JPS60143355A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To prevent generation of white, blur, etc. of the printed image by laminating a photoconductive layer in which a high resistance part occupies the main region and a low resistance region exists partially on a base via an intermediate layer and making the resistance value of the intermediate layer equal to or higher than the low resistance region. CONSTITUTION:A high resistance region 1A and a low resistance region 1B are both made present in a photoconductive layer 1 of a photosensitive body constituted by providing the layer 1 on a base 2. An intermediate layer 3 having the resistance value equal to or higher than the resistance value of the region 1B is made present between the layer 1 and the base 2. The layer 1 consists of a-Si: and the resistance value thereof is about 10<13>OMEGAcm. The intermediate layer 3 is formed by using a-Si:O. The resistance value of such layer 3 is about 10<14>OMEGAcm and the dielectric relaxation time is about 20sec and therefore the fast potential attenuation is suppressed even if there is the low resistance region 1B which is the cause for white etc. extisting on the layer 1. No adverse influence is thus given to the light attenuation of the region 1A. The satisfactory image is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electrophotographic photoreceptor, and particularly to an electrophotographic photoreceptor suitable for application to a laser beam printer.

[Background of the invention]

Conventionally, 5eXSe has been used as a photoconductive material for electrophotographic photoreceptors.
Alloys, inorganic substances such as CdS, and polyvinylcarbazole (P
Organic substances such as VK) are used. However, these inorganic substances have strong requirements, and there are problems in handling during production and treatment after use. Furthermore, since the surface of photoreceptors made of these materials does not have sufficient hardness, the surface is scratched during use, resulting in poor images. In order to improve these drawbacks, it has been proposed to use hydrogen-containing amorphous Si (hereinafter abbreviated as a-8i) as a photoreceptor (see, for example, Japanese Patent Laid-Open No. 78135/1983).

The structure of a general electrophotographic photoreceptor is shown in FIG. 1, and its equivalent circuit is shown in FIG. 2. The time change in the surface potential (2) of the film is expressed by the following equation.

AnV=--10A τ...(1) τ=RC 几: Resistance value of the photoconductor C: Capacitance of the photoconductor A: Constant If the resistivity of the photoconductor is ρ and the relative dielectric constant is ε, then τ =εε0
ρ...(2) εo: Dielectric constant of vacuum (8,85X10-14CF/c
It can be expressed as rn)).

τ needs to be 10(8) or more for an electrophotographic photoreceptor.

In the case of a-8i:H, ε is about 11. τ to 1Q84
To make it K1 or higher, ρ,=io” [:Ω・mouth] is required.

By the way, if a-8i:H is created by glow discharge method etc., ρ
It becomes difficult to make the value greater than 1013 [Ω·α].

For this reason, resistivity is increased by doping a-8i:H with 9, C, or N, which is doped with B or O.

In addition, even if ρ is not 10131 (Ω・03 or more) for a-8i:H, there is a method to increase the charging ability by providing a charge injection blocking layer (blocking layer) such as a-8ich between the photoreceptor and the substrate ( (see JP-A No. 56-24354, etc.).

The inventor of this application has developed a-8i:H by reactive sputtering.
t was prepared. At that time, by controlling the hydrogen partial pressure during sputtering, a-8
We succeeded in producing i:H with good reproducibility.

As a result, it was possible to obtain a photoreceptor with high charging ability without containing B or O-doped film, C or N, or without using a blocking layer.

However, when a printing test was conducted using this photoreceptor, white spots were observed on the copy sample. This is thought to be due to the presence of columnar low resistance portions IB locally on the photoreceptor, as shown in FIG.

The other part is a high resistance part IA. In fact, as a result of observing the state of charge-up of the a-8i:H film produced by the present inventor with an electron microscope, it was found that there were portions (parts that appeared black) that were not charged-up.

It is thought that the white spots on the electrophotograph in question are caused by the surface charge escaping from this low-resistance portion.

4 Of course, the formation of such a low resistance part is not a desirable thing. However, it is extremely difficult to eliminate such portions, especially when performing high-speed film formation.

[Purpose of the invention]

An object of the present invention is to provide an electrophotographic photoreceptor in which the occurrence of white spots, blurring, etc. in printed images can be prevented despite the presence of high and low resistance regions in which the photoconductive layer is made of hydrogenated amorphous silicon, etc. is to provide.

[Summary of the invention]

In the present invention, the photoconductive layer has a high-resistance portion mainly occupying a region, and a low-resistance region partially exists, and this photoconductive layer is laminated on a supporting substrate with an intermediate layer interposed therebetween. This intermediate layer has a resistance value equal to or higher than the low resistance region in the photoconductive layer.

