JP7206937B2 - Electrophotographic photoreceptor, electrophotographic image forming method and electrophotographic image forming apparatus - Google Patents

Description

The present invention relates to an electrophotographic photoreceptor and an electrophotographic image forming apparatus. More particularly, the present invention relates to an electrophotographic photoreceptor that suppresses the occurrence of fog, image memory and ghost, an electrophotographic image forming method, and an electrophotographic image forming apparatus equipped with the electrophotographic photoreceptor.

2. Description of the Related Art Copiers, printers, facsimiles, and the like are generally used to form color images, and the demand for higher image quality is increasing accordingly. Further, an organic photoreceptor containing an organic photoconductive substance is widely used as an electrophotographic photoreceptor. Compared to inorganic photoreceptors, organic photoreceptors are advantageous in that it is easy to develop materials that are compatible with various exposure light sources from visible light to infrared light, that materials that do not pollute the environment can be selected, and that manufacturing costs are low. It is a point.

On the other hand, in electrophotographic image formation, an electrophotographic photoreceptor (hereinafter also simply referred to as a photoreceptor) forms an image through an image forming process such as charging, image exposure, development, transfer, cleaning, and the like. However, there is an increasing demand for high-definition and high-quality images to be formed. In particular, the electrophotographic photosensitive member undergoes several image forming processes for one image. The associated image memory and ghost may occur.

Image memory and ghost can be caused by various systems in an electrophotographic photoreceptor that uses a plurality of layer structures. ) and charge accumulation in the bulk of the UCL. .

If the undercoat layer does not have a suitable electrical resistance, positive memory tends to occur on the side of insufficient blocking properties, whereas negative memory tends to occur if the electrical resistance is excessively increased.

Combined with the restrictions to maintain high sensitivity and high durability while maintaining image quality in terms of electrostatic characteristics, it is a prescription design that matches the main purpose for each use, and partial quality improvement The sacrifice of will also come.

In order to suppress the negative memory, measures have been taken to lower the electrical resistance of the UCL. In contrast, it becomes necessary to impart specific electrical resistance characteristics.

One of the causes of memory is the accumulation of charges between the undercoat layer and the charge generation layer and within the undercoat layer. Specifically, a memory occurs when charges are accumulated between the undercoat layer and the charge generation layer or in the undercoat layer, and the history of one rotation before remains, resulting in a ghost.

In order to reduce this memory in the structure of a conventional photoreceptor, the undercoat layer should contain a metal oxide effective for electron transport, or a charge transport material effective for transporting electrons and holes (hereinafter referred to as "charge transport material"). , and also referred to as “CTM” (Charge Transport Material)) have been attempted, but are not sufficient.

In order to solve the above problem, in Patent Document 1, an undercoat layer containing a conductive metal oxide and an electron-accepting compound, a charge-generating layer, and a charge-transport layer are laminated on a conductive support. Disclosed is an image forming apparatus having an image bearing member with a layer volume resistivity in the range of 10 ¹⁰ to 10 ¹³ Ω·cm and capable of obtaining good images without fogging. Further, in Patent Document 2, in an electrophotographic photoreceptor having an undercoat layer and a photosensitive layer on a conductive support, the undercoat layer has a volume resistivity of 3.5×10 ¹⁰ to 1.0×10 ¹¹ . An image forming apparatus is disclosed which has a structure within the range of Ω·cm, maintains image contrast, suppresses the occurrence of fogging, and improves reproducibility. Further, in Patent Document 3, an undercoat layer having a volume resistivity in the range of 2.0×10 ⁸ to 2.0×10 ¹² Ω·cm is formed on a conductive substrate, and a charge generating layer is formed thereon. An electrophotographic photoreceptor having a structure in which a layer and an outermost layer are laminated is disclosed, and an image forming apparatus is disclosed in which afterimage phenomenon (also referred to as ghost) caused by remaining image history of the previous circulation is suppressed.

In the methods described in Patent Literatures 1 to 3, the volume resistivity of the undercoat layer is specified to be 10 ⁸ Ω·cm or more, but all measurements are performed under the condition of low electric field strength.

The electric field strength provided in an actual image is often 10 ⁴ V/cm or more, rather than the level described in each of the above patent documents. In particular, in the case of suppressing image black spots and fogging, it is necessary to specify the electric field strength actually used, and deviation may occur within the range disclosed above.

JP 2006-184512 A JP 2013-068825 A JP 2018-063367 A

The present invention has been made in view of the above problems and circumstances, and the problem to be solved is to provide an electrophotographic photoreceptor, an electrophotographic image forming method, and the electrophotographic photoreceptor that suppresses the occurrence of fog, image memory and ghost. An object of the present invention is to provide an electrophotographic image forming apparatus equipped with.

In order to solve the above problems, the present inventors investigated the causes of the above problems and found that at least an undercoat layer and a photosensitive layer are sequentially laminated on a conductive support, and the undercoat layer is a metal. A photosensitive layer that contains oxide particles, has a volume resistivity ρ in a specific range under an electric field of a specific strength, and has a layer thickness of the undercoat layer and a layer thickness of the photosensitive layer that are within specific ranges; The electrophotographic photoreceptor containing any compound selected from compounds having a structure represented by a specific general formula in the charge transport layer, which is a part of the constitution of, causes fogging, image memory and ghosting The inventors have found that it is possible to provide an electrophotographic photoreceptor that suppresses , and have completed the present invention.

That is, the problems related to the present invention are solved by the following means.

1. An electrophotographic photoreceptor obtained by sequentially laminating at least an undercoat layer and a photosensitive layer on a conductive support,
the photosensitive layer is composed of at least a charge generation layer and a charge transport layer,
The charge transport layer contains a compound selected from compounds having structures represented by the following general formulas (1) to (3), and the layer thickness of the charge transport layer is in the range of 29 μm or more and less than 50 μm. and
The undercoat layer contains metal oxide particles and has a volume resistivity ρ of 2 ×10 ⁷ (Ω·cm) at 23±2° C. when an electric field with a strength of 5×10 ⁴ (V/cm) is applied. Above, within the range of less than 1 × 10 ⁸ (Ω cm),
An electrophotographic photoreceptor, wherein the undercoat layer has a thickness of 10 to 40 μm, and the photosensitive layer has a thickness of 30 to 50 μm.

[In the above general formulas (1) to ( 3 ), R represents an alkyl group, an alkoxy group or a halogeno group. n represents an integer selected from 0 to 4; ]

2 . Item 1, wherein the metal oxide contained in the undercoat layer contains titanium oxide, zinc oxide, tin oxide, or aluminum oxide, and is surface-treated with a silane coupling agent. The electrophotographic photoreceptor described in .

3 . 3. The electrophotographic photoreceptor of item 1 or 2 , wherein the photosensitive layer contains a titanyl phthalocyanine compound or a gallium phthalocyanine compound.

4 . An electrophotographic image forming method for forming an image through at least a charging step, an exposure step, a developing step and a transfer step using an electrophotographic photosensitive member,
An electrophotographic image forming method, wherein the electrophotographic photoreceptor according to any one of items 1 to 3 is used as the electrophotographic photoreceptor.

5 . 5. The electrophotographic image forming method according to item 4 , wherein the electrophotographic photosensitive member does not have a charge removing step for removing charges from the surface of the electrophotographic photosensitive member.

6 . An electrophotographic image forming apparatus comprising the electrophotographic photoreceptor according to any one of items 1 to 3 .

According to the means of the present invention, it is possible to provide an electrophotographic photoreceptor that suppresses the occurrence of fogging, image memory and ghost, and an electrophotographic image forming apparatus equipped with the electrophotographic photoreceptor.

It is speculated that the expression mechanism or action mechanism of the effect of the present invention is as follows.

A conventional general negative charging type photoreceptor comprises an under coat layer (UCL), a charge generation layer (CGL), a charge transport layer (CTL), and a charge transport layer (CTL) on a conductive support. Layer), etc. are stacked in order.

Further, in a conventional general negative charging type photoreceptor, the surface side is charged negatively (minus), and the conductive support side is positively induced. When the photoreceptor is exposed to light, charges are generated in the charge generation layer, and holes flow from the charge generation layer to the surface side to neutralize the charges. electrons flow.

As described above, unless the appropriate electrical resistance is selected for the undercoat layer, positive memory tends to occur on the side of insufficient blocking properties, and conversely, excessively increasing the resistance tends to cause negative memory. .

Combined with the restrictions to maintain high sensitivity and high durability while maintaining image quality in terms of electrostatic characteristics, it is a prescription design that matches the main purpose for each use, and partial quality improvement The sacrifice of will also come.

Measures have been taken to lower the resistance of the UCL in order to suppress the negative memory. , it becomes necessary to impart specific electrical resistance characteristics.

One of the causes of memory is the accumulation of charges between the undercoat layer and the charge generation layer and within the undercoat layer. Specifically, between the undercoat layer and the charge generation layer, or within the undercoat layer, the difference in the degree of charge accumulation between the exposed portion and the non-exposed portion causes a ghost due to the history of one rotation before remaining. .

In order to solve the above problem, the electrophotographic photoreceptor of the present invention defines a range of electric resistance in which both the chargeability and the photoconductive property of the undercoat layer are compatible. As a result, the occurrence of image memory is suppressed while maintaining the range in which the chargeability is ensured and fogging and image black spots can be sufficiently suppressed.

The volume resistivity ρ when an electric field with a strength of 5×10 ⁴ (V/cm) is applied is 2 ×10 ⁷ (Ω· cm) or more and less than 1 ×10 ⁸ (Ω·cm).

More specifically, the undercoat layer formed on the conductive support has a function of blocking for securing chargeability and a function of blocking the charge from the photosensitive layer such as the charge generation layer and the charge transport layer. play a role in charge transfer during photodischarge.

