JP2002164201A - Organic positive temperature coefficient thermistor composition and organic positive temperature coefficient thermistor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic positive temperature coefficient thermistor element, that has a low specific resistance and is suppressed in resistance change caused by oxidation and deformation. SOLUTION: This organic positive temperature coefficient thermistor element 10 contains a flat element 12. The element 12 is composed of an organic positive temperature coefficient thermistor composition. The thermistor composition is prepared by mixing conductive powder in a matrix resin, composed of a crystalline macromolecular material. The conductive powder contains secondary particles, each of which is obtained by cohering a plurality of primary particles of the metallic powder together. The means particle diameter of the secondary particles is adjusted to 5-30 times the primary particles. On both main surfaces of the element 12, electrodes 14 and 14 are respectively formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic positive temperature coefficient thermistor composition and an organic positive temperature coefficient thermistor element, and more particularly to an organic positive temperature coefficient thermistor composition used for a chip type organic positive temperature coefficient thermistor element for overcurrent protection of an electronic circuit. About things.

[0002]

2. Description of the Related Art Conventionally, carbon black has been generally used as a conductive powder to be mixed with a polymer resin material of an organic positive temperature coefficient thermistor composition, which is an element of an organic positive temperature coefficient thermistor element. In an organic positive temperature coefficient thermistor element using such an organic positive temperature coefficient thermistor composition, carbon black dispersed in a polymer resin material forms a conductive path at room temperature and shows a low resistance value. Sudden crystal melting occurs near the melting point of the resin, and the resulting rapid volume expansion cuts the conductive path and increases the resistance. Therefore, this organic positive temperature coefficient thermistor element can be used for overcurrent protection.

However, in the market for interfaces such as USB and IEEE 1394, demand for low resistance chip type organic positive temperature coefficient thermistor elements for overcurrent protection is expected to increase rapidly. Movement to use is increasing. Silver powder is a typical conductive metal powder, but has the disadvantage of being expensive. Nickel powder and copper powder, which are relatively inexpensive, can also be considered, but have the disadvantage that the surface is oxidized by the heat history and the specific resistance increases due to low oxidation resistance.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 8-88106, a method of coating a nickel powder with a metal material (palladium) having oxidation resistance and conductivity is adopted, and at a relatively low cost, the acid resistance is reduced. The chemical properties were satisfied. Further, as disclosed in Japanese Patent Application Laid-Open No. 10-303003, a method of performing a coupling treatment on a metal surface is employed, and the same effect is obtained at a lower cost.

[0005]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 8-
One of the drawbacks of the devices manufactured by these methods disclosed in JP-A-88106 and JP-A-10-303003 is that the shape retention of the matrix resin when molten is low. If the shape retention is low, the material is deformed while repeating melting and solidification, thereby increasing the resistance.

As a means of improving the shape retention, there is a method of increasing the degree of crosslinking of a crystalline polymer as a matrix resin. However, increasing the degree of cross-linking has the disadvantage that the crystallinity of the crystalline polymer is reduced, which adversely affects the thermistor characteristics of the organic positive temperature coefficient thermistor element.

There is also a method of simultaneously adding carbon black as a conductive component. The purpose of this is to give a similar cross-link to the organic positive temperature coefficient thermistor composition by utilizing the property of carbon black that forms a structure (aggregated form) in a matrix resin. However, as described above, carbon black has a higher specific resistance than metal powder. Therefore, if it is mixed in a large amount, the specific resistance at room temperature increases. Therefore, it is necessary to limit the mixing amount of carbon black to a necessary minimum.

[0008] There is also a method in which an antioxidant-treated metal powder itself to be mixed as a conductive component is converted into an aggregated powder. Thereby, an effect equivalent to the simultaneous addition of carbon black can be obtained.

SUMMARY OF THE INVENTION Accordingly, it is a main object of the present invention to provide an organic positive temperature coefficient thermistor element having a low specific resistance and suppressing a change in resistance due to oxidation and deformation, and an organic positive temperature coefficient thermistor composition used therefor.

