Nip forming unit and image forming apparatus

Abstract

To prevent an endless film from becoming a distorted shape.SOLUTION: A nip forming unit has: a flexible endless film (fixing film 20); a heat source (heater 22) that heats the endless film; a nip forming member (heater 22) that is provided contactable with an inner peripheral surface of the endless film; a pressure member (pressure roller 21) that is in pressure contact with the nip forming member to form a nip with the endless film therebetween, and is driven to rotate to cause the endless film to rotate; detection means that detects the temperature of the pressure member; and control means that controls the rotational drive of the pressure member based on the temperature of the pressure member detected by the detection means, wherein a body to be conveyed (sheet P) is conveyed through the nip. The control means drives to rotate the pressure member in a conveyance direction to convey the body to be conveyed and subsequently stops the rotation of the pressure member, and when the temperature of the pressure member of the nip forming unit at the end of a job is equal to or higher than a predetermined temperature, the control means rotates the pressure member in a direction opposite to the conveyance direction for a predetermined time and subsequently stops the rotation of the pressure member.SELECTED DRAWING: Figure 9A

Description

[Technical Field]

[0001] The present invention relates to a nip forming unit and an image forming apparatus including the nip forming unit. [Background technology]

[0002] In image forming devices such as copiers and printers, a fixing device that uses a fixing roller and a pressure roller is known as a fixing device that fixes an image formed on a recording medium such as paper (for example, Patent Document 1: JP 2008-281595 A).

[0003] The fixing device disclosed in Patent Document 1 separates the paper from the fixing roller using a separating member (separating plate 204 in FIG. 2) placed close to the fixing roller. When using such a separating member, if the gap between the fixing roller and the separating member is too narrow, the separating member will come into contact with the fixing roller and the belt will be easily damaged, which will cause abnormal images.

[0004] Conversely, if the gap between the fixing roller and the separating member is too wide, the paper will pass through this wide gap and become wrapped around the fixing roller, making it more likely to jam (reducing the margin for separation). Therefore, it is necessary to place the separating member as close as possible to the fixing roller without it coming into contact with the fixing roller. Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, in the so-called surf fixing method, which uses a thin, low-heat-capacity fixing film instead of a fixing roller for on-demand printing, as in Patent Document 2 (JP 2009-288587 A), the fixing film is supported tensionlessly by a low-heat-capacity support stay or planar heater arranged inside the fixing film facing the pressure roller, and the fixing film is rotated by the rotation of the pressure roller.

[0006] Heat-resistant resin (mainly polyimide) is often used for fixing film. Fixing film made of polyimide becomes flexible and deforms at high temperatures (above 100°C), so even if it is deformed in the fixing nip, it quickly returns to its original cylindrical shape. However, if the fixing film is left pressurized in the fixing nip for a long time, the fixing film will conform to the shape of the nip, and the normally cylindrical fixing film may become distorted (flat spot).

[0007] When the fixing device is restarted after being left unused for a long time, the fixing film may come into contact with the separating member and be damaged, or the separation performance may become inconsistent, because the fixing device has not yet warmed up sufficiently.Furthermore, irregular rotation and abnormal noise may occur due to abnormal contact between the fixing film and the pressure roller, and the toner may be fixed unevenly.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to prevent the endless film of the nip forming unit from becoming distorted in shape. [Means for solving the problem]

[0009] In order to solve the above problem, the nip formation unit of the present invention comprises a rotatable, flexible endless film, a heat source for heating the endless film, a nip forming member arranged to be in contact with the inner surface of the endless film, a pressure member that presses against the nip forming member through the endless film to form a nip and rotates to cause the endless film to rotate, a detection means for detecting the temperature of the pressure member, and a control means for controlling the rotational drive of the pressure member based on the temperature of the pressure member detected by the detection means, and is characterized in that in a nip formation unit in which a transported object is transported through the nip, the control means rotates the pressure member in the transport direction to transport the transported object, and then stops the rotation of the pressure member, and when the temperature of the pressure member at the end of a job of the nip formation unit is higher than a predetermined temperature, rotates the pressure member in the direction opposite to the transport direction for a predetermined time and then stops the rotation of the pressure member. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent the endless film from becoming irregular in shape. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a fixing device. [Figure 3] FIG. 2 is a perspective view of a heater, a heater holder, and a guide portion. [Figure 4] FIG. [Figure 5] FIG. 2 is a diagram showing a power supply circuit to a heater. [Figure 6] 10 is a flowchart showing a control operation of a heater. [Figure 7A] FIG. 2 is a cross-sectional view of a fixing device including a separating member. [Figure 7B] FIG. 2 is a cross-sectional view of a fixing device including a separating member. [Figure 7C] FIG. 3 is a cross-sectional view showing the irregular shape of the fixing film. [Figure 7D] FIG. 4 is a cross-sectional view showing a state in which the fixing film comes into contact with a separating member. [Figure 8] 10A and 10B are cross-sectional views showing a method for suppressing the irregular shape of the fixing film. [Figure 9A] 10A and 10B are cross-sectional views showing a method for preventing the fixing film from being distorted by stopping the reverse rotation of the fixing film. [Figure 9B] 10A and 10B are cross-sectional views showing a method for suppressing a distorted shape by intermittently stopping reverse rotation of the fixing film. [Figure 9C] 10 is a cross-sectional view showing a state in which the fixing film comes into contact with the separating member when the forward rotation of the fixing film is stopped. FIG. [Figure 10] 10 is a flowchart showing a method for controlling the rotation of the fixing film. [Figure 11] FIG. 1 illustrates the atomic crystal structure of graphene. [Figure 12]FIG. 1 illustrates the atomic crystal structure of graphite. [Figure 13] 10A and 10B are side cross-sectional views of a fixing device showing modified examples of the thermistor arrangement. [Figure 14] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 15] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 16] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 17] FIG. 2 is a schematic diagram illustrating the configuration of an image forming apparatus different from that in FIG. [Figure 18] 1 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. [Figure 19] FIG. 19 is a plan view of a heater in the fixing device of FIG. [Figure 20] FIG. 2 is a perspective view of a heater and a heater holder. [Figure 21] FIG. 4 is a perspective view showing a state in which a connector is attached to a heater. [Figure 22] FIG. 2 is a diagram showing the arrangement of a thermistor and a thermostat. [Figure 23] FIG. 10 is a view showing a groove portion of a flange. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and descriptions thereof will be omitted once they have been described.

[0013] (●Image forming equipment) 1 is a schematic diagram of an image forming apparatus (machine) according to an embodiment of the present invention. The image forming apparatus 100 shown in FIG. 1 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body.

[0014] Each of the imaging units 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a developer of a different color—yellow, magenta, cyan, or black—corresponding to the color separation components of a color image. Specifically, each of the imaging units 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoconductor 2 as an image carrier, a charging device 3 that charges the surface of the photoconductor 2, a developing device 4 that supplies toner as a developer to the surface of the photoconductor 2 to form a toner image, and a cleaning device 5 that cleans the surface of the photoconductor 2.

