JPH0695218B2 - Electrophotographic photoconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic photoreceptor, particularly an electrophotographic photoreceptor using amorphous silicon in a photosensitive layer.

[Prior Art] The electrophotographic method forms an electrostatic latent image by charging and exposing an image on a photoreceptor, develops it with a developer, then transfers a toner image onto a transfer paper, and fixes it to make a copy. Is the way to get. The photoconductor used in this electrophotographic method has a basic structure in which a photosensitive layer is laminated on a conductive substrate, and the material forming the photosensitive layer is selenium or a selenium alloy, cadmium sulfide, zinc oxide, or the like. And inorganic photosensitive materials such as polyvinylcarbazole, trinitrofluorenone, bisazo pigment, phthalocyanine, pyrazoline, and hydrazone are known, and the photosensitive layers are used as a single layer or a laminated layer.

In recent years, photoreceptors using amorphous silicon as the photosensitive layer have been known, and various improvements have been attempted. A photoreceptor using this amorphous silicon is one in which an amorphous silicon film is formed on a conductive substrate by glow discharge decomposition method of silane (SiH ₄ ) gas. Hydrogen atoms are incorporated into and exhibit photoconductivity. Amorphous silicon photoconductors have excellent photosensitivity such that the surface hardness of the photosensitive layer is high, scratch resistance and abrasion resistance, heat resistance and mechanical strength are excellent, and the spectral sensitivity range is wide and the photosensitivity is high. is there.

[Problems to be solved by the invention]

As described above, the amorphous silicon photoreceptor has excellent photosensitivity and has a relatively high dark resistance, but the dark resistance is not yet sufficient. Therefore, there is a drawback that the dark decay of the photosensitive layer is large and a sufficient charging potential cannot be obtained even if the photosensitive member is charged. That is, when an amorphous silicon photoconductor is charged and imagewise exposed to form an electrostatic latent image, and then this is developed, the surface charge on the photoconductor is attenuated before the image exposure, or the development process is performed. In the meantime, even the electric charge of the portion that was not irradiated with light is attenuated, and it is difficult to obtain the charging potential required for development.

This decay of the charging potential is apt to change due to the influence of environmental conditions, and particularly in a high temperature and high humidity environment, the charging potential is drastically reduced, and the charging potential is gradually reduced when the photoconductor is repeatedly used. . When a copy is produced using such a photoconductor having a large dark decay of the charging potential, the copy has low image density and poor halftone reproducibility.

The present invention has been made for the purpose of eliminating the above drawbacks in the amorphous silicon photoconductor, and provides an amorphous silicon photoconductor in which the dark decay of the charging potential is small.

[Means and Actions for Solving Problems]

In order to solve the above-mentioned problems, the present invention mainly uses amorphous silicon containing hydrogen in the photoconductive layer in an electrophotographic photoreceptor formed by sequentially stacking a photoconductive layer and a surface layer on a conductive substrate. And the surface layer is composed of two upper and lower amorphous carbon layers containing 50 atomic% or less hydrogen, both of which contain boron, and the concentration of boron in the upper layer is 10 ^−4. To 0.1 atomic%, the lower layer has a boron concentration of 0.1 to 1.0 atomic%, and the upper and lower layers have different boron concentrations.

The structure of the electrophotographic photoreceptor of the present invention is as shown in FIG. 1, in which 1 is a surface layer made of amorphous carbon containing 50 atomic% or less of hydrogen and 2 is mainly made of amorphous silicon. The photoconductive layers 3 and 3 are conductive substrates. Further, 4 and 5 are the above-mentioned upper surface layer and lower surface layer, respectively.
Make up.