[0010]

The organic positive temperature coefficient thermistor composition according to the present invention is an organic positive temperature coefficient thermistor composition obtained by adding a conductive powder to a matrix resin comprising a crystalline polymer material. The conductive powder includes secondary particles obtained by aggregating a plurality of primary particles of metal powder.
The organic positive temperature coefficient thermistor composition is characterized in that the average particle size of the secondary particles is 5 to 30 times the average particle size of the primary particles. In the organic positive temperature coefficient thermistor composition according to the present invention, the average particle size of the primary particles of the metal powder is 0.5 to 10 μm.
It is preferable that Further, in the organic positive temperature coefficient thermistor composition according to the present invention, it is preferable that the total of the matrix resin and the conductive powder is 100% by volume, and the content of the conductive powder is 25 to 60% by volume. further,
In the organic positive temperature coefficient thermistor composition according to the present invention, the conductive powder is preferably a mixed powder of a metal powder and carbon black. In this case, the total of the conductive powder is 1
The content of carbon black is preferably 15% by volume or less based on 00% by volume. In the organic positive temperature coefficient thermistor composition according to the present invention, the melting point of the matrix resin is preferably from 130 to 180 ° C. An organic positive temperature coefficient thermistor element according to the present invention is an organic positive temperature coefficient thermistor element characterized in that electrodes are formed on the surface of a body made of the organic positive temperature coefficient thermistor composition according to the present invention.

The present inventors have conducted intensive studies to achieve low specific resistance and suppression of resistance change due to oxidation and deformation in an organic positive temperature coefficient thermistor element. As a result, by using agglomerated antioxidant-treated metal powder or a mixture of agglomerated antioxidant-treated metal powder and a minimum amount of carbon black as a conductive powder, low specific resistance and oxidation and It has been found that suppression of resistance change due to deformation is achieved.

In order to achieve the above-mentioned object, first, a metal powder which has been subjected to antioxidation treatment and has been aggregated as a conductive powder was selected. Examples of the metal powder include a gold powder, a silver powder, a nickel powder, a copper powder, a magnesium powder, an aluminum powder, an iron powder, and a tungsten powder. Nickel powder is suitable in consideration of cost and conductivity. Examples of the oxidation prevention treatment of the nickel powder include a metal plating treatment, a carbon coating, a coupling treatment with an organic substance, and the like.As described above, for the purpose of aggregating the metal powder and improving the shape retention of the system,
It is desirable that the coating film of the metal powder has a certain degree of viscosity. For that reason, coupling treatment with an organic substance is desirable, and as a result of intensive studies, it has been found that treatment with a titanate coupling agent is particularly optimal. The treatment amount of the titanate-based coupling agent is desirably set so that the average agglomerated diameter of the nickel powder agglomerated thereby becomes 5 to 30 times the average primary particle size (average primary particle size and average agglomerated particle size). diameter was around each aggregate value of D ₅₀ was measured with a laser diffraction type particle size distribution meter.). If the treatment amount is as small as less than 5 times, the effect of improving the shape retention of the system is low as described above, and furthermore, oxidation resistance cannot be expected. Conversely, large throughputs, such as over 30 times, cause a reduction in the mechanical strength of the system. The average primary particle diameter of the agglomerated nickel powder used before the agglomeration is preferably 0.5 μm or more and 10 μm or less. If the thickness is less than 0.5 μm, the influence of the oxide insulating film on the surface of the particles cannot be ignored and causes an increase in the resistance value. Conversely, if it exceeds 10 μm, it becomes difficult to aggregate the particles.

Next, it is necessary to select a carbon black which efficiently increases the shape retention of the organic positive temperature coefficient thermistor composition even with a small amount of mixture. As a result of various studies, using a high-structure type carbon black,
It has been found that favorable results are obtained. Here, the high structure type carbon black has an average particle diameter of 50 nm or less and a DBP oil absorption of 130 ml / 100 g.
That is all. Here, the DBP oil absorption is an index indicating the degree of the structure of the carbon black, and it can be determined that the higher the value, the higher the structure.

With the above structure, for example, agglomeration nickel powder which has been subjected to antioxidation treatment and surface-treated with a titanate-based coupling agent is used as the conductive powder, and at the same time, a high structure type carbon black is mixed to a minimum amount. , The room temperature resistivity is low, even if a heat history is applied, the increase in room temperature resistivity due to oxidation is suppressed, and the shape retention of the organic positive temperature coefficient thermistor composition can be increased,
An increase in the room temperature specific resistance due to thermal deformation is suppressed.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the present invention.