[0015] The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoreceptor 2 to light to form an electrostatic latent image, a paper feeder 7 that supplies paper P as a transport object or recording medium, a transfer device 8 that transfers the toner image formed on each photoreceptor 2 to the paper P, a fixing device 9 that serves as a nip forming unit that fixes the toner image transferred to the paper P, and a paper discharge device 10 that discharges the paper P to the outside of the apparatus. In addition to paper P (plain paper), recording media include cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, overhead projector sheets, plastic film, prepreg, copper foil, etc.

[0016] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body stretched by multiple rollers, four primary transfer rollers 12 as primary transfer members that transfer the toner images on the photoconductors 2 onto the intermediate transfer belt 11, and a secondary transfer roller 13 as a secondary transfer member that transfers the toner images transferred onto the intermediate transfer belt 11 onto paper P. Each of the multiple primary transfer rollers 12 is in contact with the photoconductor 2 via the intermediate transfer belt 11.

[0017] As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, forming a primary transfer nip therebetween. Meanwhile, the secondary transfer roller 13 comes into contact with one of the rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0018] Also, a paper transport path 14 is formed inside the image forming apparatus 100, along which paper P sent out from the paper feeder 7 is transported. A pair of timing rollers 15 is provided on the paper transport path 14 midway from the paper feeder 7 to the secondary transfer nip (secondary transfer roller 13).

[0019] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0020] When a command to start a printing operation is issued, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the original document reader or the print information instructed to be printed from a terminal, thereby reducing the potential of the exposed area and forming an electrostatic latent image. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0021] When the toner images formed on each photoconductor 2 reach the primary transfer nip (position of primary transfer roller 12) as each photoconductor 2 rotates, they are transferred onto the intermediate transfer belt 11, which rotates counterclockwise in Fig. 1, so as to overlap one another. Then, the toner images transferred onto the intermediate transfer belt 11 are transported to the secondary transfer nip (position of secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and are transferred onto the paper P that has been transported at the secondary transfer nip.

[0022] This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeder 7 is temporarily stopped by a timing roller 15, and then transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 11 reaching the secondary transfer nip. In this way, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

[0023] The paper P onto which the toner image has been transferred is transported to a fixing device 9, which fixes the toner image onto the paper P. The paper P is then discharged outside the apparatus by a paper discharge device 10, completing the series of printing operations.

[0024] (● Fixing device) Next, an embodiment of a fixing device as a nip forming unit will be described. As shown in Fig. 2, the fixing device 9 according to this embodiment includes a fixing film 20 as an endless film, a pressure roller 21 as a pressure member that contacts the outer peripheral surface of the fixing film 20 to form a fixing nip N, a planar heater 22 as a heat source that heats the fixing film 20, a heater holder 23 as a holding member that holds the heater 22, a stay 24 as a support member that supports the heater holder 23, and a thermistor 25 as temperature detection means that detects the temperature of the fixing film 20. The heater 22 also functions as a nip forming member.

[0025] 7A to 7C, which will be described later, is omitted from Fig. 2. The separating member 310 can be disposed downstream of the fixing nip N in Fig. 2 in the same manner as in Figs. 7A to 7C.

[0026] The fixing film 20 has a cylindrical substrate made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm, for example. A release layer made of a fluorine-based resin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing film 20 to enhance durability and ensure releasability.

[0027] An elastic layer made of rubber or the like having a thickness of 50 to 500 μm may be provided between the substrate and the release layer. The substrate of the fixing film 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK, or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing film 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

[0028] The fixing film 20 can also be configured with a base material, a surface layer, and an adhesive layer, without an elastic layer. Without an elastic layer, the rigidity of the entire film is low, and it is prone to deformation when stopped, as described below. However, in this embodiment, the separating member 310, described below, swings in response to fluctuations in the film surface, so paper separation can be stabilized.

[0029] The pressure roller 21 has an outer diameter of, for example, 25 mm and is composed of a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm. To improve the release properties of the surface of the elastic layer 21b, it is desirable to form the release layer 21c, which is a fluororesin layer having a thickness of, for example, about 40 μm.

[0030] By making the diameter of the fixing film 20 larger than the diameter of the pressure roller 21, the heater 22 can be made wider, making it possible to accommodate high-productivity machines. Also, a larger film diameter reduces the overall deformation of the fixing film 20 relative to the nip width, which can suppress deformation and stabilize paper separation properties.

[0031] However, if the width of the heater 22 is too wide, the tendency to deform will increase. Therefore, it is preferable to set the width of the heater 22 to an appropriate size.

[0032] The pressure roller 21 is urged toward the fixing film 20 by the urging means, so that the pressure roller 21 is pressed against the heater 22 via the fixing film 20. This forms a fixing nip N between the fixing film 20 and the pressure roller 21. The pressure roller 21 is configured to be rotationally driven by a driving means, and when the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing film 20 is rotated accordingly.

[0033] Because the fixing film 20 is rotated by the rotation, the diameter of the fixing film 20 (film diameter) needs to be larger than the inner members such as the heater 22 and the heater holder 23. If the film diameter is increased, the trajectory fluctuation of the fixing film 20 increases accordingly, but in this embodiment, the magnitude of the trajectory fluctuation can be suppressed as described later, and therefore the paper separation ability of the separating member 310 can be stabilized.

[0034] The heater 22 is a planar heating member provided longitudinally across the width direction of the fixing film 20, and is composed of a plate-shaped substrate 30, a resistance heating element 31 provided on the substrate 30, an insulating layer 32 covering the resistance heating element 31, etc. The heater 22 is in contact with the inner circumferential surface of the fixing film 20 on the insulating layer 32 side, and the heat generated by the resistance heating element 31 is transmitted to the fixing film 20 via the insulating layer 32.

[0035] A highly thermally conductive member can be disposed between the heater 22 and the heater holder 23. One surface of this highly thermally conductive member is in contact with the rear surface of the heater 22, and the other surface is in contact with the heater holder 23.

[0036] The highly thermally conductive member can improve the uniformity of heat in the heater 22 and enhance image quality. The highly thermally conductive member can be made of a material with better thermal conductivity than the base material 30 of the heater 22, such as graphene or graphite, which will be described later with reference to Figures 11 and 12.

[0037] In this embodiment, the resistance heating element 31 and the insulating layer 32 are provided on the fixing film 20 side (fixing nip N side) of the substrate 30, but conversely, the resistance heating element 31 and the insulating layer 32 may be provided on the heater holder 23 side of the substrate 30. In that case, since the heat of the resistance heating element 31 is transferred to the fixing film 20 via the substrate 30, it is desirable that the substrate 30 be made of a material with high thermal conductivity such as aluminum nitride. Furthermore, by making the substrate 30 of a material with good thermal conductivity, it is possible to sufficiently heat the fixing film 20 even if the resistance heating element 31 is arranged on the opposite side of the substrate 30 from the fixing film 20 side.

