JP2013182932A - Method for forming electrode of ptc element, and ptc element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an electrode of a PTC element, capable of reducing interface resistance between a PTC element assembly and an electrode, the PTC element being manufactured using a semiconductor porcelain composition in which a part of Ba of BaTiOis substituted with Bi-Na.SOLUTION: A method for forming an electrode of a PTC element includes a step of preparing a semiconductor porcelain composition represented by a composition formula: [(Bi-Na)(BaR)][TiM]O(where R represents at least one selected from among rare earth elements including Y, M represents at least one selected from among Nb, Ta and Sb) while the x, y and z satisfy relationships of 0<x≤0.30, 0≤y≤0.020 and 0≤z≤0.010, coating an electrode paste on the semiconductor porcelain composition, performing heat treatment to remove a binder in the electrode paste, and then performing baking treatment. The baking treatment is performed in a condition at 500°C or above and 700°C or below for 5 minutes or more and 30 minutes or less in a non-oxidizing atmosphere with an oxygen concentration of 2% or less.

Description

  The present invention relates to a method for forming an electrode of a PTC element having a semiconductor ceramic composition having a positive resistance temperature coefficient used for a PTC thermistor, a PTC heater, a PTC switch, a temperature detector, and the like, and a PTC element.

Conventionally, semiconductor porcelain compositions obtained by adding various semiconducting elements to BaTiO ₃ have been proposed as materials exhibiting PTCR characteristics (Positive Temperature Coefficient of Resistivity). In the present invention, the PTCR characteristic is described as a jump characteristic. The jump characteristic is considered to occur because the resistance formed at the crystal grain boundary, that is, the resistance due to the Schottky barrier increases. As the characteristics of this semiconductor ceramic composition, it is required that the resistivity jump characteristic (hereinafter referred to as resistance temperature coefficient) is high, and the resistivity at room temperature (hereinafter referred to as room temperature resistivity) is stable at a low value. Yes.

  Since these semiconductor porcelain compositions have the characteristic that the resistance value increases rapidly when the temperature becomes higher than the Curie point, they are used for PTC thermistors, PTC heaters, PTC switches, temperature detectors and the like. The Curie temperature of a general semiconductor ceramic composition is around 120 ° C., but it is necessary to shift the Curie temperature depending on the application.

In order to shift the Curie temperature, it has been proposed to add SrTiO ₃ to BaTiO ₃ , but the Curie temperature shifts only in the negative direction and not in the positive direction. Currently, PbTiO ₃ is known as an additive element that shifts the Curie temperature in the positive direction. However, since PbTiO ₃ contains Pb that causes environmental pollution, a semiconducting porcelain composition that does not use Pb has recently been demanded.

In Patent Document 1, in order to solve the problem of the conventional BaTiO ₃ based semiconductor ceramic composition, the Curie temperature can be shifted in the positive direction without using Pb, and the room temperature resistivity is greatly reduced. However, a semiconductor porcelain composition exhibiting excellent jump characteristics has been proposed. Specifically, the composition formula is represented by [(BiNa) _x (Ba _1-y R _y ) _1-x ] TiO ₃ , and x and y are 0 <x ≦ 0.2, 0 <y ≦ 0.02. Or the composition formula is represented by [(BiNa) _x Ba _1-x ] [Ti _1-z M _z ] O ₃ , and x and z are 0 <x ≦ 0.2, Semiconductor porcelain compositions that satisfy 0 <z ≦ 0.005 have been proposed.

  As shown in FIG. 3, a PTC element body 1 obtained by processing a semiconductor porcelain composition into a predetermined shape is formed with an electrode 2 composed of a positive electrode and a negative electrode to form a PTC element 10. In Patent Document 2, focusing on the reduction of the interface resistance between the PTC element body 1 and the electrode 2, it is proposed to provide a first electrode layer containing Zn in Ag on both opposite sides of the PTC element body. ing. In Patent Document 2, a PTC element is manufactured by the manufacturing process shown in FIG. In other words, the semiconductor ceramic composition is manufactured in Step 1, the electrode paste is applied to the semiconductor ceramic composition in Step 2, the heat treatment in the atmosphere is performed in Step 3 to remove the binder in the electrode paste, and then in Step 4 The electrode is baked.

