JPS61198160A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To ensure distinguished high sensitivity by incorporating a cyanine dye having a specified oxidation potential as an electrostatic charge generating material in a charge generating layer and a charge transfer material having a specified oxidation potential in a charge transfer layer. CONSTITUTION:The electrophotographic sensitive body is obtained by laminating on a conductive substrate the charge generating layer contg. the cyanine dye having an oxidation potential of 0.35-0.50V, exemplified by formula (1), as the charge generating material and the charge transfer layer contg. the charge transfer material having an oxidation potential of <=0.70V, exemplified by formula (18). There is the optimum range of the oxidation potential for each of the charge generating material and the charge transfer material, and carriers can be injected into the charge transfer layer without being affected by the energy barrier of the interface between the charge generating layer and the charge transfer layer only when said conditions are satisfied.

Description

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

[Conventional technology]

Conventionally, various laminated electrophotographic photoreceptors (hereinafter sometimes referred to as laminated photoreceptors) in which a photosensitive layer is functionally separated into a charge generation layer and a charge transport layer are known. However, sufficient sensitivity has not yet been obtained in this type of photoreceptor.

In other words, the reason why the sensitivity of the laminated photoreceptor does not improve is that there are many traps in the charge generation material and charge transport material that are generated by exposure to light, and holes and electrons generated by light irradiation cannot move efficiently. It is considered that carriers are not efficiently injected from the charge generation layer to the charge transport layer.

Sensitivity is one of the most important characteristics for 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) Efficiency of carrier generation in the charge generation layer (carrier generation quantum efficiency), (3) Efficiency of carrier injection from the charge generation layer to the charge transport layer (ionization potential, oxidation potential, etc.), (4) Efficiency of carrier generation in the charge transport layer. Efficiency of carrier movement (drift mobility)
It is expressed qualitatively as a comprehensive evaluation such as .

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, if the intensity of irradiated light is constant, it is unlikely that the organic photoconductive compounds known so far will be able to dramatically increase the extinction coefficient or quantum efficiency. There is. On the other hand, the hole mobility of various organic photoconductive compounds has been measured using a charge transporting material alone or a system in which it is molecularly dispersed in an insulating polymer, and the values vary somewhat depending on the measurer. The mobility of organic photoconductive materials generally used in electrophotography is about 10 to 10/vs@c, and
At present, an organic photoconductive material with a value higher than this has not yet been found.

Therefore, the present inventors focused on the fact that carrier injection efficiency from the charge generation layer to the charge transport layer is an important factor that affects sensitivity, and as a result of measuring the oxidation potential of many organic materials, the sensitivity and It was found that there is a correlation between the oxidation potential and the oxidation potential.

By the way, 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, for example, in IE.
EE Trans magazine, Volume IA-17, page 382 (198
published in 1 year). The ionization potential, which is considered to be the most important factor in carrier injection efficiency, can be measured by various methods. For example, there are methods using mass spectra, methods using 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 calculate using molecular orbital method. be. However, the methods described above have so far only been able to determine the ionization potential of relatively low-molecular compounds such as charge-transporting materials, and the ionization potential of macromolecules such as pigments, which are commonly used as charge-generating materials. It can be said that, as far as the present invention is aware, there are no reports on experimental or calculated values of . 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 and in a good state, which poses an experimental problem. Furthermore, since pigments are generally macromolecules, it is thought that there was a limit to the computation time by the combinator when performing molecular orbital calculations.

Therefore, the present inventors focused on various cyanine dyes that are used as charge-generating materials and sensitizers for silver salts. Unlike pigments, dyes are soluble in solvents, making it possible to measure oxidation potential in a solution state.

Furthermore, the oxidation potential of commonly used charge transport materials can also be measured in a solution state. Since it is generally believed that the ionization potential and the oxidation potential are in a proportional relationship, the oxidation potential is considered to be a substitute characteristic for the ionization potential. Therefore, we measured the oxidation potential of the cyanine dye, which is a charge-generating material, and the charge-transporting material, as well as the sensitivity of the laminated photoreceptor, thereby finding the optimal combination of the charge-generating material and the charge-transporting material, and arrived at the present invention. It is something.

