JP4941026B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus and a developing device used in the image forming apparatus.

  As a developing method employed in an electrophotographic image forming apparatus, a one-component developing method using only toner as a main component of a developer and a two-component developing method using toner and a carrier as main components of a developer are known. ing.

  The developing device of the one-component development system includes a toner carrying member that carries and conveys toner, and a friction charging member that contacts the toner carrying surface of the toner carrying member. When the toner carried on the toner carrying member passes through the contact position of the frictional charging member, the toner is brought into frictional contact with the frictional charging member to be thinned and charged to a predetermined polarity. As described above, the one-component developing device has an advantage that the configuration is simple, small, and inexpensive because the toner is charged by frictional contact with the frictional charging member. However, since the toner is subject to strong stress at the contact position of the frictional charging member, the toner is liable to deteriorate, so that the chargeability of the toner is impaired relatively early. In addition, the contact pressure between the toner carrying member and the frictional charging member reduces the ability of the toner to adhere and charge the toner, resulting in a relatively short life of the developing device.

  In the developing device of the two-component developing method, the toner and the carrier are charged to a predetermined polarity by frictional contact between the toner and the carrier, so that the toner receives less stress than the one-component developing device. Since the surface area of the carrier is larger than that of the toner, the toner is less likely to be adhered and soiled. However, dirt (spent) adhering to the surface of the carrier increases due to long-term use, and therefore, the ability to charge the toner is reduced, causing the problem of fogging and toner scattering. In order to extend the life of the two-component developing device, it is conceivable to increase the amount of carrier accommodated in the developing device, but this leads to an increase in the size of the developing device.

  In order to solve the above-mentioned problem related to the two-component developing device, Patent Document 1 discloses that a carrier or carrier and toner are replenished to the developer little by little, and the developer whose charging performance is lowered is gradually discharged. A developing device that suppresses an increase in deteriorated carriers is disclosed. According to this technique, it is possible to extend the life of the developer without increasing the size of the developing device. However, a mechanism for collecting the discharged carrier is necessary. In addition, the consumption of the carrier is large, which includes cost and environmental problems. Further, it is necessary to perform a predetermined amount of printing until the ratio of the undegraded carrier and the deteriorated carrier is stabilized.

  Patent Document 2 discloses a carrier in which a resin coating layer containing resin fine particles and conductive fine powder dispersed in a matrix resin is provided on a core material, and an image forming method using the carrier. When the surface of this carrier is partially scraped by contact with other particles (carrier particles, toner particles) or members (rollers, screws), new resin fine particles are exposed on the surface, which comes into contact with the toner. The toner is charged to the required level. However, the thickness of the resin coating layer is limited, and when this resin coating layer is consumed, the carrier reaches the end of its life.

  Patent Document 3 proposes a two-component developer composed of a carrier and a toner carrying charged particles on the surface, and a developing method using the developer. The charged particles are added as an abrasive for removing dirt (spent) mainly caused by toner adhering to the surface of the carrier and extending the life of the carrier. Patent Document 3 also describes that charged particles exhibit a function of polishing the surface of the electrostatic latent image carrier in the cleaning region of the electrostatic latent image carrier. However, since charged particles have a property of being charged to a polarity opposite to the charging polarity of the toner, there is a problem that the charged particles adhere to non-image portions of the electrostatic latent image and are consumed at an early stage. In particular, when an image having a small area (for example, a character image) is created, there is a problem that a large amount of charged particles is consumed, and the ability to polish and regenerate the carrier is not sufficiently exhibited.

  Patent Document 4 has a developing device including a magnetic roller and a developing roller, and selectively selects only toner from the developer including toner and carrier held on the outer peripheral surface of the magnetic roller on the outer peripheral surface of the developing roller. There has been proposed an image forming apparatus that supplies and develops an electrostatic latent image (electrostatic latent image portion) on a photosensitive member using toner held on the outer peripheral surface of the developing roller. As a feature, the invention of Patent Document 4 is interposed between the toner and the carrier without being held on either surface of the toner and the carrier, and the pulverized fine powder of the toner adheres to the surface of the carrier to form a spent. The developer contains charged particles that prevent this. The charged particles are contained only in the developer initially introduced into the developing device. However, in the image forming apparatus, the charged particles are supplied to the developing roller together with the toner by electrical coupling with the toner, and then are gradually consumed by being attached to the non-image portion of the electrostatic latent image on the photoreceptor. For this reason, for example, when a large amount of images having a small image area ratio (black and white ratio) such as a character image are printed, only a large amount of charged particles are consumed, and stable toner chargeability cannot be obtained in the long term. As a result, there are problems that fog occurs during printing and the image density decreases.

On the other hand, a technique for preventing leakage by forming a high resistance film or an insulating film on the surface of a transport roller has been reported (Patent Document 5).
JP 59-1000047 A JP-A-9-269614 JP 2003-215855 A JP 2006-308687 A JP 2005-55853 A

  An object of the present invention is to provide a developing device and an image forming apparatus capable of suppressing the consumption of charged particles and performing stable toner charging for a long period of time.

The present invention is a developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer containing toner and a carrier,
A developer including a toner and a carrier, wherein the toner is charged to a first polarity by frictional contact between the toner and the carrier, and the carrier is charged to a second polarity different from the first polarity; ,
A first conveying member disposed in an opening of a developing tank that contains the developer;
A second conveying member facing the first conveying member via a first region and facing the electrostatic latent image carrier via a second region;
A first electric field is formed between the first transport member and the second transport member, and the toner in the developer held by the first transport member is transferred to the second transport member. First electric field forming means to be moved;
A second electric field is formed between the second transport member and the electrostatic latent image carrier, and the toner held by the second transport member is transferred to the electrostatic latent image carrier by static electricity. A second electric field forming means for making the electrostatic latent image visible by moving it to an electrostatic latent image;
The developer further includes charged particles that are charged to a polarity opposite to the charged polarity of the toner by frictional contact with the toner,
The second conveying member has a surface charged to a polarity opposite to the charged polarity of the toner by frictional contact with the toner, and an image forming apparatus including the developing device. .

  According to the present invention, the developer includes charged particles that are charged with a polarity opposite to the charged polarity of the toner, and the developing roller (second conveying member) is charged with a polarity opposite to the charged polarity of the toner. Surface. Therefore, since the developing roller has a surface having the same polarity as the charged particles, the movement of the charged particles to the surface of the developing roller can be suppressed based on the electrical repulsion between the surface and the charged particles. Accordingly, since consumption of charged particles can be suppressed, the charged particles can effectively prevent toner spent on the carrier for a long term. Even if toner spent on the carrier occurs, the charged particles are held on the surface of the carrier to promote toner charging of the carrier. As a result, it is possible to suppress a decrease in the toner charging ability of the carrier and to perform stable toner charging for a long period of time.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms. Further, in the image forming apparatus and the developing apparatus described below, the same reference numerals are used for the same or similar components.

