JPH01267551A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To enhance durability and sensitivity by allowing a combination of an electric charge generating layer and a charge transfer layer to have quantum efficiency eta being sufficiently small in dependence on an electric field E in a phototensitive body and the charge transfer layer to have a specified thickness. CONSTITUTION:The photosensitive body has n<=0.5 in the relationship between the quantum efficiency eta of the photosensitive body and the electric field E, represented by formula I where eta0 is a constant, and the charge transfer layer has a thickness of >=25mum. The photosensitive body is composed fundamentally of the charge generating layer and the charge transfer layer, and it is preferred to successively laminate the charge generating layer and the charge transfer layer on a conductive substrate, thus permitting durability and sensitivity to be enhanced.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electrophotographic photoreceptor.
, relates to an electrophotographic photoreceptor with excellent durability and improved sensitivity.

(Prior Art) Electrophotographic technology has been widely used and applied in recent years not only in the field of copying machines but also in various printer fields because of its ability to provide instantaneous and high-quality images.

Photoconductive materials for photoreceptors, which are the core of electrophotographic technology, range from conventional inorganic conductors such as selenium, arsenic-selenium alloys, cadmium sulfide, and zinc oxide to lightweight, easy-to-form, and Photoreceptors using organic photoconductive materials have been developed, which have advantages such as ease of manufacture.

Organic photoreceptors include so-called dispersion type photoreceptors in which photoconductive fine powder is dispersed in a binder resin, and laminated type photoreceptors in which a charge generation layer and a charge transfer layer are provided on a conductive support. are known, but the latter type is in practical use because of its high sensitivity and high printing durability.

(Problems to be Solved by the Invention) However, conventional organic layered photoreceptors still have insufficient sensitivity and durability compared to arsenic-selenium alloys, which are high-performance inorganic photoreceptors. Various studies are being conducted to further improve performance.

In order to improve sensitivity, new photosensitive materials with high sensitivity are being searched for, and in order to improve durability, photosensitive materials with less electrical deterioration and high strength binder materials with less mechanical damage are being sought. is being carried out. As a result, although products with sufficient sensitivity and electrical performance and durability have been developed, mechanical properties are still insufficient and have limited durability.

That is, the photosensitive layer is abraded due to practical loads such as friction with toner and paper, friction with a cleaning member, etc., although the degree varies depending on the method and load, and the film thickness is reduced. A decrease in film thickness leads to a decrease in chargeability, and if this decrease exceeds a range that can be tolerated by the developing system, the photoreceptor will reach the end of its life, resulting in poor printing durability.

This mechanical property mainly depends on the binder resin material of the charge transfer layer, and acrylic resin, methacrylic resin, polyester resin, polycarbonate resin, etc. are usually used. However, these materials have not yet been made sufficiently strong using conventional techniques, and when used in a process that uses a normal blade cleaning method, the photosensitive layer becomes severely abraded after tens of thousands of copies are made. The photoreceptor will have to be replaced. The amount of film loss due to wear varies depending on the material and process, but it is usually around 0.2~/μm in a copying process of 70,000 sheets.In order to reduce this amount of wear, we need to consider usage conditions and develop new materials. Various developments are underway.

The inventor conducted various studies on ways to improve durability while using the same materials as before, and found that
We have discovered that it is possible to prevent changes in electrical properties due to abrasion, especially a decline in chargeability, by increasing the total thickness of the photosensitive layer, more specifically by significantly increasing the thickness of the charge transfer layer, compared to conventional methods. Ta.

However, in conventional laminated photoreceptors, increasing the thickness of the charge transfer layer significantly impairs the electrical characteristics, resulting in a decrease in sensitivity and a significant increase in residual potential.
It was also found that it was not suitable for practical use. However, in a laminated photoreceptor with specific electrical characteristics, the thickness of the charge transfer layer must be made much thicker than the conventionally used film thickness of /θ to 2Ol1 m, reaching 2 to eoμm. It has been found that the electrical properties do not deteriorate even when the photoreceptor is used, that is, the increase in residual potential is small and at a level that poses no problem in practical use, and that the sensitivity is actually improved, making it possible to obtain a highly sensitive photoreceptor with excellent durability compared to conventional photoreceptors. This discovery led to the present invention.

(Means for Solving the Problems) That is, the present invention provides quantum efficiency η and electric field E as a photoreceptor.
In terms of the relationship between It is about providing.

The object is to provide a laminated organic electrophotographic photoreceptor in which a charge generation layer containing an organic charge generation substance and a charge transfer layer containing an organic charge transfer substance are laminated on a conductive support. When the relationship between the quantum efficiency η of the body as a photoreceptor and the electric field E is expressed by the following formula (1), Kn is o, s
This can be easily achieved by using an electrophotographic photoreceptor characterized in that the film thickness is less than 1J and the thickness of the charge transfer layer is 25 μm or more.

