JP6624839B2 - Image heating device - Google Patents

Description

  The present invention relates to an image heating apparatus mounted on an image forming apparatus employing an electrophotographic method, an electrostatic recording method, or the like, and heating an image on a recording material.

  Examples of the image heating device include a fixing device that fixes an unfixed image on a recording material and a gloss increasing device that increases the glossiness of an image by heating an image fixed on the recording material. .

  As such a fixing device, a fixing device of a belt fixing type using a fixing roller and a belt unit has been devised (Japanese Patent Application Laid-Open No. H11-163873). The fixing device is arranged such that the fixing roller is heated and rotated, and the endless belt is driven to rotate by bringing the fixing roller into contact with the belt unit. Then, the toner image is fixed on the recording material by heat and pressure while nipping and transporting the recording material carrying the unfixed toner image at a fixing nip portion which is a contact portion between the fixing roller and the belt.

  The belt unit has a belt, a plurality of rollers for suspending the belt, and a pressing pad for pressing the belt toward the fixing roller. In this fixing device, the nip portion is formed by pressing one of the rollers for suspending the belt (referred to as a separation roller) and the pressing pad against the fixing roller.

  The pressing pad is designed according to the shape of the fixing roller, and this fixing device can ensure a large nip width in the recording material conveyance direction. Therefore, this fixing device can surely transmit heat to the toner image on the recording material in the nip portion. The separation roller assists separation of the recording material from the fixing roller by giving the belt a curvature at the exit of the nip portion.

  Therefore, this fixing device is suitable for a full-color image forming device that needs to dissolve a large amount of toner, and is suitable for a high-productivity image forming device in which a recording material easily follows a fixing roller.

JP-A-11-045025

  By the way, in a fixing device using a belt unit that presses a belt against a fixing roller by a separation roller and a pressing pad, when a gap between the separation roller and the pressing pad is large, a pressure release part occurs in a part of the nip portion. Since the expanded air or water vapor stays in the pressure release portion, the fixation is hindered and the quality of the output image is reduced.

  On the other hand, recent image forming apparatuses are required to output higher quality images than conventional image heating apparatuses. Therefore, it is desirable that such a fixing device be designed with high accuracy so that the gap between the separation roller and the pressing pad is reduced.

  However, the members constituting the belt unit vary in accuracy and shape, and may affect the accuracy of arrangement of the separation roller and the pressing pad. Therefore, it is desirable that the fixing device be a fixing device capable of accurately arranging the separation roller and the pressing pad irrespective of the accuracy and shape variation of the components. It is desirable that the fixing device can output a high-quality image while suppressing occurrence of image defects.

  An object of the present invention is to provide an image heating device in which occurrence of image defects is suppressed.

A typical configuration of the image heating apparatus according to the present invention for achieving the above object includes a rotating body and a belt that form a nip portion for heating an image on a recording material, and the belt is attached to the rotating body. A pressing pad that presses the belt, a pressing roller that is provided downstream of the pressing pad in the recording material conveyance direction, rotatably supports the belt, and presses the belt toward the rotating body; A support member that supports the pad, and a fixing portion that adjustably fixes the relative positional relationship between the pressing pad and the supporting member, and the adjustment of the fixing portion allows the pressing pad to be attached to the supporting member. The angle relative to the support member can be changed in a supported state.

  According to the present invention, it is possible to provide an image heating device in which occurrence of an image defect is suppressed.

FIG. 4 is an explanatory diagram illustrating a posture adjustment mechanism of a belt unit in the fixing device according to the embodiment when viewed from a cross-sectional direction. FIG. 3 is an explanatory diagram of a posture adjustment mechanism of the belt unit viewed from a recording material width direction. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 3 is a schematic cross-sectional view of the fixing device when the belt unit is being moved to a fixing position by a pressing operation of a pressing mechanism. It is an external appearance perspective view of a belt unit which omitted a belt. FIG. 4 is a schematic cross-sectional view of the fixing device when the belt unit is moved to a standby position by a pressure release operation of a pressure mechanism. FIG. 5 is a diagram illustrating a pressure distribution in a recording material conveyance direction in a fixing nip portion of the belt fixing device of the embodiment and a same pressure distribution of a reference example. FIG. 4 is a diagram illustrating a pressure distribution in a width direction of a recording material in a fixing nip portion of the belt fixing device according to the embodiment and a pressure distribution in a reference example.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best embodiment of the present invention, the present invention is not limited to these examples.

"Example"
(Image forming apparatus)
FIG. 3 is a schematic diagram of the configuration of the image forming apparatus in the present embodiment. The image forming apparatus 100 includes image forming units 200Y, 200M, and 200C corresponding to respective colors of Y (yellow), M (magenta), C (cyan), and K (black) as image forming means inside the apparatus main body. , 200K are arranged in series. That is, the image forming apparatus adopts a tandem system in which processes up to visualization are performed in parallel for each color.

  Hereinafter, in order to prevent the description from becoming complicated, the four image forming units Y, M, C, and K will be described with reference to the reference numeral 200, and the same applies to the following respective process units. Further, the arrangement order of the image forming units for each of the colors Y, M, C, and K is not limited thereto.

  Each image forming unit 200 includes the following process means. It has an image carrier 120 that carries an electrostatic latent image on its surface corresponding to each color of Y, M, C, and K, a primary charging device 121, an exposure device 122, and a developing device 123. The image carrier 120 is driven to rotate counterclockwise at a predetermined peripheral speed. The primary charging device 121 uniformly charges the surface of the corresponding image carrier 120 by applying a charging bias voltage having a set potential. The charged surface is exposed by the exposure device 122 to form an electrostatic latent image. The electrostatic latent image is developed with toner by the developing device 123 and is visualized as a toner image.

  Each toner image formed and carried on the surface of the image carrier 120 is sequentially placed on an intermediate transfer body 125 by an endless belt that is rotated at a predetermined peripheral speed in a clockwise direction indicated by an arrow R2 by a primary transfer device 124. The primary transfer is performed again. The intermediate transfer belt 125 is supported by being supported by a driving roller 126, a tension roller 127, and an opposing roller 128, and is driven by the driving roller 126 to rotate in the direction of arrow R2.

  The secondary transfer roller 131 provided in the secondary transfer device 130 is in pressure contact with the intermediate transfer belt 125 supported from the inside by the opposing roller 128, and the secondary transfer roller 131 and the intermediate transfer belt 125 The transfer nip N2 is formed. Then, the toner image on the intermediate transfer body 125 on which all the colors of Y, M, C, and K are primarily transferred is secondarily transferred collectively onto the sheet (recording material) P at the secondary transfer nip N2. You. The belt cleaning device 129 rubs the cleaning web against the intermediate transfer belt 125 to remove transfer residual toner, paper dust, and the like remaining on the surface of the intermediate transfer belt 125 that has passed through the secondary transfer nip N2.

  Further, the sheet feeding device (recording material feeding device) 110 separates one sheet of paper P pulled out from one of the upper and lower two-stage sheet storage cassettes 111A and 11B by the pickup roller 112 by the separation device 113. And is sent out to the registration roller 115. The registration roller 115 receives the leading end of the paper P in a stopped state and waits, and sends the paper P to the secondary transfer nip N2 in synchronization with the toner image on the intermediate transfer belt 125.

  The paper P carrying the toner image transferred in the secondary transfer nip N2 is transported to the fixing device 1 by the belt transport device 140. In the fixing device 1, the sheet P is nipped and conveyed by the fixing nip N, and the unfixed toner image is fixed by applying heat and pressure. The sheet P sent from the fixing device 1 after the fixing process is conveyed by the pair of conveying rollers 52 toward the discharge path 150 or the two-sided conveying path 160 or the like.

  In the case of the single-sided printing mode, the paper P on which the toner image is fixed advances to the discharge path 150 and is discharged to the discharge tray 152 by the discharge roller 151 and is stacked. In the case of the double-sided printing mode, the paper P having the toner image fixed on one side thereof proceeds to the reversing path 153, is switched back, is sent to the double-sided conveying path 160, and waits at the re-feed roller 161. Thereafter, the sheet P is sent to the secondary transfer nip N2 by the registration roller 115, the toner image is secondarily transferred to the back surface, and the unfixed toner image is fixed by the fixing device 1.

  As described above, the image forming apparatus 100 executes a series of image forming processes such as charging, exposure, development, transfer, and fixing to form a color toner image on the paper P such as a plain paper or an OHP sheet. Discharge. In the case of the monochrome image forming apparatus, only the black (K) image carrier exists, and the toner image formed on the image carrier is transferred to the sheet P by the transfer device.

(Fixing device)
Next, the configuration of the fixing device (image heating device) 1 in this embodiment will be described in detail mainly with reference to FIG. The fixing device 1 is a belt fixing device having a so-called lower belt configuration, and includes a fixing roller 10 as a rotating body that forms a nip portion N for heating an image (toner image) T on a sheet P (on a recording material). A fixing belt (hereinafter, referred to as a belt) 21 which is an endless belt is provided. The belt 21 is provided in a belt unit 20 disposed below the fixing roller 10.

  Further, the belt unit 20 is swung between a fixing position where the belt unit 20 is pressed against the fixing roller 10 by pressing operation (FIG. 4) and a standby position where the belt unit 20 is separated from the fixing roller 10 by pressing operation (FIG. 6). A pressing mechanism (moving mechanism) 60 is provided.

  The fixing roller 10 has a 2 mm thick silicone rubber layer formed as an elastic layer 10b around a core metal 10a made of an aluminum alloy having a thickness of 2 mm. A 50 μm thick PFA tube as a release layer is formed on the rubber layer. 10c is coated. The outer diameter of the fixing roller 10 is φ70.

  The driving force of the drive motor (drive unit) M1 controlled by the control device (control unit) 300 is transmitted via a drive transmission mechanism (not shown) to the fixing roller 71, and a predetermined control is performed in the clockwise direction of the arrow A. It is rotationally driven at a predetermined peripheral speed at a timing.

  Inside the fixing roller 10, a heater (heating source) 11 is disposed near the center. The heater 11 receives power from the power supply unit 301 and generates heat, thereby heating the fixing roller 10 from the inside. Then, the surface temperature of the fixing roller 10 is detected by the thermistor (temperature detecting element) 12, and the detected temperature information is fed back to the control device 300. The control device 300 controls the power supplied from the power supply unit 301 to the heater 11 based on the detected temperature information so that the surface temperature of the fixing roller 10 is raised and maintained at a predetermined temperature.

  The belt unit 20 has a belt 21, and the belt 21 is stretched around a plurality of belt suspension members, namely, an inlet roller 22, a separation roller (pressing roller) 23, and a steering roller 24. Further, a pressing pad 50 is provided inside the belt 21. The pressing pad 50 is disposed at a position between the entrance roller 22 and the separation roller 23 near the separation roller 23.

  By the pressing operation of the pressing mechanism 60, the belt unit 20 is moved in a direction in which the belt unit 20 comes into pressure contact with the fixing roller 10, and the separation roller 23 and the pressing pad 50 are pressed against the fixing roller 10 via the belt 21 by a predetermined pressing force SF. , PF. Thus, the pressing pad 50 presses the belt 21 toward the fixing roller 10. The separation roller 23 is provided downstream of the pressing pad 50 in the sheet conveyance direction (recording material conveyance direction) X, rotatably supports the belt 21, and presses the belt 21 toward the fixing roller 10.

  As a result, a nip (fixing nip) N having a predetermined width is formed between the fixing roller 10 and the belt 21 in the sheet conveying direction X. Since the width of the nip can be widened, the toner of the toner image T on the sheet P can be further melted, and the configuration is suitable for an image forming apparatus using a large amount of toner in a color image forming apparatus.

  In the fixing device 1 of the present embodiment, the belt 21 rotates in the counterclockwise direction indicated by the arrow K by following the rotation of the fixing roller 10 when the belt 21 is pressed against the fixing roller 10. The pressing pad 50 is slidable on the inner surface of the belt 21 at the nip N. Then, the sheet P carrying the unfixed toner image T is introduced into the nip N from the image forming unit side, and is nipped and conveyed, whereby the toner image is fixed. The fixing roller 10 corresponds to the surface of the sheet P on which the unfixed toner image T is carried. The belt 21 corresponds to the surface of the sheet P opposite to the toner image carrying surface.

