JPS58132772A - Sheet heating device - Google Patents

Abstract

PURPOSE:To raise a thermal responding property, and also to prevent an excessive temperature rise of a heating source which varies a temperature suddenly, by providing a member having a thermal responding property which is varied by heat from the heating source, and a good heat conductor which supports the member having thermal responding property and is made contacted with a heating element. CONSTITUTION:A fixation roll 1 is heated by a heater 4 supported by an electrode 3. Subsequently, in accordance with a detected temperature of a thermistor 14 being a temperature detecting means which has been made in contacted with the surface of the fixation roll 1, a switch 16 is turned on and off by a signal from a temperature controlling circuit 15, and the surface of the roll 1 is controlled to be held at a constant temperature. In case when the heater 4 is in a state to emit heat exceeding a prescribed temperature, a fuse 8 receives this heat exceeding a rated temperature, only through a holder 5, and is fused. The fuse 8 is connected in series between the heater 4 and the electric power source to stop immediately supply of electric power to the heater 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheet heating device. Specifically, the present invention relates to a heating device with an overheat prevention function.

Hereinafter, a heat fixing device applied to an image forming apparatus such as a copying machine will be described as an example of a heating device.

In conventional heat fixing devices, the overheat prevention means is provided at a position away from a heating element, such as a roller surface, which is heated by a heat source such as a halogen heater. If a fuse that turns off a large current is used, its heat capacity is large compared to temperature detection means such as a thermistor.

There was a problem that the thermal response (reaction time) was poor.

Therefore, the present invention provides (1) a heating device that solves the above-mentioned problems of the conventional example, improves thermal responsiveness, and can also prevent excessive heating of a heating source with rapid temperature changes.

An embodiment of the present invention will be described below.

FIG. 1 is a side sectional view of a heat fixing roller of a copying machine to which an embodiment of the present invention is applied.

In the figure, the fixing roller 1 is an aluminum cylinder. This fixing roller 1 is supported by bearings 2 at both ends (
The other end (not shown) is rotatably held. A halogen heater 4 is provided inside the roller 1 over its entire width. The heater 4 is supported at the center of the roller 1 by an electrode 3 attached to a frame 7, and is connected to a power source via the electrode 3 to be energized. A temperature fuse holder 5 has a temperature fuse 8 built therein, and is elastically pressed against the circumferential surface of the fixing roller 1 by a leaf spring 10b. This fuse 8 is connected to a lead wire 9 attached to the frame body 7.
The heater 4 and the power source 17 are connected in series through the heater 4 and the power source 17 (FIG. 5).

Furthermore, the installation of the temperature fuse in this embodiment will be explained using FIGS. 2, 3, and 4. FIG. 2 is a cross-sectional view of the fixing roller 1 with the temperature fuse installed, and FIG. FIG. 4 is a schematic perspective view of a portion of the heat fixing device provided with a temperature fuse, and FIG. 4 is a perspective view of a temperature fuse holder support.

First, the temperature fuse holder 5, which is a good thermal conductor, has a thermal conductivity of 0.001Cat-ey'cd-see °CI'':
electrically insulating material such as alumina (A40.) 96
% ceramic, and has a three-dimensional shape in which the surface 5a that contacts the circumferential surface of the roller 1 is arcuate, and directly contacts and covers the temperature fuse 8. Furthermore, this temperature fuse holder 5 is supported by a holder support 10 which has high heat resistance and a lower thermal conductivity than the holder 5. This holder support 10 fixedly supports the holder 5 on the bottom plate 10m. Above the vertical plate 10d is an arch-shaped leaf spring 10b. Further, this support 10 has ear-shaped attachment portions 1 on both left and right ends of the vertical IK plate 10d.
0c is provided.

