JP2002025406A - Temperature fuse and wire material for temperature fuse element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature fuse which can secure meltdown temperature from 175 deg.C or higher to 185 deg.C or lower, and a wire material for a temperature fuse element suitable for manufacturing of this temperature fuse. SOLUTION: The temperature fuse is a temperature fuse, having a fuse element melting at a given temperature, and the fuse element is formed from a fusible alloy, consisting of bismuth of 1 weight% or more and 10 weight% or less, zinc of 3 weight% or more and 13 weight% or less and the rest of tin. Furthermore, a wire material for the temperature fuse element is also formed from a fusible alloy of similar composition. That it to say, by adjusting the bismuth content and indium content in the fusible alloy, a temperature fuse and the wire material are provided with superior fusion temperature characteristics and with moderate strength and ductility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal fuse and a wire for a thermal fuse element,
The present invention relates to a thermal fuse having a thermal fuse element formed of a lead-free fusible alloy that melts at a relatively low temperature of 85 ° C. or less, and a wire for the thermal fuse element.

[0002]

2. Description of the Related Art There are two types of fuses: an electric fuse that is blown when an overcurrent flows through an electric circuit to protect the circuit, and a thermal fuse that is blown and protected when the temperature around the electric circuit rises. Electric fuses are used in TVs, washing machines, etc.
Thermal fuses are used in mobile phones, notebook computers, etc.
Each is incorporated and has a role of protecting these electrical products. Above all, the thermal fuse must be blown reliably and quickly at the set fusing temperature to protect the electric circuit. For this reason, the thermal fuse is required to be blown with high accuracy under various temperature conditions. The fusing temperature of a fuse depends on the melting point (liquidus temperature) of the fusible alloy constituting the fuse element in the thermal fuse, and the melting point is determined by the constituent metals of the alloy and the compounding ratio thereof, that is, the composition. Therefore, the choice of composition is extremely important.

Conventionally, as a fusible alloy for a thermal fuse having a melting point of 175 ° C. or more and 185 ° C. or less, an alloy containing lead as a component metal (hereinafter referred to as a lead alloy) has been used.

[0004]

However, when electric appliances are discarded in recent years, there is a problem that lead elutes from the thermal fuse incorporated therein into the natural environment. When humans take in the lead eluted into the environment, they become poisoned, and depending on the amount of intake, toxic symptoms such as fatigue, lack of sleep, constipation, trembling, abdominal pain, anemia, neuritis, and cerebral degeneration appear. Therefore, in order to prevent environmental pollution due to lead, it is required worldwide not to use lead as an industrial material as much as possible, and studying industrial materials to replace lead is one of the important issues in the industry. I have.

Therefore, as a result of intensive studies on the fusible alloy constituting the fuse element of the thermal fuse containing no lead and the wire rod for the fuse element, the inventors of the present invention have found that even if lead is not contained, 175 ° C. or higher. It has been found that a fusible alloy that melts at a temperature of 185 ° C. or lower can be obtained.

[0006] The thermal fuse and the wire for thermal fuse element of the present invention have been made based on the above findings, and have a temperature of 175 ° C or higher without containing lead in the fusible alloy.
An object of the present invention is to provide a thermal fuse capable of securing a fusing temperature of 5 ° C. or less. It is another object of the present invention to provide a wire for a thermal fuse element suitable for manufacturing the thermal fuse.

[0007]

A thermal fuse according to the present invention is a thermal fuse having a fuse element that blows at a predetermined temperature, wherein the fuse element includes 1% by weight to 10% by weight of bismuth and 1% by weight. % To 10% by weight of indium, 3% to 13% by weight of zinc,
It is characterized by being formed of a fusible alloy composed of the remaining tin.

[0008] Further, the wire for a thermal fuse element of the present invention comprises 1 wt% to 10 wt% of bismuth, 1 wt% to 10 wt% of indium, and 3 wt% to 1 wt%.
It is characterized by being formed of a fusible alloy comprising 3% by weight or less of zinc and the balance of tin.

