JPH0969416A - Organic resistor with positive temperature characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small type resistor, having non-decreasing withstand voltage and positive temperature characteristics, which can be used for a large current. SOLUTION: This organic resistor element 7 is composed of an organic resistor layer 5, on which conductive fillers are dispersively mixed into a thermoplastic polymer, and conductive internal electrodes 6a and 6b which are alternately laminated so that the number of layers of the organic resistor layer 5 located between the internal electrodes 6a and 6b becomes two or more layers. External electrodes 8a and 8b are provided on the side face of the resistor element 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a positive temperature characteristic (PT
C) with an organic resistor.

[0002]

2. Description of the Prior Art Generally, 1 in a crystalline thermoplastic polymer.
Resistors dispersed with one or more conductive fillers, such as carbon black or finely divided metal, have a positive temperature coefficient of resistance. A well-known resistor having such a positive resistance temperature characteristic is a resistor in which carbon black is added as a conductive filler to high-density polyethylene (Japanese Patent Publication No. 64-3322). FIG. 5 shows an example thereof, in which electrodes 2 are fixed on both surfaces of a resistor PTC element body 1 in which carbon black or finely divided metal is dispersed and mixed in a thermoplastic polymer, and leads are respectively attached to the electrodes 2. The wire 3 is fixed, and the entire element body 1 provided with the electrodes 2 and the lead wires 3 is integrally molded with the mold polymer 4 except for the tip portions of the lead wires 3.

Further, in Japanese Patent Laid-Open No. 7-14702,
There is a PTC resistor as a laminated type in which a ceramic layer such as barium titanate and an internal electrode are laminated.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The organic resistor having positive temperature characteristics, which uses only carbon black as the conductive filler described in Japanese Patent No. 22 has the following problems. As described above, a practical organic resistor using carbon black as a conductive filler can have a room temperature resistivity of at most about 2 Ωcm, which is unsuitable for high current applications. Also,
If the resistance of the PTC-characteristic organic resistor can be reduced, the size can be reduced. For example, a small size that is convenient for accommodating inside or outside the battery as a device for preventing discharge or charging due to excessive current in a battery or the like. Can be provided,
As described above, the conventional carbon black using carbon black is limited in resistance reduction, so that it is not possible to achieve miniaturization and it is difficult to provide a space-saving product in terms of mounting.

Further, if the resistance can be lowered, the heat generation is suppressed even with the same current, it does not operate as a PTC, and it generates heat when used with a large current, so that it can be used with a large current. However, it is not possible to use it with a large current because it has a limitation in reducing the resistance. If the amount of the conductive filler is increased in order to reduce the resistance, the rate of change in resistance becomes small, which makes it difficult to interrupt the current in the event of an abnormality.

In order to reduce the resistance as a product,
It is necessary to make the PTC resistor thin, but in that case, there is a problem that the breakdown voltage decreases.

On the other hand, the one described in Japanese Patent Laid-Open No. 7-14702 has a high specific resistance between the internal electrodes because it uses a ceramic to obtain the PTC characteristics, and the ceramic resistance is 5 at most.
Since only about Ωcm can be obtained, it is large for increasing the amount of current and not suitable for downsizing. Further, in order to reduce the resistance value, the thickness of the ceramic layer between the internal electrodes must be reduced, which results in a low breakdown voltage.
There is a problem that it is unsuitable for use at a relatively high voltage exceeding 00V. Further, if the thickness of the ceramic layer between the internal electrodes is increased in order to increase the breakdown voltage, there is a problem in that the overall thickness is increased.

In view of the above problems, it is an object of the present invention to provide a resistor having a positive temperature characteristic which is small in withstand voltage and is small in size and used in large current applications.

[0009]

In order to achieve this object, the present invention provides an organic resistor layer in which a conductive filler is dispersed and mixed in a thermoplastic polymer, and an internal electrode made of a conductor.
The organic resistor element body is formed by alternately laminating the resistor layers between the internal electrodes so that the number of the resistor layers is two or more, and external electrodes connected to the internal electrodes facing each other on the side surfaces of the element body. Is provided.

In the present invention, the conductive filler is preferably composed of spiked metal powder, carbon black, and a whisker-shaped conductive oxide which is made conductive by being coated with a conductive substance. Further, the internal electrodes are preferably made of a metal foil or a thin film formed by a thin film forming technique.

