JPH06181102A - Manufacture of ptc resistor - Google Patents

Abstract

PURPOSE:To provide the manufacturing method of a PTC resistor which has a low specific resistance at the room temperature and excellent PTC characteristic. CONSTITUTION:A PTC resistor is manufactured by setting the temperature dropping speed of an element composed mainly of a vanadium oxide in a temperature range around the transition temperature of the element (PTC characteristic manifesting temperature) at <100 deg.C/h in the temperature dropping process after baking the element. It is preferable to start the temperature range around the transition temperature of the element after the temperature of the element drops to 300 deg.C and to set the temperature dropping seed at <=50 deg.C/h.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a PTC resistor, and more particularly to temperature control in its firing process.

[0002]

2. Description of the Related Art Conventionally, a large PTC (Positive Temperature Coefficien) has been used as a current limiting element for suppressing overcurrent.
t) ceramics having the effect of BaTiO ₃ (barium titanate) and V ₂ O ₃ (vanadium trioxide) are known.

Of these, BaTiO ₃ is widely used as a positive temperature coefficient thermistor for weak current applications, but if it has a low room temperature resistance, it has several Ω or more and a large watt loss.

The appearance of the PTC effect is related to the mechanism of the grain boundary, and although the grain boundary has a high resistance due to the rise in temperature, the grain boundary breaks due to the absorbed energy and so on. Not suitable for.

On the other hand, when Cr is added to V ₂ O ₃ in the form of an oxide and the composition of (V _1-x Cr _x ) ₂ O ₃ is within the range of 0 ≦ x ≦ 0.015, the PTC effect is not obtained. well known.

Such a V ₂ O ₃ PTC resistor is Ba
Although the specific resistance can be reduced by about four orders of magnitude as compared with TiO ₃ , it has poor sinterability as a ceramic and has a problem in thermal shock resistance when a large current is applied.

Therefore, the strength is improved by improving the sinterability by a method such as adding various metals as a sintering aid.

[0008]

However, the V ₂ O ₃ -based P
When manufacturing a TC resistor, it is necessary to fire at a temperature above the melting point of the metal added as a V ₂ O ₃ ceramics sintering aid, but due to the difference in the temperature pattern during firing, the sinterability of the ceramics and the ceramics The PTC characteristics possessed by the can vary greatly.

Therefore, there is a demand for a technique for manufacturing a PTC resistor having good characteristics by sintering an element with an appropriate temperature pattern.

The present invention has been made on the basis of the above-mentioned background, and controls the temperature pattern during firing of the device,
It is an object of the present invention to provide a method for manufacturing a PTC resistor having excellent TC characteristics.

[0011]

In order to solve the above problems, the present invention provides a method for manufacturing a PTC resistor having a baking step of baking an element containing vanadium oxide as a main component. Provided is a method for manufacturing a PTC resistor, characterized in that a temperature lowering rate in a temperature range around a device transition temperature (PTC characteristic expression temperature) is set to less than 100 (° C./h) in the process.

In the method of manufacturing the PTC resistor, the temperature range around the element transition temperature is set to 300 ° C. to the temperature at which the temperature lowering process ends, and the temperature lowering rate is set to about 50.
Also provided is a method for manufacturing a PTC resistor, which is (C / h) or less.

The present invention will be described in more detail below.

In the above firing step, temperature control of the device is important for obtaining good characteristics, and by performing this temperature control satisfactorily, a PTC resistor having a small room temperature specific resistance and excellent PTC characteristics can be obtained. To be

Generally, in a V ₂ O ₃ -based PTC element, the PTC expression temperature (transition point of the element; usually 150 ° C. to 20 ° C.)
The lattice constant changes at 0 ° C. When the device is rapidly heated or cooled around this transition point, thermal strain concentrates on the crystal grain boundaries to generate microcracks, which increases the specific resistance, particularly room temperature specific resistance, and deteriorates the PTC characteristics.

In the present invention, the concentration of thermal strain is relaxed and the generation of microcracks is suppressed by setting the cooling rate of the element to less than 100 ° C. in the temperature range around the transition point of the element.

The element transition point is 150 ° C. to 200 ° C.
The temperature range around the transition point is, for example, 150 to 200 ° C., preferably 300 ° C. to the temperature lowering process end temperature (or room temperature).

The rate of temperature decrease in the above temperature range is
It is preferable to set the temperature lower than the normal temperature lowering rate, for example, less than 100 ° C./hr, preferably about 50 ° C./hr or less.

By setting the cooling rate of the element to less than 100 ° C. in the temperature range around the transition point of the element as described above, the concentration of thermal strain is relaxed, the generation of microcracks is suppressed, and good PTC characteristics are obtained. A PTC resistor having is obtained.

[0020]

EXAMPLE In this example, the PTC resistor was fired in various temperature patterns to examine its characteristics.

First, a molded body to be fired is manufactured. This molded product can be obtained by various methods, but in this example, the molded product obtained in the following step (a) was used.

(A): V ₂ O ₃ and Cr ₂ O ₃ are weighed in a mixing ratio such that (V _{0 · 996} Cr _{0 · 004} ) ₂ O ₃ is obtained after solid solution of Cr, and the mixture is placed in alcohol for 24 hours. After wet pulverizing and mixing with, and drying, the obtained powder is calcined in a hydrogen stream at 1200 ° C. for 3 hours. To the calcined powder thus obtained, iron fine powder (average particle size 8μ) was added so that the iron equivalent amount was 10 wt% of the powder amount, wet-milled and mixed in alcohol for 12 hours, and obtained after drying. An organic binder is added to the powder and pressure molding is performed at a pressure of 1.5 ton / cm ² to obtain a molded body.

Next, using the above-mentioned molded body, firing is carried out in a hydrogen stream in the temperature pattern shown in FIG. 1 to obtain (V _{0 .996} Cr
_0.004 ) ₂ O ₃ ceramic resistor sample 1 was obtained. Further, as a conventional example, firing was performed in the conventional temperature pattern shown in FIG.

As shown in FIG. 1, in the sample 1 according to this example, in the cooling process of the fired element, the temperature decreasing rate before and after the transition point of the element (300 ° C. to room temperature) was 50 ° C./hr.
And made small. On the other hand, in Comparative Example 1, the temperature lowering rate is 100 ° C./hr even near the transition point of the device.

Table 1 shows the specific resistance values of Sample 1 and Comparative Example 1.

[0026]

[Table 1]

FIG. 3 is a graph showing the correlation between the temperature and the specific resistance value of these samples. In FIG.
The line and the line B represent the specific resistance with respect to the temperature of Sample 1 and Comparative Example 1, respectively.

As shown in this figure, the comparative example has a high specific resistance near room temperature, whereas the sample 1 has a low specific resistance near room temperature, and the specific resistance rapidly increases from around 120 ° C. It can be seen that good PTC characteristics are obtained.

[0029]

As described above, according to the present invention, the temperature lowering rate near the transition point of the element is reduced in the temperature lowering process during firing of the element.

Therefore, the PTC having a good PTC characteristic with a low room temperature specific resistance in which grain boundary destruction due to thermal strain is suppressed.
A resistor is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a firing temperature pattern according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a firing temperature pattern according to a conventional example.

FIG. 3 is a graph showing the correlation of the specific resistance with respect to the temperature of each element.

Claims (2)

[Claims] 1. A method of manufacturing a PTC resistor having a firing step of firing an element containing vanadium oxide as a main component, comprising: a temperature around an element transition temperature (PTC characteristic expression temperature) in the temperature decreasing step of the firing step. The temperature decrease rate in the range is 100 (℃
/ H), the method for producing a PTC resistor. 2. The method of manufacturing a PTC resistor according to claim 1, wherein a temperature range around the element transition temperature is set to 300 ° C. to a temperature lowering process end temperature, and the temperature lowering rate is approximately 50 (° C. /
h) A method of manufacturing a PTC resistor, characterized in that: