JP5176264B2 - Electrophotographic charging member and electrophotographic image forming apparatus using the same - Google Patents

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.
(Claim 1)
An absolute value of impedance at a frequency of 20 Hz, containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal, and conductive particles having a volume resistivity of less than 10 ² Ω · cm. There have a elastic layer is less than ⁵ × 10 5 Ω, the conductive particles, carbon powder is generated by heat-treating the heavy oil in a reducing flame atmosphere, or of 800 ° C. or higher in a non-oxidizing atmosphere A charging member for electrophotography, which is one of carbon powders produced by heat-treating a phenol resin at a temperature .
(Claim 2)
2. The charging member for electrophotography according to claim 1, wherein a content of the at least one salt in the elastic layer is 0.1% by mass or more and less than 10% by mass.
(Claim 3)
The conductive particles, and characterized in that the phenolic resin is the phenolic resin from the conductive particles remaining rate when the heat treatment at a temperature of 800 ° C. is not more than 95 wt% to 20 wt% in a nitrogen atmosphere The charging member for electrophotography according to claim 1 or 2 .
(Claim 4)
The elastic layer is an electrophotographic according to claim 1, characterized by containing a compound having an ether bond content of less than 0.5% by weight to 10% by weight Charging member.
(Claim 5)
The electrophotographic charging member according to claim 1 , wherein the electrophotographic charging member is an electrophotographic charging roll.
(Claim 6)
An electrophotographic image forming apparatus using the electrophotographic charging member according to claim 1 .
(Claim 7)
The electrophotographic image forming apparatus according to claim 6 , 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, it has an elastic body layer containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal and having an absolute value of impedance at a frequency of 20 Hz of less than 5 × 10 ⁵ Ω. By using an electrophotographic charging member characterized by the above, it has been found that adhesion of toner and external additives to the surface of the charging member can be suppressed, and the present invention has been achieved.

  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 organic photoconductive (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 semiconductor 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 rubber layer (elastic body layer) containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal and having an absolute value of impedance of less than 5 × 10 ⁵ Ω at a frequency of 20 Hz An example of the charging roll having the above will be described.

A charging roll 5 according to the present invention contains a shaft (core metal) 51 made of a stainless steel rod, and a salt containing at least one metal selected from alkali metals and alkaline earth metals on the outer periphery thereof, and has a frequency. And an elastic layer 52 made of a rubber layer whose absolute value of impedance at 20 Hz is less than 5 × 10 ⁵ Ω.

  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 contains at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal, and the absolute value of impedance at a frequency of 20 Hz is less than 5 × 10 ⁵ Ω. It has an elastic body layer. 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.

  Examples of the alkali metal salt and alkaline earth metal salt include lithium, potassium, sodium and the like as the alkali metal, and examples of the alkaline earth metal include magnesium, calcium, strontium and barium, preferably potassium, sodium and magnesium. , Calcium and barium. Examples of the salt include chlorine salt, bromine salt, iodine salt, carbonate salt, sulfate salt and the like.

  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 needs to be less than 5 × 10 ⁵ Ω. To more remarkably exhibit the effects of the present invention is preferably less than 8 × 10 ³ Omega, more preferably 8 × less than 10 ³ Omega than 1 [Omega.

  The content of at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal in the rubber layer which is an example of the elastic layer ((total of salts containing an alkali metal and a salt containing an alkaline earth metal) (Mass × 100) / (mass of the rubber layer as the base material)), but if it is contained in a large amount, it will bleed out on the surface of the charging roll and contaminate the photosensitive drum, so the content is less than 10% by mass. Is preferable, and less than 5 mass% is further more preferable. Less than 2% by mass is preferable because no problem occurs even in an environment with high humidity. Moreover, in order to exhibit the effect of this invention more notably, 0.1 mass% or more is preferable, More preferably, it is 0.5 mass% or more.

The volume resistivity of the elastic layer 52 made of a rubber layer containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal in the charging roll is 10 from the viewpoint of charging performance and leakage prevention. Those having ³ Ω · cm to 10 ¹¹ Ω · cm are preferred.

  The volume resistivity of the elastic layer containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal can be measured by the following method.

A rubber containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal is cut into a cube having a side of 5 cm, and a pressure of 10 ⁷ Pa is applied by a flat plate press heated to 140 ° C. for 20 minutes. Leave it in a sheet form. 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.

The rubber material of the charging roll of the present invention preferably contains conductive particles having a volume resistivity of less than 10 ² Ω · cm in order to adjust the volume resistivity of the rubber layer. It may be composed of the same material or a combination with a different material.

