JPH01219752A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To select an optimum combination of ionization potential easily, and to obtain a photosensitive body having high sensitivity easily by providing a charge generating layer contg. an org. dye for generating a charge and a charge transfer layer contg. a charge transfer material onto an electroconductive substrate of an electrophotographic sensitive body, and regulating a difference between an ionization potential of the charge transfer layer and that of the charge generating layer. CONSTITUTION:A charge generating layer contg. a charge generating org. dye and a charge transfer layer contg. a charge transfer material are formed on an electroconductive substrate of an electrophotographic sensitive body. A difference IpCTL-IpCGL between an ionization potential IpCTL of the charge transfer layer and an ionization potential IpCGL of the charge generating layer is regulated to +0.14-0.26eV. A nonmetallophthalocyanine is used as the org. dye generating an electric charge. Thus, the sensitivity of a sensitive body is enhanced by combining easily and optimally the ionization potential of the charge generating layer and that of the charge transfer layer.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electrophotographic photoreceptor.

(Prior Art) Conventionally, inorganic photoconductive substances such as selenium, zinc oxide, titanium oxide, and cadmium oxide have been mainly used in electrophotographic materials that utilize photoconductive substances as photosensitive materials. However, many of these are highly toxic,
There are also problems with the method of disposal.

On the other hand, photosensitive materials that use organic photoconductive compounds are generally less toxic than those that use inorganic photoconductive substances, and are also characterized by transparency, flexibility, light weight, surface smoothness, and price. Recently, it has been widely studied because of its advantages in terms of the following points. Among them, functionally separated electrophotographic photoreceptors, which separate the charge generation function (charge generation layer) and the charge transport function (charge transport/?5), are conventional photoreceptors that use organic photoconductive compounds. Rapid progress has been made in recent years because sensitivity, which had been a major drawback, can be greatly improved.

Methods for improving the sensitivity of photoreceptors include "Chemistry and Industry", No. 34, Vol. 7, pp. 489-492 (1981) and I
EEE IA-17, Nα4゜382-386 (1
981), in the case of a negatively charged photoreceptor, the ionization potential of the charge generation layer (Ip.
IL) and the ionization potential of the charge transport layer (IpoT
When the relationship (L) is IpOGL>■pOTL, it functions as a photoreceptor.

Ionization potential of charge transport material (I I)'OT
It is stated that the smaller L ) is, the better the sensitivity is.

Also, in JP-A No. 60-207142.

The ionization potential of the charge transport material is determined by polarographic measurement, and the obtained ionization potential (
Ip) describes that sensitivity can be improved by using gold as a charge transporting material with a special ionization potential.

In all of the above-mentioned documents, the ionization potential (Ip'o, rL) iL is measured by dissolving the charge transporting material in a suitable solvent, and the charge transporting material is 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 - that is, the ionization potential of the charge transport material under interaction with the matrix is not measured. Furthermore, the ionization potential of organic pigments that generate charges has not actually been measured.

(Problem to be Solved by the Invention) However, electrophotographic photoreceptors that use organic photoconductive substances as photosensitive materials generally use charge-generating organic pigments (azo pigments, phthalocyanine pigments, indigo pigments, perylene pigments, etc.). Pigments, etc.) and charge transporting substances (oxazole compounds, hydrazone compounds, butadiene compounds, styryl compounds, carbazole compounds) are mixed with binder resin solutions (polyester resins, polyvinyl butyral resins, acrylic resins, silicone resins, etc.). It is formed by dispersing or dissolving it in a solution of binder resin), coating it on a conductive substrate, and drying it.
This is because there is an ionization potential of organic pigments and charge transport agents that generate charges due to some interaction with other additives, etc.

In order to improve the sensitivity, it is necessary to clarify the ionization potential of the charge generation layer and the charge transport layer themselves in the mode in which the electrophotographic photoreceptor is actually used, and furthermore, to find the optimal combination thereof. does not suggest anything about these matters.

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

(Means for Solving the Problems) The present inventors have provided a charge generation layer containing an organic pigment that generates a charge and a charge transport layer containing a charge transport substance on a conductive substrate, and the charge generation layer The ionization potential IP of
Ionization potential IpooL of OTL and charge transport layer
The present inventors have discovered that an electrophotographic photoreceptor with excellent characteristics can be obtained by setting the difference (IpoTh - Poob) within a specific range, and have accomplished the present invention.

