JP2005115025A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage, wear and deterioration of a fixing roller rotating body, to stably fix a toner image on a sheet material, to prevent image defects such as rubbing marks of the fixed image and sheet material clogging, and to fix a heat roller type fixing device. The structure for guiding the sheet material is simplified.
SOLUTION: A planar heating element 1a that has a flat surface and generates heat upon energization, a heat-resistant belt 3 that includes the planar heating element 1a and can move in a substantially circular free state, and is disposed opposite the planar heating element. And a pressure roll 2 that sandwiches and conveys the heat-resistant belt, the pressure roll has an elastic layer on the surface, and the fixing nip portion has a heat resistance between the pressure roll 2 and the sheet heating element 1a. A flat fixing nip is formed by nipping, pressing and conveying the belt, and a sheet material having a guide slope 4c approaching the sheet material conveying surface toward the front in the conveying direction of the sheet material on the fixing nip outlet side. The guide member 4 is disposed in the vicinity, and the sheet material is passed through the fixing nip portion to fix the unfixed toner image.
[Selection] Figure 1

Description

  The present invention includes a planar heating element that has a flat surface and generates heat when energized, a heat-resistant belt that includes the planar heating element and is movable in a substantially circular free state, and is disposed opposite to the planar heating element. A pressure roll that sandwiches and conveys the heat-resistant belt, and fixes the unfixed toner image formed on the sheet material by passing the sheet material through a fixing nip formed by the heat-resistant belt and the pressure roll. The present invention relates to a fixing device and an image forming apparatus.

  In an image forming apparatus such as a copying machine, a printer, or a facsimile, in a heating roll type fixing device that heats and fixes an unfixed toner image on a transfer material (sheet material), a sheet on which an unfixed toner image is formed in the fixing nip When the material is passed and fixed, the sheet material is imparted with a curling behavior that deforms along the outer periphery of the heat fixing roll, and is easily wound around the heat fixing roll side. Therefore, a peeling means such as a peeling claw, a peeling plate, or a peeling sheet is usually provided on the sheet material discharge side of the heating roll type fixing device in order to peel the sheet material from the fixing roll (for example, Patent Documents 1 and 2). reference).

For example, Patent Document 1 discloses a plurality of flexible protrusions that are formed by a sheet-like material and are provided with means for reducing rigidity at the base of a sheet peeling claw facing a sheet transfer body such as a fixing roll. The protruding portion is bent and rubbed to have a structure for peeling the sheet material from the sheet transfer body. Japanese Patent Laid-Open No. 2004-260688 discloses a rotating body that is slidably arranged by bending a free end portion in which a plurality of slits are formed from the base of a plate-like member having elasticity, facing a pair of fixing roller rotating bodies as a peeling plate. It has a structure which peels a sheet material from. In either case, a plate-like member having elasticity with respect to the rotating body is slidably disposed by bending the free end thereof, and the sheet material is peeled off from the rotating body.
Japanese Examined Patent Publication No. 2-61030 Japanese Utility Model Publication No. 53-117249

  However, as in Patent Documents 1 and 2, in a structure in which a peeling claw or a peeling plate is brought into contact with a sheet transfer body such as a fixing roll or a fixing roller rotating body to bend and peel the sheet material, the sliding portion is slid at the sliding portion. Regardless of the rubbing pressure, there is a problem that the surface of the sheet transfer body such as the fixing roll or the fixing roller rotating body is likely to be damaged, worn, or deteriorated. In particular, in recent image forming apparatuses that have increased in speed, the phenomenon appears remarkably and the rubbing arrangement is not preferable.

  On the other hand, the sheet material carries an unfixed toner image, moves along the surface of the fixing roller rotator and is fixed, and the toner image immediately after fixing discharged from the nip exit is still in a molten state. Since the sheet material is peeled off as described above, the peeling claw and the peeling plate have their tips, i.e., the rubbing portions, wedge-shaped from the surface parallel to the original conveying direction of the sheet material. Rubbing is arranged so as to bite between the sheet materials. Therefore, when the sheet material is peeled from the fixing roller rotating body and proceeds in a predetermined direction, the toner image fixed on the surface of the sheet material rubs against the plate-like member, leaving a rubbing mark on the image, Alternatively, there is a problem that the fixed toner image moves to the plate-like member to cause an image defect, or the fixed toner image sticks to the plate-like member to prevent the progress of the sheet material, and jam: the sheet material is clogged. In recent image forming apparatuses that have been increased in speed, the fixing temperature becomes higher, and such a phenomenon appears remarkably, and the rubbing arrangement is not preferable.

