JP2007183339A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleanerless system image forming apparatus in which a specific abrasive is isolated from toner and the isolated abrasive only is stuck to an auxiliary charging member to rub a drum thereby removing discharge products, and consequently image deletion and filming are prevented. <P>SOLUTION: The image forming apparatus has a brush member comprising conductive fibers as an auxiliary charging means to which a voltage having the same polarity as the charging polarity of toner is applied, wherein the fibers have a fineness of 0.5-4 deniers and the brush has a density of 300-600 KF/inch<SP>2</SP>. To the toner for image formation, inorganic fine particles of which the charging polarity is reverse to that of the toner are added, the inorganic fine particles have an average primary particle diameter which is ≤1/20 of that of the toner base particles, the toner has an aggregation degree of ≥15%, the inorganic fine particles are added in an amount of ≥0.2% by mass based on the amount of the toner base particles, and a rate of isolation of the inorganic fine particles from the toner base particles is ≥15% by number. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a full-color image forming apparatus.

  In recent years, multifunction devices equipped with all output terminals such as copiers, printers, and fax machines have become widely accepted in the market. An electrophotographic system has been widely accepted as such a network-compatible output terminal, but one of the major problems is the duty cycle of the main body. The duty cycle is a limit number of sheets in which the main body can continue to operate normally without maintenance by a service person. One of the maximum rate limiting factors of the duty cycle is the life of the photosensitive drum.

  From an ecological point of view, it is our absolute challenge to eliminate waste, that is, reduce consumables, extend the life of consumables, and improve reliability. Digitization has progressed from conventional analog devices, and it has become an absolute challenge to make the body cost equivalent to or less than analog.

  Further, in recent years, black-and-white machines have been the mainstream of copying machines and printers in recent years, but full color printing of manuscripts or output files is also rapidly increasing in offices. Not only the analog equivalent digital machine, but also the main body cost and the running cost black and white equivalent full color printer has become our absolute issue. For this purpose, a technology that can dramatically reduce TCO (total cost required from the user's perspective) is desired.

  Under such circumstances, in recent years, a plurality of photoconductors and a transfer belt for carrying and transporting a recording material are provided, and toner images of different colors formed on the respective photoconductors are recorded on the recording material carried on the transfer belt. 2. Description of the Related Art Color image forming apparatuses that obtain a color image by sequentially transferring images in a superimposed manner and tandem color image forming apparatuses have become mainstream.

  In an image forming apparatus that repeats the process of transferring multiple toner images formed on the surface of an image carrier onto an intermediate transfer member and transferring the toner image on the intermediate transfer member to a transfer material mainly composed of paper, It is essential to sufficiently remove the residual toner that does not transfer to the intermediate transfer member and remains on the image carrier.

  For this reason, many proposals have been made as cleaning means. However, a cleaning blade made of an elastic material such as urethane rubber is used to scrape off the residual toner, which is simple, compact and inexpensive. In addition, since it has an excellent toner removal function, it has been widely put to practical use. As a rubber material for the cleaning blade, urethane rubber which is high in hardness and rich in elasticity and is excellent in wear resistance, mechanical strength, oil resistance and ozone resistance is generally used.

  Recently, from the viewpoint of extending the wear life of the photosensitive member, the cleaning device is eliminated as a system, and the residual transfer toner on the photosensitive member after the transfer process is removed and collected from the photosensitive member by “development simultaneous cleaning” in the developing device. A cleanerless system is adopted that can be reused. In this simultaneous development cleaning, the transfer residual toner on the photoreceptor after transfer is charged in the subsequent development process, that is, the photoreceptor is continuously charged and exposed to form an electrostatic latent image. Fog removal bias during development process (fogging potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor), on the surface of the photoconductor that should not be developed with toner (non-image portion) In this method, the toner remaining in the transfer is collected by the developing device. According to this method, since no cleaning means such as a counter blade is required, the number of members that rub against the photoconductor is reduced, and the wear life of the photoconductor can be dramatically improved.

  As a photoconductor, an amorphous silicon photoconductor having a photoconductive layer (including a case where the photoconductive layer is functionally separated) and a surface layer sequentially laminated on the surface of the conductive support, and a conductive support An organic material photosensitive layer and a protective layer are provided, and the surface layer containing fluorine atom resin fine particles is used, which is accepted as a photoconductor that is hard to be scraped and is suitable for extending the life. However, amorphous silicon photoconductors and the like are still expensive and have not penetrated so much. In recent years, by increasing the film strength of the outermost layer of the organic photoreceptor, it is possible to obtain a highly durable photoreceptor by improving wear resistance and scratch resistance, and to further increase the residual potential during repeated use. As an electrophotographic photosensitive member that has very little characteristic change and deterioration and can exhibit stable performance even after repeated use, it has become a mainstream to use a photosensitive member containing a curable resin in a surface layer.

  However, especially when used in high-humidity environments or in machines with high process speeds, these highly wear-resistant photoconductors are less prone to scraping of photoconductors. It is difficult to remove by scraping the body surface, and problems such as image flow, blade damage, squealing, and drowning tend to occur more remarkably.

  It is known that these problems can be improved by adding particles having an abrasive action to the toner and peeling off the charged product adhering to the surface of the photoreceptor as described above. However, conventionally used abrasive particles have a large particle size and a broad particle size distribution, so that it is necessary to add a large amount to the toner in order to uniformly polish the surface of the photoreceptor. When a large amount of particles having an abrasive action is added, problems with development characteristics (particularly scattering, reversal fogging, accumulation of abrasive particles) are likely to occur.

  As an improvement of this point, strontium titanate with a small particle size and reduced looseness has been proposed, and there are also proposals of inorganic fine powders that have an excellent polishing effect with a small amount of addition (patent document) 1).

  Similarly, in the case of an image forming apparatus having a cleaning blade, the fur brush is installed immediately before the cleaning blade to remove the transfer residual toner on the photosensitive member and the waste toner scraped off by the cleaning blade. There has also been a proposal for improving damage, chatter, squealing, and the like of the cleaning blade by supplying it to the contact nip between the cleaning blade and the photosensitive member (see Patent Document 2).

  However, in the image forming apparatus using the cleanerless method, when a photoconductor containing a curable resin with a small amount of abrasion and a long life is used in the surface layer, the rubbing effect by the cleaning blade is not exhibited. For this reason, the amount of abrasion of the photosensitive member itself is reduced, and the life due to the influence of abrasion is greatly increased. However, on the other hand, there is no rubbing with the cleaning blade, discharge products, external additives, toner fine particles, etc. gradually accumulate, and the image blurs in a high humidity environment, so-called image flow phenomenon, The occurrence of remarkable fusing and filming phenomenon is likely to occur in a low humidity environment.

  Therefore, even in an image forming apparatus using a cleanerless method, the inorganic fine particles having a polishing effect are attached to an auxiliary member, particularly a brush member, and the discharge product is polished and removed by rubbing the drum there, Proposals have been made to prevent image flow and filming (see Patent Document 3).

JP2002-162878 JP2002-318467 JP-A-11-237822

  As described above, the simultaneous development cleaning is performed after the transfer residual toner on the photosensitive member after the transfer in the subsequent development step, that is, the photosensitive member is continuously charged and exposed to form an electrostatic latent image, A portion of the photoreceptor surface that should not be developed with toner by a fog removal bias (a fog removal potential difference Vback that is a potential difference between a DC voltage applied to the developing device and the surface potential of the photoreceptor) during the development process of the electrostatic latent image. This is a method of collecting the transfer residual toner existing above (non-image portion) in the developing device. In the image forming apparatus using the cleanerless system, the toner is charged in order to return the polarity of the inverted transfer residual toner to the original toner charge polarity before the transfer residual toner reaches the developing unit again. Means are indispensable, and it is an essential technique to return the reversal toner to the normal polarity by injecting or generating a discharge current there. However, when the abrasive is attached to the brush as the toner charging means as described above, not only the abrasive but also the inverted transfer residual toner is attached, and the toner charging member can be said to be a lifeline of cleanerless. As a result, the injection and discharge current cannot be generated, and it becomes difficult to return the polarity of the toner to the normal polarity.

  As a result of intensive studies, the present inventors have been able to solve the above-described problems by using the following image forming apparatus, while maintaining a long life, and accumulating discharge products such as image flow and filming. It has been found that the problem caused by the above can be prevented by effectively rubbing and polishing the photoreceptor.

(1) An image bearing member, a charging unit that charges the surface of the image bearing member, and a developing unit that develops the formed latent image formed on the image bearing member, and the formed toner image is transferred In the image forming apparatus including the transfer unit, the image carrier is downstream of the transfer unit where the transfer unit is positioned and upstream of the charging unit where the charging unit is positioned, with respect to the rotation direction of the image carrier. As a charging auxiliary means for applying a voltage having the same polarity as the charging polarity of the toner, the brush member made of conductive fibers is used, and the fineness of the fibers constituting the brush is 0.5d. (Denier) to 4d (denier) and the density of the brush is 300 KF / inch ² or more and 600 KF / inch ² or less. The toner that forms the toner image is opposite to the charging polarity of the toner. Inorganic fine particles with a charged polarity The inorganic primary particles have an average primary particle size of 1/20 or less of the average primary particle size of the toner base particles to be added, and the toner has an aggregation degree of 15% or more. An image forming apparatus characterized by satisfying that the addition amount with respect to the particles is 0.2% by mass or more and the liberation rate of the inorganic fine particles with respect to the toner base particles is 15% by number or more.

  (2) The image forming apparatus according to (1), wherein the inorganic fine particles have an average primary particle size of 30 nm to 300 nm.

  (3) The charging auxiliary means to which a voltage having the same polarity as the charging polarity of the toner is applied is a toner charging means for charging the toner remaining after the transfer to the same polarity as the charging polarity of the toner. The image forming apparatus according to (1) or (2), wherein the charged toner is a cleanerless system in which the developing device collects the toner again.

  (4) The image forming apparatus according to any one of (1) to (3), wherein the fiber constituting the auxiliary charging means is a brush using a synthetic fiber having an official moisture content of 6% or less.

  (5) The image forming apparatus according to any one of (1) to (4), wherein the inorganic fine particles added to the toner are hydrophobized fine particles.

  (6) The image forming apparatus according to any one of (1) to (5), wherein the inorganic fine particles externally added to the toner have a cubic or cuboid particle shape.

  (7) The image forming apparatus according to any one of (1) to (6), wherein the inorganic fine particles externally added to the toner are fine particles of perovskite strontium titanate crystals.

(8) The surface of the image carrier is subjected to a hardness test using a Vickers square pyramid diamond indenter in an environment with a temperature of 25 ° C. and a humidity of 50%, and the HU (Universal Hardness Value) when pushed in with a maximum load of 6 mN. The image forming apparatus according to any one of (1) to (7), wherein the image forming apparatus is 150 N / mm ² or more and 220 N / mm ² or less and has an elastic deformation rate We of 45% or more and 65% or less.

  According to the present invention, image flow becomes a problem when a cleanerless system that realizes blade removal cleaning, which is a means for realizing a long service life, and is further problematic when using a photosensitive drum that is difficult to scrape. There is no need to use a special rubbing member for filming. That is, in the present invention, an abrasive having a polarity that easily adheres electrostatically to a brush that is a toner charging auxiliary member, which is a unique essential technology in a cleanerless system, and an appropriate particle size and free rate abrasive to be attached are selected. And adhere to the toner charging auxiliary member. As a result, an object is to provide a polishing effect, and to selectively attach only the abrasive without attaching the toner base to the brush as much as possible, and to maintain the function of the toner charging means.

