JP3376014B2 - Electrophotographic photoreceptor and electrophotographic apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member and an electrophotographic apparatus for applying a voltage by contact charging, which can be widely used in electrophotographic application fields such as an electrophotographic copying machine, a laser beam printer and a plain paper FAX. Regarding

[0002]

BACKGROUND OF THE INVENTION Electrophotography is described in US Pat. No. 2,297,691.
As shown in the specification, an electric resistance is changed according to the amount of irradiation received during image exposure, and an insulating material, that is, a photoconductive material is coated on a support in a dark place. The basic characteristics required for an electrophotographic photoreceptor using this photoconductive material are (1) being capable of being charged to an appropriate potential in a dark place. (2) The dissipation of electric charges is small in the dark. (3) It is possible to rapidly dissipate the charge by light irradiation.

Conventionally, selenium has been used as an electrophotographic photoreceptor.
Inorganic photoreceptors having a photosensitive layer containing an inorganic photoconductive material such as zinc oxide and cadmium sulfide as a main component have been widely used. However, although these satisfy the above conditions (1) to (3), they are not necessarily satisfactory in terms of thermal stability, moisture resistance, durability, productivity and the like. For example, when selenium is crystallized, its characteristics as a photoreceptor are deteriorated, so that it is difficult to manufacture, and heat, fingerprints, etc. cause crystallization to deteriorate the performance as a photoreceptor. Further, cadmium sulfide has problems in moisture resistance and durability, and zinc oxide has problems in smoothness, hardness and abrasion resistance. Further, many inorganic photoconductors have a limited photosensitive wavelength region. For example, the photosensitive wavelength region of selenium is the blue region, and it has almost no sensitivity in the red region.

Therefore, various methods have been proposed to extend the photosensitivity to the long wavelength region, but there are many restrictions on the selection of the photosensitizing wavelength region. Even when zinc oxide or cadmium sulfide is used as a photoconductor, the wavelength range of light itself is narrow and it is necessary to add various sensitizers.

In order to overcome the drawbacks of these inorganic photoconductors, electrophotographic photoconductors containing various organic photoconductive materials as main components have been actively developed in recent years. For example, U.S. Pat. No. 3,837,851 discloses a photoreceptor having a charge transport layer containing triallyl pyrazoline, and U.S. Pat. No. 3,871,882 discloses a charge generation layer comprising a derivative of a perylene pigment and 3-propylene and formaldehyde. A photoconductor or the like comprising a charge transport layer comprising a condensation product of is known.

Further, as a photoreceptor using a bisazo pigment or a trisazo pigment as a charge generating substance, JP-A-59-3
Japanese Patent No. 3445, Japanese Patent Laid-Open No. 56-46237, Japanese Patent Laid-Open No. 60-111249, etc. are already known.

Further, the organic photoconductive material can freely select the photosensitive wavelength range of the electrophotographic photosensitive member depending on the material. For example, regarding azo organic pigments, JP-A-61-272754 and JP-A-56-16.
7759 discloses a material exhibiting high sensitivity in the visible region, and JP-A-57-195767 and JP-A-61-228453 have a sensitivity in the infrared region. Materials are also shown.

Of these materials, materials having sensitivity in the infrared region are used in laser beam printers (hereinafter abbreviated as LBP) and LED printers, etc., which have made remarkable progress in recent years, and their demand frequency is increasing.

Copper phthalocyanine having a sensitivity in the infrared region has been conventionally used (Japanese Patent Laid-Open No. 38385/1975).
The phthalocyanine compound as shown in 1) has attracted attention, and in recent years, oxytitanium phthalocyanine (hereinafter abbreviated as TiOPc) has attracted attention as a material having high sensitivity in the infrared region. It is known that TiOPc takes many crystal forms, and for example, the crystal forms are shown in JP-A-63-366 and Japanese Patent Application No. 1-319934. An electrophotographic photosensitive member using TiOPc as a charge generation layer has a very high sensitivity and a sensitivity in the infrared region as well. However, since the sensitivity is high, the absolute number of carriers is large, and an electron after injection of holes is generated. Has a drawback that it tends to remain in the charge generation layer and the potential change easily occurs as a kind of memory.

