JP4519429B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic process such as an electrostatic copying machine or a laser printer.

  As a photoconductor of an image forming apparatus using an electrophotographic process, the cost is lower, the toxicity is scarce, and the film formability is easier than an inorganic photoconductor produced by vacuum deposition of a conventional selenium film. Since there are many merits, so-called organic photoreceptors are the mainstream. Among these organic photoreceptors, a laminated type in which a so-called charge generation layer and charge transport layer are laminated on a conductive substrate has become the mainstream.

  However, organic photoconductors are prone to film scraping due to repeated use, and when the photoconductive layer progresses, the photoconductor's charging potential decreases, the photosensitivity deteriorates, the surface of the photoconductor becomes soiled due to scratches, etc. Improvement in wear resistance has been desired because of a strong tendency to promote density reduction or image quality degradation.

  Furthermore, in recent years, due to the increase in the speed of electrophotographic devices and the reduction in diameter of the photoconductor due to the miniaturization of the device, there has been a further increase in speed, full color, and maintenance-free movement, so it is essential to improve the wear resistance of the photoconductor It is becoming. Therefore, in an organic electrophotographic photosensitive member, it has been cited as the most important issue particularly to achieve both high image quality and high durability.

On the other hand, attempts have been made to improve the physical properties of the photoreceptor surface by adding various substances to the charge transport layer and to improve the durability of the image quality.
For example, Patent Document 1 and Patent Document 2 listed below are used repeatedly by including an epoxy compound and a hindered amine compound having a specific structure or a hindered phenol compound having a specific structure in the photosensitive layer. In addition, it is disclosed that an electrophotographic photosensitive member having excellent durability in which electrical characteristics such as charging potential and residual potential do not change and image characteristics such as sensitivity, character thickening, and image blurring do not stably change can be obtained. ing.

  Patent Document 3 discloses that the surface layer of the photosensitive layer contains polytetrafluoroethylene powder as a lubricant and a charge transport material such as a diene compound having a di-lower alkylaminophenyl group. A highly durable electrophotographic photosensitive member that is durable against the occurrence of surface abrasion and scratches due to rubbing, and that can produce a high-quality image free from image blur. It is disclosed that an electrophotographic photosensitive member having high durability without adhesion of toner to the body surface layer can be obtained.

  Further, in Patent Document 4, in an electrophotographic photosensitive member obtained by sequentially forming a protective layer containing at least a photosensitive layer and a filler on a conductive support, the photosensitive layer contains an organic sulfur compound, and By including a compound having both a hindered amine structure and a hindered phenol structure in the protective layer, even if it is repeatedly used, there is no increase in residual potential or abnormal images such as image blurring. It is disclosed that a highly durable photoreceptor that can be obtained stably can be obtained.

However, all of these known techniques prevent the charging potential of the photoconductor, the photosensitivity, the background contamination due to scratches on the photoconductor surface, the reduction of the image density, or the deterioration of the image quality, especially high image quality and high durability. It was insufficient in terms of both.
For example, in the method described in Patent Document 3, since the polytetrafluoroethylene powder is a low surface energy polymer, it is insoluble in a solvent and its dispersibility is poor, so that a smooth photoreceptor surface is obtained. Is difficult. In addition, although the dispersibility can be improved by using a dispersant or the like, the obtained coating film has a problem that light scattering is likely to occur due to a low refractive index, resulting in deterioration of the latent image, and image blurring. Is also likely to occur.
Further, although the method described in Patent Document 4 has an effect for improving the durability of the image quality, it is not sufficient for the photoconductor used in the image forming apparatus corresponding to the high image quality shown in the present invention. Especially, the image quality deteriorates severely under high temperature and high humidity.

The reason why it is difficult to achieve both high image quality and high durability is considered as follows.
As described above, many attempts have been made so far to achieve high wear resistance, and as a result, dramatic improvement in wear resistance of organic electrophotographic photoreceptors has been realized. However, along with this, the problem that the occurrence of abnormal images such as image blurring is noticeable has become obvious. However, with the improvement in the wear resistance of the photoreceptor, it has become difficult to remove the charged product, and image blurring has been cited as a major problem that hinders high durability.

  That is, since the conventional photoconductor has low wear resistance, even if the charged product is deposited on the surface of the photoconductor, it is removed by wear, so that the image blur is not a big problem. Image blur is due to the surface resistance of the photoconductor decreasing and the electrostatic latent image blurring due to the lateral movement of the charge. This decrease in surface resistance occurs when the photoconductor is charged. This is mainly caused by the deposition and deposition of ozone and NOx gas, and ionic species (hereinafter referred to as charged products) generated by them and moisture in the atmosphere on the photoreceptor. Further, when a scratch is generated on the surface of the photoreceptor, the scratch becomes difficult to be removed as the wear resistance is improved. Therefore, if a charged product is deposited on the scratched portion, it is more difficult to remove.

  Further, apart from the adhesion of the charged product, the wear resistance of the photoconductor is improved, and the time and number of times that the surface of the photoconductor is exposed to hazards such as electrification dramatically increase as the life of the photoconductor increases. For this reason, the surface material of the photoconductor may be altered due to the hazard due to ionization or even bond breakage. In this case, even if the image is not blurred, a local resistance decrease occurs, causing dot enlargement and gradation deterioration. These phenomena are not clear whether moisture accelerates these reactions or is a medium for reducing resistance, but becomes particularly prominent under high temperature and high humidity. In any case, the influence of the surface property of the photoconductor on the image quality increases as a high image quality is required, and it becomes a big problem to achieve both wear durability and image quality durability.

  On the other hand, in an image forming apparatus using an electrophotographic method, it is possible to achieve high image quality by reducing the thickness of the photoconductor. However, if the thickness of the photoconductor is reduced, the durability of the photoconductor is lost. There is a problem that the film thickness cannot be 20 μm or less.

  That is, it is known that in an image forming apparatus using an electrophotographic system, it is necessary to make the photosensitive member film thickness small (thin) so that the developing electric field follows up to a high spatial frequency (non-patent document). Reference 1). However, as pointed out in Patent Document 5, when the photosensitive member film thickness is reduced, the durability against abrasion and scratches due to cleaning deteriorates, and the charging process and the exposure process are repeated. The problem of accelerated degradation occurs. In conventional laminated organic photoreceptors, polycarbonate is generally used as the binder resin for the charge transport layer, but due to the above problems, the thickness of the charge transport layer is set to about 20 to 30 μm.

  However, according to experiments conducted by the inventor, when a photoconductor having a charge transport layer of about 20 to 30 μm is used, when the resolution becomes 1200 dpi or more, an isolated 1 dot, 1 dot line, etc. It has become clear that such a so-called high spatial frequency image cannot be reproduced. This means that an image forming apparatus with poor reproduction of one isolated dot or one dot line cannot output a so-called bitmap image or the like without going through a complicated image processing process.

  Even when a photoconductor having a charge transport layer of about 20 to 30 μm is used, it is possible to reproduce isolated one dot or one dot line by reducing the resolution to 600 dpi, 400 dpi or the like. In this case, an isolated 1 dot or 1 dot line becomes large, resulting in an image having a rough grain. In addition, in an image including diagonal lines, a decrease in resolution is accompanied by a so-called jaggy deterioration, which leads to a decrease in image quality. In addition, there is a problem that a resolution of 1200 dpi or higher is necessary to identify various fonts for character images. As described above, an image forming apparatus using an electrophotographic method with an optical writing resolution of 1200 dpi or more has a problem of achieving both high resolution and reproduction of isolated one dot and one dot line.

Further, according to an experiment conducted by the inventor, when a photoconductor having a charge transport layer of about 20 to 30 μm is used, image data subjected to halftone processing is written with a line number of 200 lpi or more. When an image is output, there is a problem that the gradation is poor and a satisfactory image cannot be obtained for an image that requires gradation expression such as a photographic image. Further, it has been clarified that under the condition that the halftone processing of 200 lpi or more is performed and the gradation is deteriorated, so-called banding is likely to occur and only a noisy image can be obtained. As described above, an image forming apparatus using an electrophotographic method in which optical writing is performed based on image data obtained by performing halftone processing on an input image with a line number of 200 lpi or more is said to have poor gradation. There are problems, banding, and noise.
Note that when the halftone processing is less than 200 lpi, although the gradation is ensured, there is a problem that the texture of the dither is perceived visually and a fine image cannot be obtained.