η=ηoEn (1) The present invention will be explained in detail below.

It is preferable to stack the charge transfer layers in this order, and a case in which this stacking order is used will be described below, but it is not limited thereto.

Conductive supports include aluminum, stainless steel,
Metal materials such as copper and nickel, polyester films with conductive layers such as aluminum, copper, palladium, tin oxide, and indium oxide on the surface, and insulating supports such as paper are used.

A commonly used barrier layer may be provided between the conductive support and the charge generation layer. As the barrier layer, for example, a metal oxide layer such as an anodized aluminum film; a resin layer such as polyamide, polyurethane, cellulose, casein, etc. can be used. Further, the photoreceptor of the present invention may be provided with other layers.

The photoreceptor of the present invention must have specific physical properties for its photoconductivity.

That is, when the electric field dependence of the quantum efficiency η as a photoreceptor is sufficiently small and approximated by the power of the electric field E as shown in the following formula (1), η=ηoEn @醗−・−・・(1) n is o,
r is required to be less than or equal to r. The quantum efficiency of a photoreceptor referred to here is the ratio of the number of charges on the surface of the photoreceptor that are neutralized by the movement of carriers generated by being excited by the light per 1 photons of light that are incident on the photoreceptor to fully expose the photoreceptor. It is expressed by , and is also called reed, xerographic gain, and light injection efficiency.

In general, η depends on the electric field and the wavelength of incident light.

The electric field E here is the average electric field applied within the photoreceptor, and means the value obtained by dividing the surface potential by the photoreceptor film thickness.

The wavelength of the incident light is within the wavelength range of image exposure in which this photoreceptor is used, and a small electric field dependence as described above is required in the wavelength range used.

Regarding the method of measuring l, see, for example, Physical Review Magazine l/Volume, No. 72,! / It is measured by the method described on page 3/7'1 from page 6J, and is determined by the following formula.

Here, C is the capacitance of the photoreceptor, e is the electronic charge, N is the number of incident photons per unit time, and PH1nit is the initial light attenuation rate. The incident light during measurement is monochromatic light having a wavelength in the region used for image exposure.

Although it is difficult to uniquely determine the form of electric field dependence of quantum efficiency, in the present invention, the electric field and quantum efficiency are plotted logarithmically and logarithmically, and expressed by the slope when approximated as a straight line.

This slope corresponds to the power number when quantum efficiency is expressed as a power of the electric field. For this approximation, linear regression using the least squares method, which is commonly used, is effective. Generally, the electric field dependence tends to deviate from this straight line due to various factors on the low electric field side, but the electric field dependence in the present invention is in the electric field range normally used for photoreceptors /×/θ5v//
c! From IL, we will use the characteristics approximated by a straight line with V/CR, but be careful!;
It is preferable to satisfy the range from v/CTL to s x 1o5v/cm.

The quantum efficiency of a laminated photoreceptor is determined by the charge generation efficiency in the charge generation layer and the efficiency of charge injection from the charge generation layer to the charge transfer layer, but the efficiency of charge injection can be greatly improved by selecting an appropriate charge transfer material. It can be almost ignored except for the low electric field side, and is determined by the charge generation efficiency in the charge generation layer. Furthermore, if an appropriate charge transfer layer is selected, loss during transport can be ignored and does not depend on the film thickness. ′l of quantum efficiency, which is a condition of the present invention
In order to reduce the t-field dependence, a charge generation material whose charge generation efficiency has a small dependence on the electric field must be selected.

Upon investigation, it was found that the conditions of the present invention could be met by selecting an organic charge generating substance. Although such charge-generating substances have not yet been completely identified, they include azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, benzimidazole pigments, biryllium salts, thiapyrylium salt pigments, and squarelylium salt pigments. It may be conveniently selected from various organic charge-generating substances such as the following.

The charge-generating layer may be a uniform layer in which these charge-generating substances are vacuum-deposited, or may be a layer in which fine particles are dispersed in pine mite resin. In such cases, binder resins include polyvinyl acetate, polyacrylic ester, polymethacrylic ester, polyester, polycarbonate,
Various binder resins such as polyvinyl butyral, phenoxy 41[1, celluloses, and urethane resins are used, and the charge generation layer usually has a thickness of o, iμm~/11 m b
Preferably 0.1! rμTL~0. It is provided as a layer with a thickness of Aμm.

