JPH0635353A - Thermal fixing device - Google Patents

Abstract

PURPOSE:To prevent temperature from excessively rising at abnormal time and to prevent the temperature of a part where a paper does not pass from rising when a small-size paper passes for the device having a means preventing the temperature from excessively rising. CONSTITUTION:As to a thermal fixing device in which a heating roller 11 having a heating source inside and a press roller 12 pressing the heating roller 11 and forming a nip part are provided, and in which a temperature detecting means 18 detecting the surface temperature of the heating roller 11 and the means 13 for preventing the temperature from excessively rising which stops energizing the heating source based on the surface temperature of the heating roller are arranged on one end side of the heating roller; the rising of the surface temperature of the heating roller on a side where the temperature detecting means 18 and the means 13 are arranged in the longitudinal direction of the heating roller 11 is set to be equal to or a little slower than that of a central part in the longitudinal direction of the heating roller 11, and is set to be faster than that of the end of the other side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electrophotographic printer,
The present invention relates to a heat fixing device used in a copying machine, an electrostatic recording device, and the like.

[0002]

2. Description of the Related Art Conventionally, a heating roller fixing device has been widely used because of its high thermal efficiency and safety. In this type of heating roller fixing device, in order to prevent the surface temperature of the heating roller from rising excessively when the control of the energization of the heater such as the halogen heater is disabled due to some abnormality. In addition, an excessive temperature rise prevention means such as a thermo switch and a thermal fuse is provided in series with the heater to shut off energization to the heater when the surface temperature of the heating roller becomes abnormally high.

As a means for preventing the excessive temperature rise, a contact type thermoswitch is widely used for a heating roller fixing device in which the surface temperature of the heating roller rises quickly because of its quick response and high reliability. .

[0004]

However, in the above-mentioned conventional apparatus, in the thermoswitch in contact with the surface of the heating roller, toner or the like accumulates on the surface of the thermoswitch due to long-term use and is retained on the surface of the thermoswitch. The clogs of toner that can no longer be transferred from the heating roller surface onto the transfer material may cause image contamination or backside contamination of the transfer material.
It has a drawback that the toner stuck to the surface of the thermoswitch damages the surface of the heating roller. This phenomenon is particularly remarkable in the heating roller fixing device that does not have a cleaning member such as a pad or a blade. In order to eliminate this drawback, it is conceivable that the thermoswitch is not in contact with the heating roller. However, if the thermoswitch is not contacted, not only the response of the thermoswitch becomes slow, but also the gap between the heating roller surface and The mechanism for maintaining a constant state without variation among the elements becomes complicated.

Although the above-mentioned defect can be eliminated by disposing the thermoswitch outside the image area on the transfer material, the area outside the image area of the transfer material is close to the bearing portion even in the heat fixing device. It is often located at the end, and in this part not only heat escapes to the bearing, but also because the heating roller surface temperature rises closer to the end of the heating area of the heater than in the central part in the heating roller longitudinal direction. Slows down. as a result,
When the temperature of the heating roller rises during an abnormality and the thermoswitch is activated, the center of the heating roller is already very hot compared to the end in the longitudinal direction.
There is a risk of smoke and ignition from the heating and fixing device, and sufficient performance cannot be exhibited as a means for preventing excessive temperature rise. This phenomenon is particularly noticeable in a small heating roller fixing device in which the heat capacity of the heating roller is small and the axial length of the heating roller and the heat generation area of the heater are not sufficiently large with respect to the transfer material width.

Further, when such a fixing device is used in a one-sided reference device having a transfer material passing standard at one end of the image forming apparatus, a small size paper having a narrow transfer material width is passed. When this happens, there is a drawback that the temperature rise of the non-sheet passing portion becomes large.

The present invention solves the problems of the above-mentioned conventional apparatus, prevents toner stains on the thermoswitch as a means for preventing excessive temperature rise for a long period of time, and prevents excessive temperature rise at abnormal times. An object of the present invention is to provide a heat fixing device capable of preventing a temperature rise in a non-sheet passing portion when a small size sheet is passed.

