JP2008203872A - Electrophotographic photoreceptor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor which has high sensitivity to light of wavelengths from 380 to 500 nm and is excellent in charging property at a low temperature. <P>SOLUTION: The electrophotographic photoreceptor has: a charge generating layer containing a disazo compound expressed by a formula (1) on a support; and a charge transporting layer having a film thickness of 10 to 25 μm on the charge generating layer, and is exposed to light at wavelengths of 380 to 500 nm. In the formula (1), R represents a 4-20C cycloalkyl alkyl group which may have an alkyl group in the ring. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic photosensitive member that is exposed to light having a short wavelength.

  Currently, an electrophotographic apparatus using a laser as an exposure light source, such as a laser printer, is used. As a light source laser, a semiconductor laser that mainly emits light having a wavelength of 780 to 800 nm or 680 nm is used. However, in recent years, there has been a strong demand for higher resolution of output images, and various attempts have been made to meet this demand. One of them is to shorten the laser wavelength. The shortening of the wavelength of the light source makes it difficult to be affected by the curvature of field of the scanning lens. Therefore, it is relatively easy to make the small-diameter laser spot uniform, which is effective for increasing the resolution.

In order to perform exposure with light having a short wavelength, it is necessary to use a photoreceptor having excellent electrical characteristics with respect to this light. A phthalocyanine compound is mainly used as a charge generator in a laser printer having a light source wavelength of about 800 nm that is currently used. However, since the phthalocyanine compound is not sensitive to light having a wavelength of 500 nm or less, it is not suitable for exposure with light having a short wavelength of 380 to 500 nm, which is currently being studied.
One of the materials currently being studied as a charge generator for a short wavelength light source is an azo compound. For example, Patent Document 1 proposes azo compounds having various structures as charge generators for a photoreceptor of an electrophotographic apparatus using a semiconductor laser that emits light with a wavelength of 380 to 500 nm as a light source. According to the study by the present inventor, not all of these azo compounds have good sensitivity to short wavelength light, but among them, those represented by the following formula (2) It has good sensitivity to light.
JP 2000-105478 A

  However, a photoconductor using the disazo compound as a charge generator has good sensitivity to short-wavelength light, but has insufficient chargeability at low temperatures. The present invention intends to provide an electrophotographic photoreceptor having high sensitivity to light with a wavelength of 380 to 500 nm and excellent chargeability at low temperatures.

  An electrophotographic photoreceptor according to the present invention is for exposure with light having a wavelength of 380 to 500 nm, and has a charge generation layer containing a disazo compound represented by the formula (1) on a support. The charge generation layer has a charge transport layer having a thickness of 10 to 25 μm.

(In the formula, R represents a cycloalkyl group having 4 to 20 carbon atoms which may have an alkyl group in the ring;

Represents. Ring X may have a substituent. )

  According to the present invention, it is possible to provide an electrophotographic photosensitive member having high sensitivity to light having a short wavelength and excellent chargeability at low temperatures.

Charge generating agent;
In the present invention, the charge generation agent represented by the formula (1) is used. Only one kind of the compound represented by the formula (1) may be used, or some of them may be used in combination. If desired, other compounds may be used in combination with the compound represented by formula (1), but it is not usually necessary.

In the formula (1), R represents a cycloalkylalkyl group having 4 to 20 carbon atoms which may have an alkyl group in the ring. The bonding position of the —OR group to the benzene ring is arbitrary, but the meta position is preferable to the bonding carbon atom of the —CONH— group. Examples of the cycloalkylalkyl group represented by R include those shown in Table 1. The cycloalkyl group is preferably a 5- or more-membered ring, and more preferably a cyclohexylmethyl group.
The bonding position of the -CONH group with respect to the naphthalene ring is arbitrary as long as the ring is bonded to the -N = N- group, but it is in the meta position with respect to the bonding carbon atom of the -N = N- group. Is preferred.

  In the formula (1), Z represents any of the following groups.

  Ring X may have a substituent. Examples of the substituent include halogen atoms such as fluorine atom, iodine atom and chlorine atom; alkyl groups such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group and n-hexyl group; methoxy group , Alkoxy groups such as ethoxy group and n-propoxy group. Among these, a fluorine atom, a chlorine atom, and a methoxy group are preferable. Most preferably, however, no substituent is present on the benzene ring represented by X. The compound represented by the formula (1) is described as a charge generator in JP-A-9-281733, but is known to have excellent characteristics for light with a short wavelength of 380 to 500 nm. Not.

