JPS60177346A - Lamination type electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain high sensitivity by specifying the absolute value of a difference in the calculated values of the respective ionization potentials of a disazo pigment incorporated in an electric charge generating layer and a hydrazone compd. incorporated in an electric charge transfer layer. CONSTITUTION:The absolute value of the difference in the calculated values of ionization potentials (Ip), by an omega-Huckel molecular orbital method, of the disazo pigment and hydrazone compd. incorporated into a lamination type photosensitive body provided with an electric charge generating layer contg. said disazo pigment and an electric charge transfer layer contg. said hydrazone compd. on a conductive substrate is made <=0.04eV. The efficiency of the carrier implantation from the charge generating layer to the charge transfer layer of the function sepn. type photosensitive body is an important factor to govern sensitivity and the sensitivity has the correlativeness with Ip. The higher sensitivity is attained in the case of ¦Ip (charge generating material)-Ip (charge transfer material)¦<=0.04(eV). For example, Ip (disazo) is 8.08eV and Ip (hydrazone) is 8.11eV as a result of the calculation relating to Ip, by which DELTAIp0.03 is obtd. and the excellent sensitivity is obtd. The combination of the material having the higher sensitivity than the DELTAIp value is thus made selectable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic photoreceptor, which is a laminated type photoreceptor in which a charge generation layer containing a nosazo reagent and a load-transferring layer containing a hydrazone compound are provided on a conductive support. 11. In the photoreceptor, the ionization potential of the disazo pigment and hydrazone compound was determined by the molecular orbital method at 41yI.
- organic light pollution 'Fii with a difference in value of 0.04 eV or less;
The present invention relates to an electrophotographic 1+ & photomaterial characterized by using a chemical compound.

Conventionally, electrophotographic photoreceptors of the type in which a charge generation layer and a charge transport layer are laminated on a conductive support are known. However, this Yuzu layered photoreceptor has not yet achieved sufficient sensitivity.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a highly sensitive electrophotographic photoreceptor.

That is, the photoreceptor of the present invention is a laminated electrophotographic photoreceptor in which a charge generation layer containing a disazo pigment and a charge transport layer containing a hydrazone compound are provided on a conductive support.
The method is characterized in that an organic photoconductive compound is used in which the absolute value of the difference between the calculated ionization potentials of the disazo pigment and the hydrazone compound by the cke1 molecular orbital method is 0.04 eV or less.

The reason why the sensitivity of a laminated photoreceptor in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer is not improved is that there are many traps of carriers generated by exposure in the charge generation material and charge transport material. Possible reasons include that holes and electrons generated by light irradiation cannot move efficiently, and that carriers are not injected efficiently from the charge generation layer to the charge transport layer.

Sensitivity is one of the most important characteristics of a photoreceptor, but in the case of a functionally separated photoreceptor, the sensitivity is generally determined by (1) the amount of light that reaches the charge generation layer (light intensity, extinction coefficient) (2) 'f[Carrier generation efficiency at 1 m (carrier generation quantum efficiency) (3) Carrier injection efficiency from the charge generation layer to the charge transport layer (ionization potential, oxidized 4th position, etc.) (4) Eye NJ eaI The effect of moving the carrier in the stomach: 4
It is expressed qualitatively as a comprehensive result such as (drift a', motion).

Therefore, in order to improve the sensitivity, it is necessary to increase the intensity of light irradiated onto the photoreceptor, the absorption coefficient and quantum efficiency of the charge generating material, the carrier injection efficiency, the drift mobility in the charge transport layer, etc. Now, assuming that the intensity of the irradiated light is constant, for the organic photoconductive compounds known so far,
It seems unlikely that it will be possible to dramatically increase the extinction coefficient or quantum efficiency. On the other hand, the hole mobility of the divine organic photoconductive compound has been measured for a charge transport phase alone or for a system in which it is molecularly dispersed in an insulating polymer, and its value is 4 (somewhat depending on the assessor). The mobility of organic photoconductive materials generally used in electrophotography is 10-7-10-6 crnl/
%"sec, and the current situation is that no organic material with a value higher than this is known yet.

Therefore, the present inventors focused on the fact that the efficiency of carrier injection from the charge generation layer to the charge transport layer is an important factor that affects sensitivity, and as a result of conducting computer experiments on many organic materials, the sensitivity and We discovered that there is a correlation between ionization potential and ionization potential.

