JP2002258502A - Image forming method using positive-charged single layer electrophotographic sensitive body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method of a digital optical system to sufficiently cope with requests of speedup and energy saving by using a positive-charged single layer electrophotographic sensitive body with high sensitivity as an image carrier. SOLUTION: The image forming method of the digital optical system is characterized by forming a photosensitive layer consisting at least of an electric charge generation agent, a hole transportation agent, an electronic transportation agent and binder resin on a conductive base body as the image carrier and providing a positive-charged single layer electrophotographic sensitive body drum the electric charge generation agent of which is a phthalocyanine pigment, with a mobility of the hole transportation agent of >=1×10<-5> cm<2> /V/sec in field intensity of 5×10<5> V/cm and with a mobility of the electronic transportation agent of >=1/20000 and <=1/10 to the mobility of the hole transportation agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus of a digital optical system such as an electrostatic copying machine, a facsimile, a laser beam printer or the like using a positively charged single-layer type electrophotographic photosensitive drum as an image carrier. The present invention relates to an image forming method used.

[0002]

2. Description of the Related Art In the above-mentioned image forming apparatus, various organic photoconductors having sensitivity in a wavelength region of a light source used in the image forming apparatus can be used. This organic photoreceptor is easier to manufacture than conventional inorganic photoreceptors, has a wide variety of photoreceptor materials such as charge transport agents, charge generators, and binder resins, and has a high degree of freedom in functional design. Due to its advantages, it has been widely used in recent years.

[0003] The organic photoreceptor includes a single-layer type photoreceptor in which a charge transporting agent and a charge generating agent are dispersed in the same photosensitive layer;
There is a laminated photoreceptor in which a charge generating layer containing a charge generating agent and a charge transporting layer containing a charge transporting agent are laminated.

In recent years, a single-layer type photoreceptor has recently been developed because of its simple structure and easy production, suppression of film defects in forming layers, improvement of optical characteristics, and less interface between layers. Is in the limelight. The single-layer type photoreceptor can be used for both positive and negative charging types, but generally, the positive charging type is currently the mainstream due to the characteristics of the photoreceptor constituent materials.

The image forming apparatus using the single-layer type photoreceptor has the following advantages, and its market is expanding. 1) High image quality because there is no disturbance of charge transfer at the interface between the charge generation layer and the charge transport layer as in the stacked type. 2) When used with positive charge, almost no ozone harmful to human body is generated.

[0006]

In order to satisfy the demands for higher speed and energy saving of image forming apparatuses, which have been increasing in recent years, the sensitivity of the conventional single-layer type photoreceptor is already inadequate. The current situation is becoming sufficient.

That is, in a conventional positively charged single-layer type electrophotographic photoreceptor, in an image forming apparatus having a high process speed of, for example, an A4 copy speed of 50 sheets or more per minute, the amount of exposure light is small and the photoreceptor drum is exposed at an exposure position. Since the time from the start to the development position is short, a phenomenon occurs that the development process is reached during the potential decay due to the exposure.

As a result, an excessive amount of light is required to lower the light potential of the photoreceptor, a change in the light potential due to an environmental change is large because the potential is being attenuated, and a change in exposure and development due to repetition of exposure and development is caused. Problems such as increased photoreceptor fatigue occur, making it difficult to obtain good images.

An object of the present invention is to provide an image forming method for a digital optical system which uses a highly sensitive positively charged single-layer type electrophotographic photoreceptor as an image carrier and sufficiently responds to demands for high speed and energy saving. To provide.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies and as a result, as an image carrier,
At least a charge generating agent, a hole transporting agent on a conductive substrate,
A photosensitive layer comprising an electron transporting agent and a binder resin is formed, wherein the charge generating agent is a phthalocyanine pigment,
The mobility of the hole transport agent at an electric field intensity of 5 × 10 ⁵ V / cm is 1 × 10 ⁻⁵ cm ² / V / sec or more, and the mobility of the hole transport agent is more than the electron transport agent. The image forming method of the digital optical system, which comprises a positively charged single-layer type electrophotographic photosensitive drum having a mobility of 1/20000 or more and 1/10 or less, can be performed at a high speed such as a laser beam printer or a facsimile. It has been clarified that it is possible to provide an energy saving image forming apparatus.