Although not confirmed in principle, the electrons left in the charge generation layer are for some reason the interface between the charge generation layer and the charge transport layer, or the charge generation layer and the support (when there is an undercoat layer). Is likely to increase or decrease the barrier property of hole injection near the interface.

As a phenomenon to be expressed when it is actually used as an electrophotographic photosensitive member, when electrons stay at the interface between the charge transport layer and the charge generating layer, it appears as a decrease in the light potential and the residual potential during continuous printing. For example, when used in a development process (so-called reversal development system) in which the dark potential part is often used in printers and the light potential part is the development part, the sensitivity at the place exposed to light during pre-printing. When the entire image is taken at the time of the next printing, the so-called ghost phenomenon (hereinafter referred to as a positive ghost), in which the previous printed part appears black, appears remarkably.

When electrons remain at the interface between the charge generating layer and the support or the undercoat layer, it appears as an increase in the bright portion potential during printing. When used in a reversal development system, the sensitivity in the area exposed to the light during the previous print becomes slow, and when the entire black image is taken during the next print, the so-called ghost development (hereinafter referred to as negative ghost), in which the previous print part appears white, is remarkable. Will appear in.

With respect to this phenomenon, a negative ghost often appears at the beginning of printing and a positive ghost often appears during continuous printing.

This phenomenon is particularly remarkable in a photoreceptor using an undercoat layer as an adhesive layer of the charge generation layer, and the volume resistance to electrons of the charge generation layer and the undercoat layer is high in an environment such as low temperature and low humidity. As a result, the charge generation layer is likely to be filled with electrons and the ghost phenomenon is likely to occur.

This phenomenon becomes more remarkable especially in the charging method for forcibly equalizing the dark part potential, which is seen in contact charging.

Contact charging will be briefly described below.

In the conventional corona charging, the electric current directed to the electrophotographic photosensitive member is only 5 to 30% of the layer current in terms of electric power, and the charging efficiency is very poor, and ozone and nitrogen oxides are by-products. Of course, these are not only harmful to the human body, but also cause surface deterioration of the electrophotographic photoreceptor.

As a countermeasure against this, a method has been proposed in which a charging member is directly brought into contact with an electrophotographic photosensitive member to charge it (Japanese Patent Laid-Open Nos. 57-178267 and 58-40566).
Issue Bulletin).

It is general to apply a voltage to the electrophotographic photosensitive member by applying an electric field in which a DC voltage is superimposed on an AC voltage to the charging member (Japanese Patent Laid-Open No. 63-149668).

However, in this method, since the surface potential is forcibly made uniform, there is a problem that the appearance of ghost is remarkable.

[0021]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrophotographic photosensitive member and an electrophotographic apparatus which provide an image having no image defects while maintaining high sensitivity as an excellent electrophotographic characteristic. .

[0022]

That is, the present invention is used in an electrophotographic apparatus having means for superposing and applying a direct current and an alternating voltage to an electrophotographic photosensitive member by contact charging, and a photosensitive layer is formed on a conductive support. The electrophotographic photosensitive member having the photosensitive layer, wherein the photosensitive layer contains oxytitanium phthalocyanine , the frequency of the alternating voltage is 700 Hz or more, and the waveform is a rectangular wave.

Further, the present invention has means for superimposing DC and AC voltages on the electrophotographic photosensitive member by contact charging,
Further, in an electrophotographic apparatus having an electrophotographic photosensitive member having a photosensitive layer on a conductive support, the photosensitive layer is oxytitanium.
Contains um phthalocyanine, and the frequency of the AC voltage is not less than 700 Hz, and an electrophotographic apparatus, wherein the waveform is a square wave.

The present invention will be described in detail below.

It is known that the electrophotographic photosensitive member using TiOPc is very sensitive.
This means that the quantum efficiency of the body is good and many carriers are generated. The reason why many carriers are generated has not been clarified at the stage of ongoing research, but it is said that the influence of oxygen and impurities is large. When a large amount of carriers are generated in this way, if the same number of electrons as the holes injected into the charge transport layer do not immediately escape to the support side, the above-mentioned negative ghost phenomenon occurs due to the electrons remaining in the charge generation layer.

