JP2006350075A - Electrifying member for electrophotography and electrophotographic image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying member for electrophotography having a polyurethane foaming body layer which is hardly distorted by compressive force, and to provide an electrophotographic image forming apparatus using the electrifying member for electrophotography. <P>SOLUTION: The electrifying member for electrophotography is constituted by forming the insulating polyurethane foaming body layer on a conductive substance, and forming a semiconductive rubber layer on the insulating polyurethane foaming body layer. <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 copiers and printers using an electrophotographic developing method, the photosensitive member (drum) is pressed and brought into contact, and a DC voltage and an AC voltage are applied in a superimposed manner, whereby the surface of the photosensitive member is applied. A charging roll for charging is used.

  As one of such charging rolls, a conductive base layer having a solid structure formed by using a conductive rubber composition on the outer peripheral surface of a shaft body (core metal) which is a conductive base is predetermined. In addition, a resistance adjustment layer is provided on the outer peripheral surface of the conductive base layer, and if necessary, an electrode layer is provided between the base layer and the resistance adjustment layer. It is known that a protective layer is laminated on the outer peripheral surface of each layer.

  In addition, a conductive material foamed using a conductive foaming rubber composition with conductive particles such as carbon black and metal powder added on the outer peripheral surface of the shaft body as having a different structure. The conductive base layer is provided with a predetermined thickness, and a substantially thin surface smooth layer made of a thermoplastic resin material is provided on the outer peripheral surface of the conductive base layer, and on the outer peripheral surface of the surface smooth layer. It is also known that the resistance adjustment layer is configured by further laminating a protective layer on the outer peripheral surface of the resistance adjustment layer as required (see Patent Document 1).

  In the charging roll having such a structure, the conductive base layer has a sponge structure in which foam is formed, so that the reduction in hardness is advantageously achieved without containing a large amount of softening agent. In addition to being able to effectively prevent contamination of the photoconductor due to the exudation of the softening agent from the conductive base layer, it can be advantageously reduced in weight, and has a solid structure as described above. Excellent characteristics not found in the charging roll having the conductive base layer thus configured can be exhibited.

Further, the surface smoothing layer provided on the outer peripheral surface of the conductive base layer can impart smoothness to the surface of the conductive base layer that is exposed to air bubbles and is in a rough state, and the conductive base layer On the outer peripheral surface, a resistance adjusting layer and a protective layer for preventing leakage and reducing the sensitive material fixing property can be satisfactorily formed.
JP 2001-154456 A

  As is well known, these charging rolls need to be in contact with a uniform force when used in contact with the photoreceptor.

  However, it is found that in the foam added with the conductive particles of the prior art, the distortion due to the compressive force is difficult to recover, and it is slightly deformed to come into contact with the photoreceptor and cause abnormal noise. It was.

  As a result of intensive studies, the present inventors have found that the addition of conductive particles is a large factor affecting the strain due to compressive force. That is, in the prior art, the conductive particles are simply dispersed as a conductive material, and therefore, at the interface between the conductive particles and the foam, interfacial peeling or cracks occur due to external force. It is easy to assume that the distortion does not recover.

  And since such abnormal noise is smaller than the sound generated from the entire device, I have not noticed so far, but as the device improved, the generated noise level became smaller and the noise generated by the charging roll began to become a problem. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrophotographic charging member having a polyurethane foam layer which is not easily distorted by a compressive force, and an electrophotographic image forming apparatus using the same. There is.