The above-described positively charged single-layer type electrophotographic photoreceptor used in the image forming method of the present invention exhibits extremely high sensitivity. The reason why a highly sensitive positively charged single-layer type electrophotographic photoreceptor was obtained is as follows.
It is estimated as follows.

[0012] Of the photo-generated carriers, electrons reach the surface of the photosensitive layer and holes reach the conductive substrate side, resulting in light attenuation. In addition, since the charge generation distribution is unevenly distributed near the photosensitive layer surface, the hole travel distance is inevitably longer than the electron travel distance.

First, the mobility of the electron transporting agent is 1/200 with respect to the hole transporting agent having a mobility of 1 × 10 ⁻⁵ cm ² / V / sec or more at an electric field strength of 5 × 10 ⁵ V / cm.
If it is less than 00, electrons that have not reached the surface of the photosensitive layer remain in the photosensitive layer due to the mobility difference between the hole transporting agent and the electron transporting agent. For this reason, the charge generation efficiency does not increase, leading to a decrease in the sensitivity of the photosensitive member, and it becomes difficult to obtain a sufficient image density in a high-speed image forming apparatus.

Conversely, when the mobility of the electron transporting agent with respect to the hole transporting agent is greater than 1/10, the positive charges on the surface of the photosensitive layer are canceled earlier than the holes reach the conductive substrate, and Of the electric field of the device decreases. For this reason, the movement of the hole becomes more and more rate-limiting, leading to a decrease in sensitivity. In addition, since the positive charge on the surface of the photosensitive layer is canceled, the surface potential of the photosensitive member also tends to decrease, and image fogging easily occurs.

Next, the charge generating agent for the positively charged single-layer type electrophotographic photosensitive drum used in the image forming method of the digital optical system of the present invention is, for example, a metal-free phthalocyanine represented by the general formula (CG1). And phthalocyanine pigments such as oxotitanyl phthalocyanine represented by the general formula (CG2). This is because an image forming apparatus of a digital optical system such as a laser beam printer or a facsimile using a light source such as a semiconductor laser needs a photosensitive member having a sensitivity in a wavelength region of 700 nm or more.

(CG1) Metal-free phthalocyanine

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(CG2) oxotitanyl phthalocyanine

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[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A single-layer type electrophotographic photoreceptor has a single photosensitive layer provided on a conductive substrate. This photosensitive layer is formed by dissolving or dispersing a charge generating agent, a hole transporting agent, an electron transporting agent, a binder resin, and the like in an appropriate solvent, applying the obtained coating solution on a conductive substrate, and drying. You.

Next, various constituent materials of the positively charged single-layer type electrophotographic photosensitive member used in the image forming method of the present invention will be described.

<Charge Generating Agent> As the charge generating material of the electrophotographic photosensitive member used in the image forming method of the present invention, for example, a metal-free phthalocyanine represented by the general formula (CG1) or a metal phthalocyanine represented by the general formula (CG2) The phthalocyanine-based pigments such as oxotitanyl phthalocyanine represented can be used alone or in combination of two or more. The charge generating agent is used in an amount of 0.1 to 30% by weight, more preferably 0.5 to 30% by weight based on the binder resin.
It is preferable that the content is contained by 10 to 10% by weight. The crystal form of the phthalocyanine pigment is not particularly limited, and various types can be used.

<Hole transport agent> The hole transport agent of the photoreceptor used in the image forming method of the present invention has an electric field strength of 5 × 10 5
^It is necessary to have a mobility of 1 × 10 ⁻⁵ cm ² / V / sec or more at ⁵ V / cm. For example, the following general formula (H
Compounds represented by T1) to (HT3) are exemplified.

(HT1) Mobility: 1.21 × 10 ⁻⁵ cm
² / V / sec

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(HT2) Mobility: 1.69 × 10 ^-5 cm
² / V / sec

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(HT3) Mobility: 3.38 × 10 ^-5 cm
² / V / sec

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In the photoreceptor used in the image forming method of the present invention, the hole transporting agent may be used alone,
A mixture of more than one species can be used. Further, the content of the hole transporting agent is preferably 5 to 500% by weight, more preferably 25 to 200% by weight, based on the binder resin.

