JP2018105998A - Corona charger and electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corona charger having a plate-like grid electrode with a small protection film which is unpeelable and an electrophotographic device having the corona charger.SOLUTION: In a corona charger having housing with an opening facing a charged body, a discharge wire provided inside the housing, and a plate-like grid electrode provided in the opening, the plate-like grid electrode includes: a base material; and a protection film formed with a hydro generation amorphous carbon on the base material. A ratio of the number of hydrogen atoms to the sum of the number of carbon atoms and the number of hydrogen atoms is equal to or more than 30% and equal to or less than 40%, and a ratio of the number of carbon atoms adopting an sp3 hybridized orbital to the sum of the number of carbon atoms adopting the sp2 hybridized orbital and the number of carbon atoms adopting the sp3 hybridized orbital are equal to or more than 30% and equal to or less than 65% among the carbon atoms contained in the protection film.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a corona charger having a discharge wire and a plate-like grid electrode, and an electrophotographic apparatus having the corona charger.

  A corona charger having a discharge wire and a plate-like grid electrode is known as a charger for charging an electrophotographic photosensitive member in an electrophotographic image forming apparatus, that is, a so-called electrophotographic apparatus.

  When corona discharge is performed in the air using a corona charger, ionized discharge products are generated. Then, the ionized discharge product is accelerated by the electric field formed between the discharge wire and the plate-like grid electrode, and jumps to the surface of the plate-like grid electrode.

Many of the ionized discharge products contain oxygen, such as nitrogen oxide ions (NOx ⁻ ). Therefore, when the ionized discharge product reaches the base material of the plate grid electrode, the base material is corroded. In general, the substrate is made of stainless steel which is not easily corroded, but corrosion still occurs. This is presumably because the exposure by corona discharge has a strong corrosive force that corrodes stainless steel beyond the ability of the stainless steel to resist corrosion by the passive film.

  Due to the corrosion of the stainless steel, the electrical resistance of the surface of the substrate of the plate-like grid electrode increases. Due to the increase in electrical resistance, the electric charge released from the discharge wire is accumulated on the surface of the plate-like grid electrode, and charge-up is likely to occur. The charge up of the plate-like grid electrode increases the amount of charge that reaches the surface of the electrophotographic photosensitive member from the discharge wire while avoiding the plate-like grid electrode, so the charge amount of the electrophotographic photosensitive member becomes larger than the desired value. Cheap. When the charge amount of the electrophotographic photosensitive member is larger than a desired value, the image quality is likely to be deteriorated such as density fluctuation.

  In order to suppress such corrosion of the base material of the plate-like grid electrode that causes a decrease in image quality, it is preferable to form a protective film on the base material of the plate-like grid electrode. As a protective film, Patent Document 1 discloses a film (tetrahedral amorphous carbon film) formed of tetrahedral amorphous carbon (tetrahedral amorphous carbon).

JP 2011-64877 A

  The tetrahedral amorphous carbon film described in Patent Document 1 can suppress the corrosion of the base material of the plate-like grid electrode by suppressing the permeation of the ionized discharge product.

  However, the ionized discharge product reacts with the carbon atom (C), which is a constituent element of tetrahedral amorphous carbon, and is released as carbon dioxide. As a result, the thickness of the tetrahedral amorphous carbon film gradually decreases. Tend to.

  This reduction in film thickness was not particularly problematic when the conventional electrophotographic apparatus was used.

  However, in the future, when it becomes necessary to further improve the durability of the plate-like grid electrode, it is required to increase the thickness of the tetrahedral amorphous carbon film.

  However, the tetrahedral amorphous carbon film has relatively many diamond bonds and strong bonds between carbon atoms. Therefore, in the case of a tetrahedral amorphous carbon film, when the film thickness is increased, the film stress tends to increase.

  On the other hand, the plate-like grid electrode generally has a large number of holes formed by an etching process or the like. In order to efficiently perform the process of forming a large number of holes, the plate thickness of the plate-like grid electrode is preferably reduced to about several hundred to several tens of μm. Due to its thinness, when the corona charger is installed in an electrophotographic apparatus, the plate grid electrode is attached to the housing of the corona charger, or the corona charger is operated, the plate grid electrode is bent. Vibration is likely to occur.

  It is considered that the combination of such bending and vibration and the increase in the above-described film stress easily causes micro-peeling of the protective film and increases the risk of corrosion from the micro-peeled portion.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a corona charger having a plate-like grid electrode having a protective film that is hardly peeled off and an electrophotographic apparatus having the corona charger.

The present invention is a corona charger for charging an object to be charged by corona discharge,
A housing having an opening facing the body to be charged,
A discharge wire provided inside the housing; and
In the corona charger having a plate-like grid electrode provided in the opening,
The plate-like grid electrode is
A substrate, and
A protective film formed of hydrogenated amorphous carbon on the substrate;
Ratio of number of hydrogen atoms to the sum _(N C + N _H) of the number of carbon atoms contained in the protective film _{(N C)} of the number of hydrogen atoms _{(N H) (N H)} ((N H / (N _C + N _H )) × 100) [%] is 30% or more and 40% or less,
Of the carbon atoms contained in the protective film, sp3 hybrid to the sum (N _CSP3 + N _CSP2 ) of the number of carbon atoms taking the sp3 hybrid orbital (N _CSP3 ) and the number of carbon atoms taking the sp2 hybrid orbital (N _CSP2 ) The ratio of the number of carbon atoms taking an orbit (N _CSP3 ) ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] is 30% or more and 65% or less. is there.

The present invention also relates to an electrophotographic apparatus having a charged object and a corona charger for charging the charged object by corona discharge.
The charged body is an electrophotographic photosensitive member,
The electrophotographic apparatus is characterized in that the corona charger is the corona charger of the present invention.

  According to the present invention, it is possible to provide a corona charger having a plate-like grid electrode having a protective film that is difficult to peel off, and an electrophotographic apparatus having the corona charger.

It is a figure which shows the corona charger of this invention. It is a ternary phase diagram for demonstrating the structure of the film | membrane formed with hydrogenated amorphous carbon. It is a figure which shows the physical property of the protective film which the plate-shaped grid electrode of the corona charger of this invention has. It is a figure which shows the film-forming apparatus for forming the protective film which the plate-shaped grid electrode of the corona charger of this invention has. It is a figure which shows the film-forming apparatus for forming the protective film which the plate-shaped grid electrode of the corona charger of this invention has. It is a figure which shows the physical property of a protective film. It is a figure which shows the physical property of a protective film. It is a figure which shows the electrophotographic apparatus which has a corona charger of this invention.

  The corona charger of the present invention will be described with reference to FIG.

(About corona charger)
FIG. 1 is a diagram showing a corona charger according to the present invention. FIG. 1A is a cross-sectional view of a corona charger and a member to be charged arranged to charge a member to be charged (the surface of the member to be charged). In FIG. 1A, the member to be charged is an electrophotographic photosensitive member 110.

