JP2013148693A - Corona charger and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corona charger capable of preventing an abnormal image such as density unevenness and image blurring caused by the adhesion of discharge products generated from a charger using corona discharge, especially NOx to the photoreceptor surface by drastically improving the decomposition ability of discharge products and an image forming apparatus using the same.SOLUTION: There is provided a corona charger having a corona discharge electrode and a charge grid, wherein the charge grid has a coating layer containing metal oxide particles, a resistance adjustment agent and a binder resin and the metal oxide particles contains one or two or more selected from CeO, AlOor ZrOand carry rhodium.

Description

  The present invention relates to a corona charger, particularly a corona charger used in an image forming apparatus using an electrophotographic method, and more particularly to a corona charger having a grid electrode and an image forming apparatus using the same.

In general, an electrophotographic apparatus irradiates a uniformly charged photosensitive member with writing light modulated by image data to form an electrostatic latent image on the photosensitive member, and this electrostatic latent image is formed. The developing unit supplies toner to the formed photosensitive member, forms a toner image on the photosensitive member, develops the toner image, and transfers the toner image on the photosensitive member to transfer paper (recording paper or intermediate transfer member) by the transfer unit. Thereafter, the toner image is transferred onto a transfer sheet by a fixing unit, and the transferred toner image is fixed by heating and pressing.
Further, the toner remaining on the surface of the photoreceptor is collected by a method such as scraping with a cleaning blade in the cleaning unit.

A corona charger using corona discharge is widely used as a charging means for charging a photoconductor as a member to be charged. Here, the corona discharge is a continuous discharge generated by local breakdown of air performed in a non-uniform electric field.

The discharge mode of corona discharge greatly depends on the polarity of the applied voltage. In the case of normal corona discharge, a uniform discharge is formed on the corona wire surface. In the case of negative corona discharge, a discharge form in which streamer discharge is scattered is obtained. The positive corona discharge has considerably good charging uniformity, but the negative corona discharge causes discharge unevenness and is inferior to the positive corona discharge.
In addition, the amount of ozone generated by the discharge is about an order of magnitude greater in the negative corona discharge than in the positive corona discharge, and the load on the environment is greater.

The corona charger and its features will be briefly described.
The corona charger is generally configured such that a minute diameter wire is stretched in a shield case with a part of aluminum or the like opened, and corona ions are released from the opening. It is roughly divided into scorotron type corona chargers.

(1) Corotron type corona charger FIG. 1A shows the configuration of a corotron type corona charger and a charging method using the same.
The corotron-type corona charger has a structure in which a tungsten wire having a diameter of 50 to 100 μm is shielded with a metal about 1 cm apart. A high voltage of 5 to 10 kV is applied to the corona wire in a state where the opening surface is arranged to face the member to be charged, and positive or negative ions generated thereby are moved to the surface of the member to be charged and charged.
As shown in FIG. 2A, since the corotron type corona charger generates a certain amount of charge, it is not necessarily good at uniformly charging the surface of the object to be charged to a certain voltage. It is particularly effective as a transfer charger intended to give a constant charge to the recording paper.

(2) Scorotron-type corona charger The scorotron-type corona charger is devised in order to reduce the unevenness of the charged potential on the surface of the object to be charged. As shown in FIG. 1B, several wires or meshes are arranged as grid electrodes on the opening surface of the corotron. The opening surface of the scorotron charger is made to face the member to be charged, and a bias voltage is applied to the grid electrode.
FIG. 2B shows charging characteristics of the scorotron type corona charger.
A feature of the scorotron type corona charger is that the charging potential is regulated by the voltage applied to the grid electrode even when the charging time is long, and the surface potential is saturated. This saturation value can be controlled by the grid applied voltage. The scorotron type corona charger has a complicated structure and inferior charging efficiency as compared with the corotron type, but is excellent in uniformity of charging potential and widely used.

The grid electrode in the electrophotographic image forming apparatus is called a charging grid.
When a corona charger that performs negative corona discharge is used, substances in the air react with each other to generate discharge products. Among the discharge products, ozone in which oxygen is oxidized (O ₃ ) and nitrogen oxides (NOx) such as carbon monoxide (NO) and nitrogen dioxide (NO ₂ ) in which nitrogen is oxidized by ozone are included. It is.
These discharge products may adhere to, and further penetrate, the photosensitive member that is a member to be charged, thereby causing problems such as density unevenness and image blurring.

