JP6477568B2 - Electrophotographic photosensitive member, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic photosensitive member, a process cartridge, and an image forming apparatus.

  The electrophotographic photosensitive member is used in an electrophotographic image forming apparatus. The electrophotographic photoreceptor includes a photosensitive layer. As the electrophotographic photosensitive member, for example, a multilayer electrophotographic photosensitive member or a single layer type electrophotographic photosensitive member is used. The multilayer electrophotographic photoreceptor includes, as a photosensitive layer, a charge generation layer having a charge generation function and a charge transport layer having a charge transport function. The single layer type electrophotographic photosensitive member includes a single layer type photosensitive layer having a charge generation function and a charge transport function as a photosensitive layer.

  The multilayer photosensitive device described in Patent Document 1 includes an electron transport layer. The electron transport layer contains a compound represented by the chemical formula (E-1).

JP 60-69657 A

  However, with the compound represented by the chemical formula (E-1) described in Patent Document 1, it is difficult to suppress the occurrence of white spots in the formed image.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an electrophotographic photosensitive member capable of suppressing the generation of white spots in a formed image. It is another object of the present invention to provide a process cartridge and an image forming apparatus that can suppress generation of white spots in a formed image by including such an electrophotographic photosensitive member.

  The electrophotographic photoreceptor of the present invention includes a conductive substrate and a photosensitive layer. The photosensitive layer is a single layer type photosensitive layer containing a charge generating agent and an electron transporting agent. The electron transport agent includes a compound represented by the following general formula (1). The charge amount of the calcium carbonate when the photosensitive layer and the calcium carbonate are rubbed is 7.0 μC / g or more.

In the general formula (1), R ₁ is an alkyl group having 1 to 8 carbon atoms having one or more halogen atoms, a cycloalkyl group having 3 to 10 carbon atoms having one or more halogen atoms, halogen An aryl group having 6 to 14 carbon atoms which may have an alkyl group having 1 or more atoms and having 1 to 6 carbon atoms, or a 5- to 14-membered heterocyclic ring having one or more halogen atoms A group or an aralkyl group having 7 or more and 20 or less carbon atoms having at least one halogen atom;

  The process cartridge of the present invention includes the above-described electrophotographic photosensitive member.

  An image forming apparatus of the present invention includes the above-described electrophotographic photosensitive member, a charging unit, an exposure unit, a developing unit, and a transfer unit. The charging unit charges the surface of the electrophotographic photosensitive member. The exposure unit exposes the charged surface of the electrophotographic photosensitive member to form an electrostatic latent image on the surface of the electrophotographic photosensitive member. The developing unit develops the electrostatic latent image as a toner image. The transfer unit transfers the toner image from the electrophotographic photosensitive member to a recording medium. When the transfer unit transfers the toner image from the electrophotographic photosensitive member to the recording medium, the electrophotographic photosensitive member is in contact with the recording medium.

  According to the electrophotographic photosensitive member of the present invention, it is possible to suppress the occurrence of white spots in the formed image. Further, according to the process cartridge and the image forming apparatus of the present invention, it is possible to suppress the occurrence of white spots in the formed image by including such an electrophotographic photosensitive member.

(A), (b) and (c) are sectional views showing an example of an electrophotographic photoreceptor according to an embodiment of the present invention. It is a figure for demonstrating the method to measure the charge amount of a calcium carbonate when a photosensitive layer and calcium carbonate are made to rub. 1 is a diagram illustrating an example of a configuration of an image forming apparatus including an electrophotographic photosensitive member according to an embodiment of the present invention. 3 is a ¹ H-NMR spectrum of a compound represented by a chemical formula (1-3) contained in an electrophotographic photoreceptor according to an embodiment of the present invention. 3 is a ¹ H-NMR spectrum of a compound represented by a chemical formula (1-4) contained in an electrophotographic photoreceptor according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, about the location where description overlaps, although description may be abbreviate | omitted suitably, the summary of invention is not limited.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. In addition, when “polymer” is added after the compound name to indicate the polymer name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Furthermore, the reactions represented by reaction formulas (R-1) to (R-4) may be described as reactions (R-1) to (R-4), respectively. The compounds represented by the general formulas (1), (2), (3), (B) and (C) are respectively represented as compounds (1), (2), (3), (B) and (C). May be described. Chemical formulas (1-1) to (1-9), (A-1) to (A-3), (B-1) to (B-3), (B-5) to (B-9), ( C-1) to (C-9), (CGM-1), (CGM-2), (E-1), (E-2) and the compound represented by (2-1), respectively, 1-1) to (1-9), (A-1) to (A-3), (B-1) to (B-3), (B-5) to (B-9), (C- 1) to (C-9), (CGM-1), (CGM-2), (E-1), (E-2), and (2-1).

  A halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 14 carbon atoms, Unless otherwise specified, a 5- to 14-membered heterocyclic group, an aralkyl group having 7 to 20 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms have the following meanings.

  The halogen atom (halogen group) is, for example, a fluorine atom (fluoro group), a chlorine atom (chloro group), a bromine atom (bromo group), or an iodine atom (iodo group).

  The alkyl group having 1 to 6 carbon atoms is linear or branched and unsubstituted. Examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, t-butyl group, pentyl group, isopentyl group, and neopentyl group. Or a hexyl group is mentioned.

  The alkyl group having 1 to 8 carbon atoms is linear or branched and unsubstituted. Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, t-butyl group, pentyl group, isopentyl group, and neopentyl group. Hexyl group, heptyl group or octyl group.

  A cycloalkyl group having 3 to 10 carbon atoms is unsubstituted. Examples of the cycloalkyl group having 3 to 10 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group.

  Examples of the aryl group having 6 to 14 carbon atoms include an unsubstituted aromatic monocyclic hydrocarbon group having 6 to 14 carbon atoms and an unsubstituted aromatic condensed bicyclic carbon group having 6 to 14 carbon atoms. A hydrogen group or an unsubstituted aromatic condensed tricyclic hydrocarbon group having 6 to 14 elemental atoms. Examples of the aryl group having 6 to 14 carbon atoms include a phenyl group, a naphthyl group, an anthryl group, and a phenanthryl group.

  The 5- to 14-membered heterocyclic group contains at least one heteroatom in addition to the carbon atom and is unsubstituted. The hetero atom is at least one selected from the group consisting of a nitrogen atom, a sulfur atom and an oxygen atom. The 5- to 14-membered heterocyclic group includes, for example, a 5-membered or 6-membered monocyclic heterocyclic group containing 1 to 3 heteroatoms in addition to the carbon atom; A heterocyclic group in which two monocyclic rings are fused; a heterocyclic group in which such a monocyclic heterocyclic ring is fused with a 5- or 6-membered monocyclic hydrocarbon ring; and three such monocyclic heterocyclic rings A fused heterocyclic group; a heterocyclic group fused with two such monocyclic heterocycles and one 5- or 6-membered monocyclic hydrocarbon ring; or such monocyclic heterocycle 1 And a heterocyclic group formed by condensing two and five or six-membered monocyclic hydrocarbon rings. Specific examples of the 5- to 14-membered heterocyclic group include piperidinyl group, piperazinyl group, morpholinyl group, thiophenyl group, furanyl group, pyrrolyl group, imidazolyl group, pyrazolyl group, isothiazolyl group, isoxazolyl group, oxazolyl group, isoxazolyl group Group, thiazolyl group, isothiazolyl group, furazanyl group, pyranyl group, pyridyl group, pyridazinyl group, pyrimidinyl group, pyrazinyl group, indolyl group, 1H-indazolyl group, isoindolyl group, chromenyl group, quinolinyl group, isoquinolinyl group, purinyl group, pteridinyl Group, triazolyl group, tetrazolyl group, 4H-quinolidinyl group, naphthyridinyl group, benzofuranyl group, 1,3-benzodioxolyl group, benzoxazolyl group, benzothiazolyl group, benzimidazolyl group, Rubazoriru group, phenanthridinyl group, acridinyl group, phenazinyl group or include phenanthrolinyl group.

  An aralkyl group having 7 to 20 carbon atoms is unsubstituted. The aralkyl group having 7 to 20 carbon atoms is an alkyl group having 1 to 6 carbon atoms to which an aryl group having 6 to 14 carbon atoms is bonded.

  The alkoxy group having 1 to 6 carbon atoms is linear or branched and unsubstituted. Examples of the alkoxy group having 1 to 6 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, s-butoxy, t-butoxy, pentyloxy, iso A pentyloxy group, a neopentyloxy group, or a hexyloxy group may be mentioned.

<1. Photoconductor>
The present embodiment relates to an electrophotographic photoreceptor (hereinafter sometimes referred to as a photoreceptor). The photoreceptor according to this embodiment includes a conductive substrate and a photosensitive layer.

  Hereinafter, the structure of the photoreceptor 1 will be described with reference to FIG. FIG. 1 is a cross-sectional view illustrating an example of a photoreceptor 1 according to the present embodiment.

