Drum unit and image forming apparatus

Abstract

To provide a technique that can be applied to various media and prevents the occurrence of printing failure.SOLUTION: In a drum unit 20, the surface potential of a photoreceptor drum 11 is defined as V0 (V), which is measured according to a first condition that the surface of the photoreceptor drum 11 is electrostatically charged by using a voltage having a first polarity and an absolute value of 1000 (V), and is exposed at an exposure value Q within a range of 0.13-0.34 (μJ / cm2), while the photoreceptor drum 11 is rotated at a peripheral velocity of 151 (mm / s). The surface potential of the photoreceptor drum 11 is defined as V1 (V), which is measured according to the first condition again after applying, for 406 (sec), a voltage having a second polarity opposite to the first polarity and an absolute value of 2850 (V) to the surface of the photoreceptor drum 11, while the photoreceptor drum 11 is rotated at a peripheral velocity of 73 (mm / s). When the surface potentials are represented as ΔV={1-(V1 / V0)}×100 (%), ΔV≤0.489×Q-0.014 (%) is established.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a drum unit having a photosensitive drum, and an image forming apparatus including the drum unit. [Background technology]

[0002] In an image forming device using an electronic process, the surface of a photoconductor drum is charged and then exposed to light to form an electrostatic latent image. The electrostatic latent image is developed with a developer to become a developer image. A transfer member is disposed opposite the photoconductor drum, and a medium passes between the two. By applying a transfer voltage to the transfer member, the developer image on the photoconductor drum is transferred to the medium.

[0003] Here, when printing a developer image on a medium that is narrow and has a high volume resistivity, in the area outside the area where the photosensitive drum contacts the medium (outside the medium area), contact between the photosensitive drum and the transfer member causes current to flow from the transfer member to the photosensitive drum.

[0004] As a result, charges of a polarity opposite to the charging potential accumulate on the surface of the photosensitive drum, which can cause a printing defect called strong transfer history when printing on a subsequent medium.

[0005] In order to reduce such printing defects, Patent Document 1 proposes increasing the surface potential (increasing the absolute value) in the outer-medium area of ​​the photosensitive drum by exposure processing. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-160292 A (Abstract, see FIG. 7) Summary of the Invention [Problem to be solved by the invention]

[0007] However, with conventional technology, it is difficult to handle a variety of media, such as continuous media (perforated media) and irregular media.

[0008] The present disclosure has been made to solve the above problems, and aims to provide a technology that is compatible with a variety of media and suppresses the occurrence of printing defects. [Means for solving the problem]

[0009] The drum unit of the present disclosure has a photosensitive drum and a frame that holds the photosensitive drum. While rotating the photoconductor drum at a peripheral speed of 151 [mm / s], the surface of the photoconductor drum is charged with a voltage of a first polarity and an absolute value of 1000 [V] to obtain a charge of 0.13 to 0.34 [μJ / cm 2 The surface potential of the photosensitive drum measured under the first condition of exposing the photosensitive drum with an exposure amount Q within the range of [V] is defined as V0 [V]. While rotating this photosensitive drum at a peripheral speed of 73 [mm / s], a voltage of a second polarity opposite to the first polarity and having an absolute value of 2850 [V] is applied for 406 [seconds], and the surface potential of the photosensitive drum is measured again under the first conditions, and is designated as V1 [V]. When expressed as ΔV={1-(V1 / V0)}×100[%], ΔV≦0.489×Q-0.014[%] holds. Effect of the Invention

[0010] According to the present disclosure, it is possible to suppress the occurrence of printing defects and also to support a variety of media. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a configuration of an image forming unit according to the embodiment; [Diagram 3] 2A and 2B are diagrams illustrating a cross-sectional structure of a photoconductor drum according to an embodiment. [Figure 4]3A and 3B are diagrams showing cross-sectional structures of a developing roller and a supply roller according to an embodiment. [Diagram 5] 5A and 5B are schematic diagrams illustrating a method for measuring the resistance of a developing roller according to an embodiment. [Figure 6] 1A and 1B are diagrams showing cross-sectional structures of a charging roller and a developing roller according to an embodiment of the present invention. [Figure 7] 2 is a schematic diagram showing a charging position, an exposure position, a development position, and a transfer position of a photoconductor drum according to an embodiment of the present invention; [Figure 8] FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the embodiment; [Figure 9] FIG. 2 is a schematic diagram showing a photoconductor drum, a transfer roller, and a medium according to the embodiment. [Figure 10] 5A to 5E are schematic diagrams showing the movement of electric charges on the surface of the photosensitive drum according to the embodiment. [Figure 11] 1A to 1C are schematic diagrams showing examples of strong transfer hysteresis occurring in a printed image. [Figure 12] 1A and 1B are schematic diagrams showing a method for measuring the rate of change of light attenuation. [Figure 13] 1 is a table showing the evaluation results of the rate of change in light attenuation and density difference when the amount of exposure of the photosensitive drum is changed for Examples 1 to 5 and Comparative Examples 1 to 5. [Figure 14] 1 is a graph showing the relationship between the exposure amount of a photosensitive drum and the rate of change of light attenuation for Examples 1 to 5 and Comparative Examples 1 to 5. [Figure 15] 1A and 1B are schematic diagrams showing a transfer nip between a photosensitive drum and a transfer roller, and FIG. 1C is a graph showing the relationship between the area of ​​the outside-of-medium region and the surface potential of the photosensitive drum. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <Configuration of Image Forming Apparatus> First, an image forming apparatus according to an embodiment will be described. Fig. 1 is a diagram showing an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 forms a color image by electrophotography, and is, for example, a color printer. Note that the image forming apparatus 1 is not limited to a color printer, and may be a monochrome printer.

[0013] The image forming apparatus 1 has a medium supply section 40 that supplies a medium M such as printing paper, image forming units 10K, 10Y, 10M, and 10C that form toner images of black (K), yellow (Y), magenta (M), and cyan (C), a transfer unit 30 that transfers the toner image to the medium M, a fixing device 50 that fixes the toner image to the medium M, and a medium discharge section 60 that discharges the medium M.

[0014] The medium supply unit 40 has a medium tray 41, a hopping roller 42, a pair of registration rollers 43, and a pair of transport rollers 44. The medium tray 41 accommodates media M in a stacked state. The media M is, for example, printing paper, OHP sheets, envelopes, copying paper, special paper, etc. The printing paper includes plain paper, coated paper (for example, waterproof paper), etc.

[0015] The hopping roller 42 rotates by the driving force of the transport motor 45 (FIG. 8) and sends the medium M from the medium tray 41 to the transport path one by one. The registration roller pair 43 rotates by the driving force of the transport motor 45 (FIG. 8) and transports the medium M along the transport path. The registration roller pair 43 starts rotating a predetermined time after the leading edge of the medium M contacts the nip portion between the registration roller pair 43, thereby correcting skew of the medium M. The transport roller pair 44 rotates by the driving force of the transport motor 45 (FIG. 8) and transports the medium M to the transfer unit 30.

[0016] Image forming units 10K, 10Y, 10M, and 10C as image forming sections are arranged from the upstream side to the downstream side, i.e., from the right side to the left side in Fig. 1, along the transport path of medium M. When there is no particular need to distinguish between image forming units 10K, 10Y, 10M, and 10C, they will be referred to as "image forming units 10."

[0017] An exposure head 21 serving as an exposure device is disposed so as to face a photoconductor drum 11 (described later) of the image forming unit 10. The exposure head 21 has a plurality of LEDs (light emitting diodes) serving as light emitting elements arranged in the axial direction of the photoconductor drum 11, and irradiates light onto the surface of the photoconductor drum 11. The exposure head 21 is suspended and supported by a top cover 1B that covers the upper part of the housing 1A. Also, laser elements may be used instead of LEDs.

[0018] <Configuration of image forming unit> 2 is a diagram showing the configuration of image forming unit 10. Image forming unit 10 has photosensitive drum 11 as an image carrier, charging roller 12 as a charging member, developing roller 13 as a developer carrier, supply roller 14 as a supply member, developing blade 15 as a layer regulating member, cleaning member 16, and frame 17 that houses these. On frame 17, toner cartridge 18 as a developer container is attached.

[0019] In the above configuration, the photosensitive drum 11 and the frame 17 that holds it constitute a drum unit 20. The drum unit 20 and the charging roller 12 may be collectively called a charging device.

[0020] The photoconductor drum 11 is a cylindrical member in which a photosensitive layer is formed on the surface of a conductive support, and rotates clockwise in the drawing about a rotation axis. The photoconductor drum 11 carries an electrostatic latent image on its surface. The configuration of the photoconductor drum 11 will be described in detail later.

[0021] The charging roller 12 is disposed so as to be in contact with the surface of the photosensitive drum 11, and rotates following the rotation of the photosensitive drum 11. A charging voltage is applied to the charging roller 12 from a charging roller power source 131 (FIG. 8), and the charging roller 12 uniformly charges the surface of the photosensitive drum 11.

[0022] The developing roller 13 is disposed so as to contact the surface of the photosensitive drum 11, and rotates in the opposite direction (the direction in which the surface moves at the contact portion is the forward direction) to the photosensitive drum 11. A developing voltage is applied to the developing roller 13 from a developing roller power supply 132 (FIG. 8), and the electrostatic latent image on the surface of the photosensitive drum 11 is developed with toner (developer).

[0023] Supply roller 14 is disposed so as to contact the surface of developing roller 13, and rotates in the same direction as developing roller 13 (the direction in which the surface moves in the contact portion is the opposite direction). Supply roller 14 receives a supply voltage from supply roller power source 133 (FIG. 8) and supplies toner to developing roller 13.

[0024] The developing blade 15 is a blade disposed so as to come into contact with the surface of the developing roller 13. A blade voltage is applied to the developing blade 15 from a developing blade power supply 134 (FIG. 8), and the toner layer on the surface of the developing roller 13 is regulated to a constant thickness.

[0025] The cleaning member 16 is disposed so as to come into contact with the surface of the photoreceptor drum 11, and scrapes off the toner remaining on the surface of the photoreceptor drum 11. The waste toner scraped off by the cleaning member 16 is transported to a waste toner recovery section by a transport screw (not shown).

[0026] Frame 17 is a housing forming the outer periphery of image forming unit 10. Within frame 17, the area in which developing roller 13, supply roller 14, and developing blade 15 are arranged is a toner storage section 22 that stores toner. In toner storage section 22, in addition to developing roller 13, supply roller 14, and developing blade 15, crank-shaped stirring bars 19a, 19b, and 19c that stir and transport toner T are arranged.

[0027] A toner cartridge 18 serving as a developer container is removably attached to the upper portion of a frame 17 of the image forming unit 10. The toner cartridge 18 is a container that contains toner (indicated by the symbol T) serving as a developer, and supplies the toner to a toner storage section 22.

[0028] As shown in FIG. 1, the transfer unit 30 has four transfer rollers 31 arranged to face the photosensitive drums 11 of each image forming unit 10, a transfer belt 32 passing between the photosensitive drums 11 and the transfer rollers 31, and a drive roller 33 and a driven roller 34 around which the transfer belt 32 is stretched.

[0029] The transfer unit 30 also has a belt cleaning member 35 that removes residual toner from the transfer belt 32 , and a waste toner storage unit 36 ​​that stores the residual toner removed by the belt cleaning member 35 .

[0030] The transfer belt 32 is an endless belt formed of a semiconductive plastic film with high resistance. The transfer belt 32 has a glossy surface, and attracts and holds the medium M on the surface to transport it.

[0031] The driving roller 33 is rotated by the driving force of a driving motor 108 (FIG. 8), and causes the transfer belt 32 to travel in the direction indicated by the arrow B. The driven roller 34 applies a predetermined tension to the transfer belt 32.

[0032] The transfer roller 31 as a transfer member is a metal shaft with a semiconductive elastic layer formed on the surface thereof. A transfer voltage is applied to the transfer roller 31 by a transfer roller power supply 135 (FIG. 8), and the toner image on the surface of the photosensitive drum 11 is transferred to the medium M on the transfer belt 32.

[0033] The fixing device 50 has a fixing roller 51 and a pressure roller 52. The fixing roller 51 has a built-in heater such as a halogen lamp. The fixing roller 51 is rotated by the driving force of a fixing motor 53 (FIG. 8).

[0034] The pressure roller 52 is pressed against the fixing roller 51, forming a fixing nip between the fixing roller 51 and the pressure roller 52. The fixing roller 51 and the pressure roller 52 apply pressure and heat toner transferred onto the medium M to fix it to the medium M.

[0035] The medium discharge section 60 is disposed downstream of the fixing device 50 in the transport direction of the medium M. The medium discharge section 60 has a pair of discharge rollers 61 that discharges the medium M that has passed through the fixing device 50 from a paper discharge port 62. The pair of discharge rollers 61 rotate by the rotation transmitted from the fixing motor 53 (FIG. 8), and discharge the medium M from the paper discharge port 62. A stacker 63 that stacks the discharged medium M is provided on the upper part of the top cover 1B.

[0036] 1 and 2, the axial direction of the photoconductor drum 11 (i.e., the direction of the rotation axis) is defined as the X direction. The X direction is the axial direction of each roller in the image forming apparatus 1, and is also the width direction of the medium M being transported. The movement direction of the medium M as it passes through the image forming unit 10 is defined as the Y direction. The direction perpendicular to the X direction and the Y direction is defined as the Z direction. Here, the Z direction is the up-down direction.

[0037] <Components of the image forming unit> Next, each of the components of the image forming unit 10 will be described in more detail.

[0038] <Toner> First, the toner used in the image forming unit 10 will be described. The toner is a non-magnetic, single-component, negatively charged toner. The average particle size of the toner is about 6.0 [μm], and the circularity is about 0.96. The average particle size is measured using a Multisizer 3 manufactured by Coulter Corporation. The circularity is measured using a Flow Particle Image Analyzer FPIA-3000 manufactured by Sysmex Corporation.

[0039] The toner is obtained by adding an external additive (external additive) such as inorganic fine powder or organic fine powder to toner base particles containing at least a binder resin.

[0040] The binder resin is preferably a polyester resin, a styrene-acrylic resin, an epoxy resin, or a styrene-butadiene resin. A plurality of types of binder resins may be mixed. In this embodiment, a mixture of two or more types of amorphous polyester resins and a crystalline polyester resin having a crystal structure is used.

[0041] A release agent and a colorant are added to the binder resin, and in addition, additives such as a charge control agent, a conductivity adjuster, a flowability improver, or a cleaning property improver may be added.

[0042] The release agent is not particularly limited, but may be low molecular weight polyethylene, low molecular weight polypropylene, copolymers of olefins, aliphatic hydrocarbon waxes such as microcrystalline wax, paraffin wax, and 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 Montan acid ester wax, and fatty acid esters such as deoxidized carnauba wax that have been partially or completely deoxidized. The content of the release agent is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 12 parts by weight, relative to 100 parts by weight of the binder resin. A plurality of waxes may be used in combination.

[0043] The colorant is not particularly limited, but dyes, pigments, etc. generally used as yellow, magenta, cyan, and black toner colorants can be used alone or in combination. Specifically, for example, carbon black, iron oxide, phthalocyanine blue, permanent brown FG, brilliant first 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 used. The content of the colorant is preferably 2 to 25 [parts by weight], more preferably 2 to 15 [parts by weight], relative to 100 [parts by weight] of the binder resin.

[0044] The charge control agent may be a known one. For example, in the case of a negatively charged toner, there are azo complex charge control agents, salicylic acid complex charge control agents, calixarene charge control agents, etc. The content of the charge control agent is preferably 0.05 to 15 parts by weight, more preferably 0.1 to 10 parts by weight, relative to 100 parts by weight of the binder resin.

[0045] The external additive is added to improve environmental stability, charge stability, developability, fluidity, and storage stability, and known additives can be used. The content of the external additive is 0.01 to 10 parts by weight, preferably 0.05 to 8 parts by weight, per 100 parts by weight of the binder resin. In this embodiment, several types of silica (positive and negative charge polarity) with an average particle size of 14 μm, colloidal silica (negative charge) with an average particle size of 110 μm, and melamine (positive charge) with an average particle size of 200 μm are added to 100 parts by weight of the base particles, and the total amount is within the above range.

[0046] The toner charge (blow-off charge) was measured by stirring the toner and carrier by shaking. Here, Powdertech Co., Ltd.'s ferrite carrier "EF96-35" was used as the carrier, and 0.5 [g] of toner and 9.5 [g] of carrier were mixed. The toner and carrier mixture (150 [mg]) was placed in a container and shaken using Yayoi Co., Ltd.'s shaker "YS-LD". The shaking frequency was 200 [times / min], and the shaking time was 300 [seconds].

[0047] After shaking, the powder charge measuring device "TB-203" manufactured by Kyocera Chemical Corporation was used to perform suction 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 were output every 0.1 seconds to a PC (personal computer). The charge amount per unit weight of the toner particles Q / M calculated from the average charge amount and suction amount output during the last 2 seconds of the suction time (10 seconds) was approximately -35 μC / g. The measurements were performed at a temperature of 25°C and a relative humidity of 50%.

[0048] <Photoconductor drum> Next, a description will be given of the photoconductor drum 11. Fig. 3(A) is a diagram showing a cross-sectional structure of the photoconductor drum 11. Fig. 3(B) is an enlarged view showing a part of the cross section of the photoconductor drum 11 shown in Fig. 3(A).

[0049] The photoconductor drum 11 is a member that carries an electrostatic latent image on its surface (surface layer portion). As shown in FIG. 3(A), the photoconductor drum 11 is a cylindrical member that has a drum gear 11a at one axial end and a drum flange 11b at the other end. The drum gear 11a is a portion that receives a driving force from a driving motor 108 (FIG. 8). The outer diameter of the cylindrical portion of the photoconductor drum 11 (excluding the drum gear 11a and drum flange 11b) is, for example, 30 mm, and is within a range of 30.0±0.2 mm when manufacturing errors are taken into account. The axial length of the cylindrical portion of the photoconductor drum 11 is, for example, 327 mm.

[0050] 3(B), the photoconductor drum 11 has a conductive support 110 and a photosensitive layer 114 that covers the surface of the conductive support 110. The conductive support 110 is a pipe made of a metal such as aluminum or stainless steel.

[0051] The photosensitive layer 114 has a structure in which a charge generating layer 112 and a charge transport layer 113 are laminated in this order. An undercoat layer 111 may be formed between the conductive support 110 and the photosensitive layer 114. The undercoat layer 111 is also called a blocking layer.

[0052] For example, a binder resin having particles of a metal oxide or the like dispersed therein is used as the undercoat layer 111. The undercoat layer 111 may be configured as a single layer or as a multi-layer structure.

[0053] Examples of metal oxide particles used in the undercoat layer 111 include metal oxide particles containing one type of metal element, such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements, such as calcium titanate, strontium titanate, and barium titanate. These may be used alone or in any combination of two or more types in any ratio.

[0054] Among these metal oxide particles, titanium oxide and aluminum oxide are preferred, and titanium oxide is particularly preferred. The titanium oxide particles may have their surfaces treated 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.

[0055] These treatments may be performed by one kind or by two or more kinds. The crystal type of the titanium oxide particles may be, for example, any of rutile, anatase, brookite, and amorphous. The titanium oxide particles may have only one kind of crystal type, or may contain two or more kinds of crystal types in any ratio and combination.

[0056] The particle size of the metal oxide particles may be any size as long as it does not significantly impair the effects of the present disclosure, but from the viewpoint of the properties of the binder resin of the undercoat layer 111 and the stability of the solution, it is preferable that the average primary particle size is 10 nm or more and 100 nm or less, and preferably 50 nm or less. This average primary particle size can be measured, for example, by a transmission electron microscope (TEM).

[0057] The undercoat layer 111 is preferably formed, for example, by dispersing metal oxide particles in a solution in which a binder resin is dissolved, and applying the solution onto the conductive support 110. Examples of the binder resin used in the undercoat layer 111 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, polyvinylpyrrolidone resin, polyvinylpyridine resin, water-soluble polyester resin, cellulose ester resin such as nitrocellulose, cellulose ether resin, 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 any combination of two or more in any ratio. They may also be used in a cured form together with a curing agent. In particular, alcohol-soluble copolymerized polyamides, modified polyamides, etc. are preferred because they exhibit good dispersibility and applicability.

[0058] The photosensitive layer 114 may have any structure applicable to known electrophotographic photoreceptors. Specific examples include a single-layer photoreceptor having a single-layer photosensitive layer (i.e., a single-layer photosensitive layer) in which a photoconductive material is dissolved or dispersed in a binder resin, and a multi-layer photoreceptor having a photosensitive layer (i.e., a multi-layer photosensitive layer) consisting of a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance (charge transport material). It is generally known that photoconductive materials, whether single-layer or multi-layer, exhibit equivalent performance in terms of function.

[0059] The photosensitive layer 114 of the photosensitive drum 11 in this embodiment may be in any known form, but a laminated type electrophotographic photosensitive member is preferred in consideration of the mechanical properties, electrical properties, manufacturing stability, etc. of the electrophotographic photosensitive member. In particular, a normal laminated type photosensitive member in which a charge generating layer 112 and a charge transport layer 113 are laminated in this order on a conductive support 110 is more preferred.

[0060] When forming the charge transport layer 113 of a laminated photoreceptor (functionally separated photoreceptor) and the photosensitive layer of a single-layered photoreceptor, a binder resin is used to disperse the compound in order to ensure film strength. The charge transport layer of a functionally separated photoreceptor can be obtained by applying and drying a coating liquid obtained by dissolving or dispersing a charge transport material and various binder resins in a solvent. Also, a single-layered photoreceptor can be obtained by applying and drying a coating liquid obtained by dissolving or dispersing a charge generating material, a charge transport material, and various binder resins in a solvent.

[0061] Examples of the binder resin used in the charge generating layer 112 of the function separation type photoconductor include polyvinyl butyral resin, polyvinyl formal resin, polyvinyl acetal resin such as partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal or acetal, polyarylate resin, polycarbonate resin, polyester resin, modified ether polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyvinylpyridine resin, cellulose resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl a The binder resin may be selected from, but is not limited to, alcohol resin, polyvinylpyrrolidone resin, casein, vinyl chloride-vinyl acetate copolymer, hydroxy-modified vinyl chloride-vinyl acetate copolymer, carboxyl-modified vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, and other vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, styrene-alkyd resin, silicone-alkyd resin, phenol-formaldehyde resin, and other insulating resins, and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, and polyvinylperylene. In addition, one of these binder resins may be used alone, or two or more may be used in any ratio and combination.

[0062] Examples of the binder resin used in the charge transport layer 113 include polyvinyl acetal resin, polyarylate resin, polycarbonate resin, polyester resin, modified ether polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyvinylpyridine resin, cellulose resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin, polyvinylpyrrolidone resin, casein, vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, styrene-alkyd resin, silicone-alkyd resin, phenol-formaldehyde resin, and organic photoconductive resin. Examples of the vinyl chloride-vinyl acetate copolymer include vinyl chloride-vinyl acetate copolymer, hydroxy-modified vinyl chloride-vinyl acetate copolymer, carboxyl-modified vinyl chloride-vinyl acetate copolymer, and vinyl chloride-vinyl acetate-maleic anhydride copolymer. Examples of the organic photoconductive resin include poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylperylene.

[0063] The charge transport layer 113 contains, for example, at least one type of charge transport substance (charge transport material). The type of the charge transport substance is not particularly limited, but may be, for example, an aromatic amine derivative, a stilbene derivative, a butadiene derivative, a hydrazone derivative, a carbazole derivative, an aniline derivative, or an enamine derivative. The charge transport substance may be, for example, a compound to which one or more of the above-mentioned aromatic amine derivatives are bonded. The charge transport substance may be, for example, a polymer (electron donating material) having a group consisting of the above-mentioned aromatic amine derivative 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 to which one or more of them are bonded, and more preferably a compound to which an aromatic amine derivative and an enamine derivative are bonded.

[0064] The charge transport layer 113 further contains an electron transport substance (electron transport material) to reduce printing defects. For example, aromatic quinone is known as an electron transport substance. In the charge transport layer 113, if a large amount of the electron transport substance is added, the charge transport ability decreases, so the amount of the electron transport substance added is set to an extent that does not impair the image quality of the toner image.

[0065] Each layer constituting the photoreceptor drum 11 is formed by repeatedly applying a coating liquid containing the material constituting each layer onto the conductive support 110 using a known coating method and drying steps for each layer. Examples of the solvent (dispersion medium) used to dissolve the binder resin and prepare the coating liquid include 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, linear, branched, and cyclic ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone, and 4-methoxy-4-methyl-2-pentanone, methyl formate, ethyl acetate, and the like. Examples of the solvent include ester solvents such as 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 (also called THF), 1,4-dioxane, methyl cellosolve, and ethyl cellosolve, aprotic polar solvents such as acetonitrile, dimethyl sulfoxide, sulfolane, and hexamethylphosphoric acid triamide, nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, triethylenediamine, and triethylamine, mineral oils such as ligroin, and water, and those that do not dissolve the above-mentioned undercoat layer are preferably used. These may be used alone or in any ratio and combination of two or more.

[0066] The coating liquid for forming the charge transport layer of the single-layer photoreceptor and the multi-layer photoreceptor has a solid content of 5% by weight or more, preferably 10% by weight or more, and 40% by weight or less, preferably 35% by weight or less. The viscosity of the coating liquid is 10 mPa·s or more, preferably 50 mPa·s or more, and 500 mPa·s or less, preferably 400 mPa·s or less.

[0067] In the case of the charge generating layer of the multi-layer photoreceptor, the solid content is 0.1 [wt %] or more, preferably 1 [wt %] or more, and 15 [wt %] or less, preferably 10 [wt %] or less. Also, the viscosity of the coating liquid is 0.01 m [Pa·s] or more, preferably 0.1 [mPa·s] or more, and 20 [mPa·s] or less, preferably 10 [mPa·s] or less.

[0068] Examples of the coating method of the coating liquid include dip coating, spray coating, spinner coating, bead coating, wire bar coating, blade coating, roller coating, air knife coating, curtain coating, etc., but other known coating methods can also be used. These methods may be used alone or in any combination of two or more. The coating liquid is preferably dried by heating at a temperature range of 30[°C] to 200[°C] for 1 minute to 2 hours without wind or with air blowing after touch-drying at room temperature (25[°C]). The heating temperature may be constant or may be changed during drying.

[0069] The thickness of the photosensitive layer of the single-layer photoreceptor is generally 5 μm or more, preferably 10 μm or more, and generally 100 μm or less, preferably 50 μm or less. The thickness of the charge transport layer of the normal laminated photoreceptor is generally 5 μm or more and 50 μm or less, but from the viewpoint 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 preferably 10 μm or more and 30 μm or less.

[0070] <Developing roller> Next, the developing roller 13 will be described. Fig. 4(A) is a diagram showing a cross-sectional structure of the developing roller 13. The developing roller 13 includes a conductive core metal (shaft body) 13a, an elastic layer 13b formed on the surface of the core metal 13a, and a surface layer 13c covering the surface of the elastic layer 13b. The core metal 13a may be made of any material having good electrical conductivity, and may be made of, for example, iron, aluminum, stainless steel, or the like.

[0071] The elastic layer 13b may be made of a general rubber material such as silicone rubber or urethane. When polyurethane is used as the elastic layer 13b, it is preferable that the polyurethane is mainly made of polyether-based polyol. The ether-based polyurethane is a so-called cast-type polyurethane obtained by reacting a polyol mainly made of polyether-based polyol with a polyisocyanate. This is to reduce the compression set. On the other hand, when an ester-based polyurethane is used, it has poor hydrolysis characteristics and cannot be used stably for a long period of time.

[0072] Furthermore, when polyurethane is used as the elastic layer 13b, the isocyanate to be reacted with the polyol may be, for example, a trifunctional isocyanate alone such as triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, or bicycloheptane triisocyanate, or a mixture of hexamethylene diisocyanate modified polyisocyanate or polymeric MDI.

[0073] In addition, a mixture of these trifunctional or higher polyisocyanates and a general bifunctional isocyanate compound may be used. Examples of bifunctional isocyanate compounds 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 polymers such as prepolymers having these isocyanates at both ends.

[0074] The elastic layer 13b is formed by adding carbon black to the above-mentioned rubber base material, and then heat-curing the material while maintaining the carbon dispersed therein. This converts the carbon black, which has a specific resistance of about 0.1 to 10 [Ω·cm], into an elastomer (10 12 ~10 16 [Ω cm]) for 10 4 ~10 8 It is possible to form a stable medium resistance region of [Ω·cm].

[0075] The surface layer 13c is formed, for example, by impregnating the surface layer of the elastic layer 13b 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, and pentyl acetate. When such an organic solvent is used, for example, isocyanate compounds such as 2,4-tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI), as well as polymers and modified products thereof, can be used as the isocyanate component contained in the surface treatment liquid.

[0076] The surface treatment liquid may contain a polyether polymer. The polyether 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 polymers having active hydrogen include polymers having a hydroxyl group or an allyl group, such as polyols and glycols used in terminal isocyanate prepolymers.

[0077] 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 specific 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 acrylic acid ester and an alkyl fluoride acrylate, and derivatives thereof. The acrylic silicone-based polymer is, for example, a solvent-soluble silicone-based polymer, and examples thereof include a block copolymer of an acrylic acid ester and an acrylic acid siloxane ester, and derivatives thereof.

[0078] The surface treatment solution may further contain carbon black, such as acetylene black, as a conductivity imparting agent.

[0079] The polyether polymer, acrylic fluorine polymer, and acrylic silicone polymer in the surface treatment liquid are preferably adjusted so that the total amount of the polyether polymer, acrylic fluorine polymer, and acrylic silicone polymer is 10 to 70% by mass relative to the isocyanate component. If the amount is less than 10% by mass, the effect of retaining carbon black, etc. in the surface treatment liquid is reduced. On the other hand, if the amount is more than 70% by mass, there is a problem that the electrical resistance value increases or the amount of the isocyanate component is relatively reduced, making it impossible to form an effective surface treatment layer.

[0080] The elastic layer 13b is immersed in the above-mentioned surface treatment liquid, and the surface treatment liquid is applied to the elastic layer 13b by drying and curing, so that the surface layer of the elastic layer 13b is impregnated with the surface treatment liquid to form the surface layer 13c. The outer diameter of the developing roller 13 is, for example, 16.0 mm.

[0081] The resistance value of the developing roller 13 was measured by the method shown in Figures 5(A) and (B). A high resistance meter (model number: 4339B) manufactured by Hewlett-Packard was used as the measuring device 25. As shown in Figure 5(A), a load of W = 300 [g] was applied to the shaft parts 13e at both ends of the core metal 13a of the developing roller 13, and the developing roller 13 was brought into contact with a stainless steel metal roller 26 having a diameter of 30 [mm].

[0082] A potential difference of -100 [V] was applied to the shaft portion 13e of the developing roller 13 relative to the shaft portion 27 of the metal roller 26, and the metal roller 26 was rotated at a speed of 50 [rpm]. The resistance was then measured at 100 points per revolution of the developing roller 13, and the average value was taken as the resistance value of the developing roller 13. The resistance value of the developing roller 13 was 1×10 4 ~1×10 7 [Ω] is preferred, where the resistance is 1×10 5 A developing roller 13 of [Ω] was used.

[0083] <Supply roller> Next, the supply roller 14 will be described. Fig. 4(B) is a cross-sectional view showing the supply roller 14. The supply roller 14 has a conductive core metal (shaft body) 14a and a sponge-like foamed elastic layer 14b formed on the surface of the core metal 14a. The core metal 14a may be any material having good conductivity, and may be formed of, for example, iron, aluminum, stainless steel, or the like.

[0084] The rubber composition forming the foamed elastic layer 14b contains rubber, a foaming agent, and a conductive agent, and further contains additives as necessary. The rubber is preferably silicone rubber or silicone modified rubber, which has excellent heat resistance and electrostatic properties. The foaming agent may be any foaming agent used for foamed rubber. Examples of inorganic foaming agents include sodium bicarbonate and ammonium carbonate. Examples of organic foaming agents include organic azo compounds such as diazoamino derivatives, azonitrile derivatives, and azodicarboxylic acid derivatives. Inorganic foaming agents are used when continuous cells are formed in the foamed elastic layer 14b, and organic foaming agents are used when closed cells are formed. Examples of additives include fillers, colorants, and release agents.

[0085] The outer diameter of the supply roller 14 is, for example, 15.5 mm. The average cell diameter of the foamed elastic layer 14b of the supply roller 14 is preferably 200 to 500 μm. The hardness of the foamed elastic layer is preferably about 50 to 65 degrees in Asker F hardness, and is 58 degrees here.

[0086] The resistance value of the supply roller 14 is preferably 3.5 to 7.5 [log Ω]. In this example, the supply roller 14 has a resistance of 5.5 log Ω. The measurement method is the same as the measurement method of the resistance value of the developing roller 13. As explained with reference to the above.

[0087] <Developing blade> 2 is a plate-shaped elastic body made of metal. More specifically, the developing blade 15 is made of stainless steel and has a plate thickness of, for example, 0.08 mm. The developing blade 15 is formed in an elongated shape that is long in the X direction.

[0088] One end (fixed end) in the width direction of the developing blade 15 is fixed to a blade holder 23 provided on the frame 17. The other end (free end) in the width direction of the developing blade 15 is bent, and the radius of curvature of the bent portion is approximately 0.18 [mm]. The bent portion of the developing blade 15 abuts against the surface of the photosensitive drum 11. The pressure (linear pressure) between the developing blade 15 and the developing roller 13 is approximately 40 [gf / cm].

[0089] Considering the setting conditions of the developing blade 15, the surface roughness, resistance value, etc. of the developing roller 13 are set to obtain the desired toner layer thickness and toner charge amount on the developing roller 13. The surface roughness of the developing roller 13 is preferably such that the ten-point average roughness Rz (JIS B0601-1994) in the circumferential direction is 2 to 10 μm.

[0090] <Charging roller> Fig. 6(A) is a diagram showing a cross-sectional structure of the charging roller 12. As shown in Fig. 6(A), the charging roller 12 has a core (shaft body) 12a, an elastic layer 12b formed on the surface of the core 12a, and a surface layer 12c covering the surface of the elastic layer 12b.

[0091] The core metal 12a is made of a conductive material, for example, a metal such as electroless nickel-plated free-cutting steel (SUM) or stainless steel (SUS). The elastic layer 12b is made of rubber, thermoplastic elastomer, resin, or the like so as to form a nip between the core metal 12a and the photoconductor drum 11 where appropriate discharge occurs. The elastic layer 12b may be a single layer or may have a multi-layer structure of two or more layers.

[0092] The elastic layer 12b is made of, for example, epichlorohydrin rubber (CO, ECO, GECO), ethylene propylene rubber (EPM, EPDM), or acrylonitrile-butadiene rubber. It is formed from a rubber composition whose main component is one or a mixture of two or more of the following rubbers: NBR, hydrogenated acrylonitrile-butadiene rubber (H-NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), urethane rubber, and silicone rubber.

[0093] In particular, it is preferable to use rubber mainly composed of epichlorohydrin rubber (ECO) or a mixture of epichlorohydrin rubber (ECO) and acrylonitrile-butadiene rubber (NBR). In this embodiment, rubber mainly composed of epichlorohydrin rubber (ECO) is used.

[0094] If the electrical resistance of the elastic layer 12b is too high, printing defects occur due to uneven charging or overcharging of the surface of the photoconductor drum 11. Conversely, if the electrical resistance of the elastic layer 12b is too low, printing defects occur due to current leakage caused by scratches on the surface of the photoconductor drum 11. Therefore, there is an appropriate range for the electrical resistance of the elastic layer 12b. In order to set the electrical resistance of the elastic layer 12b within the appropriate range, an ion-conductive material, an ion-conductive agent, carbon black, a metallic oxide, or the like is added to the elastic layer 12b to give it a predetermined conductivity.

[0095] The elastic layer 12b may have electronic conductivity or ionic conductivity. Since partial resistance unevenness of the elastic layer 12b easily leads to charging unevenness of the photoconductor drum 11, an elastic layer having ionic conductivity is often used from the viewpoint of suppressing resistance unevenness, but an elastic layer having electronic conductivity may also be used.

[0096] The volume resistance of the elastic layer 12b is 10 6 ~10 9 When the charging roller 12 has ion conductivity, the volume resistance value changes depending on the temperature and humidity, but here, the value shown is measured in an environment with a temperature of 20° C. and a relative humidity of 50%.

[0097] The hardness of the elastic layer 12b is adjusted so that a minute gap is formed between the surface of the charging roller 12 and the surface of the photosensitive drum 11, and appropriate discharge based on Paschen's law can be generated. The hardness of the elastic layer 12b is measured by using a micro rubber hardness tester "MD-1capa" (Type_A) manufactured by Kobunshi Keiki Co., Ltd., and peak measurement is performed. When measured by this method, the hardness of the elastic layer 12b is preferably in the range of 35 degrees to 80 degrees. If the hardness of the elastic layer 12b is in this range, it can absorb eccentricity or shape variations of the charging roller 12 and the photosensitive drum 11. However, the range of hardness is not limited to the above range as long as an appropriate nip is formed between the charging roller 12 and the photosensitive drum 11.

[0098] The surface (i.e., the outer peripheral surface) of the elastic layer 12b is given a predetermined surface roughness by cutting, polishing, molding, or the like. The ten-point mean roughness Rz of the charging roller 12 depends on the applied voltage and the usage environment, but is preferably about 1 to 30 μm, for example, according to Paschen's law. The surface of the elastic layer 12b may be subjected to surface treatment, coating, ultraviolet irradiation, or electron beam irradiation. These treatments make it possible to prevent contamination of the photoconductor drum 11 or adjust the resistance of the elastic layer 12b. In addition, the toner and its external additives attached to the photoconductor drum 11 are less likely to adhere to the surface of the charging roller 12.

[0099] The surface layer 12c is formed by applying a solution of ethyl acetate (solvent) mixed with a urethane polymer and porous particles to the surface of the elastic layer 12b (see Examples 1-1 to 1-5 described later). The application is performed by dipping, spraying, or using a coater. The urethane polymer is a homopolymer or copolymer having a urethane bond formed by condensation of an isocyanate group and an alcohol group.

[0100] For the formation of the surface layer 12c, for example, toluene diisocyanate (TDI), methylene diisocyanate (MDI), xylylene diisocyanate (XDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), polyester polyol, polycarbonate polyol, silicone diol, acrylic fluorine polymer, acrylic silicone polymer, fluorine polymer, and their multiples, modified products, etc. Also, a conductive agent such as carbon black, an ionic conductive agent, or an electronic conductive agent can be added as necessary.

[0101] The porous particles contained in the surface layer 12c are, for example, urethane resin, acrylic resin, nylon resin, fluororesin, polyamide resin, polycarbonate resin, polyester resin, isocyanate resin, etc., and these can be used alone or in combination of two or more kinds.

[0102] Here, as an example, the outer diameter of the core metal 12a of the charging roller 12 is set to 8 [mm], and the outer diameter of the elastic layer 12b is set to 12 [mm].

[0103] <Cleaning materials> 2 is made of a plate-shaped elastic body. The cleaning member 16 is supported by a plate-shaped jig 24 provided on the frame 17.

[0104] The material of the cleaning member 16 is not particularly limited, but it is preferable to use an elastic composition so as not to damage the surface of the photoreceptor drum 11 when the cleaning member 16 comes into sliding contact with the surface of the photoreceptor drum 11 to scrape off the residual toner. For example, a composition containing polyurethane, silicone resin, fluororesin, fluororubber, etc., and an additive may be included. In particular, a polyurethane composition having excellent mechanical strength and elastic pressure-welding properties is preferable.

[0105] The above polyurethane composition can be obtained using a polyisocyanate, a polyol, a curing agent and a catalyst.

[0106] The polyisocyanate is not particularly limited, but examples thereof 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 uretidinedione (a dimer of 2,4-TDI), 1,5-naphthylene diisocyanate, metaphenylene diisocyanate, hexamethylene diisocyanate, 1,5-naphthylene ... Isocyanates, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate (water-added MDI), carbodiimide-modified MDI, orthotoluidine diisocyanate, xylene diisocyanate, paraphenylene diisocyanate, diisocyanates such as lysine diisocyanate methyl ester, triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, polymeric MDI, etc. can be used. These can be used alone or in combination of two or more. In particular, MDI is preferred from the viewpoint of abrasion resistance.

[0107] The polyol used together with the polyisocyanate is not particularly limited, but may be, for example, polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexylene adipate, and polyether polyols such as polycaprolactone, polyoxytetramethylene glycol, and polyoxypropylene glycol. These may be used alone or in combination of two or more. In particular, PBA is preferred because of its excellent abrasion resistance.

[0108] The curing agent used together with the polyisocyanate and polyol is not particularly limited, but examples of polyols that can be used include 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, 1,2,6-hexanetriol, and other polyols having a molecular weight of 300 or less. These can be used alone or in combination of two or more kinds.

[0109] The linear pressure of the cleaning member 16 against the photosensitive drum 11 is preferably 15 gf / cm or more and 30 gf / cm or less, and is set to 20 gf / cm here. The cleaning angle is set to 10° or more and 15° or less.

[0110] <Transfer roller> 6(B) is a cross-sectional view showing the cross-sectional structure of transfer roller 31. Transfer roller 31 has a conductive core (shaft) 31a and elastic layer 31b formed on the surface of core 31a. Core 31a is made of a conductive material such as iron, aluminum, stainless steel, etc. Elastic layer 31b is a foamed rubber layer such as acrylonitrile butadiene rubber (NBR).

[0111] <Transfer belt> 1 is an endless belt made of a semiconductive plastic film having high resistance. The transfer belt 32 is made of a resin such as polyamide, polyimide, or polyether ether ketone, or a mixture of these materials. The transfer belt 32 may have a base layer and a surface layer.

[0112] 7 is a schematic diagram for explaining the charging position, the exposure position, the development position, and the transfer position of the photoconductor drum 11 in the image forming unit 10. The charging position is the position where the photoconductor drum 11 contacts the charging roller 12. In other words, the charging position is the position where the photoconductor drum 11 is applied with a charging voltage V CH This is the position where a voltage of -1000[V] is applied.

[0113] The exposure position is a position where the photoconductor drum 11 contacts and faces the exposure head 21. In other words, the exposure position is a position where the photoconductor drum 11 is exposed to an exposure amount Q (0.13 to 0.34 [μJ / cm 2 ]) is the position where it is exposed.

[0114] The development position is the position where the photoconductor drum 11 contacts the development roller 13. In other words, the development position is the position where the probe of the electrometer 80, which will be described later, is disposed.

[0115] The transfer position is a position where the photosensitive drum 11 contacts the transfer roller 31. In other words, the transfer position is a position where the photosensitive drum 11 is applied with a transfer voltage V TR This is the position where a voltage of +2850[V] is applied.

[0116] The rotation direction of the photoconductor drum 11 (clockwise direction in the figure) is defined as the first circumferential direction. If the charging position is defined as the reference position, the exposure position is separated from the reference position by an angle P1 in the first circumferential direction. The development position is separated from the reference position by an angle P2 in the first circumferential direction. The transfer position is separated from the reference position by an angle P3 in the first circumferential direction.

[0117] Here, the angle P1 is 44.0 degrees, the angle P2 is 97.6 degrees, and the angle P3 is 224.0 degrees. These values ​​of the angles P1, P2, and P3 are merely examples and can be changed as appropriate.

[0118] <Image forming device control system> Next, we will explain the control system of the image forming apparatus 1. Fig. 8 is a block diagram showing the control system of the image forming apparatus 1. The image forming apparatus 1 has a control unit 100, a receiving memory 121, an image data editing memory 122, an operation unit 123, a sensor group 124, and a power supply circuit 130.

[0119] The control unit 100 includes a print control unit (main control unit) 101, an I / F (interface) control unit 102, a head control unit 103, a fixing control unit 104, a fixing drive control unit 105, a transport control unit 106, and a drive control unit 107.

[0120] The print control unit 101 has a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, a timer, etc. The print control unit 101 executes a predetermined program to control the overall operation of the image forming apparatus 1. Specifically, the print control unit 101 receives print data and control commands from an external device via the I / F control unit 102, and performs overall control of the head control unit 103, the fixing control unit 104, the fixing drive control unit 105, the conveyance control unit 106, the drive control unit 107, and the power supply circuit 130 to perform the printing operation.

[0121] The I / F control unit 102 receives print data and control commands from an external device such as a personal computer, and also transmits information regarding the state of the image forming apparatus 1 to the external device.

[0122] The receiving memory 121 temporarily stores print data input from an external device via the I / F control unit 102 .

[0123] The image data editing memory 122 receives the print data stored in the receiving memory 121, and records image data obtained by editing the print data.

[0124] The operation unit 123 has a display unit that displays information related to the state of the image forming apparatus 1, and an input unit that accepts operation inputs from the user. The display unit is formed of, for example, an LED lamp, and the input unit is formed of, for example, a button or a touch panel.

[0125] The sensor group 124 includes various sensors that monitor the operating state of the image forming apparatus 1. Specifically, these include a position detection sensor that detects the position of the medium M on the transport path, a temperature and humidity sensor, a print density sensor, and a toner remaining amount sensor.

[0126] The power supply circuit 130 includes a charging roller power supply 131 that applies a charging voltage to the charging roller 12, a developing roller power supply 132 that applies a developing voltage to the developing roller 13, a supply roller power supply 133 that applies a supply voltage to the supply roller 14, a developing blade power supply 134 that applies a blade voltage to the developing blade 15, and a transfer roller power supply 135 that applies a transfer voltage to the transfer roller 31.

[0127] The head control unit 103 controls the emission of each LED of the exposure head 21 based on the image data recorded in the image data editing memory 122 .

[0128] The fixing control unit 104 has a temperature adjustment circuit, and supplies a current to a heater in the fixing roller 51 based on an output signal of a temperature sensor such as a thermistor provided in the fixing device 50 .

[0129] The fixing drive control unit 105 controls the rotation of the fixing motor 53 which rotates the fixing roller 51. The pair of discharge rollers 61 is rotated by the rotation transmitted from the fixing motor 53.

[0130] The conveyance control unit 106 controls the rotation of a conveyance motor 45 that drives the hopping roller 42, the registration roller pair 43, and the conveyance roller pair 44. The rotation of the conveyance motor 45 is transmitted to the hopping roller 42, the registration roller pair 43, and the conveyance roller pair 44 via an electromagnetic clutch or the like (not shown).

[0131] The drive control unit 107 controls the rotation of a drive motor 108 that rotates and drives the photosensitive drum 11. The rotation of the photosensitive drum 11 is also transmitted to the developing roller 13, the supply roller 14, and the drive roller 33 via a gear train (not shown).

[0132] <Printing Operation of Image Forming Device> Next, the printing operation of the image forming apparatus 1 will be described with reference to Fig. 1 and Fig. 8. When the print control unit 101 receives a print command and print data from a higher-level device via the I / F control unit 102, the print operation is started.

[0133] The print control unit 101 temporarily records print data received from a higher-level device in a reception memory 121 , edits the recorded print data to generate image data, and records the image data in an image data editing memory 122 .

[0134] Furthermore, the fixing drive control unit 105 drives the fixing motor 53, and the fixing roller 51 and the pressure roller 52 start to rotate. Furthermore, the fixing control unit 104 energizes the heater in the fixing roller 51, and the fixing roller 51 is heated to a predetermined fixing temperature.

[0135] In addition, the transport control unit 106 drives the transport motor 45, and the hopping roller 42 sends out the medium M in the medium tray 41 to the transport path. In addition, the registration roller pair 43 and the transport roller pair 44 each rotate to transport the medium M to the transfer unit 30.

[0136] Further, a charging voltage, a developing voltage, a supply voltage and a blade voltage are applied from power sources 131 to 134 of a power circuit 130 to the charging roller 12, the developing roller 13, the supply roller 14 and the developing blade 15 of each image forming unit 10, respectively.

[0137] In addition, the drive control unit 107 drives the drive motor 108 to rotate the photoconductor drum 11 in each image forming unit 10. As the photoconductor drum 11 rotates, the charging roller 12, the developing roller 13, and the supply roller 14 also rotate. The charging roller 12 uniformly charges the surface of the photoconductor drum 11.

[0138] In addition, the head control unit 103 drives the exposure head 21 to irradiate light onto the surface of the photoconductor drum 11. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 11.

[0139] The electrostatic latent image formed on the surface of the photoconductor drum 11 is developed by the toner attached to the developing roller 13, and a toner image is formed on the surface of the photoconductor drum 11. Furthermore, a transfer voltage is applied to the transfer roller 31 from a power source 135 for the transfer roller.

[0140] This transfer voltage causes the toner image on the surface of the photoconductor drum 11 to be transferred to the medium M passing between the photoconductor drum 11 and the transfer roller 31. Toner that has not been transferred to the medium M is scraped off by the cleaning member 16. The toner images are transferred from the photoconductor drums 11 of the image forming units 10 to the medium M and are superimposed on each other.

[0141] In the fixing device 5, heat and pressure are applied to the medium M passing through the fixing nip between the fixing roller 51 and the pressure roller 52, and the toner image is fixed to the medium M. The medium M with the fixed toner image is sent to the medium discharge section 6.

[0142] In the medium discharge section 6, a pair of discharge rollers 61 discharges the medium M from a discharge port. The discharged medium M is stacked on a stacker 63. This completes the formation of an image on the medium M.

[0143] <Image forming unit operation> The operation of the image forming unit 10 during the above printing operation is as follows: The photosensitive drum 11, charging roller 12, developing roller 13 and supply roller 14 of the image forming unit 10 rotate in the directions indicated by the arrows in FIG.

[0144] A case will be described where a medium M, which is A4-size plain paper, is printed in a vertical feed. The printing speed is a peripheral speed of 151 [mm / s]. The outer diameter of the developing roller 13 is 16.0 [mm], and the peripheral speed is 0.3 [m / s]. The outer diameter of the supply roller 14 is 15.5 [mm], and the peripheral speed is 0.2 [m / s]. The axial length of the photoconductor drum 11 is 327 [mm], the outer diameter is 30.0±0.2 [mm], and the peripheral speed is 0.22 [m / s].

[0145] Supply roller 14 rotates while carrying toner on the outer peripheral surface of foamed elastic layer 14b and in the cells, and transports the toner to the contact portion with developing roller 13. A DC voltage of −330 [V] is applied to supply roller 14 from supply roller power supply 133, and a DC voltage of −200 [V] is applied to developing roller 13 from developing roller power supply 132. Due to the potential difference between developing roller 13 and supply roller 14, negatively charged toner is supplied to developing roller 13.

[0146] A DC voltage of −330 [V] is applied to the developing blade 15 from a developing blade power supply 134. The developing blade 15 causes the toner on the surface of the developing roller 13 to become a thin layer.

[0147] A DC voltage of −1000 [V] is applied to the charging roller 12 from a charging roller power supply 131. The charging roller 12 uniformly charges the surface of the photoconductor drum 11 to about −420±30 [V].

[0148] The uniformly charged surface of the photoconductor drum 11 is exposed to light by the exposure head 21, forming an electrostatic latent image. The electrostatic latent image formed on the surface of the photoconductor drum 11 is developed by the toner carried by the developing roller 13 into a toner image.

[0149] When printing a solid image with a print image density of 100%, the surface potential of the photoconductor drum 11 is attenuated from −420 [V] before exposure to approximately −50 to −100 [V] due to exposure by all the LEDs of the exposure head 21.

[0150] The toner on the developing roller 13 that has not been supplied to the photosensitive drum 11 is scraped off by the supply roller 14 at the portion facing the supply roller 14.

[0151] The toner image on the surface of the photosensitive drum 11 is transferred onto the medium M by a transfer roller 31 (FIG. 1) to which a predetermined transfer voltage is applied.

[0152] Meanwhile, the toner that has not been transferred to the medium M and remains on the surface of the photoconductor drum 11 and the external additives that have been separated from the toner particles and adhered to the surface of the photoconductor drum 11 are scraped off by the cleaning member 16 .

[0153] The surface of the photoconductor drum 11 is cleaned of toner and external additives by the cleaning member 16, and then is neutralized by being irradiated with neutralization light by a neutralization light unit (not shown). The neutralized surface of the photoconductor drum 11 is then charged again by the charging roller 12.

[0154] <Strong transcription history> Next, we will explain strong transfer history, which is one type of print defect. When a high resistance medium is used as the medium M, if the same transfer voltage as that for plain paper is applied, the current required for transferring the toner image cannot be obtained, resulting in insufficient transfer and transfer blur. Therefore, when using a high resistance medium, it is common to set the transfer voltage higher than when using plain paper.

[0155] A high-resistance medium is a medium with a high volume resistivity, such as coated paper (waterproof paper, etc.) with a resin coating on the paper, film media made of polyester, etc. In contrast, plain paper is a medium with a relatively low volume resistivity (low-resistance medium).

[0156] 9 is a schematic diagram showing a state in which medium M passes between photoconductor drum 11 and transfer roller 31. The area where photoconductor drum 11 contacts medium M is referred to as medium area R1. Meanwhile, in areas on both sides of medium M in the width direction, photoconductor drum 11 and transfer roller 31 face each other via transfer belt 32. This area is referred to as outside-medium area R2.

[0157] Although the case where a transfer belt 32 is used is described here, the photosensitive drum 11 and the transfer roller 31 may be in contact with each other without using the transfer belt 32, as in an image forming device that forms a monochrome image (such as a monochrome printer).

[0158] When a high resistance medium is used as the medium M as described above, a high transfer voltage is applied to the transfer roller 31, and therefore, in the outside-medium region R2 where the photosensitive drum 11 and the transfer roller 31 face each other, a current flows from the transfer roller 31 to the photosensitive drum 11. In the area where the current flows in, the photosensitive drum 11 is charged to a polarity (positive polarity) opposite to the original charging potential (negative polarity).

[0159] When printing is repeated, positive potential accumulates on the surface of the photoconductor drum 11, causing charging defects. The accumulation of positive potential does not disappear even if left for several hours, so it is called strong transfer history. When a halftone image is printed in a state where strong transfer history has occurred, the density becomes high in the areas where positive potential has accumulated, causing printing defects.

[0160] 10(A) to (F) are schematic diagrams showing the states of charges in conductive support 110, undercoat layer 111, charge generating layer 112, and charge transport layer 113 of photoreceptor drum 11. In Figs. 10(A) to (F), transfer roller 31 and transfer belt 32 are positioned above photoreceptor drum 11 in the drawings.

[0161] When a toner image is transferred to the high resistance medium M1, as shown in Figures 10(A) and (B), a strong current flows from the transfer roller 31 to the photosensitive drum 11 in the outer medium area R2, and positive charges accumulate in the charge transport layer 113.

[0162] When the transfer operation is repeated, the positive charges in the charge transport layer 113 move to the charge generation layer 112, and charges are accumulated in the charge generation layer 112, as shown in FIG. 10(C).

[0163] When charges are accumulated in the charge generation layer 112 in this way, as shown in Fig. 10(D), part of the negative charges applied from the charging roller 12 during the next printing is cancelled by the positive charges that have moved from the charge transport layer 113 to the charge generation layer 112. As a result, as shown in Fig. 10(E), a step occurs in the distribution of charges on the surface of the charge transport layer 113.

[0164] In this state, when a halftone image is printed on a wide medium M (dimension in the direction perpendicular to the transport direction F), the difference in the distribution state of the charges on the surface of the photoconductor drum 11 appears as a difference in the amount of toner adhesion, i.e., a density difference occurs in the printed image.

[0165] Therefore, for example, when an image 70 is continuously printed on a high-resistance medium M1 having a width (dimension perpendicular to the transport direction F) W1 as shown in Figure 11(A), and then a halftone image 71 is printed on a medium M2 having a width W2 (>W1) as shown in Figure 11(B), dark areas 72 will be produced at both widthwise ends of the halftone image 71 on the medium M2, i.e., outside the areas corresponding to the width W1 of the high-resistance medium M1, as shown in Figure 11(C).

[0166] Therefore, the image forming unit 10 and the drum unit 20 of this embodiment are equipped with a photoconductor drum 11 having a characteristic that positive charges are unlikely to accumulate on the surface even when a high transfer voltage is applied.

[0167] The property of making it difficult for positive charges to accumulate on the surface of the photoconductor drum 11 can be achieved, for example, by adding an electron transport material to the charge transport layer 113. Although the addition of an electron transport material to the charge transport layer 113 is a negative factor in improving the inherent capability (charge transport capability) of the charge transport layer 113, it is effective in canceling out the positive charges generated by the above-mentioned high transfer voltage.

[0168] <Measurement of the surface potential of the photoconductor drum> 12(A) and (B) are schematic diagrams for explaining a method for measuring the surface potential of the photosensitive drum 11. In Fig. 12(A), the photosensitive drum 11, the charging roller 12, the exposure head 21, and the transfer roller 31 are shown among the components of the image forming unit 10.

[0169] An electrometer 80 for measuring the surface potential of the photoconductor drum 11 was incorporated in the image forming unit 10. A surface electrometer "Model 344" manufactured by Trek Corporation was used as the electrometer 80. The probe of the electrometer 80 was placed at a position where the distance D2 from the surface of the photoconductor drum 11 was 5 [mm]. In addition, the circumferential position of the probe of the electrometer 80 (the circumferential position around the rotation axis of the photoconductor drum 11) was the same as the circumferential position of the developing roller 13.

[0170] The surface potential of the photoconductor drum 11 was measured under an environment of a temperature of 25° C. and a relative humidity of 50%. First, as shown in FIG. 12A, the photoconductor drum 11 was rotated at a peripheral speed (surface speed) of 151 mm / s while a charging voltage V CH The surface of the photoconductor drum 11 was charged by applying a charging voltage V = -1000 [V]. CH The −1000 [V] corresponds to −420±30 [V] as the surface potential of the photoconductor drum 11. The peripheral speed of 151 [mm / s] corresponds to the printing speed of the image forming apparatus 1 for printing on plain paper.

[0171] The surface of the photoconductor drum 11, which has been charged by the charging roller 12, is exposed to a charge of 0.13 to 0.34 [μJ / cm 2 The exposure was performed with an exposure amount Q of 100 [mm]. At this time, the distance D1 between the exposure head 21 and the surface of the photoconductor drum 11 was set to 10 [mm]. Then, 10 [seconds] after the photoconductor drum 11 started to rotate, the surface potential V0 of the photoconductor drum 11 was measured by an electrometer 80 having a probe disposed at the position of the developing roller 13. The condition at this time is defined as the first condition.

[0172] The exposure amount Q of the exposure head 21 is expressed in units [μJ / cm 2] corresponds to the input energy per unit area to the LED of the exposure head 21. Therefore, the exposure amount Q may be called exposure energy.

[0173] Within 5 seconds from the end of the measurement under the first condition, the charging voltage V CH (-1000[V]) is applied to the transfer roller 31 while rotating the photoconductor drum 11 at a peripheral speed of 73[mm / s]. TR was applied for 406 [seconds]. No exposure was performed by the exposure head 21. The conditions at this time are defined as the second conditions.

[0174] Note that 406 seconds is the time equivalent to printing 100 sheets of medium M, and the circumferential speed of 73 mm / s corresponds to the printing speed of waterproof paper in image forming apparatus 1. In the second condition, the circumferential speed of photoconductor drum 11 is slower than in the first condition to create a more severe condition (a condition in which strong transfer history is more likely to occur), and a strong current flows through photoconductor drum 11, making it easier for positive charges to accumulate in charge transport layer 113.

