JP2006189629A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent axial deflection or creep deformation of a belt tensioning and laying member, and to form a uniform and stable fixing nip over the entire region in the axial direction, by simple configuration. <P>SOLUTION: In a fixing device and an image forming apparatus which are provided with a thermal fixing roll 1, a pressure roll 2 for pressing against the thermal fixing roll 1, a heat resistant belt 3 wound around the outer circumference of the pressure roll 2 and moving while it is held between the thermal fixing roll 1 and the pressure roll 2, the belt tensioning and laying member 4 for tensioning and laying the heat resistant belt 3, and a sliding member 5 arranged between the belt tensioning and laying member 4 and the pressure roll 2, sliding along the outer circumference of the pressure roll 2, and biting the nip part between the thermal fixing roll 1 and the pressure roll 2, and which fix an unfixed toner image formed on a sheet member, the fixing device and the image forming apparatus include: the sliding member 5 arranged between the belt tensioning and laying member 4 and the pressure roll 2, sliding along the outer circumference of the pressure roll 2, and biting the nip part between the thermal fixing roll 1 and the pressure roll 2; and a press means 9 for pressing the belt tensioning and laying member 4 against the thermal fixing roll 1. <P>COPYRIGHT: (C)2006,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, an endless 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 another outlet is provided at the exit of the nip region. A fixing device that applies pressure larger than the portion locally to cause distortion on the elastic body on the surface of the heat fixing roll, and facilitates discharge of the sheet material from the nip portion (see, for example, Patent Document 1) ), A fixing device in which a pressing member provided with a protrusion is provided inside the endless heat-resistant belt so as to reduce a minute pressure region in the contact nip region (for example, Patent Document 2) Irradiation), and the like have been proposed.

  These require a plurality of support rolls and their rotating bearings, so that not only the fixing device is complicated and large, but also expensive, and inevitably, the image forming apparatus equipped with the fixing device is complicated, large, Make it expensive. Moreover, when the perimeter of the heat-resistant belt becomes long and moves along a predetermined path, the heat energy is taken away by the plurality of support rolls, and the natural heat dissipation increases according to the length of the perimeter. 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.

  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 strain 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.

  In addition, the roll is deflected by the pressure set between the rolls to form a nip length in contact with the roll, and a sheet material carrying an unfixed toner image is passed between the nips and fixed to match the characteristics of the sheet material. There has been proposed a fixing device (for example, see Patent Document 3) that selects and drives the roll speed as the first speed or the second speed. However, the roll has a large heat capacity and requires a long warm-up time. Not only is this not preferable, but the sheet material that passes between the long nips formed by bending the roll with pressure, like the former device, is stressed by this pressure and causes deformation of the sheet material such as curls and wrinkles. .

Therefore, as a solution to the above-described problem, the nip is formed by winding the heat-resistant belt around the heat-fixing roll from the tangent line of the pressing portion between the heat-fixing roll and the pressure roll at the upstream side in the moving direction of the heat-resistant belt. By placing it at the forming position and supporting it in a swingable manner, the structure of the heat roll type fixing device can be simplified, reduced in size and cost can be reduced, the warm-up time can be shortened, and the stress on the sheet material can be reduced. A fixing device (see, for example, Patent Document 4) that can suppress deformation of the discharged sheet material such as curling and wrinkling is proposed.
Japanese Patent No. 3084692 Japanese Patent No. 3480250 Japanese Patent Publication No. 8-40235 Japanese Unexamined Patent Publication No. 2004-4234

  However, the structure of each of the conventional fixing devices proposed so far is an effective means for improving the fixing characteristics, but in the axial direction of the heat fixing roll and the pressure roll, that is, in the longitudinal direction. It is not sufficient to form a stable contact nip area throughout. That is, the contact nip area has a delicate relationship with deformation such as axial bending of the heat fixing roll or pressure roll by pressing, or bending or warping of the pressing member or stretching member, and twisting in the axial direction. Under the present circumstances, it is difficult to eliminate the instability of the contact nip area, and the fixing characteristics cannot be improved.

  In addition, creep deformation may occur under the influence of a high temperature of about 200 ° C. generated by the heat fixing roll, particularly in the case of a stretch member formed of a plastic material having a small heat capacity that is effective for shortening the warm-up time. This phenomenon appears remarkably, and there are cases where it is not preferable for the formation of a stable fixing nip.

  SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem, and a contact nip region in which a nip is formed by wrapping a heat-resistant belt around a heat-fixing roll from a tangent line of a pressing portion between the heat-fixing roll and the pressure roll is stabilized with a simple configuration. Thus, the belt stretching member can be prevented from bending in the axial direction and creep deformation, and a uniform and stable fixing nip can be formed over the entire axial direction, thereby improving the fixing characteristics.

  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, and an image forming apparatus, comprising: a belt stretching member that stretches the heat-resistant belt; A sliding member that slides along the outer periphery of the pressure roll and bites into a nip portion between the heat fixing roll and the pressure roll, and a pressure that presses the belt stretching member toward the heat fixing roll. It has the means.

  The sliding member has a surface abutting on the nip portion side formed on a curved surface corresponding to a curvature of the heat fixing roll including a thickness of the heat-resistant belt, and the belt stretching member includes the sliding member on the curved surface. And a pressing portion that presses in the direction of the heat fixing roll, and the pressing portion has a plurality of protrusions on an integral wall portion.

  The belt stretching member is rotatably supported on the heat fixing roll side with the back edge as a fulcrum, and contacts the heat fixing roll through the heat-resistant belt, and the contact portion is flat. A plurality of slits are formed in a direction perpendicular to the axial direction in a portion excluding the contact portion, and the heat fixing is performed at a position where the sheet material is guided to the nip portion via the heat-resistant belt when entering the sheet material. It is characterized by being disposed in non-contact with the roll.

  Between the sliding member and the belt stretching member, the sliding member is pressed against the outer periphery of the pressure roll, and the belt stretching member is tensioned to the heat-resistant belt to be stretched. A spring urging means is provided, and the spring urging means is provided with a plurality of springs parallel to the axial direction of the pressure roll.

  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 belt tension member that stretches the heat-resistant belt, and is disposed between the belt tension member and the pressure roll and slides along the outer periphery of the pressure roll to Since it has a sliding member that bites into the nip portion and a pressing means that presses the belt stretching member toward the heat fixing roll, the sliding member bites into the nip portion of the heat fixing roll and the pressure roll to form a nip. It can be stabilized by a simple configuration including the contact nip region, can prevent axial deflection and creep deformation over the entire axial direction, can form a uniform and stable fixing nip, and can improve the fixing characteristics. Accordingly, it is possible to form a fixing nip in which the pressing state is continuous from a portion where the sliding member abuts along the outer periphery of the heat fixing roll to a portion where the pressure roll is pressed against the heat fixing roll.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows one embodiment of a fixing device according to the present invention. FIG. 1A is a cross-sectional view taken along the line XX of FIG. FIG. 4 is a cross-sectional view taken along the line YY in FIG. 1A and viewed in the direction of the arrow, with the right half of the device omitted. 2 is a perspective view seen from the pressure roll side of the belt stretching member of the fixing device shown in FIG. 1, and FIG. 3 is a perspective view seen from the pressure roll side of the nip pressing member of the fixing device shown in FIG. 4 is an enlarged view of a fixing nip portion of the fixing device shown in FIG. In the figure, 1 is a heat fixing roll, 2 is a pressure roll, 3 is a heat resistant belt, 4 is a belt tension member, 4a is a belt sliding surface, 4b is a protruding wall, 4c is a spring receiving portion, and 4d is an integral wall. Part, 4e is a pressing part, 4f is a wall part, 4g is an open part, 4h is a flat surface, 5 is a nip pressing member, 5a is a flange, 5b is a sliding contact part, 5c is a pressing part, 5d is a tip part, 5e is Cutout portions, 5f are spring arrangement portions (holes), 6, 9 are springs, and 7 is a frame.

  In FIG. 1, a heat fixing roll 1 is formed by, for example, using a pipe material having an outer diameter of about 25 mm and a thickness of about 0.7 mm as a roll base material 1b and covering an outer periphery of an elastic body 1c with a thickness of about 0.4 mm. The roll base 1b has a built-in rotation of 1050W as a heating source and two columnar halogen lamps 1a. The pressure roll 2 is formed by, for example, forming a pipe material having an outer diameter of about 25 mm and a wall thickness of about 0.7 mm by coating a roll base material, and further covering an outer periphery of the elastic body having a thickness of about 0.2 mm. 1 is arranged so that the pressure contact force F between the heat fixing roll 1 and the pressure roll 2 is 10 kg or less, the nip length is about 10 mm, and is rotatable in the direction of the arrow R shown in the figure. . As shown in FIG. 1B, 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.

  The heat-resistant belt 3 is an endless belt that is sandwiched between the heat fixing roll 1 and the pressure roll 2 and is stretched around the outer periphery of the pressure roll 2 and the belt stretching member 4 so as to be movable. It is composed of a metal tube such as a stainless steel tube or a nickel electroformed tube having a thickness of 0.03 mm or more, and a heat-resistant resin tube such as polyimide or silicon.

  The belt stretching member 4 is inserted into the inner periphery of the heat-resistant belt 3 to apply tension f to the heat-resistant belt 3 between the pressure roll 2 and more than the nip portion between the heat fixing roll 1 and the pressure roll 2. On the upstream side of the sheet material S in the conveying direction, a substantially half-moon-shaped sliding member (heat-resistant belt 3 is placed on the belt stretching member 4) is disposed at a position where the heat-resistant belt 3 is wound around the heat-fixing roll 1 to form a nip. The member which slides. The belt stretching member 4 is disposed so as to be swingable in the direction of the arrow W around the rotation shaft 2a of the pressure roll 2, and the heat-resistant belt 3 is attached to the heat fixing roll while the sheet material S does not pass through the fixing nip. 1 is stretched in the tangential direction.

  The nip pressing member 5 includes a slidable contact portion 5 b that slidably contacts along the outer periphery of the pressure roll 2 and a pressing portion 5 c that presses the heat-resistant belt 3 against the heat fixing roll 1 on the upstream side of the nip portion. A sliding member that slides. The nip pressing member 5 is lightly biased in the direction of the pressure roll 2, so that a frictional force acts on the outer periphery of the nip pressing member 2 along with the rotation of the pressure roll 2, and the pressing portion 5 c becomes a heat resistant belt. 3 is pressed against the heat fixing roll 1 and its tip bites into the nip portion.

  As shown in FIG. 2, the belt stretching member 4 has protruding walls 4b for restricting meandering of the heat-resistant belt 3 at both ends or one end of the belt sliding surface 4a, and a spring arrangement of a nip pressing member 5 described later. A spring receiving portion 4c is provided at a position on the back side of the belt sliding surface 4a facing the portion 5f. The pressing portion 4e contacts and presses against the edge portion of the back side wall surface of the pressing portion 5c of the nip pressing member 5 and rotates toward the heat fixing roll 1 with the edge portion serving as a rotation fulcrum to fix the heat-resistant belt 3 to heat. It is arranged so as to press against the roll 1. The relative positional relationship between the belt tension member 4 and the heat fixing roll 1 is determined in a state in which the heat-resistant belt 3 is stretched between the pressure roll 2 and the belt tension member 4 and tension is applied, and a fine relationship is established. However, it is not in a state parallel to the axial direction with respect to the heat fixing roll 1, but is a so-called skewed relative relationship, or is affected by straightness such as warping or bending of the belt stretching member 4. In such a case, if the belt tension member 4 that is lightly pressed from the inside of the heat-resistant belt 3 to the heat-fixing roll 1 has a cylindrical curved surface, the belt tension is applied from the inside of the heat-resistant belt 3 to the heat-fixing roll 1. There is a case where the fixing nip aspect cannot be uniformly formed at the portion where the frame member 4 is lightly pressed. However, if the belt tensioning member 4 is lightly pressed from the inside of the heat-resistant belt 3 to the heat fixing roll 1 with the flat surface 4c, the uneven state of the fixing nip at this portion can be alleviated. A preferable fixing nip can be easily formed.

  Furthermore, if a stable nip is formed at a site where the belt tension member 4 is lightly pressed, the sliding friction force between the heat resistant belt 3 and the belt stretching member 4 corresponds to the sliding friction force generated from the tension of the heat resistant belt 3. Added. Accordingly, when the heat-resistant belt 3 is driven by the pressure roll 2, an intermediate region between a portion where the belt tension member 4 is lightly pressed against the heat fixing roll 1 and a portion where the pressure roll 2 is pressed against the heat fixing roll 1. In the intermediate region of the fixing nip, a continuous fixing nip in a pressed state in which the heat-resistant belt 3 is pressed by the curved surface of the pressing portion 5c of the nip pressing member 5 and wound around the heat fixing roll 1 can be formed.

  As shown in FIG. 3, the nip pressing member 5 is formed with flanges 5a at both ends and extends to both end surfaces of the pressure roll 2 and the belt stretching member 4, with the pressure roll 2 and the belt stretching member 4 at the end surfaces. It is a guide part which contacts and guides. The portion of the guide portion that contacts the pressure roll 2 and the end surface of the belt stretching member 4 may be a slidable contact surface, a plurality of protrusions, a rotating ball or roller, or these may be the nip pressing member 5. You may provide in the other party. Further, the nip pressing member 5 includes a plurality of arcuate protrusions 5b 'which are arranged on the inner surface as sliding contact portions 5b at substantially equal intervals in the axial direction and are slidably contacted along the outer periphery of the pressure roll 2, and the nip portions. A slidable contact surface 5 b ″ is formed in which the entire surface is slidably contacted with the pressure roll 2 continuously at the tip of the side. It has a curved surface corresponding to the curvature of the heat-fixing roll 1 including the thickness of the heat-resistant belt 3 to be pressed, and the protruding pressing portion 4e of the belt stretching member 4 abuts on the back surface of the pressing portion 5c. It is like that.

