JPH0569216B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field to Which the Invention Pertains] The present invention relates to an electrophotographic photoreceptor having a photosensitive layer made of a selenium-based material and used in electrophotographic plain paper copying machines and optical printers. [Prior Art and Its Problems] In recent years, office automation has rapidly developed and become popular, and in conjunction with this, various printers have been actively developed as output devices. Among these, electrophotographic optical printers are attracting attention due to their high speed printing performance, high image quality, high reliability, and low noise. Recently, small optical printers with medium to low speeds (printing speeds of around 1,000 lines/minute) have been developed one after another. These small optical printers are mainly used by connecting to office computers, and are also used as output devices for Japanese word processors and optical disk file systems, and there is a movement to use them for high-speed facsimiles. . Furthermore, recently there has been a strong demand for digital plain paper copying machines that can be equipped with various intelligent functions, and this is also used as an output unit. Laser light, light emitting diodes, and the like are used as light sources for optical printers, and laser light is often used because of its high printing speed and high image quality. Although He--Ne laser light has been mainly used as the laser light, semiconductor laser light has recently come into use due to the demand for miniaturization of equipment. Optical printers use scanning laser beams or light emitting diode arrays, etc., in a direction corresponding to the image to be printed.
It consists of a part that controls on/off, and an electrophotographic part that receives the control light to form an electrostatic latent image corresponding to the print image on a charged photoreceptor and prints the latent image as a toner image. . The electrophotographic part has the same configuration as a conventional electrophotographic copier, but
The performance of the photoreceptor used here is an important factor that influences the printing speed of the printer, the quality and stability of the printed image. As described above, optical printers use semiconductor laser light and light emitting diode arrays, and the wavelength of semiconductor laser light is around 790 nm, and the wavelength of light from light emitting diodes is around 660 to 680 nm. For such long-wavelength light, photoreceptors that are conventionally applied mainly to electrophotographic copying machines cannot be used. In conventional photoreceptors, photoconductive materials are selected to have high photosensitivity in the visible wavelength region, and the structure of the photosensitive layer is also devised.
This is because the photosensitivity to longer wavelength light is extremely low. Various studies are underway regarding photoconductive materials and photosensitive layer configurations that can be used in photoreceptors suitable for such long wavelength light, but electrophotographic properties (charging potential, photosensitivity, residual potential, etc.) ), there are still many problems in terms of fatigue properties, environmental resistance, printing durability, etc. Studies are also underway on selenium photoreceptors, including a carrier transport layer made of amorphous selenium or an amorphous selenium-tellurium alloy on a conductive substrate; A functionally separated photoreceptor with a multilayer structure has been proposed in which a carrier generation layer made of a tellurium alloy and a surface protection layer made of amorphous selenium or an amorphous alloy of tellurium or arsenic and selenium are sequentially laminated. However, although the photoreceptor having such a structure has excellent electrophotographic properties with respect to long wavelength light, there is a problem in its durability. In other words, in the case of a photoreceptor made of amorphous selenium or an amorphous selenium-tellurium alloy, the surface protective layer exhibits practically sufficient characteristics in terms of initial electrophotographic characteristics and abrasion resistance during continuous printing. , the amorphous surface protective layer tends to crystallize if left at high temperatures after printing. On the other hand, in the case of a photoreceptor whose surface protective layer is made of an amorphous selenium-arsenic alloy,
The glass transition point of selenium-arsenic alloys is higher than that of selenium and selenium-tellurium alloys, and therefore transition from amorphous to crystalline, that is, crystallization, is less likely to occur, eliminating the above-mentioned drawback of easy crystallization of the surface protective layer. be able to. Furthermore, as shown in Figure 2, as the amount of arsenic added increases, the glass transition point of the selenium-arsenic alloy increases, so in order to suppress crystallization of the surface protective layer, the more amount of arsenic added, the better. become. However, because the carrier transport layer and carrier generation layer, which are the underlayers, are made of amorphous selenium or an amorphous selenium-tellurium alloy, the photoreceptor is exposed to high temperatures above the glass transition point (approximately 45°C) of the underlayer for a long time. When exposed, a disadvantage arises in that the surface protective layer wrinkles due to the difference in thermal expansion coefficient between the base layer and the surface protective layer. In order to prevent the occurrence of wrinkles, it is necessary to reduce the thickness of the surface protective layer or reduce the amount of arsenic added. However, from the viewpoint of crystallization resistance, it is not desirable to reduce the amount of arsenic added, and from the viewpoint of abrasion resistance during continuous printing, there is a problem that the film thickness cannot be made thinner than a certain level. [Object of the Invention] The object of the present invention is to solve the above-mentioned problems and to provide a material that has excellent electrophotographic properties in the long wavelength range of 660 to 800 nm, and has good abrasion resistance and crystallization resistance. in,
The object of the present invention is to provide a selenium photoreceptor for electrophotography that does not cause wrinkles. [Summary of the Invention] An object of the present invention is to provide a carrier transport layer made of amorphous selenium or an amorphous selenium-tellurium alloy on a conductive substrate, and amorphous selenium containing 20 to 50% by weight of tellurium. - In an electrophotographic photoreceptor in which a carrier generation layer made of a tellurium alloy and a surface protection layer made of an amorphous selenium-arsenic alloy are sequentially laminated, the surface protection layer is divided into two layers, and the carrier generation layer is formed by dividing the surface protection layer into two layers. This is achieved by making the arsenic content of the first surface protective layer that is in contact with the outer surface smaller than the arsenic content of the second surface protective layer that is the outer surface. [Embodiments of the Invention] One of the properties that the surface protective layer (hereinafter also referred to as lower OCL) should have is crystallization resistance, which depends on the arsenic content of the selenium-arsenic alloy that is the constituent material of OCL. The following experiment was conducted to determine the practically effective arsenic content. An aluminum cylinder with an outer diameter of 12 mm is maintained at a temperature of 60°C, and selenium is vacuum-deposited on its outer surface to a thickness of 50 μm to form a carrier transport layer (CTL).
(also referred to as). On this layer, a selenium-tellurium alloy containing 44% by weight of tellurium was flattened to a thickness of 0.3 μm to form a carrier generation layer (hereinafter also referred to as CGL). On top of this layer, the first
Photoreceptor samples No. 1 to No. 4 were prepared by flash-depositing layers having the compositions and film thicknesses shown in the table. These samples were attached to a commercially available semiconductor laser printer with a printing speed of 20 sheets per minute and a one-component developer development method, and 1,500 sheets were printed on B4 paper, and extremely clear images were stably obtained in all cases. . These samples were then heated to 50°C.
The sample was left in a constant-temperature atmosphere, and the change in chargeability (current flowing into the photoreceptor required to give a predetermined charging potential to the photoreceptor surface by corona discharge) was examined.
As a result, it was observed that the chargeability of the samples decreased as the surface crystallization progressed, but the standing time until such crystallization started varied greatly depending on the sample as shown in Table 1.

