JP2011081153A - Developing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always provide a preferable image without an abnormal image by accurately detecting a toner density and controlling a toner density with high accuracy even when the fluidity of the toner greatly changes, in an image forming apparatus including a developing device employing a two-component developing system. <P>SOLUTION: There may occur problems of decrease in the fluidity of a developer due to degradation of the developer or of significant decrease in the fluidity of a developer due to continuous printing of low-density documents, and these problems can not be sufficiently solved only by a density detecting means arranged below a stirring member, and detecting the toner density of the two-component developer. Decrease in the fluidity is preliminarily sensed and the toner density is controlled with high accuracy by arranging a back-flow plate, which allows an excess developer regulated by a layer thickness regulating member to flow from the layer thickness regulating member back to a separated position, and also by arranging a density detecting means, which detects a toner density of a two-component developer flowing over the back-flow plate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a developing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, and an image forming apparatus using the same, and more particularly, a developing device using a two-component developer and an image forming using the same. Relates to the device.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a photosensitive drum as an image carrier, and the electrostatic latent image on the surface of the photosensitive drum is developed with a developer. A toner image is formed on the surface, the toner image is transferred from the photosensitive drum to a sheet (recording paper) that is a transfer material, and the transfer material to which the toner image has been transferred is heated and pressurized to place the toner image on the transfer material. Has been established. Further, since residual toner and residual charge remain on the surface of the photosensitive drum, the residual toner is removed by a cleaning device and the residual charge is removed by a charge eliminating device.

  As a general development method for developing an electrostatic latent image on a photosensitive drum, a two-component development method using a two-component developer in which a developer is composed of toner and a magnetic carrier, and a developer is composed only of toner. There is a one-component development method using a one-component developer.

  In the two-component development system, a two-component developer composed of toner and a magnetic carrier is supported on the sleeve of the developing roller by utilizing the magnetic force of a magnet included in the developing roller as a developer bearing member, and the sleeve is rotated. Thus, the toner is conveyed to a developing area facing the photosensitive drum, and only the toner is transferred to the latent image, that is, developed, and after the development, the developer is collected in the developing tank. Therefore, in order to stabilize the development, toner that is a density detection unit that replenishes the consumed toner from the toner replenishment mechanism and controls the ratio of the toner contained in the developer, that is, the toner density to be constant. A density detection sensor is required.

  For the toner concentration detection sensor, a magnetic permeability detection sensor is generally used by paying attention to the fact that the magnetic permeability of the carrier and the toner is different, and in order to enable accurate concentration detection, for example, JP-A-2-93568 (Patent Document) In 1), a vibration waveform component corresponding to the development density is output from the sensor while rubbing the stirring sensor surface with the stirring member and the developer in the vicinity of the stirring member and stirring and mixing, and the waveform component and the reference density level are compared. However, it has been proposed to perform drive control of the toner supply mechanism.

  However, in order to perform density control with higher accuracy, it is necessary to provide a plurality of density detection means. For example, as described in JP-A-2006-293016 (Patent Document 2), stress applied to the developer In order to reduce the developer life and extend the life of the developer, it is disclosed that a density control means is provided for each stirring member, but one stirring member is driven independently so that it can be stopped if necessary. Therefore, a separate drive device is necessary and becomes large.

  In addition, as disclosed in Japanese Patent Application Laid-Open No. 2007-140291 (Patent Document 3), there is a device in which density control means are provided on the upstream side and the downstream side in the agitating / conveying direction. Since the length exceeds the length, the length in the longitudinal direction of the developing device becomes long, and the developing device becomes large.

  In addition to this, it is assumed that the developing device is not increased in size or provided with another new driving source, that is, is devised so as not to exceed the restrictions on the layout of the developing device and the image forming apparatus. JP-A-11-95537 (Patent Document 4) and JP-A-2008-129131 (Patent Document 5) are disclosed, both of which are provided with a plurality of concentration control means in the vicinity of the stirring member. There is only.

  In Patent Documents 2 to 5, by arranging a plurality of density detecting means in the vicinity of the stirring member, the toner density when the toner charge amount and bulk change are changed compared to the case where a single density detecting means is provided. The accuracy of accurate detection is improved, the image density is stable, and it is possible to obtain a good image free from abnormal images such as background contamination and toner scattering.

Japanese Patent Laid-Open No. 2-93568 JP 2006-293016 A JP 2007-140291 A JP-A-11-95537 JP 2008-129131 A

  However, by providing a plurality of density detecting means in the vicinity of the stirring member, accurate toner concentration control can be performed up to the weakly stirred portion in the vicinity of the layer thickness regulating member where the excess developer regulated by the layer thickness regulating member stays. Therefore, the flowability of the developer decreased due to deterioration of the developer due to, for example, the toner fusing to the carrier surface as well as the printing durability, or the coating agent on the carrier surface being partially peeled off.

  In addition, when a low-density original is continuously printed, the toner is hardly consumed. Therefore, the external additive of the toner is buried in the toner resin surface or the toner is not replaced while the carrier surface is charged. Therefore, it is difficult to accurately control the toner density.

  The present invention regulates a developing tank that contains a two-component developer containing toner and a carrier, a developing roller that supplies the two-component developer to the photosensitive drum, and a supply amount of the two-component developer that is supplied to the photosensitive drum. A regulating member, a plurality of agitating members for agitating the developer in the developing tank, a first toner concentration detection sensor for detecting the toner concentration of the two-component developer disposed below the agitating member, and a layer thickness regulating member A recirculation plate that recirculates the excess developer regulated by the above to a position separated from the layer thickness regulating member, a second toner concentration detection sensor that detects the toner concentration of the two-component developer that flows on the recirculation plate, and a developer tank A second toner concentration detection sensor that detects the toner concentration of the two-component developer that flows on the reflux plate and can detect a significant decrease in fluidity in advance. , More accuracy It is characterized in that to enable high toner density detection.

  Further, the present invention provides a first density detection sensor for detecting the toner density of the two-component developer disposed below the stirring member, and a second density detection for detecting the toner density of the two-component developer flowing on the reflux plate. The sensor preferably detects the concentration of the developer based on a change in the magnetic permeability of the developer.

  Further, in the present invention, it is preferable that the detection surface of the second density detection sensor for detecting the toner density of the two-component developer flowing on the reflux plate and the upper surface of the reflux plate are on the same plane.

  Furthermore, in the present invention, it is preferable that a peripheral speed of the developing roller is 314 (mm / sec) to 1382 (mm / sec).

  Furthermore, in the present invention, the average particle diameter D50 of the carrier is preferably 30 μm or more and 90 μm or less.

  Furthermore, according to the present invention, by using the image forming apparatus including the developing device, the image forming apparatus has improved chargeability and developer transportability, and improved quality of an image output after development. be able to.

  Furthermore, the image forming apparatus of the present invention forcibly applies toner onto the photosensitive drum in accordance with the density detection output result by the second density detection sensor that detects the toner density of the two-component developer flowing on the reflux plate. It is preferable to develop.

  According to the present invention, in addition to the first toner concentration detection sensor that detects the toner concentration of the two-component developer disposed below the stirring member, the excess developer regulated by the layer thickness regulating member is removed from the layer thickness regulating member. Since the second density sensor for detecting the toner density of the two-component developer flowing on the reflux plate and the reflux plate for refluxing to a position separated from the reflux plate is also provided, the developer does not stay in the weakly agitated portion. In addition, even when the developer on the reflux plate does not flow and accurate toner density control becomes difficult, it can be detected immediately, so that more accurate and accurate toner density detection is possible.

