JP2839106B2 - Electrophotographic photoreceptor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor for forming an electrostatic latent image in an electrophotographic apparatus used as a copying machine or a printer, and particularly to an electrophotographic photoconductor having excellent durability stability. The present invention relates to an electrophotographic photosensitive member (hereinafter, may be abbreviated as “photosensitive member”).

[Prior Art] Conventionally, electrophotographic photosensitive members mounted on electrophotographic apparatuses used as copiers or printers include inorganic CdS, ZnO, TiO ₂ , Se, Se-Te and α-Si. It has been known. In recent years, with the expansion of the copier or printer market,
Organic photoreceptors, which are inexpensive and have excellent mass productivity, have begun to attract attention, and their initial characteristics such as sensitivity have advanced beyond that of inorganic ones. Is that a wide range of functions can be added by chemical reforming.

Furthermore, organic materials have the advantage that their properties can be easily improved and optimized.

A general form of an organic photoreceptor is one in which a charge transporting material and a charge generating material, which are organic materials, are formed on a conductive substrate using a film-forming resin or the like. From the viewpoint of the characteristics, a function-separated type photosensitive layer in which a charge transport layer and a charge generation layer are separated and laminated is particularly excellent, and there are many examples thereof. In addition, in the case of an organic photoreceptor, when various intermediate layers are interposed between the conductive substrate and the photosensitive layer in order to improve the adhesion between the conductive substrate and the photosensitive layer and the ability to control the charge injection property, etc. There are many.

An inferior point of an organic photoreceptor having the above-mentioned features and advantages as compared with an inorganic photoreceptor is insufficient durability. Organic photosensitive materials are more susceptible to physical abrasion and damage because they are more flexible than inorganic materials. Further, the chemical stability is still lower than that of the inorganic material, and particularly, it is greatly affected by deterioration by an active corona product such as ozone generated by a charging process in a durable use. The organic photoconductive material or resin forming the organic photoreceptor is susceptible to chemical changes such as oxidation, addition, decomposition or deterioration by the active corona product.

In the organic photoreceptor that has undergone such a chemical change,
This causes a decrease in sensitivity, accumulation of residual potential, a decrease in carrier mobility, a decrease in charging ability, and the like. Further, when a reaction product or a complex of a corona product or an organic photoreceptor and a corona product acts as a charge acceptor or a charge donor,
They cause an increase in sensitivity due to generation and injection of carriers, a decrease in charging ability, an increase in dark decay, and the like.

The deterioration of the organic photoreceptor due to the corona product described above appears as an influence on the entire surface of the photoreceptor because the corona product is generated when the apparatus is operating. Further, even when the apparatus is stopped, the corona charger, NO _X, from knowing the corona products such as HNO ₃ is remained, it emerges as a partial degradation of the charger near the photoreceptor. In either case, the deterioration of the photoreceptor causes a change in the copy or print image, but when the entire photoreceptor is deteriorated, a change in the density of the entire image or blurring of the image occurs. Will occur.

Since the organic photoreceptor which has undergone such chemical deterioration needs to be replaced, it is reflected in an increase in the running cost of the copier or the printer and in a decrease in serviceability or maintenance.

This fact cancels out the inherent advantages of the organic photoreceptor, such as low cost and ease of handling, and various solutions have been proposed to solve the problem.

For example, JP-A-57-122444 or JP-A-58-1202
As disclosed in JP-A-60, there is a method of adding a deterioration inhibitor to a photosensitive layer. However, it is not a complete measure,
Particularly, in an apparatus for copying or printing a graphic image or a photographic image requiring high image quality, an organic photoconductor having high practicality has not been obtained.

[Problems to be Solved by the Invention] An object of the present invention is to prevent deterioration of an organic photoreceptor caused by a corona product, and in particular, to prevent a decrease in charging ability and image unevenness due to an increase in carriers. .

[Means for Solving the Problems] According to the knowledge obtained from the study of the present inventors, the following facts have been found.

That is, during the deterioration of the organic photoreceptor due to the corona product, the corona product itself, or a reactant or a complex formed between the organic material constituting the photosensitive layer and the corona product becomes an electron acceptor or an electron donor. The fact that it may act as a body.

When the electron acceptor or the electron donor is generated and mixed into the organic photoreceptor, the electron acceptor or the electron donor exerts an ability to generate a carrier and an injection action. And so on.

It has also been suggested that the above-mentioned adverse effects due to the generation and injection of carriers are particularly remarkable when the corona product has penetrated to the interface between the photosensitive layer and the conductive substrate.

