JP6521355B2 - Fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus provided with the same.

  As a fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or a printer, a belt fixing device using an endless fixing belt in place of a heating roller has been put to practical use. The belt fixing apparatus heats the fixing belt with a heat source and presses a nip forming member disposed inside the fixing belt against the fixing belt to form a fixing nip between the fixing belt and the pressure roller. Because the fixing belt is formed of a film material having a small heat capacity, it is characterized by being excellent in energy saving property and quick start property {see Patent Document 1 (Japanese Patent Laid-Open No. 2014-134701)}.

  As described above, the fixing device is composed of various members including the fixing belt and the pressure roller. Among them, the nip forming member is important because it largely depends on the fixing property of the image and the sheet conveying property. It is one of the members. Therefore, the inventors have developed a new nip forming member. However, when a newly developed nip forming member is mounted on a fixing device and printing is attempted, a problem occurs that a desired fixing property can not be obtained.

  As a result of intensive investigations by the inventors for these problems, the desired fixing property was not obtained because a gap was formed between the nip forming member and the fixing belt at the step portion. We came to the knowledge that there is. That is, if there is a step portion in the area forming the fixing nip of the nip forming member, the pressure roller and the fixing belt can not sufficiently deform following the shape of the step portion, whereby the nip forming member and the fixing belt There is a gap between the As a result, it was newly found that a pressure drop was partially generated at the fixing nip, and a problem that the fixing property was lowered at the pressure dropped portion was generated.

In order to solve the above problems, the present invention provides a rotation having a flexible first rotatable fixing member and an elastic layer to form a fixing nip between the first fixing member. A second fixing member, a heating source for heating the first fixing member, an inner circumferential surface of the first fixing member and the heating source, and the first fixing member And a nip forming member facing the second fixing member via the first fixing member to form the fixing nip, wherein the heat source is at least a portion of the first fixing member other than the fixing nip. A step is provided on the inner periphery of the first fixing member so as to heat directly, and a step is formed in a region forming the fixing nip of the nip forming member, and the nip forming member and the Fill the gap that occurs with one fixing member Between filling member, is interposed between said nip forming member first fixing member, the region for forming the fixing nip of the nip forming member, a first flat surface, said first flat surface A second flat surface disposed closer to the second fixing member at the exit side of the fixing nip than the fixing nip, and the step portion connecting the first flat surface and the second flat surface And the first flat surface and the second flat surface are disposed parallel to each other .

  According to the present invention, the gap between the nip forming member and the first fixing member in the stepped portion can be filled, and partial pressure loss in the fixing nip can be highly suppressed, and a good image can be obtained. It becomes possible.

FIG. 1 is a schematic view showing an entire configuration of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view of a fixing device according to the present invention. FIG. 1 is a perspective view showing a schematic configuration of main parts of a fixing device according to the present invention. FIG. 2 is a cross-sectional view of a nip forming portion used in the fixing device according to the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of a main part of a fixing device according to the present invention. FIG. 6 is a cross-sectional view showing a schematic configuration of main parts of a fixing device according to a comparative example. FIG. 6 is a cross-sectional view showing a schematic configuration of a fixing device according to another embodiment of the present invention. FIG. 5 is an enlarged view of a fixing nip.

  Hereinafter, an embodiment of the present invention will be described based on the attached drawings. In each of the drawings for describing the embodiments of the present invention, components such as members having the same function or shape and components such as components are described once by attaching the same reference numerals as much as possible. So I will omit the explanation.

First, with reference to FIG. 1, an entire configuration and an operation of an image forming apparatus according to an embodiment of the present invention will be described.
The image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided at the center of the apparatus main body. The image forming units 4Y, 4M, 4C and 4K contain developers of different colors of yellow (Y), magenta (M), cyan (C) and black (K) corresponding to color separation components of a color image. Other than the above, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photosensitive member 5 as a latent image carrier, a charging device 6 for charging the surface of the photosensitive member 5, and a surface of the photosensitive member 5. The developing device 7 that supplies toner, and a cleaning device 8 that cleans the surface of the photosensitive member 5 are provided. In FIG. 1, only the photosensitive member 5, the charging device 6, the developing device 7, and the cleaning device 8 provided in the black image forming unit 4K are denoted by reference numerals, and in the other image forming units 4Y, 4M, and 4C. The sign is omitted.