<Electron Transport Agent> The electron acceptor of the single-layer type positively charged electrophotographic photoreceptor used in the image forming method of the present invention is 1 / l of the mobility of the above-described hole transport agent.
It is necessary to have a mobility of 20,000 or more and 1/10 or less, and examples thereof include compounds represented by the following general formulas (ET1) to (ET7) with respect to the hole transporting agent.

(ET1) Mobility: 1.75 × 10 ⁻⁹ cm
² / V / sec

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(ET2) Mobility: 5.32 × 10 ⁻⁹ cm
² / V / sec

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(ET3) Mobility: 1.67 × 10 ⁻⁸ cm
² / V / sec

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(ET4) Mobility: 6.13 × 10 ⁻⁸ cm
² / V / sec

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(ET5) Mobility: 1.37 × 10 ⁻⁷ cm
² / V / sec

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(ET6) Mobility: 3.47 × 10 ⁻⁷ cm
² / V / sec

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(ET7) Mobility: 1.04 × 10 ⁻⁶ cm
² / V / sec

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In the photoreceptor used in the image forming method of the present invention, the electron transporting agent can be used alone or in combination of two or more. Further, the content of the electron transporting agent is preferably 5 to 100% by weight, more preferably 10 to 80% by weight, based on the binder resin.

It should be noted that the above mobility is normal room temperature,
It was measured by the F (TimeOfFlight) method. The electric field strength was 5 × 10 ⁵ V / cm. The measurement sample is
Binder resin (bis having a weight average molecular weight of 20,000)
-Z-type polycarbonate resin) and dissolved at a charge transport agent concentration of 40 wt%, applied on a substrate,
The heat treatment was performed for 5 minutes. The sample thickness is 7 μm.

<Binder Resin> As the binder resin for dispersing the above components, various resins conventionally used in the photosensitive layer can be used. For example, styrene-based polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, acrylic polymers, styrene-acrylic copolymers, polyethylene, ethylene-vinyl acetate copolymers Coalesce, chlorinated polyethylene, polyvinyl chloride, polypropylene, ionomer, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, Thermoplastic resin such as polyether resin, silicone resin, epoxy resin, phenol resin,
Resins such as urea resins, melamine resins, other cross-linkable thermosetting resins, and photo-curing resins such as epoxy acrylate and urethane-acrylate can be used. These binder resins can be used alone or in combination of two or more.

In the photosensitive layer, in addition to the above components, various conventionally known additives such as an antioxidant, a radical scavenger, a singlet quencher, and an ultraviolet ray may be used as long as they do not adversely affect the electrophotographic properties. Deterioration inhibitors such as absorbents, softeners, plasticizers, surface modifiers, extenders, thickeners, dispersion stabilizers, waxes, acceptors, donors, and the like can be added. Also, in order to improve the sensitivity of the photosensitive layer, for example,
Known sensitizers such as terphenyl, halonaphthoquinones, and acenaphthylene may be used in combination with the charge generator.

The thickness of the photosensitive layer in the single-layer type positively charged electrophotographic photosensitive member is 5 to 100 μm, preferably 10 to 50 μm.
It is.

In a single-layer type positively charged electrophotographic photosensitive member,
A barrier layer may be formed between the conductive substrate and the photosensitive layer as long as the characteristics of the photosensitive member are not impaired. Further, a protective layer may be formed on the surface of the photoconductor.

As the conductive substrate on which the photosensitive layer is formed, various conductive materials can be used.
For example, simple metals such as iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass, and plastic materials on which the above metals are deposited or laminated , Aluminum iodide, tin oxide,
Glass coated with indium oxide or the like can be given.

The conductive substrate may be in the form of a sheet, a drum, or the like, depending on the structure of the image forming apparatus to be used. The substrate itself has conductivity or the surface of the substrate is conductive. What is necessary is just to have the property. The conductive substrate preferably has a sufficient mechanical strength when used.

When the photosensitive layer is formed by a coating method, a hole transporting agent, a charge generating agent, an electron acceptor, a binder resin and the like described above together with a suitable solvent are mixed with a known method, for example, a roll mill. A dispersion may be prepared by dispersing and mixing using a ball mill, an attritor, a paint shaker, an ultrasonic disperser, or the like, and the dispersion may be applied by a known means and dried.

