JPH05210338A - Image forming device - Google Patents

Abstract

PURPOSE:To effectively prevent image flowing caused by corona generated substance which is generated by corona discharge and to maintain a good-quality image over a long term by providing a means for applying a substance which complements the lowering of the surface resistance of a photosensitive body to the surface of the photosensitive body. CONSTITUTION:The substance which complements the lowering of the surface resistance is applied to the surface of the photosensitive body 1. Namely, after solid paraffin whose electric resistance is >=10<14>OMEGAcm, whose dielectric constant is 1.5-4, and whose fusing point is >=55 deg.C is heated to a liquid state, an applying member is impregnated with the paraffin and wound to a core material singly to quintuply, so that an applying tool 12 is obtained. The cleaning member of a toner cleaning device 7 for removing the corona generated substance is principally composed of activated carbon fiber. Even when the corona generated substance is stuck to the surface layer of the photosensitive body 1, in such constitution, it is effectively removed by the cleaning member. Furthermore, when resistance becomes low because the surface layer of the photosensitive body 1 is damaged and the corona generated substance is stuck, the low resistance is complemented by applying the paraffin whose resistance is high and whose dielectric constant is low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine for charging a photoreceptor and transferring a toner image using a corona discharger.
The present invention relates to an image forming apparatus such as a laser printer and a facsimile, and particularly to an image forming apparatus which prevents image deletion.

[0002]

_2. Description of the Related Art In image forming apparatuses such as electrophotographic copying machines, laser printers, and facsimiles, amorphous silicon (a-Si photoconductor), Se, As ₂ Se ₃ , SeTe is formed on a conductive support.
Inorganic photoconductive material (Se photoconductor), etc., and poly-N
A photoconductor using an organic photoconductive material (OPC photoconductor) such as vinylcarbazole, trinitrofluorenone and various azo pigments is generally known.

For example, an OPC photoconductor has good electrical characteristics and spectral sensitivity, is inexpensive to produce, is non-polluting, and can be processed into a belt or drum-shaped photoconductor relatively easily. It is used a lot from low-speed machines to medium-speed machines.

On the other hand, the a-Si photoconductor is inferior in charging ability to other photoconductors, but it has high sensitivity and high abrasion resistance, and is used in high speed copying machines, laser printers and the like.

An example of an image forming apparatus using such a photoconductor is shown in FIG. The photoreceptor 1 is uniformly charged by a charging corona discharger (charging charger) 2. The corona discharger 2 has a corotron method in which a tungsten wire with a diameter of 40 to 100 μm is stretched, and a scorotron method in which a grid is stretched near the opening of the corona discharger to make the uneven discharge uniform. , 4000-8000 volts high voltage is applied. The exposure unit 3 performs image exposure to form an electrostatic latent image, and then the developing device 4 forms a toner image.

After the toner image is transferred to the copy sheet 8 by the transfer corona discharger (transfer charger) 5, the copy sheet is separated from the photoconductor by the separation corona discharger (separation charger) 6, and the fixing device 9 is used. Then it becomes a hard copy.

On the other hand, the photoconductor 1 after the transfer is cleaned by the cleaning device 7 to remove the residual toner, and the series of copying process is completed.

By the way, in an image forming apparatus using a corona discharger, a corona product, that is, a product such as ozone or nitrogen oxide, is generated during corona discharge, and this corona product adheres to the surface of the photoreceptor. Then, the surface resistance of the surface layer of the photoconductor decreases, or the photosensitivity of the photoconductor deteriorates.
It is known that image quality is degraded. In particular, the surface resistance decreases depending on the humidity, image blur occurs, and in the worst case, the image may not be formed at all. Therefore,
In order to maintain the initial image for a long time, it is necessary to eliminate the influence of corona products. In such image blur, the degree of occurrence differs depending on the material constituting the photoconductor, and there are differences in the causative substances that cause image blur, but in all cases, the corona product triggers the occurrence of image blur. There is.

The following are known to prevent the deterioration of image characteristics due to the corona product as described above.

