JP2015158597A - image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device that can reduce a difference in pressure between both ends and the central part along the generating line of a belt member when a pressure applied to a nip part is reduced, with a simple mechanism arranged in an internal space of the belt member.SOLUTION: A pressure mechanism 60 can apply a first urging force and a second urging force smaller than the first urging force between a stay 102 and a pressure roller 106 to apply a pressure to a nip part N. A pressure application auxiliary spring 120 is arranged between a guide member 103 and the stay 102. Since the pressure application spring 120 urges both ends of the guide member 103 along the generating line of a fixing belt 101 from the stay 102 toward the nip part N, when the second urging force is applied between the stay 102 and pressure roller 106, the guide member 103 is properly pressed toward the pressure roller 106 to suppress a reduction in the pressure to be applied to the nip part on both ends of the guide member 103.

Description

  The present invention relates to an image heating apparatus that heats a recording material carrying a toner image at a nip portion between an endless belt member and a rotating body.

  Widely used in an image forming apparatus that forms a toner image and transfers it to a recording material, and heats the recording material on which the toner image is formed by a fixing device as an example of an image heating device to fix the image on the recording material. It has been. As an example of a fixing device, a rotating member (roller member or belt member) is brought into contact with a belt member supported by a guide member to form a nip portion, and a recording material carrying a toner image is sandwiched and conveyed by the nip portion. A belt fixing device that performs heat treatment while being used has been put into practical use (Patent Documents 1 and 2).

  Patent Document 2 discloses a roller fixing device that can change the pressure applied to the nip portion in two stages. Here, when the envelope is selected as the recording material, the pressing force at the nip portion is lowered as compared with the case where plain paper is selected, thereby preventing the recording material from being wrinkled as the toner image is fixed. .

JP 2011-232442 A JP 2011-028298 A JP 2007-212526 A

  As described in Patent Document 3, the recording material such as thin paper or envelope tends to cause wrinkles on the recording material during the heat treatment, and therefore the pressure applied to the nip portion is lower than when forming an image on a normal recording material. It is desirable to make it. However, when the applied pressure at the nip portion is reduced in the belt fixing device, the pressure at both ends along the bus bar of the belt member is significantly lower than the pressure at the central portion, resulting in uneven glossiness on the fixed image output to the recording material. Was found to occur.

  In view of this, it has been proposed to arrange a mechanism outside the belt member so that the pressure at both ends along the bus bar of the belt member coincides with the pressure at the center when the pressure applied to the nip portion is reduced. However, the mechanism disposed outside the belt member complicates the structure of the belt fixing device, increases the manufacturing cost, and interferes with operations such as belt member replacement and inspection.

  The present invention can reduce the pressure difference between both ends and the central portion along the generatrix of the belt member when the applied pressure of the nip portion is reduced by a simple mechanism disposed in the inner space of the belt member. An object of the present invention is to provide an image heating apparatus.

  The image heating apparatus according to the present invention includes an endless belt member, a rotating body that contacts the belt member, a heating unit that heats at least one of the belt member and the rotating body, and the rotation via the belt member. A guide member that contacts the inner surface of the belt member so as to press the body and guides the belt member; a support member that is arranged in a beam shape in the inner space of the belt member and supports the guide member; A pressure mechanism capable of applying a first urging force and a second urging force smaller than the first urging force between the support member and the rotating body, the guide member, and the support member And an elastic member that urges both ends of the guide member toward the rotating body from the support member. And when the said pressurization mechanism applies said 2nd urging | biasing force, the said elastic member can compensate the fall of the applied pressure with respect to the said belt member in the both ends of the said guide member.

  In the image heating apparatus of the present invention, the elastic member expands and contracts in response to a decrease in the applied pressure at both ends of the guide member, thereby reducing the decrease in the applied pressure. For this reason, the pressure difference of the both ends along the bus line of a belt member when the pressurization force of a nip part is reduced can be made small by the simple mechanism arrange | positioned in the inner space of a belt member. As a result, gloss unevenness at both ends and the center of the output image is reduced in the recording material such as thin paper or envelope.

