JP4329563B2 - Developing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a developing device that develops an electrostatic latent image on an image carrier with toner using a two-component developer composed of toner and a magnetic carrier, and more particularly to a two-component developer. The present invention relates to a developing device that autonomously controls the toner density therein and an image forming apparatus using the same.

JP-A-63-225266 JP 07-333912 A Japanese Patent Laid-Open No. 09-022178 JP 2003-280281 A

  In general, as a developing device used in an image forming apparatus such as an electrophotographic system, an electrostatic latent image formed on an image carrier such as a photosensitive drum is visualized with a developer. Yes. As a developing method used in this type of developing device, a one-component developing method using only toner that is colorant particles as a developer, and a carrier that is magnetic particles and a toner that is colored particles are mixed as a developer. It is roughly classified into a two-component development method using a stirred one.

  2. Description of the Related Art Conventionally, as a two-component development type developing device, there are many excellent points such as image quality, maintainability and stability. Therefore, there is a magnetic brush developing method in which a developer in which toner is mixed in a magnetic carrier is conveyed and developed by a magnetic field Widely used. In this magnetic brush developing method, the toner is supported on the surface of the magnetic carrier by the electrostatic force generated by the friction between the toner and the magnetic carrier. When the toner approaches the electrostatic latent image on the image carrier, The electrostatic latent image is visualized by flying on the electrostatic latent image by an electric field formed between the electrostatic latent image carrier and the developer carrier. Further, the developer is repeatedly used while replenishing the toner consumed by the development.

  However, in such a magnetic brush developing method, if the toner concentration (mixing ratio of toner and magnetic carrier) is not controlled to be within a certain range, toner scattering and fogging occur when the toner concentration increases. On the other hand, when the toner density is reduced, density reduction, density spots, image omission, and the like occur. Therefore, it is necessary to keep the toner density constant in order to obtain a stable image.

  Therefore, in the conventional magnetic brush development method, in order to obtain a stable image, the toner density is detected using a toner density sensor, or a development patch is created to detect the toner development amount. Control is performed to keep the toner density constant by actuating it. For example, the toner density is detected by the toner density sensor, and after determining that the toner density has decreased based on the detection information, the toner supply is performed by the toner supply member.

  However, in this type of magnetic brush developing method, a toner density sensor and a toner replenishing member that can be independently driven ON / OFF are indispensable, and an increase in the size and cost of the developing device cannot be avoided. In addition, there is a problem that the toner density detection system is troublesome, such as creating a density patch to be detected.

  As a prior art for solving such a problem, there has already been proposed a developing device that keeps the toner density constant without using a toner density sensor or a toner replenishing member (see, for example, Patent Documents 1 to 4). Such a developing apparatus has a developer accommodating portion that accommodates a two-component developer, and a toner accommodating portion that communicates with the developer accommodating portion and accommodates toner, and the amount of the two-component developer on the developer carrier is reduced. The toner density is adjusted by regulating by the regulating member and autonomously controlling the toner intake of the two-component developer by changing the toner density of the two-component developer on the developer carrier.

  However, in each of the above prior arts, the toner concentration is controlled by the change in the volume of the developer corresponding to the change in the toner concentration and the movement of the developer. Needs to be active. Under such a demand, it is necessary to increase the developer density in the developer container around the developer carrier with a small amount of developer as compared with the normal two-component development method. The circulation is poor and there are portions where the developer moves actively and portions where the movement of the developer is not active, so that the toner is not uniformly taken up. Furthermore, if the magnetic carrier comes out of the main body of the developing device due to the deterioration of the charging performance or the magnetization characteristic and the amount of the magnetic carrier in the developer accommodating portion decreases, the toner amount ratio with respect to the magnetic carrier amount in the developer accommodating portion increases when the toner concentration is stable. Become. As a result, there has been a problem in that sufficient toner charging is not performed and soiling and toner scattering occur. In addition, since the amount of developer must be set low in advance because the amount of developer is small, the stress applied to one magnetic carrier is increased, the life of the magnetic carrier is shortened, and as a result, the running cost is reduced. There was also a problem of rising.

  In order to solve such a technical problem, the present inventors have previously disclosed in Japanese Patent Application No. 2003-185499 that a stable toner concentration is maintained even when the amount of the magnetic carrier is changed, so The present invention has proposed a developing device that can suppress scattering and can set a large amount of developer in advance, and that can reduce running costs, and an image forming apparatus using the developing device.

  However, in the above-described developing device, since the toner once supplied to the developer accommodating portion is stirred and then supplied to the developer carrier, a time delay is likely to occur for a large amount of continuous toner consumption. There was a problem.

