JP4386771B2 - Electrophotographic photoreceptor for wet development and image forming apparatus for wet development - Google Patents

Description

  The present invention relates to an electrophotographic photoreceptor for wet development and an image forming apparatus for wet development, and in particular, has a predetermined sensitivity over a long period of time and has excellent durability and solvent resistance, and a wet development electrophotographic photoreceptor. The present invention relates to an image forming apparatus for development.

Conventionally, as an electrophotographic photoreceptor for wet development used in an image forming apparatus or the like, an organic photoreceptor made of an organic photoreceptor material such as a charge transport agent, a charge generator, and a binder resin (binder resin) has been used. . Such an organic photoreceptor is advantageous in that it is easy to manufacture and has a wide degree of freedom in structural design because it has various options for the photoreceptor material as compared with conventional inorganic photoreceptors.
Among such organophotoreceptor materials, as a charge transfer agent having a predetermined charge mobility, an enamine compound having one diphenylenamine structure represented by the following general formula (34) and an electrophotographic photoreceptor using the same Is known (see, for example, Patent Document 1).

(In General Formula (34), D is an arylene group, a divalent heterocyclic residue, an alkylene group, or an aromatic hydrocarbon divalent group linked by an alkylene chain, Ar ¹ is an aryl group, (It is a heterocyclic group or an aralkyl group, Ar ² is an aryl group or a heterocyclic group, and Z ¹ is an atomic group necessary for forming a ring together with Ar ² and a carbon atom.)

  Similarly, an electrophotographic photoreceptor containing an enamine compound having two diphenyl enamine structures represented by the following general formula (35) as a charge transport agent is also known (for example, see Patent Document 2).

(In the general formula (35), Ar ^{3 to} Ar ⁸ represent an aryl group or a heterocyclic group, Z ² represents an atomic group that forms a ring with Ar ³ and Ar ⁴ , and Ar ^{3 to} Ar ⁸ represent an aralkyl group or an alkyl group. And Ar ⁷ and Ar ⁸ may form a ring together, R ³⁹ represents hydrogen or an alkyl group, and m represents an integer of 0 to 2.)
JP 2003-167364 A (Claims) JP2003-12629 (Claims)

  However, the electrophotographic photoreceptors described in Patent Document 1 and Patent Document 2 are each easily immersed in a hydrocarbon solvent (liquid developer) when used for a long time as an electrophotographic photoreceptor for wet development, There was a problem that the hole transport agent was easily eluted. Moreover, the problem that the charge mobility was inadequate because the stilbene structure was not included as the central structure was also observed.

Therefore, the present inventors use a stilbene compound having three specific enamine structures as a hole transport agent, so that even when used for a long time as an electrophotographic photoreceptor for wet development, The present inventors have found the fact that the elution amount of the pore transport agent and the like can be remarkably reduced and the sensitivity characteristics can be improved, and the present invention has been completed.
That is, an object of the present invention is to provide an electrophotographic photosensitive member for wet development excellent in solvent resistance and sensitivity characteristics, and an image forming apparatus provided with such an electrophotographic photosensitive member for wet development.

According to the present invention, there is provided a wet electrophotographic photoreceptor having a photoreceptor layer containing at least a binder resin and a hole transport agent, and the hole transport agent is represented by the following general formula (1). An electrophotographic photosensitive member for wet development containing a stilbene derivative having three enamine structures is provided, and the above-described problems can be solved.
That is, an electrophotographic photosensitive member having at least a single-layer type photosensitive layer containing at least a binder resin and a hole transporting agent is provided on the outermost surface, and a charging process, exposure is performed around the electrophotographic photosensitive member. Wet development characterized in that each part for carrying out a process, a development process, and a transfer process is disposed, and in the development process, image formation is performed using a liquid developer in which toner is dispersed in a hydrocarbon solvent. Image forming apparatus, comprising a stilbene derivative having three enamine structures represented by the following general formula (1) as a hole transporting agent, and a binder resin having an I / O value (inorganic value / An image forming apparatus for wet development comprising a polycarbonate copolymer having an organic value of 0.38 or more .

(In General Formula (1), several R < ¹ > -R < ⁵ > is an independent hydrogen atom, a C1-C20 alkyl group, a C2-C16 ethenyl group, and a styryl group , respectively, R < ⁶ > and R < R > ⁷ is an independent hydrogen atom , B ¹ and B ² are phenyl groups, or a carbocyclic structure formed by bonding or condensing a plurality of B ¹ and B ^2. An organic group represented by the formula (2).

  In constituting the electrophotographic photoreceptor for wet development according to the present invention, it is preferable that the molecular weight of the hole transport agent is 900 or more.

  Further, in constituting the electrophotographic photosensitive member for wet development according to the present invention, the amount of the hole transport agent added may be set to a value within the range of 10 to 80 parts by weight with respect to 100 parts by weight of the binder resin. preferable.

  Further, in constituting the electrophotographic photosensitive member for wet development of the present invention, it further contains an electron transport agent, and the addition amount of the electron transport agent is 10 to 100 parts by weight with respect to 100 parts by weight of the binder resin. A value within the range is preferable.

  In constituting the electrophotographic photosensitive member for wet development according to the present invention, it is preferable to set the I / O value (inorganic value / organic value) of the electron transfer agent to 0.5 or more.

In constructing the electrophotographic photosensitive member for wet development of the present invention, the electron transporting agent used is at least one nitro group (—NO ₂ ), substituted carboxyl group (—COOR (where R is a substituted or unsubstituted carbon). An alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms)), and a substituted carbonyl group (—COR (where R is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, substituted or unsubstituted It is preferable to have an unsubstituted aryl group having 6 to 30 carbon atoms.

  The electrophotographic photosensitive member for wet development according to the present invention further includes a charge generator, and as the charge generator, metal-free phthalocyanine (τ type or x type), titanyl phthalocyanine (α type or Y type). ), Hydroxygallium phthalocyanine (type V), and chlorogallium phthalocyanine (type II).

