JP3754630B2 - Image carrier and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a printer, and more specifically, an image carrier having excellent durability in image formation by an electrophotographic process, and an image provided with the image carrier capable of obtaining a stable image. The present invention relates to a forming apparatus.
[0002]
[Prior art]
As electrophotographic photoreceptors used in electrophotographic processes widely used in copying machines, printers, etc., organic photoreceptors made of organic materials are widely used because of their advantages such as low cost, mass productivity, and non-pollution. It is coming. However, organic photoconductors have the disadvantages of being low in wear resistance and inferior in durability as compared with inorganic photoconductors such as amorphous silicon and selenium-tellurium.
In recent years, there has been a demand for downsizing of an image forming apparatus using an electrophotographic process. As a result, the diameter of a photoconductor is inevitably reduced, and mechanical durability mainly including wear resistance is strongly demanded. It is becoming.
[0003]
For this reason, methods for improving the wear resistance of organic photoreceptors (hereinafter referred to as “photoreceptors”) have been studied. In the method disclosed in JP-A-57-30846, a protective layer containing particles (hereinafter referred to as “filler”) made of metal or metal oxide is provided on the surface of the photoreceptor, and Improves wear resistance. In this method, the average particle size of the filler is set to 0.3 μm or less to increase the transparency of the protective layer and suppress an increase in residual potential.
In addition, the method disclosed in Japanese Patent Laid-Open No. 4-281461 is a method in which a protective layer provided on the surface of the photoreceptor contains a charge transport material together with a filler, which improves wear resistance and raises the residual potential. It can be suppressed.
Further, as a means for suppressing an increase in residual potential, a protective layer containing an organic acid together with a filler (Japanese Patent Laid-Open Nos. 53-133444 and 55-157748) and an electron accepting substance are contained. And the like (JP-A-2-4275) are disclosed.
[0004]
In addition, the image forming apparatus disclosed in JP-A-8-234455 contains a filler in the charge transport layer of the photoreceptor, and the refractive index difference between the filler and the charge transport layer is 0.1 or more. Yes, 1 × 10 ⁴ to 2 × 10 ⁵ fillers having a particle diameter of 1 to ³ μm per 1 mm ² are contained. An image forming apparatus that improves the wear resistance of the photoreceptor and hardly generates interference fringes.
[0005]
[Problems to be solved by the invention]
As described above, by forming a protective layer containing a filler on the surface of the photoconductor, a photoconductor excellent in mechanical durability can be obtained. On the other hand, if the wear resistance is too high, The portion of the body surface that is chemically reacted with light or ozone cannot be removed by the cleaning means, and an abnormal image such as an image flow may occur in a high temperature and high humidity environment.
[0006]
A first developer conveying member disposed in parallel with the developer carrying member for conveying the developer in a longitudinal direction of the developer carrying member; and a developer in a direction opposite to the first developer conveying member. As a characteristic of a biaxial agitation type developing device including a second developer conveying member to be conveyed, the toner supplied from the toner replenishing port is mixed with the developer while being conveyed by the two developer conveying members, When charged by frictional charging with the carrier and supplied to the developer carrying member, the toner tends to be weakly charged on the upstream side in the developer conveying direction of the first developer conveying member. Even at a level where there is no problem, the background stain on the facing photoreceptor on the upstream side in the developer conveyance direction tends to be bad. For this reason, a deviation occurs in the longitudinal direction of the photosensitive member with respect to the toner input amount to the cleaning means, and this also causes a deviation in the abrasion amount of the photosensitive member, so that a region where the wear progresses partially is created. The life may be shortened, or an area where wear does not progress partially may occur, and an abnormal image may occur over time.
[0007]
In view of the above-mentioned problems, the present invention improves the wear resistance of the image carrier and is less likely to cause a deviation in the amount of wear on the surface of the image carrier, maintaining durability over a long period of time and providing a stable and good image. An object of the present invention is to provide an image forming apparatus that can be obtained.
[0008]
[Means for Solving the Problems]
As means for solving the above-mentioned problems, the invention described in claim 1 is an image forming apparatus comprising an image carrier, a charging means, an exposure means, a developing means, a transfer means, a fixing means, and a cleaning means, The image carrier is provided with a protective layer containing particles on the surface, and the thickness of the protective layer is produced so as to change monotonously in the longitudinal direction of the image carrier. A developer carrier disposed opposite the carrier, a first developer transport member disposed in parallel with the developer carrier and transporting the developer in the longitudinal direction of the developer carrier, And a second developer conveying member that conveys the developer in the opposite direction to the one developer conveying member, and the protective layer film of the image carrier on the upstream side of the first developer conveying member in the developer conveying direction An image forming device arranged so that its thickness is smaller than that of the downstream side. To.
[0009]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the toner used in the developing unit includes an image forming apparatus including a fixing aid and / or a lubricant.
[0010]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image carrier has a difference in film thickness in the longitudinal direction of the image carrier between 1 μm and 5 μm. Is an image forming apparatus.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic view of an image forming apparatus to which the present invention is applied. A photoreceptor 101 as an image carrier has a photosensitive layer formed on a conductive support. Although a drum-like shape is shown in FIG. 1, it may be a sheet-like shape or an endless belt-like shape. The photosensitive layer may be a single layer type or a laminated type in which a charge generation layer and a charge transport layer are separated and laminated.
The photoreceptor 101 is uniformly charged by a charging roller 102 which is a charging unit. The charging roller 102 is applied with only a DC component or a charging bias in which an AC component is superimposed on the DC component. The charging means is not limited to a roller, but may be a contact charging means such as a brush or a charger.
The uniformly charged photoreceptor 101 forms an electrostatic latent image by exposure 103 corresponding to image information emitted from an exposure unit (not shown). As the exposure means, a laser diode (LD), a light emitting diode (LED), or the like can be used.
The electrostatic latent image formed on the photoconductor 101 is developed by the developing device 104 to form a toner image. This toner image is transferred to a transfer material 105 by a transfer roller 106 serving as a transfer unit. The transfer means is not limited to a roller, but may be a contact transfer means such as a brush or a belt or a charger. The toner image transferred onto the transfer material 105 is fixed by the fixing device 109.
After the toner image is transferred to the transfer material 105, the toner remaining on the photoconductor 101 is removed from the photoconductor 101 by a cleaning blade 107 serving as a cleaning unit. The cleaning device may be a cleaning brush such as a fur brush or a mag brush, and a blade and a brush may be used in combination. The photosensitive member 101 that has passed through the cleaning blade 107 is subjected to light neutralization by a neutralization lamp 108 to prepare for the next image formation.
[0012]
Next, the developing operation in the developing device 104 will be described.
The developing device 104 is close to the developing roller 110 facing the photosensitive member 101, the first conveying screw 111 that conveys the developer from the front surface to the back surface, and from the back surface to the front surface direction. It is comprised from the 2nd conveyance screw 112 which conveys a developing agent. The developing roller 110 includes an outer rotatable sleeve and an inner magnet. A toner replenishing port (not shown) is provided on the upstream side of the second conveyance screw 112 in the conveyance direction, and a toner (not shown) according to the output of the toner concentration sensor 113 provided on the downstream side of the second conveyance screw 112 in the conveyance direction. Toner is supplied from the supply device.
The developer is a two-component developer composed of a toner and a carrier, and the carrier is surface-treated by a method such as spraying a resin such as a silicone resin on the surface of a magnetic material such as ferrite, magnetite, or iron having a particle size of about 50 μm. Things are used.
The toner is obtained by kneading and pulverizing a binder resin such as an ester resin, an acrylic resin, and a styrene resin, a pigment and a charge control agent, and adding an external additive such as silica and titania to the classified toner. It is about 7 μm.
If necessary, the toner is internally added with a fixing aid such as wax or oil and / or externally added with a lubricant such as zinc stearate or fluororesin. The fixing aid is added to prevent fixing offset, and it is not necessary to apply fixing oil such as silicone oil to the fixing roller, thereby reducing the cost. In addition, the lubricant acts to reduce the surface energy of the photoreceptor, to prevent filming of the photoreceptor due to paper powder and toner, and to prevent the occurrence of abnormal images such as transfer omission.
[0013]
The toner supplied from the toner replenishing port is mixed with the developer while being conveyed by the conveying screw, is charged by frictional charging with the carrier, and is supplied to the developing roller 110. In the biaxial agitation type developing device 104 as shown in FIG. 1, due to its configuration, the toner tends to be weakly charged upstream of the first conveying screw 111 in the developer conveying direction. Even if the background contamination is at a level where there is no problem, the background contamination on the photoconductor 101 facing this position tends to be bad.
In addition, when a lubricant or a fixing aid is added to the toner as described above, when the toner remaining on the photoreceptor 101 is scraped off by the cleaning blade 107, these additives are removed by the cleaning blade 107. Therefore, the amount of abrasion on the upstream side in the developer transport direction with a lot of background stains on the photoconductor 101 is smaller than that on the downstream side, and a deviation occurs in the wear of the photoconductor 101.