Charge transport agent;
Various charge transporting agents have been proposed that are suitable for photoconductors exposed to light having a short wavelength, and any of these may be appropriately selected and used. Currently, many of the charge transfer agents that are generally used have absorption on the short wavelength side, and therefore the sensitivity of the photoreceptor may be reduced when used in the photoreceptor according to the present invention. Preferable charge transfer agents include those described in, for example, JP-A Nos. 2000-105475 and 2001-350282. Of these, the compound represented by the formula (3) is preferable.

In the formula, Ar ^{1 to} Ar ⁴ each independently represents an aryl group which may have a substituent, and Ar ⁵ and Ar ⁶ each independently represent an arylene which may have a substituent. Indicates a group. R represents an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a 2-methylpropyl group or an n-butyl group; an aralkyl group such as a benzyl group or a phenethyl group; or a phenyl group or a tolyl group An aryl group is shown. These groups may further have a substituent.
Moreover, the compound shown by Formula (4) is also preferable. Although this compound alone does not have good solubility in a solvent, a stable solution can be obtained by using it together with the compound of the above formula (3).

In the formula, Ar ^{7 to} Ar ¹⁰ each independently represent an aryl group which may have a substituent, and Ar ¹¹ and Ar ¹² may each independently have a substituent. An arylene group is shown. Z represents a C4-C8 saturated hydrocarbon ring which may have a substituent, preferably a cyclohexane ring which may have a methyl group or an ethyl group on the ring.
In said Formula (3) and Formula (4), as Ar < ¹ > -Ar < ⁴ > and Ar < ⁷ > -Ar < ¹⁰ >, a phenyl group or a tolyl group is preferable, and a phenyl group is especially preferable. Ar ⁵ , Ar ⁶ , Ar ¹¹ and Ar ¹² are preferably a phenylene group or a tolylene group, and particularly preferably a phenylene group. The substituent of these groups is usually an alkyl group having 1 to 4 carbon atoms or an alkoxy group. When using together the compound of Formula (3) and the compound of Formula (4), it is preferable to use so that the compound of Formula (3) may be 20 to 95 weight% with respect to the total weight of both.

Composition of photosensitive layer;
As is well known, an electrophotographic photosensitive member is a normal lamination type photosensitive member in which a charge generation layer and a charge transport layer are laminated in this order on a conductive support, and a reverse lamination in which the lamination order is reversed. Type photoconductors, and further, there are single layer type photoconductors in which a charge generating agent and a charge transporting agent are mixed in one photosensitive layer. The electrophotographic photoconductor of the present invention is a sequentially laminated type photoconductor. .

Support;
As a well-known conductive support, a metal material such as aluminum, stainless steel, copper, nickel and zinc, a synthetic resin such as polyester, an insulating substrate such as paper and glass, aluminum, palladium, tin oxide, A material provided with a conductive layer such as indium oxide or a conductive polymer can be used. The surface of these conductive supports can be subjected to various conventional treatments. For example, a conductive support made of aluminum is anodized as desired. The shape of the conductive support can be any shape such as a drum, a sheet, or a seamless belt.

Formation of a photosensitive layer;
The charge generation layer can be formed by forming a charge generation agent on a support by vapor deposition such as vapor deposition or sputtering, but usually the charge generation agent and binder resin are combined with an appropriate solvent. In addition to the above, it is well dispersed with a ball mill, paint shaker, attritor, sand grinder, ultrasonic disperser, etc. to make a coating solution, which is dipping method, spray method, bar coater method, blade method, roll coater method, wire The coating is carried out by applying to a support by a conventional coating method such as a bar coating method or a knife coater coating method. The film thickness of the charge generation layer is preferably 0.01 to 5 μm, particularly preferably 0.05 to 2 μm. Examples of the binder resin include polymers and copolymers of vinyl compounds such as butadiene, styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, and ethyl vinyl ether, polyvinyl acetal, polycarbonate, polyester, polyamide, polyurethane, and cellulose. Ether, phenoxy resin, silicon resin, epoxy resin and the like are used. Some of these may be used in combination, or may be used in combination with an appropriate crosslinking agent. The binder resin is preferably used in an amount of 5 to 500 parts by weight, particularly 20 to 300 parts by weight, based on 100 parts by weight of the charge generator. Solvents include butylamine, diethylamine, ethylenediamine, isopropanolamine, triethanolamine, triethylenediamine, N, N-dimethylformamide, acetone, methyl ethyl ketone, cyclohexanone, 4-methoxy-4-methylpentanone-2, benzene, toluene, xylene Chloroform, 1,2-dichloroethane, 1,2-dichloropropane, 1,1,2-trichloroethane, dichloromethane, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, methyl alcohol, ethyl alcohol, isopropyl alcohol, normal propyl alcohol, Ethyl acetate, butyl acetate, dimethyl sulfoxide, methyl cellosolve, etc. are used. Usually some of these are used together. Conventional auxiliaries such as a plasticizer, an antioxidant, an ultraviolet absorber, and a leveling agent may be contained in the coating solution.

