JP2002296956A - Belt fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent danger of the firing of oil even when minimum size paper consecutively passes. SOLUTION: A thermistor 69 is provided at the center part of a heating roller 64, and a thermostat 68 functioning as an excessive temperature rise preventing means is provided at outside of a minimum size paper passing area separated from the thermistor 69 in the shaft direction of the roller 64 by 100 mm. By the sure actuation of the thermostat 68, a situation that the temperature at the end of the roller 64 rises and oil applied to a fixing belt is prevented from firing. A mark 63 shows a fixing roller, a mark 62 shows a pressure roller and a mark 65 shows an auxiliary roller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and a belt fixing device used in the image forming apparatus, and more particularly, to a color image forming apparatus and a color image forming apparatus. The present invention relates to a belt fixing device.

[0002]

2. Description of the Related Art In a belt fixing device of this type, for example,
A heating roller having a heat source such as a halogen heater inside,
A fixing belt is stretched between the fixing rollers, and a pressure roller disposed opposite to the fixing roller is configured to press the fixing roller with the fixing belt therebetween. A fixing nip is formed between the fixing belt and the pressure roller, and the fixing nip is fixed by heat and pressure through a recording material carrying an unfixed toner image. Temperature detecting means such as a thermistor is provided near the heating roller, and the temperature of the heating roller is controlled based on detection information from the temperature detecting means. Oil is applied to the surface of the fixing belt in order to enhance the toner offset prevention function and the recording material separability.

[0003] In this type of belt fixing device, it is considered that a heat source such as a halogen heater runs away for some reason to cause an abnormally high temperature. To address this problem, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 197849 describes a technique for preventing excessive temperature rise by using a thermal fuse. The fixing device described in this publication has a configuration in which an unfixed image is fixed by heat via a fixing film that moves in sliding contact with a heater, and a temperature fuse is provided outside the minimum paper passing area of the heater. ing. By providing the thermal fuse outside the minimum paper passing area, it is possible to suppress the influence of heat absorption by the thermal fuse on the image and prevent defective fixing.
A good image without glare can be obtained.

In general, in a monochrome image forming apparatus using a so-called heat roller type fixing device in which a fixing nip portion is formed by a heating roller and a pressure roller pressed against the heating roller, as shown in FIG. And the roller surface temperature at the time of operating the thermal fuse reaches about 400 ° C. 8, the horizontal axis represents time t, and the vertical axis represents the surface temperature of the heating roller. As is clear from this graph, the surface temperature of the heating roller rises in a short time and reaches the fuse operating temperature. Even if the temperature of the heating roller rises in a short time, the monochrome machine does not use silicon oil or the like, so that there is no problem such as ignition.

A heat roller type fixing device is also used in a color image forming apparatus. In this case, since an elastic layer made of silicon rubber or the like is provided on the surface of the heating roller by 2 mm or more, as shown in FIG. The heating rate of the surface of the heating roller is low. In FIG. 9, the horizontal axis represents time t, and the vertical axis represents the surface temperature of the heating roller. As is clear from this graph, since the temperature rise rate of the surface of the heating roller is slow, even if a temperature fuse is used, the fuse operates below the ignition point of the silicone oil, and no problem occurs.

[0006]

A belt fixing device used in a color image forming apparatus is a color machine in addition to a heat roller type fixing device used in a monochrome image forming apparatus, which has a rising speed that is at least as fast as that of the fixing device. Use silion oil for Accordingly, if a temperature fuse having a slow reaction speed is used as in the conventional case, the temperature of the fixing belt immediately reaches about 350 ° C., which is the ignition point of silicon oil. This state will be described with reference to FIG. In FIG. 10, the horizontal axis represents time t, and the vertical axis represents the surface temperature of the heating roller. As is apparent from this graph, the temperature of the fixing belt reaches the ignition point of the silicone oil before the thermal fuse is activated, which may cause a fire.

In a belt fixing device used in such a color image forming apparatus, for example, an A5 plate (A5
When the minimum specification paper such as the size) is continuously passed, the surface temperature of the fixing belt differs between the paper passing portion and the non-paper passing portion. This state will be described with reference to FIG. FIG.
Is a graph showing the temperature distribution in the longitudinal direction of the heating roller. The horizontal axis indicates the axial length l of the heating roller, and the vertical axis indicates the temperature of the heating roller. M indicates the minimum paper passing area. The broken line indicates 340 ° C., which is the ignition risk temperature of silicon oil. As is clear from this graph,
Although it depends on the paper quality and ppm, when the minimum paper is continuously passed, the temperature of the non-paper passing portion becomes higher by about 50 ° C. than the temperature of the paper passing portion.

SUMMARY OF THE INVENTION It is a main object of the present invention to provide a belt fixing device capable of preventing the risk of firing even when the minimum sheet is continuously passed, and an image forming apparatus having the belt fixing device.

[0009]

According to a first aspect of the present invention, there is provided a fixing belt to which oil is applied, and a heating roller provided inside the fixing belt and having a heat source therein. A belt fixing device comprising: a temperature detection unit for detecting a temperature of the heating roller; and an overheating prevention unit that shuts off power supply to the heat source at a predetermined temperature of the heating roller. Is a thermostat, and the thermostat is disposed in the vicinity of the heating roller and in the same direction from the central portion in the longitudinal direction of the heating roller, at a position separated by １ ／ or more of the width dimension of the recording material used. Is adopted.

According to a second aspect of the present invention, in the belt fixing device according to the first aspect, a configuration is adopted in which the heat distribution of a portion of the heating roller corresponding to the thermostat is higher than other portions. .

According to the third aspect of the present invention, the first or second aspect is provided.
In the belt fixing device described above, the thermostat is in contact with the surface of the heating roller.

According to a fourth aspect of the present invention, in the belt fixing device according to the third aspect, the sliding surface of the thermostat with respect to the heating roller is covered with a film having good slidability. I have.

According to a fifth aspect of the present invention, in the belt fixing device according to the fourth aspect, a configuration is adopted in which a sliding surface of the heating roller with respect to the thermostat is covered with a film having good slidability. I have.

According to the sixth aspect of the present invention, the first to fifth aspects are provided.
In the belt fixing device described in any one of the above, the temperature detecting means and the excessive temperature rise preventing means are mounted on a support member provided inside the fixing belt.

According to a seventh aspect of the present invention, in the belt fixing device according to the sixth aspect, the support member is connected to the heating roller.

According to the present invention, the electrostatic latent image formed on the image carrier is visualized as a toner image by a developing means, the toner image is transferred to a recording material, and the toner image is transferred. An image forming apparatus for fixing the recording material passed through a belt fixing device has a configuration in which the belt fixing device is any one of claims 1 to 7.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. First, a schematic configuration and operation of an electrophotographic color printer (hereinafter, simply referred to as a color printer) 1 as an image forming apparatus according to the present embodiment will be described with reference to FIG. The color printer 1 includes a photoreceptor unit 10, a writing optical unit 20, a developing unit 30 as a developing unit, an intermediate transfer unit 40, a secondary transfer unit 50 as a transfer unit, and a fixing unit 60 as a fixing device. And a double-sided printing paper reversing unit 70 and the like. The color printer 1 has Black: Black (hereinafter referred to as Bk), C
yan: cyan (hereinafter, referred to as C), Magenta:
Magenta (hereinafter referred to as M), Yellow: yellow (hereinafter referred to as Y) color image
Are sequentially visualized on a photoreceptor belt 11 as an image carrier, and these are superimposed to form a final four-color full-color image.

The photoreceptor belt 11 rotates clockwise as indicated by an arrow A. Around the photoreceptor cleaning device 12, the charging roller 13, the selected developing unit of the developing unit 30, and the intermediate of the intermediate transfer unit 40 A transfer belt 41 and the like are arranged. The photoreceptor belt 11 is stretched between the driving roller 14, the primary transfer opposing roller 15, and the stretching roller 16, and is rotated in the direction of arrow A by a drive motor (not shown). When the photoconductive belt 11 having a seam is used, a seam mark is provided in a non-image area at the end of the photoconductor belt 11, and a detection is performed by a sensor (not shown) to form an image while avoiding the seam.

The writing optical unit 20 converts the color image data into an optical signal, performs optical writing corresponding to each color image, and forms an electrostatic latent image on the photosensitive belt 11.
The writing optical unit 20 includes a semiconductor laser 21 as a light source, a laser emission drive control unit (not shown), a polygon mirror 22, and three reflection mirrors 23a, 23b, and 23.
c etc.

The developing unit 30 includes a Bk developing device 31K,
C developing device 31C, M developing device 31M, Y developing device 31Y,
Each developing unit is configured by a not-shown contact / separation mechanism or the like that moves the developing device in the left-right direction in the drawing to perform a contact / separation operation with respect to the photosensitive belt 11. Each of the developing units 31K, 31C, 31M, and 31Y has a developing sleeve 32K, 32 that rotates while carrying a developer on the surface to develop an electrostatic latent image on the surface of the photoreceptor belt 11.
C, 32M, and 32Y, and developer paddles 33K, 33C, 33M, and 3 that rotate to pump up and agitate the developer.
3Y, and a developer storage case 34K, 3 for storing the developer.
4C, 34M, 34Y and the like. Each of the developer accommodating cases 34K, 34C, 34M, and 34Y accommodates a one-component developer composed of a toner of each color as a developer. In the illustrated example, a Bk developing device 31K containing black toner, a C developing device 31C containing cyan toner, an M developing device 31M containing magenta toner, and a Y developing device containing yellow toner are arranged in order from the lower side of the apparatus main body. 31Y is provided.

Each of the developing units 31K, 31C, 31M, 31Y
The toner inside is charged to a predetermined polarity, and a developing bias is applied to each of the developing sleeves 32K, 32C, 32M, and 32Y by a developing bias power supply (not shown), and the developing sleeves 32K, 32C, 32M, and 32Y are transferred to the photosensitive belts. 11 is biased to a predetermined potential. Also,
The contact / separation mechanism is provided by a motor (not shown) from each developing device 31.
When an electromagnetic clutch (not shown) for transmitting drive to K, 31C, 31M, and 31Y is turned on, the drive force moves developer storage cases 34K, 34C, 34M, and 34Y to photoreceptor belt 11 side (right side in the figure). It is made to let. At the time of development, each of the developing devices 31K, 31C, 31M, 3
Any one selected from 1Y moves and comes into contact with the photoreceptor belt 11. On the other hand, when the electromagnetic clutch is turned off to cancel the drive transmission, the developing device that has been in contact with the photosensitive belt 11 moves in a direction away from the photosensitive belt 11 (left side in the figure).

In a standby state of the main body of the color printer, any of the developing units 31K, 31C, 31
M and 31Y are also set at positions separated from the photoreceptor belt 11. When the printing operation is started, optical writing using a laser beam and formation of an electrostatic latent image are started based on the color image data (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk electrostatic latent image. The same applies to Y).
In order to enable development from the front end of the Bk electrostatic latent image, the rotation of the Bk developing sleeve 32K is started before the front end of the Bk electrostatic latent image reaches the Bk development position, and the Bk electrostatic latent image is converted to Bk toner. Develop with. Thereafter, the developing operation of the Bk electrostatic latent image area is continued, but when the trailing end of the Bk electrostatic latent image passes the Bk developing position, the Bk developing device 31K separates from the photoreceptor belt 11 and immediately moves to the next position. The developing device of the color a contacts the photoreceptor belt 11. This is completed at least before the leading end of the electrostatic latent image based on the next image data reaches the developing position.

The intermediate transfer unit 40 includes an intermediate transfer belt 41, a belt cleaning device 42, a position detecting sensor 43, and the like. The intermediate transfer belt 41 is stretched around a driving roller 44, a primary transfer roller 45, a secondary transfer opposing roller 46, a cleaning opposing roller 47, and a tension roller 48, and is driven and controlled in a direction indicated by an arrow B by a driving motor (not shown). You. A plurality of position detection marks (not shown) are provided in the non-image area at the end of the intermediate transfer belt 41, and one of these position detection marks (the position detection sensor 4 when the image forming operation starts) is performed.
3 is detected by the position detection mark, and image formation is started at this detection timing.

The belt cleaning device 42 includes a cleaning brush 42a, a contact / separation mechanism (not shown), and the like, while the first color Bk image is being transferred to the intermediate transfer belt 41, and 2, 3, and 4. While the color image is being transferred to the intermediate transfer belt 41, the cleaning brush 42a is separated from the surface of the intermediate transfer belt 41 by a contact / separation mechanism. The toner cleaned from the surface of the intermediate transfer belt 41 is stored in a waste toner tank 49 provided inside the intermediate transfer unit 40.

A transfer paper as a transfer material is accommodated in a transfer paper cassette 80 provided at a lower portion of the apparatus main body.
The transfer paper is fed and conveyed toward registration roller pair 82 by paper feed rollers 81a, 81b, 81c. On the right side of the color printer 1, a manual feed tray 83 for manually feeding OHP paper or thick paper is provided.

The secondary transfer unit 50 includes a secondary transfer roller 51 and a swing mechanism (not shown) provided with a clutch and the like for bringing the secondary transfer roller 51 into and out of contact with the intermediate transfer belt 41. I have. The secondary transfer roller 51 swings about the rotation axis of the swing mechanism in synchronization with the timing at which the transfer paper reaches the transfer position. The transfer paper and the intermediate transfer belt 41 are driven by the secondary transfer roller 51 and the secondary transfer facing roller 46.
And are contacted at a constant pressure. The position accuracy of the parallelism of the secondary transfer roller 51 with the secondary transfer opposing roller 46 is maintained by a positioning member (not shown) provided in the intermediate transfer unit 40. The positioning roller (not shown) provided on the secondary transfer roller 51 causes
The contact pressure of the next transfer roller 51 is made uniform. At the same time when the secondary transfer roller 51 is brought into contact with the intermediate transfer belt 41, a transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 51, and the superimposed toner image on the intermediate transfer belt 41 is collectively transferred onto transfer paper.

Each of the above units can be easily attached to and detached from the apparatus main body. For example, in FIG. 4, when removing the intermediate transfer unit 40, the front cover (not shown) is opened, and the unit is slid from the back side to the front side of the paper.

In the color printer 1 having the above configuration, when the image forming cycle is started, first, the photosensitive belt 11
Is rotated in the clockwise direction of arrow A, and the intermediate transfer belt 41 is rotated in the counterclockwise direction of arrow B by a drive motor (not shown). A position detection mark (not shown) provided on the intermediate transfer belt 41 is detected by a position detection sensor 43,
Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed on the photoreceptor belt 11 according to the detection timing of the position detection mark, and finally Bk,
A toner image is formed on the intermediate transfer belt 41 in the order of C, M, and Y. At this time, the bias applied to the primary transfer roller 45 generally increases the voltage sequentially, but differs depending on the resistance characteristics of the intermediate transfer belt 41 and the like.

The Bk toner image is formed as follows.
The charging roller 13 uniformly charges the photoreceptor belt 11 by an applied voltage of a power supply (not shown). The laser light LD for writing performs exposure based on the Bk color image signal. When this exposure is carried out, the exposed portion of the photoreceptor belt 11 which is initially uniformly charged loses the charge proportional to the amount of exposure light, and a Bk electrostatic latent image is formed. When the Bk toner on the Bk developing sleeve 32K comes into contact with the Bk electrostatic latent image, the toner does not adhere to a portion where the charge of the photoreceptor belt 11 remains, and a portion having no charge, that is, an exposed portion Bk toner is adsorbed, and a Bk toner image similar to the electrostatic latent image is formed. The Bk toner image formed on the photoreceptor belt 11 contacts the intermediate transfer belt 41 at the primary transfer position. At this primary transfer position, a nip is formed between the intermediate transfer belt 41 and the photosensitive belt 11 by the primary transfer roller 45 and the primary transfer opposing roller 15, and the Bk toner image is formed on the primary transfer roller 45. The Bk toner image is transferred to the intermediate transfer belt 41 by applying a bias having a polarity opposite to the above.

A small amount of untransferred residual toner on the photoreceptor belt 11 is cleaned by a photoreceptor cleaning device 12 in preparation for reusing the photoreceptor belt 11. The collected toner is stored in a waste toner tank (not shown) via a collection pipe (not shown).

On the photosensitive belt 11 side, the process proceeds to the C image forming step after the Bk image forming step, and the position detecting sensor 43
Is written by the laser light LD based on the C image data in accordance with the detection timing, and a C electrostatic latent image is formed. After the rear end of the previous Bk electrostatic latent image has passed, and
Before the leading end of the C electrostatic latent image arrives, the Bk developing device 31K retracts from the developing position, the C developing device 31C is set at the developing position, and the C electrostatic latent image is developed with the C toner. Hereafter, C
The development of the electrostatic latent image area is continued, but when the rear end of the C electrostatic latent image has passed, the C developing unit 31C retreats from the developing position in the same manner as in the case of the Bk developing unit 31K, and the next. M developing unit 3
Move 1M to the development position. This is also completed before the leading end of the next M electrostatic latent image reaches the developing position. The M and Y image forming processes are the same as the processes of Bk and C described above, since the operations of forming and developing the electrostatic latent image are the same as those of the processes of Bk and C described above.

The intermediate transfer belt 41 includes the photosensitive belt 1
The toner images of Bk, C, M, and Y which are sequentially formed on the same are sequentially aligned on the same surface to form a four-color superimposed toner image. In the next two transfer steps, the four-color toner image is formed. Batch transfer to transfer paper.

At the time when the image forming operation is started, the transfer paper is fed from either the transfer paper cassette 80 or the manual feed tray 83 and stands by at the nip of the registration roller pair 82. The intermediate transfer belt 41 is attached to the secondary transfer roller 51.
When the leading edge of the four-color superimposed toner image approaches, the registration roller pair 82 is driven so that the leading edge of the transfer paper just coincides with the leading edge of the toner image, and the registration between the transfer paper and the toner image is performed. Will be Then, the transfer paper is superimposed on the toner image on the intermediate transfer belt 41 and passes through the secondary transfer position. At this time, the transfer paper is charged by the transfer bias by the secondary transfer roller 51, and most of the toner image is transferred onto the transfer paper.

The transfer paper on which the four-color superimposed toner images are collectively transferred from the intermediate transfer belt 41 is conveyed to the fixing unit 60. The toner image is melted and fixed at the nip between the fixing belt 61 and the pressure roller 62 controlled to a predetermined temperature, sent out of the apparatus main body (in the direction of arrow C), stacked on the paper output tray 84 face-down, and full-color copied. Get.

When performing double-sided printing, the fixing unit 6
The transfer paper that has passed through 0 is guided in the direction of arrow D by the double-sided switching claw 85 and sent to the double-sided printing paper reversing unit 70. After the rear end of the transfer paper has passed the reversing switching claw 71, the reversing roller pair 72 stops, and the transfer paper also stops. The reversing roller pair 72 starts reversing after a certain blank time, and the transfer paper starts to switch back. At this time, the reversing switching claw 71 is switched, and the transfer paper is guided in the direction of arrow E and sent to the registration roller pair 82. The transfer paper sent to the registration roller pair 82 is turned upside down with the registration roller pair 8
Stand by at the nip of No. 2. The registration roller pair 82 is driven at a predetermined timing, the transfer paper is sent to the secondary transfer position, and the four-color superimposed toner image is collectively transferred from the intermediate transfer belt 41, and then the toner image is fused and fixed by the fixing unit 60. Is sent out of the apparatus body.

The surface of the photoreceptor belt 11 after the primary transfer is
The photosensitive member is cleaned by the photoreceptor cleaning device 12 and is uniformly discharged by a discharge lamp (not shown). The surface of the intermediate transfer belt 41 after the transfer of the toner image onto the transfer paper is cleaned by pressing the cleaning brush 42a of the belt cleaning device 42 with a contact / separation mechanism. The toner cleaned from the intermediate transfer belt 41 is stored in a waste toner tank 49.

Next, the fixing unit 60 will be described in detail with reference to FIGS. Inside the fixing belt 61 (omitted in FIG. 2), a fixing roller 63 as a driving roller, a heating roller 64 as a driven roller, and an auxiliary roller 65 are provided. The fixing belt 61 is supported by these rollers. Has been stretched. A pressure roller 62 is provided at a position facing the fixing roller 63.
2 is in pressure contact with the fixing roller 63 with the fixing belt 61 interposed therebetween. A heat source 66 such as a halogen heater is provided inside the heating roller 64. A heat source 67 such as a halogen heater is also provided inside the pressure roller 62 to assist the heating of the heat source 66 of the heating roller 64. Auxiliary roller 6
Reference numeral 5 is for making the fixing belt 61 adhere to the pressure roller 62 and creating an angle for making it easy for the paper P as a recording material to enter the fixing nip portion.

In the vicinity of the fixing roller 63, an oil application device 90 for applying oil to the surface of the fixing belt 61 to prevent toner offset or the like is provided (omitted in FIG. 4). The oil application device 90 includes a silicone oil application unit 90a, a supply roller 90b, an application roller 90c, and an oil deriving material 90c such as a felt that supplies oil from the silicon oil application unit 90a to the supply roller 90b. Near the center of the heating roller 64, a thermistor 69 is provided as a temperature detecting means for detecting the temperature of the heating roller 64. The thermistor 69 is separated from the thermistor 69 by a distance of 90 mm or more in the axial direction of the heating roller 64. At 100 mm in the embodiment, a thermostat 68 is provided in contact with the surface of the heating roller 64 as an excessive temperature rise prevention means. Since the thermostat 68 is in direct contact with the heating roller 64, an abnormal temperature can be detected effectively. The detection information of the thermistor 69 and the thermostat 68 is sent to a control unit (not shown), and the control unit executes temperature control of the heating roller 64 and the pressure roller 62, stop of the apparatus, and the like based on the information.

In response to the contact of the thermostat 68 with the heating roller 64, as shown in FIG. 3, the sliding surface of the thermostat 68 with respect to the heating roller 64 is covered with a film 68a having good slidability. . In the present embodiment, the film 68a is formed of Teflon (registered trademark). The sliding surface of the heating roller 64 with respect to the thermostat 68 is also covered with a Teflon coating 64a. Thus, it is possible to prevent the thermostat 68 from being damaged due to wear caused by contact with the heating roller 64.
At the same time, surface damage of the heating roller 64 can be prevented. The coating 64a of the heating roller 64 may be formed only on the portion corresponding to the thermostat 68, or may be formed on the entire surface.

Next, the operation of the fixing unit 60 will be described. The paper P carrying the toner image moves in the direction of arrow a in a state where the paper P overlaps the fixing belt 61 from the gap between the pressure roller 62 and the auxiliary roller 65. At the same time, the fixing belt 61
Also rotates in the direction of arrow b. The fixing belt 61 has already
6, the fixing is started while the toner image is melted. When the paper P further enters, the paper P passes through the fixing nip portion formed by the biting of the fixing roller 63 and the pressure roller 62 while being heated and pressurized, whereby the toner image is fixed on the paper P.

When the minimum sheet such as the A5 size sheet is continuously passed, the surface temperature of the fixing belt 61 differs between the sheet passing portion and the non-sheet passing portion as described with reference to FIG. When the thermostat 68 is provided in the paper passing portion in such a state,
If an abnormality occurs in the heater control by the thermistor 69 for some reason, the temperature of the end of the fixing belt 61 becomes 340 ° C. or more before the thermostat 68 operates, and there is a risk of fire. However, in the present embodiment, as described above, since the heating roller 64 is disposed at a position 90 mm or more away from the center of the heating roller 64, the thermostat 68 operates reliably even when the heater control is abnormal at the time of minimum sheet passing. The sheet width of the A5 plate as the minimum sheet in the present embodiment is 180 mm, and the width on one side from the center of the heating roller 64 is 90 mm. Therefore, if the thermostat 68 is provided at a position 90 mm or more in the axial direction of the heating roller 64 from the center of the heating roller 64, the thermostat 6
8 is outside the minimum paper passing area. 90m from this perspective
m or more. This value differs depending on the minimum size of the paper P actually used.

Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description of the already-described configuration and function will be omitted unless otherwise required. Also, only the main part will be described (same as the following embodiment). In the first embodiment, the thermostat 68 is provided outside the minimum sheet passing area. However, if the position is larger than the A5 size sheet, for example, within the A4 size sheet passing area, the thermostat 68 is set to the heating roller. 64
Since the temperature of the heating roller 64 is lower in a portion that is in contact with a non-contact portion, there is a problem that vertical streak-like gloss unevenness occurs on a fixed image. The present embodiment aims at solving this problem.

In the present embodiment, in order to solve the above problem, the heat distribution (light distribution characteristic) of the portion of the heating roller 64 corresponding to the thermostat 68 is made higher than other portions. In FIG. 5, reference numeral 64a indicates a tungsten wire of the halogen heater 66. Specifically, a known technique for changing the light distribution characteristics at the end of the heating roller 64 is applied. FIG. 6 shows a temperature graph of an example in which the light distribution characteristic at a position 50 mm inward from both ends of the heating roller is increased from 100% to 130%. This technology is already established. Using this technique, FIG.
As shown in FIG. 7, the light distribution characteristic of the heating roller 64 at the portion where the thermostat 68 is in contact is increased from 100% to 130%. Accordingly, the surface temperature of the heating roller 64 becomes uniform, and it is possible to prevent the occurrence of vertical streak-like gloss unevenness.

Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, the thermistor 69 and the thermostat 68 are attached to a support member 92 provided inside the fixing belt 61. Support member 92
Are formed integrally with bearings 94 provided at both ends of the rotating shaft of the heating roller 64, and are connected to the heating roller 64. With such a configuration, even if an accident occurs in which the fixed wearing belt 61 is cut, it is possible to prevent the thermostat 68 from falling away from the heating roller 64 and causing a situation where the temperature runaway cannot be stopped.

[0045]

According to the first or eighth aspect of the present invention, the means for preventing excessive temperature rise is a thermostat, and the thermostat is located near the heating roller and in the same direction from the longitudinal center of the heating roller. 1/1 of the width of the recording material used
Since it is arranged at a position separated by two or more, even if there is a heater control abnormality at the time of minimum sheet passing, the operation of the thermostat can be reliably obtained, and an accident such as ignition can be prevented. . In addition, the fuse can be used any number of times as compared with the thermal fuse, and troublesome replacement after operation can be avoided.

According to the second or eighth aspect of the present invention, since the heat distribution at the portion corresponding to the thermostat of the heating roller is higher than at other portions, the surface temperature of the heating roller becomes uniform, and the vertical stripes are formed. It is possible to prevent the occurrence of uneven glossiness.

According to the third or eighth aspect of the present invention, since the thermostat is configured to be in contact with the surface of the heating roller, the abnormal temperature can be detected with high accuracy.

According to the fourth or eighth aspect of the invention, the sliding surface of the thermostat with respect to the heating roller is covered with a film having good slidability. This can prevent the thermostat from being damaged. At the same time, surface damage of the heating roller can be prevented.