(Uneven density)
As a problem caused by the discharge product generated from the corona charger, there is a density unevenness immediately below the corona charger that occurs when left after a long discharge. This is because the discharge product generated by the discharge during the image forming operation adheres to the inner wall of the corona charger and the discharge product gradually becomes a photosensitive member while the image forming apparatus is stopped. This is a problem that the surface of the body is contaminated and a difference in surface potential occurs between the portion immediately below the corona charger and the other portion of the photoreceptor, resulting in image density unevenness.

Such a phenomenon is conspicuous in the scorotron type corona charger having the above-described charging grid, and occurs more significantly in a low humidity environment of about 20% RH.

FIG. 3A is a diagram showing the state of an image when density unevenness occurs directly under the corona charger, and FIG. 3B is a diagram showing a photoreceptor surface potential corresponding to the image.
As shown in FIG. 3A, line-shaped abnormal images (AP) having different image densities are generated at predetermined intervals in the transfer paper conveyance direction (paper passing direction). The abnormal image is generated at the concave portion (X) where the surface potential of the photosensitive member is increased as shown in FIG.

(Image blur)
Another problem that can occur due to the discharge products generated from the corona charger is image blurring directly under the corona charger that occurs under high temperature and high humidity. This is because the discharge product generated by the discharge during the image forming operation adheres to the inner wall of the corona charger and the discharge product contains moisture while the image forming apparatus is stopped. This is due to the fact that it gradually adheres to the surface of the photoreceptor.
Since the discharge product is an ionic substance, the resistance on the surface of the photoreceptor is lowered, and as a result, a phenomenon called image blurring that blurs the image occurs.
Such a phenomenon is conspicuous in the scorotron type corona charger having the above-described charging grid, and occurs more significantly in a high humidity environment of about 70% RH.

The occurrence of abnormal images such as density unevenness and image blur has been confirmed to occur in any photoconductor, and in particular, a photoconductor provided with a crosslinkable cured film on the surface as a protective layer, Since the surface of the photoconductor is not easily renewed and discharge products are easily accumulated, the occurrence of uneven image density is remarkable.

In order to prevent contamination of the object to be charged by the discharge product, it is conceivable to place a shielding object between the corona charger and the object to be charged after discharge, or to move the corona charger and the object to be charged. In many cases, the corona charger and the member to be charged are fixed at a fixed interval of about 1 to 2 mm so that stable charging is performed, and a complicated configuration is required, and the apparatus is large. It will become.

Japanese Patent Application Laid-Open No. 2003-91143 of Patent Document 1 discloses that a charger is disposed on the lower side of a photoreceptor, and silica gel, activated zirconia, zeolite, activated alumina, activated carbon, activated carbon fiber, and Ti-Si-Zr-based oxidation. Materials that have an adsorption action on ozone and NOx such as titanium dioxide-lime aluminate-manganese oxide series, terpenoid series, Cu-Mn series, alumina-silica gel series, etc. are placed on the back side (lower part) of the charger However, a method for suppressing the adhesion of the corona product to the photoreceptor is disclosed.

In JP-A-11-282318 and JP-A-4176927 of Patent Document 2, a photocatalyst made of an n-type semiconductor such as titanium oxide is provided on the inner wall of the corona charger to discharge near the charger. A means for efficiently decomposing ozone and NOx generated by the above in a casing is disclosed.
These methods cannot prevent the discharge product from adhering to the charging grid, and a part of the discharge product adhering to the charging grid adheres to the photoconductor, thereby completely suppressing the occurrence of abnormal images. In particular, the use of a charger over a long period of time can cause deterioration of the image carrier when discharge products accumulate on the charging grid, and particularly in a high temperature and high humidity environment. Have the problem.

In Japanese Patent Application Laid-Open No. 2005-227470 of Patent Document 4, a discharge product absorbent such as graphite particles, nickel particles, and aluminum compound particles is applied to a charging grid, and the conductive film absorbs the generated discharge products. In the above, it is disclosed that the contamination of the object to be charged is suppressed and the corrosion of the control electrode by the discharge product is suppressed.
However, the amount of discharge product absorbent that can be absorbed by the discharge product absorbent is determined by the number of adsorption sites of the particles. It cannot be suppressed.

