JP2015141320A - Developing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing apparatus configured to prevent density of a print image from being reduced after long-time use, even when developer containing titanium oxide is used, and an image forming apparatus.SOLUTION: A developing apparatus 10 includes: a developing roller 2 as a developer carrier; a supply roller 3 as a developer supply member; and a developing blade 5 as a developer layer forming member. The developing roller 2 includes an elastic layer 22, and a surface layer 23 covering the elastic layer 22. The supply roller 3 supplies developer to the developing roller 2. The developing blade 5 forms a developer layer on a surface of the developing roller 2. The developer contains titanium oxide. A dynamic friction coefficient μ of the developing roller 2 satisfies 0.6≤μ≤1.2.

Description

  The present invention relates to a developing device including a developer carrying member and an image forming apparatus including the developing device.

  In general, a developing device used in an image forming apparatus supplies a developing roller (developer carrier) that develops an electrostatic latent image formed on the surface of a photosensitive drum with toner (developer) and toner to the developing roller. And a developing blade for forming a thin toner layer on the surface of the developing roller.

  The developing roller has a conductive shaft and an elastic layer provided on the outer peripheral surface of the shaft. The elastic layer is made of a rubber material such as urethane rubber, NBR (nitrile butadiene rubber), EPDM (ethylene propylene diene rubber) or silicone rubber, and an electronic conductive agent (for example, carbon, conductive filler, etc.) or an ionic conductive agent is dispersed. Has been.

  The surface of the elastic layer is treated with a charge imparting agent or a surface modifier to improve the chargeability of the toner and prevent chemical reaction with the photoreceptor drum (contamination of the photoreceptor drum). Thus, a surface layer is formed.

  Since the developing roller is pressed against the photosensitive drum or the like, the elastic layer of the developing roller is formed of a material that does not cause nip marks even when subjected to pressure for a long period of time (that is, a material having a small compression set). An example of such a material is urethane rubber having high ion conductivity. The surface layer is formed by surface-treating an elastic layer formed of urethane rubber with a urethane solution (see, for example, Patent Document 1).

JP 2010-152024 A (see paragraph 0016)

  However, when the developing roller configured as described above is used, when a toner containing titanium oxide is used, the toner adhesion amount on the surface of the developing roller decreases with the passage of time, and the printed image (toner image) is reduced. There is a problem that the density is lowered and blurring occurs.

  The present invention has been made to solve the above-described problems, and even when a toner containing titanium oxide is used, it is possible to suppress a decrease in density of printed images and generation of blurring after long-term use. An object of the present invention is to provide a developing device and an image forming apparatus.

  In order to solve the above problems, a developing device according to the present invention includes a developer carrier having an elastic layer and a surface layer covering the elastic layer, a developer supply member for supplying the developer to the developer carrier, A developer layer forming member for forming a developer layer on the surface of the developer carrier, the developer contains titanium oxide, and the dynamic friction coefficient μ of the surface of the developer carrier is 0.6 ≦ μ ≦ 1 .2 in the range.

  The developing device according to the present invention also includes a developer carrier having an elastic layer and a surface layer covering the elastic layer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. And a developer layer forming member for forming a developer layer, wherein the developer contains titanium oxide, and the dynamic friction coefficient μ and 10-point average roughness Rz of the surface of the developer carrier are μ ≦ 5.7−. It is characterized by satisfying 0.6Rz.

  The developing device according to the present invention also includes a developer carrier having an elastic layer and a surface layer covering the elastic layer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. And a developer layer forming member for forming a developer layer, wherein the developer contains titanium oxide, and the dynamic friction coefficient μ and 10-point average roughness Rz of the surface of the developer carrier are μ ≦ −1.8 + 0. .6Rz is satisfied.

  The developing device according to the present invention also includes a developer carrier having an elastic layer and a surface layer covering the elastic layer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. And a developer layer forming member for forming a developer layer, wherein the developer contains titanium oxide, and the dynamic friction coefficient μ and 10-point average roughness Rz of the surface of the developer carrier are μ ≧ 2.1−. 0.3 Rz is satisfied.

  The developing device according to the present invention also includes a developer carrier having an elastic layer and a surface layer covering the elastic layer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. And a developer layer forming member for forming a developer layer, the developer contains titanium oxide, and the dynamic friction coefficient μ and the 10-point average roughness Rz of the surface of the developer carrier are μ ≧ 3.3. 0.6Rz and μ ≧ −1.2 + 0.6Rz are satisfied.

  The developing device according to the present invention also includes a developer carrier having an elastic layer and a surface layer covering the elastic layer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. And a developer layer forming member for forming a developer layer, wherein the developer contains titanium oxide, and the dynamic friction coefficient μ and 10-point average roughness Rz of the surface of the developer carrier are 2.10-0. 30 Rz ≦ μ ≦ −1.80 + 0.60 Rz (4.33 <Rz <6.00), 0.30 <μ ≦ −1.80 + 0.60 Rz (6.00 ≦ Rz ≦ 6.25), and 0.30 ≦ μ ≦ 5.70-0.60 Rz (6.25 <Rz ≦ 9.00) is satisfied.

  An image forming apparatus according to the present invention includes the above developing device.

  According to the present invention, even when a developer containing titanium oxide is used, it is possible to suppress the decrease in the density of printed images and the occurrence of blurring after long-term use.

1 is a diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the developing roller in 1st Embodiment. It is sectional drawing which shows the structure of the supply roller in 1st Embodiment. It is a front view which shows the structure of the supply roller in 1st Embodiment. It is a figure which shows the contact part of the developing blade and developing roller in 1st Embodiment. 2 is a block diagram illustrating a control system of the image forming apparatus according to the first embodiment. FIG. It is a figure for demonstrating the formation process of the surface layer of a developing roller. It is a figure which shows the measuring method of the dynamic friction coefficient of a developing roller. It is the front view (A) and side view (B) which show the measuring method of the whole resistance of a developing roller. It is a figure which shows the printing pattern used for experiment. It is a figure which shows the measuring method of the toner adhesion amount on the surface of a developing roller. 6 is a diagram illustrating evaluation results of a toner adhesion amount reduction rate, a print density reduction rate, blurring, and fogging with respect to a dynamic friction coefficient of a developing roller according to Embodiment 1. FIG. FIG. 4 is a graph showing a decrease in toner adhesion amount. It is a figure which shows pre-processing in order to observe the filming of the surface of a developing roller. It is a figure which shows the state of the filming observed with the laser microscope. It is a figure which shows the printing pattern used for evaluation of the density fall rate of a printing image. It is a figure for demonstrating the density | concentration measurement position in the printing pattern of FIG. It is a figure which shows generation | occurrence | production of the blur in a printed image. FIG. 6 is a diagram illustrating a collecting position of fog toner on the surface of the photosensitive drum. It is a figure which shows the measuring method of fogging. FIG. 10 is a diagram illustrating evaluation results of a toner adhesion amount reduction rate, a print density reduction rate, blurring, fogging, and dirt with respect to the 10-point average roughness of the developing roller according to the second embodiment. FIG. 4 is a graph showing a decrease in toner adhesion amount. It is a figure which shows the halftone image used for evaluation of dirt. FIG. 24 is a diagram showing a state where the halftone image of FIG. 23 is smudged. It is a figure which shows the evaluation result of a stain | pollution | contamination with respect to the dynamic friction coefficient of a developing roller, and 10 point average roughness. It is a figure which shows the evaluation result of the density fall of a printed image with respect to the dynamic friction coefficient of a developing roller, and 10 point average roughness. It is a figure which shows the evaluation result of a fog with respect to the dynamic friction coefficient and 10-point average roughness of a developing roller. It is a figure which shows the evaluation result of a blurring with respect to the dynamic friction coefficient of a developing roller, and 10 point average roughness. It is a graph which shows the optimal range of the dynamic friction coefficient of a developing roller, and 10-point average roughness.

First embodiment.
<Configuration of image forming apparatus>
FIG. 1 is a cross-sectional view showing a basic configuration of an image forming apparatus 100 according to the first embodiment of the present invention. The image forming apparatus 100 forms an image using electrophotography. Although a monochrome printer that forms a single color image will be described here, a color printer that forms a color image may be used.

  The image forming apparatus 100 includes a medium storage unit 13, a medium transport unit 14, a developing device (also referred to as an image forming unit or an image drum unit) 10, a fixing unit 15, and a medium discharge unit 16.

  The medium storage unit 13 includes a medium cassette 13a that stores and stores paper P (medium), and a paper feed roller 13b that feeds the paper P from the medium cassette 13a one by one to the transport path 18a.

  The medium transport unit 14 transports the guide 14a that guides the paper P sent out from the medium storage unit 13 and the paper P transported along the guide 14a along the transport path 18b and feeds it into the developing device 10. A conveyance roller 14b.

  The developing device 10 includes a photosensitive drum 1 as a latent image carrier, a charging roller 4 as a charging member, a developing roller 2 as a developer carrier, a supply roller 3 as a developer supply member, and a developer. A developing blade 5 as a layer forming member (or a developer regulating member), a cleaning blade 6 as a cleaning member, a waste toner conveying portion 7, a toner cartridge 8 as a developer containing portion, and a seal member 9 are provided. ing.

  The photosensitive drum 1 has a conductive cylindrical member and a photosensitive layer provided on the surface (outer peripheral surface) of the cylindrical member. The cylindrical member is made of, for example, aluminum and has a thickness of 0.75 mm and an outer diameter of 30 mm. The photosensitive layer is formed, for example, by laminating a charge generation layer having a thickness of 0.5 μm and a charge transport layer having a thickness of 18 μm.

  Examples of the charge generation material used in the charge generation layer include selenium and its alloys, arsenic selenide compounds, cadmium sulfide, zinc oxide, and other inorganic photoconductive materials, phthalocyanines, azo dyes, quinacridones, polycyclic quinones, pyrylium salts, Various organic pigments and dyes such as thiapyrylium salt, indigo, thioindigo, anthanthrone, pyrantrone, and cyanine are desirable.

  Examples of the charge transport material used in the charge transport layer include heterocyclic compounds such as carbazole, indole, imidazole, oxazole, pyrazole, oxadiazole, pyrazoline, thiadiazole, aniline derivatives, hydrazone compounds, aromatic amine derivatives, or stilbene derivatives. Or an electron donating substance such as a polymer having a group composed of these compounds in the main chain or side chain.

  The charging roller 4 is provided in contact with the surface of the photosensitive drum 1 and rotates following the photosensitive drum 1. The charging roller 4 has a conductive shaft such as SUS (stainless steel) and a conductive elastic body (for example, epichlorohydrin) provided on the surface of the shaft. The charging roller 4 is charged with a charging voltage by a charging roller power source 46 described later, and uniformly charges the surface of the photosensitive drum 1.

  The developing roller 2 is provided so as to be in contact with the surface of the photosensitive drum 1, and in the direction opposite to the rotation direction of the photosensitive drum 1 (that is, the moving direction of the surface at the contact portion with the photosensitive drum 1 is the same direction). To rotate). The developing roller 2 holds toner (developer) on the surface thereof, attaches the toner to the surface of the photosensitive drum 1, and develops the electrostatic latent image.

  FIG. 2 is a cross-sectional view of the developing roller 2 cut along a cross section orthogonal to the axial direction. The developing roller 2 has a conductive shaft (core metal) 21, an elastic layer 22 provided on the surface of the shaft 21, and a surface layer 23 that covers the elastic layer 22.

  The shaft 21 is made of a metal such as SUS. The elastic layer 22 is made of a polyether-based urethane resin, and is added with carbon black which is an electronic conductive agent, and insulating inorganic fine particles such as calcium carbonate and silica. As will be described later, the surface layer 23 is formed by treating the surface of the elastic layer 22 with a urethane solution or an isocyanate solution.

  The supply roller 3 is provided so as to be in contact with the surface of the developing roller 2 and is in the same direction as the rotation direction of the developing roller 2 (that is, the moving direction of the surface at the contact portion with the developing roller 2 is opposite). )Rotate. The supply roller 3 holds toner (developer) on its surface and supplies it to the surface of the development roller 2.

  FIG. 3 is a cross-sectional view of the supply roller 3 cut along a cross section orthogonal to the axial direction. FIG. 4 is a front view of the supply roller 3. As shown in FIG. 3, the supply roller 3 has a conductive shaft (core metal) 31 and an elastic layer 32 provided on the surface of the shaft 31. The shaft 31 is obtained by performing electroless nickel plating on SUM (free-cutting steel). The elastic layer 32 is a foam layer made of conductive silicone rubber.

  As shown in FIG. 4, the elastic layer 32 of the supply roller 3 has a crown shape in which the outer diameter of the central portion in the axial direction is larger than the outer diameters of both ends. The ratio (D2 / D1: crown ratio) of the outer diameter D2 at both ends in the axial direction to the outer diameter D1 at the central portion in the axial direction of the elastic layer 32 of the supply roller 3 is desirably 0.943 to 0.987. For example, when the outer diameter D1 at the central portion in the axial direction of the elastic layer 32 of the supply roller 3 is 15.7 mm, the outer diameter D2 at both end portions in the axial direction is preferably 14.8 to 15.5 mm.

  As for the average cell diameter (pore diameter) of the foam which comprises the elastic layer 32, 200 micrometers-500 micrometers are desirable, for example. The cell diameter of the foam can be controlled, for example, by adjusting the amount and type of the foaming agent, the vulcanization time, and the temperature. For example, when the cell diameter is increased, there are methods such as increasing the amount of the foaming agent, extending the vulcanization time, and increasing the vulcanization temperature. The density of the foam is determined by the average cell diameter and the expansion ratio. As the foaming agent, inorganic foaming agents such as sodium bicarbonate and organic foaming agents such as azodicarbonamide are generally used. In addition, carbon black is added to the foaming agent in order to impart semiconductivity.

  When forming the supply roller 3, the shaft 31 washed with an organic solvent or the like to remove the oil and the conductive silicone rubber foam are integrated with an extrusion molding machine, and then passed through an infrared oven or the like to obtain the foam. Is foamed and cured. Next, a secondary vulcanization treatment is performed at about 180 to 225 ° C. for about 5 to 10 hours. Then, a desired crown shape is obtained by polishing the surface with a polishing machine.

  FIG. 5 is an enlarged schematic view showing a contact portion between the developing blade 5 and the developing roller 2. In FIG. 5, for convenience, the surface of the developing roller 2 is shown in a planar shape. The developing blade 5 is a plate-like member that is long in the axial direction of the developing roller 2, and is provided so as to come into contact with the surface of the developing roller 2. The developing blade 5 has a shape bent in an L shape, and the bent portion 5 a is in contact with the surface of the developing roller 2.

  The developing blade 5 is made of, for example, SUS having a thickness of 0.08 mm, and the curvature radius R of the bent portion 5a is about 0.275 mm. The developing blade 5 is pressed against the developing roller 2 with a linear pressure of 20 gf / cm per unit length in the axial direction of the developing roller 2. This linear pressure regulates the toner thickness on the surface of the developing roller 2 to form a toner thin layer (developer layer).

  Returning to FIG. 1, a region surrounded by the developing roller 2, the supply roller 3, and the developing blade 5 is a toner hopper (developer hopper) that holds toner.

  The cleaning blade 6 is a plate-like member that is long in the axial direction of the photosensitive drum 1, and is provided so as to contact the surface of the photosensitive drum 1. The cleaning blade 6 scrapes off and removes transfer residual toner remaining on the surface of the photosensitive drum 1.

