JP2015184601A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a developer carrier, which has a surface layer not containing fine particles coating the outer peripheral surface of an elastic layer, to have a surface satisfying a predetermined condition, so as to prevent a developer from being adhered to the surface of the developer carrier.SOLUTION: There is provided a developer including a developer carrier that develops a latent image on an electrostatic latent image carrier, and a developer supply member that supplies a developer to the developer carrier, where the developer carrier includes an elastic layer and a surface layer that coats the outer peripheral surface of the elastic layer and does not contain fine particles; the roughness in the circumferential direction of the surface of the developer carrier satisfies a predetermined condition.

Description

  The present invention relates to a developing device and an image forming apparatus.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and an MFP (Multi Function Printer) using an electrophotographic method, an electrostatic latent image carrier and an electrostatic latent image carrier A developing device in which an acting charging member, a developer carrying member, a cleaning mechanism and the like are integrated is mounted on the apparatus main body, and a toner image is formed on a recording medium such as printing paper.

  In general, a developing device includes a developing roller as a developer carrier for developing toner as a developer on a photosensitive drum as an electrostatic latent image carrier, supply of toner to the developing roller, and A toner supply roller that scrapes off the undeveloped toner remaining on the developing roller.

  The characteristics required for the developing roller include a uniform charging property of the toner and a uniform toner conveyance property. In order to obtain these characteristics, the developing roller has an elastic layer attached to the outer periphery of the shaft core and a surface layer that covers the surface of the elastic layer. A technique for forming convex portions on the surface of a developing roller by dispersing resin fine particles is known (see, for example, Patent Document 1).

JP 2011-180195 A

  However, in the conventional developing device, when resin fine particles are added to the surface layer in order to make the surface of the developing roller have a desired surface roughness, the hardness of the resin fine particles is higher than that of the elastic layer and the surface layer, This is a phenomenon in which the toner adheres to the surface of the developing roller because mechanical stress applied to the toner on the developing roller from the photosensitive drum, the layer regulating blade, and the toner supply roller in contact with the developing roller is locally increased. There is a problem that so-called toner filming occurs.

  The present invention solves the problems in the conventional developing device, and develops the surface of the developer carrying member having a surface layer that does not contain fine particles covering the outer peripheral surface of the elastic layer so as to satisfy a predetermined condition. It is an object of the present invention to provide a developing device and an image forming apparatus in which the developer does not adhere to the surface of the agent carrier.

  Therefore, in the developing device of the present invention, the developing device includes a developer carrying member that develops the latent image on the electrostatic latent image carrying member, and a developer supply member that supplies the developer to the developer carrying member. The developer carrier has an elastic layer and a surface layer that covers the outer peripheral surface of the elastic layer and does not contain fine particles, and is arranged in the circumferential direction on the surface of the developer carrier. The roughness satisfies the following conditions.

Average interval of unevenness Sm = 50 to 200 [μm]
Ten-point average roughness Rz = 2 to 10 [μm]
Load length ratio t _p (20 [%]): 30 [%] or more and 65 [%] or less Load length ratio t _p (90 [%]): 80 [%] or more t _p ((n + 1) × 10 [ %])-T _p (n × 10 [%]): 20 [%] or less (n: integer of 2 to 8)

  According to the present invention, the developing device can reduce the stress applied to the developer on the developer carrying member, and can improve the scraping property of the undeveloped developer by the developer supply member. As a result, the occurrence of sticking of the developer to the surface of the developer carrying member can be suppressed.

1 is a cross-sectional view illustrating a configuration of a developing device according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a control block diagram of the image forming apparatus in the embodiment of the present invention. It is sectional drawing of the developing roller in embodiment of this invention. It is a figure which shows the resistance value measuring method of the developing roller in embodiment of this invention. It is a figure which shows the continuous printing pattern in embodiment of this invention. FIG. 6 is a diagram illustrating a solid image when toner filming has not occurred on the surface of the developing roller according to the embodiment of the present invention. FIG. 10 is a diagram illustrating a solid image when toner filming occurs on the surface of the developing roller according to the embodiment of the present invention. It is a figure which shows 1by1 pattern in embodiment of this invention. It is an expanded sectional view of the developing roller which formed surface roughness by the convex and the concave in embodiment of this invention. It is an expanded sectional view of the developing roller which formed surface roughness by the convex in the embodiment of the present invention. It is an expanded sectional view of the developing roller which formed surface roughness by the concave in embodiment of this invention. It is an expanded sectional view of the developing roller in which surface roughness is formed by resin fine particles added to the surface layer in the embodiment of the present invention. It is an enlarged view showing the surface of the developing roller formed with roughness by mold transfer and addition of resin fine particles in the embodiment of the present invention. It is an enlarged view showing the surface of the developing roller formed with roughness by polishing in the embodiment of the present invention. It is a diagram for explaining a load length ratio t _p in the embodiment of the present invention. It shows a load length ratio t _p corresponding to the roughness curve of the assumptions in the embodiment of the present invention. 6 is a table showing the surface roughness of the developing roller in the embodiment of the present invention. It is a table | surface which shows the test result of Examples 1-9 in embodiment of this invention. It is a table | surface which shows the test result of Comparative Examples 1-6 in embodiment of this invention. Table showing the maximum values of the load length ratios t _p (20 [%]) and t _p (90 [%]) and the change amount of the load length ratio per cutting level 10 [%] in the embodiment of the present invention. It is.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of a developing device in the embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a schematic configuration of an image forming apparatus in the embodiment of the present invention.

