Developing device and image forming apparatus

Abstract

To prevent the occurrence of printing failure such as fogging.SOLUTION: A developing device 10 comprises: a photoreceptor drum 11 (image carrier) that carries an electrostatic latent image; and a developing roller 12 (developer carrier) that is in contact with the photoreceptor drum 11 and develops the electrostatic latent image with developer. The developing roller 12 has a surface layer 12c and an inner layer 12b. The difference RALL-Rin between the entire resistance value RALL[LogΩ] of the surface layer 12c and the inner layer 12b combined and the resistance value RIN[LogΩ] of the inner layer 12b is 0.56[LogΩ] or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a developing device that develops an electrostatic latent image, and an image forming apparatus that includes the developing device. [Background technology]

[0002] In an image forming apparatus using an electronic process, a latent image formed on the surface of a photosensitive drum (image carrier) is developed with a developer attached to a developing roller (developer carrier). For example, Patent Document 1 proposes a technology for adjusting the pressure between the photosensitive drum and the developing roller to improve image quality. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-15111 A (see abstract) Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the pressure between the photosensitive drum and the developing roller, the toner that should be held on the developing roller may adhere to the surface of the photosensitive drum, resulting in a printing defect (fog) in which the toner is scattered on a white background.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to suppress the occurrence of printing defects such as fogging. [Means for solving the problem]

[0006] The developing device of the present disclosure includes an image carrier that carries an electrostatic latent image, and a developer carrier that contacts the image carrier and develops the electrostatic latent image with a developer. The developer carrier includes a shaft body, an elastic layer that covers the shaft body, and a developing agent carrier. , bullets Coating with a protective layer and contacts the image carrier. It has a surface layer that The surface layer covers the entire periphery of the elastic layer, so that the elastic layer does not come into contact with the image carrier.The developer has a Si content of 0.98 to 1.28 [wt %] as measured by elemental analysis using energy dispersive X-ray analysis. ALL [LogΩ] is 6.15 [LogΩ] or more and 8.45 [LogΩ] or less. Overall resistance R ALL [LogΩ] and the resistance value R of the elastic layer IN Difference from [LogΩ] R ALL -R IN is greater than or equal to 0.56 [LogΩ] and less than or equal to 1.74 [LogΩ]. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to suppress a decrease in the surface potential of the developer carrier, thereby reducing printing defects such as fogging. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment; [Figure 2] FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the embodiment; [Figure 3] FIG. 2 is a diagram illustrating a cross-sectional structure of a photosensitive drum according to an embodiment. [Figure 4] FIG. 2 is a diagram showing a cross-sectional structure of a developing roller according to an embodiment. [Figure 5] 1A and 1B are schematic diagrams showing a method for measuring the resistance of a developing roller and a supply roller. [Figure 6] FIG. 2 is a diagram illustrating a cross-sectional structure of a supply roller according to an embodiment. [Figure 7] FIG. 2 is a perspective view showing a support structure for a photosensitive drum and a developing roller according to an embodiment. [Figure 8] 1A and 1B are schematic diagrams showing a method for measuring the conveying force between a photosensitive drum and a developing roller. [Figure 9] 10 is a flowchart showing a method for measuring the overall resistance and inner layer resistance of a developing roller. [Figure 10]10 is a schematic diagram showing a resistance measurement method performed in steps S12 and S15 of FIG. 9. [Figure 11] 1A and 1B are schematic diagrams showing a method for cutting the surface layer of a developing roller. [Figure 12] FIG. 4 is a diagram showing a method for measuring the residual potential of a developing roller. [Figure 13] FIG. 2 is a schematic diagram showing a printing pattern used in continuous printing. [Figure 14] FIG. 2 is a schematic diagram showing a print pattern used for test printing. [Figure 15] 1A and 1B are schematic diagrams showing print patterns used in test printing. [Figure 16] 1A, 1B, and 1C are diagrams showing a method for evaluating the effect of cutting the surface layer of a developing roller. [Figure 17] 10 is a graph showing a comparison of RALL-RIN values ​​when the surface layer of the developing roller is cut and when it is not cut. [Figure 18] 10 is a graph showing print results for RALL-RIN and RALL in the embodiment and the comparative example. [Figure 19] 1A and 1B are schematic diagrams illustrating the state of toner movement from a developing roller to a photosensitive drum. [Figure 20] Graph (A) shows the relationship between the hue difference ΔE of a printed image and the initial Q / M of the toner on the developing roller, and graph (B) shows the relationship between the initial Q / M of the toner on the developing roller and the residual potential of the developing roller. [Figure 21] 10 is a graph showing the relationship between the residual potential and the resistance value of the developing roller. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Configuration of image forming device> 1 is a diagram showing an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is a printer that forms images using an electrophotographic process. The image forming apparatus 1 includes a medium supply unit 40, a developing device 10, a fixing device 50, a medium discharge unit 60, and a housing 1A that houses these components.

[0010] The media supply unit 40 has a media tray 41 that stores media P such as printing paper, a paper feed roller 42 that sends the media P from the media tray 41 one by one onto a conveying path, a conveying roller 43 that conveys the media P sent onto the conveying path to the developing device 10, and a media guide 44 that guides the conveyed media P.

[0011] An exposure head 30 serving as an exposure device is disposed opposite a photosensitive drum 11 (described later) of the developing device 10. The exposure head 30 has an LED array in which LEDs (light-emitting diodes) serving as light-emitting elements are arranged, and a lens array, and irradiates the surface of the photosensitive drum 11 with light. The exposure head 30 is suspended and supported by a top cover 1B that covers the top of the housing 1A.

[0012] The developing device 10 has a photosensitive drum 11 as an image carrier, a charging roller 15 as a charging member, a developing roller 12 as a developer carrier, a supply roller 13 as a supply member, a regulating blade 14 as a layer regulating member, a toner cartridge 16 as a developer container, a cleaning member 17, a waste toner transport section 18, and a unit housing 20 that houses these.

[0013] The developing device 10 does not need to have all of the above components, but only needs to have at least a photosensitive drum 11 as an image carrier and a developing roller 12 as a developer carrier. In addition, the developing device 10 may have a charging roller 15 as a charging member, a supply roller 13 as a supply member, and a regulating blade 14 as a layer regulating member. Furthermore, the developing device 10 may have a toner cartridge 16 as a developer container, a cleaning member 17, a waste toner transport unit 18, and a unit housing 20 that houses these.

[0014] The photosensitive drum 11 is a cylindrical member having a photosensitive layer formed on the surface of a conductive support, and rotates clockwise in the drawing. The photosensitive drum 11 carries an electrostatic latent image on its surface. The configuration of the photosensitive drum 11 will be described in detail later.

[0015] The charging roller 15 is disposed so as to contact the photosensitive drum 11 and rotates following the rotation of the photosensitive drum 11. A charging voltage is applied to the charging roller 15 from a charging voltage power supply 105 (FIG. 2), and the surface of the photosensitive drum 11 is uniformly charged.

[0016] The developing roller 12 is disposed so as to contact the surface of the photosensitive drum 11, and rotates in the opposite direction to the photosensitive drum 11 (the direction in which the surface moves at the contact point is the forward direction). A developing voltage is applied to the developing roller 12 from a developing voltage power supply 106 (FIG. 2), and the electrostatic latent image on the surface of the photosensitive drum 11 is developed with toner (developer).

[0017] Supply roller 13 is disposed so as to contact the surface of developing roller 12, and rotates in the same direction as developing roller 12 (the direction in which the surface moves in the contact area is opposite to that of developing roller 12). Supply roller 13 receives a supply voltage from supply voltage power source 107 (FIG. 2) and supplies toner to developing roller 12.

[0018] The regulating blade 14 is a blade that is disposed so as to abut against the surface of the developing roller 12. A blade voltage is applied to the regulating blade 14 from a blade voltage power supply 108 (FIG. 2), and the toner layer on the surface of the developing roller 12 is regulated to a constant thickness.

[0019] The toner cartridge 16 is a container that contains toner (indicated by the reference numeral 9) as a developer. The toner 9 is, for example, black toner, but is not limited to this. The toner cartridge 16 is detachably attached to the top of the unit housing 20, and supplies the toner 9 to the developing roller 12 and the supply roller 13.

[0020] Within unit housing 20, above developing roller 12 and supply roller 13, there is formed a toner storage section, which is a space for storing toner 9 supplied from toner cartridge 16. Crank-shaped stirring bars 25, 26, and 27 are disposed in the toner storage section. Stirring bars 25, 26, and 27 rotate in the directions indicated by the arrows to stir and transport toner 9. Below developing roller 12, there is provided a seal member 28 to prevent toner leakage.

[0021] Cleaning member 17 is a blade or roller that is arranged to contact the surface of photosensitive drum 11, and scrapes off toner 9 remaining on the surface of photosensitive drum 11. Waste toner transport unit 18 has a screw (not shown), and transports the waste toner scraped off by cleaning member 17 to a waste toner recovery unit.

[0022] The developing device 10 is also called an image forming unit, a process unit, or an image drum unit (ID unit).

[0023] A transfer roller 19 serving as a transfer member is disposed so as to contact the surface of the photosensitive drum 11. A transfer voltage is applied to the transfer roller 19 from a transfer voltage power supply 109 (FIG. 2). This transfer voltage causes the toner image on the surface of the photosensitive drum 11 to be transferred to a medium P passing between the photosensitive drum 11 and the transfer roller 19.

[0024] The image forming apparatus 1 forms a monochrome image using the developing device 10, but is not limited to this example. A configuration may also be adopted in which multiple image forming units for yellow, magenta, cyan, black, etc. are arranged in the transport direction of the medium P to form a color image.

[0025] The fixing device (also referred to as a fixing unit) 50 is disposed downstream of the developing device 10 in the transport direction of the medium P. 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 pressure roller 52 is pressed against the fixing roller 51 to form a fixing nip. The fixing roller 51 and the pressure roller 52 apply heat and pressure to the medium P passing through the fixing nip, thereby fixing the toner image to the medium P.

[0026] The medium discharge section 60 is disposed downstream of the fixing device 50 in the transport direction of the medium P. The medium discharge section 60 has discharge rollers 61 that discharge the medium P that has passed through the fixing device 50 from an outlet, and a medium guide 62 that guides the medium P from the fixing device 50 to the outlet. A stacker 63 on which the discharged medium P is placed is formed in the top cover 1B.

[0027] In Figure 1, the axial direction of the photosensitive drum 11 is 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 P being transported. The direction of movement of the medium P as it passes through the developing device 10 is the Y direction. The direction perpendicular to the X direction and the Y direction is the Z direction. Here, the Z direction is the up-down direction.

