JP2005309073A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which maintains stable cleaning performance over a prolonged period of time while using a high durability (high strength and high wear resistance) photoreceptor, does not cause image deletion, and ensures a long operating life, high image quality and a low running cost. <P>SOLUTION: In the image forming apparatus, an image carrier has a photosensitive layer on a conductive support, when the image carrier is subjected to a hardness test with a Vickers square-pyramidal diamond indentor in an environment at 25°C and 50% RH, wherein the image carrier is indented under a maximum load of 6 mN, a universal hardness (UV) is 150-220 N/mm<SP>2</SP>and an elastic deformation ratio (We) is 40-65%, a charging means is a contact roller member, a microhardness of a surface of the contact charging roller member is 75 to <100°, and an Asker C hardness of the contact charging roller member is ≤40°. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that forms an image using an electrophotographic system, and more particularly to an image forming apparatus that cleans residual toner remaining on the surface of a photosensitive drum.

  In general, in an image forming apparatus that records an image on a recording medium such as paper such as a copying machine, a printer, and a facsimile, an electrophotographic system is employed as a system for recording the image on the recording medium. In an electrophotographic system, a photosensitive drum having a surface coated with a photosensitive material is used as an image carrier. First, after the surface of the photosensitive drum is uniformly charged, the surface of the photosensitive drum is irradiated with laser light, and a potential difference is given between the irradiated portion and the non-irradiated portion. Next, the charged toner contained in the developer adheres to the surface of the photosensitive drum, whereby a toner image is formed on the surface of the photosensitive drum. Thereafter, the toner image is transferred to a recording medium, and an image is formed on the recording medium.

  As means for uniformly charging the surface of the photosensitive drum, a corona discharge device or a contact charging device is generally used. The corona discharge device is effective as a means for uniformly charging the surface of an object to be charged such as an image carrier to a predetermined potential, but has problems such as requiring a high voltage power source and generating ozone. ing. The contact charging device is a device that directly injects electric charges into the surface of the object to be charged by bringing a conductive charging member to which a voltage is applied into contact with the surface of the object to be charged to a predetermined potential. Even if it sees generation | occurrence | production, it has the characteristics of being a trace amount compared with a corona discharge device, a structure being simple, and maintenance-free.

  In such an electrophotographic system, since the surface of the photosensitive drum is repeatedly used for forming a toner image, after the toner image is transferred to the recording medium, it is not transferred to the recording medium. It is necessary to sufficiently remove the residual toner remaining on the surface of the drum. Many methods have been proposed for removing residual toner, but a method of scraping residual toner by contacting a cleaning blade, which is a counter blade made of an elastic material, with the surface of the photosensitive drum is low cost. Since the entire electrophotographic system can be made simple and compact and has excellent toner removal efficiency, it has been widely put into practical use. As a material for the cleaning blade, urethane rubber is generally used that has high hardness and high elasticity, and is excellent in wear resistance, mechanical strength, oil resistance, ozone resistance, and the like.

  The physical properties of the cleaning blade and the manner of contact with the image carrier greatly depend on the ease of cleaning depending on the degree of adhesion of the transfer residual toner to the image carrier and the surface property of the image carrier. Also, the cleaning properties are greatly affected by the physical properties such as the toner shape, particle size, and material. Therefore, it is necessary to select a blade suitable for the properties and set an appropriate angle and contact load with respect to the image carrier. In the actual selection and setting of the cleaning blade, the present condition is that the optimum condition is found through repeated trial and error.

  Recently, demands such as higher image quality and lower running cost of output devices have increased, and the photosensitive drum as an image carrier used in the electrophotographic system has a higher photosensitive layer thickness because of the necessity of high resolution. Thin ones are used, and in addition, in order to reduce the running cost, it is necessary to extend the life of the photosensitive drum itself, so that the electrical, mechanical strength and abrasion resistance of the photosensitive member surface can be improved. It has been.

  However, an image forming apparatus using such a photosensitive drum has the following problems.

  Since highly durable and highly durable photosensitive drums with high strength and high wear resistance have come to be used, use photosensitive drums with extremely high wear resistance, especially the surface abrasion amount of the photosensitive layer is 2 mg or less with a Taber abrasion tester. In this case, the surface of the photosensitive drum is not refreshed and electrical damage due to charging, surface deterioration due to adhesion of discharge products, mechanical damage due to rubbing with a cleaning blade, etc. accumulates over a long period of time. However, the slipping property (especially the cleaning blade) on the surface of the photosensitive drum is lowered, and the cleaning blade is liable to be chattered, squealed, or squeezed. Further, since the surface of the photosensitive member cannot be scraped, the discharge product is not removed, and there is a problem in that image flow occurs. Therefore, various methods have been considered so far to solve this problem.

