Heating device, fixing device and image forming apparatus

Abstract

To provide a heating device that prevents an increase in the number of components of temperature detection means used for a heat source, and has improved heating efficiency.SOLUTION: A heating device comprises a heat source that applies radiation heating to a belt member 21 from the inside. The belt member forms a nip part N with a pressure member 22 facing the belt member. The heat source has a first glass cylinder 23a and a second glass cylinder 23b, and the first glass cylinder and the second glass cylinder each have a coil member therein over the maximum paper feed width of a recording medium. The first glass cylinder has a constant heat intensity over the width direction of the recording medium, has higher output than the second glass cylinder, is more frequently turned on than the second glass cylinder, and has a smaller heat capacity of the glass cylinder than the second glass cylinder. The second glass cylinder has a portion where the heat intensity is larger than the other portions in a part in the width direction of the recording medium. In the direction of rotation of the belt member, the first glass cylinder is arranged closer to an entrance Ne of the nip part than the second glass cylinder.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] 2. Description of the Related Art It is known that in a fixing device in an electrophotographic image forming apparatus, a fixing member such as a fixing belt is heated.

[0003] For example, as in Patent Document 1, two halogen heaters are used as a heat source for heating the fixing member. Generally, fixing results in a difference in temperature in the nip between the paper-passing and non-paper-passing areas of the recording medium. Patent Document 1 therefore discloses a heating area variable member that varies the heating area of ​​the fixing member by the heat source, provided between the heat source and the fixing member, and a heat equalizing member that receives heat from the fixing member and diffuses it in the axial direction of the nip forming member. Patent Document 1 claims that it is possible to change the heating area of ​​the fixing member to match the size of the recording medium, suppress temperature increases at the edge, and average the temperature in the axial direction. Summary of the Invention [Problem to be solved by the invention]

[0004] For example, when using two halogen heaters as in Patent Document 1, it is common to use dual heaters, one for heating the central portion in the axial direction and the other for heating the edges. However, this requires detection means such as temperature control sensors and safety devices at the heating position of each heater, resulting in an environmentally friendly device configuration in terms of the number of parts. Furthermore, in the case of low-speed printers that print a small number of sheets per unit time, the heaters are turned on less frequently and the set temperature is low, making axial temperature deviation less likely to occur. This also necessitates the use of multiple temperature detection means such as temperature control sensors. Furthermore, improved heating efficiency in heating in fixing devices is required for energy conservation and other purposes, and even Patent Document 1 calls for further improvement.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a heating device that prevents an increase in the number of components, such as temperature detection means, used in a heat source and improves heating efficiency. [Means for solving the problem]

[0006] In order to solve the above problem, the heating device of the present invention is a heating device equipped with a heat source that radiates heat from the inside of a rotatable endless belt member, wherein the belt member forms a nip portion with a pressure member facing the belt member, the heat source has a first glass cylindrical body and a second glass cylindrical body, and both the first glass cylindrical body and the second glass cylindrical body have a coil member inside them across the maximum paper passing width of the recording medium, the first glass cylindrical body has a constant heat generation intensity across the width direction of the recording medium, has a higher output than the second glass cylindrical body, is turned on more frequently than the second glass cylindrical body, and has a smaller glass cylindrical heat capacity than the second glass cylindrical body, and the second glass cylindrical body has a portion in the width direction of the recording medium where the heat generation intensity is higher than other portions, and is characterized in that, in the rotation direction of the belt member, the first glass cylindrical body is positioned closer to the entrance of the nip portion than the second glass cylindrical body. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a heating device that prevents an increase in the number of parts such as temperature detection means used in a heat source and improves heating efficiency. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. [Figure 2] 1 is a schematic cross-sectional view showing an example of a heating device and a fixing device according to the present invention. [Figure 3] 1A and 1B are diagrams for explaining an example of a heat source, where FIG. 1A is included in the present invention and FIG. 1B is not included in the present invention. [Figure 4] 1A and 1B are schematic diagrams showing an example of the heat generation intensity and lighting of a heater. [Figure 5] 10 is a schematic cross-sectional view showing another example of a heating device and a fixing device according to the present invention. FIG. [Figure 6] FIG. 2 is a schematic diagram for explaining an example of a filament coil of a main heater and a sub-heater. [Figure 7] 10 is a schematic cross-sectional view showing another example of a heating device and a fixing device according to the present invention. FIG. [Figure 8] 10 is a schematic cross-sectional view showing another example of a heating device and a fixing device according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] The heating device, fixing device, and image forming apparatus according to the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments, and can be modified, added, modified, deleted, and otherwise altered within the scope of what one skilled in the art can conceive. Any embodiment that achieves the functions and effects of the present invention is within the scope of the present invention.

[0010] The heating device of the present invention is a heating device equipped with a heat source that radiates heat from the inside of a rotatable, endless belt member, wherein the belt member forms a nip portion with a pressure member facing the belt member, the heat source has a first glass cylindrical body and a second glass cylindrical body, and both the first glass cylindrical body and the second glass cylindrical body have coil members inside them across the maximum paper passing width of the recording medium, the first glass cylindrical body has a constant heat generation intensity across the width direction of the recording medium, has a higher output than the second glass cylindrical body, is turned on more frequently than the second glass cylindrical body, and has a smaller glass cylindrical heat capacity than the second glass cylindrical body, the second glass cylindrical body has a portion in the width direction of the recording medium where the heat generation intensity is higher than other portions, and is characterized in that, in the rotation direction of the belt member, the first glass cylindrical body is positioned closer to the entrance of the nip portion than the second glass cylindrical body.

[0011] The fixing device of the present invention is characterized by comprising the belt member, the pressure member arranged opposite the belt member and applying pressure to the belt member, a nip forming member arranged inside the belt member and forming a nip portion by receiving pressure from the pressure member, a support member arranged inside the belt member and supporting the nip forming member, and the heating device of the present invention.

[0012] The image forming apparatus of the present invention is characterized by including the fixing device of the present invention. According to the present invention, there are provided a heating device and a fixing device used in an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and an image forming apparatus equipped with the same.

[0013] FIG. 1 is a schematic diagram showing an example of the overall configuration of an image forming apparatus according to this embodiment. The image forming apparatus 1 shown in Figure 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the device body. Each of the image forming units 4Y, 4M, 4C, and 4K has the same configuration, except that it contains a developer of a different color—yellow (Y), magenta (M), cyan (C), or black (K)—that corresponds to the color separation components of a color image. Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, a developing device 7 that supplies toner to the surface of the photoconductor 5, and a cleaning device 8 that cleans the surface of the photoconductor 5.

[0014] In FIG. 1, only the photosensitive member 5, charging device 6, developing device 7, and cleaning device 8 of the black image forming unit 4K are labeled with reference numerals, and the other image forming units 4Y, 4M, and 4C are not labeled with reference numerals.

[0015] Below each of the imaging units 4Y, 4M, 4C, and 4K, an exposure device 9 is disposed to expose the surface of the photosensitive member 5. The exposure device 9 has a light source, a polygon mirror, an f-θ lens, a reflecting mirror, etc., and is configured to irradiate the surface of each photosensitive member 5 with laser light based on image data.

[0016] Moreover, a transfer device 3 is disposed above each of the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer body, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

[0017] The intermediate transfer belt 30 is an endless belt, and is stretched around a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, the rotation of the secondary transfer backup roller 32 causes the intermediate transfer belt 30 to run (rotate) in the direction indicated by the arrow in the figure.

[0018] The four primary transfer rollers 31 each sandwich the intermediate transfer belt 30 between themselves and the corresponding photosensitive member 5 to form a primary transfer nip. A power supply (not shown) is connected to each primary transfer roller 31, and a predetermined direct current (DC) voltage and / or alternating current (AC) voltage is applied to each primary transfer roller 31.

[0019] The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 between itself and the secondary transfer backup roller 32 to form a secondary transfer nip. Similar to the primary transfer roller 31, the secondary transfer roller 36 is also connected to a power source (not shown) so that a predetermined direct current (DC) voltage and / or alternating current (AC) voltage is applied to the secondary transfer roller 36.

[0020] The belt cleaning device 35 has a cleaning brush and a cleaning blade arranged to contact the intermediate transfer belt 30. A waste toner transport hose (not shown) extends from the belt cleaning device 35 and is connected to the inlet of a waste toner container (not shown).

[0021] A bottle storage unit 2 is provided at the top of the printer body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishment toner are removably attached to the bottle storage unit 2. A supply path (not shown) is provided between each of the toner bottles 2Y, 2M, 2C, and 2K and each of the developing devices 7, and toner is supplied from each of the toner bottles 2Y, 2M, 2C, and 2K to each of the developing devices 7 via this supply path.

[0022] Meanwhile, at the bottom of the printer body, there are provided a paper feed tray 10 that stores paper P as a recording medium, and a paper feed roller 11 that conveys paper P from the paper feed tray 10. In addition to plain paper, recording media include cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and overhead projector sheets. Although not shown, a manual paper feed mechanism may also be provided.

[0023] A transport path R is provided within the printer body for transporting paper P from the paper feed tray 10 through the secondary transfer nip and out of the device. On the transport path R, upstream of the secondary transfer roller 36 in the paper transport direction, a pair of registration rollers 12 are provided as timing rollers for transporting paper P to the secondary transfer nip in accordance with transport timing.

