JP5374958B2 - Developing device, image forming apparatus, and developing method - Google Patents

Abstract

The present invention provides a developing device which uses a toner supporting roller which is provided with concaves and projections on a using surface, an image forming device and a developing method thereof, wherein the leakage, the diffusion of toner from the toner supporting roller and the image fog are reduced. The developing device comprises the following components: a storing part for storing toner; the toner supporting roller which is formed to an approximate cylinder that is provided with a plurality of projections regularly configured on the surface and convex surrounding the plurality of projections, supports the toner layer which is supplied from the storing part and is formed by the electrified toner at the surface and rotates simultaneously; and a restricting component which abuts on the surface of the toner supporting roller for forming a restricting clamping part and restricts the thickness of the toner layer supported on the surface of the toner supporting roller. The restricting component eliminates the toner layer of the projections from the toner layer supported by the surface of the toner supporting roller at the upstream end of the restricting clamping part in the rotation direction of the toner supporting roller.

Description

  The present invention relates to a developing device having a toner carrying roller for carrying toner on its surface, an image forming apparatus, and a developing method for developing an electrostatic latent image with toner using the roller.

  As a technique for developing an electrostatic latent image with toner, there is a technique in which toner is carried on the surface of a toner carrying roller formed in a substantially cylindrical shape. In order to improve the characteristics of the toner carried on the surface of such a toner carrying roller, the applicant of the present application has regularly arranged protrusions on the surface of the roller formed in a cylindrical shape, and the periphery of the protrusions. The structure of the toner-carrying roller provided with a concave portion surrounding the toner was previously disclosed (see Patent Document 1). Such a structure has an advantage that the thickness and charge amount of the toner layer carried on the roller surface can be easily controlled because the uneven pattern on the surface is controlled and uniform.

JP 2007-127800 A (FIG. 7)

  However, when the toner carrying roller having the above-described structure is used, the unevenness is uniform. Therefore, if the toner layer thickness on the toner carrying roller is not strictly controlled, The occurrence of fog is a problem. According to the study by the present inventor, one of the main causes of these phenomena is that when old toner having deteriorated characteristics with use is mixed with new toner having good characteristics, particularly on the surface of the toner carrying roller. It is considered that the old toner is easily carried on a layer away from the toner. The toner layer away from the surface of the toner carrying roller has a weak adhesive force to the toner carrying roller, so that toner leakage, scattering, and fogging are likely to occur.

  The present invention has been made in view of the above problems, and in a developing device, an image forming apparatus, and a developing method using a toner carrying roller having a concavo-convex surface, toner leakage, scattering, and fog from the toner carrying roller are reduced. For the purpose.

In order to achieve the above object, the developing device according to the present invention is formed in a substantially cylindrical shape having a storage portion for storing toner, a plurality of regularly arranged convex portions, and a concave portion surrounding the convex portions on the surface. A toner carrying roller that rotates while carrying a toner layer of charged toner supplied from the housing portion on the surface thereof, and forms a regulating nip in contact with the surface of the toner carrying roller, and the toner carrying roller in the regulating nip A regulating member that regulates the thickness of the toner layer carried on the surface, and the regulating member is formed of an elastic body, and includes an elastic contact body that is pressed against the surface of the toner carrying roller to form the regulating nip. An upstream end portion of the elastic contact member at the upstream end portion of the regulating nip in the rotation direction of the toner carrying roller. And it abuts the toner carrying roller surface has been the toner of the convex portion is removed out of the toner layer carried on the difference in height between said convex portion and the concave portion is on the volume average particle diameter or less of the toner. In the first aspect of the developing device according to the present invention, the distance between the elastic contact body and the recess in the regulation nip is 1 to 3 times the volume average particle diameter of the toner. In the second aspect, an interval between the elastic contact body and the recess in the regulation nip is equal to or greater than a maximum particle size of the toner .

  Although described in detail later, the knowledge obtained by the inventor based on various experiments will be briefly described. Of the toner carried on the surface of the toner carrying roller, new toner having good characteristics (hereinafter referred to as “new toner”) is accumulated near the surface of the toner carrying roller, and is laminated on these toners. The toner carried away from the surface of the toner carrying roller contains a lot of toner (hereinafter referred to as “old toner”) whose characteristics have deteriorated with long-term use. That is, a toner layer mainly composed of new toner is first formed on the surface of the toner carrying roller, and a toner layer containing a large amount of old toner is further formed on the surface. Since such old toner has little contact with the toner carrying roller, a sufficient charge amount cannot be obtained, causing leakage, scattering, or fogging.

  Therefore, in the present invention, the toner layer on the convex portion of the toner carrying roller is removed by the regulating member from the toner layer formed on the surface of the toner carrying roller. In this way, the new toner having a high charge amount out of the toner removed from the convex portion acts to push out the old toner having a weak charge amount carried on the concave portion and a weak electrostatic adsorption force to the toner carrying roller. To do. As a result, since the ratio of the old toner contained in the regulated toner layer is reduced, the occurrence of toner scattering and fogging can be suppressed.

  Further, when pressure is applied to the old toner having a low charge amount, the toner particles aggregate to form a large-diameter and low-charge aggregate, and this aggregate may leak out of the developing device. However, in the present invention, since the toner is only carried on the concave portion of the surface of the toner carrying roller, the toner carried on the concave portion is not pressurized by the regulating member. For this reason, not only the aggregate formed by aggregation of the old toner is hardly generated, but also the progress of the toner deterioration itself can be suppressed, and this also has the effect of suppressing the scattering of the toner to the outside of the developing device. can get.

  As a configuration for embodying the above, for example, the height difference between the convex portion and the concave portion is set to be equal to or larger than the volume average particle diameter of the toner, and the regulating member is formed of an elastic body on the surface of the toner carrying roller. An elastic contact body that is pressed to form the regulating nip, and an upstream end of the elastic contact body in a rotation direction of the toner carrying roller is in contact with the convex portion of the toner carrying roller. A part that scrapes off the toner of the part can be used.

According to such a configuration, one or more layers of toner can be carried in the concave portion, while the toner on the convex portion is scraped off by the elastic contact member. The scraped toner having a high charge amount pushes out the old toner carried on the toner carrying roller in front of the regulation nip in the rotation direction of the toner carrying roller. As a result, the toner is carried only in the recesses behind the regulating nip, and the ratio of the old toner contained therein is reduced, so that the occurrence of toner scattering and fogging can be suppressed. By setting the interval between the elastic contact body and the recess in the regulation nip to be equal to or larger than the volume average particle diameter of the toner, it is possible to reliably carry one layer of toner in the recess. On the other hand, if the distance between the elastic contact body and the concave portion is too large, a large amount of toner is carried by the concave portion, and the amount of old toner contained therein is also increased. Therefore, if the distance between the elastic contact body and the concave portion is set to, for example, three times or less of the volume average particle diameter of the toner, the amount of toner carried in the concave portion can be limited to an appropriate amount. Further, the interval between the elastic contact body and the recess in the regulation nip may be greater than or equal to the maximum particle size of the toner. Here, the maximum particle diameter of the toner can be defined as, for example, a value obtained by adding three times the geometric standard deviation to the number-based 50% particle diameter value in the toner particle size distribution. This is because the currently produced toner has a small variation in particle size, and the ratio of toner particles having a particle size exceeding this value is extremely low. According to such a configuration, almost all of the new toner accommodated in the accommodating portion can be carried on the toner carrying roller, and toner having a large particle diameter can be prevented from staying in the accommodating portion. Here, it is desirable that the top surfaces of the plurality of convex portions form part of the same cylindrical surface, that is, the envelope surface formed by the top surfaces of the plurality of convex portions is one cylindrical surface. Thereby, since the toner carrying roller can be regarded as a rotating cylinder on a macroscopic basis, the contact pressure with the regulating member in the circumferential direction can be made constant .