For example, there is a method of preventing image flow by preventing a reduction in resistance of the surface of the photoreceptor due to moisture adsorption by heating with a heater (see Patent Document 1). However, the provision of a heater necessitates a heat control means and the like, which not only complicates the configuration, but also makes the system complicated if the heater is used especially in the miniaturization and personalization of copying machines and printers. Moreover, a certain time is required for raising the temperature of the heater, and the time (warm-up time) from when the power is turned on until printing is long, and power consumption for that is required. Further, when the photosensitive member is heated to a temperature close to the TG temperature (glass transition temperature) of the toner, the toner adheres to the surface of the photosensitive member. Various problems occur. As another method, a method of removing the corona product by rubbing the surface of the photoreceptor with an elastic roller is considered (see Patent Document 2). In this method, the rubbing force is sufficiently exerted, but since the toner scraped off from the surface of the photosensitive drum and adhering to itself is not further scraped off by other means, it is adhered to the roller forever. Repeated rubbing between them causes fusion. Conversely, if the roller surface is sufficiently scraped and the transfer residual toner is too small, the surface of the photosensitive drum may be damaged by direct contact and rubbing against the surface of the photosensitive drum. It was.
No. 1-334205 JP-A-61-100780

  The present invention solves the above-mentioned problems, and maintains a stable cleaning performance for a long period of time while using a highly durable (high strength, high wear resistance) photosensitive member, and does not cause image flow, and has a high An object of the present invention is to provide an image forming apparatus having a long life, high image quality and low running cost.

  The above object is achieved by an image forming apparatus having the following configuration according to the present invention.

(1) In an image forming apparatus having at least an image carrier, a charging unit, an image exposing unit, a developing unit, a transfer unit, and a cleaning unit,
The image carrier has a photosensitive layer on a conductive support, and the image carrier is subjected to a hardness test using a Vickers square pyramid diamond indenter in an environment of 25 ° C. and a humidity of 50% RH, with a maximum load of 6 mN. An image carrier having a universal hardness value (HU) of 150 N / mm ² or more and 220 N / mm ² or less when pressed and an elastic deformation rate (We) of 40% or more and 65% or less,
The charging means is a contact type roller member, the micro hardness of the surface of the contact type charging roller member is 75 degrees or more and less than 100 degrees, and the Asker C hardness of the contact type charging roller member is 40 degrees or less. An image forming apparatus.

  (2) The surface of the contact-type charging roller member has a directional surface roughness, and the directionality is opposite to the rotation direction of the image carrier at the contact portion with the image carrier. The image forming apparatus according to (1), wherein the image forming apparatus is configured as described above.

  (3) The image forming apparatus according to (1) or (2), wherein a width of a contact portion between the contact-type charging roller member and the image carrier is 3 mm or more and 10 mm or less.

  (4) The image forming apparatus according to (2) or (3), wherein a surface roughness of the contact-type charging roller member is 10 μm or more and 100 μm or less in terms of a 10-point average roughness.

  (5) The image forming apparatus according to any one of (1) to (4), wherein the surface layer of the contact-type charging roller member contains an inorganic fine powder.

  (6) The image forming apparatus according to any one of (1) to (5), wherein the contact-type charging roller member and the image carrier are arranged so that their rotational axes intersect. .

  According to the present invention, even when a high-hardness photosensitive member that is difficult to clean is used, there is an effect that stable image formation can be performed without causing image flow or chattering, squeaking, or blurring of the cleaning blade over a long period of time.

  Embodiments of a cleaning device and an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment.

[overall structure]
An image forming apparatus 1 shown in FIG. 1 is an electrophotographic color copying machine, and forms an image on a recording medium S in accordance with an image signal sent from a computer (not shown). The image carrier 2 of the image forming apparatus 1 is formed by applying a photosensitive material such as an organic photoreceptor (OPC) to the outer peripheral surface of a cylindrical support such as aluminum.

  The image carrier 2 is uniformly charged to about −600 V as the dark portion potential VD by the charging unit 3 as the contact charging unit while being rotationally driven at a peripheral speed of, for example, 200 mm / sec. Next, the laser oscillator 4 scans and exposes the laser beam 5 which is ON / OFF controlled according to the image information, and an electrostatic latent image of about −200 V is formed on the image carrier 2 as the bright portion potential VL. .

  The electrostatic latent image formed in this way is developed with toner as a developer by the rotary developing device 6 and visualized. The rotary developing device 6 includes a first developing device 6y including yellow toner as a first color toner, a second developing device 6m including magenta toner as a second color toner, and a third color toner. The third developing device 6c containing cyan toner and the fourth developing device 6k containing black toner as the fourth color toner are integrated.

  First, the first electrostatic latent image is developed and visualized by a first developing device 6y containing yellow toner as a first color toner. As a developing method, a jumping developing method, a two-component developing method, a FEED developing method or the like is used, and image exposure and reversal development are often used in combination. In this embodiment, a two-component development method using a non-magnetic toner is used.