  As shown in FIG. 1A, the photoreceptor 1 includes, for example, a conductive substrate 2 and a photosensitive layer 3. The photoreceptor 1 includes a single-layer type photosensitive layer 3 c as the photosensitive layer 3. The photoreceptor 1 is a so-called single layer type photoreceptor.

  As shown in FIG. 1B, the photoreceptor 1 may include a conductive substrate 2, a single-layer type photosensitive layer 3c, and an intermediate layer 4 (undercoat layer). The intermediate layer 4 is provided between the conductive substrate 2 and the single-layer type photosensitive layer 3c. As shown in FIG. 1A, the photosensitive layer 3 may be provided directly on the conductive substrate 2, or as shown in FIG. 1B, the photosensitive layer 3 is formed on the conductive substrate 2 as an intermediate layer. 4 may be provided indirectly.

  As shown in FIG. 1C, the photoreceptor 1 may include a conductive substrate 2, a single-layer type photosensitive layer 3c, and a protective layer 5. The protective layer 5 is provided on the single-layer type photosensitive layer 3c.

  The thickness of the single-layer type photosensitive layer 3c is not particularly limited as long as the function as a single-layer type photosensitive layer can be sufficiently expressed. The thickness of the single-layer photosensitive layer 3c is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less.

  The single-layer type photosensitive layer 3c as the photosensitive layer 3 contains a charge generating agent and a compound (1) as an electron transporting agent. The single layer type photosensitive layer 3c may further contain one or more of a hole transport agent and a binder resin. The single-layer type photosensitive layer 3c may contain various additives as necessary. The charge generating agent, the electron transport agent, and the components added as necessary (for example, a hole transport agent, a binder resin, or an additive) are contained in one photosensitive layer 3 (single-layer photosensitive layer 3c). Is done.

  In order to suppress the occurrence of white spots in the formed image, the single-layer type photosensitive layer 3 c containing the compound (1) is preferably disposed as the outermost surface layer of the photoreceptor 1.

  The structure of the photoreceptor 1 has been described above with reference to FIG. Next, the elements of the photoreceptor will be described.

<1-1. Photosensitive layer>
The photosensitive layer contains compound (1) as an electron transport agent. The amount of charge of calcium carbonate (hereinafter sometimes referred to as the amount of charge of calcium carbonate) when the photosensitive layer and calcium carbonate are rubbed is 7.0 μC / g or more. As a result, the photoreceptor of this embodiment is presumed to have the following advantages.

  In order to facilitate understanding, a cause of white spots occurring in the formed image will be described. When a recording medium (for example, paper) and a photoconductor are in contact with each other in image formation, a minute component (for example, paper dust) of the recording medium may adhere to the surface of the photoconductor. When a minute component of the recording medium adheres to the surface of the photoconductor, the minute component may block light exposed to the photoconductor in the image forming exposure process. In the portion where the exposed light is blocked by the minute component, the surface potential of the photoreceptor is unlikely to decrease. Since it is difficult for toner to adhere to a portion where the surface potential is not sufficiently lowered, white spots are generated in the formed image.

  Here, when the recording medium (for example, paper) and the photosensitive member come into contact with each other in image formation, the minute component (for example, paper dust) of the recording medium is rubbed by the photosensitive member, and the minute component is negative or has a desired value. It may be charged to a lower positive polarity. However, the photosensitive layer of the photoreceptor of this embodiment contains the compound (1). Since compound (1) has a halogen atom, it has a high electronegativity. When the minute component comes into contact with the photoconductor of the present embodiment and the minute component is rubbed by the photoconductor containing the compound (1) having a high electronegativity, the minute component is charged to a positive polarity higher than a desired value. Tend to. When the surface of the photoreceptor is positively charged in the image forming charging step, the surface of the photoreceptor charged positively and the minute component having a positive polarity exceeding a desired value are electrically repelled. As the charge amount of the minute component becomes a larger positive value, the electric repulsion with the surface of the photoreceptor increases. This makes it difficult for minute components to adhere to the surface of the photoreceptor. As a result, the occurrence of white spots in the formed image can be suppressed.

  As described above, the charge amount of calcium carbonate is 7.0 μC / g or more. Calcium carbonate is the main component of paper dust, which is an example of a minute component of the recording medium. When the charge amount of calcium carbonate is less than 7.0 μC / g, the positive chargeability of the minute component is insufficient when the photosensitive member and the minute component of the recording medium rub against each other, and white spots are generated in the formed image. It becomes easy. The charge amount of calcium carbonate is preferably 7.0 μC / g or more and 15.0 μC / g or less, and more preferably 8.0 μC / g or more and 9.5 μC / g or less.

  Hereinafter, a method for measuring the charge amount of calcium carbonate when the photosensitive layer 3 and the calcium carbonate are rubbed will be described with reference to FIG. The charge amount of calcium carbonate is measured by performing the first step, the second step, the third step, and the fourth step. In the first step, two photosensitive layers 3 are prepared. One of the photosensitive layers 3 is the first photosensitive layer 30. The other of the photosensitive layers 3 is the second photosensitive layer 32. The first photosensitive layer 30 and the second photosensitive layer 32 are circular with a diameter of 3 cm. In the second step, 0.007 g of calcium carbonate is placed on the first photosensitive layer 30. Thereby, the calcium carbonate layer 24 composed of calcium carbonate is formed. Subsequently, the second photosensitive layer 32 is placed on the calcium carbonate layer 24. In the third step, the first photosensitive layer 30 is rotated for 60 seconds at a rotation speed of 60 rpm while the second photosensitive layer 32 is fixed in an environment of a temperature of 23 ° C. and a relative humidity of 50% RH. Thereby, the calcium carbonate contained in the calcium carbonate layer 24 is rubbed between the first photosensitive layer 30 and the second photosensitive layer 32 to charge the calcium carbonate. In the fourth step, the charged calcium carbonate is sucked using a charge amount measuring device. The total amount of electricity Q and mass M of the sucked calcium carbonate are measured using a charge amount measuring device, and the charge amount of calcium carbonate is calculated from the formula Q / M. The charge amount of calcium carbonate is specifically measured by the method described in the examples. The method for measuring the charge amount of calcium carbonate when the photosensitive layer 3 and the calcium carbonate are rubbed has been described above with reference to FIG.

(Electron transfer agent)
The electron transport agent includes the compound (1). The electron transfer agent, for example, transports electrons in a single-layer type photosensitive layer and imparts bipolar (bipolar) characteristics to the single-layer type photosensitive layer. When the single-layer type photosensitive layer contains the compound (1) as an electron transport agent, when the paper and the photosensitive member are in contact with each other, the photosensitive member containing the compound (1) having a high electronegativity is used to make the recording medium minute. Components (eg, paper dust) are rubbed to charge the microcomponents to a desired positive value.

  The compound (1) is represented by the following general formula (1). Compound (1) is a malononitrile derivative.

In general formula (1), R ₁ is an alkyl group having 1 to 8 carbon atoms having one or more halogen atoms; a cycloalkyl group having 3 to 10 carbon atoms having one or more halogen atoms; An aryl group having 6 to 14 carbon atoms which may have an alkyl group having 1 to 6 carbon atoms; a 5- to 14-membered heterocyclic ring having one or more halogen atoms Group: or an aralkyl group having 7 or more and 20 or less carbon atoms having at least one halogen atom.

The alkyl group having 1 to 8 carbon atoms represented by R ₁ in the general formula (1) is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 3 to 5 carbon atoms. An n-propyl group, an n-butyl group, or a neopentyl group is particularly preferable. The alkyl group having 1 to 8 carbon atoms represented by R ₁ has one or more halogen atoms. The halogen atom contained in the alkyl group having 1 to 8 carbon atoms represented by R ₁ is preferably a chloro group or a fluoro group, and more preferably a chloro group. The number of halogen atoms contained in the alkyl group having 1 to 8 carbon atoms represented by R ₁ is preferably 1 or 2.

The cycloalkyl group having 3 to 10 carbon atoms represented by R ₁ has one or more halogen atoms. The halogen atom contained in the cycloalkyl group having 3 to 10 carbon atoms represented by R ₁ is preferably a chloro group or a fluoro group. The number of halogen atoms contained in the cycloalkyl group having 3 to 10 carbon atoms represented by R ₁ is preferably 1 or 2.

The aryl group having 6 to 14 carbon atoms represented by R ₁ is preferably a phenyl group. The aryl group having 6 to 14 carbon atoms represented by R ₁ has one or more halogen atoms. The halogen atom contained in the aryl group having 6 to 14 carbon atoms represented by R ₁ is preferably a chloro group or a fluoro group, and more preferably a chloro group. The number of halogen atoms contained in the aryl group having 6 to 14 carbon atoms represented by R ₁ is preferably 1 or 2, and more preferably 1. The aryl group having 6 to 14 carbon atoms may further have an alkyl group having 1 to 6 carbon atoms in addition to the halogen atom. The alkyl group having 1 to 6 carbon atoms, which the aryl group having 6 to 14 carbon atoms has, is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group.