[Purpose and outline of the invention]

An object of the present invention is to provide an electrophotographic photoreceptor with outstandingly high sensitivity by using a newly selected combination of a charge generating material and a charge transporting material.

The above object is an electrophotographic photoreceptor having a charge generation layer and a charge transport layer on a conductive support, in which the charge generation layer has a charge generation material of 0.35 to 0.50? The electrophotographic photoreceptor of the present invention is characterized in that the electrophotographic photoreceptor of the present invention comprises a layer containing a cyanine dye having an oxidation potential of 0.70 V or less, and the charge transport layer comprises a layer containing a charge transport material having an oxidation potential of 0.70 V or less achieved.

[Detailed description and examples of the invention]

The oxidation potential used in the present invention is measured using acetonitrile as a solvent, tetraethylammonium perchlorate as a supporting electrolyte, and a saturated calomel electrode as an electrode, and the peak value of the first oxidation wave (gOX) is used as the value of the oxidation potential. Using.

Conventionally, a strong correlation has been confirmed 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, by measuring the oxidation potential of not only the charge transporting material but also the charge generating material as carried out in the present invention, it was found that high sensitivity is achieved only when the oxidation potentials of both materials fall within a certain range of values.

First, it has been found that the oxidation potential of cyanine dye, which is a charge generating material, must be in the range of 0.35 to 0.50 volts. The oxidation potential is 0.35. j? As the height becomes smaller, the dark decay of the laminated photoreceptor increases regardless of the type of charge transporting material. Furthermore, it has been found that when the oxidation potential of the cyanine dye exceeds 0.50 volts, the sensitivity of the laminated photoreceptor decreases significantly, regardless of the type of charge transport material. This is believed to be because when the oxidation potential of the cyanine dye increases, the dye itself absorbs in the ultraviolet region and no longer has sensitivity in the visible region.

On the other hand, for charge transport materials, the oxidation potential is 0.70? It turns out that it is necessary to have a range below 1.

It has been found that when the oxidation potential is greater than 0.70 volts, the sensitivity of the laminated photoreceptor deteriorates significantly, regardless of the type of cyanine dye in the charge generating material.

From the above results, it has been found that in order to obtain a highly sensitive laminated photoreceptor, there is an optimum range for the oxidation potential values of the charge generating material and the charge transporting material as described above. It is rational that only when this condition is met, holes generated in the charge generation layer by light irradiation can be efficiently injected into the charge transport layer without being affected by the energy barrier at the interface between the charge generation layer and the charge transport layer. The results are as follows.

Based on the above experimental results and considerations, the present invention has revealed for the first time a correlation between the combination of a charge generating material and a charge transporting material and sensitivity.

The oxidation potential used in the charge generation layer in the present invention is 0.35 to 0.
．． Examples of cyanine dyes in the range of 50 melt include compounds having the following chemical formulas, structural formulas, and oxidation potentials.

hard nose -
to'
−″′− Φoto＾ ＾
＾−−〇＋／−１
-I■
To er
9 Qu:+
t+”+
cQ8
ζtsu
(C) Next, in the present invention, the oxidation potential used for the charge transport layer is 0.70.
Examples of the charge transport material in the range of V or less include the compounds shown below.

F” (D
Toshin Nail Momme 40 6hi
d, = 1 , :1 8ΔJ 茗 S 8 n■tocQ of
log
Hg
Kuro et
c5m 73cQ -ノ Nノ -ノト
ψ romato ″ ω
ω^^, The charge generation layer used in the present invention can be formed by dispersing one or more cyanine dyes as the charge generation substance used in the present invention in a suitable binder, and coating this. It can also be obtained by forming a vapor deposited film using a vacuum evaporation device. Binders that can be used when forming the charge generating layer by coating can be selected from a wide variety of insulating resins, and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene. You can choose from. Preferably, polyvinyl butyral, polyarylate (condensation polymer of vinylsphenol A and phthalic acid, etc.), polycargenate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide resin, polyamide, polyvinylpyridine, cellulose resin, Examples include insulating resins such as urethane resin, epoxy resin, casein, polyvinyl alcohol, and polyvinylpyrrolidone.