Generally, it has been reported that there is a correlation between the effective injection of carriers generated in the charge generation layer into the charge transport layer and the ionization potential of the charge transport material.
It is described in Trans magazine, Volume IA-17, 382 et seq. (published in 1981). The ionization potential, which is considered to be the most important factor in carrier injection efficiency, can be measured by various methods. For example, methods using mass spectra,
There are methods that use photoelectron spectroscopy, methods that create charge transfer complexes and use their absorption spectra, methods that measure oxidation potential as a substitute physical property value, and methods that perform calculations using molecular orbital methods. However, the methods described above have so far been limited to relatively low-molecular compounds such as charge-transporting materials, and the ionization of larger to larger molecules of pigments, which are commonly used as charge-generating materials. To the best of the present inventor's knowledge, there are no reports regarding experimental values of potential or 1[n values. The reason for this is thought to be that the pigment exhibits characteristics as a molecular assembly (aggregate) rather than as a single molecule dispersed state, which poses an experimental problem. Furthermore, since pigments are generally macromolecules, it is thought that there was a limit to the amount of time required to perform molecular orbital calculations on a computer, such as 3-1 hours.

However, recent dramatic improvements in the performance of personal computers have made it possible to easily calculate even large molecules using the molecular orbital method.

Therefore, the present inventors first confirmed that there is a proportional relationship between the experimental value of the oxidation potential of a hydrazone compound, which is a charge transport material, and the divided value of the ionization potential. After that, we calculated the ionization potential of the disazo pigment, which is a charge-generating material, using the same calculation method, and measured the calculated ionization potential of the disazo pigment and hydrazone compound, and the sensitivity of the laminated electrophotographic photoreceptor.
This has led to the present invention.

Specific methods and considerations will be described below in accordance with the above order. Since it is generally believed that there is a proportional relationship between oxidation potential and ionization potential, we first conducted an experiment to confirm whether this relationship holds true for hydrazone compounds.

To measure the oxidation potential, acetonitrile was used as a solvent, tetraethylammonium perchlorate was used as a supporting electrolyte, and a saturated calomel electrode was used as an electrode.

On the other hand, as a relatively easy method to calculate the ionization potential of various molecules, the Journal of Amer
Lean Chemlcal 5occulty Magazine, No. 8
The method described in vol. 2, 4123 Sada (published in 1960) is known to be effective, and ω-HMck
It is called the EL method. Using this method, the ionization potential (■) expressed in electron delt units was determined by the following formula.

I, =7.06 +2.49λ (1st equation) where λ
is the highest occupied orbital energy of the molecule expressed in resonance integral β units. However, the ω-Huck used in the present invention
The el method is a π-electron approximation method and is therefore applicable only to conjugated molecules. However, many compounds used in electrophotographic light-sensitive materials generally have a conjugated portion and a non-conjugated portion coexisting. For example, in the case of the hydrazone compound shown in , the conjugated system in the strict sense is within the broken line, but considering that substituents other than this part actually affect the value of the oxidation potential, the conjugated system is The calculation was performed by making the area as wide as possible, as shown in the solid line. The measured values of the oxidation potential and the calculated values of the ionization potential of various hydrazone compounds will be described in Examples, and it was confirmed that a proportional relationship was established between the measured oxidation potential and the calculated value of the ionization potential. -An old book The calculations were performed assuming that all parts of the disazo pigment used in the present invention are conjugated systems.

Conventionally, it has been confirmed that there is a strong correlation between sensitivity and the ionization potential of the charge transport material, and it is believed that the smaller the ionization potential of the charge transport material, the higher the sensitivity.

However, when the ionization potential was determined not only for the charge transport material but also for the charge generation material as was done in the present invention, the energy levels shown in FIG. 11 were obtained.

Details of ionization-tension values for many compounds will be described in Examples, but the above calculation results revealed the following.

In many combinations of charge-generating materials and charge-transporting materials, IIp(ffti; charge 'j'UjE+A charge) -1, (
It was recognized that high sensitivity is achieved when the following relationship holds true: 0.04 (eV) (second formula). This means that holes generated by the excitation of positive atoms in the charge-generating material by light irradiation enter the charge-transporting material without being absorbed by the energy barrier at the interface between the charge-generating layer and the charge-transporting layer. Indicates that it will be injected. Since the sensitivity is extremely high when the relationship of the second equation holds, it is presumed that holes generated in the charge generation material are efficiently injected into the charge transport material.