[0011]

In the present invention, by forming the organic resistor antibody in which the conductive filler is dispersed and mixed in the thermoplastic polymer and the internal electrode in a laminated form, a wide electrode area can be obtained as the total area of the internal electrodes in each layer. As a result, the room temperature specific resistance can be lowered. Further, since the organic resistor is used, it is not necessary to thin the space between the internal electrodes for the purpose of large current application, and therefore the breakdown voltage is not lowered.

[0012]

1 is a sectional view showing an embodiment of an organic resistor according to the present invention. This organic resistor is formed by dispersing and mixing a conductive filler in a thermoplastic polymer made of polyvinylidene fluoride, for example. PTC resistor layer 5 and internal electrode 6
a and 6b are laminated in such a manner that the number of resistor layers between the internal electrodes 6a and 6b is two or more (three in the illustrated example) to form an organic resistor element body 7, and a side surface of the element body 7 is formed. External electrodes 8a and 8b connected to the internal electrodes 6a and 6b facing each other.

FIG. 2 is a diagram showing a manufacturing process of this organic resistor, in which polyvinylidene fluoride, which is an example of a crystalline thermoplastic polymer, carbon black as a conductive filler, and a cross-linking agent are mixed at 200.degree. Knead for 1 hour (S1),
The material kneaded in this way is formed into a sheet by an extruder or a press (S2) and cross-linked by an electron beam or the like (S3).
Foil of gold, copper, aluminum or the like is applied under pressure at 200 ° C. under pressure, or electrodes 6a and 6b made of these metals are formed by a thin film forming technique (sputtering, plating or vapor deposition) (S4). Sheet-like materials with electrodes 6a and 6b attached to them are laminated in a heated and pressurized state (S5), punched into a predetermined shape (S6), and then a conductive paste is applied or a metal cap is attached to the side surfaces of the external electrodes. 8a and 8b (S7).

Table 1 shows the internal electrodes 6a, 6 as shown in FIG.
Three organic resistor layers 5 between b, that is, internal electrodes 6a,
6 shows the initial specific resistance, the rate of resistance change, and the breakdown voltage (voltage causing a short circuit in a temperature rising state) when the number of layers of 6b is four. The resistance change rate is l
It is a value expressed by og (maximum resistance value / resistance value at 25 ° C.), and% in Table 1 to the following tables represents volume%. The element used in the test had a rectangular overall shape, and electrodes 2 were fixed to both surfaces of the resistor 1 as in the conventional case.
The layer type has a length (L) of 4.5 mm and a width (W) of 3.2.
mm, the thickness (T) was 0.5 mm, and the carbon black filling rate was 22.5% by volume. On the other hand, according to the present invention, the distance between the internal electrodes 6a and 6b, the length L and the width W are the same as those of the conventional type, and only the thickness (T) is changed to 2.0 mm.

As a result, the room temperature specific resistance (specific resistance at 25 ° C.) is 0.75 Ωcm in the case of the present invention,
The resistance change rate is about 40% of 1.8 Ωcm of the conventional product, and the resistance change rate is 5.3 in the case of the present invention as compared with 5.3 of the conventional product.
It was found that the breakdown voltage (short-circuit voltage) was almost the same as that of No. 1 and that the breakdown voltage (short-circuit voltage) was almost the same as 195V in the case of the present invention as compared with 200V of the conventional product.

Further, as described above, the internal electrodes 6a and 6b are
If the number of resistor layers 5 between the inner electrodes is 3
Since the total of the facing areas between a and 6b is about three times as large as that in the conventional case, it is possible to achieve a significant reduction in size and an increase in current. In addition, when barium titanate is used for the PTC resistor, downsizing,
If the distance between the internal electrodes 6a and 6b is narrowed to reduce the thickness, the withstand voltage becomes low, which makes it unsuitable for use at relatively high pressure. However, according to the present invention, the internal electrodes 6a and 6b are not suitable.
Since it is not necessary to narrow the interval between b, the breakdown voltage does not decrease and it can be used for high voltage.

Regarding the above-mentioned sample, DC12V-
When a repetitive energization test was conducted in which energization of 15 A was performed for 15 seconds and then stopped for 150 seconds, as shown in FIG.
After repeated 10,000 times, the room temperature resistance value after repetition increased by about 23% with respect to the initial room temperature resistance value in the conventional product, but in the case of the present invention, the change in this resistance value was about 12%.
It was found that the resistance value was suppressed to about 10% and that the low resistance value could be maintained for a long time.

The internal electrodes 6a and 6b can be formed by applying a conductive paste or the like.
As described above, by performing this by fixing the metal foil or forming it by the thin film forming technique, the thin internal electrodes 6a and 6b having low resistance can be formed, which can contribute to the thinning of the entire resistor.

As the conductive filler constituting the PTC resistor, a metal powder can be used in addition to carbon black, and a mixture of other additives as a conductive auxiliary agent can be used. And, more preferably, a metal powder as a main component of the conductive filler, carbon black as a conductive auxiliary agent for reducing the resistance at room temperature, and whisker-like conductive oxidation as a conductive auxiliary agent for increasing the resistance change rate. It is more preferable that the compound is mixed with a substance, and dispersed and mixed in a crystalline thermoplastic polymer.

In the case of using such a conductive filler composition, it is preferable to use spike-shaped nickel powder (a powder having a large number of protrusions around the particles) as the metal powder. Further, as the conductive oxide, the surface of an oxide powder such as whisker-like potassium titanate, silver, nickel,
It is preferably coated with a conductive material such as carbon or tin dioxide (SnO ₂ ).

In the organic resistor manufactured as described above, KF10 manufactured by Kureha Chemical Co., Ltd. is used as polyvinylidene fluoride.
00, nickel powder # 2 manufactured by INCO
55, carbon black EC600JD made by Ketjen Black International, carbon coated potassium titanate Dentsu BK3 made by Otsuka Chemical
In order to investigate the resistance characteristics of the resistor itself, the initial specific resistance at 25 ° C. is 0.82 Ωcm when the PTC resistor is constructed with the structure shown in FIG. Was obtained, and the initial resistivity was considerably lower than that of an organic resistor filled with a conventional carbon black as a conductive filler. Moreover, the change in the specific resistance with respect to the temperature change is as shown in FIG.
The rate of change in resistance [= log (maximum resistance value / initial resistance value)] was 8.6, that is, 6 digits or more, which was a sufficiently practical value. In addition, Comparative Examples 1 and 2 shown in FIG. 4 have the following compositions shown in Table 2, respectively. Comparative Example 1: Polyvinylidene fluoride (KF1000 above)
75% by volume, carbon black (# 4 manufactured by Tokai Carbon Co., Ltd.
500) 25% by volume Comparative Example 2: Polyvinylidene fluoride (KF1000 described above)
75% by volume, nickel powder (# 255) 15% by volume, carbon black (EC600JD) 10% by volume

As can be seen from FIG. 4, according to the present embodiment, a large resistance change rate can be obtained as compared with Comparative Examples 1 and 2, that is, the resistors having carbon black alone or the mixture of carbon black and nickel. It was Further, as in the above-mentioned Japanese Patent Application No. 6-79390, when only the metal powder was used, the resistance change rate was about 6.0 at maximum, but according to the present invention, in the case of only this metal powder. A larger rate of resistance change was obtained.

In the present invention, the material used as the metal powder is preferably one that is relatively resistant to oxidation,
Examples of compounds that are difficult to oxidize include carbides, nitrides and borides. Also, as a metal that is difficult to oxidize,
There are silver and nickel. Among them, the nickel powder, which is relatively inexpensive and has a low specific resistance, was compared with the initial specific resistance and the rate of resistance change when titanium carbide and tungsten carbide were used as the conductive filler.

As shown in Table 3, in the prototype, the polyvinylidene fluoride was used as the polymer, and the packing ratio of these metal powders to the polymer was almost the same (15.2% by volume or 16.8% by volume). The filling ratio of carbon black to the polymer is 3.0% by volume, and the filling ratio of carbon-coated potassium titanate to the polymer is 11.1% to 11.2%.
% By volume. The initial resistivity and resistance change rate of the element body using these metal powders are as shown in Table 3. As can be seen from Table 3, the spike-shaped nickel powder can significantly reduce the initial resistivity. A resistance change rate of 6 digits or more is obtained, and it is understood that it is preferable to use spike-shaped nickel powder as the metal powder. The conductive filler filling rate means, for example, that the volume of the conductive filler (nickel, carbon black or potassium titanate) is a and the volume of the polymer is b, the filling rate (%) of the polymer = {a / (A + b)} × 100.

When the spike-shaped nickel powder is used as described above, the average particle size of the nickel powder is 1.0 μm to
4.0 μm and an apparent density of 0.5 g / cm ^{3 to} 0.8
It is preferably g / cm ³ . Average particle size is 1.0μ
When it is less than m, it is easy to oxidize and secular change easily occurs, and when it exceeds 4.0 μm, the resistance value becomes high. Further, when the apparent density is less than 0.5 g / cm ³ , the resistance value increases, and when the apparent density exceeds 0.8 g / cm ³ , the rate of resistance change decreases.

On the other hand, the whisker-like conductive oxide can increase the rate of resistance change by adding it as a conductive filler, but if it is used without treatment,
The resistance value becomes high. Therefore, it is preferable to coat the surface of the whisker-like conductive oxide with a conductive material to reduce the resistance value.To reduce the resistance value, carbon, silver, tin oxide, nickel was coated with whisker-like powder of potassium titanate, Sufficient values were obtained for both the initial resistivity and the rate of resistance change. Table 4 shows the initial specific resistance and the rate of change in resistance when a whisker-like conductive oxide coated with carbon, silver or tin oxide was used as a part of the conductive filler and other conductive fillers or polymers were used as described above. Indicates. If silver is used as a coating material for the whisker-like conductive oxide, it becomes expensive, so carbon coating is sufficient for practical use.

In the present invention, the larger the specific surface area of the carbon black used as the conductive additive for lowering the resistance value, the greater the effect of lowering the resistance value. The resistance value decreases as the carbon black having a small specific surface area increases, but the resistance change rate decreases as the addition amount increases. Therefore, the point is how to reduce the resistance value with a small addition amount, and the specific surface area of carbon black, the initial specific resistance, and the rate of resistance change were examined. Table 4 is a table showing the results, and in the sample of Table 5, the same nickel powder and carbon-coated potassium titanate as those described in Table 2 were used. Further, the specific surface area in Table 5 is based on the BET method, and No. The carbon black of the sample No. 1 was No. 4500, No. 4 manufactured by Tokai Carbon Co., Ltd. 2 is Cabot (Ca
Bot) Vulcan XC-72, N
o. No. 3 is EC, No. 3 manufactured by Ketjen Black International. 4 used EC600JD manufactured by Ketjen Black International.

As shown in Table 5, the specific surface area is 58 m ² /
In the case of using carbon black of g or more, although the resistance change rate of five digits or more can be obtained, the initial specific resistance becomes high. In the composition shown in Table 5, from the relationship between the specific surface area and the initial specific resistance, if approximately 800 m ² / g or more,
It was found that the initial specific resistance can be suppressed to 2 Ωcm or less. The upper limit of the specific surface area is preferably 1300 m ² / g or less in order to obtain a resistance change rate of 5 digits or more.

Next, the result of studying the filling amount of the nickel powder as the conductive powder will be described. In order to reduce the specific resistance, it is sufficient to add a large amount of conductive filler in the polymer, but if the addition amount is too large, the contact between the conductive fillers cannot be broken even after the polymer expands. Since the resistance does not increase and the resistance change rate is small, it cannot be practically used as a PTC resistor. Therefore, as shown in Table 6, the filling ratio of carbon black to polyvinylidene fluoride is 3.0.
%, The filling rate of carbon black to polyvinylidene fluoride is 11.1% by volume, which is almost constant.
The initial specific resistance and the rate of resistance change were measured while changing the ratio of polyvinylidene fluoride and nickel powder, that is, the filling rate of nickel powder. As a result, it was found that when the filling rate of the nickel powder with respect to the polymer was less than 10% by volume, the resistance was too large, and when it exceeded 25% by volume, the rate of change in resistance was 5 digits or less, which was not practical. .

The purpose of adding whisker-like potassium titanate is to increase the rate of resistance change as compared with the case of adding nickel alone. However, if the amount of potassium titanate is too small or too large, the rate of resistance change becomes small. Therefore, the proper addition amount was examined. Table 7 shows that the filling rates of nickel powder and carbon black with respect to polyvinylidene fluoride were set to be substantially constant at 15.0% by volume to 15.1% by volume and 3.0% by volume, respectively. The results of measuring the initial specific resistance and the rate of resistance change by varying the filling rate are shown below. From the results in Table 7, potassium titanate has a filling rate of 5% to 20% by volume with respect to the polymer.
It has been found that when the value is an appropriate amount, a value of about 4 Ωcm or less can be obtained as the initial specific resistance and a rate of resistance change of 5 digits or more can be obtained.

Further, the addition of carbon black can reduce the specific resistance even with a small amount of addition, so the amount of addition was examined as an auxiliary agent for nickel powder. As in the case of nickel powder, if the carbon black filling amount is too large, the resistance change rate will be small. Table 8 shows the filling rates of nickel powder and carbon-coated potassium titanate with respect to the polymer, respectively, from 15.0% by volume to 15.1% by volume and 11.0% by volume to 11.1% by volume.
The results show that the initial specific resistance and the rate of change in resistance were measured by changing the filling rate of carbon black with respect to the polymer, and the filling rate of carbon black with respect to the polymer was 1% by volume to 5% by volume. If so, the initial resistivity is about 2
It was found that the value can be made lower than Ωcm and the rate of change in resistance can be obtained in a value of 5 digits or more.

Examples of the thermoplastic polymer used in the present invention include high density polyethylene, polypropylene, polyamide resin, polyacetal, porin vinylidene chloride, and polytetrafluoroethylene in addition to polyvinylidene fluoride. (Below margin)

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

[0039]

[Table 7]

[0040]

[Table 8]

[0041]

According to the first aspect of the present invention, an organic resistor layer in which a conductive filler is dispersed and mixed in a thermoplastic polymer and an internal electrode made of a conductor are provided, and the number of resistor layers between the internal electrodes is two or more. To be laminated alternately to form an organic resistor element body,
Since the external electrodes connected to the internal electrodes facing each other are provided on the side surfaces of the element body, the facing area between the electrodes can be increased, and the apparent specific resistance can be significantly reduced. Compared to the case of using ceramics, the resistivity of the resistor layer is low, so that a PTC organic resistor for a larger current can be provided without increasing the overall thickness and size, and without lowering the withstand voltage performance. Can be provided,
As a result, it is possible to reduce the size of the PTC organic resistor.

According to the second aspect, the metal powder, the whisker-like conductive oxide, and the carbon black are dispersed and mixed in the crystalline thermoplastic polymer to form the organic resistor having the PTC characteristic. Compared with a single conductive filler, the room temperature resistivity can be kept low, and a larger rate of change in resistance can be obtained than with metal powder alone or a conductive filler consisting of metal powder and carbon black. Available P for high current applications
An organic resistor having TC characteristics can be obtained. Further, since miniaturization can be achieved, it is possible to provide an organic resistor having a PTC characteristic which is advantageous in mounting.

According to the third aspect, since the internal electrode is formed of a metal foil or a thin film formed by a thin film forming technique, a thin internal electrode having low resistance can be formed, which contributes to thinning of the entire resistor. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an organic resistor having PTC characteristics according to the present invention.

FIG. 2 is a manufacturing process diagram of the present embodiment.

FIG. 3 is a graph showing a change in resistance value in a case where a repeated energization test is performed on the present example, in comparison with a conventional example.

FIG. 4 is a graph showing a change in resistance value with respect to temperature in the present example in comparison with a comparative example.

FIG. 5 is a cross-sectional view showing a conventional PTC characteristic organic resistor.

[Explanation of symbols]

5: PTC resistor layer, 6a, 6b: internal electrode, 7: resistor element body, 8a, 8b: external electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Shibata 1-13-1, Nihonbashi, Chuo-ku, Tokyo T-DK Corporation

Claims (3)

[Claims] 1. An organic resistor layer in which a conductive filler is dispersed and mixed in a thermoplastic polymer and an internal electrode made of a conductor, and the number of organic resistor layers interposed between the internal electrodes is two or more. An organic resistor element body having positive temperature characteristics, characterized in that an organic resistor element body is formed by alternately laminating the external element bodies, and external electrodes connected to the opposing internal electrodes are provided on the side surfaces of the element body. body. 2. The conductive filler according to claim 1, comprising spiked metal powder, carbon black, and a whisker-like conductive oxide which is made conductive by being coated with a conductive substance. An organic resistor with positive temperature characteristics. 3. The organic resistor according to claim 1, wherein the internal electrode is made of a metal foil or a thin film formed by a thin film forming technique.