JP2008292941A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming a high-quality image whose image density is very high by suppressing the occurrence of irregularities in a thin layer and soiling in the apparatus caused by scattering of developer. <P>SOLUTION: The image forming apparatus includes a photoreceptor drum 61 on which an electrostatic latent image is formed, a developing roller 71 which is arranged to be opposed to the photoreceptor drum 61 and has a rotating sleeve including a fixed magnet, and a bristle cutting blade 74 which regulates the thickness of a toner layer formed on the rotating sleeve, wherein the rotating directions of the photoreceptor drum 61 and the rotating sleeve are reverse to each other, and the bristle cutting blade 74 is arranged at ≤22 degrees on an upstream side and at ≤35 degrees on a downstream side in the rotating direction of the rotating sleeve relative to a vertical surface V including the rotary shaft of the rotating sleeve on a downside relative to a horizontal surface including the rotary shaft of the rotating sleeve, and the peak value of magnetic force at a position of the developing roller 71 opposed to the bristle cutting blade 74 is 75-150 mT. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these.

  An image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile machine, or a multifunction peripheral (MFP) of the same, for example, a photosensitive drum as an image carrier, and a surface of the photosensitive drum are made uniform. A charging device for charging, an exposure device for forming an electrostatic latent image based on image data on a photosensitive drum, a developing device for developing the electrostatic latent image on the photosensitive drum into a toner image, and a photosensitive member A process unit such as a transfer device for transferring the toner image on the drum onto a recording medium such as paper is provided. Further, there may be a case where a cleaning device for removing toner remaining on the photosensitive drum after transferring the toner image on the photosensitive drum onto the sheet is provided.

  A developing device provided in an image forming apparatus using an electrophotographic method has a rotating sleeve containing a fixed magnet, and a photosensitive roller on which an electrostatic latent image is formed by a developing roller disposed opposite to the photosensitive drum. The developer toner is supplied toward the peripheral surface of the body drum. In the developing device, a blade as a layer thickness regulating member is provided at a position upstream of the rotating sleeve facing the photosensitive drum, and the thickness of the toner layer formed thick on the rotating sleeve is adjusted with this blade. By restricting, excessive supply to the photosensitive drum is prevented.

  On the other hand, an image forming apparatus using an electrophotographic system has been studied for the arrangement configuration of each process unit and members constituting the process unit in order to cope with downsizing and high speed. For example, as an arrangement of the blades, one arranged above the horizontal plane including the rotation axis of the rotation sleeve is known. In the image forming apparatus having such a blade arrangement, it is necessary to transport the developer in the direction against the gravity by the rotating sleeve. Therefore, the developer falls during the transport, and it is difficult to secure the transport amount of the developer.

Therefore, as an image forming apparatus in which the arrangement of the blades is changed, an image forming apparatus in which the blades are arranged below the horizontal plane including the rotation shaft of the rotating sleeve has been proposed (see Patent Document 1 and Patent Document 2). Further, Patent Document 1 discloses the amount of developer carried on the rotating sleeve as an interval between the surface of the rotating sleeve and the inner surface of the developing tank facing the upstream side of the blade in the rotating direction of the rotating sleeve. The interval should be set to an amount larger than the developer amount corresponding to the layer thickness defined by the blade and smaller than the developer amount corresponding to the layer thickness immediately after being pumped from the developing tank to the rotating sleeve. Is disclosed.
JP 2005-134734 A JP 2004-29156 A

  In the image forming apparatus in which the blade is disposed below the horizontal plane including the rotation shaft of the rotating sleeve, the developer is hardly attracted to the developing roller side because force is applied to the blade side under the developer due to gravity. Therefore, the developer that is not sufficiently attracted to the developing roller side is conveyed to the layer thickness regulating position where the blade and the rotating sleeve face each other. When the layer thickness of the developer that is not sufficiently attracted to the developing roller side is regulated by the blade, the thin layer is disturbed, and the blade is disposed below the horizontal plane including the rotating shaft of the rotating sleeve. Therefore, when the thin layer is disturbed, the developer is scattered and the inside of the machine is easily contaminated.

  According to Patent Document 1, it is described that by suppressing the amount of developer reaching the blade, the rotational load of the rotating sleeve can be reduced, and the life of the component parts can be extended and the deterioration of the developer characteristics can be prevented. However, since the developer is not sufficiently attracted to the developing roller side, the layer thickness is not regulated in a state in which the developer is sufficiently attracted to the developing roller side, and the above-mentioned disturbance of the thin layer is prevented. It cannot be resolved. Further, this image forming apparatus is a two-component developing method, and the one-component developer not including a carrier and the two-component developer including a carrier are different in fluidity and the like, and thus cannot be applied to the one-component developing method.

  Patent Document 2 describes an example of an image forming apparatus using toner that can be applied to an oil-less fixing system in which a blade is disposed below a horizontal plane including a rotation shaft of a rotation sleeve. However, it is not configured to eliminate the thin layer disturbance.

