Heating device and image processing apparatus including heat transfer member contacting a heater in amounts varying with position along the heater

A heating device includes a cylindrical film a heater disposed inside the cylindrical film on an inner surface of the cylindrical film. The heater has a plurality of heating elements on a first surface that are spaced from each other at intervals along an axial direction. A heat transfer member contacts a second surface of the heater. The heat transfer member is arranged such that, in a first region of the heater that includes just a single one of the heating elements, contact between the heater and heat transfer member is greater than in a second region of the heater that includes an interval between a pair of adjacent heating elements.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-131666, filed on Aug. 3, 2020, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a heating device and an image processing apparatus.

BACKGROUND

One type of image processing apparatus is an image forming apparatus that prints an image on a sheet. One type of image forming apparatus includes a heating device to heat toner or another recording agent. The heating serves to fix or fuse the toner or other recording agent to a sheet. However, an uneven temperature distribution produced by such a heating device may cause uneven gloss on the image printed on the sheet.

DETAILED DESCRIPTION

At least one embodiment provides a heating device and an image processing apparatus capable of suppressing unevenness in a temperature distribution of a heating device used in printing of images on sheets and the like.

In general, according to one embodiment, a heating device includes a cylindrical film. A heater is disposed inside a region surrounded by the cylindrical film and contacts an inner surface of the cylindrical film. The heater has a plurality of heating elements on a first surface. The heating elements are spaced from each other at intervals along the axial direction of the cylindrical film. A heat transfer member contacts a second surface of the heater. The second surface of the heater is opposite the first surface. In a cross section orthogonal to the axial direction through a first region of the heater including just a single one of the heating elements, the heat transfer member contacts the second surface for a first length in a direction perpendicular to the axial direction. In a cross section orthogonal to the axial direction through a second region of the heater including an interval between a pair of adjacent heating elements, the heat transfer member contacts the second surface for a second length in the direction perpendicular to the axial direction. The second length is less than the first length.

Hereinafter, certain example embodiments of a heating device and an image processing apparatus incorporating a heating device will be described with reference to the drawings. In the following description, the same reference numerals are given to configurations having the same or similar functions. The descriptions of those configurations or aspects shared in the different embodiments or examples may be omitted after a first description of such configurations or aspects in the context of another embodiment or example.

FIG.1is a schematic configuration diagram for an image processing apparatus.

As shown inFIG.1, the image processing apparatus is an image forming apparatus1. The image forming apparatus1performs the processing for forming an image on a sheet S, which may be a sheet of paper or the like. The image forming apparatus1includes a housing10, a scanner unit2, an image forming unit3, a sheet feed unit4, a conveyance unit5, a sheet discharge tray7, a reversing unit9, a control panel8, and a control unit6.

The housing10forms the outer shape of the image forming apparatus1.

The scanner unit2reads image information from an object to be copied based on the reflected brightness and darkness of light from the object and generates an image signal accordingly. The scanner unit2outputs the generated image signal to the image forming unit3.

The image forming unit3forms an image with a recording agent such as toner based on the image signal received from the scanner unit2or an image signal received from an external device. The image forming unit3of the present example forms images with toner as the recording agent and the image formed by the image forming unit3is thus referred to as a toner image in this context. The image forming unit3transfers the toner image onto the surface of the sheet S. The image forming unit3heats and presses the toner image on the sheet S to fix the toner image to the sheet S.

The sheet feed unit4supplies the sheets S one by one to the conveyance unit5at a timing coordinated with the timing at which the image forming unit3forms the toner image. The sheet feed unit4includes a sheet storage unit20and a pickup roller21.

The sheet storage unit20stores sheets S of a predetermined size and type.

The pickup roller21picks up the sheets S one by one from the sheet storage unit20. The pickup roller21supplies the sheet S to the conveyance unit5.

The conveyance unit5conveys the sheet S from the sheet feed unit4to the image forming unit3. The conveyance unit5includes conveyance rollers23and registration rollers24.

The conveyance rollers23convey the sheet S from the pickup roller21to the registration rollers24. The conveyance rollers23abut the leading end of the sheet S against a nip N1formed by the registration rollers24.

The registration rollers24bend or hold the sheet S at the nip N1to adjust the position of the leading end of the sheet S along the conveyance direction. The registration rollers24convey the sheet S according to a timing at which the image forming unit3can appropriately transfer the toner image to the sheet S.

The image forming unit3includes a plurality of image forming units25. The image forming unit3also includes a laser scanning unit26, an intermediate transfer belt27, a transfer unit28, and a fixing device30.

Each image forming unit25includes a photoconductor drum29. The image forming unit25forms a toner image corresponding to the image signal (received from the scanner unit2or another device) on the photoconductor drum29. The image forming units25in this example form toner images with yellow, magenta, cyan, and black toners, respectively.

An electrostatic charger, a developing device, and the like are arranged around the photoconductor drum29. The electrostatic charger electrostatically charges the surface of the photoconductor drum29. The developing device stores a developer containing yellow, magenta, cyan, or black toner. The developing device develops an electrostatic latent image on the photoconductor drum29by supplying toner. As a result, a toner image of one color is formed on the photoconductor drum29.

The laser scanning unit26scans the electrostatically charged surface of the photoconductor drum29with a laser beam L to selectively expose the photoconductor drum29. The laser scanning unit26exposes a photoconductor drum29of an image forming unit25with one of the respectively different laser beams LY, LM, LC, and LK. As a result, the laser scanning unit26forms an electrostatic latent image on each photoconductor drum29.

The toner image on the surface of the photoconductor drum29is then transferred to the intermediate transfer belt27. This transfer is referred to as a primary transfer.

The transfer unit28then transfers the toner image from the intermediate transfer belt27onto the surface of the sheet S at a secondary transfer position.

The fixing device30heats and presses the toner image that has been transferred to the sheet S to fix the toner image on the sheet S.

The reversing unit9can operate to reverse the sheet S to permit an image to be formed on the back surface of the sheet S. The reversing unit9inverts a sheet S discharged from the fixing device30by switchback. The reversing unit9conveys the reversed sheet S back towards the registration rollers24for another printing.

A sheet S on which an image has been formed can be discharged onto the sheet discharge tray7.

The control panel8is a part of a user input unit for permitting the inputting of information and instructions by the operator for performing operations of the image forming apparatus1. The control panel8includes a touch panel and various hard keys. The control unit6is a controller that controls each unit or sub-component of the image forming apparatus1.

FIG.2depicts a hardware configuration of an image processing apparatus of an embodiment.

As shown inFIG.2, the image forming apparatus1includes a central processing unit (CPU)91, a memory92, an auxiliary storage device93connected by a bus or the like. The image forming apparatus1executes a program and functions as an apparatus including a scanner unit2, an image forming unit3, a sheet feed unit4, a conveyance unit5, a reversing unit9, a control panel8, and a communication unit90by executing the program on the CPU91.

The CPU91functions as the control unit6when executing the program(s) stored in the memory92and the auxiliary storage device93.

The auxiliary storage device93comprises a storage device such as a magnetic hard disk device (HDD) or a semiconductor storage device (SSD). The auxiliary storage device93stores information.

The communication unit90incorporates a communication interface for connecting to an external device. The communication unit90communicates with external devices via the communication interface.

FIG.3is a cross-sectional view of a heating device of an embodiment.

As shown inFIG.3, the heating device of the embodiment is a fixing device30. The fixing device30includes a pressure roller31and a film unit35.

The pressure roller31forms a nip N with the film unit35. The pressure roller31presses the toner image of the sheet S in the nip N. The pressure roller31rotates and conveys the sheet S through the nip N. The pressure roller31includes a core metal32, an elastic layer33, and a release layer (not separately depicted).

The core metal32is a columnar shape (e.g., a rod shape) and formed of a metal such as stainless steel. Both axial ends of the core metal32supported in a manner permitting rotation about the axial direction. The core metal32is rotationally driven by a motor. The core metal32comes into contact with a cam member. The cam member can rotate to cause the core metal32to approach or separate from the film unit35.

The elastic layer33is formed of an elastic material such as silicone rubber. In this example, the elastic layer33is formed with 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 layer33in this example.

The hardness of the outer peripheral surface of the pressure roller31is preferably 40° to 70° under a load of 9.8 N as measured with an ASKER-C hardness tester. As a result, the area of the nip N and the durability of the pressure roller31are ensured.

The pressure roller31can approach and separate from the film unit35by rotation of the cam member. When the pressure roller31is brought close to the film unit35and pressed by a pressure spring, the nip N is formed. On the other hand, when a sheet S is jammed in the fixing device30, the sheet S can be removed by separating the pressure roller31from the film unit35. Furthermore, when the tubular film36is to be stopped from rotating for a prolonged time, such as during a device sleep or idle state, the pressure roller31can be separated from the film unit35to prevent plastic deformation of the tubular film36.

The pressure roller31is rotationally driven by a motor and rotates on its axis. When the pressure roller31rotates while the nip N is formed, the tubular film36of the film unit35is driven to rotate by the rotation of the pressure roller31. The pressure roller31rotates so that the sheet S is conveyed in a conveyance direction W through the nip N.

The film unit35heats the toner image of the sheet S that entered the nip N. The film unit35includes a tubular film36, a heater unit40, a heat transfer member70, a support member37, a stay38, a temperature sensing element60, and a film thermometer65.

The tubular film36is formed in a tubular shape. The tubular film36includes a base layer, an elastic layer, and a release layer in this order from the inner peripheral side. The base layer is a material such as polyimide formed into a tubular shape. 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 laminated on the outer peripheral surface of the elastic layer. The release layer is formed of a material such as PFA resin.

FIG.4is a cross-sectional view of the heater unit taken along the line IV-IV ofFIG.5.FIG.5is a bottom view (viewed from the +z direction) of the heater unit.

As shown inFIGS.4and5, the heater unit40includes a substrate43, a heating element group45, and a wiring group55.

The substrate43is formed of a metal such as stainless steel or a ceramic such as aluminum nitride. The substrate43is an elongated rectangular plate. The substrate43is disposed on to inside the tubular film36in the radial direction. That is, the substrate43is disposed within the interior region surrounded by the tubular film36. The axial direction of the tubular film36corresponds to the longitudinal direction of the substrate43.

