JP5885446B2 - Positively charged single layer type electrophotographic photosensitive member and image forming apparatus - Google Patents

Description

  The present invention relates to a positively charged single layer type electrophotographic photosensitive member and an image forming apparatus.

  As an electrophotographic photoreceptor provided in an electrophotographic image forming apparatus, an inorganic photoreceptor having a photosensitive layer made of an inorganic material such as selenium or amorphous silicon, and mainly a binder resin, a charge generator, a charge transport agent, etc. And an organic photoreceptor having a photosensitive layer made of any of the above organic materials. Among these photoreceptors, organic photoreceptors are widely used because they are easier to manufacture than inorganic photoreceptors, and the material of the photosensitive layer can be selected from a wide range of materials, and the degree of freedom in design is high. Yes.

  Examples of such an organic photoreceptor include a single layer type organic photoreceptor having a photosensitive layer containing a charge generating agent and a charge transporting agent in the same layer. The single layer type organic photoconductor has a simple structure compared to a laminated type organic photoconductor in which a charge generation layer containing at least a charge generation agent and a charge transfer layer containing a charge transfer agent are laminated on a conductive substrate. Therefore, its use is progressing because it is easy to manufacture.

  In addition, it is known that when a positive charging method is employed as a charging method for an electrophotographic photosensitive member in an image forming apparatus, there is little generation of oxidizing gas such as ozone during charging. For this reason, in consideration of adverse effects on the life of the photoreceptor and the office environment due to the release of the oxidizing gas, a positive charging system is often employed as the charging system for the electrophotographic photoreceptor of the image forming apparatus. Combined with the advantages of the layer type, the use of positively charged single layer type electrophotographic photoreceptors is progressing.

  Further, the image forming apparatus can simplify the configuration of the image forming apparatus. Therefore, the image forming apparatus does not include a neutralization unit for neutralizing the surface of the electrophotographic photosensitive member (image carrier) by the neutralizing light, and is a so-called static elimination-less image. The use of a forming apparatus has been studied, and the use of a positively charged single-layer type electrophotographic photosensitive member in a static elimination-less image forming apparatus has also been proposed (see Patent Document 1).

JP 2010-113336 A

  However, in a static elimination-less type image forming apparatus, when a transfer method is a method in which a toner image formed on the surface of an image carrier such as a photosensitive drum is directly transferred to a recording medium, a positively charged single layer type When an electrophotographic photosensitive member is used, there is a problem that an image defect called white streak is likely to occur in a formed image in which a portion having a low image density is streaked.

  In a direct transfer type image forming apparatus, an electrophotographic photosensitive member (image carrier) and a transfer roller to which a transfer bias is applied are in contact with each other via a transfer belt that conveys a recording medium. The recording medium is conveyed by the transfer belt between the transfer roller to which the transfer bias is applied and the electrophotographic photosensitive member (image carrier), so that the toner image formed on the surface of the electrophotographic photosensitive member is formed. It is transferred to a recording medium.

  However, in the direct transfer type image forming apparatus, as shown in FIG. 1, when a recording medium such as paper comes into contact with the electrophotographic photosensitive member at the start of transfer, the transfer belt, the electrophotographic photosensitive member, A gap is generated between the transfer roller and the amount of current flowing from the transfer roller to the surface of the photoconductor is instantaneously reduced. For this reason, in a direct transfer type image forming apparatus, after transfer, a streaky high potential portion having a higher potential than the surroundings is formed on the surface of the electrophotographic photosensitive member.

  In the case of an image forming apparatus including a charge removal unit, the high potential portion is erased by a charge removal process performed by the charge removal unit. However, in a static elimination-less image forming apparatus, the potential difference between the high potential portion and the surrounding area is maintained in the charging process and the exposure process subsequent to the transfer process, which causes white streaks in the image.

  The present invention has been made in view of such circumstances, and can suppress the occurrence of white streaks in a formed image that is used as an image carrier in an image forming apparatus of a direct transfer type that does not include a charge eliminating portion. An object is to provide a positively charged single layer type electrophotographic photosensitive member. Another object of the present invention is to provide an image forming apparatus provided with the above positively charged single layer type electrophotographic photosensitive member as an image carrier.

  The present inventors provide at least a charging unit, an exposure unit, a developing unit, and a transfer unit in this order with respect to the rotation direction of the image carrier around the image carrier, and a direct transfer system that does not include a charge eliminating unit. In the positively charged single-layer type electrophotographic photosensitive member used as the image carrier in the image forming apparatus, the mass ratio (A) of the hole transport agent (A) and the electron transport agent (B) contained in the photosensitive layer The inventors have found that the above problem can be solved by setting / (B) within a certain range, and have completed the present invention. Specifically, the present invention provides the following.

  (1) A direct transfer type image in which at least a charging portion, an exposure portion, a developing portion, and a transfer portion are provided in this order with respect to the rotation direction of the image carrier, and no charge eliminating portion is provided around the image carrier. In a forming apparatus, a positively charged single layer type electrophotographic photosensitive member used as the image carrier, wherein the positively charged single layer type electrophotographic photosensitive member has at least a charge generating agent and a hole on a conductive substrate. A photosensitive layer having a single layer structure including a transport agent (A), an electron transport agent (B), and a binder resin is formed. In the photosensitive layer, the hole transport agent (A) and the electron transport agent (B A positively charged single layer type electrophotographic photosensitive member having a mass ratio (A) / (B) to 2.2 to 5.0.

(2) The drift mobility of the hole transport agent (A) is 1.0 × 10 ⁻⁶ cm ² / V · sec or more, and the drift mobility of the electron transport agent (B) is 2.0. ^{X10 −8} cm ² / V · sec or more, and the drift mobility is 30 masses of the hole transport agent (A) or the electron transport agent (B) formed on an aluminum substrate. % And a 5 μm thick film of a polycarbonate resin composition consisting of bisphenol Z-type polycarbonate resin having a viscosity average molecular weight of 50,000 and a thickness of 23 μm, electric field strength of 3.0 × 10 ⁵ V / The positively charged single-layer type electrophotographic photosensitive member according to (1), which is a value measured under conditions of cm.

(3) The positively charged single layer type electron according to (1) or (2), wherein the ratio of the mass of the charge generating agent to the mass of the electron transport agent (B) in the photosensitive layer is 12% by mass or less. Photoconductor.

  (4) An electrostatic latent image is formed on the surface of the image carrier by exposing the image carrier, a charging unit for charging the surface of the image carrier, and the charged surface of the image carrier. An exposure unit for developing the electrostatic latent image as a toner image, and a transfer belt for transporting the recording medium to transfer the toner image from the image carrier to the recording medium. A positively-charged single-layer electron according to any one of (1) to (3), wherein the image carrier is not provided with a charge eliminating unit for eliminating the charge on the surface of the image carrier with static elimination light. An image forming apparatus characterized by being a photographic photoreceptor.

  (5) The image forming apparatus according to (4), wherein the charging unit is a contact charging method.

  According to the present invention, in a direct transfer type image forming apparatus that includes at least a charging unit, an exposure unit, a developing unit, and a fixing unit, and that does not include a neutralization unit, white in a formed image is used. It is possible to provide a positively charged single layer type electrophotographic photosensitive member capable of suppressing the generation of stripes and an image forming apparatus capable of suppressing the generation of white stripes in a formed image.

It is a schematic diagram of a transfer process in a direct transfer type image forming apparatus. 1 is a schematic cross-sectional view showing the structure of a positively charged single layer type electrophotographic photosensitive member according to an embodiment of the present invention. 1 is a schematic diagram illustrating a configuration of an image forming apparatus including a positively charged single layer type electrophotographic photosensitive member according to an embodiment of the present invention. FIG. 3 is a schematic diagram of a drum testing machine used for evaluation of a photoreceptor in Examples.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. . In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the summary of invention is not limited.

[First Embodiment]
In the first embodiment, an image carrier is provided in a direct transfer type image forming apparatus that includes at least a charging unit, an exposure unit, a developing unit, and a transfer unit in this order around the image carrier, and does not include a charge eliminating unit. The present invention relates to a positively charged single layer type electrophotographic photosensitive member used as a photosensitive member. Specifically, the positively charged single layer type electrophotographic photosensitive member according to the first embodiment includes at least a charge generating agent, a hole transporting agent (A), an electron transporting agent (B), and a conductive substrate. A photosensitive layer having a single layer structure containing a binder resin is formed, and the mass ratio (A) / (B) of the hole transport agent (A) to the electron transport agent (B) in the photosensitive layer is 2.2 to The present invention relates to a positively charged single layer type electrophotographic photosensitive member of 5.0.

  As shown in FIG. 2, the positively charged single layer type electrophotographic photoreceptor 10 of the present invention includes a conductive substrate 12, a charge generating agent, a hole transport agent (A) formed on the conductive substrate 12, An electron transfer agent (B) and a single photosensitive layer 14 containing a binder resin are provided. The positively charged single layer type electrophotographic photoreceptor 10 is not particularly limited as long as it includes the conductive substrate 12 and the photosensitive layer 14. Specifically, for example, as shown in FIG. 2A, the photosensitive layer 14 may be provided directly on the conductive substrate 12, or as shown in FIG. An intermediate layer 16 may be provided between the photosensitive layer 14 and the photosensitive layer 14. Further, as shown in FIG. 2A and FIG. 2B, the photosensitive layer 14 may be exposed as an outermost layer, or as shown in FIG. A protective layer 18 may be provided.

  Hereinafter, the conductive substrate and the photosensitive layer will be described in order.

[Conductive substrate]
The conductive substrate is not particularly limited as long as it can be used as a conductive substrate of a positively charged single layer type electrophotographic photosensitive member. Specifically, for example, a material having at least a surface portion made of a conductive material can be used. Specifically, for example, it may be made of a conductive material, or may be a plastic material or the like whose surface is covered with a conductive material. Examples of the conductive material include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass. Moreover, as a material which has electroconductivity, the material which has electroconductivity may be used by 1 type, and may be used as an alloy etc., for example, combining 2 or more types. Further, among the above, the conductive substrate is preferably made of aluminum or an aluminum alloy. By doing so, a positively charged single layer type electrophotographic photosensitive member capable of forming a more suitable image can be provided. This is considered to be due to good charge transfer from the photosensitive layer to the conductive substrate.