  Therefore, the present invention has been made in view of the above problems, and can maintain the toner concentration stably even when the amount of the developer is decreased due to adhesion of the magnetic carrier to the photoreceptor, etc. An object of the present invention is to provide a developing device capable of realizing high responsiveness of toner supply even with rapid toner consumption and capable of reducing the cost by reducing the number of parts, and an image forming apparatus using the developing device.

  In order to achieve the above object, a developing device of the present invention includes a rotatable developer carrier that carries and conveys a two-component developer containing toner and a magnetic carrier by magnetic force, and a developer carrier that is adjacent to the developer carrier. A developer accommodating portion that accommodates the two-component developer, a toner accommodating portion that communicates with the developer accommodating portion via a toner replenishment passage, and that can supply toner through the toner replenishment passage, and a developer carrier. The layer thickness of the two-component developer carried and transported is regulated to a predetermined thickness, and a layer thickness regulating member that dams up excess developer, and upstream of the developer carrier relative to the layer thickness regulating member in the rotation direction A partition member that is disposed between the developer container and the toner container and introduces excess developer blocked by the layer thickness regulating member to the toner container according to the toner concentration. Toner density in the developer container In the developing device that autonomously adjusts the density so as to be constant, the partition member opposes the layer thickness regulating member in proximity to the developer carrier on the upstream side in the rotation direction of the developer carrier. A first facing portion, and a second facing portion that is opposed to the first facing portion in the vicinity of the developer carrying member on the upstream side in the rotation direction of the developer carrying member. And containing a two-component developer carried and transported by a developer carrier between the first facing portion and the second facing portion of the partition member and blocked by the first facing portion. The two-component developer is formed with a concave portion for natural circulation.

  The developing device configured as described above includes a developer carrier, a developer container, a toner container, a layer thickness regulating member, and a partition member, and the toner concentration in the developer container is constant. In the developing device that performs density adjustment autonomously, the partition member faces the developer carrying member in proximity to the layer thickness regulating member on the upstream side in the rotation direction of the developer carrying member. A first facing portion and a second facing portion facing the developer carrying body in the upstream of the rotation direction of the developer carrying body and facing the first facing portion; Between the first facing portion and the second facing portion of the member, the two-component developer carried and transported by the developer carrying member and blocked by the first facing portion is accommodated, and the two-component developer is accommodated. Since the recess is formed so that the developer circulates naturally, it is blocked by the first facing portion. By storing the two-component developer in the recess, it becomes possible to immediately supply the two-component developer to the developer carrying member when the toner is consumed rapidly. The responsiveness of the developing device during continuous formation of the toner is improved. In addition, since the natural circulation flow of the two-component developer is generated in the concave portion, the stirring member can be omitted, thereby providing a developing device capable of reducing the cost due to the reduction in the number of parts. it can.

  The outer periphery of the second facing portion of the partition member may form the toner replenishment path with the bottom of the developer accommodating portion.

  In this case, since the outer periphery of the second facing portion of the partition member forms a toner supply path with the bottom of the developer accommodating portion, the toner is supplied in the immediate vicinity of the developer carrier. Thus, the responsiveness of toner supply to rapid toner consumption is further improved.

  Further, the concave portion of the partition member has a volume that accommodates a developer amount such that at least the developer having a layer thickness regulated by the layer thickness regulating member covers the entire circumference of the developer carrier. Also good.

  In this case, the concave portion of the partition member has a volume that accommodates the developer amount so that at least the developer having the layer thickness regulated by the layer thickness regulating member covers the entire circumference of the developer carrying member. The amount of developer capable of supplying the developer is ensured in the concave portion of the partition member over at least the entire outer periphery of the developer carrying member, so that the toner is rapidly consumed due to the formation of a high-density image. Even in such a case, it is possible to provide a developing device that is highly responsive to supplying the developer.

  Furthermore, the gap between the first facing portion of the partition member and the developer carrying member may be narrower than the gap between the second facing portion of the partition member and the developer carrying member.

  In this case, since the gap between the first facing portion and the developer bearing member is narrower than the gap between the second facing portion and the developer bearing member, more of the first facing portion than the first facing portion. Along with the introduction of the two-component developer, a part of the introduced developer is reliably dammed by the first facing portion, and the accommodation and stirring of the damped two-component developer into the recess is smoother. Become.

  Still further, the partition member forms the first facing portion, the inclined plate that is inclined from the developer carrying member side to the toner accommodating portion side, and the second facing portion. And a horizontally disposed bottom plate.