That is, in the present invention, a charge is generated on a conductive substrate, and the difference in the tension I'OGL (p.TL - p.oL) is +
It relates to an electrophotographic photoreceptor having a voltage of 0.14 to 0.26 eV.

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

After forming a charge generation layer or a charge transport layer on a conductive substrate, the six elements emitted from an ultraviolet lamp are dispersed into arbitrary wavelengths from 200 to 360 nm using a monochromator and irradiated onto the sample surface. . 200~360n
The light of m is converted into energy using the formula E=hν=h(C/λ).

It becomes 6.2 to 3.4 eV. When this light is swept from low to high excitation energy, electron emission begins at a certain energy level due to the photoelectric effect. This energy is called a photoelectric ionization potential. In the present invention, this lii is defined as an ionization potential.

Such measurements can be suitably carried out using, for example, a surface analyzer (for example, model AC-1, manufactured by Riken Keiki). (Reference, "Electronic Materials" November issue, 125-128
(1985)). This method has the advantage of being able to directly measure the ionization potential of the entire layer compared to measurements using conventional polarography.

Also, 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 higher than the ionization potential of the charge-transporting substance, as in the case determined by polarography. Although larger than.

When compared with the state of the actual layer to which a binder is added, the charge transport layer generally has a larger ionization potential. The details of this reason are not clear.

Since the ionization potential of the entire layer changes depending on the type and content of the binder, the actual ionization potential of each layer is not the individual ionization potential of the organic pigment or charge transporting substance that generates a charge. It can be seen that the value of the binder is also involved in a complex manner. In any case, when comparing the ionization potential of the layers, the charge transport layer is larger than that of the charge generation layer.

Furthermore, the present inventors have discovered that the sensitivity of electrophotographic characteristics can be improved by combining a charge transport layer and a charge generation layer such that the difference between them is 0.14 to 0.26 eV.

In order to obtain the charge transport layer and charge generation layer that are the combination described above, an organic pigment that generates charge is used.

This can be achieved by appropriately selecting the type and amount of the charge transport agent and binder used.

Next, an electrophotographic photoreceptor according to the present invention will be described in detail.

First, in the present invention, the conductive substrate is a conductive body such as a conductive-treated paper or glass film, a plastic film laminated with a metal foil such as aluminum, a metal plate, a metal drum, or the like.

In the present invention, the charge generation layer contains an organic pigment that generates charges. Organic pigments that generate charges include azoxybenzene, disazo, trisazo, benzimidazole, polycyclic quinone, i/digoid, quinacridone, perylene, methine, α type, β type, γ
It is possible to use pigments that are already known to generate electrons, such as metal-free or metal phthalocyanine-based pigments having various crystal structures such as type, δ-type, e-type, and X-type.

These pigments are disclosed in, for example, JP-A-47-37543, JP-A-47-37544, JP-A-47-18543,
JP 47-18544, JP 48-43942 9% JP 48-70538, JP 49-1231 9% JP 49-105536, JP 50-7521
No. 4, JP-A-53-44028, JP-A-54-177
This is disclosed in Publication No. 32, etc.

In particular, τ, τ' described in Japanese Patent Application Laid-Open No. 182640/1982 and European Patent Application No. 92255 are sensitive to long wavelengths (near 800 nm).
, η and η′ type gold metal phthalocyanines are preferred. In addition to these, any organic pigment that generates charge carriers upon irradiation with light can be used.

In the present invention, two or more organic pigments that generate charges and are included in the charge generation layer may be used in combination.

What is the concentration of the organic pigment that generates charges in the charge generation layer?

If it is too low, the sensitivity tends to decrease or the residual potential increases, so it is preferably 30 to 100% by weight.

Binder and/or plasticizer, fluidity imparting agent used.

Additives such as pinhole suppressants can be included. As a binder, silicone resin, polyamide resin,
Polyurethane resin, polyester resin, epoxy resin,
Polycarbonate resin, polystyrene resin, polymethyl methacrylate resin, polyacrylamide resin, polybutadiene resin, polyisoprene resin, melamine resin,
Ethylcellulose ItJ]L Nitrocellulose ml
Examples include L-IJ chloroprene resin, vinyl acetate resin, polyacrylonitrile resin, and urea resin. Heat and/or photocurable resins can also be used. In any case, there is no particular restriction as long as the resin is electrically insulating and can form a film under normal conditions. The binder in the charge generating layer is contained in an amount of 300 parts by weight based on 100 parts by weight of the charge generating organic pigment.
'il Use in an amount of 1 part or less.

