JPH03211559A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain sufficiently high sensitivity and flatness of spectral sensitivity even in a long wavelength region by specifying an electric charge generating material in an electric charge generating layer and an electric charge transferring material in an electric charge transferring layer. CONSTITUTION:A disazo pigment represented by formula I as an electric charge generating material is incorporated into an electric charge generating layer and a biphenyl compd. represented by formula II as an electric charge transferring material into an electric charge transferring layer. In the formula I, R1 is phenyl, o-tolyl, 2-ethylphenyl, etc., and X is halogen. In the formula II, each of R2 and R3 is alkyl or alkoxy and R4 is alkyl, alkoxy, aralkyl, hydroxyl or halogen. High sensitivity and flat spectral characteristics are ensured in the oscillation wavelength region of a laser diode and stable image characteristics can be obtd. in an electrophotographic process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to an electrophotographic photoreceptor, and more particularly to a laminated electrophotographic photoreceptor having one charge generation layer and a charge transport layer.

[Prior Art] Conventionally, inorganic electrophotographic photoreceptors having a photosensitive layer mainly composed of selenium, acid tetrafluoride, zinc oxide, etc. have been widely used as electrophotographic photoreceptors. These inorganic electrophotographic photoreceptors are not necessarily satisfactory in terms of thermal stability, #A humidity, and durability, and in particular, selenium and cadmium sulfide have limitations in production and handling due to their toxicity.

On the other hand, '4# electrophotographic photoreceptors, which have a photosensitive layer containing an organic photoconductive compound as a main component, have many advantages such as overcoming the above-mentioned disadvantages of inorganic electrophotographic photoreceptors, and have attracted attention in recent years. ing.

Such organic photoreceptors include a photoconductive polymer typified by poly-N-vinylcarbazole and a charge formed from this and a Lewis acid such as 2.4.7-)dinitro-9-2-fluorenone. Electrophotographic photoreceptors having a photosensitive layer containing a transfer complex as a main component have already been put into practical use.

However, this electrophotographic photoreceptor is not necessarily satisfactory in sensitivity and durability.

On the other hand, functionally separated electrophotographic photoreceptors, in which the charge generation function and charge transport function are divided into separate substances, have brought about significant improvements in sensitivity and durability, which had been considered shortcomings of conventional organic electrophotographic photoreceptors. Ta.

Such a functionally separated electrophotographic photoreceptor has the advantage that there is a wide selection range of materials for each of the charge-generating substance and the charge-transporting substance, and it is relatively easy to manufacture an electrophotographic photoreceptor with arbitrary characteristics. have.

In particular, as electrophotographic photoreceptors have come to be used not only in copiers but also in laser beam printers, LED printers, etc. in recent years, functional separation is required to establish a spectral sensitivity range that matches the emission wavelength of the light source used. The type is suitable.

As charge-generating substances, various azo pigments, heptalocyanine pigments, polycyclic bovine non-pigments, cyanine dyes, squaric acid dyes, pyrylium salt dyes, etc. are known.

Among them, many structures have been proposed for azo pigments because of their strong light resistance, large charge generation ability, and ease of material synthesis.

For example, disazo which is similar to the charge generating substance in the present invention!
T4H To L Te JP-A-56-116040, JP-A-57-182747, JP-A-58-49952, JP-A-58-115447, JP-A-59-
Publication No. 72448, Japanese Unexamined Patent Publication No. 155848/1983,
JP-A-58-115445, JP-A-58-115
It is well known and is described in Japanese Patent Application Laid-open No. 446, Japanese Patent Application Laid-open No. 59-7365, and the like.

The azo pigment used here as a charge generating substance is required to (i) be stable against heat and light;
ii) For those that exhibit charge generation ability in a dispersed state, it is easy to measure 1 fraction, and the dispersion liquid shows little change over time;
(iii) ii Charge generation ability does not change with temperature;
C5v) No change in characteristics when used repeatedly; CV) Must have an effective spectral sensitivity range for the light source used.

(vi) The charge transport material is not limited.

Practically speaking, it is most important to satisfy these requirements at a high level on average.

Although some of the above-mentioned known pigments satisfy some of the above requirements, none satisfy all of them to a high level.