  Further, in the image forming apparatuses described in Patent Document 1 and Patent Document 2, the rotation directions of the rotating sleeve and the photosensitive drum are the same. That is, since the blade is disposed below the horizontal plane including the rotation axis of the rotation sleeve, the rotation sleeve travels upward and the photosensitive drum travels downward at a position where the rotation sleeve and the photosensitive drum face each other. To do. Therefore, since the photosensitive drum travels downward, contamination in the apparatus due to scattering of the developer is likely to occur, and units such as the LED head unit and the laser scanning unit (LSU) are contaminated. Further, since the intermediate transfer belt is configured to run close to the lower end portion of the photosensitive drum, the intermediate transfer belt is also soiled. In addition, if the rotating shaft of the photosensitive drum is below the horizontal plane including the rotating shaft of the rotating sleeve, it is easy for the developer to scatter due to the photosensitive drum traveling downward at the opposite position. Becomes prominent.

  As described above, the image forming apparatuses described in Patent Document 1 and Patent Document 2 cannot form a high-quality image due to the occurrence of thin layer disturbance or the occurrence of contamination inside the apparatus. Further, in order to prevent the image quality from being deteriorated due to in-machine contamination, it is necessary to take measures such as sealing so that the process unit does not become dirty even if the developer falls off, and the image forming apparatus becomes large.

  The present invention has been made in order to solve such conventional problems, and suppresses the occurrence of thin layer disturbance and the occurrence of in-machine contamination due to the scattering of the developer, and provides a high-quality image with a sufficiently high image density. An object of the present invention is to provide an image forming apparatus capable of forming images.

  The present invention relates to an image carrier on which an electrostatic latent image is formed, a developing roller having a rotating sleeve which is disposed opposite to the image carrier and contains a fixed magnet, and a toner formed on the rotating sleeve. A layer thickness regulating member that regulates the thickness of the layer, wherein the rotation direction of the image carrier and the rotating sleeve is opposite, and the layer thickness regulating position by the layer thickness regulating member is the rotational axis of the rotating sleeve. Lower than the horizontal plane that includes the rotation axis of the rotary sleeve and 22 degrees or less on the upstream side in the rotational direction of the rotary sleeve and 35 degrees or lower on the downstream side in the rotational direction. The image forming apparatus is characterized in that a magnetic force peak value at a position facing the layer thickness regulating member of the developing roller is 75 to 150 mT.

  According to this configuration, the rotation direction of the image carrier and the rotation sleeve is opposite, and the layer thickness regulating member is disposed below the horizontal plane including the rotation axis of the rotation sleeve. Therefore, since both the image carrier and the rotating sleeve run upward at the position where the image carrier and the rotating sleeve face each other, it is difficult for the developer to fall off from the image carrier and the rotating sleeve, and the scattering of the developer is suppressed. it can. Further, since the image carrier and the rotation sleeve run in the same direction at the position where the image carrier and the rotation sleeve face each other, so that the image carrier and the rotation sleeve rotate in a so-called trail direction. Occurrence of layer disturbance and loss of developer can be suppressed. Further, since the time for which the image carrier and the rotating sleeve are close to each other is long and development is easy, image formation can be performed under mild developing conditions such as a low developing voltage applied to the rotating sleeve. This also contributes to suppression of developer falling off.

  In addition, the layer thickness regulating position by the layer thickness regulating member is arranged to be 22 degrees or less upstream of the rotation direction of the rotation sleeve and 35 degrees or less downstream of the rotation surface of the rotation sleeve. Therefore, the developer whose layer thickness is regulated by the layer thickness regulating member can be conveyed to the development position where the image carrier and the rotating sleeve face each other without disturbing or dropping off the thin layer of the developer. Further, by arranging in this way, among the plurality of magnetic poles formed by the fixed magnet, the magnetic pole formed at the developing position and formed adjacent to the developing main pole for supplying the developer to the image carrier. Can be formed at the layer thickness regulating position facing the layer thickness regulating member. By doing so, since no other magnetic pole is formed between the magnetic pole formed at the layer thickness regulating position and the developing main pole, it is possible to further suppress the occurrence of thin layer disturbance and the developer falling off.

  Further, since the magnetic force peak value at the position facing the layer thickness regulating member of the developing roller is 75 to 150 mT, a force that attracts the developer to the developing roller side is suitable, and the layer thickness of the developer is increased by the layer thickness regulating member. Even if this is regulated, it is difficult for thin layer disturbance to occur.

  As described above, the image forming apparatus of the present invention can suppress the occurrence of thin layer disturbance and the occurrence of internal stains due to the scattering of the developer, and can form a high-quality image having a sufficiently high image density. In addition, since the occurrence of contamination inside the apparatus is suppressed, it is possible to reduce the seal and the like for preventing the process unit from becoming dirty, and to achieve downsizing of the image forming apparatus.

