JP5422433B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus including the developing device.

  Conventionally, as a developing method using dry toner in an image forming apparatus using an electrophotographic process, a one-component developing method using no carrier and a non-magnetic toner using a magnetic carrier (hereinafter also simply referred to as a carrier) are used. There is known a two-component developing system that uses a two-component developer to be charged and develops an electrostatic latent image on a photosensitive member with a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush, but toner adheres to the regulating blade, resulting in non-uniform layer formation. It sometimes caused image defects.

  In the case of color printing in which color superposition is performed, since the color toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, in a full-color image forming apparatus, a two-component development system in which toner is charged and conveyed using a carrier is often employed. However, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one means for solving these problems, a magnetic roller (toner supply member) is used to transfer the developer onto a developing roller (toner carrier) installed in a non-contact manner with respect to the photoreceptor (image carrier). When developing, a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and the toner is attached to the electrostatic latent image on the photosensitive member by an alternating electric field. A scheme has been proposed.

  In the case of the above developing method, if the surface of the developing roller is metal, the adhesion force of the toner to the surface of the developing roller is increased. As a result, the recoverability of the toner on the developing roller is reduced, so that a thin toner layer is not uniformly formed on the developing roller, resulting in uneven image density or an electrostatic latent image formed on the photoreceptor. There is a possibility that density follow-up failure may occur in which image density decreases due to insufficient toner to be supplied.

  In addition, if a toner consumption area and a non-consumption area are generated on the developing roller, a variation in the toner adhesion state and the toner potential difference occurs on the developing roller. There is a problem that a phenomenon that appears as an afterimage (ghost), that is, a so-called history phenomenon is likely to occur. Therefore, after passing through the portion facing the image carrier (development nip), it is necessary to sufficiently collect the toner thin layer that has not been used for development from the developing roller to form a new toner thin layer.

  Furthermore, when a low-resistance metal sleeve is used for the developing roller, if the AC component of the developing bias applied to the developing roller is excessively increased, the potential difference between the surface potential of the photoreceptor and the peak value of the AC voltage in the developing region is increased. Generation of noise due to current leakage between the photosensitive member and the developing roller becomes a problem.

  Therefore, various methods for reducing the adhesion of toner to the surface of the developing roller have been proposed. For example, Patent Document 1 discloses an inorganic conductive film in which conductive powder is dispersed and cured in an inorganic coating liquid. A developing roller formed on the surface is disclosed.

  By forming a coating layer on the surface of the developing roller as in Patent Document 1, the adhesion of the toner to the surface of the developing roller is reduced, so that the toner recoverability can be improved. Further, since the coating layer functions as a charge barrier layer, the leakage resistance of the developing roller is also improved.

JP-A-8-6376

  By the way, the toner used in the electrophotographic system is a toner external additive such as silica or titanium oxide (hereinafter also simply referred to as an external additive) for the purpose of stabilizing the charging property or polishing the surface of the photoreceptor. Many are surface-treated, and most of them have a primary particle size of 20 to 200 nm. Such an external additive is detached from the toner surface when the toner is put into the developing device and subjected to mechanical stress with a stirring screw or the like, and most of the toner is detached and is passed through the developing roller. It moves upward and is collected by a cleaning blade, a cleaning roller, or the like.

  However, some of the external additives detached from the toner surface may adhere firmly to the developing roller surface. If the amount of adhesion is small, there is no problem, but if the amount of adhesion (particularly, the amount of titanium oxide in the external additive) increases, the surface resistance of the developing roller decreases, leak resistance decreases, There has been a problem that the adhesion is increased and the developability is lowered. Note that the above-described problems occur similarly in the one-component development system, and there are problems in developability and leakage resistance when a metal sleeve is used for the developing roller.

  In view of the above-described problems, the present invention provides a developing device capable of obtaining a good image over a long period of time by suppressing the adhesion of titanium oxide in an external additive to the surface of the developing roller, and an image forming apparatus including the developing device. An object is to provide an apparatus.

