Fixation device

Abstract

To provide an image formation device that enables suppressing occurrence of slipping or noise of a fixation film 22 without causing temperature unevenness in the fixation film arising from a lubricant.SOLUTION: A pressure pad 21 has: an upstream side rubbing part 211 in an upstream of a fitting groove part 210; and a downstream side rubbing part 212 in a downstream thereof. The downstream side rubbing part 212 is formed into a shape in which a first slide surface 212a rubbing with an inner peripheral surface of a fixation film 22 has a curvature, and the upstream side rubbing part 211 is formed into a shape in which a second slide surface 211a rubbing with the inner peripheral surface of the fixation film 22 has a curvature. At least smaller one of [Q2 / w2] of the second rubbing surface 211a and [Q1 / w1] of the first rubbing surface 212a satisfies [5(mm2 / N) or more and 80(mm2 / N) or less]. Therefore, a film thickness of a lubricant can be kept thick between the fixation film 22 and a heater 23, so that occurrence of slipping or noise can be suppressed without causing temperature unevenness arising from the lubricant in the fixation film 22.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a fixing device suitable for use in image forming apparatuses that utilize electrophotographic technology, such as printers, copiers, facsimile machines, or multifunction devices. [Background technology]

[0002] In image forming apparatuses, a toner image is formed on a recording material, and then the toner image is fixed to the recording material by a fixing device. Conventionally, a film heating type fixing device has been proposed (Patent Documents 1 and 2) that has a fixing film heated by a heater and a pressure roller that pressurizes the fixing film to form a fixing nip, and applies heat and pressure as the toner image passes through the fixing nip to fix it to the recording material. Inside the fixing film, a pressure pad is provided to hold the heater by rubbing it against the inner surface of the fixing film, and to pressurize the fixing film by sandwiching it between the pressure roller. Furthermore, in order to reduce the sliding friction resistance between the fixing film and the heater, and between the fixing film and the pressure pad, a lubricant such as grease or oil is interposed between the fixing film, the heater, and the pressure pad.

[0003] In the apparatus described in Patent Document 1, the inner surface of the fixing film is roughened to facilitate the attachment of lubricant. In the apparatus described in Patent Document 2, multiple grooves are provided on the surface of the pressure pad to facilitate the interposition of lubricant between the fixing film and the pressure pad. This increases the thickness of the lubricant between the fixing film and the heater, and between the fixing film and the pressure pad, thereby making it less likely for the fixing film to slip or for abnormal noises such as film squeal to occur. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2001-341143 [Patent Document 2] Japanese Patent Application Publication No. 10-198200 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the apparatus described in Patent Document 1, the inner surface of the fixing film becomes smoother with use due to friction with the heater and pressure pad, making it difficult to retain lubricant on the inner surface of the fixing film, which may cause the fixing film to slip or produce abnormal noises. On the other hand, in the apparatus described in Patent Document 2, there is a risk that heat cannot be properly applied to the recording material. That is, if grooves are provided on the surface of the pressure pad, the way heat is transferred to the inner surface of the fixing film differs between the grooved areas where lubricant accumulates and the other areas. The inner surface of the fixing film in contact with areas where a lot of lubricant has accumulated does not receive heat easily because of the large amount of lubricant. Conversely, the inner surface of the fixing film in contact with areas where there is little lubricant receives heat easily because of the small amount of lubricant. Therefore, temperature unevenness occurs in the fixing film, which may result in poor fixing of the toner image on the recording material.

[0006] The present invention has been made in view of the above problems, and aims to provide an image forming apparatus that can prevent temperature unevenness in the fixing film caused by the lubricant, and can suppress slippage and noise generation of the fixing film. [Means for solving the problem]

[0007] A fixing device according to one embodiment of the present invention is a fixing device for fixing a toner image formed on a recording material to the recording material, comprising: an endless belt that carries a lubricant on its inner circumferential surface and rotates; a heating means for heating the belt; a nip portion forming member provided on the inside of the belt, which forms a nip portion for fixing the toner image to the recording material by applying heat and pressure while gripping and conveying the recording material on which the toner image has been formed; and a rotating body positioned between the nip portion forming member and the belt, which contacts the outer circumferential surface of the belt and pressurizes the belt, wherein the nip portion forming member has a groove portion that is open on the side of the rotating body when viewed in the direction of the rotation axis of the rotating body, and downstream of the groove portion with respect to the conveying direction of the recording material The belt has a downstream sliding surface formed in a curved shape, which is a first sliding surface that rubs against the inner circumferential surface of the belt to restrict the belt's trajectory, and an upstream sliding surface formed in a curved shape, which rubs against the inner circumferential surface of the belt upstream of the groove in the conveying direction to restrict the belt's trajectory. When the linear pressure in the rotation axis direction of the first sliding surface is "w1" (N / mm), the radius of curvature of the first sliding surface is "R1" (mm), the linear pressure in the rotation axis direction of the second sliding surface is "w2" (N / mm), and the radius of curvature of the second sliding surface is "R2" (mm), at least the smaller of "R1 / w1" of the first sliding surface and "R2 / w2" of the second sliding surface is "5 (mm)". 2 / N) or more 80(mm) 2 It is characterized by satisfying the condition "less than or equal to / N".

