JP2006011217A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing hot offsets from being generated at both ends of a belt. <P>SOLUTION: The fixing device 10 is equipped with a fixing roller 11, a counter roller 12 which is arranged in parallel to the fixing roller 11 and made of a nonmagnetic material, an endless belt 13 which is wound around and between the fixing roller 11 and counter roller 12, an induction coil 14 which heats the fixing belt 13 by electromagnetic induction, and a pressure roller 16 which presses the fixing roller 11 across the fixing belt 13, and passes recording paper P between the fixing belt 11 and pressure roller 16 to fix unfixed toner on the recording paper P. The fixing belt 11 has a laminated structure of a base material, an elastic layer, and a peeling layer in this order starting from the bottom, and the base material is made of a material in which magnetism stabilizing alloy is dispersed, the Curie temperature of the magnetism stabilizing alloy being set lower than the hot offset of toner. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a belt-type fixing device using electromagnetic induction heating, and an image forming apparatus such as a copying machine, a printer, and a facsimile equipped with the fixing device.

  A belt-type fixing device using electromagnetic induction heating includes a fixing roller, a counter roller made of a nonmagnetic material arranged in parallel with the fixing roller, and an endless fixing belt wound between the fixing roller and the counter roller. And an induction coil for heating the fixing belt from the outside and a pressure roller for pressing the fixing roller via the fixing belt. Then, the recording paper is passed between the fixing belt and the pressure roller, and at this time, the unfixed toner on the recording paper is fixed by the heat from the fixing belt and the pressing force by the pressure roller (see, for example, Patent Document 1). ).

  In general, the fixing belt has a laminated structure in which a base material 1, a heat generating layer 2, an elastic layer 3, and a release layer 4 are laminated in order from the bottom as shown in a cross section in FIG.

  The base material 1 consists of an endless belt and is formed of a heat resistant resin. As a material of the heat resistant resin, polyimide, polyamideimide, polyetherketone (PEEK) or the like is used. From the rigidity and heat capacity of the fixing belt, the thickness of the substrate 1 is usually set to 20 μm to 100 μm.

As the heat generating layer 2, a metal such as SUS, iron, nickel, manganese, titanium, chromium, or copper is used. The elastic layer 3 is necessary for obtaining image uniformity, and heat-resistant rubber such as silicone rubber or fluororubber of about 100 to 300 μm is used. The release layer 4 is made of a fluorine resin or the like having excellent heat resistance and durability because it is in pressure contact with the transfer paper and toner.
JP 11-329700 A

  However, in the conventional fixing device, since the fixing belt is merely heated by the induction coil and the temperature of the fixing belt is not controlled, hot offset tends to occur at both ends of the belt. In other words, when small size recording paper is continuously passed, the temperature increases at both ends of the belt because heat is not taken away by the recording paper. When large size recording paper is passed in this state, There is a problem that hot offset occurs in the area.

  Further, in the conventional fixing device, since the end portion of the opposing roller has a bearing or the like and has a large heat capacity, when the fixing belt starts to be heated by the induction coil, the heat escapes to the opposite roller end portion side. As shown in FIG. 10, the temperature rise at the end of the opposed roller is slower than the temperature rise at the center of the opposed roller, and as a result, the time until the fixing device becomes ready for use, that is, the rise time becomes longer. There is also.

  SUMMARY OF THE INVENTION A first object of the present invention is to provide a fixing device and an image forming apparatus that can prevent hot offset from occurring at both end portions of a belt.

  A second object of the present invention is to provide a fixing device and an image forming apparatus that can shorten the rise time of the apparatus.

  In order to solve the first problem, the invention described in claim 1 includes a fixing roller, a counter roller made of a nonmagnetic material arranged in parallel to the fixing roller, the fixing roller, and the counter roller. An endless fixing belt wound between the fixing belt, induction heating means for electromagnetically heating the fixing belt, and a pressure roller for pressing the fixing roller via the fixing belt, A fixing device that passes recording paper between the pressure roller and fixes unfixed toner on the recording paper. The fixing belt includes a base material, an elastic layer, and a release layer laminated in order from the bottom. The base material is formed of a material in which a magnetic shunt alloy is dispersed, and the Curie temperature of the magnetic shunt alloy is set lower than the hot offset temperature of the toner.

  According to the above configuration, the base material of the fixing belt is formed of a material in which a magnetic shunt alloy is dispersed, and the Curie temperature of the magnetic shunt alloy is set lower than the hot offset temperature of the toner. Even if the paper is continuously fed, the temperature at both ends of the fixing belt is kept below the hot offset temperature, and as a result, even if the small size recording paper is continuously fed and then the large size recording paper is passed, Hot offset does not occur at both ends of the belt.

  According to a second aspect of the present invention, there is provided a fixing roller, a counter roller arranged in parallel with the fixing roller, and an endless fixing made of a nonmagnetic material wound around the fixing roller and the counter roller. A belt, induction heating means for electromagnetically heating the counter roller, and a pressure roller that presses the fixing roller via the fixing belt, and a recording sheet is placed between the fixing belt and the pressure roller. A fixing device that passes through and fixes unfixed toner on the recording paper, wherein a magnetic shunt alloy is provided on the outer peripheral surface of the facing roller, and the Curie temperature of the magnetic shunt alloy is lower than the hot offset temperature of the toner. It is characterized by being set.

  According to the above configuration, the magnetic shunt alloy is provided on the outer peripheral surface of the opposing roller, and the Curie temperature of the magnetic shunt alloy is set lower than the hot offset temperature of the toner. However, the temperature at both ends of the fixing belt is kept below the hot offset temperature. As a result, even if a small size recording paper is continuously fed and then a large size recording paper is passed, No hot offset will occur.

  According to a third aspect of the present invention, in the first or second aspect, the opposing roller has a cylindrical portion, and the thickness of the cylindrical portion is longer than the central portion along the axial direction of the opposing roller. Is characterized by being thinly formed.

  In order to solve the second problem described above, the invention according to claim 4 includes a fixing roller, a counter roller arranged in parallel with the fixing roller, and a gap between the fixing roller and the counter roller. An endless fixing belt wrapped around the fixing roller; induction heating means for electromagnetically heating the counter roller or the fixing belt; and a pressure roller for pressing the fixing roller via the fixing belt. A fixing device for passing recording paper between a belt and the pressure roller to fix unfixed toner on the recording paper, wherein the opposing roller has a cylindrical portion, and the thickness of the cylindrical portion is Is characterized in that both end portions are formed thinner than the central portion along the axial direction of the opposing roller.

  According to the above configuration, since the thickness of the cylindrical portion of the opposing roller is formed so that both ends are thinner than the central portion along the axial direction of the opposing roller, the heat capacity at both ends of the opposing roller is reduced, It can suppress that the heat | fever by electromagnetic induction heating escapes to the opposing roller edge part side. As a result, it is possible to shorten the rise time until the fixing device becomes usable.

  The invention described in claim 5 is an invention of an image forming apparatus, wherein the fixing device according to any one of claims 1 to 4 is mounted.

  According to the present invention, the temperature of the fixing belt does not rise above the hot offset temperature of the toner. Therefore, even if the large-size recording paper is passed after the small-size recording paper is continuously fed, the belt Hot offset can be prevented from occurring at both ends.

  Further, the counter roller has a small heat capacity at both ends of the cylindrical portion, and as a result, the rising time until the fixing device is ready for use can be shortened.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a fixing device 10 according to a first embodiment of the present invention. As shown in the figure, the fixing device 10 includes a fixing roller 11, a counter roller (heating roller) 12 that is arranged in parallel with the fixing roller 11 and is made of a nonmagnetic material, and a fixing roller 11 and a counter roller 12. An endless fixing belt 13 wound around and having a magnetic material inside, an induction coil (induction heating means) 14 disposed on the side of the opposing roller 12 for electromagnetic induction heating, and a fixing belt 13 And a pressure roller 16 that presses the fixing roller 11 and forms a nip portion 15 on the fixing belt 13.

  The fixing roller 11 has a heat insulating layer on the outside of a core metal such as aluminum or iron, and has an outer diameter set to 40 mm, for example. Since the heat insulation layer needs heat resistance, silicone rubber (including sponge) is used. The lower the thermal conductivity of the material used for the heat insulating layer, the more effective it is, and it is generally preferable to be 0.2 W / m / K or less. The counter roller 12 is formed of aluminum, SUS, or the like whose core metal is a nonmagnetic material.

