JP3047005B2 - Electrophotographic recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic recording apparatus widely used as an apparatus for recording image information in the fields of copying machines, laser beam printers (LBP) and the like.

[0002]

2. Description of the Related Art In a high-grade copying machine, a digital copying machine using an LBP is used in place of a conventional analog copying machine. In high-speed fax, LBP and LED
Printers are used. The electrophotographic recording method used in such a field is characterized by a higher recording speed and better image quality than other recording methods. These characteristics largely depend on the photoreceptor used.

Conventionally, selenium-based or OPC-based photosensitive drums of conventional materials have been frequently used in general-purpose medium-speed copying machines, low-speed copying machines, LBP and PPC faxes. In high-speed copying machines and large high-speed LBP fields, amorphous silicon (a-Si) -based photosensitive drum
It has been put on the market and put to practical use.

The advantages of selenium-based and OPC-based photoconductors are that they are shorter in life than the machine life, but are excellent in mass productivity, so they are inexpensive, and have a high charging potential, so that they are easy to use. On the other hand, an a-Si based photosensitive drum is
Although the service life is longer than the machine life, it has been cited as a disadvantage that it takes a long time to form the photosensitive layer and is inferior in mass productivity at present, so that the price is high, and that the charging potential is low, so that it is difficult to use.

In recent years, with the increase in the speed of information processing, OA devices such as copiers, printers, and fax machines have been required to have higher recording speed, higher image quality, and smaller devices. . Also, the demand for improving the image quality of equipment is
Photoreceptor materials have been required to have good material properties.
Furthermore, downsizing of equipment requires downsizing (smaller diameter) of the photoreceptor (drum), sufficient recording responsiveness of the photoreceptor material to maintain the machine recording speed, and countermeasures against ghost (afterimage) more than before , And the printing durability of the photoreceptor material sufficient to secure the number of recordings of the machine has been required. On the other hand, in contrast to the conventional Carlson recording method, a new recording method (optical backside recording method) in which exposure is performed from the inside of the photosensitive drum and development is performed almost simultaneously from the outside has been developed.

The basics of the conventional Carlson-type electrophotographic recording process are seven processes of charging, exposure, development, transfer, fixing, cleaning, and static elimination. These process units are arranged around the photoconductor, and the photoconductor is rotated (in the case of a drum) to perform electrophotographic recording.

First, necessary charging is uniformly performed on the surface of the photoreceptor by a charger. Next, exposure for recording is performed by exposure means such as a writing laser or LED. Exposure with a necessary wavelength and intensity is selected and set depending on the material of the photoreceptor, sensitivity characteristics, and the like. Since the surface potential of the exposed portion greatly decreases and the decrease of the surface potential of the non-exposed portion is small (only dark decay), a latent image having a large potential contrast is formed on the photoconductor surface.

[0008] Next, in the case of a printer, the charged toner of the developing device is attracted to the surface of the photoreceptor by an exposure section whose surface potential has decreased due to the principle of reversal development in the case of a printer. In principle, the charged toner of the developing device is attracted to the surface of the photoreceptor at the non-exposed portion, and a visible image (toner image) is formed on the surface of the photoreceptor.

Next, the toner on the surface of the photoreceptor is transferred to recording paper by a transfer process. The residual toner on the surface of the photoreceptor is removed by a cleaner. Finally, the residual charge on the photoreceptor surface is erased (erased) by collective irradiation of static elimination light (static elimination process).

On the other hand, in the optical backside recording method, charging / exposure / development can be performed by one process unit, cleaning can be omitted, and static elimination can be omitted. Development), transfer, fixing,
The process can be simplified to 3 to 4 processes (static elimination). Also,
According to this recording method, it has been found that the charging process can be performed simultaneously with the development and by contact charging, so that the charging potential can be reduced.

This means a reduction in the thickness of the photosensitive material, which is to reduce the cost of the photosensitive drum.
-Shows that the effect is exhibited in the Si photosensitive drum.

