JPS6125153A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain excellent electrophotographic characteristics by providing such a gradient at which the concn. of C is low near an a-Si photoconductive layer and is higher toward the surface to the concn. of C of an a-Si overcoat layer which contains C and is provided on said photosensitive layer and incorporating oxygen into the part near the photoconductive layer. CONSTITUTION:The concn. gradient is provided to the light transmittable a-Si. C-H overcoat layer 3 provided on the photoconductive layer 2 contg. a-Si such a manner that the concn. of carbon is made low near the layer 2 and is made higher toward the surface. Oxygen is incorporated into said layer in a 35- 65at% range at the outermost surface and at <=10at% near the layer 2. The holding of electric charge is thus improved by using the a-Si.C-H in the layer 3 and the problem of the adhesion to the layer 2 and the accumulation of the charge can be solved by providing the above-mentioned gradient to the carbon content of the layer 3. Photo-fatigue and clouding are eliminated by doping the oxygen to the low carbon content part of the layer 3. The excellent photosensitivity, resolving power, gradation reproducibility, wear resistance, moisture resistance and durability are thus obtd. and the generation of white lines, white spots, etc. is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application The present invention relates to an electrophotographic photoreceptor, particularly an amorphous silicon photoreceptor.

Prior Art In recent years, amorphous silicon produced by glow discharge decomposition method or sputtering method has been developed.
The application of s 5 illicon (hereinafter abbreviated as a Si ) to photoreceptors has been attracting attention. Similarly, amorphous silicon-germanium (hereinafter referred to as a
-8i:Ge) is also attracting attention. This is because a-8i y a-8i: Ge is conventional selenium and Cd
This is because it is much better in terms of environmental pollution resistance, heat resistance, abrasion resistance, photosensitivity, etc. compared to S photoreceptors.

However, a −S i , a −S i:G
E has a drawback that it has a low dark resistance and cannot be used as it is as a photoconductive layer that also serves as a charge retention layer. For this reason,
It has been proposed to improve the dark resistance by including oxygen or nitrogen, but this has the drawback of decreasing photosensitivity, and there are limits to the content.

As a result, it has been proposed to improve charge retention by forming an a-8i insulation containing a large amount of carbon on an a-Si photoconductive layer, as shown in, for example, JP-A-57-115551. has been done. However, this technology has a high carbon content and is prone to peeling at the interface with the photoconductive layer.
In addition, with repeated copying, charges are accumulated on the interface, which tends to increase the residual potential or cause blurring of the image due to horizontal flow of the accumulated charges. Also, no consideration is given to the reduction in sensitivity due to high carbon content. Furthermore, the carbon content is 70
If the content is higher than aLolIlic% (hereinafter referred to as at%), problems due to a decrease in surface hardness (for example, white streaks occur in images during copying) cannot be avoided.

A photoreceptor using amorphous silicon containing carbon in the overcoat layer is also described in JP-A-58-108543. This technology does not suggest a carbon concentration gradient, and the carbon content is 30 at%.
The moisture resistance as an overcoat layer is very low, and if the overcoat layer contains about 10 to 25 at%, image fading is likely to occur in high humidity as the number of copies increases.

A technique for creating a gradient in the carbon concentration in amorphous silicon (photoconductive layer) is proposed in Japanese Patent Laid-Open No. 119356/1983. This technology is characterized by providing a layer region containing carbon atoms in a part of the photoconductive layer instead of an overcoat layer, and the carbon content thereof is O.
The range is as wide as 0 at%, and no proposal has been made to use amorphous silicon with a specific carbon content for an overcoat. Furthermore, no technology has been proposed to solve the problems of optical fatigue and decreased sensitivity that occur when using carbon.

The present invention improves the drawbacks of amorphous silicon-based electrophotographic photoreceptors, and provides excellent overall electrophotographic properties such as photosensitivity, charge retention properties, surface hardness, and moisture resistance. The object of the present invention is to obtain an electrophotographic photoreceptor having the following properties.

