Image forming device

Abstract

To prevent a variation in temperature of a recording medium when the recording medium is heated.SOLUTION: An image forming apparatus comprises: an image forming unit that forms an image on a recording medium P; and a fixing device 9 that fixes the image to the recording medium, and comprises cooling means 35 that cools the recording medium P before the image on the recording medium P is fixed by the fixing device 9. The cooling means 35 has a higher cooling ability at least at one end side in a width direction than at a center side in the width direction of the recording medium P.SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art As image forming apparatuses such as copying machines and printers, electrophotographic image forming apparatuses that form images using toner are known.

[0003] Generally, an electrophotographic image forming apparatus is equipped with a fixing device that fixes a transferred toner image onto a sheet of paper. The fixing device includes a heating member such as a heater that heats the sheet of paper. When the sheet of paper passes through the fixing device, the heating member heats the sheet of paper, and the toner on the sheet of paper melts due to the heat and is fixed onto the sheet of paper.

[0004] For example, Patent Document 1 (JP 2016-62024 A) discloses a fixing device equipped with a plate-shaped heater having a heating element, electrical contacts, and a conductor pattern that electrically connects these, provided on a longitudinal substrate. Summary of the Invention [Problem to be solved by the invention]

[0005] In a heater having such a conductor pattern provided on a substrate, when the heating element is heated, the conductor pattern also generates a small amount of heat due to the passage of current through the conductor pattern. Therefore, strictly speaking, the heat distribution of the entire heater is affected by the heat generated by the conductor pattern.

[0006] Therefore, depending on the heat generation distribution of the conductor pattern, there may be cases where the temperature distribution of the heater varies due to this, and in such a case, the temperature of the heated recording medium and the toner on the recording medium also varies, which may affect the glossiness or fixability of the image. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus including an image forming section that forms an image on a recording medium, and a fixing device that fixes the image on the recording medium, the fixing device including a heating member that heats the recording medium, the heating member including a base material arranged in a width direction of the recording medium perpendicular to a transport direction of the recording medium, a heating element, a first electrode portion, a second electrode portion, a first conductive path that connects the heating element and the first electrode portion, a second conductive path that extends from the heating element in a first direction of the width direction of the recording medium and is connected to the second electrode portion, and a third conductive path that branches off from the second conductive path, extends in a second direction opposite to the first direction, and is connected to the second conductive path or the second electrode portion without passing through the first conductive path, and the fixing device includes a heating member that heats the recording medium before the image is fixed on the recording medium by the fixing device, the heating member including a base material arranged in a width direction of the recording medium perpendicular to a transport direction of the recording medium, a heating element, a first electrode portion, a second electrode portion, a first conductive path that connects the heating element and the first electrode portion, a second conductive path that extends in a first direction of the width direction of the recording medium and is connected to the second electrode portion, and a third conductive path that branches off from the second conductive path, extends in a second direction opposite to the first direction, and is connected to the second conductive path or the second electrode portion without passing through the first conductive path, The side opposite to the image forming surface of The cooling means has a higher cooling capacity at least at one end side in the width direction of the recording medium than at a center side in the width direction of the recording medium. Effect of the Invention

[0008] According to the present invention, it is possible to suppress variations in the temperature of the recording medium when the recording medium is heated. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic configuration diagram of a fixing device according to the present embodiment. [Diagram 3] FIG. 2 is a perspective view of the fixing device. [Figure 4] FIG. 2 is an exploded perspective view of the fixing device. [Diagram 5] FIG. 2 is a perspective view of a heating unit included in the fixing device. [Figure 6] FIG. 2 is an exploded perspective view of the heating unit. [Figure 7] FIG. 2 is a plan view of the heater according to the embodiment. [Figure 8] FIG. [Figure 9]FIG. 4 is a perspective view showing a state in which a connector is connected to the heater. [Figure 10] FIG. [Figure 11] 13 is a diagram showing the amount of heat generated by the power supply lines for each block when all the resistive heating elements are caused to generate heat. FIG. [Figure 12] 13 is a diagram showing the amount of heat generated by the power supply lines for each block when only some of the heat generating parts are caused to generate heat. FIG. [Figure 13] FIG. 13 is a diagram showing an example in which a blower fan is used as a cooling means for cooling paper. [Figure 14] FIG. 4 is a diagram showing the positional relationship between a blower fan and paper. [Figure 15] FIG. 4 is a diagram showing the positional relationship between a blower fan and a heater. [Figure 16] FIG. 13 is a diagram showing an example in which a duct is provided to guide air from a blower fan. [Figure 17] 11A and 11B are diagrams illustrating the positional relationship between an opening of a duct and a sheet of paper. [Figure 18] FIG. 4 is a diagram showing the positional relationship between an opening of a duct and a heater. [Figure 19] 13 is a diagram showing an example in which the sizes of the openings of the duct are made different between the left and right sides. FIG. [Figure 20] 13 is a diagram showing an example in which duct openings are provided at three or more locations including the center in the width direction of the paper. FIG. [Figure 21] 13 is a diagram showing an example in which a duct opening is provided continuously from the center to both ends in the width direction of the paper. FIG. [Figure 22] FIG. 13 is a diagram showing an example in which a cooling roller is used as the cooling means. [Diagram 23] FIG. 4 is a diagram showing the positional relationship between a cooling roller and a sheet. [Figure 24] FIG. 4 is a diagram showing the positional relationship between a cooling roller and a heater. [Diagram 25] FIG. 13 is a diagram showing an example in which a cooling guide is used as the cooling means. [Figure 26] FIG. 4 is a cross-sectional view of a cooling guide. [Figure 27] 6A and 6B are diagrams illustrating the positional relationship between a contact surface of a cooling guide and a sheet of paper. [Figure 28] 6A and 6B are diagrams illustrating the positional relationship between a contact surface of a cooling guide and a heater. [Figure 29] 13A and 13B are diagrams illustrating an example in which the size of the contact surface of the cooling guide is made different across the paper width direction. [Diagram 30] FIG. 13 is a diagram showing an example in which an intermediate transfer belt is used as the cooling means. [Diagram 31] FIG. 4 is a cross-sectional view of a duct disposed in the intermediate transfer belt. [Diagram 32] FIG. 4 is a diagram for explaining a preferable position for cooling the intermediate transfer belt. [Diagram 33] 13A and 13B are diagrams illustrating other examples of arrangement of photoconductors with respect to the intermediate transfer belt. [Diagram 34] FIG. 13 is a diagram showing an example in which a flow path in a duct is divided into two by a partition plate or the like. [Diagram 35] FIG. 13 is a diagram for explaining a miniaturized heater. [Diagram 36] FIG. 13 is a diagram showing another heater configuration. [Figure 37] FIG. 13 is a diagram showing the configuration of another fixing device. [Figure 38] FIG. 13 is a diagram showing the configuration of another fixing device. [Figure 39] FIG. 13 is a diagram showing the configuration of still another fixing device. [Diagram 40] FIG. 1 is a diagram showing an example in which the present invention is applied to a direct transfer type image forming apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members or components having the same function or shape are given the same reference numerals as far as they can be distinguished, and the description thereof will be omitted after the first description.

[0011] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

[0012] The image forming apparatus 100 shown in FIG. 1 includes an image forming section 200, a transfer section 300, a fixing section 400, a recording medium supply section 500, and a recording medium discharge section 600.

[0013] The image forming section 200 is provided with four imaging units 1Y, 1M, 1C, and 1Bk, and an exposure device 6. Each imaging unit 1Y, 1M, 1C, and 1Bk is configured to be detachable from the image forming apparatus main body. Each imaging unit 1Y, 1M, 1C, and 1Bk is basically configured the same except that each imaging unit 1Y, 1M, 1C, and 1Bk contains a developer of a different color, yellow, magenta, cyan, and black, corresponding to the color separation components of a color image. Specifically, each imaging unit 1Y, 1M, 1C, and 1Bk includes a photoconductor 2, which is an image carrier that carries an image on its surface, a charging roller 3, which is a charging means for charging the surface of the photoconductor 2, a developing device 4, which is a developing means for forming a toner image on the photoconductor 2, and a cleaning blade 5, which is a cleaning means for cleaning the surface of the photoconductor 2. The exposure device 6 is a means (writing means) for exposing the charged surface of the photoconductor 2 based on image information to form an electrostatic latent image.

[0014] The transfer section 300 is provided with a transfer device 8 that transfers an image onto a recording medium, namely, paper. The recording medium onto which an image is formed (transferred) may be paper (including plain paper, thick paper, thin paper, coated paper, label paper, envelopes, etc.) or a resin sheet such as an OHP sheet. The transfer device 8 has an intermediate transfer belt 11, four primary transfer rollers 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is a transfer member that carries an image on its surface and transfers the image onto paper, and is made of an endless belt member. Each primary transfer roller 12 is in contact with a different photoconductor 2 via the intermediate transfer belt 11. As a result, a primary transfer nip is formed between the intermediate transfer belt 11 and each photoconductor 2, where the intermediate transfer belt 11 and each photoconductor 2 are in contact with each other. Meanwhile, the secondary transfer roller 13 is in contact with one of a plurality of rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11, and forms a secondary transfer nip between the intermediate transfer belt 11 and the secondary transfer roller 13.

[0015] The fixing section 400 is provided with a fixing device 9 that fixes an image onto a sheet of paper. The configuration of the fixing device 9 will be described in detail later.

[0016] The recording medium supply unit 500 is provided with a paper feed cassette 14 that stores paper P, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14.

[0017] The recording medium ejection section 600 is provided with a pair of ejection rollers 17 for ejecting paper outside the image forming apparatus, and an ejection tray 18 on which the paper ejected by the ejection rollers 17 is placed.

[0018] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to FIG.

[0019] When an instruction to start the printing operation is given, the photoconductors 2 of the imaging units 1Y, 1M, 1C, and 1Bk and the intermediate transfer belt 11 start to rotate. In addition, the paper feed roller 15 rotates to feed the paper P from the paper feed cassette 14. The fed paper P comes into contact with a pair of timing rollers 16 and is temporarily stopped.

[0020] In each of the imaging units 1Y, 1M, 1C, and 1Bk, the surface of the photoconductor 2 is first charged to a uniform high potential by the charging roller 3. Next, the exposure device 6 exposes the surface (charged surface) of each photoconductor 2 based on the image information of the document read by the document reading device or the print image information instructed to be printed from the terminal. As a result, the potential of the exposed portion decreases and an electrostatic latent image is formed on the surface of each photoconductor 2. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2. When the toner image formed on each photoconductor 2 reaches the primary transfer nip (the position of the primary transfer roller 12) as each photoconductor 2 rotates, it is transferred to the rotating intermediate transfer belt 11 so as to be overlapped in sequence. Thus, a full-color toner image is formed on the intermediate transfer belt 11. After the toner image is transferred from the photoconductor 2 to the intermediate transfer belt 11, the toner remaining on each photoconductor 2 is removed by the cleaning blade 5.

[0021] The toner image transferred onto intermediate transfer belt 11 is transported to the secondary transfer nip (the position of secondary transfer roller 13) as intermediate transfer belt 11 rotates, and is transferred onto paper P that has been transported thereto by timing rollers 16. Then, paper P onto which the toner image has been transferred is transported to fixing device 9, which fixes the toner image onto paper P. Thereafter, paper P is discharged onto paper discharge tray 18 by paper discharge rollers 17, completing a series of printing operations.

[0022] The above description of the printing operation is for forming a full-color image, but it is also possible to form a monochrome image using any one of the four image-forming units, or to form a two- or three-color image using two or three image-forming units.

[0023] Next, the configuration of the fixing device 9 according to this embodiment will be described.

[0024] As shown in FIG. 2, the fixing device 9 according to this embodiment includes a fixing belt 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, and a temperature sensor 19.

[0025] The fixing belt 20 is a rotating member disposed on the unfixed toner carrying surface side (image forming surface side) of the paper P, and is a fixing member that fixes the unfixed toner to the paper P. The fixing belt 20 is composed of an endless belt member having a cylindrical substrate with an outer diameter of 25 mm and a thickness of 40 to 120 μm, for example. The substrate may be made of heat-resistant resin such as PEEK, nickel, or metal material such as SUS, in addition to polyimide. In addition, in order to increase durability and ensure releasability, a release layer made of fluororesin such as PFA or PTFE may be provided on the outer peripheral surface of the substrate. In addition, an elastic layer made of rubber or the like may be provided between the substrate and the release layer. Furthermore, a sliding layer made of polyimide, PTFE, or the like may be provided on the inner peripheral surface of the substrate.

[0026] The pressure roller 21 is an opposing member disposed so as to face the outer circumferential surface of the fixing belt 20. The pressure roller 21 is also a pressure member that is pressed against the outer circumferential surface of the fixing belt 20 to form a nip portion N between the pressure roller 21 and the fixing belt 20. The pressure roller 21 is, for example, configured with a roller having an outer diameter of 25 mm and including an iron core, an elastic layer made of silicone rubber provided on the outer circumferential surface of the core, and a release layer made of fluororesin provided on the outer circumferential surface of the elastic layer.

[0027] The heater 22 is a heating member disposed inside the fixing belt 20 and heats the fixing belt 20 and the paper through the fixing belt 20. In this embodiment, the heater 22 is composed of a plate-shaped base material 50, a first insulating layer 51 provided on the base material 50, a conductor layer 52 provided on the first insulating layer 51, and a second insulating layer 53 covering the conductor layer 52. The conductor layer 52 has a heat generating portion 60.

[0028] The substrate 50 is made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to metal materials, ceramics, glass, and the like can also be used as the material of the substrate 50. When an insulating material such as ceramics is used for the substrate 50, the first insulating layer 51 between the substrate 50 and the conductor layer 52 can be omitted. On the other hand, metal materials are excellent in durability against rapid heating and are easy to process, so they are suitable for reducing costs. Among metal materials, aluminum or copper is particularly preferable in that it has high thermal conductivity and is less likely to cause temperature unevenness. Stainless steel also has the advantage of being cheaper to manufacture than these materials.

[0029] Each of the insulating layers 51 and 53 is made of an insulating material such as heat-resistant glass. These materials may also be ceramic, polyimide, etc. A separate insulating layer may be provided on the surface of the base material 50 opposite to the surface on which the first insulating layer 51 and the second insulating layer 53 are provided.

[0030] In this embodiment, the heat generating section 60 is disposed closer to the nip portion N than the substrate 50, but conversely, the substrate 50 may be disposed closer to the nip portion N than the heat generating section 60. In that case, however, the heat of the heat generating section 60 is transferred to the fixing belt 20 via the substrate 50, so it is desirable that the substrate 50 be made of a material with high thermal conductivity, such as aluminum nitride.

[0031] In this embodiment, in order to increase the efficiency of heat transfer from the heater 22 to the fixing belt 20, the heater 22 is arranged so as to be in direct contact with the inner circumferential surface of the fixing belt 20. However, the present invention is not limited to this, and the heater 22 may be arranged so as to be in non-contact with the fixing belt 20 or indirectly contact with the fixing belt 20 via a low-friction sheet or the like. The contact point of the heater 22 with the fixing belt 20 may be the outer circumferential surface of the fixing belt 20. However, in order to avoid deterioration of fixing quality due to scratches on the outer circumferential surface of the fixing belt 20, it is preferable that the surface with which the heater 22 comes into contact is the inner circumferential surface of the fixing belt 20.

[0032] The heater holder 23 is a holding member that holds the heater 22 inside the fixing belt 20. The heater holder 23 is desirably made of a heat-resistant material because it is likely to become hot due to the heat of the heater 22. In particular, when the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, the heat resistance of the heater holder 23 is ensured while heat transfer from the heater 22 to the heater holder 23 is suppressed, so that the fixing belt 20 can be heated efficiently.

[0033] The stay 24 is a reinforcing member disposed on the inside of the fixing belt 20. The stay 24 supports the surface of the heater holder 23 opposite to the surface on the nip portion N side, thereby preventing the heater holder 23 from being deflected by the pressure force of the pressure roller 21. As a result, the nip portion N of a uniform width is formed between the fixing belt 20 and the pressure roller 21. The stay 24 is preferably made of an iron-based metal material such as SUS or SECC to ensure its rigidity.

[0034] The temperature sensor 19 is a temperature detection unit that detects the temperature of the heater 22. The output of the heater 22 is controlled based on the detection result of the temperature sensor 19, thereby maintaining the temperature of the fixing belt 20 at a desired temperature (fixing temperature). The temperature sensor 19 may be of either a contact type or a non-contact type. For example, a known temperature sensor such as a thermopile, a thermostat, a thermistor, or an NC sensor can be used as the temperature sensor 19.

[0035] In the fixing device 9 according to the present embodiment, when a printing operation is started, power is supplied to the heater 22, causing the heat generating section 60 to generate heat and heating the fixing belt 20. Also, the pressure roller 21 is rotated and the fixing belt 20 starts to rotate driven by the pressure roller 21. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 2, a sheet of paper P carrying an unfixed toner image is conveyed between the fixing belt 20 and the pressure roller 21 (nip portion N), whereby the unfixed toner is heated and pressurized, and the toner image is fixed to the sheet of paper P.

[0036] FIG. 3 is a perspective view of the fixing device 9 according to this embodiment, and FIG. 4 is an exploded perspective view thereof.

[0037] 3 and 4, the fixing device 9 according to this embodiment includes a device frame 40 formed in a rectangular frame shape. The device frame 40 is composed of a first device frame 25 having a pair of side walls 28 and a front wall 27 integrally therewith, and a second device frame 26 having a rear wall 29. The first device frame 25 and the second device frame 26 are assembled together by engaging a plurality of engagement protrusions 28a provided on the pair of side walls 28 with a plurality of engagement holes 29a provided on the rear wall 29.

[0038] The fixing belt 20 and the pressure roller 21 are supported by a pair of side walls 28. For this purpose, each side wall 28 is provided with an insertion groove 28b for inserting the rotating shaft of the pressure roller 21 and the like. The insertion groove 28b is formed with an abutment portion that opens at one end (the rear wall 29 side) and does not open at the opposite end. A bearing 30 that rotatably supports the rotating shaft of the pressure roller 21 is provided at this abutment portion. When the pressure roller 21 is supported by each side wall 28, a drive transmission gear 31 as a drive transmission member provided at one end of the axial direction of the pressure roller 21 is arranged in a state exposed outside the side wall 28. As a result, when the fixing device 9 is mounted on the image forming apparatus main body, the drive transmission gear 31 is connected to a gear provided on the image forming apparatus main body, and is in a state in which a drive force from a drive source can be transmitted. In addition, a drive transmission member such as a pulley or a coupling mechanism that stretches the drive transmission belt may be used instead of the drive transmission gear 31.

[0039] A pair of support members 32 for supporting the fixing belt 20 and the stay 24 are provided at both ends of the fixing belt 20 in the longitudinal direction. A guide groove 32a is formed in each support member 32. As shown in FIG. 4, in a state where the pair of support members 32, the fixing belt 20, the stay 24, the heater holder 23, and the heater 22 are assembled, the support members 32 are assembled to the side wall portions 28 while the guide grooves 32a of the support members 32 are aligned with the edges of the insertion grooves 28b of the side wall portions 28, so that the fixing belt 20, the stay 24, the heater holder 23, and the heater 22 are supported by the side wall portions 28. In addition, the support members 32 are biased by a pair of springs 33 as biasing members provided between the support members 32 and the rear wall portion 29, so that the fixing belt 20 is pressed against the pressure roller 21, and a nip portion is formed.

[0040] Also, the rear wall 29 is provided with a hole 29b as a positioning portion for positioning the fixing device main body relative to the image forming device main body. Meanwhile, the image forming device main body is provided with a protrusion 101 (see FIG. 4) as a positioning portion. By inserting this protrusion 101 into the hole 29b of the fixing device 9, the protrusion 101 and the hole 29b are fitted together, and the fixing device main body is positioned relative to the image forming device main body. Note that the position at which the hole 29b is provided is preferably closer to one of the ends than the center in the longitudinal direction of the rear wall 29. By providing the hole 29b at such a position, the end side where the hole 29b is not provided is allowed to expand and contract in the longitudinal direction due to temperature changes, and it is possible to suppress distortion of the device frame 40.

[0041] FIG. 5 is a perspective view of a heating unit in which a heater 22 and other components are supported by a pair of support members 32, and FIG. 6 is an exploded perspective view of the heating unit.

[0042] As shown in FIG. 5, the heater 22 and the heater holder 23 are longitudinal members extending in the left-right direction of FIG. 5. The heater 22 and the heater holder 23 are incorporated in the fixing device, and are arranged so that the longitudinal direction of the heater 22 and the heater holder 23 corresponds to the width direction U of the paper P passing through the fixing device (hereinafter, sometimes referred to as the "recording medium width direction") when the fixing device is mounted on the image forming apparatus. Also, as shown in FIG. 6, the stay 24 is also arranged longitudinally in the recording medium width direction U, similar to the heater 22 and the heater holder 23. The width direction U of the paper P is a direction perpendicular to the conveying direction of the paper P. Also, the terms "recording medium width direction", "longitudinal direction of the heater", "longitudinal direction of the substrate", "longitudinal direction of the fixing belt", and "width direction of the paper output tray" in this specification all mean the same direction.

[0043] 5 and 6, the heater holder 23 is provided with a rectangular accommodating recess 23a for accommodating the heater 22. The accommodating recess 23a is formed in substantially the same shape and size as the heater 22. However, the longitudinal dimension L2 of the accommodating recess 23a is set to be slightly longer than the longitudinal dimension L1 of the heater 22. Therefore, even if the heater 22 expands in the longitudinal direction due to thermal expansion, interference between the heater 22 and the accommodating recess 23a can be avoided.

[0044] The pair of support members 32 have a C-shaped belt support portion 32b that is inserted inside the fixing belt 20 to support the fixing belt 20, a flange-shaped belt regulating portion 32c that contacts an end face of the fixing belt 20 to regulate longitudinal movement (deviation) of the fixing belt 20, and a support recess 32d into which portions near both longitudinal ends of the heater holder 23 and the stay 24 are inserted to support them. By inserting the belt support portions 32b into both longitudinal ends of the fixing belt 20, the fixing belt 20 is supported in a so-called free belt manner in which basically no tension acts in the circumferential direction (belt rotation direction) when the belt is not rotating.

[0045] 5 and 6, a positioning recess 23e is provided as a positioning portion on one end side of the center in the longitudinal direction of the heater holder 23. The fitting portion 32e of the support member 32 on the left side in Figs. 5 and 6 fits into this positioning recess 23e, thereby positioning the heater holder 23 and the support member 32. On the other hand, the fitting portion 32e is not provided on the support member 32 on the right side in Figs. 5 and 6, and the heater holder 23 is not positioned in the longitudinal direction. In this way, the heater holder 23 is positioned relative to the support member 32 only on one side in the longitudinal direction of the heater holder 23, so that the heater holder 23 is allowed to expand and contract in the longitudinal direction due to temperature changes.

[0046] 6, steps 24a are provided in the vicinity of both ends of the stay 24 in the longitudinal direction to restrict movement of the stay 24 relative to each support member 32. Each step 24a abuts against the support member 32 to restrict longitudinal movement of the stay 24 relative to the support member 32. However, at least one of these step portions 24a is disposed with a gap (backlash) between it and the support member 32. In this manner, by disposing at least one step portion 24a with a gap between it and the support member 32, expansion and contraction of the stay 24 due to temperature changes is permitted.

[0047] FIG. 7 is a plan view of the heater 22 according to this embodiment, and FIG. 8 is an exploded perspective view thereof.

[0048] As shown in FIG. 8, a plurality of resistance heating elements 59 constituting a heating section 60 are arranged on the base material 50 of the heater 22 via a first insulating layer 51. The resistance heating elements 59 are arranged in a line in the longitudinal direction Z of the base material 50, which is also the recording medium width direction U. The conductor layer 52 is provided with a plurality of electrode parts 61 and a plurality of power supply lines (conductive parts) 62 in addition to the plurality of resistance heating elements 59. Each resistance heating element 59 is electrically connected to any two of the plurality of electrode parts 61 via the plurality of power supply lines 62. As shown in FIG. 7, the entirety of each resistance heating element 59 and most of each power supply line 62 are covered by the second insulating layer 53 to ensure insulation. In addition, since each resistance heating element 59 is arranged at intervals from each other, an insulating region (second insulating layer 53) is interposed between adjacent resistance heating elements 59. Meanwhile, each electrode part 61 is hardly covered by the second insulating layer 53 and is exposed so that a connector described later can be connected.

[0049] The resistance heating element 59 can be formed, for example, by applying a paste of silver palladium (AgPd) or glass powder to the substrate 50 by screen printing or the like, and then firing the substrate 50. The material of the resistance heating element 59 can be a silver alloy (AgPt) or ruthenium oxide (RuO 2 ) may also be used.

[0050] The electrode portion 61 and the power supply line 62 are made of a conductor having a resistance value smaller than that of the resistance heating element 59. For example, the electrode portion 61 and the power supply line 62 are formed by screen printing a material such as silver (Ag) or silver-palladium (AgPd) on the base material 50.

[0051] FIG. 9 is a perspective view showing a state in which a connector 70 serving as a power supply member is connected to the heater 22. As shown in FIG.

[0052] 9, the connector 70 has a resin housing 71 and a plurality of contact terminals 72 provided in the housing 71. Each contact terminal 72 is made of a leaf spring. A harness 73 for power supply is connected to each contact terminal 72.

[0053] As shown in FIG. 9, the connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 together. As a result, the heater 22 and the heater holder 23 are held together by the connector 70. In this state, the tips (contact portions 72a) of the contact terminals 72 of the connector 70 are elastically brought into contact (pressed) with the corresponding electrode portions 61, so that the contact terminals 72 and the electrode portions 61 are electrically connected to each other. The connector 70 is also similarly connected to the electrode portion 61 at the end opposite to the end in the longitudinal direction of the heater 22 shown in FIG. 9. As a result, the connector 70 is in a state in which power can be supplied to the heat generating portion 60 from a power source provided in the image forming apparatus via the connector 70.

[0054] Hereinafter, the configuration of the heater 22 according to this embodiment will be described in more detail with reference to FIG.

[0055] As shown in Fig. 10, the heater 22 according to this embodiment is provided with seven resistance heating elements 59A to 59G, three electrode portions 61A to 61C, and four power supply lines 62A to 62D connecting them. Of the three electrode portions 61A to 61C, two electrode portions 61A, 61C are disposed closer to one end side of the base material 50 in the longitudinal direction Z (left side in Fig. 10) than the respective resistance heating elements 59A to 59G, and the remaining one electrode portion 61B is disposed closer to the other end side of the base material 50 in the longitudinal direction Z (right side in Fig. 10) than the respective resistance heating elements 59A to 59G. Each of the resistance heating elements 59A to 59G is electrically connected to one of the two electrode portions 61A, 61C disposed on one end side and to one electrode portion 61B disposed on the other end side.

[0056] Specifically, of the seven resistance heating elements 59A-59G, the resistance heating elements 59B-59F other than those at both ends are connected in parallel to the first electrode portion 61A via a first power supply line 62A, and are connected in parallel to the second electrode portion 61B via a second power supply line 62B. On the other hand, the resistance heating elements 59A, 59G at both ends are connected in parallel to the third electrode portion 61C via a third power supply line 62C or a fourth power supply line 62D, and are connected in parallel to the second electrode portion 61B via a second power supply line 62B.

[0057] By adopting such a connection structure, in this embodiment, it is possible to independently control the heat generation of the first heating section 60A composed of the resistive heating elements 59B-59F other than those at both ends and the second heating section 60B composed of the resistive heating elements 59A, 59G at both ends. Specifically, when a voltage is applied to the first electrode section 61A and the second electrode section 61B to generate a potential difference between the two electrodes 61A, 61B, the resistive heating elements 59B-59F other than those at both ends are energized, and only the first heating section 60A generates heat. On the other hand, when a voltage is applied to the third electrode section 61C and the second electrode section 61B to generate a potential difference between the two electrodes 61C, 61B, the resistive heating elements 59A, 59G at both ends are energized, and only the second heating section 60B generates heat. Furthermore, when a voltage is applied to all the electrodes 61A-61C to generate a potential difference between the first electrode 61A and the second electrode 61 and between the third electrode 61C and the second electrode 61B, all the resistive heating elements 59A-59G are energized, and both the first heating portion 60A and the second heating portion 60B generate heat. For example, when a relatively small width paper of A4 size (paper passing width: 210 mm) or less is passed through, only the first heating portion 60A generates heat, and when a relatively large width paper of A3 size (paper passing width: 297 mm) or more is passed through, the second heating portion 60B as well as the first heating portion 60A generates heat, making it possible to create a heating area according to the paper width.

[0058] Here, the temperature variation (temperature distribution deviation) occurring in the heater 22 according to this embodiment will be described.

[0059] Generally, in a heater in which a resistive heating element as described above is connected to an electrode portion via a power supply line, when the resistive heating element is heated, the power supply line also generates a small amount of heat due to current flow through the power supply line. Therefore, depending on the heat distribution in the power supply line, there is a risk that the temperature distribution of the heater will vary. In particular, as the speed of image forming devices increases, if the current flowing through the heating element is increased to increase the amount of heat generated, the amount of heat generated in the power supply line also increases, and the effect of this cannot be ignored.

[0060] FIG. 11 shows the amount of heat generated in each of the power feed lines 62A, 62B, and 62D in each block divided for each of the resistance heating elements 59A to 59G and the total amount of heat generated in each block when 20% of the current flows through each of the resistance heating elements 59A to 59G. Here, if the direction Y (see FIG. 10) intersecting the longitudinal direction Z along the surface of the base material 50 on which the resistance heating elements 59 are provided is referred to as the "short side direction" of the base material 50, in this embodiment, the portion of each of the power feed lines 62A, 62B, and 62D extending in the short side direction Y is short and the amount of heat generated in this portion is small, so it is ignored and only the amount of heat generated in the portion extending in the longitudinal direction Z is calculated. In addition, since the amount of heat generated (W) is expressed by the following formula (1), the amount of heat generated shown in the table of FIG. 11 is calculated as the square of the current (I) flowing through each power feed line for convenience. Therefore, the calculated value of the amount of heat generated is merely a simply calculated value and differs from the actual amount of heat generated.

[0061]

number

[0062] 11 as an example, the calculation method of the heat generation amount will be described. In the first block, the current flowing through the first power feed line 62A is 100%, and the current flowing through the fourth power feed line 62D is 20%, so the total value of the squares of these, 10400 (10000+400), is the total heat generation amount of the power feed lines in the first block. In the second block, the current flowing through the first power feed line 62A is 80%, the current flowing through the second power feed line 62B is 20%, and the current flowing through the fourth power feed line 62D is 20%, so the total value of the squares of these, 7200 (6400+400+400), is the total heat generation amount of the power feed lines in the second block. In the other blocks, the heat generation amount is calculated in a similar manner.

[0063] The graph in Figure 11 shows the total heat generation amount of each block on the vertical axis. As can be seen from this graph, the total heat generation amount of each power supply line is large in the blocks at both ends and, conversely, is low in the blocks in the center. Furthermore, the total heat generation amount of each power supply line in blocks symmetrical with respect to the center (for example, the first block and the seventh block) is also different. As such, the heat generation distribution of the power supply lines varies across the longitudinal direction Z of the substrate, and this variation also causes variation in the heat generation distribution of the heater.

[0064] In addition, such temperature variation caused by heat generation from the power supply line is not limited to the case where all the resistance heating elements are heated (example shown in FIG. 11), but may occur even when some of the resistance heating elements are heated. In particular, when unintended current shunting occurs in the power supply line due to miniaturization of the heater or speed-up of the image forming apparatus, the temperature variation may become significant. In addition, unintended current shunting is likely to occur when the resistance value of the power supply line increases as a result of reducing the width of the power supply line in the short side direction of the heater in order to miniaturize the heater in the short side direction, or when the resistance value of the resistance heating element is reduced in order to increase the heat generation amount of the resistance heating element in order to speed up the image forming apparatus. In other words, when the resistance value of the power supply line and the resistance value of the resistance heating element become relatively close to each other due to miniaturization or speed-up, it becomes possible for current to flow through paths that have not been energized before (unintended current shunting may occur).

[0065] For example, as shown in Fig. 12, when electricity is supplied to only the resistance heating elements 59B-59F (first heating portion 60A) other than those at both ends, a portion of the current that passes through the second resistance heating element 59B from the left in the figure may be unintentionally branched to flow to the opposite side to the second electrode portion 61B (the left side in the figure) at the branch portion X of the second power supply line 62B. The branched current passes through the leftmost resistance heating element 59A in Fig. 12, and then passes through the rightmost resistance heating element 59G via the third power supply line 62C, the third electrode portion 61C, and the fourth power supply line 62D, before joining the second power supply line 62B.

