JP4322789B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using a two-component developer comprising at least a toner and a carrier having a resin coating layer on the surface of a core material, and a photoreceptor having at least a photosensitive layer on a conductive support.

  In general, an electrophotographic apparatus irradiates a uniformly charged photosensitive member with writing light modulated by image data to form an electrostatic latent image on the photosensitive member, and forms this electrostatic latent image. Toner is supplied to the photosensitive member by a developing unit to form a toner image on the photosensitive member and develop. The image forming apparatus transfers the toner image on the photoconductor to transfer paper (recording paper or intermediate transfer body) at the transfer unit, and then heats and pressurizes the toner transferred onto the transfer paper at the fixing unit, and fixes it. The toner remaining on the surface of the photoreceptor is collected by a method such as scraping with a cleaning blade in a cleaning unit. The image forming process as described above is taken.

  As a developer for developing a latent image formed on a latent image carrier, a two-component developer composed of a carrier and a toner and a one-component developer that does not require a carrier (magnetic toner, nonmagnetic) Toner) is known, but many two-component developers are used because the magnetic carrier shares functions such as developer agitation, transport, and charging, and functions are separated as a developer, so that control is good. It is used. In addition, the magnetic brush development method using a two-component developer can change the development level with a development bias, has a relatively good SN ratio, and can obtain a high-resolution image with no practical problem, Since it can be made compact, it is currently used in most image forming apparatuses.

  In recent years, colorization has progressed in the field of electrophotography, and accordingly, there has been a strong demand for improvement in quality such as high resolution, sharpness, halftone reproducibility, and photographic reproducibility. Consideration is being carried out from various angles. In order to achieve high image quality, the developing unit is required to stably supply toner to the electrostatic latent image to improve gradation and solid uniformity. However, in the developing unit, there is a problem of toner spent on the carrier surface as a problem that hinders the stable supply of toner to the electrostatic latent image. When the toner spent on the carrier occurs, the charge amount of the developer becomes unstable, resulting in image deterioration such as density unevenness and fading. Further, since the toner is more likely to adhere to the portion where the toner is fixed, even if a development bias is applied at the time of development, it becomes difficult for the toner to transfer to the photoreceptor, which also leads to density unevenness and fading.

  The carrier is usually provided with a coating layer or additive made of a resin material suitable for high durability and chargeability control, and a coating layer made of a resin material containing fine particles. In order to prevent this, the resin used for the coating layer is advantageously one having a low surface free energy. In Patent Documents 1 and 2, etc., it is proposed to use a fluorine-containing resin having a low surface free energy characteristic, and in Patent Documents 3, 4 etc., it is proposed to use a silicone resin.

  However, the suppression of the toner adhesion to the carrier is still insufficient, and the chargeability instability due to the toner adhesion and the accompanying image deterioration are problems. In the future, it is anticipated that the toner particle size will be reduced for higher image quality and higher resolution. However, the smaller the toner particle size, the easier it is to spend on the carrier, so further improvement is necessary.

JP 58-208754 A JP 60-176048 A Japanese Examined Patent Publication No.59-026945 JP 05-1000049 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus for obtaining a high-quality image without causing toner to be spent on the carrier surface and without causing an abnormal image. And

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the surface free energy of the carrier coating resin layer (hereinafter also referred to as “carrier coating layer”) is 15 to 30 mN / m and is photosensitive. When the surface free energy is smaller than the surface free energy of the body surface, the chargeability due to the toner spent on the carrier does not decrease, and the toner easily moves from the carrier to the photoreceptor. It was found that there was no unevenness and as a result high quality images could be obtained.

  When the surface free energy of the carrier coat layer is 30 mN / m or less, toner adhesion to the carrier is suppressed, and charging property instability due to toner spent does not occur. However, if it is less than 15 mN / m, the adhesion between the toner and the carrier becomes too weak, and frictional charging is suppressed and the charging property is lowered. Further, when the surface free energy of the carrier coat layer is smaller than the surface free energy of the photoconductor, more preferably 5 mN / m or more, the toner tends to adhere to the photoconductor from the carrier during development. The toner to be developed is firmly developed, and the toner can be stably supplied to the electrostatic latent image. As a result, toner adhesion to the carrier can be further suppressed, and toner can be supplied to the electrostatic latent image portion without unevenness.

  In addition, when the surface free energy of the photoconductor is 45 mN / m or less, it is possible to suppress adhesion of toner to other than the electrostatic latent image portion on the photoconductor during development. The force to hold the developed toner becomes too weak, and dust is generated at the edge portion, so that the contour of the image becomes unclear. Therefore, the value is preferably more than 15 mN / m and less than 45 mN / m.

The present invention is advantageous for low potential development. In the low potential development, the charging potential of the photosensitive member is set low, so that the development bias is inevitably small. Accordingly, the force for attracting the toner to the photoreceptor during development is weakened. In the present invention, since the toner easily moves from the carrier to the photoconductor during development, the toner can be stably supplied even when the development bias is reduced.
This invention is made | formed based on the said knowledge, The aspect is as follows.

