JP2010181566A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus by which a high quality image, which is less in the lowering with time in the toner concentration of a developer supplied onto developing rollers and the lowering in the toner concentration of the developer in a rotary shaft direction and is free from nonuniform density. <P>SOLUTION: The developing device and image forming apparatus set a toner concentration difference ΔT to an appropriate value, the toner concentration difference ΔT including the toner concentration difference of developer in an axial direction, which is supplied to the developing roller in a first stage, and toner concentration difference of the developer in the axial direction, which is supplied to the developing roller in a second stage. This minimizes decrease with time in the toner concentration of developer supplied to the developing rollers in the first and second stages and decrease in the toner concentration of the developer in the direction of the rotary shaft. Accordingly, the developing device and image forming apparatus obtain an image of high quality free from nonuniform density. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device having two developing rollers and an image forming apparatus having the developing device.

  In an image forming apparatus such as an electrophotographic printer or copying machine, an image forming area is set to a predetermined potential and a non-image forming area is set to a potential other than the predetermined potential on an image carrier called a photosensitive member rotating in one direction. A latent image is formed. The electrostatic latent image formed on the photoconductor is made visible by an image visualization agent called toner supplied from the developing device. The image forming apparatus prints this visible image on a recording sheet.

  2. Description of the Related Art Conventionally, a developing device applied to this electrophotographic system uses a two-component developer in which, for example, a toner as an image visualization agent is attached to a carrier as a magnetic powder called a carrier (Patent Document 1). . In the developing device disclosed in Patent Document 1, two developing rollers are installed to face the photoconductor, and the developing roller located downstream in the photoconductor rotation direction rotates forward with respect to the rotation of the photoconductor. The developing roller positioned upstream in the direction of rotation of the photoconductor rotates in reverse to the rotation of the photoconductor. The developing device disclosed in Patent Document 1 has a configuration (hereinafter referred to as a fountain configuration) having a flow rate regulating member called a doctor blade for regulating the flow rate of a developer at a central position adjacent to the developing roller.

  In the conventional developing device, only the toner in the developer is consumed by the printing operation, so that the toner concentration defined by the weight ratio of the toner in the developer is reduced in the developing device. Therefore, in the conventional developing device, the toner is supplied from the toner storing and supplying mechanism into the developing device in order to make the toner weight ratio of the developer uniform.

  The developer supplied with the toner is agitated and conveyed by rotating in the direction of the rotation axis of a pair of spiral screw members that are mixing and agitating members, and the toner weight ratio of the developer in the axial direction of the screw is made uniform. . The mixed and agitated developer is guided from the mixing and agitating member to a developing roller via a conveying member that conveys the developer, and is divided into each developing roller by a doctor blade. Then, the developer that has been mixed and agitated is supplied with toner to an image forming portion on the photosensitive member at a position where it contacts the photosensitive member, thereby forming a visible image.

  In Patent Document 1, as a method for solving the problem that the image quality is significantly deteriorated due to an image in which the background portion is blackened due to poor stirring by the mixing stirring member, so-called background fogging, the developing roller returns to the spiral screw portion. A method is disclosed in which only a part of the developer is exchanged with the developer in the spiral screw portion, and again returned to the developing roller via the conveying member. Patent Document 1 discloses a method of defining an exchange ratio and adjusting the exchange ratio to be small. The replacement ratio is the ratio of the flow rate exchanged with the developer in the spiral screw portion to the developer flow rate returned from the developing roller to the spiral screw.

  Patent Document 2 discloses a development in which the developer on the developing roller located upstream in the rotation direction of the photosensitive member of the two developing rollers is returned to the screw member side farther than the screw member adjacent to the conveying member. An apparatus is disclosed. Further, in the cited document 2, there is further illustrated together with a configuration in which there is no barrier between a pair of helical screw members.

  In the above conventional technique, if an image having a printing rate of 100% is continuously printed, the toner concentration of the developer supplied to the developing roller is lowered.

  For example, if the replacement ratio is reduced, the developer adjusted to a predetermined toner density in the spiral screw portion becomes difficult to be supplied to the developing roller portion. Therefore, the developing roller passes through the conveying member, and again rotates around the developing roller. Developer amount increases. For this reason, when the toner consumption amount at the developing roller increases, the toner concentration of the accompanying developer decreases.

  Further, the developer exchanged according to the exchange ratio and returned to the helical screw is sequentially exchanged with the developer on the conveying member side while being conveyed in the direction of the rotation axis as the helical screw rotates. Therefore, the toner density of the developer conveyed decreases from the upstream side to the downstream side in the conveyance direction of the spiral screw. For this reason, when the toner consumption amount in the developing roller increases, the difference between the upstream toner density and the downstream toner density in the conveying direction of the spiral screw exceeds the specified toner density difference, and the axial image density is increased. There is a difference. Moreover, if the return developer of the first-stage developing roller is returned to the spiral screw member adjacent to the conveying member, the required flow rate of the developer that should go around the spiral screw becomes enormous.

  Furthermore, even when the developer returned from the first-stage developing roller is returned to the spiral screw member that is not adjacent to the conveying member, the developer conveyed by both of the pair of screw members is free. In the case of a configuration to be transferred, the developer newly supplied with toner is not sufficiently agitated in the conveyance in the rotation axis direction of the screw member not adjacent to the conveyance member, and the screw member side adjacent to the conveyance member as it is To cause background fogging due to poorly stirred developer.

  The present invention has been made in view of the above circumstances, and is intended to solve this problem. The decrease in the toner concentration over time and the decrease in the toner concentration in the rotation axis direction of the developer supplied onto the developing roller are small. An object of the present invention is to provide a developing device and an image forming apparatus capable of obtaining a high-quality image without causing unevenness.

  The present invention employs the following configuration in order to achieve the above object.

The present invention is disposed in the vicinity of a photosensitive member that forms an electrostatic latent image and circulates, and develops toner contained in the developer on the photosensitive member while rotating backward with respect to the rotation direction of the photosensitive member. A first developing roller that is disposed downstream of the first developing roller in the rotation direction of the photoconductor, and the toner is transferred to the photoconductor while rotating forward with respect to the rotation direction of the photoconductor. A second developing roller to be developed; and disposed between the first developing roller and the second developing roller; and the photosensitive member, the first developing roller, and the first developing roller. A regulating member that regulates the amount of the developer that is supplied to the vicinity of the second developing roller, a conveying member that conveys the developer to the regulating member,
A toner supply member that supplies toner to the developer, and is arranged adjacent to the transport member and arranged so that the rotation axis thereof is parallel to the first development roller and the second development roller, A first mixing and agitating member for agitating the developer, and disposed in parallel with the first mixing and agitating member between the first mixing and agitating member and the toner supply mechanism; A second mixing and stirring member that stirs the toner and the developer supplied from the developer and sets the developer to a predetermined toner concentration, and the first mixing and stirring member and the second mixing and stirring member. A partition is provided between the first and second mixing and agitating members in parallel with the rotation shafts of the first and second agitating members. Is conveyed in the direction of the rotation axis of the mixing stirring member, A developing device that is transferred only between both ends of one mixing agitating member and both ends of the second mixing agitating member, wherein the first developing roller and the second developing roller are developed on the photosensitive member. The ratio of the total amount of toner to be developed and the amount of toner to be developed on the photosensitive member by the second developing roller is a ratio β, and the developing is returned from the second developing roller to the first mixing and agitating member. A ratio between the amount of the developer and the amount of the developer returned from the conveying member to the regulating member is a ratio γ, and an adhesion amount of the toner adhering to the photosensitive member is N1, and the developer by the regulating member When the regulation amount is N2, and the ratio of the circumferential speed of the first developing roller and the circumferential speed of the second developing roller to the circumferential speed of the photosensitive member is K1 and K2, respectively.

<Equation 2>
ΔT = (1-γ) × β × N1 / {N2 × (K1 + K2) × [1- (1-γ) × K2 / K1]} + 0.001
ΔT obtained in step (b) was 0.002 (0.2 wt% as a percentage) or less.

  In the developing device of the present invention, the ΔT may be set to 0.002 (percentage 0.2 wt%) or less by changing the ratio β and the ratio γ.

  In the developing device of the present invention, the ratio β may be 0.25 or less, and the ratio γ may be in the range of 0.2 to 0.4.

  In the developing device of the present invention, the developer used for development in the first developing roller may be returned to the second mixing and agitating member.

  An image forming apparatus according to the present invention includes any one of the developing devices described above, a photoreceptor that forms an electrostatic latent image, circulates, supplies toner from the developing device, and holds an image obtained by visualizing the electrostatic latent image. And a control device that controls the ratio β and the ratio γ.

  In the image forming apparatus according to the aspect of the invention, the controller may control the ratio β to a predetermined value by changing a developing bias applied to the first developing roller and the second developing roller. Also good.

  In the image forming apparatus of the present invention, the control device may be configured to control the ratio β to a predetermined value by changing the rotation speeds of the first developing roller and the second developing roller. .

  In the image forming apparatus of the present invention, the control device may be configured to control the ratio γ to a predetermined value by changing a rotation speed of the transport member.

  According to the present invention, it is possible to obtain a high-quality image in which a decrease in toner concentration over time and a decrease in toner concentration in the rotation axis direction of the developer supplied onto the developing roller are small and density unevenness does not occur.

It is a figure for demonstrating the outline of the whole structure of the image development apparatus of 1st embodiment. It is a first diagram for explaining the flow of the developer. It is a 2nd figure for demonstrating the flow of a developing agent. It is a figure for demonstrating the balance of the flow of the developer Z in a developing device. FIG. 6 is a diagram showing a relationship between a toner consumption ratio β calculated from Expression (3) and a toner density difference ΔT in the developing device with respect to each replacement ratio γ. FIG. 6 is a diagram showing a relationship between an exchange ratio γ calculated in the developing device and a toner density difference ΔT with respect to each toner consumption ratio β. FIG. 6 is a diagram showing the relationship between the peripheral speed ratio K and the developing ability η of a forward and reverse rotating single developing roller with respect to each developing efficiency η0. It is a schematic diagram explaining a photoreceptor surface potential. FIG. 6 is a diagram illustrating a relationship between a peripheral speed ratio K and a toner consumption ratio β when the toner density T0 is changed with the development efficiency η0 = 6. FIG. 6 is a diagram showing a relationship between a peripheral speed ratio K and a toner consumption ratio β when the development efficiency η0 is changed when the toner concentration T0 = 0.05 (percentage is 5 wt%). When η0 = 6 and toner density T0 = 0.05 (percentage is 5 wt%), the difference between the first stage peripheral speed ratio K1 and the toner consumption ratio β when the second stage peripheral speed ratio K2 is changed. It is a figure which shows a relationship. FIG. 6 is a diagram showing a relationship between a toner consumption ratio β and a toner density difference ΔT with respect to each replacement ratio γ. The relationship between the exchange ratio γ and the toner density difference ΔT is shown for each toner consumption ratio β. FIG. 2 is a diagram for explaining a control device that controls the developing device and an image forming apparatus including them. It is a figure for demonstrating the outline of the image development apparatus used as a comparative example. It is a figure for demonstrating the flow volume balance in a developing device. It is the figure which showed the value of the required flow volume M in each of embodiment and a comparative example.

  In this embodiment, the toner density including the axial toner density difference in the developer supplied to the first stage developing roller and the axial toner density difference in the developer supplied to the second stage developing roller. The difference ΔT is set to an appropriate value. By appropriately setting the toner density difference ΔT, the decrease in the toner density with time and the decrease in the toner density in the direction of the rotation axis of the developer supplied onto the first and second developing rollers are small. A high-quality image without unevenness can be obtained.

(Embodiment)
A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining an outline of the overall configuration of the developing device according to the first embodiment.

  The developing device 100 according to the present embodiment includes two developing rollers 10, a developing roller 20, a doctor blade 40, a toner storage mechanism 50, a mixing stirring member 60, a mixing stirring member 70, a conveying member 80, a path plate 90, and a path plate 92. Have

  The developing roller 10 and the developing roller 20 are provided so as to face a photoreceptor 30 included in an image forming apparatus to be described later on which the developing device 100 is mounted. The developing roller 10 rotates in a direction opposite to the rotation direction of the photoconductor 30 (the direction of arrow A in FIG. 1). The rotation direction of the developing roller 10 is indicated by an arrow B in FIG. The developing roller 10 is disposed upstream of the developing roller 20 in the rotation direction of the photoconductor 30.

  The developing roller 20 is disposed downstream of the developing roller 10 in the rotation direction of the photoconductor 30. The photoconductor 30 rotates in the direction indicated by the arrow A in FIG. Hereinafter, rotation in the same direction as the rotation direction of the photoconductor 30 is referred to as forward rotation. The developing roller 20 performs forward rotation in the direction (forward direction) indicated by the arrow C in FIG. In this embodiment, the drum-shaped photoconductor 30 is used as the image carrier. However, this may be a configuration such as a photoconductor belt that circulates on a specific track.

  The doctor blade 40 is a partition plate disposed between the developing roller 10 and the developing roller 20. The doctor blade 40 regulates the flow rate of the developer Z that flows to the developing roller 10 and the developing roller 20.

  The toner storage member 50 stores toner N that is mixed with the developer Z in the developing device 100. The toner N is supplied from the toner storage member 50 to the mixing and stirring member 70.

  The mixing stirring member 70 is disposed adjacent to the mixing stirring member 60. The mixing and stirring member 60 is disposed adjacent to the conveying member 80 that supplies and conveys the developer Z from the mixing and stirring member 60 to the developing roller 10 and the developing roller 20.

  Note that the developer Z of the present embodiment is a transport agent that transports the toner N. The developer Z is composed of magnetic powder called a carrier and an image visualization agent called a toner N that forms a visible image on the photoreceptor 30. In the developer Z, the toner N is mixed in a weight ratio of 2 to 8% of the total weight. In this embodiment, the weight of the toner with respect to the total weight of the developer Z is referred to as toner density. The developer Z according to the present embodiment consumes only the toner N in the developer Z by the printing operation of the printing apparatus (not shown), and therefore becomes lower depending on the toner density of the developer Z in the developing apparatus 100 and the printing operation. .

  For this reason, in the developing device 100 of this embodiment, the toner N is supplied from the toner storage and supply mechanism 50 to the developer Z, and the supplied toner N and developer Z are mixed and stirred by the mixing and stirring member 60 and the mixing and stirring member 70. To do. The developer Z in which the toner N is mixed and stirred is conveyed to the developing roller 10 and the developing roller 20 by the conveying member 80.

  The mixing and stirring member 60 and the mixing and stirring member 70 are spiral screws (see FIG. 3), and are configured to be completely partitioned except for the vicinity of both end portions of both. Therefore, the developer Z is transferred between the mixing and stirring member 60 and the mixing and stirring member 70 only at both ends.