The resin contained in the charge generation layer is suitably 80% by weight or less, preferably 40% by weight or less. Coating δ
Examples of organic solvents used in the process include alcohols/I/s such as methanol, ethanol, and isonoronol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, and N,N-dimethylformamide, N,N-dimethylacetamide, and the like. Amides, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, esters such as methyl acetate, ethyl acetate, chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, trichloroethylene, etc. Aliphatic rhodanized hydrocarbons or aromatics such as benzene, toluene, xylene, ligroin, monochlorobenzene, dichlorobenzene, etc. can be used.

Coating methods include dip coating method, sdale coating method, spinner coach ink method, heat coating method,
This can be carried out using a coating method such as a Mayer bar coating method, a grade 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 is preferably a thin film layer, for example less than 5 microns, in order to shorten the range of the generated charge carriers. is preferably a thin film layer having a thickness of 0.01 micron to 1 micron. This means that most of the incident light is absorbed by the charge generation layer and converts many charge carriers, and that the generated charge carriers are not deactivated by recombination or trapping and are transferred to the charge transport layer. This is due to the need for injection.

The charge transport layer used in the present invention can be formed by forming a film using one or more of the charge transport substances used in the present invention.

When the charge transport material does not have film-forming properties, a film can be formed by selecting an appropriate binder. Resins that can be used as binders include acrylic resin polyarylate, polyester, etc. Licarbonate, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, delJ vinyl butyral, polyvinyl formal, polysulfone, polyacrylamide, polyamide, insulating resins such as chlorinated rubber, or BoIJ + N-vinylcarbazole, polyvinylanthracene , organic photoconductive polymers such as 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.

A photosensitive layer having such a laminated structure of a charge generation layer and a charge transport layer in an arbitrary layer order is provided on a conductive support comprising, for example, a base having a conductive layer.

Examples of the substrate having a conductive layer include those whose substrate itself is conductive, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, morphine, chromium,
Titanium, nickel, indium, gold, platinum, etc. can be used, and plastics ( (e.g., polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyfluorinated ethylene, etc.), conductive particles (e.g., Kagen black, silver particles, etc.)'ft J Coating on plastic with this binder. It is possible to use a substrate made of plastic or paper impregnated with conductive particles, a glass material containing a conductive polymer, or the like.

An undercoat layer having a barrier function and an adhesive function can also be provided between the 4-electroconductor layer and the photosensitive layer. The subbing layer is casein,
Polyvinyl alcohol, nitrocellulose, ethylene-
Acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon 610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin,
It can be formed from aluminum oxide, etc.

The thickness of the undercoat layer is suitably 0.1 micron to 5 micron, preferably 0.5 micron to 3 micron.

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

Further, the charge-generating material and the charge-transporting material used in the present invention can be used not only in the electrophotographic photoreceptor described above but also in solar cells and optical sensors. 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 in any way.

Examples 1 to 64 Eight types of cyanine dyes as the charge generating material according to the present invention and 88i of the charge transporting material according to the present invention as exemplified above were used in combination with each other, and 6
Four types of electrophotographic photoreceptors were produced.

That is, first, the exemplified compounds A (1) to (8), cyanine color fj5J, and a solution of butyral resin (butyralization degree 63 mol%) 2I dissolved in isopropyl alcohol 95- After dispersing in a sand mill, it was coated on an aluminum sheet to form a charge generation layer having a thickness of 0.1 micron after drying.

