JP7499560B2 - Fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a fixing device and an image forming device.

In image forming devices such as copiers and printers, a belt-type fixing device that uses an endless belt is known as a fixing device that fixes an image formed on a recording medium such as paper.

In this type of fixing device, a heater divided into multiple parts across the width of the belt is used as a heating member for heating the belt (see Patent Document 1 below), and multiple film guides are provided as a guide section for guiding the belt (see Patent Document 2 below).

In order to achieve good fixation, it is desirable for the temperature of the belt heated by the heating member to be uniform across its width.

However, Patent Document 1 describes a problem in that when a divided heater is used, the amount of heat distributed to the divided parts of the heater is smaller than that of the other parts, and the temperature of the belt corresponding to that part is lower than that of the other parts (see paragraph [0082] of Patent Document 1).

In addition, cited reference 2 describes an issue where the heat of the belt is partially absorbed by the film guide, causing the temperature of the area from which the heat is absorbed to drop (see paragraph [0021] of patent document 2).

As such, fixing devices with separate heaters or with film guides have the problem that the temperature of the belt drops partially across the width.

To solve the above problem, the present invention provides a fixing device including an endless belt that rotates in a circumferential direction, an opposing member that contacts the outer peripheral surface of the belt to form a nip portion, a heating member that contacts the inner peripheral surface of the belt and has a heat generating portion divided into multiple parts in the belt width direction, and a guide portion that contacts the inner peripheral surface of the belt to guide the belt, characterized in that the heat capacity of the guide portion is smaller at the portion corresponding to the divided areas of the heat generating portion than at the portion corresponding to the undivided areas of the heat generating portion.

According to the present invention, by making the heat capacity of the guide section smaller at the location corresponding to the divided area of the heat generating section than at the location corresponding to the non-divided area of the heat generating section, it is possible to reduce the amount of heat transferred from the belt to the guide section at the location corresponding to the divided area. This makes it possible to suppress local temperature drops in the belt at the location corresponding to the divided area.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a fixing device. FIG. 2 is a perspective view of a heater, a heater holder, and a guide portion. FIG. FIG. 4 is a diagram showing a power supply circuit to a heater. 4 is a flowchart showing a control operation of a heater. 13A and 13B are diagrams showing an embodiment in which the divided regions of the heat generating portion and the position of the guide portion are shifted in the belt width direction. FIG. 8 is an enlarged view of a main part of FIG. 7 . FIG. 13 is a diagram showing an example in which divided regions are formed obliquely. FIG. 13 is a diagram showing an example in which divided regions are formed in a curved manner. 13A and 13B are diagrams showing an example in which a resistive heating element is formed into a shape having a plurality of folded portions; 13 is a diagram showing an example in which guide portions are arranged at locations corresponding to divided regions. FIG. 13 is a diagram showing an example in which an upstream guide portion and a downstream guide portion are disposed at different positions in the belt width direction. FIG. 13A and 13B are diagrams showing an embodiment in which recesses are provided in the guide portion at locations corresponding to the divided regions. 15A and 15B are side views of the embodiment shown in FIG. 14, in which FIG. 15A is a side view of a guide portion at a location corresponding to a divided region, and FIG. 15B is a side view of a guide portion at a location corresponding to a non-divided region. FIG. 15 is a diagram showing a modified example of the embodiment shown in FIG. 14, in which a guide portion is provided continuously across the belt width direction. 1A and 1B are diagrams showing an embodiment in which the circumferential length of a guide portion corresponding to a divided region is shortened, where (a) is a side view of the guide portion corresponding to a divided region, and (b) is a side view of the guide portion corresponding to a non-divided region. 13A and 13B are diagrams illustrating an embodiment in which the width of a guide portion is reduced in a portion corresponding to a divided region. FIG. 2 is a perspective view showing the arrangement of a thermistor and a thermostat. FIG. 11 is a schematic diagram of another fixing device. FIG. 11 is a schematic diagram of another fixing device. FIG. 11 is a schematic diagram of yet another fixing device. FIG.

The present invention will be described below based on the attached drawings. In each drawing for explaining the present invention, components such as parts and components having the same function or shape are given the same reference numerals as far as possible to distinguish them, and the description will be omitted after the first description.

Figure 1 is a schematic diagram of an image forming device according to one embodiment of the present invention.

The image forming device 100 shown in FIG. 1 has four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming device main body. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration, except that it contains a developer of a different color, yellow, magenta, cyan, or black, which corresponds to the color separation components of a color image. Specifically, each imaging unit 1Y, 1M, 1C, and 1Bk has 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.

The image forming apparatus 100 also includes an exposure device 6 that exposes the surface of each photoconductor 2 to light to form an electrostatic latent image, a paper feed device 7 that supplies paper P as a recording medium, a transfer device 8 that transfers the toner image formed on each photoconductor 2 to the paper P, a fixing device 9 that fixes the toner image transferred to the paper P, and a paper discharge device 10 that discharges the paper P outside the apparatus.

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 image on each photoconductor 2 to the intermediate transfer belt 11, and a secondary transfer roller 13 as a secondary transfer member that transfers the toner image transferred onto the intermediate transfer belt 11 to paper P. Each of the multiple primary transfer rollers 12 contacts the photoconductor 2 via the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 and each photoconductor 2 contact each other, and a primary transfer nip is formed between them. Meanwhile, the secondary transfer roller 13 contacts 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.

In addition, a paper transport path 14 is formed within the image forming device 100 along which the paper P sent from the paper feeder 7 is transported. A pair of timing rollers 15 is provided on the paper transport path 14 midway between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

Next, the printing operation of the image forming device will be described with reference to FIG.

When an instruction to start a printing operation is given, in each of the imaging units 1Y, 1M, 1C, 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 reading device or the print information instructed to be printed from the terminal, thereby lowering the potential of the exposed portion and forming an electrostatic latent image. Toner is then supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

When the toner images formed on each photoconductor 2 reach the primary transfer nip (the position of the primary transfer roller 12) as each photoconductor 2 rotates, they are transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so that they overlap one another. Then, the toner images transferred onto the intermediate transfer belt 11 are transported to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and are transferred to the paper P that has been transported at the secondary transfer nip. This paper P is supplied from the paper supply device 7. The paper P supplied from the paper supply device 7 is stopped once by the timing roller 15, and then transported to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. Thus, 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.

The paper P with the transferred toner image is transported to the fixing device 9, which fixes the toner image onto the paper P. The paper P is then discharged from the device by the paper discharge device 10, completing the printing process.

Next, we will explain the configuration of the fixing device.

As shown in FIG. 2, the fixing device 9 according to this embodiment includes a fixing belt 20 made of an endless belt, a pressure roller 21 as an opposing member that contacts the outer peripheral surface of the fixing belt 20 to form a nip portion N, a heater 22 as a heating member that heats the fixing belt 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 a temperature detection means that detects the temperature of the fixing belt 20.

The fixing belt 20 has a cylindrical substrate made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of fluororesin such as PFA or PTFE with a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 20 to enhance durability and ensure releasability. An elastic layer made of rubber or the like with a thickness of 50 to 500 μm may be provided between the substrate and the release layer. The substrate of the fixing belt 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 belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

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. In order to improve the release properties of the surface of the elastic layer 21b, it is desirable to form a release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm.

When the pressure roller 21 is urged toward the fixing belt 20 by the urging means, the pressure roller 21 is pressed against the heater 22 via the fixing belt 20. This forms a nip N between the fixing belt 20 and the pressure roller 21. The pressure roller 21 is also configured to be driven to rotate by the driving means, and when the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is rotated accordingly.

The heater 22 is a planar heating member provided longitudinally across the width of the fixing belt 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, and the like. The heater 22 is in contact with the inner circumferential surface of the fixing belt 20 on the insulating layer 32 side, and the heat generated by the resistance heating element 31 is transferred to the fixing belt 20 through the insulating layer 32. In this embodiment, the resistance heating element 31 and the insulating layer 32 are provided on the fixing belt 20 side (nip portion N side) of the substrate 30, but conversely, the resistance heating element 31 and the insulating layer 32 may be provided on the heater folder 23 side of the substrate 30. In that case, since the heat of the resistance heating element 31 is transferred to the fixing belt 20 through 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 constructing the substrate 30 from a material with good thermal conductivity, it is possible to sufficiently heat the fixing belt 20 even if the resistive heating element 31 is placed on the opposite side of the substrate 30 from the fixing belt 20 side.

The heater folder 23 and the stay 24 are disposed on the inner periphery of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends of the stay 24 are supported by both side plates of the fixing device 9. The stay 24 supports the heater folder 23 and the heater 22 held therein, so that when the pressure roller 21 is pressed against the fixing belt 20, the heater 22 reliably receives the pressing force of the pressure roller 21, and the nip portion N is stably formed.

The heater folder 23 is desirably made of a heat-resistant material because it is likely to become hot due to the heat of the heater 22. For example, if the heater folder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP, the heat transfer from the heater 22 to the heater folder 23 is suppressed, and the fixing belt 20 can be heated efficiently. In addition, in order to reduce the contact area of the heater folder 23 with the heater 22 and reduce the amount of heat transferred from the heater 22 to the heater folder 23, the heater folder 23 contacts the base material 30 of the heater 22 via the protrusions 23a. Furthermore, as in this embodiment, the protrusions 23a of the heater folder 23 are brought into contact with the base material 30 other than the back side of the portion where the resistance heating element 31 of the base material 30 is arranged, that is, by avoiding the portion of the base material 30 where the temperature is likely to be high, the amount of heat transferred to the heater folder 23 can be further reduced and the fixing belt 20 can be heated efficiently.

The heater folder 23 is provided with guide sections 26 for guiding the fixing belt 20. The guide sections 26 are provided on the upstream side (below the heater 22 in FIG. 2) and downstream side (upper side of the heater 22 in FIG. 2) of the belt rotation direction of the heater 22. As shown in FIG. 3, the upstream and downstream guide sections 26 are arranged at intervals in the longitudinal direction (belt width direction) of the heater 22. Each guide section 26 is formed in a roughly fan shape and has a belt facing surface 260 in the shape of an arc or a convex curved surface extending in the belt circumferential direction so as to face the inner peripheral surface of the fixing belt 20 (see FIG. 2). As shown in FIG. 3, in this embodiment, the width W, the length (circumferential length) L, and the height E of each guide section 26 are formed to be the same, except that the width W of the guide sections 26 arranged at both ends of the longitudinal direction of the heater 22 is formed larger than the other guide sections 26.

In the fixing device 9 according to this embodiment, when the printing operation is started, the pressure roller 21 is driven to rotate, and the fixing belt 20 starts to rotate. At this time, the inner circumferential surface of the fixing belt 20 contacts and is guided by the belt-facing surface 260 of the guide portion 26, so that the fixing belt 20 rotates stably and smoothly. In addition, the fixing belt 20 is heated by supplying power to the resistance heating element 31 of the heater 22. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 2, the paper P carrying the unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (nip portion N), so that the unfixed toner image is heated and pressurized to be fixed to the paper P.

Figure 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 resistive heating elements 31 arranged at intervals in the longitudinal direction (belt width direction). In other words, the plurality of resistive heating elements 31 constitute a heating section 35 divided into a plurality of parts in the belt width direction. Each resistive heating element 31 is electrically connected in parallel to a pair of electrodes 34 provided at both ends of the substrate 30 in the longitudinal direction via a power supply line 33. The power supply line 33 is made of a conductor having a smaller resistance value than the resistive heating element 31. The gap between adjacent resistive heating elements 31 is preferably 0.2 mm or more, more preferably 0.4 mm or more, from the viewpoint of ensuring insulation between the resistive heating elements 31. In addition, if the gap between adjacent resistive 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, more preferably 1 mm or less.

The resistive heating element 31 is made of a material with PTC (positive temperature coefficient of resistance) characteristics, and has the characteristic that the resistance value increases (heater output decreases) as the temperature increases.

Due to this feature, for example, when a paper sheet narrower than the overall width of the heating section 35 is passed through, the heat of the fixing belt 20 is not taken away by the paper sheet in the area outside the paper width, so the temperature of the resistance heating element 31 corresponding to that part rises. Since the voltage applied to the resistance heating element 31 is constant, when the temperature of the resistance heating element 31 outside the paper width rises and its resistance value rises, the output (amount of heat generated) decreases relatively, and the temperature rise at the end is suppressed. In addition, since multiple resistance heating elements 31 are electrically connected in parallel, it is possible to suppress the temperature rise of non-paper passing parts while maintaining the printing speed. Note that the heating element constituting the heating section 35 may be something other than a resistance heating element having PTC characteristics. In addition, the heating elements may be arranged in multiple rows in the short direction of the heater 22.

The resistive heating element 31 can be formed, for example, by applying a paste made of 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 resistive heating element 31 is set to 80 Ω at room temperature. In addition to the materials mentioned above, the resistive heating element 31 may be made of resistance materials such as silver alloy (AgPt) and ruthenium oxide (RuO2). The power supply line 33 and the electrodes 34 can be made of silver (Ag) or silver palladium (AgPd) by screen printing or the like.

The material of the substrate 30 is preferably a ceramic such as alumina or aluminum nitride, which has excellent heat resistance and insulation, or a non-metallic material such as glass or mica. In this embodiment, an alumina substrate having a short side width of 8 mm, a long side width of 270 mm, and a thickness of 1.0 mm is used. Alternatively, the substrate 30 may be made of a conductive material such as a metal laminated with an insulating material. As a metal material, aluminum or stainless steel is preferable because of its low cost. In addition, in order to improve the thermal uniformity of the heater 22 and enhance image quality, the substrate 30 may be made of a material with high thermal conductivity such as copper, graphite, or graphene.

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 while maintaining their sliding properties with the fixing belt 20.

Figure 5 shows the power supply circuit to the heater in this embodiment.

As shown in FIG. 5, in this embodiment, a power supply circuit for supplying power to each resistive heating element 31 is configured by electrically connecting an AC power source 200 and the electrodes 34 of the heater 22. The power supply circuit is also provided with a triac 210 that controls the amount of power supplied. The amount of power supplied to each resistive heating element 31 is controlled by a control unit 220 via the triac 210 based on the temperature detected by a thermistor 25 as a temperature detection means. The control unit 220 is configured as a microcomputer including a CPU, ROM, RAM, I/O interface, etc.

In this embodiment, thermistors 25 as temperature detection means are disposed in the longitudinal central region of the heater 22, which is within the minimum paper passing width, and at one longitudinal end of the heater 22. Furthermore, at one longitudinal end of the heater 22, a thermostat 27 is disposed as power cut-off means for cutting off the power supply to the resistive heating element 31 when the temperature of the resistive heating element 31 reaches or exceeds a predetermined temperature. The thermistor 25 and thermostat 27 are in contact with the rear surface of the substrate 30 (the side opposite to the side where the resistive heating element 31 is disposed) to detect the temperature of the resistive heating element 31.

Next, the heater control operation according to this embodiment will be described with reference to the flowchart in FIG.

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 source 200 to each resistance heating element 31 of the heater 22 (S2 in FIG. 6). As a result, each resistance heating element 31 starts generating heat, and the fixing belt 20 is heated. At this time, the thermistor (center thermistor) 25 disposed in the center region of the heater 22 in the longitudinal direction detects the temperature _T4 of the resistance heating element 31 located in the center region of the heater 22 (S3 in FIG. 6). Then, based on the temperature _T4 obtained from the center 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).

At the same time, the temperature _T8 of the resistance heating element 31 is also detected by the 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 T _N ( _T8 ≧T _N ) (S6 in FIG. 6). If it is lower than the predetermined temperature T _N , 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 T _N , it is determined that no abnormally low temperature has occurred, and the printing operation is started (S9 in FIG. 6).

In the unlikely event that the resistive heating element 31 is damaged or disconnected, making it impossible to control the temperature based on the detection by the central thermistor 25, there is a risk that the other resistive heating elements 31, including the resistive heating elements 31 at the longitudinal ends, will become abnormally hot. In that case, when the resistive heating element 31 reaches a predetermined temperature or higher, the thermostat 27 operates to cut off the power supply to the resistive heating element 31, thereby preventing the resistive heating element 31 from becoming abnormally hot.

However, in a configuration using a thin fixing belt 20, such as the fixing device 9 according to this embodiment, the heat capacity of the fixing belt 20 is small, so the surface temperature of the fixing belt 20 is easily affected by the heat generation distribution of the heater 22. Therefore, in a configuration in which the heat generating section 35 is divided across the belt width direction, such as the fixing device 9 according to this embodiment, the temperature of the fixing belt 20 tends to be lower at the points corresponding to the divided areas of the heat generating section 35.

In addition, in a configuration in which a guide portion 26 that guides the fixing belt 20 is provided, such as the fixing device 9 according to this embodiment, the heat of the fixing belt 20 is removed by the guide portion 26, so the temperature of the fixing belt 20 tends to decrease in the area where the guide portion 26 is located.

Therefore, as in the example shown in FIG. 23, when the divided area A of the heat generating section 35 and the position of the guide section 26 overlap in the belt width direction, in addition to the temperature drop caused by the divided area A of the heat generating section 35 at the overlapping point, a temperature drop occurs due to heat transfer to the guide section 26, resulting in a particularly noticeable drop in temperature of the fixing belt 20.

In Figure 23, shown below the heater 22 is a graph of the surface temperature of the fixing belt 20 measured using a thermoviewer when 500 W of power was applied to the heater 22 for 4 seconds. The horizontal axis of the graph corresponds to the position in the belt width direction. According to the measurement results, in the example shown in Figure 23, the temperature of the fixing belt 20 drops significantly especially at the point where the divided area A of the heat generating section 35 overlaps with the position of the guide section 26, falling below the desired fixing temperature range Tf. When A4 size paper was transported vertically in this state and printing was performed, poor fixing occurred.

One possible measure to prevent the above-mentioned fixing failures is to extend the heating time of the fixing belt 20 before the paper is passed through, thereby increasing the temperature of the fixing belt 20 across the entire width. However, this method has disadvantages, such as a longer warm-up time until the fixing belt 20 is heated to a specified target temperature, and increased power consumption. In addition, if the temperature of the fixing belt 20 is raised overall, there is a risk of defects such as hot offset occurring, in which excessive heat is applied to the paper, because the margin for the upper fixing temperature is reduced.

Therefore, in the fixing device 9 according to this embodiment, as shown in FIG. 7, the divided area A of the heat generating section 35 and the position of the guide section 26 are offset in the belt width direction to suppress a partial drop in temperature of the fixing belt 20.

In the embodiment shown in FIG. 7, none of the guide portions 26 are arranged in the locations corresponding to the divided area A of the heat generating portion 35 (the belt circumferential area including the divided area A). Note that the guide portions 26 need to perform the function of guiding the fixing belt 20, and therefore need to be arranged at least within the belt width area. Therefore, the guide portions 26 are arranged within the belt width area, except for the locations corresponding to the divided area A of the heat generating portion 35.

The graph shown in FIG. 7 is a measurement result of the surface temperature of the fixing belt 20 when the heater 22 according to this embodiment is used. The measurement conditions are the same as those in the example shown in FIG. 23. According to this measurement result, the temperature of the fixing belt 20 is lowered at the position of the guide portion 26 in the belt width direction and at the divided area A of the heat generating portion 35, but there is no large temperature drop as in the example shown in FIG. 23. As a result, the temperature of the fixing belt 20 is within the desired fixing temperature range Tf over the entire area, and good fixing performance is obtained. This result is thought to be due to the fact that by making the positions of the divided area A of the heat generating portion and the guide portion 26 different in the belt width direction, the local temperature drop of the fixing belt 20, which occurs when they overlap (the example shown in FIG. 23), is suppressed, and the maximum drop in the belt temperature can be reduced.

In this way, according to the configuration of this embodiment, it is possible to suppress a local temperature drop in the fixing belt 20 by simply shifting the position of the divided area A of the heat generating section 35 and the position of the guide section 26 in the belt width direction, without increasing the heating time to increase the temperature of the entire fixing belt 20. This makes it possible to obtain good fixing performance while avoiding the extension of the warm-up time and the increase in power consumption that would otherwise accompany an extension of the heating time of the fixing belt 20, as well as the occurrence of hot offset and the like.

The "divided region" in the heat generating section 35 means the width direction region A including the entire divided portion of the heat generating section 35, as shown in FIG. 8. Here, in this embodiment, the divided region A is arranged parallel to the short side direction of the heater 22 (the vertical direction in FIG. 8), but the divided region A may be inclined with respect to the short side direction of the heater 22 as shown in FIG. 9, or may be bent in the longitudinal direction of the heater 22 as shown in FIG. 10. Also, as shown in the example in FIG. 11, the resistance heating element 31 may be formed in a shape having multiple folded parts. In these examples, the "divided region" of the heat generating section 35 means the width direction region A including the entire divided portion of the heat generating section 35, as described above. Also, in the following description, the width direction region B of the heat generating section 35 excluding the divided region A will be referred to as the "non-divided region".

In the examples shown in Figures 9, 10, and 11, similar to the configuration shown in Figure 8, it is possible to suppress a significant local temperature drop in the fixing belt 20 by arranging the guide portion 26 in a location other than the location corresponding to the divided area A.

As described above, the temperature of the fixing belt 20 tends to decrease in the area corresponding to the divided area A, and the temperature decrease of the fixing belt 20 tends to be most significant in the area corresponding to the belt width direction center position M of the divided area A (see Figures 8 to 11). Therefore, in order to reduce the maximum amount of drop in the belt temperature, it is necessary to avoid locating the guide portion 26 at least at the belt width direction center position M of the divided area A.

In other words, as long as the guide portion 26 is avoided from being placed at the belt width direction center position M of the divided region A, some effect of reducing the maximum drop in belt temperature can be expected. For this reason, the guide portion 26 only needs to be placed at a position other than the position corresponding to at least the belt width direction center position M of the divided region A, and as long as this condition is met, the guide portion 26 may be placed at a position corresponding to (a part of) the divided region A, as in the example shown in FIG. 12. However, it goes without saying that in order to effectively reduce the maximum drop in belt temperature, it is preferable to place the guide portion 26 at a position other than the position corresponding to (the entire) the divided region A, as in the above-mentioned embodiment.

In addition, in the above embodiment, the guide portion 26 arranged upstream of the heater 22 and the guide portion 26 arranged downstream are arranged at the same position in the belt width direction, but as in the example shown in FIG. 13, the guide portion 26 on the upstream side (lower side in FIG. 13) and the guide portion 26 on the downstream side (upper side in FIG. 13) may be arranged at different positions in the belt width direction. In this case, heat transfer to the upstream guide portion 26 and heat transfer to the downstream guide portion 26 occur at different positions in the belt width direction, so the maximum drop in belt temperature can be reduced compared to when these overlap.

In the example shown in FIG. 13, the upstream guide portion 26 is arranged to be offset from the divided area A of the heat generating portion 35, and the downstream guide portion 26 is arranged to overlap the divided area A of the heat generating portion 35. Generally, when the fixing belt 20 rotates, it is subjected to a force that draws it in on the upstream side of the nip portion N, and tends to come into stronger contact with the upstream guide portion 26 than the downstream guide portion 26, or to come into contact over a wider area. Therefore, the heat taken from the fixing belt 20 by the guide portion 26 is greater on the upstream side than on the downstream side. In consideration of this situation, as shown in the example shown in FIG. 13, the upstream guide portion 26, which takes in more heat, is arranged offset from the divided area A of the heat generating portion 35, at least, to effectively reduce the maximum drop in the belt temperature. Conversely, a certain degree of effect can be expected by arranging the downstream guide portion 26 offset from the divided area A of the heat generating portion 35. For greater effectiveness, it is preferable to displace both the upstream and downstream guide sections 26 relative to the divided area A of the heat generating section 35, and further displace the upstream and downstream guide sections 26 from each other in the belt width direction.

Below, we will explain an embodiment that differs from the embodiment described above. Note that the following embodiment will be explained focusing on the parts that differ from the embodiment described above, and other parts will not be explained as they are basically the same.

Figure 14 is a front view of a guide section according to another embodiment of the present invention, and Figure 15 is a side view thereof.

14 and 15, the guide portion 26A (hereinafter referred to as the "first guide portion") arranged at a location corresponding to the divided region A (the belt circumferential region including the divided region A) and the guide portion 26B (hereinafter referred to as the "second guide portion") arranged at a location corresponding to the non-divided region B (the belt circumferential region including the non-divided region B) have different shapes. Specifically, a plurality of recesses 261 are formed on the belt facing surface 260 of the first guide portion 26A. On the other hand, the belt facing surface 260 of the second guide portion 26B does not have the recesses 261 formed thereon, and is formed as a smooth convex curved surface. In this embodiment, the recesses 261 are formed as spherical holes having a diameter of φ5 and a depth of 0.5 mm, but are not limited to spherical holes, and may be groove-shaped holes (slits) extending in the belt circumferential direction, or may be through holes.

In this way, by forming the recess 261 on the belt facing surface 260 of the first guide portion 26A, the fixing belt 20 does not contact the first guide portion 26A at the recess 261. In other words, the total contact length of the guide portion with the fixing belt 20 in the belt circumferential direction at any one point in the belt width direction can be reduced in the first guide portion 26A compared to the second guide portion 26B. This makes it possible to reduce the amount of heat transferred from the fixing belt 20 to the guide portion (first guide portion 26A) at the point corresponding to the divided area A, and suppress a local temperature drop in the fixing belt 20.

The "total contact length in the belt circumferential direction" refers to the total circumferential length of the guide portion at any one point in the belt width direction where the fixing belt may come into contact with the guide portion when the fixing belt rotates. Normally, when the fixing belt rotates, the rotation trajectory changes because a different behavior occurs as the belt rotates. Therefore, if the rotation trajectory of the fixing belt changes, the total circumferential length of the maximum contact portion where the fixing belt may come into contact with the guide portion as a result of this change is defined as the "total contact length in the belt circumferential direction." The same applies below.

14 and 15, the total contact length in the belt circumferential direction with respect to the fixing belt 20 is made different, so that the contact area of the guide part with respect to the fixing belt 20 is smaller at the portion corresponding to the divided region A than at the portion corresponding to the undivided region B. The "contact area" here is equivalent to the definition of the "total contact length in the belt circumferential direction" above, and specifically means the total area of the portion of the guide part with which the fixing belt may come into contact with one guide part when the fixing belt rotates. The same applies below. In this way, by making the contact area of the guide part with respect to the fixing belt 20 smaller at the portion corresponding to the divided region A, the amount of heat transferred from the fixing belt 20 to the guide part (first guide part 26A) can be reduced at the portion corresponding to the divided region A, and therefore local temperature drops in the fixing belt 20 can be suppressed.

Figure 16 shows a modified example of the embodiment shown in Figures 14 and 15.

In the example shown in FIG. 16, the guide portion 26 is provided continuously across the belt width direction (from the location corresponding to divided region A to the location corresponding to non-divided region B). Even in this configuration, by providing a recess 261 in the guide portion 26 at the location corresponding to divided region A, it is possible to similarly reduce the amount of heat transferred from the fixing belt 20 to the guide portion 26 at the location corresponding to divided region A, and to suppress a local temperature drop in the fixing belt 20.

Although only the downstream guide portion is shown in Figures 14 to 16, the upstream guide portion may also have a recess 261 formed in a location corresponding to divided area A. Also, as described above, since the upstream guide portion tends to remove more heat from the fixing belt, forming a recess 261 in the guide portion at the location corresponding to divided area A, at least on the upstream side, can effectively suppress localized temperature drops in the fixing belt.

Another embodiment is shown in Figure 17.

In the embodiment shown in FIG. 17, in order to make the total contact length of the guide portions with respect to the fixing belt 20 in the belt circumferential direction shorter at the portion corresponding to the divided region A than at the portion corresponding to the undivided region B, the length L1 in the belt circumferential direction of the first guide portion 26A is made shorter than the length L2 in the belt circumferential direction of the second guide portion 26B. Also, in this embodiment, the widths of the first guide portion 26A and the second guide portion 26B are the same, so the belt facing surface 260 is smaller in the first guide portion 26A than in the second guide portion 26B.

In this way, the belt facing surface 260 is smaller in the first guide portion 26A than in the second guide portion 26B, and as a result, the contact area of the guide portion with the fixing belt 20 is smaller in the area corresponding to the divided region A than in the area corresponding to the undivided region B. This makes it possible to reduce the amount of heat transferred from the fixing belt 20 to the guide portion (first guide portion 26A) in the area corresponding to the divided region A compared to the area corresponding to the undivided region B, and makes it possible to suppress localized temperature drops in the fixing belt 20.

Although FIG. 17 only illustrates the downstream guide portion, the upstream guide portion may also have its circumferential length shortened at a location corresponding to divided area A. As described above, the upstream guide portion tends to remove more heat from the fixing belt, so by shortening the circumferential length of the guide portion at the location corresponding to divided area A, at least on the upstream side, it is possible to effectively suppress localized temperature drops in the fixing belt. The configuration according to this embodiment is also applicable to a configuration in which the guide portion is provided continuously across the belt width.

In each embodiment shown in FIG. 14 to FIG. 17, the guide portion is provided with a recess 261 or the length of the guide portion in the belt circumferential direction is shortened to shorten the total contact length in the belt circumferential direction with the fixing belt 20 at the portion corresponding to the divided region A, or to reduce the contact area, thereby suppressing a local temperature drop of the fixing belt 20. In contrast, in the embodiment shown in FIG. 7, etc., the guide portion 26 is not arranged at the portion corresponding to the divided region A, so there is no total contact length or contact area in the belt circumferential direction with the fixing belt 20 at that portion. However, even in this embodiment, when comparing the portion corresponding to the non-divided region B where the guide portion 26 is arranged with the divided region A where the guide portion 26 is not provided, it can be said that the total contact length in the belt circumferential direction with the fixing belt 20 is shorter (the total contact length is "0") at the portion corresponding to the divided region A than the portion corresponding to the non-divided region B, or the contact area of the guide portion 26 with the fixing belt 20 is smaller (the contact area is "0"). Therefore, in this invention, "the total contact length in the belt circumferential direction is short" also means that there is no total contact length, and in this invention, "the contact area of the guide part with the fixing belt is small" also means that there is no contact area.

In the embodiment shown in FIG. 17, the contact area with the fixing belt 20 is reduced by shortening the belt circumferential length L1 of the first guide portion 26A, but from another perspective, the size (volume) of the first guide portion 26A is smaller than that of the second guide portion 26B, so that the heat capacity of the first guide portion 26A is reduced, and as a result, the amount of heat transferred from the fixing belt 20 to the guide portion (first guide portion 26A) is reduced. In this way, in addition to the embodiment shown in FIG. 17, the following embodiment shown in FIG. 18 can be cited as a way to make the contact area of the guide portion with the fixing belt 20 or the heat capacity of the guide portion smaller at the portion corresponding to the divided region A than at the portion corresponding to the non-divided region B.

In the embodiment shown in FIG. 18, the first guide portion 26A and the second guide portion 26B are made to have different widths. That is, as shown in FIG. 18, the width W1 of the first guide portion 26A is made smaller than the width W2 of the second guide portion 26B. As a result, the belt facing surface 260 at the location corresponding to the divided region A becomes smaller, and as a result, the contact area of the guide portion with the fixing belt 20 at the location corresponding to the divided region A becomes smaller. In addition, by making the width W1 of the first guide portion 26A smaller, the size (volume) becomes smaller than that of the second guide portion 26B, and the heat capacity of the guide portion at the location corresponding to the divided region A becomes smaller. As a result, the amount of heat transferred from the fixing belt 20 to the guide portion at the location corresponding to the divided region A can be reduced more than the location corresponding to the non-divided position B, and the temperature drop of the fixing belt 20 at the location corresponding to the divided region A can be suppressed.

In FIG. 18, only the downstream guide portion is shown, but the width of the upstream guide portion may also be narrowed at the location corresponding to divided area A. As described above, the upstream guide portion tends to remove more heat from the fixing belt, so by narrowing the width of the guide portion at least on the upstream side at the location corresponding to divided area A, it is possible to effectively suppress localized temperature drops in the fixing belt.

As described above, in the embodiment shown in FIG. 17 and the embodiment shown in FIG. 18, the perimeter or width of the guide portion is reduced at the location corresponding to the divided region A, thereby reducing the heat capacity of the guide portion and reducing the amount of heat transferred from the fixing belt 20 to the guide portion (first guide portion 26A). On the other hand, in the embodiment shown in FIG. 7 and the like, the guide portion 26 is not disposed at the location corresponding to the divided region A, so the guide portion 26 does not have a heat capacity at that location. However, even in this embodiment, when comparing the location corresponding to the undivided region B with the divided region A relatively, it can be said that the heat capacity of the guide portion 26 is smaller (the heat capacity is "0") at the location corresponding to the divided region A than at the location corresponding to the undivided region B. Therefore, in the present invention, "the heat capacity of the guide portion is small" also means that there is no heat capacity.

In each of the above-described embodiments, solutions to the local temperature drop of the fixing belt 20 caused by the divided area A of the heat generating section 35 and the arrangement of the guide section 26 have been described. However, in addition to these factors, the local temperature drop of the fixing belt 20 can also be caused by heat transfer to the thermistor 25 and thermostat 27 (see FIG. 5) that are in contact with the heater 22.

Therefore, in order to suppress a local temperature drop of the fixing belt 20 due to heat transfer to the thermistor 25 and thermostat 27, as in the embodiment shown in FIG. 19, the holes 41 and 42 for attaching the thermistor 25 and thermostat 27 to the heater folder 23 may be shifted in the belt width direction from the position where the guide portion 26 is provided. In other words, the contact position of the thermistor 25 and thermostat 27 with the heater 22 and the position of the guide portion 26 are made different in the belt width direction. As a result, heat transfer to the thermistor 25 and thermostat 27 and heat transfer to the guide portion 26 occur at different positions in the belt width direction, so the maximum drop in belt temperature can be reduced compared to when these overlap.

In addition, it is preferable that the contact positions of the thermistor 25 and thermostat 27 with the heater 22 are also shifted in the belt width direction from the divided area A of the heat generating section 35. This makes it possible to suppress localized temperature drops in the fixing belt 20 caused by overlapping between the thermistor 25 and thermostat 27 and the divided area A of the heat generating section 35.

Furthermore, recesses 251, 271 may be provided on the contact surfaces of the thermistor 25 and thermostat 27 with the heater 22. This reduces the contact area of the thermistor 25 and thermostat 27 with the heater 22, and reduces the amount of heat transferred from the heater 22 to the thermistor 25 and thermostat 27, thereby suppressing local temperature drops in the fixing belt 20. Furthermore, such a configuration with recesses 251, 271 is particularly suitable when the contact position of the thermistor 25 and thermostat 27 with the heater 22 overlaps with at least one of the position of the guide portion 26 and the divided area A of the heat generating portion 35 in the belt width direction.

In addition, the thermistor 25 and thermostat 27 may be arranged in contact with the fixing belt 20, other than in direct contact with the heater 22. In this case, the above-mentioned effect can be obtained by shifting the contact position of the thermistor 25 and thermostat 27 with the fixing belt 20 from the position of the guide portion 26 or the divided area A of the heat generating portion 35, or by providing a recess in the contact surface of the thermistor 25 and thermostat 27 with the fixing belt 20.

Although the embodiments of the present invention have been described above, it goes without saying that various modifications can be made without departing from the spirit of the present invention. Therefore, the above-described embodiments and their modifications may be combined as appropriate.

In the above embodiment, a color image forming device has been described as an example, but the image forming device according to the present invention may be a monochrome image forming device. In addition, the image forming device according to the present invention includes a printer, a copier, a facsimile, or a combination machine of these.

In addition to the fixing device shown in FIG. 2, the present invention can also be applied to fixing devices such as those shown in FIGS. 20 to 22. The configuration of each fixing device shown in FIGS. 20 to 22 will be briefly described below.

First, the fixing device 9 shown in FIG. 20 has a pressure roller 44 disposed on the opposite side of the fixing belt 20 from the pressure roller 21 side, and is configured so that the fixing belt 20 is sandwiched and heated by this pressure roller 44 and heater 22. On the other hand, on the pressure roller 21 side, a nip forming member 45 is disposed on the inner circumference of the fixing belt 20. The nip forming member 45 is supported by a stay 24, and the fixing belt 20 is sandwiched between the nip forming member 45 and the pressure roller 21 to form a nip portion N. The nip forming member 45 also has a guide portion 26 that guides the fixing belt 20.

Next, in the fixing device 9 shown in FIG. 21, the pressure roller 44 described above is omitted, and the heater 22 is formed in an arc shape to match the curvature of the fixing belt 20 in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22. The rest of the configuration is the same as that of the fixing device 9 shown in FIG. 20.

Finally, in the fixing device 9 shown in FIG. 22, in addition to the fixing belt 20, a pressure belt 46 is provided, and a heating nip (first nip portion) N1 and a fixing nip (second nip portion) N2 are separately configured. That is, a nip forming member 45 and a stay 47 are arranged on the opposite side of the pressure roller 21 from the fixing belt 20 side, and the pressure belt 46 is arranged rotatably so as to include the nip forming member 45 and the stay 47. Then, a sheet of paper P is passed through the fixing nip N2 between the pressure belt 46 and the pressure roller 21, and the image is fixed by heating and pressurizing it. The rest of the configuration is the same as the fixing device 9 shown in FIG. 2.

As described above, according to the present invention, by reducing the amount of heat transfer from the fixing belt to the guide section at the location corresponding to the divided area of the heat generating section, or by eliminating heat transfer to the guide section, it is possible to suppress local temperature drops in the fixing belt at the location corresponding to the divided area. Furthermore, according to the present invention, since local temperature drops in the fixing belt can be suppressed by simply making a simple design change, it is not necessary to extend the heating time to increase the temperature of the entire fixing belt. Therefore, it is possible to obtain good fixing performance while avoiding the extended warm-up time and increased power consumption that would accompany extending the heating time of the fixing belt, as well as the occurrence of hot offset, etc.

9 Fixing device 20 Fixing belt 21 Pressure roller (opposing member)
22 Heater (heating member)
25 Thermistor (temperature detection means)
26 Guide portion 26A First guide portion 26B Second guide portion 27 Thermostat (power cutoff means)
31 Resistance heating element 35 Heating portion 100 Image forming apparatus 261 Belt facing surface 262 Recess A Divided region B Non-divided region N Nip portion

JP 2016-90606 A JP 2008-140701 A

Claims (15)

An endless belt that rotates in a circumferential direction;
an opposing member that contacts an outer circumferential surface of the belt to form a nip portion;
a heating member in contact with an inner circumferential surface of the belt and having a heat generating portion divided into a plurality of portions in a width direction of the belt;
a guide portion that contacts an inner circumferential surface of the belt to guide the belt,
1. A fixing device, comprising: a heat capacity of said guide portion being smaller at a portion corresponding to a divided region of said heat generating portion than at a portion corresponding to a non-divided region of said heat generating portion. An endless belt that rotates in a circumferential direction;
an opposing member that contacts an outer circumferential surface of the belt to form a nip portion;
a heating member in contact with an inner circumferential surface of the belt and having a heat generating portion divided into a plurality of portions in a width direction of the belt;
a guide portion that contacts an inner circumferential surface of the belt to guide the belt,
11. A fixing device, comprising: a contact area of said guide portion with said belt being smaller at a portion corresponding to a divided region of said heat generating portion than at a portion corresponding to a non-divided region of said heat generating portion. The fixing device according to claim 2, wherein the total contact length of the guide portion with the belt in the belt circumferential direction at any one point in the belt width direction is shorter at a location corresponding to the divided area of the heat generating portion than at a location corresponding to the non-divided area of the heat generating portion. The fixing device according to claim 2 , wherein a belt-facing surface of the guide portion facing the inner circumferential surface of the belt is smaller at a portion corresponding to the divided region of the heat generating portion than at a portion corresponding to the non-divided region of the heat generating portion. The fixing device according to claim 4, wherein the length of the guide portion in the belt circumferential direction is shorter at the portion corresponding to the divided region of the heat generating portion than at the portion corresponding to the non-divided region of the heat generating portion. The guide portion includes a first guide portion disposed at a position corresponding to a divided region of the heat generating portion;
a second guide portion disposed in a belt width direction and spaced from the first guide portion and disposed at a location corresponding to the non-divided region of the heat generating portion,
The fixing device according to claim 4 , wherein the first guide portion is smaller than the second guide portion in the belt width direction. An endless belt that rotates in a circumferential direction;
an opposing member that contacts an outer circumferential surface of the belt to form a nip portion;
a heating member in contact with an inner circumferential surface of the belt and having a heat generating portion divided into a plurality of portions in a width direction of the belt;
a guide portion that contacts an inner circumferential surface of the belt to guide the belt,
the guide portion is disposed on the upstream side or the downstream side of the heating member in the belt rotation direction,
A fixing device characterized in that all of the upstream and downstream guide portions are arranged within the width region of the belt, at locations other than the locations corresponding to the belt width direction central positions of the divided regions of the heat generating portions. The fixing device according to claim 7, wherein all of the upstream or downstream guide sections are disposed within the width region of the belt, except for the sections corresponding to the divided regions of the heat generating section. An endless belt that rotates in a circumferential direction;
an opposing member that contacts an outer circumferential surface of the belt to form a nip portion;
a heating member in contact with an inner circumferential surface of the belt and having a heat generating portion divided into a plurality of portions in a width direction of the belt;
a guide portion that contacts an inner circumferential surface of the belt to guide the belt,
a fixing device, wherein the guide portion is not disposed in a portion corresponding to the divided regions of the heat generating portion; the guide portions are disposed on the upstream side and the downstream side of the heating member in a belt rotation direction,
10. The fixing device according to claim 1, wherein the upstream guide portion and the downstream guide portion are positioned differently in the belt width direction. a temperature detection means that is in contact with the heating member or the belt and detects the temperature of the heating member or the belt;
11. The fixing device according to claim 1, wherein a contact position of the temperature detector with the heating member or the belt is made different from at least one of a position of the guide portion and a divided region of the heat generating portion in the belt width direction . 12. The fixing device according to claim 11, wherein a recess is provided on a contact surface of the temperature detector with the heating member or the belt . a power cut-off means for contacting the heating member or the belt and cutting off the power supply to the heating member when the temperature of the heating member or the belt reaches or exceeds a predetermined temperature;
13. The fixing device according to claim 1, wherein a contact position of the power cutoff means with the heating member or the belt is made different from at least one of a position of the guide portion and a divided region of the heat generating portion in the belt width direction . 14. The fixing device according to claim 13, wherein a recess is provided on a contact surface of the power cutoff means with respect to the heating member or the belt. An image forming apparatus comprising the fixing device according to claim 1 .

Images