  The mixing stirring member 60 rotates in the direction of arrow E in FIG. 1, and the mixing stirring member 70 rotates in the direction of arrow F in FIG. The mixing and stirring member 60 and the mixing and stirring member 70 of the present embodiment are arranged such that their spiral directions are opposite to the screw rotation direction. The mixing stirring member 70 conveys the developer Z from the toner storage member 50 side in FIG. 1 to the mixing stirring member 60 side as the screw rotates, and passes the developer Z to the mixing stirring member 60.

  The mixing stirring member 60 transports the developer Z from the mixing stirring member 70 side to the transporting member 80 side, and then passes the developer Z to the mixing stirring member 70 again. The developer Z of the present embodiment is circulated in the direction of the rotation axis of the screw of the mixing and stirring member 60 and the mixing and stirring member 70 by the operation of the mixing and stirring member 60 and stirred and conveyed. The conveying member 80 rotates in the direction of arrow D in FIG. 1 and conveys the developer Z conveyed from the mixing and agitating member 60 to the developing roller 10 and the developing roller 20.

  In the developing device 100 of this embodiment, the toner N consumed by the image forming operation by the developing roller 10 and the developing roller 20 is supplied from the toner storage and supply mechanism 50. The developer Z supplied with the toe T is mixed with the surrounding developer Z while being conveyed in the axial direction of the mixing and agitating member 70, and the toner density converges to a predetermined value.

  The toner N added to the developer Z is frictionally charged by the rubbing operation between the developers Z by the stirring of the developer Z. The developer Z is transferred to the mixing and stirring member 60 at the end 71 of the mixing and stirring member 70 (see FIG. 3). The developer Z delivered to the mixing and stirring member 60 is conveyed in the axial direction of the mixing and stirring member 60 and returned to the mixing and stirring member 70 again at the end 61 of the mixing and stirring member 60. In the mixing and stirring member 60 and the mixing and stirring member 70 of the present embodiment, the above-described circular conveyance is performed (see FIG. 3). In this embodiment, the toner N in the developer Z is finally charged to about −15 to −35 μc / g by continuing the mixing and stirring operation in the circular conveyance.

  In the following description of the present embodiment, the flow of the developer Z conveyed in the axial direction of the mixing and stirring member 60 and the mixing and stirring member 70 is referred to as a lateral flow. In the developing device 100 of the present embodiment, there is a vertical flow of the developer Z described later with respect to the horizontal flow.

  The flow of the developer Z in the developing device 100 of this embodiment will be described below with reference to FIGS. FIG. 2 is a first diagram for explaining the flow of the developer, and FIG. 3 is a second diagram for explaining the flow of the developer.

  First, the vertical flow of the developer Z will be described with reference to FIG.

  As shown in FIG. 2, the flow of the developer Z from the mixing and agitating member 60 to the conveying member 80 includes a flow M8 and a flow M7. When a later-described flow M6 is added to the flow M7 and the flow M8, a flow M1 of the developer Z guided from the conveying member 80 to the doctor blade 40 is obtained. In the doctor blade 40, the flow M1 is divided into a flow M2 flowing to the developing roller 10 and a flow M3 flowing to the developing roller 20.

  The flow M2 guided to the developing roller 10 consumes the toner N by the developing operation in the closest region R ′ with the photosensitive member 30 on the developing roller 10. The flow M <b> 2 ′ in which the toner concentration is reduced due to the consumption of the toner N is separated from the developing roller 10, and returned to the mixing and agitating member 70 (not shown) through the path plate 90.

  In the flow M3 guided to the developing roller 20, the toner N is consumed by the developing operation in the region R closest to the photosensitive member 30 on the developing roller 20. The flow M <b> 3 ′ in which the toner density is reduced due to the consumption of the toner N is separated from the developing roller 20 and enters the lower side of the conveying member 80.

  In the vicinity of the conveying member 80, an opening 85 through which the developer Z is taken in and out between the conveying member 80 and the mixing and agitating member 60 is formed. The opening 85 is formed using the path plate 92 and the bottom wall surface of the developing device 100.

  In the opening 85, there are a flow M7 and a flow M8 that are generated when the mixing and stirring member 60 rotates in the direction of arrow E in FIG. The flow M7 and the flow M8 are flows from the mixing and stirring member 60 toward the conveying member 80. Further, a flow M3 ′ conveyed by the conveying member 80 away from the developing roller 20 is present in the opening 85. Therefore, in the opening 85, the flow M7, the flow M8, and the flow M3 ′ collide with each other.

  When the flow M7, the flow M8, and the flow M3 ′ collide, the flow M5 that is a part of the flow M3 ′ is exchanged with the flow M7 that flows from the mixing and stirring member 60, and the flow M5 is guided to the lower part of the mixing and stirring member 60. .

  On the other hand, the remaining flow that has not been exchanged in the flow M3 ′ is merged with the flow M7 and the flow M8 that are newly introduced from the side of the mixing and stirring member 60 by the exchange, and is supplied to the doctor blade 40 that has become the flow M1. Is done.

  In the following description of the present embodiment, this series of flows is referred to as a longitudinal flow. In order to stabilize the longitudinal flow in the developing device 100, it is necessary to store the flow rate of the developer Z in accordance with the flow rate conservation rule. In order to establish the flow rate conservation law in the developing device 100, the flow rate of the flow M7 supplied from the mixing and stirring member 60 to the conveying member 80 side is changed instead of the flow M5 returned from the conveying member 80 to the mixing and stirring member 60. The flow rate of the flow M5 must be the same. Further, the flow rate of the flow M8 supplied to the conveyance member 80 side instead of the flow M2 ′ returned from the conveyance member 80 side to the mixing and stirring member 70 needs to be the same as the flow rate of the flow M2 ′.

  In the developing device 100, there is a flow M4 that circulates around the path plate 92. The flow M4 stabilizes the diversion and flow rate regulation of the developer Z at the doctor blade 40 as a buffer developer, and is an excess flow that is blocked by the doctor blade 40 and is not supplied to the developing roller 10 and the developing roller 20. .

  Note that the flows M2 and M3 in the developing device 100 of the present embodiment are flows generated due to flow rate regulation by the developing roller 10 and the regulating gap G1 between the developing roller 20 and the doctor blade 40. Further, the flow rates of the flow M5, the flow M6, the flow M7, and the flow M8 in the developing device 100 of the present embodiment are adjusted for the conveyance capability (rotation speed adjustment) of the conveyance member 80 and the opening amount (opening area) of the opening 85. And adjustment of the arrangement of the mixing and stirring member 60 and the conveying member 80 in the direction of gravity (downward on the paper surface). The flow M4 that is an excessive flow is generated as an excess of the conveyance amount of the conveyance member 80 with respect to the flow M1 due to the adjustment of the conveyance capability of the conveyance member 80.

  In the flow M4, since the amount of the toner N conveyed increases as the flow rate increases, the decrease in the toner density of the longitudinal flow developer Z due to toner consumption in the developing roller 10 and the developing roller 20 is alleviated. However, since the toner N contained in the flow M4 is consumed by the continuous printing operation and the toner density of the flow M4 also decreases, it can be considered that there is no toner N contained in the flow M4 over time. Therefore, when considering the stabilization of the toner density of the entire developing device 100, the flow M4 that is an excessive flow may not be included.

  Next, with reference to FIG. 3, the flow M5 and the flow M7 exchanged between the conveying member 80 and the mixing stirring member 60 of the present embodiment, and the developer in the axial direction of the mixing stirring member 60 and the mixing stirring member 70. The conveyance of Z will be described.