[0028] Regarding the Y direction, the transport direction when medium P passes through developing device 10 is defined as the +Y direction, and the opposite direction is defined as the -Y direction. Regarding the X direction, the right hand direction when facing the +Y direction is defined as the +X direction, and the left hand direction is defined as the -X direction. Regarding the Z direction, the upward direction in Figure 1 is defined as the +Z direction, and the downward direction is defined as the -Z direction.

[0029] <Image forming device control system> 2 is a block diagram showing the control system of image forming apparatus 1. Image forming apparatus 1 has a main control unit 100, an I / F (interface) control unit 101, a receiving memory 102, an image data editing memory 103, a voltage control unit 104, a head control unit 110, a drive control unit 111, a fixing control unit 112, a fixing drive control unit 113, and a paper feed / conveyance control unit 114. These control units and memories constitute a control device.

[0030] The main control unit 100 has a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, a timer, etc. The main control unit 100 receives print data and control commands from a higher-level device via the I / F control unit 101, and executes the printing operation of the image forming apparatus 1.

[0031] The main control unit 100 receives operation signals from an operation panel (operation unit) 121 and detection signals from a sensor group 122 that detects the state of the image forming apparatus 1. The sensor group 122 includes, for example, a medium sensor that detects the position of the medium P on the transport path, and a temperature and humidity sensor that detects the temperature and humidity.

[0032] Receiving memory 102 temporarily stores print data input from a higher-level device via I / F control unit 101. Image data editing memory 103 receives the print data stored in receiving memory 102 and records image data formed by editing the print data, i.e., image data.

[0033] The voltage control unit 104 controls the charging voltage applied to the charging roller 15 from the charging voltage power supply 105, the developing voltage applied to the developing roller 12 from the developing voltage power supply 106, the supply voltage applied to the supply roller 13 from the supply voltage power supply 107, the blade voltage applied to the regulating blade 14 from the blade voltage power supply 108, and the transfer voltage applied to the transfer roller 19 from the transfer voltage power supply 109.

[0034] The head control unit 110 controls the light emission of each LED of the exposure head 30 based on the image data recorded in the image data editing memory 103 .

[0035] The drive control unit 111 controls the rotation of a drive motor (drum motor) 115 that rotates the photosensitive drum 11. The rotation of the photosensitive drum 11 is also transmitted to the developing roller 12 and the supply roller 13.

[0036] The fixing control unit 112 has a temperature adjustment circuit and supplies current to the heater 53 of the fixing roller 51 based on an output signal from a temperature sensor such as a thermistor provided in the fixing device 50. The fixing drive control unit 113 controls the rotation of the fixing motor 116 that drives and rotates the fixing roller 51. The discharge roller 61 is rotated by the rotation transmitted from the fixing motor 116.

[0037] The paper feed and transport control unit 114 controls the rotation of a paper feed motor 117 that drives the paper feed roller 42 and a transport motor 118 that drives the transport roller 43 .

[0038] <Basic operation of image forming device> Next, the printing operation of the image forming apparatus 1 will be described with reference to Figures 1 and 2. When the main control unit 100 receives a print command and print data from a host device via the I / F control unit 101, it starts the printing operation.

[0039] The main control unit 100 temporarily records print data received from a host device in a reception memory 102 , edits the recorded print data to generate image data, and records the image data in an image data editing memory 103 .

[0040] Furthermore, the fixing drive control unit 113 drives the fixing motor 116, and the fixing roller 51 and the pressure roller 52 start to rotate. Furthermore, the fixing control unit 112 energizes the heater 53, and the fixing roller 51 is heated to a predetermined fixing temperature.

[0041] Furthermore, the paper feed conveyance control unit 114 drives the paper feed motor 117, and the paper feed rollers 42 send the medium P in the medium tray 41 to the conveyance path as shown by the arrow A1. Furthermore, the conveyance motor 118 rotates the conveyance rollers 43, and the medium P is conveyed to the developing device 10 as shown by the arrow A2.

[0042] Furthermore, a voltage control unit 104 applies a charging voltage, a developing voltage, a supply voltage, and a blade voltage from the respective power sources 105 to 108 to the charging roller 15, the developing roller 12, the supply roller 13, and the regulating blade 14.

[0043] Furthermore, the drive control unit 111 drives the drive motor 115 to rotate the photosensitive drum 11. As the photosensitive drum 11 rotates, the charging roller 15, the developing roller 12, and the supply roller 13 also rotate. The charging roller 15 uniformly charges the surface of the photosensitive drum 11.

[0044] Furthermore, the head control unit 110 drives the exposure head 30 to irradiate the surface of the photosensitive drum 11 with light. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 11.

[0045] The electrostatic latent image formed on the surface of the photosensitive drum 11 is developed by the toner attached to the developing roller 12, and a toner image is formed on the surface of the photosensitive drum 11. Furthermore, the voltage control unit 104 applies a transfer voltage from the transfer voltage power supply 109 to the transfer roller 19.

[0046] This transfer voltage causes the toner image on the surface of the photosensitive drum 11 to be transferred to the medium P passing between the photosensitive drum 11 and the transfer roller 19. The toner that has not been transferred to the medium P is scraped off by the cleaning member 17.

[0047] In the fixing device 50, heat and pressure are applied to the medium P passing through the fixing nip between the fixing roller 51 and the pressure roller 52, and the toner image is fixed to the medium P. The medium P with the fixed toner image is sent to the medium discharge section 60 as shown by arrow A3.

[0048] In medium discharge unit 60, discharge rollers 61 discharge medium P from a discharge port as shown by arrow A4. The discharged medium P is stacked on stacker 63. This completes the formation of an image on medium P.

[0049] <Configuration of each component of the developing device> Next, the configuration of each component of the developing device 10 will be described in detail.

[0050] <Toner> First, the toner 9 will be described. The toner 9 is a non-magnetic, single-component, negatively charged toner, and 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. Note that, although a single-component development method is used in this embodiment, a two-component development method may also be used. Furthermore, the toner is not limited to a negatively charged toner, and a positively charged toner may also be used.

[0051] The binder resin is preferably a polyester resin, a styrene-acrylic resin, an epoxy resin, or a styrene-butadiene resin. A release agent, a colorant, etc. may be added to the binder resin, and additives such as a charge control agent, a conductivity adjuster, a flowability improver, or a cleaning improver may also be added. Multiple types of binder resins may also be mixed. Here, a mixture of two or more types of amorphous polyester resins and a crystalline polyester resin having a crystalline structure is used.

[0052] The average particle size of Toner 9 is approximately 7.0 μm, and the circularity is approximately 0.93. 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.

[0053] Silica (SiO2) is used as the external additive. In this embodiment, to evaluate the amount of the external additive, the Si (silicon) content (detected amount) [wt %] in the toner 9 is measured by elemental analysis using energy dispersive X-ray spectroscopy (EDX). For the elemental analysis, an energy dispersive X-ray fluorescence analyzer "EDX-800HS" manufactured by Shimadzu Corporation is used. The measurement environment is a helium (He) gas atmosphere, and the X-ray tube voltage is 15 [kV] or 50 [kV]. The Si content in the toner 9 of this embodiment is 0.98 to 1.28 [wt %].

[0054] Generally, when a sample is irradiated with X-rays, fluorescent X-rays, which are X-rays specific to the atoms contained in the sample, are generated and emitted from the sample. Because fluorescent X-rays have wavelengths (energy) specific to each element, qualitative analysis can be performed by examining the wavelengths of the fluorescent X-rays. Furthermore, the intensity of the fluorescent X-rays is a function of concentration. Therefore, quantitative analysis can be performed by measuring the amount of X-rays at each element-specific wavelength.

[0055] In this embodiment, toner is irradiated with X-rays emitted from an X-ray tube of an energy dispersive X-ray fluorescence analyzer, and the Si content is measured based on the fluorescent X-rays emitted from Si atoms contained in the external additives of the toner. In the energy dispersive X-ray fluorescence analyzer, the atmosphere in the sample chamber is replaced with helium (He) gas, and X-rays are irradiated at a voltage of 15 kV and a current of 100 μA.

[0056] The blow-off charge of the toner 9 is -94.6 [μC / g] or less. That is, in this embodiment, a toner with lower chargeability than general toner (blow-off charge: -104.6 [μC / g]) is used. The method for measuring the blow-off charge of the toner is as follows.

[0057] That is, a mixture of 0.5 g of toner and 9.5 g of carrier ("EF96-35" manufactured by Powder Tech Co., Ltd.) is placed in a container, and the container is shaken using a shaker "YS-LD" manufactured by Yayoi Co., Ltd. The number of shakes is 200 times / minute, and the shaking time is 600 seconds.

[0058] After shaking, a powder charge measurement device (Kyocera Chemical Corporation's "TB-203") was used to perform suction for 10 seconds at a blow pressure of 7.0 kPa and a suction pressure of -4.5 kPa, and the charge amount and suction amount for 0.1 seconds were output to a PC (personal computer). The charge amount per unit weight of the toner particles, Q / M (unit: μC / g), was calculated from the average values ​​of the charge amount and suction amount output during the final 2 seconds of the suction time (10 seconds). The measurement environment was a temperature of 25°C and a relative humidity of 50%.

[0059] <Photosensitive drum> Next, the photosensitive drum 11 will be described. Fig. 3 is a diagram showing the cross-sectional structure of the photosensitive drum 11. The photosensitive drum 11 has a cylindrical conductive support 11b and a photosensitive layer 11c formed on the surface of the conductive support 11b. An undercoat layer may be formed between the conductive support 11b and the photosensitive layer 11c.

[0060] The photoreceptor constituting the photosensitive layer 11c can be a photoreceptor applicable to general electrophotographic photoreceptors. Specific examples include single-layer photoreceptors and multi-layer photoreceptors. A single-layer photoreceptor has a single photosensitive layer (i.e., a single-layer photoreceptor) in which a photoconductive material is dissolved or dispersed in a binder resin. A multi-layer photoreceptor is formed by laminating a charge generation layer containing a charge generation substance and a charge transport layer containing a charge transport substance. It is generally known that photoreceptors exhibit equivalent performance whether they are single-layer or multi-layer.

[0061] In consideration of mechanical properties, electrical properties, manufacturing stability, and the like, the photosensitive layer 11c of this embodiment is preferably a laminated type photosensitive layer. Among them, a normal laminated type photosensitive body in which a charge generation layer and a charge transport layer are laminated in this order on the conductive support body 11b is particularly preferred. Note that the laminated type photosensitive body is also called a function-separated type photosensitive body because the charge generation layer and the charge transport layer share the responsibility of generating and transporting charges.

