JP2007025647A - Electrophotographic charging member and electrophotographic image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic charging member that restrains toner or an addition agent from being stuck to the surface of a charging member, so as to solve the problem of image deterioration caused by sticking of them, and to provide an electrophotographic image forming apparatus using the electrophotographic charging member. <P>SOLUTION: The electrophotographic charging member has an elastic layer containing semiconductive particles and having a threshold of 5×10<SP>5</SP>Ω or greater in impedance at a frequency of 20 Hz. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charging member used in an electrophotographic image forming apparatus such as a copying machine or a printer using an electrophotographic developing system, and an electrophotographic image forming apparatus using the charging member.

  Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a charging roll (contact charging member) brought into contact with a photosensitive drum (image carrier) is applied with a charging voltage using a power source. A charging device that uniformly charges the surface of a photosensitive drum to a predetermined potential is known.

  Such a charging roll has a conductive solid structure rubber composition or sponge structure foam in which conductive particles such as carbon black and metal powder are added to the outer peripheral surface of a shaft (core metal). The conductive elastic body layer formed using is provided with a predetermined thickness.

  In such a charging device, if a toner such as transfer residual toner or an external additive adhering to the surface of the photosensitive drum is transferred and adheres to the surface of the charging roll and is fixed, a charging failure occurs and the image quality deteriorates. It becomes a problem.

  As a countermeasure for this, for example, a method in which dirt on the surface of the charging roll is transferred to the surface of the photosensitive drum by rubbing between the surface of the charging roll and the surface of the photosensitive drum, based on the fact that the charging roll is driven by rotation of the photosensitive drum, A method of wiping dirt off by gently pressing a cleaning member such as a sponge on the roll surface has been used, but the former has insufficient removability of toner and external additives, and the latter may damage the charging roll. is there.

  Further, in order to remove the positively charged toner adhering to the charging roll, a negative voltage is applied to the transfer roll to charge the photosensitive drum to a negative polarity, and a positive voltage is applied to the charging roll. A method of transferring a positively charged toner on a charging roll to a photosensitive drum by forming a strong electric field between the negative charging roll and the negative photosensitive drum is disclosed (for example, see Patent Document 1).

Further, a resin composition further comprising a non- (fluorine-modified) acrylate resin having a glass transition temperature higher than that of the binder resin of the toner together with a fluorine-modified acrylate resin and a fluorinated olefin resin as a protective layer of the charging roll. And a method for suppressing or preventing toner adhesion and external additive adhesion to the roll surface (see, for example, Patent Document 2).
JP-A-10-161500 JP 2001-154456 A

  The method disclosed in Patent Document 1 has a problem of increasing power consumption and increasing the size of the apparatus.

  Moreover, in the method disclosed in the above-mentioned Patent Document 2, since a fluororesin is used, there is a concern about an environmental load.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electronic device capable of suppressing the adhesion of toner and external additives to the surface of the charging member and thereby solving the problem of image degradation. It is an object to provide a photographic charging member and an electrophotographic image forming apparatus using the same.

The object of the present invention is achieved by the following configurations.
(1)
An electrophotographic charging member comprising an elastic layer containing semiconductive particles and having an impedance having an absolute value of 5 × 10 ⁵ Ω or more at a frequency of 20 Hz.
(2)
The electrophotographic charging member according to (1), wherein the content of the semiconductive particles in the elastic layer is 1% by volume or more and 30% by volume or less.
(3)
The electrophotographic charging member according to (1) or (2), wherein the semiconductive particles have a volume resistivity of 10 ³ Ω · cm to 10 ⁸ Ω · cm.
(4)
The semiconductive particles are semiconductive particles derived from an organic compound having a residual ratio of 20% by mass to 95% by mass when the organic compound is heat-treated at a temperature of 800 ° C. in a nitrogen atmosphere. The charging member for electrophotography according to any one of (1) to (3).
(5)
The electroconductive particle according to (4), wherein the semiconductive particles are semiconductive particles obtained by heat-treating the organic compound at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere. Charging member.
(6)
The electrophotographic charging member according to (4) or (5), wherein the organic compound is an organic polymer material.
(7)
The electrophotographic charging member according to (6), wherein the organic polymer material is a phenol resin.
(8)
The electrophotographic charging member according to any one of (1) to (7), wherein the electrophotographic charging member is an electrophotographic charging roll.
(9)
An electrophotographic image forming apparatus using the electrophotographic charging member according to any one of (1) to (8).
(10)
The electrophotographic image forming apparatus according to (9), wherein the electrophotographic charging member is charged in contact with a member to be charged.