  In the pressure roller 16, a heat-resistant elastic layer such as silicone rubber is formed on the outer periphery of the core metal, and a surface release layer made of fluorine resin or the like is formed on the outer periphery of the heat-resistant elastic layer. Further, the surface hardness of the pressure roller 16 is formed to be higher than the surface hardness of the fixing roller 11 in order to improve the separation of the recording paper P from the fixing belt 13. Therefore, when the fixing roller 11 is pressed by the pressure roller 16 via the fixing belt 13, a part of the fixing belt 13 is deformed in a convex shape toward the fixing roller 11, and a nip portion 15 is formed in the fixing belt 11. . The thickness of the heat resistant elastic layer of the pressure roller 16 is about 1 mm to several mm.

  The induction coil 14 is wound around an exciting core 17 made of ferrite or permalloy and having a substantially concave cross section. When a high frequency current of several kilohertz to several hundred kilohertz is passed through the induction coil 14, an induction current is generated in the fixing belt 13. Due to this induced current, the fixing belt 13 generates heat locally in the vicinity of the induction coil 14 and rapidly rises in temperature.

  Further, a temperature sensor 18 for detecting the temperature of the fixing belt 13 heated by electromagnetic induction and a control device 19 for taking in a detection signal from the temperature sensor 18 and controlling a high-frequency current flowing through the induction coil 14 are provided. Yes.

  Further, a guide plate 20 that conveys the recording paper P to the fixing device 10 is provided below the facing roller 12. Unfixed toner T adheres to the surface of the recording paper P.

  FIG. 2 is a longitudinal sectional view of the fixing belt 13. As shown in FIG. 2, the fixing belt 13 has a laminated structure in which a base material 13a, an elastic layer 13b, and a release layer 13c are laminated in order from the lower side.

  The substrate 13a is formed of an endless belt, and a magnetic shunt alloy powder is blended in the resin based on a heat resistant resin. As the material of the heat-resistant resin as a base, polyimide, polyamideimide, polyetherketone (PEEK), or the like can be used. In addition, the thickness of the base material 13a is desirably 20 μm to 100 μm from the rigidity and heat capacity of the belt.

  The elastic layer 13b is necessary for obtaining image uniformity, and heat-resistant rubber such as silicone rubber or fluororubber of about 100 to 300 μm is used.

  The release layer 13c is in pressure contact with the recording paper P and the toner T. For this reason, as the release layer 13c, a fluorine resin or the like excellent in heat resistance and durability is preferable.

  In this embodiment, as described above, the base material 13a is formed of a material in which a magnetic shunt alloy is dispersed. Here, the Curie temperature of the magnetic shunt alloy is set lower than the hot offset temperature of the toner. For example, when the hot offset temperature in the fixing device 10 is 205 ° C., a powder made of, for example, an iron-nickel alloy is dispersed in the resin of the base material 13a so that the Curie temperature of the magnetic shunt alloy is 200 ° C. (The amount of nickel is adjusted so that the Curie temperature of the magnetic shunt alloy is 200 ° C.).

  When the fixing device 10 of FIG. 1 includes the fixing belt 13 shown in FIG. 2, when a high frequency current is passed through the induction coil 14, the base material 13 a of the fixing belt 13 is heated by electromagnetic induction and the fixing belt 13 generates heat. . Then, by passing the recording paper P conveyed on the guide plate 20 between the fixing roller 11 and the pressure roller 16, unfixed toner on the recording paper P can be fixed.

  Further, in the fixing device 10 having the above-described configuration, even if small-sized recording paper is continuously fed, the temperature distribution along the width direction of the fixing belt 13 is about 200 ° C. at both ends as shown in FIG. Therefore, hot offset can be prevented from occurring at both ends of the fixing roller 13 even if a large size sheet is passed after a small size recording sheet is continuously fed.

  FIG. 4 shows a second embodiment of the present invention, and is a cross-sectional view of only the upper half of the facing roller 12. As shown in the figure, the facing roller 12 has a cylindrical portion 12a, and rotation support portions 12b are provided at both ends of the cylindrical portion 12a. The rotation support portion 12b is supported by the image forming apparatus main body via a bearing.

  In this embodiment, both end portions of the inner wall surface of the facing roller 12 are cut off, and the cylindrical portion 12a is formed so that the both end portions 12d are thinner than the central portion 12c along the axial direction of the facing roller 12. Yes. For example, the thickness of the central portion 12c is 0.6 mm, and the thickness of both end portions 12d is 0.3 mm.

  With such a configuration, the heat capacity at both end portions 12d of the opposing roller 12 is reduced, and heat from electromagnetic induction heating can be prevented from escaping to the both end portions 12d side. As a result, as shown in FIG. 5, the temperature rise at both ends 12d (opposite roller both ends) is almost equal to the temperature rise at the central portion 12c (opposite roller center), and as a result, the fixing device can be used. It is possible to shorten the time until it is, that is, the rise time.

  FIG. 6 shows Embodiment 3 of the present invention, and is a sectional view of only the upper half of the fixing roller 13 wound around the counter roller 12 and the counter roller 12.

  The fixing belt 13 has a laminated structure in which a base material 13d, an elastic layer 13b, and a release layer 13c are laminated in order from the lower side. The base 13d is formed of an endless belt made of a heat resistant resin (nonmagnetic material). As a material of the heat resistant resin, polyimide, polyamideimide, polyetherketone (PEEK) or the like can be used. From the rigidity and heat capacity of the belt, the thickness of the base material 13d is desirably 20 μm to 100 μm. The elastic layer 13b and the release layer 13c are the same as those described in the first embodiment.

  In this embodiment, the facing roller 12 has a cored bar 12e made of nonmagnetic aluminum or the like, and a magnetic shunt alloy 21 is provided on the outer peripheral surface of the cored bar 12e. Examples of the material of the magnetic shunt alloy 21 include an iron-nickel alloy, iron-nickel-chromium, iron-nickel-cobalt, and the like. Further, the amount of nickel of the magnetic shunt alloy 21 is adjusted so that its Curie temperature becomes 200 ° C.

  When the fixing device 10 of FIG. 1 includes the facing roller 12 and the fixing belt 13 shown in FIG. 6, when a high frequency current is passed through the induction coil 14, the magnetic shunt alloy 21 is heated by electromagnetic induction and the facing roller 12 generates heat. The fixing belt 13 is heated by this heat generation. Then, by passing the recording paper P conveyed on the guide plate 20 between the fixing roller 11 and the pressure roller 16, unfixed toner on the recording paper P can be fixed.

  According to the present embodiment, even if small-size recording paper is continuously fed, the temperature distribution along the width direction of the fixing belt 13 rises only to about 200 ° C. at both ends as in the first embodiment. Therefore, hot offset can be prevented from occurring at both side edges of the fixing roller 13 even if a small size recording paper is continuously fed and then a large size paper is passed.

  In the case of Example 1 or Example 2, the fixing belt 13 contains a magnetic shunt alloy, but in this embodiment, the fixing belt 13 does not contain a magnetic shunt alloy. As a result, the flexibility of the fixing belt 13 is improved, the fixing belt 13 is less likely to be cracked, and the life of the fixing belt 13 can be improved.

  FIG. 7 shows Embodiment 4 of the present invention, and is a sectional view of only the upper half of the fixing roller 13 wound around the opposing roller 12 and the opposing roller 12. In the present embodiment, as in the second embodiment, both end portions of the inner wall surface of the facing roller 12 are cut away, and the thickness of the cylindrical portion 12a is greater than the center portion 12c along the axial direction of the facing roller 12. 12d is formed thinly. For example, the thickness of the central portion 12c is 0.6 mm, and the thickness of both end portions 12d is 0.3 mm. The fixing belt 13 is the same as that of the third embodiment.

  When the fixing device 10 of FIG. 1 includes the facing roller 12 and the fixing belt 13 shown in FIG. 7, when a high frequency current is passed through the induction coil 14, the magnetic shunt alloy 21 is electromagnetically heated and the facing roller 12 generates heat. The fixing belt 13 is heated by this heat generation. Then, by passing the recording paper P conveyed on the guide plate 20 between the fixing roller 11 and the pressure roller 16, unfixed toner on the recording paper P can be fixed.

  According to the present embodiment, even if small-size recording paper is continuously fed, the temperature distribution along the width direction of the fixing belt 13 rises only to about 200 ° C. at both ends as in the first embodiment. Therefore, hot offset can be prevented from occurring at both side edges of the fixing roller 13 even if a small size recording paper is continuously fed and then a large size paper is passed.

  In the present embodiment, the cylindrical portion 12a is formed such that both end portions 12d are thinner than the central portion 12c, so that the heat capacity at both end portions 12d is reduced, and the heat from electromagnetic induction heating is on the both end 12d side. It can be suppressed to escape. As a result, as in the second embodiment, it is possible to shorten the time until the fixing device becomes usable, that is, the rise time.

  FIG. 8 is a block diagram showing the principal parts of an image forming apparatus according to Embodiment 5 of the present invention. As shown in the figure, the image forming apparatus 30 is provided with a photosensitive drum 31 on which an electrostatic latent image is formed. Around the photosensitive drum 31, a charging roller 32 that is placed in contact with or close to the photosensitive drum 31 to charge the photosensitive drum 31, and the charged photosensitive drum 31 is exposed 33 to perform exposure 33 on the photosensitive drum 31. An exposure device (not shown) that forms an electrostatic latent image on the photosensitive drum 31; a developing roller 34 that visualizes the electrostatic latent image by attaching toner to the electrostatic latent image on the photosensitive drum 31; A transfer roller 35 for transferring the toner image on the body drum 31 to the recording paper P and a cleaning device 36 for cleaning the photosensitive drum 31 after the transfer process are provided.

  A fixing device 10 is provided on the downstream side of the photosensitive drum 31 along the recording sheet conveyance direction (arrow A). The fixing device 10 is one of the fixing devices described in the first to fourth embodiments.

1 is an overall configuration diagram of a fixing device according to Embodiment 1 of the present invention. 2 is a cross-sectional view of a fixing belt. FIG. FIG. 6 is a diagram illustrating a temperature distribution in the width direction of the fixing belt. 9 is a cross-sectional view of the upper half of the facing roller, showing Embodiment 2 of the present invention. FIG. It is a figure explaining the effect by Example 2. FIG. 9 is a cross-sectional view of the upper half of the opposing roller and the fixing belt, showing Embodiment 3 of the present invention. FIG. 9 is a cross-sectional view of the upper half of the opposing roller and the fixing belt, showing Embodiment 4 of the present invention. FIG. It is a principal part block diagram of the image forming apparatus by Example 5 of this invention. It is a sectional view of a conventional fixing belt. FIG. 6 is a diagram illustrating a problem of a conventional fixing belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fixing device 11 Fixing roller 12 Opposing roller 12a Cylindrical part 12c Center part 12d End part 13 Fixing belt 13a Base material 13b Elastic layer 13c Release layer 13d Base material 14 Induction coil (induction heating means)
DESCRIPTION OF SYMBOLS 15 Nip part 16 Pressure roller 18 Temperature sensor 19 Control apparatus 21 Magnetic shunt alloy 30 Image forming apparatus P Recording paper T Toner

Claims (5)

A fixing roller; a counter roller made of a non-magnetic material arranged in parallel to the fixing roller; an endless fixing belt wound between the fixing roller and the counter roller; and electromagnetic induction of the fixing belt Induction heating means for heating and a pressure roller for pressing the fixing roller via the fixing belt, and the recording paper is passed between the fixing belt and the pressure roller so as to be unfixed on the recording paper. A fixing device for fixing toner,
The fixing belt has a laminated structure in which a base material, an elastic layer, and a release layer are laminated in order from the bottom,
The fixing device, wherein the base material is formed of a material in which a magnetic shunt alloy is dispersed, and the Curie temperature of the magnetic shunt alloy is set lower than a hot offset temperature of toner. A fixing roller; a counter roller disposed in parallel with the fixing roller; an endless fixing belt made of a nonmagnetic material wound between the fixing roller and the counter roller; and electromagnetic induction of the counter roller. Induction heating means for heating and a pressure roller for pressing the fixing roller via the fixing belt, and the recording paper is passed between the fixing belt and the pressure roller so as to be unfixed on the recording paper. A fixing device for fixing toner,
A fixing device, wherein a magnetic shunt alloy is provided on an outer peripheral surface of the facing roller, and a Curie temperature of the magnetic shunt alloy is set lower than a hot offset temperature of the toner.   The said opposing roller has a cylindrical part, The thickness of the cylindrical part is formed thinly at both ends rather than the center part along the axial direction of this opposing roller. The fixing device according to 1. A fixing roller, a counter roller arranged in parallel with the fixing roller, an endless fixing belt wound between the fixing roller and the counter roller, and electromagnetic induction of the counter roller or the fixing belt Induction heating means for heating and a pressure roller for pressing the fixing roller via the fixing belt, and the recording paper is passed between the fixing belt and the pressure roller so as to be unfixed on the recording paper. A fixing device for fixing toner,
2. The fixing device according to claim 1, wherein the facing roller has a cylindrical portion, and the cylindrical portion is formed so that both ends thereof are thinner than the central portion along the axial direction of the facing roller. An image forming apparatus comprising the fixing device according to claim 1.

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