The 5- to 14-membered heterocyclic group represented by R ₁ is a 5- or 6-membered monocyclic heterocycle containing 1 to 3 heteroatoms (preferably nitrogen atoms) in addition to the carbon atom. A cyclic group is preferred, and a pyridyl group is more preferred. The 5- to 14-membered heterocyclic group represented by R ₁ has one or more halogen atoms. The halogen atom contained in the 5-membered to 14-membered heterocyclic group represented by R ₁ is preferably a chloro group or a fluoro group, and more preferably a chloro group. The number of halogen atoms contained in the 5- to 14-membered heterocyclic group represented by R ₁ is preferably one or two, and more preferably one.

The aralkyl group having 7 to 20 carbon atoms represented by R ₁ is preferably an alkyl group having 1 to 6 carbon atoms to which a phenyl group is bonded, and more preferably a phenylmethyl group (benzyl group) or a phenylethyl group. preferable. The aralkyl group having 7 to 20 carbon atoms represented by R ₁ has one or more halogen atoms. The halogen atom contained in the aralkyl group having 7 to 20 carbon atoms represented by R ₁ is preferably a chloro group or a fluoro group. The number of halogen atoms contained in the aralkyl group having 7 to 20 carbon atoms represented by R ₁ is preferably one or two.

In the general formula (1), the bonding position (substitution position) of the group represented by the general formula “—COOR ₁ ” is not particularly limited. The group represented by the general formula “—COOR ₁ ” may be bonded to any of the 1-position, 2-position, 3-position and 4-position in the following chemical formula. The group represented by the general formula “—COOR ₁ ” is preferably bonded to the 1-position, 2-position or 4-position in the following chemical formula.

In order to suitably suppress the occurrence of white spots in the formed image, R ₁ is an alkyl group having 1 to 8 carbon atoms having one or two halogen atoms; having one or two halogen atoms An aryl group having 6 to 14 carbon atoms which may have an alkyl group having 1 to 6 carbon atoms; a 5- to 14-membered heterocyclic group having 1 or 2 halogen atoms; or halogen It preferably represents an aralkyl group having 1 or 2 carbon atoms and having 7 to 20 carbon atoms.

In one embodiment for particularly suppressing generation of white spots in the formed image, R ₁ is an alkyl group having 1 to 8 carbon atoms having two halogen atoms, or 7 or more carbon atoms having two halogen atoms. It preferably represents 20 or less aralkyl groups. This is because as the number of halogen atoms in R ₁ increases, the charge amount of the minute component tends to show a large positive value when the minute component (for example, paper dust) of the recording medium is rubbed by the photosensitive member. .

In another embodiment for particularly suppressing the occurrence of white spots in the formed image, R ₁ preferably represents an alkyl group having 1 or more and 8 or less carbon atoms having one or two halogen atoms. When R ₁ represents an alkyl group having 1 or more and 8 or less carbon atoms having one or two halogen atoms, the existence probability of the compound (1) in the vicinity of the surface of the photosensitive layer tends to increase. As a result, when the minute component (for example, paper dust) of the recording medium is rubbed by the photoconductor, the minute component is likely to have a large positive charge amount.

  Specific examples of compound (1) include compounds (1-1) to (1-9). Each of the compounds (1-1) to (1-9) is represented by the following chemical formulas (1-1) to (1-9).

[Production Method of Compound (1)]
Compound (1) is produced, for example, according to the following reactions (R-1) and (R-2) or by a method analogous thereto. In addition to these reactions, appropriate steps may be included as necessary. R ₁ in the reaction formula shown in the reaction (R-1) and (R-2) has the same meaning as R ₁ in the general formula (1).

  In the reaction (R-1), 1 molar equivalent of the compound (A) and 1 molar equivalent of the compound (B) are reacted to obtain 1 molar equivalent of the compound (C). It is preferable to add 1 mol or more and 5 mol or less of compound (B) with respect to 1 mol of compound (A). The reaction temperature for reaction (R-1) is preferably 80 ° C. or higher and 150 ° C. or lower. The reaction time for reaction (R-1) is preferably 2 hours or longer and 10 hours or shorter.

  Reaction (R-1) may be carried out in the presence of a catalyst. Examples of the catalyst include an acid catalyst, and more specifically, p-toluenesulfonic acid, camphorsulfonic acid, or pyridinium-p-toluenesulfonic acid. These catalysts may be used individually by 1 type, and may be used in combination of 2 or more type. The addition amount of the catalyst is a small amount with respect to 1 mol of the compound (A), and specifically, it is preferably 0.01 mol or more and 0.5 mol or less.

  Reaction (R-1) may be carried out in a solvent. Examples of the solvent include ethers (specifically, tetrahydrofuran, diethyl ether or dioxane), halogenated hydrocarbons (specifically, methylene chloride, chloroform or dichloroethane) or aromatic hydrocarbons (specifically, Benzene or toluene).

  In the reaction (R-2), 1 molar equivalent of the compound (C) and 1 molar equivalent of the compound (D, malononitrile) are reacted to obtain 1 molar equivalent of the compound (1). It is preferable to add 1 mol or more and 5 mol or less of compound (D) with respect to 1 mol of compound (C). The reaction temperature for reaction (R-2) is preferably 40 ° C. or higher and 120 ° C. or lower. The reaction time for reaction (R-2) is preferably from 1 hour to 10 hours.

  Reaction (R-2) may be carried out in the presence of a catalyst. Examples of the catalyst include a base catalyst, and more specifically, piperidine and piperazine.

  Reaction (R-2) may be performed in a solvent. Examples of the solvent include polar solvents, and more specifically, methanol, ethanol, n-propanol, acetone, or dioxane.

  By purifying the reaction product obtained in the reaction (R-2) as necessary, the target compound (1) can be isolated. As a purification method, a known method is appropriately employed. Purification may be performed, for example, by crystallization or silica gel chromatography. An example of the solvent used for purification is chloroform.

  In addition to the compound (1), the single-layer type photosensitive layer may further contain an electron transport agent other than the compound (1) (hereinafter sometimes referred to as other electron transport agent). Examples of other electron transport agents include quinone compounds, diimide compounds, hydrazone compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, dinitroanthracenes. Compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride or dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds. An electron transfer agent may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the compound (1) is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass with respect to the total mass of the electron transport agent.

  The content of the compound (1) as the electron transfer agent is preferably 20 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the binder resin. When the content of the compound (1) is 20 parts by mass or more with respect to 100 parts by mass of the binder resin, it is easy to improve the electrical characteristics of the photoreceptor. When the content of the compound (1) is 40 parts by mass or less with respect to 100 parts by mass of the binder resin, the compound (1) is easily dissolved in the solvent for forming the photosensitive layer, and a uniform photosensitive layer is formed. It becomes easy.

(Charge generator)
The single-layer type photosensitive layer as the photosensitive layer contains a charge generating agent. The charge generator is not particularly limited as long as it is a charge generator for a photoreceptor. Examples of the charge generator include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azurenium pigments, cyanine Pigments, inorganic photoconductive materials (for example, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide or amorphous silicon), pyrylium pigments, ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, Examples include pyrazoline pigments and quinacridone pigments. A charge generating agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the phthalocyanine pigment include metal-free phthalocyanine or metal phthalocyanine represented by the chemical formula (CGM-1). Examples of the metal phthalocyanine include titanyl phthalocyanine, hydroxygallium phthalocyanine, or chlorogallium phthalocyanine represented by the chemical formula (CGM-2). The phthalocyanine pigment may be crystalline or non-crystalline. The crystal shape of the phthalocyanine pigment (for example, α type, β type, Y type, V type or II type) is not particularly limited, and phthalocyanine pigments having various crystal shapes are used.

  Examples of the crystal of metal-free phthalocyanine include an X-type crystal of metal-free phthalocyanine (hereinafter sometimes referred to as X-type metal-free phthalocyanine). Examples of the crystal of titanyl phthalocyanine include α-type, β-type, and Y-type crystals of titanyl phthalocyanine (hereinafter sometimes referred to as α-type, β-type, or Y-type titanyl phthalocyanine). Examples of the crystal of hydroxygallium phthalocyanine include a V-type crystal of hydroxygallium phthalocyanine. Examples of chlorogallium phthalocyanine crystals include chlorogallium phthalocyanine type II crystals.

  For example, in a digital optical image forming apparatus (for example, a laser beam printer or a facsimile using a light source such as a semiconductor laser), it is preferable to use a photoreceptor having sensitivity in a wavelength region of 700 nm or more. Since it has a high quantum yield in a wavelength region of 700 nm or more, the charge generator is preferably a phthalocyanine pigment, more preferably a metal-free phthalocyanine or titanyl phthalocyanine, and even more preferably an X-type metal-free phthalocyanine or a Y-type titanyl phthalocyanine. . In order to particularly improve the electrical characteristics when the photosensitive layer contains the compound (1) as a hole transport agent, Y-type titanyl phthalocyanine is more preferable as the charge generator.

