JP2564875B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic photoreceptor.

(Prior Art) Conventionally, an inorganic photoconductive substance such as selenium, zinc oxide, titanium oxide, or cadmium oxide has been mainly used in an electrophotographic material using a photoconductive substance as a photosensitive material. However, many of them are generally highly toxic, and there is a problem in the method of disposal.

On the other hand, a photosensitive material using an organic photoconductive compound is generally less toxic than a material using an inorganic photoconductive substance, and is further transparent, flexible, lightweight, surface smooth,
Since it is advantageous in terms of price, it has been widely researched recently. Among them, the function-separated type electrophotographic photoconductor in which the charge generation function (charge generation layer) and the charge transport function (charge transport layer) are separated is a major drawback of the photoconductors using the organic photoconductive compound. Since the sensitivity can be greatly improved, rapid progress has been made in recent years.

As a method for improving the sensitivity of the photoreceptor, “Chemicals and Industry”, No. 34, Volume 7, pages 489 to 492 (1981) and IEEE IA-17, No.
As described in 4,382 to 386 (1981), in the case of a negative charging type photoreceptor, the ionization potential (Ip _CGL ) of the charge generation layer and the ionization potential (Ip _CGL ) of the charge transport layer are described.
_When the relation of _CTL ) is Ip _CGL > Ip _CTL , the function as a photoreceptor is expressed, and the ionization potential (I
It is described that the smaller the _p'CTL ), the higher the sensitivity.

Further, in Japanese Patent Application Laid-Open No. 60-207142, the ionization potential of the charge transport material is determined by polarographic measurement, and from the obtained ionization potential (Ip), the sensitivity can be improved by using a charge transport material having a specific ionization potential. Is described as being improved.

The ionization potential (Ip ′ _CTL ) in each of the above-mentioned references was measured by dissolving the charge transport material in an appropriate solvent, and the state in which the charge transport material was contained in the binder resin The ionization potential of the charge transport agent in the presence of the charge transport material in the binder resin matrix-ie, interaction with the matrix, has not been measured. Also, the ionization potential of organic pigments that generate charge has not been actually measured.

(Problems to be Solved by the Invention) However, an electrophotographic photoreceptor using an organic photoconductive substance as a photosensitive material is generally an organic pigment (azo pigment, phthalocyanine pigment, indigo pigment, perylene pigment) that generates an electric charge. Pigments) and charge transporting substances (oxazole compounds, hydrazone compounds, butadiene compounds, styryl compounds, carbazole compounds), binder resin solutions (polyester resins, polyvinyl butyral resins, acrylic resins, silicone resins, etc.) Solution), or by coating and drying these on a conductive substrate, that is, mainly in the binder matrix under the interaction with the binder resin. Ionization of organic pigments and charge transport agents that generate electric charges (some interactions due to other additives) Therefore, in order to improve the sensitivity, the ionization potential of the charge generation layer and the charge transport layer itself in the mode in which the electrophotographic photoreceptor is actually used is clarified in order to improve the sensitivity.
Furthermore, the optimum combination should be found, but there is no suggestion of these in the literature.

An object of the present invention is to provide an excellent electrophotographic photoreceptor having an optimum combination of ionization potentials of a charge generation layer and a charge transport layer.

(Means for Solving the Problems) The present inventors have a charge generation layer containing a charge-generating organic pigment and a charge transport layer containing a charge-transporting substance on a conductive substrate. Ionization Potential of Ip
Difference between ionization potential Ip _CGL of _CTL and charge transport layer (Ip
It was found that an electrophotographic photoreceptor having excellent characteristics can be obtained by setting _CTL- Ip _CGL ) within a specific range, and the present invention has been completed.

That is, the present invention has a charge generation layer containing a metal-free phthalocyanine as an organic pigment for generating a charge and a charge transport layer containing a charge transport material on a conductive substrate, and the ionization potential Ip _CTL of the charge transport layer is provided. And the difference in ionization potential Ip _CGL of the charge generation layer (Ip _CTL −Ip _CGL ) is +
The present invention relates to an electrophotographic photosensitive member which is 0.14 to 0.26 eV.

The ionization potential in the present invention can be measured by the following method.

After forming the charge generation layer or the charge transport layer on the conductive substrate, the light emitted from the ultraviolet lamp is dispersed into these samples by a monochromator to an arbitrary wavelength of 200 to 360 nm, and the sample surface is irradiated with the light. Light of 200-360nm is E = hν
== h (c / λ), the energy conversion is 6.2 ~
It will be 3.4 eV. When this light is swept from the lower excitation energy toward the higher excitation energy, electron emission due to the photoelectric effect begins at a certain energy. This energy is called a photoelectrical ionization potential, and this value is referred to as an ionization potential in the present invention.

Such a measurement can be suitably performed using, for example, a surface analyzer (for example, AC-1 type, trade name, manufactured by Riken Keiki Co., Ltd.). (Reference, "Electronic Materials" November issue, pages 125-128 (1
985)). This method has the advantage of being able to directly measure the ionization potential of the entire layer, as compared to conventional polarographic measurements.

According to this method, in the case of a charge transporting substance or an organic pigment that generates a charge alone, the ionization potential of the organic pigment that generates a charge is the same as that obtained by polarography. However, the ion transport potential of the charge transport layer is generally larger than that of the actual layer containing the binder. Although the details of this reason are not clear, the actual ionization potential of each layer varies depending on the type and content of the binder, and therefore the actual ionization potential of each layer is different from the organic pigments that generate charge and charge transport. It can be seen that not only the ionization potential of the volatile substance alone, but also the binding agent has a complexly involved value. In any case, comparing the ionization potentials as layers, the charge transport layer is larger than that of the charge generation layer, and if the difference is 0.14 to 0.26 eV, the charge transport layer and charge generation layer are combined. The inventors have found that the sensitivity of electrophotographic characteristics is good and have reached the present invention.

In order to obtain the charge transport layer and the charge generation layer which are combined as described above, it is possible to appropriately select the type and the amount of the organic pigment, the charge transport agent and the binder which generate the charge.

Next, the electrophotographic photosensitive member according to the present invention will be described in detail.

First, in the present invention, the conductive substrate is a conductor such as paper or plastic film that has been subjected to conductive processing, a plastic film in which a metal foil such as aluminum is laminated, a metal plate, a metal drum, or the like.

In the present invention, the charge generation layer contains an organic pigment that generates a charge. Organic pigments that generate electric charge include azoxybenzene, disazo, trisazo, benzimidazole, polycyclic quinone, indigoid, quinacridone, perylene, methine and α type, β type,
Pigments that are already known to generate an electric charge, such as metal-free or metal-type phthalocyanine-based pigments having various crystal structures such as γ-type, δ-type, ε-type and X-type, can be used. These pigments are disclosed, for example, in JP-A-47-37543 and JP-A-47-375.
44, JP-A-47-18543, JP-A-47-18544, and JP-A-47-18544
48-43942, JP-A-48-70538, JP-A-49-1231,
JP-A-49-105536, JP-A-50-75214, JP-A-53-4
No. 4028, JP-A No. 54-17732, and the like.

In particular, Japanese Patent Laid-Open No. 58-182640 and European Patent Application Publication No.
The γ, γ ′, η and η ′ type metal-free phthalocyanines described in 92255 are suitable. In addition to these, any organic pigment that generates a charge carrier by light irradiation can be used. However, in the present invention, metal-free phthalocyanine is always used as the organic pigment.

In the present invention, two or more kinds of charge-generating organic pigments contained in the charge generation layer may be mixed and used.

If the concentration of the organic pigment generating charges in the charge generation layer is too low, the sensitivity tends to decrease and the residual potential tends to increase, and it is preferably 30 to 100% by weight.