[0175] Charge voltage V under the second condition Ch and transfer voltage V TR Within 5 seconds after the end of application of the voltage Vcc, measurement of the surface potential of the photoconductor drum 11 was started again under the first condition described above (FIG. 12A). The surface potential of the photoconductor drum 11 at this time was set to V1.

[0176] Specifically, as shown in FIG. 12A, the photoconductor drum 11 is rotated at a peripheral speed (surface speed) of 151 [mm / s] while a charging voltage V CH =-1000 [V] was applied to uniformly charge the surface of the photoconductor drum 11. The surface of the photoconductor drum 11, which had been uniformly charged by the charging roller 12, was then exposed to a voltage of 0.13 to 0.34 [μJ / cm 2 Then, 10 seconds after the photoconductor drum 11 started to rotate, the surface potential V1 of the photoconductor drum 11 was measured by a potentiometer 80 having a probe disposed at the position of the developing roller 13.

[0177] The light attenuation change rate ΔV [%] was calculated using the following formula from the surface potential V0 of the photosensitive drum 11 measured before the application of the transfer voltage and the surface potential V1 of the photosensitive drum 11 measured after the application of the transfer voltage for 406 [seconds]. ΔV={1-(V1 / V0)}×100

[0178] <Print test> Further, the photoconductor drum 11 for which the light attenuation change rate ΔV was measured was incorporated into the cyan image forming unit 10C of the image forming apparatus 1 in FIG. 1, and continuous printing was performed.

[0179] The image forming device 1 was an LED printer C844dnw manufactured by Oki Electric Industry Co., Ltd., and the image was printed on A4-sized waterproof paper ("Laser Peach WETY-145" manufactured by Daio Paper Co., Ltd.: volume resistivity 1×10 15 The blank pattern was printed on a 100-sheet toner cartridge (or more than 1000 Ω) in a vertical feed. The blank pattern was printed on 100 sheets of paper in order to eliminate the effect of the toner on the occurrence of the strong transfer history.

[0180] After continuous printing, A4 size plain paper (Oki Electric Industry Co., Ltd. "Excellent White": volume resistivity 7.5 x 10 9 The substrate was fed horizontally and a halftone test pattern was printed using cyan toner. The print rate (duty ratio) of the test pattern was 40%, and one sheet was printed. The printed test pattern was visually inspected to determine whether there was a density difference due to a strong transfer history.

[0181] The reason for conducting the printing test using the cyan image forming unit 10C is that, among the image forming units 10K, 10Y, 10M, and 10C, the cyan image forming unit 10C is located furthest downstream, and therefore the transfer voltage is set highest taking into account the charging of the medium M.

[0182] <Example> A total of 10 types of photoconductor drums 11 were prepared for Examples 1 to 5 and Comparative Examples 1 to 5, and the light attenuation change rate ΔV was measured for each of them by the method described with reference to FIGS. 12(A) and (B).

[0183] The photoconductor drums 11 of Examples 1 to 5 and Comparative Examples 1 to 5 have the same configuration except for the composition of the charge transport layer 113. In Examples 1 to 5, an electron transport material is added to the charge transport layer 113, while in Comparative Examples 1 to 5, an electron transport material is not added to the charge transport layer 113.

[0184] In each of the photoconductor drums 11 of Examples 1 to 5 and Comparative Examples 1 to 5, the exposure amount Q of the exposure head 21 in FIG. 12(A) was set to 0.13, 0.20, 0.27, and 0.34 [μJ / cm 2 ] and changed it in four different ways.

[0185] The photosensitive drums 11 of Examples 1 to 5 and Comparative Examples 1 to 5 were mounted on the image forming unit 10C (cyan) of the image forming apparatus 1, and the exposure amount Q of the exposure head 21 was changed in four ways, and the above-mentioned printing tests (continuous printing on waterproof paper and printing on plain paper) were performed.

[0186] In the printing test, as described above, after continuous printing on 100 sheets of waterproof paper, a halftone test pattern was printed on plain paper, and the printed test pattern was visually observed to determine whether or not there were density differences.

[0187] In all of Examples 1 to 5 and Comparative Examples 1 to 5, if no density step was observed for all four exposure amounts Q, the evaluation result was rated as best (◎). If a density step was observed for any of the four exposure amounts Q, but the density step was not at a level that was easily visible, the evaluation result was rated as good (◯). If a density step was observed for any of the four exposure amounts Q, but the density step was at a level that was easily visible, the evaluation result was rated as poor (×).

[0188] FIG. 13 is a table showing the measurement results of the rate of change of light attenuation in Examples 1 to 5 and Comparative Examples 1 to 5, and the evaluation results of the printing test.

[0189] In all of Examples 1 to 5 and Comparative Examples 1 to 5, as the amount of exposure Q increases, the rate of change of light attenuation ΔV also tends to generally increase.

[0190] 13, for Examples 1 and 2, no density step was observed for any of the exposure doses Q, and the evaluation results were the best (◎). For Examples 3 to 5, density steps were observed depending on the value of the exposure dose Q, but they were not at a level that was easily visible, and the evaluation results were good (◯).

[0191] On the other hand, for Comparative Examples 1 to 5, density differences were observed depending on the value of the exposure dose Q, and were at an easily visible level, so the evaluation results were poor (×).

[0192] Fig. 14 is a graph showing the results shown in Fig. 13. The horizontal axis shows the exposure dose Q [μJ / cm 2 The vertical axis indicates the measurement results of the rate of change in light attenuation ΔV [%]. The lines connecting the plots of Examples 1 to 5 are designated as lines E1 to E5, and the lines connecting the plots of Comparative Examples 1 to 5 are designated as lines C1 to C5.

[0193] 14, the straight lines E1 to E5 representing Examples 1 to 5 are positioned below the straight lines C1 to C5 representing Comparative Examples 1 to 5. That is, in Examples 1 to 5, the rate of change in light attenuation ΔV is smaller when the exposure dose Q is the same, compared to Comparative Examples 1 to 5.

[0194] Of the lines E1 to E5 representing Examples 1 to 5 for which the evaluation results were the best (◎) or good (◯), the line E5 (line E5) for Example 5 is located at the top. The line E5 representing Example 5 is expressed by an approximation of ΔV=0.489E-0.014.

[0195] In other words, when the combination of the exposure dose Q and the rate of change of light attenuation ΔV is on line E5 or in the area below it, that is, when ΔV≦0.489×Q−0.014 is satisfied, the evaluation result is the best (◎) or fair (◯).

[0196] From this result, the exposure amount Q (0.13 to 0.34 [μJ / cm 2 ]) and the rate of change in light attenuation ΔV satisfy ΔV≦0.489×Q−0.014[%], the occurrence of density differences is suppressed.

[0197] Of the straight lines E1 and E2 representing Examples 1 and 2, which had the best evaluation results (◎), the straight line E2 is located higher. The straight line E2 representing Example 2 is expressed by the approximation formula ΔV=0.204×Q−0.001.

[0198] From this result, the exposure amount Q (0.13 to 0.34 [μJ / cm 2 ]) and the rate of change in light attenuation ΔV satisfy ΔV≦0.204×Q−0.001[%], the occurrence of density differences is most effectively suppressed.

[0199] In other words, when the exposure amount Q of the exposure head 21 and the light attenuation change rate ΔV satisfy ΔV≦0.489×Q-0.014[%] (more preferably ΔV≦0.204×Q-0.001[%]), even if a high transfer voltage is applied to the photosensitive drum 11, accumulation of positive charge is unlikely to occur, density differences are suppressed, and printing defects are reduced.

[0200] Furthermore, by using drum unit 20 of the present embodiment, it is not necessary to carry out a special exposure process as in, for example, Patent Document 1, and therefore it is possible to handle a variety of media.

[0201] <Contact area between photoconductor drum and transfer roller> By using the image forming apparatus 1 equipped with the drum unit 20 of this embodiment, printing defects due to strong transfer history are suppressed, making it possible to print on a wider medium (i.e., a medium with a narrow outer medium area R2). This point will be described below.

[0202] 15A is a schematic diagram showing the photoconductor drum 11, the transfer roller 31, and the transfer belt 32. The width of the outside-medium area R2 in the axial direction of the photoconductor drum 11 (the X direction shown in FIG. 2) is defined as L [mm].

[0203] 15(B) is a schematic diagram showing the nip portion between the photoconductor drum 11 and the transfer roller 31. The length of the nip portion between the photoconductor drum 11 and the transfer roller 31 in the transport direction of the medium M (Y direction shown in FIG. 2) is taken as the nip length N [mm]. The nip length N can be measured using a pressure sheet (sensor sheet) and is also referred to as the nip width.

[0204] In this embodiment, the axial length L of the roller portion of the transfer roller 31 is TR (FIG. 15A) is 301 [mm], and the nip length N between the photosensitive drum 11 and the transfer roller 31 (FIG. 15B) is 1.51 [mm].

[0205] The total area of ​​the outside-medium region R2 on both sides in the width direction of the medium M is defined as area S. Area S is calculated by 2×N×L [mm 2 ] is expressed as

[0206] Using four types of media with different widths (referred to as media 1, 2, 3, and 4), a transfer voltage of +2850 [V] was applied to the photosensitive drum 11 for 406 [seconds] using the method described with reference to Figures 12 (A) and (B), and then the potential of the photosensitive drum 11 was measured with the electrometer 80.

[0207] Table 1 shows the area S [mm 2 12(A) and 12(B), and the surface potential [V] of the photoconductor drum 11 after the transfer voltage is applied, which is measured by the method described with reference to FIGS.

[0208] [Table 1]

[0209] Note that medium 1 is waterproof paper of A4 size (297mm length, 210mm width) that has been cut to a size of 270mm length and 210mm width, and the transport direction is horizontal. Medium 2 is waterproof paper of A4 size (297mm length, 210mm width) and the transport direction is vertical. Medium 3 is waterproof paper of A4 size (297mm length, 210mm width) that has been cut to a size of 297mm length and 105mm width, and the transport direction is vertical. Medium 4 is waterproof paper of A4 size (297mm length, 210mm width) that has been cut to a size of 297mm length and 52.5mm width (cut to 1 / 4 widthwise) and the transport direction is vertical.