Now, as charge transport substances, hydrazone compounds, pyrazoline compounds, stilbene compounds, triarylmethane compounds, arylamine compounds, etc. are known.

These compounds are required to (i) be stable against light and heat, (ii) be stable against ozone, NOx, nitric acid, etc. generated by corona discharge, and (iii) have high Examples include exhibiting charge transport ability and (Iv) high compatibility with organic solvents and binders.

Examples of combinations of the above-mentioned known azo pigments and charge transport substances include 5, for example, JP-A-58-18636;
7-204551, JP 59-44050, JP 59-44051, JP 59-15
7844, JP 60-24549, JP 60-24550, and JP 60-24551.

Examples include the description in JP-A-60-24552.

Although electrophotographic photoreceptors made with these combinations have little potential fluctuation during repeated use, many of them have major drawbacks in image characteristics, such as image deterioration due to changes in the usage environment, which poses problems in actual use. It becomes.

[Problems to be Solved by the Invention] An object of the present invention is to provide an electrophotographic photoreceptor having a charge generation layer and a charge transport layer with sufficient high sensitivity and spectral sensitivity even in a long wavelength range such as the laser diode oscillation wavelength range. To provide an electrophotographic photoreceptor having a flatness of 1, and an electrophotographic annular body whose potential is maintained stably during repeated use, and which exhibits stable potential characteristics and image characteristics regardless of the usage environment (temperature, humidity). Another object of the present invention is to provide an electrophotographic photoreceptor using an azo pigment in which the azo pigment can be easily dispersed and the dispersion liquid has little change over time.

[Means for Solving the Problems 1 Effect] The present invention provides an electrophotographic photoreceptor having a charge generation layer and a charge transport layer on a conductive support, in which the charge generation layer is represented by the following general formula (I) as a charge generation substance. The charge transport layer contains a disazo pigment, and the charge transport layer has the following general formula (II
) is comprised of an electrophotographic photoreceptor characterized by containing a biphenyl compound shown in the following.

(In the formula, R1 is a phenyl group, 0-tolyl group, 2-ethylphenyl group, 2.5-xylyl group, 2.4-xylyl group, 2-methyl-5-nitrophenyl group, 2-methyl-4
- represents a group selected from the group consisting of methoxyphenyl group, 2-ethyl-5-nitrophenyl group, and 2-methyl-5-chlorophenyl group, and X represents a halogen atom,
) General formula (II) (In the formula, R2 and R3 represent an alkyl group or an alkoxy group, and R4 represents an alkyl group, an alkoxy group, an aralkyl group, a hydroxyl group, or a \rogen atom.) More specifically, the above As a group, alkyl groups include methyl, ethyl, propyl, and butyl, alkoxy groups include methoxy, ethoxy, and propoxy, aralkyl groups include benzyl and phenethyl, and halogen atoms include chlorine, bromine, and fluorine atoms. , is an iodine atom.

Typical examples of charge-generating substances and charge-transporting substances used in the present invention are listed below.

Examples of charge generating substances include R1 and X, which are parts that vary in the basic form.
By describing only specific examples.

Exemplary pigment G-(1) R1: one G-(2) R1 knee.

G-(3) R1: Rumor G-(4) R1: Be◇ G-(5) 9) HJ G-(10) G-(11) G-(12) G-(13) G-(14) G-(15) G-(16,) G-(17) G-(18) CH ) G-(19) C)+3-(20) G-(21) G-(22)-(23)-(24) G-(25)-(26)-(27)-(28) One( 29) - (30) G - (31) G - (32) - (33) - (34) l - (35) - (36) H3 Charge transport substance exemplified compound - (1) 1 (2) - (3 ) One (4) - (5) - (6) - (7) - (8) - (9) T-(11) T-(12) - (l 3) One (l 4) T-(15) - (l 6) - (17) - (18) T-(19) T- (20) T-(21) Disazo pigment represented by general formula (I) and biphenyl compound represented by general formula (II) in the present invention The combination of is probably due to the matching of ionization potential or the good steric weight of the charge-generating substance and the charge-transporting substance.
It is considered that since charge is well injected from the charge generating material to the charge transporting material, the sensitivity is good, the residual potential is small, and the potential stability when used for reversing is also excellent.