[0016]

DETAILED DESCRIPTION OF THE INVENTION An organic positive temperature coefficient thermistor composition according to an embodiment of the present invention comprises a high density polyethylene, polyvinylidene fluoride or a mixed resin of high density polyethylene and polyvinylidene fluoride as a matrix resin, and a conductive resin. Agglomerated nickel powder surface-treated with a titanate coupling agent, or a mixture of agglomerated nickel powder surface-treated with a titanate coupling agent and a mixed powder of high-structure type carbon black as a powder. is there. As the matrix resin, besides high-density polyethylene and polyvinylidene fluoride, low-density polyethylene and polyolefin-based crystalline polymers such as polypropylene can be used. The difference between the room temperature resistivity and the resistivity after tripping (the matrix resin Considering that crystal melting causes rapid volume expansion and cuts conductive paths between conductive particles, resulting in trips that increase the specific resistance rapidly.) Vinylidene mixed resins are suitable.

The melting point of high-density polyethylene is 130
℃ ~ 140 ℃, the melting point of polyvinylidene fluoride is 170 ℃ ~ 180 ℃, if using a mixed resin of high-density polyethylene and polyvinylidene fluoride as the matrix resin, by controlling the mixing ratio It is possible to set the apparent melting point at any temperature between 130 ° C and 180 ° C. The overcurrent protection effect of the organic positive temperature coefficient thermistor element is such that when a large current flows through the element and the element temperature rises to the melting point of the matrix resin, rapid volume expansion occurs as described above, and a conductive path between the conductive particles is formed. It is caused by being cut. Therefore, the melting point of the matrix resin is one of the most important factors for the organic positive temperature coefficient thermistor element. Particularly, in the case of a chip type organic positive temperature coefficient thermistor element for surface mounting, when the melting point of the matrix resin is 130 ° C. to 180 ° C., an optimum holding current value (maximum current that can flow without tripping the element) is obtained. It can be set.

Further, as described above, as the conductive powder, an agglomerated nickel powder surface-treated with a titanate-based coupling agent, or an agglomerated nickel powder surface-treated with a titanate-based coupling agent and a high structure type carbon black However, if the mixture of only the agglomerated nickel powder can improve the shape retention of the system, the simultaneous addition of the high structure type carbon black can be omitted.

It is desirable that the conductive powder is set in the range of 25 to 60% by volume, where the total of the matrix resin and the conductive powder is 100% by volume. The mixing amount of the conductive powder is 10 in total of the matrix resin and the conductive powder.
If the amount is less than 25% by volume relative to 0% by volume, it is difficult to sufficiently lower the room temperature specific resistance of the organic positive temperature coefficient thermistor composition, and if it exceeds 60% by volume, it takes a very long time to knead. In addition to being inefficient, the mechanical strength of the resulting organic positive temperature coefficient thermistor composition is extremely low (brittle), and the adhesion to the electrode is reduced, resulting in an increase in resistance. is there.

[0020]