As a first example, it is known that the surface resistance is prevented from being lowered by improving the constituent material of the photosensitive member itself. Specifically, there are a photoreceptor having a photosensitive layer formed on a conductive support and a photoreceptor having a protective layer further laminated on the photosensitive layer. When these photosensitive layer and protective layer are formed by spray method or coating method, antioxidants (amines, hydroxylamines) are added or rubbed from the outside to eliminate the influence of corona products. I am trying to do it.

As a second example, it is known to improve the corona discharger to suppress the generation of corona products or prevent the corona products from adhering to the photoconductor. The former is disclosed in, for example, JP-A-64-68774 and JP-A-47.
-37547, JP-A-49-40739 and JP-A-49-
No. 84660, etc., a charge wire or shield made of a metal or metal oxide such as Au, Ag, Pt, Pd, Ni, Fe, Ni ₂ O ₃ , BaO, alumina, and chromium oxide, which are ozone decomposing agents. Plate the case or grid,
The generation of corona products during corona discharge is suppressed. On the other hand, the latter is described in, for example, JP-A-63-311365, the inner wall or grid of the shield case is processed with activated carbon fibers or manganese oxide or a metal chelate compound to absorb a corona product, It is designed to prevent adhesion to the photoconductor. In addition, the grid is made of carbon fiber, an absorbing member is attached (see, for example, Japanese Patent Laid-Open No. 1-210974), or a shield case shape that takes into consideration the flow of wind is used to deal with the problem. There is also. In addition, there are some cases where Pt or Ag plating such as a shield case and an absorbent composed of activated carbon are used in combination.
This is disclosed, for example, in JP-A-50-34828 and JP-A-5-34828.
It is described in JP-A-2-133894.

As a third example, it is known that the photosensitive member is heated by a heater or dried with hot air to eliminate the influence of humidity to prevent the surface resistance of the photosensitive member from lowering. (For example, JP-A-59-208558, JP-A-60-09
5467, JP 61-132977, JP 62-2620
(See Japanese Patent Publication No. 65).

As a fourth example, a corona product adhered to the surface of the photoconductor is known to be removed by polishing or wet cleaning. For polishing, for example, a roller or blade formed by winding a steel wire in a loop shape is used (see, for example, JP-A-1-161281), and for wet cleaning, water or a solvent is used to remove the corona product on the surface of the photosensitive layer. I am trying to remove it.

In addition to the above-mentioned four examples, for the purpose of preventing image deterioration due to corona products, for example, JP-A-58-28581, JP-A-60-95459, and JP-A-60-189769. JP, JP-A-60-102659, JP-A-59-219770, JP-A-60-134254, JP-A-60-17765, JP-A-55-155369 It has been known.

(Problems to be Solved by the Invention) In an image forming apparatus such as that shown in FIG. 5, a corona discharger is used for charging, transferring and separating. Ozone (O ₃ ) and nitrogen oxides (N
Corona products such as Ox) are produced. As a result, these corona products are converted into hydrophilic compounds such as nitrogen compounds, aldehyde groups, and carboxyl groups by the action of discharge energy and atmospheric moisture, carbon dioxide gas, nitrogen gas, etc., and the photoreceptor surface is oxidized. However, there is a problem that the electrical resistance (surface resistance) of the photoconductor decreases due to the adsorption of compounds and the absorption of moisture in the atmosphere, causing white spots due to image deletion and even more severe image loss, and significantly lowering copy quality. is there.

This phenomenon occurs in most or most of the photoconductors. Particularly, in the photoconductor using the a-Si layer, a hydrophilic substance such as SiO ₂ is generated on the surface of the photoconductor to cause image deletion. Even a photoreceptor using aC: H in the protective layer, which is considered to be easily generated and has excellent durability and weather resistance,
It has been found that there is a problem similar to that of the a-Si photoconductor. In these photoconductors, the higher the humidity, the worse the image flow, and sometimes the image does not have any shape.

When the As ₂ Se ₃ photoconductor is used alone, the image deletion does not become a problem, but SnO ₂ or SnO ₂ / S is used.
It has been known that even when an organic resin such as an ester or urethane cross-linked styrene-MMA resin in which ultrafine particles such as b ₂ O ₃ or TiO ₂ are dispersed is overcoated, remarkable image deletion occurs.