  The waste toner transport unit 7 is a space provided below the cleaning blade 6. The toner (waste toner) scraped off by the cleaning blade 6 falls on the waste toner transport unit 7. The waste toner transport unit 7 is provided with a transport mechanism (such as a transport screw) and transports the waste toner to the collection container.

  The seal member 9 is a film-like member and is provided so as to come into contact with the surface of the developing roller 2. The seal member 9 prevents the toner present on the supply roller 3 side (toner hopper side) of the developing roller 2 from leaking to the photosensitive drum 1 side in the developing device 10.

  The toner cartridge 8 is detachably attached to the developing device 10 and contains unused toner. The toner cartridge 8 supplies toner to the above-described toner hopper through the toner supply port 8a.

  On the upper side of the photosensitive drum 1, an LED head 11 as an exposure device is disposed oppositely. The LED head 11 includes a lens array in which a plurality of LEDs (light emitting diodes) are arranged in the axial direction of the photosensitive drum 1, and a lens group that focuses light emitted from each LED element on the surface of the photosensitive drum 1. I have. The LED head 11 irradiates the surface of the photosensitive drum 1 with light according to the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1.

  A transfer roller 12 as a transfer member is disposed below the photosensitive drum 1 so as to face the photosensitive drum 1. The transfer roller 12 is disposed so as to form a nip portion with the photosensitive drum 1. The paper P conveyed by the medium conveyance unit 14 is fed into the nip portion between the transfer roller 12 and the photosensitive drum 1. The transfer roller 12 transfers the toner image (developer image) formed on the surface of the photosensitive drum 1 onto the paper P when the paper P passes through the nip portion.

  The fixing unit 15 is disposed on the downstream side of the developing device 10 in the conveyance direction of the paper P. The fixing unit 15 includes a heat roller 15a and a pressure roller 15b. The heat roller 15a has a built-in heater, and the pressure roller 15b is pressed against the heat roller 15a. Between the heat roller 15a and the pressure roller 15b, the paper P on which the toner image has been transferred is heated and pressed to fix the toner image on the paper P.

  The medium discharge unit 16 includes a guide 16a that guides the paper P on which the toner image is fixed by the fixing unit 15 along the conveyance path 18c, and a discharge roller 16b that discharges the paper P from the discharge port 17. . In addition, a stacker unit 19 on which the paper P discharged from the discharge port 17 by the discharge roller 16b is placed is provided on the upper portion of the image forming apparatus 100.

  The toner used in the image forming apparatus 100 is a toner manufactured by an emulsion polymerization method and containing titanium oxide as an external additive. Here, toner base particles (base toner) are formed by mixing and aggregating a styrene-acrylic copolymer resin, a colorant, and wax (paraffin wax), and silica fine particles, which are external additives, are formed on the toner base particles. A mixture of powder and titanium oxide fine powder is used. The amount of titanium oxide is 0.2 to 0.5% by weight with respect to 100% by weight of toner base particles. Here, the circularity of the toner is 0.96, and the average particle size is about 7.5 μm.

<Control system of image forming apparatus>
FIG. 6 is a block diagram illustrating a control system of the image forming apparatus 100. The image forming apparatus 100 includes a control unit 40, an I / F (interface) control unit 41, a reception memory 42, an image data editing memory 43, an operation unit 44, a sensor group 45, and a charging roller power supply 46. , Developing roller power supply 47, supply roller power supply 48, developing blade power supply 49, transfer roller power supply 50, head controller 51, fixing controller 52, drum driving controller 53, fixing driving control. A unit 54, a conveyance control unit 55, a drum drive motor 56, a fixing motor 57, and a conveyance motor 58.

  The controller 40 includes a microprocessor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output port, a timer, and the like. The control unit 40 receives print data and control commands from a host device such as a personal computer via the I / F control unit 41 and executes the printing operation of the image forming apparatus 100.

  The reception memory 42 temporarily stores print data input from the host device via the I / F control unit 41. The image data editing memory 43 receives print data stored in the reception memory 42 and records image data formed by editing the print data, that is, image data.

  The operation unit 44 includes a display unit (for example, an LED) for displaying the state of the image forming apparatus 100 and an operation unit (for example, a switch) for an operator to input an instruction. The sensor group 45 includes various sensors for monitoring the operation state of the image forming apparatus 100, such as a paper position sensor and a temperature / humidity sensor.

  The charging roller power supply 46 applies a charging voltage for uniformly charging the surface of the photosensitive drum 1 to the charging roller 4. The developing roller power supply 47 applies a developing voltage to the developing roller 2 for developing the electrostatic latent image on the surface of the photosensitive drum 1.

  The supply roller power supply 48 applies a supply voltage for supplying toner to the development roller 2 to the supply roller 3. The developing blade power supply 49 applies a blade voltage for forming a thin toner layer on the developing roller 2 to the developing blade 5. The transfer roller power supply 50 applies a transfer voltage for transferring the toner image on the photosensitive drum 1 to the paper P to the transfer roller 12.

  The head controller 51 controls the light emission of the LED head 11 based on the image data recorded in the image data editing memory 43.

  The fixing control unit (fixing control unit) 52 includes a temperature adjustment circuit, and supplies a predetermined current to the heater of the heat roller 15 a based on an output signal of a temperature sensor (for example, a thermistor) provided in the fixing unit 15.

  The drum drive control unit 53 controls the rotation of a drum drive motor 56 for rotating the photosensitive drum 1, the developing roller 2, the supply roller 3, and the like.

  The fixing drive controller 54 controls the rotation of the fixing motor 57 for rotating the heat roller 15 a of the fixing unit 15. Note that the discharge roller 16 b of the medium discharge unit 16 also rotates by the rotation transmission from the fixing motor 57.

  The transport controller 55 controls the rotation of the transport motor 58 for rotating the paper feed roller 13b and the transport roller 14b that transport the paper P.

<Basic operation of image forming apparatus>
The basic operation of the image forming apparatus 100 configured as described above is as follows. First, when the control unit 40 of the image forming apparatus 100 receives a print command and print data from the host device via the I / F control unit 41, the control unit 40 starts an image forming (printing) operation. The control unit 40 temporarily records print data in the reception memory 42, edits the recorded print data, generates image data, and records the image data in the image data editing memory 43.

  The control unit 40 also drives the conveyance motor 58 by the conveyance control unit 55. As a result, the paper feed roller 13b rotates and feeds the paper P stored in the medium cassette 13a one by one to the transport path 18a. Further, the transport roller 14b rotates to transport the paper P to the developing device 10 along the transport path 18b.

  The control unit 40 also forms a toner image in the developing device 10. That is, the control unit 40 applies a charging roller power supply 46, a developing roller power supply 47, a supply roller power supply 48, and a developing blade power supply 49 to the charging roller 4, the developing roller 2, the supply roller 3 and the developing blade 5. A charging voltage, a developing voltage, a supply voltage, and a blade voltage are applied.

  The control unit 40 also rotates the drum drive motor 56 by the drum drive control unit 53 to rotate the photosensitive drum 1. As the photosensitive drum 1 rotates, the charging roller 4, the developing roller 2, and the supply roller 3 also rotate. The charging roller 4 uniformly charges the surface of the photosensitive drum 1 with the applied charging voltage.

  The control unit 40 sends the image data recorded in the image data editing memory 43 to the head control unit 51. The head controller 51 causes the LED head 11 to emit light according to the image data, exposes the surface of the photosensitive drum 1, and forms an electrostatic latent image.

  The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed with toner attached to the developing roller 2, and a toner image is formed on the surface of the photosensitive drum 1. At the timing when the toner image on the surface of the photosensitive drum 1 reaches the nip portion between the photosensitive drum 1 and the transfer roller 12, the leading edge of the paper P reaches the nip portion. The controller 40 applies a transfer voltage from the transfer roller power source 50 to the transfer roller 12, and the toner image is transferred from the photosensitive drum 1 to the paper P. The toner that has not been transferred to the paper P is scraped off by the cleaning blade 6.

  The sheet P1 on which the toner image has been transferred is further conveyed by the rotation of the photosensitive drum 1 and the transfer roller 12, and reaches the fixing unit 15.

  In the fixing unit 15, the heat roller 15 a and the pressure roller 15 b have already been rotated, and the surface temperature of the heat roller 15 a has reached a predetermined fixing temperature by the fixing controller 52. The paper P is heated and pressed by the heat roller 15a and the pressure roller 15b, and the toner image is fixed on the paper P.

  The paper P on which the toner image has been fixed is transported along the transport path 18c, and is discharged to the outside from the discharge port 17 by the discharge roller 16b. The discharged paper P is stacked on the stacker unit 19. This completes image formation.

<Manufacturing method and characteristics of developing roller>
Next, a method for manufacturing the developing roller 2 will be described.
When the developing roller 2 is manufactured, for example, carbon black (electronic conductive agent) 2.5 to 8% by weight, calcium carbonate (insulating inorganic fine particles) 10 to 40% by weight, and silica fine particles 10 to 40% by weight. Is mixed with a polyether-based urethane resin and kneaded. The composition thus obtained is put into an extrusion molding machine and integrated with a shaft 21 made of SUS. Thereby, the roller body 2a in which the shaft 21 and the elastic layer 22 are integrated is created.

  Next, as schematically shown in FIG. 7, the roller body 2 a in which the shaft 21 and the elastic layer 22 are integrated is dipped into a treatment liquid 102 made of a urethane solution or an isocyanate solution, and the treatment liquid 102 is placed on the elastic layer 22. The surface layer 23 is formed by dipping. The processing liquid 102 is stored in, for example, a vertically long container 101 whose upper side is open, and the roller body 2a is inserted into the container 101 in the axial direction from above.

  In the present embodiment, a silicon-based or fluorine-based additive and carbon black are added to the processing liquid 102 in order to adjust the dynamic friction coefficient μ of the surface of the developing roller 2. The addition amount of the silicon-based or fluorine-based additive is adjusted within a range of, for example, 0 to 39% by weight with respect to 100% by weight of the polyether-based urethane resin constituting the elastic layer 22. Carbon black is further added. The amount of carbon black added is adjusted within a range of, for example, 5 to 30% by weight based on 100% by weight of the polyether-based urethane resin. If the dynamic friction coefficient μ can be adjusted to a desired value, only a silicon-based or fluorine-based additive and carbon black may be used.

  After the surface layer 23 is formed on the surface of the elastic layer 22, the roller body 2a is taken out from the treatment liquid 102 and dried. Thereafter, the surface of the developing roller 2 is polished to obtain a target dynamic friction coefficient μ and a 10-point average roughness Rz. Polishing is performed using, for example, polishing paper.

  Here, the outer diameter of the rubber part (the elastic layer 22 and the surface layer 23) of the developing roller 2 is 19.6 mm. The outer diameter of the shaft 21 of the developing roller 2 is 12 mm. The axial length of the shaft 21 is 348 mm.

  The dynamic friction coefficient μ of the developing roller 2 in the present embodiment is 0.6 to 1.2. The reason will be described later. Further, the 10-point average roughness Rz of the developing roller 2 is desirably 3.5 μm to 9.0 μm.

  FIG. 8 is a diagram illustrating a method for measuring the dynamic friction coefficient of the developing roller 2. The tension gauge 61 (“Digital Force Gauge ZP-50N” manufactured by Imada Co., Ltd.) is fixed to a slider 62 (“Small Linear Motion Series SPL42” manufactured by Oriental Motor Co., Ltd.) that moves in the direction of the arrow. The developing roller 2 is rotatably held at a position away from the slider 62 in the horizontal direction.

  The belt 63 is in contact with the outer peripheral surface of the developing roller 2 within an angle θ (90 degrees) with respect to the central axis of the developing roller 2. The belt 63 has a width of 50 mm and a length of 200 mm. One end of the belt 63 is fixed to the tension gauge 61 and the other end is connected to the weight 64. In this state, the slider 62 is slid in the direction of the arrow in the figure for 5 seconds at a speed of 1.2 mm / sec. At this time, the load K measured by the tension gauge 61 is read to calculate the dynamic friction coefficient μ.

As the belt 63, an excellent white paper (model name PPR-CA4NA, basis weight 80 g / cm ² ) manufactured by Oki Data Co., Ltd. is used, assuming that there are few individual differences in the surface state. As the weight 64, three kinds of weights having a weight W of 5 g, 10 g, and 15 g are used. The dynamic friction coefficient μ is calculated from the following Euler belt formula.
μ = 1 / θ × ln (K / W)

  Here, the average of the dynamic friction coefficient μ calculated using three types (5 g, 10 g, and 15 g) of the weight 64 is taken.

  The 10-point average roughness Rz of the developing roller 2 is measured using a surface roughness measuring instrument (“Surfcoder SEF3500” manufactured by Kosaka Laboratory Ltd.) in accordance with JIS B0601-1994. The surface roughness measuring device uses a stylus (measuring needle) with a radius of 2 μm, a stylus pressure of 0.7 mN, and a stylus feed speed of 0.1 mm / sec. The stylus is set to move along the circumference.

  The Asker C hardness of the elastic layer 22 is preferably about 70 to 82 degrees. The Asker C hardness of the elastic layer 22 can be measured by, for example, a hardness meter “Asker rubber hardness meter C type” manufactured by Kobunshi Keiki Co., Ltd. The Asker C hardness is measured by holding the developing roller 2 so that the axial direction is horizontal and pressing an indenter of a measuring instrument against the outer peripheral surface of the developing roller 2.

  The overall resistance of the developing roller 2 is desirably about 3 to 7 logΩ, and here it is 5 logΩ. FIG. 9 is a front view (A) and a side view (B) showing a method for measuring the overall resistance of the developing roller 2. The measurement of the developing roller 2 is performed by bringing the conductive cylinder 27 into parallel contact with the developing roller 2 and pressing it with an equal load (500 gf) in the axial direction of the developing roller 2. The conductive cylinder 27 is rotated at a constant rotation speed (60 rpm), a DC voltage of −100 V is applied to the shaft 21 of the developing roller 2, and the resistance value is measured by the measuring device 26. The measurement is performed at 100 points per rotation of the developing roller 2, and the average value is taken.

<Experimental method and experimental results>
An experiment was conducted on the relationship between the dynamic friction coefficient μ of the developing roller 2, the rate of decrease in the toner adhesion amount of the developing roller 2, the rate of decrease in the density of the printed image (toner image), and the occurrence of blurring and fogging.

  Here, when the developing roller 2 is manufactured, the presence or absence and addition amount of a silicon-based or fluorine-based additive and carbon black added to the processing liquid 102 (FIG. 7) and the polishing conditions (polishing speed, polishing) By adjusting the paper roughness, polishing push-in amount, etc., polishing rollers (No. 1 to No. 6) having a 10-point average roughness Rz constant (5 μm) and 6 dynamic friction coefficients μ were prepared. . The composition, manufacturing method and dimensions of the developing roller 2 are as described above.

  No. 1-No. 6 has a dynamic friction coefficient μ of 1.8, 1.5, 1.2, 0.9, 0.6, and 0.3 in this order. In addition, No. No silicon-based or fluorine-based additive is added to the processing liquid for the surface layer 23 when the first developing roller 2 is produced. That is, no. One developing roller 2 has the same configuration as a general developing roller 2.

  No. 1-No. The developing device 10 including each of the developing rollers 2 is mounted on the image forming apparatus 100 ("MICROLINE910PS" manufactured by Oki Data Co., Ltd.), and after printing 40000 sheets, the toner adhesion amount on the developing roller 2 is measured. did.

