JPH0239788B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic photoconductor and a method for producing photoconductive cadmium sulfide used in the photoconductor. This relates to improving ozone resistance and moisture resistance.

Conventionally, as a type of electrophotographic photoreceptor, one in which a photoconductive composition consisting of a photoconductive pigment dispersed in an electrically insulating resin medium is coated on a conductive substrate has been widely used. . In electrophotographic copying, the photoconductive layer is charged by applying a corona discharge of a constant polarity, and then imagewise exposed to form an electrostatic image, and this electrostatic image is developed with toner to form a toner image. is transferred from the photosensitive plate to copy paper, the surface of the photosensitive plate is finally cleaned, and this copying cycle is repeated.

Among the photoconductive pigments used in this photoreceptor,
Cadmium sulfide-based photoconductors have particularly excellent sensitivity and are particularly suitable for high-speed copying purposes; however, when photoconductors using cadmium sulfide-based photoconductors are used for long-term repeated copying, Particularly under high humidity conditions, there is a problem that the image density is significantly reduced, and there is a drawback that the repeated use life of the photoreceptor, that is, the printing durability is low.

The reason for this is that cadmium sulfide photoconductors are n-
type photoconductor, and therefore associated with repeated negative corona discharges, the photosensitive layer is constantly attacked by ozone, which makes it sensitive to humidity,
The reason is that the initial charging potential decreases.

As a result of extensive research into improving the oson resistance and moisture resistance of the photoconductive layer of a cadmium sulfide-based photoconductor, the present inventors found that these characteristics depend on the crystal type and particle shape of photoconductive cadmium sulfide. Therefore, if photoconductive cadmium sulfide is selected as a wurtzite crystal grain with a hexagonal prism shape and a fine and uniform particle size, the ozone It was found that the initial charging potential was maintained at a significantly high level even when subjected to repeated attacks and high humidity conditions.

That is, an object of the present invention is to provide a cadmium sulfide-based electrophotographic photoreceptor that has excellent printing durability and maintains an initial charging potential at a high level even when exposed to repeated ozone attacks and high humidity conditions. be.

An important feature of the present invention is that wurtzite-type cadmium sulfide crystal particles having the above-mentioned particle shape and particle size characteristics exhibit ozone resistance and moisture resistance that are completely absent from other cadmium sulfide photoconductors. It is based on knowledge. For example, a photosensitive layer using cadmium sulfide, which is conventionally commercially available for use as a photoconductor, is subjected to ozone treatment using negative corona discharge in a normal copying machine 2000 times, and then 30
When left for 3 hours under the humidity conditions of 85%RH and 85%RH, the initial charging potential of this photosensitive layer is 35% when untreated.
% or less. On the other hand, when cadmium sulfide defined in the present invention is selected and used for the photoconductive layer, the initial charging potential is maintained at 70% or more of the untreated case even when the same treatment is performed.

Various forms of cadmium sulfide are known, including those with a zincblende structure and an equiaxed crystal system, those with a wurtzite structure and a hexagonal crystal system, and those with a mixture thereof.

In the present invention, it is important from the viewpoint of photoconductivity, ozone resistance and moisture resistance that at least 80% of these various crystal systems are of wurtzite structure. be.

The conventional photoconductive cadmium sulfide, which has poor ozone resistance and moisture resistance, has a wurtzite crystal structure of more than 80% and contains copper and chlorine of 50 to 50% each.
Although it is similar to the cadmium sulfide of the present invention in that it contains 500 ppm and 10 to 300 ppm, it differs greatly in that the average primary particle size is 3 to 5 μm. Conventionally, in the production process of cadmium sulfide, a mixed or amorphous cadmium sulfide with an arbitrary ratio of wurtzite and zincblende crystal structures is used as a starting material, and copper and chlorine are added thereto to form wurtzite crystals. In the so-called activation process to make the structure photoconductive cadmium sulfide, the temperature is 520-600℃.
It was thought that grain growth with an average primary grain size of 3 to 5 μm was unavoidable because the calcination process at a temperature in the range of 30 to 50 μm was an essential condition for converting more than 80% to the wurtzite crystal structure.

Furthermore, when cadmium sulfide with an average primary particle size of 3 to 5 μm is crushed to make it finer, the wurtzite crystal structure returns to the sphalerite type, so the cadmium sulfide of the present invention cannot be obtained. Ta.

In contrast, the present inventors selected starting materials,
By selecting a low-temperature range for the firing temperature, which was previously thought to be ineffective, we were able to reduce the average primary particle size to a degree that was previously unachievable, and the resulting cadmium sulfide The present invention has been completed based on the discovery that an electrophotographic photoreceptor produced using the method exhibits significant improvements in ozone resistance and moisture resistance.