  Patent Document 3 describes that a semiconductor ceramic composition is heat-treated in the air or in oxygen before or after the electrode is formed on the semiconductor ceramic composition, and is excellent in change over time and has a room temperature resistance of 100 Ω · cm or less. Is obtained.

International Publication WO2006 / 118274A1 JP 2010-40560 A JP 2009-234849 A

  As described above, the semiconductor ceramic composition of Patent Document 1 shifts the Curie temperature in the positive direction without using Pb, and exhibits excellent jump characteristics while reducing the room temperature resistivity. However, the PTC element using the semiconductor ceramic composition of Patent Document 1 has a higher interface resistance than the PTC element using the semiconductor ceramic composition that does not use Pb. Therefore, even if the electrode structure of Patent Document 2 is used, the interface resistance is not reduced in the semiconductor ceramic composition of Patent Document 1. When this cause was investigated, it became clear that an oxide layer was present at the interface of the PTC element body, and this oxide layer increased the interface resistance and increased the room temperature resistivity and the change with time. This oxide layer cannot be eliminated by the heat treatment before forming the electrode described in Patent Document 3 or the heat treatment after forming the electrode.

Accordingly, an object of the present invention is to reduce the interfacial resistance between the PTC element body and the electrode in a PTC element using a semiconductor ceramic composition in which a part of BaTiO ₃ is replaced with Bi—Na. An object of the present invention is to provide an electrode forming method for a PTC element. Another object of the present invention is to provide a PTC element obtained by this electrode forming method for a PTC element, which has a small interface resistance and a small room temperature resistivity and small change with time.

An oxide layer exists at the interface of the PTC element body before the electrode is formed. When the electrode is formed, the base metal of the electrode takes in oxygen in the oxide layer, so that the oxide layer is removed. However, when the electrode is formed in the atmosphere, the base metal mainly takes in oxygen from the atmosphere, so the reducing power on the oxide layer is weakened and the oxide layer is not completely removed. Therefore, the interface resistance cannot be lowered. The oxide layer not only increases the room temperature resistivity, but also causes the change with time to increase because the electrode easily peels off due to insufficient adhesion.
Therefore, in the present invention, the electrode is baked in a non-oxygen atmosphere in order to remove the oxide layer of the PTC element body, thereby suppressing the oxidation of the base metal component from the atmosphere and maintaining the reducing power of the base metal component in a higher state. As a result, the oxide layer at the interface of the PTC element body can be reduced as compared with the prior art. As a result, the interface resistance can be reduced to 1.0 Ω / cm ² or less. As a result, it was possible to realize a PTC element having a small room temperature resistivity and a change with time.

That is, the present invention is a method for forming an electrode of a PTC element having an electrode made of an alloy of Ag and a base metal in a perovskite-based semiconductor ceramic composition containing at least Ba and Ti, wherein the semiconductor ceramic composition has the composition formula _{[(Bi-Na) x (} Ba 1-y R y) 1-x] [Ti 1-z M z] O 3 ( provided that at least one of rare earth element R, including the Y, M is Nb, Ta, At least one of Sb), and x, y, and z satisfy 0 <x ≦ 0.30, 0 ≦ y ≦ 0.020, and 0 ≦ z ≦ 0.010, and electrode paste Is applied to the semiconductor ceramic composition, followed by a heat treatment for removing the binder in the electrode paste, followed by a baking treatment, wherein the baking treatment is a non-oxidizing material having an oxygen concentration of 2% or less. 500 ° C or higher in the atmosphere 00 ° C. or less, and carrying out at least 5 minutes 30 minutes following conditions.

  The heat treatment is preferably performed in the atmosphere at a temperature of 300 ° C. to 400 ° C. for 10 minutes to 60 minutes.

  The electrode preferably has a composition in which Ag is 20% by mass or more and 65% by mass or less and the balance is a base metal element.

  The base metal is preferably one or more elements selected from Zn and Sn.

  When the base metal is Sn, it is preferable that Sn is in the range of 20% by mass to 60% by mass.

Further, the present invention is a PTC element manufactured by the above electrode forming method for a PTC element, wherein the PTC element has an interface resistance between the electrode and the semiconductor ceramic composition of 1.0 Ω / cm ² or less. It is characterized by that.

