JPH09138600A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the high-speed operation of an image forming device by pushing in a belt toward the inside and heating the pushed-in belt part from the outside. SOLUTION: In this fixing device 2, a motor drives to rotate a roller 16 in a direction shown by an arrow 22. Then, the belt 8 press-contacting with the roller 16 is moved and rollers 4 and 6 and a heating roller 10 which come in contact with the belt 8 are rotated. Meanwhile, heat from the heat source 14 of the roller 10 is transmitted to the outer peripheral surface of the belt 8 through a cylinder 12. A heat transfer amount by the contact of the belt 8 with the roller 10 becomes larger as the contact area between the belt 8 and the cylinder 2 becomes larger. Therefore, it is desirable to make the pushed-in amount of the belt 8 by the roller 10 as large as possible so that the contact area between them may be large. Concretely, it is preferable to set the central angle θ of the roller 10 corresponding to the contact length of the belt 8 with the roller 10>=30 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for heating a developer and fixing it on a sheet in an electrophotographic copying machine or printer.

[0002]

2. Description of the Related Art Generally, an electrophotographic copying machine or printer is equipped with a heating roller having a built-in heater and a pressure roller parallel to and in pressure contact with the heating roller. 2. Description of the Related Art A fixing device that heats, melts and fixes a developer is widely used. Further, as another fixing device, a heating device is provided inside a heat resistant belt supported by a plurality of rollers, and the heating device is pressed against the opposing roller via the belt and is conveyed between the belt and the opposing roller. It is known that a developer on a sheet is heated by a heating device via a belt to be fused and fixed.

[0003]

However, in the former fixing device, the roller surrounding the roller is heated by the heater, and the developer is melted by the heated roller, so that the outer peripheral surface of the roller reaches a temperature suitable for fixing. It takes a long time to rise. Therefore, there is a problem in that the roller needs to be kept at a certain temperature or higher even during the standby state in which the image forming process is not performed, and the power consumption is large. On the other hand, in a fixing device using a heat-resistant belt, if a suitable coating is applied to the surface to improve the durability and releasability of the belt, it becomes thick, and the heat of the inner heating device is transferred to the outer surface, Takes a long time to rise to a temperature suitable for fixing. As described above, in the conventional fixing device, it takes time to transfer the heat required to the portion that contacts the developer (the outer peripheral surface of the heating roller, the outer peripheral surface of the belt), and thus the speed of the image forming apparatus is increased. There was an urgent need to improve the fixing device.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device suitable for increasing the speed of an image forming apparatus. The fixing device includes an endless heat resistant belt and the belt from the inside thereof. A plurality of inner supporting members to support, a pushing member that pushes the belt portion supported by the inner supporting member toward the inner side of the belt, and heating that heats the belt portion pushed inward by the pushing member from the outside. And an outer support member that contacts the outer peripheral surface of the belt.

[0005]

In the fixing device, the belt portion pushed inward by the pushing member is heated by the heating means from the outside. Therefore, the outer peripheral surface of the belt rises to a temperature required for melting the developer in an extremely short time. When the sheet is conveyed between the belt and the outer supporting member, the heated belt comes into contact with the developer held by the sheet and melts it. The melted developer is fixed on the sheet by the contact force between the belt and the outer supporting member.

As is clear from the above, the fixing device according to the present invention pushes the belt inward and heats the pushed belt portion from the outside. Therefore, the peripheral length of the belt which is in contact with or close to the heating portion can be increased, and the outer peripheral surface of the belt is directly heated, so that the heat transfer efficiency is high. Therefore, the fixing device can be suitably used for a high-speed image forming apparatus.

