JP3003308B2 - Laminated electrophotographic photoreceptor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated electrophotographic photosensitive member having improved sensitivity and a method for producing the same.

[0002]

2. Description of the Related Art Electrophotographic photoreceptors include those using an inorganic photoconductor and those using an organic photoconductor. Of these, a photoreceptor using an organic photoconductor has been used frequently in recent years because of its advantages such as low environmental pollution, high productivity and low cost. However, among the organic photoconductors, substances that generate charges by absorbing visible light have poor charge retention, and conversely, substances that have good charge retention and are excellent in film-forming properties are generally formed by visible light. There is a disadvantage that there is almost no photoconductivity. As a method for solving this drawback, there is a method in which the photosensitive layer is functionally separated into a charge generation layer that absorbs visible light to generate charges and a charge transport layer that transports the charges, and is formed into a stacked type. By adopting such a laminated structure, the charge generation material and the charge transport material can be individually selected, and the selection criteria for each material can be broadened.

As charge generation materials, polycyclic quinone pigments,
Perylene pigments, indigo pigments, bisbenzimidazole pigments, quinacridone pigments, phthalocyanine pigments, monoazo pigments, disazo pigments, tris or higher polyazo pigments and the like are known, and as the charge transport material, amine compounds, hydrazone compounds, pyrazoline Compounds, oxazole compounds, oxadiazole compounds, stilbene compounds, carbazole compounds and the like are known. To make an electrophotographic photoreceptor using these materials,
Sensitivity, receptive potential, potential holding, potential stability, residual potential,
Electrophotographic properties such as spectral properties, and strength, durability,
It is necessary to select a material that is satisfactory over all aspects of service properties, such as stain resistance.

[0004] Among these characteristics, the sensitivity of the electrophotographic photosensitive member is the most important, and improvement of the sensitivity is always desired. The sensitivity is determined mainly by the combination of the charge generation material and the charge transport material, but also varies depending on the conditions for forming the charge generation layer and the charge transport layer, component adjustment, and the like. For example, the sensitivity can be increased to some extent by setting the thickness of the charge generation layer and / or the charge transport layer to be large. However, there is a limit due to a change in physical properties other than sensitivity, or a limitation in manufacturing technology. Increasing the proportion of the charge generation material in the charge generation layer is also effective in improving the sensitivity, but this is also limited by changes in physical properties other than the sensitivity and restrictions on manufacturing technology.

[0005]

Therefore, the type of material,
There has been a demand for a means for further improving the sensitivity without changing the component ratio, the film thickness of each layer, and the like, that is, after selecting the charge generation material and the charge transport material to certain specific types. For example, Japanese Patent Application Laid-Open No.
Japanese Patent No. 304265 describes that the sensitivity is improved by applying a dispersion obtained by adding a charge generation material together with an acid to a binder resin solution, but in this case, the amount of the acid added is reduced. When the amount is small, the sensitizing effect is small, and when the amount is too large, there is a drawback in that it is difficult to adjust the amount of the acid, for example, a secondary obstacle such as a decrease in charging potential occurs.

The present invention has been made in view of the above-mentioned problems of the prior art. That is, the object of the present invention is to
It is an object of the present invention to provide a laminated electrophotographic photoreceptor which has a simple adjustment of the amount of an acid, has improved sensitivity, and has stable characteristics, and a method for producing the same.

[0007]

Means for Solving the Problems Accordingly, the present inventors have
As a result of intensive studies to achieve the above objectives,
It has been found that by adding an excess amount of acid to the binder resin solution to disperse the charge generating material and removing the acid that has not been adsorbed by the charge generating material, sensitivity can be improved while suppressing secondary obstacles, The present invention has been completed.

That is, a feature of the present invention is that, in a laminated electrophotographic photosensitive member having at least a charge generation layer and a charge transport layer provided on a substrate, the charge generation layer converts the charge generation material into a binder resin solution. It is added and dispersed together with an excess amount of acid, and then the content of the acid in the dispersion is reduced by 10% by weight from the initial addition amount.
It has been formed by applying the reduced material.

Another feature of the present invention is that when a charge generating layer and a charge transport layer are sequentially laminated to produce a laminated electrophotographic photoreceptor, a charge generating material is used as a coating liquid for forming a charge generating layer. Is added to the binder resin solution together with an excess amount of acid to disperse, and thereafter, a coating solution in which the content of acid in the dispersion is reduced by 10% by weight or more from the initial addition amount is used.