Furthermore, when the electron concentration in the charge generation layer is increased by continuous printing and the electron concentration at the interface between the charge generation layer and the charge transport layer is increased, the energy levels of the charge transport material and TiOPc are increased. Changes and it becomes easier to inject holes into the charge transport material. As a result, it appears as a positive ghost on the screen.

In order to correct such an image defect in the electrophotographic photosensitive member, it is sufficient to reduce the number of photo carriers generated, but this has a drawback that sensitivity is deteriorated. As a result of earnestly studying a method for preventing such image defects on the apparatus, the AC applied to the primary charging
It has been found that such an image defect can be removed by setting the frequency of 2 above a certain value and making the waveform a rectangular wave . It is not certain why the image defect disappears by using such a device, but it is presumed as follows.

As described above, trapping of electrons inside the photoconductor is a cause of ghost. In order to remove the ghost, the electrons in the charge generation layer need not be concentrated at the charge transport layer interface or the undercoat layer (or support) interface. For this purpose, an electrical pulsating current may be applied to the charge generation layer during charging. In other words, it is considered that if a high frequency AC is applied at the time of primary charging, extreme transition of electrons at the interface is hindered.

Next, the structure of the photoconductor used in the present invention will be described.

As the conductive support, any material having conductivity may be used, and examples thereof include metals such as aluminum and stainless steel, metals provided with a conductive layer, plastics, paper, and the like, and the shape is cylindrical or film-like. Is mentioned.

When the image input is laser light such as LBP, it is preferable to provide a conductive layer for the purpose of preventing interference fringes due to scattering. This can be formed by dispersing conductive powder such as carbon black or metal particles in a binder resin. The thickness of the conductive layer is 5 to 40 μm, preferably 10 to 30 μm.

An intermediate layer having an adhesive function is provided thereon. Examples of the material for the intermediate layer include polyamide, polyvinyl alcohol, polyethylene oxide, ethyl cellulose, casein, polyurethane and polyether urethane. These are dissolved in a suitable solvent and applied.
The thickness of the intermediate layer is 0.1 to 5 μm, preferably 0.3 to 1
μm is suitable.

On the intermediate layer, a coating liquid prepared by dispersing TiOPc in a binder resin dissolved in a solvent is applied and dried to form a charge generation layer.

As the binder resin used here, for example, polyester resin, polyacrylic resin, polyvinylcarbazole resin, phenoxy resin, polycarbonate resin, polystyrene resin, polyvinyl acetate resin, polysulfone resin, polyarylate resin, vinylidene chloride / acrylonitrilo copolymer resin. , Polyvinyl benzal resin and the like are mainly used. The ratio of the binder resin to the pigment is preferably 1/5 to 5/1, more preferably 1/2 to 3/1.

The charge transport layer is formed mainly by applying a coating material in which a charge transport material and a binder resin are dissolved in a solvent and drying the coating material. Examples of the charge transport material used include various triarylamine compounds, hydrazone compounds, stilbene compounds, pyrazoline compounds, oxazole compounds, triallylmethane compounds and thiazole compounds. As the binder resin, the same resin as that used for the charge generation layer can be used.

As the coating method of these photosensitive layers, a dipping method, a spray coating method, a spinner coating method, a bead coating method, a blade coating method, a beam coating method and the like can be used.

Next, T used as a charge generating material in the present invention
An example of manufacturing iOPc will be shown. [Production Example 1] In 100 g of α-chloronaphthalene, 5.0 g of o-phthalodinitrile and 2.0 g of titanium tetrachloride were heated and stirred at 200 ° C. for 3 hours, cooled to 50 ° C., and the precipitated crystals were separated by filtration. A paste of dichlorotitanium phthalocyanine was obtained. Next, this was heated to 100 ° C. to obtain N, N′-dimethylformamide 1
Stir and wash with 00 ml, then methanol at 60 ° C 10
It was washed twice with 0 ml and filtered off. Further, the obtained paste was stirred in 100 ml of deionized water at 80 ° C. for 1 hour and filtered to obtain blue TiOPc crystals. Yield 4.3
g.