On the contrary, it was found that when the left side of the second equation becomes larger than 0.04 eV, the sensitivity becomes low. This shows that when the difference in the interfacial barrier between the two materials becomes too large, such as 0.04 eV or more, hole injection becomes extremely difficult. The reasonable result is that the required hole injection is unlikely to occur.

From the above calculation results and considerations, the present invention clarifies for the first time the correlation between the combination of charge-generating materials and charge-transporting materials and sensitivity. It can be seen that there is an optimal range of ionization potential as shown in the second equation. Therefore, it can be seen that by using the present invention, useful information can be obtained for selecting a charge generating material and a charge transporting material.

Examples of the disazo pigment used in the charge generation layer in the present invention include the compounds shown below.

■ p15q 巳 6 Name S 巳 , d す ＆ S 艮匁 8 Ryo 8 (8) The charge generating layer is made by dispersing the charge generating substance described above in a suitable binder and coating it on the substrate. It can also be obtained by forming a vapor-deposited film using a vacuum evaporation apparatus. The binder that can be used to form the charge generating layer by coating can be selected from a wide range of insulating resins, as well as organic photoconductive polymers such as polyvinylcarbazole, polyvinylanthracene, and polyvinylpyrene. can. Preferably, I-rivinyl pteral, polyarylate (condensation polymer of bisphenol A and phthalic acid, etc.), polycarzenate, polyester, phenoxy resin, vinyl triacetate, acrylic resin,
Examples include insulating resins such as polyacrylamide resin, polyamide, polyvinylpyridine, cellulose resin, uredan resin, epoxy resin, casein, polyvinyl alcohol, and polyvinylpyrrolidone. The resin contained in the charge generation layer has a weight ratio of 80% or less, preferably 4%.
0% by weight or less is suitable. Organic solvents used during coating include alcohols such as methanol, ethanol, isopropanol, acetone, methyl ethyl ketone,
Ketones such as cyclohexanone, amides such as N,N-dimethylformamide, N,N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, methyl acetate, ethyl acetate, etc. esters, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene, or aromatic compounds such as benzene, toluene, xylene, ligroin, monochlorobenzene, and dichlorobenzene. etc. can be used.

M technology includes Nl coating method, spray coating method, spinner coating method, bead coach ink method,
This can be carried out using a coating method such as a Mayer-Per coating method, a blade coating method, a roller coach ink method, or a curtain coating method.

The charge generation layer contains as much of the organic photoconductor as possible in order to obtain sufficient absorbance, and in order to shorten the range of the generated charge carriers, it is a thin film layer, for example 5 microns or less, Preferably, the thin film layer has a thickness of 0.01 micron to 1 micron. This means that most of the incident light is absorbed by the charge generation layer, generating many charge carriers, and that the generated charge carriers are not deactivated by recombination or trapping, but are transferred to the charge transport layer. This is due to the need for injection.

A photosensitive layer having such a laminated structure of a charge generation layer and a charge transport layer is provided on a substrate having a conductive layer. Examples of substrates having a conductive layer include those in which the substrate itself is conductive;
For example, aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium,
Nickel, indium, gold, platinum, etc. can be used, and in addition, plastics having a layer formed by vacuum evaporation of aluminum, aluminum alloy, indium oxide, tin oxide, indium oxide-tin oxide alloy, etc. (for example, Polyethylene, polynolopyrene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, ethylene fluoride, etc.), conductive particles (e.g. carbon black, silver particles, etc.) coated on plastic with a suitable binder, conductive particles A substrate impregnated with plastic or paper, a plastic containing a conductive polymer, etc. can be used.

An undercoat layer having a barrier function and an adhesive function can also be provided between the conductive layer and the photosensitive layer.゛Undercoat layer: casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6,
Nylon 66, nylon 610, co-salted nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc.