Next, the electrophotographic photoreceptor of the present invention will be explained in more detail.

The charge generation layer contains as much of the disazo pigment represented by the general formula CI) as possible in order to obtain sufficient absorbance, and is a thin film layer, for example, 5 μm or less, in order to shorten the range of the generated charge carriers. Preferably 0.01-1, pm
It is desirable to form a thin film layer with a thickness of .

The charge generation layer can be formed by dispersing the disazo pigment represented by the general formula (1) in a transparent binder and coating it on a conductive support, or by forming a vapor deposited film using a vacuum vapor deposition device. I can do it.

As a binder used when forming by coating,
One can choose from a wide variety of insulating resins and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene and polyvinylpyrene.

Preferably polyvinyl butyral, polyarylate (condensation polymer of bisphenol A and phthalic acid), polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide, polyamide, polyvinylpyridine, cellulose resin, polyurethane, epoxy Citrus fat, casein, polyvinyl alcohol,
Examples include polyvinylpyrrolidone.

The resin contained in the charge generation layer is preferably 80% by weight or less, preferably 40% by weight or less. The solvent that dissolves these resins varies depending on the type of resin, and does not dissolve the charge transport layer or undercoat layer. It is preferable to select from among the types.

Specifically, alcohols such as methanol, ethanol, and impropatol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and sulfoxides such as dimethyl sulfoxide. kind,
Ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, esters such as methyl acetate, ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, trichloroethylene, or benzene,
Aromatic compounds such as toluene, xylene, ligroin, chlorobenzene, dichlorobenzene, etc. can be used.

As the coating method, a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a Mayer-Per coating method, a blade coating method, a roller coating method, a curtain coating method, and the like can be adopted.

Drying is preferably done by drying to the touch at room temperature and then heating. Drying by heating is performed at a temperature range of 30 to 200°C for 5 minutes or more.
Testing is carried out for 2 hours in a stationary or ventilated environment.

The charge transport layer is electrically connected to the charge generation layer,
It has the function of receiving and taking charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. At this time, the charge transport layer may be laminated on or under the charge generation layer.

The charge transport layer is formed by dissolving the biphenyl compound represented by (II) together with a suitable binder and applying the solution.

Examples of the binder include acrylic resin, polyarylate, polyester, polycarbonate polystyrene,
Acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral,
Examples include insulating resins such as polysulfal formal, polysulfone, polyacrylamide, polyamide, and chlorinated rubber, and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene.

Since the charge transport layer has a limit in its ability to transport charge carriers, it cannot be made thicker than necessary. Generally, the thickness is 5 to 35 gm, but the preferred range is 8 to 30 gm.
It is Lm.

When forming the charge transport layer by coating, any suitable coating method as described above can be employed.

An electrophotographic photoreceptor having such a laminated structure of a charge generation layer and a charge transport layer is provided on a support having a conductive layer.

As the support having electrical conductivity, it is possible to use a material whose support itself is electrically conductive, such as a metal or alloy such as aluminum or aluminum column alloy.

In addition, plastics having a coating film formed by vacuum evaporation of aluminum, aluminum alloy, indium oxide, tin oxide, indium oxide-tin oxide alloy, etc., and conductive particles (e.g. carbon black, silver particles, etc.) may be used as appropriate. Examples include a conductive support in which a plastic material is coated on the metal support together with a binder, a conductive support in which plastic or paper is impregnated with conductive particles, and a plastic containing a conductive polymer.

An undercoat layer having a healer function and an adhesive function can also be provided between the conductive support and the photosensitive layer.

The undercoat layer is casein and polyvinyl alcohol.

Nitrocellulose, ethylene-acrylic acid coformer, polyamide (nylon 6, nylon 66, nylon 6)
10. It can be formed from copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin-melted aluminum, etc.

The thickness of the undercoat layer is 0.1 to 5 gm, preferably 0.5 to 3 gm.
μm is appropriate.

The electrophotographic photoreceptor of the present invention can be used in a laser diode 7' printer to fully utilize its performance, and can also be widely used in electrophotographic applications such as LED printers, a-crystalline printers, and laser engraving.