Thus, as a combination of a photosensitive member (material) and a recording method suitable for such technology and market trends, a combination of an amorphous silicon alloy-based photosensitive drum composed of a transparent substrate and a light back recording method is particularly promising. It has come to be considered.

[0013] In the present invention, the problem of a new problem (afterimage) in the combination of photoreceptors made of various materials with reduced diameters, in particular, an a-Si alloy photoreceptor and an optical backside recording method, will be described. In addition to the improvement, the solution was attempted in terms of the electrophotographic process.

In the optical backside recording method, the charging, exposure, and development processes are performed simultaneously as described above, so the mechanism of the recording process is not clear, but the process flow is the same as the Carlson process described above. Is completed in one round (one rotation) of the photoconductor.

However, recording is not completed in one round of the photosensitive member. For example, if one round of the photoconductor is shorter than the length of the paper,
It is necessary to repeat the same recording process by rotating the photoconductor twice or more for one sheet of paper. Also, when the circumference of the photoconductor is longer than the paper, usually the second and subsequent papers are often printed continuously, and the photoconductor is continuously rotated twice or more, and the image forming process is repeated. Become.

For this reason, the photosensitive member needs to be restored to the same state in the first and second rounds, and if the history of the previous image forming process remains without being erased, the second round will not. An afterimage will occur in the subsequent image formation.

In particular, since the light back exposure method is a simple process, the process unit can be simplified and the size of the apparatus can be easily reduced. Therefore, it is desired to reduce the diameter and speed of the photosensitive drum. As the diameter of the photoconductor drum is reduced, the time between successive image forming processes becomes shorter, and it becomes more difficult to recover the history of the photoconductor, and an afterimage is easily generated. For example, 30m in diameter
When the photoconductor drum of m is used, the photoconductor needs to rotate three times in the case of vertical recording on A4 paper. Note that the afterimage development as described above generally occurs on a photosensitive drum made of any material.

There are the following prior arts relating to light irradiation, all of which have completely different technical ideas from the present invention.

(1) JP-A-60-164785: In the conventional Carlson method, light is irradiated from the outside of the photosensitive drum using a toner image formed on the photosensitive member as a mask.

(2) JP-A-63-142380: In the optical backside recording method, light is irradiated from outside the photosensitive drum for the purpose of preventing carrier transfer.

[0021]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of an afterimage in an optical backside recording system.

[0022]

According to the present invention, there is provided an electrophotographic recording apparatus comprising: a photoreceptor having at least a light-transmitting conductive layer and a photosensitive layer provided in this order on a light-transmitting support; A developing means for supplying a developer to the surface of the photoreceptor, a voltage applying means for applying a voltage between the translucent conductive layer of the photoreceptor and the developing means, and a light-transmissive support side of the photoreceptor, Image signal exposure means arranged to face the developing means, and irradiating the photosensitive layer of the photoconductor with selected light to form an electrostatic latent image,
A toner image an electrostatic latent image is formed on is photosensitive member by developing means, in the electrophotographic recording apparatus equipped with a transfer unit for transferring to a transfer member, or formation of the toner image
At while leading to al transfer, provided the light irradiation means irradiating light to the photosensitive layer of a light-transmitting support side of the photosensitive member, further optical illumination means
Characterized in that a slit is provided between the substrate and the permeable support .

[0023]

FIG. 1 is an explanatory view showing an embodiment of an electrophotographic recording apparatus according to the present invention. A light-transmitting conductive layer 15 and an amorphous silicon (a-Si) -based photosensitive layer 17 are formed on a light-transmitting hollow cylindrical light-transmitting support 13 made of glass or the like. 11 are constituted.
Also, instead of the drum-shaped photoconductor 11, a belt (sheet) -shaped photoconductor may be used.

An LED array 21 as an image signal exposing means is arranged inside the translucent support 13, that is, on the back side of the photoreceptor 11, so as to face the developing unit 31 (developing means). The back exposure is performed via the light condensing element 23 (selfoc lens).

A developing unit 31 is provided around the photosensitive member 11.
Transfer unit 41 (transfer unit) and fixing unit 51
Is provided.

