JPS6255779B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor, and more particularly, to an electrophotographic photoreceptor having a photosensitive layer containing an organic photoconductive substance made of an oxadiazole compound. Conventionally, inorganic photoconductive substances such as selenium, cadmium sulfide, and zinc oxide have been widely used in the photosensitive layer of electrophotographic photoreceptors. Photoreceptors using such inorganic photoconductors have several advantages and at the same time have various disadvantages. For example, in the case of selenium, the productivity is low due to vacuum evaporation and manufacturing is difficult. Manufacturing costs are high due to difficult conditions and loss of raw materials, and the selenium vapor-deposited film itself is extremely susceptible to heat and mechanical shock.
It has problems such as being extremely susceptible to crystallization depending on environmental conditions. In the case of cadmium sulfide, it is sensitive to humidity and poses a pollution problem except for photoreceptors coated with an insulating layer. In the case of zinc oxide, since it is sensitized with a dye with a low degree of porosity, such as rose bengal, there are problems such as deterioration due to electrical conduction due to corona charging and photofading. Furthermore, since the zinc oxide particles are in a resin dispersion system, the surface smoothness, hardness, abrasion resistance, etc. of the photosensitive layer are poor. On the other hand, organic photoconductive materials have advantages over inorganic materials, such as a highly flexible photosensitive layer, easy manufacture, and the ability to obtain photoreceptors with stable electrophotographic properties at a lower cost. , many proposals have been made in recent years. Types of photoreceptors using organic photoconductive materials include: (1) those in which a charge transfer complex is formed by a combination of an electron-donating compound and an electron-accepting compound (e.g., US P3484237); Photoconductors sensitized by adding dyes (e.g.,
-25658 Publication), (3) Pigment dispersed in a hole- or electron-active matrix (e.g., JP-A-47-25658);
30328, Japanese Unexamined Patent Publication No. 18545/1983), (4) A charge generation layer and a charge transport layer separated in function (e.g.,
JP-A No. 49-105537), (5) those whose main component is a eutectic complex consisting of a dye and a resin (for example, JP-A No. 105537);
47-10785), (6) a charge transfer complex containing an organic pigment or an inorganic charge generating material;
(For example, Japanese Patent Laid-Open No. 49-91648), (7) and others. Although some of these photoreceptors are practical, the current situation is that further improvements in sensitivity, durability, environmental stability, etc. are desired. In addition, the organic photoconductive materials used in such photoreceptors include high molecular materials such as poly-N-vinylcarbazole and low molecular materials such as pyrazolone derivatives described in JP-A-49-105537. be. Polymer type coatings generally have brittle coatings and have problems with film formability, flexibility, etc. If plasticizers are added to solve this problem, problems such as decreased sensitivity arise. On the other hand, for low-molecular type products, an appropriate binder can be selected and the above-mentioned drawbacks of high-molecular type products can be overcome. In order to eliminate the above-mentioned drawbacks, the present inventors have conducted extensive research on organic low-molecular photoconductive substances, and have discovered that a specific oxadiazole compound has extremely excellent properties, and have thus arrived at the present invention. be. The oxadiazole compound used in the present invention is represented by the following general formula (1). In the formula, R ₁ and R ₂ are a linear or branched alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a benzyl group which may have a substituent,
Aralkyl groups such as phenethyl groups, (substituents include alkyl groups such as methyl groups and ethyl groups, alkoxy groups such as methoxy groups and ethoxy groups, and halogen atoms such as chlorine atoms, bromine atoms, and iotho atoms.) , or a residue that forms a ring with a nitrogen atom, such as a morpholino group, a piperazino group, or a pyrrolidino group, and R ₁ and R ₂ may be the same or different. When the oxadiazole compound used in the present invention is symmetrical (R ₁ and R ₂ are the same group), the following general formula It is easy to synthesize by heating the carboxylic acid represented by the formula (in the formula, R ₃ has the same meaning as R ₁ and R ₂ above) together with a salt such as hydrazine hydrochloride or sulfate in polyphosphoric acid. When the oxadiazole compound is asymmetric (R ₁
and groups in which R ₂ are different) have the general formula (In the formula, R ₁ has the same meaning as before. R ₄ represents a lower alkyl group such as a methyl group or an ethyl group.)