The present invention comprises the following aspects.
(1) In an image forming apparatus using a two-component developer comprising at least a toner and a carrier having a resin coating layer on the surface of a core material, and a photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, the protection An image forming apparatus characterized in that the layer has fluororesin powder as a filler material, and the surface free energy of the resin coating layer of the carrier is 15 to 30 mN / m and smaller than the surface free energy of the surface of the photoreceptor. 2) The image forming apparatus according to (1), wherein the difference between the surface free energy of the resin coating layer of the carrier and the surface free energy of the surface of the photoreceptor is 5 mN / m or more.
(3) The image forming apparatus according to (1), wherein the surface free energy of the surface of the photoreceptor is 15 mN / m or more and 45 mN / m or less.
( 4 ) The image forming apparatus according to any one of (1) to ( 3 ), further comprising a surface free energy reducing agent coating mechanism for supplying a surface free energy reducing agent to at least the photosensitive member and the surface of the photosensitive member.
( 5 ) At least a charging step for uniformly charging the photoconductor, a latent image forming step by exposure, a developing process for developing the electrostatic latent image formed on the photoconductor with a developer, and the developed developer image are transferred. The image forming apparatus according to any one of (1) to ( 4 ), wherein in the image forming apparatus performing the transfer process, the charged potential of the photoconductor is 400 V or less in absolute value.

  According to the present invention, since the toner spent on the carrier does not occur, the chargeability of the developer is stabilized, the toner is easily transferred from the carrier to the photoconductor, and the toner to be developed is reliably developed, so that it is uniform. An image forming apparatus capable of obtaining an image without unevenness can be provided.

The present invention will be described in detail below.
First, the carrier used in the present invention will be described.
As shown in FIG. 1, the magnetic carrier of the two-component developer includes a core material and a coating material.
The core material is about 30 to 90 (μm), and the coating material is about 0.5 to 4 (μm).
The core material of the carrier includes ferromagnetic materials such as iron oxide and cobalt, magnetite and hematite, and ferrite-based magnetism such as Li-based ferrite, Mn-Zn-based ferrite, Cu-Zn-based ferrite, Ni-Zn ferrite, and Ba ferrite. A powder is used, but a so-called resin dispersion carrier having a form in which magnetic powder is dispersed in a known resin such as a phenol resin, an acrylic resin, or a polyester resin can also be used. However, in recent years, there is a tendency to use a lot of ferrite having a small saturation magnetization and a low coercive force.

If the saturation magnetization is small, the heading is short and supple, and the image quality is soft and the heading is not noticeable.
The saturation magnetization is 120 to 200 (emu / g) for iron oxide, 80 to 90 (emu / g) for magnetite, and 50 to 70 (emu / g) for ferrite. However, if the saturation magnetization is too small, the earing becomes worse, the supply of toner becomes insufficient, development unevenness occurs, and the image has a low contrast.
If the saturation magnetization is too large, the ear lacks the flexibility, resulting in a noticeable image.

The carrier used as the core material can be used for development without processing, but if the carriers easily adhere to each other, or if the surface properties of the carrier change due to filming or moisture absorption, the image quality deteriorates and becomes unusable. Since the carrier is always in contact with the toner, filming occurs or moisture absorption causes the surface properties to change and the charge to become unstable.
Therefore, in order to stably obtain a good image, it is desirable to coat a film having high durability and capable of maintaining a stable charge.

The coating material is required to have functions such as the ability to retain electric charge due to frictional charging with the toner, fluidity, prevention of adhesion of foreign matters to the surface of the carrier, and less moisture adsorption. For this reason, it is desirable to use a material having a low surface energy.
Examples of the low surface energy coating material include conventionally known materials described below.
Polytetrafluoroethylene (PTFE), perfluoroalkoxy / fluororesin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), polychloro Examples thereof include ethylene fluoride (PCTFE), vinylidene fluoride (PVDF), vinyl fluoride (PVF), polyimide resin, polycarbonate resin, styrene resin, and acrylic resin. Two or more of these resins may be mixed and used.

The coating layer can contain the following substances in order to control resistance and increase the film strength. One or more of these substances may be used in an appropriate amount as required. These include materials, conductive ZnO, metal powder such as Al, SnO ₂ were made by various methods, SnO ₂ doped with various elements, borides example _{TiB 2, ZnB 2, MoB 2} , silicon carbide, conductive Polymer (polyacetylene, polyparaphenylene, poly (para-phenylene sulfide), polypyrrole, carbon black and the like.
As a method for forming the coating layer, a known method such as a spray drying method, a dipping method, or a powder coating method can be used.

