JPH0754416B2 - Fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial field of application) The present invention relates to an image forming apparatus utilizing an electrostatic recording process, such as an electrostatic copying machine and a printer, and more particularly to a fixing device thereof. is there.

(Problems to be Solved by Prior Art) As a means for fixing and fixing a toner image electrostatically adhered to a sheet-like recording material such as paper to the recording material, a pair that are heated to a predetermined temperature and are pressed against each other. Conventionally, a fixing device configured to pass through the pressure contact nip portion of the roller has been widely used.

Such a fixing device has a basic structure including a heating roller in which a heat source such as a halogen lamp is arranged, and a pressure roller arranged in pressure contact so as to have an excessive nip portion. For detecting the surface temperature of the heating roller, for example, a temperature detecting element using a thermocouple, thermistor, etc., and for preventing heating of the heating roller or its vicinity due to control error, for example, a thermoswitch, a thermal fuse, etc. A device provided with an excessive temperature rise prevention element to be used is commonly used.

As for the relational arrangement of these temperature detection element and the excessive temperature rise prevention element, the excessive temperature rise prevention element is appropriately separated from this, in other words, in the vicinity of the center of the passable region of the transfer material as viewed in the longitudinal direction of the heating roller. It is usual to use either a method of arranging the temperature detecting element near the end of the roller or, conversely, a method of arranging the former element at the center of the heating roller and the latter element at the end of the roller. Met.

After all, looking at the temperature distribution of this type of heating roller,
When the temperature rises after the operation of the roller starts, the heat dissipation due to radiation and heat conduction from the roller edge is relatively large, so the temperature near the center of the paper passage area is high and The temperature of the
Since heat is taken by the transfer material passing therethrough, the temperature of the central portion tends to decrease.

Therefore, in the case where the respective elements are arranged in the relation as in the preceding stage, when the temperature rises, the temperature at the position where the temperature rise detecting element is arranged is higher than that at the position where the temperature detecting element is arranged. In order to prevent malfunction of the element, it is necessary to set the operating temperature high.

Therefore, even if the heat source becomes uncontrollable and the overheating prevention element operates in the continuous heating state, the temperature of the heating roller becomes too high by this time and there is a risk of damage, ignition, etc. there were.

Further, in the case of the related arrangement as in the latter stage, when a small recording material that does not pass through the position on the heating roller where the excessive temperature rise prevention element exists is continuously fed, Since the temperature of the heating roller in the vicinity rises, it is necessary to set the operating temperature of the element high, and the same drawbacks as in the above case cannot be avoided.

The present invention has been made to cope with the above situation, and an object of the present invention is to provide a highly safe fixing device that can always be operated in a stable state regardless of usage conditions. It is a thing.

(2) Configuration of the Invention (Technical Means for Solving the Problems) In order to achieve the above object, the present invention provides a heating rotor.
A pressure rotating body that is in pressure contact with the heating rotating body, a temperature detecting element that detects the temperature of the heating rotating body in order to control the temperature of the heating rotating body, and an excessive temperature rise that prevents an excessive temperature rise of the heating rotating body. In a fixing device having a temperature prevention element, a recording material carrying an unfixed image conveyed by a center reference at a pressure contact portion between the heating rotator and the pressure rotator is nipped and conveyed for fixing.
It is characterized in that the temperature detecting element and the excessive temperature rise preventing element are provided in the vicinity of a central portion of a conveying region in a direction orthogonal to a recording material conveying direction.

With this configuration, it is possible to lower the rated temperature of the excessive temperature rise prevention element, prevent the excessive temperature rise of the heating roller, and reliably avoid the risk of equipment damage and ignition due to heating. it can.

(Explanation of Embodiments) FIG. 1 schematically shows a main part of a fixing device according to an embodiment of the present invention. Reference numeral 1 is a heat source 3 such as a halogen heater inside
The pressure roller 2 is in pressure contact with the heating roller, and the recording material carrying the toner image, which is formed in the image forming portion (not shown), is conveyed in the direction perpendicular to the paper surface with the central reference. Then, the fixing is carried out by passing through the pressure contact nip portion N of both rollers.

The heating roller is made of aluminum pipe with a wall thickness of 1.6 mm and an outer diameter of 25 mm coated with a release agent such as PFA.The pressure roller is made of SUS. Those with an elastic layer formed were used.

A temperature detection element 5 and an excessive temperature rise prevention element 4 are respectively arranged in the vicinity of the central portion O of the heating roller 1 and the heater 3 in the longitudinal direction in the left and right symmetrical positions A and B in the figure.

The heater 3 heats the heating roller 1 by generating heat from the power supply 7 via the excessive temperature rise prevention element 4.

The excessive temperature rise prevention element 4 can energize at a temperature lower than the normal fixing temperature and is in a cutoff state at a temperature higher than the rated temperature, and it is preferable to use a thermoswitch (manufactured by Elmwood Co., Ltd.). A thermal fuse may be used. The temperature detecting element 5 is connected to the temperature control device 6 by an NTC thermistor so that the output of the temperature detecting element becomes a predetermined value, that is,
The power supply output is controlled so that the detected temperature of the element can obtain a good fixing property.

With this configuration, when there is a temperature distribution in the longitudinal direction of the heating roller 1 as indicated by symbol a in FIG. 2, the temperature TA at the position A where the temperature detecting element 5 exists and the excessive temperature rise prevention. The relationship of TA = TB can be maintained with the temperature TB at the position B where the element 4 exists.

A curved line b shown by a dotted line in the figure shows the color temperature distribution on the surface of the halogen heater which is a heating element, and the color temperature distribution is determined in consideration of the loss due to radiation and heat transfer from the roller end. .

In the illustrated apparatus, the temperature at point A during the fixing operation is 18
It shall be set at 0 ℃. In this case, since the overshoot is about 20 ° C. in the so-called rise time after the start of energization of the heater until fixing is possible, the temperature at the point A is 200 even when the detection element 5 is operating normally.
It rises up to about ℃.

At this time, the temperature at point B at the same time also becomes 190 ± 5 ° C.

Therefore, it can be seen that if an element having a rated temperature of 210 ° C. is used as the excessive temperature rise prevention element, there is a difference of about 10 ° C. from the maximum temperature of the temperature detecting element, so that it can be sufficiently used.

FIGS. 3, 4, 5A and 5B show the temperature relationship with the position of the temperature detecting element (point A) and the position of the excessive temperature rise preventing element (point B) in the above-mentioned known fixing device. .

Note that FIG. 5B shows the distribution when a small transfer material is passed, and the other figures show the distribution when no paper is passed.

The following table shows the operation modes of the devices shown in FIGS. 3 to 5 as Comparative Examples 1, 2 and 3, respectively.

As described above, this table compares the operation modes of the embodiment shown in FIGS. 1 and 2 and the comparative experimental example shown in FIGS. 3 to 5B.

In each of the examples, an NTC thermistor having a rated temperature of 180 ° C. was used, and a transfer paper having a toner having a good fixing property at a temperature of 160 ° C. or higher was used as a fixing target. The rating of the excessive temperature rise prevention element was set to the maximum temperature reached on the surface of the heating roller plus 10 ° C.

As can be seen from the table, except for the case of FIG. 4 (Comparative Example 2) in which a good fixing property is not finally obtained, the case of the present invention has an excessive temperature rise as compared with the other cases. The rated temperature of the protection element can be set low. In other words, even if the heating element cannot be controlled and is continuously energized, the surface temperature of the heating roller can be kept as low as possible when the energization to the element is interrupted. Alternatively, there is no risk of damage or ignition of the transfer material.

(3) Effects of the Invention Since the present invention has the configuration described above, the operating temperature of the excessive temperature rise prevention element can be lowered in the fixing device having the heating means, so that the fixing device is safe. It greatly contributes to the improvement of

[Brief description of drawings]

FIG. 1 is a schematic front view showing the main part of a fixing device to which the present invention is applied, FIG. 2 is a graph showing the surface temperature distribution of the same heating roller as above, and FIGS. 3 to 5B are temperature detection elements and excessive temperature rise. 6 is a graph showing the surface temperature distribution in a heating roller having various relational arrangements with the prevention element. 1 ... Heating roller, 2 ... Pressure roller, 3 ... Halogen heater, 4 ... Excess temperature rise prevention element, 5 ... Temperature detection element,
6 ... Temperature control device, 7 ... Heating power source.

Claims (1)

[Claims] 1. A heating rotator, a pressure rotator in pressure contact with the heating rotator, a temperature detecting element for detecting the temperature of the heating rotator for controlling the temperature of the heating rotator, and the heating rotator. An excessive temperature rise prevention element for preventing excessive temperature rise of the body, and nipping and conveying a recording material carrying an unfixed image, which is conveyed at a center reference, at a pressure contact portion between the heating rotator and the pressure rotator. In the fixing device for performing the fixing, the temperature detecting element and the excessive temperature rise preventing element are provided in the vicinity of a central portion of a conveying region in a direction orthogonal to the conveying direction of the recording material.