  In order to achieve the above-described object, the present invention has a toner carrier disposed opposite to an image carrier, and an electrostatic latent image formed on the image carrier using a toner layer carried on the toner carrier. In a developing device for developing an image, a coat layer made of a resin material is formed on the outer peripheral surface of the toner carrier, and titanium oxide is added to the coat layer, and as a toner external additive, Titanium oxide having the same polarity as the added titanium oxide is added.

  In the present specification, “the same chargeability” means that the electric characteristics (positive and negative) are the same, such as positive charge or negative charge.

  According to the present invention, the primary particle diameter of titanium oxide added as an external toner additive is 20 to 200 nm in the developing device configured as described above.

  The present invention also provides an image forming apparatus equipped with the developing device having the above-described configuration.

  According to the first configuration of the present invention, as a toner external additive, titanium oxide having the same polarity as that of titanium oxide added to the coat layer of the toner carrier is added to the toner external additive. It is possible to reduce the electrostatic adhesion force of the titanium oxide to the surface of the toner carrier, thereby suppressing the increase in surface resistance of the toner carrier and the occurrence of leakage.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, the primary particle diameter of titanium oxide added as an external toner additive is set to 20 to 200 nm. While maintaining the function as an external additive, the electrostatic adhesion force of titanium oxide to the surface of the toner carrier can be reduced.

  Further, according to the third configuration of the present invention, by mounting the developing device having the first or second configuration, leakage due to an image density defect or an increase in the surface resistance of the toner carrying member does not occur, and the long configuration. The image forming apparatus can obtain a good image over a period.

1 is a schematic diagram showing an overall configuration of an image forming apparatus equipped with a developing device according to a first embodiment of the present invention. Side surface sectional drawing which shows the structure of the image development apparatus of 1st Embodiment. The figure which shows an example of the bias waveform applied to the developing roller and magnetic roller of the developing device of 1st Embodiment. Schematic showing the overall configuration of an image forming apparatus equipped with a developing device according to a second embodiment of the present invention. Side surface sectional drawing which shows the structure of the image development apparatus of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with a developing device according to a first embodiment of the present invention. Here, a tandem color printer is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and are further driven by a driving unit (not shown). The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer sheet S as an example of a recording medium, and further fixed on the transfer sheet S in the fixing unit 13 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer sheet S on which the toner image is transferred is accommodated in a sheet cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 to be described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip portion with the roller 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed downstream of the secondary transfer roller 9 in the rotation direction of the intermediate transfer belt 8.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 5. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  Then, by applying a predetermined transfer voltage to the primary transfer rollers 6 a to 6 d, yellow, cyan, magenta, and black toner images on the photosensitive drums 1 a to 1 d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer sheet S is conveyed from the registration roller 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. The full color image on the intermediate transfer belt 8 is transferred onto the transfer paper S. The transfer sheet S on which the toner image has been transferred is conveyed to the fixing unit 13.

  The transfer sheet S conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a to fix the toner image on the surface of the transfer sheet S, thereby forming a predetermined full color image. The transfer sheet S on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer sheet S, the image is directly discharged onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer sheet S, a part of the transfer sheet S that has passed through the fixing unit 13 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer sheet S is distributed to the sheet conveyance path 18 by the branching section 14 by rotating the discharge roller pair 15 in the reverse direction, and is conveyed again to the secondary transfer nip section with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer sheet S where the image is not formed, and conveyed to the fixing unit 13 and the toner image is fixed. , And discharged to the discharge tray 17.

  FIG. 2 is a side sectional view showing the configuration of the developing device according to the first embodiment. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter also simply referred to as a developer) is accommodated. The developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second stirring chambers 20b and 20c are divided into stirring chambers 20b and 20c, and the toner (positively charged toner) supplied from the toner container 4a (see FIG. 1) is mixed with the carrier and stirred to be charged. A first agitation screw 21a and a second agitation screw 21b are provided for rotation.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and the developer is passed through the developer passages (not shown) formed at both ends in the longitudinal direction of the partition wall 20a. It circulates between the 1st and 2nd stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1 on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing.

