JP2005156670A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve simplification, miniaturization, a cost reduction, a short warm-up period, a decrease in stress on a sheet material and hence restriction of deformation of the sheet material, and uniform pressure on the sheet material in a fixing nip. <P>SOLUTION: A heat-resistant belt 3 is wrapped around the external circumference of a pressure roll 2 pressed against the thermal fixing roll 1 and moved between the thermal fixing roll 1 and the pressure roll 2 while held between them. The heat-resistant belt 3 is wrapped along the thermal fixing roll 1 by a belt stretch member 4 between the pressure roll 2 and it, thereby forming the fixing nip. The rotating support point of the heat-resistant belt is set so as to be rockable in the direction of the rotating center of the thermal fixing roll 1. Tension in the direction of the tangent of a nip relative to the thermal fixing roll 1 is applied to the heat-resistant belt 3. Thereby, the heat-resistant belt 3 is stretched and pressed against the thermal fixing roll 1 with frictional force relative to the heat-resistant belt 3 and an unfixed toner image formed on the sheet material is fixed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention includes a heat fixing roll, a pressure roll that presses against the heat fixing roll, a heat-resistant belt that is attached to the outer periphery of the pressure roll and is sandwiched and moved between the heat fixing roll, and the heat-resistant roll. The present invention relates to a fixing device and an image forming apparatus that include a belt stretching member that stretches a belt and fixes an unfixed toner image formed on a sheet material.

  Mounted on image forming devices such as copiers, printers, and facsimiles, it is a heated roll type fixing device that heats and fixes unfixed toner images on a transfer material. A heat-fixing roll, a heat-resistant belt stretched by a plurality of support rolls, and a heat-resistant belt is wound around the heat-fixing roll by a predetermined angle to form a nip region, and at the exit of the nip region from other parts A fixing device is also proposed in which a large pressure is applied locally to provide a pressure means for generating distortion on the elastic body on the surface of the heat fixing roll to facilitate the discharge of the sheet material from the nip portion (see, for example, Patent Document 1). )

  In this conventional fixing device, since the surface of the heat fixing roll has distortion in advance due to the presence of pressure means, the toner is in contact with the surface of the heat fixing roll at the exit of the nip region. The surface distortion is instantaneously released. For this reason, when the sheet material is discharged from the nip portion, the adhesion force between the toner and the heat fixing roll is reduced to prevent the sheet material from being wound around the heat fixing roll. Can be easily peeled off. In this way, the above-described apparatus eliminates the peeling claw that has been conventionally required.

  Further, in the heat fixing device with two heaters using two halogen lamps for the heat fixing roll, the first heater having a larger amount of heat generation at the center of the heat fixing roll than at both ends, and at both ends of the heat fixing roll. A temperature distribution is made uniform according to the sheet passing size by combining with a second heater that generates a larger amount of heat (for example, see Patent Document 2).

  In these heat fixing devices, since the heat escape from the roll end is larger than that at the center of the roll, the axial temperature distribution tends to be higher at the center and lower at both ends. Therefore, in consideration of heat escape from the end, it has been conventionally performed to set the light distribution distribution of the halogen lamp so that the end is higher than the center, and to obtain a uniform temperature distribution in the axial direction. It was.

However, for example, when fixing continuously using narrow paper, the paper passing area is deprived of heat by the paper, while the heat supply by the halogen lamp exceeds the heat escape at the end outside the paper passing area. The temperature may rise abnormally because heat continues to accumulate on the roll. If the roll temperature becomes too high due to such a phenomenon, the life may be shortened by causing peeling at the interface between the roll mandrel and the elastic layer and damaging the roll. Therefore, conventionally, a means for locally cooling the end portion is provided, or a fixing pause period is provided to make the temperature uniform, and the heat conducting member is brought into contact with the heat fixing roll to change the temperature. There has been proposed a technique for achieving uniformization (see, for example, Patent Document 3).
Japanese Patent No. 3084692 JP-A-8-123230 JP-A-8-87191

  However, in the structure of the conventional fixing device described above, a heat-resistant belt that is stretched around a plurality of support rolls and is movable is wound around the heat-fixing roll by an angle that allows nip formation by pressure means, and locally at the outlet of the nip region. Since it is driven by applying a large pressure, a plurality of support rolls and their rotary bearings are required. Furthermore, the perimeter of the heat-resistant belt is increased, and the fixing device is not only complicated and large, but also expensive. The complicated, large and expensive construction of the fixing device inevitably makes the image forming apparatus equipped with the fixing device complicated, large and expensive.

  In addition, the heat-resistant belt is heated at the nip portion with the rotatable heat fixing roll with a built-in heating source, but in a configuration in which the circumference is extended by a plurality of support rolls, it moves along a predetermined path. When this is done, heat energy is deprived by the plurality of support rolls, and natural heat dissipation increases according to the length of the circumference. For this reason, it takes a long time to reach a predetermined temperature, and a so-called warm-up time from when the power is turned on to when fixing is required is not preferable.

