JP4897395B2 - Fixing device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a fixing device that fixes an unfixed image formed of a powder particle-like image forming substance (toner) on a sheet (recording medium), and a copying machine, printer, facsimile, printing machine, and the like provided with this fixing device. The present invention relates to an image forming apparatus.

In image forming apparatuses such as copying machines, facsimile machines, printers, and printing machines, copies and recorded articles are obtained by heating and fixing an unfixed image transferred and carried on a sheet (sheet) such as a recording medium. Can be obtained. There are also various types of recording media.
The fixing device used in the electrophotographic color image forming apparatus has only the toner melting performance because the toner thickness of the unfixed image transferred onto the paper to be heated and pressed is thicker than that at the time of monochrome image formation. In addition, image quality such as separation from the fixing roller, color developability, glossiness, gloss unevenness, and the like are in higher demand than monochrome images.

For this reason, in a conventional fixing device for a color image forming apparatus, an elastic layer (rubber layer or the like) is disposed on each of a heating roller and a pressure roller that are in pressure contact with each other to form a fixing roller, and the heating roller in the paper conveyance direction The width of the fixing nip between the pressure roller and the pressure roller is wider than that of a fixing device for a monochrome image forming apparatus.
Further, the thickness of the elastic layer on the heating roller side is made thicker than that of the pressure roller, so that the paper discharge direction of the fixing nip is different from the image surface of the recording medium, thereby increasing the separation margin.
Furthermore, there is also an auxiliary separating member that forcibly separates the recording medium from the heating roller with a separation claw or a separation plate. Further, by providing an elastic layer on the surface in contact with the toner image, it is possible to prevent uneven gloss and color unevenness by following the unevenness of the toner image and making uniform contact. As described above, in the prior art, various proposals have been made for problems in the fixing device (see, for example, Patent Documents 1 to 6).

In the fixing device, the heating roller is heated using a large-capacity heat source, and when the surface of the heating roller reaches a set temperature at which the color toner can be sufficiently melted, the warm-up is completed and the image forming apparatus can form an image. Become. If the heating roller is provided with an elastic layer, it takes a long time from the start of heating of the heating roller to the end of warm-up, and it is not possible to cope with the demand for power saving and high speed of the image forming apparatus.
In order to solve such a problem, 0.1 to 3.0 mm thick aluminum pipe or 0.3 to 3 mm thick iron pipe as in the case of the fixing device for monochrome image formation. In order to secure a thin heating roller provided with an elastic layer such as silicon rubber of ~ 3.0 mm and further having a surface coat (for example, PFA or PTFE) for improving releasability, and a fixing nip width, On the pressure roller side, there is a fixing device using an elastic layer such as silicon rubber or foamed silicon rubber of 3.0 to 10.0 mm.

In order to improve the strength, a rib is provided inside the heating roller. In this case, since the heat capacity of the heating roller is small and the elastic layer is thin, the temperature rise time is relatively short, and power saving can be achieved.
However, in the fixing device for color image formation, as described above, the elastic layer of the heating roller is thinner than the elastic layer of the pressure roller. In some cases, the toner image is discharged while being in contact with the heating roller, and a winding jam occurs. Even if the separation claw or separation plate forcibly peels off, if the wrapping force is large, the image surface may be scratched and the image quality may be significantly reduced.

Therefore, there is provided a fixing device for image formation in which a separation roller that is in pressure contact with the heating roller is provided on the downstream side of the pressure roller in the sheet conveying direction, and the fixing roller is configured by three rollers of the heating roller, the pressure roller, and the separation roller. This is proposed in Patent Document 1.
Further, the outer diameter of the peeling roller is made smaller than the outer diameter of the heating roller, and the surface hardness of the peeling roller is equal to or higher than the surface hardness of the heating roller. This is because the paper that has passed between the pair of rollers tries to wrap around the peripheral surface of the roller having a small outer diameter, and the nip portion where the elastic body on the peripheral surface of the heating roller becomes the peripheral surface of the peeling roller. This is because the sheet is deformed into a concave shape and the sheet is directed toward the peeling roller.

