JP2006023504A - Electrophotographic photoreceptor for wet development - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electrophotographic photoreceptor for wet development which is so excellent in resistance to a liquid developer that, in particular, a hole transport agent is hardly leached out in the liquid developer, and which hardly causes solvent cracking. <P>SOLUTION: The electrophotographic photoreceptor for wet development has a photosensitive layer on a conductive substrate, wherein a hole transport agent having a solubility in toluene at 25°C of ≥15 wt.% and a molecular weight of ≥900 is contained in the photosensitive layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic photoreceptor suitable for wet development.

  In an image forming apparatus using electrophotography such as an electrostatic copying machine, a laser beam printer, a plain paper facsimile machine, and a complex machine thereof, the surface of the electrophotographic photosensitive member is uniformly charged and then exposed. The method of developing the electrostatic latent image formed in this way into a toner image is roughly divided into a dry development method using a dry developer and a wet development method using a liquid developer. Widely used. However, since the particle size of the toner particles can be remarkably reduced compared with the dry development method, the development method can sufficiently cope with the high image quality, high quality, etc. required for full-color printers for which demand is increasing in recent years. The wet development method is in the spotlight again.

  In the wet development method, generally, in a liquid developer constituted by dispersing toner particles and the like in an insulating liquid, the toner particles are developed into a toner image by contacting the electrostatic latent image by electrophoresis. As the insulating liquid, for example, aliphatic hydrocarbon solvents such as isoparaffin solvents and normal paraffin solvents are widely used. In the wet development method, all or part of the electrophotographic photosensitive member is always immersed in the liquid developer, so that the electrophotographic photosensitive member has excellent resistance to the liquid developer. An inorganic photoreceptor such as selenium or amorphous silicon is generally used.

  In contrast, organic photoreceptors having a single layer or two or more photosensitive layers containing a binder resin, a charge generating agent, a charge transporting agent (hole transporting agent, electron transporting agent), etc. are widely used in dry development methods. However, since it is not sufficiently resistant to the liquid developer, it has hardly been used for wet development. However, organic photoreceptors are advantageous in that they are easier to manufacture than inorganic photoreceptors and have a high degree of freedom in design, and therefore are being considered for application to wet development methods.

Among the components contained in the photosensitive layer, in particular, the charge transport agent elutes in the liquid developer, and the point that is particularly problematic in considering the resistance of the organic photoreceptor to the liquid developer is that of the photosensitive layer. There is a change in composition and surface state, and in Patent Document 1, there is an aromatic hydrocarbon solvent contained as an impurity in an aliphatic hydrocarbon solvent generally used as an insulating liquid in a liquid developer. , That is the main cause. And in patent document 1, by selectively using the charge transport agent whose solubility in 25 degreeC with respect to toluene which is a typical example of an aromatic hydrocarbon solvent is 1 to 13 weight%, of the said charge transport agent It has been proposed to suppress elution into the liquid developer and the accompanying compositional change of the photosensitive layer.
Japanese Patent No. 3198710 (claims, columns 0006 to 0009, columns 0013 to 0016)

  However, according to a study by the inventor, among the charge transfer agents, in particular, when a hole transfer agent having a solubility of 1 to 13% by weight in toluene at 25 ° C. is used, the electrophotographic photosensitive member is used. It has been clarified that when image formation is repeatedly carried out in a state where the toner is immersed in a liquid developer, solvent cracks and image defects based thereon are likely to occur on the surface of the photoreceptor.

  An object of the present invention is to provide an organic electrophotographic photosensitive member for wet development that is superior in resistance to a liquid developer than before, and in particular, an organic electrophotographic photoreceptor for wet development, in which a hole transport agent is less likely to elute in the liquid developer and hardly causes solvent cracks. It is to provide.

  When a hole transport agent having a solubility in toluene at 25 ° C. of 1 to 13% by weight is used, the cause of the occurrence of solvent cracks in the photosensitive layer has not been clarified, but the inventors speculate as follows: is doing. That is, when the solvent of the liquid developer comes into contact with the photosensitive layer, a part of the hole transport agent on the surface of the photosensitive layer is swollen, but the solubility of the hole transport agent in aromatic components such as toluene is not sufficient. For this reason, the hole transport agent is easily crystallized, and the crystallized portion is eluted into the aliphatic hydrocarbon solvent, thereby generating minute solvent cracks.

  Therefore, if a hole transport agent having a solubility of 15% by weight or more is used, the occurrence of solvent cracks can be reliably prevented. However, when a hole transporting agent whose solubility in toluene at 25 ° C. is only 15% by weight or more is used, as described in Patent Document 1, the hole transporting agent is contained in the liquid developer. May cause a problem that the composition or surface state of the photosensitive layer changes.

  Therefore, as a result of further examination of the hole transport agent, the inventor selected a hole transport agent having a solubility in toluene at 25 ° C. of 15% by weight or more and a molecular weight of 900 or more to use as a solvent crack. It has been found that, in addition to preventing the occurrence of the above, the elution of the hole transport agent into the liquid developer can be suppressed. That is, since a hole transport agent having a large molecular weight of 900 or more has low plasticity, the binder resin can maintain its original characteristics without being affected by the addition of the hole transport agent. Therefore, even if the solubility of the hole transport agent in toluene alone is 15% by weight or more, it is difficult to elute into the liquid developer in a state where the photosensitive layer is formed by dispersing in the binder resin, for example. Elution can be suppressed.

Accordingly, the invention described in claim 1 is an electrophotographic photosensitive member for wet development having a photosensitive layer on a conductive substrate, wherein the photosensitive layer has a solubility in toluene at 25 ° C. of 15% by weight or more and a molecular weight of 900. An electrophotographic photosensitive member for wet development, comprising the hole transport agent as described above.
The photosensitive layer has various layer configurations such as a laminated photosensitive layer in which a charge generating layer containing a charge generating agent and a charge transporting layer containing a charge transporting agent are laminated on a conductive substrate. In particular, a single-layer photosensitive layer containing a charge generator, a hole transport agent, an electron transport agent, and a binder resin is preferably used because it has fewer formation steps and is excellent in productivity. .

  In addition, when the single layer type photosensitive layer and the multilayer type photosensitive layer are compared in the wet development, when the constituent materials are the same, the single layer type photosensitive layer containing both the electron transport agent and the hole transport material is better. , It has the feature that the elution amount of the constituent material is small. This seems to be because the electron transport agent and the hole transport agent interact with each other to suppress mutual elution. Also from this point, a single-layer type photosensitive layer is preferably employed.

Accordingly, the invention according to claim 2 is the electrophotographic film for wet development according to claim 1, wherein the photosensitive layer is a single layer type photosensitive layer containing a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin. It is a photoreceptor.
The molecular weight of the electron transfer agent contained in the single-layer type photosensitive layer is preferably 600 or more. Since the electron transport agent having a molecular weight of 600 or more has excellent solvent resistance, it is difficult to elute in the liquid developer in a state where it is dispersed in the binder resin to form a photosensitive layer, thereby suppressing the elution. it can.

Accordingly, the invention described in claim 3 is the electrophotographic photosensitive member for wet development according to claim 2, wherein the molecular weight of the electron transfer agent is 600 or more.
Moreover, it is preferable that the I / O value represented by the ratio of the inorganic degree I and the organic degree O of the electron transport agent contained in a single layer type photosensitive layer is 0.6 or more. Details of the inorganic degree I, the organic degree O, and the I / O value will be described later. These are numerical values specific to a specific organic compound, and the smaller the I / O value, the more organic the compound is. On the contrary, the larger the I / O value, the stronger the compound is. It means that the stronger the organic compound, the easier it is to dissolve in a strong organic solvent, and the stronger the inorganic compound, the less soluble in an organic solvent.

  In liquid developers, hydrocarbon solvents such as aliphatic hydrocarbon solvents used as insulating liquids and aromatic hydrocarbon solvents contained as impurities in the aliphatic hydrocarbon solvents are typical organic solvents. On the other hand, if a strong inorganic electron transport agent having an I / O value of 0.6 or more is selectively used, the electron transport agent is a liquid containing a hydrocarbon solvent. Since it is difficult to elute into the developer, the durability of the photoreceptor can be further improved.

Therefore, in the invention according to claim 4, the I / O value represented by the ratio between the inorganic degree I and the organic degree O of the electron transport agent is 0.6 or more. An electrophotographic photosensitive member for development.
As the binder resin contained in the single-layer type photosensitive layer, the formula (R-1):

[Wherein, A represents —O—,> C═O or a single bond directly connecting the benzene rings on both sides. R ^a and R ^b are the same or different and each represents a hydrogen atom or a methyl group. ]
A repeating unit represented by formula (R-2):

[Wherein, R ^c and R ^d are the same or different and each represents a hydrogen atom or a methyl group. ]
The copolymer polycarbonate containing the repeating unit represented by these is preferable.
Therefore, the invention described in claim 5 is a copolymer polycarbonate in which the binder resin includes a repeating unit represented by the above formula (R-1) and a repeating unit represented by the formula (R-2). Item 3. The electrophotographic photosensitive member for wet development according to Item 2.

Moreover, it is preferable that I / O value represented by ratio of the inorganic degree I and the organic degree O of a binder resin is 0.38 or more. As described above, an inorganic binder resin having an I / O value of 0.38 or more is difficult to elute into a liquid developer containing a hydrocarbon solvent that is a typical strong organic compound. The resistance of the photoreceptor can be further improved.
Accordingly, in the invention described in claim 6, the I / O value represented by the ratio between the inorganic degree I and the organic degree O of the binder resin is 0.38 or more. It is a photographic photoreceptor.

  When the electrophotographic photosensitive member for wet development of the present invention is used in, for example, a laser beam printer or a plain paper facsimile apparatus using a semiconductor laser that emits light in a wavelength region of 600 nm or more as an exposure light source, the above wavelength region is used. Various charge generating agents having sensitivity can be used, and phthalocyanine pigments are particularly preferable. Since the phthalocyanine pigment has high sensitivity in the above wavelength region and hardly dissolves in the liquid developer containing the hydrocarbon solvent, the resistance of the photoreceptor can be further improved. The phthalocyanine pigment is preferably at least one selected from the group consisting of metal-free phthalocyanine, titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine.

  Accordingly, in the invention described in claim 7, the charge generating agent is at least one selected from the group consisting of metal-free phthalocyanine, titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine. An electrophotographic photoreceptor.