  Further, in the configuration in which the heat-resistant belt is wound around the heat fixing roll at an angle capable of forming a nip, and a pressure larger than other portions is locally applied at the exit of the nip portion to form a distortion in the elastic layer of the heat fixing roll. The sheet material discharged along the strain of the elastic layer curls along the strain or is locally damaged by high pressure. It causes deformation such as occurrence.

  Further, in the case of a fixing device provided with means for cooling the end of the heat fixing roll, there is a problem that the noise of the cooling fan occurs and the heat efficiency is low because heating and cooling are performed simultaneously. A method in which the heat conducting member is brought into contact with the surface of the heat fixing roll in the sheet passing area is not preferable because it damages the outer peripheral surface of the heat fixing roll and deteriorates the image quality. Further, these systems have a drawback that the structure is complicated and the cost is increased. On the other hand, in the method of providing the fixing pause period, the longer the number of continuous fixing sheets, the more frequently the pause period must be provided, resulting in problems such as a reduction in productivity.

  The present invention solves the above-described conventional problems, and can simplify the structure of the heat roll type fixing device, reduce the size, reduce the cost, shorten the warm-up time, and reduce the stress on the sheet material. Therefore, deformation of the discharged sheet material such as curling and wrinkling can be suppressed. Further, the pressure on the sheet material at the fixing nip is made uniform to prevent a temperature rise at the end of the heat fixing roll, thereby preventing a decrease in image quality and a decrease in productivity due to a temperature increase at the end.

  Therefore, the present invention comprises a heat fixing roll, a pressure roll that presses against the heat fixing roll, a heat-resistant belt that is attached to the outer periphery of the pressure roll and is sandwiched and moved between the heat fixing roll, A fixing device for fixing an unfixed toner image formed on a sheet material, or an image forming apparatus equipped with the fixing device, the belt extending member comprising: a belt extending member for extending the heat-resistant belt; The heat-resistant belt is wound around the heat-fixing roll with the pressure roll to form a fixing nip, and a rotation fulcrum is set so as to be swingable in the rotation center direction of the heat-fixing roll. By applying a tension in the nip tangential direction to the heat fixing roll and stretching the heat-resistant belt, when the heat-resistant belt is driven to rotate, the frictional force between the belt-stretching member and the heat-resistant belt causes the bell The tension member is characterized by being configured to press lightly to the heat fixing roll.

  The rotation fulcrum is closer to the pressure roll side than the nip tangent line between the heat fixing roll and the pressure roll, and from the line connecting the nip portion with the belt stretching member from the rotation center of the heat fixing roll. It is characterized in that it is set on the pressure roll side, or the rotation fulcrum is located on the heat fixing roll side from the nip tangent line between the heat fixing roll and the pressure roll and from the rotation center of the heat fixing roll. It is characterized in that it is set on the opposite side of the pressure roll from the line connecting the nip portion with the belt stretching member, and the rotation fulcrum is in the vicinity of the nip portion tangent between the heat fixing roll and the belt stretching member. It is characterized by setting.

  The belt stretching member has pressing means for lightly pressing a nip portion with the heat fixing roll in the direction of the heat fixing roll, and the belt stretching member includes the heat fixing roll and the pressure roll. It arrange | positions in the upstream from the nip part.

  The belt stretching member has a contact portion that contacts the outer peripheral surface of the heat fixing roll at both ends, and the contact portion has a thickness of the heat-resistant belt with respect to a surface that holds the heat-resistant belt. It is higher than the thickness obtained by adding the minimum thickness of the sheet material to the thickness of the heat-resistant belt, and the contact portion has a thickness equal to the thickness of the heat-resistant belt with respect to a surface sandwiching the heat-resistant belt. It is characterized by being higher than the total thickness of the sheet material.

  The contact portion is formed integrally with the belt stretching member, and a member having a heat conductivity higher than that of the heat resistant belt is used. The contact portion is formed on an outer periphery of the heat fixing roll. A sliding surface that slides in contact with a predetermined length along the belt is formed, and the belt stretching member has a sliding surface of the heat-resistant belt that faces the heat fixing roll as the heat fixing roll. It is characterized by being formed concentrically.