  Therefore, even when a highly durable and highly durable photosensitive drum is used, image flow, fusing, and filming do not occur, stable image formation can be performed over a long period of time, and a long life and low running cost can be achieved.

The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.
FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a color laser printer using a transfer type electrophotographic process, a contact charging method, and a reversal developing method and having a maximum sheet passing size of A3 size. The image forming apparatus 100 forms a full-color image on a transfer material such as paper, an OHP sheet, or a cloth in accordance with image information from an external host device that is communicably connected to the image forming apparatus main body (apparatus main body). Can be output. The image forming apparatus 100 has a plurality of process cartridges 8, and each process cartridge 8 temporarily transfers multiple toner images to the intermediate transfer member 91 once and then transfers them onto the transfer material P at a time so that full color is obtained. This is a four-drum type (in-line) image forming apparatus for obtaining a print image. Four process cartridges 8 are arranged in the order of yellow, magenta, cyan, and black in series in the moving direction of the intermediate transfer belt 91.

  In this embodiment, the image forming portions PY, PM, and PC for each color of yellow (Y), magenta (M), and cyan (C), which are a plurality of image forming means, are the same except that the color of the developer used is different. In the following description, unless there is a particular need to distinguish, subscripts Y, M, and C that indicate elements of each image forming unit will be omitted, and a general description will be given. For example, the overall operation when a four-color full-color image is formed will be described. According to a signal from an external host device that is communicably connected to the image forming apparatus 100, a color-separated image signal is generated. Thus, toner images of the respective colors are formed in the process cartridges 8Y, 8M, and 8C of the image forming units PY, PM, and PC. The black image forming portion PBk has an image forming unit 8K that is not a cartridge, and image formation is performed. In each of the process cartridges 8Y, 8M, and 8C and the black image forming unit 8K, the electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier is charged by the charging unit 2, and the uniformly charged surface is scanned by the exposure unit 3. An electrostatic latent image is formed on the photosensitive drum 1 by exposure. Next, a toner image is formed by supplying toner as a developer to the electrostatic latent image by the developing means 4. The toner images of the respective colors formed on the respective photosensitive drums 1 are sequentially superimposed and transferred onto an intermediate transfer belt 91 as a moving intermediate transfer member (second image carrier). The full-color toner image formed on the intermediate transfer belt 91 is transferred onto the transfer material P that has been conveyed to the secondary transfer portion where the intermediate transfer belt 91 and the secondary transfer roller 10 as the secondary transfer unit face each other. Are collectively transferred. Next, the transfer material P is conveyed to the fixing unit 12 where the toner image is fixed and then discharged outside the apparatus.

  Hereinafter, each component of the image forming apparatus 100 will be described in more detail sequentially with reference to FIG.

  The image forming apparatus 100 includes a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier. In this embodiment, the photosensitive drums 1Y, 1M, and 1C are organic photoconductor (OPC) drums, and have an outer diameter of 30 mm and a process speed (peripheral speed) of 204 mm / sec centered on the central support shaft. It is rotated counterclockwise.

  Here, the photosensitive drums 1Y, 1M, and 1C will be described.

  The HU (universal hardness value) and elastic deformation rate in the present invention are the microhardness measuring device Fischerscope that continuously applies a load to the indenter and directly reads the indentation depth under the load to obtain the continuous hardness. Measurement was performed using H100V (Fischer). The indenter used was a Vickers square pyramid diamond indenter with a face angle of 136 °. The load conditions were measured stepwise up to a final load of 6 mN (273 points with a holding time of 0.1 sec for each point).

  An outline of the output chart is shown in FIG. The vertical axis represents the load (mN) and the horizontal axis represents the indentation depth h (μm), which is the result of increasing the load stepwise and applying the load to 6 mN, and then decreasing the load stepwise in the same manner.

HU (universal hardness value: hereinafter referred to as HU) is defined by the following formula (1) from the indentation depth under the same load when indented at 6 mN.

The elastic deformation rate is obtained from the work (energy) performed by the indenter on the membrane, that is, the change in energy due to the increase or decrease of the load of the indenter on the membrane, and the value can be obtained from the following equation (2). The total work amount Wt (nW) is represented by an area surrounded by ABDA in FIG. 3, and the elastic deformation work amount Wo (nW) is represented by an area surrounded by CBDC.
Elastic deformation rate We = Wo / Wt × 100 (%) (2)

  As described above, the performance required for the organic electrophotographic photosensitive member includes improved durability against mechanical deterioration. In general, the hardness of the film is higher as the amount of deformation with respect to external stress is smaller, and it is considered that the electrophotographic photosensitive member having higher pencil hardness or Vickers hardness naturally improves durability against mechanical deterioration. However, the high hardness obtained by these measurements does not necessarily improve the durability. When the values of HU and elastic deformation ratio are within a certain range, mechanical deterioration of the surface layer of the photoconductor hardly occurs. .

In other words, a hardness test is performed using a Vickers square pyramid diamond indenter, the HU when pressed at a maximum load of 6 mN is 150 N / mm ² or more and 220 N / mm ² or less, and the elastic deformation rate is 45% or more and 65% or less. By using the electrophotographic photosensitive member, which is Also, the further improvement of properties and is more preferably HU value is 160 N / mm ² or more 200 N / mm ² or less.

For example, when HU exceeds 220 N / mm ² and the elastic deformation rate is less than 45%, paper dust or toner sandwiched between charging rollers or the like may be exposed to light. When the elastic force of the body is insufficient and the elastic deformation rate is larger than 65%, the elastic deformation amount becomes small even if the elastic deformation rate is high. As a result, a large pressure acts locally and deep scratches are generated. Therefore, it is considered that a material having a high HU is not necessarily optimal as a photoconductor.

Also, when the HU is less than 150 N / mm ² and the elastic deformation rate exceeds 65%, even if the elastic deformation rate is high, the amount of plastic deformation increases, and the paper powder or toner sandwiched between the charging rollers or the like is rubbed. If it is done, it will be shaved or fine scratches will occur.

  The photosensitive drum used in the present invention is composed of an electrophotographic photosensitive member containing a compound having at least a surface layer polymerized or crosslinked and cured. As the curing means, heat, light such as visible light or ultraviolet light, and radiation can be used.

  Therefore, in this embodiment, as a method of forming the surface layer of the photoreceptor, a dip coating method using a coating solution that melts or contains a compound that can be cured by polymerization or crosslinking, which is used for the surface layer. A method in which the applied compound is cured by a curing means after being applied by spray coating, curtain coating, spin coating or the like is employed.

  Of these, the dip coating method is most preferable as a method for efficiently mass-producing photoreceptors, and the dip coating method can also be adopted in the first embodiment.

  In addition, the configuration of the photosensitive drum according to this embodiment is a single-layer type having a layer configuration in which both the charge generation material and the charge transport material are contained in the same layer on a conductive substrate having an outer diameter of, for example, about 30 mm. The charge generation layer containing a charge generation material and the charge transport layer containing a charge transport material are either stacked or sequentially stacked in reverse order. Furthermore, a surface protective layer can be formed on the photosensitive layer.

  In the embodiment of the present invention, at least the surface layer of the photoreceptor only needs to contain a compound that can be polymerized or crosslinked and cured by heat, light such as visible light and ultraviolet light, and radiation. Preferably, from the viewpoints of characteristics as a photoreceptor, particularly electrical characteristics such as residual potential and durability, a function separation type photoreceptor structure in which a charge generation layer and a charge transport layer are sequentially laminated, or this function separation. It is preferable that a surface protective layer is further formed on the photosensitive layer laminated with the type photosensitive member structure.

  In this embodiment, as a method for curing a compound in polymerization or cross-linking in the surface layer, there is little deterioration of the photoreceptor characteristics, no increase in residual potential occurs, and sufficient hardness can be exhibited. Radiation is used.

  Polymerization by radiation does not particularly require a polymerization initiator, and can form a surface layer of a very high purity three-dimensional matrix, and is preferable because a photoreceptor showing good electrophotographic characteristics can be obtained.

  The radiation used in generating the polymerization or crosslinking is preferably an electron beam or gamma ray. When using an electron beam of these, it is possible to use all types such as a scanning type, an electron curtain type, a broad beam type, a pulse type, and a laminar type as an accelerator.

  In the case of irradiation with an electron beam, the acceleration voltage is preferably 250 kV or less, preferably 150 kV or less, as an irradiation condition in order to develop the electrical characteristics and durability performance of the photoreceptor according to the first embodiment. Is more preferable. The irradiation dose is preferably in the range of 10 kJ / kg to 1000 kJ / kg, and more preferably in the range of 50 kJ / kg to 200 kJ / kg.

  When the acceleration voltage is larger than 250 kV, damage due to electron beam irradiation on the characteristics of the photoreceptor, so-called damage tends to increase. Moreover, when the irradiation dose is less than 10 kJ / kg, curing tends to be insufficient. In addition, when the dose is higher than 1000 kJ / kg, the photoreceptor characteristics are likely to be deteriorated. From this viewpoint, it is desirable to select the dose from the above range.

  Furthermore, in order to further harden the surface layer, it is good to heat at the time of the polymerization reaction by electron beam. As for the heating timing, it is sufficient that the photoconductor is at a constant temperature while radicals are present. Therefore, heating may be performed at any stage before or after electron beam irradiation. The heating temperature may be adjusted so that the temperature of the photoreceptor is from room temperature to 250 ° C., more preferably from 50 ° C. to 150 ° C. When the heating temperature is higher than 250 ° C., the material of the electrophotographic photosensitive member is deteriorated.

  Although the heating time depends on the temperature, it may be about several seconds to several tens of minutes. The atmosphere at the time of irradiation and heating may be any of air, inert gas such as nitrogen and helium, and vacuum. In an inert gas or vacuum is preferable in that the influence of radicals by oxygen can be suppressed.

  In addition, as a compound for the surface layer that can be cured by polymerization or cross-linking, unsaturated polymerizability is included in the molecule from the viewpoint of high reactivity, high reaction rate, and high hardness achieved after curing. Compounds containing functional groups are preferred.

  Further, among compounds having an unsaturated polymerizable functional group in the molecule, compounds having an acrylic group, a methacryl group and a styrene group are particularly preferable.

  The compound having an unsaturated polymerizable functional group according to the first embodiment is roughly classified into a monomer and an oligomer depending on the repeating state of the structural unit. The monomer refers to a monomer having a relatively small molecular weight without repeating a structural unit having an unsaturated polymerizable functional group.

  On the other hand, an oligomer is a polymer having about 2 to 20 repeating units of an unsaturated polymerizable functional group. Furthermore, a so-called macromer in which an unsaturated polymerizable functional group is bonded only to the terminal of the polymer or oligomer can be used as the curable compound for the surface layer according to the first embodiment.

  The compound having an unsaturated polymerizable functional group according to this embodiment is more preferably a charge transport compound in order to satisfy the charge transport function required for the surface layer. Among these charge transport compounds, an unsaturated polymerizable compound having a hole transport function is more preferable.

Next, the photosensitive layer of the electrophotographic photoreceptor in this embodiment will be described.
First, an undercoat layer having a barrier function and an adhesive function is provided on a conductive support such as aluminum, and a charge generation layer and a charge transport layer are laminated thereon. In this case, the thickness of the photosensitive layer is It is in the range of 5 μm or more and 30 μm or less. Further, the film thickness of the photosensitive layer at this time is the sum of the film thicknesses of the charge generation layer, the charge transport layer, and the surface protective layer.