A carboxylic acid ester represented by the formula and hydrazine hydrate are heated in an alcoholic solvent such as methanol or other suitable solvent, and the general formula (R ₁ has the same meaning as before) is synthesized. Next, the above hydrazide has the general formula (In the formula, R ₂ is different from R ₁ in the general formula (4), but has the same meaning as before.) It can be synthesized by condensing the carboxylic acid represented by the formula in polyphosphoric acid. The electrophotographic photoreceptor containing the oxadiazole compound represented by the general formula (1) can be applied to any of the photoreceptor types (1) to (7) using organic photoconductive substances mentioned above. can. The present invention provides an oxadiazole represented by the general formula (1) as a charge transport material for use in a charge transport layer of a photoreceptor of type (4), that is, a photoreceptor that is functionally separated into two layers: a charge generation layer and a charge transport layer. When using compounds,
In particular, the sensitivity of the photoreceptor becomes high and the residual potential is low. In addition, in this case, the surface potential during repeated use,
The decrease in sensitivity is small and the increase in residual potential is negligible, making it an extremely excellent photoreceptor. Therefore, the (4) type photoreceptor will be explained. As for the layer structure, a conductive layer, a charge generation layer, and a charge transport layer are essential, and the charge generation layer may be either above or below the charge transport layer, but in an electrophotographic photoreceptor of the type that is used repeatedly. It is preferable to laminate a conductive layer, a charge generation layer, and a charge transport layer in this order mainly from the viewpoint of physical strength and in some cases from the viewpoint of chargeability. An adhesive layer may be provided as necessary for the purpose of improving the adhesiveness between the conductive layer and the charge generation layer. As the conductive layer, a metal plate or metal foil such as aluminum, a plastic film on which a metal such as aluminum is vapor-deposited or an aluminum foil laminated with paper or plastic film, paper treated with conductivity, etc. are used. Effective materials for the adhesive layer include resins such as casein, polyvinyl alcohol, water-soluble polyethylene, and nitrocellulose. The thickness of the adhesive layer is suitably 0.1 to 5 microns, preferably 0.5 to 3 microns. For the charge generation layer, inorganic materials such as selenium, selenium-tellurium, selenium-arsenic, adomium sulfide, and amorphous silicon, which absorb light and generate charge carriers with extremely high efficiency, as well as pyrylium dyes and thiopyrylium dyes, can be used. , triarylmethane dyes, thiazine dyes, cyanine dyes,
Pigments, phthalocyanine pigments, perylene pigments,
separate deposited layers selected from a variety of charge-generating materials consisting of organic substances such as indigo pigments, thioindigo pigments, quinacridone pigments, scale acid pigments, azo pigments, polycyclic quinone pigments;
A layer made of a charge-generating material and a binder resin, or a layer made of a dye or pigment that does not contain resin can be used, and the combination with specific materials is not limited. The thickness of the charge generation layer is preferably 5 microns or less, preferably 0.01 to 1 micron. When the charge generation layer is formed by applying a resin dispersion or solution of the charge generation material, the proportion of the binder in the charge generation layer is preferably 80% or less, since a large amount of binder used will affect the sensitivity. 40% or less is desirable. Binders used include polyvinyl butyral, polyvinyl acetate, polyester, polycarbonate, phenoxy resin, acrylic resin, polyacrylamide,
Various resins such as polyamide, polyvinylpyridine resin, cellulose resin, urethane resin, epoxy resin, casein, and polyvinyl alcohol are used. A charge transport layer is formed on the charge generation layer thus formed. The thickness of the charge transport layer is 5 to 30 microns, preferably 8 to 20 microns. Since the oxadiazole compound used in the present invention does not have a film-forming ability by itself, a solution dissolved in a suitable organic solvent together with various binder resins is coated and dried by a conventional method to form a charge transport layer. As the binder, acrylic stem resin, polystyrene resin, polyester resin, phenoxy resin, polycarbonate resin, silicone resin, epoxy resin, polyurethane resin, etc. can be used. Further, a hole transporting polymer such as poly-N-vinylcarbazole can also be used as a binder. The oxadiazole compound used in the present invention has hole transport properties, and when using