The surface layer of No. 1 functions as a charge blocking layer that blocks injection of charges from the surface of the photoconductive layer to the inside during charging, and also oxygen, water vapor, moisture in air, ozone (O ₃ ). Such a surface protective layer can prevent the molecular species generally present in the environmental atmosphere from directly contacting or adsorbing to the surface of the photoconductive layer. At the same time, the above surface layer has a role as a surface protective layer that prevents the characteristics of the photoconductive layer itself from being destroyed by the action of external factors such as the addition of stress or the adhesion of reactive chemical substances. You can

Further, the above surface layer is a film for preventing film constituent atoms such as hydrogen, which are generally contained in a photoconductive layer mainly composed of amorphous silicon, from leaving from the photoconductive layer. It can serve as a layer for preventing the separation of constituent atoms.

The surface layer 1 can be formed by a method such as a glow discharge method, a sputtering method, an ion plating method, a vacuum deposition method, a CVD method, or the like. Above all, an amorphous carbon film containing 50 atomic% or less of hydrogen, which is formed by decomposing a hydrocarbon compound by a glow discharge method, has a high dark resistance and an amorphous silicon photoconductive layer required as an electrophotographic photoreceptor. It has excellent characteristics such as transparency and high hardness without damaging the characteristics.

The following materials are used as the raw materials used for forming the surface layer of the present invention. As the carbon raw material comprising mainly methane, ethane, propane, butane, pentane, etc. C _n H _{2n + 2}
A paraffinic hydrocarbon represented by the general formula: ethylene,
Propylene, butylene, pentene and other olefinic hydrocarbons represented by the general formula for C _n H _2n , acetylene, arylene, butyne and other aliphatic carbonized hydrocarbons such as acetylene represented by the general formula for C _n H _2n-2 Hydrogen; alicyclic hydrocarbons such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclobutene, cyclopentene, and cyclohexene; aromatic compounds such as benzene, toluene, xylene, naphthalene, and anthracene.

The hydrogen content in the amorphous carbon film is usually determined by the hydrogen contained in the raw material hydrocarbon, but if necessary, hydrogen gas may be introduced into the apparatus simultaneously with the raw material hydrocarbon.

Further, the amorphous carbon surface layer in the present invention has two layers of upper layer 4 and lower layer 5 as shown in FIG. 1 for the purpose of controlling dark resistance or bonding characteristics with the amorphous silicon photoconductive layer. It is characterized by Diborane (B ₂ H ₆ ) gas is mixed into the raw material hydrocarbon described above to form the amorphous carbon layer 5 containing 0.1 to 1.0 atomic% of boron (B), and then the diborane gas is added to the raw material hydrocarbon gas. Is reduced to form the amorphous carbon layer 4 containing 10 ^{−4 to} 0.1 atomic% of boron.

The glow discharge decomposition of the raw material gas is possible in either direct current or alternating current discharge, and the frequency is 0 to 30 MHz, preferably 5 to 20 MHz. The degree of vacuum during discharge is 0.1 to 5 Torr (13.
3 to 66.7 N / m ² ) and the substrate heating temperature is 100 to 400 ° C. The film thickness of the surface layer is set arbitrarily, but 10 μm or less,
Particularly, 1 μm or less is preferable.

The photoconductive layer containing amorphous silicon as the main component 2 can be formed on the substrate by a method such as a glow discharge method, a sputtering method, an ion plating method, or a vacuum deposition method. Above all, according to the method of glow discharge decomposition of silane (SiH ₄ ) gas by the plasma CVD method (glow discharge method), the film automatically contains an appropriate amount of hydrogen and has relatively high dark resistance and high photosensitivity. It is possible to obtain a photoconductive layer having optimum properties for an electrophotographic photoreceptor. Further, in this case, in order to more efficiently contain hydrogen, hydrogen (H ₂ ) gas may be introduced simultaneously with the silane gas into the plasma CVD apparatus. For the purpose of controlling the dark resistance or charging polarity of the amorphous silicon photoconductive layer film, a dopant gas such as diborane (B ₂ H ₆ ) gas or phosphine (PH ₃ ) gas is added to the above gases. It is also possible to mix them and add (doping) an impurity element such as boron (B) or phosphorus (P) into the photoconductive layer film. Furthermore,
For the purpose of increasing the dark resistance of the film, increasing the photosensitivity, or increasing the charging ability (charging ability or charging potential per unit film thickness), halogen atoms, carbon atoms, oxygen atoms, nitrogen atoms are contained in the amorphous silicon film. Etc. may be contained. Furthermore, it is also possible to add an element such as germanium (Ge) into the photoconductive layer film for the purpose of sensitizing the long wavelength region sensitivity. In order to add and contain elements other than hydrogen in the amorphous silicon photoconductive layer film, glow discharge decomposition can be performed by introducing a gasified product of those elements together with silane gas as a main raw material into the plasma CVD apparatus. Good.