The carrier used in the developer may have a weight average particle diameter of 20 to 100 [mu] m, preferably 30 to 90 [mu] m, and more preferably 35 to 50 [mu] m.
If the particle size of the carrier is small, the charge held by the carrier increases, and the toner adheres to the carrier without unevenness, so that the development efficiency for the electrostatic latent image is also increased. Therefore, fine lines can be developed well, and an image with high resolution can be easily obtained.
However, on the other hand, a phenomenon in which the carriers are aggregated or scattered occurs, and the carrier is easily pulled electrostatically. For this reason, the carrier adhering to the photoconductor adheres to the transfer paper at the time of transfer together with silica and titanium oxide added as a fluidizing agent, causing transfer omission or pressure contact during transfer to the photoconductor. A dent is formed, which causes a cleaning failure and a medaka phenomenon. When the amount of carrier attached to the photoconductor increases, not only the photoconductor but also the cleaning blade edge may be lost. Accordingly, the particle size of the carrier is preferably 20 μm or more, and preferably 30 μm or more.

As the carrier particle size increases, the charge held by the carrier becomes relatively small (Q decreases as the carrier diameter d increases), so the amount of toner that adheres electrostatically to the carrier is inevitably small. Become. Accordingly, the developing ability is lowered, so that development cannot catch up, and in the case of copying a large number of sheets, the density is lowered and development unevenness is likely to occur.
When the toner amount of the developer decreases, the carrier easily adheres to the photoconductor, so it is necessary to consider the balance between the toner and carrier particle size, the amount of dispersion, and the like. Therefore, the carrier diameter is preferably 100 μm or less, and preferably 90 μm or less.

Next, the photoreceptor used in the present invention will be described.
First, the layer structure of the electrophotographic photoreceptor of the present invention will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view of an electrophotographic photoreceptor used in the present invention, which has a function-separated type photosensitive layer constituted by laminating a charge generation layer and a charge transport layer on a conductive support, Furthermore, a protective layer is provided on the charge transport layer.

Examples of the conductive support include those having a volume resistance of 10 ¹⁰ Ω · cm or less, such as metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, and platinum, tin oxide, and indium oxide. Metal oxide coated with film or cylindrical plastic or paper by vapor deposition or sputtering, or a plate made of aluminum, aluminum alloy, nickel, stainless steel, etc. After the conversion, a tube subjected to surface treatment such as cutting, superfinishing or polishing can be used. Further, an endless nickel belt and an endless stainless steel belt disclosed in Japanese Patent Publication No. 52-36016 can be used as the conductive support.

  In addition, those obtained by dispersing and coating conductive powder in an appropriate binder resin on the support can also be used as the conductive support 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 of the present invention.

The charge generation layer is a layer mainly composed of a charge generation material, and a binder resin may be used as necessary. As the charge generation material, inorganic materials and organic materials can be used.
Inorganic materials include crystalline selenium, amorphous selenium, selenium-tellurium, selenium-tellurium-halogen, selenium-arsenic compounds, and amorphous silicon. In amorphous silicon, a dangling bond terminated with a hydrogen atom or a halogen atom, or a boron atom or a phosphorus atom doped is preferably used.

  On the other hand, a known material can be used as the organic material. For example, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, azulenium salt pigments, squaric acid methine pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, azo pigments having a diphenylamine skeleton, dibenzo An azo pigment having a thiophene skeleton, an azo pigment having a fluorenone skeleton, an azo pigment having an oxadiazol skeleton, an azo pigment having a bisstilbene skeleton, an azo pigment having a distyryl oxadiazol skeleton, and a distyrylcarbazole skeleton Azo pigments, perylene pigments, anthraquinone or polycyclic quinone pigments, quinoneimine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine pigments, Jigoido pigments, bisbenzimidazo - such as Le based pigments. These charge generation materials can be used alone or as a mixture of two or more.

  Binder resins used as necessary for the charge generation layer include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, polyarylate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, poly -N-vinylcarbazole, polyacrylamide, etc. are used. These binder resins can be used alone or as a mixture of two or more. Moreover, you may add a low molecular charge transport material as needed.

Charge transport materials that can be used in the charge generation layer include electron transport materials and hole transport materials.
Examples of the electron transport material include chloranil, bromanyl, 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. These electron transport materials can be used alone or as a mixture of two or more.

  Examples of the hole transporting material include the electron donating materials shown below and are used favorably. For example, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane, styrylanthracene, styryl Examples include pyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, and thiophene derivatives. These hole transport materials can be used alone or as a mixture of two or more.

The charge generation layer is mainly composed of a charge generation material, a solvent, and a binder resin, and may contain any additive such as a sensitizer, a dispersant, a surfactant, and silicone oil. good.
Methods for forming the charge generation layer include a vacuum thin film preparation method and a casting method from a solution dispersion system. For the former method, a vacuum deposition method, a glow discharge decomposition method, an ion plating method, a sputtering method, a reactive sputtering method, a CVD method, or the like is used, and the above-described inorganic materials and organic materials can be satisfactorily formed. . Further, in order to provide a charge generation layer by a casting method, a ball mill using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, dichloroethane, butanone together with a binder resin if necessary with the inorganic or organic charge generation material described above, It can be formed by dispersing with an attritor, a sand mill or the like and applying the solution after diluting the dispersion appropriately. The coating can be performed using a dip coating method, a spray coating method, a bead coating method, or the like.
The thickness of the charge generation layer provided as described above is suitably about 0.01 to 5 μm, preferably 0.05 to 2 μm.