[0210] 15C is a graph showing the relationship between the area of ​​the outside-medium region R2 and the surface potential of the photosensitive drum 11 after the transfer voltage has been applied for 406 [seconds]. The horizontal axis represents the contact area [mm 2 ], and the vertical axis represents the surface potential [V] of the photosensitive drum 11.

[0211] The smaller the area S of the outside-medium area R2, the higher the surface potential of the photoconductor drum 11 after the transfer voltage is applied. This is because the smaller the area S of the outside-medium area R2, the more concentrated the current flowing from the transfer roller 31 to the photoconductor drum 11 during transfer.

[0212] Regardless of which of media 1 to 4 is used, if the exposure amount Q of the exposure head 21 and the light attenuation change rate ΔV satisfy ΔV≦0.489×Q-0.014[%], density differences in the printed image can be suppressed and printing defects can be suppressed.

[0213] In other words, when the image forming apparatus 1 equipped with the drum unit 20 of the embodiment is used, the area of ​​the outside-medium region R2 is 47 to 376 mm 2 ], the occurrence of printing defects can be suppressed.

[0214] In the above description, an example has been described in which the charging roller 12 applies a charging voltage of negative polarity (first polarity) to the photosensitive drum 11, and the transfer roller 31 applies a transfer voltage of positive polarity (second polarity).

[0215] However, the present embodiment is not limited to this example, and a positive charging voltage may be applied to the photosensitive drum 11 by the charging roller 12, and a negative transfer voltage may be applied to the transfer roller 31. In this case as well, if the exposure amount Q of the exposure head 21 and the light attenuation change rate ΔV satisfy ΔV≦0.489×Q−0.014[%], it is possible to suppress density differences in the printed image and the occurrence of printing defects.

[0216] In addition, although an example has been described in which the transfer unit 30 has a transfer roller 31, a transfer belt 32, a drive roller 33 and a driven roller 34, in the case of an image forming device that prints monochrome images, it is sufficient to have a transfer roller 31 that contacts the photosensitive drum 11.

[0217] In this embodiment, a photosensitive drum 11 having an outer diameter of 30.0 mm was used, but the same effect as described above could be obtained if the outer diameter of the photosensitive drum 11 was 30.0±0.2 mm, which is within the range of manufacturing error (variation).

[0218] <Effects of the embodiment> As described above, the drum unit 20 of the present embodiment rotates the photosensitive drum 11 at a peripheral speed of 151 [mm / s] while applying a voltage (charged voltage V CH ) and charged to 0.13 to 0.34 [μJ / cm 2 The surface potential of the photoconductor drum 11 measured under the first condition of exposing the photoconductor drum 11 to an exposure amount Q within the range of 1000 to 1500 [V] is taken as V0 [V]. While rotating the photoconductor drum 11 at a peripheral speed of 73 [mm / s], a voltage (transfer voltage V TR) for 406 [seconds], the surface potential of the photoconductor drum 11 measured again under the first condition is defined as V1 [V]. When ΔV is expressed as ΔV={1-(V1 / V0)}×100[%], ΔV≦0.489×Q-0.014[%] is satisfied.

[0219] Therefore, even if a high transfer voltage is applied to the photoconductor drum 11, accumulation of positive charges is unlikely to occur, which makes it possible to suppress the occurrence of density differences and printing defects. In addition, since a special exposure process such as that described in Patent Document 1 is not required, it is possible to handle a variety of media.

[0220] In particular, when ΔV≦0.489×Q−0.014[%] is satisfied, it is possible to more effectively suppress the occurrence of density differences and improve print quality.

[0221] The present disclosure can be used in image forming apparatuses that form images on media, such as printers, copiers, facsimile machines, and MFPs (Multi Function Peripherals).

[0222] Although the preferred embodiments have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various improvements and modifications can be made.

[0223] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A photosensitive drum and a frame that holds the photosensitive drum, While rotating the photosensitive drum at a peripheral speed of 151 [mm / s], the surface of the photosensitive drum is charged with a voltage of a first polarity and an absolute value of 1000 [V] to obtain a charge of 0.13 to 0.34 [μJ / cm 2 The surface potential of the photoconductor drum measured under the first condition of exposing the photoconductor drum to an exposure amount Q within the range of V0 [V], While rotating the photosensitive drum at a peripheral speed of 73 mm / s, a voltage having a second polarity opposite to the first polarity and an absolute value of 2850 V was applied to the surface of the photosensitive drum for 406 seconds. The surface potential of the photoconductor drum measured again under the first condition is defined as V1 [V], When expressed as ΔV={1-(V1 / V0)}×100[%], ΔV≦0.489×Q-0.014[%] A drum unit characterized in that: (Appendix 2) Furthermore, ΔV≦0.204×Q-0.001[%] 2. The drum unit according to claim 1, wherein the following holds true: (Appendix 3) the first polarity is negative, The second polarity is a positive polarity. 3. The drum unit according to claim 1 or 2. (Appendix 4) When a voltage having an absolute value of 1000 [V] is applied with the first polarity, the absolute value of the potential on the surface of the photosensitive drum is 420±30 [V]. 4. The drum unit according to claim 1, (Appendix 5) In a first circumferential direction around the rotation axis of the photosensitive drum, when the position of the charge on the photosensitive drum is set as a reference position, The exposure position of the photosensitive drum is at a position of 44.0 degrees from the reference position, The measurement position of the surface potential V0 and the surface potential V1 of the photosensitive drum is at a position 97.6 degrees from the reference position, The position where the voltage is applied to the photosensitive drum is 224.0 degrees from the reference position. 5. The drum unit according to claim 1, (Appendix 6) the photosensitive layer of the photoreceptor drum has a charge transport layer and a charge generation layer, The charge transport layer contains an electron transport material. 6. The drum unit according to claim 1, (Appendix 7) A drum unit according to any one of claims 1 to 6, a charging member that contacts the surface of the photosensitive drum and applies a voltage thereto; an exposure device that exposes the surface of the photosensitive drum; a transfer member that contacts the surface of the photosensitive drum and applies a voltage thereto; An image forming apparatus comprising: (Appendix 8) A transfer nip through which a medium passes is formed between the photosensitive drum and the transfer member, If the area where the photosensitive drum and the transfer member face each other without the medium therebetween is defined as a non-medium area, The area of ​​the outside medium region is 47 to 376 mm 2 ] 8. The image forming apparatus according to claim 7, [Explanation of symbols]

[0224] 1 image forming apparatus, 10 image forming unit (image forming section), 11 photoconductor drum (image carrier), 12 charging roller (charging member), 13 developing roller (developer carrier), 14 supply roller (supply member), 15 developing blade (layer regulating member), 16 cleaning member, 17 frame (housing), 18 toner cartridge (developer container), 20 drum unit, 21 exposure head (exposure device), 22 toner storage section (developer storage section), 30 transfer unit, 31 transfer roller (transfer member), 32 transfer belt (belt body), 40 medium supply section, 50 fixing device, 60 medium discharge section, 80 electrometer, 110 conductive support, 111 undercoat layer (blocking layer), 112 charge generation layer, 113 charge transport layer 113 Photosensitive layer, M medium, M1 high resistance medium, M2 normal medium, R1 medium area, R2 outside medium area, Q exposure amount, V0,V1 surface potential of photosensitive drum, ΔV light attenuation change rate.

Claims

1. A photosensitive drum and a frame that holds the photosensitive drum, While rotating the photosensitive drum at a peripheral speed of 151 [mm / s], the surface of the photosensitive drum is charged with a voltage of a first polarity and an absolute value of 1000 [V], and a charge of 0.13 to 0.34 [μJ / cm ２ the surface potential of the photoconductor drum measured under the first condition of exposing the photoconductor drum to an exposure amount Q within the range of V0 [V]; While rotating the photosensitive drum at a peripheral speed of 73 mm / s, a voltage having a second polarity opposite to the first polarity and an absolute value of 2850 V was applied to the surface of the photosensitive drum for 406 seconds. The surface potential of the photoconductor drum measured again under the first condition is defined as V1 [V], When ΔV is expressed as {1-(V1 / V0)}×100[%], ΔV≦0.489×Q−0.014[%] A drum unit characterized in that:

2. Furthermore, ΔV≦0.204×Q−0.001 [%] 2. The drum unit according to claim 1, wherein the following expression is satisfied:

3. the first polarity is negative, The second polarity is a positive polarity.

2. The drum unit according to claim 1,

4. When a voltage having an absolute value of 1000 [V] is applied in the first polarity, the absolute value of the potential on the surface of the photosensitive drum is 420±30 [V].

2. The drum unit according to claim 1,

5. In a first circumferential direction around the rotation axis of the photosensitive drum, when the position of the charge on the photosensitive drum is defined as a reference position, The exposure position of the photosensitive drum is at a position of 44.0 degrees from the reference position, The measurement positions of the surface potentials V0 and V1 of the photosensitive drum are located at 97.6 degrees from the reference position, The position where the voltage is applied to the photosensitive drum is 224.0 degrees from the reference position.

2. The drum unit according to claim 1,

6. The photosensitive layer of the photoreceptor drum has a charge transport layer and a charge generation layer, The charge transport layer contains an electron transport material.

2. The drum unit according to claim 1,

7. A drum unit according to any one of claims 1 to 6, a charging member that contacts the surface of the photosensitive drum and applies a voltage thereto; an exposure device that exposes the surface of the photosensitive drum; a transfer member that contacts the surface of the photosensitive drum and applies a voltage thereto; An image forming apparatus comprising:

8. A transfer nip through which a medium passes is formed between the photosensitive drum and the transfer member, If the area where the photosensitive drum and the transfer member face each other without the medium therebetween is defined as a non-medium area, The area of ​​the outer region is 47 to 376 mm ２ ] 8. The image forming apparatus according to claim 7,

Images