  The hole transporting compound having an unsaturated polymerizable functional group according to this embodiment can be used as a charge transport layer on the charge generation layer described above. Alternatively, a charge transport layer composed of a charge transport layer and a binder resin can be formed on the charge generation layer and then used as a surface protective layer.

  In any case, the surface layer is generally formed by applying a solution containing a hole transporting compound, followed by polymerization or curing reaction. It is also possible to form a surface layer using a material obtained by previously reacting a solution containing a hole transporting compound to obtain a cured product and then again dispersing or dissolving it in a solvent.

  Moreover, as a method for applying the above-mentioned solution, a dip coating method, a spray coating method, a curtain coating method, a spin coating method, and the like are known. From the viewpoint of efficiency / productivity, the dip coating method is desirable as a method for applying the solution. It should be noted that other known film forming methods such as vapor deposition and plasma treatment can be appropriately selected.

The specific resistance of the surface layer is preferably in the range of 10 ⁸ Ωm to 10 ¹⁵ Ωm, and more preferably 10 ¹⁰ Ωcm to 10 ¹³ Ωcm.

  Further, in this embodiment, the surface layer contains fluorine atom-containing resin particles. Examples of the fluorine atom-containing resin particles include a tetrafluoroethylene resin, a trifluoroethylene chloride resin, a hexafluoroethylenepropylene resin, a vinyl fluoride resin, a vinylidene fluoride resin, a difluoride dichloride ethylene resin, and these. It is preferable to appropriately select at least one of the copolymers.

  And as said fluorine atom containing resin particle, a tetrafluoroethylene resin and a vinylidene fluoride resin are especially preferable. The molecular weight and particle size of the resin particles can be appropriately selected and are not necessarily limited to the molecular weight and particle size described above.

  The ratio of the fluorine atom-containing resin in the surface layer is typically 2% by mass to 40% by mass, and preferably 5% by mass to 30% by mass with respect to the total mass of the surface layer. is there. This is because when the proportion of the fluorine atom-containing resin particles is more than 40% by mass, the mechanical strength of the surface layer tends to be lowered, and when it is less than 3% by mass, the surface layer surface releasability and the surface layer are resistant to abrasion. This is because the wear and scratch resistance may be insufficient.

  In the embodiment of the present invention, it is desirable to increase the releasability of the surface of the photosensitive layer by including a fluorine atom-containing resin in the surface layer as described above, and pure water is used as an index indicating the releasability. When the contact angle C is used, the contact angle C is preferably 85 ° ≦ C ≦ 130 °. If the contact angle C is less than 85 degrees, the releasability of the surface of the photosensitive drum is too low to be collected in the development process, and toner or external additives that are moving around the surface of the photosensitive drum are fixed, and fusion or filming occurs. Is likely to occur. On the other hand, when the contact angle exceeds 130 degrees, the releasability is so high that a sufficient rubbing force cannot be applied by the brush means or the like, and the polishing effect by strontium titanate is hardly exhibited.

  In addition, the contact angle measurement was performed using a contact angle meter CX-A type manufactured by Kyowa Interface Science Co., Ltd. under normal temperature and normal humidity (23.5 ° C., 60%) environmental conditions.

  In the embodiment of the present invention, an additive such as a radical scavenger and an antioxidant can be added to the surface layer in order to further improve dispersibility, binding properties and weather resistance. In the first embodiment, the film thickness of the surface protective layer is preferably in the range of 0.2 μm to 10 μm, and more preferably in the range of 0.5 μm to 6 μm.

  When the photosensitive drum formed as described above is used in an image forming apparatus, the surface layer is roughened in order to improve the smoothness of the surface of the photoreceptor or to expose the fluororesin more firmly on the surface of the photoreceptor. Is preferred. The roughness of the surface layer is preferably from 0.1 μm to 1.5 μm in terms of Rzjis (μm). When the roughness of the surface layer is smaller than 0.1 μm, the exposure of the fluororesin tends to be insufficient. On the other hand, when the roughness of the surface layer is larger than 1.5 μm, the rubbing of the brush to the surface recess becomes insufficient. More preferably, the roughness of the surface layer is 0.2 μm or more and 0.6 μm or less.

  In order to roughen the surface of the photosensitive drum, polishing is performed with a wrapping tape having a coating particle of # 3000 or the like, or blasting using beads such as glass or alumina.

  In the following description, the surface roughness Rz in the present invention means the ten-point average roughness Rzjis, which is based on JIS B0601 (2001) and measured at a surf coder SE3400 (Kosaka Laboratory) with a measurement length of 2. The values measured at 5 mm, a measurement speed of 0.1 mm / sec, and a cutoff of 0.8 mm shall be shown.

Next, a method for producing an electrophotographic photoreceptor (photoreceptor A) will be described.
In particular, in the present embodiment, the photosensitive drums 1Y, 1M, and 1C were prepared as follows. A 30φ aluminum cylinder is prepared for the hardness test and the actual machine test. The coating material for the conductive layer was prepared by the following procedure. 50 parts of conductive titanium oxide powder coated with tin oxide containing 10% antimony oxide (mass parts, hereinafter the same), phenol resin 25 parts, methyl cellosolve 20 parts, methanol 5 parts and silicone oil (polydimethylsiloxane poly) An oxyalkylene copolymer (average molecular weight 3000) 0.002 part was dispersed for 2 hours in a sand mill using φ1 mm glass beads. This paint was applied onto the cylinder by a dip coating method and dried at 140 ° C. for 30 minutes to form a conductive layer having a thickness of 23 μm.

  Next, 5 parts of N-methoxymethylated nylon was dissolved in 95 parts of methanol to prepare an intermediate layer coating material. This paint was applied onto the conductive layer by a dip coating method and dried at 100 ° C. for 20 minutes to form a 0.6 μm intermediate layer.

  Next, 3 parts of oxytitanium phthalocyanine having a strong peak at 9.0, 14.2, 23.9, and 27.1 degrees in the black angle 2θ ± 0.2 degrees in CuKα X-ray diffraction , 3 parts of polyvinyl butyral (trade name ESREC BM2, manufactured by Sekisui Chemical Co., Ltd.) and 35 parts of cyclohexanone were dispersed for 2 hours in a sand mill using a φ1 mm glass bead, and then 60 parts of ethyl acetate was added. Thus, a charge generation layer coating material was prepared. This paint was applied on the intermediate layer by a dip coating method and dried at 50 ° C. for 10 minutes to form a charge generation layer having a thickness of 0.2 μm.

After forming the charge generation layer, 10 parts of a styryl compound of the following structural formula (4)
And 10 parts of a polycarbonate resin having a repeating unit of the following structural formula (5)
(Mv≈20000)
It was dissolved in a mixed solvent of 50 parts of monochlorobenzene and 30 parts of dichloromethane to prepare a charge transport layer coating solution. This coating solution was dip coated on the charge generation layer and dried at 120 ° C. for 1 hour to form a charge transport layer having a thickness of 20 μm.

  Next, 60 parts of the hole transporting compound of the structural formula (3) was dissolved in a mixed solvent of 50 parts of monochlorobenzene and 50 parts of dichloromethane to prepare a protective layer coating material. This protective layer coating material contained 10 wt% of tetrafluoroethylene resin as fluorine atom-containing resin particles with respect to the total weight of the protective layer.

  This coating solution was coated on the charge transport layer and irradiated with an electron beam under the conditions of an acceleration voltage of 150 KV and an irradiation dose of 50 KGy in an atmosphere having an oxygen concentration of 10 ppm. Subsequently, a heat treatment is performed for 10 minutes under the same atmosphere at a temperature of 100 ° C., and in order to further increase the degree of curing, a heat treatment is performed for 1 hour at 140 ° C. in air. A protective layer having a thickness of 5 μm was formed to obtain an electrophotographic photosensitive member (photosensitive member A).

  The contact angle of the drum surface created above with respect to pure water was 100 degrees. The contact angle was measured using a CA-X type manufactured by Kyowa Interface Science.

  As the photosensitive drum 1Bk, a photosensitive drum provided with a light receiving layer on a conductive substrate for an electrophotographic photosensitive member was used. The photoreceptive layer is composed of an a-Si lower charge injection blocking layer, a-Si: H (hydrogenated a-Si), and a photoconductive layer having photoconductivity and a-SiC in this order from the conductive substrate side. The surface layer has a free surface. The photoconductive layer is composed of a first layer region and a second layer region in order from the conductive substrate side, and the functions are separated. In addition, it is preferable to perform interface control so as to suppress interface reflection by continuously changing the interface between the photoconductive layer and the surface layer. Further, if necessary, the photoconductive layer may be formed of a-Si: (H, X) in which halogen atoms are added. Further, the surface layer may be formed of other materials such as a-SiN type and aC type.

In this embodiment, the charging roller 2 that is a contact charger is used as a charging unit in the process cartridges 8Y, 8M, and 8C of the image forming units PY, PM, and PC of the image forming apparatus 100. By applying a voltage under a predetermined condition to the charging roller 2, the photosensitive drum 1 is uniformly charged to a negative polarity. The charging roller 2 has a longitudinal length of 320 mm, and has a three-layer structure in which a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are sequentially laminated from the bottom around the outer periphery of a core metal (support member) 2a. The lower layer 2b is a foamed sponge layer for reducing charging noise, the intermediate layer 2c is a resistance layer for obtaining uniform resistance as the entire charging roller 2, and the surface layer 2d is formed on the photosensitive drum 1 with pinholes or the like. This is a protective layer provided to prevent leakage even if there is a defect. In the charging roller 2 of this embodiment, a stainless steel rod having a diameter of 6 mm is used as the core 2a, carbon is dispersed in the fluororesin as the surface layer, the outer diameter as a roller is 14 mm, and the roller resistance is 10 ^4. Ω to 10 ⁷ Ω. The charging roller 2 rotatably holds both ends of the cored bar 2a by bearing members and urges the cored bar 2a toward the photosensitive drum 1 by a pressing spring so that a predetermined pressing force is applied to the surface of the photosensitive drum 1. With pressure contact. The charging roller 2 rotates following the rotation of the photosensitive drum 1. Then, a predetermined vibration voltage (charging bias voltage Vdc + Vac) obtained by superimposing an alternating voltage of a predetermined frequency on a direct current voltage is applied to the charging roller 2 through the cored bar 2a from the power source 20 as a voltage applying unit, and rotates. The peripheral surface of the drum 1 is charged to a predetermined potential. A contact portion between the charging roller 2 and the photosensitive drum is a charging portion a. In this embodiment, the charging bias voltage applied to the charging roller 2 is a vibration voltage obtained by superimposing a DC voltage of −500 V, a frequency = 1985 Hz, a peak-to-peak voltage Vpp = 1400 V, and a sinusoidal AC voltage. The peripheral surface of 1 is uniformly contact-charged to −500 V (dark part potential Vd). A charging roller cleaning member 2 f is provided for the charging roller 2. In the present embodiment, the charging roller cleaning member 2f is a flexible cleaning film. This cleaning film 2f is arranged in parallel to the longitudinal direction of the charging roller 2 and fixed at one end to a support member 2g that reciprocates a certain amount in the longitudinal direction, and is charged on the surface near the free end side. It is arranged to form a contact nip with the roller 2. The support member 2g is driven through a gear train by a drive motor of the image forming apparatus 100, and reciprocates a certain amount in the longitudinal direction, whereby the surface layer 2d of the charging roller 2 is rubbed with the cleaning film 2f. . Thereby, the adhered contaminants (fine powder toner, external additives, etc.) on the surface layer 2d of the charging roller 2 are removed. The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller 2 and then exposed to image exposure means (color separation / imaging exposure optical system for color original image, time-series electric digital pixel signal of image information). Image exposure L by a laser scanning scanning exposure system that outputs a laser beam modulated in accordance with the above. Thereby, electrostatic latent images of color components corresponding to the respective image forming portions PY, PM, PC, and PBk of the target color image are formed.
Further, a corona charging unit is used as the charging unit in the image forming unit 8K of the Bk image forming unit PBk.

