Heater, fixing device, and image forming apparatus

Abstract

To provide a heater that can heat a fixing belt uniformly over an axial direction, while securing a necessary creepage distance.SOLUTION: A heater 33 is in contact with an inner face of a fixing belt formed in a cylindrical shape to heat the fixing belt. The heater 33 has: a substrate 36 that is formed of an insulator, and extends in an axial direction in correspondence with the fixing belt; and a plurality of resistance heating elements 38 that are arranged side by side in the axial direction with a gap G therebetween on one face of the substrate 36 that is on an inner face side of the fixing belt, and generate heat upon energization. The relationship between the gap G [mm] between the resistance heating elements 38 adjacent in the axial direction and the thermal conductivity of the inner face of the fixing belt λ [W / m K] satisfies λ≥138G-36.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a heater for heating a fixing belt, a fixing device, and an image forming apparatus. [Background technology]

[0002] A fixing device that thermally fixes a toner image to a medium includes a heating member (heater) that contacts the inner surface of an endless belt to heat the endless belt. The heating member has multiple heat generating members divided in a direction perpendicular to the medium transport direction. The multiple heat generating members are arranged on an insulator, and the creepage distance of the insulator between the multiple heat generating members is longer than the distance between the multiple heat generating members. This electrically insulates adjacent heat generating members and suppresses a drop in temperature of the endless belt in the areas corresponding to the gaps between the heat generating members. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6458119 Summary of the Invention [Problem to be solved by the invention]

[0004] In order for the heating members to heat the endless belt uniformly, it is necessary to consider not only the gap between the heat generating members but also the thermal conductivity of the inner surface of the endless belt. Specifically, the higher the thermal conductivity of the inner surface of the endless belt, the wider the gap can be. In the above-mentioned technology, the thermal conductivity of the inner surface of the endless belt is not fully taken into consideration, so depending on the thermal conductivity, it may not be possible to ensure the required creeping distance or the temperature of the endless belt may drop significantly in the part corresponding to the gap.

[0005] In consideration of the above problems, the present invention provides a heater, a fixing device, and an image forming apparatus that can heat a fixing belt uniformly in the axial direction while ensuring a necessary creepage distance. [Means for solving the problem]

[0006] The present invention provides a heater that comes into contact with the inner surface of a cylindrical fixing belt and heats the fixing belt, the heater comprising a substrate formed of an insulator and extending in the axial direction corresponding to the fixing belt, and a plurality of resistance heating elements that are arranged with gaps in the axial direction on one side of the substrate that faces the inner surface of the fixing belt and generate heat when electricity is applied, the relationship between the gaps (G [mm]) between adjacent resistance heating elements in the axial direction and the thermal conductivity (λ [W / m K]) of the inner surface of the fixing belt satisfying λ≧138G-36.

[0007] The fixing device according to the present invention includes a fixing belt formed in a cylindrical shape and rotating about its axis to heat toner on a medium, a pressure roller rotating about its axis to form a pressure area between the fixing belt and the pressure roller, and pressing the toner on the medium passing through the pressure area, and a heater in contact with an inner surface of the fixing belt facing the pressure area to heat the fixing belt, the heater having a substrate made of an insulating material and extending in the axial direction corresponding to the fixing belt, and a plurality of resistance heating elements arranged with gaps in the axial direction on one surface of the substrate that faces the inner surface of the fixing belt and that generate heat when electricity is applied, the heater having a gap (G [mm]) between adjacent resistance heating elements in the axial direction and a thermal conductivity (λ [W / m K]) of the inner surface of the fixing belt satisfying λ≧138G-36.

[0008] In this case, the inner surface of the fixing belt may be made of polyimide.

[0009] An image forming apparatus according to the present invention includes any one of the fixing devices described above. Effect of the Invention

[0010] According to the present invention, the fixing belt can be heated uniformly in the axial direction while ensuring the necessary creepage distance. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram (front view) illustrating a printer according to an embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a bottom view illustrating a heater of the fixing device according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Diagram 5] 11 is a table showing the relationship between the gap between the resistance heating element and the thermal conductivity of the inner surface of the fixing belt, and the quality of an image formed on a sheet of paper. [Figure 6] 6 is a scatter diagram showing the relationship between the gap of the resistive heating element and the thermal conductivity of the inner surface of the fixing belt. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that Fr, Rr, L, R, U, and D shown in the drawings indicate front, rear, left, right, top, and bottom. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

[0013] [Printer overall configuration] A printer 1 as an example of an image forming apparatus will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (front view) showing the printer 1.