Therefore, the present inventors have selected a method for inactivating the corona product that has entered at the interface between the photosensitive layer and the conductive substrate in order to effectively achieve the object of the present invention. Specifically, a nitrogen-containing heterocyclic compound and an aromatic carboxylic acid contained in a nitrogen-conjugated heterocyclic structure were introduced into the interface between the photosensitive layer and the conductive substrate.

One of the characteristics of these nitrogen-containing heterocyclic compounds is that the unpaired electron pairs on the nitrogen atom tend to delocalize in the conjugated ring structure, and thus have a lower electron density than ordinary nitrogen atoms. No. It has been found that such compounds are unlikely to trap electric charges, and therefore, even if they are interposed between the conductive substrate and the photosensitive layer, the decrease in sensitivity and the increase in residual potential on the photosensitive layer are small. Further, by adding an aromatic carboxylic acid, the trapped charge on the nitrogen-containing heterocyclic compound is effectively detrapped, and the decrease in sensitivity and the increase in residual potential are further reduced. A photosensitive member having a low residual potential was obtained. In addition, since nitrogen-containing heterocyclic compounds exhibit weak basicity or weak donor properties in the presence of aromatic carboxylic acids, they form complexes with acidic substances such as corona products or acceptors and inactivate them. can do.

In the present invention, to interpose a nitrogen-containing heterocyclic compound and an aromatic carboxylic acid between the conductive substrate and the photosensitive layer,
A film obtained by dissolving the nitrogen-containing heterocyclic compound and aromatic carboxylic acid in, for example, an appropriate organic solvent can be formed by a coating method. Even a compound which is difficult to form a film by itself can be applied or formed in the form of a stabilizing layer using an appropriate resin as a binder.

The amount of the nitrogen-containing heterocyclic compound and aromatic carboxylic acid introduced is usually 0.1 to 500 mg / m ² per unit area of the photoreceptor. This value depends on the electron density on the nitrogen atom of the compound and the dissociation constant of the aromatic carboxylic acid, but is preferably 1 to 200 mg / m ^2.
It is. If the amount is less than this, the ability to inactivate corona products and the like is insufficient. If the amount is larger than this, adverse effects such as a decrease in adhesion between the substrate and the photosensitive layer occur.

The ratio between the nitrogen-containing heterocyclic compound and the aromatic carboxylic acid is usually between 50/1 to 1/50, preferably 20/1 to 1/20.
Mix in the ratio of

In forming the stabilizing layer together with the binder resin, the following binder resins are preferably used: polyester resin, polycarbonate resin, polyacrylate resin, polyurethane resin, phenol resin, epoxy resin, alkyd resin, Examples include melamine resin, polystyrene resin, polyvinyl butyral resin, polyamide resin, acrylic resin, styrene-butadiene copolymer, styrene-acryl copolymer, cellulose, modified cellulose resin, polyamino acid, casein and gelatin.

The thickness of these stabilizing layers is usually 0.01 to 10 μm, preferably 0.1 to 3 μm. Further, the stabilizing layer may contain a conductive pigment, an antioxidant, a surfactant or the like.

The stabilizing layer in the photoreceptor of the present invention is the center of the improvement, and one of them is the following nitrogen-containing heterocyclic compound A or AA.

Here, X ¹ and X ² are an alkyl group, an aralkyl group, an aryl group which may have a substituent, and a heterocyclic ring which may have a substituent,
-OH, -NO _2, -COOR (where R represents H, an alkyl group, an aralkyl group and an aryl group), (Where R ¹ and R ² represent H, an alkyl group, an aralkyl group and an aryl group), Cl, Br, F, CN; Z represents an alkylene group, an alkenylene group, a nitrogen atom, an oxygen atom and a sulfur atom, When two or more coexist, they may be the same or different.

Here, Y is an alkylene group, alkenylene group, arylene group, oxygen atom and sulfur atom; Z ¹ and Z ² may be one or more as defined in Group A and may be different from each other.

 The basic skeleton of the compounds belonging to Group A is as follows.

The basic skeleton of the compounds belonging to Group AA is obtained by linking two or more nitrogen-containing heterocyclic compounds belonging to Group A by an intermediate group -Y-. An example is shown below. (Here, n is usually 1 to 10, preferably 1 to 6, more preferably 1 to 4.) Preferred compounds among these are the _{following: A 11, AA 1, AA} 2, AA 4, AA 5.

The other one of the stabilizing layers in the photoreceptor of the present invention is an aromatic carboxylic acid belonging to the following group B. The basic skeleton is, as shown in the following example, via a condensed ring such as a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring or a pyrene ring, or a diphenyl ring or a hydrocarbon group in which two or more of these rings are directly bonded. It has a structure in which one or more carboxyl groups are bonded to an aromatic nucleus such as diphenylalkane formed by bonding.