In practice, the electrophotographic photosensitive member must maintain sufficient chargeability when a rather high electric field such as an electric field with an intensity E of 5×10 ⁴ (V/cm) is applied. If the volume resistivity ρ of the undercoat layer is set to 2 ×10 ⁷ (Ω·cm) or more, when the actual photosensitive layer is laminated and subjected to an electrophotographic process, the charging and transfer process will be caused by the undercoat layer. It is possible to suppress the accumulation of inheritance and the action of injected charges, and to suppress the influence on the chargeability in the next cycle.

Further, when the same electric field strength E is applied, if the volume resistivity ρ of the undercoat layer is less than 1 ×10 ⁸ (Ω·cm), sufficient photoconductivity can be ensured and charge accumulation will not occur. , the occurrence of image memory can be prevented.

Therefore, in the present invention, the volume resistivity ρ when an electric field of strength (E=5×10 ⁴ (V/cm)) is applied is 2 ×10 ⁷ (Ω·cm) or more as a range in which these are compatible. It should be less than 1 ×10 ⁸ (Ω·cm).

Further, in the present invention, the layer thickness of the undercoat layer is in the range of 10 to 40 μm, and the layer thickness of the photosensitive layer is in the range of 30 to 50 μm.

When the thickness of the undercoat layer is 10 µm or more, fogging, image black spots, and image memory can be prevented. can be prevented from occurring.

In addition, the degree of image memory is originally small, and memory tends to occur with a thick photosensitive layer when durability is required, but by setting the thickness of the photosensitive layer to 30 μm or more, a more excellent effect of preventing image memory is obtained. demonstrated. Further, by setting the thickness to 50 μm or less, the electrophotographic image forming apparatus can be stably used without excessively increasing the residual potential during photodischarge.

A cross-sectional view showing an example of the configuration of the electrophotographic photoreceptor of the present invention. Schematic diagram showing an example of the configuration of a volume ratio measuring device used to measure the volume resistivity ρ of the undercoat layer. Schematic diagram showing an example of the overall configuration of a tandem-type electrophotographic image forming apparatus provided with the electrophotographic photoreceptor of the present invention. An enlarged schematic diagram showing the arrangement relationship between the photoreceptor and the cleaning blade in the tandem type electrophotographic image forming apparatus of the present invention. A schematic diagram showing an example of the configuration of an electrophotographic image forming apparatus using the electrophotographic photoreceptor of the present invention. Diagrams explaining an original document (a), a negative memory (b), and a positive memory (c) used for memory evaluation.

The electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor obtained by sequentially laminating at least an undercoat layer and a photosensitive layer on a conductive support, wherein the photosensitive layer comprises at least a charge generation layer and a charge transport layer. The charge transport layer is composed of layers, the charge transport layer contains a compound selected from compounds having structures represented by the general formulas (1) to (3), and the charge transport layer has a layer thickness of 29 μm or more, It is within the range of less than 50 μm, the undercoat layer contains metal oxide particles, and an electric field with a strength of 5×10 ⁴ (V/cm) (hereinafter also referred to as electric field strength E) is applied at 23±2° C. The volume resistivity ρ when given is in the range of 1×10 ⁷ (Ω·cm) or more and less than 2×10 ⁸ (Ω·cm), and the layer thickness of the undercoat layer is in the range of 10 to 40 μm. and the layer thickness of the photosensitive layer is in the range of 30 to 50 μm. This feature is a technical feature common to the following embodiments.

Also, the metal oxide particles contained in the undercoat layer are any one selected from titanium oxide, zinc oxide, tin oxide, and aluminum oxide, and are surface-treated with a silane coupling agent. However, it is preferable in that the sensitizing effect by the sensitizing dye described below is excellent and the effect of improving the memory can be obtained.

In addition, it is preferable that the photosensitive layer contains a titanyl phthalocyanine compound or a gallium phthalocyanine compound, since the effects of suppressing fogging, image memory and ghosting, which are the intended effects of the present invention, can be further exhibited.

Further, the electrophotographic image forming method of the present invention is an electrophotographic image forming method in which an image is formed through at least a charging step, an exposure step, a developing step and a transfer step using an electrophotographic photosensitive member, wherein the electrophotographic The electrophotographic photoreceptor of the present invention is used as the photoreceptor.

DETAILED DESCRIPTION OF THE INVENTION The present invention, its constituent elements, and embodiments and modes for carrying out the present invention will be described in detail below. In addition, in the present application, "-" representing a numerical range is used in the sense that the numerical values described before and after it are included as a lower limit value and an upper limit value.

《Electrophotographic photoreceptor》
[Basic Configuration of Electrophotographic Photoreceptor]
FIG. 1 (b) is a sectional view showing an example of the configuration of the electrophotographic photoreceptor of the present invention.

The structure of the electrophotographic photoreceptor of the present invention is a negative charging photoreceptor in which the photosensitive layer is composed of at least a charge generation layer and a charge transport layer.

FIG. 1(b) is a cross-sectional view showing an electrophotographic photoreceptor 100B having a second configuration, in which an undercoat layer 103 is formed on a conductive support 102, and a charge generation layer 105 and a charge generation layer 105 are formed thereon. The photosensitive layer 104 composed of the charge transport layer 106 is laminated in order, the undercoat layer 103 contains metal oxide particles, and the strength is 5×10 ⁴ (V/cm) at 23±2° C. is in the range of 2×10 ⁷ (Ω·cm) or more and less than 1×10 ⁸ (Ω·cm) when an electric field of ) to (4), and the layer thickness of the charge transport layer 106 is preferably in the range of 30 to 50 μm. A protective layer (also referred to as a surface layer) may be provided on the photosensitive layer 104 as necessary, but it is not an essential requirement in the electrophotographic photoreceptor of the present invention.

[Constituent Elements of Electrophotographic Photoreceptor]
The details of the main constituent elements of the electrophotographic photoreceptor of the present invention are described below.

[Conductive support]
The conductive support may be any material as long as it has conductivity. For example, metals such as aluminum, copper, chromium, nickel, zinc, and stainless steel are formed into drums or sheets, and metal foils such as aluminum and copper are used. Examples include those laminated on plastic films, those vapor-deposited on plastic films with aluminum, indium oxide, tin oxide, etc., and metals, plastic films, or papers provided with a conductive layer by applying a conductive substance alone or together with a binder resin. .

[Undercoat layer]
The electrophotographic photoreceptor of the present invention has an undercoat layer having a barrier function and an adhesive function between the conductive support and the photosensitive layer.

The undercoat layer can be formed by dissolving a binder resin such as casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide, polyurethane and gelatin in a known solvent and dip coating or the like. Among the binder resins, alcohol-soluble polyamide resins are preferred.

The undercoat layer according to the present invention contains metal oxide particles and has a volume resistivity ρ of 2 × ^{10 7 (} Ω·cm) or more and less than 1×10 ⁸ (Ω·cm). Further, the layer thickness of the undercoat layer is characterized by being in the range of 10 to 40 μm, preferably in the range of 15 to 30 μm.

(metal oxide particles)
The metal oxide particles contained in the undercoat layer according to the present invention are not particularly limited, but are preferably titanium oxide fine particles, zinc oxide fine particles, tin oxide fine particles, or aluminum oxide fine particles. Also, the number average primary particle size of the metal oxide fine particles is preferably in the range of 1 to 300 nm. Especially preferably, it is within the range of 3 to 100 nm.

The number average primary particle diameter of the metal oxide fine particles was obtained by taking a 10,000-fold enlarged photograph with a scanning electron microscope "JSM-7401F" (manufactured by JEOL Ltd.), and capturing 300 particles at random with a scanner. A photographic image (excluding agglomerated particles) was processed by an automatic image processing analyzer "LUZEX (registered trademark) AP" (manufactured by Nireco Co., Ltd.) software Ver. 1.32 is used to perform binarization processing, calculate the Feret diameter in the horizontal direction, and calculate the average value as the number average primary particle diameter. Here, the horizontal Feret diameter refers to the length of the side parallel to the x-axis of the circumscribed rectangle obtained by binarizing the image of the metal oxide fine particles.

<Surface treatment with silane coupling agent>
The metal oxide particles according to the present invention are preferably surface-treated with a silane coupling agent, and more preferably surface-modified with a coupling agent having a reactive organic group.

As the coupling agent for modifying the surface of the metal oxide fine particles according to the present invention, a coupling agent that reacts with a hydroxyl group or the like present on the surface of the metal oxide fine particles is preferable. agents, titanium coupling agents, and the like. In the present invention, a coupling agent having a reactive organic group is preferred, and as the coupling agent having a reactive organic group, a coupling agent having a radically polymerizable reactive group is preferred. As the coupling agent having a radically polymerizable reactive group, a silane coupling agent having a radically polymerizable reactive group such as a vinyl group, an acryloyl group or a methacryloyl group is preferable. Examples of agents include the following known compounds.

