JP3067396B2 - Rapid heating type PTC thermistor heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device for a PTC thermistor which is applied to a heater for fixing a heat of a copying machine.

[0002]

2. Description of the Related Art A PTC (positive resistance temperature characteristic) thermistor is, as shown in FIG. 6, formed with electrodes 1 on both surfaces of a PTC thermistor 2, and generates heat by applying a voltage to both electrodes. The resistance value rises sharply at
It has the feature of high safety and is used as various heaters for heating. Also, this PTC thermistor
Since an inrush current is generated at the time of incoming power, it is also suitable for applications that require a fast rise in temperature. Among these applications, a heater for heating and fixing has recently attracted attention particularly as an application requiring a rise.

[0003] As means for increasing the rising speed,
Heretofore, a method of reducing the resistance value to increase the inrush current and a method of reducing the size and thickness of the entire PTC thermistor have been considered.

[0004]

However, the method of reducing the resistance value has a range that can be used in consideration of the operating current of the breaker and the like, and the method of reducing the size and thickness of the PTC thermistor involves safety, strength and heat capacity. There was a limit from the aspect of etc. In addition, as another means,
JP-A-136193 proposes a method of forming an electrode plate as a sprayed layer, but it has not been a fundamental solution.

The problem to be solved by the present invention is to provide a PTC thermistor heating device which has a simple manufacturing process, can be manufactured stably, and has a fast heating rise time.

[0006]

In order to solve this problem, a rapid heating type PTC thermistor heat generating apparatus according to the present invention comprises a pair of electrodes having different areas formed on opposite surfaces of a flat PTC thermistor. In addition, an electrode having a smaller area is closely attached to a heat radiating plate in contact with the object to be heated.

[0007]

According to the PTC thermistor heating device of the present invention, as shown in FIG.
The area of the electrode 1a is made different, and the electrode 1a having a small area is brought into close contact with the radiator plate on the side that comes into contact with the object to be heated. This effect will be described with reference to the drawings. FIG.
(B) shows the relationship between the thickness direction and the electric field density when the PTC element 2 of (a) is viewed in the thickness direction. That is, when a voltage is applied to the PTC element 2, the concentration of the voltage is likely to occur because the resistance near the side 1a where the electrode area is small is high. Further, due to the voltage concentration, the temperature rises, the resistance value increases according to the PTC characteristic, and the voltage concentration further increases. FIG. 3 is a circuit diagram for explaining the phenomenon.
4 shows an equivalent resistance of the C element 2. This shows that the resistance values of the PTC element 2 on the electrode 1a side, the central part, and the electrode 1b side are different. In the above case, 1a having a small electrode area
The rate of temperature rise on the side is remarkably fast because the conventional PTC thermistor heat-generating device generates heat from near the center, whereas heat is generated from near the surface on the heat-dissipating side. That is, the present invention intentionally utilizes a pinch effect on the heat radiation side.

Further, the electrode 1a on the side having the smaller area is PT
Since it is near the center of the surface of the C element 2 and hardly protrudes to the end face, there is a merit that the withstand voltage is improved. Also, when joining the electrode plates, the possibility that the brazing material or the adhesive adheres to the end face is small, so that the safety is improved, the fabrication is easy, and the improvement of the yield can be expected.

[0009]

EXAMPLE A heat sink 3 was formed on a 15 × 30 × 3 mm PTC element in which electrodes 1a having three types of areas as shown in FIG. 7 were formed on one side and electrodes 1b were formed on the other side. A heater as shown in FIG. 4 was assembled. 1 for both electrodes
00V was applied and the relationship between the elapsed time and the surface temperature on the electrode 1a side was measured. As a result, as shown in FIG. 7, the conventional one (●) in which electrodes were formed on the entire surface on both sides took nearly 25 seconds to reach a steady state, whereas the one with a small electrode area (▲) took 15 seconds. It becomes steady in about seconds, and the speed of the rising temperature is remarkably improved.

[0010] In addition, when the rising characteristic of the PTC thermistor heating device of the present invention is operated more efficiently, a heat insulating material may be interposed between the electrode portion on the back of the heater and the side surface of the PTC element, or silicone resin, epoxy resin, polyamide, or the like. Resin, imide resin, ketone resin, fluorine resin,
A method of solidifying the periphery with a polyphenylene sulphite resin or the like may be used.

The present invention is not limited to the configuration shown in FIG. 1, but may be changed depending on the use conditions, as shown in FIGS. 5A, 5B, 5C, and 5C.
Shapes such as (d), (e) and (f) may be used. In short, it is only necessary that the areas of the opposed electrodes 1a and 1b are different. When an Ag electrode is used, it is not necessary to form a large area on the entire surface in consideration of Ag migration, and it may be formed slightly inside from the end face. Also,
The PTC element 2 is not limited to a rectangle, but may be a disk as shown in FIG. 5 (g). In this case, it is preferable that the electrode 1a on the side with the smaller area is formed in the center of the PTC element 2. Further, the PTC thermistor heat generating device of the present invention may be used alone or a plurality of PTC thermistor heat generating devices may be used in a concentrated manner.

[0012]

As described above, according to the present invention, PT
P is fast rising time without excessively thinning the C element
A TC thermistor heating device can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of a PTC thermistor heating device of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a thickness direction of a PTC element and an electric field density in the present invention.

FIG. 3 is an equivalent circuit diagram of a resistance of a PTC element according to the present invention.

FIG. 4 is an explanatory diagram illustrating a configuration of a heater according to the embodiment of the present invention.

FIG. 5 is a perspective view showing each example of another PTC thermistor heating device of the present invention.

FIG. 6 is a perspective view of a conventional PTC thermistor heating device.

FIG. 7 is a graph showing the rising characteristics of the PTC thermistor heating device of the present invention in comparison with a conventional example.

[Explanation of symbols]

1a, 1b: Electrode, 2: PTC element, 3: Heat sink, 4:
Electrode plate, 5: adhesive, 6, 7, 8: resistor

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05B 3/14

Claims (1)

(57) [Claims] To 1. A facing surface of the plate-like PTC thermistor,
A rapid heating type PTC thermistor heat generating apparatus, wherein a pair of electrodes having different areas are formed, and an electrode having a smaller area is brought into close contact with a heat radiating plate on a side in contact with an object to be heated.