The object of the present invention is achieved by the following configurations.
(Claim 1)
An electrophotographic charging member, wherein an insulating polyurethane foam layer is formed on a conductive substrate, and a semiconductive rubber layer is formed on the insulating polyurethane foam layer.
(Claim 2)
2. The electrophotographic charging member according to claim 1, wherein the semiconductive rubber layer has a volume resistivity of 10 ³ Ω · cm to 10 ¹¹ Ω · cm.
(Claim 3)
The charging member for electrophotography according to claim 1 or 2, wherein the density of the semiconductive rubber layer is 0.5 g / cm ³ or more and less than 2 g / cm ³ .
(Claim 4)
The charging member for electrophotography according to any one of claims 1 to 3, wherein the outermost layer is the semiconductive rubber layer.
(Claim 5)
The charging member for electrophotography according to any one of claims 1 to 4, wherein the density of the insulating polyurethane foam layer is 0.001 g / cm ³ or more and less than 0.5 g / cm ³ .
(Claim 6)
6. The electrophotographic charging member according to claim 1, wherein the insulating polyurethane foam layer has a volume resistivity of 10 ¹² Ω · cm to 10 ¹⁶ Ω · cm.
(Claim 7)
7. The electrophotographic charging member according to claim 1, wherein the layer in direct contact with the conductive substrate is an insulating polyurethane foam layer.
(Claim 8)
The electrophotographic charging member according to claim 1, wherein the layer in direct contact with the insulating polyurethane foam layer is a semiconductive rubber layer.
(Claim 9)
9. The electrophotographic charging member according to claim 1, wherein the electrophotographic charging member is an electrophotographic charging roll.
(Claim 10)
An electrophotographic image forming apparatus using the electrophotographic charging member according to claim 1.
(Claim 11)
The electrophotographic image forming apparatus according to claim 10, wherein the electrophotographic charging member is charged in contact with an object to be charged.

  The inventor of the present invention is characterized in that an insulating polyurethane foam layer is formed on a conductive substrate, and a semiconductive rubber layer is formed on the insulating polyurethane foam layer. By using the charging member, it is not necessary to add conductive particles to the insulating polyurethane foam layer, so that the polyurethane foam layer is less likely to be distorted and the outer semiconductive rubber layer is Therefore, the present invention has been achieved.

  According to the charging member of the present invention, it has good chargeability and the polyurethane foam layer of the charging member is not easily distorted by a compressive force.

  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 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 developing unit 6, and the formed developed image is transferred to the transfer body 8 that has been transported in time by the action of the transfer unit 7. 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 g / cm, and the electrical pressure is a direct current applied to the charging roll. The voltage is preferably adjusted to an absolute value of 200 to 900 V, and when an AC voltage is applied, it is adjusted to a peak-to-peak voltage of 500 to 5,000 Vp-p and a frequency of 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 photoconductor, or may have a predetermined circumference in the forward or reverse direction with respect to 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.

  In the charging roll 5, an insulating polyurethane foam layer 53 is formed in a form of being in direct contact with a shaft body (core metal) 51 made of a stainless steel rod as a conductive substrate, and directly on the polyurethane foam layer 53. A semiconductive rubber layer 54 is formed so as to come into contact. The two layers form an elastic layer, and the semiconductive rubber layer 54 is the outermost layer. Such a configuration is preferable in terms of durability improvement and prevention of contamination of the roll surface with toner and external additives.

  The charging roll 5 may be provided with another elastic body layer in addition to the polyurethane foam layer 53 and the semiconductive rubber layer 54 of the present invention as long as the object of the present invention can be achieved.

The volume specific resistance of the semiconductive rubber layer 54 is preferably 10 ³ Ω · cm or more and 10 ¹¹ Ω · cm or less from the viewpoint of charging performance and leakage prevention.

The density of the semiconductive rubber layer 54 is preferably 0.5 g / cm ³ or more and less than 2 g / cm ³ . By setting it to 0.5 g / cm ³ or more, it is not necessary to add a large amount of a softener and the like, and contamination of the roll can be prevented. On the other hand, if it is 2 g / cm ³ or more, the elastic modulus increases, which is not preferable.

The density of the insulating polyurethane foam layer 53 is preferably 0.001 g / cm ³ or more and less than 0.5 g / cm ³ . If the density is too high, the elastic modulus is increased, which is not preferable. If the density is too low, the softness becomes too soft.

It is preferable that the volume resistivity of the insulating polyurethane foam layer 53 is 10 ¹² Ω · cm or more and 10 ¹⁶ Ω · cm or less. Since almost no conductive particles need be added to the foam layer, the strain recovery is improved.

