JP2010217289A - Developing device, image forming apparatus, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain proper image quality, while preventing scattering of a toner from a toner carrying roller, in a developing device having the toner carrying roller arranging projections and recesses on the surface, and to provide an image forming method for using an image forming apparatus and the roller to form images. <P>SOLUTION: In the image forming apparatus which uses a developing roller 44, provided with regular irregularities, an interval Ho between an upstream side edge part 462e of an elastic member 462, attached to a regulation blade and the projections 441 of the surface of the developing roller 44 is larger than zero and a volume average particle size of the toner or less. An interval Hp, with the recesses 442 of the surface of the developing roller 44 is 1-2 times the volume average particle size of the toner. The image forming apparatus positively carries the toner of one layer or less on the projections 441 to obtain sufficient developing density, while preventing scattering. In addition, the apparatus makes two layers or fewer of the toner of the recesses 442 to suppress fog. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device having a toner carrying roller having a convex portion and a concave portion on the surface, an image forming apparatus, and an image forming method for forming an image 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 properties of the toner carried on the surface of such a toner carrying roller, the applicant of the present application has regularly arranged convex portions on the surface of the roller formed in a cylindrical shape, and the periphery of the convex portions. 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.

Japanese Patent Laying-Open No. 2008-299011 (for example, FIG. 7)

  In the technique described in Patent Document 1 described above, a very small amount of toner is allowed to adhere to the convex portion of the toner carrying roller surface, but almost all toner is carried in the concave portion. This is to prevent the development memory phenomenon of an image caused by developing with toner having a small particle size carried on the convex portion and having a slow rise in charging (see paragraph 0085 of Patent Document 1). In addition, it is possible to prevent the toner from being scattered by the wind pressure associated with the rotation of the roller by setting the toner in the recess recessed from the surface of the toner carrying roller.

  On the other hand, in such a configuration, since the amount of toner transport relative to the surface area of the toner carrying roller is absolutely reduced, it is difficult to obtain a high development density. In addition, the density of the toner conveyance amount on the surface of the toner carrying roller is reflected in the image, and an uneven pattern on the surface of the toner carrying roller may appear in the image. As described above, in the technique of forming an image using the toner carrying roller provided with regular irregularities, there is a problem of achieving both good prevention of toner scattering from the toner carrying roller and good image quality. .

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a developing device having a toner carrying roller having convex and concave portions on the surface, an image forming apparatus, and an image forming method for forming an image using the roller, toner carrying The object is to obtain good image quality while preventing toner scattering from the roller.

  In order to achieve the above object, a developing device according to the present invention includes a housing that accommodates toner therein, and a plurality of convex portions that are pivotally attached to the housing and each top surface forms part of the same cylindrical surface. A concave portion surrounding the convex portion, and a toner carrying roller that rotates while carrying the charged toner supplied from the housing on the surface, and abuts on the surface of the toner carrying roller in the housing. Regulating means for regulating the amount of toner carried on the surface, wherein the regulating means has a free end facing the upstream side in the rotation direction of the toner carrying roller, and an adjacent portion adjacent to the free end is the toner carrying roller. A regulating blade abutting on the surface, wherein a space between the tip of the free end and the convex portion of the toner carrying roller is larger than 0 and the volume level of the toner The sum of the distance between the tip of the free end and the convex portion of the toner-carrying roller and the height difference between the convex portion and the concave portion is one time the volume average particle size or less. It is characterized by being twice or more.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a housing that accommodates toner therein, and a plurality of shafts that are pivotally attached to the housing and whose top surfaces form part of the same cylindrical surface. Formed on the surface, and a toner carrying roller that rotates while carrying charged toner supplied from the housing on the surface, and contacts the surface of the toner carrying roller in the housing. A regulating unit that regulates the amount of toner carried on the surface in contact with the latent image carrier, and a latent image carrier that is disposed opposite to the carrying roller and carries an electrostatic latent image on the surface. Has a regulating blade that faces the upstream side in the rotation direction of the toner carrying roller and an adjacent portion adjacent to the free end contacts the surface of the toner carrying roller, and the free end The distance between the tip of the toner carrying roller and the convex part of the toner carrying roller is greater than 0 and less than or equal to the volume average particle diameter of the toner, and the gap between the tip of the free end and the convex part of the toner carrying roller; The sum of the height difference between the convex portion and the concave portion is 1 to 2 times the volume average particle size.

  In addition, in order to achieve the above object, the image forming method according to the present invention is a toner in which a plurality of convex portions each having a top surface forming part of the same cylindrical surface and concave portions surrounding the convex portions are formed on the surface. The toner is carried on the surface of the carrying roller, and a regulating means is brought into contact with the surface to regulate the amount of toner, and the latent image carrying body carrying the electrostatic latent image is opposed to the toner carrying roller. The electrostatic latent image is developed with toner, and the regulating means is configured such that the free end faces the upstream side in the rotation direction of the toner carrying roller and an adjacent portion adjacent to the free end abuts on the surface of the toner carrying roller. And a spacing between the tip of the free end and the convex portion of the toner carrying roller that is greater than 0 and less than or equal to the volume average particle diameter of the toner. The sum of the distance between the tip of the end and the convex portion of the toner carrying roller and the height difference between the convex portion and the concave portion is set to be 1 to 2 times the volume average particle diameter. Yes.

