JP2019128475A - Fixation device and heating member to be used in the same - Google Patents

Abstract

To provide a fixation device and heating member to be used in the fixation device that suppress looseness of a fixation belt on a downstream side in a revolving direction of the fixation belt, and improve separability between the fixation belt and a recording material.SOLUTION: A fixation device has: a fixation belt 301 which has a cross section orthogonal to a longitudinal direction formed into a ring shape; a heating member that, upon rotation of the fixation belt, contacts with an interior circumferential surface of the fixation belt as elastically deforming in the cross section orthogonal to the longitudinal direction, and has a base material, and a heating part for heating the fixation belt; and a facing rotor that faces the fixation belt, and forms a nip part together with the fixation belt. In the cross section orthogonal to the longitudinal direction when the fixation belt rotates, an intermediate position A between the most upstream side position of the base material and the most downstream side position thereof in the recording material conveyance direction perpendicular to the longitudinal direction is provided on an upstream side in a recording material conveyance direction with respect to a first linear line connecting a center position of the nip part in the recording material conveyance direction to a rotation center position of the facing rotor.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device that can be mounted on an image forming apparatus such as a printer and a copying machine, and a heating member used for the same.

  As a fixing device, in recent years, a heating device of a film heating system using an endless film has been put into practical use from the viewpoint of quick start and energy saving. Furthermore, as described in Patent Documents 1 and 2, the inner peripheral surface of the endless film has a thin plate-like heating member to be heated, and is brought into contact with the endless film along the circumferential direction from the inner peripheral surface. In this case, a fixing device having a so-called surface heating element configuration is known which heats an endless film in a wide range.

JP, 2015-127728, A JP, 2015-79140, A

  However, in the sheet heating element configurations of Patent Documents 1 and 2, it is conceivable that the recording material is difficult to separate from the fixing belt due to the sag of the fixing belt on the downstream side in the circumferential direction of the fixing belt.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that suppresses the slack of the fixing belt on the downstream side in the circumferential direction of the fixing belt and improves the separation property between the fixing belt and the recording material, and a heating member used therefor. .

  In order to achieve the above object, a fixing device according to the present invention is a rotatable fixing belt which is long in the longitudinal direction and whose cross section orthogonal to the longitudinal direction is formed in a ring shape; A heating member that is long in the longitudinal direction and is in contact with the inner peripheral surface of the fixing belt while being elastically deformed in a cross section perpendicular to the direction, and a base material and a heat generating portion for heating the fixing belt. A heating member having an opposing rotating body that forms a nip portion that sandwiches and conveys a recording material bearing an unfixed toner image together with the fixing belt and facing the fixing belt, and the fixing belt rotates. In the cross section orthogonal to the longitudinal direction, an intermediate position between the most upstream position and the most downstream position of the base material in the recording material transport direction orthogonal to the longitudinal direction is the recording material transport method. First straight line connecting the rotational center position of the opposing rotor and the center position of the nip in the hand, characterized in that provided on the upstream side of the recording material conveyance direction.

  Further, the heating member according to the present invention is elastically deformed in the cross section orthogonal to the longitudinal direction upon rotation of the rotatable fixing belt which is long in the longitudinal direction and the cross section orthogonal to the longitudinal direction is formed in a ring shape. A cross section orthogonal to the longitudinal direction, the heating member being long in the longitudinal direction and in contact with the inner peripheral surface of the fixing belt, and having a base material and a heat generating portion for heating the fixing belt When the base material is divided into one side and the other side by a cross section in the longitudinal direction including a predetermined straight line, the longitudinal elastic modulus of the base material is different between the one side and the other side.

  Further, another heating member according to the present invention is elastic in a cross section orthogonal to the longitudinal direction when the rotatable fixing belt, which is long in the longitudinal direction and whose cross section orthogonal to the longitudinal direction is formed in a ring shape, rotates. A heating member that is long in the longitudinal direction and is in contact with the inner peripheral surface of the fixing belt while being deformed, and has a base material and a heat generating portion for heating the fixing belt, and is orthogonal to the longitudinal direction When the base material is divided into one side and the other side by a cross section in the longitudinal direction including a predetermined straight line in the cross section, the curvature radius of the base material is changed from the one side to the other side in the cross section orthogonal to the longitudinal direction. It is characterized by increasing non-linearly toward the side.

  According to the present invention, it is possible to improve the separability of the fixing belt and the recording material by suppressing the sag of the downstream fixing belt in the circumferential direction of the fixing belt.

FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to a first embodiment. It is a schematic cross section of the longitudinal direction containing the exothermic part in a heating member. It is a typical top view which shows schematic structure of the heat-emitting part in a heating member. FIG. 3 is a schematic cross-sectional view illustrating a shape of a heating member in a state where there is no fixing belt of the fixing device according to the first embodiment. FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to a conventional configuration as a comparative example different from the upstream tension shape. It is a figure which shows the effect of the fixing device which concerns on 1st Embodiment. FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a fixing device according to a conventional configuration as a comparative example regarding a wide range of contact areas between a heating member and a fixing belt. It is a figure which shows the effect of the fixing device which concerns on 1st Embodiment. FIG. 6 is a schematic cross-sectional view showing a heating member shape in a state where there is no fixing belt of a fixing device according to a second embodiment. It is a figure which shows curvature-radius distribution of the base material of the heating member of 2nd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

First Embodiment
(Image forming device)
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a laser printer 100 (hereinafter referred to as a printer 100) using an electrophotographic process as an example of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. It is. The printer 100 forms an image in a form in which an image corresponding to information provided from an output device (not shown) such as a host computer provided outside the main body of the printer 100 is recorded on a recording material (recording medium, recording paper) P. Device. The surface of the photosensitive drum 101 as a latent image carrier is a photoconductive layer whose main component is an organic photosensitive member, and a clockwise direction indicated by an arrow A by a drive mechanism (not shown) provided in the printer 100 main body. Is driven to rotate.

  The photosensitive drum 101 is uniformly charged at a predetermined potential by the charging roller 102, and then the outer surface of the photosensitive drum 101 is exposed by laser light 103 as exposure light exposed from the exposure device 115 in accordance with information provided from the output device. An electrostatic latent image corresponding to the provided information is formed. This electrostatic latent image is visualized as a toner image by the developing sleeve 106 carrying the toner T as a developer of the developing device 104.

  Here, the recording material P is taken out one by one from the paper supply cassette 107 by the paper supply roller 112, passes through the path B, and is visualized by the toner T on the front end of the recording material P and the outer peripheral surface of the photosensitive drum 101. It is introduced (carried in) in synchronization with the tip of the image forming unit. In other words, the registration roller pair 113 introduces the toner image on the photosensitive drum 101 onto the recording material P by electrical action at a predetermined timing and is introduced into the transfer nip portion between the transfer roller 108 serving as transfer means and the photosensitive drum 101. Be done.

  The transfer residual toner on the photosensitive drum 101 after the transfer process is removed from the photosensitive drum 101 by the cleaning blade 109 and collected by the cleaning device 110. After the cleaning process, the photosensitive drum 101 repeats the image forming process (charging → exposure → development → transfer → cleaning) to form an unfixed toner image on the recording material P. On the other hand, the recording material P carrying the unfixed toner image is introduced into the fixing device 111 and is pressed and heated to fix the toner image on the recording material P.

  Regarding discharge of the recording material P from the fixing device 111, face-up (FU) discharge that is discharged from the printer 100 through the path C with the print surface up, and printer with the print surface down through the path D It is possible to select face-down (FD) paper discharge from 100. In this way, the recording material P is discharged from the printer 100.

  In the printer 100 according to the present embodiment, each device such as the photosensitive drum 101 and the developing device 104 is comprehensively controlled by an engine controller 114 provided in the printer 100 main body.

(Fixing device)
Next, the fixing device 111 will be described. FIG. 2 is a schematic cross-sectional view of the fixing device 111 according to the present embodiment. Here, a direction perpendicular to the conveyance direction of the recording material P and the thickness direction of the recording material P (vertical direction in FIG. 2) is taken as the longitudinal direction. Note that the conveyance direction of the recording material P indicates the conveyance direction of the recording material passing through the fixing nip portion and a direction parallel to the conveyance direction.

  As shown in FIG. 2, a fixing belt 301 that is long in the longitudinal direction and has a cross section perpendicular to the longitudinal direction formed in a ring shape and is rotatable, and a pressure roller 401 as an opposing rotating body facing the fixing belt 301, A nip portion for nipping and conveying the recording material P carrying an unfixed toner image is formed. That is, FIG. 2 shows a state where the fixing belt 301 and the pressure roller 401 form a nip portion for fixing processing, and a heating member 302 is provided inside the fixing belt 301. State.

  The pressure roller 401 is disposed so as to contact the outer peripheral surface of the fixing belt 301, while the backup member (nip member) 303 is disposed so as to contact the inner peripheral surface of the fixing belt 301. As a result, the fixing belt 301 is sandwiched between the pressure roller 401 and the backup member 303 disposed at a position facing the pressure roller 401.