Japanese Patent Application Laid-Open No. 2007-121460 of Patent Document 5 can suppress the adsorption of discharge products to the grid wire by coating the grid wire with gold, platinum, iridium, rhodium, ruthenium, palladium, and the like. A charger that can prevent unevenness is disclosed.
However, specific embodiments are not disclosed, and the operation and effect are not clear.

Japanese Patent Application Laid-Open No. 2011-59647 of Patent Document 6 discloses a corona charger having a charging grid on the surface of which a layer containing a zeolite, a metal catalyst, a conductive agent, and a binder resin is formed. However, although it is excellent in that the contamination of the charged body can be suppressed, it is necessary to contain zeolite as an adsorbent, and the ability to remove the discharge product of the metal catalyst is still not sufficient.

The present invention has been made in view of the above problems, and has dramatically improved the resolution of discharge products, and discharge products generated from a charger utilizing corona discharge, in particular NOx, adhere to the surface of the photoreceptor. An object of the present invention is to provide a corona charger capable of preventing abnormal images such as density unevenness and image blur caused by the above, and an image forming apparatus using the corona charger.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have supported rhodium on metal oxide particles containing one or more selected from CeO ₂ , Al ₂ O ₃ , or ZrO _2. Therefore, the resolution of the discharge product is dramatically improved, and the discharge product is provided over a long period of time by providing the charging grid with the coating layer containing the rhodium-supported metal oxide particles, the resistance adjusting agent, and the binder resin. It has been found that occurrence of abnormal images such as density unevenness and image blur caused by adhering to the surface of the photoreceptor can be prevented.

The said subject is solved by following (1)-(8) of this invention.
(1) “A corona charger having a corona discharge electrode and a charging grid, wherein the charging grid has a coating layer containing metal oxide particles, a resistance adjusting agent, and a binder resin. Corona charger characterized in that the particles contain one or more selected from CeO ₂ , Al ₂ O ₃ , or ZrO ₂ and support rhodium ”,
(2) “The coating layer contains one or more metal oxide particles supporting platinum, palladium, or lanthanum in addition to the rhodium-supporting metal oxide particles. Corona charger as described in section),
(3) "The corona charger according to (1) or (2) above, wherein the coating layer contains 5 wt% or more and 50 wt% or less of metal oxide particles",
(4) "The corona charger according to any one of (1) to (3) above, wherein the coating layer has a binder resin content of 5 wt% or more and 40 wt% or less" ,
(5) “An image forming apparatus having an electrophotographic photosensitive member, a charger, an exposure device, a developing device, a transfer device, and a cleaning device, wherein the charger is as defined in the items (1) to (4). An image forming apparatus characterized by being a corona charger according to any one of the above ”,
(6) In the above item (5), comprising a plurality of electrophotographic photosensitive members, and sequentially transferring toner images formed on the plurality of electrophotographic photosensitive members to a transfer medium. Image forming apparatus ",
(7) “A process cartridge having an electrophotographic photosensitive member and a corona charger and removable from an image forming apparatus, wherein the corona charger is any one of the items (1) to (4). A process cartridge characterized by being a corona charger as described in "
(8) “An image forming method, wherein an image is formed using the image forming apparatus according to (5) or (6)”.

  As will be understood from the following detailed and specific description, according to the present invention, the resolution of the discharge product is remarkably improved, and the discharge product generated from the charger utilizing corona discharge, particularly NOx, is reduced. It is possible to provide a corona charger having a grid electrode capable of preventing abnormal images such as density unevenness and image blur caused by adhering to the surface of the photoreceptor, and an image forming apparatus using the same.

It is a schematic diagram which shows the structure of a corotron type corona charger and a scorotron type corona charger. It is a figure which shows the charging characteristic of a corotron type corona charger and a scorotron type corona charger. It is a figure which shows the density non-uniformity right under a corona charger. 1 is a diagram illustrating a configuration example of an image forming apparatus of the present invention. It is a principal part enlarged view of a corona charger. It is a figure which shows the structural example of the process cartridge of this invention.

The corona charger of the present invention will be described in detail.
The corona charger of the present invention is a corona charger having a corona discharge electrode and a charging grid, and the charging grid has a coating layer containing metal oxide particles, a resistance adjusting agent, and a binder resin.