  In FIG. 2, reference numeral 10 denotes an image forming apparatus according to the present embodiment. For example, the image forming apparatus is a printer, a facsimile machine, a copying machine, a multi-function machine having various functions, or the like. Here, the image forming apparatus 10 will be described as an electrophotographic printer that forms an image by an electrophotographic method. The image forming apparatus 10 may be a device that forms a color image. However, for convenience of explanation, it is assumed that the image forming device 10 is a device that forms a monochrome image.

  In this case, an image forming unit 28 and a fixing device 27 are arranged inside the image forming apparatus 10 along a conveyance path of a recording medium 21 as a medium. Then, the recording media 21 stacked and set in a paper cassette or the like are fed one by one by a paper feed roller 31, transported in the direction indicated by arrow A, and sent to the paper transport roller 32. It is. Subsequently, the recording medium 21 is sent in a direction indicated by an arrow B at a predetermined timing by the paper transport roller 32, and is a developer image formed by the image forming unit 28 while being transported along the transport path. A toner image is transferred by the transfer roller 25.

  When the recording medium 21 is sent to the fixing device 27, a fixing process is performed by the fixing device 27, and the toner image is fixed on the recording medium 21. Subsequently, the recording medium 21 on which the toner image is fixed is conveyed in the direction indicated by the arrow C, discharged in the direction indicated by the arrow D by the paper discharge roller 33, and accommodated in a stacker outside the image forming apparatus 10. The

  Here, the image forming unit 28 includes the developing device 20. As shown in FIG. 1, the developing device 20 includes a toner container 22 as a developer container and a casing 23 that stores therein toner 17 as a developer replenished from the toner container 22. Prepare. Further, the developing device 20 includes a photosensitive drum 13 as an electrostatic latent image carrier, a developing roller 11 as a developer carrier disposed so as to face the photosensitive drum 13, and a toner 17 on the developing roller 11. A toner supply roller 12 as a developer supply member for supplying toner, a charging roller 14 as a charging member for charging the photosensitive drum 13, and a toner layer thickness for forming the toner 17 supplied onto the developing roller 11 into a thin layer The developing blade 15 as the regulating blade, the stirring members 24a, 24b and 24c for maintaining the fluidity of the toner 17 in the casing 23, and the transfer residual toner on the photosensitive drum 13 are scraped and collected. A cleaning blade 16 is provided.

  The developing roller 11, the toner supply roller 12, the photosensitive drum 13, and the charging roller 14 rotate in directions indicated by arrows, respectively. The agitating members 24a, 24b, and 24c are crank-shaped sacrifices, and rotate in a direction indicated by an arrow on a broken line shown in the drawing.

  Reference numeral 26 denotes an LED head as an exposure apparatus that includes an LED (Light Emitting Diode) as a light emitting element and exposes the surface of the photosensitive drum 13 based on image data to form an electrostatic latent image. .

  Next, the control device of the image forming apparatus 10 will be described.

  FIG. 3 is a control block diagram of the image forming apparatus in the embodiment of the present invention.

  In the figure, reference numeral 30 denotes a print control unit including a microprocessor, ROM, RAM, input / output port, timer, and the like. Print data and control commands are sent from a host device (not shown) via an interface (I / F) control unit 36. Then, the entire sequence of the image forming apparatus 10 is controlled to perform a printing operation.

  Reference numeral 37 denotes a reception memory that temporarily records print data input from the host device via the interface control unit 36. Reference numeral 41 denotes an image data editing memory that receives the print data recorded in the reception memory 37 and records image data formed by editing the print data, that is, image data.

  An operation unit 42 includes a display unit such as an LED for displaying the state of the image forming apparatus 10 and an input unit such as a switch for giving an instruction from the operator to the image forming apparatus 10. Further, reference numeral 43 denotes a sensor group including various sensors for monitoring the operation state of the image forming apparatus 10, such as a paper position detection sensor, a temperature / humidity sensor, a print density sensor, and a toner remaining amount detection sensor. Yes.

  Reference numeral 46 denotes a charging roller power supply, which applies a voltage to the charging roller 14 according to an instruction from the print control unit 30 to charge the surface of the photosensitive drum 13. Reference numeral 44 denotes a developing roller power source for applying a predetermined voltage to the developing roller 11 in order to attach the toner 17 to the electrostatic latent image. A toner supply roller power source 45 applies a predetermined voltage to the toner supply roller 12 for supplying the toner 17 to the developing roller 11.

  Reference numeral 47 denotes a developing blade power source for applying a predetermined voltage to the developing blade 15 for forming a thin layer of the toner 17 on the surface of the developing roller 11. A transfer roller power source 51 applies a predetermined voltage to the transfer roller 25 for transferring the toner image formed on the photosensitive drum 13 to the recording medium 21.

  The charging roller power supply 46, the developing roller power supply 44, the toner supply roller power supply 45, the developing blade power supply 47, and the transfer roller power supply 51 change the voltage applied to each member in accordance with an instruction from the print control unit 30. Can be done.

  Reference numeral 52 denotes a head drive controller that sends the image data recorded in the image data editing memory 41 to the LED head 26 and drives the LED head 26. Reference numeral 53 denotes a fixing control unit that applies a voltage to the fixing device 27 as fixing means in order to fix the transferred toner image on the recording medium 21. The fixing device 27 includes a heater (not shown) for melting the toner 17 constituting the toner image on the recording medium 21, a temperature sensor (not shown) for detecting the temperature, and the like. The fixing control unit 53 reads the sensor output of the temperature sensor, energizes the heater based on the sensor output, and controls the fixing device 27 to have a constant temperature.

  Reference numeral 54 denotes a transport motor controller that controls the paper transport motor 34 for transporting the recording medium 21. The transport motor control unit 54 transports or stops the recording medium 21 at a predetermined timing according to an instruction from the print control unit 30. The paper feed roller 31, paper transport roller 32, and paper discharge roller 33 are rotated by a paper transport motor. Then, the recording medium 21 is conveyed in the directions indicated by arrows A to D.

  Reference numeral 55 denotes a drive control unit that drives a drive motor 35 for operating the photosensitive drum 13. When the drive motor 35 is driven by the drive controller 55, as shown in FIG. 2, the photosensitive drum 13 is rotated in the direction indicated by the arrow, and the charging roller 14, the developing roller 11, and the toner are rotated. Each of the supply rollers 12 is rotated in the direction indicated by the arrow.

  Next, main components of the developing device 20 will be described in detail.

  FIG. 4 is a cross-sectional view of the developing roller in the embodiment of the present invention.

  The toner 17 in the present embodiment is a nonmagnetic one-component negatively chargeable toner manufactured by a pulverization method and using a polyester resin as a binder. The volume average particle diameter of the toner 17 particles is 5.7 [μm], the circularity is 0.92, and the blow-off charge amount is −36 [μC / g]. Note that Coulter Multisizer II (manufactured by Coulter, Inc.) was used for measurement of the volume average particle size. Moreover, the flow type | formula particle image analyzer FPIA-3000 (made by Sysmex Corporation) was used for the measurement of circularity. For measurement of the blow-off charge amount, a powder charge amount measuring device TYPE TB-203 (manufactured by Kyocera Corporation) was used. After mixing 0.5 [g] toner 17 and 9.5 [g] ferrite carrier (F-60) (manufactured by Powdertech Co., Ltd.) and stirring for 30 minutes, the blow pressure is 7.0 [kPa]. The saturation charge amount was measured under the condition of suction pressure −4.5 [kPa].

  As shown in FIG. 4, the developing roller 11 includes a conductive metal core 61, an elastic layer 62 disposed on the metal core 61, and a surface layer 63 that covers the surface of the elastic layer 62. .

  The material of the elastic layer 62 is a general rubber material such as silicone rubber, urethane, acrylonitrile butadiene rubber (NBR), and a mixture of acrylonitrile butadiene rubber and epichlorohydrin rubber (ECO).

  Generally, the rubber hardness of the elastic layer 62 is preferably 60 to 80 degrees in terms of Asker C hardness. When the Asker C hardness of the elastic layer 62 is lower than 60 degrees, when the developing device 20 is not operated for a long period of time, the contact between the photosensitive drum 13 and the developing blade 15 in the developing roller 11 There is a problem that a dent is generated and a horizontal stripe is generated on the printed image. Further, if the Asker C hardness of the elastic layer 62 is higher than 80 degrees, the load applied to the developing roller 11 is increased, and not only toner filming is likely to occur on the surface of the developing roller 11 but also the photosensitive drum 13. Since the contact pressure with the ink becomes high, there is a problem that the reproducibility when printing a fine pattern is lowered. In the present embodiment, the elastic layer 62 is made of silicone rubber having an Asker C hardness of 65 degrees.

  In addition, various additives such as a conductive agent, a filling agent, a curing agent, and a vulcanization accelerator may be appropriately added to the elastic layer 62 as necessary. As the conductive agent, a general conductive agent such as an electronic conductive agent such as carbon black or an ionic conductive agent such as a quaternary ammonium salt can be used.

  The material of the surface layer 63 needs to be selected in consideration of wear resistance, charge imparting property to the toner 17, and the like. In general, a urethane resin, an acrylic resin, a silicone resin, or the like is used. In this embodiment, a urethane resin is used, and its layer thickness is about 10 [μm].

  When a urethane resin is used for the surface layer 63, the polyol component is preferably polyether polyol, a mixture of polyether polyol and polyester polyol, a mixture of polyether polyol and polycarbonate diol, or the like. The polyisocyanate component of polyurethane is preferably MDI, HDI or the like. In addition to polyisocyanate and polyol, a urethane, a catalyst, a filler, a plasticizer, and the like can be appropriately blended and used for urethane.

  Next, a method for measuring the resistance value of the developing roller 11 will be described.

  FIG. 5 is a diagram showing a method of measuring the resistance value of the developing roller in the embodiment of the present invention.

  A high resistance meter (model number: 4339B) (manufactured by Hewlett-Packard Company) 64 was used to measure the resistance value of the developing roller 11. The developing roller 11 was brought into contact with a metal roller 65 made of a stainless steel (SUS) material having a diameter of 30 [mm] with a load of W = 500 [g] applied to both ends. The metal roller 65 is rotated at a speed of 50 [rpm], a voltage of -100 [V] is applied to the cored bar 61 of the developing roller 11, and the resistance value is measured at 100 points per rotation of the developing roller 11, The average value was used as the resistance value of the developing roller 11.

The resistance value of the developing roller 11 is preferably in the range of 1 × 10 ⁴ to 1 × 10 ⁸ [Ω]. In the present embodiment, the developing roller 11 having a resistance value of 1 × 10 ⁵ [Ω] is used.

  The developing blade 15 is made of stainless steel and has a plate thickness of 0.08 [mm]. The contact portion with the developing roller 11 is bent, and the curvature radius of the bent portion (contact portion) is The pressure (linear pressure) against the developing roller 11 is 40 [gf / cm].

  In view of the setting conditions of the developing blade 15, it is necessary to examine the surface roughness, resistance value, and the like of the developing roller 11 in order to set the toner layer thickness, the toner charge amount, and the like on the developing roller 11 to desired amounts. As for the surface roughness of the developing roller 11 used in the present embodiment, the 10-point average roughness Rz (JIS B0601-1994) in the circumferential direction is 2 to 10 [μm], and the average interval Sm of unevenness (JIS B0601-1994). Is suitably 50 to 200 [μm]. The surface roughness is measured using a surf coder SEF3500 (manufactured by Kosaka Laboratories). The measuring instrument has a stylus radius of 2 [μm], a stylus pressure of 0.7 [mN], and a stylus feed. The speed is 0.1 [mm / sec] and the measurement length is 2.5 [mm].

  If the ten-point average roughness Rz is smaller than 2 [μm], the toner layer formed on the developing roller 11 becomes thin, and the stress applied to each toner 17 particle increases. For this reason, the amount of the external additive released from the toner 17 increases, and the external additive is clogged in the contact portion between the developing roller 11 and the developing blade 15, and toner filming is likely to occur in the developing blade 15. There's a problem.

  On the other hand, if the ten-point average roughness Rz is larger than 10 [μm], the toner layer thickness on the developing roller 11 becomes large, so that the toner 17 cannot be sufficiently scraped off by the toner supply roller 12, and the developing roller 11 There is a problem that toner filming is likely to occur on the surface.

  On the other hand, when the average interval Sm between the concaves and convexes is smaller than 50 [μm], the width of the valley becomes narrow, so that the toner 17 cannot be sufficiently scraped off by the toner supply roller 12, and the toner 17 is conveyed to the surface of the developing roller 11. There is a problem that dirt and toner filming due to an increase in the amount are likely to occur.

  Further, if the average interval Sm between the concaves and convexes is larger than 200 [μm], the transportability of the toner 17 is lowered, and there is a problem that the printing density is lowered.

  The toner supply roller 12 includes a conductive metal core (not shown) and a silicone rubber sponge (not shown) disposed on the metal core.

  The silicone rubber sponge is obtained by molding an unvulcanized silicone rubber compound by a method such as extrusion and vulcanizing and foaming by heating. The silicone rubber compound is obtained by adding a reinforcing silica filler, a vulcanizing agent necessary for vulcanization and a foaming agent, to various raw rubbers such as dimethyl silicone raw rubber and methylphenyl silicone raw rubber. As the foaming agent, an inorganic foaming agent such as sodium bicarbonate and an organic foaming agent such as ADCA are used. In addition, when giving semiconductivity, acetylene black, carbon black, etc. are added. Further, the adjustment of the hardness of the toner supply roller 12 is adjusted by the addition amount of the vulcanizing agent.

  In the present embodiment, the diameter of the cells (fine holes (holes) generated by foaming) of the toner supply roller 12 is 200 to 500 [μm], and the Asker F hardness is 35 to 65 degrees. is there.

Further, the resistance value of the toner supply roller 12 is 1 × 10 ⁴ to 1 × 10 ⁸ [when the load W = 200 [g] and the applied voltage is −300 [V] in the measurement method shown in FIG. Ω] is preferable, and in this embodiment, it is 1 × 10 ⁵ [Ω].

  The toner supply roller 12 is arranged so as to bite about 0.5 to 1.5 mm with respect to the developing roller 11, and rotates in the opposite direction to the developing roller 11 at the contact portion.

  When the Asker F hardness of the toner supply roller 12 is low and the biting amount of the toner supply roller 12 with respect to the developing roller 11 is small, the scraping property of the undeveloped toner on the developing roller 11 is reduced, and therefore the developing roller 11 The undeveloped toner continues to receive stress from the contact member, and toner filming is likely to occur on the surface of the developing roller 11.

  Further, when the Asker F hardness of the toner supply roller 12 is high and the amount of biting of the toner supply roller 12 with respect to the developing roller 11 is large, the contact pressure of the toner supply roller 12 with respect to the developing roller 11 is high, and Since mechanical stress applied to the toner 17 increases, toner filming is likely to occur on the surface of the developing roller 11.

  From the above, in order to suppress the occurrence of toner filming on the surface of the developing roller 11, the stress applied to the toner 17 on the developing roller 11 is reduced, and the toner supply roller 12 does not apply the toner on the developing roller 11. It is necessary to improve the scraping property of the developing toner.

  For the developing roller 11, in order to satisfy the above-described conditions, the surface of the developing roller 11 should not be excessively hard, and the toner 17 can scrape off the circumferential surface roughness of the developing roller 11. It is mentioned to make it easy to be used.

  Next, the operation at the time of image formation of the developing device 20 having the above configuration will be described.

  When the developing roller 11 and the toner supply roller 12 rotate in the direction indicated by the arrow in FIG. 1 along with the rotation of the photosensitive drum 13, the toner supply roller 12 in which a sponge-like elastic body is disposed on the core metal is The toner 17 rotates while carrying the toner 17 on the surface of the roller and in the cell, and the toner 17 reaches a contact portion with the developing roller 11. The toner supply roller 12 is applied with a DC voltage of −300 [V] by the power supply 45 for the toner supply roller. A DC voltage of −200 [V] is applied to the developing roller 11 by the developing roller power supply 44.

  Due to the potential difference generated between the developing roller 11 and the toner supply roller 12, the negatively charged toner 17 is supplied to the developing roller 11. Further, since the developing roller 11 and the toner supply roller 12 rotate in opposite directions at the contact portion, the toner supply roller 12 also scrapes off the undeveloped toner on the developing roller 11.

  The toner 17 carried on the surface of the developing roller 11 is formed on the photosensitive drum 13 after being thinned by the developing blade 15 to which a DC voltage of −300 [V] is applied by the developing blade power supply 47. The electrostatic latent image is developed by attaching to the electrostatic latent image.

  Next, a test conducted by the inventor of the present invention in order to confirm the effect in the present embodiment will be described.

  FIG. 6 is a diagram showing a continuous printing pattern in the embodiment of the present invention, FIG. 7 is a diagram showing a solid image when toner filming is not generated on the surface of the developing roller in the embodiment of the present invention, and FIG. FIG. 9 is a diagram showing a solid image when toner filming occurs on the surface of the developing roller in the embodiment of the present invention, and FIG. 9 is a diagram showing a 1by1 pattern in the embodiment of the present invention.

  The inventor of the present invention conducted a test using an actual machine having the same configuration as that of the image forming apparatus 10 as shown in FIG. Specifically, a continuous printing test of 30000 sheets was performed under the above-described image forming conditions in an environment of a temperature of 25 ° C. and a relative humidity of 50%.

  The printing pattern at the time of continuous printing was a pattern in which ruled lines 71a and 71b parallel to the printing direction of the recording medium 21, that is, the circumferential direction of the developing roller 11, as shown in FIG. In the portion corresponding to the ruled lines 71a and 71b on the circumference of the developing roller 11, almost no undeveloped toner remains on the developing roller 11, so that toner filming does not occur. On the other hand, since the development with the toner 17 is not performed at all on the circumference of the developing roller 11 other than the portions corresponding to the ruled lines 71a and 71b, the undeveloped toner continues to stay on the developing roller 11. If the shape of the surface roughness of the developing roller 11 and the contact condition of the toner supply roller 12 are not appropriate, toner filming occurs.

  Whether or not toner filming on the surface of the developing roller 11 occurred after continuous printing of 30,000 sheets was confirmed by printing a solid pattern on the recording medium 21.

  When toner filming does not occur on the surface of the developing roller 11, a uniform solid image 72 can be printed as shown in FIG. On the other hand, when toner filming occurs on the surface of the developing roller 11, as shown in FIG. 8, the printing density of the solid portion 73 where the ruled lines 71a and 71b are not printed is equal to the developing roller 11 by toner filming. Due to the decrease in the development efficiency accompanying the increase in the resistance value of the surface, the print density of the ruled line printing portions 74a and 74b, which are the portions where the ruled lines 71a and 71b are printed, becomes thinner.

  In the solid image 72 after continuous printing, if the density difference between the ruled line printing parts 74a and 74b and the solid part 73 which is a ruled line non-printing part cannot be visually confirmed, toner filming has occurred. If the density difference could be confirmed visually, it was determined that toner filming occurred.

  After the continuous printing, a 1-by1 pattern was printed on the recording medium 21 in addition to the solid pattern for confirming whether toner filming occurred. As shown in FIG. 9, the 1by1 pattern is a pattern of 1 dot at 600 [dpi] arranged at intervals of 1 dot. By printing the 1by1 pattern, the print reproducibility of a fine pattern can be confirmed. The theoretical value of the size of one dot of 600 [dpi] is 0.042 [mm].

  When toner filming occurs on the surface of the developing roller 11, the charge amount variation of the toner layer formed on the developing roller 11 becomes large, and when the shape of the surface roughness of the developing roller 11 is not appropriate, the toner 17 As a result, the development of the fine electrostatic latent image such as the 1by1 pattern formed on the photosensitive drum 13 with the toner 17 is not performed normally.

  The printed 1by1 pattern image was magnified and observed with a microscope, and 100 dots formed on the recording medium 21 were extracted using image analysis software SALT (Lasertec Corporation). Next, the area of each dot was measured, and the equivalent circle diameter [mm] for the area was calculated. Then, whether the dot reproducibility was good or bad was determined based on the calculated standard deviation σ of 100 circle equivalent diameter data.

  When σ ≦ 0.007, the level at which dot missing is not noticeable, and when 0.007 <σ ≦ 0.01, the level at which dot missing can be confirmed in some places but does not affect actual use, 0.01 < When it is σ, it is a level at which dot missing can be confirmed over a wide range in the observation region, and missing or missing dots can be visually confirmed without magnifying observation.

  In this test, when σ ≦ 0.01, the test was accepted, and when 0.01 <σ, the test was rejected.

  Next, the developing roller 11 that has been subjected to the above test, that is, the continuous printing test will be described.

FIG. 10 is an enlarged cross-sectional view of a developing roller having surface roughness formed by protrusions and recesses in the embodiment of the present invention, and FIG. 11 is an enlarged view of the developing roller having surface roughness formed by protrusions in the embodiment of the invention. FIG. 12 is an enlarged cross-sectional view of a developing roller having a surface roughness formed by recesses in the embodiment of the present invention, and FIG. 13 is a diagram showing the surface roughness by resin fine particles added to the surface layer in the embodiment of the present invention. FIG. 14 is an enlarged cross-sectional view of the formed developing roller, FIG. 14 is an enlarged view showing the surface of the developing roller on which roughness has been formed by mold transfer and addition of resin fine particles in the embodiment of the present invention, and FIG. enlarged view showing the surface of the developing roller to form a roughness by polishing in form 16 is a diagram illustrating a load length ratio t _p in the embodiment of the present invention, FIG. 17 is the embodiment of the present invention Shows a kick load length ratio t _p corresponding to the roughness curve of the assumptions, the table showing the surface roughness of the developing roller in the embodiment of FIG. 18 is the present invention, FIG. 19 is performed in the embodiment of the present invention Table showing test results of Examples 1 to 9, FIG. 20 is a table showing test results of Comparative Examples 1 to 6 in the embodiment of the present invention, and FIG. 21 is a load length ratio t _p (in the embodiment of the present invention). 20 [%]) and t _p (90 [%]) and a table showing the maximum value of the cutting level 10 (%) load length ratio of the change amount per.

  The elastic layer 62 and the surface layer 63 of the developing roller 11 are as described above, but the inventor of the present invention develops with different surface roughness magnitudes, surface roughness shapes, and surface roughness forming methods. A continuous printing test was conducted using the roller 11 as an experimental example.

  There are two methods for forming the roughness of the developing roller 11, that is, the method of forming the surface roughness. One is a method of forming roughness on the outer peripheral surface of the elastic layer 62 and covering the elastic layer 62 with the surface layer 63. The other is a method of covering the elastic layer 62 having a smooth outer peripheral surface with a surface layer 63 to which resin fine particles 75 for roughness formation are added, as shown in FIG.

  As a method for forming the roughness on the surface of the elastic layer 62, a polishing method and a mold transfer method were used.

  When the roughness forming means is polishing, that is, in the method by polishing, it is performed in a wet state, using a water-resistant polishing paper, for example, water-resistant sand paper, and supplying a polishing liquid to the roll while rotating the roll. By making contact, roughness is formed on the outer peripheral surface of the elastic layer 62. As a result, the cross section of the developing roller 11 has a shape as shown in FIG. 10, and a number of fine vertical grooves are formed on the surface in the circumferential direction of the developing roller 11 as shown in FIG.

  In the case where the roughness forming means is mold transfer, that is, in the mold transfer method, a molding die in which minute concaves or convexes, or both concaves and convexes are present at a specific area ratio on the inner surface. The metal core 61 is set in the hollow portion of the metal mold, and a rubber material is poured into the gap between the metal mold and the metal core 61 to heat and crosslink the metal mold. By removing from the mold, roughness is formed on the outer peripheral surface of the elastic layer 62. As a result, the cross section of the developing roller 11 has a shape as shown in FIGS. 10 to 12, and the surface has a large number of minute protrusions or depressions, or a large number of protrusions and depressions, as shown in FIG. It becomes the shape to do.

When the roughness forming means is particles, that is, in the method of forming the surface roughness by adding the resin fine particles 75 to the surface layer 63, the cross section of the developing roller 11 has a shape as shown in FIG. As shown in FIG. 14, the surface has a shape in which a large number of projections exist uniformly. In the present experimental example, spherical polyurethane resin particles were used as the resin fine particles 75. The particle size of the resin fine particles 75 was 2 to 8 [μm]. Further, the fine hardness of the resin fine particles 75 alone is 0.6 [N / mm ² ] or less in Martins hardness.

Further, the surface roughness for the size, the average interval Sm of irregularities, and, as an index ten-point average roughness Rz, the shape of the surface roughness, the load length ratio t _p to (JIS B0601-1994) It was used as an index.

For load length ratio t _p, it is described with reference to FIG. 16. The load length ratio t _p (c [%]) is a percentage with respect to the measured length L of the cut portion length when the roughness curve is cut at a certain cutting level c, and is expressed by the following equation (1). Is done. At this time, the cutting level c is 0 [%] at the highest peak of the roughness curve and 100 [%] at the deepest valley bottom, and the load length ratio t _p (0 [%]) when the cutting level is 0 [%]. Is 0 [%], and the load length ratio t _p (100 [%]) at a cutting level of 100 [%] is 100 [%].

Thus, the load length ratio t _p, so and a roughness width of the convex portion of the curve in the height direction of the roughness (width of the recess) information, useful to the scope defined surface roughness It is.

Specifically, when the load length ratios t _p (10 [%]) and t _p (20 [%]) are small when the cutting level c is 10% and 20%, the roughness curve When the crest portion c has a pointed shape and the cutting level c is 80 [%] and 90 [%], the load length ratios t _p (80 [%]) and t _p (90 When [%]) is small, the width of the valley portion of the roughness curve is wide. In addition, when the change amount t _p (c ₂ ) −t _p (c ₁ ) of the load length ratio is large in the range of the cutting level c ₁ [%] to c ₂ [%], the cutting level c ₁ [%] To c ₂ [%], it means that there is a part where the slope of the roughness curve is gentle.

  If the tip of the peak of the roughness curve has a sharp shape, the pressure applied from the abutting member to the toner 17 riding on the portion becomes locally high, and toner filming is likely to occur. Further, in the roughness curve, when the width of the gentle portion near the flat or the valley portion is too wide, the scraping property of the toner 17 by the toner supply roller 12 is deteriorated, so that toner filming is likely to occur. Become.

Therefore, the load length ratio t _p, in order to improve the scraping of the toner 17 on the developing roller 11 by the toner supply roller 12 is an indicator should know.

The average interval Sm of the unevenness is an average value of the interval from one change point to the next change point, with the change point being the point where the roughness curve changes from a peak to a valley. Then, the average distance Sm of unevenness can be measured by the same measuring method and conditions as the ten-point average roughness Rz and the load length ratio t _p.

Here, assuming form 1 and form 2 of the roughness curve as shown in FIG. 17, it can be seen that the value of the load length ratio t _p is the same in both forms. That is, it can be understood that the average interval Sm of the unevenness is also necessary to accurately define the surface roughness.

  As described above, in the case of the developing roller 11 used in the present embodiment, the average interval Sm of the unevenness is 50 to 200 [μm].

18, the shape of the surface roughness of the developing roller 11 used as an experimental example in continuous printing test, roughness forming means, the ten-point average roughness Rz, and a table showing the load length ratio t _p. Here, among the experimental examples, those in which good results were obtained without causing toner filming on the surface of the developing roller 11 were designated as Examples 1 to 9, and others were designated as Comparative Examples 1 to 6. . Further, the Asker F hardness of the toner supply roller 12 is set to 30 to 70 degrees with respect to the developing roller 11 of the experimental example, and the amount of biting into the developing roller 11 is varied between 0.4 and 1.6 [mm]. The results of the continuous printing test are shown in FIGS.

The determination symbols “◯”, “□”, “Δ”, and “×” in FIGS. 19 and 20 represent the following determination results.
○: No toner filming occurred, dot diameter variation σ of 1by1 pattern is 0.007 or less □: No toner filming occurred, dot diameter variation σ of 1by1 pattern is greater than 0.007, 0.01 or less Δ: No toner filming occurred, dot diameter variation σ of 1by1 pattern is larger than 0.01 x: toner filming occurred In the above determination results, “◯” and “□” were passed, “Δ” and “X” was rejected.

  In Examples 1 to 9, if the toner supply roller 12 has an Asker F hardness of 35 to 65 degrees and the biting amount of the toner supply roller 12 with respect to the developing roller 11 is in the range of 0.5 to 1.5 [mm]. No toner filming occurred, and the dot diameter variation σ of the 1by1 pattern was 0.01 or less. In Examples 1 to 6, in the setting range of the toner supply roller 12, the dot diameter variation σ of the 1by1 pattern is 0.007 or less, which is a better result than Examples 7 to 9.

  On the other hand, in Comparative Examples 1 to 6, toner filming occurred under almost all conditions.

  In Comparative Example 2, the toner filming occurred because the pressure applied to the surface of the developing roller 11 from the contact member was locally increased by adding the resin fine particles 75 having higher hardness than the surface layer 63 to the surface layer 63. This is thought to be due to the higher price.

In the case of the developing roller 11 of other experimental examples except the comparative example 2, whether or not toner filming occurs depends on the load length ratio t _p of the surface roughness. The inventor of the present invention uses t _p (20 [%]) and t _p (90 [%]) among the load length ratios t _p shown in the table of FIG. The amount of change in the load length rate per cutting level 10 [%] shown in FIG. The table shown in FIG. 21 shows an excerpt of these numerical values.

t _p ((n + 1) × 10 [%]) − t _p (n × 10 [%]) (2)
From the table of FIG. 21, it can be seen that Examples 1 to 9 in which toner filming did not occur on the surface of the developing roller 11 satisfied all of the following conditions.

Ten-point average roughness Rz: 2 to 10 [μm]
Load length ratio t _p (20 [%]): 30 [%] or more and 65 [%] or less Load length ratio t _p (90 [%]): 80 [%] or more t _p ((n + 1) × 10 [ %])-T _p (n × 10 [%]): 20 [%] or less (n: integer of 2 to 8)
Here, the load length ratio t _p (20 [%]) is 30 [%] or more and 65 [%] or less, indicating that it is better that the surface roughness peaks are not too sharp. The load length ratio t _p (90 [%]) of 80 [%] or more indicates that the width of the valley portion of the surface roughness should not be too wide. Moreover, the amount of change in the load length ratio per cutting level 10 [%] is 20 [%] or less indicates that the slope between the peaks and valleys of the surface roughness should not be too gentle. Yes.