1 is an explanatory diagram of a configuration of an image forming apparatus. FIG. 3 is an explanatory diagram of a configuration of a vertical cross section of the fixing device. It is a side view of a fixing device. FIG. 3 is a perspective view of an internal configuration of a fixing member. It is explanatory drawing of operation | movement of the pressurization mechanism of a fixing device. FIG. 4 is a cross-sectional view of a fixing member at both ends of the fixing belt. 5 is an explanatory diagram of a bending state of a fixing member in Embodiment 1. FIG. It is explanatory drawing of the bending state of the fixing member in a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
(Image forming device)
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 1 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PK are arranged along an intermediate transfer belt 31. is there.

  In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 11 (Y) and transferred to the intermediate transfer belt 31. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 11 (M) and transferred to the intermediate transfer belt 31. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 11 (C) and 11 (K), respectively, and sequentially transferred to the intermediate transfer belt 31.

  The recording material P is taken out one by one from the recording material cassette 20 and waits at the registration roller 23. The recording material P is fed to the secondary transfer portion T2 by the registration roller 23 in synchronization with the toner image on the intermediate transfer belt 31, and the toner image is secondarily transferred from the intermediate transfer belt 31. The recording material P on which the four-color toner images are secondarily transferred is conveyed to the fixing device 40, and is heated and pressed by the fixing device 40 to fix the image, and then discharged to the external tray 64 by the discharge roller 63. The

  On the other hand, when toner images are formed on both surfaces of the recording material P, the recording material P on which the toner image on one surface is fixed by the fixing device 40 is guided upward by the flapper 61. The recording material P is turned upside down by being switched back in the transport path 73, and then transported through the duplex transport path 70 and waits at the registration roller 23. Then, a toner image is formed on the other surface at the secondary transfer portion T2, and after the toner image is fixed by the fixing device 40, it is discharged to the external tray 64.

  The image forming units PY, PM, PC, and PK are different from the toners used in the developing devices 14 (Y), 14 (M), 14 (C), and 14 (K) except for yellow, magenta, cyan, and black. The configuration is substantially the same. In the following, the yellow image forming unit PY will be described, and redundant description regarding the other image forming units PM, PC, and PK will be omitted.

  In the image forming unit PY, a corona charger 12, an exposure device 13, a developing device 14, a transfer blade 17, and a drum cleaning device 15 are arranged around the photosensitive drum 11.

  The corona charger 12 charges the surface of the photosensitive drum 11 to a uniform potential. The exposure device 13 scans the laser beam and writes an electrostatic image of the image on the photosensitive drum 11. The developing device 14 develops the electrostatic image and forms a toner image on the photosensitive drum 11. The transfer blade 17 is applied with a voltage to transfer the toner image on the photosensitive drum 11 to the intermediate transfer belt 31. The drum cleaning device 15 cleans residual toner by sliding the photosensitive drum 11 with a cleaning blade.

(Fixing device)
FIG. 2 is an explanatory diagram of the configuration of the axial vertical cross section of the fixing device. FIG. 3 is a side view of the fixing device. FIG. 4 is a perspective view of the internal configuration of the fixing member.

  As shown in FIG. 2, in the belt heating type fixing device 40, the non-rotating ceramic heater 100 heats the toner image carrying surface of the recording material via a belt member that moves integrally with the recording material. The fixing device 40 sandwiches and conveys the recording material P carrying the toner image Tn at the nip portion N where the pressure roller 106 contacts the fixing member 41, and fixes the image on the recording material.

  The fixing member 41 rotatably holds a cylindrical fixing belt 101 outside the guide member 103 provided with the ceramic heater 100. When the pressure roller 106 rotates, the fixing belt 101 is driven to rotate around the fixed guide member 103, and the heat of the ceramic heater 100 is transmitted to the recording material P through the fixing belt 101.

  As shown in FIG. 3, the fixing flanges 104 are disposed at both ends of the fixing belt 101 and regulate the rotation trajectory of the fixing belt 101. The stay 102 is disposed so as to penetrate the inner space of the fixing belt 101 in a beam shape, and continuously contacts the back surface of the guide member 103 to ensure the bending strength of the guide member 103.

  The fixing flange 104 is held in an opening formed in the side plate 108 of the fixing device 40 so as to be movable up and down. The side plate 108 is formed with an elongated hole-shaped opening so that the fixing flange 104 can be moved in the pressurizing direction. The fixing flange 104 is fitted and held in an elongated hole-shaped opening and is movable along the elongated hole shape of the opening. The fixing flange 104 is pressed downward by a pair of pressure mechanisms 60.

  As shown in FIG. 4, in the fixing member 41, the stay 102 is disposed so as to penetrate the inner space of the fixing belt 101 (not shown) in the longitudinal direction, and the guide member 103 is brought into contact with the lower surface of the stay 102. A bundle guide 118 and a thermistor (not shown) are fixed to the back surface of the guide member 103.

  As shown in FIG. 2, the fixing belt 101 is loosely fitted on the guide member 103. The fixing belt 101 is a cylindrical heat-resistant fixing film that transfers heat to the recording material P, and is made of a heat-resistant material of 100 μm or less, preferably 50 μm or less and 20 μm or more. For example, it is a single layer film of PTFE, PFA, FEP, or a composite layer film obtained by coating PTFE, PFA, FEP or the like on the outer peripheral surface of polyimide, polyamideimide, PEEK, PES, PPS or the like. Moreover, the composite layer film which coat | covered the resin material on the outer peripheral surface of thin metal films, such as 50 micrometers or less 20 micrometers or more, may be sufficient.

  The guide member 103 is provided inside the fixing belt 101. The guide member 103 is made of a material having insulating properties, heat resistance properties, and heat insulation properties. For example, resin materials such as phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, PFA resin, PTFE resin, and LCP resin are used. The guide member 103 has a function as a guide for assisting the pressing of the nip portion N formed by being in pressure contact with the pressure roller 106 and stabilizing the rotation of the fixing belt 101.

  The ceramic heater 100 is a low-heat-capacity resistance heating element that raises the temperature with a steep rise characteristic when energized to the heating resistor layer. For example, an energization heating resistor layer is formed on an elongated thin plate-like ceramic substrate. Further, the ceramic heater 100 is fitted and supported in a fitting groove 103 a provided along the longitudinal direction on the lower surface of the guide member 103.

  The stay 102 is pressed against the back surface of the relatively flexible resin-made guide member 103 to give the guide member 103 bending rigidity in the longitudinal direction and correct the bending state of the guide member 103 so that the longitudinal direction of the guide member 103 is corrected. This is a member for forming the nip portion N having an appropriate pressure distribution.

  As shown in FIG. 3, the fixing flange 104 is fitted to both ends of the stay 102, and the cylindrical portion of the fixing flange 104 is inserted into both ends of the fixing belt 101, and the rotation locus of both ends of the fixing belt 101 is observed. Hold loose. The fixing flange 104 guides the rotation of the fixing belt 101 and also serves as a thrust stopper for the fixing belt 101. The fixing flange 104 is fitted and held in the side plate 108 of the fixing device 40 to guarantee the position of the fixing member 41. The pressure roller 106 is rotationally driven by the drive motor 24 controlled by the control unit 45 via a gear 109 attached to one end portion in the longitudinal direction.

  As shown in FIG. 2, the fixing belt 101 rotates following the pressure roller 106. The pressure roller 106 is configured by concentrically and integrally covering an elastic layer 106b formed in a roller shape around a cored bar 106a. The elastic layer 106b is made of a material having heat resistance and elasticity such as silicone rubber, fluororubber, and fluororesin, and has a release layer on the surface. For the release layer, a material having good releasability and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, and FEP is selected and used.

  The pressure roller 106 has a bearing member (not shown) made of a heat-resistant resin such as PEEK, PPS, or liquid crystal polymer attached to both ends of the core metal 106a, and can rotate on a pair of side plates 108 as shown in FIG. It is held and arranged. The pressure roller 106 can rotate around a rotation axis fixed to the side plate 108.

  As described above, in the first embodiment, the pressure roller 106, which is an example of a rotating body, is in contact with the fixing belt 101, which is an example of an endless belt member, and a nip portion of a recording material that carries a toner image. N is formed. The pressure roller 106 is a roller member having an elastic layer. A ceramic heater 100 as an example of a heating unit heats at least one of the fixing belt 101 and the pressure roller 106.

  A guide member 103, which is an example of a guide member, abuts against the inner surface along the generatrix of the fixing belt 101 and guides the belt member that passes through the nip portion. The stay 102, which is an example of a support member, is arranged in a beam shape in the inner space along the generatrix of the fixing belt 101 and supports the guide member 103.

  As shown in FIG. 5, the pressurizing mechanism 60, which is an example of the pressurizing mechanism, applies a first urging force and a first urging force between the stay 102 and the pressurizing roller 106 in order to pressurize the nip portion N. It is possible to apply a second urging force smaller than the urging force.

(Pressure mechanism)
FIG. 5 is an explanatory diagram of the operation of the pressure mechanism of the fixing device. In the figure, (a) is a state of normal pressurization, and (b) is a state of pressure reduction corresponding to an envelope or the like.

  The fixing device 40 forms a nip portion of the recording material by sandwiching the fixing belt 101 between the guide member 103 provided with the ceramic heater 100 and the pressure roller 106. Since the fixing belt 101 is thin, has a small heat capacity, and has a good thermal response, the fixing device 40 can efficiently reflect the thermal response of the ceramic heater 100 in the nip portion N. Further, since the fixing device 40 reaches the target temperature for temperature adjustment in a short time after the ceramic heater 100 is turned on, the waiting time for image formation is small. Since the fixing device 40 requires less power to maintain the fixing belt 101 at the target temperature for temperature adjustment and has a short time to rise to the target temperature, it can save power compared to the conventional roller heating type fixing device. Is realized.

  On the other hand, in recent years, correspondence to various types of recording materials such as thin paper, plain paper, thick paper, coated paper, embossed paper, postcard, and envelope has been demanded. Also in the fixing device 40, in order to cope with various types of recording materials, it is necessary to change the heating conditions such as the fixing temperature and the applied pressure according to the types of the recording materials.

  For example, a recording material formed into a cylindrical shape by folding and partially bonding paper such as an envelope is distorted when passing through the nip portion N of the fixing device 40, and the surface tends to be wrinkled. . Even thin paper with low rigidity tends to generate wrinkles when it passes through the nip portion N of the fixing device 40. For this reason, when an envelope or thin paper is selected as the recording material, the fixing device 40 executes a pressure down mode in which the applied pressure is lower than the normal pressure mode applied to plain paper or the like, thereby generating wrinkles. Suppressed. When the envelope is selected as the recording material on the operation terminal, the fixing device 40 automatically reduces the pressure applied to the nip portion and shifts the normal pressure applied so far to the pressure-down state.

  As shown in FIG. 5A, the pressurizing mechanism 60 applies a predetermined pressure F <b> 1 to each fixing flange 104. As shown in FIG. 3, the pressure mechanism 60 presses the fixing belt 101 downward via the stay 102 and the guide member 103 to form a nip portion N between the fixing belt 101 and the pressure roller 106. .

  The first swing arm 110 and the second swing arm 114 are provided so as to be swingable individually with the fulcrum 111 as the center of rotation. The pressure spring 113 is a compression spring provided between the first swing arm 110 and the second swing arm 114. The spring guide 112 guides the inner diameter of the pressure spring 113 to prevent the pressure spring 113 from being detached during expansion and contraction.

  The spring guide 112 passes through a clearance hole provided in the first swing arm 110 and is fixed to the second swing arm 114. For this reason, the spring guide 112 swings integrally with the second swing arm 114 regardless of the tilt angle of the first swing arm 110.

  The cam 115 changes the inclination angle of the second swing arm 114 by rotating in contact with the second swing arm 114. The cam 115 is driven by the drive motor 116 and can rotate in the β direction in the figure.

  The fixing flange 104 is provided with a protrusion 104a. The protrusion 104 a abuts on the first swing arm 110 and transmits the pressure applied by the first swing arm 110 to the fixing flange 104.

  As shown in FIG. 5A, in the normal pressure state, when the cam 115 rotates to a predetermined angle β, the pressure spring 113 rotates together with the second swing arm 114 by a predetermined angle α. Then, the first swing arm 110 is rotated by an angle γ. When the second swing arm 114 rotates to the angle α, the first swing arm 110 biased by the pressure spring 113 rotates to the angle γ.

  The first swing arm 110 contacts the protrusion 104a and presses the fixing flange 104 toward the pressure roller 106 side. Then, the pressure spring 113 is compressed to the operating length l and applies a predetermined pressure F1 to the nip portion N.

  As shown in FIG. 5B, when thin paper or an envelope is selected as the recording material, the control unit 45 operates the drive motor 116 to reduce the pressure applied to the nip portion N to bring the pressure down. Transition. This is because, when normal pressure is applied with an envelope, wrinkles are likely to occur at the fold portion where the paper overlaps, and generation of wrinkles can be suppressed by setting the pressure down state.

  In the state where the pressure is reduced, the cam 115 is rotated to a predetermined angle β ′ and stopped, and the second swing arm 114 is rotated and held to a predetermined angle α ′. The pressure spring 113 rotates together with the second swing arm 114 to a predetermined angle α ′ to rotate the first swing arm 110 to the angle γ ′. The fixing flange 104 is pressed toward the pressure roller 106 in contact with 104a.

  However, when the pressure is reduced, the distance between the first swing arm 110 and the second swing arm 114 is large, and the operating length l ′ of the pressure spring 113 is the operating length l during normal pressurization. Longer than. Therefore, a predetermined pressurizing force F1 ′ lower than that during normal pressurization is applied to the nip portion N.

  Thus, the pressurizing mechanism 60 can change the operating length l of the spring by changing the rotation angle of the cam 115 and can change the applied pressure in two stages.

(Auxiliary pressure mechanism)
FIG. 6 is a cross-sectional view of the fixing member at both ends of the fixing belt. FIG. 7 is an explanatory diagram of a bending state of the fixing member in the first embodiment. In FIG. 7, (a) is a normal pressure state, and (b) is a pressure-down state.

  As shown in FIG. 4, in the first embodiment, at least one pair of auxiliary pressure springs 120 is disposed at both ends in the longitudinal direction of the guide member 103. The auxiliary pressure spring 120 urges both end portions of the guide member 103 toward the pressure roller 106 side.

  As shown in FIG. 6, the auxiliary pressure spring 120 has one end in the pressing direction abutted against the stay 102 and the other end abutted against the guide member 103.

  As shown in FIG. 7A, the pressure roller 106 is formed in an inverted crown shape such that the diameter of the elastic layer 106b gradually increases from the center to the end. This is because the rubber at the end portion is crushed and deforms to the outside of the roller and escapes, so that the amount of crushing required to obtain the same pressure (reaction force) differs between the center and the end portion.

(Normal pressure state)
As shown in FIG. 7A, in the normal pressure state, the stay 102 abuts with no gap across the entire length of the guide member 103, and the guide member 103 is fixed with a substantially uniform pressure distribution in the longitudinal direction. The belt 101 is pressurized. In the normal pressure state, the stay 102 is bent and deformed into an upwardly convex arch shape by the reaction force of the pressure, and the center portion is bent so as to retreat from the pressure roller 106.

  Assuming the deflection of the stay 102 in a normal pressure state, a crown shape 103a is formed on the contact surface with the positioning surface A of the guide member 103 so that the center protrudes toward the stay 102 with respect to the end portion. Yes. For this reason, when the guide member 103 is pressed against the stay 102 by the pressing force of the pressure mechanism 60, the stay 102 is bent, and a positioning surface A whose center protrudes toward the pressure roller 106 is formed.

  The positioning surface A is curved following the crown shape 103 a of the guide member 103, so that the entrance / exit is offset between the positioning surface A and the crown shape 103 a of the guide member 103. The positioning surface A of the stay 102 and the crown shape 103a of the guide member 103 are in close contact with each other, and the influence of the bending of the stay 102 in the normal pressure state is reduced. At this time, the auxiliary pressure spring 120 remains in a compressed state and does not contribute to the support or deformation of the guide member 103.

  Thereby, in a normal pressurization state, a substantially uniform pressure distribution is formed along the longitudinal direction of the nip portion N. A nip portion N having a substantially uniform pressure distribution in the longitudinal direction is formed by the difference in diameter between the crown shape 103a of the guide member 103 and the center portion and the end portion of the outer diameter of the pressure roller 106 facing each other. The fixing device 40 is provided with a crown shape 103a on the guide member 103 to reduce the influence of bending of the stay 102 that holds the guide member 103, and uniformly applies heat and pressure to the recording material in the longitudinal direction. Is possible.

  The core metal 106a of the pressure roller 106 is also bent so that the central portion is retracted from the stay 102 by the reaction force of the pressure. However, since the cored bar 106a has a higher bending rigidity (section modulus) than the stay 102, the amount of deflection of the cored bar 106a is negligible.

(Pressure down state)
As shown in FIG. 7B, in the state where the pressure is reduced, the stay 102 is separated from the guide member 103 at both ends of the guide member 103, so that effective pressure is applied at both ends of the guide member 103 as it is. It cannot be applied to the guide member 103. As shown in FIG. 6, since both end portions of the guide member 103 are separated from the positioning surface A of the stay 102, a gap is formed between the positioning surface A and the guide member 103.

  However, in the first embodiment, the auxiliary pressure spring 120 is brought into contact with the guide member 103 instead of the stay 102 to secure the applied pressure at both ends of the guide member 103. The auxiliary pressure spring 120 abuts against both end portions of the guide member 103 and the positioning surface A of the stay 102 and is positioned, and the auxiliary pressure spring 120 presses the guide member 103 toward the pressure roller 106 in a compressed state. doing.

  The auxiliary pressure spring 120 presses both ends of the guide member 103 toward the pressure roller 106 to compensate for the insufficient pressure applied at both ends of the guide member 103. As a result, even in a state where the pressurizing force is reduced, it is possible to apply a pressure equal to the longitudinal length to the nip portion N. A nip portion N having a substantially uniform pressure distribution is formed in the longitudinal direction.

(Comparative example)
FIG. 8 is an explanatory diagram of the bending state of the fixing member in the comparative example. In the figure, (a) is a normal pressure state, and (b) is a pressure down state. The comparative example is a configuration in which the auxiliary pressure spring 120 is not provided in the configuration of the first embodiment shown in FIG.

  As shown in FIG. 8A, even in the comparative example, in the normal pressure state, the difference in diameter between the crown shape 103a of the guide member 103 and the central portion and the end portion of the outer diameter of the pressure roller 106 facing each other. Thus, the nip portion N having a substantially uniform pressure distribution in the longitudinal direction is formed.

  However, as shown in FIG. 8B, when the pressure down mode is executed during image formation on the envelope and the applied pressure is reduced to a level at which the wrinkle of the envelope can be suppressed, the deflection of the stay 102 is reduced. In addition, only the center portion where the protrusion amount of the crown shape 103a is large is pressurized. As a result, the nip width at both ends of the guide member 103 is reduced. For this reason, in wide envelopes such as the square No. 2, there may be a difference in fixability between the image at the center and at the edge.

  As shown in FIG. 8B, in the comparative example, when the pressurization force of the pressurizing mechanism 60 is lowered from the normal pressurization state to the pressurization down state, the stay 102 and the stay 102 are applied more than in the normal pressurization state. The deflection of the pressure roller 106 is reduced. Therefore, the crown shape 103a of the guide member 103 set in accordance with the normal pressure state remains in a convex state on the pressure roller 106 side. As a result, the pressure reduction in the end region of the guide member 103 is remarkably lower than that in the center, resulting in a difference in image glossiness or a difference in image fixability between the center portion and the end portion.

(Configuration and effect of the first embodiment)
In the first embodiment, as illustrated in FIG. 7B, the auxiliary pressure spring 120, which is an example of an elastic member, is disposed between the guide member 103 and the stay 102. The auxiliary pressure spring 120 urges both end portions of the guide member 103 along the generatrix of the fixing belt 101 from the stay 102 toward the nip portion N. For this reason, when a second urging force is applied between the stay 102 and the pressure roller 106, the guide member 103 is appropriately pressed toward the pressure roller 106, and the guide member 103 is moved at both ends. The pressure drop at the nip can be suppressed.

  In the first embodiment, the auxiliary pressure spring 120 is a compression spring that is arranged closer to the center side than the both end positions of the guide member 103 along the generatrix of the fixing belt 101. For this reason, parts cost becomes very low. Since the heat resistance of the compression spring is high and the spring property does not easily change as the temperature rises, it is possible to ensure a stable pressure with little change with time.

  In the first embodiment, both ends of the guide member 103 abut against the stay 102 when the pressurizing mechanism 60 applies the first biasing force, and the guide member 103 when the pressurizing mechanism 60 applies the second biasing force. Both end portions of the are separated from the stay 102. For this reason, even when a thick recording material enters the nip portion, both end portions of the guide member 103 are flexibly retracted so that the pressure distribution in the longitudinal direction of the nip portion N is not greatly broken.

  In the first exemplary embodiment, at least one of the guide member 103 and the stay 102 is a cross section that gradually protrudes from the both end positions along the generatrix of the fixing belt 101 toward the pressure roller 106, which is an example of the rotating body side, toward the central portion. It has a contour shape. For this reason, a uniform pressure distribution in the longitudinal direction of the nip portion can be ensured in a normal pressure state.

  In the first embodiment, the control unit 45, which is an example of the detection unit, can detect whether the recording material is an envelope or a sheet by reading a user setting through the operation panel. The control unit 45, which is an example of a control unit, sets the first biasing force to the pressurizing mechanism 60 when the recording material is a sheet, and applies the second biasing force to the pressurizing mechanism when the recording material is an envelope. Set to 60. For this reason, wrinkles can be prevented when the envelope is used as a recording material.

  According to the first embodiment, by providing the pressure member that presses both ends of the guide member toward the pressure roller, the end fixing property is deteriorated even if the applied pressure is decreased and the central pressure is decreased. Can be prevented. Accordingly, it is possible to set an optimum pressing force for various recording materials. In other words, by providing a pressure member that presses both ends of the guide member toward the pressure roller, it is possible to prevent the pressure difference from the center from increasing due to a decrease in the applied pressure at the end when the applied pressure is reduced. it can. In the configuration in which both ends of the guide member that supports the fixing belt 1 and forms the nip portion N between the pressure roller 106 and the pressure roller 106 are pressed toward the pressure roller 106, the pressure reduction at both ends can be reduced. As a result, it is possible to maintain optimum fixing properties for various recording materials. Provided is a film heating type fixing device that achieves high image quality by forming a uniform nip width in the longitudinal direction even when the pressure is reduced to suppress wrinkling of a cylindrical recording material such as an envelope. be able to.

<Embodiment 2>
In the first embodiment, the embodiment in which the nip portion N is directly heated using the ceramic heater 100 has been described. The fixing belt 101 is in contact with the surface of the recording material carrying the toner image, and the ceramic heater 100 is a heater member that is disposed on the guide member 103 and generates heat when energized.

  On the other hand, in the second embodiment, a halogen heater is disposed in the inner space of the fixing belt 1, and the fixing belt 1 is heated from the inner side by the radiant heat of the halogen heater. Using a halogen heater, the thin fixing belt is indirectly heated using the radiant heat. A pad member, which is a nip forming member made of resin or metal, is disposed opposite to a pressure roller as a pressure member, and a nip portion is formed by sandwiching the fixing belt.

  The fixing belt 101 is in contact with the surface of the recording material carrying the toner image, and the halogen heater is disposed in the inner space of the fixing belt 101 along the stay 102, and radiates heat to the inner surface of the fixing belt 101 by energization. It is a heater member.

<Embodiment 3>
In the third embodiment, the fixing belt 1 is heated using an IH heating device. The fixing belt 101 has a layer of a material that abuts on the surface of the recording material carrying the toner image and generates heat by an incident magnetic field. The heating means in the IH heating device is a coil member that is disposed along the bus bar of the fixing belt 101 and generates a magnetic field by energization to enter the fixing belt 101. Further, the present invention can be implemented even with a configuration using other heating means.

<Other embodiments>
As long as the elastic member presses both end portions of the guide member to prevent a partial decrease in the applied pressure when the applied pressure of the entire nip portion is reduced, a part of the configuration of the embodiment or Other embodiments may be implemented in which all are replaced with the alternative configuration.

  Therefore, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified. .

  The rotating body is not limited to a roller member, and may be a belt member whose inner surface is supported by a rubbing pad or a supporting roller.

  The embodiment is not limited to the embodiment in which the belt member is heated and brought into contact with the toner image carrying surface of the recording material. In another embodiment, the fixing roller or the fixing belt is brought into contact with the toner image surface of the recording material carried on the belt member to form the nip portion.

  The image heating device is not limited to a fixing device that fixes a toner image on a recording material. It can also be implemented by a gloss processing device, a surface processing device, or the like that heat-processes a semi-fixed image or a fixed image on a recording material.

  The switching of the pressing force is not limited to two stages. It can also be implemented with a switching mechanism having three or more stages, or a mechanism for continuously changing the pressure.

  The image forming apparatus can be implemented without distinction between a single drum type and a tandem type. It can be carried out without distinction between the number of photoconductors, charging method, electrostatic latent image forming method, transfer method, fixing method, and the like. Here, only the main part relating to toner image formation / transfer is described, but the present invention adds printers, various printing machines, copiers, fax machines, composites, in addition to necessary equipment, equipment, and housing structure. The image forming apparatus can be used for various purposes such as a printer.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 11 Photosensitive drum, 12 Corona charger 13 Exposure apparatus, 14 Developing apparatus, 15 Drum cleaning apparatus 17 Transfer blade, 20 Recording material cassette, 23 Registration roller 31 Intermediate transfer belt, 35 Secondary transfer roller, 40 Fixing Device 45 Control unit, 60 Pressure mechanism 100 Ceramic heater, 101 Fixing belt, 102 Stay 103 Guide member, 104 Fixing flange, 106 Pressure roller 108 Side plate, 110 First swing arm 111 Support point, 112 Spring guide, 113 Pressurization Spring 114 Second swing arm, 115 cam, 24, 116 Drive motor 120 Pressurizing auxiliary spring

Claims (9)

An endless belt member;
A rotating body in contact with the belt member;
Heating means for heating at least one of the belt member and the rotating body;
A guide member that contacts the inner surface of the belt member so as to press the rotating body via the belt member and guides the belt member;
A support member that is arranged in a beam shape in the inner space of the belt member and supports the guide member;
A pressurizing mechanism capable of applying a first urging force and a second urging force smaller than the first urging force between the support member and the rotating body;
An elastic member that is disposed between the guide member and the support member and biases both ends of the guide member from the support member toward the rotating body,
The image heating apparatus according to claim 1, wherein when the pressurizing mechanism applies the second urging force, the elastic member compensates for a decrease in pressure applied to the belt member at both ends of the guide member.   When the pressing mechanism applies the first biasing force, both ends of the guide member abut against the support member, and when the pressing mechanism applies the second biasing force, both ends of the guide member The image heating apparatus according to claim 1, wherein the image heating apparatus is separated from the support member.   3. The image heating according to claim 1, wherein the elastic member is a compression spring disposed closer to a center side than both end positions of the guide member along a rotation axis of the rotating body. apparatus.   2. At least one of the guide member and the support member has a cross-sectional contour shape that gradually protrudes toward the rotating body from the both end positions along the rotation axis of the rotating body toward the central portion. 4. The image heating apparatus according to any one of items 1 to 3. The belt member is in contact with the surface of the recording material carrying the toner image;
The image heating apparatus according to claim 1, wherein the heating unit is a heater member that is disposed on the guide member and generates heat when energized. The belt member is in contact with the surface of the recording material carrying the toner image;
5. The heater according to claim 1, wherein the heating unit is a heater member that is disposed in an inner space of the belt member along the support member and that radiates radiant heat to the inner surface of the belt member when energized. The image heating apparatus according to claim 1. The belt member is in contact with the surface of the recording material carrying the toner image and has a layer of material that generates heat by an incident magnetic field;
5. The heating unit according to claim 1, wherein the heating unit is a coil member that is disposed along a bus bar of the belt member and generates a magnetic field by energization to be incident on the belt member. Image heating device.   The image heating apparatus according to claim 1, wherein the rotating body is a roller member having an elastic layer. A detection unit capable of detecting whether the recording material is an envelope or a sheet;
A controller that sets the first biasing force to the pressurizing mechanism when the recording material is a sheet, and sets the second biasing force to the pressurizing mechanism when the recording material is an envelope; The image heating apparatus according to claim 1, comprising: an image heating apparatus according to claim 1.

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