  Y-type titanyl phthalocyanine has a main peak at 27.2 ° of the Bragg angle (2θ ± 0.2 °) in the CuKα characteristic X-ray diffraction spectrum, for example. The main peak in the CuKα characteristic X-ray diffraction spectrum is a peak having the first or second highest intensity in a range where the Bragg angle (2θ ± 0.2 °) is 3 ° or more and 40 ° or less.

  An example of a method for measuring the CuKα characteristic X-ray diffraction spectrum will be described. A sample (titanyl phthalocyanine) is filled in a sample holder of an X-ray diffractometer (for example, “RINT (registered trademark) 1100” manufactured by Rigaku Corporation), an X-ray tube Cu, a tube voltage 40 kV, a tube current 30 mA, and CuKα. An X-ray diffraction spectrum is measured under the condition of a characteristic X-ray wavelength of 1.542 mm. The measurement range (2θ) is, for example, 3 ° to 40 ° (start angle 3 °, stop angle 40 °), and the scanning speed is, for example, 10 ° / min.

  In a photoreceptor applied to an image forming apparatus using a short wavelength laser light source (for example, a laser light source having a wavelength of 350 nm or more and 550 nm or less), an sanslon pigment is preferably used as a charge generating agent.

  The content of the charge generating agent is preferably 0.1 parts by weight or more and 50 parts by weight or less, and 0.5 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the binder resin contained in the single-layer type photosensitive layer. The amount is more preferably 0.5 parts by mass or less and particularly preferably 0.5 parts by mass or more and 4.5 parts by mass or less.

(Hole transport agent)
The single-layer type photosensitive layer contains, for example, a hole transport agent. Examples of the hole transport agent include triphenylamine derivatives and diamine derivatives (for example, N, N, N ′, N′-tetraphenylbenzidine derivatives, N, N, N ′, N′-tetraphenylphenylenediamine derivatives, N, N, N ′, N′-tetraphenylnaphthylenediamine derivative, N, N, N ′, N′-tetraphenylphenanthrylenediamine derivative, or di (aminophenylethenyl) benzene derivative), oxadiazole Compounds (eg, 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole), styryl compounds (eg, 9- (4-diethylaminostyryl) anthracene), carbazole compounds ( For example, polyvinyl carbazole), organic polysilane compound, pyrazoline compound (for example, 1-phenyl-3- (p Dimethylaminophenyl) pyrazoline), hydrazone compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compound, or triazole-based compounds. A hole transport agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  An example of the hole transporting agent is compound (2). Compound (2) is represented by general formula (2).

In general formula (2), R _{21 to} R ₂₆ each independently represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms. r, s, v, and w each independently represent an integer of 0 or more and 5 or less. t and u each independently represents an integer of 0 or more and 4 or less.

In general formula (2), R _{21 to} R ₂₆ each independently preferably represent an alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group. It is preferable that r, s, v and w each independently represent 0 or 1. t and u each independently preferably represent 0 or 1, more preferably 0.

  Specific examples of the compound represented by the general formula (2) include the compound (2-1). The compound (2-1) is represented by the following chemical formula (2-1).

  The content of the hole transport agent contained in the single-layer type photosensitive layer is preferably 10 parts by mass or more and 200 parts by mass or less, and preferably 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the binder resin. More preferably.

(Binder resin)
The single layer type photosensitive layer contains a binder resin. Examples of the binder resin include a thermoplastic resin, a thermosetting resin, and a photocurable resin. Examples of the thermoplastic resin include polycarbonate resin, polyarylate resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic acid polymer, styrene-acrylic acid copolymer, Polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer resin, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide resin, urethane resin, polysulfone resin, diallyl phthalate Examples thereof include resins, ketone resins, polyvinyl butyral resins, polyester resins, and polyether resins. As a thermosetting resin, a silicone resin, an epoxy resin, a phenol resin, a urea resin, or a melamine resin is mentioned, for example. Examples of the photocurable resin include epoxy acrylate (epoxy compound acrylic acid adduct) or urethane-acrylate (urethane compound acrylic acid adduct). These binder resins may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among these resins, a polycarbonate resin is preferable because a single-layer type photosensitive layer having an excellent balance of workability, mechanical properties, optical properties, and abrasion resistance can be obtained. Examples of the polycarbonate resin include bisphenol ZC type polycarbonate resin, bisphenol C type polycarbonate resin, and bisphenol A type polycarbonate resin. Another example of the polycarbonate resin includes a resin represented by the following general formula (3) (hereinafter sometimes referred to as resin (3)).

In General Formula (3), R _{31 to} R ₃₆ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 14 carbon atoms. However, R ₃₅ and R ₃₆ may be bonded to each other to form a cycloalkylidene group having 5 to 7 carbon atoms. m and n each independently represent a positive number. m + n = 1.00 and 0.00 ≦ m ≦ 0.90.

The alkyl group having 1 to 6 carbon atoms represented by R _{31 to} R ₃₆ in the general formula (3) is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group.

As the aryl group having 6 to 14 carbon atoms represented by R _{31 to} R ₃₆ in the general formula (3), a phenyl group is preferable.

In the general formula (3), R ₃₁ , R ₃₂ , R ₃₃ and R ₃₄ each preferably represents a hydrogen atom, and more preferably represents a hydrogen atom or a methyl group. R ₃₅ and R ₃₆ are preferably bonded to each other to represent a cycloalkylidene group having 5 to 7 carbon atoms, and more preferably bonded to each other to represent a cyclohexylidene group.

The resin (3) is composed of a repeating structural unit represented by the general formula (3a) (hereinafter may be referred to as repeating unit (3a)) and a repeating structural unit represented by the general formula (3b) (hereinafter referred to as “repeating structural unit”). Repeating unit (3b)). In general formula (3a) R ₃₁ and R ₃₂ in each has the same meaning as R ₃₁ and R ₃₂ in each general formula (3). R ₃₃ in the general formula (3b), R _34, R ₃₅ and R ₃₆ have the same meanings as R _33, R _34, R ₃₅ and R ₃₆ each general formula (3).

  In the general formula (3), m is the amount of the substance (number of moles) of the repeating unit (3a) with respect to the total amount of substances (number of moles) of the repeating unit (3a) and the repeating unit (3b) in the resin (3). Represents a ratio (molar ratio). n represents the ratio (molar ratio) of the substance amount (mole number) of the repeating unit (3b) to the total substance amount (mole number) of the repeating unit (3a) and the repeating unit (3b) in the resin (3). . More preferably, 0.00 ≦ m ≦ 0.40.

  The resin (3) may be a random copolymer in which the repeating unit (3a) and the repeating unit (3b) are randomly copolymerized. Alternatively, the resin (3) may be an alternating copolymer in which the repeating unit (3a) and the repeating unit (3b) are alternately copolymerized. Alternatively, the resin (3) may be a periodic copolymer in which one or more repeating units (3a) and one or more repeating units (3b) are periodically copolymerized. Alternatively, the resin (3) may be a block copolymer in which a block composed of a plurality of repeating units (3a) and a block composed of a plurality of repeating units (3b) are copolymerized.

  Specific examples of the resin (3) include polycarbonate resins represented by the following chemical formula (3-1) or (3-2). The polycarbonate resin represented by the chemical formula (3-1) is a resin in which m in the general formula (3) is 0.00 and n is 1.00. The polycarbonate resin represented by the chemical formula (3-1) is composed only of the repeating unit (3b). The polycarbonate resin represented by (3-2) is a resin in which m is 0.40 and n is 0.60.

  The viscosity average molecular weight of the binder resin is preferably 25,000 or more, and more preferably 25,000 or more and 52,500 or less. When the viscosity average molecular weight of the binder resin is 25,000 or more, it is easy to improve the abrasion resistance of the photoreceptor. When the viscosity average molecular weight of the binder resin is 52,500 or less, the binder resin is easily dissolved in a solvent at the time of forming the photosensitive layer, and the viscosity of the single-layer photosensitive layer coating solution does not become too high. As a result, it becomes easy to form a single-layer type photosensitive layer.

The method for producing the binder resin is not particularly limited as long as the resin (3) can be produced. As an example of the method for producing the resin (3), there is a method (so-called phosgene method) in which a diol compound for constituting a repeating unit of a polycarbonate resin and phosgene are subjected to condensation polymerization. More specifically, for example, a method of polycondensing a diol compound represented by the general formula (3c), a diol compound represented by the general formula (3d), and phosgene can be mentioned. In general formula (3c) R ₃₁ and R ₃₂ in each has the same meaning as R ₃₁ and R ₃₂ in each general formula (3). R ₃₃ in the general formula (3d), R _34, R ₃₅ and R ₃₆ have the same meanings as R _33, R _34, R ₃₅ and R ₃₆ each general formula (3). Another example of the method for producing the resin (3) is a method in which a diol compound and diphenyl carbonate are transesterified.

