Heating device, fixing device, image forming apparatus

Abstract

To improve a temperature distribution in a longitudinal direction of a rotary member.SOLUTION: A fixing device 9 comprises: a halogen heater 22; a fixing belt 20; a pressure roller 20 that applies a pressure to the fixing belt 20; a nip forming member 23 that is arranged inside the fixing belt 20 and forms a fixing nip N with the pressure roller 20 with the fixing belt 20 sandwiched therebetween; and a slide sheet 26 that is provided between the fixing belt 20 and the nip forming member 23. The slide sheet 26 has a high heat conduction part 261 that has a heat conductivity larger than that of other parts.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a heating device, a fixing device, and an image forming apparatus. [Background technology]

[0002] In a fixing device serving as a heating device, a nip forming member provided on the inner surface of a fixing belt serving as a rotating member forms a fixing nip between the fixing belt and a pressure roller serving as a pressure member.

[0003] Some of such fixing devices are provided with a sliding sheet having excellent sliding properties in order to improve the sliding properties between the nip forming member and the fixing belt and to suppress wear of the fixing belt.

[0004] For example, in the fixing device of Patent Document 1 (JP 2016-33636 A), a sliding sheet is provided between the nip forming member and the fixing belt. The nip forming member is composed of multiple members with different thermal conductivities, and highly heat-conductive members such as a heat equalizing plate and a heat absorbing member are provided to prevent excessive temperature rise in non-paper passing portions of the fixing belt.

[0005] However, the provision of the sliding sheet described above makes it difficult for heat to be transferred between the rotating member and the nip forming member, which in turn reduces the effect of uniformly heating the rotating member in the longitudinal direction, achieved by the high thermal conductivity member described above, and creates the problem of being unable to obtain an ideal longitudinal temperature distribution in each of the rotating members and other components in the heating device. Summary of the Invention [Problem to be solved by the invention]

[0006] The object is to improve the temperature distribution in the longitudinal direction of the rotating member. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a heating device comprising a heating body, a rotating member, a pressure member that presses the rotating member, a nip forming member that is disposed inside the rotating member and forms a nip between the rotating member and the pressure member via the rotating member, and a sliding sheet that is provided between the rotating member and the nip forming member, wherein the sliding sheet changes its thermal conductivity in the longitudinal direction. The heating device heats a first recording medium and a second recording medium having a length in the longitudinal direction greater than that of the first recording medium, and the sliding sheet is configured so that the thermal conductivity of a first longitudinal region, which is an area inside a passage area of ​​the second recording medium in the longitudinal direction and outside the passage area of ​​the first recording medium, is set to be greater than the thermal conductivity of a second longitudinal region, which is an area within the passage area of ​​the first recording medium. It is characterized by: [Effects of the Invention]

[0008] According to the present invention, the temperature distribution in the longitudinal direction of the rotating member can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an image forming apparatus. [Figure 2] 1 is a side cross-sectional view showing a configuration of a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the positional relationship in the longitudinal direction of a halogen heater, a sliding sheet, and a sheet of paper. [Figure 4] 1A and 1B show a fixing device different from the present invention in which small-sized paper is passed through, where FIG. 1A shows a non-paper passing area, and FIG. 1B shows the temperature distribution in the longitudinal direction of the fixing belt. [Figure 5] FIG. 2 is an exploded perspective view showing a nip forming member and a sliding sheet. [Figure 6] 10A and 10B are diagrams illustrating the positional relationship in the longitudinal direction of a halogen heater, a sliding sheet, and a paper in a fixing device according to a different embodiment. [Figure 7] 10 is a diagram showing the positional relationship in the longitudinal direction of a halogen heater, a sliding sheet, and a sheet of paper in a fixing device according to yet another embodiment. [Figure 8] 3 is a side cross-sectional view showing a fixing device according to an embodiment different from that shown in FIG. 2. [Figure 9] 3 is a side cross-sectional view showing a fixing device according to an embodiment different from that shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted. Below, a fixing device provided in an image forming apparatus will be described as a heating device according to one embodiment of the present invention.

[0011] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

[0012] The image forming apparatus 100 shown in FIG. 1 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a different color developer: yellow, magenta, cyan, or black. These color developers correspond to the color separation components of a color image. Each imaging unit 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoconductor 2 as an image carrier, a charging device 3, a developing device 4, and a cleaning device 5. The charging device 3 charges the surface of the photoconductor 2. The developing device 4 supplies toner as a developer to the surface of the photoconductor 2 to form a toner image. The cleaning device 5 cleans the surface of the photoconductor 2.