In this embodiment, a laser beam scanner 3 using a semiconductor laser is used as the exposure means. The laser beam scanner 3 outputs a laser beam modulated in accordance with an image signal sent from a host device such as an image reading device (not shown) to the image forming apparatus 100 side, and rotates the photosensitive drum 1. Laser scanning exposure (image exposure) is performed on the uniformly charged surface. By this laser scanning exposure, the potential of the surface of the photosensitive drum 1 irradiated with the laser light L is lowered, and an electrostatic latent image corresponding to the scanned and exposed image information is formed on the rotating photosensitive drum 1 surface. Is done. In this embodiment, the exposed portion potential Vl is set to −150V. The irradiation position of the image exposure L on the photosensitive drum 1 is the exposure part b. Next, the electrostatic latent image formed on the photosensitive drum 1 is developed with toner by a developing device 4 as developing means. In this embodiment, the developing device 4 is a two-component contact developing device (two-component magnetic brush developing device). The developing device 4 includes a developing container (developing device main body) 40, a developing sleeve 41 as a developer carrying member having a magnet roller fixedly disposed therein, a developer regulating blade 42 as a developer regulating member, and a developing container 40. Two-component developer (developer) 46, which is a mixture of mainly contained resin toner particles (toner) and magnetic carrier particles (carrier), and developer agitating members 43 and 44 disposed on the bottom side in the developer container 40. Etc. The developing sleeve 41 is rotatably disposed in the developing container 40 with a part of its outer peripheral surface exposed to the outside. A developer regulating blade 42 is opposed to the developing sleeve 41 with a predetermined gap, and a thin developer layer is formed on the developing sleeve 41 as the developing sleeve 41 rotates in the direction of the arrow in the figure. In this embodiment, the developing sleeve 41 is disposed opposite to the photosensitive drum 1 while keeping the closest distance (S-Dgap) to the photosensitive drum 1 at 350 μm. A facing portion between the photosensitive drum 1 and the developing sleeve 41 is a developing portion c. The developing sleeve 41 is driven to rotate in the direction opposite to the traveling direction of the photosensitive drum 1 in the developing section c. The developer thin layer on the developing sleeve 41 comes into contact with the surface of the photosensitive drum 1 at the developing portion c and rubs the photosensitive drum 1 appropriately. A predetermined developing bias voltage is applied to the developing sleeve 41 from a power source (not shown) as voltage applying means. In this embodiment, the developing bias voltage applied to the developing sleeve 41 is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, the vibration voltage is obtained by superimposing Vdc of −350 V, Vac of 1800 Vpp, and frequency = 2300 Hz. In this way, the electrostatic latent image formed on the photosensitive drum 1 by the toner in the developer 46 coated as a thin layer on the rotating developing sleeve 41 and conveyed to the developing section c is formed on the photosensitive drum 1 by the electric field due to the developing bias voltage. As a result, the electrostatic latent image is developed as a toner image. In this embodiment, the toner adheres to the exposed bright portion on the photosensitive drum 1 and the electrostatic latent image is reversely developed. The developer thin layer on the developing sleeve 41 that has passed through the developing portion c is returned to the developer reservoir in the developing container 40 as the developing sleeve 41 continues to rotate. Further, the developing device 4 is provided with stirring screws 43 and 44 as developer stirring members. The agitating screws 43 and 44 rotate in synchronization with the rotation of the developing sleeve 41, and have a function of agitating and mixing the supplied toner with a carrier to give the toner a predetermined charged charge. Further, the agitating screws 43 and 44 respectively convey the developer 46 in the opposite direction in the longitudinal direction, supply the developer 46 to the developing sleeve 41, and adjust the toner concentration (ratio of toner in the developer) by the developing process. The developer 46 having a reduced thickness is transported to the toner replenishing section, and the developer 46 is circulated in the developing container 40. A sensor 45 that detects a change in the magnetic permeability of the developer 46 and detects the toner concentration in the developer 46 is provided on the upstream side wall surface of the screw 44 of the developing device 4. A toner supply opening 47 is provided slightly downstream of 45. After performing the developing operation, the developer 46 is conveyed to the sensor 45, where the toner density is detected. According to the detection result, in order to keep the toner concentration in the developer 46 constant, the toner is appropriately rotated by the rotation of the screw 51 provided in the developer supply container (toner supply unit) 5 connected to the developing device 4. Toner is supplied from the supply unit 5 through the toner supply opening 47 of the developing device 4. The replenished toner is conveyed by the agitating screw 44, mixed with the carrier, given an appropriate charge, and then transported to the vicinity of the developing sleeve 41 to form a thin layer on the developing sleeve 41 for development. . In this embodiment, a negatively charged toner having an average particle diameter of 5.5 μm is used as the toner, and a magnetic carrier having a saturation magnetization of 205 emu / cm ³ and an average particle diameter of 35 μm is used as the carrier. Further, a mixture of toner and carrier at a weight ratio of 6:94 was used as a developer. The charge amount of the toner subjected to development on the photosensitive drum 1 is −25 μC / g. An intermediate transfer unit 9 as a transfer unit is provided so as to face the photosensitive drums 1 of the image forming portions PY, PM, PC, and PBk. In the intermediate transfer unit 9, an endless intermediate transfer belt 91 as an intermediate transfer member (second image carrier) is hung on the driving roller 94, the tension roller 95, and the secondary transfer counter roller 96 with a predetermined tension. It is passed and moves in the direction of the arrow in the figure. The toner image formed on the photosensitive drum 1 enters a primary transfer nip portion (transfer portion) d that is a portion where the photosensitive drum 1 and the intermediate transfer belt 91 are opposed to each other. In the transfer portion d, a primary transfer roller 92 as a primary transfer unit is in contact with the back side of the intermediate transfer belt 91. The primary transfer roller 92 is connected to a primary transfer bias power supply 93 as a voltage application unit so that the primary transfer bias voltage can be independently applied to each image forming unit PY, PM, PC, PBk. Yes. First, a yellow toner image formed on the photosensitive drum 1 by the above-described operation is transferred to the intermediate transfer belt 91 by the first color (yellow) image forming unit PY, and then corresponding to each color subjected to the same process. Magenta, cyan, and black toner images are sequentially transferred from the photosensitive drum 1 by the image forming units PM, PC, and PBk. In this embodiment, in consideration of the transfer efficiency with respect to the toner transferred to the exposure portion (exposure portion potential Vl: −150 V), a voltage of +350 V is applied to the first to fourth colors as the primary transfer bias voltage. The four-color full-color image formed on the intermediate transfer belt 91 is then supplied from a transfer material feeding means (not shown) by a secondary transfer roller 10 as a secondary transfer means, and as a conveying means at a predetermined timing. Are collectively transferred to the transfer material P sent from the paper feed roller 12. The transfer material P onto which the toner image has been transferred is then conveyed to a roller fixing device 13 as a fixing unit, where the toner image is fused and fixed to the transfer material P by heat and pressure. Thereafter, the transfer material P is discharged out of the apparatus to obtain a color print image. Further, the secondary transfer residual toner remaining on the intermediate transfer belt 91 is cleaned by a cleaning blade 11a as a cleaning unit provided in the intermediate transfer belt cleaner 11, and is prepared for the next image forming process. The material of the intermediate transfer belt 91 is preferably a resin-based or rubber belt with a metal core, or a belt made of resin and rubber. Of course, in consideration of image improvement without occurrence of toner scattering and voids, An intermediate transfer belt having an elastic layer may be used. In this example, a resin belt in which carbon was dispersed in PI (polyimide) and the volume resistivity was controlled to the order of 10 ⁸ Ωcm was used. The thickness is 80 μm, the longitudinal direction is 320 mm, and the entire circumference is 900 mm. The primary transfer roller 92 is made of a conductive sponge. The resistance was 10 ⁶ Ω or less, the outer diameter was 16 mm, and the longitudinal length was 315 mm. Further, each of the image forming units PY, PM, PC, and PBk is provided with a toner charge amount control unit 6 and a residual toner image equalizing unit 7 that are in contact with the photosensitive drum 1.

Next, the toner charge amount control means 6 and the residual toner equalization means 7 will be described.
In the present invention, the toner charge amount control means 6 and the residual toner equalization means 7 are both brush members made of conductive fibers. More specifically, the toner charge amount control means 6 includes a horizontally long electrode plate 62 provided with a brush portion 61. Similarly, the residual toner uniformizing means 7 is provided with a brush portion 71 on the electrode plate 72. The brush portions 61 and 71 are brought into contact with the surface of the photosensitive drum 1 and fixedly supported and arranged substantially in parallel with the longitudinal direction of the photosensitive drum 1 (direction substantially orthogonal to the surface movement direction). The brush portions 61 and 71 of the toner charge amount control means 6 and the residual toner equalization means 7 are preferably fibers having an official moisture content of 6% or less. In the case of fibers with a high moisture absorption higher than the official moisture content of 6%, if the fineness of the brush is lowered to increase the brush density, the fibers will fall back in a high humidity environment. Even if the abrasive adheres to the brush, the polishing effect is not sufficiently obtained, and the discharge product cannot be removed particularly in a high temperature and high humidity environment, thereby causing an image flow. Also, if the hygroscopic property is high, the fibers start to aggregate and aggregate in a high-temperature and high-humidity environment, and the abrasive cannot be sufficiently collected. Specifically, a synthetic fiber such as nylon or polyester in which carbon or metal powder is included and the resistance value is controlled is preferable because it has an official moisture content of 4% or less and has a low hygroscopic property and can exhibit a polishing effect.

  In general, the untransferred toner remaining on the photosensitive drum 1 without being transferred to the recording material P at the transfer portion d is mixed with reversal toner and toner with an inappropriate charge amount. Accordingly, the transfer residual toner is once neutralized by the auxiliary leveling means (uniformization means) 7, and then the transfer residual toner is again charged to the normal polarity by the leveling means (toner charge amount control means) 6. Thereby, it is possible to effectively prevent the transfer residual toner from adhering to the charging roller 2 and to completely remove and collect the transfer residual toner in the developing device 4. Therefore, generation of a ghost image of the transfer residual toner image pattern is also strictly prevented.

  In particular, when using strontium titanate with a large number of convex portions because the particle size is small and the shape is cubic or rectangular parallelepiped as in the present invention, there is an effect of polishing the drum surface uniformly and evenly. It is important to make the brush fiber holding the wire as thin and dense as possible, and selectively hold only a large amount of strontium titanate to rub the drum surface uniformly.

  As a brush used in the leveling means and the auxiliary leveling means, conductive fibers are planted in a base fabric in a W-weave and attached to a conductive base connected to a bias power source.

