JP2005115027A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the damage, the wear and the deterioration of a fixing roller rotating body, to stably fix a toner image on sheet material, to prevent an image defect such as the sliding mark of a fixed image and the jamming of the sheet material, and to simplify structure for guiding the sheet material of a thermal roller type fixing device. <P>SOLUTION: The fixing device is equipped with a thermal fixing roll 1 incorporating a heating source 1c and equipped with an elastic layer on its surface, a pressure means 2 arranged to be opposed to the roll 1 and pressing it, and a heat resistant belt 3 arranged on the outer periphery of the pressure means and moving while it is held between the roll 1 and the pressure means. In a fixing nip part formed by the pressing of the pressure means 2, a fixing nip having pressure distribution small on the exit side of the fixing nip is formed. A sheet material guiding member 8 having a guiding inclined surface 8c approaching to the carrying surface of the sheet material 5 is proximately arranged on the exit side of the fixing nip forward in the carrying direction of the sheet material 5, and the sheet material 5 is made to pass through the fixing nip part so as to fix an unfixed toner image formed on the sheet material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention includes a heat fixing roll with a built-in heat source and an elastic layer on the surface, a pressure unit that is disposed so as to face and press the heat fixing roll, and the heat fixing roll that is disposed on the outer periphery of the pressure unit. A heat-resistant belt that is held between the heat-fixing roll and the heat-fixing roll and a fixing nip formed by the heat-resistant belt, and passes the sheet material to fix the unfixed toner image formed on the sheet material. 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.

  For this purpose, the present invention includes a heat fixing roll having a built-in heat source and an elastic layer on the surface, a pressure unit that is disposed so as to face and press the heat fixing roll, and an outer periphery of the pressure unit. A non-fixed toner image formed on the sheet material by passing the sheet material through a fixing nip formed by the heat fixing roll and the heat-resistant belt. In the fixing device for fixing or in the image forming apparatus equipped with the fixing device, the fixing nip portion formed by pressing of the pressure unit forms a fixing nip having a pressure distribution in which the outlet side becomes smaller, and the fixing nip outlet side In addition, a sheet material guide member having a guide slope approaching the conveyance surface of the sheet material toward the front in the conveyance direction of the sheet material is disposed close to the sheet material.

  The pressurizing means includes a pressurizing roll that presses against the heat fixing roll, and a belt stretching member that tensions the heat-resistant belt by attaching the heat-resistant belt to the outer periphery between the pressurizing rolls. The belt stretching member is disposed downstream of the pressure roll in the sheet material conveying direction, and the heat-resistant belt is wound around the heat fixing roll to form a fixing nip.

  A part of the pressing means is formed to have a harder surface than the elastic layer of the heat fixing roll, and the heat fixing roll is provided with a PFA layer on a surface layer of the elastic layer. Features.

  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 heat fixing roll having a built-in heat source and having an elastic layer on the surface, a pressure unit that is disposed opposite to the heat fixing roll and pressed, and an outer periphery of the pressure unit are disposed on the heat fixing roll. A non-fixed toner image formed on the sheet material by passing the sheet material through a fixing nip formed by the heat fixing roll and the heat-resistant belt. In the fixing device for fixing or in the image forming apparatus equipped with the fixing device, the fixing nip portion formed by pressing of the pressure unit forms a fixing nip having a pressure distribution in which the outlet side becomes smaller, and the fixing nip outlet side In addition, since the sheet material guide member having the guide slope approaching the sheet material conveyance surface is disposed close to the front in the sheet material conveyance direction, the sheet material is disposed on the heat fixing roller by the elastic layer of the heat fixing roll. The sheet material can be elastically deformed in a direction away from the sheet to impart curling habits, and the sheet material after fixing can be peeled off without being wound around the heat fixing roll, thus eliminating the means for forcibly removing the sheet material. Very stable image fixing is possible. Further, the sheet material guide member does not rub against the heat fixing roll, the heat-resistant belt, or the image surface of the sheet material, and it is possible to prevent the surface material from being damaged such as wear or deterioration.

The pressurizing means includes a pressurizing roll that presses against the heat fixing roll, and a belt stretching member that tensions the heat-resistant belt by attaching the heat-resistant belt to the outer periphery between the pressurizing rolls. The belt stretching member is disposed downstream of the pressure roll in the sheet material conveying direction, and the heat-resistant belt is wound around the heat fixing roll to form a fixing nip.
Furthermore, with the above configuration, the outer diameters of the heat fixing member and the pressure member can be made small, and the fixing nip can be lengthened. Therefore, it is possible to achieve image fixing at a fixing nip having a sufficiently long length so that the sheet material after fixing does not wrap around the heat fixing member or the heat-resistant belt, and peeling for forcibly peeling the sheet material. Means such as a nail and a peeling plate can be omitted. In addition, an introduction port portion can be formed in which the sheet material smoothly enters, and since a large fixing pressure is finally applied at the end position after being heated in the fixing nip, stable fixing can be realized and a heat fixing member can be realized. When the side becomes concave and the curvature increases, the peelability of the sheet material from the heat fixing member also improves.

  Further, in order to stably fix an unfixed toner image formed on a sheet material, it is essential to sufficiently melt and fix the unfixed toner image, and a desired temperature and melting time are required. However, in the configuration according to the present invention, since the elastic body coated on the surface of the heat fixing member is not required to be greatly distorted to increase the nip length, there is no need to increase the nip length. It is configurable. In addition, it is not necessary to set the pressure contact pressure of the pressure member large in order to distort the elastic body, and the sheet material carrying the unfixed toner image passes when passing between the heat fixing member and the heat-resistant belt. Therefore, deformation of the sheet material such as wrinkles on the sheet material discharged after fixing the unfixed toner image is suppressed.

  Since a part of the pressing means is formed to have a harder surface than the elastic layer of the heat fixing roll, the pressing means is applied to the sheet material by the hardness balance and pressing force of the pressure roll and the heat fixing roll. The amount of curling behavior in the direction away from the heat fixing roll can be easily adjusted, and the sheet material is imparted with curling behavior in the direction away from the heat fixing roll so that the sheet material after fixing does not wrap around the heat fixing roll. By providing the PFA layer on the surface of the elastic layer, the heat fixing roll can be improved in rigidity and the sheet material and toner can be peeled off.

  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 is subjected to a lubricant treatment on at least the surface facing the sheet material. The low-cost configuration prevents damage to the surface condition such as wear or deterioration of the heat fixing member or pressure member, and the toner image fixed on the sheet material surface rubs against the sheet material guide member. Then, a rubbing mark is left on the image, or the fixed toner image is transferred 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. This can prevent clogging.

  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 roll, 1a is a halogen lamp, 1b is a roll base, 1c is an elastic body, 2 is a pressure roll, 2a is a rotating shaft, 2b is a roll base, 2c is an elastic body, and 3 is heat resistant. Belt, 4 is a belt stretching member, 4a is a protruding wall, 5 is a sheet material, 5a is an unfixed toner image, 6 is a cleaning member, 7 is a frame, 8 is a sheet material guide member, 9 is a spring, and L is a pressing portion. Indicates tangent.