  In this case, the partition member forms the first facing portion, the inclined plate that is inclined from the developer carrying member side to the toner accommodating portion side, and the substantially opposite surface that forms the second facing portion. The surplus developer blocked by the layer thickness regulating member is smoothly introduced to the outer peripheral side of the inclined plate by the inclined inclined plate, and the inside of the partition member is also provided. In the concave portion formed on the circumferential side, the two-component developer dammed up at the first facing portion falls by its own weight, collides with the bottom plate arranged substantially horizontally, and reflects, The developer flow conveyed by the developer carrier is combined with the developer, and the natural circulation flow of the developer can be generated more smoothly.

  In the above, the gap between the layer thickness regulating member and the developer carrier may be narrower than the gap between the first facing portion and the developer carrier.

  In this case, since the gap between the layer thickness regulating member and the developer carrier is narrower than the gap between the first facing portion and the developer carrier, more two-component development is performed with respect to the layer thickness regulating member. In addition to the introduction of the developer, the excess developer can be smoothly introduced into the toner storage unit or the developer storage unit via the partition member.

  An image forming apparatus according to the present invention includes the developing device.

  According to the present invention, the toner concentration can be stably maintained even when the amount of the developer is decreased due to, for example, the magnetic carrier adhering to the photoconductor, etc. It is possible to provide a developing device that is highly responsive to toner supply and can be reduced in cost by omitting a stirring member and an image forming apparatus using the same.

Embodiments of the present invention will be described below with reference to the drawings.
<First embodiment>

  First, a schematic configuration of an image forming apparatus including a developing device according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

  As shown in FIG. 1, an image forming apparatus 10 according to the present invention includes a photosensitive drum 21 on which a latent image due to a difference in electrostatic potential is formed by irradiating image light after uniform charging. Around this, a charging device 22 that uniformly charges the surface of the photosensitive drum 21, an exposure device 23 that irradiates the photosensitive drum 21 with image light to form a latent image on the surface, and the photosensitive drum 21. A transfer bias electric field is applied between the developing device 24 for selectively transferring the toner to the upper latent image to form a toner image, and the photosensitive drum 21 facing the photosensitive drum 21 with the recording medium 28 interposed therebetween. A transfer roll 26 to be generated and a cleaning device 29 for removing toner remaining on the photosensitive drum 21 after the transfer of the toner image are provided. The recording medium 28 is supplied from the upstream side of the facing portion (nip portion) between the photosensitive drum 21 and the transfer roll 26, and the unfixed image transferred onto the recording medium 28 is downstream. A fixing device 50 is provided that heats and melts the toner image and presses the toner image onto the recording medium 28. Here, the photosensitive drum 21 can be formed by forming a photosensitive layer made of an organic photosensitive material, an amorphous selenium photosensitive material, an amorphous silicon photosensitive material, or the like on the surface of a metal drum rotating in the direction of the arrow. . The charging device 22 uses, for example, a scorotron in which a high voltage is applied to a thin wire made of tungsten or the like, and a shield made of aluminum or the like spaced apart from the thin wire and a grid electrode having a gap on the photosensitive drum 21 side are arranged. it can. The exposure device 23 includes a laser writing device and an LED array, generates exposure light that blinks based on an image signal, and scans this in the main scanning direction of the photosensitive drum 21 by a polygon mirror. An electrostatic latent image is formed on the surface of the photosensitive drum 21. This electrostatic latent image is formed as a potential image by contrast with a high potential portion not exposed to light because the surface potential of the photosensitive drum 21 in the portion exposed to light is lowered. The developing device 24 accommodates a two-component developer composed of toner and magnetic carriers as colored particles in a housing 31, and supports the two-component developer on the developer carrier 32. By applying a developing bias from the bias power source 25, the developer carrier 32 is held at an intermediate potential between the high potential portion and the low potential portion of the electrostatic latent image, and the image portion of the electrostatic latent image is charged. The toner is developed with toner. Further, the transfer device 26 is constituted by, for example, a transfer roll disposed in contact with the photoconductive drum 21, and a transfer bias in a direction in which the toner image on the photoconductive drum 21 is attracted by the bias power source 27 is applied. The toner image on the photosensitive drum 21 is transferred to the recording medium 28. The toner remaining on the photosensitive drum 21 is removed by, for example, a doctor blade type cleaning device 29.

  Further, the fixing device 50 is, for example, a heat roll type, and includes a heating roll 51 and a pressure roll 52, and the recording medium 28 is passed between the heating roll 51 and the pressure roll 52, thereby toner. The image is fixed on the recording medium 28.

  Next, the basic configuration of the developing device according to the present embodiment will be described with reference to FIG. FIG. 2 is a configuration diagram showing an outline of the developing device 24 according to the present embodiment.