JP-A-10-198053 JP-A-10-301303 JP-A-8-160648 Japanese Patent Laid-Open No. 2002-139859 Japanese Patent Laid-Open No. 11-95462 Fundamentals and applications of electrophotographic technology, Corona, p. 150-151

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus using an electrophotographic method that is less likely to cause background staining, a decrease in image density, and image quality deterioration even when used repeatedly, has high image quality, and is excellent in durability. . Furthermore, the present invention provides an image forming apparatus using an electrophotographic method that achieves both high resolution and reproduction of isolated 1-dot and 1-dot lines, has excellent gradation, and produces banding and image noise. The purpose is to prevent the occurrence.

An object of the present invention is to provide an image forming apparatus using an electrophotographic system having (1) “at least a photoconductor, a charging unit, and a unit that performs optical writing on the photoconductor to form an electrostatic latent image. A laser beam having a beam diameter of 35 μm or less is used for the optical writing means, and the photoconductor includes a charge generation layer containing a charge generation material on a conductive support, and a charge containing a charge transport material. A film thickness comprising at least a transport layer, at least one selected from compounds represented by the following general formula (I), and a surface layer containing a charge transport material and a filler , and combining the charge transport layer and the surface layer Is an image forming apparatus characterized by having a thickness of 5 μm or more and 20 μm or less;

［式中、Ｒ^１、Ｒ^２は、置換又は無置換のアルキル基若しくは芳香族基を表わし、同一でも異なっていてもよい。但し、Ｒ^１、Ｒ^２のいずれか１つは置換もしくは無置換の芳香族基である。Ａｒは置換もしくは無置換の芳香族炭化水素基を表わす。］」、（２）「少なくとも、感光体と、帯電手段と、感光体に対して光書き込みを行ない静電潜像を形成する光書き込み手段と、入力画像に対して中間調処理を行なう画像処理手段とを有する電子写真方式を用いた画像形成装置であって、前記光書き込み手段にビーム径３５μｍ以下のレーザービーム光が用いられ、前記感光体が、導電性支持体上に電荷発生物質を含有する電荷発生層と、電荷輸送物質を含有する電荷輸送層と、下記一般式（Ｉ）で表わされる化合物から選ばれる少なくとも一種と、電荷輸送物質及びフィラーを含有する表面層とを少なくとも設けてなり、該電荷輸送層および表面層を合わせた膜厚が５μｍ以上２０μｍ以下であることを特徴とする画像形成装置；

[Wherein R ¹ and R ² represent a substituted or unsubstituted alkyl group or an aromatic group, and may be the same or different. However, any ^one of R ¹ and R ² is a substituted or unsubstituted aromatic group. Ar represents a substituted or unsubstituted aromatic hydrocarbon group. ], (2) “At least the photosensitive member, the charging unit, the optical writing unit that performs optical writing on the photosensitive member to form an electrostatic latent image, and the image processing that performs halftone processing on the input image An image forming apparatus using an electrophotographic method, wherein a laser beam having a beam diameter of 35 μm or less is used for the optical writing unit, and the photoconductor includes a charge generating material on a conductive support. A charge generation layer, a charge transport layer containing a charge transport material, at least one selected from compounds represented by the following general formula (I), and a surface layer containing a charge transport material and a filler. An image forming apparatus characterized in that the combined thickness of the charge transport layer and the surface layer is 5 μm or more and 20 μm or less;

［式中、Ｒ^１、Ｒ^２は、置換又は無置換のアルキル基若しくは芳香族基を表わし、同一でも異なっていてもよい。但し、Ｒ^１、Ｒ^２のいずれか１つは置換もしくは無置換の芳香族基である。Ａｒは置換もしくは無置換の芳香族炭化水素基を表わす。］」、（３）「前記電子写真感光体の表面層が、カルボン酸化合物を含有することを特徴とする前記第（１）項又は第（２）項に記載の画像形成装置」、（４）「前記帯電手段が帯電部材を感光体に接触もしくは近接配置したものであることを特徴とする前記第（１）項乃至第（３）項の何れかに記載の画像形成装置」、（５）「前記帯電手段が直流成分に交流成分を重畳し、感光体に帯電を与えるものであることを特徴とする前記第（１）項乃至第（３）項の何れかに記載の画像形成装置」によって解決される。

[Wherein R ¹ and R ² represent a substituted or unsubstituted alkyl group or an aromatic group, and may be the same or different. However, any ^one of R ¹ and R ² is a substituted or unsubstituted aromatic group. Ar represents a substituted or unsubstituted aromatic hydrocarbon group. ], ( 3 ) "The image forming apparatus according to (1) or (2), wherein the surface layer of the electrophotographic photosensitive member contains a carboxylic acid compound", ( 4) ) "the paragraph (1), second (3, wherein said charging means is obtained by contacting or disposed close to the charging member to the photosensitive member) the image forming apparatus according to any one of items", (5 The image forming apparatus according to any one of (1) to ( 3 ), wherein the charging means superimposes an alternating current component on a direct current component to charge the photosensitive member. Is solved by.

  An image forming apparatus according to the present invention is an image forming apparatus using an electrophotographic system having a photoconductor, a charging unit, and a unit that performs optical writing on the photoconductor to form an electrostatic latent image. A specific laser beam light is used for writing means, and the photoconductor contains at least one selected from a charge generation layer, a charge transport layer, and a compound represented by the general formula (I) on a conductive support. At least a surface layer, and the combined thickness of the charge transport layer and the surface layer is 20 μm or less. In addition, the image density is not lowered and the image quality is hardly deteriorated, and the image quality is high and the durability is excellent. Furthermore, even when halftone processing is performed in image processing, an image with excellent gradation can be formed.

First, a photoconductor used in the image forming apparatus of the present invention will be described with reference to the drawings.
The photoreceptor used in the present invention is selected from a charge generation layer containing a charge generation material on a conductive support, a charge transport layer containing a charge transport material, and a compound represented by the following general formula (I): And at least a surface layer containing at least one kind.

［式中、Ｒ^１、Ｒ^２は、置換又は無置換のアルキル基若しくは芳香族基を表わし、同一でも異なっていてもよい。但し、Ｒ^１、Ｒ^２のいずれか１つは置換もしくは無置換の芳香族基である。Ａｒは置換もしくは無置換の芳香族炭化水素基を表わす。］

[Wherein R ¹ and R ² represent a substituted or unsubstituted alkyl group or an aromatic group, and may be the same or different. However, R ^1, any one of R ² is Ru aromatic group der substituted or unsubstituted. Ar represents a substituted or unsubstituted aromatic hydrocarbon group. ]

  1 and 2 show examples of the layer structure of the photoreceptor of the present invention. As shown in FIG. 1, a charge generation layer (35) mainly composed of a charge generation material and a charge transport layer (37) mainly composed of a charge transport material are laminated on a conductive support (31). A protective layer (39) which is a surface layer containing a specific substance is formed thereon. In the photoreceptor used in the present invention, as shown in FIG. 2, an intermediate layer (33) may be provided between the conductive support (31) and the charge generation layer (35).

As the conductive support (31) constituting the photosensitive member used in the present invention, a conductive support having a volume resistance of 10 ¹⁰ Ω · cm or less, for example, aluminum, nickel, chromium, nichrome, copper, gold, silver Metals such as platinum, metal oxides such as tin oxide and indium oxide, film or cylindrical plastics, or paper coated by vapor deposition or sputtering, or plates made of aluminum, aluminum alloy, nickel, stainless steel, etc. In addition, pipes that have been subjected to surface treatment such as cutting, super-finishing, and polishing after forming them into a raw pipe by a method such as extrusion or drawing are included. Further, an endless nickel belt and an endless stainless steel belt disclosed in Japanese Patent Application Laid-Open No. 52-36016 can be used as the conductive support (31).

  In addition to the above, a conductive powder dispersed in a suitable binder resin and coated on the support can be used as the conductive support (31) of the present invention. Examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc, and silver, or metal oxide powder such as conductive tin oxide and ITO. It is done. The binder resin used at the same time is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, Examples thereof include thermoplastic, thermosetting resins, and photocurable resins such as melamine resin, urethane resin, phenol resin, and alkyd resin. Such a conductive layer can be provided by dispersing and coating these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, and toluene.

  Furthermore, it is electrically conductive by a heat-shrinkable tube in which the conductive powder is contained in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, Teflon (registered trademark) on a suitable cylindrical substrate. Those provided with a conductive layer can also be used favorably as the conductive support (31) of the photoreceptor used in the present invention.