In the present description, the x direction, the y direction, and the z direction are defined as follows with respect to the figures. The y direction is the longitudinal direction of the substrate43. The +y direction is the direction from a second end heating element53to a first end heating element52. The x direction is the lateral (planar width) direction of the substrate43, and the +x direction is the conveyance direction (downstream direction) for the sheet S. The z direction is the thickness direction of the substrate43. The +z direction is the direction in which the heating element group45is arranged with respect to the substrate43. The first surface41of the heater unit40faces towards the +z direction. The first surface41is in contact with inner surface of the tubular film36. The −z direction is the direction opposite to the +z direction. The di second surface42, which is in contact with the heat transfer member70,40faces towards the −z direction. An insulating layer44is formed on the +z direction surface side of the substrate43of a glass material or the like. The −z direction surface side of the substrate43is the second surface42of the heater unit40. The second surface42is formed in a planar and orthogonal to the z direction.

As shown inFIG.5, the heating element group45is arranged on the substrate43. The heating element group45is formed of a material such as a silver/palladium alloy disposed on the substrate43by screen printing. The overall outer shape of the heating element group45as a whole is a rectangular shape with the y direction as the longitudinal direction and the x direction as the lateral direction. The center hc of the heating element group45along the x direction is offset in the −x direction from the center pc of the substrate43along the x direction. The center pc can also be taken as the center or midpoint of the heater unit43along the x direction.

The heating element group45comprises a plurality of heating elements50provided at intervals along the y direction of the substrate43. The plurality of heating elements50are arranged in a row along the y direction. In this example embodiment, seven individual heating elements50are provided. The plurality of heating elements50includes the first end heating element52, a plurality of central heating elements51, and the second end heating element53. However, inFIG.5, for simplicity, the plurality of central heating elements51are collectively shown as a single heating element50. The central heating elements51are arranged on the central portion of the heating element group45in the y direction. In this example, the plurality of central heating elements51are electrically connected in parallel. The first end heating element52is on the +y direction side of the plurality of central heating elements51. That is, the first end heating element52is arranged at the +y direction end of the heating element group45. The second end heating element53is on the −y direction side of the plurality of central heating elements51. That is, the second end heating element53is arranged at the −y direction end of the heating element group45. The first end heating element52and the second end heating element53are electrically connected in parallel.

The heating element group45generates heat when supplied with electric power (energized). A sheet S having a relatively small width in the y direction may pass through just the central portion of the fixing device30. In such a case, the control unit6can be configured to generate heat using only the central heating elements51. On the other hand, the control unit6can be configured to generate heat using the entire heating element group45when the sheet S has a width in the y direction that exceeds the central portion of the fixing device30. Therefore, in the present example, the central heating element (s)51are controlled to generate heat independently from the first end heating element52and the second end heating element53. Furthermore, in this example, the first end heating element52and the second end heating element53are controlled to generate heat in the same manner as one another.

As shown inFIG.4, the heating element group45and the wiring group55are formed on the surface of the insulating layer44on the +z direction side. A protective layer46is formed of a glass material or the like so as to cover the heating element group45and the wiring group55. The protective layer46improves the slidability (reduces friction) between the heater unit40and the tubular film36.

Similar to the insulating layer44, an insulating layer may also be formed on the −z direction side of the substrate43. Similar to the protective layer46, another protective layer may be formed on the −z direction side of the substrate43. By matching protective and insulating layers on both sides of the substrate43, warping of substrate43can be suppressed or avoided.

As shown inFIG.3, the heater unit40is arranged inside the tubular film36. Typically, a grease or similar lubricant is applied to the inner peripheral surface of the tubular film36. The first surface41comes into contact with the inner peripheral surface of the tubular film36via the grease or the like. When the heater unit40generates heat, the viscosity of the grease decreases. As a result, the slidability between the heater unit40and the tubular film36is improved (friction is reduced).

As depicted inFIG.3, a straight line CL connecting the center rc of the pressure roller31and the center fc of the film unit35is defined. The center pc of the substrate43is offset in the +x direction from the straight line CL. The center hc of the heating element group45is on the straight line CL. The heating element group45is entirely contained within the region of the nip N and overlaps the center of the nip N. As a result, the heat distribution of the nip N becomes more uniform, and a sheet S passing through the nip N will be heated evenly.

The heat transfer member70is formed of a metal material having high thermal conductivity such as copper or aluminum, a graphite sheet, or the like. The outer planar shape of the heat transfer member70is substantially the same as the outer planar shape of the substrate43. The heat transfer member70is arranged to be in contact with at least a part of the second surface42.

The support member37can be formed of a resin material such as a liquid crystal polymer. The support member37is arranged so as to cover or overlap the −z direction surface of the heater as well as both x direction ends of the heater unit40. The support member37supports the heater unit40via the heat transfer member70therebetween in the z direction. Both outer x direction ends of the support member37are rounded or chamfered. The x direction ends of the support member37rest on and support the inner peripheral surface of the tubular film36.

When a sheet S passing through the fixing device30is heated, a temperature distribution can be generated in the heater unit40according to the size of the sheet S. When a portion of the heater unit40becomes locally hot during heating, the local temperature may exceed the heat resistance temperature of the support member37, which is made of a resin material. The heat transfer member70functions to average the temperature distribution across the heater unit40to avoid localized hotspots. As a result, the support member37can avoid being overheated beyond its heat resistance temperature.

The stay38is formed of a steel plate material or the like. The cross section of the stay38perpendicular to the y direction is formed in a U shape. The stay38is mounted on the −z direction side of the support member37. The U-shaped opening is thus closed by the support member37. The stay38extends in the y direction. Both ends of the stay38in the y direction can be fixed to the housing or the like of the image forming apparatus1. As a result, the film unit35is supported by the image forming apparatus1. The stay38improves (increases) the bending rigidity of the film unit35. A flange for restricting the movement of the tubular film36in the y direction can be mounted near both y direction ends of the stay38.

The temperature sensing element60is on the −z direction side of the heater unit40. In this example, the temperature sensing element60is arranged on the −z direction surface of the heat transfer member70. The temperature sensing element60or a portion thereof is disposed inside a hole that penetrates the support member37in the z direction. The wiring of the temperature sensing element60can be led out from the hole in the −z direction. The temperature sensing element60includes a heater thermometer62and a thermostat66. For example, the heater thermometer62is a thermistor.

FIG.6is a plan view (viewed from the −z direction) of the heater thermometer62and the thermostat66. InFIG.6, the depiction of the support member37is omitted.

As shown inFIG.6, the heater thermometer62includes a central heater thermometer63and an end heater thermometer64. The thermostat66includes a central thermostat67and an end thermostat68. The central heater thermometer63and the central thermostat67are arranged on the −z direction side of the central heating element51. The end heater thermometer64and the end thermostat68are arranged on the −z direction side of the first end heating element52and the second end heating element53.

In this example, the heater thermometer62detects the temperature of the heater unit40via the heat transfer member70.

The control unit6(seeFIG.1) detects or measures the temperature of the heating element group45using the heater thermometer62when the fixing device30is initially started (at startup or a return from an idle or sleep state). When the temperature of the heating element group45is lower than a predetermined temperature, the control unit6causes the heating element group45to generate heat for a short time. After that initial heating, the control unit6begins the rotation of the pressure roller31. Due to the heat generated by the heating element group45at startup or the like, the viscosity of the grease applied to the inner peripheral surface of the tubular film36decreases. As a result, the slidability between the heater unit40and the tubular film36at the start of rotation of the pressure roller31is improved (friction is reduced).

In this example, the heater thermometer62detects the temperature of the heat transfer member70.

The control unit6detects or measures the temperature of the heat transfer member70with the heater thermometer62during the operation of the fixing device30. The control unit6controls the energization of the heating element group45based on the temperature measurement results. As a result, the temperature of the heat transfer member70, which is in contact with the support member37, can be maintained below the heat resistant temperature of the support member37.

The thermostat66cuts off the power to the heating element group45when the temperature of the heater unit40(detected via the heat transfer member70) exceeds some predetermined temperature. As a result, excessive heating of the tubular film36by the heater unit40can be avoided.

As shown inFIG.3, the film thermometer65comes into contact with the inner peripheral surface of the tubular film36. In this example, the film thermometer65detects the temperature of the tubular film36.

The control unit6detects or measures the temperatures of the central portion and an end of the tubular film36during the operation of the fixing device30. The control unit6controls the energization of the central heating element51based on the temperature measurement result for the central portion of the tubular film36. The control unit6controls energization of both the first end heating element52and the second end heating element53based on the temperature measurement result for one y direction end portion of the tubular film36.

First Embodiment

The shape of the heating element group45of the first embodiment will be described.

FIG.7is a perspective view of the heater unit40and the heat transfer member70according to the first embodiment.FIG.8is a bottom view showing the heater unit40according to the first embodiment. InFIG.7, the insulating layer44, the protective layer46, and the wiring group55is omitted from the depiction. Furthermore, inFIG.8, the insulating layer44and the protective layer46are additionally omitted from the depiction.

As shown inFIGS.7and8, the plurality of heating elements50are arranged so that the +x direction edges overlap with −x direction edges of an adjacent (in the y direction) heating element50. The heating element group45is overall formed in a rectangular shape with the y direction as the longitudinal direction, but boundaries between adjacent heating elements50are not perpendicular to the y direction.

The outer planar shape of the central heating elements51is formed as a parallelogram in which a pair of sides extend in the y direction and the remaining pair of sides extend in a direction inclined with respect to the x direction when seen in a plan view from the z direction. The plurality of central heating elements51can be formed to have the same shape and the same size as each other. However, in some examples, the central heating elements51may be formed so that the dimensions in the y direction of some or all are different from one another. The +x-direction edge of each central heating element51is connected to a wiring of the wiring group55. The edge of each central heating element51in the −x direction is connected to a wiring of the wiring group55. The wiring connected to the +x direction edge of each central heating element51extends along the y direction and is integrated with the +x direction edge wiring of the other heating elements50to forma common connection wiring. The wirings connected the −x direction edge of each central heating element51extends along the y direction and are likewise integrated with one another. As a result, the central heating elements51are electrically connected in parallel with each other.

The outer planar shape of the first end heating element52is a trapezoidal shape having a pair of bases (+/−x direction edges) and a pair of legs (+/−y direction edges) in a plan view. The pair of bases extend in parallel with the y direction. The leg on the central heating element51side (−y direction end) extend in a direction inclined with respect to the x direction corresponding to the outer shape of the central heating element51adjacent to the first end heating element52. The leg on the +y direction end extends parallel to the x direction in this example. The +x direction edge and the −x direction edge of the first end heating element52are respectively connected to wirings of the wiring group55.

The outer planar shape of the second end heating element53is a trapezoidal shape having a pair of bases (+/−x direction edges) and a pair of legs (+/−y direction edges) in a plan view. The pair of bases extend in parallel with the y direction. The leg on the central heating element51side (+y direction end) extends in a direction inclined with respect to the x direction corresponding to the outer shape of the central heating element51adjacent to the second end heating element53. The leg on the −y direction end extends parallel to the x direction in this example. The +x direction edge and the −x direction edge of the second end heating element53are respectively connected to the wiring of the wiring group55.

In some examples, the heating element50may have the above-described general outer planar shape, but details of the structure inside the outer planar shape is not particularly limited to a solid filing of the overall outline of the planar shape. A heating element50may be formed by material in extending or arranged in a zigzag shape or other pattern so as to fill the inside of the described outline.

As depicted inFIG.8, an interval G (gap) is left between the pairs of adjacent heating elements50. The interval G extends in a direction inclined with respect to the x direction and has a constant width in this example. The interval G between a pair of heating elements50extends so that the +x direction end and the −x direction end do not overlap one another when viewed from the x direction. As a result, the adjacent pair of heating elements50also overlap each other when viewed from the x direction. The intervals G extend in parallel with each other in this example. The individual intervals G are formed so as not to overlap each other when viewed from the x direction. In the present embodiment, the plurality of intervals G are formed to have the same shape and the same size. However, the plurality of intervals G may be formed so that, for example, the width and the inclination direction of different intervals G are different.

In the following description, the region of which the heating element group45in which an interval G is formed between a pair of adjacent heating elements50is referred to as a first region X. A region of a heating element50directly adjacent to and continuous with a first region X in they direction and is referred to as a second region Y. The second regions Y are portions of a heating element50which do not overlap with another heating element50when viewed from the x direction. In the present embodiment, the second region Y is a region in which the heating element50extends along the y direction at a constant width (dimension in the x direction).

The heat transfer member70of the first embodiment will be described.

As shown inFIG.7, the heat transfer member70is arranged on the side opposite to the heating element group45with the substrate43interposed therebetween. The heat transfer member70has a facing surface71facing the heater unit40. The facing surface71faces in the +z direction. The facing surface71is formed in a plane orthogonal to the z direction. The facing surface71is formed in a rectangular shape with the y direction as the longitudinal direction. The facing surface71overlaps the entire heating element group45when viewed from the z direction. In the present embodiment, the heat transfer member70is formed to have the same shape and size as the substrate43of the heater unit40when viewed from the z direction. Further, the facing surface71is formed to have the same overall shape and size as the second surface42of the heater unit40.

FIG.9is a plan view showing a part of the heater unit40and the heating elements50according to the first embodiment.FIG.10is a cross-sectional view taken along the line X-X ofFIG.9.FIG.11is a cross-sectional view taken along the line XI-XI ofFIG.9.

As shown inFIGS.9to11, the facing surface71of the heat transfer member70includes a contact surface72and a recess73. The contact surface72comes into surface contact with the second surface42of the heater unit40. The contact surface72may be in direct contact with the second surface42or may be in contact with the second surface42via thermal grease, paste, or the like. The contact surface72is positioned so as to correspond to the entirety of the second regions Y between both x direction edges of the facing surface71. The contact surface72overlaps the entire heating element50in the second region Y when viewed from the z direction. The recess73is adjacent to the contact surface72. The recess73is recessed in the −z direction so as to avoid contact with the heater unit40. Each recess73is provided in a first region X. A separate recess73is provided at both the x direction sides of the first regions X. Each recess73is open on the side surface of the heat transfer member70in the x direction. Each recess73has a rectangular opening on the facing surface71. The recess73overlaps the second surface42of the heater unit40in a plan view. The recess73overlaps the heating element50in a plan view. The y-direction edge (sidewall) of each recess73is located at a y-direction edge boundary of a first region X.

The heat transfer member70is in contact with the second surface42of the heater unit40with a constant first length A in a zx cross section orthogonal to the y direction in the entire second region Y. The heat transfer member70is in contact with the second surface42of the heater unit40with a constant second length B in the zx cross section in the entire first region X. The second length B is shorter than the first length A. Specifically, for example, among the contact lengths of the heater unit40and the heat transfer member70in the zx cross section, the longest contact length in the first region X is shorter than the shortest contact length in the second region Y. Due to the above relationship, the heat transfer member70is in contact with the heater unit40in the second region Y at a first contact area ratio. The heat transfer member70is in contact with the heater unit40in the first region X at a second contact area ratio that is less than the first contact area ratio. The contact area ratio is the ratio of the contact area between the heat transfer member70and the heater unit40per unit area.

FIGS.9to11show the peripheral structure of the interval G between a pair of adjacent central heating elements51among the plurality of heating elements50. However, the above configuration is applicable to all or part of the peripheral structure of the intervals G between any pair of adjacent heating elements50in the example.

FIG.12is a graph showing the glossiness of an image on a sheet printed by an image forming apparatus. A solid image was formed on the entire printing surface of the sheet S using the fixing devices of certain examples including a comparative example. The glossiness of the image was measured with a glossiness measuring device. In the fixing device of the comparative example, a recess was not formed in the heat transfer member70. In the fixing device of Example 1, a recess73of the first embodiment is formed in the heat transfer member70. In the fixing device of Example 2, the heat transfer member70is formed with a penetrating portion80of a second embodiment (described further below).

InFIG.12, the horizontal axis indicates the image position on a sheet S along the y direction as passed through the fixing device. The label “1 cell” on the horizontal axis corresponds to the position of a central heating element51arranged in the most +y direction end among the plurality of central heating elements51. The label “5 cells” on the horizontal axis corresponds to the position of a central heating element51arranged in the most −y direction end among the plurality of central heating elements51. That is, each increment from 1 cell to from “1 cell” to “5 cells” on the horizontal axis corresponds to a second region Y. The labels “GAP1” to “GAP4” on the horizontal axis are positions of intervals G between the adjacent central heating elements51. Thus, each label “GAP1” to “GAP4” respectively corresponds to a first region X.

As shown inFIG.12, in the fixing device of the comparative example, the portion of the image on the sheet S passed through one of the first regions X has a lower glossiness than the portion of the image passed through one of the second regions Y. As a result, the image on the sheet S from the comparative example has uneven gloss.

On the other hand, in the fixing device of Example 1, the decrease in the glossiness of the first region X with respect to the glossiness of the second region Y is suppressed as compared with the fixing device of the comparative example. As a result, the uneven gloss of the image on the sheet S from Example 1 is suppressed.

As described above, the fixing device30includes the heater unit40including the heating element group45, and the heat transfer member70in contact with the heater unit40. The heating element group45includes a plurality of heating elements50provided at intervals along the y direction. The heating element group45has an interval G between at least one pair of adjacent heating elements50among the plurality of heating elements50in the first region X. The heating elements50do not overlap with each other in the second regions Y between adjacent first regions X. Therefore, since the interval G between a pair of heating elements50is in the first region X, there is a difference in heat generation by the heater unit40in the first regions X and the second regions Y.

However, the heat transfer member70contacts the heater unit40with a first length A in the zx cross section in the second region Y. The heat transfer member70contacts the heater unit40in the zx cross section in the first region X with a second length B shorter than the first length A. According to this configuration, the contact area of the heat transfer member70is reduced in the first region X as compared with a configuration in which a heat transfer member simply evenly contacts with the heater unit40over the entire area. Therefore, the heat transfer from the heater unit40to the heat transfer member70is reduced in the first region X, where the degree of heat generation of the heater unit40is relatively small, as compared to the second region Y. Therefore, the temperature of the heater unit40can be made more uniform during the initial stage of heating by the heater unit40in which the temperature difference between the heater unit40and the heat transfer member70is relatively large. Therefore, it is possible to suppress the occurrence of an uneven temperature distribution of the heater unit40.

A pair of adjacent heating elements50overlap each other when viewed from the x direction. With this configuration, there is no region in which at least one heating element50is not provided along the y direction. As a result, the occurrence of an uneven temperature distribution of the heater unit40can be additionally suppressed.

The heat transfer member70includes the recesses73in the first regions X adjacent to the contact surface72. According to this configuration, by providing the recesses73, the contact between the heater unit40and the heat transfer member70on the zx cross section passing through the recesses73can be reduced (length dimension of the contact surface in the x direction is reduced). Therefore, the above-mentioned effects can be obtained.

Further, the volume of the heat transfer member70can be increased as compared with a configuration in which the heat transfer member70is provided with a penetrating portion instead of the recess73. Therefore, the strength of the heat transfer member70can be ensured.

Certain modifications of the first embodiment will be described. In general, the aspects other than those described below for a modification can be considered to be the same as those already described for the first embodiment.

FIG.13is a plan view showing a part of a heater unit and the heating elements according to a first modification of the first embodiment.

The heat transfer member70of the first modification is formed with a pair of recesses74instead of the pair of recesses73of the first embodiment. The recess74is provided in just the first regions X. The recess74is opened in a semi-elliptical shape on the facing surface71. The recess74overlaps the heating element50in a plan view. The y-direction end of each recess74is located at the y-direction end of the first region X. As a result, the heat transfer member70is in contact with the heater unit40in the zx cross section in the entire first region X with the second length B shorter than the first length A, as in the first embodiment. The second length B changes in a range shorter than the first length A depending on the position in the y direction. According to this configuration, the same effect as that of the first embodiment can be obtained.

FIG.14is a plan view showing a part of a heater unit and the heating elements according to a second modification of the first embodiment.

The heat transfer member70of the second modification is formed with a pair of recesses75instead of the pair of recesses73of the first embodiment. The recess75is provided in just the first regions X. The recess75is opened in a triangular shape on the facing surface71. The recess75overlaps the heating element50in a plan view. The y-direction end of each recess75is located at the y-direction end of the first region X. As a result, the heat transfer member70is in contact with the heater unit40in the zx cross section in the entire first region X with the second length B shorter than the first length A, as in the first embodiment. According to this configuration, the same effect as that of the first embodiment is obtained.

FIG.15is a plan view showing a part of a heater unit and the heating elements according to a third modification of the first embodiment.

The heat transfer member70of the third modification is formed with a recess76instead of the pair of recesses73of the first embodiment. The recess76is provided in just the first regions X. The recess76is opened in a rectangular shape in the facing surface71. However, entire outer periphery of the recess76is surrounded by the contact surface72. The recess76is thus closed (surrounded) by the second surface42of the heater unit40. The recess76overlaps the adjacent heating elements50in a plan view. The y-direction end of each recess76is located at the y-direction edge of the first region X. As a result, the heat transfer member70is in contact with the heater unit40in the zx cross section in the entire first region X with the second length B shorter than the first length A (since the middle portion of length B is absent from the contacting length), as in the first embodiment. When the contact portion between the heat transfer member70and the heater unit40is divided on the zx cross section as in this modification, the second length B is taken as the total length of the contacting portions. According to this configuration, the same effect as that of the first embodiment is obtained.

Furthermore, since the entire periphery of recess76is surrounded by the contact surface72and is closed by the second surface42of the heater unit40, the recess76is not exposed (open) to the outside of the fixing device30. As a result, heat dissipation in the first regions X of the heat transfer member70can be suppressed. Therefore, the temperature of the heater unit40can be raised more uniformly.

FIG.16is a plan view showing a part of the heater unit and the heating element according to a fourth modification of the first embodiment.

The heat transfer member70of the fourth modification is formed with a plurality of recesses77instead of the pair of recesses73of the first embodiment. All the recesses77are provided in just the first regions X. The entire periphery of at least one recess77(center one) is surrounded by the contact surface72. In the illustrated example, some of the recesses77are open to the facing surface71in a circular shape. At least one recess77overlaps the adjacent heating elements50in a plan view. The inner surface of each recess77may be formed by a plurality of planes or a curved surface.

The plurality of recesses77can be arranged without gaps over the entire first region X when viewed from the x direction in some examples. The heat transfer member70can thus be in contact with the heater unit in the zx cross section in the entire first region X with the second length B shorter than the first length A, as in the first embodiment. According to this configuration, the same effect as that of the first embodiment is obtained.

FIG.17is a plan view showing a part of a heater unit and the heating elements according to a fifth modification of the first embodiment.

The heat transfer member70of the fifth modification is formed with a plurality of recesses78instead of the pair of recesses73of the first embodiment. All the recesses78are provided in a first region X. At least one recess78is inside the outer edge of the facing surface71. In the illustrated example, the recess78is open to the facing surface71in a circular shape. At least one recess78overlaps a heating element50in a plan view. Among the plurality of recesses78, the recess78located in the most +y direction is located in the −y direction from the end of the first region X in the +y direction. Among the plurality of recesses78, the recess78located in the most to the −y direction is located within the −y direction edge of the first region X. The plurality of recesses78are arranged so as to leave a gap therebetween when viewed from the x direction. However, the heat transfer member70will be in contact with the heater unit40in a part of the first region X in the zx cross section with the second length B shorter than the first length A. In this case as well, the heat transfer member70contacts the heater unit40in the first region X at the second contact area ratio smaller than the first contact area ratio, as in the first embodiment. According to this configuration, the same effect as that of the first embodiment is obtained.

FIG.18is a plan view showing a part of a heater unit and the heating elements according to a sixth modification of the first embodiment.

The heat transfer member70of the sixth modification is formed with a pair of recesses79instead of a pair of recesses73of the first embodiment. Each recess79is provided spanning the first region X into to an adjacent second region Y. The recess79overlaps a portion of the adjacent heating elements50in a plan view. Both y direction ends of each recess79are located within a second region Y. As a result, the heat transfer member70is in contact with the second surface42of the heater unit40with a maximum first length A in the zx cross section in a part of the second region Y. Further, the heat transfer member70is in contact with the heater unit40in the zx cross section in the entire first region X with the second length B shorter than the first length A. In this case as well, the heat transfer member70contacts the heater unit40in the first region X at the second contact area ratio smaller than the first contact area ratio as in the first embodiment. According to this configuration, the same effect as that of the first embodiment is obtained.

FIG.19is a plan view showing a part of a heater unit and the heating elements according to a seventh modification of the first embodiment.

The heater unit40of the seventh modification is provided with a heating element group47instead of the heating element group45of the first embodiment. The heating element group47includes a plurality of heating elements54provided at intervals along the y direction. The interval G left between pairs of adjacent heating elements54has a constant width in the y direction. As a result, the pair of adjacent heating elements54do not overlap each other when viewed from the x direction. By providing the recesses73on the facing surface71of the heat transfer member70as in the first embodiment, the similar effects as that of explained already for the first embodiment can be obtained.

Second Embodiment

A heat transfer member170of the second embodiment will be described. The aspects other than those described below for the second embodiment can be considered to be the same as those of already described for the first embodiment.

FIG.20is a plan view showing a part of a heater unit40and the heating elements50according to a second embodiment.

As shown inFIG.20, a penetrating portion80that is adjacent to the contact surface72in the first region X. The penetrating portion80penetrates through the heat transfer member170in the z direction. In the first region X, the penetrating portion80extends to the level of the facing surface71of the heat transfer member170. In the present example, penetrating portions80are provided at both x direction sides in each first region X. Each penetrating portion80reaches in the x direction to the outside side surface of the heat transfer member170. An opening81for each penetrating portion80is formed in a rectangular shape in the heat transfer member170. The opening81for the penetrating portion80is overlapped by the second surface42of the heater unit40in a plan view. The opening81also overlaps with the adjacent heating elements50in a plan view. The y direction end of the opening81of each penetrating portion80is located at they direction end of the first region X. The penetration portion80is formed of a material that has lower thermal conductivity than the heat transfer member170overall.

Similar to the heat transfer member70of the first embodiment, the heat transfer member170is in contact with the heater unit40within the first region X with the second length B that is less than the first length A for which the heat transfer member170is in contact with heater unit40in the second region Y. Specifically, for example, among the contact lengths of the heater unit40and the heat transfer member170in the zx cross section, the longest contact length in the first region X is shorter than the shortest contact length in the second region Y. As a result, the heat transfer member170is in contact with the heater unit40in the second region Y with a first contact area ratio. The heat transfer member170is in contact with the heater unit40in the first region X with a second contact area ratio that is smaller than the first contact area ratio.

As shown inFIG.12, in the fixing device of Example 2 (corresponding to this second embodiment), a decrease in the glossiness of the first region X with respect to the glossiness of the second region Y is suppressed as compared with the fixing device of the comparative example. As a result, the uneven gloss of the image on the sheet S is suppressed.

As described above, the heat transfer member170contacts the heater unit40with the first length A in the zx cross section in the second region Y. The heat transfer member70contacts the heater unit40in the zx cross section in the first region X with the second length B shorter than the first length A. According to this configuration, the contact area of the heat transfer member170with respect to the heater unit40can be reduced in the first region X as compared with a configuration in which a heat transfer member is evenly contacted with the heater unit40without inclusion of the penetrating portions80with the heat transfer member. However, with inclusion of the penetrating portions80, the heat transfer from the heater unit40to the heat transfer member170is suppressed in the first region X where the degree of heat generation of the heater unit40is relatively small as compared with the second region Y. Therefore, the temperature of the heater unit40can be raised more uniformly during the initial stage of heating of the heater unit40in which the temperature difference between the heater unit40and the heat transfer member170is relatively large. Therefore, as in the first embodiment, it is possible to suppress the occurrence of an uneven temperature distribution of the heater unit40.

A penetrating portion80that reaches to the level of the contact surface72in the first region X is provided. According to this configuration, the contact length between the heater unit40and the heat transfer member170on the zx cross section passing through the opening81for the penetrating portion80can be reduced. Therefore, the above-mentioned effect can be obtained.

Modifications of the second embodiment will be described. In general, the aspects other than those described below for a modification can be considered to be the same as those already described for the second embodiment.

FIG.21is a plan view showing a part of a heater unit40and the heating elements50according to a first modification of the second embodiment.

The first modification has a penetrating portion82instead of the pair of penetrating portions80of the second embodiment. The penetrating portion82is provided in the first region X. The penetrating portion82is at the +z direction level of the facing surface71of the heat transfer member170. An opening83for the penetrating portion82is formed in a rectangular shape. The entire periphery of opening83is surrounded by the contact surface72. The opening83overlaps the adjacent heating elements50in a plan view. The y-direction end of the opening83is located at the y-direction edge of the first region X. As a result, the heat transfer member170is in contact with the heater unit40in the zx cross section in the first region X with a second length B that is shorter than the first length A. According to this configuration, the same effect as that of the second embodiment can be obtained.

FIG.22is a plan view showing a part of a heater unit40and heating elements50according to a second modification of the second embodiment.

The heat transfer member170of the second modification is formed with a plurality of penetrating portions84instead of just the pair of penetrating portions80. All the penetrating portions84are provided in the first region X. The penetrating portion84are at the +z direction level of the facing surface71. An opening85for each penetrating portion84is formed in a rectangular shape with the y direction as the longitudinal direction. The entire periphery of each penetrating portions84is surrounded by the contact surface72. The opening85of at least one penetrating portion84overlaps the adjacent heating elements50in a plan view. The y-direction end of the opening85is located at the y-direction edge of the first region X. As a result, the heat transfer member170is in contact with the heater unit40in the zx cross section in the first region X with a second length B that is shorter than a first length A. According to this configuration, the same effect as that of the second embodiment is obtained.

Similarly to the various modifications of the first embodiment with respect to recess shape, the shape of the opening for the penetrating portion(s) is not particularly limited to any shape. For example, the shape of the opening for the penetrating portion(s) may match the shape of the recess(es) as depicted for in the modifications of the first embodiment.

In the above embodiments and the modifications thereof, the openings of the recesses or for the penetrating portions overlap at least one heating element50in a plan view. However, the openings of the recesses and for the penetrating portions do not necessarily have to overlap a heating element50in a plan view.

The image processing apparatus of an embodiment is the image forming apparatus1, and the heating device is a fixing device30. However, in other examples, the image processing apparatus may be a decolorizing device, and the heating device may be a decolorizing unit. The decolorizing device performs the processing for decolorizing (erasing) an image formed on a sheet with a decolorable toner. The decolorizing unit heats and decolorizes the decolorable toner image formed on the sheet passing through the nip.

According to at least one embodiment described above, a heating element group has a plurality of heating elements spaced at intervals along a row a direction on a first side of a substrate. An interval in the row direction is left between a pair of adjacent heating elements among the plurality of heating elements. There is a region (overlap region) in the heating element group in which end portions of the adjacent heating elements overlap one another in a conveyance direction along the substrate and orthogonal to the row direction. A portion of each heating element outside the overlap region does not overlap with any other heating element in the heating element group in the conveyance direction. A heat transfer member, which is formed of a material with high thermal conductivity, comes into contact with a back side of the substrate. In the overlap region, the heat transfer member contacts the back side of the substrate such that a first contact length of the heat transfer member taken along the conveyance direction is less than a second contact length of the heat transfer member taken along the conveyance direction outside the overlap region. For example, the heat transfer member is formed such that a recess, hole, or protrusion limits contact between the heat transfer member and the back side of the substrate in the first region X as compared to the second region Y. Therefore, heat transfer from the heater unit to the heat transfer member is suppressed in the first region X where the heat generation by the heater unit is relatively small. Therefore, the temperature of the heater unit can be raised more uniformly during an initial stage of heating (startup or the like) of the heater unit for which the temperature difference between the heater unit and the heat transfer member is relatively large. Therefore, it is possible to suppress the occurrence of an uneven temperature distribution in the heater unit.