  According to the present invention, a heat fixing roll, a pressure roll that presses against the heat fixing roll, a heat-resistant belt that is attached to the outer periphery of the pressure roll and is sandwiched and moved between the heat fixing roll, A fixing device for fixing an unfixed toner image formed on a sheet material, or an image forming apparatus equipped with the fixing device, the belt extending member comprising: a belt extending member for extending the heat-resistant belt; The heat-resistant belt is wound around the heat-fixing roll with the pressure roll to form a fixing nip, and a rotation fulcrum is set so as to be swingable in the rotation center direction of the heat-fixing roll. By applying a tension in the nip tangential direction to the heat fixing roll and stretching the heat-resistant belt, when the heat-resistant belt is driven to rotate, the frictional force between the belt-stretching member and the heat-resistant belt causes the Belt tension Since the member is lightly pressed against the heat-fixing roll, a member with which the heat-resistant belt slides is used as the belt tension member, and the structure is small and simple, the circumference of the heat-resistant belt is shortened, and the nip length is reduced. It can be configured to be long, can reduce wasteful heat dissipation, increase the heating efficiency, and shorten the warm-up time. Furthermore, it reduces the impact on the sheet material tip when entering the nip, reduces the stress on the sheet material, suppresses deformation of the discharged sheet material such as curling and wrinkles, and prevents jamming. Can do.

  The rotation fulcrum is closer to the pressure roll side than the nip tangent line between the heat fixing roll and the pressure roll, and from the line connecting the nip portion with the belt stretching member from the rotation center of the heat fixing roll. The belt support member is set on the pressure roll side, or the rotation fulcrum is on the heat fixing roll side with respect to the nip tangent line between the heat fixing roll and the pressure roll, and from the rotation center of the heat fixing roll. Since the rotation fulcrum is set in the vicinity of the nip portion tangent between the heat fixing roll and the belt stretching member, the tension of the heat-resistant belt is set. Is maintained properly, and the rotational force that presses the belt stretching member almost uniformly against the heat fixing belt can be generated, and the pressure on the sheet material can be made almost uniform regardless of the variation in the thickness of the sheet material. Melting Unevenness can be eliminated.

  The belt stretching member has pressing means for lightly pressing a nip portion with the heat fixing roll in the direction of the heat fixing roll, and the belt stretching member is a nip between the heat fixing roll and the pressure roll. As the heat-resistant belt is driven to rotate, the belt tension member is lightly pressed against the heat fixing roll by the friction force between the belt tension member and the heat-resistant belt as the heat-resistant belt rotates. The toner can be made almost uniform and uneven melting of the toner can be eliminated.

  The belt stretching member has contact portions that contact the outer peripheral surface of the heat fixing roll at both ends, so that the belt stretching member contacts the heat fixing roll at the contact portion. It can function as a squeeze member and efficiently release heat from the end of the heat fixing roll to prevent the end temperature from rising. The contact portion is higher than the thickness of the heat-resistant belt with respect to the surface sandwiching the heat-resistant belt, and lower than the thickness obtained by adding the minimum thickness of the sheet material to the thickness of the heat-resistant belt. Depending on the thickness of the belt tension member, the belt tension member swings to generate a rotating force that presses the belt tension member almost evenly against the heat fixing belt, and the pressure on the sheet material is almost uniform regardless of variations in the thickness of the sheet material. Thus, uneven melting of the toner can be eliminated. Further, the abutting portion is higher than the thickness of the heat-resistant belt plus the maximum thickness of the sheet material with respect to the surface sandwiching the heat-resistant belt, so that the end of the heat fixing roll is always at the end of the fixing operation. Heat can be efficiently released from the part to prevent the end temperature from rising, and even if the number of continuous fixing sheets increases, it is possible to prevent a decrease in productivity by providing a rest period without frequent rest periods. be able to. Furthermore, with these configurations, a desired gap can be formed between the belt stretching member and the heat fixing roll with the heat resistant belt interposed therebetween, and an amount of heat taken as heat insulating layer from the heat fixing roll via the heat resistant belt. Can be reduced, heat loss can be reduced, and warm-up time can be shortened.

  The contact portion is formed integrally with the belt stretching member, and a member having a heat conductivity higher than that of the heat resistant belt is used. The contact portion has a predetermined length along the outer periphery of the heat fixing roll. Since the sliding surface that slides in contact with each other is formed, it acts as a temperature fixing member of the heat fixing roll, and can efficiently release heat from the end of the heat fixing roll to prevent the end temperature from rising. The belt tension member has a sliding surface of the heat-resistant belt facing the heat fixing roll formed concentrically with the heat fixing roll, so that the belt tension member presses the belt tension member almost uniformly against the heat fixing belt. It can be generated, and the pressure on the sheet material can be made substantially uniform regardless of the variation in the thickness of the sheet material, thereby eliminating uneven melting of the toner.

  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. Is different between a fixing nip portion wound around the heat fixing roll 1 and a portion where the belt stretching member 4 slides on the heat fixing roll 1, and a wide sheet material and a narrow sheet material. Temperature control under conditions can be easily performed.

  The heat-resistant belt 3 may be made of a rubber material such as PFA or silicon, for example, in consideration of the influence on the surface layer of the opposing heat-fixing roll 1 or the contact with the toner image surface during double-side fixing to the sheet material. 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 upstream side in the conveyance 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 initial position where the sheet material 5 enters the fixing nip when the sheet material 5 does not pass through the fixing nip. . 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. When the belt stretching member 4 is stretched in the tangential direction of the heat fixing roll 1 on the upstream side in the conveying direction of the sheet material 5, an introduction port portion in which the sheet material 5 smoothly enters can be formed and is stable. The sheet material 5 can enter. 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 becomes concave and the curvature becomes large, the sheet material 5 is difficult to be wound around the heat fixing roll 1 and is easily peeled off from the heat fixing roll 1.

  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. The belt-sliding member (a heat-resistant belt 3 slides on the belt stretching member 4) is disposed in a position where the belt is formed. 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, the surface of this plastic belt sliding member is subjected to metal coating treatment such as copper plating, nickel plating or vapor deposition for the purpose of improving thermal conductivity, and the axial length is heated. When the length of the elastic layer covering portion of the fixing roll 1 is shorter than the axial length, it is possible to further exhibit characteristics excellent in thermal response under a small heat capacity.

  The belt stretching member 4 is disposed at a position where the heat-resistant belt 3 is wound around the pressing portion tangent L between the heat-fixing roll 1 and the pressure roll 2 toward the heat-fixing roll 1 to form a nip. It has the protruding wall 4a formed. The protruding wall 4a has an abutting portion that abuts on the outer peripheral surface of the heat fixing roll 1 outside the sheet passing region, and serves as a temperature leveling member that releases heat from both ends of the heat fixing roll 1 to prevent an end temperature increase. Works as a gap adjusting member that adjusts the gap between the sliding surface of the belt stretching member 4 on which the heat-resistant belt 3 slides and the heat fixing roll 1, or when the heat-resistant belt 3 approaches one side It acts as a belt deviation regulating member that abuts against the protruding wall 4a and regulates the deviation of the heat-resistant belt 3. Therefore, the belt stretching member 4 is provided with a spring 9 between the heat fixing roll 1 of the protruding wall 4a and the frame at the opposite end, and is lightly pressed against the heat fixing roll 1 by the spring 9, so that the heat fixing roll 1 and is 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 unstable factors against aging and disturbance can be eliminated, and the heat-resistant belt 3 is stabilized with a pressure roll. And 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 belt stretching member 4 is lightly pressed against the heat fixing roll 1 as the nip initial position, whereby the unfixed toner image 5a is fixed. The position where the pressure roll 2 is pressed against the heat fixing roll 1 is set as the nip end position, and the sheet is conveyed in the direction of the pressing portion tangent L between the heat fixing roll 1 and the pressure roll 2. 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.

  An unfixed toner image formed on a sheet material by pressing and pressing the pressure roll 2 having a harder surface than the elastic layer coated on the surface of the heat fixing roll 1 and further forming a concave fixing nip. Is fixed to the sheet material 5 that has passed through the fixing nip, and a pressure roll that is harder than the elastic layer coated on the surface of the heat fixing roll 1 and its own restoring force (commonly referred to as the waist of the sheet material). By pressing 2, the elastic layer of the heat fixing roll 1 can be elastically deformed in a direction in which the sheet material 5 is separated from the heat fixing roll 1, thereby imparting curl 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 releasability are improved. can do.

  Even if the wrapping 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 has an unexpected characteristic in a moisture absorption state, a sheet fiber state, or a constituent material. In addition, the sheet material guide member 8 may be disposed on the fixing nip outlet side in consideration of safety, although it does not need to exhibit its function until it is forcibly removed as an unexpected measure such as a sheet material jam. It is effective for a trouble-free configuration to determine the conveyance path by being arranged in proximity to each other. 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.

  Next, a support structure for the pressure roll 2 and the belt stretching member 4 will be described. FIG. 2 is a cross-sectional view taken in the direction of the arrow along the YY line in FIG. 1, and the right half of the apparatus is omitted. As shown in FIG. 2, 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.

  3 shows an example in which the rotation fulcrum of the belt stretching member is set on the heat fixing roll side, and FIG. 4 shows an example in which the rotation fulcrum of the belt stretching member is set on the pressure roll side. FIG. 4 is a view showing an example in which the rotation fulcrum of the belt stretching member is set on the pressure roll side and on the fixing nip side with respect to the line connecting the closest fixing nip portion of the belt stretching member and the pressure roll rotation center. It is.