[1. Image forming apparatus]
FIG. 1 shows a portion related to image formation of an electrophotographic image forming apparatus according to the present invention. The image forming apparatus may be any of a copier, a printer, a facsimile machine, and a multi-function machine having a combination of these functions. The image forming apparatus 1 includes a photoreceptor 12 that is an electrostatic latent image carrier. In the embodiment, the photoconductor 12 is formed of a cylindrical body, but the present invention is not limited to such a form, and an endless belt type photoconductor can be used instead. The photoreceptor 12 is drivingly connected to a motor (not shown), and is rotated in the direction of arrow 14 based on the driving of the motor. Around the photoconductor 12, a charging station 16, an exposure station 18, a developing station 20, a transfer station 22, and a cleaning station 24 are arranged along the rotation direction of the photoconductor 12.

  The charging station 16 includes a charging device 26 that charges a photosensitive layer, which is the outer peripheral surface of the photosensitive member 12, to a predetermined potential. In the embodiment, the charging device 26 is represented as a cylindrical roller. However, instead of this, other types of charging devices (for example, a rotary or fixed brush-type charging device or a wire-discharge-type charging device) may be used. Can be used. In the exposure station 18, the image light 30 emitted from the exposure device 28 disposed in the vicinity of the photosensitive member 12 or away from the photosensitive member 12 travels toward the outer peripheral surface of the charged photosensitive member 12. A passage 32 is provided. On the outer peripheral surface of the photoconductor 12 that has passed through the exposure station 18, an electrostatic latent image is formed that includes a portion where the image light is projected and the potential is attenuated and a portion where the charged potential is substantially maintained. In the embodiment, the portion where the potential is attenuated is the electrostatic latent image portion, and the portion where the charged potential is substantially maintained is the electrostatic latent image non-image portion. The developing station 20 includes a developing device 34 that visualizes the electrostatic latent image using a powder developer. Details of the developing device 34 will be described later. The transfer station 22 includes a transfer device 36 that transfers a visible image formed on the outer peripheral surface of the photoreceptor 12 to a sheet 38 such as paper or film. In the embodiment, the transfer device 36 is represented as a cylindrical roller, but other types of transfer devices (for example, wire discharge transfer devices) can also be used. The cleaning station 24 includes a cleaning device 40 that collects untransferred toner remaining on the outer peripheral surface of the photoconductor 12 without being transferred to the sheet 38 at the transfer station 22 from the outer peripheral surface of the photoconductor 12. In the embodiment, the cleaning device 40 is shown as a plate-like blade, but other types of cleaning devices (for example, a rotary type or a fixed type brush type cleaning device) may be used instead.

  When the image forming apparatus 1 having such a configuration forms an image, the photoconductor 12 rotates clockwise based on the driving of a motor (not shown). At this time, the outer peripheral portion of the photoreceptor passing through the charging station 16 is charged to a predetermined potential by the charging device 26. The charged outer periphery of the photoconductor is exposed to image light 30 at an exposure station 18 to form an electrostatic latent image. The electrostatic latent image is conveyed to the developing station 20 along with the rotation of the photosensitive member 12, where it is visualized as a developer image by the developing device 34. The visualized developer image is conveyed to the transfer station 22 along with the rotation of the photosensitive member 12, and is transferred to the sheet 38 by the transfer device 36 there. The sheet 38 to which the developer image has been transferred is conveyed to a fixing station (not shown), where the developer image is fixed to the sheet 38. The outer peripheral portion of the photosensitive member that has passed through the transfer station 22 is conveyed to the cleaning station 24 where the developer remaining on the outer peripheral surface of the photosensitive member 12 without being transferred to the sheet 38 is recovered.

[2. Development device]
The developing device 34 includes a developing tank (housing) 42 that houses a two-component developer containing non-magnetic toner as first component particles and a magnetic carrier as second component particles, and various members described below. ing. In order to facilitate understanding of the invention by simplifying the drawing, a part of the developing tank 42 is omitted. The developing tank 42 includes a series of openings (44, 52) opened toward the photosensitive member 12, and a toner conveying member (second conveying member) is formed in a space 46 formed in the vicinity of the opening 44. A developing roller 48 is provided. The developing roller 48 is a cylindrical member (second rotating cylindrical body), and is arranged in parallel to the photosensitive member 12 and rotatably via the outer peripheral surface of the photosensitive member 12 and a predetermined developing gap 50. .

  In the present invention, the developing roller 48 has a surface that is charged to a polarity opposite to the charging polarity of the toner by contact with the toner. From the viewpoint of ease of production, those having a surface layer that is charged to a polarity opposite to the charged polarity of the toner by contact with the toner are used, and are usually opposite to the charged polarity of the toner by contacting with the carrier. Those having a surface layer charged to the polarity of

  Specifically, for example, when using a toner that is negatively charged by frictional contact with a carrier, a developing roller having a surface layer that is positively charged by contact with the toner is used. Those having a surface layer that is positively charged by frictional contact are used. Examples of such a positively chargeable surface layer include a positively chargeable organic layer made of a nitrogen-containing resin and a positively chargeable inorganic layer made of strontium titanate, barium titanate, and alumina. The nitrogen-containing resin is not particularly limited as long as it is a polymer containing a nitrogen atom, and examples thereof include a nitrogen-containing silicone resin, a nitrogen-containing acrylic resin, polyimide, and polyamide.

で表されるアミノアクリル変性シリコーン樹脂が挙げられる。 Specific examples of the nitrogen-containing silicone resin include, for example, the following general formula (I);

The aminoacryl modified silicone resin represented by these is mentioned.

In formula (I), R < ¹ > -R < ³ > is respectively independently a C1-C5 alkyl group, More preferably, it is a methyl group simultaneously. Specific examples of preferable alkyl groups include, for example, a methyl group, an ethyl group, an isopropyl group, and an n-propyl group.
R ⁴ is an alkylene group having 1 to 3 carbon atoms, preferably an ethylene group.
R ⁵ is an alkyl group having 1 to 3 carbon atoms. Specific examples of preferable alkyl groups include, for example, a methyl group, an ethyl group, an isopropyl group, and an n-propyl group.
m is 10-25.

で表されるポリアミノアクリル酸エステル樹脂、ならびにアクリル酸２−ジメチルアミノエチル、アクリル酸２−ジエチルアミノエチル、メタクリル酸２−ジメチルアミノエチル、メタクリル酸２−ジエチルアミノエチル、ビニルピリジン、Ｎ−ビニルカルバゾールおよびビニルイミダゾールからなる群から選択される１種類またはそれ以上の含窒素モノマーからなる単独重合体または共重合体が挙げられる。 Specific examples of the nitrogen-containing acrylic resin include, for example, the following general formula (II);

And 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole and vinyl A homopolymer or copolymer comprising one or more nitrogen-containing monomers selected from the group consisting of imidazoles.

