JP7062450B2 - Fixing device and heating member used for it - Google Patents

Description

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

As a fixing device, a film heating type heating device using an endless film has been put into practical use in recent years from the viewpoint of quick start and energy saving. Further, as described in Patent Documents 1 and 2, a thin plate-shaped heating member to be heated is provided on the inner peripheral surface of the endless film, and the endless film is brought into contact with the endless film from the inner peripheral surface in the circumferential direction. Therefore, a fixing device having a so-called planar heating element structure, which heats an endless film in a wide range, is known.

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

However, in the planar heating element configuration of Patent Documents 1 and 2, it is considered that the recording material is difficult to separate from the fixing belt due to the slack of the fixing belt on the downstream side in the circumferential direction of the fixing belt.

An object of the present invention is to provide a fixing device for suppressing slack of the fixing belt on the downstream side in the circumferential direction of the fixing belt to improve the separability between the fixing belt and the recording material, and a heating member used for the fixing device. ..

In order to achieve the above object, the fixing device according to the present invention has a rotatable fixing belt which is long in the longitudinal direction and has a ring-shaped cross section orthogonal to the longitudinal direction, and the longitudinal portion when the fixing belt is rotated. 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 orthogonal to the direction, and has a base material and a heat generating portion for heating the fixing belt. It has a heating member and an opposed rotating body that forms a nip portion that faces the fixing belt and holds and conveys a recording material carrying an unfixed toner image together with the fixing belt, and when the fixing belt rotates. In the cross section orthogonal to the longitudinal direction, the intermediate position between the most upstream side position and the most downstream side position of the base material in the recording material transport direction orthogonal to the longitudinal direction is the center of the nip portion in the recording material transport direction. The longitudinal direction including a predetermined straight line in a cross section orthogonal to the longitudinal direction, which is provided on the upstream side in the recording material transport direction with respect to the first straight line connecting the position and the rotation center position of the opposed rotating body. When the base material is divided into one side and the other side according to the cross section of the above, the one side is provided on the upstream side in the recording material transport direction with respect to the other side, and the longitudinal elasticity coefficient of the base material is the one side. Is larger than the other side .

Further, the heating member according to the present invention is elastically deformed in the cross section orthogonal to the longitudinal direction when the rotatable fixing belt, which is long in the longitudinal direction and has a ring-shaped cross section orthogonal to the longitudinal direction, is rotated. A cross section orthogonal to the longitudinal direction, which is a heating member long in the longitudinal direction that is in contact with the inner peripheral surface of the anchoring belt and has a base material and a heat generating portion for heating the anchoring belt. When the base material is divided into one side and the other side by the cross section in the longitudinal direction including a predetermined straight line in the above, the longitudinal elasticity coefficient of the base material is different between the one side and the other side.

According to the present invention, it is possible to suppress the slack of the fixing belt on the downstream side in the circumferential direction of the fixing belt and improve the separability between the fixing belt and the recording material.

It is a schematic cross-sectional view which shows the schematic structure of the image forming apparatus equipped with the fixing apparatus which concerns on embodiment of this invention. It is a schematic cross-sectional view which shows the schematic structure of the fixing device which concerns on 1st Embodiment. It is a schematic cross-sectional view in the longitudinal direction including a heat generating part in a heating member. It is a schematic top view which shows the schematic structure of the heat generating part in a heating member. It is a schematic cross-sectional view which showed the shape of the heating member in the state which there is no fixing belt of the fixing device which concerns on 1st Embodiment. It is a schematic cross-sectional view which shows the schematic structure of the fixing device which concerns on the conventional structure as a comparative example different from the upstream side tension shape. It is a figure which shows the effect of the fixing device which concerns on 1st Embodiment. It is a schematic cross-sectional view which shows the schematic structure of the fixing device which concerns on the conventional structure as a comparative example about securing the contact area of a heating member and a fixing belt in a wide range. It is a figure which shows the effect of the fixing device which concerns on 1st Embodiment. It is a schematic cross-sectional view which showed the shape of the heating member in the state which there is no fixing belt of the fixing device which concerns on 2nd Embodiment. It is a figure which shows the radius of curvature 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 preferably showing an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. Is. The printer 100 forms an image 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. It is a device. The surface of the photosensitive drum 101 as a latent image carrier is a photoconducting layer whose main component is an organic photosensitive member, and the drive mechanism (not shown) provided in the printer 100 main body causes the clockwise direction of arrow A. It is driven to rotate.

