JP2001312176A - Image fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image fixing device capable of making a heating roll in press contact with a pressure roll in an axial direction by uniform pressuring force, fixing a toner image on a recording sheet with sufficient strength and preventing the recording sheet from being wrinkled. SOLUTION: In this image fixing device by which the unfixed toner image T is fixed on the recording sheet P by inserting the sheet P through space between the heating roll 1 and the pressure roll 2, the roll 2 is constituted of a hollow cylindrical pressure sleeve 20 having an elastic layer 23 formed on its surface and rotating to follow the roll 1, a metallic pressing shaft 21 inserted into the hollow part of the sleeve 20 so as to make the sleeve 20 in press contact with the roll 1 and formed so that the shape of its outer peripheral surface in contact with the inner peripheral surface of the sleeve 20 is gradually more slender toward both shaft ends from the center in the axial direction and an elastic coating layer 24 formed on the outer peripheral surface of the shaft 21 with a uniform thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording sheet which is inserted between a heating roll and a pressure roll which are pressed against each other.
The present invention relates to an image fixing device that heats and presses an unfixed toner image transferred onto a recording sheet to fix the unfixed toner image on the recording sheet. Specifically, the image fixing device uniformly presses a pressure roll along an axial direction of the heating roll. It relates to the improvement to make it.

[0002]

2. Description of the Related Art Conventionally, as an image fixing device for fixing an unfixed toner image transferred onto a recording sheet by an electrophotographic copying machine or a laser beam printer to a recording sheet, a heating roll having a built-in heater and an elastic roller are used. It is generally known that a pressure roll covered with a layer is pressed against each other, and a recording sheet is inserted between the heating roll and the pressure roll. In this conventional fixing device, by pressing a pressure roll covered with an elastic layer against a heating roll, the elastic layer is crushed to form a nip area that sandwiches a recording sheet, and carries an unfixed toner image. While the recording sheet passes through the nip area, the toner on the recording sheet is melted by the thermal energy of the heater, and the melted toner is pressed against the recording sheet, thereby firmly fixing the toner image to the recording sheet. It is possible to do.

[0003] However, when a heating roll and a pressure roll, which are rotatably supported, are simply pressed against each other, a large pressing force is obtained near both ends in the axial direction of these rolls, but a large pressing force is obtained near the center in the axial direction. The pressing force was slightly insufficient, and a nip region having a uniform width could not be formed along the axial direction of the heating roll. For this reason, the toner image cannot be fixed on the recording sheet with sufficient strength, and the recording sheet that has passed through the nip region is likely to be wrinkled. In particular, in recent years, in order to shorten the print waiting time at the time of starting the printer, etc., measures have been taken to reduce the heat capacity by reducing the thickness of the heating roll, and apply a force to both shaft ends of the heating roll and the pressure roll. When the two rolls are pressed and brought into contact with each other, the heating roll tends to bend, so that the pressing force tends to become increasingly insufficient near the center of the heating roll in the axial direction.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 9-68883 and Japanese Patent Application Laid-Open No.
An image fixing device disclosed in Japanese Patent No. 38811 has been proposed. In this image fixing device, by improving the structure of the pressure roll, care is taken to obtain a uniform pressing force along the axial direction of the heat roll, and the heat roll is unchanged from the conventional configuration. The pressure roller has a hollow cylindrical pressure sleeve formed with an elastic layer on the surface and is rotated by the heating roll. The pressure roller is inserted into the hollow portion of the pressure sleeve and presses the pressure sleeve against the heating roll. The pressing shaft is formed such that the outer diameter gradually decreases from the center in the axial direction to both ends. When the pressing shaft is pressed to bring the heating roll and the pressing sleeve into pressure contact with each other, the elastic layer on the surface of the pressing sleeve is crushed to form a nip area of the recording sheet. Since it is the largest at the center, even if the heating roll is bent, a uniform pressing force is obtained along the axial direction of the heating roll, and a nip region having a uniform width along the axial direction is obtained. Considered to be formed.

