JP2729616B2 - Electrophotographic photoreceptor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member used in an electrophotographic copying machine, and more particularly, to an electrophotographic photosensitive member provided with an electrophotographic photosensitive layer containing a charge generating substance and a charge transporting substance. It relates to an electrophotographic photosensitive member. 2. Description of the Related Art Conventionally, as an electrophotographic photoreceptor, one using an inorganic photoconductive material such as selenium, cadmium sulfide, and zinc oxide has been known. It is true that these inorganic materials have many advantages as well as various disadvantages. For example, selenium, which is widely used at present, has excellent electrophotographic properties (eg, chargeability, dark decay, light sensitivity, residual potential, etc.), but the production conditions are difficult, and the production cost is high. There are drawbacks such as lack of flexibility.
Cadmium sulfide is used by being dispersed in a binder resin. However, it is known that a dielectric layer is provided on the surface due to poor mechanical strength or toxicity. However, in this method, a complicated electrophotographic method must be used, and the manufacturing cost increases. Although zinc oxide has no toxicity, it is hard to say that the photosensitivity is sufficient. In recent years, in order to solve these disadvantages of inorganic substances, electrophotographic photosensitive members using various organic substances have been proposed and put to practical use. For example, an electrophotographic photosensitive member comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorenone (U.S. Pat. No. 3,484,237);
Examples thereof include those obtained by sensitizing vinyl carbazole with a pyrylium salt dye (JP-A-48-25648) and those containing a eutectic complex composed of a dye and a resin as a main component (JP-A-47-10735). These organic electrophotographic photoreceptors have improved the mechanical properties and the like of the inorganic electrophotographic photoreceptor to some extent, but still have insufficient sensitivity and are not suitable for repeated use. Was not fully satisfied. In order to solve this problem, a stacked type in which a function is separated into a charge generation layer that absorbs light and generates a charge and a charge transport layer that transports the charge is known.
This has the advantage that by performing charge generation and charge transport with different substances, the electrophotographic characteristics of the electrophotographic photoreceptor, such as sensitivity and accepting potential, can be improved, and the material can be selected from a wide range. ing. However, when a stacking type electrophotographic photoreceptor is manufactured using a conventionally known material, there is no material having an excellent electron transporting property as a charge transporting substance, and thus a charge generating layer and a charge transporting layer are stacked in this order. Then, it has a disadvantage that it must be used with negative charge. That is, conventionally known charge transporting materials include amine compounds, hydrazone compounds, pyrazoline compounds, oxazole compounds, and stilbene compounds, all of which are hole transporting materials.
Further, conventionally, as a material having an electron transporting property, a fluorenone-based compound such as 2,4,7-trinitrofluorenone, a quinone-based compound, and the like are known, but these have extremely high electron mobility. It is slow and not practical enough. Therefore, as a method of preparing a positively charged electrophotographic photosensitive member using a hole transporting material, an electrophotographic photosensitive member in which a charge generation layer is laminated on a charge transport layer has been proposed.