  Note that a toner concentration sensor (not shown) is disposed in the developing container 20 so as to face the first agitating screw 21a. From the toner container 4a to the toner supply port according to the toner concentration detected by the toner concentration sensor. The toner is supplied into the developing container 20 through 20d.

  The magnetic roller 22 includes a non-magnetic rotating sleeve 22a and a fixed magnet body 22b having a plurality of magnetic poles contained in the rotating sleeve. In the present embodiment, the magnetic poles of the fixed magnet body 22 b have a five-pole configuration including a main pole 35, a regulation pole (head cutting pole) 36, a transport pole 37, a separation pole 38, and a pumping pole 39.

  Further, a regulating blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the regulating blade 25 rotates in the rotation direction of the magnetic roller 22 (clockwise in the figure). In FIG. 2, the developing roller 23 and the magnetic roller 22 are positioned upstream of the facing position. A slight gap (gap) is formed between the tip of the regulating blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 includes a cylindrical developing sleeve 23a and a magnet member 23b fixed in the developing sleeve 23a. The magnetic roller 22 and the developing roller 23 have a predetermined gap at the facing position (opposite position). Are facing each other. The magnet member 23b is different in polarity from the opposing magnetic pole (main pole) 35 of the fixed magnet body 22b.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected. The first bias circuit 30 and the second bias circuit 31 are grounded to a common ground.

  A voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC), Vslv (AC) applied to the developing roller 23 and Vmag (DC) applied to the magnetic roller 22. ), Vmag (AC) can be varied.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Since the restricting pole 36 of the fixed magnet body 22b faces the restricting blade 25, a nonmagnetic material or a magnetic material is used as the restricting blade 25, so that a magnetic field in a direction attracting the gap between the tip of the restricting blade 25 and the rotating sleeve 22a. Will occur.

  Due to this magnetic field, a magnetic brush is formed between the regulating blade 25 and the rotating sleeve 22a. When the thickness of the magnetic brush on the magnetic roller 22 is regulated by the regulating blade 25 and then moves to a position facing the developing roller 23, a magnetic field attracted by the main pole 35 of the fixed magnet body 22b and the developing roller side magnetic pole 23b is generated. Therefore, the magnetic brush comes into contact with the surface of the developing roller 23. Then, a toner thin layer is formed on the developing roller 23 by a potential difference ΔV between Vmag (DC) applied to the magnetic roller 22 and Vslv (DC) applied to the developing roller 23 and a magnetic field.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 23 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 3 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. Further, the magnetic roller 22 has a second combined waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a rectangular wave Vmag (AC) having a phase different from Vslv (AC). Applied from the bias circuit 31.

  Accordingly, the voltage applied between the magnetic roller 22 and the developing roller 23 (hereinafter referred to as MS) is a composite waveform Vmag-Vslv having Vpp (max) and Vpp (min) as shown in FIG. Become. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to the opposite portion between the photosensitive drum 1a and the developing roller 23 by the rotation of the developing sleeve 23a. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  When the rotating sleeve 22a further rotates clockwise, this time, the magnetic brush is pulled away from the surface of the developing roller 23 by the horizontal (roller circumferential direction) magnetic field generated by the different polarity peeling pole 38 adjacent to the main pole 35. The remaining toner that is not used for is collected from the developing roller 23 onto the rotating sleeve 22a. When the rotating sleeve 22a further rotates, a repulsive magnetic field is applied by the peeling pole 38 of the fixed magnet body 22b and the scooping pole 39 having the same polarity, so that the toner is detached from the rotating sleeve 22a in the developing container 20. Then, after being stirred and conveyed by the second agitating screw 21b, a magnetic brush is again formed on the rotating sleeve 22a by the scooping pole 39 as a two-component developer that is uniformly charged again with an appropriate toner concentration, and the regulating blade 25 It is conveyed to.

  Next, the developing sleeve 23a constituting the developing roller 23 will be described in detail. The developing sleeve 23a has a coating layer formed on the outer peripheral surface of an aluminum or aluminum alloy sleeve body. The coat layer suppresses adhesion of the toner supplied on the developing sleeve 23a, and allows the toner to be transferred from the developing roller 23 to the surface of the photosensitive drum relatively easily. Further, since the mechanical stress applied to the developer by the coat layer is less than that on the metal surface, both improvement in toner recoverability from the developing roller 23 and prevention of developer deterioration when the developer transport amount is increased are achieved. Can be achieved.