According to the present invention, in an electrophotographic photoreceptor comprising a photoconductive layer formed by dispersing photoconductive cadmium sulfide in an electrically insulating resin medium on a conductive substrate, the photoconductive cadmium sulfide comprises: It has at least 80% wurtzite crystal structure, the average primary grain size is between 1.5 and 2.5 μm, and the copper is between 50 and 50%.
Provided is an electrophotographic photoreceptor characterized in that it is made of cadmium sulfide containing 500 ppm and 10 to 300 ppm of chlorine.

In addition, according to the present invention, a compound containing copper and chlorine is added to cadmium sulfide powder, which has a wurtzite crystal structure of 60% or more and an average primary particle size of 1.3 to 2.3 μm, and is heated under an inert gas atmosphere. 400~500℃
Provided is a method for producing the photoconductive cadmium sulfide, which comprises firing the photoconductive cadmium sulfide.

The average primary particle size of the photoconductive cadmium sulfide used in the present invention is 1.5 to 2.5 μm, preferably 1.8 to 2.2 μm.
The average primary particle size must be within the range of 2.5
It exhibits significantly superior ozone resistance and moisture resistance compared to photoconductive cadmium sulfide, which is larger than a micron. Moreover, if it is less than 1.5 μm, crystallinity is low and photoconductivity is low, making it unsuitable for electrophotography.

The starting material for the photoconductive cadmium sulfide used in the present invention is wurtzite-type CdS produced by the method described in Japanese Patent Publication No. 12911/1983 by Mitsubishi Metals Co., Ltd., one of the applicants of the present invention, which has an average primary particle size. 1.3~
The first feature is the use of CdS powder with a diameter of 2.3 μm and at least 60% wurtzite type. If the average primary particle size of the starting material is out of the above range, the average primary particle size will be changed in the subsequent firing process for activation treatment.
It cannot be controlled within 1.5-2.5 μm. Furthermore, if the wurtzite crystal content is less than 60%, the average primary particle size will exceed the required upper limit of 2.5 μm when the wurtzite crystal content reaches 80% in the above firing step.
The content of copper and chlorine for activation of cadmium sulfide is also determined in the wurtzite type CdS of the present invention.
50~500ppm and 10~300ppm respectively as before
is preferable, and after adding cadmium sulfide and a copper salt such as copper sulfate or copper chloride to the starting material powder, it is heated at 400 to 500 ml under an inert gas atmosphere to avoid grain growth.
This is achieved by firing at a temperature range of .

The second feature of the method for producing photoconductive cadmium sulfide of the present invention is that such a temperature range, which was conventionally thought to be ineffective for activation, has been found. If the firing temperature is lower than 400°C, the average primary particle size will not reach the required lower limit of 1.5μ, making it impossible to achieve 80% wurtzite crystal structure. On the other hand, if the temperature exceeds 500°C, the particle will grow beyond the required upper limit of 2.5 μm.

In the present invention, the photoconductive cadmium sulfide described above is used as a solid content of an electrically insulating resin as a binder.
It is used in an amount of 100 to 500 parts by weight per 100 parts by weight.

The binder resin used to form the photoconductive layer includes epoxy resins, silicone resins, urethane resins, acrylic resins, saturated polyester resins, alkyd resins, vinyl resins, etc. used to disperse this type of photoconductor. All binders listed can be used. Binder resins that have good dispersibility of cadmium sulfide and are suitable for the purpose of the present invention are epoxy resins, silicone resins, and acrylic resins.

The coating composition for forming a photoconductive layer is prepared by mixing the above-mentioned binder resin with a suitable solvent, such as aromatic solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; tetrahydrofuran, and butyl acetate. It can be obtained by dissolving the CdS-based photoconductor and, if necessary, higher saturated fatty acids in this solution using means such as ultrasonic irradiation or a homomixer. At this time, there is no particular problem with the order of addition of the higher saturated fatty acids; for example, they may be added to the binder resin solution in advance, or may be added at the same time as CdS, or may be added later. The solid content concentration of the coating composition varies depending on the coating method, but is generally preferably in the range of 20 to 50% by weight. This coating composition,
It is coated on a conductive substrate known per se and dried to form a photosensitive plate. When applying the photosensitive layer, the thickness after drying is
The thickness is preferably 10 to 100μ, particularly 20 to 50μ.

The invention is illustrated by the following example.

