Image carrier unit and image forming apparatus

Abstract

To achieve size reduction while maintaining printing quality.SOLUTION: A developing device 20 is provided with a photoconductor drum 34 as a cylindrical image carrier that develops a latent image formed thereon with developer, and an electrifying roller 26 and a developing roller 32 as contact members that are in contact with the surface of the photoconductor drum 34. The element tube diameter / the element tube thickness of the photoconductor drum 34 being the ratio of the outer diameter to the thickness of the photoconductor drum 34 is 16.2 or less, and the difference in characteristic frequency between the photoconductor drum 34 and the contact members is 0.10 or more.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] Embodiments of the present invention relate to an image carrier unit and an image forming apparatus, and are suitable for application to, for example, an electrophotographic printer.

Background Art

[0002] Conventionally, in an image forming apparatus using an electrophotographic process such as a printer, a copier, a facsimile machine, or a multifunction machine, a charging roller built in a developing device as an image carrier unit uniformly charges the surface of a photosensitive drum as an image carrier built in the developing device, irradiates the surface of the photosensitive drum with light from an exposure device to form an electrostatic latent image on the surface of the photosensitive drum, and further attaches toner as a developer from a developing roller as a developer carrier built in the developing device to the electrostatic latent image to develop a toner image, thereby printing an image, which has been widely spread.

[0003] As such an image forming apparatus, there is one in which a silencer as a vibration damping member is inserted into a photosensitive drum to suppress vibration of the photosensitive drum (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when the image carrier is made smaller to miniaturize the developing device, it is difficult to insert a vibration damping member into the image carrier, and due to resonance between the image carrier and a contact member that contacts the image carrier, jitter may occur when transferring the developer on the image carrier onto a medium, and the print quality may not be maintained.

[0006] The embodiments of the present invention have been made in consideration of the above points, and an image carrier unit and an image forming apparatus that can be downsized while maintaining print quality are proposed.

Means for Solving the Problems

[0007] In the image carrier unit according to the embodiment of the present invention for solving such problems, a cylindrical image carrier that develops a formed latent image with a developer and a contact member that contacts the surface of the image carrier are provided, and the ratio of the outer diameter to the wall thickness of the image carrier is 8.0 or more and 16.2 or less, and the natural frequencies of the image carrier and the contact member When the degree of inconsistency is obtained from the absolute value of (1 - (the third natural frequency of the contact member) / (the first natural frequency of the image carrier)), are set to be 0.10 or more and 0.17 or less.

[0008] Furthermore, in the image forming apparatus according to the embodiment of the present invention, the above-described image carrier unit is provided.

[0009] In the embodiments of the present invention, by increasing the wall thickness with respect to the outer diameter of the image carrier, the weight of the entire image carrier can be increased, the difference between the natural frequency of the developer carrier and the natural frequency of the image carrier can be widened, and the jitter during transfer from the image carrier to the medium due to the resonance between the developer carrier and the contact member that contacts the developer carrier can be suppressed, and the image carrier can be downsized while maintaining print quality.

Effects of the Invention

[0010] According to the embodiments of the present invention, an image carrier unit and an image forming apparatus that can be downsized while maintaining print quality can be realized.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 8

Figure 9

[0012] Hereinafter, embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0013] [1. Configuration of Image Forming Apparatus] As shown in FIG. 1, the image forming apparatus 1 is, for example, a printer using an electrophotographic method, and forms a black-and-white image on a medium P such as paper or film by performing an image forming operation using a developer such as toner. Various components are arranged inside the apparatus main body 2 which is a housing formed in a substantially box shape. Hereinafter, a position close to the paper cassette 4 as viewed from an arbitrary position on the conveyance path along which the medium P is conveyed, or a direction toward the paper cassette 4 is referred to as upstream. Also, a position close to the stacker 18 where the medium P is discharged and stacked as viewed from an arbitrary position on the conveyance path, or a direction toward the stacker 18 is referred to as downstream. Further, the direction from upstream to downstream is referred to as the conveyance direction.

[0014] Inside the image forming apparatus 1, an image forming unit 6 and a fixing device 8 are arranged along the conveyance path of the medium P. The medium P stacked and set in the paper cassette 4 is fed one by one in a separated state by the paper feed roller 10, conveyed in the direction indicated by the arrow A, and sent to the paper conveyance roller 12. Subsequently, the medium P is sent out in the direction indicated by the arrow B at a predetermined timing by the paper conveyance roller 12, and while being conveyed on the transfer belt along the conveyance path, the toner image, which is the developer image formed by the image forming unit 6, is transferred by the transfer roller 14.

[0015] Then, when the medium P is sent into the fixing device 8, the fixing process is performed by the fixing device 8, and the toner image is fixed on the medium P. Subsequently, the medium P on which the toner image is fixed is conveyed in the direction indicated by the arrow C, discharged in the direction indicated by the arrow D by the paper discharge roller 16, and stored in the stacker 18 outside the apparatus main body 2.

[0016] As shown in FIG. 2, the image forming unit 6 includes a developing device 20 and a toner storage unit 22. The toner storage unit 22 stores toner TN. The developing device 20 has a casing 24 that houses the toner TN as a developer replenished from the toner storage unit 22. The developing device 20 also has a charging roller 26, a toner supply roller 28, a developing blade 30, a developing roller 32, a photosensitive drum 34, a cleaning blade 36, and stirring members 38a, 38b, and 38c.

[0017] The charging roller 26 rotates in the direction indicated by the arrow to charge the photosensitive drum 34. The toner supply roller 28 rotates in the direction indicated by the arrow to supply toner TN to the developing roller 32. The developing blade 30 forms the supplied toner TN on the developing roller 32 into a thin layer. The developing roller 32 is disposed opposite to the photosensitive drum 34 and rotates in the direction indicated by the arrow to develop the electrostatic latent image formed on the surface of the photosensitive drum 34 with the toner TN carried by the developing roller 32. The photosensitive drum 34 is a member that carries the electrostatic latent image on its surface (surface layer portion), and rotates in the direction indicated by the arrow to transfer the toner image developed on the surface of the photosensitive drum 34 to the medium P. The cleaning blade 36 scrapes off and collects the residual toner on the photosensitive drum 34. The stirring members 38a, 38b, and 38c are crank-shaped rods, and rotate in the direction indicated by the arrow on the broken line shown in the figure to maintain the fluidity of the toner TN in the casing 24.

[0018] Also, the LED head 40 (Fig. 1) has an LED (Light Emitting Diode) and is an exposure device that exposes the surface of the photosensitive drum 34 based on image data to form an electrostatic latent image.

[0019] [2. Configuration of Developing Device] Next, the main components of the developing device 20 will be described in detail.

[0020] [2-1. Configuration of Toner] The toner TN used in this embodiment is a non-magnetic one-component negatively charged toner, which is obtained by adding external additives (hereinafter referred to as external additives), such as inorganic fine powders and organic fine powders, to toner mother particles containing at least a binder resin. Although there is no particular limitation on this binder resin, polyester resins, styrene-acrylic resins, epoxy resins, or styrene-butadiene resins are preferred. A release agent, a colorant, etc. are added to this binder resin, and other additives such as a charge control agent, a conductivity adjuster, a fluidity improver, or a cleaning property improver may be appropriately added. Further, a plurality of types may be mixed as the binder resin. In this embodiment, a crystalline polyester resin having a crystal structure is used in addition to a plurality of amorphous polyester resins. The average particle size of the toner TN is 6.0 [μm], and the circularity is 0.96. For the measurement of the average particle size, a Coulter Multisizer III (manufactured by Beckman Coulter, Inc.) was used, and for the measurement of the circularity, a flow-type particle image analyzer FPIA-3000 (manufactured by Sysmex Corporation) was used.

[0021] Although there is no particular limitation on the release agent, known ones such as low molecular weight polyethylene, low molecular weight polypropylene, copolymers of olefins, microcrystalline wax, paraffin wax, aliphatic hydrocarbon waxes such as Fischer-Tropsch wax, oxides of aliphatic hydrocarbon waxes such as oxidized polyethylene wax, or block copolymers thereof, waxes mainly composed of fatty acid esters such as carnauba wax and montanic acid ester wax, and those obtained by partially or completely deoxidizing fatty acid esters such as deacidified carnauba wax can be mentioned. And the content is effectively added in an amount of 0.1 to 20 parts by weight, preferably 0.5 to 12 parts by weight, based on 100 parts by weight of the binder resin. It is also preferable to use a plurality of waxes in combination.

[0022] As the colorant, although not particularly limited, dyes, pigments, etc. that have been used as colorants for conventional black, yellow, magenta, and cyan toners can be used alone or in combination of two or more. For example, carbon black, iron oxide, phthalocyanine blue, permanent brown FG, brilliant fast scarlet, pigment green B, rhodamine-B base, solvent red 49, solvent red 146, pigment blue 15:3, solvent blue 35, quinacridone, carmine 6B, disazo yellow, etc. can be mentioned. The content of this colorant is added in an amount of 2 to 25 parts by weight, preferably 2 to 15 parts by weight, based on 100 parts by weight of the binder resin.

[0023] As the charge control agent, known ones can be used. For example, in the case of a negatively charged toner, azo complex charge control agents, salicylic acid complex charge control agents, calixarene-based charge control agents, etc. can be mentioned. The content of this charge control agent is added in an amount of 0.05 to 15 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the binder resin.