  The shape of the conductive substrate can be appropriately selected according to the structure of the image forming apparatus to be used. For example, a sheet-like or drum-like substrate can be suitably used.

(Photosensitive layer)
The photosensitive layer provided in the positively charged single layer type electrophotographic photosensitive member can be used as a photosensitive layer of the positively charged single layer type electrophotographic photosensitive member, and includes at least a charge generating agent, a hole transporting agent (A), and an electron transporting agent. (B) and a photosensitive layer having a single layer structure made of a binder resin, and the mass ratio (A) / (B) of the hole transport agent (A) to the electron transport agent (B) in the photosensitive layer is 2 If it is 2-5.0, it will not specifically limit.

(Charge generator)
The charge generating agent is not particularly limited as long as it can be used as a charge generating agent for a positively charged single layer type electrophotographic photosensitive member. Specifically, for example, X-type metal-free phthalocyanine (x-H2Pc), Y-type oxotitanyl phthalocyanine (Y-TiOPc) represented by the following formula (I), perylene pigment, bisazo pigment, dithioketopyrrolopyrrole pigment, Powders of inorganic photoconductive materials such as metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, trisazo pigments, indigo pigments, azurenium pigments, cyanine pigments, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, and amorphous silicon , Pyrylium salts, ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments, and the like.

  Moreover, a charge generation agent may be used independently so that it may have an absorption wavelength in a desired area | region, and may be used in combination of 2 or more type. Further, among the above-mentioned charge generating agents, in particular, in a digital optical image forming apparatus such as a laser beam printer or a facsimile using a light source such as a semiconductor laser, a positively charged single layer having sensitivity in a wavelength region of 700 nm or more Since a type electrophotographic photoreceptor is required, for example, phthalocyanine pigments such as metal-free phthalocyanine and oxotitanyl phthalocyanine are preferably used. The crystal form of the phthalocyanine pigment is not particularly limited, and various types can be used. In addition, an image forming apparatus of an analog optical system such as an electrostatic copying machine using a white light source such as a halogen lamp needs a positively charged single layer type electrophotographic photosensitive member having sensitivity in the visible region. For example, perylene pigments and bisazo pigments are preferably used.

(Hole transport agent (A))
The hole transport agent (A) used in the present invention can be appropriately selected from hole transport agents (A) conventionally used in positively charged single layer type electrophotographic photoreceptors. Examples of the hole transport agent (A) conventionally used in the photosensitive layer of a positively charged single-layer type electrophotographic photoreceptor include, for example, benzidine derivatives, oxadiazole compounds, styryl compounds, carbazole compounds, and organic polysilane compounds. , Pyrazoline compounds, hydrazone compounds, triphenylamine compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, triazole compounds, etc. Examples thereof include nitrogen cyclic compounds and condensed polycyclic compounds. Among these compounds used as the hole transport agent (A), styryl compounds, triphenylamine compounds, and hydrazone compounds are more preferable.

The hole transporting agent (A) used in the present invention, the drift mobility are measured according to the following method, it is preferably at ^{1.0 × 10 -6 cm 2 / V} · sec or more, 5.0 × 10 ^- More preferably, it is ⁶ cm ² / V · sec or more. The drift mobility of the hole transport agent (A) can be measured according to the following method.

<Drift mobility measurement method>
A bisphenol Z-type polycarbonate resin having a viscosity average molecular weight of 50,000 and a hole transport agent (A) of 30% by mass with respect to the total mass of the sample are added to an organic solvent, and the polycarbonate resin and the hole transport agent (A ) Is dissolved to prepare a coating solution. The obtained coating solution was applied onto a substrate made of aluminum, subjected to heat treatment at 80 ° C. for 30 minutes, and the solvent was removed to form a 7 μm thick coating film. Next, a semi-transparent gold electrode was formed on the coating film by a vacuum deposition method to obtain a measurement sample. Using the obtained sample, the drift mobility is measured according to the TOF (Time of Flight) method under the conditions of a temperature of 23 ° C. and an electric field strength of 3.0 × 10 ⁵ V / cm.

The viscosity average molecular weight [M] of the polycarbonate resin can be calculated from [η] = 1.23 × 10 ⁻⁴ M ^{0.83 according} to Schnell's equation, by obtaining the intrinsic viscosity [η] with an Ostwald viscometer. [Η] can be measured using a polycarbonate resin solution obtained by dissolving a polycarbonate resin at 20 ° C. using methylene chloride as a solvent so that the concentration becomes 6.0 g / dm ³ .

(Electron transfer agent (B))
The electron transfer agent (B) is not particularly limited as long as it can be used as the electron transfer agent (B) contained in the photosensitive layer of the positively charged single layer type electrophotographic photosensitive member. Specifically, for example, quinone derivatives such as naphthoquinone derivatives, diphenoquinone derivatives, anthraquinone derivatives, azoquinone derivatives, nitroantharaquinone derivatives, dinitroanthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, trinitrothioxanthone derivatives, 3, 4, 5, 7-tetranitro-9-fluorenone derivative, dinitroanthracene derivative, dinitroacridine derivative, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, succinic anhydride, maleic anhydride, dibromoanhydride And maleic acid. An electron transfer agent (B) may be used independently and may be used in combination of 2 or more type.