  Thus, the tip 5d of the nip pressing member 5 has a wedge-shaped acute angle with a predetermined curvature as shown in FIGS. The entire surface in the axial direction is slidably contacted with the outer periphery with a constant width, and the pressing portion 5c presses against the heat fixing roll 1 over the entire surface in the axial direction via the heat-resistant belt 3, and bites into the nip portion between the heat fixing roll 1 and the pressure roll 2. Even if the rigidity is reduced due to this, since the deformation of the shape is restricted by the heat fixing roll 1 and the pressure roll 2, a plastic material with low rigidity that has a small heat capacity and is effective in shortening the warm-up time, etc. Even with this member, it is possible to maintain the desired stable shape by preventing the contact of the nip portion from becoming unstable due to insufficient rigidity of the tip 5d or due to thermal deformation, and ensuring sufficient nip pressing force even at the tip 5d. Can be thin, lightweight In addition, a notch portion 5e is provided in a portion other than the nip portion of the nip pressing member 5, that is, a portion on the opposite side to the heat fixing roll 1 side to form a discontinuous and open portion. As a result, even if the nip pressing member 5 is heated from the heat fixing roll 1 side and a temperature difference occurs between the nip pressing member 5 and the opposite side, distortion and deformation due to the difference in thermal expansion can be prevented.

  Further, in the present embodiment, the nip pressing member 5 has a spring arrangement portion (hole) 5f formed on the back side of the sliding contact portion 5b, and the spring 6 is provided between the belt arrangement member 4 and the spring arrangement portion 5f. It is arranged. Then, as shown in FIG. 1B, with the flange 5a as a guide portion, the end face of the pressure roll 2 and the flange 5a are in contact with each other, and the pressure roll 2 and the belt stretching member 4 are connected between the flanges 5a of the nip pressing member 5. The nip pressing member 5 and the belt stretching member 4 are positioned with respect to the pressure roll 2. With this configuration, a tension corresponding to the urging force of each spring 6 acts on the belt stretching member 4, and a tension f is applied to the heat-resistant belt 3. At the same time, the rotational force of the pressure roll 2 is transmitted to the nip pressing member 5 by the frictional force with the sliding contact portion 5b, and the heat-resistant belt 3 can be pressed against the heat fixing roll 1 via the pressing portion 5c.

  Further, as the heat-resistant belt 3 is driven, the belt stretching member 4 is oscillated and biased toward the heat fixing roll 1 by the frictional force between the heat-resistant belt 3 and the belt sliding surface 4a. Since the part 4e presses the back side of the pressing part 5c of the nip pressing member 5, the pressing force of the pressing part 5c is added. Further, if the urging force of the spring 9 is applied to the flange 5a in the direction of the arrow W as shown in FIGS. 1B and 4, the pressing force of the pressing portion 5c can be further increased.

  FIG. 5 is a cross-sectional view showing a modification of the fixing device of FIG. 1, and FIG. 6 is a diagram showing changes in the nip passage position and fixing pressure. In FIG. 1, a protruding sliding contact portion 5b having a curvature surface substantially the same as the outer peripheral surface of the pressure roll 2 is formed on the inner surface of the nip pressing member 5, and the pressure roll 2 is interposed via the sliding contact portion 5b. However, in the embodiment shown in FIG. 5, the sliding contact portion 5 b has a vector resultant force at two positions 5 b ′-1 and 5 b ′-2 along the outer peripheral surface of the pressure roll 2. The nip pressing member 5 is in sliding contact.

  The fixing pressure corresponding to the nip passing position varies depending on the sheet material thickness as shown in FIG. 6, but the portion where the nip pressing member 5 presses from the portion where the belt stretching member 4 presses from the initial nip position. The fixing pressure is increased by pressing with the pressure roll 2 at the nip end position, and a more stable fixing nip can be formed. The change in the fixing pressure is indicated by a dotted line for the thick sheet material, a solid line for the standard thickness sheet, and a two-dot chain line for the thin sheet material.

  7 is a view showing another embodiment in which the heat-resistant belt is pressed against the heat fixing roll by the nip pressing member and the belt stretching member, and FIG. 8 is a view from the pressure roll side of the belt stretching member of the fixing device shown in FIG. FIG. 9 is a diagram showing changes in the nip passage position and the fixing pressure, and FIG. 10 is a diagram showing changes in the nip passage position and the fixing pressure when the spring urging force of the belt stretching member is increased.

  7, the belt stretching member 4 is disposed in a non-contact manner with the heat fixing roll 1 at a position where the sheet material S is guided to the nip portion via the heat-resistant belt 3 when the sheet material enters, and as shown in FIG. On the fixing roll 1 side, that is, on the downstream side of the belt sliding surface 4a, an axially integral wall portion 4d and a plurality of protruding pressing portions 4e that press against the nip pressing member 5 on the wall portion 4d are pressed. In addition to being provided at intervals, a wall portion 4f on the upstream side of the belt sliding surface 4a and an open portion (slit portion, notch portion) 4g opened discontinuously on the belt sliding surface 4a are provided. If the fixing pressure is large at the initial position where the sheet material S enters the fixing nip, the entry may not be smoothly performed and the sheet material S may be fixed with the leading end of the sheet material S broken. When the roll 1 is stretched in the tangential direction, an introduction port portion in which the sheet material S can smoothly enter can be formed, and the sheet material S can be stably entered.

  As shown in FIG. 9, the fixing pressure at the nip passing position becomes a fixed fixing pressure by the pressing of the nip pressing member 5 from the initial nip position in the nip region, and the fixing pressure by the pressing roll 2 at the nip end position. Get higher. The change in fixing pressure is indicated by a dotted line for a thick sheet material, a solid line for a standard thickness sheet, and a two-dot chain line for a thin sheet material.

  In the previous embodiment, the spring 9 is disposed at a portion where the nip pressing member 5 is lightly pressed against the heat fixing roll 1, but at the end of the protruding wall 4 b of the belt stretching member 4 opposite to the heat fixing roll 1. It is good also as a light press urging means which is arrange | positioned between frames and spring-biased the belt stretching member 4 in the direction lightly pressed to the heat fixing roll 1 from the inner side of the heat-resistant belt 3. The belt tensioning member 4 presses the back side of the pressing portion 5 c of the nip pressing member 5 by such an urging of the spring 9, and the pressing portion 5 c of the nip pressing member 5 is lightly applied to the heat fixing roll 1 from the inside of the heat-resistant belt 3. When pressed and brought into sliding contact with the thermal fixing roll 1, the fixing pressure can be increased even at the initial nip position as shown in FIG. Of course, even if the spring 9 is omitted, it is possible to perform positioning with a desired pressing force by the frictional force between the pressure roll 2 and the nip pressing member 5 and the frictional force between the heat-resistant belt 3 and the stretching member 4.

  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.

  Furthermore, according to this 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 S after fixing is wound around the heat fixing roll 1 or the heat-resistant belt 3. Since it is not attached, means for forcibly peeling the sheet material S becomes unnecessary. If a PFA layer of about 30 μm is provided on the surface of the elastic body 1 c of the heat fixing roll 1, the rigidity is improved by that amount and a substantially uniform elastic deformation is formed to form a so-called horizontal nip, thereby forming the heat fixing roll 1. Thus, there is no difference in the conveying speed of the heat-resistant belt 3 or the sheet material S with respect to the peripheral speed, and extremely stable image fixing is possible.

  If the belt stretching member 4 is a non-rotating member that slides the heat-resistant belt 3 as in the present embodiment, a bearing structure or the like is not necessary because the belt stretching member 4 is not a rotating member, and thus 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 on the pressure roll 2 side in the direction of the half-moon notch, and is arranged close to the pressure roll 2 to the limit. Is possible. 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.

  Since the heat-resistant belt 3 moves along the minimum necessary path, it is heated at the nip portion with the heat fixing roll 1 that has a built-in heating source and can be rotated, and the thermal energy lost when moving along the predetermined path is minimized. Can be suppressed. Furthermore, since the perimeter can be shortened, there is little temperature drop due to natural heat dissipation, and so-called warm-up time from when the power is turned on to when a desired temperature is reached and fixing becomes possible can be shortened. In addition, as shown in FIG. 1, 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 nip. The length can be increased, the structure is simplified, and the size can be reduced and the cost can be reduced.

  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.

  Further, in order to stably fix the unfixed toner image formed on the sheet material S, it is essential to sufficiently melt and fix the unfixed toner image, and a desired temperature and melting time are required. However, according to the configuration of the present embodiment, as shown in FIG. 1, the heat-resistant belt 3 is stretched by the belt stretching member 4 to apply tension, and is wound around the heat fixing roll 1 to form a nip. An elastic body coated on the surface of the heat fixing roll 1 in order to make the nip length long by pressing with the pressure roll 2 from inside 3 and lightly pressing with the nip pressing member 5 and the belt stretching member 4. There is no need for a means for greatly distorting and increasing the nip length, and the elastic body 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 S 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 is small, deformation of the sheet material S such as wrinkles on the sheet material 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.

  The belt stretching member 4 has a crown shape in which the vicinity of the center in the axial direction in which the heat-resistant belt 3 slides protrudes slightly convex so that the tension f applied to the heat-resistant belt 3 near the center is increased. The heat-resistant belt 3 can be smoothly slid on the sliding surface of the belt stretching member 4 and the belt stretching member 4 is deformed so as to obtain a substantially straight state. It can also be. It is effective for forming a stable fixing nip that the crown shape is formed not only in the direction in which the heat-resistant belt 3 is stretched but also in the direction in which the heat-fixing roll 1 is lightly pressed.