[0024] The external additives of toner TN are added to improve environmental stability, charge stability, developability, fluidity, and storage stability, and known ones can be used. The content of the external additives is added in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 8 parts by weight, based on 100 parts by weight of the binder resin. In this embodiment, several types of silica with an average particle size of 14 [nm] (positive and negative charge polarities) and colloidal silica with an average particle size of 110 [μm] (negatively charged) and melamine with an average particle size of 200 [μm] are added to 100 parts by weight of the mother particles, and the total amount is made to fall within the above-mentioned range.

[0025] The charge amount (blow-off charge amount) of toner TN was measured by agitating the toner and the carrier by vibration. Here, as the carrier, ferrite carrier EF96-35 (manufactured by Powdertech Co., Ltd.) was used, and 0.5 [g] of toner and 9.5 [g] of carrier were mixed. A mixture of toner and carrier (150 [mg]) was placed in a container and vibrated using a shaker YS-LD (manufactured by Yayoi Co., Ltd.). The vibration frequency was 200 [times / min], and the vibration time was 300 seconds. After vibration, a powder charge amount measuring device TB-203 (manufactured by Kyocera Chemical Corporation) was used, and suction was performed for 10 seconds with a blow pressure of 7.0 [kPa] and a suction pressure of -4.5 [kPa], and the charge amount and suction amount per 0.1 second were output to a PC (personal computer). The charge amount Q / M per unit weight of toner particles calculated from the average values of the charge amount and suction amount output in the last 2 seconds of the suction time (10 seconds) was approximately -35 [μC / g]. The measurement was performed at a temperature of 25 [°C] and a relative humidity of 50 [%].

[0026] [2-2. Configuration of Developing Roller] The developing roller 32 as a contact member in the embodiment of the present invention has a conductive mandrel as a shaft, an elastic layer disposed on the mandrel, and a surface layer covering the surface of the elastic layer. The rubber hardness of the elastic layer in the roll shape is generally preferably 55 to 80 [°] in Asker C hardness. If the Asker C hardness of the elastic layer is lower than 55 [°], when the developing device 20 is not operated for a long period of time, dents are generated at the contact portions of the developing roller 32 with the photosensitive drum 34 and the developing blade 30, and there is a problem that horizontal streaks occur on the printed image. On the other hand, if the Asker C hardness of the elastic layer is higher than 80 [°], the mechanical load applied to the developing roller 32 increases, and toner filming is likely to occur on the surface of the developing roller 32. Toner filming on the developing roller 32 means that the toner TN on the developing roller 32 is damaged by mechanical load, making it difficult to develop from the developing roller 32 to the photosensitive drum 34, and at the same time, it becomes difficult for the toner supply roller 28 to scrape off the toner TN on the developing roller 32 that has not been supplied to the photosensitive drum 34, resulting in a state of deposition on the developing roller 32.

[0027] As the material of the elastic layer, general rubber materials such as silicone rubber and urethane can be used. When polyurethane is used as the elastic layer, it is preferably a polyurethane mainly composed of polyether polyol. Ether-based polyurethane is a so-called cast type polyurethane obtained by reacting a polyol mainly composed of polyether polyol with polyisocyanate. This is to reduce the compression set. On the other hand, when ester-based polyurethane is used, the hydrolysis characteristics are poor and it cannot be stably used over a long period. Also, when polyurethane is used as the elastic layer, as the isocyanate to react with the polyol, for example, trifunctional isocyanate monomers such as triphenylmethane triisocyanate, tris(isocyanatophenyl) thiophosphate, and bicycloheptane triisocyanate, mixtures such as neolate-modified polyisocyanate of hexamethylene diisocyanate and polymeric MDI can be used. Further, a mixture of these trifunctional or higher polyisocyanates and a general bifunctional isocyanate compound may also be used. Examples of the bifunctional isocyanate compound include 2,4-tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), paraphenylene diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI), 3,3-dimethyldiphenyl-4,4-diisocyanate (TODI), and modified products and multimers such as prepolymers having these isocyanates at both ends. The elastic layer is formed by adding carbon black to the rubber base material as described above and heat-curing while maintaining the dispersion state of the carbon. Thereby, carbon black showing about 0.1 to 10 [Ω·cm] as the specific resistance can be dispersed in an elastomer (1012 to 1016 [Ω·cm]) which can be regarded as an insulator to form a stable medium resistance region of 104 to 108 [Ω·cm].

[0028] In this embodiment, the surface layer is formed by impregnating the surface layer portion of the elastic layer with a surface treatment liquid. The surface treatment liquid is obtained by dissolving at least an isocyanate component in an organic solvent. Examples of the organic solvent include methyl acetate, butyl acetate, pentyl acetate, and the like. When using such an organic solvent, for example, as the isocyanate component contained in the surface treatment liquid, isocyanate compounds such as 2,4-tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI), and the above-described multimers and modified products can be used.

[0029] The surface treatment liquid may contain a polyether-based polymer. Here, the polyether-based polymer is preferably soluble in an organic solvent, and preferably has active hydrogen and can react with an isocyanate compound to form a chemical bond. Suitable polyether-based polymers having active hydrogen include polymers having a hydroxyl group or an allyl group, such as polyols and glycols used in terminal isocyanate prepolymers. Further, the surface treatment liquid may contain a polymer selected from an acrylic fluorine-based polymer and an acrylic silicone-based polymer. The acrylic fluorine-based polymer and the acrylic silicone-based polymer are soluble in a predetermined solvent and can react with an isocyanate compound to form a chemical bond. The acrylic fluorine-based polymer is, for example, a solvent-soluble fluorine-based polymer having a hydroxyl group, an alkyl group, or a carboxyl group, and examples thereof include a block copolymer of an acrylate ester and an alkyl fluoride acrylate and derivatives thereof. The acrylic silicone-based polymer is a solvent-soluble silicone-based polymer, and examples thereof include a block copolymer of an acrylate ester and a siloxane acrylate ester and derivatives thereof. Further, carbon black such as acetylene black may be added as a conductivity-imparting material to the surface treatment liquid. The total amount of the polyether-based polymer, the acrylic fluorine-based polymer, and the acrylic silicone-based polymer in the surface treatment liquid is preferably 10 to 70% by mass with respect to the isocyanate component. If these are less than 10% by mass, the effect of retaining carbon black or the like in the surface treatment liquid becomes small. On the other hand, if these are more than 70% by mass, there are problems such as an increase in the electrical resistance value or a relatively small amount of the isocyanate component, resulting in the inability to form an effective surface treatment layer. By immersing the elastic layer in the above-described surface treatment liquid, applying it, and drying and curing it, the surface treatment liquid is impregnated into the surface layer portion of the elastic layer to form a surface layer.

[0030] The resistance value of the developing roller 32 was measured by the method shown in FIG. 3, and a high resistance meter: 4339B (manufactured by Hewlett-Packard Japan, Ltd.) 60 was used. In this measurement, a load of W = 300 [g] was applied to both ends in the longitudinal direction of the developing roller 32, and it was brought into contact with a metal roller 61 made of SUS (Steel Use Stainless) material with a diameter of 30 [mm]. The metal roller 61 was rotated at a speed of 50 [rpm], a voltage of -100 [V] was applied to the core metal 62 of the developing roller 32, and 100 points were measured for each rotation of the developing roller 32, and the average value was taken as the resistance value of the developing roller 32. At this time, the resistance value of the developing roller 32 preferably ranges from 1 × 104 to 1 × 107 [Ω]. In this embodiment, a developing roller 32 with a resistance value of 1 × 105 [Ω] was used. In this measurement method, the resistance value between the core metal 62, the developing roller 32, and the metal roller 61 is measured. However, since the resistance values of the core metal 62 and the metal roller 61 with respect to the developing roller 32 which is rubber are sufficiently low, it is considered that only the resistance value of the developing roller 32 is measured, and the resistance values of the core metal 62 and the metal roller 61 are ignored.

[0031] [2-3. Configuration of the Developing Blade] The developing blade 30 is made of a stainless steel material with a plate thickness of 0.08 [mm], and a bent portion is formed by bending the contact portion with the developing roller 32, and the radius of curvature of the bent portion is 0.18 [mm]. The pressure (linear pressure) of the developing blade 30 against the developing roller 32 was set to 40 [gf / cm].

[0032] In view of the setting conditions of the developing blade 30, it is necessary to consider the surface roughness and resistance value, etc. of the developing roller 32 in order to make the toner layer thickness and toner charge amount on the developing roller 32 the desired amounts. In this embodiment, it is appropriate that the surface roughness of the developing roller 32 has a ten-point average roughness Rz (standard: JIS B0601-1994) in the circumferential direction of 2 to 10 [μm].

[0033] [2-4. Configuration of the Cleaning Blade] The cleaning blade 36 has one end thereof in contact with the surface of the photosensitive drum 34, and scrapes off the toner TN remaining on the surface of the photosensitive drum 34 without being transferred to the transfer belt. This cleaning blade 36 is made of, for example, a flexible rubber material, a plastic material, or the like.

[0034] The cleaning blade 36 is composed of a plate-shaped elastic body and a conductive plate-shaped holder for holding it. The material for forming the plate-shaped elastic body is not particularly limited, but when scraping off residual toner by slidingly contacting the surface of the photosensitive drum 34, it is common to use an elastic body composition so as not to damage the surface of the photosensitive drum 34. Examples of the material for forming the plate-shaped elastic body include compositions in which appropriate additives are blended with polyurethane, silicone resin, fluororesin, fluororubber, etc. Among them, a polyurethane composition is preferable in terms of excellent mechanical strength, elastic pressure contact property, etc. This polyurethane composition can usually be obtained using a polyisocyanate, a polyol, a curing agent, and a catalyst. The polyisocyanate is not particularly limited, and examples include 4,4′-diphenylmethane diisocyanate (MDI), 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 3,3′-tolylene-4,4′-diisocyanate, 3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, 2,4-tolylene diisocyanate urethidine dione (dimer of 2,4-TDI), 1,5-naphthylene diisocyanate, metaphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate (water-added MDI), carbodiimide-modified MDI, orthotoluidine diisocyanate, xylene diisocyanate, para-phenylene diisocyanate, lysine diisocyanate methyl ester, etc. diisocyanates, triphenylmethane-4,4′,4″-triisocyanate, etc. triisocyanates, polymeric MDI, etc. These can be used alone or in combination of two or more. Among them, MDI is preferable as the polyisocyanate from the viewpoint of wear resistance. Further, the polyol used together with the polyisocyanate is not particularly limited, and examples include polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexylene adipate, polycaprolactone, polyether polyols such as polyoxytetramethylene glycol and polyoxypropylene glycol.These are used alone or in combination of two or more. Among the polyols, PBA is preferred in terms of excellent abrasion resistance. The curing agent used together with the polyisocyanate and the polyol is not particularly limited, and examples include polyols having a molecular weight of 300 or less such as 1,4-butanediol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, xylene glycol, triethylene glycol, trimethylolpropane, glycerin, pentaerythritol, sorbitol, and 1,2,6-hexanetriol. These are used alone or in combination of two or more. The line pressure of the cleaning blade 36 against the photosensitive drum 34 is desirably 15 [gf / cm] or more and 30 [gf / cm] or less, and in this embodiment, it is set to 20 [gf / cm]. Also, the cleaning angle is set to be 10 to 15 degrees.

[0035] [2-5. Configuration of Photosensitive Drum] As shown in FIG. 4, the photosensitive drum 34 has a laminated structure in which an undercoat layer 75, a charge generation layer 76, and a charge transport layer 77 are laminated in this order from the surface on a conductive support 74 processed into a cylindrical shape. The photosensitive layer 73 is composed of the charge generation layer 76 and the charge transport layer 77. Hereinafter, the conductive support 74 is also referred to as a bare tube. Also, a drum gear 71 and a drum flange 72 are provided at the longitudinal ends of the photosensitive drum 34.

[0036] Between the conductive support 74 and the photosensitive layer 73 described later, an undercoat layer 75 may be provided to improve adhesion, blocking properties, etc. As the undercoat layer 75, for example, a resin or a resin in which particles such as metal oxides are dispersed is used. Further, the undercoat layer 75 may be a single layer or a plurality of layers may be provided. Examples of the metal oxide particles used for the undercoat layer 75 include metal oxide particles containing one kind of metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing a plurality of metal elements such as calcium titanate, strontium titanate, and barium titanate. These may be used alone or in any ratio and combination of two or more.

[0037] Among these metal oxide particles, titanium oxide and aluminum oxide are preferable, and titanium oxide is particularly preferable. The titanium oxide particles may be treated on their surface with an inorganic substance such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, or silicon oxide, or an organic substance such as stearic acid, polyol, or silicone. Any one of these treatments may be used, or two or more treatments may be applied. As the crystal form of the titanium oxide particles, for example, any of rutile, anatase, brookite, or amorphous can be used. Note that the crystal form of the titanium oxide particles may be only one kind, or two or more crystal forms may be included in any ratio and combination. The particle size of the metal oxide particles is arbitrary as long as the effects of the present invention are not significantly impaired. However, from the viewpoints of the properties of the binder resin, which is the raw material of the undercoat layer 75, and the stability of the solution, the average primary particle size is usually 10 [nm] or more and usually 100 [nm] or less, preferably 50 [nm] or less. This average primary particle size can be measured, for example, by a transmission electron microscope (TEM).

[0038] The undercoat layer 75 is preferably formed by dispersing metal oxide particles in a binder resin. Such an undercoat layer 75 is preferably formed, for example, by dispersing metal oxide particles in a solution in which a binder resin is dissolved, and applying the solution in which these metal oxide particles are dispersed (hereinafter, appropriately referred to as "coating solution for forming undercoat layer"). Examples of the binder resin used for the undercoat layer 75 include epoxy resin, polyethylene resin, polypropylene resin, acrylic resin, methacrylic resin, polyamide resin, vinyl chloride resin, vinyl acetate resin, phenol resin, polycarbonate resin, polyurethane resin, polyimide resin, vinylidene chloride resin, polyvinyl acetal resin, vinyl chloride-vinyl acetate copolymer, polyvinyl alcohol resin, polyurethane resin, polyacrylic acid resin, polyacrylamide resin, polyvinyl pyrrolidone resin, polyvinyl pyridine resin, water-soluble polyester resin, cellulose ester resins such as nitrocellulose, cellulose ether resins, casein, gelatin, polyglutamic acid, starch, starch acetate, amino starch, organic zirconium compounds such as zirconium chelate compounds and zirconium alkoxide compounds, organic titanyl compounds such as titanyl chelate compounds and titanyl alkoxide compounds, and silane coupling agents. These may be used alone or in combination of two or more in any ratio. Further, the binder resin of the undercoat layer 75 may be used in a cured form together with a curing agent. Among them, alcohol-soluble copolymer polyamides, modified polyamides, etc. exhibit good dispersibility and coatability and are preferable.

[0039] The structure of the photosensitive layer 73 can adopt any structure applicable to a known electrophotographic photoreceptor. To give a specific example, a so-called single-layer type photoreceptor having a single-layer photosensitive layer (i.e., a single-layer type photosensitive layer) in which a photoconductive material is dissolved or dispersed in a binder resin, and a photosensitive layer composed of a plurality of layers formed by laminating a charge generation layer 76 containing a charge generating substance and a charge transport layer 77 containing a charge transport substance (i.e., a laminated type photosensitive layer), such as a so-called laminated type photoreceptor, etc. are mentioned. Generally, it is known that photoconductive materials exhibit equivalent performance as a function, whether in a single-layer type or a laminated type.

[0040] The photosensitive layer of the electrophotographic photoreceptor of the present invention may be in any known form. However, in consideration of the mechanical properties, electrical properties, manufacturing stability, etc. of the electrophotographic photoreceptor, a laminated electrophotographic photoreceptor is preferred. In particular, a sequential lamination type photoreceptor in which a charge generation layer 76 and a charge transport layer 77 are laminated in this order on a conductive support 74 is more preferred.

[0041] When forming the charge transport layer of a function-separated type photoreceptor (i.e., a laminated photoreceptor) having a charge generation layer 76 and a charge transport layer 77 and the photosensitive layer of a single-layer type photoreceptor, in order to ensure film strength, a binder resin is usually used to disperse a compound. The charge transport layer of the function-separated type photoreceptor can be obtained by applying and drying a coating solution obtained by dissolving or dispersing a charge transport material and various binder resins in a solvent. Further, the single-layer type photoreceptor can be obtained by applying and drying a coating solution obtained by dissolving or dispersing a charge generating material, a charge transport material, and various binder resins in a solvent.

[0042] Examples of binder resins commonly used in the charge generation layer 76 of the function-separated photoreceptor include polyvinyl butyral resins, polyvinyl formal resins, partially acetalized polyvinyl butyral resins in which a part of butyral is modified with formal or acetal, etc., polyvinyl acetal resins, polyarylate resins, polycarbonate resins, polyester resins, modified ether-based polyester resins, phenoxy resins, polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl acetate resins, polystyrene resins, acrylic resins, methacrylic resins, polyacrylamide resins, polyamide resins, polyvinyl pyridine resins, cellulose-based resins, polyurethane resins, epoxy resins, silicone resins, polyvinyl alcohol resins, polyvinyl pyrrolidone resins, casein, vinyl chloride-vinyl acetate copolymers, hydroxy-modified vinyl chloride-vinyl acetate copolymers, carboxyl-modified vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, etc., vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, styrene-alkyd resins, silicone-alkyd resins, phenolic-formaldehyde resins, etc., insulating resins, and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, and polyvinyl perylene. These can be selected and used, but are not limited to these polymers. Further, these binder resins may be used alone or in combination of two or more in any ratio and combination.

[0043] Examples of the binder resin used in the charge transport layer 77 include, for example, polyvinyl acetal resins, polyarylate resins, polycarbonate resins, polyester resins, modified ether-based polyester resins, phenoxy resins, polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl acetate resins, polystyrene resins, acrylic resins, methacrylic resins, polyacrylamide resins, polyamide resins, polyvinyl pyridine resins, cellulose-based resins, polyurethane resins, epoxy resins, silicone resins, polyvinyl alcohol resins, polyvinyl pyrrolidone resins, casein, vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, styrene-alkyd resins, silicone-alkyd resins, phenol-formaldehyde resins, and organic photoconductive resins. Vinyl chloride-vinyl acetate copolymers include, for example, vinyl chloride-vinyl acetate copolymers, hydroxy-modified vinyl chloride-vinyl acetate copolymers, carboxyl-modified vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinyl acetate-maleic anhydride copolymers. Organic photoconductive resins include, for example, poly-N-vinylcarbazole, polyvinyl anthracene, and polyvinyl perylene.

[0044] Examples of those used as the charge transport agent include, for example, those containing any one or two or more of the charge transport substances. The type of the charge transport substance is not particularly limited, and examples thereof include aromatic amine derivatives, stilbene derivatives, butadiene derivatives, hydrazone derivatives, carbazole derivatives, aniline derivatives, and enamine derivatives. In addition, the charge transport substance may be, for example, a compound in which any one or two or more of the above-mentioned aromatic amine derivatives are bonded. Further, the charge transport substance may be, for example, a polymer (electron-donating material) having a group composed of the above-mentioned aromatic amine derivatives or the like as a main chain or a side chain. Among them, the charge transport substance is preferably an aromatic amine derivative, a stilbene derivative, a hydrazone derivative, an enamine derivative, or a compound in which any one or two or more of them are bonded, and more preferably a compound in which an aromatic amine derivative and an enamine derivative are bonded.

