JP2007108673A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that prevents degradation of carrier for a long term even if successively forming an image with a comparatively small image area ratio, and to provide an image forming apparatus. <P>SOLUTION: The developing device 2a includes: a developer tank 16 for receiving a developer 24 including toner, the carrier for charging the toner and reverse polarity particles charged in reverse polarity with respect to the charge polarity of the toner by means of the carrier; a developer carrier 11 on the surface of which the developer supplied from the developer tank is carried; and a separation mechanism 22 for separating the toner or the reverse polarity particles from the developer on the developer carrier. In this arrangement, the reverse polarity particles are collected into the developer tank, and the image forming apparatus is provided with the developing device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine or a printer, and a developing apparatus used for developing an electrostatic latent image formed on an image carrier, particularly from two components of a toner and a carrier. The present invention relates to a developing device using the developer and an image forming apparatus using the same.

  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, generally, toner is charged by passing toner through a regulating portion formed by a toner carrier and a regulation plate pressed against the toner carrier, and a desired toner thin layer can be obtained. Therefore, it is advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus. On the other hand, the deterioration of the toner is likely to be promoted due to the strong stress of the regulating portion, and the charge acceptability of the toner is likely to be lowered. Further, the toner regulating member and the surface of the toner carrying member are contaminated with the toner and the external additive, so that the charge imparting property to the toner is also lowered, causing problems such as fogging. As a result, the life of the developing device is shortened. End up.

  In comparison, 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, which is a charge imparting member for the toner, has a large surface area, it is relatively resistant to contamination by toner and external additives, and is advantageous in extending the service 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 by supplying a small amount of carrier together with toner or by itself and discharging a deteriorated developer having reduced chargeability accordingly. Has been disclosed to suppress the increase in the deteriorated carrier ratio. 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. However, 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 there is an aspect that it cannot be said that the initial characteristics are maintained and utilized.

On the other hand, Patent Document 2 discloses a two-component developer comprising a toner externally added with carrier and particles having a chargeability opposite to the toner charge polarity, and a developing method using the same. In the developing method of Patent Document 2, the reverse polarity charged particles are added for the purpose of acting as abrasives and spacer particles, and it is shown that the effect of removing the spent on the carrier surface is effective in suppressing deterioration. Further, the cleaning portion of the image carrier is effective for improving the cleaning property and polishing the image carrier. However, in the disclosed developing method, the consumption amount of the toner and the reverse polarity charged particles differs depending on the image area ratio, and particularly when the image area ratio is small, the consumption of the reverse polarity charged particles becomes excessive, and the carrier in the developing device There is a problem that the deterioration suppressing effect is lowered.
JP 59-1000047 A Japanese Patent Laid-Open No. 2003-215855

  An object of the present invention is to provide a developing device and an image forming apparatus that suppress the deterioration of a carrier over a long period of time even when images having a relatively small image area ratio are continuously formed.

  The present invention relates to a developer tank containing a toner, a carrier for charging the toner, and a developer containing reverse polarity particles that are oppositely charged with respect to the charge polarity of the toner, and a developer carried on the surface. A developer comprising a developer carrying member to be conveyed, and a separation mechanism for separating toner or reverse polarity particles from the developer on the developer carrying member, wherein the reverse polarity particles are collected in a developer tank. The present invention relates to an apparatus and an image forming apparatus having the developing device.

  The present invention also provides a developer tank containing toner, a carrier for charging the toner, and a developer containing reverse polarity particles that are charged in the opposite polarity to the charged polarity of the toner, and supplied from the developer tank. A developer that carries at least the toner in the developer to be conveyed and transports it to the development area, and a separation mechanism that separates the toner and the reverse polarity particles contained in the developer. The reverse polarity particles are separated after being supplied to the carrier or by supplying the developer to the carrier, and at least the reverse polarity particles after being separated from the toner are collected in a developer tank. The present invention relates to a developing device and an image forming apparatus having the developing device.

  In the present invention, since the consumption of the reverse polarity particles is suppressed, it is possible to reduce the influence of the fluctuation of the consumption amount of the reverse polarity particles depending on the image area ratio. It is possible to suppress excessive consumption. In addition, the opposite polarity particles can effectively compensate for the chargeability of the carrier, and as a result, the deterioration of the carrier can be suppressed over a long period of time. Therefore, the toner charge amount is effectively maintained for a long time even when images having a relatively small image area ratio are continuously formed.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a main part of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus is a printer that performs image formation by transferring a toner image formed on an image carrier (photoconductor) 1 to a transfer medium P such as paper by an electrophotographic method. This image forming apparatus has an image carrier 1 for carrying an image, and a charging member 3 as a charging unit for charging the image carrier 1 and an image carrier around the image carrier 1. A developing device 2a for developing the electrostatic latent image on the image 1, a transfer roller 4 for transferring the toner image on the image carrier 1, and a cleaning blade 5 for removing residual toner on the image carrier 1 It arranges in order along the rotation direction A of the body 1.