The electron transport agent (B) used in the present invention preferably has a drift mobility of 2.0 × 10 ⁻⁸ cm ² / V · sec or more according to the following method, and is 1.2 × 10 ^−7. More preferably, it is cm ² / V · sec or more. The drift mobility of the electron transfer agent (B) can be measured by the same method as that for the hole transfer agent (A).

(Binder resin)
The binder resin is not particularly limited as long as it can be used as a binder resin contained in the photosensitive layer of the positively charged single layer type electrophotographic photosensitive member. Specific examples of the resin suitably used as the binder resin include polycarbonate resin, styrene resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-acrylic acid copolymer. Polymer, acrylic copolymer, polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer, vinyl chloride-vinyl acetate copolymer, polyester resin, alkyd resin, polyamide resin , Polyurethane resins, polycarbonate resins, polyarylate resins, polysulfone resins, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, polyether resins, polyester resins, etc .; silicone resins, epoxy resins Phenolic resins, urea resins, melamine resins, thermosetting resins such as other crosslinking thermosetting resins, epoxy acrylate resins, urethane - include photocurable resins such as acrylate copolymer resin. These resins may be used alone or in combination of two or more.

  Among these resins, a photosensitive layer having a good balance of processability, mechanical properties, optical properties, and abrasion resistance can be obtained. Therefore, bisphenol Z-type polycarbonate resins, bisphenol ZC-type polycarbonate resins, and bisphenol C-type polycarbonates are obtained. A resin and a polycarbonate resin such as a bisphenol A type polycarbonate resin are more preferable.

(Additive)
The photosensitive layer of the positively charged single-layer type electrophotographic photosensitive member is in addition to the charge generating agent, the hole transporting agent (A), the electron transporting agent (B), and the binder resin as long as the electrophotographic characteristics are not adversely affected. Various additives may be included. Additives that can be incorporated into the photosensitive layer include, for example, antioxidants, radical scavengers, singlet quenchers, UV absorbers and other deterioration inhibitors, softeners, plasticizers, surface modifiers, extenders, Examples thereof include a sticking agent, a dispersion stabilizer, a wax, an acceptor, a donor, a surfactant, and a leveling agent.

(Method for producing positively charged single layer type electrophotographic photoreceptor)
The method for producing the positively charged single layer type electrophotographic photosensitive member is not particularly limited as long as the object of the present invention is not impaired. A preferred example of a method for producing a positively charged single layer type electrophotographic photosensitive member includes a method of forming a photosensitive layer by applying a coating solution for a photosensitive layer on a conductive substrate. Specifically, a conductive substrate is obtained by dissolving or dispersing a charge generating agent, a hole transporting agent (A), an electron transporting agent (B), a binder resin, and various additives as required in a solvent. A photosensitive layer can be produced by applying the solution on the substrate and drying it. The application method is not particularly limited, and examples thereof include a method using a spin coater, applicator, spray coater, bar coater, dip coater, doctor blade and the like. Moreover, as a drying method of the coating film formed on the electroconductive base | substrate, the method of hot-air drying etc. on the conditions for 15 to 120 minutes at 80-150 degreeC are mentioned, for example.

  In the positively charged single layer type electrophotographic photosensitive member, the hole transport agent (A) and the electron transport agent (B) are the masses of the hole transport agent (A) and the electron transport agent (B) in the photosensitive layer. It is used so that ratio (A) / (B) may be 2.2-5.0. Specifically, the content of the hole transporting agent (A) is preferably 5 to 500 parts by mass and more preferably 25 to 200 parts by mass with respect to 100 parts by mass of the binder resin. An electron transfer agent (B) is used so that it may become the said ratio with respect to the usage-amount of a hole transfer agent (A).

  The content of the charge generating agent in the photosensitive layer is not particularly limited as long as the object of the present invention is not impaired. The content of the charge generating agent is preferably 0.1 to 50 parts by mass and more preferably 0.5 to 30 parts by mass with respect to 100 parts by mass of the binder resin. Moreover, it is preferable that it is 12 mass% or less with respect to the usage-amount of an electron transport agent (B), and, as for the usage-amount of a charge generating agent, it is more preferable that it is 7-12 mass%. When the charge generating agent is used in such a ratio with respect to the amount of the electron transporting agent (B) used, even when images are formed repeatedly, the surface potential of the photoreceptor is hardly increased, and a good image is formed over a long period of time. Cheap.

  Furthermore, the total amount of the hole transport agent (A) and the electron transport agent (B), that is, the content of the charge transport agent is preferably 20 to 500 parts by mass with respect to 100 parts by mass of the binder resin. It is more preferable that it is 30-200 mass parts.

  The thickness of the photosensitive layer of the positively charged single layer type electrophotographic photosensitive member is not particularly limited as long as it can sufficiently function as the photosensitive layer. Specifically, for example, 5 to 100 μm is preferable, and 10 to 50 μm is preferable.