  As in the above-described embodiment, the belt stretching member 4 is disposed so as to be able to swing on the upstream side in the conveying direction of the sheet material 5 from the nip portion between the heat fixing roll 1 and the pressure roll 2, and the pressure roll 2 and the belt tension. The heat-resistant belt 3 is tensioned to the heat-resistant belt 3 in cooperation with the frame member 4 in a tangential direction with the heat-fixing roll 1 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. When the heat-resistant belt 3 is rotationally driven by the formation, a rotational force is generated that presses the belt-stretching member 4 against the heat fixing roll 1 by a frictional force between the belt-stretching member 4 and the heat-resistant belt 3.

  When the position of the rotation fulcrum O is observed, the position is on the nip tangent LN1 between the heat fixing roll 1 and the pressure roll 2 on the heat fixing roll 1 side as shown in FIG. 3, for example. In this case, the rotational force is generated in the direction in which the belt stretching member 4 is separated from the heat fixing roll 1 by receiving the rotational force from the heat-resistant belt 3. Further, if the belt tension member 4 rotates in the direction away from the pressure roll 2, the belt tension increases, and if the belt tension increases, the belt ride-on occurs, or the belt buckles or breaks, which is not preferable.

  Therefore, when the rotation fulcrum O is positioned on the pressure roll 2 side with respect to the nip tangent LN1 between the heat fixing roll 1 and the pressure roll 2, as shown in FIG. Rotation force is generated to press the toner onto the heat fixing roll 1. The above-described embodiment uses the rotation shaft 2a of the pressure roll 2 around which the swing arm 4b rotates as the rotation fulcrum O of the belt stretching member 4. When the position of the rotation fulcrum O is set on the pressure roll 2 side with respect to the nip tangent LN1, the belt tension member 4 is not rotated in the direction away from the pressure roll 2, and the belt tension increases. Nor. Further, as shown in FIG. 5, the position of the rotation fulcrum O of the belt stretching member 4 is on the pressure roll 2 side with respect to the nip tangent LN1 between the heat fixing roll 1 and the pressure roll 2, and the heat fixing. It is preferable that the belt tension member 4 is on the opposite side of the line LO1 connecting the most upstream portion of the nip portion of the roll 1 and the pressure roll 2 and the rotation center of the pressure roll 2. Alternatively, conversely, from the nip tangent LN1 between the heat fixing roll 1 and the pressure roll 2 on the heat fixing roll 1 side, from the line connecting the center of rotation of the heat fixing roll 1 and the nip portion with the belt stretching member 4. The pressure roll 2 may be set on the opposite side.

  When the belt stretching member 4 is pressed almost uniformly against the heat fixing roll 1, the sheet material can be pressed against the heat fixing roll 1 from the belt stretching member 4 via the heat-resistant belt 3 with a substantially uniform pressure. This is preferable because the melting of the toner is stable. Even if the thickness of the sheet material 5 changes, the belt stretching member 4 is changed by swinging according to the thickness, and the belt stretching member 4 is pressed so as to press the sheet material 5 against the heat fixing roll 1 with a substantially uniform pressure. In order to rotate (oscillate), basically, at the center position of the nip portion between the belt stretching member 4 and the heat fixing roll 1, the direction perpendicular to the tangent portion of the nip portion, that is, the rotation of the heat fixing roll 1. The position of the rotation fulcrum O for rotating the belt stretching member 4 that can swing in the center direction is set. This is when the position of the pivot fulcrum O is on or near the nip tangent.

  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.

  In the present embodiment, as shown in FIG. 1, a spring 9 that assists as a swing urging means is pressed by a pressing portion between a heat fixing roll 1 and a pressure roll 2 that is away from a 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.

  6 to 8 show the detailed structure of the fixing device shown in FIG. 1. FIG. 6 is a cross-sectional view of the fixing device shown in FIG. 8 is a partially enlarged cross-sectional view in which the heat-resistant belt is removed by the fixing device shown in FIG. 8, and FIG.

  As shown in FIGS. 6 and 7, the belt stretching member 4 slides with the protruding walls 4a coming into contact with both ends of the heat fixing roll 1 at both ends in the axial direction of the heat fixing roll 1 at the heat fixing roll sliding surfaces 4g. Then, the heat fixing roll sliding surface 4 g and the belt sliding surface 4 h of the protruding wall 4 a are formed concentrically with the fixing roll 1. The protruding wall 4a functions as a temperature leveling member that releases heat from the end of the heat fixing roll 1 and prevents the temperature of the end from rising, and the belt sliding member 4 of the belt stretching member 4 on which the heat-resistant belt 3 slides. It functions as a gap adjusting member that adjusts the gap G between the moving surface 4 h and the heat fixing roll 1. Further, when the heat-resistant belt 3 comes to one side including the upstream side of the heat-resistant belt 3 from the sliding surface 4g of the heat fixing roll, a belt-side regulating member that regulates the deviation of the heat-resistant belt 3 by contacting the protruding wall 4a. work.