(Here, m is 1 to 10, preferably 1 to 4.) A substituent may be bonded to this basic skeleton. Examples of the substituent include the following. These may be present in combination of two or more types: an alkyl group, an aralkyl group, an amino group, a substituted amino group, an aryl group, a halogen atom, a hydroxyl group, an alkoxy group, a nitro group, and a cyano group.

Examples of preferred aromatic carboxylic acids belonging to Group B are as follows: mononitrobenzoic acid, monochlorobenzoic acid, dichlorobenzoic acid, chloronitrobenzoic acid, mononitronaphthoic acid, dinitronaphthoic acid, methylnaphthalenedicarboxylic acid, nitro Naphthalenedicarboxylic acid.

As the charge transporting material used in the present invention, a polycyclic aromatic compound or a nitrogen-containing compound generally used for an organic photoreceptor is sufficient. Specifically, as shown in FIG. 1, a phenanthrene derivative, an anthracene derivative, Triphenylmethane derivative, triphenylamine derivative, carbazole derivative, fluorenone derivative, pyrazoline derivative, hydrazone derivative, triazole derivative, oxazole derivative,
Examples include an imidazole derivative, an oxadiazole derivative, and a stilbene derivative.

The charge generating material used in the present invention is, for example, as follows: phthalocyanine pigment, polycyclic quinone pigment, bisazo pigment, disazo pigment, azo pigment, indigo pigment, quinacridone pigment, athrenium salt dye, squarylium dye,
Cyanine dye, pyrylium dye, thiopyrylium dye,
Examples include xanthene dyes, quinoneamine dyes, triphenylmethane dyes, styryl dyes, selenium, selenium-tellurium, amorphous silicon (amorphous silicon or α-Si), cadmium sulfide, and the like.

The photoreceptor in the present invention comprises a conductive substrate and a photosensitive layer. The photosensitive layer is basically composed of the charge transporting material and the charge generating material and a binder resin for forming them. As the layer configuration, there are a single-layer type and a laminated type, and the latter is more general. In the case of a single layer type, the charge transporting material, the charge generating material and the binder resin are mixed at an appropriate ratio.

On the other hand, in the case of a stacked type, a charge transport material and a charge generation material are separately formed with a binder resin, and then they are stacked to form a laminate of a charge transport layer and a charge generation layer. At this time, any layer may be formed on the conductive substrate side,
Generally, the charge generation layer is formed first. Further, the charge transport layer may contain a charge generating material, and the charge generating layer may contain a charge transport material. The following are used as binder resins for film formation, for example: polyester resin, polyarylate resin, acrylic resin, acrylonitrile resin, methacryl resin, polycarbonate resin, polyamide resin, vinyl chloride resin, vinyl acetate resin , Epoxy resin, phenolic resin, polyurethane resin, styrene-butadiene copolymer, styrene
Acrylonitrile copolymer and the like.

The ratio of the charge generation material to the binder resin in the laminate type is usually 0.5 / 1 to 10/1, and preferably 1/1 to 5/1.
The thickness of the charge generation layer is usually 0.01 to 5 μm, preferably 0.05 to 3 μm.

Similarly, the ratio of the charge transporting material of the charge transporting layer and the binder resin is usually 5/10 to 50/10, preferably usually 7/10 to 30/10.
It is. The thickness of the charge transport layer is usually 5 to 50 μm, preferably 10 to 30 μm.

As the conductive substrate of the photoreceptor used in the present invention,
For example, metals such as aluminum, iron, copper, zinc, nickel, chromium, titanium, and indium, and alloys thereof, or plastics, paper, glass, or the like can be used.

As the conductive treatment, a method of depositing a layered conductive material, a method of forming a film by containing or dispersing in a binder resin, and the like are generally used.

As the conductive material contained and dispersed in the binder resin, for example, the metal or alloy powder, carbon, tin oxide,
A powder such as zinc oxide, antimony oxide or silicon oxide, a conductive plastic, or the like is used.

Examples of the shape of the conductive substrate include a film, a sheet, a belt, a cylinder, a column, and the like.

A general coating (coating) method can be used as a film forming method used to form the photoreceptor in the present invention. That is,
The photoreceptor material can be used in the form of a liquid by dispersing or dissolving it in a suitable solvent together with a binder resin or the like.
These liquids can be formed into a film by a coating method such as spray coating, dip coating, blade coating, Meyer bar coating, roller coating, spinner coating, and curtain coating.