  In these inventions, the distance between the free end of the regulating blade and the convex portion of the toner carrying roller is set to be greater than 0 and equal to or less than the volume average particle diameter of the toner. That is, the gap between the free end tip of the regulating blade and the convex portion of the toner carrying roller is larger than 0 and smaller than the volume average particle diameter of the toner. For this reason, the convex portion is allowed to carry toner having a particle diameter equal to or smaller than the distance (opening height) between the regulating blade and the toner carrying roller in the opening.

  On the other hand, in the concave portion, the value obtained by adding the distance between the tip of the free end and the convex portion of the toner carrying roller to the height difference from the convex portion is 1 to 2 times the volume average particle diameter of the toner. This means that the opening height between the free end of the regulating blade and the concave portion of the toner carrying roller is 1 to 2 times the volume average particle diameter of the toner. Therefore, the toner layer of 1 layer or more and 2 layers or less is carried in the recess.

  The toner having a relatively small particle size carried on the convex portion has a high charge amount per mass and directly contacts the surface of the toner carrying roller, so that the electrostatic adsorption force to the toner carrying roller surface is relatively strong. The possibility of scattering due to wind pressure caused by the rotation of the toner carrying roller is low. Further, the amount of charge is expected to increase even when the toner is low-charged by rubbing between the toner carrying roller and the regulating blade.

  In the concave portion, the toner having a relatively high charge amount is strongly attracted to the surface of the toner carrying roller and is carried at a position close to the surface, while the toner having a low charge amount has a charge amount in contact with the surface of the toner carrying roller. It will adhere to high toner. In the present invention, since the toner carried in the concave portion is made up of two layers or less, the toner having a low charge amount that does not directly contact the surface of the toner carrying roller is rubbed by the regulating blade and the charge amount is improved. Because of this and the toner being conveyed in the form of being contained in the recess, scattering due to wind pressure is less likely to occur.

  The regulating blade increases the charge amount by contacting the toner carried on the convex part and the toner carried on the concave part that is not in direct contact with the toner carrying roller surface (that is, the charge quantity is low). The toner having a high charge amount that is in contact with the surface of the toner carrying roller in the concave portion has no effect. Therefore, it also has a function of reducing the variation in the toner charge amount on the surface of the toner carrying roller. This has the effect of suppressing fogging due to the low-charged toner. In this way, by developing the electrostatic latent image using both the toner carried on the convex portion and the concave portion, it is possible to obtain a sufficient development density and to prevent the uneven pattern from appearing in the image. As described above, according to the present invention, it is possible to obtain good image quality while preventing toner scattering from the toner carrying roller.

  The present invention is particularly effective when the volume average particle diameter of the toner is 5 μm or more. Since such a toner tends to increase the charge amount as compared with a toner having a smaller particle diameter, it can be suitably combined with the structure of the present invention in which toner is carried on a convex portion and used for development. On the other hand, the toner having a large average particle size has a large particle size distribution and spread of the charge amount distribution. However, in the present invention, the toner of the convex portion and the concave portion is rubbed against the regulating blade to suppress the variation in the charge amount. Therefore, it is possible to suppress the fog caused by the variation in the charge amount and obtain a good image quality.

  In these inventions, the height difference between the convex portion and the concave portion may be equal to or greater than the volume average particle size. However, even in this case, the sum of the height difference and the opening height at the convex portion must be not more than twice the volume average particle diameter of the toner. In this way, it is possible to reliably carry one or more layers of toner in the recess, and to ensure a sufficient development density.

  Further, the regulation blade may be formed of an elastic material having conductivity. By doing so, the charge transfer of the toner on the surface of the toner carrying roller can be promoted, the uniformity of the toner charge amount can be further improved, and the image quality can be improved.

  Further, the surface of the toner carrying roller may be made of metal. By doing so, the toner carrying roller can attract the charged toner to its surface by mirror image force, and toner scattering can be prevented more reliably.

  In this case, the toner carrying roller may be formed by forming the convex portion and the concave portion by rolling on the surface of a metal cylinder or column. In this way, the surface of the original cylinder or column forms a convex portion, while the groove cut by rolling functions as a concave portion, so that the top surface of each convex portion forms a single cylindrical surface. Since it can be easily obtained and the height difference between the convex portion and the concave portion can be easily controlled, toner layer regulation by the regulation blade can be performed with high accuracy.

1 is a diagram showing an 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 in FIG. 1. The figure which shows the external appearance of a developing device. The figure which shows the structure of a developing device, and a development bias waveform. The figure which shows the image development roller and the elements on larger scale of the surface. The figure which shows the relationship between a toner particle diameter and the adhesive force to a developing roller. FIG. 6 is a diagram for explaining toner layer regulation in the embodiment. The figure which represents the detail of a control nip typically. FIG. 6 is a diagram schematically illustrating a state of toner layer regulation in the embodiment. The figure which shows the evaluation result by the various combination of a toner and a regulation condition. The figure which shows the preferable range of opening height.