(Additive)
The single-layer type photosensitive layer may contain various additives as necessary. Examples of additives include deterioration inhibitors (for example, antioxidants, radical scavengers, singlet quenchers or ultraviolet absorbers), softeners, surface modifiers, extenders, thickeners, dispersion stabilizers. , Waxes, acceptors, donors, surfactants, plasticizers, sensitizers or leveling agents. Antioxidants include, for example, hindered phenols (eg, di (tert-butyl) p-cresol), hindered amines, paraphenylenediamine, arylalkanes, hydroquinones, spirochromans, spirodinones or their derivatives, organic sulfur compounds or An organic phosphorus compound is mentioned.

<1-2. Conductive substrate>
The conductive substrate is not particularly limited as long as it can be used as the conductive substrate of the photoreceptor. The conductive substrate may be formed of a material having at least a surface portion having conductivity. An example of the conductive substrate is a conductive substrate formed of a conductive material. Another example of the conductive substrate is a conductive substrate coated with a conductive material. Examples of the conductive material include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass. These conductive materials may be used alone or in combination of two or more (for example, as an alloy). Among these materials having conductivity, aluminum or an aluminum alloy is preferable because charge transfer from the photosensitive layer to the conductive substrate is good.

  The shape of the conductive substrate is appropriately selected according to the structure of the image forming apparatus. Examples of the shape of the conductive substrate include a sheet shape or a drum shape. The thickness of the conductive substrate is appropriately selected according to the shape of the conductive substrate.

<1-3. Intermediate layer>
The intermediate layer (undercoat layer) contains, for example, inorganic particles and a resin (intermediate layer resin) used for the intermediate layer. The presence of the intermediate layer is considered to suppress the increase in resistance by smoothing the flow of current generated when the photosensitive member is exposed while maintaining an insulating state capable of suppressing the occurrence of leakage.

  Examples of the inorganic particles include metal (for example, aluminum, iron or copper), metal oxide (for example, titanium oxide, alumina, zirconium oxide, tin oxide or zinc oxide) particles or non-metal oxide (for example, silica). Particles. These inorganic particles may be used individually by 1 type, and may use 2 or more types together.

  The resin for the intermediate layer is not particularly limited as long as it can be used as a resin for forming the intermediate layer. The intermediate layer may contain various additives. The additive is the same as the additive for the photosensitive layer.

<1-4. Photoconductor manufacturing method>
The photoreceptor is manufactured, for example, as follows. The photoreceptor is produced by applying a coating solution for a single-layer type photosensitive layer on a conductive substrate and drying it. The coating solution for a single-layer type photosensitive layer dissolves or disperses a charge generator, an electron transport agent, and components added as necessary (for example, a hole transport agent, a binder resin, and various additives) in a solvent. Manufactured by.

  The solvent contained in the single-layer photosensitive layer coating solution is not particularly limited as long as each component contained in the coating solution can be dissolved or dispersed. Examples of solvents include alcohols (eg, methanol, ethanol, isopropanol or butanol), aliphatic hydrocarbons (eg, n-hexane, octane or cyclohexane), aromatic hydrocarbons (eg, benzene, toluene or xylene), Halogenated hydrocarbons (eg dichloromethane, dichloroethane, carbon tetrachloride or chlorobenzene), ethers (eg dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or propylene glycol monomethyl ether), ketones (eg acetone, Methyl ethyl ketone or cyclohexanone), esters (eg ethyl acetate or methyl acetate), dimethylformaldehyde, dimethylform Amide or dimethyl sulfoxide. These solvents are used alone or in combination of two or more. In order to improve the workability during the production of the photoreceptor, it is preferable to use a non-halogen solvent (a solvent other than the halogenated hydrocarbon) as the solvent.

  The coating solution is prepared by mixing each component and dispersing in a solvent. For mixing or dispersing, for example, a bead mill, a roll mill, a ball mill, an attritor, a paint shaker, or an ultrasonic disperser can be used.

  The single-layer photosensitive layer coating solution may contain, for example, a surfactant in order to improve the dispersibility of each component.

  The method for applying the single-layer photosensitive layer coating solution is not particularly limited as long as the coating solution can be uniformly applied onto the conductive substrate. Examples of the coating method include a dip coating method, a spray coating method, a spin coating method, and a bar coating method.

  The method for drying the single-layer photosensitive layer coating solution is not particularly limited as long as the solvent in the coating solution can be evaporated. For example, the method of heat-processing (hot-air drying) is mentioned using a high-temperature dryer or a vacuum dryer. The heat treatment conditions are, for example, a temperature of 40 ° C. or higher and 150 ° C. or lower and a time of 3 minutes or longer and 120 minutes or shorter.

  In addition, the manufacturing method of a photoreceptor may further include one or both of a step of forming an intermediate layer and a step of forming a protective layer as necessary. A known method is appropriately selected in the step of forming the intermediate layer and the step of forming the protective layer.

<2. Image forming apparatus>
Next, the image forming apparatus 100 including the photoreceptor 1 according to the present embodiment will be described with reference to FIG. FIG. 3 shows an example of the configuration of the image forming apparatus 100.

  The image forming apparatus 100 is not particularly limited as long as it is an electrophotographic image forming apparatus. For example, the image forming apparatus 100 may be a monochrome image forming apparatus or a color image forming apparatus. When the image forming apparatus 100 is a color image forming apparatus, the image forming apparatus 100 employs, for example, a tandem method. Hereinafter, the tandem image forming apparatus 100 will be described as an example.

  The image forming apparatus 100 includes image forming units 40a, 40b, 40c, and 40d, a transfer belt 50, and a fixing unit 52. Hereinafter, when it is not necessary to distinguish, each of the image forming units 40a, 40b, 40c, and 40d is referred to as an image forming unit 40.

  The image forming unit 40 includes the photoreceptor 1, a charging unit 42, an exposure unit 44, a developing unit 46, and a transfer unit 48. The photoreceptor 1 is provided at the center position of the image forming unit 40. The photoreceptor 1 is provided so as to be rotatable in the arrow direction (counterclockwise). Around the photosensitive member 1, a charging unit 42, an exposure unit 44, a developing unit 46, and a transfer unit 48 are provided in order from the upstream side in the rotation direction of the photosensitive member 1 with respect to the charging unit 42. The image forming unit 40 may further include one or both of a cleaning unit (not shown) and a charge removal unit (not shown).

  The charging unit 42 charges the surface of the photoreceptor 1. The charging unit 42 is a non-contact method or a contact method. An example of the non-contact charging unit 42 is a corotron charger or a scorotron charger. An example of the contact-type charging unit 42 is a charging roller or a charging brush.

  The image forming apparatus 100 can include a charging roller as the charging unit 42. When charging the surface of the photoreceptor 1, the charging roller contacts the photoreceptor 1. When a minute component (for example, paper powder) of the recording medium P (for example, paper) is attached to the surface of the photoreceptor 1, the minute component is pressed against the surface of the photoreceptor 1 by the charging roller that has come into contact. Thereby, a minute component is easily fixed on the surface of the photoreceptor 1. However, the image forming apparatus 100 includes the photoreceptor 1 that can suppress the generation of white spots caused by the adhesion of minute components. For this reason, even when the image forming apparatus 100 includes a charging roller as the charging unit 42, it is difficult for minute components to adhere to the surface of the photoreceptor 1, and the occurrence of white spots in the formed image is suppressed. it can.

  The charging unit 42 preferably charges the surface of the photoreceptor 1 to a positive polarity. When the photoreceptor 1 of this embodiment and the recording medium P come into contact with each other and are rubbed, the recording medium P tends to be positively charged. When the surface of the photoreceptor 1 is positively charged by the charging unit 42, the surface of the photoreceptor 1 and the recording medium P that is frictionally charged to the positive polarity are electrically repelled. As a result, minute components (for example, paper dust) of the recording medium P are difficult to adhere to the surface of the photoreceptor 1, and the generation of white spots in the formed image can be suitably suppressed.

  The exposure unit 44 exposes the surface of the charged photoreceptor 1. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 1. The electrostatic latent image is formed based on image data input to the image forming apparatus 100.

  The developing unit 46 supplies toner to the electrostatic latent image formed on the photoreceptor 1. As a result, the electrostatic latent image is developed as a toner image. The photoreceptor 1 corresponds to an image carrier that carries a toner image.

  The developing unit 46 can develop the electrostatic latent image as a toner image while in contact with the photoreceptor 1. That is, the image forming apparatus 100 can employ a so-called contact development method. When a minute component (for example, paper dust) of the recording medium P adheres to the surface of the photoreceptor 1, the minute component is pressed against the surface of the photoreceptor 1 by the developing unit 46 that has come into contact. Thereby, a minute component is easily fixed on the surface of the photoreceptor 1. However, the image forming apparatus 100 includes the photoreceptor 1 that can suppress the generation of white spots caused by the adhesion of minute components. For this reason, the image forming apparatus 100 can suppress the occurrence of white spots in the formed image because the minute components are difficult to adhere to the surface of the photoreceptor 1 even when the contact development method is employed.