[0062] When forming the charge transport layer of a function-separated photoreceptor or the photosensitive layer of a single-layer photoreceptor, it is common to disperse a compound (such as a charge transport material) in a binder resin to ensure film strength. The charge transport layer of a function-separated photoreceptor is formed by applying and drying a coating liquid obtained by dissolving or dispersing a charge transport material and a binder resin in a solvent. Similarly, a single-layer photoreceptor is formed by applying and drying a coating liquid obtained by dissolving or dispersing a charge generation material, a charge transport material, and various binder resins in a solvent.

[0063] Examples of binder resins generally used in the charge generation layer of a function-separated photoreceptor include polyvinyl acetal resins such as polyvinyl butyral resin, polyvinyl formal resin, and partially acetalized polyvinyl butyral resin in which a portion 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, and silica. The binder resin may be selected from among silicone resins, polyvinyl alcohol resins, polyvinylpyrrolidone resins, casein, vinyl chloride-vinyl acetate copolymers such as vinyl chloride-vinyl acetate copolymers, hydroxy-modified vinyl chloride-vinyl acetate copolymers, carboxyl-modified vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinyl acetate-maleic anhydride copolymers; insulating resins such as styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, styrene-alkyd resins, silicone-alkyd resins, and phenol-formaldehyde resins; and organic photoconductive resins such as poly-N-vinylcarbazole, polyvinyl anthracene, and polyvinylperylene. However, the binder resin is not limited to these resins. These binder resins may be used alone or in any combination and ratio.

[0064] Examples of binder resins used in the charge transport layer include polyvinyl acetal resins, polyarylate resins, polycarbonate resins, polyester resins, modified ether-based polyester resins, phenoxy resins, polyvinyl chloride resins, polyvinylidene chloride resins, polyvinyl acetate resins, polystyrene resins, acrylic resins, methacrylic resins, polyacrylamide resins, polyamide resins, polyvinylpyridine resins, cellulose-based resins, polyurethane resins, epoxy resins, silicone resins, polyvinyl alcohol resins, polyvinylpyrrolidone resins, casein, vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, styrene-alkyd resins, silicone-alkyd resins, phenol-formaldehyde resins, and organic photoconductive resins. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate copolymers, hydroxy-modified vinyl chloride-vinyl acetate copolymers, carboxyl-modified vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinyl acetate-maleic anhydride copolymers. Examples of organic photoconductive resins include poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylperylene.

[0065] The compound contained in the charge transport layer includes, for example, one or more charge transport materials. The type of charge transport material is not particularly limited, but examples include aromatic amine derivatives, stilbene derivatives, butadiene derivatives, hydrazone derivatives, carbazole derivatives, aniline derivatives, and enamine derivatives. The charge transport material may be, for example, a compound to which one or more of the above-mentioned aromatic amine derivatives are bonded. The charge transport material may also 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 side chain. In particular, the charge transport material is preferably an aromatic amine derivative, a stilbene derivative, a hydrazone derivative, an enamine derivative, or a compound to which one or more of these are bonded, and more preferably a compound to which an aromatic amine derivative and an enamine derivative are bonded.

[0066] The photosensitive layer 11c of the photoreceptor drum 11 is generally formed by repeating a process for each layer, in which a coating liquid containing materials for each layer is applied onto the conductive support 11b by a known coating method and then dried. Examples of solvents or dispersion media for dissolving the binder resin when preparing 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, and methyl formate. Examples of solvents that do not dissolve the undercoat layer include ester solvents such as ethanol, ethyl acetate, and n-butyl acetate, halogenated hydrocarbon solvents such as methylene chloride, chloroform, and 1,2-dichloroethane, chain and cyclic ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, 1,4-dioxane, methyl cellosolve, and ethyl cellosolve, aprotic polar solvents such as acetonitrile, dimethyl sulfoxide, sulfolane, and hexamethylphosphoric triamide, nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, triethylenediamine, and triethylamine, mineral oils such as ligroin, and water. These solvents may be used alone or in any combination and ratio.

[0067] Examples of methods for applying the coating liquid include dip coating, spray coating, spinner coating, bead coating, wire bar coating, blade coating, roller coating, air knife coating, and curtain coating, but other coating methods may also be used. These methods may be used alone or in any combination of two or more. The coating liquid is preferably dried to the touch at room temperature (usually 25°C), and then heated at a temperature in the range of 30 to 190°C for a drying time of 1 minute to 2 hours, with or without airflow. The heating temperature may be constant, or the heating temperature may be varied while drying.

[0068] The thickness of the charge transport layer of a normal layered photoreceptor is generally in the range of 5 to 50 μm, but from the viewpoints of long life and image stability, it is preferably 10 to 45 μm. Furthermore, from the viewpoint of improving resolution, it is more preferably 10 to 30 μm. The outer diameter of the photoreceptor drum 11 in this embodiment is 30.0 mm.

[0069] <Developing roller> Next, we will explain the developing roller 12. Figure 4 is a diagram showing the cross-sectional structure of the developing roller 12. The developing roller 12 includes a conductive shaft 12a, an inner layer (elastic layer) 12b that covers the surface of the shaft 12a, and a surface layer (coating layer) 12c that covers the surface of the inner layer 12b.

[0070] The inner layer 12b can be formed from a common rubber material such as silicone rubber or urethane. When polyurethane is used as the rubber material, polyurethanes based on polyether-based polyols (ether-based polyurethanes) are preferred. Ether-based polyurethanes are cast-type polyurethanes obtained by reacting polyols based on polyether-based polyols with polyisocyanates. This is to reduce compression set. On the other hand, ester-based polyurethanes have poor hydrolysis properties, making them difficult to use stably over long periods of time.

[0071] The inner layer 12b is formed by adding carbon black to a rubber base material made of the above-mentioned rubber material, and then heat-curing the rubber base while maintaining the dispersed state of the carbon black.

[0072] The surface layer 12c is formed by impregnating the surface of the inner layer 12b with a surface treatment liquid. The surface treatment liquid is prepared by dissolving isocyanate in an organic solvent, and further dissolving acrylic resin and urethane resin in a certain ratio. If the total of the acrylic resin and urethane resin in the surface treatment liquid is taken as 100%, it is desirable that the acrylic resin be contained in an amount of 40 to 60% (more desirably 50%). Carbon black, such as acetylene black, is added to the surface treatment liquid as a conductivity imparting agent.

[0073] By immersing the inner layer 12b in the surface treatment solution, the surface layer portion of the inner layer 12b is impregnated with the surface treatment solution. Thereafter, the inner layer 12b is dried and hardened, and the surface layer portion of the inner layer 12b becomes the surface layer 12c. The thickness of the surface layer 12c is 10 μm to 20 μm (i.e., 0.01 mm to 0.02 mm).

[0074] The roller portion of the developing roller 12 (excluding the shaft end portion 12e described below) may have a straight shape with a constant outer diameter, or may have a shape in which the outer diameter varies between the axial center and the end portions (for example, a crown shape). A shape in which the contact pressure between the developing roller 12 and the photosensitive drum 11, the supply roller 13, and the regulating blade 14 is uniform in the axial direction is desirable. In this example, the roller portion of the developing roller 12 has a straight shape and an outer diameter of 12.0 mm.

[0075] The rubber hardness (Asker C hardness) of the inner layer 12b is preferably 55 to 85 degrees. If the Asker C hardness of the inner layer 12b is lower than 55 degrees, when the developing device 10 is stopped for a long period of time, a depression may occur at the contact point between the developing roller 12 and the photosensitive drum 11 or the regulating blade 14, possibly resulting in horizontal streaks in the image. If the Asker C hardness of the inner layer 12b is higher than 85 degrees, the mechanical load on the developing roller 12 increases, making it more likely that toner will adhere to the surface of the developing roller 12 (known as filming). Here, the Asker C hardness of the inner layer 12b is 82 degrees.

[0076] The surface roughness Rz (ten-point average roughness: JIS_B0601-1994) of the developing roller 12 is preferably 2.0 to 7.0 μm. If the surface roughness Rz is less than 2.0 μm, the toner layer on the surface of the developing roller 12 becomes thin, and the stress applied to each toner particle becomes large. As a result, the amount of external additives that separates from the toner increases, and the external additives may become stuck between the developing roller 12 and the regulating blade 14, causing filming on the surface of the regulating blade 14. If the surface roughness Rz exceeds 7.0 μm, the toner layer on the surface of the developing roller 12 becomes thick, which may prevent the supply roller 13 from sufficiently scraping off the toner, causing filming on the surface of the developing roller 12. Furthermore, more toner than necessary may move to the photosensitive drum 11, causing image contamination.

[0077] The surface roughness Rz of the developing roller 12 is measured using a surface roughness measuring instrument "Surfcorder SEF3500" manufactured by Kosaka Laboratory Co., Ltd. The stylus radius of the surface roughness measuring instrument is 2 μm, the stylus pressure is 0.7 mN, and the measurement is performed by moving the stylus in the axial direction of the developing roller 12 a distance of 4.0 mm at a speed of 0.1 mm / sec. The cutoff value is 0.8 mm.

[0078] The resistance value (total resistance, described later) of the developing roller 12 is preferably 6.15 to 8.45 [log Ω]. The method for measuring the resistance of the developing roller 12 is as follows.

[0079] 5(A) and (B) are schematic diagrams showing a method for measuring the resistance of the developing roller 12. A "High Resistance Meter" (model number: 4339B) manufactured by Hewlett-Packard Co., Ltd. is used as the measuring device 71. As shown in FIG. 5(A), stainless steel bearings 72 with a diameter of 10.0 mm are pressed as contacts against the surface of the developing roller 12 at six locations in the longitudinal direction of the developing roller 12 with a load W1 of 20±0.5 gf.

[0080] As shown in Figure 5(B), a measuring device 71 is connected to the shaft end 12e of the developing roller 12 and the bearing 72, the developing roller 12 is rotated at a speed of 50 rpm, and a DC voltage of -40 V is applied to the shaft end 12e of the developing roller 12 relative to the bearing 72. In this state, the resistance value of the developing roller 12 is obtained from the current flowing between the shaft end 12e of the developing roller 12 and the bearing 72. The measurement environment is a temperature of 20°C and a relative humidity of 50%.

[0081] <Supply roller> Next, the supply roller 13 will be described. Fig. 6 is a cross-sectional view showing the supply roller 13. The supply roller 13 has an electrically conductive shaft 13a and a foamed elastic layer 13b formed on the surface of the shaft 13a. The shaft 13a may be made of any material as long as it has good electrical conductivity, and iron, aluminum, stainless steel, etc. are generally used.