According to the present invention, the PTC element using a semiconductor ceramic composition in which a part of Ba of BaTiO ₃ is substituted with Bi-Na, may provide an electrode forming method of a PTC element that can reduce the interfacial resistance . Thereby, a PTC element with a small change with time and room temperature resistivity can be provided.

It is a figure for demonstrating the manufacturing process of baking of the electrode of this invention. It is a figure for demonstrating the measuring method of interface resistance. It is an example of a PTC element. It is a figure for demonstrating the manufacturing process of the baking of the conventional electrode. It is a figure for demonstrating resistance temperature coefficient (alpha).

Hereinafter, the PTC element of the present invention and the manufacturing method thereof will be described.
FIG. 1 is an example of a flowchart of the manufacturing method of the present invention. In Step 1, a semiconductor ceramic composition having the above composition is manufactured. Then, electrode paste is apply | coated to a semiconductor ceramic composition by step2. In Step 3, heat treatment in air is performed to remove the binder in the electrode paste. The heat treatment temperature in the air heat treatment is preferably 300 ° C. to 400 ° C. Thereafter, in Step 4, the electrode is baked in a non-oxidizing atmosphere. By this manufacturing process, a PTC element having a low interface resistance using the semiconductor ceramic composition having the above composition can be manufactured.

The semiconductor ceramic composition for use in the PTC device of the present invention, the composition formula _{[(Bi-Na) x (} Ba 1-y R y) 1-x] [Ti 1-z M z] O 3 ( where, R represents At least one of rare earth elements (including Y), M is represented by at least one of Nb, Ta, and Sb), and x and y are 0 <x ≦ 0.30, 0 ≦ y ≦ 0.020, 0 ≦ z ≦ 0.010 is satisfied.
Here, the Curie temperature can be set to 130 ° C. to 200 ° C. by setting the range of x to exceed 0 and not more than 0.30. If x exceeds 0.30, a different phase is easily formed, which is not preferable. The room temperature resistivity can be reduced by setting the range of y to 0 to 0.020 and the range of z to 0 to 0.010. If x = 0, the interface resistance does not increase so much in the first place, and the effect of reducing changes with time cannot be fully utilized. When y + z = 0, the room temperature resistivity is close to 100 Ω · cm, and the efficiency as a heater element is relatively poor. Therefore, it is preferable to satisfy y + z> 0. It is assumed that y is 0.020 and z is 0.010 or less. If both values exceed this value, the room temperature resistivity becomes high, so the efficiency as a heater element becomes low, which is not preferable.

  In joining the semiconductor ceramic composition used for the PTC element of the present invention and an electrode, if an electrode made of only a noble metal such as Ag, Au, or Pt is used, the interface resistance increases. In order to reduce the interface resistance, it is effective to use an electrode having a composition in which a noble metal contains a base metal such as Zn or Sn. That is, oxygen in the oxide layer formed at the interface of the PTC element body is reduced by the base metal in the electrode, whereby the oxide layer is reduced and the PTC element body and the electrode are in ohmic contact. As a result, the interface resistance is reduced.

  A precious metal such as Ag can be further used as the cover electrode in order to prevent a change with time due to oxidation of the base metal electrode.

Since the PTC element body of the present invention has a problem that when it is exposed to a high temperature exceeding 700 ° C., the resistance increases, the baking temperature of the electrode is desirably 700 ° C. or less. It has been found that a base metal element having a melting point of 200 to 500 ° C. provides excellent ohmic characteristics, and elements such as Zn and Sn are suitable as the base metal component.
Further, if the Ag ratio in the electrode exceeds 65% by mass, base metal components such as Zn and Sn are reduced, and the oxide layer cannot be sufficiently removed, which is not preferable. On the other hand, when the Ag ratio is less than 20% by mass, the ratio of the base metal is excessively increased and the change with time increases, which is not preferable.

  When using Sn as a base metal component, it is preferable that the ratio in an electrode shall be 60 mass% or less. If it exceeds 60% by mass, the change with time increases, which is not preferable.

  The heat treatment for removing the binder in the electrode paste is preferably performed in the air at a temperature of 300 ° C. or higher and 400 ° C. or lower and 10 minutes or longer and 60 minutes or shorter. When the temperature is less than 300 ° C. and the retention time is less than 10 minutes, the organic components in the electrode paste are not sufficiently decomposed and the adhesion of the electrode is hindered. Further, heat treatment exceeding 400 ° C. or heat treatment longer than 60 minutes is not preferable because base metal oxidation starts and the oxide layer cannot be sufficiently removed. The amount of organic binder in a general electrode paste is 0.1% by mass or more and 30% by mass or less, and the binder can be sufficiently removed from the electrode paste by heat treatment under the above conditions.

  The conditions for electrode baking will be described. The oxide layer at the interface of the PTC element body is reduced by baking the electrode by holding it in a non-oxidizing atmosphere with an oxygen concentration of 2% or less under conditions of 500 ° C. or more and 700 ° C. or less for 5 minutes or more and 30 minutes or less. Resistivity and change with time can be reduced. If the temperature during baking is less than 500 ° C. or the holding time is less than 5 minutes, sufficient adhesion strength cannot be obtained. Also, if the baking temperature is higher than 700 ° C. or the holding time exceeds 30 minutes, the base metal component takes in a very small amount of oxygen in the atmosphere and the reducing power on the oxide layer is reduced, so that the room temperature resistivity is the same as described above. Becomes higher.

Next, an example of a semiconductor ceramic composition used in the present invention and a manufacturing method for obtaining this PTC element will be described. The method of manufacturing a semiconductor ceramic composition, in the production of the composition formula _{[(Bi-Na) x (} Ba 1-y R y) 1-x] [Ti 1-z M z] O 3, (BaR) TiMO 3 Provisional Each calcined powder composed of calcined powder (hereinafter referred to as BaT calcined powder) and calcined powder composed of (Bi-Na) TiO ₃ calcined powder (hereinafter referred to as BNT calcined powder) are prepared separately. Then, a molded object is manufactured using the mixed calcined powder which mixed the said BaT calcined powder and BNT calcined powder suitably. Thus, it is preferable to employ a manufacturing method (hereinafter, divided calcining method) in which BaT calcined powder and BNT calcined powder are separately prepared, and mixed calcined powder obtained by mixing these is formed and sintered.

BaT calcined powder and BNT calcined powder are obtained by calcining each raw material powder at an appropriate temperature according to each. For example, TiO ₂ , Bi ₂ O ₃ , and Na ₂ CO ₃ are usually used as the raw material powder for BNT calcined powder, but Bi ₂ O ₃ has the lowest melting point among these raw material powders, and thus volatilizes by firing. Is more likely to occur. Therefore, the Bi is calcined at a relatively low temperature of 700 ° C. or more and 950 ° C. or less so that Bi is not volatilized as much as possible and there is no overreaction of Na. The holding time is preferably 0.5 hours or more and 10 hours or less. Once the BNT calcined powder is formed, the melting point of the BNT powder itself is stabilized at a high temperature, so that even when mixed with the BaT calcined powder, it can be fired at a higher temperature. As described above, the advantage of the divided calcining method is that the volatilization of Bi and the overreaction of Na are suppressed, and a BNT calcined powder having a small composition deviation of Bi-Na with respect to the measured value can be obtained. On the other hand, the BaT calcined powder is calcined at a temperature of 900 ° C. to 1300 ° C. and higher than the BNT calcined powder. The holding time is preferably 0.5 hours or more.

  By using the divided calcining method, the volatilization of Bi in the BNT calcined powder is suppressed, the compositional deviation of Bi-Na can be prevented as much as possible, and the molar ratio Bi / Na Bi / Na can be accurately controlled. By mixing, calcining and sintering these calcined powders, a semiconductor porcelain composition having a low resistivity at room temperature and a suppressed Curie temperature variation can be obtained. However, the split calcination method is not necessarily used. The ratio of Bi to Na is basically 1: 1, but it may be one in which Bi is volatilized and the ratio of Bi to Na is shifted in a calcining process or the like by a batch mixing method or the like. That is, the Bi / Na ratio is 1: 1 at the time of blending, but the case of not being 1: 1 in the sintered body is also included in the composition of the present invention.

  10% by mass of PVA was added to the pulverized powder of the calcined powder, mixed, and granulated by a granulator. Molding is performed with a single-screw press machine, and after binder removal at 400 ° C. to 700 ° C. for 0.1 hours to 12 hours, the sintering temperature is 1200 ° C. to 1450 ° C., and the sintering time is 2 hours to 6 hours. Sintering is performed under conditions to obtain a sintered body. The obtained sintered body is cut into a PTC body having a predetermined shape.

  The temperature conditions for baking the electrodes are as described above.

  The thickness of the electrode may be about 5 to 30 μm. Further, the present invention defines only the electrode directly formed on the PTC element body, but an Ag electrode or the like is used as the second layer electrode (cover electrode) for preventing oxidation of the base metal electrode and improving the wettability of the solder. Can also be used. Further, an electrode structure having three or more layers can be formed.

The evaluation method is as follows.
(Resistance temperature coefficient α)
The resistance temperature coefficient α was calculated by measuring the resistance-temperature characteristics while raising the temperature to 260 ° C. in a thermostatic bath.
The resistance temperature coefficient α is defined by the following equation.
α = (lnR ₁ −lnR _c ) × 100 / (T ₁ −T _c )
As shown in FIG. 5, R ₁ is the maximum resistivity, T ₁ is the temperature indicating R ₁ , T _c is the Curie temperature, and R _c is the resistivity at T _c . Here, _Tc is a temperature at which the resistivity becomes twice the resistivity at room temperature.

(Room temperature resistivity R ₂₅ )
The room temperature resistivity R ₂₅ was measured by a four-terminal method at 25 ° C.

(change over time)
The energization test was carried out for 500 hours by applying 13V while cooling at a wind speed of 4 m / s while being incorporated in a heater with aluminum fins. The room temperature resistivity at 25 ° C. after the energization test was measured, and the resistance change rate (%) was obtained by dividing the difference between the room temperature resistivity before the energization test and after 500 hours energization by the room temperature resistivity before the energization test, The change with time was examined.
Therefore, the rate of change with time is defined by the following equation.
{(Room temperature resistivity when energized for 500 hours) − (initial room temperature resistivity)} / (initial room temperature resistivity) × 100 (%)

(Interface resistance)
Since the interface resistance between the PTC element body and the electrode cannot be measured directly, it was defined as follows. First, a plurality of PTC elements having different thicknesses provided with electrodes on both end faces are prepared, and the resistance values of the respective semiconductor ceramic compositions at 25 ° C. are measured. As shown in FIG. The data obtained by plotting the thickness and the resistance value on the vertical axis are taken. An approximate straight line between the thickness and the resistance value is obtained from this data, the resistance value when the thickness of the approximate straight line at room temperature of 25 ° C. is 0 is obtained for convenience, and the resistance value when the thickness is 0 is formed on both surfaces of the element. The interface resistance (Ω / cm ² ) at the interface was defined by dividing by half the value of the electrode area. In FIG. 2, the slope of the approximate straight line indicates the resistance value of the PTC element body per unit thickness, and the vertical axis intercept (value of y when x = 0) is between the PTC element body 1 and the electrode 2. It was considered to indicate interfacial resistance.

The higher the numerical value of the temperature coefficient of resistance α, the better the jump characteristics and the wider the application. For example, if the temperature coefficient of resistance α is 5% / ° C. or more, it can be sufficiently used as a PTC element for sensor use or heater use. The room temperature resistivity is desirably stable at a low value of 100 Ω · cm or less in an in-vehicle auxiliary heater or the like. If it is higher than that, it can be used for applications such as a steam generating module up to about 1000 Ω · cm, for example, a heater for a hybrid vehicle, an electric vehicle, and a heat generating module that require high withstand voltage at 1000 Ω · cm or higher. Since the Curie temperature has a temperature suitable for the use of the PTC element, for example, a temperature range of about 130 ° C. to 200 ° C. is applicable to various uses. The smaller the change over time, the better. However, if the change over time in the room temperature resistivity when energized at 13 V for 500 hours is 10% or less, there is no practical problem.
In the following invention, the room temperature resistivity R ₂₅ is 100 Ω · cm or less, the temperature coefficient of resistance α is 5% / ° C. or more, and the interface resistance is 1.0 Ω / cm ² or less for the purpose of use in an in-vehicle auxiliary heater or the like. The characteristic value with a time-dependent change of room temperature resistivity when energized at 13 V for 500 hours was 10% or less was set as a target value.

Example 1
The following semiconductor porcelain compositions were obtained using the division calcination method. Raw material powders of BaCO ₃ , TiO ₂ , and La ₂ O ₃ were prepared, blended so as to be (Ba _0.994 La _0.006 ) TiO _3, and mixed with pure water. The obtained mixed raw material powder was calcined in the atmosphere at 900 ° C. for 4 hours to prepare BaT calcined powder.

Raw material powders of Na ₂ CO ₃ , Bi ₂ O ₃ and TiO ₂ were prepared, weighed and blended so as to be Bi _0.5 Na _0.5 TiO _3, and mixed in ethanol. The obtained mixed raw material powder was calcined in the air at 800 ° C. for 2 hours to prepare BNT calcined powder.

  The prepared BaT calcined powder and BNT calcined powder are blended in a molar ratio of 73: 7, and the center particle size of the mixed calcined powder is 1.0 μm to 2.0 μm by a pot mill using pure water as a medium. After mixing and pulverizing until dry, it was dried. 10% by mass of PVA was added to the pulverized powder of the mixed calcined powder, mixed, and granulated by a granulator. The obtained granulated powder was molded with a uniaxial press machine to obtain a molded body. This molded body was debindered at 700 ° C. for 1 hour, held in a nitrogen atmosphere with an oxygen concentration of 0.01% (100 ppm) at 1360 ° C. for 4 hours, and then gradually cooled in a furnace to obtain a sintered body. Obtained.

  The obtained sintered body (40 mm × 25 mm × 4 mm) was processed into a plate shape of 10 mm × 10 mm × 1 mm, 10 mm × 10 mm × 0.75 mm, 10 mm × 10 mm × 0.50 mm, 10 mm × 10 mm × 0.25 mm. Thus, four types of test PTC bodies were prepared. Next, an electrode paste in which the mass percentage of Ag and Zn was 50:50 when the metal component of the electrode material was 100 mass% was produced and applied to the 10 mm × 10 mm surface of the PTC element body by screen printing. Furthermore, Ag paste was applied as a cover electrode and applied by screen printing. The coated electrode is dried at 150 ° C. and then heat-treated in the air at 350 ° C. for 30 minutes. Thereafter, the temperature rise rate is 24 ° C./min, 600 in a nitrogen atmosphere with an oxygen concentration of 0.01% (100 ppm). The electrode was formed by holding at 10 ° C. for 10 minutes and baking at a temperature drop rate of 24 ° C./min. The time during which the PTC element was exposed to a temperature of 300 ° C. or higher was 34 minutes. The electrode paste was prepared by uniformly adding 3% by mass of glass frit and 25% by mass of organic binder to 100% by mass of the metal component. The same applies to the following examples and comparative examples, and the influence of metal components was evaluated.

The obtained results are shown in Table 1.
As a result, the room temperature resistivity R ₂₅ was 35.1 Ω · cm, the Curie temperature was 161 ° C., the resistance temperature coefficient α was 6.1% / ° C., the interface resistance was 0.20 Ω / cm ² , and the change with time was 6.5%. there were.

(Examples 2 to 11)
Examples 2 to 11 are examples in which the conditions for electrode formation were changed. In Examples 2 to 5, the heat treatment conditions in the atmosphere were changed, and in Examples 6 to 11, the baking conditions in the non-oxidizing atmosphere after the heat treatment were changed. The semiconductor porcelain composition production method, electrode formation method, and evaluation method other than changing the electrode formation conditions were also the same as in Example 1. The obtained results are shown in Table 1.
In the results of Examples 2 to 11, the room temperature resistivity R ₂₅ , the temperature coefficient of resistance α, the interface resistance, and the change with time satisfy the target characteristic values.

(Comparative Examples 1-9)
Comparative Examples 1 to 9 are examples in which the electrode formation conditions are outside the scope of the present invention. A method for producing a semiconductor ceramic composition, a method for forming an electrode, and an evaluation method were also performed in the same manner as in Example 1 except that the electrode formation conditions were changed. The obtained results are shown in Table 1.
From Examples 3, 6, and 7 and Comparative Example 5, it was found that when the oxygen concentration during electrode baking was higher than 2%, the interface resistance exceeded 1.0 Ω / cm ² and the change with time exceeded 10%. I understand. Moreover, from Example 3, 8-11, and Comparative Examples 6-9, when the temperature at the time of electrode baking is lower than 500 degreeC, higher than 700 degreeC, baking time is shorter than 5 minutes, or from 30 minutes As the length increases, the interfacial resistance exceeds 1.0 Ω / cm ² and the change with time exceeds 10%.
Furthermore, from the results of Examples 1 to 5 and Comparative Examples 1 to 4, the heat treatment temperature in the atmosphere was 300 ° C. or lower, or 420 ° C. or higher, or the heat treatment time was shorter than 10 minutes or longer than 60 minutes. Then, it can be seen that the interface resistance exceeds 1.0 Ω / cm ² and the change with time is more than 10%.
If the temperature of the electrode is out of the range of the above-mentioned temperature and holding time, the change over time is worse than when it is out of the preferable range of the heat treatment for debinding. is important.

(Examples 12 to 16)
Examples 12 to 16 are examples in which the composition of the semiconductor ceramic composition was changed. Except for changing the composition of the semiconductor ceramic composition, the production method of the semiconductor ceramic composition, the electrode formation method, and the evaluation method were also performed in the same manner as in Example 3. The obtained results are shown in Table 2.
In the results of Examples 12 to 16, the room temperature resistivity R ₂₅ , the temperature coefficient of resistance α, the interface resistance, and the change with time satisfy the target characteristic values.

(Comparative Examples 10-12)
Comparative Examples 10 to 12 are examples in which the composition of the semiconductor ceramic composition was out of the scope of the present invention. A method for producing a semiconductor ceramic composition, a method for forming an electrode, and an evaluation method were performed in the same manner as in Example 3 except that the composition of the semiconductor ceramic composition was out of the scope of the present invention. The obtained results are shown in Table 2.
From the results of Examples 12 to 14 and Comparative Example 10, it can be seen that if the range of x exceeds 0.3, the room temperature resistivity exceeds 100 Ω · cm. Further, from Examples 15 and 16 and Comparative Example 11, it can be seen that if the value of y exceeds 0.020, the temperature coefficient of resistance α falls below 5.0.

(Example 17)
Example 17 is an example in which a part of Ti is replaced with Ta without using a rare earth element as a semiconducting element. A semiconductor porcelain composition was obtained as follows using the division calcination method.
Raw material powders of BaCO ₃ , TiO ₂ , and Ta ₂ O ₅ were prepared, blended so as to be Ba (Ti _0.991 Ta _0.009 ) O _3, and mixed with pure water. The obtained mixed raw material powder was calcined in the atmosphere at 900 ° C. for 4 hours to prepare BaT calcined powder.

In the production of the BNT calcined powder, the manufacturing method of the semiconductor ceramic composition, the electrode formation method, and the evaluation method were the same as in Example 1 except that the heat treatment temperature was 400 ° C. The obtained results are shown in Table 2.
The room temperature resistivity R ₂₅ is 83.4 Ω · cm, the Curie temperature is 158 ° C., the resistance temperature coefficient α is 7.2% / ° C., the interface resistance is 0.54 Ω / cm ² , and the change over time is 7.5%. The characteristics were satisfied.

(Examples 18 to 19)
Examples 18 to 19 are examples in which the amount of Ta substitution was changed. Other semiconductor ceramic composition production methods, electrode formation methods, and evaluation methods were the same as in Example 17. The obtained results are shown in Table 2.
As a result of Examples 18 and 19, the room temperature resistivity R ₂₅ , the Curie temperature, the resistance temperature coefficient α, the interface resistance, and the change with time satisfy the target characteristic values.

(Comparative Example 13)
Comparative Example 13 is an example in which the amount of Ta substitution is outside the scope of the present invention. Other semiconductor ceramic composition production methods, electrode formation methods, and evaluation methods were the same as in Example 17. The obtained results are shown in Table 2.
From the results of Examples 17 to 19 and Comparative Example 12, if the substitution amount z of Ti exceeds 0.010, the room temperature resistivity R ₂₅ exceeds the target 100 Ω · cm, and the target characteristic value can be satisfied. I understand that it will disappear. To make a semiconductor, a part of Ti is replaced with Ta. However, the reason why the resistance does not decrease monotonously as the amount of replacement increases is considered to be because the number of different phases increases.
However, Comparative Examples 10 to 12 described above show satisfactory values when only changes with time are taken. In these examples, the interface resistance value of 1.0 Ω / cm ² or less is considered to contribute to the reduction of the change over time, and the effect of the reduction of the change over time is not necessarily limited to the composition of the semiconductor ceramic composition. It can be said that it is not involved in. Therefore, when the purpose is only to reduce the change over time, the comparative examples 10 to 12 can be said to be examples or reference examples.

(Examples 20 to 25)
Examples 20 to 25 are examples in which the composition of the electrode components was changed. Except for changing the composition of the electrode components and the heat treatment temperature, the production method of the semiconductor ceramic composition, the electrode formation method, and the evaluation method were also performed in the same manner as in Example 1. The obtained results are shown in Table 3.
In the results of Examples 20 to 25, the room temperature resistivity R ₂₅ , the temperature coefficient of resistance α, the interface resistance, and the change with time satisfy the target characteristic values.

(Comparative Examples 13-15)
Comparative Examples 13 to 15 are examples in which the composition of the electrode components is outside the scope of the present invention. A method for producing a semiconductor ceramic composition, a method for forming an electrode, and an evaluation method were also performed in the same manner as in Example 20 except that the composition of the electrode component was changed. The obtained results are shown in Table 3.
From Examples 20 to 22 and Comparative Examples 13 and 14, if the Ag ratio of the electrode is 20 to 65 mass% and the Zn ratio of the ohmic electrode component is 35 mass% or more and 80 mass% or less, the target characteristics can be satisfied. I understand. Moreover, from Examples 24 to 25 and Comparative Example 15, it can be seen that when the proportion of Sn as an ohmic component exceeds 60% by mass, the interface resistance exceeds 1.0 Ω / cm ² .

(Comparative Examples 16 and 17)
In Comparative Examples 16 and 17, the amount of BNT was set to 0. In Comparative Example 16, the oxygen concentration was 0.01% during electrode baking, and in Comparative Example 17 was 21% (in the atmosphere). Production methods and evaluation methods other than adding BNT were the same as in Example 19. The obtained results are shown in Table 3.
The values of the obtained interface resistance are almost the same in Comparative Examples 16 and 17, and it can be seen that the PTC element body containing no BNT has little effect of baking in a non-oxidizing atmosphere. Further, since the Curie temperature is as low as 130 ° C., it cannot be put to practical use in applications such as a PTC thermistor, a PTC heater, a PTC switch, and a temperature detector.

  The PTC element obtained by the present invention is most suitable for a PTC thermistor, a PTC heater, a PTC switch, a temperature detector, and the like. Moreover, it can utilize for the heat generating module which uses a PTC element as a component.

10: PTC element,
1: Semiconductor porcelain composition (PTC body),
2: Electrode

Claims (6)

A method for forming an electrode of a PTC element having an electrode made of an alloy of Ag and a base metal in a perovskite-based semiconductor ceramic composition containing at least Ba and Ti,
The semiconductor ceramic composition, a composition formula _{[(Bi-Na) x (} Ba 1-y R y) 1-x] [Ti 1-z M z] O 3 ( where, R represents a rare earth element including Y At least one of them, M is at least one of Nb, Ta, and Sb), and x, y, and z are 0 <x ≦ 0.30, 0 ≦ y ≦ 0.020, and 0 ≦ z ≦ 0. 010 is satisfied,
Applying the electrode paste to the semiconductor ceramic composition, performing a heat treatment to remove the binder in the electrode paste, and then performing a baking process;
The electrode forming method for a PTC element, wherein the baking treatment is performed in a non-oxidizing atmosphere having an oxygen concentration of 2% or less under conditions of 500 ° C. or higher and 700 ° C. or lower and 5 minutes or longer and 30 minutes or shorter. 2. The method for forming an electrode of a PTC element according to claim 1, wherein the heat treatment is performed in air at a temperature of 300 ° C. to 400 ° C. for 10 minutes to 60 minutes. 3. The method for forming an electrode of a PTC element according to claim 1, wherein the electrode has a composition in which Ag is 20% by mass or more and 65% by mass or less and the balance is a base metal. The method for forming an electrode of a PTC element according to claim 3, wherein the base metal is one or more elements selected from Zn and Sn. 5. The electrode forming method for a PTC element according to claim 4, wherein when the base metal is Sn, Sn is in a range of 20 mass% to 60 mass%. A PTC element manufactured by the electrode forming method for a PTC element according to any one of claims 1 to 5,
The PTC element is characterized in that an interface resistance between the electrode and the semiconductor ceramic composition is 1.0 Ω / cm ² or less.