EXAMPLES (Examples 1 to 12) In Examples 1 to 3, high-density polyethylene (density: 0.968 g / cm) was used as the matrix resin component of the organic positive temperature coefficient thermistor composition which is the element of the organic positive temperature coefficient thermistor element. ³ ) Used. Aggregated nickel powder A whose surface has been treated with a titanate-based coupling agent
(Average primary particle size: 2 μm, average aggregation diameter: 30 μm, density: 8.8 g / cm ³ ), and Toka Black # 450 manufactured by Tokai Carbon Co., Ltd. as carbon black.
0 (average particle size: 40 nm, DBP oil absorption: 168 ml /
100 g, density: 1.8 g / cm ³ ). The mixing ratio is 100% by volume of the whole organic positive temperature coefficient thermistor composition.
The high-density polyethylene was 50% by volume and the conductive powder was 50% by volume. The volume ratio of the agglomerated nickel powder surface-treated with the titanate-based coupling agent to the carbon black among the conductive powders was 95: 5 in Example 1, 90:10 in Example 2, and 10:10 in Example 3.
0: 0 was set. In Examples 4, 5 and 6, the matrix resin component was polyvinylidene fluoride (density: 1.77 g / c
m ³ ), except that they were the same as in Examples 1, 2, and 3, respectively. Examples 7, 8, and 9 are the same as Examples 1, 2, and 3, respectively, except that the matrix resin component is a mixed resin of the above-described high-density polyethylene and the above-mentioned polyvinylidene fluoride (weight ratio: 50/50). And Instead of the agglomerated nickel powder A surface-treated with the titanate coupling agent used in Examples 1 to 9, in Example 10, agglomerated nickel powder B (average primary particle size: 2 μm) surface-treated with a titanate coupling agent , Average aggregation diameter: 12μ
m, density: 8.8 g / cm ³ ), except that agglomerated nickel powder C surface-treated with a titanate coupling agent (average primary particle size: 2 μm, average) Aggregation diameter: 50 μm, density: 8.8 g /
cm ³ ) except that cm ³ ) was used. In Example 12, Examples 1, 2, 4, 5, 7, 8, 10, 1
In place of the carbon black used in No. 1, Toka Black # 4400 (average particle size: manufactured by Tokai Carbon Co., Ltd.)
Example 1 was the same as Example 1 except that 38 nm, DBP oil absorption: 135 ml / 100 g, and density: 1.8 g / cm ³ ). After blending, 1 to 2 in Examples 1 to 3 and 10 to 12 by a two-roll kneader (manufactured by Nissin Kagaku Co., Ltd.)
Kneading was performed at 50 ° C. for 10 minutes, and in Examples 4 to 9, kneading was performed at 190 ° C. for 15 minutes. Furthermore, Examples 1-3 and 10
In No. 12, for the purpose of chemical crosslinking, 1% by weight of dicumyl peroxide was added to the high-density polyethylene and kneaded again for 5 minutes. After completion of kneading, the sheet was taken out as a sheet having a thickness of about 0.7 mm, and a copper foil (thickness: 18 μm) having one surface roughened was set on both sides of the sheet so that the rough side was on the sheet side. 180 for 1-3 and 10-12
At 10 ° C. for 10 minutes.
Pressed for 0 minutes. In this case, the thickness of the spacer is 0.
5 mm. Then, cool to room temperature, thickness 0.5m
Thus, m samples with electrodes were obtained. The obtained sample was cut into a size of 5 mm square with a sheet cutter to obtain an organic positive temperature coefficient thermistor element 10 shown in FIG. Thereafter, the resistance was measured by a four-terminal method in a temperature-variable thermostat, and the specific resistance was calculated from the thickness and the area. The organic positive temperature coefficient thermistor element 10 shown in FIG. 1 includes a plate-shaped element body 12 made of an organic positive temperature coefficient thermistor composition. Electrodes 14 and 14 are respectively formed on both main surfaces of the element body 12.

The temperature profile of the measurement is shown in Examples 1-3.
And 10 to 12 at 30 to 150 ° C., and Examples 4 to 9 at 30 to 190 ° C. in 10 ° C. steps, and the waiting time at each measurement temperature was 3 minutes. After the measurement was completed, the sample was allowed to cool to 30 ° C., and the same measurement was performed again.
The measurement was repeated five times.

For comparison, the following Comparative Examples 1, 2,
Samples of 3, 4, 4 ', 4 ", 5 and 6 were prepared. The preparation and measurement of the samples were performed in Examples 1-3 and 10-12.
Method.

Comparative Example 1 Comparative Example 1 was the same as Example 1 except that only carbon black was blended as the conductive powder.

Comparative Example 2 Comparative Example 2 was the same as Example 1 except that untreated nickel powder was blended in place of the agglomerated nickel powder surface-treated with a titanate coupling agent.

Comparative Example 3 In Comparative Example 3, instead of using the agglomerated nickel powder A surface-treated with a titanate-based coupling agent, non-agglomerated nickel powder D (average primary particles) surface-treated with a titanate-based coupling agent Example 2 was the same as Example 1 except that the diameter: 2 μm and the density: 8.8 g / cm ³ ).

Comparative Example 4 In Comparative Example 4, a titanate-based
Use agglomerated nickel powder A surface-treated with a coupling agent
Surface treatment with titanate coupling agent instead of using
Aggregated nickel powder D (average primary particle size: 2 μm, average
Aggregation diameter: 80 μm, density: 8.8 g / cm ^ThreeUse
The other conditions were the same as in Example 1.

(Comparative Example 4 ') In Comparative Example 4', agglomerated nickel powder A surface-treated with a titanate coupling agent was used.
Agglomerated nickel powder E (average primary particle size: 0.2 μm) surface-treated with a titanate coupling agent instead of
m, average aggregation diameter: 5 μm, density: 8.8 g / cm ³ ).

(Comparative Example 4 ″) In Comparative Example 4 ″, the aggregated nickel powder A surface-treated with a titanate coupling agent was used.
Was used in the same manner as in Example 1 except that nickel powder F (average primary particle size: 15 μm, no aggregation, density: 8.8 g / cm ³ ) surface-treated with a titanate coupling agent was used instead of .

Comparative Example 5 In Comparative Example 5, the entire organic positive temperature coefficient thermistor composition was 100% by volume, the high density polyethylene was 80% by volume, and the agglomerated nickel surface-treated with the titanate coupling agent was used. 1 powder A
7% by volume, and 3% by volume of the above carbon black (Toka Black # 4500 manufactured by Tokai Carbon Co., Ltd.).