  The inventors of the present invention have considered as follows to arrive at the present invention.

  As a result of intensive studies, the present inventors have found that the absolute value of the impedance in the low frequency region of the elastic layer is a large factor affecting the adhesion of toner and external additives.

That is, to a charging member by using an electrophotographic charging member containing a semiconductive particle and having an elastic layer having an impedance having an absolute value of 5 × 10 ⁵ Ω or more at a frequency of 20 Hz. The present inventors have found that the adhesion of toner and external additives can be suppressed, and have reached the present invention.

  According to the charging member of the present invention, adhesion of toner and external additives to the surface of the charging member is suppressed, the charging member is less likely to become dirty, and a good image can be obtained.

  Although the example of embodiment regarding this invention is shown below, the aspect of this invention is not limited to these.

<Electrophotographic image forming apparatus>
First, an electrophotographic image forming apparatus using the charging member according to the present invention will be described. In this example, a charging roll is used as a charging member, and a photoconductor is used as a member to be charged.

  FIG. 1 is a sectional view showing an example of an electrophotographic image forming apparatus of the present invention. Reference numeral 4 denotes a photosensitive drum as a member to be charged, which is formed by forming an organic photoconductor (OPC) as a photosensitive layer on the outer peripheral surface of an aluminum drum base, and rotates at a predetermined speed in the direction of an arrow. .

  In FIG. 1, exposure light is emitted from a semiconducting laser light source 1 based on information read by a document reading device (not shown). This is distributed in the direction perpendicular to the paper surface of FIG. 1 by the polygon mirror 2 and irradiated onto the surface of the photoreceptor through an fθ lens 3 that corrects image distortion, thereby forming an electrostatic latent image. The photosensitive drum 4 is uniformly charged by the charging roll 5 in advance, and starts rotating clockwise in accordance with the timing of image exposure.

  The electrostatic latent image on the surface of the photosensitive drum is developed by the negatively charged toner in the developing device 6, and the formed developed image is transferred to the transfer body 8 that has been conveyed in time by the action of the transfer device 7. The Further, the photosensitive drum 4 and the transfer body 8 are separated by a separator (separation pole) 9, but the developed image is transferred and supported on the transfer body 8, guided to the fixing device 10, and fixed.

  Untransferred toner or the like remaining on the surface of the photoreceptor is cleaned by a cleaning blade type cleaning device 11, the residual charge is removed by pre-charge exposure (PCL) 12, and again by the charging roll 5 for the next image formation. Uniformly charged.

  A power supply unit 14 applies a voltage to the charging roll 5 and supplies a predetermined voltage to a shaft body (core metal) 51 of the charging roll 5. The applied voltage is preferably a DC voltage superimposed with an AC voltage.

  Further, the mechanical pressure applied between the charging roll and the electrophotographic photoreceptor is such that the contact pressure of the charging roll to the photoreceptor is 5 to 500 Pa, and the electrical load is the DC voltage applied to the charging roll. When an alternating voltage is applied to an absolute value of 200 to 900 V, it is desirable that the peak-to-peak voltage is adjusted to 500 to 5,000 Vp-p and the frequency is 50 to 3,000 Hz. For example, it is preferable that the applied voltage has a peak-to-peak voltage value that is at least twice the charging start voltage value for the photoreceptor.

  The charging roll may be driven or driven non-rotatingly by a surface-driven driven photoconductor, or a predetermined circumference in the forward or reverse direction in the surface movement direction of the photoconductor at the contact portion. You may make it actively rotate at a speed.

  The transfer member is typically plain paper, but is not particularly limited as long as it can transfer an unfixed image after development, and of course includes an OHP PET base.