  FIG. 1 is a diagram showing an 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 positioned at predetermined developing positions facing the photosensitive member 22. Then, 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 with a predetermined gap, and the developing roller 44 to the photosensitive member 22 at the opposite position. Toner is applied to the surface. 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 shows the structure of the developing device and the developing bias waveform. More specifically, FIG. 4A is a cross-sectional view showing the structure of the developing device. FIG. 4B shows the relationship between the developing bias waveform and the photoreceptor surface potential. Each of the developing devices 4Y, 4C, 4M, and 4K has the same structure. Therefore, here, the configuration of the developing device 4K will be described in more detail with reference to FIG. 3 and FIG. 4A, but 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 rotatably attached to a housing 41 that accommodates a nonmagnetic one-component toner T therein, and the developing device 4K is positioned at the developing position. The developing roller 44 is positioned so as to face the photosensitive member 2 with a development gap DG therebetween, and these rollers 43 and 44 are engaged with a rotation driving unit (not shown) provided on the main body side in a predetermined direction. Rotate to. 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 or alloy such as copper, aluminum, and stainless steel. In this embodiment, an iron cylinder surface that has been subjected to electroless nickel / phosphorus plating is used. Then, when the two rollers 43 and 44 are rotated 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 agitated 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 second chamber 412 having a relatively small volume is provided by surrounding the supply roller 43 and the developing roller 44 with the side wall of the housing 41 and the partition wall 41a. 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. Conductive particles such as carbon particles are dispersed in the elastic member 462, and the resistivity is adjusted to about 10 ⁵ Ωcm.

  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 shown by the arrow in FIG. The member 461 is disposed on the upstream side of the rear end portion. In other words, the regulating blade 46 is attached such that one end (rear end portion) is fixed and the front end portion, which is the free end on the opposite side, is directed upstream in the rotation direction D4 of the developing roller 44. The elastic member 462 elastically contacts the surface of the developing roller 44 in the so-called counter direction 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 contact pressure of the regulating blade 46 on the surface of the developing roller 44, that is, the regulating load is adjusted to 15 gf / cm.

  The toner layer formed on the surface of the developing roller 44 in this way is sequentially conveyed to a position facing the photoreceptor 22 on which the electrostatic latent image is formed by the rotation of the developing roller 44. A developing bias from a bias power source 140 controlled by the engine controller 10 is applied to the developing roller 44. As shown in FIG. 4B, the surface potential Vs of the photosensitive member 22 is about the residual potential Vr in the exposed portion that is uniformly charged by the charging unit 23 and then irradiated with the light beam L from the exposure unit 6. The non-exposed portion where the light beam L is not irradiated has a substantially uniform potential Vo. On the other hand, the developing bias Vb applied to the developing roller 44 is a rectangular wave AC voltage on which a DC potential is superimposed, and the peak-to-peak voltage is represented by the symbol Vpp. By applying such a developing bias Vb, the toner carried on the developing roller 44 flies in the developing gap DG and partially adheres to each surface portion of the photosensitive member 22 according to the surface potential Vs, Thus, the electrostatic latent image on the photosensitive member 22 is visualized as a toner image of the toner color.

As the development bias voltage Vb, for example, a rectangular wave voltage having a peak-to-peak voltage Vpp of 1000 V and a frequency of about 3 to 4 kHz can be used. Of the repetition period Tc of the alternating current component of the developing bias Vb, the period in which the potential swings to the positive side is represented by the symbol Tp, the period in which the potential swings to the negative side is represented by the symbol Tn, and the waveform duty WD of the developing bias Vb is :
WD = Tp / (Tp + Tn) = Tp / Tc
In this embodiment, the bias waveform is determined so that Tp> Tn, that is, the waveform duty WD is larger than 50%. Typically, WD can be about 60%.

  The weighted average voltage Vave of the developing bias Vb obtained by adding the direct current component generated due to the waveform duty to the direct current component superimposed on the rectangular wave alternating current voltage has a potential difference with the residual potential Vr of the photoreceptor 22 so-called development contrast. Since this affects the image density, it can be set to a value necessary for obtaining a predetermined image density. Typically, for example, it can be set to about (-200) V.

  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 is a belt-like film formed of a flexible resin material such as polyethylene, nylon, or fluororesin and extending along a direction X parallel to the rotation axis of the developing roller 44 and orthogonal to the longitudinal direction X. One end in the short direction (the direction along the rotation direction of the developing roller 44) is fixed to the housing 41, and the other end is in contact with the surface of the developing roller 44. The other end is in contact with the developing roller 44 in the so-called trail direction so as to go downstream in the rotation direction D 4 of the developing roller 44, and remains on the surface of the developing roller 44 that has passed the position facing the photoconductor 22. In addition to guiding the toner in the housing 41, the toner in the housing is prevented from leaking outside.