  The present invention solves the above-described conventional problems, eliminates the need for a means for forcibly peeling the sheet material in the fixing device, prevents damage, wear and deterioration of the surface of the fixing unit rotating body, and prevents toner images. Is stably fixed to the sheet material, and image defects such as rubbing marks and clogging of the sheet material are prevented from occurring in the fixed image. The structure for guiding the sheet material of the heat roller type fixing device is simplified to reduce the size and cost of the fixing device and the image forming apparatus.

  Therefore, the present invention provides a planar heating element that has a flat surface and generates heat when energized, a heat-resistant belt that includes the planar heating element and is movable in a substantially circular free state, and is disposed opposite to the planar heating element. An unfixed toner image formed on the sheet material by passing the sheet material through a fixing nip portion formed by the heat-resistant belt and the pressure roll. The pressure roll has an elastic layer on the surface thereof, and the fixing nip portion conveys the pressure roll with the heat-resistant belt sandwiched between the pressure roll and the sheet heating element. In this way, a flat fixing nip is formed, and a sheet material guide member having a guide slope approaching the sheet material conveying surface toward the front in the sheet material conveying direction is arranged close to the fixing nip outlet side. Special To.

  The sheet material guide member is formed of a plate-like member, forms a plurality of projecting wall portions extending in the sheet material guide direction, and has a lubricant treatment applied to at least the surface of the surface facing the sheet material. And

  According to the present invention, a planar heating element that has a flat surface and generates heat when energized, a heat-resistant belt that includes the planar heating element and is movable in a substantially circular free state, and is disposed opposite to the planar heating element. An unfixed toner image formed on the sheet material by passing the sheet material through a fixing nip portion formed by the heat-resistant belt and the pressure roll. The pressure roll has an elastic layer on the surface thereof, and the fixing nip portion conveys the pressure roll with the heat-resistant belt sandwiched between the pressure roll and the sheet heating element. In this way, a flat fixing nip is formed, and a sheet material guide member having a guide slope approaching the sheet material conveying surface toward the front in the sheet material conveying direction is arranged close to the fixing nip outlet side. So flat The sheet material after fixing passing through the fixing nip portion by the contact nip can be discharged from the fixing nip portion without imparting curl habits to either the heat-resistant belt side or the pressure roll side, forcibly. The means for peeling off can be eliminated. In addition, the sheet material after fixing, which is discharged from the fixing nip outlet, is in contact with the guide slope by the guide slope of the sheet material guide member disposed close to the fixing nip exit side without using a pressure roll or a heat-resistant belt. However, it is possible to guide in the transport direction along the transport surface without rubbing the image surface. Therefore, it is possible to prevent rubbing marks on the image, or to prevent the fixing toner image from moving to the plate-like member and causing an image defect or a sheet material clogging. It is possible to prevent damage, wear and deterioration on the surface of the heat-resistant belt.

  The sheet material guide member is formed of a plate-like member, forms a plurality of protruding wall portions extending in the sheet material guide direction, and is provided with a lubricant treatment on at least the surface facing the sheet material. With a simple configuration, the sheet material can be smoothly guided in the conveyance direction along the conveyance surface, and the toner image fixed on the sheet material surface rubs against the sheet material guide member and rubs against the image. It may leave a mark, or the fixed toner image may move to the plate-like member and cause an image defect, or the fixed toner image may stick to the plate-like member and prevent the sheet material from proceeding. Can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of a fixing device of the present invention. In the figure, 1 is a heat fixing member, 1a is a sheet heating element, 1b is a belt guide member, 2 is a pressure roll, 2b is a roll base, 2c is an elastic layer, 3 is a heat resistant belt, and 4 is a sheet material guiding member. 4a is a mounting member, 4b is a sheet material guide plate, 4c is a guide slope, and L is a pressing portion tangent.

  In FIG. 1, a heat fixing member 1 is composed of a sheet heating element 1a having a flat surface and generating heat upon energization, and a belt guide member 1b made of, for example, a ceramic base that supports the sheet heating element 1a. An endless belt that includes the heat fixing member 1 and is movable in a substantially circular free state. The pressure roll 2 is a pressure member in which, for example, a pipe material is used as a roll base material 2b, and an elastic body is formed on the outer periphery thereof to form an elastic layer 2c. In the fixing nip, the pressure roll 2 is disposed opposite to the sheet heating element 1a from above the heat-resistant belt 3 slidably disposed on the surface of the sheet heating element 1a, and pressed with a predetermined pressing force. It is formed by. Since the heat-resistant belt 3 is slid and moved on the surface of the sheet heating element 1a by pressing and urging the heat-resistant belt 3 from the pressure roll 2, the friction coefficient between the pressure roll 2 and the heat-resistant belt 3 is large. The friction coefficient between the sheet heating element 1a and the heat-resistant belt 3 is composed of a combination of small materials. Further, since the heat-resistant belt 3 is heated to a predetermined temperature by the sheet heating element 1a to fix the unfixed toner image on the sheet, the heat-resistant belt 3 is preferably excellent in thermal conductivity.

  The heat-resistant belt 3 is an endless belt that is slidably arranged on the surface of the sheet heating element 1a following the rotation of the pressure roll 2, has a thickness of 0.03 mm or more, and is made of polyimide. A heat-resistant resin such as a tube or silicon, rubber, or the like may be used, but a metal belt made of a stainless base material or a nickel electroformed tube having excellent thermal conductivity is preferable. In consideration of the effect of contacting the pressure roller 2 facing the toner image surface of the sheet material, for example, a rubber material such as PFA or silicon is preferably used as the surface layer.

  The sheet material guide member 4 guides the sheet material from the fixing nip exit, and is held on the base by a fixing means such as a heat-resistant double-sided tape and is attached to the main body frame by the attachment portion 4a. The gap between the pressure roll 1 and the heat-resistant belt 3 is disposed close to the fixing nip exit side with a gap without rubbing. The sheet material guide plate 4b is formed by bending a plate member made of a heat-resistant resin such as polyimide, polyamideimide, PPS, or a metal steel plate material such as a stainless steel plate material, a phosphor bronze plate material, or a thin steel plate material. There is a guide slope 4c that approaches the sheet material conveyance surface L from the fixing nip outlet toward the front in the sheet material conveyance direction.

  When the heat-resistant belt 3 is pressed in the direction of the planar heating element 1a by the pressure roll 2, the elastic layer 2c is provided on the surface of the pressure roll 2, so that the heat-resistant belt 3 follows the surface of the planar heating element 1a. In the pressing portion, a flat nip is formed as a fixing nip with the surface of the heat-resistant belt 3 along the surface of the flat sheet heating element 1a as a reference.

  Originally, when a sheet material on which an unfixed toner image is formed is passed through the fixing nip and is heated and melted and fixed by the heat-resistant belt 3, the sheet material is imparted with a curling behavior that deforms along the outer periphery of the heat-resistant belt 3 and is heat-resistant. It becomes easy to wind around the belt 3 side. According to the present embodiment, since the heat-resistant belt 3 including the sheet heating element 1a is pressed and urged by the pressure roll 2 to form a flat nip, the sheet material passing through the fixing nip is the heat-resistant belt 3. No curling habit is imparted to either the side of the pressure roller 2 or the pressure roll 2, the sheet material after fixing is not wrapped around the heat-resistant belt 3, and a peeling claw or a peeling plate for forcibly peeling the sheet material The stripping means is unnecessary.

  However, even if the wrapping of the sheet material is basically eliminated in the configuration of the flat nip as described above, the sheet material may bring about unexpected characteristics in the moisture absorption state, the sheet fiber state, or the constituent material. The sheet material guide member 4 is transported in the vicinity of the fixing nip exit side in consideration of safety, although it does not need to exhibit its function until it is forcibly removed as an unexpected measure such as jamming of the sheet material. Establishing a route is effective for trouble-free configurations.