Example 1 50 g of cadmium sulfide with a primary particle size of 1.8 μm, 94% of which is wurtzite, was mixed with 10 g of cadmium chloride and 30 g of copper sulfate.
The mixed powder was thoroughly mixed with mg in deionized exchange water, vacuum dried, and then ground at 450℃ in a _N2 gas atmosphere for 30 minutes.
Activation treatment for 45g of photoconductive layer CdS powder (yield
90%).

This powder was 96% wurtzite type, the copper and chlorine contents were 227 ppm and 130 ppm, respectively, and the primary particle size measured by air transmission method and electron microscopy was in good agreement and was 2.0 μm.

12g of this cadmium sulfide powder, 8g of cyclohexanone and acrylic resin (manufactured by Rohm & Hass Co., Ltd.)
Add 9.6 g of AT50 (solid content 50%) and 1.2 g of epoxy resin (#600 manufactured by Thermoset Co., Ltd.), disperse with an ultrasonic dispersion machine, and place wire bar No. It was applied at 28. Then put this plate in the oven
Heat curing was performed at 100° C. for 1 hour to produce a photosensitive plate with a layer thickness of 27 μm after heat treatment. Next, we conducted a durability test on this photosensitive plate using a DC-15 copying machine manufactured by Sanda Kogyo with a partially modified charging section.
150,000 good copies were obtained at room temperature and humidity. On the other hand, in high humidity (30℃80%), 8
More than 10,000 good copies were obtained, and the photoreceptor had excellent ozone resistance and humidity resistance.

Example 2 50 g of cadmium sulfide with a primary particle size of 1.3 μm, 60% of which is wurtzite, was mixed with 10 g of cadmium chloride and 20 g of copper sulfate.
The mixed powder was thoroughly mixed with mg in deionized exchange water, dried under vacuum, and then _ground .
The photoconductive powder of the present invention was activated at ℃ for 60 minutes.
40g (80% yield) was obtained. This powder is 85% wurtzite type, with copper and chlorine contents each
The primary particle size measured by the 151 ppm and 89 ppm air permeation method was 1.5 μm.

On the other hand, 50 g of cadmium sulfide with a primary particle size of 0.7 μm, 30% of which is wurtzite, was mixed in the same manner as above, dried,
After grinding, the mixed powder was heated at 520℃ under _N2 gas atmosphere.
24g of photoconductive powder for comparison after activation for 30 minutes
(yield 48%). The powder is 90% wurtzite, with copper and chlorine contents of 148 ppm and 87 ppm, respectively, and a primary particle size measured by air permeation method.
It was 3.5 μm.

Next, 4 g of tetrahydrofuran, 2.6 g of epoxy resin (#600 manufactured by Thermoset), and 1.4 g of a hardening agent (#65 manufactured by Thermoset) were added to 8 g of each cadmium sulfide powder, and thoroughly dispersed using an ultrasonic dispersion machine. Each coating solution was coated on an 80 μm aluminum plate using a wire bar No. 28. Furthermore, place this plate in the oven for 100 minutes.
Heat curing was carried out under conditions of 1 hour at °C to produce a photosensitive plate having a layer thickness of 28 μm after heat treatment.

Next, the amount of charge on these photoreceptors was measured using an electrostatic paper analyzer manufactured by Kawaguchi Electric Co., Ltd. under the following conditions. Measurement condition
STAT measurement, applied voltage (-) 6KV, as a result of the above measurements, when the cadmium sulfide powder of the present invention is used, the initial charge (V ₁ ) is 1070 volts, and when the comparative cadmium sulfide powder is used (V ₁ ') is 770 volts.
It was hot. Next, in order to perform corona treatment on these photosensitive plates, these photosensitive plates were installed in a copier DC-15 manufactured by Sanda Kogyo Co., Ltd., with the developing unit removed.
The process of charging, exposing, charging (for transfer), and removing static electricity was repeated 2000 cycles without passing through the transfer paper.

Next, these ozone-treated photosensitive plates were heated at 30°C and 80°C.
% in a constant temperature and humidity chamber for 5 hours to adjust the humidity. The amount of charge on the photosensitive plate after humidity conditioning was measured in the same manner as described above. As a result, when the cadmium sulfide powder of the present invention was used, the charge amount (V ₂ ) after ozone treatment and humidity conditioning was 750 volts, and when the comparative cadmium sulfide powder was used (V ₂ ') was 170 volts.
It was hot. Comparing the charged states of V ₁ , V ₂ and V ₁ ′, V ₂ ′, the potential of the photosensitive plate using the cadmium sulfide powder of the present invention after ozone treatment and humidity control is the same as that of the untreated photosensitive plate (V ₁ ), but when a comparison cadmium sulfide powder was used, it was about 80% lower. Next, when we actually created images on these photosensitive plates using a DC-15 machine equipped with a developing machine, the photosensitive plates of the present invention produced images with high contrast, whereas the comparative photosensitive plates produced almost no images. I couldn't get an image.