[0005]

However, the pressing shafts of the image fixing devices disclosed in these publications have a metal shaft having a constant outer diameter, which is provided with a coating layer made of an elastic material on the surface thereof. Since the outer shape of the pressing shaft described above is formed by adjusting the thickness, there are the following problems. That is, since the thickness of the coating layer constituting the pressing shaft is different between the center and the end in the axial direction, when the pressing shaft is pressed against the heating roll via the pressing sleeve, the elasticity of the coating layer is increased. As a result, the deformation amount is different between the center and the end in the axial direction, and it is difficult to form the nip region with a uniform width along the axial direction. Further, when the temperature of the coating layer is increased by the heat energy given from the heating roll, the expansion amount of the coating layer is different between the center and both ends in the axial direction of the pressing shaft,
Again, it is difficult to obtain a uniform pressure distribution along the axial direction. Furthermore, the coating layer made of an elastic body gradually wears out due to contact with the inner peripheral surface of the pressure sleeve, but since the width of the nip region is different between the center in the axial direction and both ends as described above, The abrasion amount of the coating layer also became non-uniform, and the non-uniform distribution of the pressing force tended to increase as the fixing device was used over time. Furthermore, it is necessary to form the coating layer of the pressing shaft on a convex curved surface so that a desired pressure distribution can be obtained between the heating roll and the pressing sleeve, but the elastic body is processed into such a shape. However, there is a problem that the production cost increases.

The present invention has been made in view of such a problem, and an object of the present invention is to enable a heating roll and a pressure roll to be pressed against each other with a uniform pressing force along an axial direction. It is an object of the present invention to provide an image fixing device which can fix a toner image on a recording sheet with sufficient strength and does not cause wrinkles or the like on the recording sheet.

[0007]

In order to achieve the above object, an image fixing apparatus of the present invention has a recording sheet inserted between a heating roll and a pressure roll which are in pressure contact with each other, and is transferred to the recording sheet. Assuming an image fixing device for fusing and pressing the unfixed toner image to the recording sheet, the pressure roll has a hollow cylinder that has an elastic layer formed on its surface and rotates following the heating roll. Pressurized sleeve, while being inserted into the hollow portion of the pressurized sleeve and pressing the pressurized sleeve against the heating roll,
A metal pressing shaft formed so that the shape of the outer peripheral surface in contact with the inner peripheral surface of the pressing sleeve becomes gradually narrower from the center in the axial direction toward both axial ends, and the outer peripheral surface of the pressing shaft or the pressing. And an elastic coating layer formed on the inner peripheral surface of the sleeve with a uniform thickness.

According to such technical means, the shape of the outer peripheral surface of the metal pressing shaft is formed so as to gradually decrease from the center in the axial direction toward both ends of the shaft. Since an elastic coating layer having a uniform thickness is formed on the outer peripheral surface or the inner peripheral surface of the pressing sleeve, when the pressing shaft is pressed against the inner peripheral surface of the pressing sleeve, the elastic coating layer is heated by a heating roll. Since the elastic deformation occurs substantially uniformly along the axial direction of the recording sheet, the heating roll and the pressure roll can be pressed against each other with a substantially uniform pressing force along the axial direction, and the nip area of the recording sheet can be axially moved. It can be formed with a substantially uniform width along the direction. Thus, the toner image on the recording sheet can be reliably fixed to the recording sheet, and a trouble such as wrinkling of the recording sheet can be avoided.

Here, the coating elastic layer formed on the outer peripheral surface of the pressing shaft or the inner peripheral surface of the pressing sleeve ensures that the pressing shaft made of metal and the inner peripheral surface of the pressing sleeve are in close contact with each other without any gap. And reduces noise caused by the contact between the pressing shaft and the pressing sleeve. Therefore, the coating elastic layer may be formed on the outer peripheral surface of the pressing shaft or may be formed on the inner peripheral surface of the pressing sleeve.

On the other hand, from the viewpoint that the pressing shaft formed so that the outer diameter at the central portion in the axial direction is larger than the outer diameters at both shaft ends presses the pressing sleeve against the heating roll, the pressing sleeve is formed by the pressing shaft. It is necessary that the pressing shaft is not easily deformed by the reaction force of pressing the pressing sleeve against the heating roll. Further, if the heating roll is easily deformed when the pressure sleeve is pressed against the heating roll, it is not possible to apply a sufficient pressing force between the heating roll and the pressure sleeve. Therefore, it is preferable that the rigidity in the direction perpendicular to the axial direction of the heating roll, the pressing sleeve, and the pressing shaft, that is, the rigidity in the radial direction decreases in the order of the pressing shaft, the heating roll, and the pressing sleeve. With this configuration, the pressure sleeve easily deforms following the shape of the outer peripheral surface of the pressing shaft when pressed against the heating roll, so that the inner peripheral surface of the pressing sleeve is tightly attached to the outer peripheral surface of the pressing shaft. As a result, the pressing sleeve and the heating roll can be more uniformly pressed along the axial direction.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image fixing device according to the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 are a schematic front view and a schematic side view showing an embodiment of an image fixing apparatus to which the present invention is applied. The image fixing device of this embodiment includes a heating roll 1 having a built-in heater 10,
The recording sheet P to which the unfixed toner image T has been transferred is inserted between the heating roll 1 and the pressure roll 2 so that the toner is transferred to the recording sheet P. The toner image T is fused and pressed onto the surface of the toner image T to fix the toner image T thereon. The pressure roll 2 includes a hollow cylindrical pressure sleeve 20 that rotates following the heating roll 1, and a pressure sleeve 20.
And a pressing shaft 21 inserted into the hollow portion of the heating roll 1. The pressing sleeve 21 is pressed against the heating roll 1 so that the pressing sleeve 20 is pressed against the heating roll 1.

First, the heating roll 1 is formed as a release layer 12 on the outer peripheral surface of a steel core 11 formed in a cylindrical shape.
The core 11 is coated with FA (perfluoroalkyl vinyl ether copolymer resin), and the core 11 has a diameter of 35 mm, a thickness of 0.4 mm, and an effective length of 34 in the axial direction.
The release layer 12 is about 30 mm while being formed to 5.5 mm.
Coated to a thickness of μm. The core 11 has both ends supported on the fixed frame 3 via bearings 13, and is driven by a drive motor (not shown) to about 300 mm.
It is driven to rotate at a peripheral speed of mm / s.
Further, a Colts lamp (100 V, 1000 W) as the heater 10 is built in the hollow portion of the core 11, and the heater 10 is fixedly arranged so as to penetrate the core 11. A temperature sensor 14 is in contact with the surface of the heating roll 1, and on / off of the heater 10 is controlled based on a detection value of the temperature sensor 14, so that the surface temperature of the heating roll 1 is always a fixed fixing temperature. (For example, 170 ° C.).

On the other hand, a pressure sleeve 20 constituting the pressure roller 2 has a hollow cylindrical stainless steel core 22.
The core 22 is formed to have an outer diameter of 29 mm, a thickness of 0.3 mm, and an effective length of 318 mm, while the elastic layer 23 has a thickness of 3mm, rubber hardness 60 ° (JIS A)
Is formed. The pressure sleeve 20 is only suspended by the pressing shaft 21 penetrating through the hollow portion, and is not supported on the fixed frame 3 or the movable frame 4 itself.

As shown in FIG. 3, the pressing shaft 21
Is a member made of stainless steel having a shape that gradually becomes narrower from the center in the axial direction to the ends of both shafts, and the outer peripheral surface is formed in a convex curved shape. The effective length of the pressing shaft 21 is 319 mm, the minimum outer diameter within the effective length is 19 mm, and the outer peripheral surface is covered with an elastic coating layer 24 made of silicon rubber having a thickness of 1 mm. This pressing shaft 2
A shaft part 25 is protruded from both shaft ends of the shaft part 1.
5 is supported on the movable frame via bearings 26.

In order to restrict the axial movement of the pressing sleeve 20, a side guide member 27 is fitted on the shaft portion 25 of the pressing shaft 21, and the pressing sleeve 20 is provided on the side surface of the side guide member 27. Is restricted from moving in the axial direction (thrust direction). When the side guide member 27 and the elastic layer 23 of the pressure sleeve 20 come into contact with each other, the frictional resistance between them causes the pressure sleeve 2
0, the toner image T on the recording sheet P fluctuates, and image defects such as rubbing occur. Therefore, in the fixing device of this embodiment, the elastic layer 23 of the pressure sleeve 20 is connected to the side guide member 27. It is kept out of contact. Specifically, as shown in FIG. 4, the core 22 of the pressure sleeve 20 is projected from the elastic layer 23 at both ends in the axial direction, and only the core 22 contacts the side guide member 27 and The movement in the direction is restricted. Thereby, the frictional resistance acting between the side guide member 27 and the pressure sleeve 20 is reduced, and the rotation of the pressure sleeve 20 with respect to the heating roll 1 is performed smoothly.