As described above, the fineness and density of the conductive fibers are such that, as described above, the small-abrasive abrasive having a small particle size is retained and rubbed, and the toner base is not retained as much as possible, and only the abrasive is selectively retained. Is selected from the viewpoint of The fineness of the conductive fibers is preferably 0.55 × 10 ⁻⁷ kg / m or more and 4.4 × 10 ⁻⁷ kg / m or less (0.5 denier or more and 4 denier or less) finer than fibers used as a general cleaning brush. density is preferably denser than fibers used as the cleaning brush, it is desirable that the 300 KF / inch ² or more 600KF / inch ² or less (300,000 / inch ² or more 600,000 / inch ² or less) . When the fineness of the conductive fiber is finer than 0.55 × 10 ⁻⁷ kg / m (0.5 denier), when the density is increased, each fiber is densely packed into the space. However, it is difficult to retain a toner having a large particle size such as a toner, but similarly, it becomes impossible to retain an abrasive having an average primary particle size of 30 nm or more and 300 nm or less, and only the abrasive is selectively retained. The purpose cannot be achieved. Further, in such a case, the transfer residual toner as a leveling brush is scattered and the leveling effect tends to be reduced. In the case the fineness of the electrically conductive fibers are thicker than ^{4.4 × 10 -7 kg / m (} 4 denier) is reversed, difficult to the manufacturing issues 300 KF / inch ² or more 600KF / inch ² or less and a high density Even if it is made dense, each fiber is not densely packed into the space. Therefore, in such a case, the adhesion of the toner is promoted, so that the polishing effect is not achieved, and the function as the toner charging unit is also lost.

Further, as described above, the brush density is preferably higher than the normal brush fiber density because only the abrasive having a small particle diameter is held on the brush and rubbed, as described above. 300KF / inch ² or more 600KF / inch ² or less. When the brush density is lower than 300KF / inch ² , each fiber is not densely packed into the space, so the toner base enters the gap, starts agglomeration, and toner with a larger particle size takes precedence over the photoreceptor. Therefore, the contact between the abrasive attached to the brush and the photosensitive member is hindered, and the rubbing ability is weakened. In addition, the toner aggregated on the brush raises the resistance of the brush, thereby hindering the toner charging function. If the brush density is higher than 600KF / inch ^2, on the other hand, it is necessary to increase the density with a fine fiber, but one single fiber is filled with very dense with respect to space, the toner into the gap Since the penetration of not only the base material but also the abrasive is prevented, the abrasive does not sufficiently adhere to the fibers, and the polishing effect cannot be obtained. In addition, since the hair is too thin, even if synthetic fibers with low water absorption and high rigidity under high temperature and humidity are used, the hair of each hair becomes weak and the toner image is made uniform as well as the polishing effect. The effect to do is lost.

FIG. 4 shows an image diagram of the above-mentioned brush fibers in a close-packed state.
Further, the brush portions 61 and 71 were brought into contact with the surface of the photosensitive drum 1 so that the penetration amount was 1 mm, and the width of the contact nip portion with the photosensitive drum 1 was set to 5 mm.

  As shown in FIG. 2, in this embodiment, the residual toner is located downstream from the transfer portion d in the rotation direction of the photosensitive drum 1 and upstream from the charging portion a, and sequentially from the upstream in the rotation direction of the photosensitive drum 1. The uniformizing means 7 and the toner charge amount control means 6 are arranged, and a contact portion e between the residual toner equalization means 7 and the photosensitive drum 1 and a contact portion f between the toner charge amount control means 6 and the photosensitive drum 1 are formed. Yes. As will be described in detail later, a predetermined voltage is applied to the residual toner equalizing means 7 and the toner charge amount control means 6 from power sources 22 and 21 as voltage applying means, respectively. Voltage application means such as power supplies 20, 21, and 22 provided in the image forming apparatus 100 are controlled by a control circuit 130 that is included in the main body of the image forming apparatus and serves as a control means that controls the overall operation of the apparatus. In this embodiment, the photosensitive drum 1, the charging roller 2, the charging roller cleaning member 2 f, the developing device 4, the residual toner uniformizing means 7, the toner charging means 6, and the like are constituted by the charging unit frame body 111 and the developing frame body 112. The process cartridge 8 is formed by integrally forming a cartridge. The process cartridge 8 is detachably mounted via a mounting means 110a provided in the image forming apparatus main body. Further, in a state where the process cartridge 8 is mounted on the image forming apparatus main body, a driving means (not shown) provided on the image forming apparatus main body and a driving transmission means on the process cartridge 8 side are connected, and the photosensitive drum 1 and the developing The device 4 and the charging roller 2 are ready to be driven. Further, with the process cartridge 8 mounted in the main body of the image forming apparatus, power is applied to the charging roller 2, the toner charge amount control unit 6, and the residual toner uniformizing unit 7. Various voltage applying means such as a power source (not shown) for applying a bias are electrically connected through contacts provided on the process cartridge 8 side and the image forming apparatus main body side, respectively. On the other hand, the toner replenishing unit 5 is detachably attached to the developing device 4 and the image forming apparatus main body via the attaching means 110b.

Next, conventional actions other than the above-described rubbing function of the residual toner uniformizing means 7 and the toner charge amount control means 6 will be described in more detail.
There is untransferred toner on the photosensitive drum 1 after the transfer process. This transfer residual toner includes negative polarity toner in the image area, positive polarity toner in the non-image area, and toner whose polarity has been reversed to positive polarity due to the positive voltage in the transfer process (reversal toner). It is.

  In this embodiment, the voltage condition applied to the residual toner equalizing unit 7 is set so as to improve the toner recoverability of the residual toner equalizing unit 7 for such normal polarity and reverse polarity toners. As a result, the transfer residual toner is collected by the residual toner equalizing means 7 and basically the toner is not sent to the contact portion (charging portion) a between the charging roller 2 and the photosensitive drum 1.

  In this embodiment, an AC voltage on which a DC voltage is superimposed is applied from the power source 22 to the residual toner equalizing means 7 during image formation.

  By applying a DC voltage having a polarity opposite to the normal polarity of the toner to the residual toner equalizing means 7 so as to be superimposed on the AC voltage, the electrostatic latent image on the photosensitive drum 1 is neutralized to prevent a positive ghost. To do. Further, a negative voltage having the same polarity as the normal polarity of the toner is applied from the power source 21 to the toner charging unit 6 during image formation. This is to prevent the toner slightly slipping from the residual toner image uniformizing means 7 from contaminating the charging roller 2. In order to avoid this, in this embodiment, by applying a DC voltage of −700 V or higher, which is equal to or higher than the discharge start voltage, the transfer residual toner passing through the toner charging unit 6 is negatively charged (regular) due to sufficient discharge. Polarity).

  Thereafter, in the charging process in the charging unit a described above, the surface of the photosensitive drum 1 is charged from above the transfer residual toner. The polarity of the transfer residual toner is uniformly made negative by the toner charging unit 6. Therefore, no toner adheres to the charging roller 2. Further, the charged charge of the transfer residual toner is appropriately neutralized by the AC bias applied to the charging roller 2. However, since the toner charging means is in contact with the image carrier, even if the density and fineness of the current brush are defined, the transfer residual toner passing therethrough is trapped. If the trapped toner is accumulated as it is, the toner charging capability will be hindered, so that it is essential to discharge the toner from the charging auxiliary means. The toner discharge operation will be described. As a pre-operation in which the residual developer uniformization control unit 7 and the toner charge amount control unit 6 perform the discharge operation substantially simultaneously, only the AC voltage is applied to the charging roller 2 to The voltage applied to the residual developer equalization control means 7 and the toner charge amount control means 6 when the discharge operation is performed is performed so that the potential on the surface of the photosensitive drum 1 is approximately 0 V by the discharge operation. A voltage that does not fluctuate is applied (± 300 V in this embodiment), and the charging roller 2 is set to approximately 0 V with respect to the discharged photosensitive drum 1 surface.

  Here, the voltage at which the potential of the surface of the photosensitive drum 1 of approximately 0 V does not fluctuate due to the discharging operation is preferably a voltage equal to or lower than the charging start voltage during the image forming operation.

Most of the discharged toner is basically recovered by electrostatic and physical rubbing by a developing device using contact two-component counter development. However, there is a case where the developer is not completely recovered for a toner having a small charge amount or a reverse polarity toner even with a normal polarity. However, these are transferred to the intermediate transfer belt from the photosensitive drum by pressure transfer at the transfer nip, and are removed from the belt by the intermediate transfer belt cleaner. During the discharging operation of the toner charge amount control means 6, if a voltage having a polarity opposite to the normal polarity (negative polarity) is applied to the transfer bias by the primary transfer bias source, the positive polarity toner is easily transferred, which is more effective. .
As a result, it is possible to allow the discharged toner having both normal polarity and reverse polarity to pass through the charging nip portion without adhering to the charging roller 2.
By performing the discharging operation under such conditions, it is possible to prevent the charging roller from being contaminated by the discharged toner and to always perform good image formation.

  Subsequently, in the exposure process in the exposure part b, exposure is performed from the transfer residual toner, but since the amount of transfer residual toner is small, there is no influence. Then, in the developing process in the developing unit c, the transfer residual toner adhering to the unexposed part (non-image part) on the photosensitive drum 1 that should not be developed is completely in the negative polarity, and the charging roller 2 As a result, it is possible to reduce the mirror power with respect to the photosensitive drum 1 by appropriate neutralization. Therefore, the surface potential (unexposed portion potential: −500 V) of the photosensitive drum 1 and the DC component (−350 V) of the developing bias (fogging potential difference Vback) are reliably recovered in the developing device 4. . As described above, in the present embodiment, the developing sleeve 41 of the developing device 4 is rotated in the developing unit c in a direction opposite to the traveling direction of the surface of the photosensitive drum 1, and the developer layer carried thereon is used as the photosensitive drum. 1 is rubbed (contact two-component counter development method). This is advantageous for collecting the transfer residual toner on the photosensitive drum 1.

Next, the configuration of the Bk developing device 400 in the fixed developing device 4Bk will be described with reference to FIG.
In the fixed developing device 4Bk, the developing container 400 has an opening extending in the longitudinal direction of the device, and a developing sleeve 401 serving as a fixed developer carrier is installed in the opening. The developing sleeve 401 is made of a material such as aluminum or SUS. Further, the developing sleeve 401 has a substantially left half circumferential surface that protrudes into the developing container 400 as seen in the drawing of the opening, and a right substantially half circumferential surface is exposed to the outside of the developing container 400 so as to face the photosensitive drum 1. It is rotatably arranged. A small gap (S-Dgap) is provided between the developing sleeve 401 and the photosensitive drum 1, and the developing sleeve 401 is rotationally driven in the direction of the arrow R4a with respect to the rotational direction Rl of the photosensitive drum 1.

The minute gap S-Dgap is variable while the Bk developer 400 is pressed in the direction of the arrow R4c against the fixed developing device 4a by a variable means (not shown).
A magnet 402 is provided as a magnetic field generating means in the developing sleeve 401. In the present embodiment, the magnet 402 is a permanent magnet. The magnet 402 is disposed non-rotatingly in the developing sleeve 401 so that a fixed magnetic field can be generated regardless of the rotation of the developing sleeve 401.

In the vicinity of the developing sleeve 401 in the developing container 400, a plate-like magnetic blade 403 is provided as a developer regulating member, with a fixed end supported by the opening of the developing container 400 and an opposing free end close to the developing sleeve 401. The magnetic blade 403 is positioned so that one of the magnetic poles of the magnet 402 is substantially opposed to the magnetic blade 403.

The magnetic toner 405 carried on the developing sleeve 401 by the stirring member 404 is then conveyed to a portion of the magnetic blade 403 facing the developing sleeve 401 as the developing sleeve 401 rotates. Then, the magnetic regulation formed in the gap between the magnetic blade 403 and the developing sleeve 401: the layer thickness is regulated by S-Bgap, and after the thin layer is formed on the developing sleeve 401, the regulating part: S- The toner is discharged from the Bgap and conveyed to the developing area facing the photosensitive drum 1 with a small gap: S-Dgap. In the developing area, a bias applying unit (not shown) applies an alternating voltage in which an alternating current is superimposed on a direct current as a developing bias voltage between the developing sleeve 401 and the photosensitive drum 1. Transfers and adheres to the electrostatic latent image on the photosensitive drum 1 to visualize and develop the electrostatic latent image as a toner image.