  In the image forming apparatus, the electrostatic latent image formed on the image carrier is developed into a toner image with the toner of the developer, the developed toner image is transferred, and the transferred toner image is transferred to the recording medium. It is preferable that the intermediate transfer member to be transferred is provided, and the position where the image carrier and the intermediate transfer member are close to each other is above the horizontal plane including the rotation axis of the image carrier.

  According to this configuration, since the intermediate transfer member is located above the layer thickness regulating position where the rotating sleeve and the layer thickness regulating member face each other, even when the developer scatters, the intermediate transfer member is soiled by the developer. And a high-quality image can be formed. Further, since measures for preventing the intermediate transfer member from being soiled due to the scattering of the developer are almost unnecessary, the size can be further reduced.

  It is preferable that a rotation axis of the rotation sleeve is above a horizontal plane including a rotation axis of the image carrier. According to this configuration, the position at which the image carrier and the rotation sleeve face each other is above the horizontal plane that includes the rotation axis of the image carrier, so that the developer is placed above the horizontal plane that includes the rotation axis of the image carrier. Toner is supplied to the image carrier to form a toner image. Further, the formed toner image is transferred to the intermediate transfer member above the horizontal plane including the rotation axis of the image carrier. Therefore, the toner is hardly transported below the horizontal plane including the rotation axis of the image carrier, and the toner is not easily dropped from the image carrier.

  Further, the rotation shaft of the rotation sleeve is disposed above the horizontal plane including the rotation shaft of the image carrier, so that a space is formed below the developing roller. In that space, there is almost no need to provide a seal or the like for preventing the process unit from being soiled by the developer, so that the exposure light can pass through the space. By doing so, the size can be further reduced.

  Further, in the image forming apparatus, by using a magnetic one-component developer as the developer, it is possible to suitably exhibit the effect that it is possible to suppress the occurrence of thin layer disturbance and the occurrence of internal contamination due to the scattering of the developer.

  The image forming apparatus of the present invention can suppress the occurrence of thin layer disturbance and the occurrence of internal stains due to the scattering of the developer, and can form a high-quality image having a sufficiently high image density.

  Hereinafter, an embodiment according to an image forming apparatus of the present invention will be described in detail with reference to the drawings. Here, a tandem image forming apparatus will be described as an example of the image forming apparatus. However, the image forming apparatus may be any image forming apparatus using an electrophotographic method, and is not limited to a tandem image forming apparatus. Further, as a type of the image forming apparatus, a color printer will be described as an example. However, for example, a copying machine, a facsimile machine, and a multifunction machine may be used.

  FIG. 1 is a schematic cross-sectional view showing the overall configuration of a color printer 1 according to an embodiment of the present invention. First, an overall configuration of a tandem color printer 1 according to an embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the color printer 1 has a box-shaped device body 1a. In the apparatus main body 1a, a paper feeding unit 2 that feeds the paper P, an image forming unit 3 that transfers an image to the paper P while conveying the paper P fed from the paper feeding unit 2, and A fixing unit 4 that performs a fixing process on the image transferred to the paper P by the image forming unit 3 is provided. Further, a paper discharge unit 5 for discharging the paper P subjected to the fixing process by the fixing unit 4 is provided on the side surface (left side surface in FIG. 1) of the device main body 1a.

  The paper feed unit 2 includes a paper feed cassette 21, a pickup roller 22, a paper feed roller 23, and a registration roller 24. The paper feed cassette 21 is provided so as to be detachable with respect to the apparatus main body 1a, and stores the paper P of each size. The pickup roller 22 is provided at the upper right position of the paper feed cassette 21 shown in FIG. 1 and takes out the paper P stored in the paper feed cassette 21 one by one. The paper feed roller 23 sends out the paper P taken out by the pickup roller 22 to the main transport path L1. The registration roller 24 temporarily waits for the paper P sent to the main transport path L1 by the paper feed roller 23, and then supplies the paper P to the image forming unit 3 at a predetermined timing.

  The paper feeding unit 2 further includes a manual feed tray 26 and a pickup roller 27. The manual feed tray 26 is attached to the side surface (the right side surface in FIG. 1) opposite to the paper discharge unit 5 of the apparatus main body 1a so as to be detachable and foldable, and places the paper P of each size. The pickup roller 27 takes out the paper P placed on the manual feed tray 26 one by one. The paper P taken out by the pickup roller 27 is sent out to the main transport path L1 by the paper feed roller 23 as in the case of the paper P taken out from the paper feed cassette 21, and the image forming unit 3 at a predetermined timing by the registration roller 24. To be supplied.

  The image forming unit 3 includes an image forming unit 6 corresponding to each color of magenta (M), cyan (C), yellow (Y), and black (K), and a surface (contact surface) formed by these image forming units 6. An intermediate transfer belt 31 to which a toner image based on image data sent from a computer or the like is primarily transferred, and a sheet on which the toner image primarily transferred onto the intermediate transfer belt 31 is fed from a paper feed cassette 21 or the like. And a secondary transfer roller 32 for secondary transfer to P.