  FIG. 5 is a diagram showing a partially enlarged view of the developing roller and its surface. The developing roller 44 is formed in a substantially cylindrical roller shape, and a shaft 440 is provided coaxially with the roller at both ends in the longitudinal direction. The shaft 440 is supported by the developing device 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. Eggplant. The convex portion 441 and the concave portion 442 surrounding the convex portion 441 are connected by a gentle side surface 443. That is, the normal line of the side surface 443 has a component in a direction outward in the radial direction of the developing roller 44 (upward in the drawing), that is, in a direction away from the rotation axis of the developing roller 44.

  In this embodiment, the arrangement pitch P of the convex portions 441 on the surface of the developing roller 44 is 80 μm in both the circumferential direction and the axial direction (X direction). The depth of the concave portion 442, that is, the height difference between the convex portion 441 and the concave portion 442 is 8 μm. Further, the gap (development gap) between the photosensitive member 22 and the development roller 44 at the development position is 100 μm.

  The developing roller 44 having such a structure can be manufactured by a manufacturing method using a so-called rolling process described in, for example, Japanese Patent Application Laid-Open No. 2007-140080. Thereby, a regular and uniform uneven part can be formed on the cylindrical surface of the developing roller 44. Therefore, the obtained developing roller 44 can carry a uniform and optimum amount of toner on its cylindrical surface, and the rolling property (ease of rolling) of the toner on the cylindrical surface of the developing roller 44 is also uniform. Can be. As a result, it is possible to prevent poor local charging and conveyance of the toner and to exhibit excellent development characteristics. Further, since the concavo-convex portion is formed using a mold, unlike the general developing roller obtained by blasting, the obtained concavo-convex portion can have a relatively large width at the tip of the convex portion. Such uneven portions have excellent mechanical strength. In particular, since the mechanical strength of the portion pressed by the mold is improved, the obtained concavo-convex portion has excellent mechanical strength as compared with that obtained by processing such as cutting. The developing roller 44 having such a concavo-convex portion can exhibit excellent durability. In addition, if the width of the tip of the convex part of the concave and convex part is relatively large, there will be little change in shape even if it is worn out, so it will be possible to prevent development characteristics from abruptly decreasing and to exhibit excellent development characteristics over a long period of time Can do.

  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 rollers 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 has the toner image fixed 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 reverse 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, it is placed again on the transport path F before the gate roller 81. At this time, the image is transferred first on the surface of the sheet S on which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2. 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 and the remaining amount of the built-in toner. 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, non-contact data transmission / reception is performed using electromagnetic means such as wireless communication. However, a connector is provided on the main body side and each developing device side, and the connector is mechanically fitted. By doing so, you may make it mutually transmit / receive data.

  In addition, as shown in FIG. 2, the apparatus includes a display unit 12 that is controlled by the CPU 111 of the main controller 11. The display unit 12 is configured by, for example, a liquid crystal display, and in response to 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 is brought into contact with 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, the toner used in this embodiment will be described. The toner is a non-magnetic one-component toner manufactured by a known pulverization method, and has a property of being negatively charged by frictional charging. In the pulverization method, it is difficult to produce a toner having a very small particle diameter, and the circularity is relatively low, but the particle size distribution (variation in particle diameter) is large. In this embodiment, the one having a volume average particle diameter (Dave) of about 8 μm, a standard deviation (σ) of about 1.5, and a circularity of about 0.92 is used. Toner particles having a large particle size have good developability in a low electric field and can bear a large amount of pigment, so that a high development density can be obtained. There are also the following advantages.

  FIG. 6 is a diagram showing the relationship between the toner particle diameter and the adhesion force to the developing roller. The forces acting to adhere the toner particles to the surface of the developing roller 44 are mainly contact charging adhesion force and van der Waals force that are electrostatic attraction acting on the charged toner. As shown in FIG. 6, 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, when the toner particle diameter is small, especially when it is 5 μm or less, the van der Waals force increases rapidly. Even with toner having the same charge amount, the image force generated by the adjacent conductor increases as the particle size decreases. For these reasons, the toner having a large particle size is higher in the ease of flying from the surface of the developing roller 44 (flying property). For this reason, the toner having a large particle diameter may have a smaller amplitude of the developing bias Vb than that having a small particle diameter.

  On the other hand, the fact that the toner is easy to fly also means that the toner is easily scattered from the developing roller 44. Although toner with a small particle size is difficult to scatter, it is difficult to obtain a high development density unless the amount of toner supplied to the development gap is increased. On the other hand, a toner having a large particle diameter can easily obtain a high development density, but is easily scattered. Thus, it is not easy to achieve both sufficient development density and prevention of scattering. In the present embodiment, toner having a relatively large particle diameter is used, and toner layer regulation on the developing roller 44 is performed as follows to achieve both of them.