The reason why white spots occur in copy samples as described above can be considered as follows. It is assumed that σ of the low resistance portion is 1012 [:Ω·mouth]. It can be seen from equation (2) that the surface potential decay is 10 times faster.

This rapid potential attenuation can be suppressed by using a multilayer structure, but let us consider how the charge attenuates in a multilayer structure.

The two-layer structure is shown in FIG. 3, and its complete equivalent circuit is shown in FIG. The equation for charge decay is as follows:

QIIVIIC+ and 几1 are the charge amount, potential difference, capacitance, and resistance value of the layer (photoconductive layer 1) shown in FIG. 2, respectively. Q2, V
2, C2, and R2 are the charge amounts of the intermediate layer 2.

They are potential difference, capacitance, and resistance value. Furthermore, QI and Q2 are the first-order differentials of QI and Q2 with respect to time, respectively.

Solving equation (3) and calculating the time change in the surface potential of this photoreceptor results in the following equation.

V = V r + V2 ... (4) Here, VO
IIVO2 is an integral constant, τ1. τ2 is the light 4 in the figure, respectively.
It is expressed by the I-electric relaxation time of the electric layer 1 and the intermediate layer 3. V1@V2 are photoconductive layer 1,
The voltage applied to the intermediate layer 3 is the surface potential. (
As is clear from equation 4), even if 7ri is small, if τ2 is larger than it, the surface potential decays slowly.

Further, assuming that the currents flowing through the photoconductive layer 1 and the intermediate layer 3 are equal as an initial condition, the initial value of V(+Vx is as follows.

SVI = VORt / (Rt + Rz) where V
o is the initial potential applied to the photoreceptor.

In order to prevent white spots, it is necessary that (2) be equal to or higher than vl in the low resistance portion. In other words, it is necessary that R2 be equal to or greater than R1.

If the photoconductive layer 1 is a-8i:H, the resistivity is 1013Ω.
The relaxation time of Sen and Ryoden is about 10 degrees. It is assumed that there is a low resistance part in this layer with a resistivity of 1012 Ωm and a dielectric relaxation time of type 1.

The intermediate layer 3 is made of oxygenated amorphous silicon (hereinafter referred to as a-8i).
:O), its resistivity is 1014Ωm1, and the dielectric relaxation time is about 20 degrees.

The sixth figure shows how the potential attenuation was calculated using equations (4) and (6), assuming that the photoconductive layer 1 was 10 μm and the intermediate layer 3 was 0.1 μm.
It is a diagram. The curve shown in the figure is the potential attenuation curve of the low resistance part when the layer 3 is not present. The curve B is the potential decay curve of the low resistance part when layer 3 is introduced.

C and D are the potential decay curves of the high resistance part, respectively, dark decay and
Represents light attenuation.

From this figure, it can be seen that the introduction of the photoconductive layer 1 slows down the rate of potential attenuation in the low resistance part and does not adversely affect the optical attenuation in the high resistance part.

[Embodiments of the invention]

Examples will be described below with reference to the drawings.

Example 1 FIG. 7 shows an apparatus for producing an a-8i photoconductor containing hydrogen according to the present invention.

The method for manufacturing the a-8i photoconductor is as shown in FIG. 7: the reaction tank is evacuated to I x 10-6 T□rr, and the 120φ A4 drum substrate 5 is heated with a heater. The At drum was heated to 113,001" and degassed. Thereafter, it was cooled to 200C and kept warm. On the other hand, the gas was adjusted as follows: 11 argon cylinders and 12 hydrogen cylinders, each with mass flow. The flow rate is adjusted to a predetermined value via the controller 9.10, and sent to the gas mixer 8. Thereafter, the inside of the reaction tank 4 is adjusted to IX 10-3 TOrr by the needle pulp 13, and finally the main pulp 11 is fed. 5 x 1
Adjusted to 0-sTQrr.

Fukoku 9 Yuka →] I soup-001 person r Bufunokutsu i-kari 1
The non-1P silicon target 7 used was 99.99% or more. During sputtering, cooling and heating were performed as appropriate to keep the temperature of the AA drum substrate constant.

The mixed gas ratio of argon gas and hydrogen gas to the reaction tank was defined as the flow rate of hydrogen to the total flow rate of argon and hydrogen.

FIG. 8 shows the electrical resistivity when a film was formed to a thickness of 5 μm using the above method at a mixed gas ratio of 0.2 to 0.8.

It was found that when the mixed gas ratio was 0.4 or more, the electrical resistivity of the photoconductor was 1013Ω or more.

Example 2 A 10 μm thick A-8I light guide was produced on an At drum with an outer diameter of 120 φ at a mixed gas ratio of 0.5 using the method shown in Example 1, and the results of the T Yu printing test were as follows. White spots were observed on the print sample.

The surface of this a-8i photoconductor was observed with an electron microscope without gold vapor deposition. A black spot with a diameter of about 10 μm was observed on the sample surface. This is thought to be because the sample charges up, but in areas with low electrical conductivity, the charge escapes and appears black.

In order to further quantitatively investigate the state of charge-up,
PMA (Electron Probe Micro
o Ana-lyser) was used for the experiment.

The dependence of the ratio of the amount of α-rays generated to Si- on the electron acceleration voltage was measured.

The amount of X-rays generated can be considered as follows.

Let Eb be the voltage threshold for X-ray generation. If the electron acceleration voltage is {circle around (2)} and the absorption current is {circumflex over (x)}, then the amount of X-ray generation Ix can be approximately expressed by the following equation.

Ixoc(VEb)2・I-(7)Here, by rough approximation, I-(V-Eb)...(8) If Ix ''(VEb) 3-(9) Low resistance part and it In other parts, it is thought that differences in charge-up cause differences in the value of Eb and differences in Ix.

FIG. 9 shows the dependence of the IxO ratio of the low resistance part and other parts on the electron acceleration voltage. According to equation (9), Eb in the low resistance part and other parts are 2.2KV and 2KV, respectively.
．． It was estimated to be 4KV. It is thought that the low resistance part has a smaller charge-up amount by about 200V than the other parts.

It is thought that the electric charge was removed from this low-resistance portion, causing white spots to appear in the printing test.

Example 3 Using the same method as Example 1, using 5i02 as the target,
On an At drum with an outer diameter of 120φ, a deer a of about 0.1 μm thick was placed.
-8i:O was produced. At this time, the sputtering gas was only Ar, which was flowed at 30 sCCm. Other conditions are the same as in Example 1.

After that, the target was replaced with 84 target and Example 2
A 10 μm thick a Si photoconductor was prepared in the same manner as described above.

A printing test was conducted using the a-8i photoconductor obtained as described above, and as a result, a printing sample with excellent image quality and no white spots could be obtained.

The surface of this photoreceptor was observed with an electron microscope in the same manner as in Example 2, without gold vapor deposition. As a result, particles similar to those observed in Example 2 were observed. However, the charge did not come out of this area and it did not become a black spot. This is thought to be because the intermediate layer 3 suppressed charge leakage.

〔Effect of the invention〕

As explained above, according to the present invention, there is an effect that it is possible to eliminate white spots on an electrophotograph and to obtain a good image.

[Brief explanation of drawings]

Figures 1 and 5 are schematic cross-sectional views of a single-layer electrophotographic photoreceptor;
2 is an equivalent circuit diagram of the electrophotographic photoreceptor shown in FIG. 1, FIG. 3 is a schematic sectional view of an electrophotographic photoreceptor according to an embodiment of the present invention, and FIG. 4 is an equivalent circuit diagram of the electrophotographic photoreceptor shown in FIG. 3. Equivalent circuit diagram of 6th
The figures are surface potential decay curve diagrams of each of the electrophotographic photoreceptors shown in FIGS. 1 and 3, FIG. The figure shows the resistivity characteristics of the electrophotographic photoreceptor with respect to the gas mixture ratio.
Figure 9 shows the Si-
2 is an α-ray intensity ratio characteristic diagram. 1... Photoconductive layer, 2... Supporting substrate, 3... Intermediate/intermediate layer, IA Continued from page 1 of Ukonreirikijinshishi 0 Inventor: Toshi Ohno, 3-chome, Saiwaimachi, Hitachi City Inventor: Mitsuru Chikazaki, 3-chome, Saiwaimachi, Hitachi City 0 Inventor: Masanobu Hanazono Hitachi City Saiwaimachi 3-chome premises

Claims (1)

[Scope of Claims] 1. In an electrophotographic photoreceptor comprising a photoconductive layer provided on its supporting substrate, the photoconductive layer has both a high resistance region and a low resistance region; An electrophotographic photoreceptor characterized in that an intermediate layer having a resistance value equal to or higher than that of the low resistance region is provided between the layer and the support base. 2. The electrophotographic photoreceptor according to claim 1, wherein the photoconductive layer is made of a hydrogenated amorphous silicon material and has a resistivity of 10'3 Ω·m or more. 3. In claim 1 or 2,
An electrophotographic photoreceptor, wherein the intermediate layer is made of amorphous silicon oxide.