JPH04269776A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a sharp image of high resolution by preventing deterioration of image characteristic due to an edge effect by developing by a pressurized contact developing method after an electrostatic latent image is formed on a high gamma type photosensitive body. CONSTITUTION:A developing roll 9 is brought into a pressurized contact with a surface a photosensitive layer 3 of a latent image bearing member 1 at a specified pressure and toner 8 on the roll 9 is carried to the pressurized contact part. The toner 8 electrified according to developing electric field by potential contrast of the bearing member 1 and a developing bias impressing means 14 is stuck to the photosensitive layer 3 and the electrostatic latent image is visualized. Furthermore, an image by the toner is transferred to a recording paper 16 utilizing a transferring device 15, and the transferred toner is fixed to the recording paper forming a desired image on the recording paper 16 with heat or pressure. At this time, the high gamma type photosensitive body, etc., showing a photosensitivity characteristic which is an avalanche like phenomenon is utilized as material constituting the photosensitive layer 3.

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 with excellent resolution mainly using a monocomponent toner.

0002

[Prior Art] As a developing device used in a conventional image forming method using an electrophotographic process, for example, US Pat.
As disclosed in No. 121931, a magnetic brush made of one-component magnetic toner is formed on the sleeve using a developing roller equipped with a magnetic roller inside a non-magnetic cylindrical sleeve, and the one-component magnetic toner is conveyed and This method performs development and is known as a one-component magnetic brush development method.

[0003] Further, as a developing method that improves the above-mentioned one-component magnetic brush developing method, US Pat. No. 4,564,28
No. 5, the so-called FEED development method improves the image quality of line images and solid images by providing a floating electrode on the developing roller, or a magnetic roller as disclosed in U.S. Pat. No. 4,851,874. A developing method has been proposed in which a toner layer formed on the surface of a belt-shaped latent image carrier is transported and developed on a belt-shaped latent image carrier.

Furthermore, focusing on photoreceptors that form latent images, as disclosed in Japanese Patent Application Laid-Open No. 1-169454, photoreceptors for digital light input are conventionally used as photoreceptors for digital light input.
Materials having so-called high γ characteristics have been proposed.

[0005]

[Problems to be Solved by the Invention] Conventional image forming methods each have a characteristic in that development can be performed while maintaining a certain image quality, but they are not capable of further improving image characteristics such as resolution. It is not always completely satisfactory. For example, in the conventional one-component magnetic brush development method and FEED development method, the developing roller consists of a developing sleeve and a magnetic roller, which not only makes the structure complicated, but also causes uneven density and image edges due to fluctuations in the magnetic field of the magnetic roller. The problem is that there are relatively many causes of image quality deterioration, such as trailing (edge effect). Furthermore, problems similar to those described above occur also in a developing method in which a thin layer of toner is conveyed and developed on the surface of a magnetic roller.

[0006] The present invention has been made in view of the above-mentioned prior art, and in particular, it is an image method for effectively preventing deterioration of image characteristics caused by edge effects and the like to obtain sharp, high-resolution images. The purpose is to provide a formation method.

[0007]

[Means for Solving the Problems] The present invention has been made based on the knowledge that the resolution of formed images is improved by combining a high γ type photoreceptor and a pressure-contact development method. According to the knowledge of By controlling the range, the formed image can be made sharper and the resolution can be further improved.

The present invention has been made based on the above-mentioned findings, and more specifically relates to an electrophotographic process in which an electrostatic latent image is formed on a photoreceptor and an image is formed by developing this electrostatic latent image. This image forming method is characterized by forming an electrostatic latent image on a high γ type photoreceptor and then developing this electrostatic latent image by a pressure development method to form an image with excellent resolution. The present invention relates to an image forming method.

Furthermore, in the present invention, when performing development by the pressure contact development method, the speed ratio A of the circumferential speed of the photoreceptor to the circumferential speed of the developing roller (peripheral speed of the developing roller/peripheral speed of the photoreceptor) is set to 1. The present invention relates to an image forming method characterized in that control is performed within a range of ≦A≦5.

The present invention will be explained in more detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus including a developing device used in the method of the present invention. In this embodiment, the latent image carrier 1 includes a photoconductive photosensitive layer 3 formed on a conductive support 2, and the photosensitive layer 3 is connected to a charger such as a corona charger or a charging roller. After charging the photosensitive layer 3 using a laser or LED, light from a light source 5 such as a laser or LED is selectively irradiated onto the photosensitive layer 3 according to the image through an imaging optical system 6 to obtain a potential contrast. An electrostatic latent image is formed in layer 3.