In the formula (II), R ⁶ is an alkyl group having 1 to 8 carbon atoms, preferably 1 to 5 carbon atoms. Specific examples of preferable alkyl groups include, for example, methyl group, ethyl group, propyl group, butyl group and the like.
n is 40-180.

  The positively chargeable organic layer may contain a positive charge control agent that is positively charged by contact with the toner. As the positive charge control agent, the positive charge control agent exemplified in the description of the charged particles described later can be used. When the positively chargeable organic layer contains a positive charge control agent, the constituent resin of the organic layer is not limited to the above nitrogen-containing resin, and other resins such as a styrene-methacrylic acid ester copolymer and an epoxy resin may be used. May be used.

  The positively chargeable surface layer is preferably an organic layer from the viewpoint of ease of production, and from the viewpoint of more effectively suppressing the consumption of charged particles, is made of a nitrogen-containing silicone resin, a nitrogen-containing acrylic resin, or polyimide. An organic layer, in particular, an aminoacryl-modified silicone resin represented by the above general formula (I), a polyaminoacrylic acid ester resin represented by the above general formula (II), or an organic layer made of polyimide is preferable.

Preferred combinations of the binder resin constituting the negatively chargeable toner and the resin constituting the positively chargeable surface layer are as follows.
(Negatively chargeable toner-Positively chargeable surface layer)
Styrene-methacrylate ester resin-nitrogen-containing silicone resin (especially aminoacryl-modified silicone resin represented by the above general formula (I))
Styrene-methacrylate ester resin-nitrogen-containing acrylic resin (especially polyaminoacrylic ester resin represented by general formula (II))
Styrene-methacrylate ester resin-polyimide polyester-nitrogen-containing silicone resin (especially aminoacryl-modified silicone resin represented by the above general formula (I))
Polyester-nitrogen-containing acrylic resin (especially polyaminoacrylic ester resin represented by general formula (II))
Polyester-polyimide

  In addition, for example, when using toner that is positively charged by frictional contact with the carrier, a developing roller having a surface layer that is negatively charged by contact with the toner is used. Those having a surface layer that is negatively charged by contact are used. Examples of such a negatively chargeable surface layer include a negatively chargeable organic layer made of a fluorine-containing resin and a negatively chargeable inorganic layer made of fluorosilicate glass. The fluorine-containing resin is not particularly limited as long as it is a polymer containing a fluorine atom, and examples thereof include a fluorine-containing olefin resin and a fluorine-containing acrylic resin.

  Specific examples of the fluorine-containing olefin resin include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride.

  Polytetrafluoroethylene is available as DuPont PTFE 851-212.

  Specific examples of the fluorine-containing acrylic resin include, for example, polyfluorinated methacrylate.

  The negatively chargeable organic layer may contain a negative charge control agent that is negatively charged by contact with the toner. As the negative charge control agent, the negative charge control agent exemplified in the description of the charged particles described later can be used. When the negatively chargeable organic layer contains a negative charge control agent, the constituent resin of the organic layer is not limited to the above-mentioned fluorine-containing resin, but other polyesters, epoxy resins, styrene-methacrylate ester copolymers, etc. Resins may be used.

  The negatively chargeable surface layer is preferably an organic layer from the viewpoint of ease of production, and from the viewpoint of more effectively suppressing the consumption of charged particles, an organic layer composed of a fluorine-containing silicone resin, particularly an organic layer composed of PTFE. A layer is preferred.

Preferred combinations of the binder resin constituting the positive and negative chargeable toner and the resin constituting the negative chargeable surface layer are as follows.
(Positively chargeable toner-negatively chargeable surface layer)
Styrene acrylic resin-fluorine-containing olefin resin (especially PTFE)
Epoxy resin-fluorine-containing olefin resin (especially PTFE)

The organic layer can be produced by dissolving a predetermined resin in a solvent and applying the solution to the surface of a predetermined aluminum tube or stainless steel (SUS) tube and drying. When using a resin such as PTFE which is difficult to dissolve in a solvent, it can be produced by using it in an emulsion form, applying it, and baking it.
The inorganic layer can be manufactured by performing a vacuum deposition method or the like using a predetermined inorganic substance.

  The thickness of the surface layer of the developing roller 48 is not particularly limited as long as the object of the present invention is achieved. From the viewpoint of more effectively preventing the decrease in image density while preventing the occurrence of fogging, the thickness of the surface layer is set to 0. It is preferable to set it as 05-0.5 micrometer.

  Behind the developing roller 48, another space 52 is formed as an opening. In the space 52, a transport roller 54 that is a developer transport member (first transport member) is disposed in parallel with the developing roller 48 and through an outer peripheral surface of the developing roller 48 and a predetermined supply / recovery gap 56. . The conveyance roller 54 includes a magnet body 58 that is fixed so as not to rotate, and a cylindrical sleeve 60 (first rotating cylinder body) that is rotatably supported around the magnet body 58. Above the sleeve 60, a restricting plate 62 fixed to the developing tank 42 and extending in parallel with the central axis of the sleeve 60 is disposed so as to oppose a predetermined restricting gap 64.

  The magnet body 58 has a plurality of magnetic poles facing the inner surface of the transport roller 54 and extending in the direction of the central axis of the transport roller 54. In the embodiment, the plurality of magnetic poles are opposed to the magnetic pole S <b> 1 facing the upper inner peripheral surface portion of the transport roller 54 near the regulating plate 62 and the left inner peripheral surface portion of the transport roller 54 near the supply and recovery gap 56. Magnetic pole N1, magnetic pole S2 facing the lower inner peripheral surface portion of the transport roller 54, and two adjacent magnetic poles N2, N3 of the same polarity facing the right inner peripheral surface portion of the transport roller 54.

  A developer stirring chamber 66 is formed behind the transport roller 54. The stirring chamber 66 has a front chamber 68 formed in the vicinity of the transport roller 54 and a rear chamber 70 separated from the transport roller 54. A front screw 72 that is a pre-stirring and conveying member that conveys the developer while stirring the developer from the front surface to the back surface of the drawing is rotatably disposed in the front chamber 68, and the rear chamber 70 is rotated from the back surface to the front surface of the drawing. A rear screw 74 that is a rear stirring member transporting member that transports the developer while stirring is disposed rotatably. As shown in the figure, the front chamber 68 and the rear chamber 70 may be separated by a partition wall 76 provided therebetween. In this case, the partition portions near both ends of the front chamber 68 and the rear chamber 70 are removed to form a communication passage, and the developer that has reached the downstream end of the front chamber 68 passes through the communication passage. The developer that has been fed to 70 and reaches the downstream end of the rear chamber 70 is fed to the front chamber 68 via a communication passage.