In this case, since the charge transporting layer is on the lower side, a hole transporting charge transporting material can be used. However,
The electrophotographic photoreceptor having such a configuration has the disadvantages of low sensitivity and high residual potential. That is,
In order to uniformly apply the charge generation layer on the charge transport layer, it is necessary to use a solvent that does not dissolve the charge transport layer as a dispersion solvent for the charge generation layer. At the interface with the charge transport layer, the two are not sufficiently joined to each other, and the injection of charges is significantly inhibited, so that the above-described drawbacks occur. Further, since the charge generation layer is brought to the upper side, there is a disadvantage that the mechanical strength is insufficient and the printing durability is poor. Further, the electrophotographic photoreceptor of the laminate type requires at least two layers of coating, and has a drawback that a lot of labor is required in the production and a production cost is increased. The positive charging type electrophotographic photosensitive member is required for the following reasons. That is, when a negatively charged electrophotographic photosensitive member is used in an electrophotographic copying machine, there are the following disadvantages. 1. It is difficult to obtain uniform discharge of the charger. For this reason,
Although a charger called a scorotron and having a grid line provided between a photoreceptor and a corona line is often used, it is still difficult to obtain uniform charging, and it is easy to cause image density unevenness. 2. A large amount of ozone is generated. Negative charging generates an amount of ozone several times larger than positive charging, so that the deterioration of the photoreceptor due to ozone is easily promoted, and an ozone filter such as an ozone filter is used to prevent the ozone from being discharged out of the copying machine. Parts
Must be installed inside the copier. 3. When using a negatively charged photoreceptor, it is necessary to use a positively charged toner. However, there is no excellent charge control agent that is positively charged, and image defects such as fogging and image density reduction at high temperatures are likely to occur. For 1,2,3 reasons, the copier system is complicated,
There is a problem that it causes an increase in cost. Therefore, an organic electrophotographic photoreceptor having excellent characteristics that can be used by positive charging has been desired. In order to solve such a problem, a positively charged organic electrophotographic photosensitive member comprising a perylene pigment, a photoconductive polymer, and an electron accepting substance has been proposed. (Japanese Patent Laid-Open No. 59
JP-A-31957, JP-A-59-140456, JP-A-59-174849 and JP-A-59-224846) Further, a specific amount of an n-type photoconductive pigment and a p-type charge transport material are contained. Further, a positively charged photoconductor has been proposed. (JP-A-60-254142, JP-A-61-48861, JP-A-61-48862
SUMMARY OF THE INVENTION Problems to be Solved by the Invention However, in the former positively chargeable electrophotographic photoreceptor, although sensitivity, environment and repetition stability are improved as compared with the conventional one, it is still practically unsatisfactory. It was enough. Such defects are considered to be due to the fact that the hole mobility of the photoconductive polymer is low, and electrons remain as space charges in the photosensitive layer, which adversely affects the photogeneration process and the charge transport process. Further, the latter positively charged type photoconductor is still insufficient for practical use in terms of the repetition stability of the receiving potential and the large optical memory effect. In view of the circumstances described above, an object of the present invention is to provide an electrophotographic photosensitive member having excellent characteristics in which conventional disadvantages are improved as an organic electrophotographic photosensitive member that can be used in a positive charging system. Means for Solving the Problems The object of the present invention is to provide an electrophotographic method in which a charge generation pigment and a charge transport material are dispersed and dissolved in a binder resin as a photosensitive layer on a conductive support. In the body, as a charge generating pigment, at least one type of photoconductive pigment having its own electron transporting ability is used at a ratio of 5 to 15% by weight based on the binder resin, and as a charge transporting substance. This is achieved by using at least one compound having a hole transporting ability in a proportion of 50 to 180% by weight based on the binder resin. Next, the present invention will be described in more detail. The general configuration of the present invention is as shown in FIG. The basic components include a conductive support 1 and a photosensitive layer 2 provided on the conductive support. In the photosensitive layer, a charge generation pigment 3, a charge transport material 4, and a binder resin 5
Is contained. As the conductive support, aluminum, nickel, chromium, a metal plate made of stainless steel, a metal drum, or a metal foil, and aluminum, titanium, nickel,
Chromium, SUS, gold, vanadium, tin oxide, indium oxide, plastic films provided with thin films such as ITO, etc.