The present invention is described below.
As described above, the electrophotographic photosensitive member for wet development of the present invention comprises a photosensitive layer on a conductive substrate, and this photosensitive layer has a solubility in toluene at 25 ° C. of 15% by weight or more and a molecular weight of 900 or more. It is characterized by containing the hole transport agent which is. Here, the solubility in toluene at 25 ° C. is determined as defined in Patent Document 1. That is, a supersaturated solution is prepared by heating and dissolving a hole transport agent in toluene, and allowed to stand at 25 ° C. for 10 days. At this time, since a part of the charge transport agent is crystallized and precipitated, a certain amount of the solution portion is weighed out so that this crystal does not enter, and the remaining hole transport agent is weighed by distilling off toluene from the solution portion. And the weight ratio (weight%) with respect to a toluene solution is calculated | required, and this value is defined as the solubility in 25 degreeC with respect to toluene.

  The inorganic degree I, the organic degree O, and the I / O value are values conceptually treating the polarities of various organic compounds. 1954); Chemistry, Volume 11, No. 10, pages 719-725 (1957); Fragrance Journal, No. 34, pages 97-111 (1979); Fragrance Journal, No. 50, No. 79-82 (1981); and the like.

  According to these documents, the I / O value is that the organic degree of one carbon is 20, and the inorganic degree (I) and organic degree (O) values of various polar groups are as shown in Table 1 below. Then, it can be calculated from the ratio of the sum of the inorganicity (I) and the sum of the organicity (O) in the compound.

In Table 1, R ₄ mainly represents an alkyl group, and φ mainly represents an alkyl group or an aryl group.
The concept of the I / O value is that the properties of organic compounds are classified into “inorganic groups” that exhibit ionic bonding properties and “organic groups” that exhibit covalent bonding properties. It is expressed by positioning one point at a time on an orthogonal coordinate named an axis.

  The degree of inorganicity I is obtained by quantifying the magnitude of the influence on the boiling point of various substituents and bonds of an organic compound, based on the hydroxyl group. Specifically, when the distance between the boiling point curve of a linear alcohol and the boiling point curve of a linear paraffin is about 100 ° C., the influence of one hydroxyl group is set to 100 as a numerical value. Based on this numerical value, the value obtained by quantifying the influence of various substituents or various bonds on the boiling point is the inorganic degree I of the substituent that the organic compound has. For example, as shown in Table 1 above, the inorganicity of the —COOH group is 150, and the inorganicity of the double bond is 2.

On the other hand, the organic degree O is determined based on the influence of the methylene group in the molecule as a unit and the boiling point of the carbon atom representing the methylene group. That is, in the vicinity of 5 to 10 carbon atoms of the linear saturated hydrocarbon, the average value of the boiling point increase due to the addition of one carbon atom is 20 ° C. Next, based on this, the degree of organicity of one carbon atom is set to 20, and the value obtained by quantifying the influence on the boiling point of various substituents and bonds to this value is the degree of organicity O. For example, as shown in Table 1 above, the organicity of the nitro group (—NO ₂ ) is 70.

  Next, a method for calculating an I / O value will be described using a naphthoquinone derivative represented by the following general formula (ETM-2) as an example.

[Organicity O]
The naphthoquinone derivative of the above general formula (ETM-2) has 23 carbon atoms with an organic degree of 20 and one nitro group with an organic degree of 70, and the sum of these is 20 × 23 + 70 × 1 = 530.
[Nonpolarity I]
The naphthoquinone derivative of the above general formula (ETM-2) has one naphthalene ring having a nonpolarity of 60, two benzene rings having a nonpolarity of 15, three ketone groups having a nonpolarity of 65, and a nonpolarity of 70. Each of which has a total of 60 × 1 + 15 × 2 + 65 × 3 + 70 × 1 = 355.
[I / O value]
From the organic degree O and the inorganic degree I, the I / O value of the naphthoquinone derivative of the general formula (ETM-2) is 355/530 = 0.6698.
(Binder resin)
In the case of a binder resin, the method for calculating the I / O value is slightly different. A repeating unit represented by the formula (R-11) and a repeating unit represented by the formula (R-21), which will be described later, have a molar ratio (R-11) :( R-21) = 15: 85. Taking the (I) copolymerized polycarbonate resin as an example, the I / O value of this resin is calculated as follows.
[Organicity O]
-It has 13 × 0.15 + 15 × 0.85 = 14.7 carbon atoms with an organic degree of 20.
-It has 1 × 0.85 = 0.85 iso branches with an organicity of −10.

Therefore, the organic degree O is 20 × 14.7−10 × 0.85 = 285.5.
[Inorganicity I]
-It has 2 × 0.15 + 2 × 0.85 = 2 benzene rings with an inorganic degree of 15.
-It has 1 × 0.15 + 1 × 0.85 = 1 O-COO with an inorganic degree of 80.
Therefore, the inorganic degree I is 15 × 2 + 80 = 110.

Therefore, the I / O value of the (I) copolymer polycarbonate resin is 110 / 285.5 = 0.3853.
<Photosensitive layer>
As the photosensitive layer,
A single-layer type photosensitive layer containing a charge generating agent and a charge transporting agent, and a laminated photosensitive layer comprising a charge generating layer containing a charge generating agent and a charge transporting layer containing a charge transporting agent,
In particular, among the former single-layer type photosensitive layers, a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin, in which a hole transporting agent and an electron transporting agent are used in combination as charge transporting agents, A monolayer type photosensitive layer is preferred.