  Further, in constituting the electrophotographic photosensitive member for wet development according to the present invention, the amount of the charge generating agent is set to a value within the range of 0.2 to 40 parts by weight with respect to 100 parts by weight of the binder resin. Is preferred.

  In constituting the electrophotographic photoreceptor for wet development of the present invention, the binder resin includes a polycarbonate copolymer having an I / O value (inorganic value / organic value) of 0.38 or more. It is preferable.

  In constituting the electrophotographic photoreceptor for wet development of the present invention, the photoreceptor layer is preferably a single layer type.

  Another aspect of the present invention includes the electrophotographic photosensitive member for wet development described in any one of the above, and a charging step, an exposure step, a developing step, and a transfer around the electrophotographic photosensitive member for wet development. This is an image forming apparatus for wet development in which parts for performing the steps are arranged and image formation is performed using a liquid developer in which a toner is dispersed in a hydrocarbon solvent in the development step.

According to the electrophotographic photoreceptor for wet development of the present invention, a stilbene derivative having an enamine structure at each of three symmetrical positions in the molecule as represented by the general formula (1) as a hole transport agent. By using this, it is possible to provide an electrophotographic photoreceptor for wet development that has not only excellent compatibility with the binder resin but also high charge mobility and a predetermined sensitivity over a long period of time.
That is, the stilbene derivative represented by the general formula (1) has a specific enamine structure at each of three symmetrical positions at the molecular end, so that the three-dimensional It is characterized by good compatibility with the binder resin due to the obstacle and high charge mobility. Therefore, the electrophotographic photoreceptor for wet development using such a stilbene derivative can exhibit excellent sensitivity characteristics, durability and solvent resistance over a long period of time.

  In addition, according to the electrophotographic photoreceptor for wet development of the present invention, by setting the molecular weight of the hole transport agent to a predetermined value or more, the hydrocarbon solvent used as a developer for wet development can be used for a long time. Even when immersed, the elution amount of the hole transport agent is reduced. Further, since the compatibility with the binder resin is also good, it is possible to provide an electrophotographic photoreceptor for wet development that is further excellent in durability and solvent resistance.

  Further, according to the electrophotographic photoreceptor for wet development of the present invention, by limiting the addition amount of the hole transport agent to a predetermined range, crystallization of the hole transport agent can be effectively prevented, and further sensitivity characteristics In addition, it is possible to provide an electrophotographic photosensitive member for wet development that is excellent.

  In addition, according to the electrophotographic photoreceptor for wet development of the present invention, while further containing an electron transport agent, by limiting the addition amount to a specific range, predetermined durability and sensitivity characteristics can be obtained, The crystallization of the electron transport agent in the electrophotographic photoreceptor for wet development can also be effectively prevented.

  Further, according to the electrophotographic photosensitive member for wet development of the present invention, by limiting the I / O value (inorganic value / organic value) of the electron transport agent to a predetermined range, durability and solvent resistance can be further improved. An excellent electrophotographic photoreceptor for wet development can be provided.

  In addition, according to the electrophotographic photoreceptor for wet development of the present invention, an electrophotographic photoreceptor for wet development having excellent solvent resistance at the time of development is provided because the electron transport agent used has a specific substituent. be able to.

  In addition, according to the electrophotographic photoreceptor for wet development, by using a specific compound such as a metal-free phthalocyanine as a charge generating agent, when a hole transporting agent and an electron transporting agent are used in combination, sensitivity characteristics and electrical properties are improved. It is possible to provide an electrophotographic photosensitive member for wet development having more excellent characteristics and the like.

  In addition, according to the electrophotographic photoreceptor for wet development of the present invention, the effect of increasing the quantum yield is improved by limiting the amount of the charge generator added to a predetermined range, and further, red, infrared, or near An effect of increasing the absorption coefficient for light having an absorption wavelength in the infrared region can be maintained, and an electrophotographic photoreceptor for wet development having further excellent sensitivity characteristics and electrical characteristics can be provided.

  Further, according to the electrophotographic photoreceptor for wet development of the present invention, the solvent resistance is further improved by limiting the I / O value (inorganic value / organic value) of the binder resin to be used within a predetermined range. An excellent electrophotographic photoreceptor for wet development can be provided.

  In addition, according to the electrophotographic photoreceptor for wet development of the present invention, the solvent resistance during development can be determined with high accuracy by limiting the elution amount of the hole transport agent to a specific range. For example, it is possible to accurately estimate the solvent resistance when 100,000 images are formed from the elution amount of the hole transport agent obtained by such a 2,000-hour immersion test.

  In addition, according to the electrophotographic photosensitive member for wet development of the present invention, an electrophotographic photosensitive member having a predetermined sensitivity over a long period of time can be obtained by making the photosensitive layer a single layer type, although it is easy to configure and manufacture. You can get a body.

  Further, according to the image forming apparatus for wet development of the present invention, since the electrophotographic photosensitive member for wet development using a specific stilbene derivative is provided as the hole transport agent, the image forming apparatus for wet development is provided. Even when the electrophotographic photosensitive member for wet development is immersed in a hydrocarbon solvent used as a wet developer for a long time, the elution amount of the hole transport agent is small and the predetermined sensitivity is maintained. An image forming apparatus can be provided.

  Hereinafter, embodiments of the electrophotographic photoreceptor for wet development according to the present invention will be specifically described with reference to the drawings as appropriate.

[First embodiment]
The first embodiment is a wet electrophotographic photosensitive member provided with at least a binder resin and a hole transport agent, and has 3 enamine structures represented by the following general formula (1) as the hole transport agent. An electrophotographic photoreceptor for wet development containing a stilbene derivative.

(In General Formula (1), several R < ¹ > -R < ⁵ > is an independent hydrogen atom, a C1-C20 alkyl group, a C2-C16 ethenyl group, and a styryl group , respectively, R < ⁶ > and R < R > ⁷ is an independent hydrogen atom , B ¹ and B ² are phenyl groups, or a carbocyclic structure formed by bonding or condensing a plurality of B ¹ and B ^2. An organic group represented by the formula (2).