[Table] This difference in crystallization start time is due to the fact that as the amount of arsenic added to OCL increases, the thermal stability of OCL improves.
If it is above, it is sufficiently stable for practical use. Another property that OCL should have is wear resistance.
Photoreceptor sample No. 5, in which up to CGL was formed according to sample 1, and OCL with a thickness of 2.2 μm made of a selenium-arsenic alloy containing 3 at % arsenic was formed on top of the CGL.
Continuous printing tests were conducted using a semiconductor laser printer using a two-component developer, reversal development, and a furbrush cleaning method. After printing on 140,000 sheets of paper with a width of 18 inches and a length of 11 inches, the OCL film thickness was examined using an optical interference thickness gauge, and 0.05 μm of wear was observed. Practically speaking, printing durability of at least 100,000 sheets is required, so the OCL film thickness is 0.1 μm, taking into account variations and allowing a slight margin.
The above is necessary. Based on the above results, in order to maintain good heat resistance and abrasion resistance of the photoreceptor, OCL should be made of a selenium-arsenic alloy containing 3 at.% or more of arsenic.
The layer must be 0.1 μm or larger. However, when a photoreceptor having such an OCL is exposed to a high temperature atmosphere, wrinkles occur on the OCL surface. The present invention further eliminates this wrinkling by dividing the OCL into two layers with different concentrations of arsenic. The present invention will be explained below by way of examples with reference to drawings and comparative examples. FIG. 1 shows a conceptual cross-sectional view of the photoreceptor of the present invention, in which 10 is a conductive substrate, 20
is the carrier transport layer (CTL), 30 is the carrier generation layer (CGL), and 40 is the first surface protection layer (OCL1) 4
This is a surface protective layer consisting of a first surface protective layer (OCL2) and a second surface protective layer (OCL2) 42. Examples 1 and 2 An aluminum cylinder with an outer diameter of 120 mm serving as the conductive substrate 10 was maintained at a temperature of 60° C., and selenium (Se) was vacuum-deposited on its outer surface to a thickness of 50 μm to form a CTL 20. On top of this, a selenium-tellurium alloy containing 44% by weight of tellurium (Te) was flash-deposited to a thickness of 0.3 μm to obtain CGL30. OCL1 on top of this layer
In Example 1, layers with the composition and film thickness shown in Table 2 were sequentially formed as OCL2 by flash vapor deposition.
And a photoreceptor of Example 2 was produced. Comparative Examples 1, 2, 3, 4 OCL20 and CGL30 on conductive substrate 10
The steps up to this point were formed according to Example 1, and then OCL was formed on top of that.
Comparative Examples 1 and 2, in which a layer having the composition and film thickness shown in Table 2 as 1 were formed by flash vapor deposition, but OCL 2 was not formed, that is, a single layer OCL;
Photoreceptors Nos. 3 and 4 were produced. The above six types of photoreceptors were left in a constant temperature bath at a temperature of 65° C. for 60 minutes, and then taken out into a room temperature atmosphere to examine the occurrence of wrinkles on the surface of the photoreceptors. The results were compared to the composition and film thickness of OCL1 and OCL2, and a second
Shown in the table.