[Examples] Example 1 An undercoat layer using a 0.1 pm vinyl chloride-maleic anhydride-vinyl acetate copolymer was formed on an aluminum plate.

Next, add 5 g of one example of Kao-zuki G-(26) to cyclohexano
'95 ml of butyral resin (butyralization degree 63
2 g (mol%, number average molecular weight: 20,000) was added to the solution and dispersed in a sand mill for 20 hours.

The film thickness after drying this dispersion was applied to a base plate of 0.4. p
A charge generating layer was formed by applying Mayer per coat to give a thickness of m and drying.

Next, 5 g of exemplified biphenyl compound T-(1) and bisphenol Z-type colicarbonate (viscosity average molecular weight 30,000) were added.
5 g of the solution was dissolved in 70 ml of chlorobenzene, and Mayer Per coating was applied onto the charge generation layer so that the film thickness after drying was 17 m, followed by drying to form a charge transport layer.

The produced electrophotographic photoreceptor is referred to as photoreceptor 1.

Photoreceptor lt-electrostatic copying paper testing device ModelSP-42
-5 by static method using 8 (Using mouthpiece 1! made by Koji),
After corona charging at 5 KV and holding for 1 second in a dark place, the sample was exposed to light using a halogen lamp with an illuminance of 2 lux, and the charging characteristics were measured.

As for charging characteristics, the surface potential (Vo) and the exposure amount (El/6) required to attenuate the potential (VD) to 1/6 when dark decayed for 1 second were measured.

Show the results.

VO Knee 710V v,, Knee 702V El/6: 1.56 iuxesec In addition, remove the photoreceptor l from the -5.6KV corona charger, exposure optical system, developer, transfer charger! It was attached to the cylinder of an electrophotographic copying machine equipped with an exposure optical system and a cleaner, and image characteristics were investigated.

This copying machine is configured to produce an image on transfer paper as a cylinder is driven.

Image evaluation was performed in three environments: 10% humidity, 5°C air temperature, 50% humidity, 18°C air temperature, 80% humidity, and 35°C air temperature.

Good images faithful to the original were obtained in both environments. No blurring or blurring of the image was observed even after the 10,000th copy, indicating that photoreceptor 1 exhibited good image characteristics.

770-800n which is the laser oscillation wavelength range of the photoreceptor 1
It was found that the sensitivity change over m was +1+('/'/Llnm) ΔE-0.97, which was extremely small.

Comparative Examples 1 to 3 Electrophotographic photoreceptors were produced in exactly the same manner as in Example 1, except that the following comparative pigments (1), (2), and (3) described in JP-A-62-147463 were used. . Each,
Comparative photoreceptors 1.2 and 3.

Comparative Pigment (1) Comparative Pigment (2) Comparative Face #(3) In the same manner as in Example 1, the charging characteristics of Comparative Photoreceptors 1.2 and 3 were investigated.

Furthermore, the sensitivity change ΔE from 760 to 800 nm was calculated. Show the results.

(1) 630 609 4.5 0.81
(2) 650 629 4.0 0.77 (
3) From the results of 670 641 7.1 0.62, it was found that the electrophotographic photoreceptor of the present invention exhibits high sensitivity and full spectral sensitivity in the laser diode oscillation wavelength range.

In Example 1, the dark potential (Vo
) is set to -700V, and the light intensity of the laser diode is set so that the bright area potential (VL) is -200V at 760nm, the surface potential at 800nm with the same light intensity is as follows, and the electron of the present invention It can be seen that the photographic photoreceptor exhibits little variation in contrast potential even when the laser oscillation wavelength changes, and is an electrophotographic photoreceptor with extremely excellent image characteristics.

Photoreceptor IVL (800nm): -204V Comparative photoreceptor IVL (800nm): -315V Comparative photoreceptor 2 VL (800nm): -351V Comparative photoreceptor 3 VL (800nm): -450V Examples 2 to 4
3 An electrophotographic photoreceptor was produced in the same manner as in Example 1 by combining the exemplified pigment and the exemplified biphenyl compound, and the exposure iE1/6 was measured.