  The solvent contained in the coating solution for the photosensitive layer is not particularly limited as long as each component constituting the photosensitive layer can be dissolved or dispersed. Specifically, alcohols such as methanol, ethanol, isopropanol and butanol; aliphatic hydrocarbons such as n-hexane, octane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; dichloromethane, dichloroethane and tetrachloride Halogenated hydrocarbons such as carbon and chlorobenzene; ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as ethyl acetate and methyl acetate Aprotic polar organic solvents such as dimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide. These solvents may be used alone or in combination of two or more.

  As described above, the positively charged single layer type electrophotographic photosensitive member according to the first embodiment includes at least a charging unit, an exposure unit, a developing unit, and a transfer unit around the image carrier in the rotation direction of the image carrier. On the other hand, it is used as an image carrier in an image forming apparatus of a direct transfer type that is provided in this order and does not have a charge eliminating portion. In the above-described image forming apparatus, white stripes are likely to occur in the formed image. However, by using the positively charged single layer type electrophotographic photosensitive member according to the first embodiment as an image carrier, white stripes are generated in the formed image. Can be suppressed.

[Second Embodiment]
In the second embodiment, an electrostatic latent image is formed on the surface of the image carrier by exposing the surface of the image carrier, the charging unit for charging the surface of the image carrier, and the surface of the charged image carrier. An exposure unit for developing the electrostatic latent image as a toner image, and a transfer unit for transferring the recording medium from the image carrier to the recording medium by conveying the recording medium by a transfer belt. And an image forming apparatus using the positively charged single-layer type electrophotographic photosensitive member according to the first embodiment as an image carrier without a neutralization unit for neutralizing the surface of the image carrier with static elimination light.

  The image forming apparatus of the present invention is preferably a tandem color image forming apparatus using a plurality of colors of toner as described later. Here, a tandem color image forming apparatus will be described.

  The image forming apparatus including the positively charged single layer type electrophotographic photosensitive member according to the present embodiment is arranged in parallel in a predetermined direction in order to form toner images with different colors of toner on each surface. A plurality of image carriers, and a developing roller that is arranged opposite to each image carrier, carries toner on the surface and conveys the toner, and supplies the conveyed toner to the surface of each image carrier. The positively charged single layer type electrophotographic photosensitive member according to the first embodiment is used as each image carrier.

  FIG. 3 is a schematic view showing a configuration of an image forming apparatus provided with a positively charged single layer type electrophotographic photosensitive member according to an embodiment of the present invention. Here, the color printer 1 will be described as an example of the image forming apparatus.

  As shown in FIG. 3, the color printer 1 has a box-shaped device body 1a. In the apparatus main body 1a, a toner image based on image data and the like is transferred to the paper P while feeding the paper P fed from the paper feeding unit 2 and the paper P fed from the paper feeding unit 2. An image forming unit 3 and a fixing unit 4 for performing a fixing process for fixing the unfixed toner image transferred onto the paper P by the image forming unit 3 to the paper P are provided. Further, on the upper surface of the apparatus main body 1a, a paper discharge unit 5 for discharging the paper P subjected to the fixing process by the fixing unit 4 is provided.

  The paper feed unit 2 includes a paper feed cassette 121, a pickup roller 122, paper feed rollers 123 and 124, and a registration roller 125. The paper feed cassette 121 is provided so as to be detachable from the apparatus main body 1a, and stores the paper P of each size. The pickup roller 122 is provided at the upper left position of the paper feed cassette 121 shown in FIG. 3 and takes out the paper P stored in the paper feed cassette 121 one by one. The paper feed rollers 123 and 124 send out the paper P taken out by the pickup roller 122 to the paper transport path. The registration roller 125 temporarily waits for the paper P sent to the paper transport path by the paper feed rollers 123 and 124 and then supplies the paper P to the image forming unit 3 at a predetermined timing.

  The paper feeding unit 2 further includes a manual feed tray (not shown), a pickup roller, and a paper feeding roller that are attached to the left side surface of the device main body 1a shown in FIG. This pickup roller takes out the paper P placed on the manual feed tray. The paper P taken out by the pickup roller is sent out to the paper transport path by the paper feed roller, and is supplied to the image forming unit 3 by the registration roller 126 at a predetermined timing.

  The image forming unit 7 includes a black unit 7K, a yellow unit 7Y, a cyan unit 7C, and a magenta unit 7M which are sequentially arranged from the upstream side (left side in FIG. 3) to the downstream side. ing. Each of the units 7K, 7Y, 7C and 7M has a positively charged single layer type electrophotographic photosensitive member 37 (hereinafter referred to as a photosensitive member 37) as an image carrier capable of rotating in the direction of an arrow (clockwise) at the center position. Has been placed. Around each photoconductor 37, a charging unit 39, an exposure unit 38, a developing unit 71, and a cleaning unit (not shown) are sequentially arranged from the upstream side in the rotation direction. As the photoreceptor 37, the positively charged single layer type electrophotographic photoreceptor according to the first embodiment is used. In addition, since the image forming apparatus according to the second embodiment has a structure without static elimination, the color printer 1 does not include a static elimination unit around the photoreceptor 37.