The inventor of the present invention has found that lead-free and 17
A fusible alloy for a fuse that melts at a temperature of 5 ° C. or more and 185 ° C. or less was studied, and a tin-zinc binary alloy was considered with a focus on tin and zinc, which have relatively low melting points and are inexpensive. However, the eutectic point of the Sn—Zn binary alloy is 19
Since the temperature is 8.5 ° C., a fuse that melts below this temperature cannot be made from the Sn—Zn alloy. In order to obtain an alloy that melts at 175 ° C or more and 185 ° C or less, Sn-Z
It is necessary to add a third component to the n alloy to lower the melting point. Therefore, the inventor of the present invention focused on bismuth. Bismuth has a property of lowering the melting point of the alloy when contained in the alloy. The inventor of the present invention has found that the melting point of the alloy can be reduced to 185 ° C. or lower by preparing the Sn—Zn—Bi alloy by adding bismuth to the Sn—Zn alloy. However, bismuth has high hardness but poor ductility and is brittle, so this property appears in alloys with a high bismuth content. Therefore,
Further, the inventor of the present invention focused on indium. Indium has a role of lowering the melting point of the alloy similarly to bismuth, but has a property of being symmetrically rich in ductility and having low hardness in comparison with bismuth. Therefore, indium is further contained in the Sn-Zn-Bi alloy to make Sn-Zn-Bi-I
By preparing an n alloy and adjusting the bismuth and indium contents in this alloy, a lead-free fusible alloy having a melting temperature and ductility equivalent to those of a lead alloy can be obtained.

[0010] However, in order to obtain such a lead-free fusible alloy, it is necessary to overcome the following new problems that arise. First, if the indium content is too high relative to the bismuth content, the alloy becomes too soft. Further, since indium is more expensive than bismuth, zinc and tin, it is desirable to set the indium content as low as possible within the range in which the object of the present invention can be achieved. Further, as described above, the fusing temperature of the fuse is determined by the melting point of the fusible alloy. However, when the temperature around the electric circuit reaches the solid phase temperature of the fusible alloy, the fuse begins to melt, so if the difference between the liquid phase temperature and the solid phase temperature of the alloy (hereinafter referred to as ΔT) is large, the solid phase It takes time to reach the liquidus temperature after reaching the temperature. A large ΔT means that it takes a long time to blow the fuse, and if the blow takes a long time, there is a possibility that electronic components such as semiconductors may be damaged. For this reason, the fuse is required to have a quick-disconnect property to quickly melt at a desired temperature, and the ΔT of the fusible alloy is required to be within 30 ° C.

[0011] The thermal fuse of the present invention made of the above-mentioned fusible alloy can be used as a thermal fuse of a conventional lead alloy.
This is a practical thermal fuse capable of securing a fusing temperature of not less than ℃ and not more than 185 ° C and overcoming the above-mentioned problems. In addition, compared to a wire for a thermal fuse element made of an alloy having a high bismuth content, the wire for a thermal fuse element of the present invention made of the above-mentioned fusible alloy has an appropriate ductility and can be thinned. It can be used for electronic components with low heat resistance, small electronic devices, and the like.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a thermal fuse and a wire for a thermal fuse element according to the present invention will be described below with reference to the drawings for each item of a fusible alloy, a thermal fuse, and a wire for a thermal fuse element. I do.

<Fusible Alloy> First, an embodiment of a fusible alloy which is a material for forming a thermal fuse and a wire for a thermal fuse element of the present invention will be described. The fusible alloy used for the thermal fuse and the wire rod of the present invention includes bismuth of 1 wt% to 10 wt%, indium of 1 wt% to 10 wt%, and zinc of 3 wt% to 13 wt%. And the balance of tin. The reason why the fusible alloy has such a composition will be described with reference to the drawings.