  In the transport path of the developer Z in the axial direction of the mixing and stirring member 60 and the mixing and stirring member 70 shown in FIG. 3, the flow point where the developer Z is passed from the mixing and stirring member 70 to the mixing and stirring member 60 is defined as an IN point. In addition, a point where the developer Z is passed from the mixing and stirring member 60 to the mixing and stirring member 70 is defined as an OUT point.

  Between the IN point and the OUT point, the flow M5 and the flow M7 are exchanged everywhere. The toner concentration in the flow M5 is lower than the toner concentration in the lateral flow M0 that circulates around the mixing and stirring member 60 and the mixing and stirring member 70 as the toner in the developing roller 20 is consumed. As the flow M5 in which the toner concentration is reduced is sequentially mixed with the horizontal flow M0, the toner concentration in the horizontal flow M0 also gradually decreases.

  Therefore, when an image forming operation is performed such that the toner N is consumed in the entire area in the axial direction of the developing roller 20, the lateral flow M0 and the flow M5 in which the toner density is decreased in the entire area in the axial direction of the mixing and stirring member 60. Will be exchanged. For this reason, the toner density at the IN point is highest in the lateral flow M0, and the toner density at the OUT point is lowest.

  In this case, the developer Z supplied to the developing roller 10 and the developing roller 20 is a developer Z having a different toner density in the axial direction. When the difference in toner density in the developer Z is large, images having different densities in the axial direction are printed.

  Further, when the exchange amount of the flow M5 and the flow M7 is large, the ratio of the developer Z conveyed in the mixing and stirring member 60 supplied to the developing roller 10 and the developing roller 20 along the vertical flow increases. When the ratio of the developer Z sent to the longitudinal flow increases, the developer Z may be supplied to the developing roller 10 and the developing roller 20 without being sufficiently stirred. The toner N supplied into the mixing and stirring member 70 is stirred and charged when it goes around the mixing and stirring member 60 and the mixing and stirring member 70. Therefore, in the developer Z that is not sufficiently stirred, the toner N may not be sufficiently charged. When an image is formed with the toner N that is not sufficiently charged, the background portion other than the image area is more likely to be developed as a fog component, resulting in a decrease in image quality.

  In the developing device 100 of the present embodiment, the above situation is taken into consideration, and the balance between the flow rate of the developer Z and the flow rate of the toner N accompanying the flow of the developer Z is made appropriate.

  The flow rate balance in the present embodiment will be described below with reference to FIG. FIG. 4 is a diagram for explaining the balance of the flow of the developer Z in the developing device 100.

  As described above, the longitudinal flow has a width in the axial direction of the mixing and stirring member 60 and the mixing and stirring member 70. The unit of each flow rate in the unit length in the width direction is [g / s / cm].

  Here, the flow rate (unit: [g / s]) of the longitudinal flow in which the width directions of the mixing and stirring member 60 and the mixing and stirring member 70 are grouped will be described.

  In FIG. 4, the flow M <b> 5 and the cross flow M <b> 0 of the longitudinal flows merge at a point Q. The IN point and OUT point shown in FIG. At the point Q, the toner density of the lateral flow M0 is changed at a stretch by the longitudinal flow collected in the width direction with respect to the flowing lateral flow M0. The lateral flow M0 ′ with the changed toner density flows out from the point Q. Accordingly, the difference between the toner concentration of the lateral flow M0 flowing in from the point Q and the toner concentration of the lateral flow M0 'flowing out from the point Q is the toner concentration in the width direction (IN point and OUT point) of the mixing stirring member 60 and the mixing stirring member 70. It corresponds to the difference.

  In FIG. 4, the flow M6, the flow M7, and the flow M8 out of the longitudinal flows merge at the point P, become the flow M1, and flow out from the point P. At this time, the flow rate of the flow M1 is defined as M [g / s], and the toner density of the flow M1 is defined as T0. However, the toner concentration T0 is not a percentage unit but a ratio of the toner weight to the weight of the developer Z.

  A point at which the flow M1 is divided into the developing roller 10 and the developing roller 20 in the doctor blade 40 is defined as a point S, and a dividing ratio when the developer Z is divided into the developing roller 10 and the developing roller 20 at the point S is represented by α. It was. The diversion ratio α is a ratio at which the flow M1 is diverted as the flow M3, and the diversion ratio of the flow M2 diverted to the developing roller 10 is (1−α).

  In the developing roller 10 and the developing roller 20, the toner N is consumed by the developing operation. A point of consumption of toner N on the developing roller 10 is a point R, and a point of consumption of toner N on the developing roller 20 is a point R ′. If the toner consumption flow rate at the points R and R ′ is t [g / s] and the ratio of the toner N consumed by the developing roller 20 (toner consumption ratio) is defined as β, the developing roller 10 at the point R ′ is defined as β. The toner consumption ratio is (1-β). Therefore, the toner consumption flow rate of the developing roller 10 is (1−β) × t [g / s], and the toner consumption flow rate at the point R is β × t [g / s].

  The flow M3 becomes the flow M3 ′ in which the toner N is consumed at the point R, and is divided into the flow M5 and the flow M6 at the point X. The flow M5 divided at the point X joins the cross flow M0 at the point Q. The flow M6 divided at the point X joins the flow M7 and the flow M8 at the point P again as a longitudinal flow. The ratio at which the flow M3 ′ is split at the point X is defined as an exchange ratio γ that separates the longitudinal flow and leads to the transverse flow M0.

  The flow M <b> 2 becomes a flow M <b> 2 ′ where the toner is consumed at the point R ′ and is guided to the mixing and stirring member 70. The flow M2 ′ returns to the point Q after the toner N is replenished from the toner storage member 50 in the mixing and agitating member 70 to the prescribed toner concentration S0 and then becomes a lateral flow M0.

  As described above, the lateral flow M0, the flow M1, the flow M2, the flow M3, the flow M5, the flow M6, the flow M7, the flow M8, the lateral flow M0 ′, the flow M2 ′, and the flow M3 ′ of the developer Z are respectively unique. Toner density. The flow M1, the flow M2, and the flow M3 are the developer Z before the toner N is consumed, and the toner density is T0. In the flow M3 ′, the flow M5, and the flow M6, the toner N is consumed by the developing roller 20, and the toner density is T1.

  The toner concentrations of the flow M7, the flow M8, and the lateral flow M0 are the prescribed toner concentration S0. The toner concentration in the flow M0 ′ was changed to the toner concentration S1 changed from the specified toner concentration S0 by the replacement of the developer Z.

  The toner density multiplied by the flow rate of each flow of the developer Z is a flow rate of toner flow m0, m1, m2, m3, m5, m6, m7, m8, and m0 ′ in each flow shown in FIG. m3 '.

  Next, consider the balance of the flow rate of toner N (hereinafter referred to as toner flow rate) at each point marked in FIG. At each point shown in FIG. 4, the balance between the points P and Q where a plurality of flows coexist and the balance between the flow rates at the point R where the toner N is consumed are important.

  Since the flow rate conservation law holds at each point, m1 = m6 + m7 + m8 holds at the toner flow rate at point P. At the toner flow rate at point Q, m0 + m5 = m0 ′ + m7 + m8 holds. At the toner flow rate at point R, m3 = β × t + m3 ′ holds.

  Here, the difference between the toner density S0 and the toner density T0 (S0−T0) is defined as the toner density difference ΔR1, and the difference between the toner density S0 and the toner density S1 (S0−S1) is defined as the toner density difference ΔR2. The following formulas (1) and (2) are obtained from the three formulas.

ΔR1 = (1−γ) × β × t / [M × {1− (1−γ) × α}] (1) Expression ΔR2 = γ × β × t / [(1-γ) × α-1] / [(1−α) × M−m] (2) Formula In the present embodiment, ΔR1 is the specified toner concentration S0 and the toner concentration of the developer Z that is actually supplied to the developing roller 10 and the developing roller 20. This is the difference from T0.

  When the toner density difference ΔR1 is large, the density of the printed image is greatly different, and the image quality is deteriorated. Further, the toner density difference ΔR2 indicates a difference in toner density in the axial direction between the developing roller 10 and the developing roller 20. When the toner density difference ΔR2 is large, the printed image is shaded in the axial direction as described above. Accordingly, the sum of these values, that is, the value defined by toner density difference ΔT = toner density difference ΔR1 + toner density difference ΔR2 is axially applied in the developer Z actually supplied to the developing roller 10 and the developing roller 20. This is a toner density difference including a density difference. In the present embodiment, the toner density difference ΔT is made smaller than a predetermined value, thereby reducing the toner density reduction and the toner density reduction in the rotation axis direction, and obtaining a high-quality image with no density unevenness. .

  In recent years, the allowable range of color difference on the photoreceptor 30 is 3 or less. Some image forming apparatuses in recent years have improved the fineness of image quality by reducing the particle size of the toner N to suppress the toner adhesion amount on the photoreceptor to about 0.4 to 0.5 mg / cm 2. .

  In an image formed by this image forming apparatus, in order to make the color difference within an allowable range, it is necessary to suppress the fluctuation of the toner adhesion amount difference in the image to 5% or less. In order to suppress the toner adhesion amount difference, it is necessary to suppress the toner density difference (corresponding to ΔT described above) of the developer supplied to the developing roller to 0.2 or less. When the developing device is configured so that ΔR1 = 0 at this time, ΔR2, which is the toner density difference in the axial direction of the developing roller, can be allowed to be 0.002 (0.2 wt% in percentage).

  However, the value of the fluctuation range of the toner density difference due to the printing operation in which various printing patterns are switched as needed and the toner density control operation associated therewith is about 0.1. Therefore, in order to make the color difference within the allowable range, it is necessary to suppress the toner density difference in the axial direction of the developing roller to about 0.1.

  Therefore, in this embodiment, the developing device 100 is configured such that ΔT is 0.002 (0.2 wt% as a percentage) or less and ΔR2 is 0.001 (0.1 wt% as a percentage) or less.

  In the developing device 100 of the present embodiment, the restriction amount of the developer Z in the doctor blade 40 is N2 [g / cm ^ 2], the peripheral speed of the photosensitive member 30 is V [cm / s], the developing roller 10, and the developing roller 20 Assuming that the width in the axial direction is L [cm], the peripheral speed ratio of the developing roller 10 with respect to the peripheral speed of the photoconductor 30 is K1, and the peripheral speed ratio of the developing roller 20 with respect to the peripheral speed of the photoconductor 30 is K2, Is α = K2 / K1, and the flow rate M of the developing roller 10 and the developing roller 20 is M = N2 × (K1 + K2) × V × L [g / s].

  Further, if the toner adhesion amount printed on the photosensitive member 30 is N1 [g / cm 2], the toner consumption amount t is t = N1 × V × L [g / s]. From the above values and the expressions (1) and (2), the following expressions (3) and (4) are obtained.

ΔT = (1−γ) × β × N1 / {N2 × (K1 + K2) × [1- (1-γ) × K2 / K1]} + 0.001 Formula (3)
m = (1−K2 / K1) × N2 × (K1 + K2) × V × L−γ × β × N1 × V × L / {[(1-γ) × K2 / K1-1] × 0.2} (4)
In the developing device 100 of this embodiment, the regulated amount N2 of the developer Z is 0.055 g / cm ^ 2, the peripheral speed V of the photosensitive member 30 is 76.2 cm / s, the axial width L is 50.8 cm, and development is performed. The peripheral speed ratio K1 of the roller 10 and the peripheral speed ratio K2 of the developing roller 20 are the same 1.4, the toner adhesion amount N1 = 0.0006 g / cm 2 (however, the transfer efficiency from the photoreceptor 30 to the sheet is 81%) In this case, the toner adhesion amount on the photoconductor is 0.0045 g / cm 2. As can be seen from Equation (3), ΔT does not depend on the peripheral speed V and the axial width L of the photoreceptor 30.

  In the developing device 100 of the present embodiment, the value of the parameter to be substituted into Expression (3) is the above value, but is not limited to this. In the developing device 100 of the present embodiment, each value may be set so that the toner density difference ΔT defined by Expression (3) is 0.2 or less.

In the developing device 100 of this embodiment, the toner density difference ΔT can be adjusted by adjusting the toner consumption ratio β in the developing roller 10 and the developing roller 20. The toner consumption ratio β of the developing roller 10 and the developing roller 20 may be adjusted, for example, by changing the rotation speed of the developing roller by a control device or the like that controls the developing device 100. FIG. FIG. 6 is a diagram showing the relationship between the toner consumption ratio β calculated from (1) and the toner density difference ΔT with respect to each replacement ratio γ. FIG. 6 is a graph showing the relationship between the replacement ratio γ calculated in the developing device and the toner density difference ΔT with respect to each toner consumption ratio β. 5 and 6, the toner density difference ΔT can be reduced by decreasing the toner consumption ratio β or increasing the replacement ratio γ. The toner consumption ratio β is 0.25 or less, and the replacement ratio γ is 0.3. With the above, the toner density difference ΔT can be set to 0.2 or less.

  Hereinafter, the toner consumption ratio β in the developing device 100 will be described.

  The developing device 100 of the present embodiment has a fountain type configuration (hereinafter referred to as a fountain configuration) having a doctor blade 40. In the fountain configuration, the first-stage developing roller 10 rotates in the reverse direction with respect to the rotation of the photosensitive member 30, and the second-stage developing roller 20 rotates in the forward direction with respect to the photosensitive member 30. In the developing device 100 having the fountain structure, the resistance of the developer Z to be used, the development gaps G10 and G20 (see FIG. 1), and the amount of the developer Z occupying the development gaps G10 and G20 (unit [g / cm ^ 3]) Are the same, the developing ability η is different. The developing gap G10 is the closest distance between the photosensitive member 30 and the developing roller 10 in the developing unit 12 (see FIG. 1) of the developing roller 10. The development gap G20 is the closest distance between the photoconductor 30 and the development roller 20 in the development unit 22 (see FIG. 1) of the development roller 20.

  The developing ability η in the developing gaps G10 and G20 is the toner adhesion amount N0 [mg / cm ^ 2] to be developed, the toner concentration T0 of the developer Z supplied to the developing roller 10 and the developing roller 20, the developing unit 12 and the developing unit. Assuming that the developing potential ΔP in the portion 22 and the charge amount Q [μC / g] of the toner N to be developed, N0 = proportional constant represented by η × T0 × ΔP / Q. The developing potential ΔP is the difference between the voltage VB applied to the developing roller 10 and the developing roller 20 and the image area potential VR on the photoconductor 30.

  FIG. 7 is a graph showing the relationship between the peripheral speed ratio K and the developing ability η of the forward and reverse rotating single developing roller with respect to each developing efficiency η0. The development efficiency η0 varies depending on the resistance of the developer to be used, the amount of developer showing in the development gap, and the like.