  The charging unit 39 uniformly charges the peripheral surface of the electrophotographic photosensitive member 37 rotated in the direction of the arrow. The charging unit 39 is not particularly limited as long as the peripheral surface of the electrophotographic photosensitive member 37 can be uniformly charged, and may be a non-contact type or a contact type. Specific examples of the charging unit include a corona charging device, a charging roller, and a charging brush, and a contact-type charging device such as a charging roller and a charging brush is more preferable. By using the contact type charging unit 39, the discharge of the active gas such as ozone and nitrogen oxide generated from the charging unit 39 is suppressed, and the photosensitive layer of the electrophotographic photosensitive member is prevented from being deteriorated by the active gas. Designed with the environment in mind.

  When the charging unit 39 includes a contact type charging roller, the charging roller is not particularly limited as long as it can charge the peripheral surface (surface) of the electrophotographic photosensitive member 37 while being in contact with the electrophotographic photosensitive member 37. Examples of the charging roller include a roller that rotates while depending on the rotation of the electrophotographic photosensitive member 37 while being in contact with the electrophotographic photosensitive member 37. Moreover, as a charging roller, the roller etc. which the surface part was comprised with resin at least are mentioned, for example. More specifically, for example, a core metal that is rotatably supported, a resin layer formed on the metal core, and a voltage application unit that applies a voltage to the metal core may be used. The charging unit including such a charging roller can charge the surface of the electrophotographic photosensitive member 37 that is in contact with the cored bar by applying a voltage to the cored bar by the voltage applying unit.

  The resin constituting the resin layer of the charging roller is not particularly limited as long as the peripheral surface of the electrophotographic photoreceptor 37 can be charged satisfactorily. Specific examples of the resin used for the resin layer include a silicone resin, a urethane resin, and a silicone-modified resin. Further, the resin layer may contain an inorganic filler.

  The voltage applied to the charging roller by the voltage application unit is preferably only a DC voltage. The DC voltage applied to the electrophotographic photosensitive member by the charging roller is preferably 1000 to 2000V, more preferably 1200 to 1800V, and particularly preferably 1400 to 1600V. The amount of abrasion of the photosensitive layer tends to be smaller when only the DC voltage is applied to the charging roller than when the AC voltage or the superimposed voltage obtained by superimposing the AC voltage on the DC voltage is applied to the charging roller.

  The exposure unit 38 is a so-called laser scanning unit, and irradiates the peripheral surface of the photoreceptor 37 uniformly charged by the charging unit 39 with laser light based on image data input from a personal computer (PC) as a host device. Then, an electrostatic latent image based on the image data is formed on the photoreceptor 37. The developing unit 71 supplies toner to the circumferential surface of the photoreceptor 37 on which the electrostatic latent image is formed, thereby forming a toner image based on the image data. Then, this toner image is transferred to the paper P conveyed by the transfer belt 31. The cleaning unit cleans the toner remaining on the peripheral surface of the photoconductor 37 after the transfer of the toner image onto the paper P is completed. The peripheral surface of the photoreceptor 37 cleaned by the cleaning unit is directed to the charging unit for a new charging process, and a new charging process is performed.

  The transfer belt 31 is an endless belt-like rotating body, and includes a driving roller 33, a driven roller 34, a backup roller 35, and a surface (contact surface) side so as to be in contact with the peripheral surface of each electrophotographic photoreceptor 37. It is stretched over a plurality of rollers such as a transfer roller 36. The transfer belt 31 is configured to rotate endlessly by a plurality of rollers while being pressed against the electrophotographic photosensitive member 37 by a transfer roller 36 disposed opposite to each electrophotographic photosensitive member 37. The driving roller 33 is rotationally driven by a driving source such as a stepping motor, and gives a driving force for rotating the transfer belt 31 endlessly. The driven roller 34, the backup roller 35, and the transfer roller 36 are rotatably provided, and are driven to rotate with the endless rotation of the transfer belt 31 by the driving roller 33. These rollers 34, 35, 36 are driven to rotate via the transfer belt 31 according to the main rotation of the drive roller 33 and support the transfer belt 31. The sheet P supplied from the registration roller 125 is adsorbed on the transfer belt 31 by the adsorption roller 126, and the sheet P adsorbed on the transfer belt is transferred to each photoconductor 37, the transfer roller 36 and the transfer belt 31. Pass between.

The transfer roller 36 applies a transfer bias (a polarity opposite to the charging polarity of the toner) to the transfer belt 31. By doing so, the toner image formed on each photoconductor 37 is transferred between each photoconductor 37 and the transfer roller 36 in the direction of the arrow (clockwise) by driving the drive roller 33. The images are sequentially transferred onto the upper paper P in a state of overcoating. Thereafter, each photoconductor 37 is further rotated, and the process proceeds to the next process.

  The fixing unit 4 performs a fixing process on the transfer image transferred to the paper P by the image forming unit 3. The fixing unit 4 is disposed opposite to the heating roller 41 heated by the energized heating element and the heating roller 41. Is provided with a pressure roller 42 that is pressed against the peripheral surface of the heating roller 41.

