JP2001242655A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrification single layer type electrophotographic photoreceptor which does not generate transfer image memory even when it is used for a reversal developing type image forming device. SOLUTION: In the positive electrification single layer type electrophotographic photoreceptor, the charge generating layer of the photosensitive layer contains a phthalocyanine pigment and one kind of compound expressed by general formula (1), (2) or (3) and a perylene pigment expressed by general formula (4) as an electron transfer agent. The weight ratio of the perylene pigment to the phthalocyanine pigment is <=1.

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 used for an image forming apparatus such as an electrophotographic copying machine, a facsimile, a laser beam printer, and the like, and an image forming method using the same.

More specifically, the present invention relates to a positively charged single-layer type electrophotographic photosensitive member which does not generate a transfer memory image even when used in a reversal developing digital image forming apparatus, and a reversal developing digital image forming method using the same. It is.

[0003]

2. Description of the Related Art Organic photoreceptors are easier to manufacture than conventional inorganic photoreceptors, are inexpensive, and have a wide variety of photoreceptor materials such as charge transport agents, charge generators and binder resins. In recent years, it has been widely used because it has an advantage that the degree of freedom in functional design is high.

The organic photoreceptor includes a single-layer type photoreceptor in which a charge transporting agent (a hole transporting agent and an electron transporting agent) is dispersed in the same photosensitive layer together with a charge generating agent, and a charge generating agent containing a charge generating agent. There is a laminated photoconductor in which a layer and a charge transport layer containing a charge transport agent are laminated.

On the other hand, an image forming apparatus using an electrophotographic system charges a photosensitive member (main charging step), forms an electrostatic latent image by exposing the image (exposure step), and develops the electrostatic latent image. The toner is developed with a bias voltage applied (developing step), the formed toner image is transferred onto a transfer sheet (transfer step), and fixed to form an image. Further, the residual toner on the photoconductor is cleaned by a urethane blade or the like (cleaning process), and the residual charge on the photoconductor is erased by an LED or the like (static elimination process).

Image forming apparatuses utilizing the electrophotographic method include digital and analog copying machines, facsimile machines, laser beam printers, and the like. In particular, toner having the same polarity as a charging voltage applied to a photosensitive member in a charging step is used. The reversal developing method of developing by using is widely used in digital image forming apparatuses.

When an electrophotographic photoreceptor is used in a reversal developing digital image forming apparatus, the transfer voltage applied to the photoreceptor in the transfer step is not directly applied to the photoreceptor but via a transfer medium (paper). It is applied and is not applied when the transfer medium does not pass through the transfer process.

However, it is very difficult to turn on and off the transfer voltage, and the front and rear ends of the transfer medium often have portions directly applied to the photosensitive member. That is, before the leading end of the transfer medium covers the transfer device, the transfer voltage starts to be applied, and the transfer voltage continues to be applied even when a part of the transfer device is exposed by the passage of the rear end of the transfer medium. In this portion, a transfer voltage is directly applied to the photosensitive member.

In the case of a positively charged single-layer type electrophotographic photosensitive member, since the polarity of the voltage applied by the transfer device is negative, a negative space charge remains on the surface of the photosensitive member to which the negative voltage is applied, so-called, Transfer memory occurs. In general, since the single-layer type photoconductor has sensitivity to both polarities, negative space charges are erased in the next neutralization step.

However, if the sensitivity of the positively charged single-layer type photoreceptor to the negative polarity is very low (the half-exposure amount is very large), the negative space charge is not sufficiently erased and the next charging step is not performed. However, even if the surface is positively charged, a potential drop is caused by the effect of space charge, and furthermore, it appears as a difference in sensitivity in the developing process, and a so-called transfer memory image occurs in which the portion becomes black in the image.

[0011]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a positively charged single-layer type electrophotographic photosensitive member having a very small transfer memory even when used in a reversal developing digital image forming apparatus. .

Another object of the present invention is to provide a reversal-developing digital image forming apparatus using the positively charged single-layer type electrophotographic photosensitive member of the present invention.

[0013]

Means for Solving the Problems As a result of intensive studies, the present inventors have formed a photosensitive layer on a conductive substrate, and the photosensitive layer has a phthalocyanine pigment as a charge generating agent. Formulas (1) and (2) as electron transporting agents
Or a weight ratio of the content of the perylene pigment to the content of the phthalosinine pigment, containing at least one compound represented by the formula (3) and the perylene pigment represented by the formula (4): Has been found to have a very small transfer memory.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A positively charged single-layer type electrophotographic photosensitive member 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 materials used for the positively charged single-layer type electrophotographic photosensitive member of the present invention will be described in detail.

<Charge Generating Agent> In a digital image forming apparatus, an LED and a semiconductor laser are generally used, but their oscillation wavelength is about 740 nm or more and is limited to an infrared region. Therefore, at least 700-8
An organic photoreceptor having sensitivity in a wavelength region around 50 nm is required.

As the charge generator used in the organic photoreceptor satisfying the above requirements, for example, polycyclic quinone pigments, pyrylium pigments, squarium pigments, phthalocyanine pigments, etc. have been proposed or put into practical use. However, various phthalocyanine pigments are used in the positively charged single-layer type electrophotographic photoreceptor of the present invention.

Generally, phthalosinine-based pigments include metal-free phthalosinin (CGM-1) having no central metal.
In recent years, research and development on aluminum phthalocyanine, vanadium phthalosinine, cadmium phthalocyanine, antimony phthalosinine, chromium phthalosinine, copper 4-phthalosinine, germanium phthalosinine, iron phthalosinine, chloroaluminum phthalosinine, titanyl phthalosinine Chloroindium phthalocyanine, chlorogallium phthalosinine, magnesium phthalosinine, dialkylphthalosinine, tetramethylphthalosinine, metal phthalocyanines having a central metal such as tetraphenylphthalosinine, and α-form, β
There are various crystal types such as type, γ-type, δ-type, ε-type, σ-type, and x-type, and any of them can be used. These phthalocyanine pigments can be used alone or as a blend of two or more.

(CGM-1)

Embedded image

Further, the positively charged single-layer type electrophotographic photoreceptor of the present invention contains a perylene pigment represented by the general formula (4) in addition to the phthalosinine pigment in order to reduce transfer memory. Features.

The reason for the decrease in transfer memory when the perylene-based pigment is contained is not clear, but the perylene-based compound shows almost no light absorption at 740 nm or more, and thus becomes a trap that causes transfer memory. It is considered that they do not increase the generation of carriers, but rather play a role in releasing carriers generated more than necessary.

The phthalocyanine pigment is used in an amount of 0.1 to 20% by weight, especially 0.5 to 1% by weight based on the weight of the binder resin.
It is preferable to contain 0 wt%.

The content of the perylene pigment is as defined in claim 1.
As described, the weight ratio must be 1 or less based on the content of the phthalosinin-based pigment. The weight ratio is 1
If it is larger, the problem that the photosensitivity of the photoreceptor is remarkably deteriorated occurs, although the reason is not clear (see FIG. 1).

<Electron Transport Agent> The electron transport agent used in the positively charged single-layer type electrophotographic photoreceptor of the present invention has a large electron mobility and an improved negative sensitivity in order to reduce transfer memory. General formulas (1), (2), and (3) described in 1.
Alternatively, the compound represented by (4) is used.

When the above compounds are used as the electron transporting agent, they may be used alone or in at least one kind. That is, various electron transporting agents may be contained together with the compound.

Examples of various electron transporting agents include pyrene compounds, carbazole compounds, hydrazone compounds, N, N-dialkylaniline compounds, diphenylamine compounds, triphenylamine compounds, triphenylmethane compounds, tetraphenyl compounds, and the like. Cyanoethyl, tetracyanoquinodimethane, chloranil, bromoanil, 2,
4,7-trinitro-9-fluorenone, 2,4,5,7-
Tetranitro-9-fluorenone, 2,4,7-trinitro-9-dicyanomethylenefluorenone, 2,4,5,7
And electron-withdrawing substances such as -tetranitroxanthone, 2,4,8-trinitrothioxanthone, and those obtained by polymerizing these electron-withdrawing substances.

The content of the electron transporting agent is 5 to 100% by weight, more preferably 10 to 80% by weight based on the weight of the binder resin.
Is preferred.

<Hole transporting agent> The hole transporting agent used in the single-layer type electrophotographic photoreceptor of the present invention is preferably a compound represented by formula (5) or (6) according to claim 2 for reducing transfer memory. The compounds shown are preferably used.

When the above compounds are used as the hole transporting agent, they may be used alone or in at least one kind. That is, various hole transporting agents may be contained together with the compound.

Oxadiazole compounds such as 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole; styryl compounds such as 9-4 (-diethylaminostyryl) anthracene; Carbazole compounds such as polyvinyl carbazole, organic polysilane compounds, pyrazoline compounds such as 1-phenyl-3 (p-dimethylaminophenyl) pyrazoline, hydrazone compounds, triphenylamine compounds, indole compounds, oxazole compounds, iso Examples thereof include nitrogen-containing cyclic compounds such as oxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds. These hole transporting agents can be used alone or as a blend of two or more.

The content of the hole transporting agent is 5 to 500 wt% based on the weight of the binder resin, and more preferably 25 to 200 watts.
t% is preferred.

<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-butadiene copolymer,
Styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic copolymer, styrene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, ionomer, Thermoplastic resin such as vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, silicone resin, epoxy resin , Phenolic 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 as a blend of two or more.