  The image carrier 1 is charged by the charging member 3 and then exposed by an exposure device 30 equipped with a laser emitter or the like at the point E in the figure, and an electrostatic latent image is formed on the surface thereof. . The developing device 2a develops the electrostatic latent image into a toner image. The transfer roller 4 transfers the toner image on the image carrier 1 to the transfer medium P, and then discharges it in the direction of arrow C in the figure. The cleaning blade 5 removes the residual toner on the image carrier 1 after the transfer with its mechanical force. For the image carrier 1, the charging member 3, the exposure device 30, the transfer roller 4, the cleaning blade 5 and the like used in the image forming apparatus, a well-known electrophotographic technique may be arbitrarily used. For example, although a charging roller is shown in the drawing as the charging means, a charging device that is not in contact with the image carrier 1 may be used. Further, for example, there may be no cleaning blade.

  In the present embodiment, the developing device 2a includes a developer tank 16 that contains the developer 24, a developer carrier 11 that carries and conveys the developer 24 supplied from the developer tank, and the developer carrier. A separation mechanism for separating toner or reverse polarity particles from the developer on the body is provided, and the reverse polarity particles are collected in the developer tank 16. As a result, consumption of the reverse polarity particles can be suppressed, and the reverse polarity particles can effectively compensate for the chargeability of the carrier, and as a result, the deterioration of the carrier can be suppressed over a long period of time. Therefore, the toner charge amount can be effectively maintained over a long period even when images having a relatively small image area ratio are continuously formed.

  If the developing device does not have the separation mechanism, the carrier deterioration suppressing effect in the developing device is reduced particularly when the image area ratio is small. The expression of this phenomenon is considered to be based on the following mechanism. In a two-component developing device, a strong electric field is formed by applying an oscillating electric field or the like in the developing region, thereby improving toner separation from the carrier in the developer and improving development efficiency. When the developer is included, the carrier, toner, and reverse polarity particles are separated, and the carrier remains on the developer carrier by the magnetic attraction force, but the toner has reverse polarity particles in the image portion of the electrostatic latent image. Each non-image part is consumed. Therefore, the consumption balance between the toner and the reverse polarity particles is not stable depending on the image area ratio, and particularly when a large amount of images having a large background area are printed, the reverse polarity particles in the developer are preferentially consumed, It is considered that the chargeability cannot be compensated and the effect of suppressing carrier deterioration is reduced.

  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. By incorporating reverse polarity particles in the two-component developer and accumulating the reverse polarity particles in the developer with durability by the separation mechanism, the chargeability of the carrier can be increased by spending the toner or the post-treatment agent on the carrier. Even if it decreases, the reverse polarity particles can also charge the toner to the normal polarity, so that the chargeability of the carrier can be effectively compensated, 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 weight with respect to 100 parts by weight 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 weight with respect to 100 parts by weight 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 weight with respect to 100 parts by weight 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 weight with respect to 100 parts by weight of the toner. The number average primary particle size of the external additive is 9 to 100 nm. Preferably, at least one external additive (inorganic fine particles) having a number average primary particle size of 20 to 40 nm is included. More preferably, an external additive (inorganic fine particles) having a number average primary particle size of 9 to 16 nm is further included.

  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 weight 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 into 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. The toner ratio is 3 to 50% by weight, preferably 6 to 30% by weight based on the total amount of the toner and the 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 weight, particularly 0.01 to 100 parts by weight with respect to 100 parts by weight of the carrier. 2.00 parts by weight 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.

  In the developing device 2a, as a separation mechanism 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 The collection member 22 is employed. As shown in FIG. 1, the reverse polarity particle recovery member 22 is provided on the upstream side in the developer movement direction from the development region 6 in the developer carrier 11, and the 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 recovery member 22. After the reverse polarity particles are separated by the reverse polarity particle recovery 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 6. Develop the image.

  The reverse polarity particle recovery member 22 is connected to a power source (not shown), and a predetermined reverse polarity particle separation bias is applied, whereby the reverse polarity particles in the developer are electrically separated on the surface of the reverse polarity particle recovery member 22.・ It is collected.

  The reverse polarity particle separation bias applied to the reverse polarity particle recovery member 22 differs depending on the charge polarity of the reverse polarity particles, that is, when the toner is negatively charged and the reverse polarity particles are positively charged, When the toner is positively charged and the reverse polarity particles are negatively charged, the average value is lower than the average value of the applied voltage. Is a voltage having a high average value. The difference between the average voltage applied to the reverse polarity particle recovery member and the average voltage applied to the developer carrier is 20 to 500 V, even when the reverse polarity particles are charged to either positive or negative polarity. In particular, 50 to 300V is preferable. 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, the carriers held by the magnetic force on the developer carrier are separated by the electric field, and the original developing function may be impaired in the developing region.

In the developing device 2a, it is further preferable that an alternating electric field is formed between the reverse polarity particle recovery member and the developer carrier. 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 to further improve the reverse polarity separation and recovery. It becomes possible.