[Table] In the table, ◯ indicates that no wrinkles were observed, △ indicates that some wrinkles were observed, and × indicates that many wrinkles occurred. As mentioned above, the OCL or at least the outer surface of the OCL must be a layer of selenium-arsenic alloy containing at least 3 atomic percent arsenic with a thickness of 0.1 μm or more, but if the OCL is a single layer, Wrinkles were already observed in Comparative Example 1 with a film thickness of 0.1 μm, and the wrinkles tended to increase as the film thickness increased in Comparative Examples 2, 3, and 4. On the other hand, according to the present invention, OCL
is divided into two layers, and the inner layer is in contact with CGL.
When the arsenic content of OCL1 is reduced, no wrinkles are observed even if the thickness of OCL2, which is the outer surface, is increased as in Examples 1 and 2, and the effect is extremely significant. Examples 3, 4, 5 Up to CGL30 were formed according to Example 1, and layers with the compositions and film thicknesses shown in Table 3 as OCL1 and OCL2 were sequentially formed thereon by flash vapor deposition. Photoreceptors Nos. 4 and 5 were produced. Comparative Examples 5 and 6 Comparative Examples 5 and 6 were carried out in the same manner as in Example 3, except that the composition and film thickness of OCL1 were changed as shown in Table 3.
A photoreceptor was fabricated. The above five types of photoreceptors were subjected to the same heating test as in the case where the results shown in Table 2 were obtained, and the occurrence of wrinkles was investigated. The results are also summarized in Table 3.