First, the zinc content in the alloy will be described. FIG. 1 is a composition diagram of a Sn—Zn binary alloy. As can be seen, the alloy was 91.2% by weight Sn-8.
It has a eutectic point A with a composition of 8% by weight Zn and a temperature of 19%.
8.5 ° C. Therefore, this alloy does not melt at temperatures below 198.5 ° C. Therefore, in order to set the melting temperature of the fusible alloy to 175 ° C. to 185 ° C., it is necessary to contain another metal (Bi, In) in this alloy to lower the melting point of the alloy. However, since the Sn-Zn binary alloy has a low production cost and good mechanical properties, the content of other metals should be as low as possible. In order to lower the content of other metals, it is effective to add other component metals to the Sn-Zn alloy having a composition near the eutectic point having the lowest melting point. For these reasons, the zinc content is set to 3% by weight or more and 13% by weight or less.

Next, the bismuth content in the alloy will be described. As described above, bismuth has properties of high hardness but poor ductility and brittleness. Therefore, if the bismuth content in the alloy is too high, the properties of bismuth will appear in the alloy. This is because, in cooling the combined liquid in which bismuth, indium, zinc, and tin are melt-mixed in the alloy manufacturing process, if the bismuth content is high, bismuth is crystallized as a primary crystal from the melt. Therefore,
In order not to crystallize bismuth as a primary crystal, the lower the bismuth content, the better. On the other hand, if it is too low, the purpose of containing bismuth, that is, lowering the melting point of the alloy, cannot be achieved. For these reasons, the bismuth content is set to 1% by weight or more and 10% by weight or less.

Next, the indium content will be described. Indium is an element contained in the alloy (Bi, In, Z
n, Sn) is the most expensive. On the other hand, if the indium content is too high, the properties of indium such as softness and high ductility may appear in the alloy. For these reasons, the lower the indium content, the better. On the other hand, if the indium content is too low, the indium-containing purpose of neutralizing the embrittlement of the alloy by bismuth may not be achieved. For these reasons, the indium content is set to 1% by weight or more and 10% by weight or less.

For the above reasons, the fusible alloy forming the wire for the thermal fuse and the fuse element of the present invention contains bismuth at 1 wt% to 10 wt%, indium at 1 wt% to 10 wt%, and zinc at 1 wt% to 10 wt%. 3% by weight or more and 13% by weight
Hereinafter, the remainder has a composition of tin.

By changing the mixing ratio of bismuth, tin, zinc and indium within this composition range, the melting point of the alloy can be freely controlled.
Thermal fuses and wires corresponding to any target temperature between ℃ and 185 ℃ can be provided.

Incidentally, it is conceivable that unavoidable impurities from the raw metal and the like are mixed into the fusible alloy. The fusible alloy constituting the fuse and the wire according to the present invention does not specifically exclude mixing of impurities, and the alloy having the above composition also includes a case where unavoidable impurities are mixed in the alloy.

<Thermal Fuse> An embodiment of the thermal fuse of the present invention will be described with reference to the drawings. FIG.
FIG. 1 shows a sectional view of a cylindrical thermal fuse as an example of the thermal fuse of the present invention. The thermal fuse 1 shown in FIG. 2 includes a fuse element 10 that blows at a constant temperature and a fuse element 10.
And a flux 1 filled around the fuse element 10 in a columnar shape and covering the fused surface after the fuse element is blown to prevent conduction again.
1 and a cylindrical ceramic case 12 for housing a part of the fuse element 10, the flux 11 and the lead wire 2.

In an electronic device, the thermal fuse 1 is provided between a power supply such as a battery and an electric circuit. When the temperature around the thermal fuse 1 rises for some reason and reaches the set temperature of the thermal fuse 1, the fuse element 10
Is melted, the flux 11 covers the melted section, and the conduction between the power supply and the circuit is cut off. In this way, the thermal fuse 1 can protect a power supply, an electric circuit, and the like.

The method of manufacturing the thermal fuse 1 of the present embodiment can be manufactured by various methods conventionally used for manufacturing a fuse. For example, a wire to be described later is cut to form a fuse element 10, and the fuse element 10 and the lead wire 2 are joined to form a fuse element 10.
And a method in which a ceramic case 12 for protecting the fuse element 10 and the like from the outside is provided by filling a flux 11 around the surroundings.