[0045] Each layer constituting the photosensitive drum 34 is usually formed by repeatedly applying and drying a coating solution containing the materials constituting each layer onto the conductive support 74 using a known coating method for each layer and sequentially applying them. As the solvent and dispersion medium for dissolving the binder resin and used for preparing the coating solution, for example, saturated aliphatic solvents such as pentane, hexane, octane, and nonane, aromatic solvents such as toluene, xylene, and anisole, halogenated aromatic solvents such as chlorobenzene, dichlorobenzene, and chloronaphthalene, amide solvents such as dimethylformamide and N-methyl-2-pyrrolidone, alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, and benzyl alcohol, aliphatic polyhydric alcohols such as glycerin and polyethylene glycol, chain, branched, and cyclic ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone, and 4-methoxy-4-methyl-2-pentanone, ester solvents such as methyl formate, ethyl acetate, and n-butyl acetate, halogenated hydrocarbon solvents such as methylene chloride, chloroform, and 1,2-dichloroethane, chain and cyclic ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran (hereinafter, appropriately referred to as "THF"), 1,4-dioxane, methyl cellosolve, and ethyl cellosolve, aprotic polar solvents such as acetonitrile, dimethyl sulfoxide, sulfolane, and hexamethylphosphoric triamide, nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, triethylenediamine, and triethylamine, mineral oils such as ligroin, and water, etc. are mentioned, and those that do not dissolve the undercoat layer 75 described above are preferably used. These may be used alone or in combination of two or more in any ratio and combination.

[0046] For the coating liquid for layer formation, in the case of the charge transport layer of a single-layer photoreceptor and a laminated photoreceptor, the solid content concentration is usually 5% by weight or more, preferably 10% by weight or more, and the upper limit is usually 40% by weight or less, preferably 35% by weight or less. Also, the viscosity of the coating liquid is usually 10 [mPa·s] or more, preferably 50 [mPa·s] or more, and the upper limit is usually 500 [mPa·s] or less, preferably 400 [mPa·s] or less.

[0047] In the case of the charge generation layer of a laminated photoreceptor, the solid content concentration is usually 0.1% by weight or more, preferably 1% by weight or more, and the upper limit is usually 15% by weight or less, preferably 10% by weight or less. Also, the viscosity of the coating liquid is usually 0.01 m[Pa·s] or more, preferably 0.1 [mPa·s] or more, and the upper limit is usually 20 [mPa·s] or less, preferably 10 [mPa·s] or less.

[0048] Examples of the coating method of the coating liquid include, for example, dip coating method, spray coating method, spinner coating method, bead coating method, wire bar coating method, blade coating method, roller coating method, air knife coating method, curtain coating method, etc., but it is also possible to use other known coating methods. These methods may be used alone or in any combination of two or more. The drying of the coating liquid is preferably carried out by heating and drying under no wind or blowing for usually 1 minute or more and 2 hours or less in a temperature range of usually 30 [°C] or more and 200 [°C] or less after dry to the touch at room temperature (usually 25 [°C]). Also, the heating temperature may be constant or may be changed during drying.

[0049] The film thickness of the photosensitive layer of the single-layer photoreceptor is usually 5 μm or more, preferably 10 μm or more, and its upper limit is usually 100 μm or less, preferably 50 μm or less. Further, the film thickness of the charge transport layer of the sequential lamination type photoreceptor is usually used in the range of 5 μm or more and 50 μm or less. From the viewpoints of long life and image stability, it is preferably 10 μm or more and 45 μm or less, and from the viewpoint of high resolution, it is more preferably 10 μm or more and 30 μm or less.

[0050] [3. Configuration of the control mechanism] Here, with reference to FIG. 5, the control mechanism of the image forming apparatus 1 will be described. The image forming apparatus 1 is provided with a control unit 42, a reception memory 44, an image data editing memory 46, an operation unit 48, a sensor group 50, and a power supply circuit 52 as control mechanisms. The image forming apparatus 1 is further provided with a paper conveyance motor 53 and a drive motor 54. The paper conveyance motor 53 drives the paper feed roller 10, the paper conveyance roller 12, and the paper discharge roller 16 (FIG. 1), and conveys the medium P in the directions indicated by arrows A to D. The drive motor 54 drives and rotates the photosensitive drum 34, the charging roller 26, the developing roller 32, and the toner supply roller 28 (FIG. 2).

[0051] The control unit 42 includes an interface (I / F) control unit 64, a main control unit 58, a head drive control unit 40S, a fixing control unit 8S, a conveyance motor control unit 53S, and a drive control unit 54S. The main control unit 58 is composed of a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, etc., and controls the entire processing operation in the image forming apparatus 1 by executing a predetermined program, for example. Specifically, the main control unit 58 receives print data and control commands from the I / F control unit 56, and performs a printing operation by comprehensively controlling the head drive control unit 40S, the fixing control unit 8S, the conveyance motor control unit 53S, and the drive control unit 54S. The I / F control unit 56 receives print data and control commands from an external device such as a PC, or transmits a signal regarding the state of the image forming apparatus 1.

[0052] The reception memory 44 temporarily stores print data from an external device such as a PC via the I / F control unit 56. The image data editing memory 46 receives the print data stored in the reception memory 44 and stores the image data obtained by editing the print data. The operation unit 48 includes, for example, an LED lamp for displaying information such as the state of the image forming apparatus 1, and an input unit (buttons or touch panel) for the user to give instructions to the image forming apparatus 1. The sensor group 50 includes various sensors for monitoring the operating state of the image forming apparatus 1, such as a position detection sensor for the medium P, a temperature and humidity sensor, a print density sensor, and a toner remaining amount detection sensor.

[0053] The head drive control unit 40S sends the image data recorded in the image data editing memory 46 to the LED head 40 and controls the driving of the LED head 40. The fixing control unit 8S controls the voltage applied to the fuser 8 when fixing the toner image transferred to the medium P onto the medium P. The conveyance motor control unit 53S controls the operation of the paper conveyance motor 53 to rotate the paper feed roller 10, the paper conveyance roller 12, and the paper discharge roller 16 in the directions indicated by the arrows, respectively, to convey the medium P. The drive control unit 54S controls the operation of the drive motor 54 to rotate the photosensitive drum 34 in the direction indicated by the arrow and to rotate the charging roller 26, the developing roller 32, and the toner supply roller 28 in the directions indicated by the arrows, respectively.

[0054] The power supply circuit 52 has a charging roller power supply of 26V, a toner supply roller power supply of 28V, a developing roller power supply of 32V, a developing blade power supply of 30V, and a transfer roller power supply of 14V. Here, the charging roller power supply of 26V, the toner supply roller power supply of 28V, the developing roller power supply of 32V, the developing blade power supply of 30V, and the transfer roller power supply of 14V apply voltages based on the instructions of the main control unit 58 to the charging roller 26, the toner supply roller 28, the developing roller 32, the developing blade 30, and the transfer roller 14, respectively. The charging roller power supply of 26V charges the surface of the photosensitive drum 34 by applying a voltage to the charging roller 26. The toner supply roller power supply of 28V supplies the toner TN from the toner storage unit 22 to the developing roller 32 by applying a voltage to the toner supply roller 28. The developing roller power supply of 32V develops the electrostatic latent image formed on the surface of the photosensitive drum 34 with the toner TN carried by the developing roller 32 by applying a voltage to the developing roller 32. The transfer roller power supply of 14V transfers the toner image developed on the surface of the photosensitive drum 34 to the medium P by applying a voltage to the transfer roller 14.

[0055] [4. Operation of the developing device] Next, the operation of the developing device 20 during image formation will be described. The developing device 20 in the present embodiment has at least a photosensitive drum 34, a charging roller 26, and a developing roller 32. As the drive motor 54 rotates, the photosensitive drum 34, the developing roller 32, the toner supply roller 28, and the charging roller 26 rotate in the directions indicated by the arrows in FIG. 2. In the present embodiment, the printing speed of the image forming apparatus 1 is equivalent to 40 [ppm] in vertical printing on A4 paper for the medium P, the peripheral speed of the developing roller 32 with an outer diameter of 16.0 [mm] is 0.3 [m / s], and the peripheral speed of the toner supply roller 28 with an outer diameter of 15.5 [mm] is 0.2 [m / s].

[0056] In the developing device 20, the toner supply roller 28 having a foamed elastic layer which is a spongy elastic body rotates while carrying the toner TN on its outer peripheral surface and in the cells, and reaches the contact portion with the developing roller 32. A DC voltage of -330 [V] is applied to the toner supply roller 28 by the toner supply roller power source 28V. Also, a DC voltage of -200 [V] is applied to the developing roller 32 by the developing roller power source 32V. Then, due to the potential difference generated between the developing roller 32 and the toner supply roller 28, the negatively charged toner TN is supplied to the developing roller 32. The toner TN carried on the surface of the developing roller 32 is thinned by the developing blade 30 to which a DC voltage of -330 [V] is applied by the developing blade power source 30V. Also, a DC voltage of -1000 [V] is applied to the charging roller 26 by the charging roller power source 26V. Thereby, the surface of the photosensitive drum 34 is uniformly charged. Then, the toner TN carried by the developing roller 32 is supplied to the electrostatic latent image formed on the photosensitive drum 34 by the exposure of the LED head 40, and the electrostatic latent image is developed. The toner TN on the developing roller 32 that has not been supplied to the photosensitive drum 34 is scraped off by the toner supply roller 28 at the opposing portion of the toner supply roller 28. The toner TN that has been developed on the photosensitive drum 34 and not transferred to the medium P, and the external additive that has been released from the toner mother particles and adhered to the surface of the photosensitive drum 34 are conveyed to the contact portion of the cleaning blade 36 and scraped off.