  In FIG. 1, a heat fixing roll 1 is formed by covering a pipe member having an outer diameter of about 25 mm and a wall thickness of about 0.7 mm as a roll base material 1b, and an elastic body 1c having a thickness of about 0.4 mm on its outer periphery. This is a heat fixing member as a rotary moving body on the heating side in which 1050 W as a heating source and two columnar halogen lamps 1 a are incorporated inside the roll base 1 b and are rotatable. The pressure roll 2 is a pressure member that is disposed opposite to the heat fixing roll 1 and presses and urges to form a fixing nip, and covers the surface of the heat fixing roll 1 that is a rotary moving body on the heating side with an elastic body 1c. This is a rotationally movable body on the other side having a hard surface with respect to the formed elastic layer. The heat-resistant belt 3 is an endless belt which is sandwiched between the heat fixing roll 1 and the pressure roll 2 and is stretched around the outer circumference of the pressure roll 2 and the belt stretching member 4 so as to be movable. It has a thickness of 03 mm or more. The material may be a heat resistant resin such as a polyimide tube or silicon, rubber, or the like, but a metal belt made of a stainless steel base material or a nickel electroformed tube excellent in thermal conductivity is preferable. The heat-resistant belt 3 is tensioned by the cooperation of the pressure roll 2 and the belt stretching member 4 to stretch the heat-resistant belt 3, and the heat-resistant belt 3 is wound around the heat-fixing roll 1 to form a fixing nip. Thus, the sheet material 5 on which the unfixed toner image 5a is formed is passed through the fixing nip and fixed. The pressure contact force between the heat fixing roll 1 and the pressure roll 2 is 10 kg or less, the nip length is about 10 mm, and it is rotatable in the direction of the arrow shown.

  By arranging the pressure roll 2 having a surface harder than the elastic layer on the surface of the heat fixing roll 1 so as to be pressed and urged, the elastic layer of the heat fixing roll 1 is elastically deformed to have a concave and concave shape. When the fixing nip is formed, the sheet material 5 after fixing is imparted with curling behavior on the opposite side to the heat fixing roll 1 at the exit of the fixing nip, so that the heat fixing roll 1 is not wound around the heat fixing roll 1. Sent in a direction away from 1. The pressure roll 2 having a hard surface is made of, for example, a pipe material having a wall thickness of about 0.7 mm, having an outer diameter of about 25 mm, or 24.8 mm, which is smaller than the roll base material 1b of the heat fixing roll 1. It consists of material 2b. Further, the pressure roll 2 is made thinner than the elastic layer of the heat fixing roll 1 on the outer periphery thereof, and covers the elastic body 2c having a thickness of, for example, about 0.2 to 0.3 mm to form an elastic layer. Since the surface can be made harder than the elastic layer of the fixing roll 1, if the surface is harder than the elastic layer of the heat fixing roll 1, the surface of the fixing roll 1 has an elastic layer as well as the roll base. May be.

  In the present embodiment, two heat sources 1a are built in the heat fixing roll 1, and when the heating elements of the halogen lamp are configured in different arrangements and selectively lit, a heat-resistant belt 3 described later. Different conditions such as a fixing nip portion wound around the heat fixing roll 1 and a portion where the belt stretching member 4 is in sliding contact with the heat fixing roll 1, or a wide sheet material and a narrow sheet material. Temperature can be easily controlled under different conditions.

  The heat-resistant belt 3 is made of a rubber material such as PFA or silicon, for example, in consideration of the influence on the surface layer of the opposite heat fixing roll 1 and the contact with the toner image surface during double-side fixing to the sheet material. It's also good. When the heat fixing roll 1 is heated to a predetermined temperature by warming up, the heat-resistant belt 3, the pressure roll 2, and the belt stretching member 4 are also raised to the predetermined temperature and stored. When a member having high thermal conductivity is used for the heat-resistant belt 3, the pressure roll 2, and the belt stretching member 4, the heat-resistant belt 3 is deprived of the sheet material 5 at the fixing nip by fixing the toner image on the sheet material 5. Since heat can be efficiently returned from the pressure roll 2 and the belt stretching member 4 to the heat-resistant belt 3, the temperature reduction of the heat-resistant belt 3 is suppressed particularly when fixing is performed through a plurality of sheet materials. be able to.

  The belt stretching member 4 is disposed on the downstream side in the conveying direction of the sheet material 5 with respect to the nip portion between the heat fixing roll 1 and the pressure roll 2, and in the direction of arrow P around the rotation shaft 2 a of the pressure roll 2. Is swingably disposed. The belt stretching member 4 is configured to stretch the heat-resistant belt 3 in the tangential direction of the heat fixing roll 1 at an end position where the sheet material 5 is discharged from the fixing nip while the sheet material 5 does not pass through the fixing nip. The fixing nip portion forms a fixing nip having a pressure distribution that becomes smaller on the outlet side. When the sheet material 5 on which the unfixed toner image is formed is passed through the fixing nip having a small pressure distribution on the outlet side and is fixed, there is no stress on the sheet material 5 at the fixing nip outlet, and therefore the sheet material 5 that has passed through the fixing nip. The sheet material 5 after fixing does not wrap around the heat fixing roll 1 by its own restoring force (commonly referred to as the waist of the sheet material), and the extension line of the fixing nip tangential line (virtual sheet material conveyance direction) Will be discharged along. Therefore, a peeling means such as a peeling claw or a peeling plate for forcibly peeling the sheet material from the heat fixing roll 1 becomes unnecessary.

  The belt stretching member 4 is inserted into the inner periphery of the heat-resistant belt 3 and applies a tension f to the heat-resistant belt 3 in cooperation with the pressure roll 2, and the heat-resistant belt 3 is wound around the heat-fixing roll 1 to nip the belt. Is a substantially half-moon shaped belt sliding member (the heat-resistant belt 3 slides on the belt stretching member 4). The configuration of the belt sliding member may be made of a metal such as an aluminum alloy having excellent thermal conductivity, but is preferably made of a plastic having excellent thermal conductivity from the viewpoint of shortening the warm-up time. As a more preferable condition, if a metal coating process such as copper plating, nickel plating or vapor deposition is performed on the surface of the plastic belt sliding member for the purpose of improving thermal conductivity, heat is generated under a small heat capacity. The characteristics excellent in responsiveness can be further exhibited.

  The belt stretching member 4 is disposed at a position where the heat-resistant belt 3 is wound around the heat fixing roll 1 side from the tangent line between the heat fixing roll 1 and the pressure roll 2 to form a nip. The projecting wall 4a is provided so as to project from one end or both ends of the belt stretching member 4, and when the heat-resistant belt 3 approaches one side, the projecting wall 4a comes into contact with the projecting wall 4a to regulate the deviation. The belt stretching member 4 is provided with a spring 9 between the heat fixing roll 1 of the protruding wall 4 a and the frame at the opposite end, and is lightly pressed against the heat fixing roll 1 by the spring 9. Positioned in sliding contact.

  In order to stretch the heat-resistant belt 3 by the pressure roll 2 and the belt stretching member 4 and drive it stably with the pressure roll 2, the friction coefficient between the pressure roll 2 and the heat-resistant belt 3 is set to the belt stretching member 4. However, the friction coefficient may become unstable due to the intrusion or wear of foreign matter. On the other hand, the winding angle of the belt tension member 4 and the heat-resistant belt 3 is smaller than the winding angle of the pressure roll 2 and the heat-resistant belt 3, and the diameter of the belt tension member 4 is smaller than the diameter of the pressure roll 2. Is set to be small, the length that the heat-resistant belt 3 slides on the belt stretching member 4 is shortened, and it is possible to avoid unstable factors against changes with time, disturbances, etc. Can be driven.

  The cleaning member 6 is disposed between the pressure roll 2 and the belt stretching member 4 and is slidably brought into contact with the inner peripheral surface of the heat-resistant belt 3 to clean foreign matter, wear powder, etc. on the inner peripheral surface of the heat-resistant belt 3. The heat-resistant belt 3 is refreshed by cleaning such foreign matter, wear powder, etc., and the instability factor is removed. Further, the recess 4f provided in the belt stretching member 4 is suitable for storing the removed foreign matter, abrasion powder, and the like.

  The sheet material 5 passes between the heat-resistant belt 3 and the heat-fixing roll 1 with the position where the pressure roll 2 is pressed against the heat-fixing roll 1 as the initial position of the nip, whereby the unfixed toner image 5a is fixed, and the belt tension. The pressure distribution on the exit side of the fixing nip is reduced by setting the position where the mounting member 4 is lightly pressed against the heat fixing roll 1 to reduce the pressure distribution on the fixing nip outlet side, and the pressing portion tangent L between the heat fixing roll 1 and the belt stretching member 4 is reduced. Transport in the direction. A pressing part tangent L is a fixing nip tangent and indicates a conveyance surface of the sheet material 5 in the virtual sheet material conveyance direction.

  The sheet material guide member 8 guides the conveying direction of the sheet material 5 from the fixing nip exit, is held on the base portion by a fixing means such as a heat-resistant double-sided tape, and is attached to the main body frame by the attachment portion 8a. The tip of 8b is disposed close to the fixing nip exit side with a gap without rubbing against the surface of the heat fixing roll 1 and the heat-resistant belt. The sheet material guide plate 8b 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 8c that approaches the conveyance surface L of the sheet material 5 from the fixing nip exit toward the front in the conveyance direction of the sheet material 5. The angle of the guide slope 8c ranges from an angle parallel to the tangent line L of the pressing portion to the tangent of the heat fixing roll 1 and the belt stretching member 4 at the tip of the guide slope 8c, that is, the tip of the guide slope 8c is heated. This is the range from the center of rotation of the fixing roll 1 toward the inside and the fixing nip.

  For example, when the guide slope 8c is at an angle away from the conveyance surface L of the sheet material 5 from the fixing nip exit toward the front in the conveyance direction of the sheet material 5, that is, the direction of the tip of the sheet material guide plate 8b is the heat. When the angle is directed inward from the tangent line of the fixing roll 1, the fixing toner image surface is aligned with the guide slope 8c when the leading edge of the sheet material 5 advances along the guide slope 8c, as in the case of the conventional peeling claw or release plate. Rubbing. When the extended line at the front end of the guide slope 8c passes through the outer side opposite the fixing nip from the rotation center of the heat fixing roll 1, the surface facing the sheet material 5 is tangent to the heat fixing roll 1 at the front end. Since the angle is smaller than 90 ° with respect to the surface, when the sheet material 5 discharged from the fixing nip exit leaves the heat fixing roll 1 and comes into a substantially circular free state and comes into contact with the guide slope 8c, heat fixing is performed. It is wound in the direction of the roll 1.

  Originally, when the sheet material 5 on which the unfixed toner image 5a is formed is passed through the fixing nip and fixed, the sheet material 5 is imparted with a curl habit that deforms along the outer periphery of the heat fixing roll 1, and the heat fixing roll 1 side. It becomes easy to wind around. According to the present embodiment, since the outer diameters of the heat fixing roll 1 and the pressure roll 2 are configured to be as small as about 25 mm, the sheet material 5 after fixing is wound around the heat fixing roll 1 or the heat-resistant belt 3. There is no need for means such as a peeling claw or a peeling plate for forcibly peeling the sheet material 5.

  The pressure roll 2 having a harder surface than the elastic layer coated on the surface of the heat fixing roll 1 is pressed and urged, and further, a concave fixing nip is formed to form an unfixed image formed on the sheet material. When fixing, the sheet material 5 that has passed through the fixing nip has its own restoring force (commonly referred to as the waist of the sheet material) and the pressure roll 2 that is harder than the elastic layer coated on the surface of the heat fixing roll 1. The elastic layer of the heat fixing roll 1 can be elastically deformed in the direction of separating the sheet material 5 from the heat fixing roll 1 by applying the pressure to impart a curling behavior to the sheet material 5. Moreover, the amount of curling behavior in the direction away from the heat fixing roll 1 is easily applied to the sheet material 5 with respect to the moving direction of the heat-resistant belt 3 due to the balance between the hardness of the pressure roll 2 and the heat fixing roll 1 and the pressing force. It can be adjusted. As a result, it is possible to eliminate the means for forcibly removing the sheet material 5 after fixing without being wound around the heat fixing roll 1 and the heat-resistant belt 3, and extremely stable image fixing is possible. Furthermore, if a PFA (peroxy-alkoxy-fluoro resin) layer of about 30 μm is provided on the surface layer of the elastic body 1 c of the heat fixing roll 1, the rigidity is improved by that much and the sheet material 5 and the toner are easily peeled. be able to.

  However, even if the winding of the sheet material 5 is basically eliminated by the configuration of the heat fixing roll 1 and the pressure roll 2 as described above, the sheet material 5 is expected to be in a moisture absorption state, a sheet fiber state, or a constituent material. In addition, the sheet material guide member 8 is not fixed to the fixing nip in consideration of safety. It is effective for a trouble-free configuration that the transport path is determined by being arranged close to the exit side. According to the present embodiment, the sheet material 5 that has passed through the fixing nip is discharged away from the fixing nip outlet without being wound around the heat fixing roll 1 and the heat-resistant belt 3. What is necessary is just to be able to correct in the conveyance direction.

  According to the sheet material guide plate 8 b of the sheet material guide member 8, the sheet material guide plate 8 b is disposed close to the surface of the heat fixing roll 1 and the heat-resistant belt 3 without being rubbed, and the sheet material from the front end that becomes the fixing nip outlet side. The guide can be guided by a guide slope 8c having an angle parallel to the conveying direction (direction of the tangent L of the pressing portion between the heat fixing roll 1 and the pressure roll 2) or an angle passing through the rotation center of the heat fixing roll 1. In addition, by setting the guide slope 8c at a predetermined angle, the sheet material 5 can be guided in a desired conveying direction only by rubbing the leading edge, and the toner image of the sheet material 5 slides on the sheet material guide plate 8b. Without rubbing, a fixed rubbing mark is left on the fixed image, or the fixed toner image moves to the sheet material guide plate 8b to cause an image defect, or the fixed toner image sticks to the sheet material guide plate 8b. It prevents jamming of the sheet material and does not cause 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. For example, as shown in FIG. 2, a sheet material guide plate 8b having a guide slope 8c is provided as a sheet material guide member 8 disposed close to the exit side of the fixing nip without rubbing against the heat fixing roll 1 and the heat-resistant belt 3. There are mounting portions 8a on both sides, and the sheet material guide plate 8b 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 8d may be formed in parallel to the sheet material guiding direction. The winding of the sheet material 5 is basically eliminated by the roller configuration as described above, and the sheet material guide member 8 that guides the conveyance of the sheet material 5 disposed on the fixing nip outlet side is substantially equal to the fixing nip width. Since the heat fixing roll 1 and the heat-resistant belt 3 are formed with the same width and are provided with a gap, the heat-fixing roll 1 and the heat-resistant belt 3 are worn or deteriorated without relatively rubbing against these surfaces. Does not cause damage to the surface condition.

  Since the leading edge of the sheet material 5 that has passed through the fixing nip is guided by the sheet material guiding member 8 and the traveling direction is corrected to a desired direction (conveyance direction), the leading edge of the sheet material 5 is the sheet material guiding member. As a reaction force that is guided and guided by contact with 8, a reverse curl behavior that is opposite to the curl direction immediately after passing through the fixing nip passage portion is imparted. When the advancing posture of the sheet material 5 is corrected and guided to the desired relationship by the guide slope 8c, the sheet material 5 is normally guided by rubbing only at the front end in this guiding process, and the fixed toner image is transferred to the sheet material. There is no relative rubbing with the guide member 8. Accordingly, a rubbing mark is left on the fixed image, or the fixed toner image is transferred to the sheet material guide member 8 to cause an image defect. Further, the fixed toner image sticks to the sheet material guide member 8 and the sheet material advances. Jam: Prevents jamming of sheet material. Even if the toner image surface touches the sheet material guiding member 8 due to an unexpected factor such as a moisture absorption state, a sheet fiber state, or a constituent material, and the toner image surface may touch the sheet material guiding member 8, a plurality of When the sheet material guide member 8 having the protruding wall portion 8d is arranged, the contact area of the toner image surface can be minimized, and troubles with respect to the fixed image can be reduced as much as possible.