  Then, the transfer image transferred to the paper P by the transfer roller 36 in the image forming unit 3 is fixed to the paper P by a fixing process by heating when the paper P passes between the heating roller 41 and the pressure roller 42. Is done. The paper P subjected to the fixing process is discharged to the paper discharge unit 5. Further, in the color printer 1 of the present embodiment, the transport roller 6 is disposed at an appropriate position between the fixing unit 4 and the paper discharge unit 5.

  The paper discharge unit 5 is formed by recessing the top of the device main body 1a of the color printer 1, and a paper discharge tray 51 for receiving the discharged paper P is formed at the bottom of the concave portion. .

  The color printer 1 forms an image on the paper P by the image forming operation as described above. The tandem type image forming apparatus as described above includes the positively charged single-layer type electrophotographic photosensitive member according to the first embodiment as an image carrier. Despite the device configuration in which white stripes are likely to occur, the occurrence of white stripes in the formed image can be suppressed.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

In Examples, Reference Examples, and Comparative Examples, HTM-A or HTM-B represented by the following formula is used as the hole transport agent (A), and ETM represented by the following formula is used as the electron transport agent (B). -A or ETM-b was used. The numerical value on the lower right of the structural formula is the drift mobility (unit: cm ² / V · sec).

[Hole transport agent (A)]

[Electron transfer agent (B)]

[ Reference Example 1]
2 parts by weight of metal-free phthalocyanine, 50 parts by weight of hole transport agent (HTM-A), 10 parts by weight of electron transport agent (ETM-a), 100 parts by weight of bisphenol Z-type polycarbonate resin having a viscosity average molecular weight of 50,000, and tetrahydrofuran 800 parts by mass was added to a ball mill and mixed and dispersed for 50 hours to prepare a coating solution for a photosensitive layer. The obtained coating solution is applied on a conductive substrate by a dip coating method, treated at 100 ° C. for 40 minutes to remove tetrahydrofuran from the coating film, and a positively charged single layer type electrophotographic film having a photosensitive layer with a thickness of 30 μm. A photoreceptor was obtained. Using the positively charged single layer type electrophotographic photosensitive member obtained in Reference Example 1, white stripes were evaluated and the surface potential of the photosensitive member after continuous printing was measured according to the following method. Table 1 shows the evaluation results of the positively charged single layer type electrophotographic photosensitive member of Reference Example 1.

<White stripe evaluation>
Using an image forming apparatus that is a static transfer-less and direct transfer system and includes a scorotron charger as a charging unit, an A4 size image formed at a print density of about 0.8 is visually observed to determine the degree of white streaks. The determination was made according to the following criteria. A practically acceptable determination is LV1.

(Criteria)
Level 1: White streaks are not observed in the formed image.
Level 2: Very pale white streaks are observed in the formed image.
Level 3: Pale white streaks are observed in the formed image.
Level 4: A clear white streak is observed in the formed image.

<Surface potential of photoconductor>
The surface potential of the positively charged single layer type electrophotographic photosensitive member was measured using the drum testing machine shown in FIG. The drum testing machine includes a charger 102 (a scorotron charger) that applies a positive voltage to the photoconductor 101 and a transfer charger 105 (a corotron charger) that applies a negative voltage to the photoconductor. In addition, the drum testing machine includes a light source 103 that exposes the photoconductor 101 adjacent to the charger 102 in a downstream direction with respect to the rotation direction of the photoconductor 101, and a potential measurement probe that measures the surface potential of the photoconductor 101. 104 in this order. In this drum tester, the positively charged single layer type electrophotographic photosensitive member of Reference Example 1 is set, and the photosensitive member 101 is rotated in a predetermined direction (clockwise in FIG. 4), and charging → exposure → transfer → charging. The test was repeated for 30 minutes, and the change in surface potential (ΔV ₀ (V)) obtained by subtracting the surface potential of the photoconductor after the continuous test for 30 minutes from the initial surface potential of the photoconductor was measured. In the drum tester, the applied voltage in the charging process is 800 V, the exposure amount in the exposure process is 1.0 μJ · cm ² , the applied voltage in the transfer process is −1.2 kV, and the peripheral speed of the photoconductor Was 100 mm / sec. The evaluation results are shown in Table 1. A case where the absolute value of ΔV ₀ was less than 20V was judged as ◯, and a case where the absolute value was 20V or more was judged as Δ.

[Examples 1-8 , Reference Examples 2-5, and Comparative Examples 1-8]
A positively charged single layer type electrophotographic photosensitive member is obtained in the same manner as in Reference Example 1 except that the types and amounts of the hole transport agent and electron transport agent are changed to the types and amounts shown in Table 1. It was. Using the obtained photoreceptor, as in Reference Example 1, white stripe evaluation, white stripe evaluation, and measurement of the surface potential of the photoreceptor after continuous printing were performed. Table 1 shows the evaluation results of the positively charged single layer type electrophotographic photosensitive members of Examples 1 to 8 , Reference Examples 2 to 5, and Comparative Examples 1 to 8.