  As shown in FIG. 2, the developing device 24 includes a housing 31 that opens toward the photosensitive drum 21, and a developer carrier 32 is disposed facing the opening of the housing 31. Among these, a developer accommodating portion 33 that accommodates the two-component developer G is disposed in a portion adjacent to the developer bearing member 32, and a developer bearing member that is adjacent to the developer bearing member 32 and is located with respect to the developer accommodating portion 33. A two-component developer that has flowed out of the toner T and the developer retracting portion 34 and communicated with the developer carrying member 32 through the developer retracting portion 34 provided on the downstream side of the developer conveying direction 32 and the developer containing portion 33. A toner storage portion 35 for storing G is formed. Here, the developer carrier 32 includes a rotatable sleeve 321 that is rotatably formed, and a magnetic pole roll 322 that is fixedly disposed inside the rotatable sleeve 321 and includes a plurality of magnetic poles. Further, with respect to the development region where the photosensitive drum 21 and the developer carrier 32 are opposed to each other, the layer thickness regulation is performed so that the developer carrier 32 is opposed to the developer carrier 32 on the upstream side in the rotation direction. A member 41 is provided. The layer thickness regulating member 41 has the same width as that of the developer carrier 32, one end is supported by the housing 31, and the tip end portion is formed on the developer carrier 32 with a gap of about several tens μm to several hundreds μm. It is close. In the present embodiment, the two-component developer G is a developer composed of toner T and a magnetic carrier, and the toner T uses, for example, a non-magnetic toner. Magnetic toner may be used.

  The developer accommodating portion 33 has a space for accommodating the two-component developer G, and the bottom shape of the developer accommodating portion 33 is formed in a substantially square shape so as to cover the outer peripheral bottom portion of the developer carrier 32. ing.

  The toner container 35 is provided with a toner agitation / conveying member 351 for agitating and conveying the toner T to be accommodated and the two-component developer G flowing out from the developer retracting part 34. The two-component developer G flowing out from the toner T and the developer retracting portion 34 is swept out along the bottom wall surface of the toner containing portion 35 formed in a curved shape.

  Further, above the connecting portion between the developer containing portion 33 and the toner containing portion 35 and on the upstream side in the rotation direction of the developer carrying member 32 with respect to the layer thickness regulating member 41, the developer containing portion 33 and the developing portion are developed. A partition member 39 formed in a substantially U-shape is provided between the developer retracting portion 34 and the developer retracting portion 34 so as to partition the both and to cover the outer periphery of the developer carrying member 32 on the toner accommodating portion 35 side. The partition member 39 has a facing surface 39 s that faces the low wall surface of the developer accommodating portion 33, and includes a bottom plate 39 </ b> A disposed substantially horizontally and an end portion on the toner accommodating portion 35 side of the bottom plate 39 </ b> A. The side plate 39B extends in the vertical direction, and the inclined plate 39C is inclined from the upper end of the side plate 39B toward the developer carrier 32. Each of these plates 39A, 39B, and 39C is formed to have the same width as the developer carrier 32, and between the facing surface 39s of the bottom plate 39A and the bottom of the developer accommodating portion 33, A toner replenishment path 37 that enables toner replenishment from the toner containing portion 35 is formed, and the end 39d of the bottom plate 39A on the developer carrying member 32 side is close to the developer carrying member 32 and the second portion 39d. The opposite part is formed. Further, in the inclined plate 39C, the upper end portion 39u located on the developer carrier 32 side is upstream of the layer thickness regulating member 41 in the developer transport direction (upstream in the rotation direction of the developer carrier 32). The upper surface 39u forms a first facing portion with respect to the developer carrying member 32 while being arranged to face the surface of the developer carrying member 32 with a gap of several hundred μm to several mm. . Further, a bypass 45 is formed between the upper end 39 u and the housing 31 so that the developer blocked by the layer thickness regulating member 41 can flow into the developer retracting portion 34. The gap between the upper end 39 u of the partition member 39 and the developer carrier 32 is supplied to the layer thickness regulating member 41 in order to supply more two-component developer G. It is set wider than the gap with the body 32.

  Further, a concave portion 47 facing the outer peripheral surface of the developer carrier 32 on the toner accommodating portion 35 side is provided between the developer carrier 32 and the plates 39A, 39B, and 39C constituting the partition member 39. Is formed.

  The recess 47 has a storage capacity sufficient to supply the developer to the developer carrier 32 immediately when the toner is consumed rapidly. Specifically, it has at least a layer capacity that is regulated by the layer thickness regulating member 41 and has a developer volume accommodation volume that can cover the outer circumference (entire circumference) of the developer carrier 32. preferable.

  As a result, even when the toner is consumed rapidly, at least the amount of the developer that covers the outer periphery of the developer carrier 32 is transferred by the developer contained in the recess 47 disposed in the immediate vicinity of the developer carrier 32. Therefore, it is possible to improve the responsiveness of supplying the developer when the toner is rapidly consumed.

