Fixing device and image forming apparatus

Abstract

To provide a fixing device that can efficiently transfer heat to a fixing belt.SOLUTION: A fixing device comprises: a fixing pad 34 that is in contact with an inner face of a fixing belt and forms, with a pressure roller, a nip part for applying pressure to a sheet; and a heater 40 that is attached to the fixing pad 34 and has positive temperature characteristics. The heater 40 is provided with a heat generation surface 43a that generates heat on a side facing the nip part, and an insulating layer (substrate 41) is provided between the heat generation surface 43a and the inner face of the fixing belt.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a fixing device and an image forming apparatus that heat and press a sheet to fix an image.

Background Art

[0002] Conventionally, in a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a toner image is fixed by pressing and heating a sheet on which an unfixed toner image is formed. In recent years, a fixing device using an endless fixing belt has been proposed, and the fixing belt is heated by a heater. In addition, in an image forming apparatus, sheets of various sizes are used. However, when fixing is repeated, there is a problem that the temperature gradually rises in a region where the sheet does not pass (non-sheet passing region). Therefore, a method for suppressing uneven heat generation distribution in the width direction of the sheet has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A heater in a conventional image forming apparatus includes a substrate, a first conductor provided on the substrate along the longitudinal direction of the substrate, a second conductor provided on the substrate at a position different from the first conductor in the short-side direction of the substrate, and a plurality of heating resistors connected in parallel between the first conductor and the second conductor, and a heating block having the plurality of heating resistors is formed. And, in one heating block, the heating resistor disposed at the end has a higher resistance value than the heating resistor disposed at the center in the longitudinal direction.

[0005] In a conventional image forming apparatus, electrodes are provided on the side surface of a heating resistor, and the entire area between the electrodes generates heat. Due to the diffusion of heat, there is a problem that the fixing belt cannot be efficiently heated.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide a fixing device and an image forming apparatus that can efficiently transfer heat to a fixing belt.

Means for Solving the Problems

[0007] The fixing device according to the present disclosure is a fixing device that heats and presses a sheet sandwiched between a cylindrical fixing belt and a pressing member to fix an image on the sheet, and includes a fixing member that abuts on the inner surface of the fixing belt and forms a nip portion that presses the sheet together with the pressing member, and a heater attached to the fixing member and having a positive temperature characteristic. The heater is provided on a side where a heat generating surface that generates heat faces the nip portion, and an insulating layer is provided between the heat generating surface and the inner surface of the fixing belt.

[0008] In the fixing device according to the present disclosure, the heater may be configured to have a plurality of heating elements arranged along the axial direction of the pressing member.

[0009] In the fixing device according to the present disclosure, the insulating layer may be configured such that a power supply electrode for supplying power to the heater is provided on the heat generating surface side.

[0010] In the fixing device according to the present disclosure, the heater may be configured such that an electrode is formed on the back surface opposite to the heat generating surface, and a conduction path for conducting power from the back surface to the heat generating surface is formed on the side surface.

[0011] In the fixing device according to the present disclosure, the heater may be configured such that a sliding layer is provided on a surface that abuts on the inner surface of the fixing belt.

[0012] In the fixing device according to the present disclosure, the heater may be configured to be longer than the nip portion in the paper conveyance direction.

[0013] The image forming apparatus according to the present disclosure is characterized by including the fixing device according to the present disclosure.

Effects of the Invention

[0014] According to the present disclosure, by providing the heat generating surface on the fixing belt side, heat can be efficiently transferred to the fixing belt.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0016] (First Embodiment) Hereinafter, a fixing device and an image forming apparatus according to the first embodiment of the present disclosure will be described with reference to the drawings.

[0017] FIG. 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus according to the first embodiment of the present disclosure.

[0018] The image forming apparatus 100 is a multifunction machine having a copying function, a scanner function, a facsimile function, and a printer function, and transmits the image of the document read by the image reading apparatus 130 to the outside, or forms the image of the document read by the image reading apparatus 130 or the image received from the outside in color or monochrome on a recording medium such as paper.

[0019] Above the image reading apparatus 130, a document conveying apparatus 110 supported so as to be openable and closable is provided. The document conveying apparatus 110 conveys one or a plurality of documents one by one in order. The image reading apparatus 130 reads the document placed on the document placement table 130a by scanning the scanning optical system 130b, or reads the document conveyed by the document conveying apparatus 110 to generate image data.

[0020] The image forming apparatus 100 is provided with a fixing device 1, a developing device 2, a photosensitive drum 3, a drum cleaning device 4, a charger 5, an intermediate transfer belt device 7, a secondary transfer device 11, an optical scanning device 12, a paper feeding unit 18, and the like.

[0021] In the image forming apparatus 100, image data corresponding to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y), or a monochrome image using a single color (for example, black) is handled. The image forming apparatus 100 is provided with four each of a developing device 2, a photosensitive drum 3, a drum cleaning device 4, and a charger 5 for forming four types of toner images, and each is associated with black, cyan, magenta, and yellow, and four image stations Pa, Pb, Pc, and Pd are configured.

[0022] The optical scanning device 12 exposes the surface of the photosensitive drum 3 to form an electrostatic latent image. The developing device 2 develops the electrostatic latent image on the surface of the photosensitive drum 3 to form a toner image on the surface of the photosensitive drum 3. The drum cleaning device 4 removes and collects the residual toner on the surface of the photosensitive drum 3. The charger 5 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. By the above-described series of operations, toner images of each color are formed on the surface of each photosensitive drum 3.

[0023] The intermediate transfer belt device 7 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer driving roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. Four intermediate transfer rollers 6 are provided inside the intermediate transfer belt 71, respectively, so as to form four types of toner images corresponding to each color. The intermediate transfer roller 6 transfers the toner images of each color formed on the surface of the photoreceptor drum 3 to the circumferentially moving intermediate transfer belt 71.

[0024] The intermediate transfer belt 71 is stretched between the intermediate transfer driving roller 72 and the intermediate transfer driven roller 73. In the image forming apparatus 100, the toner images of each color formed on the surface of each photoreceptor drum 3 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 71. The cleaning device 9 removes and collects the waste toner remaining on the surface of the intermediate transfer belt 71 without being transferred to the paper.

[0025] The secondary transfer device 11 sandwiches and conveys the paper conveyed through the paper conveyance path 21 at the transfer nip portion TN between the secondary transfer roller 11a and the intermediate transfer belt 71. When the paper passes through the transfer nip portion TN, the toner image on the surface of the intermediate transfer belt 71 is transferred and the paper is conveyed to the fixing device 1.

[0026] The fixing device 1 includes a fixing belt 31 that rotates around an axis and a pressure roller 32 (an example of a pressure member). The fixing device 1 sandwiches the paper with the toner image transferred at the nip portion N between the fixing belt 31 and the pressure roller 32, heats and pressurizes it, and fixes the toner image on the paper. Although not shown in FIG. 1, the fixing device 1 also has constituent members other than the fixing belt 31 and the pressure roller 32. Details of this fixing device 1 will be described later.

[0027] The paper feeding unit 18 is provided with a paper feeding cassette for loading a recording medium (paper) used for image formation, and is provided below the optical scanning device 12. The paper is pulled out from the paper feeding unit 18 by the pickup roller 16 and conveyed to the paper conveyance path 21. The paper conveyed to the paper conveyance path 21 is discharged to the paper discharge tray 19 by the discharge roller 17 via the secondary transfer device 11 and the fixing device 1.

[0028] In the paper conveyance path 21, a conveyance roller 13, a registration roller 14, and a discharge roller 17 are arranged. The conveyance roller 13 promotes the conveyance of the paper. The registration roller 14 conveys the paper at a speed equal to the process speed of performing image formation on the paper. This registration roller 14 is provided between the paper feeding unit 18 and the secondary transfer device 11, and adjusts the conveyance timing of the paper so that the toner image is transferred to the paper by the secondary transfer device 11. For example, the registration roller 14 waits (stops temporarily) while sandwiching the paper conveyed from the paper feeding unit 18, and starts the conveyance of the paper at a constant speed in synchronization with the secondary transfer device 11.

[0029] When performing image formation not only on the front surface but also on the back surface of the paper, the conveyance direction of the paper is changed by the discharge roller 17, and the paper is conveyed to the reverse conveyance path 22. In the reverse conveyance path 22, the paper is guided to the registration roller 14 in a state where the front and back surfaces are reversed by the reverse conveyance roller 15. The image forming apparatus 100 forms an image on the back surface of the paper guided to the registration roller 14 in the same manner as the front surface, and discharges it to the paper discharge tray 19.

[0030] FIG. 2 is a schematic cross-sectional view showing the configuration of the fixing device according to the first embodiment of the present disclosure.

[0031] The fixing device 1 includes a fixing belt 31 and a pressure roller 32. As shown in FIG. 2, the fixing device 1 further includes a support member 33 and a fixing pad 34 inside the fixing belt 31. Further, the fixing device 1 includes a fixing temperature sensor 38 and a separation plate 39 outside the fixing belt 31.

[0032] The fixing belt 31 is an endless flexible belt and is formed in a substantially annular shape. The fixing belt 31 has a configuration in which a release layer is provided on the surface of a belt-shaped base material formed of a synthetic resin such as polyimide or a metal such as nickel. The fixing belt 31 is rotatably provided about an axis along a direction perpendicular to the plane of the paper in FIG. 2. The axial direction of the fixing belt 31 is substantially parallel to the width direction W of the paper P to be conveyed (see FIG. 3 described later). In the present embodiment, the width direction W of the paper P coincides with the axial direction of the pressure roller 32.

[0033] The fixing pad 34 is formed in a long plate shape extending along the axial direction (width direction W described later) of the fixing belt 31 and is formed of, for example, a synthetic resin. The length of the fixing pad 34 is substantially equal to the length of the fixing belt 31 in the width direction W. A heater 40, which is a member for heating the fixing belt 31 and has a positive temperature coefficient (PTC) characteristic, is attached to the fixing pad 34. Specifically, the heater 40 is a PTC heater.

[0034] In the present embodiment, a heater 40 extending along the width direction W of the paper P to be conveyed is attached to the fixing pad 34. The detailed configuration of the heater 40 will be described with reference to FIGS. 3 and 4 described later.

[0035] The support member 33 is a member that supports the fixing pad 34 while pressing it against the inner peripheral surface of the fixing belt 31. The support member 33 has a substantially L-shaped cross section and includes a long plate-shaped fixing portion 33a to which the fixing pad 34 is fixed and a long plate-shaped standing portion 33b standing from an end of the fixing portion 33a.

[0036] The pressure roller 32 is disposed at a position facing the fixing pad 34 with the fixing belt 31 interposed therebetween. The pressure roller 32 rotates about a rotation axis parallel to the axial direction of the fixing belt 31 and is arranged to extend substantially parallel to the fixing belt 31. At the nip portion N between the pressure roller 32 and the fixing belt 31, the fixing belt 31 is pressed against the pressure roller 32 by the fixing pad 34. The pressure roller 32 has a configuration in which the surface of a cylindrical core material formed of a metal such as aluminum is covered with an elastic material such as rubber.

[0037] A driving force from a driving source such as a motor (not shown) is transmitted to the pressure roller 32 via gears or the like. The pressure roller 32 is rotationally driven by receiving this driving force, and as the pressure roller 32 rotates, the fixing belt 31 is driven to rotate in a direction opposite to the rotation direction of the pressure roller 32. The sheet P passes through the nip portion N between the pressure roller 32 and the fixing belt 31 along the conveyance direction S.

[0038] The fixing temperature sensor 38 detects the fixing temperature, which is the surface temperature of the fixing belt 31. The separation plate 39 is disposed on the downstream side of the nip portion N in the conveyance direction S to prevent the sheet P from being wound around the fixing belt 31.

[0039] FIG. 3 is a side view showing the heater, and FIG. 4 is a plan view showing the heater.

[0040] The heater 40 has a base 41 extending along the width direction W, an electric wire 42 (an example of a power supply electrode 42a), and a heating element 43. In the present embodiment, the base 41 is a flat plate long in the width direction W and is formed of a material having insulation properties, for example, alumina. The electric wire 42 is provided at both ends of the base 41 along the respective long sides. Note that the electric wire 42 only needs to be configured to be energized, and in the portion facing the heating element 43, it is formed thinly so that the distance between the base 41 and the heating element 43 does not increase significantly. A plurality of heating elements 43 are arranged along the width direction W and are attached onto the base 41 with the electric wire 42 interposed therebetween. In the present embodiment, the number of heating elements 43 can be appropriately adjusted according to the range to be heated, and heating can be performed efficiently.

[0041] FIG. 5 is a cross-sectional view of the heater in a state of being attached to the fixing pad, and FIG. 6 is a plan view of the heating element viewed from the heating surface side. In FIG. 5, hatching is omitted in consideration of the visibility of the drawing.

[0042] The heater 40 (particularly, the heating element 43) is provided on the side where the heat-generating surface 43a that generates heat faces the nip portion N (downward in FIG. 5). The heating element 43 and the base 41 are adhered by an adhesive layer 45. On the heat-generating surface 43a, as shown in FIG. 6, element electrodes 44 are provided at both ends in the conveyance direction S of the sheet P so as to overlap the power supply electrode 42a. Note that the element electrode 44 can energize the heating element 43 as long as a part thereof overlaps the power supply electrode 42a. By providing the heat-generating surface 43a on the fixing belt 31 side in this way, heat can be efficiently transferred to the fixing belt 31.

[0043] As described above, the base 41 is provided with a power supply electrode 42a for supplying power to the heater 40 on the heat-generating surface 43a side. By providing the power supply electrode 42a in the insulating layer in this way, power can be supplied to the heater 40 with a simple configuration.

[0044] The heater 40 is provided with a sliding layer 46 on the surface that contacts the inner surface of the fixing belt 31. The sliding layer 46 may be formed of a material that reduces friction with the fixing belt 31. In this embodiment, it is formed of glass. By providing the sliding layer 46 in this way to improve the slipperiness, torque reduction can be achieved and durability can be improved.

[0045] Also, the heater 40 is longer than the nip portion N in the paper P conveyance direction S. By heating a wider range than the nip portion N in this way, the toner image can be reliably transferred onto the paper P.

[0046] Note that, for the heater 40, a portion of the base 41 where the heating element 43 is not attached may be fixed to the fixing pad 34, or the back surface 43b of the heating element 43 may be adhered to the fixing pad with an adhesive or the like.

[0047] In FIG. 6, a configuration in which the element electrodes 44 are provided only at both ends of the heating element 43 is shown, but the present invention is not limited to this, and a configuration in which the element electrodes 44 are extended to the central portion of the heating element 43 may also be used. Next, a modified example in which the shape of the element electrode 44 is changed will be described with reference to FIG. 7.

[0048] FIG. 7 is a plan view of the heating element as viewed from the heat generating surface side in the modified example.

[0049] In FIG. 7, the heat generating surface 43a of the heating element 43 in the modified example is shown. In the modified example, the element electrodes 44 are provided along both ends of the heat generating surface 43a, and the element electrodes 44 have extending portions 44a that extend from both ends toward the center. The extending portions 44a are provided alternately from each of the ends. As a result, the portion where the heat generating surface 43a is exposed has a meandering shape. By providing the extending portions 44a in this way, portions far from the element electrodes 44 can be eliminated, and power can be stably supplied to the entire heat generating surface 43a.