The peripheral surface of the pressure roller is sufficiently flexible compared to the peripheral surface of the heating roller to ensure a wide nip width, thereby enhancing the melting property of the color toner, and the toner on the peripheral surface of the heating roller by the peeling roller. The releasability of the paper and the peelability of the paper can be improved.
Further, since it is necessary to make the outer diameter of the peeling roller smaller than that of the heating roller, bending occurs when pressing the peeling roller against the heating roller, and the width of the peeling nip formed by the peeling roller and the heating roller is not uniform, In some cases, it is not possible to ensure stable paper separation.
Patent Documents 2 and 3 describe a heat supply roller that is pressed against the fixing roller downstream of the nip portion, and a peeling member that forms the nip portion with the fixing roller. Further, in order to prevent such unevenness of the peeling nip, in Patent Documents 4 to 6, the peeling roller is pressed by a backup roller from a substantially opposite side to the nip formed as a heating roller to prevent bending.
Japanese Utility Model Publication No. 4-87866 JP 2003-005551 A JP 2004-085625 A JP 2005-195649 A JP 2005-173030 A JP 2005-173032 A

However, since the heating roller is thinned and the heat capacity is reduced in order to shorten the heating time, in the case of Patent Documents 4 to 6, if paper having a narrow paper width is continuously passed, The temperature of the central portion of the heating roller, which is the paper region, decreases, and the end portion, which is the non-paper passing region, becomes high temperature.
If a wide sheet is passed in this state, the edge portion is at a high temperature, so uneven glossiness or hot offset of toner occurs, and the image quality is significantly degraded. In addition, the elastic layer and the release layer of the heating roller itself may be deteriorated and destroyed at a high temperature.

Further, in Patent Documents 2 and 3, the paper does not pass through the nip portion formed by the heat supply roller or the peeling member and the fixing roller, and the function of making the heat in the axial direction uniform, the concrete for making the heat uniform No specific means is described, and neither the temperature variation in the axial direction of the fixing member or the peeling member, nor the separation of the paper and the prevention of the temperature rise at the edge are described. In addition, when a thin heating roller is used, since the heat capacity is small, temperature unevenness in the axial direction occurs depending on the paper width during continuous paper passing, and gloss unevenness and poor fixing are likely to occur.
Accordingly, an object of the present invention is to fix the temperature unevenness in the axial direction of the heating roller in the entire region in consideration of the above-described situation, and to obtain a high-quality image at low energy and low cost regardless of the paper size. And an image forming apparatus including the fixing device.

In order to solve the above-described problems, a first aspect of the present invention is a fixing roller having a heat-resistant elastic layer, a pressure member in pressure contact with the fixing roller, a fixing roller and the pressure member. In the fixing device having a separation member that forms a second nip by being pressed against the fixing roller at a downstream side of one nip and separates the sheet from the fixing roller by deforming the heat-resistant elastic layer, the separation member includes: heat equalizing member der axial is, the material constituting the heat equalizing member is characterized by a heat pipe embedded in at least a metal or metal, a combination of hard insulation.
According to a second aspect of the present invention, in the fixing device according to the first aspect, the heat pipe includes a plurality of heat pipes .
According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the separation member is a crown-shaped roller .

According to a fourth aspect of the present invention, there is provided an image forming apparatus including the fixing device according to any one of the first to third aspects .

  According to the present invention, when the paper width is narrow, even when the temperature difference between the non-sheet passing area and the sheet passing area becomes large, the separation member is made of a heat uniformizing member having high thermal conductivity such as metal. Since the heat in the direction can be made uniform, abnormal images such as a difference in glossiness of the image (gloss unevenness) and hot offset (fixing failure) can be prevented, and the life of the fixing roller itself can be extended.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing the configuration of the fixing device according to the first embodiment of the present invention and the layer configuration of each roller. In FIG. 1, the fixing device is composed of three rollers.
That is, the fixing roller 1 arranged so as to form a first nip into which the paper P conveyed from the upstream side enters therebetween, the pressure roller 2 provided to face the fixing roller 1, and further downstream in the conveying direction. And a separation roller 3 provided opposite to the fixing roller 1 and forming a second nip therebetween.
A halogen heater 4 serving as a heat source is arranged in the fixing roller 1, and the surface of the fixing roller 1 is arranged outside by a temperature sensor and a control device (not shown) provided at the center in the substantially axial direction of the fixing roller 1. The temperature is controlled to an arbitrary temperature by controlling on / off.
The fixing roller 1 has an outer diameter of 30 to 40, and a silicon rubber of 0.2 to 1.0 mm is provided as a heat-resistant elastic layer 12 on a core metal 13 made of Al or Fe having a thickness of 0.4 to 1.0 mm. Further, a release layer 11 made of PFA or PTFE, which is a fluororesin of 10 to 50 μm, is provided on the outermost layer. The cored bar 13 is provided with a ring-shaped rib in order to improve the bending strength, whereby the cored bar 13 can be thinned, and the heat capacity can be reduced and the strength can be improved.