  On the other hand, Comparative Example 1 in which toner filming occurred on the surface of the developing roller 11 and Comparative Examples 3 to 6 do not satisfy all of the above conditions.

  From the above results, in the developing roller 11 having the elastic layer 62 and the surface layer 63 covering the surface of the elastic layer 62, the surface roughness of the developing roller 11 is expressed by the unevenness formed on the surface of the elastic layer 62. The surface roughness in the circumferential direction of the developing roller 11 measured in accordance with JIS B-0601-1994 is not the one expressed by adding fine particles to the surface layer 63. If all the conditions are satisfied, it can be said that the occurrence of toner filming on the surface of the developing roller 11 is suppressed.

  In addition, regarding the variation σ of the dot diameter of the 1by1 pattern, Examples 1 to 6 are smaller than Examples 7 to 9 because the shape of the surface roughness of the developing roller 11 is smaller than the fine vertical groove shape. It is considered that the shape having a large number of minute protrusions and depressions can suppress the variation in the thickness of the toner layer formed on the developing roller 11.

  Furthermore, in order to form a rough shape satisfying the above conditions by mold transfer, it seems easier to mix convex and concave than only convex or concave.

  Thus, in this embodiment, the developing roller 11 having the elastic layer 62 and the surface layer 63 that covers the outer peripheral surface of the elastic layer 62 and does not contain fine particles has an elastic surface roughness. When the surface roughness in the circumferential direction of the developing roller 11 expressed by the unevenness formed on the outer peripheral surface of the layer 62 and measured in accordance with JIS B0601-1994 satisfies the following conditions, the surface of the developing roller 11 is returned to. The occurrence of toner filming can be suppressed.

Average interval of unevenness Sm = 50 to 200 [μm]
Ten-point average roughness Rz = 2 to 10 [μm]
Load length ratio t _p (20 [%]): 30 [%] or more and 65 [%] or less Load length ratio t _p (90 [%]): 80 [%] or more t _p ((n + 1) × 10 [ %])-T _p (n × 10 [%]): 20 [%] or less (n: integer of 2 to 8)
The Asker F hardness of the toner supply roller 12 is preferably 35 to 65 degrees, and the amount of biting of the toner supply roller 12 with respect to the developing roller 11 is preferably 0.5 to 1.5 [mm].

  Further, the shape of the roughness formed on the outer peripheral surface of the elastic layer 62 is a convex shape close to a hemisphere by mold transfer, rather than forming many fine grooves extending in the circumferential direction of the developing roller 11 by polishing. In the case where a concave pattern is formed and a fine pattern such as a 1by1 pattern is printed, variation in the size of the toner image developed on the photosensitive drum 13 can be suppressed.

  In the present embodiment, the case where the image forming apparatus 10 is a printer that forms a monochrome image of the direct transfer method having one developing device 20 has been described. However, in the present invention, a plurality of image forming apparatuses 10 are provided. The present invention can also be applied to a device for forming a color image having the developing device 20 on the stage or an intermediate transfer type device.

  Furthermore, the present invention can also be applied when the image forming apparatus 10 is an MFP, a facsimile machine, and a copier.

  The present invention is not limited to the above-described embodiment, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

  The present invention can be used in a developing device and an image forming apparatus.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Developing roller 12 Toner supply roller 13 Photosensitive drum 17 Toner 20 Developing apparatus 62 Elastic layer 63 Surface layer

Claims (7)

A developer carrier for developing a latent image on the electrostatic latent image carrier;
A developing device comprising a developer supplying member for supplying the developer to the developer carrying member,
The developer carrier has an elastic layer and a surface layer that covers the outer peripheral surface of the elastic layer and does not contain fine particles,
The developing device according to claim 1, wherein the roughness of the surface of the developer carrying member satisfies the following conditions.
Average interval of unevenness Sm = 50 to 200 [μm]
Ten-point average roughness Rz = 2 to 10 [μm]
Load length ratio t _p (20 [%]): 30 [%] or more and 65 [%] or less Load length ratio t _p (90 [%]): 80 [%] or more t _p ((n + 1) × 10 [ %])-T _p (n × 10 [%]): 20 [%] or less (n: integer of 2 to 8)   The developing device according to claim 1, wherein the roughness in the circumferential direction of the surface of the developer carrying member is expressed by the roughness formed on the outer circumferential surface of the elastic layer.   The developing device according to claim 2, wherein the roughness of the outer peripheral surface of the elastic layer is formed by mold transfer.   The developing device according to claim 2, wherein the shape of roughness of the outer peripheral surface of the elastic layer is a shape in which convexity and concaveness are mixed.   The developing device according to claim 1, wherein the developer supply member has an Asker F hardness of 35 degrees or more and 65 degrees or less.   The developing device according to claim 1, wherein an amount of biting of the developer supply member with respect to the developer carrying member is 0.5 [mm] or more and 1.5 [mm] or less.   An image forming apparatus comprising the developing device according to claim 1.

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