JP2003077705A - Polymer ptc thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer PTC thermistor which can be electrically insulated with reliability even when the polymer PTC thermistor is destroyed. SOLUTION: This polymer PTC thermistor has a conductive polymer 1 having a PTC characteristic, electrode foils 2a, 2b bonded to the conductive polymer 1, and a pair of conductive leads 3a, 3b. The conductive leads 3a, 3b are bonded to the electrode foils so that, when the upper conductive lead 3a is projected on a surface of the electrode foil 2b to which the lower conductive lead 3b is bonded, the lower conductive lead 3b does not overlap with the other projected conductive lead. A reduced cross-sectional area portion 7, which is electrically insulated even when destroyed due to application of a voltage exceeding a maximum rated voltage, is provided between these conductive leads 3a, 3b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive resistance temperature characteristic, that is, PTC (Positive Temperature Coefficient).
The present invention relates to a polymer PTC thermistor having characteristics, and a secondary battery such as a lithium ion secondary battery using the same, and an electric device such as a microwave oven.

[0002]

2. Description of the Related Art Conventionally, a polymer PTC switch (polymer PTC thermistor) having a PTC characteristic (positive resistance temperature characteristic) has been used as an overcurrent protection element in order to prevent overcharge of a secondary battery. There is. Examples of the secondary battery include a lithium-ion secondary battery, a nickel hydrogen secondary battery, and a nicad secondary battery. Hereinafter, a lithium ion secondary battery will be described as an example.

An example of the polymer PTC switch will be described below with reference to FIG. FIG. 9 is a schematic view of a conventional polymer PTC switch, (a) is a side view and (b) is a plan view. Reference numeral 101 is a conductive polymer, 102a and 102b are electrode foils joined to the conductive polymer 101, 103
Reference characters a and b are conductive leads joined to the electrode foil.

The conductive polymer 101 has a rectangular parallelepiped shape, and is obtained by, for example, kneading polyethylene and carbon black and then cross-linking with radiation. The conductive polymer 101 has a large number of conductive paths through which an electric current flows due to the mixed carbon black, and has good conductivity at room temperature. However, when an overcurrent flows, the conductive polymer 101 causes self-heating due to Joule heat and expands, and the distance between the mixed carbon blacks increases, so that the conductive path between the carbon blacks is cut, and as a result, The resistance value is rapidly increasing. Such a state in which the resistance value of the conductive polymer rapidly increases due to overcurrent or overheating is hereinafter referred to as “trip state”.

The electrode foils 102a and 102b are nickel-plated copper foils having a thickness of about 35 μm, and are bonded to almost the entire opposite surfaces (upper and lower surfaces in the figure) of the conductive polymer 101. Conductive lead 103
Each of a and b is made of Ni and has a thickness of about 125 μm, and is joined to the upper and lower surfaces of the electrode foils 102a and 102b by soldering. As shown in FIG. 9B, the upper conductive lead 103 a is connected to the upper electrode foil 1
02a extends from one end 102c to the other end 102d along the longitudinal direction. In this way, the pair of conductive leads 103a and 103b are arranged at the bottom (one) in the figure.
The lower electrode foil 1 to which the conductive lead 103b is joined
When the upper (other) conductive lead 103a is projected on the surface of 02b, the upper conductive lead 103a and the lower conductive lead 103b are overlapped with each other.
It is joined to a and b.

The polymer PTC switch thus constructed operates as follows. Hereinafter, a case where the polymer PTC switch having the above structure is attached as an overcurrent protection element for a lithium ion secondary battery will be described. Since the conductive polymer 101 has a low resistance at room temperature, overcurrent does not flow during normal charging, and the temperature does not rise. However, if an overcurrent flows for some reason, the conductive leads 103a, 103b, the electrode foil 10
Overcurrent flows into the conductive polymer 101 via 2a and 2b. Then, the conductive polymer 101 is generated by Joule heat.
Generates heat and expands thermally. When the conductive polymer 101 thermally expands, the distance between the carbon blacks that functioned as a conductive path for passing an electric current increases, and the conductive path is cut, so that the resistance value rapidly increases. When the resistance value increases, the current naturally stops flowing.

This is illustrated in FIG. In the figure, the horizontal axis is the temperature (° C.) and the vertical axis is the logarithmic resistance value (Ω), which is a semi-logarithmic graph. As can be seen from the figure, the resistance value gradually increases from room temperature to about 100 ° C., and the low resistance of 0.1Ω or less is maintained. When the temperature further rises, the resistance value sharply rises up to about 10 ⁴ to 10 ⁵ times the resistance value at room temperature around 130 ° C., and a trip state occurs. And further 150 ℃
When the temperature rises above, the resistance value gradually rises.
As described above, the resistance-temperature characteristic draws a substantially S-shaped curve. With such resistance-temperature characteristics, when an overcurrent flows through the conductive polymer 101 and the temperature rises, the resistance sharply rises at a predetermined operating temperature (see arrow A in the figure).

When the power applied to the polymer PTC switch is cut off, the conductive polymer 10 is heated by Joule heat.
The thermal expansion of No. 1 stops, the conductive polymer 101 is cooled by the ambient temperature, and since the conductive polymer 101 is pre-crosslinked, it thermally contracts and returns to the initial state. Along with this, carbon blacks approach each other again,
By re-forming the conductive path, the resistance value returns to the initial state (see arrow B in the figure).

As described above, the polymer PTC switch utilizes the PTC characteristics of the conductive polymer 101, so that the current can be interrupted when an overcurrent occurs and the current can be re-applied when the power source is removed. It has a switch function of returning to the normal state. As a result, the lithium ion secondary battery equipped with the polymer PTC switch is protected from overcharging and the like.

[0010]

As described above, if the extent of the overcurrent is within the range expected at the time of designing, the temperature at which the resistance rises rapidly in the resistance-temperature curve shown in FIG. Range (about 130-140 ℃)
In the above, since the polymer PTC switch repeatedly generates heat and heat with the surroundings, it is possible to maintain a high resistance value. However, it was unexpectedly used, for example, to directly connect a 3.6V-compatible lithium-ion secondary battery to a household power supply having a voltage (100V) exceeding the maximum rated voltage without passing through a transformer. In this case, a large current larger than the designed current is flown in the circuit, and the heat generated thereby increases the resistance value, which in turn applies an overvoltage to the PTC switch. In this case, the conductive polymer 10
The heat generated by No. 1 exceeds the heat released to the surroundings, the PTC switch thermally runs away, and the temperature of the conductive polymer 101 is, for example, 30.
The temperature rises to 0 ° C. or higher (see arrow C in FIG. 10), and eventually the destruction occurs. Even if the polymer PTC switch is destroyed, there is no particular problem as long as it is electrically insulated so as not to recover after the destruction. However, even after the breakage, the conductive leads 103a and 103b may come into direct contact with each other to cause a short circuit. With this, the function of the polymer PTC switch as the overcurrent protection element cannot be fulfilled.

Still another problem is as follows. The PTC characteristic can be used not only as an overcurrent protection element but also as an overheat protection element. This is because the resistance value increases as the temperature rises. For example, a control box of a microwave oven is provided with a bimetal for shutting off an electric circuit when the box is exposed to a high temperature. However, for applications such as microwave ovens that handle high currents of 15 A during normal use, the structure is inevitably large and complicated even though it is a bimetal. On the other hand, there is no thermal fuse suitable for such a high current. Therefore, a compact and inexpensive device having an overheat protection function has been desired.

The present invention has been made in view of the above circumstances and has the following objects. An object of the present invention is to provide a polymer PTC thermistor that can be reliably electrically insulated even if the polymer PTC thermistor is destroyed. Also,
It is an object of the present invention to provide a secondary battery that can be reliably electrically insulated even if it is unexpectedly charged by a high voltage higher than a design value and is broken or destroyed. Another object of the present invention is to provide a polymer PTC thermistor having an overheat protection function, which is compact and can be used at low cost for electric devices such as a microwave oven that normally use a high current.

[0013]

The present invention adopts the following means in order to solve the above problems. The present invention is PT
In a polymer PTC thermistor having a conductive polymer having C characteristics, an electrode foil bonded to the conductive polymer, and a pair of conductive leads bonded to the electrode foil, each conductive lead is When the other conductive lead is projected on the surface of the electrode foil to which the conductive lead of is joined, the electrode foil in a state where the one conductive lead does not overlap with the projected other conductive lead. It is characterized in that an insulating portion is provided between the conductive leads and is electrically insulated even if a voltage exceeding the maximum rated voltage is applied and destroyed.

When another conductive lead is projected onto the surface of the electrode foil to which the one conductive lead is joined, the one conductive lead does not overlap the projected other conductive lead. The pair of conductive leads are arranged, that is, the pair of conductive leads are arranged in a three-dimensionally offset manner. Therefore, even if the electrode foil or the conductive polymer existing between these conductive leads is in a trip state due to overcurrent or overheating, and even if an overvoltage is applied and destroyed or burned out, these conductive leads directly overlap each other, There is no short circuit. If the electrode foil or the conductive polymer remained between the conductive leads after a voltage exceeding the maximum rated voltage was applied and the PTC switch was destroyed, it was connected without being completely electrically insulated. As a result, the external device connected to the PTC switch is adversely affected. Therefore, in the present invention, an insulating portion is provided between each conductive lead, which is electrically insulated even if a voltage exceeding the maximum rated voltage is applied and destroyed. As a result, the PTC switch is not left electrically connected even after it is destroyed. The maximum rated voltage in the present invention means the maximum value of the voltage applied to both ends of the conductive polymer when the polymer PTC thermistor is in the trip state. If a voltage exceeding this value is applied, the PTC switch may be destroyed.