  In addition, a first concentration detection sensor that detects the toner concentration of the two-component developer disposed below the stirring member, and a second concentration detection sensor that detects the toner concentration of the two-component developer flowing on the reflux plate, By using a magnetic permeability sensor that detects the developer concentration based on the change in the magnetic permeability of the developer, the developer toner concentration can be detected with high sensitivity.

  In addition, according to the present invention, the development surface on the reflux plate is formed by making the detection surface of the second density detection sensor for detecting the toner concentration of the two-component developer flowing on the reflux plate and the upper surface of the reflux plate on the same plane. Since the flow of the agent is not hindered and the developer is not deposited on the detection surface, the developer toner concentration can be detected with high sensitivity.

  Further, according to the present invention, the developer in the developing device can be stably conveyed by setting the peripheral speed of the developing roller within the range of 314 (mm / sec) to 1382 (mm / sec). Therefore, the toner density in the developing device can be detected with high accuracy.

  In addition, according to the present invention, the quality of the output image can be improved by setting the average particle diameter D50 of the carrier to a fine carrier in the range of 30 μm to 90 μm.

  Further, according to the present invention, by including the developing device of the present invention, the image forming apparatus can improve the chargeability and developer transportability, and can realize the improvement in the quality of the image output after the development over a long period of time. it can.

  Further, according to the present invention, the toner is forcibly developed on the photosensitive drum according to the density detection output result of the second density detection sensor, so that the external additive of the toner is buried in the toner resin surface. The toner and the toner that has not been replaced while being charged on the surface of the carrier are also developed and consumed, so that the fluidity of the developer is restored, and the toner density can be detected with higher accuracy and accuracy.

1 is a schematic diagram showing an overall configuration of an image forming apparatus equipped with a developing device according to the present invention. It is sectional drawing which shows typically the structure of the developing device which concerns on this embodiment. FIG. 10 is a diagram illustrating output characteristics of a toner concentration detection sensor attached to the developing device according to the present embodiment. FIG. 3 is a block diagram schematically showing an electrical configuration related to toner replenishment operation control of an image forming apparatus equipped with a developing device according to the present invention. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus according to an exemplary embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing the configuration of an image forming apparatus equipped with a developing device according to the present invention, which is an example of an embodiment of the invention.

  As shown in FIG. 1, in this embodiment, a photosensitive drum (electrostatic latent image carrier) 15 on which an electrostatic latent image is formed, a charging device 16 for charging the surface of the photosensitive drum 15, and a photosensitive An exposure device 17 that forms an electrostatic latent image on the surface of the photosensitive drum 15; a developing device 1 that supplies toner to the electrostatic latent image on the surface of the photosensitive drum 15 to form a toner image; and a toner that is on the surface of the photosensitive drum 15 A transfer device 18 for transferring an image to a recording medium, a fixing device 20 for fixing the transferred toner image to the recording medium, a cleaning device 19, a paper feed tray 23, a scanner unit 24, and a paper discharge tray 25. The developing device 1 employs the configuration of the developing device according to the present invention.

  The image forming apparatus 100 that forms an image using toner by an electrophotographic method forms a single color image on a predetermined sheet based on, for example, image data transmitted from each terminal device on the network.

  The photosensitive drum 15 is a roller-like member having a photosensitive film on which a latent electrostatic image and, consequently, a toner image is formed. For the photosensitive drum 15, for example, a roller-shaped member including a conductive substrate (not shown) and a photosensitive film (not shown) formed on the surface of the conductive substrate can be used. As the conductive substrate, a conductive substrate having a cylindrical shape, a columnar shape, a sheet shape or the like can be used, and among them, the cylindrical conductive substrate is preferable. Examples of the photosensitive film include an organic photosensitive film and an inorganic photosensitive film.

  As an organic photosensitive film, a laminate of a charge generation layer, which is a resin layer containing a charge generation material, and a charge transport layer, which is a resin layer containing a charge transport material, a charge generation material and a charge transport material in one resin layer And a resin layer (single layer body). Examples of the inorganic photosensitive film include films containing one or more selected from zinc oxide, selenium, amorphous silicon and the like. A base film may be interposed between the conductive substrate and the photosensitive film, and a surface film (protective film) for mainly protecting the photosensitive film may be provided on the surface of the photosensitive film.

  The charging device 16 is connected to a power source (not shown) and applies a voltage to the charging device 16. The charging device 16 receives a voltage from a power source and charges the surface of the photosensitive drum 15 to a predetermined polarity and potential. In this embodiment, a charger-type charger is used, but the present invention is not limited to this, and a charger such as a charging brush-type charger, a roller-type charger, a saw-tooth type charger, an ion generator, or a magnetic brush can be used.

  The exposure device 17 receives image information of a document read by the scanner unit 24 (reading unit 105 shown in FIG. 5) or image information from an external device, and is in a charged state with signal light corresponding to the image information. Irradiate the surface of the photosensitive drum 15. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 15.

  As the exposure device 17, a laser scanning device including a light source is used. The laser scanning device is a device that combines, for example, a light source, a polygon mirror, an fθ lens, a reflection mirror, and the like. As the light source, for example, a semiconductor laser, an LED array, an electroluminescence (EL) element, or the like can be used.

  The transfer device 18 is a roller-like member provided so as to be in pressure contact with the photosensitive drum 15, is rotatably supported by a support member (not shown), and is rotatably provided by a driving unit (not shown). For the transfer device 18, for example, a roller-shaped member including a metal core with a diameter of 8 to 10 mm and a conductive elastic layer formed on the surface of the metal core is used.

  As the metal forming the metal core, stainless steel, aluminum, or the like can be used. As the conductive elastic layer, a rubber material in which a conductive material such as carbon black is blended with a rubber material such as ethylene-propylene rubber (EPDM), foamed EPDM, or foamed urethane can be used.

In synchronism with the toner image being conveyed by the rotation of the photosensitive drum 15 to a pressure contact portion (hereinafter referred to as “transfer nip portion”) 18 n between the transfer device 18 and the photosensitive drum 15, the paper feed tray 23 is synchronized. The recording medium is supplied one by one through a pickup roller and a registration roller (not shown). As the recording medium passes through the transfer nip portion 18n of the transfer device 18, the toner image on the surface of the photosensitive drum 15 is transferred to the recording medium.
A power supply (not shown) is connected to the transfer device 18, and a voltage having a polarity opposite to the charging polarity of the toner constituting the toner image is applied to the transfer device 18 when the toner image is transferred to a recording medium. As a result, the toner image is smoothly transferred to the recording medium. In this manner, the toner image on the surface of the photosensitive drum 15 is transferred to the recording medium by the transfer device 18.

  The cleaning device 19 includes a cleaning blade (not shown) and a toner storage tank (not shown). The cleaning blade is a plate-like member that extends in parallel to the longitudinal direction of the photosensitive drum 15 and is provided so that one end in the short direction abuts the surface of the photosensitive drum 15. The cleaning blade removes toner, paper dust, and the like remaining on the surface of the photosensitive drum 15 from the surface of the photosensitive drum 15 after transferring the toner image to the recording medium. The toner storage tank is a container-like member having an internal space, and temporarily stores the toner removed by the cleaning blade. In this manner, the surface of the photosensitive drum 15 after the toner image is transferred is cleaned by the cleaning device 19.

