JP2007232904A - Positive charge monolayer type electrophotographic photoreceptor and image forming apparatus of contact charging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of uneven charges and to obtain stable charging characteristics in a positive charge monolayer type electrophotographic photoreceptor used for an image forming apparatus of a contact charging system. <P>SOLUTION: In the positive charge monolayer type electrophotographic photoreceptor to be applied to an image forming apparatus equipped with a charging means of a contact charging system type charging means, and an image forming apparatus using the photoreceptor, a value represented by IP1-IP2, with IP1 (eV) being the ionization potential of a hole transporting agent and IP2 (eV) being the ionization potential of a charge generating agent, is set to a range of 0.1 to 0.4 (eV), and the surface potential of the positive charge monolayer type electrophotographic photoreceptor upon superposing a DC voltage and an AC voltage is set to 300 V or more during contact charging in the positive charge monolayer type electrophotographic photoreceptor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a positively charged single layer type electrophotographic photosensitive member and a contact charging type image forming apparatus, and in particular, to a positively charged single layer type electrophotographic photosensitive member and a contact charging type image forming capable of obtaining a stable charging potential. Relates to the device.

In general, organic photoconductors are often used as electrophotographic photoconductors used in electrophotographic machines such as copying machines and laser printers due to demands for low price and environmental pollution.
In addition, the surface of such an organic photoreceptor is charged (main charging step) and an electrostatic latent image is formed (exposure step), and then the electrostatic latent image is applied with a developing bias voltage. An image forming process is performed in which toner development (development process) is performed, and the formed toner image is transferred to transfer paper by a reversal development method (transfer process), which is heated and fixed to form a predetermined image. ing.
The residual toner on the organic photoconductor is removed using a cleaning blade (cleaning step), and the residual charge on the organic photoconductor is erased by an LED or the like (static elimination step). .
However, in such an organic photoreceptor, since the organic photoreceptor is rotated and used, the potential (bright potential) of the portion exposed in the previous round remains and the charging process in the next round is performed. In such a portion, a phenomenon (exposure memory) in which a desired charging potential (dark potential) cannot be obtained was observed.
For this reason, there has been a problem that the image density is changed between the portion with and without the exposure memory, and a good image cannot be obtained.

Therefore, in order to provide an electrophotographic photoreceptor with little potential fluctuation even when it is repeatedly used, a substance used as a charge transport agent is specified, and the difference in ionization potential between the charge transport layer and the charge generation layer is determined. There has been disclosed a negatively charged laminate type electrophotographic photosensitive member defined to a value within a predetermined range (for example, Patent Document 1).
JP-A-7-36204 (Claims)

However, the electrophotographic photosensitive member disclosed in Patent Document 1 is a negatively charged laminated type, which has a complicated structure and a problem that the exposure memory cannot be sufficiently erased and cannot be stably charged. It was.
Therefore, as a result of intensive studies, the inventors of the present invention have determined that, in a positively charged single layer type electrophotographic photosensitive member used for a contact charging type image forming apparatus, the ionization potential of a hole transport agent and the ionization potential of a charge generation agent. The difference in voltage between the two is controlled to a value within a predetermined range, and the surface potential when the DC voltage and the AC voltage are superimposed at the time of contact charging is set to a predetermined value. The title and the present invention have been completed.

  That is, the object of the present invention is to stably charge even a positively charged single layer type electrophotographic photosensitive member that has a long electron transport distance and easily generates an exposure memory, even when a system without a photostatic charge is employed. It is an object of the present invention to provide a positively charged single layer type electrophotographic photosensitive member and a contact charging type image forming apparatus.

According to the present invention, there is provided a positively charged single layer type electrophotographic photosensitive member that is applied to an image forming apparatus provided with a charging means of a contact charging method, on a substrate, at least a charge generating agent, a hole transporting agent, IP1-IP2 when the ionization potential of the hole transporting agent is IP1 (eV) and the ionization potential of the charge generating agent is IP2 (eV), which includes an electron transporting agent and a binder resin. The numerical value is set to a value within the range of 0.1 to 0.4 (eV), and the surface potential at the time of superimposing the DC voltage and the AC voltage at the time of contact charging in the positively charged single layer type electrophotographic photosensitive member is set to 300V. A positively charged single layer type electrophotographic photosensitive member having the above values is provided, and the above-mentioned problems can be solved.
That is, as illustrated in FIG. 1, even when a positively charged single-layer type electrophotographic photosensitive member is used, the difference in ionization potential between the charge generating agent and the hole transporting agent is By setting the value within the predetermined range, it is possible to provide a positively charged single-layer type electrophotographic photosensitive member that generates less exposure memory and can be stably charged.
In addition, since the generation of the exposure memory is small, stable image formation is possible even when the light static elimination-less system is adopted.
Furthermore, since it is a positively charged single layer type electrophotographic photosensitive member that is applied to an image forming apparatus equipped with a contact charging method charging means, the overall configuration is simpler than that of the non-contact charging method, and harmful substances such as ozone are used. It can be said that it has excellent environmental characteristics.

In constituting the positively charged single layer type electrophotographic photosensitive member of the present invention, it is preferable to use a metal-free phthalocyanine as a charge generating agent.
With this configuration, it is easy to adjust the difference between the ionization potential of the hole transport agent and the ionization potential of the charge generation agent. Moreover, since the metal-free phthalocyanine is excellent in dispersibility in the photosensitive layer, the occurrence of exposure memory can be more effectively suppressed.

In constituting the positively charged single layer type electrophotographic photosensitive member of the present invention, the hole transport agent is preferably at least one of the following general formulas (1) to (3).
Such a configuration not only makes it easier to adjust the difference between the ionization potential of the hole transport agent and the ionization potential of the charge generation agent, but also provides excellent sensitivity.
In addition, as an alkyl group as a substituent in General formula (1)-General formula (3), a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl, for example C1-C6 alkyl groups, such as a group, t-butyl group, pentyl group, isopentyl group, neopentyl group, and hexyl group. Examples of the alkoxy group as a substituent include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, s-butoxy, t-butoxy, pentyloxy, isopentyloxy, neopentyloxy, hexyloxy and the like. And an alkoxy group having 1 to 6 carbon atoms.

(In General Formula (1), R ^{a1 to} R ^a4 are an alkyl group, an alkoxy group which may have a substituent, a halogen atom, or a hydrogen atom, and at least one of R ^{a1 to} R ^a4 has 3 carbon atoms. These are the above alkyl groups or alkoxy having 3 or more carbon atoms.)

(In General Formula (2), R ^{b1 to} R ^b5 are an alkyl group, an alkoxy group which may have a substituent, a halogen atom, or a hydrogen atom, and at least one of R ^{b1 to} R ^b5 has 3 carbon atoms. These are the above alkyl groups or alkoxy having 3 or more carbon atoms.)

(In General Formula (3), R ^{c1 to} R ^c6 are an alkyl group, an alkoxy group which may have a substituent, a halogen atom, or a hydrogen atom, and at least one of R ^{c1 to} R ^c6 has 3 carbon atoms. These are the above alkyl groups or alkoxy having 3 or more carbon atoms.)

According to another aspect of the present invention, there is provided an image forming apparatus in which a contact charging type charging unit, a developing unit, and a transfer unit are sequentially arranged around a positively charged single layer type electrophotographic photosensitive member. The charged single layer type electrophotographic photosensitive member includes at least a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin on a substrate, and the ionization potential of the hole transporting agent is IP1 (eV ), And when the ionization potential of the charge generating agent is IP2 (eV), the numerical value represented by IP1-IP2 is set to a value within the range of 0.1 to 0.4 (eV) and positively charged. In this image forming apparatus, the surface potential at the time of superimposing a DC voltage and an AC voltage at the time of contact charging in a single-layer type electrophotographic photosensitive member is set to a value of 300 V or more.
That is, even when a positively charged single layer type electrophotographic photosensitive member is used, the difference in ionization potential value between the charge generating agent and the hole transporting agent should be within a predetermined range. Therefore, it is possible to provide an image forming apparatus that can generate images stably with less exposure memory.
Since the image forming apparatus includes a contact charging type charging unit, the overall configuration is simpler than that of the non-contact charging type, and no harmful substances such as ozone are generated. It can be said that.

In configuring the image forming apparatus of the present invention, it is preferable to employ an optical static elimination-less system that does not use an optical static eliminating unit as the static eliminating unit in the image forming apparatus.
With this configuration, it is possible to prevent the generation of residual charges due to exposure from the photostatic means in the photosensitive layer. Therefore, more stable charging is possible.
Further, by omitting the light neutralizing means, the image forming apparatus can be reduced in size and the manufacturing cost can be reduced.

In configuring the image forming apparatus of the present invention, it is preferable to use a static elimination brush as the static elimination means.
With this configuration, it is possible to efficiently eliminate the influence of the exposure memory while maintaining stable charging characteristics.

[First Embodiment]
A first embodiment of the present invention is a positively charged single layer type electrophotographic photosensitive member applied to an image forming apparatus provided with a charging unit of a contact charging method, and includes at least a charge generating agent and a hole on a substrate. IP1-IP2 when the transporting agent, the electron transporting agent and the binder resin are included, the ionization potential of the hole transporting agent is IP1 (eV) and the ionization potential of the charge generating agent is IP2 (eV). Is a value within the range of 0.1 to 0.4 (eV), and at the time of superimposing the DC voltage and the AC voltage at the time of contact charging in the positively charged single layer type electrophotographic photosensitive member. A positively charged single layer type electrophotographic photosensitive member having a surface potential of 300 V or more.
Hereinafter, the positively charged single layer type electrophotographic photosensitive member of the first embodiment will be described separately for each component.

1. Basic Configuration As shown in FIG. 2A, the single-layer type photoreceptor 11 is obtained by providing a single photoreceptor layer 11a on a substrate (conductive substrate) 11b. The photosensitive layer 11a is characterized by containing a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin in the same layer.
This is because the charge generated from the charge generating agent at the time of exposure can be efficiently transported by including both the hole transporting agent and the electron transporting agent in the same photosensitive layer. .
Further, as shown in FIG. 2B, a photosensitive member 11 ′ in which a barrier layer 11c is formed between the conductive substrate 11b and the photosensitive layer 11a within a range that does not impair the characteristics of the photosensitive member may be used. Further, as shown in FIG. 2C, a photosensitive member 11 ″ having a protective layer 11d formed on the surface of the photosensitive layer 11a may be used.

2. Charge generator (1) type It is preferable to use metal-free phthalocyanine as the charge generator used in the electrophotographic photosensitive member of the present invention.
This is because the difference between the ionization potential of a metal-free phthalocyanine and the ionization potential of a hole transport agent described later can be easily adjusted within a predetermined range.
That is, by setting the difference in ionization potential within a predetermined range, not only the exposure memory in the photosensitive layer can be suppressed and the sensitivity can be improved, but also the charging characteristics can be improved.
A more specific description of setting the difference between the ionization potential of the charge generating agent and the ionization potential of the hole transport agent within a predetermined range will be described in the section of the hole transport agent described later.
In addition, since metal-free phthalocyanine is excellent in dispersibility in the photosensitive layer, the occurrence of exposure memory can be more effectively suppressed.
That is, since the metal-free phthalocyanine can be uniformly dispersed in the photosensitive layer, it is possible to generate charges efficiently for exposure and to efficiently transfer charges between the charge transport agent. Because it can be done.
Moreover, as a specific example of such a metal-free phthalocyanine, a compound represented by the following formula (4) is preferably used.

(2) Ionization potential Moreover, it is preferable to make the value of the ionization potential in a charge generator into the value within the range of 5.0-5.5 eV.
The reason for this is that when the value of the ionization potential is less than 5.0 eV, the difference from the value of the ionization potential in the hole transport agent described later becomes excessively large, so that efficient charge transport becomes difficult. Because there is. As a result, the sensitivity of the photosensitive member is lowered and the exposure memory is caused. On the other hand, when the value of the ionization potential exceeds 5.5 eV, the difference from the value of the ionization potential in the hole transport agent described later becomes excessively small, and the charging characteristics in the photoconductor may deteriorate. Because.
Therefore, the value of the ionization potential in such metal-free phthalocyanine is more preferably set to a value in the range of 5.0 to 5.4 eV, and further preferably set to a value in the range of 5.0 to 5.2 eV.
Note that a method for measuring the ionization potential will be described in a later example.

(3) Addition amount The addition amount of the charge generating agent is preferably set to a value within the range of 0.6 to 3.0% by weight with respect to the total amount.
The reason for this is that by setting the amount of charge generator added within this range, the metal-free phthalocyanine can efficiently generate charges when exposed to a photoconductor, and charge transport can be performed. This is because charge transport to and from the agent is also efficiently performed.
That is, when the amount of the charge generator added is less than 0.6% by weight, the charge generation amount becomes insufficient, and it may be difficult to form a predetermined electrostatic latent image on the photoreceptor. Because there is. On the other hand, when the added amount of the charge generating agent exceeds 3% by weight, it may be difficult to uniformly disperse in the photosensitive layer coating solution.
Therefore, it is more preferable that the addition amount of the charge generating agent is a value within the range of 0.8 to 2.8% by weight with respect to the total amount.

3. Hole Transport Agent (1) Ionization Potential Further, as the hole transport agent, the ion transport potential (eV) of the hole transport agent is preferably set to a value within the range of 5.1 to 6.0 eV.
The reason for this is that the ionization potential (eV) in the hole transport agent is set to a value in the range of 5.1 to 6.0 eV, as described in detail in the next section. This is because it becomes easy to adjust the value obtained by subtracting the value of ionization potential (eV) in metal-free phthalocyanine from the value of (eV) within a predetermined range. Therefore, the value of ionization potential (eV) in such a hole transport agent is more preferably in the range of 5.2 to 5.8 eV, and is preferably in the range of 5.3 to 5.7. Is more preferable.

Moreover, as a hole transport agent, the value which subtracted the value of the ionization potential (eV) in a charge generating agent from the value of the ionization potential (eV) in the said hole transport agent is the range of 0.1-0.4 (eV). A hole transporting agent having a value within the range is used.
This is because a hole transport agent having an ionization potential (eV) value of 0.1 to 0.4 eV higher than that of a metal-free phthalocyanine as a charge generating agent is used. This is because not only the exposure memory in the photosensitive layer can be suppressed and the sensitivity can be improved, but also the charging characteristics can be improved.
That is, when the difference between the ionization potential (eV) of the hole transport agent and the ionization potential (eV) of the metal-free phthalocyanine is less than 0.1 eV, the ionization potential of the hole transport agent and the ionization of the metal-free phthalocyanine This is because the difference between the potential and the potential becomes excessively small, and the charging characteristics of the photosensitive member may deteriorate.

On the other hand, when the difference between the ionization potential (eV) of the hole transport agent and the ionization potential (eV) of the metal-free phthalocyanine exceeds 0.4 eV, efficient charge transport becomes difficult, and the sensitivity This is because there is a case where the image quality decreases or an exposure memory is generated.
Therefore, the difference between the ionization potential (eV) of the hole transport agent and the ionization potential (eV) of the metal-free phthalocyanine is more preferably set to a value within the range of 0.12 to 0.35 eV. More preferably, the value is in the range of -0.3 eV.
In addition, the measuring method of the ionization potential in a hole transport agent is described in a later Example.

(2) Type The hole transporting agent used in the present invention is preferably at least one of the compounds represented by the general formulas (1) to (3) described above.
The reason for this is that a compound having such a specific structure not only facilitates adjustment of the difference between the ionization potential of the hole transport agent and the ionization potential of the charge generation agent, but also can provide excellent sensitivity. Because.
That is, in the case of a compound having a structure represented by the general formulas (1) to (3), the difference between the ionization potential and the ionization potential of the metal-free phthalocyanine as the charge generator is likely to be within a predetermined range. Because. Therefore, the exposure memory in the photosensitive layer can be suppressed and the charging characteristics can be improved.
Moreover, if it is a compound which has a structure represented by General formula (1)-(3), since it is excellent in a hole transport ability, the movement of an electric charge becomes efficient and the sensitivity of a photoreceptor can be improved further. Because.

  Moreover, as a specific example of the hole transport agent represented by the general formulas (1) to (3), the hole transport agents (HTM-A to D) represented by the following formulas (5) to (8) are used. ). Moreover, as hole transport agents other than the hole transport agents represented by the general formulas (1) to (3), a hole transport agent (HTM-E) represented by the following formula (10) may be used. preferable.

(3) Addition amount The addition amount of the hole transport agent is preferably set to a value in the range of 20 to 500 parts by weight with respect to 100 parts by weight of the binder resin.
This is because when the amount of the hole transporting agent added is less than 20 parts by weight, the hole transporting function in the photosensitive layer is lowered, which may adversely affect image characteristics. On the other hand, when the added amount of the hole transport agent exceeds 500 parts by weight, the dispersibility is lowered and crystallization is likely to occur.
Therefore, the amount of the hole transport agent added is more preferably set to a value within a range of 30 to 200 parts by weight, and a value within a range of 40 to 100 parts by weight with respect to 100 parts by weight of the binder resin. Is more preferable.

4). Electron Transfer Agent (1) Type As the electron transfer agent, any of various conventionally known electron transfer compounds can be used. In particular, benzoquinone compounds, diphenoquinone compounds, naphthoquinone compounds, malononitrile, thiopyran compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, fluorenone compounds [for example, 2,4,7-trinitro-9-fluorenone, etc. ], Dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, succinic anhydride, maleic anhydride, dibromomaleic anhydride, 2,4,7-trinitrofluorenone imine compound, ethylated nitrofluorenone imine compound, tryptoanthone Thrin compound, tryptoanthrin imine compound, azafluorenone compound, dinitropyridoquinazoline compound, thioxanthene compound, 2-phenyl-1,4-benzoquinone compound, 2- Electrons such as salts of anion radicals and cations of phenyl-1,4-naphthoquinone compounds, 5,12-naphthacenequinone compounds, α-cyanostilbene compounds, 4, '-nitrostilbene compounds, and benzoquinone compounds Inhalable compounds are preferably used. These may be used alone or in combination of two or more.

  Specific examples of the electron transport agent described above include electron transport agents (ETM-A to D) represented by the following formulas (10) to (13).

(2) Addition amount The addition amount of the electron transfer agent is preferably set to a value within the range of 20 to 500 parts by weight with respect to 100 parts by weight of the binder resin.
This is because, when the amount of the electron transfer agent added is less than 20 parts by weight, the sensitivity is lowered and a practical problem may occur. On the other hand, when the added amount of the electron transport agent exceeds 500 parts by weight, the electron transport agent is easily crystallized, and it may be difficult to form an appropriate film as the photosensitive layer. Therefore, it is more preferable that the addition amount of the electron transport agent is a value within a range of 30 to 200 parts by weight, and a value within a range of 40 to 100 parts by weight with respect to 100 parts by weight of the binder resin. Is more preferable.

5). Binder resin As the binder resin, for example, styrene polymer, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic polymer, styrene-acrylic copolymer, Polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone Thermoplastic resins such as resins, polyvinyl butyral resins, and polyether resins, silicone resins, epoxy resins, phenol resins, urea resins, melamine resins, and other crosslinkable thermosetting resins, and epoxy-acrylates, and Examples thereof include a photocurable resin such as urethane-acrylate. These binder resins can be used alone or in combination of two or more.
Further, in constituting the electrophotographic photosensitive member of the present invention, one of preferable binder resins is a Z-type polycarbonate resin represented by the following formula (14).

6). Other additives In addition to the above-mentioned components, various additives such as a sensitizer, a fluorene compound, an ultraviolet absorber, a plasticizer, a surfactant, and a leveling agent are added to the photosensitive layer. You can also In order to improve the sensitivity of the photoreceptor, sensitizers such as terphenyl, halonaphthoquinones, and acenaphthylene may be used in combination with the charge generator.

7). Substrate As the substrate on which the above-described photosensitive layer is formed, various conductive materials can be used. For example, a conductive substrate formed of a metal such as iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass; Examples include a substrate made of a plastic material on which a metal is deposited or laminated, or a glass substrate coated with aluminum iodide, tin oxide, indium oxide, or the like.
That is, it is only necessary that the substrate itself has conductivity or the surface of the substrate has conductivity. Further, it is preferable that the substrate has sufficient mechanical strength when used.
The shape of the substrate may be any of a sheet shape and a drum shape according to the structure of the image forming apparatus to be used.

8). Photosensitive Layer Film Thickness and Charging Characteristics (1) Photosensitive Layer Film Thickness It is preferable to set the film thickness of the photosensitive layer to a value within the range of 5.0 × 10 ^{−6 to} 1.0 × 10 ⁻⁴ m.
This is because a photoconductor excellent in practicality can be obtained by setting the film thickness in the photosensitive layer to a value in the range of 5.0 × 10 ^{−6 to} 1.0 × 10 ⁻⁴ m. It is.
That is, when the film thickness in the photosensitive layer is less than 5.0 × 10 ⁻⁶ m, the mechanical strength as the photoreceptor may be insufficient. On the other hand, if the film thickness of the photosensitive layer exceeds 1.0 × 10 ⁻⁴ m, it may be easy to peel from the substrate.
Therefore, it is more preferable to set the film thickness in the photosensitive layer to a value within the range of 1.0 × 10 ^{−5 to} 8.0 × 10 ⁻⁵ m, and 2.0 × 10 ^{−5 to} 4.0 × 10. More preferably, the value is within the range of ⁻⁵ m.

(2) Charging characteristics The surface potential when the DC voltage and the AC voltage are superimposed when the photosensitive layer of the positively charged single layer type electrophotographic photosensitive member is contact-charged is set to a value of 300 V or more.
That is, as shown in FIG. 1, when alternating voltage is gradually superimposed, even if the line A corresponds to the present invention (Example 1) or the line B corresponds to Comparative Example 1 of the present invention, Up to about 1.5 kV, the surface potential of the photoconductor tends to increase linearly. In the case of line A, the surface potential value of the photosensitive member is saturated at around 350 V and shows a constant value until the AC voltage exceeds 1.5 kV and reaches about 2.5 kV.
However, in the case of line B, when the AC voltage exceeds 1.5 kV, the value of the surface potential of the photoconductor decreases rapidly, and when it exceeds 1.7 kV, it drops to about 100V. In this case, it goes without saying that when the surface potential of the photosensitive member becomes 100 V, stable image formation cannot be performed.
Therefore, in the present invention, the superposed AC voltage is within the range of 1.5 to 2.5 kV so that the surface potential at the time of superimposing the DC voltage and the AC voltage when the photosensitive layer is contact-charged is 300 V or more. The value is preferably set to a value within the range of 1.7 to 2.3 kV, and more preferably set to a value within the range of 1.8 to 2.2 kV.

