JP2008225276A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device having a fixing roll having an elastic material layer on a surface thereof, an endless belt pressed against the fixing roll, and a pressure member pressing the endless belt against the fixing roll, the surface of the fixing roll being prevented from being damaged by side edges of a recording medium repeatedly passing through a press-contact part between the fixing belt and endless belt. <P>SOLUTION: The pressure member 2 has a pressure pad 20 upstream in a revolving movement direction of the endless belt 3 and also has a pressure applying member 21 made of a material having higher rigidity than that of the pressure pad downstream. The pressure applying member is pressed against the elastic material layer 1c of the fixing roll across the endless belt to cause the elastic material layer to have large elastic deform. On a surface of the pressure applying member 21, recessed portions 21a and 21b reducing pressing force to the fixing roll 1 are provided at positions opposed to side edges of the recording medium conveyed between the fixing roll 1 and endless belt 3. Those recessed portions are formed of gently curved surfaces. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes an unfixed toner image held on a recording medium to a recording medium in an image forming apparatus such as a printer, a copying machine, and a facsimile that forms an image using toner.

  As a fixing device of an image forming apparatus that forms a visible image using toner, one having a fixing roll having a heat source and an endless belt supported so as to be capable of circular movement while being pressed against the fixing roll. Are known. A pressure member is disposed inside the endless belt, and the endless belt is pressed against the fixing roll by the pressure member. A so-called nip is formed in which the endless belt and the fixing roll are pressed against each other. Yes. Then, the recording medium onto which the toner image is transferred is sandwiched in the nip portion, and the toner image is fixed on the recording medium by heating and pressurizing the toner.

  As the pressure member used in the fixing device, for example, a pad-shaped member made of an elastic material is used. By pressing such a pad-shaped member from the inside of the endless belt, the endless belt can be pressed against the fixing roll in a wide range. Accordingly, the toner image can be sufficiently heated even when the conveyance speed of the recording medium passing through the nip portion is high.

  On the other hand, as the fixing roll, one in which an elastic body layer made of silicone rubber or the like is formed on the surface of a metal cylindrical metal core is known. In addition, a material in which the surface of the elastic layer is coated with a release layer made of a fluororesin or the like is widely used. When the endless belt is pressed against the fixing roll having such an elastic layer, the elastic layer is deformed to improve the adhesion to the toner image, and the toner on the recording medium is heated evenly to achieve good fixing. It can be performed.

Patent Document 1 describes a fixing device in which a pressure member is provided so that a large elastic deformation occurs in the elastic layer at a downstream portion of a nip portion.
The pressure member used in the fixing device is a pressure applying member made of a material having a large rigidity in a downstream portion of the pressure contact portion, where a pad-like elastic member is disposed upstream of a region where the fixing roll and the endless belt are pressure contacted. Is arranged. When this pressure member is pressed against the fixing roll from the inside of the endless belt, a sufficiently long pressure contact portion is formed in the circumferential direction. Further, the pressure applying member causes a larger deformation in the elastic body layer of the fixing roll than the upstream portion where the elastic member is pressed. When passing through the part where the large elastic deformation occurs, a minute speed difference occurs between the conveyance speed of the recording medium and the moving speed of the surface of the fixing roll, and the recording medium on which the toner image is fixed becomes the surface of the fixing roll. It becomes easy to peel from.
JP 2002-132080 A

When the recording medium is repeatedly sent to the pressure contact portion between the fixing roll and the endless belt as described above, the outermost surface of the fixing roll may be damaged at the position where the side edge of the recording medium passes. The cause of this damage can be considered as follows.
As shown in FIG. 6, when the recording medium P is sandwiched between the fixing roll 101 and the endless belt 103 and strongly pressed from the back surface of the endless belt 103 by the pressure applying member 102, the side edge of the recording medium P, that is, At the position where the edge Pe is pressed, the amount of deformation of the elastic layer 101a of the fixing roll 101 changes suddenly, and stress concentrates. As the thickness of the recording medium P increases, the amount of deformation of the elastic layer and the resulting stress also increase. Such deformation repeatedly causes damage to the surface, and when the fixing roll 101 has a release layer 101b made of a fluororesin or the like, the release layer is damaged or peeled off, Cause image defects.