  The content of conductive particles in the rubber layer, which is an example of the elastic layer ((total volume of conductive particles × 100) / (volume of the base rubber layer)), but considering the mechanical properties of the charging roll 30 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 this invention more notably, electroconductive particle is preferable 1 volume% or more.

  Although the composition is controlled by the absolute value of the impedance, other components such as a crosslinking agent, a surfactant, a mat material, an anti-degradation agent, an antioxidant, and an ultraviolet absorber are included within the scope of the present invention as necessary. It may be added.

The volume resistivity of the conductive particles is measured by the 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 manufacturing 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.

  Further, the conductive particles have a residual ratio ((mass of residue after heat treatment × 100) when the organic compound is heat-treated at a temperature of 800 ° C. in a nitrogen atmosphere because of control of volume resistivity, ease of production, and cost. ) / (Mass of organic compound before heat treatment)) is preferably conductive particles derived from an organic compound having a mass ratio of 20% by mass to 95% by mass. It is particularly important that the residual ratio is 20% by mass or more in that the production cost can be reduced. Moreover, being 95 mass% or less is important in the point which carbonizes an organic compound.

  Specifically, the conductive 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. Further, the organic compound may be heat-treated (fired) in a reducing flame atmosphere.

  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 conductive 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, coke and pitch can be used. A mixture or the like is used. In the solid phase, a cross-linked material such as a wood raw material, a furan resin, a phenol resin, cellulose, polyacrylonitrile, or rayon is 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, but graphitizable carbon materials are preferably selected from the viewpoint that the volume resistivity can be lowered.

  The graphitizable carbon material is obtained by heat-treating an organic compound that generates graphitizable carbon in a non-oxidizing atmosphere as described above.

  In addition, by using an organic polymer material, particularly a phenol resin, porous conductive particles can be easily obtained, and by increasing the surface area of the interface between the material constituting the elastic layer such as rubber and the conductive particles, The cross-linking points are increased, and the strength of an elastic layer such as rubber containing conductive particles can be improved.

  The phenol resin suitably used in the present invention includes, for example, alkylphenols and other substituted phenols, polyhydric phenols and aldehydes such as formaldehyde and paraformaldehyde as raw materials, in addition to phenol, and generally known ordinary methods 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 conductive particles after previously molding an organic compound into a fibrous shape and then performing a carbonization process by the heat treatment described above. 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 method for mixing the salt containing at least one metal selected from alkali metals and alkaline earth metals with rubber is not particularly limited.

  Also, the rubber layer contains a compound containing an ether bond at a content of 0.5% by mass or more and less than 10% by mass ((mass of compound containing an ether bond × 100) / (mass of the rubber layer as a base)). This is preferable because it can more effectively prevent bleed out of a salt containing an alkali metal or an alkaline earth metal. As for the compound containing an ether bond, it may be a polyether polymer whose main chain is composed of an ether bond, or a polymer in which a polyether group is grafted on a side chain, and includes an alkali metal or an alkaline earth metal. In order to effectively prevent salt bleed out, the molecular weight is preferably 500 or more in terms of mass average molecular weight, and a molecular weight of less than 300,000 is selected in order to avoid phase separation of rubber accompanying crystallization. Considering the viscosity at the time of kneading, it is preferably less than 100,000, bleed-out does not occur, process suitability is good, and the most preferable range is 1000 or more and less than 10,000.

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.
<Manufacture of electroconductive particle 1>
A gas burner is attached to one end of an alumina cylinder having a diameter of 10 cm, and combustion is performed under conditions where the reducing flame region is the widest. In the reducing flame region, heavy oil having a viscosity of 8000 poise is added at a rate of 1 ml / s to generate soot. Operation was performed in this state, and the soot produced was recovered to produce conductive particles 1. Soot was obtained as agglomerated particles, and had an average particle size of 0.2 μm and a volume resistivity of 2 × 10 ⁻² Ω · cm.
<Production of conductive particles 2>
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 for 4 hours at the reflux temperature, vacuum dehydration concentration was further performed under heating, and an uncured softening point of 110 ° C. 1 kg of novolak resin was obtained. 50 g of uncured novolak resin was heated and melted and stirred to obtain an uncured novolak resin.

  This uncured novolak resin is dropped into a cured aqueous solution containing formaldehyde and hydrochloric acid as main components until the viscosity of the aqueous solution increases to 300 poise. This cured aqueous solution was heated to 95 ° C. at a rate of 0.5 ° C./min, held for 8 hours, filtered and dried to obtain a cured novolak resin. 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 resin was heat-treated in a nitrogen atmosphere at 1000 ° C. to obtain carbon powder. The carbon powder was pulverized with a jet mill to produce conductive particles 2. The volume resistivity of the particles was measured and found to be 20 Ω · cm.
Example 1
<Preparation of charging roll 1>
The charging roll 1 of the present invention was produced in the following manner.
{Invention rubber layer formulation A}
Epichlorohydrin rubber terpolymer 100 parts by weight conductive particles 1 10 parts by weight sodium sulfate salt 2 parts by weight zinc oxide 5 parts by weight fatty acid 2 parts by weight or more of materials were kneaded for 10 minutes in a closed mixer adjusted to 60 ° C. Thereafter, 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 mass of epichlorohydrin rubber as a raw material rubber was added 1 part by mass of sulfur as a vulcanizing agent, 1 part by mass of Noxeller DM as a vulcanization accelerator, and 0.5 parts by mass 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, subjected to heat vulcanization molding, and then polished.

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

  A surface layer was attached to the roll obtained here to obtain a charging roll 1.

That is, as a material for the surface 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 (CCR1) 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 the 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 distortion 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 a calcium carbonate salt was used instead of the sodium sulfate salt.

The resulting rubber layer A had a volume resistivity of 10 ⁷ Ω · cm.
(Example 3)
In Example 1, a charging roll 3 and an impedance evaluation sheet were prepared and evaluated in the same manner except that 5 parts by mass of a polyether having a mass average molecular weight of 1000 was further added to the rubber layer A of the present invention.

The resulting rubber layer A had a volume resistivity of 10 ⁷ Ω · cm.
(Reference example)
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 compounded B is spread by 5 mm and polished after heat vulcanization molding. The charging roll 4 was manufactured by processing. An impedance evaluation sheet was prepared in the same manner as in Example 1 and evaluated in the same manner.

The obtained rubber layer B had a volume resistivity of 10 ⁷ Ω · cm.
{Invention rubber layer blend B}
Epichlorohydrin rubber terpolymer 100 parts by weight conductive particles 2 10 parts by weight conductive tin oxide (made 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 (Comparative Example 1)
100 parts by mass of styrene-ethylene / butylene-olefin copolymer resin (trade name: Dynalon, manufactured by Nippon Synthetic Rubber), 20 parts by mass of polyethylene, and 80 parts by mass of carbon black (trade name: Ketjen Black EC, manufactured by Lion Akzo) Was mixed in a V-type blender for several minutes. 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.

  As the material for the inner layer, 100 parts by mass of polyurethane elastomer, 10 parts by mass of magnesium oxide and 1 part by mass 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 the impedance and image were evaluated in the same manner.

Ketjen Black EC had a volume resistivity of 10 ⁻² Ω · cm, and the outer rubber layer obtained had a volume resistivity of 10 ⁶ Ω · cm.

  The evaluation results of Examples and Comparative Examples are summarized in Table 1.

  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

DESCRIPTION OF SYMBOLS 1 Semiconductor laser light source 2 Polygon mirror 3 f (theta) lens 4 Photosensitive drum 5 Charging roller 51 Shaft body (core metal)
6 Developing Device 7 Transfer Device 8 Transfer Material 9 Separation Electrode 10 Fixing Device 11 Cleaning Device 12 Pre-Charge Exposure (PCL)
13 Cleaning blade 14 Power supply

Claims (7)

An absolute value of impedance at a frequency of 20 Hz, containing at least one salt selected from a salt containing an alkali metal and a salt containing an alkaline earth metal, and conductive particles having a volume resistivity of less than 10 ² Ω · cm. There have a elastic layer is less than ⁵ × 10 5 Ω,
The conductive particles are either carbon powder produced by heat treating heavy oil in a reducing flame atmosphere, or carbon powder produced by heat treating a phenol resin at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere. A charging member for electrophotography characterized by the above.   2. The charging member for electrophotography according to claim 1, wherein a content of the at least one salt in the elastic layer is 0.1% by mass or more and less than 10% by mass. The conductive particles, and characterized in that the phenolic resin is the phenolic resin from the conductive particles remaining rate when the heat treatment at a temperature of 800 ° C. is not more than 95 wt% to 20 wt% in a nitrogen atmosphere The charging member for electrophotography according to claim 1 or 2 . The elastic layer is an electrophotographic according to claim 1, characterized by containing a compound having an ether bond content of less than 0.5% by weight to 10% by weight Charging member. The electrophotographic charging member according to claim 1 , 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 6 , wherein the electrophotographic charging member is charged in contact with a member to be charged.

Images