Further, the invention is characterized in that the insulating portion is a part of the electrode foil formed so as to be broken prior to other portions.

The conventional electrode foil is formed so that the current density does not differ in any part, that is, it has a constant cross-sectional area. Therefore, when a voltage exceeding the maximum rated voltage is applied, it is not possible to specify from which part the electrode foil will be destroyed, and it is impossible to control the insulating location. On the other hand, in the present invention, a part of the electrode foil is burnt out before the other part, so that the current is surely cut off in this part.

Further, the insulating portion of the present invention is characterized in that it is a reduced cross-sectional area portion in which the cross-sectional area of the electrode foil is reduced.

Since it is decided to provide the cross-sectional area decreasing portion in which the cross-sectional area of the electrode foil is reduced, when a large current flows through the PTC thermistor, the cross-sectional area decreasing portion has the largest current density in the electrode foil. Becomes As a result, the cross-sectional area reduced portion is destroyed first. In addition,
The cross-sectional area reduced portion may be formed so as to increase the current density in the electrode foil, and can be achieved, for example, by reducing the width and thickness of the electrode foil.

The cross-sectional area reduced portion of the present invention is characterized by being formed by partially removing the electrode foil.

The electrode foil is partially removed, and the cross-sectional area of the electrode foil in that portion is reduced to form a cross-sectional area reduced portion. For example, to partially remove the electrode foil so that cuts are made from both sides of the electrode foil toward the center so that the width of the electrode foil decreases (only the center of the electrode foil remains). As a result, the cross-sectional area reduced portion is formed. Further, the cross-sectional area reduced portion can be formed even if only the central portion of the electrode foil is removed. Also,
These methods can be combined appropriately. For example, when electrode foils are bonded to the upper surface and the lower surface of the conductive polymer, both sides of the electrode foil on the upper surface may be removed, and only the central portion of the electrode foil on the lower surface may be removed. Etching is suitable as a method for partially removing the electrode foil. The thickness of the electrode foil is preferably 20 μm.

The cross-sectional area reduced portion of the present invention is characterized by being formed by a thin portion.

By providing a thin portion on the electrode foil, the thickness of the electrode foil in this portion is reduced to form a cross-sectional area reduced portion. The thin portion may be provided over the entire width direction of the electrode foil, or may be partially provided without being formed over the entire width direction. The thinness is, for example, 35 μm in thickness.
If the electrode foil has a thickness of m, a thickness of about 20 μm is suitable. However, this thickness is set for an expected overcurrent. As a method for forming the thin portion, there are etching, pressing and the like, and etching is particularly preferable.

Further, the present inventor focuses on a conductive polymer as described below, in addition to the case of focusing on the above-mentioned electrode foil, as an insulating portion which is electrically insulated when a current or temperature exceeds a predetermined value. I also found a case. Therefore,
The insulating part of the present invention is characterized in that it is formed as a part of a conductive polymer formed so as to be burned off before the other part.

Since the insulating portion is formed as a part of the conductive polymer formed so as to be burnt out before the other portions, no current flows through the burned-out conductive polymer portion. Therefore, the portion to be insulated first is secured in advance, and the PTC thermistor is surely insulated.

Part of the conductive polymer of the present invention is characterized in that it is a low PTC part in which the rate of increase in resistance value with respect to temperature rise is set lower than in other parts.

Since the resistance value of the low PTC portion does not increase more than the other portions even when the temperature rises, for example, an overcurrent flows to the PTC thermistor, which causes a trip state and an overvoltage is applied. In this case, the resistance value of the low PTC portion does not increase as compared with the other portions even if the temperature rises. Therefore, a large amount of current flows into the low PTC portion, the temperature becomes higher, and finally the element is burned out.

The low PTC part of the present invention is characterized in that it is a part that is cross-linked to a lower degree than other parts.

The conductive polymer depends on the degree of crosslinking.
The rate of increase of the resistance value with respect to the temperature rise changes. Therefore, low cross-linking will result in low PTC properties.

The low PTC portion of the present invention is characterized in that it is a portion which is pressed more than other portions.

Even if the conductive polymer itself expands due to overcurrent or overheating, if the expansion is restrained by being pressurized, the distance between the conductive materials dispersed in the conductive polymer is not separated. , The resistance value does not increase. Therefore, the portion pressed in this way has a low PTC.
It becomes a part.

