JP6206256B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device that performs development by an electrophotographic developing method using a one-component magnetic developer (toner) and an image forming apparatus including the developing device, and more particularly, a fixed magnet roller having three magnetic poles as a toner carrier. The present invention relates to a developing device using a developing sleeve in which is installed.

  There is known a jumping development method in which a single component magnetic toner is used to cause the toner to fly to a photoreceptor (drum side). In this jumping development, a magnetic toner having a predetermined charge is held on a non-magnetic toner carrier (developing sleeve), and between the developing sleeve and a photoreceptor on which an electrostatic latent image is formed. By applying an alternating electric field, toner is selectively ejected to a portion corresponding to an image and developed. For this reason, the magnetic toner does not fly to the non-image area, and as a result, high image quality without fogging is obtained. However, in the case of this jumping development, since the alternating electric field flies between the triboelectric charge possessed by the toner and the electrostatic latent image formed on the photoreceptor, the amount of charge possessed by the toner greatly contributes to the development. come. Therefore, if the charge amount of the toner is large, it is easy to fly. Conversely, if the charge amount is small, it becomes difficult to fly.

  In general, since toner has a predetermined particle size distribution, a toner having a large particle size has a smaller specific surface area than a toner having a small particle size, and thus generally the amount of charge held tends to be small. On the other hand, toner with a large particle size has a large magnetic attractive force to the sleeve surface, and conversely, toner with a small particle size has a small magnetic attractive force. Therefore, when a developing device employing the above-described jumping development method is used, toner having a large charge amount and a small magnetic attractive force (toner having a small particle diameter) is preferentially developed. There is a tendency that toner having a large particle diameter remains on the sleeve. Then, a so-called “selective development” problem occurs in which the amount of toner developed gradually decreases and as a result, the image density decreases. This tendency becomes more prominent when the life of the developing device is extended with the extension of the life of the image forming apparatus in recent years.

  In the following Patent Document 1, as a means for preventing a phenomenon of developing density reduction caused by the use of a developing device of the one-component magnetic jumping developing system, a timing at which image formation is not performed is used according to the usage status of the developing device. It has been proposed to perform so-called refresh development for forcibly transferring the toner on the sleeve to the photoreceptor.

  Also, in Patent Document 2 below, in order to keep the toner charge amount constant (to eliminate image quality deterioration due to excessive charging), the magnetic flux density of the transport pole is 40 to 70% of the development pole, and the half-value width is 45 to 60 degrees. It has been proposed that the angle between the transport pole and the regulation pole is set to 100 to 110 degrees to reduce the toner transport force and prevent excessive charging of the small diameter toner.

JP 2000-310909 A JP 2000-187390 A

However, since it forcibly removed residual toner on the sleeve by performing a refresh developed as disclosed in Patent Document 1, although capable of obtaining a stable development over a long period, the toner unnecessarily Will consume. This leads to an increase in container capacity and a decrease in the number of printable sheets, and thus measures that do not depend on such processing are required.

  In addition, as in the above-mentioned Patent Document 2, when the toner conveying force is reduced to prevent excessive charging of the toner and the amount of toner around the blade is reduced, in high density printing, there is a problem such as image omission due to insufficient toner supply. Is likely to occur. In addition, a separate measure for stabilizing the toner amount around the blade is required.

  The present invention has been made in order to solve the above-described problems, and it is possible to improve the circulation of the toner around the blade so as to stably charge the toner while stabilizing the amount of toner around the blade without performing refresh development. The purpose is to improve.