  The visualized first color toner image is electrostatically applied to the surface of the intermediate transfer member 7 at the first transfer portion 7a facing the intermediate transfer member 7 as a second image carrier to be rotated. Transferred (primary transfer). The intermediate transfer member 7 is formed of a conductive elastic layer and a surface layer having releasability, and has a circumferential length slightly longer than the length of the maximum recording medium that can be conveyed. While being pressed by pressure, it is driven to rotate in a direction opposite to the rotation direction of the image carrier 2 (that is, in the same direction at the contact portion) with a circumferential speed substantially equal to the peripheral speed of the image carrier 2. Is done.

  The intermediate transfer member 7 is primarily transferred onto the surface of the intermediate transfer member 7 by applying a voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner to the cylinder portion by the high voltage power source 7c. The toner remaining on the surface of the image carrier 2 after the primary transfer is removed by a cleaning device 8 described later. Subsequently, the above process is repeated for each color, and four color toner images are transferred and superimposed on the intermediate transfer member 7.

  The recording medium S is loaded on the cassette 9 and is separated and fed one by one by the pickup roller 10. After the skew is corrected by the registration roller pair 11, the cassette 9 reaches the transfer portion 7 b. Accordingly, the transfer belt 12 that is in a separated state with respect to the surface of the intermediate transfer member 7 is pressed against and rotated by the surface of the intermediate transfer member 7 with a predetermined pressing force. The transfer belt 12 is stretched by a bias roller 12a and a tension roller 12b, and a voltage (secondary transfer bias) having a polarity opposite to the charging polarity of the toner is applied to the bias roller 12a by a high voltage power source 12c.

  As a result, the toner image on the intermediate transfer body 7 is batch transferred (secondary transfer) onto the surface of the recording medium that has been conveyed to the second transfer portion 7b at a predetermined timing, and is then sent to the fixing means 14 for heat and pressure. After the image is fixed by being added, the paper is discharged out of the apparatus by the discharge roller pair 15. The toner remaining on the surface of the intermediate transfer body 7 after the secondary transfer is completed is removed by the intermediate transfer body cleaning device 13 that comes into contact with the surface of the intermediate transfer body 7 at a predetermined timing.

[Image carrier]
A photoconductor that is an image carrier used in the present invention will be described below (hereinafter, the image carrier is referred to as a photoconductor or a photosensitive drum).

  The photoconductor used in the present invention is preferably an electrophotographic photoconductor containing a compound in which at least the surface layer is polymerized or cross-linked and cured, and the curing means is heat or visible light, Light such as ultraviolet rays and further radiation can be used. Therefore, in order to form a surface layer in the present invention, a coating solution containing a compound that can be polymerized or crosslinked and cured for the surface layer and melted is used, a dip coating method, a spray coating method, a curtain coating method, The procedure is such that coating is performed by spin coating or the like, and this is cured by the above-described curing means. The dip coating method is the best for efficient mass production of photoreceptors, and the dip coating method is also preferably used in the present invention.

  The structure of the photoreceptor used in the present invention is, for example, a single layer type in which both a charge generation material and a charge transport material are contained in the same layer on a conductive support having an outer diameter of about 62 mm, or a charge generation material. The charge generation layer containing a charge transport layer and the charge transport layer containing a charge transport material are either stacked in this order or in the reverse order. Furthermore, a surface protective layer can be formed on the photosensitive layer. In the present invention, it is preferable that at least the surface layer of the photoreceptor contains a compound that can be polymerized or crosslinked and cured by heat, light such as visible light, ultraviolet light, or radiation. However, from the viewpoint of characteristics as a photoreceptor, particularly electrical characteristics such as residual potential and durability, a charge generation layer / charge transport layer is laminated in this order, or a functionally separated photoreceptor is laminated in this structure. A configuration in which a surface protective layer is formed on the photosensitive layer is preferable.

  In the present invention, it is preferable to use radiation because the surface layer is polymerized or the compound to be crosslinked is cured without causing deterioration of the photoreceptor characteristics, without increasing the residual potential, and exhibiting sufficient hardness. It is.

  At this time, the radiation used is an electron beam and a gamma ray. In the case of irradiating an electron beam, any type such as a scanning type, an electron curtain type, a broad beam type, a pulse type, and a minor type can be used as an accelerator. In the case of irradiating an electron beam, in the photoreceptor used in the present invention, the acceleration condition is preferably 250 kV or less, and optimally 150 kV or less, in order to develop good electrical characteristics and durability. . The irradiation dose is preferably in the range of 10 kGy to 1000 kGy, more preferably in the range of 30 kGy to 500 kGy. By setting the acceleration voltage in the case of using an electron beam within the above range, the surface layer can be sufficiently cured while suppressing the damage of the electron beam irradiation on the characteristics of the photoreceptor.

  The compound for the surface layer that can be polymerized or crosslinked and cured includes an unsaturated polymerizable functional group in the molecule from the viewpoint of high reactivity, high reaction rate, and high hardness achieved after curing. Among them, compounds having an acrylic group, a methacryl group, and a styrene group are particularly preferable.