  The image forming unit 6 includes a black unit 6K, a yellow unit 6Y, a cyan unit 6C, and a magenta unit 6M which are sequentially arranged from the downstream side toward the upstream side. Each unit 6 includes a photosensitive drum 61, and a toner image corresponding to each color is formed on the photosensitive drum 61 based on image data, and is primarily transferred to the intermediate transfer belt 31. The configuration of the image forming unit 6 will be described later.

  The intermediate transfer belt 31 is an endless belt-like rotating body, and includes a drive roller 33, a belt support roller 34, a backup roller 35, a front surface (contact surface) side so as to be in contact with the peripheral surface of each photosensitive drum 61, respectively. It is stretched around a plurality of rollers such as a primary transfer roller 36, a cleaning roller 37, a tension roller 38, and a driven roller 39. The intermediate transfer belt 31 is configured to rotate endlessly by the plurality of rollers in a state where the intermediate transfer belt 31 is pressed against the photosensitive drum 61 by a primary transfer roller 36 disposed to face each photosensitive drum 61. The driving roller 33 is rotationally driven by a driving source such as a stepping motor, and gives a driving force for rotating the intermediate transfer belt 31 endlessly. The belt support roller 34, the backup roller 35, the primary transfer roller 36, the cleaning roller 37, the tension roller 38, and the driven roller 39 are rotatably provided, and are driven as the intermediate transfer belt 31 is rotated endlessly by the driving roller 33. Rotate. These rollers 34 to 39 are driven to rotate via the intermediate transfer belt 31 according to the main rotation of the driving roller 33 and support the intermediate transfer belt 31.

  Further, the cleaning roller 37 removes the toner remaining on the surface of the intermediate transfer belt 31 after the toner on the surface of the intermediate transfer belt 31, that is, the toner image on the surface of the intermediate transfer belt 31 is transferred onto the paper. . The tension roller 38 applies tension (tension) to the intermediate transfer belt 31 so that the intermediate transfer belt 31 does not loosen. The tension roller 38 is biased by, for example, a biasing member such as a spring body, so that the intermediate transfer belt 31 is moved from the back surface (inner peripheral side) to the front surface (outer peripheral side). The tension is generated by applying a pressing force to the belt 31.

  The primary transfer roller 36 applies a primary transfer bias (a polarity opposite to the toner charging polarity) to the intermediate transfer belt 31. By doing so, the toner image formed on each photosensitive drum 61 circulates in the arrow (clockwise) direction between each photosensitive drum 61 and the primary transfer roller 36 by driving of the driving roller 33. The intermediate transfer belt 31 is sequentially transferred (primary transfer) in an overcoated state.

  The secondary transfer roller 32 applies a secondary transfer bias having a polarity opposite to that of the toner image to the paper P. By doing so, the toner image primarily transferred onto the intermediate transfer belt 31 is transferred onto the paper P between the secondary transfer roller 32 and the backup roller 35, whereby a color transfer image is transferred onto the paper P. It is formed.

  The fixing unit 4 performs a fixing process on the transfer image transferred to the paper P by the image transfer unit 3. The fixing unit 4 is disposed opposite to the heating roller 41 heated by the energized heating element and the heating roller 41. And a pressure roller 42 whose surface is pressed against the peripheral surface of the heating roller 41.

  The transferred image transferred to the paper P by the secondary transfer roller 12 in the image forming unit 3 is subjected to a fixing process by heating when the paper P passes between the heating roller 41 and the pressure roller 42. Fixed to P. Then, the paper P subjected to the fixing process is discharged to the paper discharge unit 5. Further, in the color printer 1 of the present embodiment, a conveyance roller 81 that conveys the paper P subjected to the fixing process to the paper discharge unit 5 is disposed between the fixing unit 4 and the paper discharge unit 5. Yes.

  The paper discharge unit 5 includes a paper discharge tray 51 and a paper discharge roller 52. The paper discharge tray 51 is attached to the side surface (left side surface in FIG. 1) of the device main body 1a so as to be detachable and foldable, and receives the paper P discharged from the device main body 1a. The paper discharge roller 52 discharges the paper P transported by the transport roller 7 to the paper discharge tray 51. Further, the paper discharge roller 52 can pull out the fixed sheet P from the apparatus main body 1a to some extent and then rotate the paper P to the apparatus main body 1a by reverse rotation, thereby conveying it to the switchback conveyance path L2. By doing so, it is configured so that it can be transported again to the paper feed unit 2 by the transport roller 82 appropriately disposed in the switchback transport path L2, and the back side not printed can be printed.

  Further, the color printer 1 according to the present embodiment conveys the paper P to the switchback conveying path L2 by the conveying roller 81 between the fixing unit 4 and the paper discharging unit 5 instead of conveying the paper P to the paper discharging unit 5. You can also. By doing so, the paper P that can be transported to the paper feeding unit 2 again by the transport roller 83 appropriately disposed in the switchback transport path L2 and has passed through the image forming unit 3 or the like without printing, or once printed The printed paper P is further printed on the surface.

  Next, the image forming unit 6 will be described. The arrangement of each unit 6 is as follows. The unit 6K is disposed such that the position where the photosensitive drum 61 and the intermediate transfer belt 31 are close to each other is above the horizontal plane including the rotation axis of the photosensitive drum 61. The units 6Y, 6C, and 6M are the photosensitive drums. It arrange | positions so that it may become lower than the horizontal surface containing 61 rotating shafts. In FIG. 1, the unit 6K is disposed on the lower right side of the intermediate transfer belt 31, and the units 6Y, 6C, and 6M are disposed on the upper left side of the intermediate transfer belt 31, respectively.

  In each of the units 6K, 6Y, 6C, and 6M, a photosensitive drum 61 serving as an image carrier is disposed at the center position so as to be rotatable in the direction of an arrow (counterclockwise in FIG. 1). First, the configuration of the unit 6K will be described. FIG. 2 is an enlarged view of the periphery of the image forming unit 6K of the color printer 1 shown in FIG. Around the photosensitive drum 61 of the unit 6K, a charger 62, an exposure device 63, a developing device 64, a cleaning device 65, and the like are sequentially arranged from the upstream side in the rotation direction of the photosensitive drum 61.

  The charger 62 uniformly charges the peripheral surface of the photosensitive drum 61 rotated in the direction of the arrow. Examples of the charger 62 include a non-contact discharge type corotron type and scorotron type charger, a contact type charging roller, a charging brush, and the like. The exposure device 63 irradiates the peripheral surface of the photosensitive drum 61 uniformly charged by the charger 62 with laser light based on the image data input from the image reading device or the like, and converts the image data onto the photosensitive drum 61. Forming an electrostatic latent image based thereon; Examples of the exposure device 63 include an LED head unit and a laser scanning unit (LSU).

  The developing device 64 includes a developing roller 71, a paddle mixer 72, a stirring mixer 73, and a spike cutting blade 74. The developing roller 71 includes a rotating sleeve and a fixed magnet disposed inside the rotating sleeve. The paddle mixer 72 and the agitation mixer 73 have spiral blades and agitate while conveying toner in opposite directions to charge the toner, and the paddle mixer 72 supplies the charged toner to the developing roller 71. The developing roller 71 adsorbs the charged toner on the surface of the rotating sleeve by the magnetic force generated by the fixed magnet to form a toner layer. The developing roller 71 conveys the toner by rotating the rotating sleeve on which the toner layer is formed. The ear cutting blade 74 is a layer thickness regulating member that regulates the thickness of the toner layer formed on the developing roller 71.

  The developing device 64 regulates the thickness of the toner layer conveyed by the developing roller 71 by the spike cutting blade 74 when passing between the spike cutting blade 74 and the development roller 71. Then, the toner layer whose thickness is regulated is further conveyed to the vicinity of the photosensitive drum 61, and an electrostatic latent image is formed by the potential difference generated between the photosensitive drum 61 and the developing roller 71. A toner image based on the image data is formed on the peripheral surface of the photosensitive drum 61. Then, the toner image is primarily transferred to the intermediate transfer belt 31.

  For example, a photosensitive drum having a diameter of 40 mm is used as the photosensitive drum 61, and a developing roller 71 having, for example, a rotating sleeve having a diameter of 25 mm is used. The linear speeds of the photosensitive drum 61 and the rotating sleeve are set to, for example, 440 and 660 mm / sec, respectively, and the linear speed ratio between the rotating sleeve and the photosensitive drum 61 (rotating sleeve linear speed / photosensitive drum linear speed). Is, for example, 1.5.

  The cleaning device 65 includes a cleaning roller 76 and a cleaning blade 75. The cleaning blade 75 and the cleaning roller 76 remove the toner remaining on the peripheral surface of the photosensitive drum 61. The peripheral surface of the photosensitive drum 61 cleaned by the cleaning device 65 goes to the charger 62 for a new charging process, and a new primary transfer is performed. In the image forming unit 6, a static eliminator (not shown) may be disposed around the photosensitive drum 61, and the cleaning device 65 remains on the peripheral surface of the photosensitive drum 61 after static elimination by the static eliminator. The toner that is being removed may be removed.

  Further, in the image forming unit 6K, the rotation directions of the rotating sleeves of the photosensitive drum 61 and the developing roller 71 are opposite, and the earbrushing blade 74 is positioned below the horizontal plane including the rotating shaft of the rotating sleeve. Is arranged. That is, both the photosensitive drum 61 and the rotating sleeve travel upward at a position where the photosensitive drum 61 and the rotating sleeve face each other. Therefore, the toner as the developer is not easily dropped from the photosensitive drum 61 and the rotating sleeve, and the scattering of the toner can be suppressed.