The thickness of the undercoat layer is suitably 0.1 to 5 microns, preferably 0.5 to 3 microns.Next, the hydrazonated metal used in the charge transport layer in the present invention is N-methyl-N-phenylhydra. Dino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylcarbazole
O-ethylphenothiazone, N,N-diphenylhydrano-3-methylidene-10-ethylphenoxazine,
P-diethylaminobenzaldehyde-N,N-diphenylhydrazino, P-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone, P-pyrrolidinylbenzaldehyde-N,N-diphenylhydrazone, 1,3.3-) Tumethylindolenine-ω-
Examples include aldehyde-N,N-diphenylhydrazone, P-zoethylpenzaldehyde 3-methylbenzthiazolinone-2-hydrazone, and the like.

Further, these charge transport substances can be used alone or in combination of two or more.

When the charge transport material does not have film-forming properties, a film can be formed by selecting an appropriate binder. Examples of resins that can be used as binders include acrylic resin polyarylate, polyester, precarbonate, polystyrene, acrylonitrile styrene copolymer, acrylonitrile-butadiene, copolymer, polyvinyl butyral, polyvinyl formal, trisulfone, polyacrylamide, 19-lyamide, chlorinated rubber, etc. or organic photoconductive polymers such as polyvinyl anthracene, 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. Typically it is 5 microns to 30 microns, with a preferred range of 8 microns to 20 microns. When forming the charge transport layer by coating, an appropriate coating method as described above can be used.

The electrophotographic photoreceptor provided by the present invention can be used not only for electrophotographic copying machines, but also for laser printers and CRTs.
It can also be widely used in electrophotographic applications such as printers.

Further, the organic photoconductor of the present invention can also be used in solar cells and optical sensors in addition to the above-mentioned electrophotographic photoreceptor.

Solar cells can be prepared, for example, by sandwiching the aforementioned organic photoconductors with indium oxide and aluminum.

Next, the present invention will be explained with reference to examples, but the present invention is not limited thereto.

Examples 1 to 3 Cisazo pigment (1) having the following structure 5.9 and butyral resin (degree of butyralization 63 mol%)2. ! i' was dispersed with a solution of 95 ml of ethanol and then coated on an aluminum sheet to form a charge generation layer having a thickness of 0.1 micron after drying.

To the country - 〇In addition, NEC's PC-9801 is used to calculate the ionization potential (engineering). -Used a personal computer.

The I of this pigment (1) was 8.08 sV.

Monochlorobencef was prepared by mixing a hydrazone compound having the structural formula shown in Table 1 and an acrylic resin (trade name: Seiko Kagakuten J-899) as a binder in a weight ratio of 1:1 on the above-mentioned charge generation layer. A charge transport layer was formed by applying a 20% weight solution onto the charge generation layer using a wire bar so that the film thickness after drying would be 16 microns.

The electrophotographic photoreceptor thus formed was manufactured by Kawaguchi Electric Co., Ltd.
Electrostatic copying paper tester Model 5P-428 was used to perform dynamic corona charging, and after holding for 1 second in a dark place, exposure was performed for 4 seconds at an illuminance of 5 lux to determine the charging characteristics.
I was able to shave it off.

As for the charging characteristics, Fukiko i (
E1/6) was measured. By the above method, the oxidation potential and ionization potential (I
), I of disazo pigment (1), and I of hydrazone compound
The results of the difference (ΔI,) are summarized in Table 1.

Furthermore, Figure 2 shows ΔI obtained in Table 1 and E1/
showed a correlation with 6. As is clear from the above results, all the materials of Examples 1 to 3 in which the difference between the ionization potential of the charge generation charge and the charge transporting material was within the range of -004 to 0.04 eV had high sensitivity. It can be seen that It is understood that the range of -0.04 to 0.04 eV is the optimum condition for a combination of highly sensitive materials, since sensitivity rapidly decreases when the value deviates from this range.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the ion potential of the ion generation control,
FIG. 2 is a diagram showing the relationship between the electric potential and ion potential obtained in Table 1. Figure 1

Claims (1)

[Claims] 'j; I:Ij, containing a disazo pigment on a sexual support'
In a Kasu-Isso-type Ichi-Ichiko photographic photoreceptor provided with a charge transport layer containing tr'i and a hydrazone compound,
It n of each ionization potential of disazo pigment and hydrazone compound by ω-HMcke 1 minute orbital method
The difference i, +:: of the difference of &i is a C4 body whose result is that the pair sum 1 is 0.04 eV or less.