JP3020334B2 - Organic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor having an organic photoreceptor layer formed on a surface-treated aluminum substrate, and more particularly to an organic photoreceptor excellent in halftone reproducibility. .

[0002]

2. Description of the Related Art As an electrophotographic photoreceptor, a photoreceptor in which various inorganic or organic photoconductor layers are provided on a conductive substrate is widely used. As one of such organic photoconductors, a so-called functional separation type photoconductor in which a charge generating substance and a charge transporting substance are combined in a laminated type or a dispersed type is known. As a conductive substrate for forming the organic photoreceptor, an aluminum raw tube is often used commercially. From the viewpoint of the adhesion to the organic photoreceptor layer, this aluminum tube is generally subjected to a surface treatment such as anodizing treatment, so-called alumite processing.

[0003]

Generally, in either the analog or digital electrophotographic system, the reproduction sensitivity, that is, the γ (gamma) value of a character image (high contrast image) is used to reproduce a halftone image. There is a demand for a developing method which is lower than the case and which is within a certain range. Here, the γ value is defined as a gradient when the relationship between the image density and the electrostatic latent image potential (or bias potential) is plotted on the ordinate and the image density is on the ordinate. In particular, digital PPC
In the (plain paper copy) method, in reproducing pseudo halftones by the multi-valued dither matrix method,
Severe control of J and γ values is required. Conventionally, the γ value in electrophotography naturally depends on the constitution and characteristics of the photosensitive layer, but when the photosensitive layer is constant, it often depends on the characteristics of the developer and the conditions of the developing system.

Incidentally, the inventors of the present invention conducted a manufacturing experiment for providing a certain organic photosensitive layer on an aluminum tube and found that the structure and electrical characteristics of the manufactured photosensitive members were almost the same. Nevertheless, the development sensitivity γ under the same development conditions
Often encountered unexplained facts of fluctuation. In the course of elucidating this trouble, the present inventors have found that the impedance characteristics of the anodized film present on the surface of the aluminum substrate greatly affect the development sensitivity and γ-value of the organic photoreceptor. Reached. That is, an object of the present invention is to provide an electrophotographic photoreceptor comprising a surface-treated aluminum substrate and an organic photosensitive layer provided thereon and having improved intermediate layer reproducibility. Another object of the present invention is to provide an organic photoreceptor for electrophotography capable of forming a halftone image without being significantly affected by the type of developer or the developing system.

[0005]

[Equation 1]

250 ≧ Z ₂ ≧ 100 and 4 ≦ Z ₂ / Z ₃ ≦ 5.5 (where Z ₂ is the impedance (KΩ) when the cell is measured at a frequency of 100 Hz, and Z ₃ is the cell at a frequency of 1000 Hz. Impedance (K
Ω). The present invention provides an organic photoreceptor characterized by having a surface treatment layer having electric characteristics satisfying (3).

The anodic oxide film was also measured in the above cell, and the formulas ( ₂ ) C ₂ > 4 and 3 ≧ C ₂ / C ₃ ≧ 1 (where C ₂ is the cell measured at a frequency of 100 Hz) When the capacity (nF), C ₃ is the cell at a frequency of 1000H
Represents the capacitance (nF) as measured by z. ) Is satisfied, and the measurement is performed using the same cell, and the following equation (3) is used. R ₂ <500 (where R ₂ is the AC resistance when the cell is measured at a frequency of 100 Hz. KΩ)).

[0007]

According to the present invention, in a photoreceptor having an organic photosensitive layer provided on a surface-treated aluminum substrate, the development sensitivity γ of the photoreceptor is affected by the specific impedance characteristic of the surface treatment layer. That is, it is based on the finding that a halftone image can be reproduced by selecting and using an aluminum base material that satisfies the above “Equation 1”. FIG. 1 shows the development sensitivity γ of photoconductors A, B, and C in which organic photosensitive layers are provided on various surface-treated aluminum tubes A, B, and C (for details, see examples described later).
It is what was asked. The results of measuring the AC resistance (KΩ) capacity (nF) and impedance (absolute value, KΩ) of these photoreceptors and element tubes are shown in Table 1, Table 2, and Table 3, respectively. The following interesting facts became clear.

