elastic layer 11 and a magnetic field generating layer 12 concentrically formed on the outer periphery of a shaft 10. Are arranged in a shape,
The magnetic toner 8 is formed by the leakage magnetic flux around the magnetic field generating layer 12.
Is held directly on the developing roller, and the developing roller 9 is rotated while the plate-shaped elastic blade 22 made of non-magnetic or magnetic metal or resin is regulated to an appropriate amount to convey the thin layer toner 8. It is.

In the present invention, the developing roller 9 made of a specific elastic material is pressed against the surface of the photosensitive layer 3 of the latent image carrier 1 at a predetermined pressure, and the toner 8 on the developing roller 9 is pressed against the pressing portion. When the toner 8 is conveyed, the toner 8 charged in accordance with the potential contrast of the latent image carrier 1 and the developing electric field by the developing bias applying unit 14 adheres to the photoconductor 3, whereby the electrostatic latent image is visualized. . Further, an image formed by the toner is transferred onto the recording paper 16 using a transfer device 15 such as a corona transfer device or a transfer roller, and the transfer toner is fixed on the recording paper by heat or pressure to form a desired image on the recording paper. Can be. In the above embodiment, the developing roller 9 is made of an elastic material. However, the present invention is not limited to this.
It suffices if a pressure contact state is realized between the developing roller and the developing roller. For example, when a belt-shaped photoconductor is used, the developing roller 9 does not necessarily need to be formed of an elastic body.

The above is an outline of the image forming apparatus. In the method of the present invention, the material constituting the photosensitive layer 3 is, for example, a high γ type photoreceptor exhibiting avalanche-like photosensitivity characteristics, particularly a simple material. The layer effect is effectively reduced by using a positively charged organic photoreceptor and employing the above-described pressure contact development for development, thereby achieving a significant improvement in resolution.

In the present invention, the above “high γ-type photoreceptor”
Means those satisfying the following conditions. That is, the high γ-type photoreceptor is a photoreceptor having light attenuation characteristics as shown in FIGS. 3A and 3C, and attenuates the surface potential by 25%, 50%, and 75%. exposure required _{E 25, E 50,} and _{E 7 5}
Satisfies the following relationship: E ₂₅ ≧ 0.5 · E ₅₀ E ₇₅ ≦ 2 · E ₅₀ More preferably, E ₂₅ ≧ 0.75 · E ₅₀ E ₇₅ ≦ 1.25 · E ₅₀ Shall do.

The above-mentioned high γ-type photoreceptor has its own photosensitivity characteristics, but when combined with pressure contact development, can significantly contribute to improvement in resolution. Hereinafter, this point will be described.

FIG. 4 is a contour line showing the distribution of the amount of light on the photosensitive member when the exposure is performed.
These are contour lines of the light amount distribution when a photoconductor is exposed to 600 DPI line pairs (12 line pairs / mm) using an I laser head. As shown in this figure, normally, the light-exposed portion on the photosensitive member shows a gentle light amount distribution. In the figure, X indicates the line center.

On the other hand, FIG. 5 and FIG. 6 are contour lines showing the distribution of the absolute value of the surface potential when the exposure as shown in FIG. 4 is performed. Among these, FIG. 5 is a contour line of the surface potential of the conventional photoconductor shown in FIG. 3B. In the conventional photoconductor, only a gentle surface potential distribution is obtained. No sharp developing electric field is formed even when the image is brought into close proximity, and therefore, the edge of the image is blurred.

On the other hand, FIG. 6 shows the surface potential distribution in the case of the high γ-type photosensitive member shown in FIG. 3A. As shown in FIG. A surface potential distribution such that the surface potential changes steeply at the boundary with the image area.If the development electrode is brought into close contact with the development electrode, a sharp development electric field is obtained. A high-contrast, high-resolution image can be formed.

The pressing pressure in the above-described pressing development is suitably in the range of 2 to 20 g / mm, and more preferably 4 to 20 g / mm.
A range of 10 g / mm is preferred. If the pressing pressure is less than 2 g / mm, it is difficult to maintain a stable pressing state, and the resolution tends to decrease. On the other hand, press contact with a pressure exceeding 20 g / mm is not preferable because it adversely damages the toner, causes filming of the developing roller, and requires excessive driving torque.

By employing the above-described method, the edge effect is significantly reduced, whereby the amount of developed toner per dot is stabilized, the resolution is improved, and the area gradation is improved. This is also advantageous in reducing consumption.