[0050] Regarding the element electrode 44, the shape of the modification may be appropriately applied according to the size of the heating element 43. When the size of the heating element 43 is large, it is preferable to apply a shape provided with an extension part 44a.

[0051] (Second Embodiment) Next, an image forming apparatus according to a second embodiment of the present disclosure will be described with reference to the drawings.

[0052] In the second embodiment, the configuration of the heater 40 is different from that of the first embodiment. Since the second embodiment has substantially the same configuration as the first embodiment shown in FIGS. 1 to 7, the description thereof will be omitted, and only the different points will be described.

[0053] FIG. 8 is a cross-sectional view of the heater attached to the fixing pad in the second embodiment of the present disclosure.

[0054] The second embodiment is different from the first embodiment in that the base 41 is not provided. In the present embodiment, the heater 40 has its back surface 43b attached to the fixing pad 34 by an adhesive layer 45. Further, an element electrode 44 is provided on the back surface of the heater 40, and a power supply electrode 42a is provided so as to overlap it. The power supply electrode 42a has an electric wire 42 connected to an end portion that does not face the heating element 43. Further, the heating element 43 has a conduction path formed on a side surface for conducting electric power from the back surface 43b to the heating surface 43a. The conduction path formed on the side surface is insulated from the heating element 43 and is configured to limit heat generation between the conduction paths. On the other hand, on the heating surface 43a, the conduction path and the heating element 43 are configured to be conductive, and the heating surface 43a is configured to generate heat. Thus, by providing electrodes on the back surface 43b, the heating surface 43a can be widely used and efficient heating can be achieved. And in the present embodiment, the sliding layer 46 is attached to the heating surface 43a without passing through the base 41.

[0055] Note that the embodiments disclosed this time are illustrative in all respects and are not a basis for restrictive interpretation. Therefore, the technical scope of the present disclosure is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Also, all changes within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0056] 1 Fixing device 31 Fixing belt 32 Pressing roller (an example of a pressing member) 34 Fixing pad (an example of a fixing member) 40 Heater 41 Substrate (an example of an insulating layer) 42 Electric wire 43 Heating element 43a Heating surface 43b Back surface 44 Element electrode 44a Extension part 45 Adhesive layer 46 Sliding layer 100 Image forming apparatus W Width direction

Claims

1. A fixing device that heats and presses a sheet sandwiched between a cylindrical fixing belt and a pressing member to fix an image on the sheet, a fixing member that abuts against the inner surface of the fixing belt and forms a nip portion that presses the sheet together with the pressing member, and a heater having a positive temperature characteristic, attached to the fixing member. The heater has a heat generating surface that generates heat provided on the side facing the nip portion, and an insulating layer is provided between the heat generating surface and the inner surface of the fixing belt. A fixing device characterized by this.

2. The fixing device according to Claim 1, wherein the heater has a plurality of heating elements arranged along the axial direction of the pressing member. A fixing device characterized by this.

3. The fixing device according to Claim 1, wherein a power supply electrode for supplying power to the heater is provided on the insulating layer on the heat generating surface side. A fixing device characterized by this.

4. The fixing device according to Claim 1, wherein an electrode is formed on the back surface of the heater on the side opposite to the heat generating surface, and a conduction path for conducting power from the back surface to the heat generating surface is formed on the side surface. A fixing device characterized by this.

5. The fixing device according to Claim 1, wherein a sliding layer is provided on the surface of the heater that abuts against the inner surface of the fixing belt. A fixing device characterized by this.

6. The fixing device according to Claim 1, wherein the heater is longer than the nip portion in the sheet conveyance direction. A fixing device characterized by this.

7. An image forming apparatus including the fixing device according to Claim 1.

Images