For the volume resistivity, polyurethane foam or semiconductive rubber is cut into a cube of 5 cm on a side, and is applied to a pressure of 10 ⁷ Pa 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 foam, 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 density is measured by a known method.

  The polyurethane foam used in the present invention is a known soft polyurethane foam having a polyether polyol or polyester polyol, or a mixture of both, an isocyanate compound, a catalyst, a surfactant, and a foaming agent as a basic formulation. The polyurethane resin handbook (Iwata Keiji Nikkan Kogyo Shimbun; ISBN: 4526022349; (1987/09)), the basis of functional polyurethane, except that it relates to a polymerization catalyst in the novel electrophotographic charging roll manufacturing technology which is an embodiment of the invention And application (Katsuharu Matsunaga; CMC; ISBN: 4882312972; (2000/11)) and new edition polyurethane raw materials and product comprehensive survey New material and new material series (CMC; ISBN: 48823316404; new edition version (2000/09) ) Etc. Manufactured with raw materials and manufacturing techniques described in known literature.

  Specifically, a polyurethane foam is formed using a polyol and a polyfunctional isocyanate, a surfactant, a polymerization catalyst, and a foaming agent. The production method thereof is conventionally known and known to those skilled in the art. Although it can be produced by any method such as (1) prepolymer method, (2) one-shot method, and (3) partial prepolymer method, the one-shot method is preferably used in the present invention.

  Here, for the one-shot method, reference can be made to, for example, published by Kobunshi Publishing Co., Ltd., Yoshio Imai, “Polyurethane Foam”, (1987) and the like.

  Hereinafter, each component of the polyurethane foam of this invention is demonstrated concretely.

<Polyol component>
Polyether polyols include polyhydric alcohols such as ethylene glycol, glycerin, and trimethylolpropane, addition polymers obtained by addition polymerization of alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide to these polyhydric alcohols, and the like. A mixture is mentioned.

  Examples of polyester polyols include condensates obtained from the condensation reaction of polyvalent carboxylic acids such as adipic acid, phthalic acid, and succinic acid with polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, and trimethylolpropane. , And mixtures thereof.

  Examples of the polymer polyol include those obtained by polymerizing and stably dispersing vinyl monomers such as acrylonitrile and styrene in the presence of a radical polymerization initiator in at least one of the polyols listed above, and mixtures thereof.

  Other polyol components include polyols and phosphorus-containing polyols in which melamine or ammonium polyphosphate is dispersed, polylactone-based polyols obtained by ring-opening polymerization of lactone using polyhydric alcohol as an initiator, polycarbonate polyols, polygen-based polyols, and the like. These mixtures are mentioned.

  Furthermore, the polyol may be used as an OH group-terminated prepolymer reacted with a polyfunctional isocyanate described below.

  Water resistance is imparted by using the hydrophobic polyol described below, which is preferable. As a hydrophobic polyol, it passes in the compatibility test of the polyol mentioned later. Specifically, as dimer acid polyol, dimer acid and esterified product of polyfunctional hydroxide such as ethylene glycol, diethylene glycol, trimethylolpropane, glycerin, castor oil and castor oil modified product, polybutadiene polyol and hydrogenated product thereof Products, polyisoprene-based polyols and hydrogenated products thereof. Examples of these polyols include, but are not limited to, an OH group-terminated prepolymer previously reacted with a polyfunctional isocyanate described later or an NCO group-terminated.

<Multifunctional isocyanate>
Examples of the polyfunctional isocyanate include aromatic polyisocyanates and aliphatic polyisocyanates containing two or more isocyanate groups in the molecule, or modified products thereof, specifically, toluene diisocyanate ( TDI), diphenylmethane isocyanate (MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tetramethylxylylene diisocyanate (TMXDI), etc., and mixtures thereof. Moreover, the NCO group terminal prepolymer etc. which were made to react with the said polyol, these mixtures, etc. are mentioned.

<Polymerization catalyst>
As a polymerization catalyst, a general primary amine compound to a tertiary amine compound or a salt thereof can be used. An aromatic amine such as pyridine can also be used. Among these amine compounds, triethylenediamine is preferable. It is also preferable to use these amine compounds and tin-containing compounds in combination for the reaction.