  The operation of the developing device 34 configured as described above will be described. During image formation, the developing roller 48 and the sleeve 60 rotate in the directions of arrows 78 and 80, respectively, based on driving of a motor (not shown). The front screw 72 rotates in the direction of arrow 82 and the rear screw 74 rotates in the direction of arrow 84. Thereby, the developer 2 accommodated in the developer stirring chamber 66 is stirred while being circulated and conveyed through the front chamber 68 and the rear chamber 70. As a result, the toner and the carrier contained in the developer come into frictional contact with each other and are charged with opposite polarities. In the embodiment, it is assumed that the carrier is positively charged and the toner is negatively charged. As shown in FIG. 2, the carrier 4 is considerably larger than the toner 6. Therefore, as shown in FIG. 3, the negatively charged toner 6 adheres around the positively charged carrier 4 mainly based on the electrical attraction force of both.

  Returning to FIG. 1, the charged developer 2 is supplied to the transport roller 54 in the process of being transported through the front chamber 68 by the front screw 72. The developer 2 supplied from the front screw 72 to the conveyance roller 54 is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnetic pole N3 in the vicinity of the magnetic pole N3. The developer 2 held by the sleeve 60 constitutes a magnetic brush along the magnetic field lines formed by the magnet body 58, and is conveyed in the counterclockwise direction based on the rotation of the sleeve 60. The amount of developer 2 held by the magnetic pole S <b> 1 in the area facing the restriction plate 62 (restriction area 86) is regulated by the restriction plate 62 to a predetermined amount. The developer 2 that has passed through the regulation gap 64 is conveyed to a region (supply / recovery region) 88 where the developing roller 48 and the conveying roller 54 are opposed to each other, where the magnetic pole N1 is opposed. As will be described in detail later, in the supply / recovery region 88, an upstream region (supply region) 90 mainly in the rotation direction of the sleeve 60, the presence of an electric field formed between the developing roller 48 and the sleeve 60. Thus, the toner 6 adhering to the carrier 4 is electrically supplied to the developing roller 48. Further, in the supply / recovery area 88, a region (collection area) 92 on the downstream side mainly in the rotation direction of the sleeve 60, as will be described later, the development sent back to the supply / recovery area 88 without contributing to the development. The toner on the roller 48 is scraped off by a magnetic brush formed along the magnetic field lines of the magnetic pole N1 and collected in the sleeve 60. The carrier 4 is held on the outer peripheral surface of the sleeve 60 by the magnetic force of the magnet body 58 and does not move from the sleeve 60 to the developing roller 48. When the developer 2 that has passed through the supply / recovery region 88 is held by the magnetic force of the magnet body 58 and passes through the opposing portion of the magnetic pole S2 along with the rotation of the sleeve 60, it reaches the opposing region of the magnetic poles N2 and N3 (release region 94). The repulsive magnetic field formed by the magnetic poles N2 and N3 is discharged from the outer peripheral surface of the sleeve 60 to the front chamber 68 and mixed with the developer 2 being conveyed through the front chamber 68.

The toner 6 held on the developing roller 48 in the supply area 90 is conveyed in the counterclockwise direction along with the rotation of the developing roller 48, and is an area (developing area) 96 where the photosensitive body 12 and the developing roller 48 face each other. It adheres to the electrostatic latent image portion formed on the outer peripheral surface. In the image forming apparatus according to the embodiment, a predetermined negative potential V _H is applied to the outer peripheral surface of the photoreceptor 12 by the charging device 26, and the electrostatic latent image image portion on which the image light 30 is projected by the exposure device 28 is predetermined. attenuated until the potential V _L, an electrostatic latent image non-image portion of the image light 30 is not projected by the exposing device 28 maintains a substantially charge potential V _H. Accordingly, in the developing region 96, the negatively charged toner 6 adheres to the electrostatic latent image portion due to the action of the electric field formed between the photosensitive member 12 and the developing roller 48, and the electrostatic latent image portion. The latent image is visualized as a developer image.

  When the toner 6 is consumed from the developer 2 in this way, it is preferable to supply the developer 2 with an amount of toner corresponding to the consumed amount. For this purpose, the developing device 34 includes means for measuring the mixing ratio of the toner and the carrier stored in the developing tank 42. In addition, a toner replenishment section 98 is provided above the rear chamber 70. The toner supply unit 98 includes a container 100 for storing toner. An opening 102 is formed at the bottom of the container 100, and a supply roller 104 is disposed in the opening 102. The replenishing roller 104 is drivingly connected to a motor (not shown), and the motor is driven based on the output of the means for measuring the mixing ratio of toner and carrier so that the toner drops and replenishes the rear chamber 70. In the present invention, since the consumption of charged particles is sufficiently suppressed, the replenishment toner can be set with the charged particle ratio being lower than the charged particle content ratio relative to the toner in the initially filled developer.

[3. Electric field forming means]
In order to efficiently move the toner 6 from the sleeve 60 to the developing roller 48 in the supply region 90, the developing roller 48 and the sleeve 60 are electrically connected to the electric field forming device 110. Specific examples of the power supply are shown in FIGS.

The electric field forming apparatus 110 of Embodiment 1 shown in FIG. 5A includes a first power source 112 (corresponding to second electric field forming means) connected to the developing roller 48 and a second power source 114 (corresponding to the second electric field forming unit). Corresponding to first electric field forming means). The first power supply 112 includes a DC power supply 118 connected between the developing roller 48 and the ground 116, and a first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner 6. Is applied to the developing roller 48. The second power supply 114 has a DC power supply 120 connected between the sleeve 60 and the ground 116, and has the same polarity as the charging polarity of the toner 6 and a second DC voltage that is higher than the first DC voltage. V _DC2 (eg, −400 volts) is applied to the sleeve 60. As a result, in the supply region 90, the negatively charged toner 6 is electrically attracted from the sleeve 60 to the developing roller 48 under the action of a DC electric field formed between the developing roller 48 and the sleeve 60. Is done. At this time, the positively charged carrier 4 is not attracted to the developing roller 48 from the sleeve 60. In the developing region 96, the negative toner held on the developing roller 48 is, as shown in FIG. 5B, the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L :−). It adheres to the electrostatic latent image portion based on the potential difference of 80 volts). At this time, the negative polarity toner adheres to the electrostatic latent image non-image portion due to a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image non-image portion (V _H : −600 volts). There is nothing.

In the electric field forming apparatus 122 of FIG. 6A according to the second embodiment, the first power supply 124 (corresponding to the second electric field forming means) is provided between the developing roller 48 and the ground 126, similarly to the power supply of the first embodiment. The first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner 6 is applied to the developing roller 48. The second power source 130 includes a DC power source 132 and an AC power source 134 between the sleeve 60 and the ground 126. The DC power supply 132 applies a second DC voltage V _DC2 (for example, −400 volts) having the same polarity as the charging polarity of the toner 6 and higher than the first DC voltage to the sleeve 60. As shown in FIG. 6B, the AC power supply 134 applies an _AC voltage VAC having a peak-to-peak voltage V _PP of, for example, 300 volts between the sleeve 60 and the ground 126. As a result, in the supply region 90, the negatively charged toner 6 is electrically transferred from the sleeve 60 to the developing roller 48 under the action of a pulsating electric field formed between the developing roller 48 and the sleeve 60. Sucked. At this time, the positively charged carrier 4 is held by the sleeve 60 by the magnetic force of the fixed magnet inside the sleeve 60 and is not supplied to the developing roller 48. In the developing region 96, the negative toner held on the developing roller 48 is caused by a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). Based on the electrostatic latent image portion.