According to the study of the present inventor, the speed ratio of the peripheral speed of the photoreceptor to the peripheral speed of the developing roller (the peripheral speed of the developing roller / the peripheral speed of the photoreceptor) is specified in the above-mentioned press-contact development. It has been found that by controlling the resolution, the formed image can be sharpened and the resolution can be further improved. That is, in performing the development by the above-described pressure contact development method, the speed ratio A of the peripheral speed of the photosensitive member to the peripheral speed of the developing roller A
(The peripheral speed of the developing roller / the peripheral speed of the photoreceptor) is 1 ≦ A
By controlling the range of ≦ 5, a good resolution can be obtained. FIG. 2 is a graph showing the relationship between the speed ratio A and the resolution, in which a 300 [DPI] line image is formed using the image forming apparatus shown in FIG. The solid line graph is for the one-component non-magnetic toner, and the broken line graph is for the one-component magnetic toner. The resolution in this case is obtained by measuring the maximum value (Max) and the minimum value (Min) of the optical reflection density of the formed line image and plotting a value given according to the following equation. Resolution (%) = (Max−Min) / (Max + Mi)
n) As is clear from this figure, when the speed ratio A is in the range of 1 to 5, good resolution can be obtained. In particular, in the case of a non-magnetic toner, the toner tends to be oversupplied when the speed ratio is 4 or more, while in the case of a magnetic toner, the toner is oversupplied when the speed ratio is 5 or more. Tended to be in the state. The oversupply refers to a state in which the toner is excessively supplied to the developing area and overflows. In this state, it is difficult to continue the development. Therefore, in consideration of the problem of oversupply, in the case of a one-component non-magnetic toner, it is preferable to control the speed ratio A in the range of 1 ≦ A ≦ 4. Ratio A
Is preferably controlled within the range of 1 ≦ A ≦ 5.

Hereinafter, the present invention will be described based on actual embodiments, but the present invention is not limited to the description of these embodiments.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus shown in FIG.
Under the conditions shown in the table, a 300 [DPI] line image and a 600 [DPI] line image were formed, and the resolution was measured.

Table 1 Example Photoconductor Photoconductor Development bias Development method Speed ratio resolution (%) No. type Charge voltage Voltage 300 DPI 600 DPI 1 high γ type + 400V + 225V a 2 75 60 2 high γ type + 400V + 175V a 4 60 45 3 High γ type + 400V + 350V a 0.7 25 - 4 high γ type + 400V + 150V a 10 − − 5 High γ type + 400V + 250V b280806 6 High γ type + 400V + 200V b560 407 7 High γ type + 400V + 150V b10 − −8 High γ type + 550V + 500V c420 − 9 High γ type + 550V + 400V (AC) d 140 -10 Conventional type -400V -225V e240 20 11 Conventional type -550V -500V c 420-12 Conventional type -550V -400V (AC) d 140 −13 High γ type + 400V -200V e27040 14 High γ type + 400V -200V f27550 15 High γ type -400V -225V a26540 16 High γ type -400V -275V b26540 40 In the example, No. 1, 2, 5, 6, 13 to 16 are examples of the present invention, and the others are comparative examples.

Further, No. As the high γ-type photoreceptors 1 to 9 and 13 and 14, a phthalocyanine-based single-layer positively charged organic photoreceptor shown in FIG.
No. As the 15 and 16 high γ type photoreceptors, FIG.
A two-layer negatively-charged organic photoreceptor of the function-separated type shown in FIG. 3B is used, and a conventional two-layered organic photoreceptor of the function-separated type shown in FIG. It was used.

The developing methods in Table 1 are as follows. Developing method a: Pressure contact / reversal development with one-component non-magnetic toner Developing method b: Pressure contact / reversal development with one-component magnetic toner Developing method c: Reversal development with one-component magnetic brush Developing method d: Non-contact with one-component non-magnetic toner・ Reversal development Developing method e: Pressure contact with one-component non-magnetic toner ・ Regular development Developing method f: Pressure contact with one-component magnetic toner ・ Regular development

[0027]

According to the image forming method of the present invention,
A single-layer positively charged organic photoreceptor height is used as the photoreceptor for forming an electrostatic latent image, and the above-described press-contact development is used for development, so that the edge effect is effectively reduced and the resolution is reduced. It can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment used in an image forming method according to the present invention.

FIG. 2 is a graph showing a relationship between a speed ratio of a peripheral speed of a photosensitive member to a peripheral speed of a developing roller and resolution.

FIG. 3 is a graph showing light attenuation characteristics of a photoconductor.

FIG. 4 is a contour line showing a distribution state of a light amount on a photoconductor.

FIG. 5 is a contour line showing a distribution state of an absolute value of a surface potential when a conventional photoconductor is exposed.

FIG. 6 is a contour line showing a distribution state of an absolute value of a surface potential when a high γ-type photoconductor is exposed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Latent image carrier 2 Support part 3 Photosensitive layer 4 Charger 5 Light source 8 Toner 9 Developing roller

Claims (1)

[Claims] 1. An image forming method for forming an image by forming an electrostatic latent image on a photoreceptor and developing the electrostatic latent image, the method comprising: An image forming method, comprising: forming an electrostatic latent image, and developing the electrostatic latent image by a pressure contact developing method to form an image having excellent resolution.