Here, the electrophotographic photosensitive member for wet development includes a single layer type and a laminated type, and the electrophotographic photosensitive member for wet development of the present invention is applicable to both.
However, it can be used for both positive and negative chargeability, has a simple structure and is easy to manufacture, and suppresses film defects when forming the photoreceptor layer, so there are few interfaces between layers, improving optical characteristics For reasons such as being possible, it is more preferable to apply to a single layer type.

1. Single Layer Type Photoreceptor (1) Basic Configuration As shown in FIG. 1A, the single layer type photoreceptor 10 is obtained by providing a single photoreceptor layer 14 on a conductive substrate 12.
This photoreceptor layer is made of, for example, a binder resin, a hole transporting agent represented by the general formula (1), an electron transporting agent, a charge generating agent, and, if necessary, a leveling agent and the like in an appropriate solvent. It can be formed by dissolving or dispersing in, applying the obtained coating solution on a conductive substrate and drying. Such a single layer type photoreceptor is characterized in that it can be applied to either a positive or negative charge type with a single configuration, has a simple layer configuration, and is excellent in productivity.

(2) Hole transport agent (2) -1 type Moreover, it contains the stilbene derivative which has three enamine structures represented by General formula (1) as a hole transport agent.
The reason for this is that by using a stilbene compound with an enamine structure introduced at a predetermined position in the molecule as a hole transporting agent, the solvent resistance to paraffinic solvents represented by Isopar (trade name) is remarkably improved. It is because it can be made. Therefore, stable image formation can be carried out over a long period of time by the electrophotographic photoreceptor for wet development.
In addition, by using a stilbene compound having such a specific structure introduced at the molecular end, not only the sensitivity characteristics can be further improved, but also the mechanical characteristics and film formability can be improved.

In constituting the stilbene derivative of the present invention, the trivalent organic group represented by the symbol A in the general formula (1) is an organic group represented by the following general formula (2). .
This is because such a specific carbocyclic structure can improve electrical characteristics and heat resistance, and the electron distribution is delocalized and planar. This is because the charge mobility can be increased and the charge injection property from the charge generating agent can be enhanced.

(In the general formula (2), R ^{8 to} R ¹⁰ are each an independent hydrogen atom. )

In constituting the stilbene derivative of the present invention, a plurality of R ¹ , R ² , R ⁴ , R ⁵ , R ⁶ and R ^{7 in} the general formula (1) are each an independent hydrogen atom or 1 carbon atom. It is preferably a -20 substituted or unsubstituted alkyl group.
This is because the production of a stilbene derivative having a predetermined structure is facilitated, and such a derivative can be obtained stably.

In constituting the stilbene derivative of the present invention, a plurality of R ³ in the general formula (1) are each independently an hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or the following general formula ( It is preferable that it is a substituent represented by 3).
The reason for this is that when a plurality of R ³ in the general formula (1) are each an alkyl group or the like, it becomes easy to produce a stilbene derivative having a predetermined structure, and such a stilbene derivative can be obtained stably. In addition, when a plurality of R ³ are substituents represented by the general formula (3), intramolecular conjugation can be expanded, and as a result, as a hole transport agent in an electrophotographic photoreceptor. This is because when used, stability and durability can be improved, and excellent sensitivity can be exhibited for a longer time.

(In General Formula (3), R ^{20 to} R ²⁶ are each an independent hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and a substituted or unsubstituted halogen group having 1 to 20 carbon atoms. An alkyl group, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.)

Moreover, it is preferable that the molecular weight of a hole-transporting agent shall be 900 or more. The reason for this is that if the molecular weight is above such a value, the compatibility with a specific binder resin will be good, and the elution amount of the hole transport agent into the developer will be small, and the solvent resistance will be reduced. This is because it is possible to provide an electrophotographic photoreceptor for wet development that is excellent in durability and durability.
In addition, the molecular weight of the hole transport agent and the molecular weight of the electron transport agent described later can be calculated based on the structural formula, or can be measured by a mass spectrum obtained with a mass spectrometer.

(2) -2 Specific Examples As specific examples of stilbene derivatives having three stilbene derivatives having three ethenyl structures represented by the general formula (1), stilbenes represented by the following structural formulas (4) to (12) Derivatives (HTM-A to I) are shown.

  It is also preferable to use a conventionally known hole transport agent in combination. Examples of such hole transporting agents include N, N, N ′, N′-tetraphenylbenzidine derivatives, N, N, N ′, N′-tetraphenylphenylenediamine derivatives, N, N, N ′, N ′. -Tetraphenylnaphthylenediamine derivatives, N, N, N ', N'-tetraphenylphenanthrylenediamine derivatives, 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole, etc. Oxadiazole compounds, styryl compounds such as 9- (4-diethylaminostyryl) anthracene, carbazole compounds such as polyvinylcarbazole, organic polysilane compounds, pyrazolines such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline Compounds, hydrazone compounds, indole compounds, oxazole compounds, isoxazols System compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and nitrogen-containing cyclic compounds such as triazole compounds, and condensed polycyclic compounds.

(2) -3 Addition amount Further, regarding the addition amount of the hole transport agent, it is preferable to set the value within the range of 10 to 80 parts by weight with respect to 100 parts by weight of the binder resin.
The reason for this is that when the added amount of the hole transport agent is less than 10 parts by weight, the sensitivity is lowered and a practical problem may occur. On the other hand, when the added amount of the hole transport agent exceeds 80 parts by weight, the hole transport agent is likely to be crystallized, and an appropriate film as a photoreceptor may not be formed.
Therefore, it is more preferable to set the addition amount of the hole transport agent to a value within the range of 30 to 70 parts by weight.