[0082] The rubber composition forming the foamed elastic layer 13b contains rubber, a foaming agent, and a conductivity imparting agent, and further contains additives as necessary. The rubber is preferably silicone rubber or silicone-modified rubber, which has excellent heat resistance and electrostatic charge characteristics. The foaming agent may be any foaming agent used in 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 to form open cells in the foamed elastic layer 13b, and organic foaming agents are used to form closed cells. Examples of additives include fillers, colorants, and release agents.

[0083] The roller portion of the supply roller 13 may have a straight shape with a constant outer diameter, or may have a shape (for example, a crown shape) in which the outer diameter varies between the axial center and the ends. A shape that ensures uniform contact pressure between the supply roller 13 and the developing roller 12 in the axial direction is desirable. In this example, the roller portion of the supply roller 13 has a crown shape with an outer diameter of 16.2 mm at the axial center and 15.8 mm at the ends.

[0084] The outer diameter of the shaft 13a of the supply roller 13 is, for example, 6.0 mm. The average cell diameter of the elastic foam layer is preferably 200 to 500 μm, but is not limited to this range. The hardness of the elastic foam layer is preferably about 53 to 63 degrees on the Asker F hardness scale, and one with 58 degrees is used here.

[0085] The resistance value of the supply roller 13 is preferably 6.0 to 8.0 [log Ω]. Here, a supply roller 13 with a resistance value of 7.0 [log Ω] is used. The method for measuring the resistance of the supply roller 13 is the same as the resistance measurement method described with reference to Figures 5(A) and (B).

[0086] As shown in FIG. 5A, stainless steel bearings 72 having a diameter of 10.0 mm are pressed against the surface of the supply roller 13 at six points in the longitudinal direction of the supply roller 13 with a load W1 of 10.5 gf.

[0087] 5(B), measuring device 71 is connected to shaft end 13e of supply roller 13 and bearing 72, supply roller 13 is rotated at a speed of 63 rpm, and a DC voltage of -300 V is applied to shaft end 13e of supply roller 13 relative to bearing 72. In this state, the resistance value of supply roller 13 is determined from the current flowing between shaft end 13e of supply roller 13 and bearing 72. The measurement environment is a temperature of 20°C and a relative humidity of 50%.

[0088] The supply roller 13 is made by integrally molding the shaft 13a, which has been washed with an organic solvent or the like to remove oil, with a conductive silicone rubber foam using an extrusion molding machine, and then expanding and curing the foam in an infrared oven or the like. After that, a secondary vulcanization process is performed at a temperature of about 180 to 225°C for about 5 to 10 hours, and the surface of the foamed elastic body is polished with a polishing machine to obtain the desired outer diameter.

[0089] <Regulatory blade> 1 is a plate-shaped member made of stainless steel, and has a plate thickness of, for example, 0.08 mm. The regulating blade 14 is bent at the contact portion with the developing roller 12, with the radius of curvature of the bent portion being approximately 0.15 to 0.35 mm. The pressure (linear pressure) between the regulating blade 14 and the developing roller 12 is approximately 25 to 50 gf / cm.

[0090] <Support structure for photosensitive drum and developing roller> 7 is a schematic diagram showing a support structure for the photosensitive drum 11 and the developing roller 12 in the developing device 10. The axial direction of the photosensitive drum 11 and the developing roller 12 is the X direction.

[0091] The unit housing 20 of the developing device 10 has side frames 21 and 22 on both sides of the photosensitive drum 11 and the developing roller 12 in the X direction. The photosensitive drum 11 and the developing roller 12 are supported by the side frames 21 and 22. The supply roller 13 and the regulating blade 14 (FIG. 1) are also supported by the side frames 21 and 22, but are omitted in FIG. 7.

[0092] The photosensitive drum 11 has a shaft 11a that axially penetrates a conductive support 11b (FIG. 3). Both end portions 11e of the shaft 11a are fitted into holes 21a and 22a formed in the side frames 21 and 22. This fixes the shaft 11a to the side frames 21 and 22. The shaft 11a does not rotate by itself.

[0093] The conductive support 11b (FIG. 3) of the photosensitive drum 11 is rotatably supported on the shaft 11a by a bearing (not shown) provided on the inner periphery of the support 11b. A drum flange 11f is provided at the end of the photosensitive drum 11 in the -X direction (side frame 21 side), and a drum gear 11g is provided at the end in the +X direction (side frame 22 side).

[0094] The drum flange 11f and the drum gear 11g are located on both sides of the photosensitive layer 11c in the X direction. The drum gear 11g meshes with a gear (not shown) to which rotation from the drive motor 115 (FIG. 2) is transmitted, thereby rotating the photosensitive drum 11.

[0095] The developing roller 12 has shaft end portions 12e at both ends in the X direction of the shaft body 12a (FIG. 4) supported by bearings disposed in holes 21b and 22b of the side frames 21 and 22. As a result, the developing roller 12 is rotatably supported by the side frames 21 and 22.

[0096] A roller gear 12g that meshes with the drum gear 11g is fixed to a shaft end 12e in the +X direction of the developing roller 12. When the photosensitive drum 11 rotates, the developing roller 12 also rotates due to the meshing of the drum gear 11g and the roller gear 12g.

[0097] The photosensitive layer 11c of the photosensitive drum 11 and the surface layer 12c of the developing roller 12 are in contact with each other. The distance L1 between the centers of the photosensitive drum 11 and the developing roller 12 is determined by the center-to-center distance between the holes 21a and 21b of the side frame 21 (i.e., the center-to-center distance between the holes 22a and 22b of the side frame 22). The contact pressure between the photosensitive drum 11 and the developing roller 12 is determined by this distance L1.

[0098] Next, we will explain the transport force exerted by the photosensitive drum 11 and the developing roller 12. The transport force is the force with which an object (here, a film) inserted between the photosensitive drum 11 and the developing roller 12 is pulled by the rotating photosensitive drum 11 and the developing roller 12. The transport force is also called the pulling force or the feed force.

[0099] Fig. 8(A) is a schematic diagram showing a method for measuring the conveying force between the photosensitive drum 11 and the developing roller 12. Fig. 8(B) is a schematic diagram showing a measuring jig 80 used for measuring the conveying force.

[0100] As shown in FIG. 8(A), a film 82 is inserted between the photosensitive drum 11 and the developing roller 12, and the photosensitive drum 11 and the developing roller 12 are rotated. The force with which the film 82 is pulled is measured with a force gauge 81, thereby measuring the conveying force.

[0101] The longitudinal direction of the film 82 is the tangent direction to the surface of the photosensitive drum 11 at the contact portion (indicated by the symbol N) between the photosensitive drum 11 and the developing roller 12. The width direction of the film 82 is the X direction.

[0102] 8(B), a support plate 83 is fixed to the upper end portion (the end portion away from the contact portion N) of the film 82. One end of a hook 85 is attached to the support plate 83, and the other end of the hook 85 is attached to the force gauge 81.

[0103] The film 82 is made of, for example, PET (polyethylene terephthalate). The length of the film 82 is 95 mm, the width is 5 mm, and the thickness is 1 mm. The width direction of the film 82 is the X direction.

[0104] Support plate 83 is, for example, an acrylic plate, and is fixed to one longitudinal end of film 82. Support plate 83 is 20 mm long and 12 mm wide. Support plate 83 is formed with a hole 84 into which one end of hook 85 is hooked.

[0105] As shown in Figure 8(A), with film 82 inserted between photosensitive drum 11 and developing roller 12, photosensitive drum 11 and developing roller 12 are rotated. The rotational speed (circumferential speed) of photosensitive drum 11 is 234.0 mm / sec, which corresponds to a printing speed of 49 ppm. The peripheral speed of developing roller 12 is 1.26 times the peripheral speed of photosensitive drum 11.

[0106] The peripheral speed ratio between the photosensitive drum 11 and the developing roller 12 (here, 1.26) is determined by the outer diameter ratio between the photosensitive drum 11 and the developing roller 12 and the tooth number ratio between the drum gear 11g and the roller gear 12g shown in FIG.

[0107] With the photosensitive drum 11 and the developing roller 12 rotated as described above, the value [N] of the force gauge 81 is read. The force gauge 81 is a digital force gauge in this case, and the measured value is output to a personal computer.

[0108] The conveying force is measured at three locations: the center of the developing roller 12 in the X direction and both sides of that center in the X direction. At each location, the output value of the force gauge 81 is recorded at a sampling interval of 10 [ms], and the average value over a 5 [second] period is calculated. This gives the conveying force [N] at each location. The maximum value of the conveying force at the three locations is then defined as the conveying force [N].

[0109] Although the maximum value of the conveying forces at the three locations is used here, it is not limited to this, and for example, the average value of the conveying forces at the three locations may be used. Alternatively, since the conveying forces at both sides in the X direction tend to be higher than at the center of the developing roller 12, the average value of the conveying forces at both sides (two locations) in the X direction may be used.

[0110] <Total resistance and inner layer resistance of developing roller> Next, the overall resistance and inner layer resistance of the developing roller 12 will be described. Fig. 9 is a flowchart showing a method for measuring the overall resistance and inner layer resistance of the developing roller 12. First, the outer diameter of the developing roller 12 is measured (step S11). An automatic roller measuring machine manufactured by Apollo Seiko Co., Ltd. is used to measure the outer diameter.

[0111] Next, the overall resistance of the developing roller 12 is measured (step S12). Fig. 10 is a schematic diagram showing a resistance measurement method. As a measuring device 71, a "High Resistance Meter" (model number: 4339B) manufactured by Hewlett-Packard Co., Ltd. is used.

[0112] The resistance measurement method is substantially the same as that described with reference to Figures 5(A) and (B), but uses only one bearing 72. As shown in Figure 10, a stainless steel bearing 72 with a diameter of 10.0 [mm] is pressed as a contact against the axial center part M of the developing roller 12 with a load W1 of 20±0.5 [gf].

[0113] A measuring device 71 is connected to the shaft end 12e of the developing roller 12 and the bearing 72, and the developing roller 12 is rotated at a speed of 50 rpm, and a DC voltage of -40 V is applied to the shaft end 12e of the developing roller 12 relative to the bearing 72. In this state, the resistance of the developing roller 12 is calculated from the current flowing between the bearing 72 and the shaft end 12e. The average value of the resistance over two revolutions of the developing roller 12 is taken as the overall resistance R ALL Let it be [LogΩ].

[0114] Next, the surface of the developing roller 12 is cut (step S13). Figures 11(A) and (B) are schematic diagrams showing the cutting process of the developing roller 12. As shown in Figure 11(A), a flat blade 90 (made of cutlery tool steel, width 20 mm, blade length 25 mm) manufactured by Toho Co., Ltd. is used for cutting. The shaft end 12e of the developing roller 12 is rotatably supported by a shaft holder 92, and the flat blade 90 is pressed against the surface of the center portion M of the developing roller 12.