Then, it was attached to the cylinder of an electrophotographic copying machine equipped with a corona charger, an exposure optical system, a developing device, a transfer charger, a 41t, an exposure optical system, and a cleaner.

This copying machine is configured to produce an image on transfer paper as a cylinder is driven.

Using this copying machine, the initial bright area potential (VL) and dark area potential (Vp) were set to -200v and -700v, respectively, and the amount of variation Δ in the bright area potential and dark area potential after 10,000 times of use.
VL and ΔVO were measured.

Show the results.

Combination composition of exemplified pigment and exemplified biphenyl compound
-Bifnyl 2 2 G-(1) T-(1)
3 3 G-(1) T-(9)4
4 G-(2) T-(1)5
5 G-(2) T-(9) 0 1 2 3 4 5 6 7 8 Engineering 9 0 1 2 3 4 5 0 1 Engineering 2 3 4 5 6 7 8 9 0 1 2 3 4 5 G-(3) G-(4) G-(5) G-(6) G-(6) G-(7) G-(9) G-(10) G-(10) G-(11) G-(11) G-(12) G-(13) G-(14) G-(14) G-(17) G-(17) G-(18) G-(18) G-(19) T-(2) T-(2) T-(15) T-(5) T-(3) T-(6) T-(3) T-(14) T-(9) T-(1) T-(11) T-(12) T-(13) T-(1) T-(15) T-(1) T-(16) T-(2) T-(3) T-(6) 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 9 0 G-(19) G-(20) G-(21) G-(22 ) G-(23) G-(25) G-(25) G-(26) G-(26) G-(27) G-(27) G-(28) G-(29) G-(30 ) G-(30) G-(31) G-(33) G-(35) T-(9) T-(11) T-(4) T-(17) T-(18) T-(19 ) T-(1) T-(2) T-(19) T-(4) T-(20) T-(21) T-(13) T-(5) T-(15) T-(14 ) T-(16) T-(6) 0 1 2 3 4 5 6 7 8 9 0 1 i, si 1 , 81 1 , 61 2 , 41 1 , 60 1 , 51 1 , 95 1.70 2, 10 2 , 05 2 , l 9 1 , 71 2 , 41 1 , 69 2 , 49 2 , 00 2 , 10 1.60 1.90 1 , 75 4 14 7 11 6 7 20 4 = 14 16 17 9 12 8 13 15 16 11 = 6 3 ~ 11 2 12 7 4 11 7 14 15 11 8 19 6 18 17 14 5 14 5 2 23 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 E, 90 1.80 2 , 24 2 , 00 2 , 10 2 , 49 1 , 69 1 , 95 1 , 99 2 , 75 1 , 60 1 , 70 2 , 49 1 , 81 2 , 70 2 , 80 2 , 89 1 , 64 1 , 96 1 , 60 18 4 15 15 14 16 2 17 10 10 4 7 16 6 15 13 14 7 = 14 11 14 6 18 18 10 11 = 1 18 17 16 9 7 17 4 14 14 17 6 18 18 42 2.01 -19 -174
3 1.98 -5 -2
Comparative Examples 4 to 6 ΔVD and ΔVL were measured in the same manner as in Example 2 using comparative photoreceptors 1, 2, and 3. Show the results.

4 1 -51
-405 2 -39
-156 3 -31
-21 From the above results, the electrophotographic photoreceptor of the present invention.

It can be seen that the fluctuation in potential during repeated use is small.

Comparative Examples 7 to 11 In place of the biphenyl compound in Example 1.

Compounds H-(1), H-(2), H-(3
), H-(4), and H-(5) were used as the charge transport materials, electrophotographic photoreceptors were produced in exactly the same manner as in Example 1, and comparative photoreceptors 4, 5.6, and 5.6 were produced, respectively. .7
and 8, and the charging characteristics were measured.

Further, the amount of potential fluctuation was measured in exactly the same manner as in Example 2.

Show the results.