9. Manufacturing method In addition, in manufacturing a single-layer type photoreceptor, a binder resin, a charge generating agent, a hole transporting agent, and an electron transporting agent are added to a solvent, dispersed and mixed, and coated for a photosensitive layer. Use liquid. That is, when a single layer type photoreceptor is formed by a coating method, phthalocyanine as a charge generating agent, a hole transporting agent, an electron transporting agent, a binder resin and the like together with an appropriate solvent are known methods such as a roll mill. A dispersion is prepared by dispersing and mixing using a ball mill, an attritor, a paint shaker, an ultrasonic disperser or the like, and this is applied by a known means and dried.
Moreover, as a solvent for making the coating liquid for photosensitive layers, 1 type (s) or 2 or more types, such as tetrahydrofuran, a dichloromethane, toluene, 1, 4- dioxane, and 1-methoxy-2-propanol, are mentioned.
Furthermore, in order to improve the dispersibility of the charge transport agent and the charge generator and the smoothness of the surface of the photoreceptor layer, a surfactant, a leveling agent, and the like may be added to the photosensitive layer coating solution. .

[Second Embodiment]
The second embodiment of the present invention is an image forming apparatus in which a contact charging type charging unit, a developing unit, and a transfer unit are sequentially arranged around a positively charged single layer type electrophotographic photosensitive member. The charged single layer type electrophotographic photosensitive member includes at least a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin on a substrate, and the ionization potential of the hole transporting agent is IP1 (eV ), And the ionization potential of the charge generator is IP2 (eV), the numerical value represented by IP1-IP2 is set to a value within the range of 0.1 to 0.4 (eV), This is an image forming apparatus in which the surface potential when a DC voltage and an AC voltage are superimposed at the time of contact charging in a layer type electrophotographic photosensitive member is set to a value of 300 V or more.
Hereinafter, the contents already described in the first embodiment will be omitted, and the second embodiment will be described focusing on differences from the first embodiment.

The basic configuration and operation of the image forming apparatus according to the present invention will be described with reference to FIG.
First, the photoconductor 111 of the image forming apparatus 100 is rotated at a predetermined process speed (peripheral speed) in the direction indicated by the arrow A, and then the surface is charged to a predetermined potential by the charging unit 112 of the contact charging method. As the contact charging type charging means 112, a charging roll is used.
Next, the exposure unit 113 exposes the surface of the photoconductor 111 through a reflection mirror or the like while being optically modulated according to image information. By this exposure, an electrostatic latent image is formed on the surface of the photoreceptor 111.
Next, based on the electrostatic latent image, latent image development is performed by the developing unit 114. The developing means 114 contains toner, and the toner adheres corresponding to the electrostatic latent image on the surface of the photoconductor 111 to form a toner image.
Further, the recording paper 120 is conveyed to the lower part of the photoconductor along a predetermined transfer conveyance path. At this time, a toner image can be transferred onto the recording material 120 by applying a predetermined transfer bias between the photosensitive member 111 and the transfer unit 115.

Next, the recording paper 120 on which the toner image has been transferred is separated from the surface of the photoreceptor 111 by a separating unit (not shown) and conveyed to a fixing device by a conveying belt. Next, the toner image is fixed on the surface by being heated and pressed by the fixing device, and then discharged to the outside of the image forming apparatus 100 by a discharge roller.
On the other hand, the photoconductor 111 after the transfer of the toner image continues to rotate, and residual toner (adhered matter) that has not been transferred to the recording paper 120 at the time of transfer is removed from the surface of the photoconductor 111 by the cleaning device 117. Further, the electric charge remaining on the surface of the photoconductor 111 is erased by the charge eliminating means 102 and used for the next image formation.

In the image forming apparatus according to the present invention, as described in the first embodiment, the difference between the ionization potential of the hole transport agent and the ionization potential of the charge generator is within a predetermined range, and at the time of charging. A positively charged single layer type electrophotographic photosensitive member having a surface potential within a predetermined range is used.
Therefore, it is possible to obtain an image forming apparatus that can generate images stably with less exposure memory. In addition, since it is an image forming apparatus equipped with a contact charging type charging means, the overall configuration is simpler than that of the non-contact charging type, and no harmful substances such as ozone are generated. It can be said that.

Further, it is preferable to employ an optical static elimination-less system that does not use the optical static elimination means as the static elimination means in the image forming apparatus.
The reason for this is that by not using a light neutralizing unit as the neutralizing unit 102, it is possible to prevent the generation of residual charges in the photosensitive layer due to exposure from the light neutralizing unit, and as a result, more stable charging can be achieved. This is because it becomes possible.