The elemental analysis values of this compound were as follows.

Elemental analysis value (C ₃₂ H ₁₆ N ₈ TiO) C H N Cl calculated value (%) 66.68 2.80 19.44 0.00 measured value (%) 66.50 2.99 19.42 0.47 Next, this crystal was dissolved in 30 ml of concentrated sulfuric acid, dropped into 300 ml of deionized water at 20 ° C. under stirring, re-precipitated, filtered, and sufficiently washed with water to obtain amorphous TiOPc. This amorphous TiOPc (4.0 g) was suspended and stirred in 100 ml of methanol at room temperature (22 ° C.) for 8 hours, filtered, and dried under reduced pressure to obtain low crystalline TiOPc. Furthermore, T with low crystallinity
To 2.0 g of iOPc, 40 ml of n-butyl ether was added and milled with 1 mmφ glass beads at room temperature (22
C) 20 hours. The solid content was taken out from this dispersion, thoroughly washed with methanol and water, and dried. Yield 1.8
g.

Diffraction angle 2θ ± in X-ray diffraction of this crystal
0.2 ° is 9.0 °, 14.2 °, 23.9 °, 27.
It had a strong peak at 1 °.

[Manufacturing Example 2] According to the manufacturing example disclosed in Japanese Patent Application Laid-Open No. 61-239248 (USP 4,728,592), a so-called α-type crystal system T is used.
iOPc was obtained.

Next, the charging conditions for the photoconductor thus prepared will be described.

Charging is performed by the DC component on which the AC component is superimposed. The DC component is for controlling the potential on the electrophotographic photosensitive member, and the developing condition of the toner depends on the condition.

The AC component has parameters of the frequency, the peak voltage, and the waveform, but the particular problem is the frequency.
In other words, how many times you go to the plus side is a problem. The effect is great when the frequency is 700 Hz or more. There is no particular upper limit, but if it is 700 Hz or more, especially 1 kHz or more, there is no frequency dependence and the same effect is obtained. The peak voltage may be any value as long as the primary charging can be made uniform, but the peak voltage is preferably 1 kV or more, and more preferably 1.5 kV or more. The waveform does not have an extreme effect, but if possible, a shorter rise time such as a rectangular wave is more effective than a sine wave.

FIG. 1 shows an example of a contact charging type electrophotographic apparatus. This example is a transfer type copying machine or printer.

Reference numeral 1 is a drum type electrophotographic photosensitive member which is the object of the present invention. This electrophotographic photosensitive member 1 has a predetermined peripheral speed (process speed) in the clockwise direction of arrow A.
Is driven to rotate.

A charging roller 2 is a contact charging member as a charging means. The charging roller 2 is rotated by the rotation of the photosensitive member 1 which is pressed against the charging roller, and a DC voltage superimposed with an AC voltage is applied from the bias power source 2A. By the charging roller 2, the peripheral surface of the photoconductor 1 is uniformly charged to a predetermined polarity and potential by a contact charging method.

Exposure 3 of the target image information is performed on the charging surface of the photoconductor 1 by an unillustrated exposing means (image forming exposure means for a document image, laser beam scanner, etc.) and the photoconductor 1
An electrostatic latent image corresponding to the target image information is formed on the surface.

The formed electrostatic latent image is visualized as a transferable particle image (toner image) 5a by normal development or reversal development with the charged particles (toner) 5 of the developing device 4.

Then, the toner image is fed from the paper feed cassette 9 to the paper feed roller 10 and the registration roller 11 at the nip portion (transfer portion) between the photoconductor 1 and the transfer roller 7 as the transfer means which is pressed against the photoconductor. Thus, the sheets 5 are transferred 5b one by one at a predetermined timing. Transfer roller 7
A bias voltage having a polarity opposite to that of the charge held by the toner 5 is applied from the bias power source 7A.