[0013] The image forming apparatus 100 also includes an exposure device 6, a paper feed device 7, a transfer device 8, a fixing device 9, and a paper discharge device 10. The exposure device 6 exposes the surface of each photoconductor 2 to light and forms an electrostatic latent image on that surface. The paper feed device 7 supplies paper P as a recording medium to a paper transport path 14. The transfer device 8 transfers the toner image formed on each photoconductor 2 to the paper P. The fixing device 9 fixes the toner image transferred to the paper P to the surface of the paper P. The paper discharge device 10 discharges the paper P outside the apparatus. The imaging units 1, photoconductors 2, charging devices 3, exposure device 6, transfer device 8, etc. constitute image forming means for forming an image on paper.

[0014] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body, four primary transfer rollers 12 as primary transfer members, and a secondary transfer roller 13 as a secondary transfer member. The intermediate transfer belt 11 is stretched by multiple rollers. The primary transfer rollers 12 transfer the toner images on the photoconductors 2 to the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 to paper P. Each of the multiple primary transfer rollers 12 contacts the photoconductors 2 via the intermediate transfer belt 11. This brings the intermediate transfer belt 11 and each photoconductor 2 into contact with each other, forming a primary transfer nip between them. Meanwhile, the secondary transfer roller 13 contacts one of the rollers stretching the intermediate transfer belt 11 via the intermediate transfer belt 11. This forms a secondary transfer nip between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0015] Further, a pair of timing rollers 15 is provided in the paper transport path 14 between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

[0016] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0017] When a command to start a printing operation is issued, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the charging device 3 charges the surface of the photoconductor 2 to a uniform high potential. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the document reading device or the print information instructed to be printed from the terminal. This reduces the potential of the exposed area, forming an electrostatic latent image. Toner is then supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0018] The toner images formed on each photoconductor 2 rotate with the rotation of the photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are then transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so that they overlap one another. The toner images transferred onto the intermediate transfer belt 11 are then transported to the secondary transfer nip (the position of the secondary transfer roller 13) with the rotation of the intermediate transfer belt 11. The toner images are then transferred to the paper P transported at the secondary transfer nip. This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeder 7 is temporarily stopped by timing roller 15 and then transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 11 reaching the secondary transfer nip. In this way, a full-color toner image is carried on the paper P. After the toner image is transferred, any toner remaining on each photoconductor 2 is removed by the cleaning devices 5.

[0019] The paper P onto which the toner image has been transferred is transported to a fixing device 9, which fixes the toner image onto the paper P. The paper P is then discharged outside the apparatus by a paper discharge device 10, completing the series of printing operations.

[0020] As shown in FIG. 2 , the fixing device 9 according to this embodiment includes a fixing belt 20 as a rotating or fixing member, a pressure roller 21 as a counter rotating or pressing member, a halogen heater 22 as a heating element, a nip forming member 23, a stay 24 as a support member, a reflecting member 25, a sliding sheet 26, and a separating member 27. The fixing belt 20 is an endless belt. The pressure roller 21 contacts the outer surface of the fixing belt 20 to form a fixing nip N between the fixing belt 20 and the pressure roller 21. The halogen heater 22 heats the fixing belt 20. The stay 24 supports the nip forming member 23. The fixing member provided in the fixing device is one example of a rotating member provided in a heating device. The fixing device 9 according to this embodiment is provided with the fixing belt 20 as a specific example of this fixing member. The pressure member provided in the fixing device is one example of a counter rotating member provided in a heating device. The fixing device 9 according to this embodiment is provided with the pressure roller 21 as a specific example of this pressure member.

[0021] 2 is the longitudinal direction of the fixing belt 20, pressure roller 21, halogen heater 22, nip forming member 23, stay 24, sliding sheet 26, etc., and hereinafter this direction will be simply referred to as the longitudinal direction. Note that this longitudinal direction also corresponds to the width direction of the paper being conveyed, the belt width direction of the fixing belt 20, and the axial direction of the pressure roller 21.

[0022] The fixing belt 20 is composed of an endless belt member. This belt member is thin and flexible. The belt member includes a film. Specifically, the fixing belt 20 is composed of a substrate on the inner circumferential side and a release layer on the outer circumferential side. This substrate is made of a metal material such as nickel or SUS, or a resin material such as polyimide (PI). The release layer is made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like. An elastic layer made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber may be interposed between the substrate and the release layer.

[0023] The pressure roller 21 is composed of a core 21a, an elastic layer 21b made of foamed silicone rubber, silicone rubber, fluororubber, or the like provided on the surface of the core 21a, and a release layer 21c made of PFA, PTFE, or the like provided on the surface of the elastic layer 21b. The pressure roller 21 is urged toward the fixing belt 20 by a urging means and abuts against the nip forming member 23 via the fixing belt 20. At the location where the pressure roller 21 and the fixing belt 20 come into pressure contact, the elastic layer 21b of the pressure roller 21 is compressed, thereby forming a fixing nip N of a predetermined width. The pressure roller 21 is configured to be rotationally driven by a drive source such as a motor provided in the printer body. When the pressure roller 21 is rotationally driven, the drive force is transmitted to the fixing belt 20 at the nip N, causing the fixing belt 20 to rotate.

[0024] In this embodiment, the pressure roller 21 is a solid roller, but it may also be a hollow roller. In this case, a heating element such as a halogen heater may be disposed inside the pressure roller 21. Furthermore, if the pressure roller 21 does not have an elastic layer, its thermal capacity is reduced, improving fixation. On the other hand, when crushing unfixed toner to fix it, minute irregularities on the belt surface may be transferred to the image, resulting in gloss unevenness in solid areas of the image. To prevent this, it is desirable to provide the pressure roller 21 with an elastic layer with a thickness of 100 μm or more. By providing the pressure roller 21 with an elastic layer with a thickness of 100 μm or more, the elastic deformation of the elastic layer can absorb minute irregularities, thereby preventing gloss unevenness. The elastic layer 21b may be solid rubber, but if the pressure roller 21 does not have a heating element inside, sponge rubber may also be used. Using sponge rubber for the elastic layer of the pressure roller 21 is preferable because it improves thermal insulation and makes it more difficult for heat to be removed from the fixing belt 20. Furthermore, the fixing member and the pressure member are not limited to being pressed against each other, and may be simply in contact with each other without applying pressure.

[0025] A shielding member that blocks part of the heat from the halogen heater 22 may be disposed between the fixing belt 20 and the halogen heater 22. This makes it possible to suppress an excessive temperature rise in the non-paper passing areas of the fixing belt 20, particularly when paper is continuously passed through, and to prevent deterioration or damage to the fixing belt 20 due to heat.

[0026] The nip forming member 23 is made of a heat-resistant material with a heat resistance temperature of 200°C or higher. This prevents deformation of the nip forming member 23 due to heat in the toner fixing temperature range, ensures a stable fixing nip N, and stabilizes the output image quality. The nip forming member 23 can be made of common heat-resistant resins such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), and polyetheretherketone (PEEK).

[0027] A sliding sheet 26 is provided between the nip forming member 23 and the inner surface of the fixing belt 20 .

[0028] The stay 24 supports the nip forming member 23. The end of the stay 24 is fixed to the housing of the fixing device. This prevents the nip forming member 23 from bending due to the pressure of the pressure roller 21. As a result, a uniform nip width can be obtained along the rotational axis of the pressure roller 21. Furthermore, in order to satisfy the function of preventing the nip forming member 23 from bending, the stay 24 is preferably made of a metal material with high mechanical strength, such as stainless steel or iron. However, the stay 24 can also be made of resin.

[0029] The reflecting member 25 is disposed between the stay 24 and the halogen heater 22. In this embodiment, the reflecting member 25 is fixed to the stay 24. Furthermore, since the reflecting member 25 is directly heated by the halogen heater 22, it is desirable that it be formed from a high-melting-point metal material or the like. By disposing the reflecting member 25, light radiated from the halogen heater 22 toward the stay 24 is reflected toward the fixing belt 20. This increases the amount of light irradiated onto the fixing belt 20, enabling the fixing belt 20 to be heated efficiently. Furthermore, since the transfer of radiant heat from the halogen heater 22 to the stay 24 and the like can be suppressed, energy savings can be achieved.

[0030] Instead of providing the reflecting member 25 as in this embodiment, a reflecting surface may be formed by polishing or applying a mirror finish such as painting to the surface of the stay 24 on the halogen heater 22 side. The reflectance of the reflecting surface of the reflecting member 25 or the stay 24 is preferably 90% or more.

[0031] Furthermore, the shape and material of the stay 24 cannot be freely selected in order to ensure its strength. For this reason, providing the reflective member 25 separately, as in this embodiment, allows for greater freedom in selecting the shape and material, and allows the reflective member 25 and stay 24 to specialize in their respective functions. Furthermore, by providing the reflective member 25 between the halogen heater 22 and the stay 24, the position of the reflective member 25 becomes closer to the halogen heater 22, which allows the halogen heater 22 to heat the fixing belt 20 efficiently.

[0032] Next, the basic operation of the fixing device according to this embodiment will be described. When the power switch of the image forming apparatus main body is turned on, power is supplied to the halogen heater 22, and the pressure roller 21 starts to rotate clockwise in FIG. 2. As a result, the fixing belt 20 is rotated counterclockwise in FIG. 2 due to the frictional force with the pressure roller 21.

[0033] Thereafter, the paper P bearing the unfixed toner image T in the image forming process described above is conveyed in the direction of arrow A1 in Fig. 2 and sent into the nip N between the fixing belt 20 and the pressure roller 21, which are in a pressure-contact state. Then, the toner image T is fixed to the surface of the paper P by the heat of the fixing belt 20 heated by the halogen heater 22 and the pressure force between the fixing belt 20 and the pressure roller 21.

[0034] The sheet P on which the toner image T has been fixed is conveyed out of the fixing nip N in the direction of the arrow in Figure 2. At this time, the leading edge of the sheet P comes into contact with the leading edge of the separating member 27, so that the sheet P is separated from the fixing belt 20.

[0035] The fixing device 9 of this embodiment has two halogen heaters 22. More specifically, as shown in FIG. 3, the fixing device 9 has a center heater 22a whose main heat-generating region is located at the center in the longitudinal direction, and end heaters 22b whose main heat-generating regions are located at both longitudinal end portions. The main heat-generating region of the center heater 22a or end heater 22b is the portion where the filament provided inside the glass tube of the halogen heater 22 is tightly wound. Dotted line D in FIG. 3 indicates the widthwise center position of the paper passing through the fixing device, and is also the longitudinal center position of the main heat-generating region of the center heater 22a or the center position of the sliding sheet 26.

[0036] When narrow sheets of paper such as sheets P1 and P2 are passed through the fixing device 9, only the center heater 22a is turned on. When wide sheets of paper such as sheet P3 are passed through the fixing device 9, the center heater 22a and the edge heater 22b are turned on. Sheet P1 is, for example, an A6 size sheet of paper.

[0037] Here, the problem of excessive temperature rise of the fixing belt in the non-paper passing area will be explained using the fixing device of Fig. 4, which has a different configuration from this embodiment. Fig. 4(a) is a diagram showing the positional relationship between the center heater 22a in the longitudinal direction, the sliding sheet 26', and the paper P1, and Fig. 4(b) is a diagram showing an example of the temperature distribution in the longitudinal direction of the fixing belt when the paper P1 is passed through.

[0038] 4(a), in a fixing device having a different configuration from the present embodiment, the sliding sheet 26' is formed of the same material in the longitudinal direction and has the same thermal conductivity. Another difference from the fixing device of the present embodiment is that the nip forming member does not include a high thermal conductivity member, which will be described later.

[0039] In such a fixing device, when a sheet of paper having a width smaller than the main heating area of ​​the halogen heater 22 is passed through, the fixing belt overheats. For example, as shown in FIG. 4(a), when a sheet of paper P1 is passed through the fixing device 9, only the center heater 22a is turned on. At this time, in the non-paper passing area B, which is an area within the main heat generating area of ​​the center heater 22a but outside the paper passing area of ​​the sheet of paper P1, the fixing belt 20 is heated by the center heater 22a, but the temperature of the fixing belt 20 is not absorbed by the sheet of paper. For this reason, as shown in FIG. 4(b), the fixing belt 20 overheats in the non-paper passing area B, which can cause damage to the fixing belt.

[0040] In contrast, the fixing device 9 of this embodiment is provided with a highly heat-conductive member in the nip forming member 23, thereby promoting heat transfer in the longitudinal direction of the fixing belt 20 and suppressing excessive temperature rise in the non-paper passing areas of the fixing belt 20. The configuration of the nip forming member 23 will be described in more detail below with reference to FIG.

[0041] As shown in FIG. 5, the nip forming member 23 includes a heat equalizing member 31 as a highly thermally conductive member, a first heat absorbing member 32, a second heat absorbing member 33, a first heat insulating member 34, and a second heat insulating member 35.

[0042] The heat equalizing member 31 has bent portions 31b bent at approximately right angles on both sides of the metal plate. The contact portion 31a provided in the center is the portion that contacts the inner surface of the fixing belt 20 via the sliding sheet 26.

[0043] The sliding sheet 26 is provided below the contact portion 31a of the heat equalizing member 31 on the fixing belt 20 side in FIG. 5, and is disposed between the heat equalizing member 31 and the fixing belt 20. Both ends of the sliding sheet 26 are folded back at the tip of each bent portion 31b of the heat equalizing member 31, and are held inside the bent portions 31b. Alternatively, the sliding sheet 26 may be adhered to the contact portion 31a and the bent portions 31b on both sides with double-sided tape or the like.

[0044] The first heat absorption member 32 is made of a material with a higher thermal conductivity than the first heat insulating member 34 or the second heat insulating member 35. The first heat absorption member 32 is provided on the opposite side of the nip forming member 23 from the fixing nip N in the thickness direction. The first heat absorption member 32 is provided over the entire heating region C of the halogen heater 22 in the longitudinal direction. The heating region C of the halogen heater 22 refers to the range in which the main heat generating regions of the center heater 22a and end heaters 22b in the longitudinal direction are provided.

[0045] The second heat absorption member 33 is made of a material with a higher thermal conductivity than the first heat insulating member 34 or the second heat insulating member 35. The second heat absorption member 33 is provided on both sides outside the paper passage area of ​​the paper P1 in the longitudinal direction. In other words, when the paper P1 is passed through the fixing device 9 and the center heater 22a is turned on, the second heat absorption member 33 is provided opposite the non-paper passage area B (see FIG. 4) that is outside the paper P1 in the longitudinal direction within the main heat generation area of ​​the center heater 22a.

[0046] The second heat insulating member 35 is formed of a material, such as a resin material, having a lower thermal conductivity than the heat equalizing member 31. The second heat insulating member 35 is provided at a position in the longitudinal direction where the second heat absorbing member 33 is provided, and overlaps with the second heat absorbing member 33.

[0047] The first heat insulating member 34 is formed from a material with lower thermal conductivity than the heat equalizing member 31, for example, a resin material. The first heat insulating member 34 is provided between the heat equalizing member 31 and the first heat absorption member 32 in the thickness direction of the nip forming member 23. The first heat insulating member 34 is also provided at a position in the longitudinal direction where the second heat absorption member 33 and the second heat insulating member 35 are not provided. In other words, the first heat insulating members 34 or the second heat absorption members 33 and the second heat insulating members 35 are provided alternately in the longitudinal direction of the nip forming member 23.

[0048] The provision of the heat equalizing member 31 promotes heat transfer in the longitudinal direction of the fixing belt 20, thereby making the temperature of the fixing belt 20 uniform in the longitudinal direction. This prevents excessive temperature rise in the non-paper-passing region B of the fixing belt 20. The provision of the first heat absorption member 32 and the second heat absorption member 33 also promotes heat transfer from the heat equalizing member 31 toward the thickness direction of the nip forming member 23. In other words, the first heat absorption member 32 and the second heat absorption member 33 can compensate for the lack of heat capacity of the heat equalizing member 31. The provision of the first heat insulating member 34 also prevents excessive heat removal from the fixing belt 20 in the paper passing region, preventing a temperature drop in the paper passing portion of the fixing belt 20. The provision of the second heat insulating member 35 adjusts the amount of heat transfer in the thickness direction of the nip forming member 23 in the non-paper passing region B in the longitudinal direction. Therefore, it is possible to prevent the nip forming member 23 from excessively removing heat from the fixing belt 20 at the position in the longitudinal direction where the second heat absorption member 33 is provided.

[0049] With this configuration of nip forming member 23, as described above, the temperature of fixing belt 20 can be made uniform in the longitudinal direction and excessive temperature rise can be suppressed in non-paper passing areas of fixing belt 20. However, since fixing belt 20 and heat equalizing member 31 abut against each other via sliding sheet 26, it becomes difficult for heat to transfer from fixing belt 20 to heat equalizing member 31, which causes a problem that the effect of uniforming the temperature of fixing belt 20 in the longitudinal direction and the effect of suppressing excessive temperature rise of fixing belt 20 are reduced.

