JP2010175764A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably charge a replenished toner and use it for developing even when forming an image at high speed by using a developing unit using the developer that contains toner and carrier. <P>SOLUTION: The developing unit 4 has the developer agitated and transported in a developer supplying section 42 for supplying the developer to a developer carrier 41 for supplying the toner in developer d to an image carrier 1. Then, toner density in the developer is detected by a first density detecting means 60 which is provided upstream of the transporting direction of the developer transporting path when the developer that is fed out from a feeding out opening 42a which is on the downstream side of the transporting direction of the developer is returned to the developer supplying section from a returning opening 42b by agitating and transporting in the developer transporting paths 44 to 47. Next, the necessary amount of toner is replenished while divided into a plurality of times to the portion of the developer in which the toner density is deteriorated from a toner replenishing means 61 that is provided on the downstream side by a first control means 63. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a composite machine of these, and in particular, in an image forming apparatus using a developing device using a developer containing toner and a carrier, the toner density is lowered. When new toner is replenished to the developed developer, the new toner is appropriately replenished to the portion of the developer whose toner density has decreased, and even when the image forming speed is increased. The toner is used for development in a state of being appropriately charged so that a good image can be stably obtained.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a composite machine of these, an image is carried by supplying toner from a developing device to an electrostatic latent image formed on an image carrier such as a photoconductor. The electrostatic latent image formed on the body is developed.

  As such a developing device, a one-component developing type developing device using only toner as a developer and a two-component developing type developing device using a developer containing toner and a carrier are known. The two-component developing system using a developer containing a toner and a carrier is excellent in that the toner is quickly and appropriately charged to form a high-speed image.

  Here, in a two-component developing type developing device using a developer containing toner and a carrier, the developer is generally conveyed while being stirred by a stirring and conveying member in a developer conveying path in the developing device. Then, the toner is charged by bringing the toner and the carrier into contact with each other, and the developer charged with the toner is led to a developer supplying unit that supplies the developer carrying member, and the developer supplying unit supplies the developer described above. The developer is supplied to the developer carrier, and the toner is supplied from the developer carrier to the electrostatic latent image formed on the image carrier for development, and the developer is agitated and conveyed in the developer supply unit. In this method, the developer is conveyed while being stirred so that the developer is circulated between the developer conveyance path and the developer supply unit.

  When toner is supplied from the developer carrier to the electrostatic latent image formed on the image carrier as described above and development is performed, the density of the toner in the developer gradually decreases, and an image is formed. Therefore, when the toner concentration in the developer decreases to some extent, new toner is supplied to the developer.

  Here, the new toner replenished in this manner is in an uncharged state, and the replenished toner is supplied from the developer supply unit to the developer carrier in a state where the replenished toner is not sufficiently charged and used for development. In other words, there are problems such as toner scattering and fogging in the formed image.

  For this reason, conventionally, as disclosed in Patent Document 1, a developer supply unit that supplies a developer to a developer carrying member while agitating and conveying the developer by the agitating and conveying member, and a developer by the agitating and conveying member It has been proposed to increase the length of the developer transport direction in the developer transport section to be stirred and transported, to increase the distance to transport the developer while mixing and stirring, and to sufficiently charge the replenished toner. Yes.

  In recent years, there has been a demand for image formation at high speed by increasing the image formation speed in the image forming apparatus.

  When the image is formed at such a high speed as described above, the length of the developer feeding direction in the developer supplying unit and the developer conveying unit is increased as described above to sufficiently charge the supplied toner. In order to supply the developer to the developer carrying member, it is necessary to lengthen the length of the developer supply unit and the developer transport unit very much, and the developing device becomes larger and the image forming apparatus There was a problem that the whole was enlarged.

  In addition, when replenishing new toner as described above, if the new toner is not properly replenished to the portion of the developer where the toner concentration has been lowered, only the toner concentration in the developer where the new toner has been replenished is obtained. Toner concentration in the developer that is abnormally high and used for development in the state where the new toner that has been replenished is not properly charged, or in the portion where the new toner has been replenished, and the developer in the portion where the toner density has decreased There is a problem that the difference between the two becomes large and density unevenness occurs in the formed image.