The sheet 6 to which the toner image has been transferred is separated from the surface of the photosensitive member 1 and conveyed to a fixing means (not shown) to be subjected to a toner image fixing process.

After the transfer of the toner image, the surface of the photosensitive member 1 is cleaned by a cleaner (cleaning device) 8 to remove adhering contaminants such as untransferred toner, and is made into a cleaning surface to be repeatedly used for image formation.

[0053]

EXAMPLES Examples will be described below. (Example 1) An aluminum cylinder having a diameter of 30 mm and a diameter of 260 mm was used as a support, and a coating material composed of the following materials was applied to the support by a dipping method and heat-cured at 140 ° C. for 30 minutes to obtain a conductive layer of 15 μm. Was formed.

Conductive pigment: tin oxide coated titanium oxide: 10 parts (parts by weight, hereinafter the same) Resistance adjusting pigment: titanium oxide: 10 parts Binder resin: phenol resin: 10 parts Leveling agent: Silicon Oil: 0.001 part Solvent: Methanol / methyl cellosolve = 1/1: 20 parts Next, 3 parts of N-methoxymethylated nylon and 3 parts of copolymerized nylon are mixed with 65 parts of methanol and n. -A solution dissolved in 30 parts of butanol was applied by the dipping method to form a 0.5 μm intermediate layer.

Next, the charge generation material 3 produced in Production Example 1
Parts by weight and polyvinyl butyral (trade name: S-REC B
M-2, manufactured by Sekisui Chemical Co., Ltd.) and 80 parts of cyclohexanone were dispersed in a sand mill using φ1 mm glass beads for 4 hours, and then 115 parts of methyl ethyl ketone was added to obtain a charge generation layer dispersion liquid. This was applied onto the intermediate layer by a dipping method to form a 0.2 μm charge generation layer.

Next, 7 parts of an amine compound having the following structural formula

[0057]

[Chemical 1]

And 3 parts of an amine compound of the following structural formula and

[0059]

[Chemical 2]

12 parts of bisphenol Z polycarbonate resin (viscosity average molecular weight 22000) was dissolved in 55 parts of monochlorobenzene and 12 parts of dichloromethane. This coating material was applied on the above charge generation layer by a dipping method and dried at 110 ° C. for 1 hour to form a 20 μm charge transport layer.

Image evaluation was performed using this photoreceptor.
Next, the device used for evaluation will be described. The equipment is Hewlett-Packard LBP "LaserJet III S".
i ”was modified and used. In the modification, the high voltage on the primary charging side was separated from the main unit, and the frequency etc. could be freely controlled by an external power supply. With this device, the frequency was changed and an image was displayed.

Sampling was performed as follows. Temperature 1
In an environment of 8 ° C. and a humidity of 20%, an appropriate character pattern was printed for one round of the drum at the beginning, and then a halftone image was taken over the entire surface to confirm whether a ghost phenomenon occurred.
Next, the following durability pattern was continuously printed on 5,000 sheets, and a halftone image was taken on the entire surface after the durability test, and it was confirmed whether or not a ghost phenomenon after the durability occurred.

The image evaluation method was as follows. The endurance pattern was printed with lines having a width of about 2 mm every 7 mm in length and width. An image sample was used in which the entire surface was black and an image having a dot density of 1 dot and 1 space was used, and each was sampled at a development volume of a machine, F5 (center value) and F9 (light density).

The evaluation criteria are rank 5 when ghost is not visible, rank 4 when 1 dot 1 space F9 is visible, rank 3 when 1 dot 1 space F5 is visible, and rank 2 when visible in all black F9. The one that can be seen with all black F5 was ranked. Further, the initial bright portion potential of the photoconductor and the bright portion potential after the endurance were measured, and the value obtained by subtracting the absolute value of the initial bright portion potential from the absolute value of the end light portion potential was V.
The amount was increased by 1.

The primary charging condition is -70 for the DC component.
The peak voltage of the AC component was 0 kV, the peak voltage was 2 kV, and the waveform was a rectangular wave.

The results are shown in Table 1.