  The fixing device 20 includes a fixing roller 21 and a pressure roller 22. The fixing roller 21 is a roller-like member, and is rotatably supported by a support member (not shown), and is provided so as to be rotatable around an axis line by a drive unit (not shown).

  The fixing roller 21 has a heating member (not shown) inside, and heats and melts the toner constituting the unfixed toner image carried on the recording medium conveyed through the transfer nip portion 18 n of the transfer device 18. To fix on the recording medium. As the fixing roller 21, for example, a roller-shaped member including a cored bar and an elastic layer is used. The core metal is formed of a metal such as iron, stainless steel, or aluminum. The elastic layer is formed of an elastic material such as silicone rubber or fluorine rubber, for example. The heating member receives heat from a power source (not shown) and generates heat. A halogen lamp, an infrared lamp, etc. can be used for a heating member.

  The pressure roller 22 is a roller-like member, is rotatably supported, and is provided so as to be in pressure contact with the fixing roller 21 by a pressure member (not shown). The pressure roller 22 rotates following the rotation of the fixing roller 21. A pressure contact portion between the fixing roller 21 and the pressure roller 22 is a fixing nip portion 20n.

  The pressure roller 22 promotes fixing of the toner image to the recording medium by pressing the toner in a molten state against the recording medium when the fixing roller 21 heat-fixes the toner image to the recording medium. For the pressure roller 22, a roller-like member having the same configuration as that of the fixing roller 21 can be used. A heating member may also be provided inside the pressure roller 22. A heating member similar to the heating member inside the fixing roller 21 can be used.

  The fixing device 20 passes the recording medium onto which the toner image has been transferred to the fixing nip portion 20n, melts the toner constituting the toner image, and presses the recording medium against the recording medium, thereby fixing the toner image on the recording medium. To print.

  The recording medium on which the image is printed is discharged and stacked on a discharge tray 25 provided on the side surface in the vertical direction of the image forming apparatus 100 in FIG. Note that the sheet feeding tray 23 accommodates a recording medium.

  The scanner unit 24 is provided with a document setting tray (not shown), an automatic document feeder (RADF), and the like, and a document reading device (not shown).

  The automatic document feeder conveys a document placed on a document set tray to a document placing table of a document reading device. The document reading device includes a document placing table, a document scanning device, a reflecting member, a photoelectric conversion device (hereinafter referred to as “CCD”) line sensor, and the like, and is placed on the document placing table. The image information of the original is read every plural lines, for example every ten lines.

The document placing table is a glass plate-like member for placing a document for reading image information.
The document scanning device includes a light source (not shown) and a first reflection mirror, and reciprocates at a constant speed V in parallel along the lower surface in the vertical direction of the document placement table, thereby forming an image of the document placed on the document placement table. Irradiate the surface with light. A reflected light image is obtained by this light irradiation.

  The light source is a light source for irradiating a document placed on the document table. The first reflecting mirror reflects the reflected light image toward a reflecting member (not shown).

  The reflecting member includes a second reflecting mirror, a third reflecting mirror, and an optical lens (not shown), and forms a reflected light image obtained by the document scanning device on the CCD line sensor. The reflecting member reciprocates at a speed of V / 2 following the reciprocating movement of the document scanning device.

  The second and third reflection mirrors reflect the reflected light image so that the reflected light image faces the optical lens. The optical lens forms a reflected light image on the CCD line sensor.

  The CCD line sensor includes a CCD circuit (not shown) that photoelectrically converts a reflected light image formed by the optical lens into an electric signal, and outputs an electric signal as image information to an image processing unit in the control means. The image processing unit converts image information input from an external device such as a document reading device or a personal computer into an electrical signal and outputs the electrical signal to the exposure device 17.

  Next, a characteristic configuration of the developing device 1 according to the present embodiment will be described in detail with reference to the drawings. FIG. 2 is an explanatory diagram showing the configuration of the developing device according to the present embodiment.

  The developing device 1 includes a developing tank 2, a developing roller 3, a first stirring member 4, a second stirring member 5, a conveying member 6, a layer thickness regulating member 7, a regulating member support 8, and a reflux plate. 9, a first toner concentration detection sensor 12, a second toner concentration detection sensor 13, and a toner supply roller 14.

  Inside the developing tank 2, a developing roller 3, a first stirring member 4, a second stirring member 5, a conveying member 6, a layer thickness regulating member 7, a reflux plate 9, and the like are accommodated. The developer is a two-component developer containing toner and a carrier that is magnetic powder. Further, in the developing tank 2, when the developing device 1 is mounted on an electrophotographic image forming apparatus, an opening 2a is formed on a side surface facing a photoreceptor provided in the image forming apparatus. A toner replenishing port 2 b is formed on the top surface of the developing tank 2 in the vertical direction.

  A toner cartridge and a toner hopper (not shown) are provided above the developing tank 2 in the vertical direction. More specifically, the toner cartridge, the toner hopper, and the developing tank 2 are provided in this order from the top to the bottom in the vertical direction. The toner cartridge accommodates toner in its internal space and is detachably attached to an image forming apparatus main body (not shown) on which the developing device 1 is mounted. Further, the toner cartridge is rotationally driven around the axis by a driving unit (not shown) provided in the image forming apparatus. An elongated opening extending in the longitudinal direction is formed on the side surface in the longitudinal direction of the toner cartridge, and the toner falls from the elongated opening and is supplied to the toner hopper as the toner cartridge rotates.

  The toner hopper is provided, for example, such that a toner supply port that is an opening formed in the bottom surface in the vertical direction communicates with a toner supply port 2 b that is an opening formed in the top surface in the vertical direction of the developing tank 2 in the vertical direction. In the toner hopper, a toner supply roller 14 is provided above the toner supply port in the vertical direction. The toner replenishing roller 14 is rotatably supported by a toner hopper and is rotationally driven by a driving unit (not shown). The rotational driving of the toner replenishing roller 14 is controlled by a control means (not shown) provided in the image forming apparatus according to the detection result of the toner density in the developing tank 2 by the toner density sensors 12 and 13. The toner is replenished into the developing tank 2 through the toner supply port and the toner supply port 2b by the rotational driving of the toner supply roller 14.

  The toner replenishing roller 14 is provided with a cylindrical porous elastic member such as foamed urethane around a core metal, and the toner held by the porous elastic member of the toner replenishing roller 14 in the toner hopper is The toner replenishing port 2b and the toner replenishing roller 14 are rubbed off from the toner replenishing roller 14 and replenished into the developing tank 2.

  The developing roller 3 is a roller-like member that is at least partially supported by the developing tank 2 so as to be rotatable, and is driven to rotate about an axis by a driving unit (not shown). Further, the developing roller 3 faces the photosensitive drum 15 through the opening 2 a of the developing tank 2.

  In this embodiment, the developing roller 3 is provided so as to be separated from the photosensitive drum 15 with a gap, and the closest portion where the developing roller 3 and the photosensitive drum 15 face each other is the developing nip portion 3n. It is.