Nitrogen-containing heterocyclic compound 9 parts by weight of the Example 1 the following structures A _1, 9 parts by weight of the aromatic carboxylic acid of structure B ₁ and 100 parts by weight of a soluble polyamide [trade name: Toresin EF-30 (manufactured by Teikoku Chemical)], 920 parts by weight of methanol and 430 parts by weight of isopropanol were stirred and dissolved.

On a mirror-finished aluminum cylinder 80 mm in diameter x 375 mm in length and 1.0 mm in thickness, dip and apply the above solution at 90 ° C.
After drying for 10 minutes, a stabilized layer having a thickness of 1.0 μm was obtained.

Next, the following azo pigment 10 parts by weight, Polycarbonate resin (bisphenol A type: molecular weight
(M _N = 13,000) 20 parts by weight and 1000 parts by weight of cyclohexanone were subjected to sand milling using a glass bead having a diameter of 1 mm to obtain 2 parts by weight.
Mixing and dispersion at 2,000 rpm for 5 hours at 5 ° C.

The contents were washed out with 500 parts by weight of cyclohexanone to remove glass beads, and after centrifugation at 10,000 rpm, the mixture was diluted with 500 parts by weight of tetrahydrofuran and 200 parts by weight of cyclohexanone.

After spray-coating this dispersion on the stabilizing layer, 70
A charge generation layer having a thickness of 0.15 μm was formed by drying at 10 ° C. for 10 minutes.

Further, 20 parts by weight of the following stilbene compound, Polycarbonate resin (bisphenol Z type: M _N = 14,
000) 25 parts by weight and 200 parts by weight of benzene were mixed and dissolved. After dip coating this solution on the charge generation layer, 11
By drying at 0 ° C. for 80 minutes, a charge transport layer having a thickness of 25 μm was formed to obtain a photosensitive drum. Table 1 shows the durability test results.

Comparative Example 1 A photoconductor drum was obtained in the same manner as in Example 1, except that the stabilizing layer did not contain any of the nitrogen-containing heterocyclic compound and the aromatic carboxylic acid.

Evaluation of Characteristics Fluctuation by Endurance Test For the endurance test, a copying machine [trade name: NP-3525 (manufactured by Canon)] was used.

The copying machine was driven after the photoconductor drum was mounted thereon, and the primary charging grid bias was adjusted so that the dark potential (Vd) of the photoconductor was -800 V by a potential measurement sensor arranged at the developing position. Furthermore, the voltage of the document reading halogen lamp was adjusted such that the light potential (V1) of the photoconductor when using a solid white document was -100V.

After the initial settings described above, a continuous durability test was performed on a solid white document in an A4 size side-by-side flow to 10,000 sheets. After the durability test, Vd and Vl were measured again, and V1 was measured when the grid bias was readjusted to Vd = -800V. Table 1 shows the results of the durability test.

As a result, in the photoreceptor of Comparative Example 1, the decrease of Vd was 50 V and Vd.
l decreased to 50 V, but in the photoconductor of Example 1, Vd
It was found that the fluctuation of the potential was small as a result of the decrease of 10 V and the decrease of Vl of 5 V. Also, the amount of light required for the initial Vl setting changes only smaller than in Comparative Example 1, and
It was found that the sensitivity reduction width was also small. That is, it can be said that a good photoconductor was obtained.

Before and after the durability test, a change in density of a halftone image and occurrence of image unevenness were evaluated. Comparative Example 1
In Example 2, the image density decreased and the density unevenness occurred after the durable use, but in Example 1, a stable halftone image was obtained even after the durable use.

In Example 1, to create a photosensitive drum using the same method in except for using aromatic carboxylic acids having the following structure a ₂ stabilizing layer containing heterocyclic compound and structure b _2, durable The test was performed. Good results were obtained for both the potential and the image, which are shown in Table 1.

Example 3 In Example 1, by the exception of using the aromatic carboxylic acid of a nitrogen-containing heterocyclic compound and structure b ₃ of the following structure a ₃ to stabilization layer similar operation, durable create a photoreceptor drum The test was performed. Good results were obtained for both the potential and the image, which are shown in Table 1.

Example 4 In Example 1, by the exception of using the aromatic carboxylic acid of a nitrogen-containing heterocyclic compound and structure b ₄ of the following structure a ₄ stabilizing layer similar operation, durable create a photoreceptor drum The test was performed. Good results were obtained for both the potential and the image, which are shown in Table 1.

Example 5 Example 1, by the exception of using the aromatic carboxylic acid of a nitrogen-containing heterocyclic compound and structure b ₅ of the following structure a ₅ to stabilization layer similar operation, durable create a photoreceptor drum The test was performed. Good results were obtained for both the potential and the image, which are shown in Table 1.

