JP7569013B2 - Fixing device and image forming apparatus - Google Patents

Description

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

Image forming devices such as copiers and printers are equipped with a fixing device that fixes the toner image onto the paper.

Typically, a fixing device has a pair of rotating bodies that come into contact with each other, and by passing paper between the rotating bodies (the fixing nip), the paper is heated and pressurized, and the toner image on the paper is fixed.

In recent years, in order to save energy or shorten warm-up times, fixing devices have been developed that use a fixing belt, which has a smaller heat capacity than a roller, as the rotating body. However, this type of fixing device has a problem in that when small-sized paper is continuously passed through, the temperature of the fixing belt increases significantly in non-paper passing areas where no paper passes through.

To address this issue, Patent Document 1 (JP 2018-169467 A) proposes a method of contacting a heat transfer assistant member with good thermal conductivity with the fixing belt to transfer heat from the fixing belt in its longitudinal direction, thereby suppressing temperature increases in non-paper passing areas.

As described above, by providing a heat transfer assisting member, it is possible to suppress localized temperature increases in the fixing belt in non-paper passing areas. However, even in a configuration that includes such a heat transfer assisting member, there is a risk of localized temperature increases in the fixing belt when the number of sheets passing per unit time increases as the image forming device becomes faster.

On the other hand, if the volume of the heat transfer assistant member is increased, the amount of heat transfer in the heat transfer assistant member can be increased, and localized temperature increases in the fixing belt can be more effectively suppressed. However, increasing the volume of the heat transfer assistant member causes the device to become larger. Also, if the volume of the heat transfer assistant member is increased, the heat from the fixing belt is taken away by the heat transfer assistant member during warm-up after the image forming device is turned on, which causes a problem of longer warm-up times.

In order to solve the above problem, the present invention provides a fixing device comprising a rotatable endless fixing belt, a rotatable pressure member that contacts the outer peripheral surface of the fixing belt to form a fixing nip, a heat source that heats the fixing belt, and a heat transfer auxiliary member that directly or indirectly contacts the inner peripheral surface of the fixing belt at the position of the fixing nip, wherein the heat transfer auxiliary member has a base portion that directly or indirectly contacts the inner peripheral surface of the fixing belt, a connecting portion that extends from a part of an end extending in the longitudinal direction of the base portion to the side opposite the pressure member side, and a planar portion that extends from the tip of the connecting portion in a direction intersecting the extension direction of the connecting portion, wherein the width of the connecting portion in the longitudinal direction of the base portion is smaller than the width of the planar portion in the longitudinal direction of the base portion, and the connecting portion is positioned at least outside the smallest recording medium passing area of the passing area of the recording medium passing through the fixing nip .

According to the present invention, it is possible to effectively suppress localized temperature increases in the fixing belt while avoiding an increase in the size of the device and an increase in the heating time of the fixing belt during warm-up, etc.

1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 2 is a schematic configuration diagram of a fixing device according to the present embodiment. FIG. 2 is a perspective view of a heat equalizing plate according to the embodiment. 4 is a plan view showing the arrangement of protruding pieces in a fixing device of a center reference transport system; FIG. 4 is a plan view showing the arrangement of protruding pieces in a fixing device using an end-based transport method; FIG. 13 is a plan view showing an example in which a plurality of pairs of protruding pieces are arranged corresponding to paper passing areas of different widths. FIG. 4 is a plan view showing a state in which the heat equalizing plate is attached to the nip forming member. FIG. FIG. 11 is a cross-sectional view for explaining a method for attaching a heat equalizing plate. FIG. 11 is a cross-sectional view for explaining a method for attaching a heat equalizing plate. FIG. 13 is a plan view for explaining a method for attaching the heat equalizing plate. FIG. 13 is a plan view for explaining a method for attaching the heat equalizing plate. 4 is a cross-sectional view showing a state in which a heat equalizing plate is attached to a nip forming member. FIG. 13A and 13B are cross-sectional views showing modified examples of the protrusions. 4 is an enlarged plan view showing an engagement portion between a heat equalizing plate and a nip forming member. FIG. 13 is a schematic diagram showing an example in which a protruding piece is provided at a downstream end of a base portion in a paper transport direction. FIG.

The present invention will be described below with reference to 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.

As shown in FIG. 1, the image forming device 1 according to this embodiment is an electrophotographic printer that includes an image forming unit 2, a recording medium supply unit 3, a transfer unit 4, a fixing unit 5, and a recording medium discharge unit 6. The image forming device according to the present invention may be a printer, a copier, a facsimile, or a multifunction device that has two or three of these functions.

The image forming section 2 includes four imaging units 7Y, 7M, 7C, and 7K that form images, and an exposure device 8 that forms an electrostatic latent image on the surface of the photoconductor 10 of each imaging unit 7Y, 7M, 7C, and 7K. In addition to the photoconductor 10 as an image carrier, each of the four imaging units 7Y, 7M, 7C, and 7K includes a charging member 11 that charges the surface of the photoconductor 10, a developing device 12 that supplies developer to the surface of the photoconductor 10, and a cleaning member 13 that cleans the surface of the photoconductor 10. Each imaging unit 7Y, 7M, 7C, and 7K has the same configuration, except that it contains developers of different colors, yellow (Y), magenta (M), cyan (C), and black (K), which correspond to the color separation components of the color image. The exposure device 8 includes a light source, a polygon mirror, an f-θ lens, a reflecting mirror, and the like.

The recording medium supply unit 3 is provided with a paper feed tray 18 that stores paper P as a recording medium, and a paper feed roller 19 that feeds paper P one sheet at a time from the paper feed tray 18. The paper P stored in the paper feed tray 18 includes plain paper, thick paper, thin paper, postcards, envelopes, coated paper (coated paper or art paper, etc.), tracing paper, etc. In addition to paper, resin sheets such as overhead projector sheets may also be used as recording media.

The transfer section 4 is provided with a transfer device 14 that transfers an image onto paper P supplied from a paper feed tray 18. The transfer device 14 includes an intermediate transfer belt 15, a primary transfer roller 16, and a secondary transfer roller 17. The intermediate transfer belt 15 is an endless belt member that is stretched by a plurality of support rollers. Four primary transfer rollers 16 are provided on the inside of the intermediate transfer belt 15 corresponding to each photoconductor 10. Each primary transfer roller 16 contacts each photoconductor 10 via the intermediate transfer belt 15, thereby forming a primary transfer nip between the intermediate transfer belt 15 and each photoconductor 10. The secondary transfer roller 17 contacts the outer peripheral surface of the intermediate transfer belt 15 to form a secondary transfer nip.

The fixing section 5 is provided with a fixing device 20 that fixes an image onto the paper P. The fixing device 20 includes an endless fixing belt 21 and a pressure roller 22 as a pressure member. The fixing belt 21 and the pressure roller 22 are pressed against each other, forming a fixing nip between them.

The recording medium ejection section 6 is provided with a pair of ejection rollers 23 that eject the paper P outside the device.

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

When an instruction to start a printing operation is given, the photoconductor 10 in each of the imaging units 7Y, 7M, 7C, and 7K starts to rotate, and the surface of the photoconductor 10 is charged to a uniform high potential by the charging member 11. Next, the exposure device 8 irradiates the surface of each photoconductor 10 with laser light 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. This reduces the potential of the area irradiated with the laser light, and an electrostatic latent image is formed on the surface of each photoconductor 10. Toner is then supplied from the developing device 12 to this electrostatic latent image, and a toner image is formed on each photoconductor 10.

The toner image formed on each photoconductor 10 reaches the primary transfer nip (position of the primary transfer roller 16) as each photoconductor 10 rotates, and is transferred onto the rotating intermediate transfer belt 15 so that they overlap one another. The toner image transferred onto the intermediate transfer belt 15 then reaches the secondary transfer nip (position of the secondary transfer roller 17) as the intermediate transfer belt 15 rotates, and is transferred onto the paper P.

This paper P is supplied from the recording medium supply unit 3. In the recording medium supply unit 3, after an instruction to start the printing operation is given, the paper feed roller 19 rotates, and paper P is sent out one sheet at a time from the paper feed tray 18. The sent-out paper P is then temporarily stopped by a pair of timing rollers 24, and then transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 15 reaching the secondary transfer nip. In this way, a full-color toner image is transferred onto the paper P. In addition, after the toner image is transferred, the toner remaining on each photoconductor 10 is removed by each cleaning member 13.

The paper P with the transferred toner image is transported to the fixing unit 5. In the fixing unit 5, the paper P is conveyed while being sandwiched between the fixing belt 21 and the pressure roller 22, so that the toner image is fixed to the paper P. The paper P is then conveyed to the recording medium discharge unit 6, and is discharged outside the device by the paper discharge rollers 23. This completes the series of printing operations.

The configuration of the fixing device 20 according to this embodiment will be described in detail below with reference to FIG. 2.

As shown in FIG. 2, the fixing device 20 according to this embodiment includes a fixing belt 21 and a pressure roller 22, as well as a halogen heater 25, a nip forming member 26, a stay 27, a reflecting member 28, a temperature sensor 29, and a heat equalizing plate 30.

The fixing belt 21 is disposed on the unfixed image bearing surface of the paper P, and is a fixing member that fixes the unfixed image on the paper P. The fixing belt 21 is composed of an endless belt member, and is rotatably held by a pair of belt holding members inserted into both ends of the longitudinal direction. Therefore, the fixing belt 21 is held in a so-called free belt manner in which no tension is applied to the fixing belt 21 when it is not rotating. In addition, a halogen heater 25 is disposed on the inside of the fixing belt 21 as a heat source. Therefore, when the halogen heater 25 generates heat, the fixing belt 21 is heated from the inside.

The pressure roller 22 is a rotating body that contacts the outer peripheral surface of the fixing belt 21. Specifically, the pressure roller 22 is composed of a core metal, an elastic layer made of foamed silicone rubber, silicone rubber, or fluororubber, etc., provided on the surface of the core metal, and a release layer made of PFA, PTFE, etc., provided on the surface of the elastic layer. The pressure roller 22 is pressed (pressed) against the fixing belt 21 by a biasing member such as a spring, and a fixing nip N is formed between the fixing belt 21 and the pressure roller 22. The pressure roller 22 is configured to be rotated by a drive source provided in the image forming apparatus body. When the pressure roller 22 is rotated, the driving force is transmitted to the fixing belt 21 at the fixing nip N, and the fixing belt 21 is rotated. Therefore, as shown in FIG. 2, when paper P carrying an unfixed image enters between the fixing belt 21 and the pressure roller 22 (fixing nip N), the paper P is transported in the direction of arrow Y by the rotating fixing belt 21 and pressure roller 22, and is heated and pressurized, so that the unfixed image is fixed to the paper P.

In this embodiment, the pressure roller 22 is a solid roller, but the pressure roller 22 may be a hollow roller. When the pressure roller 22 is a hollow roller, a heater may be disposed inside the pressure roller 22. In addition, when the pressure roller 22 does not have an elastic layer, the heat capacity is reduced, and the fixing property is improved. On the other hand, when the pressure roller 22 does not have an elastic layer, when the unfixed toner is fixed, minute irregularities on the belt surface may be transferred to the image, and uneven gloss may occur in the solid part of the image. To prevent this, it is preferable that the pressure roller 22 has an elastic layer having a thickness of 100 μm or more. When the pressure roller 22 has an elastic layer having a thickness of 100 μm or more, the surface of the pressure roller 22 is in close contact with the minute irregularities of the fixing belt 21, and the occurrence of uneven gloss can be suppressed. In addition, the material used for the elastic layer of the pressure roller 22 may be solid rubber, but if there is no heater inside the pressure roller 22, sponge rubber can also be used. Sponge rubber is preferable to solid rubber because it has better insulating properties and is less likely to lose heat to the fixing belt 21.

The halogen heater 25 is a heat source that irradiates the inner peripheral surface of the fixing belt 21 with infrared light to heat the fixing belt 21. The heat source may be a halogen heater or another radiant heat type heater such as a carbon heater or a ceramic heater. It is also possible to use an electromagnetic induction heating type heat source. In this embodiment, two halogen heaters 25 are arranged inside the fixing belt 21, but the number of heat sources may be one or three or more.

The nip forming member 26 is a member that forms the fixing nip N by receiving the pressure of the pressure roller 22 from the inside of the fixing belt 21. It is preferable to use a heat-resistant material with a heat resistance temperature of 200°C or more as the material of the nip forming member 26. For example, general heat-resistant resins such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), or polyetheretherketone (PEEK) can be mentioned. By using such a heat-resistant material as the material of the nip forming member 26, thermal deformation of the nip forming member 26 in the fixing temperature range can be prevented, and the shape of the fixing nip N can be stabilized.

The stay 27 is a support member that supports the nip forming member 26 from the side opposite the pressure roller 22. The stay 27 supports the nip forming member 26, thereby suppressing bending of the nip forming member 26 due to pressure from the pressure roller 22 (particularly bending in the longitudinal direction of the fixing belt 21). This allows a fixing nip N of uniform width to be obtained. In order to ensure rigidity, the material of the stay 27 is preferably an iron-based metal material such as SUS or SECC.

The reflecting member 28 is a member that reflects heat or infrared light radiated from the halogen heater 25. The reflecting member 28 reflects the heat or infrared light of the halogen heater 25 toward the fixing belt 21, thereby efficiently heating the fixing belt 21. The reflecting member 28 is also interposed between the stay 27 and the halogen heater 25, and serves to suppress heat transfer to the stay 27. The stay 27 may also have the function of the reflecting member 28. For example, by mirror-finishing the surface of the stay 27 facing the halogen heater 25, the heat or infrared light from the halogen heater 25 can be reflected toward the fixing belt 21 by the mirror-finished portion of the stay 27. In this case, it is not necessary to provide a separate reflecting member 28, which allows the device to be made smaller and less expensive.

The temperature sensor 29 is a temperature detection member that detects the temperature of the fixing belt 21. Based on the temperature detected by the temperature sensor 29, the heat generation of the halogen heater 25 is controlled, and the temperature of the fixing belt 21 is maintained at a predetermined temperature (fixing temperature). In this embodiment, two temperature sensors 29 are arranged at positions facing each halogen heater 25 across the fixing belt 21, but the number and arrangement of the temperature sensors 29 can be changed as appropriate. As the temperature sensor 29, for example, a known contact or non-contact temperature sensor such as a thermopile, thermostat, thermistor, or NC sensor can be used.

The heat equalizing plate 30 is a heat transfer auxiliary member that contacts the inner peripheral surface of the fixing belt 21 at the fixing nip N and transfers the heat of the fixing belt 21 in its longitudinal direction to equalize the temperature. The heat equalizing plate 30 is made of a material with a higher thermal conductivity than the nip forming member 26. Specifically, the heat equalizing plate 30 is made of a highly thermally conductive material such as copper, aluminum, or silver. In this embodiment, the heat equalizing plate 30 is in direct contact with the inner peripheral surface of the fixing belt 21, but may be in indirect contact via a lubricant such as grease. By the heat equalizing plate 30 being in direct or indirect contact with the inner peripheral surface of the fixing belt 21, the heat of the fixing belt 21 is transferred to the heat equalizing plate 30 and diffused in the longitudinal direction.

The fixing belt 21 is heated to an almost uniform temperature overall by the halogen heater 25, but when paper passes through the fixing nip N, the heat of the fixing belt 21 is absorbed by the paper in the paper-passing area through which the paper passes. On the other hand, in the non-paper-passing area where paper does not pass, the heat of the fixing belt 21 is not absorbed by the paper as easily. Therefore, when paper is continuously passed through, heat is accumulated in the fixing belt 21, and there is a risk of an excessive temperature rise. In particular, in a configuration using a fixing belt 21 that has a smaller heat capacity than a roller and is more likely to rise in temperature, the temperature rise in the non-paper-passing area is likely to be significant.

Therefore, in this embodiment, a heat equalizer plate 30 as a heat transfer auxiliary member is arranged along the longitudinal direction of the fixing belt 21, thereby transferring heat from the fixing belt 21 in the non-paper passing areas in the longitudinal direction, thereby suppressing localized temperature increases in the fixing belt 21. However, even in a configuration using such a heat equalizer plate 30, if the number of sheets of paper passing per unit time increases, the amount of heat stored in the fixing belt 21 in the non-paper passing areas exceeds the amount of heat transferred by the heat equalizer plate 30, and there is a risk of localized temperature increases in the fixing belt 21.

Therefore, in this embodiment, the following measures are taken to increase the amount of heat transfer in the heat equalizer plate 30. The configuration of the heat equalizer plate 30 according to this embodiment is described in detail below.

Figure 3 is a perspective view of the heat equalizer plate 30 according to this embodiment.

First, in FIG. 3, the arrow Y direction is the paper transport direction (recording medium transport direction) in which the paper P passes through the fixing nip N, and the arrow X direction is the paper width direction (recording medium width direction) perpendicular to the paper transport direction Y. As shown in FIG. 3, when the paper P passes through the fixing nip N, the temperature of the fixing belt 21 tends to rise in the non-paper passing area Q (especially the hatched area H near the widthwise end of the paper passing area) where the paper P does not pass. For this reason, in this embodiment, a protrusion 32 that releases heat is provided in the non-paper passing area Q of the heat equalizing plate 30.

The protruding piece portion 32 has a planar portion 33 arranged parallel or approximately parallel to the base portion 31 of the heat equalizing plate 30, and a connecting portion 34 connecting the planar portion 33 and the base portion 31. The base portion 31 has a planar portion that directly or indirectly contacts the inner peripheral surface of the fixing belt 21 to form the fixing nip N, and is arranged to extend continuously in the longitudinal direction (paper width direction X) of the fixing belt 21. In addition, both ends 31a, 31b of the base portion 31 in the paper transport direction Y and their neighboring parts are formed to be curved in accordance with the fixing belt 21. The connecting portion 34 is provided to protrude from a part of the end 31a on the upstream side in the paper transport direction of both ends 31a, 31b extending in the longitudinal direction (paper width direction X) of the base portion 31. The connecting portion 34 extends from the end 31a of the base portion 31 on the paper transport direction flow side toward the opposite side to the pressure roller 22 side (the direction of the arrow Z in FIG. 3), and a planar portion 33 is provided at the tip of the connecting portion 34 in the extending direction. The planar portion 33 is provided so as to bend from the tip of the connecting portion 34 toward the paper transport direction Y, and is formed so as to expand in a direction (paper transport direction Y and paper width direction X) that intersects with the direction Z in which the connecting portion 34 extends.

In this manner, in this embodiment, the heat equalizing plate 30 has a protrusion 32 in the non-paper passing area Q that dissipates heat, and the heat in the non-paper passing area Q of the fixing belt 21 can be effectively dissipated via this protrusion 32. Therefore, in this embodiment, even when a large number of sheets of paper P are passed continuously, heat accumulation in the non-paper passing area Q of the fixing belt 21 can be suppressed, and an excessive rise in temperature of the fixing belt 21 can be avoided. This also makes it unnecessary to take measures such as stopping paper passing or reducing the paper passing speed until the temperature of the fixing belt 21 drops. Alternatively, since there is less need for such measures, productivity can be improved.

As shown in FIG. 4, in this embodiment, a so-called center-based transport method is adopted in which paper P of various width sizes W1, W2 is transported based on the center C in the width direction, and so the protrusions 32 are arranged symmetrically with respect to the center C in the width direction. In other words, in the case of the center-based transport method, the outsides of each paper-passing area R1, R2 corresponding to the various width sizes W1, W2 become non-paper-passing areas Q1, Q2, so a total of two protrusions 32 are arranged, one each in each of the non-paper-passing areas Q1, Q2 on both outsides.

In contrast, as shown in FIG. 5, in the case of a so-called end-based transport method in which paper P of various width sizes W1, W2 is transported based on one widthwise end of each paper, mainly only the outer area on one side of the paper passing areas R1, R2 becomes the non-paper passing area Q1, Q2. Therefore, in the case of the end-based transport method, it is sufficient that the protrusion 32 is arranged only on one side of the paper passing areas R1, R2 (non-paper passing area Q1, Q2).

Also, as shown in FIG. 6, when there are many types of paper P to be passed through, four or more protruding pieces 32 may be arranged. Specifically, in the example shown in FIG. 6, paper P of various width sizes, namely B5 vertical width size W1, A4 vertical width size W2, B4 vertical width size W3, and A3 vertical width size W4, which are standard sizes, are passed through. Among these width sizes, protruding pieces 32 are arranged near both ends (non-paper passing areas) of the paper passing areas of A4 vertical width size W2 and B4 vertical width size W3. In this case, the temperature rise in the non-paper passing areas when B5 vertical width size W1 and A4 vertical width size W2 are passed through is mainly suppressed by each of the inner protruding pieces 32B. Also, the temperature rise in the non-paper passing areas when B4 vertical width size W3 is passed through is mainly suppressed by each of the outer protruding pieces 32A.

The position of each protrusion 32 can be changed as appropriate depending on the width size or number of types of paper P that can be passed through. However, in order to suppress temperature rise in the non-paper passing area, the protrusion 32 needs to be positioned at least outside the minimum paper passing area (non-paper passing area). Also, since it is sufficient for the protrusion 32 to be able to dissipate heat in the non-paper passing area, the surface portion 33 may be within the paper passing area for the minimum width paper as long as at least the connecting portion 34 is in the non-paper passing area for the minimum width paper.

As described above, by providing the protruding portion 32 on the heat equalizing plate 30, the temperature rise in the non-paper passing area during continuous paper passing can be effectively suppressed. In particular, when the planar portion 33 is formed large, the amount of heat transferred to the planar portion 33 increases, which is more effective. However, during warm-up in which the fixing belt 21 is heated from a room temperature state to the fixing temperature, it is preferable to suppress the transfer of heat from the fixing belt 21 to the planar portion 33 so that the fixing belt 21 can be effectively heated to shorten the warm-up time. Therefore, in this embodiment, as shown in FIG. 3, the width D1 of the connecting portion 34 in the longitudinal direction (paper width direction X) of the base portion 31 is made smaller than the width D2 of the planar portion 33 in the longitudinal direction (paper width direction X) of the base portion 31. In other words, the width of the heat transfer path in the connecting portion 34 is made smaller. As a result, during warm-up when the temperature variation is small and the thermal gradient of the fixing belt 21 is low, the transfer of heat to the planar portion 33 via the connecting portion 34 is suppressed. This allows the fixing belt 21 to be heated efficiently, shortening the warm-up time.

As shown in FIG. 3, in this embodiment, the planar portion 33 is arranged to extend from the tip of the connecting portion 34 in a direction intersecting the direction in which the connecting portion 34 extends (the direction of the arrow Z in FIG. 3), so that the heat equalizing plate 30 does not become thicker. That is, in this embodiment, the planar portion 33 is not arranged to extend in the same direction as the connecting portion 34 (the direction of the arrow Z), so that the size of the planar portion 33 can be ensured while suppressing an increase in the thickness of the heat equalizing plate 30 in the direction of the arrow Z (the dimension in the direction intersecting both the paper transport direction Y and the paper width direction X). This makes it possible to suppress localized temperature increases in the fixing belt while minimizing the size of the fixing device.

In addition, in this embodiment, since the planar portion 33 is bent from the tip of the connecting portion 34 toward the paper transport direction Y, as shown in FIG. 4, the planar portion 33 is arranged to overlap the base portion 31 when viewed from a direction intersecting the base portion 31. In this way, in this embodiment, since the planar portion 33 is arranged to overlap the base portion 31, the heat equalizing plate 30 can be made smaller in the paper transport direction Y and the paper width direction X. In addition, since the planar portion 33 is arranged to overlap the base portion 31, the planar portion 33 is arranged to avoid the area E (see FIG. 2) where the infrared light of the halogen heater 25 is directly irradiated. In this way, in this embodiment, since the planar portion 33 is arranged outside the area directly irradiated by the halogen heater 25, it is possible to prevent the planar portion 33 from being heated by the halogen heater 25. As a result, heat can be reliably transferred from the fixing belt 21 to the planar portion 33, so that a local temperature rise of the fixing belt 21 can be effectively suppressed. The portion where the planar portion 33 overlaps with the base portion 31 does not have to be the entire planar portion 33, but may be only a part of it.

The heat equalizer plate 30 according to this embodiment is configured to be attachable to the nip forming member 26. As shown in FIG. 2, when the heat equalizer plate 30 is attached to the nip forming member 26, the nip forming member 26 is sandwiched and held (contained) between the base portion 31 and the planar portion 33 of the heat equalizer plate 30.

Figure 7 is a plan view showing the heat equalizer plate 30 attached to the nip forming member 26.

As shown in FIG. 7, the surface portion 33 of the heat equalizer 30 is provided with a hole 35 as an engagement portion that can engage with the nip forming member 26. Meanwhile, the nip forming member 26 is provided with a protrusion 36 that can engage with the hole 35. In addition, the nip forming member 26 is formed with a recess 37 to avoid interference with the surface portion 33 when the heat equalizer 30 is attached to the nip forming member 26.

To attach the heat equalizer plate 30 to the nip forming member 26, first, as shown in FIG. 8, the planar portion 33 of the heat equalizer plate 30 is inserted into the recess 37 of the nip forming member 26. Next, as shown in FIG. 9, the heat equalizer plate 30 is rotated so that the base portion 31 of the heat equalizer plate 30 approaches or contacts the nip forming member 26.

Figure 10 is a view of the state after rotation shown in Figure 9 from a direction intersecting the base portion 31. In the state shown in Figure 10, a pair of planar portions 33 are arranged in each recess 37 of the nip forming member 26. Then, from this state, as shown in Figure 11, the heat equalizer 30 is slid in the longitudinal direction of the nip forming member 26, and the protrusions 36 of the nip forming member 26 are engaged with the holes 35 of each planar portion 33. At this time, each planar portion 33 can smoothly overcome each protrusion 36 due to the inclined surface 33a (see Figure 3) provided at its tip. Therefore, the tip of each planar portion 33 does not get caught on each protrusion 36, and the protrusions 36 can be engaged with the holes 35. Through the above procedure, the attachment of the heat equalizer 30 to the nip forming member 26 is completed.

As shown in the cross-sectional view of FIG. 12, when the heat equalizing plate 30 is attached, the convex portion 36 of the nip forming member 26 engages with the hole portion 35 of the heat equalizing plate 30, and the nip forming member 26 is held between the planar portion 33 and the base portion 31 of the heat equalizing plate 30, preventing the heat equalizing plate 30 from coming off the nip forming member 26. In addition, in this embodiment, the heat equalizing plate 30 itself has an engagement portion (hole portion 35) that engages with the nip forming member 26, so there is no need to provide a separate member for attaching the heat equalizing plate 30 to the nip forming member 26, and the heat equalizing plate 30 can be easily attached.

Contrary to this embodiment, the nip forming member 26 may be provided with a hole as an engagement portion, and the heat equalizing plate 30 may be provided with a protrusion that can engage with the hole. The shape of the protrusion 36 may be a hemisphere as shown in FIG. 12, or a cylinder as shown in FIG. 13. The hole 35 is not limited to a through hole without a bottom, and may be a hole with a bottom.

Here, the heat equalizing plate 30 is made of a metal material such as aluminum that does not easily expand thermally, whereas the nip forming member 26 is made of a resin material that easily expands thermally. Therefore, due to the difference in linear expansion coefficients, if the position of the hole 35 relative to the convex portion 36 changes in the longitudinal direction of the base portion 31, the convex portion 36 and the hole 35 may interfere with each other, and the heat equalizing plate 30 or the nip forming member 2 may be deflected. Therefore, in this embodiment, as shown in FIG. 14, the hole 35 is formed as a long hole extending in the longitudinal direction of the base portion 31 (horizontal direction in the figure). As a result, even if the heat equalizing plate 30 expands thermally and the position of the hole 35 relative to the convex portion 36 changes, interference between the convex portion 36 and the hole 35 can be avoided, and deflection of the heat equalizing plate 30 or the nip forming member 26 can be prevented. The hole 35 formed in the long hole may be either one of the two holes 35 provided in each planar portion 33.

As shown in FIG. 2, in this embodiment, the protrusion 32 is provided at the upstream end of the base portion 31 in the paper transport direction Y. Therefore, even if the heat equalizer plate 30 receives a moving force in the rotational direction as the fixing belt 21 rotates, the contact of the protrusion 32 with the nip forming member 26 can restrict the movement of the heat equalizer plate 30 in the rotational direction (paper transport direction Y).

Also, as shown in the example in FIG. 15, the protrusion 32 may be provided at the downstream end of the base portion 31 in the paper transport direction Y. This configuration is suitable, for example, when the pressure in the fixing nip N is greater downstream than upstream in the paper transport direction Y. In other words, when the pressure in the fixing nip N is greater downstream, the temperature downstream of the fixing nip N tends to be high. Therefore, by adopting the configuration shown in FIG. 15, the heat on the downstream side can be effectively released via the protrusion 32.

Although the embodiment and examples of the present invention have been described above, the present invention is not limited to the above-mentioned embodiment or examples, and various modifications can of course be made without departing from the spirit of the invention. In addition, the above-mentioned embodiment has been described using a free-belt type fixing device in which the fixing belt is held by a pair of belt holding members inserted at both ends of the length of the fixing belt, but the present invention is not limited to the free-belt type configuration, and can also be applied to a configuration in which the fixing belt is stretched around multiple rollers, etc.

1 Image forming apparatus 20 Fixing device 21 Fixing belt 22 Pressure roller (pressure member)
25 Halogen heater (heat source)
26 Nip forming member 30 Heat equalizing plate (heat transfer auxiliary member)
31 Base portion 32 Projection portion 33 Planar portion 34 Connecting portion 35 Hole portion (engagement portion)
36 Convex portion 37 Concave portion P Paper (recording medium)

JP 2018-169467 A

Claims (10)

a rotatable endless fixing belt;
a rotatable pressure member that contacts an outer peripheral surface of the fixing belt to form a fixing nip;
a heat source for heating the fixing belt;
a heat transfer assistance member that directly or indirectly contacts an inner circumferential surface of the fixing belt at a position of the fixing nip;
A fixing device comprising:
The heat transfer assistance member is
a base portion that directly or indirectly contacts an inner circumferential surface of the fixing belt;
a connecting portion extending from a part of an end of the base portion extending in a longitudinal direction toward an opposite side to the pressing member;
a planar portion extending in a direction intersecting a direction in which the connecting portion extends from a tip of the connecting portion;
having
a width of the connecting portion in the longitudinal direction of the base portion is smaller than a width of the planar portion in the longitudinal direction of the base portion,
The fixing device, wherein the connection portion is disposed at least outside a minimum passing area of the recording medium passing through the fixing nip . a rotatable endless fixing belt;
a rotatable pressure member that contacts an outer peripheral surface of the fixing belt to form a fixing nip;
a heat source for heating the fixing belt;
a heat transfer assistance member that directly or indirectly contacts an inner circumferential surface of the fixing belt at a position of the fixing nip;
A fixing device comprising:
The heat transfer assistance member is
a base portion that directly or indirectly contacts an inner circumferential surface of the fixing belt;
a connecting portion extending from a part of an end of the base portion extending in a longitudinal direction toward an opposite side to the pressing member;
a planar portion extending in a direction intersecting a direction in which the connecting portion extends from a tip of the connecting portion;
having
a width of the connecting portion in the longitudinal direction of the base portion is smaller than a width of the planar portion in the longitudinal direction of the base portion,
The fixing device, wherein the connecting portion is provided in a plurality of portions along a longitudinal direction of the base portion . a nip forming member disposed between the base portion and the planar portion,
The fixing device according to claim 1 , wherein the surface portion has an engaging portion that is engageable with the nip forming member . The engaging portion is a hole portion that can be engaged with a protrusion portion provided on the nip forming member, or a protrusion portion that can be engaged with a hole portion provided on the nip forming member,
The fixing device according to claim 3 , wherein the hole is an elongated hole extending in the longitudinal direction of the base portion . The fixing device according to claim 3 , wherein the nip forming member has a recess for preventing interference between the heat transfer assistance member and the planar portion when the heat transfer assistance member is attached to the nip forming member . The fixing device according to claim 1 , wherein the connecting portion is provided at an upstream end of the base portion in a transport direction of the recording medium passing through the fixing nip . The fixing device according to claim 1 , wherein the connecting portion is provided at a downstream end of the base portion in a transport direction of the recording medium passing through the fixing nip . The fixing device according to claim 1 , wherein the planar portion is disposed so as to overlap the base portion when viewed from a direction intersecting the base portion . The fixing device according to claim 1 , wherein the planar portion is disposed outside an area directly irradiated with light from the heating source . An image forming apparatus comprising the fixing device according to claim 1 .

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