  In the developing nip portion 3n, toner is supplied to the surface of the photosensitive drum 15 from a developer layer (not shown) on the surface of the developing roller 3. In the developing nip portion 3n, a developing bias voltage is applied to the developing roller 3 from a power source (not shown) connected to the developing roller 3, and toner is transferred from the developer layer on the surface of the developing roller 3 to the surface of the photosensitive drum 15. Proceed smoothly.

  The developing roller 3 includes a magnet roller 10 and a sleeve 11. The magnet roller 10 has both ends in the longitudinal direction supported by the developing tank wall of the developing tank 2, and magnetic poles, which are a plurality of bar magnets having a rectangular cross section, are spaced apart from each other at the circumferential position of the developing roller 3. 3 is a multi-pole magnetized magnet roller arranged radially in the radial direction.

  The sleeve 11 is a cylindrical member that is externally fitted to the magnet roller 10, is rotatably supported by the developing tank 2 and a support member (not shown), and is rotatably provided by a drive unit (not shown). The sleeve 11 is not particularly limited as long as it is a non-magnetic material, and aluminum, aluminum alloy, SUS304, which is stainless steel defined in JIS-G4305, or the like is preferably used. Furthermore, in order to satisfactorily carry and transport the developer, it is preferable that moderate irregularities are formed on the surface of the sleeve 11. For example, the surface roughness Rz (JIS B0601: 10-point average roughness) is 5 Blasting is performed so as to be equal to or larger than (μm) and equal to or smaller than 10 (μm). In the present embodiment, the sleeve 11 rotates counterclockwise, and the photosensitive drum 15 rotates clockwise.

  Each of the first stirring member 4 and the second stirring member 5 is a roller-like member that is rotatably supported by the developing tank 2 and can be driven to rotate about an axis by a driving unit (not shown).

  In the present embodiment, the first stirring member 4 rotates counterclockwise and the second stirring member 5 rotates clockwise. The first stirring member 4 is provided at a position that faces the photosensitive drum 15 via the developing roller 3 and that is vertically lower than the developing roller 3. The second agitating member 5 is provided at a position facing the developing roller 3 via the first agitating member 4 and being vertically lower than the developing roller 3. The first agitating member 4 and the second agitating member 5 agitate the developer stored in the developing tank 2 to give a uniform charge to the toner, and pump up the charged developer to Supply to the surroundings.

  The conveyance member 6 is a roller-like member that is rotatably supported by the developing tank 2 and is rotatably driven by a driving unit (not shown). The conveying member 6 is provided opposite to the first stirring member 4 with the second stirring member 5 interposed therebetween, and is provided below the toner supply port 2b in the vertical direction. The conveying member 6 conveys the toner replenished into the developing tank 2 through the toner replenishing port 2 b around the second stirring member 5.

  The layer thickness regulating member 7 is a plate-like member extending parallel to the axial direction of the developing roller 3, and one end in the short direction is supported by the developing tank 2 and the regulating member support 8 above the developing roller 3 in the vertical direction. And the other end is provided so as to be separated from the surface of the developing roller 3 with a gap.

  The layer thickness regulating member 7 is formed of, for example, stainless steel such as SUS304 or SUS316, a nonmagnetic metal having elasticity such as aluminum, or a synthetic resin. In the present embodiment, a thin plate-like stainless steel is used for the layer thickness regulating member 7.

  The regulating member support 8 supports the layer thickness regulating member 7 together with the developing tank 2. Specifically, one end of the layer thickness regulating member 7 in the short direction and the vicinity thereof are supported so as to be sandwiched between the regulating member support 8 and the developing tank 2. The restricting member support 8 is formed of a material such as synthetic resin or metal. In this embodiment, it is formed from a synthetic resin. The layer thickness regulating member 7 removes excess developer (surplus developer) from the developer layer carried on the surface of the developing roller 3, and regulates the layer thickness of the developer layer to keep the developer transport amount constant. Adjust. Further, the layer thickness regulating member 7 imparts electric charge to the developer that is insufficiently charged in the developer layer by rubbing between the other end in the short side direction and the developer layer, and is contained in the developer layer. Charge the developer sufficiently.

  The reflux plate 9 is a plate provided in the developing tank 2 upstream of the layer thickness regulating member 7 in the rotation direction of the developing roller 3 and above the first stirring member 4 and the second stirring member 5 in the vertical direction. It is a shaped member. The reflux plate 9 has one end 9 b 1 in the short direction facing the surface of the developing roller 3, spaced apart with a gap, and the other end 9 b 2 extending in a direction away from the developing roller 3.

  In the present embodiment, the upper surface in the vertical direction of the reflux plate 9 is parallel to the horizontal direction at the end portion 9b1 on the developing roller 3 side in the short side direction of the reflux plate 9 and the vicinity thereof, and at other portions. It is provided so as to descend downward in the vertical direction as it is separated from the developing roller 3.

  In the present embodiment, the reflux plate 9 is supported by a support member 9a that is formed so as to penetrate in the longitudinal direction of the reflux plate 9 in the lower part in the vertical direction and is inserted into the through hole.

  By providing the reflux plate 9, the developer does not stay in the weakly agitated portion in the vicinity of the layer thickness regulating member 7, so that a smooth flow of the developer in the developing tank 2 occurs, and the toner is uneven. Generation of charging, toner blocking, etc. is prevented.

  More specifically, the developer removed from the surface of the developing roller 3 by the layer thickness regulating member 7 temporarily stays in the space above the developing roller 3, but when the amount increases, the upper surface in the vertical direction of the reflux plate 9 is separated from the developing roller 3. It begins to flow in the direction of separation. The developer flows along the upper surface of the reflux plate 9, and falls toward the second stirring member 5 from the end portion 9 b 2 opposite to the developing roller 3 side in the short direction of the reflux plate 9. The dropped developer is uniformly mixed with the other developer and newly supplied toner by the first stirring member 4 and the second stirring member 5, and is conveyed toward the developing roller 3. In this way, a smooth flow of the developer in the developing tank 2 occurs.

The dimensions of the first stirring member 4, the second stirring member 5, the conveying member 6, the layer thickness regulating member 7, and the reflux plate 9 are appropriately determined from an appropriate range according to the dimensions of the developing roller 3.
For example, the first toner concentration detection sensor 12 is mounted on the bottom surface of the developing tank 2 below the second stirring member 5 in the vertical direction so that the first toner concentration detection sensor 12 sensor detection surface 12a is exposed inside the developing tank 2. Provided.

  The second toner concentration detection sensor 13 is mounted on the upper surface of the reflux plate 9 in the vertical direction.

  The first toner concentration detection sensor 12 and the second toner concentration detection sensor 13 are electrically connected to control means (not shown). The control means controls to rotate the toner cartridge according to the detection results of the first toner concentration detection sensor 12 and the second toner concentration detection sensor 13 and replenish the toner into the developing tank 2 via the toner hopper. . That is, when it is determined that the detection results by the first toner concentration detection sensor 12 and the second toner concentration detection sensor 13 are lower than the toner concentration setting value, a control signal is sent to the driving means for rotating the toner cartridge, and the toner cartridge is rotated. Drive. As the first toner concentration detection sensor 12 and the second toner concentration detection sensor 13, a general toner concentration detection sensor can be used, and examples thereof include a transmitted light detection sensor, a reflected light detection sensor, and a magnetic permeability detection sensor. Among these, a magnetic permeability detection sensor is preferable.

  A power supply (not shown) is connected to the toner concentration detection sensor. The power supply applies a drive voltage for driving the toner concentration detection sensor and a control voltage for outputting a detection result of the toner concentration to the control means. Application of a voltage to the magnetic permeability detection sensor by the power source is controlled by the control means. The permeability detection sensor is a type of sensor that receives the control voltage and outputs the toner density detection result as an output voltage value. Basically, the sensitivity near the median value of the output voltage is good. It is used by applying a control voltage to obtain a voltage. Examples of this type of toner concentration detection sensor include TS-L, TS-A, and TS-K (all are trade names, manufactured by TDK Corporation).

  The control unit may be provided exclusively for the developing device 1 or may also be a control unit provided in an image forming apparatus to which the developing device 1 is attached.

  Further, it is difficult for the second toner concentration detection sensor 13 to achieve accurate concentration control only with the first toner concentration detection sensor 12 mounted on the bottom surface of the developing tank 2 below the second stirring member 4 in the vertical direction. It was added to eliminate the problem.

  In other words, the developer fluidity decreases due to the deterioration of the developer due to, for example, the toner fusing to the carrier surface as well as the printing durability, or the coating agent on the carrier surface is partially peeled off. When a low-density original is continuously printed, the toner is hardly consumed. Therefore, the external additive of the toner is buried in the toner resin surface, or the toner is not replaced while the carrier surface is charged. The fluidity of the agent is greatly reduced. Although the reflux plate is arranged to allow the accumulated developer in the vicinity of the layer thickness regulating member to flow in the direction away from the developing roller 3 on the vertical upper surface of the reflux plate 9, If it decreases significantly and eventually stops flowing, the detection output from the first toner concentration detection sensor 12 will not be output, and accurate concentration detection will not be possible. This is because, if the two-toner density detection sensor 13 is also provided on the reflux plate 9, it is possible to quickly detect a significant decrease in the fluidity on the reflux plate and to detect the density with higher accuracy.

  Further, it is preferable that the sensor detection surface 13 a of the second toner concentration detection sensor 13 is provided so as to be flush with the top surface of the reflux plate 9.

  On the sensor (on the same plane), if the sensor detection surface 13a of the second toner concentration detection sensor 13 protrudes from the top surface of the reflux plate 9, a sufficient flow of the developer is made on the reflux plate. Unless it is, the flow of the developer on the reflux plate is only hindered. Conversely, if the developer is disposed at a position recessed from the top surface of the reflux plate 9, only a small amount of developer flows on the reflux plate. This is because, although it becomes possible to detect, if the developer deteriorates and the fluidity decreases, the developer accumulates in a recessed position, which hinders density detection.

  However, if the developer fluidity gradually decreases due to the deterioration of the developer due to, for example, the toner fusing to the carrier surface along with the printing durability or the coating agent on the carrier surface partially peeling off The second toner density detection sensor 13 can detect the density at any time. However, since the low density original is continuously printed and the toner is hardly consumed, the toner external additive is applied to the toner resin surface. If the developer fluidity drops significantly because it is buried or the toner is not replaced while the carrier surface is charged, the developer that should flow on the reflux plate stops flowing all at once. In some cases, it is impossible to detect the density with high accuracy by using only the first toner density detection sensor 12 and the second toner density detection sensor 13.

  In such a case, the density detection output itself of the second toner density detection sensor 13 is not output. At this time, the printing is stopped and the toner is forcibly developed on the photosensitive drum 15 to consume the toner. In this case, the toner in the developer in the developing tank 2 is replaced with the undegraded toner supplied from the toner hopper, so that the fluidity of the developer in the developing tank 2 is restored.

  Hereinafter, operation control related to toner density control will be described in more detail.

  FIG. 3 is a diagram showing output characteristics of the toner density detection sensor, and FIG. 4 is a block diagram showing a simplified electrical configuration relating to toner replenishment operation control.

  Usually, a non-magnetic material is used for the toner of the two-component developer, and a magnetic material such as iron powder or ferrite is used for the carrier. The magnetic permeability detects the magnetic property of the magnetic material in the developer. When the mixing ratio of the magnetic material and the non-magnetic material in the developer, that is, the relative concentration of the magnetic material changes, the detection output changes. Therefore, by detecting the magnetic permeability of the developer, it is possible to measure the concentration of the carrier that is a magnetic material in the developer, and conversely, the concentration of the toner that is a non-magnetic material in the developer.

  FIG. 3 illustrates the relationship between the toner concentration in the developer (T / D: T is toner, D is developer) in the toner concentration detection sensor and the magnetic permeability detection output voltage of the sensor. Reference numeral 50 denotes an output characteristic of the toner density detection sensor. The proper use toner density Ts is determined according to the type of the two-component developer, the reference voltage Vs corresponding to the toner density Ts in the output characteristics of the toner density detection sensor is obtained, and the proper use toner density Ts and the reference voltage Vs are obtained. It can be stored in advance in the storage unit 52 of the control unit 51 provided in the developing device 1. When the toner density detection sensor outputs a detection value lower than the reference voltage Vs, the density of the magnetic material in the developer, that is, the carrier, is low, that is, the density of the toner that is a non-magnetic material is high. Does not output replenishment operation instructions. On the contrary, when the toner concentration detection sensor outputs a detection value higher than the reference voltage Vs, since the carrier concentration in the developer is high, that is, the toner concentration is low, the control unit 51 causes the toner hopper to A replenishment operation instruction is output, and toner is replenished into the developing tank 2 from the toner hopper via the toner replenishment roller 14.

In the developing tank 2, there are two toner density detection sensors that operate as described above, that is, the toner density of the developer in the developing tank 2 by the first toner density detection sensor 12 and the second toner density detection sensor 13. The toner concentration of the two-component developer flowing on the reflux plate can be measured.
The toner concentration in the developing tank 2 is uniform regardless of the location unless the flowability of the developer is significantly reduced due to the deterioration of the developer. The detection values of the two toner density detection sensors 13 are the same.

  However, if the developer fluidity is significantly reduced due to the deterioration of the developer, the density detection output itself of the second toner density detection sensor 13 is not output and becomes 0 (V). At this time, printing is stopped and toner is forcibly developed on the photosensitive drum 15. As described above, if the toner is consumed, the toner in the developer in the developing tank 2 is replaced with the non-deteriorated toner replenished from the toner hopper, so that the fluidity of the developer in the developing tank 2 is restored. As a result, the density detection output of the second toner density detection sensor 13 is output.

  Next, the electrical configuration of the image forming apparatus 100 according to the present embodiment will be described in detail with reference to a block diagram. FIG. 5 is a block diagram showing an electrical configuration of the image forming apparatus according to the present embodiment.

  As shown in FIG. 5, the image forming apparatus 100 is, for example, a multifunction machine including a scanner unit 24, a printer main body 100 </ b> A, and a peripheral device 100 </ b> B, a reading unit 105 that reads a document image, and an appropriate document image that has been read. An image processing unit 106 that generates image data by converting it into an electrical signal, an image forming unit 107 that visualizes the generated image data using toner and forms an image on a recording medium (transfer paper), an image forming unit A fixing unit (not shown) for fixing by heating and fixing to the recording medium visualized in 107, and a peripheral device control unit 108 for controlling a peripheral device 100B such as a finisher or a sorter as a post-processing device are provided.

  The printer main body 100A includes a control unit 101, a storage unit 102, an input unit 103, a display unit 104, an image processing unit 106, an image forming unit 107, a calculation unit 109, and the like.

  In the storage unit 102, a print command via an input unit (for example, an operation panel) 103 disposed on the upper surface of the image forming apparatus 100, detection results from various sensors (not illustrated) disposed at various locations inside the image forming apparatus 100, and the like. , Image information input from an external device via USB (registered trademark) / LAN, various setting values and data tables for controlling the operation of each device in the image forming apparatus 100, and various controls Programs can be entered.

  Further, a memory or the like commonly used in this field can be used as the storage unit 102. For example, a read only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), Blu-ray (registered trademark). Disk etc. As the external device, an electric / electronic device that can form or acquire image information and can be electrically connected to the image forming apparatus 100 can be used, and examples thereof include a computer and a digital camera.

  The arithmetic unit 109 retrieves various data (print command, detection result, image information, etc.) stored in the storage unit 102 and a program for performing various controls, and performs various detections and / or determinations.

  The control unit 101 sends a control signal to the corresponding device according to various determination results, calculation results, and the like in the calculation unit 109 to perform operation control. The control unit 101 and the calculation unit 109 are, for example, processing circuits realized by a microcomputer, a microprocessor, or the like that includes a central processing unit (CPU).

  The control unit configured as described above includes a main power supply together with the storage unit 102, the calculation unit 109, and the control unit 101. The main power supply supplies power not only to the control means but also to each device in the image forming apparatus 100.

  Next, the developer used in the image forming apparatus 100 of this embodiment will be described.

  The developer used in the developing device 1 of the image forming apparatus 100 is a two-component developer composed of toner and carrier.

  For example, the toner may be a melt kneading and pulverizing method in which a binder resin, a colorant, a charge control agent (charge control agent), a wax as an offset preventive agent, and the like are melted and kneaded and then solidified by cooling and pulverization classification. It can be obtained by a polymerization method such as a turbid polymerization method or an emulsion polymerization method. In general, inorganic particles such as silica and aluminum oxide are added to the toner as an external additive for the purpose of improving fluidity and charging stability.

  As the binder resin, those commonly used as toner binder resins can be used, for example, polyester resins, styrene resins such as polystyrene, acrylic resins, methacrylic resins, acrylic resins such as polystyrene-acrylate copolymers, and the like. Examples thereof include thermoplastic resins such as resins, vinyl chloride resins, phenol resins, epoxy resins, polyether polyol resins, polyurethane resins, and polyvinyl butyral resins.

  Among these, a polyester resin is preferably used. As the polyester resin, known resins can be used, and among them, a polyester resin obtained by polycondensation of a polyol and a polybasic acid is preferable. The polyester resin may have a cross-linked structure that is cross-linked by polymerizing at least one of a polyol and a polybasic acid using a trifunctional or higher polyfunctional component. Here, the polyol is a compound having two or more hydroxyl groups, and includes both alcohols having an alcoholic hydroxyl group and phenols having a phenolic hydroxyl group. Polybasic acids are compounds having two or more carboxyl groups and derivatives thereof.

  Known polyols can be used for the synthesis of the polyester resin. Among the polyols, divalent alcohols, that is, diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, , 3-propylene glycol, dipropylene glycol, trimethylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,7- Examples include heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol.

  Among the polyols, divalent phenols include bisphenol A alkylenes such as 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A), hydrogenated bisphenol A, and polyoxyethylenated bisphenol A. An oxide adduct, hydroquinone, etc. are mentioned.

  Examples of the trivalent or higher polyol that is a trifunctional or higher polyfunctional component related to the crosslinking of the polyester resin include glycerin, 1,2,4-butanetriol, 1,2,5-pentanetriol, and 2-methyl. Propanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,3,6-hexanetetraol, sorbitol , Alcohols such as 1,4-sorbitan and sucrose, and phenols such as 1,2,4-benzenetriol.

  As the polybasic acid used for the synthesis of the polyester resin, known ones can be used. Among the polybasic acids, as the dibasic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, Isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and anhydrides or lower alcohols of these acids (e.g. , Esters with lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol, propanol and butanol).

  Examples of the tribasic or higher polybasic acid that is a trifunctional or higher polyfunctional component related to the crosslinking of the polyester resin include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1 , 2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexatricarboxylic acid, and anhydrides or lower alcohols of these acids ( Examples thereof include esters with methanol, ethanol, propanol, butanol and the like (lower alcohols having 1 to 4 carbon atoms).

  As the colorant, dyes and pigments commonly used as toner colorants can be used. For example, nigrosine dyes, carmine dyes, various basic dyes, acid dyes, oily dyes, anthraquinone dyes, benzidine yellow organic pigments, quinanthrine And carbon black such as zinc organic pigment, rhodamine organic pigment, phthalocyanine organic pigment, zinc oxide, titanium oxide, furnace black, acetylene black, and thermal black. Among these, carbon black is preferable. The two-component developer of the present invention can be used for development of both black and white images and color images by appropriately selecting the color of the colorant contained in the toner. One type of colorant may be used alone, or two or more types may be used in combination.

  As the charge control agent, those commonly used as charge control agents for toners can be used, and examples include nigrosine dyes, metal azo compounds, metal salicylic acid salts, and quaternary ammonium salts. One type of charge control agent may be used alone, or two or more types may be used in combination. The amount of the charge control agent used is not particularly limited, and can be appropriately selected from a wide range according to various conditions such as the type of binder resin, the type and content of the colorant.

  As the anti-offset agent, those commonly used as a toner release agent can be used. Among them, petroleum waxes such as paraffin wax and microcrystalline wax, synthetic waxes such as polyethylene wax, Fischer Tropus wax and amide wax. Waxes such as animal and plant waxes such as carnauba wax, candelilla wax and rice wax are preferred.

  The offset preventive agent is dispersed in the toner, and dissolves (bleeds) on the surface of the toner when the toner is heated by the fixing member to cause the toner to exhibit releasability, thereby acting as an offset preventive agent that prevents the hot offset phenomenon. The amount of the offset inhibitor used is not particularly limited, and can be appropriately selected from a wide range according to various conditions such as the type of binder resin, the type and content of the colorant.

  The external additive may be attached to the surface of the toner particles, or a part thereof may be embedded in the toner particles. Known external additives can be used, and examples thereof include colloidal silica, alumina powder, titanium oxide powder, and calcium carbonate powder. One type of external additive may be used alone, or two or more types may be used in combination. The amount of the external additive used is not particularly limited, and can be appropriately selected from a wide range according to various conditions such as the type of binder resin, the type and content of the colorant.

  As the carrier, a coated carrier composed of magnetic particles called core material (core material particles) and a coating material containing a synthetic resin covering the core material is used. The coating material covering the core material increases the volume resistivity of the carrier to improve the performance of imparting triboelectric charge to the toner, and determines the adhesion state of the toner to the carrier. Further, the surface condition of the carrier can be made suitable, and toner deterioration in which the external additive is embedded in the toner by friction between the toner and the carrier can be prevented.

  Examples of the core material include hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, lithium ferrite, copper-zinc ferrite, and mixtures thereof.