The charge generation layer (35) provided on the conductive support (31) is a layer mainly composed of a charge generation material and a binder resin, and the charge generation material and the binder resin are dispersed in an appropriate solvent. Or it melt | dissolves, it forms by apply | coating and drying this on an electroconductive support body (31). The charge generation layer (35) contains a charge generation material and a binder resin as main components, but may contain any additive such as a sensitizer, a dispersant, a surfactant, and silicone oil.
An undercoat layer may be provided between the conductive support (31) and the charge generation layer (35), or between the conductive support (31) and the intermediate layer (33).

  As the charge generation material constituting the charge generation layer (35), a known charge generation material can be used. Representative examples include phthalocyanine pigments such as titanyl phthalocyanine, vanadyl phthalocyanine, copper phthalocyanine, chlorogallium phthalocyanine, hydroxygallium phthalocyanine, and metal-free phthalocyanine, monoazo pigments, disazo pigments, asymmetric disazo pigments, azo pigments such as trisazo pigments, and perylene pigments. , Perinone pigments, indigo pigments, pyrrolopyrrole pigments, anthraquinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squalium pigments, and the like, and these are useful. These charge generating materials can be used alone or in combination of two or more.

  The binder resin used for the charge generation layer (35) as necessary may be polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone, poly -N-vinyl carbazole, polyacrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinyl pyridine, cellulosic resin, casein, polyvinyl alcohol, polyvinyl pyrrolidone Etc. The amount of the binder resin is suitably 0 to 500 parts by weight, preferably 10 to 300 parts by weight with respect to 100 parts by weight of the charge generating material. The binder resin may be added before or after dispersion.

  In the charge generation layer (35), the charge generation material is dispersed in a suitable solvent together with a binder resin if necessary using a ball mill, attritor, sand mill, ultrasonic wave, etc., and this is applied onto the conductive support. And formed by drying.

  Solvents used to form the charge generation layer (35) include isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene, Xylene, ligroin and the like can be mentioned, and ketone solvents, ester solvents and ether solvents are particularly preferably used. These may be used alone or in combination of two or more.

  The film thickness of the charge generation layer (35) is suitably about 0.01 to 5 μm, preferably 0.1 to 2 μm. As a coating method of the coating liquid for forming the charge generation layer (35), methods such as dip coating, spray coating, beat coating, nozzle coating, spinner coating, and ring coating can be used.

  The charge transport layer (37) constituting the photoreceptor used in the present invention is obtained by dissolving or dispersing a charge transport material and a binder resin in an appropriate solvent, and applying and drying the solution on the charge generation layer (35). It is formed by. In addition, the charge transport layer (37) is useful because it is possible to add one or two or more kinds of plasticizers, leveling agents, antioxidants, lubricants, and the like as necessary.

  The charge transport material constituting the charge transport layer (37) is classified into a hole transport material and an electron transport material. Examples of the electron transporting material include chloroanil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7-tri Examples thereof include electron-accepting substances such as nitrodibenzothiophene-5,5-dioxide and benzoquinone derivatives.

  Examples of the hole transport material include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, Oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazolines Derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, etc. Other known materials may be used.

  Among these hole transport materials, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, and benzidine derivatives are preferable. More preferably, triarylamine compounds represented by the following general formulas (II) and (III) are preferably used from the viewpoints of carrier mobility, compatibility with the resin, and matching properties with the charge generation material. These charge transport materials may be used alone or in combination of two or more.

In the formula (II), Ar ¹ and Ar ² represent a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group, and R ³ , R ⁴ and R ⁵ represent a hydrogen atom, substituted or unsubstituted. Represents an alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, and R ⁴ and R ⁵ may be bonded to each other to form a ring. , Ar ³ represents a substituted or unsubstituted arylene group, and n represents 0 or 1.

In the above formula (III), R ⁶ , R ⁸ and R ⁹ are a hydrogen atom, amino group, alkoxy group, thioalkoxy group, aryloxy group, methylenedioxy group, substituted or unsubstituted alkyl group, halogen atom or substituted Alternatively, an unsubstituted aryl group, R ⁷ represents a hydrogen atom, an alkoxy group, a substituted or unsubstituted alkyl group, or a halogen. ^However, when R ^6, R 7, ^{R 8} and ^{R 9} are all hydrogen atoms is excluded. R ⁶ and R ⁷ may be bonded to each other to form a ring. K, l, m and n are integers of 1, 2, 3 or 4, and when each is an integer of 2, 3 or 4, the R ⁶ , R ⁷ , R ⁸ and R ⁹ are the same or different. It may be.

  Examples of the binder resin constituting the charge transport layer (37) include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-acetic acid. Vinyl copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, Thermoplastic or thermosetting resins such as epoxy resins, melamine resins, urethane resins, phenol resins, alkyd resins and the like can be mentioned.

  For the charge transport layer (37), a polymer charge transport material having a function as a binder resin and a function as a charge transport material is also preferably used. The charge transport layer composed of these polymer charge transport materials is excellent in wear resistance and effective for high durability. In the charge transport layer (37), these polymer charge transport materials can be mixed with the aforementioned binder resin or low molecular charge transport material. As the polymer charge transport material, known materials can be used, and in particular, a polycarbonate containing a triarylamine structure in the main chain and / or side chain is preferably used.

  These polymer charge transport materials are disclosed in JP-A-8-269183, JP-A-9-71642, JP-A-9-104746, JP-A-9-272735, JP-A-11-29634, JP-A-11-29634. JP-A-9-235367, JP-A-9-87376, JP-A-9-110976, JP-A-9-268226, JP-A-9-221544, JP-A-9-227669, JP-A-9- No. 157378, JP-A-9-302084, JP-A-9-302085, JP-A2000-26590, and the like.

  The content of the charge transport material is 20 to 300 parts by weight, preferably 40 to 150 parts by weight, based on 100 parts by weight of the binder resin. However, when a polymer charge transport material is used, it can be used alone or in combination with a binder resin.

  A leveling agent and a plasticizer can be added to the charge transport layer (37) as necessary. Leveling agents that can be used in combination include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the side chain, and the amount used is 0 with respect to 100 parts by weight of the binder resin. About 1 part by weight is appropriate. In addition, as plasticizers that can be used in combination, those used as plasticizers for general resins such as dibutyl phthalate and dioctyl phthalate can be used as they are, and the amount used is 0 to 30 weights with respect to 100 parts by weight of the binder resin. Part is appropriate.

  The thickness of the charge transport layer (37) is 20 μm or less, including the thickness of the surface layer (that is, the protective layer (39)) described later. When the total thickness of the charge transport layer (37) and the surface layer is 20 μm or less, excellent resolution can be obtained. The lower limit varies depending on the system to be used (particularly charging potential), but is preferably 5 μm or more.

  Solvents used for coating the charge transport layer (37) include those that dissolve well charge transport materials and binder resins such as tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, and acetone. Used. These may be used alone or in combination of two or more.

  The coating liquid for forming the charge transport layer (37) can be applied by a known method such as a dip coating method, spray coating, bead coating, or ring coating method in the same manner as the charge generation layer (35). .

  In the photoreceptor used in the present invention, a protective layer containing an arylmethane compound having at least an alkylamino group as a surface layer on the charge transport layer (37) for the purpose of improving wear durability and image quality durability. A layer (39) is formed.

  The protective layer (39) as the surface layer preferably contains a filler material in order to improve wear durability and image quality durability. Examples of the filler material include an organic filler and an inorganic filler. Examples of the organic filler material include fluororesin powder such as polytetrafluoroethylene, silicone resin powder, a-carbon powder, and the like. Inorganic filler materials doped with metal powder such as copper, tin, aluminum, indium, silica, tin oxide, zinc oxide, titanium oxide, alumina, zirconia, indium oxide, antimony oxide, bismuth oxide, calcium oxide, antimony Examples thereof include metal oxides such as tin oxide and tin-doped indium oxide, metal fluorides such as tin fluoride, calcium fluoride, and aluminum fluoride, and inorganic materials such as potassium titanate and boron nitride. Among these fillers, it is preferable to use an inorganic material, particularly a metal oxide, from the viewpoint of filler hardness and light scattering property, since the abrasion resistance of the photoreceptor can be improved and a high-quality image can be obtained. Furthermore, when a metal oxide is used, the quality of the coating film is also improved. Since the coating film quality greatly affects the image quality and wear resistance, obtaining a good coating film is effective for high durability and high image quality.

Further, among these metal oxides, a filler having high electrical insulation is preferable as a filler that hardly causes image blur. When the conductive filler is contained in the outermost surface of the photoreceptor, the surface resistance is lowered, and the charge is laterally moved, so that the image blur easily occurs. In particular, the specific resistance of the filler is preferably 10 ¹⁰ Ω · cm or more from the viewpoint of resolution, and examples of such a filler include alumina, zirconia, titanium oxide, and silica. On the other hand, as the conductive filler having a specific resistance of 10 ¹⁰ Ω · cm or less or the filler having a relatively low specific resistance, tin oxide, zinc oxide, acid value indium, acid value antimony, tin oxide doped with antimony, tin Indium oxide or the like doped with, and in the present invention, image blur tends to occur, which tends to be undesirable.

  However, even if the filler is made of the same material, the specific resistance of the filler may be different. Therefore, it is not completely classified according to the type of filler, but it is important to determine the specific resistance of the filler. It is also possible to use a mixture of two or more of these fillers, whereby the surface resistance can be controlled. Furthermore, in order to enhance the effect of suppressing image blur, it is preferable to select a filler having a pH at an isoelectric point of at least 5 or more, and the more basic the filler, the higher the effect. The filler dispersed in the liquid is positively or negatively charged, and the chargeability may affect the stability and resolution of the filler particles. A filler whose pH at the isoelectric point is more basic is effective for suppressing image blur from the viewpoint of chargeability and resistance. Examples of the metal oxide having a pH of 5 or more at the isoelectric point include titanium oxide, zirconia, and alumina among the fillers described above. In particular, since the basicity increases in the order of titanium oxide <zirconia <alumina, More preferably, it is used. Furthermore, α-alumina, a hexagonal close-packed structure with high light transmission, high thermal stability and excellent wear resistance, suppresses image blur and improves wear resistance, coating film quality, light transmission It can be used particularly effectively in view of the above.

  The same applies to the refractive index of the filler. When the refractive index of the filler is less than 1.0 and greater than 2.0, the transmittance of the protective layer (39) decreases, and the reproducibility of the written dot in the latent image Decreases and the image quality deteriorates. The refractive index of the filler can be obtained, for example, from the refractive index of a liquid in which particles are immersed in a liquid in which the value of the refractive index can be changed little by little and the particle interface becomes unclear. The refractive index of the liquid can be obtained by an Abbe refractometer or the like.

  Furthermore, these fillers can be surface-treated with at least one kind of surface treatment agent. In a photoreceptor containing a filler, the occurrence of image blur due to exposure to ozone or NOx gas is considered to be caused by the adsorption of the image on the filler surface. The surface treatment agent can change the specific resistance of the filler and the pH at the isoelectric point, and the effect of suppressing image blur can be greatly enhanced by the surface treatment agent. The surface treatment of the filler not only has the effect of suppressing image blur but also has the effect of improving the dispersibility of the filler, improving the transparency of the coating film, suppressing coating film defects, and further improving the wear resistance and uneven wear. It is also effective for suppressing the above.

As the surface treatment agent for the filler, a conventionally used surface treatment agent can be used, but a surface treatment agent capable of maintaining the specific resistance of the filler and the pH at the isoelectric point is preferable. The pH at the isoelectric point of the filler can be changed by surface treatment. That is, the filler treated with the acidic treatment agent moves to the acidic side, and the filler treated with the basic treatment agent moves to the basic side, so in the configuration of the present invention, the surface treatment agent is also more basic. It is preferable to use a treatment agent exhibiting the above from the viewpoint of filler dispersibility and image blur suppression.
For example, titanate coupling agents, aluminum coupling agents, zircoaluminate coupling agents and the like can be used particularly effectively. Also, Al ₂ O ₃ , TiO ₂ , ZrO ₂ , silicone, aluminum stearate, etc., or a mixture thereof is preferably used from the viewpoint of filler dispersibility and image blur. The treatment with the silane coupling agent is strongly affected by image blur, but the influence may be reduced by performing a mixing treatment of the surface treatment agent and the silane coupling agent. Moreover, even if the pH at the isoelectric point of the filler exhibits an acidity of 5 or less, it is possible to obtain the desired effect in the present invention by using the above basic treatment agent as the surface treatment agent. .

  The average primary particle size of the filler is preferably 0.01 to 0.9 μm from the viewpoint of light transmittance and wear resistance, and more preferably 0.1 to 0.5 μm. If the average primary particle size of the filler is smaller than this, not only will the filler aggregate or wear resistance will decrease, but the effect of image blur may increase due to an increase in the specific surface area of the filler. . In addition, when the average primary particle size of the filler is larger than this, the sedimentation property of the filler may be promoted, or the image quality may deteriorate or an abnormal image may occur.

  In order to suppress the increase in residual potential caused by the inclusion of these fillers, it is preferable to add one kind of carboxylic acid compound to the surface layer. The carboxylic acid compound in the present invention may be one having a non-volatile content of 100% or one previously dissolved in an organic solvent or the like.

As said carboxylic acid compound, if it is a compound which contains a carboxyl group in molecular structure, such as generally known organic fatty acid, high acid value resin, or a copolymer, it can be used.
For example, saturated and unsaturated fatty acids such as lauric acid, stearic acid, arachidic acid, behenic acid, adipic acid, oleic acid, maleic acid, maleic anhydride, salicylic acid, phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, Any carboxylic acid such as an aromatic carboxylic acid can be used. Furthermore, saturated polyester, unsaturated polyester, terminal carboxylic acid unsaturated polyester, or acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, styrene-acrylic acid copolymer, styrene-acrylic acid-acrylic ester copolymer Polymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride, etc. A polymer, oligomer or copolymer to which one or more carboxyl groups are bonded can be used, and it is used more effectively because it not only suppresses the increase in residual potential but also improves the dispersibility of the filler. It is done. Among these carboxylic acid compounds, polycarboxylic acid compounds having a plurality of carboxylic acid residues have a high acid value and tend to improve the adsorptivity to the filler, which reduces the residual potential and improves the dispersibility of the filler. Is particularly effective and useful.

  The reduction in the residual potential is considered to be due to the fact that these compounds have an acid value and adsorbability to the filler. The increase in residual potential due to the addition of filler is considered to occur due to the polar group on the filler surface becoming a charge trap site, and these carboxyl groups are likely to be adsorbed to the polar group of this filler, thereby reducing the residual potential. Is considered to increase. In addition, these carboxylic acid compounds have an affinity for both the filler and the binder resin to increase the wettability, and reduce the interaction between the fillers by giving steric hindrance or electrical repulsion. Has the effect of improving the dispersibility of the filler.

  As the binder resin contained in the protective layer (39) as the surface layer of the photoreceptor, those mentioned for the charge transport layer (37) can be used. As the solvent used for forming the protective layer (39), the solvents mentioned in the charge transport layer (37) can be used, and two or more kinds of solvents can be mixed and used.

  The protective layer (39) may further contain a charge transport material. By containing the charge transport material in the protective layer (39), it is possible to reduce the residual potential and suppress the sensitivity deterioration. It is also possible to use a polymer charge transport material as the charge transport material. As the charge transport material and the polymer charge transport material used for the protective layer, all the materials described for the charge transport layer (37) or similar materials can be used.

  The film thickness of the protective layer (39) is preferably 0.5 μm to 10 μm, and more preferably 2 μm to 6 μm. However, in the present invention, as described above, the total thickness of the charge transport layer (37) and the protective layer (39) is 20 μm or less.

  For the formation of the protective layer (39), conventional coating methods such as dip coating, spray coating, beat coating, nozzle coating, spinner coating, ring coating and the like can be used, but spray coating is most preferable. In addition, it is possible to form the protective layer by coating the required thickness of the protective layer at one time, but the method of forming the protective layer by applying two or more layers is the uniformity of the filler in the film From the standpoint of this, it is more preferable. By doing so, a further effect may be obtained with respect to reduction of residual potential, improvement of resolution, and improvement of wear resistance. In addition, it has the effect of improving the quality of the coating film and suppressing the occurrence of coating film defects.

  The protective layer (39) as the outermost surface layer constituting the photoreceptor used in the present invention contains at least one selected from compounds represented by the following general formula (I).

［式中、Ｒ^１、Ｒ^２は、置換又は無置換のアルキル基若しくは芳香族基を表わし、同一でも異なっていてもよい。但し、Ｒ^１、Ｒ^２のいずれか１つは置換もしくは無置換の芳香族基である。Ａｒは置換もしくは無置換の芳香族炭化水素基を表わす。］

[Wherein R ¹ and R ² represent a substituted or unsubstituted alkyl group or an aromatic group, and may be the same or different. However, R ^1, any one of R ² is Ru aromatic group der substituted or unsubstituted. Ar represents a substituted or unsubstituted aromatic hydrocarbon group. ]

Specific examples of the substituent in the compound represented by the general formula (I) are shown below.
In the definition of R ¹ and R ^{2 in} the general formula (I), specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. Similarly, specific examples of the aromatic group include an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, an anthryl group, and a pyrenyl group, unsubstituted or substituted with 2 or 5 substituents. Aromatic heterocyclic groups such as pyridyl group, quinolyl group, thienyl group, furyl group, oxazolyl group, oxadiazolyl group, carbazolyl group having ˜5 substituents can be mentioned. Further, as these substituents, those mentioned in the specific examples of the alkyl group, or alkoxy groups such as a methoxy group, an ethoxy group, a propoxy group, and a butoxy group, or a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom A halogen atom, an aromatic ring group, etc. are mentioned .

  The addition amount of the compound represented by the general formula (I) is preferably 1 wt% to 50 wt% with respect to the binder resin, and more preferably 2 to 20 wt%. When the addition amount of the compound is small, the resistance to image quality deterioration suppression is insufficient, and when it is too large, the film strength is lowered and the wear resistance is deteriorated.

When the compound represented by the general formula (I) is contained in the surface layer of the photoreceptor, when it is repeatedly used, it is possible to prevent the occurrence of background staining, a decrease in image density, and the occurrence of image quality deterioration. The R ¹ and R ² substituted amino groups (dialkylamino groups) contained in the molecular structure of the compound of general formula (I) are effective against oxidizing gases such as ozone and NOx that are generated when the photoreceptor is charged. It is presumed that this is to suppress the generation of radical substances. Further, it is considered that it also has a protective function for the surface layer constituent material and suppresses the acid value of the acidic ionic species generated by the oxidizing gas and moisture in the air. In addition, since the compound represented by the general formula (I) also has a charge transport capability, it does not act as a trap for the charge bile itself, and electrical characteristics such as residual potential increase due to the addition are not deteriorated. It becomes almost unseen. Further, it is presumed that the effect is generated by reducing the adhesion with a so-called image-flowing substance, which is generated in a particularly large amount under high temperature and high humidity.

  In the photoreceptor used in the present invention, an intermediate layer (33) is provided between the conductive support (31) and the charge generation layer (35) or between the charge transport layer (37) and the protective layer (39). It is also possible to provide it. In the intermediate layer, a binder resin is generally used as a main component. Examples of these resins include polyamide, alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinyl butyral, and polyvinyl alcohol. As a method for forming the intermediate layer, a generally used coating method as described above is employed. In addition, about 0.05-2 micrometers is suitable for the thickness of an intermediate | middle layer.

  In the photoreceptor used in the present invention, an undercoat layer is provided between the conductive support (31) and the charge generation layer (35), or between the conductive support (31) and the intermediate layer (33). be able to. The undercoat layer generally comprises a resin as a main component, but these resins have a high solvent resistance with respect to a general organic solvent in consideration of coating the charge generation layer (35) thereon with a solvent. A resin is desirable. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, and epoxy. Examples thereof include a curable resin that forms a three-dimensional network structure such as a resin. Further, a metal oxide fine powder pigment exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide and the like may be added to the undercoat layer in order to prevent moire and reduce residual potential.

These undercoat layers can be formed using an appropriate solvent and coating method, such as the charge generation layer (35) and the charge transport layer (37) described above. Furthermore, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like can be used as the undercoat layer of the present invention. In addition, in the undercoat layer of the present invention, Al ₂ O ₃ is provided by anodization, organic substances such as polyparaxylylene (parylene), SiO ₂ , SnO ₂ , TiO ₂ , ITO, CeO ₂ A material provided with an inorganic material such as a vacuum thin film can also be used favorably. In addition, known ones can be used. The thickness of the undercoat layer is suitably from 0 to 5 μm.

  Next, an image forming apparatus using the electrophotographic system of the present invention will be described. The image forming apparatus of the present invention includes a first aspect and a second aspect. The image forming apparatus according to the first aspect includes at least the photosensitive member, a charging unit, and a unit that performs optical writing on the photosensitive member to form an electrostatic latent image. The image forming apparatus according to the second aspect includes the photosensitive member, the charging unit, the optical writing unit that performs optical writing on the photosensitive member to form an electrostatic latent image, and halftone processing on the input image. Image processing means for performing at least.

  In the image forming apparatuses according to the first and second aspects, the charging device used for the charging unit generally includes a corona charging device that charges the photosensitive member using corona discharge. In addition, there are a charging device (JP-A-8-20210, JP-A-6-301286), a contact charging device, and the like that perform charging using a sawtooth electrode as a discharge electrode.

  In the image forming apparatuses according to the first and second aspects, a laser beam having a beam diameter of 35 μm or less is used for the optical writing unit as a unit for performing optical writing on the photosensitive member to form an electrostatic latent image. It is done. When a laser beam of 35 μm or less is used as the optical writing means, it is possible to achieve high image quality excellent in gradation, 1-dot reproducibility, jaggy, banding, and the like. On the other hand, if the beam diameter exceeds 35 μm, the font can be identified. However, since the dod itself is large, the gradation is lowered and the reproducibility of a halftone image such as a photographic image is remarkably lowered. There is a fear. This optical writing means will be specifically described in the embodiments.

  In the image forming apparatus according to the first aspect of the present invention, an optical writing unit that performs optical writing with a resolution of 1200 dpi or more on the photosensitive member to form an electrostatic latent image is preferable. When the resolution is less than 1200 dpi, an isolated 1 dot or 1 dot line becomes large, resulting in an image with a rough grain. In addition, in an image including a diagonal line, image quality is degraded due to deterioration of jaggy. In addition, various fonts may not be identified for character images.

  In the image forming apparatus according to the second aspect of the present invention, the electrostatic latent image is written on the photoconductor based on the image data obtained by applying halftone processing to the input image with a line number of 200 lpi or more. An optical writing means for forming an image is preferred. When halftone processing is performed at less than 200 lpi, the gradation is ensured, but the texture of the dither is perceived visually and a fine image cannot be obtained.

Next, the outline of the image forming apparatus using the electrophotographic process of the present invention will be described in detail with reference to FIG. 3, FIG. 4, FIG. 5, FIG.
In FIG. 3, the photosensitive drum (1) has a charge generation layer, a charge transport layer, a surface layer (protective layer) containing the compound of the above general formula (I), etc. on the surface of the conductor (conductive support). It is formed by coating and rotates in the direction of the arrow in FIG. The image forming apparatus forms an image in the following procedure.

1. The charging means (2) charges the surface of the photoreceptor to a desired potential.
2. The exposure means (3) exposes the photoconductor to form an electrostatic latent image corresponding to a desired image on the photoconductor.
3. Developing means (4) develops the electrostatic latent image produced by the exposing means with toner to form a toner image on the photoreceptor.
4). The transfer means (5) transfers the toner image on the photoreceptor onto a recording sheet (6) such as paper conveyed by a conveyance means (not shown).
5). The cleaning means (7) cleans the toner that is not transferred onto the recording sheet by the transfer means but remains on the photoreceptor.
6). The recording sheet onto which the toner image has been transferred by the transfer means (5) is conveyed to the fixing means (8). In the fixing means (8), the toner is heated and fixed on the recording sheet.
Since the photosensitive drum rotates in the direction of the arrow in FIG. 1, a desired image is formed on the recording sheet by repeating the steps 1 to 6 described above.

The charging device used in the image forming apparatus of the present invention can be a known device as a charging device used in an electrophotographic process, and is not particularly limited. Hereinafter, these charging devices will be described.
As a charging device in an electrophotographic process, a corona charging device that charges a photosensitive member using corona discharge using a wire has been conventionally used. FIG. 5 is a schematic diagram of an example of a corona charging device. In the corona charging device as shown in FIG. 4, a wire (82) made of tungsten or the like and having a wire diameter of about 60 μm is usually used. The wire (82) is stretched in the axial direction of the photosensitive drum (1) at the center of the charging case (80), and a voltage (high voltage) of about −7 kV is applied. The charging case (80) is formed of stainless steel which is not easily oxidized. A grid (81) is stretched between the wire (82) and the photosensitive drum (1), and a voltage of about -0.6 kV is applied. The grid (81) is obtained by cutting a stainless steel plate having a thickness of about 0.1 mm into a mesh shape.

  In the corona charging device shown in FIG. 4, the photosensitive member is charged as follows. In the vicinity of the stretched wire, a strong electric field is formed, air breakdown occurs, and ions are generated. Some of these ions move by the electric field between the wire and the photoconductor, and the surface of the photoconductor is charged. Since the charging of the photoconductor continues until the surface potential becomes substantially equal to the potential applied to the grid, the surface potential of the photoconductor can be controlled by the potential applied to the grid.

As a corona charging device other than the corona charging device using a wire, there is one using a sawtooth electrode as a discharge electrode (Japanese Patent Laid-Open Nos. Hei 8-20210 and Hei 6-301286).
FIG. 5 is a schematic view of an example of a corona charging device using the sawtooth electrode. The sawtooth electrode (90) has a shape as shown in FIG. 6 and is made of a stainless steel plate having a thickness of 0.1 mm, and the apex pitch is 3 mm. As shown in FIG. 5, the sawtooth electrode (90) is fixed to the support member (91), and a high voltage (-5 kV) is applied by a power source. Similarly to the corona charging device using the wire shown in FIG. 4, the corona charging device using the sawtooth electrode is covered with a charging case (92) made of stainless steel, and the sawtooth electrode (90) and the photosensitive device are photosensitive. A grid (93) is arranged between the body drum (1). The charging of the photoconductor with the corona charging device using the sawtooth electrode is the same as when using a wire, and corona discharge occurs near the apex of the sawtooth electrode (90). Other corona charging devices have been devised in which the discharge electrode is a needle-like (pin-like) electrode.

  A corona charging device using a sawtooth electrode has advantages of small size and low ozone generation compared to the case of using a wire. In the sawtooth electrode, corona discharge occurs with directionality (the flow of ions toward the charging case is smaller than the flow of ions toward the grid (photoreceptor)). The opening width on the photoconductor side) can be reduced. This is important for downsizing of the entire image forming apparatus. In addition, since the corona discharge has directionality, the charging efficiency of the photosensitive member is increased, and the current flowing through the corona charging device can be reduced. As a result, the amount of ozone generated is reduced.

In addition to these corona charging devices, there are so-called contact charging devices as charging devices for image forming apparatuses. This contact charging device can improve the following problems of the corona charging device.
1. A lot of ozone is generated. Large applied voltage (5-7 kV)
For this reason, it is widely used as a charging device in low- and medium-speed electrophotographic image forming apparatuses.

FIG. 7 is an example of a contact charging device, and shows a cross-sectional view thereof. The contact charging device charges the photosensitive member (1a) by bringing the charging member (2) into contact with the photosensitive drum (1), which is a member to be charged, and applying a voltage to the charging member. The charging member (2) has a roller shape and a diameter of 5 to 20 mm and a length of about 300 mm, and an elastic layer (2b) is formed on the conductor (2a). The photosensitive drum (1) has a diameter of 30 to 80 mm and a length of about 300 mm, and the photosensitive member (1b) is formed on the conductor (1a). The charging member comes into contact with the rotating photosensitive drum and rotates in a driven manner. The elastic layer of the charging member is made of a material having a resistivity of 10 ⁷ to 10 ⁹ Ωcm. In addition, a surface protective layer having a thickness of about 10 to 20 μm may be formed on the surface of the charging member (surface of the elastic layer). A voltage is applied to the charging member by a power source (30) to charge the photoreceptor. The applied voltage is -1.5 to -2.0 kV in direct current. With such a configuration, the contact charging device can uniformly charge the photosensitive member to −500 to −800V.

  Further, in the contact charging device, since the charging member is in contact with the photosensitive member, the toner or foreign matter adheres to the charging member, and the charging member is contaminated to reduce the charging property, or the charging member is contaminated. Of the photosensitive member surface is promoted by re-adhering to the surface of the photosensitive member, wear of the photosensitive member or uneven wear is promoted by contamination of the charging member, or the surface of the photosensitive member is pressed by the charging member. The charging member is placed close to the photoconductor because there is a problem that the removal efficiency of the foreign matter is reduced, and the charging roller trace remains on the photoconductor or an abnormal image is generated due to deformation of the charge roller. A charging device is also used. The charging member itself may be the same as the contact charging member, but from the viewpoint of charging stability and suppression of charging unevenness, the applied voltage is used by superimposing an alternating current of −300 to −1000 V with a direct current. There are many cases. As for the gap with the photosensitive member required for the proximity arrangement, a charging roller is formed by winding a gap tape on the charging member side, providing a step at the end of the roller, or providing a step at the drum end from the photosensitive member side. And the gap can be maintained.

The gap material can be in any form such as tape, seal or tube. The thickness of the gap is preferably 10 to 200 μm, more preferably 20 to 100 μm, and further preferably 40 to 80 μm. If the gap is smaller than this, there will be more contact between the charging member and the photoconductor, and the merit of placing them closer will not be obtained, and the effect of image quality degradation will increase. If the gap is larger than this, charging will be stable. The charging voltage may be reduced and charging unevenness may occur, and it is necessary to increase the applied voltage to maintain the required charge level. May increase.
Further, the charging member can be charged with a charge by superimposing an AC component on a DC component. By superimposing an alternating current component, it is possible to reduce charging unevenness, thereby suppressing image density unevenness and contrast deterioration, which is useful.

  An example of the exposure means in the image forming apparatus of the present invention is the apparatus shown in FIG. 8 (details of the apparatus in FIG. 8 will be described later). The apparatus of FIG. 8 performs light modulation by making a so-called LD (laser diode) correspond to an output image, and the laser light emitted from the LD is a so-called collimating lens, aperture, cylindrical lens, polygon mirror, f An image is formed on the photoreceptor via a -θ lens. The polygon mirror is a rotating polygon mirror, and the laser beam is scanned on the photosensitive member by this rotation. Therefore, the photosensitive member can be exposed to form an electrostatic latent image corresponding to a desired image on the photosensitive member.

An outline of the image forming apparatus used in the embodiment will be described with reference to FIG. The image forming apparatus of the present invention contains the compound of the general formula (I) in the photoreceptor surface layer, but the basic configuration is the same as the conventional one.
The photosensitive drum (1) is formed by applying a photosensitive layer coating solution (UL, CGL, CTL, protective layer) on the surface of a conductor (aluminum or the like), and rotates in the direction of the arrow in FIG. The diameter of the photosensitive drum is 60 mm, and the peripheral speed is 230 mm / sec. The charging means (2) is a so-called contact roller charging device, and a charging roller having a configuration in which a so-called medium-resistance conductive elastic layer (thickness 3 mm) is formed on a cored bar is supplied with a DC voltage (−1 .21 kV) is applied to charge the photoreceptor uniformly (-550 V).

The exposure means (3) forms an electrostatic latent image by irradiating the surface of the photoreceptor uniformly charged by the charging means (2) with light corresponding to the target image. The light source of the exposure means is a laser diode, and the photosensitive member is scanned while being irradiated with a laser beam by a polygon mirror. The so-called beam diameter is 35 μm in the main scanning direction and 35 μm in the sub-scanning direction. The beam diameter indicates the diameter at 1 / e ² of the maximum value of the profile expressed by a Gaussian function. In general, the radius of the Gaussian distribution is from the optical axis where the intensity is reduced to some extent from the value on the axis. Can be defined by the distance.

  The developing means is a so-called two-component developing device, and a developer in which a toner (volume average particle diameter of 6.8 μm) and a carrier (particle diameter of 50 μm) are mixed to a toner concentration of 5.0% is stored in a developing container. Yes. In the developing device, the developer is conveyed to the photosensitive member-developing sleeve facing portion by the developing sleeve. The distance between the photoreceptor and the developing sleeve (so-called developing gap) is 0.3 mm. Since a DC voltage (−400 V) is applied to the developing sleeve from the power source, toner adheres to the photosensitive member corresponding to the electrostatic latent image on the photosensitive member (so-called reverse development). The peripheral speed of the developing sleeve is 460 mm / sec (so-called peripheral speed ratio is 2.0).

  The transfer means (5) transfers the toner image developed by the developing means onto the recording sheet (6) conveyed from the paper supply means (not shown). The transfer unit of the image forming apparatus used in the embodiment includes a transfer belt and a power source, and a voltage is applied from the power source to the transfer belt. The applied voltage is constant current control and is 30 μA.