On the other hand, the movable frame 4 is urged toward the fixed frame 3 by a pressing means (not shown), whereby the pressing shaft 21 is pressed against the heating roll 1 and the pressing sleeve 20 is And the pressing shaft 21. As a result, the pressure sleeve 20 is pressed against the heating roll 1, and when the heating roll 1 rotates, it rotates with the rotation. When the heating roll 1 and the pressing sleeve 20 are pressed against each other, the elastic layer 23 formed on the outer peripheral surface of the pressing sleeve 20 is crushed, and the heating roll 1 and the pressing sleeve 2 are pressed.
A nip area for sandwiching the recording sheet P is formed between the recording sheet P and the recording sheet P. The recording sheet P is given heat energy from the heating roll 1 while passing through the nip area, and the unfixed toner T transferred to the recording sheet P is melted. Further, the melted toner is crushed by the pressure contact between the heating roll 1 and the pressure sleeve 20 and is pressed against the recording sheet P. Thus, when the recording sheet P passes through the nip area, the toner image T transferred to the recording sheet P is fixed on the recording sheet P.

In order to obtain a good fixed image without defective fixing or rubbing of the toner image T, it is important that the heating roll 1 and the pressure sleeve 20 are pressed against each other with a uniform pressing force along the axial direction. It is. Further, when the nip region is formed with an uneven width along the axial direction, the transportability of the recording sheet P is deteriorated, and wrinkles are easily generated on the recording sheet P passing through the fixing device. It is also important that such a nip region is formed with a uniform width along the axial direction.

However, since the heating roll 1 is not completely rigid, when the heating roll 1 is pressed against the pressing sleeve 20 with both shaft ends supported by the fixed frame 3, as shown in FIG. Bends. Further, since the thickness of the core 11 of the heating roll 1 is reduced in order to suppress the heat capacity thereof, the heating roll 1 is crushed in the radial direction by the pressing of the pressing sleeve 20. Therefore, in order to generate a substantially uniform distribution of the pressing force in the axial direction in the nip region, it is necessary to determine the shape of the outer peripheral surface of the pressing shaft 21 in consideration of the amount of bending and crushing of the heating roll 1. is there. For this reason, in the fixing device of this embodiment, the amount of bending and crushing of the heating roll 1 generated when a constant load is applied to the heating roll 1 is obtained, and based on this, the outer peripheral surface of the pressing shaft 21 is determined. Shape is determined. FIG. 5 assumes that a load of 800 N is applied to both shaft ends of the heating roll 1 supported on the fixed frame 3, and the amount of displacement in the radial direction of the nip region caused by bending and crushing of the heating roll 1. Determined by the finite element method,
Are shown along the axial direction of FIG. That is, when the load is applied to the heating roll 1 from the radial direction, the nip region formed by the pressure contact between the heating roll 1 and the pressing sleeve 20 is bent as shown by the graph line in FIG. Become. Therefore, if the shape of the outer peripheral surface of the pressing shaft 21 is formed into a convex curved shape along the graph line, the distribution of the pressing force along the axial direction in the nip region can be made substantially uniform.

Further, even when the pressing shaft 21 is formed in a specific shape in this manner, the pressing sleeve 20 which is actually pressed against the heating roll 1 is deformed according to the shape of the pressing shaft 21 and heats. If it does not adhere to the roll 1, it becomes difficult to generate a uniform pressure distribution in the axial direction in the nip region. For this reason, in the fixing device of this embodiment, the rigidity of the pressing sleeve 20 in the radial direction is set smaller than those of the pressing shaft 21 and the heating roll 1. Since the heating roll 1 also needs to be deformed following the shape of the pressing shaft 21, the rigidity of the heating roll 1 in the radial direction is set to be smaller than that of the pressing shaft 21.
That is, when comparing the rigidity in the radial direction between the heating roll 1, the pressing sleeve 20, and the pressing shaft 21, the rigidity decreases in the order of the pressing shaft 21, the heating roll 1, and the pressing sleeve 20. Thereby, the heating roll 1 and the pressing sleeve 20 can be deformed along the specific shape given to the pressing shaft 21, and both can be pressed tightly.

The pressing shaft 21 of this embodiment is formed by processing a stainless steel rod into the above-described shape.
Elastic coating layer 24 having a uniform thickness with respect to the outer peripheral surface pressed against
Is covered. For this reason, when a uniform pressure distribution is obtained along the axial direction of the nip region, the amount of deformation of the elastic coating layer 24 also becomes uniform along the axial direction, and the width of the nip region is reduced in the axial direction. Along the line, it can be substantially uniform. Further, even in a case where the heat energy of the heating roll 1 flows into the elastic coating layer 24 to cause the thermal expansion of the elastic coating layer 24, the distribution of the thermal expansion amount of the elastic coating layer 24 is in the axial direction. Therefore, the pressure distribution in the nip region does not become uneven due to the thermal expansion of the elastic coating layer 24. Furthermore, since the pressure distribution in the axial direction in the nip region is uniform, even if the elastic coating layer 24 is worn with the use of the fixing device over time, the amount of wear is uniform along the axial direction. It is also possible to avoid the disadvantage that the pressure distribution becomes non-uniform over time.

FIG. 6 is a graph showing the result of measuring the pressure distribution in the nip region of the fixing device of the present embodiment having the above-described configuration, and the horizontal axis shows the position of the heating roll 1 in the axial direction. . As shown in this graph, in the fixing device of the present embodiment, the heating roll 1 and the pressure sleeve 20 could be pressed against each other with a substantially uniform pressing force along the axial direction. When the width of the nip region at this time was measured, it was 4 mm at the center in the axial direction and 4.2 mm at both ends, and a nip region having a substantially uniform width could be formed.
The fixing strength of the toner image T and the occurrence of wrinkles on the recording sheet P were observed by actually inserting the recording sheet P through the fixing device of this embodiment. Was satisfactory, and no wrinkles occurred on the recording sheet P.

Next, FIG. 7 shows another embodiment of the pressure sleeve 20. In the above embodiment, the pressing shaft 21
The elastic coating layer 24 is formed on the outer peripheral surface of the pressing shaft 21 and the pressing sleeve 20.
It is not necessarily formed on the outer peripheral surface of the pressing shaft 21 because it is for tightly contacting the pressure shaft and for preventing generation of noise due to such contact. That is, as shown in FIG. 7, an elastic coating layer 28 having a uniform thickness may be provided on the inner peripheral surface of the core 22 constituting the pressure sleeve 20. In this case, it is not necessary to form the elastic coating layer 24 on the outer peripheral surface of the pressing shaft 21.

FIG. 8 shows another embodiment of the pressing shaft. As described above, the pressing shaft 21 has an outer peripheral surface formed in a convex curved shape, and has a maximum outer diameter at a central portion in the axial direction, and a minimum outer diameter at both ends. The perimeter of the surface is different at the center and at both ends. However, the pressing sleeve 20 against which the pressing shaft 21 is pressed is connected to the heating roll 1.
In the above embodiment, the pressing shaft 2 is used to absorb the difference in the circumferential length.
1 and the pressure sleeve 20 have slipped. For this reason, the elastic coating layer 24 or 2 formed on the outer peripheral surface of the pressing shaft 21 or the inner peripheral surface of the pressure sleeve 20.
8 will be worn, and the amount of wear will be different at the axial center and at both ends. Therefore, in the above embodiment, as the use time of the fixing device is cumulatively increased, the elastic coating layer 24 or 28 is unevenly worn, the pressure distribution in the nip region is changed, and the width of the nip region is also changed. There was a concern.

Therefore, in the pressing shaft 5 shown in FIG.
A plurality of pressing disks 50 having different diameters are arranged on the support shaft 51, and these pressing disks 50 are rotatably supported on the support shaft 51, and a rotational speed difference due to a difference in circumference is determined for each pressing disk 50. It was configured to absorb. In other words,
The pressing shaft 21 of the embodiment is divided into a plurality of disk members, and the individual disk members are arranged rotatably with respect to the support shaft. With this configuration, the pressing disks 50 having different circumferential lengths can freely rotate with respect to the support shaft 51, so that when the pressing shaft 5 is rotated along with the pressing sleeve 20, each pressing disk 50 There is no slippage between the sleeve and the pressure sleeve 20, and wear of the elastic coating layer 24 or 28 is prevented. Accordingly, it is possible to prevent the pressure distribution in the nip region from fluctuating due to the use of the fixing device over time, and also possible to avoid a trouble that the width of the nip region changes.

FIG. 9 shows another example of the contact structure between the pressure sleeve 20 and the side guide member 27. As shown in FIG. In the embodiment shown in FIG. 4, only the core 22 of the pressure sleeve 20 is configured to contact the side guide member, and the frictional resistance between the pressure sleeve 20 and the side guide member 27 is reduced. However, in the example shown in FIG. 9, the surface and side surfaces of the elastic layer of the pressure sleeve 20 are covered with a PFA layer 29 having a thickness of 30 μm, and the PFA layer 29 is in contact with the side guide member 27. Since the friction resistance of the surface of the PFA layer 29 is lower than that of the elastic layer 23, the frictional resistance acting between the side guide member 27 and the pressure sleeve 20 is reduced in this example as well.
Is smoothly carried out with respect to the heating roll 1.