Hereinafter, the present invention will be described in detail. FIG. 1 is a schematic view showing a cross-sectional view of the electrophotographic photoreceptor of the present invention, in which a charge generation layer is shown in an enlarged manner. A charge generation layer 2 and a charge transport layer 3 are provided on a substrate 1, and the charge generation layer 2 contains a charge generation material 4 and an acid 5. FIG. 2 is a schematic view of another embodiment of the present invention, in which a barrier layer 6 is provided between the base 1 and the charge generation layer 2.

As the substrate in the electrophotographic photosensitive member of the present invention, those conventionally used in the electrophotographic photosensitive member can be used. A charge generation layer is formed on a substrate by applying a dispersion of a powdery charge generation material in a binder resin solution.In the present invention, an acid is added during dispersion of the charge generation material. It is characterized in that an acid is removed from the dispersion obtained by addition and the amount is reduced by 10% by weight or more from the initial addition amount. If the amount of acid removed is less than 10% by weight, the dispersion is not stable, and an electrophotographic photosensitive member having good sensitivity cannot be obtained.

The types of acids used include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, phosphoric acid, formic acid, acetic acid,
Organic acids such as propionic acid, butyric acid, lactic acid, benzoic acid, and sulfonic acid, and halogen-substituted, nitro-substituted, and alkyl-substituted products thereof. Among these, an organic acid that is easily compatible with an organic solvent is preferable, and mono, di, or trifluoroacetic acid is particularly preferable because of its remarkable effect of improving sensitivity.

Known pigments can be used as the charge generating material. For example, polycyclic quinone pigments, perylene pigments, indigo pigments, bisbenzimidazole pigments, quinacridone pigments, phthalocyanine pigments, monoazo pigments, disazo pigments, tris or higher polyazo pigments can be used.

As the dispersing means for dispersing these charge generating materials, those used in a conventional manner such as a ball mill, a roll mill, a sand mill, an attritor and the like can be used.

Examples of the binder resin include polycarbonate, polystyrene, polyester, polyvinyl butyral, methacrylate polymer or copolymer, vinyl acetate polymer or copolymer, cellulose ester or ether, polybutadiene, polyurethane, and epoxy resin. And the like.

The acid may be added when dispersing the charge generating material in the binder resin solution. However, in order to further enhance the action of the acid, the charge generating material is dispersed in an acid solution in advance to carry out the acid treatment. And then adding and dispersing a resin solution therein. The amount of the acid added is about 0.1 to 2 mol% based on the solid content of the dispersion. In the case of an acid containing water such as hydrochloric acid or nitric acid, it is necessary to calculate by excluding water.
Although water will be mixed into the dispersion, it is not a problem because it is extremely small compared to the total amount of the dispersion. When dispersing the charge generating material in a solvent, the dispersion is performed by adding an acid, and then the dispersion is performed together with the binder resin solution. Are sensitized more than in the case where are mixed and dispersed.

As a means for reducing the content of the added acid, for example, a method of evaporating the acid from the dispersion can be adopted. At this time, it is effective to use means such as stirring, heating, and decompression. It is also possible to adopt a method in which an acid is adsorbed on a highly adsorptive substance such as zeolite to reduce the concentration of the acid in the dispersion.

On the other hand, the charge transport layer comprises the above-described charge transport material and a resin having a film forming property. Examples of such a resin include resins for general binder resins such as polycarbonate, polyarylate, polystyrene, polyester, styrene-acrylonitrile copolymer, polysulfone, polymethacrylates, and styrene-methacrylate copolymer. . The compounding ratio of the charge transport material and the resin is about 5: 1 to 1: 5, preferably about 3: 1 to 1: 3. When the former is too large, the mechanical strength of the charge transporting layer decreases, and when the former is too small, the sensitivity decreases.
The thickness of the charge generation layer is about 0.05 μm to 5 μm, and the thickness of the charge transport layer is about 5 μm to 50 μm.

As shown in FIG. 2, a barrier layer 6 may be formed between the charge generation layer and the substrate. The barrier layer is effective to prevent unnecessary charge injection from the substrate,
The chargeability of the photosensitive layer can be increased. Further, the adhesiveness between the photosensitive layer and the substrate can be improved. Examples of the material of the barrier layer include polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl pyridine, cellulose esters, cellulose ethers, polyamide, polyurethane, casein, gelatin, polyglutamic acid, starch acetate, amine starch, polyacrylate, polyacrylamide, and the like. can give. The resistivity of the material is 10
^It is preferably about ⁵ to 10 ¹⁴ Ω · cm. The thickness of the barrier layer is
It is about 0.05 μm to 2 μm.