First, referring to the columns of photoreceptor samples A, B and C in Tables 1 and 2, the electrical characteristics of these photoreceptors, that is, the AC resistance and static electricity, despite the difference in development sensitivity in FIG. Almost no difference is found in the capacitance. On the other hand, A, B and C without the photosensitive layer shown in Tables 1 and 2
Column, there is a marked difference in the AC resistance and capacitance of these samples A, B, and C. Further, with reference to Table 3, the AC resistance and capacitance of these samples are combined. It is clear that there is a correlation between the impedance characteristic and the development sensitivity of the photosensitive member.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

In the present specification, the measurement of various electrical characteristics was performed using the above-mentioned cell and the following measuring apparatus under the following conditions. That is, using an LCR meter Model AG-4311B manufactured by Ando Electric Co., Ltd.
V, measured by waveform SIN wave.

In the present invention, the impedance characteristic of the surface treatment layer of the aluminum substrate is set so as to satisfy the above (Equation 1) by preventing a sharp rise in the gradient of the development sensitivity curve and maintaining a gentle constant range. It was surprising to have the effect of controlling the slope of the road. Conventionally, an alumite layer is formed on the surface of the base tube by anodic oxidation, but this alumite layer merely serves to improve the adhesion of the organic photosensitive layer and prevent carrier injection during reversal development. It was not known at all that it affected the developing performance of the electrostatic latent image formed on the surface of the photosensitive layer.

The effect of optimizing the development sensitivity γ in reproducing halftones in the present invention has been found as a phenomenon from the results of numerous experiments and measurements, and the reason has not yet been elucidated. Not in. However, the present inventors presume this point as follows. The surface treatment layer formed on the substrate surface by anodic oxidation or the like is a layer composed of an aluminum oxide or a hydrated oxide, and has a structure ranging from a dense one to a relatively porous one. The hydrated oxide has a relatively high electric resistance and a relatively low electric resistance, and also has a capacitance as a film.

In FIG. 6 showing an equivalent circuit of this surface treatment layer, generally, this layer is formed as shown in FIG.
The circuit comprises a circuit in which a capacitor C and a resistor Rs are connected in series, and a circuit of a resistor Rp connected in parallel to the circuit. This circuit has a C-R in FIG. 6B on the high impedance side.
It can be approximated as a parallel circuit, while on the low impedance side
It can be approximated to the CR series circuit of (C).

In the case of a low-impedance (high-capacitance) surface-treated aluminum substrate used in the present invention, static electricity can be effectively removed through the surface-treated layer even when the charge generated in the photosensitive layer during exposure is relatively small. Is performed, and the surface potential is maintained until development.
It is considered that a sharp rise of the γ-value is prevented and the slope becomes gentle.

[0017]

Preferred embodiments of the present invention are described below. The organic photoreceptor according to the present invention comprises a surface-treated aluminum substrate and an organic photosensitive layer formed on the substrate, and the organic photosensitive layer may have a charge generation layer and a charge transport layer separated from each other, or may have a single layer. It may be.

Aluminum substrate When the substrate is used for a photosensitive drum, it is mainly an aluminum tube, and the surface of the tube is subjected to a surface treatment such as anodic oxidation. In the surface treatment, for example, an oxide film is formed by immersing in an aqueous solution of an acid such as oxalic acid, sulfuric acid, or chromic acid using the aluminum tube as an anode and applying a current. By anodizing the surface layer to form a fine porous layer in this way, in addition to enhancing the adhesion with the photosensitive layer described later, it also prevents carrier injection and the like and prevents discharge breakdown of the photoconductor layer. However, in the present invention, the surface treatment conditions are set so as to satisfy the above “Equation 1”, more preferably “Equation 2” and “Equation 3” during the surface treatment as described above. .

In general, the more densely the alumite film is formed, the higher the impedance becomes, and conversely, the thinner the film becomes, the lower the impedance becomes. This is related to the current density at the time of anodic oxidation, and the coating tends to be sparse at high current density. Also, as the thickness of the alumite film increases, the impedance of the film increases. This is related to the contact time. Further, if the alumite film after the electrolytic treatment is subjected to the sealing treatment, the impedance of the coating increases depending on the conditions of the sealing treatment. Therefore, the adjustment of the thickness and the density of the processing film may be performed by setting the current density, the voltage, the electrolysis time, the electrolysis temperature, the electrolyte concentration, and the like so as to obtain the impedance characteristics.