  The toner used for printing was prepared by mixing a styrene acrylic copolymer resin, a colorant of 2.5 to 7.5% by weight, and a paraffin wax of 2.5 to 7.5% by weight by an emulsion polymerization method. Particles are prepared, and 0.5 to 5% by weight of silica fine powder, 0.5% by weight of titanium oxide fine powder and 0.1 to 0.3% by weight of melamine are added to a mixer with respect to 100% by weight of the toner base particles. And mixed.

  The printing environment was a temperature of 22 ° C. and a humidity of 50%. Further, a developing voltage of −200 V is applied to the developing roller 2, a supply voltage of −320 V is applied to the supply roller 3, a charging voltage of −1100 V is applied to the charging roller 4, and a − A blade voltage of 320 V was applied.

Further, as the paper P, A4 size plain paper (basis weight 68 to 75 g / cm ² ) was used, and single-sided printing was performed by lateral feeding. The printing speed was 37 ppm (page per minutes).

  As shown in FIG. 10, the pattern used for printing was a linear strip pattern 71 extending in a direction perpendicular to the printing direction (paper transport direction). The printing area of the band pattern 71 was 1% of the total area of the printing area 70.

  At the start of printing and after the completion of printing 40,000 sheets, one blank sheet was printed, the developing device 10 was taken out of the image forming apparatus 100, and the toner adhesion amount of the developing roller 2 was measured.

FIG. 11 is a diagram illustrating a method for measuring the toner adhesion amount on the surface of the developing roller 2. When measuring the toner adhesion amount of the developing roller 2, a probe 66 connected to a power source 65 is used. The probe 66 has a facing surface 67 that faces the surface of the developing roller 2, and the area of the facing surface 67 is 1 cm ² .

The shaft 21 of the developing roller 2 was grounded, a DC voltage of +300 V was applied to the probe 66, and the toner on the surface of the developing roller 2 was attracted to the probe 66 and collected. The weight (mg) of the toner adsorbed on the facing surface 67 (1 cm ² ) of the probe 66 was measured and used as the toner adhesion amount (mg / cm ² ).

  In FIG. 1-No. 6 shows a measurement result of the toner adhesion amount of the developing roller 2. In FIG. 1, no. 3 and no. 5 is a graph showing a change in the toner adhesion amount of the developing roller 2 of FIG.

  As shown in FIG. 1 and no. In the case of using 2 developing roller 2 (dynamic friction coefficient μ is 1.5 or more), the decrease rate of the toner adhesion amount after printing 40000 sheets was as high as 63% and 45%, respectively.

  In contrast, no. 3-No. 6 development roller 2 (dynamic friction coefficient μ is 0.3 to 1.2), the rate of decrease in toner adhesion after printing 40,000 sheets is 16% to 28%, and the decrease in toner adhesion is reduced. Was suppressed.

  From this result, it can be seen that by reducing the dynamic friction coefficient μ of the surface of the developing roller 2 to 1.2 or less, it is possible to obtain an effect of suppressing a decrease in the toner adhesion amount after long-term use.

  This is because, when the dynamic friction coefficient μ is large, filming (fusion) of the toner and titanium oxide (external additive) on the surface of the developing roller 2 occurs, causing the toner to be insufficiently charged. It is considered that the toner holding ability on the surface of the roller 2 is lowered, and the toner adhesion amount is reduced.

  On the other hand, when the dynamic friction coefficient μ is small, filming of the toner and titanium oxide on the surface of the developing roller 2 is difficult to occur, and as a result, a sufficient amount of toner can be held on the surface of the developing roller 2, It is considered that the decrease in the toner adhesion amount is suppressed.

  Further, by reducing the dynamic friction coefficient μ on the surface of the developing roller 2, the release of titanium oxide from the toner (peeling of the titanium oxide from the toner mother particles) is reduced, and even if the release of titanium oxide occurs. It is considered that the amount of fusion to the surface of the developing roller 2 is reduced.

  Next, the state of filming on the surface of the developing roller 2 was observed. First, the developing roller 2 is taken out from the developing device 10 and, as schematically shown in FIG. 14, only the developing roller 2 and the photosensitive drum 1 are brought into contact with each other and a developing voltage is applied to the developing roller 2 while rotating. . As a result, the toner adhered to the surface of the developing roller 2 was adhered to the surface of the photosensitive drum 1 by electrostatic force. In this state, only the toner and the external additive (titanium oxide) fused to the surface of the developing roller 2 by filming remain on the surface of the developing roller 2.

  The surface of the developing roller 2 treated in this way was observed with a laser microscope. FIG. 15 shows the state of filming on the surface of the developing roller 2. FIG. 15A shows the surface of the developing roller 2 in which filming is noticeable. FIG. 15B shows the surface of the developing roller 2 with a slight filming.

  Compared to FIG. 15B, in FIG. 15A, the toner and the external additive are fused to many portions of the surface of the developing roller 2. As described above, the toner and the external additive fused to the surface of the developing roller 2 cause a charging failure of the toner, which causes a decrease in the toner adhesion amount.

  It was confirmed by elemental analysis that, in the developing roller 2 having a large dynamic friction coefficient μ, titanium oxide was liberated from the toner and fused to the surface of the developing roller 2 (filming).

  Next, the density reduction in the printed image was measured. The print pattern (solid image) shown in FIG. 16 is applied to a print sheet of A3 Nobi (size that is one margin larger than A3) at the start of printing the print pattern (FIG. 10) and after the completion of printing 40000 sheets. Printed.

  Then, the density ρ1 of the solid image printed at the time of starting the printing of the above 40,000 sheets and the density ρ2 of the solid image printed after the printing of 40,000 sheets were measured by a spectral densitometer “X-Rite500” manufactured by Canon Itech Co., Ltd. . As shown in FIG. 17, the density measurement location was the upper part of the printed image (near the tip in the printing direction). And ((rho) 1- (rho) 2) / (rho) 1 was made into density | concentration reduction rate (rho).

  When the concentration reduction rate ρ thus obtained was 15% or less, it was determined as good (◯). Moreover, when the density reduction rate ρ was 15 to 20%, it was determined that the density was substantially good (Δ). Moreover, when the density reduction rate ρ exceeded 20%, it was determined as defective (×).

  The reason why the density reduction rate ρ exceeds 20% is determined to be defective. In the solid image, if there is a portion where the density is reduced to about 80% with respect to the high density portion, the density unevenness is noticeable visually. Because.

  No. 1-No. The determination result of the density reduction rate when the developing roller 2 is used is shown in FIG.

  As shown in FIG. 1 and no. No. 2 developing roller 2 (dynamic friction coefficient μ is 1.5 or more), a density drop (defect level) exceeding 20% was observed. 3-No. 6 was used (dynamic friction coefficient μ was 0.3 to 1.2), the density reduction was 20% or less (good or almost good level).

  This is because, by reducing the dynamic friction coefficient μ of the surface of the developing roller 2 to 1.2 or less, filming of toner and titanium oxide on the surface of the developing roller 2 is suppressed, and a sufficient amount of the surface of the developing roller 2 is provided. Since the toner can be held, it is considered that the decrease in density of the printed image is suppressed.

  As can be seen from FIG. 13 described above, when the dynamic friction coefficient μ of the surface of the developing roller 2 is reduced, the decrease in the toner adhesion amount after long-term printing is suppressed, but the toner adhesion amount at the beginning of printing is small. Tend to be. Therefore, it is necessary to consider the possibility of blurring and fogging.

  Then, the evaluation of the blur was performed next. The blur is caused by the fact that the amount of toner adhering to the developing roller 2 is small, so that an amount of toner necessary for image formation is not supplied to the photosensitive drum 1. As described above, when the print pattern (solid image) in FIG. 16 is printed on the A3 nob print paper, the lower part of the print image (near the rear end in the printing direction) is blurred as shown in FIG. .

  After the completion of the printing of 40000 sheets of the above printing pattern (FIG. 10), the printing pattern (solid image) of FIG. 16 was printed, and the presence or absence of blur was visually observed. When the blur was visually confirmed, it was judged as defective (x), and when the blur was not visually confirmed, it was judged as good (◯).