The present invention provides an electrophotographic photoreceptor in which a light-transmitting overcoat layer of amorphous silicon containing carbon is provided on a photoconductive layer containing 7 mol 7 as silicon, in which the overcoat layer is adjacent to the photoconductive layer. It has a carbon concentration gradient of 35% to 65% on the outermost surface, and a carbon concentration gradient of 10% at least in the vicinity of the photoconductive layer.
The present invention relates to an electrophotographic photoreceptor characterized by containing oxygen of aL% or less.

The basic configuration of the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1 is a schematic partial cross-sectional view of the electrophotographic photoreceptor of the present invention.
1) represents a substrate, (2) represents a photoconductive layer, and (3) represents an overcoat layer.

The substrate is a conductive material commonly used in ordinary electrophotographic photoreceptors, such as an AI drum, and the present invention is not characterized in this respect.

The photoconductive layer (2) is an amorphous silicon-based photosensitive layer, and is made of amorphous silicon-hydrogen (hereinafter a-8i: H
), but it may also be partially supplemented with oxygen, nitrogen, halogen (especially fluorine), etc.
Material a-8i: It may be a Ge layer, and boron, phosphorus, etc. may be added to perform P and N control.

The photoconductive layer containing a-8i may be formed by a conventional method such as a glow discharge decomposition method.The thickness of the photoconductive layer is 10 to 100 .mu.m, preferably 10 to 60 .mu.m.

An underfoot layer may be provided between the substrate (1) and the photoconductive layer (2).

In the present invention, an overcoat layer is further provided on the photoconductive layer. The overcoat layer is amorphous silicon.
It is formed from carbon (hereinafter referred to as a-8i.C-H).

The carbon content of a-8i-C-H is high as it reaches the surface layer, and in the outermost layer, it is set in the range of 35 to 65aL% (number of IC atoms/(number of C atoms + number of Si atoms)) x 100). is preferred. If the carbon concentration in the outermost layer is less than 35%, the sensitivity will be insufficient and optical fatigue will occur, and the expected moisture resistance stability will not be obtained. Further, if the content is 6Sat% or more, the surface hardness decreases and white streak-like image defects occur. Carbon content 35
The ~65 at% layer has a thickness of 0.01 to 1.5 μm, more preferably 0.03 to 0.5 μm. If the layer thickness is thinner than this, the function as a protective layer will be insufficient in terms of moisture resistance and printing durability, and if it is too thick, the sensitivity will decrease and the residual potential will increase.

The carbon content is tapered as one approaches the photoconductive layer so that there is virtually no gap in carbon concentration between the overcoat layer and the photoconductive layer.

This improves the adhesion between the overcoat layer and the photoconductive layer and prevents them from peeling off, and also prevents an increase in residual potential due to the accumulation of charges at the interface between the two and blurring of the image due to horizontal flow of accumulated charges. To prevent. From the viewpoint of adhesion, it is preferable that the layer thickness of the carbon concentration gradient part be thicker in order to have a concentration gradient as gentle as possible, but in consideration of photoconductive properties, it is preferable to make the layer thickness about 200 to 9000. If the thickness is too small, defects similar to virtually no concentration gradient will occur;
Even if the above is done, the above effects cannot be further achieved, and the a-8i/C-H layer becomes too thick, which tends to cause other problems such as a decrease in sensitivity.

In the a-3i-CH layer, the portion where the carbon concentration is low (ie, the carbon concentration gradient portion) has a large amount of light absorption, which inhibits the transmission of light to the photoconductive layer, resulting in a decrease in sensitivity and, at the same time, a tendency to cause optical fatigue.

In order to solve the above problem, in the present invention, the carbon concentration gradient portion is doped with oxygen. By doping with oxygen, a Si・
The light transmittance in the C-H portion where the carbon concentration is low is improved, optical fatigue is reduced, and the adhesion with the photoconductive layer can be further improved. Although it is not necessary to intentionally dope oxygen in the carbon concentration range of 35 to G5aL%, it is possible to further improve the surface hardness by doping a small amount (for example, up to several percent).