[0014]
In order to solve the above problems, the wear resistance of the photoconductor is improved, the wear amount on the photoconductor surface is less likely to vary, the durability is maintained over a long period of time, and a stable good image is obtained. The photoconductor as the image carrier of the present invention has the following configuration.
FIG. 2 is a cross-sectional view showing a schematic configuration of the photoconductor according to the present invention, and a laminated electrophotographic photoconductor will be described as an example as an embodiment.
On the conductive support 1, a charge generation layer 3 mainly composed of a charge generation material and a charge transport layer 4 mainly composed of a charge transport material are laminated. A protective layer 5 is formed as a surface layer of the photoreceptor.
[0015]
The conductive support 1 has a volume resistance of 10 ¹⁰ Ωcm or less, for example, a metal such as aluminum or stainless steel processed into a tube, or a metal such as nickel processed into an endless belt, or A film or cylindrical plastic coated with a metal such as nickel or a metal oxide such as tin oxide by vapor deposition or sputtering is used.
[0016]
The charge generation material that is the main component of the charge generation layer 3 is an inorganic or organic material. Typical examples include monoazo pigments, diazo pigments, trisazo pigments, phthalocyanine pigments, selenium, selenium-tellurium alloys, Examples include selenium-arsenic alloys and amorphous silicon. These charge generation materials can be formed by dispersing the charge generating material together with a binder resin such as polycarbonate using a solvent such as tetrahydrofuran or cyclohexanone by a ball mill or the like and applying the dispersion. Application is performed by dip coating, spray coating, or the like. The film thickness of the charge generation layer 3 is usually 0.01 to 5 μm, preferably 0.1 to 2 μm.
[0017]
The charge transport layer 4 can be formed by dissolving or dispersing a charge transport material and a binder resin in a suitable solvent such as tetrahydrofuran, toluene, dichloroethane, and applying and drying the solution. Moreover, a plasticizer, a leveling agent, etc. can also be added as needed.
Among charge transport materials, low molecular charge transport materials include electron transport materials and hole transport materials. Examples of the electron transport material include chloroanil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 1, Examples include electron-accepting substances such as 3,7-trinitrodibenzothiophene-5,5-dioxide.
Examples of hole transport materials include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, thiophene derivatives, etc. These electron donating substances are listed.
When a polymer charge transport material is used as the charge transport material, it may be dissolved or dispersed in an appropriate solvent, and coated and dried to form a charge transport layer. The polymer charge transport material may be a polymer material having a charge transport substituent in the main chain or side chain as mentioned in the low molecular charge transport material.
As the binder resin used for the charge transport layer 4 together with the charge transport material, polystyrene resin, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, polyester resin, polyarylate resin, polycarbonate resin, acrylic resin, epoxy resin, Examples thereof include thermoplastic or thermosetting resins such as melamine resin and phenol resin. The film thickness of the charge transport layer 4 may be appropriately selected in the range of 5 to 30 μm according to the desired photoreceptor characteristics.
[0018]
In the laminated electrophotographic photoreceptor, an undercoat layer may be formed between the conductive support 1 and the photosensitive layer 2. The undercoat layer is generally composed of a resin as a main component. These resins are solvent-resistant resins that are insoluble in general organic solvents in consideration of applying the photosensitive layer 2 using a solvent. It is desirable to be. Examples of such resins include water-soluble resins such as polyvinyl alcohol resins, alcohol-soluble resins such as copolymer nylon, polyurethane resins, alkyd-melamine resins, and curable resins that form a three-dimensional network structure such as epoxy resins. .
Similar to the photosensitive layer 2, the undercoat layer can be formed by a coating method using an appropriate solvent. The thickness of the undercoat layer is suitably 5 μm or less.
[0019]
In the multilayer electrophotographic photoreceptor of the present invention, a protective layer 5 containing a filler is formed on the photosensitive layer 2 as a surface layer for the purpose of protecting the photosensitive layer 2 and improving durability.
As the binder resin, a polycarbonate resin is preferable, and a filler is dispersed therein to form the protective layer 5.
As the filler, it is possible to form a uniform particle diameter, and transparent and homogeneous materials are preferable, and metal oxides such as alumina, silica, and titanium oxide are particularly preferable. The average particle size is preferably one that can maintain transparency of about 0.3 μm.