<Metal oxide particles>
The metal oxide particles carry rhodium, and metal oxides such as cerium oxide, zirconium oxide, and aluminum oxide can be used as the metal oxide forming the metal oxide particles.
The particle diameter of the metal oxide particles is preferably 1 μm or less, and particularly preferably 0.05 μm or more and 0.5 μm or less from the viewpoint of the strength and translucency of the surface layer.

The particle size of rhodium supported on the metal oxide particles is preferably a small particle size so as to increase the surface area and obtain sufficient activity. However, since the catalytic activity decreases due to aggregation, it is 2 nm to 30 nm. It is preferable that it is 2 nm or more and 10 nm or less.
The amount of rhodium supported on the metal oxide particles is preferably 0.1 wt% or more and 10 wt% with respect to the metal oxide particles, from the viewpoint of the manifestation and sustainability of the effect as a discharge product removal catalyst.

As a rhodium raw material for supporting rhodium on the metal oxide particles, a compound containing rhodium can be used. For example, rhodium nitrate, rhodium chloride, rhodium acetate, hexaammine rhodium, or the like can be preferably used. Examples of the method for supporting rhodium on the metal oxide particles include a sol-gel method, an alkoxide method, a reverse micelle method, and a hydrothermal synthesis method.

In addition to the metal oxide particles supporting rhodium, the coating layer contains metal oxide particles supporting one or more of platinum, palladium, and lanthanum, thereby improving the discharge product removal rate. This is preferable.
Rhodium and other catalysts such as platinum may be supported on one metal oxide particle, but the removal rate of discharge products is improved when rhodium and platinum are completely separated. .
The content of the metal oxide particles supporting one or more of platinum, palladium and lanthanum is preferably 60 wt% or less in the metal oxide particles.

The content of the metal oxide particles in the coating layer is preferably 5 wt% or more and 50 wt% or less from the viewpoints of adhesion between the charging grid and the coating layer, discharge product removal ability, and transparency.
If it is less than 5 wt%, the discharge product removal ability may be lowered, and if it exceeds 50 wt%, the adhesion between the coating layer and the charging grid may be lowered.

<Binder resin>
The binder resin in the present invention is contained in the coating layer formed on the charging grid, and binds the rhodium-supported metal oxide particles and the resistance control agent to the charging grid, and further disperses the coating layer coating liquid. It also plays a role in improving stability and forming a uniform film.

The type of the binder resin is not particularly limited. For example, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride. -Vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, Thermoplastic or thermosetting resins such as silicone resin, epoxy resin, melamine resin, urethane resin, phenol resin, alkyd resin can be used, but thermosetting resin composed of alkyd resin and amino resin, or Polyamide resin, heat resistance, adhesion to a charging grid, and excellent in dispersibility of the metal oxide particles are on the charging grid over a long term can be retained compositions can be used satisfactorily.

The binder resin content of the coating layer is preferably 5 wt% or more and 40 wt% or less, and more preferably 10 wt% or more and less than 30 wt%. If it exceeds 40 wt%, the metal oxide particles may be covered and the discharge product removal function may be deteriorated. If it is less than 5 wt%, the adhesion between the coating layer and the charging grid is reduced, and film peeling occurs. It becomes easy to do.

<Resistance adjuster>
The charged grid base material is made of a processed product of a wire or a metal plate, and is originally conductive, but since it is covered with a coating layer containing rhodium-supported metal oxide particles and a binder resin, the electrical resistance increases, and the surface Potential control ability decreases.
Therefore, a resistance control agent is dispersed in the binder resin for the purpose of imparting conductivity to the coating layer.

Examples of the resistance control agent include metal fine particles such as graphite, nickel, copper, and silver, and metal oxides such as antimony-doped tin oxide (ATO), indium tin oxide (ITO), tin oxide, and zinc antimonate. In addition, conductive particles such as activated carbon and binder resin exhibiting conductivity can be used, and two or more of these may be used.
Among them, metals such as graphite and nickel, and undoped metal oxides such as tin oxide and zinc antimonate have high durability against discharge, are stable against use over time and environmental fluctuations, and can be preferably used. The resistance control agent preferably has high conductivity and a small particle size.

The resistance control agent content of the coating layer is preferably 5 wt% or more and 50 wt% or less, and more preferably 10 wt% or more and 40 wt% or less. If it is less than 5 wt%, the surface potential control ability may be lowered, and if it exceeds 50 wt%, the adhesion of the coating layer and the discharge product removal function may be lowered.