  A charging bias is applied to the discharge wire 101 by a high voltage power supply (not shown). A grid bias is applied to the substrate 105 of the plate-like grid electrode by a grid bias power source (not shown). The housing 102 is grounded. As a result, electric charges are discharged from the discharge wire 101 by an electric field formed by the discharge wire 101 and the grounded casing 102 and the base plate 105 of the plate-like grid electrode.

  The electric charge discharged from the discharge wire 101 passes through the opening (hole) 106 of the plate-like grid electrode due to the grid bias applied to the substrate 105 of the plate-like grid electrode, and the surface (surface) of the electrophotographic photoreceptor 110. The number reaching the surface of the layer 111 is controlled.

  FIG. 1B is a view of the plate-like grid electrode 103 viewed from the electrophotographic photosensitive member side. The openings (holes) 106 of the plate-like grid electrode are formed in a mesh shape at a desired angle and a desired opening width with respect to the longitudinal direction as shown in FIG. As a method for forming the opening 106, for example, a method of performing an etching process on a plate-like member made of stainless steel can be cited. In order to perform an etching process efficiently, it is preferable to make a plate-shaped member thin, and material cost can also be suppressed by making it thin.

When the corona charger is operated in the air with a negative polarity in particular, the charge released from the discharge wire 101 reacts with the air to be ionized including oxygen such as nitrogen oxide ions (NOx ⁻ ). A discharge product is generated in the vicinity of the discharge wire 101. Some of these ionized discharge products pass through the opening 106 and fly to the electrophotographic photosensitive member 110, but some fly to the plate-like grid electrode 103.

  When the ionized discharge product flying to the plate-like grid electrode 103 reaches the substrate 105 of the plate-like grid electrode, the substrate 105 is corroded. However, the protective film 104 covering the base material 105 of the plate-like grid electrode suppresses the arrival of ionized discharge products to the base material 105 of the plate-like grid electrode, and prevents the base material 105 from corroding.

  In the corona charger according to the present invention, the protective film 104 covering the base material 105 of the plate-like grid electrode is formed of hydrogenated amorphous carbon having a specific structure.

  FIG. 2 is a ternary phase diagram for explaining the structure of a film formed of hydrogenated amorphous carbon.

(About the ternary phase diagram)
First, the ternary phase diagram of FIG. 2 will be described.

  The carbon atoms constituting the film formed of hydrogenated amorphous carbon take an orbital state of either the sp2 hybrid orbital or the sp3 hybrid orbital.

  The vertex g of the ternary phase diagram shows a film (graphite) in which there are no hydrogen atoms contained in the film and all the carbon atoms take sp2 hybrid orbitals. The vertex d indicates a film (diamond) in which no hydrogen atoms are contained in the film and all the carbon atoms have sp3 hybrid orbitals. Hereinafter, a carbon atom having an sp2 hybrid orbital is also referred to as “sp2 carbon atom”, and a carbon atom having an sp3 hybrid orbital is also referred to as “sp3 carbon atom”.

The film on the side connecting the apex g and the apex d is a ratio of hydrogen atoms (N _H ) to the sum (N _C + N _H ) of the number of carbon atoms (N _C ) and the number of hydrogen atoms (N _H ) in the film. ((N _H / (N _C + N _H )) × 100) [%] is 0%, that is, a film formed of only carbon atoms. Move on this side from vertex g to vertex d. Then, the ratio of the number of sp3 carbon atoms in the film _{(N CSP 3)} and sp2 number of sp3 carbon atoms to the sum _(N CSP3 ₊ N _CSP2) of the number of carbon atoms _{(N CSP2) (N CSP3)} ((N CSP3 / ( N _CSP3 + N _CSP2 )) × 100) [%] shifts from 0% to 100%.

The vertex h indicates a state where the ratio ((N _H / (N _C + N _H )) × 100) [%] is 100%. However, the region Z on the apex h side from the line segment z is a region that becomes a gas and cannot exist as a film. The ratio ((N _H / (N _C + N _H )) × 100) [%] in the film shifts from 0% to 100% from the side connecting the vertex g and the vertex d toward the vertex h. The line segment “a” on the way indicates a film having the above ratio ((N _H / (N _C + N _H )) × 100) [%] of 30%. A line segment b on the apex h side with respect to the line segment a indicates a film having the above ratio ((N _H / (N _C + N _H )) × 100) [%] of 40%. A film in which the ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is 0% at the intersection of the line connecting the vertex g and the vertex h in both the line segment a and the line segment b Indicates that Further, in both the line segment a and the line segment b, the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is 100% at the intersection of the side connecting the vertex d and the vertex h. It shows that it is a film.

The line segment c indicates that the ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is 30%, and the line segment e indicates 65%. In the respective intersections of the edges connecting the vertex g and the vertex h, the ratio ((N _H / (N _C + N _H )) × 100) [%] becomes 0%, and the ratio ( The value of (N _H / (N _C + N _H )) × 100) [%] increases. The structure that the hydrogenated amorphous carbon film can take is a region obtained by excluding the gas region Z from the triangular region connecting the vertex d, vertex g, and vertex h if the defect density in the film is ignored. Be inside.

(Discharge corrosion resistance)
The protective film made of hydrogenated amorphous carbon suppresses the permeation of ionized discharge products generated by corona discharge, and also suppresses the corrosion of the plate-like grid electrode base material, also expressed as “discharge corrosion resistance” To do. A protective film formed of hydrogenated amorphous carbon is also referred to as a “hydrogenated amorphous carbon protective film”.

As a condition of the structure of the protective film having high discharge corrosion resistance, first, the ratio ((N _H / (N _C + N _H )) × 100) [%] needs to be 40% or less. Referring to the ternary phase diagram of FIG. 2, when the ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film is more than 40%, the discharge corrosion resistance is poor. It will be enough. That is, in the case of the protective film in the region excluding the region Z that becomes a gas in the region on the vertex h side from the line segment b in FIG. 2, the discharge corrosion resistance is insufficient.

This is because the protective film in this region is considered to contain a lot of structures such as so-called polymers having a chain-like one-dimensional structure with a carbon atom as a skeleton in a random arrangement. Since structures such as polymers are randomly arranged, they are connected only by weak intermolecular forces, and therefore the film density of the protective film is also low. Due to the low film density, the ionized discharge product flying to the plate grid electrode cannot be sufficiently prevented from transmitting to the base material of the plate grid electrode. Conversely, by reducing the value of the above ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film, the skeleton of the carbon atoms in the protective film has a two-dimensional structure or a three-dimensional structure. Start taking structure. Thereby, since the film density of the protective film increases, it becomes easy to suppress permeation of ionized discharge products to the base material of the plate-like grid electrode.

Furthermore, even if the ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film is 40% or less, the above ratio ( (N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] needs to be 30% or more.