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

Here, the recording material P is taken out one by one from the paper feed cassette 107 by the paper feed roller 112, passes through the path B, and is visualized by the toner T on the tip of the recording material P and the outer peripheral surface of the photosensitive drum 101. It is introduced (carried in) so as to be synchronized with the tip of the image forming part. That is, it is introduced into the transfer nip portion of the transfer roller 108, which is a transfer means, and the photosensitive drum 101 at a predetermined timing by the resist roller pair 113, and the toner image on the photosensitive drum 101 is transferred onto the recording material P by an electric action. Will be done.

The transfer residual toner on the photosensitive drum 101 that has completed the transfer step is removed from the photosensitive drum 101 by the cleaning blade 109 and collected by the cleaning device 110. The photosensitive drum 101 that has completed the cleaning step repeats the image forming process (charging-> exposure-> development-> transfer-> cleaning) again 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, pressurized and heated, and the toner image is fixed on the recording material P.

Regarding the ejection of the recording material P from the fixing device 111, the face-up (FU) paper ejected from the printer 100 with the print surface facing up through the path C and the printer with the printing surface facing down through the path D. Face-down (FD) paper ejection from 100 can be selected. In this way, the recording material P is discharged from the printer 100.

Further, in the present embodiment, in the printer 100, each device such as the photosensitive drum 101 and the developing device 104 is collectively controlled by the 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, the direction orthogonal to the transport direction of the recording material P and the thickness direction of the recording material P (the direction perpendicular to the paper surface in FIG. 2) is defined as the longitudinal direction. The transport direction of the recording material P shall indicate the transport direction of the recording material passing through the fixing nip portion and the direction parallel to the transport direction.

As shown in FIG. 2, a fixing belt 301 that is long in the longitudinal direction and has a ring-shaped cross section orthogonal to the longitudinal direction and is rotatable, and a pressure roller 401 as an opposed rotating body facing the fixing belt 301. A nip portion for sandwiching and transporting the recording material P carrying the unfixed toner image is formed. That is, FIG. 2 shows a state in which 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. It is in a state.

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

The fixing belt 301 is a film-like member having a base layer made of heat-resistant resin polyimide and a surface layer made of a fluororesin PFA laminated on the base layer, and is formed in an endless shape with the surface layer on the outside. .. The thickness of the base layer is 70 μm, and the thickness of the surface layer is 15 μm. The fixing belt 301 has a cylindrical shape (ring shape) having a substantially circular cross section orthogonal to the longitudinal direction in a free state where no external force is applied. 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 this embodiment, the outer diameter is 25 mm and the dimensions are 340 mm in the longitudinal direction.

In the pressure roller 401, the outer peripheral surface of the core metal 401c made of aluminum metal is covered with the elastic layer 401b, and the outer peripheral surface of the elastic layer 401b is covered with the surface layer 401a made of a fluororesin PFA tube. The elastic layer 401b is an elastic member made of silicone rubber, 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 pressurizing roller 401 is connected to a motor as a drive source and is rotationally driven. The fixing belt 301 is driven to rotate when its peripheral surface comes into contact with the pressure roller 401 rotating at the nip portion. That is, the fixing belt 301 functions as a rotating body in which the pressure roller 401 rotates the fixing belt 301.

The backup member 303 is a long-axis member long in the longitudinal direction that forms 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.

Further, the support portion 304 is formed into a long-axis rod shape long in the longitudinal direction by combining members bent so that the cross-sectional shape is substantially L-shaped, and the support portion 304 is in the longitudinal direction (axis direction). It is located inside the fixing belt 301 so as to support the backup member 303. Then, the backup member 303 is supported at both ends in the longitudinal direction, and a pressing force is applied so that the backup member 303 is pressed against the pressurizing roller 401 side. 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 positioned by being supported at both ends in the recording material transport direction by the L-shaped tip portion of the support portion 304 and the sheet metal 304b fixed by being screwed to the support portion 304. It is fixed.