In the present invention, oxygen doping is mainly performed on the carbon concentration gradient section. The amount of oxygen doped is 0.05-10 at% (
Number of IOM children/(number of S1 atoms + number of C atoms, tens of atoms) lx
loo), more preferably 0°1 to 5 aL%.

The oxygen doping may be constant or may be increased as the carbon content decreases if necessary. Oxygen content is 5 at%,
In particular, if it exceeds 10 at%, it will cause residual potential to occur.

FIG. 2 schematically shows the above embodiment. The axis indicates the thickness from the outermost surface of the overcoat layer (3) to the interface with the photoconductive layer, and the latitude axis indicates the carbon concentration and oxygen concentration. The region (OPQR3O) schematically shows the approximate range of the carbon concentration of the present invention corresponding to the depth of the overcoat layer. In this region, the carbon concentration is on lines (4) and (5)
It may be changed as shown in . Line (4) shows a carbon concentration of 50a from the overcoat layer surface to a depth of 0.5μI11.
It is shown that the carbon concentration is composed of asi-c-H containing t%, and thereafter the carbon concentration gradually decreases and becomes substantially 0 at the interface with the photoconductive layer. #i(5) indicates that the carbon concentration decreases linearly from the outermost layer toward the interface.

The region (OVTUO) indicates the amount of oxygen doped. Line (6) is a diagram showing that a certain amount (0.3 at%) of oxygen is doped into the carbon content reduced region shown by line (4).

As shown by line (7), the amount of oxygen doped may be increased closer to the interface.

Effects of the Invention The present invention solves the drawback of low dark resistance of a-3i-H electrophotographic photoreceptors by using a5i-CH having a specific amount of carbon in the overcoat layer to improve charge retention; a
The problems of adhesion and charge accumulation between -8i-C-H and the photoconductive layer were solved by creating a gradient in the carbon content of the overcoat layer; Fatigue and opacity are overcome by doping the low carbon content with oxygen. Therefore, the obtained electrophotographic photoreceptor has excellent sensitivity, resolution, gradation reproducibility, sharpness, abrasion resistance, moisture resistance, and durability.
The occurrence of white streaks, white spots, etc. that tend to occur when copying using an electrophotographic photoreceptor overcoated with 8i-CH is suppressed.

Example 1 In the glow discharge decomposition apparatus shown in FIG. 3, first, the rotary pump (23) is operated, followed by the diffusion pump (24), and the interior of the reaction chamber (25) is brought to a high vacuum of about 10-6 Torr. After setting the first to third and fifth regulating valves (13
), (14), (15), and (17) are opened, H2 gas is supplied from the first tank (8), 100% 5iH=gas is supplied from the second tank (9), and H2 is supplied from the third tank (10). B2H' diluted to 200 pp+n, gas, and 02 gas from the 5th tank (12) are added to the output pressure gauge IKg/
Mass 70-controller (38) under cm2, (1
, 9), (20), and (22). Then, adjust the scale of each square 70-controller to
Flow rate of 486.5 sccm, SiH, 90 sec
m, B2H6 22.5sec, 02 1. Os
ccm and flowed into the reaction chamber (25). After each flow rate stabilizes, the internal pressure of the reaction chamber (25) reaches 1. I adjusted it to OTorr. On the other hand, as the conductive substrate (27), an aluminum drum with a diameter of 80III11 is preheated to 240°C, and the high frequency power source (26) is turned on when the flow rate of each gas is stable and the internal pressure is stable. Insert 250 u+ into the electrode plate (28)
Atts power (frequency 13.56 MHz) was applied to generate glow discharge. This glow discharge was continued for about 6 hours to form an a-Si photoconductive layer (29) (Fig. 4) with a thickness of about 20 μM containing hydrogen, boron, and a trace amount of oxygen on the conductive substrate (27). .

a Once the Si photoconductive layer is formed, a high frequency power source (26
) The transition layer is continuously deposited without stopping the power application from ). That is, 0. The gas is quickly < 3 sec + n, and the main t-mass 70 - controller < 20) j: from B
, I-1, and gas were also set to Osc c +n at the same time, flowing into or stopping the reaction chamber (25), and maintained in this state for about 2 minutes.