The developing unit 31 is disposed on the photosensitive layer 17 side of the photosensitive member 11 and supplies a developer 61 to the surface of the photosensitive member 11. The conductive sleeve 35 of the developing unit 31 includes
A developing bias power supply 37 (voltage applying means) for applying a voltage is connected between the translucent conductive layer 15 of the photoconductor 11 and the developing unit 31. The developing unit 31 has a conductive sleeve 35 containing a mag roller 33 having several magnetic poles (N and S poles), and conveys and supplies the developer 61 to the surface of the photoconductor 11 by rotation.

In forming an image, the developer 61 is conveyed to the surface of the photoconductor 11 by the sleeve 35, and a positive developing bias voltage is applied to the conductive sleeve 35 from the developing bias power source 37. In this embodiment, a positively chargeable toner is used. However, the chargeability of the toner and the polarity of the bias voltage are determined by the characteristics of the photoconductor. Photosensitive layer 1
After the contact of the photoconductor 7 with the developer 61, the charge is injected into the photoconductor 11 by the developing bias power supply 37 via the developer 61, and is charged. The residual toner thus removed is cleaned by the magnetic brush.

The LED array 2 disposed on the light-transmitting support 13 side of the photoconductor 11 so as to face the developing unit 31
By (1), an image signal is exposed in the vicinity of the opposing portion between the developing unit 31 and the photoconductor 11. Since the charging and the exposure are almost simultaneous processes, the charging potential may be small (for example, several tens V).

When exposure is performed by the LED array 21 in accordance with the image information, the potential of the photosensitive layer 17 in the exposed portion rapidly decreases, the toner is reversely developed, and a toner image 63 is formed on the surface of the photoconductor 11.

Next, the L provided inside the photoreceptor 11 is
Light irradiation equipment (light irradiation means) for countermeasures such as ED arrays
25, the entire surface of the photoconductor 11 on which the toner image 63 is formed is irradiated with light. This light irradiation is performed immediately after the end of the development step, but at the latest before the transfer step. Exposure energy in light irradiation may be almost the same level as image exposure, and a
In the case of a -Si type photoreceptor, it is about 0.1 to 2.0 [mu] J / cm < ² >. By evaluating the recorded image, the amount of light irradiation can be adjusted. It is desirable that the wavelength of the light irradiation be substantially equal to the image exposure. Further, the light irradiation device 25 may be mounted on the head of the LED array 21 for image exposure and incorporated. The slit 27 prevents light from the light irradiation device 25 from being irradiated on the photoconductor 11 before the development process. The operation of the light irradiation of the present invention will be described later in detail.

Next, the toner image 63 on the photoconductor 11 is
In the transfer unit 41, the image is transferred onto the plain paper 71 (transfer member) by the transfer roller 43 to which a negative bias voltage is applied by the transfer bias power supply 45. Next, the transfer toner is fixed on the plain paper 71 by the fixing roller 53 (heating roller) in the fixing unit 51. 55 indicates a pressure roller. The residual toner on the photoconductor 11 after the transfer is removed by magnetism when the photoconductor 11 comes into contact with the developer 61 at a position facing the developing unit 31, and there is no need to provide a separate cleaning member. Of course, a separate cleaning unit may be provided in a stage preceding the developing unit 31.

Next, light is irradiated by a charge elimination light source 29 (charge elimination means) provided between the transfer unit 41 and the development unit 31 to make the charge of the photosensitive layer 17 disappear. In the present invention, the charge elimination operation (the charge elimination light source 29) can be omitted.

Next, the light irradiation of the present invention will be described with reference to FIGS. In this case, the static elimination light source 29 is not used. FIGS. 2A to 2C are schematic diagrams showing the state of the trap carrier and the surface potential of the photoconductor when the light irradiation of the present invention is not performed (conventional example).

FIGS. 2 (D) to 2 (F) show a case where the light irradiation of the present invention is performed. FIGS. 3A and 3B are graphs showing the number of trapped optical carriers in each process, wherein FIG. 3A is a conventional example and FIG. 3B is the present invention. In general, the quality of a photoconductor material is determined by the product of μτ, that is, the product of carrier mobility and lifetime.