[0008] A fixing device according to one embodiment of the present invention is a fixing device for fixing a toner image formed on a recording material to the recording material, comprising: an endless belt that rotates with a lubricant carried on its inner circumferential surface; a heating means for heating the belt; a nip portion forming member provided on the inside of the belt, which forms a nip portion for fixing the toner image to the recording material by applying heat and pressure while gripping and conveying the recording material on which the toner image has been formed; and a rotating body positioned between the nip portion forming member and the belt, which contacts the outer circumferential surface of the belt and pressurizes the belt, wherein the nip portion forming member, when viewed in the direction of the rotation axis of the rotating body, has a groove portion that is open on the side of the rotating body, a downstream sliding portion formed in a shape having curvature which slides against the inner circumferential surface of the belt downstream of the groove portion with respect to the conveying direction of the recording material and restricts the trajectory of the belt, and upstream of the groove portion with respect to the conveying direction of the belt The first sliding surface has an upstream sliding portion formed in a curved shape, wherein the linear pressure in the direction of the rotation axis on the first sliding surface is "w1" (N / mm), the radius of curvature of the first sliding surface is "R1" (mm), the radius of curvature of the belt on the first sliding surface is "G1" (mm), and the equivalent radius of curvature of the first sliding surface "Q1" (mm) is "1 / Q1 = 1 / R1 - 1 / G1". When the linear pressure in the rotational axis direction on the second sliding surface is "w2" (N / mm), the radius of curvature of the second sliding surface is "R2" (mm), the radius of curvature of the belt on the second sliding surface is "G2" (mm), and the equivalent radius of curvature "Q2" (mm) on the second sliding surface is "1 / Q2 = 1 / R2 - 1 / G2", then at least the smaller of "Q1 / w1" of the first sliding surface and "Q2 / w2" of the second sliding surface is "5 (mm) 2 / N) or more 80(mm) 2 It is characterized by satisfying the condition "less than or equal to / N". [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress belt slippage and abnormal noise generation without causing temperature unevenness in the belt due to the lubricant, with a simple configuration. [Brief explanation of the drawing]

[0010] [Figure 1] Schematic diagram showing a suitable image forming apparatus using the fixing device of the present embodiment. [Figure 2] Schematic diagram showing a fixing device. [Figure 3] Schematic diagram showing a heater and a control block of a heater control system. [Figure 4] Perspective view showing a pressure pad. [Figure 5] Cross-sectional view showing the pressure pad of the present embodiment, (a) state before pressurization, (b) state after pressurization. [Figure 6] Graph showing the relationship between the equivalent radius of curvature and the line load in the width direction. [Figure 7] Cross-sectional view showing a pressure pad of a comparative example, (a) state before pressurization, (b) state after pressurization.

Mode for Carrying Out the Invention

[0011] <Image Forming Apparatus> An image forming apparatus suitable for using the fixing device of the present embodiment will be described with reference to FIG. 1. The image forming apparatus 100 shown in FIG. 1 forms an image corresponding to image information sent from an external device (not shown) such as a computer or a document reading device provided outside the apparatus main body 100A on a recording material P. Examples of the recording material P include various types of sheet materials such as plain paper, cardboard, rough paper, embossed paper, coated paper, plastic film, cloth, and the like.

[0012] The photosensitive drum 1 is an electrophotographic photoreceptor having a photosensitive layer formed on the outer peripheral surface of, for example, an aluminum cylinder, and is rotated in the direction of arrow F1 at a predetermined process speed by a motor (not shown). After the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging roller 2, an electrostatic latent image is formed on the surface by laser light output from the exposure device 3 according to image information from an external device. This electrostatic latent image is developed into a toner image using a developer by the developing device 4.

[0013] - The recording material P is pre-loaded into a cassette 5 and supplied one sheet at a time from the cassette 5 to the transport path 8a by a supply roller 6. It is then transported by a pair of register rollers 7 toward the transfer nip T formed when the transfer roller 9 and the photosensitive drum 1 come into contact at a predetermined timing. As the recording material P passes through the transfer nip T, a transfer voltage is applied to the transfer roller 9 by a power supply (not shown), and the toner image on the photosensitive drum 1 is transferred onto the recording material P. Any remaining toner on the photosensitive drum 1 that is not transferred to the recording material P is removed from the photosensitive drum 1 by a cleaning device 10.

[0014] The recording material P that has passed through the transfer nip section T is transported to the fixing device 11, where heat and pressure are applied to fix the toner image onto the recording material P. The recording material P that has passed through the fixing device 11 then travels along the transport path 8c and is discharged from the discharge port 13 to the mounting section 14 located on the upper surface of the main body 100A of the device.

[0015] In this embodiment, the image forming unit 300, which forms a toner image on the recording material P, is composed of the photosensitive drum 1, charging roller 2, exposure device 3, developing device 4, transfer roller 9, and a motor and power supply (not shown). The image forming unit 300 and the fixing device 11 are controlled by a control unit 200 provided in the main body 100A of the device.

[0016] Here, we will explain the transfer roller 9 and the transfer voltage control for the transfer roller 9. Generally, the transfer roller 9 is made of a core metal 9b made of stainless steel (SUS), iron, etc., with carbon, ion conductive filler, etc., on its outer circumference, resulting in a "1 × 10" 6 ~1 × 10 10 An elastic sponge roller is used, which has a semiconducting elastic layer 9a formed on it that is adjusted to have a resistance of approximately Ω. In this embodiment, an ion-conductive transfer roller 9 is used, in which an elastic layer 9a is formed in a roller shape on the outer circumference of a metal core 9b using a conductive sponge formed by reacting NBR rubber with a surfactant or the like.

[0017] The resistance value of the elastic layer 9a is "1 × 10 8 ~5×108 The value was set to Ω. Generally, the resistance of the transfer roller 9 tends to fluctuate depending on the temperature and humidity inside the device body 100A, and fluctuations in the resistance of the transfer roller 9 may cause transfer failures. Therefore, in this embodiment, in order to suppress the occurrence of transfer failures caused by fluctuations in the resistance of the transfer roller 9, a transfer voltage control is employed that detects the resistance value of the transfer roller 9 in advance and appropriately controls the transfer voltage applied to the transfer roller 9 according to the detection result. "ATVC (Active Transfer Voltage Control)" has been conventionally proposed as such a transfer voltage control, and "ATVC" is also adopted as the transfer voltage control in this embodiment.

[0018] "ATVC" is a control system that optimizes the transfer voltage applied to the transfer roller 9 during transfer. Simply put, while the image forming apparatus 100 is in standby mode, a voltage is applied that causes a predetermined current (constant current) to flow from the transfer roller 9 to the photosensitive drum 1. The resistance of the transfer roller 9 is detected from the voltage value at that time, and a transfer voltage corresponding to the detected resistance value is applied to the transfer roller 9 during transfer. This "ATVC" system can suppress the occurrence of transfer defects due to fluctuations in the resistance of the transfer roller 9.