In addition, as the laminated photosensitive layer, for example,
A layer in which a charge generation layer containing a charge generation agent and a charge transfer layer containing a hole transfer agent as a charge transfer agent are laminated in this order on a conductive substrate (the charge generation layer may contain an electron transfer agent) Good),
A laminate of the charge generation layer and the charge transport layer in the reverse order;
A layer in which a charge generating layer containing a charge generating agent and a hole transporting agent and a charge transporting layer containing an electron transporting agent as a charge transporting agent are laminated in this order on a conductive substrate; and A laminate of charge transport layers in the reverse order,
Etc.

  The content of the charge generating agent in the single-layer type photosensitive layer is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight with respect to 100 parts by weight of the binder resin. If the content of the charge generator is less than this range, the sensitivity of the single-layer type photosensitive layer may be insufficient. If the content exceeds this range, the content of the binder resin is relatively reduced. There is a possibility that a strong single-layer type photosensitive layer in which the generator is uniformly dispersed in the binder resin cannot be formed.

  The content of the charge transport agent in the single-layer type photosensitive layer is preferably less than 50% by weight of the total amount of all solids, that is, the total amount of the charge generator, charge transport agent and binder resin. When the content of the charge transport agent in the single-layer type photosensitive layer is 50% by weight or more, the charge transport is carried out when all or part of the electrophotographic photoreceptor is repeatedly immersed in a liquid developer and repeatedly used for image formation. The elution amount of the developer into the liquid developer increases, and the composition and surface state of the photosensitive layer may change.

  However, if the content of the charge transport agent is too small, the sensitivity of the single layer type photosensitive layer may be insufficient. Therefore, the content of the charge transport agent in the single layer type photosensitive layer is the total amount of the total solid content. It is preferably 15% by weight or more. The content of the charge transport agent referred to here is the content of the hole transport agent when one or more hole transport agents are used as the charge transport agent. When one or two or more hole transport agents and one or two or more electron transport agents are used in combination, the content is the total content of both transport agents.

The thickness of the single-layer type photosensitive layer is preferably 5 to 100 μm, and more preferably 10 to 50 μm.
On the other hand, the charge generation layer of the multilayer type photosensitive layer may be formed of a charge generator alone, or a charge generator may be contained in a binder resin. The amount is preferably 1 to 500 parts by weight, more preferably 10 to 300 parts by weight, based on 100 parts by weight of the resin.

  In addition, the content of the charge transport agent in the charge transport layer in the multilayer photosensitive layer is the same as that in the case of the single layer photosensitive layer, and is the total amount of the total solids, that is, the total amount of the charge transport agent and the binder resin. , Preferably less than 50% by weight, more preferably 15% by weight or more. In addition, when the charge generation layer of the multilayer photosensitive layer contains a charge transport agent, the content of the charge transport layer can be favorably transported to the charge transport layer or the like without hindering charge generation by the charge generation agent. In view of this, the amount is preferably 1 part by weight or less with respect to 100 parts by weight of the charge generating agent.

The thickness of the charge generation layer in the multilayer photosensitive layer is preferably 0.01 to 5 μm, more preferably 0.1 to 3 μm. The thickness of the charge transport layer is preferably 2 to 100 μm, and more preferably 5 to 50 μm.
<Hole transport agent>
The reason why the solubility of the hole transport agent used in the present invention in toluene at 25 ° C. is limited to 15% by weight or more and the molecular weight is limited to 900 or more is as described above. When the solubility of the hole transport agent in toluene at 25 ° C. is too high, all or part of the electrophotographic photoreceptor is always immersed in the liquid developer even if the molecular weight is 900 or more. When it is repeatedly used for image formation in the state, the amount of elution into the liquid developer increases, and the composition and surface state of the photosensitive layer may change. For this reason, the solubility of the hole transport agent in toluene at 25 ° C. is preferably 100% by weight or less.

  Moreover, when the molecular weight of the hole transport agent is too large, the solubility in an organic solvent used for forming the photosensitive layer is lowered, so that there is a possibility that it cannot be uniformly dispersed in the photosensitive layer. For this reason, the molecular weight of the hole transport agent is preferably 3,000 or less, and more preferably 1,600 or less. The molecular weight of the hole transport agent can be calculated based on the structural formula or can be calculated using a mass spectrum.

  Examples of hole transporting agents include N, N, N ′, N′-tetraphenylbenzidine derivatives, N, N, N ′, N′-tetraphenylphenylenediamine derivatives, N, N, N ′, N′-tetra. Oxazis such as phenylnaphthylenediamine derivatives, N, N, N ′, N′-tetraphenylphenanthrylenediamine derivatives, 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole Azole compounds, styryl compounds such as 9- (4-diethylaminostyryl) anthracene, carbazole compounds such as polyvinylcarbazole, organic polysilane compounds, pyrazoline compounds such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline , Hydrazone compounds, indole compounds, oxazole compounds, isoxazole compounds Among conventionally known various electron-donating compounds such as nitrogen-containing cyclic compounds such as thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, triazole compounds, and condensed polycyclic compounds Therefore, those satisfying the above conditions are selected and used, and among them, a compound having a substituent at the ortho position of the phenyl group substituted with a nitrogen atom is particularly preferably used because of its excellent compatibility with the binder resin. . Preferable examples of such hole transporting agents include compounds represented by the following formulas (HTM-1) to (HTM-4).

