Heating device and image forming apparatus including heat pipe having flat outer surface

A heating device includes a rotating unit, a transport belt, a heater, and a heat pipe. The rotating unit rotates. The transport belt rotates together with the rotating unit while nipping a heated member together with the rotating unit so as to transport the heated member. The heater has a contact surface in contact with an inner peripheral surface of the transport belt and a flat non-contact surface not in contact with the inner peripheral surface, and generates heat so as to heat the heated member via the transport belt. The heat pipe has a flat outer surface in contact with the non-contact surface of the heater and an interior having a cross-sectionally-circular space filled with a working fluid, and transfers heat in a belt width direction of the transport belt in accordance with a function of the working fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2020-058591 filed Mar. 27, 2020.

BACKGROUND

(i) Technical Field

The present disclosure relates to heating devices and image forming apparatuses.

(ii) Related Art

Japanese Unexamined Patent Application Publication No. 2013-142834 discloses an image forming apparatus that causes a heated member to pass through a fixation nip formed by a heater, a film member rotatably disposed in pressure contact with the heater, and a presser disposed in pressure contact with the heater with the film member interposed therebetween. In this image forming apparatus, the heater is a plate-like heat pipe, a heating element is printed on the fixation-nip-facing surface of a heat pipe substrate with an insulation layer interposed therebetween, and the outermost surface is coated with the insulation layer.

SUMMARY

In a conceivable configuration that uses a heater to heat a heated member, transported by a rotating unit and a transport belt, via the transport belt, a heat pipe is used to transfer heat from a high temperature section to a low temperature section of the heater (referred to as “configuration A” hereinafter).

In the aforementioned configuration A, if the heat pipe used is cylindrical, the contact area with the heater tends to be small since the outer peripheral surface of the heat pipe is circular in cross section.

Aspects of non-limiting embodiments of the present disclosure relate to ensuring a sufficient contact area with a heater, as compared with a configuration that uses a cylindrical heat pipe.

According to an aspect of the present disclosure, there is provided a heating device including a rotating unit, a transport belt, a heater, and a heat pipe. The rotating unit rotates. The transport belt rotates together with the rotating unit while nipping a heated member together with the rotating unit so as to transport the heated member. The heater has a contact surface in contact with an inner peripheral surface of the transport belt and a flat non-contact surface not in contact with the inner peripheral surface, and generates heat so as to heat the heated member via the transport belt. The heat pipe has a flat outer surface in contact with the non-contact surface of the heater and an interior having a cross-sectionally-circular space filled with a working fluid, and transfers heat in a belt width direction of the transport belt in accordance with a function of the working fluid.

DETAILED DESCRIPTION

Image Forming Apparatus10

The configuration of an image forming apparatus10according to an exemplary embodiment will now be described.FIG. 1schematically illustrates the configuration of the image forming apparatus10according to this exemplary embodiment. In the following description, the height direction, the depth direction, and the left-right direction of the image forming apparatus10will be referred to as, “apparatus height direction”, “apparatus depth direction”, and “apparatus width direction”, respectively. The apparatus height direction, the apparatus depth direction, and the apparatus width direction are orthogonal to one another. In the drawings, the apparatus height direction is indicated by an arrow X, the apparatus depth direction is indicated by an arrow Z, and the apparatus width direction is indicated by an arrow Y. Because these directions are defined for the sake of convenience, the apparatus configuration is not to be limited to these directions.

As shown inFIG. 1, the image forming apparatus10includes an apparatus body11, a container12that contains at least one sheet P, a transport unit14that transports the sheet P, an image forming unit16that forms a toner image G onto the sheet P, and a fixing device30.

The sheet P is an example of a recording medium as well as a heated member. The toner image G is an example of an image. The image forming unit16is an example of an image forming unit. The transport unit14transports the sheet P upward from the container12in the apparatus height direction along a transport path T. For example, the image forming unit16performs a known electrophotographic process including an electrostatic charging step, an exposure step, a developing step, and a transfer step by using a single-color toner or multicolor toners, so as to form the toner image G onto the sheet P transported by the transport unit14.

The fixing device30shown inFIG. 1is an example of a heating device. The fixing device30heats the toner image G formed on the sheet P by the image forming unit16, so as to fix the toner image G onto the sheet P. In detail, as shown inFIG. 1, the fixing device30has a device body50, a pressing roller40, and a heating belt60. Furthermore, as shown inFIG. 2, the fixing device30has a heater70, a supporter80, and a heat pipe90. These components of the fixing device30will be described below in detail.

The device body50shown inFIG. 1is detachable from the apparatus body11of the image forming apparatus10. Accordingly, the entire fixing device30is detachable from the apparatus body11of the image forming apparatus10. The device body50has a support frame (not shown) that supports the individual components of the fixing device30.

The pressing roller40is an example of a rotating unit. The heating belt60is an example of a transport belt.

The pressing roller40and the heating belt60are disposed facing each other.

The heating belt60is annular, specifically, endless. For example, the heating belt60is a polyimide-resin member with a fluorine-coated outer peripheral surface. The opposite ends of the heating belt60in the belt width direction are rotatably supported by a support member (not shown).

The belt width direction intersects with (specifically, orthogonal to) a rotational direction in which the heating belt60rotates, and is parallel to the Z direction. This belt width direction may also be regarded as a direction parallel to a rotational axis (also referred to as “axial direction” hereinafter) of the pressing roller40.

The pressing roller40has a shaft45whose axial direction is aligned with the apparatus depth direction (i.e., the Z direction), an elastic layer46provided around the outer periphery of the shaft45, and a separation layer47provided around the outer periphery of the elastic layer46. The shaft45is pressed toward the heater70by a presser including a spring (not shown). Accordingly, a contact region50S (i.e., a fixation nip) where the heating belt60and the pressing roller40are in contact with each other is formed. In other words, the contact region50S is formed between the heating belt60and the pressing roller40.

Furthermore, with regard to the pressing roller40, the shaft45is supported by a bearing (not shown) and is rotated by a driver (not shown). On the other hand, the heating belt60rotates by being driven by the pressing roller40. Accordingly, the heating belt60rotates together with the pressing roller40while nipping the sheet P together with the pressing roller40, thereby transporting the sheet P. This sheet P is pressed by the pressing roller40and the heating belt60and is also heated by the heater70, so that the toner image G formed on the sheet P is fixed thereon.

As shown inFIG. 2, the heater70is disposed inside the heating belt60and is supported by the supporter80to be described later. The heater70has a planar shape (i.e., a tabular shape) whose thickness direction is aligned with the apparatus width direction (i.e., the Y direction), and extends longitudinally in the belt width direction (i.e., the Z direction) of the heating belt60.

As shown inFIG. 3, the heater70has a contact surface70A in contact with an inner peripheral surface60A of the heating belt60, and also has a flat non-contact surface70B not in contact with the inner peripheral surface60A. The non-contact surface70B is disposed at the opposite side from the heating belt60relative to the contact surface70A. In other words, the non-contact surface70B is opposed to the contact surface70A. Moreover, the non-contact surface70B is disposed parallel to the contact surface70A. Specifically, the distance between the non-contact surface70B and the contact surface70A is fixed in the apparatus height direction (i.e., the X direction).

Furthermore, as shown inFIG. 3, the heater70has a substrate72, a resistor74, and a protection layer76. The substrate72is formed of a rectangular plate that is long in the apparatus depth direction (i.e., the Z direction) and short in the apparatus height direction (i.e., the X direction). The substrate72is formed of, for example, an alumina molded body. The thickness of the substrate72in the apparatus width direction (i.e., the Y direction) is, for example, about 1 mm.

The resistor74is provided on a surface72A at the pressing roller40side of the substrate72. The opposite ends of the resistor74in the apparatus depth direction are provided with electrodes (not shown). The electrodes are connected to a power supply (not shown). Electricity is applied to the resistor74from the power supply, so that Joule heat occurs in accordance with an internal resistance of the resistor74, whereby the resistor74generates heat.

The protection layer76is provided on the surface72A of the substrate72and covers the resistor74. This protection layer76serves as the contact surface70A of the heater70. In the heater70, the sheet P is heated via the heating belt60by the heat generated by the resistor74.

The supporter80shown inFIG. 2has a function of supporting the heating belt60. Moreover, the supporter80has a function of supporting the heater70. In detail, the supporter80has a support frame82and a retaining member84.

The support frame82extends longitudinally in the apparatus depth direction (i.e., the Z direction). When viewed from the apparatus depth direction, the support frame82has a U shape in cross section that has an opening facing toward the pressing roller40. Furthermore, the opposite ends of the support frame82in the apparatus depth direction are supported by the device body50.

The retaining member84is, for example, a crystal polymer member extending longitudinally in the apparatus depth direction. Furthermore, the retaining member84is attached to a pressing-side section of the support frame82and retains the heater70.

As shown inFIG. 2, the heat pipe90is a single pipe provided on the non-contact surface70B of the heater70. As shown inFIG. 4, the heat pipe90extends in the longitudinal direction (i.e., the Z direction) of the heater70. Specifically, the axial direction of the heat pipe90is aligned with the longitudinal direction of the heater70. Moreover, the heat pipe90is disposed at the center of the heater70in the lateral direction (i.e., the X direction).

As shown inFIG. 5, the heat pipe90includes a pipe body96having an interior94and an outer peripheral surface95, and also includes wires97. InFIG. 2, the wires97are not shown.

The interior94of the heat pipe90is provided with a cross-sectionally-circular space93filled with a working fluid. The space93extends in the axial direction of the heat pipe90. The space93is filled with the working fluid in a state where the space93is decompressed.

The outer peripheral surface95of the heat pipe90includes a flat first outer surface91in contact with the non-contact surface70B of the heater70, and a second outer surface92having a cross-sectionally circular-arc shape extending along a part of a cross-sectionally-circular inner peripheral surface93A of the space93. In detail, the second outer surface92has a circular arc shape concentric with the inner peripheral surface93A. Moreover, the second outer surface92is not in contact with the non-contact surface70B of the heater70. More specifically, the second outer surface92is not in contact with other components in the fixing device30, and is exposed in a space surrounded by the support frame82of the supporter80(seeFIG. 2).

In this exemplary embodiment, the first outer surface91of the heat pipe90is formed by cutting a part of a cylindrical body190(seeFIG. 6). In detail, as shown inFIG. 6, in a cross-sectional view of the cylindrical body190(corresponding to the heat pipe90prior to being cut), as viewed from the axial direction thereof, the cylindrical body190is cut along a cutting line N3located between a tangent line N1and a tangent line N2and parallel to the tangent lines N1and N2, so that the heat pipe90having the first outer surface91is formed. The tangent line N1is tangent to an inner peripheral surface190A of the cylindrical body190. The tangent line N2is parallel to the tangent line N1and is tangent to an outer peripheral surface190B of the cylindrical body190.

As shown inFIG. 5, in the heat pipe90, a thickness S1at the first outer surface91is smaller than a thickness S2at the second outer surface92. The thicknesses S1and S2are thicknesses in the radial direction of the heat pipe90. Moreover, the heat pipe90has an outer radius ranging between, for example, 1 mm and 5 mm inclusive at the second outer surface92. The dimension at the first outer surface91in the lateral direction (i.e., the X direction) of the heater70is smaller than or equal to the outer radius.

Furthermore, as shown inFIG. 7, the heat pipe90has cylindrical axial ends. In detail, the heat pipe90has opposite axial ends90B that are cylindrical. In other words, the heat pipe90has a cross-sectionally-circular outer peripheral surface99at each of the opposite axial ends90B. More specifically, the aforementioned outer peripheral surface95is provided in a central part between the opposite axial ends90B in the axial direction. At each of the opposite axial ends90B, the heat pipe90has a gap98relative to the non-contact surface70B.

The opposite axial ends90B of the heat pipe90have an outer diameter smaller than that of the central part in the axial direction. Furthermore, for example, the opposite axial ends90B of the heat pipe90have an inner diameter that is the same as that of the central part in the axial direction. The opposite axial ends90B of the heat pipe90are closed by being crimped from the cylindrical state.

The wires97shown inFIG. 5are an example of a forming member. The wires97are disposed in the space93of the heat pipe90. The wires97are a bundle of multiple wires disposed in the space93and extending in the axial direction of the heat pipe90. Consequently, a capillary tube that moves the working fluid in the axial direction is formed. Accordingly, in this exemplary embodiment, a capillary structure (i.e., a so-called wick) is formed by the wires97.

In detail, the wires97are disposed at the non-contact surface70B side in the space93of the heat pipe90. In other words, the wires97are disposed along the inner peripheral surface93A of the heat pipe90at a position opposed to the first outer surface91. The wires97are retained by a retaining member (not shown) in a state where the wires97are in contact with the entire inner peripheral surface93A of the heat pipe90.

Due to the function of the working fluid enclosed in the interior94, the heat pipe90transfers heat in the belt width direction of the heating belt60. In detail, the heat of the heater70is transferred as follows. The working fluid is boiled by heat applied to the heat pipe90by a high temperature section of the heater70. Vapor of the working fluid generated as a result of the boiling moves to a low temperature section of the heater70in accordance with a pressure difference. The vapor condenses at the low temperature section, so that condensation heat is released to the heater70. Then, the condensed working fluid is returned to the original position (i.e., the high temperature section of the heater70) in accordance with a capillary phenomenon caused by the capillary tube formed by the wires97.

Operation According to Exemplary Embodiment

Next, the operation according to this exemplary embodiment will be described.

In the image forming apparatus according to this exemplary embodiment, the image forming unit16forms a toner image G onto a sheet P transported by the transport unit14. In the fixing device30, the toner image G formed on the sheet P by the image forming unit16is pressed by the pressing roller40and the heating belt60and is heated by the heater70, so as to become fixed onto the sheet P.

In this exemplary embodiment, when a temperature distribution occurs in the heater70, the heat pipe90transfers heat in the belt width direction of the heating belt60from the high temperature section to the low temperature section of the heater70in accordance with the function of the working fluid enclosed in the interior94.

A temperature distribution of the heater70occurs when, for example, an image is fixed onto a sheet P having a dimension smaller than that of the heater70in the belt width direction. In this case, the heat is surrendered to the sheet P in an area of the heater70in the belt width direction, so that a temperature distribution occurs in the heater70.

The heat pipe90has the interior94having the cross-sectionally-circular space93filled with the working fluid, and also has the flat first outer surface91in contact with the non-contact surface70B of the heater70.

In a configuration that uses a rectangular heat pipe (referred to as “first configuration” hereinafter), the internal space of the heat pipe is rectangular in cross section, so that pressure occurring from expansion of the working fluid acts lopsidedly on a part of the heat pipe, sometimes causing the heat pipe to break.

In contrast, in the heat pipe90, the space93in the interior94of the heat pipe90is circular in cross section, so that pressure occurring from expansion of the working fluid may vary less in the circumferential direction, as compared with the first configuration. Therefore, the heat pipe90may have improved durability against expansion of the working fluid, as compared with the first configuration.

In a configuration that uses a cylindrical heat pipe (referred to as “second configuration” hereinafter), the outer peripheral surface of the heat pipe is circular in cross section, so that the contact area with the heater70tends to be small.

In contrast, in the heat pipe90, the flat first outer surface91is in contact with the non-contact surface70B of the heater70, so that a sufficient contact area with the non-contact surface70B of the heater70may be ensured. As a result, heat is efficiently transferred from the high temperature section to the low temperature section of the heater70, so that temperature variations in the belt width direction of the heating belt60may be reduced. Accordingly, fixation variations in the fixing device30may be suppressed.

Furthermore, in the heat pipe90, the second outer surface92has a cross-sectionally circular-arc shape extending along a part of the cross-sectionally-circular inner peripheral surface93A of the space93. Therefore, the thickness between the second outer surface92and the inner peripheral surface93A may vary less than in a configuration where the second outer surface92is polygonal in cross section. More specifically, the second outer surface92has a circular-arc shape that is concentric with the inner peripheral surface93A. Therefore, the thickness between the second outer surface92and the inner peripheral surface93A may vary less than in a configuration where the center of the inner peripheral surface93A and the center of the second outer surface92are not aligned with each other.

Furthermore, in this exemplary embodiment, the first outer surface91of the heat pipe90is formed by cutting a part of a cylinder. In a configuration where a first outer surface is formed by pressing on a part of the outer periphery of a cylindrical heat pipe (referred to as “third configuration” hereinafter), the heat pipe may sometimes recover its cylindrical shape due to expansion pressure of the working fluid.