  Examples of the material of the coating layer include urethane-modified resin, acrylic resin, melamine resin, silicone resin, fluorine resin, etc. in addition to silicone-modified polyurethane. Good urethane resin and acrylic resin are preferable. Among these, the use of a silicon-modified polyurethane resin in which a part of carbon of the urethane resin is replaced with silicon is preferable because the hygroscopic property of the urethane resin is improved and the change in charging characteristics of the coat layer with respect to environmental changes is suppressed.

In addition, the coating layer contains titanium oxide as a resistance adjusting agent, adjusts the volume resistance value of the coating layer, and suppresses uneven resistance. Thereby, stabilization of the charged state of the toner layer and releasability at the time of toner collection can be achieved. The volume resistance value is preferably about 10 ⁴ to 10 ⁸ Ω · cm, which can appropriately retain the residual charge on the surface of the developing roller 23.

  The surface roughness (arithmetic mean roughness) Ra of the coating layer is the surface roughness normally obtained when the coating agent is applied by spraying, dipping, roll coating, or the like, or the surface roughness of urethane beads or the like is adjusted. It is adjusted to 0.4 to 1.5 μm by applying an agent.

  Moreover, before forming the coat layer, the outer peripheral surface of the sleeve body may be anodized to form the anodized layer. According to this configuration, since the alumite layer formed on the sleeve surface has a function as a charge barrier layer, it is possible to prevent the occurrence of leakage when a developing bias is applied to the developing roller 23.

  Next, the two-component developer used in the developing device of the present invention will be described. The two-component developer contains a toner and a carrier. The weight ratio (T / C) between the toner and the carrier in the two-component developer is preferably 5 to 20 parts by weight, more preferably 8 to 15 parts by weight with respect to 100 parts by weight of the carrier.

  The toner is obtained by adding an external additive to toner base particles. The toner base particles contain a binder resin and a colorant. The toner base particles may contain a release agent, a charge control agent, magnetic powder and the like as necessary. The weight average particle diameter of the toner base particles is preferably 5 to 12 μm, and more preferably 6 to 10 μm. The weight average particle diameter of the toner base particles is measured by a particle size distribution measuring device (for example, Multisizer II type manufactured by Coulter, Inc.). The toner base particles are produced by a known method such as a pulverization classification method, a melt granulation method, a spray granulation method, or a polymerization method. The addition amount of the external additive is usually 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.

  As the carrier, magnetic particles or resin particles in which a magnetic material is dispersed in a binder resin are used. Examples of magnetic materials include magnetic metals such as iron, nickel, cobalt, alloys thereof, alloys containing rare earths, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium Examples thereof include soft ferrites such as ferrite and lithium ferrite, iron-based oxides such as copper-zinc ferrite, and mixtures thereof.

  Examples of the binder resin include vinyl resins, polyester resins, epoxy resins, phenol resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, polyether resins, and mixtures thereof. Magnetic particles are produced by a known method such as a sintering method or an atomizing method. The carrier may have a coating layer made of a coating resin on its surface.

  The present invention is characterized in that titanium oxide having a primary particle diameter of 20 to 200 nm and having the same polarity as titanium oxide added to the coating layer of the developing sleeve 23a is used as an external additive for the toner. The cause of the external additive adhering to the surface of the developing sleeve 23a is that the particle size of the external additive is very small, so that the physical adhesion between the coat layer on the sleeve surface and the external additive becomes very large, In addition, electrostatic adhesion acts between the coat layer on the sleeve surface and the external additive.

  Among these, since the function as an external additive largely depends on the particle size, the particle size cannot be increased to decrease the physical adhesion. However, the electrostatic adhesion can be reduced by making the external additive and the coating layer have the same polarity. Specifically, titanium oxide having the same polarity as that of titanium oxide added to the coating layer of the developing sleeve 23a is used as the titanium oxide treated as an external additive to the toner base particles.