  According to the present embodiment, the pressure roll 2 having the elastic layer 2c is pressed and urged from above the heat-resistant belt 3 to the planar heating element 1a to form a flat nip, so that the heat-resistant belt 3 is flat. When released from the close contact state along the surface of the sheet heating element 1a, it becomes a substantially circular free state, and the sheet material at its shape-arranged part has its own return force (commonly referred to as the waist of the sheet material). Can be easily separated from the heat-resistant belt 3. The sheet material that has passed through the fixing nip in this manner is discharged away from the fixing nip exit without being wound around the pressure roll 2 and the heat-resistant belt 3, so that the leading edge is guided and corrected in the desired conveying direction. I can do it. Therefore, the angle of the guide slope 4c of the sheet material guide member 4 is a range that is perpendicular to the tangent of the surface of the pressure roll 2 and heat-resistant belt 3 at the tip of the guide slope 4c from the angle parallel to the pressing part tangent L, that is, It is preferable that the leading end of the guide slope 4c be in a range in which the tip of the pressure roll 2 is directed to the inside from the rotation center of the pressure roll 2 and from the center of curvature of the heat-resistant belt 3 to the inside of the fixing nip.

  For example, when the guide slope 4c is at an angle away from the sheet material conveying surface L from the fixing nip exit toward the front in the sheet material conveying direction, that is, the direction of the leading edge of the sheet material guiding plate 4b is the heat resistant belt 3. In the case where the angle is inward from the tangent line, the fixing toner image surface is rubbed against the guide slope 4c when the leading edge of the sheet material advances along the guide slope 4c, as in the case of conventional peeling claws and peeling plates. End up. When the extended line at the tip of the guide slope 4c passes through the outer side opposite to the fixing nip from the center of curvature of the heat-resistant belt 3, the surface facing the sheet material is in contact with the tangential surface of the heat-resistant belt 3 at the tip. Therefore, when the sheet material discharged from the fixing nip exit is separated from the heat-resistant belt 3 and is in a substantially circular free state and comes into contact with the guide slope 4c, the sheet material is caught in the direction of the heat-resistant belt 3. It comes to be.

  According to the sheet material guide plate 4 b of the sheet material guide member 4, the sheet material guide plate 4 b is disposed close to the surface of the pressure roll 2 and the heat-resistant belt 3 without being rubbed, and the sheet material is guided from the leading end on the fixing nip outlet side. The guide can be guided by a guide slope 4c having an angle parallel to the conveying direction (direction of the tangent L of the flat nip portion) or the angle of rotation of the pressure roll 2 and the center of curvature of the heat-resistant belt 3. In addition, by setting the guide slope 4c at a predetermined angle, the sheet material can be guided in a desired conveyance direction only by rubbing the leading edge, and the toner image of the sheet material slides on the sheet material guide plate 4b. Without leaving rubbing marks on the fixed image, the fixed toner image is transferred to the sheet material guide plate 4b to cause an image defect, or the fixed toner image is stuck on the sheet material guide plate 4b. This prevents jamming and jamming of the sheet material, and enables extremely stable image fixing.

  FIG. 2 is a perspective view of a sheet material guide member disposed close to the fixing nip exit side. The sheet material guide member 4 disposed in the vicinity of the fixing nip outlet side without sliding against the pressure roll 2 and the heat-resistant belt 3 is, for example, a sheet material guide plate 4b having a guide slope 4c as shown in FIG. 2a, and the sheet material guide plate 4b is not only a flat plate member as shown in FIG. 2 (A), but also squeezes the plate member into a rib shape as shown in FIG. 2 (B). The plurality of protruding wall portions 4d may be formed in parallel to the sheet material guiding direction. As described above, the winding of the sheet material is basically eliminated by the configuration of the fixing nip, and the sheet material guiding member 4 that guides the conveyance of the sheet material arranged on the fixing nip outlet side is substantially equal to the fixing nip width. Since the pressure roll 2 and the heat-resistant belt 3 are formed with the same width and are disposed with a gap, the pressure roll 2 and the heat-resistant belt 3 are worn or deteriorated without relatively rubbing against the surfaces. Does not cause damage to the surface condition.

  Since the leading edge of the sheet material that has passed through the fixing nip is guided by the sheet material guiding member 4 and the traveling direction is corrected to a desired direction (conveying direction), the leading edge of the sheet material is guided to the sheet material guiding member 4. A reverse curl behavior that is opposite to the curl direction immediately after passing through the fixing nip passing portion is given as a reaction force that is guided and guided by contact. When the guide material 4 is guided by the guide slope 4c so that the traveling posture of the sheet material is corrected to a desired relationship, the sheet material is originally guided by rubbing only at the front end in this guidance process, and the fixed toner image is transferred to the sheet material guide member. No relative rubbing with 4. Accordingly, a rubbing mark is left on the fixed image, or the fixed toner image is transferred to the sheet material guide member 4 to cause an image defect. Further, the fixed toner image sticks to the sheet material guide member 4 and the sheet material advances. Jam: Prevents jamming of sheet material. Even if the toner image surface touches the sheet material guiding member 4 due to unexpected factors such as the moisture absorption state, the sheet fiber state, or the constituent material, and the toner image surface may come into contact with the sheet material guiding member 4, a plurality of protrusions may occur. When the sheet material guide member 4 having the wall portion 4d is disposed, the contact area of the toner image surface can be minimized, and troubles to the fixed image can be reduced as much as possible.

  Further, if the surface of the sheet material guide member 4 facing at least the surface of the sheet material is subjected to a lubricant treatment comprising, for example, coating, painting, or plating of a fluorine material, the sliding resistance of the sheet material is reduced. Therefore, stable guidance and guidance of the sheet material can be performed. Further, even if the toner image surface touches the sheet material guide member 4 and a part of the toner image adheres to a part of the sheet material guide member 4, the sheet material guide is obtained by applying a lubricant treatment. The toner can be easily peeled off from the member 4.

  FIG. 3 is a diagram for explaining the behavior in which the sheet material curled and discharged to the heat-resistant belt side is guided by the sheet material guide member, and FIG. 4 is the sheet material curled and discharged to the pressure roll side. It is a figure for demonstrating the behavior guided by a material guide member. The basic curling behavior of the sheet material 5 after fixing is that the sheet material 5 has a moisture absorption state, a sheet fiber state or a constituent material, a paper quality, a thickness, an image or a line drawing having a relatively large amount of toner that is almost solid like a photograph. Sheet material discharged from the exit of the fixing nip, depending on whether the image has a relatively small amount of toner, or the image on the front surface or the image on the back surface has a large or small amount of toner. Even if 5 is peeled off without being wound around the heat-resistant belt 3, it is curled and discharged to either the heat-resistant belt 3 side or the pressure roll 2 side.

  When the sheet material 5 discharged from the fixing nip exit is curled toward the heat-resistant belt 3 with respect to the conveyance surface L of the sheet material 5 that is a tangent to the fixing nip and is in the direction of conveying the virtual sheet material as shown in FIG. First, when the leading edge of the sheet material 5 comes into contact with the guide slope 4c of the sheet material guide member 4 disposed close to the heat-resistant belt 3 side (a), the leading edge remains in contact with the guide slope 4c. It is guided and proceeds (b), and a reverse curl behavior is given as its contact reaction force (c), and finally guided in the virtual sheet material conveyance direction (d). During this time, the fixing toner image surface of the sheet material 5 is separated from the guide slope 4c by being guided so as to approach the conveying surface L of the sheet material 5 while the leading edge of the sheet material 5 is in contact with the guide slope 4c. Guided without rubbing. Since the leading edge of the sheet material 5 is guided and advanced in this manner, the leading edge of the sheet material 5 can be advanced with a smoother behavior by applying a lubricant treatment to the contact surface. .

  Conversely, as shown in FIG. 4, the sheet material 5 discharged from the fixing nip outlet is curled toward the pressure roll 2 with respect to the conveyance surface L of the sheet material 5 which is the tangent line of the fixing nip and is in the virtual sheet material conveyance direction. When the sheet material 5 advances, the tip of the sheet material 5 comes into contact with the guide slope 4c of the sheet material guide member 4 disposed close to the pressure roll 2 side (a). Guided as it is and proceeds (b), a reverse curling behavior is given as the contact reaction force (c), and finally guided in the virtual sheet material conveyance direction (d). During this time, the front surface of the sheet material 5 is guided so as to approach the conveying surface L of the sheet material 5 while the leading end of the sheet material 5 is in contact with the guide slope 4c, so that even if the back surface of the sheet material 5 is the fixed toner image surface. It is guided without being rubbed away from the guide slope 4c.