  The core material of the carrier can be manufactured by a manufacturing method such as a sintering method or an atomizing method. In addition, if necessary, granulation is performed so that the distribution range of the magnetic particle size distribution is narrowed, or the sintering temperature, the heating rate, the heating and holding time, etc. are controlled to have predetermined magnetic characteristics. Magnetic core particles (core material) can be produced.

  The carrier is obtained by coating the surface of the core material with a coat resin and forming a coat resin layer. For example, coating resins having different volume resistivity can be obtained by dispersing conductive fine powder in different amounts in the coating resin.

  Examples of the conductive fine powder include powders of metals such as aluminum, copper, nickel, and silver, powders of alloys or mixtures of these metals, scaly metal powders or short metal fibers of these metals, and antimony oxide. , Conductive metal oxides such as indium oxide and tin oxide, polymer conductive agents such as polymer electrolytes, carbon fiber, carbon black, graphite powder or conductive powder whose surface is coated with these conductive substances, etc. Can be mentioned.

  Examples of the polymer conductive agent such as a polymer electrolyte include polyamide, polyamine, polyalkylene oxide, polyester, polyalkylene sulfide, polyphosphazene and derivatives thereof, polypyrrole, polythiophene, polyaniline, polyacetylene, polyparaphenylene, polyparaffin. Examples include phenylene vinylene and polythiophene vinylene.

  The resin used for the coating resin can be a thermoplastic resin or a thermosetting resin, and is preferably an insulating resin. Examples of the thermoplastic resin include styrene resins such as polystyrene, acrylic resins such as polymethyl methacrylate and styrene-acrylic acid copolymers, styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, and vinyl chloride resins. , Vinyl acetate resin, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose , Cellulose derivatives such as hydroxypropyl cellulose, novolak resin, low molecular weight polyethylene, saturated alkyl polyester resin, polyethylene Terephthalate, polybutylene terephthalates, aromatic polyester resins such as polyarylate, polyamide resin, polyacetal resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin, polyether ketone resin. Thermosetting resins include, for example, phenol resins, modified phenol resins, maleic resins, alkyd resins, epoxy resins, acrylic resins, specifically, non-polymerization obtained by polycondensation of maleic anhydride-terephthalic acid-polyhydric alcohol. Saturated polyester, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, acetoguanamine resin, gliptal resin, furan resin, silicone resin, polyimide resin, polyamideimide resin, polyether Examples thereof include imide resins and polyurethane resins.

  The above-described resins can be used alone or in combination of two or more. In addition, for the purpose of improving durability, it is possible to use a thermoplastic resin mixed with a curing agent and cured.

  As a method of forming the coat resin layer of the carrier, when coating the core material, the coat resin is quickly coated so that the core materials do not adhere to each other, and the coating and drying are performed in such a way that the core material always flows. It is preferable to use a processing method in which the process proceeds simultaneously.

  As a method for producing a coated carrier, a fluidized bed coating apparatus is used to spray a coating resin solution in which a coating resin is uniformly dispersed in a solvent such as ethyl acetate, toluene, xylene, while the carrier core particles are suspended and flowed. A method of forming a coating film on the surface of the core material particles is preferable.

  Specifically, (a) a fluidized bed made of a core material is formed by a gas flow rising in a cylindrical tube, and (b) a coating layer resin solution is supplied from a direction perpendicular to the moving direction of the fluidized bed. (C) and the coating resin solution is applied to the magnetic core material particles by spraying. A coated resin-coated carrier that has excellent properties efficiently by sufficiently controlling conditions such as selection of a solvent for dissolving the coated resin, processing temperature, processing time, and using the methods (a) to (c) described above. Can be manufactured.

  Moreover, it is preferable that the coating resin solution used for coating the coating resin is supplied to the spray nozzle so as to continuously change from a high volume resistivity to a low one. In such a coating resin solution supply apparatus, such supply that continuously changes from a high volume resistivity to a low one can achieve the following effects, for example.

  When the carrier is provided with such a coating resin, the durability is improved, and the toner can be stably supplied to the photosensitive drum 15 even in long-term use, so that a high-quality image can be secured.

  In order to stabilize the coat resin layer formed on the surface of the core material, baking is preferably performed. An apparatus used for baking may be an external heating system or an internal heating system, and examples thereof include a fixed electric furnace, a fluid electric furnace, a rotary electric furnace, and a burner furnace.

  The coat carrier coated with the coat resin preferably has an average particle diameter D50 of 30 to 90 μm. By using such a minute carrier, it is possible to improve the quality of the output image.

  When the average particle diameter D50 of the carrier is smaller than 30 μm, the fluidity is deteriorated and the stirring property is lowered. On the other hand, when the average particle size of the carrier is larger than 90 μm, a high-definition image cannot be obtained.

  The two-component developer of the present invention is produced by mixing the carrier and toner obtained as described above with a mixer. A well-known thing can be used as a mixer, for example, a V type mixer and a W type mixer are mentioned.

  Next, image formation by the developing device 1 in the image forming apparatus 100 of the present embodiment will be described in detail with reference to examples.

  Tables 1 and 2 show the effect on the image after the actual shooting test, after 50K sheets and after 100K sheets, by measuring the image density and image fogging, and visually judging the presence or absence of image blurring. Using a copier MX-M1100 manufactured by Sharp Corporation, and changing the particle size of the carrier of the two-component developer in the developing tank 2 of the image forming apparatus 100 having the configuration of the developing device 1 according to the present invention. The A4 original with an area ratio of 1% was used, and a real paper test was performed by passing plain paper (cata paper) horizontally continuously.

  The image area ratio is calculated from the image data of the document read by the scanner unit 24.

  Table 1 shows test results when the first toner concentration detection sensor 12 and the second toner concentration detection sensor 13 are provided. Table 2 is a comparative example with respect to Table 1. Although the first toner concentration detection sensor 12 is provided, the second toner concentration detection sensor 13 for detecting the toner concentration of the two-component developer flowing on the reflux plate is provided. It is a test result when not arranged.

  The image evaluation was performed under the following conditions. As the developer, a two-component developer containing a toner having a toner concentration of 6 (% by weight) and a carrier was used. As the toner, a polyester toner having a volume average particle diameter of 6.5 μm was used. As the carrier, a resin-coated ferrite carrier was used.

  The developing conditions were set in the image forming apparatus, the gap between the photosensitive drum 15 and the developing roller 3 was 0.4 mm, and the outer diameter of the developing roller 3 was Φ30. The layer thickness regulating member 7 had a thickness of 1.5 mm, and the gap between the layer thickness regulating member 7 and the developing roller 3 was 0.7 mm.

  The photosensitive drum 15 has a process speed of 540 (mm / sec), and the developing roller 3 has a peripheral speed of the sleeve 11 of 1080 (mm / sec).