A developing device according to one aspect of the present invention includes a fixed magnet roller having three magnetic poles, a developing roller having a developing sleeve in which the fixed magnet roller is incorporated, and
A blade disposed on the developing sleeve on the upstream side in the rotation direction of the developing sleeve from the developing position by the developing roller,
A developing device that restricts passage of the one-component magnetic toner carried on the developing sleeve by the magnetic force of the fixed magnet roller by the blade and conveys the toner to the developing position;
The magnetic pole of the fixed magnet roller has a developing pole disposed in the vicinity of the developing position, a position different from the developing pole, and a position facing the developing container bottom surface on the downstream side of the developing position in the rotation direction of the developing sleeve. A shield pole disposed on the surface, and a polarity different from that of the development pole, and the three poles of the blade pole disposed at a position facing the blade,
The distribution in the circumferential direction where the magnetic flux density of the blade pole is 80% of the peak value is relative to the reference axis connecting the center of the fixed magnet roller and the peak position of the magnetic flux density of the blade pole. The upstream side is set wider than the rotation direction downstream ,
Circumferential angle which the magnetic flux density is 80% of the peak value of the blade electrode, 12 ° downstream in the rotation direction of the developing sleeve from the reference axis, is 24 ° der shall upstream in the rotational direction .

  According to the present invention, with respect to the developing roller magnetized with three poles, the toner circulation property around the blade is maintained so that the toner is stably charged while the amount of toner around the blade is stabilized without performing refresh development. Improved. As a result, even when the developing device is used for a long time, a new toner is always kept on the surface of the sleeve, so that the toner average particle diameter does not change greatly. As a result, it is possible to suppress the selective development of the toner held on the sleeve surface, and the image density is hardly lowered even after long-term use.

1 is a left side cross-sectional view illustrating a structure of an image forming apparatus including a developing device according to an embodiment of the present invention. 1 is a cross-sectional configuration diagram of a developing device according to an embodiment of the present disclosure. FIG. 3 is a diagram in which the magnetic flux density distribution of each magnetic pole of the fixed magnet roller is superimposed on FIG. 2. It is a graph which shows transition of the image density at the time of durability. 3 is a graph of particle size distribution of toner in a developing device.

  Hereinafter, a developing device and an image forming apparatus including the developing device according to an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a left side sectional view showing the structure of an image forming apparatus provided with a developing device according to an embodiment of the present invention.

  The image forming apparatus 1 according to an embodiment of the present disclosure is, for example, a printer. In the present embodiment, the side (the right side in FIG. 1) on which a manual feed tray 65 to be described later is disposed is the front side of the image forming apparatus 1.

  The image forming apparatus 1 includes a housing M, an image forming unit that forms a predetermined image on a sheet (transfer material) T based on predetermined image information, a sheet T that is fed to the image forming unit, and an image that is And a paper supply / discharge unit that discharges the formed paper T.

  As shown in FIG. 1, the image forming unit includes a photosensitive drum 2, a charging unit 10, a laser scanner unit 4, a developing device 16, a toner cartridge 5, a toner supply device 6, a transfer roller 8, A fixing device 9 and a drum cleaning unit 11 are provided. The paper supply / discharge unit includes a paper supply cassette 52, a manual feed tray 65, a registration roller pair 80, and a conveyance path L for the paper T.

  The photosensitive drum 2 is made of a cylindrical member and functions as an image carrier. The photosensitive drum 2 is disposed in the housing M in such a manner that it can rotate around a rotation axis perpendicular to FIG. An electrostatic latent image is formed on the surface of the photosensitive drum 2.

  The charging unit 10 is disposed above the photosensitive drum 2. The charging unit 10 uniformly charges the surface of the photosensitive drum 2 positively (plus polarity).

  The laser scanner unit 4 is disposed above the photosensitive drum 2 and spaced from the photosensitive drum 2. The laser scanner 4 includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  The laser scanner unit 4 scans and exposes the surface of the photosensitive drum 2 based on image information output from an external device such as a PC (personal computer). By performing scanning exposure with the laser scanner unit 4, electric charges charged on the surface of the photosensitive drum 2 are removed. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 2.

  The developing device 16 is disposed in front of the photosensitive drum 2 (on the right side in FIG. 1). The developing device 16 develops a monochrome (usually black) toner image on the electrostatic latent image formed on the photosensitive drum 2. The developing device 16 includes a developing roller 17 that can be disposed to face the photosensitive drum 2 and a stirring spiral 18 for stirring the toner.

