Heating device, image processing apparatus, and method for manufacturing the heating unit

A heating device includes a cylindrical film, a heater arranged inside the cylindrical film and extending along a longitudinal direction of the cylindrical film, a heat conductor extending along the longitudinal direction, and a first grease layer between the heater and the heat conductor and having a consistency grade less than or equal to three.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-159387, filed on Sep. 2, 2019, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a heating device, an image processing apparatus, and a method for manufacturing the heating device.

BACKGROUND

An image forming apparatus for forming an image on a sheet has a fixing unit that heats the sheet to fix toner to the sheet. The fixing unit includes a rotatable cylindrical drum and a heating unit that abuts the inner surface of the cylindrical drum. In such a fixing unit, it is required to reduce deteriorations which might increase sliding friction between the heating unit and the cylindrical drum.

DETAILED DESCRIPTION

One or more embodiments provide a heating device, an image processing apparatus, and a manufacturing method of a heating unit.

A heating device according to an embodiment includes a cylindrical film configured to be rotated about an axis. The heating device includes a heater having a first side facing an inner surface of the cylindrical film. The heater extending along a longitudinal direction parallel to the axis. A heat conductor is on a second side of the heater opposite the first side. The heat conductor extends along the longitudinal direction. A first grease layer is between the heat conductor and the second side of the heater and has a consistency grade less than or equal to three

A heating unit, an image processing apparatus, and a heating unit according to embodiments will now be described with reference to the drawings.

FIG. 1is a schematic diagram of an image processing apparatus1according to an embodiment. For example, the image processing apparatus1is an image forming apparatus such as a multifunction printer (MFP). The image processing apparatus1is configured to form an image on a sheet of paper S. The image processing apparatus1includes a housing10, a scanner unit2, an image forming unit3, a sheet supply unit4, a conveyance unit5, a sheet discharge tray7, an inversion unit9, a control panel8, and a control unit or a controller6.

The housing10houses each component of the image processing apparatus1.

The scanner unit2reads an image formed on a sheet as light and dark signals and generate an image signal of the image. The scanner unit2outputs the generated image signal to the image forming unit3.

The image forming unit3forms an output image (such as a toner image) by using a recording agent (such as toner) according to the image signal received from the scanner unit2or an image signal received from another apparatus via a network. The image forming unit3transfers the output image onto the surface of the sheet S. When the output image is a toner image, the image forming unit3then heats and presses the toner image against the surface of the sheet S to fix the toner image to the sheet S.

The sheet supply unit4supplies sheets S one by one to the conveying unit5at a time synchronized with the timing at which the image forming unit3forms the toner image. The sheet supply unit4includes a sheet storage unit20and a pickup roller21.

The sheet storage unit20stores a sheet S having a particular size and type.

The pickup roller21takes out the sheets S one by one from the sheet storage unit20. The pickup roller21supplies the taken-out sheet S to the conveying unit5.

The conveying unit5conveys the sheet S from the sheet supply unit4to the image forming unit3. The conveying unit5includes a pressing roller23and registration rollers24.

The conveying roller23conveys the sheet S from the pickup roller21to the registration rollers24. The conveying roller23presses the leading end of the sheet S against a nip N formed by the registration rollers24.

The registration rollers24adjust the sheet S position at the nip N to adjust the position of the leading end of the sheet S along the conveying direction. The registration rollers24then convey the sheet S along the conveying direction in accordance with the timing at which the image forming unit3transfers the toner image to the sheet S.

The image forming unit3includes a plurality of image forming units25, a laser scanning unit26, an intermediate transfer belt27, a transfer unit28, and a heating unit30.

Each of the image forming units25includes a photosensitive drum25d. Each image forming unit25forms a toner image corresponding to the image signal received from the scanner unit2or another apparatus on the corresponding photosensitive drum25d. The image forming units25Y,25M,25C and25K form toner images of yellow, magenta, cyan and black toners, respectively.

A charging device, a developing device, and the like are disposed around each photosensitive drum25d. The charging device electrostatically charges the surface of the corresponding photosensitive drum25d. Each developing device contains developer including one of yellow, magenta, cyan and black toners. The developing device develops an electrostatic latent image formed on the photosensitive drum25d. As a result, a toner image is formed on each photosensitive drum25dby the corresponding color of toner.

The laser scanning unit26scans each charged photosensitive drum25dwith a laser beam L to selectively expose the photosensitive drum25daccording to image data to be printed. The laser scanning unit26exposes the photosensitive drum25dof each of the image forming units25Y,25M,25C and25K with the corresponding laser beam LY, LM, LC and LK. In this manner, the laser scanning unit26forms the electrostatic latent image on each photosensitive drum25d.

The toner image formed on the surface of each photosensitive drum25dis first transferred (primary transfer) to the intermediate transfer belt27.

The transfer unit28next transfers the toner image on the intermediate transfer belt27onto the surface of the sheet S at a secondary transfer position.

The heating unit30heats the toner image that has been transferred to the sheet S to fix the toner image on the sheet S.

The inversion unit9inverts the sheet S in order to form an image on the back surface of the sheet S. The inversion unit9reverses the sheet S after the sheet S has passed the heating unit30by a switch-back or the like. The inversion unit9conveys the inverted sheet S back to the registration rollers24by a switch-back route or path.

The sheet discharge tray7holds the printed sheets S after discharge from the heating unit30.

The control panel8is an input unit for an operator to input information to operate the image processing apparatus1. The control panel8includes a touch panel and various hardware keys.

The control unit6controls each unit of the image processing apparatus1.

FIG. 2is a hardware block diagram of the image processing apparatus1. The image processing apparatus1includes the scanner unit2, the image forming unit3, the sheet supply unit4, the conveyance unit5, the inversion unit9, the control panel8, the control unit6, an auxiliary storage device93, and a communication unit90. Those components are connected by a bus. The control unit6includes a CPU (Central Processing Unit)91and a memory92, and is configured to execute a program or programs to control each unit of the image processing apparatus1.

The CPU91executes programs stored in the auxiliary storage device93and loaded onto the memory92. The CPU91controls the operation of each unit of the image processing apparatus1.

The auxiliary storage device93is a storage device such as a magnetic hard disk device (HDD) or a semiconductor storage device (SSD). The auxiliary storage device93stores programs to be executed by the CPU91and information required or generated by the programs.

The communication unit90is a network interface for communicating with an external apparatus via a network.

FIG. 3is a cross-sectional view of the heating unit30according to an embodiment. For example, the heating unit30is a fixing unit. The heating unit30includes a pressing roller30pand a heated roller30h. The heated roller30hmay be referred to in some contexts as a heating drum, fixing belt, or a film unit.

The pressing roller30pforms a nip N with the heated roller30h. The pressing roller30ppresses the toner image formed on the sheet S that has entered the nip N. The pressing roller30protates to convey the sheet S. The pressing roller30pincludes a core metal32, an elastic layer33, and a release layer (not separately depicted).

The core metal32is formed in a columnar shape by a metal material such as stainless steel. Both end portions in the axial direction of the core metal32are rotatably supported. The core metal32is driven to rotate by a motor or the like. The core metal32comes into contact with a cam member or the like. The cam member can be rotated to move the core metal32toward and away from the heated roller30h.

The elastic layer33is formed of an elastic material such as silicone rubber. The elastic layer33has a constant thickness on the outer peripheral surface of the core metal32.

The release layer is formed of a resin material such as PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer). The release layer is formed on the outer peripheral surface of the elastic layer33.

For example, the hardness of the outer peripheral surface of pressing roller30pis 40°-70° at a load of 9.8 N by an ASKER-C hardness meter. Thus, the area of the nip N and the durability of the pressing roller30pare secured.

The pressing roller30pis able to move toward and away from the heated roller30hby rotation of the cam member. The pressing roller30pis moved toward the heated roller30hand presses it with a pressing spring to form a nip N. On the other hand, when the sheet S is jammed in the heating unit30, the pressing roller30pcan be separated from the heated roller30h, whereby the jammed sheet S can be removed. Further, during sleep or an idle state, rotation of the cylindrical film35is stopped and the pressing roller30pis moved away from the heated roller30h, thereby preventing unnecessary plastic deformation of the cylindrical film35.

The pressing roller30pis rotated by a motor. When the pressing roller30protates while the nip N is formed, the cylindrical film35of the heated roller30his driven to rotate. The pressing roller30protates to convey the sheet S in the conveying direction W through the nip N.

The heated roller30hheats the toner image on the sheet S in the nip N. The heated roller30hincludes a cylindrical film35, a heater40, a heat conductor49, a support member36, a stay38, a heater temperature sensor62, a thermostat68, and a film temperature sensor64.

The cylindrical film35has a cylindrical shape. The cylindrical film35includes a base layer, an elastic layer, and a release layer in this order from the inner peripheral side thereof. The base layer is a material such as nickel (Ni) or the like. The elastic layer is laminated on the outer peripheral surface of the base layer. The elastic layer is formed of an elastic material such as silicone rubber. The release layer is applied on the outer peripheral surface of the elastic layer. The release layer is formed of a material such as a PFA resin.

FIG. 4is a cross-sectional view of the heating unit30taken along the IV-IV line ofFIG. 5.FIG. 5is a bottom view of the heating unit when viewed from the +z direction. The heater40includes a substrate41, a heating element group45, and a ring set55.

The substrate41is made of a metal material such as stainless steel or a ceramic material such as aluminum nitride. The substrate41has a long rectangular plate shape. The substrate41is arranged inside the cylindrical film35. The longitudinal direction of the substrate41is parallel to the axis of the cylindrical film35.

In the present disclosure, the x direction, the y direction, and the z direction are defined as follows. The y direction is parallel to the longitudinal direction of the substrate41. The +y direction is a direction from a central heating element45atoward a first end heating element45b1. The x direction is parallel to the lateral direction of the substrate41. The +x direction corresponds to the transport direction of the sheet S during printing operations. The z direction is a normal direction of the substrate41. The +z direction is the direction from the substrate41to the heating element group45. The insulating layer43is formed on the surface of the substrate41on the +z direction side by a glass material or the like.

As shown inFIG. 5, the heating element group45is disposed above the substrate41. The heating element group45is formed of a silver-palladium alloy or the like. The heating element group45has a rectangular shape in which the long side extends along the y direction and the short side extends along the x direction. The center45cin the x direction of the heating element group45is offset to the −x direction from the center41cof the substrate41(the heater unit40).

The heating element group45includes a first end heating element45b1, a central heating element45a, and a second end heating element45b2arranged side by side along the y direction. The central heating element45ais disposed in the center portion of the heating element group45in the y direction. The first end heating element45b1is located at the end of the heating element group45in the +y direction adjacent to the central heating element45a. The second end heating element45b2is arranged adjacent to the central heating element45ain the −y direction and at the end of heating element group45in the −y direction.

The heating element group45generates heat when energized. A sheet S having only a small width in the y direction can be positioned to pass through the center portion of the heating unit30. In such a case, the control unit6causes only the central heating element45ato generate heat. On the other hand, when a sheet S has a large width in the y direction, the control unit6causes the entire heating element group45to be energized. The central heating element45aand the first and second end heating elements45b1and45b2can be independently controlled in heat generation. Also, the first end heating element45b1and the second end heating element45b2can be similarly controlled to one another during heat generation.

As shown inFIG. 4, the heating element group45and the ring set55are formed on the surface of the insulating layer43on the +z direction side. A protective layer46is formed of a glass material or the like so as to cover the heating element group45and the ring set55. The protective layer46improves the sliding property (reduces friction) between the heater40and the cylindrical film35.

Similarly to the insulating layer43formed on the substrate41on the +z direction side, an insulating layer may be formed on the substrate41on the −z direction side. Similarly to the protective layer46formed on the substrate41on the +z direction side, a protective layer may be formed above the substrate41on the −z direction side. Thus, the warpage of the substrate41is suppressed.

As shown inFIG. 3, the heater40is disposed inside the cylindrical film35. That is, the heater40is disposed inside a region surrounded by the cylindrical film35. A straight line CL connecting the center pc of the pressure roller30pand the center hc of the heating drum30his depicted inFIG. 3. The center41cin the x direction of the substrate41is shifted in the +x direction from the straight line CL. The center45cof the heating element group45in the x direction is disposed on the straight line CL. The heating element group45is entirely included within the region of the nip N, and is disposed at the center of the nip N. Thus, the heat distribution of the nip N becomes more uniform, and a sheet S passing through the nip N will be more uniformly heated.

The heat conductor49is formed of a metal material having high thermal conductivity, such as copper. The outer shape (planar shape when viewed from the z direction) of the heat conductor49is matches the outer shape (planar shape when viewed from the z direction) of the substrate41of the heater40. The heat conductor49is disposed in contact with at least a part of the second surface40bon the −z direction side of the heater40.

The support member36is made of a resin material such as a liquid crystal polymer. The support member36is disposed so as to cover the surface on the −z direction side of the heater40and the both sides in the x direction. The support member36supports the heater40via the heat conductor49. Both end portions in the x direction of the support member36are curved to support the inner peripheral surface of the cylindrical film35at both end portions in the x direction of the heater40.

