JPH0567504A - Manufacture of ptc resistance element - Google Patents

Abstract

PURPOSE:To provide a PTC resistance element manufacturing method by which a PTC element having a high PTC characteristic can be obtained by uniformly dispersing Cr against V2O3. CONSTITUTION:This PTC resistance element is manufactured by mixing vanadium trioxide (NH4)2Cr2O7 which is an alcohol-soluble chromium compound, and alcohol and performing calcination, baking, etc., on the mixture after the (NH4)2 Cr2O7 is resolved by heating the mixture.

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 resistance element.

[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) obtained by adding a compound of chromium (V _1-x Cr _x ) ₂ O ₃ (0 <X ≤0.01
5) etc. are known.

Of these, BaTiO ₃ is widely used as a positive temperature coefficient thermistor for low-voltage applications, but even if it has a low room temperature resistance, it has a large watt loss of several Ω or more, and P
The appearance of the TC effect is related to the mechanism of the grain boundary, and although the grain boundary becomes high resistance due to the temperature rise, it is not suitable for electric power because it causes grain boundary destruction due to absorbed energy. ..

On the other hand, (V _1-x Cr _x ) ₂ O ₃ is suitable for electric power because it can reduce the specific resistance by about four digits compared with BaTiO ₃ , but it has poor sinterability as a ceramic. There was a problem with thermal shock resistance when a large current was applied.

[0005]

Therefore, in order to solve the above-mentioned problems, the applicant of the present invention first applies V ₂ O ₃ and Cr ₂ O.
Fe ₂ O ₃ or a simple substance of Fe is added as a sintering aid to a powder obtained by mixing ₃ and ₃ in alcohol and then calcining, so that PT having good sinterability and excellent strength can be obtained.
They found that a C-resistive element could be obtained and proposed it.

However, in this manufacturing method, Cr ₂ O
_{Since 3} is insoluble in alcohol, V ₂
The dispersibility when mixed with O ₃ is poor, and it is difficult to uniformly disperse Cr.

Therefore, the PTC resistance element obtained by the above manufacturing method has a problem that the PTC characteristic is deteriorated.

The present invention has been made under such a background, and a PT in which Cr is uniformly dispersed in V ₂ O ₃ is obtained.
Provided is a method for manufacturing a C-resistive element, which has high PTC characteristics.
The purpose is to obtain a C resistance element.

[0009]

Means and Actions for Solving the Problems The present inventors have
In the process of manufacturing a PTC resistance element, when Cr is dispersed in V ₂ O ₃ in alcohol, when Cr is mixed in a form that dissolves Cr in alcohol, Cr is uniformly dispersed in V ₂ O ₃ . As a result of repeated earnest experiments,
The present invention has been completed.

That is, according to the present invention, a chromium compound and an alcohol are added to vanadium oxide and mixed, and in the method for producing a PTC resistance element in which the mixture is baked, ammonium dichromate [(NH ₄ ) _{2 is} used as the chromium compound. Cr
₂ O ₇ ] is used.

As described above, Cr is used as a compound soluble in alcohol, and this compound, alcohol and V ₂ O ₃ are added.
When Cr is mixed with Cr, Cr is uniformly dispersed in V ₂ O ₃ , so that moldability is improved and good PTC characteristics are obtained. Therefore, the PTC characteristics of the PTC resistance element can be improved regardless of the type of sintering aid.

As such a chromium compound, (NH ₄ ) ₂
There are Cr ₂ O ₇ , copper dichromate (CuCr ₂ O ₇ ) and the like, both of which improve the dispersibility of Cr in V ₂ O ₃ , but (NH ₄ ) ₂ Cr ₂ O ₇
Is easily decomposed by heating it to 185 ° C. or higher, so that residual components do not remain. Therefore, a PTC resistance element having particularly good PTC characteristics can be obtained.

[0013]

EXAMPLES Generally, PT containing vanadium oxide as a main component
The composition of the C resistance _{element, (V 1-x Cr x} ) 2 O 3 (0 <x ≦ 0.015)
In this example, the composition is (V _{0 .995}
A PTC resistance element was manufactured as Cr _0.005 ) ₂ O ₃ .

That is, the composition of V ₂ O ₃ (Mitsuwa Chemical Co., Ltd., purity 99%) and (NH ₄ ) ₂ Cr ₂ O ₇ (Kokusan Kagaku Co., Ltd., purity 99%) were used. It is weighed so as to be (V _{0 .995} Cr _{0 .005} ) ₂ O ₃ and wet-mixed and ground in alcohol for 24 hours.

Next, this powder was dried in a vacuum to obtain (N
To decompose H ₄ ) ₂ Cr ₂ O ₇
After heating for a period of time, calcination is performed at 1200 ° C. for 3 hours in a reducing atmosphere to obtain a calcined powder.

A particle size of 8 μm was added to the calcined powder as a sintering aid.
Fe powder (Mitsuwa Chemicals, purity 99.5%)
5 wt% of (V _{0 .995} Cr _{0 .005} ) ₂ O _{3 was} added, and the mixture was wet-milled and mixed for 12 hours and then dried in vacuum. .

Further, an organic binder is added to the crushed mixture, pressure molding is performed at a pressure of 1.5 ton / cm ² , and the molded body is fired in a reducing atmosphere at 1600 ° C. for 3 hours to obtain a PTC resistance element. To get In this example, a hydrogen atmosphere was used as the reducing atmosphere. This manufacturing process is shown in FIG.

As a comparative example, Cr ₂ O ₃ was used instead of (NH ₄ ) ₂ Cr ₂ O ₇ in the above manufacturing process,
A PTC resistance element was manufactured by omitting the step of heating at 0 ° C. This manufacturing process is shown in FIG.

FIG. 1 shows the temperature characteristics of each PTC resistance element manufactured by the above method. In this figure, lines A and B represent the temperature characteristics of the PTC resistance element according to the present embodiment and the PTC resistance element according to the conventional example, respectively.

In FIG. 1, the graph of the conventional PTC resistance element rises comparatively gently at low temperatures, whereas the PTC resistance element of this embodiment has a smaller specific resistance at low temperatures than the conventional example. In addition, the specific resistance rapidly increases around 80 ° C., and the maximum value of the specific resistance is larger than that of the conventional example.

Therefore, it can be seen that in this embodiment, a PTC resistance element having better PTC characteristics than the conventional example is obtained.

In the above process, V ₂ O ₃ and (NH ₄ ) ₂
The heating temperature of a mixture of Cr ₂ O _7, in order to decompose the _{(NH 4) 2 Cr 2 O} 7, it is preferable that the 185 ° C. or higher is a decomposition temperature of the compound.

The calcining step is preferably performed at 1100 ° C. or higher in order to improve the reaction of solid solution of Cr in V ₂ O ₃ , and the upper limit of the calcining temperature is not particularly limited.
It is preferable to set the upper limit to 1400 ° C. due to the durability of calcination equipment and the like. The amount of Fe added is 1.5 to 20 w relative to the weight of the final sintered body in order to keep the PTC ratio high.
It is preferably t%.

Further, regarding the firing temperature, the sintering aid F
In order to melt e and improve the sinterability, the temperature is preferably 1500 ° C. or higher. Although the upper limit of the firing temperature is not particularly limited, it may be 1650 depending on the durability of the firing equipment and the like.
It is preferable to set the upper limit to ° C.

[0025]

In the present invention, vanadium trioxide and
A PTC resistance element is manufactured by mixing (NH ₄ ) ₂ Cr ₂ O ₇ and alcohol and firing the mixture.

The PTC resistance element obtained by the above manufacturing method has a small specific resistance at low temperatures, but the specific resistance rapidly increases above a predetermined temperature, and the maximum specific resistance is large.

Therefore, according to the present invention, a PTC resistance element having good PTC characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing temperature characteristics of a PTC resistance element.

FIG. 2 is a graph showing the relationship between the Cr addition amount and temperature characteristics.

FIG. 3 is a graph showing the relationship between sintering temperature and temperature characteristics.

Claims (1)

[Claims] 1. Vanadium trioxide, a chromium compound,
A method for manufacturing a PTC resistance element, which comprises a step of mixing with alcohol and firing the mixture, wherein ammonium bichromate is used as the chromium compound.