JP2017090541A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that can suppress an increase in the amount of charge of a developer that is absorbed on a magnet provided on a lateral face of a regulation member, and an image forming apparatus including the developing device.SOLUTION: A developing device comprises: a housing that stores a developer including a magnetic toner; a developing roller 54 that includes a first magnet 542 that attracts the developer inside the housing to a peripheral surface 54C with magnetic force; a regulation member 55 that includes a projection part 55B provided separated from the peripheral surface 54C of the developing roller 54 with a gap and regulates the thickness of the developer attached to the peripheral surface 54C; and a second magnet 56 that includes an opposing part 56A provided on a lateral face of the regulation member 55 on the upstream side of the rotation direction 54B of the developing roller 54, separated farther from the peripheral surface 54C than the regulation member 55, and is arranged opposite to the peripheral surface 54C, where the thickness T2 of the rotation direction 54B of the opposing part 56A is equal to or less than half the thickness T1 in the rotation direction 54B of the projection part 55B of the regulation member 55.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electrophotographic image forming apparatus and a developing device mounted on the image forming apparatus.

  In an image forming apparatus such as a printer capable of forming an image by electrophotography, an image may be formed using a developer containing magnetic toner. This type of image forming apparatus includes a developing device. The developing device includes a developing roller that draws the developer inside to a peripheral surface by a magnetic force, and a regulating member that regulates the thickness of the developer attached to the peripheral surface of the developing roller. 2. Description of the Related Art Conventionally, a developing device is known that includes a magnet on the upstream side surface of the regulating member in the rotation direction of the developing roller (see Patent Document 1). In the developing device, the developer passing through the position facing the regulating member on the peripheral surface is compressed by the developer attracted by the magnet. Thereby, the thickness variation in the thin layer of the developer formed by the regulating member is suppressed.

JP 2014-219694 A

  By the way, when the magnet is provided on the side surface of the regulating member, the developer roller rotates, so that the developer adsorbed on the magnet and the developer attached to the peripheral surface of the developer roller are rotated. The rubbing is repeated. As a result, the charge amount of the developer adsorbed on the magnet may become excessive. When the developer having such an excessive charge amount is separated from the magnet and used for image formation, problems such as black streaks appear in the formed image.

  An object of the present invention is to provide a developing device and an image forming apparatus capable of suppressing an increase in the charge amount of a developer adsorbed by a magnet provided on a side surface of a regulating member.

  A developing device according to one aspect of the present invention includes a housing, a developing roller, a regulating member, and a second magnet. The housing contains a developer containing magnetic toner. The developing roller includes a first magnet that is rotatably provided in the housing and draws the developer in the housing to a peripheral surface by a magnetic force. The regulating member has a first facing portion provided with a gap with respect to the circumferential surface of the developing roller, and regulates the thickness of the developer attached to the circumferential surface. The second magnet is provided on the side surface of the regulating member on the upstream side in the rotation direction of the developing roller, and has a second facing portion that is farther from the circumferential surface than the regulating member and faces the circumferential surface. And the thickness of the said rotation direction in the said 2nd opposing part is 1/2 or less of the thickness of the said rotation direction in the said 1st opposing part of the said limitation member.

  An image forming apparatus according to another aspect of the present invention includes a developing device and an image forming unit. The developing device includes a housing, a developing roller, a regulating member, and a second magnet. The housing contains a developer containing magnetic toner. The developing roller includes a first magnet that is rotatably provided in the housing and draws the developer in the housing to a peripheral surface by a magnetic force. The regulating member has a first facing portion provided with a gap with respect to the circumferential surface of the developing roller, and regulates the thickness of the developer attached to the circumferential surface. The second magnet is provided on the side surface of the regulating member on the upstream side in the rotation direction of the developing roller, and has a second facing portion that is farther from the circumferential surface than the regulating member and faces the circumferential surface. And the thickness of the said rotation direction in the said 2nd opposing part is 1/2 or less of the thickness of the said rotation direction in the said 1st opposing part of the said limitation member. On the other hand, the image forming unit can form an image based on image data.

  According to the present invention, it is possible to suppress an increase in the charge amount of the developer attracted by the magnet provided on the side surface of the regulating member.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of the developing device of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram illustrating a partial configuration of the developing device of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of the developing roller, the regulating member, and the second magnet of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram showing the configuration of the first magnet of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram showing an experimental result using the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

[Configuration of Image Forming Apparatus 10]
First, the configuration of an image forming apparatus 10 according to an embodiment of the present invention will be described with reference to FIG. Here, FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 10.

  The image forming apparatus 10 is a multifunction machine having a plurality of functions such as a facsimile function and a copy function, as well as a scan function for reading image data from a document and a print function for forming an image based on the image data. The present invention is applicable to image forming apparatuses such as printers, facsimile machines, and copiers.

  As shown in FIG. 1, the image forming apparatus 10 includes an automatic document feeder (ADF) 1, an image reading unit 2, an image forming unit 3, and a paper feeding unit 4.

  The ADF 1 includes a document setting unit, a plurality of conveyance rollers, a document pressing unit, and a paper discharge unit. In the ADF 1, the document P set on the document setting unit is conveyed by the plurality of conveyance rollers to the paper discharge unit via the image reading position by the image reading unit 2.

  The image reading unit 2 includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD. The image reading unit 2 reads image data from the document P placed on the document table or the document P conveyed by the ADF 1. Specifically, in the image reading unit 2, image data of the document P is input by inputting light reflected on the document P from the light source to the CCD via the plurality of mirrors and the optical lens. Is read.

  The image forming unit 3 can form an image by electrophotography based on the image data read by the image reading unit 2. The image forming unit 3 can also form an image based on image data input from an information processing apparatus such as an external personal computer. As shown in FIG. 1, the image forming unit 3 includes a photosensitive drum 31, a charging device 32, an optical scanning device (LSU) 33, a developing device 5, a developer supply unit 34, a transfer roller 35, a cleaning device 36, and a fixing roller. 37, a pressure roller 38, and a paper discharge tray 39.

  The paper feeding unit 4 feeds the sheet S on which an image is formed in the image forming unit 3. As shown in FIG. 1, the paper feed unit 4 includes a paper feed cassette 41 that stores sheets S. In the paper feeding unit 4, the sheets S stored in the paper feeding cassette 41 are taken out one by one and fed to an image forming position by the image forming unit 3.

  In the image forming unit 3, an image is formed on the sheet S supplied from the paper feeding unit 4 according to the following procedure, and the sheet S after the image formation is discharged to the paper discharge tray 39. The sheet S is a sheet material such as paper, coated paper, postcard, envelope, and OHP sheet.

  First, the surface of the photosensitive drum 31 is uniformly charged to a predetermined potential by the charging device 32. Next, the light scanning device 33 irradiates the surface of the photosensitive drum 31 with light based on the image data. Thereby, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 31. The electrostatic latent image on the photosensitive drum 31 is developed (visualized) as a toner image by the developing device 5. The developing device 5 is replenished with a developer from a developer replenishing unit 34 that can be attached to and detached from the image forming unit 3.

  Subsequently, the toner image formed on the photosensitive drum 31 is transferred onto the sheet S by the transfer roller 35. Thereafter, the toner image transferred to the sheet S is heated and fixed by the fixing roller 37 when the sheet S passes between the fixing roller 37 and the pressure roller 38. The toner remaining on the surface of the photosensitive drum 31 is removed by the cleaning device 36.

[Configuration of Developing Device 5]
Next, the developing device 5 will be described in detail with reference to FIGS. Here, FIG. 2 is a schematic cross-sectional view showing the configuration of the developing device 5. FIG. 3 is a schematic plan view showing the configuration of the first housing portion 51B and the second housing portion 51C of the housing 51. FIG. 4 is a schematic cross-sectional view showing the configuration of the developing roller 54, the regulating member 55, and the second magnet 56. FIG. 5 is a schematic cross-sectional view showing the configuration of the first magnet 542. In FIGS. 4 and 5, the first magnetic pole 542A, the second magnetic pole 542B, the third magnetic pole 542C, and the fourth magnetic pole 542D of the first magnet 542 are indicated by alternate long and short dash lines. In FIG. 5, straight lines L1 to L3 passing through the center P4 of the rotation shaft 54A of the developing roller 54 are indicated by broken lines. 4 and 5, for convenience of explanation, hatching applied to the cross sections of the developing roller 54, the regulating member 55, and the second magnet 56 is omitted.

  The developing device 5 develops the electrostatic latent image on the photosensitive drum 31 using toner contained in the developer. Specifically, the developer is a one-component developer mainly composed of magnetic toner. For example, the developer includes an external additive such as titanium oxide and silica for adjusting the transportability and chargeability of the magnetic toner together with the magnetic toner.