[0115] 11(B), the developing roller 12 is rotated in one direction (counterclockwise in the figure) at a rotational speed of 150 rpm or more. The cutting edge 91 of the flat blade 90 is pressed against the surface of the developing roller 12 below the center of rotation in a counter direction to the direction of movement of the surface of the developing roller 12. The orientation of the cutting edge 91 of the flat blade 90 is at 45 degrees with respect to the vertical direction.

[0116] The cutting depth, which is set to 0.03 mm here, is sufficient as long as it is deeper than the thickness (here, 0.01 to 0.02 mm) of the surface layer 12c of the developing roller 12. By cutting, the surface layer 12c is removed from the center portion M (width 20 mm) of the developing roller 12, exposing the inner layer 12b.

[0117] After cutting, the shavings remaining on the surface of the developing roller 12 are blown away by air blowing, and are then removed by pressing a nonwoven fabric wiper "BEMCOT" (registered trademark) manufactured by Asahi Chemical Industry Co., Ltd. against the surface.

[0118] Next, the outer diameter of the center portion M of the developing roller 12 after cutting is measured (step S14). An automatic roller measuring device manufactured by Apollo Seiko Co., Ltd. is used for the outer diameter measurement. At this time, it is confirmed that the difference between the outer diameter measured in step S11 and the outer diameter measured in step S14 (i.e., the cutting depth of the center portion M of the developing roller 12) is 0.03 mm or more, and if the outer diameter difference is less than 0.03 mm, the cutting in step S13 is repeated. Note that, although the center portion M of the developing roller 12 is cut in this embodiment, other locations may also be cut as long as the surface layer 12c is formed.

[0119] Next, the resistance of the center portion M of the developing roller 12 after cutting is measured (step S15). The resistance measurement method is the same as in step S12. That is, as shown in Fig. 10, the bearing 72 is pressed against the center portion M of the developing roller 12, the developing roller 12 is rotated at a speed of 50 rpm, and a DC voltage of -40 V is applied to the shaft end portion 12 e of the developing roller 12 with respect to the bearing 72.

[0120] In this state, the resistance of the developing roller 12 is calculated from the current flowing between the bearing 72 and the shaft end 12e. The average value of the resistance for two revolutions of the developing roller 12 is taken as the resistance value R of the inner layer 12b. IN Since the surface layer 12c is removed at the center M of the developing roller 12, the resistance of the inner layer 12b (i.e., the resistance value R IN ) can be obtained.

[0121] Next, the total resistance value R calculated in step S12 ALL From [LogΩ], the resistance value R of the inner layer 12b calculated in step S15 is calculated. IN Subtract [LogΩ] and R ALL -R IN Obtain the value of [LogΩ].

[0122] The resistance value R ALL and resistance value R IN is in logarithmic notation. For example, R ALL = 7.27 [LogΩ], converting the unit to [Ω], R ALL =10 7.27 [Ω]. Because logarithmic notation is used, R ALL -R IN The value of [LogΩ] is also called the resistance ratio.

[0123] In this embodiment, the overall resistance value R ALL and the resistance value R of the inner layer 12b IN A plurality of developing rollers 12 (Examples 1 to 10 and Comparative Examples 1 to 10) with different properties were prepared, and test printing was carried out using each of them to evaluate the relationship with the occurrence of print defects such as uneven density, fogging, and fading.

[0124] <Residual potential of developing roller> Next, we will explain how to measure the residual potential of the developing roller 12. Figure 12 is a schematic diagram showing a method for measuring the residual potential of the developing roller 12. The measuring device 300 used to measure the residual potential of the developing roller 12 is a dielectric relaxation measuring device "DRA2000" manufactured by Quality Engineering Associates.

[0125] The measuring device 300 has a carrier 301, a corona discharge electrode 302, a probe 303, and a surface electrometer 304. The corona discharge electrode 302 and the probe 303 are supported by the carrier 301. The carrier 301 is movable along the surface of the developing roller 12 in the axial direction of the developing roller 12. The probe 303 is connected to the surface electrometer 304. The distance between the corona discharge electrode 302 and the probe 303 is 23 mm.

[0126] When measuring the residual potential, the shaft end 12e of the developing roller 12 is grounded via a resistor 305. In this state, the carrier 301 is moved to a predetermined position (for example, the center position in the axial direction of the developing roller 12), and corona discharge is performed by the corona discharge electrode 302. The corona discharge voltage is set to 6.0 [KV].

[0127] Thereafter, the carrier 301 is moved 23 mm, and the probe 303 is positioned at the position of the corona discharge electrode 302 during corona discharge. The residual potential [-V] is then measured 2.15 seconds after the corona discharge. The reason for measuring the residual potential after 2.15 seconds is that the residual potential of the developing roller 12 varies greatly immediately after the corona discharge (especially before 0.2 seconds has elapsed). The residual potential can be measured after the variation in the residual potential has become small, and may be measured after 2.10 seconds or 2.30 seconds, for example.

[0128] As will be described later, the residual potential is measured for a plurality of types of developing rollers 12 (Examples 1 to 10 and Comparative Examples 1 to 10) using a measuring device 300. Note that, because a negative developing voltage is applied to the developing roller 12, the unit of the residual potential is [-V]. Hereinafter, a large absolute value of the potential (residual potential, surface potential) is referred to as a "high potential," and a small absolute value of the potential is referred to as a "low potential."

[0129] <Test print> Next, test printing will be described. In recent years, image forming apparatuses using electrophotographic processes have been considered for printing using toner with fewer external additives. When toner with fewer external additives is used, the toner tends to have a lower chargeability. Therefore, when the surface potential of the developing roller 12 decreases, the toner is not retained on the developing roller 12 and tends to adhere to the unexposed portions of the photosensitive drum 11 that are not exposed by the exposure head 30. As a result, a phenomenon occurs in which toner is printed scattered on white paper (fog).

[0130] Furthermore, if the toner transfer from the developing roller 12 to the photosensitive drum 11 is insufficient, the image density will be partially reduced, resulting in a printing defect called "blurring." Furthermore, if the voltage responsiveness of the developing roller 12 is low, the surface potential of the developing roller 12 will fluctuate, resulting in uneven density.

[0131] Here, continuous printing and subsequent test printing were performed using the image forming apparatus 1 to determine the presence or absence of fogging, blurring, and density unevenness. The image forming apparatus 1 used was an LED printer "B820" manufactured by Oki Electric Industry Co., Ltd., and the developing device 10 was previously refilled with 15 g of toner.

[0132] Black toner was used for the continuous printing and test printing. The desirable range of the Si content in the toner is 0.98 to 1.28 [wt%], but here it was set to 0.98 [wt%]. The Si content was measured by elemental analysis using energy dispersive X-ray spectroscopy (EDX) as described above.

[0133] Figure 13 shows the medium P1 used for continuous printing. The medium P1 is A4-sized plain paper. The transport direction was horizontal, and the transport speed (circumferential speed) was 202.5 mm / sec, which corresponds to a printing speed of 45 ppm. The printing environment was a temperature of 28°C and a relative humidity of 80%.

[0134] The charging voltage applied to the charging roller 15 was -1050 [V], the developing voltage applied to the developing roller 12 was -200 [V], the supply voltage applied to the supply roller 13 was -350 [V], the blade voltage applied to the regulating blade 14 was -350 [V], and the transfer voltage applied to the transfer roller 19 was +1500 [V]. Note that the potential of the portion of the surface of the photosensitive drum 11 exposed by the exposure head 30 drops to -30 [V] to -50 [V].

[0135] In the continuous printing, an image LP with a duty ratio of 1.25% was printed on the medium P1. The image LP with a duty ratio of 1.25% (i.e., a print image density of 1.25%) is a line-shaped solid image as shown in FIG.

[0136] The duty ratio is also called print image density and is defined as follows: Print image density (duty ratio) = [Cm(i) / (Cd×C0)] × 100 Cm(i) is the number of dots emitted by the exposure head 30 while the photosensitive drum 11 rotates Cd. C0 is the number of dots that the exposure head 30 can emit while the photosensitive drum 11 rotates once. Cd x C0 is the number of dots that the exposure head 30 can emit while the photosensitive drum 11 rotates Cd.

[0137] In other words, if a solid image is printed over the entire printable area of ​​the medium P1, the print image density will be 100%. If an image with an area of ​​1% of this print image density of 100% is printed, the print image density will be 1%.

[0138] Continuous printing was performed on 10,000 sheets of the medium P1, and three types of test patterns described below were printed every 2,000 sheets.

[0139] FIG. 14 shows the medium P2 and test pattern used for the test printing. Medium P2 was A3-sized plain paper. The transport direction was vertical, and the transport speed (circumferential speed) was 202.5 mm / sec, which corresponds to a printing speed of 45 ppm. A halftone image HT was printed on medium P2 as a test pattern. The halftone image HT is a 2x2 pattern. The 2x2 pattern forms 4 dots in 2 vertical dots D and 2 horizontal dots D, out of 16 squares formed by 4 dots in the vertical direction and 4 dots in the horizontal direction.

[0140] Fig. 15(A) shows the medium P3 and test pattern used for test printing. Medium P3 is the same as medium P2 shown in Fig. 14, and the transport direction and transport speed are also the same. A solid image SD with a duty ratio of 100% was printed on medium P3 as the test pattern.

[0141] Figure 15(B) shows the medium P4 and test pattern used in the test printing. Medium P4 was A3-sized glossy paper. The transport direction and transport speed were the same as those of medium P2 shown in Figure 14. Image WH with a duty ratio of 0% was printed on medium P3 as the test pattern.

[0142] As will be described later, the resistance value R ALL ,R IN After creating a plurality of developing rollers 12 with different sizes, each developing roller 12 was incorporated into the developing device 10 of the image forming apparatus 1, and the above-mentioned continuous printing was carried out. After completing the continuous printing of 2000 sheets, test patterns (images HT, SD, WH) were printed on the media P1, P2, and P3, respectively, and the surfaces of the media P1, P2, and P3 after printing were visually observed to evaluate the presence or absence of fog, fading, and uneven density.

[0143] A total of five test prints were performed after each 2000-sheet continuous print run. If even one sheet was judged to be defective as a result of visual fogging, the fogging evaluation was given an "X"; if all five sheets were judged to be good, the fogging evaluation was given an "O".

[0144] Similarly, in a total of five test prints, if even one sheet was judged to be defective through visual inspection, the smearing was rated as "X", and if all five sheets were judged to be good, the smearing was rated as "O".