  In this configuration, it is preferable that the upstream end surface of the elastic contact body in the rotation direction of the toner carrying roller is erected substantially perpendicular to the surface of the toner carrying roller. By doing so, it is possible to prevent the toner adhering to the convex portion from being drawn into the regulating nip and being pressed by the elastic contact body to be aggregated or fixed to the surface of the toner carrying roller. Further, the toner scraped off from the surface of the toner carrying roller by the elastic contact member stays in the vicinity of the upstream end surface of the elastic contact member, so that the replacement of the old toner with the new toner on the toner carrying roller surface is further promoted. Therefore, the ratio of the old toner remaining on the surface of the toner carrying roller after the regulation can be further reduced.

  For example, the distance between the elastic contact body and the recess in the regulation nip can be greater than or equal to the sum of the volume average particle diameter and the maximum particle diameter of the toner. In this way, it is possible to carry a toner particle having the maximum particle size on the surface of the concave portion, and further, the toner having a large particle size that has entered the concave portion is pressed by the elastic contact body. It is possible to prevent problems such as degradation and aggregation. Further, such a large particle diameter toner can be contributed to development efficiently.

  Further, it is preferable that the deformation amount of the elastic contact body that is elastically deformed by contact with the toner carrying roller is maximized at an upstream end portion in the rotation direction of the toner carrying roller. The elastic contact body is elastically deformed by pressing the elastic contact body against the surface of the toner carrying roller. More specifically, when the elastic contact body is pressed against the surface of the convex portion and the portion is elastically depressed, the thickness of the elastic contact body in the direction perpendicular to the surface of the toner carrying roller is reduced. The “deformation amount of the elastic contact body” referred to in the present invention represents the reduction amount of the thickness. When this is viewed microscopically, the amount of contraction of the elastic contact body at the portion facing the concave portion of the toner carrying roller is smaller than the amount of contraction at the portion pressed against the convex portion. That is, in the space above the recess, the surface of the elastic contact body is bent toward the bottom of the recess. The elastic contact body bent in this way pressurizes the toner carried in the recess. The amount of bending of the elastic contact body into the recessed space is considered to increase as the deformation amount of the elastic contact body viewed macroscopically increases. Further, the larger the deformation amount of the elastic contact body, the greater the contact pressure against the convex portion.

  Here, as described above, if the amount of deformation of the elastic contact member is maximized at the upstream end portion in the rotation direction of the toner carrying roller, the contact pressure on the convex portion becomes the upstream end portion of the regulation nip. And the toner can be removed more reliably from the convex portion. In addition, since the amount of the elastic contact body to be bent into the concave portion is reduced toward the downstream side in the regulating nip, the pressure on the toner carried in the concave portion is weakened toward the downstream side in the regulating nip, and unnecessary pressure is applied to the toner. Can be avoided.

Further, for example, the height difference between the convex portion and the concave portion may be twice or more the volume average particle diameter of the toner.

  In the invention configured as described above, since the toner on the convex portion of the surface of the toner carrying roller is removed by the regulating member, similarly to the developing device described above, the toner with insufficient charge amount leaks or scatters. Can be suppressed. On the other hand, two or more layers of toner can be carried in the concave portion of the toner carrying roller. For this reason, there is toner that is carried in the concave portion without being in direct contact with the surface of the toner carrying roller. By making it possible to carry such toner on the toner carrying roller, in the present invention, it is possible to obtain an effect of improving the developing efficiency when developing the electrostatic latent image.

  In the developing device of each aspect described above, the surface of the toner carrying roller may be formed of a conductive material. According to the experiment by the present inventor, the above phenomenon, that is, a phenomenon in which a layer mainly composed of new toner and a layer mainly composed of old toner are laminated on the surface of the toner carrying roller (hereinafter referred to as “layer separation phenomenon”). Is particularly prominent when the surface of the toner carrying roller is formed of a conductive material. If the idea of the present invention is applied to the developing device having such a configuration, it is more effective.

  The effect of the present invention is also remarkable when the storage unit has a supply port for supplying toner from the outside. In the developing device having such a configuration, a phenomenon may occur in which a large amount of new toner is injected from the replenishing port with respect to the old toner in the storage unit that has been used for a long time. In such a case, the above-described layer separation phenomenon is likely to occur, and toner scattering and fogging are likely to occur. By applying the concept of the present invention to the developing device having such a configuration, it is possible to suppress toner scattering and fogging.

  The storage section includes a plurality of toner storage chambers for storing toner, and at least a part of the surface of the toner carrying roller is exposed inside one of the plurality of toner storage chambers. The same applies to a case where a toner transfer mechanism is provided for feeding toner stored in another toner storage chamber to one toner storage chamber. Even in such a configuration, the new toner is sent from the other toner storage chambers to the old toner in the vicinity of the toner carrying roller.

  In addition, the present invention is applicable to the case where a toner having a volume average particle size of 5 μm or less is used, or the particle size of an external additive added to the toner in order to improve the fluidity of the toner is 50 nm or less and the toner base particles are coated. A particularly remarkable effect is obtained when a toner having a rate of 100% or more is used. For example, when the volume average particle diameter of the toner is 5 μm or less, the van der Waals force between the toner particles becomes strong, so that the old toner tends to adhere to the toner layer on the toner carrying roller. Even in such a case, the old toner is likely to be scattered or fogged, so that the effect of the present invention is increased. Further, in the toner to which the above external additive is added, since the change in the fluidity of the toner with time is large, the layer separation phenomenon is particularly likely to occur, so that the effect when the present invention is applied is great.

In order to achieve the above object, an image forming apparatus according to the present invention has an image carrier that carries an electrostatic latent image, a plurality of regularly arranged convex portions, and concave portions that surround the convex portions on the surface. A toner carrying roller which is formed in a substantially cylindrical shape and carries a toner layer of charged toner on the surface thereof , and the convex portion of the toner layer which is in contact with the surface of the toner carrying roller and carried on the surface of the toner carrying roller A developing device having a regulating member that removes the toner layer, and the regulating member has an elastic contact body that is formed of an elastic body and is pressed against the surface of the toner carrying roller to form a regulating nip, At the upstream end portion of the regulation nip in the rotation direction of the toner carrying roller, the upstream end portion of the elastic contact body comes into contact with the convex portion of the toner carrying roller, and the toner carrying roller The toner on the convex portion of the toner layer carried on the surface of the roller is removed, and the height difference between the convex portion and the concave portion is equal to or greater than the volume average particle diameter of the toner, and the elastic contact in the regulation nip is increased. The distance between the contact body and the concave portion is 1 to 3 times the volume average particle diameter of the toner .

According to another aspect of the image forming apparatus of the present invention, in order to achieve the above object, an image carrier that carries an electrostatic latent image, a plurality of regularly arranged convex portions, and surrounding the convex portions. A toner carrying roller which is formed in a substantially cylindrical shape having a concave portion on its surface and carries a toner layer of charged toner on its surface, and a toner layer carried on the surface of the toner carrying roller in contact with the surface of the toner carrying roller A developing device having a regulating member that removes the toner layer of the convex portion, and the regulating member is formed of an elastic body, and an elastic contact body that is pressed against the surface of the toner carrying roller to form a regulating nip. An upstream end of the elastic contact member abuts on the convex portion of the toner carrying roller at an upstream end of the restriction nip in the rotation direction of the toner carrying roller, The toner of the convex portion is removed from the toner layer carried on the surface of the toner carrying roller, and the height difference between the convex portion and the concave portion is equal to or larger than the volume average particle diameter of the toner, and the elasticity in the regulation nip The distance between the contact body and the concave portion is greater than the maximum particle size of the toner .

In order to achieve the above object, the developing method according to the present invention has, on the surface, a plurality of regularly arranged convex portions and concave portions surrounding the convex portions on the surface of the image carrier carrying the electrostatic latent image. substantially cylindrical shape formed with the toner carrying roller disposed face to face bearing the toner layer by the charged toner on the surface thereof, the electrostatic latent image is developed by the toner, prior Symbol the image bearing member and the counter of the toner layer having Prior to the toner layer, a toner layer is supported on the convex portion and the concave portion on the surface of the toner carrying roller, and the toner layer on the convex portion is removed by a regulating member in contact with the surface of the toner carrying roller. In addition, the restricting member has an elastic contact body that is formed of an elastic body and is pressed against the surface of the toner carrying roller to form a restricting nip, and is arranged in the rotation direction of the toner carrying roller. The upstream end portion of the elastic contact member abuts the convex portion of the toner carrying roller at the upstream end portion of the regulation nip, and the convex portion of the toner layer carried on the toner carrying roller surface. The height difference between the convex portion and the concave portion is equal to or greater than the volume average particle size of the toner, and the distance between the elastic contact body and the concave portion in the regulation nip is the volume of the toner. It is characterized by being 1 to 3 times the average particle size .

  According to these inventions, as in the developing device described above, the amount of old toner carried on the toner carrying roller can be reduced, and toner scattering and fogging from the toner carrying roller can be suppressed.

  FIG. 1 is a diagram showing a first embodiment of an image forming apparatus to which the present invention is applied. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus forms a full color image by superposing four color toners (developers) of yellow (Y), cyan (C), magenta (M), and black (K), or only black (K) toner. The image forming apparatus forms a monochrome image using In this image forming apparatus, when an image signal is given to the main controller 11 from an external device such as a host computer, the CPU 101 provided in the engine controller 10 controls each part of the engine unit EG in response to a command from the main controller 11. Then, a predetermined image forming operation is executed, and an image corresponding to the image signal is formed on the sheet S.

  In the engine unit EG, the photosensitive member 22 is provided to be rotatable in the arrow direction D1 in FIG. A charging unit 23, a rotary developing unit 4 and a cleaning unit 25 are arranged around the photosensitive member 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes the toner remaining on the surface of the photosensitive member 22 after the primary transfer, and collects it in a waste toner tank provided inside. The photosensitive member 22, the charging unit 23, and the cleaning unit 25 integrally constitute the photosensitive member cartridge 2, and the photosensitive member cartridge 2 is detachably attached to the apparatus main body as a whole.

  Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 22 charged by the charging unit 23. The exposure unit 6 exposes the light beam L onto the photosensitive member 22 in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided about a rotation axis center orthogonal to the paper surface of FIG. A yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Based on the control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoreceptor 22 or have a predetermined gap. When the developing roller 44 is positioned at a predetermined developing position facing the space, the developing roller 44 provided in the developing unit and carrying the toner of the selected color is disposed to face the photosensitive member 22, and the developing roller 44 is disposed at the facing position. Then, toner is applied to the surface of the photosensitive member 22. As a result, the electrostatic latent image on the photosensitive member 22 is visualized with the selected toner color.

  FIG. 3 is a view showing the appearance of the developing device. FIG. 4 is a cross-sectional view showing the structure of the developing device. Each of the developing devices 4Y, 4C, 4M, and 4K has the same structure. Therefore, although the structure of the developing device 4K will be described in more detail with reference to FIGS. 3 and 4, the structures and functions of the other developing devices 4Y, 4C, and 4M are the same. In the developing device 4K, a supply roller 43 and a developing roller 44 are axially attached to a housing 41 that accommodates toner T therein. When the developing device 4K is positioned at the developing position, the developing roller 44 is photosensitive. While being in contact with the body 2 or opposed to each other with a predetermined gap, these rollers 43 and 44 are engaged with a rotation driving unit (not shown) provided on the main body side and rotated in a predetermined direction. . The supply roller 43 is formed in a cylindrical shape by an elastic material such as foamed urethane rubber or silicon rubber. The developing roller 44 is formed in a cylindrical shape from a metal such as copper, aluminum, or stainless steel or an alloy. Then, when the two rollers 43 and 44 rotate while being in contact with each other, the toner is rubbed against the surface of the developing roller 44 and a toner layer having a predetermined thickness is formed on the surface of the developing roller 44. In this embodiment, negatively charged toner is used, but positively charged toner may be used.

  The internal space of the housing 41 is partitioned into a first chamber 411 and a second chamber 412 by a partition wall 41a. Both the supply roller 43 and the developing roller 44 are provided in the second chamber 412, and the toner in the second chamber 412 flows and is stirred and supplied to the surface of the developing roller 44 as these rollers rotate. On the other hand, since the toner stored in the first chamber 411 is isolated from the supply roller 43 and the developing roller 44, the toner does not flow due to their rotation. The toner is mixed and agitated with the toner stored in the second chamber 412 as the developing unit 4 rotates while holding the developing device.

  As described above, in this developing device, the interior of the housing is divided into two chambers, and the supply roller 43 and the developing roller 44 are surrounded by the side wall of the housing 41 and the partition wall 41a to provide the second chamber 412 having a relatively small volume. Even when the remaining amount of toner decreases, the toner is efficiently supplied to the vicinity of the developing roller 44. Further, by supplying the toner from the first chamber 411 to the second chamber 412 and stirring the whole toner by rotating the developing unit 4, a stirring member (auger) for stirring the toner is omitted in the developing device. The augerless structure that had been realized.

  In the developing device 4K, a regulating blade 46 for regulating the thickness of the toner layer formed on the surface of the developing roller 44 to a predetermined thickness is disposed. The regulating blade 46 includes a plate member 461 having elasticity such as stainless steel or phosphor bronze, and an elastic member 462 made of a resin member such as silicon rubber or urethane rubber attached to the tip of the plate member 461. ing. The rear end portion of the plate-like member 461 is fixed to the housing 41, and an elastic member 462 attached to the front end portion of the plate-like member 461 is plate-like in the rotation direction D4 of the developing roller 44 indicated by an arrow in FIG. The member 461 is disposed on the upstream side of the rear end portion. The elastic member 462 elastically contacts the surface of the developing roller 44 to form a restriction nip, and finally the toner layer formed on the surface of the developing roller 44 is restricted to a predetermined thickness.

  The toner layer thus formed on the surface of the developing roller 44 is sequentially conveyed to a position facing the photoconductor 22 on which the electrostatic latent image is formed by the rotation of the developing roller 44. When a developing bias from a bias power supply (not shown) is applied to the developing roller 44, the toner carried on the developing roller 44 is partially applied to each surface of the photoreceptor 22 in accordance with the surface potential. Thus, the electrostatic latent image on the photosensitive member 22 is visualized as a toner image of the toner color.

  Further, the housing 41 is provided with a seal member 47 pressed against the surface of the developing roller 44 on the downstream side of the position facing the photoconductor 22 in the rotation direction of the developing roller 44. The seal member 47 guides the toner remaining on the surface of the developing roller 44 that has passed through the position facing the photoconductor 22 into the housing 41 and prevents the toner in the housing from leaking outside.

  FIG. 5 is a diagram showing a developing roller and a partially enlarged view of the surface thereof. The developing roller 44 is formed in a substantially cylindrical roller shape, and a shaft 440 is provided at both ends in the longitudinal direction coaxially with the roller. The shaft 440 is supported by the developing device main body and is developed. The whole is freely rotatable. A central portion 44a of the surface of the developing roller 44 has a plurality of regularly arranged convex portions 441 and concave portions surrounding the convex portions 441, as shown in a partial enlarged view (in a dotted circle) of FIG. 442.