[0019] <Fusing device> Next, the fixing device 11 of this embodiment will be described with reference to Figure 1 and using Figure 2. As shown in Figure 2, the fixing device 11 of this embodiment is broadly composed of a fixing film unit 110 and a pressure roller 24.

[0020] The pressure roller 24, as a rotating body, is held by bearings on an unillustrated device frame of the fixing device 11 so that both ends in the direction of the rotation axis can rotate. The pressure roller 24 is also provided to contact the fixing film 22 of the fixing film unit 110 and pressurize the fixing film 22. When the pressure roller 24 pressurizes the fixing film 22, a fixing nip portion N is formed between the pressure roller 24 and the fixing film 22. The pressure roller 24 has, for example, a metal core made of aluminum, an elastic layer of silicone rubber or the like with a thickness of "approximately 3 mm" on its outer circumference, and a release layer of perfluoroalkoxyalkane (PFA) or polytetrafluoroethylene (PTFE) or the like with a thickness of "approximately 30 μm" on the outer circumference of the elastic layer.

[0021] When the pressure roller 24 is rotated by a motor (not shown), the rotational force of the pressure roller 24 is transmitted to the fixing film 22 by the frictional force generated at the fixing nip section N, and the fixing film 22 moves along with the pressure roller 24. The recording material P is held and conveyed at the fixing nip section N, and at that time heat and pressure are applied, fixing the toner image to the recording material P. After passing through the fixing nip section N, the recording material P separates from the fixing film 22 and the pressure roller 24.

[0022] <Fusing film unit> Next, the fixing film unit 110 will be described. The fixing film unit 110 is provided on the main body 100A so as to be movable toward the pressure roller 24 side. The fixing film unit 110 has a fixing film 22, a pressure pad 21 and a stay 50 which are non-rotatably arranged inside the fixing film 22, and a heater 23 which is held by the pressure pad 21.

[0023] <Fixing film> The fixing film 22 is an endless belt member formed in the form of a thin, flexible, and heat-resistant film. The fixing film 22 has a cylindrical nickel base layer with a thickness of 40 μm, manufactured, for example, by electroforming. In addition to nickel, iron alloys, copper, silver, etc. may be appropriately selected and used for the base layer. Alternatively, a heat-resistant resin (such as polyimide) may be used. The thickness of the base layer is preferably set in the range of 20 to 60 μm. A lubricating layer with a thickness of 10 to 50 μm is provided on the inner circumference of the base layer using fluororesin, polyimide, etc., to reduce sliding friction with the pressure pad 21 and heater 23. In this embodiment, a lubricating layer with a thickness of 10 μm is provided using polyimide.

[0024] On the other hand, an elastic layer is provided on the outer periphery of the base layer, for example, made of heat-resistant silicone rubber. The thickness of the elastic layer is preferably set in the range of "100 to 800 μm". As the silicone rubber material for forming the elastic layer, for example, one with a JIS-ASKER-C hardness of "20 degrees" and a thermal conductivity of "0.8 W / mK" is used. On the outer periphery of this elastic layer, a surface release layer with a thickness of "30 μm" is provided, for example, made of a fluororesin such as PFA or PTFE. In this embodiment, a PFA tube was used for the surface release layer. Furthermore, in order to reduce the heat capacity of the fixing film 22, shorten the warm-up time required to raise the temperature of the fixing film 22 to the desired temperature at startup, and obtain a suitable fixed image when fixing a color image, the thickness of the elastic layer is set to "300 μm".

[0025] The fixing film 22 is supported so as to be rotatable and so as to restrict movement in the width direction by flange portions (not shown) located at both ends in the width direction intersecting the rotation direction of the fixing film 22. Although not shown, the flange portions have a cylindrical portion that is fitted inside the width direction end of the fixing film 22 and supports the width direction end so as to be rotatable, and a contact portion that can contact the width direction edge of the fixing film 22. The cylindrical portion guides the rotation of the fixing film 22 while holding the width direction end of the fixing film 22 in a cylindrical state from the inside. In other words, the fixing film 22 is not stretched across multiple tension rollers, but is in a so-called free belt configuration.

[0026] In addition, the pressure roller 24 and the fixing film 22 may be positioned slightly off-parallel due to mounting errors of the pressure roller 24 or the fixing film unit 110. In such cases, the fixing film 22 may rotate and move towards the width direction. When the fixing film 22 moves towards the width direction, the contact portion of the flange receives the width direction end of the fixing film 22 and restricts its movement in the width direction.

[0027] <Compression pads> The pressure pad 21, which serves as a nip-forming member, is provided on the inside of the fixing film 22 and forms the fixing nip portion N described above. The pressure pad 21 is a molded product that extends in the width direction and is formed to hold a heater 23 as a heating means. The pressure pad 21 is formed from a high heat-resistant resin such as polyimide, polyamide-imide, PEEK, PPS, or liquid crystal polymer, or from a composite material of these resins with ceramics, metal, glass, etc. In this embodiment, a pressure pad 21 molded by injecting liquid crystal polymer into a mold was used.

[0028] The heater 23, held by the pressure pad 21, contacts the inner circumferential surface of the fixing film 22, thereby heating the fixing film 22. In this embodiment, the pressure pad 21 not only holds the heater 23 but also has the function of guiding the fixing film 22. As shown in Figure 2, the pressure pad 21 guides the fixing film 22 by restricting its trajectory from the inside on both the upstream and downstream sides in the transport direction of the recording material P (arrow X direction). The shape of the pressure pad 21 in this embodiment will be described later (see Figures 4 to 5(b)).

[0029] <Stay> The stay 50 is a rigid member (sheet metal, for example) made of metal that extends in the width direction along the fixing film 22, and is formed in a substantially U-shape in cross-section with an opening on the side facing the pressure pad 21. The stay 50 reinforces the pressure pad 21 so that it does not deform due to the pressure applied by the pressure roller 24. The flange portions described above are fixed to both ends of the stay 50 in the width direction. The flange portions may be pressed toward the pressure roller 24.