  The toner cartridge 5 stores toner supplied to the developing device 16.

  The toner supply device 6 supplies the toner contained in the toner cartridge 5 to the developing device 16.

  The drum cleaning unit 11 is disposed behind the photosensitive drum 2 (on the left side in FIG. 1). The drum cleaning unit 11 removes toner and deposits remaining on the surface of the photosensitive drum 2, and transports the removed toner and the like to a predetermined recovery mechanism for recovery.

  The transfer roller 8 functions as a transfer device that transfers the toner image developed on the surface of the photosensitive drum 2 to the paper T. A transfer bias for transferring the toner image developed on the photosensitive drum 2 to the paper T is applied to the transfer roller 8 by a voltage application unit (not shown).

  The transfer roller 8 is brought into contact with and separated from the photosensitive drum 2. Specifically, the transfer roller 8 is configured to be movable between a contact position where the transfer roller 8 is in contact with the photosensitive drum 2 and a separation position where the transfer roller 8 is separated from the photosensitive drum 2. Specifically, the transfer roller 8 is moved to the contact position when the toner image developed on the photosensitive drum 2 is transferred to the paper T, and is moved to the separation position in other cases.

  The paper T is sandwiched between the photosensitive drum 2 and the transfer roller 8 and pressed against the surface of the photosensitive drum 2 (the side on which the toner image is developed). In this way, the transfer nip N is formed, and the toner image developed on the photosensitive drum 2 is transferred onto the paper T.

  The fixing device 9 melts the toner constituting the toner image transferred onto the paper T and fixes it on the paper T. The fixing device 9 includes a heating roller 9a and a pressure roller 9b pressed against the heating roller 9a. The heating roller 9a and the pressure roller 9b convey the paper T on which the toner image is transferred so as to be sandwiched. By transporting the paper T so as to be sandwiched between the heating roller 9a and the pressure roller 9b, the toner transferred onto the paper T is melted and fixed.

  The paper feed cassette 52 is disposed at the bottom of the housing M. The paper feed cassette 52 is arranged on the front side (right side in FIG. 1) of the housing M so as to be able to be pulled out in the horizontal direction. The paper feed cassette 52 includes a placement plate 60 on which the paper T is placed. The paper feed cassette 52 stores the paper T in a state where the paper T is stacked on the placement plate 60. The cassette paper feed unit 51 is disposed at the paper feed side end (the right side end in FIG. 1) of the paper feed cassette 52. The cassette paper feed unit 51 sends out the paper T stored in the paper feed cassette 52 to the transport path L.

  The cassette paper feeding unit 51 includes a multi-feed prevention mechanism including a forward feed roller 61 that takes out the paper T placed on the placement plate 60 and a roller pair 63 that feeds the paper T to the transport path L one by one.

  A transport path L for transporting the paper T is formed between the cassette paper feed unit 51 or the manual paper feed unit 64 and the paper discharge unit 50. The conveyance path L is transferred from the first conveyance path L1 from the cassette paper feeding unit 51 to the first merge part P1, the second conveyance path L2 from the first merge part P1 to the registration roller pair 80, and the transfer from the registration roller pair 80. A third conveyance path L3 to the roller 8, a fourth conveyance path L4 from the transfer roller 8 to the fixing device 9, a fifth conveyance path L5 from the fixing device 9 to the branching portion P3, and a discharge portion from the branching portion P3. The sixth transport path L6 up to 50 and the seventh transport path L7 from the manual feed tray 65 to the first junction P1.

  The first merging portion P1 is a merging portion between the first conveyance path L1 that conveys the paper T from the cassette paper feeding section 51 and the seventh conveyance path L7 that conveys the paper T from the manual feed tray 65.

  A second junction P2 is disposed in the middle of the second transport path L2. Furthermore, the conveyance path L has a return conveyance path Lb from the branching part P3 to the second joining part P2. The second junction P2 is a junction between the second conveyance path L2 and the return conveyance path Lb.