a photoreceptor in which a conductive layer, a charge generation layer, and a charge transport layer are laminated in this order, the surface of the charge transport layer must be negatively charged. When exposed to light after being charged, holes generated in the charge generation layer in the exposed area are injected into the charge transport layer, and then reach the surface and neutralize the negative charge, causing a decrease in the surface potential and creating static between the exposed area and the unexposed area. Electrocontrast occurs. A visible image can be obtained by developing the electrostatic latent image thus formed with a positively charged toner. This can be directly fixed, or the toner image can be transferred to paper or plastic film and then developed and fixed. Alternatively, a method may be used in which the electrostatic latent image on the photoreceptor is transferred onto an insulating layer of transfer paper, then developed and fixed. The type of developer, the developing method, and the fixing method may be any known one or any known method and are not limited to a specific one. Photoreceptors other than the (4) type are described in detail in the respective exemplified documents, so they will be briefly explained. Type (1) photoreceptors form a charge transfer complex when the oxadiazole compound used in the present invention is combined with an electron-withdrawing substance. It can be obtained by coating and drying a conductive layer or a conductive layer provided with an adhesive layer by a conventional method. Examples of electron-withdrawing substances include chloranil, bromoanil,
Tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitrofluorene,
Low molecular weight substances such as 2,4,7-trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone and those described in US P.4122113. There are polymers of electron-withdrawing monomers. As the binder, the various binders exemplified for the (4) type photoreceptor can be used. The (2) type photoreceptor can be prepared by dissolving the oxadiazole compound used in the present invention and the binder for the charge transport layer exemplified for the (4) type photoreceptor in a suitable solvent. It can be obtained by adding the various exemplified dyes, applying this liquid to a conductive layer or a conductive layer provided with an adhesive layer by a conventional method, and drying it. (3) type photoreceptor uses the oxazole compound used in the present invention as a hole matrix,
(4) Type: Obtained by adding the various pigments exemplified for photoreceptors. (5) type photoreceptor uses pyrylium dyes such as 2,6-diphenyl-4-(N·N-dimethylaminophenyl)thiapyrylium perchlorate and resins that form eutectic complexes with such dyes. For example, it can be manufactured from polycarbonate resin and the oxadiazole compound used in the present invention. The charge transfer complex in the (6) type photoreceptor is similar to the (1) type charge transfer complex, and the charge generating material to be added can be any of the materials exemplified for the (4) type photoreceptor. be. The electrophotographic photoreceptor of the present invention can be used not only for electrophotographic copying machines, but also for laser printers, CRTs, etc.
It can also be widely used in electrophotographic applications such as printers and electrophotographic plate making systems. Next, a synthesis example of the oxadiazole compound used in the present invention will be shown. 2,5-bis(p-diethylaminostyryl)-
Synthesis of 1,3,4-oxadiazole. Polyphosphoric acid was prepared by mixing 44.7 g of phosphorus pentoxide and 28.8 ml of 85% phosphoric acid and stirring the mixture at a liquid temperature of 100°C for 2 hours. Next, in this polyphosphoric acid, hydrazine sulfate 4.33
g (0.033 mol), p-diethylaminocinnamic acid
14.58g (0.067mol) was added and the liquid temperature was 140℃.
A time reaction was performed. After lowering the liquid temperature to 80°C, the reaction liquid was poured into ice water, and the precipitated solid content was filtered off. The obtained solid content was thoroughly stirred in a 5% sodium carbonate solution, filtered, washed with water, and dried to obtain 12.00 g of a solid content with a melting point of 155.5 to 160°C. Recrystallization from methyl ethyl ketone gave 6.85 g of crystals with a melting point of 167-168.5°C. Yield 49.5% Elemental analysis Molecular formula C ₂₆ H ₃₂ N ₄ O Calculated value Analytical value C 74.95% 74.91% H 7.76〃 7.70〃 N 13.45〃 13.42〃 IR absorption spectrum =C-O-C=stretching 970cm ^-1 , 1015cm ^{- 1} (Weak) Other oxadiazole compounds used in the present invention can be synthesized in the same manner. Next, examples of the present invention will be shown. Example 1 An ammonia aqueous solution of casein (11.2 g of casein, 1 g of 28% ammonia water, 222 g of water) was placed on an aluminum plate.