In the electric field forming device 136 shown in FIG. 7A, the first power source 138 includes a DC power source 142 and an AC power source 144 between the developing roller 48 and the ground 140. The DC power supply 142 applies a first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner 6 to the sleeve 60 and the developing roller 48. The AC power supply 144 applies an _AC voltage VAC having an amplitude (peak-to-peak voltage) _VP-P of, for example, 1,600 volts between the sleeve 60 and the developing roller 48 and the ground 146. The second power source 146 (corresponding to the first electric field forming means) has a DC power source 150 connected between the terminal 148 between the developing roller 48 and the AC power source 144 and the sleeve 60. The DC power supply 150 can output a predetermined DC voltage V _DC2 , and the anode is connected to the terminal 148 and the cathode is connected to the sleeve 60, whereby the sleeve 60 is biased to the negative polarity with respect to the developing roller 48. (See FIG. 7B). Accordingly, in the supply region 90, the negatively charged toner 6 is electrically attracted from the sleeve 60 to the developing roller 48 due to the action of the pulsating electric field formed between the developing roller 48 and the sleeve 60. Is done. In the developing region 96, the negative toner on the developing roller 48 is statically charged based on the potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). It adheres to the electrostatic latent image portion.

An electric field forming device 152 shown in FIG. 8 is obtained by adding AC power sources 154 and 156 to the first power source 112 and the second power source 114, respectively, in the electric field forming device 110 of Embodiment 1 shown in FIG. 5A. The output voltages of the AC power supplies 154 and 156 are V _AC1 and V _AC2 . The voltages V _AC1 and V _AC2 may be the same or different. An electric field forming device 158 shown in FIG. 9 is obtained by adding an AC power source 160 to the first power source 112 in the power source of the embodiment shown in FIG. 5A. The output voltage of the AC power supply 160 is _{V AC.} Similarly to the electric field forming devices 110, 122, and 136, the electric field forming devices 152 and 158 of these forms also receive the action of the pulsating electric field formed between the developing roller 48 and the sleeve 60, and in the supply region 90. The negatively charged toner 6 is supplied from the sleeve 60 to the developing roller 48, and the negatively charged toner 6 is supplied from the developing roller 48 to the electrostatic latent image portion (V _L : −80) in the developing region 96. Based on the potential difference with respect to the voltage (volt).

[4. Developer)
In general, in a two-component developer containing toner and carrier as main components, dirt (spent) is generated by the toner adhering to the surface of the carrier, and this reduces the life of the carrier. In order to solve this problem, in the present invention, charged particles (implant particles) are added as a third component to the two-component developer.

  2 to 4, the image forming apparatus and the developing apparatus according to the present invention make the toner 6 have a normal polarity (not shown) by frictional contact with the toner 6 in addition to the toner 6 and the carrier 4. In this case, charged particles 8 having a diameter smaller than that of the toner 6 are included. In the embodiment, the charged particles 8 are detachably held on the outer peripheral surface of the toner 6 and are replenished together with the toner 6 from the toner replenishing unit 98.

  At the time of image formation, the charged particles 8 are transported in the developing tank 42 together with the toner 6 and the carrier 4, and then are held by the sleeve 60 and move in the regulation region 86, the supply / recovery region 88, and the discharge region 94. In this conveyance process, when the charged particles 8 held on the surface of the toner 6 are placed in the electric field of the supply / recovery region 88, an electric force in a direction opposite to the electric force acting on the toner 6 is obtained. In response, the toner 6 is detached from the outer peripheral surface. The separated charged particles 8 are held or driven on the outer peripheral surface of the carrier 4 by stress acting between the separated charged particles 8 and the carrier 4. As shown in FIG. 4, when a part or the whole of the outer peripheral surface of the carrier 4 is covered with the spent 10, the charged particles 8 are driven into the spent 10. The charged particles 8 held or driven on the outer peripheral surface of the carrier 4 are charged to a polarity opposite to that of the toner 6 by frictional contact with the toner 6. In the embodiment, since the toner 6 is charged to a negative polarity, the charged particles 8 are charged to a positive polarity. As a result, the carrier 4 into which the charged particles 8 are implanted maintains the same chargeability as the state without the spent 10 even if at least a part of the outer peripheral surface thereof is covered with the spent 10, and the toner 6 is preliminarily provided. Charged to the polarity.

  As described above, the charged particles 8 are charged with a polarity opposite to that of the toner 6. Therefore, in the supply / recovery area 88, the toner 6 moves from the sleeve 60 to the developing roller 48 based on the electric field formed between the developing roller 48 and the sleeve 60. Further, the charged particles 8 separated from the toner 6 are quickly held on the carrier surface of the developer that is relatively carrier-rich by the toner 6 being taken away in the supply region 90 and supplied to the developing roller 48 together with the toner 6. Even if not supplied or supplied to the developing roller 6, the amount is extremely small.

  In the embodiment, the toner 6 is charged to a negative polarity and the carrier 4 is charged to a positive polarity by frictional contact between the toner 6 and the carrier 4. Further, the charged particles 8 are charged negatively by contact with the toner 6, and the charged particles 8 are charged positively. The chargeability of the toner, carrier, and charged particles used in the present invention is not limited to such a combination. Specifically, the toner 6 is charged positively by the frictional contact between the toner 6 and the carrier 4, the carrier 4 is charged negatively, and the charged particles 8 are charged positively by the contact with the toner 6. A combination in which the charged particles 8 are negatively charged is also conceivable.

[5. Specific materials)
Specific materials of the toner, carrier, charged particles, and other particles contained in the developer will be described.

[Charged particles]
The charged particles preferably used are appropriately selected according to the charging polarity of the toner, and particles charged to a polarity opposite to the charging polarity of the toner by frictional contact with the toner are used. Particles that are charged to the opposite polarity to the charged polarity of the toner by contact are used. The average primary particle size of the charged particles is, for example, 100 to 1000 nm. Specifically, for example, when using a toner that is negatively charged by frictional contact with the carrier, charged particles are particles that are positively charged by contact with the toner, and are usually positively charged by frictional contact with the carrier. Particles that are electrically charged are used. Such particles include, for example, inorganic particles such as strontium titanate, barium titanate, magnesium titanate, calcium titanate, and alumina, and thermoplastic resins such as acrylic resin, benzoguanamine resin, nylon resin, polyimide resin, and polyamide resin. Or it can comprise with a thermosetting resin. The resin constituting the charged particles may contain a positive charge control agent that is positively charged by contact with the toner. As the positive charge control agent, for example, nigrosine dye, quaternary ammonium salt and the like can be used. The charged particles may be composed of nitrogen-containing monomers. Examples of the material constituting the nitrogen-containing monomer include 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole, There is vinylimidazole. A preferred combination of the binder resin constituting the negatively chargeable toner and the material constituting the positively chargeable charged particles is as follows.
(Negatively charged toner-positively charged charged particles)
Polyester-SrTiO ₃
Styrene-methacrylate resin-SrTiO ₃
Polyester-CaTiO ₃
Styrene-methacrylate resin-CaTiO ₃

