JP6131814B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that heats a sheet as a recording medium during image formation.

  An image forming apparatus that prints an image on a sheet (printing sheet) by electrophotography includes a fixing device that heats the sheet onto which the toner image is transferred. The toner, which is a color material, is melted by heating and fixed on the paper. The roller-type fixing device includes a heating roller (also referred to as a fixing roller) and a pressure roller that contacts the heating roller to form a nip portion. The sheet is conveyed to the nip portion and heated while passing through the nip portion while being pressurized.

  Generally, an image forming apparatus is configured to be able to use a plurality of sizes of paper. For example, an image forming apparatus in which the dimension in the width direction of the sheet conveyance path (direction perpendicular to the conveyance direction) corresponds to the short side dimension (297 mm) of A3 size conveys sheets of A3 size and smaller size than A3 size. Is possible.

  The fixing device is basically temperature-controlled so that the temperature of the nip portion is uniform over the entire length in the width direction of the conveyance path. In this case, when a sheet having a size in the width direction smaller than the width of the conveyance path is continuously used, a non-sheet passing region in the nip portion where the sheet does not pass is likely to be overheated. This is because, in the non-sheet passing area, unlike the sheet passing area through which the sheet passes, thermal diffusion to the sheet does not occur.

  A method for suppressing overheating of a non-sheet passing region in a fixing device has been proposed. Patent Document 1 discloses an image forming apparatus that includes a cooling fan that blows air from an air outlet in a unit that heats paper, and regulates the opening width of the air outlet according to the width of the paper. Patent Document 2 discloses an image forming apparatus that suppresses a temperature rise at both ends in the width direction of the fixing belt by switching whether the fixing belt is brought into contact with or separated from the plate / heat pipe according to the sheet size. Have been described.

JP 2008-014986 A JP 2006-003804 A

  In the above prior art for preventing overheating of the non-sheet passing region in the fixing device, the fixing device is increased in size because a moving means such as a mechanism for switching the position of the cooling fan or the heat pipe is assembled. Inevitably, a large space for assembling the fixing device inside the image forming apparatus is required, and it is difficult to reduce the size of the image forming apparatus. In addition, it is necessary to control the on / off of the cooling fan by detecting the presence or absence of overheating, or to control the position of the heat pipe. From the viewpoint of energy saving, the use of a cooling fan is particularly disadvantageous. If the positions of the heat pipes are switched uniformly according to the size of the paper to be used, there is a possibility that the heat pipe is brought into contact with the fixing belt in a temperature state that does not require cooling to cool the fixing belt wastefully.

  SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to prevent an excessive temperature rise in a fixing device without using a movable unit that requires external control.

  A fixing device that achieves the above object is a fixing device that heats a sheet when an image is formed on the sheet, and rotates around an axis extending along a width direction of a conveyance path along which the sheet is conveyed. And a rotating body in contact with the sheet, a heating means for heating the rotating body, a heat dissipating body located in the vicinity of the rotating body, and between the rotating body and the heat dissipating body, And a phase change member that is supported by the heat radiating body and expands so that there is no gap between the rotating body and the heat radiating body when a phase change occurs due to temperature rise.

  According to the present invention, the amount of heat conduction between the rotating body and the heat radiating member is switched by increasing or decreasing the volume of the phase change member, so that excessive temperature rise in the fixing device can be achieved without using movable means that requires external control. Can be prevented.

1 is a diagram illustrating an example of a configuration of an image forming apparatus including a fixing device according to an embodiment of the present invention. FIG. 3 is a diagram illustrating an internal structure of a fixing device and a configuration of a control unit. FIG. 3 is a diagram schematically illustrating a first example of a heat dissipation structure of a fixing device. FIG. 3 is a diagram illustrating a configuration of a main part of a fixing device. It is a figure which shows typically the 2nd example of the thermal radiation structure of a fixing device. It is a figure which shows the example of the surface processing of the end surface facing a phase change member. It is a figure which shows typically the 3rd example of the thermal radiation structure of a fixing device. It is a figure which shows typically the 4th example of the thermal radiation structure of a fixing device. It is a figure which shows the modification of a structure of a phase change member. It is a figure which shows the example of the guide member which regulates the direction of the volume change by a phase change. It is a figure which shows typically the 5th example of the structure of the thermal radiation part of a fixing device. It is a graph which shows the relationship between the temperature change in a thermoelectric conversion element, and the electric power generation amount. It is a figure which shows the relationship between the thermal resistance in connection with a thermoelectric conversion element, and a temperature change.

  An image forming apparatus 1 illustrated in FIG. 1 is an electrophotographic color printer. The image forming apparatus 1 includes four imaging stations 11, 12, 13, and 14, which are arranged in parallel with four color toner images of yellow (Y), magenta (M), cyan (C), and black (K). Can be formed. Each of the imaging stations 11, 12, 13, and 14 includes devices necessary for forming a toner image, such as a cylindrical photosensitive member, a charging charger, a developing device, a cleaner, and an exposure light source.

  In color printing, a total of four toner images formed by the imaging stations 11, 12, 13, and 14 are primarily transferred in sequence to the intermediate transfer belt 16 and are superimposed on the intermediate transfer belt 16. In monochrome printing, a black toner image formed by the imaging station 14 is primarily transferred to the intermediate transfer belt 16. The toner image on the intermediate transfer belt 16 is secondarily transferred from the lower stacker 10 to the paper P that is transported along a transport path 15 indicated by a broken line in the drawing. After the secondary transfer, the paper P passes through the inside of the fixing device 20 and is sent to the upper paper discharge tray 18. When passing through the fixing device 20, the toner image is fixed on the paper P by heating and pressing.

  In the illustration of FIG. 2, the fixing device 20 is of an induction heating (IH) type and includes a magnetic flux generator 24 that heats a cylindrical flexible fixing belt 23. The fixing belt 23 rotates with the fixing roller 21 while being supported by the fixing roller 21 and the guide plate 231. The magnetic flux generator 24 has a bobbin 242 along the peripheral surface of the fixing belt 23 and an excitation coil 243 supported by the bobbin 242. Excitation power is supplied to the excitation coil 243 by an AC input unit 41 and an IH (Induction Heating: IH) power source 42.

  In the fixing device 20, a fixing roller 21 disposed inside the fixing belt 23 and a pressure roller 22 disposed outside form a nip portion for fixing with the fixing belt 23 interposed therebetween. The axial direction of the rotation shafts of the fixing roller 21 and the pressure roller 22 is a direction orthogonal to the transport direction M1 of the paper P. For example, when the pressure roller 22 is driven to rotate at a predetermined peripheral speed in a direction (clockwise in the drawing) of feeding the paper P by a driving mechanism (not shown), the fixing belt 23 and The fixing roller 21 rotates following the rotation of the pressure roller 22.

  The fixing roller 21 includes a cored bar 25 made of a nonmagnetic material and a cylindrical elastic body layer 26 surrounding the cored bar 25. The cored bar 25 is a cylindrical body having an outer diameter of about 20 mm made of aluminum, iron, stainless steel, or other metal. The metal core 25 is longer than the elastic body layer 26 and protrudes on both sides of the elastic body layer 26 in the axial direction. The material of the elastic body layer 26 is a foamed elastic body that is excellent in heat resistance and heat insulation, such as silicone rubber and fluororubber. When the thickness of the elastic layer 26 is about 8 mm, the outer diameter of the fixing roller 21 is about 36 mm.

  The pressure roller 22 includes a cylindrical cored bar 27, an elastic body layer 28, and a release layer 29. The material of the core metal 25 is aluminum, for example. The elastic body layer 28 is made of, for example, silicon sponge rubber. The release layer 29 is made of a material such as PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene) coat. The outer diameter of the pressure roller 22 is about 35 mm, for example.

  The fixing device 20 is controlled by a main controller 30 provided in the image forming apparatus 1. The main controller 30 includes a CPU (Central Processing Unit) 31 that comprehensively controls the processing operation of the image forming apparatus 1, a ROM (Read Only Memory) 32 that stores a program for control by the CPU 31, and a program execution work. A RAM (Random Access Memory) 32 used as an area is included. The CPU 31 is connected to the operation input unit 35 and acquires instructions and setting information input by the user.

  In the control of the fixing device 20, the CPU 31 maintains the fixing temperature at the nip portion at a temperature suitable for fixing the unfixed toner image. Specifically, the CPU 31 controls the IH power source 42 so that the temperature detected by the thermistor 43 disposed in the vicinity of the peripheral surface of the fixing roller 21 approaches the target temperature set according to the type of paper. The IH power source 42 increases or decreases the power supplied to the exciting coil 243 of the magnetic flux generator 24 in accordance with a command from the CPU 31. When the fixing belt 23 is heated, the fixing roller 21 and the pressure roller 22 are heated by heat conduction from the fixing belt 23. In other words, the fixing roller 21 and the pressure roller 22 are indirectly heated by the magnetic flux generator 24.

  The heat generation method of the fixing device 20 is not limited to the IH method, and may be a method using a halogen lamp or a ceramic heater as a heat source.