  Below each image forming unit 4Y, 4M, 4C, 4K, an exposure device 9 for exposing the surface of the photosensitive member 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photosensitive member 5 with a laser beam based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, and a secondary transfer backup roller 32. A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33 and a tension roller 34. Here, by driving the secondary transfer backup roller 32 to rotate, the intermediate transfer belt 30 travels (rotates) in the direction indicated by the arrow in the figure.

  The four primary transfer rollers 31 respectively sandwich the intermediate transfer belt 30 with the respective photosensitive members 5 to form a primary transfer nip. Further, a power supply is connected to each primary transfer roller 31, and a predetermined DC voltage (DC) and / or an alternating voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, as in the case of the primary transfer roller 31, a power supply is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or an AC voltage (AC) is applied to the secondary transfer roller 36. It is supposed to be.

  The belt cleaning device 35 has a cleaning brush and a cleaning blade disposed to abut the intermediate transfer belt 30. The waste toner collected by the belt cleaning device 35 is stored in a waste toner storage container through a waste toner transfer hose.

  In the upper part of the image forming apparatus main body, a bottle housing portion 2 is provided, and in the bottle housing portion 2, four toner bottles 2Y, 2M, 2C, 2K for containing toner for replenishment are detachably mounted. ing. The toners are replenished from the toner bottles 2Y, 2M, 2C, 2K to the developing devices 7 through the replenishment paths provided between the toner bottles 2Y, 2M, 2C, 2K and the developing devices 7.

  On the other hand, at the lower part of the image forming apparatus main body, a sheet feeding tray 10 accommodating sheets P as a recording medium, a sheet feeding roller 11 for discharging the sheet P from the sheet feeding tray 10 and the like are provided. The recording medium includes, in addition to plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, etc. In addition, a manual sheet feeding mechanism may be provided.

  In the image forming apparatus main body, a conveyance path R for discharging the sheet P from the sheet feeding tray 10 through the secondary transfer nip to the outside of the apparatus is disposed. On the transport path R, on the upstream side of the position of the secondary transfer roller 36 in the sheet transport direction with respect to the position of the secondary transfer roller 36, a pair of registration rollers 12 as timing rollers for transporting the sheet P to the secondary transfer nip is disposed. ing.

  Further, a fixing device 20 for fixing the unfixed image transferred to the sheet P is disposed downstream of the position of the secondary transfer roller 36 in the sheet conveyance direction. Further, on the downstream side of the fixing device 20 in the sheet conveyance direction of the conveyance path R, a pair of sheet discharge rollers 13 for discharging the sheet to the outside of the apparatus is provided. Further, a sheet discharge tray 14 for stocking sheets discharged to the outside of the apparatus is provided on the upper surface portion of the apparatus body.

Subsequently, the basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, each photosensitive member 5 in each image forming unit 4Y, 4M, 4C, 4K is rotationally driven clockwise in the figure, and the surface of each photosensitive member 5 is set to a predetermined polarity by the charging device 6. It is uniformly charged. Laser light is irradiated from the exposure device 9 on the surface of each charged photosensitive member 5 to form an electrostatic latent image on the surface of each photosensitive member 5. At this time, the image information to be exposed on each photosensitive member 5 is monochrome image information in which a desired full color image is separated into color information of yellow, magenta, cyan and black. Thus, the electrostatic latent image is visualized (visualized) as a toner image by supplying toner to each electrostatic latent image formed on each photosensitive member 5 by each developing device 7 .

  Further, when the image forming operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the figure to cause the intermediate transfer belt 30 to run in the direction shown by the arrow in the figure. In addition, a primary transfer nip between each primary transfer roller 31 and each photosensitive member 5 is applied by applying to each primary transfer roller 31 a constant voltage or a constant current controlled polarity opposite to the charging polarity of the toner. A transfer electric field is formed at.

  Thereafter, when the toner image of each color on the photosensitive member 5 reaches the primary transfer nip as the photosensitive member 5 rotates, the toner image on each photosensitive member 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photosensitive member 5 that can not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photosensitive member 5 is discharged by the discharging device, and the surface potential is initialized.

  At the lower part of the printer, the sheet feeding roller 11 starts to rotate and the sheet P is fed out from the sheet feeding tray 10 to the conveyance path R. The conveyance of the sheet P fed to the conveyance path R is temporarily stopped by the registration roller 12.