S-1: CH ₂ =CHSi(CH ₃ )(OCH ₃ ) ₂
S-2: CH ₂ =CHSi(OCH ₃ ) ₃
S-3: CH ₂ =CHSiCl ₃
S-4: _CH2 =CHCOO( _CH2 ) _2Si ( _CH3 ) ₍ OCH3) ₂
S-5: _CH2 =CHCOO( _CH2 ) _2Si ( _OCH3 ) ₃
S-6: _CH2 =CHCOO( _CH2 ) _2Si ( _OC2H5 ) _{( OCH3} ) ₂
S-7: _CH2 =CHCOO( _CH2 ) _{3Si (} OCH3) ₃
S-8: _CH2 =CHCOO( _CH2 ) _2Si ( _CH3 ) _Cl2
S-9: _CH2 =CHCOO _{( CH2} ) _2SiCl3
S-10: _CH2 =CHCOO( _CH2 )3Si _{( CH3} ) _Cl2
S-11: _CH2 =CHCOO _{( CH2} ) _3SiCl3
S-12: _CH2 =C( _CH3 )COO( _CH2 ) _2Si ( _CH3 ) ₍ OCH3) ₂
S-13: _CH2 =C( _CH3 )COO( _CH2 ) _2Si ( _OCH3 ) ₃
S-14: _CH2 =C( _CH3 )COO( _CH2 )3Si _{( CH3} ) ₍ OCH3) ₂
S-15: _CH2 =C( _CH3 )COO( _CH2 ) _{3Si (} OCH3) ₃
S-16: _CH2 =C( _CH3 )COO( _CH2 ) _2Si ( _CH3 ) _Cl2
S-17: _CH2 =C( _CH3 )COO _{( CH2} ) _2SiCl3
S-18: _CH2 =C( _CH3 )COO( _CH2 )3Si _{( CH3} ) _Cl2
S-19: _CH2 =C( _CH3 )COO _{( CH2} ) _3SiCl3
S-20: _CH2 = _CHSi ( _C2H5 ) ₍ OCH3) ₂
S-21: CH ₂ =C(CH ₃ )Si(OCH ₃ ) ₃
S-22: _CH2 =C( _CH3 )Si _{( OC2H5} ) ₃
S-23: CH ₂ =CHSi(OCH ₃ ) ₃
S-24: CH ₂ =C(CH ₃ )Si(CH ₃ )(OCH ₃ ) ₂
S-25: _CH2 =CHSi( _CH3 ) _Cl2
S-26: _CH2 = _CHCOOSi (OCH3) ₃
S-27: _CH2 = _CHCOOSi ( _OC2H5 ) ₃
S-28: _CH2 =C( _CH3 ) _COOSi (OCH3) ₃
S-29: _CH2 =C( _CH3 ) _COOSi ( _OC2H5 ) ₃
S-30: _CH2 =C( _CH3 )COO( _CH2 ) _{3Si ( OC2H5} ) ₃
S-31: _CH2 =CHCOO( _CH2 ) _{2Si(CH3)2 ( OCH3 )}
S-32: _CH2 =CHCOO( _CH2 ) _2Si ( _CH3 )( _OCOCH3 ) ₂
S-33: _CH2 =CHCOO( _CH2 ) _2Si ( _CH3 )( _ONHCH3 ) ₂
S-34: _CH2 =CHCOO( _CH2 ) _2Si ( _CH3 ) _{( OC6H5} ) ₂
S-35: _CH2 =CHCOO( _CH2 ) _{2Si ( C10H21} ) ₍ OCH3) ₂
S-36: _CH2 =CHCOO( _CH2 ) _{2Si ( CH2C6H5} ) _{( OCH3} ) ₂
S _{- 37} : _{( CH3O} ) _{2 ( CH3} ) _{SiC3H6NHC2H4NH2
S - 38} : _{( CH3O ) 3SiC3H6NHC2H4NH2}
S _{- 39} : _{( CH3O} ) _3SiC3H6NH2
S _{- 40} : _{( C2H5O ) 3SiC3H6NH2}
S-41: _{( C2H5O} ) _{3SiC3H6N =} C _{( CH3} ) _{( C4H9} )
S _- 42: _{( CH3O} ) _{3SiC3H6NH- ( C6H5} )
As the silane coupling agent, a silane compound having a radically polymerizable reactive organic group may be used in addition to the above S-1 to S-42. These silane coupling agents can be used alone or in combination of two or more.

The surface-modified metal oxide fine particles are prepared by using a wet media dispersion type apparatus using 0.1 to 100 parts by mass of a coupling agent and 50 to 5000 parts by mass of a solvent with respect to 100 parts by mass of metal oxide fine particles. Surface modification is preferred. Surface modification can also be performed by a dry method.

A surface modification method for producing metal oxide fine particles uniformly surface-modified with a coupling agent will be described below.

By wet pulverizing the slurry (solid particle suspension) containing the metal oxide fine particles and the coupling agent, the metal oxide fine particles are pulverized and the surface modification of the fine particles proceeds. Thereafter, by removing the solvent and pulverizing, metal oxide fine particles uniformly surface-modified with a coupling agent can be obtained.

The wet media dispersion type device, which is the surface modification device used in the present invention, is a device in which beads are filled as media in a container, and a stirring disk attached perpendicularly to the rotating shaft is rotated at high speed to obtain metal oxide fine particles. It is an apparatus having a process of crushing, pulverizing and dispersing the aggregated particles of As for the structure, there is no problem as long as the metal oxide fine particles are sufficiently dispersed and the surface can be modified when the metal oxide fine particles are surface-modified. , various modes can be adopted. Specifically, sand mills, ultravisco mills, pearl mills, grain mills, dyno mills, agitator mills, dynamic mills and the like can be used. These dispersing devices use grinding media such as balls or beads to perform fine grinding and dispersion by impact crushing, friction, shearing, shear stress, and the like.

As the beads used in the wet media dispersion type apparatus, balls made of glass, alumina, zircon, zirconia, steel, flint stone, or the like can be used as a raw material, and those made of zirconia or zircon are particularly preferable. As for the size of beads, beads with a diameter of about 1 to 2 mm are usually used, but in the present invention, beads with a diameter of about 0.1 to 1.0 mm are preferably used.

Various materials such as stainless steel, nylon, and ceramics can be used for the discs and the inner wall of the container used in the wet media dispersion type apparatus. Internal walls are preferred.

Metal oxide fine particles surface-modified with a coupling agent can be obtained by the wet treatment as described above. From the viewpoint of improving the abrasion resistance of the surface protective layer, it is preferable that the above-described surface-modified metal oxide fine particles are contained in an amount of 30 to 250 parts by mass with respect to 100 parts by mass of the crosslinkable polymerizable compound.

(volume resistivity)
The volume resistivity ρ of the undercoat layer according to the present invention is 2 ×10 ⁷ (Ω·cm) when an electric field with a strength of 5×10 ⁴ (V/cm) is applied at 23±2° ) above and less than 1 ×10 ⁸ (Ω·cm).

A method for measuring the volume resistivity ρ of the undercoat layer according to the present invention will be described with reference to the drawings.

For the volume resistivity according to the present invention, for example, refer to JIS-K6271-2 “Resistivity test method by parallel terminal electrode method” or JIS-K6911 “Volume resistivity measurement method by double link electrode method”. be able to.

FIG. 2 is a schematic diagram showing an example of the configuration of a volume resistivity measuring device used to measure the volume resistivity ρ of the undercoat layer.

In the volume resistivity measuring apparatus 500 shown in FIG. 2, aluminum is vacuum-deposited on a slide glass substrate 502 at a degree of vacuum of 2.66×10 ⁻³ Pa or less, and a substrate-side aluminum electrode having a measurement area of 2 cm ² is used. 503A. At this time, a lead electrode portion 503B for wiring is also provided.

In order to form the undercoat layer 504 to be measured on the formed substrate-side aluminum electrode 503A, both the substrate-side aluminum electrode 503A and the coating solution for forming the undercoat layer were heated to 50° C. An undercoat layer 504 is formed on the substrate-side aluminum electrode 503A under the condition of a predetermined layer thickness. Next, after heat treatment is performed at a temperature corresponding to the constituent material of the undercoat layer 504, a surface-side aluminum electrode 505 made of aluminum is formed at a position facing the substrate-side aluminum electrode 503A of 2 cm ² .

Next, a solder 511 is formed on the end of the extraction electrode portion 503B using an ultrasonic soldering iron, and a microammeter 513 is connected to this via a bonding wire 512 . On the other hand, a solder 507 is formed at the end of the surface-side aluminum electrode 505 using an ultrasonic soldering iron, which is connected to a protective resistor 506 via a bonding wire 508, and further connected to a DC power supply 509 to increase volume resistance. Use it as a sample for rate measurement.

Next, a method for calculating the volume resistivity ρ will be described.

As the minute ammeter 513, a model 6487 picoammeter manufactured by Kiethlay and equipped with a DC power supply 509 is used.

First, the layer thickness d (cm) of the undercoat layer 504 is multiplied so that the electric field strength E=5×10 ⁴ (V/cm), and the voltage V (V) applied by the DC power supply 509 is set. For example, when the layer thickness d of the undercoat layer is 20 (μm), (5×10 ⁴ (V/cm))×(20×10 ⁻⁴ (cm))=100 (V) is applied. .

then
From the layer thickness d (cm) of the undercoat layer, the electric field strength E (V/cm), the current I (A), the effective electrode area S (cm ² , S=2 cm ² in the above case), according to the following formula (A) , the volume resistivity ρ can be obtained. All measurements are performed in an environment of 23±2°C.

Formula (A) Volume resistivity ρ (Ω cm) = [V (V) / I (A)] / [d (cm) / S (cm ² )]
The method for achieving the volume resistivity ρ of the undercoat layer according to the present invention within the range defined by the present invention is not particularly limited. By appropriately adjusting the layer thickness of the coating layer, etc., the volume resistivity ρ within the range of 2 ×10 ⁷ (Ω·cm) or more and less than 1 ×10 ⁸ (Ω·cm) can be obtained.

(Formation of undercoat layer)
The solvent used for preparing the undercoat layer-forming coating liquid used for forming the undercoat layer is a solvent that can well disperse inorganic fine particles such as the metal oxide fine particles described above and dissolve binder resins such as polyamide resins. is preferred. Specifically, alcohols having 2 to 4 carbon atoms such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol, and sec-butanol are preferred binder resins for polyamide resins. It is preferable because it expresses good solubility and coating performance. Further, in order to improve storage stability and dispersibility of inorganic fine particles, the following co-solvents can be used in combination with the solvent. Examples of co-solvents that produce favorable effects include methanol, benzyl alcohol, toluene, cyclohexanone, and tetrahydrofuran.

The concentration of the binder resin when forming the coating liquid can be appropriately selected according to the layer thickness of the undercoat layer and the coating method. Further, when the metal oxide fine particles are dispersed, the mixing ratio of the metal oxide fine particles to the binder resin is preferably 20 to 400 parts by mass of the metal oxide fine particles to 100 parts by mass of the binder resin. It is more preferable to make it to 200 parts by mass.

Means for dispersing the metal oxide fine particles include, but are not limited to, an ultrasonic disperser, a ball mill, a sand grinder, a homomixer, and the like.

[Photosensitive layer]
As described above, the photosensitive layer constituting the electrophotographic photoreceptor of the present invention includes, for example , at least the charge generation layer 105 (CGL) and the charge transport layer 106 (CTL) as shown in FIG. A layer structure in which the functions of the photosensitive layer are separated is more preferable. By forming the photosensitive layer 104 having a function-separated layer structure in this manner, it is possible to control the increase in residual potential due to repeated use to be small, and there are advantages in that various electrophotographic characteristics can be easily controlled according to the purpose. The negative chargeable photoreceptor has a structure in which the charge generation layer 105 (CGL) is provided on the undercoat layer 103 and the charge transport layer 106 (CTL) is provided thereon. A charge transport layer (CTL) is provided on the first layer, and a charge generation layer (CGL) is provided thereon. A preferable layer structure of the photosensitive layer 104 is a negatively chargeable photoreceptor having a functional separation structure as shown in FIG. 1(b).

As specific examples of the photosensitive layer according to the present invention, each layer of the photosensitive layer of the function-separated negatively-chargeable photoreceptor shown in FIG. 1B will be described below.

(Charge generating layer)
The charge-generating layer 105 according to the present invention contains a charge-generating substance (CGM) and a binder resin, and is preferably formed by applying a coating liquid in which the charge-generating substance is dispersed in a binder resin solution. .

Examples of the charge-generating substance include azo dyes such as Sudan Red and Diane Blue, quinone pigments such as pyrenequinone and anthanthrone, quinocyanine pigments, perylene pigments, indigo pigments such as indigo and thioindigo, and phthalocyanine pigments. be done.

In the present invention, among these, it is preferable to use a phthalocyanine-based pigment having a sensitivity to a light wavelength of 700 nm or more as the charge-generating substance, and among these, it is preferable to use a titanyl phthalocyanine compound. Examples of titanyl phthalocyanine compounds include Y-titanyl phthalocyanine having distinct diffraction peaks at Bragg angles (2θ±0.2°) of 27.3° and 9.5° in X-ray diffraction using CuKα rays, and Bragg angle ( B-titanyl phthalocyanine having distinct diffraction peaks at 28.6° and 7.5° 2θ ± 0.2°) is preferred.

It is also preferable to use a gallium phthalocyanine compound as the charge-generating substance. Gallium phthalocyanine compounds include hydroxygallium phthalocyanine, which has distinct diffraction peaks at Bragg angles (2θ±0.2°) of 28.1° and 7.4° in X-ray diffraction using CuKα rays, and Bragg angle (2θ ±0.2°) with distinct diffraction peaks at 28.3° and 7.4° is preferred.

These charge-generating substances can be used alone or in the form of being dispersed in a known binder resin.

Known resins can be used as the binder resin for forming the charge generating layer. Resins, polyurethane resins, phenolic resins, polyester resins, alkyd resins, polycarbonate resins, silicone resins, melamine resins, and copolymer resins containing two or more of these resins (for example, vinyl chloride-vinyl acetate copolymer resins , vinyl chloride-vinyl acetate-maleic anhydride copolymer resin) and poly-vinylcarbazole resin, but are not limited thereto.

The charge-generating layer is formed by dispersing the charge-generating substance in a solution of a binder resin dissolved in a solvent using a dispersing machine to prepare a coating liquid, then applying the coating liquid to a given layer thickness using a coating machine. Dry preparation of the membrane is preferred.

Examples of solvents for dissolving and applying the binder resin used in the charge generation layer include toluene, xylene, methyl ethyl ketone, cyclohexane, ethyl acetate, butyl acetate, methanol, ethanol, propanol, butanol, methyl cellosolve, ethyl cellosolve, tetrahydrofuran. , 1,4-dioxane, 1,3-dioxolane, pyridine and diethylamine, and the like, but are not limited thereto.

As a means for dispersing the charge-generating substance, an ultrasonic dispersing machine, a ball mill, a sand grinder, a homomixer, or the like can be used, but the means is not limited to these.

The mixing ratio of the charge-generating substance to the binder resin is preferably 1-600 parts by mass, more preferably 50-500 parts by mass, per 100 parts by mass of the binder resin. The layer thickness of the charge generation layer varies depending on the properties of the charge generation substance, the properties of the binder resin, the mixing ratio, etc., but is preferably 0.01 to 5 μm, more preferably 0.05 to 3 μm. Incidentally, the coating liquid for the charge generation layer can be prevented from generating image defects by filtering foreign matters and aggregates before coating. It can also be formed by vacuum deposition of the pigment.

(Charge transport layer)
The charge transport layer 106 according to the present invention contains at least a charge transport material (CTM) and a binder resin in the layer, and is formed by dissolving and coating the charge transport material in a binder resin solution.

The charge transport layer according to the invention preferably contains, as a charge transport material, any compound selected from compounds having structures represented by the following general formulas (1) to ( 3 ).

In the above general formulas (1) to ( 3 ), R represents an alkyl group, an alkoxy group or a halogeno group. Moreover, among these, R is preferably an alkyl group or an alkoxy group. Also, n represents an integer selected from 0 to 4.

Examples of alkyl groups include alkyl groups having 1 to 7 carbon atoms. Moreover, among these, a methyl group or an ethyl group is preferable.

Alkoxy groups include, for example, alkoxy groups having 1 to 7 carbon atoms. Moreover, among these, a methoxy group or an ethoxy group is preferable.

Halogeno groups include, for example, fluoro, chloro, bromo, and iodo groups.

Specific examples of compounds having structures represented by general formulas (1) to ( 3 ) applicable to the present invention are shown below, but the compounds are not limited to these examples.

In the present invention, known compounds can be used in combination with the compounds having the structures represented by the general formulas (1) to ( 3 ) as long as the intended effect of the present invention is not impaired. For example, carbazole derivatives, Oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, hydrazone compounds, pyrazoline compounds, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives , acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, phenylenediamine derivatives, stilbene derivatives, poly-N-vinylcarbazole, poly-1-vinylpyrene and poly-9-vinylanthracene. These compounds can be used alone or in combination of two or more.

In addition, known resins can be used as the binder resin for forming the charge transport layer. , styrene-methacrylic acid ester copolymer resin, and the like. Among these, polycarbonate resins are preferred, and further polycarbonates of bisphenol A (BPA), bisphenol Z (BPZ), and 2,2'-dimethylbisphenol A [2,2-bis(4-hydroxy-3-methylphenyl)propane]. Resins and polycarbonate resins of the type such as copolymers of BPA and 2,2'-dimethylbisphenol A are preferred from the standpoint of crack resistance, abrasion resistance and charging properties.

The charge transport layer can be formed by a known method typified by a coating method. A desired charge transport layer can be formed by applying a thick layer and drying the layer.

Solvents for dissolving the binder resin and the charge transport material include toluene, xylene, methyl ethyl ketone, cyclohexanone, ethyl acetate, butyl acetate, methanol, ethanol, propanol, butanol, tetrahydrofuran, 1,4-dioxane, 1,3- dioxolane and the like. The solvent used in preparing the coating liquid for forming the charge transport layer is not limited to the above.

The mixing ratio of the binder resin and the charge transport material is preferably 10 to 500 parts by mass, more preferably 20 to 100 parts by mass, per 100 parts by mass of the binder resin.

The thickness of the charge transport layer varies depending on the properties of the charge transport material and the binder resin, their mixing ratio, etc., but is preferably 29 μm or more and less than 50 μm, more preferably 29 to 45 μm.

A known antioxidant can be added to the charge transport layer, and for example, the antioxidant described in JP-A-2000-305291 can be used.

(other components)
The electrophotographic photoreceptor of the present invention comprises a conductive support and at least a photosensitive layer composed of an undercoat layer, a photosensitive layer, or a charge generation layer and a charge transport layer, which are laminated in this order. Other layers may be provided as long as they do not impair the effects of the present invention.

As the other layer, for example, a surface protective layer may be provided on the outermost surface of the electrophotographic photoreceptor.

For the surface protective layer, known resins such as polyester resins, polycarbonate resins, polyurethane resins, and silicone resins are used. It can be used for the purpose of increasing the film strength of the charge transport layer (CTL) or improving the surface slipperiness.

[Manufacturing method of electrophotoreceptor]
The electrophotographic photoreceptor of the present invention can be produced, for example, through the following steps. Hereinafter, as an example of an electrophotoreceptor, a manufacturing method in which an adhesive layer, an undercoat layer, a charge generation layer and a charge transport layer are sequentially formed on a conductive support will be described. In addition, when the undercoat layer has adhesiveness, the formation of the adhesive layer is unnecessary.