  The compound having an unsaturated polymerizable functional group in the present invention is roughly classified into a monomer and an oligomer based on repetition of the structural unit. The monomer means that the structural unit having an unsaturated polymerizable functional group is not repeated, and indicates a relatively small molecular weight, and the oligomer is a structural unit having an unsaturated polymerizable functional group having about 2 to 20 repeating units. It is a polymer. Moreover, the macronomer which has an unsaturated polymerizable functional group only in the terminal of a polymer or an oligomer can also be used as a curable compound for the surface layer of this invention.

  Further, the compound having an unsaturated polymerizable functional group in the present invention is more preferably a charge transport compound in order to satisfy a charge transport function necessary for the surface layer. Among these, an unsaturated polymerizable compound having a hole transport function is more preferable.

  Next, the photosensitive layer of the electrophotographic photoreceptor according to the present invention will be described.

  The support for the electrophotographic photosensitive member may have any conductivity, such as aluminum, copper, chromium, nickel, zinc and stainless steel or alloys formed in a drum or sheet, aluminum and copper, etc. A metal film laminated with a plastic film, aluminum, indium oxide, tin oxide or the like deposited on a plastic film, a metal with a conductive layer applied alone or with a binder resin, or a plastic film And paper.

  In the present invention, an undercoat layer having a barrier function and an adhesive function can be provided on the conductive support.

  The undercoat layer is used for improving the adhesion of the photosensitive layer, improving the coatability, protecting the support, covering defects on the support, improving the charge injection from the support, and protecting the photosensitive layer from electrical breakdown. Formed for. Materials for the undercoat layer include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, ethylene-acrylic acid copolymer, casein, polyamide, N-methoxymethylated 6 nylon, copolymer nylon, glue, gelatin, etc. Can be used. These are dissolved in a solvent suitable for each and coated on a support. The film thickness at that time is preferably 0.1 to 2 μm.

  When the photoreceptor of the present invention is a function separation type photoreceptor, a charge generation layer and a charge transport layer are laminated. Examples of the charge generation material used in the charge generation layer include selenium-tellurium, pyripium, thiapyrylium dyes, various central metals and crystal systems, specifically crystal types such as α, β, γ, ε, and X types. Phthalocyanine compounds, anthanthrone pigments, dibenzpyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, monoazo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine pigments, quinocyanines, and JP-A No. 54-143645 Examples include amorphous silicon.

  In the case of a function-separated type photoconductor, the charge generation layer comprises the charge generation material 0.3 to 4 times the binder resin and solvent on a mass basis, a homogenizer, an ultrasonic dispersion, a ball mill, a vibration ball mill, a sand mill, an attritor, and the like. The film is well dispersed by means such as a roll mill, and is formed by applying a dispersion and drying, or formed as a single composition film such as a vapor deposition film of the charge generation material. The film thickness is preferably 5 μm or less, and particularly preferably in the range of 0.1 to 2 μm.

  As binder resin, polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, trifluoroethylene, polyvinyl alcohol, polyvinyl acetal, polycarbonate, polyester , Polysulfone, polyphenylene oxide, polyurethane, cellulose resin, phenol resin, melanin resin, silicon resin, epoxy resin and the like.

  The hole transporting compound having an unsaturated polymerizable functional group in the present invention is a charge transport layer comprising a charge transport layer and a binder resin on the charge generation layer, as a charge transport layer, or on the charge generation layer. After forming, it can also be used for the surface protective layer.

  When used for the surface protective layer, the charge transport layer underneath is a suitable charge transport material, for example, a polymer compound having a heterocyclic ring or a condensed polycyclic aromatic compound such as poly-N-vinylcarbazole or polystilanthracene, or pyrazoline. Appropriate binding of heterocyclic compounds such as imidazole, oxador, triazole, carbazole, triarylamine derivatives such as triphenylamine, low molecular weight compounds such as phenylenediamine derivatives, N-phenylcarbazole derivatives, stilbene derivatives, hydrazone derivatives, etc. A solution dispersed / dissolved in a solvent together with a resin (which can be selected from the above-mentioned resins for charge generation layers) can be applied by the above-mentioned known method and dried. In this case, the ratio of the charge transport material to the binder resin is preferably selected in the range of 30 to 100, preferably 50 to 100, when the total mass of both is 100. If the amount of the charge transport material is smaller than that, the charge transport ability is lowered, and problems such as a decrease in sensitivity and an increase in residual potential occur. Also in this case, the thickness of the photosensitive layer is in the range of 5 to 30 μm, and 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.

  In any case, the surface layer is generally formed by applying a solution containing the hole transporting compound, followed by polymerization / curing reaction, but the solution containing the hole transporting compound is reacted in advance. It is also possible to form the surface layer by using a material obtained by dispersing and dissolving in a solvent after obtaining a cured product. As a method for applying these solutions, 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 preferable. Moreover, vapor deposition, plasma, and other known film forming methods can be appropriately selected.

  Conductive particles may be mixed in the surface protective layer in the present invention.