As described above, the process of image deletion depends on the constitution of the photoconductor, but in any case, it occurs due to the corona product.

This phenomenon does not occur when the photoconductor used is new, but the photoconductor surface is contaminated during repeated use in the image forming apparatus, lacking water repellency, and the hardness of the photoconductor surface. It is considered that the hydrophilic substance remains indefinitely because it is large and difficult to scrape.

The band-shaped white spots under the corona discharger, which occur even at a relative humidity of 30% or more, disappears after copying several tens of sheets, and the overall image deletion under high humidity is about 65%. Humidity tends to recover. All of these recover because the surface of the photoconductor is dried, and when the humidity rises again, it tends to recur.

As described above, if the surface of the photoconductor becomes hydrophilic or a low resistance substance is attached, image deletion easily occurs. The corona product generated by the corona discharge becomes mist and adheres to the photoconductor, but the corona product is relatively easy to remove when the photoconductor has almost no scratches. However, when a mark is formed on the surface of the photoconductor, the corona product penetrates into the mark and the removal rate decreases. For example, when an aC: H layer is laminated on an OPC photosensitive member, the film hardness can be varied between about 20 and 2000 kg / mm ² depending on the manufacturing method, but the film hardness affects how the surface marks are formed. As a result, the image quality characteristics are also affected. That is, when abrasion occurs and scratches are generated earlier, abnormal images such as band-shaped white spots tend to be generated earlier. Therefore, it is desirable that the film hardness be as hard as possible. However, considering the conditions of film formation at room temperature and the necessary conditions such as light transmittance and electric resistance to be established as an electrophotographic photoreceptor, the hardness is 300 to 1500 kg / mm ² It will be about. This value is O
This corresponds to a value 12 to 65 times that of a PC photoconductor. However, even with such a hard film, scratches are likely to occur if there is a hard foreign matter or a defect of the cleaning blade.

It is an object of the present invention to provide an image forming apparatus capable of effectively preventing image deletion due to corona products generated by corona discharge and maintaining high quality images for a long period of time.

[0023]

In order to achieve the above object, the present invention firstly comprises (1) a means for coating a surface of a photoreceptor with a substance that complements the decrease in the surface resistance of the photoreceptor. To do. Then, as a substance that complements the decrease in the surface resistance of the photoconductor, the electric resistance is 10 ¹⁴ Ω · cm or more, and the relative dielectric constant is
Paraffin with a melting point of 1.5 to 4 and a melting point of 55 ° C or higher can be used.
Next, (2) a means for applying a substance that complements the reduction in the surface resistance of the photoconductor to the surface of the photoconductor, and a cleaning means for removing the corona product adhering to the surface of the photoconductor are also provided. The cleaning member for removing the corona product attached to the surface of the photoconductor is mainly composed of activated carbon fiber.

[0024]

[Effect] Even if the corona product adheres to the surface layer of the photoconductor, it can be effectively removed by the cleaning member mainly composed of activated carbon fiber. In the case of resistance reduction, by applying paraffin having high resistance and low relative dielectric constant, the resistance reduction can be complemented.

[0025]

Embodiments will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Reference numeral 1 is a photoconductor, 2 is a corona discharger, and 7 is a toner cleaning device for removing residual toner. These are the same as those in the conventional example. .. Reference numeral 11 denotes a coating device that coats the surface of the photoconductor with a substance that complements the reduction of the surface resistance of the photoconductor 1. As the applicator 12, a roller as shown in FIG. 2 is used here. The applicator 12 comprises a core 13 and a flexible applicator 14 which is impregnated with a substance that complements the reduction of the surface resistance of the photoconductor. As the core material 13, aluminum, a plastic product such as polyethylene or polypropylene, or a paper product is used. Application member 14
As the fiber, a single fiber such as polyester, polyurethane, polypropylene or nylon, or a mixed-spun cloth product or cotton product is used. As a substance that supplements the decrease in the surface resistance of the photoconductor, the electric resistance is 10 ¹⁴ Ωcm or more, and the relative dielectric constant is 1.5 to
4. Solid paraffin having a melting point of 55 ° C. or higher is used, which is heated to a liquid state, impregnated in a coating member 14, and wound 1 to 5 times around a core material 13 to form a coating tool 12.