  Further, the gap between the side end 39d of the bottom plate 39A and the developer carrier 32 is set wider than the gap between the upper end 39u of the inclined plate 39C and the developer carrier 32.

  Thereby, a large amount of the two-component developer G is supplied to the gap between the inclined plate 39C and the developer carrier 32, and a part of the supplied developer is reliably dammed by the upper end portion 39u of the inclined plate 39C. The damped two-component developer G is accommodated in the recess 47, and a circulating flow of the two-component developer G can be generated in the recess 47.

  In order to generate the circulation flow of the two-component developer G, it has been confirmed that the circulation effect is higher when the bottom plate 39A is closer to the developer carrier 32. In addition, when this bottom part plate 39A does not exist, it has also been confirmed that the above-mentioned circulation flow does not occur.

  As schematically shown in FIG. 3, this is because the two-component developer G that could not pass through the gap between the upper end 39u of the inclined plate 39C, which is the first facing portion, and the developer carrier 32 is self-weighted. The developer flows onto the bottom plate 39A, collides with the bottom plate 39A and is reflected, and the gap between the side end 39d of the bottom plate 39A, which is the second opposing portion, and the developer carrier 32 is formed. The developer flow that passes and is conveyed by the developer carrier 32 is combined and circulated in the recess 47 formed by the inner peripheral surfaces of the bottom plate 39A, the side plate 39B, and the inclined plate 39C. It is thought that this is because a circulating flow is generated.

  Thus, by forming the concave portion 47 in the partition member 39, a circulating flow of the two-component developer G is generated, and thereby, the same effect as that provided by the stirring and conveying member in the developer containing portion 33 is obtained. It is possible to obtain such a stirring member. The shape of the recess 47 does not have to be substantially U-shaped as formed by the bottom plate 39A, the side plate 39B, and the inclined plate 39C as in the present embodiment. When the two-component developer G blocked by the facing portion falls by its own weight, it may be an arc-shaped recess having a lower end portion that collides and reflects.

  Next, an outline of the operation of the developing device 24 configured as described above will be described below.

  In FIG. 2, the two-component developer G in the developer accommodating portion 33 is captured by the magnetic pole disposed in the developer carrier 32 and is conveyed in the rotation direction of the developer carrier 32 (rotating sleeve 321). Is done. When the transported two-component developer G reaches the vicinity of the layer thickness regulating member 41, a spike is formed by the transport magnetic pole that acts as a trimming magnetic pole. By being regulated by the thickness regulating member 41, a developer layer is formed on the developer carrier 32, and this developer layer is conveyed to a development area facing the photosensitive drum 21. Further, the developer layer of the two-component developer G transported to the development area forms a magnetic brush by the magnetic attraction force of the developing magnetic pole, and the toner T in the two-component developer G that forms this magnetic brush is photosensitive. The electrostatic latent image on the photosensitive drum 21 is visualized by a developing electric field formed between the photosensitive drum 21 and the developer carrier 32.

  Here, in the developing device 24 according to the present embodiment, the gap between the upper end portion 39u of the partition member 39 and the developer carrier 32 is the gap between the downstream layer thickness regulating member 41 and the developer carrier 32. Therefore, the gap between the layer thickness regulating member 41 and the developer carrier 32 in the two-component developer G that has passed through the gap between the upper end portion 39u of the partition member 39 and the developer carrier 32 is set. As a result, surplus developer that cannot be passed through this gap is generated. When the toner concentration in the two-component developer G is high, the surplus developer that is blocked and cannot pass through the bypass 45 is more than the pressure at which it flows out to the developer retracting portion 34 via the bypass 45. The magnetic attraction force by the magnetic pole roll 322 trying to keep in the vicinity is overcome, and the excess developer does not flow out to the detour 45. On the other hand, when the toner concentration in the two-component developer G accommodated in the developer accommodating portion 33 decreases with toner consumption, the concentration of the magnetic carrier in the developer relatively increases, and the two-component developer Compared to the case where the toner density in G is high, the magnetic attractive force received from the external magnetic field of the developer increases. As a result, the developer carrying force of the developer carrying body 32 having the magnetic pole roll 322 is increased and the developer carrying force is increased, and the layer thickness regulating member 41 is used to dam the toner density in the two-component developer G. The pressure at which the surplus developer to be stopped flows out to the detour 45 is superior to the magnetic attractive force to be retained in the vicinity of the detour 45, and the surplus developer passes through the detour 45 and the developer is retracted on the partition member 39. It flows out to the part 34. That is, when the toner concentration in the developer is low, the two-component developer G flows out on the inclined plate 39C of the partition member 39 through the bypass 45, so that there is an empty space in the developer accommodating portion 33. As a result, the toner T on the toner container 35 side can be taken into the developer container 33 side through the toner supply path 37. On the other hand, when the toner concentration in the developer is high, the magnetic carrier concentration is relatively low, and the magnetization of the two-component developer G is weak, so that a large conveying force cannot be obtained. The pressure of the excess developer blocked by the thickness regulating member 41 becomes smaller than the magnetic attraction force to be held in the vicinity of the detour 45, and the developer does not flow out through the detour 45. As described above, the toner is supplied to the two-component developer G having a low toner concentration and is not supplied to the two-component developer G having a high toner concentration. The toner density in the two-component developer G in the section 33 is autonomously optimized. In a two-component developer that uses toner and a magnetic carrier, the toner concentration has a strong correlation with the charge amount. By optimizing the toner concentration, the toner charge amount can be optimized and the image density can be stabilized. Can be made.

  Further, by storing the two-component developer G blocked by the upper end portion 39u of the inclined plate 39C of the partition member 30 in the concave portion 47, when the toner is consumed rapidly, the two-component developer G is removed. It is possible to immediately supply the developer to the developer carrying member 32, thereby improving the responsiveness of the developing device 24 when continuously forming a high-density image. In addition, since the natural circulation flow of the two-component developer G is generated in the recess 47, it is possible to omit the stirring member, thereby providing a developing device capable of reducing the cost due to the reduction in the number of parts. be able to.

  In addition, the toner in the toner storage unit 35 or a high-concentration developer having a very high toner concentration is directly supplied to the vicinity of the developer carrier 32 via the toner replenishment path 37 to replenish the toner or the high-concentration developer. Is carried out at a position close to the developer carrying member 32, so that even with a large amount of continuous toner consumption, it is possible to supply toner or a high-density developer with high responsiveness without time delay.

  Next, the results of comparison verification with Comparative Configuration Example 1 and Comparative Configuration Example 2 based on the conventional configuration of the developing device 24 according to the present invention configured as described above will be described below as an example.

  First, the schematic configuration of the developing device according to Comparative Configuration Example 1 will be described with reference to FIG.

  As shown in FIG. 8, the main part of the developing device 100 according to the comparative configuration example 1 has a developing housing 131 that opens toward the photosensitive drum 120, and the developing roll faces the opening of the developing housing 131. 132 is provided, and a layer thickness regulating member 133 for regulating the layer thickness of the two-component developer G on the developing roll 132 is provided at the upper edge of the opening of the developing housing 131. A developer container 134 that contains developer G and a toner container 135 that communicates with the developing roll 132 via the developer container 134 and that contains toner are disposed at a portion adjacent to the developer container 134. Yes.

  In the developing device 100 configured as described above, when the toner concentration of the developer G is high, the developer volume is large and the developer stays in the vicinity of 134, but when the toner concentration of the developer G is low, the developer is high. As a result, the boundary line between the developer G and the toner moves to the stirring member 140 side. In the vicinity of the agitating member 140, the developer flows by the rotation of the agitating member 140, and the toner near the boundary line is drawn into the flow and taken into the developer G, and the toner density increases. By repeating this, the toner density is kept substantially constant. As a result, the toner charge amount and the development density are kept almost constant. However, in such an apparatus, since toner replenishment and non-replenishment are determined by the volume of the developer G, when the developer material decreases due to carrier adhesion to the photoreceptor or developer spillage, the same volume as in the initial state When the developer amount decreases with time, the toner concentration increases, and the toner charge amount decreases, resulting in the occurrence of background fogging due to the generation of reverse polarity toner. It was.

  Next, a schematic configuration of the developing device according to Comparative Configuration Example 2 will be described with reference to FIG.

  The developing device 200 of the comparative configuration example 2 improves the above-described problems in the comparative configuration example 1, and as shown in FIG. 9, the developing housing 231 that opens toward the electrostatic latent image carrier 221. The developer carrying member 232 is disposed facing the opening of the developing housing 231, and the two-component developer G is accommodated in a portion of the developing housing 231 adjacent to the developer carrying member 32. A developer accommodating portion 233; a developer retracting portion 234 that is adjacent to the developer carrying member 232 and provided downstream of the developer carrying member 232 in the developer transport direction with respect to the developer carrying portion 233; The toner container 232 communicates with the developer carrying member 232 via 233 and is configured by a toner container 235 that stores the toner T and the two-component developer G that has flowed out of the developer retracting part 234.