  No. 1-No. FIG. 12 also shows the result of determination of blur when the developing roller 2 is used.

  As shown in FIG. 1-No. When any of the development rollers 2 of No. 6 was used, no generation of blur was observed.

  Next, the fogging was evaluated. Fog is caused by toner adhering to the background portion (non-printing portion) of an image due to undercharged toner or reversely charged toner (toner charged with reverse polarity).

  The fog was evaluated as follows. First, after the printing of 40000 sheets of the above printing pattern (FIG. 10) is completed, printing of a blank image is started by the image forming apparatus 100 in an environment of a temperature of 28 degrees and a humidity of 80%, and the image forming apparatus is in the middle of development. 100 was stopped. Then, as shown in FIG. 19, an adhesive tape 81 was pasted on the surface of the photosensitive drum 1 in a region downstream of the developing roller 2 and upstream of the transfer roller 12. As the adhesive tape 81, “Scotch tape” manufactured by Sumitomo 3M Limited was used.

  When the adhesive tape 81 is peeled off from the surface of the photosensitive drum 1, the toner attached to the surface of the photosensitive drum 1 is adsorbed to the adhesive tape 81. The adhesive tape 81 is attached to the white recording paper 82. The color difference ΔE from when only the adhesive tape was applied to the recording paper 82 was measured with a spectrocolorimeter (“CM-2600d” manufactured by Konica Minolta, Inc.). The measurement was performed at five locations (ΔE1, ΔE2, ΔE3, ΔE4, and ΔE5 shown in FIG. 20) equally from both ends of the photosensitive drum 1, and an average value was taken.

  When the value of the color difference ΔE is small, it indicates that there is little fogging, that is, there is little toner with insufficient charge or reverse charge. When ΔE obtained by the above method was less than 3.5, it was judged as good (◯), and when ΔE was 3.0 or more and less than 3.5, it was judged as Δ (almost good). . Further, when ΔE was 3.5 or more, it was determined to be defective (x).

  No. 1-No. FIG. 12 also shows the determination result of the fog when the developing roller 2 is used.

  As shown in FIG. 1-No. No fogging was observed when the developing roller 2 (dynamic friction coefficient μ was 0.6 to 1.8) was used. When the developing roller 2 of No. 6 (dynamic friction coefficient μ is 0.3) was used, the occurrence of fogging was observed.

Summarizing the above results, it can be seen that by reducing the dynamic friction coefficient μ on the surface of the developing roller 2, it is possible to suppress a decrease in the toner adhesion amount after long-term printing. Furthermore, the range of the dynamic friction coefficient μ that can clear all the determination criteria for the density reduction, blurring, and fogging of the printed image shown in FIG. 12 can be expressed by the following equation (1).
0.6 ≦ μ ≦ 1.2 (1)

  Generally, the toner adhesion amount on the surface of the developing roller 2 is controlled by adjusting the developing voltage applied to the developing roller 2 and the supply voltage applied to the supply roller 3. However, if a large amount of toner or titanium oxide released from the toner is filmed (fused) on the surface of the developing roller 2, the toner adhesion amount does not correspond to the development voltage and the toner adhesion amount becomes difficult to control. . Therefore, in order to maintain good print quality, it is necessary to suppress as much as possible a decrease in the amount of toner adhesion after long-term printing.

  According to the present embodiment, by reducing the dynamic friction coefficient μ on the surface of the developing roller 2, a decrease in the toner adhesion amount after long-term printing is suppressed, so that the toner adhesion amount can be sufficiently controlled. And good print quality can be maintained over a long period of time.

  As described above, according to the first embodiment of the present invention, even when a toner containing titanium oxide is used, the dynamic friction coefficient μ of the developing roller 2 is set to 0.6 ≦ μ ≦ 1.2. By making it within this range, it is possible to suppress a decrease in the density of the printed image without causing blurring or fogging and to maintain good print quality.

Second embodiment.
Next, a second embodiment of the present invention will be described.
In the first embodiment described above, the dynamic friction coefficient μ of the developing roller 2 is changed. However, in the second embodiment, the surface roughness (10-point average roughness Rz) of the developing roller 2 is further changed. Let Note that the configurations of the image forming apparatus 100 and the developing apparatus 10 are the same as those in the first embodiment.

  The 10-point average roughness Rz of the developing roller 2 can be changed by properly using several types of polishing paper when the surface of the developing roller 2 is polished, and adjusting the polishing speed and the polishing push-in amount. Here, first, the dynamic friction coefficient μ of the developing roller 2 is kept constant at 1.2, and the 10-point average roughness Rz is varied in 10 ways. 11-No. Twenty developing rollers 2 were prepared.

  Generally, when the 10-point average roughness Rz changes, the dynamic friction coefficient μ also changes. Here, the presence or absence of a silicon-based additive or a fluorine-based additive and carbon black when forming the surface layer 23 of the developing roller 2 In addition, by adjusting the addition amount, the 10-point average roughness Rz is changed while keeping the dynamic friction coefficient μ constant.

  Then, as described in the first embodiment, the reduction rate of the toner adhesion amount, the density reduction rate ρ, the blurring, and the rash after the printing of the print pattern shown in FIG. .

  No. 11-No. FIG. 21 shows the evaluation results of the reduction rate of the toner adhesion amount, the density reduction rate ρ of the printed image, the blur, and the rash when the 20 developing rollers 2 are used.

  From the results shown in FIG. 21, it can be seen that by increasing the 10-point average roughness Rz of the surface of the developing roller 2, it is possible to suppress a decrease in the amount of toner adhesion after long-term printing. This is considered to be because if the unevenness of the surface of the developing roller 2 is large, even if a certain amount of toner filming occurs, the unevenness is not completely filled with the toner and the toner can be held.

  FIG. No. 15 developing roller 2 (10-point average roughness Rz is 6.5 μm) FIG. 6 is a graph showing a decrease in toner adhesion after printing 40,000 sheets when 18 developing rollers 2 (10-point average roughness Rz is 5.0 μm) are shown.

  From FIG. 22, No. 10 having a large value of 10-point average roughness Rz. It can be seen that, with the 15 developing roller 2, the rate of decrease in the adhesion amount after printing 40000 sheets is reduced, but the toner adhesion amount at the beginning of printing is increased. This is considered to be due to an increase in toner charge amount due to friction as the 10-point average roughness Rz increases. An increase in the toner adhesion amount at the beginning of printing causes stains and the like.

  Therefore, here, dirt was also evaluated. This is because as the 10-point average roughness Rz increases, the possibility of occurrence of contamination increases. Dirt is most likely to occur in a low humidity environment. Accordingly, 1000 print patterns shown in FIG. 10 were printed, and then the image forming apparatus 100 was left in a low humidity environment (temperature 10 ° C., humidity 20%) for 24 hours. In general, the smear appears most prominently around 1000 sheets from the start of printing, and then tends to ease.

  After leaving for 24 hours in this way, a halftone image (print density 30% to 50%) shown in FIG. 23 is printed in a low humidity environment (temperature 10 ° C., humidity 20%). The stain is mainly printed on the image as the stain as shown in FIG. 24 because the toner that could not be regulated by the developing blade 5 on the developing roller 2 adheres to the photosensitive drum 1. Therefore, when a halftone image is printed, dirt is most easily found.

  The printed halftone was observed, and when no stain was visually observed, it was judged as good (◯). In addition, when the stain was found but the degree was good and no problem was observed visually, it was judged to be almost good (Δ). Those in which the dirt could be clearly confirmed visually were judged as defective (x). The evaluation results of dirt are also shown in FIG.

From the results shown in FIG. 21, when the dynamic friction coefficient μ is 1.2, the range of the 10-point average roughness Rz that clears all the determination criteria for the density reduction rate, blurring, fogging, and dirt is as follows: 2).
5.0 μm ≦ Rz ≦ 7.5 μm (2)

  In the present embodiment, the range of the dynamic friction coefficient μ and the 10-point average roughness Rz that can suppress all of stains, a decrease in print density, blurring, and fogging has been studied.