  FIG. 7 is a view for explaining toner layer regulation in the present embodiment. More specifically, FIG. 7A is a diagram showing a state in which the regulating blade 46 is in contact with the surface of the developing roller 44, and FIG. 7B is a partially enlarged view thereof. As shown in these figures, a free end 46a of the regulating blade 46 opposite to one end fixed to the developing device housing 41 extends toward the upstream side in the rotation direction D4 of the developing roller 44, Of the elastic member surface 462 a facing the developing roller 44, the edge portion 462 e that is the upstream tip is not in contact with the developing roller 44 surface, but is in contact with the developing roller 44 slightly downstream. Here, the nip Nr formed by the contact between the developing roller 44 and the elastic member 462 is referred to as a “regulation nip”, and its length Ln is referred to as a “regulation nip length”.

  The edge portion 462e of the elastic member 462 and the surface of the developing roller 44 are slightly separated from each other, and the developing roller 44 along a virtual line R connecting the rotation center of the developing roller 44 and the edge portion 462e of the elastic member 462 The distance from the elastic member 462 is referred to as “opening height” and is represented by the symbol Ho. Further, the length from the upstream end portion of the regulation nip Nr to the edge portion 462e is referred to as “opening length” and is represented by the symbol Lo. In this embodiment, the mounting position of the regulating blade 46 with respect to the housing 41 is variable in the adjustment direction indicated by the arrow in FIG. 7B, and thereby the opening length Ho is increased or decreased to increase or decrease the opening height Ho. Can be adjusted.

  FIG. 8 is a diagram schematically showing details of the restriction nip. As described above, the space between the developing roller 44 and the elastic member 462 is open on the upstream side of the regulation nip Nr. More specifically, as shown in FIG. 8A, the surface of the developing roller 44 closest to the edge portion 462e of the elastic member 462 is convex at each position along the axial direction (X direction) of the developing roller 44. There are a case where it is 441 and a case where the concave portion 442 is closest to the edge portion 462e as shown in FIG. The opening height Ho shown in FIG. 7B is a macroscopic opening height when the surface of the developing roller 44 is regarded as a cylinder. Strictly speaking, as shown in FIG. The distance between the convex portion 441 and the edge portion 462e of the elastic member 462. In the following, when it is necessary to clarify this point, the opening height Ho is referred to as “convex opening height”. On the other hand, as shown in FIG. 8B, the interval between the concave portion 442 of the developing roller 44 and the edge portion 462e of the elastic member 462 is larger, and this interval is referred to as “recess opening height” and is represented by the symbol Hp. As is apparent from the relationship shown in FIG. 8C, the recess opening height Hp is obtained by adding the height difference Hd between the protrusion 441 and the recess 442 to the protrusion opening height Ho.

  In this embodiment, the convex opening height Ho is set to a value greater than 0 and equal to or less than the volume average particle diameter Dave of the toner, while the concave opening height Hp is greater than the convex opening height Ho and the toner The value is 1 to 2 times the volume average particle diameter Dave. Specifically, for the toner having a volume average particle diameter Dave of 8 μm, the convex opening height Ho is set to 5 μm, which is smaller than this. As described above, since the height difference Hd between the convex portion 441 and the concave portion 442 is 8 μm, the total concave opening height Hp is 13 μm, which is larger than the volume average particle diameter Dave of the toner and smaller than twice that. . In this way, as described below, this embodiment suppresses scattering and leakage due to toner dropping from the developing roller 44 and fogging on the image while obtaining a sufficient development density. It is possible to do.

  FIG. 9 is a diagram schematically showing the state of toner layer regulation in this embodiment. In the opening between the convex portion 441 on the surface of the developing roller 44 and the edge portion 462e of the elastic member 462 shown in FIG. 9A, the opening height Ho is equal to or less than the volume average particle diameter Dave of the toner. For this reason, only toner Ts having a particle size equal to or smaller than the opening height Ho (indicated by a circle with hatching in the drawing) Ts enters between the developing roller 44 and the elastic member 462 and is carried on the convex portion 441. The Rukoto. On the other hand, a toner having a particle diameter larger than the opening height Ho, that is, a toner Ta having an average particle diameter indicated by white circles, or a volume average particle diameter Dave indicated by hatched circles with halftone dots. The toner Tl having a particle size is not carried on the convex portion 441.

  On the other hand, at the opening between the recess 442 on the surface of the developing roller 44 and the edge 462e of the elastic member 462, the recess opening height Hp is equal to or larger than the volume average particle diameter Dave of the toner, as shown in FIG. Accordingly, the concave portion 442 carries toner having a particle size equal to or smaller than the concave opening height Hp. Here, for example, assuming that the recess opening height Hp is twice the volume average particle diameter Dave of the toner, which is the upper limit of the requirements of the present invention, a toner layer consisting of two layers of toner is formed on the recess 442 on average. It will be. In addition, since the toner having the convex portion opening height Ho or less adheres to the top surface of the convex portion 441 and enters the elastic member 462, the interval between the concave portion 442 and the elastic member 462 is also within the regulation nip. It is maintained at a value substantially close to the recess opening height Hp. In particular, in this embodiment, the regulated load is set to a relatively low value (15 gf / cm), so that the toner is not crushed between the convex portion 441 and the elastic member 462.