[Solubility in toluene at 25 ° C .: 25 wt%, molecular weight: 1057.41]

[Solubility in toluene at 25 ° C .: 55% by weight, molecular weight: 1057.41]

[Solubility in toluene at 25 ° C .: 60% by weight, molecular weight: 1057.41]

[Solubility in toluene at 25 ° C .: 20% by weight, molecular weight: 1041.29]
As the hole transport agent, hole transport agents satisfying the above conditions may be used alone or in combination of two or more. In addition, a hole transport agent that satisfies the above conditions and another hole transport agent that does not satisfy one or both of the conditions can be used in combination as long as the effects of the present invention are not impaired. Examples of other hole transporting agents that may be used in combination include those described above among the nitrogen-containing compounds exemplified above and condensed polycyclic compounds.
<Charge generator>
Examples of the charge generator include phthalocyanine pigments, perylene pigments, bisazo pigments, diketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, trisazo pigments, indigo pigments, azurenium pigments, Organic photoconductors such as cyanine pigments, pyrylium pigments, ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, A conventionally known charge generating agent such as an inorganic photoconductive material such as amorphous silicon can be used. Each of the charge generating agents may be used alone or in combination of two or more so as to have an absorption wavelength in a desired region.

  When the electrophotographic photosensitive member for wet development of the present invention is used in, for example, a laser beam printer or a plain paper facsimile apparatus using a semiconductor laser that emits light in a wavelength region of 600 nm or more as an exposure light source, In particular, phthalocyanine pigments are preferred. Examples of the phthalocyanine pigment include the following formula (CGM-1):

Metal-free phthalocyanine represented by the formula (CGM-2):

A titanyl phthalocyanine represented by the formula (CGM-3):

And hydroxygallium phthalocyanine represented by the formula (CGM-4):

And chlorogallium phthalocyanine represented by the formula: The crystal form of the phthalocyanine pigment is not particularly limited, and various types can be used. For example, as the metal-free phthalocyanine, X-type or τ-type can be mentioned, and as the titanyl phthalocyanine, α-type or Y-type is preferably used. Further, the hydroxygallium phthalocyanine is preferably a V type, and the chlorogallium phthalocyanine is preferably a II type.
<Electron transport agent>
Examples of the electron transport agent include diphenoquinone derivatives, benzoquinone derivatives, anthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, trinitrothioxanthone derivatives, 3,4,5,7-tetranitro-9-fluorenone derivatives, dinitroanthracene derivatives, dinitroacridine derivatives, Nitroantharaquinone derivatives, dinitroanthraquinone derivatives, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, dibromoanhydride maleic Examples include various compounds having an electron accepting property such as an acid.

  The electron transfer agent preferably has a molecular weight of 600 or more, an I / O value of 0.6 or more, or satisfies both conditions. The reason for this is as described above. In addition, when the molecular weight of the electron transfer agent is too large, the solubility in an organic solvent used when forming the photosensitive layer is lowered, so that there is a possibility that it cannot be uniformly dispersed in the photosensitive layer. For this reason, the molecular weight of the electron transport agent is preferably 2,000 or less, and more preferably 1,200 or less.

  In addition, when the I / O value of the electron transfer agent is too high and the inorganic property is too strong, the solubility in an organic solvent used in forming the photosensitive layer is also lowered, and therefore, it may not be uniformly dispersed in the photosensitive layer. There is. For this reason, the I / O value of the electron transport agent is preferably 1.2 or less. Preferable examples of the electron transport agent that satisfies these conditions include compounds represented by the following formulas (ETM-1) to (ETM-3).

[Molecular weight: 658.65, I / O value: 0.6488]

[Molecular weight: 383.35, I / O value: 0.6698]

[Molecular weight: 684.95, I / O value: 0.3098]
One electron transport agent may be used alone, or two or more electron transport agents may be used in combination.
<Binder resin>
Examples of the binder resin include polycarbonate resins such as bisphenol Z type, bisphenol ZC type, bisphenol C type, bisphenol A type, polyarylate resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer. Polymer, acrylic copolymer, styrene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, ionomer, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide , Polyurethane, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, etc., silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, etc. Bridge thermosetting resin, epoxy acrylate, urethane - photocurable resin such as acrylate. Among these polycarbonate resins, especially the formula (R-1):

[Wherein, A represents —O—,> C═O or a single bond directly connecting the benzene rings on both sides. R ^a and R ^b are the same or different and each represents a hydrogen atom or a methyl group. ]
A repeating unit represented by formula (R-2):

[Wherein, R ^c and R ^d are the same or different and each represents a hydrogen atom or a methyl group. ]
The copolymer polycarbonate containing the repeating unit represented by these is preferable.
The binder resin preferably has an I / O value of 0.38 or more. The reason for this is as described above. However, when the I / O value of the binder resin is too high and the inorganic property is too strong, the solubility in an organic solvent used when forming the photosensitive layer is lowered, and thus there is a possibility that a uniform photosensitive layer cannot be formed. For this reason, the I / O value of the binder resin is preferably 0.45 or less.

Specific examples of the binder resin include copolymer polycarbonate resins represented by the following (I) to (V).
(I) Formula (R-11):

A repeating unit represented by formula (R-21):

A copolymeric polycarbonate resin having a molar ratio (R-11) :( R-21) = 15: 85 and an I / O value of 0.3853.
(II) Formula (R-12):

And a repeating unit represented by the formula (R-21) in a molar ratio (R-12) :( R-21) = 25: 75, and an I / O value of 0 Copolymer polycarbonate resin which is 3761.
(III) Formula (R-3):

The repeating unit represented by formula (I), the repeating unit represented by formula (R-11), and the repeating unit represented by formula (R-21) have a molar ratio (R-3): (R-11). ): (R-21) = 0.3: 15: 84.7 A copolymer polycarbonate resin having an I / O value of 0.3858.
(IV) Formula (R-13):

And a repeating unit represented by the formula (R-21) at a molar ratio (R-13) :( R-21) = 50: 50, I / O value: 0 Copolycarbonate resin which is 4138.
(V) Formula (R-14):

And a repeating unit represented by the formula (R-21) in a molar ratio (R-14) :( R-21) = 20: 80, I / O value: 0 Copolymer polycarbonate resin which is 4271.
The viscosity average molecular weight of the binder resin is 18,000 to 100 in consideration of reliably preventing elution into the liquid developer while maintaining good solubility in the organic solvent used when forming the photosensitive layer. Is preferably 30,000, more preferably 30,000 to 60,000. Moreover, binder resin may be used individually by 1 type, respectively, and may use 2 or more types together.
<Others>
In the photosensitive layer, in addition to the components described above, various conventionally known additives such as an antioxidant, a radical scavenger, a singlet quencher, and an ultraviolet ray are used as long as the electrophotographic characteristics are not adversely affected. Deterioration inhibitors such as absorbents, softeners, plasticizers, surface modifiers, extenders, thickeners, dispersion stabilizers, waxes, acceptors, donors, and the like can be blended. In order to improve the sensitivity of the photosensitive layer, a known sensitizer such as terphenyl, halonaphthoquinones, and acenaphthylene may be used in combination with the charge generator. A barrier layer may be formed between the conductive substrate and the photosensitive layer, or between the laminated layers as long as the characteristics of the photosensitive member are not impaired.

  As the conductive substrate, those made of various conductive materials can be used. For example, iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium , Metal such as indium, stainless steel, and brass, plastic materials on which the above metal is vapor-deposited or laminated, glass formed by coating with aluminum iodide, tin oxide, indium oxide, or the like.

The shape of the conductive substrate may be any of a sheet shape, a drum shape, etc. according to the structure of the image forming apparatus to be used. The conductive substrate itself has conductivity or the surface of the conductive substrate is What is necessary is just to have electroconductivity. Further, the conductive substrate is preferably one having sufficient mechanical strength when used.
When the photosensitive layer is formed by a coating method, the above-exemplified charge generating agent, charge transporting agent, binder resin and the like together with a suitable solvent are known methods such as a roll mill, ball mill, attritor, paint shaker, super A coating solution may be prepared by dispersing and mixing using a sonic disperser or the like, and this may be applied by a known means and dried.

  As the solvent for preparing the coating solution, various organic solvents can be used, for example, alcohols such as methanol, ethanol, isopropanol, and butanol, aliphatic hydrocarbons such as n-hexane, octane, and cyclohexane, Aromatic hydrocarbons such as benzene, toluene, xylene, halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,4-dioxane Ethers such as 1,3-dioxolane, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and methyl acetate, dimethylformaldehyde, dimethylform Le formamide, dimethyl sulfoxide and the like. These solvents are used alone or in combination of two or more.

  Furthermore, in order to improve the dispersibility of the charge generating agent, the charge transporting agent and the like and the smoothness of the photosensitive layer surface, a surfactant, a leveling agent and the like may be added to the coating solution.

Hereinafter, the present invention will be described based on examples and comparative examples.
Example 1:
4 parts by weight of an X-type metal-free phthalocyanine represented by the above formula (CGM-1) as a charge generating agent and a compound represented by the above formula (HTM-1) as a hole transporting agent [25 with respect to toluene Solubility at 25 ° C .: 25% by weight, molecular weight: 1057.41] 40 parts by weight and a compound represented by the above formula (ETM-1) as an electron transport agent [molecular weight: 658.65, I / O value: 0 6488] 50 parts by weight, 100 parts by weight of the above-mentioned copolymeric polycarbonate resin (I) as a binder resin [viscosity average molecular weight 50,000, I / O value: 0.3853], and dimethyl silicone as a leveling agent 0.1 part by weight of oil [KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.] is mixed and dispersed together with 750 parts by weight of tetrahydrofuran using an ultrasonic disperser, and coating for a single-layer type photosensitive layer A liquid was prepared.

This coating solution is applied to the entire outer periphery of an aluminum tube having a diameter of 30 mmφ and a length of 245 mm, and then dried with hot air at 140 ° C. for 20 minutes to have a single-layer type photosensitive layer having a thickness of 22 μm. A photoreceptor was manufactured.
Examples 2-4:
As a charge generating agent, Y-type titanyl phthalocyanine represented by the formula (CGM-2) (Example 2), V-type hydroxygallium phthalocyanine represented by the formula (CGM-3) (Example 3), or the above For wet development having a single-layer type photosensitive layer having a thickness of 22 μm in the same manner as in Example 1 except that the same amount of type II chlorogallium phthalocyanine represented by the formula (CGM-4) (Example 4) was used. An electrophotographic photoreceptor was produced.

Example 5:
Example 1 except that the same amount of the compound represented by the formula (HTM-2) (solubility in toluene at 25 ° C .: 55 wt%, molecular weight: 1057.41) was used as the hole transport agent. Thus, an electrophotographic photosensitive member for wet development having a single-layer type photosensitive layer having a thickness of 22 μm was produced.