Particularly preferred resins are bisphenol Z-type polycarbonates derived from bisphenol Z-type monomers such as Panlite manufactured by Teijin Chemicals Ltd. and PCZ manufactured by Mitsubishi Gas Chemical Co., Ltd. and phosgene.

The binder resin of the above example has a weight average molecular weight of 5,000 to 200,000, more preferably 15,000 to 200,000.
100,000 is preferred.

The thickness of the positively charged single-layer type electrophotographic photosensitive member of the present invention is preferably from 5 to 50 μm, particularly preferably from 15 to 35 μm.

In the positively charged single-layer type electrophotographic photosensitive member of the present invention, 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.

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 shape of the conductive substrate may be sheet-like or drum-like depending on the structure of the image forming apparatus to be used. The substrate itself has conductivity or the surface of the substrate has conductivity. 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 may be used in a known method.
For example, a dispersion may be prepared by dispersing and mixing using a roll mill, 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.

As the solvent for preparing the dispersion, various organic solvents can be used, for example, alcohols such as methanol, ethanol, isopropanol and butanol, and aliphatic solvents such as n-hexane, octane and cyclohexane. 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 smoothness of the surface of the photosensitive layer, a leveling agent such as silicone oil may be used.

On the other hand, the image forming apparatus of the present invention has the following features.
Using the positively charged single-layer type electrophotographic photoreceptor described in the above, and including at least a main charging step, an exposure step, a development step, a transfer step, a charge removal step, and a cleaning step along a traveling direction of the photoreceptor; The voltage applied in the process is a reversal-developed digital image forming apparatus, which has a polarity opposite to that of the voltage applied in the charging process, and examples thereof include a digital copying machine, a facsimile, and a laser beam printer. Can be

The positively charged single-layer type electrophotographic photoreceptor of the present invention comprises:
As described above, since the transfer memory is very small, no memory image is generated even when used in the image forming apparatus.

[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 12> 2.0 parts by weight of an X-type metal-free phthalocyanine (CGM-1) as a charge generator and a compound represented by the general formula (4) [PE-1,
1) (1.0 parts by weight) selected from the group consisting of general formula (1) [ET-101] and general formula (2)
[ET-201], one kind (32 parts by weight) selected from general formulas (3) and [ET-301], and as a hole transport agent, general formulas (5) [HT-501] and general formulas (6) [ HT-6
01], and bis-Z having a weight average molecular weight of 50,000 as a binder resin.
100 parts by weight of a mold polycarbonate resin and 770 parts by weight of tetrahydrofuran were dispersed or dissolved in a ball mill for 22 hours to prepare a coating solution for a single-layer type photosensitive layer.
Then, this coating solution is applied on an aluminum pipe as a support by a dip coating method, and dried with hot air at 135 ° C. for 35 minutes to obtain a positively charged monolayer having a single photosensitive layer having a thickness of 23.5 μm. A layer type photoreceptor was prepared.

Tables 1 to 3 show the structural formulas of the compounds used in the examples.

<Perylene Compound>

[Table 1]

<Electron transport agent>

[Table 2]

<Hole transport agent>

[Table 3]

<Comparative Examples 1 and 2> ET- as an electron transporting agent
A positively charged single-layer type photoreceptor was produced in the same manner as in Examples 1 to 12, except that Examples 1 and 2 were used.

<Comparative Examples 3 to 8> Positively charged single-layer type photoconductors were prepared in the same manner as in Examples 1 to 12, except that no perylene pigment was added.

<Comparative Examples 9 and 10>
Except for adding 4 parts by weight, a positively charged single-layer type photoreceptor was prepared in the same manner as in Examples 1 to 12.

Table 4 shows the structural formulas of the compounds used in Comparative Examples 1 and 2.

<Electron transport agent>

[Table 4]

The following characteristics were evaluated for the positively charged single-layer type electrophotographic photoreceptors of the above Examples and Comparative Examples. The evaluation results are shown in Tables 5 and 6.

<Evaluation of Light Sensitivity>
C) Drum sensitivity tester (Gentec Cynthia 3)
0M), an applied voltage was applied to the photoreceptors of Examples and Comparative Examples, and the surfaces thereof were charged to + 725V.

Next, monochromatic light having a wavelength of 780 nm (half-width 20 nm, extracted from white light of a halogen lamp, which is an exposure light source of the tester, using a band-pass filter).
A light intensity of 15 μW) was applied to the charged surface of the photoreceptor (exposure time: 40 msec). Then, the surface potential at the point when 330 msec had elapsed from the start of exposure was measured as the post-exposure potential VL (V). That is, the smaller the potential after exposure, the higher the sensitivity of the photoconductor. VL is not allowed to be 250 V or more.