[Table] From Table 3, the arsenic content of OCL1 must be 0.5 at% or more. Also, the arsenic content of OCL1 is 2
If it exceeds atomic %, the arsenic content of OCL 1 will be too close to the arsenic content of OCL 2, and the effect of dividing OCL into two layers will be reduced, so it is preferable that the arsenic content of OCL 1 is 2 atomic % or less. Examples 6 and 7 Photoreceptors of Examples 6 and 7 were produced in the same manner as in Example 5, except that the film thickness of OCL1 was changed to 0.4 μm and 2.0 μm, respectively. Comparative Example 7 A photoconductor of Comparative Example 7 was produced which was the same as Example 6 except that the film thickness of OCL1 was 2.3 μm. The above three types of photoreceptors were similarly investigated for the occurrence of wrinkles, and no wrinkles were observed in Examples 6 and 7, while some wrinkles were observed in Comparative Example 7, OCL1 As the film thickness of
It is preferably 2.0 μm or less. On the other hand, the thickness of the OCL 40 is required to be 0.5 μm or more in view of the charging ability of the photoreceptor, and considering the case where the thickness of the OCL 2 is 0.1 μm, the thickness of the OCL 1 is required to be 0.4 μm or more. Examples 8, 9, 10 Up to CGL30 were formed according to Example 1, and layers with the compositions and film thicknesses shown in Table 4 as OCL1 and OCL2 were sequentially formed thereon by flash vapor deposition. Photoreceptors Nos. 9 and 10 were prepared. Comparative Example 8 A photoconductor of Comparative Example 8 was produced which was the same as Example 9 except that the film thickness of OCL2 was 0.8 μm. Comparative Example 9 A photoreceptor was prepared in Comparative Example 9, which was the same as Example 10 except that the film thickness of OCL2 was 0.7 μm. The occurrence of wrinkles was similarly investigated for the above five types of photoreceptors. The results are summarized in Table 4.

〔Effect of the invention〕

According to the present invention, a carrier transport layer made of amorphous selenium or an amorphous selenium-tellurium alloy is provided on a conductive substrate, and a carrier transport layer made of an amorphous selenium-tellurium alloy containing 20 to 50% by weight of tellurium. In an electrophotographic photoreceptor in which a carrier generation layer and a surface protection layer made of an amorphous selenium-arsenic alloy are sequentially laminated, the surface protection layer is divided into two layers, and a first surface protection layer in contact with the carrier generation layer is used. The layer has a low arsenic concentration, and the second surface protection layer on the side that becomes the outer surface has a high arsenic concentration. By having such a configuration,
It has excellent electrophotographic properties in the long wavelength region of 660 to 800 nm, and has good abrasion resistance and crystallization resistance.
Moreover, a photoreceptor without wrinkles can be obtained. By interposing a first surface protective layer having a thermal expansion coefficient intermediate between the carrier generation layer and the second surface protective layer, the difference in thermal strain between the two layers is alleviated and wrinkles on the surface of the photoreceptor are caused. Even if the carrier generation layer contains a large enough amount of tellurium to have sufficient photosensitivity to long wavelength light, the surface can be covered with selenium, which has a high arsenic concentration and has good crystallization resistance.
This is because it has become possible to protect the film with an arsenic alloy layer that is thick enough to provide sufficient printing durability. The present invention has an extremely large effect in that it can provide an excellent electrophotographic photoreceptor for optical printers or intelligent digital plain paper copying machines, which are expected to rapidly develop and become popular in the future.

[Brief explanation of drawings]

FIG. 1 is a conceptual cross-sectional view showing one embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the arsenic content and the glass transition point of a selenium-arsenic alloy. DESCRIPTION OF SYMBOLS 10... Conductive substrate, 20... Carrier transport layer, 30... Carrier generation layer, 40... Surface protective layer, 41... First surface protective layer, 42... Second surface protective layer.

Claims (1)

[Claims] 1 A carrier transport layer made of amorphous selenium or an amorphous selenium-tellurium alloy containing 10% by weight or less tellurium on a conductive substrate, and amorphous selenium-tellurium containing 20 to 50% by weight tellurium. The carrier generation layer consists of an alloy and an amorphous selenium-arsenic alloy containing 0.5 to 2.0 at% arsenic.
Consisting of a first surface protective layer of 0.4 to 2.0 μm and an amorphous selenium-arsenic alloy containing 3 to 5 at% arsenic,
A selenium photoreceptor for electrophotography, characterized in that a second surface protective layer having a thickness of 0.1 to 0.7 μm is laminated in this order.