JP2018146706A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing apparatus configured to prevent the change in nip width between a fixing member and a pressure member, which is caused by reduction in hardness of the pressure member.SOLUTION: A fixing apparatus 7 includes: an endless rotatable fixing belt 22; a pressure roller 23 pressed by the fixing belt 22 to form a nip part N with the fixing belt 22; a contact/separation mechanism 50 which biases the pressure roller 23 toward the fixing belt 22; and a nip forming member 30 which is arranged on an inner periphery side of the fixing belt 22. In the fixing apparatus for fixing an image on a sheet P, the nip forming member 30 comes into contact with the pressure roller 23 via the fixing belt 22 and has a nip forming surface 30a where the nip part N is formed, and the pressure roller 23 comes into contact with a downstream end 30a1 in a sheet P conveyance direction of the nip forming surface 30a, via the fixing belt 22. When the pressure roller 23 biased by the contact/separation mechanism 50 comes close to the fixing belt 22, a guide hole 42a in the fixing apparatus 7 guides the pressure roller 23 toward a downstream side in the conveyance direction.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device.

  In the fixing device, the fixing member and the pressure member are brought into contact with each other, and a nip portion is formed between them. The developer image on the recording medium is fixed by pressing and heating the recording medium at the nip portion.

  In order to form the nip portion, a biasing mechanism that biases the pressure member toward the fixing member is provided, and the pressure member is pressed against the fixing member by the biasing force of the biasing mechanism, thereby A fixing device for forming a portion is already known.

  As this type of fixing device, for example, the pressing member is pressed against the fixing member by the biasing force of a spring connected to the pressing member, and the biasing force against the pressing member is provided by a cam provided in the biasing mechanism. There is a configuration in which the pressure member is adjusted and brought into contact with and separated from the fixing member (for example, Patent Documents 1 and 2).

  In the configurations of Patent Document 1 and Patent Document 2, when the repulsive force against the urging force of the pressure member decreases due to aging degradation or the like, the pressure member is more strongly pressed toward the fixing member, and the width of the nip portion is increased. Become. When the width of the nip portion is increased, the recording medium passing through the nip portion is overheated, causing problems such as hot offset.

  By the way, in recent years, a low-hardness pressure member provided with an elastic layer made of rubber or sponge has been adopted for the purpose of downsizing the apparatus. In other words, the elastic layer of the pressure member elastically deforms along the shape of the outer peripheral surface of the fixing member at the time of press contact with the fixing member, so that the nip width can be widened. Even with a member, a sufficient nip width can be ensured. However, with such a low-hardness pressure member, the repulsive force is particularly lowered due to the above-mentioned deterioration over time, and problems such as hot offset due to an increase in the nip width are likely to occur.

  Under such circumstances, an object of the present invention is to provide a fixing device that can suppress a change in the nip width between the fixing member and the pressure member caused by a decrease in the hardness of the pressure member. .

  In order to solve the above problems, the present invention includes a rotatable endless fixing member, a pressure member that is pressed against the fixing member and forms a nip portion between the fixing member, and the pressure member. In a fixing device that includes an urging mechanism that urges toward the fixing member and a nip forming member that is disposed on the inner peripheral surface side of the fixing member, the nip forming member fixes the image on the recording medium. A nip forming surface that contacts the pressure member through the fixing member to form the nip portion, and the pressure member passes through the fixing member in a recording medium conveyance direction of the nip forming surface. A guide mechanism that contacts the one end and guides the pressure member to one side in the transport direction when the pressure member is biased by the biasing mechanism and approaches the fixing member; It is characterized by that.

  In the present invention, the approaching direction of the pressure member to the fixing member is inclined to one side in the recording medium conveyance direction. As a result, even when the pressure member is strongly pressed by the fixing member due to a decrease in the hardness of the pressure member, the pressure member is moved to the opposite side to the other side of the recording medium conveyance direction in which the nip width increases. Therefore, the increase in the nip width can be offset, and the change in the nip width can be suppressed.

1 is a schematic configuration diagram of an image forming apparatus. 1 is a schematic configuration diagram of a fixing device. 2 is a plan view of the fixing device. FIG. FIG. 4 is a schematic diagram illustrating a relationship between a pressure roller and a nip forming member in a fixing device having a configuration different from that of the present invention. FIG. 3 is a schematic diagram illustrating a relationship between a pressure roller and a nip forming member of the fixing device according to the first embodiment of the present invention. It is a figure which shows the guide mechanism of the pressure roller of the fixing device which concerns on 1st embodiment. FIG. 6 is a schematic diagram illustrating a configuration of a pressure roller and a nip forming member of a fixing device according to a second embodiment. FIG. 10 is a schematic diagram illustrating a configuration of a pressure roller and a nip forming member of a fixing device according to a third embodiment. It is the schematic which shows the structure of the pressure roller and nip formation member of the fixing device which concerns on 4th embodiment. FIG. 6 is a cross-sectional view showing a fixing device having a different configuration according to the present invention.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

  In the center of the color image forming apparatus 1 shown in FIG. 1, an image forming unit 2 in which four process units 9Y, 9M, 9C, 9K are detachably provided is arranged. Each process unit 9Y, 9M, 9C, 9K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each process unit 9 includes a photosensitive drum 10 that is a drum-like rotating body capable of carrying toner as a developer on the surface, and a charging roller 11 that uniformly charges the surface of the photosensitive drum 10. A developing device 12 having a developing roller for supplying toner to the surface of the photosensitive drum 10, a cleaning unit 13, and the like.

  Below the process unit 9, the exposure unit 3 is arranged. The exposure unit 3 is configured to emit laser light based on the image data.

  A transfer unit 4 is disposed above the image forming unit 2. The transfer unit 4 includes an endless intermediate transfer belt 16, a primary transfer roller 17 disposed at a position facing the photosensitive drum 10 of each process unit 9 with the intermediate transfer belt 16 interposed therebetween, and a secondary transfer roller 18, a secondary transfer backup roller 14, a cleaning backup roller 15, a tension roller 27, and a belt cleaning device 28.

  The intermediate transfer belt 16 is an endless belt, and is stretched around the secondary transfer backup roller 14, the cleaning backup roller 15, and the tension roller 27. Here, the secondary transfer backup roller 14 is rotationally driven, so that the intermediate transfer belt 16 runs around (rotates) in the direction of arrow A in the figure.

  Each of the four primary transfer rollers 17 sandwiches the intermediate transfer belt 16 from each of the photosensitive drums 10 to form a primary transfer nip. Each primary transfer roller 17 is connected to a power source so that a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to each primary transfer roller 17.

  The secondary transfer roller 18 sandwiches the intermediate transfer belt 16 with the secondary transfer backup roller 14 to form a secondary transfer nip. Similarly to the primary transfer roller 17, a power source is also connected to the secondary transfer roller 18, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 18. It is like that.

  The belt cleaning device 28 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 16. The waste toner collected by the belt cleaning device 28 is accommodated in a waste toner container via a waste toner transfer hose.

  The paper feed unit 5 is located below the image forming apparatus 1 and includes a paper feed cassette 19 that stores paper P as a recording medium, a paper feed roller 20 that carries the paper P out of the paper feed cassette 19, and the like. ing.

  The conveyance path 6 is a conveyance path that conveys the paper P carried out from the paper feeding unit 5, and the conveyance roller pair is located in the middle of the conveyance path 6 until it reaches the paper discharge unit 8 described later in addition to the pair of registration rollers 21. Are appropriately arranged.

  The fixing device 7 includes a fixing belt 22 as a fixing member heated by a heating source, a pressure roller 23 as a pressure member capable of pressing the fixing belt 22, and the like.

  The paper discharge unit 8 is provided on the most downstream side of the conveyance path 6 of the image forming apparatus 1. The paper discharge unit 8 is provided with a pair of paper discharge rollers 24 for discharging the paper P to the outside and a paper discharge tray 25 for stocking the discharged paper P.

  At the upper part of the image forming apparatus 1, toner bottles 29Y, 29C, 29M, and 29K filled with yellow, cyan, magenta, and black toners are detachably provided. Each color toner is supplied to each color developing device 12 through a supply path provided between the toner bottles 29Y, 29C, 29M, and 29K and each developing device 12.

  The basic operation of the image forming apparatus 1 will be described below with reference to FIG.

  In the image forming apparatus 1, when an image forming operation is started, electrostatic latent images are formed on the surfaces of the photosensitive drums 10 of the process units 9Y, 9C, 9M, and 9K. The image information exposed to each photosensitive drum 10 by the exposure unit 3 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. An electrostatic latent image is formed on each photoconductor drum 10, and the toner stored in each developing device 12 is supplied to the photoconductor drum 10 by a drum-shaped developing roller, whereby the electrostatic latent image becomes visible. It is visualized as a toner image (developer image) which is an image.

  In the transfer unit 4, the intermediate transfer belt 16 is driven to run in the direction of arrow A in the figure by the rotational drive of the secondary transfer backup roller 14. Further, each primary transfer roller 17 is applied with a constant voltage or a constant current-controlled voltage having a polarity opposite to the charging polarity of the toner. As a result, a transfer electric field is formed in the primary transfer nip, and the toner images formed on the respective photosensitive drums 10 are sequentially superimposed and transferred onto the intermediate transfer belt 16 in the primary transfer nip.

  On the other hand, when the image forming operation is started, the sheet P stored in the sheet feeding cassette 19 is moved to the transport path 6 by rotating the sheet feeding roller 20 of the sheet feeding unit 5 below the image forming apparatus 1. Sent out. The sheet P sent to the conveyance path 6 is timed by the registration roller 21 and is sent to the secondary transfer nip between the secondary transfer roller 18 and the secondary transfer backup roller 14. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 16 is applied, and a transfer electric field is formed in the secondary transfer nip. The toner images on the intermediate transfer belt 16 are collectively transferred onto the paper P by the transfer electric field formed in the secondary transfer nip.

  The sheet P on which the toner image is transferred is conveyed to the fixing device 7, and the sheet P is heated and pressed by the fixing belt 22 and the pressure roller 23, so that the toner image is fixed on the sheet P. Then, the paper P on which the toner image is fixed is separated from the fixing belt 22, transported by a pair of transport rollers, and discharged to a paper discharge tray 25 by a paper discharge roller 24 in the paper discharge unit 8.

  The above description is an image forming operation when a full-color image is formed on the paper P. A single color image can be formed using any one of the four process units 9Y, 9C, 9M, and 9K. It is also possible to form two or three color images using two or three process units 9.

Next, a more detailed configuration of the fixing device 7 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 7 includes a fixing belt 22 and a pressure roller 23 pressed against the fixing belt 22.

  On the inner peripheral surface side of the fixing belt 22, a nip forming member 30, a support member 31 that supports the nip forming member 30, a heat transfer member 32 disposed so as to face the inner peripheral surface of the fixing belt 22, A heater 33 is provided as a heating source. Further, a temperature sensor 34 is provided facing the outer peripheral surface of the fixing belt 22.

  The fixing belt 22 is formed by laminating a base material layer, an elastic layer, and a release layer from the inner peripheral surface side. The base material layer has a layer thickness of 30 to 100 μm and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.

  The elastic layer of the fixing belt 22 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. By providing the elastic layer on the fixing belt 22, minute irregularities on the surface of the fixing belt 22 at the nip portion (fixing nip) N are not formed, and heat is uniformly transmitted to the toner image T on the paper P, so Occurrence is suppressed.

  The release layer of the fixing belt 22 has a layer thickness of 10 to 50 μm, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES ( Polyether sulfide) and the like. By providing the release layer, the releasability (peelability) for the toner (toner image) T is secured.

  The diameter of the fixing belt 22 is set in a range of 15 to 120 mm, and is set to about 30 mm as an example.

  The pressure roller 23 is formed by forming an elastic layer 23b on a hollow core metal 23a, and the diameter thereof is set to about 30 mm. The pressure roller 23 contacts the outer peripheral surface of the fixing belt 22 to form a nip portion N.

  The elastic layer 23b of the pressure roller 23 is formed of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. In order for the pressure roller 23 to have a certain elasticity, the elastic layer 23b is preferably formed with a thickness of 2 mm or more.

  The surface hardness of the pressure roller 23 is preferably an ASKER-C hardness of 60 or less. By providing an elastic layer on the pressure roller 23 and reducing its surface hardness, when the pressure roller 23 is pressed against the fixing belt 22, the pressure roller 23 is elastically deformed and is in close contact with the fixing belt 22. The nip width formed between the pressure roller 23 and the fixing belt 22 can be increased. Therefore, even with the small-diameter pressure roller 23 and the fixing belt 22, a sufficient nip width can be secured, and the fixing operation can be speeded up without causing a fixing failure.

  By forming the elastic layer 23b with a sponge-like material such as foamable silicone rubber, the applied pressure acting on the nip portion can be adjusted, and the bending of the nip forming member 30 can be reduced. Thereby, the heat insulation of the pressure roller 23 can be improved, and the heating efficiency of the fixing belt 22 is improved.

  Note that a heat source such as a halogen heater may be provided inside the pressure roller 23. Further, a thin release layer made of PFA, PTFE or the like may be provided on the surface layer of the elastic layer 23b.

  In the present embodiment, the diameter of the fixing belt 22 is set to be approximately the same as the diameter of the pressure roller 23. However, by setting the diameter of the fixing belt 22 smaller than the diameter of the pressure roller 23, the curvature of the fixing belt 22 in the nip portion N is made smaller than that of the pressure roller 23, and the paper P is separated from the nip portion N. It can also be made easier. In addition, the diameter of the fixing belt 22 may be set larger than the diameter of the pressure roller 23.

  As shown in FIG. 3, the pressure roller 23 is rotatably held by a side plate 42 as a casing of the fixing device 7 via bearings 41 on both sides in the axial direction. Further, the bearing 41 is provided so as to be movable in a guide hole formed in the side plate 42, and the pressure roller 23 can be brought into contact with and separated from the fixing belt 22 by this movement.

  A gear 43 is provided on one end side in the axial direction of the pressure roller 23. The pressure roller 23 rotates when a driving force is transmitted through the gear 43. As shown in FIG. 2, when the pressure roller 23 rotates in the direction of the arrow B2, the fixing belt 22 contacting the pressure roller 23 is driven to rotate in the direction of the arrow B1.

  As shown in FIG. 3, the nip forming member 30, the support member 31, the heat transfer member 32, and the heater 33 are provided over the axial direction of the pressure roller 23, and are supported by side plates 42 on both sides thereof.

  The nip forming member 30 is a plate-like member extending in the axial direction, and is made of, for example, a heat resistant resin material such as a liquid crystal polymer. The nip forming member 30 is supported by the side plate 42 so that the paper P is positioned in the transport direction.

  The support member 31 has an axial length that is set to be approximately the same as that of the nip forming member 30. As shown in FIG. 2, the support member 31 abuts against the back surface (surface opposite to the nip forming surface 30 a) 30 b of the nip forming member 30, thereby supporting the nip forming member 30 from the back surface side. Thereby, it is possible to prevent the nip forming member 30 from being bent due to the pressure applied by the pressure roller 23, and to form a uniform nip width in the entire axial direction of the opposed region of the fixing belt 22 and the pressure roller 23. .

  In order to satisfy the functions described above, the support member 31 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron. Further, a heat insulating member can be provided on the surface of the support member 31 facing the heater 33, or BA treatment or mirror polishing treatment can be performed. Thereby, the amount of heat transmitted from the heater 33 to the support member 31 is reduced, and the heater 33 can heat the fixing belt 22 more efficiently.

  The heat transfer member 32 is a cylindrical member having a wall thickness of 0.2 mm or less. The heat transfer member 32 is formed in a concave shape toward the inner peripheral surface of the fixing belt 22 at the position of the nip portion N, and is provided so that the pressure applied by the pressure roller 23 does not act on the heat transfer member 32. . As a material of the heat transfer member 32, a metal material having thermal conductivity such as aluminum, iron, stainless steel or the like can be used.

  The heat transfer member 32 is disposed at a position excluding the nip portion N so as to be close to or in contact with the inner peripheral surface of the fixing belt 22. Accordingly, the heat transfer member 32 supports the fixing belt 22 from the inner peripheral surface side, and the flexible fixing belt 22 can maintain a substantially circular cross-sectional shape. Further, the heat transfer member 32 is provided on the inner peripheral surface side so as to face the heater 33, and is heated by the heater 33 to transmit the heat to the fixing belt 22.

  By the way, if the heat transfer member 32 and the fixing belt 22 are too close to each other, the fixing belt 22 is easily worn when the fixing belt 22 rotates. On the other hand, if the heat transfer member 32 and the fixing belt 22 are too far apart, the heat transfer efficiency from the heat transfer member 32 to the fixing belt 22 is reduced. Accordingly, it is preferable that the heat transfer member 32 and the fixing belt 22 be arranged with an appropriate gap, for example, the heat transfer member 32 is arranged with a gap of 1 mm or less between the fixing belt 22. Is preferred.

  Further, the sliding surface side of the heat transfer member 32 is formed of a low friction member, or a sliding layer made of a material containing fluorine, for example, is provided to reduce the sliding resistance generated between the heat transfer member 32 and the fixing belt 22. be able to.

  The heater 33 is composed of, for example, a halogen heater or a carbon heater. As shown in FIG. 2, in this embodiment, two halogen heaters 33 are provided. The heater 33 heats the heat transfer member 32 by radiant heat when supplied with electric power.

  The temperature sensor 34 is provided on the outer peripheral surface side of the fixing belt 22 and at a position facing the heater 33 with the heat transfer member 32 interposed therebetween. The temperature sensor 34 detects the surface temperature of the fixing belt 22 at this facing position. Based on the detected temperature, the amount of heat generated by the heater 33 is controlled, and the fixing belt 22 is controlled to a predetermined temperature.

  The fixing device 7 includes a contact / separation mechanism (biasing mechanism) 50 that contacts and separates the pressure roller 23 with respect to the fixing belt 22. The contact / separation mechanism 50 includes a pressure lever 51, an eccentric cam 52, a pressure spring 53, a holding plate 54, and the like.

  The pressure lever 51 is provided to be rotatable around a support shaft 51a on one end side thereof. A pressure spring 53 is connected to the other end side of the pressure lever 51. Further, the pressure lever 51 is in contact with a bearing 41 (see FIG. 3) supporting the pressure roller 23 at the center side. As shown in FIG. 2, the pressure spring 53 abuts the eccentric cam 52 via the holding plate 54 at the end opposite to the side connected to the pressure lever 51.

  During the fixing operation, the pressure lever 51 receives a force in the pulling direction toward the pressure spring 53 by the elastic force of the pressure spring 53. The pressure lever 51 transmits the force received from the pressure spring 53 to the pressure roller 23 via the bearing 41 (see FIG. 3), and urges the pressure roller 23 toward the fixing belt 22. . As shown in FIG. 2, the pressing roller 23 is pressed against the fixing belt 22 by this urging force to form a nip portion N.

  When the eccentric cam 52 rotates except during the fixing operation, the holding plate 54 in contact with the eccentric cam 52 moves in a direction away from the fixing belt 22. As a result, the tensile force of the pressure spring 53 against the pressure lever 51 decreases, the urging force received by the pressure roller 23 from the pressure lever 51 decreases, and the pressure roller 23 separates from the fixing belt 22. In this way, the pressure roller 23 can be brought into contact with and separated from the fixing belt 22 by changing the urging force from the contact / separation mechanism 50 to the pressure roller 23.

  When the image forming operation is started, electric power is supplied to the fixing device 7 and the heater 33 generates heat, and the fixing belt 22 rotates in the direction of arrow B1 and the pressure roller 23 rotates in the direction of arrow B2. Radiant heat of the heater 33 is transmitted to the fixing belt 22 through the heat transfer member 32, and the fixing belt 22 is heated to a temperature necessary for the fixing operation.

  Then, the paper P on which the unfixed image (toner image) T is formed is conveyed in the arrow Y1 direction (paper conveyance direction), guided to the nip portion N, and heated and pressurized in the nip portion N. As a result, the toner image is fixed on the paper P. Thereafter, the paper P is conveyed in the direction of the arrow Y2 and further sent to a downstream process.

  The heat transmitted from the heater 33 to the heat transfer member 32 is also transmitted in the circumferential direction of the heat transfer member 32, and moves in a direction in which the amount of heat becomes uniform inside the heat transfer member 32. The heat uniformed in the circumferential direction is transmitted from the heat transfer member 32 to the fixing belt 22 that faces the heat transfer member 32 in the circumferential direction. Thus, only a part of the fixing belt 22 is not locally heated, but is almost entirely heated in the circumferential direction. Therefore, even when the fixing operation of the fixing device 7 is speeded up, the fixing belt 22 is sufficiently heated and the occurrence of fixing failure can be suppressed. That is, since the fixing belt 22 can be efficiently heated with a relatively simple configuration, the warm-up time and first print time can be shortened, and the fixing device 7 can be downsized.

  FIG. 4 is a diagram showing a positional relationship between the pressure roller and the nip forming member, and is a diagram showing a conventional configuration different from the present embodiment. In FIG. 4, the illustration of the fixing belt is omitted for convenience.

  As shown in FIG. 4, the pressure roller 23 moves in the direction of the arrow D1 when the bearing 41 is urged by the contact / separation mechanism, and moves to the nip forming member 30 via the fixing belt 22 (see FIG. 2). The nip portion N is formed by pressure contact. At this time, as shown in FIG. 4, on the downstream side of the nip forming surface 30a in the sheet conveying direction, the pressure roller 23 contacts the downstream end 30a1. On the other hand, a non-contact portion 30a3 to which the pressure roller 23 does not contact is provided on the upstream side of the nip forming surface 30a in the sheet conveyance direction. Note that the direction of the arrow D1 is a direction different from the paper transport direction among the directions perpendicular to the longitudinal direction of the pressure roller 23 (the front and back direction in FIG. 4).

  By the way, when the rubber hardness of the elastic layer of the pressure roller 23 decreases due to deterioration over time and the repulsive force of the pressure roller 23 against the urging force from the contact / separation mechanism weakens, the pressure roller 23 is applied to the nip forming member 30. Further, the elastic layer is crushed and the amount of crushing is increased (the state of the pressure roller 23 ′ indicated by the dotted line in FIG. 4). Accordingly, the pressure roller 23 is pressed in a wider range on the upstream side of the nip forming surface 30a in the paper conveyance direction, the range of the non-contact portion 30a3 is narrowed, and the nip width N2 on the upstream side of the paper conveyance direction is increased. . In the normal pressure contact state (the state of the pressure roller 23 indicated by the solid line in the figure), there is no non-contact portion on the downstream side of the nip forming surface 30a in the sheet conveying direction, so that the pressure roller 23 further forms a nip. Even when pressed against the member 30 side, the nip width N1 on the downstream side in the paper transport direction does not increase.

  As described above, when the nip width of the nip portion N becomes larger than the initial target due to the decrease in the rubber hardness of the elastic layer of the pressure roller 23, the toner image T of the paper P passing through the nip portion N is overheated and hot. Problems such as offset will occur.

  As a configuration for solving such a problem, the configuration of the fixing device of this embodiment will be described with reference to FIG. In the following description, the upstream side in the paper transport direction or the downstream side in the paper transport direction is also simply referred to as the upstream side or the downstream side, respectively. Also, in FIG. 5, the illustration of the fixing belt is omitted as in FIG.

  As shown in FIG. 5, in the fixing device of the present embodiment, the direction in which the pressure roller 23 approaches the fixing belt 22 (nip forming member 30) is an angle with respect to the direction of the arrow D1 (see FIG. 4). It is set in the direction of arrow D2 inclined by θ. The direction of the arrow D2 is a direction toward the downstream side in the paper conveyance direction (one side in the recording medium conveyance direction) while approaching the fixing belt 22. Further, when the pressure roller 23 is separated from the nip forming member 30, it moves in the direction opposite to the arrow D2.

  The pressure roller 23 is pressed against the nip forming member 30 via the fixing belt 22 by the movement in the direction of the arrow D2 to form the nip portion N. At this time, the pressure roller 23 is in contact with the downstream end 30a1 on the downstream side of the nip forming surface 30a of the nip forming member 30. On the other hand, a non-contact portion 30a3 is provided on the upstream side.

  In this embodiment, when the rubber hardness of the elastic layer of the pressure roller 23 decreases and the repulsive force of the pressure roller 23 against the urging force from the contact / separation mechanism weakens, the pressure roller 23 further moves in the direction of the arrow D2. The pressed state is reached (the state of the pressure roller 23 ′ indicated by the dotted line in FIG. 5).

  In this case, the nip width of the nip portion N does not change greatly between the pressure roller 23 and the pressure roller 23 '. That is, in this embodiment, when the pressure roller 23 is further pressed against the nip forming member 30 side, the pressure roller 23 moves to the downstream side, so that the upstream nip width N2 is reduced. It will be. Therefore, the nip width N2 is equal to the amount by which the nip width decreases due to the movement of the pressure roller 23 and the amount by which the pressure roller 23 is pressed more strongly against the nip forming member 30 to increase the nip width. The amount of change in the nip width is kept small. On the downstream side, the pressure roller 23 is already in contact with the downstream end 30a1 of the nip forming surface 30a, so that the downstream nip width N1 even if the pressure roller 23 moves further downstream. Will not change.

  As described above, in this embodiment, the approaching direction of the pressure roller 23 to the nip forming member 30 is set in the direction of the arrow D2, and the nip width increases due to the decrease in the rubber hardness of the elastic layer (upstream in the sheet conveying direction). ) And the pressure roller 23 is moved in the opposite direction. Thereby, the change of the nip width by the fall of the rubber hardness of the elastic layer of the pressure roller 23 can be suppressed, and generation | occurrence | production of the hot offset mentioned above can be prevented. Therefore, in the fixing device 7, the pressure roller 23 having a low hardness elastic layer can be employed, and the nip portion N having a sufficient width can be formed even with the pressure roller 23 having a small diameter.

  The approaching direction inclination θ of the pressure roller 23 is preferably provided at an angle of 10 degrees or more in order to secure a certain amount of the decrease in the nip width N2. On the other hand, in order to bring the pressure roller 23 into and out of contact with the nip forming member 30, it is necessary to secure a certain amount or more of movement in the contact and separation direction of the pressure roller 23 so that the angle does not become too large. It is necessary to.

  The downstream side of the nip forming surface 30a is formed in a curved shape that partially curves toward the pressure roller 23 so as to follow the shape of the outer peripheral surface of the pressure roller 23. Thereby, the downstream side of the nip forming surface 30a can be brought into close contact with the pressure roller 23 via the fixing belt 22, and the width of the nip portion N can be increased.

  Further, the downstream end 30a1 of the nip forming member 30 is formed in an R shape. Thereby, the sliding resistance generated between the downstream end portion 30a1 and the fixing belt 22 can be reduced, and even when the pressure state from the pressure roller 23 to the fixing belt 22 is maintained for a long time, It is possible to prevent the fixing belt 22 from being deformed. On the other hand, if the R shape is too large, depending on the pressure contact state of the pressure roller 23 to the fixing belt 22, the pressure roller 23 and the downstream end 30a1 are separated from each other, and the nip width on the downstream side in the transport direction varies. . Therefore, the R shape is preferably formed with a radius in the range of 0.3 to 2.0 mm.

Next, a configuration for guiding the pressure roller in the direction of the arrow D2 will be described with reference to FIG.
As shown in FIG. 6, bearings 41 provided on both sides in the axial direction of the pressure roller 23 are held by the side plate 42, and are provided so as to be movable in guide holes (guide mechanisms) 42 a of the side plate 42. The guide hole 42a is provided toward the downstream side (upper side in the figure) of the sheet conveyance direction as it goes toward the fixing belt 22 (left side in the figure), and guides the bearing 41 in the extending direction of the guide hole 42a. Thus, the direction of the pressure roller 23 relative to the fixing belt 22 can be set to the direction (the direction of arrow D2 in FIG. 5 and the opposite direction thereof).

  Next, a modification of the nip forming member will be described for the fixing device of the present invention.

  As shown in FIG. 7, the nip forming member 30 of the second embodiment has an inclined surface 30b on the upstream side of the nip forming surface 30a. The inclined surface 30b is inclined in a direction away from the pressure roller 23 toward the upstream side.

  In the present embodiment, since the nip forming member 30 has the inclined surface 30b, the upstream nip width N2 is reduced. Further, the amount of increase in the nip width N2 when the pressure roller 23 is pressed more strongly against the nip forming member 30 and the amount of decrease in the nip width N2 due to the movement of the pressure roller 23 downstream in the conveying direction are also included. Get smaller. Therefore, the change amount of the nip width N2 can be reduced with respect to the change of the pressing amount of the pressure roller 23 against the nip forming member 30.

  Further, a part of the nip forming member 30 can be constituted by another member. For example, as shown in FIG. 8, the nip forming member 30 of the third embodiment includes a second member 35, a part of which is a separate member from the other parts. The second member 35 constitutes a part of the nip forming surface 30a. Thereby, a part of the nip forming surface 30a is replaced with a member having a small friction coefficient to reduce the frictional force generated between the nip forming member 30 and the fixing belt 22, or a part of the nip forming surface 30a is more heat resistant. It can be composed of highly functional members.

  In the above embodiment, the configuration in which the nip width N2 on the upstream side in the transport direction is changed has been described. However, the present invention is not limited to this, and a configuration in which the nip width N1 on the downstream side in the transport direction may be changed.

  Specifically, as shown in FIG. 9, in the fixing device according to the fourth embodiment of the present invention, the pressure roller 23 contacts the upstream end 30a2 on the upstream side (one side) of the nip forming surface 30a. . On the other hand, a non-contact portion 30a3 to which the pressure roller 23 does not contact is provided on the downstream side of the nip forming surface 30a. The upstream side of the nip forming surface 30 a is provided in a curved shape along the outer peripheral surface of the pressure roller 23.

  The pressure roller 23 is urged by the contact / separation mechanism, moves in the direction of an arrow D3 inclined with respect to the transport direction, and is pressed against the nip forming member 30.

  In such a configuration, when the pressure roller 23 is more strongly pressed against the nip forming member 30 due to a decrease in rubber hardness of the elastic layer of the pressure roller 23, the pressure roller 23 moves upstream. . Thereby, the amount of change in the downstream nip width N1 is suppressed. Further, the nip width N2 on the upstream side in the transport direction is provided with a constant width regardless of the pressing amount of the pressure roller 23.

  In the fixing device of the fourth embodiment, regardless of the pressing amount of the pressure roller 23, the upstream end position of the nip portion N in the transport direction is fixed to the upstream end 30a2. For this reason, the behavior at the time of entry of the paper P to be passed through the nip portion N to the fixing device 7 is easily stabilized.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a complex machine thereof.

  Recording media include paper P (plain paper), thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, plastic film, prepreg, copper foil, etc. included.

  The fixing device of the present invention is not limited to the configuration shown in FIG. For example, as shown in FIG. 10, the fixing device 7 is not provided with a heat transfer member, and the fixing belt 22 is directly heated by the heater 33. The pressure roller 23 includes a cored bar 23a, an elastic layer 23b, and a release layer 23c. In addition, a contact / separation mechanism 50 that contacts and separates the pressure roller 23 from the fixing belt 22 is provided. The pressure roller 23 is pressed toward the fixing belt 22 by the contact / separation mechanism 50 to form a nip portion N with the fixing belt 22 (nip forming member 30).

  The heater 33 is composed of a single halogen heater. However, two or three or more may be provided as in the above-described embodiment. A reflective member 36 is provided between the support member 31 and the heater 33. The reflection member 36 reflects heat radiated from the heater 33 toward the support member 31, and the fixing belt 22 is heated more efficiently.

  In the fixing device 7 employing such a low heat capacity fixing member, the fixing belt 22 can be heated to a temperature necessary for the fixing operation with a slight heating by the heater 33. On the other hand, the temperature of the fixing belt 22 increases. And the above-described hot offset problem is likely to occur.

  Also in the fixing device having the above-described configuration, the pressing amount of the pressure roller 23 against the nip forming member 30 due to a decrease in rubber hardness or the like by adopting the configuration of the present invention described with reference to FIGS. Even in the case of increasing, it is possible to suppress the fluctuation amount of the nip width and prevent the occurrence of hot offset. The contact / separation mechanism shown in FIGS. 2 and 10 is an example, and any structure that can apply an appropriate urging force to the pressure roller 23 can be used, and the configuration can be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 7 Fixing apparatus 22 Fixing belt (fixing member)
23 Pressure roller (Pressure member)
30 Nip forming member 30a Nip forming surface 30a1 Downstream end (end on one side in the recording medium conveyance direction)
30b Inclined surface 42 Side plate (Fusing device casing)
42a guide hole (guide mechanism)
50 Contact / separation mechanism (biasing mechanism)
N nip P Paper (recording medium)

JP 2013-164451 A JP 2014-199386 A

Claims (10)

A rotatable endless fixing member;
A pressure member which is pressed against the fixing member and forms a nip portion with the fixing member;
An urging mechanism for urging the pressing member toward the fixing member;
A fixing device including a nip forming member disposed on an inner peripheral surface side of the fixing member, and fixing an image on a recording medium,
The nip forming member has a nip forming surface that contacts the pressure member through the fixing member and forms the nip portion,
The pressure member abuts against one end of the nip forming surface in the recording medium conveyance direction via the fixing member,
A fixing device further comprising a guide mechanism that guides the pressing member to one side in the transport direction when the pressing member is biased by the biasing mechanism and approaches the fixing member. .   The approach direction of the pressure member to the fixing member is a direction having an inclination of 10 degrees or more with respect to a direction different from a conveyance direction of the recording medium among directions perpendicular to a longitudinal direction of the pressure member. The fixing device according to 1. The pressure member is rotatably held in a casing of the fixing device via bearings provided on both sides in the axial direction of the pressure member,
The fixing device according to claim 1, wherein the guide mechanism guides the pressure member in the direction by guiding the bearing to one side in the transport direction.   4. The fixing device according to claim 1, wherein the nip forming surface has an inclined surface that is inclined in a direction away from the pressure member toward the other end side in the conveyance direction.   5. The nip forming surface according to claim 1, wherein the nip forming surface has an R shape at one end portion in the conveyance direction of the recording medium, and a radius thereof is set in a range of 0.3 to 2.0 mm. Fixing device.   The fixing device according to claim 1, wherein the nip forming member is formed of a heat resistant resin material. The pressure member is rotatably held in a casing of the fixing device via bearings provided on both sides in the axial direction of the pressure member,
The fixing device according to claim 1, wherein the nip forming member is held by the housing.   The fixing device according to claim 1, wherein the pressure member has an elastic layer having a thickness of 2 mm or more.   The fixing device according to claim 1, wherein a surface hardness of the pressure member is set to 60 or less in terms of ASKER-C hardness.   An image forming apparatus comprising the fixing device according to claim 1.

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