Also, for example, in the case of toner charged to positive polarity by frictional contact with a carrier, charged particles are particles that are negatively charged by contact with toner, and usually negative polarity due to frictional contact with the carrier. Particles that are electrically charged are used. As such particles, for example, inorganic particles such as silica and titanium oxide, and particles made of thermoplastic resin or thermosetting resin such as fluororesin, polyolefin resin, silicone resin, and polyester resin can be used. A negative charge control agent that is negatively charged by contact with the toner may be contained in the resin constituting the charged particles. Examples of negative charge control agents include salicylic acid-based and naphthol-based chromium complexes, aluminum complexes, iron complexes, and zinc complexes. The charged particles may be a copolymer of a fluorine-containing acrylic monomer or a fluorine-containing methacrylic monomer. Preferred combinations of the binder resin constituting the positively chargeable toner and the material constituting the negatively chargeable charged particles are as follows.
(Positively chargeable toner binder resin-negatively charged charged particles)
Styrene acrylic resin-Silica Polyaminoacrylic ester-Polyfluorinated acrylic beads Polyaminoacrylic ester-PTFE beads Styrene acrylic resin-Polyfluorinated acrylic beads Styrene acrylic resin-PTFE beads

  In order to control the chargeability and hydrophobicity of the charged particles, the surface of the inorganic particles may be surface-treated with a silane coupling agent, a titanium coupling agent, silicone oil, or the like. In particular, when imparting positive electrode chargeability to inorganic particles, it is preferable to surface-treat with an amino group-containing coupling agent. When imparting negative chargeability to the particles, it is preferable to surface-treat with a fluorine group-containing coupling agent.

  The content of the charged particles is not particularly limited as long as the object of the present invention is achieved. For example, 0.1 to 5.0% by weight, particularly 0.5 to 2.0% by weight is preferable with respect to the toner. is there.

〔toner〕
As the toner, a known toner that has been conventionally used in an image forming apparatus can be used. The toner particle size is, for example, about 3 to 15 μm. A toner containing a colorant in a binder resin, a toner containing a charge control agent or a release agent, and a toner holding an additive on the surface can also be used.

  The toner can be produced by a known method such as a pulverization method, an emulsion polymerization method, or a suspension polymerization method.

[Binder resin]
The binder resin used for the toner is not limited. For example, styrene resin (monopolymer or copolymer containing styrene or styrene-substituted product), polyester resin, epoxy resin, vinyl chloride resin, phenol resin. , Polyethylene resin, polypropylene resin, polyurethane resin, silicone resin, styrene acrylic resin, nitrogen-containing acrylic resin, or any mixture of these resins. The binder resin preferably has a softening temperature in the range of about 80 to 160 ° C and a glass transition point in the range of about 50 to 75 ° C.

[Colorant]
For the colorant, a known material such as carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultramarine blue, rose bengal, lake red, etc. should be used. Can do. In general, the addition amount of the colorant is preferably 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

[Charge control agent]
As the charge control agent, materials conventionally known as charge control agents can be used. Specifically, for the positively charged toner, for example, nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazole compounds, and polyamine resins can be used as charge control agents. For the negatively charged toner, metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curixarene compounds can be used as charge control agents. The charge control agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  As the release agent, a known release agent conventionally used as a release agent can be used. As the material for the release agent, for example, polyethylene, polypropylene, carnauba wax, sazol wax, or a mixture of them as appropriate is used. The release agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

[Other additives]
In addition, a fluidizing agent that promotes fluidization of the developer may be added. As the fluidizing agent, for example, inorganic fine particles such as silica, titanium oxide, and aluminum oxide, and resin fine particles such as acrylic resin, styrene resin, silicone resin, and fluorine resin can be used. In particular, it is preferable to use a material hydrophobized with a silane coupling agent, a titanium coupling agent, silicone oil, or the like. The fluidizing agent is preferably added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The number average primary particle size of these additives is preferably 9 to 100 nm, particularly preferably 9 to less than 100 nm.

[Carrier]
As the carrier, a known carrier that has been generally used can be used. Either a binder type carrier or a coat type carrier may be used. The carrier particle size is not limited, but is preferably about 15 to 100 μm.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and those having fine particles or a coating layer charged positively or negatively on the surface can be used. The charging characteristics such as the polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, and the type of the surface coating layer.

  The binder resin used for the binder type carrier is a thermoplastic resin such as a vinyl resin, a polyester resin, a nylon resin, or a polyolefin resin typified by a polystyrene resin, a polyacrylic resin, and a styrene-methacrylate copolymer. And curable resins such as phenol resins.

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape of the carrier may be granular, spherical, or needle-shaped. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added in an amount of 50 to 90% by weight in the magnetic resin carrier.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material for the binder type carrier. The charge imparting ability of the carrier can be improved by coating and curing these resins on the carrier surface to form a coat layer.

  For example, the charging fine particles or the conductive fine particles can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly and adhering the fine particles to the surface of the magnetic resin carrier. This is done by driving fine particles into the magnetic resin carrier by applying a strong impact force. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier. Organic and inorganic insulating materials are used for the chargeable fine particles. Specifically, organic insulating materials include polystyrene, styrene-based copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof such as organic insulating fine particles. is there. The charge imparting ability and the charge polarity can be adjusted to the material of the chargeable fine particles, the polymerization catalyst, the surface treatment and the like. As the inorganic insulating material, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  The coat type carrier is a carrier in which carrier core particles made of a magnetic material are coated with a resin, and like the binder type carrier, chargeable fine particles that are charged positively or negatively can be fixed to the surface of the carrier. The charging characteristics such as the polarity of the coated carrier can be adjusted by selecting the type of surface coating layer and the electrifying fine particles. As the coating resin, the same resin as the binder resin of the binder type carrier can be used.

  The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount, and the toner ratio is preferably 3 to 50% by weight, preferably 6 to 30% by weight based on the total amount of the toner and the carrier. .

(Carrier A)
A carrier A was prepared by coating a polyacrylic resin on a 40 μm particle diameter Mn · Zn ferrite sphere.

(Carrier B)
500 parts of zinc-based ferrite powder having a particle size of 0.3 to 0.6 μm are mixed with 100 parts of the polyester resin by a super mixer, and the mixture is melt-kneaded. After cooling, the mixture is coarsely pulverized to 2 mm, and further, a carrier having an average diameter of 40 μm is obtained by fine pulverization and classification.