The cleaning means (7) is constituted by a blade formed of an elastic body, and cleans the residual toner image (so-called transfer residual toner) on the photoconductor.
The toner image transferred onto the recording sheet (paper or the like) by the transfer unit is conveyed to the fixing unit, and is heated and pressed by the fixing unit to fix the toner image on the recording sheet. Is output to the output image.
By repeating the above steps, a desired image is formed on the recording sheet.

FIG. 8 shows a writing unit of the image forming apparatus used in the embodiment. In the image forming apparatus, a 4ch (4 channel) type LD array having four LDs (laser diodes) (51) having a wavelength of 780 nm is mounted. Laser light from the LD is irradiated to the polygon mirror (56) via a so-called collimating lens (52), ND filter (53), aperture (54), and cylindrical lens (cylinder lens) (55). In the image forming apparatus, the polygon mirror (56) is a six-sided type and rotates at a rotational speed of 27165 rpm.
The laser beam reflected by the polygon mirror (56) forms an image on the photosensitive member via the folding mirrors (58) and (59) and the f-θ lenses (57) and (60). . In the image forming apparatus, the so-called beam diameter on the photosensitive of the laser beam is adjusted to be 35 μm (main scanning direction) × 35 μm (sub-scanning direction). In the image forming apparatus, the f-θ lens is a plastic lens obtained by molding plastic, and the lens shape is designed by a so-called AC surface. As a result, 35 μm (main scanning direction) × 35 μm (sub-scanning direction) An extremely narrow beam diameter is achieved. Further, the laser beam scans on the photosensitive member as the polygon mirror rotates. The resolution of the image forming apparatus is 1200 dpi, and the size of 1pixel is 21.3 μm × 21.3 μm. In the image forming apparatus, the photosensitive member is irradiated with a laser beam while moving around 1pixel in a time of 16.9 nsec. At this time, the so-called pixel clock is 59.2 MHz, which means that the LD is optically modulated at a frequency of 59.2 MHz.

  In the image forming apparatus, as described above, the laser beam scans the photosensitive member by the rotation of the polygon mirror. When the laser beam is positioned in the non-image area, the synchronization detection plate (shown in FIG. 62), the laser beam is incident. This synchronization detection plate (62) has a mechanism for generating a reference signal by the incidence of a laser beam, and based on this reference signal, resets the timing of the image writing position, that is, the clock signal forming a so-called pixel clock. To do. As a result, the light-modulated laser beam can be incident on a predetermined position on the photosensitive member.

  Further, in the image forming apparatus, the pulse width of the LD is changed in four stages so that four-level writing can be performed, which can express four gradations per pixel, and such a large number is obtained. The value is written.

Next, photoconductors used in Examples and Comparative Examples are shown. All parts are parts by weight.
(Photoreceptor 1)
Undercoat layer coating solution, charge generation layer coating solution, and charge transport layer coating solution of the following composition are sequentially applied on a φ60 aluminum cylinder by dip coating, dried, and undercoated with a thickness of 4.5 μm. A layer, a 0.2 μm charge generation layer, and a 15 μm charge transport layer were formed.

[Undercoat layer coating solution]
Titanium dioxide powder 400 parts Melamine resin 65 parts Alkyd resin 120 parts 2-butanone 400 parts

[Coating liquid for charge generation layer]
Y-type oxotitanium phthalocyanine pigment 2 parts Polyvinyl butyral (ESREC BM-2: manufactured by Sekisui Chemical) 2 parts Tetrahydrofuran 50 parts

[Charge transport layer coating solution]
Bisphenol Z polycarbonate (Panlite TS-2050, manufactured by Teijin Chemicals Ltd.) 10 parts Low molecular charge transport material having a structure represented by the following formula (1) 6 parts Tetrahydrofuran 100 parts

  On the charge transport layer, a protective layer coating solution having the following composition was further applied by spray coating to form a protective layer having a total film thickness of 5 μm, thereby producing an electrophotographic photoreceptor.

[Coating liquid for protective layer]
Bisphenol Z polycarbonate (Panlite TS-2050, manufactured by Teijin Chemicals Co., Ltd.) 10 parts Low molecular charge transport material having the structure shown in the following formula (2) 7 parts Exemplified compound (I) -4 1 part α alumina (Sumicorundum AA-03) ,
Average primary particle size: 0.3 μm, pH 8-9, manufactured by Sumitomo Chemical Co., Ltd.) 3 parts (refractive index: 1.76, pH: 5.5)
Polycarboxylic acid compound (BYK-P104,
0.12 part Tetrahydrofuran 400 parts Cyclohexanone 120 parts

(Photoreceptor 2)
The photoreceptor 2 was prepared in the same manner as the photoreceptor 1 except that the exemplified compound (I) -2 was used in place of the exemplified compound (I) -4 contained in the protective layer coating solution in the photoreceptor 1. Created.

(Photoreceptor 3)
The photoreceptor 3 was prepared in the same manner as the photoreceptor 1 except that the exemplified compound (I) -10 was used instead of the exemplified compound (I) -4 contained in the protective layer coating solution in the photoreceptor 1. Created.

(Photoreceptor 4)
The photoreceptor 4 was prepared in the same manner as the photoreceptor 1 except that the exemplified compound (I) -7 was used in place of the exemplified compound (I) -4 contained in the protective layer coating solution in the photoreceptor 1. Created.

(Photoreceptor 5)
Photoreceptor 5 was prepared in the same manner as Photoreceptor 1 except that Exemplified Compound (I) -4 contained in the protective layer coating solution was removed from Photoreceptor 1.

(Photoreceptor 6)
Photoreceptor 1 is the same as Photoreceptor 1 except that a hindered amine compound having the structural formula shown in the following formula (3) is used instead of the exemplified compound (I) -4 contained in the protective layer coating solution. Thus, a photoreceptor 6 was produced.

(Photoreceptor 7)
Instead of the exemplified compound (I) -4 contained in the protective layer coating solution in the photoreceptor 1, a compound having both a hindered amine structure and a hindered phenol structure represented by the following formula (4) is used. A photoconductor 7 was produced in the same manner as the photoconductor 1 except that.

(Photoreceptor 8)
Photoreceptor 1 is the same as Photoreceptor 1 except that 2 parts by weight of Lubron L-2 is used as polytetrafluoroethylene fine particles instead of the exemplified compound (I) -4 contained in the protective layer coating solution. Thus, a photoreceptor 8 was produced.

The photoreceptor thus obtained was mounted on the image forming apparatus, images were formed in Examples 1 to 32 and Comparative Examples 1 to 3, and evaluated as follows.
(Image quality evaluation method)
The image quality evaluation was performed by a method of measuring gradation which is an important item of image quality. Tone evaluation was performed by outputting a patch (17 steps) subjected to halftone processing by changing the number of lines and measuring the lightness (L *) of this patch. As halftone processing, an image was output at a so-called line number of 200 lpi. A spectral density colorimeter (X-Rite 938) was used to measure the lightness (L *).

The numerical value of the gradation is calculated from the linearity of the brightness value obtained by measuring the 17-step patch with respect to the input (area ratio on the data), so-called R ² (the autocorrelation coefficient in the linear approximation). This was done by calculating (square). The value of R ² becomes a value close to 1.0 (see FIG. 9) if the relationship between the above-mentioned input data and lightness (L *) is linear (see FIG. 9), and becomes smaller as it deviates from the straight line (see FIG. 10) become.
In addition, the inventor made a condition of excellent gradation property that the value of R ² is 0.98 or more by performing subjective evaluation of an image such as a natural image that requires high gradation property. Further, the value of R ² tends to be larger in a so-called low line number image. However, when the number of lines is 200 lpi or less, a so-called dither texture can be recognized, and an unnatural impression is given in a natural image or the like, resulting in image quality deterioration. From this, the inventor determined that the image quality is high when the number of lines of halftone processing is 200 lines or more and the gradation R ² value is 0.98 or more.

  The recording density is related to the image quality of characters and line drawings, and is particularly effective for jaggy characteristics. It is necessary for the jaggy to become inconspicuous, and 900 dpi or more is necessary. In order to achieve high image quality, 1200 dpi or more is necessary.

For the photoconductor obtained above, image evaluation was performed using the above-described experimental machine: RICOH MF4570 modified to 1200-bit or 1800-dpi 2-bit writing. The beam diameter was 25, 35, the writing density was 1200, 1800 dpi, and as the halftone processing, an image was output at a so-called line number of 200, 240 lpi. The image quality of the image output by the above means was evaluated. Also, as an evaluation procedure, first, an image is output by an experimental machine and image quality is evaluated, and then a 30K running evaluation is performed at 1 to 2 under high temperature and high humidity (30 ° C / 90% RH) (A bright part) The potential (VD = -600V)) and an image were again output by the experimental device, and the image quality was evaluated.
The beam diameter was measured with a beam scan manufactured by PHOTON, and the OPC film thickness was measured with a film thickness meter manufactured by Fisherscope.

  Table 2 shows the measurement results.

  The photoconductors of Examples and Comparative Examples containing α-alumina as a filler had a wear amount of 0.4 to 0.6 μm in a 40K running test, whereas the wear amount of the photoconductor excluding the fillers. Was 3.0 μm, and was extremely inferior in wear durability. After running test, background stains and half-tone streaky irregularities occurred.

Example 33
As a charging member of the image forming apparatus used for the evaluation, a charging member for proximity arrangement in which an insulating tape having a thickness of 50 μm is wound around both ends of a charging roller as shown in FIG. 11 (the gap between the photoreceptor and the surface of the charging member is 50 μm). The evaluation was performed in the same manner as in Example 3 except that the evaluation was performed using the photosensitive member 1.
Charging conditions:
DC bias: -550V
AC bias: 2.0 kV (peak to peak), frequency: 2.0 kHz

Example 34
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photoconductor 2 was used instead of the photoconductor 1.

Example 35
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photosensitive member 3 was used instead of the photosensitive member 1.

Example 36
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photoconductor 4 was used instead of the photoconductor 1.

Comparative Example 33
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photoconductor 5 was used instead of the photoconductor 1.

Comparative Example 34
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photoconductor 2 was used instead of the photoconductor 1.

Comparative Example 35
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photosensitive member 3 was used instead of the photosensitive member 1.

Comparative Example 36
In Example 33, evaluation was performed in the same manner as in Example 33 except that the photoconductor 4 was used instead of the photoconductor 1.
The results are shown in Table 3.

Tables 2 and 3 show the measurement of gradation (the above-mentioned R ² ) when at least one compound selected from the compounds represented by the general formula (I) shown in the present invention is contained in the surface layer, and other It is the result of evaluating image quality. As can be seen from the results, by including the compound represented by the general formula (1) of the present invention, an image having excellent gradation can be formed, as well as the wear resistance is improved and the floor is improved. It was confirmed that an image with extremely little deterioration in tonality can be obtained and the stability of image quality is improved.

Further, as can be seen from Table 2, in order to form a high-resolution and high-definition image, a high-quality image cannot be obtained only with a resolution of 1200 dpi or higher and a halftone process of 200 lpi or higher. It can be seen that, in order to form a higher quality image, it can be achieved only by using the compound of the general formula (I) of the present invention in addition to setting the beam diameter and the OPC film thickness to specific values. That is, even if the same beam diameter, OPC film thickness, writing density and number of lines are set, depending on the use of hindered amine or hindered phenol, as shown in the comparative example, an image with excellent gradation can be obtained. Cannot be provided.
It was also confirmed that good image quality can be maintained, such as little deterioration in gradation even under high temperature and high humidity, and no occurrence of abnormal images.
Furthermore, although there is little charging unevenness and excellent image quality uniformity, even if charging means that superimposes an AC component on a DC component that has a large hazard and is likely to cause image blurring, the surface layer can be When at least one compound selected from the compounds represented by the general formula (I) shown in the invention is contained, it is possible to form an image having excellent gradation properties, as well as to improve wear resistance and tonality. It was confirmed that an image with extremely little deterioration can be obtained and the stability of the image quality is improved.

That is, for example, an image forming apparatus using an electrophotographic method with an optical writing resolution of 1200 dpi or higher and / or image data that has been subjected to halftone processing with an input image having a line number of 200 lpi or higher. In the image forming apparatus using the electrophotographic method performed based on the above, the light writing means is a laser beam having a beam diameter of 35 μm or less, and the photosensitive member contains at least a charge generating substance on the conductive support. A charge transport layer containing a charge generation layer and a charge transport material, the surface layer of the photoreceptor containing at least one selected from the compounds represented by formula (I), and the charge If the total thickness of the transport layer and the surface layer is 20μm or less, it is possible that the value of the gradation R ² is ensured 0.98 or more, and wear Sex even less deterioration of good and image quality, stable high-quality image was found to be obtained.

  Furthermore, it has been clarified that the present invention can improve the problem of image quality degradation under high temperature and high humidity that could not be solved so far, and provides an image forming apparatus that realizes both high durability and high image quality including the environment. It became possible to do.

It is sectional drawing which shows an example of the photoreceptor used by this invention. It is sectional drawing which shows another example of the photoreceptor used by this invention. It is explanatory drawing of the image forming apparatus using the electrophotographic process of this invention. It is the schematic which shows an example of the corona charging device using a wire. It is the schematic which shows an example of the corona charging device using a sawtooth electrode. It is the schematic which shows an example of a sawtooth electrode. It is the schematic which shows an example of a contact charging device. It is explanatory drawing which shows an example of the writing unit of this invention. It is explanatory drawing which shows an example with a favorable gradation property. It is explanatory drawing which shows the example with a bad gradation property. It is a figure which shows an example of the proximity charging mechanism which has arrange | positioned the gap formation member in the charging member side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 1a Photoconductor 1b Conductor 2 Charging means (charging device)
2a Elastic layer 2b Conductor 3 Exposure means 4 Developing means 5 Transfer means 6 Recording sheet 7 Cleaning means 8 Fixing means 20 Charging roller 21 Gap forming member 22 Metal shaft 23 Image forming area 24 Non-image forming area 30 Power supply 31 Conductive support 33 Intermediate layer 35 Charge generation layer 37 Charge transport layer 39 Protective layer 51 4chLD (laser diode)
52 Collimating lens 53 ND filter 54 Aperture 55 Cylinder lens 56 Polygon mirror 57 f-θ lens 1
58 Folding mirror 1
59 Folding mirror 2
60 f-θ lens 2
61 Photosensitive member surface 62 Synchronization detection plate 80 Charging case 81 Grid 82 Wire (tungsten)
83, 84 Power supply 90 Sawtooth electrode 91 Support member 92 Charging case 93 Grid 94, 95 Power supply

Claims (5)

An image forming apparatus using an electrophotographic system having at least a photosensitive member, a charging unit, and a unit that performs optical writing on the photosensitive member to form an electrostatic latent image, wherein the optical writing unit has a beam diameter. A laser beam of 35 μm or less is used, and the photoconductor includes a charge generation layer containing a charge generation material on a conductive support, a charge transport layer containing a charge transport material, and the following general formula (I) At least one selected from the represented compounds and a surface layer containing a charge transport material and a filler , and the combined thickness of the charge transport layer and the surface layer is 5 μm or more and 20 μm or less. Image forming apparatus.

[Wherein R ¹ and R ² represent a substituted or unsubstituted alkyl group or an aromatic group, and may be the same or different. However, any ^one of R ¹ and R ² is a substituted or unsubstituted aromatic group. Ar represents a substituted or unsubstituted aromatic hydrocarbon group. ] An electrophotographic system having at least a photosensitive member, a charging unit, an optical writing unit that performs optical writing on the photosensitive member to form an electrostatic latent image, and an image processing unit that performs halftone processing on an input image A laser beam having a beam diameter of 35 μm or less is used for the optical writing unit, and the photoconductor includes a charge generation layer containing a charge generation material on a conductive support, and a charge A charge transport layer containing a transport material, at least one selected from compounds represented by the following general formula (I), and a surface layer containing a charge transport material and a filler, and the charge transport layer and the surface An image forming apparatus, wherein the combined thickness of the layers is 5 μm or more and 20 μm or less.

[Wherein R ¹ and R ² represent a substituted or unsubstituted alkyl group or an aromatic group, and may be the same or different. However, any ^one of R ¹ and R ² is a substituted or unsubstituted aromatic group. Ar represents a substituted or unsubstituted aromatic hydrocarbon group. ] The image forming apparatus according to claim 1, wherein the surface layer of the electrophotographic photoreceptor contains a carboxylic acid compound. The image forming apparatus according to any one of claims 1 to 3, wherein the charging unit is obtained by contacting or disposed close to the charging member to the photosensitive member. The charging unit is superimposing an AC component on a DC component, the image forming apparatus according to any one of claims 1 to 3, characterized in that to provide a charged photoconductor.

Images