[0020]

The reason why the sensitivity is improved when an acid is contained in the charge generation layer is unknown in detail, but the acid changes the surface properties of the charge generation material and the acid changes the charge transport described above. It has the property of forming a charge transfer complex with materials (all of them are electron donating compounds). Further, the acid tends to collect around the charge generating material. At the interface between the charge generation layer and the charge transport layer, a charge transport complex is formed due to the contact between the acid and the charge transport material, and a low-resistance portion having reduced electrical resistance is generated. Since the acid is a substance having a lower resistance than the binder resin from the beginning, when the charge generation layer is irradiated with light, the photo charge is injected from the charge generation material directly into the charge transport layer. It is considered that, when the photocharge is injected from the charge generation material through the low-resistance portion of the acid and the charge transfer complex, the charge flows more easily, the injection property is improved, and the sensitivity is improved.

When the content of the acid is small, the sensitizing effect is small, and when it is too large, inconveniences such as a decrease in physical properties other than sensitivity, for example, a decrease in charging potential and a decrease in repetition stability are liable to occur. Further, depending on the combination with the undercoat layer, when the content of the acid is too large, a phenomenon that the sensitivity is conversely lowered may occur.

In the present invention, the acid is once added in excess, and the acid is effectively adsorbed on the charge generating material.
By removing the excess acid, a stable coating solution can be obtained. In this case, the effect is diminished unless the amount of the acid added in excess is at least 10% by weight or more with respect to the optimum amount of the acid.

[0023]

The present invention will be specifically described below with reference to examples. Here, “parts” means “parts by weight” unless otherwise specified.

Examples 1 and 2 1 part of a polyvinyl butyral resin (trade name: manufactured by BMI Sekisui Chemical Co., Ltd.) was dissolved in 20 parts of cyclohexanone.
To this solution is added dibromant anthrone pigment (CI.
Pigment Red 168) and 0.015 part of trifluoroacetic acid. In this case, the solids content of the acid is 0.15% by weight. Next, dispersion was performed with a sand mill having a diameter of 1 mm using glass beads as a dispersion medium. Cyclohexanone was further added to the dispersion to prepare a coating solution having a solid content of 10%. Thereafter, the trifluoroacetic acid was evaporated by stirring the coating solution for 20 hours while contacting the coating solution with air, and the amount of acid to solid content was reduced to 0.1% each.
A coating solution was prepared in which the amount was reduced to 12% by weight and 0.13% by weight. At this time, the reduction amount of the acid was 20% (Example 1) and 13% (Example 2) of the initial addition amount, respectively.

The acid was quantitatively measured using an ion chromatograph (2000i / sp, manufactured by DIONEX).
The procedure was as follows. First, 2 g of the dispersion was put into a centrifuge tube together with the extract (a 10% aqueous solution of methanol), and the mixture was shaken with a tube mixer for 3 minutes to extract the acid into the aqueous solution. Next, the solid content was removed by a centrifuge, and 1 ml of the supernatant was diluted 25-fold with an eluent (aqueous solution of 1.8 mM sodium carbonate and 1.7 mM sodium hydrogen carbonate) to remove the remaining solid content. And filtered through a filter. The acid in the sample thus prepared was measured by ion chromatography, and the acid was quantitatively measured by comparing it with a standard sample that had been measured in advance.

On the other hand, a methanol / butanol mixed solution of nylon 8 resin (trade name: lactamide, manufactured by Dainippon Ink) was applied to an 84 mmφ × 310 mm aluminum pipe to form a 0.8 μm barrier layer. On top of that, the coating liquid was applied by a ring coating machine,
The resultant was dried by heating at 10 ° C. for 10 minutes to form a charge generation layer having a thickness of 0.8 μm.

On the other hand, N, N'-diphenyl-N, N'-
Bis (3-methylphenyl)-[1,1′-biphenyl] -4,4′-diamine (5 parts) is used as a charge transport material, and monochlorobenzene 4 is used together with 6 parts of a polycarbonate Z resin.
Dissolved in 0 parts. The obtained solution was applied by a dip coating method, and dried at 110 ° C. for 1 hour to form a 20 μm charge transport layer.