[0066] In this way, the unintended branching current reaches the second power supply line 62B through the path indicated by the dashed line K3 in Fig. 12 from the branching portion X. In addition, such an unintended branching current may occur if the conductive path of the heater 22, such as the heater 22 according to this embodiment, has at least a first conductive path K1 connecting each of the resistance heating elements 59B to 59F (first heating portion 60A) other than both ends to the first electrode portion 61A, a second conductive path K2 extending from each of the resistance heating elements 59B to 59F other than both ends in a first direction S1 (rightward in Fig. 12) of the longitudinal direction of the heater 22 (or the width direction of the paper) and connected to the second electrode portion 61B, and a third conductive path K3 branching from the second conductive path K2 and extending in a second direction S2 (leftward in Fig. 12) opposite to the first direction S1 and connected to the second conductive path K2 or the second electrode portion 61B without passing through the first conductive path K1. In this embodiment, the parts constituting the third conductive path K3 include a part of the second power supply line 62B (the part from the branch point X to the left in FIG. 12), the third power supply line 62C, and the fourth power supply line 62D, as well as the resistive heating elements 59A, 59G (second heating portion 60B) at both ends and the third electrode portion 61C. However, even if the third conductive path K3 is only a power supply line that does not include a resistive heating element and an electrode portion, unintended shunting may occur.

[0067] The table and graph in Fig. 12 show the amount of heat generated in each of the power feed lines 62A, 62B, 62D for each block and the total amount of heat generated when unintended current shunting occurs. In this example, when 20% of the current flows evenly to each of the resistance heating elements 59B to 59F other than at both ends, a portion of the current is assumed to be shunted by 5% at the branch part X, and the amount of heat generated in each of the power feed lines 62A, 62B, 62D for each block (second block to sixth block) is calculated. The method of calculating the amount of heat generated is the same as the method described in the example shown in Fig. 11.

[0068] As shown in the table and graph in Fig. 12, in this case as well, the total heat generation amount of the power supply line is large in the blocks at both ends and is low in the block in the center, resulting in variation. However, in the case of Fig. 12, contrary to Fig. 11, the temperature of the block on the left side of the graph is higher than that of the block on the right side. Note that Figs. 11 and 12 show a state in which the current flows in one direction, but the current flowing through the heater 22 may be either DC or AC.

[0069] As described above, in the fixing device according to the present embodiment, temperature variation occurs along the length of the heater 22, and therefore the temperature of the toner on the heated paper also varies. As a result, the glossiness or density of the image also varies, which may result in a deterioration in image quality.

[0070] Therefore, in the image forming apparatus according to the present embodiment, in order to suppress the variation in glossiness or density of the image caused by the variation in the temperature distribution of the heater as described above, the following measures are taken.

[0071] FIG. 13 is a diagram showing an example in which a blower fan (blower means) is used as a cooling means for cooling the paper.

[0072] 13, in the image forming apparatus according to this embodiment, a blower fan 35 is provided as a cooling means for cooling the paper P between a transfer position A (secondary transfer nip) where an image is transferred to the paper P and a fixing position B (fixing nip) where the image is fixed to the paper P. The blower fan 35 blows air onto the paper P between the transfer position A and the fixing position B to cool the paper P. At this time, it is preferable that the surface of the paper P onto which the air is blown is the surface opposite to the image forming surface onto which the unfixed toner T adheres, so that the unfixed toner T on the paper P is not disturbed by the blown air.

[0073] 14, the blower fans 35 are provided at positions corresponding to both ends e in the width direction U of the paper P transported in the direction of the arrow V in the figure. Therefore, when air is blown from each blower fan 35 to the paper P, the blown air mainly cools both ends e in the width direction of the paper P and the surrounding areas. As a result, the paper P is cooled so that the temperature is lower on the both ends e side than on the center m side in the width direction. In other words, the paper P is cooled so that the temperature is lower on the both ends e side, opposite to the temperature distribution of the heater 22 described above (see FIGS. 11 and 12).

[0074] In this manner, in this embodiment, the both ends e of the width direction of the paper P, which are heated to a high temperature by the heater 22, are cooled in advance to a low temperature, so that when the paper P enters the fixing position B (fixing nip) and is heated, it is possible to prevent the both ends e of the width direction of the paper P from becoming at a higher temperature than the center m of the width direction. This makes it possible to prevent variations in the glossiness or density of the image caused by the paper P being heated at different temperatures across the width direction U.

[0075] In addition, in order to effectively lower the temperature on both ends e of the width direction of the paper P, it is preferable that the blower fan 35 is disposed closer to both ends e of the width direction than the center m of the width direction of the paper P. More specifically, it is preferable that the blower fan 35, particularly the blower port 35a (see FIG. 14), is disposed closer to both ends e of the width direction than the center m of the width direction of the paper P. Here, disposing the blower port 35a at a position closer to both ends e of the width direction than the center m of the width direction of the paper P means that the distance in the paper width direction U from each end e of the width direction of the paper P to the closest part of the blower port 35a is shorter than the distance in the paper width direction U from the center m of the width direction of the paper P to the closest part of the blower port 35a. For example, in the example shown in FIG. 14, the distance in the paper width direction U from the center m of the width direction of the paper P to the closest part of the blower port 35a is the distance β in the figure, while the distance in the paper width direction U from each end e of the paper P to the closest part of the blower port 35a is 0 because the blower port 35a is disposed so as to overlap each end e of the paper P.

[0076] The position of the blower fan 35 may be determined based on the temperature distribution of the heater 22. For example, in the example shown in Fig. 11 above, the temperature (total heat generation amount) is highest in the seventh block at one end of the heater 22 in the longitudinal direction, and in the example shown in Fig. 12 above, the temperature (total heat generation amount) is highest in the second block on the opposite side. Therefore, in either case, it is preferable to arrange the blower port 35a of each blower fan 35 at a position corresponding to at least one of the second block J2 and the seventh block J7 among the seven blocks J1 to J7 obtained by dividing the heater 22 into the resistance heating elements 59A to 59G, as shown in Fig. 15, so as to prevent the temperature from becoming high at both ends in the width direction of the paper P.

[0077] Furthermore, since the heat generation temperature of each of the blocks J1 to J7 of the heater 22 corresponds to the total value of the current flowing through the resistance heating elements 59 and the power supply lines 62 in each of the blocks J1 to J7, the position of the air outlet 35a of the blower fan 35 may be determined based on the total value of the current flowing through each of the blocks J1 to J7. In other words, by arranging the air outlet 35a at a position corresponding to the block with the largest total value of the current flowing through each of the blocks J1 to J7, it is possible to prevent the temperature at both ends e in the width direction of the paper P from becoming too high.

[0078] 11 or 12, when the heat generation temperature differs between one end and the other end in the longitudinal direction of the heater 22 depending on the way the heater 22 generates heat, the cooling capacity may be adjusted by changing the air volume (air speed) of each blower fan 35. In this case, by making the air volume of the blower fan 35 on the end side where the heat generation temperature is high greater than the air volume of the blower fan 35 on the end side where the temperature is low, the cooling capacity on the side where the heat generation temperature is high can be increased and the variation in temperature of the paper P can be suppressed.

[0079] Further, the blower fan 35 may be provided only on one end side in the width direction of the paper P. For example, as in the example shown in Fig. 11 or 12, when the temperature differs between one end side and the other end side in the longitudinal direction of the heater 22, the blower fan 35 may be provided only at a position corresponding to the end side of the heater where the temperature is higher.

[0080] In addition, when the blower fan 35 cannot be disposed near the paper P, as in the example shown in FIG. 16, the cooling means may include, in addition to the blower fan 35, a duct 36 as a guide path for guiding air from the blower fan 35 to the paper P. In this case, as shown in FIG. 17, by disposing the openings 36a of the duct 36 at positions corresponding to both ends e in the width direction U of the paper P, the air from the blower fan 35 can be blown mainly to both ends e in the width direction of the paper P and their neighboring parts. As a result, the paper P is cooled so that the temperature is lower on both ends e in the width direction, and therefore, when the paper P is heated by the fixing device 9, it is possible to prevent the both ends e in the width direction of the paper P from becoming higher in temperature than the center m in the width direction. In addition, by using the duct 36, the air blown out from one blower fan 35 can be distributed to both ends e in the width direction of the paper P, and therefore the number of blower fans 35 installed can be reduced, leading to miniaturization and cost reduction.

[0081] Furthermore, in order to effectively reduce the temperature on both ends e of the width direction of the paper P, it is preferable that the openings 36a of the duct 36 are located closer to both ends e in the width direction than to the width direction center m of the paper P. In other words, it is sufficient that the distance in the paper width direction U from each end e in the width direction of the paper P to the closest part of the openings 36a of the duct 36 is shorter than the distance in the paper width direction U from the width direction center m of the paper P to the closest part of the openings 36a of the duct 36.

[0082] As with the position of the blower fan 35 described above, the position of the opening 36a of the duct 36 may also be determined based on the temperature distribution of the heater 22 or the total value of the current flowing in each block. For example, as shown in Fig. 18, by arranging each opening 36a of the duct 36 at a position corresponding to the seventh block J7 which has the highest temperature (the largest total value of the current) in the example shown in Fig. 11 and the second block J2 which has the highest temperature (the largest total value of the current) in the example shown in Fig. 12, it becomes possible to prevent the temperature from becoming too high on both ends e of the width direction of the paper P in either case.

[0083] In addition, when there is a variation in the heat generation temperature between one end side and the other end side of the heater 22 in the longitudinal direction, the sizes d1, d2 of one opening 36a of the duct 36 and the other opening 36a in the paper transport direction (recording medium transport direction) V may be made different from each other, as in the example shown in Fig. 19. In this case, by making the size d1 of the opening 36a at the end side where the heat generation temperature is high larger than the size d2 of the opening 36a at the end side where the heat generation temperature is low, the cooling capacity on the side where the heat generation temperature is high can be increased and the variation in the temperature of the paper P can be suppressed. In addition, when the heat generation temperature of the heater 22 changes, the opening area of ​​each opening 36a of the duct 36 can be changed in response to the temperature change, or the amount of air (wind speed) of air blown out from each opening 36a of the duct 36 can be changed using multiple blower fans 35, thereby making it possible to adjust the cooling capacity.

[0084] 20, the openings 36a of the duct 36 may be disposed in three or more locations including the center m and both ends e of the width direction of the paper P. In this case, by making the size d in the paper transport direction V larger for the openings 36a disposed closer to the end e of the width direction of the paper P, the cooling capacity at the end e of the width direction of the paper P can be increased.

[0085] 21, the openings 36a of the duct 36 may be provided continuously from the center m of the width of the paper P to both ends e of the width of the paper P. In this case as well, the size d of each opening 36a in the paper transport direction V is larger on the both ends e of the width of the paper P than on the center m of the width of the paper P, thereby improving the cooling capacity on the ends e of the width of the paper P.

[0086] In the example shown in Figure 20 or the example shown in Figure 21, the opening 36a of the duct 36 is formed symmetrically with respect to the widthwise center m of the paper P, but if the heat generation temperature differs between one end and the other end of the heater 22 in the longitudinal direction, the size d of the openings 36a on the one end and the other end in the paper transport direction V may be made different depending on the heat generation temperature, so that the opening 36a of the duct 36 is asymmetric.

[0087] Furthermore, the opening 36a of the duct 36 may be provided only on one end side in the width direction of the paper P. For example, the opening 36a of the duct 36 may be provided only at a position corresponding to the end side with a higher temperature among both ends in the width direction of the paper P.

[0088] Next, the examples shown in Figs. 22 to 24 are examples in which a cooling member that cools the paper by coming into contact with the paper is used as the cooling means.

[0089] 22, in this example, a rotatable cooling roller 37 is provided as a cooling member between transfer position A and fixing position B. At least the surface (outer circumferential surface) of cooling roller 37 is made of a metal material or the like having better thermal conductivity than paper P. Therefore, as shown in FIG. 22, when cooling roller 37 comes into contact with paper P, heat is transferred from paper P to cooling roller 37, thereby cooling paper P.

[0090] 23, the cooling rollers 37 are provided at positions corresponding to both ends e of the width direction U of the paper P. Therefore, when the paper P comes into contact with each cooling roller 37, the paper P is mainly cooled at both ends e of the width direction and the adjacent portions thereof. As a result, the paper P is cooled so that the temperature is lower at both ends e than at the center m of the width direction. That is, in this case as well, the paper P is cooled so that the temperature is lower at both ends e, in contrast to the temperature distribution of the heater 22, so that the temperature of both ends e of the width direction of the paper P can be prevented from becoming higher than that of the center m of the width direction. This makes it possible to prevent variations in the glossiness or density of the image caused by variations in the temperature distribution of the heater 22.

[0091] Furthermore, when the paper P comes into contact with the cooling roller 37, the cooling roller 37 rotates, and the surface of the cooling roller 37 that comes into contact with the paper P changes (because the same surface does not come into contact), so that heat can be effectively transferred from the paper P to the cooling roller 37. The cooling roller 37 may be rotated by contact with the paper P, or may be configured to be rotated by a drive source. Furthermore, as shown in FIG. 22, the surface of the paper P that comes into contact with the cooling roller 37 is preferably the surface opposite the image forming surface to which the unfixed toner T adheres, so that the unfixed toner T on the paper P is not disturbed by contact with the cooling roller 37.

[0092] In this example, in order to make the cooling roller 37 contact the paper P more reliably, as shown in FIG. 22, the cooling roller 37 (contact surface 37a) is disposed at a position that is further into the image forming surface side (left side in the figure) of the paper P than the straight line α that passes through the transfer position A and the fixing position B. Furthermore, the speed at which the paper P is transported at the fixing position B is set to be slightly faster than the speed at which the paper P is transported at the transfer position A so that tension acts on the paper P between the transfer position A and the fixing position B. Therefore, when the paper P is transported between the transfer position A and the fixing position B, tension acts on the paper P, and the paper P is pressed against the cooling roller 37 by the tension. This ensures that the paper P and the cooling roller 37 come into contact with each other, and the paper P is effectively cooled. In addition, between the cooling roller 37 and the transfer position A, or between the cooling roller 37 and the fixing position B, there may be another pair of rotating bodies such as a pair of transport rollers. In this case, the straight line α may be a straight line passing through the nip portions of the pair of rotating bodies closest to the upstream side and the downstream side of the cooling roller 37 in the paper transport direction.

[0093] Furthermore, in order to effectively lower the temperature on both ends e of the width direction of the paper P, it is preferable that the contact surface 37a (see FIG. 23) of the cooling roller 37 that comes into contact with the paper P is positioned closer to both ends e in the width direction than to the width direction center m of the paper P. In other words, it is only necessary that the distance in the paper width direction U from each end e of the paper P to the closest part of the contact surface 37a of the cooling roller 37 is shorter than the distance in the paper width direction U from the width direction center m of the paper P to the closest part of the contact surface 37a of the cooling roller 37.

[0094] Also, similarly to the above example, the position of the cooling roller 37 and its contact surface 37a may be determined based on the temperature distribution of the heater 22 or the total value of the current flowing in each block. For example, as shown in Fig. 24, by arranging the cooling roller 37 and its contact surface 37a at a position corresponding to the seventh block J7 having the highest temperature (the largest total value of the current) in the example shown in Fig. 11 and the second block J2 having the highest temperature (the largest total value of the current) in the example shown in Fig. 12, it becomes possible to prevent the temperature from becoming high at both ends in the width direction of the paper P in either case.

[0095] In order to increase the cooling capacity of the cooling roller 37, a blower fan for cooling the cooling roller 37 may be provided, or the cooling roller 37 may be a heat pipe roller. As in the above example, the cooling roller 37 may be provided only at one end side in the width direction of the paper P, or may be provided at three or more locations across the paper width direction U. Furthermore, a plurality of cooling rollers 37 may be provided across the paper transport direction V between the transfer position A and the fixing position B.

[0096] Next, the example shown in Figs. 25 to 29 is an example in which a cooling guide 38 that makes sliding contact with the paper P relatively is used as the cooling member.

[0097] In this way, a non-rotating member such as cooling guide 38 may be used as the cooling member. As with cooling roller 37 described above, cooling guide 38 is made of a metal material or the like having a higher thermal conductivity than paper P at least on the surface that contacts paper P. Therefore, as shown in Fig. 25, when cooling guide 38 contacts paper P, heat is transferred from paper P to cooling guide 38, and paper P is cooled.

[0098] Also, in this example, the surface of the cooling guide 38 is formed with a curved surface with a smaller curvature (larger radius of curvature) than the above-mentioned cooling roller 37, so that the contact area with the paper P (contact range in the paper transport direction V) is larger. This increases the cooling capacity and allows the paper P to be cooled effectively. Note that, similar to the above-mentioned example, it is preferable that the surface of the paper P that the cooling guide 38 contacts is the surface opposite to the image forming surface to which the unfixed toner T adheres, so that the unfixed toner T on the paper P is not disturbed.

[0099] 26, the cooling guide 38 is formed unevenly across the paper width direction U, and is configured to contact only both ends e of the paper P in the width direction and their adjacent areas. As a result, when the paper P comes into contact with the cooling guide 38, mainly both ends e of the paper P in the width direction and their adjacent areas are cooled, and similarly to the above example, the both ends e of the paper P in the width direction are prevented from becoming higher in temperature than the center m of the paper P in the width direction.

[0100] Also in this example, in order to ensure contact between the paper P and the cooling guide 38, as shown in Fig. 25, the cooling guide 38 (contact surface 38a) is positioned closer to the image forming surface side of the paper P (left side in the figure) than the straight line α passing through the transfer position A and the fixing position B. Therefore, the tension acting on the paper P presses the paper P against the cooling guide 38, ensuring contact between the paper P and the cooling guide 38 and allowing the paper P to be effectively cooled.

[0101] 27, in order to effectively lower the temperature on both ends e of the width direction of the paper P, it is preferable that the contact surface 38a of the cooling guide 38 that comes into contact with the paper P is positioned closer to both ends e of the width direction than to the width direction center m of the paper P. That is, as in the above example, it is sufficient that the distance in the paper width direction U from each end e of the width direction of the paper P to the closest part of the contact surface 38a of the cooling guide 38 is shorter than the distance in the paper width direction U from the width direction center m of the paper P to the closest part of the contact surface 38a of the cooling guide 38.

[0102] The position of the contact surface 38a of the cooling guide 38 may be determined based on the temperature distribution of the heater 22 or the total value of the current flowing in each block. For example, as shown in Fig. 28, by disposing the contact surface 38a of the cooling guide 38 at a position corresponding to the seventh block J7 which has the highest temperature (the largest total value of the current) in the example shown in Fig. 11 and the second block J2 which has the highest temperature (the largest total value of the current) in the example shown in Fig. 12, it becomes possible to prevent the temperature from becoming too high at both ends in the width direction of the paper P in either case.

[0103] 29, the size f of the contact surface 38a of the cooling guide 38 in the paper transport direction V may be made larger on both ends e of the width direction of the paper P than on the center m of the width direction of the paper P. In this case, the cooling capacity on the ends e of the width direction of the paper P can be increased.

[0104] Also, in order to increase the cooling capacity of the cooling guide 38, a blower fan for cooling the cooling guide 38 may be provided. Also, the cooling guide 38 may be configured to contact the paper P only at one end side in the width direction, or may be configured to contact the paper P at three or more points in the width direction U. Furthermore, multiple cooling guides 38 may be provided across the paper transport direction V between the transfer position A and the fixing position B.

[0105] Furthermore, the examples shown in FIGS. 30 to 34 are examples in which an intermediate transfer belt 11 is used as a cooling means.

[0106] As shown in Fig. 30, in this example, the intermediate transfer belt 11, a blower fan (blower means) 41 that blows air to the intermediate transfer belt 11, and a duct 42 that serves as a guide path for guiding air from the blower fan 41 to the intermediate transfer belt 11 are provided as cooling means (cooling members) for cooling the paper. When air is blown out from the blower fan 41, the air is blown through the duct 42 to the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 is first cooled. Then, the cooled intermediate transfer belt 11 comes into contact with the paper P, so that the paper P is cooled.

[0107] 31, a part of the duct 42 arranged inside the intermediate transfer belt 11 opens at a position corresponding to or near both ends g of the intermediate transfer belt 11 in the width direction W (paper width direction U). Therefore, air blown out from the opening 42a of the duct 42 is blown mainly onto both ends g of the intermediate transfer belt 11 in the width direction and the parts in their vicinity. This causes the intermediate transfer belt 11 to be cooled so that the temperature on both ends g side in the width direction is lower than that on the center i side in the width direction.

[0108] In this way, mainly both widthwise end g sides of the intermediate transfer belt 11 are cooled, and when the intermediate transfer belt 11 comes into contact with the paper P, mainly both widthwise end e sides of the paper P are cooled. That is, the lower temperature parts of the intermediate transfer belt 11 on both widthwise end g sides come into contact with the parts of the paper P on both widthwise end e sides, so that both widthwise end e sides of the paper P are effectively cooled. As a result, similar to the above example, the temperature of both widthwise end e sides of the paper P becomes lower than the temperature of the widthwise center m side, and the widthwise end e sides of the paper P are prevented from becoming higher in temperature than the widthwise center m side.

[0109] 30, the surface of the intermediate transfer belt 11 onto which the air is blown is preferably the inner peripheral surface of the intermediate transfer belt 11 so as not to disturb the image (toner) carried on the outer peripheral surface. In that case, the duct 42 is disposed inside the intermediate transfer belt 11, which also contributes to space saving and size reduction.

[0110] 32, the position where the intermediate transfer belt 11 is cooled (the position where air is blown) is preferably any position within a range H1 from the nip portion (primary transfer nip) with the most downstream photoconductor 2 to the transfer position A (secondary transfer nip) where an image is transferred to the paper P in the rotation direction C of the intermediate transfer belt 11. On the other hand, if the position where the intermediate transfer belt 11 is cooled is a range H3 from the transfer position A to the nip portion with the most downstream photoconductor 2, the intermediate transfer belt 11 comes into contact with the cleaning member 55 and the photoconductor 2, and the temperature deviation due to cooling is alleviated, and the paper P cannot be effectively cooled. Therefore, by setting the position where the intermediate transfer belt 11 is cooled within the above range H1, it is possible to prevent the cooled portion from coming into contact with the photoconductor 2 and the cleaning member 55, and the paper P can be effectively cooled. More preferably, the position where the intermediate transfer belt 11 is cooled is within a range H2 from the transfer position A shown in Fig. 32 to a quarter of the length of the intermediate transfer belt 11 in the direction opposite to the rotation direction C. In this case, the intermediate transfer belt 11 can be cooled at a position close to or immediately before the transfer position A, so that the paper P can be cooled even more effectively.

[0111] Furthermore, such an arrangement of the duct 42 with respect to the intermediate transfer belt 11 is not limited to the example in which the photoconductors 2 are arranged above the intermediate transfer belt 11 as shown in Fig. 32, but can also be applied to a configuration in which the photoconductors 2 are arranged below the intermediate transfer belt 11 as shown in Fig. 33. In the example shown in Fig. 33, the range H1 from the nip between the most downstream photoconductor 2 and the intermediate transfer belt 11 to the transfer position A is shorter than in the example shown in Fig. 32, but if possible, the duct 42 can be arranged so that the intermediate transfer belt 11 can be cooled within this range H1, thereby making it possible to effectively cool the paper P in the same manner as described above.

[0112] 17, the openings 42a of the duct 42 that blows air onto the intermediate transfer belt 11 are preferably disposed in positions close to both ends e of the width direction of the paper P or in positions close to both ends g of the width direction of the intermediate transfer belt 11. The shape, size, or number of the openings 42a of the duct 42 can also be changed as appropriate following the examples shown in the above-mentioned FIGS.

[0113] 34, the flow path in the duct 42 may be divided into two by a partition plate or the like so that air can be guided from one duct inlet to each of one end side and the other end side in the width direction of the intermediate transfer belt 11. In this case, air blown out from one blower fan 41 can be blown to both ends in the width direction of the intermediate transfer belt 11, so that the blower fan 41 can be provided only on one side in the width direction W of the intermediate transfer belt 11, thereby achieving size reduction and cost reduction.

[0114] As described above, the image forming apparatus according to the present invention is provided with a cooling means having a higher cooling capacity at the widthwise ends of the paper than at the widthwise center, and thus can pre-cool the paper so that the temperature at the widthwise ends of the paper is lower, in contrast to the heater temperature distribution. This makes it possible to suppress variations in the glossiness or density of the image caused by variations in the heater temperature distribution, and ultimately improves the image quality. In addition, by improving the deterioration of image quality caused by variations in the heater temperature distribution, it becomes possible to accommodate configurations using small heaters that are prone to variations in temperature distribution, or heaters that have increased heat generation for higher speeds.

[0115] Therefore, the present invention is expected to be particularly effective when applied to an image forming apparatus equipped with a small heater as described below. Specifically, the present invention is expected to be particularly effective when applied to a heater 22 in which the ratio (R / Q) of the short-side dimension R of the resistance heating element 59 to the short-side dimension Q of the substrate 50 as shown in FIG. 35 is 25% or more. Furthermore, the effect of applying the present invention is even greater for a heater 22 in which the short-side dimension ratio (R / Q) is 40% or more. In the example shown in FIG. 35, the substrate 50 of the heater 22 is formed in a rectangular shape, so that the short-side dimension Q of the substrate 50 is the same at any longitudinal position. However, when the substrate 50 has an uneven edge and the short-side dimension Q changes depending on the position in the longitudinal direction Z, the above-mentioned short-side dimension ratio (R / Q) may be established for the portion in the longitudinal range in which the resistance heating element 59 is disposed, where the short-side dimension Q of the substrate 50 is the smallest.

[0116] Also, in order to suppress the temperature variation in the heater, a resistance heating element having a PTC characteristic may be used. The PTC characteristic is a characteristic in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). By using a heating part having a PTC characteristic, it is possible to achieve high output at low temperatures and suppress excessive temperature rise with low output at high temperatures. For example, if the TCR coefficient of the PTC characteristic is set to about 300 to 4000 ppm / degree, it is possible to reduce costs while ensuring the resistance value required for the heater. It is more preferable to set the TCR coefficient to 500 to 2000 ppm / degree.

[0117] The temperature coefficient of resistance (TCR) can be calculated using the following formula (3). In formula (3), T0 is a reference temperature, T1 is an arbitrary temperature, R0 is a resistance value at the reference temperature T0, and R1 is a resistance value at the arbitrary temperature T1. For example, in the heater 22 described above shown in FIG. 10, if the resistance value between the first electrode portion 61A and the second electrode portion 61B is 10Ω (resistance value R0) at 25°C (reference temperature T0) and 12Ω (resistance value R1) at 125°C (arbitrary temperature T1), the temperature coefficient of resistance is 2000 ppm / °C from formula (3).

[0118]

number

[0119] Furthermore, the heater provided in the fixing device is not limited to a heater 22 having a block-shaped (square-shaped) resistive heating element 59 as shown in FIG. 35, but may be a heater 22 having a resistive heating element 59 shaped like a folded straight line as shown in FIG. 36, or a heater having a resistive heating element of another shape.

[0120] Further, the fixing device provided in the image forming apparatus is not limited to the above-mentioned fixing device, but may be a fixing device as shown in Figures 37 to 39. The configuration of each fixing device shown in Figures 37 to 39 will be briefly described below.

[0121] 37 differs from the above-described fixing devices in that a pressure roller 90 is disposed on the side of fixing belt 20 opposite to the pressure roller 21 side. In this case, the fixing belt 20 is sandwiched and heated by the pressure roller 90 and heater 22. Meanwhile, on the pressure roller 21 side, a nip forming member 91 is disposed on the inner periphery of fixing belt 20. Nip forming member 91 is supported by stay 24, and nip portion N is formed by nipping fixing belt 20 between nip forming member 91 and pressure roller 21.

[0122] 38, the above-mentioned pressure roller 90 is omitted, and in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22, the heater 22 is formed in an arc shape in accordance with the curvature of the fixing belt 20. The rest of the configuration is the same as that of the fixing device 9 shown in FIG.

[0123] 39, a pressure belt 92 is provided in addition to the fixing belt 20, and a heating nip (first nip portion) N1 and a fixing nip (second nip portion) N2 are separately configured. That is, a nip forming member 91 and a stay 93 are also arranged on the opposite side of the pressure roller 21 from the fixing belt 20 side, and the pressure belt 92 is arranged so as to enclose the nip forming member 91 and the stay 93. The rest of the configuration is the same as that of the fixing device 9 shown in FIG.

[0124] By applying the present invention to an image forming apparatus equipped with a fixing device such as that shown in Figures 37 to 39, it becomes possible to suppress variations in image gloss or density caused by variations in heater temperature distribution, thereby improving image quality and enabling miniaturization or high speed printing.

[0125] In the above embodiment, the present invention is applied to a so-called intermediate transfer type image forming apparatus in which an image on the photoreceptor 2 is transferred to the paper P via the intermediate transfer belt 11. However, the present invention can also be applied to a direct transfer type image forming apparatus in which an image on the photoreceptor 2 is directly transferred to the paper P without the intermediate transfer belt as shown in FIG. 40. As shown in FIG. 40, even in the direct transfer type image forming apparatus, it is possible to suppress the variation in the glossiness or density of the image caused by the variation in the temperature distribution of the heater by arranging a cooling means such as the above-mentioned blower fan 35 between the transfer position A where the image is transferred from the photoreceptor 2 to the paper P and the fixing position B where the image on the paper P is fixed. In addition, the present invention is not limited to a color image forming apparatus, but can also be applied to a monochrome image forming apparatus. [Explanation of symbols]

[0126] 9 Fixing device 35 Blower fan (blower means) 36 Duct (taxiway) 36a opening 37 Cooling roller (cooling member) 37a Contact surface 38 Cooling guide (cooling member) 38a Contact surface 41 Blower fan (blower means) 42 Duct (taxiway) 50 Base material 59 Resistance heating element (heating element) 60 Heating Part 61A 1st electrode part 61B 2nd electrode part 100 Image forming device 200 Image forming section P Paper (recording medium) K1 First conductive path K2 Second conductive path K3 Third conductive path S1 1st direction S2 2nd direction [Prior art documents] [Patent documents]

[0127] [Patent Document 1] JP 2016-62024 A

Claims

1. an image forming unit that forms an image on a recording medium; a fixing device for fixing an image onto the recording medium; An image forming apparatus comprising: the fixing device includes a heating member for heating the recording medium, The heating member is A substrate disposed in a width direction of the recording medium perpendicular to a conveying direction of the recording medium; A heating element; A first electrode portion; A second electrode portion; A first conductive path connecting the heating element and the first electrode portion; a second conductive path extending from the heating element in a first direction among the width directions of the recording medium and connected to the second electrode portion; a third conductive path that branches off from the second conductive path, extends in a second direction opposite to the first direction, and is connected to the second conductive path or the second electrode portion without passing through the first conductive path; having a cooling unit for cooling a surface of the recording medium opposite to an image forming surface thereof before the image is fixed to the recording medium by the fixing device; The image forming apparatus has a cooling capacity higher at least at one end side in the width direction of the recording medium than at a center side in the width direction of the recording medium.

2. An image forming apparatus as described in claim 1, wherein the cooling means is provided with an air blowing means for blowing air onto the recording medium.

3. The cooling means includes an induction path for guiding air from the blowing means to the recording medium, 3. The image forming apparatus according to claim 2, wherein the opening of the guide path for blowing air onto the recording medium is disposed at a position closer to at least one end in the width direction of the recording medium than to a center in the width direction of the recording medium.

4. The cooling means includes an induction path for guiding air from the blowing means to the recording medium, 3. The image forming apparatus according to claim 2, wherein an opening of the guide path for blowing air onto the recording medium is formed larger at least on one widthwise end side of the recording medium than on a widthwise center side of the recording medium.

5. An image forming unit that forms an image on a recording medium; a fixing device for fixing an image onto the recording medium; An image forming apparatus comprising: the fixing device includes a heating member for heating the recording medium, The heating member is A substrate disposed in a width direction of the recording medium perpendicular to a conveying direction of the recording medium; A heating element; A first electrode portion; A second electrode portion; A first conductive path connecting the heating element and the first electrode portion; a second conductive path extending from the heating element in a first direction among the width directions of the recording medium and connected to the second electrode portion; a third conductive path that branches off from the second conductive path, extends in a second direction opposite to the first direction, and is connected to the second conductive path or the second electrode portion without passing through the first conductive path; having a cooling unit that cools the recording medium before the image is fixed on the recording medium by the fixing device; the cooling means includes a cooling member that comes into contact with the recording medium to cool it; The image forming apparatus has a cooling capacity higher at least at one end side in the width direction of the recording medium than at a center side in the width direction of the recording medium.

6. An image forming apparatus as described in Claim 5, wherein the cooling member contacts the recording medium at a position that is at least closer to one width end than to the width center of the recording medium.

7. An image forming apparatus as described in Claim 5, wherein the contact surface of the cooling member with the recording medium is larger at least at one widthwise end side of the recording medium than at the widthwise center side.

8. An image forming apparatus as described in Claim 5, wherein the cooling member is a transfer member that transfers an image onto the recording medium.

9. The transfer member is an endless belt member, 9. The image forming apparatus according to claim 8, wherein the cooling unit includes a blowing unit that blows air onto the belt member.

10. The cooling means has a guide path for guiding air from the blowing means to the transfer belt, The image forming apparatus according to claim 9 , wherein the guide path is disposed inside the transfer belt.

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