で表されるアミノ基含有アクリル変性シリコーン樹脂２０ｇを溶解した。この溶液をディッピング法により、現像ローラに用いるアルミ管に塗布し、乾燥させた。ローラの抵抗は、市販のテスターを用い、管の内面と外面に電極を当てて測定した。この塗布アルミ管の抵抗を測定したところ、０．０１６Ωであった。ローラ表面の帯電極性は、図１０のように前記キャリアＡ（４）を載せた回転するスリーブ６０に、スリーブ６０より周速度が遅くスリーブ６０と同方向に回転する現像ローラ４８を接触させ一周した後、表面電位を、プローグ１８１を有する表面電位計１８０を用いて測定し検出する。本ローラの表面電位は＋５０Ｖであり、本塗布材料はキャリアＡに対して正帯電性であることが明らかであった。このローラをＲ１とする。なお、以下に示す現像ローラの抵抗、表面電位および厚みの測定方法は、現像ローラＲ１における方法と同様である。 (Developing roller R1)
To 400 g of methyl ethyl ketone, the following structural formula:

20 g of an amino group-containing acrylic modified silicone resin represented by This solution was applied to an aluminum tube used for a developing roller by a dipping method and dried. The resistance of the roller was measured using a commercially available tester and applying electrodes to the inner and outer surfaces of the tube. When the resistance of this coated aluminum tube was measured, it was 0.016Ω. As shown in FIG. 10, the charging polarity on the surface of the roller made one turn by contacting a rotating sleeve 60 carrying the carrier A (4) with a developing roller 48 rotating at a lower peripheral speed than the sleeve 60 and rotating in the same direction as the sleeve 60. Thereafter, the surface potential is measured and detected using a surface potentiometer 180 having a probe 181. The surface potential of this roller was +50 V, and it was clear that this coating material was positively charged with respect to carrier A. Let this roller be R1. The method for measuring the resistance, surface potential and thickness of the developing roller described below is the same as the method for the developing roller R1.

(Developing rollers R2 to R4)
Each of the developing rollers R2 to R4 was manufactured by the same method as the developing roller R1, except that coating and drying were performed twice, five times, and eight times.

(Developing roller R5)
The developing roller R5 was manufactured by the same method as the developing roller R1, except that the solution prepared by the following method was used.
A solution was prepared by dissolving 5 g of an amino group-containing acrylic modified silicone resin in 400 g of methyl ethyl ketone.

(Developing roller R6)
The developing roller R6 was produced by the same method as the developing roller R1, except that the solution prepared by the following method was used and coating and drying were performed 5 times.
A solution was prepared by dissolving 100 g of an amino group-containing acrylic modified silicone resin in 400 g of methyl ethyl ketone.

(Developing roller R7)
The developing roller R7 was produced by the same method as the developing roller R1, except that a solution prepared by the following method was used and coating and drying were performed 6 times.
A solution was prepared by dissolving 40 g of an amino group-containing acrylic-modified silicone resin in 400 g of methyl ethyl ketone.

(Developing roller R8)
The developing roller R8 was produced by the same method as the developing roller R1, except that the solution prepared by the following method was used.
A solution was prepared by dissolving 10 g of an amino group-containing acrylic modified silicone resin in 400 g of methyl ethyl ketone.

(Developing roller RC1)
The aluminum tube used in the production of the developing roller R1 was used as it was.

で表されるポリアミノアクリル酸エステル樹脂４０ｇを溶解した。この溶液をディッピング法により、現像ローラに用いるアルミ管に塗布し、乾燥させた。ローラ表面の電位を、現像ローラＲ１と同様の方法により測定し検出する。本ローラの表面電位は＋４５Ｖであり、本塗布材料はキャリアＡに対して正帯電性であることが明らかであった。 (Developing roller R9)
To 400 g of methyl ethyl ketone, the following structural formula:

40 g of a polyaminoacrylate resin represented by the formula: This solution was applied to an aluminum tube used for a developing roller by a dipping method and dried. The potential of the roller surface is measured and detected by the same method as that for the developing roller R1. The surface potential of this roller was +45 V, and it was clear that this coating material was positively charged with respect to carrier A.

(Developing roller R10)
The developing roller R10 was manufactured by the same method as the developing roller R9, except that coating and drying were performed three times.

(Developing rollers R11 to R12)
The developing rollers R11 to R12 were manufactured by the same method as the developing roller R9, except that the solution prepared by the following method was used and coating and drying were performed once and six times, respectively.
A solution was prepared by dissolving 100 g of polyaminoacrylate resin in 400 g of methyl ethyl ketone.

(Developing roller R13)
40 g of bisallyldiimide (BANI-M manufactured by Maruzen Petrochemical Co., Ltd.) is dissolved in methyl ethyl ketone and applied to an aluminum tube by dipping. This is left to cure at 250 ° C. for 24 hours. The surface potential of the roller is detected by the same method as that for the developing roller R1. The surface potential of this roller was +65 V, and it was clear that this material was positively charged with respect to carrier A.

(Developing roller R14)
The developing roller R14 was manufactured by the same method as the developing roller 13 except that coating and curing were repeated three times.

(Developing roller R15)
PTFE is coated on the aluminum tube. First, a primer (PTFE paint 850-314 manufactured by DuPont) is spray-coated on the tube and dried at 150 ° C. Thereafter, an emulsion of PTFE (Teflon paint 851-214 manufactured by DuPont) is applied by spraying, followed by drying and baking at 300 ° C. The surface potential of the roller is detected by the same method as that for the developing roller R1, except that the carrier B is used. The surface potential of this roller was −65 V, and it was clear that this material was negatively charged with respect to carrier B.

(Charged particle A)
As the charged particles A, strontium titanate (SW-series; manufactured by Titanium Industry Co., Ltd.) having an average primary particle size of 0.6 μm was used. This strontium titanate was mixed with carrier A at a weight mixing ratio (charged particle / carrier) of 20/80 and measured by the blow-off method. As a result, it was +70 μC / g and exhibited positive chargeability with respect to carrier A. .

(Charged particle B)
Silica (manufactured by Nippon Aerosil Co., Ltd.) having an average primary particle size of 0.5 μm was used as the charged particle B. This silica was mixed with carrier B at a weight mixing ratio (charged particle / carrier) of 20/80 and measured by the blow-off method. As a result, it was −45 μC / g, and showed negative chargeability with respect to carrier B.

(Toner A: negatively chargeable toner)
Styrene-methacrylate ester resin (Mw: 220,000, Mn: 8300, Tg: 58 ° C.) is mixed with 100 parts by weight of carbon black (6 parts by weight) and S34 (manufactured by Orient Chemical Co., Ltd.) with a high-speed shear mixer. After kneading, cooling, pulverization, and classification were performed to obtain toner particles having a weight average particle diameter of 6 μm. Toner A is obtained by mixing 0.5% by weight of hydrophobized silica having an average primary particle size of 30 nm and 2% by weight of charged particles A with respect to the toner particles.