Alternatively, paper or a plastic film coated or impregnated with a conductivity-imparting agent is used. In the present invention, an organic charge generating pigment having an electron transporting ability is used as the charge generating pigment itself. Many charge generation pigments have been proposed for use in organic electrophotographic photoreceptors. Usually,
As the name implies, only the charge generation efficiency of the charge generation material is a problem, and its charge transport performance has not been sufficiently studied. That is, in an electrophotographic photoreceptor in which only a charge generating substance is dispersed in a resin to form a photosensitive layer, a charge receiving property and a charge retention property are extremely poor, and the electrophotographic photoreceptor is not practically usable. It was common to use the charge generation layer and the charge transport layer separately. And
As the charge generation layer, it is sufficient that the charge generation material absorbs light and generates an electric charge. Therefore, the charge generation layer is often used as a thin layer of about 0.1 to 2 μm, Charge transport capacity was not a concern. However, these photoconductive pigments have properties as a semiconductor, and it is known that they are classified into electron transporting pigments and hole transporting pigments depending on each substance. These evaluations as n-type and p-type semiconductors are made by examining the rectifying properties of the pigment in the form of pellets. However, simply, a large amount of the pigment is dispersed in the binder resin, The determination can also be made by providing a photosensitive layer on a support and evaluating the photoconductive properties thereof. That is, when the photosensitive layer is positively charged and illuminated with light, the sensitivity is a p-type semiconductor (hole transporting property) if the sensitivity is shown. (Electron transporting property). The present inventors have found that among these charge-generating pigments, the use of a pigment exhibiting the properties of n-type semiconductor (charge-transporting property) exhibits extremely excellent electrophotographic properties. Charge-generating pigments having such properties differ depending on the individual material and should be evaluated individually. Generally, those containing a large number of electron-absorbing groups exhibit such properties. it is conceivable that. Examples of the electron-withdrawing functional group include those having a nitro group, those having a fluorenone or quinone skeleton, and those having a functional group substituted with a halogen such as chlorine or bromine or oxygen. Etc. are known. Examples of the charge generation pigment used in the present invention include pigments known as charge generation materials. The ratio of the charge generation pigment to the binder resin is 5 to 15% by weight. If the ratio is too small, the sensitivity will decrease,
It causes an increase in the residual potential, and if it is too much, it causes a decrease in charge acceptability, a decrease in mechanical strength, an increase in the optical memory effect, and a decrease in cyclic stability. For example, in the composition described in JP-A-60-254142, the ratio of the charge generation pigment is 10 to 50% by weight based on the entire photosensitive layer.
And, in the one described in JP-A-61-48862,
Although the content ratio to the binder resin is set to 20: 100 to 50: 100, in these cases, the above-described disadvantages occur. It is considered that the cause is above all that the absolute amount of the pigment is too large. As a result of investigations by the present inventors, it has been found that the optimum amount exists separately from the range in the above-described conventional technique, and the above range is most preferable. As the charge transporting substance, a compound having a hole transporting property can be used. Examples of these compounds include amine compounds, hydrazone compounds, pyrazone compounds, oxazole compounds, stilbene compounds, and carbazole compounds. The ratio of the charge transport material to the binder resin is 50 to 180.
It must be in weight percent. If this ratio is too low, charge transport is hindered, causing a decrease in sensitivity and an increase in the residual potential. If it is too high, the mechanical strength decreases. Since most of these charge generation pigments and charge transport substances do not themselves have a film-forming property, they are usually used by being dispersed or dissolved in a binder resin. As the binder resin, any resin can be used as long as it has high compatibility with the charge transport material, can disperse the charge generation pigment, and has a high film-forming property. Examples include polycarbonate, polyacrylate, polyester, polystyrene, styrene-acrylonitrile copolymer, polysulfone, polymethacrylate, styrene-methacrylate copolymer, vinyl polymer, polyurethane, epoxy resin and the like. The photosensitive layer is used by dispersing and dissolving the charge generating pigment and the charge transport material in a binder resin. As a dispersion method, a conventional method such as a ball mill, a roll mill, a sand mill, and an attritor is used. Any solvent can be used as long as it has good dispersibility with respect to the charge generation pigment and dissolves the charge transport material and the binder resin. In the present invention, the thickness of the photosensitive layer is preferably about 5 to 50 μm. In the electrophotographic photoreceptor of the present invention, it is possible to form a layer containing no charge generating pigment between the conductive support and the photosensitive layer. That is, as long as the photosensitive layer has a sufficient charge generating ability, a hole transport layer can be provided on the lower side to prevent generation of unnecessary heat-generated carriers, and to generate electrons from the conductive support. Injection can also be prevented. As the hole transporting layer, the charge transporting substance and the binder resin used in the present invention can be used as they are. However, it does not need to be exactly the same as the material used for the photosensitive layer. The thickness is desirably about 2 to 30 μm. FIG. 3 shows a schematic configuration in that case, in which a hole transport layer 6 composed of a charge transport material 4 and a binder resin 5 is provided between the photosensitive layer 2 and the conductive support 1. I have. Further, in the electrophotographic photoreceptor of the present invention, it is preferable to provide an undercoat layer between the conductive support and the photosensitive layer or the hole transport layer. The undercoat layer is effective for improving the adhesion between the photosensitive layer or the hole transport layer and the support, covering the support with defects (preventing image quality defects), and removing unnecessary charges from the support. Injection can also be prevented. Materials for the undercoat layer include polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl pyridine, cellulose ethers, cellulose esters, polyamide, polyurethane, casein, gelatin, polyglutamic acid, starch, starch acetate, amino starch, polyacrylamide, polyester, and silane. Coupling agent, zirconium chelate,
Titanium chelates and the like. The resistivity of these materials is preferably about 10 ⁵ to 10 ¹⁴ Ω · cm. The thickness of the undercoat layer is about 0.01 to 2 μm. FIG. 2 shows a schematic configuration in that case, in which an undercoat layer 7 is provided between the photosensitive layer 2 and the conductive support 1. FIG. 4 shows an electrophotographic photosensitive member of the present invention.