[0145] Similarly, in a total of five test prints, if even one sheet was judged to be defective through visual inspection of the density unevenness, the density unevenness was rated as "X", and if all five sheets were judged to be good, the density unevenness was rated as "O".

[0146] As a result, the overall resistance value R of the developing roller 12 ALL and the resistance value R of the inner layer 12b IN It is possible to evaluate the correlation between the resistance characteristics, including the above, and print defects such as uneven density, fogging, and blurring.

[0147] <Resistance value R of inner layer 12b IN Correction of> Before explaining the relationship between the resistance characteristics of the developing roller 12 and print quality, the resistance value R of the inner layer 12b IN The correction of the resistance value R of the inner layer 12b will be described. IN When measuring the resistance R of the inner layer 12b (steps S13 to S15 shown in FIG. 9), the surface layer 12c of the developing roller 12 is cut to expose the inner layer 12b. IN The effect of cutting on the

[0148] Here, the resistance value R of the inner layer 12b is calculated as follows. IN First, as shown in Fig. 16(A), the inner layer 12b is formed on the surface of the shaft body 12a (not shown in the figure), and before the surface layer 12c is formed, the resistance value R of the inner layer 12b is measured by bringing the bearing 72 into contact with the inner layer 12b (point A) using the resistance measurement method described with reference to Fig. 10. IN was measured.

[0149] Next, as shown in FIG. 16(B), a surface layer 12c is formed on the surface of the inner layer 12b of FIG. 16(A), and the overall resistance value R of the developing roller 12 is measured by pressing a bearing 72 against the surface layer 12c (point A) using the resistance measurement method described with reference to FIG. ALL was measured.

[0150] Furthermore, as shown in FIG. 16(C), the surface layer 12c of FIG. 16(B) is cut with a flat blade 90 to expose the inner layer 12b, and the resistance value R of the inner layer 12b is measured by pressing the bearing 72 against the inner layer 12b (point A) using the resistance measurement method described with reference to FIG. IN was measured.

[0151] The overall resistance R measured in Figure 16(B) ALL The resistance value R of the inner layer 12b measured in FIG. IN By subtracting this, the R when the surface layer 12c is not cut ALL -R IN On the other hand, the total resistance R measured in Figure 16(B) ALL The resistance value R of the inner layer 12b measured in FIG. 16(C) IN By subtracting this, R when the surface layer 12c is removed ALL -R IN is required.

[0152] Here, 12 types of developing rollers 12 were created by varying the content of acrylic resin and urethane resin in the surface treatment liquid used to form the surface layer 12c of the developing roller 12, as well as the amount of carbon black added. ALL -R IN and R when the surface layer 12c is removed. ALL -R IN asked for.

[0153] Figure 17 shows the R when the surface layer 12c is not removed. ALL -R IN and R when the surface layer 12c is removed. ALL -R IN The vertical axis is a graph showing the relationship between R when the surface layer 12c is not scraped. ALL -RIN (y), and the horizontal axis shows R when the surface layer 12c is scraped. ALL -R IN (x) is shown.

[0154] The 12 plots shown in Figure 17 are on the approximate line of y = 0.998x + 0.417, and the coefficient of determination R 2 is 0.954. The slope of the line, 0.998, can be considered roughly 1, indicating a high correlation.

[0155] On the other hand, the y-intercept of the above straight line, 0.417, is due to the influence of cutting the surface layer 12c, more specifically, the increase in the surface roughness of the inner layer 12b due to cutting the surface layer 12c.

[0156] The surface roughness Rz of the inner layer 12b in Fig. 16(A) was measured using the above-mentioned surface roughness measuring instrument (Kosaka Manufacturing Co., Ltd.'s "Surfcorder SEF3500") and was found to be Rz = 6.3 [μm]. In contrast, the surface roughness Rz of the inner layer 12b in Fig. 16(C) was measured and found to be Rz = 20.3 [μm].

[0157] From this, it can be seen that the y-intercept of the straight line shown in Figure 17, 0.417, is due to the fact that the surface roughness Rz of the inner layer 12b becomes rough due to the cutting of the surface layer 12c, and the degree of adhesion between the inner layer 12b and the bearing 72 (Figure 10) decreases.

[0158] From the above, in this embodiment, the resistance value R of the inner layer 12b measured in step S15 of FIG. IN By subtracting 0.417 from the value of IN is corrected.

[0159] <Example> Next, Examples 1 to 10 and Comparative Examples 1 to 10 will be described. The developing rollers 12 of Examples 1 to 10 and Comparative Examples 1 to 10 were manufactured by adjusting the amount of carbon black added to the rubber material of the inner layer 12b and the amount of carbon black added to the surface treatment liquid used to form the surface layer 12c, thereby achieving an overall resistance value R ALLand the resistance value R of the inner layer 12b IN This is a result of the above differences.

[0160] The developing roller 12 of Example 1 has an overall resistance value R ALL is set to 7.27 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.45 [LogΩ]. ALL -R IN The value of was 0.82 [LogΩ] and the residual potential was 3.66 [-V].

[0161] The developing roller 12 of the second embodiment has an overall resistance value R ALL is set to 7.29 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.07 [LogΩ]. ALL -R IN The value of was 1.22 [LogΩ] and the residual potential was 2.98 [-V].

[0162] The developing roller 12 of the third embodiment has an overall resistance value R ALL is set to 7.84 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.34 [LogΩ]. ALL -R IN The value of was 1.50 [LogΩ] and the residual potential was 9.33 [-V].

[0163] The developing roller 12 of Example 4 has an overall resistance value R ALL is set to 8.00 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.26 [LogΩ]. ALL -R IN The value of was 1.74 [LogΩ] and the residual potential was 21.3 [-V].

[0164] The developing roller 12 of Example 5 has an overall resistance value R ALL is set to 6.69 [LogΩ], and the resistance value R of the inner layer 12b INis set to 6.13 [LogΩ]. R ALL -R IN The value of was 0.56 [LogΩ] and the residual potential was 3.83 [-V].

[0165] The developing roller 12 of Example 6 has an overall resistance value R ALL is set to 7.19 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.39 [LogΩ]. ALL -R IN The value of was 0.80 [LogΩ] and the residual potential was 5.08 [-V].

[0166] The developing roller 12 of Example 7 has an overall resistance value R ALL is set to 6.15 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 4.89 [LogΩ]. ALL -R IN The value of was 1.26 [LogΩ] and the residual potential was 3.02 [-V].

[0167] The developing roller 12 of Example 8 has an overall resistance value R ALL is set to 6.15 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 5.45 [LogΩ]. ALL -R IN The value of was 0.70 [LogΩ] and the residual potential was 3.06 [-V].

[0168] The developing roller 12 of Example 9 has an overall resistance value R ALL is set to 8.45 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 7.34 [LogΩ]. ALL -R IN The value of was 1.11 [LogΩ] and the residual potential was 8.01 [-V].

[0169] The developing roller 12 of Example 10 has an overall resistance value R ALL is set to 8.45 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.90[LogΩ].ALL -R IN The value of was 1.55 [LogΩ] and the residual potential was 13.20 [-V].

[0170] In the developing rollers 12 of Examples 1 to 10, the weight ratio (also referred to as the A / U ratio) of the acrylic resin to the urethane resin in the surface layer 12c was set to 50:50. This is the weight ratio of the acrylic resin to the urethane resin contained in the surface treatment liquid used when the inner layer 12b is surface-treated to form the surface layer 12c.

[0171] The developing roller 12 of Comparative Example 1 has an overall resistance value R ALL is set to 6.26 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 7.05 [LogΩ]. ALL -R IN The value of was -0.79 [LogΩ] and the residual potential was 1.36 [-V].

[0172] The developing roller 12 of Comparative Example 2 has an overall resistance value R ALL is set to 6.52 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.61 [LogΩ]. ALL -R IN The value of was -0.09 [LogΩ] and the residual potential was 1.81 [-V].

[0173] The developing roller 12 of Comparative Example 3 has an overall resistance value R ALL is set to 6.49 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 6.99 [LogΩ]. ALL -R IN The value of was -0.50 [LogΩ] and the residual potential was 4.83 [-V].

[0174] The developing roller 12 of Comparative Example 4 has an overall resistance value R ALL is set to 7.69 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 8.63 [LogΩ]. ALL -R INThe value of was -0.94 [LogΩ] and the residual potential was 5.84 [-V].

[0175] The developing roller 12 of Comparative Example 5 has an overall resistance value R ALL is set to 7.52 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 8.89 [LogΩ]. ALL -R IN The value of was -1.37 [LogΩ] and the residual potential was 5.64 [-V].

[0176] The developing roller 12 of Comparative Example 6 has an overall resistance value R ALL is set to 5.70 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 5.45 [LogΩ]. ALL -R IN The value of was 0.25 [LogΩ] and the residual potential was 3.05 [-V].

[0177] The developing roller 12 of Comparative Example 7 has an overall resistance value R ALL is set to 8.50 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 8.39 [LogΩ]. ALL -R IN The value of was 0.11 [LogΩ] and the residual potential was 8.02 [-V].

[0178] The developing roller 12 of Comparative Example 8 has an overall resistance value R ALL is set to 7.20 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 4.73 [LogΩ]. ALL -R IN The value of was 2.47 [LogΩ] and the residual potential was 5.43 [-V].

[0179] The developing roller 12 of Comparative Example 9 has an overall resistance value R ALL is set to 6.05 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 4.29 [LogΩ]. ALL -R INThe value of was 1.76 [LogΩ] and the residual potential was 5.02 [-V].

[0180] The developing roller 12 of Comparative Example 10 has an overall resistance value R ALL is set to 9.08 [LogΩ], and the resistance value R of the inner layer 12b IN is set to 7.78 [LogΩ]. ALL -R IN The value of was 1.30 [LogΩ] and the residual potential was 16.28 [-V].

[0181] Of these, the developing roller 12 of Comparative Example 1 had a surface layer 12c with a weight ratio of acrylic resin to urethane resin of 20:80.The developing rollers 12 of Comparative Examples 2 to 10 had a surface layer 12c with a weight ratio of acrylic resin to urethane resin of 50:50.

[0182] The developing rollers 12 of Examples 1 to 10 and Comparative Examples 1 to 10 were incorporated into the developing device 10 of the image forming apparatus 1, and continuous printing and test printing were carried out under the conditions described above, and uneven density, blurring, and fogging were evaluated. The results are shown in Tables 1 and 2.