[0020]
The amount of the filler added to the protective layer 5 is 10 to 40%, preferably 20 to 30%, based on the weight. If the amount of the filler is less than 10%, the photoreceptor 101 is greatly worn and inferior in durability, and if it exceeds 40%, a decrease in sensitivity or an increase in residual potential cannot be ignored.
In order to satisfy the above requirements, the filler content needs to have an area occupancy in an arbitrary cross section of the protective layer 5 of 2% or more and 6% or less in terms of the above-mentioned weight-based value.
[0021]
Further, the thickness of the protective layer 5 is monotonously changed in the longitudinal direction of the photoconductor 101 in order to make it difficult for the wear amount of the photoconductor 101 to vary. Specifically, the film thickness of the protective layer 5 is set so that the film thickness of the protective layer 5 becomes small at a place where the background of the photoconductor 101 facing the upstream side in the developer conveying direction in the developing device 104 is heavily stained. Change monotonically in the longitudinal direction. By arranging the photosensitive member 101 and the developing device 104 having such a protective layer 5 formed thereon, even if a deviation occurs in the wear amount in the longitudinal direction of the photosensitive member 101, the film of the protective layer 5 in the longitudinal direction of the photosensitive member 101 is obtained. It shall be compensated by the thickness difference. With such a configuration, it is possible to maintain the durability of the photoconductor 101 over a long period of time and obtain a stable image.
However, if the film thickness difference of the protective layer 5 is too large, the sensitivity difference in the longitudinal direction of the photoconductor 101 becomes large and toner density unevenness occurs. Accordingly, the film thickness difference of the protective layer 5 in the longitudinal direction of the photoreceptor 101 is preferably 1 μm or more and 5 μm or less.
[0022]
Spray coating can be used to form the protective layer 5 of the photoreceptor 101 shown above.
Formation of a protective layer having a uniform film thickness on a conventional photoreceptor is generally performed by moving the spray gun in the longitudinal direction of the photoreceptor while spraying the coating liquid while rotating the photoreceptor in the circumferential direction. A protective layer having an arbitrary film thickness can be formed by repeating this spray coating, heating and drying to remove the solvent.
In order to change the film thickness of the protective layer 5 in the longitudinal direction of the photoconductor 101 as in the present invention, a plurality of spray guns may be used. Using a plurality of spray guns having different discharge amounts, the protective layer 5 whose film thickness varies in the longitudinal direction of the photoconductor 101 is formed by spraying and coating so that part of the coating liquid overlaps. Can be formed. In addition, the amount of change in the thickness of the protective layer 5 can be adjusted by adjusting the intervals between the plurality of spray guns, the discharge amount, and the like.
[0023]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited by these Examples.
(Example 1)
An undercoat layer, a charge generation layer, and a charge transport layer are each applied in that order by a dip coating method on an aluminum substrate having a diameter of 30 mm, dried, and then an undercoat layer of 3.5 μm and a charge generation of 0.15 μm are generated. A 20 μm charge transport layer was formed.
Then, the protective layer which made the polycarbonate resin contain the alumina as a filler was formed by the spray coating method. The content of alumina was 4.2% in terms of area occupancy in an arbitrary cross section of the protective layer. Further, at this time, the protective layer was applied by changing the film thickness monotonously in the longitudinal direction of the photoconductor so that the film thickness was reduced on the upstream side in the developer conveying direction in the developing device. When the cross section of the protective layer of the photoreceptor was observed with an SEM and the thickness of the protective layer was examined, the protective layer thickness on the upstream side in the developer transport direction was 3 μm, and the protective layer thickness on the downstream side was 7 μm.
The photoconductor produced as described above was mounted on the image forming apparatus shown in FIG. 1 and durability was evaluated.
Image exposure was laser exposure at 655 nm, and charging was applied by superimposing AC (2 kHz, 1.8 kVpp) on DC (−750 V) on a charging roller.
As the developer, a two-component developer composed of a carrier having an average particle diameter of 50 μm and a toner having an average particle diameter of 6.8 μm was used. The toner was externally added with 1.2 parts by weight of silica and 0.15 parts by weight of zinc stearate in order to improve fluidity and prevent transfer loss.
The process speed of this process was 125 mm / s.
As a result, the output image was almost good even after the initial and continuous 100,000 sheets, and slight halftone unevenness was recognized after 100,000 sheets. Further, the wear amount of the photosensitive member after 100,000 sheets of continuous paper was about 1.5 μm on the upstream side in the developer conveying direction and about 6 μm on the downstream side.
