JP2007327998A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for forming excellent images over a long period of time in a developing device using a two-component developer. <P>SOLUTION: The developing device using the developer including toner, a carrier and reverse polarity particles charged in a reverse polarity to a charge polarity of the toner comprises a separation means for separating the toner or the reverse polarity particles and has a control means for controlling a separation ratio of the reverse polarity particles in response to printing sheet number. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a developing device that develops a latent image on an image carrier using a developer containing toner and a carrier.

  Conventionally, in an image forming apparatus using an electrophotographic method, as a developing method of an electrostatic latent image formed on an image carrier, a one-component developing method using only toner as a developer and a two-component using a toner and a carrier Development methods are known.

  In the one-component development method, a predetermined charge amount is generally obtained by using a toner carrier and a regulation plate pressed toward the toner carrier, and regulating the film thickness while pressing the toner on the toner carrier with the regulation plate. A thin toner layer can be formed. With this toner thin layer, the electrostatic latent image on the image carrier is developed. This method is excellent in dot reproducibility and is a method in which a uniform image with little image unevenness can be easily obtained. In addition, it is considered advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus. However, in order to give a strong stress to the toner in the restricting portion, the toner surface is denatured, or toner or an external additive adheres to the surface of the toner restricting member or the toner carrying member, and the charge amount of the toner is reduced. This causes problems such as fogging on the image and dirt in the aircraft due to scattering. As a result, there is a problem that the life of the developing device is shortened.

  On the other hand, in the two-component development system, the toner is charged by frictional charging by mixing with the carrier, so that the stress is small and it is advantageous for the deterioration of the toner. Furthermore, since the carrier as a charge imparting member to the toner has a large surface area, it is relatively resistant to contamination by the toner and external additives, and is advantageous for extending the life.

  However, even when a two-component developer is used, the surface of the carrier is contaminated by toner and external additives, and the toner charge amount is reduced by long-term use, such as fogging and toner scattering. Problems arise and their lifetime is by no means sufficient, and a longer lifetime is desired.

  As a method for extending the life of a two-component developer, Patent Document 1 discloses that a carrier is supplied in small amounts together with toner or alone, and accordingly, a deteriorated developer having reduced chargeability is discharged and the carrier is replaced. A developing device is disclosed that suppresses the ratio of deteriorated carriers. In this apparatus, since the carrier is replaced, it is possible to suppress a decrease in toner charge amount due to carrier deterioration at a certain level, which is advantageous in extending the service life.

  Patent Document 2 discloses a two-component developer comprising a toner and a carrier externally added with reverse polarity particles having chargeability opposite to the toner charge polarity, and a developing method using the same. The reverse polarity particles in this development method act as abrasives and spacer particles, and the effect of suppressing carrier deterioration is shown by the effect of removing spent matter on the carrier surface.

Patent Document 3 discloses a so-called hybrid development system in which a latent image on an image carrier is developed using a toner carrier that carries only toner from a two-component developer. The hybrid development system does not cause uneven brushing of images with a magnetic brush, excels in dot reproducibility and image uniformity, and the image carrier and the magnetic brush are not in direct contact with each other, so that carrier transfer to the image carrier (carrier consumption) ) Also does not occur. In the hybrid development system, the toner is charged by frictional charging with the carrier. Therefore, maintaining the charge imparting performance of the carrier is important for stabilizing the chargeability of the toner and maintaining the image quality over a long period of time.
JP 59-1000047 A JP 2003-215855 A JP-A-9-185247

  However, in Patent Document 1, there is a problem in terms of cost and environment because a mechanism for collecting the discharged carrier is necessary and the carrier becomes a consumable item. Further, it is necessary to repeat a predetermined amount of printing until the new and old ratio of the carrier is stabilized, and the initial characteristics cannot always be maintained. Further, in Patent Document 2 and Patent Document 3, there remains a problem that the carrier surface is contaminated with toner, a post-treatment agent, and the like together with the number of printed sheets, and the charge imparting performance of the carrier is lowered.

  An object of the present invention is to provide an image forming apparatus using a two-component developer and capable of forming a good image over a long period of time.

  In order to solve the above problems, the present invention has the following features.

1.
A developer tank containing a toner, a carrier, and a developer containing reverse polarity particles that are charged in the opposite polarity to the charged polarity of the toner;
A developer carrying member for carrying and carrying the developer supplied from the developer tank to the surface;
Separation means for separating toner or the reverse polarity particles from the developer on the developer carrying member;
A recovery unit that recovers the reverse polarity particles separated by the separation unit in the developer tank;
In an image forming apparatus including the developing device and an image carrier that is arranged via a development region and carries an electrostatic latent image,
The separation means includes a separation member, and a separation voltage application means for applying a bias voltage for separating the toner or reverse polarity particles between the separation member and the developer carrier,
An image forming apparatus comprising: control means for controlling the separation rate of the reverse polarity particles so as to increase according to the number of printed sheets.

2.
The separation voltage application means applies an alternating voltage to at least one of the separation member and the developer carrier,
2. The image forming apparatus according to 1, wherein the control unit controls at least one parameter among an amplitude value, a frequency, an average potential difference, and a duty ratio of the alternating voltage.

3.
3. The image forming apparatus according to claim 1, wherein the control unit controls a distance between the separation member and the developer carrying member.

4).
The separation member is provided on the upstream side in the developer movement direction with respect to the development area in the developer carrier, and before the developer on the developer carrier develops the electrostatic latent image on the image carrier. The image forming apparatus according to any one of claims 1 to 3, wherein the reverse polarity particles are separated from the developer on the developer carrying member.

5).
The separation member is a toner carrier that is provided between the developer carrier and the image carrier and separates the toner from the developer on the developer carrier. The image forming apparatus according to any one of 1 to 3, wherein the electrostatic latent image on the carrier is developed.

6).
6. The image forming apparatus according to any one of claims 1 to 5, further comprising background portion potential control means for controlling the background portion potential of the image carrier by the number of printed sheets.

7).
7. The image forming apparatus according to claim 1, further comprising a development gap control unit that controls a development gap in the development area based on the number of printed sheets.

  According to the present invention, since there is a control means for controlling the separation rate separated by the separating means to increase according to the number of printed sheets, the toner or post-treatment agent spent on the carrier or the like occurs as the number of printed sheets increases. Even in such a case, the charge imparted to the toner by the reverse polarity particles is exhibited to an appropriate degree. As a result, it is possible to provide an image forming apparatus that can compensate for a decrease in toner charge amount due to carrier deterioration, maintain a stable toner charge amount over a long period of time, and form a high-quality image.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

(First embodiment)
FIG. 1 is a sectional view showing an example of an image forming apparatus according to the first embodiment of the present invention. As shown in FIG. 1, a charging device 3, a laser exposure optical system 4, a developing device 2 a, a cleaning device 8, and a transfer device 5 are arranged around an image carrier (photosensitive member) 1. An image forming process using this image forming apparatus is performed as follows. The surface of the photosensitive member 1 is uniformly charged by the charging device 3, and then the image is exposed by the laser exposure optical system 4 to form a latent image. The latent image is visualized with toner by the developing device 2 a, and the visualized toner image is transferred onto the transfer paper 7 using the transfer device 5. The toner image on the transfer paper 7 is fixed on the transfer paper by the fixing device 6. The residual toner remaining on the photoreceptor 1 after the transfer is cleaned by the cleaning device 8. The cleaned surface of the photoreceptor 1 is again subjected to the image forming process.

  The photosensitive member 1 is a drum-shaped substrate made of a conductive material such as aluminum, and is rotatably supported by a rotating shaft 11 and a photoconductive layer made of OPC or the like is formed on the peripheral surface of the substrate. The substrate is grounded via a rotating shaft 11, and the photoreceptor 1 is configured to rotate in the direction of the arrow.

  The charging device 3 may be a corona charging device using a discharge wire, a contact charging device using a conductive roller, a conductive brush, conductive particles, or a needle charging device using a sawtooth electrode.

(Configuration of the developing device 2a)
The configuration of the developing device 2a will be described in detail.