[0008]

According to the present invention, the above object is provided with a heating roller having a heating source therein and a pressing roller for pressing the heating roller to form a nip portion. In a heating and fixing device in which a temperature detecting means for detecting a temperature and an excessive temperature rise preventing means for shutting off energization to a heating source depending on the surface temperature of the heating roller are arranged at one end side of the heating roller, Set so that the temperature rise of the heating roller surface on the side where the temperature detection means and the excessive temperature rise prevention means are arranged is equal to or slightly slower than the central portion in the longitudinal direction of the heating roller and faster than the other side end. It is achieved by being done.

[0009]

In the present invention having such a structure, the temperature of the heating roller surface rises quickly in the portion having the excessive temperature rise prevention means, so that the excessive temperature rise of the heating roller surface temperature at the time of abnormality can be prevented. . In addition, since the temperature rise peak is in the center, uniform fixing property can be secured, and the temperature at the end opposite to the temperature detection element and the overheat prevention device is low, so the size is small. The temperature rise in the non-sheet-passing area during paper-passing can be kept low.

[0010]

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

<First Embodiment> FIG. 1 is a sectional view taken along a plane including the axis of the apparatus of this embodiment, and FIG. 2 is a sectional view taken along a plane perpendicular to the axis.

The heating roller 11 has a release layer made of a fluororesin such as PTFE or PFA on an aluminum cored bar, and a halogen heater 14 provided therein receives a signal from a thermistor 18, which is a surface temperature detecting means. The surface temperature is controlled to a predetermined temperature by controlling energization by a control means (not shown). Furthermore, the heating roller 1
1 is supported by bearings 15 on both sides, and is rotationally driven in the direction of arrow A via a drive system (not shown) from the image forming apparatus. The pressure roller 12 is formed by forming an elastic layer of silicone rubber, silicone sponge or the like on a cored bar of iron, stainless steel or the like, and bearings 16 are provided on both sides of the cored bar.
The heating roller 11 is pressed against the heating roller 11 with a constant load by the pressing spring 17 to form a desired nip portion with the heating roller 11. In addition, the heating roller 1
The surface of 1 has a thermoswitch 13 as a means for preventing overheating.
Are in contact with each other, and in the present embodiment, the thermistor 1
8. The thermo switch 13 is outside the image area of the transfer material,
They are arranged in the circumferential direction at substantially the same position in the longitudinal direction.

With such a heat fixing device, the toner image T formed on the transfer material P by the well-known electrophotographic image forming process is permanently fixed on the transfer material.

Next, the apparatus of the embodiment will be described in more detail with specific numerical values.

As the heating roller 11, a cored bar made of aluminum having an outer diameter of 24 mm and a wall thickness of 2 mm is coated with a PFA layer having a thickness of 30 μm. Further, the end portion of the heating roller 11 on the side where the thermistor 18 and the thermoswitch 13 are arranged (the non-driving side in this embodiment) has the thickness of the core bar cut to 1 mm on the outer surface, and the outer diameter is 22 mm. There is.

On the other hand, in the pressure roller 12, a silicone rubber layer having a thickness of 6 mm is formed on an iron rod having an outer diameter of 6 mm, and a PFA tube having a thickness of 50 μm is coated thereon, and the hardness on the roller is 50. Degree (Asker C). The thermistor 18 and the thermoswitch 13 are arranged outside the image area for the transfer material having the maximum size. In this embodiment, the transfer material having the maximum size width is letter size (width 216 mm ×
The length is 279 mm), the position of 108 mm from the center of the image is the transfer material edge, and the position of 103 mm is the image area edge. On the other hand, the thermistor 18 has a contact surface width of 6 mm.
The edge portion of the thermistor 18 is 2 mm outside from the image area by arranging the thermistor center at a position 108 mm from the image center. The thermoswitch has a heating roller 1 with a cap for bimetal protection.
The portion contacting 1 has a disk shape with a diameter of 10 mm, and by arranging the center of the thermoswitch at a position 110 mm from the center of the image, the end of the thermoswitch escapes 2 mm outside the image area.

FIG. 3 shows the temperature distribution on the surface of the heating roller in this embodiment. In particular, after the power source of the image forming apparatus main body is turned on, the surface temperature of the thermistor arrangement portion of the heating roller is a predetermined temperature (warm). It shows the state when the temperature rises). As can be seen from this graph, the surface temperature distribution of the heating roller of the present embodiment has almost no temperature difference between the thermistor / thermoswitch arrangement portion and the central portion, and the central portion has a slightly higher temperature (about 10 ° C).
° C). Further, the surface temperature of the heating roller on the side opposite to the side where the thermistor and the thermoswitch are in contact is lower than that of the thermistor and thermoswitch arrangement section. The surface temperature of the heating roller in the portion (A portion) positioned symmetrically with is about 25 ° C lower.