  Next, development by the Bk developing device 400 in this embodiment will be described.

  First, the surface of the photosensitive drum 1 is uniformly charged by the primary charger 2 to the drum surface potential vd = + 400V. Next, the surface of the photosensitive drum 1 is exposed to PWM exposure L at 600 dpi by a semiconductor laser having a wavelength of 680 μm, and an electrostatic latent image is formed on the photosensitive drum 1. The laser power at this time is set so that the electrostatic latent image becomes V1 = + 50V.

  Subsequently, development is performed by the Bk developing device 400 with S-Bgap: 250 μm and S-Dgap: 250 μm, and visualized as a toner image. In the above-described conventional example, the color image formation by the normal development has been described, but in this embodiment, the case where the reverse development is adopted will be described.

  The developer used in this embodiment is a negative magnetic one-component toner, and the development bias voltage Vdc superimposes an AC voltage of 2700 Hz, 1500 Vpp, and 50% Duty on a DC voltage of +200 V to realize jumping development. This is because the Bk development contrast Vcont (= Vd−Vdc) = 200 V and the fog removal bias Vback (= Vdc−Vl) = + 150 V in the reversal development are set.

  Next, the cleaning device 7Bk used in the black image forming portion Pbk of this embodiment will be described with reference to FIG. The cleaning device 7Bk includes a cleaning container 109a, a cleaning blade 109b held by the cleaning container 109a and in contact with the surface of the photosensitive drum 1, and an upstream side of the cleaning blade 109b (relative to the rotational direction of the photosensitive drum 1). A magnet roller 109c as a magnetic roll, a regulating roller 109d, and a screw 109e are provided on the upstream side) with a predetermined gap with respect to the photosensitive drum 1. A cleaner pre-exposure device 108 is disposed upstream of the magnet roller 109c in the rotation direction of the photosensitive drum 1, and a separation claw 113 is disposed upstream of the cleaner pre-exposure device 108. Yes.

  The cleaning blade 109b is made of urethane rubber having a thickness of 3 mm, and the magnet roller 109c is made of an 18 mm diameter roller having eight magnetic poles each having a magnetic flux density of 1000 gauss.

  The photosensitive drum 1 is rotationally driven at a predetermined speed in the direction of the arrow R1 shown in the drawing. After the surface of the photosensitive drum 1 is neutralized by the pre-exposure device 2, the surface is uniformly charged by the primary charger 2Bk. When the image exposure light L is irradiated on the surface of the photosensitive drum 1, an electrostatic latent image corresponding to the image is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed by the developing device 5 and visualized as a toner image.

  By the way, the photosensitive drum 1 has an amorphous silicon photosensitive layer having a thickness of 30 μm formed by glow discharge on an aluminum cylinder having a diameter of 108 mm and a thickness of about 5 mm. Then, a sheet heating element heater 114 of about 80 W is arranged in the inside of the photosensitive drum 1 and the power is controlled so that the temperature of the aluminum cylinder becomes 42 ° C.

Next, the configuration of the cleaning device 7bk will be further described.
The cleaning device 9 will be described in more detail with reference to FIG. The cleaning blade 109b is an elastic blade mainly composed of urethane, has a hardness of 70 ° (Hs), a rebound resilience of 41 (%) (a rebound resilience of 63% at 40 ° C.), and a 300% modulus of 200 (kg / cm ^2). ) (Both according to JIS standards), the edge portion A is disposed opposite the photosensitive drum 1 at a contact angle of 24 ° and a contact pressure of 10 (g / cm). The magnet roller 109c rotates in the forward direction with respect to the rotation direction of the photosensitive drum 1 at a peripheral speed of 10% relative speed. The magnet roller 9c is disposed with a gap of 1.0 mm with respect to the photosensitive drum 1. The regulating roller 109d is disposed with a gap of 1.8 mm with respect to the magnet roller 109c, and rotates in the forward direction at a relative speed of 10% with the magnet roller 109c.

Hereinafter, the developer used in this embodiment and the added inorganic fine particles will be described.
The two-component developer (developer) 4e in the developing container 4a is mainly a mixture of a non-magnetic toner and a magnetic carrier, and is stirred by the developer stirring member 4f.
The developer used in the image forming apparatus according to this embodiment is a two-component developer that is a mixture of a non-magnetic toner produced by a polymerization method or a pulverization method and a magnetic carrier.

The developer has a T / D ratio (weight Wt%) of 8%. As the magnetic carrier, the magnetization intensity in the magnetism of (4π) ⁻¹ × 10 6 A / m ( ¹ kOe) is 4π × 10 ⁻² Wb / m ² (100 emu / cm ³ ). Resistance is about 10 ¹³ Ωcm, particle size (volume average particle size: measured using laser diffraction particle size distribution measuring device HEROS (manufactured by JEOL Ltd.) in a range of 0.5 μm to 350 μm divided into 32 logarithms. The volume average particle diameter with a 50% median diameter is about 40 μm.

  The toner used in the image forming apparatus according to this embodiment preferably has an average primary particle size in the range of 4 μm to 9 μm. If the toner has an average primary particle size of less than 4 μm, it becomes difficult to differentiate the level of adhesion to a brush having a particle size of about 100 nm with an abrasive, and only the abrasive is selectively attached to the brush. Is difficult. In addition, if the average primary particle size is larger than 9 μm, it is difficult to form high-resolution dots for realizing high image quality.

  The weight average particle diameter of the toner was measured using Coulter Multisizer II (manufactured by Coulter). An interface (manufactured by Nikka) and a PC9801 personal computer (manufactured by NEC) are connected to Coulter Multisizer II, and a 1% NaCl aqueous solution is prepared using first-grade sodium chloride. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, a surfactant, preferably alkylbenzene sulfonate, is added in an amount of 0.1 to 5 ml as a dispersant in 100 to 150 ml of the electrolytic aqueous solution, and further 2 to 20 mg of a measurement sample is added. The electrolyte in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toners of 2 μm or more are measured using the 100 μm aperture as an aperture with the Coulter Multisizer. Volume distribution and number distribution were calculated. Then, the weight-average particle diameter based on the weight based on the volume distribution according to the present invention (representing the representative value of each channel as the representative value for each channel) was obtained.

  The toner used in the image forming apparatus of the present invention is a toner that has been made spherical after being manufactured by a pulverization method or the like, and has a circularity of 0.96.

<Measurement of average toner circularity>
The average circularity of the toner is measured using a flow type particle image measuring device “FPIA-2100 type” (manufactured by Sysmex Corporation), and is calculated using the following equation.

  Here, the “particle projected area” is the area of the binarized toner particle image, and the “peripheral length of the particle projected image” is the length of the contour line obtained by connecting the edge points of the toner particle image. Define. The measurement uses the perimeter of the particle image when image processing is performed at an image processing resolution of 512 × 512 (pixels of 0.3 μm × 0.3 μm).

  In the present invention, the circularity is an index indicating the degree of unevenness of the toner particles, and is 1.000 when the toner particles are completely spherical. The more complicated the surface shape, the smaller the circularity.

The average circularity C _{AVE. Which} means the average value of the circularity frequency distribution is calculated from the following equation, where ci is the circularity (center value) at the dividing point i of the particle size distribution and m is the number of measured particles. The

  In addition, “FPIA-2100”, which is a measuring apparatus used in the present invention, calculates the circularity of each particle, and then calculates the average circularity and the circularity standard deviation. The degree of 0.4 or more and 1.0 or less is divided into equal classes every 0.01, and the average circularity and circularity standard deviation are calculated using the center value of the division points and the number of measured particles.

  As a specific measuring method, 10 ml of ion-exchanged water from which impure solids have been removed in advance is prepared in a container, and a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant therein, followed by further measurement. Add 0.02 g of sample and disperse uniformly. As a means for dispersion, an ultrasonic disperser “Tetora 150 type” (manufactured by Nikka Ki Bios Co., Ltd.) is used, and dispersion treatment is performed for 2 minutes to obtain a dispersion for measurement. In that case, it cools suitably so that the temperature of this dispersion may not be 40 degreeC or more. In order to suppress variation in circularity, the installation environment of the apparatus is controlled at 23 ° C. ± 0.5 ° C. for a certain period of time so that the in-machine temperature of the flow type particle image analyzer FPIA-2100 is 26 ° C. or higher and 27 ° C. or lower. In other words, the autofocus is preferably performed every 2 hours using 2 μm latex particles.

  To measure the circularity of the toner particles, the flow type particle image measuring apparatus is used, and the dispersion concentration is readjusted so that the toner particle concentration at the time of measurement is 3000 / μl or more and 10,000 / μl or less, 1000 or more toner particles are measured. After the measurement, using this data, data having an equivalent circle diameter of less than 2 μm is cut to determine the average circularity of the toner particles.

  In this embodiment, the toner is triboelectrically charged to the negative polarity by rubbing with the magnetic carrier.

  In the embodiment of the present invention, strontium titanate is used in order to stably use a photoconductor having a surface protection layer with high elasticity and hardness. As in the present invention, the toner charging means has a surface layer formed of a highly elastic organic material, and when used in a cleanerless system, the toner charging means itself has a certain degree of friction, In order to capture the external additive and rub the surface of the photosensitive drum, it is preferable that the external additive has an appropriate hardness, strontium titanate is preferable also in terms of Mohs hardness, and the following are preferable. .

  Strontium titanate, which is an inorganic fine powder containing 50% by number or more of perovskite crystals having an average primary particle size of 30 nm to 300 nm and having a substantially cubic or cuboid particle shape, is preferred. It is 0.2 mass% or more with respect to 100 mass parts of resin, More preferably, 0.5 mass%-1.0 mass% are externally added.

  Further, the release rate of the inorganic fine particles with respect to the toner base particles is preferably 15% by number or more. When the release rate is 15% by number or less, most of the strontium titanate contained adheres to the surface of the toner base, and the drum It will move up and adhere to the brush, and a sufficient rubbing effect will not be achieved. In order to obtain a sufficient polishing effect, it is important that strontium titanate alone adheres to the brush.

  However, even if the liberation ratio is 15% by number or more, if the amount of external addition is less than 0.2% by mass, the polishing performance on the surface of the photosensitive drum, which is the purpose of external addition of the above strontium titanate, cannot be exhibited sufficiently. On the other hand, if the amount of the external additive is more than 1.0% by mass, the coverage on the toner surface is excessively increased and affects the developability and fixability.

  The measurement method of the content T (Wt%) of the strontium titanate with respect to the total mass of the toner was performed by fluorescent X-ray measurement. Specifically, RIX3000 manufactured by Rigaku Denki Kogyo Co., Ltd. is used, and two strontium nets of toner, which are not externally added to the toner, and toner in which 1 part by weight of strontium titanate is externally added to 100 parts by weight of the toner resin. The strength was measured, a calibration curve was created from both, and the strength ratio of each measurement sample was taken as the content rate T (Wt%).