On the other hand, the fixing roller 1 is mounted on the side plate 11 of the fixing device F, which faces the fixing roller 1 and the pressure roller 12 in the longitudinal direction.
In this installation, the body 13 is fixed to the part opposite to which the holder support 10 is attached.In this installation, the body 13 is provided with openings 13c and 13d at its bent portions 13m and 13b. . Therefore, the mounting of the support body 10 is carried out in part 1.
0c into the openings 13c and 13d of the mounting plate 13, the support body 10 is supported by the side plate 11 with the mounting portion 10c as a pivot point. At this time, the plate spring 10b comes into contact with the rear plate 13e of the mounting glue 13, and the support body 10 receives an elastic force in the direction of the roller 1 (in the direction of the arrow) by the plate spring 10b. Therefore, the holder 5 fixed to the support 10 has its arcuate surface 5a aligned with the roller 1.
It will press elastically against the circumferential surface. Therefore holder 5
can reduce wear without hindering the rotation of the roller 1. In addition, when removing the holder 5, the mounting part 10c is narrowed by its elasticity to open the opening 1.
Remove from 3e and 13d or bend parts 13a-13b
Just spread it out and remove it. Further, the leaf spring 10b does not need to be made of a particularly springy material, but may be any elastic material.

Here, the temperature fuse holder 5 is preferably made of a variety of materials that have high insulation and heat resistance, such as inorganic materials or organic materials such as resin, but the temperature increase rate of the heating source is 10t"!0 ℃/see, in order to quickly operate the temperature fuse switch,
It is necessary to have thermal conductivity, and for that purpose 0.0
01CI! Lt-51I martyrdom・8ec・℃ or more, preferably 0.05Cs1. -cq/d・see・Tg2fJ
A material having a thermal conductivity of C) or higher is preferable. In other words, if you use ceramics such as beryllia, alumina, or silicon carbide, you can obtain high electrical insulation with a thickness of about 0.3 dew, and the thermal conductivity is also much better than other materials.
The temperature until the temperature fuse blows out is significantly shortened. Furthermore, ceramics such as alumina have PFA, a heat-resistant resin, on the surface that comes into contact with the circumferential surface of the roller as a heating element.
Coat about 20μ of fluororesin such as (5b in Figure 4).
If it is coated with a fluororesin), it will be non-adhesive and will not damage the fluororesin coated roller, etc., and it will be possible to improve the abrasion resistance of the contact side. The material to be coated may be not only fluorine resin but also silicone resin, or may be covered with a heat-resistant film such as polyimide resin, although its non-adhesiveness is inferior.

Here, temperature control of the fixing device F will be explained using FIG. 5.

First, the fixing roller 1 is heated by the heater 4 supported by the electrode 3. Then, according to the temperature detected by the thermistor 14 as a temperature detection means that is in contact with the surface of the fixing roller 1, a switch 16 is turned ON/OFF by a signal from the temperature control circuit 15 to control the surface of the roller 1 to be maintained at a constant temperature. be done. At this time, the temperature control circuit 15 controls the halogen heater 4 to output its maximum rated output when raising the surface temperature of the row 21 from room temperature to the temperature required for fixing, and once the temperature reaches the temperature required for fixing. Then, from then on, the phase control will be applied to 1/! control to output the following output.

In the event that the heater 4 generates heat exceeding the rated temperature, the fuse 8 receives heat exceeding the rated temperature only through the holder 5 and blows out. If the fuse 8 blows out due to heat, the fuse 8 is connected in series between the heater 4 and the power supply, so the heater 4 immediately
The supply of power to is stopped. At this time, in this embodiment, in particular, the fuse 8 is provided so that the heat from the heater 4 is transferred to the fuse via the holder, which has a much better thermal conductivity than air. It is possible to quickly respond to the rising heat and fuse, and the abnormal state can be quickly resolved. Note that 9 in the figure is a lead wire that supplies power to the heater 4.

Next, referring to FIG. 6, an example of the fixing device F using the above embodiment will be shown. In 1-, 12 is a pressure roller,
Sheet P having an unfixed image 21 between it and the fixing roller 1
be held and transported. Then, the unfixed image 21 is heated onto the sheet P using heat from the heater 4. The roller 12 has a core metal 12m covered with an elastic member 12b such as rubber. The fixing row 21 is operated by a motor M-'
The driving force of the chain 2 is transmitted by gears 22 and 23 and rotates, and the pressure roller 12 is rotated as a result of the fixing roller 1. Note that the driving force from the motor M is applied to the pressure roller 1.
It may be transmitted to 2. In the drawings, the frame, side plates, bearings, etc. are omitted.

In this way, the above-mentioned embodiment does not heat the -H roller and detect its side radiation heat as in the conventional example, so the temperature fuse can be heated more quickly.
The present invention can be rapidly fused and cut with a fixed heat of 196° C. Next, using FIG. 7, experimental results showing the good effects of the present invention will be shown.

First, in the above-mentioned example, the applicant conducted an experiment using a device in which a 1.2 KW halogen heater was installed inside a fixing roller made of aluminum with a wall thickness of 2 m 1 m. 1.2
When the fixing roller was heated with the output of KW, as shown in the graph of FIG. 7, the surface temperature of the roller rose over the course of one hour, and for example, rose to 200° C. in about 20 seconds.

Furthermore, the applicant assumed an abnormal situation and conducted an experiment in which power was continuously supplied, but after about 70 seconds, the temperature exceeded 660°C (0 in the figure), which is the melting point of aluminum, and the fixing roller 1 melted. It turns out.

Therefore, we determined that the thermal conductivity is 0.05CaJL-stop-・se
Volume resistivity 1014Ω at e・℃ (at 20℃)
-1 (at 300℃), and dielectric strength 10KV/-
An experiment was conducted to make a holder 5 made of ceramic with an alumina content of 96 degrees Celsius, and the short distance between the fixing roller 1 and the temperature fuse 8 was 0.3.
Temperature fuses rated at ±1.67°C (high-density temperature fuses 4000A series manufactured by Microtemp) are approximately 60
The temperature rise of the holder 5 is shown in the graph (note that it melted in seconds). Also, ■ is the point at which the fuse blows. )
This was 10 seconds shorter than the experimental result of about 70 seconds conducted using a 0.125μ polyimide sheet, and the fixing roller surface temperature was about 600°C, about 10θ°C lower. Therefore, in the event of an abnormality, it is possible to stop energizing the heater 4 before the fixing roller 1 is deformed.

In addition, in order to safely use a heating source that causes a temperature change of at least 10°C/sec, the intermediate member that transfers heat to the overheating prevention device must have a temperature of 0.001Cat-cyy'c.
It is preferable that the temperature is d-8ee·°C or higher. However, it is not limited to this.

As described above, the present invention can also be applied to a heating source with a rapid temperature rise rate. The present invention provides a fixing device having an overheat prevention means.

4. Year-by-year explanation of the drawings Figure 1 is a side sectional view of the heat-fixing roller of a copying machine, Figure 2 is a cross-sectional view of the fuser roller with a temperature fuse installed, and Figure 3 is a heat-fixing device with a temperature fuse installed. 4 is a perspective view of the temperature fuse holder support, FIG. 5 is a block diagram, FIG. 6 is a perspective view of the fixing device, and FIG. 7 is a graph showing experimental results. 00 In the figure, 1...Fixing roller, 3...[&b 4...Halogen heater %5...Temperature fuse holder, 8...Temperature fuse 10d...Vertical plate, 11... Side plate, 12...
・Pressure roller, 13... Mount on body, 13a, 13b.
...Bending portion, 13c, 13d...Opening, 14...Thermistor, 15...Temperature control circuit, 16...Switch〇Applicant Canon Co., Ltd.

Claims (1)

[Scope of Claims] (1) A heating source, a heating element that is heated by the heat from the heating source for heating the sheet, and a heating element that is connected between the heating source and the power source and that is heated by the heat from the heating source. A sheet heating device comprising: a thermally responsive member that changes; and a good thermal conductor that supports the thermally responsive member and contacts a heating element. (2) The sheet heating device according to claim (1), wherein the thermal conductor is made of ceramics. (8) The sheet heating device according to claim (1), wherein the thermal conductor is electrically insulating. (4) The sheet heating device according to claim (1), wherein a heat-resistant resin is coated on the surface of the thermally conductive material that comes into contact with the heating element. (5) The sheet heating device according to claim (4), wherein the heat-resistant resin is a fluororesin. (6) The sheet heating device according to claim 4, wherein the heat-resistant resin is a silicone resin (γ) Claim 1, wherein the heat-resistant resin is a polyimide resin
The sheet heating device according to item 4). (8) As the thermal conductor, the thermal conductivity is 0.001C&t-
The sheet heating device according to claim (1), characterized in that an electrically insulating material having a temperature of 1-.11 ee.° C. or higher is used.