H-(1) H-(2) - (3) - (4) H-(5) 98 30 00 92 99 57 87 80 54 71 2.5 2.7 4.8 2.9 3, 8 Power Δv v ΔVL V7
4 -38 -358
5 -28 +IO
96-10-85 107-35+20 11 8 -50 -
69 Comparative Examples 12 to 25 The above charge transport materials H-(1), H-(2), H-(3)
, H-(4), H-(5) and Example 6゜9.15.35
．． Comparative photoreceptors 9 to 22 were manufactured in the same manner as in Example 1 by combining the charge generating substances used in Example 41 as shown below, and the charging characteristics and potential fluctuation amount were measured. Show the results.

Wei 12 9 G-(3) H-(1) 13
10 G-(3) H-(3)14 11
G-(3) H-(5) 15 12
G-(6) H-(2)16 13' G-
(6) H-(4) 17 14 G-(6)
H-(5) 8 19 0 1 2 3 4 5 5 Engineering 6 7 8 9 0 1 2 G-(l 1) G-(11) G-(11) G-(27) G-(27) G- (27) G-(31) G-(31) H-(2) H-(3) H-(4) H-(1) H-(3) H-(5) H-(2) H- (3) 2 3 4 5 6 7 8 9 0 1 2 2 , 4 4 , 7 4.0 2 , 4 2.1 3 , 4 2.5 3.7 2.0 2.5 3 , 8 49 = 78 40 34 40 70 42 49 37 60 61 9 -104 80 +30 +IO 81 +15 84 +15 50 0 23 4.0 -54 -7024
2.5 -60 +4025
3.9 -34 -98 From the above results, the electrophotographic photoreceptor of the present invention.

It can be seen that the sensitivity and repeatability are excellent.

Actual Noodle Examples 44-48 Photoreceptor 6,719.21 which is an electrophotographic photoreceptor of the present invention
and 35 were exposed to 120 ppm ozone for 30 minutes and further exposed to aoppm HNO3 gas for 1 hour, and then the charging characteristics were measured in exactly the same manner as in the experiment. Show the results.

44 6 704 699 1.71
45 7 700 694 1.79
46 19 709 700 1.58
47 21 701 681 1.514
8 35 710 700 1.81 Comparative Examples 26 to 30 Charging characteristics were measured in the same manner as in Example 44 using Comparative Photoreceptors 3.10.12.21 and 23. Show the results.

26 3 640 530 3.
627 10 610 560 3.1
28 12 600 550 4.92
9 21 610 500 4.73
0 23 640 570 4.4 From the above results, the electrophotographic photoreceptor of the present invention.

It is found that the photoreceptor is extremely stable against oxidizing substances caused by corona charging, such as ozone and nitric acid.

[Effects of the Invention] The electrophotographic photoreceptor of the present invention is produced by combining a specific charge-generating substance and a specific charge-transporting substance.

It has the remarkable effects of: (1) high sensitivity and flat spectral characteristics in the oscillation wavelength range of a laser diode, (2) stable image characteristics in the electrophotographic process, and (2) excellent potential stability.

Claims (1)

[Scope of Claims] 1. In an electrophotographic photoreceptor having a charge generation layer and a charge transport layer on a conductive support, the charge generation layer contains at least one disazo pigment represented by the following general formula (I) as a charge generation substance. 1. An electrophotographic photoreceptor comprising a layer containing at least one biphenyl compound represented by the following general formula (II) as a charge transporting substance. General formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_1 is a phenyl group, o-tolyl group, 2-ethylphenyl group, 2,5-xylyl group, 2,4-xylyl group, 2 -Methyl-5-nitrophenyl group, 2-methyl-
It represents a group selected from the group consisting of 4-methoxyphenyl group, 2-ethyl-5-nitrophenyl group and 2-methyl-5-chlorophenyl group, and X represents a halogen atom. ) General formula (II) ▲There are numerical formulas, chemical formulas, tables, etc.▼ (In the formula, R_2 and R_3 represent an alkyl group or an alkoxy group, and R_4 represents an alkyl group, an alkoxy group, an aralkyl group, a hydroxyl group, or a halogen atom. ) 2. The charge transport layer has the following general formula (III
2. The electrophotographic photoreceptor according to claim 1, comprising a layer containing at least one of the biphenyl compounds represented by the following. General formula (III) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_5, R_6 and R_7 represent an alkyl group or an alkoxy group.)