  A registration roller pair 80 is arranged on the upstream side (right side in FIG. 1) of the transfer direction of the paper T in the transfer roller 8.

  The return conveyance path Lb is a conveyance path that is provided so that the opposite surface (non-printing surface) to the surface that has already been printed faces the photosensitive drum 2 when performing duplex printing on the paper T.

  A manual paper feed unit 64 is provided on the front side of the housing M (on the right side in FIG. 1) and above the paper feed cassette 52. The manual paper feed unit 64 includes a manual tray 65 that is a paper placement unit, and a paper feed roller 66 that is a paper feed roller.

  On the opening side of the paper discharge unit 50, a paper discharge stacking unit M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the housing M. The paper discharge stacking portion M1 is a portion formed by the upper surface of the housing M being depressed downward. The bottom surface of the paper discharge stacking unit M1 constitutes a part of the top surface of the housing M. In the paper discharge stacking unit M1, the paper T discharged from the paper discharge unit 50 and having a predetermined image transferred thereon is stacked and stacked.

  Next, the configuration of the developing device 16 will be described. FIG. 2 is a cross-sectional configuration diagram of the developing device 16 according to an embodiment of the present invention.

  The developing device 16 has a developing container 21 in which one-component magnetic toner is accommodated, and a developing roller 17 facing the photosensitive drum 2 at the developing position is disposed in the developing container 21.

  The developing roller 17 includes a fixed magnet roller 17a having three magnetic poles (N, S1, S2), and a developing sleeve 17b in which the fixed magnet roller 17a is housed. The developing sleeve 17b is formed of, for example, a nonmagnetic material such as aluminum or stainless steel, and is driven to rotate counterclockwise in FIG.

  In the developing container 21, a blade 23 is disposed on the developing sleeve 17b on the upstream side of the developing position in the rotation direction of the developing sleeve 17b. The blade 23 charges the toner and regulates the amount of toner passing to form a thin toner layer on the developing sleeve 17b. A magnet body 24 is fixed to the rear surface of the blade 23 (the surface located upstream in the rotation direction of the developing sleeve 17b as viewed from the developing position).

  A pair of agitation spirals 18 a and 18 b are arranged in the developing container 21. The rotation axes of the pair of stirring spirals 18 a and 18 b are arranged horizontally or above the rotation axis of the developing roller 17. A partition wall 27 extending in the longitudinal direction of the developing roller 17 is disposed between the pair of stirring spirals 18a and 18b. Between the both ends in the longitudinal direction of the partition wall 27 and the inner surface of the developing container 21, a passage path through which the toner passes is defined. The toner in the developing container 21 is agitated by the rotational driving of the agitating screws 18a and 18b, and the toner is conveyed in the direction of the developing roller 17.

  The toner replenished from the toner replenishing port 28 to the developing container 21 is conveyed to the agitating spiral 18a side through the above passage while being agitated by the rotational drive of the agitating spiral 18b. Then, the toner is supplied to the developing roller 17 by the stirring spiral 18a. The toner separated from the developing sleeve 17b is collected by the stirring spiral 18a and sent to the stirring spiral 18b side through the passage. That is, as indicated by the thick arrow in the figure, the toner is circulated in the order of the stirring spiral 18b, the passage, the stirring spiral 18a, and the passage along the partition wall 27 to supply the toner to the developing sleeve 17b. The toner separated from the developing sleeve 17b is collected.

  As described above, when toner is supplied to the peripheral surface of the developing sleeve 17b, the toner adheres to the peripheral surface of the developing sleeve 17b by the magnetic force of the fixed magnet roller 17a. As the developing sleeve 17b rotates, the toner adhering to the peripheral surface of the developing sleeve 17b is frictionally charged and restricted in passage when passing through the gap between the developing sleeve 17b and the blade 23, and the periphery of the developing sleeve 17b. A thin toner layer is formed on the surface.