  The cleaning blade 13 uses a rubber-like elastic body having a thickness of about 1 to 30 mm, and urethane rubber is most often used as the material. Since this is used in pressure contact with the photoconductor, it is easy to transfer heat, and it is desirable to provide a release mechanism and keep it away from the photoconductor when no image forming operation is performed.

<Charging roll>
Next, the charging roll according to the present invention will be described in detail.

Hereinafter, a charging roll having a rubber layer (an example of an elastic body layer) containing semiconductive particles and having an impedance having an absolute value of 5 × 10 ⁵ Ω or more at a frequency of 20 Hz will be described as an example.

The charging roll 5 according to the present invention includes a shaft body (core metal) 51 made of a stainless steel rod and semiconductive particles on the outer periphery thereof, and an absolute value of impedance at a frequency of 20 Hz is 5 × 10 ⁵ Ω or more. And an elastic layer 52 made of a rubber layer.

  In addition to the rubber layer, the elastic layer may be a foam layer such as polyurethane.

  Further, the charging roll may be provided with one elastic body layer of the present invention as long as the object of the present invention can be achieved, and a plurality of other elastic body layers may be combined in addition to this layer.

  In the present invention, there is no particular limitation on the combination of the elastic layers, but it is preferable that the elastic layer of the present invention is installed from the outermost layer or from the outer side to the second layer in terms of enhancing the antifouling effect. . For example, a resistance adjusting layer or a protective layer may be provided on the elastic layer of the present invention.

The charging roll of the present invention has a material design by introducing a new evaluation method, and surprisingly, the presence of a rubber layer in which the balance between conductivity and chargeability is controlled. Adhesion of toner and external additives could be suppressed. That is, the charging roll of the present invention has an elastic body layer containing semiconductive particles and having an absolute value of impedance of 5 × 10 ⁵ Ω or more at a frequency of 20 Hz. Although the mechanism for suppressing toner adhesion and external additive adhesion is not clear, it is presumed that electrostatic repulsion occurs between the toner or external additive and the charging roll.

  In the present invention, material design was performed using the values obtained by the following new measurement method. As a result, the present invention was completed by overcoming the dirt obstacle without sacrificing the charging performance of the charging roll.

  The absolute value of impedance can be measured with good reproducibility by the method described below.

  The thickness of the measurement sample is preferably less than 0.5 mm, more preferably less than 0.2 mm, but if the thickness is corrected during measurement, the reproducibility is good as long as it is less than 1 mm. If it is 1 mm or more, the error becomes large, and if it is extremely thin, it becomes wrinkled during measurement, thereby increasing the measurement error. Therefore, at least 0.02 mm or more is necessary, and preferably 0.1 mm or more.

  That is, the elastic layer used for the charging roll of the present invention is molded into a sheet having a thickness of 0.02 mm or more and less than 1 mm to obtain a measurement sample.

  Regarding the apparatus, it is an apparatus that combines an impedance measuring apparatus capable of measuring at a frequency of 1 Hz or more and used for measuring a dielectric constant of an electronic component and a sheet measuring electrode. Specifically, it is a combination of Yokogawa Hewlett-Packard (hereinafter, YHP) Precision LCR meter HP4284A and HP16451B.

  An example of obtaining the absolute value of the impedance at 20 Hz with this combination of devices will be described in detail. Using a precision LCR meter HP4284A to which HP16451B having two electrodes constituted by parallel planes and a guard electrode is connected, the absolute value of the impedance of the sheet material is measured by a void method in an atmosphere of 23 ° C. and 20% RH. Regarding the measurement of the void method, the electrode non-contact method described in the instruction manual of HP16451B is followed. The size of the sample is not particularly limited as long as it is larger than the electrode plane. However, when the diameter of the main electrode is 3.8 cm, a square sample having a size of 5 cm × 5 cm to 6 cm × 6 cm is preferable. If the surface resistivity measured using the DC current of the sample is the same on the front and back, either side may be up, but if it is not equal on the front and back, the surface with a low surface resistivity is up. A sample is placed between two electrodes composed of parallel planes, and measurement is performed by the air gap method while applying an AC voltage.

Here, the absolute value of impedance at a frequency of 20 Hz measured using an electrode having an area of 11 to 12 cm ² is required to be 5 × 10 ⁵ Ω or more. In order to exhibit the effect of the present invention more remarkably, it is preferably 8 × 10 ⁵ Ω or more, more preferably 1 × 10 ⁶ Ω or more and 10 ²⁰ Ω or less.