  As shown in FIGS. 2 to 5, the developing device 5 includes a housing 51, a first conveying member 52, a second conveying member 53, a developing roller 54, a regulating member 55, and a second magnet 56.

  The housing 51 houses the constituent members of the developing device 5 and the developer. The housing 51 is elongate along the left-right direction of the image forming apparatus 10 (the depth direction in FIG. 2). As shown in FIGS. 2 and 3, the interior of the housing 51 is divided into a first housing part 51B and a second housing part 51C by a partition wall 51A. The partition wall 51 </ b> A is provided in a long shape along the longitudinal direction of the housing 51. At both ends in the longitudinal direction of the partition wall 51A, communication passages 51F to 51G are provided for communicating the first storage portion 51B and the second storage portion 51C.

  As shown in FIG. 2, an opening 51 </ b> D is provided on the upper wall surface of the first housing 51 </ b> B of the housing 51. The opening 51D is a through hole that guides the developer replenished from the developer replenishing portion 34 to the first accommodating portion 51B. The developer supplied from the developer supply unit 34 is stored in the first storage unit 51B via the opening 51D.

  As shown in FIG. 2, an opening 51 </ b> E is provided at the rear end portion of the second accommodating portion 51 </ b> C of the housing 51. In the image forming apparatus 10, the developing device 5 is disposed at a position where the opening 51 </ b> E faces the photosensitive drum 31.

  The 1st conveyance member 52 is rotatably provided in the 1st accommodating part 51B of the housing 51. As shown in FIG. For example, as shown in FIGS. 2 and 3, the first transport member 52 is a transport screw having spiral blades 52 </ b> B formed along the rotation shaft 52 </ b> A. A driving force is supplied to the first transport member 52 from a driving source (not shown) such as a motor. As a result, the first transport member 52 is rotated in the rotation direction 52C, and the developer stored in the first storage portion 51B is transported along the transport direction 52D while being stirred by the spiral blade 52B. The developer is triboelectrically charged by stirring with the spiral blade 52B.

  The developer conveyed by the first conveying member 52 is accommodated in the second accommodating portion 51C via a communication path 51F provided on the downstream side in the conveying direction 52D of the first accommodating portion 51B.

  The second conveying member 53 is rotatably provided in the second accommodating part 51 </ b> C of the housing 51. For example, as shown in FIGS. 2 and 3, the second transport member 53 is a transport screw having a spiral blade 53 </ b> B formed along the rotation shaft 53 </ b> A. Similarly to the first transport member 52, the second transport member 53 is supplied with driving force from the drive source (not shown). Accordingly, the second transport member 53 is rotated in the rotation direction 53C, and the developer stored in the second storage section 51C is transported along the transport direction 53D while being stirred by the spiral blade 53B. The developer is triboelectrically charged by stirring with the spiral blade 53B.

  A part of the developer conveyed by the second conveying member 53 is supplied to the developing roller 54. Of the developer transported by the second transport member 53, the remaining portion that is not supplied to the developing roller 54 passes through the communication path 51G provided on the downstream side in the transport direction 53D of the second storage section 51C. 1 is accommodated in the accommodating portion 51B. That is, in the developing device 5, a circulation transport path through which the developer is circulated is formed by the first storage portion 51B, the communication passage 51F, the second storage portion 51C, and the communication passage 51G. In the developing device 5, the developer accommodated in the housing 51 is circulated and conveyed in the circulation conveyance path by the first conveyance member 52 and the second conveyance member 53.

  The developing roller 54 is rotatably provided in the housing 51. As shown in FIG. 2, the developing roller 54 is positioned at the rear side of the image forming apparatus 10 with respect to the second conveying member 53 in the second accommodating portion 51 </ b> C, and the rotation shaft 54 </ b> A is provided by the second conveying member 53. Arranged along the conveyance direction 53D. A part of the peripheral surface 54 </ b> C of the developing roller 54 is exposed to the outside of the housing 51 through the opening 51 </ b> E and faces the photosensitive drum 31.

  As shown in FIG. 2, the developing roller 54 includes a developing sleeve 541 and a first magnet 542. The developing sleeve 541 has a cylindrical shape and is rotatably provided in the housing 51. For example, the developing sleeve 541 is made of a nonmagnetic material such as aluminum. For example, the peripheral surface of the developing sleeve 541 is subjected to a roughening process in order to adjust the amount of developer retained and the amount of friction.