On the other hand, the developing device 21 conveys and develops the magnetic toner 8, and the developing roller 9 conveying the toner 8 has an elastic layer 11 and a magnetic field generating layer 12 concentrically arranged around the outer periphery of the shaft 10. It is arranged in a shape,
The magnetic toner 8 is generated by leakage magnetic flux around the outer periphery of the magnetic field generation layer 12.
A thin layer of toner 8 is conveyed by rotating the developing roller 9 while holding the toner directly on the developing roller and controlling the amount to an appropriate amount by a plate-like elastic blade 22 made of non-magnetic or magnetic metal or resin. 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 with a predetermined pressure, and the toner 8 on the developing roller 9 is pressed against the surface of the photosensitive layer 3 of the latent image carrier 1. When transported, the toner 8 charged according to the potential contrast of the latent image carrier 1 and the developing electric field by the developing bias applying means 14 adheres to the photoreceptor 3, thereby making the electrostatic latent image visible. . Furthermore, the toner image is transferred onto the recording paper 16 using a transfer device 15 such as a corona transfer device or a transfer roller, and the transferred toner is fixed onto the recording paper by heat or pressure to form a desired image on the recording paper. Can be done. In the above embodiment, the developing roller 9 is made of an elastic body, but the present invention is not limited to this, and the developing roller 9 is made of an elastic material.
It is sufficient if a state of pressure contact is achieved between the developing roller and the developing roller. For example, when a belt-shaped photoreceptor is used, the developing roller 9 does not necessarily have to be made of an elastic body.

The above is an outline of the image forming apparatus. In the method of the present invention, a high γ type photoreceptor or the like exhibiting avalanche-like photosensitivity characteristics is used as the material constituting the photosensitive layer 3. Furthermore, by employing the above-mentioned pressure-contact development during development, edge effects are effectively reduced and resolution is significantly improved.

[0014] In the present invention, the above-mentioned "high γ type photoreceptor"
means that the following conditions are satisfied. In other words, a high γ type photoreceptor is a photoreceptor that has light attenuation characteristics as shown in A and C of FIG. The relationship between the exposure amounts E25, E50, and E75 required for It refers to something that satisfies E50.

The above-mentioned high γ type photoreceptor has its own unique photosensitivity characteristics, but when combined with pressure development, it can make a significant contribution to improving resolution. This point will be explained below.

FIG. 4 is a contour line showing the distribution of the amount of light on the photoreceptor when exposure is carried out.
600DPI line pair (
These are contour lines of the light amount distribution when the photoreceptor is exposed to light at a rate of 12 line pairs/mm). As shown in this figure, the exposed portion on the photoreceptor usually exhibits a gentle light amount distribution. In the figure, X indicates the center of the line.

On the other hand, FIGS. 5 and 6 are contour lines showing the distribution state of the absolute value of the surface potential when exposure as shown in FIG. 4 is performed. Of these, FIG. 5 shows the contour lines of the surface potential of the conventional photoreceptor shown in FIG. Even if they are placed in close proximity, a sharp developing electric field will not be formed, resulting in blurred edges of the image.

On the other hand, FIG. 6 shows the surface potential distribution in the case of the high γ type photoreceptor shown in A of FIG. The surface potential distribution is such that the surface potential changes sharply at the boundary with the image area, and when pressure development is performed and the development electrode is placed closest, a sharp developing electric field can be obtained. A high-contrast, high-resolution image can be formed.

The contact pressure in the above-mentioned pressure development is suitably in the range of 2 to 20 g/mm, more preferably in the range of 4 to 20 g/mm.
A range of 10 g/mm is preferred. Contact pressure is 2g/mm
If it is less than this, it is difficult to maintain a stable press-contact state, and the resolution tends to decrease, which is not preferable. On the other hand, 20g/
Pressing with a pressure exceeding 1 mm is undesirable because problems such as damaging the toner, causing filming on the developing roller, and requiring excessive driving torque occur.

[0020] By adopting the above method, the edge effect is significantly reduced, the amount of developed toner per dot is stabilized, the resolution is increased and the area gradation property is improved, and furthermore, the toner It is also advantageous in reducing consumption.