Although not limited to the following examples, as an example, in the case of a sulfuric acid film, a sulfuric acid having a concentration of 10 to 18% is used, a current density is 1 to 4 A / dm ² in a bath at a temperature of 15 to 25 ° C.
A condition that satisfies the above-mentioned electrical characteristics may be selected from a processing time of about 5 to 20 minutes. In addition, the sealing treatment may be similarly selected from conditions of about 5 to 30 minutes in water of 95 ° C. to boiling point. In addition, the thickness of the treatment film is generally preferably in the range of 2 to 20 μm.

In the present invention, the value of Z ₂ is preferably 250 KΩ or less.
It is preferably KΩ or more, and the value of Z ₂ / Z ₃ is preferably 4 or more, and more preferably 5.5 or less. Further, the value of C ₂ is preferably 10 nF or less and 4.5 nF or more. Further, the value of R ₂ is 500 KΩ or less, 100 KΩ
It is good to be above. Note that FIG. 7 shows 100 Hz (or 2 log Hz) to 100,000 Hz (or 5 log).
FIG. 3 is a characteristic diagram of a capacitance change depending on the frequency of the raw tube at (gHz).

Organic Photosensitive Layer The present invention can be applied to a laminated electrophotographic photoconductor and a monolayer dispersed electrophotographic photoconductor. For example, a charge generation layer (CGL) can be formed on a surface-treated aluminum tube, and a charge transport layer (CTL) can be provided on the charge generation layer. Alternatively, conversely, a charge transport layer may be provided on a base tube, and a charge generation layer may be provided on the charge transport layer. Further, a material in which a charge generating substance is dispersed in a charge transport medium on a base tube can be provided as a single layer as a photosensitive layer.

Examples of the charge generation material include selenium, selenium-tellurium, amorphous silicon, pyrylium salts, azo pigments, disazo pigments, ansanceron pigments, phthalocyanine pigments, indigo pigments, slen pigments, and toluidine. Pigments, pyrazoline pigments, perylene pigments, quinacridone pigments and the like are exemplified, and one kind or a mixture of two or more kinds is used so as to have an absorption wavelength range in a desired region.

This charge generation material can be applied in the form of a layer by means such as vapor deposition, or can be applied as a layer in a form dispersed in a binder resin. As such a binder resin, various resins can be used, for example, a styrene-based polymer, an acrylic-based polymer, a styrene-acryl-based copolymer, an ethylene-vinyl acetate copolymer, a polypropylene,
Olefin polymers such as ionomers, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester,
Alkyd resin, polyamide, polyurethane, epoxy resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, polyether resin,
Various polymers such as a phenol resin and a photocurable resin such as an epoxy acrylate can be exemplified. These binder resins may be used alone or in combination of two or more.

The charge transporting material is dispersed in the above-mentioned binder resin and a known material is used. For example, stilbene, N, N '-(o, p-dimethylphenyl) -N,
N '-(diphenyl) benzidine, 1,1-bis (p-
Diethylaminophenyl) -4,4-diphenyl-1,
3-butadiene, N, N-diethylaminobenzaldehyde-N, N-diphenylhydrazone, N, N-dimethylaminobenzaldehyde-N, N-diphenylhydrazone, N-methyl-N-phenylaminobenzaldehyde-N, N-diphenylhydrazone, 4-diphenylamino-α-phenylstilbene, triphenylamine and the like.

In such a configuration, the photoreceptor layer is formed by applying a coating solution using a solvent known per se and applying the coating solution to the surface layer of the base tube. In the photoreceptor formed in this way, even if the organic photosensitive layer is changed variously, its development sensitivity affects the impedance of the surface of the tube, and the AC resistance and capacity of the entire photoreceptor actually differ. It should be understood that this is not possible.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments. Example 1 Preparation of conductive substrate A pure aluminum drum was treated under the following anodic oxidation conditions to form an alumite layer on the surface thereof. Current density: 2.0 A / dm ² Voltage: 12 V Electrolyte free sulfuric acid: Sulfuric acid concentration 15% Temperature: 25 ° C. Time: 15 minutes The tube was sealed in 98 ° C. boiling water for 15 minutes. The obtained raw tube is referred to as a raw tube B (corresponding to the sample B in Table 1, Table 2, Table 3, and FIG. 1).

Preparation of Electrophotographic Photoreceptor 100 parts by weight of polyvinyl butyral as a binder resin and X-type metal-free phthalocyanine 2 as a charge generating material
Then, 00 parts by weight and a predetermined amount of dichloromethane were charged into a ball mill, and stirred and mixed for 24 hours to prepare a coating solution for the charge generation layer. The prepared solution was applied to the base tube B as a conductive substrate by a dipping method. The resultant was dried with hot air at 30 ° C. for 30 minutes to be cured, thereby forming a charge generation layer having a thickness of 0.5 μm. Next, a polycarbonate resin 10 is used as a binder resin.
0 parts by weight, 100 parts by weight of diethylaminobenzaldehyde-1,1-diphenylhydrazone as a charge transport material, and a predetermined amount of toluene were stirred and mixed with a homomixer to prepare a coating solution for a charge transport layer. This coating solution was applied to the surface of the charge generation layer by a dipping method, and then dried with hot air at 100 ° C. for 30 minutes to form a charge transport layer having a thickness of about 20 μm, thereby producing an electrophotographic photoreceptor. A photoreceptor corresponding to the photoreceptor sample B in Tables 1, 2 and 3 is obtained. The light attenuation characteristics of this photoreceptor are shown in Table 4.
It is as follows.

Example 2 An electrophotographic photosensitive member was prepared in the same manner as in Example 1 except that a τ-type metal-free phthalocyanine was used in place of the X-type metal-free phthalocyanine as the charge-generating material in the coating solution for the charge-generating layer. The body was made.

Comparative Example 1 Preparation of conductive substrate Current density: 1.0 A / dm ² Voltage: 12 V Electrolyte free sulfuric acid: Sulfuric acid concentration 15% Temperature: 25 ° C. Time: 30 minutes This tube was sealed in the same manner as in Example 1. The holes were treated. The obtained tube is referred to as a tube A (corresponding to the sample A in Table 1, Table 2, Table 3, and FIG. 1).

Preparation of Electrophotographic Photoreceptor An electrophotographic photoreceptor was prepared in the same manner as in Example 1 except that the base tube A was used as the conductive substrate. A photoreceptor corresponding to photoreceptor sample A in Tables 1 and 2 is obtained.

Comparative Example 2 Comparative Example 1 was repeated except that a τ-type metal-free phthalocyanine was used in place of the X-type metal-free phthalocyanine as the charge-generating material in preparing the coating solution for the charge-generating layer.
An electrophotographic photoreceptor was produced in the same manner as described above.

(Evaluation method) Using a light-attenuating electrophotographic copying machine (manufactured by Mita Kogyo Co., Ltd .: LPX2 modified machine (using a semiconductor laser as a light source)), exposure was performed by changing the light intensity (LD) of the semiconductor laser. The surface potential of each electrophotographic photosensitive member was measured for each of the above light intensities, and the results are shown in Tables 4 to 5 and FIGS. The optical attenuation characteristics of Example 1 and Comparative Example 1 and those of Example 2 and Comparative Example 2 were almost the same.

[0034]

[Table 4]

[0035]

[Table 5]

Developing sensitivity (γ) Using an electrophotographic copying machine {Mita Kogyo Co., Ltd .: LPX2 remodeling machine (using a semiconductor laser as a light source)}, copying is performed by changing the bias potential, and the image density for each of the above bias potentials (ID) with an image densitometer (Tokyo Denshoku Co., Ltd .: TC-
6D), and the results are shown in Table 6 and FIG.

[0037]

[Table 6]

In the gradation digital PPC, in order to obtain good gradation, when area gradation is used, its area and image density (I
Ideally, the ratio of D) is linear. That is, in the exposure of the electrophotographic photosensitive member, by modulating the LD pulse width, the LD emission time can be reduced to the normal 0/4, 1/4, 2/4, 3 /
4, 4/4, 5 values (PWM), and the above 5 values (PWM)
Each image density (ID) is measured, and the ID in PWM is measured.
If the relationship becomes linear, it is determined that the image has ideal gradation characteristics. The results are shown in Table 7, Table 8, and FIG.
As shown in FIG.