300! If the amount is exceeded, the electrophotographic properties will deteriorate.

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

When using only the organic pigment as described above, the charge generation layer can be formed by vacuum deposition, and the charge generation organic pigment, binder and other additives are added to acetone, methyl ethyl ketone.

Tetrahydrofuran, toluene, xylene, methanol, methylene chloride, isopropyl alcohol.

Isobutyl alcohol, n-butyl alcohol.

After uniformly dissolving or dispersing in a solvent such as trichloroethane, this solution is dip coated onto a conductive substrate.

Spray coating method, roll coating method, applicator coating method,
It can also be formed by coating using a coating method such as a wire bar coating method and drying.

The thickness of the charge generation layer is preferably 0.001 to 10 μm, particularly preferably 0.01 to 5 μm.

If it is less than 0.001 μm, it becomes difficult to uniformly form a charge generation layer, and if it exceeds 10 μm, photographic characteristics tend to deteriorate.

The charge transport layer contains a charge transport substance.

Examples of the charge transporting substance include polymer compounds such as poly-N-vinylcarbazole, polyvinylpyrene, and polyvinylpyrazoline, carbazole, 3-phenylcarbazole, and 2-phenylindole.

Oxadiazole, 1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline, hydrazone, butadiene, enamine, 2
-phenyl-4-(4-diethylaminophenyl)-5
- Low molecular weight compounds such as phenyloxazole, triphenylamine, imidazole, and derivatives thereof.

The charge transport layer may also contain the same binders and additives as used in the charge generation layer, such as a plasticizer, a fluidity imparting agent, and a pinhole inhibitor, if necessary. The binder is preferably 400 parts by weight or less per 100 parts by weight of the charge transporting substance so as not to deteriorate the electrophotographic properties, and when only a low-molecular charge transporting substance is used, from the viewpoint of film properties,
The substance 100]! It is preferable to use at least 50'x parts of binder per part by volume. Other additives are 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, particularly preferably 8 to 20 μm.

Further, the thickness of the charge transport layer is less than 5 μm.

If the thickness exceeds 50 μm, the charging property tends to be poor.

Sensitivity tends to decrease.

To form the charge transport layer, a coating solution prepared by uniformly dissolving or dispersing the charge transporting substance constituting the '+1 charge transport layer in the above-mentioned solvent is applied onto the charge generation layer and dried. This can be done by

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

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

Next, make 8 rows of each material used for taxidermy below. Abbreviations are shown in parentheses.

(1) Charge-transporting substance oxazole derivative 1 (OXZ-1) Oxazole derivative 2 (OXZ-2) Hydrazone derivative 1 () (DZ-1) Charge-transporting substance oxazole derivative 1 (OXZ-1) Enamine derivative (ENM) Butadiene derivative (BUT) (3) Binder binder Binder silicone varnish for charge generation layer: Product name KR214 (KR214)
(Solid content 70wt) [Shin-Etsu Chemical Co., Ltd.] (B) Binder polycarbonate resin for charge transport layer: Trade name Kneepilon S-3000
(UP3000) (Solid content 100% by weight) [Mitsubishi Gas Chemical ■] Example 1 0.5 g of τ-H2PC, 5 g of KR2140, and tetrahydrofuran 709 were milled in a ball mill (Nippon Kagaku Togyo 3).
The mixture was kneaded for 8 hours using a small pot mill.

The obtained pigment dispersion was applied onto an aluminum plate (thickness: 0.1 mm) as a conductive substrate using an applicator, and dried at 100°C for 30 minutes to form a charge generation layer with a thickness of 0.5 μm. did.

Next, the ionization potential Ip of this charge generation layer. O
When L was determined using a surface analyzer (product name: AC-1 model, Riken Keiki ■), it was #Ipo. 1 is 5.20eV
Met.

Next, set BUT69 and UP3000 149 to 1, 1.2
- Mixed in 1:1 mixed solvent 809 of trichloroethane and methylene chloride to completely dissolve. The obtained solution was applied onto the charge generation layer using an applicator, and 1
It was dried at 20° C. for 30 minutes to form a charge transport layer with a thickness of 15 μm.

The solution used to form the above charge transport layer was applied onto an aluminum plate (thickness: 0.1 mm) using an applicator, and dried at 120° C. for 30 minutes to form a charge transport layer of 15 μm. Ionization potential Ipo of this charge transport layer
? When h was determined using the same surface analyzer as above, +
IpOTL was 5.40eV.