[0024]
(Comparative Example 1)
In Example 1, a photoconductor was prepared in the same manner as in Example 1 except that the thickness of the protective layer was 4 μm over the entire width in the longitudinal direction of the photoconductor. Durability evaluation was performed.
As a result, the output image was generally good on the upstream side in the developer transport direction even after 100,000 continuous sheets were passed, and a slight unevenness occurred in the halftone. The abrasion amount of the photoreceptor was 1.8 μm.
However, black streaks due to poor cleaning occurred on the downstream side in the developer transport direction. The abrasion amount of the photosensitive member was 8.3 μm, and the protective layer disappeared due to abrasion.
[0025]
(Comparative Example 2)
A photoconductor was prepared in the same manner as in Example 1 except that coating was performed so that the protective layer thickness was 2 μm on the upstream side in the developer transport direction and 10 μm on the downstream side in the developer transport direction. The durability of the image forming apparatus shown in FIG. 1 was evaluated.
As a result, in the output image, density unevenness occurred in the longitudinal direction of the photoconductor in the middle tone due to the sensitivity difference of the photoconductor in the initial stage. As the paper was passed, the density unevenness in the longitudinal direction of the photoconductor became inconspicuous. The abrasion amount of the photoreceptor was 1.3 μm on the upstream side in the developer conveying direction and 6.2 μm on the downstream side.
[0026]
【The invention's effect】
As described above, according to the present invention, the protective layer containing particles made of metal oxide or the like is exposed so that the film thickness becomes small at the position of the photoconductor facing the upstream side in the developer transport direction. By changing monotonically in the longitudinal direction of the body and forming it on the surface of the photoreceptor, the wear resistance of the photoreceptor is improved, and even if there is a deviation in the amount of wear on the surface of the photoreceptor, the protective layer in the longitudinal direction of the photoreceptor It is possible to provide a photoreceptor that can compensate for the difference in film thickness, maintain durability over a long period of time, and obtain a stable and good image.
Further, the content of the particles contained in the protective layer is 2% or more and 6% or less in the area occupancy ratio in the arbitrary cross section of the protective layer, so that the sensitivity of the photoreceptor is not lowered, the residual potential is not increased, etc. It is possible to provide a photoreceptor capable of giving a good image and obtaining durability over a long period of time.
Further, by setting the difference in thickness of the protective layer in the longitudinal direction of the photoreceptor to 1 μm or more and 5 μm or less, toner density unevenness due to the thickness difference of the protective layer does not occur, and a stable and stable image is always given. It is possible to provide a photoreceptor that maintains durability for a long period of time.
Further, by mounting the photoconductor having the above structure as an image carrier in an image forming apparatus, it is possible to provide an image forming apparatus capable of maintaining durability over a long period of time and obtaining a stable and good image.
[Brief description of the drawings]
FIG. 1 is a schematic view of an image forming apparatus to which the present invention is applied.
FIG. 2 is a cross-sectional view showing a schematic configuration of a photoreceptor according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Conductive support body 2 Photosensitive layer 3 Charge generation layer 4 Charge transport layer 5 Protective layer 101 Photoconductor 102 Charging roller 103 Exposure 104 Developing device 105 Transfer material 106 Transfer roller 107 Cleaning blade 108 Static elimination lamp 109 Fixing device 110 Developing roller 111 First One conveying screw 112 Second conveying screw 113 Toner concentration sensor

Claims (3)

An image forming apparatus having an image carrier, a charging unit, an exposure unit, a developing unit, a transfer unit, a fixing unit, and a cleaning unit,
The image carrier is provided with a protective layer containing particles on the surface, and the thickness of the protective layer is produced so as to change monotonously in the longitudinal direction of the image carrier,
The developing means includes at least a developer carrying member disposed to face the image carrying member;
A first developer conveying member that is arranged in close proximity to the developer carrying member and conveys the developer in the longitudinal direction of the developer carrying member;
A second developer conveying member that conveys the developer in the opposite direction to the first developer conveying member;
An image forming apparatus, wherein the protective layer of the image carrier on the upstream side in the developer transport direction of the first developer transport member is disposed so as to be smaller than that on the downstream side. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the toner used in the developing unit includes a fixing auxiliary agent and / or a lubricant. The image forming apparatus according to claim 1, wherein
The image forming apparatus, wherein the image carrier has a difference in film thickness of the protective layer in the longitudinal direction of the image carrier from 1 μm to 5 μm.

Images