  The gap G has a thickness of the heat-resistant belt 3 on the heat-fixing roll sliding contact surface 4g of the protruding wall 4a with respect to the belt-sliding surface 4h on which the heat-resistant belt 3 slides and the sheet material 5 enters while facing the heat-fixing roll 1. It is formed to be higher than the thickness obtained by adding the minimum thickness of the sheet material 5 to the thickness of the heat-resistant belt 3. For example, when the heat-resistant belt 3 is formed with a thickness of about 80 μm, if the step is formed by setting the height of the gap G to about 110 μm, stable fixing is possible even with a sheet material having a thickness of 60 μm. The heat fixing roll sliding surface 4g is slidably brought into contact with the heat fixing roll 1 between so-called papers between the sheet materials to efficiently release heat from both ends of the heat fixing roll 1 to prevent the temperature rise at both ends. Can do.

  When passing through the sheet material 5 to which the heat-resistant belt 3 is attached, the heat-resistant belt 3 and the sheet material 5 are pressed against the nip portion between the heat fixing roll 1 and the pressure roll 2 as shown in FIG. The heat-resistant belt 3 is wound around the heat fixing roll 1 by the belt stretching member 4 and the sheet material 5 is lightly pressed to the heat fixing roll 1 through the heat-resistant belt 3 at the initial nip position.

  It is practical to match the speed of the process step for forming an unfixed toner image on the sheet material 5 on the sheet material 5 in the previous step of the fixing step with the speed of the fixing step in consideration of variations in various parts dimensions in mass production. is not. 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 5, and is set to either one of the processes before and after the process. However, it is necessary to securely grip the sheet material 5 at the initial position where the sheet material 5 enters the fixing nip to clarify the entry speed of the sheet material 5. When configured as described above, This objective is achieved.

  The surface of the elastic body of the heat fixing roll 1 and the surface of the heat-resistant belt 3 are moved at the same peripheral speed to fix the unfixed toner image formed on the sheet material 5. If the sheet material 5 is in a shape or the leading end of the sheet material 5 is in a wave shape, the fixing start state may become unstable. Therefore, if the heat-resistant belt 3 is lightly pressed against the heat fixing roll 1 at the initial nip position, the combined state of both is stabilized, so that an extremely stable unfixed toner image can be fixed.

  In this embodiment, since the 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, the gap G is formed as a heat insulating layer during warming up. Thus, the amount of heat taken from the heat fixing roll 1 via the heat-resistant belt 3 is reduced, heat loss is reduced, and warm-up time can be shortened.

  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 addition, the belt stretching member 4 transmits the heat of the end portion of the heat fixing roll 1 to the heat resistant belt 3 on the upstream side of the fixing nip, so that the sheet material before fixing is preheated via the heat resistant belt 3 and applied to the sheet material. It can improve heat transfer efficiency and save energy.

  9 shows another embodiment of the fixing device shown in FIG. 1, FIG. 9 (A) is a sectional view, and FIG. 9 (B) is seen in the direction of the arrow along the YY line of FIG. 9 (A). It is sectional drawing. 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.

  The present embodiment differs from the embodiment shown in FIG. 1 in that, in the embodiment shown in FIG. 1, the belt stretching member 4 is set at a predetermined angle with a common axis with the rotation shaft 2 a of the pressure roll 2. In this embodiment, the belt stretching member 4 can be swung by a predetermined angle on a shaft 7b different from the rotating shaft 2a of the pressure roll 2 in this embodiment. It is the point which constitutes.

  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.

  As a result, the rotational moment acting on the belt stretching member 4 can be changed (in the embodiment shown in FIG. 9, the rotational moment is increased), and the heat-resistant belt 3 and the heat fixing roll 1 are pressed against each other depending on the position of the shaft 7b. The pressure contact force can be adjusted. In this embodiment as well, as shown in FIG. 6, the heat-resistant belt 3 and the belt sliding surface 4h facing the heat-fixing roll 1 with the sheet material interposed therebetween are higher than the thickness of the heat-resistant belt 3 and the heat-resistant belt. The gap (step) G is provided by making the sliding surface 4g of the belt stretching member 4 lower than the thickness obtained by adding the minimum thickness of the sheet material 5 to the thickness of 3.

  FIG. 10 is a cross-sectional view showing another embodiment of the fixing device shown in FIG. In this embodiment, the belt stretching member 4 is a roll-shaped non-rotating member. Also in this embodiment, as shown in FIG. 6, the heat-resistant belt 3 is opposed to the heat-fixing roll 1, and the belt sliding surface 4h into which the sheet material 5 enters is higher than the thickness of the heat-resistant belt 3. Further, the gap (step) G is provided by lowering the sliding surface 4g of the belt stretching member 4 from the thickness of the heat-resistant belt 3 plus the minimum thickness of the sheet material 5.