Further, according to the research of the present inventor, during the above-mentioned pressure-contact development, the speed ratio of the circumferential speed of the photoreceptor to the circumferential speed of the developing roller (peripheral speed of the developing roller/peripheral speed of the photoreceptor) is set within a specific range. It has been found that the formed image can be made even sharper and the resolution can be improved by controlling the amount of light. That is, when performing development by the above pressure contact development method, the speed ratio A (
Circumferential speed of developing roller/peripheral speed of photoreceptor), 1≦A≦
Good resolution can be obtained by controlling it within the range of 5. FIG. 2 is a graph showing the relationship between the speed ratio A and the resolution when a line image of 300 [DPI] is formed using the image forming apparatus shown in FIG. The solid line graph is for a one-component non-magnetic toner, and the broken line graph is for a one-component magnetic toner. The resolution in this case is obtained by measuring the maximum value (Max) and minimum value (Min) of the optical reflection density of the formed line image, and plotting the given values according to the following formula. Resolution (%) = (Max-Min)/
(Max+Min) As is clear from this figure, good resolution can be obtained when the speed ratio A is in the range of 1 to 5. In addition, especially in the case of non-magnetic toner, there is a tendency for toner to be oversupplied when the speed ratio is 4 or more, whereas in the case of magnetic toner, toner is oversupplied when the speed ratio is 5 or more. There was a tendency for the situation to be This oversupply refers to a state in which toner is supplied to the developing area so much that it overflows, and in this state, it is difficult to continue developing. Therefore, considering this problem of oversupply, 1
In the case of component non-magnetic toner, it is preferable to control the speed ratio A in the range of 1≦A≦4, while in the case of one-component magnetic toner, the speed ratio A is preferably controlled in the range of 1≦A≦5. It is preferable.

The present invention will be explained below based on actual examples, but the present invention is not limited by the description of these examples.

[0023]

[Example] Using the 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 their resolutions were measured.

[0024]
Table 1
Example Photoconductor Photoconductor development bias Development method Speed ratio Resolution (%) No. Type of charging voltage Voltage
300DPI 600DPI 1
High γ type +400V +225V
a 2 75
60 2 High γ type +400V
+175V a4
60 45 3 High γ type
+400V +350V a
0.7 25-4
High γ type +400V +150V
a10-
−5 High γ type +400V
+250V b 2
80 65 6 High γ type +4
00V +200V b
5 60 40 7
High γ type +400V +150V
b10-
−8 High γ type +550V
+500V c 4
20 - 9 High γ type +5
50V +400V (AC) d
1 40-10
Conventional type -400V -225V
e 2 40
20 11 Conventional type -550V
-500V c 4
20 - 12 Conventional type -5
50V -400V (AC) d
1 40-13
High γ type +400V -200V
e 2 70
40 14 High γ type +400V
-200V f2
75 50 15 High γ type −
400V -225V a
2 65 40 1
6 High γ type -400V -275V
b 2 65
40 In the above example, No. 1, 2, 5, 6,
Nos. 13 to 16 are examples of the present invention, and the others are comparative examples.

[0025] Also, No. As the high γ type photoreceptor in Nos. 1 to 9, 13, and 14, a phthalocyanine-based single-layer positively charged organic photoreceptor shown in A of FIG. 3 was used,
No. As the high γ type photoreceptor of Nos. 15 and 16, C in Fig. 3 is used.
A conventional photoreceptor is a functionally separated two-layer negatively charged organic photoreceptor shown in FIG. It was used.

The developing method shown in Table 1 above is as follows. Development method a: Pressure/reversal development using a one-component nonmagnetic toner Development method b: Pressure/reversal development using a one-component magnetic toner Development method c: Reversal development using a one-component magnetic brush Development method d: Non-contact using a one-component non-magnetic toner・Reversal development development method e: Pressure contact/regular development using one-component non-magnetic toner Development method f: Pressure contact/regular development using one-component magnetic toner

[0027]

[Effects of the Invention] In the image forming method according to the present invention,
By using a high-gamma type photoreceptor as the photoreceptor that forms the electrostatic latent image, and using the pressure-contact development described above for development, the edge effect is effectively reduced and the resolution is significantly increased. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-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 the relationship between the speed ratio of the circumferential speed of a photoreceptor to the circumferential speed of a developing roller and resolution.

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

FIG. 4 is a contour line showing the distribution of light amount on a photoreceptor.

FIG. 5 is a contour line showing the distribution of absolute values of surface potential when a conventional photoreceptor is exposed to light.

FIG. 6 is a contour line showing the distribution of absolute values of surface potential when a high γ type photoreceptor is exposed to light.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. An image forming method using an electrophotographic process in which an image is formed by forming an electrostatic latent image on a photoreceptor and developing the electrostatic latent image, the method comprising: An image forming method characterized by forming an image and then developing the electrostatic latent image by a pressure contact development method to form an image with excellent resolution. 2. When performing development by the pressure contact development method, the speed ratio A of the circumferential speed of the photoreceptor to the circumferential speed of the developing roller (peripheral speed of the developing roller/peripheral speed of the photoreceptor) is set to 1≦A≦5. The image forming method according to claim 1, wherein the image forming method is controlled within the range of .