The low PTC part of the present invention is characterized by being made of a material different from that of the other parts.

The low PTC portion can also be formed by changing the material of the conductive polymer. For example,
It can be formed by changing the amount of the conductive material dispersed in the polymer or by adopting polymers having different melting points.

The polymer PTC thermistor of the present invention can be used as a circuit protection element due to its switching function, and is particularly suitable for a secondary battery such as a lithium ion battery.

If the polymer PTC thermistor of the present invention is used as an overcharge protection device for a secondary battery, the current can be cut off reliably even if it is connected to an unexpectedly high voltage power source.

The polymer PTC thermistor of the present invention can be used as a temperature protection element, and is particularly suitable for use in electric equipment such as a microwave oven.

The polymer PTC thermistor has a low resistance even under a high current if the operating current is set high at the time of design. In contrast, there is no suitable thermal fuse for such a high current. On the other hand, the polymer PTC thermistor also has the characteristic that the resistance rapidly increases as the temperature rises. Therefore, if the polymer PTC thermistor of the present invention is installed as a temperature protection element in a circuit such as a microwave oven through which a high current of about 15 A flows, even if an abnormally high temperature is generated in the circuit, the circuit is reliably cut off. can do.

In the present invention described above, either the electrode foil or the conductive polymer may be modified, or both may be appropriately combined.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described below with reference to the drawings. Figure 1
FIG. 3 shows a PTC switch (polymer PTC thermistor) according to the first embodiment of the present invention, (a) is a side view, (b) is a plan view, and (c) is a bottom view. This PT
The C switch is a lithium ion secondary battery (not shown).
When the lithium ion secondary battery has a rectangular parallelepiped shape, the lithium ion secondary battery is mounted along a narrow side surface thereof in a substantially straight line.

Reference numeral 1 is a conductive polymer, 2a and 2b are electrode foils bonded to the conductive polymer 1, and 3a and b are conductive leads bonded to the electrode foil.

The conductive polymer 1 has a rectangular parallelepiped shape, and is obtained by, for example, kneading polyethylene and carbon black which is a conductive material, molding the mixture, and then crosslinking by radiation. The conductive polymer 1 has a large number of conductive paths in which an electric current flows due to the mixed carbon black, and has good conductivity at room temperature (about 20 ° C.). However, when an overcurrent flows, the conductive polymer 1 causes self-heating due to Joule heat and expands, and the distance between the mixed carbon blacks increases, so that the conductive path between the carbon blacks is cut, resulting in The resistance value is rapidly increasing.

The electrode foils 2a and 2b are nickel-plated copper foils having a thickness of about 20 μm, which is thinner than the conventionally used 35 μm. These electrode foils 2a,
2b are joined so as to face each other over the entire upper surface 1a and lower surface 1b of the conductive polymer 1. Conductive polymer 1 for electrode foils 2a and 2b
A nodular surface on which a large number of small protrusions are formed is formed on the surface contacting with, whereby the electrode foils 2a and 2b are firmly bonded to the conductive polymer 1.

The upper electrode foil 2a has a width W of the electrode foil 2a.
In order to reduce the cross sectional area, the notches 5 and 5 are formed on both sides to partially remove the electrode foil 2a to form a cross sectional area reduced portion 7 (see FIG. 1B). By thus making the cut 5 in the electrode foil 2a, the cross-sectional area of the electrode foil 2a cut in the thickness direction is reduced. The cut 5 is formed by etching.

The lower electrode foil 2b is provided with a rectangular removal portion 9 in which the electrode foil 2b is partially removed along the width direction so as not to reach the edge 11 of the electrode foil 2b (FIG. 1 (c)). The portion left after the removal portion 9 is formed in this manner becomes the cross-sectional area reduction portion 7. The removed portion 9 formed on the lower electrode foil 2b is the same as the upper electrode foil 2
It is formed at a position corresponding to the cross-sectional area reduction portion 7 formed in a. More specifically, when the lower electrode foil 2b is viewed from the cross-sectional area reduction portion 7 formed on the upper electrode foil 2a (when viewed in the direction perpendicular to the paper surface of FIG. 1B), the upper electrode foil 2a The cross-sectional area reduction portion 7 overlaps the lower removal portion 9. As a result, even if the portion of the conductive polymer 1 corresponding to the reduced cross-sectional area 7 is burnt out, the upper and lower electrode foils 2a and 2b do not come into contact with each other at this portion.

The conductive leads 3a, 3b are made of Ni having a thickness of about 125 μm, and the upper and lower electrode foils 2 are formed.
They are joined to a and 2b by soldering.