  The toner thin layer moves in accordance with the rotation of the developing sleeve 17b, and is a position where the photosensitive drum 2 and the developing roller 17 are closest to each other by an AC electric field applied between the photosensitive drum 2 and the developing roller 17. At the developing position, the toner on the developing sleeve 17b flies to the electrostatic latent image on the photosensitive drum 2, and the electrostatic latent image is developed to form a toner image. At the developing position, the toner remaining on the developing sleeve 17b without flying on the photosensitive drum 2 moves with the rotation of the developing sleeve 17b, and is peeled off from the developing sleeve 17b by the rotating action of the stirring spiral 18a. Then, new toner is supplied to the developing sleeve 17b by the stirring spiral 18a. As described above, the toner peeled off from the developing sleeve 17b is mixed with newly supplied toner while circulating through the pair of stirring spirals 18a and 18b.

  FIG. 3 is a diagram in which the distribution of the magnetic flux density of each magnetic pole of the fixed magnet roller 17a is superimposed on the cross section of the developing device 16 shown in FIG. In the present embodiment, the fixed magnet roller 17a has, as magnetic poles, (1) a developing pole (N pole) arranged in the vicinity of the developing position and (2) a polarity different from the developing pole (N pole). And a shield pole (S1 pole) disposed at a position facing the bottom surface of the developing container 21 on the downstream side in the rotation direction of the developing sleeve 17b, and (3) a blade 23 having a polarity different from that of the developing pole (N pole). It consists of three poles of blade poles (S2 poles) arranged at positions facing each other. The blade 23 is disposed in a direction along a reference axis that connects the center of the fixed magnet roller 17a and the peak position of the magnetic flux density of the blade pole. As a result, the toner passing through the gap between the developing sleeve 17b and the blade 23 is sufficiently restricted, and a thin toner layer can be formed on the peripheral surface of the developing sleeve 17b.

  Here, the distribution in the circumferential direction where the magnetic flux density of the blade pole is 80% of the peak value is conventionally related to the reference axis connecting the center of the fixed magnet roller 17a and the peak position of the magnetic flux density of the blade pole. It was almost symmetrical about the reference axis. In the present embodiment, the distribution in the circumferential direction where the magnetic flux density of the blade pole is 80% of the peak value is asymmetrical more widely upstream than the downstream side in the rotation direction of the developing sleeve 17b with the reference axis as the center. It is set. Specifically, the distribution in the circumferential direction where the magnetic flux density of the blade pole is 80% of the peak value is 12 ° on the downstream side in the rotational direction of the developing sleeve 17b and the upstream side in the rotational direction. It exists in the region of 24 °. As described above, by broadening the magnetic force distribution of the blade pole upstream in the rotation direction of the developing sleeve 17b, the magnetic force distribution of the blade pole is expanded on the stirring spiral 18a side, and the toner circulation around the blade 23 is improved. .

  FIG. 4 is a graph showing the transition of image density during endurance. The plot expressed as “conventional” has a distribution in the circumferential direction where the magnetic flux density of the blade pole is 80% of the peak value as a reference axis connecting the center of the fixed magnet roller 17a and the peak position of the magnetic flux density of the blade pole. This is an example (hereinafter referred to as a conventional configuration) in which it is symmetrical (region of an angle of 18 ° from the reference axis to the downstream side and the upstream side in the rotation direction of the developing sleeve 17b). As is apparent from the graph, in the conventional configuration, the image density continues to decrease as the number of printed sheets increases. This is because the selective development described above has occurred. On the other hand, in this embodiment, the image density decreases until the number of printed sheets exceeds 1000, but the image density does not decrease thereafter. That is, selective development is suppressed.