  As shown in FIG. 7, the higher the development efficiency η0, the larger the development capability η. When the single developing roller rotates in the reverse direction, the developing ability η shows a tendency to increase with respect to the absolute value of the peripheral speed ratio K, with the developing efficiency η0 being a proportional constant in the range where the absolute value of the peripheral speed ratio K is 1-2. . When the peripheral speed ratio K is set to a value greater than that shown in FIG. 7, for example, the tendency to saturation occurs due to the restriction by the toner concentration. In FIG. 7, when the peripheral speed ratio K is a positive value, it indicates that the developing roller is rotating in the forward direction. When the peripheral speed ratio K is a negative value, the developing roller is rotated by the photosensitive member. On the other hand, it shows rotating in the opposite direction.

  When the single developing roller rotates forward, the developing ability η exhibits an unstable behavior in a region where the peripheral speed ratio K is smaller than 1. The developing ability η starts to increase monotonously after the peripheral speed ratio K becomes 1 or more. When the peripheral speed ratio K is in the range of 1 to 2, the developing ability η shows an increasing tendency with respect to a value obtained by subtracting 0.5 from the peripheral speed ratio K with the development efficiency η0 as a proportional constant. The developing capacity η tends to be saturated when the peripheral speed ratio K is 2 or more, for example, due to the restriction by the toner concentration.

  Next, the developing ability η in the case where the developing device 100 of this embodiment has a two-stage configuration will be described.

  In the case of the two-stage developing device 100 having the developing roller 10 and the developing roller 20 as in the present embodiment, in the development with the first developing roller 10, the developing ability η is (T0 × ΔP / Q). The toner N multiplied by is developed as it is. Hereinafter, development by the second-stage developing roller 20 will be described with reference to FIG.

  FIG. 8 is a schematic diagram for explaining the photoreceptor surface potential. In the development by the development roller 20 at the second stage, the development potential of the development unit 22 is ΔV ′. The developing potential ΔV ′ is a potential (Q × N0 × d / ε, d = photosensitive member 30) generated from the developing potential ΔP of the developing portion 11 by the charge of the toner N adhering to the photosensitive member 30 by the developing roller 10. Is the potential obtained by subtracting the thickness of the dielectric layer (ε = dielectric constant). Therefore, in the development by the development roller 20 at the second stage, the toner N obtained by multiplying the development ability η by (T0 × ΔV ′ / Q) is developed.

Considering the above, the toner adhesion amount N01 developed in the first stage developing unit 12 is
N01 = η0 × T0 / Q × K1 × ΔP
It becomes. Further, the toner adhesion amount N02 developed by the second stage developing unit 22 is
N02 = η0 × T0 / Q × (K2-0.5) × (1-η0 × T0 × K1 × d / ε) × ΔP
It becomes. Therefore, the toner consumption ratio β between the first developing roller 10 and the second developing roller 20 can be obtained. Toner consumption ratio β is
β = N02 / (N01 + N02)
It becomes. If this is rearranged, the following formula (5) is obtained.

β = 1 / [1 + K1 / (K2-0.5) / (1-η0 × T0 × K1 × d / ε)] Formula (5)
As can be seen from the equation (5), the toner consumption ratio β does not depend on the development potential ΔP and the charge amount Q of the toner N, and the peripheral speed ratio K1 and the peripheral speed ratio K2 of the developing roller 10 and the developing roller 20 It depends on efficiency η0 and toner density T0. Therefore, in the developing device 100 of this embodiment, the toner consumption ratio β can be adjusted by changing the peripheral speed ratio K1 and the peripheral speed ratio K2 by changing the peripheral speeds of the developing roller 10 and the developing roller 20.

  9 and 10 show that the peripheral speed ratio K and the toner consumption ratio β are the same under the condition that the peripheral speed ratio K1 and the peripheral speed ratio K2 of the developing roller 10 and the developing roller 20 are the same (K = K1 = K2). FIG. FIG. 9 is a diagram showing the relationship between the peripheral speed ratio K and the toner consumption ratio β when the toner density T0 is changed at the development efficiency η0 = 6, and FIG. 10 shows the toner density T0 = 0.05 (percentage). FIG. 5 is a graph showing the relationship between the peripheral speed ratio K and the toner consumption ratio β when the development efficiency η0 is changed at 5 wt%.

  As shown in FIGS. 9 and 10, when the toner density T0 is larger than 0.05 and the development efficiency η0 is larger than 6, the toner consumption ratio β does not exceed 0.25. In this embodiment, the peripheral speed ratio K1 of the developing roller 10 and the peripheral speed ratio K2 of the developing roller 20 may be set so that the toner consumption ratio β does not exceed 0.25.

  Further, in the fountain configuration of the developing device 100 of the present embodiment, the peripheral speed ratio between the first-stage developing roller 10 and the second-stage developing roller 20 can be freely set.

  FIG. 11 shows the peripheral speed ratio K1 and the toner consumption of the first stage when the peripheral speed ratio K2 of the second stage is changed when η0 = 6 and the toner density T0 = 0.05 (percentage 5 wt%). It is a figure which shows the relationship with ratio (beta).

  In FIG. 11, the peripheral speed ratio K2 is changed to 1.2, 1.4, 1.6, and 1.8. In this case, the toner consumption ratio β does not exceed 0.25 when the relationship between the circumferential speed ratio K1 and the circumferential speed ratio K2 is at least K1 ≧ K2.

  In FIGS. 5 and 6, the peripheral speed ratio K1 of the developing roller 10 and the peripheral speed ratio K2 of the developing roller 20 are set to the same 1.4. A case where the speed ratio K2 is 1.4 will be described. From the results shown in FIG. 11, when the peripheral speed ratio K1 is 1.9 and the peripheral speed ratio K2 is 1.4, the toner consumption ratio β is less than 0.25. The regulated amount N2 of the developer Z is 0.055 g / cm ^ 2, the peripheral speed V of the photosensitive member 30 is 76.2 cm / s, the axial width L is 50.7 cm, and the toner adhesion amount N1 = 0. 0056 g / cm ^ 2, which is the same as the example shown in FIGS.

  12 and 13 show the results when the peripheral speed ratio K1 is 1.9 and the peripheral speed ratio K2 is 1.4. FIG. 12 is a diagram showing the relationship between the toner consumption ratio β and the toner density difference ΔT with respect to each replacement ratio γ. FIG. 13 shows the relationship between the replacement ratio γ and the toner density difference ΔT with respect to each toner consumption ratio β.

  As shown in FIGS. 12 and 13, when the toner consumption ratio β is 0.25 or less, ΔT ≦ 0.002 (0.2 wt% in percentage) even when the replacement ratio γ is 0.2.

  As described above, when the toner consumption ratio β is 0.25 or less and the replacement ratio γ is 0.3 or more, the toner density difference ΔT is 0.2 in a condition range that satisfies the peripheral speed ratio K1 ≧ the peripheral speed ratio K2. Can not be exceeded. In this case, the expression (4) shows that the flow rate M of the developer Z to be transported by the mixing and stirring member 60 and the mixing and stirring member 70 needs to be 546 g / s or more.

  Based on the conditions studied above, in the developing device 100 of the present embodiment, the development gaps G10 and G20, the resistance of the developer Z, the amount of the developer Z occupying the development gaps G10 and G20, and the development efficiency η0 is 6. The peripheral speed ratio K2 and the peripheral speed ratio K2 of the developing roller 10 and the developing roller 20 are the same 1.4, the specified toner concentration S0 is 5 wt%, and the toner consumption ratio β is 0.25. Adjusted as follows.