Further, the charge generation layer may contain additives such as a binder and / or a plasticizer, a fluidity imparting agent, and a pinhole inhibitor, which are commonly used in electrophotographic photoreceptors. As the binder, silicone resin, polyamide resin, polyurethane resin, polyester resin, epoxy resin, polycarbonate resin, polystyrene resin, polymethylmethacrylate resin, polyacrylamide resin, polybutadiene resin, polyisoprene resin, melamine resin, ethylcellulose resin, nitro Cellulose resin, polychloroprene resin, vinyl acetate resin, polyacrylonitrile resin, urea resin and the like can be mentioned. Also, heat and / or light curable resins can be used. In any case, there is no particular limitation as long as it is an electrically insulating resin that can form a film in a normal state. The binder is used in the charge generation layer in an amount of 300 parts by weight or less based on 100 parts by weight of the charge-generating organic pigment.
If it exceeds 300 parts by weight, the electrophotographic properties will deteriorate.

Examples of the plasticizer include halogenated paraffin, dimethylnaphthalene, dibutyl phthalate and the like. Examples of the fluidity-imparting agent include Modaflow (manufactured by Monsanto Chemical Co., Ltd.) and Acronal 4F (manufactured by Basuf Co.). Examples of the pinhole inhibitor include benzoin and dimethyl phthalate. Each of these additives is preferably used in an amount of 5% by weight or less based on the organic pigment generating the electric charge.

As a method for forming the charge generation layer, when only the above-mentioned organic pigment is used, it can be carried out by vacuum deposition, and the charge-generating organic pigment, the binder and other additives are added to acetone, methyl ethyl ketone, tetrahydrofuran, toluene. , Xylene, methanol, methylene chloride, isopropyl alcohol, isobutyl alcohol, n-butyl alcohol, trichloroethane, etc. after being uniformly dissolved or dispersed, this solution is applied onto the conductive substrate by dip coating, spray coating, roll coating. It can also be formed by coating using a coating method such as a coating method, an applicator coating method, or a wire bar coating method, and drying.

The thickness of the charge generation layer is preferably 0.001 to 10 μm, and particularly preferably 0.01 to 5 μm. 0.001 μm
If it is less than 10 μm, it becomes difficult to uniformly form the charge generation layer, and if it exceeds 10 μm, the electrophotographic properties tend to deteriorate.

The charge transport layer contains a charge transport material. Examples of the charge transport material include poly-N-vinylcarbazole,
Polymer compounds such as polyvinylpyrene and polyvinylpyrazoline, carbazole, 3-phenylcarbazole, 2-phenylindole, oxadiazole, 1-phenyl-3-
(4-Diethylaminostyryl) -5- (4-diethylaminophenyl) pyrazolin, hydrazone, butadiene, enamine, 2-phenyl-4- (4-diethylaminophenyl) -5-phenyloxazole, triphenylamine, imidazole, etc. Low molecular weight compounds and derivatives thereof.

If necessary, the charge transport layer may contain the same binders and additives as those used in the charge generation layer, such as a plasticizer, a fluidity imparting agent and a pinhole inhibitor. The binder is
To 100 parts by weight of the charge transporting substance, 400 parts by weight or less is preferable so that the electrophotographic properties are not deteriorated. On the other hand, it is preferable to use 50 parts by weight or more of the binder. Each of the other additives is preferably used in an amount of 5% by weight or less based on the charge transporting substance.

The thickness of the charge transport layer is preferably 5 to 50 μm,
It is particularly preferably 8 to 20 μm. Further, if the thickness of the charge transport layer is less than 5 μm, the charging property tends to be poor, and if it exceeds 50 μm, the sensitivity tends to decrease.

To form the charge transport layer, a coating solution prepared by uniformly dissolving or dispersing the charge transporting substance or the like constituting the charge transport layer in the above-mentioned solvent is applied on the charge generating layer and dried. It can be carried out.

The electrophotographic photoreceptor according to the present invention may have a conventionally known protective layer on its surface. The electrophotographic photosensitive member according to the present invention may further have an undercoat layer, an adhesive layer and / or a barrier layer between the conductive substrate and the charge generation layer.

(Examples) Next, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

The materials used in the following examples are listed below. Abbreviations are shown in parentheses.

(1) Organic pigment that generates electric charge γ-type metal-free phthalocyanine (γ-H ₂ Pc) (2) Charge-transporting substance (3) Binder (A) Binder for charge generation layer Silicone varnish: trade name KR214 (KR214) (70 wt% solids) [Shin-Etsu Chemical Co., Ltd.] (B) Binder for charge transport layer Polycarbonate resin: Product name Iupilon S-3000 (UP
3000) (solid content 100% by weight) [Mitsubishi Gas Chemical Co., Inc.] Example 1 γ-H ₂ Pc 0.5 g, KR214 0.5 g and tetrahydrofuran 70
g was kneaded using a ball mill (3 inch pot mill manufactured by Nippon Kagaku Sangyo) for 8 hours. An aluminum plate (thickness 0.1 m
m) and then dried at 100 ° C. for 30 minutes to form a charge generation layer having a thickness of 0.5 μm.

Next, the ionization potential Ip _CGL of this charge generation layer
Ip _CGL was 5.20 eV when measured using a surface analyzer (trade name AC-1 type Riken Keiki Co., Ltd.).

Next, 6 g of BUT and 14 g of UP3000 were mixed in 80 g of a 1: 1 mixed solvent of 1,1,2-trichloroethane and methylene chloride and completely dissolved. The resulting solution was applied onto the charge generation layer with an applicator and dried at 120 ° C. for 30 minutes to form a 15 μm charge transport layer.

The solution used to form the charge transport layer above was coated on an aluminum plate (thickness 0.1 mm) with an applicator and the temperature was 120 ° C.
And dried for 30 minutes to form a 15 μm charge transport layer. The ionization potential Ip _CTL of this charge transport layer was determined by using the same surface analyzer as above, and the Ip _CTL was 5.40 eV.

Atsuta in accordance connexion _{Ip CTL -Ip CGL = 5.40-5.20 = 0.20eV} .

Example 2 Ip _CGL 5.20e was formed on an aluminum plate in the same manner as in Example 1.
A V charge generation layer was formed.

Next, a charge transport layer of Ip _CTL 5.36 eV was formed on the above charge generation layer in the same manner as in Example 1 except that 5 g of ENM and 15 g of UP3000 were used.

In this electrophotographic photosensitive member, Ip _CTL −Ip _CGL is 5.36−
It was 5.20 = 0.16 eV.

Example 3 Ip _CGL 5.20e was formed on an aluminum plate in the same manner as in Example 1.
A V charge generation layer was formed.

Next, a charge transport layer of Ip _CTL 5.42 eV was formed on the above charge generation layer in the same manner as in Example 1 except that BUT 4 g, OXZ-12 g and UP3000 14 g were used.

In this electrophotographic photoreceptor, Ip _CTL −Ip _CGL is 5.42−
It was 5.20 = 0.22 eV.

Example 4 Ip _CGL 5.20e was formed on an aluminum plate in the same manner as in Example 1.
A V charge generation layer was formed.

Next, a charge transport layer of Ip _CTL 5.46 eV was formed on the charge generation layer in the same manner as in Example 1 except that BUT 4 g, HDZ-22 g and UP3000 14 g were used.

In this electrophotographic photosensitive member, Ip _CTL −Ip _CGL is 5.46−
It was 5.20 = 0.26 eV.

Example 5 Ip _CGL 5.20e was formed on an aluminum plate in the same manner as in Example 1.
A V charge generation layer was formed.

Next, a charge transport layer of Ip _CTL 5.43 eV was formed on the charge generation layer in the same manner as in Example 1 except that BUT 6 g, HDZ-12 g and UP3000 12 g were used.

In this electrophotographic photoreceptor, Ip _CTL −Ip _CGL is 5.43−
It was 5.20 = 0.23 eV.

Comparative Example 1 The same charge generation layer of Ip _CGL 5.20 eV as in Example 1 was formed on the same conductive substrate (aluminum plate) as in Example 1.

Next, 8 g of HDZ-1 and 12 g of UP3000 were mixed in 80 g of a 1: 1 mixed solvent of 1,1,2-trichloroethane and methylene chloride and completely dissolved. The obtained solution was applied on the charge generation layer with an applicator and dried at 100 ° C for 30 minutes.
A 15 μm charge transport layer was formed.

The above solution was applied on an aluminum plate (thickness 0.1 mm) with an applicator and dried at 100 ° C. for 30 minutes to form a 15 μm charge transport layer. The ionization potential Ip _CTL of this charge transport layer was determined using a surface analyzer.
_{The CTL} was 5.25 eV.

Accordance connexion, Atsuta in _{Ip CTL -Ip CGL = 5.25-5.20 = 0.05eV} .

Comparative Example 2 Ip _CTL 5.24eV was prepared in the same manner as in Example 1 except that the same charge generation layer was formed on the same conductive substrate as in Example 1 and OXZ-2 8g and UP3000 12g were used. A charge transport layer was formed on the charge generating layer.

In this electrophotographic photosensitive member, Ip _CTL −Ip _CGL is 5.24−
It was 5.20 = 0.04 eV.

Comparative Example 3 Same as Example 1 except that exactly the same charge generation layer was formed on the same conductive substrate as in Example 1, 5 g of HDZ-2 and 15 g of UP3000 were used and the drying temperature was 90 ° C. Then, a charge transport layer of Ip _CTL 5.54 eV was formed on the charge generation layer.

In this electrophotographic photoreceptor, Ip _CTL −Ip _CGL is 5.54−
5.20 = 0.34 eV Comparative Example 4 Same as Comparative Example 1 except that exactly the same charge generation layer was formed on the same conductive substrate as in Example 1 and HDZ-1 5g and UP3000 15g were used. Then, a charge transport layer of Ip _CTL 5.58 eV was formed on the charge generation layer.

In this electrophotographic photoreceptor, Ip _CTL −Ip _CGL is 5.58−
It was 5.20 = 0.38 eV.

Comparative Example 5 The same charge generation layer was formed on the same conductive substrate as in Example 1, and OXZ-1 5g and UP3000 15g were used.
I was prepared in the same manner as in Example 1 except that the drying temperature was 115 ° C.
A charge transport layer of p _CTL 5.48 eV was formed on the charge generating layer.

In this electrophotographic photosensitive member, Ip _CTL −Ip _CGL is 5.48−
It was 5.20 = 0.28 eV.

Example 6 γ-H ₂ Pc 0.4 g, KR214 0.6 g and tetrahydrofuran 70
g was kneaded in the same manner as in Example 1 using a ball mill for 8 hours. The obtained pigment dispersion was applied onto an aluminum plate as a conductive substrate with an applicator and dried at 100 ° C. for 30 minutes to form a charge generation layer having a film thickness of 0.5 μm. The Ip _CGL of this charge generation layer was 5.22 eV.

Next, on this charge generation layer, Ip having the same composition as in Example 1 was formed.
A charge transport layer of _CTL 5.40 eV was formed.

In this electrophotographic photoreceptor, Ip _CTL -Ip _CGL = 5.40-5.
It was 22 = 0.18 eV.

Example 7 γ-H ₂ Pc 0.7 g, KR214 0.3 g and tetrahydrofuran 70
g was kneaded in the same manner as in Example 1 using a ball mill for 8 hours. The obtained pigment dispersion was applied onto an aluminum plate as a conductive substrate with an applicator and dried at 100 ° C. for 30 minutes to form a charge generation layer having a film thickness of 0.5 μm. The Ip _CGL of this charge generation layer was 5.13 eV.

Next, on this charge generation layer, Ip having the same composition as in Example 2 was formed.
A charge transport layer of _CTL 5.36 eV was formed.

In this electrophotographic photosensitive member, Ip _CTL -Ip _CGL = 5.36-5.
It was 13 = 0.23 eV.

