JP2002175903A - 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 can suppress resistance value fluctuations due to oxidation and deformation. SOLUTION: This organic positive temperature coefficient thermistor element 10 contains a plat-like elemental body 12. The body 12 is formed of a material prepared, by mixing conductive powder composed of nickel powder treated for oxidation prevention with a titanate-based coupling agent, in a matrix composed of a mixed resin of a high-density polyethylene resin and polyvinylidene fluoride. A film of a thermosetting resin 16, such as epoxy resin, etc., is formed not only on the side faces of the elemental body 12, but also on the end sections of electrodes 14 and 14 formed on both main surfaces of the body 12.

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 element, and more particularly to a chip type organic positive temperature coefficient thermistor element for protecting an electronic circuit from overcurrent.

[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.

Therefore, Japanese Patent Application Laid-Open Nos. 8-88106 and 10-303003 disclose an organic positive temperature coefficient thermistor element using a metal powder as a conductive powder.

[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, and therefore causes an increase in room temperature specific resistance depending on the mixing amount.

Therefore, a main object of the present invention is 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.

[0009]

An organic positive temperature coefficient thermistor element according to the present invention comprises: a body made of a matrix resin in which conductive powder is dispersed; An organic positive temperature coefficient thermistor element, wherein a metal powder is used as a conductive powder, and a thermosetting resin is formed on at least a part of a surface other than a surface provided with an electrode.

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, the metal powder is used as the conductive powder, and in the obtained organic positive temperature coefficient thermistor element, at least a part of the surface other than the surface provided with the electrodes for preventing deformation during melting is thermosetting. It has been found that by forming a resin, low specific resistance and suppression of resistance change due to oxidation and deformation are achieved.

In order to achieve the above-mentioned object, first, a metal powder having been subjected to an antioxidant treatment was selected as a conductive powder. 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 metal plating treatment, carbon coating, coupling treatment with an organic substance, and the like, and for the purpose of improving wettability with a matrix resin and reducing cost, coupling treatment with an organic substance is desirable. , After careful study,
It has been found that treatment with a titanate coupling agent is optimal. The purpose of the present invention can be achieved even if the metal powder used is not subjected to an antioxidant treatment.

Next, a thermosetting resin formed in the organic positive temperature coefficient thermistor element was examined. JP-A-10-28
JP-A-4302, JP-A-10-284304, JP-A-11-111506 and JP-A-11-23
JP 8601 employs a method of covering the entire element with a thermosetting resin. However, a problem with this method is "reduction in the number of trip digits of the resistor". The resistance trip of the organic positive temperature coefficient thermistor element is caused by volume expansion due to melting of the matrix resin. By coating the entire element with a thermosetting resin, volume expansion during melting of the matrix resin is inhibited, and trips are reduced. As a result, there is a possibility that sufficient overcurrent protection cannot be performed. Another problem is “reduction of the holding current value”. Since the entire element is covered with the thermosetting resin, the heat radiation effect of the element is reduced, and even if a small amount of current flows, the element temperature rises and trips. This means
This leads to a decrease in the holding current value (maximum current value that can be passed to the element without tripping), and the USB and IEEE
Considering the increasing demand for large current type devices in the interface market such as E1394, the disadvantage is large. Then, as a result of examining a coating method using a thermosetting resin, it was found that an effect can be obtained by forming the thermosetting resin on at least a part of the surface other than the surface provided with the electrodes. This makes it possible to impart an effect of improving shape retention (preventing deformation after melting) without completely suppressing expansion of the element at the time of melting and without sacrificing heat dissipation. At this time, for example, in the organic positive temperature coefficient thermistor element 10 shown in FIG. 1, not only the surface (side surface) of the plate-shaped body 12 but also both main surfaces of the body 12 as shown by the hatched portion in FIG. It is desirable that the thermosetting resin 16 is also formed on the ends of the formed electrodes 14 and 14.
This makes it possible to simultaneously suppress separation between the electrodes 14 and the element body 12 that occurs during melting and solidification.
As described above, the thermosetting resin is preferably formed so as to partially cover both of the pair of electrodes. By doing so, the adhesion between the element body and the electrode can be further improved. The thermosetting resin used includes epoxy resin, silicone resin, urethane resin, phenol resin,
Polyamide resin, polyimide resin and the like,
Epoxy resin is suitable in consideration of cost and handling.

With the above arrangement, for example, nickel powder surface-treated with a titanate-based coupling agent is used as the conductive powder, and at least a portion of the surface other than the surface provided with the electrodes of the element is made of epoxy, for example. When a thermosetting resin such as a resin is formed, the room temperature specific resistance is low, the increase in room temperature specific resistance due to oxidation is suppressed even when a heat history is applied, and the resin is melted without significantly lowering the holding current value. The shape retention of the element can be improved, and an increase in room temperature specific resistance due to thermal deformation can be 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.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An element of an organic positive temperature coefficient thermistor element 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; The conductive powder is obtained by mixing nickel powder which has been subjected to a surface treatment with a titanate coupling agent as the conductive powder. 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 a sudden volume expansion occurs due to crystal melting, the conductive path between the conductive particles is cut, and a trip in which the specific resistance increases sharply is observed). 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.

It is preferable that the total amount of the matrix resin and the conductive powder is 100% by volume, and the conductive powder is set in the range of 25 to 60% by volume. By setting the mixing amount of the conductive powder in the above range, the non-resistance at room temperature of the organic positive temperature coefficient thermistor composition can be sufficiently reduced, the mechanical strength is high, and the adhesion to the electrode is high. It can be.

[0018]

EXAMPLES (Examples 1 to 3) In Example 1, a high-density polyethylene (density: 0.968 g / cm ³ ) was used as a matrix resin component of an organic positive temperature coefficient thermistor composition serving as an element of an organic positive temperature coefficient thermistor element. It was used. As the conductive powder, a nickel powder (average primary particle diameter: 2 μm, density: 8.8 g / cm ³ ) surface-treated with a titanate-based coupling agent was used as an antioxidant metal powder. The compounding ratio was 100 vol% for the whole organic positive temperature coefficient thermistor composition, 50 vol% for high density polyethylene, and 50 vol% for conductive powder. In Example 2, the matrix resin component was polyvinylidene fluoride (density: 1.77 g)
/ Cm ³ ), except that it was the same as Example 1. In Example 3, the matrix resin component was a mixed resin of high-density polyethylene and polyvinylidene fluoride (weight ratio: 5
0/50) was the same as in Example 1. After blending, in Example 1, kneading was performed at 150 ° C. for 10 minutes using a two-roll kneader (manufactured by Nissin Chemical Co., Ltd.).
In Nos. 3 and 3, kneading was performed at 190 ° C. for 15 minutes. Further, in Examples 1 and 3, 1% by weight of dicumyl peroxide was added to high-density polyethylene for the purpose of chemical crosslinking, and the mixture was kneaded again for 5 minutes. After kneading, thickness is about 0.7m
The sheet was taken out as a sheet of m, and a copper foil (thickness: 18 μm) having one side roughened was set on both sides of the sheet such that the rough side was on the sheet side, and was pressed at 180 ° C. for 10 minutes in Example 1. In Examples 2 and 3, pressing was performed at 220 ° C. for 10 minutes. In this case, the thickness of the spacer is 0.5 mm
And Then, it cooled to room temperature and obtained the sample with 0.5-mm-thick electrode. The obtained sample is 5
After being cut to the size of mm square, a thermosetting epoxy resin (main component: bisphenol A type epoxy, curing agent: microcapsule type imidazole) is used as the thermosetting resin 16.
Was applied to two surfaces of the element body 12 other than the surfaces of the electrodes 14 and 14 as shown in FIG. 3, and the epoxy resin was cured by heating in an oven at 120 ° C. for 30 minutes. 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 temperature profile of the measurement was 30 to 150 ° C. for Example 1, 30 to 190 ° C. for Examples 2 and 3 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.

Example 4 In Example 4, the above-mentioned thermosetting epoxy resin was used as the thermosetting resin 16 on one surface of the element body 12 other than the surfaces of the electrodes 14, 14, as shown in FIG. It was the same as Example 1 except that it was applied.

(Embodiment 5) In Embodiment 5, the above-mentioned thermosetting epoxy resin is used as the thermosetting resin 16 on the three surfaces of the element body 12 other than the surfaces of the electrodes 14 and 14, as shown in FIG. It was the same as Example 1 except that it was applied.

Example 6 In Example 6, the above-mentioned thermosetting epoxy resin was used as the thermosetting resin 16 on the four surfaces of the element body 12 other than the surfaces of the electrodes 14 and 14, as shown in FIG. It was the same as Example 1 except that it was applied.

For comparison, the following two comparative examples 1
And 2 samples were made. Sample preparation and measurement
According to the methods of Examples 1 to 6.

Comparative Example 1 Comparative Example 1 was the same as Example 1 except that the above-mentioned thermosetting epoxy resin was not applied as the thermosetting resin 16.

(Comparative Example 2) In Comparative Example 2, the above-mentioned thermosetting epoxy resin was used as the thermosetting resin 16, and as shown in FIG. 7, the entire device (excluding the four-terminal contact portion of the resistance measuring device) was used.
The procedure was the same as in Example 1 except that the composition was applied to

Table 1 shows the results of the measurement of the initial room temperature resistivity and the room temperature resistivity and the number of trip digits of the resistance after five measurements of Examples 1 to 6 and Comparative Examples 1 and 2.

[0027]

[Table 1]

Table 1 shows Examples 1 to 6 and Comparative Example 1.
Also, the rate of change of the room temperature resistivity and the pass / fail judgment from the initial stage of Nos. 2 and 5 to the end of the measurement five times are shown. In this case, the pass / fail judgment is based on the fact that the rate of change of the room temperature resistivity from the initial stage to the end of five measurements is + 200% or less and the number of trip digits (condition: 30 ° C.-1)
50 ° C or 30 ° C-190 ° C) with 5 digits or more as “Pass” and “X” with other things as “Fail”
Indicated by

From Table 1, it can be seen that, in Examples 1 to 6, the rate of change of the room temperature resistivity is small even after the application of the thermal history, indicating high stability against the thermal history. In Examples 1 to 6,
It can also be seen that it shows a trip of sufficient resistance. On the other hand, in Comparative Example 1, since the element deformation preventing treatment by applying the thermosetting resin was not performed, the rate of change in the room temperature resistivity after the application of the thermal history was large. Further, in Comparative Example 2, since the entire element was solidified with a thermosetting resin, and the volume expansion of the matrix resin upon melting was suppressed, the number of trip digits of the resistance was small.

FIG. 8 is a perspective view showing another example of the organic positive temperature coefficient thermistor element according to the present invention. In the organic positive temperature coefficient thermistor element 10 shown in FIG. 8, the element body 12 is formed in a quadrangular prism chip type as compared with the organic positive temperature coefficient thermistor element 10 shown in FIG. Electrodes 14 and 14 are formed on both end surfaces of the element body 12, respectively. Further, the element 12
Thermosetting resins 16, 16 are formed not only on the two side surfaces, but also on the ends of the electrodes 14, 14, respectively. The organic positive temperature coefficient thermistor element 10 shown in FIG. 8 also achieves the effects of the present invention, similarly to the organic positive temperature coefficient thermistor elements described above.

The organic positive temperature coefficient thermistor element and the method of manufacturing the same 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.

[0032]

According to the present invention, in the organic positive temperature coefficient thermistor element, the metal powder is used as the conductive powder, and the surface other than the surface provided with the electrodes for preventing deformation during melting. Since the thermosetting resin is formed at least partially, low specific resistance and suppression of resistance change due to oxidation and deformation can be realized. Further, according to the present invention, in the organic positive temperature coefficient thermistor element, since the thermosetting resin is formed on at least a part of the surface other than the surface provided with the electrodes, the volume expansion at the time of melting of the matrix resin is achieved. Is not completely suppressed, so that it is possible to obtain a sufficient resistance trip, and it is possible to prevent a decrease in the holding current value because the heat radiation property does not decrease.

[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.

FIG. 2 is an illustrative view showing one example of an organic positive temperature coefficient thermistor element according to the present invention;

FIG. 3 is a perspective view showing an organic positive temperature coefficient thermistor element of Examples 1 to 3.

FIG. 4 is a perspective view showing an organic positive temperature coefficient thermistor element of Example 4.

FIG. 5 is a perspective view showing an organic positive temperature coefficient thermistor element of Example 5.

FIG. 6 is a perspective view showing an organic positive temperature coefficient thermistor element of Example 6.

FIG. 7 is a perspective view showing an organic positive temperature coefficient thermistor element of Comparative Example 2.

FIG. 8 is a perspective view showing another example of the organic positive temperature coefficient thermistor element according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Organic positive temperature coefficient thermistor element 12 Element body 14 Electrode 16 Thermosetting resin

Claims (3)

[Claims] 1. An organic positive temperature coefficient thermistor element comprising a matrix formed by dispersing a conductive powder in a matrix resin and comprising a pair of electrodes, wherein a metal powder is used as said conductive powder, and said electrode is provided. Characterized in that a thermosetting resin is formed on at least a part of the surface other than the surface that is formed,
Organic positive temperature coefficient thermistor element. 2. The organic positive temperature coefficient thermistor element according to claim 1, wherein said metal powder is nickel powder. 3. The organic positive temperature coefficient thermistor element according to claim 1, wherein said thermosetting resin is an epoxy resin.