  Specifically, as shown in FIG. 25, the dynamic friction coefficient μ is changed to 7 types in the range of 0.3 to 2.1, and the 10-point average roughness Rz is set to 12 types in the range of 3.5 μm to 9.8 μm. In total, 84 types of developing rollers 2 were prepared.

  As described above, the dynamic friction coefficient μ and the 10-point average roughness Rz are adjusted by the presence / absence and addition amount of a silicon-based additive or a fluorine-based additive and carbon black when forming the surface layer 23 of the developing roller 2. And adjusting the kind of polishing paper, polishing speed, and polishing push-in amount when polishing the developing roller 2.

  FIG. 25 shows the evaluation results of dirt when 84 types of developing rollers 2 are used. The dirt evaluation method is as described above.

  In FIG. 25, when the dynamic friction coefficient μ is 2.1, dirt is confirmed when the 10-point average roughness Rz is 6.0 or less, and when the dynamic friction coefficient μ is 1.8, the 10-point average roughness Rz. Is 5.5 or less, and contamination is confirmed. When the dynamic friction coefficient μ is 1.5, dirt is confirmed when the 10-point average roughness Rz is 5.0 or less, and when the dynamic friction coefficient μ is 1.2, the 10-point average roughness Rz is 4. Dirt is confirmed at 5 or less. When the dynamic friction coefficient μ is 0.9, dirt is confirmed when the 10-point average roughness Rz is 4.0 or less, and when the dynamic friction coefficient μ is 0.6, the 10-point average roughness Rz is 3. Dirt is confirmed at 5 or less. When the dynamic friction coefficient μ is 0.3, there is no stain that can be clearly recognized visually.

  From this result, it can be seen that the larger the dynamic friction coefficient μ is, the smaller the 10-point average roughness Rz is. On the contrary, when the dynamic friction coefficient μ is large, it can be seen that the occurrence of dirt can be suppressed by increasing the 10-point average roughness Rz. It can also be seen that when the 10-point average roughness Rz is small, the occurrence of dirt can be suppressed by reducing the dynamic friction coefficient μ.

From the result of FIG. 25, the range of the dynamic friction coefficient μ and the 10-point average roughness Rz that can clear the determination criterion for dirt can be expressed by the following equation (3).
μ ≦ 5.7−0.6Rz (3)

  FIG. 26 shows the evaluation result of the density reduction of the printed image when 84 types of developing rollers 2 are used. The evaluation method of the decrease in the density of the printed image is as described with reference to FIGS.

  In FIG. 26, when the dynamic friction coefficient μ is 2.1, the 10-point average roughness Rz is 6.5 or more, and the density decrease is large (that is, the defect level at which the density decrease rate ρ exceeds 20), and the dynamic friction coefficient μ is In the case of 1.8, the 10-point average roughness Rz is 7.0 or more, and the density reduction is large. When the dynamic friction coefficient μ is 1.5, the 10-point average roughness Rz is 7.5 or more and the density drop is large. When the dynamic friction coefficient μ is 1.2, the 10-point average roughness Rz is 8. The density drop is large at 0 or more. When the dynamic friction coefficient μ is 0.9, the 10-point average roughness Rz is 8.5 or more and the density drop is large. When the dynamic friction coefficient μ is 0.6, the 10-point average roughness Rz is 9. The density drop is large at 0 or more. When the dynamic friction coefficient μ is 0.3, no significant decrease in density is observed.

  From this result, it can be seen that as the dynamic friction coefficient μ is larger and the 10-point average roughness Rz is larger, the density reduction of the printed image is larger. On the contrary, when the dynamic friction coefficient μ is large, it can be seen that the decrease in the density of the printed image can be suppressed by reducing the 10-point average roughness Rz. It can also be seen that when the 10-point average roughness Rz is large, the decrease in the density of the printed image can be suppressed by reducing the dynamic friction coefficient μ.

From the result of FIG. 26, the range of the dynamic friction coefficient μ and the 10-point average roughness Rz that can clear the criterion for determining the density reduction of the printed image can be expressed by the following equation (4).
μ ≦ −1.8 + 0.6Rz (4)

  FIG. 27 shows the evaluation results of the fog when 84 types of developing rollers 2 are used. The fogging evaluation method is as described with reference to FIG.

  In FIG. 27, when the dynamic friction coefficient μ is 1.2 or more, the fog is at a good level regardless of the 10-point average roughness Rz. On the other hand, when the dynamic friction coefficient μ is 0.9, the 10-point average roughness Rz is 3.5 and fogging occurs. When the dynamic friction coefficient μ is 0.6, fogging occurs when the 10-point average roughness Rz is 4.5 or less. When the dynamic friction coefficient μ is 0.3, fogging occurs when the 10-point average roughness Rz is 5.5 or less.

  From this result, it can be seen that the smaller the dynamic friction coefficient μ and the smaller the 10-point average roughness Rz, the more likely fogging occurs. Conversely, when the dynamic friction coefficient μ is small, it can be seen that the occurrence of fogging can be suppressed by increasing the 10-point average roughness Rz. It can also be seen that when the 10-point average roughness Rz is small, the occurrence of fogging can be suppressed by increasing the dynamic friction coefficient μ.

From the results of FIG. 27, the range of the dynamic friction coefficient μ and the 10-point average roughness Rz that can clear the fogging criterion can be expressed by the following equation (5).
μ ≧ 2.1−0.3Rz (5)

  FIG. 28 shows the evaluation result of blurring when 84 types of developing rollers 2 are used. The blur evaluation method is as described with reference to FIG.

  In FIG. 28, when the dynamic friction coefficient μ is 2.1, the 10-point average roughness Rz is 5.0 or less, and the blur is confirmed. When the dynamic friction coefficient μ is 1.8, the 10-point average roughness Rz Was less than 4.5, and a blur was confirmed. When the dynamic friction coefficient μ is 1.5, a 10-point average roughness Rz is 4.0 or less, and a blur is confirmed. When the dynamic friction coefficient μ is 0.9 to 1.2, a defective level of blur is It was not confirmed. When the dynamic friction coefficient μ is 0.6, blurring is confirmed when the 10-point average roughness Rz is 4.0 or less, and when the dynamic friction coefficient μ is 0.3, the 10-point average roughness Rz is 4. Scratch was confirmed at 5 or less.

  From this result, it can be seen that blurring is likely to occur when the dynamic friction coefficient μ is large and small. This is because, when the dynamic friction coefficient μ is large, scumming due to filming of toner and titanium oxide (external additive) on the surface of the developing roller 2 is likely to occur, and when the kinetic friction coefficient μ is small. This is considered to be due to the occurrence of blurring (initial blurring) due to the small amount of toner attached at the beginning of printing. Moreover, in any case, it can be seen that generation of blurring can be suppressed by increasing the 10-point average roughness Rz.

From the result of FIG. 28, the range of the dynamic friction coefficient μ and the 10-point average roughness Rz that can clear the determination criterion of blur can be expressed by the following expressions (6) and (7).
μ ≧ 3.3-0.6Rz (6)
μ ≧ −1.2 + 0.6Rz (7)

  Equation (6) is the range of the dynamic friction coefficient μ and the 10-point average roughness Rz for suppressing the initial blur, and the equation (7) is the dynamic friction coefficient μ and the 10-point average for suppressing the aging blur. It is the range of the roughness Rz.

Although the dynamic friction coefficient μ is controlled according to the polishing conditions of the developing roller 2 as described above, it is practically difficult to make the dynamic friction coefficient μ less than 0.3. Therefore, here, the lower limit of the dynamic friction coefficient μ is set to 0.3 as represented by the following formula (8).
μ ≧ 0.3 (8)

  FIG. 29 is a graph representing the equations (3) to (8) described in the present embodiment. The vertical axis represents the dynamic friction coefficient μ, and the horizontal axis represents the 10-point average roughness Rz (μm).