  In general recording media such as PPC paper, the above-mentioned image defects do not occur up to about 200000 sheets. However, when a thick recording medium is used repeatedly, the elastic body of the fixing roll The load acting on the layer and the release layer is increased. For this reason, fixing failure due to damage of the release layer or the like occurs earlier than the above number.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to prevent the fixing roll from being damaged by the side edge of the recording medium that sequentially passes through the press contact portion, and to fix a good image over a long period of time. And a fixing device capable of maintaining the peelability of the recording medium.

  In order to solve the above problem, the invention according to claim 1 is provided such that a fixing roll that is supported so as to be rotatable around an axis and at least a peripheral surface is heated, and a part of the fixing roll is pressed against the outer peripheral surface of the fixing roll. An endless belt that presses the recording medium holding the unfixed toner image in a pressure contact area with the fixing roll, and is in contact with the inner peripheral surface of the endless belt. A pressure member that presses the endless belt against the fixing roll, and the fixing roll includes an elastic body layer that is deformed by the pressing force of the pressure member over the entire circumference. A pressure pad that is in pressure contact with an inner peripheral surface of the endless belt at an upstream portion in a circumferential direction of the endless belt, and is pressed against the fixing roll via the endless belt at the downstream portion, Pad is pressed A pressure applying member that causes a large deformation in the elastic layer of the fixing roll than the portion to be formed, and the recording medium side conveyed between the fixing roll and the endless belt on the surface of the pressure applying member Provided is a fixing device in which a concave portion for reducing the pressing force to the fixing roll is formed at a position corresponding to the edge.

  According to a second aspect of the present invention, there is provided the fixing device according to the first aspect, wherein the concave portion is a recording medium having a size smaller than a maximum size recording medium that can be conveyed at least between the fixing roll and the endless belt. It shall be formed in the position corresponding to a side edge.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the concave portion is formed by a curved surface that is gently continuous in the width direction of the recording medium that passes therethrough.

  According to a fourth aspect of the present invention, in the fixing device according to the first, second, or third aspect, the pressure contact force between the fixing roll and the endless belt in the region where the concave portion is formed in the pressure applying member is: It is assumed that the pressure pad is substantially the same as or greater than the pressure contact force in the region where the fixing roll is pressed via the endless belt.

  According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the maximum depth of the concave portion is 80 μm to 120 μm.

  By providing the configuration as described above, in the invention according to claim 1, when the recording medium to be conveyed is sandwiched between the fixing roll and the endless belt and passes the position where the pressure applying member is pressed. Then, the vicinity of the side edge of the recording medium is deformed so that the endless belt is pushed into the recess formed in the pressure applying member. As a result, the force of pressing the side edge against the fixing roll is reduced, and the amount of deformation of the elastic layer of the fixing roll is alleviated from suddenly changing at a position corresponding to the side edge of the recording medium. Therefore, it is possible to suppress the occurrence of damage on the surface of the fixing roll.

  In the invention according to claim 2, when a recording medium having a size smaller than the maximum size is repeatedly used, damage to the surface of the fixing roll can be suppressed at a position where the side edge of the recording medium of the small size passes. . The position where the small-size side edge passes is within the image area when the maximum-size recording medium passes, and it becomes easy to notice when a defect occurs in the image, but at this position, damage to the surface of the fixing roll is effectively suppressed. As a result, it is possible to suppress the occurrence of image defects such as a line entering the image and to form a good image over a long period of time.

  In the invention according to claim 3, since the concave portion is formed on the surface of the pressure applying member by a gentle curved surface, the pressure contact force does not change suddenly at the boundary between the concave portion of the pressure applying member and its peripheral portion, and the image is displayed. It can prevent the trace of a recessed part arising.

