JP2008209515A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device preventing image irregularities by improving contact of transfer paper with a pressure roller and achieving self-separation of the transfer paper. <P>SOLUTION: The fixing device is equipped with: an endless fixing belt provided with an elastic layer; a rotatable heating roller having a heating means and supporting the fixing belt from the inside; a separation roller driven to rotate, arranged on a downstream side from the heating roller and supporting the fixing belt from the inside; and the pressure roller press-contacting with the heating roller and the separation roller through the fixing belt and also pressing the fixing belt positioned between the heating roller and the separation roller to form a fixing nip. The separation roller has an elastic layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device that melts and fixes an unfixed toner image.

  In an image forming apparatus such as a copying machine or a facsimile, a toner image formed on the surface of a photosensitive drum is transferred onto a transfer sheet and fixed by a fixing device. The fixing device includes a heating roller that heats and melts the toner on the transfer paper, a pressure roller that presses and contacts the heating roller to fix the toner onto the transfer paper, and the heating roller from the inside. A heat roller fixing device including a supported endless fixing belt or the like is generally used.

  In such a heat roller fixing device, in order to secure a sufficient fixing nip width for fixing the toner on the transfer paper, conventionally, an endless fixing belt is used for forming the fixing nip. Specifically, two support rollers that support the belt from the inner peripheral side of the fixing belt and a pressure roller are brought into contact with each other through the fixing belt, and the outer peripheral surface of the fixing belt is brought into contact with the pressure roller by this contact. The fixing nip is formed by abutting against the fixing nip. When the transfer paper passes through the fixing nip and the toner is fixed, the transfer paper is separated by the curvature of the separation roller that is one of the support rollers.

  However, in the conventional fixing device, there is a case where the contact state between the transfer paper and the pressure roller is poor in a portion where the fixing belt is in contact with only the pressure roller in the fixing nip. In this case, there is a problem that the toner is not sufficiently fixed, and the separation roller affects the image at the time of separation, causing image disturbance such as toner peeling.

  In order to solve this problem, Patent Document 1 discloses that the fixing belt is driven by a support roller (separation roller) in order to increase the degree of adhesion of the transfer paper to the pressure roller, and the fixing belt is attached to the nip portion (fixing nip). A fixing device driven by pulling is disclosed.

  In this fixing device, the support roller (separation roller) is composed of a hard roller having no elastic layer, and the opposing roller (pressure roller) is a soft roller having an elastic layer in order to ensure the separation of the transfer paper. It consists of With this configuration, the pressure roller is distorted at the exit of the fixing nip (on the separation roller side), and separation is performed by changing the traveling direction of the transfer paper.

  However, in the fixing device described in Patent Document 1, since the separation roller is constituted by a hard roller, only the pressure roller is distorted in the fixing nip, and in particular, in the case of a color image having a large amount of toner to be transferred. The problem remains that it is difficult to ensure separation performance only by the pressure roller strain.

JP 2003-330295 A

  The present invention has been made to solve the above-mentioned problems of the prior art, and improves the degree of adhesion of the transfer paper to the pressure roller, enables self-separation of the transfer paper, and prevents image disturbance. It is an object of the present invention to provide a fixing device that can be prevented.

  The invention according to claim 1 includes an endless fixing belt provided with an elastic layer, a heating unit having a heating unit, and a rotatable heating roller that supports the fixing belt from the inside. A separation roller that is disposed further downstream and supports the fixing belt from the inside, is in pressure contact with the heating roller and the separation roller via the fixing belt, and is positioned between the heating roller and the separation roller. The present invention relates to a fixing device including a pressure roller that presses the fixing belt to form a fixing nip, wherein the separation roller includes an elastic layer.

  The invention according to claim 2 relates to the fixing device according to claim 1, wherein the pressure roller is driven to rotate, and the fixing belt is driven together with the rotation of the separation roller.

  The invention according to claim 3 is characterized in that the pressure at the portion where the separation roller and the pressure roller are in pressure contact is stronger than the pressure at the portion where the heating roller and the pressure roller are in pressure contact. Item 3. The fixing device according to Item 1 or 2.

  In the invention according to claim 4, the heating roller is a roller having no elastic layer, the pressure roller and the separation roller are rollers having an elastic layer, and the hardness of the surface of the heating roller is h1, 4. The fixing according to claim 3, wherein when the hardness of the surface of the pressure roller is h2 and the hardness of the surface of the separation roller is h3, the magnitude relationship of these hardnesses is h1> h2> h3. Relates to the device.

  The invention according to claim 5 relates to the fixing device according to any one of claims 1 to 4, wherein a driving rotation speed of the separation roller is higher than a driving rotation speed of the pressure roller.

  A sixth aspect of the present invention relates to the fixing device according to any one of the first to fifth aspects, further comprising a tension roller that supports the fixing belt from the inside.

  According to the first aspect of the present invention, there is provided an endless fixing belt provided with an elastic layer, a heating roller and a separation roller for supporting the fixing belt from the inside, and a pressure roller. Since the separation roller has an elastic layer, the separation roller is distorted by the curvature of the separation roller, the pressure contact with the pressure roller, and the driving of the separation roller itself, and the fixing belt supported by the separation roller is also distorted. As a result, the driving speed of the fixing belt changes and a minute difference is generated between the transfer paper and the moving speed of the transfer paper. Therefore, the degree of contact between the transfer paper and the fixing belt is reduced, and the transfer paper is easily separated. Therefore, the transfer paper can be self-separated by the curvature of the separation roller.

  According to the second aspect of the invention, not only the separation roller but also the pressure roller is driven and rotated, so that the fixing belt is driven without bending. As a result, the degree of adhesion of the transfer paper conveyed to the fixing belt to the pressure roller is increased, and the toner is sufficiently fixed on the transfer paper, so that the image is hardly disturbed and the gloss of the toner is increased.

  According to the third aspect of the invention, the pressure at the portion where the separation roller and the pressure roller are in pressure contact is stronger than the pressure at the portion where the heating roller and the pressure roller are in pressure contact, so that the separation serving as the exit of the fixing nip is performed. On the roller side, along with the curvature of the separation roller, the transfer paper is bent and the transfer paper is self-separated. Further, since the pressure at the outlet of the fixing nip is strong, the transfer paper is strongly pressed by the separation roller via the fixing belt, so that the toner can firmly penetrate the transfer paper and is firmly fixed. .

  According to the invention of claim 4, the heating roller does not have an elastic layer, and the pressure roller and the separation roller have an elastic layer. When the hardness of the surface of the heating roller is h1, the hardness of the surface of the pressure roller is h2, and the hardness of the surface of the separation roller is h3, the magnitude relationship between these hardnesses is h1> h2> h3. Since the heating roller does not have an elastic layer, the heat from the heating means is transmitted to the transfer paper without passing through the elastic layer, so that the toner image can be sufficiently dissolved. Since h2> h3, the pressure on the separation roller side of the fixing nip is strong, and the separation roller has an elastic layer, so that the separation roller is at the pressure contact portion between the separation roller and the pressure roller. It will be distorted. As the separation roller is distorted as described above, the fixing belt supported by the separation roller is also distorted. As a result, the driving speed of the fixing belt changes, and a minute difference is generated between the transfer paper and the moving speed of the transfer paper. Therefore, the degree of adhesion between the transfer paper and the fixing belt is reduced, and the transfer paper is easily separated. .

  According to the fifth aspect of the present invention, since the driving rotation speed of the separation roller is higher than the driving rotation speed of the pressure roller, distortion occurs in the driving direction of the fixing belt in the separation roller. As a result, the fixing belt supported by the separation roller is also distorted, and the driving rotation speed of the fixing belt changes, so that a slight difference is generated between the transfer belt and the moving speed. As a result, the degree of adhesion between the transfer paper and the fixing belt decreases, and the transfer paper is easily separated.

  According to the invention which concerns on Claim 6, the tension roller which supports a fixing belt from an inner side is further provided. As a result, the fixing belt can be driven stably.

Hereinafter, a preferred embodiment of a fixing device according to the present invention will be described with reference to the drawings.
FIG. 1 is a side view showing a schematic configuration example of an embodiment of a fixing device (1) according to the present invention.
The fixing device (1) according to this embodiment includes a heating roller (2), a pressure roller (3), a separation roller (4), a tension roller (5), and a fixing belt (6).

The heating roller (2) is a rotatable roller that supports the fixing belt (6) from the inside. The heating roller (2) is pressed by a pressing spring (not shown) and is connected to the pressure roller (3) via the fixing belt (6). Press contact. This pressure contact portion is located at the entrance of the fixing nip (7). The heating roller (2) is a cylindrical hollow rigid body (21) made of a metal having high thermal conductivity such as aluminum. In order to prevent sticking of the transfer paper (50) and the molten toner, the surface thereof is covered with a material having good releasability such as a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) tube. The outer diameter of the heating roller (2) is preferably 20 to 40 mm.
The inner surface of the rigid body (21) of the heating roller (2) is painted black, and a halogen lamp (8) as heating means is provided at the center of the roller. When the halogen lamp is turned on and the inner surface of the black-colored heating roller (2) is irradiated, the radiant heat is absorbed by the heating roller (2). Thereby, the heating roller (2) is efficiently heated. When the heating roller (2) is heated, it supplies heat to the fixing belt (6) while rotating.

  In addition, as a heating means, it is not restricted to this, The heating apparatus using the induction heating method may be sufficient. This device is provided with a coil wound in a spiral. By causing a high frequency current to flow through the coil, an induced eddy current is generated in the heating roller (2) by the generated high frequency magnetic field, and Joule heat is generated in the heating roller (2) itself by the skin resistance of the heating roller (2). According to this apparatus, it is possible to raise the temperature of the heating roller (2) in a short time compared to indirect heating such as a halogen lamp, and energy loss due to heat generation, light leakage, etc. other than the heating roller (2) is reduced. Less.

The pressure roller (3) is a rotatable roller that drives the fixing belt (6). The pressure roller (3) presses the heating roller (2) through the fixing belt (6) and supports the fixing belt (6). Drive. The pressure roller (3) is also driven and rotated to drive the fixing belt (6) without bending. The pressure roller (3) is a hollow rigid body (31), and includes a halogen lamp (8) as heating means inside. An elastic layer (32) made of, for example, silicon rubber is provided on the outer surface of the rigid body (31). The rubber hardness of the elastic layer (32) of the pressure roller (3) is about “ASKER C 50-60” (Japan Rubber Association Standard (SRIS) 0101), and its outer diameter is 35-50 mm. Is preferred.
The heating roller (2) is pressed by the pressure roller (3) to form the fixing nip (7). The transfer paper (50) on which the unfixed toner image is formed is conveyed to the fixing nip (7) and passes through the fixing nip (7) by the rotation of the heating roller (2) and the pressure roller (3). . When the transfer paper (50) passes through the fixing nip (7), it is heated and pressurized by the heating roller (2) and the pressure roller (3), so that the unfixed image on the transfer paper (50) is unfixed. The toner image is melted and fixed on the transfer paper (50).

  The separation roller (4) is a roller that is driven and rotated, and is positioned downstream of the heating roller (2), that is, at the exit of the fixing nip (7), and supports the fixing belt (6). The rotation speed of the separation roller (4) is about 1.005 to 1.02 when the rotation speed of the pressure roller is 1. If this speed is too small, the amount of strain tends to decrease. On the other hand, if the speed is too high, the image is rubbed to cause image defects. The separation roller (4) is a hollow roller made of an elastic layer. As the elastic layer, for example, an elastic body such as sponge or rubber, foamed rubber or the like is used. The rubber hardness of the elastic layer of the separation roller (4) is about “ASKER C 25-40” (Japan Rubber Association Standard (SRIS) 0101). Since the separation roller (4) has an elastic layer, the separation roller (4) is distorted by the curvature of the separation roller (4), the pressure contact with the pressure roller (3), and the driving of the separation roller (4) itself. The fixing belt (6) supported by the separation roller (4) is also distorted.

  As described above, distortion occurs in the fixing belt (6), so that the driving speed of the fixing belt (6) is changed, and a minute difference is generated between the moving speed of the transfer paper (50). As a result, the degree of adhesion between the transfer paper (50) and the fixing belt (6) decreases, and the transfer paper (50) is easily separated.

  The separation roller (4) has a predetermined radius of curvature and presses the fixing belt (6). When the separation roller (4) has a predetermined radius of curvature, the transfer paper (50) is separated from the fixing belt (6) by the curvature separation when the fixing belt (6) is pressed. In order to perform the curvature separation, it is necessary to make the outer diameter of the separation roller (4) below a certain value. This is because if the outer diameter is too large, it is difficult to reliably peel the transfer paper (50) from the fixing belt (6). On the other hand, if the outer diameter of the separation roller (4) is too small, the durability of the fixing belt (6) will be affected. For this reason, it is preferable that the outer diameter of the separation roller (4) is 10 to 20 mm.

  As described above, the heating roller (2) is a rigid body, the pressure roller (3) has a rubber hardness of ASKER C 50-60, and the separation roller (4) has a rubber hardness of ASKER C 25-40. It is. Therefore, the magnitude relationship of the hardness (h1, h2, and h3) of the surfaces of the heating roller (2), the pressure roller (3), and the separation roller (4) is h1> h2> h3. This causes the separation roller (4) to be distorted at the pressure contact portion between the separation roller (4) and the pressure roller (3), coupled with the strong pressure on the separation roller side of the fixing nip (7). It becomes. As the separation roller (4) is distorted as described above, the fixing belt (6) supported by the separation roller (4) is also distorted. As a result, the driving speed of the fixing belt (6) is changed, and a minute difference is generated between the moving speed of the transfer paper (50), so that the degree of adhesion between the transfer paper (50) and the fixing belt (6) is increased. As a result, the transfer paper (50) is easily separated.

  The rotation speed of the separation roller (4) is 1.005 to 1.02 when the pressure roller speed is 1, and the rotation speed of the separation roller (4) is the pressure roller (3 ), The distortion occurs in the driving direction of the fixing belt (6) in the separation roller (4). For this reason, the fixing belt (6) supported by the separation roller (4) is also distorted, the driving speed of the fixing belt (6) is changed, and a minute amount between the moving speed of the transfer paper (50). There is a difference. As a result, the degree of adhesion between the transfer paper (50) and the fixing belt (6) decreases, and the transfer paper (50) is easily separated.

  The fixing belt (6) is an endless belt provided with an elastic layer, and is supported from the inside of the belt by a heating roller (2), a separation roller (4), and a tension roller (5). The fixing belt (6) has a three-layer structure including a base material layer, an elastic layer, and a surface layer. The base material layer has a thickness of about 30 to 100 μm and is formed of polyimide resin, nickel, SUS (stainless steel), or the like. The elastic layer has a thickness of about 100 to 500 μm and is formed of silicon resin or the like. The surface layer is formed of a PTFE (polytetrafluoroethylene) coat, a fluororesin such as a PFA tube, or the like in consideration of releasability with respect to the toner. When the fixing belt (6) is pressed against the separation roller (4), the elastic layer is deformed. Due to the deformation of the elastic layer, the transfer paper (50) is prevented from being wound around the fixing belt (6), and separability from the fixing belt (6) is obtained.

  The tension roller (5) is a support member that supports the fixing belt (6), and is pulled by the spring (10) to apply tension to the fixing belt (6). By providing the tension roller (5), fatigue of the fixing belt (6) can be reduced. The tension roller (5) may be made of a metal having high thermal conductivity such as aluminum, and the surface thereof may be covered with a fluororesin or the like. The outer diameter of the tension roller (5) is preferably 10 to 20 mm as in the outer diameter of the separation roller (4) or slightly smaller than the separation roller (4).

  FIG. 2 is a view showing a pressure distribution in the fixing nip (7) in the embodiment of the fixing device (1) according to the present invention. As shown in the figure, the pressure at the pressure contact portion (separation roller side) between the separation roller (6) and the pressure roller (3) is the pressure contact portion (heating roller side) between the heating roller (2) and the pressure roller (3). ) Is stronger than the pressure in By applying a strong pressing force to the separation roller side, the fixing belt (6) is distorted, and a minute difference is generated between the moving speed of the transfer paper (50) and the moving speed of the fixing belt (6). As a result, on the separation roller side, the degree of adhesion between the transfer paper (50) and the fixing belt (6) decreases, and the transfer paper (50) is bent together with the curvature of the separation roller (4), whereby the transfer paper (50 ) Self-separate.

  In addition, since a predetermined pressure is applied to a portion between the fixing nip outlet and the inlet, that is, a portion where the pressure roller (3) is in contact with the fixing belt (6), image roughness due to pressure loss is also caused. Does not occur.

  Further, on the separation roller side, the transfer paper (50) is strongly pressed against the separation roller (4) via the fixing belt (6), so that the toner can penetrate into the transfer paper (50) firmly and be strong. To settle.

  The present invention is suitably used in a heat roller fixing apparatus in which toner is heated and melted by a heat roller.

1 is a side view illustrating a schematic configuration example of an embodiment of a fixing device according to the present invention. FIG. 4 is a diagram illustrating a pressure distribution at a fixing nip in the embodiment of the fixing device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Heating roller 3 Pressure roller 4 Separation roller 5 Tension roller 6 Fixing belt 7 Fixing nip 8 Halogen lamps 21, 31 Rigid body 32 Elastic layer

Claims (6)

An endless fixing belt provided with an elastic layer;
A rotatable heating roller having heating means and supporting the fixing belt from the inside;
A driving roller and a separation roller disposed downstream of the heating roller and supporting the fixing belt from the inside;
A pressure roller that is in pressure contact with the heating roller and the separation roller via the fixing belt and that presses the fixing belt located between the heating roller and the separation roller to form a fixing nip; A fixing device,
The fixing device, wherein the separation roller has an elastic layer.   The fixing device according to claim 1, wherein the pressure roller is driven to rotate, and the fixing belt is driven together with the rotation of the separation roller.   3. The fixing according to claim 1, wherein a pressure at a portion where the separation roller and the pressure roller are in pressure contact is stronger than a pressure at a portion where the heating roller and the pressure roller are in pressure contact. apparatus. The heating roller is a roller having no elastic layer, and the pressure roller and the separation roller are rollers having an elastic layer,
When the hardness of the surface of the heating roller is h1, the hardness of the surface of the pressure roller is h2, and the hardness of the surface of the separation roller is h3, the magnitude relationship between these hardnesses is h1>h2> h3. The fixing device according to claim 3.   The fixing device according to claim 1, wherein a driving rotation speed of the separation roller is higher than a driving rotation speed of the pressure roller.   The fixing device according to claim 1, further comprising a tension roller that supports the fixing belt from the inside.

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