  Examples of the conductive particles include metals, metal oxides, and carbon black. Examples of the metal include aluminum, zinc, copper, chromium, nickel, stainless steel, and silver, and those obtained by depositing these metals on the surface of plastic particles. Examples of the metal oxide include zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin-doped indium oxide, antimony-doped tin oxide, and antimony-doped zirconium oxide. These can be used alone or in combination of two or more. When two or more kinds are combined, they may be simply mixed or formed into a solid solution or a fused form.

  The average particle size of the conductive particles used in the present invention is preferably 0.3 μm or less, and particularly preferably 0.1 μm or less, from the viewpoint of the transparency of the protective layer.

  In the present invention, among the conductive particles as described above, it is particularly preferable to use a metal oxide in terms of transparency.

The ratio of the conductive metal oxide particles in the surface protective layer is one of the factors that directly determine the resistance of the surface protective layer, and the resistance of the protective layer is in the range of 10 ¹⁰ to 10 ¹⁵ Ω · cm. Preferably there is.

  The surface layer in the present invention may contain fluorine atom-containing resin particles.

  Fluorine atom-containing resin particles include tetrafluoroethylene resin, trifluorinated ethylene resin, hexafluoroethylene propylene resin, vinyl fluoride resin, vinylidene fluoride resin, difluorodiethylene chloride resin, and their co-polymers. It is preferable to select one or two or more from the coalesced, but particularly preferred are tetrafluoroethylene resin and vinylidene fluoride resin. The molecular weight and particle size of the resin particles can be appropriately selected and are not particularly limited.

  The proportion of the fluorine atom-containing resin in the surface layer is preferably 5 to 70% by mass, more preferably 10 to 60% by mass with respect to the total mass of the surface layer. When the proportion of fluorine atom-containing resin particles is more than 70% by mass, the mechanical strength of the surface layer tends to be lowered, and the surface layer releasability of the surface layer in which the proportion of fluorine atom-containing resin particles is less than 5% by mass, Wear resistance and scratch resistance may not be sufficient.

  In the present invention, additives such as a radical scavenger and an antioxidant may be added to the surface layer for the purpose of further improving dispersibility, binding properties and weather resistance.

  The film thickness of the surface protective layer used in the present invention is preferably in the range of 0.2 to 10 μm, more preferably in the range of 0.5 to 6 μm.

  In the present invention, the universal hardness value (HU) and elastic deformation rate are continuously applied by applying a load to the indenter in an environment of 25 ° C. and a humidity of 50% RH, and directly reading the indentation depth under the load. The measurement was made using a microhardness measuring device Fischerscope H100V (Fischer) that is required to have hardness. 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 s for each point).

  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). Here, Wt (nW) is the total work, and Wo (nW) is the work of elastic deformation.

      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 has not always been expected to improve durability.

As a result of intensive studies, we have found that mechanical deterioration of the surface layer of the photoreceptor is less likely to occur when the values of HU and elastic deformation ratio are within a certain range, and the present invention has been achieved. That is, 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 40% or more and 65% or less By using the electrophotographic photosensitive member, which is

  The amount of wear on the surface of the photoreceptor, which is an image carrier used in the present embodiment, is 2 mg or less in the Taber abrasion tester, but if it is 6 mg or less, sufficient effects can be obtained. The test method of the Taber abrasion test is as follows. A sample is mounted on a sample stand of a Taber abrasion tester (YSS Taber Yasuda Seisakusho), and wrapping tape (Fuji Film product name: C2000) is attached to two surfaces. In this method, a load of 500 gr is applied to each of the attached rubber wear wheels (CS-0), and the mass reduction of the sample after 1000 revolutions is measured with a precision balance.

  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, it was found that the high hardness obtained by these measurements did not necessarily improve the durability, and the above range was good.

Although the HU and the elastic deformation rate cannot be separated, for example, when the HU exceeds 220 N / mm ² , if the elastic deformation rate is less than 40%, the paper dust sandwiched between the cleaning blade, the charging, and the transfer roller As a result, the amount of elastic deformation is small even if the elastic deformation rate is high, because the elastic deformation rate is larger than 65%. As a result, a large pressure is applied to the surface, so that scratches are likely to occur, and the amount of wear of the photoreceptor increases. Therefore, it is considered that the one with a high HU is not necessarily optimal as the photosensitive member.

Also, if 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 dust sandwiched between the cleaning blade, the charging, and the transfer roller If the toner or the toner is rubbed, it will be scraped off or fine scratches will occur, resulting in a shortened durability life.

[Developer]
The developer used in the image forming apparatus of the present embodiment is a two-component developer that is a mixture of a nonmagnetic polymer toner (T) produced by a polymerization method and a resin magnetic carrier (D). The developer has a T / D mass ratio of 8%, and the resin magnetic carrier has a magnetization amount of 100 emu / cm ³ in a magnetic field of 1 kilo Oersted and a number average particle diameter of 40 μm. A resistor having a resistance of 10 ¹³ Ω · cm is used.