  In the present embodiment, the developing device 2a includes a developer tank 16 that contains a toner, a carrier, and a developer 24 that has reverse polarity particles that are oppositely charged to the toner, and a developer 24 that is supplied from the developer tank 16. Is provided on the surface of the developer carrying body 11 and a separating means for separating the reverse polarity particles from the developer on the developer carrying body 11. The separation means includes a reverse polarity particle separation member 22 as a separation member for separating reverse polarity particles, and a separation voltage for applying a bias voltage for separating the reverse polarity particles from the developer carrier 11 to the reverse polarity particle separation member 22. And a power source Vb1 as an application unit. The reverse polarity particle separation member 22 is provided on the upstream side in the developer moving direction with respect to the developing region 100 in the developer carrier 11, and the developer on the developer carrier 11 is an electrostatic latent image on the image carrier 1. Before developing, the reverse polarity particles are separated from the developer on the developer carrier 11. The output voltage of the power supply Vb1 is controlled in accordance with the number of printed sheets printed by the developing device 2a. With this controlled voltage, the separation rate of the reverse polarity particles from the developer on the developer carrier 11 is controlled in accordance with the number of printed sheets. Controls to increase. The reverse polarity particles on the reverse polarity particle separation member 22 separated and collected from the developer carrier 11 are switched to the developer carrier 11 side by switching the output voltage of the power source Vb1 between the print image and the print image. And collected in the developer tank 16.

  As described above, the reverse polarity particles are separated before being developed and the number of reverse polarity particles transferred to the image carrier 1 is reduced, and the separation rate is increased according to the number of printed sheets. The amount of the reverse polarity particles to be collected can be made appropriate. Therefore, an image forming apparatus capable of compensating for the charging performance of the carrier, which deteriorates with an increase in the number of printed sheets, with the reverse polarity particles, preventing a decrease in the charge amount of the toner, and forming a stable image for a long period of time. be able to.

(Separation voltage control)
FIG. 2 shows a flowchart of the control means for controlling the separation voltage so that the separation rate of the reverse polarity particles increases in accordance with the number of printed sheets. The operation of the control means described below can be performed by a CPU, a memory, a power supply circuit, and the like included in the image forming apparatus.

  First, at the start of printing, it is determined whether or not the developing unit set in step S1 is a new one. If the developing unit is new, the print number integrated value N = 0 is written in the memory in step S2. The memory at this time may be attached to the developing device 2a, or may be attached to the image forming apparatus main body side together with the individual recognition of the developing device 2a. Next, in step S3, 1 is added to the print number integrated value N, and in step S4, it is determined whether N <A. If N <A, the output condition from the power source Vb1 is set to X in step S8, the image forming operation is started in step S11, and printing is performed. When the print number integrated value N is not less than A and less than B, the output condition is printed as Y (S5, S9, S11). Similarly, when the print number integrated value N is B or more and less than C, the output condition is set to Z (S6, S10). If the print number integrated value N is greater than or equal to C, a display prompting replacement of the developing unit is displayed on the display unit of the image forming apparatus in step 7. Here, the output condition from Vb1 is such a condition that the separation rate of the reverse polarity particles increases as it proceeds to X, Y, and Z. In this flowchart, the output condition is changed for every fixed number of sheets A, B, and C, but may be changed for each sheet.

  As the separation rate control means, in addition to controlling the output condition of the power source as the separation voltage application means as described above, means for controlling the gap between the reverse polarity particle separation member 22 and the developer carrier 11. May be used in combination.

(Developer)
In the present embodiment, the developer 24 includes toner, a carrier for charging the toner, and reverse polarity particles. The reverse polarity particles can be charged with a polarity opposite to the charging polarity of the toner by the carrier used. For example, when the toner is negatively charged by the carrier, the opposite polarity particles are positively charged particles that are positively charged in the developer. Also, for example, when the toner is positively charged by the carrier, the reverse polarity particles are negatively charged particles that are negatively charged in the developer. The reverse polarity particles are contained in the two-component developer, and the reverse polarity particles are accumulated in the developer as the number of printed sheets is increased by the separating means. Even if the chargeability is lowered, the reverse polarity particles can charge the toner to the normal polarity, so that the chargeability of the carrier can be compensated for, and as a result, the deterioration of the carrier can be suppressed.

  The reverse polarity particles preferably used are appropriately selected depending on the charging polarity of the toner. When a negatively chargeable toner is used as the toner, fine particles having positive chargeability are used as the reverse polarity particles. For example, inorganic fine particles such as strontium titanate, barium titanate, and alumina, acrylic resin, benzoguanamine resin, and nylon resin are used. Fine particles composed of thermoplastic resin such as polyimide resin and polyamide resin or thermosetting resin can be used, and a positive charge control agent imparting positive charge property can be contained in the resin, or a nitrogen-containing monomer You may make it comprise the copolymer of these. Here, as the positive charge control agent, for example, a nigrosine dye, a quaternary ammonium salt, or the like can be used, and as the nitrogen-containing monomer, 2-dimethylaminoethyl acrylate, 2-acrylic acid 2- Diethylaminoethyl, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinyl pyridine, N-vinyl carbazole, vinyl imidazole and the like can be used.

  On the other hand, in the case of using a positively chargeable toner, fine particles having negative chargeability are used as the reverse polarity particles. For example, in addition to inorganic fine particles such as silica and titanium oxide, fluorine resin, polyolefin resin, silicone resin, polyester resin Fine particles composed of thermoplastic resins such as thermoplastic resins or thermosetting resins can be used, and a negative charge control agent that imparts negative chargeability to the resin can be contained, or fluorine-containing acrylic monomers and fluorine-containing methacrylates can be used. You may make it comprise the copolymer of a system monomer. Here, as said negative charge control agent, a salicylic acid type, a naphthol type chromium complex, an aluminum complex, an iron complex, a zinc complex etc. can be used, for example.

  In order to control the chargeability and hydrophobicity of the reverse polarity particles, the surface of the inorganic fine particles may be surface-treated with a silane coupling agent, a titanium coupling agent, silicone oil, etc. When imparting positive chargeability, surface treatment with an amino group-containing coupling agent is preferred, and when imparting negative chargeability, surface treatment with a fluorine group-containing coupling agent is preferred.

  The number average particle diameter of the reverse polarity particles is preferably 100 to 1000 nm.

  The toner is not particularly limited, and a commonly used known toner can be used. The binder resin contains a colorant or, if necessary, a charge control agent or a release agent, and is added externally. What processed the agent can be used. The toner particle diameter is not limited to this, but is preferably about 3 to 15 μm.

  In manufacturing such a toner, it can be manufactured by a publicly known method, for example, a pulverization method, an emulsion polymerization method, a suspension polymerization method, or the like.

  The binder resin used in the toner is not limited to this. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene-substituted product), polyester resin, epoxy resin, vinyl chloride Resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins and the like can be mentioned. It is preferable to use those having a softening temperature in the range of 80 to 160 ° C. and those having a glass transition point in the range of 50 to 75 ° C., depending on the resin alone or the composite.

  Further, as the colorant, known ones that are generally used can be used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultra Marine blue, rose bengal, lake red, or the like can be used, and it is generally preferable to use 2 to 20 parts by mass with respect to 100 parts by mass of the binder resin.

  As the charge control agent, known ones can be used. Examples of the charge control agent for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazoles. System compounds and polyamine resins. Examples of the charge control agent for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curlyx arene compounds. In general, the charge control agent is preferably used at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  In addition, as the above-mentioned mold release agent, known ones that are generally used can be used. For example, polyethylene, polypropylene, carnauba wax, sazol wax and the like can be used alone or in combination of two or more. In general, it is preferably used at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  Also, as the above external additives, publicly known ones can be used, and fluidity improvement, for example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin In addition, resin fine particles such as a fluororesin can be used, and it is particularly preferable to use a resin that has been hydrophobized with a silane coupling agent, a titanium coupling agent, silicon oil, or the like. Such a fluidizing agent is added at a ratio of 0.1 to 5 parts by mass with respect to 100 parts by mass of the toner. The number average primary particle size of the external additive is preferably 10 to 100 nm.

  The carrier is not particularly limited, and a commonly used carrier can be used, and a binder type carrier, a coat type carrier, and the like can be used. Although it is not limited to this as a carrier particle size, 15-100 micrometers is preferable.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and positive or negative chargeable fine particles can be fixed to the carrier surface or a surface coating layer can be provided. Charging characteristics such as 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.

  Examples of the binder resin used for the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, 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 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 mass in the magnetic resin carrier.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material of the binder type carrier, and these resins are coated on the surface and cured to form a coating layer, thereby providing a charge imparting ability. Can be improved.

  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. By applying a strong impact force and fixing the fine particles so as to be driven into the magnetic resin carrier. 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. As the chargeable fine particles, organic or inorganic insulating materials are used. Specifically, organic insulating fine particles such as polystyrene, styrene copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof may be used as the organic type. Regarding the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, a surface treatment or the like. Further, as the inorganic type, 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.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and in a coated carrier, similarly to a binder-type carrier, positive or negatively chargeable fine particles are fixed to the carrier surface. it can. Charging characteristics such as polarity of the coat type carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, the coating resin can be the same resin as the binder resin of the binder type carrier.

  The charged polarity of the toner and the reverse polarity particles by the combination of the reverse polarity particles, the toner and the carrier is obtained by mixing and stirring each to form a developer, and then separating the toner or the reverse polarity particles from the developer using the apparatus of FIG. It can be easily known from the direction of the electric field.

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

  The amount of the reverse polarity particles contained in the developer is not particularly limited as long as the object of the present invention is achieved. For example, 0.01 to 5.00 parts by mass, particularly 0.01 to 100 parts by mass with respect to 100 parts by mass of the carrier. 2.00 parts by mass is preferred.

  The developer can be prepared, for example, by externally adding reverse polarity particles to the toner in advance and then mixing with a carrier.

(Separation / collection operation)
In the developing device 2a, as the separating means for separating the toner or the reverse polarity particles from the developer on the developer carrier 11, the reverse polarity particles for separating and collecting the reverse polarity particles from the developer on the developer carrier 11 A separation member 22 is employed. As shown in FIG. 1, the reverse polarity particle separation member 22 is provided on the upstream side in the developer movement direction from the development region 100 in the developer carrier 11, and a developer is applied by applying a reverse polarity particle separation bias. The reverse polarity particles therein are electrically separated and collected on the surface of the reverse polarity particle separation member 22. After the reverse polarity particles are separated by the reverse polarity particle separation member 22, the remaining developer on the developer carrier 11, that is, the toner and the carrier are continuously conveyed, and the electrostatic latent image on the image carrier 1 is developed in the development region 100. Develop the image.

  The reverse polarity particle separation member 22 is connected to the power source Vb1, and a reverse polarity particle separation bias controlled according to the number of printed sheets is applied, whereby the reverse polarity particles in the developer are electrically reversed. Separated and collected on the surface.

  The reverse polarity particle separation bias applied to the reverse polarity particle separation member 22 is controlled in accordance with the number of printed sheets, but is preferably controlled within the following range.

  The reverse polarity particle separation bias differs depending on the charged polarity of the reverse polarity particles, that is, when the toner is negatively charged and the reverse polarity particles are positively charged, the average value of the voltage applied to the developer carrier 11 is more than When the toner is positively charged and the reverse polarity particles are negatively charged, the voltage becomes a higher average value than the average value of the voltage applied to the developer carrier 11. is there. The difference between the average voltage applied to the reverse polarity particle separation member 22 and the average voltage applied to the developer carrier 11 is 20 even when the reverse polarity particles are charged to either positive or negative polarity. It is preferable to be -500V, especially 50-300V. If the potential difference is too small, it will be difficult to sufficiently collect the reverse polarity particles. On the other hand, if the potential difference is too large, carriers held by the magnetic force on the developer carrier 11 are separated by an electric field, and the original developing function in the developing region 100 may be impaired.

In the developing device 2 a, it is preferable that an alternating electric field is formed between the reverse polarity particle separating member 22 and the developer carrier 11. Since the toner reciprocates due to the formation of the AC electric field, the reverse polarity particles adhering to the toner surface can be effectively separated, and the recovery of the reverse polarity particles can be improved. At that time, an electric field of 2.5 × 10 ⁶ V / m or more is preferably formed. By forming an electric field of 2.5 × 10 ⁶ V / m or more, it becomes possible to separate the reverse polarity particles from the toner even by the electric field, and it is possible to further improve the reverse polarity separation and recovery. It becomes possible.

  In this specification, an electric field formed between the reverse polarity particle separation member 22 and the developer carrier 11 is referred to as a reverse polarity particle separation electric field. Such a reverse polarity particle separation electric field is usually obtained by applying an alternating voltage to one or both of the reverse polarity particle separation member 22 and the developer carrier 11. In particular, when an AC voltage is applied to the developer carrier 11 in order to develop the electrostatic latent image with toner, an AC voltage applied to the developer carrier 11 is used to form a reverse polarity particle separation electric field. It is desirable. At this time, the reverse polarity particle separation electric field may have a maximum absolute value within the above range.

  For example, when the charged polarity of the reverse polarity particles is positive, the DC voltage and the AC voltage are applied to the developer carrier 11, and only the DC voltage is applied to the reverse polarity particle separation member 22, the reverse polarity particle separation is performed. Only a DC voltage lower than the average value of the voltages (DC + AC) applied to the developer carrier 11 is applied to the member 22. Further, for example, when the charged polarity of the reverse polarity particles is negative, the DC voltage and the AC voltage are applied to the developer carrier 11, and only the DC voltage is applied to the reverse polarity particle separation member 22, the reverse polarity particles Only a DC voltage higher than the average value of the voltages (DC + AC) applied to the developer carrier 11 is applied to the separating member 22. In these cases, the maximum absolute value of the reverse polarity particle separation electric field is the potential difference between the voltage applied to the developer carrier 11 (DC + AC) and the voltage applied to the reverse polarity particle separation member 22 (DC). Is the value obtained by dividing the maximum value by the closest gap between the opposite polarity particle separation member 22 and the developer carrier 11, and it is desirable that this value be in the above range.

  Further, for example, when the charged polarity of the reverse polarity particles is positive, only the DC voltage is applied to the developer carrier 11, and the AC voltage and DC voltage are applied to the reverse polarity particle separation member 22, the reverse polarity particles A DC voltage on which an AC voltage is superimposed is applied to the separating member 22 so that the average voltage is lower than the DC voltage applied to the developer carrier 11. Further, for example, when the charged polarity of the reverse polarity particles is negative, only the DC voltage is applied to the developer carrier 11 and the AC voltage and DC voltage are applied to the reverse polarity particle separation member 22, the reverse polarity particles are applied. A DC voltage on which an AC voltage is superimposed is applied to the separating member 22 so that the average voltage is higher than the DC voltage applied to the developer carrier 11. At these times, the maximum absolute value of the reverse polarity particle separation electric field is the potential difference between the voltage applied to the developer carrier 11 (DC) and the voltage applied to the reverse polarity particle separation member 22 (DC + AC). Is the value obtained by dividing the maximum value by the closest gap between the opposite polarity particle separation member 22 and the developer carrier 11, and it is desirable that this value be in the above range.

  Further, for example, when the charged polarity of the reverse polarity particles is positive and a DC voltage in which an AC voltage is superimposed on both the developer carrier 11 and the reverse polarity particle separation member 22 is applied, A voltage (DC + AC) having an average voltage smaller than the average value of the voltage (DC + AC) applied to the developer carrier 11 is applied. Further, for example, when the charged polarity of the reverse polarity particles is negative and a DC voltage in which an AC voltage is superimposed on both the developer carrier 11 and the reverse polarity particle separation member 22 is applied, A voltage (DC + AC) having an average voltage larger than the average value of the voltage (DC + AC) applied to the developer carrier 11 is applied. At these times, the voltage (direct current + alternating current) applied to the developer carrier 11 and the opposite polarity particle separation member 22 are generated due to differences in the amplitude, phase, frequency, duty ratio and the like of the alternating voltage components applied to each. The value obtained by dividing the maximum value of the potential difference from the applied voltage (DC + AC) by the closest gap between the opposite polarity particle separation member 22 and the developer carrier 11 is the absolute value of the opposite polarity particle separation electric field. It is the maximum value, and it is desirable that the value be in the above range.

  The reverse polarity particles separated and collected by the reverse polarity particle separation member 22 are collected in the developer tank 16. When collecting the reverse polarity particles from the reverse polarity particle separation member 22 to the developer tank, the average value of the voltage applied to the reverse polarity particle separation member 22 and the average value of the voltage applied to the developer carrier 11 are small or large. It is sufficient to reverse the relationship, and the timing at the time of non-image formation, such as the interval between sheets before the start of image formation or after the end of image formation, during image formation during continuous operation (between pages between the previous page and the subsequent page). Can be done.

(Developing device 2a component)
The reverse polarity particle separation member 22 may be made of any material as long as the voltage can be applied. For example, an aluminum roller subjected to surface treatment may be used. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this. Further, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

  The developer carrying member 11 includes a magnet roller 13 that is fixedly arranged, and a rotatable sleeve roller 12 that contains the magnet roller 13. The magnet roller 13 has five magnetic poles N1, S2, N3, N2, and S1 along the rotation direction B of the sleeve roller 12. Of these magnetic poles, the main magnetic pole N1 is disposed at the position of the developing region 100 facing the image carrier 1, and also generates the repulsive magnetic field for peeling off the developer 24 on the sleeve roller 12. The pole portions N3 and N2 are disposed at positions facing the inside of the developing tank 16.

  The developer tank 16 is formed of a casing 18 and normally contains a bucket roller 17 for supplying developer to the developer carrier 11 therein. An ATDC (Automatic Toner Density Control) sensor 20 for detecting toner concentration is preferably disposed at a position facing the bucket roller 17 of the casing 18.

  The developing device 2a normally has a replenishment section 27 for replenishing toner in the developer tank 16 for the amount of toner consumed in the development area 100, and a developer thin film for regulating the amount of developer on the developer carrier 11. It has a regulating member 15 for stratification. The replenishing unit 27 includes a hopper 21 that stores the replenishing toner 23 and a replenishing roller 19 for replenishing the toner into the developer tank 16.

  As the replenishment toner 23, it is desirable to use a toner having externally treated reverse polarity particles. By using the toner to which the reverse polarity particles are externally added, it becomes possible to effectively assist the decrease in the chargeability of the carrier that gradually deteriorates due to durability. The external addition amount of the reverse polarity particles in the replenishing toner 23 is preferably 0.1 to 10.0% by mass, particularly preferably 0.5 to 5.0% by mass with respect to the toner.

(Developer movement)
The movement of the developer in the developing device 2a will be described.

  The developer 24 in the developer tank 16 is mixed and stirred by the rotation of the bucket roller 17 and is frictionally charged. Then, the developer 24 is pumped up by the bucket roller 17 and supplied to the sleeve roller 12 on the surface of the developer carrier 11. The developer 24 is held on the surface side of the sleeve roller 12 by the magnetic force of the magnet roller 13 inside the developer carrier 11, is rotated with the sleeve roller 12, and is provided to face the developer carrier 11. The passage amount is regulated by the regulating member 15. Thereafter, only the reverse polarity particles contained in the developer are separated and collected by the reverse polarity particle separation member 22 at the portion facing the reverse polarity particle separation member 22 as described above. The remaining developer from which the reverse polarity particles have been separated is conveyed to the developing area 100 facing the image carrier 1. In the development region 100, developer spikes are formed by the magnetic force of the main magnetic pole N1 of the magnet roller 13, and formed between the electrostatic latent image on the image carrier 1 and the developer carrier 11 to which a development bias is applied. The toner in the developer moves to the electrostatic latent image side on the image carrier 1 by the force applied to the toner by the applied electric field, and the electrostatic latent image is developed into a visible image. The development method may be a reversal development method or a regular development method. The developer 24 that has consumed the toner in the developing region 100 is conveyed toward the developer tank 16 and is applied to the developer carrier 11 by the repulsive magnetic fields of the magnet roller equipolar portions N3 and N2 provided facing the bucket roller 17. It is peeled off from above and collected into the developer tank 16. When a supply control unit (not shown) provided in the supply unit 27 detects from the output value of the ATDC sensor 20 that the toner concentration in the developer 24 has become equal to or lower than the minimum toner concentration for ensuring image density, the toner supply is performed. A drive start signal is sent to the drive means of the roller 19. Then, the toner replenishing roller 19 starts rotating, and with this rotation, the replenishing toner 23 stored in the hopper 21 is supplied into the developer tank 16. On the other hand, the reverse polarity particles collected by the reverse polarity particle separation member 22 reverse the direction of the electric field applied to the developer carrier 11 and the reverse polarity particle separation member 22 during non-image formation, thereby developing the developer carrier. 11 is returned to the developer tank 11, transported together with the developer as the developer carrier 11 rotates, and returned to the developer tank.

  In FIG. 1, the reverse polarity particle separation member 22 is provided separately from the restriction member 15 and the casing 26, but the reverse polarity particle separation member 22 may also serve as at least one of the restriction member 15 and the casing 26. That is, the regulating member 15 and / or the casing 26 may be used as the reverse polarity particle separation member 22. In that case, a reverse polarity particle separation bias may be applied to the regulating member 15 and the casing 26. Thereby, space saving and low cost can be realized.

  In the developing device 2a, not all the reverse polarity particles are necessarily collected by the reverse polarity particle separation member 22, but some of the reverse polarity particles are not collected but are supplied to the developing unit together with the toner. The toner and the reverse polarity particles are further separated by the action of the developing electric field in the developing portion, but a part remains without being separated and attached to the toner. The reverse polarity particles that are not separated from the toner are consumed together with the toner in the image portion, and the separated reverse polarity particles are consumed in the non-image portion (background portion). Therefore, the separation rate of the reverse polarity particles depends on the background potential, and the consumption changes. Further, since the developing electric field changes due to the change in the gap of the developing region, the separation rate of the reverse polarity particles is influenced and the consumption amount changes. For this reason, the background potential control means or the development gap control means may be used together to control the reverse polarity particle separation rate in accordance with the number of printed sheets. For example, as the background portion potential control means, the surface potential of the photoreceptor 1 charged by the charging device 3 may be controlled according to the number of printed sheets. Further, as the development gap control means, means for controlling the distance between the photoreceptor 1 and the developer carrier 11 may be used.

(Second Embodiment)
Next, an example of an image forming apparatus according to the second embodiment of the present invention is shown in FIG. In FIG. 3, members having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

(Configuration of the developing device 2b)
A developing device 2b shown in FIG. 3 uses a developer carrier as a separating means for separating toner or reverse polarity particles from the developer on the developer carrier 11 instead of the reverse polarity particle separation member 22 shown in FIG. A toner carrier 25 that separates and carries the toner from the developer on 11 is employed. The toner carrier 25 is provided between the developer carrier 11 and the image carrier 1, and a toner separation bias controlled according to the number of printed sheets is applied by the power source Vb4, whereby the toner carrier 25 is placed on the developer carrier 11. The toner is electrically separated and carried on the surface of the toner carrier 25 from the developer.

  The toner separated and carried by the toner carrier 25 is conveyed by the toner carrier 25 and develops the electrostatic latent image on the image carrier 1 in the development region 100.

  As described above, in the developing device 2 b, unlike the embodiment shown in FIG. 1, the toner carrier 25 carries the toner separately from the developer on the developer carrier 11. The electrostatic latent image is being developed. The reverse polarity particles are separated from the toner by the toner separation bias, remain on the developer carrier 11 side, and are collected in the developer tank 16. The collected reverse polarity particles accumulate in the developer tank 16 to compensate for the charging performance of the carrier that deteriorates due to printing durability. Further, the reverse polarity particles are still attached to the toner surface on the separated toner carrier 25, and the reverse polarity particles attached to the toner are in the background portion of the image carrier 1 in the developing region 100. Is consumed. By controlling the amount of the reverse polarity particles consumed in the background portion, the amount of the reverse polarity particles existing on the toner carrier 25 after passing through the development region 100 can be controlled. The reverse polarity particles on the toner carrier 25 after passing through the development region 100 are transferred to the developer carrier 11 and collected in the developer tank 16. Thus, by controlling the amount of the reverse polarity particles consumed in the background portion of the image carrier 1 according to the number of printed sheets, the amount of the reverse polarity particles in the developer tank 16 can be controlled. This can contribute to compensation of charging performance.

(Separation voltage control)
FIG. 4 shows a flowchart for controlling the separation voltage in accordance with the number of printed sheets. Since the control method is the same as in the first embodiment, details are omitted. The separation voltage applied to the toner carrier 25 is controlled so that a voltage corresponding to the number of printed sheets of the developing device 2b to be used is output from the power supply Vb4.

(Separation / collection operation)
Next, the separation and recovery operation in the developing device 2b will be described with reference to FIG.

  The toner carrier 25 is connected to the power source Vb4, and the developer carrier 11 is connected to the power source Vb3. A toner separation bias controlled according to the number of printed sheets of the developing device 2b is applied to Vb4, whereby the toner from the developer on the developer carrier 11 is electrically separated and carried on the surface of the toner carrier 25. . The toner separation bias at this time is performed within the following range.

  The toner separation bias applied to the toner carrier 25 varies depending on the charging polarity of the toner, that is, when the toner is negatively charged, the average value is higher than the average value of the voltage applied to the developer carrier 11. When the toner is positively charged, the voltage is an average value lower than the average value of the voltage applied to the developer carrier 11. The difference between the average voltage applied to the toner carrier 25 and the average voltage applied to the developer carrier 11 is 20 to 500 V, especially when the toner is charged to either positive or negative polarity. It is preferable that it is 50-300V. If the potential difference is too small, the amount of toner on the toner carrier 25 is small and a sufficient image density cannot be obtained. On the other hand, if the potential difference is too large, the toner supply becomes excessive, and wasteful toner consumption may increase.

In the developing device 2b, an AC electric field is preferably formed between the toner carrier 25 and the developer carrier 11. By forming an alternating electric field, the toner reciprocally vibrates, so that the toner and the reverse polarity particles can be effectively separated. At that time, an electric field of 2.5 × 10 ⁶ V / m or more is preferably formed. By forming an electric field of 2.5 × 10 ⁶ V / m or more, it becomes possible to separate the reverse polarity particles from the toner even by the electric field, and it becomes possible to further improve the toner separation property. .

  In the present specification, an electric field formed between the toner carrier 25 and the developer carrier 11 is referred to as a toner separation electric field. Such a toner separation electric field is usually obtained by applying an alternating voltage to one or both of the toner carrier 25 and the developer carrier 11. In particular, when an AC voltage is applied to the toner carrier 25 in order to develop the electrostatic latent image with toner, it is desirable to form a toner separation electric field using the AC voltage applied to the toner carrier 25. At this time, the maximum value of the absolute value of the toner separation electric field may be within the above range.

  For example, when the charging polarity of the toner is positive, a DC voltage and an AC voltage are applied to the developer carrier 11, and only a DC voltage is applied to the toner carrier 25, the developer is applied to the toner carrier 25. Only a DC voltage lower than the average value of the voltages (DC + AC) applied to the carrier 11 is applied. Further, for example, when the charging polarity of the toner is negative, a DC voltage and an AC voltage are applied to the developer carrier 11, and only a DC voltage is applied to the toner carrier 25, the toner carrier 25 is developed. Only a DC voltage higher than the average value of the voltages (DC + AC) applied to the agent carrier 11 is applied. At these times, the maximum value of the absolute value of the toner separation electric field is the maximum value of the potential difference between the voltage applied to the developer carrier 11 (DC + AC) and the voltage applied to the toner carrier 25 (DC). It is a value divided by the closest gap between the toner carrier 25 and the developer carrier 11, and it is desirable that this value is in the above range.

  Further, for example, when the charging polarity of the toner is positive, only a DC voltage is applied to the developer carrier 11 and an AC electric field and a DC voltage are applied to the toner carrier 25, the toner carrier 25 is developed. A DC voltage on which an AC electric field is superimposed is applied so that the average voltage is lower than the DC voltage applied to the agent carrier 11. Further, for example, when the charging polarity of the toner is negative, only a DC voltage is applied to the developer carrier 11 and an AC electric field and a DC voltage are applied to the toner carrier 25, the toner carrier 25 is developed. A DC voltage on which an AC electric field is superimposed is applied so that the average voltage is higher than the DC voltage applied to the agent carrier 11. At these times, the maximum absolute value of the toner separation electric field is the maximum value of the potential difference between the voltage applied to the developer carrier 11 (DC) and the voltage applied to the toner carrier 25 (DC + AC). It is a value divided by the closest gap between the toner carrier 25 and the developer carrier 11, and it is desirable that this value is in the above range.

  Further, for example, when the charging polarity of the toner is positive and a DC voltage in which an AC voltage is superimposed is applied to both the developer carrier 11 and the toner carrier 25, the toner carrier 25 has the developer carrier 11. A voltage (DC + AC) having an average voltage smaller than the average value of applied voltages (DC + AC) is applied. Further, for example, when the toner charge polarity is negative and a DC voltage on which an AC voltage is superimposed is applied to both the developer carrier 11 and the toner carrier 25, the toner carrier 25 has the developer carrier 11. A voltage (DC + AC) having an average voltage larger than the average value of applied voltages (DC + AC) is applied. At these times, the voltage (direct current + alternating current) applied to the developer carrier 11 and the toner carrier 25 are generated due to differences in the amplitude, phase, frequency, duty ratio, etc. of the alternating voltage components applied to each. The value obtained by dividing the maximum value of the potential difference from the voltage (DC + AC) by the closest gap between the toner carrier 25 and the developer carrier 11 is the maximum value of the absolute value of the toner separation electric field. Is preferably within the above range.

  The remaining developer on the developer carrier 11 from which the toner has been separated by the toner carrier 25, that is, the carrier and the reverse polarity particles, are conveyed by the developer carrier 11 as they are and are collected in the developer tank 16. In this embodiment, after separation of the toner, the reverse polarity particles are collected as they are in the developer tank by the developer carrier 11, and thus collected by the reverse polarity particle separation member 22 described in the embodiment of FIG. The step of returning the reverse polarity particles to the developer tank at the time of non-image formation can be omitted.

(Developing device 2b component)
The toner carrier 25 may be made of any material as long as the voltage can be applied. For example, an aluminum roller subjected to surface treatment may be used. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this. Further, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

  As other constituent members of the developing device 2b, the same components as those in the first embodiment can be used.

(Developer movement)
The movement of the developer in the developing device 2b will be described.

  As in the developing device 2a, the developer 24 in the developer tank 16 is mixed and agitated by the rotation of the bucket roller 17, frictionally charged, and then pumped up by the bucket roller 17 to be a sleeve roller on the surface of the developer carrier 11. 12 is supplied. The developer 24 is held on the surface side of the sleeve roller 12 by the magnetic force of the magnet roller 13 inside the developer carrier 11, is rotated with the sleeve roller 12, and is provided to face the developer carrier 11. The passage amount is regulated by the regulating member 15. Thereafter, only the toner contained in the developer is separated and carried on the toner carrier 25 at the portion facing the toner carrier 25 as described above. The separated toner is conveyed to the developing area 100 facing the image carrier 1. In the developing region 100, the toner on the toner carrier 25 is imaged by the force applied to the toner by the electric field formed between the electrostatic latent image on the image carrier 1 and the toner carrier 25 to which the developing bias is applied. It moves toward the electrostatic latent image on the carrier 1, and the electrostatic latent image is developed into a visible image. The development method may be a reversal development method or a regular development method. The toner layer on the toner carrier 25 that has passed through the development region 100 is transported to the development region 100 through toner supply / recovery by a magnetic brush at the facing portion between the toner carrier 25 and the developer carrier 11. On the other hand, the developer separated from the toner and remaining on the developer carrying member 11 is conveyed to the developer tank 16 as it is, and is supplied to the magnet roller equipolar portions N3 and N2 provided facing the bucket roller 17. It is peeled off from the developer carrier 11 by the repulsive magnetic field and collected into the developer tank 16. When a supply control unit (not shown) provided in the supply unit 27 detects that the toner concentration in the developer 24 has become equal to or lower than the minimum toner concentration for securing the image density, as in FIG. A drive start signal is sent to the driving means of the roller 19, and the replenishment toner 23 is supplied into the developer tank 16.

  In the developing device 2 b, not all the reverse polarity particles are necessarily collected by the developer carrier 11, and some of the reverse polarity particles move to the toner carrier 25 together with the toner and are supplied to the development region 100. The In the developing region 100, most of the toner and the reverse polarity particles are further separated by the action of the developing electric field, but a part of the toner remains attached to the toner without being separated from the toner. The reverse polarity particles remaining on the toner are consumed together with the toner in the image portion, and most of the separated reverse polarity particles are consumed in the non-image portion (background portion). Further, the reverse polarity particles that have not been consumed in the image area and the non-image area are returned to the developer tank 16 via the developer carrier 11.

  For this reason, the consumption of reverse polarity particles also changes depending on the background potential in the development region 100. In the developing region 100, the developing electric field also changes due to the change in the gap between the image carrier 1 and the toner carrier 25, and the separation rate of the opposite polarity particles is influenced. Therefore, the background portion potential control means or the development gap control means may be used together to control the separation rate to increase in accordance with the number of printed sheets. For example, as the background portion potential control means, the surface potential of the photoreceptor 1 charged by the charging device 3 may be controlled according to the number of printed sheets. Further, as a developing gap control means, a means for controlling the distance between the photosensitive member 1 and the toner carrier 25 may be used to control the separation rate according to the number of printed sheets.

  Furthermore, by providing the developing device 2b with the reverse polarity particle separation member 22 provided in the developing device 2a shown in the embodiment of FIG. 1, the reverse polarity particle recovery property is further improved, and the number of printed sheets can be increased. It becomes possible to collect an appropriate amount of reverse polarity particles in the developer tank 16.

(Effect of reverse polarity particles)
Next, the carrier charge assisting effect by the reverse polarity particles, the range of effective addition amount, and its influence will be discussed. FIG. 5 shows an example of a change in toner charge amount with respect to the amount of reverse polarity particles added to the carrier. For evaluation, a carrier for bizhub C350 manufactured by Konica Minolta Co., Ltd. was used, and the carrier was pretreated by changing the addition amount of strontium titanate as reverse polarity particles in advance. The developer for bizhub C350 was mixed with a carrier having a different amount of reverse polarity particles so that the toner mass ratio would be 8% to obtain a developer. For each carrier having a different processing amount of the reverse polarity particles, the toner charge amount is measured using the apparatus shown in FIG. 6, and the difference from the toner charge amount of the developer using the carrier not processed with the reverse polarity particles is measured. (Change) was determined. To measure the toner charge amount, the measured developer was placed on the entire surface of the conductive sleeve 31 so as to be uniform, and the rotation speed of the magnet roll 32 provided in the conductive sleeve 31 was set to 1000 rpm. Then, a bias voltage of 2 kV is applied from the bias power source 33 to the polarity opposite to the charging potential of the toner, the conductive sleeve 31 is rotated for 15 seconds, and the potential at the cylindrical electrode 34 at the time when the conductive sleeve 31 is stopped. While reading Vm, the mass of toner adhering to the cylindrical electrode 34 was weighed with a precision balance to determine the charge amount of the toner. FIG. 5 shows that the toner charge amount is increased by attaching the reverse polarity particles to the carrier. The effect of assisting the chargeability of the carriers by the reverse polarity particles can be obtained by adding a very small amount, and the effect increases as the addition amount increases. When the addition amount is further increased, the effect of the reverse polarity particles starts to decrease, and when the addition amount exceeds about 5% by mass, the effect is lost. The decrease in the effect when the amount added is large is due to the fact that the amount of reverse polarity particles is large, making it difficult to hold on the carrier surface, and the movement of excess reverse polarity particles together with the toner cancels the toner charge. it seems to do. From the above, when strontium titanate is used as reverse polarity particles, the amount of reverse polarity particles adhering to the carrier surface is in the range of about 0.01% by mass to 2% by mass in order to obtain the carrier charge assist effect. Is appropriate. Even within an appropriate range, the magnitude of the carrier charge assist effect due to the reverse polarity particles varies with the amount of the reverse polarity particles. It can be seen that it is effective for obtaining the toner charge amount. Here, the addition amount of the reverse polarity particles is expressed as a ratio to the carrier.

(Explanation of reverse polarity particle separation behavior)
Here, the reverse polarity particle separation behavior in the reverse polarity particle recovery unit and the development unit will be described.

  The opposite polarity particles contained in the developer and the toner have different charging polarities, so the electrostatic force due to the electric field acts in the opposite direction and some of them are separated, but the toner and the opposite polarity particles are completely separated. It is difficult to do.

  In the reverse polarity particle separation portion of the developing device 2 a, the toner and a part of the reverse polarity particles are separated by the electric field formed between the reverse polarity particle separation member 22 and the developer carrier 11, and the developer on the developer carrier 11. Only the reverse polarity particles are separated from the two-component developer, and then, in the development portion, some of the reverse polarity particles that have not been separated by the reverse polarity particle separation member 22 are further separated from the toner by the action of the developing electric field. Is consumed. Further, the reverse polarity particles that are not separated from the toner by the developing electric field are consumed as a toner image in the image portion together with the toner.

  Similarly, in the reverse polarity particle separation portion of the developing device 2b, the toner and the reverse polarity particles are partly separated by the electric field formed between the toner carrier 25 and the developer carrier 11, and a part of the reverse polarity particles is a developer. Although it is collected in the developer tank 16 by the carrier 11, the remainder is supplied together with the toner to the toner carrier 25, and the toner and the reverse polarity particles are further separated by the developing electric field in the developing part and consumed in the background part. The reverse polarity particles that are not separated even by the developing electric field are consumed as a toner image in the image portion together with the toner.

(Separation rate control factor)
Next, factors that can control the separation rate of the reverse polarity particles in the reverse polarity particle separation portion and the development region 100 are shown below. Separation of opposite polarity particles is achieved by separation of opposite polarity particles or toner from a two-component developer layer containing opposite polarity particles, toner and carrier, or separation of opposite polarity particles or toner from a toner layer containing opposite polarity particles. Is called. Therefore, the separation of opposite polarity particles from the two-component developer layer and the separation of opposite polarity particles from the toner layer were evaluated. For the evaluation, the apparatus shown in FIG. 7 was used. The evaluation apparatus in FIG. 7 uses the configuration of the developing apparatus in FIG.

  In FIG. 7, the separation rate of the opposite polarity particles from the two-component developer layer is evaluated at the gap A1 formed by the developer carrier 11 and the toner carrier 25, and the toner carrier 25, the image carrier 1 and The separation rate of the reverse polarity particles from the toner layer was evaluated at the position of the gap B1 formed in step 1). The separation rate was determined by measuring the amount of reverse polarity particles contained in the developer or toner in each of the regions a, b, c, d, and e in FIG. 7, and setting the respective amounts as Ga, Gb, Gc, Gd, and Ge. . The amount of reverse polarity particles was measured by ICP analysis.

  The separation rate when applying an electric field in the direction of separating the reverse polarity particles from the two-component developer layer (corresponding to the reverse polarity particle separation portion and the background portion of the development region in the developing device 2a) is (Ga−Gb) / Ga, Separation when an electric field in the direction of separating the toner from the two-component developer layer is applied (corresponding to the image area in the developing area of the developing device 2a, the opposite portion between the toner carrier 25 and the developer carrier 11 of the developing device 2b). The rate is (Ga−Gc) / Ga, and the separation rate is (Gc−Gd) / Gc when an electric field in the direction of separating the opposite polarity particles from the toner layer is applied (corresponding to the background portion of the developing region of the developing device 2b) The separation rate when an electric field in the direction of separating the toner from the toner layer is applied (corresponding to the image portion in the developing area of the developing device 2b) is expressed as (Gc-Ge) / Gc.

  For evaluation, a carrier for bizhub C350 manufactured by Konica Minolta Co., Ltd. and a negatively chargeable toner for bizhub C350 externally treated with strontium titanate as a reverse polarity particle are prepared so that the toner ratio in the developer is 8%. did.