  Each of the plurality of convex portions 441 protrudes toward the front side of the paper surface of FIG. 5, and the top surface of each convex portion 441 is a part of a single cylindrical surface that is coaxial with the rotation axis of the developing roller 44. Each is made. The concave portion 442 is a continuous groove surrounding the convex portion 441 in a mesh shape, and the entire concave portion 442 also has one cylindrical surface that is coaxial with the rotation axis of the developing roller 44 and different from the cylindrical surface formed by the convex portion. Make it. The developing roller 44 having such a structure can be manufactured by a manufacturing method described in, for example, Japanese Patent Application Laid-Open No. 2007-140080. In addition, you may process further so that all the top surfaces of the convex part 441 may become a plane.

  The length L1 of one side of the top surface of each convex portion 441 and the interval L2 between the convex portions can be, for example, about 10 to 100 μm, but are not limited thereto. Further, the shape of the convex portions 441 and the arrangement thereof are not limited to those described here. The height difference between the convex portion 441 and the concave portion 442 will be described later.

  Returning to FIG. 1, the description of the image forming apparatus will be continued. The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched between a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotationally driving the roller 73. It has. When a color image is transferred to the sheet S, each color toner image formed on the photosensitive member 22 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 along the conveyance path F.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing of feeding the sheet S to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. S is sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet S on which the color image is formed in this manner is fixed with the toner image by the fixing unit 9 and is conveyed to the discharge tray portion 89 provided on the upper surface portion of the apparatus main body via the pre-discharge roller 82 and the discharge roller 83. The Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reversal position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is conveyed in the direction of the arrow D3 along the reverse conveyance path FR. Then, the sheet is again placed on the transport path F before the gate roller 81. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2 is first transferred. It is the opposite surface. In this way, images can be formed on both sides of the sheet S.

  Further, as shown in FIG. 2, each of the developing devices 4Y, 4C, 4M and 4K is provided with memories 91 to 94 for storing data relating to the manufacturing lot and usage history of the developing devices, the remaining amount of the built-in toner, and the like. ing. Further, the developing devices 4Y, 4C, 4M, and 4K are provided with wireless communication devices 49Y, 49C, 49M, and 49K, respectively. Then, if necessary, these selectively communicate with the wireless communication device 109 provided on the main body side in a non-contact manner, and data is transmitted between the CPU 101 and each of the memories 91 to 94 via the interface 105. Various information such as consumables management for the developing device is managed by sending and receiving. In this embodiment, data is transmitted and received in a non-contact manner using electromagnetic means such as wireless communication. However, a connector is provided on the main body side and each developer side, and the connector is mechanically fitted. By doing so, you may make it mutually transmit / receive data.

  Further, as shown in FIG. 2, this apparatus includes a display unit 12 that is controlled by the CPU 111 of the main controller 11. The display unit 12 is constituted by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, etc. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112. Reference numeral 106 is a ROM for storing a calculation program executed by the CPU 101, control data for controlling the engine unit EG, and the like. Reference numeral 107 is a RAM for temporarily storing calculation results in the CPU 101 and other data. is there.

  A cleaner 76 is disposed in the vicinity of the roller 75. The cleaner 76 can be moved toward and away from the roller 75 by an electromagnetic clutch (not shown). Then, the blade of the cleaner 76 abuts on the surface of the intermediate transfer belt 71 that is stretched over the roller 75 while moving to the roller 75 side, and the toner that remains on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove.

  Further, a density sensor 60 is disposed in the vicinity of the roller 75. The density sensor 60 is provided to face the surface of the intermediate transfer belt 71 and measures the image density of the toner image formed on the outer peripheral surface of the intermediate transfer belt 71 as necessary. Based on the measurement results, this apparatus uses the operating conditions of each part of the apparatus that affect the image quality, such as the developing bias applied to each developing device, the intensity of the exposure beam L, and the tone correction characteristics of the apparatus. Adjustments are being made.

  The density sensor 60 is configured to output a signal corresponding to the density of a predetermined area on the intermediate transfer belt 71 using, for example, a reflective photosensor. The CPU 101 can detect the image density of each part of the toner image on the intermediate transfer belt 71 by periodically sampling the output signal from the density sensor 60 while rotating the intermediate transfer belt 71.

  Next, details of the toner layer regulation on the developing roller 44 in the developing device 4K and the like of the image forming apparatus configured as described above will be described. As described above, in the developing device 4K and the like of this image forming apparatus, the supply roller 43 contacts the surface of the developing roller 44 inside the housing 41 containing the toner T, and the regulating blade is downstream in the developing roller rotation direction. 46 abuts against the toner layer on the developing roller, thereby defining the thickness of the toner layer carried on the surface of the developing roller 44. If the thickness is not appropriate, the image forming operation is affected. That is, if the toner layer is too thin, the amount of toner transported to the position facing the photoreceptor 22 is reduced, and a sufficient image density cannot be obtained. If the toner layer is too thick, the toner may fall from the surface of the developing roller 44 and leak into the apparatus, or may be scattered from the developing roller 44 as a cloud, or may adhere to the photoreceptor 22 and cause fogging. (Hereinafter, these phenomena are collectively referred to as “toner scattering etc.”).

  First, the principle of toner layer regulation in this embodiment will be described. The inventor of the present application has various causal relationships between the surface state of the developing roller 44 on which the toner layer is formed and the toner scattering, etc., in a state where the toner layer is relatively thick (about several times the volume average particle diameter of the toner). The experiment was conducted. As a result, it became clear that the generation mechanism of toner scattering and the like can be explained by the following model, for example.

  FIG. 6 is a diagram illustrating a model for explaining a generation mechanism such as toner scattering. The developing device is initially filled with new toner. However, as the image forming operation using the developing device is repeated, the developing device contains unused toner that retains the original characteristics (in this specification, “ New toner ”) and used toner (characterized as“ old toner ”in this specification) that has been once carried on the surface of the developing roller 44 but has not been used for development and has been deteriorated by being returned to the developing device again. Will be mixed). Therefore, as shown in FIG. 6A, the periphery of the developing roller 44 is in a state where the new toner Tn and the old toner To are mixed. In FIG. 6, the new toner Tn is represented by a white circle, and the old toner To is represented by a hatched circle.

  Among these, the new toner Tn has a high fluidity and a high charge amount, and therefore is attracted to the surface of the developing roller 44 by the electrostatic force Ft. On the other hand, since the old toner is inferior in fluidity and chargeability due to causes such as embedding and peeling of the external additive, the force attracted to the developing roller 44 is weaker than that of the new toner. As a result, as shown in FIG. 6B, most of the toner that directly contacts the developing roller 44 becomes the new toner Tn. That is, of the toner layer formed on the surface of the developing roller 44, the first layer immediately adjacent to the developing roller 44 is formed with the new toner.

  On the other hand, in the layer deposited on the first layer thus formed, the new toner Tn and the old toner To are mixed as shown in FIG. 6C. This is because when the surface of the developing roller 44 is covered with a new toner layer, the influence of the electrostatic force of the developing roller itself is weakened on the upper layer, so that the charge of the new toner attracts new toner, resulting in a new toner. This is because not only the toner but also the old toner which has deteriorated due to deterioration and has been charged to the opposite polarity is attracted to such charge. In this specification, a phenomenon in which new toner concentrates in a layer close to the surface of the developing roller 44 and a large amount of old toner is contained in a layer far from the surface is referred to as a “layer separation phenomenon”.

  Depending on the electrostatic force of the developing roller 44 and the charging characteristics of the toner itself, two or more new toner layers may be formed on the surface of the developing roller 44 as shown in FIG. Even in such a case, the new toner Tn and the old toner To are mixed in the layer far from the surface of the developing roller 44, and the layer separation phenomenon occurs.

  Thus, the ratio of the old toner To increases in the outer layer far from the developing roller 44 in the toner layer formed on the surface of the developing roller 44. Since the old toner To has a low charge amount, the adhesion force to the surface of the developing roller 44 or the toner layer thereon is weak, and as a result, the toner is peeled off from the surface of the developing roller 44 in the course of toner conveyance by the rotation of the developing roller 44. Will be scattered. In addition, the toner charged to a polarity opposite to the original charged polarity adheres to a region of the electrostatic latent image on the photosensitive member 22 where the toner should not be originally attached, thereby causing fogging.

  This model can explain the following experimental facts. For example, when new toner is replenished to a developing device that has been used for a long time and the remaining amount of toner is reduced, it was observed that toner scattering and fogging temporarily increased and then gradually decreased. This is because a large amount of new toner is mixed in the deteriorated toner in the developing unit, so that the vicinity of the surface of the developing roller 44 is occupied by the new toner, and the outermost surface of the toner layer contains a lot of old toner. It is done. If the toner is further used, the new toner is selectively used. As a result, the difference in characteristics from the old toner is reduced and the layer separation phenomenon is alleviated. Therefore, it is considered that the level of toner scattering and the like also decreases. .

  This is further supported by experiments in which a toner of a color different from the original toner color is replenished. For example, new cyan toner is replenished to the cyan developing device 4C where the remaining amount of toner is low, and the surface of the developing roller 44 is observed. As a result, a toner layer with a color close to green, in which cyan toner and yellow toner are mixed, was formed on the surface of the developing roller, but the surface toner was removed by blowing air or brushing the surface. Over time, the color of the surface of the developing roller 44 gradually changed to yellow. In particular, the toner of the first layer that is in direct contact with the surface of the developing roller 44 is almost the same yellow color as the original toner color. On the other hand, when an image forming operation is executed using such a developing device, it was mainly cyan toner that was scattered around the developing device or fogged on the photosensitive member 22. .

  For these reasons, the layer close to the surface of the developing roller 44 is mainly occupied by new toner, while the layer far from the surface contains a large amount of old toner. It can be seen that this is caused by the old toner.

  Here, “new toner” and “old toner” are concepts representing a relative characteristic difference between toner particles in the developing device, and are not necessarily related to whether or not the toner itself is new. For example, even if it is a new toner, there may be some toner that does not have sufficient characteristics as in the case of the old toner described above. In such a case, the toner is referred to as “old toner”. Will work in the same way. Further, even if the toner is not new, it can be considered as “new toner” if the relative characteristic difference between the toner particles is small.

  The same phenomenon occurs not only when the developer is provided with a supply port for supplying toner, but also when it is not. For example, as in the present embodiment, when the developer is divided into two or more chambers and toner is supplied from one chamber to another chamber at a certain timing, the supply timing is the same. Mixing of new toner and old toner occurs. In this embodiment, the auger is not provided in the developing device. However, when the developing device 4K is rotated with the rotation of the rotary developing unit 4, the new toner stored in the first chamber 411 has the ratio of the old toner. Mixing occurs by flowing into the increased second chamber 412. The same applies to a configuration in which a toner transport mechanism such as an auger is provided in the developing device or a configuration in which toner is periodically replenished from a toner tank provided separately from the developing device.

  FIG. 7 is a diagram showing the relationship between the toner particle diameter and the adhesion force to the developing roller. As the force that acts to adhere the toner particles to the surface of the developing roller 44 or the toner layer on the surface, the contact charging adhesion force and van der Waals force that are electrostatic attraction acting on the charged toner are the main ones. . As shown in FIG. 7, when the toner particle diameter is large, there is no significant difference in the size between the contact charging adhesion force and the van der Waals force. On the other hand, the van der Waals force becomes dominant when the toner particle diameter is small, particularly 5 μm or less. When Van der Waals force becomes strong, the toner particles tend to adhere to each other.

  As described above, the above-mentioned layer separation phenomenon becomes a particular problem when using a toner having a small particle size in which van der Waals force acts strongly. This is because if the van der Waals force is weak, toner adheres to the surface of the developing roller 44 mainly due to electrostatic attraction, so that old toner with a small charge amount does not collect on the surface of the developing roller 44. On the other hand, when the van der Waals force is strong, further toner adheres to the toner layer on the developing roller 44 regardless of the amount of charge. Such toner inevitably contains a lot of old toner, and causes the above-mentioned layer separation phenomenon. Further, the old toners are easily aggregated by van der Waals force to easily form a large toner lump. Since such a toner lump has a smaller charge amount than its particle size, it easily falls from the surface of the developing roller 44, and the toner scatters. cause. Thus, it can be seen that the problem caused by the layer separation phenomenon is particularly remarkable when the particle size of the toner T to be used is small.

  Therefore, in this embodiment, toner is not carried on the convex portion 441 of the surface of the developing roller 44, and a thin and uniform toner layer of new toner is carried only on the concave portion 442. The reason why the toner is not carried on the convex portion 441 is as follows. When toner is carried on the convex portion 441, the toner is aggregated by being pressed by the regulating blade 46 in the regulating nip, and is fixed to the surface of the developing roller 44 to cause a filming phenomenon. It may be scattered. This is remarkable when the old toner is carried on the convex portion 441, and particularly when the toner T is a small particle diameter toner having a volume average particle diameter of 5 μm or less as described above. In order to avoid such a problem, the toner carried on the convex portion 441 on the surface of the developing roller 44 in the housing 41 is scraped off by the regulating blade 46.

  Further, the following effects can be obtained by carrying the toner only in the concave portion 442. The toner carried in the recess 442 is not pressed or rubbed by the regulating blade 46, and therefore hardly aggregates or deteriorates. This is advantageous in that toner characteristics such as charge amount and fluidity can be maintained in a state close to that of a new product over a long period of time. Further, by suppressing the generation of “old toner” having deteriorated characteristics, it is possible to further suppress toner scattering and the like.

  FIG. 8 is a diagram showing a contact state between the developing roller and the regulating blade. In this embodiment, as shown in FIG. 8A, a regulating blade 46 is in contact with the surface of the developing roller 44 in a so-called counter direction with respect to the rotational direction D4, and an elastic member 462 provided at the tip of the developing roller 44 develops. A regulating nip N <b> 1 where the surface of the developing roller 44 and the elastic member 462 come into contact is formed by being pressed against the surface of the roller 44 and partially elastically deforming. Further, the upstream end 462a of the elastic member 462 in the rotation direction D4 of the developing roller 44 includes an upper edge thereof in the regulation nip N1, and regulates the toner by so-called edge regulation.

  As shown in FIG. 8B, the upstream end 462a of the elastic member 462 is located upstream in the rotation direction D4 of the developing roller 44 with respect to the perpendicular line extending from the rotation center of the developing roller 44 to the upper surface of the elastic member 462. Is located. For this reason, the deformation amount Db of the elastic member 462 due to the elastic deformation in the vicinity of the upstream end portion 462a is somewhat smaller than the maximum deformation amount Da of the elastic member 462 in the vicinity of the foot of the perpendicular line. In this way, the elastic member 462 comes into contact with the developing roller 44 in a wide range on the upper surface thereof, and the regulation nip width Wn1 becomes relatively large.

  FIG. 9 is an enlarged schematic view of the restriction nip in this embodiment. In the region upstream of the regulation nip N1 in the movement direction D4 of the surface of the developing roller 44, which is marked “before regulation” in FIG. 9, a layer made of a new toner Tn indicated by a white circle is formed immediately below the surface of the developing roller 44. On the other hand, a layer in which the new toner Tn and the old toner To indicated by hatched circles are mixed is formed on the surface of the toner layer. On the other hand, in the regulation nip N1, the elastic member 462 of the regulation blade 46 is in pressure contact with the surface of the developing roller 44, in particular, the projection 441. Therefore, the toner carried on the projection 441 before regulation is old and new. Regardless, it is scraped off at the upstream end 462a of the elastic member 462.

  New toner and old toner are mixed in the toner scraped off from the convex portion 441 in this way, and among these, the toner removed from the vicinity of the surface of the convex portion 441 has a particularly high charge amount. This is because most of the toner adhering to the surface of the convex portion 441 is a new toner having good chargeability, and the amount of charge is increased due to sliding and rolling with the regulating blade 46 when scraped from the convex portion 441. This is because a strong electrostatic force attracted to the developing roller 44 acts due to the rise. On the other hand, there is also an old toner with a low charge amount behind the contact position with the regulating blade 46 (leftward in FIG. 9). When the toner with a high charge amount scraped from the vicinity of the surface of the convex portion 441 collides with such an old toner, the new toners Tn1 and Tn2 with a high charge amount eject the old toners To1 and To2 with a low charge amount behind. . Thus, the old toner existing in the vicinity of the surface of the developing roller 44 is gradually replaced by the new toner Tn, and the old toner is driven backwards. As a result, in the regulation nip N1 and on the downstream side in the developing roller rotation direction D4 from the regulation nip N1, the toner is carried only by the concave portion 442, and the ratio of the old toner contained therein is extremely low.

  In order to promote such a phenomenon, it is preferable that the upstream end portion 462a of the elastic member 462 has a wall standing upright substantially perpendicular to the surface of the developing roller 44. If the angle θ formed by the end portion of the elastic member 462 is an acute angle, the scraped toner is separated from the surface of the developing roller 44, so that the replacement of the old toner with the new toner is less likely to occur. If the angle θ is an obtuse angle, the scraped toner is pushed into the regulation nip N1 and pressed. When the angle θ is about 90 degrees, the scraped toner stays in the vicinity of the upstream end 462a of the elastic member 462, and the replacement of the toner is promoted.

  FIG. 10 is a diagram showing the toner charge amount distribution measured before and after the regulation. When plotting the number ratio of the toner collected from the surface of the developing roller 44 before the regulation by the regulation blade 46 for each charge amount, the distribution curve is relatively broad and electrically neutral as shown by the solid line in FIG. While toner and positively charged toner were also included in a high ratio, the toner collected from the surface of the developing roller 44 after the regulation nip N1 has a sharp distribution curve as shown by the broken line in FIG. The ratio of positively charged toner is remarkably reduced. From this result, it can be seen that the toner layer after the regulation is composed of a well-charged toner by the toner regulation of the present embodiment. By transporting the toner layer thus regulated to a position facing the photoconductor 22 and developing the electrostatic latent image, in this embodiment, a good image with less fog can be formed and the charge amount can be increased. It is also possible to prevent the old toner having a low value from scattering outside the developing device.

  Next, the height difference between the convex portion 441 and the concave portion 442 on the surface of the developing roller 44 will be examined. In this embodiment, the toner on the convex portion 441 is removed by contact with the regulating blade 46, and the toner is carried only on the concave portion 442. Therefore, the amount of toner transported to the position facing the photoreceptor 22 is determined by the amount of toner carried in the recess 442, and this difference in height is an important factor in obtaining good image quality.

  FIG. 11 is a schematic diagram showing the relationship between the height difference of the developing roller surface and the toner to be carried. In this embodiment, since the toner is carried in the concave portion 442 in a state where the elastic member 462 is in contact with the convex portion 441, the level difference between the convex portion 441 and the concave portion 442, more strictly, the concave portion 442 and the elastic member. It is necessary that the distance from 462 be equal to or greater than the volume average particle diameter of the toner. More specifically, if the elastic deformation of the elastic member 462 in the restriction nip N1 is not so large because the hardness of the elastic member 462 is relatively high and the area of the restriction nip N1 is relatively large, the convex portion 441 Since the height difference from the concave portion 442 is almost equal to the distance between the concave portion 442 and the elastic member 462, there is substantially no problem if attention is paid to any of them. However, when elastic deformation of the elastic member 462 is large at the regulation nip N1 and protrudes toward the bottom of the concave portion 442, attention is paid to the interval between the concave portion 442 and the elastic member 462, and this interval is set as the toner. It is preferable that the volume average particle size be greater than or equal to. Hereinafter, the volume average particle diameter of the toner is represented by the symbol Dave. Here, as shown in FIG. 11A, when the distance between the recess 442 and the elastic member 462 is a value G1 that is twice or more the volume average particle diameter Dave of the toner, the recess 442 has an average of two layers. More than a minute of toner is carried.

The toner of the first layer that is in contact with the surface of the developing roller 44 adheres to the developing roller 44 with a strong electrostatic force, but the second and subsequent layers adhering on the toner of the first layer Since the electrostatic force acting on the toner is weaker than this, the toner easily separates from the developing roller 44 and plays a major role in developing the electrostatic latent image at a position facing the photoreceptor 22. That is, by forming the second and subsequent toner layers in the recesses 442 in this way, the development efficiency can be increased as compared with the case where only one toner layer is carried. This is particularly effective when using a toner having a small particle size (for example, a volume average particle size of 5 μm or less) in which the adhesion between toner particles due to van der Waals force is high. In this respect, it is more preferable that the interval between the concave portion 442 and the elastic member 462 be at least twice the volume average particle diameter Dave of the toner. However, if the interval is too large, mixing of old toner is permitted. The volume average particle diameter Dave of 3 times or less is appropriate. That is, the following formula:
Dave ≦ G1 ≦ 3Dave (Formula 1)
It is better to establish the relationship. In particular, this is preferable for a toner having a small toner particle size variation.

In order to secure sufficient development efficiency, it is preferable to carry two or more layers of toner in the concave portion 442 on the surface of the developing roller 44. That is,
2Dave ≦ G1 (Formula 1a)
It is more preferable that

On the other hand, considering the particle size variation of the toner, as shown in FIG. 11B, the concave portion 442 and the elasticity are adjusted so as to be equal to or larger than the maximum particle size Tm of the toner T. A gap G2 with the member 462 may be determined. Here, the maximum particle diameter of the toner can be statistically determined as follows. In other words, the maximum particle diameter Dm is expressed by the following equation, where the number standard of toner T is 50% particle diameter D50 and the geometric standard deviation σ.
Dm = D50 + 3σ (Formula 2)
Can be defined by In a commonly used toner, the ratio of toner having a particle size exceeding the maximum particle size Dm is extremely small.

If the distance between the concave portion 442 and the elastic member 462 is small, the toner having a large particle size that has entered the concave portion 442 is pressed by the elastic member 462 and deteriorates. In addition, the toner having a large particle diameter is not taken into the concave portion 442 and remains in the developing device indefinitely, and the particle size distribution of the toner in the developing device gradually shifts to the large particle size side and cannot be used for development. On the other hand, as described above, when the distance between the concave portion 442 and the elastic member 462 is set to the maximum particle diameter Dm or more, most of the toner particles contained in the toner T accommodated in the developing device are carried on the concave portion 442. Thus, the toner in the developing device can be used up effectively to the end. That is, the following formula:
G2 ≧ Dm = D50 + 3σ (Formula 3)
Should be satisfied.

Further, as shown in FIG. 11C, the toner Tm having the maximum particle diameter may be supported on the first layer of the toner layer supported by the recess 442. That is, the gap G3 between the recess 442 and the elastic member 462 is expressed by the following formula:
G3 ≧ Dave + Dm = Dave + D50 + 3σ (Formula 4)
The interval G3 may be set so that is established. In this way, even the toner Tm having the maximum particle diameter can be carried on the toner layer in contact with the developing roller 44, and therefore, the large particle diameter toner can be used for development more efficiently. .

  As described above, in this embodiment, the toner carried on the convex portion 441 on the surface of the developing roller 44 is scraped off by the regulating blade 46 in the regulating nip N1, and the toner is carried only on the concave portion 442. In this way, pressure is applied to the toner in the regulation nip N1, and the toner is prevented from aggregating or deteriorating. By not deteriorating the toner in this way, it is possible to reduce the scattering of the toner from the developing roller 44 to the outside of the developing device due to the deteriorated toner. In addition, the upstream end surface of the regulating blade 462 is a wall that stands substantially vertically from the developing roller 44, and the scraped toner is retained to replace the old toner that has entered the recess 442 with the new toner. Reduce the percentage of old toner contained. As a result, the amount of old toner conveyed outside the developing device is reduced, and the effect of suppressing toner scattering and fogging is further improved.