(3) Electron Transfer Agent (3) -1 Type In addition, the type of electron transfer agent preferably includes at least one compound selected from the group consisting of naphthalenecarboxylic acid diimide derivatives, naphthoquinone derivatives, and azoquinone derivatives. .
This is because by using a specific compound as the electron transport agent, it is possible to provide an electrophotographic photoreceptor for wet development that has excellent electron acceptability and excellent sensitivity characteristics and solvent resistance. is there.

(3) -2 I / O value (inorganic value / organic value)
In selecting an electron transfer agent, the I / O value is preferably 0.5 or more.
The reason for this is that by limiting the I / O value of the electron transport agent to a specific range, the inorganicity of the electron transport agent is increased, and the solvent resistance is excellent with respect to hydrocarbon solvents that are organic solvents. Is obtained. However, when the value of the I / O value becomes excessively large, the solubility in the solvent and the binder resin may be lowered.
Therefore, the I / O value of the electron transport agent is more preferably set to a value within the range of 0.6 to 1.7, and further preferably set to a value within the range of 0.7 to 1.5.
Specifically, it is preferable that the inorganic value (I value) of the electron transfer agent is a value in the range of 240 to 900, and the organic value (O value) is a value in the range of 240 to 1000.

  Here, the inorganic value (I value) and the organic value (O value) used in the present invention, and the I / O value that is the ratio thereof are values that treat the polarity of various organic compounds in an organic concept. . For example, KUMAMOTO PHARMACEUTICAL BULLETIN, No. 1, No. 1-16 (1954); Area of Chemistry, Vol. 11, No. 10, 719-725 (1957); Fragrance Journal, No. 34, No. 97 ˜111 pages (1979); Fragrance Journal, No. 50, pp. 79-82 (1981); and the like, and as a reference value, one carbon (C) is organic 20 It is stipulated. On the other hand, the inorganic and organic values of typical polar groups are determined as shown in Table 1. Based on Table 1, etc., the sum of inorganic values of various polar groups contained in the compound (I value) And the sum (O value) of the organic value, and the ratio (I / O value) between the sum of the inorganic value and the sum of the organic value is calculated to obtain the I / O value. is there.

That is, the concept of the I / O value will be described in more detail. The properties of a compound are divided into an organic group representing a covalent bond and an inorganic group representing an ionic bond. Each point on the orthogonal coordinates named inorganic axis is shown.
In this case, the inorganic value (I value) is a value obtained by quantifying the magnitude of the influence on the boiling point of various substituents and bonds of the organic compound based on the hydroxyl group. Specifically, when the distance between the boiling point curve of the linear alcohol and the boiling point curve of the 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 value of the substituent that the organic compound has. For example, the inorganic value of the —COOH group is 150, and the inorganic value of the double bond is 2. Therefore, the inorganic value of a certain organic compound means the sum of inorganic values such as various substituents and bonds of the compound.
On the other hand, the organic value (O value) 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, since the average value of the boiling point rise is 20 ° C. when adding one carbon in the vicinity of 5 to 10 carbon atoms of the linear saturated hydrocarbon, the organic value of one carbon atom is set to 20 on the basis of this. A value obtained by quantifying the influence of various substituents and bonds on the boiling point based on this value is an organic value. For example, the organic value of a nitro group (—NO ₂ ) is 70. Therefore, the organic value of a certain type of organic compound means the sum of various substituents and bonds of the compound.
Therefore, as an example, the I / O value of the naphthoquinone derivative represented by the electron transfer agent (ETM-B) represented by the formula (14) described later is calculated as follows.
That is, the compound has 23 carbon atoms (organic 20) and 1 nitro group (organic 70), and the organic value is 20 × 23 + 70 = 530. It also has one naphthalene ring (inorganic 60), two benzene rings (inorganic 15), two ketone groups (inorganic 65), and one nitro group (inorganic 70). Since it has one and one carboxyl group (inorganic 60), the inorganic value is 60 × 1 + 15 × 2 + 65 × 2 + 70 + 60 = 350. Therefore, the I / O value of such a compound is 350/530 = 0.6604.

In addition, the specific electron transport agent may be at least one nitro group (—NO ₂ ), a substituted carboxyl group (—COOR (where R is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted carbon number). 6-30 aryl groups)), and substituted carbonyl groups (-COR (R is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms)) It is preferable.
The reason for this is that an electrophotographic photosensitive member for wet development having excellent solvent resistance can be provided when the electron transfer agent used has a specific substituent.

  In addition, when it is desired to obtain further excellent solvent resistance, the above-described electron transporting agent excludes two or more substituted carboxyl groups or two or more substituted carbonyl groups (however, the quinone moiety ketone group is excluded). ) Is more preferable.

(3) -3 Specific Examples Specific examples of these electron transfer agents include compounds (ETM-A to ETM-E) represented by the following formulas (13) to (17).

It is also preferable to use a conventionally known electron transport agent in combination. Examples of such electron transporting agents 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 And various compounds having electron-accepting properties such as dibromomaleic anhydride, and preferably used alone or in combination of two or more.
Of these compounds, the concentration is adjusted to 40% by weight with respect to 60% by weight of the resin, and the electron mobility at an electric field strength of 5 × 10 ⁵ v / cm is 1.0 × 10 ^−8. An electron transfer agent having a cm ² / V / sec or more is more preferable.

(3) -4 Addition amount In constituting the electrophotographic photoreceptor for wet development, the addition amount of the electron transport agent is a value within the range of 10 to 100 parts by weight with respect to 100 parts by weight of the binder resin. It is preferable to do.
The reason for this is that when the added amount of the plurality of electron transfer agents is less than 10 parts by weight, the sensitivity is lowered and a practical problem may occur. On the other hand, when the added amount of the plurality of electron transfer agents exceeds 100 parts by weight, the electron transfer agent is likely to be crystallized, and an appropriate film as a photoreceptor may not be formed.
Therefore, it is more preferable to set the addition amount of the electron transfer agent to a value within the range of 20 to 80 parts by weight.