The upper conductive lead 3a is arranged so that the tip portion 24a of the conductive lead 3a does not exceed the central portion (the position where the cross-sectional area reduction portion 7 is present) in the longitudinal direction of the upper electrode foil 2a. In (b), the left side is the bonding surface, which is bonded to the upper surface of the upper electrode foil 2a.
The lower conductive lead 3b is arranged so that the tip end portion 24b of the lower conductive lead 3b does not exceed the central portion (the position where the cross-sectional area reduction portion 7 exists) in the longitudinal direction of the lower electrode foil 2b.
In (c), the right side is the joining surface, and it is joined to the lower surface of the lower electrode foil 2b. In this way, the pair of conductive leads 3a and 3b is obtained by projecting the upper (other) conductive lead 3a onto the surface of the electrode foil 2b to which the lower (one) conductive lead 3b is joined in the figure. To
The lower conductive lead 3b is joined to the upper conductive lead 3a without overlapping. Since the pair of conductive leads 3a and 3b are arranged as described above,
The cross-sectional area reduced portion 7 is formed between the tip portions 24a and 24b of the conductive leads 3a and 3b.

The operation and effect of the PTC switch of the present invention having the above structure will be described below. At room temperature of about 20 ° C., when a lithium ion secondary battery using a PTC switch as a circuit protection element is applied with a normal use voltage of about 3.6 V, the resistance value of the conductive polymer 1 does not rise sharply. Electric current flows, and the electric circuit including the PTC switch operates normally. However, when a high voltage of about 100 V, which exceeds the maximum rated voltage that is not normally assumed in the lithium ion secondary battery, is applied, P
The TC switch trips due to a sudden flow of a large current and enters a high resistance state. In this state, a voltage of 100V will be applied between the terminals of the PTC switch,
Eventually, the conductive polymer 1 is ignited and burned out. If the conductive polymer 1 is burnt out, the upper and lower electrode foils 2a and 2b may come into contact with each other and the circuit may be short-circuited. If short-circuited, a voltage as high as 100 V will be applied to the lithium-ion secondary battery, destroying the secondary battery. On the other hand, in the PTC switch according to the present embodiment, since the cross-sectional area reduction portion 7 is formed, when a large current flows, this portion is destroyed first. That is, since the cross-sectional area reduction portion 7 has a smaller cross-sectional area than the other portions of the electrode foils 2a and 2b, the current density inevitably increases. Since the electrode foils 2a and 2b are destroyed from the place where the current density is large, the cross-sectional area reduction portion 7 is surely destroyed before the other portions, and the PTC switch is electrically insulated in this portion. That is, the PT according to the present embodiment
The cross-sectional area reduction portion 7 of the C switch is an insulating portion that is electrically insulated when a large current of a predetermined value or more flows through the PTC switch.

Further, as described above, the PTC switch according to the present embodiment is attached in such a state that the conductive leads 3a and 3b do not overlap each other, so that the conductive polymer 1 and the electrode foils 2a and 2b are not attached. Even if they are destroyed, the conductive leads 3a and 3b do not come into direct contact with each other. Therefore, it is possible to surely avoid the inconvenience that the conductive leads 3a and 3b come into direct contact with each other to cause a short circuit.

Also, the cross-sectional area reduction portion 7 of the upper electrode foil 2a
Is provided at a position corresponding to the removed portion 9 formed on the lower electrode foil 2b, so that even if the conductive polymer 1 located between them is burned out, the upper and lower electrodes The foils 2a and 2b do not come into direct contact with each other.

As described above, even if a high voltage is applied to the lithium-ion secondary battery, if the PTC switch according to the present embodiment is used as a circuit protection element, even if the PTC switch is destroyed, it will never be short-circuited and can be reliably performed. It can be insulated.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a PTC switch according to this embodiment.
(A) is a side view and (b) is a plan view. The present embodiment is different from the first embodiment only in the configuration of the electrode foils 2a and 2b including the cross-sectional area reduction portion 7. Conductive polymer 1
The conductive leads 3a and 3b are the same as those in the first embodiment. Therefore, the electrode foils 2a and 2b including the cross-sectional area reduced portion 7 will be mainly described.

The electrode foils 2a and 2b are nickel-plated copper foils whose thickness other than the thin portion 13 is 35 μm as in the conventional case. A thin portion 13 is formed over the entire width direction at the central portion in the longitudinal direction of the upper and lower electrode foils 2a and 2b. The thin portion 13 is formed to be thinner than the other electrode foils 2a and 2b. More specifically, the other electrode foils 2a and 2b have a thickness of 35 μm, while the thin portion has a thickness of 20 μm. However, this value is determined according to the current density at which the electrode foil should be destroyed. This thin portion is formed by etching. In this way, the cross-sectional area reduced portion 7 is formed by the thin portion 13 in which the electrode foils 2a and 2b are thinned. The action and effect of ensuring the insulation by the cross-sectional area reduction portion 7 are the same as those in the first embodiment.