The charge transport layer can be formed by dissolving or dispersing a mixture or copolymer mainly composed of a charge transport component and a binder component in an appropriate solvent, and applying and drying the mixture.
In the present invention, examples of the polymer compound that can be used as the binder component include 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, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic resin, silicone resin, fluorine resin, epoxy resin , Thermoplastic or thermosetting resins such as melamine resin, urethane resin, phenol resin, alkyd resin, etc., but are not limited thereto. These polymer compounds can be used singly or as a mixture of two or more kinds, or copolymerized with a charge transport material.

  Examples of the material that can be used as the charge transport material include the above-described low molecular weight electron transport materials and hole transport materials. The amount of the charge transport material used is 20 to 200 parts by weight, preferably about 50 to 100 parts by weight, based on 100 parts by weight of the polymer compound.

  Examples of the dispersion solvent that can be used in preparing the charge transport layer coating solution include ketones such as methyl ethyl ketone, acetone, methyl isobutyl ketone, and cyclohexanone, ethers such as dioxane, tetrahydrofuran, and ethyl cellosolve, toluene, xylene, and the like. Examples include aromatics, halogens such as chlorobenzene and dichloromethane, and esters such as ethyl acetate and butyl acetate.

In the present invention, a protective layer is provided on the photosensitive layer. Materials used for the protective layer include ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, aryl resin, phenol resin, polyacetal, polyamide, polyamideimide, polyacrylate, polyallylsulfone, polybutylene, Polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethylbenten, polypropylene, polyphenylene oxide, polysulfone, polystyrene, polyarylate, AS resin, butadiene-styrene copolymer, polyurethane, polychlorinated Examples thereof include resins such as vinyl, polyvinylidene chloride, and epoxy resin.

A filler material is added to the protective layer . As the filler material, a fluororesin powder such as polytetrafluoroethylene is used as an essential component .

The filler material can be dispersed using a conventional method such as a ball mill, an attritor, a sand mill, or an ultrasonic wave together with a charge transport material, a binder resin, a solvent, and the like. The average primary particle size of the filler is preferably 0.01 to 0.8 μm from the viewpoint of the transmittance of the protective layer and the wear resistance. In addition, the addition of the charge transport material mentioned in the charge transport layer to the protective layer is an effective means for improving the image quality.
As a method for forming the protective layer, conventional methods such as dip coating, spray coating, beat coating, nozzle coating, spinner coating, and ring coating can be used.

In the present invention, the surface free energy on the surface of the photoreceptor is preferably more than 15 mN / m and not more than 45 mN / m. When the surface free energy on the surface of the photoreceptor is not within the above range, the surface free energy reducing agent is sensitized. By applying to the body surface, it can be within the above range.
As a solid-type material having a function of a surface free energy reducing agent, lead oleate, zinc oleate, copper oleate, zinc stearate, cobalt stearate, iron stearate, copper stearate, zinc palmitate , Metal fatty acids such as copper palmitate, zinc linolenate, talc, fluorine-containing polymer, polytetrafluoroethylene (trade name: Teflon (registered trademark)), polychlorotrifluoroethylene, tetrafluoro Fluorine such as copolymer of ethylene and ethylene, polyvinylidene fluoride, copolymer of tetrafluoroethylene and oxafluoropropylene, polychlorotrifluoroethylene, polytrifluorochloroethylene, dichlorodifluoroethylene, polytrifluoroethylene, etc. Resin, fluororesin Fibrillated fluorocarbon fibers to polyfluorocarbon, there are fibers of such as polytetrafluoroethylene. Examples of the powder type include polyvinylidene fluoride powder, the above-mentioned fluororesin powder, and talc powder.

In the liquid type, animal oils such as silicone oil, fluorine-based synthetic oils, whale oil and squalane oil, vegetable oils such as rapeseed oil, safflower oil, sesame oil, coconut oil, coconut oil, paraffinic and naphthenic mineral oils, petroleum Type, ester type, polyether type, hydrocarbon type, silicone type, and fluorine type synthetic oil type. However, in consideration of long-term stability, it is desirable to use synthetic oils such as silicone oil and fluorine-based oil. Silicone oil includes methylphenyl silicone oil, dimethyl silicone oil, silicone polyether copolymer oils, and modified silicone oil includes fluorine-modified, epoxy-modified, alcohol-modified, alkyl-modified, amino-modified silicone oils, etc. Yes, the oil shows good lubricity, although there are some differences in its effect. Examples of the fluorinated oil include fluorocarbon oil and perfluoroether oil.
As the surface free energy reducing agent, various types can be used as described above, and zinc stearate, WAX, and fluorinated oil are particularly suitable.