In addition, when determining the addition amount of an electron transport agent, it is preferable to consider the addition amount of a hole transport agent mentioned above. More specifically, the addition ratio (total ETM / total HTM) of the electron transport agent (total ETM) is a value within the range of 0.25 to 1.3 with respect to the hole transport agent (total HTM). It is preferable to do.
This is because if the ratio of all ETMs / all HTMs is outside this range, the sensitivity is lowered, which may cause practical problems.
Therefore, it is more preferable that the ratio of the total ETM / total HTM is set to a value within the range of 0.5 to 1.25.

(4) Charge generator (4) -1 type As the charge generator used in the electrophotographic photoreceptor of the present invention, metal-free phthalocyanine (τ type or x type), titanyl phthalocyanine (α type or Y type), It is preferable to include at least one compound selected from the group consisting of hydroxygallium phthalocyanine (type V) and chlorogallium phthalocyanine (type II).
The reason for this is that by specifying the type of charge generating agent, an electrophotographic photosensitive member for wet development that has better sensitivity characteristics, electrical characteristics, stability, etc. when a hole transporting agent and an electron transporting agent are used in combination. This is because it can be provided.

(4) -2 Specific Example Among these charge generators, it is more preferable to use phthalocyanine pigments (CGM-A to CGM-D) represented by the following formulas (18) to (21). preferable.

  It is also preferable to use a conventionally known charge generating agent. Such charge generators include phthalocyanine pigments such as oxo titanyl phthalocyanine, perylene pigments, bisazo pigments, diketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, trisazo pigments, indigo Organic photoconductors such as pigments, azulenium pigments, cyanine pigments, pyrylium pigments, ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments, selenium, selenium-tellurium, selenium- One kind of inorganic photoconductive agent material such as arsenic, cadmium sulfide, and amorphous silicon, or a mixture of two or more kinds may be used.

(4) -3 Addition The addition amount of the charge generator is preferably set to a value within the range of 0.2 to 40 parts by weight with respect to 100 parts by weight of the binder resin.
The reason for this is that when the added amount of the plurality of charge generating agents is less than 0.2 parts by weight, the effect of increasing the quantum yield becomes insufficient, and the sensitivity, electrical characteristics, stability, etc. of the electrophotographic photosensitive member are reduced. This is because it cannot be improved. On the other hand, when the added amount of the plurality of charge generating agents exceeds 40 parts by weight, the absorption coefficient for light having an absorption wavelength in the red and infrared to near infrared regions decreases, and the sensitivity of the photoreceptor, This is because electrical characteristics, stability, and the like may be reduced accordingly.
Therefore, it is more preferable to set the addition amount of the charge generating agent to a value within the range of 0.5 to 20 parts by weight.

Further, among the charge generating agents used in the present invention, when the compound (CGM-B) represented by the formula (19) is used, a dispersion aid represented by the following formula (22) (for example, C.I. IPigment Orange 16) may be added.
This is because the charge generating agent (CGM-B) and the dispersion auxiliary agent (C. IPigment Orange 16) are used together to improve the dispersibility of CGM-B in the coating solution, and the coating solution pot This is because the life can be lengthened.
In addition, when using the dispersion | distribution adjuvant represented by Formula (22), it is preferable to make the addition amount into the value within the range of 30-200 weight part with respect to 100 weight part of all the electric charge generating agents.
This is because when the amount of the dispersion aid added is less than 30 parts by weight, the solubility in the solvent and the binder resin becomes insufficient, and an appropriate film as a photoreceptor cannot be produced. On the other hand, when the dispersion aid exceeds 200 parts by weight, the effect of increasing the quantum yield of the charge generating agent becomes insufficient, and the sensitivity characteristics, electrical characteristics, stability, etc. of the electrophotographic photoreceptor can be improved. It is because it becomes impossible.

(5) Binder Resin (5) -1 Type As the binder resin for dispersing the charge generator and the like, a polycarbonate having an I / O value (inorganic value / organic value) of 0.38 or more. It is preferred to use a copolymer.
This is because the copolymer polycarbonate having such a structure can further improve the solvent resistance of the organic photoreceptor.

Further, in constituting the stilbene derivative of the present invention, a polycarbonate copolymer composed of bis (4-hydroxyphenyl) ether or bis (4-hydroxyphenyl) methanone represented by the following general formulas (23) and (24): Preferably there is.
This is because such a copolymer polycarbonate is hardly soluble in a hydrocarbon solvent without introducing a siloxane structure or the like, and has high oil repellency. As a result, the interaction between the surface of the photoreceptor layer and the above-mentioned hydrocarbon solvent is reduced, and the change in the appearance of the surface of the photoreceptor layer is reduced over a long period of time.

(In the general formula (23), a plurality of R ²⁷ , R ²⁸ , R ²⁹ , R ³⁰ , R ³¹ , and R ³² are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted carbon number of 1 -12 alkyl group, substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, substituted or unsubstituted aryl group having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl group having 6 to 30 carbon atoms, Or it is a C10-30 condensed polycyclic hydrocarbon group, and the molar ratio represented by m / (m + n) is a value within the range of 0.05-0.6.)

(In the general formula (24), a plurality of R ³³ , R ³⁴ , R ³⁵ , R ³⁶ , R ³⁷ , and R ³⁸ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted carbon number of 1 -12 alkyl group, substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, substituted or unsubstituted aryl group having 6 to 30 carbon atoms, substituted or unsubstituted alkenyl group having 6 to 30 carbon atoms, Or it is a C10-30 condensed polycyclic hydrocarbon group, and the molar ratio represented by m / (m + n) is a value within the range of 0.05-0.6.)

(5) -2 Specific Example Further, specific examples of the copolymer polycarbonate represented by the general formula (23) and the general formula (24) include, for example, compounds represented by the following formulas (25) to (32) (Resin -A to Resin-H).