In addition, the organic charge transfer substance in the charge transfer layer is 1,2
．． &, 7-) Electron-withdrawing substances such as linitrofluorenone and tetracyanoquinodimethane, heterocyclic compounds such as carbazole, indole, imidazole, oxazole, thiazole, oxadiazole, pyrazole, pyrazoline, and thiadiazole, derivatives of aniline, Examples include electron-donating substances such as hydrazone derivatives, conjugated compounds having a stilbene skeleton, and polymers having a group consisting of these compounds in the main chain or side chain.

Furthermore, a binder resin may be blended into the charge transfer layer together with these charge transfer substances, but examples of the binder resin include thermoplastic resins such as polycarbonate resin, acrylic resin, methacrylic resin, polyester resin, polystyrene resin, and silicone resin. Various curable resins are used. Particularly preferred are polycarbonate resins and polyester resins, which cause few scratches even if they are abraded. As the bisphenol component of the polycarbonate resin, various known components such as bisphenol A, bisphenol C, and bisphenol 2 can be used, but polycarbonate containing bisphenol C and bisphenol Z as the bisphenol component is preferred.

Further, the charge transfer layer of the present invention may contain well-known additives such as additives for improving film formability, flexibility, etc., and additives for suppressing accumulation of residual potential. .

The thickness of the charge transfer layer must be 25 μm or more, and J
More preferably, it is 60 μm from Opll.

(Effects of the Invention) The thus obtained photoreceptor of the present invention has excellent sensitivity, greatly improved durability, and extremely high performance characteristics.

In addition to electrophotographic copying machines, the photoreceptor of the present invention can also be used in a wide range of electrophotographic application fields, including as a photoreceptor for printers and facsimiles that use lasers, light emitting diodes (LEDs), LCD shutters, cathode ray tubes, etc. as light sources. .

(Examples) Next, all embodiments of the present invention will be explained in more detail, but the present invention is not limited to these examples as long as they do not exceed the gist thereof. In addition, in the following, "part" means "part by weight"
shows.

Example 1 100 parts of ethylene glycol dimethyl ether was added to part IIO of a bisazo compound having the following structure, and a dispersion treatment was carried out using a sand grind mill. This liquid and phenoxy resin (manufactured by Union Carbide, trade name PKHH)
J part, polyvinyl butyral resin (Denka Kogyo #1,00
0) S part f A solution dissolved in 100 parts of ethylene glycol dimethyl ether was mixed to obtain a charge generation layer coating solution. This coating solution was applied by dip coating onto an aluminum cylinder with a diameter of 01 N and whose surface was mirror-finished to provide a charge generation layer. The film thickness after drying was 0.5 μm.

Bisazo Compound I 100 parts of N-methylcarbazole-3-aldehyde diphenylhydrazone and 100 parts of bisphenol A polycarbonate resin (manufactured by Mitsubishi Chemical Corporation, Tubarex ■702!;k) / 00 parts were added on the charge generation layer thus obtained. , 0.5 part of a cyanide compound having the following structure, 8 parts of ditertiarybutylhydroxytoluene (BHT) dissolved in q-dioxane was applied onto the charge generation layer, which had a dry film thickness of 10 pz/7 μm. 2! rμ@, 30
It was coated by dipping so that the thickness was 0 μm or 0 μm.

I These photoreceptors are respectively /-A, /-B% l-C, /-
Let D, /-E. For the photoreceptor of /-B, the incident light wavelength is 3! Using monochromatic light of r Onm, the initial potential decay rate was measured, and the capacitance of this photosensitive layer was determined to determine the quantum efficiency as a photoreceptor and its electric field dependence. The results are shown in Figure 1. On the other hand, measurements were made in the same manner for /-A and /-D, and almost the same results were obtained, which are shown in the same figure. From these, it can be seen that the quantum efficiency of the photoreceptor does not depend on the film thickness.
When the electric field dependence of the quantum efficiency of this photoreceptor is approximated by a total power, the electric field o, 4 can be approximated by a multiplicative approximation, and it can be seen that the electric field dependence is small.

Next, samples i-A, i-B, /-C, /-D.

/-E white light, and! r! The sensitivity at r Onm was determined as a half exposure amount (exposure amount required to attenuate the initial surface potential of 700 V by half) E//2. These results and electrophotographic properties such as chargeability and residual potential are listed/
Shown below.

Table / It can be seen that in these photoreceptors, by increasing the thickness of the charge transfer layer, in addition to an increase in the υ chargeability, the sensitivity also increases, and disadvantages such as an increase in residual potential are not as noticeable. The relationship between the film thickness (horizontal axis) and the reciprocal of the sensitivity E//l in SSOnm is shown in the figure.