  11 to 12 show another embodiment of the fixing device according to the present invention. FIG. 11A is a cross-sectional view, and FIG. 11B is an arrow direction along the line Y-Y in FIG. FIG. 12 shows a state when the sheet material is not passed, FIG. 12A is a partially enlarged sectional view of FIG. 11A, and FIG. It is sectional drawing cut | disconnected by the X-ray and seen in the arrow direction. In addition, about the same structure as the said embodiment, the same number is attached | subjected and description is abbreviate | omitted.

  In the above embodiment, the belt stretching member 4 is disposed on the upstream side in the conveying direction of the sheet material 5 from 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 swung in the direction of arrow P about the rotation shaft 2a of the pressure roll 2 on the downstream side in the conveying direction of the sheet material 5 from the pressing portion of the heat fixing roll 1 and the pressure roll 2. It is possible to arrange. 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 a nip end 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 conveyed in the direction of the pressing part tangent L at the end position.

  As shown in FIG. 12, the protruding wall 4a of the belt stretching member 4 is positioned in sliding contact with the heat fixing roll 1 with a sliding surface 4g, and the heat fixing roll sliding surface 4g and the belt sliding surface 4h are positioned on the heat fixing roll 1. And concentric circles. The heat fixing roll sliding surface 4g of the protruding wall 4a is higher than the thickness of the heat resistant belt 3 with respect to the belt sliding surface 4h facing the heat fixing roll 1 with the heat resistant belt 3 and the sheet material interposed therebetween, and the heat resistant belt 3 The gap (step) G is provided by making the sliding surface 4g of the belt stretching member 4 lower than the thickness obtained by adding the minimum thickness of the sheet material 5 to the thickness. Specifically, for example, when the heat-resistant belt 3 is configured with a thickness of about 80 μm, a stable fixing is possible even with a sheet material having a thickness of 60 μm by forming a step by setting the height of the gap G to about 110 μm. Yes, the heat fixing roll sliding surface 4g is slidably brought into contact with the heat fixing roll 1 between so-called papers between the sheet material, and heat is efficiently released from both ends of the heat fixing roll 1, so Temperature rise can be prevented.

  The heat-resistant belt 3 is pressed against the nip portion between the heat fixing roll 1 and the pressure roll 2, and the belt stretching member 4 winds the heat-resistant belt 3 around the heat fixing roll 1 on the downstream side and heat-fixes at the nip end position. The roll sliding surface 4 g is pressed against the heat fixing roll 1. Also in this embodiment, since the gap G is formed between the heat-resistant belt 3 and the belt stretching member 4 in this state in which the sheet material 5 does not pass, the gap G is formed at the time of warming up. As a heat insulating layer, the amount of heat taken from the heat fixing roll 1 through the heat-resistant belt 3 is reduced, heat loss is reduced, and warm-up time can be shortened.

  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 addition, since the belt stretching member 4 transmits the heat of the end of the heat fixing roll 1 to the heat resistant belt 3 on the downstream side of the fixing nip, the sheet material before fixing is preheated via the heat resistant belt 3 and applied to the sheet material. It can improve heat transfer efficiency and save energy.

  FIG. 13 shows another embodiment of the fixing device shown in FIG. 11, FIG. 13A is a sectional view, and FIG. 13B is seen in the direction of the arrow along the YY line of FIG. It is sectional drawing. The present embodiment is different from the embodiment shown in FIG. 11 in that, in the above-described embodiment, the belt stretching member 4 is swung by a predetermined angle on 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 embodiment shown in FIG. 13, the rotational moment is increased), and the heat-resistant belt 3 and the heat fixing roll 1 are pressed against each other depending on the position of the shaft 7b. The pressure contact force can be adjusted.

  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. Thus, 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.

  FIG. 14 is a schematic cross-sectional view of the overall configuration showing an embodiment of an image forming apparatus according to 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. 14, an 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.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the gap G between the belt sliding surface 4h of the belt stretching member 4 on which the heat-resistant belt 3 slides and the heat fixing roll 1 is set to the belt sliding surface 4h with respect to the heat fixing of the protruding wall 4a. The roll sliding contact surface 4g is formed to be higher than the thickness of the heat-resistant belt 3 and lower than the thickness of the heat-resistant belt 3 plus the minimum thickness of the sheet material 5, but the protruding wall 4a is formed against the belt sliding surface 4h. The heat fixing roll sliding contact surface 4g may be formed higher than the thickness of the heat-resistant belt 3 plus the maximum thickness of the sheet material 5. Moreover, although it comprised so that the gap G might be formed with the protrusion wall 4a, you may comprise using a gap roller.