[0057] [5. Configuration of Drive Transmission Mechanism] By the way, the photosensitive drum 34, the charging roller 26, the developing roller 32, the toner supply roller 28, etc. are connected to a drive motor 54 which is a drive source for image formation, and rotate by receiving the rotation of the drive motor 54. For this purpose, the photosensitive drum 34, the charging roller 26, the developing roller 32, the toner supply roller 28, etc. are each connected to the drive motor 54 via a drive transmission device.

[0058] In addition, in order to transmit the rotation of the drive motor 54 to the photosensitive drum 34, the charging roller 26, the developing roller 32, the toner supply roller 28, etc., the output shaft of the drive motor 54 and a rotation transmission system composed of a gear train are connected. However, so that vibrations generated in the charging roller 26, the developing roller 32, the toner supply roller 28, etc. are not transmitted to the photosensitive drum 34, the rotation transmission system that transmits rotation to the photosensitive drum 34 and the rotation transmission system that transmits rotation to the charging roller 26, the developing roller 32, the toner supply roller 28, etc. are made independent of each other.

[0059] Next, the drive transmission device 80 shown in FIGS. 6 and 7 will be described. Since each drive transmission device that connects the photosensitive drum 34, the charging roller 26, the developing roller 32, the toner supply roller 28, and the drive motor 54 has the same structure, hereinafter, the photosensitive drum drive transmission device 81 that connects the drive motor 54 and the photosensitive drum 34 and the developing roller drive transmission device 82 that connects the drive motor 54 and the developing roller 32 will be described, and the description of the drive transmission device that connects the drive motor 54 and the charging roller 26, the toner supply roller 28, etc. will be omitted.

[0060] [5-1. Configuration of Photosensitive Drum Drive Transmission Device] The photosensitive drum drive transmission device 81 is composed of a drum drive gear 83, a drum drive shaft 84, a drum driven shaft 85, a drum coupling device 86, and a drum spring 87.

[0061] The drum drive gear 83 is rotatably disposed on the apparatus main body 2 and rotates by the driving force of the drive motor 54. At the end of the drum drive gear 83 on the image forming unit 6 side, a post 83p that protrudes toward a drum driven side coupling 86F (described later) is formed. The post 83p connects the drum drive side coupling 86D (described later) and the drum drive gear 83 so as not to move in the circumferential direction and to be movable in the axial direction.

[0062] The drum drive shaft 84 rotatably supports the drum drive gear 83 and rotates in the direction of arrow A as the drum drive gear 83 rotates. The drum driven shaft 85 is rotatably disposed corresponding to the drum drive shaft 84 on the image forming unit 6 side, transmits the rotation of the drum drive shaft 84 to the photosensitive drum 34, and rotates the photosensitive drum 34 in the direction of arrow A.

[0063] The drum coupling device 86 is composed of a drum drive side coupling 86D and a drum driven side coupling 86F, and selectively couples the drum drive shaft 84 and the drum driven shaft 85. The drum drive side coupling 86D is connected to the drum drive gear 83 via a post 83p on the apparatus main body 2 side. A plurality of (for example, three) teeth 86Dg are formed at equal pitches at the end of the drum drive side coupling 86D on the drum driven side coupling 86F side. On the other hand, the drum driven side coupling 86F is connected to the drum driven shaft 85 on the image forming unit 6 side. A plurality of (for example, three) teeth 86Fg are formed at equal pitches at the end of the drum driven side coupling 86F on the drum drive side coupling 86D side. When the image forming unit 6 is not attached to the apparatus main body 2, as shown in FIG. 6, the meshing between the teeth 86Dg and the teeth 86Fg is released, and the drum drive side coupling 86D and the drum driven side coupling 86F are in a non-connected state where they are not connected. On the other hand, when the image forming unit 6 is attached to the apparatus main body 2, as shown in FIG. 7, the teeth 86Dg and the teeth 86Fg mesh with each other, and the drum drive side coupling 86D and the drum driven side coupling 86F are in a connected state where they are connected.

[0064] The drum spring 87 is disposed so as to surround the post 83p between the drum drive gear 83 and the drum drive side coupling 86D. When the image forming unit 6 is attached to the apparatus main body 2 and the drum drive side coupling 86D and the drum driven side coupling 86F are in a connected state, the drum spring 87 presses the drum drive side coupling 86D against the drum driven side coupling 86F with a predetermined biasing force.

[0065] [Configuration of Developing Roller Drive Transmission Device] On the other hand, the developing roller drive transmission device 82 is composed of a developing drive gear 88, a developing drive shaft 89, a first developing driven shaft 90, a second developing driven shaft 91, a first developing driven gear 92, a second developing driven gear 93, a developing connecting device 94, and a spring 95.

[0066] The developing drive gear 88 is rotatably disposed on the apparatus main body 2 and rotates by the driving force of a drive motor 54 transmitted from a drive transmission mechanism (not shown). The developing drive shaft 89 rotatably supports the developing drive gear 88 and is rotated in the direction of arrow A as the developing drive gear 88 rotates. The first developing driven shaft 90 is rotatably disposed corresponding to the developing drive shaft 89 on the image forming unit 6 side, is rotated by receiving the rotation of the developing drive shaft 89, and rotates the first developing driven gear 92. The second developing driven shaft 91 is disposed in parallel with the first developing driven shaft 90 and rotatably supports the developing roller 32. Elastic bodies (not shown) are disposed at both ends of the second developing driven shaft 91, and the elastic bodies press the developing roller 32 against the photosensitive drum 34 with a predetermined biasing force F.

[0067] The first developing driven gear 92 is supported by the first developing driven shaft 90. The second developing driven gear 93 is supported by the second developing driven shaft 91. The second developing driven gear 93 meshes with the first developing driven gear 92, reverses the rotation transmitted to the first developing driven shaft 90, transmits it to the second developing driven shaft 91, and rotates the developing roller 32 in the direction of arrow B.

[0068] The developing connection device 94 is composed of a developing driving-side coupling 94D and a developing driven-side coupling 94F, and selectively connects the developing driving shaft 89 and the first developing driven shaft 90. The developing driving-side coupling 94D is connected to the developing driving gear 88 via the developing driving shaft 89 on the device main body 2 side. At the end of the developing driving-side coupling 94D on the developing driven-side coupling 94F side, a fitting convex portion 94Db with a predetermined shape (for example, a triangular prism shape) is formed. On the other hand, the developing driven-side coupling 94F is connected to the first developing driven shaft 90 on the image forming unit 6 side. At the end of the developing driven-side coupling 94F on the developing driving-side coupling 94D side, a fitting concave portion 94Fd with a predetermined shape (for example, a triangular prism shape) is formed corresponding to the fitting convex portion 94Db. When the image forming unit 6 is not attached to the device main body 2, as shown in FIG. 6, the fitting between the fitting convex portion 94Db and the fitting concave portion 94Fd is released, and the developing driving-side coupling 94D and the developing driven-side coupling 94F are in a non-connected state where they are not connected. On the other hand, when the image forming unit 6 is attached to the device main body 2, as shown in FIG. 7, the fitting convex portion 94Db and the fitting concave portion 94Fd are fitted, and the developing driving-side coupling 94D and the developing driven-side coupling 94F are in a connected state where they are connected.

[0069] The spring 95 is built in the developing driving-side coupling 94D. When the image forming unit 6 is attached to the device main body 2 and the developing driving-side coupling 94D and the developing driven-side coupling 94F are in a connected state, the developing driving-side coupling 94D is pressed against the developing driven-side coupling 94F with a predetermined biasing force.

[0070] [5-3. Configuration of the coupling intermittent mechanism] The device main body 2 is provided with a coupling intermittent mechanism (not shown) that switches between the connected state and the non-connected state of the drum driving-side coupling 86D and the drum driven-side coupling 86F, and also switches between the connected state and the non-connected state of the developing driving-side coupling 94D and the developing driven-side coupling 94F.

[0071] The coupling intermittent mechanism is provided with an actuator. When the operator activates the coupling intermittent mechanism, the actuator pushes the drum drive-side coupling 86D toward the drum drive gear 83 against the biasing force of the drum spring 87, and at the same time, pushes the developing drive-side coupling 94D toward the developing drive gear 88 against the biasing force of the spring 95. As a result, the drum drive-side coupling 86D and the drum driven-side coupling 86F become uncoupled, and the developing drive-side coupling 94D and the developing driven-side coupling 94F become uncoupled.

[0072] On the other hand, when the operator releases the activation of the coupling intermittent mechanism, the actuator stops pushing the drum drive-side coupling 86D toward the drum drive gear 83 and stops pushing the developing drive-side coupling 94D toward the developing drive gear 88. For this reason, the drum drive-side coupling 86D is pushed toward the drum driven-side coupling 86F by the biasing force of the drum spring 87, and the developing drive-side coupling 94D is pushed toward the developing driven-side coupling 94F by the biasing force of the spring 95. As a result, the drum drive-side coupling 86D and the drum driven-side coupling 86F become coupled, and the developing drive-side coupling 94D and the developing driven-side coupling 94F become coupled.