  The fixing belt 301 is a film-like member having a base layer made of a heat-resistant resin polyimide and a surface layer made of a fluororesin PFA laminated on the base layer, and is formed endlessly with the surface layer facing outside. . The thickness of the base layer is 70 μm, and the thickness of the surface layer is 15 μm. In a free state where no external force is applied, the fixing belt 301 has a cylindrical shape (ring shape) whose cross section perpendicular to the longitudinal direction is substantially a perfect circle. The free state in which no external force is applied is the state of the fixing belt 301 alone. That is, the heating member 302 and the backup member 303 are not provided inside the fixing belt 301 and are not in contact with the pressure roller 401. In the present embodiment, the outer diameter is 25 mm, and the longitudinal direction is 340 mm.

  The pressure roller 401 covers the outer peripheral surface of a core metal 401c made of aluminum metal with an elastic layer 401b and the outer peripheral surface of the elastic layer 401b with a surface layer 401a made of a fluorine resin PFA tube. The elastic layer 401b is an elastic member made of silicone rubber and has a thickness of about 10 mm and is formed on the outer peripheral surface of the core metal 401c. The surface layer 401a has a thickness of 10 μm, and the outer diameter of the pressure roller 401 is 25 mm.

  Here, the pressure roller 401 is connected to a motor as a drive source, and is rotationally driven. The fixing belt 301 is driven to rotate by contacting the pressure roller 401 whose peripheral surface is rotating at the nip portion. That is, in the fixing belt 301, the pressure roller 401 functions as a rotating body that rotates the fixing belt 301.

  The backup member 303 is a long-axis-shaped member that is long in the longitudinal direction forming a nip portion by being pressed by the support portion 304 from the inner peripheral surface of the fixing belt 301 toward the pressure roller 401, and is made of silicone rubber. The formed elastic material having heat resistance is used.

  In addition, the support portion 304 is a long rod-like rod shape that is long in the longitudinal direction by combining members obtained by bending a metal plate so that the cross-sectional shape is substantially L-shaped. The longitudinal direction (axial direction) To position the fixing belt 301 so as to support the backup member 303. A pressing force is applied so that the backup member 303 is pressed against the pressure roller 401 by being supported at both ends in the longitudinal direction. In this embodiment, the pressing force is 150 N on one side and 300 N on both sides in total.

  The backup member 303 is supported at both ends in the recording material conveyance direction by the L-shaped tip end of the support portion 304 and the sheet metal 304 b fixed by being screwed to the support portion 304, thereby providing a position. It is fixed.

(Heating member)
In the present exemplary embodiment, when the fixing belt 301 is rotated, the fixing belt 301 is heated by contacting the inner peripheral surface of the fixing belt 301 while elastically deforming in a cross section orthogonal to the longitudinal direction. A heating member 302 is provided. The heating member 302 has a base 302a and a heat generating layer 302b as a heat generating portion for heating the fixing belt 301, as described in detail later with reference to FIG. The base material 302a is formed of a thin sheet metal and is long in the longitudinal direction, and a cross section orthogonal to the longitudinal direction has a ring shape.

  With such a configuration, when the pressure roller 401 is rotationally driven, the fixing belt 301 is driven to rotate, and the recording material P onto which the toner image T has been transferred has the surface on which the toner image T is placed facing the fixing belt 301 side. In this state, it is sent to the nip portion between the pressure roller 401 and the fixing belt 301. The toner image T on the recording material P is heated by the fixing belt 301 heated by the heating member 302 and is pressed from the pressure roller 401 side, so that the toner image T is pressed against the recording material P. Thereafter, the recording material P is separated from the fixing belt 301 in the separation area Z (FIG. 2) and discharged.

  FIG. 3 shows the longitudinal sectional shape of the heating member 302 including the base material 302a, and FIG. 4 shows the heating member 302 (including the base material 302a) including the position V (FIG. 2) as viewed from above. When the base material 302a divides the base material into one side and the other side by a longitudinal cross section including a predetermined straight line in a cross section orthogonal to the longitudinal direction in an unloaded state, as described in detail later, The modulus of elasticity is configured differently on one side and the other side.

  The heating member 302 is a thin plate-like member in which the base material 302a can be elastically deformed. In this embodiment, a metal material such as stainless steel is used as the material. An insulating layer 302c is formed on the base 302a so as to sandwich the heat generating layer 302b.

  As shown in FIG. 4, the heat generating layer 302b functions as an example of a heat generating portion that draws a predetermined pattern. In FIG. 4, the insulating layer 302c is not shown, and the base material 302a has a size of 320 mm in the longitudinal direction and a size of 55 mm in the short direction (recording material conveyance direction).

  Furthermore, power supply portions 302d and 302e electrically connected to the heat generating layer 302b are formed on both side regions in the longitudinal direction orthogonal to the fixing belt circumferential direction of the base material 302a. The AC power supply unit of the image forming apparatus is electrically connected to the heat generation layer 302b and the power supply unit 302e via the power supply unit 302d, whereby electric power is supplied to the heat generation layer 302b and the heating member 302 generates heat. The fixing belt 301 is heated by the fixing belt 301 and the heating member 302 coming into contact with each other on the inner peripheral surface.

  In the present embodiment, the heat generating layer 302b is made of a stainless steel foil having a thickness of 30 μm. For example, SUS430, SUS330, or the like can be used, and heat is generated more uniformly by drawing a predetermined pattern. Here, as shown in FIG. 4, the predetermined pattern is formed by continuously connecting from a U-shaped basic pattern consisting of a location on an arc and a linear location.

  The insulating layer 302c is also a layer for insulating the heat generating layer 301b and protecting the heat generating layer 301b from being bent. In the present embodiment, a two-layer structure is employed with the heat generating layer 301b interposed therebetween. At this time, the heat generation layer 301b is sandwiched between the upper layer and the lower layer of the heat generation layer 301b and thermocompression bonding is performed, so that the heat generation layer 301b is included in the insulating layer 302c.

  In addition, as shown in FIG. 2, the heating member 302 has a downstream end region fixed to and supported by the support unit 304 via a screw X with respect to the position V in the circumferential direction of the fixing belt 301. There is. That is, the heating member 302 has a relationship in which the area of the downstream end with respect to the position V in the circumferential direction of the fixing belt 301 is fixed to the L-shaped sheet metal 304 a and the I-shaped sheet metal 304 c. And the fixed places in the longitudinal direction are at least three places (one each at the center part and both ends).

  On the other hand, the heating member 302 has a free end at the upstream end when the position V in the circumferential direction of the fixing belt 301 is a reference, and the fixing belt 301 is caused by the elastic repulsive force of the base member 302 a of the heating member 302. The contact is made along the inner surface of the That is, as shown in FIG. 5, the heating member 302 does not have the fixing belt 301, and in the state where the downstream end in the fixing belt 301 circumferential direction is supported by the fixing support portion, the downstream direction of the recording material conveyance direction. It has a shape that overhangs.

  In the present embodiment, the longitudinal elastic modulus (hereinafter referred to as Young's modulus) of the base material 302a is expressed by the region U in FIG. 4 (upstream side in the rotation direction of the fixing belt with respect to the position V) and the region D (position V). It is changed on the downstream side in the fixing belt rotation direction when used as a reference. The boundary position between the region U and the region D is the position of V described above with reference to FIG.

  In FIG. 4 showing the base material 302a, the region U indicates 20 mm between the position of 10 mm from the upstream end and 35 mm with respect to the circumferential direction of the fixing belt. A region D indicates a 20 mm region between a position 10 mm from the downstream end and 35 mm in the circumferential direction of the fixing belt.

  In this embodiment, the Young's modulus of the region U is 250 GPa and the Young's modulus of the region D is 200 GPa. However, the present invention is not limited to this value. The Young's modulus of the region U> the Young's modulus of the region D It is important to have a relationship. When this relationship is satisfied, the elastic repulsive force of the base material 302a generated by being restrained by the fixing belt 301 on the upstream side in the circumferential direction of the fixing belt is generated by being restrained by the fixing belt 301 on the downstream side. And the elastic repulsive force of the base material 302a. As a result, the fixing belt 302 has a shape stretched toward the upstream side in the recording material conveyance direction.

  That is, in FIG. 2, the point that protrudes most upstream in the recording material conveyance direction of the base material 302a (most upstream position) is R, and the point that protrudes most downstream (most downstream position) is L. , A and a central point (intermediate position) of a straight line connecting R and L. At this time, the center point (intermediate position) A is transported by the recording material rather than the straight line (first straight line) connecting the rotation center position B of the pressure roller 401 and the center position C in the recording material transport direction of the nip portion. Therefore, the fixing belt 301 also follows this shape.

  In FIG. 2, a straight line (second straight line) connecting the position V as the boundary between the area U and the area D and the center point (intermediate position) A is the rotation center point B of the pressure roller 401 and the recording of the nip portion. It is parallel to a straight line (first straight line) connecting the center point C in the material transport direction. The position V is on the side opposite to the nip portion with respect to the center point (intermediate position) A.

  Here, as a virtual shape of the fixing belt, a symmetrical shape with respect to the first straight line is used as a reference shape, and the fixing belt is divided into an upstream shape and a downstream shape in the rotation direction of the fixing belt with respect to the second straight line. become that way. That is, both the upstream shape and the downstream shape are provided upstream in the recording material conveyance direction with respect to the corresponding upstream shape and downstream shape in the reference shape.

  The following effects can be obtained as long as at least the above-described relationship is satisfied, but a more preferable configuration is the following configuration. That is, the center point (intermediate position) A of the recording material is a straight line (first straight line) connecting the rotation center position B of the pressure roller 401 and the center position C of the nip portion in the recording material conveyance direction. It is more preferable to set it as the structure which offsets 5.0 mm or more to the upstream in the conveyance direction. As shown in FIG. 7, when the radius of curvature of the fixing belt 301 at the recording material separation position exceeds 25 mm, separation failure occurs. In the present embodiment, the radius of curvature of the fixing belt 301 at the initial recording material separation position is 20 mm, and without the configuration of the present embodiment, the radius of curvature may be increased by 10 mm and may be increased to 30 mm. Therefore, the center point (intermediate position) A is offset by 5.0 mm or more at least upstream in the conveyance direction of the recording material with respect to the first straight line in advance (that is, in a state where the nip portion is formed in the initial fixing device 111). Keep it. Accordingly, it is considered that the possibility that the fixing belt 301 does not sag more than 10 mm−5.0 mm = 5.0 mm or more and that the radius of curvature of the fixing belt 301 exceeds 25 mm is low.

  The effect obtained by the upstream side stretch shape of the base material 302a will be described below by comparing with the conventional example. FIG. 6 shows the path of the belt on the downstream side in the fixing belt circumferential direction in the conventional configuration. In the conventional configuration, with respect to the base material 302a, the center point of a straight line connecting the most protruding point on the upstream side in the recording material conveyance direction and the most protruding point on the downstream side is as follows. That is, it is configured to exist on a straight line (first straight line) connecting the rotation center point of the pressure roller 401 and the center point of the nip portion in the recording material conveyance direction.

  In this conventional configuration, the fixing belt has a shape indicated by a solid line in FIG. However, the fixing belt is in a free state in a region excluding the nip portion region and the contact region between the heating member and the fixing belt. That is, when the operation from the drive state to the stop operation is performed a plurality of times, the fixing belt is drawn to the downstream end side in the fixing belt circumferential direction, and is slackened at the downstream end in the fixing belt circumferential direction (FIG. 6). As shown by the dotted line). When the recording material is passed in the state where the fixing belt is slack, it becomes difficult to separate the fixing belt and the recording material, resulting in poor separation.

  Specifically, a toner image is placed on the surface of the recording material in contact with the fixing belt, and this toner image functions like an adhesive between the fixing belt and the recording material. Then, a behavior of winding around the fixing belt is shown, and the recording material enters the gap between the exit guide 305 (FIG. 6) and the fixing belt, and a paper jam occurs.

  As a countermeasure, it is known that the recording material is forcibly separated from the fixing belt by its own weight by reducing the radius of curvature of the fixing belt at the nip exit at the downstream side in the conveyance direction. By this action, the recording material separation position can be brought close to the nip portion and prevented from entering the gap between the exit guide 305 and the fixing belt.

  In the present embodiment, in view of this effect, the fixing belt is formed in an upstream-side stretch shape in the recording material conveyance direction by adopting the configuration of the base material 302a as described above. That is, the fixing belt in the free state area of the fixing belt in the area excluding the nip area of the fixing belt and the contact area of the heating member and the fixing belt is suppressed, and as a result, the fixing belt connected with the downstream side of the nip The radius of curvature of the fixing belt at the downstream end in the circumferential direction is reduced.

(Separation of recording material from fixing belt)
With regard to the separation of the recording material from the fixing belt, comparative experiments were conducted between the conventional configuration shown in FIG. 6 and the configuration of the present embodiment. Specifically, the radius of curvature of the fixing belt in the separation region Z (FIG. 6) connected to the downstream side of the nip portion when the recording material is passed after repeating the rotation driving and rotation stop of the pressure roller a plurality of times. (Mm) was compared at each repetition of driving and stopping.

  Note that the radius of curvature of the portion where separation occurs is a radius of curvature within a range of ± 5 mm along the circumferential direction of the fixing belt, centering on the point where the recording material starts to separate from the outer peripheral surface of the fixing belt. Further, as described above, the fixing belt has a diameter of 25 mm in both the conventional configuration and the present embodiment, has a cylindrical shape with a substantially circular cross section in a free state where no external force is applied, and uses polyimide as a base material. Except for the configuration of the base material of the heating member, all are the same in the conventional configuration and the configuration of the present embodiment.

  The results of the comparative experiment are shown in FIG. As a result, in the conventional configuration, a large belt slack does not occur until the first and tenth repetitions of rotation driving and stopping, and no poor separation occurs. However, when the number of times exceeds 100, sagging occurs in the free state portion of the fixing belt (region other than the nip portion in the circumferential direction), the radius of curvature of the fixing belt in the separation region Z increases, and separation failure occurs. Occur. Since the fixing belt is configured to be driven to rotate along the circumferential surface of the pressure roller, the fixing belt is pulled into the nip portion in the area of the fixing belt upstream of the nip portion in the recording material conveyance direction during driving. Force acts so that the fixing belt is pulled out from the nip portion in the region of the fixing belt downstream of the nip portion. As a result, as rotation of the pressure roller is repeated, the slack produced in the region downstream of the nip portion of the fixing belt increases.

  On the other hand, in the present embodiment, the fixing belt in the free state portion is not slackened from the initial state by forming the fixing belt in the upstream tension shape in the recording material conveyance direction by the configuration of the base material 302a described above (FIG. 2). Can be maintained. This is because the free state portion (the portion other than the nip portion in the circumferential direction) of the fixing belt is pulled upstream (substantially not in the free state) in the recording material conveyance direction (upstream in the fixing belt circumferential direction of the substrate 302a). This is because the shape of the fixing belt on the downstream side in the circumferential direction is formed by the side.

  This makes it possible to maintain the shape of the fixing belt even if the number of repetitions of driving stop is increased, that is, even if the recording material on which the toner image is placed is continuously fed from the image forming unit to the fixing device. It is possible to suppress (prevent) separation failure of the recording material in

  Further, in the present embodiment, in addition to suppressing the separation failure, it is possible to secure a wide contact area between the heating member 302 and the fixing belt 301. The conventional configuration shown in FIG. 8 will be described as a comparative example. In the configuration of FIG. 8, the thin plate-shaped heating member 80 is pressed toward the Z direction in order to stabilize the trajectory of the fixing belt 61. The pressure roller, the nip member, the support member, and the like as other configurations are substantially the same as those in the present embodiment. For example, the fixing belt uses the same material as that of the present embodiment, and has a cylindrical shape with a substantially round cross section in a free state where no external force is applied, and has an outer diameter of 25 mm.

  In such a conventional configuration, by pressing the fixing belt in the Z direction, the deflection in the free state region of the fixing belt (excluding the contact region between the fixing belt and the heating member and the nip portion region) is caused to be upstream and downstream. Both can be suppressed (prevented). However, since the structure is pressed toward the Z direction, the upstream direction in the direction orthogonal to the Z direction (recording material transport direction) and the tension toward the downstream direction are insufficient, so the upstream side in the recording material transport direction, The contact area between the fixing belt and the heating member on the downstream side has become smaller.

  When the fixing belt is driven to rotate by driving the pressure roller, the contact area can be secured about 12 mm in the conventional configuration, whereas the present embodiment can secure about 17 mm. That is, the heat generation amount per unit area of the heating member necessary for fixing the toner of the recording material on which the toner image conveyed to the nip portion is fixed can be reduced in this embodiment.

  The result of comparing the required temperature per unit area of the heating member (heating member temperature control temperature) necessary for securing a predetermined amount of fixing strength of the recording material-like toner image between this embodiment and the conventional configuration (FIG. 8). Is shown in FIG. The toner fixing strength (%) in FIG. 9 is ((image density before rubbing) − (after rubbing) when the image portion on which the toner image is placed is rubbed 5 times while applying a load with a 200 g weight. Image density)) / (image density before rubbing) × 100.

  In the conventional configuration, for example, a temperature adjustment temperature of 200 ° C. is necessary to secure a fixing strength of 20%, but in this embodiment, it can be lowered to 191 ° C. That is, it leads to energy saving and it is also possible to suppress the temperature rise of the non-sheet passing portion of the heating member during continuous feeding of small size recording materials. And since it becomes possible to reduce the highest reached temperature of the heating member at the time of temperature rise of a non-sheet passing part by about 9 ° C., it is possible to suppress (prevent) thermal deterioration of components.

  In the present embodiment, Young's modulus of region U of base material 302a> Young's modulus of region D, but as a means for this, the thickness of region U of base material 302a is made thicker than the thickness of region D (region U And region D are the same material). Alternatively, the material of the region D and the region U may be changed so that the Young's modulus of the region U of the base material 302a> the Young's modulus of the region D.

Second Embodiment
In the first embodiment, the Young's modulus of the region U of the base material 302 a in the heating member is the Young's modulus of the region D. In the present embodiment, the Young's modulus of the base material 302a is the same value (for example, 200 GPa) in the entire area, and the radius of curvature of the base material 302a is defined for each area. That is, with respect to the second straight line including the above-described intermediate position and parallel to the first straight line, the curvature radius of the base material 302a is increased nonlinearly from the upstream side to the downstream side in the rotation direction of the fixing belt.

  Thus, the base 302a of the present embodiment adopts the following configuration when the base 302a is divided into one side and the other side by a cross section in the longitudinal direction including a predetermined straight line in a cross section orthogonal to the longitudinal direction. . That is, in the cross section orthogonal to the longitudinal direction, the radius of curvature of the base material 302a increases nonlinearly from one side to the other side.

  The radius of curvature here is the radius of curvature in the state where the fixing belt 301 is not present as shown in FIG. 10 and the downstream end in the circumferential direction of the fixing belt 301 is supported by the fixed support portion. In FIG. 10, the shape of the heating member is indicated by a dotted line (the radius of curvature of the substrate is nonlinearly increased) in the present embodiment, and a solid line (the radius of curvature of the substrate linearly increases) in the conventional configuration.

  Here, as a virtual shape of the fixing belt, a symmetrical shape with respect to the first straight line is used as a reference shape, and the fixing belt is divided into an upstream shape and a downstream shape in the rotation direction of the fixing belt with respect to the second straight line. become that way. That is, only the upstream side shape is provided on the upstream side in the recording material conveyance direction with respect to the corresponding upstream side shape in the reference shape.

  FIG. 11 shows a curvature radius distribution of the base material 302a in the fixing belt circumferential direction (y direction) of the present embodiment shown in FIG. 10 and the conventional configuration. The reference position in the fixing belt circumferential direction (the position in which the y direction is zero) corresponds to the position V in FIG. In the conventional configuration, by increasing the radius of curvature linearly in the y direction, a contact area between the heating member and the fixing belt in the rotation direction of the fixing belt is secured. On the other hand, in this embodiment, the radius of curvature is increased nonlinearly (in a quadratic curve) in the y direction.

  Here, in the conventional configuration, the elastic repulsion force of the base material 302a on the upstream side in the fixing belt rotation direction is equal to the elastic repulsion force of the base material 302a on the downstream side in the fixing belt rotation direction. On the other hand, in this embodiment, when the position V (FIG. 2) is used as a reference, the elastic repulsion force of the base material 302a on the upstream side in the fixing belt rotation direction is the elastic repulsion force of the base material 302a on the downstream side in the fixing belt rotation direction. It is bigger than power.

  Due to the elastic repulsive force of the base material 302a on the upstream side in the fixing belt rotation direction, the fixing belt is stretched in the upstream direction in the recording material conveyance direction, and the sag in the free state portion of the fixing belt is suppressed (prevented), and the separation region The radius of curvature of the fixing belt at Z (FIG. 2) can be reduced. In addition, it is possible to suppress (prevent) the sag of the fixing belt due to repeated driving rotation and stoppage of the pressure roller, as in the first embodiment.

(Modification)
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

(Modification 1)
In the present embodiment described above, the pressure roller is shown as the counter rotating member that forms the nip portion that faces the fixing belt and sandwiches and conveys the recording material carrying the unfixed toner image together with the fixing belt. Not limited. For example, an endless belt suspended by a plurality of rollers can be used as the opposing rotating body. The endless belt may press the fixing belt, or the endless belt may be pressed by the fixing belt.

(Modification 2)
In the embodiment described above, the recording paper has been described as a sheet that is a recording material. However, the sheet in the present invention is not limited to paper. Generally, a recording material is a sheet-like member on which a toner image is formed by an image forming apparatus. For example, regular or irregular plain paper, cardboard, thin paper, envelope, postcard, seal, resin sheet, OHP sheet, Includes glossy paper. In the embodiment described above, for the sake of convenience, the handling of the recording material (sheet) P has been described using terms such as paper feeding and paper feeding. However, the sheet in the present invention is not limited to paper.

(Modification 5)
In the above-described embodiment, the fixing device that fixes an unfixed toner image to a sheet has been described as an example. However, the present invention is not limited to this, and the toner image that is supposedly attached to the sheet is used to improve the gloss of the image. The present invention is similarly applicable to a heating and pressing device (also referred to as a fixing device in this case).

301 .. Fixing belt 302.. Thin plate heating member 302 a. Base material 302 b Heat generation layer 401 Pressure roller

Claims (12)

A rotatable fixing belt that is long in the longitudinal direction and in which a cross section perpendicular to the longitudinal direction is formed in a ring shape;
A heating member long in the longitudinal direction that contacts the inner peripheral surface of the fixing belt while being elastically deformed in a cross section orthogonal to the longitudinal direction when the fixing belt rotates, and the fixing belt A heating member having a heating portion for heating;
A counter-rotating member that forms a nip portion that sandwiches and conveys a recording material bearing an unfixed toner image together with the fixing belt, facing the fixing belt;
Have
In a cross section orthogonal to the longitudinal direction when the fixing belt rotates,
An intermediate position between the most upstream position and the most downstream position of the base material in the recording material conveyance direction orthogonal to the longitudinal direction, the center position of the nip portion in the recording material conveyance direction, and the rotation center of the opposite rotating member A fixing device, wherein the fixing device is provided upstream of the first straight line connecting the positions in the recording material conveyance direction.   The longitudinal elastic modulus of the base material in the cross section perpendicular to the longitudinal direction is that of the upstream region in the rotation direction of the fixing belt with respect to the second straight line including the intermediate position and parallel to the first straight line. The fixing device according to claim 1, wherein the fixing device is larger than the downstream region.   The thickness of the base material is greater in the upstream region in the rotation direction of the fixing belt than the second straight line including the intermediate position and parallel to the first straight line in a cross section perpendicular to the longitudinal direction. The fixing device according to claim 2, wherein the fixing device is larger than a downstream area.   In the cross section orthogonal to the longitudinal direction, the virtual shape of the fixing belt is a symmetrical shape with respect to the first straight line as a reference shape, and the fixing belt is upstream in the rotation direction of the fixing belt with respect to the second straight line. When divided into the side shape and the downstream shape, both the upstream shape and the downstream shape are provided upstream in the recording material conveyance direction with respect to the corresponding upstream shape and downstream shape in the reference shape. The fixing device according to claim 2 or 3, characterized in that: In a cross section orthogonal to the longitudinal direction when the fixing belt rotates,
The radius of curvature of the base material increases non-linearly from the upstream side to the downstream side in the rotation direction of the fixing belt with respect to a second straight line including the intermediate position and parallel to the first straight line. The fixing device according to claim 1.   In a cross section orthogonal to the longitudinal direction, a symmetric shape with respect to the first straight line as a virtual shape of the fixing belt is used as a reference shape, and a second straight line including the intermediate position and parallel to the first straight line is used. When the fixing belt is divided into an upstream shape and a downstream shape in the rotation direction of the fixing belt, only the upstream shape is provided upstream in the recording material conveyance direction with respect to the corresponding upstream shape in the reference shape. The fixing device according to claim 5, wherein the fixing device is provided.   The heat generating portion is a cross section orthogonal to the longitudinal direction, and is on a side opposite to the nip portion with respect to the intermediate position and overlaps with a second straight line including the intermediate position and parallel to the first straight line. The fixing device according to claim 1, wherein the fixing device is provided.   8. The heating member according to claim 1, wherein the heating member is provided with the heat generating portion on the base material and has an insulating layer on the heat generating portion in a cross section orthogonal to the longitudinal direction. The fixing device according to Item.   The fixing device according to claim 1, wherein the base material is a sheet metal formed of a metal material.   A cross-section perpendicular to the longitudinal direction has a backup member that contacts the inner peripheral surface of the fixing belt in the nip portion, and the counter-rotating body is a pressure roller that pressurizes the backup member. The fixing device according to any one of claims 1 to 9. When the rotatable fixing belt which is long in the longitudinal direction and whose cross section perpendicular to the longitudinal direction is formed in a ring shape is rotated, the inner peripheral surface of the fixing belt is elastically deformed in the cross section perpendicular to the longitudinal direction. Said longitudinally elongated heating member in contact, wherein
A substrate, and a heat generating portion for heating the fixing belt;
When the base material is divided into one side and the other side by the longitudinal cross section including a predetermined straight line in the cross section orthogonal to the longitudinal direction,
The heating member, wherein the longitudinal elastic modulus of the substrate is different on the one side and the other side. When the rotatable fixing belt which is long in the longitudinal direction and whose cross section perpendicular to the longitudinal direction is formed in a ring shape is rotated, the inner peripheral surface of the fixing belt is elastically deformed in the cross section perpendicular to the longitudinal direction. Said longitudinally elongated heating member in contact, wherein
A substrate, and a heat generating portion for heating the fixing belt;
When dividing the base material into one side and the other side by a cross section in the longitudinal direction including a predetermined straight line in a cross section perpendicular to the longitudinal direction, in the cross section perpendicular to the longitudinal direction, the radius of curvature of the base material is A heating member characterized by nonlinearly increasing from one side to the other side.