<Coating layer forming method>
The coating layer can be formed by preparing a coating layer coating solution containing metal oxide particles, a resistance adjusting agent, and a binder resin, coating the coating layer coating solution on a charging grid, and drying.
In addition, the resistance control agent may be included in the coating layer coating liquid in advance as described above, but after coating and drying the coating layer coating liquid not including the resistance control agent, the resistance control agent is applied, The covering layer may be formed by driving.
Examples of the method for applying the coating layer coating solution to the charging grid include a dipping method, a roller coating method, an electrophoretic electrodeposition method, and the like, but a spray method is preferable with little coating unevenness.

<Image forming apparatus>
The corona charger of the present invention and an image forming apparatus using the corona charger will be described.
First, an example of an image forming apparatus using the corona charger of the present invention is shown in FIG.
The image forming apparatus includes a scorotron-type corona charger (101) that uniformly charges the surface of the photoconductor (100) around the drum-type photoconductor (100) that is an image carrier, and a photoconductor ( 100) is exposed to writing light (L) modulated by image data to form an electrostatic latent image, and the surface of the photosensitive member (100) formed by the exposure device (102) is electrostatically exposed. A developing device (103) for supplying toner to the latent image to form a toner image is provided. Further, the image forming apparatus transfers a toner image formed on the surface of the photosensitive member (100) onto a transfer sheet (109) conveyed one by one from a sheet feeding device (not shown), and a transfer sheet (104). 109) a cleaning device (105) comprising a cleaning brush (106) and a cleaning blade (107) for removing toner remaining on the surface of the photoconductor (100) from the surface of the photoconductor (100) after the toner image is transferred to it. ) And a charge removal device (108) for removing charges remaining on the surface of the photoconductor (100) after cleaning.

In addition, the image forming apparatus stops the transfer paper (109) conveyed one by one from a paper supply device (not shown), and transfers the transfer paper (109) to the transfer device (104) and the photoconductor (100) at a predetermined timing. ) And a fixing device that heats and presses the toner image transferred onto the transfer paper (109) by the transfer device and fixes the toner image on the transfer paper (109).

In the image forming apparatus of the present invention, conventionally known members can be used as other constituent members such as a photoreceptor and a developer. In the present invention, metal oxide particles contained in the coating layer of the charging grid are used. Since it has a high ability to remove discharge products, it is possible to suppress contamination of the charged body, and a photoreceptor provided with a crosslinkable cured film can be preferably used.

<Image forming method>
The image forming method of the present invention will be described.
First, the image carrier (100) is charged to (±) 600 to 1400 V by the charger (101). After the charge is applied (charged), a latent image is formed by the image exposure system (102).
Here, in the case of an analog copying machine, an original image irradiated by an exposure lamp is projected onto a photosensitive member in the form of a reverse image by a mirror and formed into an image, whereas in the case of a digital copying machine, a CCD (charge) is formed. The original image read by the coupling element) is converted into a digital signal, projected by an LD or LED having a wavelength of 400 to 780 nm, and formed on the photoreceptor. Therefore, the wavelength range of the analog copying machine and that of the digital copying machine are different.
The photoreceptor (100) on which the latent image corresponding to the document is formed is developed with a developer by the developing device (103), and is visualized (toner image). Next, the toner image on the photosensitive member is transferred to the transfer paper (109) by applying a voltage to the transfer device (104).
The voltage applied in the transfer may be constant current control so that the current flowing through the photoconductor is constant.
On the other hand, the toner (100) after the toner image is transferred is cleaned by the cleaning device (105), and the latent image (original image) remaining on the photoconductor after the cleaning is removed by a static eliminator (generally a red light). (Used) (108), the charge on the surface of the photosensitive member is made uniform, the preparation of the next latent image formation is completed, and a series of copying processes is completed.

In the corona charger of the present invention, the discharge product accumulated in the corona charger by the image forming process does not adhere to the surface of the photoreceptor directly under the corona charger even after the image forming process is completed. As shown in FIG. 5, it is adsorbed to the coating layer (2c) applied to the charging grid (2d) disposed between the discharge electrode (2a) and the surface (1a) of the photoreceptor (1). Disassembled. As a result, the discharge product generated in the corona charger (2) is prevented from adhering to the surface (1a) of the photoreceptor (1) in the region facing the corona charger, thereby suppressing density unevenness. It is possible to do.
Although not shown, the corona charger may have means for cleaning foreign matters such as dust and scattered toner attached to the wire electrode and the charging grid.