[0030] <Lubricant> The fixing film 22 rotates with a lubricant carried on its inner circumferential surface in order to slide smoothly against the pressure pad 21 or heater 23. By interposing the lubricant between the fixing film 22 and the pressure pad 21 or heater 23, the sliding friction resistance at the sliding surfaces between the fixing film 22 and the pressure pad 21 or heater 23 is reduced. In this embodiment, silicone oil (for example, viscosity of 1000 cSt at a temperature of 23°C) was used as the lubricant. However, the lubricant is not limited to silicone oil; fluorine oil or perfluoropolyether (PEPE) grease may also be used.

[0031] <Heater> Next, the heater 23 will be explained using Figure 3. In Figure 3, to make the explanation easier to understand, the heater 23 is shown divided into a film sliding surface 23A that rubs against the fixing film 22 and a film non-sliding surface 23B that is on the opposite side of the film sliding surface 23A and does not rub against the fixing film 22.

[0032] The heater 23 is a planar heating element such as a ceramic heater, and as shown in Figure 3, it has a ceramic substrate 27 on the film sliding surface 23A side with a heating resistor 26 formed along the width direction. The ceramic substrate 27 is positioned so that its longitudinal direction substantially coincides with the direction that intersects the transport direction of the recording material P (arrow X direction). A material with good heat resistance, insulation, and thermal conductivity is used for the ceramic substrate 27, and in this embodiment, aluminum nitride is used. The dimensions of the ceramic substrate 27 are, for example, 7 mm in width, 360 mm in length, and 1 mm in thickness.

[0033] On the ceramic substrate 27, the surface of the heating resistor 26 is protected by an overcoat layer 28. The overcoat layer 28 is provided to ensure the electrical insulation of the heater 23 and the sliding properties of the fixing film 22. In this embodiment, a heat-resistant glass layer with a thickness of approximately 50 μm was used as the overcoat layer 28. Power supply electrodes 29 and 30 are formed at both ends of the heating resistor 26. The power supply electrodes 29 and 30 are connected to an AC power supply 33, and power is supplied from the AC power supply 33. In this embodiment, the power supply electrodes 29 and 30 are formed at both ends of the heating resistor 26 by a silver-palladium screen printing pattern. That is, the heating resistor 26 is formed in a linear strip shape on the ceramic substrate 27 by screen printing a paste made by mixing silver, palladium, glass powder (inorganic binder), and an organic binder. In addition to silver-palladium (Ag / Pd), other electrical resistance materials such as RuO2 and Ta2N may be used as the material for the heating resistor 26. Furthermore, the resistance value of the heating resistor 26 was set to "20Ω" at room temperature.

[0034] In this embodiment, the temperature of the heater 23 is configured to be detectable by a thermistor 25. Although not shown in the figure, the thermistor 25 is configured by placing heat-insulating ceramic paper on top of a highly heat-resistant liquid crystal polymer and fixing a chip thermistor element on top of it. By pressing the chip thermistor element side of the thermistor 25 against the non-sliding surface 23B of the film, the temperature of the heater 23 can be measured. The thermistor 25 is located within the minimum paper feed area and is connected to the CPU 31. The heater 23 is held on the pressure pad 21 with the non-sliding surface 23B of the film facing the stay 50 side (see Figure 1). As a result, the inner circumferential surface of the heater 23 and the fixing film 22 rub against each other, and heat can be applied from the heater 23 to the toner image on the recording material P via the fixing film 22.

[0035] Next, the temperature control of the heater 23 will be explained using Figure 3. In this embodiment, the control unit 200 capable of controlling the temperature of the heater 23 may be connected to various motors, power supplies, etc., in addition to those shown in the figure, but since this is not the main point of the invention, their illustration and explanation will be omitted here.

[0036] The control unit 200 performs various controls on the image forming apparatus 100 (see Figure 1), such as image forming operations, and includes, for example, a CPU (Central Processing Unit) 31 and a memory 32. The memory 32 is composed of ROM (Read Only Memory) and RAM (Random Access Memory), and stores various programs and data for controlling the image forming apparatus 100. The CPU 31 can execute various programs stored in the memory 32, such as image forming jobs (not shown), and can operate the image forming apparatus 100 to form an image on the recording material P. In this embodiment, the control unit 200 can adjust the temperature of the heater 23 by controlling the power supply to the heater 23 by the AC power supply 33. The memory 32 can temporarily store calculation results and other data associated with the execution of various programs.

[0037] When the AC power supply 33 energizes the heating resistor 26 through the power supply electrodes 29 and 30 and the heater 23 heats up, the thermistor 25 detects the increase in the heater 23's temperature. The output of the thermistor 25 is then converted to digital and the resulting signal is input to the control unit 200. Based on this signal, the control unit 200 controls the power supplied to the heating resistor 26 by the triac 34 using phase control or wavenumber control, etc. This controls the temperature of the heater 23.

[0038] The control unit 200 controls the power supply to the heater 23 by the AC power supply 33 so that the heater 23 is heated if the temperature detected by the thermistor 25 is lower than a predetermined set temperature, and cooled if it is higher than the set temperature, thereby making it possible to maintain the heater 23 at a constant temperature. In this embodiment, the power supplied to the heating resistor 26 is changed in 21 steps in 5% increments within the range of "0 to 100%" by phase control. Output 100% is the output when the heater 23 is fully energized. Once the temperature of the heater 23 has risen to the predetermined temperature and the rotation speed of the fixing film 22 has stabilized, the control unit 200 transports the recording material P to the fixing nip portion N of the fixing film 22 and the pressure roller 24. In this embodiment, a belt ceramic heater is used to heat the fixing film 22, but it is not limited to this, and other types of heaters such as halogen heaters or induction heating heaters may also be used.