As described above, by disposing the thermistor 18 and the thermoswitch 13 outside the image area, the surfaces of the thermistor 18 and the thermoswitch 13 are prevented from being contaminated with toner due to long-term use. On the other hand, by disposing the thermistor 18 and the thermoswitch 13 at the end portion of the heating roller 11, the rise of the surface temperature of the heating roller 11 at that portion is delayed as compared with that at the central portion. In particular, regarding the phenomenon that the surface temperature of the central portion of the heating roller 11 becomes extremely high when the thermoswitch 13 is operated in an abnormal state, the end portion of the heating roller 11 is contacted from the outside of the contact portion of the thermoswitch 13 through the bearing portion. By reducing the core metal thickness in the area up to, the heating roller surface temperature of the thermoswitch arrangement part can obtain the same rise as in the central part, so when the thermoswitch operates during an abnormal condition, the heating roller over the entire length of the heating roller, There is no place where the temperature becomes very high. As a result, when abnormality occurs in the energization control of the heater and the thermoswitch located at the same position in the longitudinal direction as the thermistor section operates, the heating roller surface temperature of the thermoswitch placement section of the heat fixing device of the present embodiment is 350 ° C. At that time, the peak temperature in the longitudinal direction of the heating roller is suppressed to 370 ° C.

By thus reducing the thickness of the core metal at the end of the heating roller, the heat capacity at the end of the heating roller is reduced, so that the temperature of the end of the heating roller rises relatively quickly, resulting in a heating roller. Uniformization of the surface temperature distribution in the longitudinal direction can be achieved. By doing so, in the configuration in which the contact-type thermoswitch is provided outside the image area, not only can the peak surface temperature of the heating roller during the thermoswitch operation be suppressed to a low level, but also the thermal efficiency can be increased and the heating roller can be fixed. The effect that the time (wait-up time) required to reach the predetermined temperature required for the above can be shortened is obtained.

FIG. 4 shows the heat fixing device of the present embodiment.
When letter size (width 216 x length 279 mm) transfer material is passed (solid line a), envelope (width 105 x length 24)
It is a heating roller surface temperature distribution when 1 mm) is passed (broken line b).

When the letter size (maximum sheet passing width in this embodiment) is passed, the transfer material takes heat from the heating roller, and the transfer of heat in the longitudinal direction within the core metal of the heating roller causes heating. The temperature distribution in the longitudinal direction of the roller is more likely to be uniform than when it rises (graph in FIG. 3), and the temperature distribution is such that the temperature is slightly higher in the central portion than at both ends. As a result, even if the temperature distribution is uneven at the start-up, at the time of actual paper passing, the surface temperature drops even if heat is removed during paper passing because the end of the opposite side to the thermistor with a low temperature has a large heat capacity. It is difficult to cause poor fixing property due to relatively uniform temperature distribution.

In particular, since the peak of the temperature distribution at the time of rising is near the central portion, the fixing force is weak even in the central portion where the nip is weak and the temperature tends to decrease, and the fixing ability is unstable. Is obtained. On the other hand, when a small size paper such as an envelope is passed, the lower the heat supply amount in the non-sheet passing area is, the smaller the temperature rise in the non-sheet passing area becomes. The higher the heat capacity of the non-sheet passing area, the smaller the temperature rise of the non-sheet passing section. Each of these manifests itself as a surface temperature distribution at the time of rising, so the lower the temperature of the non-paper passing region at the time of rising, the smaller the temperature rise of the non-paper passing portion. Therefore, by reducing the heat capacity on the thermistor side as in the present embodiment, the temperature rise at the opposite side end is delayed compared to the temperature rise at the thermistor arrangement part at the time of rise, thereby raising the temperature of the non-sheet passing part. Can be suppressed. Specifically, as shown by the broken line b in the graph of FIG. 4, the peak of the temperature rise in the non-sheet passing area is about 40 ° C. lower than that in the thermistor section. On the other hand, when the end portion of the heating roller 11 is not thinly machined, the peak temperature of the non-sheet passing region of the heating roller 11 when the envelope is passed is increased by about 60 ° C as compared with the thermistor portion.

<Second Embodiment> Next, a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view of the device of this example, taken along a plane including the axis.

In this embodiment, in order to reduce the heat capacity of the end portion of the heating roller core bar, the inner surface of the core bar made of a pipe material is cut to reduce its thickness. Specifically, the heating roller 5
As 1, a core metal made of an aluminum tube having an outer diameter of 24 mm and a wall thickness of 2 mm and coated with a PFA layer with a thickness of 30 μm is used, and the core at the end where the thermistor 18 and the thermoswitch 13 are arranged is used. 1m thick inside gold
The inner diameter is 22 mm. The arrangement of the pressure roller, the thermistor, and the thermoswitch in the longitudinal direction is the same as in the case of the apparatus of the first embodiment described above, and the description thereof is omitted.

The graph of FIG. 6 shows the temperature distribution of the heating roller surface during warm-up in the heating and fixing device of this embodiment.

As can be seen from the graph of FIG. 6, in this embodiment, the difference between the surface temperature of the thermistor arrangement portion of the heating roller during warm-up and the peak temperature in the longitudinal direction of the heating roller was only 5 ° C., which was abnormal. When the thermoswitch operates, the heating roller surface temperature of the thermoswitch arrangement is 350 ° C, the peak temperature in the longitudinal direction of the heating roller is 365 ° C, and the paper is pinched between the heating roller and the pressure roller. Even if it was done, a slight amount of smoke was generated. At this time, the temperature (A portion) when the temperature of the heating roller on the opposite side to the thermistor / thermoswitch arrangement portion rises is about 25 ° C. lower than that of the thermistor / thermoswitch arrangement portion. In this state, the temperature distribution of the heating roller surface when the letter-size transfer material is passed in the same manner as in the previous embodiment has a relatively uniform temperature for the same reason as in the previous embodiment as indicated by the solid line a in the graph of FIG. Distribution,
Good fixability was secured. In addition, the temperature rise in the non-sheet-passing portion during envelope passage can be suppressed to a low level. Even when an envelope having a width of 106 mm is continuously passed, the peak temperature of the heating roller surface in the non-sheet-passing area is higher than that in the thermistor portion. It was settled at about 40 ° C higher. On the other hand, in the case of the same configuration as the heating roller of the present embodiment, but the inner peripheral surface of the core bar end portion is not cut, the heating roller surface in the non-paper passing area when an envelope of the same size is passed under the same conditions. The temperature peak is about 60 ° C higher than that of the thermistor arrangement part.

Furthermore, in this embodiment, the rise of the surface temperature of the heating roller is also accelerated, and the rise is improved by about 15% as compared with the case where the inner surface of the core metal is not ground. As a result, the wait time is shortened.

As described above, the reason why the excellent effect is obtained compared to the previous embodiment is that the core metal is thinned to the contact area of the thermistor and the thermoswitch in order to scrape the inner peripheral surface of the core metal. This is because it is possible to reduce the heat capacity of the region from the armistor / thermoswitch contact portion to the end portion of the cored bar to a smaller value than in the previous embodiment.

Further, in this embodiment, since the inner peripheral surface of the core metal is cut, the inner diameter of the core metal becomes large. For example, when a halogen heater is used as the heat generating member, the core metal cutting portion is the sealing portion of the halogen heater. Since it corresponds to the position, the temperature rise of the sealing portion of the halogen heater can be small, and the halogen heater can be shortened, which contributes to downsizing of the device.

<Third Embodiment> Next, a third embodiment will be described with reference to FIG.

In this embodiment, the inner peripheral surface of the core metal is cut on both the driving side (right side) and the non-driving side (left side) of the heating roller, and the driving side is the driving side on the non-driving side where the thermistor and the thermoswitch are arranged. On the other hand, the cutting area is made larger. Specifically, the heating roller 81 has an outer diameter of 24 m.
m, a core metal made of an aluminum tube having a wall thickness of 2 mm and coated with a PFA layer with a thickness of 30 μm. At this time, at the non-driving side end portion, the inner peripheral surface is shaved by 1 mm, the thickness thereof is set to 1 mm, and the cutting width is set to 25 mm, so that the cutting region covers the abutting portion of the thermistor and the thermoswitch. On the other hand, on the driving side, the inner peripheral surface is cut by 1 mm to make the thickness 1 mm and the cutting width 10 mm. The arrangements of the pressure roller 12, the thermistor, and the thermoswitch are the same as those in the first and second embodiments described above, and the description thereof will be omitted.

FIG. 9 is a graph showing the temperature distribution of the heating roller surface when the heating and fixing device of this embodiment warms up. As can be seen from this graph, the heating roller surface temperature distribution during warm-up becomes extremely uniform in the longitudinal direction within the image area. Furthermore, in the part A located on the opposite side of the thermistor arrangement part, it is about 15 compared to the thermistor part.
° C is low. As a result, the peak temperature in the longitudinal direction in the heating roller and the rising speed of the heating roller surface temperature when the thermoswitch operates at the time of abnormality are the same as in the case of the second embodiment described above, and are shown in the graph of FIG. As shown in the figure, a very uniform temperature distribution is obtained during letter-size paper passing (solid line a), and the temperature rise in the non-paper-passing area when continuous narrow-width transfer material such as envelopes is continuously fed to the thermistor placement area. Compared to a heating roller that uses a core bar that has not been cut, it is kept out of contact by approximately 10 ° C. It was possible to lower the temperature rise in the paper area.

By thus cutting both ends of the core metal to reduce the heat capacity, a uniform temperature distribution can be obtained in the longitudinal direction of the heating roller, and the lengths of the heating roller and the heater can be minimized. It will be composed. In addition, the heat capacity of the end of the core on the side where the thermistor and thermoswitch are arranged is smaller than the heat capacity of the end on the opposite side. It is also possible to minimize the temperature rise in the non-sheet passing area.

[0034]

As described above, according to the present invention, in the heating roller fixing device, the heat capacity of the end portion of the core metal on the side where the thermoswitch and thermistor of the heating roller are arranged is reduced.
Even if the length of the heating roller fixing device is reduced, a uniform temperature distribution can be obtained over the transfer material image area from the thermistor with the outer edge of the image area and the thermoswitch arrangement part. The heating roller surface temperature can be kept low, and at the same time, the heating roller surface temperature can rise faster, the wait time can be shortened, and the temperature rising on the opposite side of the thermistor can be delayed. Thus, it is possible to suppress the temperature rise in the non-sheet passing area at the time of passing the small size sheet, which is a problem in the one-sided reference image forming apparatus. Further, in the present invention, in order to reduce the heat capacity of the core of the heating roller, it can be carried out by a simple means of thinning the wall thickness by simply cutting the end of the heating roller core, It is also very advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a device according to a first embodiment of the present invention in a plane including an axis.

FIG. 2 is a cross-sectional view taken along a plane perpendicular to the axis of the device shown in FIG.

FIG. 3 is a diagram showing a temperature distribution when the apparatus of FIG. 1 is warmed up.

FIG. 4 is a diagram showing a temperature distribution when the apparatus of FIG.

FIG. 5 is a cross-sectional view taken along a plane including the axis of the second embodiment device.

FIG. 6 is a diagram showing a temperature distribution when the apparatus of FIG. 5 is warmed up.

FIG. 7 is a diagram showing a temperature distribution when the apparatus of FIG.

FIG. 8 is a cross-sectional view taken along a plane including the axis of the third embodiment device.

9 is a diagram showing a temperature distribution when the apparatus of FIG. 8 is warmed up.

FIG. 10 is a diagram showing a temperature distribution when the apparatus of FIG.

[Explanation of symbols]

 11; 51; 81 heating roller 12 pressure roller 13 excessive temperature rise prevention means (thermo switch) 18 temperature detection means (thermistor)

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yuko Tanaka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. A heating roller having a heating source inside and a pressing roller for pressurizing the heating roller to form a nip portion, and temperature detecting means for detecting the heating roller surface temperature and heating roller surface temperature. In the heat fixing device in which the excessive temperature rise preventing means for cutting off the power supply to the heating source is arranged at one end side of the heating roller, the side where the temperature detecting means and the excessive temperature rise preventing means are arranged in the longitudinal direction of the heating roller. The heating and fixing device is characterized in that the rise of the heating roller surface temperature is set to be equal to or slightly slower than that of the central portion in the longitudinal direction of the heating roller and faster than that of the other side end.