  From FIG. 29, the optimum range A that satisfies all the expressions (3) to (8) satisfies the straight line of the expression (3), the straight line of the expression (4), the straight line of the expression (5), and the expression (8). It can be seen that the region is surrounded by straight lines.

The optimum range A shown in FIG. 29 can be expressed by the following formula (9).
2.10-0.30Rz ≦ μ ≦ −1.80 + 0.60Rz (4.33 <Rz <6.00)
0.30 <μ ≦ −1.80 + 0.60Rz (6.00 ≦ Rz ≦ 6.25)
0.30 ≦ μ ≦ 5.70-0.60 Rz (6.25 <Rz ≦ 9.00)
... (9)

  No. described in the first embodiment. The developing roller 2 (general developing roller) 1 has a dynamic friction coefficient μ of 1.80 and a 10-point average roughness Rz of 5.00 μm. It can be seen that it is far from A.

  As described above, according to the second embodiment of the present invention, by controlling the 10-point average roughness Rz of the developing roller 2, the dynamic friction coefficient μ is wider than that in the first embodiment. In addition, it is possible to suppress a decrease in the toner adhesion amount after long-term printing.

In the second embodiment,
When the dynamic friction coefficient μ and the 10-point average roughness Rz satisfy the following expression (3), it is possible to suppress the occurrence of stains in the printed image.
μ ≦ 5.7−0.6Rz (3)

Further, when the dynamic friction coefficient μ and the 10-point average roughness Rz satisfy the following expression (4), it is possible to suppress a decrease in the density of the printed image.
μ ≦ −1.8 + 0.6Rz (4)

Further, when the dynamic friction coefficient μ and the 10-point average roughness Rz satisfy the following formula (5), the occurrence of fogging on the photosensitive drum 1 can be suppressed.
μ ≧ 2.1−0.3Rz (5)

Further, when the dynamic friction coefficient μ and the 10-point average roughness Rz satisfy the following formulas (6) and (7), blurring of the printed image can be suppressed.
μ ≧ 3.3-0.6Rz (6)
μ ≧ −1.2 + 0.6Rz (7)

In addition, when the dynamic friction coefficient μ and the 10-point average roughness Rz satisfy the following expression (9), all of the above-described dirt, density reduction, fogging and blurring can be suppressed.
2.10-0.30Rz ≦ μ ≦ −1.80 + 0.60Rz (4.33 <Rz <6.00)
0.30 <μ ≦ −1.80 + 0.60Rz (6.00 ≦ Rz ≦ 6.25)
0.30 ≦ μ ≦ 5.70-0.60 Rz (6.25 <Rz ≦ 9.00)
... (9)

  In the first and second embodiments described above, the direct transfer type image forming apparatus that directly transfers the toner image (developer image) formed on the photosensitive drum to the medium has been described. The present invention can also be applied to an intermediate transfer type image forming apparatus using a belt or the like.

  The present invention can be applied not only to a printer but also to an MFP (Multi Function Peripheral), a facsimile machine, and a copying machine.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum, 2 Developing roller (developer carrier), 21 Shaft, 22 Elastic layer, 23 Surface layer, 2a Roller body, 3 Supply roller (developer supply member), 31 Shaft, 32 Elastic layer, 4 Charging roller (Charging member), 5 developing blade (developer layer forming member), 6 cleaning blade (cleaning member), 8 toner cartridge (developer container), 9 seal member, 10 developing device (developing device), 11 LED head ( Exposure apparatus), 13 medium supply unit, 14 medium transport unit, 15 fixing unit, 16 medium discharge unit, 40 control unit.

Claims (16)

A developer carrier having an elastic layer and a surface layer covering the elastic layer;
A developer supply member for supplying a developer to the developer carrier;
A developer layer forming member for forming a developer layer on the surface of the developer carrying member,
The developer contains titanium oxide;
The dynamic friction coefficient μ of the surface of the developer carrying member is
0.6 ≦ μ ≦ 1.2
A developing device in the range of A developer carrier having an elastic layer and a surface layer covering the elastic layer;
A developer supply member for supplying a developer to the developer carrier;
A developer layer forming member for forming a developer layer on the surface of the developer carrying member,
The developer contains titanium oxide;
The dynamic friction coefficient μ and the 10-point average roughness Rz of the surface of the developer carrying member are as follows:
μ ≦ 5.7-0.6Rz
A developing device characterized by satisfying A developer carrier having an elastic layer and a surface layer covering the elastic layer;
A developer supply member for supplying a developer to the developer carrier;
A developer layer forming member for forming a developer layer on the surface of the developer carrying member,
The developer contains titanium oxide;
The dynamic friction coefficient μ and the 10-point average roughness Rz of the surface of the developer carrying member are as follows:
μ ≦ −1.8 + 0.6Rz
A developing device characterized by satisfying A developer carrier having an elastic layer and a surface layer covering the elastic layer;
A developer supply member for supplying a developer to the developer carrier;
A developer layer forming member for forming a developer layer on the surface of the developer carrying member,
The developer contains titanium oxide;
The dynamic friction coefficient μ and the 10-point average roughness Rz of the surface of the developer carrying member are as follows:
μ ≧ 2.1−0.3Rz
A developing device characterized by satisfying A developer carrier having an elastic layer and a surface layer covering the elastic layer;
A developer supply member for supplying a developer to the developer carrier;
A developer layer forming member for forming a developer layer on the surface of the developer carrying member,
The developer contains titanium oxide;
The dynamic friction coefficient μ and the 10-point average roughness Rz of the surface of the developer carrying member are as follows:
μ ≧ 3.3-0.6Rz, and μ ≧ −1.2 + 0.6Rz
A developing device characterized by satisfying A developer carrier having an elastic layer and a surface layer covering the elastic layer;
A developer supply member for supplying a developer to the developer carrier;
A developer layer forming member for forming a developer layer on the surface of the developer carrying member,
The developer contains titanium oxide;
The dynamic friction coefficient μ and the 10-point average roughness Rz of the surface of the developer carrying member are as follows:
2.10-0.30Rz ≦ μ ≦ −1.80 + 0.60Rz (4.33 <Rz <6.00),
0.30 <μ ≦ −1.80 + 0.60Rz (6.00 ≦ Rz ≦ 6.25), and 0.30 ≦ μ ≦ 5.70-0.60 Rz (6.25 <Rz ≦ 9.00)
A developing device characterized by satisfying   The developing device according to claim 1, wherein the surface layer of the developer carrying member is formed by dipping the elastic layer into a processing liquid.   The developing device according to claim 7, wherein the processing liquid is a urethane solution or an isocyanate solution.   9. The developing device according to claim 7, wherein a silicon-based additive, a fluorine-based additive, or carbon black is added to the processing solution.   The dynamic friction coefficient μ and the 10-point average roughness Rz of the developer carrier are adjusted according to the amount of the silicon-based additive or fluorine-based additive or carbon black added and the polishing conditions of the surface of the developer-carrying member. The developing device according to claim 9.   The developing device according to claim 1, wherein the developer is generated by an emulsion polymerization method.   12. The development according to claim 1, wherein the developer contains 0.2 to 0.5 wt% of titanium oxide with respect to 100 wt% of developer base particles. apparatus.   13. The developer carrier according to claim 1, wherein the developer carrying member is a developing roller provided with the elastic layer on a surface of a shaft, and the surface layer is provided so as to cover the elastic layer. 2. The developing device according to item 1.   The developing device according to claim 1, wherein the developer supply member is a supply roller having an elastic layer formed of a foam material. The developer layer forming member is a blade having a bent portion,
The developing device according to claim 1, wherein the bent portion of the blade is pressed against the developer carrier. An image forming apparatus comprising the developing device according to claim 1.

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