[0039] <Compression pad shape> Next, the shape of the pressure pad 21 of this embodiment will be described using Figures 4 to 5(b) with reference to Figure 2. As shown in Figure 4, the pressure pad 21 has a fitting groove 210 extending along the width direction on the side opposite to the stay 50, into which the heater 23 can be fitted and held. With respect to the transport direction of the recording material P (arrow X direction), the pressure pad 21 has an upstream sliding portion 211 upstream of the fitting groove 210 and a downstream sliding portion 212 downstream of the fitting groove 210. The upstream sliding portion 211 slides against the inner circumferential surface of the fixing film 22 upstream of the fitting groove 210 to restrict the trajectory of the fixing film 22, and the downstream sliding portion 212 slides against the inner circumferential surface of the fixing film 22 downstream of the fitting groove 210 to restrict the trajectory of the fixing film 22.

[0040] Figures 5(a) and 5(b) are cross-sectional views showing the pressure pad 21 of this embodiment, where Figure 5(a) shows the state before pressurization by the pressure roller 24, and Figure 5(b) shows the state after pressurization by the pressure roller 24. As shown in Figures 5(a) and 5(b), when viewed from the width direction (direction of the rotation axis of the pressure roller 24), the downstream sliding portion 212 of the pressure pad 212 protrudes downstream of the fitting groove portion 210 with respect to the transport direction of the recording material P (arrow X direction), extending from the bottom surface of the fitting groove portion 210 toward the pressure roller 24 side (rotating body side) beyond the heater 23. Also, the upstream sliding portion 211 protrudes upstream of the fitting groove portion 210 with respect to the transport direction of the recording material P (arrow X direction), extending from the bottom surface of the fitting groove portion 210 toward the pressure roller 24 side beyond the heater 23. This is because the downstream sliding portion 212 and the upstream sliding portion 211 of the heater 23 protrude towards the pressure roller 24, making it less likely for the fixing film 22 to get caught on the edge of the heater 23.

[0041] Furthermore, the downstream abrasive portion 212 is formed with a first abrasive surface 212a that rubs against the inner circumferential surface of the fixing film 22 having a curved shape, and the upstream abrasive portion 211 is formed with a second abrasive surface 211a that rubs against the inner circumferential surface of the fixing film 22 having a curved shape. The first abrasive surface 212a of the downstream abrasive portion 212 and the second abrasive surface 211a of the upstream abrasive portion 211 will be described below.

[0042] <Comparative Example> First, the comparative example will be described. Figures 7(a) and 7(b) are cross-sectional views showing the comparative example's pressure pad 21A, where Figure 7(a) shows the state before pressurization by the pressure roller 24, and Figure 7(b) shows the state after pressurization by the pressure roller 24. The comparative example's pressure pad 21A also has an upstream abrasive portion 211 upstream of the fitting groove 210, and a downstream abrasive portion 212 downstream of the fitting groove 210. The downstream abrasive portion 212 has a first abrasive surface 2121 that rubs against the inner circumferential surface of the fixing film 22 and is formed with a curved shape, while the upstream abrasive portion 211 has a second abrasive surface 2111 that rubs against the inner circumferential surface of the fixing film 22 and is formed with a curved shape.

[0043] Here, the equivalent radius of curvature (Q) is expressed by the following equation 1, where R is the radius of curvature at the tip of the upstream (or downstream) sliding portion of the pressure pad, and G is the radius of curvature at the sliding surface of the upstream (or downstream) sliding portion. 1 / Q=1 / R-1 / G ··· Formula 1

[0044] In this specification, the radius of curvature "R" at the tip of the upstream abrasion portion (or downstream abrasion portion) is the radius of curvature of an approximate curve that passes through three points with respect to the transport direction of the recording material P: the central point of the abrasion surface, the uppermost point of the abrasion surface that abrades with the fixing film, and the lowermost point of the abrasion surface that abrades with the fixing film (also called the radius of curvature of the abrasion surface). Furthermore, the radius of curvature "G" at the abrasion surface of the upstream abrasion portion (or downstream abrasion portion) is the radius of curvature of an approximate curve that passes through three points in the fixing film 22 with respect to the transport direction of the recording material P: the central point of the abrasion surface, a point on the upstream side where there is a gap of "10 to 20 μm" between the upstream abrasion portion (or downstream abrasion portion) and the fixing film, and a point on the downstream side where there is a gap of "10 to 20 μm" between the upstream abrasion portion (or downstream abrasion portion) and the fixing film.

[0045] In the comparative example, the radius of curvature (R2A) of the second abrasive surface 2111 is, for example, "0.6 mm", and the radius of curvature (G2A) of the fixing film 22 on the second abrasive surface 2111 is a sufficiently large value compared to the radius of curvature (R2A) of the second abrasive surface 2111. Therefore, the equivalent radius of curvature (Q2A) on the second abrasive surface 2111 is approximately "0.6 mm".

[0046] In the comparative example, the radius of curvature (R1A) of the first abrasive surface 2121 is "0.4 mm," which is smaller than the radius of curvature (R2A) of the second abrasive surface 2111. In contrast, the radius of curvature (G1A) of the fixing film 22 on the first abrasive surface 2121 is sufficiently larger than the radius of curvature (R1A) of the first abrasive surface 2121, so the equivalent radius of curvature (Q1A) on the first abrasive surface 2121 is approximately "0.4 mm."

[0047] In the comparative example, when pressure is applied by the pressure roller 24, the loads applied to the fixing film 22, the upstream rubbing portion 211, and the downstream rubbing portion 212 are all "45 N". The linear loads in the width direction (w2, w1) are calculated and are "0.14 N / mm". Here, when the parameter for the ease of lubricant circulation is defined as "Q / w", it has been found by the inventors' experiments that the larger "Q / w" is, the easier the lubricant circulates by the fixing film 22. In the case of the comparative example, "Q2A (≈R2A) / w2" of the second rubbing surface 2111 is "about 4.3 mm 2 / N", and "Q1A (≈R1A) / w1" of the first rubbing surface 2121 is "about 2.9 mm 2 / N".

[0048] On the other hand, in the case of the present embodiment, the radius of curvature (R2, see Fig. 5(a)) of the second rubbing surface 211a is larger than that of the comparative example, which is "2.5 mm". And the radius of curvature (G2) of the fixing film 22 on the second rubbing surface 211a is a sufficiently large value compared to the radius of curvature (R2) of the second rubbing surface 211a. Therefore, the equivalent radius of curvature (Q2; "1 / Q2 = 1 / R2 - 1 / G2") on the second rubbing surface 211a is substantially the same as the radius of curvature (R2) of the second rubbing surface 211a, which is "2.5 mm".