JP 2001-109265 A

  An object of the present invention is to solve various problems as described above in an image forming apparatus using a developing device using a developer containing a toner and a carrier.

  That is, according to the present invention, in the above image forming apparatus, when new toner is replenished to the developer having a lowered toner concentration, the new toner is appropriately applied to the portion of the developer having the lowered toner concentration. In addition to being replenished, even when the image forming speed is increased, the replenished toner is used for development in a properly charged state so that a good image can be stably obtained. It is to be an issue.

  In the present invention, in order to solve the above-described problems, in the developer supply unit that supplies the developer to the developer carrier that supplies the toner in the developer to the image carrier, the toner and the carrier are mixed. The developer contained is agitated and conveyed by the agitating and conveying member, and the developer sent from the delivery port located downstream in the developer conveying direction in the developer supply unit is agitated and conveyed by the agitating and conveying member in the developer conveying path. In the image forming apparatus using the developing device in which the developer is returned to the developer supply unit from the return port located upstream in the developer transport direction in the developer supply unit, the developer transport described above In order from the upstream side of the developer conveying direction in the path, a first density detecting means for detecting the toner density in the developer, a toner supplying means for supplying toner to the developer, and a toner in the developer Second density detecting means for detecting the degree of toner, and a toner amount required for replenishing toner from the toner replenishing means to the developer portion where the toner density detected by the first density detecting means is lowered is supplied a plurality of times. The first control means for replenishment is provided.

  In the image forming apparatus of the present invention, the second density detecting unit is provided with a second control unit that restricts image formation based on the toner density in the developer detected by the second density detecting unit. When the toner density in the developer detected by the above is out of the predetermined density range and when the fluctuation of the toner density is not less than the predetermined range, the image forming can be restricted by the second control means. .

  Further, in the image forming apparatus of the present invention, the developing device includes a plurality of the developer transport paths described above so that the replenished toner is appropriately charged even when the image forming speed is increased. Each of the developer transport sections, and an introduction section for guiding the developer to the next developer transport section is provided on the downstream side of the developer transport direction in each developer transport section, and the developer transport section in the final developer transport section It is preferable to use one provided with a return port for returning the developer to the upstream side in the developer conveyance direction in the developer supply unit on the downstream side in the conveyance direction.

  In the image forming apparatus of the present invention, as described above, the first density detecting means for detecting the toner density in the developer in order from the upstream side of the developer conveying direction in the developer conveying path of the developing device, and the developer A toner replenishing means for replenishing the toner and a second density detecting means for detecting the toner density in the developer, and the developer portion where the toner density detected by the first density detecting means is reduced, The first control means supplies the required amount of toner from the toner replenishing means in a plurality of times.

  As a result, new toner is replenished in a plurality of divided portions and dispersed over the entire portion of the developer having a reduced toner concentration, and a large amount of toner is supplied to the developer having a decreased toner concentration. Compared to a case where the toner is replenished as a whole, the replenished new toner is appropriately agitated with the carrier by the agitating / conveying member and appropriately charged in the developer conveying path.

  In addition, when the toner is replenished in a plurality of times as described above, even when the timing of replenishing the toner deviates from the developer portion where the toner concentration is lowered, the portion where the new toner is replenished The toner concentration in the developer is prevented from being abnormally high, and the replenished new toner is used for development in a state where it is not properly charged, or the developer and toner concentration in the portion where the new toner is replenished An increase in the difference in toner density between the developer and the developer in the lowered portion is suppressed, and uneven density and the like are prevented from occurring in the formed image.

  Further, as described above, there is provided second control means for restricting image formation based on the toner density in the developer detected by the second density detection means, and in the developer detected by the second density detection means. If the toner density is outside the predetermined density range and the fluctuation of the toner density is more than the predetermined range, the image formation is restricted, so that the formation of an image with an image defect such as density unevenness is suppressed, and a good image is always obtained. It can be obtained stably.