  In this specification, the electric field formed between the reverse polarity particle recovery member and the developer carrier 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 AC voltage to one or both of the reverse polarity particle recovery member and the developer carrier. In particular, when an AC voltage is applied to the developer carrier to develop the electrostatic latent image with toner, an AC voltage applied to the developer carrier can be used to form a reverse polarity particle separation electric field. 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 charge polarity of the reverse polarity particles is positive, the DC voltage and the AC voltage are applied to the developer carrier, and only the DC voltage is applied to the reverse polarity particle recovery member, the reverse polarity particle recovery member Only a DC voltage lower than the average value of the voltages (DC + AC) applied to the developer carrier is applied. Further, for example, when the charged polarity of the reverse polarity particles is negative, a DC voltage and an AC voltage are applied to the developer carrier, and only a DC voltage is applied to the reverse polarity particle recovery member, the reverse polarity particle recovery member Only a DC voltage higher than the average value of the voltages (DC + AC) applied to the developer carrier is applied. In these cases, the maximum absolute value of the reverse polarity particle separation electric field is the maximum potential difference between the voltage applied to the developer carrier (DC + AC) and the voltage applied to the reverse polarity particle recovery member (DC). The value is a value obtained by dividing the value by the closest gap between the reverse polarity particle recovery member and the developer carrier, and it is desirable that the 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, and the AC voltage and the DC voltage are applied to the reverse polarity particle recovery member, the reverse polarity particle recovery member A DC voltage on which an AC voltage is superimposed is applied so that the average voltage is lower than the DC voltage applied to the developer carrier. Also, for example, when the charged polarity of the reverse polarity particles is negative, only the DC voltage is applied to the developer carrier, and the AC voltage and DC voltage are applied to the reverse polarity particle recovery member, the reverse polarity particle recovery member A DC voltage on which an AC voltage is superimposed is applied so that the average voltage is higher than the DC voltage applied to the developer carrier. In these cases, the maximum absolute value of the reverse polarity particle separation electric field is the maximum potential difference between the voltage applied to the developer carrier (DC) and the voltage applied to the reverse polarity particle recovery member (DC + AC). The value is a value obtained by dividing the value by the closest gap between the reverse polarity particle recovery member and the developer carrier, and it is desirable that the value be in the above range.

  Also, for example, when the charged polarity of the reverse polarity particles is positive and a DC voltage with an AC voltage superimposed on both the developer carrier and the reverse polarity particle recovery member is applied, the reverse polarity particle recovery member is loaded with the developer. A voltage (DC + AC) having an average voltage smaller than the average value of the voltage (DC + AC) applied to the body is applied. In addition, for example, when the polarity of the reverse polarity particles is negative and a DC voltage in which an AC voltage is superimposed on both the developer carrier and the reverse polarity particle recovery member is applied, the reverse polarity particle recovery member is loaded with the developer. A voltage (DC + AC) having an average voltage larger than the average value of the voltage (DC + AC) applied to the body is applied. At these times, the voltage applied to the developer carrier (direct current + alternating current) caused by the difference in the amplitude, phase, frequency, duty ratio, etc. of the alternating voltage component applied to each is applied to the reverse polarity particle recovery member. The value obtained by dividing the maximum value of the potential difference from the voltage (direct current + alternating current) by the closest gap between the reverse polarity particle collecting member and the developer carrier is the maximum absolute value of the reverse polarity particle separation electric field, It is desirable that the value falls within the above range.

  The reverse polarity particles on the surface of the member separated and collected by the reverse polarity particle recovery member 22 are recovered in the developer tank 16. When recovering reverse polarity particles from the reverse polarity particle recovery member to the developer tank, the magnitude relationship between the average value of the voltage applied to the reverse polarity particle recovery member and the average value of the voltage applied to the developer carrier is reversed. It may be performed at the timing at the time of non-image formation such as the interval between images during the continuous operation before the start of image formation or after the end of image formation (between pages between the previous page and the subsequent page). Can do.

  The reverse polarity particle recovery member 22 may be made of any material as long as the voltage can be applied. For example, an aluminum roller subjected to a 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, S1, N3, N2, and S2 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 6 facing the image carrier 1 and generates a repulsive magnetic field for peeling off the developer 24 on the sleeve roller 12. The pole portions N3 and N2 are arranged 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 7 for replenishing toner in the developer tank 16 for the amount of toner consumed in the development area 6, and a developer thin film for regulating the amount of developer on the developer carrier 11. It has a regulating member (regulating blade) 15 for stratification. The supply unit 7 includes a hopper 21 that stores supply toner 23 and a supply roller 19 for supplying 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 weight, particularly preferably 0.5 to 5.0% by weight, based on the toner.