The discharge conditions effective in the amorphous silicon photoconductive layer film forming method for glow discharge decomposition of silane (SiH ₄ ) gas by the above plasma CVD method, that is, the effective conditions for forming an amorphous silicon film are, for example, in the case of AC discharge. Take as an example: The frequency is usually 0.1-30MHz, preferably 5-20MHz,
The degree of vacuum during discharge is 0.1 to 5 Torr (13.3 to 66.7 N / m ² ), and the substrate heating temperature is 100 to 400 ° C.

The thickness of the photoconductive layer mainly composed of amorphous silicon is arbitrarily set, but 1 μm to 200 μm, particularly 10 μm to 100 μm is preferable.

The conductive substrate 3 in the attached drawings is a substrate made of a metal such as Al, Ni, Cr, Fe, stainless steel, brass, or In.
_A substrate made of an intermetallic compound such as ₂ O ₃ , SnO ₂ , CuI, or CrO ₂ can be used. Also, the substrate shape is cylindrical,
It is possible to obtain any shape such as an endless belt shape.

Further, as shown in FIG. 2, a charge injection blocking layer 6 can be provided between the photoconductive layer 2 and the conductive substrate 3 if necessary. As a material for forming this layer, for example, hydrogenated amorphous silicon to which a trace amount of boron is added or hydrogenated amorphous silicon to which a trace amount of phosphorus is added is used depending on the charge code used for the photoreceptor.

〔Example〕

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Comparative Example 1 Using a capacitively coupled plasma CVD apparatus capable of forming an amorphous silicon film on a cylindrical substrate, silane (Si
A so-called i-type amorphous material with relatively high dark resistance containing hydrogen and a trace amount of boron on a cylindrical Al substrate by glow discharge decomposition of a mixed gas of H ₄ ) gas and diborane (B ₂ H ₆ ) gas. A silicon film was produced. The conditions for forming the amorphous silicon film at this time were as follows.

A cylindrical Al substrate was installed at a predetermined position in the reaction chamber of the plasma CVD apparatus, the substrate temperature was maintained at a predetermined temperature of 250 ° C., and 100% silane (SiH ₄ ) gas was supplied in the reaction chamber at 120 cc / min.
Dichlorosilane (B ₂ H ₆ ) gas diluted with hydrogen of 20 cc / min and 100% hydrogen (H ₂ ) gas of 90 cc / min were introduced to bring the internal pressure of the reactor to 0.5 Torr (66.7 N / m ² ). After maintaining 13.56
High frequency power of MHz was applied to cause glow discharge, and the output of high frequency power was maintained at 85W. In this way, a so-called i-type amorphous silicon photoconductor having a high dark resistance containing 25 μm thick hydrogen and a very small amount of boron was obtained on the cylindrical Al substrate.

The photoconductor was positively charged to have an initial potential of 550V. this
The operation of exposing with light having a wavelength of 650 nm was repeated at a rate of 40 times per minute. The residual potential at this time was stable at 0 V, but the charging potential tended to decrease as the number of repetitions increased,
The charge potential decreased to 75% of the initial charge potential after 1000 repeated operations.