[0049] Also, the radius of curvature (R1, see Fig. 5(a)) of the first rubbing surface 212a is "2.0 mm", which is smaller than the radius of curvature (R2) of the second rubbing surface 211a but larger than that of the comparative example. And the radius of curvature (G1) of the fixing film 22 on the first rubbing surface 212a is a sufficiently large value compared to the radius of curvature (R1) of the first rubbing surface 212a. Therefore, the equivalent radius of curvature (Q1; "1 / Q1 = 1 / R1 - 1 / G1") on the first rubbing surface 212a is substantially the same as the radius of curvature (R1) of the first rubbing surface 212a, which is "2.0 mm".

[0050] In this embodiment, when pressure is applied by the pressure roller 24, the load on the fixing film 22, the upstream abrasion portion 211, and the downstream abrasion portion 212 is "20N", and the line load in the width direction (w2, w1) is calculated to be "0.06N / mm". In this embodiment, the "Q2 / w2" (effectively "R2 / w2") of the second abrasion surface 211a is "approximately 42mm 2 The ratio of the first friction surface 212a, "Q1 / w1" (effectively "R1 / w1"), is smaller than the ratio of the second friction surface 211a, "approximately 33 mm". 2 It is " / N".

[0051] <Experimental Study> The inventors conducted comparative experiments between the comparative example and this embodiment. The results of these experiments are shown in Table 1. [Table 1]

[0052] The first aspect of the experiment is to suppress slippage that occurs when the image forming apparatus 100 is started while the fixing film 22 and pressure roller 24 are cold. For example, if the power to the image forming apparatus 100, which has been stopped overnight, is turned on first thing in the morning, the fixing film 22 and pressure roller 24 will have cooled to room temperature, and due to the high viscosity of the lubricant, the sliding resistance between the fixing film 22 and the heater 23 will be high. In this case, when the pressure roller 24 is started to move, the torque of the motor (not shown) that drives the pressure roller 24 becomes high. As a result, the fixing film 22 may not be able to keep up with the rotation of the pressure roller 24, and slippage may occur. For example, the pressure applied to the pressure roller 24 is set to "300N", and the rotation speed of the pressure roller 24 is set to "300mm / s".

[0053] In Comparative Example 1, the motor's rotational torque at startup was 2.4 kg·cm, while in this embodiment, the motor's rotational torque at startup was 2.0 kg·cm. Although this embodiment showed a decrease in rotational torque compared to the comparative example, no slip occurred in either case. Upon investigating the factors contributing to the decrease in motor rotational torque, it was found that the amount of lubricant blocked by the upstream sliding part 211 and the downstream sliding part 212 differed between Comparative Example 1 and this embodiment.

[0054] In Comparative Example 1, the amount of lubricant blocked in the upstream sliding portion 211 was smaller than the amount blocked in the downstream sliding portion 212. On the other hand, in this embodiment, the amount of lubricant blocked in the upstream sliding portion 211 was smaller than the amount blocked in the downstream sliding portion 212, but it was found that the amount of blocked lubricant in each portion was even smaller than in Comparative Example 1.

[0055] From this, it was confirmed that the larger "Q / w" is, the less lubricant is blocked and the larger the lubricant film thickness that can pass through. Therefore, it is thought that the reason why the rotational torque decreases is that the larger "Q / w" is, the greater the film thickness of the lubricant passing through the upstream sliding surface 211 and the downstream sliding surface 212, bringing the fixing film 22 and the heater 23 closer to fluid lubrication through the lubricant. In other words, to suppress slip, the smaller of "Q2 / w2" of the second sliding surface 211a of the upstream sliding surface 211 and "Q1 / w1" of the first sliding surface 212a of the downstream sliding surface 212 should be made as large as possible.

[0056] In a free-belt configuration like that of this embodiment, it is necessary to provide protrusions such as the upstream abrasive portion 211 and the downstream abrasive portion 212 in order to restrict the trajectory of the fixing film 22, and a certain amount of linear load is applied to the upstream abrasive portion 211 and the downstream abrasive portion 212. In such a configuration, there is a risk of blocking the lubricant as described above, but by increasing the equivalent radius of curvature "Q" or decreasing the linear pressure "w", it is possible to maintain the film thickness of the lubricant that penetrates the fixing nip portion N.

[0057] The second aspect of the experiment is the suppression of abnormal noises such as film squeal that occur when the heater 23 is heated. As the temperature of the fixing film 22 rises in response to the heating of the heater 23, the viscosity of the lubricant decreases, the film thickness of the lubricant passing through the upstream sliding part 211 and the downstream sliding part 212 decreases, and less lubricant is supplied to the heater 23. Therefore, the film thickness of the lubricant between the fixing film 22 and the heater 23 becomes thinner. As a result, the proportion of areas where the fixing film 22 and the heater 23 slide against each other without the lubricant increases, resulting in a mixed lubrication state where fluid lubrication via the lubricant and boundary lubrication, which is contact between solids, are mixed, causing stick-slip and abnormal noise. In the experiment to confirm this abnormal noise, the pressure force of the pressure roller 24 is set to "300N", the temperature of the heater 23 is set to "220℃", and the rotation speed of the pressure roller 24 is gradually reduced from "300mm / s". Furthermore, the rotation speed of the pressure roller 24 when an abnormal noise occurs can be used to evaluate the film thickness of the lubricant.

[0058] In Comparative Example 1, the rotational speed of the pressure roller 24 when abnormal noise occurred was "90 mm / s". In contrast, in this embodiment, no abnormal noise occurred even when the rotational speed of the pressure roller 24 was reduced to "10 mm / s". This is because, in this embodiment, a thicker film of lubricant was maintained between the fixing film 22 and the heater 23, thereby maintaining fluid lubrication through friction between the fixing film 22 and the heater 23 via the lubricant. As described above, it was found that this embodiment, with its larger "Q / w", has an advantage in terms of suppressing slip and abnormal noise.