  Further, the photosensitive drum 61 and the rotating sleeve rotate in a so-called trail direction that travels in the same direction at the position where the photosensitive drum 61 and the rotating sleeve face each other. Therefore, it is possible to suppress the occurrence of thin layer disturbance and toner dropout due to the difference in the traveling direction of the photosensitive drum 61 and the rotating sleeve. In addition, since the photosensitive drum 61 and the rotating sleeve are close to each other for a long time and development is easy, image formation can be performed under mild developing conditions such as a low developing voltage applied to the rotating sleeve. This also contributes to suppression of developer falling off.

  Further, the layer thickness regulating position by the ear cutting blade 74 is arranged within a range of 22 degrees or less on the upstream side in the rotation direction of the rotary sleeve and 35 degrees or less on the downstream side with respect to the vertical plane V including the rotation axis of the rotary sleeve. Is done. That is, when the angle α formed by the layer thickness regulating position by the panicle cutting blade 74 and the vertical plane V including the rotation axis of the rotary sleeve is located upstream of the vertical plane V in the rotation direction of the rotary sleeve, 22 degrees or less, and 35 degrees or less when downstream. FIG. 2 shows an example in which the rotary sleeve is arranged at a position of approximately 15 degrees on the upstream side in the rotational direction. By doing so, the toner whose layer thickness is regulated by the spike cutting blade 74 can be conveyed to the developing position where the photosensitive drum 61 and the rotating sleeve face each other without disturbing or dropping off the toner layer. Further, by arranging in this way, among the plurality of magnetic poles formed by the fixed magnet, the magnetic pole formed at the developing position and formed adjacent to the developing main pole for supplying the developer to the image carrier. Can be formed at the layer thickness regulating position facing the ear cutting blade 74. By doing so, since no other magnetic pole is formed between the magnetic pole (blade magnetic pole) formed at the layer thickness regulation position and the developing main pole, it is possible to further suppress the occurrence of thin layer disturbance and toner dropout. It should be noted that the layer thickness regulating position by the ear cutting blade 74 is an edge portion on the upstream side in the rotation direction of the rotation sleeve of the ear cutting blade 74 facing the rotation sleeve.

  Further, the magnetic force peak value at the layer thickness regulation position is selected to be any value within the range of 75 to 150 mT. If it is less than 75 mT, the toner attracting force to the developing roller 71 is too weak, and the toner layer is separated from the developing roller 71. On the other hand, if it is larger than 150 mT, the force to attract the toner to the developing roller 71 is too strong, the magnetic brush (magnetic toner chain) generated by the magnetic force at the layer thickness regulating position becomes too strong, and the layer thickness regulating position is clogged with toner. Occurs and thin layer disturbance occurs. Therefore, when the magnetic force peak value at the layer thickness regulation position is in the range of 75 to 150 mT, the force to attract the toner to the developing roller 71 is suitable, and even if the layer thickness of the toner layer is regulated by the ear cutting blade 74, Thin layer turbulence hardly occurs.

  Further, in the image forming unit 6K, as described above, the position where the photosensitive drum 61 and the intermediate transfer belt 31 are close to each other is above the horizontal plane including the rotation axis of the photosensitive drum 61. Therefore, since the intermediate transfer belt 31 is located above the layer thickness regulating position where the rotating sleeve and the earbrushing blade 74 are opposed to each other, even when the toner scatters, the intermediate transfer belt 31 is not contaminated by the toner. High-quality images can be formed. Further, since measures such as a seal for preventing contamination of the intermediate transfer belt 31 due to toner scattering are almost unnecessary, the size can be reduced.

  Further, the rotation axis of the rotation sleeve is above the horizontal plane including the rotation axis of the photosensitive drum 61. Therefore, since the layer thickness regulating position where the photosensitive drum 61 and the rotating sleeve face each other is above the horizontal plane including the rotating shaft of the photosensitive drum 61, the developing is performed above the horizontal plane including the rotating shaft of the photosensitive drum 61. The toner of the agent is supplied to the photosensitive drum 61 to form a toner image. Further, the formed toner image is transferred to the intermediate transfer belt 31 above the horizontal plane including the rotation axis of the photosensitive drum 61. Therefore, the toner is hardly transported below the horizontal plane including the rotation axis of the photosensitive drum 61, and the toner is not easily dropped from the photosensitive drum 61.

  Further, the rotation shaft of the rotation sleeve is disposed above the horizontal plane including the rotation shaft of the photosensitive drum 61, so that a space is formed below the developing roller 71. In that space, there is almost no need to provide a seal or the like for preventing the process unit from being contaminated by the developer, so that the exposure light from the exposure device 63 can pass through the space. By doing so, the size can be further reduced.

