JP2008251769A - Overcurrent protecting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcurrent protecting element which can maintain its insulated condition without being broken or deteriorated even when its heat generating state is maintained or it is brought back to the room temperature after being kept under a high temperature atmosphere for a long time and which can obtain a low resistance value again when it is brought back to the room temperature. <P>SOLUTION: A macromolecular matrix is sandwiched between a pair of opposed pieces of metal foil. The macromolecular matrix contains multiple conductive particles and also contains at least either one of metal oxide and metal nitride. A compound of either one of alumina and magnesium oxide which can be easily treated is used. Since the macromolecular matrix contains the metal oxide and/or metal nitride, the overcurrent protecting element itself can be cooled in a short time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an overcurrent protection element that protects circuits, batteries, components, and the like built in various electric devices.

  In a conventional resin-type overcurrent protection element, a polymer matrix is sandwiched between a pair of metal foils (not shown) facing each other, and the polymer matrix contains a large number of conductive fine particles. The characteristics are required to be sufficiently low, the rate of change between the room temperature resistance value and the resistance value during operation is sufficiently large, and the change in resistance value during repeated operation is small (see Patent Documents 1 and 2). ).

Such an overcurrent protection element is such that the element itself is heated during operation in a high-temperature atmosphere or at high current energization, and the polymer matrix thermally expands at a high temperature, and the conductive particles dispersed in the polymer matrix. Individual distances between them are separated to form an insulating state.
JP 2000-80216 A JP-A-10-303003

  By the way, a conventional overcurrent protection element using a polymer matrix, as seen in the aging test in UL1434 (Thermistor Standard), keeps an overcurrent for a long time and maintains a heat generation state or a high temperature for a long time. When the temperature is returned to room temperature after being placed in an atmosphere, it takes time to cool the element itself, and thus there is a problem that the resistance value is significantly increased from the initial state.

  The present invention has been made in view of the above, and can maintain a stable insulating state without being broken or deteriorated even if the heat generation state is maintained or the temperature is returned to room temperature after being in a high temperature atmosphere for a long time. In addition, an object of the present invention is to provide an overcurrent protection element that can obtain a low resistance value again at the time of returning to room temperature.

In the present invention, in order to solve the above problems, a polymer matrix is sandwiched between a pair of opposing conductive foils, and the polymer matrix contains conductive fine particles,
The polymer matrix contains at least one of a metal oxide and a metal nitride.

Note that nickel or copper is preferably used as the conductive foil.
Moreover, it is preferable that a crystalline resin is contained in the polymer matrix.
In addition, the polymer matrix contains one or more types of elastomers composed of ethylene-α olefin-diene copolymer and styrene-butadiene polymer in which maleic anhydride is added to the modified elastomer. It is preferable to do.
Furthermore, any compound of alumina (aluminum oxide) and magnesium oxide can be used as the metal oxide.

  Here, the metal oxide and the metal nitride in the claims are contained in the polymer matrix in an amount of 5 to 20 wt%, preferably 5 to 15 wt%, more preferably 5 to 10 wt% from the viewpoint of facilitating production. Good to be done. As a method for manufacturing an overcurrent protection element, a polymer matrix, conductive particles, and a metal oxide or metal nitride are stirred at a predetermined temperature, a crystalline resin is added while maintaining this temperature, and these are added. A kneaded product is manufactured by pressure mixing, and the kneaded product is formed into a sheet having a predetermined thickness. The obtained sheet is sandwiched between a pair of conductive foils and heated and pressed to form a polymer matrix with the pair of conductive foils. A sandwich laminate may be formed, and this laminate may be irradiated with an electron beam or the like to crosslink the polymer blend of the laminate.

  According to the present invention, there is an effect that a stable insulating state can be maintained without being destroyed or deteriorated even if the heat generation state is maintained or the temperature is returned to room temperature after being in a high temperature atmosphere for a long time. . Further, there is an effect that a low resistance value can be obtained again at the time of returning to room temperature.