Next, 5 g of each of the charge transporting materials of the above-mentioned compounds Muα to ) and a styrene-acrylic resin (trade name: Nippon Steel Chemical MS-200) as a binder were mixed at 0.5 g.
A charge transport layer was formed by coating a 20!1 ft % solution of monochlorobenzene mixed at a weight ratio of 95:1 on the charge generation layer so that the film thickness after drying was 16 microns.

The 64 types of electrophotographic photoreceptors created in this way were tested using Seiden copying paper testing equipment iiModelSP- manufactured by Kawaguchi Electric Co., Ltd.
428 using a dynamic method, the sample was held in a dark place for 1 second, and then exposed to light at an illuminance of 5 lux for 4 seconds to examine the charging characteristics.

As for the band t% property, we measured the surface position and the exposure it (Ey) (lu:c-see) required to attenuate the potential (Vo = 600s) to '4 when dark decayed for 1 second. is. In addition, the residual potential (v
8) was also measured. The results of the photoreceptor obtained by the above method are summarized in Table 1. The numbers in [ ] in Table 1 are VR (
s lt) is shown.

In addition, in this table, the area surrounded by a large frame: is an electrophotographic photoreceptor within the scope of the present invention, * represents a large dark decay (200 melt or more), and - represents no sensitivity. It is something.

From the results in Table 1, it can be seen that for each compound, the oxidation potential of the cyanine dye of the charge generation material is in the range of 0.35 to 0.50 volts, and the oxidation potential of the charge transport material is in the range of more than 0.7 ON volts. It can be seen that the electrophotographic photoreceptor of the present invention using a combination of the above has low residual potential and high sensitivity.

Example 65 The charge generating material used in this example was the exemplified compound A (4
), and the charge transport material was a combination of the above-mentioned exemplified compounds M and A. Photoreceptors were prepared in the same manner as in Examples 1 to 64. However, in this example, a charge transport layer was first formed on an aluminum sheet, and then a charge generation layer was laminated on the charge transport layer, and the positive corona band iti characteristics were measured. The results are shown in Table 2.

Table 2 Table 2 also shows the characteristics of the e-charging photoreceptors made of the same material combinations shown in Examples 1 to 64.

The results of this example show that regardless of the order in which the charge generation layer and the charge transport layer are stacked, a highly sensitive photoreceptor can be obtained by using a combination of materials that meet the scope of the claims.

Example 66 The cyanine color $511 of the exemplified compound A (9) and a solution of 2N butyral resin (degree of butyralization 63 mol %) dissolved in Inglobil alcohol 9511j were dispersed in a sand mill, and then coated on an aluminum sheet. A charge generation layer having a thickness of 0.2 microns after drying was formed.

Next, charge transport material 5.9 of the above-mentioned exemplified compound Ya4 and polyarylate resin (bisphenol A and terephthalic acid) were combined.
5 g of iso-7-talic acid condensation polymer) was added to 7 g of tetrahydrofuran.
Apply the solution dissolved to 0m on the charge generation layer so that the film thickness after drying is 1.
It was applied to a thickness of 5 microns and dried to form a charge transport layer.

The charging characteristics of the photoreceptors thus prepared were measured in the same manner as in Examples 1 to 64, and the following results were obtained.

This example differs from the previous examples in that the structures of the charge generation material and the charge transport material are significantly different. Nevertheless, it clearly shows that the invention is well established.

〔Effect of the invention〕

According to the present invention, by optimizing the combination of charge generating material and charge transporting material, even in a laminated photoreceptor,
An electrophotographic photoreceptor with higher sensitivity can be provided.

Claims (1)

[Claims] In an electrophotographic photoreceptor having a charge generation layer and a charge transport layer on a conductive support, the charge generation layer comprises a layer containing a cyanine dye having an oxidation potential of 0.35 to 0.50 volts as a charge generation material. , the charge transport layer is 0.7
An electrophotographic photoreceptor comprising a layer containing a charge transport material having an oxidation potential of 0 volts or less.