  In general, the polymer toner has a higher degree of sphericity than the pulverized toner. The degree of sphericity of the shape of the toner particles is expressed using shape factors SF-1 and SF-2 calculated from the following equation (3). As for the toner shape factors SF-1 and SF-2, 100 toner images are randomly sampled using Hitachi FE-SEM (S-800), and the image information is obtained from an image analyzer (Luxex 3) manufactured by Nireco. And is calculated from the following equation (3).

  Of the toner shape factors, SF-1 indicates the degree of sphericity. When SF-1 is 100, the toner is a true sphere, and when SF-1 exceeds 100 to 140, the toner is Is substantially spherical. When SF-1 is larger than 140, the toner gradually changes from a substantially spherical shape to an indefinite shape. The shape factor SF-2 indicates the degree of unevenness of the toner particle surface. When SF-2 is 100 to 120, the toner surface is smooth, and SF-2 is larger than 120. In this case, the unevenness of the toner surface becomes remarkable. As the polymerized toner used in the image forming apparatus of the present embodiment, a substantially spherical toner having an average particle diameter of 6 μm to 10 μm, a shape factor SF-1 of 100 to 140, and SF-2 of 100 to 120. However, it is preferable for maintaining high transfer efficiency.

  The toner used in the present embodiment is manufactured by a polymerization method, and silica, titanium oxide, or the like having a particle diameter of 20 nm is externally added to stabilize charged performance against environmental fluctuations and improve fluidity.

  In this embodiment, the spherical toner having good transferability is described by the polymerization method. However, the present invention is not limited to this, and for example, the toner prepared by a conventional mechanical pulverization classification method is used. It is also possible to use toner that has been subjected to thermal or mechanical post-treatment and rounded.

[Cleaning device]
FIG. 3 shows a diagram relating to the cleaning blade. The cleaning blade 8a is made of polyurethane rubber that is integrally held at the tip of a sheet metal (not shown), and is in contact with the photoreceptor 2 under conditions of a predetermined penetration amount δ and a set angle θ. As a result of repeating trial and error in this embodiment and finding optimum conditions, the rubber hardness is preferably 50 to 85 degrees (JISA), more preferably 60 to 80 degrees (JISA), and in this embodiment 70 degrees (JISA). ), Θ = 22 degrees, δ = 1.2 mm, and the contact pressure to the photosensitive member 2 was about 30 g / cm.

[Charging]
2A is a front view showing the mutual relationship between the charging roller and the photosensitive member, and FIG. 2B is a sectional view thereof.

  The charging roller 3 as a flexible contact charging member as a charging means in the present embodiment is formed by forming a middle resistance layer of rubber or foam on a cored bar.

  The middle resistance layer was formulated with a resin (urethane in this embodiment), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and formed in a roller shape on the core metal. Thereafter, the surface was polished.

Here, it is important that the charging roller 3 as a contact charging member functions as an electrode. In other words, it is necessary to provide a sufficient contact state with the photoconductor by providing elasticity, and at the same time, have a sufficiently low resistance to charge the moving photoconductor. On the other hand, it is necessary to prevent voltage leakage when there is a low breakdown voltage defect portion such as a pinhole in the photoreceptor. In order to obtain sufficient chargeability and leakage resistance, a resistance of 10 ⁴ to 10 ⁷ Ω is desirable. In this embodiment, a resistance of 10 ⁶ Ω is used. The resistance value of the charging roller 3 was measured as follows. The photoconductor 2 of the printer is replaced with an aluminum drum. Thereafter, a voltage of 100 V was applied between the aluminum drum and the cored bar 3a of the charging roller 3, and the resistance value of the charging roller 3 was determined by measuring the current value flowing at that time. This resistance measurement was performed in an environment of a temperature of 25 ° C. and a humidity of 60% RH.