When a sheet S passing through the heating unit30is heated, a temperature distribution is generated across the heater40in accordance with the size of the sheet S. The local temperature of parts of the heater40may become a locally high temperature, such temperatures may exceed the upper-temperature limit of the support member36formed of resin material. The heat conductor49functions to average or smooth the local temperature distribution of the heater40. Thus, the support member36can be prevented from being overheated locally.

The stay38is formed of a steel sheet material or the like. A cross section of the stay38perpendicular to the y direction has a U shape. The stay38is mounted on the support member36on the −z direction side so as to cover the opening of the U shape along with the support member36. The stay38extends along the y direction. Both end portions in the y direction of the stay38are fixed to the housing of the image processing apparatus1. As a result, the heating drum30his supported by the image processing apparatus1. The stay38improves the rigidity of the heated roller30h. A flange for restricting the movement of the cylindrical film35in the y direction is provided in the vicinity of both end portions in the y direction of the stay38.

The heater temperature sensor62is disposed on the heat conductor49. The heater temperature sensor62is mounted on a surface of the support member36on the −z direction side. The heater temperature sensor62contacts the heat conductor49through a hole through the support member36in the z direction. The heater temperature sensor62measures the temperature of the heater40via the heat conductor49.

The thermostat68is arranged similarly to the heater temperature sensor62. The thermostat68interrupts the energization to the heating element group45when the temperature of the heater40detected through the heat conductor49exceeds a predetermined temperature.

The film temperature sensor64is disposed inside the cylindrical film35and adjacent to the support member36in the +x direction. The film temperature sensor64is brought into contact with the inner peripheral surface of the cylindrical film35to measure the temperature of the cylindrical film35.

The grease applied to the heating unit30will now be described.FIG. 6is an enlarged view of the heating unit30. The heating unit30includes a first grease layer49gand a second grease layer35g. The second grease layer35gcovers the entire inner surface of the cylindrical film35. The first surface40aon the +z direction side of the heater comes into contact with the inner surface of the cylindrical film35via the second grease layer35g. When the heater40generates heat, the viscosity of the second grease layer35gdecreases. Thus, the sliding between the heater40and the cylindrical film35is improved (friction is reduced).

The second grease layer35gincludes fluoro-grease comprising a fluorinated oil as a base oil. The fluoro-grease has high heat resistance, low viscosity, and long life (good stability). The second grease layer35gcontains, for example, PTFE (polytetrafluoroethylene) as a thickening agent. The consistency grade of the second grease layer35gis two or less, which corresponds to 265 ( 1/10 mm) or more in working penetration as measured by a test method specified in Japanese Industrial Standard (JIS) K2220:2013. For example, the consistency grade of the second grease layer35gis zero or less, which corresponds to 355 ( 1/10 mm) or more in the working penetration.

In general, in order to improve heat transfer between adjacent objects, a high thermal conductivity grease can be applied between the objects. The high thermal conductivity grease typically includes: thermally conductive filler material such as silicon, carbon, aluminum or zinc. The thermal conductivity of the high thermal conductivity grease is on the order of 5.0 W/m·K on average, and can be about 10.0 W/m·K at maximum. The thermally conductive filler material typically has a large particle diameter and a high hardness. When a thermally conductive filler is on a sliding surface (friction surface), abrasion of the sliding surface proceeds rapidly, and properties of the sliding surface are ultimately worsened. For such a reason, unlike a thermally conductive grease, the second grease layer35gdoes not include a thermally conductive filler material. The thermal conductivity of the second grease layer35gis, as a result, equal to or less than 1.0 W/m·K.

The first grease layer49gis disposed between the heater40and the heat conductor49. The second surface40bon the −z direction side of the heater40comes into contact with the heat conductor49via the first grease layer49g. Various irregularities are present at the contacting surfaces of the heater40and the heat conductor49. In particular, when a glass layer is formed on the second surface40bof the heating unit30, a large unevenness is typically present on the surface of the glass layer. When the first grease layer49gcovers and fills the concave and convex portions of the surface, the heat conductivity between the heater40and the heat conductor49is improved.

However, the first grease49gis not a high thermal conductivity grease and does not contain a thermally conductive filler. The thermal conductivity of the first grease layer49gis equal to or less than 1.0 W/m·K. For example, the thermal conductivity of the first grease layer49gis about 0.01 W/m·K. As described above, a high thermal conductivity grease improves heat conductivity between adjacent objects. In order to prevent the high thermal conductivity grease from flowing out from between the objects to which it is applied, the high thermal conductivity grease is generally fairly viscous even at high temperatures. The consistency grade of the high thermal conductivity grease is four or more, which corresponds to 205 ( 1/10 mm) or less in the working penetration.

The first grease layer49gincludes fluoro-grease comprising a fluorinated oil as a base oil. The first grease layer49gcontains PTFE (polytetrafluoroethylene) as a thickening agent. The consistency grade of the first grease layer49gis three or less, which corresponds to 220 ( 1/10 mm) or more in the working penetration. By adjusting the blending ratio of the base oil and the thickener, the consistency of the first grease layer49gcan be adjusted.

For example, the first grease layer49gcan be the same as the second grease layer35g. In such a case, the consistency grade of the first grease layer49gis not more than two, preferably not more than zero. The first grease49galso does not include a thermally conductive filler. The thermal conductivity of the first grease layer49gis equal to or less than 1.0 W/m·K. Since the same type of grease can be used for the first grease layer49gand the second grease layer35g, the manufacturing cost is reduced.

When the heater40generates heat, the viscosity of the first grease layer49gdecreases. Accordingly, a part of the first grease layer49gmay flow out from the second surface40bside of the heater40and reach the first surface40a. The consistency grade of the first grease layer49gis three or less and is approximately the same as that of the second grease layer35g. Since the first grease layer49gdoes not include a thermally conductive filler, potential abrasion of the sliding surface by such a thermally conductive filler can be avoided.

Table 1 is a comparative table of characteristics of a high thermal conductivity grease as a comparative example and a fluoro-grease according the example embodiments described above. Table 1 shows measurement results relating to various performance parameters when these different grease types are utilized as to the first grease layer49gin an image processing apparatus.

The “Return Time” column in Table 1 includes values indicating how long the heater40took to change from room temperature to the fixing temperature for. The measured return time for the comparative example is 9.9 seconds, whereas the measured return time for the example embodiments is 9.6 seconds. For the embodiments, it is considered that the heat from the heater40is less transmitted to the heat conductor49(via the fluoro-grease) than in the comparative example (using the high thermal conductivity grease), so that the return time is shortened.

The “Average Power” column group in Table 1 provides values for power consumption calculated from the on-off ratio of the heating element group45during the relevant time period. For the column “In WU (warm-up)” in Table 1, the value represents the average power utilized by the heater in a return to the fixing temperature from room temperature. In the experiments presented in Table 1, for both “In WU” and “In Printing,” time periods, the entire heat generating element group45is energized (that is, the center heat generating element45a, the first end heat generating element45b1, and the second end heat generating element45b2are each turned on to generate heat). The columns labeled “Whole” in Table 1 indicates the total power consumption for the entire heating element group45. The column labeled “central portion” in Table 1 indicates the power consumption of just the central heating element45afrom among the heating element group45. The “End Portion” column in Table 1 indicates the power consumption of the first end heating element45b1and second end the heating element45b2from among heating element group45.

In general, there is little difference between the comparative example and the embodiments in the measured average power utilized for heating.

The “Heater End Temperature” column group in Table 1 records the maximum temperature of the second surface40bof the heater40in a non-paper passing region (such as a region beyond the sheet S passing region of the heater40in the y direction) of the heating unit30. The “Front Side” column in Table 1 provides measured temperature values of the front side (one side in the y direction) of the image processing apparatus1. The “Rear side” column provides measured temperatures of the rear side (the other side in the y direction opposite the front side) of the image processing apparatus1. The reason why there is a temperature difference between the front side and the rear side is that the center of the passing sheet S in the y direction is shifted with respect to the center in the y direction of the heating unit30.

Since the non-sheet-passing area of the heating unit30is not cooled by the passing sheet S, this area tends to reach a high temperature. In comparison with the comparative example, since the thermal conductivity of the first grease layer49gis small, heat is less well transferred from the heater40to the heat conductor49. Therefore, in the embodiments, as compared to the comparative example, the second surface40bof the heater40in the non-sheet-passing region tends to become a higher temperature. However, in the results shown in Table 1, the temperature difference between the front side and the rear side is small in comparison with the comparative example. Since the spacing distance between the heater40and the heat conductor49is small, even when the first grease layer49gof the embodiments has low thermal conductivity, heat transfer is not greatly inhibited.

A method of manufacturing the heating unit30will now be described.

The second grease layer35gis applied to the entire inner surface of the cylindrical film35. Thereafter, the heater40is inserted inside the cylindrical film35. Thus, the second grease layer35gcan always be interposed between the rotating cylindrical film35and the heater40.

The first grease layer49gis disposed between the heater40and the heat conductor49. That is, the first grease layer49gis applied to either one or both of the second surface40bof the heater40and the first surface49aof the heat conductor49before these elements are brought together. Subsequently, the heat conductor49is disposed on the second surface40bof the heater40. As a result, the first grease layer49gis disposed between the heater40and the heat conductor49. Therefore, heat transfer between the heater40and the heat conductor49is improved by the presence of the first grease layer49g.

When the first grease layer49gand the second grease layer35gare formed of the same material, the following manufacturing method may be adopted. The first grease layer49gis not disposed between the heater40and the heat conductor49in advance. The heat conductor49is then arranged on the second surface40bof the heater40. Next, the heating element group45is caused to generate heat. For example, the heating element group45is heated by the heating device30. Accordingly, the viscosity of the second grease layer35gapplied to the inner surface of the cylindrical film35is reduced, so that the second grease layer35gcan flow into the gap between the second surface40band the heat conductor49. That is, the second grease layer35gflows from the first surface40aof the heater40to the second surface40b, and enters between the heater40and the heat conductor49. Thus, the second grease layer35gthat flows to the second surface40bfrom the first surface40acan function as the first grease layer49g.

In this manufacturing method, the first grease layer49gis not required to be applied between the heater40and the heat conductor49in advance. Therefore, the manufacturing process can be simplified and the manufacturing cost reduced.

As described above, the heating unit30of the embodiments includes the cylindrical film35, the heating element group45, the heater40, the heat conductor49, and the first grease layer49g. The heating element group45is located inside the cylindrical film35. The heater40has the heating element group45. The heater40has a longitudinal direction in the y direction. The heater40is in contact with the inner surface of the cylindrical film35on the first surface40a. The heat conductor49is disposed on the second surface40bopposite to the first surface40aof the heater40. The heat conductor49extends in the y direction along the heater40. The first grease layer49gis disposed between the heater40and the heat conductor49. The first grease layer49ghas a consistency grade of no more than three.

When the heater40generates heat, the viscosity of the first grease layer49gdecreases. Accordingly, a part of the first grease layer49gmay flow out from between the heater40and the heat conductor49, and may reach into the sliding surface between the heater40and the cylindrical film35. However, since the first grease layer49ghas a consistency grade of no more than three, it is possible to suppress any deterioration in the slidability between the heater40and the cylindrical film35.

The first grease layer49gdoes not include thermally conductive filler. The first grease layer49ghas a thermal conductivity of 1.0 W/m·K or less.

As described above, the first grease layer49gmay enter the sliding surface between the heater40and the cylindrical film35. However, since the first grease layer49gdoes not include a thermally conductive filler, the potential abrasion of the sliding surface by a thermally conductive filler is avoided. Therefore, it is possible to avoid sliding friction increases between the heater40and the cylindrical film35.

While the first grease layer49ghas a thermal conductivity of 1.0 W/m·K or less, the gap left between the heater40and the heat conductor49is relatively small, so that heat will still be able to be sufficiently transferred between these elements via the first grease layer49g. Since the temperature distribution across the length heater40is still averaged by the presence of heat conductor49, the temporary suspension of the printing or other operations of the image processing apparatus1to permit cooling of the heater40can suppressed. Therefore, a decrease in productivity of the user of the image processing apparatus1is suppressed. Heat can still be transferred from the end of the heater40in the y-direction to the center through the heat conductor49. Since the heat generation amount of the central heat generating element45acan be suppressed in this manner, an increase in power consumption of the heating unit30is suppressed.

The first grease layer49gcan be formed of the same material as the second grease disposed on the inner surface of the cylindrical film35. Accordingly, the manufacturing cost is reduced.

In some embodiments, the image processing apparatus1may be a decoloring apparatus, and the heating unit may be a decoloring unit. The decoloring apparatus is configured to decolor or erase an image formed on a sheet by a decolorable toner. The decoloring unit heats the decoloring toner image formed on the sheet passing through the nip to decolorize the toner image.

According to at least one embodiment described above, the heating unit30has the first grease layer49gdisposed between the heater40and the heat conductor49. The first grease layer49ghas a consistency grade of no more than three. As a result, it is possible to suppress a decrease in sliding performance between the heater40and the cylindrical film35.