The schematic configuration in the case where both the hole transport layer 6 and the undercoat layer 7 are provided between the photosensitive layer 2 and the conductive support 1 is shown. Function In the electrophotographic photoreceptor of the present invention, electron-hole pairs are generated in the pigment by light irradiation, holes are injected and transported into the charge transport material, and electrons are uniformly distributed in the photosensitive layer. It is believed that it will be transported through the dispersed pigment. Therefore,
Applicable to both positively charged type and negatively charged type. However, this electrophotographic photoreceptor exhibits extremely excellent characteristics especially when used in a positive charging type. Although the reason for this has not yet been fully understood, the present inventors think as follows. First, in the case of positive charging, light irradiation causes light to be absorbed not only near the surface of the photosensitive layer but also to some extent inside, causing charge generation. (The depth at which light absorption occurs depends on the absorptivity, Of the generated charges, holes are injected into the charge transport material and move,
It takes a sufficiently short time to reach the substrate from the surface of the photosensitive layer. In addition, since electrons are generated on the side relatively closer to the surface, their movement distance is short, and even relatively slow conduction through the pigment is considered to pose almost no problem in practical use. However, when used with negative charge, the moving distance of charges (hole electrons) is reversed, so that potential decay does not occur promptly, lowering the sensitivity. In addition, charge is gradually accumulated by repeated use. , Its properties are likely to be degraded. Examples Hereinafter, the present invention will be described with reference to examples. Example 1 A disazo pigment represented by the following general formula was prepared as a charge generation pigment. For 10 g of this pigment, 1 g of polyvinyl butyral (trade name: BM-1 manufactured by Sekisui Chemical Co., Ltd.) and 40 g of cyclohexanone
g was mixed and then dispersed well by a paint shaker, which was applied to an aluminum sheet with an applicator and dried. The film thickness after drying was 6 μm. This was tested using an "Electrostatic Copying Paper Testing Apparatus SP-428" (manufactured by Kawaguchi Electric Works) to evaluate its photoconductive properties. That is, + 6k
Each voltage of V and -6 kV was applied to the surface of the photoreceptor, respectively. One second after charging, exposure was performed using a tongue lamp.
In the case of the positive charging, almost no light attenuation occurred, whereas in the case of the negative charging, rapid light attenuation was exhibited. Therefore, it was found that the disazo pigment has an electron transporting ability. Next, a compound of the following structural formula showing excellent properties as a hole transport material 8 g of polycarbonate resin (trade name: Lexan 145 GE, molecular weight 35,000 to 40,000) was dissolved in 150 g of monochlorobenzene, 1 g of the above disazo pigment was mixed therein, and then dispersed by a ball mill for 24 hours. Then
This was applied to the surface of an aluminum pipe having a diameter of 84 × 338 mm by a ring color coating machine described in JP-A-53-22544. The film thickness after drying at 100 ° C. × 1 hour was 19 μm. The electrophotographic photoreceptor thus prepared is charged so that the current flowing into the drum becomes +15 μA, and the potential (Vpo) at that time is measured. Then, white light is irradiated with a halogen lamp to emit light. The sensitivity (d) is measured by measuring the exposure amount E (erg / cm ² ) and the potential attenuation amount (V) at that time.