The reason is that, in the region where the above ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] is less than 30%, they are merely bonded to each other with a relatively weak van der Waals force 2. This is because the dimensional structure is considered to form the main part of the protective film. Therefore, the film density of the protective film becomes insufficient, and the permeation of ionized discharge products flying to the plate grid electrode to the substrate of the plate grid electrode cannot be sufficiently suppressed. Note that the region where the above ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] is less than 30% is a region on the vertex g side from the line segment c in FIG. In addition, a two-dimensional structure that is only bonded to each other with a relatively weak van der Waals force may be a graphene structure composed of sp2 carbon atoms.

Conversely, in the _region where the above ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] is 30% or more, the three-dimensional structure formed by sp3 carbon atoms is in the protective film as such. Therefore, the film density of the protective film is increased. Therefore, the permeation | transmission to the base material of the plate-like grid electrode of the ionized discharge product is suppressed, and sufficient discharge corrosion resistance is obtained. Note that the region in which the above ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] is 30% or more is a region on the vertex d side from the line segment c in FIG.

That is, the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] needs to be 30% or more and 40% or less.

(About elastic deformation)
The ability of the protective film coated on the substrate of the plate grid electrode to elastically deform against deformation such as bending or vibration of the substrate of the plate grid electrode is also referred to as “elastic deformation”.

The region on the side connecting the vertex g and the vertex d with respect to the line segment a in FIG. 2, that is, the ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film is 30%. When the protective film in the region below is thickened to about 5 μm, sufficient elastic deformability cannot be obtained. That is, the protective film in the region where the ratio ((N _H / (N _C + N _H )) × 100) [%] is less than 30% is elastic against deformation such as bending or vibration of the base material of the plate-like grid electrode. Difficult to deform. As a result, plastic deformation, cracking or cleavage occurs, and micro-peeling associated therewith easily occurs.

On the contrary, if the ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film is 30% or more, it is sufficient even if the thickness of the protective film is as thick as about 5 μm. Elastic deformation is obtained.

(About volume resistivity)
It is preferable to suppress corrosion of the base material of the plate-like grid electrode by the protective film and to lower the volume resistivity of the protective film.

  The reason is that if the volume resistivity of the protective film is large, the charge discharged from the discharge wire and reaching the plate grid electrode during operation of the corona charger passes through the protective film and passes through the protective film. This is because it is difficult to flow into the base material. As a result, the surface of the protective film is easily charged up. By this charge-up, the amount of electric charge that reaches the surface of the electrophotographic photosensitive member avoiding the plate-like grid electrode among the electric charges emitted from the discharge wire increases. As a result, when continuously outputting images from the electrophotographic apparatus, the density changes according to the number of output sheets. For example, when negative charge and negative toner are used and IAE (Image Area Exposure) is adopted, the density becomes lower than the desired density.

Therefore, it is preferable to reduce the volume resistivity of the protective film. Specifically, it is preferably 10 ⁸ Ωcm or less.

The volume resistivity of the hydrogenated amorphous carbon protective film also depends on the density of structural defects such as dangling bonds present in the protective film. Therefore, although it is not uniquely determined on the ternary phase diagram, there is a general tendency depending on the position on the ternary phase diagram. That is, a structure having more sp3 carbon atoms than sp2 carbon atoms has a large band gap, and the volume resistivity of the protective film increases as the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] increases. Tend to grow. The volume resistivity of the protective film can be about 10 ⁸ Ωcm or more and about 10 ⁹ Ωcm or less at the density of structural defects of the protective film formed by the method described later. Even within that range, the volume resistivity can be lowered by _{setting the} ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] to 65% or less. That is, a region closer to the vertex g than the line segment e in FIG.

  Based on the above, the protective film having sufficient elastic deformation and sufficient discharge corrosion resistance and difficult to charge up is a region partitioned by line segments a, b, c and e in FIG. , A protective film having a structure in region A. If the protective film is in this region, minute peeling is suppressed, corrosion of the base material of the plate-like grid electrode is suppressed, charge-up is suppressed, and the image quality of the output image can be kept good.

Among the regions A, a more preferable protective film is a film in the region B in FIG. In other words, the line segment f in FIG. 3 has the above ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] of 50%. The film in the region B, that is, the region B is preferable.

In the case of employing negative charging, it is preferable to include Group 13 atoms of the periodic table such as boron atoms in the protective film of hydrogenated amorphous carbon. In this case, the conductivity of the protective film against electrons emitted from the discharge wire can be increased, and the volume resistivity of the protective film can be lowered to 10 ⁷ Ωcm or less.

That is, the ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is preferably 30% or more and 65% or less, and more preferably 30% or more and 50% or less.

(About film formation method)
Examples of a method for forming a protective film of hydrogenated amorphous carbon include a plasma CVD method.

  As the plasma CVD method, for example, RF (Radio Frequency) power is applied to one of two electrodes facing each other, plasma is generated between the electrodes, and the source gas flowing between the electrodes is decomposed. And an RF plasma CVD method for forming a film. Alternatively, a rectangular wave voltage having a frequency of 1 MHz or less may be applied to one of two opposing electrodes to generate plasma between the electrodes.

  When the hydrogenated amorphous carbon protective film is formed by plasma CVD, a hydrocarbon gas can be used as the source gas. Examples of the hydrocarbon gas include saturated hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, heptane, octane, isobutane, isopentane, and neopentane. In addition, saturated hydrocarbons such as isohexane, neohexane, dimethylbutane, methylhexane, ethylpentane, dimethylpentane, triptan, methylheptane, dimethylhexane, trimethylpentane, and isonone are also included. Further, unsaturated hydrocarbons containing a double bond or a triple bond such as ethylene, acetylene and benzene are also included.

When the protective film contains periodic group 13 atoms such as boron atoms, together with the hydrocarbon gas, periodic table group 13 such as diborane (B ₂ H ₆ ) and boron trifluoride (BF ₃ ). A gas containing atoms can be used.

The ratio of sp2 carbon atoms and sp3 carbon atoms in the protective film can be adjusted by conditions such as the type of gas, power (RF power), pressure during reaction, and temperature of the substrate. In addition, the above-described ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film and the content of a structure such as a polymer can be adjusted.

Further, during the formation of the protective film by the plasma CVD method, hydrogen atoms contained in the formed protective film are obtained by diluting a hydrocarbon-based gas, which is a raw material gas introduced into the film forming apparatus, with hydrogen gas. May be pulled out. Therefore, the ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film can be controlled to some extent by dilution with hydrogen gas.

  It is also possible to control the structure of the protective film by using an inert gas such as argon gas or helium gas as a diluent gas for the hydrocarbon-based gas that is a raw material gas introduced into the film forming apparatus. It is.

  A film forming apparatus for forming a protective film of the plate-like grid electrode by RF plasma CVD will be described with reference to FIG.