ml) with a Mayer bar and dry, coating amount 1.0
An adhesive layer of g/m ² was formed. Next, a pigment having the following structural formula, 5g and 2g of butyral resin (degree of butyralization 63 mol%) dissolved in 95ml of ethanol were dispersed in a ball mill, and then coated on the adhesive layer with a Mayer bar, resulting in a coating weight of 0.2g/m ² after drying. A charge generation layer was formed. Next, 5 g of 2,5-bis(p-diethylaminostyryl)-1,3,4-oxadiazole, poly-4,4'-dioxydiphenyl-
2,2'-propane carbonate (molecular weight 30000)
A solution obtained by dissolving 5 g in dichloromethane 70 ml was applied onto the charge generation layer and dried to form a charge transport layer with a coating weight of 11 g/m ² . After conditioning the electrophotographic photoreceptor thus prepared at 20°C and 65% (relative humidity), it was statically charged with corona at 5KV using an electrostatic copying paper tester Model SP-428 manufactured by Kawaguchi Electric Co., Ltd. After holding it in the dark for 10 seconds, it was exposed to light at an illuminance of 5 lux to examine its charging characteristics. The initial potential is Vo (-V), the potential retention rate for 10 seconds in the dark is Vk (%), and the half-decay exposure is E1/
2 (lux, sec) to show the charging characteristics of this photoreceptor. Vo605V, Vk97% E1/29.0lux.sec Examples 2 to 8 On a 100μ thick aluminum plate, selenium-tell (10% tellurium) was vapor deposited to a thickness of 0.8μ to form a charge generation layer. Next, polyester resin (Vyron
200 (manufactured by Toyobo Seki Co., Ltd.) and 5 g of the oxadiazole compound listed in the following table dissolved in 70 ml of dichloromethane was applied onto the charge generation layer and dried to form a charge transport layer with a coating amount of 10 g/m ² was formed. The charging characteristics of the electrophotographic photoreceptor thus prepared were examined in the same manner as in Example 1, and the results are shown in the following table.

【table】

[Table] Example 9 2,5-bis(p-diethylaminostyryl)
-1,3,4-oxadiazole 5g and poly-N
- Add the following pigment to a solution of 5 g of vinyl carbazole (molecular weight 300,000) dissolved in 70 ml of dichloromethane. After adding 1.0 g and dispersing it in a ball mill, it was applied and dried on the adhesive layer of an aluminum plate provided with the adhesive layer described in Example 1 to form a photosensitive layer of 12 g/m ² . Charge measurement of the photoreceptor thus prepared was carried out in the same manner as in Example 1. However, the charging characteristics are the same. Vo520V, Vk89%, E1/216lux.sec Example 10 A 0.2mm thick aluminum substrate was set in a vacuum device, and after sufficient evacuation, hydrogen gas and silane gas (15% by volume relative to hydrogen gas) were introduced. Then
A charge generation layer of amorphous silicon with a thickness of 0.3 μm was formed on the substrate by glow discharge by applying a high frequency electric field of 13.5 MHz. After returning the inside of the vacuum apparatus to atmospheric pressure, the sample was taken out and a charge transport layer was formed on the charge generation layer in exactly the same manner as in Example 2. The photoreceptor thus obtained was placed in a charging/exposure experimental device, corona discharged at 5 KV, and a light image was immediately irradiated.
The light image was illuminated through a transmission test chart using a tungsten lamp light source. Immediately afterwards a positively charged developer (including toner and carrier)
A good toner image was obtained on the surface of the photoreceptor by cascading the toner onto the surface of the photoreceptor. Example 11 The same charge transport layer and charge generation layer as in Example 10 were sequentially laminated on an aluminum plate having a thickness of 0.2 mm. A good toner image was obtained by performing the same operations as in Example 10 using the thus obtained photoreceptor. However, the corona charge was set to 5KV, and a negatively charged developer was used.

Claims (1)

[Claims] 1. General formula (In the formula, R ₁ and R ₂ are alkyl groups, aralkyl groups, or residues that form a ring together with a nitrogen atom, and R ₁ and R ₂
may be the same or different). 2. The electrophotographic photoreceptor according to claim 1, comprising at least three layers: a conductive layer, a charge generation layer, and a charge transport layer containing a charge transport material represented by formula (1).