[0059] In contrast, Comparative Examples 2 and 3, shown in Table 1, attempt to address this issue by changing the viscosity of the lubricant. When a low-viscosity lubricant is used, the lubricant viscosity is low at the first start-up in the morning, which allows for lower motor rotation torque and thus makes slippage less likely. However, as the temperature rises, the viscosity decreases, reducing the film thickness of the lubricant passing through the upstream sliding parts 211 and downstream sliding parts 212. This reduces the amount of lubricant supplied between the fixing film 22 and the heater 23, making high-temperature noise more likely. Conversely, when a high-viscosity lubricant is used, while it can suppress the occurrence of abnormal noise, it makes slippage more likely.

[0060] Figure 6 shows the results of this experiment, where "Q / w" was varied. In Figure 6, "○" indicates that neither slipping nor abnormal noise occurred, and "×" indicates that at least one of slipping or abnormal noise occurred. As can be seen from Figure 6, when "Q / w" is "5mm 2 If the value is above " / N", slippage and abnormal noise can be suppressed.

[0061] Table 2 shows, as an example, the "Q / w" for an image forming apparatus with a front margin (mm) of "3.5 mm" and the "Q / w" for an image forming apparatus with a front margin (mm) of "5.5 mm". In Table 2, "○" indicates that there is no slippage or abnormal noise, and furthermore, the separation between the recording material P and the fixing film 22 is good and there is no temperature unevenness in the fixing film. "△" indicates that there is no slippage or abnormal noise, and furthermore, the separation between the recording material P and the fixing film 22 is good, but there is temperature unevenness in the fixing film. "×" indicates that at least one of slippage or abnormal noise occurs, and in addition, the separation between the recording material P and the fixing film 22 is not good. [Table 2]

[0062] When "Q / w" is large, that is, when the equivalent radius of curvature "Q" is large or the linear pressure "w" is small, the trajectory of the fixing film 22 becomes gentler in the downstream friction portion 212, which reduces the separation between the recording material P and the fixing film 22.

[0063] Therefore, in this embodiment, at least the smaller of "Q2 / w2" of the second sliding surface 211a of the upstream sliding portion 211 and "Q1 / w1" of the first sliding surface 212a of the downstream sliding portion 212 is "5(mm) 2 / N) or more 80(mm) 2 It is sufficient if the value of "Q1 / w1" on the first friction surface 212a and "Q2 / w2" on the second friction surface 211a are both "5(mm)". 2 / N) or more 80(mm) 2 The condition "less than or equal to / N" must be met.

[0064] This is because either "Q1 / w1" or "Q2 / w2" is "5(mm) 2 If it is smaller than "Q1 / w1" or "Q2 / w2", the lubricant will be more easily scraped off by the upstream sliding surface 211 and the downstream sliding surface 212 (i.e., the amount of blockage will be large), and the amount of lubricant carried on the fixing film 22 will be too small, resulting in a thin film thickness of lubricant penetrating the fixing nip N. On the other hand, if either "Q1 / w1" or "Q2 / w2" is "80(mm 2 If the value is greater than " / N"), the lubricant will not be easily scraped off by the upstream friction portion 211 and the downstream friction portion 212 (i.e., the amount of blockage will be small), but if there is too much lubricant carried on the fixing film 22, it will not be easily carried on, and as a result the film thickness of the lubricant that penetrates the fixing nip portion N will be thin. Note that "Q1 / w1" of the first friction surface 212a is set to "10(mm)" from the viewpoint of the separation of the recording material P. 2 / N) or more and 30 or less (mm 2 It is preferable to set it to " / N". When "Q1 / w1" is "10 (mm2 / N) or more and 30 or less (mm2 / N)", the separation properties of the recording material P will be good.

[0065] As described above, in this embodiment, with respect to the pressure pad 21, at least the smaller of "Q2 / w2" of the second sliding surface 211a of the upstream sliding portion 211 and "Q1 / w1" of the first sliding surface 212a of the downstream sliding portion 212 is "5 (mm) 2 / N) or more 80(mm) 2 The condition " / N) or less" is satisfied. To achieve this, a pressure pad 21, which has an upstream sliding portion 211 and a downstream sliding portion 212, is non-rotatably arranged inside the fixing film 22. By doing so, a thicker film thickness of lubricant can be maintained between the fixing film 22 and the heater 23, preventing temperature unevenness in the fixing film 22 caused by the lubricant and suppressing slippage and noise generation of the fixing film 22.

[0066] <Other Embodiments> In the embodiments described above, a direct transfer method was described in which the toner image formed on the photosensitive drum is directly transferred to the recording material. However, this method can also be applied to an intermediate transfer method in which the toner image formed on the photosensitive drum is transferred to an intermediate transfer belt.