  As described above, the color printer 1 can suppress the occurrence of thin layer disturbance and the occurrence of internal contamination due to the scattering of the developer, and can form a high-quality image having a sufficiently high image density. In addition, since the occurrence of dirt inside the machine is suppressed, the number of seals for preventing the process unit from becoming dirty can be reduced, and downsizing can be achieved.

  Further, in the image forming unit 6K, an angle β formed by the layer thickness regulation position by the panning blade 74 and the virtual plane P including the rotation axis of the rotation sleeve and the rotation axis of the photosensitive drum 61 is 30 degrees or more and 90 degrees or less. It is preferable to arrange within the range. In FIG. 2, the example arrange | positioned at about 60 degree | times is shown. By doing so, the toner whose layer thickness is regulated by the trimming blade 74 can be conveyed to the developing position where the photosensitive drum 61 and the rotating sleeve face each other without disturbing or dropping off the thin layer of toner. The effect that can be demonstrated more suitably. Further, by arranging in this way, among the plurality of magnetic poles formed by the fixed magnet, the magnetic pole formed at the development position and formed adjacent to the development main pole for supplying toner to the photosensitive drum 61. Can be formed at the layer thickness regulating position facing the ear cutting blade 74. By doing so, since no other magnetic pole is formed between the magnetic pole (blade magnetic pole) formed at the layer thickness regulation position and the developing main pole, it is possible to further suppress the occurrence of thin layer disturbance and toner dropout.

  Further, the configuration of the image forming unit 6K as described above is such that when a magnetic toner that is a magnetic one-component developer is used as a developer, the above-described thin layer disturbance occurs and the developer scatters. The effect that generation | occurrence | production of dirt can be suppressed can be exhibited suitably. Since the other image forming units 6K, 6Y, and 6C generally use a two-component developer including toner and carrier, the configuration may be the same as the configuration of the image forming unit 6K. It may be a configuration of a forming unit. For example, FIG. 1 shows an image forming unit using a developing device of a hybrid developing system.

  The magnetic toner used in the image forming unit 6K preferably has a circularity of 0.96 or less by a flow type particle image analyzer (FPIA). If the circularity is too high, the magnetic brush (magnetic toner chain) generated by the magnetic force at the layer thickness regulation position is not likely to have an appropriate strength, and charging tends to be insufficient or thin layer formation failure tends to occur. is there. The volume average particle size of the magnetic toner is preferably 4 to 7.8 μm. Further, the CV value based on the number representing the sharp difference in the particle size distribution of the magnetic toner is preferably 28% or less, more preferably 25% or less, and even more preferably 22% or less. If the CV value is too large, small-diameter toner having a small saturation magnetization is difficult to be conveyed by the developing roller 71 and tends to accumulate in the developing device 64 such as on the ear cutting blade 74. In addition, when the earbrushing blade 74 is installed below the rotation axis of the photosensitive drum 61 as in the present invention, the pressure is more likely to be applied to the toner at the layer thickness regulating position than when the earbrushing blade 74 is installed above. If the toner is accumulated in the toner, toner fusing is likely to occur.

[Examination example]
Hereinafter, in the color printer 1 according to the embodiment of the present invention, the results of studying the positional relationship between the photosensitive drum 61 and the developing roller 71 and the magnetic force peak value at the layer thickness regulation position will be described.

(Examination example 1)
First, the results of examining the positional relationship between the photosensitive drum 61 and the developing roller 71 will be described. The relationship between the angle α and the disordered state of the magnetic brush generated by the magnetic force at the layer thickness regulating position is shown in Table 1 below. The disordered state of the magnetic brush was evaluated as follows.

The thickness (layer thickness) (mg / cm ² ) of the toner layer formed on the rotating sleeve is measured along the longitudinal direction of the rotating sleeve, and the average value of the measured layer thickness and the maximum value of the layer thickness are measured. If the ratio is less than 50%, it is determined that no disturbance has occurred, and is evaluated as “◯”, and if it is 50% or more, it is determined that disturbance has occurred. , “×”.

  From Table 1, when the photosensitive drum 61 and the developing roller 71 are arranged within an angle α of 22 degrees or less on the upstream side and 35 degrees or less on the downstream side, the arrangement of the developing main pole and the blade magnetic pole becomes suitable. It can be seen that the magnetic brush is stable. If the photosensitive drum 61 and the developing roller 71 are arranged so that the angle α is larger than 22 degrees on the upstream side, the angle between the developing magnetic pole and the blade magnetic pole becomes narrow, and the magnetic brush is disturbed. If the photosensitive drum 61 and the developing roller 71 are arranged so that the angle α is larger than 35 degrees on the downstream side, the angle between the developing magnetic pole and the blade magnetic pole becomes too wide, and the angle between the developing magnetic pole and the blade magnetic pole is increased. Further, it is necessary to form one or more magnetic poles as the conveying poles, and the magnetic brush is disturbed and the toner layer is disturbed.