The thin portion 13 of this embodiment is the electrode foil 2
Although it is formed over the entire width direction of a and 2b, the present invention is not limited to this, and the electrode foils 2a and 2b are not limited thereto.
You may form in a part of b. Moreover, you may form the cross-sectional area reduction part by combining the notch 5 and the removal part 9 of 1st Embodiment, and the thin part 13 of this embodiment.

Next, modified examples of the first and second embodiments will be described with reference to FIGS. 3 and 4. 3A and 3B show a modification in which the conductive leads 3a and 3b are arranged so as not to overlap each other. FIG. 3A is a side view and FIG. 3B is a plan view. As shown in FIG. 3, each of the conductive leads 3a and 3b is connected to the electrode foil 3
They are arranged so as to be offset in the width direction of a and 3b so that they do not overlap. That is, the upper conductive lead 3
a is brought close to the one end 15 side of the upper electrode foil 2a and joined, and the lower conductive lead 3b is brought close to the other end 16 side of the lower electrode foil 2b and joined. By arranging in this way,
The conductive leads 3a, 3b can be attached even when the tip ends of the conductive leads 3a, 3b exceed the central portions of the electrode foils 2a, 2b in the longitudinal direction.

On the upper electrode foil 2a, a stepped thin portion 18 is formed so as to surround the upper conductive lead 3a. In other words, the thin portion 18 has one end 15 of the electrode foil 2a.
From the first thin portion 18 toward the center of the electrode foil 3a in the width direction
a, a second thin portion 18b connected to the first thin portion and extending in the longitudinal direction of the electrode foil 3a, and a second thin portion connected to the second thin portion 18b,
The third extending along the width direction to the other end 16 of the electrode foil 2a
It is composed of a thin portion 18c. The lower electrode foil 2b also has a thin portion having a similar shape formed at a position corresponding to the thin portion 18. In this way, the conductive lead 3
A cross-sectional area reduced portion 7 is formed by a thin portion 18 so as to separate the portions a and 3b.

FIG. 4 shows the following modification.
(A) is a side view and (b) is a plan view. This modified example is different from the first embodiment in the cross-sectional area reduction portion 7.
That is, a plurality of holes 20 are formed in the electrode foils 2a and 2b. The holes 20 are formed in the width direction of the electrode foils 2a and 2b. A plurality of holes 20 are also formed in the lower electrode foil 2b. By forming the holes 20 in this way,
The cross-sectional area reduction part 7 can also be formed.

[Third Embodiment] Next, a third embodiment of the present invention will be described with reference to FIG. The PTC switch according to the present embodiment is used as a temperature protection element used in an electric circuit of a microwave oven (electric device) in which high current is normally used. PTC shown in FIG.
The switch does not differ from the first and second embodiments with respect to the conductive leads 3a and 3b. The electrode foil 2 is similar to the conventional electrode foils 103a and 103b in that the cross-sectional area reduction portion 7 is not provided.

The conductive polymer 1 in this embodiment is
It differs from each of the above-described embodiments in that the degree of cross-linking is changed during manufacturing. That is, the central portion 1b of the conductive polymer 1
Are crosslinked by a lower level of radiation than the side 1a of the conductive polymer 1.

Depending on the degree of radiation crosslinking applied to the conductive polymer 1, the rate of increase in resistance value with respect to temperature rise can be varied. This will be described with reference to FIG. For example, when the conductive polymer 1 is not exposed to any radiation, the resistance slightly increases as shown by the curve L1 in FIG. 6, but a rapid change in resistance cannot be expected. On the other hand, when radiation of about 10 Mrad is applied, L
As shown in FIG. 3, a resistance value increase of about 5 digits can be obtained. Further, when a radiation amount smaller than the above radiation dose is applied, a resistance temperature characteristic L2 located between L1 and L3 is obtained. By varying the degree of radiation crosslinking in this way, the positive resistance temperature characteristic can be adjusted.

The side portion 1a of the conductive polymer 1 in this embodiment is radiation-crosslinked so that the resistance value can be increased by about 5 digits. That is, the PTC characteristic shown in FIG. 6 L3 is shown. On the other hand, the central portion 1b of the conductive polymer 1 has a lower degree of radiation crosslinking than the side portion 1a, and thus exhibits the PTC characteristic shown by L2 in FIG. That is, the PTC characteristic of the central portion 1b of the conductive polymer 1 is set lower than that of the side portion 1a, which is a low PTC portion.

The operation and effect of the above configuration will be described below. If the microwave oven is normally used, PT
The C switch maintains a low resistance, and a high current of about 15 A is passed through the PTC switch. When the electric circuit portion provided with the PTC switch is exposed to a high temperature of about 80 ° C. due to some failure, the PTC switch according to the present embodiment operates as follows. The resistance value of the side portion 1a of the conductive polymer 1 rapidly increases. On the other hand, since the central portion 1b of the conductive polymer is the low PTC portion, the resistance value does not increase as compared with the side portion 1a.
Then, the current intensively flows into the central portion 1b having a low resistance, and the central portion 1b further generates heat,
The melting point of the conductive polymer 1 is far exceeded, reaching the ignition point, and finally burned out. Thus, the PTC switch is insulated by first burning out the central portion 1b of the conductive polymer 1. Thus, the PTC according to the present embodiment
The switch can be used as a temperature protection element in an electric circuit of a microwave oven in which a high current flows.

When the temperature of the conductive polymer 1 becomes high,
As described above, since the electric current flows intensively in the central portion 1b, the electrode foils 2a, 2 bonded to the central portion 1b are formed.
The electric current also flows intensively to the part b, and the electrode foil 2
The parts of a and 2b are also destroyed. In order to make the destruction of the electrode foils 2a and 2b more reliable, the electrode foils of the first and second embodiments may be combined.

As a modification of this embodiment, the material of the conductive polymer 1 may be changed as shown in FIG.
That is, the material is changed so that the central portion 1b of the conductive polymer 1 has a lower PTC portion than the side portion 1a. More specifically, a method of using a polymer having a low melting point as the polymer of the central portion 1b, or increasing the abundance ratio of carbon black is used.

[Fourth Embodiment] The fourth embodiment of the present invention will be described below with reference to FIG. The present embodiment is different from the third embodiment in the method of achieving the low PTC part. The conductive polymer 1 has a similar positive resistance temperature characteristic throughout as in the first and second embodiments. The electrode foils 2a and 2b and the conductive leads 3a and 3b are the same as those in the third embodiment.

The present embodiment is characterized in that the band 22 is provided between the tips of the conductive leads 3a and 3b. This band 22 is made of conductive polymer 1 and electrode foil 2.
It is wound so as to bind a and 2b. The band 22 partially applies pressure to the conductive polymer 1. An insulating material such as rubber is used as the material of the band 22.

The conductive polymer 1 portion pressed by the band 22 becomes a low PTC portion as described below. This is because, when the conductive polymer 1 is pressurized by the band 22, even if the ambient temperature of the PTC switch rises and thermal expansion is attempted, the conductive polymer 1 is restrained by the band 22 and does not expand. If the conductive polymer 1 does not expand, the carbon blacks dispersed in the conductive polymer 1 are not separated from each other, so that the conductive path is not cut. Therefore, the resistance value of the portion pressed by the band 22 does not increase so much even if the temperature rises. Due to the band 22 that partially restrains the thermal expansion of the conductive polymer 1, the low PTC having the positive resistance temperature characteristic as shown by L2 in FIG.
Parts will be formed. According to this embodiment, since the low PTC portion can be obtained by attaching the band 22, it is possible to easily and inexpensively manufacture.

Although the nickel foil-plated copper foil has been used as the electrode foils 2a and 2b in each of the above-described embodiments, the invention is not limited to this and may be nickel foil, for example.

[0067]

As described above, according to the polymer PTC thermistor of the present invention, the following effects can be obtained. Since an insulating part is provided between the conductive leads that is electrically insulated even if a voltage exceeding the maximum rated voltage is applied and destroyed, short-circuiting should occur even if the polymer PTC thermistor is destroyed. There is no. Further, when another conductive lead is projected on the surface of the electrode foil to which the one conductive lead is joined, the electrode is formed in a state where the one conductive lead does not overlap with the projected other conductive lead. Since it is bonded to the foil, even if the conductive polymer and the electrode foil are burned out, the conductive leads do not come into direct contact with each other to cause a short circuit.

Since a part of the electrode foil is destroyed before the other part, it is possible to select a part to be insulated in advance and avoid a situation in which an unexpected part is broken and an unexpected short circuit is caused. can do.

Since the insulating portion is formed by the cross-sectional area reduced portion in which the cross-sectional area of the electrode foil is reduced, the cross-sectional area of the electrode foil may be determined according to the current density to be destroyed, and the insulating portion can be simplified. Can be set.

Since the insulating portion is formed by burning off a part of the conductive polymer prior to the other portion, it is possible to select the portion to be insulated in advance, and the unexpected portion is destroyed. It is possible to avoid a situation in which an unexpected short circuit is caused.