Example 6:
Example 1 except that the same amount of the compound represented by the formula (HTM-3) [solubility in toluene at 25 ° C .: 60 wt%, molecular weight: 1057.41] was used as the hole transport agent. Thus, an electrophotographic photosensitive member for wet development having a single-layer type photosensitive layer having a thickness of 22 μm was produced.

Example 7:
Example 1 except that the same amount of the compound represented by the formula (HTM-4) [solubility in toluene at 25 ° C .: 20 wt%, molecular weight: 1041.29] was used as the hole transport agent. Thus, an electrophotographic photosensitive member for wet development having a single-layer type photosensitive layer having a thickness of 22 μm was produced.

Example 8:
Except for using the same amount of the compound represented by the above formula (ETM-2) [molecular weight: 383.35, I / O value: 0.7] as the electron transfer agent, the same as in Example 1, An electrophotographic photoreceptor for wet development having a single-layer type photosensitive layer having a thickness of 22 μm was produced.
Examples 9-12:
As the binder resin, the copolymer polycarbonate resin (II) [viscosity average molecular weight 49,000, I / O value: 0.3761] (Example 9), the copolymer polycarbonate resin (III) [viscosity average molecular weight 50 1,000, I / O value: 0.3858] (Example 10), the copolymer polycarbonate resin of the above (IV) [viscosity average molecular weight 51,000, I / O value: 0.4138] (Example 11), Alternatively, the thickness of the copolymer polycarbonate resin (V) (viscosity average molecular weight 50,000, I / O value: 0.4271) (Example 12) was the same as in Example 1 except that the same amount was used. An electrophotographic photoreceptor for wet development having a single-layer type photosensitive layer of 22 μm was produced.

Comparative Example 1:
As a hole transport agent, the following formula (HTM-5):

A single-layer photosensitive layer having a thickness of 22 μm is obtained in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 14% by weight, molecular weight: 1001.30] is used. An electrophotographic photoreceptor for wet development was produced.
Comparative Example 2:
As a hole transport agent, the following formula (HTM-6):

A single-layer photosensitive layer having a thickness of 22 μm in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 9.5 wt%, molecular weight: 1013.23] was used. An electrophotographic photosensitive member for wet development having the following characteristics was produced.
Comparative Example 3:
As a hole transport agent, the following formula (HTM-7):

A single-layer photosensitive layer having a thickness of 22 μm in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 0.5 wt%, molecular weight: 1157.44] was used. An electrophotographic photosensitive member for wet development having the following characteristics was produced.
Comparative Example 4:
As a hole transport agent, the following formula (HTM-8):

A single-layer photosensitive layer having a thickness of 22 μm is obtained in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 13 wt%, molecular weight: 700.95] is used. An electrophotographic photoreceptor for wet development was produced.
Comparative Example 5:
As a hole transport agent, the following formula (HTM-9):

A single-layer photosensitive layer having a thickness of 22 μm in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 3.3 wt%, molecular weight: 700.95] was used. An electrophotographic photosensitive member for wet development having the following characteristics was produced.
Comparative Example 6:
As a hole transport agent, the following formula (HTM-10):

A single-layer type photosensitive layer having a thickness of 22 μm is obtained in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 53 wt%, molecular weight: 644.84] is used. An electrophotographic photoreceptor for wet development was produced.
Comparative Example 7:
As a hole transport agent, the following formula (HTM-11):

A single-layer type photosensitive layer having a thickness of 22 μm was obtained in the same manner as in Example 1 except that the same amount of the compound represented by the formula (solubility in toluene at 25 ° C .: 62% by weight, molecular weight: 343.46) was used. An electrophotographic photoreceptor for wet development was produced.
Comparative Example 8:
As a hole transport agent, the following formula (HTM-12):

A single-layer photosensitive layer having a thickness of 22 μm is obtained in the same manner as in Example 1 except that the same amount of the compound represented by the formula [solubility in toluene at 25 ° C .: 23 wt%, molecular weight: 638.88] is used. An electrophotographic photoreceptor for wet development was produced.
Initial sensitivity test:
The light potential of the electrophotographic photoreceptor for wet development produced in each of the above Examples and Comparative Examples was measured using a drum sensitivity tester (manufactured by GENTEC). That is, after the surface of the photosensitive member is charged to +850 V in the dark, monochromatic light having a wavelength of 780 nm extracted from the white light of the halogen lamp using a bandpass filter (half-value width: 20 nm, light intensity: 1.0 μJ.cm ⁻² ) The surface potential [bright potential (V)] was measured after 0.5 seconds from the start of exposure. The photoreceptor is more sensitive as the light potential is smaller.

Solvent resistance test:
The whole electrophotographic photosensitive member for wet development produced in each of the above examples and comparative examples was immersed in 500 ml of an isoparaffin solvent (registered trademark Isopar L manufactured by Exxon Chemical Co., Ltd.) in a dark place for 2000 hours. (The liquid temperature is maintained at 25 ± 1 ° C.) After being pulled up, the remaining liquid is subjected to ultraviolet absorption analysis, and the concentration of the hole transport agent eluted in the liquid (elution amount, 1 × 10 ⁻⁷ g / cm ³ ). The smaller the amount of elution, the better the photoconductor is in solvent resistance.