The electrical resistance and the relative permittivity are characteristics necessary for complementing the surface resistance of the photoconductor, and the above characteristics can be obtained by using high-grade paraffin, but when paraffin containing a large amount of impurities is used, the electrical resistance becomes higher. It becomes low and the initial characteristics cannot be maintained.

On the other hand, the photoconductor sometimes rises to about 40 to 45 ° C. due to heat generated by exposure, fixing, driving devices and the like. Therefore, it is desirable that the melting point of solid paraffin is higher, but for practical use, it may be 55 ° C. or higher (solid paraffins with various melting points are available depending on the application, and commercially available products with a melting point of about 71 to 73 ° C. The manufacturing method of the applicator 12 is as described above, but solid paraffin is put in a container and sufficiently heated and melted, and a coating member 14, for example, a non-woven fabric or a gauze cloth product using ultrafine fibers of polyester and polyurethane. Put into a container so that there is no crease, and pull up slowly to obtain a substantially uniform sheet-shaped impregnated cloth. This is wound 1 to 5 times around the core material 13, and the whole is further heated to make the impregnated cloth fit in. Further, the applicator 12 is obtained by fitting the bases on both end surfaces. By doing so, paraffin can be uniformly applied to the photoconductor.

The applicator 12 is used in contact with the photoconductor, but the number of rotations is not particularly limited. It is desirable that the applicator 12 be released from the photoconductor after the copying is completed.

FIG. 3 shows another embodiment of the applicator 12, which is composed of a core material 15, an applicator member 16 and a press fitting 17 and is used by being fixed. In this method, if the front surface is coated on the surface of the photoconductor after the completion of copying, band-shaped white spots can be prevented after being left for a long time, and if it is coated every time, sudden changes in the humidity environment can be sufficiently dealt with. When the coating member 16 wears and the coating amount becomes insufficient, a good image can be reproduced again by replacing with a new one.

Liquid paraffin also exists as liquid paraffin, but it has a viscosity when it adheres to the photoconductor, so the transferability of the toner deteriorates, the image cannot be reproduced sufficiently, and a cleaning blade or a cleaning blade is used. It is unsuitable because it may stain the developing device and the photoconductor. It is also possible to add an antioxidant or the like into the paraffin. However, addition of more than necessary deteriorates the characteristics of the paraffin, and the effect of preventing the photoconductor from being oxidized cannot be obtained.

Next, a concrete example will be shown. Knoop hardness of 750-800kg / mm ² and film thickness of about 7,000Å a-C: H on OPC photoconductor
Layer (raw material gas C ₂ H ₄ 100%) plasma CV at room temperature
The photoconductors laminated by the D method are mounted on an experimental laser printer.

On the other hand, solid paraffin (electrical resistance ρv = 8 × 10 ¹⁵ Ω · cm, relative permittivity 2.2, melting point 6) was placed in a stainless steel container.
6-68 ℃, Wako Pure Chemicals) put in an appropriate amount and heat to dissolve. After sufficiently dissolving, a gauze cloth having a width of 200 mm and a length of 150 mm is put therein, and slowly pulled up to prepare a coating member having a thickness of about 2.5 mm.

This coating member is wound around a plastic roller of 20 mm in diameter twice and the whole is exposed to an atmosphere of 85 ° C. for 1 to 2 minutes. Both ends of the coating member were wound with ordinary cotton thread about 10 times for edge treatment.

The applicator thus obtained is mounted on the laser printer, and is rotationally driven at about 10 rpm through a gear. However, this time, the release mechanism after the stop is not added. Further, only half of the roller is used as the coating member, and the coating portion and non-coating portion on the photosensitive member are formed to facilitate the determination. Furthermore, the contact pressure of the applicator with the photoconductor is 10
A constant pressure was applied to give a thickness of ~ 30 μm. In addition,
As the image pattern at the time of determination, 2 to 3 types of patterns including a 2 × 2 dot pattern were used.

As an implementation method, 22 to 25 ° C., 60 to 65% RH
The image test was conducted for 5 days at a rate of 4000 sheets / day under the environment of No., but up to 2000 sheets, the applicator was not attached, and the applicator was 40
I replaced it every time after 00 sheets were finished.