[0039]

[Table 7]

[0040]

[Table 8]

As is apparent from FIGS. 5 and 6, the raw tube B (AC resistance, capacitance and impedance of the raw tube surface are shown in Table 1, Table 2 and Table 3). Sample B
Of the electrophotographic photoreceptors of Examples 1 and 2 using the tube A (the AC resistance value, the capacitance value and the impedance of the surface of the tube are described as samples A in Tables 1, 2 and 3).
Compared with the photoreceptors of Comparative Examples 1 and 2 using
It can be seen that the relationship D is close to the ideal ID relationship in PWM and shows good gradation. From Tables 4 and 5, it can be seen that the light attenuation characteristics of the electrophotographic photosensitive member are related only to the characteristics of the photosensitive layer regardless of the characteristics of the conductive substrate. Further, it can be seen from Table 6 that the development sensitivity is related only to the characteristics of the conductive substrate.

[0042]

As described above, according to the present invention, since the impedance Z of the surface-treated layer is formed within a specific range during the surface treatment of the raw tube, the developing sensitivity of the photoreceptor becomes constant. Thus, an image with gradation can be obtained regardless of the physical properties of the developer and the system conditions.

[Brief description of the drawings]

FIG. 1 shows the image density ID and bias voltage of a photoreceptor obtained by forming a photosensitive layer having the same prescription on three types (A, B, and C) of raw tubes under the same system conditions and developer. FIG. 9 is a characteristic diagram showing the development sensitivity when the value is changed.

FIG. 2 is a characteristic diagram of light attenuation of a photoconductor.

FIG. 3 is a characteristic diagram of light attenuation of a photoconductor.

FIG. 4 is a characteristic diagram of the development sensitivity of the photoconductor according to the present invention and the photoconductor of a comparative example.

FIG. 5 is a characteristic line diagram of a gradation characteristic showing a relationship between an image density and a light emission time taking five values.

FIG. 6 is a characteristic diagram of gradation showing the relationship between image density and emission time taking five values.

FIG. 7: 100 Hz (or 2 log Hz) to 100
It is a characteristic diagram of the capacity | capacitance change of the base tube in 000Hz (or 5logHz).

FIG. 8 is an equivalent circuit diagram of an aluminum substrate surface treatment layer used for a photoreceptor.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-116162 (JP, A) JP-A-2-226162 (JP, A) JP-A-1-312554 (JP, A) JP-A-1- 280768 (JP, A) JP-A-63-316060 (JP, A) JP-A-63-311260 (JP, A) JP-A-2-111955 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) G03G 5/14 101

Claims (7)

(57) [Claims] 1. An electrophotographic organic photoreceptor having an aluminum substrate having a surface treatment layer and an organic photosensitive layer provided on the surface treatment layer, wherein the aluminum substrate has a surface area of 1 cm ² of gold. Is measured in the form of a cell on which is vapor-deposited, and the expressions 250 ≧ Z ₂ ≧ 100 and 4 ≦ Z ₂ / Z ₃ ≦ 5.5 (where Z ₂ is the impedance (KΩ) when the cell is measured at a frequency of 100 Hz. ), Z ₃ is the impedance (K) when the cell is measured at a frequency of 1000 Hz.
Ω). An organic photoreceptor having a surface treatment layer having electric characteristics satisfying (3). 2. The surface treatment layer of the substrate is measured by the cell according to the following formulas: C ₂ > 4 and 3 ≧ C ₂ / C ₃ ≧ 1 (where C ₂ is a frequency of 100 Hz in volume when measured (nF), C ₃ frequencies 1000H said cell
Represents the capacitance (nF) as measured by z. 2. The organic photoreceptor according to claim 1, which has an electrical property satisfying (1). 3. The surface layer of the substrate is measured by the cell as follows: R ₂ <500 (where R ₂ is an AC resistance (KΩ) when the cell is measured at a frequency of 100 Hz. 3. The photosensitive member according to claim 1, which has an electrical characteristic satisfying the following. 4. The surface treatment layer has a thickness of 2 to 20 μm.
4. The photoreceptor according to claim 1, wherein the photoreceptor comprises an anodic oxide film of aluminum. 5. The photoreceptor according to claim 1, wherein the organic photosensitive layer comprises a composition in which a charge generating substance is dispersed in a charge transport medium. 6. The photoreceptor according to claim 1, wherein the organic photosensitive layer comprises a laminate of a charge generation layer provided on the surface treatment layer and a charge transport layer provided on the charge generation layer. 7. The photoreceptor according to claim 1, wherein the organic photoreceptor comprises a laminate of a charge transport layer provided on the surface treatment layer and a charge generation layer provided thereon.