The thermal fuse according to the present invention may be various types of thermal fuses conventionally used, such as a fuse with a claw, a tubular fuse and a plug-type fuse, in addition to the cylindrical fuse shown in FIG. .

The thermal fuse of the present invention has a temperature of 175 ° C.
Fusing can be performed quickly at any temperature in the range of 185 ° C. or less. Therefore, it can be used in a wide variety of applications such as protection of electronic devices having low heat resistance.

<Temperature Fuse Element Wire> Next, an embodiment of the temperature fuse element wire of the present invention used for the above-described temperature fuse will be described. The wire of the present invention can be manufactured by various methods conventionally used for manufacturing wires. The drawing method will be described as an example.

The drawing method includes a compounding step of mixing the raw material of the fusible alloy constituting the wire into a melting furnace, a step of melting the compounded raw material, preparing an alloy and pouring the alloy into a mold to form a billet, and forming a rough wire from the billet. It consists of an extrusion step for producing and a drawing step for forming a fine wire from a coarse wire.

First, in a raw material blending step, tin, zinc, bismuth, and indium raw materials, which are raw materials for a wire, are weighed and blended so as to have a desired composition, and then charged into a melting furnace. next,
In the billet production step, the raw materials are melted at a temperature of 300 to 350 ° C. to prepare an Sn—Zn—Bi—In alloy, and the prepared alloy in a molten state is poured into a mold to produce a columnar billet. Next, in the extrusion step, the billet is taken out of the mold, set in an extruder, and extruded to form a coarse wire. Finally, in the wire drawing step, the coarse wire is applied to a drawing forming machine, and a thin alloy, that is, a wire is formed by drawing a linear alloy from a die hole provided in the forming machine. The diameter of the dice is gradually reduced so that a predetermined diameter can be obtained while passing through a large number of dice.
The alloy is tensioned by the die and becomes the wire of the present embodiment.

In the method of forming a wire by tension as in the above-mentioned drawing method, if the bismuth content in the wire is high, the wire is cut during the drawing. On the other hand, the wire for a thermal fuse element of the present embodiment has a low bismuth content and has an appropriate ductility because it contains indium, and the wire can be formed by tension as in the above-described drawing method. It is possible. Wires formed by tension are compared to wires manufactured by other forming methods such as extrusion.
It is possible to make it thinner. Such a thin wire can be wound around a bobbin or the like, for example, and can be stored compactly, so that it has excellent storage properties. The wire may have various cross-sectional shapes conventionally used, such as an elliptical shape and a polygonal shape, in addition to a true circular shape in a cross section in a direction perpendicular to the axial direction.

The wire of the present invention, which can be made thinner than wires manufactured by other methods, can meet the following requirements when used. A thermal fuse used at a relatively low temperature is required to have a quick disconnection property with respect to a set temperature in order to protect electronic components such as a semiconductor having low heat resistance. In order to ensure quick disconnection, a fuse element made of a wire is often installed in the fuse with a constant tension applied. Since the fuse element installed in this state blows faster as the cross-sectional area is smaller,
Wires used for low-temperature thermal fuses are required to have a small cross-sectional area. Since the wire of the present invention is thinner than a wire manufactured by another method, that is, has a smaller cross-sectional area, it can sufficiently meet this demand.

Furthermore, the wire of the present invention has a fusing temperature of 1
Fuse having a wire material that is 75 ° C. or more and 185 ° C. or less but melts in this temperature range has been increasingly demanded for electronic devices such as mobile phones, video cameras, and notebook computers. In recent years, these electronic devices have been continually being miniaturized because of the convenience of use.To reduce the size of the devices, it is required that the thermal fuses also be small, and that the cross-sectional area of the thermal fuse element wire be small. Is required. From the above needs, the cross-sectional area of the wire is required to be 0.3 mm ² or less. Since the wire of the present invention is thinner than a wire manufactured by another method, it can sufficiently meet this demand.

[0031]

EXAMPLES Based on the above embodiment, an ingot having a predetermined composition was produced, and a sample was taken from this ingot for an experiment. This will be described as an example.