[0183] [Table 1]

[0184] [Table 2]

[0185] Tables 1 and 2 show the ratio of the acrylic resin to the urethane resin in the surface layer 12c of the developing roller 12 (A / U ratio), the overall resistance value R ALL , the resistance value R of the inner layer 12b IN , the difference between these (resistance ratio) R ALL -R IN , the residual potential of the developing roller 12, and the image evaluation results (shading unevenness, blur, fogging).

[0186] In Comparative Example 1, R ALL -RIN The resistance value R of the inner layer 12b was -0.79 [LogΩ], and fogging was observed. This is due to the following reason. IN is the total resistance R ALL Since the resistance of the surface layer 12c of the developing roller 12 is higher than that of the inner layer 12b, the charge applied to the surface layer 12c of the developing roller 12 does not easily move to the inner layer 12b, which has a higher resistance. Therefore, the charge applied to the surface layer 12c is easily dissipated into the atmosphere, and the surface potential of the developing roller 12 decreases.

[0187] Here, as in Examples 1 to 10, the overall resistance value R ALL is the resistance value R of the inner layer 12b IN In the above cases, the charge applied to the surface layer 12c is likely to move to the inner layer 12b and is therefore unlikely to dissipate into the atmosphere, and therefore the charge is likely to be retained throughout the entire developing roller 12.

[0188] On the other hand, the overall resistance value R ALL is the resistance value R of the inner layer 12b IN If the temperature is lower than 100°C, the charge applied to the surface layer 12c is likely to dissipate into the atmosphere, resulting in less charge being held on the entire developing roller 12. As a result, fogging is more likely to occur.

[0189] When the surface potential of the developing roller 12 decreases, toner (e.g., positively charged toner) that would normally be retained on the developing roller 12 is not retained on the developing roller 12 and instead adheres to the photosensitive drum 11. Such toner also adheres to the non-exposed portions of the photosensitive drum 11, causing fogging in the printed image. The fact that the charge on the developing roller 12 is easily dissipated is consistent with the low residual potential in Comparative Example 1.

[0190] In Comparative Example 2, R ALL -R IN The resistance value R of the inner layer 12b was −0.09 [LogΩ], and fogging was observed. This was due to the same reason as in Comparative Example 1. IN is the total resistance R ALLSince the resistance of the developing roller 12 is higher than that of the developing roller 12, the charge applied to the surface layer 12c of the developing roller 12 does not easily move to the highly resistive inner layer 12b and is easily dissipated into the atmosphere, resulting in a decrease in the surface potential of the developing roller 12. The fact that the charge on the developing roller 12 is easily dissipated is also consistent with the low residual potential in Comparative Example 2.

[0191] In Comparative Examples 3 to 5, R ALL -R IN The values ​​of the resistance R of the inner layer 12b were -0.50 [LogΩ], -0.94 [LogΩ], and -1.37 [LogΩ], respectively, and fogging was observed in all cases. This is for the same reason as in Comparative Examples 1 and 2. That is, IN is the total resistance R ALL Since the surface potential of the developing roller 12 is higher than the surface potential of the developing roller 12, the charge applied to the surface layer 12c of the developing roller 12 does not easily move to the highly resistive inner layer 12b and is easily dissipated into the atmosphere, resulting in a decrease in the surface potential of the developing roller 12.

[0192] In Comparative Example 6, the overall resistance value R ALL The total resistance R ALL and the resistance value R of the inner layer 12b IN This is because both of these are low, and therefore the amount of conductive agent (carbon black) added is large. When a large amount of conductive agent is added, the attenuation rate of the development voltage applied to the developing roller 12 increases, and as a result, the charge in the entire developing roller 12 is more likely to dissipate via the shaft 12a, and the surface potential of the developing roller 12 decreases.

[0193] In Comparative Example 7, the overall resistance value R ALL The total resistance R ALL and the resistance value R of the inner layer 12b IN This is because both of these are high, resulting in a decrease in the voltage responsiveness of the developing roller 12. When the voltage responsiveness decreases, the surface potential of the developing roller 12 does not rise sufficiently even when a developing voltage is applied, resulting in an insufficient amount of toner on the developing roller 12 and an insufficient amount of toner adhering to the photosensitive drum 11, causing blurring.

[0194] In Comparative Example 8, R ALL -R IN The value of R was 2.47 [LogΩ], and density unevenness was observed. ALL -R IN This is because the value of is large, and therefore the content of the conductivity imparting agent (carbon black) in the surface layer 12c is low. If the content of the conductivity imparting agent is low, the conductivity imparting agent is dispersed sparsely in the surface layer 12c, causing variations in the charge on the surface of the developing roller 12, resulting in uneven density.

[0195] In Comparative Example 9, the overall resistance value R ALL The total resistance R was 6.05 [LogΩ], and fogging was observed. This was due to the same reason as in Comparative Example 6. ALL and the resistance value R of the inner layer 12b IN Since both of these are low and therefore the amount of conductive agent (carbon black) added is large, the decay rate of the development voltage applied to the development roller 12 becomes high, and as a result, the charge is easily dissipated through the shaft 12a of the entire development roller 12, and the surface potential of the development roller 12 decreases.

[0196] In Comparative Example 10, the overall resistance value R ALL The total resistance value R ALL and the resistance value R of the inner layer 12b IN This is because the voltage response of the developing roller 12 is reduced due to the high voltages.

[0197] In contrast, in Examples 1 to 10, the evaluation results for fog, blur, and unevenness in density were all good. ALL -R IN Since the value is 0.56 to 1.74 [LogΩ], the charge on the surface of the developing roller 12 is less likely to dissipate (and therefore the surface potential is less likely to decrease), and charge variation due to an insufficient amount of the conductive agent in the surface layer 12c is less likely to occur, which is thought to have suppressed the occurrence of fog and unevenness in density.

[0198] In addition, in Examples 1 to 10, the overall resistance value R ALL Since the value of the voltage is 6.15 to 8.45 [LogΩ], the charge is less likely to dissipate across the entire developing roller 12, and the voltage response of the developing roller 12 is also sufficient, which is thought to have prevented the occurrence of blurring.

[0199] Figure 18 is a graph showing the evaluation results shown in Tables 1 and 2. The vertical axis is R ALL -R IN The horizontal axis shows the total resistance R ALL In Figure 18, R ALL -R IN is 0.56~1.74[LogΩ], and the overall resistance R ALL The range of 6.15 to 8.45 [LogΩ] is a range in which blurring, fogging, and density unevenness do not occur.

[0200] On the other hand, in Figure 18, R ALL -R IN In the range R1 where the value exceeds 1.74 [LogΩ], the content of the conductivity imparting agent (carbon black) in the surface layer 12c is small, and therefore density unevenness occurs.

[0201] In addition, the overall resistance R ALL A range R2 where the voltage responsiveness of the developing roller 12 exceeds 8.45 [LogΩ] is a range where blurring occurs due to a decrease in the voltage responsiveness of the developing roller 12.

[0202] Also, R ALL -R IN In the range R3 where the value is below 0.56 [LogΩ], the charge on the surface of the developing roller 12 is likely to dissipate, and the surface potential of the developing roller 12 decreases, causing fogging.

[0203] In addition, the overall resistance R ALL In the range R4 where the resistance is below 6.15 [LogΩ], the charge of the entire developing roller 12 is likely to dissipate, and the surface potential of the developing roller 12 decreases, causing fogging.

[0204] <Consideration> Here, the relationship between the surface potential of the developing roller 12 and fogging will be further examined. Figure 19(A) is a schematic diagram showing the state of toner movement from the developing roller 12 to the photosensitive drum 11. Figure 19(B) is a schematic diagram showing the state of toner retention on the surface of the developing roller 12. In this embodiment, toner with a small amount of external additives is used, and the blow-off charge amount is 94.6 [μC / g] or less.

[0205] When the amount of external additive in the toner is small, the toner tends to have low chargeability. In this case, too, as shown in Figure 19(B), if the surface potential of the developing roller 12 is high, there is a large amount of charge on the surface layer 12c of the developing roller 12, and the toner can be held on the developing roller 12 by electrostatic force. On the other hand, if the surface potential of the developing roller 12 decreases, the ability to hold the toner on the developing roller 12 decreases.

[0206] 19(A), the surface potential of the developing roller 12 is highest at the contact point with the regulating blade 14 and decreases as it approaches the contact point N with the photosensitive drum 11. If the circumferential distance from the regulating blade 14 to the photosensitive drum 11 on the developing roller 12 is L1, the time it takes for the developing roller 12 to rotate by the distance L1 is approximately 0.12 seconds.

[0207] If the surface potential of the developing roller 12 drops while the developing roller 12 rotates from the regulating blade 14 to the photosensitive drum 11, the positively charged toner, which is supposed to be held on the surface of the developing roller 12 by electrostatic force (and not move to the photosensitive drum 11), may leave the developing roller 12 and move to the photosensitive drum 11. Such toner also adheres to the non-exposed parts of the photosensitive drum 11, causing toner to scatter over white characters and cause printing fog.

[0208] In particular, if the conveying force exerted by the photosensitive drum 11 and the developing roller 12 is increased (for example, to 1.0 [N] or more), the pressure between the photosensitive drum 11 and the developing roller 12 is high, so the amount of toner adhering to the photosensitive drum 11 increases, making fogging even more likely to occur.

[0209] Here, the relationship between the residual potential of the developing roller 12, the residual charge of the toner on the developing roller 12, and fogging will be described. First, in addition to Examples 1 to 10 and Comparative Examples 1 to 10, several types of developing rollers 12 with different compositions of the surface layer 12c (for example, the amount of carbon black added) were produced.

[0210] The developing roller 12 was mounted in the developing device 10 of the image forming apparatus 1 (LED printer "B820" manufactured by OKI Electric Industry Co., Ltd.), and the pattern (image LP) shown in Figure 13 was printed on A4-sized plain paper. The transport direction was horizontal, and the transport speed (circumferential speed) was 202.5 [mm / sec], which corresponds to a printing speed of 45 [ppm]. The charging voltage was -1050 [V], the developing voltage was -200 [V], the supply voltage was -300 [V], and the transfer voltage was +1500 [V]. The printing environment was a temperature of 28 [°C] and a relative humidity of 80 [%].

[0211] During this printing operation, the image forming apparatus 1 was stopped, the developing roller 12 was removed from the image forming apparatus 1, and the charge Q / M [μC / g] of the toner on the developing roller 12 was measured. The charge Q / M measured in this manner is referred to as the "initial Q / M."

[0212] The toner charge Q / M was measured using the measuring device 300 shown in Fig. 12. Corona discharge was performed while moving the carrier 301 at a speed of 230 mm / s, and the charge was measured 0.1 seconds after the corona discharge.