[0038] The heater holder 23 and the stay 24 are disposed on the inner circumferential side of the fixing film 20. The stay 24 is made of a metal channel material, and both ends thereof are supported by both side plate portions of the fixing device 9. Since the heater holder 23 and the heater 22 held thereby are supported by the stay 24, when the pressure roller 21 is pressed against the fixing film 20, the heater 22 reliably receives the pressing force of the pressure roller 21, and the fixing nip N is stably formed.

[0039] The heater holder 23 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 22. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP, heat transfer from the heater 22 to the heater holder 23 is suppressed, and the fixing film 20 can be heated efficiently.

[0040] Furthermore, in order to reduce the contact area of ​​the heater holder 23 with the heater 22 and reduce the amount of heat transferred from the heater 22 to the heater holder 23, the heater holder 23 is in contact with the base material 30 of the heater 22 via the protrusions 23a. Furthermore, as in this embodiment, by bringing the protrusions 23a of the heater holder 23 into contact with a portion of the base material 30 other than the back side of the portion where the resistance heating element 31 is located, i.e., by avoiding a portion of the base material 30 where the temperature is likely to become high, the amount of heat transferred to the heater holder 23 can be further reduced and the fixing film 20 can be heated efficiently.

[0041] The heater holder 23 is also provided with guide portions 26 that guide the fixing film 20. The guide portions 26 are provided on the upstream side (below the heater 22 in FIG. 2) and downstream side (above the heater 22 in FIG. 2) of the film rotation direction of the heater 22.

[0042] 3, the upstream and downstream guide portions 26 are arranged at intervals along the longitudinal direction (film width direction) of the heater 22. Each guide portion 26 is formed in a generally fan shape, and has an arc-shaped or convexly curved film-facing surface 260 that extends in the film circumferential direction so as to face the inner circumferential surface of the fixing film 20 (see FIG. 2). Also, as shown in FIG. 3, in this embodiment, the width W of the guide portions 26 arranged at both longitudinal end portions of the heater 22 is larger than that of the other guide portions 26, and the width W, length (circumferential length) L in the film circumferential direction, and height E of each guide portion 26 are the same.

[0043] In the fixing device 9 according to this embodiment, when a printing operation is started, the pressure roller 21 is driven to rotate, and the fixing film 20 starts to rotate accordingly. At this time, the inner circumferential surface of the fixing film 20 contacts and is guided by the film-facing surface 260 of the guide portion 26, so that the fixing film 20 rotates stably and smoothly.

[0044] Furthermore, power is supplied to the resistance heating element 31 of the heater 22, thereby heating the fixing film 20. Then, when the temperature of the fixing film 20 reaches a predetermined target temperature (fixing temperature), the paper P carrying an unfixed toner image is transported between the fixing film 20 and the pressure roller 21 (fixing nip N) as shown in FIG.

[0045] (● Heater configuration) Fig. 4 is a plan view of the heater according to this embodiment. As shown in Fig. 4, the heater 22 according to this embodiment has a plurality of resistance heating elements 31 arranged at intervals in the longitudinal direction (film width direction).

[0046] In other words, a heating section 35 divided into a plurality of sections in the width direction of the film is formed by a plurality of resistance heating elements 31. The heating section 35 can be divided into at least three or four or more sections, namely, end heaters that heat both end sections and a central heater that heats the central section.

[0047] When the heater is divided into sections, it is necessary to widen the heater width in the paper feed direction. This increases the width of the fixing nip N, which increases the deformation tendency of the film and the trajectory fluctuation. However, in this embodiment, the magnitude of the trajectory fluctuation can be suppressed as described below, so a divided heater can be used without any problems.

[0048] Each resistance heating element 31 is electrically connected in parallel to a pair of electrode portions 34 provided at both longitudinal ends of the substrate 30 via a power supply line 33. The power supply line 33 is made of a conductor having a smaller resistance value than the resistance heating element 31.

[0049] The gap between adjacent resistance heating elements 31 is preferably 0.2 mm or more, and more preferably 0.4 mm or more, from the viewpoint of ensuring insulation between the resistance heating elements 31. Furthermore, if the gap between adjacent resistance heating elements 31 is too large, a temperature drop is likely to occur in the gap, so from the viewpoint of suppressing temperature unevenness across the longitudinal direction, the gap is preferably 5 mm or less, and more preferably 1 mm or less.

[0050] The resistance heating element 31 is made of a material with a PTC (positive temperature coefficient of resistance) characteristic, and has the characteristic that its resistance value increases (heater output decreases) as the temperature increases. Due to this characteristic, for example, when a paper sheet narrower than the entire width of the heating section 35 is passed through, the paper sheet does not take heat from the fixing film 20 in the area outside the paper width, and the temperature of the resistance heating element 31 corresponding to that area increases.

[0051] Because the voltage applied to the resistance heating elements 31 is constant, when the temperature of the resistance heating elements 31 outside the paper width rises and their resistance value rises, the output (amount of heat generated) decreases relatively, suppressing the rise in temperature at the edges. In addition, by electrically connecting multiple resistance heating elements 31 in parallel, it is possible to suppress the rise in temperature in non-paper passing areas while maintaining the printing speed.

[0052] The heating element constituting the heating section 35 may be something other than a resistance heating element having PTC characteristics. The heating elements may be arranged in a single row in the short side direction of the heater 22 as shown in FIG. 4, or in multiple rows.

[0053] The resistance heating element 31 can be formed, for example, by applying a paste prepared by mixing silver palladium (AgPd) and glass powder to the substrate 30 by screen printing or the like, and then firing the substrate 30. In this embodiment, the resistance value of the resistance heating element 31 is set to 80 Ω at room temperature.

[0054] In addition to the materials mentioned above, resistance materials such as silver alloy (AgPt) and ruthenium oxide (RuO2) may be used for the material of the resistance heating element 31. The material of the power supply line 33 and the electrode part 34 can be formed by screen printing or the like using silver (Ag) or silver palladium (AgPd).

[0055] The material of the substrate 30 is preferably a ceramic such as alumina or aluminum nitride, which has excellent heat resistance and insulation properties, or a non-metallic material such as glass or mica. In this embodiment, an alumina substrate having a width of 8 mm, a length of 270 mm, and a thickness of 1.0 mm is used.

[0056] Alternatively, the substrate 30 may be formed by laminating an insulating material onto a conductive material such as a metal. Aluminum, stainless steel, or other metal materials are preferred because they are low cost. Furthermore, to improve the uniform heating of the heater 22 and enhance image quality, the substrate 30 may be formed from a material with high thermal conductivity, such as copper, graphite, or graphene.

[0057] The insulating layer 32 is made of heat-resistant glass having a thickness of, for example, 75 μm. The insulating layer 32 covers the resistance heating element 31 and the power supply line 33, insulating and protecting them and maintaining sliding properties with the fixing film 20.

[0058] FIG. 5 is a diagram showing a power supply circuit to the heater according to this embodiment.

[0059] 5, in this embodiment, a power supply circuit for supplying power to each resistance heating element 31 is configured by electrically connecting an AC power source 200 and the electrode portions 34 of the heaters 22. The power supply circuit also includes a triac 210 for controlling the amount of power supply.