Comparative Example 6 In Comparative Example 6, the total volume of the organic positive temperature coefficient thermistor composition was 100% by volume, the above-mentioned high-density polyethylene was 35% by volume, and the agglomerated nickel was surface-treated with the above-described titanate-based coupling agent. Powder A 4
5% by volume, and 20% by volume of the above-described carbon black (Toka Black # 4500 manufactured by Tokai Carbon Co., Ltd.)
And

Table 1 shows the measurement results of the above-mentioned Examples 1 to 12 and Comparative Examples 1 to 6 with respect to the initial room temperature resistivity and the room temperature resistivity after five measurements.

[0032]

[Table 1]

Table 1 also shows the rate of change of the room temperature specific resistance and the pass / fail judgment of Examples 1 to 12 and Comparative Examples 1 to 6 from the beginning to the end of five measurements. In this case, the pass / fail judgment is that the room temperature resistivity at the initial stage and after the application of the thermal history is 0.020 Ω · cm or less, and the change rate of the room temperature resistivity from the initial stage to the end of five measurements is 150%. % Were accepted as "pass", and the others were rejected as "x".

From Table 1, it can be seen that in Examples 1 to 12, the initial room temperature resistivity was low, and the low room temperature resistivity was maintained even after the heat history was applied. On the other hand, in Comparative Examples 1, 4, 4 'and 5, the initial room temperature resistivity is high, and in Comparative Examples 2, 3, 4 ", 5 and 6, the rate of change of the room temperature resistivity is large.

The organic positive temperature coefficient thermistor composition and the organic positive temperature coefficient thermistor element according to the present invention are not limited to the above-described embodiments, but may be variously modified within the scope of the present invention. Good.

[0036]

According to the present invention, in the organic positive temperature coefficient thermistor composition, since a crystalline polymer is used as a matrix resin, rapid crystal melting near the melting point occurs. Due to the resulting rapid volume expansion,
The conductive path formed by the conductive particles is cut, and a sharp increase in specific resistance is observed. This phenomenon is preferable for the purpose of overcurrent protection. According to the present invention, in the organic positive temperature coefficient thermistor composition, as the conductive powder, for example, an antioxidant-treated aggregated metal powder, or a mixed powder of an antioxidant-treated aggregated metal powder and a high-structure type carbon black Is used, an increase in resistance due to oxidation and deformation is suppressed even after receiving a low specific resistance and thermal history, and the resistance of the organic positive temperature coefficient thermistor element at room temperature can be kept low. further,
By setting the melting point of the matrix resin at 130 ° C. to 180 ° C. in the organic positive temperature coefficient thermistor composition according to the present invention, it is possible to set a holding current value suitable as a chip type organic positive temperature coefficient thermistor element for surface mounting. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an organic positive temperature coefficient thermistor element to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Organic positive temperature coefficient thermistor element 12 Element body 14 Electrode

Claims (7)

[Claims] 1. An organic positive temperature coefficient thermistor composition comprising a matrix resin made of a crystalline polymer material and a conductive powder added thereto, wherein said conductive powder is formed by aggregating a plurality of primary particles of a metal powder. Including the secondary particles, wherein the average particle size of the secondary particles is 5 to 30 times the average particle size of the primary particles,
Organic positive temperature coefficient thermistor composition. 2. The organic positive temperature coefficient thermistor composition according to claim 1, wherein the average particle size of the primary particles of the metal powder is 0.5 to 10 μm. 3. The method according to claim 1, wherein a total of the matrix resin and the conductive powder is 100% by volume, and a content of the conductive powder is 25 to 60% by volume. 3. The organic positive temperature coefficient thermistor composition according to item 1. 4. The method according to claim 1, wherein the conductive powder is a mixed powder of a metal powder and carbon black.
The organic positive temperature coefficient thermistor composition according to claim 3. 5. The organic positive temperature coefficient thermistor composition according to claim 4, wherein the content of said carbon black is 15% by volume or less, with the total of said conductive powder being 100% by volume. 6. The melting point of the matrix resin is 130 to
The organic positive temperature coefficient thermistor composition according to claim 1, wherein the temperature is 180 ° C. 7. 7. An organic positive temperature coefficient thermistor element comprising an element formed of the organic positive temperature coefficient thermistor composition according to claim 1 and an electrode formed on a surface of the element body.