  The belt 21 is configured to have a polyimide base layer having a thickness of 100 μm. A 0.2 mm thick silicone rubber layer is coated on this base layer. The outer diameter of the belt 21 is φ80. The belt 21 of this embodiment is a seamless belt.

  The entrance roller 22 is a metal roller made of stainless steel, and is disposed on the entrance side where the paper P enters the fixing device 1, and has a rotation center position that is freely rotatable so that the conveyance path of the paper P does not change.

  The separation roller 23 is a metal roller made of stainless steel and has a diameter smaller than the diameter of the fixing roller 10 ". The separation roller 23 is pressed toward the fixing roller 10 via the belt 21 by a spring (first pressing member) 64 of the pressing mechanism 60 described later. Due to this pressure, the elastic layer 10 b of the fixing roller 10 is deformed by the pressure contact of the separation roller 23. In particular, at the end in contact with the separation roller 23, the circular arc shape of the elastic layer 10b is in the opposite direction. Since the toner T on the paper P is melted and pressed at the nip N, the toner T and the surface layer of the fixing roller 10 are stuck by the surface tension.

  However, since the arc shape of the elastic layer 10b of the fixing roller 10 is reversed by the separating roller 23, the toner T stuck to the fixing roller 10 is peeled off, and the paper P is separated from the fixing roller 10. That is, the separation roller 23 rotates while supporting the back surface of the belt 21 at the sheet separation position (recording material separation position) on the downstream side of the nip N in the sheet conveyance direction.

  FIG. 5 is an external perspective view of the belt unit 20. However, the belt 21 is omitted. In the belt unit 20, a belt front side plate 30 on one end side and a belt rear side plate 40 on the other end side in the unit width direction (longitudinal direction) are fixed to a pressing pad 50. The entrance roller 22 is rotatably supported by the belt front side plate 30 and the belt rear side plate 40. A bearing 23c is provided at one end 23a of the separation roller 23, and is attached to the elongated hole 30a of the belt front side plate 30. The separation roller 23 is supported movably in the direction of arrow B with respect to the elongated hole 30a of the belt front side plate 30.

  Similarly, a bearing 23 d is provided on the other end 23 b of the separation roller 23 on the belt rear side plate 40 side, and is attached to the elongated hole 40 a of the belt rear side plate 40. The separation roller 23 is supported movably in the direction of arrow B with respect to the elongated hole 40a of the belt rear side plate 40.

  A bearing 24c is provided at one end 24a of the steering roller 24, and is attached to the elongated hole 35a of the front pressure contact arm 35. The steering roller 24 is supported movably in the direction of arrow C with respect to the elongated hole 35a of the front pressure contact arm 35. Further, the front pressure contact arm 35 presses the steering roller 24 in the direction of arrow D by the pressure spring 32, thereby applying tension to the belt 21.

  Similarly, a bearing 24d is provided on the other end 24b of the steering roller 24 on the belt rear side plate 40 side, and is attached to the elongated hole 45a of the rear pressure contact arm 45. The steering roller 24 is supported movably in the direction of arrow C with respect to the elongated hole 45a of the rear pressure contact arm 45. The rear pressure contact arm 45 presses the steering roller 24 in the direction of arrow D by a pressure spring (not shown), thereby applying tension to the belt 21.

  As will be described later, when the belt unit 20 is separated from the fixing roller 10 by the pressing release operation of the pressing mechanism 60, the pressing spring 32 presses the steering roller 24 in the direction of arrow D, so that the steering roller 24 is pressed. Moves in the D direction. The movement of the steering roller 24 applies tension to the belt 21. Therefore, even if the belt unit 20 is separated from the fixing roller 10, the belt 21 is stretched by the entrance roller 22, the separation roller 23, and the steering roller 24 without sagging.

  As described above, the steering roller 24 functions as a tension roller that constantly applies tension to the belt 21. One end of the steering roller 24 is movable in the direction of arrow C, and one end of the steering roller 24 is moved to a predetermined position by a steering mechanism (not shown) controlled by the control device 8, thereby rotating the belt 21. Is corrected for the shift in the width direction.

  The pressing pad 50 is configured such that the pressing pad 51 is fixed to a pad holder 52. The pad holder 52 is made of metal such as SUS for suppressing the deflection of the pressure pad 51.

  The pressure pad 51 has a two-layer structure in which an elastic layer 51a is attached to a base 51b. The base 51a is a member made of aluminum, and the elastic layer 51b is made of silicone rubber having a rubber hardness Hs of 30 °. The pressure pad 51 has a shape having a radius of curvature of 30 mm, and is in contact with a straight line parallel to the pressure pad base 51a at the entrance Na of the nip N. The rubber thickness is 3 mm.

  In order to reduce the sliding resistance between the pressure pad 51 and the belt 21, that is, to reduce the sliding resistance between the surface of the elastic layer 51 a and the inner surface of the belt 21, the sliding is performed so as to cover the entire area of the elastic layer 51 a. A moving sheet 53 is provided. As the sliding sheet 53, a polyimide sheet coated with PTFE is used. In this embodiment, the thickness of the sliding sheet 53 is set to 100 μm.

  Next, the pressing mechanism 60 of the belt unit 20 with respect to the fixing roller 10 will be described. Pressing mechanisms 60 are provided at one end and the other end of the belt unit 20, respectively (FIG. 2). Since these two pressing mechanisms 60 have a symmetrical structure, only one of them will be described as a representative in FIGS.

  A bearing 61 a is provided at an end of the separation roller 23, and a bearing 61 a is arranged on a roller pressing plate (a support member that supports the separation roller 23) 61. The end portion of the pad holder 52 of the pressing pad 50 is disposed on a pad pressing plate (a supporting member that supports the pressing pad 50) 62. A belt pressing plate 63 is arranged below the roller pressing plate 61 and the pad pressing plate 62. The roller pressing plate 61, the pad pressing plate 62, and the belt pressing plate 63 are configured to be rotatable around a rotation shaft 69.

  A roller pressing spring (first pressing member) 64 is disposed between the belt pressing plate 63 and the roller pressing plate 61, and a guide shaft 65 fixed to the belt pressing plate 63 is It passes through the inside and is provided on the roller pressing plate 61 and is arranged through the hole.

  A pad pressing spring (second pressing member) 66 is disposed between the belt pressing plate 63 and the pad pressing plate 62, and a guide shaft 67 fixed to the belt pressing plate 63 is It passes through the inside and is provided on the pad pressing plate 62 and is arranged through the hole.

  A receiving portion 68 is provided on a side surface of the belt pressing plate 63, and a pressing cam 72 is provided on a rotating shaft 71 below the receiving portion 68. The pressing cam 72 comes into contact with the receiving portion 68.

  The rotating shaft 71 is driven to rotate by a driving force of a driving motor (driving unit) M2 controlled by the control device 300 being transmitted via a driving transmission mechanism (not shown). That is, the pressure cam 72 is rotated. As shown in FIG. 4, the pressing cam 72 is stopped with the rotation angle posture in which the long-diameter portion (large protruding portion) 72 a is directed upward, so that the receiving portion 68 is pushed upward and the rotating shaft 69. , The belt pressing plate 63 rotates in the direction of arrow E.

  As a result, the roller pressing plate 61 is rotated around the rotation shaft 69 by the roller pressing spring 64, and the separation roller 23 is pressed against the fixing roller 10 via the belt 21 with the pressing force SF. Similarly, the pad pressing plate 62 is rotated around the rotation shaft 69 by the pad pressing spring 66, and the pressing pad 50 is pressed against the fixing roller 10 via the belt 21 with the pressing force PF. That is, by the pressing operation of the pressing mechanism 60, the belt unit 20 is lifted, and the belt 21 is moved to and held at the fixing position where the belt 21 is pressed against the fixing roller 10 in a predetermined manner.

  In this embodiment, 490 N (50 kgf) is applied to the pressing pad 50 and 392 N (40 kgf) is applied to the separation roller 23. As a result, the pressing pad 50 and the elastic layer of the fixing roller 10 form a bending nip N.

  On the other hand, as shown in FIG. 6, the pressurizing cam 72 is stopped with the rotation angle posture in which the short diameter portion (small protruding portion) 72b is directed upward, so that the receiving portion 68 is moved from the push-up position in FIG. The belt pressing plate 63 is rotated downward about the rotation shaft 69 in the direction of arrow F.

  Therefore, the urging force of the roller pressing spring 64 is not applied by the stopper of the guide shaft 65, and the roller pressing holder 61 rotates about the rotation shaft 69, and the separation roller 23 is separated from the fixing roller 10. . Similarly, the urging force of the pad pressing spring 66 is not applied by the stopper of the guide shaft 67, and the pad pressing plate 62 rotates about the rotation shaft 64, so that the pressing pad 50 is separated from the fixing roller 10. That is, the belt unit 20 is lowered by the pressure release operation of the pressure mechanism 60, and the belt 21 is moved to and held at the standby position separated from the fixing roller 10.

  Next, a posture adjusting mechanism of the pressing pad 50 will be described with reference to FIGS. This posture adjustment mechanism has fixing portions 31, 32, 41, and 42 for fixing the relative positional relationship between the pressing pad 50 and the pad pressing plate 62 in an adjustable manner. By adjusting the fixing portion, the pressing pad 50 can be relatively moved with respect to the pad pressing plate 62 while being supported by the pad pressing plate 62. By adjusting the fixing portion, the pressing pad 50 can change the relative angle with respect to the pad pressing plate 62 while being supported by the pad pressing plate 62.

  The fixing portion has first fixing portions 31 and 41 provided on one end side in the belt width direction, and second fixing portions 32 and 42 provided on the other end side in the belt width direction.

  Further, there are height adjusting mechanisms 81, 82, 83, 84 that can adjust the relative height of one end side and the other end side in the width direction of the pressing pad 50.

  The above mechanism configuration will be described more specifically below. V-shaped grooves 52 a are provided at both longitudinal ends of the pad holder 52 as a center of rotation of the pressing pad 50, and are supported by arc-shaped projections 62 a provided on the pad pressing plate 62. That is, the pressing pad 50 is supported so as to be movable in the arrow G direction about the arc-shaped projection 62a.

  The pad pressure plate 62 supporting both ends of the pressing pad 50 includes a pad height adjusting plate (posture support member) 81 at one end as a height adjusting member of the pressing pad 50 and a pad rear height at the other end. An adjustment plate (posture support member) 82 is provided. Both of the adjusting plates 81 and 82 are provided rotatably about a rotation center (rotation center portion) 62b. That is, both the adjusting plates 81 and 82 are rotatable about the rotation center 62b and are provided at positions separated from the rotation center 62b by a predetermined distance.

  The front height adjustment plate 81 and the rear height adjustment plate 82 are provided with adjustment screws 83 and 84 as adjustment members. The front height adjustment plate 81 and the rear height adjustment for the pad pressure plate 62 are provided. The height of the plates 82 can be independently adjusted.

  When the adjusting screws 83 and 84 provided on the height adjustment plate 81 before the pad and the height adjustment plate 82 after the pad are turned in the tightening direction, the pressing pad 50 of the belt unit 20 is turned by the arrow on the outlet side Nb of the nip N. G is inclined upward. When the adjusting screws 83 and 84 are turned in the loosening direction, the pressing pad 50 of the belt unit 20 is configured such that the outlet side Nb of the nip N is inclined downward as indicated by the arrow G. Therefore, the contact angle of the pressing pad 50 with respect to the fixing roller 10 can be adjusted.

  In the present embodiment, the reference line H of FIG. 1 is used to adjust the contact point between the V-shaped groove 52a of the pad holder 52 and the center of rotation 62b and the adjusting screws 32, 42 of the height adjustment plate 81 before the pad and the height adjustment plate 82 after the pad. Is a line where the height difference at the tip landing point becomes zero. This line is adjusted to be ± 1 ° or less with respect to the reference line H.

  Further, a pad front support shaft 31 and a pad rear support shaft 41 as a position adjusting unit of the pressing pad 50 are provided downstream of the pressing pad 50 of the belt front side plate 30 and the belt rear side plate 40 in the sheet conveying direction. Adjustment screws 32 and 42 are provided on the support shaft 31 before the pad and the support shaft 41 after the pad, and the downstream side of the pressing pad 50 with respect to the height adjustment plate 81 before the pad and the height adjustment plate 82 after the pad in the sheet conveyance direction. Height can be adjusted independently of each other.

  This adjusts the height of the tip ends of the adjusting screws 32 and 42 of the belt unit 20 with respect to the V-shaped grooves 52 a provided at both ends of the pad holder 52. The angle of the plane formed by the two V-shaped grooves 52a and the tips of the adjusting screws 32 and 42 in the sheet conveying direction and the sheet width direction (direction orthogonal to the sheet conveying direction) is adjusted to be a predetermined angle.

  In this embodiment, the angle in the sheet conveying direction and the sheet width direction is adjusted so as to be ± 1 ° or less with respect to the reference line H in FIG.

  That is, since the pressing pad 50 is adjusted within a predetermined angle range with respect to the reference line H, even when the belt unit 20 is replaced, the contact angle of the pressing pad 50 with the fixing roller 10 greatly changes, The posture of the pressing pad 50 does not become unstable.

  In the present embodiment, the V-shaped groove 52a and the rotation center 62b are provided on the upstream side in the paper transport direction (fixing nip), and the adjustment screws 32 and 42 and the adjustment screws 83 and 84 are provided on the downstream side in the paper transport direction (fixing nip). It is. This is because, since the rotation center 69 of the belt unit 20 is on the upstream side in the paper transport direction (fixing nip), the workability is improved by providing the attitude adjustment mechanism on the downstream side in the paper transport direction (fixing nip). .

  As described above, the angle of the pressing pad 50 in the sheet conveying direction and the sheet width direction is adjusted by the posture adjusting mechanism. As a result, the pressure distribution in the sheet conveyance direction can be set as shown by the solid line a in FIG. 7 so that a pressure drop portion does not locally occur from the upstream side to the downstream side of the fixing nip. As shown by the solid line a in FIG. 8, the pressure distribution in the paper width direction can be set so that the pressure difference between the front end and the rear end in the longitudinal direction can be reduced, and the pressure distribution does not tilt.

  In other words, the center of rotation is provided on a side plate supporting both ends in the longitudinal direction of the pressing member, and the angle of the pressing member in the recording material conveyance direction and the recording material width direction at the fixing nip portion is adjusted, so that the pressing member The contact posture to the fixing roller can be stabilized. By doing so, the pressure distribution in the recording material conveyance direction and the pressure distribution in the recording material width direction at the fixing nip are stabilized, and it is possible to prevent the occurrence of image defects such as uneven gloss and image deviation.

  Here, when a pressure release portion occurs between the separation roller and the pressing pad as in Reference Example 1 indicated by a dotted line b in FIG. 7, an icicle-shaped low gloss portion (hereinafter, referred to as gloss unevenness) is displayed on the solid image. Easy to occur. The same applies to the case where the pressure on the entrance side of the fixing nip is high and the pressure is low at the center of the fixing nip as in Reference Example 2 indicated by the dashed line c. Further, when the pressure distribution of the pressing pad is inclined as in the reference example 3 of the dotted line b and the reference example 3 of the dashed line c in FIG. 8, there is a problem that the image is shifted or distorted at the end in the sheet width direction. there were.

  This is because, when a sheet of low air permeability, such as coated paper, is used as the sheet, image distortion occurs due to expansion of air in the belt nip and generation of water vapor. When fixing an unfixed toner image on a sheet of low air permeability such as coated paper, the air existing in the unfixed toner layer stays in a low pressure portion in the nip. This air partially creates a gap at the interface between the sheet and the fixing roller, and disturbs the toner image that has not been sufficiently fixed.

  In the case of plain paper, the air existing in the toner layer is retained inside the porous paper, which is a large-volume porous material, or escapes by passing through, since the air permeability is large, so that image disturbance is caused. It is considered that occurrence is small.

  Further, as another problem of the belt fixing device as described above, when the width of the fixing nip portion is widened, a hot offset or a separation failure due to excessive fixing may occur on thin paper. Further, by narrowing the nip portion, the fixing property becomes insufficient with thick paper, and the toner layer may peel off when the recording material after the solid image is fixed is bent.

  The pressure release portion indicated by the dotted line b and the dashed line c in FIG. 7 occurs when the contact angle of the pressing pad with respect to the fixing roller in the paper transport direction is unstable. The inclination of the pressure distribution shown by the dotted line b and the one-dot chain line c in FIG. 8 occurs when the contact angle of the pressing pad with respect to the fixing roller in the paper width direction is unstable.

  Since the belt fixing device has a plurality of rollers as belt suspension members and pressurizing means for the members, the accuracy and shape variation of the members constituting the belt fixing device cause the pressing pad to move in the sheet conveying direction and the sheet width direction. There was a problem that the contact angle became unstable.

  In the present embodiment, the posture of the pressing pad 50 in the paper conveying direction and the paper width direction is adjusted by the posture adjusting mechanism to optimize the pressure distribution. Thereby, even when the paper to be used is coated paper, it is possible to prevent the occurrence of image defects such as gloss unevenness and image misalignment, and to expand the applicable range of the paper while maintaining productivity, and to provide the belt fixing device. It is possible to improve the merchantability of the image forming apparatus.

  Thus, when the belt is pressed against the fixing roller by the separating roller and the pressing pad, the posture of the pressing member in the recording material conveying direction and the recording material width direction can be stabilized, and the pressure loss portion and the inclination of the pressure distribution can be eliminated. Thereby, even when the recording material to be used is coated paper in which image defects are most likely to occur, the occurrence of image defects is prevented, and the application range of the recording materials is expanded while maintaining productivity, and the belt fixing device is used. The image quality of the image forming apparatus provided with is improved.

  In the above-described embodiment, the fixing device that heats and fixes the unfixed toner image formed on the sheet (on the recording material) is described as an example of the image heating device, but is not limited thereto. The present invention can be applied to an apparatus for increasing the gloss (gloss) of an image by reheating a toner image fixed or assumed on a sheet P.

  1. Image heating device, 10. Fixing roller (heating rotating body), 21. Endless belt, N. Nip, P .. Recording material, T .. Image, 50 .. Press pad, 62 .. Pressure support plate, 23 separation roller (pressing roller), 31, 32, 41, 42 fixed part, 81, 82, 83, 84 height adjustment mechanism

Claims (10)

A rotating body and a belt that form a nip for heating an image on a recording material, and a pressing pad that presses the belt toward the rotating body,
A pressing roller provided downstream of the pressing pad in the recording material transport direction to rotatably support the belt and press the belt toward the rotating body;
A support member for supporting the pressing pad,
A fixing portion that adjustably fixes the relative positional relationship between the pressing pad and the support member,
The adjustment of the fixed portion, the pressing pad image heating apparatus, characterized in that the changeable relative angle with respect to the support member in a state of being supported by the support member. The image heating apparatus according to claim 1, wherein the adjustment of the fixing portion is performed by a screwdriver of an adjustment screw . The image heating apparatus according to claim 1, further comprising a height adjustment mechanism capable of adjusting a relative height between one end and the other end in the width direction of the pressing pad . The height adjustment mechanism is configured to be rotatable around a rotation center provided on the support member and provided at a position separated by a predetermined distance from the rotation center, and a posture support member, The image heating apparatus according to claim 3, further comprising a height adjusting member for adjusting a position . 5. The apparatus according to claim 4, wherein the rotation center portion is provided on an upstream side of the nip portion in a recording material conveyance direction, and the posture support member is provided on a downstream side of the nip portion in a recording material conveyance direction. 6. Image heating device. The image heating apparatus according to claim 4, wherein the height adjustment member is an adjustment screw that is screwed . The pressing pad has a pad holder and a pressing pad fixed to the pad holder,
The pad holder is provided with a V-shaped groove comprises an arc-shaped projection on the support member, according to the V-shaped groove in any one of claims 1 to 6, characterized in that the support at the arcuate projection Image heating device. The image heating apparatus according to claim 1, further comprising a first pressing member that presses the pressing roller and a second pressing member that presses the support member . The said fixing part has the 1st fixing part provided in the one end side of a belt width direction, and the 2nd fixing part provided in the other end side of a belt width direction, The Claims 1 thru | or 1 characterized by the above-mentioned. 9. The image heating device according to any one of items 8 to 8. The image heating apparatus according to claim 1, wherein a diameter of the pressing roller is smaller than a diameter of the rotating body .