JPH0462579B2 - - 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 photoconductive layer made of amorphous silicon.

[Prior art and its problems]

Conventionally, electrophotographic photoreceptors have been used, for example, amorphous Se, photoreceptors made by doping amorphous Se with impurities such as As, Te, and Sb, or ZnO and CdS.
A photoreceptor, etc., in which the compound is dispersed in a resin binder, is used. However, these photoreceptors have problems in terms of environmental pollution, thermal stability, and mechanical strength.
In order to solve these problems, in recent years amorphous silicon (hereinafter referred to as a-Si) has been used as a photoconductive layer.
It is proposed to use However, a-Si produced by vapor deposition or sputtering
has a low specific resistance of 10 ⁵ Ωcm in the dark and extremely low photoconductivity, making it undesirable as an electrophotographic photoreceptor. In such a-Si, a so-called dangling bond, in which the Si-Si bond is broken, is generated, and many localized levels exist within the energy gap due to this defect. For this reason, hopping conduction of thermally excited carriers occurs, resulting in a decrease in dark specific resistance, and photoconductivity is deteriorated because photoexcited carriers are captured in localized levels. On the other hand, amorphous silicon hydride (a-Si:H) created by glow discharge decomposition of silane gas (SiH ₄ )
By capturing the above defects with hydrogen atoms (H) and bonding H to Si, the number of dangling bonds can be greatly reduced, resulting in extremely good photoconductivity and improved p-type and n-type valences. Although electronic control has become possible, the dark resistivity value is at most 10 ⁸ to ^{10 9} Ωcm, which is still low compared to the resistivity value of 10 ¹² Ωcm or more, which is sufficient for an electrophotographic photoreceptor. Therefore, such a-Si:H
The photoreceptor has a high dark decay rate of surface potential and a low initial charging potential. Therefore, such a-Si:H
By doping an appropriate amount of boron to impart charge retention ability to the material, the specific resistance can be increased to over 10 ¹² Ωcm, making it possible to apply it to the Carlson copying process. Although a photoreceptor with such an a-Si:H surface can initially produce good images, it often shows poor images when the images are evaluated after being stored in the air or high humidity for a long period of time. It is known that this occurs. It has also been found that repeating the copying process many times gradually causes image blurring. It has been confirmed that such deteriorated photoreceptors are prone to image blurring, especially in high humidity environments, and that as the number of copies increases, the critical humidity at which image blurring begins to occur tends to gradually decrease. To check for such image blurring, it is necessary to repeatedly make tens of thousands of copies using an actual copying machine and then visually inspect the images, which requires a huge amount of effort. As mentioned above, a-Si: Photoreceptors are chemical species (ozone, nitrogen oxides, nascent oxygen, etc.) that are generated when exposed to the atmosphere or moisture over a long period of time, or due to corona discharge during the copying process.
It is believed that the outermost surface of the photoreceptor is easily affected by this, and some kind of chemical alteration causes image defects. Although the deterioration mechanism has not been sufficiently investigated to date, in order to prevent the occurrence of such image defects and improve printing durability, a protective layer is applied to the surface of the a-Si:H photoreceptor. Attempts have been made to provide chemical stabilization. For example, as a surface protective layer, amorphous silicon hydrocarbon (a-Si _x C _1x :H, 0<x<1) or amorphous silicon nitride (a-
A known method is to prevent deterioration of the photoreceptor surface layer due to the copying process or environmental atmosphere by providing Si _x N _1-x :H, 0<x<1. It is true that printing durability can be considerably improved by selecting the optimal carbon or nitrogen concentration in the surface protective layer, but it is not possible to maintain moisture resistance in a high-humidity atmosphere, and tens of thousands of sheets In the copying process, image blurring occurs at relative humidity levels of 60%, and even with these surface protective layers, printing durability and moisture resistance cannot be significantly improved.