  Next, a second embodiment of the image forming apparatus to which the invention is applied will be described. In the apparatus of the second embodiment, the state of contact of the regulating blade 46 with the developing roller 44 is different from that of the first embodiment. Other configurations and operations are the same as those in the first embodiment. Therefore, the components common to the first and second embodiments are denoted by the same reference numerals and description thereof is omitted, and the second embodiment will be described focusing on the differences from the first embodiment.

  FIG. 12 is a diagram showing a contact state between the developing roller and the regulating blade in the second embodiment. As shown in FIG. 12A, also in this embodiment, the regulating blade 46 is brought into contact with the surface of the developing roller 44 in the counter direction to form the regulating nip N2. However, as shown in FIG. 12B, the upstream end 462 a of the elastic member 462 is located in the rotation direction D 4 of the developing roller 44 with respect to a perpendicular line that extends from the rotation center of the developing roller 44 to the upper surface of the elastic member 462. Located downstream. For this reason, the amount of deformation of the elastic member 462 due to elastic deformation is the maximum value Dc at the upstream end 462a. That is, the elastic member 462 has the largest elastic deformation at the upstream end. Further, the contact area between the elastic member 462 and the developing roller 44 is also reduced, and the regulation nip width Wn2 is smaller than the nip width Wn1 in the first embodiment.

FIG. 13 is an enlarged schematic view of the restriction nip in this embodiment. As described above, since the elastic member 462 is most elastically deformed at the upstream end portion 462a, the elastic member 462 faces the convex portion 441 of the developing roller 44 in the elastic member 462 in the vicinity of the upstream end portion of the restriction nip N2. The largest contact pressure is applied to the location. On the other hand, no pressure is applied at a location facing the recess 442 of the developing roller 44. For this reason, as shown in FIG. 13, the portion of the elastic member 462 facing the concave portion 442 is bent toward the bottom of the concave portion 442 (upward in FIG. 13), and the elastic member 462 is in the space where the concave portion 442 faces. The surface protrudes. The amount of bending is greatest at the upstream end of the regulation nip N2 having the highest contact pressure, and decreases toward the downstream side. That is, the following formula:
M1>M2> M3 (Formula 5)
The relationship is established. This relationship is also established when there is only one concave portion 442 included in the regulation nip, and the amount of bending becomes smaller toward the downstream in one concave portion 442.

  The elastic member 462 protruding toward the concave portion 442 allows the toner layer having a thickness corresponding to the distance between the tip of the elastic member 462 and the bottom portion of the concave portion 442 among the plurality of layers of toner carried in the concave portion to be allowed. However, since the amount of deflection becomes smaller toward the downstream side in the moving direction D4 of the developing roller 44 as described above, the pressure applied to the toner does not rise in the regulating nip, and the concave portion is restricted. The toner does not adhere to the bottom of 442. Further, when the distance between the tip of the elastic member 462 and the bottom of the concave portion 442 is larger than that on the downstream side, the toner layer that has entered the regulation nip is applied with pressure, and the toners are deformed and fixed. However, such a problem does not occur as described above.

  Also with such a configuration, as in the first embodiment described above, the toner on the convex portion 441 is removed by the regulating blade 46, so that it is possible to prevent toner deterioration due to pressing. In addition, the old toner contained in the concave portion 442 can be replaced with new toner, so that the amount of old toner conveyed outside the developing device can be reduced. For this reason, also in the apparatus of the second embodiment, it is possible to suppress the occurrence of toner scattering and fog as in the first embodiment. Moreover, the consideration about the height difference between the convex portion 441 and the concave portion 442 in the first embodiment is similarly established in the present embodiment.

  As described above, in each of the above embodiments, the developing device 4K and the like correspond to the “developing device” of the present invention, and the housing 41, the developing roller 44, and the regulation blade 46 are each the “accommodating portion” of the present invention. , “Toner carrying roller” and “regulating member”. Further, the elastic member 462 attached to the regulating blade 46 functions as the “elastic contact body” of the present invention. In each of the above-described embodiments, the first chamber 411 and the second chamber 412 in the developing device 4K correspond to the “toner storage chamber” of the present invention, while the toner in the first chamber is removed by rotating the entire developing device. The rotary developing unit 4 fed into the second chamber functions as the “toner transfer mechanism” of the present invention. In the image forming apparatus of the above-described embodiment, the photosensitive member 22, the developing device 4K, and the like function as the “image carrier” and the “developing device” of the invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the convex portion 441 of the developing roller 44 of the above embodiment is formed in a substantially rhombus shape, but the present invention is not limited to this. For example, the convex portion may have another shape such as a circle or a triangle. .

  Further, although the developing roller 44 of the above embodiment is a metal cylinder, the present invention can also be applied to an apparatus having a developing roller formed of a material other than this. However, according to the experiments of the present inventor, the above-mentioned layer separation phenomenon is noticeable when a developing roller whose surface is formed of a conductive material such as a developing roller made of metal or non-metal is subjected to metal plating is used. The present invention is particularly effective when applied to an apparatus having a developing roller having such a conductive surface. In this respect, the present invention is also effective for an apparatus provided with a developing roller made conductive by dispersing conductive material such as carbon black or fine metal powder in a rubber or resin cylinder. is there.

  In addition, the regulation blade 46 in the above embodiment is obtained by attaching a resin elastic member 462 to a metal plate member 461, but is not limited to such a structure. For example, a metal plate coated with an elastic resin can be used. Further, an appropriate bias potential may be applied to the regulating blade.

  The toner used in the above embodiment is not particularly limited, but the effect of the present invention is particularly remarkable when a one-component toner having a relatively large change in charging characteristics with time is used. In addition, since the problem such as toner scattering is more serious with toner having a small average particle diameter, it is effective to apply the present invention to an apparatus using such toner. In particular, in recent years, a reduction in toner particle size has been demanded from the viewpoints of higher image definition and reduction in toner consumption. For example, fine toner particles having a volume average particle size of 5 μm or less have been manufactured. Such fine powder toner easily causes toner scattering and the like, but the problem can be solved by applying the present invention.

  In particular, the effect of the present invention becomes remarkable when a toner in which the particle size of the external additive added to the toner is 50 nm or less and the coverage of the toner base particles is 100% or more is used. In the toner to which such an external additive is added, the fluidity is high in the initial stage, but the change in fluidity with time is large, and the fluidity tends to be greatly lowered due to durability (long-term use). In such a toner, the layer separation phenomenon is likely to occur due to the difference in fluidity between the new toner and the old toner, so that the effect of applying the present invention is great.

  The image forming apparatus of the above embodiment is a color image forming apparatus in which the developing unit 4K and the like are mounted on the rotary developing unit 4, and an apparatus that mixes toner in the developing unit by rotating the developing unit 4K and the like. However, as described above, the application target of the present invention is not limited to this. For example, the present invention can also be applied to a monochrome image forming apparatus that includes only one developing device and forms a monochrome image. In particular, the toner is supplied from a replenishment port provided in the developing device by a user or a dedicated operator. The present invention can be suitably applied to an apparatus capable of replenishing toner or an apparatus configured to periodically replenish toner from a toner tank or the like separate from the developing device.