  Further, when the surface of the sheet material guide member 8 facing at least the sheet material 5 is subjected to a lubricant treatment such as coating, painting, plating, etc. of a fluorine material, the sliding resistance of the sheet material 5 is reduced. The sheet material 5 can be stably guided and guided. Further, even if the toner image surface touches the sheet material guide member 8 and a part of the toner image adheres to a part of the sheet material guide member 8, the sheet material guide is obtained by applying a lubricant treatment. The toner can be easily peeled off from the member 8.

  Next, a support structure for the pressure roll 2 and the belt stretching member 4 will be described. FIG. 3 is a cross-sectional view taken along the line YY of FIG. 1 in the direction of the arrow, and the right half of the apparatus is omitted. As shown in FIG. 3, the rotary shafts 2a at both ends of the pressure roll 2 are rotatably supported by the left and right frames 7 via bearings 7a. A swing arm 4b is rotatably fitted on both sides of the rotary shaft 2a of the pressure roll 2, and a guide groove 4c is formed on the belt stretching member 4 side of the swing arm 4b. On the other hand, guide portions 4d extending toward the pressure roll 2 are formed at both ends of the belt stretching member 4, and the guide portions 4d are guided through the springs 4e to guide grooves 4c of the swing arm 4b. It is inserted inside. As a result, the belt stretching member 4 is urged in a direction away from the pressure roll 2 by the spring 4 e and has a structure in which a tension f is applied to the heat-resistant belt 3.

  In the present embodiment, since a non-rotating member that slides the heat-resistant belt 3 is used as the belt stretching member 4, a bearing or the like is not required instead of the rotating member, and the support structure is simplified. In addition, by arranging the belt tension member 4 in a substantially half-moon shape, the belt tension member 4 is arranged in the direction of the half-moon notch on the pressure roll 2 side, and can be arranged close to the pressure roll 2 to the limit. This also makes it possible to configure the heat-resistant belt 3 with a reduced circumferential length. Therefore, the heat roll type fixing device can be made simple and small and inexpensive. In addition, since the heat-resistant belt 3 moves along the minimum necessary path, the heat-resistant belt 3 is heated at the nip portion with the heat fixing roll 1 that is rotatable with a built-in heating source, and is taken away when moving along a predetermined path. The thermal energy generated can be minimized and the perimeter is short, so there is little temperature drop due to natural heat dissipation, and so-called warm-up time from when the power is turned on until it reaches the desired temperature and can be fixed is shortened. Is possible. Furthermore, since the heat-resistant belt 3 is tensioned by the cooperation of the pressure roll 2 and the belt stretching member 4 and is wound around the heat fixing roll 1 to form a fixing nip, the nip length is easily increased. In addition, the structure can be simplified, and the size can be reduced and the cost can be reduced.

  Further, in order to stably fix the unfixed toner image formed on the sheet material 5, it is essential to sufficiently melt and fix the unfixed toner image, and a desired temperature and melting time are required. However, in the configuration according to the present embodiment, there is no need for a means for greatly increasing the nip length by greatly distorting the elastic body coated on the surface of the heat fixing roll in order to increase the nip length. Can be made thin. In addition, it is not necessary to set the pressure contact pressure of the pressure roll 2 large in order to distort the elastic body, and when the sheet material 5 carrying the unfixed toner image passes between the heat fixing roll 1 and the heat-resistant belt 3. Since the stress on the passing sheet material 5 is small, deformation of the sheet material 5 such as generation of wrinkles on the sheet material 5 discharged after fixing the unfixed toner image is suppressed.

  Therefore, not only the mechanical rigidity of the heat roll type fixing device is not required, but also the heat fixing roll 1 can be thinned, and the heating speed for heating the heat-resistant belt 3 from the heating source is improved. Similarly, the pressure roll 2 can be made thin and thick, and the heat capacity can be made small. Therefore, the heat energy absorption from the heat-resistant belt 3 is small, and it can be fixed by reaching a desired temperature when the power is turned on. It is possible to shorten the so-called warm-up time.

  4 is a cross-sectional view taken along the line XX of FIG. 1 and viewed in the direction of the arrow, FIG. 5 shows a state when the sheet material is not passed, and FIG. 5 (A) is a partially enlarged cross-section of FIG. 5B is a cross-sectional view taken along the line XX of FIG. 5A and viewed in the direction of the arrow, FIG. 6 shows a state when the sheet material is passed, and FIG. 6A is a partially enlarged cross-sectional view of FIG. 6A, and FIG. 6B is a cross-sectional view taken along the line XX of FIG. In addition, about the same structure as the said embodiment, the same number is attached | subjected and description is abbreviate | omitted.

  As shown in FIGS. 4 and 5, the protruding wall 4a of the belt stretching member 4 is slidably contacted with the heat fixing roll 1 by a sliding contact surface 4g and positioned. A gap (step) G larger than the thickness of the heat-resistant belt 3 is provided between the sliding surface 4g of the belt stretching member 4 and the pressure surface 4h that presses the heat-resistant belt 3 and presses the sheet material against the heat fixing roll 1. The pressing surface 4 h is formed concentrically with the fixing roll 1. Specifically, the gap is formed with a step of about 110 μm, the heat-resistant belt 3 is formed with a thickness of about 80 μm, thereby securing a gap of about 30 μm, and stable fixing even with a sheet material having a thickness of about 60 μm. It is possible.

  The heat-resistant belt 3 is brought into pressure contact with the nip portion between the heat fixing roll 1 and the pressure roll 2 and is wound around the heat fixing roll 1 at the downstream side thereof and is attached to the heat fixing roll 1 by the belt stretching member 4 at the nip end position. It is pressed. In this embodiment, a gap G is formed between the heat-resistant belt 3 and the belt stretching member 4 in this state where the sheet material 5 does not pass. Therefore, when warming up, the gap G becomes a heat insulating layer, and the amount of heat taken from the heat fixing roll 1 via the heat-resistant belt 3 is reduced, so that heat loss is reduced and the warming up time can be shortened.

  On the other hand, when the sheet material 5 passes through the fixing nip, as shown in FIG. 6, the protruding wall 4 a of the belt stretching member 4 is separated from the heat fixing roll 1, and the heat resistant belt 3 and the belt stretching member 4 are separated from each other. The gap G is eliminated, and the sheet material 5 is pressed between the heat-resistant belt 3 and the heat-fixing roll 1 at the fixing nip portion. Therefore, if the pressing force is adjusted to a desired pressure by the spring 9, an appropriate value is obtained. Fixing can be achieved.

  In addition, because of the presence of the gap G, the belt stretching member 4 is heated from the heat fixing roll 1 and has a small amount of heat to be stored, so that the undetermined formed on the sheet material 5 when the sheet material 5 enters the fixing nip. The opposite surface of the toner image 5a cools the heat-resistant belt 3 having a small heat capacity, but the amount of heat heated from the belt stretching member 4 side is small. Therefore, in the case of double-sided image fixing in which the unfixed toner image formed on the first surface on the sheet material 5 is fixed and then the unfixed toner image is fixed again on the opposite second surface, the second surface is fixed. Sometimes the image on the first surface that has been fixed first is not heated more than necessary to disturb the image.

  In the present embodiment, a spring 9 that assists as a swing urging means is downstream in the moving direction of the heat-resistant belt 3 from the pressing portion of the heat fixing roll 1 and the pressure roll 2 that are separated from the swing fulcrum of the belt stretching member 4. Arranged on the side. When one of the heat fixing roll 1 or the pressure roll 2 is driven, the heat-resistant belt 3 is driven, and the belt tension member 4 is moved from the heat-fixing roll 1 by this driving force and the sliding frictional force between the heat-resistant belt 3 and the belt tension member 4. It swings and moves away, but it overcomes this swinging force and urges the belt stretching member 4 toward the heat fixing roll 1 with a desired urging force to set a desired fixing pressure. It is possible to fix the toner image.

  FIG. 7 shows the fixing pressure when assisting the swing movement force of the belt stretching member 4. In the present embodiment, since the spring 9 is disposed on the downstream side in the moving direction of the heat-resistant belt 3 from the pressing portion of the heat fixing roll 1 and the pressure roll 2 that are separated from the swing fulcrum of the belt stretching member 4, As shown in FIG. 7 by the lever mechanism, it is possible to continuously reduce the applied pressure from the pressing portion of the heat fixing roll 1 and the pressure roll 2 and to have an inflection point in the sheet material. Since no stress is applied, fixing unevenness or the like does not occur in the fixed image, and it becomes possible not only to fix an extremely stable unfixed toner image, but also to cause wrinkles in the sheet material discharged after fixing the unfixed toner image. Sheet material deformation can be suppressed.

  At this time, the pressing force at the nip end position is P1, the pressing force at the pressing portion where the pressure roll 2 presses the heat fixing roll 1 is P3, and the pressing force between the nip end position and the pressing portion is P2. Then, the relationship of P1 <P2 <P3 is established, and the pressing force P3 at the pressing portion where the pressure roll 2 presses the heat fixing roll 1 becomes the maximum pressure.

  8 shows a modification of the embodiment of FIG. 1, FIG. 8 (A) is a cross-sectional view, and FIG. 8 (B) is a cross-sectional view taken in the direction of the arrow along the YY line of FIG. 8 (A). It is.

  The present embodiment is different from the embodiment of FIG. 1 in that, in the above-described embodiment, the belt stretching member 4 is swung by a predetermined angle with a common shaft with the rotation shaft 2a of the pressure roll 2. In contrast to this, in the present embodiment, the belt stretching member 4 is configured to be swingable by a predetermined angle on a shaft 7b different from the rotation shaft 2a of the pressure roll 2. Is a point.

  That is, the swing arm 4b is rotatably fitted on both sides of the shaft 7b disposed at a position different from the axis of the rotary shaft 2a, and a guide groove is formed on the belt stretching member 4 side of the swing arm 4b. 4c is formed. On the other hand, guide portions 4d extending toward the pressure roll 2 are formed at both ends of the belt stretching member 4, and the guide portions 4d are guided through the springs 4e to guide grooves 4c of the swing arm 4b. It is inserted inside. As a result, the belt stretching member 4 is urged in a direction away from the pressure roll 2 by the spring 4 e and has a structure in which a tension f is applied to the heat-resistant belt 3.

  Thereby, the rotational moment acting on the belt stretching member 4 can be changed (in the example of FIG. 8, the rotational moment is increased), and the pressure contact force between the heat-resistant belt 3 and the heat fixing roll 1 can be adjusted. it can.

  In this embodiment, the heat fixing roll or the pressure roll is the driving roll. In this case, in order to achieve stable driving, the harder roll is the driving side and the softer roll is the driven side. Is preferred. The pressure roll 2 is driven by pressing the heat-resistant belt 3 against an elastic body 1c having a heat-resistant belt 3 attached to the outer periphery thereof and covering the surface of the heat-fixing roll 1, and the heat-fixing roll 1 is driven. It becomes. The pressure roll 2 determines the conveyance speed of the heat-resistant belt 3, that is, the sheet material 5 carrying the unfixed toner image 5a, and therefore has a surface harder than at least the elastic body 1c coated on the surface of the heat fixing roll 1. The configuration is as follows. Accordingly, the conveyance speed can be stably driven without deformation.

  In this embodiment, in addition to the above-described structure, selection of the rotation speed can be combined. The control of the driving speed will be described. The driving means has two rotation speeds for driving the heat fixing roll 1 and the pressure roll 2, and the heat fixing roll 1 and the pressure roll 2 are driven by the first rotation speed and the rotation speed according to the sheet material characteristics. Selective drive is performed at a slow second rotational speed. This rotation speed is provided with a detecting means for detecting the sheet material characteristics, and is provided with setting means for setting selection information such as a rotation speed in accordance with the sheet material characteristics in advance, and the sheet material 6 carrying the unfixed toner image 5a. When the sheet material characteristic is detected during the conveyance process, the sheet material 5 carrying the unfixed toner image 5a is set according to the sheet material characteristic in the fixing command process, and the rotation speed is selected and driven according to the setting content. The As the setting means, a part interlocked with the heat roll type fixing device may be manually operated prior to the fixing command, or remotely operated by an electrical signal or the like.

  The sheet material 5 carrying the unfixed toner image 5a must be applied to various uses such as a general sheet material such as paper, a thick sheet material having a large heat capacity, and a transparent sheet material (OHP sheet material). is there. Compared to general sheet materials, the unfixed toner image 5a is sufficiently melted particularly in thick sheet materials having a large heat capacity, laminated sheet materials such as envelopes, and transparent sheet materials (OHP sheet materials). In order to fix to the sheet material, a desired melting time is required. In such a case, the unfixed toner image 5a is melted by selectively driving the heat fixing roll 1 and the pressure roll 2 at the first rotation speed and the second rotation speed slower than the heat fixing roll 1 and the pressure roll 2 in accordance with the sheet material characteristics. It is optimized and a desired fixing can be achieved.

  Even when the sheet material 5 carrying the unfixed toner image 5 a passes between the heat fixing roll 1 and the heat-resistant belt 3 even when selectively driven at the first rotation speed or the second rotation speed, the sheet material 5 passes. Since the stress on the sheet material 5 to be applied is not changed and is small, deformation of the sheet material such as wrinkles on the sheet material 5 discharged after fixing the unfixed toner image 5a is suppressed. Therefore, it is not necessary to increase the mechanical rigidity of the heat roll type fixing device, and it is possible to reduce the thickness of the heat fixing roll, and the heating rate for heating the heat-resistant belt from the heating source is improved. Similarly, the pressure roll 2 can also be thinned and can be achieved with a small heat capacity. Therefore, the heat energy absorption from the heat-resistant belt 3 is small, and it can be fixed by reaching a desired temperature when the power is turned on. It is possible to shorten the so-called warm-up time. As the selection means for selectively driving, for example, a means for selectively changing the rotational speed of the drive motor is suitable.

  In the above embodiment, the fixing nip portion reduces the pressure distribution on the outlet side to form a concave fixing nip on the heat fixing roll 1 side, and the sheet toward the front side in the sheet material conveyance direction on the fixing nip outlet side. Although the sheet material guide member having a guide slope approaching the material conveyance surface is arranged close to the sheet material, the sheet material can be used even if the belt tension member 4 is arranged upstream in the sheet material conveyance direction to increase the pressure distribution on the outlet side. The problem can be solved in the same manner by preventing the toner from being wound around the heat fixing roll 1. 9 shows another embodiment of the fixing device, FIG. 9A is a cross-sectional view, and FIG. 9B is a cross-sectional view taken along the line Y-Y in FIG. 10 is a partially enlarged cross-sectional view with the heat-resistant belt removed in FIG. 9, FIG. 11 is a view with the heat-resistant belt 3 attached in FIG. 10, and FIG. 12 is a view showing a state when the sheet material passes in FIG. .

  In the above embodiment, the belt stretching member 4 is disposed on the downstream side in the conveyance direction of the sheet material 5 with respect to the pressing portion of the heat fixing roll 1 and the pressure roll 2, whereas this embodiment is shown in FIG. As described above, the belt stretching member 4 is disposed on the upstream side in the conveying direction of the sheet material 5 with respect to the pressing portions of the heat fixing roll 1 and the pressure roll 2, and the arrow P around the rotation shaft 2 a of the pressure roll 2. It is arranged so that it can swing in the direction. The belt stretching member 4 is inserted into the inner periphery of the heat-resistant belt 3 and applies a tension f to the heat-resistant belt 3 in cooperation with the pressure roll 2, and the heat-resistant belt 3 is wound around the heat-fixing roll 1 to nip the belt. It is a half-moon shaped belt sliding member arranged in the position which forms. The belt stretching member 4 is disposed at a position in contact with the tangent L of the heat fixing roll 1 at an initial nip position where the heat-resistant belt 3 is wound around the heat fixing roll 1 to form a nip. The sheet material 5 is fixed with the unfixed toner image 5a by passing between the heat-resistant belt 3 and the heat fixing roll 1 with the position where the belt stretching member 4 is in pressure contact with the heat fixing roll 1 as the initial position of the nip. It is discharged in the direction of the pressing part tangent L at the end position.

  4 and 10, the protruding wall 4a of the belt stretching member 4 is positioned in sliding contact with the heat fixing roll 1 at the sliding contact surface 4g. A gap (step) G larger than the thickness of the heat-resistant belt 3 is provided between the sliding surface 4g of the belt stretching member 4 and the pressure surface 4h that presses the heat-resistant belt 3 and presses the sheet material against the heat fixing roll 1. The pressing surface 4 h is formed concentrically with the fixing roll 1. Specifically, the gap is formed with a step of about 110 μm, the heat-resistant belt 3 is formed with a thickness of about 80 μm, thereby securing a gap of about 30 μm, and stable fixing even with a sheet material having a thickness of about 60 μm. It is possible.

  FIG. 11 is a view in which the heat-resistant belt 3 is mounted. The heat-resistant belt 3 is pressed against the nip portion between the heat fixing roll 1 and the pressure roll 2 and is wound around the heat fixing roll 1 to be in the fixing nip portion. The belt stretching member 4 is pressed against the heat fixing roll 1 at the upstream nip initial position.

  If the fixing pressure is large at the initial position where the sheet material 5 enters the fixing nip, the sheet material 5 may not enter smoothly and may be fixed with the leading edge of the sheet material broken. If it is configured to be stretched in the tangential direction of the heat fixing roll 1, an introduction port portion in which the sheet material 5 can smoothly enter can be formed, and the sheet material 5 can be stably entered. In addition, if the fixing pressure is large at the end position where the sheet material 5 is discharged from the fixing nip, the sheet material 5 enters and is heated at the fixing nip, and finally the large fixing pressure is applied at the end position. In addition, since the heat fixing roll 1 side is concave and the curvature is increased, the peelability of the sheet material 5 from the heat fixing roll 1 is improved.

  It is practical to match the speed of the process step for forming an unfixed toner image on the sheet material on the sheet material before the fixing step and the speed of the fixing step in consideration of variations in various parts dimensions in mass production. Absent. Therefore, considering this variation, the speed of the fixing process is increased or decreased as compared with the speed of the process process for forming an unfixed toner image on the sheet material, and is set to either one of the processes before and after the process. Although the speed balance is established, if it is necessary to clearly grip the sheet material at the initial position where the sheet material enters the fixing nip to clarify the sheet material entry speed, The objective is achieved.

  Further, the elastic surface of the roll and the surface of the heat-resistant belt move at the same peripheral speed to fix the unfixed toner image formed on the sheet material, but the surface of the heat-resistant belt is wave-shaped or the sheet material If the tip is wave-shaped, the fixing start state may become unstable. Therefore, if the heat-resistant belt 3 is pressed against the heat-fixing roll 1 at the initial nip position, the merged state of both is stabilized, so that an extremely stable unfixed toner image can be fixed.

  In this embodiment, a gap G is formed between the heat-resistant belt 3 and the belt stretching member 4 in this state where the sheet material 5 does not pass. Therefore, when warming up, the gap G becomes a heat insulating layer, and the amount of heat taken from the heat fixing roll 1 via the heat-resistant belt 3 is reduced, so that heat loss is reduced and the warming up time can be shortened.

  On the other hand, when the sheet material 5 passes through the fixing nip, as shown in FIG. 12, the protruding wall 4 a of the belt stretching member 4 is separated from the heat fixing roll 1, and the heat resistant belt 3 and the belt stretching member 4 are separated from each other. The gap G is eliminated, and the sheet material 5 is pressed between the heat-resistant belt 3 and the heat-fixing roll 1 at the fixing nip portion. Therefore, if the pressing force is adjusted to a desired pressure by the spring 9, an appropriate value is obtained. Fixing can be achieved.

  In addition, because the gap G exists, the belt tension member 4 is heated from the heat fixing roll 1 so that the amount of heat stored is small, so that the undetermined formed on the sheet material 5 when the sheet material 5 enters the fixing nip. The opposite surface of the toner image 5a cools the heat-resistant belt 3 having a small heat capacity, but the amount of heat heated from the belt stretching member 4 side is small. Therefore, in the case of double-sided image fixing in which the unfixed toner image formed on the first surface on the sheet material 5 is fixed and then the unfixed toner image is fixed again on the opposite second surface, the second surface is fixed. Sometimes, the image on the first surface fixed first is not heated more than necessary to disturb the image.

  In the present embodiment, as shown in FIG. 9, a spring 9 that assists as a swing urging means is pressed by a pressing portion between the heat fixing roll 1 and the pressure roll 2 that is away from the swing fulcrum of the belt stretching member 4. The heat-resistant belt 3 is arranged on the upstream side in the moving direction. When one of the heat fixing roll 1 or the pressure roll 2 is driven, the heat-resistant belt 3 is driven, and the belt tension member 4 moves in the direction of the heat fixing roll 1 by this driving force and the sliding frictional force between the heat-resistant belt 3 and the belt tension member 4. However, the fixing pressure for fixing the unfixed toner image formed on the sheet material 5 may be insufficient only by this swinging movement force. Therefore, when the swinging force is assisted and set to a desired fixing pressure, an extremely stable unfixed toner image can be fixed.

  13A and 13B are diagrams for explaining the features of the present embodiment. FIG. 13A is a cross-sectional view, and FIG. 13B is a diagram showing the fixing pressure at the nip passage position. In the present embodiment, the spring 9 as the swinging biasing means is located upstream from the pressing portion of the heat fixing roll 1 and the pressure roll 2 away from the swinging fulcrum of the belt stretching member 4 in the moving direction of the heat-resistant belt 3. Therefore, as shown in FIG. 13B, the pressing force can be continuously increased from the initial nip position toward the pressing portion between the heat fixing roll 1 and the pressure roll 2 by the lever mechanism. The sheet material is not subjected to stress with an inflection point, so that the fixing image does not cause uneven fixing and the fixing of the unfixed toner image is possible not only stably but also the unfixed toner image. It is possible to suppress deformation of the sheet material such as wrinkles in the sheet material discharged after fixing.

  At this time, the pressing force at the initial nip position is P1, the pressing force at the pressing part where the pressure roll 2 presses the heat fixing roll 1 is P3, and the pressing force between the initial nip position and the pressing part is P2. Then, the relationship of P1 <P2 <P3 is established, and the pressing force P3 at the pressing portion where the pressure roll 2 presses the heat fixing roll 1 becomes the maximum pressure. For example, if the surface of the sheet material is uneven, or if the toner image melted with a material having a very smooth and airtight surface, such as an OHP sheet, is difficult to penetrate, the last time the sheet material passes through the nip. Since a higher pressure is applied to the toner melted in the stage than in the melting stage, the surface of the melted toner can be made smoother and the permeation action into the sheet material can be promoted to further stabilize the fixed image. .

  FIG. 14 shows a modification of the fixing device of FIG. 9, FIG. 14A is a cross-sectional view, and FIG. 14B is a cross-sectional view taken along the line Y-Y of FIG. It is. In the following description, the same components as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  9 differs from the embodiment of FIG. 9 in that in the embodiment of FIG. 9, the belt stretching member 4 is swung by a predetermined angle on a shaft common to the rotary shaft 2a of the pressure roll 2. In contrast, the belt tension member 4 is configured to be swingable by a predetermined angle on a shaft 7b different from the rotation shaft 2a of the pressure roll 2 in this example. Is a point.

  That is, the swing arm 4b is rotatably fitted on both sides of the shaft 7b disposed at a position different from the axis of the rotary shaft 2a, and a guide groove is formed on the belt stretching member 4 side of the swing arm 4b. 4c is formed. On the other hand, guide portions 4d extending toward the pressure roll 2 are formed at both ends of the belt stretching member 4, and the guide portions 4d are guided through the springs 4e to guide grooves 4c of the swing arm 4b. It is inserted inside. As a result, the belt stretching member 4 is urged in a direction away from the pressure roll 2 by the spring 4 e and has a structure in which a tension f is applied to the heat-resistant belt 3.

  Thereby, the rotational moment acting on the belt stretching member 4 can be changed (in the example of FIG. 14, the rotational moment is increased), and the pressure contact force between the heat-resistant belt 3 and the heat fixing roll 1 is pressed depending on the position of the shaft 7b. Can be adjusted. Also in this example, as shown in FIGS. 4 and 10, the sliding surface 4 g of the belt stretching member 4 and the pressing surface 4 h that presses the heat-resistant belt 3 and presses the sheet material against the heat fixing roll 1. A gap (step) G larger than the thickness of the heat-resistant belt 3 is provided therebetween.

  FIG. 15 is a cross-sectional view showing a modification of the fixing device of FIG. In this example, the belt stretching member 4 is a roll-shaped non-rotating member. Also in this example, as shown in FIGS. 4 and 10, the sliding surface 4 g of the belt stretching member 4 and the pressing surface 4 h that presses the heat-resistant belt 3 and presses the sheet material against the heat fixing roll 1. A gap (step) G larger than the thickness of the heat-resistant belt 3 is provided therebetween.

  FIG. 16 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. 16, the image forming apparatus 10 includes a housing 10a, a paper discharge tray 10c formed on the upper portion of the housing 10a, and a door body 10b attached to the front surface of the housing 10a so as to be opened and closed. 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.

  FIG. 17 is a diagram for explaining the behavior in which the sheet material that is curled and discharged to the heat fixing roll side is guided by the sheet material guide member, and FIG. 18 is a diagram illustrating the sheet material that is curled and discharged to the pressure roll side. It is a figure for demonstrating the behavior guided by a sheet 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 fixing roll 1, it is curled and discharged to either the heat fixing roll 1 side or the pressure roll 2 side.

  As shown in FIG. 17B, the sheet material 5 discharged from the fixing nip outlet is curled toward the heat fixing roll 1 with respect to the conveyance surface L of the sheet material 5 that is a tangent to the fixing nip and is in the virtual sheet material conveyance direction. As shown in FIG. 17A, first, the sheet material 5 comes into contact with the guide slope 8c of the sheet material guide member 8 disposed close to the heat fixing roll 1 side (a). Then, the tip is guided and advanced along the guide slope 8c in the contact state (b), and the reverse curl behavior is given as the contact reaction force (c), and finally in the virtual sheet material conveyance direction. Guided (d). During this time, the fixed toner image surface of the sheet material 5 is separated from the guide slope 8c 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 8c. Guided without rubbing. As described above, since the leading end of the sheet material 5 is guided and advanced in the contact state, if the lubricant treatment is applied to the contact surface, the leading end of the sheet material 5 can be smoothly advanced.

  Conversely, as shown in FIG. 18B, the sheet material 5 discharged from the fixing nip exit is tangent to the fixing nip, and is on the side of the pressure roll 2 with respect to the conveyance surface L of the sheet material 5 in the virtual sheet material conveyance direction. 18A, the sheet material 5 comes into contact with the guide slope 8c of the sheet material guide member 8 that is disposed close to the pressure roll 2 side as shown in FIG. ), The tip is guided and advanced along the guide slope 8c in the contact state (b), and the reverse curl behavior is given as the contact reaction force (c), and finally in the virtual sheet material conveyance direction. (D) During this time, 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 8c, so that even if the back surface of the sheet material 5 is the fixed toner image surface. The guide is guided without being rubbed away from the guide slope 8c.

  FIG. 19 is a diagram showing an embodiment of a fixing device constituted by various combinations of a heat fixing member and a pressure member.

  In the embodiment shown in FIG. 19A, a fixing nip is formed by pressing a pressing roll 2 with a predetermined pressing force on a heat fixing roll 1 having a built-in heating source, and the fixing nip is formed on a sheet material. 2 is a two-roll fixing device that passes and fixes an unfixed toner image formed on the toner. The surface of the heat fixing roll 1 has an elastic layer 1c, and the surface of the pressure roll 2 is harder than the elastic layer 1c of the heat fixing roll 1, and the pressure roll 2 is pressed against the heat fixing roll 1. By doing so, the elastic layer 1c of the heat fixing roll 1 is elastically deformed into a concave shape, and a curling behavior is imparted in a direction in which the sheet material is separated from the heat fixing roll 1.

  FIG. 19B shows an embodiment applied to a so-called surf fixing device. A planar heating element 51 is provided on a flat surface such as a ceramic substrate, and a heat-resistant belt 53 is provided on the surface of the planar heating element 51 so as to be slidable. In this belt fixing device, a fixing nip pressed with a predetermined pressing force is formed, and an unfixed toner image formed on the sheet material is passed through the fixing nip to be fixed. An elastic layer 52c is provided on the surface of the pressure roll 52, and when the heat-resistant belt 53 is pressed in the direction of the sheet heating element 51, the heat-resistant belt 53 adheres along the surface of the sheet heating element 51 and heat transfer is improved. The fixing nip is a flat nip because the surface of the heat-resistant belt 53 along the surface of the flat sheet heating element 51 is a reference. The sheet material passing through the flat nip has a structure in which no curl behavior is imparted to either the heat-resistant belt 53 side or the pressure roll 52 side. However, the sheet material may cause unexpected characteristics due to the toner characteristics of the unfixed toner image, the moisture absorption state of the sheet material, the sheet fiber state, or the constituent material. When the sheet material travels along the shape of the sheet material, it is released from the state in which the heat-resistant belt 53 is in close contact with the surface of the flat sheet-like heating element 51 to be in a substantially circular free state, and the sheet material has its own restoring force ( It is easily separated from the heat-resistant belt 53 by a common name called a waist of the sheet material). However, the function is not required until it is forcibly removed as an unexpected measure such as a sheet material jam, but in consideration of safety, the sheet material guide member 58 is disposed close to the fixing nip outlet side. It is effective for a trouble-free configuration to determine the transport route.

  In the embodiment shown in FIG. 19C, a heat-resistant belt 63 is provided on a heat-fixing roll 61 incorporating a heating source 61a, and the heat-resistant belt 63 presses the heat-fixing belt 63 toward the heat-fixing roll 61 with a predetermined pressing force. A pressing member 62 is built in, and is configured to be driven by being wound around a heat fixing roll 61 by a predetermined angle, so that a fixing nip is formed, and the fixing nip is passed through an unfixed toner image formed on a sheet material. This is a belt fixing device. An elastic layer 61c is provided on the surface of the heat fixing roll 61, and a pre-nip member 62c made of an elastic member for pressing the heat-resistant belt 63 against the heat fixing roll 61 to form a wide fixing nip on the pressing member 62; A peeling nip member 62 d formed with a curvature smaller than the curvature of the outer diameter of the heat fixing roll 61 for locally deforming the elastic layer on the surface of the heat fixing roll 61 to enhance the peelability of the sheet material from the heat fixing roll 61. Have a structure.

  With the above structure, the sheet material after fixing does not wrap around the heat fixing roll 61 or the heat-resistant belt 63, and means such as a peeling claw and a peeling plate for forcibly peeling the sheet material are unnecessary. However, the sheet material may bring unexpected characteristics in the toner characteristics of the unfixed toner image, the moisture absorption state of the sheet material, the sheet fiber state, or the constituent material, and as an unexpected response such as a sheet material jam. The function is not required until it is forcibly removed, but in consideration of safety, it is trouble-free that the sheet material guide member 68 is disposed close to the fixing nip outlet side to determine the conveyance path. It is effective for.

  In the embodiment shown in FIG. 19D, a fixing nip is formed by pressing a pressure roll 72 against a metal heat generating belt 71 capable of generating heat by applying a high frequency current to the coil 71a and pressing it with a predetermined pressing force. The heat generating belt fixing device forms and fixes an unfixed toner image formed on a sheet material through the fixing nip. The heat generating belt 71 is made of a metal member such as a thin SUS pipe or a nickel electroformed tube as a base, a heat-resistant elastic layer such as silicon rubber is formed on the surface, and a PFA surface layer is provided on the surface. It is configured to be possible. On the other hand, the pressure roll 72 is not an essential component, but has an elastic layer on the surface, and has a sufficient surface synthesis to deform the entire heat generating belt 71 when it is pressed against the heat generating belt 71. A concave fixing nip is formed on the belt 71. Therefore, when the unfixed toner image formed on the sheet material is fixed, the sheet material is elastically deformed in a direction away from the heat generating belt 71 and imparts curling behavior to the sheet material. A means for forcibly peeling the sheet material from the heat generating belt 71 and the pressure roll 72 is not required without being wound around the pressure roll 72. The curl behavior amount in the direction away from the heat generating belt 71 to which the sheet material is applied and the pressure roll 72 can be easily adjusted by the balance between the hardness of the pressure roll 72 and the heat generating belt 71 and the pressing force. With such a configuration, the sheet material after fixing does not wrap around the heat generating belt 71 and the pressure roll 72, and means such as a peeling claw or a peeling plate for forcibly peeling the sheet material is unnecessary. The sheet material may cause unexpected properties such as the toner characteristics of the unfixed toner image, the moisture absorption state of the sheet material, the sheet fiber state, or the constituent material, and is also forced as an unexpected measure such as a sheet material jam. It is effective for a trouble-free configuration that the sheet material guide member 68 is disposed close to the fixing nip outlet side and the conveying path is determined in consideration of safety. It is.

  In the embodiment shown in FIG. 19 (E), a pressure roller 82 is disposed opposite to a heat fixing roller 81 in which a heat-resistant belt 83 is stretched between a heat roller 84 having a built-in heating source 84a, and a predetermined pressing force is applied. This is a belt fixing device that forms a pressed fixing nip, and passes and fixes an unfixed toner image formed on a sheet material through the fixing nip. The surface of the heat fixing roll 81 has an elastic layer 81 c, and the surface of the pressure roll 82 is harder than the elastic layer 81 c of the heat fixing roll 81, and the pressure roll is attached to the heat fixing roll 81 via the heat-resistant belt 83. By pressing 82, the elastic layer 81c of the heat fixing roll 81 is elastically deformed into a concave shape, and the curling behavior is imparted in a direction in which the sheet material is separated from the heat fixing roll 81.

  In the embodiment shown in FIG. 19 (F), a fixing roll 91 in which a heat-resistant belt 93 is stretched between a heating roll 94 having a built-in heating source 94a is provided, and a pressure roll 92 is disposed opposite to the heat-resistant belt 93. In this belt fixing device, a fixing nip pressed with a predetermined pressing force is formed, and an unfixed toner image formed on the sheet material is passed through the fixing nip to be fixed. The surface of the pressure roll 92 presses the heat-resistant belt 93 stretched between the heating roll 94 and the fixing roll 91 to a position where the heat-resistant belt 93 is deformed into a concave shape from the tangential state, and imparts curl behavior in the direction in which the sheet material is separated from the heat-resistant belt 93. Structure.

  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 sectional drawing seen in the arrow direction along the YY line of FIG. It is sectional drawing which showed the detailed structure of FIG. 1, and cut | disconnected by the XX line and looked at the arrow direction. 1 shows a state when the sheet material is not passed, FIG. 5 (A) is a partially enlarged sectional view of FIG. 1 (A), and FIG. 5 (B) is cut along line XX of FIG. 5 (A). It is sectional drawing seen in the arrow direction. 1 shows a state when the sheet material is passed, FIG. 6 (A) is a partially enlarged sectional view of FIG. 1 (A), and FIG. 6 (B) is an arrow cut along line XX of FIG. 6 (A). It is sectional drawing seen in the direction. FIG. 7 is a diagram illustrating an example of a fixing pressure that changes in accordance with a nip passage position in FIG. 6. FIG. 8A is a cross-sectional view, and FIG. 8B is a cross-sectional view taken in the direction of the arrow along the YY line of FIG. 8A. FIG. 9A is a cross-sectional view, and FIG. 9B is a cross-sectional view taken along the line YY of FIG. 9A in the arrow direction. FIG. 10 is a partially enlarged cross-sectional view with the heat-resistant belt removed in FIG. 9. It is the figure which attached the heat-resistant belt 3 in FIG. It is a figure which shows the state at the time of passage of a sheet | seat material in FIG. It is a figure which shows the example of the fixing pressure which changes according to a nip passage position. FIG. 14A is a cross-sectional view, and FIG. 14B is a cross-sectional view taken along the line Y-Y in FIG. 14A in the arrow direction. FIG. 10 is a cross-sectional view illustrating a modification of the fixing device in FIG. 9. 1 is a schematic cross-sectional view showing an embodiment of an image forming apparatus of the present invention. It is a figure for demonstrating the behavior by which the sheet material curled and discharged to the heat fixing roll 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. It is a figure which shows embodiment of the fixing apparatus comprised by various combinations of a heat fixing member and a pressurizing member.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Thermal fixing roll, 1a ... Halogen lamp, 1b ... Roll base material, 1c ... Elastic body, 2 ... Pressure roll, 2a ... Rotary shaft, 2b ... Roll base material, 2c ... Elastic body, 3 ... Heat-resistant belt, 4 ... belt tension member, 4a ... projecting wall, 5 ... sheet material, 5a ... unfixed toner image, 6 ... cleaning member, 7 ... frame, 8 ... sheet material guide member, 9 ... spring, L ... pressing part tangent

Claims (8)

A heat fixing roll having a built-in heating source and provided with an elastic layer on the surface, a pressurizing means arranged to face and press against the heat fixing roll, and an outer periphery of the pressurizing means arranged between the heat fixing rolls A fixing device for fixing an unfixed toner image formed on the sheet material by passing the sheet material through a fixing nip formed by the heat fixing roll and the heat-resistant belt, The fixing nip portion formed by the pressing of the pressurizing unit forms a fixing nip having a pressure distribution that becomes smaller on the exit side, and the sheet material toward the front side in the conveying direction of the sheet material on the exit side of the fixing nip. A fixing device characterized in that a sheet material guide member having a guide slope approaching the conveying surface is disposed in proximity. The pressurizing means includes a pressurizing roll that presses against the heat fixing roll, and a belt stretching member that tensions the heat-resistant belt by attaching the heat-resistant belt to the outer periphery between the pressurizing rolls. 2. The fixing according to claim 1, wherein the belt stretching member is disposed downstream of the pressure roll in the sheet conveyance direction, and the heat-resistant belt is wound around the heat fixing roll to form a fixing nip. apparatus. 3. The fixing device according to claim 1, wherein a part of the pressure unit has a surface harder than an elastic layer of the heat fixing roll. The fixing device according to claim 1, wherein the heat fixing roll includes a PFA layer on a surface layer of the elastic layer. 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. The fixing device according to claim 1, wherein the sheet material guide member is obtained by subjecting at least a surface of the surface facing the sheet material to a lubricant treatment. An image forming apparatus comprising the fixing device according to claim 1.

Images