<Process cartridge>
An example of the process cartridge is shown in FIG. The process cartridge incorporates an image carrier (photoreceptor), and in addition, a unit selected from a charging unit, an exposure unit, a developing unit, a transfer unit, and a cleaning unit is integrally connected to be removable from the main body of the image forming apparatus. One device (component). Therefore, if this process cartridge is pulled out from the main body of the image forming apparatus, maintenance, inspection and replacement of these apparatuses can be performed easily and reliably. The corona charger (101), the developing device (103), the cleaning device (105), and the charge removal device (108) may be incorporated independently into the image forming apparatus, but it is preferable to use a process cartridge as described above. .

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to what is illustrated here. The part in an Example represents a weight part.

(Preparation of rhodium-supported metal oxide particles A)
Ceria-containing zirconia powder (containing 10 wt% of CeO ₂ ) was impregnated in an aqueous rhodium nitrate solution, dried at 120 ° C. for 2 hours, and then fired at 400 ° C. for 1 hour. Next, this powder was mixed with water and pulverized using a bead mill to obtain a slurry solution.
Further, boehmite was added to the slurry solution, and the mixture was sufficiently mixed and stirred, then dried at 370 ° C. and then calcined at 550 ° C. for 3 hours to obtain rhodium-supported metal oxide particles A.
The obtained rhodium-supported metal oxide particles were a powder having an average particle size of 0.3 μm composed of rhodium 1 wt% -ceria 5 wt% -zirconia 44 wt% -alumina 50 wt%.

(Preparation of rhodium-supported metal oxide particles B) Zirconyl nitrate aqueous solution was impregnated with γ-alumina, dried at 150 ° C. and then fired at 400 ° C. for 1 hour to obtain zirconia-containing alumina powder (containing 3 wt% of ZrO ₂ ). .
This powder was impregnated with an aqueous rhodium nitrate solution, dried at 120 ° C. for 2 hours, and then fired at 400 ° C. for 1 hour to obtain rhodium-supported metal oxide particles B.
The obtained rhodium-supported metal oxide particles were powder having an average particle diameter of 0.4 μm composed of rhodium 1 wt% -zirconia 3 wt% -alumina 96 wt%.

(Preparation of palladium-supported metal oxide particles)
Ceria and barium oxide-containing zirconia powder (containing 10 wt% CeO2 and 2 wt% BaO) was impregnated in an aqueous palladium nitrate solution, dried at 120 ° C for 2 hours, and then calcined at 400 ° C for 1 hour. Next, this powder was mixed with water and pulverized using a bead mill to obtain a slurry solution having a median diameter of 150 nm.
Further, boehmite was added to the slurry solution, and the mixture was sufficiently mixed and stirred, then dried at 370 ° C. and then fired at 550 ° C. for 3 hours to obtain palladium-supported metal oxide particles.
The obtained palladium-supported metal oxide particles were powder having an average particle size of 0.3 μm composed of 5 wt% palladium, 5 wt% ceria, 1 wt% barium oxide, 34 wt% zirconia, and 55 wt% alumina.

(Preparation of platinum-supported metal oxide particles)
A zirconia-containing ceria powder (containing 20 wt% of ZrO ₂ ) was impregnated in a dinitrodiamine platinum aqueous solution, dried at 120 ° C. for 2 hours, and then fired at 400 ° C. for 1 hour.
Next, this powder was mixed with water and pulverized using a bead mill to obtain a slurry solution having a median diameter of 150 nm.
Further, boehmite was added to the slurry solution, and after sufficiently mixed and stirred, dried at 370 ° C. and then fired at 550 ° C. for 3 hours to obtain platinum-supported metal oxide particles.
The obtained platinum-supported metal oxide particles were a powder having an average particle size of 0.3 μm composed of platinum 1 wt% -zirconia 10 wt% -ceria 39 wt% -alumina 50 wt%.

In addition to drying and baking when preparing the catalyst-supporting metal oxide particles, all drying when forming a coating layer described later was performed in an air atmosphere.

(Preparation of coating layer coating solution)
The binder resin was dissolved in a solvent to prepare a binder resin solution of about 5 to 10 wt%, and the coating resin coating solution was prepared by adding metal oxide particles and a resistance control agent while stirring the binder resin solution. The coating solution solid content concentration during spray coating was 30 wt% or less.