Also, during this 2 minute period, the mass 70-controller (21
) with C2H, gas from 0 to 45 sccI.

It was gradually changed so that In this way, about 0°1μ
A 5i-C transition layer (30') (FIG. 4) of 1 was formed. After applying the high frequency for about 3 minutes, the mass 70-controller turned the 5IH4 to 90%.
From sec to 30 sec, 02〃 3 sec
It was uniformly decreased from m to Oscc■. During this time, the C2Haws continues to flow for 45 seconds. Thus approximately 0.1 μm a-3i-C transition layer (30”) (fourth
Figure) was formed.

Furthermore, by stopping B2) (6 gas while applying high frequency power and maintaining this state for 6 minutes, approximately 0°1 μmn
An overcoat outermost layer (31) is formed.

Immediately thereafter, high frequency power application was stopped.

The overcoat outermost layer (31) thus formed contains about 40 at% carbon, and the transition layer (30) contains up to about 3 at% oxygen.

The thus obtained photoreceptor was used for powder image transfer type copying (EP-6).
50Z: Set in Minolta Camera Co., Ltd.), (+)
When copied using electrostatic charging, a clear, high-density image with excellent resolution and good gradation reproducibility was obtained.

Furthermore, even after 400,000 sheets were continuously copied, no deterioration in image characteristics such as white streaks or white spots was observed, and good copies were obtained to the end. Further, even when copying was performed under conditions of high temperature and high humidity of 30° C. and 85%, the electrophotographic characteristics and image characteristics were no different from those under normal temperature conditions.

A photoreceptor was prepared according to the procedure of Example 1. However, in the transition layer (30'), the ethylene flow rate is changed from O to Z S (!0
111, the transition layer (30″) and the surface layer (
In 31), oxygen was not used and ethylene was directly passed through Zsec to form a film.

Table 1 shows the results of quantification of the amount of carbon in the overcoat layer by Auger analysis by changing Z.

Table 1: The obtained photoreceptor was printed on the same copying machine as in Example 1.
, I made continuous copies of OOO sheets. As a result, with the photoreceptor of Reference Example 8, white streaks occurred in the copied image, and
℃, 85% environment, reference example 1
Image deletion occurred in photoreceptors No. 2 and 2. Accordingly, it has been found that when the amount of carbon in the oval coat layer is small, the moisture resistance is insufficient, and when it is too large, the surface hardness decreases, resulting in problems such as white streaks during actual copying. Therefore, the appropriate amount of carbon is 35 to 65 at%.

Examples 2 to 6 and Comparative Examples 1 and 2 Photoreceptors were produced according to the procedure of Example 1. However, in the transition layer (30'), the oxygen flow rate is rapidly increased from 1 to Ysccm, and in the transition layer (30''), the oxygen flow rate is increased from Y to Oseem.
The film was formed so that the surface layer (31) contained oxygen in a monotonically decreasing manner.

Table 2 shows the results of quantification of the maximum amount of oxygen in the transition layer by Auger analysis by varying Y.

Table 2 The obtained photoreceptor was placed in a photoreceptor testing machine, and corona charging and erasing tests were repeated.

As a result, Comparative Example 1 in which oxygen was not added to the transition layer
A decrease in surface potential was observed for the photoreceptor. It was also found that increasing the amount of oxygen added tends to suppress the rate of decrease in surface potential. This rate of decrease in surface potential is called photofatigue (L1BhtFaLigue), and based on the difference between the surface potential at the first rotation (Vow) and the surface potential at the 10th rotation (VO, , )), the rate of decrease in surface potential is The degree of fatigue was determined.

Light fatigue level “I (V'o+ Voto) / VOll
x 100 FIG. 5 shows the relationship between this degree of optical fatigue and the amount of oxygen in the transition layer.