1 is a diagram showing a first embodiment of an image forming apparatus to which the invention is applied. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The figure which shows the external appearance of a developing device. Sectional drawing which shows the structure of a developing device. The figure which shows the image development roller and the elements on larger scale of the surface. The figure which shows the model explaining the generation | occurrence | production mechanism of toner scattering. The figure which shows the relationship between a toner particle diameter and the adhesive force to a developing roller. The figure which shows the state of contact | abutting with a developing roller and a control blade. The expansion schematic diagram of the control nip in 1st Embodiment. The figure which shows the charge amount distribution of the toner measured before and behind regulation. FIG. 3 is a schematic diagram showing a relationship between a difference in height on the surface of a developing roller and a carried toner. The figure which shows the state of contact | abutting with the developing roller of 2nd Embodiment, and a control blade. The expansion schematic diagram of the control nip in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Rotary developing unit (toner transfer mechanism), 22 ... Photoconductor (image carrier), 4C, 4K, 4M, 4Y ... Developing device (developing device, developing device), 41 ... Housing (accommodating portion), 44 ... Developing Roller (toner carrying roller) 46 ... Restriction blade (regulation member) 411 ... First chamber (toner accommodation chamber) 412 ... Second chamber (toner accommodation chamber) 441 ... Convex part (on developing roller surface) 442 ... concave portion (on developing roller surface), 461 ... plate-like member (regulating member), 462 ... elastic member (elastic contact body)

Claims (15)

A storage section for storing toner;
A toner that is formed in a substantially cylindrical shape having a plurality of regularly arranged convex portions and concave portions surrounding the convex portions on its surface, and rotates while carrying a toner layer of charged toner supplied from the housing portion on the surface. A carrying roller;
A regulating member that abuts against the surface of the toner carrying roller to form a regulating nip, and regulates the thickness of the toner layer carried on the surface of the toner carrying roller at the regulating nip,
The restricting member includes an elastic contact body that is formed of an elastic body and is pressed against the surface of the toner carrying roller to form the restricting nip. The upstream end of the restricting nip in the rotation direction of the toner carrying roller The upstream end portion of the elastic contact member is in contact with the convex portion of the toner carrying roller to remove the toner on the convex portion of the toner layer carried on the surface of the toner carrying roller;
The height difference between the convex portion and the concave portion is equal to or greater than the volume average particle size of the toner, and the interval between the elastic contact body and the concave portion in the regulation nip is one or more times the volume average particle size of the toner. A developing device characterized in that it is 3 times or less. A storage section for storing toner;
A toner that is formed in a substantially cylindrical shape having a plurality of regularly arranged convex portions and concave portions surrounding the convex portions on its surface, and rotates while carrying a toner layer of charged toner supplied from the housing portion on the surface. A carrying roller;
A regulating member that abuts against the surface of the toner carrying roller to form a regulating nip, and regulates the thickness of the toner layer carried on the surface of the toner carrying roller at the regulating nip,
The restricting member includes an elastic contact body that is formed of an elastic body and is pressed against the surface of the toner carrying roller to form the restricting nip. The upstream end of the restricting nip in the rotation direction of the toner carrying roller The upstream end portion of the elastic contact member is in contact with the convex portion of the toner carrying roller to remove the toner on the convex portion of the toner layer carried on the surface of the toner carrying roller;
The height difference between the convex portion and the concave portion is not less than the volume average particle size of the toner, and the interval between the elastic contact member and the concave portion in the regulation nip is not less than the maximum particle size of the toner. A developing device.   The developing device according to claim 2, wherein a distance between the elastic contact body and the concave portion in the regulation nip is equal to or larger than a sum of a volume average particle diameter and a maximum particle diameter of the toner.   The developing device according to claim 1, wherein the top surfaces of the plurality of convex portions form part of the same cylindrical surface. The upstream end surface of the elastic abutting member in the rotation direction of the toner carrier roller, a developing device according to any one of the toner carrier roller claims 1 are towering substantially perpendicular to the surface 4. Deformation amount of the elastic abutting member which is elastically deformed by the contact with the toner carrying roller, according to any one of the claims 1 and has a maximum at the upstream-side end portion in the rotation direction of the toner carrier roller 5 Development device. An apparatus according to any one of the height difference between said convex portion and the concave claims 1 to more than twice the volume average particle diameter of the toner 6. An apparatus according to any one of the toner carrying roller surface of claims 1 are formed of a conductive material 7. The accommodating unit, a developing device according to any one of claims 1 and has a supply opening for supplying the toner 8 from the outside. The storage section has a plurality of toner storage chambers for storing toner, and at least a part of the surface of the toner carrying roller is exposed inside one of the plurality of toner storage chambers, and the one toner an apparatus according to any one of accommodating claims 1 comprises a toner transfer mechanism for feeding toner contained in other toner storage chamber to the chamber 8. An apparatus according to any one of 1 0 to volume average particle diameter of toner claims 1 is 5μm or less. The particle size has been added following external additive 50nm to the toner, the developing device according to the external additive coverage to the toner base particles claims 1 to 100% or more to any one of 1 1 . An image carrier for carrying an electrostatic latent image;
A toner carrying roller formed in a substantially cylindrical shape having a plurality of regularly arranged convex portions and concave portions surrounding the convex portions on the surface, and carrying a toner layer of charged toner on the surface, and the surface of the toner carrying roller A developer having a regulating member for removing the toner layer of the convex portion of the toner layer carried on the surface of the toner carrying roller in contact with the toner carrying roller,
The restricting member includes an elastic contact body that is formed of an elastic body and is pressed against the surface of the toner carrying roller to form the restricting nip. The upstream end of the restricting nip in the rotation direction of the toner carrying roller The upstream end portion of the elastic contact member is in contact with the convex portion of the toner carrying roller to remove the toner on the convex portion of the toner layer carried on the surface of the toner carrying roller;
The height difference between the convex portion and the concave portion is equal to or greater than the volume average particle size of the toner, and the interval between the elastic contact body and the concave portion in the regulation nip is one or more times the volume average particle size of the toner. An image forming apparatus characterized by being 3 times or less. An image carrier for carrying an electrostatic latent image;
A toner carrying roller formed in a substantially cylindrical shape having a plurality of regularly arranged convex portions and concave portions surrounding the convex portions on the surface, and carrying a toner layer of charged toner on the surface, and the surface of the toner carrying roller A developer having a regulating member for removing the toner layer of the convex portion of the toner layer carried on the surface of the toner carrying roller in contact with the toner carrying roller,
The restricting member includes an elastic contact body that is formed of an elastic body and is pressed against the surface of the toner carrying roller to form the restricting nip. The upstream end of the restricting nip in the rotation direction of the toner carrying roller The upstream end portion of the elastic contact member is in contact with the convex portion of the toner carrying roller to remove the toner on the convex portion of the toner layer carried on the surface of the toner carrying roller;
The height difference between the convex portion and the concave portion is not less than the volume average particle size of the toner, and the interval between the elastic contact member and the concave portion in the regulation nip is not less than the maximum particle size of the toner. An image forming apparatus. An image carrier that carries an electrostatic latent image is formed in a substantially cylindrical shape having a plurality of regularly arranged convex portions and concave portions surrounding the convex portions on the surface, and a toner layer made of charged toner is carried on the surface. A toner carrying roller to be opposed, and developing the electrostatic latent image with the toner;
Prior to making the toner layer face the image carrier, the toner layer is supported on the convex portion and the concave portion on the surface of the toner carrying roller, and the toner layer on the convex portion is further transferred to the toner carrying roller. Removed by the regulating member that is in contact with the surface,
The restricting member includes an elastic contact member that is formed of an elastic member and is pressed against the surface of the toner carrying roller to form a restricting nip, and at an upstream end portion of the restricting nip in the rotation direction of the toner carrying roller. The upstream end portion of the elastic contact member contacts the convex portion of the toner carrying roller to remove the toner on the convex portion of the toner layer carried on the surface of the toner carrying roller;
The height difference between the convex portion and the concave portion is equal to or greater than the volume average particle size of the toner, and the interval between the elastic contact body and the concave portion in the regulation nip is one or more times the volume average particle size of the toner. A developing method characterized by being 3 times or less.

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