Since a part of the conductive polymer is a low PTC part in which the rate of increase in resistance value with respect to temperature rise is set lower than other parts, when the temperature of the polymer PTC thermistor rises, this low The PTC portion will be selectively burned down, and the insulation can be ensured.

Since the polymer PTC thermistor according to the present invention is used as a circuit protection element in a secondary battery, even if there is an overcharge which is not assumed at the time of design, the secondary battery main body is not affected, and the secondary battery main body is reliably protected. It can be insulated.

Since the polymer PTC thermistor according to the present invention is used in an electric device as a temperature protection element, it is possible to provide an electric device which is inexpensive and can be reliably insulated even in an environment where a high current of, for example, about 15 A is always used. You can

[Brief description of drawings]

FIG. 1 is a PTC switch shown as a first embodiment of the present invention, in which (a) is a side view and (b) is a plan view.
(C) is a bottom view.

FIG. 2 is a PTC switch shown as a second embodiment of the present invention, in which (a) is a side view and (b) is a plan view.

FIG. 3 is a PTC switch shown as a modified example of the present invention, in which (a) is a side view and (b) is a plan view.

FIG. 4 is a PTC switch shown as a modified example of the present invention, in which (a) is a side view and (b) is a plan view.

FIG. 5 is a side view of the PTC switch shown as the third embodiment of the present invention.

FIG. 6 is a diagram showing a positive resistance temperature characteristic of a conductive polymer according to a third embodiment.

FIG. 7 is a side view of a PTC switch shown as a modified example of the third embodiment.

FIG. 8 is a PTC switch shown as a fourth embodiment of the present invention, in which (a) is a side view and (b) is a plan view.

FIG. 9 shows a conventional PTC switch, (a) is a side view and (b) is a plan view.

FIG. 10 is a diagram showing a positive resistance temperature characteristic of a PTC switch.

[Explanation of symbols]

1 Conductive polymer 1b Low PTC part 2a, 2b electrode foil 3a, 3b conductive lead 7 Cross-section area reduction part 13 Thin part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naofumi Miyasaka             2414 Amada, Oita, Sakuragawa Village, Inashiki District, Ibaraki Prefecture               Electronics Raychem Co., Ltd. Chiku             Nami Business Office (72) Inventor Masatoshi Sakamoto             2414 Amada, Oita, Sakuragawa Village, Inashiki District, Ibaraki Prefecture               Electronics Raychem Co., Ltd. Chiku             Nami Business Office F-term (reference) 5E034 AA09 AB01 AC09                 5H022 AA04 AA09 KK01

Claims (13)

[Claims] 1. A conductive polymer having PTC characteristics,
Polymer PT having an electrode foil bonded to the conductive polymer and a pair of conductive leads bonded to the electrode foil
In the C thermistor, when each conductive lead projects another conductive lead on the surface of the electrode foil to which the one conductive lead is joined, the one conductive lead projects another conductive lead. In addition to being bonded to the electrode foil without overlapping the conductive leads, there is an insulating part between these conductive leads that is electrically insulated even if a voltage exceeding the maximum rated voltage is applied and destroyed. A polymer PTC thermistor, which is provided. 2. The polymer PTC thermistor according to claim 1, wherein the insulating part is a part of the electrode foil formed so as to be broken prior to other parts. 3. The polymer PTC thermistor according to claim 2, wherein the insulating portion is a cross-sectional area reduced portion in which the cross-sectional area of the electrode foil is reduced. 4. The polymer PTC thermistor according to claim 3, wherein the cross-sectional area reduced portion is formed by partially removing the electrode foil. 5. The polymer PTC thermistor according to claim 4, wherein the electrode foil has a thickness of 20 μm or less. 6. The thermistor according to claim 3, wherein the cross-sectional area reduced portion is formed by a thin portion. 7. The polymer PTC according to claim 1, wherein the insulating portion is formed as a part of the conductive polymer formed so as to be burned off before the other portion.
Thermistor. 8. The low PTC portion, wherein a part of the conductive polymer has a resistance increase rate with respect to a temperature rise set to be lower than that of the other part.
The polymer PTC thermistor described. 9. The polymer PTC thermistor according to claim 8, wherein the low PTC portion is a portion that is cross-linked to a lower degree than the other portions. 10. The polymer PTC thermistor according to claim 8, wherein the low PTC portion is a portion which is pressed more than other portions. 11. The polymer PTC thermistor according to claim 8, wherein the low PTC portion is made of a material different from that of other portions. 12. A secondary battery comprising the polymer PTC thermistor according to any one of claims 1 to 11 as a circuit protection element. 13. An electric device using the polymer PTC thermistor according to any one of claims 1 to 11 as a temperature protection element.