  Specifically, in the developing device 2 a shown in FIG. 1, the developer 24 in the developer tank 16 is mixed and stirred by the rotation of the bucket roller 17, is frictionally charged, and is then pumped up by the bucket roller 17 to be surface of the developer carrier 11. To the sleeve roller 12. 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 carrying member (developing roller) 11, rotates together with the sleeve roller 12, and is provided to face the developing roller 11. The passing amount is regulated by the regulated member 15. Thereafter, only the reverse polarity particles contained in the developer are separated and collected by the reverse polarity particle recovery member at the portion facing the reverse polarity particle recovery member 22 as described above. The remaining developer from which the reverse polarity particles have been separated is conveyed to a developing area 6 facing the image carrier 1. In the developing region 6, developer spikes are formed by the magnetic force of the main magnetic pole N <b> 1 of the magnet roller 13, and are formed between the electrostatic latent image on the image carrier 1 and the developing roller 11 to which a developing bias is applied. Due to the force applied to the toner by the electric field, the toner in the developer moves toward the electrostatic latent image on the image 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 developer 24 that has consumed the toner in the developing region 6 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 7 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 recovery member 22 are returned onto the development roller by reversing the direction of the electric field applied to the developing roller and the reverse polarity particle recovery member during non-image formation. As the roller rotates, it is transported together with the developer and returned to the developer tank.

  In FIG. 1, the reverse polarity particle recovery member 22 is provided separately from the restriction member 15 and the casing 26, but the reverse polarity particle recovery member 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 collecting member. 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 have to be collected by the reverse polarity particle collecting member, but some of the reverse polarity particles are not collected but are used for development together with the toner and consumed. Also good. Since the reverse polarity particles in the other parts are collected and the reverse polarity particles are replenished, the carrier charge assisting effect by the reverse polarity particles can be obtained even if the reverse polarity particles cannot be completely recovered.

  Next, the main part of an image forming apparatus according to another embodiment of the present invention is shown in FIG. In FIG. 2, members having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  A developing device 2b shown in FIG. 2 uses a developer carrier as a separation mechanism for separating toner or reverse polarity particles from the developer on the developer carrier 11 instead of the reverse polarity particle recovery member 22 shown in FIG. A toner carrier 25 that separates and carries the toner from the developer on 11 is employed. As shown in FIG. 2, the toner carrier 25 is provided between the developer carrier 11 and the image carrier 1, and a toner separation bias is applied to electrically remove the toner in the developer. It is designed to be separated and carried on the surface of the carrier. 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 developing area 6.

  As described above, in the developing device 2b, unlike the embodiment shown in FIG. 1, instead of separating the reverse polarity particles from the developer, the toner is separated from the developer by the toner carrier 25 and carried. The toner separated and carried on the toner carrier 25 is used for developing the electrostatic latent image on the image carrier 1.

  The toner carrier 25 is connected to a power source (not shown), and a predetermined toner separation bias is applied, whereby the toner in the developer is electrically separated and carried on the surface of the toner carrier 25.

  The toner separation bias applied to the toner carrier 25 differs depending on the charging polarity of the toner. That is, when the toner is negatively charged, the voltage becomes an average value higher than the average value of the voltage applied to the developer carrier. When the toner is positively charged, the voltage is an average value lower than the average value of the voltage applied to the developer carrying member. Even when the toner is charged to either positive or negative polarity, the difference between the average voltage applied to the toner carrier and the average voltage applied to the developer carrier is 20 to 500 V, particularly 50 to It is preferable that it is 300V. If the potential difference is too small, the amount of toner on the toner carrier 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 and the developer carrier. 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 is possible to further improve the toner separation property. .

  In this specification, the electric field formed between the toner carrier and the developer carrier is referred to as a toner separation electric field. Such a toner separation electric field is usually obtained by applying an AC voltage to one or both of the toner carrier and the developer carrier. In particular, when an AC voltage is applied to the toner carrier 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. 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, and only a DC voltage is applied to the toner carrier, the toner carrier is loaded with the developer carrier. Only a DC voltage lower than the average value of applied voltages (DC + AC) 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, and only a DC voltage is applied to the toner carrier, the developer carrier is applied to the toner carrier. Only a DC voltage higher than the average value of the voltages (DC + AC) applied to is applied. In these cases, the maximum value of the absolute value of the toner separation electric field is the maximum value of the potential difference between the voltage (DC + AC) applied to the developer carrier and the voltage (DC) applied to the toner carrier. It is a value divided by the closest gap between the carrier and the developer carrier, and it is desirable that this value is in the above range.

  Also, for example, when the charging polarity of the toner is positive, only a DC voltage is applied to the developer carrier, and an AC electric field and a DC voltage are applied to the toner carrier, the developer carrier is applied to the toner carrier. 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. Also, for example, when the charging polarity of the toner is negative, only a DC voltage is applied to the developer carrier, and an AC electric field and a DC voltage are applied to the toner carrier, the developer carrier is applied to the toner carrier. 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. In these cases, the maximum value of the absolute value of the toner separation electric field is the maximum value of the potential difference between the voltage (DC) applied to the developer carrier and the voltage (DC + AC) applied to the toner carrier. It is a value divided by the closest gap between the carrier and the developer carrier, and it is desirable that this value is in the above range.

  In addition, for example, when the charging polarity of the toner is positive and a DC voltage in which an AC voltage is superimposed on both the developer carrier and the toner carrier is applied, the voltage applied to the developer carrier is applied to the toner carrier. A voltage (DC + AC) having an average voltage smaller than the average value of (DC + AC) is applied. In addition, for example, when the charging polarity of the toner is negative and a DC voltage in which an AC voltage is superimposed on both the developer carrier and the toner carrier is applied, the voltage applied to the developer carrier is applied to the toner carrier. A voltage (DC + AC) having an average voltage larger than the average value of (DC + AC) is applied. At these times, the voltage applied to the developer carrier (DC + AC) and the voltage applied to the toner carrier, which are caused by differences in the amplitude, phase, frequency, duty ratio, etc. of the AC voltage components applied to the respective components. A value obtained by dividing the maximum value of the potential difference from (DC + AC) by the closest gap between the toner carrier and the developer carrier is the maximum absolute value of the toner separation electric field, and this value is within the above range. It is desirable to do.

  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 recovered as they are into the developer tank by the developer carrier 11, so that the reverse polarity collected by the reverse polarity particle recovery member described in the embodiment of FIG. The step of returning the polar particles to the developer tank at the time of non-image formation can be omitted.

  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.

  Specifically, in the developing device 2b shown in FIG. 2, the developer 24 in the developer tank 16 is mixed and stirred by the rotation of the bucket roller 17 and frictionally charged, and then pumped up by the bucket roller 17 as in the developing device 2a. Then, it is 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 carrying member (developing roller) 11, rotates together with the sleeve roller 12, and is provided to face the developing roller 11. The passing amount is regulated by the regulated 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 a developing area 6 facing the image carrier 1. In the developing area 6, 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 carrying member that has passed through the developing region 6 is transported to the developing region through toner supply / recovery by a magnetic brush at the facing portion between the toner carrying member and the developer carrying member. 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 7 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 2b, not all of the reverse polarity particles have to be collected by the reverse polarity particle collecting member, but some of the reverse polarity particles are not collected but are used for development together with the toner and consumed. Also good. Since the reverse polarity particles in the other parts are collected and the reverse polarity particles are replenished, the carrier charge assisting effect by the reverse polarity particles can be obtained even if the reverse polarity particles cannot be completely recovered.
Further, by providing the developing device 2b also to the reverse polarity particle recovery member 22 provided in the development device 2a shown in the embodiment of FIG. 1, it is possible to further improve the reverse polarity particle recovery property.

Experimental example 1
A toner produced by the following method was used.
Toner A:
For 100 parts by weight of a toner base material having a volume average particle diameter of about 6.5 μm prepared by a wet granulation method, 0.2 parts by weight of the first hydrophobic silica and 0.5 parts by weight of the second hydrophobic silica Toner A was obtained by subjecting 0.5 part by weight of hydrophobic titanium oxide to a surface treatment for 3 minutes at a speed of 40 m / s using a Henschel mixer (manufactured by Mitsui Metal Mining Co., Ltd.).
The first hydrophobic silica used here is a silica (# 130: manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 16 nm and surface-treated with hexamethyldisilazane (HMDS) as a hydrophobizing agent. is there. The second hydrophobic silica is obtained by surface-treating silica having a number average primary particle size of 20 nm (# 90G: manufactured by Nippon Aerosil Co., Ltd.) with HMDS. Hydrophobic titanium oxide is obtained by surface-treating anatase-type titanium oxide having a number average primary particle size of 30 nm with isobutyltrimethoxysilane as a hydrophobizing agent in an aqueous wet process.

Toner B:
2 parts by weight of strontium titanate having a number average particle diameter of 350 nm as the opposite polarity particles in the toner A with respect to 100 parts by weight of the toner base particles contained in the toner A, and 3 at a speed of 40 m / s using the Henschel mixer. Toner B was obtained by external addition treatment for a minute.

Toner C:
2 parts by weight of strontium titanate having a number average particle diameter of 350 nm as the opposite polarity particles in the toner A to 100 parts by weight of the toner base material particles contained in the toner A, 1 at a speed of 30 m / s using the Henschel mixer. Toner C was obtained by external addition for a minute.

<Example 1>
A developing device having the configuration shown in FIG. 1 was used, and a carrier for bizhub C350 (volume average particle diameter of about 33 μm) manufactured by Konica Minolta Business Technologies and toner B were used as developers. The toner ratio in the developer was 8% by weight. The toner ratio is the ratio of the total amount of toner, post-treatment agent and reverse polarity particles to the total amount of developer (hereinafter the same). A rectangular wave developing bias having an amplitude of 1.4 kV, a DC component of −400 V, a duty ratio of 50%, and a frequency of 2 kHz was applied to the developer carrying member. A DC bias of −550 V, which is a potential difference of −150 V with respect to the average potential of the developing bias and a potential difference of 850 V with respect to the maximum potential of the developing bias, was applied to the reverse polarity particle recovery member. As the reverse polarity particle recovery member, an aluminum roller having an alumite treatment on the surface was used, and the gap at the closest part between the developer carrying member and the reverse polarity particle recovery member was set to 0.3 mm. The background potential of the electrostatic latent image formed on the image bearing member was −550V, and the image portion potential was −60V. The gap at the closest part between the image carrier and the developer carrier was 0.35 mm. The maximum absolute value of the reverse polarity particle separation electric field formed between the reverse polarity particle recovery member and the developer carrying member was 850 V / 0.3 mm = 2.8 × 10 ⁶ V / m. Recovery of the reverse polarity particles collected by the reverse polarity particle recovery member into the developer tank was performed by reversing the voltage applied to the developer carrier and the reverse polarity particle recovery member at the timing between the sheets.

<Example 2>
In Example 1, a developing device in which the reverse polarity particle recovery member was removed and the function of the reverse polarity particle recovery member was also used as a regulating member was used. A rectangular wave developing bias having an amplitude of 1.4 kV, a DC component of −400 V, a duty ratio of 50%, and a frequency of 2 kHz was applied to the developer carrying member. A DC bias of −700 V, which is a potential difference of −300 V with respect to the average potential of the developing bias and a potential difference of 1000 V with respect to the maximum potential of the developing bias, was applied to the regulating member. The regulating member was made of stainless steel (SUS430). The closest gap between the developer carrying member and the regulating member was 0.4 mm. The background potential of the electrostatic latent image formed on the image bearing member was −550V, and the image portion potential was −60V. The gap at the closest part between the image carrier and the developer carrier was 0.35 mm. The maximum value of the absolute value of the electric field formed between the regulating member (reverse polarity particle collecting member) and the developer carrying member was 1000 V / 0.4 mm = 2.5 × 10 ⁶ V / m. Recovery of the reverse polarity particles collected by the reverse polarity particle recovery member into the developer tank was performed by reversing the voltage applied to the developer carrier and the reverse polarity particle recovery member at the timing between the sheets.

<Example 3>
The developing device having the configuration shown in FIG. 2 was used, and a carrier for bizhub C350 (volume average particle diameter of about 33 μm) manufactured by Konica Minolta Business Technologies and toner C were used as the developer. The toner ratio in the developer was 8% by weight. A DC voltage of −400 V was applied to the developer carrying member. A rectangular wave developing bias having an amplitude of 1.6 kV, a DC component of −300 V, a duty ratio of 50%, and a frequency of 2 kHz was applied to the toner carrier. The average potential of the toner carrier has a potential difference of 100V with respect to the potential of the developer carrier, and the maximum potential difference is 900V. An aluminum roller having an alumite treatment on the surface was used for the toner carrier, and the gap at the closest part between the developer carrier and the toner carrier was 0.3 mm. The background potential of the electrostatic latent image formed on the image carrier is −550 V, the image part potential is −60 V, and the gap between the image carrier and the toner carrier is 0.15 mm. The maximum value of the absolute value of the toner separation electric field formed between the toner carrier and the developer carrier was 900 V / 0.3 mm = 3.0 × 10 ⁶ V / m.

<Example 4>
A developing device having the configuration shown in FIG. 2 was used, and a carrier for bizhub C350 (volume average particle diameter of about 33 μm) manufactured by Konica Minolta Business Technologies and toner B were used as the developer. The toner ratio in the developer was 10% by weight. A DC voltage of −250 V was applied to the developer carrying member. A development bias in which a rectangular wave having an amplitude of 1.4 kV, a duty ratio of 60%, and a frequency of 4 kHz is superimposed on a DC voltage of −300 V is applied to the toner carrier. The average potential of the toner carrier is −160 V, has a potential difference of 90 V with respect to the potential of the developer carrier, and the maximum potential difference is 750 V. An aluminum roller having an alumite treatment on the surface was used for the toner carrier, and the gap at the closest part between the developer carrier and the toner carrier was 0.3 mm. The background potential of the electrostatic latent image formed on the image carrier is −550 V, the image part potential is −60 V, and the gap between the image carrier and the toner carrier is 0.15 mm. The maximum value of the absolute value of the toner separation electric field formed between the toner carrier and the developer carrier was 750 V / 0.3 mm = 2.5 × 10 ⁶ V / m.

<Comparative Example 1>
A developing device having the same configuration as in Example 1 was used except that toner A was used as the toner.
<Comparative example 2>
A developing device having the same configuration as in Example 3 was used except that toner A was used as the toner.
<Comparative Example 3>
A developing device having the same configuration as in Example 1 was used except that the reverse polarity particle recovery member was omitted.

  Using the image forming apparatus in which the copier bizhub C350 manufactured by Konica Minolta Business Technologies, Inc. was modified as described above, durability evaluation of 50,000 sheets was performed using an image chart having an image area ratio of about 5% under each condition. Table 1 shows the results of evaluating the toner charge amount of the developer sampled at each point of durability evaluation using the apparatus of FIG. In any of the image forming apparatuses, the toner described in each of the examples and comparative examples was used as the replenishing toner. The developer sampling was performed from the developer tank.

  Further, the amount of strontium titanate adhering to the carrier surface after the above 50,000 durability tests was calculated from the amount of strontium by ICP analysis and quantified. After separating the toner from the developer using the apparatus shown in FIG. 4, the carrier is subjected to ultrasonic vibration in an aqueous solution to which a surfactant is added to remove excess deposits on the carrier surface, and then the analysis is performed. It was. The value is the ratio of strontium titanate to the carrier weight.

  According to Table 1, the toner charge amount after the initial printing and after printing 50,000 sheets changed very little in the examples, whereas in the comparative examples, the toner charge amount change reached a level exceeding 5 μC / g. ing. Further, in the example, 0.01% by weight or more is secured as the amount of strontium titanate on the carrier surface after printing 50,000 sheets, whereas in Comparative Example 3, it is greatly lower than that of the example. In Comparative Examples 1 and 2 using a toner containing no strontium titanate, it was not detected.

Experimental example 2
The carrier charge assist effect by the reverse polarity particles and the range of effective addition amount will be discussed. FIG. 3 shows 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 carrier for bizhub C350 was mixed with a carrier having a different amount of reverse polarity particles so that the toner weight ratio would be 8% to obtain a developer. For each carrier having a different treatment amount of the reverse polarity particles, the toner charge amount is measured using the apparatus shown in FIG. 4, and the difference from the toner charge amount of the developer using the carrier not treated 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 weight of the toner adhering to the cylindrical electrode 34 was weighed with a precision balance to determine the charge amount of the toner. FIG. 3 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 2% by weight, 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 0.01% to 2% by weight in order to obtain the carrier charge assist effect. It turns out to be appropriate. The amount of the reverse polarity particles added is expressed as a ratio to the carrier.

Experimental example 3
A toner layer containing reverse polarity particles was formed on one of the parallel plate electrodes. As the toner, the toner B in Experimental Example 1 described above was used. The amount of strontium titanate, which is the reverse polarity particles contained in toner B, is 2% by weight. When the amount of reverse polarity particles separated by an electric field was evaluated from the toner layer formed on the electrode, the result shown in FIG. 5 was obtained. As shown in FIG. 5, the amount of the reverse polarity particles separated by the electric field rose from about 2.5 × 10 ⁶ V / m, and it was found that the amount of separation increased when the electric field was increased. From the above, it can be seen that an electric field of 2.5 × 10 ⁶ V / m or more is necessary to separate the reverse polarity particles contained in the toner by an electric field, and this improves the reverse polarity particle separation and recovery. It can be seen that application of an electric field of 2.5 × 10 ⁶ V / m or more is effective.

Examples 5-10
Toners D to I were prepared in the same manner as Toner B except that the external addition treatment described in Table 2 below was performed.

The toner D is obtained by removing the hydrophobic titanium oxide subjected to the external addition treatment from the toner B.
In the toner E, the reverse polarity particles of the toner D are changed to barium titanate having a number average primary particle size of 300 nm, and the rotation speed and processing time of the Henschel mixer are changed to 20 m / s for 3 minutes.
In the toner F, the number average primary particle diameter of the hydrophobic titanium oxide externally added to the toner B is reduced to 13 nm.
In the toner G, the number average primary particle diameter of the second hydrophobic silica of the toner D is increased to 40 nm.
The toner H is obtained by further removing the second hydrophobic silica from the toner D.
In the toner I, the particle size of the first hydrophobic silica of the toner H is increased to 20 nm.

  For the toners D to I, the toner charge amount was evaluated in the same manner as in Example 1. The results are shown in Table 3 below.

In Table 3, the toner charge amount change evaluation was ranked according to the following criteria.
○: Change amount is less than 3 μC / g.
Δ: Change amount is less than 3 to 5 μC / g.
Δ-: Change amount is less than 5-7 μC / g.

  In toners D and E, the effect of maintaining the charge is slightly reduced by removing hydrophobic titanium oxide (30 nm) from toner B. Further, in the toner F, when the hydrophobic titanium oxide is changed from the toner B to one having a small diameter, the effect of maintaining the charge is slightly lowered. Further, in the toner H, the effect of maintaining the charge was reduced by removing the second hydrophobic silica (20 nm).

  On the other hand, the toner G is obtained by increasing the diameter of the second hydrophobic silica of the toner D. In this case, the effect of maintaining the charge is improved.

  From the above, it can be seen that, in addition to the reverse polarity particles, as the external additive externally added to the toner, it is preferable that inorganic fine particles having a relatively large diameter and a number average primary particle size of 20 to 40 nm are contained. The reason for this is that the relatively large diameter particles are difficult to be fixed (embedded) in the toner, and the reverse polarity particles that are externally added the second time are prevented from coming into direct contact with the toner base material. This is presumably because it is presumably present as being externally added in an easy state, and the reverse polarity particles are easily detached from the toner under an alternating electric field and easily collected.

  In the case of Toner I, a slight amount of background fogging occurred. As a result of increasing the diameter of the first hydrophobic silica having a toner charging function to 20 nm, the initial average charge amount is lowered, the charge amount distribution is widened, and the low charge amount toner is increased. The effect of maintaining the charge is not much different from that of toner D and toner E, but in order to enhance the charging function, inorganic fine particles having a relatively small diameter and a number average primary particle size of 9 to 16 nm are also used. It can be seen that both are preferably externally added to the toner.

1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to an embodiment of the present invention. 6 is a graph showing a change in toner charge amount with respect to the amount of reverse polarity particles added to a carrier. It is a schematic block diagram which shows the measuring device of the amount of charge. It is a graph which shows the change of the amount of reverse polarity particle separation from toner by an electric field.

Explanation of symbols

1: image carrier, 2a: 2b: developing device, 3: charging member, 4: transfer roller, 5: cleaning blade, 6: developing area, 7: replenishing section, 11: developer carrier, 12: sleeve roller, 13: Magnet roller, 15: Restriction member, 16: Developer tank, 17: Bucket roller, 18: Casing, 19: Toner supply roller, 20: ATDC sensor, 21: Hopper, 22: Reverse polarity particle recovery member, 23: Supply toner, 24: developer, 25: toner carrier.

Claims (15)

  A developer tank containing toner, a carrier for charging the toner, and a developer containing particles having opposite polarity charged to a polarity opposite to the charging polarity of the toner, and the developer supplied from the developer tank on the surface A developer carrier that is carried on the developer carrier and a separation mechanism that separates the toner or the reverse polarity particles from the developer on the developer carrier, and the reverse polarity particles are collected in the developer tank. A developing device.   The separation mechanism includes a reverse polarity particle recovery member that separates and recovers the reverse polarity particles from the developer on the developer carrier, and is provided upstream of the development region in the developer carrier in the developer movement direction. 2. The developing according to claim 1, wherein the remaining developer on the developer carrying member from which the reverse polarity particles are separated by the reverse polarity particle collecting member develops the electrostatic latent image on the image carrying member. apparatus.   When the reverse polarity particles are positively charged, a voltage that is lower than the average value of the voltage applied to the developer carrier is applied to the developer carrier when the reverse polarity particles are negatively charged. The developing device according to claim 2, wherein a voltage having an average value higher than the average value of the applied voltages is applied to the reverse polarity particle recovery member.   An AC voltage is further applied to at least one of the developer carrying member and the reverse polarity particle collecting member, and a reverse polarity particle separation electric field composed of an AC electric field is formed between the reverse polarity particle collecting member and the developer carrying member. The developing device according to claim 3, wherein: The reverse polarity particle separation electric field having a maximum absolute value of 2.5 × 10 ⁶ V / m or more is formed between the reverse polarity particle recovery member and the developer carrying member. Development device.   The developing device according to claim 2, wherein the reverse polarity particle recovery member also serves as at least one of a regulating member and a casing of the developing device.   The separation mechanism includes a toner carrier that separates and carries the toner from the developer on the developer carrier, and is provided between the developer carrier and the image carrier and separated by the toner carrier. The developing device according to claim 1, wherein the toner develops the electrostatic latent image on the image carrier.   When the toner is negatively charged, the voltage that is higher than the average value of the voltage applied to the developer carrier is equal to the voltage applied to the developer carrier when the toner is positively charged. 8. The developing device according to claim 7, wherein a voltage having an average value lower than the average value is applied to the toner carrier.   9. The AC voltage is further applied to at least one of the toner carrier and the developer carrier, and a toner separation electric field composed of an AC electric field is formed between the toner carrier and the developer carrier. The developing device according to 1. The developing device according to claim 9, wherein a toner separation electric field having a maximum absolute value of 2.5 × 10 ⁶ V / m or more is formed between the toner carrier and the developer carrier.   In a developer tank containing a toner, a carrier for charging the toner, and a developer containing reverse polarity particles charged in the opposite polarity to the charging polarity of the toner, and in the developer supplied from the developer tank And a separation mechanism that separates the toner contained in the developer and the reverse polarity particles, and supplies the developer after the reverse polarity particle separation to the support. Alternatively, the developing device is characterized in that after the developer is supplied to the carrier, the reverse polarity particles are separated and at least the reverse polarity particles after being separated from the toner are collected in a developer tank.   The developing device according to claim 1, wherein toner having externally added reverse polarity particles is replenished.   The developing device according to claim 1, wherein the toner contains at least one inorganic fine particle having a number average primary particle size of 20 to 40 nm as an external additive.   The developing device according to claim 1, wherein the toner contains at least one inorganic fine particle having a number average primary particle size of 9 to 16 nm as an external additive.   The image bearing member, an electrostatic latent image forming unit for forming an electrostatic latent image on the image bearing member, and the electrostatic latent image on the image bearing member for developing the electrostatic latent image. An image forming apparatus.

Images