JPH03223879A - Device for preventing excessive rise of temperature - Google Patents

Abstract

PURPOSE:To improve detecting accuracy by providing a softening member whose softening point is higher than the actuating temperature of a temperature excessive rise preventing element and which softens before the temperature excessive rise preventing element actuates in the case that the temperature abnormally rises on a part of a spacer member. CONSTITUTION:The temperature excessive rise preventing element 4 which shuts off an energizing path to a heater when the temperature excessively rises is attached to a shaft 16 and the spacer 15 made of heat resistant resin exist at both ends of the shaft 16, so that the shaft 16 and the temperature excessive rise preventing device 4 maintain a fixed gap with a fixing roller 1. The substance which is not softened in a conventional specification state but softened in a state where the temperature excessively rises is selected for the spacer 15. When the spacer 15 is softened, the element 4 is immediately abuts on the roller 1 and actuates to shut off energizing for the heater 3. Thus, the energizing for the heater 3 is early shut off when the temperature excessively rises and fuming and firing are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an excessive temperature rise prevention device used in a fixing device or the like to prevent excessive temperature rise of a rotating body.

[Prior Art] FIG. 4 is a schematic perspective view of a conventional heat roller fixing device.

In Fig. 4, 1 is a fixing roller as a heating fixing member, which is a layer of tetrafluoroethylene resin or the like provided on a core metal material such as aluminum, and 2 is an elastic body such as silicone rubber on a core metal 2a such as stainless steel. This is a pressure roller provided with layer 2b.

A heater 3 as a heating means is disposed inside the fixing roller 1 along its longitudinal direction, and this heater 3 detects when the fixing roller 1 is overheated beyond a predetermined temperature and cuts off the circuit. It is connected to a power source 7 via an over-temperature rise prevention element 4 that contacts the roller and a relay 6 that turns on and off electricity to the heater 3 under the control of a temperature control circuit 5 as a control means. 5 is fixing roller 1
The relay 6 is controlled to be turned on or off in accordance with the output of a temperature sensing element 8, which serves as a detection means for detecting the temperature.

The fixing roller 1 is rotationally driven by a motor M via gears 10, 11, 12 and a chain 13, and as the fixing roller 1 rotates, the pressure roller 2 is driven to rotate.

P is a recording material having an unfixed image 14, and a fixing roller 1
The unfixed image is fixed by being conveyed while being held between the roller 2 and the pressure roller 2 while being heated.

In the above configuration, if the relay 6 fails and the heater 3 continues to be energized, the fixing roller 1 is heated to a predetermined temperature or higher, and the excessive temperature rise prevention element 4 is activated, thereby cutting off the energization to the heater 3.

A temperature fuse or thermoswitch is used as the overheating prevention element.

Since the excessive temperature rise prevention element is used in contact with the fixing roller, toner and paper powder may accumulate on the contact surface with the fixing roller, and the surface layer of the fixing roller may be coated with PF.
There was a problem that the release layer of A and the like was worn out, causing offset.

Additionally, there was a problem in that the accumulated toner spilled out and adhered to the recording material, staining the image.

As a countermeasure against these problems, it has been considered to place an excessive temperature rise prevention device close to the fixing roller without contacting it.

[Problems to be Solved by the Invention] However, when an overheating prevention element is provided on the fixing roller in a non-contact manner, heat conduction is slow, so it is difficult to detect overheating and cut off power to the heater. This was causing a problem as it slowed down and produced smoke. Further, in order to improve the detection accuracy, it is necessary to make the gap with the fixing roller extremely accurate, but this is technically difficult and results in an increase in cost.

[Means for Solving the Problems] The present invention, which solves the above problems, includes a rotating body heated by a heating source, and an energizing path to the heating source when the rotating body has an abnormal product temperature, which is disposed in a non-contact manner on the rotating body. In an overtemperature-rise prevention device having an over-temperature-rise prevention element that blocks the It is characterized by having a softening member which softens before the overheating prevention element is activated in the event of an abnormal product temperature.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a perspective view of an embodiment of the invention. In the figure,
Reference numeral 1 denotes a fixing roller, which has a core made of aluminum or iron coated with a heat-resistant release layer such as PFA or PTFE. A heater (not shown) is contained in the core metal to heat it. Both ends of the fixing roller 1 are rotatably held by bearings 21a and 21b.
It is supported by b. 2 is a pressure roller, which has a heat-resistant elastic layer such as silicone rubber formed around a core metal such as stainless steel. Both ends of the core are bearings 19
The fixing roller 1 is supported by a pressure spring 20 and is pressed against the fixing roller 1 by a pressure spring 20. The surface temperature of the fixing roller 1 is maintained at a predetermined temperature by a heat-sensitive element and a control circuit (not shown).

With this configuration, the overtemperature rise prevention element 4, which cuts off the current supply path to the heater in the event of an overtemperature rise, is attached to the shaft 16. There are spacers 15a and 15b made of heat-resistant resin at both ends of the shaft 16, thereby maintaining a constant gap between the shaft 16 and the excessive temperature rise prevention device 4 with respect to the fixing roller 1. The surface of the fixing roller 1 that the spacer 15 comes into contact with is coated with PF to prevent wear.
Preferably, the material is coated with A or PTFH.

Further, it is preferable to contact the spacer 15 outside the paper passing area to prevent toner and paper dust from accumulating on the spacer 15. Spacer 15
Select a material that does not soften under normal specification conditions, but softens under excessive temperature conditions. In a typical fixing device, the temperature of the fixing roller is 200° C. or less, and it is best to select a resin that softens when the temperature is higher than that.

Examples include polyamideimide (softening temperature 274°C), glass fiber-containing polyether sulfone (softening temperature 216°C),
Glass fiber-filled polyethylene terephthalate (softening temperature 235℃), glass fiber-filled polyamide (softening temperature 22℃)
A resin having a softening temperature exceeding 200°C, such as 8°C), can be used as the spacer 15.

In addition, the softening temperature is based on the J I 5K2531 ring and ball method.

Further, in this embodiment, the softening temperature T of the spacer is set higher than the operating temperature T2 of the overheating prevention element.

Therefore, when the spacer softens, the excessive temperature rise prevention element immediately comes into contact with the roller and operates to turn off the power to the heater.

Further, the fixing roller 1 may have a temperature distribution in the roller axial direction.

FIG. 7 is an example of the roller temperature distribution during overheating. Between the spacer position and the excessive temperature rise prevention element position, the roller temperature at the excessive temperature rise prevention element position is higher by ΔT.

When there is such a temperature difference ΔT, it is preferable to select the spacer resin and the excessive temperature rise prevention element so that T1ΔT>T2.

[Example of Practical Experiment] The same fixing roller heater as in the above-mentioned example was used, and the distance between the thermoswitch and the fixing roller was maintained at 0.5 mm with a spacer made of glass fiber-containing polyethylene terephthalate (softening temperature: 235° C.). As a result, the relationship between the operating temperature of the thermoswitch and the excessive temperature rise of the fixing roller was as shown by the solid line A in FIG. As a result, a thermoswitch with an operating temperature of 200°C to 230°C can be used, and even a thermoswitch with the lowest operating temperature of 20.0°C will not be erroneously activated during printing.

[Comparative Experimental Example] A fixing roller with a length of 260 mm, an outer diameter of 30 mm, and a wall pressure of 3. 25μm PFA on Omm aluminum core metal
A coated one was prepared and a 750W heater was placed inside. As an excessive temperature rise prevention device, a thermoswitch was held at a distance of 0.5 mm from the fixing roller. Thermoswitches with different operating temperatures were attached to this fixing device, the temperature was forcibly raised from room temperature 20° C., and the temperature of the fixing roller when the thermoswitches were activated was measured. The results are shown by broken line B in FIG. Operating temperature σ of 200°C] When the thermoswitch was used, the temperature of the fixing roller rose to 420°C, causing smoke. On the other hand, if a thermoswitch with an operating temperature of 190°C is used, the temperature rise will decrease to 380°C, or
The thermo switch warmed up during printing, and even though the temperature did not rise too much, the thermo switch activated, making the printer unable to operate.

FIG. 6 shows another embodiment of the invention.

In the above embodiment, the entire spacer 15 was made of heat-resistant resin, but as shown in FIG. By using a resin with lower heat resistance, it is possible to prevent excessive temperature rise at a lower temperature than in the above-mentioned embodiments, and to produce a spacer at a lower cost. The portion 24 that comes into contact with the fixing roller can be made of polyamideimide or the like as in the previous embodiment. Further, for the portion 25, Boacarbo, glass 18M polybutylene terephthalate, polyarylate, etc. can be used. By configuring the spacer 15 with two or more parts in this way, when the temperature rises too much, the part 25 melts quickly, and the overheating prevention device approaches the fixing roller 1 to quickly stop energizing the heater. . On the other hand, under normal conditions, the temperature of the fixing roller 25 can be kept below the heat distortion temperature, and the excessive temperature rise prevention device will not accidentally approach the fixing roller and operate. It is also possible to reduce costs by reducing the amount of expensive heat-resistant resin used.

FIG. 3 shows yet another embodiment of the invention. In this configuration, the excessive temperature rise prevention element 4 is fixed, and when the temperature rises excessively, the heat insulating bushing 23 melts and the fixing roller 1
is pushed up by the pressure roller 2, and the fixing roller l approaches the excessive temperature rise prevention device 4, causing the excessive temperature rise prevention device 4 to operate quickly. The pressing direction of the pressure roller 2 and the direction of the excessive temperature rise prevention element 4 are adjusted so that when the heat insulating bushing 23 is melted, it is pushed by the pressure roller 2 and moves in the direction in which the fixing roller 1 moves or approaches the excessive temperature rise prevention element 4. The location can be determined. Most preferably, the excessive temperature rise prevention device 4 is provided on the extension of the pressure roller in the pressing direction. FIG. 3(a) shows a normal state, and FIG. 3(b) shows a state in which the heat insulating bushing 23 melts when the temperature rises excessively and the fixing roller 1 and the excessive temperature rise prevention device 4 come into contact with each other.

[Effects of the Invention] As explained above, by making the excessive temperature rise prevention device non-contact with the fixing roller under normal conditions, the coating of the fixing roller is not damaged and the toner and paper This also solved the problem of powder accumulating and spilling out, staining recording materials. Furthermore, when the temperature rises excessively, the fixing roller and the overheating prevention element come into contact with each other, so that the current supply to the heater can be cut off at an early stage, thereby making it possible to prevent smoke and ignition.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, FIGS. 2(a) and 2(b) are longitudinal sectional views of an embodiment of the present invention, FIGS. 3(a) and 3(b), )? S A vertical sectional view of another embodiment of the present invention, FIG. 4 is a perspective view of a conventional example, FIG. 5 is a correlation diagram between the operating temperature of the thermoswitch and the temperature of the fixing roller, and FIG. FIG. 7 is a vertical cross-sectional view of the embodiment, and FIG. 7 is an axial distribution diagram of the temperature of the fixing roller during excessive temperature rise. 1 is the fixing roller 2, the pressure roller 3, the heater 4, the overheating prevention element 15, the spacer 16, the shaft 17, the wing 18, the long size 20, the pressure wing 21, the hair ring 22, the side plate 23, the heat insulating bushing. (ρ) (Siri (ku) Ru) Figure 5 βν Otsu V Otsu? h51UL made by IC Nobumonui-j

Claims (3)

[Claims] (1) An overtemperature rise prevention element that includes a rotating body that is heated by a heating source and an overtemperature rise prevention element that is disposed in a non-contact manner on the rotating body and cuts off the energization path to the heating source when the temperature of the rotating body increases abnormally. In the prevention device, at least a part of the spacer member that guarantees the distance between the rotating body and the overheating prevention element has a softening point higher than the operating temperature of the overheating prevention element, and An excessive temperature rise prevention device comprising a softening member that softens before the temperature rise prevention element is activated. (2) The excessive temperature rise prevention device according to claim 1, wherein the softening member is a bearing made of resin. (3) The excessive temperature rise prevention device according to claim 1, wherein the softening member is a heat insulating bush.