JPH05299204A - Manufacture of ptc resistor - Google Patents

Abstract

PURPOSE:To obtain a PTC resistor manufacturing method with which a PTC resistor can be calcined uniformly and easily at low cost. CONSTITUTION:A subsidiary ingredient, which induces PTC characteristics, is mixed with vanadium oxide of main raw material, and after graphite has been added to the obtained mixture, a granulation and molding operation is conducted. Then, the obtained molded body is calcined in a vacuum atmosphere, and a PTC resistor is manufactured.

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 a PTC {Positive Temperature Coeffic which can be used as a current limiting resistor for suppressing overcurrent (short circuit current).
The present invention relates to a method for producing a resistor composition having the effect of “ientient”.

[0002]

2. Description of the Related Art Conventional ceramics having a large PTC effect are BaTiO ₃ (barium titanate) and V ₂ O.
₃ (vanadium trioxide) is known.

The BaTiO ₃ is widely used as a posistor (positive characteristic thermistor) for weak electric current, but cannot be used for electric power for the following two reasons.

1. A few Ω even if the resistivity value at room temperature is small
Since it is more than cm, the watt loss becomes large when used for electric power.

2. The appearance of the PTC effect is related to the mechanism of the grain boundary, and the resistance of the grain boundary becomes high due to the rise of temperature, but if the temperature becomes too high, the energy absorbed will cause the grain boundary destruction.

On the other hand, although the specific resistance of V ₂ O ₃ can be reduced by about 4 orders of magnitude as compared with BaTiO ₃ , it has poor sinterability as a ceramic and has a problem in thermal shock resistance when a large current is applied. Therefore, it is desired to improve the strength of V ₂ O ₃ .

[0007]

Usually, V ₂ O ₃ -based PT is used.
The C-resistive resistor is obtained by adding vanadium oxide such as V ₂ O ₃ or V ₂ O ₅ with a trace amount of an auxiliary component such as Cr ₂ O ₃ , Al ₂ O ₃ or Sc ₂ O ₃ which induces PTC characteristics. This can be obtained by reduction firing in a hydrogen atmosphere.

[0008] In the above firing step, since it is necessary to flow hydrogen at a high temperature of about 1300 ° C to 1700 ° C, running costs are high and equipment costs are high.

In addition, in the current reduction method such as hydrogen reduction, reduction is performed from the surface of the resistor, and therefore, when the resistor itself has a large diameter or a thick shape, a shape effect occurs, so that it is uniform. It is difficult to obtain various characteristics.

Therefore, the PTC resistor resistor has a large capacity P.
The uniformity of the resistor, which is important when the TC resistor resistor is applied to a circuit breaker or the like, is poor, and therefore heat loss is large at all times. Further, when the short-circuit current generated when the circuit breaker is short-circuited is limited by the PTC resistance resistor, the PTC magnification is large because the inside of the resistor is non-uniform, and the resistor itself is destroyed by thermal strain. ..

The present invention has been made based on the above background, and an object of the present invention is to provide a method for manufacturing a PTC resistor which is easy and inexpensive, and which can uniformly sinter the resistor.

[0012]

In order to solve the above-mentioned problems, the present invention uses vanadium oxide as a main raw material and P
In a method for producing a PTC resistor in which a subcomponent that induces TC characteristics is mixed, and a mixture obtained thereby is granulated and then molded and fired, after adding graphite to the mixture, granulation and molding are performed, Further, the firing is performed in a vacuum atmosphere.

The present invention will be described in more detail below.

[0014] vanadium oxide for use in the invention, for example, _{V 2 O 5, V 2 O} 3 and the like, preferably using a V ₂ O _3. Examples of the accessory component that induces the PTC characteristic include Cr, Al, Fe and compounds thereof, and preferably Cr ₂ O ₃ is added.

Next, Fe, Ni, Cu or the like is preferably added as a sintering aid to the mixture of the vanadium oxide and the subcomponents.

Graphite powder is added to this, and wet pulverized and mixed in alcohol to obtain a slurry. The addition of graphite powder causes a reaction of reducing metal oxide according to the following formula.

[0017]

## STR1 ## MO + C → M + CO (1) (MO _Y + YC → M + YCO) As described above, this reaction requires C (graphite) in the same mole as oxygen in the metal oxide to be reduced. At this time, generally, if the addition amount of graphite is small, the reduction will be insufficient and the PTC characteristics will be deteriorated. On the other hand, if the addition amount is too large, graphite that could not be completely oxidized during firing will remain inside the resistor to cause voids. Then
The PTC characteristics will deteriorate.

Therefore, the amount of graphite added is preferably about equimolar to the oxygen atoms in the metal to be reduced. Generally, as described above, in the PTC resistor containing vanadium oxide as the main component, the amount of graphite added. A good PTC characteristic can be obtained by setting the ratio to 0.01% to 10%.

Further, in order to improve the reactivity between the metal and the graphite, it is preferable that the particle size of the graphite is about the same as that of the raw material powder such as V ₂ O ₃ , and preferably 30 μm or less. Good PTC characteristics can be obtained.

In the method of manufacturing the PTC resistor, the graphite and the sintering aid may be added after mixing V ₂ O ₃ and the subcomponents in advance.

Next, the PTC resistor is obtained by granulating, molding and firing the slurry obtained by adding the auxiliary component, the sintering aid and the graphite to the main raw material as described above and wet pulverizing and mixing. ..

Preferably, the above slurry is dried by, for example, a spray dryer to produce appropriate granules, and the granules and molding are carried out by press-molding the granules with a die press, CIP or the like. Further, when firing is performed, it is preferable that the molded body be fired at 1000 ° C. to 1700 ° C. in vacuum.

[0023]

EXAMPLE In this example, a PTC resistor was manufactured by using V ₂ O ₃ as a main component, adding a small amount of Cr ₂ O ₃ , and further adding Fe. The details are shown below.

First, Cr ₂ O ₃ and Fe were added to V ₂ O ₃ , the basic composition was (V _{0 .996} Cr _{0 .004} ) ₂ O ₃ , and 5 wt% Fe was added to this, and further graphite powder was added. After the addition, the mixture was wet milled and mixed in alcohol to obtain a slurry.

An organic binder is added to this slurry and mixed, and then dried with a spray drier to obtain appropriate granules. This was pressure-molded with a die press, CIP, etc., and the obtained molded body was baked at 1000 ° C. to 1700 ° C. in vacuum to obtain a PTC resistor.

In the present embodiment, the resistor samples a to h were prepared by adding graphite in an amount of 0 to 15 wt% in the above manufacturing method.
Was manufactured.

Further, in the method for producing the PTC resistor, samples i and j were produced without adding graphite and the firing atmosphere was H ₂ and N ₂ , and the PTC characteristics of each of the samples a to j were examined. .. The results are shown in Table 1.

[0028]

[Table 1]

From Table 1 above, when the amount of graphite added is small, the reduction is insufficient and the PTC characteristics deteriorate, and when the amount of graphite added is too large, graphite that cannot be fully oxidized during firing remains inside the resistor. It can be seen that voids are generated and the PTC characteristics deteriorate.

Therefore, the amount of graphite added is preferably approximately equimolar to the oxygen atoms in the metal to be reduced. Generally, in the PTC resistor containing vanadium oxide as the main component as described above, the amount of graphite added is A good PTC characteristic can be obtained by setting the ratio to 0.01% to 10%.

Further, in order to improve the reactivity between the metal and the graphite, it is preferable that the particle size of the graphite is as large as that of the raw material powder such as V ₂ O ₃ , and in this embodiment, it is at least 30 μm or less. By doing so, good PTC characteristics were obtained.

[0032]

As described above, according to the present invention, PT
In the method for producing a C resistor, graphite is mixed in advance with a molded body and then the molded body is fired to reduce the resistor during firing.

Therefore, in the past, since the above reduction was performed by firing in a reducing atmosphere such as a hydrogen atmosphere,
While it was very difficult to reduce the surface of the resistor and the inside of the resistor uniformly, in the present invention, the reduction is performed by the graphite in the resistor, so that the resistor can be easily and uniformly reduced. You can

Further, the running cost is lower than the method of firing in a hydrogen atmosphere, and no special equipment is required, which is economically advantageous.

Further, since the uniform reduction reaction occurs from the inside of the resistor as described above, the PTC ratio (ratio of the room temperature resistivity and the resistivity after high temperature transition) of the resistor is improved.

Therefore, for example, when this resistor is incorporated in a distribution breaker, the short-circuit current can be sufficiently suppressed. Further, since the uniformity is improved, the columnar resistor can be used as a resistor having a large diameter and a large capacity.

Claims (1)

[Claims] 1. A method for producing a PTC resistor, comprising mixing vanadium oxide as a main raw material with a sub-component that induces PTC characteristics, granulating the mixture thus obtained, and then molding and firing the mixture. P is characterized by performing granulation and molding after adding graphite, and further performing the firing in a vacuum atmosphere.
Method for manufacturing TC resistor.