JPH11125918A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of improving resolution and obtaining high image quality by adopting a novel constitution for an image carrier, without changing the performance of an exposure device in the image forming device and the mechanical accuracy of a whole device. SOLUTION: In the image forming device for forming an electrostatic latent image on the surface of a photoreceptive drum 1 (image carrier), in such a manner that on the surface of the drum 1, an image is spot-formed and the surface of the drum 1 is scanned with laser light from a laser light source, the drum 1 is provided with a surface layer having a large number of divided photoreceptor pieces 1a smaller than the diameters of beam spots and the resistance value of the surface layer is smaller than 1.0×10<12> Ω.cm.

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 using an electrophotographic process, and more particularly, to an image forming apparatus using digital signals used for a full-color printer or the like as image information.

[0002]

2. Description of the Related Art A laser beam printer employing an electrophotographic system is known as a printer which is characterized by high speed and low noise in an image forming apparatus. A typical image forming method of this laser beam printer forms an image such as a character or a figure by applying or not applying a laser beam to a photosensitive member.
This is a value recording method.

In order to improve the resolution, it is necessary to reduce the diameter of the laser spot. Even when the density pattern method is used after increasing the pixel density, or when a binary image is simply formed, the laser spot diameter is reduced. It is necessary to reduce the spot diameter.

[0004]

Here, in order to reduce the laser spot diameter, it is necessary to shorten the laser wavelength and increase the diameter of the incident light laser. Since the cost is high and the depth of focus is narrow, it is difficult to stably form the image dots on the image carrier due to the limitation of the mechanical accuracy. Overall accuracy) needed to be improved.

On the other hand, there has been proposed a method of increasing the resolution by reducing the sensitivity at the bottom of the light amount distribution of a laser beam using a so-called high γ photoreceptor disclosed in, for example, JP-A-1-169454. I have.

However, even in this method, since the sensitivity of the photoreceptor is not constant depending on the light amount, a sufficient latent image cannot be obtained due to the fluctuation of the light amount, and the potential at the bottom of the light amount distribution is also greatly reduced. Problems such as an increase in the dot shape of the image occur, and there is a problem that the effect of high resolution cannot be obtained simply by replacing the conventional photoconductor with the above photoconductor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide an image bearing apparatus without changing the performance of an exposure apparatus of an image forming apparatus or the mechanical accuracy of the entire apparatus. By making the body a new composition,
An object of the present invention is to provide an image forming apparatus capable of improving resolution and obtaining high image quality.

[0008]

In order to achieve the above object, according to the present invention, light from a light source is spot-formed and scanned on the surface of an image carrier, and the surface of the image carrier is scanned. In an image forming apparatus for forming an electrostatic latent image on a surface, the image carrier includes a surface layer having a large number of photoreceptor pieces divided into smaller beam spot diameters, and
The resistance value of the surface layer is smaller than 1.0 × 10 ¹² Ω · cm.

According to this, a dot latent image smaller than the exposure spot diameter on the photoreceptor can be formed, the reproducibility of a high-resolution image can be further improved, and a high-quality image can be obtained. .

Further, the image carrier has a small light sensitivity and a small amount of potential decay at a low light quantity, and has a sensitivity section where the light sensitivity increases and the potential decay quantity increases as the light quantity increases. It is also preferable to use a photoconductor having characteristics.

The image bearing member may further include a light-shielding means between the photosensitive member and the adjacent photosensitive member on the surface layer of the image bearing member to suppress light leaking from each photosensitive member from entering the adjacent photosensitive member. It is suitable.

It is also preferable that each photoreceptor piece is partitioned by a member having a lower refractive index than the electron transport layer as the light shielding means.

It is also preferable that each photoreceptor piece is partitioned by a member having a high light-shielding property or a high light-absorbing property as the light-shielding means.

It is also preferable that the member used as the light-shielding means has a higher electric resistance than the electron transport layer of the photoreceptor piece.

The surface layer of the image carrier has a plurality of photoreceptor pieces formed by cutting and dividing the surface of the integrally formed photoreceptor. It is also preferable to have

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) A first embodiment of the present invention will be described below. FIG. 1 is a diagram showing the basic concept of the present invention. FIG. 2 is a cross-sectional configuration diagram of a printer PR1 as an embodiment of an image forming apparatus according to the present invention, and FIG. 3 is a diagram schematically illustrating a schematic configuration of a laser exposure optical system 4 in FIG. is there.

The image forming apparatus PR1 according to the first embodiment has a digital color image reader section at the top and a digital color image printer section at the bottom.

In the reader section, an original is placed on an original platen glass, and is exposed and scanned by an exposure lamp, so that a reflected light image from the original is condensed on a CCD sensor by a lens to obtain a decomposed image signal. The decomposed image signal passes through an amplification circuit (not shown) (not shown), is processed by a video processing unit, and is sent to a printer unit.

In the printer section, a photosensitive drum 1 as an image carrier is rotatably supported in the direction of an arrow. Around the photosensitive drum 1, a pre-exposure lamp 2, a charging device 3, a laser exposure optical system 4, a developing device 5, The transfer device 6 and the cleaning device 7 are arranged.

The laser exposure optical system 4 uses a laser drive circuit 4a based on the decomposed image signal input from the reader unit.
(Emission signal generator) is driven to emit a laser beam L by causing a laser light source 4b as a light source to emit light.

The laser beam L passes through a collimator 4c, a polygon mirror 4d, and an fθ lens group 4e.
The upper surface is scanned, and a beam spot is formed on the surface of the photosensitive drum 1 to form an electrostatic latent image.

At the time of image formation in the printer section, an image is recorded on recording paper through a well-known electrophotographic process. The photosensitive drum 1 is rotated in the direction of an arrow, Is uniformly charged by the charger 3 and exposed by the laser beam L to form an electrostatic latent image.

Next, the developing device 5 is operated to develop the latent image on the photosensitive drum 1 to form a toner image on the photosensitive drum 1 using a resin as a base.

Further, the recording paper is supplied from the sheet cassette 8 to the position facing the photosensitive drum 1 by the conveying means, and the toner image on the photosensitive drum 1 is transferred to the recording paper by the transfer device 6.

The recording paper onto which the toner image has been transferred is conveyed to a fixing device 10 by a conveyance belt 9, and the toner image is heated and pressed to be discharged to a discharge tray 11.

On the other hand, the photosensitive drum 1 after the transfer is cleaned by a cleaning device 7 to remove the residual toner on the surface, and then subjected to the image forming process again.

The photosensitive drum 1 according to the present embodiment
Is characterized in that it has a surface layer having a large number of photoreceptor pieces divided into sections smaller than the beam spot diameter, and that the resistance value of the surface layer is smaller than 1.0 × 10 ¹² Ω · cm.

FIG. 4 shows a conceptual diagram of the spot diameter of the light beam in the printer PR1 of the present invention. The spot diameter of the light beam is represented by a portion until it decreases to 1 / e ² (E1) of the peak intensity (E0). The light beam used includes an exposure scanning optical system using a semiconductor laser, a solid-state scanner such as an LED and a liquid crystal shutter, and the like. The light intensity distribution also includes a Gaussian distribution, a Lorentz distribution, and the like. Let the spot diameter be the portion up to / e2.

The light spot generally has an elliptical shape as shown in FIG. 4, and the spot diameter of the present invention means the main scanning spot diameter and the sub-scanning spot diameter in the drawing. Applicable.

However, it is known that light actually reaches a wide area far exceeding the spot diameter due to light scattering inside the photosensitive member. 1200dp as it is
When a high resolution such as i or higher is required, the integrated light amount between spots due to light scattering increases and exceeds the E1 level, so that the spot diameter becomes apparently large and dot reproducibility deteriorates. Will be.

As a method for solving the above-mentioned problems and maximizing the effect of reducing the diameter of the latent image spot, a photosensitive drum 1 composed of a large number of photosensitive members 1a as shown in FIG. 1 is used. It is effective to do.

However, in practice, the way of hitting the beam spot is usually disturbed to some extent. This is called jitter. Under this phenomenon, if the photosensitive member having the structure shown in FIG. The degree of disturbance is further emphasized, and it is expected that an image that is worse than usual is output.

Therefore, a study was made to provide a resistive layer on the surface of the photoreceptor. For example, the surface layer is a coating layer of a material in which ultrafine SnO ₂ is dispersed in a photocurable acrylic resin.

Specifically, antimony is doped,
A coating layer of a material in which SnO ₂ particles having a reduced resistance of about 0.03 μm and having a particle diameter of about 0.03 μm are dispersed in a resin by 70% by weight. It was coated to about 2 μm to form the surface layer.

Further, the amount of the acrylic resin and the ultrafine particles S
Samples (a) having different surface resistance values by adjusting the ratio of the amount of dispersion of nO ₂ (a) 1.0 × 10 ¹¹ Ω · cm, sample (b) 1.
0 × 10 ¹² Ω · cm, sample (c) 1.0 × 10 ¹³ Ω · cm
cm were prepared, and the image formation quality of each was evaluated comparatively.

In the case of the sample (c), when the beam spot is slightly displaced in the photoreceptor piece 1a due to mechanical accuracy or the like, the beam spot is faithfully reproduced. However, in the case of a low-resistance material such as sample (a) or sample (b), the entire photosensitive member 1a has a constant potential, so that the photosensitive member 1a is always
It turned out that the dots which were tidy according to the pattern were obtained.

As described above, in particular, a photoreceptor piece having a size smaller than the beam spot diameter is used, and the resistance value of the surface layer of the photoreceptor is smaller than 1.0 × 10 ¹² Ω · cm. In addition to solving the above-mentioned problems by the image forming apparatus characterized by the above, the diameter of the latent image spot can be easily reduced at a low cost without preparing an optical system having an expensive minute spot diameter as described above. Was.

It is also possible to use an area gradation method such as the dither method, even if the grid-shaped photoreceptor piece 1a as in this embodiment is used.

(Embodiment 2) In the second embodiment, as shown in FIG. 5A, the photoreceptor piece of the photosensitive drum 1 has a small light sensitivity and a small amount of potential decay at a low light quantity. The light intensity-charge potential decay characteristic (E) has a sensitivity section in which the light sensitivity increases and the potential attenuation increases as the light intensity increases.
−V characteristic).

At this time, the shape of the beam spot is
This is shown in FIG. The photoreceptor exposed with the laser exposure distribution of FIG. 5B, according to the EV characteristic of FIG. 5A, forms a latent image with a potential decay like L1 in FIG. Formed at

Here, L2 in FIG. 5C is the shape of the laser exposure distribution shown in FIG. 5B, and the shape of the latent image of the potential decay changes from the original shape of the laser exposure distribution. It is displayed as a reference for indicating.

In FIG. 5C, the potential decay amount and the light amount scale on the vertical axis are shown such that the maximum value of the potential decay amount distribution and the maximum value of the laser exposure distribution are the same. As shown here, since the bottom of the laser beam corresponds to the low sensitivity region of the EV characteristic, the bottom of the latent image is reduced, and as a result, FIG.
The resolution can be increased by forming the latent image of FIG. 5C having a spot diameter substantially smaller than the shape of the beam spot of FIG.

However, as described above, in practice, light reaches a wide range far exceeding the spot diameter due to light scattering inside the photosensitive member, and thus the photosensitive member has such a binary characteristic. Therefore, it is easily affected by the light scattering.

Therefore, a photoreceptor piece having a size smaller than the beam spot diameter of the present invention is used, and the resistance value of the surface layer of the photoreceptor is smaller than 1.0 × 10 ¹² Ω · cm. It has been confirmed that the above-described problems can be solved by the image forming apparatus described above, and that the diameter of the latent image spot can be reduced with a synergistic effect.

(Embodiment 3) As another embodiment, a printer PR as an image forming apparatus employing a multiple development batch transfer electrophotographic system as shown in FIG.
2 can also be applied.

The multiple development batch transfer electrophotographic system is a multiple development process in which a toner image is superimposed directly on a photoreceptor to form a color image, and is a system capable of forming a color image.

The same components as those in the printer PR1 of the first embodiment are denoted by the same reference numerals.

To explain this process, first, the photosensitive drum 1 is uniformly charged by the charger 3. After that, a latent image is written from above the photosensitive drum 1 by the laser exposure optical system 4 and only the portion irradiated with the laser is developed by reversal development. This process is performed by developing units 5a, 5b,
By repeating 5c and 5d, three or four colors of magenta, cyan, yellow, and (black) are repeated, and the toner images are superposed on the photosensitive drum 1 to form a color image.

Then, the toner image is collectively transferred to recording paper by the transfer device 6 and fixed by passing through the fixing device 10 to obtain a color image. The residual charge on the photosensitive drum 1 is removed by a pre-exposure lamp.

By applying the photoreceptor 1 having the small photoreceptor piece 1a to the printer PR1 of such a system, the resolution of an image can be improved and a high-quality image can be formed. .

(Embodiment 4) FIG. 7 shows a fourth embodiment in which the present invention is applied to a multiple drum system. In the present embodiment, the image forming apparatus is a full-color laser beam printer. However, unlike the previous embodiment, a dedicated image carrier for each color, that is, in the present embodiment, the photosensitive drum 1Y (yellow ), 1M (magenta), 1C (cyan), and 1BK (black), around which dedicated laser beam scanners 4Y, 4M, 4C, 4B
K, developing units 5Y, 5M, 5C, 5BK, transfer discharger 6
Y, 6M, 6C, 6BK, cleaning units 7Y, 7M,
7C and 7BK are arranged.

The recording paper to be transferred is a sheet cassette 8
Then, the sheet is conveyed through the sheet feeding guide 8a and sequentially through the sheet feeding roller and the sheet feeding guide, receives corona discharge from an unillustrated adsorption charger, and is surely adsorbed to the conveyor belt 12.

Thereafter, the images formed on the respective photosensitive drums are transferred by the transfer dischargers 6Y, 6M, 6C, and 6BK.
The charge is removed from the conveyor belt 12 by the charge remover and fixed by the fixing device 10 to obtain a full-color image.

In the present embodiment, a plurality of laser beam scanners and image carriers are arranged for the main purpose of high-speed output of a full-color image. In this case, however, each laser beam scanner and the mechanical Due to limitations in accuracy and the like, dot resolution is more important than the configurations used in some of the above-described embodiments. Therefore,
By improving the dot resolution by the method of the present invention, the above-mentioned problem can be more effectively solved.

In the above embodiment, a digital copying machine has been mainly described as an example, but the present invention is also applied to an image forming apparatus (an analog copying machine or the like) having another configuration using a similar electrophotographic process. The invention can be applied.

(Embodiment 5) The shape of the photoreceptor piece 1a can be circular as shown in FIG. 8 as an example, but is not limited to this shape. Further, as an example of a method of arranging the photoreceptor pieces 1a as shown in FIG. 9, higher density recording is possible, but the arrangement method is not limited to this.

(Embodiment 6) In the sixth embodiment,
A method for manufacturing the photoconductor 1 will be briefly described. For example, in the case of the image exposure process, the photoreceptor piece 1a shown in FIG.
Grid portion 1b serving as a light shielding means for suppressing light leaking from the photoreceptor piece around the photoreceptor piece from entering the adjacent photoreceptor piece
May be the ground substrate 1c, and the cross-sectional view is shown in FIG.
It becomes like.

When producing the photoreceptor 1 of the present invention, a conventional photoreceptor drum is prepared, and then a cutting member is applied to the photoreceptor to make a cut, and the photoreceptor layer (including the charge generation layer and the charge transport layer) is cut. Can be formed by carving.

(Embodiment 7) The structure of the photoreceptor according to the seventh embodiment shown in FIG. 11 is, for example, used in a background exposure process.
In (a), a grid member 1b includes a shielding member 1d.
Are embedded as insulating members.

The method of manufacturing the shield member 1d is as follows. After forming the photoreceptor piece 1a as in the sixth embodiment, a resin ball (polyester thermoplastic resin) 1e of several μm is dusted on the photoreceptor drum 1, and It was obtained by applying great heat and fusing the resin balls gathered in the grooves (see FIG. 11A).