  FIG. 5 is a graph of the particle size distribution of the toner in the developing device 16. The plot expressed as “initial” represents the particle size distribution of the toner in the developing device 16 when the number of printed sheets is zero. Initially, the average diameter is 7.561 μm and the median diameter (d50) is 7.414 μm. The plot expressed as “Conventional 28K” represents the particle size distribution of the toner in the developing device when the number of printed sheets is 28,000 with the conventional configuration. When the number of printed sheets is 28,000 with the conventional configuration, the average diameter is 9.693 μm and the median diameter (d50) is 9.805 μm. The plot expressed as “Embodiment 28K” represents the particle size distribution of the toner in the developing device 16 when the number of printed sheets is 28,000. In this embodiment, when the number of printed sheets is 28,000, the average diameter is 9.002 μm and the median diameter (d50) is 8.935 μm. As apparent from the graph, in the conventional configuration, the particle size distribution of the toner is largely shifted to the plus side, whereas in this embodiment, the shift width of the toner particle size distribution is suppressed to be small.

  As described above, according to the present embodiment, the developing roller magnetized with three poles is configured so that the toner is stably charged without stabilizing the amount of toner around the blade 23 without performing refresh development. The circulation property of the toner around 23 is improved. As a result, even when the developing device 16 is used for a long time, the toner on the surface of the developing sleeve 17b is constantly renewed, so that the average particle diameter does not change greatly. As a result, it is possible to suppress the selective development of the toner held on the surface of the developing sleeve 17b, and the image density is hardly lowered even after long-term use.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, a printer is used as an embodiment of the image forming apparatus according to the present invention. However, this is only an example, and other electronic devices such as a copier, a facsimile machine, and a composite Other image forming apparatuses such as a printer may be used.

  Moreover, in the said embodiment, the structure shown by the said embodiment using FIG. 1 thru | or FIG. 5 is only one Embodiment of this invention, and is not the meaning which limits this invention to the said structure.

1 Image forming apparatus 2 Photosensitive drum (image carrier)
8 Transfer roller (transfer device)
9 Fixing Device 16 Developing Device 17 Developing Roller 17a Fixed Magnet Roller 17b Developing Sleeve 18a Stirring Spiral 18b Stirring Spiral 21 Developing Container 23 Blade N Developing Electrode S1 Shielding Electrode S2 Blade Electrode

Claims (4)

A fixed magnet roller having three magnetic poles, and a developing roller having a developing sleeve in which the fixed magnet roller is incorporated;
A blade disposed on the developing sleeve on the upstream side in the rotation direction of the developing sleeve from the developing position by the developing roller,
A developing device that restricts passage of the one-component magnetic toner carried on the developing sleeve by the magnetic force of the fixed magnet roller by the blade and conveys the toner to the developing position;
The magnetic pole of the fixed magnet roller has a developing pole disposed in the vicinity of the developing position, a position different from the developing pole, and a position facing the developing container bottom surface on the downstream side of the developing position in the rotation direction of the developing sleeve. A shield pole disposed on the surface, and a polarity different from that of the development pole, and the three poles of the blade pole disposed at a position facing the blade,
The distribution in the circumferential direction where the magnetic flux density of the blade pole is 80% of the peak value is relative to the reference axis connecting the center of the fixed magnet roller and the peak position of the magnetic flux density of the blade pole. The upstream side is set wider than the rotation direction downstream ,
The circumferential angle of the magnetic flux density is 80% of the peak value of the blade electrode, the 12 ° downstream in the rotation direction of the developing sleeve from the reference axis, the developing device Ru 24 ° der upstream in the rotational direction.   The developing device according to claim 1, wherein the blade is disposed in a direction along the reference axis. A pair of stirring spirals for stirring the toner supplied from the toner supply device;
The developing device according to claim 1, wherein a rotation shaft of the pair of stirring spirals is disposed at a position that is horizontal with or above the rotation shaft of the developing roller. A developing device according to any one of claims 1 to 3 ,
An image carrier on which an electrostatic latent image is formed on the surface, and a toner image is developed on the electrostatic latent image by the developing device;
A transfer device that abuts against the image carrier and sandwiches a sheet to transfer the toner image onto the sheet;
The image forming apparatus having the toner image and a fixing device for fixing the toner image on the paper by heating the paper that has been transferred to melt the toner forming the toner image thermocompression bonding.