  Further, as shown in FIG. 1, if the line passing through the axis of the spring 6 is set on the line passing through the position shifted outward from the axis of the rotary shaft 2a of the pressure roll 2 with respect to the heat fixing roll 1, the belt tension. The direction in which the frame member 4 is urged is a direction in which the component of the urging force presses the heat-resistant belt 3 against the heat fixing roll 1. In this case, the reaction force acting on the nip pressing member 5 by the spring 6 is in a direction opposite to the sliding direction with the rotation of the pressure roll 2, so that at least the rotation of the pressure roll 2 is caused by the reaction force. Accordingly, the frictional force acting on the sliding contact portion 5b of the nip pressing member 5 is set to be larger. As a result, the component force of the urging force applied to the belt stretching member 4 is added to the pressing force for lightly pressing the heat-resistant belt 3 against the heat fixing roll 1. From the portion where the nip pressing member 5 is lightly pressed to the heat fixing roll 1 to the portion where the pressure roll 2 is pressed to the heat fixing roll 1, the heat-resistant belt 3 is wound around the heat fixing roll 1 to form a continuous fixing nip. As a result, a more stable fixing nip can be formed.

  When a heat-resistant belt 3 that is attached to the outer periphery of the pressure roll 2 and is sandwiched and moved between the heat-fixing roll 1 is stretched by the belt-stretching member 4 and wound around the heat-fixing roll 1, a belt tension is formed. The frame member 4 is deflected in the axial direction, or creep deformation occurs due to the influence of the heat fixing roll 1 having a high temperature of about 200 ° C. In particular, when the belt stretching member 4 is made of a plastic material having a small heat capacity as effective for shortening the warm-up time, this phenomenon appears remarkably and is not preferable for forming a stable fixing nip. In the present embodiment, the belt tension member 4 is subjected to a tension according to the urging force of each spring 6 over the entire axial direction. Since it can be prevented by the width, a uniform and stable fixing nip can be formed over the entire axial direction.

  FIG. 11 is a diagram illustrating a setting example of the fixing pressure distribution by the spring. When a configuration in which a plurality of springs 6 are provided between the belt stretching member 4 and the nip pressing member 5 to apply tension to the heat-resistant belt 3 as in the present embodiment is adopted, the biasing force of the plurality of springs 6 is reduced. Depending on the selected combination of adjustment and biasing force, a desired fixing pressure distribution can be arbitrarily set in the axial direction of the belt stretching member 4 according to the purpose.

  FIG. 11A shows the urging forces of the plurality of springs 6 that are selectively arranged so as to have an evenly distributed fixing pressure. When an unfixed toner image formed on a sheet material is fixed by passing through the fixing nip portion, fixing characteristics such as fixing strength and fixing gloss depend on the temperature and pressure of the fixing nip portion. Therefore, a uniform fixed image can be obtained over the entire area of the sheet material by configuring at an evenly distributed fixing pressure.

  In FIG. 11B, the urging forces of the plurality of springs 6 are selectively arranged so that the fixing pressure distribution is large at the center and small at both ends. When axial deformation of the heat fixing roll 1, the pressure roll 2, the belt stretching member 4, and the nip pressing member 5 occurs, the fixing pressure at the center portion decreases and an undesirable state occurs. By setting the central portion of the belt stretching member 4 to be large and the both end portions to be small, it is possible to obtain a fixed image having a uniform fixing characteristic over the entire sheet material.

  In FIG. 11C, the biasing forces of the plurality of springs 6 are selectively arranged so that the fixing pressure distribution is large at both ends and small at the center. When an unfixed toner image formed on a sheet material is fixed by passing through the fixing nip portion, wrinkles or the like may occur in the center portion of the sheet material due to the balance between the fixing pressure and the sheet material conveyance force. As countermeasures in this case, generally, a roll pair having a reverse crown shape in which the central portion of the outer diameter of the pressure roll or the heat fixing roll is thinned to increase the conveying force at both ends of the sheet material can be coped with. However, according to the present embodiment, the urging force of the plurality of springs 6 is set so that both ends of the belt stretching member 4 are large and the center is small, thereby increasing the sheet material conveying force at both ends. It can be generated at the center of the sheet material by increasing the conveying force at both ends of the sheet material using the reverse crown-shaped roll pair in which the center part of the outer diameter of the pressure roll or heat fixing roll is thinned. The effect equivalent to the content of preventing wrinkles can be exhibited.

  FIG. 11D shows a case where the urging forces of the plurality of springs 6 are set so as to increase at both end portions and the central portion of the belt stretching member 4, and the fixing pressure obtained by combining FIGS. 11B and 11C. It has a distribution, and can increase the fixing pressure at the center and increase the sheet material conveying force at both ends.

  FIG. 12 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, 21b is a rotary polygon mirror, 29 is a transfer belt unit, 30 is a paper feed unit, 40 is fixing means, W is an exposure unit, and D is an image forming unit.

  The image forming apparatus 10 of the present embodiment includes a housing 10a, a paper discharge tray 10c formed on the top of the housing 10a, and a door body 10b that is attached to the front surface of the housing 10a so as to be openable and closable. 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, and a paper feed unit 30, and a paper conveyance unit 11 is arranged in the door body 10b. Yes. 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. Each of the image forming stations Y, M, C, and K includes an image carrier 17 composed of a photosensitive drum, and a charging unit 19 and a developing unit 20 disposed around the image carrier 17. 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 roller 13 disposed obliquely above the drive roller 12, and a backup roller (tension roller). ) 14, an image transfer conveyance means 18 comprising an intermediate transfer belt that is stretched between these three or at least two rollers and driven to circulate in the direction indicated by the arrow (counterclockwise direction X), and an image transfer conveyance means 18 And a cleaning means 15 that abuts against the surface. The driven roller 13, the backup roller 14, and the image transfer / conveying means 18 are disposed in a direction inclined to the left in the drawing with respect to the driving roller 12, so that the belt conveying direction X 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 driving roller 12. Then, the image carrier 17 contacts 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 figure. 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 can be adjusted by controlling the tension applied to the image transfer / conveying means 18 by the tension roller 14, the arrangement interval of the image carrier 17, the winding angle (arch curvature), and the like. .

The drive roller 12 also serves as a backup roller for the secondary transfer roller 39. For example, a rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roller 12, and the secondary transfer roller is grounded through a metal shaft. This is a conductive path for the secondary transfer bias supplied through the terminal 39. Further, by making the diameter of the driving roller 12 smaller than the diameters of the driven roller 13 and the backup roller 14, the recording paper after the secondary transfer can be easily separated by the elastic force of the recording paper itself. Further, the driven roller 13 is also used as a backup roller for the cleaning means 15 described later.

  The primary transfer member 16 is disposed at a position in contact with the inner side of the image transfer / conveyance means as a transfer bias applying means for forming an image by sequentially superimposing and transferring the toner images. For example, a conductive roller or a rigid contactor rotated in contact with the image transfer conveying means, a conductive elastic member such as a leaf spring, or a conductive group formed by a fiber group such as a resin. It can also be configured with a nature brush or the like.

  As described above, in the image forming apparatus according to the present embodiment, a plurality of image carriers 17 are arranged in parallel, and the endless sleeve-like shape is flexible with a posture having substantially the same winding angle with respect to each image carrier 17. The image transfer / conveying means 18 is placed in contact and is stretched and rotated around at least two rollers 12 and 13. The image transfer / conveying means 18 is tensioned by any of the rollers 12 and 13 to carry the image. The toner image of the body 17 is configured to be sequentially superimposed and transferred, and substantially the same nip is easily formed at the contact portion between the image carrier 17 and the image transfer conveying means 18 according to substantially the same winding angle. The contact pressure is also substantially the same.

  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 roller 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 present embodiment, the scanning optical system B is disposed below the apparatus, and the scanner means 21 is disposed at the bottom of the case to minimize the vibration that the polygon motor 21a itself gives to the entire case. By reducing the number of polygon motors 21a to one, vibration applied to the entire case is minimized. Further, the image stations Y, M, C, and K are arranged in an oblique direction, and the image carrier 17 is arranged in parallel upward along an oblique arched line so that the toner storage container 26 is inclined obliquely downward. Arranged.

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

  In the present embodiment, the fixing unit 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 formation 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. Further, since the image transfer conveying means 18 is arranged in a direction inclined with respect to the drive roller 12, a large space is generated in the right side space in the figure, and the fixing means 40 can be arranged in the space, thereby making the apparatus compact. And the heat generated by the fixing unit 40 is prevented from being transmitted to the exposure unit W, the image transfer / conveying unit 18 and the image forming stations Y, M, C, and K located on the left side. be able to. Since the exposure unit W can be arranged in the lower left space of the image forming unit D, the vibration of the scanning optical system B 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. And deterioration of image quality can be prevented.

  In the above embodiment, the intermediate transfer belt is configured to come into contact with the image carrier 17 as the image transfer conveyance unit 18. However, the sheet material is adsorbed and conveyed on the surface, and the toner images are sequentially superimposed on the surface of the sheet material. Alternatively, a sheet material conveying belt that forms and conveys an image by transferring the image may be configured to contact the image carrier 17 as the image transfer conveying means 18. In this case, the difference from each of the above embodiments is that the belt conveyance direction of the sheet material conveyance belt which is 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-described embodiment, a spring is disposed between the belt stretching member and the nip pressing member, tension is applied to the heat-resistant belt by the belt stretching member, and the reaction force causes the nip pressing member to the pressure roll. Although configured to be lightly pressed, each may be configured to be biased separately. Further, the guide portion by the flange of the nip pressing member may be provided only in any one of them by a configuration in which the belt stretching member and the nip pressing member are supported and spring-biased. Furthermore, although a substantially half-moon-shaped sliding member is used as the belt stretching member, it may be configured using one or more stretching rolls. For example, the nip pressing member of this embodiment may be added between a belt stretching member using a sliding member or a roll member of a fixing device proposed in Patent Document 4 and a pressure roll. The nip pressing member is configured so as to be similarly arranged upstream of the fixing nip between the pressure roll and the heat fixing roll in the fixing apparatus having the conventional configuration including the fixing apparatus in which no other heat-resistant belt is interposed. May be.

1 is a diagram for explaining an embodiment of a fixing device of the present invention. FIG. FIG. 2 is a perspective view of a belt stretching member of the fixing device illustrated in FIG. 1 viewed from a pressure roll side. FIG. 2 is a perspective view of a nip pressing member of the fixing device shown in FIG. 1 viewed from a pressure roll side. FIG. 2 is an enlarged view showing a fixing nip portion of the fixing device shown in FIG. 1. FIG. 8 is a view showing a modification of the fixing device shown in FIG. 1. It is a figure which shows the change of a nip passage position and fixing pressure. It is a figure which shows the change of a heat fixing roll nip passage position and fixing pressure with a heat-resistant belt by a nip pressing member and a belt stretching member. It is a figure which shows other embodiment pressed against. It is the perspective view seen from the pressure roll side of the belt stretching member of the fixing device shown in FIG. It is a figure which shows the change of a nip passage position and fixing pressure. It is a figure which shows the change of the nip passage position and fixing pressure which enlarged the spring urging | biasing force of the belt stretching member. It is a figure which shows the example of a setting of the fixing pressure distribution by a spring. 1 is a schematic cross-sectional view illustrating an example of an image forming apparatus according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Thermal fixing roll, 2 ... Pressure roll, 3 ... Heat-resistant belt, 4 ... Belt tension member, 4a ... Belt sliding surface, 4b ... Projection wall, 4c ... Spring receiving part, 4d ... Integrated wall part, 4e ... Pressing part, 4f ... Wall part, 4g ... Open part, 4h ... Flat surface, 5 ... Nip pressing member, 5a ... Flange, 5b ... Sliding contact part, 5c ... Pressing part, 5d ... Front end, 5e ... Notch part 5f: Spring arrangement part (hole), 6, 9 ... Spring, 7 ... Frame

Claims (11)

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 that fixes an unfixed toner image formed on a sheet material, and is disposed between the belt stretching member and the pressure roll and extends along an outer periphery of the pressure roll. And a sliding member that slides into the nip portion between the heat fixing roll and the pressure roll, and a pressing unit that presses the belt stretching member toward the heat fixing roll. 2. The fixing device according to claim 1, wherein a surface of the sliding member that abuts on the nip portion side is formed as a curved surface corresponding to a curvature of the heat fixing roll including a thickness of the heat-resistant belt. . The fixing device according to claim 2, wherein the belt stretching member includes a pressing portion that presses the sliding member on the back side of the curved surface in the heat fixing roll direction. The fixing device according to claim 3, wherein the pressing portion is provided with a plurality of protrusions on an integral wall portion. The belt stretching member is rotatably supported on the heat fixing roll side with the edge portion on the back side as a fulcrum, and abuts on the heat fixing roll through the heat-resistant belt. 5. The fixing device according to any one of 4 above. The fixing device according to claim 5, wherein the belt stretching member is formed with a flat surface at the abutting portion. The fixing device according to claim 5, wherein the belt stretching member is provided with a plurality of slits in a direction orthogonal to the axial direction in a portion excluding the contact portion. 5. The belt fixing member according to claim 1, wherein the belt stretching member is disposed in a non-contact manner with the heat fixing roll at a position where the sheet material is guided to the nip portion via the heat-resistant belt when entering the sheet material. The fixing device according to any one of the above. Between the sliding member and the belt stretching member, a spring is attached in a direction in which the sliding member is pressed against the outer periphery of the pressure roll and tension is applied to the heat-resistant belt. 9. The fixing device according to claim 1, further comprising a spring urging unit that urges. The fixing device according to claim 9, wherein the spring urging unit includes a plurality of springs arranged in parallel with an axial direction of the pressure roll. An image forming apparatus comprising the fixing device according to claim 1.

Images