  Evaluation of factors that change the separation rate from the two-component developer layer is as follows: the gap A1 is 0.35 mm, the toner carrier 25 is grounded, the developer carrier 11 has a frequency of 4 kHz, a duty ratio of 50%, and an amplitude of 1 This standard is based on the condition that a DC bias superimposed voltage of 200 V is applied to the AC bias of .5 kV rectangular wave when separating reverse polarity particles from the developer layer, and −200 V is applied to the toner. This was done by measuring the separation rate when changing each factor from the conditions. Tables 1 to 5 show the separation rates when the AC bias amplitude, the duty ratio, the frequency, the DC bias, and the gap A1 are changed. In both cases, the separation rate is shown for the direction of the electric field in both the reverse polarity separation direction (reference: 200 V) and the toner separation direction (reference: −200 V).

  Similarly, the factors that change the separation rate from the toner layer are evaluated in the same manner. The gap B1 is 0.15 mm, the image carrier 1 is grounded, the toner carrier 25 has a frequency of 4 kHz, a duty ratio of 50%, an amplitude of 1. Based on the condition of applying a DC bias superimposed voltage of 200 V when separating the reverse polarity particles from the toner layer to the 4 kV rectangular wave AC bias, and -200 V when separating the toner. This was done by measuring the separation rate when each factor was changed.

  The toner layer formation on the toner carrier 25 is the same as the reference condition for toner separation from the two-component developer layer (that is, toner supply to the toner carrier 25), and is applied to the developer carrier 11. By superimposing the bias on the bias applied to the toner carrier 25, a -200V DC bias is superimposed on the toner carrier 25 on a rectangular wave AC bias having a frequency of 4 kHz, a duty ratio of 50%, and an amplitude of 1.5 kV. The applied voltage was applied. Tables 6 to 10 show the separation ratio when the AC bias amplitude, the duty ratio, the frequency, the DC bias, and the gap B1 are changed. In both cases, the separation rate is shown for the direction of the electric field in both the reverse polarity separation direction (reference: 200 V) and the toner separation direction (reference: −200 V).

  As described above, it can be seen that the separation ratio between the toner and the reverse polarity particles can be changed by changing each factor in the reverse polarity particle separation portion and the image portion and background portion of the development region. By changing the direction of accumulation of reverse polarity particles in the developer according to the number of printed sheets of the developing device using these factors, the charging ability of the carrier that deteriorates with the number of printed sheets is compensated, and the charge amount of the toner is reduced. It becomes possible to maintain it stably.

  Here, when changing the factor that can change the separation rate of the reverse polarity particles, it must be performed within a range that does not hinder image formation. These factors may be changed alone or in combination. It is possible to expand the range of change in the separation rate by changing it in combination. Furthermore, by combining the change in the separation rate in the reverse polarity particle separation part, the image part and the background part, it becomes possible to stabilize the amount of reverse polarity particles contained in the developer in the developer tank, and for a long time. It is possible to maintain a stable toner charge amount.

  The timing for changing the separation rate of the reverse polarity particles is not particularly limited, and may be set according to the deterioration rate of the carrier depending on the use conditions. For example, every time a certain number of prints such as 100 sheets or 10,000 sheets are printed. You may change continuously for every sheet according to a space | interval or the number of printed sheets. Further, the interval may be shortened as the number of printed sheets increases, for example, 50,000 sheets, 80,000 sheets, 100,000 sheets.

  Examples are shown below.

  As the developer, a carrier and toner for bizhub C350 manufactured by Konica Minolta were used. The toner is a negatively chargeable toner to which strontium titanate is externally added as reverse polarity particles. The toner ratio in the developer was 8% by mass.

A copy machine bizhub C350 manufactured by Konica Minolta Co., Ltd. was modified to print 200,000 sheets of a chart with an image area ratio of 5%. The setting conditions of the device are shown below.
<Condition 1>
Using the developing device 2a shown in FIG. 1, a developer carrier 11 is applied with a rectangular wave developing bias having an amplitude of 1.5 kV, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −400 V, and a reverse polarity particle collecting member. A DC bias of −550 V was applied to 22. As the reverse polarity particle recovery member 22, an aluminum roller having an alumite treatment on the surface was used, and the gap at the closest part between the developer carrier 11 and the reverse polarity particle recovery member 22 was set to 0.3 mm. The background portion potential of the electrostatic latent image formed on the photoreceptor 1 was −550 V, and the image portion potential was −60 V. The gap at the closest portion between the photoreceptor 1 and the developer carrier 11 was set to 0.35 mm.
<Condition 2>
Using the developing device 2a shown in FIG. 1, a developer carrier 11 is applied with a rectangular wave developing bias having an amplitude of 1.8 kV, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −400 V, and a reverse polarity particle collecting member. A DC bias of −600 V was applied to 22. As the reverse polarity particle recovery member 22, an aluminum roller having an alumite treatment on the surface was used, and the gap at the closest part between the developer carrier 11 and the reverse polarity particle recovery member 22 was set to 0.3 mm. The background portion potential of the electrostatic latent image formed on the photoreceptor 1 was −500 V, and the image portion potential was −60 V. The gap at the closest portion between the photoreceptor 1 and the developer carrier 11 was set to 0.35 mm.
<Condition 3>
Using the developing device 2a shown in FIG. 1, a developer carrier 11 is applied with a rectangular wave developing bias having an amplitude of 1.5 kV, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −400 V, and a reverse polarity particle collecting member. A rectangular wave bias having an amplitude of 250 V, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −550 V was applied to 22. At this time, the phase of the bias applied to the developer carrying member 11 and the reverse polarity particle collecting member 22 is reversed, that is, the oscillating electric field between the developer carrying member 11 and the reverse polarity particle collecting member 22 is strengthened. As the reverse polarity particle recovery member 22, an aluminum roller having an alumite treatment on the surface was used, and the gap at the closest part between the developer carrier 11 and the reverse polarity particle recovery member 22 was 0.25 mm. The background portion potential of the electrostatic latent image formed on the photoreceptor 1 was −550 V, and the image portion potential was −60 V. The gap at the closest portion between the photoreceptor 1 and the developer carrier 11 was set to 0.35 mm.
<Condition 4>
Using the developing device 2a shown in FIG. 1, a developer carrier 11 is applied with a rectangular wave developing bias having an amplitude of 1.5 kV, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −400 V, and a reverse polarity particle collecting member. A rectangular wave bias having an amplitude of 500 V, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −600 V was applied to 22. At this time, the phase of the bias applied to the developer carrying member 11 and the reverse polarity particle collecting member 22 is reversed, that is, the oscillating electric field between the developer carrying member 11 and the reverse polarity particle collecting member 22 is strengthened. As the reverse polarity particle recovery member 22, an aluminum roller having an alumite treatment on the surface was used, and the gap at the closest part between the developer carrier 11 and the reverse polarity particle recovery member 22 was 0.25 mm. The background portion potential of the electrostatic latent image formed on the photoreceptor 1 was −550 V, and the image portion potential was −60 V. The gap at the closest portion between the photoreceptor 1 and the developer carrier 11 was set to 0.35 mm.
<Condition 5>
Using the developing device 2b shown in FIG. 2, a DC voltage of -400V is applied to the developer carrier 11, and the toner carrier 25 has an amplitude of 1.4 kV, a duty ratio of 60%, a frequency of 4 kHz, and a DC component of -340V. A rectangular wave developing bias was applied. An aluminum roller having an alumite treatment on the surface was used as the toner carrier, and the gap at the closest part between the developer carrier 11 and the toner carrier 25 was set to 0.3 mm. The background potential of the electrostatic latent image formed on the photosensitive member 1 is −550 V, the image portion potential is −60 V, and the gap at the closest portion between the photosensitive member 1 and the toner carrier 25 is 0.15 mm. .
<Condition 6>
Using the developing device 2b shown in FIG. 2, a DC voltage of −400V is applied to the developer carrier 11, and the toner carrier 25 has an amplitude of 1.4 kV, a duty ratio of 55%, a frequency of 2 kHz, and a DC component of −270V. A rectangular wave developing bias was applied. The toner carrier 25 is an aluminum roller with an alumite treatment on the surface, and the closest gap between the developer carrier 11 and the toner carrier 25 is 0.3 mm. The background portion potential of the electrostatic latent image formed on the photoreceptor 1 is −500 V, the image portion potential is −60 V, and the gap between the photoreceptor 1 and the toner carrier 25 is 0.15 mm. .
<Condition 7>
Using the developing device 2b shown in FIG. 2, a rectangular wave bias having an amplitude of 500 V, a duty ratio of 45%, a frequency of 4 kHz, and a DC component of -375 V is applied to the developer carrier 11, and an amplitude of 1.V is applied to the toner carrier 25. A rectangular wave developing bias of 4 kV, a duty ratio of 55%, a frequency of 4 kHz, and a DC component of −270 V was applied. The rectangular waves applied to the developer carrier 11 and the toner carrier 25 are out of phase so as to increase the electric field between the developer carrier 11 and the toner carrier 25. The toner carrier 25 is an aluminum roller with an alumite treatment on the surface, and the closest gap between the developer carrier 11 and the toner carrier 25 is 0.3 mm. The background potential of the electrostatic latent image formed on the photosensitive member 1 is −550 V, the image portion potential is −60 V, and the gap at the closest portion between the photosensitive member 1 and the toner carrier 25 is 0.15 mm. .
<Condition 8>
Using the developing device 2b shown in FIG. 2, a rectangular wave bias having an amplitude of 800 V, a duty ratio of 50%, a frequency of 4 kHz, and a DC component of −400 V is applied to the developer carrier 11, and the toner carrier 25 has an amplitude of 1.. A rectangular wave developing bias of 4 kV, duty ratio 50%, frequency 4 kHz, DC component −200 V was applied. The rectangular waves applied to the developer carrier 11 and the toner carrier 25 are out of phase so as to increase the electric field between the developer carrier 11 and the toner carrier 25. The toner carrier 25 is an aluminum roller with an alumite treatment on the surface, and the closest gap between the developer carrier 11 and the toner carrier 25 is 0.3 mm. The background potential of the electrostatic latent image formed on the photosensitive member 1 is −550 V, the image portion potential is −60 V, and the gap at the closest portion between the photosensitive member 1 and the toner carrier 25 is 0.15 mm. .
<Example 1> The durability test was performed by switching from condition 1 to 10 to 200,000 sheets to condition 2 up to 100,000 printed sheets.
Example 2 An endurance test was performed by switching from condition 1, 10 to 150,000 sheets to condition 3, and from 15 to 200,000 sheets to condition 4, up to 100,000 printed sheets.
<Example 3> The durability test was performed by switching from condition 5 up to 100,000 to condition 6 up to 100,000 sheets.
<Example 4> The durability test was performed by switching up to 100,000 prints on condition 5, switching from 10 to 150,000 on condition 7, and changing from 15 to 200,000 on condition 8.
<Comparative Example 1> Durability tests were conducted under condition 1 up to 200,000 sheets.
<Comparative Example 2> Durability tests were conducted under condition 2 up to 200,000 sheets.
<Comparative Example 3> Durability tests were conducted under condition 3 up to 200,000 sheets.
<Comparative Example 4> Durability tests were conducted under condition 4 up to 200,000 sheets.
<Comparative Example 5> Durability tests were performed on condition 5 up to 200,000 sheets.
<Comparative Example 6> Durability tests were conducted under condition 6 up to 200,000 sheets.
<Comparative Example 7> A durability test was performed under condition 7 up to 200,000 sheets.
<Comparative Example 8> An endurance test was conducted under condition 8 up to 200,000 sheets.
<Comparative Example 9> The durability test was performed by switching the condition up to 100,000 sheets from condition 2 to 10 to 200,000 sheets to condition 1.
<Comparative Example 10> Durability tests were conducted by switching from 100,000 sheets to Condition 4, 10 to 150,000 sheets to Condition 3, and from 15 to 200,000 sheets to Condition 1.

  Table 11 summarizes the results of evaluating the toner charge amount of the developer sampled every 20,000 printed sheets using the apparatus shown in FIG.

  From Table 11, in the example of the present invention, the change amount of the toner charge amount is suppressed to 4 μC / g or less over a long period from the initial printing to 200,000 sheets, whereas in the comparative example, the toner charge The amount change width reached a level exceeding 5 μC / g, confirming the effect of the present invention.

  As described above, by controlling the separation voltage so as to increase the separation rate of the reverse polarity particles according to the number of printed sheets, the carrier charge assist effect by the reverse polarity particles can be effectively acted and stabilized over a long period of time. It can be seen that the toner charging characteristics can be maintained. As a result, the deterioration of the carrier can be suppressed over a long period of time, a stable toner charge amount can be realized through the printing durability, the life of the developing device can be extended, and a good image can be formed over a long period of time. An image forming apparatus can be provided.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the flowchart which controls a separation voltage by the image area ratio concerning the 1st Embodiment of this invention. It is a schematic block diagram which shows the image forming apparatus which is the 2nd Embodiment concerning this invention. It is a figure which shows the flowchart which controls a separation voltage by the image area rate concerning the 2nd Embodiment of this invention. It is a figure which shows an example of the toner charge amount change with respect to the reverse polarity particle addition amount to a carrier. It is a schematic block diagram which shows the measuring device of the amount of charge. It is a schematic block diagram which shows a part of developing apparatus used for evaluation.

Explanation of symbols

1 Image carrier (photoreceptor)
2a, 2b Developing device 3 Charging device 4 Transfer roller 5 Cleaning blade 6 Developing area 100
7 Toner Supply Device 11 Developer Carrier 12 Sleeve Roller 13 Magnet Roller 14 Power Supply 15 Regulatory Member 16 Developer Tank 17 Bucket Roller 18 Casing 19 Supply Roller 20 ATDC Sensor 21 Hopper 22 Reverse Polarity Particle Separation Member 23 Supply Toner 24 Developer 25 Toner carrier 31 Conductive sleeve 32 Magnet roll 33 Bias power supply 34 Cylindrical electrode A Image carrier rotation direction B Sleeve roller rotation direction C, D Gap a, b, c, d, e Measurement region for separation rate evaluation Ga, Gb, Gc, Gd, Ge Amount of opposite polarity particles in each region

Claims (7)

A developer tank containing a toner, a carrier, and a developer containing reverse polarity particles that are charged in the opposite polarity to the charged polarity of the toner;
A developer carrying member for carrying and carrying the developer supplied from the developer tank to the surface;
Separation means for separating toner or the reverse polarity particles from the developer on the developer carrying member;
A recovery unit that recovers the reverse polarity particles separated by the separation unit in the developer tank;
In an image forming apparatus including the developing device and an image carrier that is arranged via a development region and carries an electrostatic latent image,
The separation means includes a separation member, and a separation voltage application means for applying a bias voltage for separating the toner or reverse polarity particles between the separation member and the developer carrier,
An image forming apparatus comprising: control means for controlling the separation rate of the reverse polarity particles so as to increase according to the number of printed sheets. The separation voltage application means applies an alternating voltage to at least one of the separation member and the developer carrier,
The image forming apparatus according to claim 1, wherein the control unit controls at least one parameter among an amplitude value, a frequency, an average potential difference, and a duty ratio of the alternating voltage. The image forming apparatus according to claim 1, wherein the control unit controls a distance between the separation member and the developer carrier. The separation member is provided on the upstream side in the developer movement direction with respect to the development area in the developer carrier, and before the developer on the developer carrier develops the electrostatic latent image on the image carrier. The image forming apparatus according to claim 1, wherein the reverse polarity particles are separated from the developer on the developer carrying member. The separation member is a toner carrier that is provided between the developer carrier and the image carrier and separates the toner from the developer on the developer carrier. The image forming apparatus according to claim 1, wherein the electrostatic latent image on the carrier is developed. 6. The image forming apparatus according to claim 1, further comprising a background portion potential control unit configured to control a background portion potential of the image carrier based on the number of printed sheets. The image forming apparatus according to claim 1, further comprising a development gap control unit that controls a development gap in the development region based on a number of printed sheets.

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