  The measurement of the hardness of the charging roller in the present invention was performed in an environment of 23.5 ° C./60% RH using an ASKER-C hardness meter and a micro hardness meter MD-1 type (both manufactured by Kobunshi Keiki Co., Ltd.). is there. The measurement method using the ASKER-C hardness tester is to place a charging roller on a metal plate, place a metal block, and fix the roller easily so that it does not roll. The ASKER-C hardness tester is pressed with a weight of 1 kg (9.8 N) so as to accurately hit the center, and the value after 5 seconds is read. An average value is calculated by measuring a total of nine points at three positions in the circumferential direction at both ends and the center at a position 40 mm from the rubber end of the charging roller. In the case of the micro hardness tester, the value is measured in the peak hold mode, and the measurement terminal is made to vertically contact the central portion of the charging roller as in the case of the above-described ASKER-C hardness. As for the measurement position and the number of measurements, the average value of 9 points is calculated in the same manner as in ASKER-C. In the present invention, the micro hardness of the surface of the charging roller is 75 degrees or more and less than 100 degrees, and the Asker C hardness of the charging roller is 40 degrees or less. If the hardness of the charging roller 3 is too high, the width of the charging contact portion (nip width N) cannot be ensured between the charging roller 3 and the photosensitive member, and stable chargeability cannot be obtained. In the present invention, by increasing the micro hardness of the surface layer of the charging roller to 75 degrees or higher, the effect of refreshing the surface of the highly durable drum is given, and the Asker C hardness of the charging roller as a whole is lowered to 40 degrees or less to reduce the nip The width N is sufficient. As a result, not only good charging performance can be secured, but a higher refreshing effect can be achieved by combining with a hard surface layer. On the contrary, if the micro hardness is less than 75 degrees and the Asker C hardness is more than 40 degrees, a sufficient nip width cannot be secured, so that a sufficient effect for refreshing the surface of the highly durable photosensitive drum used in the present invention cannot be obtained. Satisfactory image quality cannot be obtained. The nip width N between the photosensitive member and the charging roller is sufficient if the contact portion width is 1 mm or more in order to obtain good chargeability. In the present invention, since the effect of refreshing the surface of the photoreceptor on the surface of the charging roller is required, it is preferable to widen the nip width N, and 3 mm to 10 mm is preferable in order to stably obtain a high rubbing ability. It is a range. A configuration in which the nip width N exceeds 10 mm is not practical because it is necessary to extremely increase the diameter of the charging roller or extremely increase the pressing force of the charging roller against the photosensitive member. The material of the charging roller 3 is not limited to the elastic foam as long as the above-described hardness and charging performance can be satisfied. The material of the elastic body may be EPDM, urethane, NBR, silicone rubber, IR, or the like. In addition, a rubber material in which a conductive material such as carbon black or a metal oxide is dispersed for resistance adjustment, and those obtained by foaming these materials may be mentioned. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive substance.

  The charging roller 3 is disposed in parallel with the photosensitive drum 2 while the cored bar 3a is supported by the bearing 22 at both ends in the longitudinal direction, and the photosensitive drum 2 by a spring 23 as a pressure member attached to the bearing 22. Pressed against the surface. In this embodiment, the contact pressure by the pressure spring to the surface of the photosensitive drum 2 at this time is set to about 40 [g / cm]. With this setting, a sufficient contact width (nip width N) between the photosensitive drum 2 and the charging roller 3 can be secured, and a stable charging property can be obtained. The contact pressure is not limited to those described above, and there is no problem as long as satisfactory chargeability, the surface of the photoreceptor, the surface of the charging roller, etc. are not damaged and satisfactory durability is obtained.

  As a method for measuring the contact pressure, two thin plates made of SUS are inserted into the contact nip region between the photosensitive drum 2 and the charging roller 3 and required when the thin plate having a width of 1 [cm] is pulled out. It was obtained by measuring the force with only a spring.

  By increasing the surface roughness Rz of the charging roller, even when the surface layer of the charging roller is contaminated with an external additive or toner, the surface can be rubbed effectively at the edge portion. However, even if Rz is made too large, the effect does not change so much and the chargeability may be affected. Therefore, the preferred range is 10 μm or more and 100 μm or less. It is a 10-point average surface roughness (Rz jis 1994) defined in JIS standard B0601 (1994). Further, the charging roller surface has a directional surface roughness, and the direction of the charging roller is opposite to the rotation direction of the image carrier at the contact portion with the image carrier. As a result, a more effective refreshing effect can be achieved. Further, if the rotation axis of the charging roller is not arranged parallel to the rotation axis of the image carrier, but is provided so as to intersect with a predetermined crossing angle, it is effective in preventing the charging roller from being contaminated, and the charging roller and image Since the vector in the rotational direction differs from that of the carrier, a refreshing effect is obtained by the rubbing force generated at the nip portion.

  The charging roller 3 rotates following the rotation of the photosensitive member 2. For example, the charging roller is subjected to constant current control with a frequency of 1.8 kHz and a total current of 2000 μA from a high voltage power supply for charging, and the photosensitive member potential is determined by the superimposed DC bias.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, although these Examples are examples of the best example in this invention, this invention is not limited to these Examples.

[Example 1]
The outline of the image forming apparatus used in the present embodiment is as described in the above embodiment. Here, the charging member has a micro hardness in the range of 75 to 95 degrees and an Asker C hardness of 30 degrees. The outer diameter of the roller was 14 mm, and the width of the contact portion between the charging roller and the photosensitive member was set to 3 mm. The charging roller has a surface roughness of Rz of 10 μm. A photoconductor with HU = 200 N / mm ² and elastic deformation rate = 50% was used. Table 1 shows the results of evaluating the endurance of 50,000 sheets printed at high temperature and high humidity (30 ° C., 80% RH) with the above configuration.

[Comparative Example 1]
An ordinary organic photoreceptor that does not cure the surface layer was used as the photoreceptor. HU = 190 N / mm ² and elastic deformation rate = 37%. Other configurations are the same as those in the first embodiment. When the same evaluation as in Example 1 was performed, the photosensitive member was scratched with a durable number of about 10,000 sheets, resulting in an image defect.