  The liberation rate of the external additive is included in the toner particles with respect to the sum of the number of carbon atoms contained in the toner particles and atoms contained in the lubricating compound (for example, fluorine atoms for fluororesin and zinc atoms for zinc stearate). It is represented by the ratio of the number of atoms contained in the non-lubricating compound. The liberation rate can be measured according to the principle described on pages 65 to 68 of the “Japan Hardcopy97” paper collection. Specifically, each toner particle is introduced into the plasma one by one, and the element in the toner particle, the number of toner particles, and the particle size of the toner particle can be known from the obtained emission spectrum, and the above-mentioned release rate is measured from this emission spectrum. can do.

According to the above measurement method, the liberation rate of the lubricating compound is determined by the following formula (iii) from the emission of carbon atoms, which are constituent elements of the binder resin contained in the toner particles, and the emission of atoms of the lubricating compound. It is done.
(Iii) Free rate of external additive (number%) = (Number of light emission of only atoms contained in external additive) × 100 / (Number of light emission of atoms contained in external additive that emitted light simultaneously with carbon atom) + (Number of light emission of atoms in external additive)

  In the above formula, “simultaneously emitted” means emission of atoms contained in a compound having lubricity and emission within 2.6 msec from emission of a carbon atom, and is included in a compound having lubricity after that. The emission of atoms is the emission of only atoms contained in the compound having lubricity. Further, simultaneous emission of carbon atoms and atoms contained in the external additive means synchronization with the toner particles, and light emission of only the atoms contained in the external additive means that the external additive is removed from the toner particles. It means that it is free. The liberation rate was measured using a particle analyzer (PT1000: manufactured by Yokogawa Electric Corporation) using an emission spectrum.

  The specific measurement method is as follows. First, using helium gas containing 0.1% oxygen, measurement is performed in an environment with a temperature of 23 ° C. and a humidity of 60%, and the toner sample is left in the same environment overnight to adjust the humidity. In the measurement, carbon atoms are measured in channel 1 (measurement wavelength 247.860 nm, K factor is the recommended value), and atoms contained in the external additive are measured in channel 2, and the number of emission of carbon atoms in one scan is measured. Sampling is performed so as to be 1,000 times or more and 1,400 times or less, and scanning is repeated until the total number of light emission of carbon atoms becomes 10,000 or more, and the number of light emission is integrated. At this time, in the distribution in which the number of light emission of the carbon atom is on the vertical axis and the cube root voltage of the carbon atom is on the horizontal axis, the distribution has one maximum and further has a valley-free distribution. Sampling and measuring. Based on this data, the noise cut level of all atoms is set to 1.50 V, and the liberation rate of the external additive is calculated using the above formula (iii).

  The liberation rate of the external additive in this example is defined as an integrated value of the liberation rates of all the external additives contained other than the toner base. In this example, strontium titanate as an external additive (average particle size of primary particles: 100 nm) At this time, the liberation rate is calculated for the Sr element, and the value obtained by integrating these is the liberation rate of the total external additive.

  The toner aggregation degree is desirably 15 or more. When the degree of aggregation of the toner is too low, the toner particles exist alone and the probability of forming an aggregate is reduced, and not only the abrasive but also the toner base particles are likely to adhere to the brush. As a method for measuring the degree of toner aggregation, a powder tester and a digital vibrometer (Digivibro MODEL 1332) manufactured by Hosokawa Micron Corporation are used.

As a measuring method, a sieve having an opening of 38 μm, a sieve having an opening of 75 μm, and a sieve having an opening of 150 μm are set on a vibration table. Add 5 g of accurately weighed sample on the set top sieve of 150 μm, adjust the displacement value of the digital vibration meter of the shaking table to 0.500 ± 0.015 mm, and vibrate for about 15 seconds. Add. Then, the mass of the residual sample of the sieve having an opening of 150 μm is ag, the mass of the residual sample of the sieve having an opening of 75 μm is bg, and the mass of the remaining sample of the sieve having an opening of 38 μm is cg. obtain.
Aggregation degree (%) = ((a + b) × 0.6 + c × 0.2) / 5

The inorganic fine powder of the perovskite crystal used in the present invention should have an average primary particle size of 30 nm to 300 nm, more preferably 100 nm to 180 nm.
If the average particle size is less than 30 nm, the polishing effect of the particles is insufficient. On the other hand, if the average particle size is 300 nm or more, the polishing effect is too strong, causing a problem that the drum is scratched.
In addition, about the particle size of the inorganic fine powder in this invention, it measured by measuring 100 particle size from the photograph image | photographed with the magnification of 50,000 times with the electron microscope.

  Further, the abrasive described in the present invention is preferably hydrophobized, and when using a fiber brush with low hygroscopicity such as nylon, the hydrophobized inorganic fine particles are more and stronger. It is known to adhere to fibers. Therefore, the effect of the present invention of adhering only the abrasive without adhering the toner base is further promoted.

In addition, when the particle diameter of the inorganic fine powder that is approximately cubic or rectangular parallelepiped is the longest length (T1) and the shortest short side (S1) in the shape of the fine powder, The particle size of the inorganic fine powder was calculated using the formula.
Particle size of inorganic fine powder = (T1 + S1) / 2

  Further, it is preferable that the inorganic fine powder of the present invention contains 50% by number or more of the particles whose shape is approximately cubic or rectangular parallelepiped because the charged product can be more efficiently removed.

  The schematic cubic and cuboid (dice, cubic shape) shape of the inorganic fine powder is a shape as shown in FIG. 7 showing a photograph taken with an electron microscope at a magnification of 50,000 times.

  In addition, in order to improve the developability and the responsiveness to a brush member to which a bias is applied, the charged polarity of the inorganic fine powder of the perovskite crystal subjected to the surface treatment of the present invention is opposite to that of the toner. Is preferred.

  If it is opposite to the charging polarity of the toner, the inorganic fine powder is likely to adhere to the toner charge amount control means 6 that is charged to the same polarity as the toner, and the normal non-reversed transfer residual toner is difficult to adhere. Only the inorganic fine powder can be selectively adhered to the brush as the charge amount control means, and the polishing ability of the photoreceptor can be exhibited. In addition, the bias applied to the primary transfer means is the opposite polarity to the charging polarity of the toner, so the toner is easily transferred, but if the added inorganic fine powder has the opposite polarity to the toner, it is difficult to transfer at the primary transfer portion. Thus, it is possible to generate a transfer residual toner richly containing inorganic fine powder and to attach a lot of inorganic fine powder to the brush.

The method for measuring the charge amount is as follows.
Using DSP 138 (manufactured by Dowa Iron Industries Co., Ltd.) as a carrier under an environment of a temperature of 23 ° C. and a relative humidity of 50%, a mixture obtained by adding 0.1 g of the sample to be measured to 9.9 g of the carrier is put into a 50 ml capacity polyethylene bottle. Shake 100 times. Next, as shown in FIG. 8, about 0.5 g of the mixture is put in a metal measuring container 172 having a metal mesh screen 173 having a mesh opening of 32 μm at the bottom, and a metal lid 174 is formed. At this time, the mass of the entire measurement container 172 is weighed and is defined as W1 g. Next, in the suction machine 171 (at least a part in contact with the measurement container 172 is suctioned), the pressure of the vacuum gauge 175 is set to 250 mmAq by suction from the suction port 177 and adjusting the air volume control valve 176. In this state, suction is performed for 2 minutes to remove the developer by suction. The potential of the electrometer 179 at this time is set to V (volt). Here, 178 is a capacitor, and the capacity is C (μF). Moreover, the mass of the whole measuring machine after suction is weighed and is defined as W2 (g). The triboelectric charge amount (mC / kg) of the developer is calculated as follows:
Frictional charge amount = CV / (W1-W2)

  Further, the relationship between the adhesion amount of strontium titanate, which is an abrasive, to the brush, the adhesion amount of the toner base to the brush, and the image flow will be described below.

  As described above, in order to effectively rub the surface of the photoreceptor in order to prevent filming and image flow, the toner should not be attached to the brush as the toner charging means as much as possible, and the abrasive. It is important to deposit strontium titanate. Therefore, it is necessary to release strontium titanate, which is an abrasive, from the toner base as much as possible, to behave alone, and to add as much as possible. In addition, by differentiating the primary average particle size between the toner base and an abrasive such as strontium titanate and optimizing the fineness and density of the brush, the toner base can be adhered to the strontium titanate as much as possible. Only the abrasive is selectively attached to the brush, and the polishing effect can be obtained.

  Further, as shown in FIG. 7, the strontium titanate of the perovskite crystal used this time has a cubic or rectangular parallelepiped shape, which is effective for a brush or the like even in a cleaningless system having no cleaning blade. If it is made to adhere, a very high polishing ability can be obtained as compared with a conventional amorphous one. When the ratio of the number of adhered toner to the brush and the number of adhered abrasive is plotted on the horizontal axis, the average particle size of the toner and the abrasive is varied, and the release rate of the abrasive with respect to the toner base particles is varied. FIGS. 9, 10, 11, and 12 show the cases where the amount of the abrasive added to the toner base is varied and the degree of aggregation of the toner is varied.

  In the examples, the ratio of the number of adhered toner base particles and abrasive particles is shown as an adhesion amount ratio F as a barometer indicating whether or not the abrasive is selectively attached to the brush. The adhesion amount ratio F is expressed by the following equation, and the larger F is, the higher the polishing effect is. F = (Number of adhered abrasives to the brush) / (Number of adhered toner base particles)

  Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The rate was 40% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 1-1 shows the results of the evaluation where “0” indicates that no image flow occurred, “Δ” indicates a slight occurrence, and “×” indicates a clear occurrence.

  Since the toner base particle size and the abrasive particle size are differentiated, and a sufficient amount of abrasive is added and the abrasive is free, the abrasive can be selectively attached to the brush. The adhesion ratio F exceeded 300, which has a sufficient effect on the image flow, so that a rubbing effect was produced and the image flow could be suppressed.

  Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 250 nm as a polishing agent added to the toner mass is added. The ratio was 35% by number, and the toner aggregation degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 2-1 shows the results of the evaluation where “0” indicates that no image flow occurred, “Δ” indicates a slight occurrence, and “×” indicates a clear occurrence.

  Since the toner base particle size and the abrasive particle size are differentiated, and a sufficient amount of abrasive is added and the abrasive is free, the abrasive can be selectively attached to the brush. The adhesion ratio F exceeded 300, which has a sufficient effect on the image flow, so that a sufficient rubbing effect was obtained and the image flow could be suppressed.

[Comparative Example 1]
Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of the strontium titanate having a cubic shape with an average primary particle size of 600 nm as a polishing agent added to the toner mass is added to the toner. The ratio was 30% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 1-2 shows the results of the evaluation when the image was not generated as ◯, when the image occurred slightly as Δ, and when it occurred clearly as ×.

  Due to the excessively large abrasive particles, the high-density brush cannot adhere to the toner base particles together with the toner base particles, and the adhesion ratio F is sufficiently effective for the image flow even if the abrasive is separated. Since there was no over 300, sufficient polishing effect could not be achieved, and image spill occurred.

  Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.2% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The rate was 40% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 3-1 shows the results of evaluations where “0” indicates that no image flow has occurred, “Δ” indicates that it has occurred somewhat, and “×” indicates that it has clearly occurred.

  The toner base particle size and the abrasive particle size were differentiated, and there was a little, but a sufficient amount of abrasive was added and the abrasive was free, so the abrasive was selected for the brush Since the adhesion ratio F sufficiently exceeded 300 in the image flow, a sufficient rubbing effect was obtained and the image flow could be suppressed.

[Comparative Example 2]
Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.1% by mass of strontium titanate having a cubic shape with an average primary particle size of 110 nm as a polishing agent added to the toner mass is added in an amount of 0.1% by mass. The ratio was 50% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 2-2 shows the results of the evaluation when the image was not generated as ◯, when the image occurred slightly as Δ, and when it occurred clearly as ×.