The charge transport layer can also be formed by applying a coating solution prepared by dissolving a charge transport agent and a binder resin in an appropriate solvent in the same manner as the charge generation layer. In the coating solution, various auxiliary agents can be contained as in the case of forming the charge generation layer. As the binder resin and the solvent, those described above may be used. The binder resin is preferably used in an amount of 10 to 500 parts by weight, particularly 30 to 300 parts by weight, based on 100 parts by weight of the charge transfer agent. The thickness of the charge transport layer is preferably 10 to 50 μm, particularly 13 to 25 μm.
In the case of producing a single-layer type photoreceptor, the binder resin, the charge generator and the charge transport agent are added in the above-mentioned appropriate solvent, and the charge generator is 1 to 20 parts by weight with respect to 100 parts by weight of the binder resin. And a coating solution prepared by adding and dispersing the charge transfer agent in a proportion of 30 to 300 parts by weight.

Other layers;
The electrophotographic photoreceptor according to the present invention consists essentially of a conductive support and a photosensitive layer formed thereon, and further comprises an undercoat layer, an intermediate layer, a transparent insulating layer, and a surface protective layer. For example, the electrophotographic photosensitive member may have a known additional layer. For example, as the undercoat layer, a resin such as polyamide resin, phenol resin, melamine resin, casein, polyurethane resin, epoxy resin, cellulose, nitrocellulose, polyvinyl alcohol, polyvinyl butyral or the like dissolved in an appropriate solvent, or oxidized in this If an inorganic fine particle such as titanium, aluminum oxide, zirconia, or silicon oxide is added to a conductive support so that the film thickness after drying is 0.01 to 50 μm, preferably 0.01 to 10 μm. Good. When a surface protective layer is provided, the film thickness is preferably 0.01 to 20 μm, particularly preferably 0.1 to 10 μm.

Exposure light source;
The electrophotographic photosensitive member according to the present invention is exposed with light having a short wavelength of 380 to 500 nm, particularly 400 to 450 nm. As the light source, a so-called blue laser emitting monochromatic light having this wavelength is preferable, but a blue LED can also be used.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In addition, a part is a weight part.
Example 1
A film obtained by depositing aluminum on a 75 μm thick polyester film is used as a support, and the film thickness after drying the following charge generation layer coating solution is 0.4 g / m 2 (about 0.4 μm). As described above, the film was applied with a wire bar and dried to form a charge generation layer. The following charge transport layer coating solution was applied on this with an applicator and dried at room temperature for 30 minutes and then at 125 ° C. for 20 minutes to produce a photoreceptor having a charge transport layer with a thickness of 25 μm.

Charge generation layer coating solution;
30 parts of 1,2-dimethoxyethane was added to 1.5 parts of the azo compound of the following formula (5), and the mixture was pulverized with a sand grind mill for 8 hours for dispersion treatment. Subsequently, 0.75 parts of polyvinyl butyral (Denka Butyral # 6000C) and 0.75 part of phenoxy resin (Union Carbide, “PKHH”) were added to 28.5 of 1,2-dimethoxyethane. And 13.5 parts of a mixed solution of 1,2-dimethoxyethane and 4-methoxy-4-methylpentanone-2 is finally added. Finally, 1,2-dimethoxy is added. A coating solution having a solid content (pigment + resin) concentration of 4.0% by weight was prepared in a mixed solvent of ethane and 4-methoxy-4-methylpentanone-2 (weight ratio 9: 1).

Charge transport layer coating solution;
In 600 parts of an 8: 2 mixed solvent of tetrahydrofuran and toluene, 35 parts of a charge transfer agent of the following formula (6), 35 parts of a charge transfer agent of the formula (7), and 100 parts of a polycarbonate resin of the formula (8) are added. It melt | dissolved and it was set as the coating liquid.

Comparative Example 1
In Example 1, the following formula (10) is used as a charge generator.