  A film forming apparatus 400 shown in FIG. 4 is a diode type plasma CVD apparatus. In the film forming apparatus 400, a plate-like grid electrode base material 431 is disposed on the base-side electrode 403 inside a container 407 made of an insulating member. The base material 431 is electrically connected to the electrode 403 on the base material side. The substrate-side electrode 403 includes a heater 405 disposed therein and a substrate-side electrode conductive member 404, and the substrate-side electrode conductive member 404 is grounded. A counter electrode 401 is disposed to face the electrode 403 on the substrate side. When RF power is applied from the RF power source 406 to the counter electrode 401, plasma is generated in the space 410. The counter electrode 401 includes a conductive member 402 serving as a counter electrode. The conductive member 402 of the counter electrode is provided with a gas flow path 408 for introducing the raw material gas and the dilution gas into the space 410 from a gas supply facility (not shown). The gas flow path 408 is connected to a gas supply facility (not shown) through a gas supply pipe 421. The space 410 is evacuated through an exhaust pipe 422 to an appropriate pressure below atmospheric pressure for generating desired radical species and ion species by plasma generation from the source gas by an exhaust facility (not shown). . A non-illustrated detoxification device is arranged at the rear stage of the unillustrated exhaust equipment, and the gas discharged from the space 410 is exhausted to the atmosphere after being sufficiently detoxified by the detoxification device.

The ratio ((N _H / (N _C + N _H )) × 100) [%] of the protective film formed by diode type plasma CVD tends to be large.

The main contribution to film formation by diode-type plasma CVD is the diffusion of radicals such as CH ₂ generated in the plasma in the space 410 into the substrate 431 of the plate-like grid electrode.

When radicals such as CH ₂ diffuse and adhere to the surface of the protective film that is being formed on the substrate 431 of the plate-like grid electrode, sp2 hybrid orbitals are formed at the bonds between the carbon atoms in the protective film. Cheap.

  On the other hand, sp3 hybrid orbitals in bonds between carbon atoms are easily formed by allowing carbon atoms to enter into the protective film that has already been formed with a kinetic energy reduced to an appropriate value.

  However, in the diode type plasma CVD, the sheath voltage formed on the electrode 403 on the substrate side is difficult to increase.

Therefore, even if ions containing carbon atoms are generated in the plasma generated in the space 401, it is difficult to accelerate the ions to a sufficient kinetic energy to form sp3 hybrid orbitals in the protective film forming the ions. Therefore, the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] tends to be relatively small.

Therefore, in order to control the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] larger, it is also preferable to use a triode type RF plasma CVD apparatus as shown in FIG.

A film forming apparatus 500 shown in FIG. 5 is a triode type RF plasma CVD apparatus. An intermediate electrode 541 is disposed between the substrate-side electrode 503 and the counter electrode 501. The intermediate electrode 541 is grounded. A base-side power source 542 is connected to the base-side electrode 503. The voltage applied from the substrate-side power source 542 to the substrate-side electrode 503 only needs to have a period during which a negative bias is applied to the intermediate electrode 541, and may be a voltage in which the negative bias is applied in a pulsed manner. At this time, the plasma generated in the triode type RF plasma CVD apparatus 500 is isolated from the surface of the base material 531 of the plate-like grid electrode, and is mostly confined in the space 511. For this reason, diffusion of radicals such as CH ₂ does not easily reach the surface of the base material 531 of the plate-like grid electrode, and it is difficult to contribute to film formation. Therefore, it is relatively easy to suppress an increase in sp2 hybrid orbitals.

On the other hand, ions containing carbon atoms generated in the space 511 can be accelerated by the electric field formed in the space 512 to impart kinetic energy necessary for rushing into the protective film that is being formed. . Therefore, in the triode type RF plasma CVD, the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] is relatively easy to control.

In order to increase the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] of the protective film, the _{filtered cathodic} vacuum arc method (FCVA method) may be good.

In this method, carbon plasma is generated from a carbon target material by vacuum arc discharge, only carbon ions are extracted by a magnetic filter, and the film is being formed to be focused to an appropriate energy by a bias voltage applied to the substrate. Rush into. Therefore, it is easy to increase the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%].

  Further, an ionized vapor deposition method, an arc ion plating method, or the like can also be used.

  However, the plasma CVD method can easily form a film uniformly over a large area compared to other methods. Further, since the structure of the film forming apparatus is simple, there is an advantage in the simplicity of work when maintenance of the film forming apparatus accompanied by the decomposition of the film forming apparatus at the time of mass production is entered.

(About image formation)
An electrophotographic apparatus 800 in FIG. 8 is an electrophotographic apparatus having a corona charger 802 having a plate-like grid electrode 805 having the above-described protective film.

  When forming an image with the electrophotographic apparatus 800, the electrophotographic photosensitive member 801 is rotated and the surface of the electrophotographic photosensitive member 801 is charged by the corona charger 802. Thereafter, the image exposure device 806 irradiates the surface of the electrophotographic photoreceptor 801 with image exposure light, thereby forming an electrostatic latent image on the surface of the electrophotographic photoreceptor 801. Next, a developing device 807 forms a toner image corresponding to the electrostatic latent image on the surface of the electrophotographic photosensitive member 801. Thereafter, the charge of the toner image before primary transfer is adjusted by the pre-transfer charger 818 to facilitate primary transfer, and the toner image is transferred to the intermediate transfer member 808 by the primary transfer roller 809. The pre-transfer charger 818 imparts a charge having an appropriate polarity to the toner depending on whether the image exposure / development method is IAE (Image Area Exposure) or BAE (Background Area Exposure). The primary transfer roller 809 is also applied with a voltage having an appropriate polarity depending on whether the image exposure / development method is IAE or BAE, thereby performing good primary transfer. Then, after secondary transfer by the secondary transfer unit 810 to the paper transported by the paper transport body 811 from the paper feed cassette 812, the toner image is fixed by the fixing unit 813 to form an image. On the other hand, the transfer residual toner is removed from the surface of the electrophotographic photosensitive member 801 that has undergone the primary transfer by the cleaning unit 814. Thereafter, the pre-exposure device 815 irradiates the surface of the electrophotographic photosensitive member 801 with pre-exposure light, whereby the remaining carriers remaining on the electrophotographic photosensitive member 801 are neutralized.

[Example 1 and Comparative Example 1]
In Example 1, a protective film in which the value of the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] was within the region A in FIG. 2 was formed. For forming the protective film, a triode type RF plasma CVD apparatus shown in FIG. 5 was used.

  First, a plate-like grid electrode substrate was placed on the substrate-side electrode in FIG. Thereafter, the electrode on the base material side was heated to 150 ° C., and the pressure of 13.3 Pa was maintained while cyclopropane as a raw material gas was introduced into the plasma CVD apparatus at a flow rate of 15 ccm. Then, RF power of 400 W was applied to the counter electrode, and a rectangular wave voltage with a frequency of 2 kHz and −100 V was applied to the electrode on the substrate side. Thus, plasma was generated in the space between the intermediate electrode and the counter electrode. Then, ions and radicals containing carbon atoms pass through the counter electrode and reach the substrate of the plate-like grid electrode installed on the electrode on the substrate side, so that the hydrogenated amorphous carbon A protective film was formed.

  In Example 1-1, a plate-like grid electrode having a protective film with a film thickness of 1 μm was produced by repeating twice per side of the substrate. In Example 1-2, a plate-like grid electrode was produced in the same manner as in Example 1-1 except that the thickness of the protective film was changed to 2 μm.

Also in Examples 1-3 and 1-4, the value of the ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is the same value as in Examples 1-1 and 1-2. A protective film was formed. However, in Example 1-3, the ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a lower protective film in the region A. Further, in Example 1-4, the ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a protective film on the higher side in the region A.

In Example 1-3, a plate-like shape is obtained in the same manner as in Example 1-1 except that 5 ccm of hydrogen gas as a dilution gas is flowed together with cyclopropane as the raw material gas and the RF power is changed from 400 W to 500 W. A grid electrode was produced. By introducing hydrogen gas and increasing RF power, hydrogen radicals and the like are increased in the plasma. Thereby, a protective film is formed while hydrogen atoms are selectively etched. In this way, in Example 1-3, the value of the ratio _{((N H / (N C} + N H)) × 100) [%] forms a low protective film.

In Example 1-4, a plate-like grid electrode was produced in the same manner as in Example 1-1 except that the internal pressure of the plasma CVD apparatus was changed from 13.3 Pa to 26.6 Pa. As the pressure inside the plasma CVD apparatus increases, radicals containing hydrogen atoms increase in the plasma and adhere to the base of the plate-like grid electrode. By doing so, a protective film having a high value of the above ratio ((N _H / (N _C + N _H )) × 100) [%] was formed.

  In Comparative Examples 1-1 and 1-2, a hydrogenated amorphous carbon protective film was formed on the base of the plate-like grid electrode by the FCVA method. That is, carbon plasma was generated from a solid carbon target by vacuum arc discharge. And only the ionized carbon atom was extracted with the magnetic filter, and the base material of the plate-shaped grid electrode applied to -100V was irradiated. By this method, the formation of the protective film on the substrate of the plate-like grid electrode was repeated twice per side, and in Example 1-1, a plate-like grid electrode having a protective layer with a film thickness of 0.3 μm was produced. did. In Comparative Example 1-2, a plate-like grid electrode was produced in the same manner as Comparative Example 1-1 except that the thickness of the protective layer was changed to 1 μm.

The hydrogenated amorphous carbon film formed by this method usually has a high value of the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%], and the above ratio ((N _H / (N _C + N _H )) × 100) [%] value is a very low film. Such a film is generally called a tetrahedral amorphous carbon film and has been used as a protective film for a conventional plate grid electrode.

In Comparative Examples 1-3 and 1-4, the value of the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is the same value as in Examples 1-1 and 1-2. A protective film was formed. However, in Comparative Example 1-3, the ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a lower protective film outside the region A. Further, in Comparative Example 1-4, the ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a protective film on the higher side outside the region A.

  In Comparative Example 1-3, 10 ccm of hydrogen gas as a dilution gas was flowed together with cyclopropane as the raw material gas, and the RF power was changed from 400 W to 600 W. Except for these, a protective film was formed in the same manner as in Example 1-1.

  In Comparative Example 1-4, a plate-like grid electrode was produced in the same manner as in Example 1-1 except that the pressure inside the plasma CVD apparatus was changed from 13.3 Pa to 133.3 Pa.

  The physical property values of the protective films of Example 1 and Comparative Example 1 were measured by the following measurement methods.

(Measurement method of the above ratio ((N _H / (N _C + N _H )) × 100) [%])
A sample was cut out from a plate-like grid electrode having a protective film. Using RBS (Rutherford backscattering method), the backscattering measurement device (trade name: AN-2500, manufactured by Nissin High Voltage Co., Ltd.), atoms with respect to the scattering energy of carbon atoms in the sample in the RBS measurement area Number distribution was measured.

  Furthermore, the atomic number distribution with respect to the scattering energy of the hydrogen atom in the sample in the measurement area of HFS was measured by the backscattering measurement apparatus using HFS (hydrogen forward scattering method) simultaneously with RBS.

  Then, from the film thickness of the protective film measured by ellipsometry, which will be described later, and the atomic number distribution with respect to the scattering energy of hydrogen atoms and carbon atoms, the distribution with respect to the distance in the film thickness direction of each atom number in the measurement area of RBS and HFS Calculated.

  That is, the energy of the scattered atoms is reduced according to the distance passing through the medium, but the thickness direction of each number of atoms is obtained by associating the distribution of the resulting number of atoms with respect to the energy and the thickness of the protective film. The distribution of was calculated.

Then, the average value in the film thickness direction of the ratio ((N _H / (N _C + N _H )) × 100) [%] in the protective film was calculated.

In Example 1 and Comparative Example 1, the deviation from the average value of the maximum value and the minimum value in the film thickness direction of the above ratio ((N _H / (N _C + N _H )) × 100) [%] The value is less than 3%, and it is considered that there is no significant influence.

Specific measurement conditions for RBS and HFS are incident ion: ⁴ He ⁺ , incident energy: 2.3 MeV, incident angle: 75 °, sample current: 35 nA, and incident beam length: 1 mm. The RBS detector has a scattering angle of 160 ° and an aperture diameter of 8 mm. The detector of HFS has a recoil angle of 30 ° and an aperture diameter of 8 mm + Slit.

(Measurement method of the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%])
A sample was cut out from a plate-like grid electrode having a protective film. Using XPS (X-ray photoelectron spectroscopy), the sample was introduced into a measurement position in a measurement apparatus (trade name: VersaProbe II, manufactured by ULVAC-PHI).

  Thereafter, the sample is irradiated with X-rays, and the excited electrons emitted along with the sample are received by a detector. From the received binding energy spectrum of the number of excited electrons per unit time, the carbon atoms contained in the protective film are The ratio of electron orbital state was calculated.

  Specifically, the binding energy spectrum was measured by limiting the binding energy range that can be taken by the excited electrons from the 1s orbital of the carbon atom to 278 eV or more and 298 eV or less. By doing so, it was possible to obtain spectral data with high resolution within a realistic measurement time.

In the sp2 carbon atom, the excited electron from the 1s orbit takes a peak at a binding energy of 284.5 eV, and in the sp3 carbon atom, the excited electron from the 1s orbit takes a peak at a binding energy of 285.4 eV. From this, the binding energy spectrum of the excited electrons from the carbon atom 1s orbit was measured (waveform separation) by superimposing the distribution functions having peaks at the binding energies of 284.5 eV and 285.4 eV. Each distribution function is a convolution of a Lorentz distribution function and a Gaussian distribution function. The ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] from the integrated value (area) of the distribution function corresponding to the fitted sp2 hybrid orbitals and sp3 hybrid orbitals with respect to the binding energy. ] Was calculated.

Furthermore, the protective film was shaved little by little by performing argon sputtering, and the above measurement was repeated. This was repeated until all the protective film was removed and averaged in the film thickness direction. This is because electrons excited by X-rays are emitted only from the region of the extreme outermost layer such as several nanometers, and thus the above ratio of the entire protective film ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [%] It is done to ask for.

(Measurement method of volume resistivity)
It was measured by the double ring electrode method.

  Specifically, a circular back electrode having a diameter of 83 mm is mask-deposited on a glass substrate by vapor deposition of chromium, and then a hydrogenated amorphous carbon with a diameter of 100 mm is formed under the same film formation conditions as in the above-described Examples and Comparative Examples. A film was formed. On the hydrogenated amorphous carbon film, a mask electrode is formed by chromium deposition on a surface electrode composed of a circular inner electrode having a diameter of 50 mm and an outer electrode having a ring shape having an inner diameter of 70 mm and an outer diameter of 80 mm surrounding the inner electrode. did.

  A potential difference was applied between the front electrode and the back electrode, and the volume resistivity was calculated from the relationship between the potential difference and the current flowing through the internal electrode.

Of the physical property values of the protective film, the ratio ((N _H / (N _C + N _H )) × 100) [%] and the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [% The positions on the ternary phase diagram of Example 1 and Comparative Example 1 are shown in FIG.

  Next, the performance (elastic deformation, discharge corrosion resistance, durability, concentration deviation) of the protective film of Example 1 and Comparative Example 1 is evaluated by the following evaluation methods and standards, and from A according to the results of each evaluation. D was ranked. In this rank, C is the same level as that of Comparative Example 1-1, indicating that it is at the same level as the prior art. D shows that it is inferior to the comparative example 1-1, and shows that it does not reach the level of the prior art. A and B show that the performance of the present invention is improved by the present invention as compared with the prior art, and the effect of the present invention is shown.

(Evaluation method for elastic deformation)
Bend with a radius of curvature of 100 mm and hold for 5 seconds so that the front side (discharge wire side) of the center part in the longitudinal direction of the plate-like grid electrode having a protective film is outside, and then return to the original state. It was bent and returned under the same conditions. This was repeated 20 times.

  Such bending with a radius of curvature is a stronger bending than the bending that occurs when the plate-like grid electrode is attached to or removed from the housing of the corona charger, and is evaluated under severe conditions.

  Thereafter, a corona charger equipped with a plate-like grid electrode was operated. Specifically, a current (−1000 μA) flowing through the discharge wire and a voltage (−500 V) applied to the plate-like grid electrode necessary for obtaining a desired amount of charge on the surface of the electrophotographic photosensitive member are applied, The corona charger was operated for 10 hours.

  About the protective film of the plate-like grid electrode which passed through the above evaluation process, the front side and the back side (electrophotographic photoreceptor side) of the central part in the longitudinal direction were observed with an optical microscope to confirm the presence or absence of micro-peeling. When there is micro-peeling, it indicates that the elastic deformation of the protective film is not sufficient.

And according to the observation results, the ranking was as follows.
A: Elastic deformation (no micro-peeling).
D: No elastic deformation (with minute peeling).

  In order to avoid the adverse effect on the measurement environment due to scattering of the film pieces generated by peeling, the protective film finely peeled in this evaluation was not subjected to the following evaluation.

(Evaluation method for discharge corrosion resistance)
After 10 hours of operation of the corona charger performed in the above-described evaluation of elastic deformability, the plate grid electrode was removed from the corona charger, and a sample was cut out from the plate grid electrode. Using XPS (X-ray photoelectron spectroscopy), a sample was introduced into a measurement position in a measurement apparatus (trade name: VersaProbe II, manufactured by ULVAC-PHI).

  Thereafter, the sample is irradiated with X-rays, and the excited electrons emitted by the sample are received by the detector. From the received binding energy spectrum of the number of excited electrons per unit time, the atomic ratio contained in the protective film is calculated. Calculated.

  Specifically, the binding energy spectrum was measured by limiting to a binding energy range that can be taken by excited electrons from atoms assumed to be contained in the base material of the protective film and the plate-like grid electrode. By doing so, it was possible to obtain spectral data with high resolution within a realistic measurement time. Here, it corresponds to iron atoms (Fe) and chromium atoms (Cr) which are constituent atoms of the base material of the plate-like grid electrode, and carbon atoms (C) and oxygen atoms (O) which are constituent atoms of the protective film. The measurement was limited to the binding energy spectrum.

And for each atom, from the integrated value (area) of the number of detected excitation electrons per unit time with respect to the binding energy,
Oxygen atoms relative to the sum of the number of carbon atoms (N _C ), the number of oxygen atoms (N _O ), the number of iron atoms (N _Fe ), and the number of chromium atoms (N _Cr ) (N _C + N _O + N _Fe + N _Cr ) ratio of the number of _{(N O) ((N O} / (N C + N O + N Fe + N Cr)) × 100) [%]
Was calculated.

Further, by performing argon sputtering, the protective film and part of the base material of the plate-like grid electrode were scraped little by little, and the above measurement was repeated. In this way, the ratio _{((N O / (N C} + N O + N Fe + N Cr)) × 100) [%] thickness direction of the distribution is obtained.

Oxygen atoms are often contained in ionized discharge products generated in the vicinity of the discharge wire by corona discharge in the air. Therefore, the ratio _{((N O / (N C} + N O + N Fe + N Cr)) × 100) from the thickness direction of the distribution of [%], discharge products are ionized and flying to the protective layer of the plate-like grid electrode Can pass through the protective film and determine whether or not the base material of the plate-like grid electrode has been reached. If the ionized discharge product passes through the protective film, iron atoms and chromium atoms which are constituent atoms of the base material of the plate-like grid electrode are oxidized. Then, the peak of their binding energy shifts. Furthermore, oxygen atoms are detected at the interface between the protective film and the substrate of the plate-like grid electrode, and in some cases, the above ratio ((N 2 _O / (N 2 _C + N 2 _O + N 2 _Fe + N _Cr )) × 100) [% ] In the film thickness direction may have a peak at the interface. Therefore, it can be determined whether or not the protective film has a discharge corrosion resistance.

The results were ranked as follows.
A: Resistance to discharge corrosion.
D: No discharge corrosion resistance.

  When it was determined that there was no discharge corrosion resistance in this evaluation, the following evaluation was not performed.

(Durability evaluation method)
As a method for evaluating the durability of the corona charger, a reduction in the thickness of the protective film by operating the corona charger was measured. Specifically, in the same manner as described above, a current (−1000 μA) flowing through the discharge wire and a voltage (−500 V) applied to the plate-like grid electrode were applied, and the corona charger was operated for 10 hours. Then, after measuring the thickness of the protective film before and after the operation of the corona charger, the operation time of the corona charger is converted into the number of operating sheets assuming that it is used for an electrophotographic apparatus equivalent to 150 sheets / min. The film thickness reduction rate of the protective film was calculated from the film thickness measured before and after operation. A value obtained by integrating the film thickness reduction rate of the protective film with the film thickness before operation of the protective film was defined as the durability value.

  For the evaluation method, the durability value of the protective film in each production condition with respect to the durability value of Comparative Example 1-1 was used as the durability evaluation value, and the durability of the corona charger was determined from this durability evaluation value. The greater the durability evaluation value, the more the protective film can withstand the operation of the corona charger for a long time.

  In addition, the film thickness of the protective film was measured by spectroscopic ellipsometry (manufactured by JA Woollam: high-speed spectroscopic ellipsometry M-2000). Specific measurement conditions of spectroscopic ellipsometry are incident angles: 60 °, 65 °, 70 °, measurement wavelengths: 195 nm to 700 nm, and beam diameter: 1 mm × 2 mm.

  First, using a plate-like grid electrode base material having no protective film as a reference base material, the relationship between the wavelength, the amplitude ratio Ψ, and the phase difference Δ was determined at each incident angle.

  Next, using the result as a reference, the wavelength and amplitude ratio Ψ and phase difference Δ at each incident angle were measured by spectroscopic ellipsometry on a base plate electrode having a protective film before and after the operation of the corona charger. Sought the relationship.

  Then, the volume ratio between the protective film of the roughness layer and the air layer was changed by analysis software, and the relationship between the wavelength at each incident angle, the amplitude ratio Ψ, and the phase difference Δ was obtained by calculation. The mean square error of the relationship between the wavelength and the amplitude ratio Ψ and the phase difference Δ obtained by the above calculation at each incident angle and the relationship between the wavelength and the amplitude ratio Ψ and the phase difference Δ obtained by measuring the measurement sample is minimized. The calculation model was selected. The film thickness of the protective film was calculated by the selected calculation model, and the obtained value was used as the film thickness of the protective film. The analysis software is J.I. A. WVASE32 (trade name) manufactured by Woollam was used. The volume ratio of the protective film of the roughness layer to the air layer was calculated by changing the ratio of the air layer in the roughness layer by 1 from 10: 0 to 1: 9 in the protective film: air layer. In Example 1 and Comparative Example 1, the relationship between the wavelength, the amplitude ratio Ψ, and the phase difference Δ obtained by calculation when the volume ratio of the protective film of the roughness layer to the air layer was 9: 1 was obtained by measurement. The mean square error of the relationship between wavelength, amplitude ratio Ψ and phase difference Δ was minimized.

And according to the above-mentioned durability evaluation value, it ranked as follows.
A: The durability evaluation value is 3.0 or more.
B: The durability evaluation value is 2.0 or more and less than 3.0.
C: The durability evaluation value is 1.0 or more and less than 2.0.
D: The durability evaluation value is less than 1.0.

(Evaluation method of density deviation)
This was carried out using a modified machine of a digital electrophotographic apparatus “image RUNNER ADVANCE C7065” (trade name) manufactured by Canon Inc. The image data can be directly output without using a printer driver, and the area gradation image (that is, the image) of the area gradation dot screen at a line density of 45 °, 212 lpi (212 lines per inch) by image exposure light. The area gradation of the dot portion to be exposed) was output.

  As the area gradation image, gradation data uniformly distributed in 17 levels was used. The darkest gradation is set to 17, the thinnest gradation is set to 0, and a number is assigned to each gradation to make a gradation step.

  The modified machine is an IAE system using a negative charging electrophotographic photosensitive member and a negative toner.

  Next, the prepared corona charger was installed in the modified machine, and output to A3 paper using the gradation data using the text mode. In order to exclude the influence of high-humidity flow, the condition that the surface of the electrophotographic photosensitive member is kept at about 40 ° C. with the heater for the electrophotographic photosensitive member turned on in an environment of a temperature of 22 ° C. and a relative humidity of 50%. Output 100 images. Then, at the central portion in the longitudinal direction of the corona charger, the average value of the last three image densities of the 100 images output by the reflection densitometer (X-Rite Inc: 504 spectral densitometer) is calculated for each floor. Measured for each key.

  A value obtained by averaging the absolute value of the difference between the average value of the image density at each gradation and the gradation value obtained in this way at 17 gradations was calculated. This value was defined as a density deviation value. The larger the density deviation value from 0.00, the larger the deviation from the desired image density.

  For the evaluation method, the ratio of the density deviation value in the protective film in each production condition is the density deviation evaluation value with respect to the density deviation value of the corona charger produced in Comparative Example 1-1. Then, it was evaluated whether or not the concentration was output appropriately. That is, as the density deviation evaluation value is closer to 0.00, a desired density is output, indicating that the protective film of the corona charger is more excellent.

The ranking was as follows.
A: The density deviation evaluation value is 0.50 or less.
B: Density deviation evaluation value is larger than 0.50 and 0.75 or less.
C: Density deviation evaluation value is larger than 0.75 and 1.00 or less.
D: The density deviation evaluation value is larger than 1.00.

  Among the ranks given by the above evaluations, the lowest rank was set as the overall evaluation rank. Table 1 shows the measurement results of the physical property values of the protective film of hydrogenated amorphous carbon formed in Example 1 and Comparative Example 1, and the evaluation results of the performance of the corona charger having the protective film on the plate-like grid electrode. Show.

The protective film of tetrahedral amorphous carbon formed in Comparative Example 1-1 is comparable to the prior art. From this, it was found that when the film thickness is increased with the aim of further extending the life (Comparative Example 1-2), minute peeling occurs and the elastic deformability becomes insufficient. Further, even in the hydrogenated amorphous carbon film (Comparative Example 1-3) in which the ratio ((N _H / (N _C + N _H )) × 100) [%] was less than 30%, micro-separation occurred. Further, in the hydrogenated amorphous carbon film (Comparative Example 1-4) in which the ratio ((N _H / (N _C + N _H )) × 100) [%] is larger than 40%, the substrate of the plate-like grid electrode is used. The surface was corroded. In Example 1-2, the film thickness was increased in order to extend the life compared to Example 1-1, but micro-peeling did not occur, and both the maintenance of elastic deformability and the improvement of durability were achieved. .

[Example 2 and Comparative Example 2]
In Example 2-1, a protective film was formed in which the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] value was within the region B in FIG. A diode type plasma CVD apparatus shown in FIG. 4 was used for forming the protective film.

  First, a plate-like grid electrode substrate was placed on the substrate-side electrode of FIG. Thereafter, the electrode on the substrate side was heated to 150 ° C., and the pressure of 13.3 Pa was maintained while introducing methane as a raw material gas into the plasma CVD apparatus at a flow rate of 100 ccm. Then, 400 W of RF power was applied to the counter electrode.

Also in Examples 2-2 and 2-3, the protective film was formed so that the value of the above ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] was the same value as in Example 2-1. Formed. However, in Example 2-1, the above ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a protective film on the higher side in the region B. Further, in Example 2-2, the ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a lower protective film in the region B.

  In Example 2-2, a plate-like grid electrode was produced in the same manner as in Example 2-1, except that the internal pressure of the plasma CVD apparatus was changed from 13.3 Pa to 26.6 Pa.

  In Example 2-3, a plate-like grid is formed in the same manner as in Example 2-1, except that 20 ccm of hydrogen gas as a dilution gas is flowed together with methane as the raw material gas, and the RF power is changed from 400 W to 500 W. An electrode was produced.