  FIG. 5 is a schematic cross-sectional view of the overall configuration showing an embodiment of the image forming apparatus of the present invention. In the figure, 10 is an image forming apparatus, 10a is a housing, 10b is a door, 11 is a paper transport unit, 15 is a cleaning means, 17 is an image carrier, 18 is an image transfer transport means, 20 is a developing means, and 21 is a scanner. Means, 30 is a paper feeding unit, 40 is fixing means, W is an exposure unit, and D is an image forming unit.

  In FIG. 5, the image forming apparatus 10 includes a housing 10a, a paper discharge tray 10c formed on the top of the housing 10a, and a door 10b that is openably and detachably mounted on the front surface of the housing 10a. 1 includes an exposure unit (exposure means) W, an image forming unit D, a transfer belt unit 29 having an image transfer and conveyance means 18, and a paper feed unit 30, and a paper conveyance unit 11 is arranged in the door body 10b. ing. Each unit has a configuration that can be attached to and detached from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The image forming unit D includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. In each of the image forming stations Y, M, C, and K, an image carrier 17 that is a photosensitive drum, a charging unit 19 that is a corona charging unit and a developing unit that are disposed around the image carrier 17 are provided. Means 20 are included. These image forming stations Y, M, C, and K are arranged in parallel on the lower side of the transfer belt unit 29 so that the image carrier 17 faces upward along an oblique arched line. The order of arrangement of the image forming stations Y, M, C, and K is arbitrary.

  The transfer belt unit 29 is disposed below the housing 10a and is driven to rotate by a drive source (not shown), a driven roll 13 disposed obliquely above the drive roll 12, a tension roll 14, An image transfer conveying means 18 composed of an intermediate transfer belt that is stretched between these three and at least two rolls and driven to circulate in the direction of the arrow in the figure, and a cleaning means 15 that contacts the surface of the image transfer conveying means 18. I have. The driven roll 13, the tension roll 14, and the image transfer / conveying means 18 are arranged in a direction inclined to the left in the drawing with respect to the drive roll 12, and thereby the belt conveying direction when driving the image transfer / conveying means 18 is downward. The belt surface 18a is positioned below, and the belt surface 18b whose transport direction is upward is positioned above.

  Accordingly, the image forming stations Y, M, C, and K are also arranged in a direction inclined to the left in the drawing with respect to the drive roll 12. Then, the image carrier 17 is brought into contact with the belt surface 18a facing downward in the transport direction of the image transfer transport unit 18 along the arched line, and is rotationally driven in the transport direction of the image transfer transport unit 18 as indicated by the arrows in the drawing. The The flexible endless sleeve-shaped image transfer / conveyance means 18 is brought into contact with the image carrier 17 from substantially the same wrapping angle so as to be covered from above, so that the image carrier 17 and the image transfer / conveyance means 18 are in contact with each other. The contact pressure and the nip width between them can be adjusted by controlling the tension applied to the image transfer / conveying means 18 by the tension roll 14, the arrangement interval of the image carrier 17, the winding angle (arch curvature), and the like. .

The drive roll 12 also serves as a backup roll for the secondary transfer roll 39. A rubber layer having a thickness of, for example, about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roll 12, and the secondary transfer roll is grounded through a metal shaft. This is a conductive path for the secondary transfer bias supplied via the line 39. Thus, by providing the drive roll 12 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet material enters the secondary transfer portion to be transmitted to the image transfer conveying means 18, and the image quality is deteriorated. Can be prevented. Further, by making the diameter of the driving roll 12 smaller than the diameter of the driven roll 13 and the backup roll 14, the sheet material after the secondary transfer can be easily peeled off by the elastic force of the sheet material itself. Further, the driven roll 13 is also used as a backup roll for the cleaning means 15 described later.

  The image transfer / conveying means 18 is arranged in a direction inclined to the right in the drawing with respect to the drive roll 12, and correspondingly, each of the image forming stations Y, M, C, K is also illustrated with respect to the drive roll 12. And may be arranged along an oblique arch shape in a direction inclined to the right side.

  The cleaning unit 15 is provided on the side of the belt surface 18a facing downward in the transport direction, and a cleaning blade 15a that removes toner remaining on the surface of the image transfer transport unit 18 after the secondary transfer, and a toner transport that transports the collected toner A member 15b is provided. The cleaning blade 15 a is in contact with the image transfer / conveyance means 18 at a portion where the image transfer / conveyance means 18 is wound around the driven roll 13. Further, a primary transfer member 16 is brought into contact with the back surface of the image transfer conveying unit 18 so as to face an image carrier 17 of each of the image forming stations Y, M, C, and K described later. A transfer bias is applied.

  The exposure means W is disposed in a space formed obliquely below the image forming unit D disposed in the oblique direction. A paper feeding unit 30 is disposed below the exposure unit W and at the bottom of the housing 10a. The exposure means W is entirely housed in a case, and the case is disposed in a space formed obliquely below the belt surface facing downward in the transport direction. A single scanner means 21 comprising a polygon mirror motor 21a and a polygon mirror (rotating polygon mirror) 21b is horizontally disposed at the bottom of the case, and a plurality of laser light sources 23 modulated by image signals of respective colors. In the optical system B that reflects and scans the laser beam by the polygon mirror 21b and deflects and scans the image carrier, the single f-θ lens 22 and the scanning light path of each color are not parallel to the image carrier 17 respectively. A plurality of reflecting mirrors 24 are arranged so as to be folded.

  In the exposure means W configured as described above, an image signal corresponding to each color is emitted from the polygon mirror 21b with a laser beam modulated and formed based on a common data clock frequency, and the f-θ lens 22 and the reflection mirror 24 are passed through. After that, the image carrier 17 of each image forming station Y, M, C, K is irradiated to form a latent image. By providing the reflection mirror 24, the scanning optical path can be bent, the height of the case can be lowered, and the optical system can be made compact. In addition, the reflection mirror 24 is arranged so that the scanning optical path lengths to the image carrier 17 of the image forming stations Y, M, C, and K are the same. In this way, the length of the optical path from the polygon mirror 21b of the exposure means W to the image carrier 17 to the image carrier 17 (optical path length) for each image forming unit D is configured to be substantially the same, thereby scanning in each optical path. The scanning widths of the emitted light beams are also substantially the same, and no special configuration is required for image signal formation. Therefore, the laser light source can be modulated and formed based on a common data clock frequency even though it is modulated corresponding to images of different colors by different image signals, and uses a common reflecting surface. Color misregistration caused by a relative difference in the sub-scanning direction can be prevented, and a simple and inexpensive color image forming apparatus can be configured.

  Further, in this embodiment, by arranging the scanning optical system below the apparatus, the vibration of the scanning optical system due to the vibration that the drive system of the image forming means gives to the frame that supports the apparatus can be minimized. Degradation of image quality can be prevented. In particular, by arranging the scanner means 21 at the bottom of the case, the vibration that the polygon motor 21a itself gives to the entire case can be minimized, and deterioration of the image quality can be prevented. Further, by making the number of polygon motors 21a, which are vibration sources, one, vibration applied to the entire case can be minimized.

  The sheet feeding unit 30 includes a sheet feeding cassette 35 in which sheet materials are stacked and held, and a pickup roll 36 that feeds sheet materials from the sheet feeding cassette 35 one by one. The paper transport unit 11 includes a pair of gate rolls 37 (one roll is provided on the housing 10a side) that regulates the timing of feeding the sheet material to the secondary transfer unit, the drive roll 12 and the image transfer transport means 18. A secondary transfer roll 39 serving as a secondary transfer unit pressed against the main recording medium, a main recording medium conveyance path 38, a fixing unit 40, a discharge roll pair 41, and a duplex printing conveyance path 42.