[0073] By the way, in order to accurately form a toner image on the photosensitive drum 34, when the operator attaches the image forming unit 6 to the apparatus main body 2, the drum drive shaft 84 and the drum driven shaft 85 are connected to place the photosensitive drum 34 at a reference position, and then, the positioning of the developing roller 32 with respect to the photosensitive drum 34 is performed. Here, if there are manufacturing errors, assembly errors, etc. in the image forming unit 6, the photosensitive drum drive transmission device 81, the developing roller drive transmission device 82, etc., or if the positioning of the image forming unit 6 is not performed accurately, the developing drive shaft 89 and the first developing driven shaft 90 in the developing roller drive transmission device 82 may be eccentric to each other and shaft misalignment may occur. In this case, the rotation of the drive motor 54 is not smoothly transmitted to the developing roller 32, vibrations may occur in the image forming unit 6, or the image quality may deteriorate.

[0074] In contrast, in the present embodiment, by using an Oldham coupling as the developing drive side coupling 94D of the developing roller drive transmission device 82, the axial displacement between the developing drive shaft 89 and the first developing driven shaft 90 is absorbed.

[0075] Thus, in the image forming apparatus 1, instead of the second developing driven shaft 91 and the drum driven shaft 85 directly meshing with each other via gears, a drum driven side coupling 86F and a second developing driven gear 93 are provided as drive units that are respectively arranged on the photosensitive drum 34 and the developing roller 32 and receive the drive of the drive motor 54 from the outside device main body 2 side to drive the photosensitive drum 34 and the developing roller 32 respectively.

[0076] [Regarding Jitter, Spot Stains, and Horizontal Streaks] Next, jitter, spot stains, and horizontal streaks caused by distortion of the developing roller 32, which are problems to be solved by the present invention, will be described.

[0077] [6-1. Regarding Jitter] First, jitter will be described. When transferring the developer on the image carrier onto the medium, the vibration of the drive motor 54 is transmitted to the photosensitive drum 34 and the developing roller 32. At this time, when the natural frequencies of the photosensitive drum 34 and the developing roller 32 are close values, the photosensitive drum 34 and the developing roller 32 resonate, and the distance between the photosensitive drum 34 and the transfer roller 14 varies periodically. When the distance between the photosensitive drum 34 and the transfer roller 14 is large, the toner TN on the photosensitive drum 34 is not sufficiently transferred onto the medium P, so the density becomes low and it becomes a horizontal white band with a width of several millimeters. Therefore, when the photosensitive drum 34 and the developing roller 32 resonate, the distance between the photosensitive drum 34 and the transfer roller 14 changes periodically, so horizontal white bands occur periodically. This phenomenon is called jitter. The natural frequencies of the photosensitive drum 34 and the developing roller 32 were calculated by the following formula (1).

[0078] [Equation]

[0079] · When calculating the natural frequency of the photosensitive drum 34 f: Natural frequency of the photosensitive drum 34 λ: Constant determined by the order of the natural frequency of the photosensitive drum 34 L: Length of the bare tube of the photosensitive drum 34 E: Young's modulus of the bare tube of the photosensitive drum 34 I: Second moment of area of the bare tube of the photosensitive drum 34 ρ: Mass density of the bare tube of the photosensitive drum 34 A: Cross-sectional area of the bare tube of the photosensitive drum 34 · When calculating the natural frequency of the developing roller 32 f: Natural frequency of the developing roller 32 λ: Constant determined by the order of the natural frequency of the developing roller 32 L: Length of the shaft of the developing roller 32 E: Young's modulus of the shaft of the developing roller 32 I: Second moment of area of the shaft of the developing roller 32 ρ: Mass density of the shaft of the developing roller 32 A: Cross-sectional area of the shaft of the developing roller 32

[0080] Although the developing roller 32 is composed of a rubber part and a shaft part (shaft body), since the Young's modulus of the rubber part is sufficiently smaller than that of the shaft part, the natural frequency of the developing roller 32 was calculated based on the shape of the shaft part. Since the third natural frequency of the developing roller 32 is close to the first natural frequency of the photosensitive drum 34, the evaluation of the natural frequency was performed using the first natural frequency of the photosensitive drum 34 and the third natural frequency of the developing roller 32. In order to vary the value of the first natural frequency of the photosensitive drum 34, samples with the variable tube wall thickness (i.e., the thickness of the tube) of the photosensitive drum 34 were prototyped and evaluated. As an index of the deviation between the natural frequency of the photosensitive drum 34 and the natural frequency of the developing roller 32, the degree of disagreement of the natural frequency was defined as follows. First, the ratio of the third natural frequency of the developing roller 32 to the first natural frequency of the photosensitive drum 34 was obtained, and the difference between the obtained ratio and 1 (when the natural frequencies match), that is, the absolute value of (1 - (the third natural frequency of the developing roller 32) / (the first natural frequency of the photosensitive drum 34)) was defined as the degree of disagreement of the natural frequency.

[0081] [6-2. About spot stains] Next, the spot stain will be described. The spot stain is a printing defect in which the halftone (2×2 pattern) becomes spotty. This is caused by the temperature rise of the toner TN in the developing device 20, which causes the external additive on the surface of the toner TN to peel off. When the external additive peels off, it becomes difficult to electrically control the development of the toner TN onto the photosensitive drum 34, and excess toner TN adheres to the photosensitive drum 34. Also, the toner TN particles are more likely to aggregate, and the aggregated toner TN adheres to the photosensitive drum 34, resulting in spotty stains. This is called spot stain. Usually, the external additive adheres to the surface of the toner TN. However, when the temperature of the toner TN increases, the viscosity of the toner TN decreases, and the holding force of the external additive decreases, making it easier for the external additive to peel off. Also, when the base tube wall thickness of the photosensitive drum 34 increases, the base tube weight and the heat capacity of the base tube increase. Even when the heat of the base tube moves to the medium P during paper feeding, the temperature of the base tube is less likely to decrease. Therefore, when the base tube wall thickness of the photosensitive drum 34 increases, the temperature of the base tube and the temperature of the toner TN in the developing device 20 increase during continuous printing, making it easier for spot stains to occur. In order to evaluate the occurrence of spot stains due to the base tube wall thickness, samples with variable base tube wall thicknesses of the photosensitive drum 34 were prototyped and evaluated.

[0082] [6-3. Horizontal streaks] Next, the horizontal streaks caused by leaving the developing device 20 after installation will be described. Note that "installation" refers to the state in which a sample with a variable base tube wall thickness of the photosensitive drum 34 is incorporated into the developing device 20 as shown in Fig. 2 together with the developing roller 32. When the hardness of the rubber part of the developing roller 32 is low, the vibration of the photosensitive drum 34 is absorbed by the rubber part of the developing roller 32, so jitter is less likely to occur. However, if the hardness of the rubber part of the developing roller 32 is below a certain level, the mechanical strength decreases, and during the storage period after installing the developing device 20, dents occur in the rubber part, which causes a printing defect called horizontal streaks.

[0083] In order to evaluate the presence or absence of horizontal streaks caused by the hardness of the developing roller 32, samples with variable hardness of the developing roller 32 were prototyped and evaluated. As a device for measuring the hardness of the developing roller 32, an Asker rubber hardness tester type C (manufactured by Kobunshi Keiki Co., Ltd.) was used, and the relationship between the Asker C hardness value and the occurrence of horizontal streaks was evaluated.

[0084] [7. Evaluation] Using the image forming apparatus 1 having the above-described configuration, the photosensitive drum 34 and the developing roller 32 were evaluated. In this evaluation, as shown in FIG. 8, six types of photosensitive drums 34 of Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6, and two types of photosensitive drums 34 of Comparative Example 1 and Comparative Example 2 were created, and evaluation was made as to whether or not jitter, spot stains, and horizontal streaks occurred. The printer used in each evaluation was C650dnw (manufactured by Okidata Co., Ltd.).

[0085] In FIG. 8, "×" was marked when jitter occurred, and "〇" was marked when jitter did not occur. Regarding the evaluation of jitter, evaluation was performed by combining two types of printing speeds and three types of test environments. When jitter was confirmed in any combination of printing speed and test environment, "×" was indicated, and when jitter was not confirmed in all combinations of printing speed and test environment, "○" was marked. Also in FIG. 8, "×" was marked when spot stains occurred, and "〇" was marked when spot stains did not occur. Further in FIG. 8, "×" was marked when horizontal streaks occurred due to leaving the developing device 20 mounted, and "〇" was marked when horizontal streaks did not occur due to leaving the developing device 20 mounted.

[0086] [7-1. Evaluation of Jitter] First, the method for evaluating jitter will be described. The image printing conditions for evaluating jitter are as follows. · Printing speed: 35 [ppm], 16 [ppm] in the vertical direction of A4 · Printing pattern: Halftone (2×2 pattern) · Test environment: Air temperature 25 [°C], relative humidity 50 [%], Air temperature 27 [°C], relative humidity 80 [%], Temperature 10 [°C], Relative Humidity 20 [%] · Visually evaluate the evaluation images for each printing speed and test environment, and check for the presence or absence of jitter

[0087] [7-2. Evaluation of Spot Stains] Next, the method for evaluating spot stains will be described. In this evaluation, after continuous printing under the following continuous printing conditions in a high-temperature and high-humidity environment where the temperature in the developing device 20 tends to rise, image printing was performed under the following evaluation image printing conditions for evaluating spot stains

[0088] Continuous Printing Conditions · Printing speed: 35 [ppm] in the vertical direction of A4 · Number of printed sheets: 200 sheets · Printing pattern: 0.3 [%] Duty (printing image density) · Test environment: Temperature 27 [°C], Relative Humidity 80 [%]

[0089] Evaluation Image Printing Conditions · Printing speed: 35 [ppm] in the vertical direction of A4 · Printing pattern: Halftone (2×2 pattern) · Test environment: Temperature 27 [°C], Relative Humidity 80 [%] · Visually evaluate the evaluation images and check for the presence or absence of spot stains

[0090] Here, the printing image density is a value representing the ratio of the number of pixels to which the developer is transferred to the medium P out of the total number of pixels when the image is decomposed into pixel units. For example, when solid printing is performed over the entire printable range of a predetermined area (one circumference of the photosensitive drum 34, one page of the printing medium, etc.), the area ratio 100 [%] printing is referred to as printing image density 100 [%], and printing corresponding to an area of 1 [%] with respect to this printing image density 100 [%] is referred to as printing image density 1 [%]. When the printing image density DPD is expressed by a mathematical formula using the number of used dots Cm, the rotation speed Cd, and the total number of dots CO, it can be expressed as in the following formula (2).