Comparative Example 6 γ-H ₂ Pc 0.15 g, KR214 0.85 g and tetrahydrofuran
70 g was kneaded in the same manner as in Example 1 using a ball mill for 8 hours. The pigment dispersion obtained is applied onto an aluminum plate, which is a conductive substrate, with an applicator and the temperature is maintained at 100 ° C for 30
After drying for a minute, a charge generation layer having a thickness of 0.5 μm was formed. The Ip _CGL of this charge generation layer was 5.42 eV.

Next, on this charge generation layer, an Ip having the same composition as in Example 4 was formed.
A charge transport layer of _CTL 5.46 eV was formed.

In this electrophotographic photosensitive member, Ip _CTL -Ip _CGL = 5.45-5.
It was 42 = 0.03 eV.

Comparative Example 7 γ-H ₂ Pc 0.4 g, KR214 0.6 g and tetrahydrofuran 70
g was kneaded in the same manner as in Example 1 using a ball mill for 8 hours. The obtained pigment dispersion was applied onto an aluminum plate as a conductive substrate with an applicator and dried at 100 ° C. for 30 minutes to form a charge generation layer having a film thickness of 0.5 μm. The Ip _CGL of this charge generation layer was 5.22 eV.

Next, on this charge generation layer, Ip having the same composition as in Comparative Example 4 was formed.
A charge transport layer of _CTL 5.58 eV was formed.

In this electrophotographic photoreceptor, Ip _CTL -Ip _CGL = 5.58-5.
It was 22 = 0.36 eV.

An electrostatic recording test device (SP-42 manufactured by Kawaguchi Denki Co., Ltd.) was used to measure the spectral sensitivity of the electrophotographic photoreceptors obtained in Examples 1 to 7 and Comparative Examples 1 to 7.
8) was used. The results are shown in Table 1.

The spectral sensitivity (S780) of 780 nm is obtained by irradiating a monochromatic light of 780 nm through a monochromator with a halogen lamp as the light source, and irradiating the light with a potential of half after the irradiation, t (s), The energy of the irradiation light (mW
/ m ² ).

FIG. 1 shows the relationship between the spectral sensitivity and the difference (ΔIp) between the ionization potential of the charge generation layer and the ionization potential of the charge transport layer.

As is clear from FIG. 1, the electrophotographic photosensitive member having ΔIp of 0.14 to 0.26 exhibits excellent sensitivity.

(Effects of the Invention) According to the present invention, the optimum combination of ionization potentials of the charge generation layer and the charge transport layer can be easily selected, so that an electrophotographic photoreceptor having high sensitivity can be easily obtained.

[Brief description of drawings]

FIG. 1 is a relationship diagram of the spectral sensitivity (S780 (mJ / m ² )) and the difference ΔIp (eV) (Ip _CTL −Ip _CGL ) between the ionization potential of the charge generation layer and the ionization potential of the charge transport layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Kageyama Akira Kageyama 4-13-1, Higashimachi, Hitachi City, Ibaraki Hitachi Chemical Co., Ltd. Yamazaki Factory (72) Inventor Takayuki Akimoto 4-13-1, Higashimachi, Ibaraki Prefecture Issue Hitachi Chemical Co., Ltd. Ibaraki Research Laboratory (72) Inventor Shigeo Tachiki 4-13-1, Higashimachi, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Ibaraki Research Laboratory (56) Reference JP-A-60-19153 (JP, A) ) JP-A-60-237454 (JP, A) JP-A-58-182639 (JP, A) JP-A-60-19144 (JP, A) JP-A-61-34547 (JP, A)

Claims (1)

(57) [Claims] 1. A charge generating layer containing a metal-free phthalocyanine as an organic pigment for generating a charge and a charge transporting layer containing a charge transporting substance on a conductive substrate, and an ionization potential Ip _CTL of the charge transporting layer. The difference in the ionization potential Ip _CGL of the charge generation layer (Ip _CTL −Ip _CGL ) is +0.14 to
An electrophotographic photoreceptor of 0.26 eV.