[0067]

Example 2 A photoconductor was prepared and evaluated in the same manner as in Example 1 except that the charge generation material prepared in Production Example 2 was used. The results are shown in Table 2.

[0069]

Reference Example 1 A photoconductor was prepared and evaluated in the same manner as in Example 1 except that the waveform of the AC component was a sine wave. The results are shown in Table 3.

[0071]

Example 3 A photoconductor was prepared and evaluated in the same manner as in Example 1 except that the frequency of the AC component was fixed at 700 Hz and the peak voltage was changed as shown in Table 4. The results are shown in Table 4.

[0073]

(Comparative Example 1) A photoconductor was prepared and evaluated in the same manner as in Example 1 except that the following charge generating materials were used and the laser output was increased 7 times. The results are shown in Table 5.

[0075]

[Chemical 3]

[0076]

As described above in the first and second embodiments and the first reference example , the frequency is set to 700 Hz or higher and the waveform is a rectangular wave to suppress ghost development and further suppress potential fluctuation. be able to.

Further, as shown in Example 3 , it is clear that even if the peak voltage is varied to some extent, the effect continues and the frequency effect has priority. It is also apparent that the frequency dependence is reduced by lowering the sensitivity as compared with Comparative Example 1.

Therefore, even if a phthalocyanine pigment is used in the charge generation layer of the electrophotographic photosensitive member and contact charging is performed, it is possible to obtain an image without a ghost phenomenon while maintaining high sensitivity.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an electrophotographic apparatus of the present invention.

Continued front page    (72) Inventor Hideyuki Ainotani               3-30-2 Shimomaruko, Ota-ku, Tokyo               Within Canon Inc. (72) Inventor Yamasaki               3-30-2 Shimomaruko, Ota-ku, Tokyo               Within Canon Inc. (72) Inventor Hidetoshi Hirano               3-30-2 Shimomaruko, Ota-ku, Tokyo               Within Canon Inc. (72) Inventor Mayumi Kimura               3-30-2 Shimomaruko, Ota-ku, Tokyo               Within Canon Inc.                (56) References JP-A-5-100458 (JP, A)                 Japanese Patent Laid-Open No. 1-267667 (JP, A)                 JP-A-7-191517 (JP, A)                 Japanese Patent Laid-Open No. 6-289687 (JP, A)                 JP-A-6-130703 (JP, A)                 JP-A-6-3847 (JP, A)                 JP-A-4-7567 (JP, A)                 JP-A-5-35051 (JP, A)                 JP-A-4-372955 (JP, A)                 JP-A-4-324450 (JP, A)                 JP-A-5-34961 (JP, A)

Claims (4)

(57) [Claims] 1. An electrophotographic photoreceptor having a photosensitive layer on a conductive support, which is used in an electrophotographic apparatus having means for superposing and applying a DC and AC voltage to the electrophotographic photoreceptor by contact charging. Oxytitanium phthalocyanine
An electrophotographic photoreceptor containing nin, having a frequency of the alternating voltage of 700 Hz or more, and having a rectangular waveform. 2. The Bragg angle 2θ ± 0.2 ° in X-ray diffraction of CuKα, wherein the oxytitanium phthalocyanine is
But 9.0 °, 14.2 °, electrophotographic photosensitive member according to claim 1 which is oxytitanium phthalocyanine having strong peaks at 23.9 ° and 27.1 °. 3. An electrophotographic apparatus having an electrophotographic photosensitive member having means for applying a direct current and an alternating voltage to the electrophotographic photosensitive member by contact charging, and having a photosensitive layer on a conductive support. Oxytitanium phthalocyanine layer
An electrophotographic apparatus containing nin, having a frequency of the alternating voltage of 700 Hz or higher, and having a rectangular waveform. 4. The Bragg angle 2θ ± 0.2 ° in X-ray diffraction of CuKα, wherein the oxytitanium phthalocyanine is
But 9.0 °, 14.2 °, electrophotographic apparatus according to claim 3 which is oxytitanium phthalocyanine having strong peaks at 23.9 ° and 27.1 °.