  The first magnet 542 is fixedly provided inside the developing sleeve 541. As shown in FIGS. 4 and 5, the first magnet 542 has a first magnetic pole 542A, a second magnetic pole 542B, a third magnetic pole 542C, and a fourth magnetic pole 542D. For example, the first magnetic pole 542A is an N pole and generates a peak magnetic force at a position facing the second transport member 53. The second magnetic pole 542B is an S pole, and generates a peak magnetic force at a position facing the second magnet 56 or the like. The second magnetic pole 542B will be described later. The third magnetic pole 542 </ b> C is an N pole, and generates a peak magnetic force at a position facing the photosensitive drum 31. The fourth magnetic pole 542D is an S pole, and generates a peak magnetic force at a position downstream of the third magnetic pole 542C in the rotational direction 54B and upstream of the first magnetic pole 542A.

  In the developing roller 54, the developer having magnetism is attracted to the peripheral surface 54C at a supply position P1 (see FIG. 4) where the second conveyance member 53 and the peak position of the magnetic force of the first magnetic pole 542A face each other. On the other hand, the developer is frictionally charged by agitation by the first conveying member 52 and the second conveying member 53, and is attracted to the peripheral surface 54C by electrostatic force. Therefore, a part of the developer conveyed by the second conveying member 53 adheres to the peripheral surface 54C at the supply position P1.

  A driving force is supplied to the developing roller 54 from the driving source (not shown). Accordingly, the developing roller 54 is rotated in the rotation direction 54B, and the developer attached to the peripheral surface 54C is conveyed from the supply position P1 along the rotation direction 54B.

  The regulating member 55 regulates the thickness of the developer attached to the peripheral surface 54 </ b> C of the developing roller 54. As shown in FIGS. 2 and 4, the regulating member 55 is provided at a position downstream of the supply position P1 in the rotation direction 54B. The restricting member 55 is provided in a long shape along the longitudinal direction of the housing 51. For example, the restricting member 55 is formed in a blade shape with a magnetic metal or the like.

  As shown in FIG. 4, the regulating member 55 has a base portion 55A and a protruding portion 55B. As shown in FIG. 2, the base portion 55 </ b> A is formed in a shape in which a plate-like member long in the longitudinal direction of the housing 51 is bent substantially at a right angle. A portion on one side from the bent portion of the base portion 55A is fixed to the inner surface of the upper wall of the housing 51 by a fixing tool (not shown). The other side portion of the base portion 55 </ b> A extends downward toward the peripheral surface 54 </ b> C of the developing roller 54. The protruding portion 55B is provided integrally with the base portion 55A at the lower end portion 55A1 (see FIG. 5) of the base portion 55A. The protruding portion 55B is a plate-like member that is thinner than the thickness at the lower end portion 55A1 of the base portion 55A. In the present embodiment, the thickness (thickness in the rotation direction 54B) T1 of the protrusion 55B is 1.0 millimeter. The protruding portion 55B protrudes downward from the lower end portion 55A1 of the base portion 55A so as to be flush with the front side (right side in FIG. 2) of the lower end portion 55A1 of the base portion 55A. The protrusion 55B does not reach the peripheral surface 54C, and protrudes upward from the peripheral surface 54C to a position separated by a gap G1. That is, the protruding portion 55B is provided on the base portion 55A so that the protruding end 55B1 faces the circumferential surface 54C of the developing roller 54 with a gap G1 therebetween. The protruding end 55B1 of the protruding portion 55B is generally located on a vertical line passing through the center of the rotating shaft 54A. In the present embodiment, the gap G1 between the protruding end 55B1 of the protruding portion 55B and the peripheral surface 54C is 0.3 millimeters. The dimensions of the thickness T1 and the gap G1 are merely examples, and are not limited to the above dimensions.

  A magnetic field is formed by the second magnetic pole 542B of the first magnet 542 at the facing position P2 (see FIG. 4) where the protrusion 55B and the peripheral surface 54C face each other. Further, the protrusion 55B is magnetized by the second magnetic pole 542B to have a polarity (N pole) opposite to that of the second magnetic pole 542B.