Therefore IPOTL-IpooL=5.40-5.20
=0.20eV.

Example 2 Ip was deposited on an aluminum plate in the same manner as in Example 1. OL5
．． A charge generation layer of 20 eV was formed.

Next, a charge transport layer with an IPOTL of 5.36 eV was formed on the charge generation layer in the same manner as in Example 1 except that ENM5G and UP3000 15G were used.

In this electrophotographic photoreceptor, p IporL-”pO
GL was 5.36-5.20=0.16 eV.

Example 3 ■pOGL5 was placed on an aluminum plate in the same manner as in Example 1.
．． A charge generation layer of 20 eV was formed.

Next, BUT4G, 0XZ-129 and UP3000
Ipo
A charge transport layer with a TL of 5.42 eV was formed on the charge generation layer.

In this electrophotographic photoreceptor, p. TL I pO
GL was 5.42-5.20=0.22 eV.

Example 4 Ip was deposited on an aluminum plate in the same manner as in Example 1. A charge generation layer of 01°5.20 eV was formed.

Next, BUT4g, HDZ-22g and UP3000
Ipo was prepared in the same manner as in Example 1 except that i4g was used.
A charge transport layer with a TL of 5.46ev was formed on the charge generation layer.

In this electrophotographic photoreceptor, IPOTL”p
oot.

was 5.46-5.20=0.26 eV.

Example 5 I pOGL was deposited on an aluminum plate in the same manner as in Example 1.
A charge generation layer of 5.20 eV was formed.

Next, BUT69. HDZ-129 and UP3000
Ipo' was prepared in the same manner as in Example 1 except that 129 was used.
A charge transport layer with rl, s, 43 eV was formed on the charge generation layer.

In this electrophotographic photoreceptor, p. TL-Eng p. OL
was 5.43-5.20=0.23 eV.

Comparative Example 1 A charge generation layer having the same IpooL of 5.20 eV as in Example 1 was formed on the same conductive substrate (aluminum plate) as in Example 1.

Next, HDZ-1sg and UP3000 129 at 1.1
．． The mixture was mixed in 80 g of a 1=1 mixed solvent of 2-trichloroethane and methylene chloride to completely dissolve it. The resulting solution was applied onto the charge generation layer using an applicator and dried at 100° C. for 30 minutes to form a charge transport layer with a thickness of 15 μm.

The above solution was applied onto an aluminum plate (thickness: 0.1 am) using an applicator, and dried at 100° C. for 30 minutes to form a charge transport layer of 15 μm. The ionization potential (IpoTL) of this charge transport layer was determined using a surface analyzer and was found to be 5.25 eV.

Therefore? IpOTI, 'poot, = 5.2
5", 20 = 0.05 eV.

Comparative Example 2 The same charge generation layer was formed on the same conductive substrate as in Example 1, and 0XZ-28g and UP3000 1
IPOTL was prepared in the same manner as in Example 1 except that 29 was used.
9. A charge transport layer of 5.24 eV was formed on the charge generation layer.

In this electrophotographic photoreceptor, IPOTL Ip.

OL was 5.24-5.20=0.04 eV.

Comparative Example 3 The same charge generation layer was formed on the same conductive substrate as in Example 1, and HDZ-2sg and UP3000 1 were also formed.
Example 1 except that 59 was used and the drying temperature was 90°C.
A charge transport layer with an IpoTL of 5.54 eV was formed on the charge generation layer in the same manner as above.

In this electrophotographic photoreceptor, p. TL-Eng p. OL
was 5.54-5.20 = 0.34 eV.

Comparative Example 4 The same charge generation layer was formed on the same conductive substrate as in Example 1, and HDZ-1sg and UP3000 1 were also formed.
1poTL in the same manner as Comparative Example 1 except that 59 was not used.
A 5.58 eV charge transport layer was formed on the charge generation layer.

In this electrophotographic photoreceptor, IPOTL-IPO
GL was 5.58-5.2020, 38 eV.

Comparative Example 5 The same charge generation layer was formed on the same conductive substrate as in Example 1, and 0XZ-159 and UP3000 1 were also formed.
A charge transport layer with an IPOTL of 5.48 eV was formed on the charge generation layer in the same manner as in Example 1, except that 59 was used and the drying temperature was 115°C.

In this electrophotographic photoreceptor, p. TL ”pOG
L was 5.48-5.20=0.28 eV.