  As a result, at the regulation nip Nr and the downstream side thereof, as shown in FIG. 9C, the top surface of the convex portion 441 of the developing roller 44 has mainly one small particle size (convex portion opening height Ho or less). ), A thin toner layer (one or less in terms of average particle size) is formed, while the recess 442 has an average particle size corresponding to the recess opening height Hp. Thus, a toner layer of 1 layer or more and 2 layers or less is formed.

  According to the knowledge of the inventors of the present application, among the toners carried on the surface of the developing roller 44, those having a relatively high charge amount are carried in a state of being in direct contact with or close to the surface of the developing roller 44, but the charge amount is inferior. The toner tends to be carried at a position away from the surface of the developing roller 44, that is, in a state of being attached on the highly charged toner that is in direct contact with the surface of the developing roller 44. This is presumably because the higher the charge amount of toner, the stronger the force attracted to the developing roller 44 which is a conductor.

  As described above, the toner having a low charge amount and weak adhesion to the surface of the developing roller 44 may be separated from the surface of the developing roller 44 due to the wind pressure received due to the rotation of the developing roller 44, and may cause scattering and leakage. With respect to this problem, in this embodiment, only a relatively small particle size toner having a strong mirror force acts on the convex portion 441, and the toner layer is made thin so that almost all the toner is removed from the surface of the developing roller 44. To make direct contact. Thereby, the detachment of the toner from the convex portion 441 can be suppressed. In particular, since the toner with insufficient charge amount can be expected to increase the charge amount by being rubbed against the elastic member 462, separation from the surface of the developing roller 44 can be effectively suppressed.

  Further, in the concave portion 442, since the toner is carried in a region retracted inward (side closer to the central axis) from the outer peripheral surface of the enveloping developing roller 44 including the top surface of each convex portion 441, the toner has wind pressure. Is less affected by In addition, since the toner layer is not more than two layers, the toner having a low charge amount and not in contact with the surface of the developing roller 44 is surely rubbed from the elastic member 462, so that the charge amount is increased. For these reasons, the detachment of the toner from the developing roller 44 is also suppressed in the concave portion 442, and scattering and leakage can be prevented.

  In addition, when only the toner that is not in direct contact with the surface of the developing roller 44 in the concave portion 442 is rubbed against the elastic member 462 and the charge amount of such toner is increased, the charge that is originally in direct contact with the surface of the developing roller 44 is high. It also has the effect of reducing the difference in charge amount with the toner having the amount and reducing the variation in charge amount. In this way, a sufficient developing density can be obtained by causing the toner carried on both the convex portion 441 and the concave portion 442 to contribute to development with a small variation in charge amount.

  FIG. 10 is a diagram showing evaluation results based on various combinations of toner and regulation conditions. As shown by the broken line in FIG. 10A, the convex opening height Ho increases as the opening length Lo increases. On the other hand, since the height difference Hd between the convex portion 441 and the concave portion 442 is added to the concave portion opening height Hp, the concave portion opening height Hp also varies depending on the opening length Lo, similarly to the convex portion opening height Ho. To do. Further, it varies depending on the height difference Hd between the convex portion 441 and the concave portion 442.

  Various combinations of the toner volume average particle diameter Dave and the regulation conditions (opening heights Ho and Hp) were changed to evaluate the development density, toner scattering / leakage from the developing roller 44, and the degree of fogging on the image. . More specifically, the amount of toner scattering / leakage and fog generated when an image is formed at a predetermined development density was determined. A part of the result is shown in FIG. The opening heights Ho and Hp and the height difference Hd are normalized by the volume average particle diameter Dave of the toner. In the figure, a circle indicates that the result is the best, a triangle indicates that the result is slightly inferior, and a cross indicates that the result is inferior. The column with two crosses indicates that the state was the worst.

  The sample A has a so-called edge restriction in which the convex opening height Ho is 0, that is, the edge 462e of the elastic member 462 is brought into contact with the convex 441 and included in the regulation nip Nr. In this case, the recess opening height Hp coincides with the height difference Hd. At this time, since no toner is carried on the convex portion 441, there is no problem with scattering and leakage, but the amount of fogging is slightly large, particularly when the height difference Hd between the convex portion 441 and the concave portion 442 is large. This is because when the height difference Hd is increased and the toner layer carried on the recess 442 is thickened, the amount of toner passing through the regulation nip Nr increases without contacting any of the developing roller 44 and the elastic member 462. This is considered to be due to the fact that the effect of suppressing the variation in charge is not obtained, and the toner conveyed to the development gap contains a large amount of toner having a low charge amount.

  In sample B, the convex opening height Ho was 0.6 times the volume average particle diameter Dave of the toner. In this case, good results were obtained for both scattering / leakage and fogging, but the height difference Hd between the convex portion 441 and the concave portion 442 was increased, and the concave opening height Hp was twice the volume average particle diameter Dave of the toner. Above this, there was a tendency for fog to increase. The reason for this is the same as described above, and it is considered that the toner having more than two layers held in the concave portion 442 and the toner having a low charge amount increased.