  As shown in FIG. 3, the fixing device 20 includes phase change members 51, 52, 53, 54 and heat radiators 61, 62. The phase change members 51 and 52 are attached to both end faces of the core metal 25 of the fixing roller 21, and the phase change members 53 and 54 are attached to both end faces of the core metal 27 of the pressure roller 22. The radiator 61 is provided at a position about several millimeters away from the phase change members 51 and 53 when in the solid phase, and similarly the radiator 62 is located at a position away from the phase change members 52 and 54 when in the solid state. Is provided. The radiators 61 and 62 are, for example, a housing of the fixing device 20, a metal frame that supports the fixing device 20 inside the housing of the image forming apparatus 1, or a metal plate that is thermally connected to the frame. A structure having excellent thermal conductivity and a large heat dissipation capacity can be used as a heat dissipation body.

  The phase change members 51, 52, 53, 54 are members obtained by molding a phase change material that changes phase at a predetermined temperature into a predetermined shape. In this example, it is formed into a cylindrical shape having substantially the same diameter as the diameters of the core bars 25 and 27. The shape of the phase change members 51, 52, 53, 54 is not limited to a cylindrical shape, and may be other shapes such as a truncated cone, a cube, a rectangular parallelepiped.

  Phase change materials include organic compounds and inorganic compounds. Various substances are known, from substances that cause a phase change from a solid phase to a liquid phase at a low temperature below room temperature depending on the composition, to substances that cause a phase change from a solid phase to a liquid phase at a high temperature exceeding 300 ° C. Yes.

  For example, when the temperature control temperature of the fixing device 20 is set to 160 ° C., a compound of sodium hydroxide and potassium hydroxide that changes phase at about 170 ° C. is used. The phase can be changed when the fixing device 20 is excessively heated. Also. When the temperature control temperature is set to 180 ° C., pentaerythritol that changes phase at about 187 ° C. can be used.

  The phase change members 51, 52, 53, and 54 may be manufactured by selecting a substance that changes phase at a temperature at which the fixing device 20 is desired to start cooling or at a temperature close thereto. Using a substance whose phase change temperature is slightly higher than the temperature control temperature, such as a compound of lithium hydroxide and sodium hydroxide that changes phase at about 210 ° C., the function of the rotating body of the fixing device 20 deteriorates due to excessive temperature rise. There is also a method of performing heat dissipation before it fails or breaks down.

  The phase change material includes a material that expands in volume by 10% to 20% or more with respect to the solid phase during the phase change from the solid phase to the liquid phase. When the ambient temperature falls from the phase change temperature or lower to the phase change temperature or higher, the volume expands, and when the ambient temperature falls from the phase change temperature or higher to the phase change temperature or lower, the volume shrinks to the solid phase volume.

  4A and 4B schematically show the volume change of the phase change member 52. FIG. The volumes of the other phase change members 51, 53, 54 change in the same manner as the phase change member 52.

  As illustrated, the fixing roller 21 is rotatably supported by a support body 82 having a bearing 81 that engages with an end portion of the core metal 25. One end surface of the columnar phase change member 52 is fixed to the end surface of the cored bar 25 slightly protruding from the bearing 71 so as to extend the cored bar 25. An adhesive can be used for fixing. The cored bar 25 corresponds to a part of a rotating body 213 (see FIG. 3) configured by the fixing roller 21 and the fixing belt 23.

  In FIG. 4A, the temperature of the fixing roller 21 and the phase change member 52 is a normal temperature (for example, 20 ° C.) lower than the temperature adjustment temperature. At this time, the phase change member 52 is in a solid phase, and a gap having a gap length g1 exists between the phase change member 52 and the radiator 62. That is, the phase change member 52 is separated from the heat radiating body 62. Therefore, in this state, the heat radiation of the fixing roller 21 is mainly radiation (heat dissipation) around the fixing roller 21. Since the contact area between the bearing 81 and the cored bar 25 is very small, the heat conducted to the bearing 81 is small.

  In FIG. 4B, the temperature at the end of the cored bar 25 is higher than the phase change temperature from the solid phase to the liquid phase of the phase change member 52, and the phase change member 52 is in the liquid phase state. As can be seen from a comparison with FIG. 4A, the expanded phase change member 52 is in contact with the radiator 62. That is, the phase change member 52 and the heat radiator 62 are thermally connected. In this state, heat from the cored bar 25 through the phase change member 52 to the heat radiating body 62 is conducted, and thereby further temperature rise of the cored bar 25 is suppressed.

  The liquid phase change member 52 has moderate plasticity that keeps its volume without flowing down. In this case, when the fixing roller 21 rotates, the portion of the phase change member 52 that is fixed to the cored bar 25 rotates with the cored bar 25. However, the portion of the phase change member 52 that comes into contact with the radiator 62 hardly rotates. The axial center portion of the phase change member 52 is deformed so as to be twisted, and the phase change member 52 remains between the metal core 25 and the heat radiating body 62 without being twisted as a whole.

  The thermal conductivity of air depends on the temperature, but is about 0.02 to 0.03 W / m · K in the environment where the image forming apparatus 1 is used. On the other hand, the thermal conductivity of the phase change material is about 0.3 to 0.5 W / m · K when it is an organic compound, and 1.0 W when it is a hydrated salt or a similar substance. / M · K. Among products marketed as thermal boundary materials, there are products having a thermal conductivity exceeding 5.0 W / m · K.

  By filling the voids with the phase change material, the thermal conductivity increases from about 0.02 W / m · K for air to 5.0 W / m · K for the phase change material, and the thermal conductivity is about 100 to 200 times larger. Can be expected.

  An example in which erythritol is used as the material of the phase change members 51, 52, 53, 54 will be described.

Erythritol changes phase from a solid phase to a liquid phase at 119 ° C. The density of erythritol is about 1480 kg / m ³ in a 20 ° C. environment, and becomes a density of about 1300 kg / m ³ at 140 ° C. when the phase change to the liquid phase is completed. That is, a volume expansion of about 13.8% occurs due to the change from the solid phase to the liquid phase.

  The distance D between the cored bar 25 and the heat radiating body 62 shown in FIG. 4A is usually about 10 mm. Therefore, when erythritol is used as the material of the phase change member 52, the length (column height) L of the phase change member 52 needs to be 8.8 mm or more and the gap length g1 needs to be 1.2 mm or less. is there. The space between the cored bar 25 and the radiator 62 is filled with the phase change member 52 that expands in volume as the phase change member 52 changes from the solid phase to the liquid phase. The thermal resistance between 25 and the heat radiating body 62 decreases.

  When the thermal conductivity of air is 0.027 W / (m · K) and the thermal conductivity when erythritol is changed to a liquid phase is 0.338 W / (m · K), The combined thermal resistance of the resistance and the thermal resistance of erythritol is about 31.2 K / W. On the other hand, the thermal resistance when filled with erythritol is about 0.3 K / W, and is reduced to 10% or less as compared with the thermal resistance when there is a void.

  The material of the phase change members 51, 52, 53, 54 is not limited to erythritol. Even when a substance other than erythritol is used, the same effect as when erythritol is used can be obtained by setting the gap length g1 according to the volume expansion coefficient of the phase change members 51, 52, 53, and 54. .

  It is not restricted to the structure which attaches phase change member 51,52,53,54 to the edge part of the metal cores 21 and 22. FIG. The phase change member can be arranged as follows.

  In the example of FIG. 5, the phase change members 51, 52, 53, 54 are attached not to the cores 25, 27 of the rotating body in the fixing device 20 b but to the positions facing the cores 25, 27 in the radiators 61, 62. It has been.

  In a normal temperature environment, the phase change members 51, 52, 53, 54 are separated from the radiators 61, 62 by a gap length g2. When the phase change member 51, 52, 53, 54 rises in temperature and undergoes a phase change, the phase change member 51, 52, 53, 54 becomes the core metal 25, due to the volume expansion accompanying the phase change as described with reference to FIG. 27, the thermal resistance between the metal cores 25, 27 and the radiators 61, 62 decreases.

  In the configuration of FIG. 5, the form of temperature increase of the phase change members 51, 52, 53, 54 is radiation from the core bars 25, 27 that are heat sources. That is, the phase change members 51, 52, 53, and 54 are less likely to rise in temperature compared to the heat conduction in the example of FIG. Therefore, it is preferable to make the gap length g2 smaller than the gap length g1.

  Processing to increase the water repellency on the end faces of the core bars 25 and 27 that come into contact with or separate from the phase change members 51, 52, 53, 54 with the volume change of the phase change members 51, 52, 53, 54. Can be applied.

  FIG. 6 shows an example of the water repellent finish. In FIG. 6, an end surface S <b> 27 on the side close to the radiator 61 in the core metal 27 is drawn as a representative of the end surfaces of the core bars 25 and 27.

  The end surface S27 is subjected to fine surface processing in which convex portions and concave portions are repeatedly arranged at a constant pitch p. The height of the convex portion (depth of the concave portion) d is about 5 to 20 μm. When the width of the concave portion is a, the width of the convex portion is b, and the sum of the width a and the width b is the pitch p, the ratio of the width a and the width b is the Lotus effect. The water repellency is selected so as to be 2 or less.

  By imparting water repellency, when the phase change members 51, 52, 53, 54 change from the liquid phase to the solid phase and the volume decreases, the phase change members 51, 52, 53, 54 are separated from the end faces of the core bars 25, 27 that have been in contact with each other. It becomes easy. That is, the switching of the thermal resistance between the core bars 25 and 27 and the heat radiating bodies 61 and 62 becomes steep. Not only physical processing, but also chemical processing in which a material having excellent water repellency is coated on the end faces of the phase change members 51, 52, 53, 54 may be used.

  In the fixing device 20 c of FIG. 7, phase change members 55 and 56 are attached to a heat radiator 63 disposed in the vicinity of the pressure roller 22. The heat radiating body 63 faces the circumferential surface of the large diameter portion of the pressure roller 22 over the entire length in the width direction M1 of the sheet conveyance. Phase change members 55 and 56 are disposed on both sides of the small-size sheet passing region As, which is the central portion in the width direction M2, of the portion of the heat radiating body 63 that faces the large diameter portion of the pressure roller 22.

  The small-size sheet passing area As corresponds to a portion through which the sheet passes in the transport path 15 when a sheet having a small size in the width direction M2 is used for printing. When using small size paper, the temperature of the non-sheet passing area on both sides of the small size sheet passing area As is likely to increase on the peripheral surface of the large diameter portion of the pressure roller 22 compared to the small size sheet passing area As. . By disposing the phase change members 55 and 56 in such a non-sheet passing region, overheating of the non-sheet passing region in the pressure roller 22 can be suppressed.

  In FIG. 7, the phase change members 55 and 56 are arranged on the downstream side in the conveyance direction M <b> 1 with respect to the pressure roller 22, but the arrangement position may be on the upstream side in the conveyance direction M <b> 1 or below the pressure roller 22.

  In the example of FIG. 7, the distance between the pressure roller 22 and the radiator 63 is about 10 mm. When erythritol is used as the material of the phase change members 55 and 56 as in the above example, the height of the phase change members 55 and 56 may be 8.8 mm or more and the gap length g3 may be 1.2 mm or less. Due to the change of erythritol from the solid phase to the liquid phase, the phase change members 55 and 56 come into contact with the pressure roller 22, and the thermal resistance between the pressure roller 22 and the radiator 63 is reduced to 10% or less before the contact. To do.

  Also in the configuration of FIG. 7, the material of the phase change members 55 and 56 is not limited to erythritol. Even when a substance other than erythritol is used, the same effect as when erythritol is used can be obtained by setting the gap length g3 according to the volume expansion amount of the phase change members 55 and 56.

  In the example of FIG. 8, phase change members 57 and 58 are disposed inside the heating roller 22d. The elastic body layer 281 exists inside the release layer 291 that is the outermost layer in the large diameter portion of the heating roller 22d. The phase change members 57 and 58 are fixed to the cored bar 27 at portions on both sides of the small size paper passing region As inside the elastic layer 281.

  At normal temperature, a gap exists between the peripheral surface of the cylindrical phase change members 57 and 58 concentric with the core metal 27 and the elastic layer 281. At a temperature higher than normal temperature but lower than the temperature adjustment temperature for fixing, the phase change members 57 and 58 remain in a solid phase and voids remain.

  When the temperature of the phase change members 57 and 58 exceeds the temperature control temperature or a phase change temperature close thereto, the phase change members 57 and 58 change to a liquid phase, and there is no gap between the elastic layer 281 due to volume expansion. Since the release layer 291 and the cored bar 27 overlapping the elastic layer 281 are thermally connected via the phase change members 57 and 58, the heat release performance of the release layer 291 is improved.

  Thereafter, when the heat release from the release layer 291 sufficiently proceeds, the volume of the phase change members 57 and 58 decreases so as to form a gap between the release layer 291 and the release layer 291 and the core metal 27. It returns to the state where the thermal resistance between them is high.

  The case where erythritol is used as the material of the phase change members 57 and 58 as in the above example will be described. Here, it is assumed that the diameter of the core metal 27 is 10 mm and the inner diameter of the elastic body layer 281 of the pressure roller 22d is about 18 mm. In erythritol, volume expansion of about 13.8% occurs during the transition from the solid phase to the liquid phase. Therefore, if the thickness of the phase change members 57 and 58 in the solid phase is 3.6 mm and the outer diameter is approximately 17.2 mm. Good. A gap having a gap length of 0.4 mm that exists between the phase change members 57 and 58 and the elastic body layer 281 in the solid phase can be eliminated by the phase change of the phase change members 57 and 58.

  By setting it as such attachment conditions, a space | gap is lose | eliminated by the volume expansion of the phase change members 57 and 58, and the thermal resistance between the mold release layer 291 and the metal core 27 becomes low. The thermal resistances of air and erythritol are calculated from 1 / (length × thermal conductivity), respectively. When voids are present, the combined thermal resistance of the voids and erythritol is about 93.4 K / W. On the other hand, the thermal resistance when there is no gap is about 0.7 K / W, which is significantly lower than the thermal resistance when there is a gap.

  The material of the phase change members 57 and 58 is not limited to erythritol. Even when a substance other than erythritol is used, the same effect as when erythritol is used can be obtained by setting the gap length in consideration of the volume expansion of the phase change members 57 and 58.

  5, 7 and 8, the heat of the rotating body in the fixing device is transmitted to the phase change member in the form of convection or radiation through the air in the gap. Therefore, a substance having a phase change temperature from the solid phase to the liquid phase lower than the temperature control temperature of the fixing device can be used as the material of the phase change member. Examples of substances that satisfy the condition that the phase change temperature must be higher than room temperature include paraffinic substances and sodium acetate hydrate.

  FIG. 9 shows a modification of the configuration of the phase change member. FIG. 9A is a perspective view schematically showing the overall shape, and FIG. 9B is a cross-sectional view.

  In FIG. 9, the phase change member 59 includes a main body 591 made of a phase change substance and a cylindrical thin container 592 that houses the main body 591. The container 592 has heat resistance that can withstand abnormal temperature rise of the fixing device, abrasion resistance that can withstand rubbing with a surface that contacts the volume expansion, and elasticity that can be deformed in accordance with the volume change of the main body 591. . Examples of the material of the container 592 include resin materials such as polytetrafluoroethylene and polyimide. The shape of the phase change member 59 is not limited to a cylindrical shape.

  FIG. 10 shows an example of the guide member. The exemplary guide member 70 is cylindrical and has a size that allows the phase change member 59 of FIG. As illustrated in FIG. 10C, when the phase change member 59 is attached to, for example, the end surface of the core metal 25, the guide member 70 is disposed so as to surround the phase change member 59. In FIG. 10C, the end face positions on the heat radiating body 61 side of the phase change member 59 and the guide member 70 are aligned, but the present invention is not limited to this. In a normal temperature state, the guide member 70 may slightly protrude from the phase change member 59, and conversely, the phase change member 59 may slightly protrude from the guide member 70. In other words, the axial dimension of the guide member 70 may be a value close to that of the phase change member 59.

  As shown in FIG. 10D, when the volume of the phase change member 59 increases due to the phase change, the guide member 70 prevents the phase change member 59 from expanding in all directions in the radial direction. Thereby, the phase change member 59 mainly expands toward the radiator 61. Guide member 70 serves to regulate the direction of volume change of phase change member 59 in a direction in which the gap between heat radiator 61 and phase change member 59 increases or decreases.

  When the guide member 70 regulates the direction of volume change of the phase change member 59, the increase / decrease in the gap dimension with the radiator 61 due to the volume change of the phase change member 59 becomes significant. In other words, the gap having a predetermined dimension can be eliminated or returned by the phase change member 59 having a smaller volume expansion coefficient than that in the case where the guide member 70 is not used. That is, the choice of the material of the phase change member 59 increases.

  Examples of the material of the guide member 70 include resins having excellent heat resistance such as polyimide resin, polyamideimide resin, and allyl resin.

  FIG. 11 shows another example of the structure of the heat radiating portion in the fixing device. The basic configuration of the illustrated fixing device 20e is the same as the example of FIG.

  The fixing device 20e in FIG. 11 includes a thermoelectric conversion element 72 as a feature thereof. The illustrated thermoelectric conversion element 72 is attached to the radiator 62 so as to face the phase change member 52 attached to one end face of the cored bar 25 in the fixing roller 21. Although not shown, the fixing device 20e further includes three thermoelectric conversion elements in addition to the thermoelectric conversion elements 72. These three thermoelectric conversion elements are attached to the radiators 61 and 62 so as to face the phase change members 51, 53 and 54 attached to the other end face of the core metal 25 and both end faces of the core metal 27 of the pressure roller 22. It is attached.

  There is a gap having a gap length g1 between the phase change member 52 and the thermoelectric conversion element 72 when in the solid phase. In this state, since the thermal resistance of the air in the gap is large, almost no heat is transmitted from the fixing roller 21 to the heat radiating body 62. This means that there is no influence of the phase change member 52 on the heating by the magnetic flux generator 24 immediately after the image forming apparatus 1 is turned on or during the period in which the temperature control is performed before the sheet is passed. The phase change member 52 does not lengthen the time required for raising the temperature of the fixing belt 23.

  When the phase change member 52 expands due to a phase change from the solid phase to the liquid phase, the phase change member 52 and the thermoelectric conversion element 72 come into contact with each other, and one of the thermoelectric conversion elements 72 of the thermoelectric conversion element 72 passes through the phase change member 52 from the core metal 25. Heat is conducted to the surface (heat source side). Then, electric power corresponding to the temperature difference between the heat source side and the heat dissipation side in the thermoelectric conversion element 72 is output from the thermoelectric conversion element 72. The electric power generated by the thermoelectric conversion element 72 is used as part of driving power for various loads in the image forming apparatus 1.