<Foam stabilizer>
Examples of the foam stabilizer include organic silicone foam stabilizers, surfactants, and the like, and mixtures thereof. In the former case, it is preferable not to use them depending on the application, but if used intentionally, a polyfunctional isocyanate and It is preferable to use a silicone foam stabilizer having an active group such as a hydroxyl group, a mercapto group, an amino group, an epoxy group, or a carboxyl group that reacts, because it becomes non-migratory. In the latter case, diethylamino oleate, sorbitan monostearate, glycerin monooleate, vinyl pyrrolidone, fluorine, organic compound, etc., and mixtures thereof can be mentioned.

<Foaming agent>
Examples of the blowing agent include water; inert gases such as nitrogen, carbon dioxide, and air that are gaseous at normal pressure; halogenated alkanes such as monofluorinated trichloromethane and dichloromethane; and low-boiling alkanes such as butane and pentane. And azobisisobutylnitrile that generates cracked nitrogen gas and the like, and mixtures thereof.

  As other additives, a crosslinking agent, a colorant, a resin modifier, a flame retardant, an ultraviolet absorber, a durability improver, and the like can be arbitrarily used as necessary.

  The insulating polyurethane foam used in the present invention does not need to contain conductive particles, and can produce a foam with low compression set even at a low density, thus completing the present invention. That is, in the present invention, the density of the polyurethane foam can be reduced, and the low elastic modulus required for the charging roll can be achieved with almost no plasticizer, and the layer for adjusting conductivity (the semiconductor shown below). Material design such as a rubber layer).

The conductive polyurethane may be added to the insulating polyurethane foam used in the present invention within a range that does not affect the compression set.
<Semiconductive rubber layer>
Hereinafter, the semiconductive rubber layer will be described.

  The semiconductive rubber layer can be produced by adding a carbon powder typified by carbon black to a general rubber material and adjusting the volume resistivity. A foaming agent may be used as necessary, but it is preferable for the purpose of the present invention not to use a foaming agent. The carbon powder used in the present invention is appropriately selected from materials described in the Carbon Black Handbook edited by the Carbon Black Association.

  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 a charged body.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.
Example 1
(Formation of insulating polyurethane foam layer)
A component is 49 g of TDI-80, B component is 100 g of PPG-BM (glycerin-based polyoxypropylene triol: Mw = 3000: OH number 56), 1.2 g of silicon surfactant (L520), water and catalyst (A compound of triethylenediamine and tin).

When a metal rod was installed at the center of the mold in the shape of a charging roll, the A component and the B component were vigorously mixed, poured into a 1 g mold and heated to 50 ° C., a foaming reaction occurred. After removing from the mold and aging at 80 ° C. for 4 hours, the surface was polished flat, taking care not to expose the cell to the outside. The density of the insulating polyurethane foam layer was 0.2 g / cm ³ and the volume resistivity was 10 ¹⁵ Ω · cm.

(Formation of semiconductive rubber layer)
Rubber layer formulation A
Epichlorohydrin rubber terpolymer 100 parts by mass carbon black (trade name: Ketjen Black EC, manufactured by Lion Akzo)
20 parts by weight quaternary ammonium salt 1 part by weight zinc oxide 5 parts by weight fatty acid 2 parts by weight After kneading for 10 minutes in a closed mixer in which the composition A of the rubber layer was adjusted to 60 ° C., sebacin was added to 100 parts by weight of epichlorohydrin rubber 5 parts by weight of an acid polyester plasticizer was added, and the mixture was further kneaded for 20 minutes in 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 formed into a roll shape on a polished polyurethane foam by an extrusion molding machine, wound, heat-vulcanized, and then polished. The semiconductive rubber layer had a density of 1.0 g / cm ³ and a volume resistivity of 10 ⁷ Ω · 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
As a result, although the image was slightly stained from about 500 sheets, it was almost satisfactory. Thereafter, the charging roll is removed and sandwiched between two 10 cm square plates, and a 1 kg load is applied for 24 hours. After removing the load and leaving it for 24 hours, the difference between the average of the three outer diameters of the part sandwiched between the plates and the average of the three outer diameters of the parts not sandwiched (evaluation of strain due to compression) was obtained. , 0.
(Example 2)
The charging roll of Example 1 was further provided with a surface layer to form a charging roll. 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 coating material for dipping was applied onto the roll so as to have a film thickness of 10 μm by dipping, and then air-dried for 10 minutes and then dried at 160 ° C. for 1 hour with a heating dryer to obtain a charging roll. .

When durability evaluation similar to that in Example 1 was performed, the image was free from smudges and was a good result. Thereafter, the strain was evaluated in the same manner as in Example 1. As a result, a strain of 0.05 mm was observed.
(Comparative Example 1)
A polyurethane foam was formed in the same manner as in the formation of the polyurethane foam layer of Example 1, except that 30 parts by mass of carbon black (trade name: Ketjen Black EC, manufactured by Lion Akzo) was added to the polyurethane foam layer of Example 1. A comparative charging roll having only one foam layer was produced.

When the same durability evaluation as in Example 1 was performed, a phenomenon in which abnormal noise was generated after 800 sheets were observed. Thereafter, the strain was evaluated in the same manner as in Example 1. As a result, a strain of 1.5 mm was observed.
(Comparative Example 2)
A charging roll was produced in the same manner as in Example 1 except that the formation order of the semiconductive rubber layer and the polyurethane foam layer in Example 1 was reversed. That is, the semiconductive rubber layer of Example 1 was wrapped around a metal and vulcanized, and then the insulating polyurethane foam layer of Example 1 was formed thereon. The surface layer was carefully polished so that the cells did not appear outside to produce a charging roll.

When the same durability evaluation as in Example 1 was performed, the function was not sufficient and a dirty image appeared on the first printed sheet, so the evaluation was stopped.
(Comparative Example 3)
In Example 1, a charging roll was produced in the same manner as in Example 1 except that the polyurethane foam layer was not provided and only the semiconductive rubber layer was provided.

  When the durability evaluation similar to that in Example 1 was performed, the semiconductive rubber layer was stiff, so that it did not function sufficiently as a charging roll, and a dirty image appeared on the first printed sheet. . When the photoreceptor was confirmed, it was scratched by contact with the semiconductive rubber layer.

  From the above examples and comparative examples, the charging roll of the present invention has good durability test results, and since it is difficult to be distorted by compression even in the sample after the durability test, it does not deform even when used for a long time, The object of the present invention has been achieved.

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 roll 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 Unit 53 Insulating Polyurethane Foam Layer 54 Semiconducting Rubber Layer

Claims (11)

An electrophotographic charging member, wherein an insulating polyurethane foam layer is formed on a conductive substrate, and a semiconductive rubber layer is formed on the insulating polyurethane foam layer. 2. The electrophotographic charging member according to claim 1, wherein the semiconductive rubber layer has a volume resistivity of 10 ³ Ω · cm to 10 ¹¹ Ω · cm. The charging member for electrophotography according to claim 1 or 2, wherein the density of the semiconductive rubber layer is 0.5 g / cm ³ or more and less than 2 g / cm ³ . The charging member for electrophotography according to any one of claims 1 to 3, wherein the outermost layer is the semiconductive rubber layer. The charging member for electrophotography according to any one of claims 1 to 4, wherein the density of the insulating polyurethane foam layer is 0.001 g / cm ³ or more and less than 0.5 g / cm ³ . 6. The electrophotographic charging member according to claim 1, wherein the insulating polyurethane foam layer has a volume resistivity of 10 ¹² Ω · cm to 10 ¹⁶ Ω · cm. 7. The electrophotographic charging member according to claim 1, wherein the layer in direct contact with the conductive substrate is an insulating polyurethane foam layer. The electrophotographic charging member according to claim 1, wherein the layer in direct contact with the insulating polyurethane foam layer is a semiconductive rubber layer. 9. 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 10, wherein the electrophotographic charging member is charged in contact with an object to be charged.

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