Various evaluation and measurement methods are described below.
First, regarding image density,
“X” is less than 1.20,
“△” is 1.20 or more and less than 1.29,
“◯” was 1.30 or more.
For the measurement, a spectrocolorimetric densitometer (X-Rite 938, manufactured by X-Rite) was used.
For image cover,
“×” is 1.6 or more,
“△” is 1.1 or more and less than 1.6;
“◯” was set to 1.0 or less.
For the measurement, whiteness of A4 size white paper is measured in advance with a whiteness meter (Hunter Whiteness Meter, manufactured by Nippon Denshoku Industries Co., Ltd.), and the measured value is the first measured value. This value is obtained from a value obtained by subtracting the value of the second measurement value from the first measurement value.
Regarding image blurring,
“×” means that the image blur is visible even a little,
“◯” indicates that no image blur is visible.
Regarding the measurement method of the carrier average particle diameter D50,
300 or more samples were randomly extracted with an optical microscope, and measured as a carrier average particle size D50 with a horizontal ferret diameter using an image processing analyzer Luzex3 manufactured by Nireco Corporation.

  As is apparent from the evaluation results in Tables 1 and 2, when continuous printing is performed with an A4 original having an image area ratio of 1% and a low image area ratio, the toner concentration of the two-component developer flowing on the reflux plate is detected. In the case of Table 2 where the second toner concentration detection sensor 13 is not provided, a significant decrease in developer fluidity cannot be detected for any carrier particle size, and accurate toner concentration detection is possible. As a result, the image density is greatly reduced.

  On the other hand, as shown in Table 1, when the second toner concentration detection sensor 13 is disposed on the reflux plate, it is possible to immediately detect a significant decrease in the flowability of the developer. Yes.

  On the other hand, when the carrier average particle diameter D50 is smaller than 30 μm, the fluidity is too poor and the stirring property is greatly lowered, so that not only the image density is lowered, but also the image fogging occurs. On the other hand, if it is larger than 90 μm, the fluidity is greatly improved, so that there is no reduction in image density or image fogging, but charging performance is reduced and image blurring occurs, resulting in a high-definition image. I can no longer get it.

  Next, Table 3 shows test results when printing is stopped and solid images are continuously developed on the photosensitive drum 15 until the determination of the image density obtained in Table 1 becomes “◯”. is there.

  That is, for example, after 50K sheets, printing is stopped until the item for which the image density determination is “Δ” becomes “◯” immediately after printing 50K sheets in Table 1 and obtaining the evaluation result, and the photosensitive drum 15 is a test result when printing is resumed after a solid image is continuously developed on 15.

  As is clear from the evaluation results in Table 3, a solid image is formed on the photosensitive drum 15 even when the low-density original is continuously printed and the toner remains charged on the carrier surface. By continuously developing and consuming the toner, the toner in the developer is replaced with a newly supplied toner that is not deteriorated, and the fluidity is improved. Therefore, the output is recovered so that the output can be seen in the output result of the second toner concentration detection sensor 13 for detecting the toner concentration of the two-component developer flowing on the reflux plate, and the state can be accurately detected. The occurrence of image fog can be resolved over a long period of time.

  Finally, Tables 4 and 5 show test results when the average particle diameter of the carriers shown in Tables 1 and 2 is 40 μm and the peripheral speed of the developing roller is changed.

  Table 4 shows the test results when the first toner concentration detection sensor 12 and the second toner concentration detection sensor 13 are provided. Table 5 is a comparative example for Table 4. Although the first toner concentration detection sensor 12 is provided, the second toner concentration detection sensor 13 for detecting the toner concentration of the two-component developer on the reflux plate is arranged. It is a test result when it is not installed.

  As is apparent from the results in Tables 4 and 5, when the peripheral speed of the developing roller is 314 (mm / sec) or more, the image density after 100K printing durability is improved. On the other hand, if it is 1382 (mm / sec) or less, the image fog after 50K and 100K printing durability is improved.

  As is clear from the evaluation results in Table 4, when the peripheral speed of the developing roller exceeds 1382 (mm / sec), stress due to friction between carriers in the developing tank 2 and stirring members and other inner peripheral walls of the developing tank 2 Due to excessive stress due to collision, peeling of the coating material of the carrier is accelerated at a stretch, the toner cannot be sufficiently charged, and image fogging due to poor charging has occurred. In addition to this, since the toner rotates at a high speed, the toner scatters, which hinders accurate density control in the developing tank 2.

  On the contrary, when the peripheral speed of the developing roller is less than 314 (mm / sec), as is apparent from the evaluation results in Table 5, the decrease in image density and the occurrence of image fog can be eliminated over a long period of time. .

  In the above-described embodiment, the example in which the developing device 1 according to the present invention is applied to the image forming apparatus 100 as illustrated in FIG. 1 has been described. However, the image forming apparatus uses a developing device that uses a two-component developer. If so, the present invention is not limited to the image forming apparatus and the copying machine having the above-described configuration, and can be developed to other image forming apparatuses.

  For example, the development device can be applied to full-color image forming devices by arranging four colors (yellow, cyan, magenta, black) or six colors (yellow, cyan, magenta, black, light cyan, light magenta). Is possible.

  As described above, any embodiment obtained by combining technical means appropriately changed without departing from the gist of the present invention is included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Developing apparatus 2 Developing tank 2a Opening 2b Toner replenishing port 3 Developing roller 3n Developing nip part 4 1st stirring member 5 2nd stirring member 6 Conveying member 7 Layer thickness regulating member 8 Regulating member support 9 Reflux plate 9a Support member 10 Magnet Roller 11 Sleeve 12 First toner concentration detection sensor 12a Sensor detection surface 13 Second toner concentration detection sensor 13a Sensor detection surface 14 Toner supply roller 15 Photosensitive drum 16 Charging device 17 Exposure device 18 Transfer device 18n Transfer nip portion
DESCRIPTION OF SYMBOLS 19 Cleaning apparatus 20 Fixing apparatus 20n Fixing nip part 21 Fixing roller 22 Pressure roller 23 Paper feed tray 24 Scanner part 25 Paper discharge tray 50 Line 51 Control part 52 Storage part 100 Image forming apparatus 100A Printer main body 100B Peripheral equipment 101 Control part 102 Storage unit 103 Input unit 104 Display unit 105 Reading unit 106 Image processing unit 107 Image forming unit 108 Peripheral device control unit 109 Calculation unit

Claims (7)

  A developing roller including a magnet roller, carrying a two-component developer including a toner and a carrier on its surface, rotating, supplying toner to the electrostatic latent image on the surface of the photosensitive drum, and developing, and a developer on the surface of the developing roller A layer thickness regulating member that regulates the amount of the toner, a stirring member that supplies the developer to the developing roller, a first density detecting unit that detects the toner concentration of the two-component developer disposed below the stirring member, and a layer A reflux plate for refluxing excess developer regulated by the thickness regulating member to a position separated from the layer thickness regulating member, and a second density detecting means for sensing the toner concentration of the two-component developer flowing on the reflux plate are provided. A developing device.   2. The developing device according to claim 1, wherein the first density detecting unit and the second density detecting unit detect the concentration of the developer based on a change in magnetic permeability of the developer.   2. The developing device according to claim 1, wherein a detection surface of the second density detection unit and an upper surface of the reflux plate are on the same plane.   The developing device according to claim 1, wherein a peripheral speed of the developing roller is 314 (mm / sec) to 1382 (mm / sec).   The developing device according to claim 1, wherein the carrier has an average particle diameter D50 of 30 μm or more and 90 μm or less.   6. The image forming apparatus according to claim 1, wherein the developing device is the developing device according to any one of claims 1 to 5.   The image according to claim 6, wherein printing is stopped and toner is forcibly developed on the photosensitive drum when output is no longer seen in the density detection result by the second density detection unit. Forming equipment.