This value is in the band gap (forbidden band).
It is preferable that the localized level density is small. The localized level density in this band gap (forbidden band) generally deteriorates electrostatic characteristics in various forms.

For example, a localized level near the band gap edge causes the surface potential after charging to gradually decrease (called dark decay). Further, an increase in the environmental temperature causes a decrease in the charging potential. These phenomena are caused by heat carriers excited from localized levels near the band gap edge.

The localized level deep from the band gap end traps optical carriers excited by long-wavelength writing exposure, which causes an afterimage.

In other words, the localized level at a deep position is always present even if there is a difference in size, and traps optical carriers generated by writing exposure (see FIG. 2B). (The mobile photocarriers excited in the conduction band contribute to lowering the sensitivity, that is, the charge potential (see FIG. 2A).) The trapped photocarriers pass over time (several msec to tens of s).
ec) Most are emitted and become mobile optical carriers and recombine, but some remain trapped (see FIG. 2C).

The rotation speed of the photosensitive drum of a normal high-speed printer, in this case, the process time from exposure to next charging is about 1 second. The trapped photocarriers are finally discharged by the electric field at the time of next charging. However, such photocarriers act in the direction of canceling charge injection and hinder the charging process. This effect is only a decrease of several volts with respect to the charged potential of about 50 V (unexposed portion). It seems to overlap with the image information of the week thinly, especially,
It is easy to appear in images of halftone density.

About one second after this, the number of light carriers ejected (the number of light carriers trapped by exposure) is a-Si: H
Although it can be reduced by improving the photosensitive material, it cannot be essentially eliminated.

On the other hand, in the present invention, after development and before transfer, the entire surface is illuminated collectively from the back side of the photoreceptor.
Before the charging / exposure / development process in the second cycle, the difference between the trapped photocarriers in the image-exposed area and the non-exposed area in the first cycle can be made extremely small, and is stable in each cycle. Therefore, an afterimage can be prevented and an image can be formed with good reproducibility.

As shown in FIGS. 2D and 2E, first, the exposure unit receives the sum of the exposure energy hν and the irradiation energy hν ′ (about twice the exposure energy). The non-exposed portion receives only the irradiation energy (close to the exposure energy and almost one time).

The number of photocarriers trapped in the a-Si: H film is slightly affected by the amount of light, but since there is a sufficient time from the irradiation of the first cycle to the charging of the second cycle, the number of photocarriers is reduced. Due to emission and recombination, the difference in the number of photocarriers in the trapped state at the time of the second round charging in both portions is extremely small (see FIG. 2E → 2F).

This is because the trap density in the a-Si: H film is a finite value, and the a-Si: H
This is because the number of photocarriers trapped in the H film tends to be saturated. When the trap density (occupation density) in the a-Si: H film is sufficient and a large number of photocarriers are generated in the trap level, the number of emitted (excited) photocarriers is proportional to the carrier concentration of this trap level. Therefore, the effect is large at the beginning, but is small after a sufficient time (during the second round of charging).

Thus, it can be seen that the number of residual photocarriers during the second round of charging becomes substantially equal between the image-exposed portion and the non-exposed portion in the first round due to the addition of light irradiation immediately after the writing and exposing step.

FIG. 3 is a graph showing the above relationship focusing on the change in the number of trapped photocarriers. The graph of the present invention (FIG. 3A) is compared with a conventional example (FIG. 3A) in which light irradiation is not performed.
In B), it can be seen that the difference in the number of trapped light carriers between the exposed part and the non-exposed part during the second round of charging is small.

In the conventional example as well, it is conceivable that after the transfer and before the charging in the second round, the charge is removed with a strong light amount by the charge removing device 29 (see FIG. 1). However, in this method, strong static elimination light of 4 to 10 times that of the writing exposure is required, so that the next charging process has a large adverse effect on charging. In other words, it takes several milliseconds to several tens of seconds for the trapped photocarriers to be discharged, but the charging drop during charging is remarkable in the first process. The value is settled to a constant value from several times to several tens of times, but the charging potential becomes lower as the amount of the charge removing light increases or as the wavelength increases.

In the case of the present invention, since the potential of the unexposed portion is reduced by light irradiation (see FIG. 2E), the amount of charge removal is much smaller than in the conventional case. Accordingly, there is little charge reduction and the charging efficiency is improved. It is also possible to delete the charge elimination process. An image was formed using the apparatus shown in FIG. However, the static elimination light source 29 was not used.

The photoreceptor 11 used had an outer diameter of 30 mm, and the translucent conductive layer 15 was an ITO thin film.
Further, as the photosensitive layer 17, a carrier injection blocking layer (a-
Si: H: O: N: B), photoconductive layer (a-Si: H),
A layered structure (thickness of about 3 μm) composed of a surface protective layer (a-SiC: H) was used. As the photosensitive material of the photoreceptor layer 17, in addition to the a-Si type, Se type, Cas type, As
₂ Se system, inorganic and organic photoconductive materials such as PVK-TNF system applicable.

The wavelength of the LED array 21 is 685 nm.
And the surface of the photoreceptor was positively charged with the potential of the developing unit being positive, and developed using a positively chargeable toner according to the principle of reversal development.

[0051] Using the LED array of the same 685nm and LED array 21 for exposure as a light irradiation device 25, the light irradiation device 25 to be substantially the same irradiation power as writing exposure energy (about 0.5μJ / cm ²⁾ Supply current was adjusted. When image formation was repeated using plain paper, high-quality images were obtained continuously from the first sheet to many sheets without residual images, and the halftone images were also good.

[0052]

According to the present invention, in an optical backside recording system, after development and before transfer, light is irradiated from the back of the photoreceptor, thereby improving or eliminating afterimages from images without adversely affecting charging characteristics. In particular, excellent image quality with good halftones can be obtained.

Accordingly, it is possible to cope with downsizing of the photoconductor and speeding up of the apparatus. In addition, since light is irradiated from the back of the photoconductor, a light source for light irradiation can be housed inside the photoconductor, and the apparatus does not become large.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of an electrophotographic recording apparatus according to the present invention.

FIGS. 2A to 2C are schematic diagrams showing the generation state and surface potential of trap carriers of a photoreceptor in each image forming process, wherein FIGS. 2A to 2C are conventional examples, and FIGS. 2D to 2F are the present invention. .

FIG. 3 is a graph showing a change in a trap light carrier between an exposed portion and a non-exposed portion in each image forming process;
(A) is a conventional example, and (B) is the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Photoreceptor 13 Translucent support 15 Translucent conductive layer 17 Photosensitive layer 21 LED array 23 Condensing element 25 Light irradiation device 27 Slit 29 Static elimination light source 31 Developing unit 33 Mag roller 35 Sleeve 37 Developing bias power supply 41 Transfer unit 43 Transfer Roller 45 Transfer bias power supply 51 Fixing unit 53 Fixing roller 55 Pressure roller 61 Developer 63 Toner image 71 Plain paper

Claims (1)

(57) [Claims] 1. A photoconductor in which at least a light-transmitting conductive layer and a photosensitive layer are sequentially provided on a light-transmitting support, and a developing device which is disposed on the photoconductor side of the photoconductor and supplies a developer to the surface of the photoconductor. Means for applying a voltage between the light-transmitting conductive layer of the photoreceptor and the developing means; and a photoreceptor disposed on the light-transmitting support side of the photoreceptor so as to face the developing means. An image signal exposing unit for forming an electrostatic latent image by irradiating the photosensitive layer with a selected light, and a toner image formed on the photoreceptor by developing the electrostatic latent image by the developing unit. in electrophotographic recording apparatus equipped with a transfer unit for transferring the at while reaching the transfer from the formation of the toner image, it is provided a light irradiation means irradiating light to the photosensitive layer of a light-transmitting support side of the photosensitive body, further A slit is provided between the light irradiation means and the transparent support.
Electrophotographic recording apparatus characterized in that arranged the door.