(Heating member)
Then, in the present embodiment, when the fixing belt 301 is rotated, it is in contact with the inner peripheral surface of the fixing belt 301 while being elastically deformed in a cross section orthogonal to the longitudinal direction, so that the fixing belt 301 is heated in a thin plate shape. A heating member 302 is provided. The heating member 302 has a base material 302a and a heat generating layer 302b as a heat generating portion for heating the fixing belt 301, as will be described in detail later with respect to FIG. The base material 302a is made of a thin plate-shaped sheet metal, is long in the longitudinal direction, and has a ring-shaped cross section orthogonal to the longitudinal direction.

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 to which the toner image T is transferred has the surface on which the toner image T is placed turned toward the fixing belt 301 side. In this state, it is sent to the nip portion between the pressurizing roller 401 and the fixing belt 301. Then, the toner image T on the recording material P is heated by the fixing belt 301 heated by the heating member 302 and pressed from the pressure roller 401 side, so that the toner image T is pressed against the recording material P. After that, the recording material P is separated from the fixing belt 301 in the separation region Z (FIG. 2) and discharged.

FIG. 3 shows the longitudinal cross-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) viewed from above. When the base material 302a is divided 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 a no-load state, the base material 302a is vertically formed as described in detail later. The elastic modulus has a different configuration on one side and the other side.

The heating member 302 is a thin plate-shaped member in which the base material 302a is elastically deformable, and in the present embodiment, a metal material such as stainless steel is used as the material. An insulating layer 302c is formed on the base material 302a so as to sandwich the heat generating layer 302b.

Then, as shown in FIG. 4, the heat generating layer 302b functions as an example of a heat generating unit that draws a predetermined pattern. Note that the insulating layer 302c is not shown in FIG. 4, and the base material 302a has dimensions of 320 mm in the longitudinal direction and 55 mm in the lateral direction (recording material transport direction).

Further, feeding 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. By conducting power from the AC power supply unit of the image forming apparatus to the heat generating layer 302b and the power feeding unit 302e via the power feeding unit 302d, electric power is supplied to the heat generating layer 302b and the heating member 302 generates heat. Then, the fixing belt 301 is heated by the contact between the fixing belt 301 and the heating member 302 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 the U-shaped basic pattern consisting of the arcuate portion and the linear portion.

Further, the insulating layer 302c is also a layer for insulating the heat generating layer 301b and protecting the heat generating layer 301b from bending. In the present embodiment, a two-layer structure is adopted so as to sandwich the heat generating layer 301b. Further, at this time, the heat generating layer 301b is sandwiched between the upper layer and the lower layer of the heat generating layer 301b, and thermocompression bonding is performed so that the heat generating layer 301b is included in the insulating layer 302c.

Further, as shown in FIG. 2, in the heating member 302, the region of the downstream end portion when the position V in the circumferential direction of the fixing belt 301 is used as a reference is fixedly supported by the support portion 304 via the screw X. There is. That is, the heating member 302 has a relationship in which the region of the downstream end portion with respect to the position V in the circumferential direction of the fixing belt 301 is fixed to the L-shaped sheet metal 304a and the I-shaped sheet metal 304c. There are at least three fixing points in the longitudinal direction (one at the center and one at 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 used as a reference, and the fixing belt 301 is caused by the elastic rebound force of the base material 302a of the heating member 302. It is in contact with the inner peripheral surface of the. That is, as shown in FIG. 5, in the state where the heating member 302 does not have the fixing belt 301 and the downstream end portion in the circumferential direction of the fixing belt 301 is supported by the fixed support portion, the downstream side direction in the recording material transport direction. It has a shape that overhangs.

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

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

In the present embodiment, the Young's modulus of the region U is 250 GPa and the Young's modulus of the region D is 200 GPa, but the present invention is not limited to this value, and the Young's modulus of the region U> the Young's modulus of the region D. It is important that the relationship is. When this relationship is satisfied, the elastic rebound 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. It becomes larger than the elastic rebound 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 transport direction.

That is, in FIG. 2, the point most protruding to the upstream side (most upstream position) in the recording material transport direction of the base material 302a is R, and the most protruding point to the downstream side (most downstream position) is L. , Let A be the center point (intermediate position) of the straight line connecting R and L. At this time, the center point (intermediate position) A is the recording material transfer 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 transfer direction of the nip portion. It will be located on the upstream side in the direction, and the fixing belt 301 will follow this shape.

In FIG. 2, the 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 pressurizing roller 401 and the recording of the nip portion. It is parallel to the straight line (first straight line) connecting the center point C in the material transport direction. The position V is on the opposite side of the nip portion with respect to the center point (intermediate position) A.

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

The following effects can be obtained as long as at least the above-mentioned relationship is satisfied, but a more preferable configuration is the following configuration. That is, the center point (intermediate position) A is the recording material with respect to the straight line (first straight line) connecting the rotation center position B of the pressurizing roller 401 and the center position C in the recording material transport direction of the nip portion. It is better to have a configuration that is offset by 5.0 mm or more toward the upstream side in the transport direction. As shown in FIG. 7, if the radius of curvature of the fixing belt 301 at the separation position of the recording material exceeds 25 mm, separation failure occurs. In this embodiment, the radius of curvature of the fixing belt 301 at the initial recording material separation position is 20 mm, and if the configuration of this embodiment is not provided, the radius of curvature may increase by 10 mm and increase to 30 mm. Therefore, in advance (that is, in the state where the nip portion is formed in the initial fixing device 111), the center point (intermediate position) A is offset from the first straight line by at least 5.0 mm or more on the upstream side in the transport direction of the recording material. Keep it. As a result, it is considered unlikely that the fixing belt 301 will not sag for 10 mm-5.0 mm = 5.0 mm or more and the radius of curvature of the fixing belt 301 will exceed 25 mm.

The effect obtained by such an upstream side tension shape of the base material 302a will be shown below by comparing with a conventional example. FIG. 6 shows the trajectory of the belt on the downstream side in the circumferential direction of the fixing belt in the conventional configuration. In the conventional configuration, with respect to the base material 302a, the center point of the straight line connecting the most protruding point on the upstream side in the recording material transport 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 transport direction.

In this conventional configuration, the fixing belt has a shape as shown by a solid line in FIG. 6 at the initial stage of arrival when the number of sheets of recording material to be passed is small. However, the fixing belt is in a free state except for the nip portion region and the contact region between the heating member and the fixing belt. That is, when the stop operation is performed a plurality of times from the driving state, the fixing belt is pulled toward the downstream end side in the fixing belt circumferential direction, and is in a state of being slackened at the downstream end portion in the fixing belt circumferential direction (FIG. 6). It becomes the state shown by the dotted line of. If the recording material is passed through the fixing belt in a slack state, it becomes difficult to separate the fixing belt and the recording material, resulting in poor separation.

Specifically, the toner image is placed on the surface of the recording material on the side in contact with the fixing belt, and this toner image acts like an adhesive between the fixing belt and the recording material. Then, the recording material exhibits a behavior of winding while being adhered to the fixing belt, and the recording material enters the gap between the outlet guide 305 (FIG. 6) and the fixing belt, causing a paper jam.

As a countermeasure, it is known that the recording material is forcibly peeled off from the fixing belt by the weight of the recording material by reducing the radius of curvature of the fixing belt at the outlet of the nip portion on the downstream side in the transport direction. By this action, the recording material separation position can be brought closer to the nip portion, and it can be prevented from entering the gap between the outlet guide 305 and the fixing belt.

In view of this effect, the present embodiment has the structure of the base material 302a as described above, so that the fixing belt has an upstream side tension shape in the recording material transport direction. That is, the fixing belt is connected to the downstream side of the nip portion by suppressing the slack in the free state portion of the fixing belt in the region excluding the nip portion region of the fixing belt and the contact region between the heating member and the fixing belt. 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)
Regarding the separation of the recording material from the fixing belt, a comparative experiment was 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 drive and rotation stop of the pressure roller multiple times. (Mm) was compared for each number of repetitions of drive and stop.

The radius of curvature of the portion where the separation occurs is set to the radius of curvature in the 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, both the conventional structure and the present embodiment have a diameter of 25 mm, a tubular shape having a substantially perfect circular cross section in a free state without external force, and a polyimide as a base material. Except for the configuration of the base material of the heating member, the conventional configuration and the configuration of the present embodiment are all the same.

The results of the comparative experiment are shown in FIG. As a result, in the conventional configuration, the large belt slack does not occur until the first and tenth repetition of the rotation drive and the stop, and the separation failure does not occur. However, after the 100th time, slack occurs in the free state portion of the fixing belt (the region other than the nip portion in the circumferential direction), the radius of curvature of the fixing belt in the separation region Z becomes large, and separation failure occurs. Occur. Since the fixing belt is configured to rotate in accordance with the peripheral surface of the pressure roller, the fixing belt is pulled into the nip portion in the region of the fixing belt upstream of the nip portion in the transport direction of the recording material during driving. A force acts so that the fixing belt is pulled out from the nip portion in the region of the fixing belt on the downstream side of the nip portion. As a result, as the rotational drive of the pressurizing roller is repeated, the slack generated in the region downstream of the nip portion of the fixing belt becomes larger.

On the other hand, in the present embodiment, according to the configuration of the base material 302a described above (FIG. 2), the fixing belt has an upstream side tension shape in the recording material transport direction, so that the fixing belt in the free state portion does not sag from the initial state. Can be maintained at. 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 in the recording material transport direction (substantially, the free state portion is not in the free state), and the substrate 302a is upstream in the circumferential direction of the fixing belt. This is because the shape of the fixing belt on the downstream side in the circumferential direction is formed depending on the side.

As a result, the shape of the fixing belt can be maintained even if the number of times the drive is stopped is increased, that is, even if the recording material on which the toner image is placed is continuously passed through the fixing device from the image forming portion, and the separation region Z can be maintained. It is possible to suppress (prevent) poor separation of the recording material in.

Further, in the present embodiment, in addition to suppressing poor separation, it is possible to secure a wide contact area between the heating member 302 and the fixing belt 301. As a comparative example, the conventional configuration shown in FIG. 8 will be described. In the configuration of FIG. 8, the thin plate-shaped heating member 80 is pressed in the Z direction in order to stabilize the trajectory of the fixing belt 61. Other configurations such as the pressure roller, the nip member, the support member, and the like are substantially the same as those of the present embodiment. For example, the fixing belt uses the same material as that of the present embodiment, and has a tubular shape with a substantially perfect circular 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 increased to the upstream side and the downstream side. Both can be suppressed (prevented). However, due to the configuration of pressing in the Z direction, tension is insufficient in the upstream and downstream directions in the direction orthogonal to the Z direction (recording material transport direction), so that 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 and rotated by the pressure roller drive, it is possible to secure a contact area of about 12 mm in the conventional configuration, whereas it is possible to secure about 17 mm in the present embodiment. That is, in the present embodiment, the calorific value per unit area of the heating member required to fix the toner of the recording material on which the toner image transferred to the nip portion is placed can be reduced.

The result of comparing the required temperature per unit area of the heating member (heating member temperature control temperature) required to secure the fixing strength of the toner image in the form of a recording material between the present embodiment and the conventional configuration (FIG. 8). Is shown in FIG. The toner fixing strength (%) in FIG. 9 is obtained when the image portion on which the toner image is placed is rubbed 5 times with a weight of 200 g while applying a load ((image density before rubbing)-(after rubbing). Image density)) / (Image density before rubbing) × 100 is calculated from the formula.

In the conventional configuration, for example, a temperature control temperature of 200 ° C. was required to secure a fixing strength of 20%, but in the present embodiment, the temperature 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-passing portion of the heating member during continuous paper passing of the small size recording material. Further, since it is possible to reduce the highest temperature reached by the heating member when the temperature of the non-passing portion is raised by about 9 ° C., it is possible to suppress (prevent) thermal deterioration of the parts.

In this embodiment, the Young's modulus of the region U of the base material 302a> the Young's modulus of the region D, but as a means thereof, the thickness of the region U of the base material 302a is made thicker than the thickness of the region D (region U). And area D are the same material). Alternatively, the materials 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 302a in the heating member> the Young's modulus of the region D. In the present embodiment, the Young's modulus of the base material 302a is set to the same value in all regions (for example, 200 GPa), and the radius of curvature of the base material 302a is defined for each region. That is, with respect to the second straight line including the above-mentioned intermediate position and parallel to the first straight line, the radius of curvature of the base material 302a is non-linearly increased from the upstream side to the downstream side in the rotation direction of the fixing belt.

As described above, the base material 302a of the present embodiment adopts the following configuration when the base material 302a is divided 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. .. That is, in the cross section orthogonal to the longitudinal direction, the radius of curvature of the base material 302a increases non-linearly from one side to the other side.

As shown in FIG. 10, the radius of curvature here is the radius of curvature in a state where there is no fixing belt 301 and the downstream end portion of the fixing belt 301 in the circumferential direction is supported by the fixed support portion. In FIG. 10, the shape of the heating member is shown by a dotted line (the radius of curvature of the base material is increased non-linearly) in the present embodiment and a solid line (the radius of curvature of the base material is linearly increased) in the conventional configuration.

Here, as a virtual shape of the fixing belt, a shape symmetrical with respect to the first straight line is used as a reference shape, and the fixing belt is divided into an upstream side shape and a downstream side 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 transport direction with respect to the corresponding upstream side shape in the reference shape.

FIG. 11 shows the radius of curvature distribution of the base material 302a in the circumferential direction (y direction) of the fixing belt according to the present embodiment shown in FIG. 10 and the conventional configuration. The reference position in the circumferential direction of the fixing belt (the position where the y direction is zero) corresponds to the position V in FIG. In the conventional configuration, the radius of curvature is linearly increased in the y direction to secure the contact region between the heating member and the fixing belt in the circumferential direction of the fixing belt. On the other hand, in the present embodiment, the radius of curvature is increased non-linearly (quadratic curve) in the y direction.

Here, in the conventional configuration, the elastic repulsive force of the base material 302a on the upstream side in the fixing belt circumferential direction and the elastic repulsive force of the base material 302a on the downstream side in the fixing belt circumferential direction are equivalent. On the other hand, in the present embodiment, the elastic repulsive force of the base material 302a on the upstream side in the fixing belt circumferential direction and the elastic repulsion of the base material 302a on the downstream side in the fixing belt circumferential direction when the position V (FIG. 2) is used as a reference. It is greater than force.

Due to the elastic repulsive force of the base material 302a on the upstream side in the circumferential direction of the fixing belt, the fixing belt is formed into an upstream side tension shape in the recording material transport direction, and the slack in the free state portion of the fixing belt is suppressed (prevented) and the separation region is formed. The radius of curvature of the fixing belt at Z (FIG. 2) can be reduced. Further, the slack of the fixing belt due to repeated drive rotation and stop of the pressure roller can be suppressed (prevented) as in the first embodiment.

(Modification example)
Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and modifications can be made within the scope of the gist thereof.

(Modification 1)
In the above-described embodiment, the pressure roller is shown as an opposed rotating body that forms a nip portion that faces the fixing belt and holds and conveys a recording material carrying an unfixed toner image together with the fixing belt. Not limited. For example, an endless belt suspended from a plurality of rollers can be used as an opposed rotating body. The endless belt may be configured to pressurize the fixing belt, or the endless belt may be configured to be pressurized by the fixing belt.

(Modification 2)
In the above-described embodiment, the recording paper has been described as a sheet as a recording material, but the sheet in the present invention is not limited to paper. Generally, the recording material is a sheet-like member on which a toner image is formed by an image forming apparatus, for example, standard or irregular plain paper, thick paper, thin paper, envelopes, postcards, stickers, resin sheets, transparencies, etc. Glossy paper etc. are included. In the above-described embodiment, for convenience, the handling of the recording material (sheet) P has been described using terms such as paper feeding and paper passing, but the sheet in the present invention is not limited to paper.

(Modification 5)
In the above-described embodiment, the fixing device for fixing the unfixed toner image to the sheet has been described as an example, but the present invention is not limited to this, and the toner image presumed to be attached to the sheet is used to improve the gloss of the image. It can also be applied to a device for heating and pressurizing (also referred to as a fixing device in this case).

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

Claims (11)

A rotatable fixing belt that is long in the longitudinal direction and has a ring-shaped cross section orthogonal to the longitudinal direction.
A heating member that is long in the longitudinal direction and is in contact with the inner peripheral surface of the anchoring belt while being elastically deformed in a cross section orthogonal to the longitudinal direction when the anchoring belt rotates. A heating member having a heat generating portion for heating, and
An opposed rotating body that forms a nip portion that faces the fixing belt and that holds and conveys a recording material that carries an unfixed toner image together with the fixing belt.
Have,
In a cross section orthogonal to the longitudinal direction when the fixing belt rotates,
The intermediate position between the most upstream side position and the most downstream side position of the base material in the recording material transport direction orthogonal to the longitudinal direction is the center position of the nip portion and the rotation center of the opposed rotating body in the recording material transport direction. It is provided on the upstream side in the recording material transport direction with respect to the first straight line connecting the positions.
When the base material is divided into one side and the other side by the cross section in the longitudinal direction including a predetermined straight line in the cross section orthogonal to the longitudinal direction.
The one side is provided on the upstream side in the recording material transport direction with respect to the other side.
A fixing device characterized in that the Young's modulus of the substrate is larger on one side than on the other side . The longitudinal elasticity coefficient of the base material is a region on the upstream side in the rotational direction of the fixing belt with respect to a second straight line including the intermediate position and parallel to the first straight line in a cross section orthogonal to the longitudinal direction. The fixing device according to claim 1, wherein the fixing device is larger than the area on the downstream side. The thickness of the base material is larger in the region on the upstream side in the rotational direction of the fixing belt with respect to the second straight line including the intermediate position and parallel to the first straight line in the cross section orthogonal to the longitudinal direction. The fixing device according to claim 2, wherein the fixing device is larger than the area on the downstream side. In the cross section orthogonal to the longitudinal direction, the shape symmetric with respect to the first straight line is used as a reference shape as a virtual shape of the fixing belt, and the fixing belt is moved upstream in the rotation direction of the fixing belt with respect to the second straight line. When dividing into a side shape and a downstream side shape, both the upstream side shape and the downstream side shape are provided on the upstream side in the recording material transport direction with respect to the corresponding upstream side shape and downstream side shape in the reference shape. The fixing device according to claim 2 or 3, wherein the fixing device is characterized. 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 rotational 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. In the cross section orthogonal to the longitudinal direction, the shape symmetric with respect to the first straight line is used as a reference shape as a virtual shape of the fixing belt, and the 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 side shape and a downstream side shape in the rotation direction of the fixing belt, only the upstream side shape is provided on the upstream side in the recording material transport direction with respect to the corresponding upstream side shape in the reference shape. The fixing device according to claim 5, wherein the fixing device is provided. The heat generating portion has a cross section orthogonal to the longitudinal direction, is located on the opposite side of the nip portion with respect to the intermediate position, and is located in a region including the intermediate position and overlapping with a second straight line parallel to the first straight line. The fixing device according to any one of claims 1 to 6, wherein the fixing device is provided. One of claims 1 to 7, 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 described in the section. The fixing device according to any one of claims 1 to 8, wherein the base material is a sheet metal made of a metal material. It has a backup member having a cross section orthogonal to the longitudinal direction and abutting on the inner peripheral surface of the fixing belt at the nip portion, and the opposed 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 has a cross section orthogonal to the longitudinal direction formed in a ring shape, is elastically deformed in the cross section orthogonal to the longitudinal direction, the inner peripheral surface of the fixing belt is formed. A heating member that is long in the longitudinal direction and is in contact with each other.
It has 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 the cross section in the longitudinal direction including a predetermined straight line in the cross section orthogonal to the longitudinal direction.
A heating member characterized in that the Young's modulus of the base material differs between the one side and the other side.

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