  The developer conveyed from the supply position P1 by the developing roller 54 is attracted to the facing position P2 by the magnetic field formed at the facing position P2. The developer attracted to the facing position P2 comes into contact with the protruding portion 55B of the regulating member 55 when passing through the facing position P2. As a result, the developer attached to the peripheral surface 54C of the developing roller 54 is regulated to a thickness corresponding to the gap G1, and a thin layer of the developer is formed on the peripheral surface 54C. Further, the developer comes into contact with the protruding portion 55B and is frictionally charged. The gap G1 may be arbitrarily set according to the thickness of the developer thin layer formed by the regulating member 55.

  As shown in FIG. 4, the second magnet 56 is provided on the upstream side surface of the regulating member 55 in the rotation direction 54 </ b> B of the developing roller 54. The second magnet 56 is provided in a long shape along the longitudinal direction of the housing 51, similarly to the restriction member 55. For example, the second magnet 56 is formed in a plate shape from neodymium. The second magnet 56 has a facing portion 56A. The lower end portion of the second magnet 56 is a facing portion 56A. 56 A of opposing parts are spaced apart from 54 C of peripheral surfaces rather than the lower end part of the limitation member 55, and are facing 54 C of peripheral surfaces. A gap G2 of 0.8 mm is provided between the facing portion 56A and the peripheral surface 54C.

  The second magnet 56 is disposed such that the facing portion 56A side in the direction perpendicular to the peripheral surface 54C has the same polarity (S pole) as the second magnetic pole 542B of the developing roller 54. Thereby, a magnetic field is formed between the protruding portion 55 </ b> B of the regulating member 55 and the facing portion 56 </ b> A of the second magnet 56. Further, the protruding portion 55B is magnetized by the facing portion 56A of the second magnet 56 in addition to the second magnetic pole 542B. For example, the magnetic flux density at the tip portion facing the peripheral surface 54C of the protruding portion 55B is adjusted to be 30 millitesla by the second magnetic pole 542B and the second magnet 56.

  In the facing portion 56 </ b> A of the second magnet 56, the developer is attracted by a magnetic field formed between the protruding portion 55 </ b> B of the regulating member 55. As a result, the developer pool is formed in the space between the facing portion 56A and the peripheral surface 54C. The developer pool formed in the space compresses the developer passing through the facing position P2. Thereby, the thickness variation in the thin layer of the developer formed by the regulating member 55 is suppressed.

  The developer that has passed the facing position P2 is conveyed by the developing roller 54 to the developing position P3 (see FIG. 4) where the photosensitive drum 31 and the peak position of the magnetic force of the third magnetic pole 542C face each other. On the other hand, a superimposed voltage obtained by superimposing a DC voltage and an AC voltage is applied to the developing roller 54 from a power source (not shown). As a result, a part of the developer conveyed to the developing position P3 is supplied to the photosensitive drum 31 from the peripheral surface 54C. Of the developer transported to the development position P3, the remaining portion that is not supplied to the photosensitive drum 31 is held on the peripheral surface 54C by the magnetic force of the fourth magnetic pole 542D and accommodated in the housing 51.

  By the way, when the second magnet 56 is provided on the side surface of the regulating member 55, the developing roller 54 rotates, and the developer adsorbed to the facing portion 56 </ b> A of the second magnet 56 and the peripheral surface 54 </ b> C of the developing roller 54. The rubbing is repeated with the attached developer. As a result, the charge amount of the developer adsorbed on the facing portion 56A of the second magnet 56 may become excessive. When the developer having such an excessive charge amount is used for forming an image away from the second magnet 56, a problem such as black streaks occurs in the formed image. On the other hand, in the image forming apparatus 10 according to the embodiment of the present invention, as described below, the charge amount of the developer that is attracted to the second magnet 56 provided on the side surface of the regulating member 55 is increased. It is possible to suppress.

  Specifically, in the image forming apparatus 10, the thickness T <b> 2 (see FIG. 4) in the rotation direction 54 </ b> B in the facing portion 56 </ b> A is formed thinner than the thickness T <b> 1 in the rotation direction 54 </ b> B in the protruding portion 55 </ b> B. That is, in the image forming apparatus 10, the thickness T2 in the facing portion 56A (thickness in the rotation direction 54B) is set to be equal to or less than half the thickness T1 of the protruding portion 55B. For example, in the image forming apparatus 10, the thickness T1 of the protruding portion 55B is 1.0 millimeter as described above, whereas the thickness T2 of the facing portion 56A is 0.5 millimeter. Thereby, the amount of the developer adsorbed on the facing portion 56A is reduced. Note that the thickness T2 of the facing portion 56A may be arbitrarily set, for example, in the range of 0.1 millimeters to 0.5 millimeters. Here, the protruding portion 55B is an example of the first facing portion in the present invention. The facing portion 56A is an example of a second facing portion in the present invention.

  Here, when the thickness T2 of the facing portion 56A is formed thinner than the thickness T1 of the protruding portion 55B, the amount of the developer pool formed in the space between the peripheral surface 54C and the facing portion 56A is small. Accordingly, the compressive force applied to the developer passing through the facing position P2 due to the developer pool may be reduced.

  Therefore, in the image forming apparatus 10, two magnetic pole peaks are provided on the second magnetic pole 542 </ b> B of the first magnet 542. Specifically, as shown in FIGS. 4 and 5, the second magnetic pole 542B has a first magnetic force peak X1 facing the facing portion 56A, and a first magnetic force upstream of the first magnetic force peak X1 in the rotational direction 54B. It has a second magnetic force peak X2 adjacent to the peak X1. Here, the second magnetic pole 542B is an example of the magnetic pole in the present invention.

  For example, as shown in FIG. 5, the first magnetic force peak X1 includes a straight line L1 connecting the center P4 of the rotation shaft 54A of the developing roller 54 and the upstream end in the rotation direction 54B of the regulating member 55, the center P4, The angle C1 formed by the straight line L2 connecting one magnetic peak X1 is set to be 10 degrees. The second magnetic force peak X2 is provided so that the angle C2 formed by the straight line L1 and the straight line L3 connecting the center P4 and the second magnetic force peak X2 is 25 degrees.

  As a result, the developer pool is formed by the developer attracted to the second magnetic peak X2 of the second magnetic pole 542B, and the developer pool is supplied to the facing position P2. Accordingly, it is possible to suppress a reduction in the compressive force applied to the developer passing through the facing position P2 due to the thickness T2 of the facing portion 56A being made thinner than the thickness T1 of the protruding portion 55B.

[Example]
In the image forming apparatus 10 according to the above-described embodiment, an experiment was conducted to investigate the uniformity of the density of the printed image. The experimental results are shown in FIG.

  The experiment was conducted according to the following procedure. First, the image forming apparatus 10 is installed in an environment of a temperature of 25 degrees and a humidity of 50%, and the image forming apparatus 10 is caused to execute a toner installation process for supplying toner to the developing device 5, and printing is performed after the toner installation process is performed. An image with a rate of 20% was printed, and the uniformity of the image density was investigated based on the printing result. Subsequently, in a state where the installation environment of the image forming apparatus 10 is maintained, an image with a printing rate of 5% is printed for 2000 sheets by double-sided printing, and then an image with a printing rate of 20% is printed. The uniformity of image density was investigated. Subsequently, the image forming apparatus 10 is left in an environment of a temperature of 30 degrees and a humidity of 90%, and after 24 hours, 48 hours, 72 hours, 120 hours, and 144 hours have elapsed, respectively. At this timing, an image with a printing rate of 20% was printed, and the uniformity of the image density was investigated based on the printing result. In the experiment, the uniformity of the density of the printed image was visually confirmed and evaluated in 13 stages from the lowest value 1 to the highest value 13.

The specifications of the image forming apparatus 10 at the time of the experiment are as follows.
Thickness T1: 1.0 mm of protrusion 55B
Opposite portion 56A thickness T2: 0.5 mm
Printing speed: 30 ppm (pages / minute)
Development method: magnetic one component Linear speed of photosensitive drum 31: 180 mm / sec
Linear speed ratio between the photosensitive drum 31 and the developing roller 54: 1.5
Distance between photosensitive drum 31 and developing roller 54: 0.3 mm
Material of photosensitive drum 31: amorphous silicon Superposed voltage applied to developing roller 54: frequency 3.0 kHz, duty ratio 50%, peak-to-peak voltage 1200V, DC component 150V
Toner: particle size 8.0 μm, positive chargeability

[Comparative Example 1]
In the image forming apparatus 10, instead of the second magnet 56, an experiment similar to the above was performed using another magnet having a thickness T2 of the facing portion 56A of 2.5 millimeters. The experimental results are shown in FIG. In addition, the magnetic force of the other magnet was adjusted so that the magnetic flux density at the tip portion facing the peripheral surface 54C of the protruding portion 55B coincided with the example.