Further, by mixing a coloring material or the like in a resin ball or in a resin ball, light leaking from each photoconductor piece 1a is admitted to the adjacent photoconductor piece 1a.
a, and a material having a lower refractive index than the charge transport layer (or air) is disposed in the grid portion 1b around the photoreceptor piece 1a to prevent light leakage. The effect of the present invention is further enhanced by such a measure, and by disposing a highly insulating material in the grid portion 1b to prevent carriers such as electrons as well as light from diffusing.

The method of forming the shield member 1d is not limited to this, and as shown in FIG. 11B, it is possible to apply the present invention by processing the ground substrate 1c with masking and photoresist to make it uneven. I can do it.

[0063]

According to the present invention, the diameter of the substantially effective beam spot on the image carrier can be further reduced, and the resolution can be increased.

Since the density and gradation are maintained, the reproducibility of a high-resolution digital image can be further improved, and a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating characteristics of a photosensitive drum according to a first embodiment.

FIG. 2 is an explanatory cross-sectional configuration diagram of the printer device according to the first embodiment.

FIG. 3 is a diagram showing a configuration of an exposure optical system in FIG. 2;

FIG. 4 is a diagram illustrating a beam spot diameter.

FIG. 5 is a diagram illustrating characteristics of a photoconductor.

FIG. 6 is an explanatory cross-sectional configuration diagram of a printer device having another configuration to which the present invention is applied.

FIG. 7 is a cross-sectional configuration explanatory view of a printer device having another configuration to which the present invention is applied.

FIG. 8 is a view showing the shape of a photoreceptor piece;

FIG. 9 is a diagram showing an arrangement configuration of photoconductor pieces.

FIG. 10 is a diagram illustrating a relationship between a photoreceptor piece and a grid portion.

FIG. 11 is a diagram illustrating an example of a method of manufacturing a grid portion.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 1a photoreceptor piece 1b grid part (light shielding means) 1c ground substrate 1d shield member 1e resin ball 2 pre-exposure lamp 3 charger 4 laser exposure optical system 4a laser drive circuit 4b laser light source (light source) 4c Collimator 4d Polygon mirror 4e fθ lens group 5 Developing device 6 Transfer device 7 Cleaning device 8 Sheet cassette 9 Conveying belt 10 Fixing device 11 Discharge tray PR1 Printer device (image forming device) L Laser beam

Claims (7)

[Claims] 1. An image forming apparatus for forming an electrostatic latent image on the surface of an image carrier by causing light from a light source to form a spot image on a surface of the image carrier and scanning the image carrier. Comprises a surface layer having a large number of photoreceptor pieces divided into sections smaller than the beam spot diameter, and the resistance of the surface layer is smaller than 1.0 × 10 ¹² Ω · cm. Forming equipment. 2. The image carrier according to claim 1, wherein the image carrier has a small light sensitivity and a small amount of potential decay at a low light amount, and has a sensitivity section in which the light sensitivity increases and the potential decay amount increases as the light amount increases. The image forming apparatus according to claim 1, wherein a photoconductor having characteristics is used. 3. A light shielding means for preventing light leaking from each photoreceptor piece from entering the adjacent photoreceptor piece between a photoreceptor piece and an adjacent photoreceptor piece on the surface layer of the image carrier. The image forming apparatus according to claim 1, wherein: 4. The image forming apparatus according to claim 3, wherein each of the photoreceptor pieces is partitioned by a member having a lower refractive index than that of the electron transport layer as the light shielding means. 5. The image forming apparatus according to claim 3, wherein each of the photoreceptor pieces is partitioned by a member having a high light-shielding property or a high light-absorbing property as the light-shielding means. 6. The image forming apparatus according to claim 3, wherein the member used as the light shielding unit has an electric resistance greater than that of the electron transport layer of the photoreceptor piece. apparatus. 7. The surface layer of the image bearing member has a plurality of photoreceptor pieces formed by cutting and dividing a surface of a photoreceptor integrally formed, and a light shielding means is provided in the cut. The image forming apparatus according to any one of claims 3 to 6, further comprising: