Fixing device and image forming apparatus

Abstract

To provide a fixing device that can make a temperature distribution uniform with a simple configuration.SOLUTION: A fixing device comprises: a rotatable endless fixing belt; a heater 23 that heats the fixing belt; a holding member 25 that holds the heater 23 so as to bring a front side surface into contact with an inner peripheral surface of the fixing belt; and a pressing member that is pressed by the heater 23 with the fixing belt therebetween and forms, with the fixing belt, a pressure area for applying heat and pressure to a sheet to which a toner image is transferred. The holding member 25 has a recess 41 for accommodating the heater 23, and a seating face 41c in contact with a rear face of the heater 23 is formed in the recess 41. The seating face 41c is formed such that the area of a contact surface with the heater 23 in a circumferential direction of the fixing belt 21, is smaller or larger in one portion than the other portion, in a width direction intersecting the circumferential direction.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fixing device that fixes a toner image on a sheet of paper and an image forming apparatus equipped with the fixing device. [Background technology]

[0002] The sliding type fixing device is equipped with an endless fixing belt heated by a heater and a pressure member that contacts the fixing belt to form a pressure area, and fixes a toner image on a sheet of paper transported to the pressure area by rotating the fixing member and the pressure member. In this type of fixing device, it is necessary to make the temperature distribution of the fixing belt uniform in order to eliminate uneven fixing.

[0003] Generally, the heater is held by a holding member so as to be in contact with the inner circumferential surface of the fixing belt. In addition, the fixing device may be provided with a temperature sensor for measuring the temperature of the heater. In this way, the heater is in contact with the holding member and the temperature sensor in addition to the fixing belt. In this case, the heat generated by the heater is transmitted to members other than the fixing belt, and the temperature of the fixing belt is difficult to increase at the contact points between these members and the heater. In particular, when the contact points are locally present in the width direction of the fixing belt, the temperature distribution of the fixing belt in the width direction becomes non-uniform, and image defects due to temperature unevenness may occur.

[0004] In the fixing device described in Patent Document 1, a highly thermally conductive member is disposed between the heater and a heat-insulating support member that holds the heater. By disposing the highly thermally conductive member in this manner, even if there is variation in the temperature rise distribution of the heater, heat is conducted along the highly thermally conductive member, making the temperature distribution uniform. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-84919 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the fixing device described in Patent Document 1 has a problem in that the number of parts increases by the amount of the highly heat-conductive member, which increases costs and the number of manufacturing steps.

[0007] SUMMARY OF THE PRESENT DISCLOSURE In consideration of the above circumstances, an object of the present invention is to provide a fixing device capable of achieving uniform temperature distribution with a simple configuration, and an image forming apparatus including the fixing device. [Means for solving the problem]

[0008] In order to solve the above problem, the fixing device of the present invention comprises a rotatable endless fixing belt, a heater for heating the fixing belt, a holding member for holding the heater so that its front surface is in contact with the inner surface of the fixing belt, and a pressure member that is pressed against the heater across the fixing belt to form a pressure area between the fixing belt and the heater for heating and pressurizing paper onto which a toner image has been transferred, the holding member having a recess for accommodating the heater, the recess having a seating surface formed therein for contacting the rear surface of the heater, and the seating surface being formed so that the area of ​​the contact surface with the heater in the circumferential direction of the fixing belt is narrower or wider in some locations than in other locations in a width direction intersecting the circumferential direction.

[0009] In the present invention, the heater may further include a contact member that contacts a rear surface of the heater, and the retaining member may be formed so that the area of ​​the contact surface between the heater and the seat surface at the contact point between the contact member and the heater is narrower than at other points.

[0010] In the present invention, the contact member may be a temperature sensor that detects the temperature of the heater.

[0011] In the present invention, the heater may be formed with a heating layer divided into multiple parts along the width direction, a predetermined gap is formed at the boundary between adjacent heating layers, and the retaining member may be formed so that the area of ​​the contact surface between the heater and the seat surface in the gap is narrower than at other locations than the gap.

[0012] In the present invention, the heater may be formed with a heat generating layer extending along the width direction, and the retaining member may be formed so that the area of ​​the contact surface between the heater and the seat surface near both ends of the heat generating layer in the width direction is larger than at any other location.

[0013] The image forming apparatus of the present invention is characterized by comprising: an image forming section that forms a toner image on a sheet of paper; and a fixing device that fixes the toner image on the sheet of paper. Effect of the Invention

[0014] According to the present invention, the contact area between the heater and the holding member is narrowed in the portion of the fixing belt where the temperature is difficult to increase, so the amount of heat transferred from the heater to the member (holding member) other than the fixing belt can be reduced, which makes it easier to make the temperature distribution of the fixing belt uniform. [Brief description of the drawings]

[0015] [Figure 1] 1 is a front view showing a schematic internal configuration of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a bottom view of a holding member of the fixing device according to an embodiment of the present invention. [Figure 4A] FIG. 2 is a cross-sectional view of FIG. [Figure 4B] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Diagram 5]4 is a graph showing the relationship between the position in the longitudinal direction of the fixing belt and the temperature of the fixing belt in the fixing device according to one embodiment of the present invention. [Figure 6] FIG. 13 is a bottom view of a holding member of a conventional fixing device. [Figure 7] 5 is a graph showing the relationship between the contact area between a holding member and a heater and the temperature of a fixing belt in a fixing device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an image forming apparatus and a fixing device of the present invention will be described with reference to the drawings.

[0017] First, the overall configuration of the image forming apparatus 1 will be described with reference to Fig. 1. Fig. 1 is a front view that shows a schematic internal configuration of the image forming apparatus 1. Hereinafter, the front side of the paper in Fig. 1 is the front side (front side) of the image forming apparatus 1.

[0018] The device body 3 of the image forming device 1 is provided with a paper feed cassette 5 in which paper S is stored, a paper feed device 7 that feeds paper S from the paper feed cassette 5, an image forming section 9 that forms a toner image on paper S by electrophotography, a fixing device 11 that fixes the toner image on paper S, a paper discharge device 13 that discharges paper S, and a paper discharge tray 15 on which the discharged paper S is stacked. Furthermore, the device body 3 is formed with a transport path 17 for paper S that runs from the paper feed device 7 through the image forming section 9 and the fixing device 11 toward the paper discharge device 13.

[0019] Next, the fixing device 11 will be described with reference to Figures 2, 3, 4A, and 4B. Figure 2 is a cross-sectional view of the fixing device 11, Figure 3 is a bottom view of the holding member 25, and Figures 4A and 4B are cross-sectional views of the holding member 25, the heater 23, and the temperature sensor 27. Figure 4A shows a cross-section taken along line II in Figure 3, and Figure 4B shows a cross-section taken along line II-II in Figure 3.

[0020] As shown in FIG. 2, the fixing device 11 includes a fixing belt 21, a heater 23 for heating the fixing belt 21, a holding member 25 for holding the heater 23, a temperature sensor 27 for detecting the temperature of the fixing belt 21, a pressure roller 29 as a pressure member for forming a pressure area N between the fixing belt 21 and the pressure roller 29, and a guide 31 for guiding the paper S to the pressure area N.

[0021] The fixing belt 21 is an endless belt, and has a predetermined inner diameter and a width greater than the width of the paper S. The fixing belt 21 is made of a flexible material, and has a base layer, an elastic layer provided on the outer peripheral surface of the base layer, and a release layer provided on the outer peripheral surface of the elastic layer. The base layer is made of a metal such as SUS or Ni. The elastic layer is made of silicone rubber or the like. The release layer is made of a PFA tube or the like. A sliding layer may be formed on the inner peripheral surface of the base layer. The sliding layer is made of polyimide amide, PTFE or the like.

[0022] Both ends of the fixing belt 21 are supported by end holders (not shown). The both end holders are rotatably supported by a fixing housing (not shown). A stay 33 passes through the hollow portion of the fixing belt 21. Both ends of the stay 33 are supported by the fixing housing.

[0023] The heater 23 is a flat plate-shaped member, and has a width equal to the width of the fixing belt 21 (length along the width direction Y intersecting with the circumferential direction X), and a predetermined length and thickness. The heater 23 has a laminated structure in which a stainless steel or ceramic substrate, a glass electrical insulating layer, a resistance heating layer having electrodes, and a protective layer are laminated in this order from the back side to the front side. As shown in FIG. 3, the resistance heating layer is divided in the width direction Y into a central heating layer 23a and end heating layers 23b and 23c arranged on both sides of the central heating layer 23a in the width direction Y. A predetermined gap is provided between the central heating layer 23a and the end heating layers 23b and 23c to maintain insulation from each other. The surface of the protective layer is formed flat, and serves as a sliding surface 23x that contacts the inner circumferential surface 21a of the fixing belt 21. The resistance heating layer generates heat by passing electricity through the electrodes.

[0024] The holding member 25 is a substantially semi-cylindrical member having a width equal to that of the fixing belt 21 and a predetermined length along the circumferential direction X. The holding member 25 is formed of a heat-resistant resin such as a liquid crystal polymer.

[0025] As shown in FIG. 2, the outer peripheral surface 25a of the holding member 25 is curved to follow the inner peripheral surface 21a of the fixing belt 21. The outer peripheral surface of the top 25b of the holding member 25 is formed flat. A recess 41 for accommodating the heater 23 is formed in the top 25b along the width direction Y. As shown in FIG. 3 and FIG. 4A, the recess 41 has an outer recess 41a that is long in the circumferential direction X, and an inner recess 41b that is shorter in the circumferential direction X than the outer recess 41a. On both sides of the inner recess 41b in the circumferential direction X, a seat surface 41c that is parallel to the top 25b of the holding member 25 is formed.

[0026] 4A, the heater 23 is accommodated in the outer recess 41a. The sliding surface 23x of the heater 23 is flush with the outer circumferential surface of the top 25b of the holding member 25, and the back surface of the heater 23 is in contact with the seat surface 41c of the recess 41.

[0027] As shown in FIGS. 3 and 4B, one end of the holding member 25 in the width direction Y is formed with a rectangular through-hole 43 that penetrates the recess 41 (the outer recess 41a and the inner recess 41b) in the thickness direction.

[0028] The temperature sensor 27 is a thermistor, a thermo-cut, or the like, and is supported by the stay 33, as shown in FIG. 2, and is disposed in the area where the central heating layer 23a and the end heating layer 23c are formed, and contacts the rear surface of the heater 23 through the through hole 43 of the holding member 25 (see also FIG. 3 and FIG. 4B). The length of the temperature sensor 27 along the circumferential direction X is shorter than the length of the through hole 43 along the circumferential direction X. Therefore, there is a space on both sides of the temperature sensor 27 in the circumferential direction X, and the heater 23 and the holding member 25 are not in contact. On the other hand, as shown in FIG. 4A, the heater 23 is in contact with the seat surface 41c of the recess 41 of the holding member 25 at a location other than the through hole 43. In this way, the area of ​​the contact surface between the holding member 25 and the heater 23 at the contact location between the temperature sensor 27 and the heater 23 (see FIG. 4B) is narrower than the area other than the contact location (see FIG. 4A).

[0029] 2 again, the pressure roller 29 has a core, an elastic layer provided on the outer peripheral surface of the core, and a release layer provided on the outer peripheral surface of the elastic layer. The elastic layer is made of silicone rubber or the like. The release layer is made of a PFA tube or the like.

[0030] The pressure roller 29 is supported so as to be pressed against the heater 23 from below the fixing belt 21. As a result, a pressure region N is formed between the fixing belt 21 and the pressure roller 29. The pressure roller 29 is driven by a motor (not shown) to rotate in the counterclockwise direction in FIG. 2. When the pressure roller 29 is driven to rotate by the motor, the fixing belt 21 is driven to rotate in the clockwise direction in FIG. 2, which is opposite to the clockwise direction of the pressure roller 29. As a result, the paper S transported along the transport path 17 passes through the pressure region N.

[0031] The guide 31 is disposed upstream of the pressure region N in the transport direction of the sheet S, and guides the sheet S transported along the transport path 17 to the pressure region N.

[0032] The fixing operation of the fixing device 11 having the above configuration will be described. First, the pressure roller 29 is driven by a motor to rotate, and the fixing belt 21 rotates in the opposite direction to the rotation direction of the pressure roller 29 (clockwise direction in FIG. 2) by following the pressure roller 29. At the same time, the heater 23 is driven to heat the fixing belt 21. The temperature of the heater 23 is detected by the temperature sensor 27. The heater 23 is heated until the detected temperature becomes a predetermined control temperature (for example, 160° C.), and heats the fixing belt 21. After the fixing belt 21 is heated in this manner, the paper S on which the toner image has been transferred is guided by the guide 31 and transported to the pressure region N. When the paper S passes through the pressure region N, it is heated by the fixing belt 21 and pressed by the pressure roller 29 and the fixing belt 21, and the toner image is fixed to the paper S. The paper S on which the toner image has been fixed is transported from the pressure region N along the transport path 17.

[0033] Incidentally, the heat generated from the heater 23 moves to the fixing belt 21 to heat it, but also moves to the holding member 25. Furthermore, as described above, the temperature sensor 27 is in contact with the rear surface of the heater 23, so the heat also moves to the temperature sensor 27. Since the temperature sensor 27 is disposed at one end in the width direction Y, the amount of heat transferred from the heater 23 to parts other than the fixing belt 21 increases locally at the contact point between the temperature sensor 27 and the heater 23. As a result, the temperature of the fixing belt 21 is less likely to increase at the contact point between the temperature sensor 27 and the heater 23, and the temperature distribution of the fixing belt 21 in the width direction Y becomes non-uniform.

[0034] As described above, according to the fixing device 11 of the present invention, the heater 23 does not come into contact with the holding member 25 (seat surface 41c) at the contact point between the temperature sensor 27 and the heater 23 (see FIG. 4B), where the temperature of the fixing belt 21 is unlikely to rise. In other words, the amount of heat transferred from the heater 23 to a member other than the fixing belt 21 (holding member 25) can be reduced at the contact point between the temperature sensor 27 and the heater 23. This makes it easier to uniformize the temperature distribution of the fixing belt 21 in the width direction Y.

[0035] The results of temperature measurement of the fixing belt 21 in the examples will be described with reference to Fig. 5. The examples show the fixing device 11 described in the above embodiment. As a comparative example, a conventional fixing device (see Fig. 6) is shown in which the length of the through hole 43 along the circumferential direction X is the same as the length of the inner recess 41b of the recess 41, and the back surface of the heater 23 is in contact with the seat surface 41c of the recess 41 of the holding member 25 at the contact point between the temperature sensor 27 and the heater 23.

[0036] 5 is a graph showing the relationship between the position in the width direction Y of the fixing belt 21 and the temperature of the fixing belt 21. The horizontal axis of the graph shows the position in the width direction Y of the fixing belt 21, and the vertical axis shows the temperature of the fixing belt 21. The solid line of the graph shows the working example, and the dashed line shows the comparative example. The vertical axis explains the difference between the working example and the comparative example, and does not show the actual temperature.

[0037] As can be seen from the graph, the area between the temperature baseline (indicated by the dashed line) and the measured temperature at the contact point between heater 23 and temperature sensor 27 is smaller in the example than in the comparative example. In other words, the degree of temperature drop at the contact point is smaller in the example. In other words, the temperature of fixing belt 21 is more likely to rise.

[0038] Next, the relationship between the contact area between heater 23 and holding member 25 and the temperature of fixing belt 21 will be described with reference to Fig. 7. Fig. 7 is a graph showing the relationship between the contact area between heater 23 and holding member 25 and the temperature of fixing belt 21. The horizontal axis of the graph indicates the contact area, and the vertical axis indicates the temperature of fixing belt 21.

[0039] As can be seen from the graph, when the contact area is narrow, the temperature of the fixing belt 21 is more likely to rise, and as the contact area is wider, the temperature of the fixing belt 21 is less likely to rise. In other words, the narrower the contact area, the more likely the temperature of the fixing belt 21 is to rise.

[0040] As described above, the contact area between the temperature sensor 27 and the heater 23 is a location where the temperature of the fixing belt 21 is unlikely to increase. In other words, the contact area between the temperature sensor 27 and the heater 23 is a location where it is desired to increase the temperature of the fixing belt 21. By narrowing the contact area between the holding member 25 and the heater 23 at such a location, it is possible to reduce the amount of heat transferred from the heater 23 to members other than the fixing belt 21 (the holding member 25). In other words, by widening the contact area between the holding member 25 and the heater 23 at a location where it is desired not to increase the temperature of the fixing belt 21, it is possible to increase the amount of heat transferred from the heater 23 to members other than the fixing belt 21.

[0041] As described above, there is no resistance heating element between the central heating layer 23a and both end heating layers 23b, 23c of the resistance heating layer of the heater 23, so the amount of heat transferred to the fixing belt 21 between the adjacent heating layers 23a, 23b, 23c is reduced. Therefore, as shown in Fig. 3, a region 44 in which the contact area between the heater 23 and the holding member 25 is narrowed is formed between the adjacent heating layers 23a, 23b, 23c. In the narrow contact area region 44, the seating surface 41c is cut out by a predetermined width in the width direction Y, and does not contact the rear surface of the heater 23.

[0042] Alternatively, in the non-paper passing region (both ends in the width direction Y of the resistance heating layer of the heater 23), the temperature does not transfer from the fixing belt 21 to the paper S, so the temperature of the fixing belt 21 rises. Therefore, as shown in FIG. 3, in the non-paper passing region, a wide contact width region 45 is formed in which the contact area between the holding member 25 and the heater 23 is widened. In the wide contact width region 45, the opposing seating surfaces 41c extend toward each other, so that the area of ​​the seating surface 41c that contacts the rear surface of the heater 23 is widened. This increases the amount of heat that transfers from the heater 23 to the holding member 25, so that the temperature rise in the non-paper passing region can be suppressed.

[0043] In this way, the temperature of the fixing belt 21 can be controlled by the contact area between the heater 23 and the holding member 25. In the above embodiment, the seating surface 41c of the recess 41 of the holding member 25 does not contact the back surface of the heater 23 at the contact point between the temperature sensor 27 and the heater 23, but the width of the seating surface 41c may be narrowed to narrow the contact area with the heater 23. Also, in the above embodiment, the contact member that contacts the back surface of the heater 23 is the temperature sensor 27, but in some cases it may be a stay, a connector, or the like, other than the temperature sensor 27.

[0044] Furthermore, the above description of the embodiments of the present invention describes preferred embodiments of the present invention, and therefore may include various technically preferable limitations. However, the technical scope of the present invention is not limited to these aspects unless there is a specific description that limits the present invention. [Explanation of symbols]

[0045] 1. Image forming device 9. Image forming section 11 Fixing device 21 Fixing belt 23 Heater 23a, 23b, 23c Heating layer 25 Retaining member 27 Temperature sensor (contact member) 29 Pressure roller (pressure member) 41 Recess 41c Seat

Claims

1. a rotatable endless fixing belt; a heater for heating the fixing belt; a holding member that holds the heater such that a front surface of the heater is in contact with an inner circumferential surface of the fixing belt; a pressure member that is pressed by the heater across the fixing belt to form a pressure region between the fixing belt and the sheet of paper onto which a toner image has been transferred, and heats and presses the sheet of paper onto which a toner image has been transferred; the holding member has a recess for accommodating the heater, and the recess is formed with a seat surface that comes into contact with a back surface of the heater, A fixing device characterized in that the seat surface is formed so that the area of ​​the contact surface with the heater in the circumferential direction of the fixing belt is narrower or wider in some locations than other locations in a width direction intersecting with the circumferential direction.

2. Further comprising a contact member that contacts a rear surface of the heater, 2. The fixing device according to claim 1, wherein the holding member is formed so that the area of ​​the contact surface between the heater and the seat surface at the contact point between the contact member and the heater is narrower than the area other than the contact point.

3. 3. The fixing device according to claim 2, wherein the contact member is a temperature sensor that detects the temperature of the heater.

4. The heater is formed with a plurality of divided heating layers along the width direction, and a predetermined gap is formed at the boundary between adjacent heating layers, 2. The fixing device according to claim 1, wherein the holding member is formed such that an area of ​​a contact surface between the heater and the seat surface in the gap is narrower than an area outside the gap.

5. The heater is provided with a heat generating layer extending along the width direction, The fixing device according to claim 1 , wherein the holding member is formed so that the area of ​​the contact surface between the heater and the seat surface is wider near both ends of the heat generating layer in the width direction than at any other location.

6. an image forming unit that forms a toner image on a sheet; 2. An image forming apparatus comprising: a fixing device according to claim 1 for fixing the toner image onto the paper.

Images