  In sample C, the convex opening height Ho was larger than the volume average particle diameter Dave of the toner. In this case, scattering / leakage and fogging were the worst results regardless of the recess opening height Hp. This is because the toner having a large particle diameter and easily coming off from the developing roller 44 is carried on the convex portion 441, and the concave portion 442 is deepened and a multilayer toner is carried, thereby increasing the charge amount. This is thought to be due to the increased variation.

In this way, like the range surrounded by the thick line in the figure,
0 <Ho ≦ Dave (Formula 1)
Dave ≦ Hp = Ho + Hd ≦ 2Dave (Formula 2)
Good results were obtained in a range where both were satisfied. In these samples, when the recess opening height Hp was made smaller than the volume average particle diameter Dave of the toner, the amount of toner transport was remarkably reduced, and sufficient development density could not be obtained.

  FIG. 11 is a view showing a preferable range of the opening height. From the experimental results as described above and the considerations described so far, it can be said that the preferred ranges for the combination of the convex opening height Ho and the concave opening height Hp are as follows. That is, as shown in FIG. 11, the convex opening height Ho is desirably larger than 0 and equal to or smaller than the volume average particle diameter Dave of the toner (Formula 1). The recess opening height Hp obtained by adding the height difference Hd between the projections 441 and the recesses 442 is preferably not less than twice the volume average particle diameter Dave of the toner (Formula 2).

  On the other hand, when considering the image forming apparatus described in Patent Document 1 (Japanese Patent Laid-Open No. 2008-299011) described above as a comparative example, the toner has a volume average particle diameter Dave of 4.6 μm and a convex opening. The height Ho is 2 μm, and the height difference Hd between the convex part and the concave part is 8 μm. Accordingly, the requirement of the above (Equation 1) that the convex opening height Ho is larger than 0 and equal to or smaller than the volume average particle diameter Dave of the toner is satisfied, but the height difference Hd between the convex portion and the concave portion is added thereto. The concave opening height Hp is 10 μm, which exceeds twice the volume average particle diameter Dave of the toner, and the requirement of (Equation 2) is not satisfied. Therefore, in the configuration of Patent Document 1, it is expected that the fog increases when a toner having a larger particle diameter is used.

  As described above, in this embodiment, in the image forming apparatus using the developing roller 44 having regular irregularities on the surface, the toner layer carried on the developing roller 44 is the volume average particle size of the toner for the convex portion 441. In terms of diameter, it is 1 layer or less, and the recess 442 is 1 layer or more and 2 layers or less. More specifically, when the regulating blade 46 is brought into contact with the developing roller 44, the opening height on the uppermost stream side is equal to or less than the volume average particle diameter Dave of the toner in the convex portion 441 and the volume average particle diameter of the toner in the concave portion 442. It is set to be 1 to 2 times that of Dave. By doing so, scattering, leakage, fogging, and the like of the toner from the developing roller 44 can be suppressed while obtaining a sufficient developing density. Therefore, in this embodiment, it is possible to obtain good image quality.

  Such a configuration is particularly suitable when a toner having a large particle size and a large particle size distribution, for example, a toner having a volume average particle size of 5 μm or more is used. A toner having a large spread of particle size distribution, that is, a toner having a large variation in particle size, is not easy to achieve both development density and prevention of scattering, etc., but in this embodiment, development with regular unevenness that manages the height difference is performed. The roller 44 is used, and a toner having a relatively small particle size contained in the toner is selectively carried on the convex portion 441, and the other is carried on the concave portion 442, so that both development density and prevention of scattering are compatible. Can be made.

  In the above embodiment, the elastic member 462 constituting the regulating blade 46 is made of a resin material that is originally an insulator. However, since the resistivity is adjusted to provide conductivity, the regulating nip Nr It is possible to promote the movement of charges between toners and reduce the variation in charge amount.

  In this embodiment, since the developing roller 44 is made of metal and has irregularities formed by rolling, it is possible to precisely manage the level difference of the irregularities. As a result, the toner layer can also be controlled with high accuracy, and a great effect is achieved in making the effect of the present invention more reliable.

  As described above, in this embodiment, the photosensitive member 22, the developing roller 44, and the regulating blade 46 function as the “latent image carrier”, “toner carrying roller”, and “regulating means” of the present invention, respectively. . Further, the developing devices 4Y, 4M, 4C and 4K provided with these correspond to the “developing device” of the present 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 above-described embodiment is a so-called jumping development type image forming apparatus in which the photosensitive member 22 and the developing roller 44 are opposed to each other with a predetermined gap therebetween, and the toner is caused to fly between them. The present invention can also be applied to an apparatus that applies an AC developing bias in a state.

  Further, for example, the convex portion 441 of the developing roller 44 of the above embodiment is formed in a substantially rhombus shape, but is not limited to this, and for example, the convex portion may have another shape such as a circle or a triangle. Also good. Moreover, the shape of each convex part does not need to be the same, The thing of a different shape may be mixed. However, in any case, in order to obtain the effect of controlling the toner layer according to the present invention, at least the top surface of each convex portion has a structure that forms a part of the same cylindrical surface. Is desirable. Further, it is desirable that the depth of the recess is substantially constant. In this respect, a structure in which concaves and convexes are originally formed by carving concaves on a smooth cylindrical surface is particularly effective.

  In the above embodiment, pulverized toner having a volume average particle diameter of 5 μm or more is used. This is because the present invention exhibits a particularly excellent effect when a pulverized toner having a large variation in particle size and low circularity is used. However, the toner that can be used in the image forming apparatus to which the present invention is applied is not limited to the above. For example, a toner manufactured by a polymerization method or an apparatus using a toner having a smaller particle diameter may be used. The present invention is effective.

  The image forming apparatus of the above embodiment is a color image forming apparatus in which the developing device 4K and the like are mounted on the rotary developing unit 4, but the application target of the present invention is not limited to this. For example, the present invention is also applied to a so-called tandem color image forming apparatus in which a plurality of developing devices are arranged along an intermediate transfer belt, and a monochrome image forming device that includes only one developing device to form a monochrome image. Is possible.

  DESCRIPTION OF SYMBOLS 22 ... Photosensitive body (latent image carrier), 41 ... Housing, 44 ... Developing roller (toner carrying roller), 46 ... Restricting blade (regulating means), 46a ... Free end of regulating blade, 441 ... (Developing roller surface) ) ... convex part 442 ... concave part (on the surface of the developing roller) 462 ... elastic member (regulating means), 462e ... edge part (of the elastic member), Hd ... height difference between the convex part and the concave part, Ho ... convex part Part opening height, Hp: recess opening height, T: toner

Claims (8)

A housing that contains toner therein;
A plurality of convex portions that are pivotally attached to the housing and each top surface forms a part of the same cylindrical surface and a concave portion that surrounds the convex portions are formed on the surface, and the charging supplied from the housing to the surface A toner carrying roller that rotates while carrying toner;
A regulating means for regulating the amount of toner carried on the surface in contact with the toner carrying roller surface in the housing;
The regulating means has a regulating blade whose free end faces the upstream side in the rotation direction of the toner carrying roller and an adjacent portion adjacent to the free end contacts the surface of the toner carrying roller,
The distance between the free end and the convex portion of the toner carrying roller is greater than 0 and less than or equal to the volume average particle diameter of the toner, and
The sum of the distance between the tip of the free end and the convex portion of the toner carrying roller and the height difference between the convex portion and the concave portion is 1 to 2 times the volume average particle size. A developing device.   The developing device according to claim 1, wherein the toner has a volume average particle diameter of 5 μm or more.   The developing device according to claim 1, wherein a height difference between the convex portion and the concave portion is equal to or greater than the volume average particle diameter.   The developing device according to claim 1, wherein the regulating blade is formed of an elastic material having conductivity.   The developing device according to claim 1, wherein a surface of the toner carrying roller is made of metal.   The developing device according to claim 5, wherein the toner carrying roller has the convex portion and the concave portion formed on a surface of a metal cylinder or column by rolling. A housing that contains toner therein;
A plurality of convex portions that are pivotally attached to the housing and each top surface forms a part of the same cylindrical surface and a concave portion that surrounds the convex portions are formed on the surface, and the charging supplied from the housing to the surface A toner carrying roller that rotates while carrying toner;
A regulating means for regulating the amount of toner carried on the surface in contact with the toner carrying roller surface in the housing;
A latent image carrier that is disposed opposite the carrier roller and carries an electrostatic latent image on the surface;
The regulating means has a regulating blade whose free end faces the upstream side in the rotation direction of the toner carrying roller and an adjacent portion adjacent to the free end contacts the surface of the toner carrying roller,
The distance between the free end and the convex portion of the toner carrying roller is greater than 0 and less than or equal to the volume average particle diameter of the toner, and
The sum of the distance between the tip of the free end and the convex portion of the toner carrying roller and the height difference between the convex portion and the concave portion is 1 to 2 times the volume average particle size. An image forming apparatus. The toner is carried on the surface of a toner carrying roller having a plurality of convex portions whose top surfaces form a part of the same cylindrical surface and concave portions surrounding the convex portions on the surface, and a regulating means is applied to the surface. To regulate the amount of toner,
Developing the latent electrostatic image with toner with the latent image bearing member carrying the latent electrostatic image facing the toner bearing roller; and
The restricting means has a structure having a restricting blade in which a free end faces an upstream side in the rotation direction of the toner carrying roller and an adjacent portion adjacent to the free end contacts the surface of the toner carrying roller. The interval between the tip and the convex portion of the toner carrying roller is greater than 0 and less than or equal to the volume average particle diameter of the toner, the interval between the tip of the free end and the convex portion of the toner carrying roller, and the convex An image forming method, wherein the sum of the height difference between the portion and the concave portion is 1 to 2 times the volume average particle size.

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