Furthermore, it can be seen from FIG. 6 that by increasing the amount of oxygen in the transition layer, the spectral sensitivity, particularly the short wavelength sensitivity, is improved.

However, in the photoreceptor of Comparative Example 2 which contains a large amount of oxygen, the image is blurred even in an environment at room temperature, and a clear image cannot be obtained by a normal electrophotographic process. Furthermore, although the photoreceptor of Example 6 does not have the above-mentioned drawbacks, when it was set in the copying machine described in Example 1 for continuous copying, image fogging was observed after several thousand copies. It became noticeable.

From the above, a particularly preferable range of the amount of oxygen in the transition layer is 0.1 to 5 at%.

Comparative Examples 3 to 8 After forming a Si photoconductive layer (29) under the same conditions as in Example 1, the application of high-frequency power was stopped, and the flow rates of all mass rollers were set to 0, and the reaction chamber was closed. (25) The inside was sufficiently degassed. After that, the first tongue, ri (
8) from H2w 486. 5 sec, 100% 5iH4ff from the second tank (9) 309QCm
, C2H4 gas from the fourth tank (11) for 120 seconds
The scale of the mass 70-controller was adjusted so that the mass 70-controller became 100 m, and after each flow rate became stable, high-frequency power of 250 u+atts was applied again, and after 6 minutes of open film formation, high-frequency power application was stopped. This is the third example in Example 1 (30
) without the transition layer.

Table 3 shows the results of fabricating several types of photoreceptors by similarly changing only the c2H4 gas flow rate.

As a result of continuous copying of 40,000 sheets using the same copying machine as in Example 1, all of the photoreceptors obtained from Comparative Examples 5, 6, 7 and 8 had white streaks on the images. this is,
This is because the adhesion between the overcoat layer and the photoconductive layer is poor, and the overcoat layer peels off during the cleaning process inside the copying machine.

After copying 40,000 sheets, actual copying was performed at 30° C. under high temperature and high humidity conditions of 85%, and image deletion occurred in the photoreceptors obtained from Comparative Examples 3 and 4.

Therefore, it was found that the transition layer (29-) is necessary in order to satisfy both the prevention of peeling of the overcoat layer and the high moisture resistance.

[Brief explanation of the drawing]

Fig. 1 is a schematic partial cross-sectional view of the electrophotographic photoreceptor of the present invention, Fig. 2 is a schematic diagram showing the carbon concentration and oxygen concentration in the overcoat layer, and Fig. 3 is a schematic diagram showing the carbon concentration and oxygen concentration in the overcoat layer. A schematic diagram of the apparatus, FIG. 4 is a partial sectional view of a photoreceptor for explaining an example, FIG. 5 is a graph showing the oxygen concentration in the overcoat layer and the degree of optical fatigue, and FIG. 6 is a photoreceptor of the present invention. Graph showing sensitivity versus wavelength. (1) Substrate, (2) Photoconductive layer, (3) Overcoat layer. Figure 1 2nd cause

Claims (1)

[Claims] 1. In an electrophotographic photoreceptor in which a transparent overcoat layer of amorphous silicon containing carbon is provided on a photoconductive layer containing amorphous silicon, the overcoat layer is low near the photoconductive layer; It has a high carbon concentration gradient toward the surface, in the range of 35 to 65 at% at the outermost surface, and at least 10 at% in the vicinity of the photoconductive layer.
An electrophotographic photoreceptor characterized by containing the following oxygen: 2. The electrophotographic photoreceptor according to item 1, wherein the overcoat layer has a total thickness of 0.05 to 1.5 μm, and the carbon concentration gradient portion has a thickness of 0.02 to 1 μm. 3. The electrophotographic photoreceptor according to item 1, wherein the overcoat layer has an oxygen concentration of 0.1 to 5 at%. 4. Third, the oxygen concentration increases as it approaches the photoconductive layer.
The electrophotographic photoreceptor described in .