  In the invention according to claim 4, since the pressing force to the fixing roll is maintained even in the region where the concave portion of the pressure applying member is formed, the state of gloss or the like of the image is compared with the region where the concave portion is not formed. An image with little change and high uniformity can be obtained.

  In the invention according to claim 5, the depth of the concave portion is appropriately set, and the damage of the surface of the fixing roll can be effectively suppressed, and good fixing property can be maintained and a highly uniform image can be obtained.

Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic front view of the fixing device.
The fixing device includes a heat source therein and is supported so as to be able to rotate around an axis, and the fixing roll 1 is supported in parallel with the axis of the fixing roll 1 and pressed against the fixing roll 1. The pressure member 2 and the endless belt 3 sandwiched between the fixing roll 1 and the pressure member 2 and wound around the pressure member 2 in a state where no tension is introduced constitute a main part. .

  The fixing roll 1 includes a metal cylindrical member having a high thermal conductivity as a core metal 1b, and a heat-resistant elastic body layer 1c made of silicone rubber having a thickness of 0.6 mm on the outer peripheral surface of the core metal 1b. As a surface layer, a release layer 1d having a thickness of about 30 μm and covered with a fluororesin tube is laminated. These layers are formed over the width of the maximum size recording medium in the axial direction of the cored bar 1b. A heating source 1a such as a halogen heater is provided inside the metal core 1b.

  A temperature sensor 8 is disposed near the surface of the fixing roll 1, and the temperature of the peripheral surface of the fixing roll 1 is adjusted by controlling ON / OFF of the halogen heater based on the detected value of the temperature sensor 8. Yes.

The endless belt 3 has a two-layer structure of a base layer and a surface layer. In consideration of heat resistance, strength, and surface smoothness, the base layer includes a heat-resistant resin such as polyimide, polyamide, and polyamide-imide. Metal such as aluminum and stainless steel is used, and the surface layer is made of silicone rubber, fluorine rubber, or the like, which has high heat resistance and high releasability from the toner.
The endless belt 3 is pressed against the outer peripheral surface along the axial direction of the fixing roll 1 by a pressing member 2 disposed on the inner side. Then, the fixing roll 1 is driven by being rotationally driven, and moves around while sliding with the pressure member 2. In addition, the code | symbol 4 shown in FIG. 1 is a belt guide which controls the position when the said endless belt 3 carries out a circular movement.

  Further, in order to reduce the frictional resistance between the inner peripheral surface of the endless belt 3 and the pressing member 2, the sliding sheet 7 is disposed on the surface of the pressing member 2 on which the endless belt 3 is rubbed. Although this sliding sheet 7 can also use a sheet-like member having a smooth surface such as polyimide, in the present embodiment, it is made by weaving fluororesin fibers in a cloth shape and having a thickness of 50 μm to 100 μm. A thing is used as the sliding sheet 7.

The sliding sheet 7 is wound around the pressure member 2 so that the upstream end of the endless belt 3 in the rotation direction is fixed to the support member 22 and is in contact with the inner peripheral surface of the endless belt 3. . The other end is not restricted and is a free end.
As a result, the sliding sheet 7 is sandwiched between the pressing member 2 and the inner peripheral surface of the endless belt 3 along the circumferential movement direction of the endless belt 3, and the endless belt 3 that circulates is rubbed. This also reduces the frictional resistance.

  Further, lubricating oil is applied to the inner peripheral surface of the endless belt 3 by the lubricating oil applying member 6. The lubricating oil application member 6 is disposed in contact with the inner peripheral surface of the endless belt 3, supplies lubricating oil over the entire width of the region where the pressure member 2 is pressed, and the sliding between the endless belt 3 and the pressure member 2. The dynamic resistance is further reduced, and the smooth circumferential movement of the endless belt 3 is promoted.