[0067] Furthermore, this technology can also be configured as follows. (1) A fixing device for fixing a toner image formed on a recording material to the recording material, An endless belt that rotates with a lubricant carried on its inner circumference, A heating means for heating the belt, A nip-forming member is provided on the inside of the belt and forms a nip section that holds and transports the recording material on which a toner image has been formed, while applying heat and pressure to fix the toner image to the recording material. The system comprises a rotating body positioned between the nip portion forming member and the belt, which contacts the outer circumferential surface of the belt and applies pressure to the belt, The nip-forming member, when viewed from the direction of the rotation axis of the rotating body, The rotating body side has an open groove, With respect to the conveying direction of the recording material, the downstream sliding portion is formed in a curved shape, and the first sliding surface that slides against the inner circumferential surface of the belt downstream of the groove to restrict the trajectory of the belt is a downstream sliding portion, With respect to the conveying direction, the upstream side sliding portion has a curved shape and a second sliding surface that slides against the inner circumferential surface of the belt upstream of the groove to regulate the belt's trajectory. When the linear pressure in the direction of the rotation axis on the first sliding surface is "w1" (N / mm), the radius of curvature of the first sliding surface is "R1" (mm), the linear pressure in the direction of the rotation axis on the second sliding surface is "w2" (N / mm), and the radius of curvature of the second sliding surface is "R2" (mm), Of the "R1 / w1" of the first sliding surface and the "R2 / w2" of the second sliding surface, at least the smaller of the two is "5 (mm 2 / N) or more 80(mm) 2 Satisfying the condition " / N) less than or equal to", A fixing device characterized by the following features. (2) Both the "R1 / w1" of the first sliding surface and the "R2 / w2" of the second sliding surface are "5(mm 2 / N) or more 80(mm) 2 Satisfying the condition " / N) less than or equal to", The fixing device according to (1) above, characterized in that (3) The "R1 / w1" of the first friction surface is "10 (mm 2 / N) or more and 30 or less (mm 2 / N)」 The fixing device according to (1) or (2) above, characterized in that (4) The "R1 / w1" of the first friction surface is smaller than the "R2 / w2" of the second friction surface. A fixing device according to any one of (1) to (3) above, characterized in that (5) The heating means is a planar heating element, which is disposed in the groove so as to slide against the inner circumferential surface of the belt. A fixing device according to any one of (1) to (4) above, characterized in that (6) A fixing device for fixing a toner image formed on a recording material to the recording material, An endless belt that rotates with a lubricant carried on its inner circumference, A heating means for heating the belt, A nip-forming member is provided on the inside of the belt and forms a nip section that holds and transports the recording material on which a toner image has been formed, while applying heat and pressure to fix the toner image to the recording material. The system comprises a rotating body positioned between the nip portion forming member and the belt, which contacts the outer circumferential surface of the belt and applies pressure to the belt, The nip-forming member, when viewed from the direction of the rotation axis of the rotating body, The rotating body side has an open groove, With respect to the conveying direction of the recording material, the downstream sliding portion is formed in a curved shape, and the first sliding surface that slides against the inner circumferential surface of the belt downstream of the groove to restrict the trajectory of the belt is a downstream sliding portion, With respect to the conveying direction, the upstream side sliding portion has a curved shape and a second sliding surface that slides against the inner circumferential surface of the belt upstream of the groove to regulate the belt's trajectory. Let w1 (N / mm) be the linear pressure in the direction of the rotation axis on the first friction surface, R1 (mm) be the radius of curvature of the first friction surface, G1 (mm) be the radius of curvature of the belt on the first friction surface, and Q1 (mm) be the equivalent radius of curvature on the first friction surface, given by 1 / Q1 = 1 / R1 - 1 / G1. When the linear pressure in the direction of the rotation axis on the second friction surface is "w2" (N / mm), the radius of curvature of the second friction surface is "R2" (mm), the radius of curvature of the belt on the second friction surface is "G2" (mm), and the equivalent radius of curvature on the second friction surface "Q2" (mm) is "1 / Q2 = 1 / R2 - 1 / G2", Of the "Q1 / w1" of the first abrasive surface and the "Q2 / w2" of the second abrasive surface, at least the smaller of the two is "5 (mm 2 / N) or more 80(mm) 2 Satisfying the condition " / N) less than or equal to", A fixing device characterized by the following features. [Explanation of Symbols]

[0068] 11... Fixing device, 21... Nip forming member (pressure pad), 22... Belt (fixing film), 23... Heating means (heater), 24... Rotating body (pressure roller), 210... Groove (fitting groove), 211... Upstream sliding part, 211a... Second sliding surface, 212... Downstream sliding part, 212a... First sliding surface, P... Recording material

Claims

1. A fixing device for fixing a toner image formed on a recording material to the recording material, comprising: an endless belt that rotates while carrying a lubricant on its inner peripheral surface; a heating unit that heats the inner peripheral surface of the belt; a nip portion forming member that abuts against the inner peripheral surface of the belt and forms a nip portion that sandwiches and conveys the recording material on which the toner image is formed while applying heat and pressure to fix the toner image to the recording material; a rotating body that is disposed with the belt interposed therebetween with respect to the nip portion forming member and that abuts against the outer peripheral surface of the belt to press the belt; wherein the nip portion forming member has a holding portion that holds the heating unit along the rotation axis direction of the rotating body; a downstream rubbing portion having a first rubbing surface that receives rubbing from the inner peripheral surface of the belt on the downstream side of the holding portion with respect to the rotation direction of the belt; an upstream rubbing portion having a second rubbing surface that receives rubbing from the inner peripheral surface of the belt on the upstream side of the holding portion with respect to the rotation direction of the belt; the holding portion holds the heating unit so as not to protrude toward the rotating body side beyond a line connecting a portion that receives rubbing from the belt on the first rubbing surface and a portion that receives rubbing from the belt on the second rubbing surface when viewed from the rotation axis direction; The second rubbing surface is formed in a curved shape, and when the force applied to the belt is "w2" (N / mm) with respect to the length of the second rubbing surface in the direction of the rotation axis, and the radius of curvature of the second rubbing surface is "R2" (mm), "R2 / w2" of the second rubbing surface is "5 (mm ２ / N) or more and 80 (mm ２ / N) or less". A fixing device characterized by the above.

2. The first rubbing surface is formed in a curved shape. When the force applied to the belt is "w1" (N / mm) with respect to the length of the first rubbing surface in the rotation axis direction, and the radius of curvature of the first rubbing surface is "R1" (mm), "R1 / w1" of the first rubbing surface is "5 (mm2 / N) or more and 80 (mm2 / N) or less". The fixing device according to claim 1, characterized by the above.

3. "R1 / w1" of the first rubbing surface is "10 (mm ２ / N) or more and 30 or less (mm ２ / N)". The fixing device according to claim 2, characterized by the above.

4. The radius of curvature "R2" of the second rubbing surface is larger than the radius of curvature "R1" of the first rubbing surface. The fixing device according to claim 3, characterized by the above.

5. "R2 / w2" of the second rubbing surface is larger than "R1 / w1" of the first rubbing surface. The fixing device according to claim 3, characterized by the above.

6. The heating unit is a ceramic heater. The fixing device according to claim 1, characterized by the above.

Images