[0060] The amount of power supplied to each resistance heating element 31 is controlled by a control unit 220 via a triac 210 based on the temperature detected by a thermistor 25 serving as a temperature detection means. The control unit 220 is configured as a microcomputer including a CPU, ROM, RAM, an I / O interface, etc.

[0061] In this embodiment, thermistors 25 serving as temperature detection means are disposed in a central region in the longitudinal direction of the heater 22, which is within the minimum paper passing width, and at one longitudinal end side of the heater 22. Furthermore, at one longitudinal end side of the heater 22, a thermostat 27 is disposed as power cut-off means that cuts off the power supply to the resistance heating element 31 when the temperature of the resistance heating element 31 reaches or exceeds a predetermined temperature. The thermistor 25 and thermostat 27 contact the back surface of the substrate 30 (the side opposite to the side on which the resistance heating element 31 is disposed) and detect the temperature of the resistance heating element 31.

[0062] (● Flowchart) Next, the heater control operation according to this embodiment will be described with reference to the flowchart of Fig. 6. First, when a printing operation is started in the image forming apparatus (S1 in Fig. 6), the control unit 220 starts supplying power from the AC power supply 200 to each resistance heating element 31 of the heater 22 (S2 in Fig. 6).

[0063] As a result, each resistance heating element 31 starts to generate heat, thereby heating the fixing film 20. At this time, a thermistor (central thermistor) 25 disposed in the longitudinal central region of the heater 22 detects a temperature T4 of the resistance heating element 31 located in the central region of the heater 22 (S3 in FIG. 6). Then, based on the temperature T4 obtained from the central thermistor 25, the control unit 220 controls the amount of power supplied to each resistance heating element 31 by the triac 210 so that each resistance heating element 31 reaches a predetermined temperature (S4 in FIG. 6).

[0064] At the same time, the temperature T8 of the resistance heating element 31 is also detected by a thermistor (end thermistor) 25 arranged on the longitudinal end side of the heater 22 (S5 in FIG. 6). Then, it is determined whether the temperature T8 detected by the end thermistor 25 is equal to or higher than a predetermined temperature TN (T8≧TN) (S6 in FIG. 6). If the temperature T8 is less than the predetermined temperature TN, an abnormally low temperature has occurred (a wire break has occurred), and the power supply to the heater 22 is cut off (S7 in FIG. 6), and an error message is displayed on the operation panel of the image forming apparatus (S8 in FIG. 6). On the other hand, if the detected temperature T8 is equal to or higher than the predetermined temperature TN, it is determined that an abnormally low temperature has not occurred, and the printing operation is started (S9 in FIG. 6).

[0065] Furthermore, if temperature control based on detection by the central thermistor 25 becomes impossible due to damage or a disconnection of the resistance heating element 31, there is a risk that the other resistance heating elements 31, including the resistance heating elements 31 at the longitudinal ends, will reach an abnormally high temperature. In this case, when the resistance heating element 31 reaches a predetermined temperature or higher, the thermostat 27 will operate and cut off the power supply to the resistance heating element 31, thereby preventing the resistance heating element 31 from reaching an abnormally high temperature.

[0066] (●Separation member) 7A is a conceptual diagram of a fixing device equipped with a separating member 310 that separates the paper P that has passed through the fixing nip N from the fixing film 20. In FIG. 7A, this separating member 310 is disposed in the form of a separating plate on the downstream side (right side) of the fixing nip N. The paper P is separated from the fixing film 20 by the separating member 310.

[0067] The separating member 310 can be made of a heat-resistant metal or resin, such as stainless steel.

[0068] Examples of heat-resistant resins that can be used include polyimide, PEEK, etc. The separating member 310 may be made of a material other than metal or resin as long as it is heat-resistant.

[0069] The separating member 310 can be fixedly disposed as shown in Fig. 7A, or rotatably supported by a separating shaft 322 as shown in Fig. 7B. The separating member 310 extends parallel to the axial direction of the fixing film 20 with a width greater than the paper size. The size of the gap between the tip of the separating member 310 and the fixing film 20 can be set within the range of 0.2 to 2.0 mm, for example.

[0070] 7B, by rotating the separating member 310 in response to the movement of the fixing film 20, it is possible to prevent the separating member 310 from coming into contact with the fixing film 20. The separating member 310 in FIG. 7B has both longitudinal ends rotatably supported by separating shafts 322 protruding from the inner surfaces of a pair of left and right side plate portions.

[0071] (●Deformation of the fixing film) As mentioned above, the fixing film 20 can be made of a heat-resistant resin such as polyimide, but because it is thin, it is prone to large deformation while the rotation is stopped. If the fixing film 20 is rotated in this state, the trajectory of the fixing film 20 will fluctuate irregularly.

[0072] That is, in the fixing nip N while the rotation is stopped, the fixing film 20 is sandwiched between the planar heater 22 and the pressure roller 21, and a flat deformation occurs as shown on the right side of Fig. 7C. The fixing film 20 and the heater 22 have a large difference in cooling time, which makes this deformation more likely to occur. Since there is no member inside the fixing film 20 to restrict film deformation, when the fixing film 20 starts to rotate in a deformed state as shown on the right side of Fig. 7C, the rotational orbit of the fixing film 20 fluctuates irregularly and in a distorted shape as shown by the chain line in Fig. 7D (occurrence of fluttering).

[0073] (●Movement of separation parts) If the rotational path of the fixing film 20 fluctuates irregularly in an irregular shape as shown by the dotted line in Fig. 7D, the fixing film 20 will come into contact with nearby components such as the separating member 310. To prevent the fixing film 20 from coming into contact with the separating member 310, it is necessary to separate the separating member 310 from the rotational path of the fixing film 20 as shown by the dotted line, but this will degrade the separation performance. Furthermore, separating nearby components from the rotational path of the fixing film 20 will restrict space-saving layouts.

[0074] (● Suppression of deformation) 8 is one possible method for suppressing deformation of the fixing film 20. This method is basically the same as the method disclosed in Patent Document 1 (JP 2008-281595 A) for suppressing deformation of a fixing roller.

[0075] That is, each time the rotation of the pressure roller 21 is stopped, the stopping position of the fixing film 20 is shifted little by little. By doing so, the irregular shape (flat spot) is dispersed in the circumferential direction of the fixing film 20 as shown on the right side of FIG.

[0076] 7C, the fixing film 20 can be prevented from being significantly deformed. Also, the compression set of the pressure roller 21 can be suppressed.

[0077] (● Pressure roller reverse rotation stop) However, even when the flat spots are dispersed in the circumferential direction of the fixing film 20 as in Fig. 8, tension and deflection remain before and after the fixing nip N when the fixing film 20 is stopped. That is, when the fixing film 20 is rotated (forward) in the conveying direction as in Fig. 9C and then stopped, "tension" remains on the upstream side of the fixing nip N, and "deflection" remains on the downstream side.

[0078] In this state, if the pressure roller 21 is restarted to rotate clockwise and rotate the fixing film 20, the "deflection" on the downstream side will expand further in the downstream direction, increasing the possibility of contact with the separating member 310. Here, "starting" or "restarting" means that the pressure roller 21, which has once stopped, returns to a state in which it can rotate the fixing film 20.

[0079] Therefore, in the embodiment of the present invention, after the fixing film 20 is stopped (heater 22 is off), the pressure roller 21 is driven in the reverse direction opposite to the conveying direction for a predetermined time and then stopped as shown in Figure 9A. As a result, "flexure" remains on the upstream side of the fixing nip N, and "tension" remains on the downstream side.

[0080] 9A, even if the pressure roller 21 is restarted to rotate clockwise and the fixing film 20 is rotated by the pressure roller 21, the downstream side of the "pulling" does not expand downstream but slides to the left along the guide portion 26. Therefore, the fixing film 20 can be prevented from coming into contact with the separating member 310.

[0081] The rotation speed of the pressure roller 21 when driven in the reverse direction can be set lower than the rotation speed when rotating in the conveying direction. Driving the pressure roller 21 in the reverse direction at such a low speed reduces the load on the sliding portion of the fixing film 20, thereby extending the life of the film.

[0082] (● Intermittent reverse rotation stop of pressure roller) In FIG. 9B, after the fixing film 20 is stopped (heater 22 is off), the pressure roller 21 is intermittently reverse-driven in the direction opposite to the conveying direction for a predetermined time, and then stopped. This intermittent reverse drive can be minute intermittent reverse drive. This allows residual heat from the heater 22 and guide portion 26 in the fixing nip N to be released upstream by the intermittent reverse movement of the fixing film 20.

[0083] This reduces the temperatures of the heater 22 and the guide portion 26, and averages the cooling of the fixing film 20 in the circumferential direction, thereby reducing curling. This reduces the temperature difference between the fixing nip N and the fixing film 20 before and after it, and suppresses irregular fluctuations (fluttering) of the fixing film 20 after restarting the pressure roller 21.

[0084] 9A, if the pressure roller 21 is continuously driven in the reverse direction, the greater the amount of rotation, the greater the risk of damage to the fixing film 20 at the sliding portion. In contrast, if the pressure roller 21 is driven in the reverse direction (very slightly) intermittently as shown in FIG. 9B, the fixing film 20 rotates by the minimum amount, thereby reducing the risk of damage to the fixing film 20.

[0085] In the intermittent reverse driving, for example, the fixing film 20 is rotated in the reverse direction by 80 degrees at a time. After a predetermined stop time (for example, 15 seconds), the fixing film 20 is rotated in the reverse direction by 80 degrees again. Such reverse driving can be repeated several times.

[0086] (● Pressure roller drive control) Next, the drive control of the pressure roller 21 will be described with reference to the flowchart of Fig. 10. This flowchart can be executed by the control unit 220 as the control means described above, or by the control unit of the machine 100.

[0087] As described above in Figures 9A and 9B, by driving the pressure roller 21 in the reverse direction for a predetermined period of time after stopping it, it is possible to prevent the fixing film 20 from expanding downstream of the fixing nip N when the pressure roller 21 is restarted and the fixing film 20 is rotated by the pressure roller 21.

[0088] However, in order to increase the productivity of the machine 100, the reverse rotation of the pressure roller 21 must be kept to a minimum. According to experiments conducted by the inventors of the present application, when the temperature of the pressure roller 21 is high at the end of printing (end of job), a large amount of heat accumulates in the nip portion. If the fixing film 20 is allowed to cool naturally in this state, it tends to become more warped, resulting in greater irregular fluctuations (fluttering) when the next printing starts. Note that "end of job" refers to the point at which image formation for the number of prints specified on the operation panel of the image forming apparatus 100, including the nip formation unit, has been completed.

[0089] Conversely, if the temperature of the pressure roller 21 is low at the end of printing, the heat stored in the nip portion is small, and even if the nip portion is allowed to cool naturally, the temperature difference between the nip portion and other portions is small, and the curling of the fixing film 20 is reduced.

[0090] In this embodiment, based on the above findings, the pressure roller 21 is controlled and driven as shown in the flowchart of Fig. 10. That is, after the printing operation is started in step S11, power is supplied to the heater 22 in step S12, and the printing operation is started in step S13. Immediately after the printing operation is completed in step S14 (immediately after the job is completed), the temperature T1 is indirectly detected by a thermistor attached to the pressure roller 21 in step S15.

[0091] Then, it is determined whether the temperature T1 of the pressure roller 21 is high or not in step 16. Here, the temperature T1 of the pressure roller 21 is determined to be high when it is above 60° C., and low when it is 60° C. or less.

[0092] When the temperature T1 of the pressure roller 21 is low (T1 ≤ 60°C), it is determined whether the number of printed sheets at the end of the printing operation (step S15) in step S17 is 3 sheets or less. If the number of printed sheets is 3 sheets or less, the process ends without reverse control of the pressure roller 21.

[0093] When it is determined in step S16 that the temperature T1 of the pressure roller 21 is high (60°C < T1), the pressure roller 21 is reversely controlled for 60 seconds and then stopped (ended) in step S18. The reverse control at this time can be performed in either FIG. 9A or FIG. 9B. Also, when the number of printed sheets is 4 sheets or more, reverse control of the pressure roller 21 is performed.

[0094] That is, it is determined in step S19 whether the number of printed sheets is 10 sheets or less. If the number of printed sheets is 10 sheets or less, the pressure roller 21 is reversely controlled for 30 seconds and then stopped (ended) in step S20. The reverse control at this time can be performed in either FIG. 9A or FIG. 9B as described above.

[0095] When it is determined in step S19 that the number of printed sheets is 11 sheets or more, the pressure roller 21 is reversely controlled for 60 seconds and then stopped (ended) in step S18. The reverse control at this time can be performed in either FIG. 9A or FIG. 9B as described above.

[0096] The position where the fixing film 20 stops after the reverse control of the pressure roller 21 described above can be shifted little by little from the previous stop position as shown in FIG. 8. Thereby, the uneven shape (flat spot) of the fixing film 20 can be dispersed in the circumferential direction of the fixing film 20. Also, the compression set of the pressure roller 21 can be suppressed.

[0097] Of course, the above-described conditions (such as the determination of high or low temperature T1, reverse drive time, number of printed sheets, etc.) can be adjusted according to the state of the machine 100. Also, when the machine 100 has a function of shifting to the sleep mode if it does not operate for a predetermined time, the reverse control of the pressure roller 21 being executed can be aborted simultaneously when the machine 100 shifts to the sleep mode.

[0098] (Graphene sheet) The high thermal conductivity member can be made of a graphene sheet. This allows the formation of a high thermal conductivity member with high thermal conductivity in a predetermined direction along the graphene surface, i.e., in the arrangement direction rather than the thickness direction. Therefore, temperature unevenness in the arrangement direction of the heater 22 and the fixing film 20 can be effectively suppressed.

[0099] Graphene is a thin flake powder. As shown in Figure 11, which will be described later, graphene consists of a planar hexagonal lattice structure of carbon atoms. A graphene sheet is a sheet of graphene, usually a single layer. The single layer of carbon may contain impurities.

