JP2603485B2 - Electrophotographic photoreceptor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor mainly composed of amorphous silicon, and more particularly to improvement of its use environment characteristics.

(Prior art) Conventional electrophotographic photoreceptor mainly composed of amorphous silicon,
For example, as shown in FIG. 1, a positively charged photoreceptor has a conductive substrate (1), a lower barrier layer (2), a potential holding layer (3), and an upper barrier layer (3) formed on the conductive substrate (1). 4), and each layer except the conductive substrate (1) is generally formed as follows. That is, the lower barrier layer (2) is formed of amorphous Si, H, B, O, and N, each having a uniform atomic concentration distribution in the thickness direction as shown in FIG.
Prevents electrons injected from the conductive substrate (1) from reaching the potential holding layer (3) and the barrier layer (4) thereover by being made to have a strong P-type conductivity with a thickness of 10 μm. I do.
As shown in FIG. 2, the potential holding layer (3) is mainly composed of amorphous Si and H and B, each having a uniform atomic concentration distribution in the thickness direction, and has a dark resistance ρ _D of 10 ¹¹ to 10 ¹⁶ Ω.・ Cm (at the time of light irradiation
It has a photoconductivity of 10 ⁴ to 10 ¹⁰ Ω · cm, and can be made to hold a potential of about 500 to 1500 V in the dark.
The upper barrier layer (4) has a thickness of 500 ° to 5 μm and is mainly formed of amorphous Si, C and H whose atomic concentration distribution is uniform in the thickness direction as shown in FIG. Are made to have a high energy barrier to holes so that positively charged charges can be prevented from being injected into the potential holding layer (3).

(Prior Art and Problems Thereof) However, in the above-described conventional photoconductors, generally, the higher the humidity in the use environment, the worse the reproducibility of the original image becomes, and the sharper the image becomes. For example, according to the results of the copy cycle test for those having the photosensitive characteristics shown in Table 1 below, a normal image can be obtained even after the 500,000-sheet copy cycle test at a room temperature of 25 ° C. and a relative humidity of 50%. However, if the room temperature is 25 ° C. and the relative humidity is 95%, the reproducibility of the original image is completely lost after a 500,000 copy cycle test, resulting in a so-called image flow.

Moreover, in the conventional photoreceptor, the concentrations of Si and H forming the upper barrier layer (4) and the potential holding layer (3) are discontinuous at the interface between them, and particularly, C atoms are contained in the potential holding layer (3). On the other hand, on the upper barrier layer side, the concentration rapidly changes to 30 to 95% within a layer thickness of about 0 to 100 ° from the interface, compared to 5% or less (not shown in the figure because the amount is small). This indicates that the difference in optical energy gap between the upper barrier layer (4) and the potential holding layer (3) is large, and the interface structure has a large lattice mismatch of the microscopic crystal structure. This indicates that the charging potential decreases due to the increase in the interface state based on this, and the residual potential increases, deteriorating the photosensitive characteristics, indicating that there is room for improvement in the photosensitive characteristics.

(Object of the Invention) The present invention relates to an electrophotographic photosensitive member mainly composed of amorphous silicon, which has improved photosensitive characteristics such as an increase in a charging potential and a decrease in a residual potential, in addition to an improvement in use environment characteristics. It was made for the purpose of providing. Hereinafter, the present invention will be described in detail with reference to the drawings.

(Means of the Invention for Solving the Problems) The inventor of the present invention has conducted various studies on the development of the image flow as described above, and has found that the cause is as follows. That is, in the conventional photoreceptor, as described above with reference to FIG. 2, the concentration distribution of Si atoms in the upper barrier layer (4) is uniform in the thickness direction and the Si
Atoms are exposed.

For this reason, the surface Si exposed to the positive corona discharge for charging performed every time of copying has high hygroscopicity, and is inferior to mechanical contact with paper, toner, and other mechanical, chemical, and physical stimuli.
Changed to SiOx surface. Therefore, as described above, under a high humidity condition such as a relative humidity of 95%, the moisture content adsorbed on the surface and the ionic components such as NOx in the atmosphere usually cause the humidity to drop to 1%.
The lateral resistance of 0 ¹¹ to 10 ¹⁶ Ω · cm is degraded to 10 ⁸ Ω · cm or less. As a result, the electrostatic charge latent image of the original image after positive charging by positive corona discharge is spread laterally through the low resistance area on the surface, and as a result, the image flow is lost, and it is apparent that the reproducibility of the original image is lost. Was.

