JPH0447814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention provides a composite electrophotographic photoreceptor having high sensitivity in the long wavelength region, which is formed by forming a charge generation layer and a charge transport layer on a conductive support. In particular, the present invention relates to an electrophotographic photoreceptor that has high sensitivity and is suitable for improving the stability of long-term repeatability.

[Background of the invention]

Conventionally, charge-generating substances for composite electrophotographic photoreceptors include moriazo dyes, disazo dyes, and squaric acid derivative dyes soluble in organic primary amines as disclosed in JP-A No. 52-55643, and squaric acid derivative dyes. Showa 53-
A large number of organic substances have been proposed, such as quinocyanine pigments shown in JP-A No. 42830 and JP-A-53-41230, and copper phthalocyanine pigments shown in JP-A-51-11763. In addition, tellurium-arsenic-glassy selenium series shown in Japanese Patent Publication No. 50-15137,
Japanese Patent Publication No. 49-14272 discloses polymers having imide bonds and inorganic substances such as amorphous selenium.

On the other hand, as a charge transport material, Japanese Patent Application Laid-Open No. 52-77730
Poly N-vinylcarbazole series shown in JP-A No. 52-753929, etc., JP-A-1987-
Pyrazophosphoric acid conductors shown in JP-A No. 105537, trinitrofluorenone shown in JP-A-46-4484, and various nitro- and cyano-substituted compounds shown in JP-A-53-301 are proposed. Electrophotographic photoreceptors using these materials all have good electrophotographic properties, but they exhibit high sensitivity to visible light in the wavelength range of 400 to 700 nm.
There is no sensitivity at all to near-infrared light (750 nm or more), or even if there is sensitivity, the sensitivity is low.
It has the disadvantage that it cannot be used as an electrophotographic photoreceptor that uses near-infrared light as a light source (for example, a semiconductor laser).

In recent years, as a type of high-speed printer, a method of printing using an electrophotographic method using a laser as a light source has been devised. In particular, when a semiconductor laser is used as a light source, the light source section can be made very small, making it possible to miniaturize the printer, significantly reduce power consumption, and increase functionality.
It is attracting a lot of attention. Since the oscillation wavelength of a semiconductor laser is a long wavelength of 770 nm or more, conventional charge transport materials as described above cannot be used in electrophotographic photoreceptors. Therefore, it is desired to develop an electrophotographic photoreceptor that has high sensitivity to specific wavelengths.

The inventors of the present invention have conducted intensive studies to provide an electrophotographic photoreceptor that has excellent various electrophotographic properties and has sufficient properties for practical use. The present inventors have discovered that the drawbacks of the conventional method can be improved by doing so, leading to the present invention.

[Purpose of the invention]

An object of the present invention is to provide an electrophotographic photoreceptor having sufficient sensitivity in the oscillation wavelength range of a semiconductor laser.

[Summary of the invention]

The electrophotographic photoreceptor according to the present invention has surface potential that can be easily removed, improved image clarity, gradation, etc., high sensitivity, and improved stability of long-term repeatability.

The composite electrophotographic photoreceptor of the present invention is composed of a layer containing a charge generating substance and a charge transporting substance on a conductive support, and the charge generation substance has a hiding rate of 5% or more with respect to the conductive support. The charge generating material is laminated in 10 or more layers, and the porosity of the pores created by the lamination is 90% or less.
Preferably, the porosity on the surface of the charge generation layer is 75%.
It is as follows.

In the present invention, the above-mentioned hiding rate refers to the area covered by the charge-generating substance existing on the surface area, assuming that the surface area of the electrophotographic photoreceptor having the charge-generating layer on the conductive support is 100. Expressed as a percentage (%).