  The developing unit 46 can clean the surface of the photoreceptor 1. In other words, the image forming apparatus 100 can employ a so-called cleaner-less method. The developing unit 46 can remove components remaining on the surface of the photoreceptor 1 (hereinafter, sometimes referred to as “residual components”). An example of the residual component is a toner component, and more specifically, a toner or a free external additive. Another example of the residual component is a non-toner component, and more specifically, a minute component (for example, paper dust) of the recording medium P. In the image forming apparatus 100 that employs the cleaner-less method, residual components on the surface of the photoreceptor 1 are not scraped off by a cleaning unit (for example, a cleaning blade). For this reason, in the image forming apparatus 100 that employs the cleaner-less method, a residual component usually tends to remain on the surface of the photoreceptor 1. However, the photoreceptor 1 of this embodiment can suppress the generation of white spots caused by the adhesion of minute components. Therefore, even if the image forming apparatus 100 including such a photoreceptor 1 adopts a cleaner-less method, residual components, particularly minute components (for example, paper dust) of the recording medium P hardly remain on the surface of the photoreceptor 1. . As a result, the image forming apparatus 100 can suppress the occurrence of white spots in the formed image.

In order for the developing unit 46 to efficiently clean the surface of the photoreceptor 1, it is preferable to satisfy the following conditions (a) and (b).
Condition (a): A contact developing method is adopted, and a circumferential speed (rotational speed) difference is provided between the photoreceptor 1 and the developing unit 46.
Condition (b): The surface potential of the photoreceptor 1 and the potential of the developing bias satisfy the following formulas (b-1) and (b-2).
0 (V) <potential of developing bias (V) <surface potential of unexposed area of photoreceptor 1 (V) (b-1)
Potential of developing bias (V)> surface potential of exposed area of photoreceptor 1 (V)> 0 (V) (b-2)

  When the contact development method shown in the condition (a) is employed and a peripheral speed difference is provided between the photosensitive member 1 and the developing unit 46, the surface of the photosensitive member 1 comes into contact with the developing unit 46, and the photosensitive member 1 The adhering component on the surface is removed by friction with the developing section 46. The peripheral speed of the developing unit 46 is preferably faster than the peripheral speed of the photoreceptor 1.

  Condition (b) assumes a case where the development method is a reversal development method. In order to improve the electrical characteristics of the photoreceptor 1 which is a single layer photoreceptor, the charging polarity of the toner, the surface potential of the unexposed area of the photoreceptor 1, the surface potential of the exposed area of the photoreceptor 1 and the potential of the developing bias Are preferably positive. It should be noted that the surface potential of the unexposed area and the exposed area of the photoreceptor 1 are the same as the surface potential of the photoreceptor 1 in which the transfer section 48 transfers the toner image from the photoreceptor 1 to the recording medium P and then the charging section 42 performs the next round. Measured before charging the surface.

  When the mathematical expression (b-1) of the condition (b) is satisfied, the electrostatic force acting between the toner remaining on the photoreceptor 1 (hereinafter sometimes referred to as “residual toner”) and the unexposed area of the photoreceptor 1. The repulsive force is larger than the electrostatic repulsive force acting between the residual toner and the developing unit 46. Therefore, the residual toner in the unexposed area of the photoreceptor 1 moves from the surface of the photoreceptor 1 to the developing unit 46 and is collected.

  When the mathematical expression (b-2) of the condition (b) is satisfied, the electrostatic repulsive force acting between the residual toner and the exposed area of the photoreceptor 1 acts on the electrostatic force acting between the residual toner and the developing unit 46. Smaller than the repulsive force. Therefore, the residual toner in the exposed area of the photoconductor 1 is held on the surface of the photoconductor 1. The toner held in the exposure area of the photoreceptor 1 is used as it is for image formation.

  The transfer belt 50 conveys the recording medium P between the photoreceptor 1 and the transfer unit 48. The transfer belt 50 is an endless belt. The transfer belt 50 is provided to be rotatable in the arrow direction (clockwise).

  The transfer unit 48 transfers the toner image developed by the developing unit 46 from the photoreceptor 1 to the recording medium P. When the toner image is transferred from the photoreceptor 1 to the recording medium P, the photoreceptor 1 is in contact with the recording medium P. That is, the image forming apparatus 100 employs a so-called direct transfer method. The transfer unit 48 is, for example, a transfer roller.

  Each of the image forming units 40a to 40d sequentially superimposes toner images of a plurality of colors (for example, four colors of black, cyan, magenta, and yellow) on the recording medium P on the transfer belt 50. When the image forming apparatus 100 is a monochrome image forming apparatus, the image forming apparatus 100 includes an image forming unit 40a, and the image forming units 40b to 40d are omitted.

  The fixing unit 52 heats and / or pressurizes the unfixed toner image transferred to the recording medium P by the transfer unit 48. The fixing unit 52 is, for example, a heating roller and / or a pressure roller. The toner image is fixed on the recording medium P by heating and / or pressurizing the toner image. As a result, an image is formed on the recording medium P.

<3. Process cartridge>
Next, with reference to FIG. 3 again, a process cartridge including the photoreceptor 1 of the present embodiment will be described. The process cartridge corresponds to each of the image forming units 40a to 40d. The process cartridge includes a unitized photoconductor 1. The process cartridge employs a configuration in which at least one selected from the group consisting of the charging unit 42, the exposure unit 44, the developing unit 46, and the transfer unit 48 is unitized in addition to the photoreceptor 1. The process cartridge may further include one or both of a cleaning device (not shown) and a static eliminator (not shown). The process cartridge is designed to be detachable from the image forming apparatus 100. Therefore, the process cartridge is easy to handle, and when the sensitivity characteristics of the photoconductor 1 deteriorate, the process cartridge including the photoconductor 1 can be replaced easily and quickly.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the scope of the examples.

<1. Photosensitive Material>
The following charge generating agent, hole transporting agent and electron transporting agent were prepared as materials for forming the single-layer type photosensitive layer of the photoreceptor.

<1-1. Charge generator>
A compound (CGM-1X) was prepared as a charge generator. The compound (CGM-1X) was a metal-free phthalocyanine represented by the chemical formula (CGM-1) described in the embodiment. In addition, the crystal structure of the compound (CGM-1X) was X-type.

<1-2. Hole transport agent>
The compound (2-1) described in the embodiment was prepared as a hole transport agent.

<1-3. Binder resin>
Resins (3-1a) and (3-2a) were prepared as binder resins.

  The resin (3-1a) was a polycarbonate resin represented by the chemical formula (3-1) described in the embodiment. The viscosity average molecular weight of the resin (3-1a) was 30000.

  The resin (3-2a) was a polycarbonate resin represented by the chemical formula (3-2) described in the embodiment. The viscosity average molecular weight of the resin (3-2a) was 30000.

<1-4. Electron transport agent>
As the electron transport agent, the compounds (1-1) to (1-9) described in the embodiment were prepared. Compounds (1-1) to (1-9) were each produced by the following method.

(Production of Compound (1-1))
Compound (1-1) was produced according to the following reactions (R-3) and (R-4).

  In reaction (R-3), compound (A-1) and compound (B-1) were reacted to obtain compound (C-1). Hereinafter, the compound (A-1) may be referred to as a first raw material for the reaction (R-3), and the compound (B-1) may be referred to as a second raw material for the reaction (R-3). 2.24 g (0.01 mol) of compound (A-1), 3.26 g (0.03 mol) of compound (B-1) and toluene (100 mL) were added to the flask to dissolve the contents of the flask. . P-Toluenesulfonic acid (0.001 mol) was added into the flask. The flask was set in a Dean-Stark apparatus. The contents of the flask were refluxed at 90 ° C. for 5 hours while dehydrating. The contents of the obtained flask were decompressed, and toluene was distilled off. Ion exchange water was added to the mixture after distillation under reduced pressure, and the mixture was extracted with chloroform. After the obtained organic layer was dried, the organic layer was depressurized and chloroform was distilled off. As a result, compound (C-1) was obtained as a crude product. The yield of compound (C-1) was 2.84 g, and the yield of compound (C-1) from compound (A-1) was 90 mol%.

  In reaction (R-4), compound (C-1) and compound (D, malononitrile) were reacted to obtain compound (1-1). Hereinafter, the compound (C-1) may be referred to as a first raw material for the reaction (R-4) and the compound (D) may be referred to as a second raw material for the reaction (R-4). 1.57 g (0.005 mol) of compound (C-1) and 0.66 g (0.01 mol) of compound (D) were added to methanol (100 mL) to obtain a methanol solution. To the methanol solution, 0.08 g (0.001 mol) of piperidine was added to obtain a mixture. The mixture was stirred at 80 ° C. for 3 hours at reflux. Subsequently, the mixture was added to ion exchange water (200 mL) to precipitate a solid, and the solid was collected by filtration. The obtained solid was purified by silica gel column chromatography using chloroform as a developing solvent. As a result, compound (1-1) was obtained. The yield of compound (1-1) was 1.45 g, and the yield of compound (1-1) from compound (C-1) was 80 mol%.