  The secondary image (unfixed toner image) secondarily transferred to the sheet material is fixed at a predetermined temperature at the nip portion formed by the fixing unit 40. In this example, the fixing means 40 is disposed in a space formed obliquely above the belt surface 18b facing upward in the transfer belt conveyance direction, in other words, in a space opposite to the image forming station with respect to the transfer belt. Therefore, heat transfer to the exposure unit W, the image transfer conveyance unit 18, and the image forming unit can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced. In particular, the exposure means W is located farthest from the fixing means 40, and the displacement of the scanning optical system components due to heat can be minimized, thereby preventing color misregistration. In the present embodiment, the image transfer / conveyance means 18 is arranged in a direction inclined with respect to the drive roll 12, so that a wide space is created in the right side space in the drawing, and the fixing means 40 can be arranged in that space. In addition, downsizing can be realized, and heat generated by the fixing unit 40 is transmitted to the exposure unit W, the image transfer conveyance unit 18 and the image forming stations Y, M, C, and K located on the left side. Can be prevented. Further, since the exposure unit W can be arranged in the space on the lower left side of the image forming unit D, the vibration of the scanning optical system of the exposure unit W due to the vibration applied to the housing 10a by the drive system of the image forming means is minimized. The image quality can be suppressed and deterioration of the image quality can be prevented.

  Further, the corona charging means 19 is adopted as the charging means in accordance with the absence of the cleaning means. When the charging unit is a roll, a small amount of primary transfer residual toner that is present on the image carrier 17 accumulates on the roll to cause a charging failure, but the corona charging unit 19 that is a non-contact charging unit. Can prevent toner from adhering and can prevent charging failure.

  Further, in this embodiment, the intermediate transfer belt is configured to contact the image carrier 17 as the image transfer conveyance unit 18, but the sheet material is adsorbed to the surface to be conveyed and moved, and a toner image is formed on the surface of the sheet material. A sheet material conveyance belt that forms and conveys an image by sequentially superimposing and transferring the image may be configured to contact the image carrier 17 as the image transfer conveyance means 18. In this case, the belt conveyance direction of the sheet material conveyance belt as the image transfer conveyance means 18 is upward in the opposite direction on the lower surface in contact with the image carrier 17.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, a planar plate-like member having a certain angle is used as the guide slope, but a curved shape or a bent shape along the guide direction of the sheet material may be used. In addition, the pair of sheet material guide members are arranged symmetrically on both sides of the sheet material conveyance surface, but may be asymmetric in accordance with the apparatus configuration, such as in the case of a single-sided apparatus that does not form an image on both sides. The sheet material guide member may be disposed only on one side.

1 is a cross-sectional view showing an embodiment of a fixing device according to the present invention. FIG. 6 is a perspective view of a sheet material guide member that is disposed close to the fixing nip exit side. It is a figure for demonstrating the behavior in which the sheet material curled and discharged to the heat-resistant belt side is guided by the sheet material guide member. It is a figure for demonstrating the behavior by which the sheet material curled and discharged to the press roll side is guided by the sheet material guide member. 1 is a schematic cross-sectional view showing an embodiment of an image forming apparatus of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Thermal fixing member, 1a ... Planar heating element, 1b ... Belt guide member, 2 ... Pressure roll, 2b ... Roll base material, 2c ... Elastic layer, 3 ... Heat-resistant belt, 4 ... Sheet material guide member, 4a ... Mounting member, 4b ... sheet material guide plate, 4c ... guide slope, L ... pressing part tangent

Claims (5)

A planar heating element that has a flat surface and generates heat when energized; a heat-resistant belt that includes the planar heating element and is movable in a substantially circular free state; and the heat-resistant belt disposed opposite to the planar heating element. A fixing device that includes a pressure roll that is nipped and conveyed, and that fixes an unfixed toner image formed on the sheet material by passing the sheet material through a fixing nip formed by the heat-resistant belt and the pressure roll. The pressure roll has an elastic layer on the surface, and the fixing nip portion is fixed flat by the pressure roll sandwiching the heat-resistant belt between the sheet heating element and conveying it. A fixing device characterized in that a nip is formed, and a sheet material guide member having a guide slope approaching the sheet material conveyance surface toward the front in the sheet material conveyance direction is disposed close to the fixing nip outlet side. apparatus. The fixing device according to claim 1, wherein the sheet material guide member is formed of a plate-like member. The fixing device according to claim 1, wherein the sheet material guide member is formed with a plurality of protruding wall portions extending in a sheet material guide direction. 4. The fixing device according to claim 1, wherein the sheet material guide member is obtained by applying a lubricant treatment to a surface of at least a surface facing the sheet material. 5. An image forming apparatus comprising the fixing device according to claim 1.

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