Generally, the wavelength range to which a photoreceptor is sensitive depends on the absorption wavelength range of the charge-generating material, as long as the charge-transporting material used does not interfere with the light absorbed by the charge-generating material.
Many studies have been carried out on long-wave absorbing charge-generating substances, and for example, for Se, Cds, etc., a method has been found to increase the sensitivity in the long wavelength region by adding a sensitizer, but It has insufficient environmental resistance and also has problems in terms of hygiene. Among the various organic photoconductive materials mentioned above, various phthalocyanine compounds have relatively good sensitivity in a long wavelength range. Generally, a charge generating substance generates charges due to light passing through a charge transport layer, and the generated charges must be efficiently transferred into the charge transport layer by an electric field. Therefore, it is necessary to disperse the charge generating substance on the conductive support in such a form that the generated charges are efficiently transferred to the charge transport layer. This dispersion form is a major controlling factor for various electrophotographic properties of an electrophotographic photoreceptor, and particularly has a great influence on sensitivity, sharpness, and gradation. Therefore, for electrophotographic photoreceptors, it is most important to control the dispersion form of the charge generating substance on the conductive support more appropriately.

The charge generation layer in the electrophotographic photoreceptor of the present invention has the following structure. In other words, the charge generating substance supported on the conductive support,
The charge-generating material has a hiding rate of 5% or more on the surface of the conductive support and is laminated in 10 or less layers, and the interstitial pores created by the lamination communicate with each other or partially communicate with each other, and the porosity is The porosity is 90% or less, preferably 75% or less. In addition, in the formed charge generation layer, if necessary, in order to properly support the charge generation substance on the conductive support,
It is desirable to contain resin. Furthermore, a film-forming aid may be added to improve film-forming properties during the formation of a charge-generating layer, or an adhesion-improving agent or a sensitizing aid may be added to improve the adhesion between a charge-generating substance and a conductive support or charge transport layer. There are no restrictions on the addition of various auxiliary agents that are effective in improving various properties of the electrophotographic photoreceptor. Furthermore, conventionally known techniques can be used to form the charge transport layer and the protective film formed on the charge transport layer.

The reason why the dispersion state of the charge generating substance is limited in the present invention is based on the following reason. It is preferable that the hiding rate for the surface of the conductive support is 5% or more; if it is less than 5%, the amount of charge generation will be low and sufficient sensitivity will not be obtained. Moreover, since the necessary amount of contact area between the charge-generating substance and the conductive support is not secured, the electrical insulation of the photoreceptor increases more than necessary, and the residual potential on the surface of the photoreceptor increases, resulting in an image The sharpness and gradation of the image are significantly reduced. Technical means for increasing the hiding rate to 5% or more can be adjusted by adjusting the concentration of the charge generating substance contained in the charge generating coating liquid (described in the examples of the present specification).
Furthermore, when the concentration of the charge generating substance is low, this can be achieved by applying the coating process multiple times. In addition, the number of stacked layers of charge generating material was limited to 10 or less.
If more layers are stacked, secondary aggregation of the charge-generating substance will increase, and the pore diameter per layer will become too large. On the other hand, when the porosity exceeds 90%, the contact area between adjacent charge-generating materials becomes small, and the transfer time of the generated charges increases, making it impossible to efficiently transfer the charges to the charge transport layer, and furthermore, the charge generation Charge remains within the layer. The technical means to reduce the porosity to 90% or less is to reduce the boiling point of the diluent that dissolves the charge-generating substance when forming the charge-generating layer to 100°C, which is a guideline for the evaporation rate.
(ordinary pressure), and can be adjusted by setting the pulling rate during dip coating to 1 to 100 mm/sec. Further, the reason why it is desirable that the porosity on the surface of the charge generation layer be 75% or less is as follows. This is particularly because when the charge generating material has a multilayer structure and the surface area is less than 25%, the contact area with the charge transport layer becomes small. As a result, the transfer efficiency of the generated charges to the charge transport layer deteriorates,
Sufficient sensitivity cannot be obtained. Furthermore, when the photoreceptor is irradiated with light, the light passes through the charge transport layer and reaches the charge generating substance, but the distance it takes for the light to reach the charge generating substance present in the gap becomes long. As a result, the light becomes weaker and the amount of charge generated becomes smaller, resulting in lower sensitivity. Therefore, if the charge-generating substance or charge-generating layer is made as described above, it can be used as a photoreceptor for electrophotography without any restrictions on the type of charge-generating substance or the method of forming the charge-generating layer and charge transport layer. It has excellent electrophotographic properties.