The pressure roller 2 has an outer diameter of φ20 to 40, and 5 to 10 mm of foamed silicon rubber is provided as an elastic layer 15 on the outer side of a solid metal core 16 made of Fe or stainless steel (SUS) of φ10 to 20, and the outermost layer is formed on the outermost layer. As the release layer 14, a tube made of PFA or PTFE is coated.
The pressure roller 2 is pressed against the fixing roller 1 by a spring (not shown) to form a first nip. The first nip has a nip width of 5 to 10 mm and a surface pressure of about 0.5 to ² kgf / cm ² . Further, the pressure roller 2 has an inverted crown shape in which the outer diameter is smaller at the center than at the end.
With such a configuration, when the nip is formed with the pressure roller 2 and the fixing roller 1, the deformation amount of the foamed silicon rubber that is the elastic layer 15 can be different between the center and the end. As a result, the conveyance speed of the paper continuously changes between the center and the edge, the center is slow, the edge is fast, and the force that pulls the paper P from the center to the edge works to prevent the generation of wrinkles. .

A separation roller 3 having a diameter of 8 to 18 is provided on the downstream side of the first nip. The outermost layer is coated with a fluororesin such as PFA or PTFE or tube-like as a release layer 17 for improving the release property with the toner.
The material of the solid core 18 is made of Fe, stainless steel (SUS), Al or Cu having high thermal conductivity. The separation roller 3 is pressed against the fixing roller 1 by a spring (not shown) to form a second nip.
The second nip is set to such a load that the nip width is 0.5 to 3 mm and the surface pressure is 2 kgf or more. In order to form a stable nip width, an elastic layer such as silicon rubber of about 0.05 to 0.2 mm may be provided between the core metal 18 and the release layer 17.
In this case, it is necessary to use an elastic layer that is thinner than the elastic layer 12 of the fixing roller 1 and has a high hardness, and the deformation of the elastic layer 12 of the fixing roller 1 can be larger than that of the separation roller 3 at the second nip. The paper direction can be set to the separation roller 3 side.

FIG. 2 is a schematic view showing an image forming apparatus that implements the fixing device of the present invention. An example of the fixing device 21 and the image forming apparatus 20 according to the present invention will be described with reference to FIG.
A paper feed tray 22 is disposed at the lower part of the main body of the image forming apparatus 20, and transfer paper P is stacked thereon. A paper feed roller 24 is disposed above the paper feed tray 22, and the transfer paper P is conveyed to the registration roller 26 after being separated one by one by a friction pad 25 pressed against the paper feed roller 24.
The sheet feeding tray 22, the sheet feeding roller 24, and the friction pad 25 constitute sheet feeding means. Above the registration roller 26, a photoconductor (image carrier) 27 and a transfer roller 28 are disposed across the vertical conveyance path B, and on the transfer paper P moving upward in the vertical conveyance path B, the photoconductor. 27, the toner image is transferred.