According to Table 1, the photosensitive layer, the mass ratio of the hole transport agent (A) and the electron transporting agent (B) (A) / ( B) is 2.2 to 5.0, Example 1 When the image is formed by an image forming apparatus that uses the electrophotographic photoconductors of No. 8 and Reference Examples 1 to 5 and is a static transfer-less and direct transfer type, the white stripes are evaluated as LV1. It can be seen that the occurrence of is suppressed satisfactorily. In addition, according to Examples 1 to 8 and Reference Examples 1 to 5 , the hole transport agent (A) has a drift mobility of 1.0 × 10 ⁻⁶ cm ² / V · sec or more. By using the agent (A) and the electron transport agent (B) having a drift mobility of 2.0 × 10 ⁻⁸ cm ² / V · sec or more in a predetermined ratio, the generation of white streaks is improved. It can be seen that a positively charged single layer type electrophotographic photosensitive member can be obtained.

  On the other hand, Comparative Examples 1 to 8 in which the mass ratio (A) / (B) of the hole transport agent (A) and the electron transport agent (B) in the photosensitive layer is out of the range of 2.2 to 5.0. When an image is formed by an image forming apparatus that is a static transfer-less and direct transfer system using the electrophotographic photosensitive member of No. 1, the evaluation of white stripes is LV2 to LV4, and it can be seen that generation of white stripes cannot be suppressed.

For example, according to the comparison between Examples 1 and 2 and Reference Examples 1 and 2 , the ratio of the mass of the charge generating agent to the mass of the electron transporting agent (B) in the photosensitive layer is 12% by mass or less. Then, it can be seen that an electrophotographic photosensitive member can be obtained in which the surface potential after charging is hardly changed even when the charging, transfer, and exposure cycles are repeated.

[Examples 9 and 10, Reference Examples 6 and 7, and Comparative Examples 9 to 14]
A positively charged single layer type electrophotographic photosensitive member was prepared in the same manner as in Reference Example 1 except that the amounts of the hole transport agent (HTM-A) and the electron transport agent (ETM-a) shown in Table 2 were used. Obtained. The white streaks of the positively charged single layer type photoreceptor thus obtained were evaluated in the same manner as in Example 1 except that an image forming apparatus in which the charging portion was replaced from a scorotron charger to a charging roller was used. Table 2 shows the evaluation results of white stripes.

According to Table 2, Example 9 wherein the mass ratio (A) / (B) of the hole transport agent (A) to the electron transport agent (B) in the photosensitive layer is 2.2 to 5.0. 10 and the electrophotographic photoreceptors of Reference Examples 6 and 7 , it can be seen that the occurrence of white streaks is satisfactorily suppressed even in an image forming apparatus including a contact charging type charging unit.

  On the other hand, the electrons of Comparative Examples 9 to 15 in which the mass ratio (A) / (B) of the hole transfer agent (A) and the electron transfer agent (B) in the photosensitive layer deviates from 2.2 to 5.0. It can be seen that the photographic photoreceptor cannot suppress the occurrence of white streaks even in an image forming apparatus including a contact charging type charging unit.

DESCRIPTION OF SYMBOLS 10 Positively charged single layer type electrophotographic photosensitive member 12 Conductive substrate 14 Photosensitive layer 16 Intermediate layer 18 Protective layer

Claims (4)

Around the image carrier, a charging unit, an exposure unit, a developing unit, and a transfer unit are provided in this order with respect to the rotation direction of the image carrier, and a recording medium is conveyed by a transfer belt that does not include a charge eliminating unit. In a direct transfer type image forming apparatus in which a toner image is transferred from the image carrier to the recording medium by a transfer unit, the positively charged single-layer type electrophotographic photosensitive member is used as the image carrier. And
The positively charged single-layer type electrophotographic photosensitive member has a single-layered photosensitive layer containing at least a charge generating agent, a hole transporting agent (A), an electron transporting agent (B), and a binder resin on a conductive substrate. Formed,
The content of the electron transfer agent (B) is 20 to 22 parts by mass with respect to 100 parts by mass of the binder resin,
Wherein in the photosensitive layer, the mass ratio of the hole transport agent (A) and the electron transporting agent (B) (A) / ( B) is Ri der 2.2 to 2.5,
The hole transport agent (A) is the following HTM-A or HTM-B:

And the electron transfer agent (B) is the following ETM-a or ETM-b:

And
The positively charged single layer type electrophotographic photosensitive material, wherein the photosensitive layer does not contain the combination of the HTM-B as the hole transport agent (A) and the ETM-b as the electron transport agent (B). body. Wherein said electron transport agent in the photosensitive layer to the mass of (B), the ratio of the mass of the charge generating material is less than 12 wt%, positively charged monolayer type electrophotographic photoreceptor according to claim 1 Symbol placement. An image carrier, a charging unit for charging the surface of the image carrier, and exposure for forming an electrostatic latent image on the surface of the image carrier by exposing the charged surface of the image carrier. A developing unit for developing the electrostatic latent image as a toner image, and a transfer unit for transporting the recording medium by a transfer belt to transfer the toner image from the image carrier to the recording medium. When provided with a not include the static eliminator for neutralizing the surface of the image bearing member by discharging light, wherein the image bearing member, that is positively charged single-layer type electrophotographic photoreceptor according to claim 1 or 2, wherein An image forming apparatus. The image forming apparatus according to claim 3 , wherein the charging unit is a contact charging method.

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