V / dE). As a result, Vpo = + 780 [Volts] and dV / dE = 112 [V · cm ² / erg]. Further, the electrophotographic photoreceptor was repeatedly charged and exposed 1000 times, and the same measurement was carried out. As a result, it was found that Vpo = + 750 Volts and dV / dE = 113 V · cm ² / erg, which were extremely stable. Was. Comparative Example 1 An electrophotographic photosensitive member was prepared in exactly the same manner as in Example 1 except that the amount of the disazo pigment was changed to 2 g, and its characteristics were evaluated. The thickness was 20 μm. As shown in the following table, the characteristics were low in the received potential, and were not endurable for repeated use. Examples 2 to 4 Brominated anthantrone (Example 2) Disazo pigment shown below (Example 3) in exactly the same manner as in Example 1. The following disazo pigment (Example 4) When the charge transporting property of the pigment was evaluated, the pigment showed n-type properties. Further, an electrophotographic photoreceptor was prepared in the same manner, and its characteristics were evaluated. The results shown in Table 1 were obtained. Comparative Examples 2-3 An electrophotographic photoreceptor sample was prepared in exactly the same manner as in Example 1 except that the charge generating pigment was changed to the following substances, and the characteristics were evaluated. β-Cu phthalocyanine (Comparative Example 2) χ-H ₂ phthalocyanine (Comparative Example 3) As a result, the substances of Comparative Examples 2-3 were p-type. The properties of the electrophotographic photosensitive member are shown in Table 1. Comparative Example 4 The procedure of Example 1 was repeated, except that 1.5 g of the charge-generating pigment used in Example 4 and 4 g of the hole-transporting substance used in Example 1 were dispersed in 12 g of the polycarbonate resin of Example 1. Thus, an electrophotographic photosensitive member was prepared, and the electrophotographic characteristics were evaluated in the same manner. As a result, VPO = + 810 [Volts] and dV / dE = 98 [V · cm ² / erg]. After 1000 times of charging and exposure, VPO = + 860
[Volts], dV / dE = 55 [V · cm ² / erg]. From this, the light sensitivity was remarkably reduced by repeated use, and was not practical. It is considered that the reason for this is that the rise in the residual potential after 1000 times to 160 [Volts] led to a decrease in photosensitivity. Effect of the Invention The electrophotographic photoreceptor of the present invention can be applied to both positively charged type and negatively charged type, and especially when used in positively charged type, has extremely excellent characteristics in sensitivity, environment and stability in repeated use. Is shown. The electrophotographic photoreceptor of the present invention can be effectively used in an electrophotographic copying machine, but can also be applied to various printers, microfilm readers, electrophotographic plate making systems and the like to which xerography technology is applied.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 are schematic cross-sectional views of examples of an electrophotographic photosensitive member according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Conductive support, 2 ... Photosensitive layer, 3 ... Charge generation pigment, 4 ... Charge transport material, 5 ... Binder resin, 6 ... Hole transport layer, 7 ... Undercoat layer .

Continuation of front page    (56) References JP-A-61-48861 (JP, A)                 JP-A-60-254142 (JP, A)                 JP-A-57-202349 (JP, A)                 JP-A-60-102634 (JP, A)                 JP-A-60-258547 (JP, A)

Claims (1)

(57) [Claims] In an electrophotographic photoreceptor having a layer in which a charge generating pigment and a charge transporting substance are dispersed and dissolved in a binder resin as a photosensitive layer on a conductive support, the charge generating pigment itself may be used. At least one kind of photoconductive pigment having an electron-transporting ability, and the ratio of the charge-generating pigment to the binder resin is 5 to 15% by weight, and the charge-transporting substance is at least one kind. An electrophotographic photoreceptor, which is a compound having a hole transporting ability, and wherein the ratio of the charge transporting substance to the binder resin is 50 to 180% by weight.