[0100] Graphene may also have a fullerene structure, which is generally recognized as a polycyclic compound in which equal numbers of carbon atoms are fused together in a cage-like fashion with five- and six-membered rings, such as C60, C70, and C80 fullerenes or other closed cage structures with three-coordinate carbon atoms.

[0101] Graphene sheets are artificial and can be produced, for example, by chemical vapor deposition (CVD). Commercially available graphene sheets can be used. The size and thickness of graphene sheets, as well as the number of layers of graphite sheets (described later), can be measured, for example, by a transmission electron microscope (TEM).

[0102] Furthermore, graphite, which is made up of multiple layers of graphene, has a large thermal conductivity anisotropy. As shown in Figure 12, which will be described later, graphite has a crystalline structure in which layers of fused six-membered rings of carbon atoms extend in a planar fashion, and these layers are stacked multiple times.

[0103] In this crystal structure, adjacent carbon atoms within a layer form covalent bonds, while adjacent carbon atoms between layers form van der Waals bonds. Covalent bonds have a stronger bonding strength than van der Waals bonds, and there is a large anisotropy between the bonds within a layer and the bonds between layers.

[0104] That is, by constructing the high thermal conductivity member from graphite, the heat transfer efficiency in the arrangement direction of the high thermal conductivity member is greater than in the thickness direction (i.e., the direction in which the members are stacked), and heat transfer to heater holder 23 can be suppressed. Therefore, it is possible to efficiently suppress temperature unevenness in the arrangement direction of heater 22 and minimize heat leakage to heater holder 23. Furthermore, by constructing the high thermal conductivity member from graphite, it is possible to provide the high thermal conductivity member with excellent heat resistance that does not oxidize up to approximately 700 degrees.

[0105] The physical properties and dimensions of the graphite sheet can be appropriately changed depending on the functions required of the high thermal conductivity member. For example, the anisotropy of thermal conductivity can be increased by using high-purity graphite or single-crystal graphite, or by increasing the thickness of the graphite sheet.

[0106] Furthermore, in order to increase the speed of the fixing device 9, a thin graphite sheet may be used to reduce the heat capacity of the fixing device 9. Furthermore, if the width of the fixing nip N or the heater 22 is large, the width of the highly thermally conductive member in the arrangement direction may be increased accordingly.

[0107] From the viewpoint of increasing the mechanical strength, the number of layers of the graphite sheet is preferably at least 11. The graphite sheet may partially include a single layer portion and a multi-layer portion.

[0108] Graphene is a flake-like powder. Graphene consists of a planar hexagonal lattice structure of carbon atoms, as shown in Figure 11. A graphene sheet is a sheet of graphene, usually a single layer.

[0109] Graphene sheets may also contain impurities in a single layer of carbon, or may have a fullerene structure, which is generally recognized as a polycyclic compound in which equal numbers of carbon atoms are fused together in a cage-like fashion with five- and six-membered rings, such as C60, C70, and C80 fullerenes, or other closed cage structures with three-coordinate carbon atoms.

[0110] Graphene sheets are artificial and can be produced, for example, by chemical vapor deposition (CVD). Commercially available graphene sheets can be used. The size and thickness of graphene sheets, as well as the number of layers of graphite sheets (described later), can be measured, for example, by a transmission electron microscope (TEM).

[0111] Furthermore, graphite, which is made by multi-layering graphene, has a large thermal conductivity anisotropy. As shown in Figure 12, graphite has a crystalline structure in which layers of fused six-membered rings of carbon atoms extend in a planar fashion, and these layers are stacked multiple times.

[0112] In this crystalline structure, adjacent carbon atoms within a layer form covalent bonds, while adjacent carbon atoms between layers form van der Waals bonds. Covalent bonds have stronger bonding strength than van der Waals bonds, and there is significant anisotropy between the bonds within a layer and the bonds between layers. In other words, by constructing the high thermal conductivity member from graphite, the heat transfer efficiency in the longitudinal direction of the high thermal conductivity member is greater than in the thickness direction (i.e., the stacking direction of the member), thereby suppressing heat transfer to the heater holder 23.

[0113] Therefore, it is possible to efficiently suppress temperature unevenness in the longitudinal direction of the heater 22 and minimize heat leakage to the heater holder 23. Furthermore, by using graphite for the high thermal conductivity member, it is possible to provide the high thermal conductivity member with excellent heat resistance that does not oxidize up to approximately 700 degrees.

[0114] The physical properties and dimensions of the graphite sheet can be appropriately changed depending on the functions required of the high thermal conductivity member. For example, the anisotropy of thermal conductivity can be increased by using high-purity graphite or single-crystal graphite, or by increasing the thickness of the graphite sheet.

[0115] In order to increase the speed of the fixing device, a thin graphite sheet may be used to reduce the heat capacity of the fixing device. In addition, if the widths of the fixing nip N and heater 22 are large, the longitudinal width of the high thermal conductivity member may be increased accordingly.

[0116] From the viewpoint of increasing the mechanical strength, the number of layers of the graphite sheet is preferably at least 11. The graphite sheet may partially include a single layer portion and a multi-layer portion.

[0117] In the above description, the present invention has been described as being applied to a fixing device, which is an example of a film-type heating device (rotary body driving device). However, the present invention is not limited to fixing devices, and may also be applied to heating devices such as a drying device that dries a liquid such as ink applied to paper, a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, and a heat sealer that thermocompresses a seal portion of a packaging material.

[0118] (Modified embodiment of the fixing device) Next, modified embodiments of the fixing device 9 will be described with reference to Figures 13 to 23. Note that the separating member 310 described above with reference to Figures 9A to 9C is omitted from Figures 13 and thereafter. The separating member 310 can be disposed, for example, downstream of the fixing nip N in Figures 13 to 16, in the same manner as in Figures 9A to 9C.

[0119] 13 shows a modified arrangement of the thermistor. In this embodiment, the thermistor 25 is provided upstream of the center position NA of the fixing nip N in the cross-array direction in the rotation direction of the fixing film 20, in other words, on the entrance side of the fixing nip N. The entrance side of the fixing nip N is an area that is particularly susceptible to heat loss by the paper P, so by having the thermistor 25 detect the temperature of this area, the fixability of the fixing device 9 can be ensured and the fixing offset can be effectively suppressed.

[0120] 14, a pressure roller 44 is disposed on the opposite side of the pressure roller 21 with respect to the fixing film 20. The pressure roller 44 is an opposing rotating member that rotates opposite the fixing film 20, which is a rotating member. The pressure roller 44 and the heater 22 are configured to sandwich and heat the fixing film 20.

[0121] On the other hand, on the pressure roller 21 side, a nip forming member 45 is disposed on the inner periphery of the fixing film 20. The nip forming member 45 is supported by a stay 24. The nip forming member 45 and the pressure roller 21 sandwich the fixing film 20 to form a fixing nip N.

[0122] 15, the above-mentioned pressure roller 44 is omitted, and in order to ensure the circumferential contact length between the fixing film 20 and the heater 22, the heater 22 is formed in an arc shape to match the curvature of the fixing film 20. The rest of the configuration is the same as that of the fixing device 9 shown in FIG.

[0123] Finally, a description will be given of the fixing device 9 shown in Fig. 16. The fixing device 9 comprises a heating assembly 92, a fixing roller 93 which is a fixing member, and a pressure assembly 94 which is an opposing member.

[0124] The heating assembly 92 includes the heater 22, heater holder 23, stay 24, and heating belt 120 as a rotating member, which are described in the previous embodiment. The fixing roller 93 is a counter rotating member that rotates opposite the heating belt 120 as a rotating member. The fixing roller 93 is composed of a solid iron core 93a, an elastic layer 93b formed on the surface of the core 93a, and a release layer 93c formed on the outside of the elastic layer 93b.

[0125] A pressure assembly 94 is provided on the opposite side of the heating assembly 92 with respect to the fixing roller 93. The pressure assembly 94 has a nip forming member 95 and a stay 96 arranged therein, and a pressure belt 97 rotatably arranged so as to enclose the nip forming member 95 and the stay 96. A sheet of paper P is passed through the fixing nip N2 between the pressure belt 97 and the fixing roller 93, and heat and pressure are applied to fix the image thereon.

[0126] 14 and 15, the amount of heat generated by the heater 22 is similarly small in the divided area B (see FIG. 19) between the resistance heating elements 31 of the heater 22. Therefore, as in the above-described embodiment, by providing a temperature detection element of the temperature detection member at a position corresponding to the divided area B of the heater 22, it is possible to sufficiently heat the portion of the rotating member corresponding to the divided area. This ensures sufficient image fixability and prevents problems such as fixing offset.

[0127] Furthermore, the present invention is not limited to the fixing device described in the above embodiment, but can also be applied to heating devices such as a drying device that dries ink applied to paper, a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, and a heat sealer that thermocompresses a seal portion of a packaging material. By applying the present invention to such devices, the portion corresponding to the divided region of the rotating member can be sufficiently heated.

[0128] The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in Fig. 1, but may also be a monochrome image forming apparatus, a copier, a printer, a facsimile, or a combination machine of these. For example, as shown in Fig. 17, the image forming apparatus 100 of this embodiment includes an image forming means 50 including a photosensitive drum or the like, a paper transport unit including a pair of timing rollers 15 or the like, a paper feeder 7, a fixing device 9, a paper discharge device 10, and a reading unit 51. The paper feeder 7 includes multiple paper feed trays, each of which accommodates paper of a different size.

[0129] The reading unit 51 reads an image of the document Q. The reading unit 51 generates image data from the read image. The paper feeder 7 stores a plurality of sheets of paper P and sends the sheets of paper P to a conveyance path. The timing rollers 15 convey the sheets of paper P on the conveyance path to the image forming means 50.

[0130] The image forming means 50 forms a toner image on a sheet of paper P. Specifically, the image forming means 50 includes a photosensitive drum, a charging roller, an exposure device, a developing device, a replenishing device, a transfer roller, a cleaning device, and a discharging device. The toner image represents, for example, an image of a document Q.

[0131] The fixing device 9 applies heat and pressure to the toner image to fix the toner image to the paper P. The paper P with the fixed toner image is transported to the paper discharge device 10 by a transport roller or the like. The paper discharge device 10 discharges the paper P outside the image forming apparatus 100.

[0132] Next, the fixing device 9 of this embodiment will be described. Descriptions of the configurations common to the fixing devices of the above-described embodiments will be omitted as appropriate.

[0133] 18, the fixing device 9 includes a fixing film 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, a thermistor 25, etc. A fixing nip N is formed between the fixing film 20 and the pressure roller 21. The nip width of the fixing nip N is 10 mm, and the linear speed of the fixing device 9 is 240 mm / s.

[0134] The fixing film 20 has a polyimide base and a release layer, but does not have an elastic layer. The release layer is made of a heat-resistant film material such as fluororesin. The outer diameter of the fixing film 20 is approximately 24 mm.

[0135] The pressure roller 21 includes a core metal 21a, an elastic layer 21b, and a release layer 21c. The pressure roller 21 has an outer diameter of 24 to 30 mm, and the elastic layer 21b has a thickness of 3 to 4 mm.

[0136] The heater 22 includes a base material, a heat insulating layer, a conductor layer including a resistance heating element, and an insulating layer, and is formed to a total thickness of 1 mm. The width Y of the heater 22 in the array crossing direction is 13 mm.

[0137] 19, the conductor layer of the heater 22 includes a plurality of resistance heating elements 31, power supply lines 33, and electrode portions 34A to 34C. In this embodiment as well, the plurality of resistance heating elements 31 are divided into divided regions B in the arrangement direction (however, although FIG. 19 shows only the enlarged range of the divided regions B, in reality, divided regions are provided between all of the resistance heating elements 31).

[0138] Three heat generating sections 35A to 35C are formed by the resistance heating element 31. Heat generating sections 35A and 35C generate heat when current is applied to electrode sections 34A and 34B. Heat generating section 35B generates heat when current is applied to electrode sections 34A and 34C. For example, when performing a fixing operation on small-sized paper, heat generating section 35B is made to generate heat, and when performing a fixing operation on large-sized paper, all of the heat generating sections are made to generate heat.

[0139] 20, the heater holder 23 holds the heater 22 in its recess 23b. The recess 23b is provided on the heater 22 side of the heater holder 23. The recess 23b is composed of a surface 23b3 that is approximately parallel to the substrate 30 and is recessed toward the stay 24 side more than the other surfaces of the heater 22, wall portions 23b1 provided inside the heater holder 23 on both sides in the arrangement direction of the heater holder 23 (or on one side), and wall portions 23b2 provided inside the heater holder 23 on both sides in the intersecting direction of the arrangement.

[0140] The heater holder 23 has a guide portion 26. The heater holder 23 is made of LCP (liquid crystal polymer).

[0141] 21, the connector 160 includes a housing made of resin (for example, LCP) and a plurality of contact terminals provided inside the housing. The connector 160 is attached so as to sandwich the heater 22 and the heater holder 23 together from the front and back sides.

[0142] In this state, each contact terminal comes into contact (pressure-contact) with each electrode portion of the heater 22, electrically connecting the heat generating portion 35 to the power supply provided in the image forming apparatus via the connector 160. This enables power to be supplied from the power supply to the heat generating portion 35. Note that, in order to ensure connection with the connector 160, at least a portion of each electrode portion 34 is not covered with an insulating layer and is exposed.

[0143] The flanges 53 are provided on both sides of the fixing film 20 in the arrangement direction and hold both ends of the fixing film 20 from the inside of the film. The flanges 53 are fixed to the housing of the fixing device 9. The flanges 53 are inserted into both ends of the stays 24 (see the arrow directions from the flanges 53 in Figure 18).