  In the developing device 200 configured as described above, as in the developing device 24 according to the present invention, when the toner concentration is high, the opening 250 is closed by the magnetic force of the developer. As the magnetic carrier concentration of the developer increases, the magnetization of the entire developer increases, and the conveying force by the developing roll 220 overcomes the force to close the opening 250 and the developer flows out of the opening 250. Due to this outflow, the amount of developer at the lower part of the partition plate 213 decreases, and the toner is supplied from the toner supply path 260. As a result, when the toner density of the developer increases, the magnetization of the developer decreases, and the developer conveyed by the developing roll 220 cannot be discharged from the opening 250. At this time, the toner replenishment path 260 is filled with the developer, and new toner is not replenished. By repeating this, the toner concentration in the developer is kept substantially constant. In this system, there is no problem even if the carrier enters the toner accommodating portion, and in the drawing, a developer including the carrier is shown by a cross in the lower part of the toner accommodating portion. That is, the high-concentration developer in which the carrier is mixed in the toner is replenished from the toner replenishment path 260. In this method, since the toner concentration does not depend on the amount of carrier existing in the developing device 200 in the initial stage, a large amount of carrier can be put in advance in anticipation that the developer decreases with time. However, this method has a problem in that since the toner is once replenished to the developer, stirred and supplied to the developing roll, there is a delay with respect to continuous large amount of toner consumption.

  Image formation (print test) using the developing device 100 according to the comparative configuration example 1 configured as described above, the developing device 200 according to the comparative configuration example 2 and the developing device 24 according to the present invention configured as described above. A comparative evaluation between the developing devices was performed.

  The conditions of the print test are shown below.

  The toner used was a pulverized polyester with a particle size of 9 μm, and the carrier used was a 50 μm coated carrier.

  The development bias was DC, the image portion side potential difference was set to 300V, and the background portion side potential difference was set to 100V.

  The gap between the developing roll and the photosensitive drum was 0.3 mm, and the peripheral speed ratio between the developing roll and the photosensitive drum was set to 2: 1.

  An image forming apparatus to which each developing device was attached and subjected to a print test was DocuPrint 360 manufactured by Fuji Xerox Co., Ltd.

  The toner density was measured by the blow-off method, and the image density was measured using X-RITE 404.

  Under these conditions, using these developing devices 24, 100, and 200, first, a change in toner density with time and a change in background fogging amount when A4 paper is continuously printed at an image density of 5%. Comparative verification was performed. FIG. 4 shows changes with time in the toner density, and FIG. 5 shows changes in the background fogging amount at that time.

  As shown in FIG. 4, in the developing device 100 according to the comparative configuration example 1, the toner concentration in the developer increases as the number of passing sheets increases, and in particular, after passing 5,000 sheets, It can be seen that this increase in toner density is noticeable. Similarly, as shown in FIG. 5, the background fogging amount is found to be extremely increased after passing 5,000 sheets in Comparative Configuration Example 1.

  This is because the amount of developer decreased as the number of sheets passed increased, resulting in a relative increase in toner density, accompanied by the occurrence of reverse polarity toner and the like, and an increase in background fog. Conceivable.

  Next, using these developing devices 24, 100, and 200, 20 sheets of A4 white paper were passed, and then 5 solid images with an image density of 100% were formed continuously, and then 20 sheets of white paper were passed. The toner density change and the solid image density change were compared and verified. The change in toner density is shown in FIG. 6, and the density change of the solid image before and after this is shown in FIG.

  Note that the density of a solid image after passing a blank sheet was measured by forming a 10 mm square patch in the image so as not to affect the toner density. The toner density was measured by taking out the developing device from the image forming apparatus every time one sheet was printed and sampling a very small amount of developer on the developing roll.

  As can be understood from FIG. 6, regarding the developing devices 100 and 200 in Comparative Example 1 and Comparative Example 2, it is understood that when a solid image is formed after the blank image is formed, the toner density rapidly decreases.

  This is considered to be due to a rapid delay in toner consumption, which caused a time delay because the developer supply was not in time, and the toner concentration in the developer was rapidly reduced accordingly.

  In contrast, it is understood that the developing device 24 according to the present invention maintains a stable toner density even with rapid toner consumption due to solid image formation after blank image formation.

  This is because the two-component developer G accommodated in the concave portion 47 provided in the partition member 39 and the toner supply path 37 close to the developer carrier 32 are responsive to the rapid supply of the developer even for rapid toner consumption. This is thought to be due to the improvement.

  Similarly, as shown in FIG. 7, regarding the developing devices 100 and 200 in Comparative Example 1 and Comparative Example 2, it is understood that when a solid image is formed after the blank image is formed, the image density is rapidly decreased. .

  In contrast, it can be seen that the developing device 24 according to the present invention maintains a stable image density even with rapid toner consumption due to solid image formation after blank image formation.

  This is because in the developing devices 100 and 200 according to the comparative configuration examples 1 and 2, it is considered that the image density of the formed image is decreased as the toner density is rapidly decreased. In the developing device 24 according to the invention, the toner concentration is kept constant, and the contained developer is sufficiently agitated and supplied by the concave portion 47 formed by the partition member 39, thereby preventing a change in image density. It is thought that this is because.

  As described above, according to the developing device 24 of the present invention, it is possible to suppress the occurrence of background fogging due to toner scattering and the like over time, and to stably maintain the toner concentration in the developer. It was verified that a high-quality image with little change in toner density and density change of the formed image can be obtained even with rapid toner consumption.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. 1 is a configuration diagram showing a configuration of an embodiment of an image forming apparatus according to the present invention. It is a figure which shows the flow of a developer typically. FIG. 6 is a diagram illustrating a change in toner density with time in each developing device when A4 paper is continuously printed at an image density of 5%. FIG. 6 is a diagram showing a change with time of a background fogging amount in each developing device when A4 paper is continuously printed at an image density of 5%. FIG. 10 is a diagram illustrating a change in toner density in each developing device when five continuous images having an image density of 100% are continuously formed after passing 20 A4 blank sheets and then 20 blank sheets are passed. . FIG. 10 is a diagram showing a density change of a solid image in each developing device when five continuous images having an image density of 100% are continuously formed after passing 20 A4 blank papers and then 20 blank papers are subsequently passed. is there. It is a block diagram which shows the structure of the developing device which concerns on the comparative structural example 1 based on a conventional structure. It is a block diagram which shows the structure of the image development apparatus which concerns on the comparative structural example 2 based on a conventional structure.

Explanation of symbols

  10: Image forming device, 21: Photosensitive drum, 22: Charging device, 23: Exposure device, 24: Developing device, 25: Bias power supply, 26: Transfer device, 27: Bias power supply, 28: Recording medium, 29: Cleaning device, 31: housing, 32: developer carrier, 33: developer accommodating portion, 34: developer retracting portion, 35: toner accommodating portion, 37: toner supply path, 39: partition member, 39A: bottom plate, 39B: Side plate, 39C: Inclined plate, 39u: Upper end, 39d: Side end, 39s: Opposing surface, 41: Layer thickness regulating member, 45: Detour, 47: Recess, 50: Fixing device, 51: Heating roll, 52: Pressure roll

Claims (7)

A rotatable developer carrying member for carrying and conveying a two-component developer containing toner and a magnetic carrier by magnetic force, a developer containing portion for containing the two-component developer adjacent to the developer carrying member, and development The toner accommodating portion communicates with the developer accommodating portion via the toner replenishing passage, and the layer thickness of the two-component developer carried and conveyed by the developer carrying member is set to a predetermined thickness. A layer thickness regulating member that blocks excess developer, and upstream of the layer thickness regulating member in the rotation direction of the developer carrying member, between the developer accommodating portion and the toner accommodating portion. And a partition member that introduces excess developer blocked by the layer thickness regulating member to the toner containing portion side according to the toner concentration so that the toner concentration in the developer containing portion becomes constant. Development device that adjusts the density autonomously In,
The partition member includes a first facing portion facing the developer carrying member in proximity to the layer thickness regulating member on the upstream side in the rotation direction of the developer carrying member, and the first facing portion. In contrast, a second facing portion facing the developer carrying member in the vicinity of the developer carrying member on the upstream side in the rotation direction of the developer carrying member,
Between the first facing portion and the second facing portion of the partition member, the two-component developer carried and transported by the developer carrying member and blocked by the first facing portion is accommodated. A developing device in which a recess is formed so that the two-component developer circulates naturally.   2. The developing device according to claim 1, wherein an outer periphery of a second facing portion of the partition member forms the toner supply path with a bottom portion of the developer accommodating portion.   The concave portion of the partition member has a volume that accommodates a developer amount such that at least the developer of the layer thickness regulated by the layer thickness regulating member covers the entire circumference of the developer carrier. The developing device according to claim 1, wherein the developing device is characterized in that:   2. The gap between the first facing portion of the partition member and the developer carrying member is narrower than the gap between the second facing portion of the partition member and the developer carrying member. The developing device according to claim 3.   The partition member forms the first facing portion, and is disposed in a substantially horizontal manner that forms an inclined plate inclined from the developer carrying member side to the toner accommodating portion side, and forms the second facing portion. The developing device according to claim 1, further comprising a bottom plate that is formed.   6. The gap between the layer thickness regulating member and the developer carrier is narrower than the gap between the first facing portion and the developer carrier. Development device.   An image forming apparatus comprising the developing device according to claim 1.

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