In contrast, in the heat pipe90according to this exemplary embodiment, the first outer surface91is formed by cutting a part of a cylinder, so that deformation of the heat pipe90into a cylindrical shape due to expansion pressure of the working fluid may be suppressed, as compared with the third configuration.

Furthermore, in the heat pipe90according to this exemplary embodiment, the thickness S1at the first outer surface91is smaller than the thickness S2at the second outer surface92. Therefore, as compared with a configuration where the thickness S1at the first outer surface91is equal to the thickness S2at the second outer surface92, heat is efficiently transferred from the high temperature section to the low temperature section of the heater70, so that temperature variations in the belt width direction of the heating belt60may be reduced.

Furthermore, in this exemplary embodiment, the heat pipe90has the gap98relative to the non-contact surface70B of the heater70at each of the opposite axial ends90B. Therefore, the working fluid may less likely to expand at the opposite axial ends90B of the heat pipe90, as compared with a configuration where the opposite axial ends90B of the heat pipe90are in contact with the non-contact surface70B of the heater70. Accordingly, an increase in internal pressure may be suppressed at the opposite axial ends90B of the heat pipe90, whereby damage to the opposite axial ends90B may be suppressed.

Furthermore, in this exemplary embodiment, the opposite axial ends90B of the heat pipe90are cylindrical, as shown inFIG. 7. Therefore, even if the opposite axial ends90B come into contact with the non-contact surface70B of the heater70due to, for example, vibrations, the contact area between the opposite axial ends90B and the non-contact surface70B may be reduced, as compared with a configuration where the non-contact surface70B side of each of the opposite axial ends90B of the heat pipe90is flat.

In the heat pipe90according to this exemplary embodiment, the wires97are disposed at the non-contact surface70B side in the space93of the heat pipe90, as shown inFIG. 5. Therefore, heat is efficiently transferred from the high temperature section to the low temperature section of the heater70, so that temperature variations in the belt width direction of the heating belt60may be reduced, as compared with a configuration where the wires97are disposed opposite the non-contact surface70B side in the space93.

Modifications

As an alternative to this exemplary embodiment in which the wires97are used as an example of a forming member, for example, a mesh member may be used as an example of a forming member, so long as the member forms a capillary tube.

As an alternative to this exemplary embodiment in which a single heat pipe90is provided in the heater70, multiple heat pipes90may be provided in the heater70.

As an alternative to this exemplary embodiment in which the second outer surface92of the heat pipe90has a cross-sectionally circular-arc shape extending along a part of the cross-sectionally-circular inner peripheral surface93A of the space93, for example, the second outer surface92may be elliptical or polygonal in a cross-sectional view from the axial direction. Moreover, for example, the second outer surface92may be partially flat.

Furthermore, as an alternative to this exemplary embodiment in which the second outer surface92has a circular-arc shape that is concentric with the inner peripheral surface93A, for example, the center of the inner peripheral surface93A and the center of the second outer surface92may be offset from each other.

As an alternative to this exemplary embodiment in which the first outer surface91of the heat pipe90is formed by cutting a part of a cylinder, for example, the first outer surface91may be formed by pressing on a part of the outer periphery of a cylindrical heat pipe.

As an alternative to this exemplary embodiment in which the thickness S1at the first outer surface91of the heat pipe90is smaller than the thickness S2at the second outer surface92of the heat pipe90, for example, the thickness S1at the first outer surface91may be equal to the thickness S2at the second outer surface92.

As an alternative to this exemplary embodiment in which the heat pipe90has the gap98relative to the non-contact surface70B of the heater70at each of the opposite axial ends90B, for example, the opposite axial ends90B of the heat pipe90may be in contact with the non-contact surface70B of the heater70.

As an alternative to this exemplary embodiment in which the heat pipe90is cylindrical at the opposite axial ends90B, as shown inFIG. 7, for example, the non-contact surface70B side of each of the opposite axial ends90B of the heat pipe90may be flat.

The present disclosure is not limited to the above-described exemplary embodiment and permits various modifications, alterations, and improvements within the scope of the disclosure. For example, multiple modifications of the modifications described above may be combined, where appropriate.