[0213] Furthermore, the hue difference ΔE, which is an index of fog, was measured for the image printed in the above printing operation (before the image forming apparatus 1 was stopped). The hue difference ΔE was measured as follows.

[0214] First, the fog toner was collected by sticking an adhesive tape ("Scotch Mending Tape" manufactured by Sumitomo 3M Limited) to the surface of the developing roller 12 and then peeling it off. This adhesive tape is referred to as the collecting adhesive tape.

[0215] This collection adhesive tape was attached to a white recording paper (Oki Electric Industry Co., Ltd. "Excellent White A4": basis weight 80 [g / m 2 ]) and a standard adhesive tape for comparison (hereinafter referred to as standard adhesive tape) was attached to another part of the same recording paper.

[0216] Then, using a spectrophotometer (Konica Minolta, Inc.'s "CM-2600d"), the hue difference ΔE (L*a*b color system chromaticity) between the sample adhesive tape and the reference adhesive tape was calculated using the following formula (1).

[0217]

number

[0218] Generally, if the hue difference ΔE is 1.5 or less, the fog evaluation result can be considered to be good.

[0219] 20(A) is a graph showing the relationship between the hue difference ΔE of the printed image measured as described above and the initial Q / M of the toner on the developing roller 12. The vertical axis represents the hue difference ΔE, and the horizontal axis represents the initial Q / M [μC / g] of the toner on the developing roller 12.

[0220] As shown in FIG. 20A, the hue difference ΔE(y) of the printed image and the initial Q / M(x) of the toner on the developing roller 12 are in a relationship that can be approximated by a curve of y=-1.386Ln(x)+5.9571, and the coefficient of determination R 2 is 0.88. The hue difference ΔE of the printed image can be made 1.5 or less (that is, fog can be suppressed) when the initial Q / M of the toner on the developing roller 12 is 30 [μC / g] or more.

[0221] 20(B) is a graph showing the relationship between the initial Q / M of the toner on the developing roller 12 and the residual potential of the developing roller 12. The vertical axis represents the initial Q / M [μC / g] of the toner on the developing roller 12, and the horizontal axis represents the residual potential [V] of the developing roller 12.

[0222] The residual potential of the developing roller 12 is a potential measured by the method described with reference to FIG. 12 after the developing roller 12 is produced and before it is incorporated into the developing device 10.

[0223] As shown in FIG. 20B, the initial Q / M(y) of the toner on the developing roller 12 and the residual potential (x) of the developing roller 12 are in a relationship that can be approximated by a curve of y=7.9155Ln(x)+17.697, and the coefficient of determination R 2 is 0.834. The initial Q / M of the toner on the developing roller 12 can be made equal to or greater than 30 μC / g when the residual potential of the developing roller 12 is equal to or greater than 4.4 −V.

[0224] 21 is a graph showing the relationship between the residual potential of the developing roller 12 and the resistance value of the developing roller 12. The vertical axis represents the residual potential [-V] of the developing roller 12, and the horizontal axis represents the resistance value [LogΩ] of the developing roller 12.

[0225] The residual potential of the developing roller 12 was measured by the method described with reference to Fig. 12. The resistance value of the developing roller 12 was measured by the method described with reference to Fig. 10. In Fig. 21, the circular plots show the measurement results for nine types of developing rollers 12 having the surface layer 12c. The square plots show the measurement results for eight types of developing rollers 12 not having the surface layer 12c.

[0226] As shown in FIG. 21, the developing roller 12 is provided with a surface layer 12c covering the inner layer 12b, and the overall resistance value R ALL [LogΩ] is the resistance value R of the inner layer 12b IN It can be seen that by making it higher than [LogΩ], the residual potential [−V] of the developing roller 12 increases, the residual charge of the toner on the developing roller 12 increases, and this leads to the suppression of fogging.

[0227] In this embodiment, the developing roller 12 has an inner layer 12b and a surface layer 12c, and the total resistance value R of the inner layer 12b and the surface layer 12c is ALL [LogΩ] and the resistance value R of the inner layer 12b IN Difference from [LogΩ] R ALL -R inis 0.56 to 1.7 4 Since it is [LogΩ], the decrease in the surface potential of the developing roller 12 is suppressed, and therefore printing defects such as fogging can be reduced.

[0228] Here, the Si content in the toner is set to a range of 0.98 to 1.28 [wt %]. If the amount of external additive in the toner is greater than 1.28 [wt %], the pressure applied to the toner between the photosensitive drum 11 and the developing roller 12 causes the external additive to fall off from the toner base particles, resulting in poor charging of the toner.

[0229] Furthermore, if the amount of external additives in the toner is less than 0.98% by weight, most of the surface of the toner particles is exposed and not covered with the external additives, making it easier for the toner particles to adhere to each other. As a result, the toner particles are less likely to separate from the surface of the developing roller 12, and less toner moves to the photosensitive drum 11, resulting in smearing.

[0230] In the test printing using the developing rollers 12 of Examples 1 to 10 described above, the Si content of the toner was set to 0.98% by weight, and the evaluation results for smearing were good in all cases. The lower the Si content of the toner, the more likely smearing occurs, and the higher the Si content, the less likely smearing occurs. Therefore, it can be seen that smearing does not occur at least when the Si content is in the range of 0.98 to 1.28% by weight.

[0231] Furthermore, in the developing rollers 12 of Examples 1 to 10 described above, the weight ratio of the acrylic resin to the urethane resin in the surface layer 12c was 50:50. In other words, the weight ratio of the acrylic resin to the total of the acrylic resin and the urethane resin was 50%. However, it has been confirmed that similar results to those described above can be obtained if the weight ratio of the acrylic resin to the total of the acrylic resin and the urethane resin is in the range of 40% to 60%.

[0232] Furthermore, when the developing roller 12 of Examples 1 to 10 described above was used, the conveying force between the photosensitive drum 11 and the developing roller 12 measured by the method shown in Figures 8(A) and (B) was 1.0 [N] or more. By making the conveying force 1.0 [N] or more, the pressure between the photosensitive drum 11 and the developing roller 12 can be made sufficiently high, and white voids can be suppressed when a solid image is printed.

[0233] If the conveying force is too large, the temperature may rise during continuous printing due to friction between the photosensitive drum 11 and the developing roller 12, which may result in print defects such as blurring. Therefore, it is desirable that the conveying force be 1.4 [N] or less.

[0234] <Effects of the embodiment> As described above, in the developing device 10 of this embodiment, the developing roller 12 has the inner layer 12b and the surface layer 12c, and the total resistance value R ALL [LogΩ] and the resistance value R of the inner layer 12b IN Difference from [LogΩ] R ALL -R in Since the value of the surface potential of the developing roller 12 is 0.56 [LogΩ] or more, the decrease in the surface potential of the developing roller 12 can be suppressed, thereby reducing the occurrence of fogging.

[0235] In addition, the overall resistance value R of the developing roller 12 ALL [LogΩ] and the resistance value R of the inner layer 12b IN Difference from [LogΩ] R ALL -R in is 1.7 4 Since the value is [LogΩ] or less, it is possible to suppress uneven density that occurs when the amount of the conductivity-imparting agent is too small (that is, occurs due to uneven distribution of the conductivity-imparting agent).

[0236] In addition, the overall resistance value R of the developing roller 12 ALL is 6.15 [LogΩ] or more, the decrease in surface potential due to dissipation of charge over the entire developing roller 12 is suppressed, thereby reducing the occurrence of fogging.

[0237] In addition, the overall resistance value R of the developing roller 12 ALL Since the voltage responsiveness of the developing roller 12 is 8.45 [LogΩ] or less, the occurrence of blurring due to a decrease in the voltage responsiveness of the developing roller 12 can be suppressed.

[0238] Furthermore, since the surface layer 12c contains an acrylic resin and a urethane resin, and the weight ratio of the acrylic resin to the total of these is 40% or more and 60% or less, a decrease in the surface potential of the developing roller 12 can be suppressed.

[0239] Furthermore, by setting the Si content of the toner, as measured by elemental analysis using energy dispersive X-ray spectroscopy, to 0.98 to 1.28 [wt %], it becomes difficult for external additives containing Si to separate from the toner base particles, thereby reducing printing defects due to poor toner charging.

[0240] The present disclosure can be used in image forming apparatuses such as printers, copiers, facsimile machines, and MFPs (Multi Function Peripherals) that form images on media. [Explanation of symbols]

[0241] 1 image forming apparatus, 10 developing device, 11 photosensitive drum (image carrier), 12 developing roller (developer carrier), 12a shaft, 12b inner layer, 12c surface layer, 13 supply roller (supply member), 14 regulating blade (layer regulating member), 15 charging roller (charging member), 16 toner cartridge (developer container), 19 transfer roller (transfer member), 30 exposure head (exposure device), 40 medium supply unit, 50 fixing device, 60 medium discharge unit, 80 measuring jig, 90 flat blade, 100 main control unit, 300 measuring device, R ALL Resistance (total resistance), R ALL -R IN Difference between the total resistance and the inner layer resistance (resistance ratio), R IN Resistance value (inner layer resistance value).

Claims

1. an image carrier that carries an electrostatic latent image; a developer carrier that contacts the image carrier and develops the electrostatic latent image with a developer; Equipped with The developer carrier is A shaft body, an elastic layer covering the shaft body; a surface layer that covers the elastic layer and contacts the image carrier; and The surface layer covers the entire periphery of the elastic layer, so that the elastic layer does not come into contact with the image carrier, the developer has a Si content of 0.98 to 1.28 [wt %] as measured by elemental analysis using energy dispersive X-ray analysis, The total resistance value R of the surface layer and the elastic layer ＡＬＬ [LogΩ] is equal to or greater than 6.15 [LogΩ] and equal to or less than 8.45 [LogΩ], The overall resistance value R ＡＬＬ [LogΩ] and the resistance value R of the elastic layer ＩＮ Difference from [LogΩ] R ＡＬＬ -R ＩＮ is equal to or greater than 0.56 [Log Ω] and equal to or less than 1.74 [Log Ω] A developing device characterized by:

2. The conveying force exerted by the image carrier and the developer carrier is 1.0 [N] or more.

2. The developing device according to claim 1.

3. the surface layer contains an acrylic resin and a urethane resin, The weight ratio of the acrylic resin to the total of the acrylic resin and the urethane resin is 40% or more and 60% or less.

3. The developing device according to claim 1, wherein the developing device is a developing unit.

4. The surface roughness Rz of the developer carrier is 2.0 μm or more and 7.0 μm or less.

4. The developing device according to claim 1, wherein the developing device is a developing unit.

5. A developing device according to any one of claims 1 to 4; a fixing device that fixes the developer image developed with the developer onto a medium; An image forming apparatus comprising:

Images