(Formation of coating layer)
Tension is applied to both ends of the charging grid in the longitudinal direction, and the charging grid is installed with the surface of the cylindrical substrate lifted from the substrate by about 3 mm in order to coat both sides in the longitudinal direction of the cylindrical substrate with a diameter of 30 mm. The coating was carried out by rotating at a speed of 10 mm / s in the horizontal direction.
After spray coating, the film was fixed by heating at 130 ° C. for 40 min and drying. As the coating film, a coating film having a thickness of 35 μm was formed on the front and back surfaces of the grid.

[Example 1]
Using the materials shown below, a coating solution for charging grit coat was prepared.
The weight ratio of metal oxide / resistance control agent / binder resin was 5/3/2, and the solid content concentration of the liquid was adjusted to 30 wt%.
・ Metal oxide: Rhodium-supported metal oxide particles A
・ Resistance control agent: Zinc antimonate (Sellnax CX-Z210IP manufactured by Nissan Chemical Industries)
・ Binder resin: Oil-free alkyd resin
(Beckolite 46-118 manufactured by Dainippon Ink and Chemicals)
Melamine resin
(Super Becamine G-821-60 manufactured by Dainippon Ink and Chemicals)
(Alkyd resin / melamine resin = 3/2 weight ratio)
Dispersion medium: 2-butanone The above coating solution was applied by spray onto a charging grid of a corona charger used in a commercially available image forming apparatus (imagio MP 1350 manufactured by Ricoh Co., Ltd.).

[Example 2]
A coating solution was obtained in the same manner as in Example 1 except that the weight ratio of metal oxide / resistance control agent / binder resin was changed to 4/3/3.

[Example 3]
A coating solution was obtained in the same manner as in Example 1 except that the following was used as the metal oxide.
・ Metal oxide: Rhodium-supported metal oxide particles B

[Example 4]
A coating solution was obtained in the same manner as in Example 2 except that the following was used as the metal oxide.
Metal oxide: rhodium-supported metal oxide particles A + palladium-supported metal oxide particles (rhodium-supported metal oxide particles A / palladium-supported metal oxide particles = 2/1 weight ratio)

[Example 5]
A coating solution was obtained in the same manner as in Example 2 except that the following was used as the metal oxide.
Metal oxide: rhodium-supported metal oxide particles A + palladium-supported metal oxide particles (rhodium-supported metal oxide particles A / palladium-supported metal oxide particles = 9/1 weight ratio)

[Example 6]
A coating solution was obtained in the same manner as in Example 2 except that the following was used as the metal oxide.
Metal oxide: rhodium-supported metal oxide particles A + palladium-supported metal oxide particles + platinum-supported metal oxide particles (rhodium-supported metal oxide particles A / palladium-supported metal oxide particles / platinum-supported metal oxide particles = (3/1/1 weight ratio)

[Example 7]
A coating solution was obtained in the same manner as in Example 2 except that the following was used as the metal oxide.
Metal oxide: rhodium-supported metal oxide particles A + palladium-supported metal oxide particles + platinum-supported metal oxide particles (rhodium-supported metal oxide particles A / palladium-supported metal oxide particles / platinum-supported metal oxide particles = (8/1/1 weight ratio)

[Example 8]
A coating solution was obtained in the same manner as in Example 1 except that the weight ratio of metal oxide / resistance control agent / binder resin was changed to 6/2/2.

[Comparative Example 1]
A coating solution was obtained in the same manner as in Example 1 except that the following was used as the metal oxide.
・ Metal oxide: palladium-supported metal oxide particles

[Comparative Example 2]
A coating solution was obtained in the same manner as in Example 1 except that the following was used as the metal oxide.
・ Metal oxide: Platinum-supported metal oxide particles

[Comparative Example 3]
Using the materials shown below, a coating solution for charging grit coat was prepared. The weight ratio of zeolite / resistance control agent / binder resin was 5/3/2, and the solid content concentration of the liquid was adjusted to 30 wt%.
・ Zeolite ... Y-type zeolite (HSZ-320HOA manufactured by Tosoh Corporation)
・ Resistance control agent: Zinc antimonate (Sellnax CX-Z210IP manufactured by Nissan Chemical Industries)
・ Binder resin: Oil-free alkyd resin
(Beckolite 46-118 manufactured by Dainippon Ink and Chemicals)
Melamine resin
(Super Becamine G-821-60 manufactured by Dainippon Ink and Chemicals)
(Alkyd resin / melamine resin = 3/2 weight ratio)
・ Dispersion medium ... 2-butanone

[Comparative Example 4]
A coating solution was obtained in the same manner as in Example 1 except that rhodium fine particles (average particle size 10 nm) were used in place of the rhodium-supported metal oxide particles A.