(Toner B: Positively chargeable toner)
Styrene acrylic resin (Mw: 240,000, Mn: 9000, Tg: 59 ° C.) 100 parts by weight, 6 parts by weight of carbon black and 4 parts by weight of nigrosine base EX (manufactured by Orient Chemical Co., Ltd.) are mixed with a high-speed shear mixer. After kneading, cooling, pulverization, and classification were performed to obtain toner particles having a weight average particle diameter of 7 μm. Toner B is made by mixing 0.5 wt% of hydrophobized silica having an average primary particle size of 30 nm and 2 wt% of charged particles B with respect to the toner particles.

(Example / Comparative Example)
The developer obtained by mixing the toner shown in Table 2 at a mixing ratio of 10% and the developing roller shown in Table 2 were mounted on an image forming apparatus having the form shown in FIG. Using this image forming apparatus, 100,000 samples with an image ratio of 5% were printed.

In Examples 1 to 14 and Comparative Example 1, the development conditions are as follows. The electric field forming apparatus employs the form shown in FIG. 9, and a DC voltage V _{DC2 of} −500 volts is applied to the conveying roller, and an AC voltage of DC voltage V _{DC1 of} −300 volts is applied to the developing roller. AC voltage frequency: 2 kHz, the amplitude _V P-P: 1,600 volts, minus the duty ratio (toner collecting duty ratio): 40%, plus a duty ratio (toner supply duty ratio): was 60% of the rectangular wave . The development gap 50 was set to 0.3 mm, the supply / recovery gap 56 was set to 0.6 mm, and the regulating portion was set so that the developer conveyance amount of the conveyance roller was 50 mg / cm ² . The charged potential (non-image portion) of the photoreceptor was −550 volts, and the potential of the electrostatic latent image (image portion) formed on the photoreceptor was −60 volts.

In Example 15, the development conditions are as follows. The electric field forming apparatus employs the form shown in FIG. 8, and a DC voltage V _DC2 : +600 volts and an AC voltage are applied to the conveying roller. The AC voltage frequency: 2 kHz, the amplitude _V P-P: 1500 volts, minus the duty ratio (toner collecting duty ratio): 50%, plus a duty ratio (toner supply duty ratio): a 50% square wave, the developing roller The AC voltage was 90 ° out of phase with the AC voltage. A DC voltage V _DC1 : +400 volts and an AC voltage were applied to the developing roller. The AC voltage frequency: 2 kHz, the amplitude _V P-P: 1500 volts, minus the duty ratio (toner collecting duty ratio): 50%, plus a duty ratio (toner supply duty ratio): was 50% of the rectangular wave. The developing gap 50 was set to 0.25 mm, the supply / recovery gap 56 was set to 0.5 mm, and the regulating portion was set so that the developer carrying amount of the carrying roller was 50 mg / cm ² . The charged potential (non-image portion) of the photoreceptor was +500 volts, and the potential of the electrostatic latent image (image portion) formed on the photoreceptor was +20 volts.

-Fog The image after printing was visually observed and evaluated by comparison with a limit sample.
The level is good in the order of × → △ → ○ → ◎. ◎ is a level at which toner is hardly seen on the background even with a loupe, ◯ is a level that can not be detected with the eyes but can be detected slightly with the loupe, △ cannot be detected with the eyes, but a level at which the toner is slightly noticeable when viewed with the loupe (practically No problem), x is a level at which fogging is detected even with the eyes.

-Image density The image density was measured using a Macbeth transmission densitometer.
A; concentration ≧ 1.5;
○; 1.3 ≦ Concentration <1.5;
Δ: 1.1 ≦ concentration <1.3 (no problem in practical use);
X: Concentration <1.1.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention and a cross section of a developing device according to the present invention. The figure which illustrates the composition of a developer typically. The figure which shows typically the state in which the toner which hold | maintained the charged particle has adhered to the surface of a carrier. The figure which shows typically the state by which the charged particle was bombarded on the surface of the carrier to which the spent adhered. The figure which shows one Embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 5A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 6A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown to FIG. 7A. The figure which shows other embodiment of an electric field formation apparatus. The figure which shows other embodiment of an electric field formation apparatus. Schematic for demonstrating the method to detect the charging polarity of the developing roller surface.

Explanation of symbols

  1: image forming apparatus, 2: developer, 4: carrier, 6: toner, 8: charged particles, 10: spent, 12: photoconductor, 16: charging station, 18: exposure station, 20: developing station, 22: Transfer station, 24: cleaning station, 26: charging device, 28: exposure device, 30: image light, 32: passage, 34: developing device, 36: transfer device, 38: sheet, 40: cleaning device, 42: developing tank (Housing), 44: opening, 46: second space, 48: developing roller, 50: developing gap, 52: opening (second space), 54: transport roller, 56: supply / recovery gap, 58: Magnet body, 60: sleeve, 62: regulating plate, 64: regulating gap, 66: developer stirring chamber, 68: front chamber, 70: rear chamber, 72: front screw, 74: rear screen -, 76: partition wall, 86: restriction area, 88: supply / recovery area, 90: supply area, 92: collection area, 94: discharge area, 96: development area, 98: toner replenishing section, 100: container, 102: opening 104: Supply roller 110: Electric field forming device 112: First power source 114: Second power source 116: Ground 118: DC power source 120: DC power source 122: Electric field forming device 124: First 1 power supply, 126: ground, 128: DC power supply, 130: second power supply, 132: DC power supply, 134: AC power supply, 136: electric field forming device, 138: first power supply, 140: ground, 142: DC Power supply, 144: AC power supply, 146: Second power supply, 148: Terminal, 150: DC power supply, 152: Electric field forming device, 154: AC power supply, 156: AC power supply, 158: Electric field forming device, 60: AC power supply.

Claims (2)

A developing device that visualizes an electrostatic latent image on an electrostatic latent image carrier using a developer including toner and a carrier,
A developer including a toner and a carrier, wherein the toner is charged to a first polarity by frictional contact between the toner and the carrier, and the carrier is charged to a second polarity different from the first polarity; ,
A first conveying member disposed in an opening of a developing tank that contains the developer;
A second conveying member facing the first conveying member via a first region and facing the electrostatic latent image carrier via a second region;
A first electric field is formed between the first transport member and the second transport member, and the toner in the developer held by the first transport member is transferred to the second transport member. First electric field forming means to be moved;
A second electric field is formed between the second transport member and the electrostatic latent image carrier, and the toner held by the second transport member is transferred to the electrostatic latent image carrier by static electricity. A second electric field forming means for making the electrostatic latent image visible by moving it to an electrostatic latent image;
The developer further includes charged particles that are charged to a polarity opposite to the charged polarity of the toner by frictional contact with the carrier ,
The developing device according to claim 1, wherein the second conveying member has a surface that is charged to a polarity opposite to a charging polarity of the toner by frictional contact with the carrier .   An image forming apparatus comprising the developing device according to claim 1.

Images