Various organic solvents can be used as a solvent for preparing the above-mentioned dispersion liquid, for example, alcohols such as methanol, ethanol, isopropanol and butanol, and aliphatic solvents such as n-hexane, octane and cyclohexane. Hydrocarbons, aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, and chlorobenzene; dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. Ethers, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and methyl acetate, dimethylformaldehyde, dimethylformamide, dimethyls Rufoxide and the like. These solvents are used alone or in combination of two or more.

Further, in order to improve the dispersibility of the charge generating agent, the hole transporting agent and the electron transporting agent, and the smoothness of the surface of the photosensitive layer, a surfactant, a leveling agent and the like may be used.

[0045]

The present invention will be described below with reference to examples and comparative examples. Note that the following embodiments are merely examples embodying the present invention, and do not limit the technical scope of the present invention.

Examples 1 to 11 4.5 parts by weight of an X-type metal-free phthalocyanine (CGM) as a charge generating agent and a hole transporting agent [select one from the above (HT1) to (HT3)]
65 parts by weight and an electron transporting agent [(ET1) to (ET)
7), 30 parts by weight, 100 parts by weight of a bisphenol Z type polycarbonate resin (Resin) having a weight average molecular weight of 30,000 as a binder resin, and 760 parts by weight of tetrahydrofuran are mixed in a ball mill for 27 times.
After dispersing or dissolving for time, a coating solution for a single-layer type photosensitive layer was prepared. Then, this coating solution was applied on an aluminum tube as a support by a dip coating method.
Drying with hot air at 40 ° C. for 40 minutes was performed to prepare a single-layer type photoreceptor having a single photosensitive layer having a thickness of 27.5 μm.

[Comparative Examples 1 to 7] (E)
T8)-(ET11)
A single-layer photoreceptor was produced in the same manner as in Examples 1 to 11.

(ET8) Mobility: 6.00 × 10 ⁻¹⁰ c
m ² / V / sec

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(ET9) Mobility: 7.56 × 10 ⁻¹⁰ c
m ² / V / sec

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(ET10) Mobility: 2.08 × 10 ⁻⁶ c
m ² / V / sec

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(ET11) Mobility: 2.77 × 10 ^-6 c
m ² / V / sec

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[Comparative Examples 8 to 14] As hole transporting agents,
A single-layer photoreceptor was produced in the same manner as in Examples 1 to 11, except that (HT4) was used.

(HT4) Mobility: 1.60 × 10 ⁻⁶ cm
² / V / sec

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With respect to the electrophotographic photosensitive members of the above Examples and Comparative Examples, the following tests were performed to evaluate the characteristics.

<Evaluation of Initial Sensitivity>
Using a drum sensitivity tester (trade name: Gentec Cynthia 30M) manufactured by EC), an applied voltage was applied to the electrophotographic photosensitive members of the respective examples and comparative examples, and the surfaces thereof were charged to +800 V.

Next, monochromatic light (half width: 20 nm, light intensity: 15 μW) having a wavelength of 780 nm extracted from white light of a halogen lamp, which is an exposure light source of the tester, using a band-pass filter is applied to the charged photosensitive member. Was exposed (exposure time: 40 msec). Then, the surface potential at the time when 500 msec had elapsed from the start of exposure was measured as the post-exposure potential V _L (V). That is, the smaller the potential after exposure, the higher the sensitivity of the photoconductor.

The post-exposure potential must be 170 V or less in order to obtain a sufficient image density in a high-speed image forming apparatus having an A4 copy speed of 50 sheets or more per minute.

<Evaluation of Initial Charging> Using the drum sensitivity tester, the initial surface potential V ₀ (V) of each of the electrophotographic photosensitive members of each of Examples and Comparative Examples at a flowing current value of 12 μA was measured. Charging was performed by a corotron method.

The initial surface potential must be 750 V or more in order to obtain an image without fogging in an image forming apparatus having an A4 copy speed of 50 sheets or more per minute.

<Evaluation of Image> The electrophotographic photoreceptors obtained in each of the examples and comparative examples were prepared by using a high-speed digital copying machine having an A4 copy speed of 50 sheets per minute [Creage 735 manufactured by Mita Kogyo KK]
0], a real-photographing test was performed, and the solid reflection density was measured using a reflection density measuring device manufactured by Nippon Denshoku Co., Ltd.