1 is a cross-sectional view showing an embodiment of a fixing device according to the present invention. FIG. 2 is a cross-sectional view of the fixing device shown in FIG. 1 as viewed in the direction of an arrow along line YY. It is a figure which shows the example which set the rotation fulcrum of the belt stretching member to the heat fixing roll side. It is a figure which shows the example which set the rotation fulcrum of the belt stretching member to the pressurization roll side. FIG. 6 is a diagram showing an example in which the rotation fulcrum of the belt stretching member is set on the pressure roll side and on the fixing nip side with respect to the line connecting the closest fixing nip portion of the belt stretching member and the pressure roll rotation center. is there. FIG. 2 is a cross-sectional view showing a detailed structure of the fixing device shown in FIG. FIG. 2 is a partially enlarged cross-sectional view of the fixing device shown in FIG. 1 with a heat-resistant belt removed. FIG. 7 is a view showing a state when the sheet material to which the heat-resistant belt 3 is attached passes. FIG. 9A shows another embodiment of the fixing device shown in FIG. 1, FIG. 9A is a cross-sectional view, and FIG. 9B is a view taken in the direction of the arrow along the YY line of the fixing device shown in FIG. FIG. FIG. 5 is a cross-sectional view illustrating another embodiment of the fixing device illustrated in FIG. 1. FIG. 11A is a cross-sectional view, and FIG. 11B is a cross-sectional view taken along the line YY of FIG. 11A in the direction of the arrow. . 11 shows a state when the sheet material is not passed, FIG. 12A is a partially enlarged cross-sectional view of FIG. 11A, and FIG. 12B is cut along line XX of FIG. It is sectional drawing seen in the arrow direction. 11 shows another embodiment of the fixing device shown in FIG. 11. FIG. 13A is a cross-sectional view, and FIG. 13B is a cross-sectional view taken along the line Y-Y in FIG. is there. 1 is a schematic cross-sectional view showing an embodiment of an image forming apparatus according to the present invention.

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 (13)

A heat-fixing roll, a pressure roll that presses against the heat-fixing roll, a heat-resistant belt that is attached to the outer periphery of the pressure roll and is sandwiched and moved between the heat-fixing roll, and the heat-resistant belt is stretched A fixing device for fixing an unfixed toner image formed on a sheet material, wherein the belt extending member is attached to the heat fixing roll between the heat fixing roll and the heat fixing roll. A fixing nip is formed by winding a belt, and a rotation fulcrum is set so as to be swingable in the direction of the rotation center of the heat fixing roll, and a tension in a tangential direction of the nip portion with the heat fixing roll is applied to the heat resistant belt. By stretching the heat-resistant belt, when the heat-resistant belt is rotationally driven, the belt-stretching member is pressed lightly against the heat fixing roll by the frictional force between the belt stretching member and the heat-resistant belt. The fixing device according to claim and. The rotation fulcrum is closer to the pressure roll side than the nip tangent line between the heat fixing roll and the pressure roll, and from the line connecting the nip portion with the belt stretching member from the rotation center of the heat fixing roll. The fixing device according to claim 1, wherein the fixing device is set on a pressure roll side. The rotation fulcrum is closer to the heat fixing roll side than the nip tangent line between the heat fixing roll and the pressure roll, and from the line connecting the nip portion with the belt stretching member from the rotation center of the heat fixing roll. The fixing device according to claim 1, wherein the fixing device is set on a side opposite to the pressure roll. The fixing device according to claim 1, wherein the rotation fulcrum is set in the vicinity of a tangent line between the heat fixing roll and the belt stretching member. The fixing device according to claim 1, wherein the belt stretching member includes a pressing unit that lightly presses a nip portion with the heat fixing roll in a direction of the heat fixing roll. The fixing device according to claim 1, wherein the belt stretching member is disposed upstream of a nip portion between the heat fixing roll and the pressure roll. The fixing device according to claim 1, wherein the belt stretching member has a contact portion that contacts an outer peripheral surface of the heat fixing roll at both ends. The contact portion is higher than a thickness of the heat-resistant belt with respect to a surface sandwiching the heat-resistant belt and lower than a thickness obtained by adding a minimum thickness of the sheet material to the thickness of the heat-resistant belt. The fixing device according to 7. The fixing device according to claim 7, wherein the contact portion is higher than a thickness obtained by adding a maximum thickness of the sheet material to a thickness of the heat resistant belt with respect to a surface sandwiching the heat resistant belt. The fixing device according to claim 7, wherein the contact portion is formed integrally with the belt stretching member and uses a member having a thermal conductivity higher than that of the heat-resistant belt. . The fixing device according to claim 7, wherein the contact portion forms a sliding surface that slides in contact with a predetermined length along an outer periphery of the heat fixing roll. The fixing device according to claim 1, wherein the belt stretching member has a sliding surface of the heat-resistant belt facing the heat fixing roll formed concentrically with the heat fixing roll. . An image forming apparatus comprising the fixing device according to claim 1.

Images