As a result, in the image after 4000 sheets were left overnight, there were no scratches on the photoconductor and no band-shaped white spots under the corona discharger were generated, but with 8000 sheets, the width of the uncoated portion was about 12 mm. Although the image density decreased, it did not occur in the coating part. After the completion of 20,000 sheets, the coating portion had many scratches, but the image was normal. However, in the non-coated area, band-shaped white spots under the corona discharger occurred, and at 30 ° C, 90%
In the test in the RH environment, no image was observed in the non-coated portion, but the coated portion was at a level that was not a problem in practical use.
Further, the paraffin was never softened and attached to the photoconductor.

Although it was mentioned above that the corona products adhered to the photoconductor are relatively easy to remove when the photoconductor has no scratches, the toner cleaning blade and the developer generally used in the copying process are used. It is insignificant to be removed, and means for removing it is necessary.

As a result of examining various materials as the cleaning member, it has been found that it is most effective to use the activated carbon fiber. Therefore, in the present invention, the cleaning member of the cleaning device for removing the corona product. Is mainly composed of activated carbon fiber.

By the way, activated carbon fibers include cellulose-based, polyacrylonitrile-based fibers, phenol resin,
Manufactured using pitch as a raw material, but ozone and NOx
Polyacrylonitrile-based activated carbon fibers are excellent in absorbing and decomposing corona-generating substances such as. Fiber diameter is 10
It is about 20 μm. In recent years, activated carbon fibers have also been diversified, and those having different effects depending on the type of gas have been announced, such as those having particularly enhanced NOx adsorption capacity.

As a cleaning member used in the cleaning device, 100% activated carbon fiber has a higher removal efficiency, but it is more fragile, and therefore it is desirable to insert a protective member between the cleaning member and the photosensitive member. Preferred as the protective member is a nonwoven fabric of fibers such as polyester and polypropylene. Since the effect of the activated carbon fiber decreases as the density increases, a relatively coarsely made product should be made 1 to 5 layers depending on the roughness. To use. The reason why the non-woven fabric is used is that it is preferable to use it as a protective layer in terms of durability, contact with the photoconductor, thinness of the sheet and the like.

By keeping this activated carbon fiber-based cleaning member in contact with the surface of the photoconductor at all times, contaminants such as corona products adhering to the surface of the photoconductor can be efficiently removed. This effect can be continued until the surface of the photoconductor is scratched and contaminants enter the scraped valleys to lower the cleaning efficiency. Therefore,
A high hardness such as aC: H is used on the photosensitive layer. As the hardness increases, the cleaning effect continues and a high quality image can be maintained.

However, when the film is formed at room temperature, a-
The hardness of the C: H layer is at most when considering the electrophotographic characteristics.
It is about 1500 to 1800 kg / mm ² (Knoop hardness). This value is about 60 to 70 times that of the OPC photoconductor and about 10 to 12 times that of the As ₂ Se ₃ photoconductor, which is considerably large. However, the thickness of the protective layer is 1
Even if the hardness is about μm, no matter how large the hardness, dust or lumps of toner or scratches on the cleaning blade may occur. The number of the scratches generated varies greatly depending on the process and the material of the member used.

When a flaw is generated on the surface of the photoconductor, a contaminant easily adheres, and when the contaminant that has entered the valley of the flaw remains without being removed, it causes deterioration of image quality such as image deletion. When the protective layer is scraped and contaminants act to deteriorate the protective layer and reduce the resistance, it is necessary to take measures such as scraping off the part or drying the surface layer sufficiently to make a sufficient improvement. Can not. This low resistance surface layer is eliminated by supplementing the surface layer with one layer of a high resistance material.

FIG. 4 shows another embodiment of the present invention, which is equipped with a coating device 11 for coating a substance that complements the reduction in the surface resistance of the photoreceptor 1 of the embodiment of FIG. In addition, a corona product cleaning device 21 is further provided in front of the coating device 11.