[0007]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of a fixing device according to the present invention, an enlarged view of which is shown in FIG.
Shown in The fixing device 2 includes a roller 4 and a roller 6 above the roller 4 and arranged in parallel at a predetermined interval. An endless heat resistant belt 8 is wound around the rollers 4 and 6.
The belt 8 is made of a thin sheet of silicon rubber or nickel having a high thermal conductivity, which is subjected to a high mold release treatment such as Teflon coating or silicon coating, or a sheet of a heat resistant resin such as polyimide. Those that have been subjected to a mold release treatment are preferably used. A heating roller 10 is arranged between the rollers 4 and 6. This heating roller 1
Reference numeral 0 denotes a heat source 14 housed in a metal cylindrical body 12 made of a material having a high surface hardness such as stainless steel, aluminum, or iron, which is pressed against a belt portion 15 supported between rollers 4 and 6, Is pushed inward toward the belt 8. The roller 16 is arranged below the roller 4 in parallel therewith, and is pressed against the roller 4 via the belt 8 by a pressing means such as a spring 18. Further, the roller 16 is connected to the motor 20. The outer peripheral portion of the roller 16 and at least one of the rollers 4 opposed to the roller 16 via the belt 8 is formed of an elastic material such as rubber in order to increase the nip length between the belt 8 and the roller 16. preferable.

In the fixing device 2, the roller 16 is rotated in the direction of arrow 22 by driving the motor 20. As a result, the belt 8 pressed against the roller 16 moves in the direction of the arrow 24, the rollers 4 and 6 in contact with the belt 8 rotate in the directions of the arrows 26 and 28, respectively, and the heating roller 10 moves in the direction of the arrow 3.
Rotate in the 0 direction. On the other hand, the heat from the heat source 14 of the heating roller 10 is transferred to the outer peripheral surface of the belt 8 via the cylinder 12. Here, the amount of heat transfer due to contact with the heating roller 10 is greatly affected by the contact area between the belt 8 and the cylinder 12, and the larger the contact area, the greater the amount of heat transfer to the belt.
Therefore, it is desirable to increase the pressing amount of the belt 8 by the heating roller 10 as much as possible to increase the contact area between the two. Specifically, the belt 8 and the heating roller 10
It is preferable to set the central angle θ of the heating roller 10 with respect to the contact length with 30 degrees or more.

In this state, the sheet on which the unfixed developer is placed is indicated by the arrow 34 in the nip region 32 between the belt 8 and the roller 16.
When conveyed from the direction, the developer comes into contact with the heated belt 8 and melts. Further, the melted developer is fixed on the sheet by the pressing force of the roller 16.

As shown in FIG. 3, the heating roller 10 is urged toward the inside of the belt 8 by a spring 36,
It is desirable to always apply a constant tension to the belt 8. In addition, as shown in FIG. 4, a scraper 38 is pressed against the heating roller 10, and a container 39 is provided below the scraper 38 to scrape off the developer and the like adhering to the belt 8 with the scraper 38 when a trouble occurs. This in container 39
It is preferable to collect it. The means for removing the developer and the like from the heating roller 10 is not limited to the scraper, and, for example, a brush, a web, or a roller-shaped member thereof can be used.

In addition, in the above-described embodiment, the roller 16 that contacts the outer peripheral surface of the belt 8 is driven by being connected to the motor 20, but the roller 4 or 6 may be driven and connected to the motor.

FIG. 5 shows a fixing device 40 of the second embodiment.
In this fixing device 40, three rollers 42, 44, 46
The heat-resistant belt 48 is wound around the belt 42, and the belt portion 50 extending from the rollers 42 to 46 is pushed inward by the heating roller 52 disposed between the rollers 42 and 46, and the belt 50 is attached to the outer peripheral surface of the heating roller 52. Are in contact. Particularly, in this embodiment, the line 5 connecting the centers of the rollers 42 and 46 is used.
By arranging the heating roller 52 inside the belt as compared with 3, the contact length between the heating roller 52 and the belt 50 is significantly lengthened. The roller 54 is in pressure contact with the rollers 42 and 44 via the belt 48, and the belt portion 56 extending from the rollers 42 to 44 is in contact with the outer peripheral surface of the roller 54.

In the fixing device 40, when the roller 54 is rotated in the direction of arrow 58 by a motor (not shown), the belt 48 pressed by this moves in the direction of arrow 60, and the movement of the belt 48 causes the rollers 42, 44, Four
6 rotates in the directions of 62, 64, and 66, respectively, and the heating roller 52 rotates in the direction of arrow 66. Further, the belt 48 is heated at the contact portion with the heating roller 52. In particular, since the contact length between the two is long in this embodiment, the outer peripheral surface of the belt 48 is heated to the required temperature in a short time. In this state, when the sheet on which the unfixed developer is placed is conveyed from the direction of arrow 68 to the contact portion (nip portion) 70 between the roller 54 and the belt portion 56, the sheet comes into contact with the belt heated as described above. The developer melts and is fixed on the sheet.

The belt portion 5 in the nip portion 70
The temperature of 6 is higher on the roller 42 side (upstream side) and lower on the roller 44 side (downstream side). Therefore, the fixed developer is sufficiently hardened on the downstream side of the nip portion 70, and therefore, when passing through the nip portion 70, the belt 4 is conveyed.
Easily separated from 8. Further, the separability can be further improved by reducing the diameter of the roller 44.

FIG. 6 shows a modification of the second embodiment. In this fixing device 72, the heating roller 52 is provided on the line 53 connecting the centers of the rollers 42 and 46. In addition, the heating roller 5
2 is pressed against the roller 42 by the spring 74 along the line 53. Therefore, even if the roller 42 vibrates when the sheet enters the nip area 68, not only the vibration but also the vibration of the belt 48 is suppressed to the minimum, and the belt 48 is not overloaded. Further, the heat of the heating roller 52 is transferred to the roller 4 via the belt 48.
2 to thereby stabilize the heating temperature at the entrance portion of the nip portion 68. Further, the heating roller 52 and the belt 48 are pressed by pressing the heating roller 52 against the roller 42.
Since the transmission rate of the rotational force due to the friction between the heating roller 52 and the outer peripheral surface of the heating roller 52 is not required to be increased (rubber coating, blast treatment, etc.), the outer peripheral surface of the belt 48 is removed. Damage is also eliminated. When the belt is not normally used, the driving of the belt is stopped, but when the rollers 52 and 42 are separated from each other, the roller 4
2 is cooled, heat is taken by the roller 42 the next time it is driven, and the time lag until the required fixing temperature is reached increases. However, in the apparatus of this embodiment, since the roller 42 is warmed even while stopped, such a time lag hardly occurs.

FIG. 7 shows a fixing device according to the third embodiment. The fixing device 80 includes rollers 82 and 84 arranged above and below.
And a roller 86 disposed on the side of these and a roller 88 disposed on the side of the roller 86. Further, the heat resistant belt 90 has four rollers 82, 84,
A heater 96 is disposed between a belt portion 92 wound around 86, 88 and extending from the rollers 82 to 88 and a belt portion 94 extending from the rollers 88 to 84. Pressure roller 9
Reference numeral 8 is connected to a motor (not shown) and is in pressure contact with the roller 84 via a belt 90.

In the fixing device 80, the belt 90 moves in the direction of the arrow 102 as the pressure roller 98 rotates in the direction of the arrow 100. As a result, the rollers 82, 8
4, 86 and 88 are arrows 104, 106 and 10 respectively.
It rotates in the 8,110 direction. And the belt portion 92,
94 is heated by the heater 96, and the nip portion 112 where the pressure roller 98 and the belt 90 come into contact with each other melts and fixes the developer on the sheet conveyed in the direction of the arrow 104.

[Brief description of the drawings]

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

FIG. 2 is an enlarged cross-sectional view of the fixing device in FIG.

FIG. 3 is a cross-sectional view showing an improved example of the fixing device in FIG.

FIG. 4 is a sectional view showing another modification of the fixing device shown in FIG.

FIG. 5 is a sectional view of a fixing device according to a second embodiment.

FIG. 6 is a cross-sectional view of a modified example of the fixing device in FIG.

FIG. 7 is a cross-sectional view of a fixing device according to a third embodiment.

[Explanation of symbols]

2 ... Fixing device, 4, 6 ... Roller, 8 ... Belt, 10 ... Heating roller, 16 ... Roller.

Claims (1)

[Claims] 1. An endless heat resistant belt, a plurality of inner supporting members for supporting the belt from the inside thereof, a pushing member for pushing the belt portion supported by the inner supporting member toward the inner side of the belt, and A fixing device provided with a heating means for heating a belt portion pushed inward by a pushing member from the outside thereof, and an outer supporting member in contact with an outer peripheral surface of the belt.