[0091] DPD [%] = Cm / (Cd × CO) × 100......(2)

[0092] However, the number of dots used Cm is the number of dots actually used to form an image when the photosensitive drum 34 rotates Cd times, and is the total number of dots exposed by the LED head 40 during the formation of the image. Also, the total number of dots CO is the total number of dots per one rotation of the photosensitive drum 34, that is, regardless of the presence or absence of exposure, it is the total number of dots that can potentially be used to form an image during one rotation of the photosensitive drum 34. In other words, the total number of dots CO is the total value of the number of dots used when forming a solid image that transfers the developer to all pixels. Therefore, the value (Cd × CO) represents the total value of the number of dots that can potentially be used to form an image while the photosensitive drum 34 rotates Cd times.

[0093] Furthermore, as shown in FIG. 9, the halftone (2×2 pattern) forms dots in 4 out of 16 squares, both vertically and horizontally, where the vertical and horizontal dot counts are 2 dots each.

[0094] [7-3. Evaluation of horizontal streaks] Next, a method for evaluating horizontal streaks due to the distortion of the developing roller 32 will be described. In this evaluation, in order to reproduce the state after the development device 20 is mounted and left, a standing test was performed under the following standing test conditions using a thermostatic chamber, and then image printing was performed under the following evaluation image printing conditions for evaluating horizontal streaks.

[0095] Standing test conditions · Standing environment: Temperature 47 [°C], Relative humidity 66 [%] · Standing period: 1 month

[0096] Evaluation image printing conditions · Printing speed: A4 vertical direction 35 [ppm] · Printing pattern: Halftone (2×2 pattern) · Test environment: Temperature 25 [°C], Relative humidity 50 [%]

[0097] [8. Judgment result] When the degree of mismatch (i.e., the difference in natural frequencies) between the natural frequency of the photosensitive drum 34 and the natural frequency of the developing roller 32 is small, the value of the natural frequency of the photosensitive drum 34 and the value of the natural frequency of the developing roller 32 become close, and jitter is likely to occur. From Comparative Example 1 and Examples 1 to 6 in which the raw tube wall thickness was varied, in order to suppress jitter, the degree of mismatch in natural frequencies needs to be 0.10 or more.

[0098] Also, when the raw tube wall thickness of the photosensitive drum 34 is large, the temperature inside the developing device 20 is likely to rise, and uneven stains are likely to occur. From Comparative Example 1 and Examples 1 to 6 in which the raw tube wall thickness was varied, in order to suppress uneven stains, the raw tube wall thickness needs to be 2.99 [mm] or less.

[0099] Furthermore, when the hardness of the developing roller 32 is low, vibration is absorbed by the rubber part, so jitter is less likely to occur. Therefore, from the perspective of jitter, it is preferable that the hardness of the developing roller 32 is lower. However, when the hardness of the developing roller 32 is low, the mechanical strength of the developing roller 32 becomes weak and the life of the developing roller 32 becomes short. Furthermore, since the hardness of the developing roller 32 is low, when the developing device 20 is left after being mounted, the developing roller 32 is likely to be deformed due to the pressure contact between the developing roller 32 and the photosensitive drum 34, so horizontal streaks are likely to appear. From Comparative Example 1 and Examples 5 and 6 in which the hardness of the developing roller 32 was varied, in order to suppress horizontal streaks due to leaving the developing device 20 after mounting, the Asker C hardness of the developing roller 32 needs to be 73.5 [°] or more. Also, when the Asker C hardness becomes 85.0 [°] or more, the pressure acting between the developing roller 32, the photosensitive drum 34, and the toner supply roller 28 increases, and the torque required to drive the developing roller 32 becomes large. Therefore, the upper limit of the Asker C hardness is set to 85.0 [°].

[0100] In addition, in order to reduce the size of the developing device 20, if the outer diameter of the base tube of the photosensitive drum 34, i.e., the base tube diameter (hereinafter also referred to as φ in this embodiment), is reduced, it is necessary to increase the base tube wall thickness of the photosensitive drum 34 in order to shift the natural frequency of the photosensitive drum 34 with respect to the natural frequency of the developing roller 32. Therefore, the base tube diameter / base tube wall thickness of the photosensitive drum 34 is calculated as an index of the relationship between the scale of the developing device 20 and the base tube wall thickness of the photosensitive drum 34. From Comparative Example 1 and Examples 1 to 6, in order to achieve both miniaturization and suppression of jitter, the base tube diameter / base tube wall thickness of the photosensitive drum 34 needs to be 16.2 or less.

[0101] In order to simultaneously achieve both miniaturization of the developing device 20 and suppression of jitter and suppression of mottling, from Examples 1, 2, and 3, the base tube wall thickness of the photosensitive drum 34 needs to be 1.48 [mm] or more and 2.99 [mm] or less. At this time, the range of the natural frequency mismatch degree is 0.10 or more and 0.17 or less, and the base tube diameter / base tube wall thickness of the photosensitive drum 34 is 8.0 or more and 16.2 or less. The base tube wall thickness (the wall thickness of the image carrier) and the base tube diameter (the outer diameter of the image carrier) of the photosensitive drum 34 were measured using a caliper. As described above in paragraph

[0049] , since the film thickness of the photosensitive layer of the photosensitive drum 34 is on the order of μm, the base tube wall thickness and the base tube diameter may be measured in a state where the photosensitive layer is formed on the base tube. Also, even if the photosensitive layer of the photosensitive drum 34 is scraped off with sandpaper or the like and only the base tube is measured using a caliper, the base tube wall thickness and the base tube diameter can be measured.

[0102] In addition, in order to widen the difference in natural frequencies between the photosensitive drum 34 and the developing roller 32, for example, it is also conceivable to increase the weight of the shaft body of the developing roller 32. However, if the shaft body of the developing roller 32 is thickened to increase its weight, the developing roller 32 will become larger, making it difficult to miniaturize the developing device 20. Also, although the developing device 20 can be miniaturized if the rubber portion provided on the surface of the shaft body of the developing roller 32 is thinned, thinning the rubber portion will shorten the life of the developing roller 32. Furthermore, if the rubber portion of the developing roller 32 is thin, when the photosensitive drum 34 and the developing roller 32 are in pressure contact, there is a possibility that the rubber portion cannot absorb the pressure contact force and the photosensitive drum 34 may be deformed.

[0103] Also, in the present embodiment, the length of the photosensitive drum 34 was evaluated at 246 [mm], and the axial length of the developing roller 32 was evaluated at 235 [mm]. Looking at the formula for the natural frequency in equation (1), it is possible to widen the natural frequency difference by changing the length of the photosensitive drum 34 and the axial length of the developing roller 32. However, considering the miniaturization of the developing device 20, if either one is made shorter than this, the printing area will be less than letter size (216 [mm]), which is not preferable.

[0104] [9. Effects, etc.] In the above configuration, the developing device 20 sets the ratio of the tube wall thickness to the tube diameter of the photosensitive drum 34 (the ratio of the tube diameter to the tube wall thickness), i.e., the tube diameter / tube wall thickness, to 16.2 or less, and sets the degree of mismatch between the natural frequencies of the photosensitive drum 34 and the developing roller 32 to 0.10 or more. For this reason, the developing device 20 can increase the overall weight of the photosensitive drum 34 by increasing the wall thickness relative to the outer diameter of the photosensitive drum 34, and widen the difference between the natural frequency of the developing roller 32 and the natural frequency of the photosensitive drum 34. Thereby, the developing device 20 can suppress the resonance between the photosensitive drum 34 and the charging roller 26 and the developing roller 32 as contact members that come into contact with the photosensitive drum 34. Thus, the developing device 20 can suppress the jitter on the medium P that occurs when transferring the toner TN on the photosensitive drum 34 onto the medium P while maintaining the printing quality, by suppressing the uneven contact between the transfer belt and the photosensitive drum 34 due to the vibration of the photosensitive drum 34, and can miniaturize the photosensitive drum 34.

[0105] Furthermore, when the developing device 20 sets the tube diameter / tube wall thickness to 8.0 or more and sets the degree of mismatch between the natural frequencies of the photosensitive drum 34 and the developing roller 32 to 0.17 or less, it can suppress the spot stains caused by continuous printing in a high-temperature and high-humidity environment.

[0106] In addition to this, the developing device 20 is configured such that the degree of mismatch between the natural frequencies of the photosensitive drum 34 and the developing roller 32 is 0.10 or more and 0.17 or less, the tube wall thickness of the photosensitive drum 34 is 1.48 [mm] or more and 2.99 [mm] or less, the Asker C hardness of the developing roller 32 is 73.5 [°] or more and 85.0 [°] or less, and the ratio of the tube wall thickness to the tube diameter of the photosensitive drum 34 (the ratio of the tube diameter to the tube wall thickness), i.e., the tube diameter / tube wall thickness, is 8.0 or more and 16.2 or less.