[Comparative Example 2]
In the image forming apparatus 10, instead of the second magnet 56, an experiment similar to the above was performed using another magnet having a thickness T2 of the facing portion 56A of 2.0 mm. The experimental results are shown in FIG. In addition, the magnetic force of the other magnet was adjusted so that the magnetic flux density at the tip portion facing the peripheral surface 54C of the protruding portion 55B coincided with the example.

[Comparative Example 3]
In the image forming apparatus 10, instead of the second magnet 56, an experiment similar to the above was performed using another magnet having a thickness T2 of the facing portion 56A of 1.5 mm. The experimental results are shown in FIG. In addition, the magnetic force of the other magnet was adjusted so that the magnetic flux density at the tip portion facing the peripheral surface 54C of the protruding portion 55B coincided with the example.

[Comparative Example 4]
In the image forming apparatus 10, instead of the second magnet 56, an experiment similar to the above was performed using another magnet having a thickness T2 of the facing portion 56A of 1.0 millimeter. The experimental results are shown in FIG. In addition, the magnetic force of the other magnet was adjusted so that the magnetic flux density at the tip portion facing the peripheral surface 54C of the protruding portion 55B coincided with the example.

[Comparative Example 5]
In the image forming apparatus 10, the same experiment as described above was performed using another member having a thickness T <b> 1 of the protruding portion 55 </ b> B of 0.65 mm instead of the regulating member 55. The experimental results are shown in FIG. In addition, the magnetic force of the 2nd magnet 56 was adjusted so that the magnetic flux density in the front-end | tip part which opposes the surrounding surface 54C of the protrusion part 55B may correspond with an Example.

  According to the experimental result shown in FIG. 6, the uniformity of the density of the printed image is improved as the thickness T2 of the facing portion 56A is reduced. This is presumably because the amount of the developer adsorbed on the facing portion 56A was reduced, and the increase in the charge amount of the developer adsorbed on the facing portion 56A was suppressed.

  Further, according to the experimental result shown in FIG. 6, compared with the image forming apparatus 10 of the comparative example 5, the image forming apparatus 10 of the example improves the uniformity of the density of the printed image. From this result, the amount of the developer adsorbed on the facing portion 56A is not the absolute value of the thickness T2 of the facing portion 56A, but is based on the relative relationship between the thickness T2 of the facing portion 56A and the thickness T1 of the protruding portion 55B. Presumed to be determined.

  As described above, in the image forming apparatus 10, the thickness T2 at the facing portion 56A is set to be equal to or less than half the thickness T1 of the protruding portion 55B. Thereby, an increase in the charge amount of the developer attracted by the second magnet 56 provided on the side surface of the regulating member 55 is suppressed.

1 ADF
2 Image Reading Unit 3 Image Forming Unit 4 Paper Feeding Unit 5 Developing Device 10 Image Forming Device 51 Housing 52 First Conveying Member 53 Second Conveying Member 54 Developing Roller 542 First Magnet 55 Restricting Member 55B Protruding Portion 56 Second Magnet 56A Opposing Part

Claims (4)

A housing for containing a developer containing magnetic toner;
A developing roller having a first magnet that is rotatably provided in the housing and draws the developer in the housing to a peripheral surface by a magnetic force;
A regulating member that has a first facing portion provided with a gap with respect to the circumferential surface of the developing roller, and regulates the thickness of the developer attached to the circumferential surface;
The regulating member is provided on a side surface on the upstream side in the rotation direction of the developing roller, and has a second facing portion that is farther from the circumferential surface than the regulating member and faces the circumferential surface, and the second facing A second magnet in which the thickness in the rotational direction at the portion is less than or equal to one half of the thickness in the rotational direction at the first opposing portion of the restriction member;
A developing device comprising:   The first magnet includes a first magnetic force peak facing the second facing portion and a magnetic pole having a second magnetic force peak adjacent to the first magnetic force peak upstream of the first magnetic force peak in the rotation direction. The developing device according to claim 1. The first facing portion has a thickness in the rotational direction of 1.0 mm,
The developing device according to claim 1, wherein the second facing portion has a thickness in the rotation direction of 0.5 mm or less. An image forming apparatus comprising the developing device according to claim 1, and comprising an image forming unit capable of forming an image based on image data.

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