However, it is also preferable to use various resins conventionally used in electrophotographic photoreceptors for wet development. For example, polycarbonate resin 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, acrylic copolymer 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, polyurethane resin, polysulfone resin, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin and other thermoplastic resins, silicone resin, epoxy resin, phenol resin, urea resin, melamine Fat, other crosslinking thermosetting resins, epoxy acrylate, urethane - resin such as photocurable resin such as acrylate can be used.
Of these binder resins, it is more preferable to use a copolymer polycarbonate resin.
This is because a copolymer polycarbonate resin is generally poorly soluble in a hydrocarbon solvent and has high oil repellency. As a result, the interaction between the surface of the photoreceptor layer and the above-mentioned hydrocarbon solvent is reduced, and the change in the appearance of the surface of the photoreceptor layer is reduced over a long period of time.

(6) Additive In addition to the above-mentioned components, the photoreceptor layer has various conventionally known additives such as an antioxidant, a radical scavenger, a singlet as long as it does not adversely affect the electrophotographic characteristics. Deterioration inhibitors such as quenchers and ultraviolet absorbers, 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 photoreceptor layer, known sensitizers such as terphenyl, halonaphthoquinones, and acenaphthylene may be used in combination with the charge generator.

(7) Structure The thickness of the photoreceptor layer in the single-layer photoreceptor is usually a value in the range of 5 to 100 μm, preferably a value in the range of 10 to 50 μm.
As the conductive substrate on which such a photoreceptor layer is formed, various conductive materials can be used, for example, iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium. , Cadmium, titanium, nickel, palladium, indium, stainless steel, brass, etc., plastic materials on which these metals are vapor-deposited or laminated, carbon black and other conductive fine particles, plastic materials, aluminum iodide And glass coated with tin oxide, indium oxide and the like.

Further, the shape of the conductive substrate may be any of a sheet shape, a drum shape, or the like in accordance with the structure of the image forming apparatus to be used. The substrate itself is conductive or the surface of the substrate is conductive. As long as it has. The conductive substrate preferably has sufficient mechanical strength when used. When the photoreceptor layer is formed by a coating method, a known method such as a roll mill, a ball mill, an attritor, a paint shaker, an ultrasonic wave is used together with an appropriate charge generating agent, charge transport agent, binder resin and the like in an appropriate solvent. A dispersion liquid may be prepared by dispersing and mixing using a disperser or the like, and this may be applied and dried by a known means.
Further, regarding the configuration of the single-layer type photoreceptor 10, as shown in FIG. 1B , a barrier layer 16 is formed between the conductive substrate 12 and the photosensitive layer 14 as long as the characteristics of the photoreceptor are not impaired. It may be.

(8) Manufacturing method Various organic solvents can be used as a solvent for preparing the dispersion. For example, alcohols such as methanol, ethanol, isopropanol, and butanol; aliphatic systems such as n-hexane, octane, and cyclohexane Hydrocarbons: 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, dioxane, Ethers such as dioxolane; ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and methyl acetate; dimethylformaldehyde, dimethylform Amides, dimethyl sulfoxide and the like. These solvents are used alone or in combination of two or more.
Further, a surfactant, a leveling agent or the like may be used in order to improve the dispersibility of the charge transport agent or the charge generator and the smoothness of the surface of the photoreceptor layer.

2. Laminated Photoreceptor (1) Basic Structure As shown in FIG. 2A, the laminated photoreceptor 20 generates a charge containing a charge generating agent on a conductive substrate 12 by means of vapor deposition or coating. A layer 24 is formed, and then a coating liquid containing at least one stilbene derivative as a hole transport agent and a binder resin is applied onto the charge generation layer 24 and dried to form the charge transport layer 22 It is produced by doing.
In contrast to the above structure, as shown in FIG. 2B, the charge transport layer 22 may be formed on the conductive substrate 12, and the charge generation layer 24 may be formed thereon.
However, since the charge generation layer 24 is much thinner than the charge transport layer 22, for protection, the charge transport layer 22 is formed on the charge generation layer 24 as shown in FIG. It is more preferable to form

  The charge generating agent, hole transporting agent, electron transporting agent, binder and the like can be basically the same as those of the single-layer type photoreceptor. However, in the case of a multilayer photoreceptor, the amount of charge generator added may be set to a value within the range of 0.5 to 150 parts by weight with respect to 100 parts by weight of the binder resin constituting the charge generation layer. preferable.

In addition, a positive or negative charge type is selected depending on the formation order of the charge generation layer and the charge transport layer and the kind of the charge transport agent used in the charge transport layer. For example, when a charge generation layer is formed on a conductive substrate and a charge transport layer is formed thereon, a positive charge such as a stilbene derivative represented by the general formula (1) is used as a charge transport agent in the charge transport layer. When a hole transport agent is used, the photoreceptor becomes a negatively charged type. In this case, the charge generation layer may contain an electron transport agent. In the case of a multilayer electrophotographic photoreceptor, the residual potential of the photoreceptor is greatly reduced, and the sensitivity can be improved.
Regarding the thickness of the photoreceptor layer in the multilayer photoreceptor, the charge generation layer is about 0.01 to 5 μm, preferably about 0.1 to 3 μm, and the charge transport layer is 2 to 100 μm, preferably 5 to 5 μm. It is about 50 μm.

[Second Embodiment]
The second embodiment includes the electrophotographic photosensitive member for wet development (hereinafter sometimes simply referred to as a photosensitive member) according to the first embodiment, and is provided around the electrophotographic photosensitive member for wet development. A charging device 32 for carrying out the charging step, an exposure light source 33 for carrying out the exposure step, a wet developing device 34 for carrying out the developing step, and a transfer device 35 for carrying out the transferring step, In addition, the image forming apparatus for wet development performs image formation using a liquid developer in which a toner is dispersed in a hydrocarbon solvent in a development step.
In the following description of the image forming apparatus for wet development, it is assumed that a single-layer type photoreceptor is used as the electrophotographic photoreceptor.