The present invention has been conceived from the above study results that the concentration of Si atoms in the surface of the upper barrier layer, which is easily affected by moisture, and the depth in the vicinity thereof may be reduced to zero in order to improve the use environment characteristics. The present invention is characterized in that it has a configuration as shown in the sectional structural view of FIG. 3 (the same reference numerals in FIGS. 1 and 2 denote the same parts). .

That is, first, the concentration of the Si principle in the upper barrier layer (4) is gradually reduced from the interface with the potential holding layer (3) toward the surface, and is reduced to zero on the surface, and the concentration of C atoms is reduced. At the interface with the potential holding layer (3), for example, 5%
Hereinafter, the distribution is such that the concentration is increased toward the surface so as to be 95 to 30% on the surface. Moreover, in addition to this, C
Unbonded unpaired electrons of Si-C and C-C bonds (dangling bond DANGLING BON
To prevent the increase in the number of trap centers due to D),
The concentration of H atoms is set to, for example, 500 from the surface of the upper barrier layer (4).
The H concentration at the surface is set to, for example, 15 to 50% so that the H atoms are bonded to the dangling bonds by making the distribution state uniform at the highest concentration within the thickness of 1010 μm, or a distribution state that continues to increase toward the surface. To inactivate. As described above, the C / Si ratio is increased while deactivating dangling bonds by H atoms to increase the optical energy gap, thereby reducing the Si atom concentration to at least zero at the surface as described above. The surface of the barrier layer (4) has the property of an amorphous carbon film, that is, the optical energy gap Eg is Eg 2.0 eV, and the dark resistance ρ _D is ρ _D 10 ¹³ Ω · cm.
To be presented. And, so that there is no Si, which becomes SiOx that easily adsorbs moisture by corona discharge, on the surface,
Even in a copy cycle test under a high humidity condition such as a relative humidity of 95%, the surface lateral resistance ρ _D is ρ _D
The image flow is prevented from deteriorating to 10 ¹¹ Ω · cm or less (deterioration to 10 ⁸ Ω · cm or less in the conventional structure). In addition, by making the surface an amorphous carbon film that is more resistant to mechanical, chemical and physical stimuli than Si, it is possible to form a surface that is more resistant to stimuli such as toner contact and paper contact. .

Second, the decreasing distribution of the concentration of Si atoms and the increasing distribution of the concentration of H atoms in the upper barrier layer (4) correspond to the potential holding layer (3).
Is performed gently and continuously from the same concentration as the concentration at the interface. As a result, the interface state density is reduced to reduce the occurrence of distortion in the film, and the potential holding layer (3) and the upper barrier layer (4) as in the conventional photoreceptor described above with reference to FIG. In this case, the reduction of the charging potential due to the discontinuity of the density at the interface of the layer and the increase of the residual potential are suppressed to improve the working environment characteristics and the photosensitive characteristics.

Of course, it is conceivable that the entire upper barrier layer (4) is made of an amorphous carbon film. However, this causes a large discontinuity with the Si atom concentration of the potential holding layer (3) at the interface. It is not preferable because it causes deterioration of photosensitive characteristics such as reduction. Also, when a part including the surface is made of an amorphous carbon film, if the amorphous carbonization is performed from the surface to a deep position as shown by a dotted line in FIG. For example, when the thickness of the upper barrier layer (4) is set to 500 ° to 5 μm, the amorphous carbon film is formed within a range of 100 to 5000 ° from the surface. Is good.

 Next, examples of the present invention will be described.

(Example) Table 2 shows the characteristics of the photoreceptor produced by using the reaction apparatus according to the high frequency glow discharge CVD method shown in FIG. About 10 r. In the reaction chamber (5) by the motor (6).
An aluminum cylindrical conductive material having an outer diameter of 100 mm and a length of 300 mm was placed on a substrate holder (8) rotated at pm and capable of heating the substrate (1) at 300 ° C. ± 2 ° C. by an internal heating device (7). The base (1) is mounted. The counter electrode (10) is opposed to the substrate (1) at a concentric distance of about 5 cm, and is connected to a 13.5 MHz high frequency power supply (9) ((9a) is an oscillator, (9b) is a matching adjuster). ) Are provided on the surface of the high-pressure cylinder (11).
a) The pressure is reduced from (11b), (11c), and (11d), and the flow rate is precisely adjusted by the mass flow controller (12), and SiH ₄ , H ₂ ,
The required gas such as B ₂ H ₆ / H ₂ , C ₂ H _{2 is} supplied to the pressure regulating valve (13
a), the gas is exhausted by a mechanical booster pump (13b) and a rotary pump (13c) and sent into a reaction chamber (5) in which the gas pressure is constantly regulated. Then, as shown in Table 3, the thickness of Si, H, B, O, N was 3 μm on the conductive substrate (1) according to the conditions such as flow rate, pressure, high frequency output, deposition time, etc. After the lower barrier layer (2) made of is formed, a potential holding layer (3) made of Si, H, and B having a thickness of 20 μm is further formed thereon. Finally, Si, H, and C atoms are deposited thereon in accordance with the atomic composition ratio of the potential holding layer (3). Then, Si atoms decrease in the thickness direction, and H and C atoms increase in the thickness direction. 3000 to distribute the concentration
Å Form a thick upper barrier layer (4).