[0050] To address this problem, in this embodiment, the thermal conductivity of the portion of the sliding sheet 26 corresponding to the non-paper passing region is increased. Specifically, as shown in FIG. 3 , the sliding sheet 26 has a high thermal conductivity portion 261 as a first longitudinal region, which has a higher thermal conductivity than other regions of the sliding sheet 26, at a position facing the non-paper passing region B in the longitudinal direction. In other words, if the region corresponding to region B, which is inside the paper passing region for paper P2, the second recording medium, and outside the paper passing region for paper P1, in the longitudinal direction of the sliding sheet 26, is defined as the first longitudinal region 261 of the sliding sheet 26, and the region facing the paper passing region for paper P1 is defined as the second longitudinal region 262, the thermal conductivity of the first longitudinal region 261 is set to be higher than the thermal conductivity of the second longitudinal region 262. The non-sheet passing area B here refers to an area within the main heat generating area of ​​the central heater 22a where the sheet P1 does not pass when the sheet P1 is passed as described above.

[0051] By providing the high thermal conductivity portion 261 in the longitudinal region of the sliding sheet 26 facing the non-paper-passing region B, heat can be more easily transferred from the fixing belt 20 to the heat equalizing member 31 in the non-paper-passing region B. This enhances the heat equalizing effect of the nip forming member 23 across the fixing belt 20, thereby preventing excessive temperature rise in the non-paper-passing region B of the fixing belt 20 when the paper P1 is passed through. By varying the thermal conductivity of the sliding sheet 26 along its longitudinal direction, the temperature distribution across the fixing belt 20 can be improved, achieving a more ideal temperature distribution. Furthermore, if the above configuration provides sufficient heat equalization across the fixing belt 20, the number of components in the nip forming member 23 can be reduced, for example by omitting the first heat absorption member 32. This improves assembly ease and reduces costs for the nip forming member. The high thermal conductivity portion 261 does not need to be provided across the entire non-paper-passing region B; it can be provided only in a portion of it.

[0052] The sliding sheet 26 is formed from a material that is highly abrasion-resistant and slides smoothly with the fixing belt 20. The high thermal conductivity portion 261 of the sliding sheet 26 can be made of, for example, metal fibers and fluorine-based resin fibers. On the other hand, the portions of the sliding sheet 26 other than the high thermal conductivity portion 261 can be made of, for example, only fluorine-based resin fibers. This allows the thermal conductivity of the high thermal conductivity portion 261 to be higher than that of other portions such as the second longitudinal region 262.

[0053] Metal fibers have a higher thermal conductivity than resin fibers, but have poorer sliding properties. Therefore, by changing the ratio of metal fibers to fluorine-based resin fibers that make up the high thermal conductivity portion 261, it is possible to adopt an optimal ratio that balances the heat transfer effect and sliding properties of the sliding sheet 26. Also, the thermal conductivity of the high thermal conductivity portion 261 can be increased by making the thickness of the high thermal conductivity portion 261 smaller than that of the other portions of the sliding sheet 26. Furthermore, the thermal conductivity of the high thermal conductivity portion 261 can be increased by increasing the diameter of the fibers that make up the high thermal conductivity portion 261 or by increasing the ratio of fibers to increase the density.

[0054] Next, a method for calculating the thermal conductivity will be described. When calculating the thermal conductivity, first, the thermal diffusivity of the object is measured, and then the thermal conductivity is calculated using the measured thermal diffusivity.

[0055] The thermal diffusivity was measured using a thermal diffusivity / thermal conductivity measuring device (trade name: ai-Phase Mobile 1u, ai-Phase Corporation).

[0056] To convert the thermal diffusivity to thermal conductivity, the density and specific heat capacity values ​​are required. A dry-type automatic densitometer (product name: Accupyc 1330, manufactured by Shimadzu Corporation) was used to measure the density. A differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) was used to measure the specific heat capacity, using sapphire as a reference material with a known specific heat capacity. In this example, the specific heat capacity was measured five times, and the average value at 50°C was used. When the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be calculated from the thermal diffusivity α obtained from the thermal diffusivity measurement using the following equation (1):

[0057]

number

[0058] The configuration of the high thermal conductivity portion of the sliding sheet described above is an example, and the present invention is not limited to this. Below, modifications of the high thermal conductivity portion provided on the sliding sheet will be described.

[0059] 6, the fixing device 9 of this embodiment corresponds to a third recording medium, namely, a sheet P4, which is wider than the sheet P1 but narrower than the sheet P2. In this embodiment, when the sheet P1 is passed through the fixing device 9, the longitudinal range B1, which is the same range as in the previous embodiment, is within the main heat generation area of ​​the center heater 22a, and the temperature of the fixing belt 20 increases in the non-sheet passing area B1, which is an area outside the area through which the sheet P1 is passed. On the other hand, when the sheet P4 is passed through the fixing device 9, the temperature of the fixing belt 20 increases in the non-sheet passing area B2, which is within the main heat generation area of ​​the center heater 22a but outside the area through which the sheet P4 is passed.

[0060] As described above, in this embodiment, there are three types of paper P1, P2, and P4 for which only the central heater 22a is turned on, and the range of the non-paper passing area also differs depending on the size of the paper being passed.

[0061] In contrast, in the sliding sheet 26 of this embodiment, the high thermal conductivity portion 261 is composed of an inner high thermal conductivity portion 261a and an outer high thermal conductivity portion 261b. The inner high thermal conductivity portion 261a is provided in a region within the longitudinal non-paper passing region B1 and outside the longitudinal non-paper passing region B2. The outer high thermal conductivity portion 261b is provided in a region within the longitudinal non-paper passing region B2. The inner high thermal conductivity portion 261a is set to have a higher thermal conductivity than the outer high thermal conductivity portion 261b.

[0062] As the width of the non-paper-passing region increases, the area of ​​the fixing belt 20 that is not affected by paper heat is larger, and the temperature of the fixing belt 20 is more likely to increase. In other words, the temperature of the fixing belt 20 is more likely to increase in the non-paper-passing region B1 when paper P1 is passed than in the non-paper-passing region B2 when paper P2 is passed. Furthermore, when the fixing belt 20 is heated, the temperature tends to increase toward the center. For these reasons, in this embodiment, the thermal conductivity of the inner high thermal conductive portion 261a, which corresponds to the area of ​​the fixing belt 20 where the temperature is more likely to increase, is set higher than the thermal conductivity of the outer high thermal conductive portion 261b. This allows the longitudinal thermal conductivity distribution of the sliding sheet 26 to be set to a more appropriate value that matches the temperature distribution of the fixing belt 20 when small-sized paper is passed. Therefore, excessive temperature rise of the fixing belt 20 can be effectively suppressed. Thus, the thermal conductivity of the high thermal conductive portion 261 of the sliding sheet 26 does not need to be uniform in the longitudinal direction but can be adjusted to match the longitudinal temperature distribution of the fixing belt 20.

[0063] 7 corresponds to sheet P5, which is wider than sheet P2 and narrower than sheet P3. When sheet P5 is passed through the fixing device, both center heater 22a and edge heater 22b are turned on.

[0064] In the fixing device of this embodiment, similar to the previous embodiments, a non-paper passing area B1 is formed when paper P1 is passed through. Then, when paper P5 is passed through the fixing device 9, the temperature of the fixing belt 20 rises in a non-paper passing area B3, which is an area outside paper P5 in the longitudinal direction and within the main heat generation area of ​​the end-side heater 22b.

[0065] Therefore, in this embodiment, the sliding sheet 26 has a second high thermal conductivity portion 262 provided in a range facing the non-paper-passing region B3 in the longitudinal direction, in addition to a first high thermal conductivity portion 261 provided in a range facing the non-paper-passing region B1 in the longitudinal direction. This makes it possible to prevent excessive temperature rise of the fixing belt 20 in the non-paper-passing region B3 when the paper P5 passes through the fixing device. In this way, if the fixing device 9 can accommodate multiple sizes of paper 3 and P5 in the main heat-generating region of the end-side heater 22b, the sliding sheet 26 can also be provided with a high thermal conductivity portion facing the main heat-generating region of the end-side heater 22b. In this way, the sliding sheet 26 can be provided with high thermal conductivity portions in multiple regions in the longitudinal direction.

[0066] The number of halogen heaters provided in the fixing device 9 is not limited to two. For example, as shown in FIG. 8 , the sliding sheet of the present invention can be applied to a fixing device having one halogen heater 22. A temperature sensor 28 is provided facing the outer peripheral surface of the fixing belt 20 on the side opposite the fixing nip N. In the fixing device of FIG. 8 , a high thermal conductivity portion 261 can be provided on the sliding sheet 26 for the halogen heater in FIG. 8 , just as a high thermal conductivity portion 261 is provided in the main heat-generating region of the center heater 22a in the longitudinal direction, facing its non-paper passing region, as shown in FIGS. 3 and 6 of the above-mentioned embodiment. Furthermore, as shown in FIG. 9 , the sliding sheet of the present invention can be applied to a fixing device having three halogen heaters 22. These halogen heaters 22 include a heater corresponding to the center heater 22a in FIG. 3 , a heater corresponding to one end heater 22b, and a heater corresponding to the other end heater 22b. Even in such a fixing device, a high thermal conductivity portion can be provided on the sliding sheet 26, as shown in FIGS. 3 and 7 .

[0067] In these fixing devices, the application of the sliding sheet of the present invention can improve the temperature distribution in the longitudinal direction of the fixing belt 20 as a rotating member. In other words, the temperature of the fixing belt 20 can be made uniform in the longitudinal direction and excessive temperature rise in non-paper passing areas can be suppressed.

[0068] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0069] The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may also be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0070] Recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, etc.

[0071] Furthermore, the present invention is not limited to the fixing device described in the above embodiment, but can also be applied to a drying device that dries ink applied to paper, and further to heating devices such as a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, and a heat sealer that thermocompresses the seal portion of a packaging material. By applying the sliding sheet of the present invention to such devices, the temperature distribution in the longitudinal direction of the rotating member can be improved. [Explanation of symbols]

[0072] 1. Image forming device 9 Fixing device (heating device) 20 Fixing belt (rotating member or fixing member) 21 Pressure roller (opposing rotating member or pressure member) 22 Halogen heater (heating element) 22a Center heater 22b End side heater 23 Nip forming member 26 Sliding Sheet 261 High thermal conductivity section (first longitudinal region) 262 Second Longitudinal Region B Non-paper passing area P Paper (recording medium) P1 Paper (first recording medium) P2 Paper (secondary recording medium) P4 paper (third recording medium) X: Longitudinal direction of the sliding sheet [Prior art documents] [Patent documents]

[0073] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-33636

Claims

1. A heating element; A rotating member; a pressure member that applies pressure to the rotating member; a nip forming member disposed inside the rotary member and forming a nip between the rotary member and the pressure member via the rotary member; A heating device including a sliding sheet provided between the rotating member and the nip forming member, The sliding sheet changes its thermal conductivity in the longitudinal direction, the heating device heats a first recording medium and a second recording medium having a length in the longitudinal direction greater than that of the first recording medium; A heating device characterized in that the thermal conductivity of the sliding sheet is set to be greater in a first longitudinal region, which is an area inside the passing area of ​​the second recording medium in the longitudinal direction and outside the passing area of ​​the first recording medium, than in a second longitudinal region, which is an area within the passing area of ​​the first recording medium.

2. The heating device according to claim 1 , wherein the first longitudinal region of the sliding sheet includes metal fibers.

3. 3. The heating device according to claim 1, wherein the first longitudinal region has a thickness smaller than that of the second longitudinal region.

4. the first longitudinal region and the second longitudinal region of the sliding sheet are formed of a fibrous material, The heating device according to claim 1 , wherein the first longitudinal region has a higher fiber density than the second longitudinal region.

5. the first longitudinal region and the second longitudinal region of the sliding sheet are formed of a fibrous material, The heating device according to claim 1 , wherein the first longitudinal region has a larger diameter of fibers than the second longitudinal region.

6. 6. The heating device according to claim 1, wherein the heating device corresponds to a third recording medium, the third recording medium having a length in the longitudinal direction that is greater than that of the first recording medium and smaller than that of the second recording medium, A heating device in which the thermal conductivity of the sliding sheet in the first longitudinal region, in a region inside the region through which the third recording medium passes, is greater than the thermal conductivity of the region outside the region through which the third recording medium passes.

7. A fixing device that heats and fixes toner on a recording medium using the heating device according to claim 1 .

8. An image forming apparatus comprising the fixing device according to claim 7.

Images