FIG. 10 also shows another example of the contact structure between the pressure sleeve 20 and the side guide member 27. In this example, the side guide member itself is constituted by the thrust ball bearing 30, and the side guide member 30 is configured to be able to support the rotation of the pressure sleeve 20 while restricting the axial movement thereof. In this example, the pressure sleeve 2
Since the frictional resistance hardly acts between the pressure guide sleeve 20 and the side guide member 30, the pressure sleeve 20 rotates more smoothly than in the example shown in FIG. 4 or FIG. Defects could be completely eliminated. In the example shown in FIG. 10, the thrust ball bearing itself is used as the side guide member. However, the thrust ball bearing is fixed to both ends of the pressurizing sleeve 20, and the thrust ball bearing is brought into contact with the mere plate side guide member 27. , The same result was obtained.

[0027]

As described above, according to the image fixing apparatus of the present invention, the shape of the outer peripheral surface of the metal pressing shaft is gradually reduced from the center in the axial direction to both ends. At the same time, an elastic coating layer having a uniform thickness is formed on the outer peripheral surface of the pressing shaft or the inner peripheral surface of the pressing sleeve, and the heating roll and the pressing roll are pressed with a substantially uniform pressing force along the axial direction. Since the nip area of the recording sheet is formed with a substantially uniform width along the axial direction while being pressed, the toner image can be fixed to the recording sheet with sufficient strength. It is possible to avoid a trouble that wrinkles and the like occur in the horn.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing an embodiment of an image fixing device of the present invention.

FIG. 2 is a schematic side view showing an embodiment of the image fixing device of the present invention.

FIG. 3 is a cross-sectional view illustrating a pressing shaft according to the embodiment.

FIG. 4 is an enlarged view showing a contact structure between a pressure sleeve and a side guide member according to the embodiment.

FIG. 5 is a graph showing a result of obtaining a displacement amount of a heating roll of an example by a finite element method.

FIG. 6 is a graph showing a pressure distribution in a nip region of the fixing device according to the embodiment.

FIG. 7 is a front sectional view showing another example of the pressure sleeve.

FIG. 8 is a front view showing another example of the pressing shaft.

FIG. 9 is an enlarged view showing a second embodiment of the contact structure between the pressure sleeve and the side guide member.

FIG. 10 is an enlarged view showing a third embodiment of a contact structure between a pressure sleeve and a side guide member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating roll, 20 ... Pressing sleeve, 21 ... Pressing shaft, 23 ... Elastic layer, 24 ... Elastic coating layer, 27 ... Side guide member

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Atsushi Endo 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Takashi Ohashi 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. Ebina Works F-term (reference) 2H033 AA15 AA31 BB15 BB28 BB33 BB35

Claims (6)

[Claims] 1. An image fixing device in which a recording sheet is inserted between a heating roll and a pressure roll that are in pressure contact with each other, and an unfixed toner image transferred to the recording sheet is melted and pressed against the recording sheet. In the pressure roll, a hollow cylindrical pressure sleeve having an elastic layer formed on its surface and rotating in accordance with the heating roll, and the pressure sleeve inserted into the hollow portion of the pressure sleeve Press contact with the heating roll, and a metal pressing shaft formed such that the shape of the outer peripheral surface in contact with the inner peripheral surface of the pressure sleeve gradually becomes narrower from the center in the axial direction toward both shaft ends, and An image fixing device comprising: an elastic coating layer formed with a uniform thickness on an outer peripheral surface of a pressing shaft or an inner peripheral surface of a pressure sleeve. 2. The image fixing device according to claim 1, wherein the rigidity of the heating roll, the pressing sleeve, and the pressing shaft in the radial direction decreases in the order of the pressing shaft, the heating roll, and the pressing sleeve. 3. A nip area of a recording sheet formed by press-contact of the heating roll and the pressure sleeve has a substantially uniform width along the axial direction of the heating roll. 3. The image fixing device according to 1 or 2. 4. The image fixing device according to claim 1, wherein the pressing shaft includes a support shaft and a plurality of driven disks rotatably arranged around the support shaft. apparatus. 5. A side guide member for restricting the axial movement of the pressure sleeve, and the side guide member and the elastic layer on the surface of the pressure sleeve are held in a non-contact manner. Item 2. The image fixing device according to Item 1. 6. The image fixing device according to claim 5, wherein a low friction member is interposed between the side guide member and the elastic layer of the pressure sleeve.