Next, a method for forming the charge generation layer and charge transport layer on the conductive support will be described. First, the charge generation layer is prepared by thoroughly mixing and stirring an organic solvent such as tetrahydrofuran, ethyl acetate, acetone, methyl ethyl ketone, halogenated hydrocarbon, etc. that can disperse the charge generation substance well or dissolve the resin and additives used as necessary. Adjust the coating liquid of the charge generating material. The conductive support is immersed in this liquid, or this liquid is dropped onto the conductive support and coated using a bar coater, roll coater, applicator, casting method, etc., and the solvent is removed by three-dimensional curing or heating. Remove and form a film. As the resin, a known three-dimensional curing resin or thermoplastic resin can be used. For the charge transport layer, a coating liquid of the charge transport material is prepared by mixing and stirring a charge transport substance and a resin in a solvent such as tetrahydrofuran, halogenated hydrocarbon, benzene, dioxane, dimethyl formamide, etc. and dissolving it. Using this solution, a charge transport layer was formed on the charge generation layer by the same method as for forming the charge generation layer.

In addition, examples of the conductive support for the composite electrophotographic photoreceptor of the present invention include metals such as aluminum, aluminum to other metal alloys, steel, iron, and copper, as well as conductive plastics and plastics.
Materials such as paper and glass imparted with electrical conductivity can be used, and these supports may be cylindrical, sheet, etc., and are not limited to any shape.

[Embodiments of the invention]

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto in any way.

Example 1 ε-type copper phthalocyanine pigment (manufactured by Toyo Ink Co., Ltd.,
Weighed 0.2, 5.0 g of Lionol Blue ES), 0.2, 5.0 g of silicone resin (KR-5240, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.005 g of methylphenyl-based siloxane compound (manufactured by Shin-Etsu Chemical Co., Ltd., KP-323). was placed in a glass container together with 80.8 g of tetrahydrofuran (solid content concentration: 0.5 to 5%), and the mixture was stirred and dispersed using an ultrasonic vibrator for 15 hours to prepare a charge generation layer coating solution. This coating liquid was dropped onto a 100 μm thick aluminum plate to form a film using an automatic applicator, and then placed in a hot air dryer for 30 minutes at 90°C.
The mixture was dried for a minute to form a charge generation layer with a hiding rate of 2 to 100%.

Next, an oxazole compound represented by the following structural formula 3g, polycarbonate resin (manufactured by GE, Lexan
141) 10g, silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KP-
323) 0.007 g and 35 g and 52 g of methylene chloride were placed in a glass container and stirred by vibration using an ultrasonic vibrator until the contents were completely dissolved to prepare a charge transport material coating liquid. This coating liquid was dropped onto the previously formed charge generation layer to form a film using an automatic applicator, and the solvent was removed by heating and drying at 110° C. for 1 hour. After drying, electrophotographic properties were measured. The electrophotographic properties were measured using an electrostatic recording paper tester (Kawaguchi Electric Co., Ltd., SP-428).
In this case, conduct corona discharge of minus 5 kV for 10 seconds to charge (surface potential V ₀ immediately after charging for 10 seconds)
(V) is the initial potential), and after being left in the dark for 30 seconds (the potential at this time is expressed as V ₃₀ (V), (V ₃₀ /V ₀ )×
100 (%) is the dark decay), expose the surface to 2x illuminance with a tungsten lamp, record the decay of the surface potential at this time and the time, and record the amount of time required for V ₃₀ to decrease to 1/2. The sensitivity (half-reduced exposure amount, E ₅₀ (x, s) was expressed as the product of the time t (seconds) and the illuminance. The results are shown in Figure 1. The curve in Figure 1 shows the example. The curve shows Comparative Example 1.

Comparative Example 1 ε-type copper phthalocyanine pigment 10 used in Example 1
Weight parts and silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR-
A charge generation layer and a charge transport layer were formed using 5 parts by weight of 5240) and the same conditions as in Example 1 except for the following conditions.
Further, the electrophotographic characteristics of this photoreceptor were measured under the same conditions as in Example 1. The results are shown in Figure 1.