  Further, in the developing device 100 of the present embodiment, in addition to the above setting, the regulated amount N2 of the developer Z at the doctor blade 40 is 0.055 g / cm ^ 2, the peripheral speed V of the photoconductor 30 is 76.2 cm / s, The width L in the axial direction was set to 50.8 cm, and the toner adhesion amount N1 of the target print image was set to 0.0056 g / cm 2.

  In the developing device 100 of the present embodiment, the rotation speed of the conveying member 80, the opening amount (opening area) of the opening 85, and the mixing and stirring member 60 and the conveying member 80 are set so that the exchange ratio γ is 0.3. Set the placement. In the developing device 100 of the present embodiment, by setting in this way, the ratio that the developer Z that is not sufficiently stirred is supplied to the developing unit 12 and the developing unit 22 and developed as a fog component in the background portion of the image. Can be reduced.

  Furthermore, in the developing device 100 of the present embodiment, the outer diameter of the mixing and stirring member 60 and the mixing and stirring member 70 is 45 mm, and the rotation speed is 500 rpm, thereby ensuring 600 g / s or more as the transport amount of the lateral flow M0.

  In the model of the developer Z flow described in the present embodiment, the circumferential flow (lateral flow M0) of the mixing and stirring member 60 and the mixing and stirring member 70 is established, and the both ends of the mixing and stirring member 60 and 70 are mixed. Only in the configuration in which the developer Z is transferred between the two. That is, in the flow model described in the present embodiment, the developer Z adjusted to the specified toner concentration S0 flows from the upstream end of the mixing and stirring member 60, which is the merging point of the longitudinal flow and the lateral flow, and the mixing stirring member 60 This is the case in the configuration that flows out from the downstream end.

  The developer flow model described in the present embodiment has a configuration in which no barrier is provided between the mixing and stirring member 60 and the mixing and stirring member 80, and the developer Z is freely transferred except at both ends. Does not hold. The reason is that in the configuration in which no barrier is provided between the mixing and stirring member 60 and the mixing and stirring member 70, all are longitudinal flows, and it is not necessary to balance the lateral flow and the longitudinal flow. However, in the configuration in which the barrier is not provided, the developer cannot be sufficiently stirred by the lateral flow, and the developer that is not sufficiently stirred reaches the developing portion, thereby causing deterioration in image quality.

  In the developing device 100 of the present embodiment, a negatively charged OPC (organic photoreceptor) is used as the photosensitive member 30, and the potentials of the image forming region and the non-image forming region on the surface of the photosensitive member 30 are −100 V and −700 V, and development is performed. Printing was performed under the condition that the bias potentials of the roller 10 and the developing roller 20 were set to the same −350V and the developing potential ΔP was 250V.

  As a result, with respect to the prescribed toner concentration S0 = 0.05 (percentage of 5 wt%) of the developer Z supplied to the development roller 10 and the development roller 20, the variation of the toner concentration difference ΔT is 0.002 (percentage is 0). .2 wt%), and the toner density difference ΔR2 in the axial direction of the developing roller 10 and the developing roller 20 can be 0.001 (percentage 0.1 wt%) or less, and the density of the printed image is generated. It was possible to obtain good quality image quality.

  Further, in the developing device 100 of this embodiment, since the exchange ratio γ is suppressed to about 0.3, supply of the developer with insufficient stirring to the developing roller can be prevented, and the image quality can be improved.

  Furthermore, when considering keeping the image quality high in the long term, it is necessary to stabilize the toner consumption ratio β and stabilize the replacement ratio γ even during long-time use.

  In general, the developing efficiency η0 of the developer Z decreases as the usage time increases. The main reason for the decrease in the development efficiency η0 is an increase in the resistance value of the developer Z.

  In the above-described embodiment, when the potential (development bias) applied to the developing roller 10 and the developing roller 20 is the same, the toner consumption ratio β is a result that does not depend on the developing potential ΔP.

  In this embodiment, when the developing bias applied to the developing roller 10 and the developing roller 20 are different, the toner consumption ratio β can be adjusted by the value of the developing bias.

  For example, when the developing efficiency η0 of the developer Z decreases and the toner consumption ratio β increases due to long-term use of the developing device 100, control is performed to change the developing bias applied to the developing roller 10 and the developing roller 20, and a predetermined toner The consumption ratio β can be set.

  When the toner consumption ratio β is set to a predetermined value, control is performed so as to decrease the toner consumption ratio β. Therefore, it is preferable to control the absolute value of the developing bias applied to the developing roller 10 to be larger than the absolute value of the developing bias applied to the developing roller 20. The control timing may be accumulated by storing the developer usage time, and the control may be started when the accumulated value reaches a predetermined value. In this case, it is assumed that the above control is performed by a control device that controls the developing device 100.

  Further, as a method of adjusting the toner consumption ratio β, there is a method of changing K1 / K2, which is a ratio of the peripheral speed ratio K1 and the peripheral speed ratio K2 between the developing roller 10 and the developing roller 20. In this case, in order to change the conveyance flow rate of the developer Z in the conveyance member 80, the mixing and stirring member 60, and the mixing and stirring member 70, the rotation speeds of the conveyance member 80, the mixing and stirring member 60, and the mixing and stirring member 70 are changed, and the exchange ratio is changed. It is also necessary to change γ.

  Further, the developing device 100 of the present embodiment may be mounted on the image forming apparatus 300. FIG. 14 is a diagram for explaining a control device that controls the developing device and an image forming apparatus including them.

  The image forming apparatus 300 is, for example, an electrophotographic printer, a copying machine, or the like. In addition to the developing device 100, the image forming apparatus 300 includes a charger, a transfer unit, and a fixing device (not shown). Here, the process of outputting the input image by the image forming apparatus 300 will be described. The developing apparatus 100 visualizes the electrostatic latent image formed on the photosensitive member as a toner image by supplying toner. The The toner image formed on the photoreceptor is transferred to a recording medium such as paper by a transfer device (not shown), and the recording medium onto which the toner image is transferred is given heat and pressure by a fixing device (not shown). The toner image is fixed. Then, the recording medium on which the toner image is fixed is output as an image outside the image forming apparatus 300. The above-described technique used for the image forming apparatus 300 is a generally known technique.

  The image forming apparatus 300 is, for example, an electrophotographic printer, a copying machine, or the like. The image forming apparatus 300 forms an electrostatic latent image on the photosensitive member by the developing device 100 based on the input image data. The image forming apparatus 300 fixes the electrostatic latent image formed on the photosensitive member onto a recording sheet by a fixing device (not shown) and outputs the recording sheet.

  The image forming apparatus 300 includes a control device 310 that controls the developing device 100. In this embodiment, the control device 310 performs control for changing the rotation speeds of the developing roller 10 and the developing roller 20 of the developing device 100, control for changing the developing bias applied to the developing roller 10 and the developing roller 20, and the like. Control is performed to set the toner consumption ratio β to a predetermined value. The control for setting the toner consumption ratio β to a predetermined value is not limited to the method described above.

  Further, in the present embodiment, the control device 310 controls, for example, the rotational speed of the transport member 80 so that the replacement ratio γ is a predetermined value. The control for setting the exchange ratio γ to a predetermined value is not limited to the method described above.

  The image forming apparatus 300 can obtain a high-quality image by including the developing device 100 of the present embodiment.

(Comparative example)
In the developing device of the present embodiment, the developer Z supplied to the first-stage developing roller 10 is returned to the mixing and stirring unit 70 as shown in FIG. Hereinafter, the result produced by this configuration will be described using a comparative example.