The image density (ID) is a measured value of the density of a solid black portion. The fog density (FD) is a density obtained by subtracting the reflection density of blank white paper before copying from the reflection density of the non-image portion after copying.

As for the image density, 1.3 or more is acceptable.
Less than 1.3 is not possible, fog density is 0.005
The following were evaluated as acceptable, and 0.006 or more were evaluated as unacceptable.

Table 1 shows the evaluation results. Comparative Examples 8 to 14
When the mobility of the hole transporting agent at an electric field strength of 5 × 10 ⁵ V / cm is smaller than 1 × 10 ⁻⁵ cm ² / V / sec as shown in FIG. _L
Was higher than 170 V, and a sufficient image density could not be obtained.

[0064]

[Table 1]

FIG. 2 shows that the mobility of the hole transporting agent at an electric field strength of 5 × 10 ⁵ V / cm is 1 × 10 ⁻⁵ cm ² / V / s.
ec or more, the relationship between the post-exposure potential V _L (V) and the mobility ratio [electron transport agent (ETM) / hole transport agent (HTM)] is shown in FIG. 3, and the initial surface potential V ₀ and the mobility ratio are shown in FIG. (Examples 1 to 11 and Comparative Examples 1 to 7).

2 and 3, the mobility ratio is 1/20000.
In the case of not less than 1/10 or less, the post-exposure potential _VL of the photoreceptor becomes 170 V or less, the initial surface potential V ₀ becomes 750 V or more, and from Table 1, it is found that the A4 copy speed is 50 sheets per minute in a high-speed image forming apparatus. Also in the actual shooting test, there was no image fog, and a sufficient image density with an ID of 1.3 or more was obtained.

On the other hand, when the mobility ratio was smaller than 1/20000, the post-exposure potential V _L of the photosensitive member was higher than 170 V, and a sufficient image density could not be obtained. When the mobility ratio was larger than 1/10, the initial surface potential V ₀ of the photosensitive member was smaller than 750 V, and image fogging occurred.

[0068]

According to the present invention, a photosensitive layer comprising at least a charge generating agent, a hole transporting agent, an electron transporting agent and a binder resin is formed on a conductive substrate as an image carrier.
The charge generating agent is a phthalocyanine pigment, the mobility of the hole transporting agent at an electric field intensity of 5 × 10 ⁵ V / cm is 1 × 10 ⁻⁵ cm ² / V / sec or more, and the hole transporting is performed. A positively charged single-layer electrophotographic photosensitive drum in which the mobility of the electron transport agent is 1/20000 or more and 1/10 or less with respect to the mobility of the agent; The method enables the provision of high speed and energy saving imaging devices such as laser beam printers and facsimile machines.

[0069]

[Brief description of the drawings]

FIG. 1 Post-exposure potential of photoreceptor and hole transport agent (HTM)
Relationship to mobility

[Figure 2] mobility of the hole transport agent in the field strength 5 × 10 ⁵ V / cm is 1 × 10 ^- In the case of more than ⁵ cm ² / V / sec, the mobility ratio and the post-exposure potential of the photosensitive member [electron transfer agent (ET
M) / Hole transport agent (HTM))]

[Figure 3] field strength ⁵ × 10 5 V / mobility of the hole transport agent in cm is ^{1 × 10 - 5 cm 2 /} V / sec or more in the case, the initial surface potential and mobility ratio of the photosensitive member [electron transfer agent (E
TM) / Hole transport agent (HTM))]

Claims (2)

[Claims] A photosensitive layer comprising at least a charge generating agent, a hole transporting agent, an electron transporting agent and a binder resin is formed on a conductive substrate as an image carrier, wherein the charge generating agent is a phthalocyanine pigment. Electric field strength is 5 × 10 ⁵ V
/ Cm of the hole transport agent at 1 × 10 ⁻⁵ / cm
cm ² / V / sec or more, and the mobility of the electron transporting agent is 1/20 of the mobility of the hole transporting agent.
An image forming method for a digital optical system, comprising a positively charged single-layer electrophotographic photosensitive drum having a size of 000 or more and 1/10 or less. 2. A digital optical system image forming method according to claim 1, wherein said phthalocyanine pigment is metal-free phthalocyanine or oxotitanyl phthalocyanine.