  The pressure member 2 is supported by the support member 22 so as to press the fixing roll 1. The pressure pad 20 is curved along the circumferential surface of the fixing roll 1, and the pressure pad 20. The pressure applying member 21 is provided so as to protrude from the surface of the fixing roll 1 on the downstream side in the circumferential movement direction of the endless belt 3. The pressure member 2 is pressed against the fixing roll 1 via the endless belt 3 so that the fixing roll 1 and the endless belt 3 are pressed against each other with a sufficient width in the circumferential direction of the endless belt 3. ing.

The pressure pad 20 is formed of an elastic body such as silicone rubber or fluorine rubber, and is supported by the support member 22 so as to press the endless belt 3 against the fixing roll 1 with a predetermined load.
The material constituting the pressure applying member 21 is not particularly limited, but is preferably a material that is not easily deformed, such as heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, and polyamide, or a metal such as iron, aluminum, copper, or magnesium. , And an alloy containing these can be used. The pressure applying member 21 is also pressed against the fixing roll 1 by the support member 22 via the endless belt 3, and has a shape having a gently curved protrusion as shown in FIG.

Since the pressure applying member 21 is made of a material having a hardness higher than that of the pressure pad 20, the pressure applying member 21 gives a larger deformation to the elastic body layer 1 c of the fixing roll 1 than a deformation caused by pressing of the pressure pad 20. It is. When a large strain is locally applied to the elastic layer 1c of the fixing roll 1 in this way, a minute slip occurs between the surface of the fixing roll 1 and the recording medium P, and the adhesion force to the fixing roll 1 is reduced. The recording medium is easily peeled off.
Note that reference numeral 9 shown in FIG. 1 indicates a peeling auxiliary member for more reliably peeling the recording medium P from the fixing roll 1. The peeling assisting member 9 is in contact with the recording medium P that is easily peeled from the fixing roll 1 by the pressure applying member 21 and mechanically peels the recording medium P from the fixing roll 1.

  On the surface of the pressure applying member 21, as shown in FIG. 2, concave portions 21 a and 21 b are formed at a plurality of positions in the axial direction of the fixing roll 1. These positions correspond to the side edges of the recording medium that passes through, and the positions corresponding to the side edges when the recording medium passes to the maximum size used in the image forming apparatus and higher than this are smaller. A concave portion is provided at a position corresponding to a side edge when a recording medium used at a frequency passes.

  FIG. 3 is an enlarged cross-sectional view of the recesses 21a and 21b, that is, an enlarged cross-sectional view of the A part and the B part shown in FIG. FIG. 3A shows the shape of the recess 21a formed corresponding to the side edge of the maximum size recording medium that can be conveyed by this apparatus, and FIG. 3B shows the size smaller than that of the maximum size recording medium. The shape of the recess 21b formed at a position corresponding to the side edge of the recording medium is shown. FIG. 4 shows a cross section in a direction perpendicular to the axis of the fixing roll 1 at a portion where the pressure applying member 21 is pressed against the fixing roll. As shown in these drawings, the concave portions 21 a and 21 b are formed by gentle curved surfaces continuous from the surface of the pressure applying member 21.

In this embodiment, the recess 21a formed at a position corresponding to the side edge of the maximum size recording medium has a depth of 0.13 mm and a width of 10 mm, as shown in FIG. . Further, as shown in FIG. 3B, the recess 21b corresponding to the side edge when the passing recording medium is smaller than the maximum size recording medium has a depth of 0.08 mm and a width of 20 mm. Yes, the range of width 4mm at the bottom is the same depth.
As described above, the concave portion 21b corresponding to the small size recording medium has a curved surface with a smaller curvature and a smaller depth than the concave portion 21a corresponding to the maximum size recording medium. Thus, when fixing the toner image on the maximum size recording medium, the image uniformity is suppressed from being deteriorated by the concave portion 21b corresponding to the side edge of the small size recording medium.

Note that the depth, width, curvature of the curved surface, and the like of the concave portion can be appropriately determined based on the thickness and hardness of the elastic body layer 1 c of the fixing roll 1, the configuration of the endless belt 3, and the like. Further, it is desirable to determine in consideration of the configuration of the sliding sheet 7.
The depth and shape of the concave portion is such that the fixing image is not affected by the provision of the concave portion, for example, a pressure contact force that is substantially the same as or greater than the area where the pressure pad 20 in the upstream portion is pressed. It is desirable to determine it to act on the surface of P. Accordingly, it is possible to suppress a change in gloss or the like between the region where the recess is provided and the region where the recess is not provided.
In addition, in the present embodiment, the positions where the concave portions are provided are provided at positions corresponding to the side edges of the recording medium of the maximum size and positions corresponding to the side edges of one recording medium of a smaller size. More or less recesses may be provided depending on the type of size of the recording medium. Furthermore, the present embodiment describes an apparatus that employs a so-called center register that controls the position of the recording medium at its center, but is an apparatus that employs a side register that regulates the position at the side edge of the recording sheet. Even if it exists, a recessed part can be provided in the position where a side edge passes corresponding to the size of the recording medium to be used.

Next, the operation of the fixing device will be described.
The fixing roll 1 is rotationally driven by a drive motor (not shown), and the endless belt 3 is rotated around the fixing roll 1. The fixing roll 1 is controlled so that the surface thereof has a predetermined temperature by energization control to the heating source 1a. The recording medium P holding the toner image is fed into the press contact portion N between the fixing roll 1 and the endless belt 3 and is sandwiched between the fixing roll 1 and the endless belt 3 and conveyed. At this time, the toner image comes into contact with the fixing roll 1 and is heated, and at the same time, the toner image is pressed against the endless belt 3 and the softened toner image is pressed against the recording medium.

  The recording medium P that has passed through the upstream portion of the press contact portion N, that is, the region where the pressure pad 20 is pressed against the endless belt 3, is conveyed to the downstream portion where the pressure applying member 21 presses the endless belt 3. At this time, concave portions 21a and 21b are formed on the surface of the pressure applying member 21 with gentle curved surfaces at portions corresponding to the side edges of the recording medium to be conveyed. Specifically, when a recording medium of the maximum size that can be used, for example, an A3 size recording medium is fed into the press contact portion N, the passing positions of the side edges of the A3 size recording medium are at both ends of the pressure applying member. This corresponds to the concave portion 21a provided at a position close to the portion. Further, when a B4 size or A4 vertical size recording medium is fed into the press contact portion, the passing position of the side edge of these recording media corresponds to the position of the concave portion 21b provided on the center side in the width direction from the concave portion. ing. Then, the vicinity of the side edge of the recording medium P is pushed into the recesses 21a and 21b by the pressing force acting between the fixing roll 1 and the pressure applying member 21, as shown in FIG.

  Thereby, the sudden change in the deformation amount of the elastic layer 1c due to the side edge Pe (edge) of the recording medium P being strongly pressed against the fixing roll 1 is alleviated. Accordingly, the stress generated in the vicinity of the surface of the fixing roll 1 is suppressed to be small, and even when the thick recording medium P passes repeatedly, the surface is hardly damaged.

  Further, the concave portions 21a and 21b are formed by gentle curved surfaces. Further, even in these concave portions, the pressure contact force when being pressed by the pressure pad 20 in the upstream portion of the pressure contact portion N is equal to or more than this. Is exerted on the surface of the recording medium P. As a result, good fixing is possible even in the region where the concave portion is formed, and there is almost no difference in gloss between the region where the concave portion is provided and the region where the concave portion is not provided, and a good image is formed. be able to. In particular, when using the maximum size recording medium, the position corresponding to the side edge of the small size recording medium is within the range of the image formed on the maximum size recording medium, but the shape, depth, etc. of the recesses. By setting appropriately, it is possible to reduce the influence due to the provision of the recess.

On the other hand, the pressure applying member 21 protrudes toward the fixing roll 1 and causes a large elastic deformation in the elastic body layer 1c of the fixing roll 1. When the recording medium P passes through this portion, the surface of the fixing roll 1 is obtained. And a slight difference in the moving speed between the recording medium P and the surface of the recording medium P. As a result, the separation of the toner image on the recording medium P from the surface of the fixing roll 1 is promoted, and the recording medium P is easily separated from the surface of the fixing roll 1 when fed from the pressing portion of the pressure applying member 21. The peeling assisting member 9 also assists this.
At this time, the deformation amount of the elastic layer 1c is small in the portion where the concave portion is provided in the pressure applying member 21, but the region where the concave portion is provided is limited to a part in the width direction of the recording medium P. Therefore, the peelability of the recording medium P is not affected.

  The invention according to the present application is not limited to the embodiment described above, and can be implemented with appropriate modifications within the scope of the claims.

1 is a schematic configuration diagram illustrating a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic front view of the fixing device shown in FIG. 1. It is an expanded sectional view of the position in which the recessed part of the A part and B part, ie, a pressure provision member, shown in FIG. 2 was provided. FIG. 4 is an enlarged cross-sectional view in a direction perpendicular to the axis of the fixing roll at a portion where the pressure applying member is pressed against the fixing roll. FIG. 6 is an enlarged cross-sectional view illustrating a state when a side edge portion of a recording medium passes through a portion where a concave portion is provided in a pressure applying member. FIG. 9 is an enlarged cross-sectional view illustrating a state in the vicinity of a side edge portion of the recording medium when the recording medium passes between the fixing roll and the pressure member, for explaining a problem to be solved by the present invention. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Fixing roll, 1a: Heat source, 1b: Core metal, 1c: Elastic body layer, 1d: Release layer, 2: Pressurizing member, 3: Endless belt, 4: Belt guide, 6: Lubricating oil application member, 7: sliding sheet, 8: temperature sensor, 9: peeling assist member, 20: pressure pad, 21: pressure applying member, 21a, 21b: recess provided in the pressure applying member, 22: support member, P: recording Medium

Claims (5)

A fixing roll that is supported so as to be capable of rotating about an axis, and at least a peripheral surface is heated;
An endless belt that is supported so as to be capable of rotating in a state where a part thereof is pressed against the outer peripheral surface of the fixing roll and sandwiches and presses a recording medium in which an unfixed toner image is held in a pressure contact area with the fixing roll;
A pressure member that is in contact with the inner peripheral surface of the endless belt and presses the endless belt against the fixing roll;
The fixing roll is provided with an elastic body layer that is deformed by the pressing force of the pressure member over the entire circumference,
The pressure member has a pressure pad in pressure contact with the inner peripheral surface of the endless belt at an upstream portion in the circumferential direction of the endless belt, and is pressed against the fixing roll via the endless belt at the downstream portion. A pressure applying member that causes a large deformation in the elastic layer of the fixing roll from a portion where the pressure pad is pressed,
A recess for reducing the pressing force to the fixing roll is formed at a position corresponding to the side edge of the recording medium conveyed between the fixing roll and the endless belt on the surface of the pressure applying member. A fixing device characterized by the above.   2. The concave portion is formed at a position corresponding to a side edge of a recording medium having a size smaller than that of a recording medium having a maximum size that can be conveyed between at least the fixing roll and the endless belt. The fixing device according to 1.   The fixing device according to claim 1, wherein the concave portion is formed by a curved surface that is gently continuous in a width direction of the recording medium that passes therethrough.   The pressure contact force between the fixing roll and the endless belt in the region where the concave portion is formed in the pressure applying member is substantially the same as the pressure contact force in the region where the pressure pad presses the fixing roll via the endless belt, or The fixing device according to claim 1, wherein the fixing device is larger than a pressing force.   The fixing device according to claim 1, wherein a maximum depth of the concave portion is 80 μm to 120 μm.

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