(Production of compounds (1-2) to (1-9))
The reaction (R-3) was carried out in the same manner as in the production of the compound (C-1) except that the following points were changed. Subsequently, the reaction (R-4) was carried out in the same manner as in the production of the compound (1-1) except that the following points were changed. As a result, compounds (1-2) to (1-9) were obtained.

  The 1st raw material of reaction (R-3) was changed into the 1st raw material shown in Table 1 from the compound (A-1) in manufacture of a compound (C-1). The 2nd raw material of reaction (R-3) was changed into the 2nd raw material shown in Table 1 from the compound (B-1) in manufacture of a compound (C-1). The addition mass of the second raw material in the reaction (R-3) was changed from 3.26 g in the production of the compound (C-1) to the addition mass of the second raw material shown in Table 1. In addition, the number of moles of each raw material used in the production of the compounds (C-2) to (C-9) was the same as the number of moles of the corresponding raw material used in the production of the compound (C-1). . As a result, compounds (C-2) to (C-9) were obtained as reaction products of reaction (R-3) instead of compound (C-1). Table 1 shows the yields of the compounds (C-2) to (C-9) obtained in the reaction (R-3). Table 1 shows the yields of the compounds (C-2) to (C-9) from the first raw material of the reaction (R-3).

  Compounds (A-1) to (A-3), (B-1) to (B-3), (B-5) to (B-9) and (C-1) to (C-) in Table 1 Each of 9) has the following chemical formulas (A-1) to (A-3), (B-1) to (B-3), (B-5) to (B-9) and (C-1) It is represented by ~ (C-9).

  Next, the 1st raw material of reaction (R-4) was changed into the 1st raw material shown in Table 2 from the compound (C-1) in manufacture of a compound (1-1). The addition mass of the first raw material in the reaction (R-4) was changed from 1.57 g in the production of the compound (1-1) to the addition mass of the first raw material shown in Table 1. In addition, the number of moles of each raw material used in the production of the compounds (1-2) to (1-9) is the same as the number of moles of the corresponding raw material used in the production of the compound (1-1). As a result, as the reaction product of reaction (R-4), compounds (1-2) to (1-9) as final target compounds were obtained instead of compound (1-1). Table 2 shows the yields of the compounds (1-2) to (1-9) obtained by the reaction (R-4). In addition, Table 2 shows the yields of the compounds (1-2) to (1-9) from the first raw material of the reaction (R-4).

Next, with reference to ¹ H-NMR (proton nuclear magnetic resonance spectroscopy), it was analyzed by ¹ H-NMR spectrum of the compound prepared (1-1) to (1-9). The magnetic field strength was set to 300 MHz. Deuterated chloroform (CDCl ₃ ) was used as the solvent. Tetramethylsilane (TMS) was used as an internal standard substance.

As representative examples of the compounds (1-1) to (1-9), the chemical shift values of ¹ H-NMR spectra of the compounds (1-1), (1-3) and (1-4) are as follows: Show. Moreover, the < ¹ > H-NMR spectrum of compound (1-3) and (1-4) is shown in FIG.4 and FIG.5. From the measured ¹ H-NMR spectrum and chemical shift value, it was confirmed that each of the compounds (1-1), (1-3) and (1-4) was obtained. The other compounds (1-2) and (1-5) to (1-9) were similarly analyzed from the measured ¹ H-NMR spectrum and chemical shift value, and the compounds (1-2) and (1-5) ) To (1-9) were confirmed to be obtained.

Compound (1-1): ¹ H-NMR (300 MHz, CDCl ₃ ) δ = 8.53 (dd, 1H), 8.39 (d, 1H), 8.18 (d, 1H), 7.85 ( dd, 1H), 7.49 (dt, 1H), 7.35 (t, 1H), 7.34 (dt, 1H), 4.45 (t, 2H), 3.63 (t, 2H), 1.90-2.07 (m, 4H).

Compound (1-3): ¹ H-NMR (300 MHz, CDCl ₃ ) δ = 8.62 (dd, 1H), 8.46 (d, 1H), 8.21 (d, 1H), 7.92 ( dd, 1H), 7.53 (dt, 1H), 7.35-7.45 (m, 2H), 4.69-4.85 (m, 2H), 4.38-4.47 (m, 1H), 3.80-3.93 (m, 2H).

Compound (1-4): ¹ H-NMR (300 MHz, CDCl ₃ ) δ = 8.30 (d, 1H), 7.68-7.72 (m, 2H), 7.47-7.60 (m , 3H), 7.36 (dt, 1H), 4.47 (t, 2H), 3.62 (t, 2H), 1.90-2.03 (m, 4H).

  Compounds (E-1) and (E-2) were also prepared as electron transport agents. Compounds (E-1) and (E-2) are represented by the following chemical formulas (E-1) and (E-2), respectively.

<2. Manufacture of photoconductor>
Photoconductors (P-1) to (P-24) were produced using a material for forming a single-layer type photosensitive layer.

<2-1. Production of photoconductor (P-1)>
In the container, 2 parts by mass of the compound (CGM-1X) as a charge generating agent, 50 parts by mass of the compound (2-1) as a hole transporting agent, 30 parts by mass of the compound (1-1) as an electron transporting agent, 100 parts by mass of the resin (3-1a) as a binder resin and 600 parts by mass of tetrahydrofuran as a solvent were added. The contents of the container were mixed for 12 hours using a ball mill to disperse the material in the solvent. This obtained the coating liquid for single layer type photosensitive layers. The single layer type photosensitive layer coating solution was coated on an aluminum drum-shaped support (diameter: 30 mm, total length: 238.5 mm) as a conductive substrate using a dip coating method. The applied coating liquid for single-layer type photosensitive layer was dried with hot air at 120 ° C. for 80 minutes. As a result, a single-layer type photosensitive layer (thickness 30 μm) was formed on the conductive substrate. As a result, a photoreceptor (P-1) was obtained.

<2-2. Production of photoconductors (P-2) to (P-24)>
Each of the photoreceptors (P-2) to (P-22) was produced by the same method as the production of the photoreceptor (P-1) except that the following points were changed. The compound (1-1) as the electron transport agent used for the production of the photoreceptor (P-1) was changed to the type of electron transport agent shown in Table 3. The content (addition amount) of the electron transport agent with respect to 100 parts by mass of the binder resin was changed from 30 parts by mass in the production of the photoreceptor (P-1) to the content (addition amount) shown in Table 3. The resin (3-1a) as the binder resin used for the production of the photoreceptor (P-1) was changed to the type of binder resin shown in Table 3.

<3. Evaluation of electrical characteristics>
The electrical characteristics of each of the manufactured photoreceptors (P-1) to (P-24) were evaluated. The electrical characteristics were evaluated in an environment at a temperature of 23 ° C and a relative humidity of 50% RH. First, the surface of the photosensitive member was charged to +600 V using a drum sensitivity tester (manufactured by Gentec Corporation). Next, monochromatic light (wavelength 780 nm, half-value width 20 nm, light energy 1.5 μJ / cm ² ) was extracted from the white light of the halogen lamp using a bandpass filter. The surface of the photoreceptor was irradiated with the extracted monochromatic light. The surface potential of the photoreceptor was measured when 0.5 seconds had elapsed after the irradiation was completed. The measured surface potential was defined as a sensitivity potential (V _L , unit: + V). Table 3 shows the measured sensitivity potential (V _L ) of the photoreceptor. Note that the smaller the absolute value of the sensitivity potential (V _L ), the better the electrical characteristics of the photoreceptor.

<4. Evaluation of triboelectric chargeability>
The triboelectric chargeability of each of the manufactured photoreceptors (P-1) to (P-24) was evaluated.

  Hereinafter, referring to FIG. 2 again, a method of measuring the charge amount of calcium carbonate when the photosensitive layer 3 (corresponding to the single-layer type photosensitive layer 3c) and calcium carbonate are rubbed will be described. The charge amount of calcium carbonate was measured by performing the following first step, second step, third step and fourth step. A jig 10 was used to measure the charge amount of calcium carbonate.

  The jig 10 includes a first table 12, a rotation shaft 14, a rotation drive unit 16 (for example, a motor), and a second table 18. The rotation drive unit 16 rotates the rotation shaft 14. The rotation shaft 14 rotates around the rotation axis S of the rotation shaft 14. The first table 12 is integrated with the rotation shaft 14 and rotates about the rotation axis S. The second base 18 is fixed without rotating.