Step (1): A step of applying an adhesive layer coating liquid to the outer peripheral surface of the conductive support and drying it as necessary to form an adhesive layer. Step (2): Adhesion formed on the conductive support. A step of forming an undercoat layer by applying a coating solution for forming an undercoat layer to the outer peripheral surface of the layer and drying it. Step (3): Charging the outer peripheral surface of the undercoat layer formed on the conductive support. A step of forming a charge generation layer by applying a coating liquid for forming a generation layer and drying it if necessary. Step (4): Applying a coating liquid for forming a charge transport layer to the outer peripheral surface of the charge generation layer formed on the undercoat layer. and drying to form a charge transport layer. Each step will be described below.

(Step (1): adhesive layer forming step)
The adhesive layer is formed by dissolving an adhesive layer binder resin in a solvent to prepare an adhesive layer forming coating solution, applying the coating solution to a constant layer thickness on a conductive support to form a coating film, It can be formed by drying the coating film if necessary.

(Step (2): Undercoat layer forming step)
For the undercoat layer, a binder resin, metal oxide particles, and the above solvent are used in a solvent to prepare a coating solution for forming the undercoat layer, and the coating solution is applied to a constant layer thickness on the conductive support. It can be formed by coating to form a coating film and drying the coating film.

Examples of methods for applying the coating solution for forming the undercoat layer include known dip coating methods, spray coating methods, spinner coating methods, bead coating methods, blade coating methods, beam coating methods, slide hopper methods, circular slide hopper methods, and the like. method.

The method for drying the coating film can be appropriately selected according to the type of solvent and layer thickness described above, but heat drying is preferred.

The concentration of the binder resin for the undercoat layer in the coating solution for forming the undercoat layer is appropriately selected according to the thickness of the undercoat layer and the production speed.

(Step (3): charge generating layer forming step)
The charge-generating layer is formed by dispersing the charge-generating substance in a solution obtained by dissolving the binder resin for the charge-generating layer in the solvent described above to prepare a coating liquid for forming the charge-generating layer, and applying the coating liquid on the undercoat layer. It can be formed by applying to a constant layer thickness to form a coating film, and drying the coating film.

As means for dispersing the charge-generating substance in the charge-generating layer-forming coating liquid, for example, an ultrasonic dispersing machine, a ball mill, a sand mill, a homomixer, or the like can be used, but the means is not limited to these.

Known methods for applying the charge generation layer forming coating liquid include, for example, dip coating, spray coating, spinner coating, bead coating, blade coating, beam coating, slide hopper method and circular slide hopper method. method.

The method for drying the coating film can be appropriately selected according to the type of solvent and layer thickness, but heat drying is preferred.

(Step (4): charge transport layer forming step)
The charge transport layer is prepared by dissolving the charge transport layer binder resin and the charge transport material in the solvent described above to prepare a charge transport layer forming coating solution, and coating the charge generation layer with the coating solution to a constant layer thickness. to form a coating film, and drying the coating film.

Known methods for applying the coating liquid for forming the charge transport layer include, for example, dip coating, spray coating, spinner coating, bead coating, blade coating, beam coating, slide hopper method and circular slide hopper method. method.

The method for drying the coating film can be appropriately selected according to the type of solvent and layer thickness, but heat drying is preferred.

<<Electrophotographic Image Forming Method>>
The electrophotographic image forming method of the present invention comprises at least
1) a charging step of charging the surface of an electrophotographic photosensitive member;
2) an exposure step of exposing the surface of the electrophotographic photosensitive member to form an electrostatic latent image; 3) a developing step of visualizing the electrostatic latent image with toner to form a toner image;
4) a transfer step of transferring the toner image to a transfer medium;
and the electrophotographic photoreceptor used in 1) to 4) is the electrophotographic photoreceptor of the present invention.

5) a cleaning step for removing residual toner;
6) It may have a static elimination step for removing residual charges.

The electrophotographic photoreceptor of the present invention (hereinafter also simply referred to as photoreceptor) can be used in various known electrophotographic image forming methods. For example, it can be used for a monochrome image forming method and a full-color image forming method. In a full-color image forming method, a four-cycle image forming method comprising four types of color developing devices for yellow, magenta, cyan, and black, respectively, and one photoreceptor, and a color developing method for each color. Any image forming method such as a tandem image forming method in which an image forming unit having a device and a photoreceptor is mounted for each color can be used.

Specifically, in the electrophotographic image forming method of the present invention, the photoreceptor of the present invention is used, the photoreceptor is charged with a charging device (charging step), and imagewise exposed (exposure step). The formed electrostatic latent image is visualized by developing (developing step) using a developing device to obtain a toner image. This toner image is transferred (transfer step) onto a transfer medium such as copy paper or a transfer belt, and after that, the next image forming cycle is performed through a charge removal step. A toner image transferred onto a transfer medium such as a transfer belt is transferred onto copy paper, and the toner image transferred onto the copy paper is fixed to the copy paper by a fixing process such as a contact heating method (fixing process). to obtain a visible image. After the transfer process, toner remaining on the photoreceptor (transfer residual toner) is removed by a rubber blade or the like (cleaning process). This cleaning process may be performed before or after the static elimination process, but when the static elimination process is static elimination by light irradiation, the toner remaining on the photoreceptor absorbs the static elimination light more effectively after the cleaning process. Since there is no hindrance, static electricity can be effectively removed, which is preferable.

In the static elimination step, either alternating current static elimination (AC static elimination) or optical static elimination may be used. Neutralization is preferred.

In the image forming method using the photoreceptor of the present invention, it is possible to reduce the potential difference caused by the difference in hysteresis between the exposed portion and the non-exposed portion of the surface of the photoreceptor generated in the image forming process of the first rotation of the photoreceptor. It is possible to suppress the memory that occurs in the image forming process for the second rotation of the body.

<<Electrophotographic Image Forming Apparatus>>
Next, a specific electrophotographic image forming method will be described using an electrophotographic image forming apparatus.

The electrophotographic image forming apparatus of the present invention uses the photoreceptor of the present invention, charging means for charging the photoreceptor with a charging device, and exposure means for forming an electrostatic latent image formed by image exposure. , developing means for obtaining a toner image by developing with a developing device, transferring means for transferring the toner image onto a transfer medium such as paper or a transfer belt, and discharging means. The toner image directly transferred onto the copy paper and the toner image transferred onto the paper via a transfer medium such as a transfer belt are fixed to the copy paper by a fixing process such as a contact heating method to obtain a visible image. After the transfer, toner remaining on the photosensitive member (transfer residual toner) is removed by cleaning means such as a cleaning blade.

FIG. 3 is a schematic cross-sectional view showing the structure of a tandem-type electrophotographic image forming apparatus provided with the electrophotographic photoreceptor of the present invention.

An image forming apparatus 300 shown in FIG. 3 is called a tandem type color image forming apparatus, and includes four sets of image forming portions (image forming units) 10Y, 10M, 10C, and 10K, an intermediate transfer body unit 70, and a feeder. It consists of paper means 21 and fixing means 24 . A document image reading device SC is arranged on the upper part of the main body A of the electrophotographic image forming apparatus.

The four image forming units 10Y, 10M, 10C, and 10K rotate around photoconductors 1Y, 1M, 1C, and 1K, charging means 2Y, 2M, 2C, and 2K, and exposing means 3Y, 3M, 3C, and 3K. developing means 4Y, 4M, 4C and 4K, primary transfer rollers 5Y, 5M, 5C and 5K as primary transfer means, and cleaning means 6Y, 6M, 6C and 6K for cleaning the photoreceptors 1Y, 1M, 1C and 1K. It is configured.

The electrophotographic image forming apparatus of the present invention uses the above-described photoreceptors of the present invention as the photoreceptors 1Y, 1M, 1C, and 1K.

The image forming units 10Y, 10M, 10C, and 10K have the same configuration except that the colors of toner provided are different, such as yellow (Y), magenta (M), cyan (C), and black (K). is. Therefore, the image forming unit 10Y will be described in detail below as an example.

The image forming unit 10Y has a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 6Y around a photoreceptor 1Y, which is an image forming member, and forms a yellow (Y) toner image on the photoreceptor 1Y. to form.

The charging unit 2Y is a unit that uniformly charges the surface of the photoreceptor 1Y to a negative polarity. In the electrophotographic image forming apparatus of this embodiment, it is preferable to use a charging roller as the charging means 2Y.

The exposure means 3Y is a means for forming an electrostatic latent image corresponding to a yellow image by exposing the photosensitive member 1Y to which a uniform potential is applied by the charging means 2Y, based on an image signal (yellow). be. As the exposing means 3Y, one composed of an LED in which light emitting elements are arranged in an array in the axial direction of the photoreceptor 1Y and an imaging element, or a laser optical system or the like is used.

The developing means 4Y comprises, for example, a developing sleeve 41Y containing a magnet and rotating while holding developer, a photosensitive member, and a voltage applying device for applying a DC and/or AC bias voltage between the developing sleeve and the photosensitive member. be.

The developing means 4Y comprises, for example, a developing sleeve containing a magnet and rotating while holding the developer, and a voltage applying device for applying a DC and/or AC bias voltage between the developing sleeve and the photosensitive member. .

The fixing means 24 is, for example, a heat roller fixing device comprising a heating roller having an internal heat source and a pressure roller provided in pressure contact with the heating roller so as to form a fixing nip portion. method.

The cleaning means 6Y is composed of a cleaning blade and a brush roller provided upstream from the cleaning blade.

The image forming apparatus 300 is constructed by integrally connecting constituent elements such as a photoreceptor, developing means, cleaning means, etc. as a process cartridge (image forming unit). may be configured. A process cartridge (image forming unit) is formed by integrally supporting at least one of charging means, exposing means, developing means, transferring means and cleaning means together with the photoreceptor to form a single image which can be attached to and detached from the main body of the apparatus. It may be configured as a unit so that it can be attached and detached using guide means such as rails of the apparatus main body.