Example 2 5 to 240 parts by weight of metal-free phthalocyanine, epoxy resin [(manufactured by Ciel Petrochemical Co., Ltd., Epicoat 1001)
100 parts by weight, 21 parts by weight of Resin M (manufactured by Maruzen Oil Co., Ltd.),
Composition consisting of 20 parts by weight of 2-ethyl-4-methylimidazole (manufactured by Shikoku Kasei Co., Ltd.)] 5 to 150 parts by weight,
3 parts by weight of methylphenyl siloxane compound (manufactured by Shin-Etsu Chemical Co., Ltd., KP-323), tetrahydrofuran
2,700 parts of the mixture was placed in a glass container and stirred under vibration for 24 hours in an ultrasonic vibrator to prepare a charge generation layer coating liquid. The coating liquid was applied to a 120 mm conductive drum using the dip coating method, and then heated in a hot air dryer at 100℃ for 2 hours.
A charge transport layer was formed by drying for a period of time and curing by heating. The surface occupancy rate (100 - porosity) of the charge generation layer is
The percentages were 27% (Figure 2), 52%, 70% (Figure 3), and 90%. Further, the concealment ratio of these charge generation layer arrangements was all 5% or more.

Next, the oxazole compound 30 used in Example 1
Parts by weight, polycarbonate resin (Lexan 141)
300 parts by weight and 2,700 parts by weight of a diluent (a mixed solvent consisting of 1,1,2,2 tetrachloroethane: 30% and methylene chloride: 70%) were placed in a glass container, and the mixture was stirred with vibration using an ultrasonic vibrator for 50 hours. A coating liquid for a charge transport layer was prepared. A charge transport layer forming drum was immersed in the coating solution and coated, and dried in a hot air dryer at 130° C. for 2 hours to form a charge transport layer to produce a photoreceptor forming drum.

The drum was attached to a semiconductor laser beam copying machine (SL-1000, manufactured by Hitachi, Ltd.), and the electrophotographic characteristics were measured. Corona applied voltage is -5.2kv
It is. The results are shown in Figure 5. In FIG. 5, the curves indicate Example 2, and the curves indicate Comparative Examples 2 and 3.

Comparative Examples 2 and 3 Metal-free phthalocyanine 300 as a charge generating substance
A charge generation layer was formed under the same conditions as in Example 2 except for the parts by weight, 150 parts by weight of the epoxy resin used in Example 2, and the drum pulling speed described below. The drum pulling speed was increased 2 and 5 times compared to Example 2 to change the surface area of the charge generating material. As the pulling speed increases, the balance between the vapor velocity of the diluent and the charge-generating substance supported on the drum is lost, and the surface area becomes smaller. The surface area of the charge transport layer thus obtained was 23% (shown in Figure 4).
It was 18%. A charge transport layer was formed on this charge generation layer under the same conditions as in Example 2, and furthermore, this photoreceptor was evaluated under the same conditions as in Example 2. The results are shown in Figure 5.

[Effects of the Invention] From the above results, it can be seen that the electrophotographic photoreceptor of the present invention is an excellent electrophotographic photoreceptor having practically sufficient electrophotographic properties.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the hiding rate and sensitivity of a charge-generating substance, and Figures 2 to 4 are electron microscopes showing the particle structure of phthalocyanine in a charge-generating layer formed on a conductive support. The photograph, FIG. 5, is a surface charging characteristic diagram of an electrophotographic photosensitive drum device used in a copying machine.

Claims (1)

[Scope of Claims] 1. A composite electrophotographic photoreceptor in which a layer containing a charge-generating substance and a charge-transporting substance is provided on a conductive support, wherein the charge-generating substance has a hiding rate with respect to the conductive support. 5% or more, the charge generating material is laminated in 10 or less layers, and the porosity of the voids formed by the lamination is 90% or less. 2. The electrophotographic photoreceptor according to claim 1, wherein the charge generating substance is a phthalocyanine pigment. 3. The electrophotographic photoreceptor according to claim 2, wherein the phthalocyanine pigment is metal-free or copper phthalocyanine.