(First step)
In the first step, two photosensitive layers 3 were prepared. Hereinafter, one of the photosensitive layers 3 is referred to as a first photosensitive layer 30, and the other of the photosensitive layers 3 is referred to as a second photosensitive layer 32. First, the 1st film 20 provided with the 1st photosensitive layer 30 whose film thickness L1 is 30 micrometers was prepared. Moreover, the 2nd film 22 provided with the 2nd photosensitive layer 32 whose film thickness L2 is 30 micrometers was prepared. Specifically, overhead projector (OHP) films were used as the first film 20 and the second film 22. The first film 20 and the second film 22 each had a circular shape with a diameter of 3 cm. On each of the first film 20 and the second film 22, the single-layer photosensitive layer coating solution used for the production of the photoreceptor (P-1) was applied. The applied coating liquid for single-layer type photosensitive layer was dried with hot air at 120 ° C. for 80 minutes. As a result, the first film 20 including the first photosensitive layer 30 and the second film 22 including the second photosensitive layer 32 were obtained.

(Second step)
In the second step, 0.007 g of calcium carbonate was placed on the first photosensitive layer 30. Thereby, a calcium carbonate layer 24 composed of calcium carbonate was formed on the first photosensitive layer 30. Then, the second photosensitive layer 32 was placed on the calcium carbonate layer 24. The specific procedure of the second step was as follows.

  First, the 1st film 20 was fixed to the 1st stand 12 using the double-sided tape. On the first photosensitive layer 30 provided in the first film 20, 0.007 g of calcium carbonate was placed. Thereby, a calcium carbonate layer 24 composed of calcium carbonate was formed on the first photosensitive layer 30. The second film 22 was fixed to the second base 18 using a double-sided tape so that the calcium carbonate layer 24 was in contact with the second photosensitive layer 32. Thereby, the 1st stand 12, the 1st film 20, the 1st photosensitive layer 30, the calcium carbonate layer 24, the 2nd photosensitive layer 32, the 2nd film 22, and the 2nd stand 18 were arranged in order from the bottom. The centers of the first table 12, the first film 20, the first photosensitive layer 30, the second photosensitive layer 32, the second film 22, and the second table 18 are arranged so as to pass through the rotation axis S.

(Third step)
In the third step, the first photosensitive layer 30 was rotated at a rotational speed of 60 rpm for 60 seconds in an environment of a temperature of 23 ° C. and a relative humidity of 50% RH while the second photosensitive layer 32 was fixed. Specifically, the rotation drive unit 16 is driven to rotate the rotation shaft 14, the first base 12, the first film 20, and the first photosensitive layer 30 around the rotation axis S at a rotation speed of 60 rpm for 60 seconds. It was. Thereby, the calcium carbonate contained in the calcium carbonate layer 24 was rubbed between the first photosensitive layer 30 and the second photosensitive layer 32, and the calcium carbonate was charged.

(Fourth step)
In the fourth step, the calcium carbonate charged in the third step was taken out from the jig 10 and sucked using a charge amount measuring device (a suction type small charge amount measuring device, “MODEL 212HS” manufactured by Trek). The total amount of electricity Q (unit: + μC) and mass M (unit: g) of the sucked calcium carbonate were measured using a charge amount measuring device. From the formula “charge amount = Q / M”, the charge amount of calcium carbonate (friction charge amount, unit: + μC / g) was calculated.

  The triboelectric chargeability of each of the photoconductors (P-2) to (P-24) was evaluated by the same method as the triboelectric chargeability evaluation of the photoconductor (P-1) except that the following points were changed. . In the first step, instead of the photosensitive layer coating solution used in the production of the photoreceptor (P-1), the photosensitive layer coating solution used in the production of the photoreceptors (P-2) to (P-24). Each was used.

  Table 3 shows the calculated charge amount of calcium carbonate for each of the photoreceptors (P-1) to (P-24). In addition, it shows that calcium carbonate is easy to be positively charged with respect to the 1st photosensitive layer 30 and the 2nd photosensitive layer 32, so that the charging amount of calcium carbonate is a large positive value.

<5. Evaluation of image characteristics>
Image characteristics were evaluated for each of the manufactured photoreceptors (P-1) to (P-24). Evaluation of image characteristics was performed in an environment of a temperature of 32.5 ° C. and a relative humidity of 80% RH. As an evaluation machine, an image forming apparatus (a modified machine of “monochrome printer FS-1300D” manufactured by Kyocera Document Solutions Co., Ltd.) was used. Specifically, the non-contact development method was modified to the contact development method. The blade cleaning method has been modified to a cleaner-less method. The Scorotron charger was modified to a charging roller. The image forming apparatus employs a direct transfer method. As a recording medium, “Kyocera Document Solutions Brand Paper VM-A4” (A4 size) sold by Kyocera Document Solutions Inc. was used. A one-component developer (prototype) was used for evaluation by the evaluation machine.

  Using an evaluator, images I (images with a printing rate of 1%) were continuously printed on 20000 sheets of recording media under the condition that the rotational speed of the photoconductor was 168 mm / sec. Subsequently, the image II (A4 size black solid image) was printed on one recording medium. The recording medium on which the image II was formed was observed with the naked eye, and the number of white spots appearing in the image II was counted. As the minute component (for example, paper dust) of the recording medium adheres to the photoreceptor, the number of white spots in the image II tends to increase. Table 3 shows the number of white spots appearing in the image II.

In Table 3, ETM and _VL represent an electron transport agent and a sensitivity potential, respectively. ETM content (addition amount) shows content (addition amount) of the electron transport agent with respect to 100 mass parts binder resin.

  The photosensitive layers of the photoreceptors (P-1) to (P-18), (P-23), and (P-24) are single-layer photosensitive layers containing a charge generator, a binder resin, and the compound (1). Met. As the compound (1), any one of the compounds (1-1) to (1-9) was contained. The amount of charge of calcium carbonate when the photosensitive layer and calcium carbonate were rubbed was +7.0 μC / g or more. Therefore, as is apparent from Table 3, in these photoreceptors, the number of white spots in the formed image was small, and the generation of white spots was suppressed. Further, in these photoreceptors, it was possible to suppress the occurrence of white spots in the formed image without impairing the electrical characteristics of the photoreceptor.

  On the other hand, the photosensitive layers of the photoreceptors (P-19) to (P-22) did not contain the compound (1). Specifically, the compound (E-1) did not have a halogen atom. Compound (E-2) had a halogen atom but did not have a skeleton of the compound represented by the general formula (1). The photosensitive layers of the photoreceptors (P-19) to (P-22) had a calcium carbonate charge amount of less than +7.0 μC / g. Therefore, as is clear from Table 3, in these photoreceptors, the number of white spots in the formed image was large in these photoreceptors, and the generation of white spots in the formed image could not be suppressed.

  From the above, it has been shown that the photoreceptor according to the present invention suppresses the generation of white spots in the formed image. Further, it has been shown that the process cartridge and the image forming apparatus according to the present invention suppress the occurrence of white spots in the formed image.

  The photoreceptor according to the present invention can be used in an image forming apparatus. The process cartridge and the image forming apparatus according to the present invention can be used for forming an image on a recording medium.

DESCRIPTION OF SYMBOLS 1 Electrophotographic photoreceptor 2 Conductive base | substrate 3 Photosensitive layer 3c Single layer type photosensitive layer 42 Charging part 44 Exposure part 46 Developing part 48 Transfer part 100 Image forming apparatus P Recording medium

Claims (8)

An electrophotographic photosensitive member comprising a conductive substrate and a photosensitive layer,
The photosensitive layer is a single-layer type photosensitive layer containing a charge generator and an electron transport agent,
The electron transport agent includes a compound represented by the following chemical formula (1-5) ,
The photosensitive layer further contains a binder resin, and the content of the compound represented by the chemical formula (1-5) is 20 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the binder resin. ,
The electrophotographic photosensitive member, wherein a charge amount of the calcium carbonate when the photosensitive layer and the calcium carbonate are rubbed is 7.0 μC / g or more.

  The electrophotographic photosensitive member according to claim 1, wherein the binder resin includes a polycarbonate resin represented by the following chemical formula (3-1) or (3-2).

To claim 1 or 2 comprising an electrophotographic photosensitive member according the process cartridge. An electrophotographic photosensitive member according to claim 1 or 2, a charging unit, an exposing unit, a developing unit, an image forming apparatus including a transfer unit,
The charging unit charges the surface of the electrophotographic photosensitive member,
The exposing unit exposes the charged surface of the electrophotographic photosensitive member to form an electrostatic latent image on the surface of the electrophotographic photosensitive member;
The developing unit develops the electrostatic latent image as a toner image,
The transfer unit transfers the toner image from the electrophotographic photosensitive member to a recording medium,
The image forming apparatus, wherein the electrophotographic photosensitive member is in contact with the recording medium when the transfer unit transfers the toner image from the electrophotographic photosensitive member to the recording medium. The image forming apparatus according to claim 4 , wherein the developing unit develops the electrostatic latent image as the toner image while being in contact with the electrophotographic photosensitive member. The developing unit cleans the surface of the electrophotographic photoreceptor, an image forming apparatus according to claim 4 or 5. The charging unit is a charging roller, the image forming apparatus according to any one of claims 4-6. The image forming apparatus according to any one of claims 4 to 7 , wherein the charging unit charges the surface of the electrophotographic photosensitive member to a positive polarity.

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