  The graph of FIG. 12 shows the relationship between the temperature change in the thermoelectric conversion element and the amount of power generation. The thermal resistance of the heat conduction path from the cored bar 25 to the thermoelectric conversion element 72 in the configuration of FIG. 11 varies greatly depending on whether or not the phase change member 52 and the thermoelectric conversion element 72 are in contact with each other.

  In FIG. 12, before the time t1, the temperature of the phase change member 52 is equal to or lower than the temperature control temperature, and the phase change member 52 is a solid phase. At this time, air having low thermal conductivity is interposed in the heat conduction path, so that the thermal resistance is large. It is assumed that, before time t1, for example, both ends in the width direction of the fixing belt 23 are excessively heated due to the passage of small-size paper. When the temperature of the phase change member 52 rises to the phase change temperature at time t1, the phase change of the phase change member 52 from the solid phase to the liquid phase starts. As the phase change member 52 expands and approaches the thermoelectric conversion element 72 in the course of the phase change, the thermal resistance gradually decreases.

  When the gap between the phase change member 52 and the thermoelectric conversion element 72 disappears at time t <b> 2, the thermal resistance between the cored bar 25 and the thermoelectric conversion element 72 becomes the thermal resistance of the phase change member 52. After time t2, as long as the contact state between the phase change member 52 and the thermoelectric conversion element 72 does not change, the value of the thermal resistance remains constant at the time t2, which is lower than the time t1.

  When heat from the cored bar 25 is conducted to the thermoelectric conversion element 72 at time t2, the temperature Th on the heat source side of the thermoelectric conversion element 72 starts to rise. The value of the temperature Th before the rise starts is the same as the value of the temperature Tc on the heat dissipation side of the thermoelectric conversion element 72. As the temperature Th rises, the difference from the temperature Tc increases and the amount of power generation increases. After the temperature Th rises to a saturated value, power generation with a certain amount of power generation continues.

  The graph of FIG. 13 illustrates the relationship between the thermal resistance related to the thermoelectric conversion element and the temperature change. In FIG. 13, in two cases where the values of the thermal resistance R between the heat source, the thermoelectric conversion element, and the radiator are different (one is R = 1 K / W and the other is R = 5 K / W), the constant amount of heat Q The temperature change of the thermoelectric conversion element when injecting the heat of is shown.

  Since the heat quantity Q is expressed as Q = (Th−Tc) / R, if the temperature Tc on the heat radiating side is the same, the thermal resistance R is smaller than that when the thermal resistance R is relatively small at 1 K / W. The temperature Th on the heat source side is higher when it is relatively large, such as 5 K / W. In general, the thermoelectric conversion element has a characteristic that the power generation efficiency is better as the temperature difference ΔT between the temperature Th on the heat source side and the temperature Tc on the heat radiation side is larger.

  Here, the phase change member 52 is in a liquid phase, and the thermal resistance R in a state where there is no gap in the heat transfer path from the cored bar 25 (heat source) through the thermoelectric conversion element 72 to the radiator 62 is 1 K / W. Suppose there is. The thermal resistance R is 5 K / W when the phase change member 52 is a solid phase and there is a gap in the heat transfer path from the cored bar 25 to the radiator 62.

  When there is no gap in advance and the thermal resistance R is as low as 1 K / W, the heat applied to heat the fixing belt 23 escapes from the cored bar 25 to the radiator 62 and is necessary for temperature control. The amount of heat increases. Low energy saving. In addition, when generating heat by thermoelectric conversion, if the thermal resistance R is small, the temperature difference ΔT is small, so the power generation efficiency is low.

  On the other hand, when the thermal resistance R is as high as 5 K / W, the amount of heat taken from the cored bar 25 is small as in the case where the surroundings are covered with air, and thus the influence on the heating of the fixing device is small. That is, if the temperature is not excessively increased, the thermal resistance R should be high. When an abnormal temperature rise occurs in the fixing device, heat is dissipated through the thermoelectric conversion element 72, so that the thermoelectric conversion element 72 can generate power at a high power generation efficiency, and energy saving can be improved. .

  According to the above embodiment, during normal fixing operation in which abnormal temperature rise does not occur, there is a gap between the heat source and the heat radiating body and the heat resistance is high, so that heat escape is suppressed and warm-up is performed. There is no effect on the time and power required. On the other hand, when the abnormal temperature increase occurs, the expansion of the phase change member eliminates the gap and lowers the thermal resistance. Therefore, the abnormal temperature increase can be eliminated without requiring power supply or special control. The self-heat dissipation function of the fixing device is realized.

  In the above-described embodiment, the configuration in which the phase change member is arranged on the heat source side as shown in FIG. 3 and the configuration in which the phase change member is arranged on the heat dissipation side as in FIGS.

  The number of phase change members 51 to 59 may be one or more. In the above-described embodiment, a general conveyance format in which the center of the sheet P is positioned at the center in the width direction M2 of the conveyance path 15 is assumed, and both are likely to be overheated when a small size sheet is used in the fixing rotating body. Although the phase change member is arranged with respect to each end, the present invention is not limited to this. When small size paper is conveyed toward one end in the width direction M2 of the conveyance path 15, the phase change member is disposed only on one end opposite to the side where the small size paper is gathered. Good.

  The material, shape and dimensions of the phase change members 51 to 59 are arbitrary, and can be selected according to various conditions such as the distance between the roller and the radiator and the shape of the mounting surface. In the configurations of FIGS. 7 and 8, it is not absolutely necessary to arrange the phase change members 55 to 58 so as to exclude the small-size sheet passing region As. Depending on the temperature distribution characteristics in the width direction M2 of the heat source, the phase change members 55 to 58 may be arranged so as to exclude a range wider than the small-size sheet passing region As or conversely a narrow range.

  The shape and size of the guide member 70 may be selected according to the shape and size of the phase change member 59. The attachment location of the thermoelectric conversion element 72 is not limited to the position on the heat radiating body 62 but may be a position on the heat source side such as the end face of the cored bar 25.

  The configuration of the fixing devices 20, 20b, 20c, and 20e can be changed as appropriate within the scope of the gist of the present invention.

  A type in which the fixing roller 21 directly contacts the paper P without providing the fixing belt 23 may be used. In contrast to driving the pressure rollers 22 and 22d to rotate the fixing roller 20 as illustrated, the fixing roller 20 may be driven to rotate the pressure rollers 22 and 22d. Moreover, you may drive both.

  For the fixing belt 155, for example, a polyimide film containing silver particles is used as a base material (heat generation layer), and an elastic layer made of silicone rubber and a surface release layer of single or mixed resin such as PTFE and PFA are sequentially formed thereon. It can be configured by overlapping. Examples of the material of the substrate include copper, nickel, stainless steel, and a magnetic shunt alloy (for example, Fe—Ni alloy).

1 Image forming apparatus 20, 20b, 20c, 20e Fixing device P Paper (sheet)
15 Conveyance path M2 Width direction 213 Rotating body 21 Fixing roller (rotating body)
22 Pressure roller (rotating body)
24 Magnetic flux generator (heating means)
61, 62, 63 Radiator 51, 52, 53, 54 Phase change member 55, 56, 57, 58, 59 Phase change member 25, 27 Core metal S27 End face 591 Main body (phase change material)
592 Container 70 Guide member 72 Thermoelectric conversion element

Claims (8)

A fixing device that heats a sheet when an image is formed on the sheet,
A rotating body that rotates around an axis extending along a width direction of a conveyance path through which the sheet is conveyed and that contacts the sheet;
Heating means for heating the rotating body;
A heat radiating body located in the vicinity of the rotating body;
Arranged between the rotator and the heat radiating body, supported by the rotator or the heat radiating body, and when there is a phase change due to temperature rise, the gap between the rotator and the heat radiating body is eliminated. And a phase change member that expands. The rotating body has a metal core whose both ends are longer than the width of the conveyance path supported by the support through a bearing,
The radiator is adjacent to at least one end face of the cored bar,
The fixing device according to claim 1, wherein the phase change member is disposed between the end surface of the cored bar adjacent to the heat radiator and the heat radiator. The fixing device according to claim 2, wherein the phase change member is attached to the end face of the cored bar. The fixing device according to claim 1, wherein the phase change member includes a container having elasticity and a phase change substance accommodated in the container. 5. The guide member according to claim 1, further comprising a guide member that partially covers an outer peripheral surface of the phase change member so that a volume change of the phase change member is regulated by a change in a direction in which the length of the gap increases or decreases. The fixing device described. When the phase change member in the rotating body or the heat radiating member expands, a surface treatment that makes the phase change member easy to separate when the volume of the phase change member decreases is applied to the surface that contacts the phase change member. The fixing device according to claim 1. The fixing device according to claim 1, wherein a thermoelectric conversion element is disposed between the phase change member and the heat radiator. An image forming apparatus comprising: a fixing device according to claim 1, wherein the fixing device includes a mechanism for conveying paper, and the fixing device fixes an unfixed image on the paper.

Images