JPH0661010A - Manufacture of positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE:To obtain a sintered body having semiconductor characteristics, uniform and not irregular, by a method wherein a calcination-molded body is immersed in a solution wherein a soluble agent for turning into semiconductor is resolved in a solvent having the affinity to raw material powder. CONSTITUTION:Raw material powder having perovskite crystal forms are molded and calcinated to obtain a porous calcination-molded body 1. Next, a soluble agent for turning into semiconductor is resolved into a solvent having the affinity to the raw material powder to prepare a solution 2 of the soluble agent. Next, the calcination-molded body 1 is immersed in the solution 2 for making the solution 2 adhere to the surface of the calcination-molded body 1 as well as permeate in the pores thereof to be dried up for removing the solvent so that an immersion-molded body 4 may be formed. Later, the immersion-molded body 4 is finally baked to obtain a sintered body 5 turned into semiconductor. Through these procedures, the additive amount of the agent can be precisely controlled thereby enabling the semiconductor characteristics such as set up PTC property, etc., to be stably secured.

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 positive temperature coefficient thermistor having a positive temperature characteristic when the temperature exceeds a predetermined temperature.

[0002]

2. Description of the Related Art Conventionally, a positive temperature coefficient thermistor (hereinafter referred to as P
As a TC thermistor), a polymer PTC thermistor in which a conductive material such as carbon black is mixed in a polymer material such as polyethylene resin has been developed, but semiconductor barium titanate ceramics is the mainstream.

The above barium titanate ceramics are
For example, barium carbonate (BaCO ₃ ) crushed to a few microns
It is manufactured by uniformly mixing a powder and a titania (TiO ₂ ) powder with a semiconducting agent such as antimony oxide and firing. There is a fixed limit (about 0.5 mol%) to the amount of the above-mentioned semiconducting agent added, and if the amount exceeds the limit, no semiconductor is formed.

[0004]

However, in the above manufacturing method, it is difficult to uniformly disperse the semiconducting agent having a small amount of addition into the barium carbonate powder and the titania powder. Also, there is a problem in that the semiconductor characteristics such as the PTC characteristics greatly change due to the weighing error of the semiconducting agent, and the obtained semiconductor characteristics become unstable.

[0005]

In order to solve the above-mentioned problems, the method for producing a positive temperature coefficient thermistor of the present invention comprises forming a raw material powder having a perovskite type crystal form and calcining it to obtain a porous calcination. After obtaining the shaped body, a solution of a soluble semiconducting agent dissolved in a solvent having an affinity for the raw material powder is permeated into the calcined shaped body to obtain an immersion shaped body having the soluble semiconducting agent, The above-mentioned immersion molded body is subjected to main firing to obtain a semiconductorized sintered body.

As the above raw material powder, ABO ₃ (A,
B is a metal element, O is oxygen) and is a metal oxide having a perovskite type crystal form, and is not particularly limited as long as it is converted into a semiconductor by adding a trace amount of a semiconducting agent, for example, antimony. Examples thereof include barium titanate (BaTiO ₃ ).

Furthermore, in order to adjust the Curie temperature, which is a transition temperature at which positive temperature characteristics begin to rise when the temperature is raised, to a predetermined temperature, strontium titanate (SrTiO ₃ ) or titanium which is a perovskite type metal oxide is used. Lead oxide (PbTiO
₃ ) may be added.

The above-mentioned solvent is not particularly limited as long as it has an affinity for the raw material powder and dissolves the soluble semiconducting agent described later, but alcohols such as ethanol can be mentioned.

The soluble semiconducting agent is not particularly limited as long as it can be dissolved in the solvent and the raw material powder can be converted into a semiconductor. For example, triphenylantimony [Sb (C ₆ H ₅ ) ₃ ] , Triphenylbismuth [Bi (C ₆ H
₅ ) ₃ ] can be mentioned. In addition, as a sintering aid at the time of firing, silicon dioxide (SiO ₂ ) or manganese oxide (Mn
O) and the like may be added at the time of molding.

[0010]

According to the above method, the solution having a uniform concentration is infiltrated into the pre-baked form, so that the soluble semiconducting agent can be uniformly distributed and added to the pre-baked form, so that uniform semiconductor characteristics can be obtained. It is possible to obtain a sintered body having
Moreover, by diluting the above solution, the concentration of the soluble semiconducting agent can be accurately and quickly adjusted, and by adjusting the number of times the preliminarily fired body is immersed in the solution, the concentration of the soluble semiconducting agent in the dipping molded body can be adjusted. The added amount can be controlled accurately and can be stabilized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe each embodiment of the present invention with reference to FIGS. Example 1 Barium titanate powder (particle size 2 to 3 μm) 3 as a raw material powder having a perovskite type crystal form 3
g was filled in a mold and pressed at 1 ton / cm ² to obtain a molded body. By calcining this molded body at 1150 ° C. for 2 hours, as shown in FIG. 1 (a), for example, a density of 3.85 g /
A disk-like shape having a cm ³ diameter, a diameter of 12 mm, and a thickness of 3 mm, in which only the abutting surface of each raw material powder was adhered, and a porous pre-baked form 1 having continuous pores was obtained. The density in this specification was calculated by weight (g) / measured dimension volume.

Next, triphenyl antimony [Sb (C ₆ H ₅ )
₃ ] (Soluble semiconducting agent) is dissolved in ethanol (solvent) to a concentration of 0.05 g / liter to prepare a semiconducting agent solution 2, and the semiconducting agent solution 2 contains 1 part of the pre-baked form 1 By soaking for a period of time, the above-mentioned semiconducting agent solution 2 was added to the surface of the calcined shaped body 1 and permeated into the inside of the porous body.

After that, the pre-fired shaped body 1 was pulled up from the semiconducting agent solution 2. The residual capacity of the semiconducting agent solution 2 after pulling up the calcinated body 1 was measured, and the amount of triphenylantimony added to the calcinated body 1 was calculated from the remaining capacity.

Subsequently, the calcined shaped body 1 in which the semiconducting agent solution 2 has been permeated is dried to remove ethanol, and then, as shown in FIG.
As shown in (1), a dip molded body 4 having the above-mentioned triphenylantimony layer 3 uniformly provided on the surface and the pore surface inside the porous body was formed.

Thereafter, the above-mentioned dipping molded body 4 is baked at 1150 ° C. for 2 hours in the atmosphere to volatilize the phenyl groups in triphenylantimony to oxidize antimony, and to swell the surface of the dipping molded body 4 and the pores in the porosity. An antimony oxide layer as a semiconducting agent was formed on the surface (not shown) to obtain an additional molded body.

Subsequently, the above-mentioned additional molded body is heated at 1360 ° C. for 15 minutes for main firing, and as shown in FIG. 1 (c), it is a barium titanate-based ceramic which is semiconducting, and is disc-shaped. Consolidation 5 was obtained. The density of the above-mentioned sintered body 5 is 5.
It was 88 g / cm ³ , and the amount of added antimony was 0.04 in terms of molar concentration (mol%), which is the molar amount of antimony (Sb) per 100 mol of barium titanate. The amount of antimony was calculated based on the amount of added triphenylantimony described above.

The term "calcining" refers to heating at a temperature lower than that in the main calcination described later and at which only the abutting surface of each raw material powder adheres to form a porous body. That is, the heating is performed at a temperature which is not higher than the melting point of the raw material powder but is a temperature at which each raw material powder of the porous molded body grows and becomes a dense body with few pores.

Next, on both surfaces of the obtained sintered body 5,
Although not shown, silver paste (manufactured by DuPont) was applied to each and baked at 560 ° C. to form each electrode. The specific resistance values of the thus-obtained sintered bodies were measured at different temperatures. The result is shown in FIG. 2 (indicated by ◯ in the figure). The above-mentioned sintered body is electrically conductive at room temperature (25 ° C), that is, the room temperature resistivity which is the resistivity at room temperature is 7.58.
It shows kΩcm, and the resistance value increases with increasing temperature P
It had TC characteristics.

Example 2 The pre-baked shaped body 1 was immersed in the semiconducting agent solution 2 for 1 hour and dried, and then 1150.
The step of baking at 2 ° C. for 2 hours was repeated twice to obtain an additional molded body with an increased amount of added antimony. 2 at 1150 ℃
Antimony oxide produced by the step of firing for a period of time is insoluble in the above-mentioned semiconductor agent solution 2.

The additional molded body thus obtained was sintered in the same manner as in Example 1, and electrodes were formed on both surfaces of the sintered body to obtain a specific resistance value with respect to temperature. The measurement was performed, and the results are also shown in FIG. 2 (indicated by □ in the figure). The above sintered body has a density of 5.65 g / cm ³ , an antimony amount (mol%) of 0.08, and a room temperature resistivity of 51 Ωcm, and has a PTC characteristic in which the resistance value increases with increasing temperature. Was there.

[Example 3] The pre-sintered shaped body 1 was dipped in the semiconducting agent solution 2 for 1 hour, dried and then heated to 1150 ° C.
The step of firing for 2 hours was repeated three times to increase the amount of antimony in the additional molded body, and thereafter, a sintered body was obtained in the same manner as in Example 1. An electrode was formed on the sintered body in the same manner as in Example 1, and the specific resistance value with respect to temperature change was measured. The result is also shown in FIG. 2 (indicated by Δ in the figure). The sintered body has a density of 5.55 g / cm ³ , an antimony amount (mol%) of 0.12, and a room temperature resistivity of 34 Ωcm, and exhibits a PTC characteristic in which the resistance value increases with increasing temperature. Had.

Example 4 The pre-baked shaped body 1 was dipped in the semiconducting agent solution 2 for 1 hour, dried and then heated to 1150 ° C.
The step of firing for 2 hours was repeated four times to increase the amount of antimony in the additional molded body, and thereafter, a sintered body was obtained in the same manner as in Example 1. An electrode was formed on the sintered body in the same manner as in Example 1, and the specific resistance value with respect to the temperature change was measured. The result is also shown in FIG. 2 (indicated by □ in the figure). The curve showing the above result was almost the same as the result of the above-mentioned Example 2, so that it was shown overlaid with the curve showing the result of the above Example 2. The density of the sintered body is 5.50.
g / cm ³ , its antimony amount (mol%) was 0.16, its room temperature resistivity was 52 Ωcm, and it had a PTC characteristic in which its resistance value increased with increasing temperature.

[Embodiment 5] The pre-sintered shaped body 1 is immersed in the semiconducting agent solution 2 for 1 hour and dried, and then at 1150 ° C.
The step of firing for 2 hours was repeated 5 times to increase the amount of antimony in the additional molded body, and thereafter, a sintered body was obtained in the same manner as in Example 1. An electrode was formed on the sintered body in the same manner as in Example 1, the specific resistance value with respect to the temperature change was measured, and the result is also shown in FIG. 2 (indicated by ⋄ in the figure). The above sintered body has a density of 5.16 g / cm ³ , an antimony amount (mol%) of 0.19, and a room temperature resistivity of 178 Ωcm.
It had a PTC characteristic in which the resistance value increased with increasing temperature.

As described above, the sintered bodies in the manufacturing methods of Examples 1 to 5 have PTC characteristics that show positive temperature characteristics when the temperature exceeds a predetermined temperature, and can be suitably used as, for example, PTC thermistors. .

In addition, in the method of each of the above-mentioned embodiments, since the pre-baked form 1 is immersed in the semiconducting agent solution 2, when the semiconducting agent is added, it is weighed in a weighing unit having a small weighing error and then diluted. Since it is good, it is possible to accurately control the amount of addition of the semiconducting agent and to stably manufacture a positive temperature coefficient thermistor having expected semiconductor characteristics such as PTC characteristics by reducing the weighing error instead of the minute amount as in the past. be able to.

In each of the above methods, the semiconducting agent 1 is immersed in the semiconducting agent solution 2 having a uniform concentration of the semiconducting agent, so that the semiconducting agent can be uniformly dispersed in the immersion molding 4. As a result, the obtained sintered body can have excellent semiconductor characteristics such as uniform PTC characteristics with reduced variations. Further, since it can be made into a semiconductor after molding, the room temperature resistance value, PTC characteristics, etc. can be changed quickly.

Further, in each of the above methods, fine adjustment of the concentration of the semiconducting agent solution 2 can be performed accurately and quickly by dilution or the like, so that the set PTC characteristic can be obtained with certainty and the PTC characteristic Different positive temperature coefficient thermistors can be stably and quickly obtained.

When the density of the sintered body in each of the above-mentioned examples is shown in a graph as shown in FIG. 3, the density showed a tendency to decrease slightly as the antimony concentration increased. It was considered that this was due to a decrease in the pore reduction rate in the sintered body as the antimony concentration increased.

On the other hand, when the room temperature resistivity of the sintered body in each of the above-mentioned Examples is shown in a graph as shown in FIG. 4, the antimony concentration shows a minimum value at about 0.1 mol%, which shows a change in the antimony concentration. It was shown that the room temperature resistivity can be easily set and the room temperature resistivity can be easily adjusted.

The above method is also applied to the addition of a trace amount of a component for modifying the lead zirconate titanate [Pb (Zr, Ti) O ₃ type piezoelectric ceramics according to the purpose of use. be able to.

[0031]

As described above, the method for producing a positive temperature coefficient thermistor according to the present invention comprises the steps of forming a raw material powder having a perovskite type crystal form and calcining it to obtain a porous calcinated body, and After obtaining a dip molded body having the soluble semiconducting agent by infiltrating the solution obtained by dissolving the soluble semiconducting agent in a solvent having an affinity for powder into the calcined shaped body,
It is a method of obtaining a semiconductor-made sintered body by subjecting the above-mentioned immersion molded body to main firing.

Therefore, according to the above method, the soluble semiconducting agent can be uniformly dispersed in the pre-sintered form to form a semiconductor.
By adjusting the concentration of the soluble semiconducting agent in the solution and the number of times the pre-baked article is immersed in the solution, the amount of the soluble semiconducting agent added in the immersion molded article can be accurately controlled. The effect of being able to obtain is stable.

[Brief description of drawings]

FIG. 1 is a schematic process diagram in a method of manufacturing a positive temperature coefficient thermistor of the present invention.

FIG. 2 is a graph showing the relationship between temperature and resistance value in each positive temperature coefficient thermistor obtained in each of the above examples.

FIG. 3 is a graph showing the density of each PTC thermistor.

FIG. 4 is a graph showing a room temperature resistance value of each of the positive temperature coefficient thermistors.

[Explanation of symbols]

 1 Preliminary Firing Form 2 Semiconductor Agent Solution (Solution) 4 Immersion Formed Body 5 Sintered Body

Claims (1)

[Claims] 1. A raw material powder having a perovskite crystal form is molded and calcined to obtain a porous calcined body, and then a soluble semiconducting agent is dissolved in a solvent having an affinity for the raw material powder. The obtained solution is permeated into the preliminarily fired form to obtain an immersion molded body having the soluble semiconducting agent, and then the immersion molded body is subjected to main firing to obtain a semiconductorized sintered body. Method of manufacturing characteristic thermistor.