EXAMPLES The samples of the examples were 6% by weight bismuth, 6% by weight indium, 8% by weight zinc, 80% by weight.
It is composed of a fusible alloy having a composition of weight percent tin. This sample was manufactured by the following method. First, bismuth with a purity of 99.99%, indium with a purity of 99.99%, zinc with a purity of 99.99%, and purity of 99.99%
% Tin was weighed and placed in a melting furnace. Next, the raw material was melted and stirred at a temperature of 300 ° C. in a melting furnace to prepare an alloy, and the prepared alloy was poured into a mold, allowed to cool, and demolded. A sample was collected from the ingot thus manufactured, and this was used as an example. When the prepared alloy was poured into a mold, the composition of the alloy was confirmed by chemical analysis.

<Experiment method> In the experiment, the sample of the example was gradually heated in a heating furnace, and the sample was melted using a thermal analyzer (hereinafter referred to as TA) and a differential scanning calorimeter (hereinafter referred to as DSC). This was performed by examining the temperature characteristics. The heating pattern of the heating furnace was such that the temperature before the experiment was 50 ° C. and the heating rate was 10 minutes per minute.
° C and the final holding temperature was 200 ° C.

<Experimental Results> FIG. 3 shows the results of measurement by TA when the temperature of the sample of the embodiment was increased according to this heating pattern. FIG. 3 shows that the temperature curve has an inflection point when the temperature is about 183 ° C. FIG. 4 shows the measurement results by DSC. From FIG. 4, it can be seen that there is a peak start point in the differential thermal curve when the temperature is about 162 ° C. From these facts, the fusible alloy constituting the sample of the example is about 16
It can be seen that the phase changes from a single phase of the solid phase alone to a two-phase coexistence state of the solid phase and the liquid phase at 2 ° C., and changes from a coexistence state of the two phases to a single phase state of the liquid phase alone at about 183 ° C. That is, in the example, about 162 ° C. is the solidus temperature, about 183 ° C. is the liquidus temperature, and ΔT is about 21 ° C. From the above experiments, it was found that the liquid phase temperature was within the temperature range of 175 ° C. or more and 185 ° C. or less, and ΔT was within 30 ° C. in the examples.

[0035]

The thermal fuse of the present invention is a thermal fuse having a fuse element that blows at a predetermined temperature,
The fuse element is a fusible alloy comprising 1% by weight to 10% by weight of bismuth, 1% by weight to 10% by weight of indium, 3% by weight to 13% by weight of zinc, and the balance of tin. Characterized by the following.

Further, the wire for a thermal fuse element of the present invention comprises:
It is formed of a fusible alloy comprising 1% by weight to 10% by weight of bismuth, 1% by weight to 10% by weight of indium, 3% by weight to 13% by weight of zinc, and the balance of tin. It is characterized by the following.

Thus, Sn-Zn-
By selecting the Bi-In alloy and adjusting the bismuth content and the indium content in the alloy, a thermal fuse having the same fusing temperature characteristics and ductility as a thermal fuse made of a lead alloy can be obtained.

[Brief description of the drawings]

FIG. 1 is a phase diagram of a Sn—Zn binary alloy.

FIG. 2 is a sectional view of a thermal fuse.

FIG. 3 is a graph showing a measurement result by TA in Examples.

FIG. 4 is a graph showing a measurement result by DSC of an example.

[Explanation of symbols]

 A: Sn-Zn binary alloy eutectic point 1: Thermal fuse 10: Fuse element 11: Flux 12: Ceramic case 2: Lead wire

Claims (2)

[Claims] 1. A thermal fuse having a fuse element that is blown at a predetermined temperature, wherein the fuse element includes 1% by weight to 10% by weight of bismuth and 1% by weight to 1% by weight.
0% by weight or less of indium and 3% by weight or more and 13% by weight
A thermal fuse characterized by being formed of a fusible alloy comprising the following zinc and the balance of tin. 2. Bismuth of 1% by weight or more and 10% by weight or less, indium of 1% by weight or more and 10% by weight, 3% by weight
A wire for a thermal fuse element formed of a fusible alloy comprising at least 13% by weight of zinc and the balance of tin.