  Next, a method for controlling the polarity (charging characteristics) of titanium oxide will be described. The charging property of titanium oxide can be adjusted by the degree of hydrophobic treatment. That is, as the degree of hydrophobic treatment increases, the number of hydroxyl groups (—OH groups) on the titanium oxide surface decreases and the positive chargeability increases. Conversely, the smaller the degree of hydrophobic treatment, the greater the number of hydroxyl groups on the titanium oxide surface and the greater the negative chargeability.

  As a method of hydrophobizing treatment, after titanium oxide is stored in a desiccator and dehydrated, titanium oxide fine powder and a silane coupling agent are reacted in toluene to hydrophobize hydroxyl groups on the surface of titanium oxide. Can be mentioned. Examples of the silane coupling agent include hexamethyldisilazane, methyltrimethoxysilane, octyltrimethoxysilane, and the like.

  FIG. 4 is a schematic configuration diagram showing the overall configuration of an image forming apparatus equipped with the developing device according to the second embodiment of the present invention, and the right side is illustrated as the front side of the image forming apparatus. Portions common to those in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 4, a sheet cassette 16 that accommodates the stacked transfer sheets is disposed at the bottom of the main body of the monochrome printer 101. Above the paper cassette 16, a paper conveyance path is formed that extends substantially horizontally from the front of the main body to the rear of the main body and further extends upward to the discharge tray 17 formed on the upper surface of the main body. A feed roller 12a, a registration roller pair 12b, an image forming unit P, a fixing unit 13 and a discharge roller pair 15 are arranged in this order from the upstream side.

  The image forming unit P includes a photosensitive drum 1 rotatably supported in FIG. 4, a scorotron charger 2, a developing device 3, and a cleaning unit 7 disposed around the photosensitive drum 1. The image forming apparatus includes a transfer roller 6 disposed so as to face the photosensitive drum 1 across the paper conveyance path and an exposure device 5 disposed above the photosensitive drum 1. A toner container 4 for supplying toner to the developing device 3 is disposed.

  By applying a predetermined voltage to the charger 2, the surface of the photosensitive drum 1 is uniformly charged. Next, an electrostatic latent image based on the image data input on the photosensitive drum 1 is formed by light irradiation from the exposure device 5, and toner is attached to the electrostatic latent image by the developing device 3. A toner image is formed on the surface. Transfer paper (not shown) is supplied from the registration roller pair 12b to the nip portion (transfer position) between the photosensitive drum 1 and the transfer roller 6 at a predetermined timing, and the photosensitive drum 1 is transferred onto the transfer paper by the transfer roller 6. The toner image on the surface is transferred.

  The transfer sheet on which the toner image is transferred is separated from the photosensitive drum 1 and conveyed toward the fixing unit 13. The transfer paper on which the toner image has been transferred in the image forming unit P is heated and pressed by a pair of fixing rollers 13 a including a heating roller provided in the fixing unit 13 and a pressure roller pressed against the heating roller 21. The toner image transferred to is fixed.

  Then, the transfer paper on which the image is formed in the image forming unit P and the fixing unit 13 is discharged to the discharge tray 17 by the discharge roller pair 15. On the other hand, the toner remaining on the surface of the photosensitive drum 1 after the transfer is removed by the cleaning unit 7. The photosensitive drum 1 is charged again by the charger 2, and image formation is performed in the same manner.

  FIG. 5 is a side sectional view of the developing device according to the second embodiment. Portions common to FIG. 2 of the first embodiment are denoted by the same reference numerals. As shown in FIG. 5, the developing device 3 includes a first agitating screw 21a, a second agitating screw 21b, a developing roller 23, and a regulating blade 25 in a developing container 20 that contains a one-component developer made of magnetic toner. Is provided.

  The inside of the developing container 20 is partitioned into a first stirring chamber 20b and a second stirring chamber 20c by a partition wall 20a extending in the longitudinal direction (paper surface direction in the drawing), and the first stirring chamber 20b includes a first stirring chamber 20b. A stirring screw 21a is disposed in the second stirring chamber 20c, and a second stirring screw 21b is disposed in the second stirring chamber 20c. Further, the partition wall 20a is not provided at both ends in the longitudinal direction of the developing container 20, and this portion is a passage (developer delivery portion) through which the toner moves between the first stirring chamber 20b and the second stirring chamber 20c. It has become.