(Examination example 2)
In addition, the result of studying the angle β will be described. If the photosensitive drum 61 and the developing roller 71 are arranged so that the angle β is less than 30 degrees, the magnetic field lines are disturbed, and it becomes difficult to convey the toner. This is because the flow of magnetic lines of force between the magnetic poles formed on the developing roller, for example, the flow of magnetic lines of force from the N pole to the S pole and the flow of magnetic lines of force from the S pole to the N pole are disturbed. If the photosensitive drum 61 and the developing roller 71 are arranged so that the angle β is 90 degrees or more, the angle between the developing magnetic pole and the blade magnetic pole becomes too wide, and the conveyance between the developing magnetic pole and the blade magnetic pole is carried out. It is necessary to form one or more magnetic poles as poles, and the magnetic brush is disturbed and the toner layer is disturbed.

(Examination example 3)
Next, the result of examining the magnetic force peak value at the layer thickness regulation position will be described. The relationship between the magnetic force peak value and the layer state of the toner layer formed on the rotating sleeve is shown in Table 2 below. In addition, the layer state was evaluated as follows similarly to the disordered state of the magnetic brush.

The thickness (layer thickness) (mg / cm ² ) of the toner layer formed on the rotating sleeve is measured along the longitudinal direction of the rotating sleeve, and the average value of the measured layer thickness and the maximum value of the layer thickness are measured. If the ratio is less than 50%, it is judged that no disturbance has occurred, and is evaluated as “◯”. If the ratio is 50% or more and less than 60%, a little disturbance has occurred. However, it was determined that there was no problem in image formation, and was evaluated as “Δ”, and when it was 60% or more, it was determined that disorder occurred and was evaluated as “×”.

  From Table 2, it can be seen that when the magnetic force is 75 to 150 mT, image quality deterioration due to thin layer disturbance does not occur. Moreover, it turns out that it is hard to generate | occur | produce a thin layer disorder more as magnetic force is 75-100 mT, and it turns out that it is more preferable. Furthermore, if the magnetic force is 60 mT or less, the magnetic force is too weak, the magnetic brush is separated from the rotating sleeve, the thin layer is disturbed, and if the magnetic force is 160 mT or more, the magnetic force is too strong, and the cutting blade 74 It can be seen that the toner adheres firmly, and the thin layer disturbance occurs due to the adhesion.

  As described above, by optimizing the positional relationship between the photosensitive drum 61 and the developing roller 71 and the magnetic force peak value at the layer thickness regulating position as in the present invention, the occurrence of thin layer disturbance and the scattering of the developer are caused. Generation of high-quality images with sufficiently high image density can be formed by suppressing the occurrence of internal stains.

1 is a schematic cross-sectional view showing an overall configuration of a color printer 1 according to an embodiment of the present invention. 2 is an enlarged view of a peripheral portion of an image forming unit 6K of the color printer 1 shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 2 Paper feed part 3 Image transfer part 4 Fixing part 5 Paper discharge part 6 Image forming unit 21 Paper feed cassette 22, 27 Pickup roller 23 Paper feed roller 24 Registration roller 31 Intermediate transfer belt 32 Secondary transfer roller 33 Drive roller 34 Belt Support Roller 35 Backup Roller 36 Primary Transfer Roller 37 Cleaning Roller 38 Tension Roller 39 Driven Roller 41 Heating Roller 42 Pressure Roller 51 Paper Discharge Tray 61 Photosensitive Drum 62 Charger 63 Exposure Device 64 Development Device 71 Development Roller 72 Paddle Mixer 73 Stirring mixer 74 Ear cutting blade 75 Cleaning blade 76 Cleaning roller

Claims (4)

An image carrier on which an electrostatic latent image is formed, a developing roller disposed opposite to the image carrier and including a fixed magnet, and a developer layer thickness formed on the rotary sleeve A layer thickness regulating member that regulates
The rotation direction of the image carrier and the rotation sleeve is the reverse direction,
The layer thickness regulating position by the layer thickness regulating member is below the horizontal plane including the rotation axis of the rotary sleeve, and the rotation of the rotary sleeve relative to the vertical plane including the rotation axis of the rotary sleeve It is arranged to be 22 degrees or less upstream in the direction and 35 degrees or less downstream.
An image forming apparatus, wherein a peak value of magnetic force at a position of the developing roller facing the layer thickness regulating member is 75 to 150 mT. An intermediate transfer body is provided that develops the electrostatic latent image formed on the image carrier into a toner image with toner of the developer, transfers the developed toner image, and transfers the transferred toner image to a recording medium. ,
The image forming apparatus according to claim 1, wherein a position where the image carrier and the intermediate transfer member are close to each other is above a horizontal plane including a rotation axis of the image carrier.   The image forming apparatus according to claim 2, wherein a rotation axis of the rotation sleeve is above a horizontal plane including a rotation axis of the image carrier.   The image forming apparatus according to claim 1, wherein the developer is a magnetic one-component developer.

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