The photoreceptor 27, the developing unit 29, the charging unit 30, the cleaning unit 31, and the transfer roller 28 constitute an image forming unit A. A writing optical system 32 is arranged in the horizontal direction of the image forming unit A.
A fixing device 21 including a fixing roller 1 and a pressure roller 2 is disposed above the image forming unit A including the photoconductor 27 and fixes an unfixed toner image on the transfer paper P by heat and pressure.
The first and second paper discharge trays 31 and 32 are positioned above the image forming unit A and below the scanner unit 33 that reads the document image on the contact glass CG, and It is located near the end of the vertical conveyance path B.
A first paper discharge roller 34 is disposed immediately before the first paper discharge tray 31, and a second paper discharge roller 35 is disposed immediately before the second paper discharge tray 32. The first paper discharge tray 31 is a tray for normal use, and the second paper discharge tray 16 is an auxiliary tray used when sorting facsimiles, printer images, and the like.

Next, the operation will be described with reference to FIG. 1 and FIG. When the print signal is received, the fixing roller 1 starts rotating at a predetermined speed by a driving device (not shown). Following this, the pressure roller 2 and the separation roller 3 rotate.
In addition, the fixing roller 1 is heated by the halogen heater 4 inside the fixing roller 1, and paper can be passed at a predetermined temperature of 130 to 180 ° C. An unfixed toner image T is formed on the paper P by the image forming unit A and conveyed to the fixing device 21.

FIG. 3 is a schematic view showing an enlarged nip portion. Referring to FIG. 3, the paper P having the unfixed toner image T is sent to the first nip, and the toner image T is fixed to the paper P by heat and pressure. At this time, the paper discharge direction of the first nip is on the fixing roller 1 surface side, and the paper is discharged along the fixing roller 1.
The discharged paper passes through the second nip, and the elastic layer 12 of the fixing roller 1 is deformed into a concave shape by the pressing force of the separation roller 3, so that the direction C in FIG. The discharged paper P is reliably peeled off from the surface of the fixing roller 1 to prevent the occurrence of jam or the like.

When paper having a size smaller than that of the fixing roller 1 is continuously passed, the temperature of the paper passing area (center portion) of the fixing roller 1 is continuously taken away by the paper. Therefore, the halogen heater 4 (FIG. 1) is continuously turned on.
At this time, since the heat is not removed from the sheet P at the end of the fixing roller 1 in the non-sheet passing region, the temperature rises, but the heat is conducted to the separation roller 3 that is in pressure contact with the fixing roller 1, and the separation roller Since the heat conductivity 3 is higher in the axial direction, the heat at the end portion moves to the central portion, and temperature unevenness in the axial direction of the fixing roller 1 can be prevented to achieve a uniform temperature.
As a result, even when the fixing roller 1 is deteriorated or sheets of different sizes are continuously fed, temperature unevenness in the axial direction does not occur, and abnormal images such as uneven gloss of the image and hot offset can be prevented.

FIG. 4 is a schematic view showing the shape of the separation roller used in FIG. 2 for comparison. FIG. 5 is a schematic view showing a separation roller having a shape different from that in FIG. In the second embodiment of the fixing device, the configuration of the separation roller 3 is changed as shown in FIG. 5 with substantially the same configuration as in the first embodiment.
In FIG. 4, as described above, the separation roller 3 is configured by the solid cored bar 18 made of Fe, stainless steel (SUS), Al, or Cu, which has a high thermal conductivity. In FIG. 5, the separation roller 3 is provided with a heat pipe 36 at the center of the separation roller 3 so as to contact the hollow core metal 19.
Since the heat pipe 36 has a thermal conductivity 100 times or more that of Cu or Al, the temperature difference in the axial direction can be made smaller than that of the metal solid core 18 in the first embodiment.

FIG. 6 is a schematic view showing a configuration in which a plurality of heat pipes are arranged in the separation roller. In the third embodiment, the configuration of the separation roller 3 is changed with substantially the same configuration as in the second embodiment.
The separation roller 3 is provided with a plurality of heat pipes 37 having a diameter smaller than that of the second embodiment in the vicinity of the outer periphery of the cored bar 39 of the separation roller 3. A heat pipe 37 is disposed in the vicinity of the outer periphery, and by using a plurality of heat pipes, the heat in the axial direction can be made more efficient and more axial than in the second embodiment. The temperature difference can be reduced.

FIG. 7 is a schematic view showing a separation roller having a hard heat insulating material in the center. In the fourth embodiment, the configuration of the separation roller 3 is changed with substantially the same configuration as that of the third embodiment.
At the center of the separation roller 3, a hard heat insulating material 38 is bonded with a heat insulating material such as a hollow bead, ceramic fiber, or an embossed film laminated member with a silicon-based adhesive, or a hollow ceramic that is a porous ceramic. This hard heat insulating material 38 hardly contains an elastic body, is hard, has a high air content due to hollow glass beads and bubbles, has a heat conductivity of 0.2 W / mK or less, and has high heat insulating properties.

A plurality of heat pipes 37 having a small diameter are provided on the outer periphery in the vicinity of the outer periphery of the separation roller 3 as shown in FIG. Since the heat pipe 37 is in the vicinity of the outer periphery and the inside thereof is insulated, the apparent heat capacity can be reduced, so that the temperature rise time at the start-up of the apparatus can be shortened and the temperature difference in the axial direction can be reduced. Reduction is possible.
Thus, by using the hard heat insulating material 38 for a part of the separating member (separating roller) 3, the apparent heat capacity of the separating roller 3 is reduced and the heating time of the fixing roller 1 is shortened. Further, the axial heat of the fixing roller 1 can be made uniform by combining with a member having high thermal conductivity such as metal or heat pipe.

FIG. 8 is a schematic view showing a separation roller having a heat pipe inside the cored bar. As in the second to fourth embodiments, the separation roller 3 according to the fifth embodiment includes a heat pipe 36 inside the cored bar 39, and the diameter of the cored bar 39 differs in the longitudinal direction.
As shown in FIG. 8, the cored bar 39 has a crown shape in which the central part is the thickest (diameter a) and the diameter becomes narrower (diameter b) toward the end part. By adopting such a shape, the bending of the separation roller 3 is corrected when pressed against the fixing roller 1 (FIG. 3), and the pressure is pressed with a uniform pressure in the axial direction.
Accordingly, since the fixing roller 1 and the separation roller 3 are in contact with each other with a uniform nip width, the bias of heat conduction from the fixing roller 1 is smaller than in the second to fourth embodiments, and the shaft is more efficiently used. The temperature difference in the direction can be reduced.

  Thus, by forming the cored bar 39 of the separation roller 3 into a crown shape and using a metal or a heat pipe, it is possible to reduce bending and heat conduction unevenness caused by the bending and to uniformize heat in the axial direction. Become.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of the fixing device according to the first embodiment and a layer configuration of each roller according to the present invention. 1 is a schematic diagram illustrating an image forming apparatus that implements a fixing device of the present invention. It is the outline which expands and shows a nip part. It is the schematic which shows the shape of the separation roller used in FIG. 2 shown for a comparison. It is the schematic which shows the separation roller which has a shape different from FIG. It is the schematic which shows the structure which has arrange | positioned the several heat pipe in the separation roller. It is the schematic which shows the separation roller which has a hard heat insulating material in the center. It is the schematic which shows the separation roller provided with a heat pipe inside a metal core.

Explanation of symbols

A Image forming apparatus
T Toner (toner image)
P paper (recording medium)
1 Fixing roller 2 Pressure member (Pressure roller)
3 Separation member (separation roller, heat equalization member)
4 Halogen heater 12 Elastic layer (heat-resistant elastic layer, silicon rubber)
13 Core metal (for fixing roller 1)
18 Solid metal core (for separation roller 3)
19 Hollow metal core (for separation roller 3)
36 heat pipe 37 heat pipe 38 hard heat insulating material 39 cored bar (for the separation roller 3)

Claims (4)

A fixing roller having a heat-resistant elastic layer, a pressure member pressed against the fixing roller, and a second nip pressed against the fixing roller at a downstream side of the first nip formed by the fixing roller and the pressure member. In a fixing device having a separating member that separates a sheet from the fixing roller by forming and deforming the heat-resistant elastic layer,
The separating member is Ri heat uniformizing member der axial, the material constituting the heat equalizing member is characterized by a heat pipe embedded in at least a metal or metal, a combination of rigid insulation material Fixing device. The fixing device according to claim 1, wherein the heat pipe includes a plurality of heat pipes . The fixing device according to claim 1, wherein the separating member is a crown-shaped roller . An image forming apparatus comprising the fixing device according to claim 1 .

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