When this photoreceptor was negatively charged and the same operation was performed, the same phenomenon as in the case of positive charging was observed. further,
The image resolution gradually decreased as the copying operation was repeated.

Example 1 After forming a photoconductive layer mainly composed of amorphous silicon under the same method and under the same conditions as in Comparative Example 1, the reaction tank was evacuated. Next, 50 cc of a mixed gas of methane (CH ₄ ) gas and 0.5% diborane (B ₂ H ₆ ) gas was flowed in at a rate of 0.2 Torr (26.7N) in the reaction tank.
/ m ² ), then about 40% by glow discharge decomposition
0.3 μm of a surface layer made of amorphous carbon containing hydrogen was provided. The boron concentration in the surface layer was 0.3 atomic%.

Next, 50 cc of a mixed gas containing methane (CH ₄ ) gas and 10 ppm of diborane (B ₂ H ₆ ) gas was flowed in at a rate of 0.2 Torr in the reaction tank.
r26.7N / m ² ), followed by glow discharge decomposition to obtain a surface layer of amorphous carbon containing 40% hydrogen by 0.1%.
μ was provided. The boron concentration in the surface layer was 1.2 × 10 ⁻³ atom%.

This surface layer was a film having high surface hardness and excellent abrasion resistance, transparency, and heat resistance.

The photoconductor was positively charged and the initial potential was set to 550V. This operation of exposing with light having a wavelength of 650 nm was repeated at a rate of 40 times per minute. At this time, the residual potential is stable at 10 V,
The charging potential retained 98% of the initial charging potential even after 1000 repeated operations. Further, even after 1,000 times of copying operation, a copy excellent in image density and resolution was obtained.

Comparative Example 2 Using a device similar to that of Comparative Example 1, a mixed gas of silane (SiH ₄ ) gas and diborane (B ₂ H ₆ ) gas was decomposed by glow discharge to decompose hydrogen and a trace amount of hydrogen on a cylindrical Al substrate. A so-called P-type amorphous silicon film containing boron and a so-called i-type amorphous silicon film containing hydrogen and a very small amount of boron were sequentially formed. The generation conditions at this time were as follows.

A cylindrical Al substrate was installed at a predetermined position in the reaction chamber of the plasma CVD apparatus, the substrate temperature was maintained at a predetermined temperature of 250 ° C., and 100% silane (SiH ₄ ) gas was supplied in the reaction chamber at 120 cc / min.
100 ppm diborane (B ₂ H ₆ ) gas diluted with hydrogen was added at 100 cc / min, and 100% hydrogen (H ₂ ) gas was introduced at 90 cc / min to maintain the internal pressure of 0.5 Torr (66.7 N / m ² ) in the reaction tank. After that, 13.56
Turn on the high frequency power of MH to cause glow discharge,
The output of the high frequency power supply was maintained at 85W. Thus, a so-called P-type amorphous silicon film containing hydrogen and boron having a thickness of 0.2 μm was formed on the cylindrical Al substrate.

Next, 100% silane (SiH ₄ ) gas is fed into the reaction chamber at a rate of 120 per minute.
cc, hydrogen-diluted 100ppm diborane (B ₂ H ₆ ) gas at 20c / min
c, 100% hydrogen (H ₂ ) gas is introduced at 90 cc / min,
After maintaining the internal pressure of the reactor at 0.5 Torr (66.7N / m ² ),
Similar to the P layer, discharge was performed to obtain a photoconductor in which a so-called i-type layer containing 25 μm thick hydrogen and a very small amount of boron was laminated.

The photoconductor thus obtained was placed in a copying machine, and the image quality was evaluated by a positive corona charging method. As a result, an image density of practically no problem was obtained in the initial stage, but the image density was gradually increased as the copying operation was repeated. The image density decreased.