That is, as shown in FIG. 3, the image forming apparatus for wet development includes a charger 32 for performing a charging process, an exposure light source 33 for performing an exposure process, and a developing process around a photosensitive member 31. It is preferable to include at least a wet developing device 34 for carrying out the transfer and a transfer device 35 for carrying out the transfer step.
The photoconductor 31 rotates at a constant speed in the direction of the arrow, and the electrophotographic process is performed on the surface of the photoconductor 31 in the following order. More specifically, the photosensitive member 31 is entirely charged by the charger 32, and then the print pattern is exposed by the exposure light source 33. Next, the toner is developed by the wet developing device 34 corresponding to the print pattern, and the toner is transferred onto the transfer material (paper) 36 by the transfer device 35. Finally, excess toner remaining on the photoconductor 31 is scraped off by the cleaning blade 37 and the photoconductor 31 is neutralized by the neutralizing light source 38.

Here, the liquid developer 34a in which the toner is dispersed is conveyed by the developing roller 34b, and the toner is attracted onto the surface of the photoconductor 31 by applying a predetermined developing bias, and developed on the photoconductor 31. Will be. Moreover, it is preferable to make the solid content concentration in the liquid developer 34a into a value within the range of 5 to 25% by weight, for example. Further, as the liquid (toner dispersion solvent) used in the liquid developer 34a, a hydrocarbon solvent or a silicone oil is preferably used.
In the photoreceptor 31, by using a specific stilbene derivative as a hole transport agent, a single layer type electrophotographic photoreceptor for wet development having excellent solvent resistance and sensitivity characteristics can be obtained, and it can be used for a long time. , Excellent image characteristics can be maintained.

[Example 1]
(1) Preparation of electrophotographic photosensitive member for wet development As a charge generating agent, 4 parts by weight of X-type metal-free phthalocyanine (CGM-A) represented by formula (18) and a hole transporting agent are used. 40 parts by weight of the stilbene derivative (HTM-B) represented by the formula (13), and 50 parts by weight of the naphthoquinone derivative (ETM-A) represented by the formula (13) as the binder resin. 100 parts by weight of the copolymer polycarbonate resin (Resin-A) represented by the formula (25) and 0.1 part by weight of KF-96-50CS (manufactured by Shin-Etsu Chemical Co., Ltd.) which is a dimethyl silicone oil as a leveling agent. And 750 parts by weight of tetrahydrofuran as a solvent were mixed and dispersed for 1 hour with an ultrasonic disperser to prepare a coating solution.
The obtained coating solution was applied by dip coating on a conductive base material (anodized aluminum base tube) having a diameter of 30 mm and a length of 254 mm. Thereafter, it was dried with hot air at 130 ° C. for 30 minutes to obtain an electrophotographic photoreceptor for wet development having a single-layer photoreceptor layer with a thickness of 22 μm.

(2) Evaluation (2) -1 Sensitivity Measurement The light potential in the obtained electrophotographic photoreceptor for wet development was measured. That is, using a drum sensitivity tester (produced by GENTEC), it was charged to 700 V, and then monochromatic light with a wavelength of 780 nm (half-value width: 20 nm, light amount) extracted from the light of the halogen lamp using a hand pulse filter. : 1.0 μJ / cm ² ). The potential after 330 msec after exposure was measured and used as the initial sensitivity.
The obtained electrophotographic photoreceptor for wet development was immersed in Isopar L (isoparaffinic solvent) used as a developer for wet development at a temperature of 25 ° C. for 2000 hours. Thereafter, the electrophotographic photosensitive member for wet development was taken out from the isopar solution, the sensitivity was measured in the same manner, and the difference between the initial sensitivity and the sensitivity after isopar soaking was calculated to determine the sensitivity change. The obtained results are shown in Table 2.

(2) -2 Evaluation of solvent resistance The obtained electrophotographic photoreceptor for single layer type wet development is immersed in 500 ml of Isopar L (trade name) at a temperature of 25 ° C. for 2000 hours so that the entire surface of the photosensitive layer is immersed. It was immersed in the conditions of. On the other hand, the concentration of the hole transport agent was changed and dissolved in Isopar L. In this state, the absorbance at the ultraviolet absorption peak wavelength was measured, and a concentration-absorbance calibration curve for the hole transport agent was prepared in advance. Next, for the electrophotographic photoreceptor for wet development immersed in Isopar L, ultraviolet absorption measurement is performed, and the elution amount of the hole transport agent is calculated from the absorbance at the ultraviolet absorption peak wavelength of the hole transport agent in light of the calibration curve. did. The obtained results are shown in Table 2.

(2) -3 Appearance Evaluation Further, the appearance of the electrophotographic photoreceptor for wet development after the solvent resistance evaluation was visually observed for occurrence of cracks, and the appearance was evaluated according to the following criteria. The obtained results are shown in Table 2.
A: No change in appearance is observed.
○: No significant change in appearance is observed.
Δ: Some change in appearance is observed.
X: A remarkable change in appearance is observed.

[Examples 2 to 4]
In Examples 2 to 4, instead of the metal-free phthalocyanine (CGM-A) represented by Formula (18) as the charge generator used in Example 1, it is represented by Formulas (19) to (21). A single-layer photoreceptor was prepared and evaluated in the same manner as in Example 1 except that each of the compounds (CGM-B to CGM-D) was used.

[Examples 5 and 6]
In Examples 5 and 6, instead of the stilbene derivative (HTM-B) represented by Formula (5) as the hole transport agent used in Example 1, it is represented by Formula (6) and (7). A single-layer photoreceptor was prepared and evaluated in the same manner as in Example 1 except that stilbene compounds (HTM-C and HTM-D) were used.

[Examples 7 to 9]
In Examples 7 to 9, instead of the stilbene derivative (HTM-B) represented by Formula (5) as the hole transport agent used in Example 1, a stilbene compound (HTM) represented by Formula (7) was used. -D), and instead of the naphthoquinone derivative (ETM-A) represented by the formula (13) as an electron transport agent, the electron transport agent (ETM-) represented by the formulas (14) to (16) A single-layer photoreceptor was prepared and evaluated in the same manner as in Example 1 except that each of BD) was used.