The coating liquids of Examples 1 to 8 and Comparative Examples 1 to 4 were applied to a charging grid of a corona charger used in a commercially available image forming apparatus (Imagio MP 1350, manufactured by Ricoh Co., Ltd.) by spraying. The following evaluation was performed.

(Film adhesion evaluation)
Whether the adhesion of the film applied to the charging grid can withstand actual use is determined by the degree of peeling when the coated surface is wiped 30 times with a cloth when rubbed with force and with a load sufficient to place a finger. evaluated. The degree of each symbol is shown below.
◎ ・ ・ ・ Does not adhere to waste even when rubbed ○ ・ ・ ・ Absorbs to a small amount of waste when rubbed, but has a level that does not pose a problem for actual use

(Evaluation of discharge product removal function)
A corona charger coated with a coating solution for charging grit coat was attached to imgio MP 1350 manufactured by Ricoh Co., Ltd. As the photoreceptor, developer, and toner, those mounted on imgio MP 1350 were used as they were.
The image forming operation was performed to discharge the corona charger for 5 hours, and then the machine was turned off and left for 20 hours. After that, the machine was turned on again, a halftone image was output, and the entire character image was output to check whether density unevenness and image flow occurred immediately below the corona charger. In addition, the environment of the said evaluation was implemented in two types of environments, 10 degreeC / 15% RH and 30 degreeC / 90% RH, respectively.
◎ ・ ・ ・ No density unevenness or image blur directly under the corona charger ○ ・ ・ ・ Density unevenness or image blur directly under the corona charger, but acceptable level × ・ ・ ・ Uneven density directly under the corona charger, Or image blur is clearly generated and unacceptable level

(About Figure 4)
DESCRIPTION OF SYMBOLS 100 Photoconductor 101 Corona charger 102 Exposure apparatus 103 Developing apparatus 104 Transfer apparatus 105 Cleaning apparatus 106 Cleaning brush 107 Cleaning blade 108 Static elimination apparatus 109 Transfer paper

(About Figure 5)
DESCRIPTION OF SYMBOLS 1 Photoconductor 1a Photoconductor surface 2 Corona charger 2a Discharge electrode 2c Coating layer 2d Charging grid

JP 2003-91143 A JP-A-11-282318 Japanese Patent No. 4176927 Japanese Patent Laid-Open No. 2005-227470 JP 2007-121460 A JP 2011-59647 A

Claims (8)

A corona charger having a corona discharge electrode and a charging grid, the charging grid having a coating layer containing metal oxide particles, a resistance adjusting agent, and a binder resin, the metal oxide particles being CeO A corona charger comprising one or more selected from ₂ , Al ₂ O ₃ , or ZrO ₂ and supporting rhodium. 2. The corona charging according to claim 1, wherein the coating layer includes one or more metal oxide particles supporting platinum, palladium, or lanthanum in addition to the rhodium-supporting metal oxide particles. vessel. The corona charger according to claim 1, wherein the coating layer contains 5 wt% or more and 50 wt% or less of metal oxide particles. The corona charger according to any one of claims 1 to 3, wherein the coating layer has a binder resin content of 5 wt% or more and 40 wt% or less. An image forming apparatus having an electrophotographic photosensitive member, a charging device, an exposure device, a developing device, a transfer device, and a cleaning device, wherein the charging device is the corona charger according to any one of claims 1 to 4. An image forming apparatus. 6. The image forming apparatus according to claim 5, comprising a plurality of electrophotographic photosensitive members, and sequentially transferring toner images formed on the plurality of electrophotographic photosensitive members to a transfer medium. A process cartridge having an electrophotographic photosensitive member and a corona charger, and detachable from an image forming apparatus, wherein the corona charger is the corona charger according to any one of claims 1 to 4. To process cartridge. An image forming method comprising forming an image using the image forming apparatus according to claim 5.

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