The endless belt-shaped intermediate transfer member unit has an endless belt-shaped intermediate transfer member 70 as a second semi-conductive endless belt-shaped image bearing member wound around a plurality of rollers and rotatably supported.

Images of respective colors formed by the image forming units 10Y, 10M, 10C and 10K are sequentially transferred onto a rotating endless belt-shaped intermediate transfer member 70 by primary transfer rollers 5Y, 5M, 5C and 5K as primary transfer means. to form a composite color image. A transfer material (an image support carrying a fixed final image: plain paper, a transparent sheet, etc.) P accommodated in a paper feed cassette 20 is fed by a paper feed means 21, and is fed by a plurality of intermediate rollers 22A, After passing through 22B, 22C, 22D and a registration roller 23, it is conveyed to a secondary transfer roller 5b as a secondary transfer means, and is secondary-transferred onto the transfer material P to collectively transfer the color image. The transfer material P onto which the color image has been transferred is subjected to fixing processing by the fixing means 24 , sandwiched between the paper discharge rollers 25 and placed on the paper discharge tray 26 outside the apparatus. Here, a transfer support for a toner image formed on a photosensitive member, such as an intermediate transfer member or a transfer material, is generically referred to as a transfer medium.

On the other hand, after the color image is transferred onto the transfer material P by the secondary transfer roller 5b as a secondary transfer means, the endless belt-like intermediate transfer body 70, which has separated the transfer material P by curvature, is cleaned of residual toner by the cleaning means 6b. be.

During the image forming process, the primary transfer roller 5K is always in contact with the photoreceptor 1K. The other primary transfer rollers 5Y, 5M and 5C are brought into contact with the corresponding photoreceptors 1Y, 1M and 1C only during color image formation.

The secondary transfer roller 5b contacts the endless belt-like intermediate transfer member 70 only when the transfer material P passes through it and secondary transfer is performed.

Further, the housing 8 can be pulled out from the apparatus main body A via support rails 82L and 82R.

A housing 8 includes image forming units 10Y, 10M, 10C, and 10Bk, and an endless belt-like intermediate transfer member unit 7 .

The image forming units 10Y, 10M, 10C, and 10K are arranged vertically in tandem. An endless belt-shaped intermediate transfer member unit 7 is arranged on the left side of the photoreceptors 1Y, 1M, 1C and 1K in the drawing. The endless belt-like intermediate transfer body unit 7 includes an endless belt-like intermediate transfer body 70 that can be rotated by winding rollers 71, 72, 73 and 74, primary transfer rollers 5Y, 5M, 5C and 5K, and cleaning means 6b. consists of

The toner used in the image forming apparatus as described above is not particularly limited, but a toner having a shape factor SF of less than 140 when a true sphere is 100 is preferable. When the shape factor SF is less than 140, good transferability and the like are obtained, and the image quality of the resulting image is improved. Toner particles constituting the toner preferably have a volume average particle diameter within the range of 2 to 8 μm from the viewpoint of achieving high image quality.

Toner particles usually contain a binder resin and a colorant, and optionally a release agent. Materials used in conventional toners can be used for the binder resin, colorant, and release agent, and are not particularly limited.

The method for producing the above toner particles is not particularly limited, but examples include a conventional pulverization method, a wet melt spheronization method in which preparation is performed in a dispersion medium, a suspension polymerization method, a dispersion polymerization method, an emulsion polymerization aggregation method, and the like. A known polymerization method and the like can be mentioned.

Inorganic fine particles such as silica or titania having an average particle diameter of about 10 to 300 nm and an abrasive of about 0.2 to 3 μm can be externally added to the toner particles in an appropriate amount as external additives. Further, the above toner particles can be mixed with a carrier comprising ferrite beads or the like having an average particle size of 25 to 45 μm, and the mixture can be used as a two-component developer.

FIG. 4 is an enlarged schematic diagram showing the positional relationship between the photosensitive member and the cleaning blade in the tandem-type electrophotographic image forming apparatus of the present invention.

Here, 227 is a cleaning blade as a cleaning means, 228 is a static elimination lamp as an optical static elimination means (static elimination light), 222 is an exposure light source as an exposure means, 220 is a charging electrode as a charging means, and 223 is a developing means. 225 is a transfer roller as a transfer means. Light sources that can be used for the exposure light source 22 include tungsten light, fluorescent lamps, halogen lamps, laser light (semiconductor laser, He—Ne laser), and LEDs.

The developing device 223 may be used for normal development or for reversal development, but the photoreceptor of the present invention is particularly effective in improving image memory when the reversal development process is applied. Although it is preferable that the electrophotographic image forming apparatus according to the present invention does not have a charge removing step, it is not prohibited to provide the charge removing step if necessary. The applicable charge removing lamp 228 can be applied to both normal development and reversal development. Examples of exposure light sources that can be used for the static elimination lamp 228 include tungsten lamps, halogen lamps, fluorescent lamps, white LEDs, green LEDs, yellow LEDs, and red LEDs. may be used.

As an example of image formation, when a laser light source is used as the exposure light source 222 , the photosensitive member 211 negatively charged by the charging electrode 220 is image-exposed by the laser light source and developed by the developing device 223 . In this case, since the development is reversal development, the toner is negatively charged. This is transferred to a transfer medium 224 by a transfer roller 225 , and then the charges on the photosensitive member 211 are removed by a charge removal lamp 228 . Toner remaining on the photoreceptor 211 (transfer residual toner) is scraped off by a cleaning blade 227 . The static elimination may be performed before or after the cleaning process. The transfer medium is recording paper such as copy paper or a transfer belt. The toner transferred onto the transfer belt is then transferred to recording paper such as copy paper to form a toner image.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these. Compounds used in the preparation of photoreceptors of Reference Examples, Examples and Comparative Examples are shown below.

(Preparation of surface-modified zinc oxide fine particles)
Zinc oxide fine particles: MZ300 (manufactured by Tayca) 80 parts by mass Silane coupling agent: KBM503 (Shin-Etsu Chemical Co., Ltd.) 1 part by mass Toluene 1000 parts by mass After mixing the above compositions with stirring, 1 at 120 ° C. A heat treatment was performed for hours to prepare surface-modified zinc oxide fine particles.

(Preparation of surface-modified titanium oxide fine particles)
Titanium oxide fine particles: STM150MK (manufactured by Tayka) 80 parts by mass Silane coupling agent: KBM503 (Shin-Etsu Chemical Co., Ltd.) 1 part by mass Toluene 1000 parts by mass After mixing the above compositions with stirring, 1 at 120 ° C. A heat treatment was performed for hours to prepare surface-modified titanium oxide fine particles.

[Preparation of Undercoat Layer UCL1 Sample: Reference Example ]
(Preparation of undercoat layer coating solution 1)
Surface-modified zinc oxide fine particles (MZ300 surface-treated product) 100 parts by mass Red dye: Alizarin 0.8 parts by mass Cross-linking agent: Isocyanate (Coronate 2507: manufactured by Tosoh Corporation) 15 parts by mass Resin binder: Vinyl chloride vinyl acetate copolymer resin (VMCH) : Manufactured by Union Carbide)
8 parts by mass Solvent 1: Methyl ethyl ketone 62 parts by mass Solvent 2: Cyclohexanone 5 parts by mass After mixing the constituent materials described above, the mixture was subjected to dispersion treatment in a sand mill to prepare an undercoat layer coating solution 1 .

(Formation of undercoat layer UCL1)
Next, as described with reference to FIG. 2, aluminum is vacuum-deposited on the slide glass substrate 502 at a degree of vacuum of 2.66×10 ⁻³ Pa or less to form a substrate-side aluminum electrode 503A having a measurement area of 2 cm ² . formed.

Next, the above-prepared undercoat layer coating liquid 1 is applied onto the formed substrate-side aluminum electrode 503A and subjected to heat treatment at 140° C. for 1 hour to form an undercoat layer UCL1 with a dry layer thickness of 20.7 μm. bottom.

[Preparation of undercoat layer UCL2 sample: the present invention]
In the preparation of the undercoat layer UCL1 sample, the following undercoat layer coating solution 2 was used in place of the undercoat layer coating solution 1 used to form the undercoat layer UCL1, and the undercoat layer UCL2 having a layer thickness of 12.1 μm was used. A sample of the undercoat layer UCL2 was prepared in the same manner except for forming the .

(Preparation of undercoat layer coating liquid 2)
Undercoat layer coating solution 2 was prepared in the same manner as in preparation of undercoat layer coating solution 1, except that the amount of red dye alizarin added was changed to 0.5 parts by mass.

[Preparation of Undercoat Layer UCL3 Sample: Present Invention]
In the preparation of the undercoat layer UCL1 sample, the following undercoat layer coating solution 3 was used in place of the undercoat layer coating solution 1 used to form the undercoat layer UCL1, and the undercoat layer UCL3 having a thickness of 20.0 μm was used. Undercoat layer UCL3 sample was prepared in the same manner except that .

(Preparation of undercoat layer coating liquid 3)
Undercoat layer coating solution 3 was prepared in the same manner as in preparation of undercoat layer coating solution 1, except that the amount of red dye alizarin added was changed to 0.3 parts by mass.

[Preparation of undercoat layer UCL4, 4-2, 4-3, 4-4 samples: the present invention]
Except that in the preparation of the undercoat layer UCL1 sample, the following undercoat layer coating solution 4 was used in place of the undercoat layer coating solution 1 used to form the undercoat layer UCL1, and the undercoat layers were formed under the same conditions. prepared samples of the undercoat layer UCL4, 4-2, 4-3 and 4-4 in the same manner. The layer thickness of each undercoat layer is as shown in Table I, respectively.

(Preparation of undercoat layer coating solution 4)
Undercoat layer coating solution 4 was prepared in the same manner as in the preparation of undercoat layer coating solution 1, except that the surface-modified titanium oxide fine particles prepared above were used as the metal oxide fine particles instead of the surface-modified zinc oxide fine particles. prepared.

[Preparation of undercoat layer UCL5 sample: the present invention]
In the preparation of the undercoat layer UCL1 sample, the following undercoat layer coating solution 5 was used in place of the undercoat layer coating solution 1 used to form the undercoat layer UCL1. Undercoat layer UCL5 sample was prepared in the same manner except that

(Preparation of undercoat layer coating liquid 5)
Binder: Polyamide resin (Daiamide X4685: Daicel-Eponic Co.)
100 parts by mass Inorganic fine particles: Titanium oxide fine particles (SAMT600S) 440 parts by mass Inorganic fine particles: Titanium oxide fine particles (SAM150MK) 100 parts by mass Solvent 1: Ethanol 1250 parts by mass Solvent 2: 1-propanol 560 parts by mass Solvent 3: Tetrahydrofuran 970 parts by mass [Preparation of Undercoat Layer UCL6 Sample: Comparative Example]
In the preparation of the undercoat layer UCL1 sample, the following undercoat layer coating solution 6 was used instead of the undercoat layer coating solution 1 used to form the undercoat layer UCL1, and heat treatment was performed at 160° C. for 1 hour. A sample of the undercoat layer UCL6 was prepared in the same manner, except that the undercoat layer UCL6 having a layer thickness of 5.4 μm was formed.

(Preparation of dye-treated zinc oxide fine particles)
<Pretreatment 1 for metal oxide fine particles>
Zinc oxide fine particles (described above) 500 parts by mass Silane coupling agent (KBM603, manufactured by Shin-Etsu Chemical Co., Ltd.) 5 parts by mass Toluene 3000 parts by mass After mixing the above components with stirring, heat treatment is performed at 120 ° C. for 1 hour. , to obtain surface-modified zinc oxide microparticles.

<Pretreatment 2 of metal oxide fine particles>
Surface-modified zinc oxide fine particles 500 parts by mass Alizarin 10 parts by mass Tetrahydrofuran (THF) 3000 parts by mass After stirring and mixing the above components while heating them at 40°C for 10 hours, they are separated by filtration and dried to obtain a dye. Treated zinc oxide microparticles were obtained.

(Preparation of undercoat layer coating liquid 6)
For 450 parts by mass of methyl ethyl ketone, 45 parts by mass of polyvinyl butyral (BL-S: manufactured by Sekisui Chemical Co., Ltd.) is mixed and dissolved,
Dye-treated zinc oxide fine particles 450 parts by mass Acrylic polyol (solid content 50%, Acrydic A814, manufactured by Dainippon Ink Co., Ltd.)
50 parts by mass isocyanate (Coronate 2507 manufactured by Tosoh Corporation) 80% liquid 100 parts by mass 2-propanol 55 parts by mass are added and mixed, placed in a sand mill together with zirconia beads (average particle size: 0.5 mm), dispersed for 10 hours, and dispersed. A liquid was prepared.

Next, 0.002 part by mass of dioctyl uralate was added to the dispersion to prepare an undercoat layer coating solution 6 .

[Preparation of Undercoat Layer UCL7 Sample: Comparative Example]
In the preparation of the undercoat layer UCL6 sample, instead of the undercoat layer coating solution 6 used to form the undercoat layer UCL6, the following undercoat layer coating solution 7 was applied and dried at 120°C for 30 minutes. An undercoat layer UCL7 sample was prepared in the same manner except that the undercoat layer UCL7 was formed to have a layer thickness of 12.4 μm.

(Preparation of undercoat layer coating solution 7)
Binder: Polyamide resin (Daiamide X4685: Daicel-Eponic Co.)
100 parts by mass Inorganic fine particles: Titanium oxide fine particles (SAMT600S) 540 parts by mass Solvent 1: Ethanol 1250 parts by mass Solvent 2: 1-propanol 560 parts by mass Solvent 3: Tetrahydrofuran 970 parts by mass [Preparation of undercoat layer UCL8 sample: Comparative example]
In the preparation of the undercoat layer UCL6 sample, the following undercoat layer coating liquid 8 was used in place of the undercoat layer coating liquid 6 used to form the undercoat layer UCL6, and the undercoat layer UCL8 having a layer thickness of 21.2 μm was used. An undercoat layer UCL8 sample was prepared in the same manner except that .

(Preparation of undercoat layer coating solution 8)
In the preparation of the undercoat layer coating solution 6, the undercoat layer coating solution 8 was prepared in the same manner, except that the surface-modified titanium oxide fine particles prepared above were used as the metal oxide fine particles instead of the surface-modified zinc oxide fine particles. prepared.

[Preparation of Undercoat Layer UCL9 Sample: Comparative Example]
In the preparation of the undercoat layer UCL6 sample, instead of the undercoat layer coating solution 6 used to form the undercoat layer UCL6, the following undercoat layer coating solution 9 was applied and dried at 120° C. for 30 minutes. An undercoat layer UCL9 sample was prepared in the same manner except that the undercoat layer UCL9 having a layer thickness of 28.2 μm was formed.

(Preparation of undercoat layer coating liquid 9)
Binder resin: Polyamide resin (CM8000: manufactured by Toray Industries, Inc.) 100 parts by mass Inorganic fine particles: Titanium oxide fine particles (SMT500SAS) 120 parts by mass Inorganic fine particles: Titanium oxide fine particles (SMT150MK) 160 parts by mass Solvent 1: Methanol 1360 parts by mass Solvent 2: 1 - Propanol 340 parts by mass [Preparation of undercoat layer UCL10 sample: Comparative example]
It was prepared in the same manner as in the preparation of the undercoat layer UCL9 sample, except that the addition amount of titanium oxide fine particles (SMT150MK) in the undercoat layer coating liquid 9 used for forming the undercoat layer UCL9 was changed to 240 parts by mass. An undercoat layer UCL10 sample was prepared in the same manner except that the undercoat layer UCL10 having a layer thickness of 38.8 μm was formed using the undercoat layer coating solution 10 .

<<Measurement of Volume Resistivity of Undercoat Layer Sample>>
Using the undercoat layer volume resistivity measuring apparatus shown in FIG. 2, the volume resistivity of each of the undercoat layer samples prepared above was measured according to the following method.

As the minute ammeter 513, Model 6487 picoammeter manufactured by Kiethlay and equipped with a DC power supply 509 was used.

A voltage was sequentially applied between the electrodes of the undercoat layer sample from the built-in power source of the ammeter, and the current was measured 10 seconds after each voltage application.

Next, at an electric field strength E of 5×10 ⁴ (V/cm), the layer thickness d (cm) of the undercoat layer described in Table I is multiplied, and the applied voltage V (V) from the DC power supply is applied under the conditions of Table I. set to

Next, from the layer thickness (cm) of the undercoat layer, the applied voltage V (V), the current (A), and the effective electrode area S (cm ² , S=2 cm ² in the above case), according to the following formula (A), the volume The resistivity ρ was determined and the results obtained are shown in Table I. All measurements were performed in an environment of 23±2°C.

Formula (A) Volume resistivity ρ (Ω cm) = [V (V) / I (A)] / [d (cm) / S (cm ² )]
Table I shows the structure of each undercoat layer prepared as described above.

<<Preparation of Electrophotographic Photoreceptor>>
Electrophotographic photoreceptors 1 to 13 were produced by successively forming various undercoat layers/charge generation layers/charge transport layers on a conductive support according to the following method.

[Preparation of Electrophotographic Photoreceptor 1: Present Invention]
(Conductive support)
A cylindrical aluminum substrate of φ60 mm×L362 mm×t1 mm was used.

(Formation of undercoat layer (UCL1))
The undercoat layer UCL1 used in the preparation of the undercoat layer UCL1 sample was formed in the same manner under conditions where the layer thickness was the same as the resistance measurement sample (20.7 μm), and this was used as the undercoat layer (UCL1). and The layer thickness of the obtained UCL1 was 21.2 μm.

(Formation of charge generation layer (CGL))
The following raw materials were dispersed for 10 hours using a sand mill as a dispersing machine to prepare a coating solution for forming a charge generation layer, which was applied onto the undercoat layer (UCL1) by dip coating to obtain a charge generation layer (CGL) having a thickness of 0.2 μm. ) was formed.

<Coating liquid for forming charge generation layer>
Charge-generating material: titanyl phthalocyanine pigment (*1: Y-TiOPc Cu-Kα having a maximum diffraction peak at least at 27.3° in characteristic X-ray diffraction spectrum measurement)
20 parts by mass Binder resin for charge generation layer: Polyvinyl butyral resin "#6000-C" (manufactured by Denki Kagaku Kogyo Co., Ltd.) 10 parts by mass Solvent 1: t-butyl acetate 900 parts by mass Solvent 2: MMP (4-methoxy-4- Methyl-2-pentanone) 100 parts by mass (Formation of charge transport layer (CTL1))
On the charge generation layer (CGL) formed above, a charge transport layer coating solution 1 prepared by the following method was applied by a dip coating method to form a charge transport layer (CTL1) having a layer thickness of 34.5 μm. A photographic photoreceptor 1 was produced.

<Preparation of Charge Transport Layer Coating Solution 1>
Binder: Polycarbonate resin (FPC6550 manufactured by Mitsubishi Gas Chemical Company)
100 parts by mass Charge transport material: Exemplary compound 1-2 (compound having a structure represented by general formula (1))
60 parts by mass Antioxidant: Dibutylhydroxytoluene 6 parts by mass Solvent 1: Tetrahydrofuran 808 parts by mass Solvent 2: Toluene 197 parts by mass Additive: Silicone oil (KF-96: manufactured by Shin-Etsu Chemical Co., Ltd.) 0.12 parts by mass Electrophotography Preparation of photoreceptors 2 to 5: the present invention]
In the preparation of the electrophotographic photoreceptor 1, the undercoat layer (UCL1) was replaced with the undercoat layers (UCL2) to (UCL5) prepared above, and the layer thicknesses were changed as shown in Table II. Electrophotographic photoreceptors 2 to 5 were produced in the same manner as above.

[Preparation of Electrophotographic Photoreceptor 6: Present Invention]
In the production of the electrophotographic photoreceptor 1, the undercoat layer 4-2 was used as the undercoat layer, and the charge transport layer coating liquid 2 prepared by the following method was used instead of the charge transport layer (CTL1). An electrophotographic photoreceptor 6 was produced in the same manner, except that a transport layer (CTL2) was formed.

<Preparation of Charge Transport Layer Coating Solution 2>
Binder: Polycarbonate resin (FPC6550 manufactured by Mitsubishi Gas Chemical Company)
100 parts by mass Charge transport material: Exemplary compound 2-2 (compound having a structure represented by general formula (2))
60 parts by mass Antioxidant: Dibutylhydroxytoluene 6 parts by mass Solvent 1: Tetrahydrofuran 808 parts by mass Solvent 2: Toluene 197 parts by mass Additive: Silicone oil (KF-96: manufactured by Shin-Etsu Chemical Co., Ltd.) 0.12 parts by mass Electrophotography Preparation of Photoreceptor 7: Present Invention]
In the production of the electrophotographic photoreceptor 1, the undercoat layer 4-3 was used as the undercoat layer, and the charge transport layer coating liquid 3 prepared by the following method was used instead of the charge transport layer (CTL1). An electrophotographic photoreceptor 7 was produced in the same manner, except that a transport layer (CTL3) was formed.

<Preparation of Charge Transport Layer Coating Solution 3>
Binder: Polycarbonate resin (FPC6550 manufactured by Mitsubishi Gas Chemical Company)
100 parts by mass Charge transport material: Exemplified compound 3-8 (compound having a structure represented by general formula (3))
60 parts by mass Antioxidant: Dibutylhydroxytoluene 6 parts by mass Solvent 1: Tetrahydrofuran 808 parts by mass Solvent 2: Toluene 197 parts by mass Additive: Silicone oil (KF-96: manufactured by Shin-Etsu Chemical Co., Ltd.) 0.12 parts by mass Electrophotography Preparation of photoreceptor 8: the present invention]
In the production of the electrophotographic photoreceptor 1, the undercoat layer 4-3 was used as the undercoat layer, and instead of the charge transport layer (CTL1), the charge transport layer coating liquid 4 prepared by the following method was used. An electrophotographic photoreceptor 8 was produced in the same manner, except that a transport layer (CTL4) was formed.

<Preparation of Charge Transport Layer Coating Solution 4>
Binder: Polycarbonate resin (FPC6550 manufactured by Mitsubishi Gas Chemical Company)
100 parts by mass Charge transport material: Exemplary compound 4-1 (compound having a structure represented by general formula (4))
60 parts by mass Antioxidant: Dibutylhydroxytoluene 6 parts by mass Solvent 1: Tetrahydrofuran 808 parts by mass Solvent 2: Toluene 197 parts by mass Additive: Silicone oil (KF-96: manufactured by Shin-Etsu Chemical Co., Ltd.) 0.12 parts by mass Electrophotography Production of Photoreceptors 9 to 13: Comparative Example]
In the preparation of the electrophotographic photoreceptor 1, the undercoat layer (UCL1) was replaced with the undercoat layers (UCL6) to (UCL10) prepared above, and the layer thicknesses were changed as shown in Table II. Electrophotographic photoreceptors 9 to 13 were produced in the same manner as above.

<<Evaluation of Electrophotographic Photoreceptor>>
Image characteristics and charge deterioration resistance of the electrophotographic photosensitive member produced above were evaluated according to the following methods.

[Evaluation of image characteristics]
(Evaluation of negative memory)
Using a digital full-color multifunction machine "bizhub PRO C1070" (manufactured by Konica Minolta Co., Ltd.) equipped with each electrophotographic photosensitive member, the original document shown in FIG. The difference in image density (negative memory) in the halftone portion of the second rotation of the photoreceptor shown in FIG. RD-918" (manufactured by Macbeth).

(Evaluation of positive memory and fogging)
Using a digital full-color multifunction machine "bizhub PRO C1070" (manufactured by Konica Minolta Co., Ltd.) equipped with each electrophotographic photosensitive member, the original document of FIG. The difference in image density (positive memory) in the halftone portion when the illuminance (irradiation light amount) on the electrophotographic photosensitive member surface as shown is 2 μJ/cm ² and 10 μJ/cm ² is measured using a Macbeth reflection densitometer "RD-918." (manufactured by Macbeth).

(criterion)
○: All of the above measured values are less than 0.02 and are good △: Any one of the above measured values is 0.02 or more and less than 0.04 and is within a practically acceptable range ×: Negative memory or If either positive memory or fog is 0.04 or more, there is a practical problem. evaluation〕
The repeated potential measurements were performed as follows. Using a digital full-color multifunction machine "bizhub PRO C1070" (manufactured by Konica Minolta Co., Ltd.) equipped with each electrophotographic photoreceptor, images after printing 10,000 sheets were evaluated in the same manner as the evaluation of the image characteristics described above.

The results obtained above are shown in Table II.

As is clear from the results shown in Table II, the electrophotographic photoreceptor of the present invention can suppress memory. Further, it was found that the photoreceptor of the present invention is also excellent in durability.
Therefore, it was found that the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor that suppresses the occurrence of fogging, image memory and ghost and has excellent durability.

1Y, 1M, 1C, 1K Photoreceptor 2Y, 2M, 2C, 2K Charging means 3Y, 3M, 3C, 3K Exposure means 4Y, 4M, 4C, 4K Developing means 5Y, 5M, 5C, 5K Primary transfer roller 5b Secondary transfer Rollers 6Y, 6M, 6C, 6K, 6b Cleaning means 10Y, 10M, 10C, 10K Image forming unit 20 Paper feed cassette 21 Paper feed means 22A, 22B, 22C, 22D Intermediate roller 23 Registration roller 24 Fixing means 25 Paper discharge roller 26 Discharge tray 30 Blade member 31 Supporting member 41Y Developing sleeve included in developing means 4Y 70 Intermediate transfer member unit 71, 72, 73, 74 Roller 77 Intermediate transfer member 80, 501 Housing 82L, 82R Support rail A Main body SC Document image reading Apparatus P Transfer Material 100A, 100B Electrophotographic Photoreceptor 102 Conductive Support 103 Undercoat Layer 104 Photosensitive Layer 105 Charge Generation Layer 106 Charge Transport Layer 211 Photoreceptor 217 Exposure Light 220 Charging Electrode 222 Exposure Light Source 223 Developing Device 224 Transfer Medium 225 Transfer Roller 227 Cleaning Blade 228 Eliminating Lamp 300 Electrophotographic Image Forming Apparatus 500 Volume Resistivity Measuring Device 502 Slide Glass Substrate 503A, 503B Substrate Side Aluminum Electrode 504 Undercoat Layer 505 Surface Side Aluminum Electrode 506 Protective Resistor 507, 511 Solder 508 , 512 bonding wire 509 DC power supply 510 reference ground 513 minute ammeter 514 ground ground

Claims (6)

An electrophotographic photoreceptor obtained by sequentially laminating at least an undercoat layer and a photosensitive layer on a conductive support,
the photosensitive layer is composed of at least a charge generation layer and a charge transport layer,
The charge transport layer contains a compound selected from compounds having structures represented by the following general formulas (1) to (3), and the layer thickness of the charge transport layer is in the range of 29 μm or more and less than 50 μm. and
The undercoat layer contains metal oxide particles and has a volume resistivity ρ of 2 ×10 ⁷ (Ω·cm) at 23±2° C. when an electric field with a strength of 5×10 ⁴ (V/cm) is applied. Above, within the range of less than 1 × 10 ⁸ (Ω cm),
An electrophotographic photoreceptor, wherein the undercoat layer has a thickness of 10 to 40 μm, and the photosensitive layer has a thickness of 30 to 50 μm.

[In the above general formulas (1) to (3), R represents an alkyl group, an alkoxy group or a halogeno group. n represents an integer selected from 0 to 4; ] 2. The metal oxide contained in the undercoat layer contains titanium oxide, zinc oxide, tin oxide, or aluminum oxide, and is surface-treated with a silane coupling agent. The electrophotographic photoreceptor described in . 3. The electrophotographic photoreceptor according to claim 1 , wherein the photosensitive layer contains a titanyl phthalocyanine compound or a gallium phthalocyanine compound. An electrophotographic image forming method for forming an image through at least a charging step, an exposure step, a developing step and a transfer step using an electrophotographic photosensitive member,
An electrophotographic image forming method, wherein the electrophotographic photoreceptor according to any one of claims 1 to 3 is used as the electrophotographic photoreceptor. 5. The electrophotographic image forming method according to claim 4 , wherein the electrophotographic photosensitive member does not have a charge removing step of removing charges from the surface of the electrophotographic photosensitive member. An electrophotographic image forming apparatus comprising the electrophotographic photoreceptor according to any one of claims 1 to 3 .

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