  The developing roller 23 includes a metal developing sleeve 23a and a magnet member 23b having a plurality of magnetic poles (here, three poles) fixed inside the developing sleeve 23a. The developing roller 23 includes a first stirring screw 21a and a second stirring screw 21a. It is rotatably supported in the first stirring chamber 20b so as to be substantially parallel to the stirring screw 21b. A first bias circuit 30 that applies Vslv (DC) and Vslv (AC) is connected to the developing roller 23, and the first bias circuit 30 is grounded. A voltage variable device 33 is connected to the first bias circuit 30.

  When the developing sleeve 23a rotates in accordance with the rotation of the photosensitive drum 1, toner is attached (carried) to the surface of the developing sleeve 23a by the magnetic force of the magnet member 23b, and a toner layer is formed. Then, the toner adhering to the developing sleeve 23 a is caused by the potential difference between the surface potential of the photosensitive drum 1 and the developing bias applied to the developing roller 23 at the developing nip portion where the developing roller 23 and the photosensitive drum 1 face each other. It flies to the drum 1 and adheres to the photosensitive layer, and a toner image is formed on the surface of the photosensitive drum 1.

  The regulating blade 25 regulates the amount of toner supplied to the photosensitive drum 1, that is, the amount of toner adhering to the developing roller 23. For example, a magnetic material such as SUS (stainless steel) is used. The regulating blade 25 is disposed so that a predetermined gap (0.2 to 0.3 mm) is formed between the tip of the regulating blade 25 and the developing roller 23. The amount of toner adhering to the developing roller 23 is regulated by the magnetic field generated in the gap and the gap, and a thin toner layer of several tens of microns is formed on the surface of the developing roller 23. Since the configuration of other parts is the same as that of the first embodiment, description thereof is omitted.

  Also in the present embodiment, the developing roller 23 is constituted by the developing sleeve 23a having a coating layer formed on the outer peripheral surface, and the surface of the toner is formed using titanium oxide having the same polarity as the titanium oxide in the coating layer as an external additive. By performing the treatment, it is possible to reduce the electrostatic adhesive force acting between the external additive (titanium oxide) and the coating layer, thereby suppressing the adhesion of titanium oxide to the developing sleeve 23a.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the present invention is not limited to the tandem color printer or monochrome printer shown in FIGS. 1 and 4, but a digital or analog monochrome copying machine, a rotary developing color printer and color copying machine, a facsimile layer, etc. The present invention can be applied to various image forming apparatuses on which a developing device including a developing roller having the above is mounted. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

Reference example

(Titanium oxide hydrophobic treatment)
After 100 g of titanium oxide (manufactured by Titanium Industry Co., Ltd.) was stored in a desiccator for 24 hours and dehydrated, 10 g of titanium oxide and hexamethyldisilazane (manufactured by Organic Synthetic Chemical Co., Ltd.) were reacted in 500 mL of toluene for a predetermined time, and titanium oxide The surface hydroxyl group was hydrophobized.

  Thereafter, 10 g of non-coated ferrite carrier (manufactured by PTK) and 0.1 g of titanium oxide were put into a 50 mL glass bottle and mixed for 30 minutes in a ball mill. The charge amount of the mixture was measured with a QM meter (manufactured by Trek). Table 1 shows the charge amounts (μC / g) of titanium oxides A to F with the hydrophobizing treatment times set to 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, and 180 minutes, respectively.

  From Table 1, it was confirmed that the charge changes from negative to positive because the hydroxyl group on the surface of titanium oxide is hydrophobized and decreases as the hydrophobization time increases.