[0144] The direction in which the connector 160 is attached to the heater 22 and heater holder 23 is the direction that intersects the heater arrangement (see the direction of the arrow from the connector 160 in FIG. 21). When the connector 160 is attached to the heater holder 23, a convex portion provided on one of the connector 160 and the heater holder 23 may engage with a concave portion provided on the other, and the convex portion may move relatively within the concave portion. The connector 160 is attached to the heater 22 and heater holder 23 on one side of the arrangement direction, opposite to the side on which the drive motor of the pressure roller 21 is provided.

[0145] 22, thermistors 25 are provided on the center side and end side of the arrangement direction of the fixing film 20, facing the inner circumferential surface of the fixing film 20. The heater 22 is controlled based on the temperatures of the center side and end side of the arrangement direction of the fixing film 20 detected by the thermistors 25. Note that one of these thermistors 25 is provided at a position corresponding to the divided region between the resistance heating elements of the heater 22, as in the above-described embodiment.

[0146] Thermostats 27 are provided facing the inner circumferential surface of the fixing film 20, at the center and end of the arrangement direction of the fixing film 20. When the temperature of the fixing film 20 detected by the thermostat 27 exceeds a predetermined threshold, the power supply to the heater 22 is stopped.

[0147] Flanges 53 are provided on both ends of the fixing film 20 in the arrangement direction to hold the respective ends of the fixing film 20. The flanges 53 are made of LCP (liquid crystal polymer).

[0148] 23 , a slide groove 53a is provided in the flange 53. The slide groove 53a extends in the direction in which the fixing film 20 approaches and separates from the pressure roller 21. An engagement portion of the housing of the fixing device 9 engages with the slide groove 53a. The engagement portion moves relatively within the slide groove 53a, allowing the fixing film 20 to move in the direction in which the fixing film 20 approaches and separates from the pressure roller 21.

[0149] In the fixing device 9 described above, by providing a temperature detection element of the thermistor 25 at a position corresponding to the divided area B of the heater 22, it is possible to sufficiently heat the portion of the fixing film 20 corresponding to the divided area. This ensures sufficient fixability of the image and prevents problems such as fixing offset from occurring.

[0150] In particular, in an image forming apparatus that performs image formation operations using a single color toner, hot offset is relatively less likely to occur compared to an image forming apparatus that performs image formation operations using multiple color toners. Therefore, even if the heating member is controlled based on the detection results of the temperature detection element disposed at a position corresponding to the divided area, as in the present invention, there is an advantage that hot offset is relatively less likely to occur in an image forming apparatus that uses a single color toner.

[0151] Although the present invention has been described above as an embodiment, it is needless to say that the present invention is not limited to the above-described embodiment and various modifications are possible. For example, instead of the heater 22 that heats the fixing film 20, a halogen heater may be disposed behind the stay 24, and a support stay with low heat capacity and no heater may be disposed as a nip forming member.

[0152] Furthermore, the separating member 310 can be arranged to be movable in a direction toward and away from the fixing film 20, and in addition to being rotatable as in the above-described embodiment, the separating member 310 may be configured to be movable in parallel in a direction toward and away from the fixing film 20 while maintaining a parallel state with the heater holder 23. Furthermore, in the above-described embodiment, the fixing film 20 of the fixing device 9 has been described as an example of an endless film, but the endless film may also be used for purposes other than fixing. [Explanation of symbols]

[0153] 1Y, 1M, 1C, 1Bk: Imaging unit 2: Photoconductor 3: Charging device 4: Developing device 5: Cleaning device 6: Exposure device 7: Paper feeder 8: Transfer device 9: Fixing unit 10: Paper ejection unit 11: Intermediate transfer belt 12: Primary transfer roller 13: Secondary transfer roller 13: Secondary transfer nip 14: Paper transport path 15: Timing roller 20: Fixing film (endless film) 21: Pressure roller (pressure member) 21a: Core metal 21b: Elastic layer 21c: Release layer 22: Heater (heat source, nip forming member) 23: Heater holder 23a: Protrusion 23b: Recessed portion 23b1 to 23b3: Wall portion 24: Stay 25: Thermistor 26: Guide part 27: Thermostat 30: Base material 31: Resistance heating element 32: Insulation layer 33: Power supply line 34: Electrode part 34A~34C: Electrode part 35: Heat generating part 35A~35C: Heat generating part 44: Pressure roller 45: Nip forming member 50: Image forming means 51: Reading unit 53: Flange 53a: Slide groove 56: Resistive heating element 92: Heating assembly 93: Fixing roller 93a: Core metal 93b: Elastic layer 93c: Release layer 94: Pressure assembly 95: Nip forming member 96: Stay 97: Pressure belt 100: Image forming device 120: Heating belt 160: Connector 200: AC power supply 210: Triac 220: Control unit 260: Belt facing surface 310: Separation plate (separation member) 322: Separation axis P: Paper (transferred object) [Prior art documents] [Patent documents]

[0154] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-281595 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-288587

Claims

1. a rotatable flexible endless film; a heat source for heating the endless film; a nip forming member provided so as to be able to come into contact with an inner peripheral surface of the endless film; a pressure member that is in pressure contact with the nip forming member via the endless film to form a nip, and that is rotationally driven to rotate the endless film; a detection means for detecting the temperature of the pressure member; a control means for controlling the rotational driving of the pressure member based on the temperature of the pressure member detected by the detection means, In a nip forming unit in which an object to be conveyed passes through the nip, The control means drives the pressure member to rotate in the transport direction to transport the transported object, and then stops the rotation of the pressure member, and when the temperature of the pressure member at the end of the job of the nip formation unit is equal to or higher than a predetermined temperature, turns off the heat source, drives the pressure member to rotate in the direction opposite to the transport direction for a predetermined time, and then stops the rotation of the pressure member.

2. 2. The nip forming unit according to claim 1, wherein the rotation of said pressure member in the reverse direction is continuously performed.

3. 2. The nip forming unit according to claim 1, wherein the rotation of the pressure member in the reverse direction is intermittently performed.

4. 4. The nip forming unit according to claim 1, wherein the pressure member is driven to rotate in the reverse direction so that the stop position of the endless film after the pressure member rotates in the reverse direction is different from the previous stop position.

5. 5. The nip forming unit according to claim 1, wherein the rotation speed of the pressure member in the reverse direction is set to be slower than the rotation speed of the pressure member when the transported object is transported.

6. 6. The nip forming unit according to claim 1, wherein the pressure member is rotated in the reverse direction only when the number of the transported objects is equal to or greater than a predetermined number.

7. A nip formation unit according to any one of claims 1 to 6, characterized in that the nip formation unit has a sleep mode which it enters if the transported object is not transported for a predetermined period of time, and when the nip formation unit transitions to the sleep mode, it stops rotating the pressure member in the reverse direction.

8. The nip forming unit according to any one of claims 1 to 7, wherein the nip forming member has the heat source.

9. 9. The nip forming unit according to claim 1, further comprising a separating member that separates the transported object from the endless film after the transported object has passed through the nip.

10. An image forming apparatus comprising the nip forming unit according to any one of claims 1 to 9.

Images