[0014] The printer 1 includes a device main body 2 that has a generally rectangular parallelepiped exterior. A paper feed cassette 3 that stores paper P (medium) is provided at the bottom of the device main body 2. A paper output tray 4 is provided on the top surface of the device main body 2. Note that the paper P is not limited to being made of paper, and may be made of resin or the like.

[0015] Inside the device body 2, a transport path 8 is formed as a passage for the paper P. The transport path 8 is formed in a substantially S-shape between the paper feed cassette 3 and the paper discharge tray 4. At the upstream end of the transport path 8, a paper feeder 5 that takes out the paper P from the paper feed cassette 3 is provided. An image forming device 6 is provided in the middle of the transport path 8, and a fixing device 20 is provided downstream of the transport path 8.

[0016] The imaging device 6 includes a toner container 10, a drum unit 11, and an optical scanning device 12. The toner container 10 contains, for example, black toner (developer). The drum unit 11 includes a photoconductor drum 13, a charging device 14, a developing device 15, and a transfer roller 16. The charging device 14, the developing device 15, and the transfer roller 16 are arranged around the photoconductor drum 13 in the order of the image formation process. The transfer roller 16 contacts the photoconductor drum 13 from below to form a transfer nip. The toner may be a two-component developer in which a toner and a carrier are mixed, or a one-component developer made of a magnetic toner.

[0017] A control device (not shown) of the printer 1 appropriately controls each device to execute an image forming process as follows. The charging device 14 charges the surface of the photoconductor drum 13. The photoconductor drum 13 receives scanning light emitted from the optical scanning device 12 and carries an electrostatic latent image. The developing device 15 develops the electrostatic latent image on the photoconductor drum 13 into a toner image using toner supplied from the toner container 10. The paper P is sent from the paper feed cassette 3 to the transport path 8 by the paper feed device 5, and the toner image on the photoconductor drum 13 is transferred to the paper P passing through the transfer nip. The fixing device 20 thermally fixes the toner image to the paper P. The paper P is then discharged to the paper output tray 4.

[0018] [Fixing device] Next, the fixing device 20 will be described with reference to Fig. 2 to Fig. 4. Fig. 2 is a cross-sectional view that shows a schematic view of the fixing device 20. Fig. 3 is a bottom view that shows a schematic view of the heater 33. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3.

[0019] 2, the fixing device 20 includes a fixing belt 31, a pressure roller 32, and a heater 33. The fixing belt 31 and the pressure roller 32 are provided inside a housing 30 (see FIG. 1). The heater 33 is provided inside the fixing belt 31.

[0020] <Fixing belt> The fixing belt 31 is an endless belt, and is formed in a generally cylindrical shape that is long in the front-rear direction (axial direction). The fixing belt 31 is disposed in the upper part inside the housing 30. A pair of generally cylindrical caps (not shown) are attached to both ends of the fixing belt 31 in the axial direction. Note that a belt guide (not shown) for maintaining the generally cylindrical shape of the fixing belt 31 may be provided inside the fixing belt 31.

[0021] The fixing belt 31 is made of a synthetic resin material having heat resistance and elasticity. As a specific example, the fixing belt 31 is formed by laminating an outer layer made of PFA (perfluoroalkoxyalkane) on an inner layer made of polyimide. Note that an intermediate layer made of silicone resin or the like may be formed between the inner layer (polyimide) and the outer layer (PFA).

[0022] (Pressing member, holding member) A pressing member 34 and a holding member 35 are provided inside the fixing belt 31. The pressing member 34 is formed in an axially long, approximately rectangular tube shape made of a metal material such as an aluminum alloy or stainless steel. The pressing member 34 penetrates the fixing belt 31 (and the cap) in the axial direction (front-rear direction), and both front and rear ends of the pressing member 34 protruding from the fixing belt 31 are supported by the housing 30. The fixing belt 31 described above is supported rotatably relative to the pressing member 34. The holding member 35 is formed in an axially long, approximately semi-cylindrical shape made of a heat-resistant resin material, for example. The holding member 35 is formed slightly shorter in the axial direction than the fixing belt 31, and is disposed inside the fixing belt 31. The holding member 35 is fixed to the lower surface of the pressing member 34, and has a curved surface that fits along the lower inner surface of the fixing belt 31. A fitting portion 35A into which the heater 33 is fitted is recessed in the lower portion of the holding member 35.

[0023] <Pressure roller> The pressure roller 32 is formed in a generally cylindrical shape that is long in the front-rear direction (axial direction). The pressure roller 32 is disposed at the lower inside of the housing 30. The pressure roller 32 has a core 32A made of an aluminum alloy, stainless steel, or the like, and an elastic layer 32B made of silicone sponge or the like laminated on the outer circumferential surface of the core 32A. Both axial ends of the core 32A are rotatably supported by the housing 30. A drive motor (not shown) is connected to the core 32A via a gear train or the like, and the pressure roller 32 is rotationally driven by the drive motor.

[0024] The fixing device 20 also has a pressure adjustment unit (not shown) that adjusts the contact pressure of the pressure roller 32 against the fixing belt 31 by raising and lowering the pressure roller 32. The pressure roller 32 is pressed against the fixing belt 31, forming a pressure region N between the fixing belt 31 and the pressure roller 32. The fixing belt 31 heats the toner on the paper P passing through the pressure region N while rotating around its axis, and the pressure roller 32 pressurizes the toner on the paper P passing through the pressure region N while rotating around its axis. The toner image is fixed on the paper P by the paper P passing through the pressure region N. The pressure region N refers to a region from an upstream position in the conveying direction of the paper P where the pressure is 0 Pa, through a position where the pressure is maximum, to a downstream position in the conveying direction of the paper P where the pressure is 0 Pa again. In this specification, the terms "upstream" and "downstream" and similar terms refer to "upstream" and "downstream" in the conveying direction of the paper P and similar concepts.

[0025] The paper P is transported with the center of its front-to-rear width roughly aligned with the center of the pressure area N in the front-to-rear direction (axial direction). For this reason, the fixing belt 31 (or the pressure area N) has a passing area A1 in the axial center that contacts the paper P, and non-passing areas A2 on both sides in the axial direction that do not contact the paper P (see FIG. 3). The paper P being transported always contacts the vicinity of the axial center of the passing area A1, regardless of the size of the paper P (dimension in the front-to-rear direction). In contrast, normal size paper P (e.g. A4 size) contacts both sides of the passing area A1 in the axial direction, but small size paper P (e.g. A5, B5 size, etc.) does not contact them.

[0026] <Heater> 2, the heater 33 is provided inside the fixing belt 31. Specifically, the heater 33 is fitted into the fitting portion 35A of the holding member 35, and is in contact with the inner surface of the fixing belt 31 facing the pressure region N. The heater 33 heats the fixing belt 31 from the inside. As shown in FIGS. 3 and 4, the heater 33 has a substrate 36 and a heat generating portion 37.

[0027] (substrate) The substrate 36 is formed of an insulator (electrically insulating material) such as ceramic. The substrate 36 is formed in a substantially rectangular plate shape that is elongated in the axial direction to correspond to the fixing belt 31. The substrate 36 is formed to be slightly shorter than the fixing belt 31 in the axial direction, and is disposed inside the fixing belt 31.

[0028] (heat generating part) The heat generating section 37 is provided on the lower surface (one surface) of the substrate 36 which is the inner surface side of the fixing belt 31 (see FIG. 4). As shown in FIG. 3, the heat generating section 37 is composed of three resistance heating elements 38A to 38C arranged in a row with a gap G therebetween in the axial direction. The three resistance heating elements 38A to 38C are each formed in a substantially rectangular shape from a metal material with a high electric resistance value. The entire heat generating section 37 is formed shorter than the entire axial length of the fixing belt 31 and longer in the axial direction than the passing area A1 of the fixing belt 31. In other words, both sides in the axial direction of the resistance heating elements 38B and 38C located on both outer sides in the axial direction face the non-passing area A2 of the fixing belt 31. The resistance heating element 38A located in the center in the axial direction corresponds to the front-rear width of a small size paper P, and all the resistance heating elements 38A to 38C correspond to the front-rear width of a normal size paper P. In this specification, in the explanation common to the three resistance heating elements 38A to 38C, only Arabic numerals are used as reference numerals.

[0029] Three individual electrodes 40A-40C and a common electrode 40D are formed on the lower surface of the substrate 36 (see FIGS. 3 and 4). The three individual electrodes 40A-40C and the common electrode 40D are formed, for example, from a metal material having a lower electric resistance value than the resistance heating element 38. In this specification, in a description common to the three individual electrodes 40A-40C and the common electrode 40D, they will be simply referred to as "electrode portion 40" and will be marked with only Arabic numerals.

[0030] As shown in Fig. 3, the individual electrode 40A is connected to the downstream end (right end) of the resistance heating element 38A located in the center in the axial direction. The other individual electrodes 40B, 40C are connected to the downstream ends of the resistance heating elements 38B, 38C, respectively. The common electrode 40D is connected to the upstream ends (left ends) of all the resistance heating elements 38A to 38C. Each of the multiple electrode portions 40 extends from a portion connected to the heating element 37 to both outer sides of the heating element 37 in the axial direction. The multiple electrode portions 40 are electrically connected to external devices (not shown), such as a power source, on both sides of the substrate 36 in the axial direction.

[0031] The heat generating portion 37 and the electrode portion 40 are covered with a coating layer 41 (see FIG. 4). The coating layer 41 is made of a material, such as ceramic, that has electrical insulation properties and has a small sliding friction force against the inner surface of the fixing belt 31. The coating layer 41, the heat generating portion 37, and the electrode portion 40 can be formed with high precision on the substrate 36 by, for example, a film formation technique such as sputtering, a printed circuit board manufacturing technique, a screen printing technique, or a combination of these techniques.

[0032] The heater 33 is fitted into the fitting portion 35A of the holding member 35 with the heat generating portion 37 (coat layer 41) facing the pressure roller 32, and the coat layer 41 is brought into contact with the inner surface of the fixing belt 31 (see FIGS. 2 and 4). The heater 33 receives the fixing belt 31 pressed against the pressure roller 32, so that a pressure region N is formed at the contact portion between the fixing belt 31 and the pressure roller 32.

[0033] The fixing device 20 is provided with a temperature detection unit 42 that detects the temperature of the heater 33 and cuts off power supply to the heater 33 if the temperature is abnormal. The temperature detection unit 42 is, for example, a heat-sensitive element such as a Thermocut, and is provided in contact with the heater 33. In detail, the temperature detection unit 42 is attached to the top surface of the fitting portion 35A of the holding member 35, and the lower part of the temperature detection unit 42 is in contact with the upper surface of the substrate 36 (see also FIG. 2). The temperature detection unit 42 is in contact with the substrate 36 slightly rearward of the center in the axial direction (not shown).

[0034] [Function of the fixing device] Here, we will briefly explain the operation (fixing process) of the fixing device 20. The electrode portion 40 of the heater 33, the drive motor, etc. are electrically connected to a power source (not shown) and a control device via various drive circuits (not shown).

[0035] The control device drives and controls the drive motor and heater 33. The pressure roller 32 rotates by receiving the driving force of the drive motor, and the fixing belt 31 rotates following the pressure roller 32 (see the solid thin arrow in FIG. 2). The heat generating section 37 (each resistance heating element 38) generates heat when electricity is applied via the electrode section 40, and the fixing belt 31 (pressure region N) is heated.

[0036] At this time, the control device changes the resistance heating elements 38A-38C to be heated (energized) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure region N, the control device executes control to cause all of the resistance heating elements 38A-38C to generate heat. Also, when a small-sized paper P passes through the pressure region N, the control device executes control to cause one resistance heating element 38A to generate heat. This makes it possible to heat only the necessary portion of the fixing belt 31 (pressure region N) in accordance with the size of the paper P. As a result, it is possible to keep the power used to a minimum. It is also possible to prevent excessive temperature rise at both ends of the fixing belt 31 in the axial direction.

[0037] When the fixing belt 31 reaches the set temperature, the image forming process described above starts. While the paper P onto which the toner image has been transferred passes through the pressure region N, the toner image is heated and pressed, and is fixed to the paper P.

[0038] Incidentally, the three resistance heating elements 38 arranged in a line in the axial direction must be electrically insulated from one another. Therefore, a creepage distance required for insulation is determined for the substrate 36 (insulator) exposed between the resistance heating elements 38 adjacent in the axial direction. If the creepage distance is increased (lengthened) to ensure the electrical insulation state, the distance between the resistance heating elements 38 adjacent in the axial direction (hereinafter simply referred to as "gap G") also becomes large (longer). In this embodiment, the creepage distance [mm] is approximately the same as the gap G [mm]. As the gap G becomes larger (longer), the problem that the temperature of the fixing belt 31 drops at the position corresponding to the gap G becomes more pronounced. As a result, the temperature of the fixing belt 31 (pressure region N) becomes non-uniform along the axial direction, and there is a risk that proper thermal fixing cannot be performed.

[0039] In addition, in order for the heater 33 to heat the fixing belt 31 uniformly in the axial direction, it is necessary to consider not only the gap G but also the thermal conductivity λ [W / m·K] (hereinafter simply referred to as "thermal conductivity λ") of the inner surface (material constituting the inner layer) of the fixing belt 31. For example, if the inner surface of the fixing belt 31 is made of a metal (stainless steel, nickel, etc.) with a high thermal conductivity λ, the fixing belt 31 heats up easily, so the gap G can be widened. On the other hand, if the inner surface of the fixing belt 31 is made of a synthetic resin (polyimide, etc.) with a low thermal conductivity λ, the fixing belt 31 does not heat up easily, so if the gap G is widened, the temperature does not become uniform in the axial direction and temperature spots are likely to occur. For this reason, if the thermal conductivity λ of the inner surface of the fixing belt 31 is low, the gap G must be narrowed while ensuring the above-mentioned electrical insulation state. However, since it is necessary to secure the above-mentioned creepage distance, there is a limit to narrowing the gap G. In this specification, the term "uniform" does not mean only a completely constant state, but also means that some error is allowed.

[0040] [experiment] The applicant conducted an experiment to confirm the relationship between the gap G and the thermal conductivity λ in order to heat the fixing belt 31 uniformly in the axial direction while ensuring the necessary creepage distance. The experiment conducted by the applicant and the results of the experiment will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a table showing the relationship between the gap G, the thermal conductivity λ, and the quality of the image formed on the paper P. Fig. 6 is a scatter diagram showing the relationship between the gap G and the thermal conductivity λ.

[0041] The applicant formed an image on paper P using three types of fixing belts 31 with different materials for the inner surface (inner layer) of the fixing belt 31 and three types of heaters 33 with different gaps G between the resistance heating elements 38, and confirmed the condition of the image (see FIG. 5). The materials for the inner surface (inner layer) of the three types of fixing belts 31 are polyimide (λ=0.3 W / m·K), stainless steel (λ=30 W / m·K), and nickel (λ=90 W / m·K). The gaps G between the three types of resistance heating elements 38 are 0.25 mm, 0.5 mm, and 0.9 mm. The applicant visually inspected for defects such as gloss streaks and peeling of the image, marking them as "X" when defects were found and "O" when no defects were found (good).

[0042] 5, when the gap G was 0.25 mm, no defective images were observed for any of the three types of fixing belts 31 (good images were obtained). When the gap G was 0.5 mm, no defective images were observed for the fixing belt 31 whose inner surface was made of stainless steel and nickel, but defective images were observed for the fixing belt 31 whose inner surface was made of polyimide. When the gap G was 0.9 mm, no defective images were observed for the fixing belt 31 whose inner surface was made of nickel, but defective images were observed for the fixing belt 31 whose inner surface was made of stainless steel and polyimide.

[0043] FIG. 6 is a scatter diagram based on the results shown in FIG. 5, with the horizontal axis representing the size of the gap G and the vertical axis representing the size of the thermal conductivity λ. In FIG. 6, a straight line (approximation line) is drawn as a boundary between points where good images were obtained (see white circles) and points where bad images were recognized (see black circles). This straight line is expressed as "λ=138G-36". Considering the above experimental results (FIGS. 5 and 6), it is considered that a good image can be obtained by setting the gap G and the thermal conductivity λ in a range equal to or greater than the straight line, and a bad image will be obtained by setting them in a range less than the straight line. In other words, it was confirmed that the fixing belt 31 can be heated uniformly in the axial direction while securing the necessary creepage distance by setting the gap G and the thermal conductivity λ so as to satisfy λ≧138G-36.

[0044] In the heater 33 (fixing device 20) according to the present embodiment described above, the relationship between the gap G [mm] between the axially adjacent resistance heating elements 38 and the thermal conductivity λ [W / m·K] of the inner surface of the fixing belt 31 satisfies λ≧138G-36. With this configuration, the appropriate gap G can be determined by determining the inner surface material (thermal conductivity λ) of the fixing belt 31. This makes it possible to electrically insulate the adjacent resistance heating elements 38 from each other, and to suppress a temperature drop in the fixing belt 31 at the portion corresponding to the gap G between the resistance heating elements 38. As a result, the fixing belt 31 can be heated uniformly in the axial direction while ensuring a necessary creepage distance in the substrate 36 (insulator) corresponding to the gap G.

[0045] Furthermore, in the fixing device 20 according to this embodiment, by using polyimide as the material for the inner surface of the fixing belt 31, the fixing belt 31 can be constructed at a lower cost and lighter weight than when metals such as stainless steel or nickel are used. Furthermore, since the thermal conductivity λ of polyimide is lower than that of metals, the gap G between the resistance heating elements 38 becomes narrower, but by satisfying the above formula, the necessary creepage distance can be ensured.

[0046] In the fixing device 20 according to the present embodiment, the inner surface (inner layer) of the fixing belt 31 is made of polyimide, but the present invention is not limited to this. The inner surface (inner layer) of the fixing belt 31 may be made of a metal such as stainless steel or nickel. Even in this case, it is preferable to set the gap G and the thermal conductivity λ so as to satisfy λ≧138G-36.

[0047] In addition, in the fixing device 20 according to the present embodiment, the heat generating section 37 is divided into three resistance heating elements 38A to 38C, but the present invention is not limited to this. The heat generating section 37 may be divided into two or more resistance heating elements 38 (not shown).

[0048] In addition, in the fixing device 20 according to the present embodiment, the paper P passes through the center of the pressure region N in the axial direction, but this is not limiting, and the paper P may pass through a position closer to one side in the axial direction of the pressure region N. In this case, the non-passage region A2 is set only on one side in the axial direction of the fixing belt 31 (or the pressure region N).

[0049] In addition, in the fixing device 20 according to the present embodiment, the pressure roller 32 is rotationally driven and the fixing belt 31 is rotated accordingly, but the present invention is not limited to this, and the fixing belt 31 may be rotationally driven and the pressure roller 32 may be rotated accordingly. In addition, the pressure roller 32 is raised and lowered (moved in a direction approaching or separating) relative to the fixing belt 31, but the present invention is not limited to this, and the fixing belt 31 may be moved in a direction approaching or separating relative to the pressure roller 32 (not shown).

[0050] In addition, in the description of this embodiment, a case where the present invention is applied to a monochrome printer 1 has been shown as an example, but the present invention is not limited to this, and may be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device, etc.

[0051] The above embodiment shows one aspect of the heater, fixing device, and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiment. The present invention may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea, and the claims include all embodiments that may be included within the scope of the technical idea. [Explanation of symbols]

[0052] 1. Printer (image forming device) 20 Fixing device 31 Fixing belt 32 Pressure roller 33 Heater 36 Substrate 38A~38C Resistance heating element G Gap N pressure area P Paper (media) λ Thermal conductivity

Claims

1. A heater that contacts an inner surface of a fixing belt formed in a cylindrical shape and heats the fixing belt, a substrate formed of an insulating material and extending in an axial direction corresponding to the fixing belt; a plurality of resistance heating elements that are arranged with gaps between them in the axial direction on one surface of the substrate that is the inner surface side of the fixing belt, and generate heat when electricity is applied thereto; A heater characterized in that the relationship between the gap (G [mm]) between the axially adjacent resistive heating elements and the thermal conductivity (λ [W / m K]) of the inner surface of the fixing belt satisfies λ≧138G-36.

2. a fixing belt formed in a cylindrical shape and rotating about an axis to heat the toner on the medium; a pressure roller that rotates around an axis to form a pressure area between the pressure roller and the fixing belt and pressurizes the toner on the medium passing through the pressure area; a heater that contacts an inner surface of the fixing belt facing the pressure region and heats the fixing belt, The heater is a substrate formed of an insulating material and extending in an axial direction corresponding to the fixing belt; a plurality of resistance heating elements that are arranged with gaps between them in the axial direction on one surface of the substrate that is the inner surface side of the fixing belt, and generate heat when electricity is applied thereto; A fixing device characterized in that the relationship between the gap (G [mm]) between adjacent resistance heating elements in the axial direction and the thermal conductivity (λ [W / m·K]) of the inner surface of the fixing belt satisfies λ≧138G-36.

3. 2. The fixing device according to claim 1, wherein the inner surface of the fixing belt is made of polyimide.

4. 4. An image forming apparatus comprising the fixing device according to claim 2.

Images