The cleaning device 21 has a cleaning tool 22,
The cleaning tool is a core material (roller) made of aluminum, iron, plastic, paper, etc. wound with activated carbon fibers in 2 to 5 layers, and a non-woven fabric in 2 to 4 layers. Alternatively, the shaft may be wound on the shaft in 2 to 5 layers, and only the surface in contact with the photoconductor may be further wound with a nonwoven fabric in 2 to 4 layers. This cleaning tool is
It is desirable to keep it in contact with the photoconductor at all times and to release it at rest.

The cleaning tool 22 is also brought into contact with the photoconductor while the image forming apparatus is in operation, but it is not necessary to keep it in contact with the photoconductor at all times, and it can be operated in combination with a humidity sensor when the humidity rises.

A specific example will be shown below. Knoop hardness of 1200 to 1300 kg / mm ² and film thickness of about 9000Å a-C: H on OPC photoconductor
Layer (raw material gas C ₂ H ₄ 100%) plasma CV at room temperature
The photoconductors laminated by the D method are mounted on an experimental laser printer.

The activated carbon fiber as a cleaning member used in the cleaning device 21 has a specific surface area of 700 m ² / g and a basis weight of 100 g.
/ M ² felt-like activated carbon fiber (Fineguard felt; manufactured by Toho Rayon), with a basis weight of 25 g / as a protective layer
m ^2, a thickness of 0.12mm polyester nonwoven fabric; a (Syntex manufactured by Mitsui Petrochemical Industries), overlapping the two sheets in the roller of aluminum 12mm, was prepared in the quadruple winding.

On the other hand, the applicator 12 was the same as in the embodiment of FIG. 1, and the cleaning device 21 and the applicator 11 were mounted on the experimental laser printer. However, initially, only the cleaning tool 22 is brought into contact with the photoconductor, and when the image deletion occurs, the coating tool 12
Decided to contact. The rotation speed of the cleaning tool 22 is about 80 rp
m, the rotation speed of the applicator 12 is about 10 rpm.

As an implementation method, 24-26 ° C., 80-85% RH
In the above environment, the paper was passed at a rate of 3000 sheets / day for 15 days, but although the image deletion did not occur, slight scratches occurred. Furthermore, the image deletion was locally generated during the 10-day paper passing, and countless scratches were generated. at this point,
When the applicator was operated and 1000 sheets were passed, a better image than the first sheet was obtained. No particular abnormality was found in the coating member.

[0051]

As described above, according to the present invention,
By applying paraffin having appropriate characteristics to the low-resistance photoconductor, it is possible to prevent band-shaped blank areas and the entire image flow at high humidity. In addition, the corona product adhered to the surface layer of the photoconductor is cleaned with a cleaning member mainly composed of activated carbon fiber, and further, when the surface layer of the photoconductor is damaged and the corona product is fixed to reduce the resistance, the resistance is reduced. By applying the complementary paraffin having high resistance and low relative dielectric constant, it becomes possible to maintain high image quality for a long period of time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of an applicator.

FIG. 3 is a configuration diagram of another applicator.

FIG. 4 is a configuration diagram of another embodiment of the present invention.

FIG. 5 is a configuration diagram of an image forming apparatus to which the present invention can be applied.

[Explanation of symbols]

1 ... Photoreceptor, 2 ... Corona discharger, 7 ... Toner cleaning device, 11 ... Coating device, 12 ... Coating tool, 1
4, 16 ... Coating member, 21 ... Corona product cleaning device, 22 ... Cleaning tool.

Claims (4)

[Claims] 1. An image forming apparatus in which a photoconductor that rotates or circulates is precharged using a corona discharger, and the photoconductor is exposed to form an electrostatic latent image, thereby reducing the surface resistance of the photoconductor. An image forming apparatus comprising means for applying a complementary substance to the surface of a photoconductor. 2. The image forming apparatus according to claim 1, further comprising cleaning means for removing corona products adhering to the surface of the photoconductor. 3. The material for compensating for the reduction of the surface resistance of the photoreceptor is paraffin having an electric resistance of 10 ¹⁴ Ω · cm or more, a relative dielectric constant of 1.5 to 4 and a melting point of 55 ° C. or more. The image forming apparatus according to claim 1 or 2. 4. The image forming apparatus according to claim 2, wherein the cleaning member for removing the corona product adhering to the surface of the photosensitive member is mainly composed of activated carbon fiber.