[Example 10, Reference Example 11, and Examples 12 to 13]
In Example 10, Reference Example 11 and Examples 12 to 13 , instead of the naphthoquinone derivative (ETM-A) represented by the formula (13) as the electron transport agent used in Example 1, the formula (15 ), An electron transfer agent (ETM-C) represented by formula (27), and, as a binder resin, instead of the copolymer polycarbonate resin (Resin-A) represented by formula (25), formula (27) A single layer type photoreceptor was prepared and evaluated in the same manner as in Example 1 except that the binder resins (Resin-C to Resin-F) represented by (30) were used.

[Example 14]
In Example 14, instead of the naphthoquinone derivative (ETM-A) represented by Formula (13) as the electron transport agent used in Example 1, an electron transport agent (ETM-E) represented by Formula (17) is used. 1) was used, and a single-layer type photoreceptor was prepared and evaluated in the same manner as in Example 1.

[Reference Example 15]
In Reference Example 15 , instead of the naphthoquinone derivative (ETM-A) represented by Formula (13) as the electron transport agent used in Example 1, an electron transport agent (ETM-E) represented by Formula (17) is used. ), And as a binder resin, instead of the copolymer polycarbonate resin (Resin-A) represented by the formula (25), a binder resin (Resin-D) represented by the formula (28) is used. A single layer type photoreceptor was prepared and evaluated in the same manner as in Example 1 except that it was used.

[Comparative Example 1]
In Comparative Example 1, triphenyl represented by the following formula (33) instead of the stilbene derivative (HTM-B) represented by formula (5) as a hole transport agent in the coating liquid of Example 1 An electrophotographic photoreceptor for wet development was prepared and evaluated in the same manner as in Example 1 except that the amine derivative (HTM-J) was used.

As described above in detail, in the stilbene derivative as a hole transport agent, the compatibility with the binder resin is excellent by symmetrically introducing a specific diphenylamine structure including an enamine structure at multiple locations in the molecule. Therefore, it is possible to maintain a predetermined sensitivity for a long time and to obtain excellent durability and solvent resistance.
Therefore, the electrophotographic photoreceptor for wet development according to the present invention is expected to contribute to speeding up and performance enhancement of various image forming apparatuses.

(A)- (b) is a figure provided in order to demonstrate the basic structure and deformation | transformation structure of a single layer type photoreceptor. (A)-(b) is a figure provided in order to demonstrate the basic structure and deformation | transformation structure of a laminated type photoreceptor. It is a figure provided in order to demonstrate the image forming apparatus provided with the electrophotographic photoreceptor for wet development.

Explanation of symbols

10: Single layer type photoreceptor 12: Conductive substrate 14: Photosensitive layer
16: Barrier layer
20: Laminated photoreceptor 22: Charge transport layer 24: Charge generation layer 31: Photoreceptor 32: Charger 33: Exposure light source 34: Wet developer 34a: Liquid developer 34b: Developing roller 35: Transfer device 36: Transfer material 37: Cleaning blade 38: Static elimination light source 39: Probe

Claims (8)

With an electrophotographic photoreceptor having an outermost surface, a single-layer type photoreceptor layer containing at least a binder resin and a hole transport agent,
Around the electrophotographic photosensitive member, a part for carrying out a charging step, an exposure step, a development step, and a transfer step is disposed, and in the development step, a liquid developer in which toner is dispersed in a hydrocarbon solvent is added. An image forming apparatus for wet development characterized in that image formation is performed using
As the hole transport agent, containing a stilbene derivative having three enamine structures represented by the following general formula (1),
An image forming apparatus for wet development, wherein the binder resin contains a polycarbonate copolymer having an I / O value (inorganic value / organic value) of 0.38 or more.

(In General Formula (1), a plurality of R ^{1 to} R ⁵ are each an independent hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an ethenyl group having 2 to 16 carbon atoms, and a styryl group, and R ⁶ and R ⁷ is an independent hydrogen atom, B ¹ and B ² are phenyl groups, or a carbocyclic structure formed by bonding or condensing a plurality of B ¹ and B ^2. (It is an organic group represented by the formula (2).)

(In the general formula (2), R ^{8 to} R ¹⁰ are each an independent hydrogen atom.)   The image forming apparatus for wet development according to claim 1, wherein the molecular weight of the hole transport agent is 900 or more.   3. The image for wet development according to claim 1, wherein the addition amount of the hole transport agent is set to a value within a range of 10 to 80 parts by weight with respect to 100 parts by weight of the binder resin. Forming equipment.   The photoconductor layer further includes an electron transport agent, and the addition amount of the electron transport agent is set to a value within a range of 10 to 100 parts by weight with respect to 100 parts by weight of the binder resin. The image forming apparatus for wet development according to any one of claims 1 to 3.   The value (I / O value) obtained by dividing the inorganic value (I value) of the electron transfer agent by the organic value (O value) is 0.5 or more as the electron transfer agent. Item 5. The image forming apparatus for wet development according to Item 4. As the electron transfer agent, at least one nitro group (—NO ₂ ), substituted carboxyl group (—COOR (R is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, substituted or unsubstituted carbon number 6). To 30 aryl groups)), and substituted carbonyl groups (-COR (R is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms)) The image forming apparatus for wet development according to claim 4, wherein the image forming apparatus has wet development.   The photoconductor layer further contains a charge generator, which includes metal-free phthalocyanine (τ type or x type), titanyl phthalocyanine (α type or Y type), hydroxygallium phthalocyanine (V type), and chloro. The image forming apparatus for wet development according to any one of claims 1 to 6, comprising at least one compound selected from the group consisting of gallium phthalocyanine (type II).   8. The image forming for wet development according to claim 7, wherein the addition amount of the charge generating agent is set to a value within a range of 0.2 to 40 parts by weight with respect to 100 parts by weight of the binder resin. apparatus.