The elution amount of the hole transport agent was determined by the following procedure. That is, a plurality of predetermined concentration solutions prepared by dissolving the same hole transporting agent used in each example and comparative example in an isoparaffin solvent were prepared, and ultraviolet absorption analysis was performed on each of the solutions, and the holes were A calibration curve showing the relationship between the peak height at a specific wavelength of the transport agent and the concentration of the hole transport agent (1 × 10 ⁻⁷ g / cm ³ ) was prepared. Then, the liquid after pulling up the photoreceptors of each Example and Comparative Example was obtained by ultraviolet absorption analysis. From the height of the peak at the specific wavelength, the calibration curve was used to elute the hole transport agent. The amount (1 × 10 ⁻⁷ g / cm ³ ) was determined.

  The electrophotographic photosensitive members for wet development in Examples and Comparative Examples were immersed in the same isoparaffinic solvent for 4000 hours in the dark (the liquid temperature was maintained at 25 ± 1 ° C.) and then sufficiently dried. For the body, the light potential (V) was measured in the same manner as in the initial sensitivity test, and the amount of change (V) in the light potential from the light potential during the initial sensitivity test was determined. The smaller the change amount of the bright potential, the better the photoreceptor is resistant to the liquid developer.

Appearance evaluation In a dark place, immerse in the same isoparaffinic solvent used in the solvent resistance test for 4000 hours and 6000 hours (both maintain the liquid temperature at 25 ± 1 ° C.), then pull it up and dry thoroughly. The surfaces of the electrophotographic photoreceptors for wet development in the examples and comparative examples were observed. And what was not changed from before the test was described as “good”, those where cracks were generated were described as “cracks” and the number of the cracks was described, and those whose color was lightened by elution of the components were described as “light”.

  The results are shown in Table 2. Further, FIG. 1 shows the relationship between the molecular weight of the hole transport agent and the elution amount in a system using the same charge generating agent, electron transport agent, and binder resin. From the figure, it was found that the larger the molecular weight of the hole transporting agent, the smaller the elution amount from the photosensitive layer.

From the table, the photoreceptors of Comparative Examples 1 to 3 using a hole transport agent having a solubility in toluene at 25 ° C. of less than 15% by weight and a molecular weight of 900 or more are all transported by holes when immersed for 2000 hours. The agent hardly eluted, but cracks occurred after immersion for 4000 hours.
The photoreceptors of Comparative Examples 4 and 5 using a hole transporting agent having a solubility in toluene at 25 ° C. of less than 15% by weight and a molecular weight of less than 900 were both immersed in 2000 hours. Was dissolved in a large amount, and cracking occurred after immersion for 4000 hours, and the light potential increased greatly, resulting in a decrease in sensitivity.

  Furthermore, the photoreceptors of Comparative Examples 6 to 8 using a hole transport agent having a solubility in toluene at 25 ° C. of 15% by weight or more and a molecular weight of less than 900 were all immersed in 2000 hours for the hole transport agent. As a result, the hole transport agent was eluted in a large amount, and the bright potential was further increased and the sensitivity was significantly lowered.

  On the other hand, the photoconductors of Examples 1 to 11 using the hole transport agent having a solubility in toluene at 25 ° C. of 15% by weight or more and a molecular weight of 900 or more are all exposed to holes after being immersed for 2000 hours. It was confirmed that the transport agent was hardly eluted, cracks did not occur even after immersion for 4000 hours, the bright potential did not increase greatly, and the sensitivity was hardly changed.

  Further, when each example is compared, Example 5 using a compound of (HTM-2) or (HTM-3) having a high solubility in toluene at 25 ° C. within the above range as a hole transport agent. No. 6 was found to have excellent resistance to the liquid developer since no cracks were generated even after 6000 hours of immersion.

It is a graph which shows the relationship between the molecular weight of the hole transport agent used by the Example and comparative example of this invention, and the elution amount from a photosensitive layer.

Claims (7)

  In the electrophotographic photoreceptor for wet development having a photosensitive layer on a conductive substrate, the photosensitive layer contains a hole transport agent having a solubility in toluene at 25 ° C. of 15% by weight or more and a molecular weight of 900 or more. An electrophotographic photoreceptor for wet development characterized by the above.   2. The electrophotographic photosensitive member for wet development according to claim 1, wherein the photosensitive layer is a single-layer type photosensitive layer containing a charge generating agent, a hole transport agent, an electron transport agent, and a binder resin.   The electrophotographic photosensitive member for wet development according to claim 2, wherein the molecular weight of the electron transfer agent is 600 or more.   The electrophotographic photosensitive member for wet development according to claim 2 or 3, wherein the electron transfer agent has an I / O value represented by a ratio of the inorganic degree I to the organic degree O of 0.6 or more. The binder resin has the formula (R-1):

[Wherein, A represents —O—,> C═O or a single bond directly connecting the benzene rings on both sides. R ^a and R ^b are the same or different and each represents a hydrogen atom or a methyl group. ]
A repeating unit represented by formula (R-2):

[Wherein, R ^c and R ^d are the same or different and each represents a hydrogen atom or a methyl group. ]
The electrophotographic photosensitive member for wet development according to claim 2, which is a copolymerized polycarbonate containing a repeating unit represented by the formula:   The electrophotographic photosensitive member for wet development according to claim 2, wherein the binder resin has an I / O value represented by a ratio of the inorganic degree I to the organic degree O of 0.38 or more.   The electrophotographic photosensitive member for wet development according to claim 2, wherein the charge generating agent is at least one selected from the group consisting of metal-free phthalocyanine, titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine.

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