  If necessary, an undercoat layer may be provided between the conductive support and the photosensitive layer. The provided undercoat layer is provided for the purpose of improving adhesiveness, preventing moire, improving the coatability of the upper layer, and reducing residual potential. In general, the undercoat layer is mainly composed of a resin, but these resins are resins having high resistance to dissolution in general organic solvents in consideration of applying a photosensitive layer thereon using a solvent. It 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, alkyd-melamine resin, and epoxy resin. And a curable resin that forms a three-dimensional network structure. Further, fine powders such as metal oxides exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide and the like, or metal sulfides and metal nitrides may be dispersed and contained. These undercoat layers can be formed using a suitable solvent and coating method.

Furthermore, a metal oxide layer formed by, for example, a sol-gel method using a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like is also useful as the undercoat layer of the present invention. In addition, the undercoat layer of the present invention is provided with Al ₂ O ₃ by anodic oxidation, organic substances such as polyparaxylylene (parylene), SnO ₂ , TiO ₂ , ITO, CeO _2, etc. What provided the inorganic substance with the vacuum thin film preparation method can also be used favorably. The thickness of the undercoat layer is suitably from 0.1 to 20 μm, preferably from 1 to 10 μm.

Next, the image forming apparatus of the present invention will be described.
FIG. 3 shows an electrophotographic apparatus provided with means for supplying a lubricant to a photoreceptor. The photoconductor 101 is charged with (±) 400 to 1400 V by a charging device (here, a roll-shaped contact charging device) 102. After the charge is applied (charged), a latent image is formed by the image exposure system 103. In the case of an analog copying machine, a document image irradiated with an exposure lamp is projected onto a photosensitive member in the form of a reverse image by a mirror and formed into an image, but in the case of digital, it is read by a CCD (Charge Coupled Device). The original image is converted into a digital signal of LD or LED of 400 to 780 nm and formed on the photosensitive member. Therefore, the analog and digital wavelength ranges are different. By image formation, charge separation is performed in the photosensitive layer, and a latent image is formed on the photosensitive member. The photosensitive member 101 on which the latent image has been formed according to the original is developed with a developer by the developing device 104, and the current draft image is visualized (toner image).

  Next, the toner image on the photosensitive member is transferred to the copy sheet 109 by the transfer device 105 and sent to the fixing device 108 for hard copy. On the other hand, after the transfer, the toner image is cleaned and cleaned by the cleaning device 106 (consisting of the cleaning brush 106b and the elastic rubber cleaning blade 106a). Since the latent image (original image) after the toner image is formed is held on the photosensitive member after cleaning, a neutralization device (generally, red light is used) 107 for erasing and uniformizing. Then, the preparation for the next latent image formation is completed and a series of copying processes is completed. In FIG. 3, reference numeral 201 denotes a supply device of the lubricant to the surface of the photoreceptor, and FIG. 3 shows a state where the lubricant application brush is in contact with the surface of the photoreceptor after cleaning to apply the lubricant.

Next, a method for supplying the surface free energy reducing agent (lubricant) to the photoreceptor will be described.
It is preferable that the lubricant application device is installed between the cleaning device and the static eliminator in the copying process, or in combination with the cleaning device. Here, a method in which the cleaning brush is not used as an applicator, that is, a method of installing a dedicated lubricant applicator will be described. If the influence of the toner stain on the image can be avoided, a method of installing in the cleaning device is also possible. A schematic diagram of the lubricant application unit is shown in FIG. Moreover, the schematic of the example which incorporated the lubricant application apparatus in the upper end part of the cleaning apparatus is shown to Fig.5 (a) and (b).

The application member 201a is a lubricant-impregnated member impregnated with a lubricant or a solid lubricant and has a structure in contact with the application brush 201c. The application brush 201c is a brush-like rotating body. The reason for using the coating brush 201c is to apply the brush to the brush and to uniformly spread and polish the surface of the photoreceptor after coating. In other words, the liquid film is thick only by application, and there is no uniformity at all, so that the toner is likely to adhere and the image is likely to be disturbed.
Therefore, in order to obtain a normal image, a uniform thin film is necessary, and unnecessary lubricants must be removed. For this purpose, a brush-like rotating body is used. The material of the brush is not particularly limited, but it is preferable that the brush ears are closely planted in order to obtain a uniform film, which is durable and does not damage the photosensitive member (chemical fiber). System) is effective.

  After the lubricant is applied to the rotating application member intermittently or continuously over about 1 to 3 turns, the lubricant-impregnated member 201a is separated from the application brush 201c, and the application member 201c is rotated. The lubricant adhering to the surface of the photoconductor is uniformly spread and thinned. Therefore, it is preferable that the amount of lubricant applied to the photoconductor 101 is as small as possible. The coating operation is preferably performed before and after the completion of copying, but can be performed even during copying when several hundred copies are made.