These electrophotographic photoreceptors are charged to -800 V, then irradiated with white light to attenuate the light, and the exposure E (erg / cm ² ) and the potential attenuation V at that time are measured. Then, the sensitivity dV / dE was determined. After repeating the above operations of charging and white light irradiation 20 times, the sensitivity was determined in the same manner. Further, the dark decay rate was calculated from the surface potential when 1 second had elapsed without performing light irradiation. Table 1 shows the results.
Shown in

Comparative Examples 1 and 2 Except that the amount of solids relative to the acid was reduced to 0.14% by weight by adjusting the amount of contact with air and that the coating solution was kept at 0.15% by weight, An electrophotographic photosensitive member was prepared and evaluated in the same manner as in Example 1. At this time, the amount of acid reduction was 7% (Comparative Example 1) and 0% (Comparative Example 2) of the initial addition amount, respectively.
It is. Table 1 shows the evaluation results.

Comparative Example 3 The initial addition amount of the acid was 0.012 parts (the solid content ratio was 0.12 parts).
% By weight) , an electrophotographic photosensitive member was prepared in the same manner as in Example 1 except that the coating solution was sealed so that the acid did not evaporate, and stirred for the same time as in Example 1.
evaluated. Table 1 shows the evaluation results.

Examples 3 and 4 Instead of the trifluoroacetic acid in Example 1, 0.028 parts of 35% hydrochloric acid were used. In this case, the amount of the acid (hydrogen chloride) with respect to the solid content was 0.10% by weight. The stirring time was 70 hours, the amount of air contact was changed, and the solid content of the acid was 0.085% by weight (Example 3) and 0.090% by weight (Example 4), respectively.
An electrophotographic photosensitive member was prepared in the same manner as in Example 1. Table 1 shows the results.

Comparative Examples 4 and 5 Except that the amount of contact with air was adjusted to 0.095% by weight (Comparative Example 4) and 0.10% by weight (Comparative Example 5) with respect to the solid content of the acid, respectively. An electrophotographic photosensitive member was prepared and evaluated in the same manner as in Example 3. Table 1 shows the evaluation results.

Comparative Example 6 The initial addition amount of hydrochloric acid was 0.024 parts (the solid content ratio was 0.0
85% by weight), an electrophotographic photoreceptor was prepared in the same manner as in Example 3 except that the coating solution was sealed so that the acid did not evaporate and stirred for the same time as in Example 3. ,evaluated. Table 1 shows the evaluation results.

[0034]

[Table 1] As is evident from the results shown in Table 1, the electrical properties and the electrical properties and the concentration of the acid after the addition of an excessive amount of the acid were lower than those from the initial addition of the desired amount of the acid. It can be seen that its stability is good, and it is better to use the one in which the amount of acid is reduced by 10% by weight or more from the initial addition amount.

[0035]

As described above, in the electrophotographic photoreceptor of the present invention, the charge generation layer forms a dispersion obtained by adding a charge generation material to a binder resin solution together with an excess amount of acid, Thereafter, the dispersion is applied in a state where the content of the acid in the dispersion is reduced by 10% by weight or more from the initial addition amount, so that the sensitivity is stable. Therefore, the electrophotographic photoreceptor according to the present invention is effectively used in an electrophotographic copying machine, but can be further applied to various printers, microfilm readers, electrophotographic plate making systems, etc. to which xerographic technology is applied. is there.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of an electrophotographic photosensitive member of the present invention.

FIG. 2 is a schematic view of another embodiment of the present invention.

[Explanation of symbols]

 1: substrate 2: charge generation layer 3: charge transport layer 4: charge generation material 5: acid 6: barrier layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-304265 (JP, A) JP-A-60-254139 (JP, A) JP-A-2-189559 (JP, A) JP-A-2- 204751 (JP, A) JP-A-60-178672 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 5/00

Claims (2)

(57) [Claims] In a laminated electrophotographic photoreceptor comprising at least a charge generation layer and a charge transport layer provided on a substrate, the charge generation layer comprises a charge generation material added to a binder resin solution together with an excess amount of acid. A multilayer electrophotographic photoreceptor formed by applying the mixture in a state where the content of the acid in the dispersion is reduced by 10% by weight or more from the initial addition amount. 2. A method for producing a laminated electrophotographic photosensitive member by sequentially laminating at least a charge generation layer and a charge transport layer on a substrate, wherein a charge generation material is used as a coating liquid for forming a charge generation layer. The solution is added and dispersed together with an excess amount of acid, and then the content of the acid in the dispersion is reduced by 1 from the initial addition amount.
A method for producing an electrophotographic photoreceptor, comprising using a coating solution reduced by 0% by weight or more.