<Evaluation of Transfer Memory> Using a digital copying machine CREAGE630 manufactured by Kyocera Mita Co., Ltd., the photoconductors of the respective examples and comparative examples were uniformly charged to +850 V by a main charger, and the reflection optical density was reduced. After outputting a halftone of about 0.5 and performing image exposure, a developing bias of +650 V was applied, and reversal development was performed with a two-component developer using positively charged toner. Then, the image was transferred to a transfer sheet at a transfer output of 6 kV, and after fixing, an image for evaluation was obtained.

That is, the image density difference (ΔID) between the dark portion (transfer memory image) of the image which appears in a band shape in the longitudinal direction of the photosensitive drum of the evaluation image and other portions.
Is larger, the transfer memory of the photoconductor is larger.

[0061]

[Table 5]

[0062]

[Table 6]

Tables 5 and 6 show that the presence of the electron transporting agent according to claim 1 has a great effect on reducing the transfer memory. Further, when the perylene pigment is added at a content within the range described in claim 1, ΔID is higher than when not added.
Was further reduced, that is, the transfer memory was reduced. However, perylene pigment content / phthalocyanine pigment (CGM
-1) When the content ratio was 1.2, the light sensitivity was deteriorated.

FIG. 1 shows that ET-10 was used as an electron transporting agent.
1. Photosensitivity when HT-601 was used as the hole transport agent and PE-1 was used as the perylene pigment (the positively charged single-layer type electrophotographic photoreceptor of Example 7 and Comparative Example 9), and the perylene pigment content / The relationship with the phthalocyanine pigment (CGM-1) content ratio is shown.

From the figure, it can be understood that when the content ratio of perylene pigment / phthalocyanine pigment (CGM-1) exceeds 1, the photosensitivity of the photoreceptor is significantly deteriorated.

[0066]

The electrophotographic photoreceptor of the present invention has a very small transfer memory and does not generate a transfer memory image even when used in a digital image forming apparatus of a reversal developing system.

[0067]

[Brief description of the drawings]

FIG. 1 shows a case where ET-101 is used as an electron transporting agent, HT-601 is used as a hole transporting agent, and PE-1 is used as a perylene pigment (positive-charged single-layer electrophotographic photoreceptor of Example 7 and Comparative Example 9). Relationship between the light sensitivity of the above and the ratio of the perylene pigment content / the phthalocyanine pigment (CGM-1) content.

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Claims (3)

[Claims] 1. A photosensitive layer is formed on a conductive substrate. The photosensitive layer comprises a phthalocyanine pigment as an electrification generator and a compound represented by the general formula (1), (2) or (3) as an electron transporting agent. It contains at least one kind of perylene pigment represented by the general formula (4), and the weight ratio of the content of the perylene pigment to the content of the phthalosinine pigment is 1 or less. Positively charged single-layer electrophotographic photosensitive member. General formula (1): (In the general formula (1), R ¹ and R ² are the same or different and represent a monovalent hydrocarbon group which may have a substituent.) The general formula (2): (In the general formula (2), R ³ and R ⁴ are the same or different and are an alkyl group, a halogenated alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, an aralkyloxy group, an acyl group, an alkoxycarbonyl group. , An aryloxycarbonyl group, an aralkyloxycarbonyl group or a nitro group, and n represents an integer of 0 to 3.) General formula (3): (In the general formula (3), R ⁵ and R ⁶ are the same or different and represent a monovalent hydrocarbon group which may have a substituent.) A general formula (4): (In the general formula (4), R ⁷ , R ⁸ , R ⁹ , and R ¹⁰ are the same or different and each represent a hydrogen atom or an optionally substituted alkyl group, aryl group, aralkyl group, or amino group. .) 2. The positively charged single-layer type electrophotographic photoreceptor according to claim 1, wherein the hole transporting agent contains at least one compound represented by the general formula (5) or (6). General formula (5): (In the general formula (5), R ¹¹ and R ¹³ are the same or different, and may have an alkyl group which may have a substituent, an aryl group which may have a substituent, and a substituent. an aralkyl group or an alkoxy group, R ¹² and R ¹⁴ are the same or different, a hydrogen atom may have a substituent, an alkyl group or an alkoxy group. However, R ¹² and R
^When the substitution position of ¹⁴ is para, R ¹² and R ¹⁴ are hydrogen atoms. General formula (6): (In the general formula (6), R ¹⁵ and R ¹⁷ represent the same or different alkyl groups, and R ¹⁶ and R ¹⁸ represent the same or different hydrogen atoms or alkyl groups.) 3. The method according to claim 1, wherein the positively charged single-layer type electrophotographic photoreceptor is used along a traveling direction of the electrophotographic photoreceptor.
It comprises at least a main charging step, an exposure step, a developing step, a transferring step, a discharging step and a cleaning step, wherein the polarity of the voltage applied in the transferring step is negative and the polarity of the voltage applied in the charging step is positive. A reversal-developing digital image forming apparatus.