Also in Comparative Examples 2-1 and 2-2, the protective film was formed so that the ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] was the same value as in Example 2-1. Formed. However, in Comparative Example 2-1, the above ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a protective film on the higher side outside the region B. Further, in Comparative Example 2-2, the ratio ((N _H / (N _C + N _H )) × 100) [%] was set to be a lower protective film outside the region B.

  In Comparative Example 2-1, a plate-like grid electrode was produced in the same manner as in Example 2-1, except that the internal pressure of the plasma CVD apparatus was changed from 13.3 Pa to 133.3 Pa.

  In Comparative Example 2-2, a plate-like grid electrode was prepared in the same manner as in Example 2-1, except that 60 ccm of hydrogen gas as a dilution gas was flowed together with methane as the raw material gas and the RF power was changed from 400 W to 600 W. Was made.

  Each physical property value of the protective film of Example 2 and Comparative Example 2 was measured by the same measurement method as in Example 1 and Comparative Example 1.

Of the physical property values of the protective film, the ratio ((N _H / (N _C + N _H )) × 100) [%] and the ratio ((N _CSP3 / (N _CSP2 + N _CSP3 )) × 100) [% The positions on the ternary phase diagram of Example 2 and Comparative Example 2 are shown in FIG.

  Further, the performances (elastic deformation property, discharge corrosion resistance, durability, concentration deviation) of the protective films of Example 2 and Comparative Example 2 were evaluated by the same evaluation methods and standards as in Example 1 and Comparative Example 1.

In the hydrogenated amorphous carbon film (Comparative Example 2-2) in which the ratio ((N _H / (N _C + N _H )) × 100) [%] was less than 30%, micro-separation occurred. Further, in the hydrogenated amorphous carbon film (Comparative Example 2-1) in which the above ratio ((N _H / (N _C + N _H )) × 100) [%] is larger than 40%, the substrate of the plate-like grid electrode is used. The surface was corroded. Moreover, in Example 2-1, the volume resistivity has decreased with respect to Example 1-1. Therefore, the density deviation is improved. This is because the protective film of Example 2-1 is a hydrogenated amorphous carbon film having a small ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%]. It is thought that it was possible to suppress. As a result, the protective film of Example 2-1 is a high-performance protective film that is less susceptible to concentration shift than the protective film of Example 1-1.

Example 3
In Example 3, in order to further improve the concentration shift with respect to the protective film of Example 2, the conductivity for electrons was increased by doping the hydrogenated amorphous carbon of the protective film with boron atoms.

Specifically, with respect to the sum of the number of carbon atoms contained in the protective film _{(N C)} and the number of boron atoms _{(N B) (N C +} N B), the number of boron atoms _{(N B)} The ratio ((N _B / (N _C + N _B )) × 10 ⁶ )
0.1 ppm (Example 3-1),
5 ppm (Example 3-2),
3000 ppm (Example 3-3)
Then, a protective film was formed by flowing diborane simultaneously with methane as the raw material gas. As the physical properties of the protective film, the above ratio ((N _B / (N _C + N _B )) × 10 ⁶ ) was measured by the following method.

(Measurement method of the above ratio ((N _B / (N _C + N _B )) × 10 ⁶ ))
A sample was cut out from a plate-like grid electrode having a protective film. Distribution of the number of atoms per unit volume of boron atoms and carbon atoms in the protective film in the film thickness direction using a measuring device (trade name: IMS-6f, manufactured by CAMECA) using SIMS (secondary ion mass spectrometry) Was measured.

Then, to calculate the average value of the film thickness direction of the ratio in the protective layer _{((N B / (N C} + N B)) × 10 6).

Each physical property value other than the above-mentioned ratio ((N _B / (N _C + N _B )) × 10 ⁶ ) of the protective film of Example 3 was measured by the same measurement method as in Example 1 and Comparative Example 1.

  Moreover, the performance (elastic deformation property, discharge corrosion resistance, durability, concentration shift) of the protective film of Example 3 was evaluated by the same evaluation method and standard as Example 1 and Comparative Example 1.

In Example 3, by doping boron atoms into the hydrogenated amorphous carbon of the protective film, the volume resistivity is further suppressed as compared with the protective film of Example 2, and thus the concentration deviation is further improved. In addition, as the ratio ((N _B / (N _C + N _B )) × 10 ⁶ ) increases to 0.1 ppm, 5 ppm, and 3000 ppm, the volume resistivity of the protective film decreases, and the charge increases. It is difficult to protect. On the other hand, no other adverse effects were found. Therefore, it was found that a more preferable protective film can be formed by doping boron atoms into hydrogenated amorphous carbon within the range of 0.1 ppm to 3000 ppm.

DESCRIPTION OF SYMBOLS 100 Corona charger 101 Discharge wire 102 Housing 103 Plate-like grid electrode 104 Protective film 105 Base material of plate-like grid electrode 106 Opening 110 Electrophotographic photoreceptor 111 Surface layer 112 Upper charge injection blocking layer 113 Photoconductive layer 114 Lower charge injection Blocking layer 115 Base of electrophotographic photosensitive member

Claims (8)

A corona charger for charging an object to be charged by corona discharge,
A housing having an opening facing the body to be charged,
A discharge wire provided inside the housing; and
In the corona charger having a plate-like grid electrode provided in the opening,
The plate-like grid electrode is
A substrate, and
A protective film formed of hydrogenated amorphous carbon on the substrate;
Ratio of number of hydrogen atoms to the sum _(N C + N _H) of the number of carbon atoms contained in the protective film _{(N C)} of the number of hydrogen atoms _{(N H) (N H)} ((N H / (N _C + N _H )) × 100) [%] is 30% or more and 40% or less,
Of the carbon atoms contained in the protective film, sp3 hybrid to the sum (N _CSP3 + N _CSP2 ) of the number of carbon atoms taking the sp3 hybrid orbital (N _CSP3 ) and the number of carbon atoms taking the sp2 hybrid orbital (N _CSP2 ) A corona charger, wherein the number of carbon atoms taking an orbit (N _CSP3 ) ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is 30% or more and 65% or less. 2. The corona charger according to claim 1, wherein the ratio ((N _CSP3 / (N _CSP3 + N _CSP2 )) × 100) [%] is 30% or more and 50% or less. The corona charger according to claim 1 or 2, wherein the protective film has a volume resistivity of 10 ⁸ Ωcm or less.   The corona charger according to claim 1, wherein the protective film contains Group 13 atoms of the periodic table.   The corona charger according to claim 4, wherein the group 13 atom of the periodic table is a boron atom. The corona charger according to claim 5, wherein a ratio of the number of boron atoms (N _B ) to the number of carbon atoms (N _C ) contained in the protective film is 0.1 ppm or more and 3000 ppm or less.   The corona charger according to claim 1, wherein the substrate is a substrate formed of stainless steel. In an electrophotographic apparatus having an object to be charged and a corona charger for charging the object to be charged by corona discharge,
The charged body is an electrophotographic photosensitive member,
An electrophotographic apparatus, wherein the corona charger is the corona charger according to any one of claims 1 to 7.

Images