Example 6 0.4 g of τ-H2PC, 6 g of KR2140, and 709 tetrahydrofuran were kneaded using a ball mill in the same manner as in Example 1 for 8 hours. The obtained pigment dispersion was applied onto an aluminum plate as a conductive substrate using an applicator and dried at 100° C. for 30 minutes to form a charge generation layer with a thickness of 0.5 μm.

The IpooLFi of this charge generation layer was 5.22ev.

Next, p of the same composition as in Example 1 was placed on this charge generation layer.
A charge transport layer with an oTL of 5.40ev was formed.

In this electrophotographic photoreceptor, IpotL"pOGL =
It was 5.40-5.22=0.18 eV.

Example 7 7 g of τ-HtPc O, KR2140,39, and tetrahydrofuran 709 were kneaded in the same manner as in Example 1 for 8 hours using a ball mill. The obtained pigment dispersion was applied onto an aluminum plate, which is a conductive substrate, using an applicator and dried at 100°C for 30 minutes to give a film thickness of 0.5 μm.
A charge generation layer was formed.

The IpOGL 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 applied.
A charge transport layer with OTI, s, 36 eV was formed.

In this electrophotographic photoreceptor, IPOTL Ip. GL
=5.36 5.13=0.23eV.

Comparative Example 6 τ-HhPco, i5g, KR2140,85
g and tetrahydrofuran 709 were kneaded for 8 hours using a ball mill in the same manner as in Example 1. The obtained pigment dispersion was applied onto an aluminum plate, which is a conductive substrate, using an applicator and dried at 100°C for 30 minutes until the film thickness was 0.
．． A charge generation layer of 5 μm was formed. I of this charge generation layer
pooL was 5.42 eV.

Next, on this charge generation layer, an IP layer having the same composition as in Example 4 is applied.
A charge transport layer with an OTL of 5.46 eV was formed.

In this electrophotographic photoreceptor, IPOTL IpOGL
=5.45-5.42=0.03 eV.

Comparative Example 7 4 g of τ-HzPc O, 6 g of KR2140, and 709 tetrahydrofuran were 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, which is a conductive substrate, using an applicator and dried at 100°C for 30 minutes to give a film thickness of 0.5 μm.
A charge generation layer was formed.

II'OGL of this charge generation layer was 5.22 eV.

Next, on this charge generation layer, an IP having the same composition as in Comparative Example 4 was applied.
A charge transport layer with an OTL of 5.58 eV was formed.

In this electrophotographic photoreceptor, IPOTL'p. OL
=5.58-5.22=0.36 eV.

The spectral sensitivities of the electrophotographic photoreceptors obtained in Examples 1 to 7 and Comparative Examples 1 to 7 were measured using an electrostatic recording tester (5P-4 manufactured by Kawaguchi Denki).
28). The results are shown in Table 1.

The spectral sensitivity of 780 nm (8780) is determined by using a halogen lamp as the light source and passing it through a monochromator.
The time t (s) required for the electric potential to be halved after irradiation was determined by irradiating m monochromatic light with light that was spectrally divided, and by multiplying this by the energy of the irradiated light (mW/m''). It is something.

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 Figure 1, ΔIp is 0.14 to 0.2
The electrophotographic photoreceptor No. 6 is excellent and exhibits +sensitivity.

(Effects of the Invention) According to the present invention, it is possible to easily select the optimum combination of 'fM, ionization potential of the load-generating waste generation layer and the load-transporting layer, and therefore it is possible to easily obtain an electrophotographic photoreceptor exhibiting high sensitivity. can.

[Brief explanation of the drawing]

Figure 1 shows the spectral sensitivity (8780 (mJ/m)) and the difference between the ionization potential of the charge generation layer and the ionization potential of the charge transport layer ΔI p (eV) (II)O
TL-Ip. GL) is a relationship diagram. blllev) (1, crL-z, cGt)th
1 figure

Claims (1)

[Scope of Claims] 1. A charge-generating layer containing an organic pigment that generates a charge and a charge-transporting layer containing a charge-transporting substance on a conductive substrate,
Ionization potential I_P_O_T of the charge transport layer
_L and the ionization potential I_P_ of the charge generation layer
Difference in O_G_L (I_P_O_T_L - I_P_O_G
_L) is +0.14 to 0.26 eV. 2. The electrophotographic photoreceptor according to claim 1, wherein the organic pigment that generates charges is a phthalocyanine organic pigment. 3. The electrophotographic photoreceptor according to claim 2, wherein the phthalocyanine organic pigment is a metal-free phthalocyanine.