  The content of semiconductive particles in the rubber layer which is an example of the elastic layer ((total volume of semiconductive particles × 100) / (volume of the base rubber layer)). Considering 30% by volume or less is preferable. If importance is attached to the durability of rubber, 20% by volume or less is preferable. Moreover, in order to exhibit the effect of the present invention more remarkably, the semiconductive particles are preferably 1% by volume or more, more preferably 5% by volume or more, and further preferably 7% by volume or more.

  The rubber material of the charging roll of this embodiment is composed of semiconductive particles and rubber as basic components, and its composition is controlled by the absolute value of the impedance. However, if necessary, the crosslinking agent is within the scope of the present invention. In addition, other components such as a surfactant, a mat material, a deterioration preventing agent, an antioxidant, and an ultraviolet absorber may be added.

The volume resistivity of the elastic layer 52 made of a rubber layer containing semiconductive particles in the charging roll is preferably 10 ⁵ Ω · cm to 10 ¹¹ Ω · cm from the viewpoint of charging performance and leakage prevention.

  The volume resistivity of the elastic layer containing the semiconductive particles can be measured by the following method.

A rubber containing semiconductive particles is cut into a cube having a side of 5 cm, and a pressure of 10 ⁷ Pa is applied with a flat plate press heated to 140 ° C. for 20 minutes to form a sheet. An intermediate portion of this sheet is cut out with a width of 1 cm to obtain a sample for measuring volume resistivity. Since the thickness of the sample differs depending on the density of the rubber, it is measured with a thickness meter. Four copper wires having a diameter of 0.2 mm and a length of 4 cm are adhered to the surface of a sample cut into a 1 cm × 5 cm strip shape by using dootite and sufficiently dried. Using the electrode thus formed, volume resistivity is measured by a four-terminal method in an environment adjusted to a temperature and humidity of 25 ° C. and 50% RH.

In order to exert the effects of the present invention more remarkably, the volume resistivity of the semiconductive particles is preferably 10 ³ Ω · cm or more and 10 ⁸ Ω · cm or less, and even if they are made of the same material, It may be a combination with materials.

The volume resistivity of the semiconductive particles is measured by a two-terminal method in an environment adjusted to a temperature and humidity of 25 ° C. and 50% RH after being molded into a tablet. About the preparation method of a tablet, it shape | molds with a hydrostatic pressure pressurization of 10 < ⁸ > Pa or more after shape | molding with a tablet molding machine. Hydrostatic pressure pressurization of 5 × 10 ⁸ Pa or more may be applied, but if the pressure is too high, it is difficult to release from the rubber mold, and therefore preferably less than 5 × 10 ⁸ Pa. More preferably, it is 3 × 10 ⁸ Pa or less.

  In addition, the semiconducting particles have a residual ratio ((mass of residue after heat treatment × mass of the residue after heat treatment) at a temperature of 800 ° C. in a nitrogen atmosphere because of control of volume resistivity, ease of production, and cost. 100) / (mass of organic compound before heat treatment) is preferably a semiconducting particle derived from an organic compound having a mass ratio of 20 mass% or more and 95 mass% or less. In addition, it is important in terms of carbonizing the organic compound to be 95% by mass or less.

  Specifically, the semiconductive particles can be obtained by heat-treating the organic compound at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include an inert gas atmosphere such as nitrogen or argon.

  The mass of the organic compound residue is measured by thermal mass spectrometry (hereinafter referred to as TGA) in a nitrogen atmosphere. Measure at a heating rate of 10 ° C./min up to 800 ° C. and read the mass of the residue at 800 ° C. A sample once heat-treated in air at 100 ° C. for 60 minutes is used.

  When the organic compound used in the present invention is heat-treated at 800 ° C. in a nitrogen atmosphere among the organic materials, (mass of carbon after heat treatment × 100) / (mass of organic compound before heat treatment) is 20% by mass or more of carbon. An organic compound that can generate carbon is preferable, more preferably 30% by mass or more, more preferably 35% by mass or more, and most preferably an organic compound that generates 40% by mass or more of carbon. The greater the amount of carbon produced, the easier it is to control the volume resistivity of the semiconductive particles.