Example 6 Example 1, in addition to using four parts by weight of the aromatic carboxylic acids, nitrogen-containing heterocyclic compound and structure b ₆ of the following structure a ₆ to stabilization layer creates a photosensitive drum in the same manner Endurance test. Good results were obtained for both the potential and the image, which are shown in Table 1.

Example 7 Example 1, the same operations in except for using 1 part by weight of aromatic carboxylic acids, nitrogen-containing heterocyclic compound 2 parts by weight and structure b ₇ of the following structure a ₇ to the stabilization layer, a photoreceptor A drum was prepared and a durability test was performed. Good results were obtained for both the potential and the image, which are shown in Table 1.

Example 8 The following thermosetting polyurethane was used as a stabilizing layer binder. That is, trifunctional polyether polyol [trade name: Nipporan 800 (manufactured by Nippon Polyurethane)] 50
Parts, polyfunctional blocked isocyanate [product name: Coronate 240 (manufactured by Nippon Polyurethane) 50 parts by weight, 6 parts by weight of a nitrogen-containing heterocyclic compound having the following structure a _8, aromatic carboxylic acid 4 parts by weight and cyclohexanone of structure b ₈ 700 parts by weight, 300 parts by weight of methyl ethyl ketone
After being applied on an aluminum cylinder, it was cured at 150 ° C. for 60 minutes to form a 0.8 μm-thick polyurethane-stabilized layer.

The preparation and durability evaluation of the photoreceptor were the same as in Example 1,
The results were also good. The results are shown in Table 1.

Comparative Example 2 The same photoreceptor drum preparation and durability test were carried out as in Example 8, except that a polyurethane intermediate layer containing no nitrogen-containing complex compound and no aromatic carboxylic acid was used. The results are shown in Table 1. As a result, adverse effects such as a decrease in potential and image unevenness occurred.

Example 9 Example 8, the same operations other than using the nitrogen-containing heterocyclic compound 6 parts by weight and 6 parts by weight of the aromatic carboxylic acid of structure b ₉ of the following structure a ₉ to the stabilization layer, a photoreceptor A drum was prepared and a durability test was performed. Good results were obtained for both the potential and the image, which are shown in Table 1.

6 parts by weight of the aromatic carboxylic acids, nitrogen-containing heterocyclic compound 8 parts by weight of the structure b ₁₀ Example 10 The following structures a _10, methanol 50 parts by weight of n
An aluminum cylinder was dip-coated with a solution of 50 parts by weight of butanol, and dried at 80 ° C. for 20 minutes.
The solid content attached to the aluminum cylinder was 40 mg / m ² . Thereafter, as in the other examples, photoconductor drum preparation and durability tests were performed. The results are shown in Table 1.

Comparative Example 3 In the same manner as in Example 1, except that the intermediate layer did not contain a nitrogen-containing heterocyclic compound, the same photoreceptor and durability test were performed. The results are shown in Table 1.

In Example 11 Example 10, the same operations other than using the aromatic carboxylic acid of a nitrogen-containing heterocyclic compound and structure b ₁₁ of the following structure a ₁₁ stabilizing layer, durable create a photoreceptor drum The test was performed. The results were good for both the potential and the image, and are shown in Table 1.

[Effects of the Invention] The photoreceptor drum of the present invention has a nitrogen-containing heterocyclic compound present at the interface between the photosensitive layer and the conductive substrate or as an intermediate stabilizing layer, thereby preventing a decrease in the potential of the photosensitive layer during a durability test. It is a photosensitive drum that is unlikely to occur.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masafumi Hisamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Fumio Sumino 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-1-314253 (JP, A) JP-A-63-167373 (JP, A) JP-A-62-279345 (JP, A) JP-A-62-270962 (JP, A) A) JP-A-2-146555 (JP, A) JP-A-63-212942 (JP, A) JP-A-62-99762 (JP, A) JP-A-64-88553 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G03G 5/14 101

Claims (2)

(57) [Claims] 1. An organic electrophotographic photoreceptor comprising a conductive substrate and a photosensitive layer containing at least a charge generating material and a charge transporting material present on the surface thereof, wherein an organic electrophotographic photosensitive member is provided between the conductive substrate and the photosensitive layer. An electrophotographic photoreceptor, wherein a layer containing a nitrogen-containing heterocyclic compound and an aromatic carboxylic acid is interposed as a stabilizing layer. 2. The electrophotographic photosensitive member according to claim 1, wherein said stabilizing layer comprises at least two layers of a layer comprising a nitrogen-containing heterocyclic compound and a layer comprising an aromatic carboxylic acid. body.