According to the fifth or eighth aspect of the present invention, the sliding surface of the heating roller with respect to the thermostat is covered with a film having good slidability. This can prevent the thermostat from being damaged. At the same time, surface damage of the heating roller can be prevented.

According to the sixth or eighth aspect of the present invention, the temperature detection means and the excessive temperature rise prevention means are configured to be attached to the support member provided inside the fixing belt. Space can be saved by common use.

According to the seventh or eighth aspect of the present invention, since the support member is connected to the heating roller, the thermostat is separated from the heating roller even if an accidental breakage of the fixed belt occurs. Falling, and a situation where the temperature runaway cannot be stopped can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view of a fixing device.

FIG. 3 is a sectional view of a main part showing a contact configuration between a heating roller and a thermostat.

FIG. 4 is a schematic front view of a color printer as an image forming apparatus.

FIG. 5 is a diagram illustrating light distribution characteristics of a heating roller according to a second embodiment.

FIG. 6 is a diagram showing a change in light distribution characteristics of a conventional heating roller.

FIG. 7 is a schematic perspective view of a fixing device according to a third embodiment.

FIG. 8 is a graph showing an operating relationship between a temperature of a heat roller type heating roller and a temperature fuse in a monochrome machine.

FIG. 9 is a graph showing the relationship between the temperature of a heat roller type heat roller in a color machine and the operation of a temperature fuse.

FIG. 10 is a graph showing the relationship between the temperature of a fixing belt and the operation of a thermal fuse in a belt fixing system of a color machine.

FIG. 11 is a graph showing a temperature distribution of a heating roller in minimum sheet passing.

[Explanation of symbols]

 Reference Signs List 30 Developing unit as developing means 61 Fixing belt 64 Heating roller 64a, 68a Coating 66 Halogen heater as heat source 68 Thermostat as overheating prevention means 69 Thermistor as temperature detecting means 92 Supporting member P Paper as recording material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 3/00 335 H05B 3/00 335 F term (Reference) 2F056 CE01 2H033 AA42 BA11 BA25 BA27 BA31 BA32 BA38 BA42 BA43 BA59 BB05 BB18 BB28 CA07 CA45 3K058 AA12 AA14 BA18 CA12 CA23 CA51 CA61 CA71 CB02 DA01

Claims (8)

[Claims] 1. A fixing belt to which oil is applied, a heating roller provided inside the fixing belt and having a heat source therein, temperature detecting means for detecting the temperature of the heating roller, A belt fixing device having an overheating prevention means for interrupting power supply to the heat source according to the temperature of the heating roller, wherein the overheating prevention means is a thermostat, and the thermostat is in the vicinity of the heating roller and in the longitudinal direction of the heating roller. A belt fixing device, which is disposed at a position separated from a central portion of the recording medium by at least half the width of a recording material used in the same direction. 2. The belt fixing device according to claim 1, wherein a heat distribution at a portion of the heating roller corresponding to the thermostat is higher than at other portions. 3. The belt fixing device according to claim 1, wherein the thermostat is in contact with a surface of the heating roller. 4. The belt fixing device according to claim 3, wherein a sliding surface of the thermostat with respect to the heating roller is covered with a film having good slidability. 5. The belt fixing device according to claim 4, wherein a sliding surface of the heating roller with respect to the thermostat is covered with a film having good slidability. 6. A fixing device according to claim 1, wherein said temperature detecting means and said excessive temperature preventing means are attached to a support member provided inside said fixing belt. A belt fixing device, characterized in that: 7. The belt fixing device according to claim 6, wherein the support member is connected to the heating roller. 8. An electrostatic latent image formed on an image carrier is visualized as a toner image by a developing means, the toner image is transferred to a recording material, and the recording material on which the toner image is transferred is a belt. An image forming apparatus for fixing by passing through a fixing device, wherein the belt fixing device is one according to any one of claims 1 to 7.