  As the organic compound that can be used in the present invention, any organic compound can be used as long as the residual rate of 800 ° C. is satisfied. For example, in the liquid phase, pitch, coal tar, or coal can be used. -Mixtures of coke and pitch are used, and in the solid phase, cross-linked materials such as wood raw materials, furan resins, phenol resins, cellulose, polyacrylonitrile, rayon are used. Carbonaceous materials can be broadly divided into petroleum pitch and other starting materials, generally heat treated at a high temperature of 2000 ° C. or higher, so-called graphitizable carbon materials having a developed graphite structure, and phenol resins and furan resins. There is a so-called non-graphitizable carbon material having a turbulent structure by heat treatment at a relatively low temperature of 2000 ° C. or less using a thermosetting polymer as a starting material.

  In the present invention, any carbon material may be used as long as the object of the invention is not impaired. However, a non-graphitizable carbon material is preferably selected from the viewpoint of easy control of electric conductivity, and an organic compound that generates such a carbon material is organic. Polymer materials, particularly phenolic resins are preferred.

  Also, by using organic polymer material, especially phenol resin, porous semiconductive particles can be easily obtained, and the surface area of the interface between the semiconductive particles and the material constituting the elastic layer such as rubber is increased. As a result, the number of crosslinking points increases, and the strength of an elastic layer such as rubber containing semiconductive particles can be improved.

  The phenol resin suitably used in the present invention is, for example, alkylphenols, other substituted phenols, polyhydric phenols and aldehydes such as formaldehyde and paraformaldehyde as raw materials, in addition to phenol. Can be obtained by reacting under an acidic catalyst (novolak type) or an alkaline catalyst (resol type).

  In the present invention, it is preferable to obtain semiconductive particles through a carbonization process by heat treatment as described above after an organic compound is molded into a fiber shape in advance. Moreover, carbonization may be promoted while stretching to form a fibrous material.

  However, the heat treatment temperature for carbonization is preferably 800 ° C. or higher, more preferably 1200 ° C. or higher. A temperature of 2000 ° C. or higher is preferable, but a temperature of 3000 ° C. or higher is not economically preferable. The heating rate up to this heat treatment temperature and the holding time of the heat treatment temperature are not particularly limited because they differ depending on the shape and composition of the carbon material to be treated, but the heating rate is 1 ° C./min or more and less than 50 ° C./min. Is preferably 1 minute or more and less than 24 hours. Moreover, you may perform processes, such as a grinding | pulverization and a classification, after heat processing.

  In the present invention, no particular limitation is imposed on rubber. Any material may be used as long as it can be used for general rubber products, and the composition may be anything obtained by blending a plurality of rubbers.

  Further, the mixing method of the semiconductive particles and the rubber is not particularly limited.

  In the above embodiment, the example of the charging roll is shown as the charging member. However, the present invention can be applied to charging members such as a blade type, a rod type, and a belt type in addition to the roll type.

  Further, in the above-described embodiment, an example in which the charging roll contacts the photosensitive member that is the charged body to charge the photosensitive body is shown, but the charged body for the charging member of the present invention is not limited to the photosensitive body. For example, the present invention can also be applied to a transfer member (for example, a transfer roll) that charges a transfer material that is an object to be charged.

EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by an Example.
<Method for producing semiconductive particle X>
3 g of 10% toluenesulfonic acid aqueous solution and 50 g of resol type phenol resin (PR-51107, Sumitomo Bakelite Co., Ltd.) are mixed for 20 seconds with a laboratory mixer and then heat-treated with a spray dryer (atmosphere 80 ° C.). The obtained powder was subjected to thermal mass spectrometry in a nitrogen atmosphere, the mass of the residue at 800 ° C. was determined, and the residual ratio was determined to be 48% by mass.

This powder was heat-treated in an electric furnace at 800 ° C. for 30 minutes in a nitrogen atmosphere. The powder thus obtained was pulverized and classified using a jet mill, and a powder having an average particle size of 0.3 μm and a volume resistivity of 2 × 10 ⁵ Ω · cm was obtained.
<Method for producing semiconductive particle Y>
A fibrous carbon material was produced as the semiconductive particles Y by the method shown below.