[Purpose of the invention]

In view of this, the present invention provides an electrophotographic photoreceptor with excellent moisture resistance and corona resistance and a long life by providing a suitable surface protective layer on a photoconductive layer made of amorphous silicon. With the goal.

[Key points of the invention]

The present invention has discovered that the contact angle of pure water measured in air on the surface of the surface protective layer of a photoreceptor has a correlation with moisture resistance and corona resistance. angle between 40 degrees and 75
The above-mentioned objective is achieved by providing a surface protective layer that is of a certain degree.

[Embodiments of the invention]

The present invention is based on the test results described below. The surface protective layer transmits the irradiated light well,
The energy gap of the photoconductive layer, for example, in the case of boron-doped a-Si:H, must be larger than 1.6 to 1.8 eV. Surface protective layers were formed using combinations of various elements, and the relationship between moisture resistance and contact angle was investigated. Figure 1 schematically shows the layer structure of the photoreceptor that was tested.
A photoconductive layer 2 is formed by depositing boron-doped a-Si:H on a conductive substrate 1 made of aluminum to a thickness of 15 to 30 μm by capacitively coupled RF glow discharge, and then a photoconductive layer 2 is formed on the conductive substrate 1 made of aluminum. Apply surface protective layer 3 in the same manner as above.
was formed into a film with a thickness of 0.1 to 2 μm. A 13.56MHz high frequency power source was used to generate glow discharge. Table 1 shows the manufacturing conditions for the surface protective layer 3 of the photoreceptor that was the subject of the test.

【table】

[Table] Table 2 shows the initial contact angle of each of these surface protective layers, the contact angle and subsequent image quality after exposure to corona for 10 and 60 minutes in an atmosphere of 25°C and 70% humidity. It shows. Here, the contact angle refers to the relationship between the surface protective layer 3, pure water droplet 4, and air 5, as shown in Figure 2.
This is the angle θ created at the interface with. "◎" in Table 2 means that extremely clear images were obtained;
"O" indicates that a good image was obtained, "△" indicates that the image was partially blurred, and "x" indicates that blur occurred over the entire surface.

[Table] In this way, the surface protective layer with an initial contact angle of 45 degrees to 70 degrees, that is, a-SiN:H, a-
The SiC:F: and a-SiC:O:F:H films have small contact angle changes and good moisture resistance. Copying tests were conducted on photoreceptors with these surface protective layers under high humidity using actual equipment, and no blurring of the images occurred even after copying 100,000 copies. In other words, the moisture resistance of a photoreceptor is not determined solely by the energy gap, component elements, and their composition, but can be determined clearly by evaluating the contact angle with water. This is considered to be because the moisture resistance of the photoreceptor surface is related to water repellency, and therefore can be estimated from the value of the contact angle with pure water. However, even when measuring the tangent angle using other liquids instead of pure water, such as non-polar ethylene iodide, it is possible to obtain upper and lower limits that indicate film quality with good moisture resistance, so it can be measured as a parameter that indicates moisture resistance. Contact angles with other liquids that are easy to use can also be used.

【Effect of the invention】

The present invention provides excellent moisture resistance and corona resistance by selecting an amorphous surface protective layer that covers the photoconductive layer of a photoreceptor having an a-Si photoconductive layer according to the contact angle that the surface makes with pure water. A photoreceptor can be obtained. Therefore, it can be effectively used for the development of new surface protective layers, and has an extremely large effect on improving the characteristics of a-Si photoreceptors.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the layer structure of an embodiment of the present invention, and FIG. 2 is an explanatory view showing the principle of contact angle measurement used in the present invention. 1: conductive substrate, 2: photoconductive layer, 3: surface protective layer, 4: water droplet, θ: contact angle.

Claims (1)

[Claims] 1 In a device having a surface protective layer made of an amorphous material on a photoconductive layer made of amorphous silicon, the surface protective layer is provided with a contact angle of pure water of 40 degrees to 75 degrees when measured in air on the surface. An electrophotographic photoreceptor characterized by: