Fixing apparatus and image forming apparatus

Abstract

To provide a fixing device that can cut off power supply to first and second heat sources before the temperature of the ends of a fixing member increases to a predetermined abnormal temperature or more, and can favorably fix images at the ends in a width direction of a recording material with the maximum width size, and to provide an image forming apparatus.SOLUTION: The ratio (maximum heat generation ratio Rp) of the calorific power at maximum heat generation parts with the largest calorific power on both sides of a second heat source such as a sub-heater to the calorific power at the center is 150% or less, and the ratio (end heat generation rate Rq) of the calorific power at parts corresponding to the width direction ends of the maximum width size of the second heat source to the calorific power at the center is 130% or more. The half value width of end areas on both sides of the second heat source and having a higher calorific power than the calorific power at the center is 65 mm or less.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Conventionally, a fixing device is known that includes a fixing member, a plurality of heating sources for heating the fixing member having different heat generation distributions from each other, and power cut-off means that is disposed opposite to the vicinity of the center in the width direction of the fixing member and cuts off the power supply to each heating source before the temperature of the fixing member reaches a predetermined abnormal temperature or higher.

[0003] Patent Document 1 describes, as the above fixing device, one that includes a first heating source and a second heating source, the second heating source having a heat generation distribution in which the heat generation amounts on both sides in the width direction are larger than the heat generation amount at the center, and the ratio of the heat generation amount at the center of the maximum heat generation portion having the largest heat generation amount on both sides of the second heating source to the heat generation amount is 125%.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a recording material with the maximum size width is passed through, there is a possibility that the image at the widthwise end of the recording material cannot be fixed well.

Means for Solving the Problems

[0005] To solve the above-mentioned problems, the present invention provides a fixing device comprising a fixing member, a plurality of heating sources for heating the fixing member having different heat distributions, and power cutting means arranged opposite each other near the center in the width direction of the fixing member, which cuts off the power supply to each heating source before the temperature of the fixing member exceeds a predetermined abnormal temperature, wherein the device comprises a first heating source having a uniform heat distribution in the width direction within the maximum size width of the paperable recording material, and a second heating source having a heat distribution in which the amount of heat generated corresponding to both sides in the width direction of the maximum size width is higher than the amount of heat generated in the center, wherein the ratio of the amount of heat generated at the maximum heat generation points on both sides of the second heating source to the amount of heat generated in the center is 150% or less, the ratio of the amount of heat generated at the ends of the second heating source in the width direction of the maximum size width to the amount of heat generated in the center is 130% or more, and the half-width of the regions on both sides of the second heating source where the amount of heat generated is higher than the amount of heat generated in the center is 65 mm or less. When each heating source experiences thermal runaway during cold start-up, the center of the fixing member in the width direction heats up faster than both sides of the fixing member. Furthermore, when each heating source experiences thermal runaway after paper feeding, the input power to each heating source is set such that the temperature of the center of the fixing member in the width direction and the temperatures of both sides of the fixing member reverse before the fixing member reaches a predetermined abnormal temperature. It is characterized by the following: [Effects of the Invention]

[0006] According to the present invention, the power supply to the first and second heating sources can be cut off before the end of the fixing member exceeds a predetermined abnormal temperature, and the image at the widthwise end of the recording material of the maximum size width can be fixed well. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the configuration of the printer according to this embodiment. [Figure 2] Schematic diagram of the fixing device. [Figure 3] A diagram showing the heat generation distribution at the widthwise ends of the subheater. [Figure 4] Temperature rise profile of the fixing belt during a thermal runaway test using the fixing device of Example 1. [Figure 5] The heating profile of the end and center of the fixing belt during cold start-up in the fixing device of Example 1. [Figure 6] Temperature rise profile of the fixing belt during a thermal runaway test in the fixing device of Comparative Example 1. [Figure 7](a) shows the temperature rise profile of the end and center of the fixing belt during cold start-up in the fixing device of Comparative Example 2, and (b) shows the temperature rise profile of the end and center of the fixing belt during cold start-up in the fixing device of Comparative Example 2. [Figure 8] Temperature rise profile of the fixing belt during the second thermal runaway test using the fixing device of Example 1. [Figure 9] Temperature rise profile of the fixing belt during the second thermal runaway test using the fixing device of Comparative Example 1. [Modes for carrying out the invention]

[0008] The following describes one embodiment of an electrophotographic printer (hereinafter simply referred to as "printer") as an image forming apparatus to which the present invention is applied. First, the general configuration of the printer will be described. Figure 1 is a schematic diagram showing the configuration of this printer. Printer 200 is a color printer that uses a tandem system in which image forming units that form multiple color images are arranged side by side along the tension direction of the belt, but the present invention is not limited to this system, and can also be applied to copiers, facsimile machines, and other devices in addition to printers.

[0009] The printer 200 has four image stations as an imaging unit, each equipped with a photosensitive drum 20Y, 20C, 20M, and 20Bk, and an optical writing device 8 positioned opposite the four image stations below. The printer 200 also has an intermediate transfer belt unit 10 positioned opposite the four image stations above.

[0010] The four imaging stations consist of photoreceptor drums 20Y, 20C, 20M, and 20Bk, arranged in this order from the upstream side in the A1 direction. Each photoreceptor drum 20Y, 20C, 20M, and 20Bk forms yellow, cyan, magenta, and black images, respectively. Devices for image formation processing are arranged around each photoreceptor drum according to its rotation. Focusing on the photoreceptor drum 20Bk, which forms the black image, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk are arranged along the rotation direction of the photoreceptor drum 20Bk to perform image formation processing.

[0011] The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, and a rotating polyface mirror as a deflection means. The optical writing device 8 emits writing light Lb corresponding to each color to each photoreceptor drum 20Y, 20C, 20M, and 20Bk to form an electrostatic latent image on the photoreceptor drums 20Y, 20C, 20M, and 20Bk. In Figure 1, for convenience, only the image station for the black image is labeled, but the same applies to the other image stations.

[0012] The intermediate transfer belt unit 10 includes an intermediate transfer belt 11, which is an endless belt, primary transfer rollers 12Y, 12C, 12M, and 12Bk, as well as elastic rollers 72 and driven rollers 73 around which the intermediate transfer belt 11 is wrapped. The driven rollers 73 are equipped with a biasing means such as a spring and also function as a tension biasing means for the intermediate transfer belt 11.

[0013] The printer 200 also includes a secondary transfer roller 5, which is a transfer roller acting as a transfer member, and an intermediate transfer cleaning device 13. The secondary transfer roller 5 is positioned opposite the intermediate transfer belt 11 and moves along with the intermediate transfer belt 11. The intermediate transfer cleaning device 13 is positioned opposite the intermediate transfer belt 11 and cleans the intermediate transfer belt 11.

[0014] The intermediate transfer cleaning device 13 has a cleaning brush and a cleaning blade arranged so as to contact the intermediate transfer belt 11. By these, foreign matters such as residual toner on the intermediate transfer belt 11 are scraped off and removed, and the intermediate transfer belt 11 is cleaned. The intermediate transfer cleaning device 13 has a discharging means for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

[0015] The transfer device 71 is constituted by the above intermediate transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, 12Bk, the secondary transfer roller 5, and the intermediate transfer cleaning device 13.

[0016] The printer 200 includes a sheet feeding device 61 on which sheets S are loaded at the lower part of the main body. The sheet feeding device 61 has a feeding roller 3 that contacts the upper surface of the uppermost sheet S. When the feeding roller 3 is rotationally driven in the counterclockwise direction, the uppermost sheet S is fed toward the registration roller pair 4.

[0017] The registration roller pair 4 feeds the sheet S conveyed from the sheet feeding device 61 toward the secondary transfer nip at a predetermined timing in accordance with the timing when the toner image on the intermediate transfer belt reaches the secondary transfer nip. The printer 200 also includes a sensor for detecting that the leading edge of the sheet S has reached the registration roller pair 4.

[0018] The printer 200 has a contact heating type fixing device 100 as a fixing unit for fixing the toner image on the sheet S (fixing target) on which the toner image has been transferred. The printer 200 also has a paper discharge roller 7 for discharging the fixed sheet S to the outside of the main body of the printer 200, and a paper discharge tray 17 arranged at the upper part of the main body of the printer 200 for stacking the sheet S discharged to the outside of the main body of the printer 200 by the paper discharge roller 7. The printer 200 also has toner bottles 9Y, 9C, 9M, 9Bk for storing the toners of yellow, cyan, magenta, and black colors below the paper discharge tray 17.

[0019] The image forming operation of the printer 200 is as follows. Visible images are formed on each of the photosensitive drums 20Y, 20C, 20M, and 20Bk at the four image forming stations. The visible images formed on each of the photosensitive drums 20Y, 20C, 20M, and 20Bk perform a primary transfer process on the intermediate transfer belt 11 that moves in the direction of arrow A1 while facing each of the photosensitive drums 20Y, 20C, 20M, and 20Bk, and the respective images are superimposed and transferred. The visible images superimposed and transferred on the intermediate transfer belt 11 are batch-transferred by performing a secondary transfer process with the secondary transfer roller 5 on the paper S. The paper S on which the toner image has been batch-transferred is fixed by the fixing device 100, and the fixed paper S is discharged to the outside of the main body of the printer 200 by the paper discharge roller 7.

[0020] Figure 2 is a schematic configuration diagram of the fixing device 100. The fixing device 100 includes an endless fixing belt 101 as a rotatable fixing member and a pressure roller 103 as a rotatable pressure member disposed opposite thereto. The fixing device 100 has a main heater 102a as a first heating source, a sub heater 102b as a second heating source, a pad 106 as a nip forming member, and a support member 107 inside the fixing belt 101. Further, the fixing device 100 has a reflector 109 as a reflecting plate and a sliding member 116 inside the fixing belt 101. All of the main heater 102a, sub heater 102b, pad 106, sliding member 116, and support member 107 disposed inside the fixing belt 101 have lengths equal to or greater than the length in the width direction of the fixing belt 101. In the figure, the paper S is conveyed from below upward, and the moving direction of the fixing belt 101 is counterclockwise in the figure.

[0021] The fixing belt 101 is composed of an endless belt or film made of a metal belt such as nickel or SUS, or a resin material such as polyimide. The surface layer of the belt has a release layer such as a PFA or PTFE layer to prevent toner from adhering. Between the belt base material made of nickel or SUS and the PFA or PTFE layer, there may be an elastic layer made of a silicone rubber layer or the like. Deformation of the silicone rubber layer absorbs minute irregularities, improving the orange peel image. Furthermore, between the belt base material and the elastic layer, there may be a high thermal conductivity layer, such as a metal layer made of copper or nickel with high thermal conductivity. By providing a high thermal conductivity layer, heat from the fixing belt can be transferred in the width direction by the high thermal conductivity layer, and the temperature of the fixing belt in the width direction can be made uniform.

[0022] The pressure roller 103 has an elastic rubber layer 104 on a core metal 105, and a release layer (PFA or PTFE layer) 103a is provided on its surface to obtain release properties. The pressure roller 103 rotates when driving force is transmitted to it via gears from a drive source such as a motor provided in the image forming apparatus. The pressure roller 103 is also pressed against the fixing belt 101 by a spring or the like, and the elastic rubber layer 104 is compressed and deformed to have a predetermined nip width. The pressure roller 103 may be a hollow roller, and the pressure roller 103 may have a heating source such as a halogen heater.

[0023] The pad 106, positioned inside the fixing belt 101 as a nip-forming member, forms a fixing nip N, which is a fixing portion, with the pressure roller 103 via the fixing belt 101. The pad 106 is provided with a sliding member 116 that slides against the inner surface of the fixing belt. This pad 106 is supported by a support member 107. The support member 107 prevents the pad 106 from deflecting when pressure is applied by the pressure roller 103, and ensures that a uniform nip width is obtained in the axial direction.

[0024] The main heater 102a and sub-heater 102b are halogen heaters, and the fixing belt 101 is directly heated from the inner circumference by the radiant heat from these heaters 102a and 102b. Here, each heater 102a and 102b only needs to be able to heat the fixing belt 101, and may be an induction heater, a resistance heating element, a carbon heater, etc.

[0025] The main heater 102a has a uniform heat distribution across the maximum width of paper that this printer can feed. On the other hand, the sub-heater 102b has a heat distribution where the amount of heat generated at both ends in the width direction is greater than the amount of heat generated in the center.

[0026] Furthermore, in this embodiment, a reflector 109 is provided between each heater 102a, 102b and the support member 107. Alternatively, the same effect can be obtained by applying heat insulation or mirror-finish treatment to the surface of the support member 107 instead of providing the reflector 109.

[0027] A temperature detection sensor 110, which is a temperature detection means for detecting the surface temperature of the fixing belt 101, is provided on the outside of the fixing belt 101. A temperature sensor with high temperature response, such as a thermopile, is used as the temperature detection sensor 110. The temperature detection sensor 110 detects the temperature of the center of the fixing belt 101 in the width direction.

[0028] Furthermore, a power cutoff device 111 is positioned outside the fixing belt 101, which is a power cutoff means that detects abnormalities in the surface temperature of the fixing belt 101 and stops the power supply to the heater. The power cutoff device 111 can be a thermostat or a thermal fuse. Alternatively, the power cutoff device 111 may be an inexpensive temperature sensor with a worse temperature response than the temperature sensor 110, which cuts off power to the heater based on the detection result of the temperature sensor. The power cutoff device 111 is positioned approximately in the center of the fixing belt 101 in the width direction.

[0029] The fixing belt 101 rotates in conjunction with the pressure roller 103. In Figure 2, the pressure roller 103 rotates due to a drive source, and the driving force is transmitted to the belt at the fixing nip N, causing the fixing belt 101 to rotate. The toner image, which is the image on the paper, is fixed at the fixing nip N by heating and pressurizing.

[0030] During the warm-up period, when the temperature of the fixing belt 101 is raised to a specified temperature (fixing temperature or standby temperature), both the sub-heater 102b and the main heater 102a are turned on to increase the amount of heat generated at the ends compared to the center. This is because, during warm-up, heat is easily lost from the fixing belt by guide members and the like that which contact the widthwise ends of the inner surface of the fixing belt and guide the fixing belt, causing the temperature at the ends of the fixing belt to become lower than the temperature at the center of the fixing belt, a phenomenon known as temperature degradation.

[0031] Therefore, in this embodiment, during warm-up, both the sub-heater 102b and the main heater 102a are lit to increase the heat generated at the edges compared to the center, thereby suppressing temperature sagging at the edges of the fuser belt 101. This allows the widthwise edges of the fuser belt 101 to be quickly raised to the same temperature as the center (fusing temperature or standby temperature). This shortens the warm-up time and thus the first print time. It also ensures proper adhesion of the paper edges during the first image formation after the warm-up is complete.

[0032] When the paper size fed to the fuser nip is large, both the sub-heater 102b and the main heater 102a are first turned on. By turning on both the sub-heater 102b and the main heater 102a in this way, it is possible to suppress the fixing operation from being performed with temperature sagging at the edges, thereby suppressing the occurrence of fixing defects at the widthwise edges of the toner image. In this embodiment, sizes of B4 portrait (width size: 257 mm) or larger are considered large sizes, and sizes smaller than B4 portrait are considered small sizes, but this is not limited to this, and the large and small sizes can be set as appropriate depending on the configuration of the device.

[0033] Then, after a predetermined time has elapsed since the start of paper feeding (start of fixing operation), and the guide member has risen to near the fixing temperature, and the conditions are met such that heat transfer from the end of the fixing belt 101 to the guide member is reduced and end temperature sagging does not occur, the sub-heater 102b is turned off. Then, only the main heater 102a is turned on and off based on the detection result of the temperature detection sensor 110 to maintain the fixing belt 101 at the fixing temperature.

[0034] When only the main heater 102a is lit, the amount of heat generated is almost uniform in the width direction, and the fixing belt 101 is heated almost uniformly. Therefore, once conditions are met to prevent temperature sagging at the edges, the lighting of the main heater 102a is controlled based on the temperature of the fixing belt 101 detected by the temperature detection sensor 110 located in the center in the width direction. This makes it possible to maintain the temperature of the fixing belt 101 at almost the fixing temperature in the width direction, thereby suppressing the occurrence of fixing failures at the edges in the width direction.

[0035] When the paper being fed is small in size, only the main heater 102a is controlled to light up based on the detection result of the temperature detection sensor 110, thereby maintaining the fuser belt 101 at the fuser temperature.

[0036] Thus, in this embodiment, by making the main heater 102a generate a uniform amount of heat across the maximum width that the printer can handle, the end temperature sensor for controlling the illumination of the sub-heater 102b, which maintains the end of the fuser belt at the fuser temperature, can be eliminated. This reduces the number of parts and lowers the cost of the device.

[0037] Very rarely, a malfunction in the control unit may cause the power supply control to the main heater 102a and sub-heater 102b to become uncontrollable, resulting in a so-called thermal runaway where the fixing belt overheats abnormally. Conventionally, a power cutoff device to handle thermal runaway of the main heater 102a was positioned opposite each other in the center of the fixing belt, and a power cutoff device to handle thermal runaway of the sub-heater 102b was positioned opposite each other at the end of the fixing belt. However, conventionally, having multiple power cutoff devices increased the number of parts, potentially leading to increased costs and a larger device size.

[0038] In this embodiment, by adjusting the heat distribution of the subheater 102b to an appropriate distribution, power to the subheater 102b can be cut off by a power cutoff device positioned approximately in the center of the width direction of the fixing belt before the end temperature of the fixing belt exceeds an abnormal temperature due to thermal runaway of the subheater 102b. A detailed explanation follows with reference to the drawings.

[0039] Figure 3 shows the heat generation distribution at the widthwise end of the subheater 102b. The heat generation distribution shown in Figure 3 was determined as follows: A constant voltage (e.g., 50V) was applied to the subheater 102b and it waited for 1 minute. Then, the optical sensor was scanned over the entire width of the subheater 102b from one end to the other in approximately 20 seconds, and the amount of infrared light at each position in the width of the subheater 102b was detected by the optical sensor. The amount of infrared light corresponds to the amount of heat generated at each position of the heater.

[0040] In this embodiment, the subheater 102b has a maximum heat generation ratio Rp of 150%, which is the ratio of the heat generation at the maximum heat generation point at the widthwise end to the heat generation at the center. In addition, the edge heat generation ratio Rq, which is the ratio of the heat generation at the edge to the center of the maximum paper size that this printer can feed (in this embodiment, SRA3 size (width: 320 mm x height: 450 mm)), is set to 130%. Furthermore, the half-width L of the edge region of the subheater 102b in this embodiment, where the amount of heat generated is greater than at the center, is set to 65 mm. Note that the above half-width is half of the central heat generation ratio (100%) of the maximum heat generation ratio Rp of 150% (125%).

[0041] Figure 4 shows the temperature rise profile of the fixing belt 101 during a thermal runaway test, which was intentionally performed using the fixing device of Example 1 equipped with a sub-heater 102b having the heat distribution shown in Figure 3. Figure 4(a) shows the temperature rise profile of the fixing belt 101 in a cold start-up thermal runaway test, and Figure 4(b) shows the temperature rise profile of the fixing belt 101 in a post-paper feed thermal runaway test. The post-paper feed thermal runaway test assumes a situation where an unexpected failure occurs after paper feed, the end surface temperature of the fixing belt 101 saturates at around 240°C, and the main heater 102a and sub-heater 102b simultaneously experience thermal runaway from a fixing belt stop state.

[0042] The cold start-up thermal runaway test was performed by turning on the main heater 102a and sub-heater 102b from a cold state with the fuser belt 101 stopped. The post-paper-feeding thermal runaway test was performed after continuously feeding 100 sheets of A4 portrait size paper, with the main heater 102a and sub-heater 102b turned on with the fuser belt 101 stopped. Specifically, the temperature of the fuser belt surface was controlled to 138°C using only the main heater 102a with the temperature detection sensor 110, while feeding A4 portrait size paper (Ricoh copy printing paper 90K, basis weight 105g / m²) at a line speed of 150mm / s. 2 ) was fed through 100 sheets of paper in a row. After that, with the fuser belt stopped, the main heater 102a and sub-heater 102b were turned on simultaneously.

[0043] The heating profile shown in Figure 4 is the heating profile of the surface temperature at position Q shown in Figure 2, before the fixing nip, where the surface temperature of the fixing belt 101 is highest in the rotational direction (hereinafter referred to as the pre-nip temperature). Multiple thermocouples were placed in the width direction at position Q shown in Figure 2, and the pre-nip temperature was measured in the width direction of the fixing belt 101 using these thermocouples to obtain the heating profile shown in Figure 4. Tc is the heating profile at the center of the fixing belt 101 in the width direction, and Te is the heating profile at a point approximately 130 mm away in the width direction from the center of the fixing belt in the width direction.

[0044] The following shows the specifications of the fixing device used in Example 1 for each thermal runaway test. • Main heater 102a: A halogen heater with a uniform heat distribution across the maximum paper size (SRA3 size) that can be fed through. • Subheater 102b: A halogen heater having the end heat distribution shown in Figure 3. • Temperature sensing sensor 110: Located in the center of the width direction of the thermopile and fixing belt. • Power cutoff device 111: Thermostat, positioned 40 mm from the center in the width direction of the fixing belt, with a gap of approximately 3 mm between it and the fixing belt. • Sliding member 116: Material: PTFE • Pressure roller 103: Outer diameter 32 mm, width (axial) length 340 mm Core metal 105:φ12mm Elastic rubber layer 104: 4mm thick foamed rubber Release layer 103a: 50 μm PFA tube • Fixing belt 101: Outer diameter 30 mm, width (axial) length 360 mm, and has an inner surface coating layer with a thickness of 10 μm, a nickel base material with a thickness of 30 μm, a high thermal conductivity layer made of copper with a thickness of 10 μm, a silicone rubber layer with a thickness of 120 μm, and a PFA coating with a thickness of 7 μm. • Nip load: 25 kgf • Fixing nip width: 10mm in the center, 10.5mm at the ends

[0045] The heater ignition conditions for each thermal runaway test are as follows: • Input voltage (maximum): 274V (rated voltage upper limit + 10%) • Main heater input power: 810W (rated power limit + 10%) • Subheater input power: 520W (rated voltage upper limit + 10%) Abnormal temperature of fixing belt 101: 400℃

[0046] In the fixing device of Example 1, which is equipped with a subheater 102b having the heat distribution shown in Figure 3 at its widthwise end, as shown in Figure 4(a), when thermal runaway occurs during cold start-up, the center of the fixing belt 101 heats up faster than the ends. As a result, the thermostat located approximately in the center can be activated and the power to each heater can be cut off before the surface temperature of the fixing belt exceeds an abnormal temperature (400°C).

[0047] As shown in Figure 4(b), in the fixing device of Example 1, even if the main heater 102a and sub-heater 102b experience thermal runaway when the pre-nip temperature Te at the end of the fixing belt 101 is higher than the pre-nip temperature Tc at the center, the pre-nip temperature Tc at the center will become higher than the pre-nip temperature Te at the end before it reaches an abnormal temperature (400°C). Therefore, even if thermal runaway occurs when the pre-nip temperature Te at the end of the fixing belt 101 is higher than the pre-nip temperature Tc at the center, such as after paper feeding, the thermostat located approximately in the center will activate before the end of the fixing belt 101 exceeds an abnormal temperature (400°C), and power to each heater can be cut off.

[0048] Furthermore, the reason why the pre-nip temperature Tc at the center of the fixing belt and the pre-nip temperature Te at the end reverse during the heating process is thought to be as follows. That is, in the initial stages of thermal runaway, the temperature at the end of the fixing belt 101 is higher than that at the center, so heat from the end of the fixing belt 101 is supplied to the center by heat conduction in the belt width direction. In particular, as mentioned above, the fixing belt 101 has a highly thermally conductive layer which is a 10 μm thick metal layer made of copper. Therefore, it has good thermal conductivity in the belt width direction, and the heat from the hotter fixing belt end can be efficiently transferred to the center in the belt width direction. In this way, as the heat from the fixing belt end moves to the center, the temperature difference between the end and the center disappears, and eventually the temperature in the width direction of the fixing belt 101 becomes uniform. After the temperature is uniform, the heat from the end of the fixing belt 101 moves to guide members and the like that come into contact with the end of the inner circumferential surface of the fixing belt 101, but the heat in the center in the width direction has fewer destinations for heat transfer compared to the end of the fixing belt 101. As a result, after the temperature becomes uniform, the pre-nip temperature Tc in the center of the fixing belt becomes higher than the pre-nip temperature Te at the ends, and it is thought that the pre-nip temperature Tc in the center of the fixing belt and the pre-nip temperature Te at the ends reverse during the heating process.

[0049] Figure 5 shows the temperature rise profile of the pre-nip temperature (temperature at position Q in Figure 2) during cold start-up in the fixing device of Example 1, between the fixing belt at the end corresponding to the maximum paper-passable width and the central section. In Figure 5, the target pre-nip temperature is the pre-nip temperature when the main heater 102a is controlled to light up so that the temperature detected by the temperature sensing sensor 110 is 138°C. In this embodiment, the target pre-nip temperature is 150°C. As shown in Figure 5, the fuser unit of Example 1 can raise the temperature of the fuser belt 101 to approximately the target pre-nip temperature at the end of the fuser belt corresponding to the maximum paper-passable width (SRA3 size) before the paper enters the fuser nip N. As a result, even if the first paper size printed after the device is powered on is the maximum paper-passable width (SRA3 size) of this printer, the toner image at the edges in the paper width direction can be properly fixed to the paper.

[0050] Figure 6 shows the temperature rise profile of the fixing belt during a thermal runaway test in the fixing device of Comparative Example 1. Figure 6(a) shows the temperature rise profile of the fixing belt 101 during a cold start-up thermal runaway test, and Figure 6(b) shows the temperature rise profile of the fixing belt 101 during a post-paper-feed thermal runaway test.

[0051] The fixing device of Comparative Example 1 has the same configuration as that of Example 1, except that the maximum heat generation ratio Rp of the subheater 102b was set to 160%. A thermal runaway test was then performed under the same conditions as in Example 1, and the pre-nip temperature Te at the end of the fixing belt and the pre-nip temperature Tc at the center were measured.

[0052] The fixing device of Comparative Example 1 has a maximum heat generation ratio Rp of subheater 102b set to 160%, which is 10% higher than the fixing device of Example 1. As a result, the amount of heat supplied to the end side of the fixing belt is greater than in Example 1, and as shown in Figure 6(a), in the case of thermal runaway during cold start-up, the end side of the fixing belt 101 heats up faster than the center. Therefore, the end side of the fixing belt 101 reaches an abnormal temperature (400°C) before the thermostat, which is positioned approximately in the center, can be activated by the surface temperature of the center of the fixing belt.

[0053] As shown in Figure 6(b), even in the case of thermal runaway after continuous printing, the ends of the fixing belt 101 reach an abnormal temperature (400°C) faster than the center. The following reasons are considered to be the cause. Specifically, the maximum heat generation ratio Rp of the sub-heater 102b is set to 160%, which is 10% higher than that of the fixing device in Example 1. As a result, the amount of heat supplied to the ends of the fixing belt 101 by the sub-heater 102b and the main heater 102a is greater than in Example 1. Consequently, the amount of heat supplied to the ends of the fixing belt 101 by the heaters is greater than the amount of heat transferred from the ends of the fixing belt 101 to the center of the belt and the guide member, and it is thought that the pre-nip temperature Te at the ends of the fixing belt 101 remained higher than the pre-nip temperature Tc at the center of the fixing belt. Therefore, it is thought that the thermostat activated based on the surface temperature of the center of the fixing belt after the ends of the fixing belt 101 exceeded an abnormal temperature (400°C). Thus, in the fixing device of Comparative Example 1, if thermal runaway occurs, the end of the fixing belt 101 may reach an abnormal temperature (400°C), and the fixing device may malfunction due to the heat.

[0054] Table 1 below shows the results of evaluating gloss unevenness and edge temperature sagging for the fixing device of Example 1 and the fixing device of Comparative Example 1.

[0055] [Table 1]

[0056] Starting from a cold state, use A3 size paper (basis weight 105g / m²). 2The relationship between the pre-nip temperature of the fixing belt 101, detected by a thermocouple at the position just before the fixing nip (position Q in Figure 2) when continuously feeding paper, and gloss unevenness was pre-evaluated. As a result, when the pre-nip temperature at the end of the fixing belt 101 exceeded +8°C (158°C) above the target pre-nip temperature of 150°C, gloss unevenness occurred with different gloss levels in the center and at the widthwise ends. Therefore, if there was a point where the pre-nip temperature at the end of the fixing belt exceeded 158°C before the paper entered the fixing nip N from a cold state, the gloss unevenness was judged as "×". On the other hand, if the pre-nip temperature at the end of the fixing belt was 158°C or lower, the gloss unevenness was judged as "〇".

[0057] If the pre-nip temperature at the end of the fixing belt 101 was less than -8°C (less than 142°C) of the target pre-nip temperature of 150°C before the paper entered the fixing nip N from a cold state, a cold offset occurred. Therefore, if the pre-nip temperature at the end of the fixing belt 101 was less than 142°C, it was judged as "×". On the other hand, if the pre-nip temperature at the end of the fixing belt was 142°C or higher, the edge temperature sag judgment was judged as "〇".

[0058] In both Comparative Example 1 and Example 1, the pre-nip temperature at the end of the fixing belt was kept within the range of 150°C ± 8°C before the paper entered the fixing nip N from a cold state. As a result, in both Comparative Example 1 and Example 1, even if the first paper size printed after turning on the device is large size paper, the difference in gloss between the edges and the center in the width direction of the paper can be suppressed. Furthermore, fixing failure at the edges in the width direction of the paper (cold offset) due to edge temperature sagging can also be suppressed.

[0059] Table 2 below shows the results of the thermal runaway tests for Comparative Example 2 and Comparative Example 3.

[0060] [Table 2]

[0061] The fixing device of Comparative Example 2 is identical to that of Example 1, except that the heat generation ratio Rq of the subheater edge is set to 120%, which is 10% lower than that of Example 1, as shown in Table 2. Comparative Example 3 is identical to that of Example 1, except that the width at half maximum is set to 75 mm, which is 10 mm longer than that of Example 1, in the width at half maximum of the subheater edge region L.

[0062] In Comparative Examples 2 and 3, similar to Example 1, the center of the fixing belt 101 reached an abnormal temperature of 400°C before the edges in both the cold start-up thermal runaway test and the post-paper-feed thermal runaway test. However, in Comparative Example 2, the edge temperature sagging was judged as "×", and in Comparative Example 3, the gloss unevenness was judged as "×".

[0063] Figure 7(a) shows the temperature rise profile of the pre-nip temperature (temperature at position Q in Figure 2) during cold start-up in the fixing device of Comparative Example 2, between the fixing belt at the end corresponding to the maximum paper width and the central section. Figure 7(b) shows the temperature rise profile of the pre-nip temperature (temperature at position Q in Figure 2) during cold start-up in the fixing device of Comparative Example 3, between the fixing belt at a point 105 mm in the width direction from the center and the central section.

[0064] In Comparative Example 2, the subheater edge heating ratio Rq was set to 120%, which is 10% lower than in Example 1. As a result, as shown in Figure 7(a), the pre-nip temperature at the point corresponding to the maximum size end of the fixing belt 101 fell below 142°C (8°C lower than the target pre-nip temperature of 150°C). Therefore, when the maximum possible paper width was fed, there was a risk of cold offset occurring in the image at the widthwise edge, resulting in a "×" judgment for edge temperature sagging.

[0065] In Comparative Example 3, the half-width was set to 75 mm, and the half-width L of the end region of the subheater was made 10 mm longer than in Example 1. As a result, the end region, which generates a large amount of heat, is longer than in Example 1. This longer end region causes the end side of the fixing belt 101 to be overheated. Consequently, as shown in Figure 7(b), a temperature exceeding 158°C (8°C above the target pre-nip temperature of 150°C) occurred at the end side of the fixing belt 101. Therefore, in Comparative Example 3, when the maximum possible paper width was fed, the gloss differed between the end side and the center side in the width direction, potentially causing uneven gloss, and the judgment for uneven gloss was "×".

[0066] Table 3 below shows the results of the thermal runaway test in Example 2.

[0067] [Table 3]

[0068] The fixing device in Example 2 is identical to that in Example 1, except that the maximum heat generation ratio Rp of the subheater was set to 145%, the edge heat generation ratio Rq to 140%, and the half-width to 60 mm, as shown in Table 3. In Example 2, as in Example 1, the center of the fixing belt 101 reached an abnormal temperature of 400°C before the edges in both the cold start-up thermal runaway test and the post-paper-feed thermal runaway test, and the thermal runaway evaluation was judged as "○". Furthermore, the pre-nip temperature at the edge of the fixing belt could be kept within the range of 150°C ± 8°C before the paper entered the fixing nip N from the cold state, and both the gloss unevenness evaluation and the edge temperature sag evaluation were judged as "○".

[0069] From the results of Examples 1-2 and Comparative Examples 1-3, the following was found: In other words, by setting the maximum heat generation ratio Rp to 150% or less, the center of the fixing belt 101 can reach an abnormal temperature (400°C) before the ends. As a result, the power to the sub-heater 102b and the main heater 102a can be cut off by a power cutoff device 111, such as a thermostat, located approximately in the center in the width direction, before the surface temperature of the fixing belt 101 exceeds the abnormal temperature (400°C). Therefore, the occurrence of malfunctions due to abnormally high temperatures in the fixing device 100 can be suppressed by a single power cutoff device 111. As a result, the number of parts can be reduced compared to a system where power cutoff devices are located at the ends and the center of the fixing belt 101 in the width direction, thereby reducing the cost of the device and making the fixing device smaller.

[0070] Furthermore, by setting the edge heating ratio Rq to 130% or higher, edge temperature sagging can be suppressed, thereby preventing poor fixing (cold offset) at the widthwise edges when feeding large-size paper. In addition, by setting the half-width L of the sub-heater edge region to 65 mm or less, the occurrence of uneven gloss between the widthwise edges and the center when feeding large-size paper can be suppressed. As a result, the toner image at the widthwise edges of large-size paper can be fixed well.

[0071] Figure 8 shows the temperature rise profile of the fixing belt 101 during the second thermal runaway test, in which only the subheater was intentionally run at 520W using the fixing device of Example 1. Figure 8(a) shows the temperature rise profile in the second thermal runaway test during cold start-up, and Figure 8(b) shows the temperature rise profile in the second thermal runaway test after paper feeding.

[0072] As shown in Figures 8(a) and 8(b), in the thermal runaway test using only the subheater 102b, the pre-nip temperature Tc at the center of the fixing belt never exceeded the pre-nip temperature Te at the end. However, the thermostat activated and cut off power to the subheater 102b before the pre-nip temperature Te at the end exceeded 400°C. In the second cold-start thermal runaway test, as shown in Figure 8(a), the thermostat activated when the pre-nip temperature Tc at the center of the fixing belt was approximately 360°C. In the second thermal runaway test after paper feeding, as shown in Figure 8(b), the thermostat activated when the pre-nip temperature Tc at the center of the fixing belt was approximately 350°C.

[0073] In the second thermal runaway test, only the sub-heater 102b was subjected to thermal runaway, resulting in a slower temperature rise compared to when both the sub-heater 102b and the main heater 102a were subjected to thermal runaway. Therefore, it is considered that the ambient temperature around the thermostat reached the temperature at which the thermostat activates, and the thermostat activated, before the pre-nip temperature Te at the end of the fixing belt 101 exceeded 400°C.

[0074] Figure 9 shows the temperature rise profile of the fixing belt 101 during the second thermal runaway test using the fixing device of Comparative Example 1. Figure 9(a) shows the temperature rise profile in the cold start-up second thermal runaway test, and Figure 9(b) shows the temperature rise profile in the second thermal runaway test after paper feeding.

[0075] As shown in Figure 9(a), in Comparative Example 1, similar to Example 1, the thermostat activated when the temperature Tc before the nip in the center of the fixing belt reached approximately 360°C during the second cold start-up thermal runaway test. Also, as shown in Figure 9(b), in the second post-paper feed thermal runaway test, similar to Example 1, the thermostat activated when the temperature Tc before the nip in the center of the fixing belt reached approximately 350°C.

[0076] However, in Comparative Example 1, the pre-nip temperature Te at the end of the fixing belt exceeded 400°C when the thermostat activated in both the cold start-up second thermal runaway test and the post-paper-feed second thermal runaway test. This is because Comparative Example 1 uses a maximum heat generation ratio Rp of 160% for the sub-heater 102b, which is 10% higher than that of the fixing device in Example 1. As a result, the amount of heat supplied to the end of the fixing belt 101 is greater than in Example 1. Consequently, as is clear from the comparison of Figures 8 and 9, the temperature rise of the pre-nip temperature Te at the end of the fixing belt is faster than in Example 1. Therefore, it is thought that the pre-nip temperature Te at the end of the fixing belt exceeded the abnormal temperature of 400°C before the thermostat, which is positioned approximately in the center, could activate due to the ambient temperature.

[0077] Table 4 below summarizes the results of the second thermal runaway test.

[0078] [Table 4]

[0079] From the second thermal runaway test, by setting the maximum heat generation ratio Rp to 150% or less, even if only the sub-heater 102b experiences thermal runaway, the power to the sub-heater can be cut off by a power cutoff device 111, such as a thermostat located approximately in the center in the width direction, before the surface temperature of the end side of the fixing belt 101 exceeds an abnormal temperature (400°C). As a result, even if only the sub-heater 102b experiences thermal runaway, the occurrence of malfunctions due to abnormally high temperatures in the fixing device can be suppressed by a single power cutoff device 111.

[0080] Furthermore, when only the main heater 102a experiences thermal runaway, the center of the fixing belt 101 will be hotter than the edges. This is because, as shown in Figure 4, when both the main heater 102a and the sub-heater 102b experience thermal runaway, the center of the belt becomes hotter. Therefore, when only the main heater 102a experiences thermal runaway, it is obvious that the center of the fixing belt will be hotter than the edges. Thus, when only the main heater 102a experiences thermal runaway, the power to the sub-heater can be cut off by a power cutoff device 111, such as a thermostat located approximately in the center in the width direction, before the surface temperature of the edges of the fixing belt 101 exceeds an abnormal temperature (400°C).

[0081] The above is just one example; each of the following embodiments produces its own unique effects. (Aspect 1) In a fixing device 100 comprising a fixing member such as a fixing belt 101, a plurality of heating sources for heating the fixing member having different heat distributions, and power cutting means such as a power cutting device 111 arranged opposite each other near the center in the width direction of the fixing member, which cuts off the power supply to each heating source before the temperature of the fixing member exceeds a predetermined abnormal temperature, the fixing device 100 comprises a first heating source such as a main heater 102a having a uniform heat distribution in the width direction within the maximum size width of the recording material that can be fed through, and a second heating source such as a sub-heater 102b having a heat distribution in which the amount of heat generated on both sides in the width direction of the maximum size width is higher than the amount of heat generated in the center, wherein the ratio of the amount of heat generated at the maximum heat generation points on both sides of the second heating source to the amount of heat generated in the center (maximum heat generation ratio Rp) is 150% or less, the ratio of the amount of heat generated at the ends in the width direction of the maximum size width of the second heating source to the amount of heat generated in the center (end heat generation ratio Rq) is 130% or more, and the half-width L of the region on both sides, such as the end region of the second heating source, where the amount of heat generated is higher than the amount of heat generated in the center is 65 mm or less. According to this, as explained in the thermal runaway tests described above, by setting the ratio of the heat output of the maximum heat output at the center of the maximum heat output points on both sides of the second heat source, such as the subheater 102b (maximum heat output ratio Rp), to 150% or less, when the second heat source experiences thermal runaway, a power cut-off means such as a thermostat located near the center in the width direction will activate before both sides of the fixing member, such as the fixing belt 101, exceed a predetermined abnormal temperature, thereby cutting off the power supply to the second heat source. Furthermore, by setting the ratio of heat generation at the widthwise edges of the second heat source to the heat generation at the center (edge ​​heat generation ratio Rq) to 130% or more, and by setting the half-width L of the region where the heat generation on both sides of the second heat source is higher than the heat generation at the center to 65 mm or less, the surface temperature on both sides of the fixing member when recording material such as paper of the maximum width is fed through can be maintained within a predetermined temperature range (150°C ± 8°C), and the toner image at the widthwise edges of the recording material of the maximum width can be fixed well.

[0082] (Aspect 2) In embodiment 1, the fixing member, such as the fixing belt 101, has a metal layer such as a high thermal conductivity layer. According to this, as described in the embodiment, the thermal conductivity in the width direction of the fixing member is improved. As a result, if thermal runaway occurs when the temperature at the end of the fixing member is higher than that at the center, the heat at the end can be efficiently transferred to the center in the belt width direction, thereby equalizing the temperature of the fixing member in the width direction. This makes it possible to prevent power cutoff means, such as a power cutoff device located in the center in the width direction, from activating after the end of the fixing member exceeds an abnormal temperature.

[0083] (Aspect 3) In embodiment 2, the metal layer, such as the high thermal conductivity layer, is made of nickel or copper. According to this, by forming a metal layer such as a high thermal conductivity layer with nickel or copper, which have high thermal conductivity, it is possible to achieve good temperature uniformity of the fixing belt.

[0084] (Aspect 4) In any of embodiments 1 to 3, the fixing member is an endless fixing belt. According to this,

[0085] (Appendix 5) An image forming unit that forms an image on a recording material such as paper, An image forming apparatus comprising a fixing device for fixing an image formed on the recording material to the recording material, wherein any fixing device from embodiment 1 to 4 was used as the fixing device. This method allows for obtaining high-quality images and reducing the number of parts. [Explanation of Symbols]

[0086] 100: Fixing device 101: Fixing belt 102a: Main heater 102b: Sub-heater 103: Pressure roller 103a: Release layer 104: Elastic rubber layer 105: Mandrel 106: Pad 107: Support member 109: Reflector 110: Temperature detection sensor 111: Power interruption device 116: Sliding member 200: Printer L: Half-width N: Fixing nip Rp: Maximum heat generation ratio Rq: End-side heating ratio S: Paper Tc: Temperature before the nip in the center of the fixing belt Te: Pre-nip temperature on the end side of the fixing belt [Prior art documents] [Patent Documents]

[0087] [Patent Document 1] Publication 2019-86618

Claims

1. Fixing member and Multiple heat sources for heating fixing members, each with different heat distributions, A fixing device comprising power cutting means arranged opposite to the center of the fixing member in the width direction, which cuts off the power supply to each heating source before the temperature of the fixing member exceeds a predetermined abnormal temperature, A first heating source having a uniform heat distribution in the width direction within the maximum size width of the recording material that can be fed through, The system includes a second heating source having a heat distribution in which the amount of heat generated corresponding to both sides in the width direction of the maximum size width is higher than the amount of heat generated in the center, The ratio of the heat output of the second heat source to the heat output of the center of the maximum heat output point, which has the highest heat output on both sides of the second heat source, is 150% or less. The ratio of the heat output to the heat output at the center of the portion corresponding to the widthwise end of the maximum size width of the second heat source is 130% or more, and the half-width of the region on both sides of the second heat source where the heat output is higher than the heat output at the center is 65 mm or less. A fixing device characterized in that, when each heating source experiences thermal runaway during cold start-up, the center of the fixing member in the width direction heats up faster than both sides of the fixing member, and when each heating source experiences thermal runaway after paper feeding, the input power to each heating source is set such that the temperature of the center of the fixing member in the width direction and the temperatures of both sides of the fixing member reverse before the fixing member reaches a predetermined abnormal temperature.

2. In the fixing device according to claim 1, The fixing device is characterized in that the fixing member has a metal layer.

3. In the fixing device according to claim 2, The fixing device is characterized in that the metal layer is made of nickel or copper.

4. In the fixing device according to claim 1, The fixing device is characterized in that the fixing member is an endless fixing belt.

5. An image forming unit that forms an image on the recording material, An image forming apparatus comprising a fixing device for fixing an image formed on the recording material to the recording material, An image forming apparatus characterized in that the fixing device is the fixing device described in claim 1.

Images