Moreover, it is preferable to use a static elimination brush as the static elimination means.
This is because the influence of the exposure memory can be efficiently eliminated while maintaining stable charging characteristics in the photosensitive member.
In other words, it is not a method of generating charges in the photosensitive layer as in the case of the photostatic means, and therefore, it is possible to prevent the generation of residual charges and maintain stable charging characteristics. On the other hand, even if only the voltage is applied by the charge eliminating brush, the generation of the exposure memory can be sufficiently suppressed if the specific photoconductor used in the present invention is used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these description content.

[Example 1]
1. Preparation of electrophotographic photoreceptor 3 parts by weight of metal-free phthalocyanine represented by formula (4) having an ionization potential of 5.15 eV and 45 parts by weight of hole transport agent (HTM-A) represented by formula (5) And 30 parts by weight of an electron transfer agent (ETM-C) represented by formula (12) and a Z-type polycarbonate represented by formula (14) having a viscosity average molecular weight of 20,000 as a binder resin (Resin- A) 100 parts by weight (manufactured by Teijin Chemicals Ltd., TS2020) was mixed and dispersed with 800 parts by weight of tetrahydrofuran using a ball mill for 50 hours to prepare a coating solution for a photosensitive layer.
Next, this photosensitive layer coating solution was applied by dip coating to an aluminum drum-shaped support having a diameter of 30 mm and a total length of 254 mm as a conductive substrate. Thereafter, it was dried with hot air at 100 ° C. for 40 minutes to prepare an electrophotographic photosensitive member having a single-layer type photosensitive layer having a film thickness of 2.5 × 10 ⁻⁵ m.

2. Ionization potential measurement In addition, each ionization potential in the metal-free phthalocyanine and the hole transport agent used was measured using an atmospheric-type ultraviolet photoelectron analyzer (manufactured by Riken Keiki Co., Ltd., AC-1). The results obtained are shown in Table 1.

3. Evaluation of Electrophotographic Photoreceptor (1) Image Evaluation In addition, evaluation of an exposure memory image when an image was formed using the obtained electrophotographic photosensitive member was performed under the following conditions.
That is, the obtained electrophotographic photosensitive member was mounted on a printer (a modified machine of the laser beam printer FS1050 manufactured by Kyocera Mita Co., Ltd.) in which a static elimination lamp was omitted, and a printing test was performed. In such a printing test, it was determined whether or not an exposure memory image was visually generated after printing 1,000 originals of 5% density text. More specifically, in the printing test, an original as shown in FIG. 4 was used, and it was determined whether a ghost image of a solid black portion was generated in the gray portion. Moreover, this judgment result was evaluated according to the following criteria. The obtained results are shown in Table 1.
A: Memory image is not observed.
○: A slight memory image is observed.
Δ: A memory image is observed.
X: A memory image is observed remarkably.

(2) Surface potential The surface potential of the obtained electrophotographic photosensitive member was measured under the following conditions.
That is, the obtained electrophotographic photosensitive member is mounted on an image forming apparatus (a modified machine of the laser beam printer FS1050 manufactured by Kyocera Mita Co., Ltd.) equipped with a charging roller, and the electrophotographic photosensitive member is developed at the developing position. A surface potential measuring device was installed on the surface of the body. Next, the electrophotographic photosensitive member is rotated at a peripheral speed of 80 mm / second, and a DC voltage 450 V and an AC voltage (frequency 700 Hz) are superimposed and applied between the surface of the photosensitive member and the charging roller, and the peak-to-peak voltage is set. It was changed to 1800 to 2000V. Then, the minimum surface potential (V) under the charging environment was measured as the surface potential (V) of the photoreceptor. The obtained results are shown in Table 1.

(3) Measurement of exposure memory potential The exposure memory potential of the obtained electrophotographic photosensitive member was measured under the following conditions.
That is, the obtained electrophotographic photosensitive member was mounted on an image forming apparatus (a modified machine of a laser beam printer FS1050 manufactured by Kyocera Mita Co., Ltd.) in which a charging roller is mounted and a charge eliminating lamp is omitted. Next, after printing a 5% density character original on 1,000 sheets, the surface potential of the unexposed portion (corresponding to the blank portion of the formed image) and the exposed portion (corresponding to the solid black portion of the formed image) after the charging process are performed. The potential was measured, and the difference was evaluated as an exposure memory potential according to the following criteria. The obtained results are shown in Table 1.
A: Memory potential is less than 30 (V).
A: The memory potential is a value less than 30 to 50 (V).
X: Memory potential is a value of 50 (V) or more.

[Examples 2 to 5]
In Examples 2 to 5, when producing the photoconductor, the hole transporting agents (HTM-B to E) represented by the formulas (6) to (9) were used, respectively. Similarly, a photoreceptor was prepared and evaluated. The obtained results are shown in Table 1.

[Comparative Examples 1-3]
In Comparative Examples 1 to 3, in place of the hole transport agent (HTM-A) used in Example 1, hole transport agents (HTM-F to FH) represented by the following formulas (15) to (17), respectively. A photoconductor was prepared and evaluated in the same manner as in Example 1 except that H) was used. The obtained results are shown in Table 1.

-Means that the surface potential was low and the exposure memory could not be measured

According to the positively charged single layer type electrophotographic photosensitive member used in the contact charging type image forming apparatus and the image forming apparatus using the same according to the present invention, the ionization potential of the hole transport agent and the ionization potential of the charge generation agent The exposure memory is erased and charging unevenness occurs by setting the surface potential when the DC voltage and the AC voltage are superimposed when the contact charging is performed to a value within a predetermined range. Can be suppressed. As a result, it is possible to provide a positively charged single layer type electrophotographic photosensitive member that can be stably charged and a contact charging type image forming apparatus even when a system without a photostatic charge is employed.
Therefore, the positively charged single layer type electrophotographic photoreceptor of the present invention and the image forming apparatus using the same are expected to contribute to further miniaturization, higher image quality, higher speed, and the like.

It is a figure provided in order to demonstrate the charging characteristic of a positively charged single layer type photoreceptor. (A)-(c) is a figure provided in order to demonstrate the structure of a single layer type photoreceptor. 1 is a diagram for explaining an image forming apparatus according to the present invention. It is a figure provided in order to demonstrate a memory image.

Explanation of symbols

11: Single layer type photoreceptor 11 ′: Single layer type photoreceptor 11 ″: Single layer type photoreceptor 11b: Substrate 11a: Photosensitive layer 11c: Barrier layer 11d: Protective layer 100: Image forming apparatus 102: Static elimination means 104: Static elimination brush 111: Electrophotographic photosensitive member 112: Charging means 113: Exposure means 114: Development means 115: Transfer means 117: Cleaning device 120: Recording paper

Claims (6)

A positively charged single layer type electrophotographic photosensitive member applied to an image forming apparatus provided with a charging means of a contact charging method,
On the substrate, at least a charge generating agent, a hole transport agent, an electron transport agent, and a binder resin,
When the ionization potential of the hole transport agent is IP1 (eV) and the ionization potential of the charge generator is IP2 (eV), the numerical value represented by IP1-IP2 is 0.1 to 0.4 (eV). ) Within the range of
A positively charged single layer type electrophotographic photosensitive member characterized in that a surface potential at the time of superimposing a DC voltage and an AC voltage at the time of contact charging in the positively charged single layer type electrophotographic photosensitive member is set to a value of 300 V or more.   2. The positively charged single layer type electrophotographic photosensitive member according to claim 1, wherein metal-free phthalocyanine is used as the charge generating agent. 3. The positively charged single layer type electrophotographic photosensitive member according to claim 1, wherein the hole transport agent is at least one of compounds represented by the following general formulas (1) to (3). .

(In General Formula (1), R ^{a1 to} R ^a4 are an alkyl group, an alkoxy group that may have a substituent, a halogen atom, or a hydrogen atom, and at least one of R ^{a1 to} R ^a4 has 3 carbon atoms. These are the above alkyl groups or alkoxy having 3 or more carbon atoms.)

(In General Formula (2), R ^{b1 to} R ^b5 are an alkyl group, an alkoxy group that may have a substituent, a halogen atom, or a hydrogen atom, and at least one of R ^{b1 to} R ^b5 has 3 carbon atoms. These are the above alkyl groups or alkoxy having 3 or more carbon atoms.)

(In General Formula (3), R ^{c1 to} R ^c6 are an alkyl group, an alkoxy group which may have a substituent, a halogen atom, or a hydrogen atom, and at least one of R ^{c1 to} R ^c6 has 3 carbon atoms. These are the above alkyl groups or alkoxy having 3 or more carbon atoms.) In an image forming apparatus in which a contact charging type charging unit, a developing unit, and a transfer unit are sequentially arranged around a positively charged single layer type electrophotographic photosensitive member.
The positively charged single-layer type electrophotographic photoreceptor includes, on a substrate, at least a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin.
When the ionization potential of the hole transport agent is IP1 (eV) and the ionization potential of the charge generator is IP2 (eV), the numerical value represented by IP1-IP2 is 0.1 to 0.4 (eV). ) Within the range of
An image forming apparatus, wherein a surface potential at the time of superimposing a DC voltage and an AC voltage at the time of contact charging in the positively charged single layer type electrophotographic photosensitive member is set to a value of 300 V or more.   5. The image forming apparatus according to claim 4, wherein an optical charge eliminating unit is not used as the charge eliminating unit in the image forming apparatus.   The image forming apparatus according to claim 5, further comprising a neutralizing brush as the neutralizing unit.