Next, samples /-13 and /-[) were used as photoreceptors in a commercially available copying machine having a blade cleaning process (manufactured by Sharp ■, 100 in SF), and a durability test was conducted. The results are shown in Table 1.

In the table, Vd is the surface potential of the unexposed area, VL is the surface potential of the exposed area, and V
r indicates a residual potential (the same applies hereinafter).

After copying 10,000 copies of both /-B and /-D photoconductors, it is approximately 6
A decrease in film thickness of about μm was observed, but the film thickness was thick/-[)
Although a slight increase in residual potential was observed in
It was found that the potential drop was small and the printing durability was sufficient for more than 100,000 copies without any change in image quality. Ten thousand
In sample B, there was no significant change in image quality until 50,000 copies were copied, but the density gradually decreased, and after 10,000 copies were copied, the potential dropped significantly and the image density decreased. In practical terms, the lifespan was estimated to be around 50,000 sheets.

Example 1 Photoconductor sample A was prepared in the same manner as in Example 1, except that azo pigment 2 having the following structure was used as the charge generating substance.
Cor B% Cor C, Cor D.

λ-E was created. The thickness of the charge transport layer is /fim% 74 μm%
-2"I'm -J OI'm 4 hirokoμm.

The quantum efficiencies of photoreceptors 1-B and 1-D were measured in the same manner as in Example 1. The results are shown in FIG. In the case of this photoreceptor, the electric field dependence is even smaller, and it can be seen that the electric field shows almost no dependence and can be approximated to the electric field to the 0.12th power.

In order to evaluate the charge transfer layer thickness dependence of this photoreceptor, electrical characteristics such as sensitivity of Samples A to E were evaluated. The results are shown in Table JIC.

Table 3 It can be seen that in these photoreceptors, there were no particular adverse effects, and as the thickness of the charge transfer layer was increased, the sensitivity increased, and the sensitivity was significantly higher at higher thicknesses.

Durability tests were conducted on sample λ-D in the same manner as in Example 1, and there was no particular change in the image after 10,000 copies were made. was found to be obtained. The potential characteristic data at this time is shown in Table DA.

Table d Comparative Example/ Photoreceptor f77/l/ in the same manner as in Example/ except that oxytitanium phthalocyanine was used as the charge generating substance.
J ”-A (J-B(j C% 3Dy3-
I created E. The thickness of each charge transfer layer is 10 μm.
s/g μ7FL 1 Ko! ;fim, JOμy
It was 1°97 μm.

The quantum efficiency of this photoreceptor was determined in the same manner as in Example.

Figure 1 shows the data obtained for sample 3 As 3 p.
IVc is shown. In the case of this photoreceptor, it was found that the dependence of the quantum efficiency on the electric field is large and is proportional to the power of E to about 0.9.

Next, in order to evaluate the relationship between photoreceptor characteristics and film thickness in this system,
The properties of samples 3-A-E were measured.

The results are shown in Table 5.

Table 5 In the case of this photoreceptor, the dependence of the quantum efficiency on the electric field is large, and as the film thickness increases, the sensitivity deteriorates, and especially when creating an image, the 5-minute/attenuation exposure, which is an indicator of the actual sensitivity. The charge transfer layer thickness (E //!; in the table) increases, and the residual potential increases significantly. It has been found that increasing the thickness to 5 μm or more significantly deteriorates the characteristics, making it difficult to put it into practical use.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the quantum efficiency and its electric field dependence of the photoreceptor of Example/, and FIG. 2 is a diagram showing the film thickness (
It is a diagram showing the relationship between the horizontal axis and the reciprocal of sensitivity E//2 (vertical axis). 3 and 3 are diagrams showing the quantum efficiency and its electric field dependence of the photoreceptors of Example 1 and Comparative Example, respectively. Applicant: Mitsubishi Chemical Industries, Ltd. Agent: Patent attorney: Mr. Hase - 7 others 11JI Electric field (taste/n) z3 t Kashi (Chi) Figure 4 Electric field (falling)

Claims (1)

[Claims] (1) A laminated organic electrophotographic photoreceptor formed by laminating a charge generation layer containing an organic charge generation substance and a charge transfer layer containing an organic charge transfer substance on a conductive support, in which the photoreceptor is When the relationship between the quantum efficiency η as a photoreceptor and the electric field E is expressed by the following formula (1), n is 0.5 or less,
An electrophotographic photoreceptor, wherein the charge transfer layer has a thickness of 25 μm or more. η=η_0E^n・・・・・・(1) (However, η is the quantum efficiency as a photoreceptor, E is the electric field, η_
0 indicates a constant. )