As is apparent from a comparison between the photosensitive characteristics of the conventional photoreceptor and Tables 1 and 2 showing that of the present invention, the photoreceptor according to the present invention has a charging potential which is increased by about 40% compared with the conventional one.
The residual voltage is also reduced by about 50%, indicating that excellent photosensitive characteristics can be obtained. In addition, according to the result of a 500,000 copy cycle test at room temperature 25 ° C and 95% relative humidity, the conventional one causes an image flow, whereas in the present invention, the original image is reproduced well and a high-resolution clear image is obtained. It was confirmed that it could be obtained.

(Effects of the Invention) As is apparent from the above, according to the present invention, the characteristics required of the upper barrier layer which plays a very important role in the electrophotographic photoreceptor, that is, the lattice formed at the interface with the potential holding layer The interface state caused by the difference in the constants is as small as possible and the interface trap density is low.

The upper barrier layer is a high-resistance substance having low conductivity of surface charge (ρ _D 10 ¹³ Ω · cm).

It has a large optical energy gap that does not absorb long-wavelength light 800 nm as a photoconductor window material.

High lateral resistance to surface charge (ρ _D 10 ¹³
Ω · cm) and maintain high lateral resistance even under the use environment conditions.

It has a long life with little deterioration of photosensitive characteristics even under mechanical, chemical and physical stimuli such as corona discharge, toner contact, paper contact and strong light irradiation.

Thus, it is possible to provide an electrophotographic photosensitive member having an upper barrier layer which can substantially satisfy the requirements such as above, and therefore, an electrophotographic photosensitive member mainly composed of amorphous silicon excellent in use environment characteristics and photosensitive characteristics.

In the above, the positive charging type photoconductor has been described as an example, but the present invention can be applied to a negative charging type photoconductor to obtain the same effect. In the examples, the high-frequency glow discharge CVD method was used.
Various known production methods such as a VD method and a DC discharge CVD method can be used.

[Brief description of the drawings]

1 and 2 are cross-sectional views of the structure of a conventional photoreceptor, FIG. 3 is a cross-sectional view of the structure of the photoreceptor of the present invention, and FIG. 4 is a diagram of an example of a reaction apparatus used for manufacturing the photoreceptor. (1) ... conductive substrate, (2) ... lower barrier layer, (3)
... potential holding layer, (4) ... upper barrier layer, (5) ... reaction chamber, (6) ... motor, (7) ... heating device,
(8)… Basic holder, (9)… High frequency power supply, (9a)
…… Oscillator, (9b) …… Matching adjuster, (10) ……
Counter electrode, (11a) (11b) (11c) (11d) ... high-pressure gas cylinder, (12) ... mass flow controller, (13a)
… Pressure adjustment valve, (13b)… Mechanical booster pump, (13c)… Rotary pump.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuru Takei 462 Osato-cho, Kofu-shi, Yamanashi Prefecture Inside Yamanashi Electronics Industry Co., Ltd. 56) References JP-A-62-182751 (JP, A) JP-A-61-219962 (JP, A) JP-A-62-170968 (JP, A) JP-A-61-130954 (JP, A)

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein a lower barrier layer, a potential holding layer,
An electrophotographic photosensitive member mainly composed of amorphous silicon in which an upper barrier layer is sequentially laminated so that an electrostatic latent image is formed on the surface of the upper barrier layer, wherein the upper barrier layer is formed of Si, H And the concentration of the Si atoms is approximately the same as the concentration of the potential holding layer at the interface with the potential holding layer, and has a distribution that decreases in the direction of the surface, and At least on the surface, the concentration of the H atoms is approximately the same as the concentration of the potential holding layer at the interface with the potential holding layer, and has a distribution that increases in the direction of the surface; The electrophotographic photoreceptor according to claim 1, wherein the concentration at the interface with the potential holding layer is 5% or less and the concentration increases in the direction of the surface.