After charging 1.2 kg of phenol, 0.6 kg of 50% formalin and 3.5 g of oxalic acid into a 3 liter flask and reacting at reflux temperature for 4 hours, vacuum dehydration concentration was further performed under heating, and an uncured softening point of 110 ° C. 1 kg of novolak resin was obtained. 200 g of uncured novolak resin and 10 g of Ketjen Black EC600JD (Ketjen Black International Co., Ltd.) were heated and melted, mixed and stirred to obtain an uncured novolak resin mixture. This uncured novolac resin mixture was melt-spun at a speed of 260 m / min using a spinneret having 20 holes and a hole diameter of 0.2 mmφ to obtain uncured novolac resin mixture fibers. This novolak resin fiber was immersed in a curing aqueous solution mainly composed of formaldehyde and hydrochloric acid, heated to 95 ° C. at a rate of 0.5 ° C./min, and held for 8 hours to obtain a cured novolac resin fiber. The obtained fiber was subjected to thermal mass spectrometry under a nitrogen atmosphere, and the amount of residue at 800 ° C. was determined to be 52% by mass. The phenol resin fiber was cut to around 1 mm and then heat-treated in an electric furnace at 1000 ° C. for 30 minutes in a nitrogen atmosphere to obtain short carbon fibers. The carbon short fibers were pulverized by jet mill to obtain carbon short fibers having a fiber length of 0.5 mm and a fiber diameter of 0.07 mm. This carbon short fiber had a volume resistivity of 5 × 10 ³ Ωcm. This short carbon fiber was designated as semiconductor particle Y.
Example 1
<Preparation of charging roll 1>
The charging roll 1 of the present invention was produced in the following manner.
{Invention}
Epichlorohydrin rubber terpolymer 100 parts by weight semiconductive particles X 38 parts by weight quaternary ammonium salt 2 parts by weight zinc oxide 5 parts by weight fatty acid 2 minutes or more in a closed mixer adjusted to 60 ° C. for 10 minutes After kneading, 5 parts by mass of a sebacic acid polyester plasticizer was added to 100 parts by mass of epichlorohydrin rubber, and the mixture was further kneaded for 20 minutes with a closed mixer cooled to 20 ° C. to prepare a raw material compound. To this compound, 100 parts by weight of epichlorohydrin rubber as a raw material rubber was added 1 part by weight of sulfur as a vulcanizing agent, 1 part by weight of Noxeller DM as a vulcanization accelerator, and 0.5 parts by weight of Noxeller TS, and then cooled to 20 ° C. It knead | mixed for 10 minutes with the roll machine. The obtained compound was molded by an extrusion molding machine so as to form a roll around a stainless steel core, heat-vulcanized, and then polished.

The resulting rubber layer A had a volume resistivity of 10 ⁷ Ω · cm.

  A charge adjusting roll 1 was obtained by attaching a resistance adjusting layer to the roll obtained here.

That is, as a material for the resistance adjustment layer,
Acrylic polyol solution (active ingredient 70% by weight) 100 parts by weight isocyanate A (IPDI, active ingredient 60% by weight) 40 parts by weight isocyanate B (HDI, active ingredient 80% by weight) 30 parts by weight conductive tin oxide (made by Ishihara Sangyo) 90 parts by mass negatively charged control resin (CCRI) 12 parts by mass Methyl isobutyl ketone (MIBK) solvent 340 parts by mass was stirred using a mixer to prepare a mixed solution. Subsequently, the mixed solution was subjected to a dispersion treatment using a circulation type bead mill disperser to prepare a dipping paint.

  The above IPDI means isophorone diisocyanate, and HDI means hexamethylene diisocyanate.

  The coating material for dipping is applied on the roll by a dipping method so that the film thickness becomes 10 μm, air-dried for 10 minutes, and then dried at 160 ° C. for 1 hour by a heating type dryer to obtain a charging roll 1. It was.

  The rubber layer A of the compound used here was heated and pressed using an iron mold having a depth of 0.2 mm and 10 cm square under the same vulcanization conditions as those of the charging roll 1 to obtain a sheet of 0.25 mm and 10 cm square. It was.