[Comparative Example 2]
Table 1 shows the configuration of the charging roller having a micro hardness of less than 75 degrees, the Asker C hardness of more than 40 degrees, and the evaluation results. A photoconductor with HU = 200 N / mm ² and elastic deformation rate = 50% was used. Other configurations are the same as those in the first embodiment. In any of the configurations in this example, a sufficient refresh effect was not obtained, and image flow occurred.

[Example 2]
In this embodiment, the surface of the charging roller member has a directional surface roughness. As shown in FIG. 4, the direction of the charging roller member is opposite to the rotation direction of the photoconductor at the contact portion with the photoconductor. It was made to become. By adopting this configuration, the catching force with the surface of the photoreceptor is increased, and a more effective refreshing action can be obtained. The charging roller had a surface roughness Rz of 15 μm. The charging roller surface had a micro hardness of 75 degrees and an Asker C hardness of 30 degrees. A photoconductor with HU = 200 N / mm ² and elastic deformation rate = 50% was used. Other configurations are the same as those in Example 1, and the results of the same evaluation are shown in Table 1.

[Example 3]
The outer diameter of the charging roller was 20 mm. A photoconductor with HU = 200 N / mm ² and elastic deformation rate = 50% was used. Other conditions were the same as in Example 1. When the outer diameter of the charging roller is increased, the contact portion between the charging roller and the photosensitive member can be widened when the contact pressure against the photosensitive member is the same. In this embodiment, the width of the contact portion is 5 mm. The results of the same evaluation as in Example 1 are shown in Table 1.

[Example 4]
In this embodiment, the rotation axis of the charging roller 3 is provided with a crossing angle of an angle θ ′ ° with respect to the rotation axis of the photosensitive drum as shown in FIG. The purpose of providing the crossing angle here is to spread the contamination of the charging roller from external additives as much as possible as disclosed in Japanese Patent No. 0245726, and to prevent local charging failure. Since the vectors in the rotation direction of the roller and the photosensitive drum are different, the refreshing effect is obtained by the rubbing force generated at the nip portion. A photoconductor with HU = 200 N / mm ² and elastic deformation rate = 50% was used. The other conditions are the same as in Example 1, and the results of a similar evaluation are shown in Table 1.

  Embodiments of the present invention are not limited to those described above. For example, a method of increasing the hardness by including an inorganic fine powder in the surface layer of the charging roller, a method of relatively increasing the surface roughness of the charging roller, and the like are also suitable. Can be used.

1 is a schematic sectional view of an image forming apparatus suitable for the present invention. FIG. 2 is a diagram illustrating a charging roller and a photosensitive drum as a charged body used in the present invention. The elements on larger scale explaining a cleaning blade. FIG. 6 is a diagram illustrating a surface of a charging roller in Embodiment 2 of the present invention. FIG. 6 is a diagram illustrating an intersection angle between a charging roller and a photosensitive drum in Embodiment 4 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoconductor 3 Charging means (charging roller)
3a Core 4 Laser oscillator 5 Laser beam 6 Rotating developing device 6y First developing device 6m Second developing device 6c Third developing device 6k Fourth developing device 7 Intermediate transfer body 7a Transfer site 7b Transfer site 7c High voltage power supply 8 Cleaning device 8a Cleaning blade 9 Cassette 10 Pickup roller 11 Registration roller pair 12 Transfer belt 12a Bias roller 12b Tension roller 12c High-voltage power supply 13 Transfer body cleaning device 14 Fixing device 15 Discharge roller pair 22 Receiving 23 Pressure spring S Recording medium

Claims (6)

In an image forming apparatus having at least an image carrier, a charging unit, an image exposing unit, a developing unit, a transfer unit, and a cleaning unit,
The image carrier has a photosensitive layer on a conductive support, and the image carrier is subjected to a hardness test using a Vickers square pyramid diamond indenter in an environment of 25 ° C. and a humidity of 50% RH, with a maximum load of 6 mN. An image carrier having a universal hardness value (HU) of 150 N / mm ² or more and 220 N / mm ² or less when pressed and an elastic deformation rate (We) of 40% or more and 65% or less,
The charging means is a contact type roller member, the micro hardness of the surface of the contact type charging roller member is 75 degrees or more and less than 100 degrees, and the Asker C hardness of the contact type charging roller member is 40 degrees or less. An image forming apparatus.   The surface of the contact-type charging roller member has a directional surface roughness, and the direction is opposite to the rotation direction of the image carrier at the contact portion with the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein a width of a contact portion between the contact-type charging roller member and the image carrier is 3 mm or more and 10 mm or less.   4. The image forming apparatus according to claim 2, wherein a surface roughness of the contact-type charging roller member is 10 μm or more and 100 μm or less in terms of a 10-point average roughness.   The image forming apparatus according to claim 1, wherein the surface layer of the contact-type charging roller member contains an inorganic fine powder. 6. The image forming apparatus according to claim 1, wherein the contact-type charging roller member and the image carrier are arranged so that their rotation axes intersect each other.

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