Example 3 50 g of cadmium sulfide with a primary particle size of 2.3 μm, 85% of which is wurtzite, was mixed with 10 g of cadmium chloride and 20 g of copper chloride.
The mixed powder, which was thoroughly mixed with mg in deionized exchange water, vacuum dried, and then ground, was heated at 400 ml under an N ₂ gas atmosphere.
The photoconductive properties of the present invention were activated at ℃ for 180 minutes.
46 g of CdS powder (yield 92%) was obtained. This powder is 92
% is wurtzite type, and the content of copper and chlorine is respectively
The primary particle size measured by 179 ppm and 122 ppm electron microscopy was 2.5 μm.

On the other hand, 50 g of cadmium sulfide with a primary particle size of 2.5 μm, 91% of which is wurtzite, was mixed in the same manner as above, dried,
43g of photoconductive CdS powder for comparison by crushing and firing
(yield 86%). This powder is 95% wurtzite and has a primary particle size of 2.6 μm as measured by electron microscopy.
It was hot.

To 10.8 g of each cadmium sulfide powder, 4.6 g of tetrahydrofuran, 4 g of polyurethane resin (Takerak U-25, manufactured by Takeda Pharmaceutical Industries, Ltd.), and 4 g of a curing agent (Takenate D-110N, manufactured by Takeda Pharmaceutical Industries, Ltd.) were added, and the mixture was processed using an ultrasonic dispersion machine. After thorough dispersion, wire bar No. 22 was placed on an alumite-treated 80μm Al plate.
Each coating liquid was coated. Furthermore, these plates were placed in an oven at 100°C.
Heat curing was carried out for 1 hour to produce a photosensitive plate having a layer thickness of 25 μm after heat treatment. Next, these photosensitive plates were subjected to measurements in the same manner as in Example 2 using an electrostatic paper analyzer manufactured by Kawaguchi Denki. As a result, when the cadmium sulfide powder of the present invention was used, the initial charge (V ₁ ) was 880 volts, and when the comparative cadmium sulfide powder was used, the initial charge (V ₁ ') was 880 volts.
It was 750 volts. Next, in order to perform corona treatment on these photosensitive plates, similar to Example 2, Mita Kogyo Co., Ltd.
2000 cycles were repeated using a copying machine DC-15.
Next, these ozone-treated photosensitive plates were heated at 30℃ and 80%
It was left in a constant temperature and humidity chamber for 5 hours to adjust the humidity. The amount of charge on the photosensitive plate after humidity conditioning was measured in the same manner as in Example 2. As a result, when the cadmium sulfide powder of the present invention was used, the charge amount (V ₂ ) after ozone treatment and humidity conditioning was 792 volts, and when the comparative cadmium sulfide powder was used (V ₂ '), it was 360 volts. _V1 ,
Comparing the charge amounts of V ₂ and V ₁ ′ and V ₂ ′, the potential (V 2 ) of the photosensitive plate using the cadmium sulfide powder of the present invention after ozone treatment and humidity conditioning is the potential (V ₂ ) of the untreated photosensitive plate ( V ₁ ), it was about a 10% decrease, but when a comparative cadmium sulfide powder was used, it was about a 60% decrease. Next, these photosensitive plates are
When an image was actually produced using a DC-15 copying machine equipped with a developing machine, the photosensitive plate of the present invention provided an image with high contrast, but the comparative photosensitive plate provided an image with only low contrast.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor comprising a photoconductive layer formed by dispersing photoconductive cadmium sulfide in an electrically insulating resin medium on a conductive substrate, wherein the photoconductive cadmium sulfide is dispersed in an electrically insulating resin medium. , with at least 80% more wurtzite crystal structure and an average primary grain size of
An electrophotographic photoreceptor characterized by being made of cadmium sulfide having a thickness of 1.5 to 2.5 μm and containing 50 to 500 ppm of copper and 10 to 300 ppm of chlorine. 2 A compound containing copper and chlorine is added to cadmium sulfide powder, which has a wurtzite crystal structure of 60% or more and an average primary particle size of 1.3 to 2.3 μm, and is heated at 400 to 500°C under an inert gas atmosphere. A method for producing photoconductive cadmium sulfide for use in a photoreceptor according to claim 1, characterized in that the photoconductive cadmium sulfide is fired in a .