A photoconductor was produced in the same manner as in Example 1 except that the compound shown in FIG.
Comparative Example 2
In Example 1, the following formula (11) is used as a charge generator.

A photoconductor was produced in the same manner as in Example 1 except that the compound shown in FIG.
Comparative Example 3
In Example 1, the following formula (12) is used as a charge generator.

A photoconductor was produced in the same manner as in Example 1 except that the compound shown in FIG.

Evaluation of the electrical properties of the photoreceptor:
Each photoconductor manufactured in Example 1 and Comparative Examples 1 to 3 was wound around an aluminum tube having a diameter of 30 mm and evaluated with an evaluation device for a drum photoconductor.
As an evaluation, the photoconductor was charged to -700 V with a scorotron charger, and white light was passed through 427, 452 and 501 nm interference filters as reference examples under conditions of a temperature of 25 ° C. and a humidity of 50%. Exposure with light, half exposure (Ea1 / 2, exposure necessary to change surface potential from -700V to -350V), 1/5 exposure (Ea1 / 5, surface potential from -700V to -140V) Exposure amount necessary to become), post-exposure potential (VL), and residual potential (Vr). The results are shown in Tables 2-4.

Reference example 1
In Example 1, as a charge transporting layer coating solution, 110 parts of a compound represented by the following formula (13) were added to 600 parts of a 65:35 mixed solvent of tetrahydrofuran and 1,4-dioxane, and the above-described formula (8). A photoconductor was produced in the same manner as in Example 1 except that 100 parts of the polycarbonate resin represented by the formula (1) was dissolved, and the charge transport layer after drying was applied to a thickness of 36 μm.

Comparative Example 4
In Example 1, a photoconductor was produced in the same manner as Example 1 except that the charge generating agent represented by the above formula (12) was used.
Evaluation of the electrical properties of the photoreceptor;
The photoreceptors produced in Reference Example 1 and Comparative Example 4 were wound around an aluminum tube having a diameter of 80 mm, and the chargeability was evaluated as follows using an evaluation apparatus for drum photoreceptors.
The photoconductor was charged to −700 V using a scorotron charger without neutralizing light in an environment of a temperature of 25 ° C. and a humidity of 50%. Next, the charged photoreceptor is exposed using a static elimination light source (white), and the surface potential after the exposure is measured. At this time, in order to prevent the change in charging potential from affecting the potential after exposure, the potential for only one rotation after exposure is measured. This measurement is performed a plurality of times while increasing the amount of light step by step, and the amount of light at which the surface potential after exposure begins to be saturated is obtained. The amount of light 6 times this amount of light was taken as the amount of charge removed for each photoconductor.
Subsequently, the scorotron grid voltage was controlled so that each photoconductor was charged to around −700 V with the respective amount of static elimination in an environment of a temperature of 25 ° C. and a humidity of 50%, and charging conditions were obtained. Subsequently, the charging potential of each photoconductor was measured under the environment of a temperature of 5 ° C. and a humidity of 10%, with the amount of charge removed and the grid voltage obtained in an environment of a temperature of 25 ° C. and a humidity of 50%. The results are shown in Table 5.

As shown in Table 5, the photoreceptor of Comparative Example 4 using the charge generating agent represented by the formula (12) has an environment of temperature 25 ° C. and humidity 50% to environment of temperature 5 ° C. and humidity 10%. In contrast, the charging potential decreases by 90 V, whereas the photoreceptor of Reference Example 1 using the charge generating agent represented by the formula (5) falls within a 50 V charging potential decrease. The decrease in the charging potential is a major factor that causes image fogging when used in the reversal phenomenon, and the small decrease in the charging potential is an important characteristic for the photoreceptor.
As described above, it can be seen that the photoconductor of the present invention is an excellent photoconductor not only having high sensitivity at a short wavelength of about 380 to 500 nm, but also excellent chargeability at low temperatures.

Claims (2)

It has a charge generation layer containing a disazo compound represented by the formula (1) on a support, and has a charge transport layer having a thickness of 10 to 25 μm on the charge generation layer. An electrophotographic photosensitive member for exposure with light having a wavelength of 500 nm.

(In the formula, R represents a cycloalkylalkyl group having 4 to 20 carbon atoms which may have an alkyl group in the ring;

Represents. Ring X may have a substituent. )   2. The electrophotographic photoreceptor according to claim 1, wherein in formula (1), R is a cycloalkylalkyl group having a 5-membered ring or more which may have an alkyl group in the ring.