  The metal developing sleeve 23a of the developing device 3a shown in FIG. 2 is coated with a silicone resin (KBC1003, manufactured by Shin-Etsu Silicone), and 100 parts by weight of the titanium oxide A is added to 100 parts by weight of the resin in the coating solution. Added. On the other hand, the titanium oxide B is added as an external additive of the toner in an amount of 1.5% by weight based on the toner base particles, and a two-component developer composed of the toner and the coated ferrite carrier is added to the toner mixing ratio (T / C) was loaded at 8% by weight into the developing device 3a.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to C and the titanium oxide added as an external additive of the toner was changed to A.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to C.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating solution of the developing sleeve 23a was changed to B.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to D and the titanium oxide added as an external additive of the toner was changed to F.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to F and the titanium oxide added as an external additive of the toner was changed to D.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating solution of the developing sleeve 23a was changed to D and the titanium oxide added as an external additive of the toner was changed to E.

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to E and the titanium oxide added as an external additive of the toner was changed to E.

Comparative Example 1

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added as an external additive of the toner was changed to D.

Comparative Example 2

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to C and the titanium oxide added as an external additive of the toner was changed to E.

Comparative Example 3

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to F and the titanium oxide added as an external additive of the toner was changed to C.

Comparative Example 4

  The developing device 3a was configured in the same manner as in Example 1 except that the titanium oxide added to the coating liquid of the developing sleeve 23a was changed to C and the titanium oxide added as an external additive of the toner was changed to D.

Test example 1

  The developing devices 3a of Examples 1 to 8 and Comparative Examples 1 to 4 are mounted on a testing machine as shown in FIG. 1 to perform a durability test (printing 10,000 test images with a printing rate of 5%), Image density (ID; image density), presence or absence of leakage, resistance value of the sleeve surface, and adhesion to the sleeve surface were investigated every 2,500 sheets.

  The image density was measured with a reflection densitometer (Spectro Eye, manufactured by Gretag Macbeth Co., Ltd.), and the occurrence of leak was visually observed as to whether or not a leak mark could be confirmed in the image. The surface resistance of the sleeve is measured by a high resistivity meter (Hirester MCP-HT450, manufactured by Mitsubishi Chemical Corporation), and the adhesive force to the sleeve surface (hereinafter referred to as sleeve adhesive force) is an interparticle adhesive force measuring device (manufactured by Nano Seeds). Was used to measure the adhesion of the measuring needle. The results are shown in Table 2.

  The voltage application conditions to the developing roller were Vslv (DC) = 50 V, Vpp of Vslv (AC) was 1.5 kV, the frequency was 4 kHz, and Duty = 50%. Further, Vmag (DC) = 250 V and Vmag (AC) Vpp of 2.0 kV were applied to the magnetic roller in reverse phase.

  As is apparent from Table 2, in Examples 1 to 8, the titanium oxide added to the coating liquid and the titanium oxide added as an external additive of the toner have the same polarity (negative and negative, or positive and positive) Even after the endurance of 10,000 sheets, the sleeve adhesion was 15 nN or less. This is because an electrostatic repulsive force acts between the titanium oxide added as an external additive and the coat layer on the developing sleeve surface, so that the titanium oxide does not adhere to the sleeve surface and the smoothness of the sleeve surface is maintained. Therefore, it is considered that the sleeve adhesion does not increase.

  Further, since titanium oxide as an external additive hardly adheres to the sleeve surface, the sleeve surface resistance hardly decreased from the beginning of the durability, and no leakage was observed. Furthermore, the toner recoverability from the developing sleeve is improved, and a uniform toner layer is formed on the developing sleeve, so that an ID of 1.3 or higher is maintained even after endurance, and a decrease in image density is recognized. There wasn't.

  On the other hand, in Comparative Examples 1 to 4 in which the titanium oxide added to the coating liquid and the titanium oxide added as the toner external additive have different polarities (negative and positive, or positive and negative), Since an electrostatic attraction force acts between the added titanium oxide and the developing sleeve surface, the sleeve adhesion force exceeded 50 nN after 10,000 sheets of durability. Further, since titanium oxide as an external additive easily adheres to the sleeve surface, the sleeve surface resistance is also greatly reduced from the initial durability stage. In Comparative Examples 1 and 3, after printing 5,000 sheets, in Comparative Examples 2 and 4, 10,000. Leakage was observed after printing. Furthermore, the ID was 0.4 to 1.1 after endurance, and a decrease in image density was also observed.