  The case holding the lubricant-impregnated member or the solid lubricant 201a is provided with a movable device 201b (mainly composed of a spring 2012b and a solenoid 2011b) that can move back and forth, and the movable device 201b operates the solenoid. It is also possible to connect a driving device 203 and a control device 204 for controlling the driving device.

FIG. 5B shows another example in which the fur brush is removed from the cleaning device. The amount of the removed cleaning device can be reduced in size, which is advantageous in terms of space. If the transfer efficiency is high and the cleaning performance is sufficient, the fur brush is not necessarily required.
The above is an example of the lubricant application method.

Next, surface free energy will be described.
Ninoaki Kitazaki, Toshio Hata et al. In Fowkes' theory describing the nonpolar intermolecular force in terms of surface free energy (synonymous with surface tension) in Journal of Japan Adhesion Association 8 (3), 131-141 (1972) On the other hand, it states that it can be further expanded to a component by polar or hydrogen-bonded intermolecular forces. By this extended Fowkes theory, the surface free energy of each substance can be obtained with three components.
This theory is based on the following three assumptions.

<Assumption 1>
The surface free energy of organic materials is expressed as the sum of three different components.

<Assumption 2>
Each surface free energy that decreases as a result of contact of two substances can be expressed as the sum of the geometric mean of the corresponding surface free energies, and if there is no corresponding component, there is no interaction between the components. Think.

<Assumption 3>
Standard substances are classified into the following three types.
(A) γ = γ ^a type: liquid and solid of saturated hydrocarbon (B) γ = γ ^a + γ ^b type: liquid and solid other than (A) and (C) (C) γ = γ ^a + γ ^b + γ ^c Types: Liquids and solids that are soluble in water or have low interfacial tension with water (γ ₁₂ <30 mN / m) and that have hydrogen bonds The Journal of Japan Adhesion Association 8 (3), 131-141 (1972) The data of is described.

Based on these assumptions, the surface free energy can be obtained as follows.
When the bonding energy of the substances 1 and 2 and W _12,

It becomes.
When the substance is a solid and a liquid, the following Young's formula (5) is established, assuming that the droplet reaches the equilibrium while maintaining the contact angle θ on the solid surface as shown in FIG.

  Therefore, the following relational expression (6) is established between the contact angle and the adhesive energy from the expressions (3) and (5).

  From equations (4) and (6)

It becomes.
In the extended Fowkes theory (7),

After all,

It becomes. Therefore, each surface free energy component (a, b, c) of solid has at least three kinds of contact angle data (y; x ₁ , x ₂ , x ₃ ) by liquids with known surface free energy components Can be obtained by linear regression from However, if the contact angle data of three types of liquids is used to determine the three unknowns from the three equations, if the contact angle of one liquid deviates greatly from the true value due to some influence, the surface free energy of the solid that is determined It will be greatly affected. In order to average the influence of the deviation of the contact angle from the true value and reduce the influence of the contact angle measurement error on the surface free energy measurement result, it is better to obtain from the contact angle data of four or more kinds of liquids.

  Moreover, when calculating | requiring by linear regression, R-2 power value (multiple correlation coefficient) can be calculated. If the R-square value is close to 1, all contact angle data are in the theoretical formula (7), and it can be determined that the obtained surface free energy of the solid is reliable. In other words, the reliability of measurement can be easily determined from the R-square value. As a criterion for judgment, the measurement result is considered reliable when the R-squared value is 0.8 or more. If it is judged that the R-2 power value is small and the reliability is low, it is considered that the contact angle cannot be measured accurately. In many cases, the cause is the surface shape of the sample, and it is necessary to devise a sample form that reduces the surface roughness and voids. As a sample preparation method with less surface roughness and voids, a resin or the like may be molded into a film, and otherwise, compression molding or heat melting may be used.

The standard substance used for the above surface free energy measurement method is a combination of each of the surface free energy components of four or more known liquids, and γ _L ^b or γ _L ^c does not become zero in all liquids. If there is no restriction | limiting in particular, it can select suitably according to the objective.

  Examples of liquids having known components of surface free energy include those shown in Tables 1 to 3 above. However, it is necessary that the reference material does not cause extended wetting. Extended wetting is a phenomenon in which wetting spreads spontaneously when a droplet is placed on a solid, and in this case, the contact angle cannot be measured. The Type A liquids listed in Table 1 for many solids (organic substances) are not preferred because they cause extended wetting.

  Therefore, the combination of standard substances for measuring the surface free energy of the solid (organic substance) is preferably a combination containing two or more types of Type B liquids and two or more types of Type C liquids without using Type A liquids. Examples of the Type B liquid include diiodomethane, α-bromonaphthalene, and Type C liquids such as glycerin, diethylene glycol, and formamide.

In the measurement of the surface free energy of the solid, the value obtained depends on the combination of the liquids used for the measurement. However, the combination of two or more Type B liquids and two or more Type C liquids shows almost the same value. Stabilize.
In the present invention, in order to determine the surface free energy, diiodomethane, α-bromonaphthalene, glycerin, and diethylene glycol were used as standard substances.

  Here, the method for measuring the contact angle is not particularly limited and can be appropriately selected according to the purpose. For example, the contact angle can be measured by a general droplet method, a meniscus method, or the like. Detailed description of the measurement method is described in “Wet Technology Handbook: Basics, Measurement Evaluation, Data” (Supervision: Ikuo Ishii, Jun Jun Koishi, Mitsuo Tsunoda Publishing Office: Techno System Co., Ltd.).

The calculation method by linear regression is as follows.
<Calculation method by linear regression>
Assuming that there are contact angle data for n types (n ≧ 3) of liquid, write as follows.

If the error is ε,

Sum of squares of this error

(A, b, c) is determined so that is minimized. The minimum requirement is

And when calculated, from (12)

From (13)

From (14)

It becomes. (A, b, c) can be obtained by solving the ternary simultaneous equations (15) to (17). The surface free energy of the solid can be obtained by squaring the obtained (a, b, c).
However, at this time, any of a, b, and c may be negative. Since a, b, and c are the square roots of the surface free energy of a solid, it is physically strange that this is negative. Therefore, the above calculation must be solved under the conditions of a ≧ 0, b ≧ 0, c ≧ 0.

Since S (a, b, c) is quadratic with respect to a, b, c, if any of a, b, c becomes negative, for example, if c becomes negative, c = It is sufficient to obtain (a, b) so that S (a, b, 0) is minimized by setting 0. Here, when b becomes negative, b = 0 is set, and a is obtained so that S (a, 0,0) is minimized. However, even if c becomes negative, S may be smaller if (a, c) is determined so that b = 0 and S (a, 0, c) is minimized. Therefore, in actuality, if any of a, b, c is negative, a = 0, b = 0, c = 0, a = b = 0, a = c = 0, b = c = 0 Calculations are respectively made such that a ≧ 0, b ≧ 0, c ≧ 0, and S having the smallest value are solutions that best match the contact angle data in the range of a ≧ 0, b ≧ 0, c ≧ 0.
The R-squared value can be obtained by the following formula.

Hereinafter, the present invention will be described by way of examples. The scope of the present invention is not limited by these specific examples. All parts are parts by weight.
<Manufacture of carriers>

・ Core material Cu-Zn ferrite particles (weight average diameter: 45 μm) 5000 parts ・ Coating material Toluene 450 parts Acrylic resin solution (solid content 50% by weight) A part Silicone resin SR2400 B part (made by Toray Dow Corning Silicone, non-volatile 50%)
Aminosilane SH6020 10 parts (made by Toray Dow Corning Silicone)
10 parts of carbon black

The coating material is dispersed with a stirrer for 10 minutes to prepare a coating solution, and the coating solution and the core material are applied to a coating apparatus that performs coating while forming a swirling flow provided with a rotating bottom plate disk and stirring blades in a fluidized bed. The coating solution was applied on the core material. The obtained coated product was baked in an electric furnace at 250 ° C. for 2 hours to obtain the carrier.
Here, the composition ratios A and B of the acrylic resin solution and the silicone resin were as follows. Further, the surface free energy was measured for each coating agent coated on an aluminum plate by a blade coating method and dried in an electric furnace at 250 ° C. for 2 hours, and the results were as shown in the following table.

<Production of developer>
A developer was prepared by uniformly mixing at 95% by weight of the prepared carrier at a ratio of 5% by weight of toner and tribocharging. A cyan toner for imgio Color 8100 manufactured by Ricoh was used as the toner.

<Preparation of photoreceptor sample>
An undercoat layer coating solution, a charge generation layer coating solution, and a charge transport layer coating solution having the following composition are sequentially applied onto an aluminum cylinder by dip coating and dried to obtain a 3.5 μm undercoat layer, 0. A 2 μm charge generation layer and a 22 μm charge transport layer were formed. All the photoreceptors in the examples have an undercoat layer thickness of 3.5 μm, a charge generation layer thickness of 0.2 μm, and a charge transport layer thickness of 22 μm.

◎ Undercoat layer coating liquid Titanium dioxide powder 400 parts Melamine resin 65 parts Alkyd resin 120 parts 2-Butanone 400 parts

◎ Charge generation layer coating solution 12 parts of bisazo pigment with the following structure

Polyvinyl butyral 5 parts 2-butanone 200 parts cyclohexanone 400 parts

◎ Charge transport layer coating solution Polycarbonate 8 parts (Z Polyca, manufactured by Teijin Chemicals)
10 parts of charge transport material of the following structural formula

      Tetrahydrofuran 100 parts

Further, the following protective layer coating solution is spray coated on the charge transport layer [spray gun: Peacecon PC308, manufactured by Olympus, air pressure: 2 kgf / cm ² ], dried at 150 ° C. for 20 minutes, and 3 μm protective layer Formed.

◎ Protective layer coating solution A solution of the following composition was circulated for 30 minutes under a 100 MPa pressure in a high-speed liquid collision dispersion device (device name: ULTIMIZER HJP-25005 manufactured by Sugino Machine Co., Ltd.), and perfluoroalkoxy (hereinafter abbreviated as PFA) A resin particle dispersion was obtained.