  FIG. 15 is a diagram for explaining the outline of a developing device as a comparative example. A developing device 200 shown in FIG. 15 includes two developing rollers 210, a developing roller 220, a doctor blade 240, a toner storage mechanism 250, a mixing and stirring member 260, a conveying member 280, a path plate 290, and a path plate 292.

  The developing device 200 has almost the same configuration as the developing device 100. The developing device 200 is different from the developing device 100 in that the return destination of the developer Z supplied to the first-stage developing roller 210 is the mixing and stirring member 260 adjacent to the conveying member 280. In the developing device 100, the developer Z supplied to the first-stage developing roller 10 is returned to the mixing and stirring member 70 that is not adjacent to the conveying member 80.

  FIG. 16 is a diagram for explaining the flow rate balance in the developing device. Also in the developing device 200, as in the developing device 100, a circumferential flow of two mixing and stirring members that is a lateral flow is established. Therefore, in the developing device 200, the delivery of the developer Z is performed only at both ends of the two mixing and agitating members.

  In the developing device 200 as well, as in the developing device 100, the balance of the toner flow rate at points P, Q, R, and R ′ is considered. In the comparative example, the flow rate of the toner at the point P is m1 = m6 + m7 + m8. At the point Q, m0 + m5 + m2 ′ = m0 ′ + m7 + m8. At the point R, m3 = β × t + m3 ′, and at the point R ′, m2 = (1−β) × t + m2 ′. By arranging these equations, the following equations (6) and (7) are obtained.

ΔR1 = (1-γ) × β × t {M × [1- (1-γ) × α]} Equation (6)
ΔR2 = t / m (7)
Since Expression (6) is the same as Expression (1), the toner density difference ΔT, which is the sum of the toner density difference ΔR1 and the toner density difference ΔR2, is 0.002 (0.2 wt% in percentage) or less. The conditions of the toner consumption ratio β and the replacement ratio γ are the same as those of the developing device 100 described in the embodiment.

  However, the flow rate M of the developer Z to be transported by the mixing and agitating member 260 and the transporting member 280 shown in Expression (7) is obtained by a ratio between the toner density difference ΔR2 and the toner consumption flow rate t.

  FIG. 17 is a diagram showing a necessary value of the flow rate M in each of the embodiment and the comparative example. The conditions for obtaining the values shown in FIG. 17 are the same as those in the embodiment. The obtained conditions are the same as in the example.

  In FIG. 17, a numerical value other than the comparative example is a value of the flow rate M necessary in the developing device 100 described in the embodiment. In the case of the developing device 100, the flow rate is 800 g / s or less under the condition that the replacement ratio γ is 0.1 to 0.5 and the toner consumption ratio β is 0.1 to 0.3. In contrast, in the comparative example, the flow rate uniformly exceeded 2000 g / s under each condition.

  In the developing device 100, when the outer diameter of the mixing and stirring member 60 and the mixing and stirring member 70 is about 45 mm and the rotation speed is 600 rpm, the transportable transport amount is about 700 g / s. Therefore, in order to obtain a flow rate comparable to that of the comparative example, the rotational speed needs to be 1800 rpm or more. However, it is not common to rotate the mixing and stirring member 60 and the mixing and stirring member 70 at such a high speed.

  As described above, the developing device 100 according to the present embodiment has the configuration in which the developer Z supplied to the first-stage developing roller 10 is returned to the mixing and stirring unit 60, thereby mixing and stirring member 60 and mixing and stirring member 70. The flow rate of the developer Z to be transported can be reduced. Therefore, in this embodiment, a general flow rate of 800 g / s or less can be obtained.

  As mentioned above, although this invention has been demonstrated based on each embodiment, this invention is not limited to the requirements shown in the said embodiment. With respect to these points, the gist of the present invention can be changed without departing from the scope of the present invention, and can be appropriately determined according to the application form.

  The present invention is applicable to a developing device having two developing rollers and an image forming apparatus having the developing device.

DESCRIPTION OF SYMBOLS 10, 20 Developing roller 30 Photoconductor 40 Doctor blade 50 Toner storage member 60, 70 Mixing stirring member 80 Conveying member 90, 92 Path plate 100 Developing device 300 Image forming device 310 Control device

JP 2004-20790 A JP 2000-267383 A

Claims (8)

A first photosensitive member is disposed in the vicinity of a rotating photoreceptor that forms an electrostatic latent image, and develops toner contained in the developer on the photoreceptor while rotating in the reverse direction with respect to the rotation direction of the photoreceptor. A development roller;
A second developing roller disposed downstream of the first developing roller in the rotation direction of the photoconductor and developing the toner on the photoconductor while rotating forward with respect to the rotation direction of the photoconductor; ,
It is disposed between the first developing roller and the second developing roller, and is supplied to a proximity portion between the photoconductor and the first developing roller and the second developing roller. A regulating member for regulating the amount of the developer,
A conveying member that conveys the developer to the regulating member;
A toner supply member for supplying toner to the developer;
A first mixing and agitating member which is adjacent to the conveying member and is arranged so that a rotation axis thereof is parallel to the first developing roller and the second developing roller and which agitates the developer by rotating; ,
Between the first mixing and agitating member and the toner supply mechanism, disposed in parallel with the first mixing and agitating member, and rotates and agitates the toner and the developer supplied from the toner supply member; A second mixing and agitating member having a predetermined toner concentration as the developer;
Have
Between the first mixing and stirring member and the second mixing and stirring member, a partition is provided in parallel with the rotation shafts of the first and second stirring members,
The developer is conveyed in the rotation axis direction of the first mixing and agitating member and between the both ends of the first and the agitating member. A developing device that is delivered only in
The ratio β of the total amount of the toner developed on the photosensitive member by the first developing roller and the second developing roller and the amount of the toner developed on the photosensitive member by the second developing roller is a ratio β,
The ratio of the amount of the developer returned from the second developing roller to the first mixing and agitating member and the amount of the developer returned from the conveying member to the regulating member is a ratio γ,
The amount of toner adhering to the photoreceptor is N1, the amount of developer regulated by the regulating member is N2, and the circumferential speed of the first developing roller and the circumferential speed of the second developing roller are the same. When the ratio to the peripheral speed of the photoreceptor is K1 and K2, respectively.
<Equation 1>
ΔT = (1-γ) × β × N1 / {N2 × (K1 + K2) × [1- (1-γ) × K2 / K1]} + 0.001
Is a developing device in which ΔT obtained in step ≦ 0.002 (0.2 wt% in percentage). ΔT is
The developing device according to claim 1, wherein the ratio β and the ratio γ are changed to 0.2 or less.   The developing device according to claim 1, wherein the ratio β is 0.25 or less, and the ratio γ is in a range of 0.2 to 0.4.   4. The developing device according to claim 1, wherein the developer used for development in the first developing roller is returned to the second mixing and agitating member. 5. A developing device according to any one of claims 1 to 4,
A photoreceptor that forms an electrostatic latent image, circulates, supplies toner from the developing device, and holds an image obtained by visualizing the electrostatic latent image;
A control device that controls the ratio β and the ratio γ. The control device includes:
The image forming apparatus according to claim 5, wherein the ratio β is controlled to a predetermined value by changing a developing bias applied to the first developing roller and the second developing roller. The control device includes:
The image forming apparatus according to claim 5, wherein the ratio β is controlled to a predetermined value by changing a rotation speed of the first developing roller and the second developing roller. The control device includes:
The image forming apparatus according to claim 5, wherein the ratio γ is controlled to a predetermined value by changing a rotation speed of the conveying member.

Images