Test example 2

  The combination of titanium oxide added to the coating liquid of the developing sleeve 23a and titanium oxide added as an external additive for the toner is the same as in Examples 1 to 8 and Comparative Examples 1 to 4, and the one component shown in FIG. The developing system 3 of the developing system was configured, and were set as Examples 9 to 16 and Comparative Examples 5 to 8, respectively.

  The developing devices 3 of Examples 9 to 16 and Comparative Examples 5 to 8 were mounted on a testing machine as shown in FIG. 4 to perform a durability test (printing 10,000 test images with a printing rate of 5%), In the same manner as in Test Example 1, image density (ID; image density), presence / absence of leakage, resistance value of the sleeve surface, and sleeve adhesion force were investigated every 2500 sheets. The results are shown in Table 3.

  As is apparent from Table 3, in Examples 9 to 16, the titanium oxide added to the coating liquid and the titanium oxide added as the external additive of the toner have the same polarity (negative and negative, or positive and positive). As in Examples 1-8, no increase in sleeve adhesion and sleeve surface resistance, occurrence of leakage, and reduction in image density were observed. On the other hand, in Comparative Examples 5 to 8 in which the titanium oxide added to the coating liquid and the titanium oxide added as the external additive of the toner are different polarities (negative and positive, or positive and negative), Comparative Examples 1 to 4 and Similarly, an increase in sleeve adhesion and sleeve surface resistance, occurrence of leakage, and a decrease in image density were observed.

  From the above results, in both the two-component development method and the one-component development method, the titanium oxide added to the coating liquid and the titanium oxide added as an external additive of the toner have the same polarity, It has been confirmed that problems such as an increase in sleeve adhesion due to adhesion, occurrence of leakage, density reduction, and history development can be effectively suppressed.

  The above embodiment is merely an example of the present invention, and the drum surface potential, conditions for applying voltage to the developing roller and the magnetic roller, and the like can be appropriately set according to the specifications of the apparatus and the usage environment.

  INDUSTRIAL APPLICABILITY The present invention can be used in a developing device that develops an electrostatic latent image on an image carrier by holding charged toner on the toner carrier, and is used as a toner external additive in a coat layer of the toner carrier. A titanium oxide having the same polarity as the added titanium oxide is added.

  Thereby, the electrostatic adhesion force of the titanium oxide in the toner external additive to the surface of the toner carrier can be reduced and the adhesion of titanium oxide to the surface of the toner carrier can be effectively suppressed. Accordingly, it is possible to provide a developing device that is less likely to cause a decrease in developability, an increase in surface resistance, a leak, and the like due to an increase in the adhesion force on the surface of the toner carrier.

1, 1a to 1d Photosensitive drum (image carrier)
3, 3a to 3d Developing device 21a First stirring screw 21b Second stirring screw 22 Magnetic roller 22a Rotating sleeve 22b Fixed magnet body 23 Developing roller (toner carrier)
23a developing sleeve 23b developing roller side magnetic pole 25 regulating blade 30 first bias circuit 31 second bias circuit 33 voltage variable device 100 color printer 101 monochrome printer P, Pa to Pd image forming unit

Claims (3)

In a developing device that has a toner carrier disposed opposite to an image carrier and develops an electrostatic latent image formed on the image carrier using a toner layer carried on the toner carrier.
An outer surface of the toner carrier is anodized to form an alumite layer, a coating layer made of a resin material is formed on the surface of the anodized layer , and titanium oxide is added to the coating layer.
As the toner external additive, titanium oxide having the same polarity as the titanium oxide added in the coating layer and having a primary particle diameter of 20 to 200 nm is added ,
The developing device characterized in that the coating layer has a volume resistance of 10 ⁴ to 10 ⁸ Ω · cm and a surface roughness of 0.4 to 1.5 μm . The developing device according to claim 1, wherein the coat layer is formed of a silicon-modified polyurethane resin .   An image forming apparatus on which the developing device according to claim 1 is mounted.