PFA resin particles (MPE-056, manufactured by Mitsui Fluorochemical) Part a Dispersing aid (Modiper F210, manufactured by Nippon Oil & Fats) 0.55 part Polycarbonate (Z Polyca, manufactured by Teijin Chemicals) Part b Tetrahydrofuran 200 parts Cyclohexanone 60 parts

  Here, the composition ratios a and b of the PFA resin particles and the polycarbonate are as shown in the following table. The surface free energy of the protective layer formed from the dispersion was as shown in Table 5 below.

<Evaluation example>
The evaluation methods and conditions in the examples are shown below.
(Evaluation of toner spent on carrier)
The produced developer and photoconductor were assembled in a Ricoh imgio Color 8100 remodeling machine, 10,000 running evaluations were performed, and the charge reduction amount of the carrier after running was evaluated. The rank improves in the order of ×, Δ, ○, ◎.
The amount of charge reduction referred to here is a general blow-off method [TB-200 manufactured by Toshiba Chemical Co., Ltd.] prepared by friction charging with a mixture of 5% by weight of toner with respect to 95% by weight of the initial carrier. ], The amount of charge (Q2) measured by the same method as that described above was subtracted from the amount of charge (Q1) measured in the above method, from the carrier from which the toner in the developer after running was removed by the blow-off device. Say the amount. Since the cause of the decrease in the charge amount is the toner spent on the carrier surface, the decrease in the charge amount can be suppressed by reducing the toner spent.

(Evaluation of uneven development)
The produced developer and the photoconductor were assembled in a remodeled imgio Color 8100 machine manufactured by Ricoh to form a solid image on the photoconductor, and the toner image on the photoconductor was transferred to a transparent tape. The tape on which the toner image was transferred was stuck on a white paper and the density was measured. The degree of density difference between the three points in the solid image was evaluated. The rank improves in the order of ×, Δ, ○, ◎.
Examples of combinations of carrier and photoreceptor and evaluation results are shown in the following table.

  As is apparent from the evaluation results, in Examples 1 to 4, which are within the scope of the present invention, there was obtained a result that the carrier charge amount did not decrease due to the toner spent and there was no uneven development. It can also be seen from Examples 3 and 4 that a better image is obtained when the difference in surface free energy between the carrier and the photoreceptor is 5 or more.

  Since the image forming apparatus of the present invention does not spend toner on the carrier surface and does not generate abnormal images associated therewith, it can be used as an image forming apparatus for obtaining high-quality images in an electrophotographic apparatus or the like.

It is a figure which shows the structure of the resin coating carrier used in the image forming apparatus of this invention. 1 is a schematic cross-sectional view of an electrophotographic photoreceptor used in the present invention. FIG. 2 is a diagram illustrating an electrophotographic apparatus including a lubricant supply unit for a photoreceptor. It is a figure which shows the outline of a structure of a lubrication agent application apparatus part. It is the schematic which shows the electrophotographic apparatus which incorporated the lubricant coating device in the upper end part of the cleaning apparatus. It is a figure which shows a state when a droplet reaches | attains equilibrium, maintaining the contact angle (theta) on the solid surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Photoconductor 102 Charging device 103 Image exposure system 104 Developing device 105 Transfer device 109 Copy paper 108 Fixing device 106 Cleaning device 106a Elastic rubber cleaning blade 106b Cleaning brush 107 Static elimination device 201 Lubricant supply device 201a Application member (solid lubricant)
201b Movable device 2011b Solenoid 2012b Spring 201c Application brush 203 Drive device 204 Control device

Claims (5)

In an image forming apparatus using a two-component developer comprising at least a toner and a carrier having a resin coating layer on the surface of a core, and a photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, the protective layer is a filler. An image forming apparatus comprising: a fluororesin powder as a material; and a surface free energy of the resin coating layer of the carrier being 15 to 30 mN / m and smaller than a surface free energy of a photoreceptor surface.   2. The image forming apparatus according to claim 1, wherein the difference between the surface free energy of the resin coating layer of the carrier and the surface free energy of the surface of the photosensitive member is 5 mN / m or more.   2. The image forming apparatus according to claim 1, wherein the surface free energy of the surface of the photosensitive member is more than 15 mN / m and not more than 45 mN / m. The image forming apparatus according to any one of claims 1 to 3, characterized in that it has a surface free energy lowering agent coating mechanism for supplying the surface free energy lowering agent in at least a photosensitive member and the photosensitive member surface. At least a charging step for uniformly charging the photosensitive member, a latent image forming step by exposure, a developing step for developing the electrostatic latent image formed on the photosensitive member with a developer, and a transfer step for transferring the developed developer image. an image forming apparatus for image forming apparatus according to any one of claims 1 to 4, wherein the charged potential of the photosensitive member is 400V or less in absolute value.

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