1 is a schematic explanatory diagram illustrating a state in which image formation is performed in an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic explanatory view showing the inside of a developing device used in the image forming apparatus according to the embodiment. In the image forming apparatus according to the above-described embodiment, a schematic explanatory view showing a state in which a necessary amount of toner is divided and replenished a plurality of times with respect to the developer portion where the toner density is lowered. In the image forming apparatus according to the above-described embodiment, when the necessary amount of toner is divided and replenished to the developer portion where the toner density is decreased, the timing for supplying the toner is shifted. It is a schematic explanatory drawing. In comparison with the image forming apparatus according to the above-described embodiment, an outline of a state in which the timing of supplying toner is shifted in supplying a necessary amount of toner to a developer portion having a lowered toner density at one time. It is explanatory drawing.

  Next, an image forming apparatus according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. Note that the image forming apparatus according to the present invention is not limited to those shown in the following embodiments, and can be implemented with appropriate modifications within a range not changing the gist thereof.

  In the image forming apparatus according to this embodiment, as shown in FIG. 1, the image carrier 1 made of a photosensitive drum is rotated, and the surface of the image carrier 1 is charged by the charging device 2. The surface of the image carrier 1 is exposed according to image information by a latent image forming apparatus 3 using a laser or the like, and an electrostatic latent image is formed on the surface of the image carrier 1.

  Then, toner is supplied from the developing device 4 to the portion of the electrostatic latent image formed on the surface of the image carrier 1 in this way, and a toner image corresponding to the electrostatic latent image is formed on the surface of the image carrier 1. After that, the recording sheet s is guided by the timing roller 6 between the image carrier 1 on which the toner image is formed and the transfer device 5, and is formed on the surface of the image carrier 1 by the transfer device 5. The toner image is transferred.

  Next, the recording sheet s to which the toner image is transferred in this way is guided between a pair of rollers 7a provided in the heating type fixing device 7, and the toner image is heated and fixed on the recording sheet s between the pair of rollers 7a. I try to let them.

  On the other hand, the cleaning member 8 is brought into pressure contact with the surface of the image carrier 1 after the toner image is transferred as described above, and the residue such as the toner remaining on the surface of the image carrier 1 after the transfer is removed. Thereafter, the image carrier 1 is charged by the charging device 2 as described above, and the above operation is repeated to continuously perform image formation.

  Here, in the developing device 4 in this embodiment, as shown in FIG. 1, the developer d containing the toner and the carrier is accommodated in the developing device 4 and is rotated as the developer carrying member 41. In the developing roller 41a, a magnet roller 41b provided with a plurality of magnetic poles N, S,... Is fixed and used.

  After the developer d is supplied from the developer supply unit 42 to the surface of the rotating developing roller 41a, the amount of the developer d supplied to the surface of the developing roller 41a is regulated by the regulating member 43. The developing roller 41a guides the developer d to a developing area facing the image carrier 1.

  The toner in the developer d thus guided to the development area by the developing roller 41a is supplied to the portion of the electrostatic latent image formed on the surface of the image carrier 1 as described above, and the image carrier After a toner image corresponding to the electrostatic latent image is formed on the surface of the body 1, the developer d on the surface of the developing roller 41 a is caused by the repulsive magnetic force between the N and N poles of the same polarity in the magnet roller 41 b. The developer is separated from the surface of the developing roller 41a and returned to the developer supply unit 42 described above.

  Here, in the developing device 4, as shown in FIGS. 1 and 2, the developer supply unit 42 and a discharge port 42 a on the downstream side in the transport direction of the developer d in the developer supply unit 42. A developer transport path constituted by four developer transport portions 44, 45, 46, 47 for transporting the guided developer d while stirring is partitioned by a partition wall 48. In addition, the developer d is transported to the developer supply section 42 and the first, second, third, and fourth developer transport sections 44, 45, 46, and 47 while stirring. Agitating and conveying members 52, 54, 55, 56, and 57 are provided.

  Then, the agitating and conveying member 52 provided in the developer supplying section 42 is rotated to convey the developer d in the developer supplying section 42 while stirring, and the developer d is supplied to the developing roller 41a as described above. While supplying the developer d, the developer d is transported to a discharge port 42a on the downstream side in the transport direction of the developer d in the developer supply unit 42, and the developer d is guided to the first developer transport unit 44 through the discharge port 42a. I have to.

  Further, in the developing device 4 described above, the first developer transport portion 44 through which the developer d is guided through the discharge port 42 a in this way is located farthest from the developer supply portion 42 and the developer supply portion 42. The second developer transport unit 45 disposed in parallel with the developer supply unit 42 is connected to the second developer transport unit 45, and the second, third, and fourth developer transport units 45, 46, and 47 are connected to each other. The second developer conveyance unit 45 is arranged in parallel so as to approach the developer supply unit 42 in order.

  Then, the agitating and conveying member 54 provided in the first developer conveying section 44 is rotated by a rotating device (not shown), and the developer d guided through the discharge port 42a is conveyed while being agitated. The developer d is guided to the second developer transport portion 45 through the first introduction portion 49a on the downstream side in the transport direction of the developer d.

  Further, the agitating and conveying members 55, 56, and 57 provided in the second, third, and fourth developer conveying portions 45, 46, and 47 are rotated so that the second, third, and fourth developers are conveyed. When the developer d is transported while being agitated in the units 45, 46, 47, the developer d is transported in the direction opposite to the developer supply unit 42 in the second and fourth developer transport units 45, 47. On the other hand, in the third developer transport section 46, the developer d is transported in the same direction as the developer supply section 42 described above.

  Here, as described above, the developer d is transported in the direction opposite to the developer supply unit 42 in the second and fourth developer transport units 45 and 47, while the development is performed in the third developer transport unit 46. In transporting the developer d in the same direction as the developer supply unit 42, in the developing device 4, the agitation transport member 52 provided in the developer supply unit 42 and the second, third, and fourth developer transport units. The gear transport mechanism 50 connects the agitating and conveying members 55, 56, and 57 provided at 45, 46, and 47.

  The gear mechanism 50 rotates the agitating and conveying members 52 and 56 in the developer supplying unit 42 and the third developer conveying unit 46 in the same direction so that the developer supplying unit 42 and the second developer conveying unit are rotated. While the developer d is conveyed in the same direction in the unit 46, the agitating and conveying members 55 and 57 in the second and fourth developer conveying units 45 and 47 are rotated in the opposite direction to the agitating and conveying members 52 and 56 described above. Thus, the developer d is conveyed in the opposite direction to the developer supply unit 42 and the third developer conveyance unit 46 in the second and fourth developer conveyance units 45 and 47. Although not shown, the stirring and conveying member 54 provided in the first developer conveying section 44 is replaced with the stirring and conveying member 55 provided in the second developer conveying section 45 and a gear mechanism (not shown). The stirring and conveying member 54 in the first developer conveying unit 44 can be rotated in conjunction with the agitating and conveying member 55 in the second developer conveying unit 45.

  In addition, a second introduction portion 49b that guides the developer d to the third developer conveyance portion 46 is provided on the downstream side in the conveyance direction of the developer d in the second developer conveyance portion 45, and this third development is performed. A third introduction portion 49 c that guides the developer d to the fourth developer transport portion 47 is provided on the downstream side in the transport direction of the developer d in the developer transport portion 46, and development in the fourth developer transport portion 47 is performed. On the downstream side in the transport direction of the developer d, a return port 42b for returning the developer d to the upstream side in the transport direction of the developer d in the developer supply unit 42 is provided.

  Then, as described above, the developer d introduced from the first developer transport section 44 to the second developer transport section 45 through the first introduction section 49a is passed through the introduction sections 49b and 49c. 3 to the fourth developer transport section, transport the developer d while stirring in the second, third, and fourth developer transport sections 45, 46, and 47, and supply the developer through the return port 42b. The developer 42 is returned to the upstream side in the conveyance direction of the developer d in the portion 42.

  Further, in this embodiment, as shown in FIGS. 1 and 2, the toner concentration in the developer d is set at the portion of the first developer transport portion 44 where the developer d is guided through the discharge port 42a. A first density detecting means 60 for detecting is provided, and development is performed through a toner replenishing port 61a as a toner replenishing means at a portion of the second developer conveying portion 45 downstream of the first density detecting means 60 in the conveying direction of the developer d. A toner replenishing device 61 for replenishing toner is provided in the device 4, and the toner concentration in the developer d is further provided in a portion of the fourth developer conveying portion 47 on the downstream side of the toner replenishing device 61 in the conveying direction of the developer d. The second concentration detecting means 62 for detecting the above is provided.

  When the first density detection means 60 detects a portion where the toner density in the developer d is reduced, this is output to the first control means 63, which is necessary for replenishment by the first control means 63. When the toner amount is calculated and the portion of the developer d having a lowered toner density is introduced to the toner replenishing port 61a, the first control means 63 causes the developer having a lowered toner density to be shown in FIG. The required amount of toner is supplied to the portion d from the toner replenishing device 61 in a plurality of times (three times in the example shown in the figure).

  In this manner, when a necessary amount of toner is divided and supplied to the portion of developer d having a lowered toner concentration, the toner thus replenished becomes the developer d having a lowered toner concentration. The toner concentration in the developer d in this portion is uniformly within a predetermined range while being quickly dispersed in the portion and being guided to the position of the second density detecting means 62 while stirring the developer d as described above. And the replenished toner is sufficiently charged.

  Even when the timing for replenishing the necessary amount of toner from the toner replenishing device 61 is deviated, the necessary amount of the developer d is reduced by the first control means 63 as described above. When the toner is replenished in a plurality of times, a certain amount of toner is replenished to the portion of the developer d having a lowered toner density as shown in FIG. 4, and the required amount is obtained as shown in FIG. Compared to the case where toner is replenished at a time, the toner concentration in the portion of developer d that has been replenished due to toner deviation does not increase significantly, and the developer d is agitated while stirring as described above. On the way to the position of the two-density detecting means 62, the toner concentration in the developer d in this portion becomes uniform within a predetermined range as in the above case, and the replenished toner It comes to be fully charged.

  For this reason, when the toner is replenished as described above with respect to the portion of the developer d where the toner concentration is lowered, the developer d in the portion where the toner is replenished in this way is supplied through the return port 42b. When the toner is returned to the portion 42, the toner concentration in the developer d in this portion becomes uniform within a predetermined range, and the supplied toner is returned to the developer supplying portion 42 in a sufficiently charged state. It becomes like this.

  As a result, in the image forming apparatus of this embodiment, in order to increase the image forming speed, the rotation speed of each of the agitating and conveying members 52, 54, 55, 56, and 57 is increased to increase the conveying speed of the developer d. Even when the speed is increased, the replenished toner is appropriately charged and the toner density in the developer d is uniformized, and a good image without density unevenness can be stably obtained.

  Further, in the image forming apparatus of this embodiment, the second density detecting means 62 detects the toner density in the developer d. In the second density detecting means 62 due to a toner replenishment error or the like. When it is detected that the toner density in the developer d is out of the predetermined density range or that the fluctuation of the toner density exceeds the predetermined range, this is output to the second control means 64, and this Image formation is restricted by the second control means 64.

  Here, when the image formation is restricted by the second control means 64, for example, when there is a portion where the toner density in the developer d is less than a predetermined density, or the toner density fluctuates within a range where one image is formed. If it is above the predetermined range, it is possible to stop the exposure by the latent image forming device 3 and prevent image formation until these portions are guided to and pass through the developer supply section 42. .

  If there is a portion where the toner density in the developer d exceeds a predetermined density, the latent image forming device 3 causes the toner to pass through the developer d until the developer d is guided to the developer supply section 42. The latent image portion to which the toner is supplied is increased, and a large amount of toner is supplied to the image carrier 1 from the developer d having a high toner concentration guided to the developer supply unit 42 to consume the toner in the developer d. On the other hand, the toner supplied to the image carrier 1 can be removed from the surface of the image carrier 1 by the cleaning member 8 without being transferred to the recording sheet s.

  In the image forming apparatus of this embodiment, the developer transport path for transporting the developer d guided to the discharge port 42a on the downstream side in the transport direction of the developer d in the developer supply section 42 while stirring is used as the developer transport path. Although the first to fourth developer conveying portions 44 to 47 are provided, the number of the developer conveying portions is not limited to four, and the developer is transported from the downstream side in the developer conveying direction in the final developer conveying portion. As long as the developer d is returned to the upstream side in the developer transport direction in the developer supply section 42 through the return port 42b, it is possible to provide more developer transport sections.

  Further, in the developing device 4 described above, the developer d is guided to the developing region facing the image carrier 1 by the developing roller 41a as described above, and the portion of the electrostatic latent image formed on the surface of the image carrier 1 In this case, the toner in developer d is supplied to develop the electrostatic latent image formed on the surface of image carrier 1, but only the toner in developer d held by developer roller 41a is used. Is held on a toner holding member (not shown), and toner is supplied from the toner holding member to a portion of the electrostatic latent image formed on the surface of the image carrier 1, so that the toner is formed on the surface of the image carrier 1. It is also possible to develop the electrostatic latent image. Further, although not shown, it is also possible to conduct development by guiding the developer to a developing area facing the image carrier with two or more developing rollers.

  Further, the developer d including the toner and the carrier used in the developing device 4 is not particularly limited, and a commonly used known developer can be used.

  Here, as the toner, a colorant in the binder resin, and if necessary, a charge control agent, a release agent, etc., which are treated with external additives can be used. Although not particularly limited, those of about 3 to 15 μm are desirable.

  And in manufacturing such a toner, it can manufacture by the well-known method generally used, for example, it can manufacture using a pulverization method, an emulsion polymerization method, a suspension polymerization method etc.

  In addition, as the binder resin used for the toner, a publicly known resin can be used. For example, a styrene resin (monopolymer or copolymer containing styrene or a styrene substitution product), a polyester resin, Epoxy resins, vinyl chloride resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins, and the like can be used, but are not limited to these. These resins can be used as a single substance or a composite, and 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. are preferably used.

  Further, as the above-mentioned colorant, publicly known publicly known ones can be used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue Ultramarine Blue, Rose Bengal, Lakey Red, etc. can be used, and it is generally preferable to use 2-20 parts by weight with respect to 100 parts by weight of the binder resin.

  As the above charge control agent, known ones can be used. Examples of charge control materials for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, Imidazole compounds, polyamine resins, etc. can be used, and charge control materials for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, Lixarene compounds can be used. In general, such a 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.

  Further, as the particles externally added to the toner, commonly used known particles can be used, and for example, silica, titanium oxide, aluminum oxide or the like is used as a fluidizing agent for improving the fluidity of the toner. In particular, it is preferable to use a silane coupling agent, a titanium coupling agent, a silicone oil or the like made water repellent. 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 fluidizing agent is preferably 10 to 100 nm.

  Further, as the carrier, a known carrier that is generally used can be used, and a binder-type carrier, a coat-type carrier, or the like can be used. The particle size of this carrier is not particularly limited, but is 15 to 100 μm. Is preferred.

  Here, the binder type carrier is one in which magnetic fine particles are dispersed in a binder resin, and positive or negative chargeable fine particles are fixed to the carrier surface or a surface coating layer is provided. You can also. Further, the charging characteristics such as the charging polarity of the binder type carrier can be controlled by the type of the binder resin material, the chargeable fine particles, and the surface coating layer.

  And as binder resin used for this binder type carrier, thermoplastic resin, such as vinyl resin represented by polystyrene resin, polyester resin, nylon resin, polyolefin resin, thermosetting properties, such as phenol resin, for example Resin can be used.

  Magnetic fine particles used for the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Magneto-plumbite type ferrite such as iron, iron or alloy particles having iron oxide on the surface can be used, and the shape thereof may be any of granular, spherical and acicular.

  In particular, when high magnetization is required for the binder type carrier, it is preferable to use iron-based ferromagnetic fine particles. In consideration of the chemical stability of the binder type carrier, 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. And the binder type | mold carrier which has desired magnetization can be obtained by selecting the kind and content of a ferromagnetic fine particle suitably. The magnetic fine particles are suitably added in an amount of 50 to 90% by weight in the binder type carrier.

  Moreover, as a material of said surface coating layer in a binder type | mold carrier, a silicone resin, an acrylic resin, an epoxy resin, a fluorine resin etc. are used, for example, these resin is coated on the surface, and it hardens | cures and forms a coating layer By doing so, the charge imparting ability can be improved.

  Further, in fixing the chargeable fine particles or the conductive fine particles to the surface of the binder type carrier, for example, after the binder type carrier and these fine particles are uniformly mixed and adhered to the surface of the binder type carrier. By applying mechanical and thermal impact force, these fine particles can be fixed by being driven into a binder type carrier. In this case, these fine particles are not completely embedded in the binder type carrier, but are fixed so as to protrude from the surface of the binder type carrier.

  Here, as the chargeable fine particles, organic or inorganic insulating materials can be used. Specifically, organic insulating materials such as polystyrene, styrene copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesins, and cross-linked products thereof, for example. Fine particles can be used. 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, and the like. As the inorganic insulating material, for example, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina can be used.

  In addition, the above-mentioned coated carrier is a carrier in which a resin coat layer is provided on the surface of carrier core particles made of a magnetic material. In this coated carrier, as in the binder-type carrier, Alternatively, negatively chargeable fine particles can be fixed.

  The charging characteristics such as polarity of the coat type carrier can be controlled by the type of the resin coat layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, a resin similar to the binder resin of the binder type carrier can be used for the resin of the resin coat layer.

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

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging device 3 Latent image forming device 4 Developing device 5 Transfer device 6 Timing roller 7 Fixing device 7a Roller 8 Cleaning member 41 Developer carrying member 41a Developing roller 41b Magnet roller 42 Developer supply portion 42a Discharge port 42b Return Port 43 Regulating member 44, 45, 46, 47 Developer conveying portion 48 Partition 49a, 49b, 49c Introducing portion 50 Gear mechanism 52, 54, 55, 56, 57 Stirring conveying member 60 First concentration detecting means 61 Toner replenishing device ( Toner supply means)
61a Toner supply port 62 Second density detecting means 63 First control means 64 Second control means d Developer s Recording sheet

Claims (4)

  The developer containing toner and carrier is agitated and conveyed by the agitating and conveying member in a developer supply unit for supplying the developer to the developer carrying body for supplying the toner in the developer to the image carrier, and this developer The developer sent from the delivery port located downstream in the developer conveyance direction in the supply unit is agitated and conveyed by the agitation conveyance member in the developer conveyance path, and upstream in the developer conveyance direction in the developer supply unit. In the image forming apparatus using the developing device in which the developer is returned to the developer supply unit from the return port located on the side, the developer in order from the upstream side in the developer transport direction in the developer transport path. A first density detecting means for detecting the toner density in the toner; a toner supplying means for supplying toner to the developer; and a second density detecting means for detecting the toner density in the developer. And a first control means for supplying a required amount of toner divided into a plurality of times for replenishing toner from the toner replenishing means to the developer portion where the toner density detected by the degree detecting means is lowered. Image forming apparatus.   2. The image forming apparatus according to claim 1, further comprising second control means for restricting image formation based on the toner density in the developer detected by the second density detecting means. apparatus.   3. The image forming apparatus according to claim 2, wherein the second control unit includes a case where the toner density in the developer detected by the second density detection unit is out of a predetermined density range, and the toner density. An image forming apparatus that restricts image formation when the variation is equal to or greater than a predetermined range.   4. The developing device according to claim 1, wherein the developer transport path in the developing device includes a plurality of developer transport units, and the developer transport direction in each developer transport unit. 5. An introduction section for introducing the developer to the next developer transport section is provided on the downstream side, and the developer is transported downstream in the developer transport direction in the final developer transport section, and the developer transport upstream in the developer supply section An image forming apparatus characterized in that a return port is provided to return to the position.

Images