  Thereafter, rotational driving of the registration roller 12 is started at a predetermined timing, and the sheet P is conveyed to the secondary transfer nip at the timing when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to that of the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip. . Then, the toner image on the intermediate transfer belt 30 is collectively transferred onto the sheet P by the transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 which can not be transferred to the sheet P is removed by the belt cleaning device 35 and conveyed to the waste toner container.

  Thereafter, the sheet P is conveyed to the fixing device 20, and the toner image on the sheet P is fixed to the sheet P by the fixing device 20. Then, the sheet P is discharged to the outside of the apparatus by the sheet discharge roller 13 and is stocked on the sheet discharge tray 14.

  The above description is an image forming operation for forming a full color image on a sheet, but a monochrome image can be formed using any one of the four image forming units 4Y, 4M, 4C, 4K, It is also possible to use two or three imaging units to form a two or three color image.

FIG. 2 is a cross-sectional view of the fixing device of the present embodiment.
The configuration of the fixing device 20 will be described below with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a first fixing member, a pressure roller 22 as a second fixing member in contact with the outer peripheral surface of the fixing belt 21, and the fixing belt 21. Reflects the heat from the halogen heater 23 as a heating source to heat, the nip forming member 24 forming the fixing nip N, the stay 25 as a supporting member supporting the nip forming member 24, and the halogen heater 23 to the fixing belt 21 And a shielding member 27 for shielding the heat from the halogen heater 23, and a temperature sensor 28 as a temperature detecting means for detecting the temperature of the fixing belt 21.

  The fixing belt 21 is formed of a flexible film-like endless belt. Specifically, the fixing belt 21 is made of an inner peripheral base material made of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) Or it is comprised by the mold release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the base and the release layer.

  When the elastic layer is not present, the heat capacity is reduced and the fixing property can be improved. However, when the unfixed toner is crushed and fixed, the minute unevenness on the belt surface is transferred to the image, and the uneven portion of the image is uneven in gloss. It may occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing the elastic layer having a thickness of 100 μm or more, fine irregularities can be absorbed by the elastic deformation of the elastic layer, so that occurrence of gloss unevenness can be avoided.

  In the present embodiment, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer that constitute the fixing belt 21 are set in the range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, respectively, and the thickness as a whole is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, and more preferably 0.16 mm or less. The diameter of the fixing belt 21 is preferably 30 mm or less.

  In the present embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. However, the present invention is not limited to this configuration. For example, the diameter of the fixing belt 21 may be smaller than the diameter of the pressure roller 22.

  As shown in FIG. 3, a belt holding member 40 is inserted in the inner circumference of both end portions of the fixing belt 21. The fixing belt 21 is rotatably supported by belt holding members 40 at both ends, and basically there is no member supporting the fixing belt 21 other than the belt holding member 40. That is, the fixing belt 21 is in a non-tensioned state in which the fixing belt 21 is not stretched over a roller or the like. The belt holding member 40 is fixed to a pair of side plates provided on both sides in the axial direction of the fixing device 20 together with the halogen heater 23 and the stay 25.

  As shown in FIG. 2, the pressure roller 22 comprises a core metal 22a, an elastic layer 22b made of a rubber material such as foamable silicone rubber, silicone rubber, or fluoro rubber provided on the surface of the core metal 22a, and elasticity. It is comprised by the release layer 22c which consists of PFA or PTFE etc. provided in the surface of the layer 22b. The pressure roller 22 is pressed toward the fixing belt 21 by the switching mechanism, and is in contact with the nip forming member 24 via the fixing belt 21. At a portion where the pressure roller 22 and the fixing belt 21 are in pressure contact with each other, the elastic layer 22 b of the pressure roller 22 is crushed to form a fixing nip N having a predetermined width.

  The pressure roller 22 is configured to be rotationally driven by a drive source such as a fixing motor provided in the apparatus main body. When the pressure roller 22 rotates, its driving force is transmitted to the fixing belt 21 at the fixing nip N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be provided inside the pressure roller 22. The elastic layer 22 b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more desirable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  The halogen heater 23 is disposed on the inner peripheral side of the fixing belt 21 and on the upstream side of the fixing nip N in the sheet conveying direction so as to heat the portion of the fixing belt 21 other than the fixing nip N. The halogen heater 23 is configured to generate an output under control of output by a power supply unit provided in the apparatus main body, and the output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 28. . By such output control of the heater 23, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired temperature. A temperature sensor for detecting the temperature of the pressure roller 22 is provided instead of the temperature sensor for detecting the temperature of the fixing belt 21, and the temperature of the fixing belt 21 is predicted by the temperature detected by the temperature sensor. It is also good.

  Although two halogen heaters 23 are provided in the present embodiment, the number of halogen heaters 23 may be one or three or more in accordance with the size of the sheet used in the printer. Besides the halogen heater, it is also possible to use an IH, a resistance heating element, a carbon heater or the like as a heating source for heating the fixing belt 21.

  The reflecting member 26 is fixedly supported by the stay 25 so as to face the halogen heater 23. By reflecting the radiant heat from the halogen heater 23 to the fixing belt 21 by the reflection member 26, the heat is prevented from being transmitted to the stay 25 or the like, and the fixing belt 21 can be efficiently heated, thereby saving energy. I am trying. As a material of the reflecting member 26, aluminum, stainless steel or the like is used. In particular, in the case of using a substrate made of aluminum on which silver having a low emissivity (high reflectance) is deposited, the heating efficiency of the fixing belt 21 can be improved.

  The shielding member 27 is configured by forming a metal plate having a thickness of 0.1 mm to 1.0 mm in an arc-like cross-sectional shape along the inner peripheral surface of the fixing belt 21. Further, the shielding member 27 is movable in the circumferential direction between the fixing belt 21 and the halogen heater 23. In the present embodiment, as shown in FIG. 2, in the circumferential direction area of the fixing belt 21, the area between the heating area α facing the halogen heater 23 and directly heated by the halogen heater 23 and the halogen heater 23 A non-heating area β which is not directly heated by the halogen heater 23 is formed by interposing other members (the reflecting member 26, the stay 25, the nip forming member 24 and the like) fixed to the side plate or the like. If the heat shielding is not necessary, as shown in FIG. 2, the shielding member 27 is moved to the non-heating area β side, and if the heat shielding is necessary, the shielding member 27 is moved to the heating area α side It has become possible.

  By rotating the shielding member 27 in this manner, the area of the heated region α of the fixing belt 21 is changed, and the heat amount of the radiant heat emitted from the halogen heater 23 to the fixing belt 21 is adjusted. As a result, it is possible to suppress an excessive temperature rise in the non-sheet passing area of the fixing belt 21 at the time of continuous sheet passing, and to prevent deterioration and damage of the fixing belt 21 due to heat. Since the shielding member 27 requires heat resistance, it is preferable to use a metal material such as aluminum, iron, stainless steel, or ceramic as its material.

  The nip forming member 24 is disposed inside the fixing belt 21 and at a position facing the pressure roller 22 via the fixing belt 21. The nip forming member 24 has a base 241 and a thin plate-like nip forming portion 242 fixed to the fixing belt 21 side of the base 241. Both the base 241 and the nip forming portion 242 are resin materials having high heat resistance, such as polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI) , Polyetheretherketone (PEEK) or the like. Besides, the base 241 and the nip forming portion 242 can also be formed of metal or ceramic. The base 241 and the nip forming portion 242 may be formed of different materials, or may be formed of the same material. In the latter case, the base 241 and the nip forming portion 242 can be integrated into one part.

  The base 241 of the nip forming member 24 is supported by the stay 25. As a result, it is possible to prevent the nip forming portion 242 from being bent by the pressure applied by the pressure roller 22, and to form a uniform nip width in the entire axial direction of the opposing region of the fixing belt 21 and the pressure roller 22. . The stay 25 is formed of a metal material such as a steel material such as stainless steel in order to satisfy the deflection preventing function of the nip forming member 24. However, the stay 25 is formed of a resin material if the deflection preventing effect is sufficient. You can also

  A low friction sheet 243 is attached to the surface of the nip forming portion 242 sliding on the fixing belt 21. When the fixing belt 21 rotates, the inner surface of the fixing belt 21 slides on the low friction sheet 243, whereby the frictional resistance acting on the fixing belt 21 can be reduced.

In FIG. 4, the cross section of the nip forming portion 242 is enlarged and shown.
As shown in FIG. 4, the surface 242 a (front surface) of the nip forming portion 242 facing the pressure roller 22 has a width that is greater than the fixing nip N in the sheet conveyance direction. A first flat surface A, a connection surface B, a second flat surface C, and a guide surface D are formed on the front surface 242 a from the inlet side (lower side in the drawing) of the fixing nip N.

  Two flat surfaces A and C of these are formed parallel to each other. One flat surface A (first flat surface) is disposed on the inlet side of the fixing nip N, and the other flat surface C (second flat surface) is an outlet of the fixing nip N than the first flat surface A. It is arranged on the side. The second flat surface C is located closer to the pressure roller 22 than the first flat surface A (right side in the drawing). It is preferable that the first and second flat surfaces A and C be formed in parallel with the inrush direction of the sheet P with respect to the entrance portion N1 of the fixing nip N. Specifically, in the present embodiment, with respect to an imaginary line m (see FIG. 4) connecting the rotation center O1 of the fixing belt 21 (the center of the belt holding member 40 shown in FIG. 3) and the rotation center O2 of the pressure roller 22. The first flat surface A and the second flat surface C are disposed along substantially orthogonal directions.

  The first flat surface A and the second flat surface C are smoothly connected via the connection surface B. The shape of the connection surface B is arbitrary, and can be formed of a flat surface, a curved surface, or a combined surface combining them. FIG. 4 exemplifies a case where the connecting surface B is formed by a compound curved surface including a first curved surface portion B1 on the inlet side of the fixing nip N and a second curved surface portion B2 on the outlet side of the fixing nip N.

  In this embodiment, the first curved surface portion B1 and the second curved surface portion B2 reverse the direction of the curvature. Specifically, the first curved surface portion B1 is a concave cylindrical surface viewed from the pressure roller 22 side having a single curvature radius R1, and the second curved surface portion B2 is a pressure having a single curvature radius R2 It is a convex cylindrical surface seen from the roller 22 side.

The shape of the guide surface D is arbitrary, and can be formed of, for example, a flat surface, a curved surface, or a combined surface combining them. The guide surface D in the present embodiment is a concave cylindrical surface having a single radius of curvature R3 and viewed from the pressure roller 22 side. The guide surface D and the second flat surface C are connected so as to have a common tangent at the boundary.
Here, although the first curved surface portion B1, the second curved surface portion B2, and the guide surface D have been described as having a single curvature radius R1, R2 and R3, respectively, the first curved surface portion B1 and the second curved surface portion B2 are described. Each of the curved surface portion B2 and the guide surface D may be configured by a plurality of curved surfaces having different curvatures.

  When the pressure roller 22 is pressed against the nip forming portion 242 described above via the fixing belt 21, the elastic layer 22 b of the pressure roller 22 is elastically deformed to fix between the fixing belt 21 and the pressure roller 22. A nip N is formed. At this time, the fixing belt 21 deforms in accordance with the shape of the front surface 242 a of the nip forming portion 242.

  In the fixing nip N, the portions formed by the first flat surface A and the second flat surface C of the nip forming portion 242 all have a planar shape corresponding to the shapes of both flat surfaces A and C. Further, the portion formed by the connection surface B of the nip forming portion 242 has a shape (curved surface shape in the present embodiment) corresponding to the shape of the connection surface B. In the following description, in the fixing nip N, a region formed by the first flat surface A of the nip forming portion 242 is referred to as a first flat portion Na, and a region formed by the connection surface B is represented by the connecting portion Nb and The area formed by the second flat surface C is referred to as a second flat portion Nc.

  In the fixing nip N, the inlet N1 is formed of the first flat portion Na (the first flat surface A of the nip forming portion 242 forms the inlet N1), and the outlet N2 is the second flat Nc. (The second flat surface C of the nip forming portion 242 forms the outlet N2). Further, the length of the second flat portion Nc is shorter than the length of the first flat portion Na.

FIG. 5 is a cross-sectional view schematically illustrating the fixing nip N formed by the nip forming portion 242 described above.
In FIG. 5, in order to clearly show the shape of the fixing nip N, the step between the first flat surface A and the second flat surface C of the nip forming member 24 is drawn exaggeratingly. Therefore, the shapes of the front surface 242a of the nip forming portion 242 and the fixing nip N are different from actual ones. Further, in FIG. 5, the fixing belt 21 is not shown in order to simplify the drawing.

  The sheet P reaches the entrance N1 of the fixing nip N with the toner T directed to the fixing belt 21 and enters the first flat portion Na. In the first flat portion Na, the compression ratio Xa of the elastic layer 22b of the pressure roller 22 increases toward the downstream side, and the surface pressure acting on the sheet P gradually increases accordingly. Then, the sheet P enters the connection portion Nb. At the connecting portion Nb, the compression ratio Xb of the elastic layer 22b rapidly increases to a maximum value, and the surface pressure acting on the sheet P becomes maximum. Thereafter, while the sheet P moves through the connection portion Nb and the second flat portion Nc, the compression ratio Xb of the elastic layer 22b decreases toward the downstream side, and the surface pressure acting on the sheet P also gradually decreases. Therefore, the toner fixing process (melting, flow, combination, permeation, solidification) mainly proceeds in the region from the connection portion Nb to the second flat portion Nc.

  The sheet P that has reached the outlet portion N2 of the fixing nip N is discharged by the guide surface D of the nip forming member 24 in the direction F slightly inclined toward the pressure roller 22 with respect to the extension direction of the second flat portion Nc. Further, it is separated from the fixing belt 21 in contact with the separation claw. A curved surface portion 242b having a small radius of curvature is provided at the downstream end of the front surface 242a of the nip forming portion 242 in the transport direction, and the fixing belt 21 has a pressure roller 22 with a large curvature along the curved surface portion 242b. It bends in the direction away from. Therefore, the separability of the sheet P discharged from the fixing nip N is good.

  As described above, in the present invention, the high surface pressure area in the fixing nip N is provided on the exit side of the fixing nip N. In order to realize this surface pressure distribution, in the fixing nip N, the portion (the connecting portion Nb in the present embodiment) where the compression ratio of the elastic layer 22b is maximum is the fixing nip N more than the rotation center O2 of the pressure roller 22. The exit side of the fixing nip N is provided on the exit side of the fixing nip N rather than the intersection when the vertical line is lowered from the rotation center O2 of the pressure roller 22 to the first flat surface A (or its extended line) of the nip forming portion 242. In the present embodiment, as shown in FIG. 4, the boundary between the first flat portion Na and the connection portion Nb is disposed in the vicinity of an imaginary line m connecting the rotation center O1 of the fixing belt 21 and the rotation center O2 of the pressure roller 22. As a result, the maximum compression portion of the elastic layer 22b can be reliably placed under the above conditions.

Hereinafter, the operation and effect of the fixing nip N configured as described above will be described.
In the first flat portion Na of the fixing nip N, wrinkles are less likely to occur on the surface of the fixing belt 21 as compared with the case where the first flat portion Na of the fixing nip N has a concave curved shape when viewed from the pressure roller 22 side. Further, in the first flat portion Na, the compression amount Xa of the elastic layer 22 b of the pressure roller 22 is small, so the linear speed difference between the fixing belt 21 and the pressure roller 22 is also small. Furthermore, even considering the displacement force acting on the unfixed toner, the influence of the displacement force is small because the first flat portion Na is a low surface pressure region. From the above reasons, it is possible to suppress the displacement of the unfixed toner on the upstream side of the fixing nip N, and to prevent the deterioration of the image quality accompanying the fixing.

  On the other hand, since the second flat surface C of the nip forming member 24 is disposed closer to the pressure roller 22 than the first flat surface A, the second flat surface C is downstream of the first flat portion Na. A compression amount larger than the compression amount Xa of the elastic layer 22b in the first flat portion Na can be obtained at least at the connection portion Nb (or both of the connection portion Nb and the second flat portion Nc). As a result, the exit side of the fixing nip N can be made to be a high surface pressure area, and sufficient heat and pressure can be applied to the toner to fix the unfixed image with certainty. In addition, by locally increasing the contact surface pressure of the fixing nip as described above, it is also possible to save energy by suppressing the amount of heating by the halogen heater 23. Further, in the present embodiment, the second flat surface C is tangential to the arc surface of the connection surface B in order to prevent damage to the fixing belt 21, the low friction sheet 243, and the nip forming member 24 due to local surface pressure increase. It is formed to be continuous.

  Thus, according to the present invention, the amount of biting of the fixing nip N into the elastic layer 22b of the pressure roller 22 is in the region where the toner T is not sufficiently heated and displacement of the unfixed image is likely to occur in the fixing nip. While the toner T is sufficiently heated, the nip forming member 24 bites deeply into the elastic layer 22b to securely fix the toner while suppressing the displacement of the unfixed image. is there. As a result, it is possible to achieve both prevention of image deterioration associated with fixing and securing of stable fixing properties.

  By the way, in the existing fixing device in which the fixing nip N is formed by bringing the rollers into pressure contact with each other, the fixing nip is a concave curved surface or a convex curved surface. Often causes wrinkles. On the other hand, in the fixing device of the present invention, since the inlet side and the outlet side of the fixing nip N are formed by the flat portions Na and Nc in parallel with each other, they extend from the first flat portion Na to the connecting portion Nb. The bending direction of the envelope up to and the bending direction of the envelope from the connecting portion Nb to the second flat portion Nc are reversed, and the bending in both directions is offset. Further, in the fixing nip N, there is no other area for curving the envelope. Therefore, the occurrence of envelope wrinkles can be prevented.

  Further, by forming the outlet portion N2 of the fixing nip N by the second flat surface C of the nip forming member 24 as described above, even when the width of the fixing nip N slightly fluctuates, the sheet discharge direction is constant. Can be That is, as shown in FIG. 6, when the outlet N2 is inclined with respect to the second flat portion Nc (for example, when the outlet N2 is formed by the guide surface D of the nip forming portion 242) Although the width of the fixing nip N fluctuates, the paper discharge direction F ′ varies, and the decurling effect decreases. However, as shown in FIG. 5, the outlet N2 has a second flat surface. Since the sheet P is discharged straight in the direction of the second flat portion Nc by forming the portion Nc, such a problem can be prevented.

  In the embodiment shown in FIG. 4, the outlet N2 of the fixing nip is formed at the downstream end of the second flat surface C, but emphasis is placed on the prevention of the variation in the discharge direction F 'due to the width variation of the fixing nip N described above. In this case, it is preferable to dispose the downstream end of the second flat surface C downstream of the outlet N2 (outside of the fixing nip N).

  FIG. 7 shows another embodiment of the present invention. In the embodiments described above (FIG. 2, FIG. 4, FIG. 5), the guide surface D of the nip forming member 24 is formed into a concaved cylindrical surface as viewed from the pressure roller 22 side. In the embodiment shown in FIG. 7, the guide surface D is formed in a flat surface flush with the second flat surface C. With such a configuration, it is possible to stabilize the discharge direction of the sheet P even under a situation where the width of the fixing nip N is wide and the guide surface D is expected to enter the fixing nip N.

  As described above, according to each embodiment of the fixing device according to the present invention, the second flat surface C of the nip forming member 24 is disposed closer to the pressure roller 22 than the first flat surface A. Therefore, the exit side of the fixing nip N can be made to be a high surface pressure area, and sufficient heat and pressure can be applied to the toner to fix the unfixed image with certainty. However, on the other hand, if there is a step (connecting surface B) between the first flat surface A and the second flat surface C, the pressure roller 22 and the fixing belt 21 are sufficient for the shape of the step. Because it can not be deformed following the gap, a gap is likely to be generated between the nip forming member 24 and the fixing belt 21, or between the fixing belt 21 and the pressure roller 22, or both of them. As a result, a partial pressure drop occurs at the fixing nip N, and a problem arises that the fixing property is reduced at the point where the pressure is lost.

  In particular, in each of the above-described embodiments, the connection surface B constituting the stepped portion has the convex second curved surface portion B2 as viewed from the pressure roller 22 side. Since the elastic layer 22b is largely compressed, the elastic layer 22b of the pressure roller 22 does not easily enter into the concave first curved surface portion B1 when viewed from the pressure roller 22 side, and a gap is easily generated. Although it is possible to improve the problem of the gap as described above by taking measures for the shape of the nip forming member 24 such as making the step portion as gentle as possible, it is difficult to completely eliminate the gap.

  Therefore, in the present embodiment, as shown in FIG. 8, the low friction sheet 243 is interposed between the nip forming member 24 and the fixing belt 21 as a gap filling member for filling the gap in the step portion between both members. ing. Since the low friction sheet 243 is a low-rigid (flexible) sheet-like member, the elastic layer 22b of the pressure roller 22 may deform following the shape of the fixing nip N which can not follow. it can. Thereby, the gap between the nip forming member 24 and the fixing belt 21 at the step portion (connection surface B) of the fixing nip N can be filled, and the adhesion between the fixing belt 21 and the pressure roller 22 is also improved. As a result, partial pressure loss at the fixing nip N is highly suppressed, and a good image can be obtained.

  When a double-sided adhesive tape is used to affix the low friction sheet 243 to the nip forming member 24, the double-sided adhesive tape is also interposed between the nip forming member 24 and the fixing belt 21. It can contribute as a gap filling member which fills up the gap of. When the double-sided pressure-sensitive adhesive tape is used, the mounting workability of the low friction sheet 243 is improved, and the double-sided pressure-sensitive adhesive tape can also function as a lubricant holding member.

  Further, in the present embodiment, since the low friction sheet 243 is used as the gap filling member, as described above, the frictional resistance acting on the fixing belt 21 can be reduced. When the low friction sheet 243 is formed of a plurality of layers, at least the surface side in contact with the fixing belt 21 may be formed of a low friction member. In addition to the low friction, a PTFE fiber or the like excellent in wear resistance may be used as the gap filling member.

  Moreover, you may use highly heat-conductive thin plate metals (9 micrometers in thickness-0.5 mm), such as copper, as a clearance gap filling member. When the pressure roller 22 is brought into contact with the nip forming member 24 by forming the sheet metal in a shape close to the shape of the fixing nip N in advance, the sheet metal is pressed by the pressure of the pressure roller 22 to fix the fixing nip N. It deforms according to the shape of and can fill up the above-mentioned crevice. In particular, in the case of using a high thermal conductivity member such as sheet metal, the heat of the fixing nip N can be dispersed in the sheet width direction, so the local area at the end of the sheet passing area generated during continuous sheet passing The temperature rise can be suppressed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment.
The image forming apparatus equipped with the fixing device according to the present invention is not limited to the color printer as shown in FIG. 1, but can be a monochrome printer. Further, not limited to the printer, a copier, a facsimile, or a complex machine of these may be used.

20 fixing device 21 fixing belt (first fixing member)
22 Pressure roller (second fixing member)
22b elastic layer 23 halogen heater (heat source)
24 nip forming member 243 low friction sheet (filling member)
A 1st flat surface B connection surface (step)
C Second flat surface D Guide surface N Fixing nip P Paper (recording medium)
T Toner (Developer)

JP 2014-134701 A

Claims (8)

A rotatable second fixing member having a flexible and rotatable first fixing member, an elastic layer and forming a fixing nip with the first fixing member; A heating source for heating one fixing member, and an inner circumferential surface of the first fixing member and the heating source, and facing the second fixing member via the first fixing member A fixing device including a nip forming member forming the fixing nip;
The heat source is disposed on the inner peripheral side of the first fixing member so as to directly heat at least a portion of the first fixing member other than the fixing nip.
A stepped portion is provided in a region forming the fixing nip of the nip forming member,
A gap filling member is interposed between the nip forming member and the first fixing member so as to fill the gap generated between the nip forming member and the first fixing member at the stepped portion ;
A first flat surface, an exit side of the fixing nip with respect to the first flat surface, and an approach side to a second fixing member in a region forming the fixing nip of the nip forming member A second flat surface and a connecting surface as the step portion connecting the first flat surface and the second flat surface are provided.
The fixing device according to claim 1, wherein the first flat surface and the second flat surface are disposed parallel to each other .   The fixing device according to claim 1, wherein the stepped portion has a curved surface portion that is convex when viewed from the second fixing member side.   The fixing device according to claim 1, wherein the gap filling member is configured by a low rigidity sheet-like member.   The fixing device according to any one of claims 1 to 3, wherein the gap filling member is formed of a high thermal conductivity member.   The fixing device according to any one of claims 1 to 4, wherein a surface of the gap filling member in contact with at least the first fixing member is formed of a low friction member. The stepped portion is composed of one or more arc surfaces,
The fixing device according to any one of claims 1 to 5, wherein the second flat surface continues in a tangent of the arc surface of the stepped portion . The fixing device according to any one of claims 1 to 6, wherein a portion where the contact surface pressure of the second fixing member with respect to the nip forming member is maximum is on the exit side of the fixing nip . An image forming apparatus comprising the fixing device according to any one of claims 1 to 7 .

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