Example 2 After forming a photoconductive layer mainly containing amorphous silicon under the same method and under the same conditions as in Comparative Example 2, the reaction tank was evacuated. Next, 20 cc of a mixed gas of ethane (C ₂ H ₆ ) gas and 0.2% diborane (B ₂ H ₆ ) gas was flowed in at a rate of 0.1 Torr (66.
30% by glow discharge decomposition after 7N / m ² )
0.1 μm of a surface layer made of amorphous carbon containing hydrogen was provided. The boron concentration in the surface layer was 0.15 atomic%.

Then, 20 cc of a mixed gas containing (C ₂ H ₆ ) gas and 20 ppm of diborane (B ₂ H ₆ ) gas was flowed in at a rate of 0.1 Torr (2
6.7 N / m ² ) and then glow discharge decomposition
A surface layer of 0.2 μm made of amorphous carbon containing hydrogen was provided. The boron concentration in the surface layer was 1.5 × 10 ⁻³ atom%.

This surface layer was a film having high surface hardness and excellent abrasion resistance, transparency, and heat resistance. Further, when the image thus obtained was placed in a copying machine and image quality was evaluated by a positive corona charging method, an image density practically no problem was obtained in the initial stage. The copying operation was repeated 50,000 times, but no decrease in image density was observed.

Example 3 After forming a photoconductive layer mainly composed of amorphous silicon according to the same method, the same conditions and the same procedure as in Comparative Example 2, the reaction tank was evacuated. Next, a mixed gas of ethylene (C ₂ H ₄ ) gas and 0.2% diborane (B ₂ H ₆ ) gas was flowed in at 30 cc per minute to make the inside of the reaction chamber 0.1 Torr (66.7 N / m ² ) and A surface layer made of amorphous carbon containing 30% hydrogen was provided by 0.2 μm by discharge decomposition. The concentration of boron in the surface layer was 0.14 atomic%.

Next, ethylene (C ₂ H ₄ ) gas and 30 ppm diborane gas were introduced at 30 cc / min to 0.1 Torr in the reaction vessel, and then glow discharge decomposition was performed to form a surface layer made of amorphous carbon containing 30% hydrogen. 0.2μ was provided. The concentration of boron in the surface layer is 2
It was × 10 ^-3 atom%.

This surface layer was a film having high surface hardness and excellent abrasion resistance, transparency, and heat resistance. Further, when the image thus obtained was placed in a copying machine and image quality was evaluated by a positive corona charging method, an image density practically no problem was obtained in the initial stage. The copying operation was repeated 50,000 times, but no decrease in image density was observed.

〔The invention's effect〕

The photoreceptor of the present invention has high surface hardness, excellent wear resistance, heat resistance and wear resistance, has a wide spectral sensitivity range, and has high photosensitivity. Further, since the dark decay is small, the charge holding power is strong, and therefore, it is possible to prevent the surface potential from remarkably lowering even after a large number of copying operations. Therefore, it is possible to prevent a decrease in copy density and resolution.

[Brief description of drawings]

1 and 2 are schematic sectional views of an electrophotographic photoreceptor to which the present invention can be applied. 1 ... Surface layer, 2 ... Photoconductive layer, 3 ... Conductive substrate, 4 ... Upper surface layer, 5 ... Lower surface layer, 6 ... Charge injection blocking layer.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Shigeru Yagi 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture Fuji Zero Tsux Co., Ltd. Takematsu Plant (56) References JP 61-94056 (JP, A) JP 61- 219961 (JP, A)

Claims (1)

[Claims] 1. An electrophotographic photoreceptor comprising a photoconductive layer and a surface layer sequentially laminated on a conductive substrate, wherein the photoconductive layer is mainly composed of amorphous silicon containing hydrogen, and the surface layer. Is composed of two upper and lower amorphous carbon layers containing 50 atomic% or less of hydrogen, and both of these amorphous carbon layers contain boron, and the concentration of boron in the upper layer is 10 ^{−4 to} 0.1 atomic%.
And a concentration of boron in the lower layer is 0.1 to 1.0 atomic%, and the concentrations of boron in the upper and lower layers are different from each other.