  Due to the extremely small amount of abrasive added to the toner particles, sufficient abrasive is not supplied to the brush, so that the abrasive cannot adhere together with the toner base particles, and the abrasive is present even if it is present. The adhesion ratio F did not exceed 300, which has a sufficient effect on image flow, so that a sufficient polishing effect could not be obtained and image flow occurred.

  Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The rate was 15% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 4-1 shows the results of the evaluation where “0” indicates that no image flow occurred, “Δ” indicates that some image flow occurred, and “×” indicates clear image generation.

  The toner base particle size and the abrasive particle size are differentiated, and a sufficient amount of abrasive is added, and the abrasive is separated by 15% or more, so that the abrasive is selectively attached to the brush. Since the adhesion ratio F exceeded 300, which has a sufficient effect on the image flow, a sufficient rubbing effect was obtained and the image flow could be suppressed.

[Comparative Example 3]
Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The ratio was 8% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 3-2 shows the results of the evaluation when the image did not occur was evaluated as ◯, when the image occurred somewhat as Δ, and when it occurred clearly as ×.

  Since the release rate of the abrasive with respect to the toner particles is extremely small at 8%, sufficient abrasive is not supplied to the brush, so that the abrasive cannot adhere together with the toner base particles, and the abrasive is present free. Even in this case, the adhesion ratio F did not exceed 300, which has a sufficient effect on the image flow, so that a sufficient polishing effect could not be obtained and an image flow occurred.

  Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as a polishing agent added to the toner mass is added. The ratio was 40% by number and the toner cohesion degree was 20%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 5-1 shows the results of evaluations where ◯ indicates that no image flow has occurred, Δ indicates that it has occurred somewhat, and X indicates that it has clearly occurred.

  Since the toner base particle size and the abrasive particle size are differentiated, and a sufficient amount of the abrasive is added and the abrasive is sufficiently separated, the abrasive can be selectively attached to the brush. Since the adhesion ratio F exceeded 300, which has a sufficient effect on the image flow, a sufficient rubbing effect was obtained and the image flow could be suppressed.

[Comparative Example 4]
Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The rate was 40% by number and the toner cohesion degree was 10%.

The material of the brush used for the toner charging means is a conductively treated nylon with an official moisture content of 4%, the brush fineness is not less than 0.5d (denier) and not more than 4d (denier), and the brush density is 300KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 4-2 shows the results of the evaluation where “0” indicates that no image flow occurred, “Δ” indicates a slight occurrence, and “×” indicates that it occurred clearly.

  The abrasive has a high release rate with respect to the toner particles, and a sufficient amount of abrasive was supplied to the brush. However, the toner particles did not aggregate together with the abrasive and the fluidity was quite high. Therefore, the adhesion ratio F did not exceed 300, which is sufficiently effective for image flow, so that a sufficient polishing effect could not be obtained and image flow occurred.

[Comparative Example 5]
Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The rate was 40% by number and the toner cohesion degree was 45%.

The material of the brush used for the toner charging means is a rayon having an official moisture content of 11% that has been subjected to conductive treatment, the fineness of the brush is not less than 0.5d (denier) and not more than 4d (denier), and the density of the brush is 300 KF / inch ² What was comprised above and below 600KF / inch ² was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 5-2 shows the results of the evaluation when the image was not generated as ◯, when the image occurred slightly as Δ, and when it occurred clearly as ×.

  The release rate of the abrasive with respect to the toner particles is also large, and a sufficient amount of abrasive was supplied to the brush. However, the abrasive was also retained, but the fiber constituting the brush was a highly hygroscopic rayon. However, in high-temperature and high-humidity places such as in H / H environments, the fibers may sag and do not produce a sufficient polishing effect, resulting in image flow. I have.

[Comparative Example 6]
Using the image forming apparatus shown in FIG. 1, the photosensitive drum A described above is used as the photosensitive drum, and the toner has an average primary particle diameter of 5.5 μm and an average circularity of 0.96. In addition to the two-component non-magnetic toner, 0.5% by mass of a strontium titanate having a cubic shape with an average primary particle size of 110 nm as an abrasive added to the toner mass is added to the toner. The rate was 40% by number and the toner cohesion degree was 45%.

The material of the brush for use in toner charging means is a moisture regain of 4% of nylon and conductive treatment, the fineness of the brush is less than 1d (denier) or more 6d (denier), and the density of the brush 50KF / inch ² or more The one composed of 200KF / inch ² or less was used.

  In the above image forming apparatus, 10,000 sheets of A4 size, 5% Duty images were continuously flowed in an HH environment (30 ° C./80%), and then left for 3 nights to evaluate image flow. Table 6-2 shows the results of the evaluation when the image did not occur was evaluated as ◯, when the image occurred somewhat as Δ, and when it occurred clearly as ×.

  Abrasion rate of the abrasive with respect to the toner particles is large, and a sufficient amount of abrasive was supplied to the brush, but the abrasive was also retained, but because the density of the fibers constituting the brush was low, not only the abrasive but also the toner particles Since the adhesion ratio F did not exceed 300, which was sufficiently effective for image flow, a sufficient polishing effect could not be obtained and image flow occurred.

1 is a schematic view of a four-drum type color electrophotographic copying apparatus described in Examples 1 to 6. FIG. FIG. 7 is a schematic cross-sectional view illustrating a configuration around a photosensitive drum of an image forming unit having the cleaningless system according to any of Embodiments 1 to 6. It is a figure which shows the outline of the output chart of Fischer scope H100V (made by Fischer). It is an image figure which shows the cross section of the density state of a toner charging means brush fiber. It is the schematic which shows the structure of a Bk developing device. FIG. 7 is a schematic cross-sectional view illustrating a configuration around a photosensitive drum of an image forming unit including the cleaning device according to any of Embodiments 1 to 6. It is the SEM photograph of the strontium titanate of the perovskite type crystal | crystallization which has the shape of the cube used as an abrasive | polishing agent in this invention, or a rectangular parallelepiped. It is the schematic of the apparatus used for the measurement of the charge amount of the toner particle in this invention. The relationship between the ratio of the number of adhering toner to the brush and the number of adhering abrasive to the brush and the ratio of the average particle size of the toner base particle to the particle size of the abrasive when the density of the brush of the toner charging means is varied was shown. FIG. FIG. 5 is a graph showing the relationship between the ratio of the number of adhered toner to the brush and the number of adhered abrasive and the release rate of the abrasive from the toner particles when the density of the brush of the toner charging unit is varied. FIG. 5 is a diagram showing a relationship between a ratio of the number of toners attached to a brush and a number of abrasives attached to the brush when the density of the brush of the toner charging unit is varied, and the amount of the abrasive added to the toner particles. FIG. 6 is a graph showing the relationship between the ratio of the number of adhered toner to the brush and the number of adhered abrasive and the degree of toner aggregation when the density of the brush of the toner charging unit is varied.

Explanation of symbols

100 Image forming apparatus 1 Electrophotographic photosensitive member (photosensitive drum)
2 Charging means (charging roller)
2a Core (support member)
2b Lower layer (foamed sponge layer)
2c Intermediate layer (resistance layer)
2d surface layer (protective layer)
2f Charging roller cleaning member 2g Support member 3 Exposure means (laser beam scanner)
4 developing means 4a developing container 4e two-component developer 4f developer stirring member 4Bk fixed developing device 5 developer supply container (toner supply unit)
6 Toner charging means (toner charge amount control means)
7 residual toner equalizing means 8 process cartridge 9a, 9b, 9c, 9d primary transfer bias source 10 secondary transfer roller 12 paper feed roller 11 intermediate transfer belt cleaner 11a cleaning blade 13 fixing means (roller fixing device)
20, 21, 22 Power supply (voltage application means)
40 Developing container 41 Developing sleeve 42 Developer regulating blade 43, 44 Developer stirring member (stirring screw)
45 Sensor 46 Two-component developer 47 Toner replenishment opening 51 Screw 61, 71 Brush part 62, 72 Electrode plate 91 Intermediate transfer member 92 Primary transfer roller 93 Primary transfer bias power supply 94 Drive roller 95 Tension roller 96 Secondary transfer counter roller 108 Pre-cleaner exposure device 109a Cleaning container 109b Cleaning blade 109c Magnet roller 109d Restriction rollers 110a and 110b Mounting means 111 Charging unit frame body 112 Development frame body 113 Separation claw 114 Planar heating element heater 130 Control circuit 171 Suction machine 172 Charge amount measurement Container 173 Screen 174 Metal lid 175 Vacuum gauge 176 Air volume control valve 177 Suction port 178 Condenser 179 Electrometer 400 Bk developer 401 Developer sleeve (fixed developer carrier)
402 Magnet 403 Magnetic blade 404 Stirring member 405 Magnetic toner a Charging part (contact part)
b Exposure unit d Transfer unit e Contact unit P Transfer material PY, PM, PC, PBk Image forming unit

Claims (8)

An image carrier, a charging unit that charges the surface of the image carrier, and a developing unit that develops the latent image formed on the image carrier, and a transfer unit to which the formed toner image is transferred. In the image forming apparatus provided,
A voltage having the same polarity as the charging polarity of the toner is applied to a position downstream of the transfer portion where the transfer means is located and upstream of the charging portion where the charging means is located with respect to the rotation direction of the image carrier. The charging auxiliary means includes a brush member made of conductive fibers, and the fineness of the fibers constituting the brush is not less than 0.5d (denier) and not more than 4d (denier), and the density of the brush is composed of 300KF / inch ² or more 600KF / inch ² or less,
The toner forming the toner image is a toner to which inorganic fine particles having a charging polarity opposite to the charging polarity of the toner are added,
The average primary particle size of the inorganic fine particles is 1/20 or less of the average primary particle size of the toner base particles to be added, the degree of aggregation of the toner is 15% or more, and the addition amount of the inorganic fine particles to the toner base particles is 0.2. An image forming apparatus, wherein the inorganic fine particles have a liberation ratio of 15% by number or more with respect to toner base particles.   The image forming apparatus according to claim 1, wherein an average primary particle size of the inorganic fine particles is 30 nm or more and 300 nm or less.   The auxiliary charging means to which a voltage having the same polarity as the charging polarity of the toner is applied is a toner charging means for charging the toner remaining after the transfer to the same polarity as the charging polarity of the toner, and is charged by the toner charging means. The image forming apparatus according to claim 1, wherein the toner is a cleanerless system in which the toner is collected again by the developing device.   The fiber constituting the charging auxiliary means is a brush using a synthetic fiber having an official moisture amount (moisture absorption rate in an environment where the temperature is 20 ° C and the humidity is 65%) of 6% or less. The image forming apparatus according to any one of the above.   5. The image forming apparatus according to claim 1, wherein the inorganic fine particles added to the toner are hydrophobized fine particles.   6. The image forming apparatus according to claim 1, wherein the inorganic fine particles added externally to the toner have a cubic or rectangular parallelepiped particle shape.   7. The image forming apparatus according to claim 1, wherein the inorganic fine particles externally added to the toner are perovskite-type strontium titanate crystal fine particles. The surface of the image carrier is subjected to a hardness test using a Vickers square pyramid diamond indenter in an environment of a temperature of 25 ° C. and a humidity of 50%, and a HU (universal hardness value) when pressed at a maximum load of 6 mN is 150 N / mm. ² or more 220 N / mm ² or less, and an image forming apparatus according to any one of claims 1 to 7 elastic deformation rate We are equal to or less than 65% more than 45%.