[0107] In this way, by optimizing the degree of mismatch between the natural frequencies of the photosensitive drum 34 and the developing roller 32, the tube wall thickness and tube diameter of the photosensitive drum 34, and the hardness of the developing roller 32, the developing device 20 can suppress jitter, spot stains, and horizontal streaks caused by leaving the developing device 20 installed. For this reason, the developing device 20 can suppress jitter that occurs during toner transfer from the photosensitive drum 34 to the medium P due to resonance between the photosensitive drum 34 and the developing roller 32, spot stains caused by continuous printing in a high-temperature and high-humidity environment, and horizontal streaks caused by leaving the developing device 20 installed. As a result, the developing device 20 can achieve both miniaturization of the developing device 20 and suppression of jitter.

[0108] In the embodiment of the present invention, the configuration is not such that the shaft of the photosensitive drum 34 and the shaft of the developing roller 32 directly mesh with each other via gears. Instead, when applied to a configuration in which the photosensitive drum 34 and the developing roller 32 are respectively driven by a drum driven-side coupling 86F and a second developing driven gear 93 that receive the drive of the drive motor 54 from the device main body 2 side, the effect is remarkable.

[0109] According to the above configuration, the developing device 20 is provided with a photosensitive drum 34 as a cylindrical image carrier that develops the formed latent image with a developer, and a charging roller 26 and a developing roller 32 as contact members that contact the surface of the photosensitive drum 34. The ratio of the tube diameter to the tube wall thickness of the photosensitive drum 34, i.e., the tube diameter / tube wall thickness of the photosensitive drum 34, is 16.2 or less, and the difference in natural frequency between the photosensitive drum 34 and the contact member is 0.10 or more.

[0110] As a result, by increasing the wall thickness of the photosensitive drum 34 with respect to its outer diameter, the weight of the entire photosensitive drum 34 can be increased, the difference between the natural frequency of the developing roller 32 and the natural frequency of the photosensitive drum 34 can be widened, and the jitter during transfer from the photosensitive drum 34 to the medium P due to resonance between the photosensitive drum 34 and the contact member in contact with the photosensitive drum 34 can be suppressed, and while maintaining the printing quality, the photosensitive drum 34 can be miniaturized.

[0111] [10. Other Embodiments] In the above-described embodiment, the case of defining the range of the degree of mismatch of the natural frequencies by focusing on the first natural frequency of the photosensitive drum 34 and the third natural frequency of the developing roller 32 has been described. The embodiment of the present invention is not limited to this, and the range of the degree of mismatch of the natural frequencies may be defined by focusing on the first natural frequency of the photosensitive drum 34 and the first natural frequency or the second natural frequency of the developing roller 32.

[0112] Also, in the above-described embodiment, in the drive transmission device 80 (FIGS. 6 and 7), the case of rotating the developing drive gear 88 by the driving force of the drive motor 54 transmitted from a drive transmission mechanism (not shown) has been described. The embodiment of the present invention is not limited to this, and the developing drive gear 88 may be rotated by the driving force of a drive motor provided separately from the drive motor 54.

[0113] Furthermore, in the above-described embodiment, the case of applying the embodiment of the present invention to the image forming apparatus 1 of a so-called direct transfer system in which the toner image is directly transferred from the photosensitive drum 34 to the medium P has been described. The embodiment of the present invention is not limited to this, and the embodiment of the present invention may be applied to an image forming apparatus of a so-called intermediate transfer system (or secondary transfer system) in which the toner images of each color are sequentially transferred from the photosensitive drum 34 to the intermediate transfer belt and the toner image is transferred from this intermediate transfer belt to the medium P.

[0114] Furthermore, in the above-described embodiment, the case where the embodiment of the present invention is applied to the image forming apparatus 1 using a developer for a one-component development system has been described. The embodiment of the present invention is not limited to this, and the embodiment of the present invention may be applied to an image forming apparatus using a developer for a two-component development system, which is a system that mixes a carrier and toner and imparts an appropriate charge amount to the toner by utilizing the friction between the carrier and the toner. In this regard, in the two-component development system, since the photosensitive drum and the developing roller are separated, resonance between the photosensitive drum and the developing roller does not occur. However, in the two-component development system, resonance may occur because the photosensitive drum and the charging roller are in contact with each other.

[0115] Furthermore, in the above-described embodiment, the case where the embodiment of the present invention is applied to the image forming apparatus 1 having one developing device 20 and forming a monochrome image using one color toner TN has been described. The embodiment of the present invention is not limited to this, and the embodiment of the present invention may be applied to an image forming apparatus having two or more developing devices 20 and forming an image using a predetermined number of color toners TN.

[0116] Furthermore, in the above-described embodiment, the case where the embodiment of the present invention is applied to the image forming apparatus 1 which is a single-function printer has been described. The embodiment of the present invention is not limited to this, and the embodiment of the present invention may be applied to other various image forming apparatuses having other functions, such as an MFP (Multi Function Peripheral) having functions of a copier or a facsimile machine. Also, the embodiment of the present invention may be applied to various electronic devices that form an image on a medium P such as paper using a developer by an electrophotographic method.

[0117] Furthermore, the embodiment of the present invention is not limited to the above-described embodiment and other embodiments. That is, the scope of application of the embodiment of the present invention extends to an embodiment in which the above-described embodiment and a part or all of the above-described other embodiments are arbitrarily combined, or an embodiment in which a part is extracted.

[0118] Furthermore, in the above-described embodiment, an image carrier unit is constituted by a photosensitive drum 34 as an image carrier and a contact member, and a developing device 20 is constituted which further includes a developing roller 32 as a developer carrier in the contact member. Further, the case where an image forming apparatus 1 as an image forming apparatus including the image carrier unit is constituted has been described. The embodiments of the present invention are not limited to this, and an image carrier unit may be constituted by a developer carrier having various other configurations, and an image forming apparatus including the image carrier unit may be further constituted.

Industrial Applicability

[0119] The embodiments of the present invention can be used when printing an image on a medium using an electrophotographic image forming apparatus.

Explanation of Signs

[0120] 1... Image forming apparatus, 2... Apparatus main body, 4... Paper cassette, 6... Image forming unit, 8... Fuser, 10... Paper feed roller, 12... Paper conveyance roller, 14... Transfer roller, 16... Paper discharge roller, 18... Stacker, 20... Developing device, 22... Toner storage section, 24... Casing, 26... Charging roller, 28... Toner supply roller, 30... Developing blade, 32... Developing roller, 34... Photosensitive drum, 36... Cleaning blade, 38a, 38b, 38c... Stirring members, 40... LED head, 42... Control unit, 44... Reception memory, 46... Image data editing memory, 48... Operation unit, 50... Sensor group, 52... Power supply circuit, 53... Paper conveyance motor, 54... Driving motor, 56... I / F control unit, 58... Main control unit, 40S... Head driving control unit, 8S... Fusing control unit, 53S... Conveyance motor control unit, 54S... Driving control unit, 26V... Power supply for charging roller, 32V... Power supply for developing roller, 28V... Power supply for toner supply roller, 30V... Power supply for developing blade, 14V... Power supply for transfer roller, TN... Toner, P... Medium, 60... High resistance meter, 61... Metal roller, 62... Core metal, 71... Drum gear, 72... Drum flange, 74... Conductive support, 75... Undercoat layer, 76... Charge generation layer, 77... Charge transport layer, 80... Driving transmission device, 81... Photosensitive drum driving transmission device, 82... Developing roller driving transmission device, 83... Drum driving gear, 83p... Post, 84... Drum driving shaft, 85... Drum driven shaft, 86... Drum coupling device, 86D... Drum driving side coupling, 86Dg... Teeth, 86F... Drum driven side coupling, 86Fg... Teeth, 87... Drum spring, 88... Developing driving gear, 89... Developing driving shaft, 90... First developing driven shaft, 91... Second developing driven shaft, 92... First developing driven gear, 93... Second developing driven gear, 94... Developing coupling device, 94D... Developing driving side coupling, 94Db... Fitting convex portion, 94F... Developing driven side coupling, 94Fd... Fitting concave portion, 95... Spring.

Claims

1. A cylindrical image carrier that develops a formed latent image with a developer, A contact member that contacts the surface of the image carrier Comprising, The ratio of the outer diameter to the wall thickness of the image carrier is 8.0 or more and 16.2 or less, and the degree of mismatch between the natural frequencies of the image carrier and the contact member is determined from the absolute value of (1 - (the third natural frequency of the contact member) / (the first natural frequency of the image carrier)), and is 0.10 or more and 0.17 or less An image carrier unit characterized by this.

2. The outer diameter of the image carrier is φ24 [mm], and the wall thickness of the image carrier is 1.48 [mm] or more and 2.99 [mm] or less The image carrier unit according to claim 1, characterized by this.

3. Drive units are further provided, which are respectively arranged on the image carrier and the contact member and are driven from the outside to drive the image carrier and the contact member respectively The image carrier unit according to claim 1 or claim 2, characterized by this.

4. The contact member is a developer carrier The image carrier unit according to any one of claims 1 to 3, characterized by this.

5. The image carrier and the developer carrier are in contact with each other to develop the developer The image carrier unit according to claim 4, characterized by this.

6. The Asker C hardness of the developer carrier is 73.5 [°] or more and 85.0 [°] or less The image carrier unit according to claim 4 or claim 5, characterized by this.

7. An image forming apparatus comprising the image carrier unit according to any one of claims 1 to 6.

Images