The absolute value of the impedance of this sheet was measured.
<Absolute impedance measurement method>
For impedance measurement, a combination of Yokogawa Hewlett-Packard (hereinafter, YHP) Precision LCR meter HP4284A and HP16451B was used. Under an atmosphere of 23 ° C. and 20% RH, the absolute value of the impedance of the sheet material was measured by the void method. Regarding the measurement of the void method, the electrode non-contact method described in the instruction manual of HP16451B (part number 16451-97000, printed December 1989) is followed. The size of the sample was cut into a 5.5 cm × 5.5 cm square using the electrode-A having a main electrode diameter of 3.8 cm.

The obtained charging roll is attached to the electrophotographic image forming apparatus of FIG. 1, and the photosensitive member is charged under the following conditions in an environment of 23 ° C./53% RH, and 1000 predetermined images are continuously printed. Printed out.
Charging condition Photoconductor contact pressure: 50 g / cm, DC voltage applied to charging roll: -600 V, AC voltage: 2,000 Vp-p, frequency: 150 Hz
Image evaluation and evaluation of the toner and external additives attached on the charging roll after printing were performed.
<Dirt and image evaluation method>
(1. Dirt evaluation method)
The dirt was evaluated based on the adhesion of the toner to the surface of the charging roll and the adhesion of the external additive.

Toner adhesion: The toner adhering to the charging roll was removed with a tape (manufactured by 3M, Scotch Mending Tape), and the density of the adhering toner transferred to the tape was visually observed and evaluated.
○: The tape remains transparent and no toner is transferred.
Δ: A portion where the toner is transferred to the tape is partially recognized.
X: The toner is transferred to the entire surface of the tape.

External additive adhesion: The concentration of the external additive adhering to the charging roll was visually observed and evaluated.
○: The roll has a black appearance, or a part where the external additive is slightly visible is only partially recognized.
(Triangle | delta): The state in which the external additive was on the roll whole surface.
X: A state in which an external additive is placed on the entire roll surface.

  In this adhesion evaluation, in both toner adhesion and external additive adhesion, 性 is two, ◯ is a combination of ○ and △, ○ and × is a combination △, and there is no ◯ is × did.

(2. Image evaluation method)
○: Good image.
Δ: Image disturbance caused by toner or external additive adhering to the charging roll was observed in a part of the image.
X: Image disturbance caused by toner or external additive adhering to the charging roll was observed in the entire image.
(Example 2)
A charging roll 2 and an impedance evaluation sheet were prepared in the same manner as in Example 1 except that the amount of the semiconductive particles X used was 25 parts by mass, and evaluated in the same manner.

The resulting rubber layer A had a volume resistivity of 10 ⁷ Ω · cm.
(Example 3)
In Example 1, the same process was performed except that the amount of the semiconductive particles X was changed to 19 parts by mass, and the charging roll 3 and the impedance evaluation sheet were prepared and evaluated in the same manner.

The resulting rubber layer A had a volume resistivity of 10 ⁷ Ω · cm.
Example 4
After blending a vulcanizing agent and a foaming agent with ethylene-propylene-diene rubber (EPDM), and applying the mixed raw rubber to a metal rod with a thickness of 5 mm, the rubber layer compounding B is spread by 5 mm and heated and vulcanized and molded. The charging roll 4 was manufactured by processing. An impedance evaluation sheet was prepared and evaluated in the same manner.

The resulting rubber layer B had a volume resistivity of 10 ⁶ Ω · cm.
{Invention rubber layer blend B}
Epichlorohydrin rubber terpolymer 100 parts by weight semiconductive particles X 20 parts by weight conductive tin oxide (manufactured by Ishihara Sangyo) 5 parts by weight quaternary ammonium salt 1 part by weight zinc oxide 5 parts by weight fatty acid 2 parts by weight (Example 5) )
In Example 1, instead of the semiconductive particle X, the same process was performed except that the amount used was changed to 5 parts by mass using the semiconductive particle Y, and the charging roll 5 and the impedance evaluation sheet were prepared. , Evaluated in the same way.

The resulting rubber layer A had a volume resistivity of 10 ⁶ Ω · cm.
(Example 6)
In Example 1, instead of the semiconductive particle X, the same process was performed except that the amount used was changed to 10 parts by mass using the semiconductive particle Y, and the charging roll 6 and the impedance evaluation sheet were prepared. , Evaluated in the same way.

The resulting rubber layer A had a volume resistivity of 10 ⁶ Ω · cm.
(Comparative Example 1)
100 parts of styrene-ethylene-butylene-olefin copolymer resin, trade name: Dynalon, manufactured by Nippon Synthetic Rubber Co., Ltd., 20 parts of polyethylene, and 15 parts of carbon black (trade name: Ketjen Black EC, manufactured by Lion Akzo Co., Ltd.) are V-shaped. Mix for a few minutes in a blender. This was further melt kneaded at 190 ° C. for 10 minutes using a pressure kneader. Furthermore, after cooling, it was pulverized by a pulverizer and pelletized by a single screw extruder.

The ketjen black EC had a volume resistivity of 10 ⁻² Ω · cm, and the rubber layer obtained had a volume resistivity of 10 ⁶ Ω · cm.

  As the material for the inner layer, 100 parts of polyurethane elastomer, 10 parts of magnesium oxide and 1 part of calcium stearate were pelletized in the same process as the material for the outer layer.

  Using a vertical extruder, these are merged into a double layer with a single crosshead, extruded into cooling water (4 to 16 ° C) at an appropriate temperature, and the distance between the tube and the cooling sizing wall becomes nearly uniform. The horizontal position of the sizing was adjusted so that it was cooled and taken out. What cut this tube was inserted in the metal roll, and was press-contacted.

A sheet was prepared in the same manner as in Example 1 using the rubber material of the outer layer material and evaluated in the same manner.
(Comparative Example 2)
In Example 1, a charging roll and a sheet were prepared in the same manner except that carbon black (trade name: Ketjen Black EC, manufactured by Lion Akzo Co., Ltd.) was used instead of the semiconductive particles X, and evaluation was performed in the same manner.

The ketjen black EC had a volume resistivity of 10 ⁻² Ω · cm, and the obtained rubber layer A had a volume resistivity of 10 ⁶ Ω · cm.

  The evaluation results of Examples and Comparative Examples are summarized in Table 1. The particles in the particle content are the semiconductive particles X in Examples 1 to 4, the semiconductive particles Y in Examples 5 to 6, and the carbon black in the comparative examples.

  From the examples and comparative examples in Table 1, the charging roll of the present invention has good dirt and image evaluation in the durability test, and achieves the object of the present invention.

1 is a perspective view showing a main part of an image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

  1 Image forming device

Claims (10)

An electrophotographic charging member comprising an elastic layer containing semiconductive particles and having an impedance having an absolute value of 5 × 10 ⁵ Ω or more at a frequency of 20 Hz. 2. The electrophotographic charging member according to claim 1, wherein the content of the semiconductive particles in the elastic layer is 1% by volume or more and 30% by volume or less. ^3. The electrophotographic charging member according to claim 1, wherein the semiconductive particles have a volume resistivity of 10 ³ Ω · cm to 10 ⁸ Ω · cm. The semiconductive particles are semiconductive particles derived from an organic compound having a residual ratio of 20% by mass to 95% by mass when the organic compound is heat-treated at a temperature of 800 ° C. in a nitrogen atmosphere. The charging member for electrophotography according to any one of claims 1 to 3. The electroconductive particle according to claim 4, wherein the semiconductive particles are semiconductive particles obtained by heat-treating the organic compound at a temperature of 800 ° C or higher in a non-oxidizing atmosphere. Charging member. 6. The charging member for electrophotography according to claim 4, wherein the organic compound is an organic polymer material. The charging member for electrophotography according to claim 6, wherein the organic polymer material is a phenol resin. The electrophotographic charging member according to any one of claims 1 to 7, wherein the electrophotographic charging member is an electrophotographic charging roll. An electrophotographic image forming apparatus using the electrophotographic charging member according to claim 1. The electrophotographic image forming apparatus according to claim 9, wherein the electrophotographic charging member is charged in contact with an object to be charged.

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