JPH0157899B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to an electrophotographic photoreceptor having a photosensitive layer made of a selenium-based material and used in laser printers and the like. Photoreceptors for laser printers particularly require long-wavelength light sensitivity, and in order to meet such requirements with a selenium-tellurium alloy, it is necessary to contain Te at a concentration of 25% by weight or more. The thickness of this charge generation layer is limited to about 2 μm or less because of the low dark resistance and charge retention ability of such Se alloys with a high Te concentration. However, it is not possible to obtain the dark potential of 500 V or more necessary for the electrophotographic process with only such a thin layer, so in order to maintain the potential, a charge transfer layer made of a Se-Te alloy with a lower Te concentration or pure Se is required. It is provided between the charge generation layer and the conductive substrate. Furthermore, it is known to provide a Se surface layer on this charge generation layer to protect it and improve its charge retention ability. This surface layer determines the life of the photoreceptor. That is, in order to extend the life of a photoreceptor, it is necessary to improve heat resistance and increase surface hardness. for that
Te, As, Sb, etc. are added to the Se surface layer, but the addition of these elements to the surface layer deteriorates the mobility of charges (electrons) to the surface layer, especially the charge against long wavelength light. This has the disadvantage that the injection efficiency of electrons from the generation layer to the surface layer becomes poor, and the charging potential fluctuations during repeated printing become large. It is an object of the present invention to eliminate this drawback, to extend the life of a photoreceptor having a functionally separated photosensitive layer, and to reduce fluctuations in charging potential during repeated copying. The purpose of this is to form an electrophotographic photoreceptor in which a charge transport layer made of pure selenium and a charge generation layer made of a selenium-tellurium alloy are laminated in this order on a conductive substrate, and a second surface layer made of pure selenium is placed on top of the charge transport layer made of pure selenium and a charge generation layer made of a selenium-tellurium alloy. This is achieved by further laminating in this order a first surface layer consisting of a selenium alloy layer containing 1 atomic % or more of either Te or Ge. Examples of the present invention will be described below with reference to figures and comparative test results. As shown in FIG. 1, the electrophotographic photoreceptor according to the present invention has a charge transfer layer 2, a charge generation layer 3, a second surface layer 4, and a first surface layer 5 sequentially laminated on a conductive substrate 1. ing. The second surface layer 4 is a pure selenium layer that may contain a trace amount of impurities compared to the first surface layer, and the first surface layer 5 contains elements to improve heat resistance and hardness. This is a selenium alloy layer containing 1 atomic % or more of added selenium. Example 1 An aluminum cylinder with a diameter of 120 mm and a length of 340 mm as the substrate 1 was maintained at 65°C, and pure Se was placed on it.
The charge transfer layer 2 was formed by vapor deposition to a thickness of 60 μm.
Next, Se alloy containing 22.5% by weight of Te was evaporated at 350°C to form a charge generation layer 3 of 0.7 μm for long wavelength light.
It was deposited to a thickness of . At that time, the topmost surface of this layer
The Te concentration was 40-50% by weight. On top of this, a second surface layer 4 with a thickness of 1.2 μm is formed by flash-depositing pure Se, and a first surface layer 5 with a thickness of 1.2 μm is further formed by flash-depositing a 5.5 wt % Te-Se alloy.
were formed sequentially. Example 2 Conductive substrate 1, charge transfer layer 2, charge generation layer 3,
The second surface layer 4 was the same as in the example, and the first surface layer 5 was a 7% by weight Te-Se alloy deposited by flash vapor deposition to a thickness of 1.5 μm. Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that the second surface layer 4 was omitted. Comparative Example 2 A sample was prepared in the same manner as in Example 2 except that the second surface layer 4 was omitted. Using the above four types of photoreceptors, corona charging is performed while rotating at a rotation speed of 14 rpm, and the corona charger
It was exposed to 780 nm monochromatic light at a position of 30°, and the surface potential was detected at a position of 100° from a corona charger. Static charge removal was performed by exposing each photoreceptor to white light with a color temperature of 2800K for an amount 10 times the half-attenuation exposure amount. For the first 25 rotations, the dark potential is measured without exposure, for the next 25 rotations, exposure is applied, and for 25 rotations again, the exposure is stopped, and in this way, after 25 rotations, the exposure is turned on and off, repeating a total of 250 cycles. , potential fluctuations at the time of stopping exposure were measured at room temperature. The results are shown in Table 1.

[Table] Example 3 A charge transfer layer 2 and a charge generation layer 3 were prepared in the same manner as in Example 1, and a surface layer was deposited thereon. Se alloy containing 1 at% Ge was used as the evaporation source, and the boat temperature of the evaporation source was set to 380°C at the start of evaporation.
In this state, Ge and Se were vapor-deposited by fractional distillation until about 1/3 of the amount of the raw material was left, and then the boat temperature was raised to 500°C and all the remaining materials were flash-deposited. The total thickness of the surface layer was 1.1 μm. Comparative Example 3 In the example, 1 atomic % Ge at the time of forming the surface layer
-The boat containing the Se alloy was heated to 500°C from the beginning for flash deposition, and the surface layer of the Se-Ge alloy was deposited.
It was formed to a thickness of 1.2 μm. Using the photoreceptors of Example 3 and Comparative Example 3, the same fatigue measurements as those used to obtain the results in Table 1 were performed. The results obtained are shown in Table 2.

[Table] Note that there is a Se-Ge alloy layer on the surface of both Example 3 and Comparative Example 3, which has not been used in the surface layer of conventional functionally separated photoreceptors. The heat resistance and printing durability were also improved compared to the pure Se surface layer. According to the present invention, fluctuations in charging potential due to repeated fatigue, which is a drawback when adding different elements such as Te and Ge to the surface layer in order to extend the life of the photoreceptor, can be reduced by the results shown in Tables 1 and 2. As shown, the amount has become almost negligible, and stable images can now be obtained. Especially when continuously copying several hundred sheets or more, there is a noticeable difference in image quality between the photoreceptor according to the present invention and a photoreceptor having a conventional surface layer. This is because when electrons generated in the charge generation layer are injected into the surface layer, the injection is incomplete due to the addition of elements to the surface layer, and these trapped electrons accumulate, causing a drop in potential. This is based on the fact that this injection property is improved by the presence of the intermediate pure selenium layer provided according to the invention, and the charging potential hardly changes since no such accumulation of electrons occurs. Moreover, the heat resistance and printing durability of the photoreceptor can be improved by the additive elements present near the surface, so the effect of the present invention is particularly great for photoreceptors having long wavelength sensitivity.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing one embodiment of the present invention. 1... Conductive substrate, 2... Charge transport layer, 3...
Charge generation layer, 4... second surface layer, 5... first surface layer.

Claims (1)

[Claims] 1 A charge transport layer made of pure selenium and a charge generation layer made of a selenium-tellurium alloy are laminated in this order on a conductive substrate, and a second layer made of pure selenium is placed on top of the charge transport layer made of pure selenium and a charge generation layer made of a selenium-tellurium alloy.
A photoreceptor for electrophotography, characterized in that a surface layer and a first surface layer made of a selenium alloy layer containing 1 atomic % or more of either Te or Ge are further laminated in this order.