[0024] Further, downstream in the paper transport direction from the position of the secondary transfer roller 36, there is disposed a fixing device 20 for fixing the unfixed image transferred onto the paper P. Furthermore, downstream in the paper transport direction of the transport path R from the fixing device 20, there is disposed a pair of paper discharge rollers 13 for discharging the paper outside the device. Also, on the top surface of the printer body, there is disposed a paper discharge tray 14 for stocking the paper discharged outside the device.

[0025] Next, the basic operation of the printer according to this embodiment will be described with reference to FIG. 1. When an image formation operation is initiated, each photoconductor 5 in each image forming unit 4Y, 4M, 4C, and 4K is rotated clockwise by a drive device (not shown), and the surface of each photoconductor 5 is uniformly charged to a predetermined polarity by a charging device 6. The charged surface of each photoconductor 5 is irradiated with laser light from an exposure device 9, forming an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information exposed to each photoconductor 5 is monochromatic image information obtained by decomposing a desired full-color image into color information for yellow, magenta, cyan, and black. When toner is supplied by each developing device 7 to the electrostatic latent image thus formed on each photoconductor 5, the electrostatic latent image is visualized as a toner image.

[0026] Furthermore, when the image formation operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, causing the intermediate transfer belt 30 to travel in the direction indicated by the arrow in the figure. Furthermore, a constant voltage or constant current controlled voltage of a polarity opposite to the charge polarity of the toner is applied to each primary transfer roller 31, thereby forming a transfer electric field in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

[0027] Thereafter, as each photoconductor 5 rotates, when the toner images of each color on the photoconductor 5 reach the primary transfer nip, the toner images on each photoconductor 5 are transferred in order onto the intermediate transfer belt 30 in a superimposed state by the transfer electric field formed at the primary transfer nip. Thus, a full-color toner image is carried on the surface of the intermediate transfer belt 30. Furthermore, any toner remaining on each photoconductor 5 that has not been transferred to the intermediate transfer belt 30 is removed by a cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by a neutralization device (not shown), and the surface potential is initialized.

[0028] At the bottom of the printer, paper feed roller 11 starts to rotate, and paper P is sent out from paper feed tray 10 to transport path R. Once paper P has been sent out to transport path R, registration roller 12 temporarily stops the transport.

[0029] Thereafter, the registration rollers 12 start to rotate at a predetermined timing, and the paper P is transported to the secondary transfer nip in time with the timing when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage of a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field at the secondary transfer nip. Then, the toner image on the intermediate transfer belt 30 is transferred onto the paper P all at once by this transfer electric field.

[0030] At this time, residual toner on the intermediate transfer belt 30 that has not been transferred to the paper P is removed by a belt cleaning device 35, and the removed toner is transported to a waste toner container (not shown) and collected. Thereafter, the paper P is transported to the fixing device 20, and the fixing device 20 fixes the toner image on the paper P to the paper P. Then, the paper P is discharged outside the apparatus by the paper discharge rollers 13 and stocked on the paper discharge tray 14.

[0031] The above description is of the image forming operation when forming a full-color image on paper, but it is also possible to form a monochrome image using any one of the four image forming units 4Y, 4M, 4C, and 4K, or to form a two-color or three-color image using two or three image forming units.

[0032] FIG. 2 is a schematic cross-sectional view of a fixing device including a heating device according to this embodiment. The heating device of this embodiment shown in Figure 2 is equipped with a heat source (halogen heater 23) that heats a rotatable endless belt member (fixing belt 21) from the inside, and the heat source has a first glass cylindrical body (main heater 23a) and a second glass cylindrical body (sub-heater 23b) that radiate heat to the belt member from the inside.

[0033] 2 includes, for example, a fixing belt 21, a pressure roller 22, a halogen heater 23, a nip forming member 24, a support member 25, a reflecting member 26, and a temperature sensor 28. The symbol N represents the nip portion, and the symbol Ne represents the entrance of the nip portion.

[0034] The fixing belt 21 is an example of a fixing member. The fixing belt 21 is a rotatable, endless belt member (including a film), which is thin and flexible. The fixing belt 21 is composed of an inner substrate made of, for example, a metal material such as nickel or SUS, or a resin material such as polyimide (PI), and an outer release layer made of, for example, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE).

[0035] 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. Without an elastic layer, the heat capacity is reduced and the fixing performance is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface may be transferred to the image, resulting in uneven gloss in the solid areas of the image. To prevent this, it is desirable to provide an elastic layer with a thickness of 100 μm or more. For example, by providing an elastic layer with a thickness of 100 μm or more, the elastic deformation of the elastic layer can absorb minute irregularities, thereby preventing uneven gloss.

[0036] In this embodiment, the fixing belt 21 is made thinner and smaller in diameter to reduce its heat capacity. Specifically, the thicknesses of the base material, elastic layer, and release layer constituting the fixing belt 21 are set to ranges of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, respectively, and the overall thickness is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. To further reduce the heat capacity, the overall thickness of the fixing belt 21 is preferably set to 0.2 mm or less, and more preferably to 0.16 mm or less. The diameter of the fixing belt 21 is preferably set to 30 mm or less.

[0037] The pressure roller 22 is an example of a pressure member, and is disposed opposite the fixing belt 21 to apply pressure to the fixing belt 21. The pressure roller 22 is in contact with the outer peripheral surface of the fixing belt 21, and may also be referred to as an opposing member.

[0038] The pressure roller 22 is composed of, for example, a core metal 22a, an elastic layer 22b, and a release layer 22c. The elastic layer 22b is made of, for example, foamed silicone rubber, silicone rubber, or fluororubber and is provided on the surface of the core metal 22a. The release layer 22c is made of, for example, PFA or PTFE and is provided on the surface of the elastic layer 22b.

[0039] Pressure roller 22 is pressed toward fixing belt 21 by a pressure means (not shown) and abuts against nip forming member 24 via fixing belt 21. At the location where pressure roller 22 and fixing belt 21 come into pressure contact, elastic layer 22b of pressure roller 22 is crushed, forming nip N of a predetermined width. Note that the fixing member and the opposing member are not limited to being in pressure contact with each other, and may be configured to simply be in contact without applying pressure.

[0040] The pressure roller 22 is configured to be rotated by a drive source such as a motor (not shown) provided in the printer body. When the pressure roller 22 is rotated, the drive force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is rotated accordingly.

[0041] In this embodiment, the pressure roller 22 is a solid roller, but it may also be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may also be used. Sponge rubber is more preferable because it has better heat insulation properties and is less likely to lose heat from the fixing belt 21.

[0042] The temperature sensor 28 is an example of a temperature detection unit that detects the temperature of the fixing belt 21 .

[0043] The halogen heater 23 is an example of a heat source (also referred to as a heating source) that radiates heat from the inside of the belt member (fixing belt 21), and has a first glass cylinder (main heater 23a) and a second glass cylinder (sub-heater 23b).

[0044] Halogen heater 23 is disposed on the inner circumferential side of fixing belt 21 and upstream of nip portion N in the paper transport direction. Halogen heater 23 is configured to generate heat under output control by a power supply unit provided in the printer body, and this output control is performed, for example, based on the detection result of the surface temperature of fixing belt 21 by temperature sensor 28. By such output control, the temperature (fixing temperature) of fixing belt 21 can be set to a desired temperature.

[0045] Instead of the temperature sensor 28 that detects the temperature of the fixing belt 21, a temperature sensor (not shown) that detects the temperature of the pressure roller 22 may be provided, and the temperature of the fixing belt 21 may be predicted based on the temperature detected by the temperature sensor. The output control described above may be performed based on the predicted temperature.

[0046] In this embodiment, two heaters, a main heater 23a and a sub-heater 23b, are provided as the halogen heater 23. A detailed example will be described later.

[0047] Nip forming member 24 is disposed inside fixing belt 21 and forms nip N when pressed by pressure roller 22. Nip forming member 24 is supported by support member 25 and slides directly against the inner surface of fixing belt 21, contacting pressure roller 22 from the inner circumferential side of fixing belt 21 to form nip N. The shape of nip N is determined by nip forming member 24 receiving the pressure from pressure roller 22. In this embodiment, nip N has a flat shape, but it may also have a concave or other shape.

[0048] The support member 25 supports the nip forming member 24. The support member 25 also serves to partition the inside of the fixing belt 21. The shape, material, etc. of the support member 25 can be selected as appropriate.

[0049] The reflecting member 26 is fixed to and supported by the support member 25 so as to face the halogen heater 23, and reflects heat from the halogen heater 23 to the fixing belt 21. The reflecting member 26 reflects the heat (or light) radiated from the halogen heater 23 to the fixing belt 21, thereby preventing the heat from being transmitted to the support member 25 and the like. Furthermore, by using the reflecting member 26, the fixing belt 21 can be heated efficiently and energy can be saved.

[0050] The reflecting member 26 is made of, for example, aluminum or stainless steel. In particular, when an aluminum substrate is used on which silver, which has low emissivity (high reflectivity), is vapor-deposited, the heating efficiency of the fixing belt 21 can be improved.

[0051] The recording medium onto which the toner image has been transferred is conveyed to the fixing device 20, and the recording medium passes through the nip portion N, whereby the toner image on the recording medium is fixed to the recording medium.

[0052] Next, a detailed example of the heating device of this embodiment, particularly the halogen heater 23, will be described. In this embodiment, the halogen heater 23 is an example of a heat source that radiates heat from the inside of the fixing belt 21, and includes a first glass cylinder (main heater 23a) and a second glass cylinder (sub-heater 23b).

[0053] The main heater 23a and the sub-heater 23b each have a glass cylinder and a coil member therein, and are examples of a first glass cylinder and a second glass cylinder, respectively. The coil member is provided across the maximum paper passing width of the recording medium (which may also be referred to as the maximum compatible paper width). The lengths of the main heater 23a and the sub-heater 23b are both equal to or greater than the maximum paper passing width of the recording medium. In this embodiment, for example, a filament coil (sometimes also referred to as a filament) is used as the coil member.

[0054] The width direction of the recording medium is a direction perpendicular to the transport direction of the recording medium and is a direction along the rotation axis direction of the fixing belt 21. In Figure 2, the rotation direction of the fixing belt 21 is indicated by an arrow. The width direction of the recording medium may also be referred to as the axial direction, the longitudinal direction, etc.

[0055] As described above, by providing the filament coils of the main heater 23a and the sub-heater 23b across the maximum paper passing width of the recording medium, it is possible to prevent an increase in the number of components, such as temperature detection means, used as the heat source. This will be explained schematically using FIG. 3A is a diagram illustrating the main heater 23a and sub-heater 23b in this embodiment, and FIG. 3B is a diagram illustrating the center heater 44a and edge heater 44b, which are not included in the present invention. In this embodiment, the main heater 23a and sub-heater 23b have filament coils provided across the maximum paper feed width of the recording medium, so only one NC sensor 41, one thermostat 42, and one thermopile 43 for temperature control are required as safety devices. On the other hand, in a configuration where the center heater 44a and edge heater 44b are provided, it is necessary to provide an NC sensor 41, one thermostat 42, and one thermopile 43 at the center and at the edge. Therefore, this embodiment can prevent an increase in the number of components for detection means such as temperature control sensors and safety devices.

[0056] Furthermore, by using two halogen heaters 23, a main heater 23a and a sub-heater 23b, as in this embodiment, it is possible to reduce the inrush current that accompanies high output and to avoid flicker caused by heating using the same power source.

[0057] The main heater 23a has a constant heat generation intensity across the width of the recording medium. On the other hand, the sub-heater 23b has a portion in the width direction of the recording medium where the heat generation intensity is greater than other portions. For example, the heat generation intensity of the sub-heater 23b is higher at both ends than at the center. In the sub-heater 23b, the heat generation intensity is higher at both ends than at the center, which can reduce the temperature deviation between the paper passing area and the non-paper passing area, for example. In this way, the heat generation intensity can be changed in a portion in the width direction by, for example, changing the winding method of the coil in the width direction.

[0058] Although not particularly limited, in this embodiment, it is preferable to control the heater heat intensity and lighting as follows. For example, when small-sized sheets are passing, the heat intensity of the main heater 23a is reduced to the minimum possible value for the non-passing area of ​​small-sized sheets, and only the main heater 23a is turned on. In this embodiment, the heating area of ​​the main heater 23a and the sub-heater 23b is set to the maximum width of the recording medium, so the non-passing area becomes larger when small-sized sheets are passing. Therefore, when the recording medium is small-sized, the temperature at the edge increases significantly. However, as described above, when small-sized sheets are passing, the heat intensity of the main heater 23a is reduced to the minimum possible value for the non-passing area of ​​small-sized sheets, and only the main heater 23a is turned on, thereby suppressing the temperature increase at the edge.

[0059] The sub-heater 23b may be configured to generate more heat at the edges than at the center, and both the main heater 23a and the sub-heater 23b may be turned on when large-size paper is fed. In this case, temperature drop at the edges of the paper can be prevented, and fixation at the edges of large-size paper can be ensured.

[0060] Because temperature sag at the edges of the paper occurs early in the paper feed, it is thought that by repeatedly feeding large-size paper with both the main heater 23a and the sub-heater 23b turned on, as described above, the temperature sag at the edges of the paper will be eliminated. For this reason, if both the main heater 23a and the sub-heater 23b are continuously turned on when feeding large-size paper, the edges may be heated more than necessary, resulting in high temperatures and poor fixing. Therefore, by turning on only the main heater 23a, whose heat generation intensity is constant in the axial direction, once the temperature sag at the edges of the paper has been eliminated, poor fixing due to high temperatures at the edges of the paper can be prevented.

[0061] The above example is shown schematically in FIG. 4. FIG. 4(a) shows when small-sized paper is passing, and FIG. 4(b) shows when large-sized paper is passing. As shown in the figure, when small-sized paper is passing, the main heater 23a is turned on and the sub-heater 23b is not turned on. On the other hand, when large-sized paper is passing, the main heater 23a and the sub-heater 23b are turned on. By doing so, the above-mentioned advantages can be obtained. In addition, the heat generation intensity represents the amount of heat generated when the heater is turned on, and the temperature of the belt member can be adjusted by controlling (duty control) the percentage at which the heater of that heat generation intensity is turned on (ON / OFF).

[0062] As mentioned above, Patent Document 1 has the problem of increasing the number of components, such as temperature detection devices, in addition to improving heating efficiency. To address this issue, we have studied and filed a patent application for a device that includes a heater that generates heat uniformly across the width of the recording medium within the maximum paper feed width, and a heater in which the heat generation intensity on both sides of the width is higher than that in the center. Such a device is believed to be effective in addressing the problem of increasing the number of components, such as temperature detection devices. However, in this case, the heat source emits light across the entire width regardless of paper size, so it is preferable to increase heating efficiency as much as possible. Therefore, the inventors conducted further research and, as described in this embodiment, arrived at the present invention by devising the arrangement of the heaters and components used.

[0063] In this embodiment, the main heater 23a has a constant heat generation intensity across the width of the recording medium, has a higher output than the sub-heater 23b, and is turned on more frequently than the sub-heater 23b. In addition, in the rotation direction of the fixing belt 21, the main heater 23a is disposed closer to the nip entrance Ne than the sub-heater 23b.

[0064] The main heater 23a has a higher output and is turned on more frequently than the sub-heater 23b, so by making the heat capacity of the glass barrel of the main heater 23a, which is turned on more frequently, smaller than the heat capacity of the glass barrel of the sub-heater 23b, the heating efficiency of the fixing belt 21 can be improved. This also makes it possible to create an energy-saving heating device. Note that the output of the main heater 23a and the sub-heater 23b mentioned above refers to the total amount of output over the entire width in the axial direction, and is not particularly limited, but for example, the output (emission intensity) of the main heater in this example can be approximately 1000 W, and the output (emission intensity) of the sub-heater can be approximately 350 W.

[0065] The reason the thermal capacity of the glass tube (also called the glass tube) of the main heater 23a can be reduced is that the light emission distribution is flat across the entire axial width, resulting in a flat temperature rise and uniform expansion across the width of the glass tube during filament heating due to current application. On the other hand, the sub-heater 23b has a difference in light emission between the center and end portions in the axial direction, resulting in a temperature difference in the glass tube along the axial direction during heating, and thus differential expansion. In this case, if the strength of the glass tube is insufficient, this differential expansion can cause microcracks in the glass tube wall. This can also cause halogen cycle failure and shorten the lifespan. Therefore, the main heater 23a is suitable for reducing its thermal capacity, and is suitable for reducing the outer diameter and thickness of the glass tube.

[0066] From the viewpoint of efficiency, it is particularly preferable to reduce the heat capacity of the glass barrel of the main heater 23a as well as the heat capacity of the glass barrel of the sub-heater 23b. However, as mentioned above, temperature deviations and expansion differences occur in the sub-heater 23b, making it difficult to reduce the diameter or thickness of the sub-heater 23b, and therefore to reduce the heat capacity. Therefore, as a guideline for reducing the heat capacity of the glass barrel of the main heater 23a as well as the heat capacity of the glass barrel of the sub-heater 23b, it is preferable to specify that the heat capacity of the glass barrel of the main heater 23a is smaller than the heat capacity of the glass barrel of the sub-heater 23b. In such a case, heating efficiency can be improved, and a highly efficient device can be obtained.

[0067] Methods for reducing the heat capacity of the glass tube of the main heater 23a include, for example, reducing the outer diameter of the glass tube, and reducing the outer diameter of the glass tube of the main heater 23a while maintaining its thickness. These methods are also called "reducing the diameter of the main heater." Other methods for reducing the heat capacity of the glass tube of the main heater 23a include reducing the thickness of the glass tube (increasing the inner diameter), or reducing the thickness of the glass tube while maintaining the outer diameter of the glass tube, which are also called thinning the main heater. Alternatively, for example, the main heater may be made thinner and have a smaller diameter.

[0068] 2 shows an example in which the diameter of the main heater 23a is reduced, that is, the outer diameter of the glass tube of the main heater 23a is made smaller than the outer diameter of the glass tube of the main heater 23a. By doing so, the heat capacity of the glass tube of the main heater 23a can be reduced, and the heat capacity of the glass tube of the main heater 23a can be made smaller than the heat capacity of the glass tube of the sub-heater 23b.

[0069] Furthermore, by reducing the diameter of the main heater 23a, the main heater 23a can be packed into the narrow space near the nip entrance, which is advantageous from the perspective of layout. Therefore, by reducing the diameter of the main heater 23a, the main heater 23a can be packed into the narrow space near the nip entrance Ne, which is partitioned by the support member 25 and the fixing belt 21, thereby making it possible to miniaturize the device. Furthermore, by reducing the diameter of the main heater 23a, it is possible to obtain the advantages of a wider irradiation angle and to reduce the distance between the filament coil of the main heater 23a and the fixing belt, thereby further improving heating efficiency.

[0070] Next, another example of this embodiment will be described. While the above example was an example in which the diameter of the main heater 23a was reduced, this example is an example in which the wall thickness of the main heater 23a was reduced. By reducing the thickness of the glass tube of the main heater 23a, which is frequently turned on, the heat capacity of the glass tube can be reduced, and heating efficiency can be improved.

[0071] 5 is a cross-sectional schematic diagram for explaining this example. As shown in the figure, the thickness of the glass tube of the main heater 23a in this example is thin. The reason why the heat capacity of the glass tube of the main heater 23a can be reduced is that the light emission distribution is flat across the entire width, so that the temperature of the glass tube also rises flatly across the width when the filament is heated by current flow, and the glass tube expands more uniformly than the sub-heater 23b. Because the glass tube of the main heater 23a expands more uniformly, the strength of the glass tube can be reduced more than that of the sub-heater 23b, making it possible to reduce the thickness of the glass tube, for example, from the outer surface side.

[0072] As mentioned above, the sub-heater 23b has a difference in light emission between the central and end portions in the axial direction, which causes a temperature difference in the glass tube in the axial direction during heating, resulting in an expansion difference. In this case, if the strength of the glass tube of the sub-heater 23b is insufficient, this expansion difference may cause microcracks in the wall of the glass tube. Furthermore, this may cause a malfunction of the halogen cycle and shorten the lifespan, so it is difficult to reduce the thermal capacity of the glass tube of the sub-heater 23b. On the other hand, the main heater 23a is suitable for reducing the thermal capacity of the glass tube by thinning it.

[0073] In this example, the thickness of the glass barrel of the main heater 23a is smaller than the thickness of the glass barrel of the sub-heater 23b. In this case, the heat capacity of the glass barrel of the main heater 23a, which is often turned on, can be sufficiently reduced, thereby improving heating efficiency.

[0074] Next, another example of this embodiment will be described. In this example, the filament coil of the main heater 23a is double-wound. FIG. 6 is a diagram for explaining this example, and is a diagram schematically showing the main heater 23a and the sub-heater 23b when viewed from a direction perpendicular to the axial direction (the width direction of the recording medium). As shown in the figure, the filament coil 40a of the main heater 23a is double-wound. By double-wounding the filament coil 40a of the main heater 23a, the heating efficiency of the heater can be further improved. In this example, by double-wounding the filament coil of the heater in conjunction with reducing the thermal capacity of the glass tube of the main heater 23a, the heating efficiency of the heater can be further improved.

[0075] Note that A in the figure represents the outer diameter of the glass barrel of the main heater 23a, and B in the figure represents the outer diameter of the glass barrel of the sub-heater 23b. In the figure, A and B appear to be the same, but in this embodiment, A is made smaller than B. Also, as in the example shown in Figure 5, it is preferable to make the thickness of the glass barrel of the main heater 23a smaller than the thickness of the glass barrel of the sub-heater 23b. In the figure, the thicker glass barrel of the sub-heater 23b is indicated by a thick line.

[0076] In this example, the wire diameter of the filament coil of the main heater 23a is preferably smaller than that of the filament coil of the sub-heater 23b. By using a thin-diameter filament in the main heater 23a and configuring it as a double-wound coil, the temperature of the filament can be increased quickly and the surface area can be increased, thereby improving heating efficiency. In the figure, the thin wire diameter of the filament coil of the main heater 23a is indicated by a thin line.

[0077] In this example, the winding of the filament coil of the sub-heater 23b may be changed depending on the location, as shown in Fig. 6. For example, it is preferable to make the heat generation intensity higher at both ends of the sub-heater 23b.

[0078] Next, another example of this embodiment will be described. In the fixing device of this embodiment, the configuration of the nip forming member can be changed as appropriate. In this embodiment, it is preferable to use a heat conductive member as the nip forming member. By using a heat conductive member, a heat uniformity effect can be achieved and temperature deviation of the fixing belt 21 in the axial direction can be reduced.

[0079] Furthermore, by adjusting the heat uniformity effect of the nip forming member in accordance with the increased heating efficiency of the heater, the temperature deviation of the fixing belt 21 in the axial direction can be further reduced, and the range of CPM (Copies Per Minute) to which this embodiment can be applied can be expanded. In the case of a high CPM machine, the temperature deviation of the fixing belt 21 in the axial direction tends to be large, so by using a heat conductive member, this embodiment can also be applied to a high CPM machine.

[0080] In this embodiment, when a thermally conductive member is used as the nip forming member, the nip forming member may consist of only the thermally conductive member, or the nip forming member may consist of multiple members including the thermally conductive member. For example, the nip forming member 24 shown in Figures 2 and 5 may be made of a material with high thermal conductivity, and the illustrated nip forming member 24 may be a thermally conductive member.

[0081] FIG. 7 shows another example of this embodiment. In FIG. 7, a heat conductive member 27 is used in addition to the nip forming member 24a. As shown in the figure, the nip forming member 24a is covered with the heat conductive member 27, and the heat conductive member 27 abuts against the fixing belt 21. In this example, the nip forming member 24a and the heat conductive member 27 form the nip forming member 24, and the nip forming member 24 in this example is made up of multiple members including the heat conductive member 27. There are no particular limitations on the material of the nip forming member 24a, and any material can be used.

[0082] The material of the heat conducting member can be selected appropriately, and for example, the following materials (good heat conductors) that are heat resistant and have high thermal conductivity can be used.

[0083] (Material) (Thermal conductivity) Carbon nanotubes: 3000~5500W / mK Graphite sheet: 700~1750W / mK Silver:420W / mK Copper:398W / mK Aluminum: 236W / mK

[0084] As described above, according to the present invention, it is possible to prevent an increase in the number of components, such as temperature detection means, used in the heat source and improve heating efficiency. Furthermore, even when using a heater that emits light across the entire axial width, it is possible to provide a highly efficient and energy-saving heating device.

[0085] Next, another example of this embodiment will be described, and a description of the same matters as above will be omitted. The examples shown in Figures 2 and 5 above are examples in which the diameter of the main heater 23a is reduced or the thickness of the main heater 23a is reduced, but both the diameter and thickness may be reduced.

[0086] FIG. 8 is a cross-sectional schematic diagram for explaining this embodiment. As shown in the figure, the outer diameter and thickness of the glass cylinder of the main heater 23a in this embodiment are reduced. By reducing the diameter and thickness in this way, the heat capacity of the glass cylinder of the main heater 23a can be further reduced, and heating efficiency can be further improved. This results in a heating device that is more efficient and energy-saving.

[0087] In this example, the outer diameter and thickness of the glass cylinder of the main heater 23a are smaller than the outer diameter and thickness of the sub-heater 23b, which makes it possible to effectively improve the heating efficiency.

[0088] Also in this example, by reducing the diameter of the main heater 23a, an advantage is obtained in that it can be disposed at a position closer to the nip entrance Ne in the rotation direction of the fixing belt 21. This makes it possible to dispose the main heater 23a in a small space near the nip entrance Ne, which is partitioned by the support member 25 and the fixing belt 21. Furthermore, in addition to being able to widen the irradiation angle of the main heater 23a, the distance between the filament and the fixing belt 21 can be reduced, improving heating efficiency. [Explanation of symbols]

[0089] 20 Fixing device 21 Fixing belt 22 Pressure roller 23 Halogen heater 23a Main heater 23b Sub-heater 24 Nip forming member 25 Support member 26 Reflective material 27 Thermal Conductive Materials 28 Temperature Sensor [Prior art documents] [Patent documents]

[0090] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-99590

Claims

1. A heating device having a heat source that radiates heat from the inside of a rotatable endless belt member, the belt member forms a nip portion with a pressure member facing the belt member, the heat source includes a first glass cylinder and a second glass cylinder; the first glass cylinder and the second glass cylinder each have a coil member therein across the maximum paper passing width of the recording medium; the first glass cylinder has a constant heat generation intensity across the width direction of the recording medium, a higher output than the second glass cylinder, a higher lighting frequency than the second glass cylinder, and a smaller heat capacity than the second glass cylinder; the second glass cylinder has a portion in the width direction of the recording medium where heat generation intensity is greater than that of other portions, A heating device, characterized in that, in the rotation direction of the belt member, the first glass cylinder is disposed closer to an entrance of the nip portion than the second glass cylinder.

2. The heating device according to claim 1 , wherein the first glass cylinder has an outer diameter smaller than that of the second glass cylinder.

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

4. 4. The heating device according to claim 1, wherein the coil member of the first glass cylinder is double-wound.

5. 5. The heating device according to claim 1, wherein the second glass cylinder has a higher heat generation intensity at both end portions in the width direction of the recording medium than at the center portion.

6. the belt member; a pressure member disposed opposite the belt member and pressing the belt member; a nip forming member disposed inside the belt member and configured to form a nip portion by receiving pressure from the pressure member; a support member disposed inside the belt member and supporting the nip forming member; A fixing device comprising: the heating device according to any one of claims 1 to 5.

7. 7. The fixing device according to claim 6, wherein the nip forming member is made up of only a heat conductive member, or is made up of a plurality of members including a heat conductive member.

8. 8. An image forming apparatus comprising the fixing device according to claim 6.

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