  Hereinafter, a preferred embodiment of the overcurrent protection element according to the present invention will be described. Although the overcurrent protection element in this embodiment is not shown, a sheet-shaped polymer matrix is sandwiched between a pair of metal foils facing each other. The polymer matrix contains a large number of conductive fine particles, and the polymer matrix contains at least one of an insulating metal oxide and a metal nitride. Built in a car or the like, the electronic circuit is protected from overcurrent.

  The pair of metal foils is formed into a substantially rectangular plate shape using, for example, rolled thin copper, aluminum, zinc, titanium, gold, silver, nickel, or an alloy, and connected to an electronic circuit via a lead wire. Is done. The material of the metal foil that is the conductive foil is not particularly limited, but the use of inexpensive nickel that is excellent in conductivity is optimal.

  The polymer matrix comprises an ethylene-α olefin-diene copolymer comprising a crystalline resin made of, for example, high-density polyethylene, polypropylene, polyvinylidene fluoride, etc., and an elastomer modified with an anhydride added with maleic anhydride One or more types of elastomers composed of a styrene-butadiene polymer are contained in an amount of 5 to 20 wt%. The conductive fine particles are not particularly limited, and for example, particles of carbon, graphite, expanded graphite, gold, silver, polyaniline, etc. are used. Among these, the use of inexpensive carbon particles having excellent weather resistance and the like is optimal.

  Examples of the metal oxide include a hard alumina or magnesium oxide compound that is easily kneaded into a polymer matrix and easy to handle. Further, examples of the metal nitride include a compound of either aluminum nitride or magnesium nitride.

  In the above, when producing an overcurrent protection element, first, the polymer matrix, the conductive particles, and the metal oxide or metal nitride are stirred with a pressure kneader or the like adjusted to a predetermined temperature to adjust the temperature. While maintaining the above, a crystalline resin such as polyethylene is added thereto and mixed under pressure to produce a kneaded product.

  Next, the kneaded product is set in a calendering machine and seated to form a sheet having a predetermined thickness, and the obtained sheet is sandwiched between a pair of metal foils and set in a press molding machine, and heated and pressurized. Thus, a laminate in which the polymer matrix is sandwiched between a pair of metal foils is manufactured. An overcurrent protection element can be manufactured by irradiating the resulting laminate with an electron beam or the like to crosslink the polymer blend of the laminate and then processing the laminate into a predetermined shape.

  According to the above configuration, since the polymer matrix contains a metal oxide and / or a metal nitride, the overcurrent protection element is continuously supplied with an overcurrent for a long time to maintain a heat generation state or for a long time under a high temperature atmosphere. The element itself can be cooled in a short time even if it is returned to room temperature after being put. Therefore, it is possible to suppress and prevent the resistance value from significantly increasing with respect to the initial state.

Examples of overcurrent protection elements according to the present invention will be described below together with comparative examples. However, the overcurrent protection elements according to the present invention are not limited to the following examples.
Examples 1-14
First, EPDM, conductive particles, and alumina or magnesium oxide according to the formulation shown in Table 1 are stirred for 30 minutes with a pressure kneader adjusted to 180 ° C., and polyethylene is added to this while maintaining the temperature adjustment at 180 ° C. The mixture was charged and mixed under pressure for 15 minutes to obtain a kneaded product.

Next, the kneaded product was set in a calendar processing machine and sheeted to form a 150 μm thick sheet. When the sheet is formed in this way, both sides of the obtained sheet are sandwiched with metal foil (Toyo Foil: nickel foil 20 μm), set in a press molding machine, heated (250 ° C.), pressurized (10 kgf / cm ² ). Thus, a laminate having a total thickness of 200 μm was obtained in which the polymer matrix was sandwiched between 25 μm thick metal foils. Then, the laminate was irradiated with an electron beam of 10 Mrad by an electron beam crosslinking apparatus to crosslink the polymer compound, and then punched into a 5 × 12 mm shape to produce an overcurrent protection element.

Comparative Example EPDM and conductive particles were stirred for 30 minutes with a pressure kneader whose temperature was adjusted to 180 ° C. according to the formulation shown in Table 1, and polyethylene was added here for 15 minutes while maintaining the temperature adjustment at 180 ° C. A kneaded product was obtained by mixing under pressure. Other parts were the same as those in Examples 1-14.

When the overcurrent protection element was manufactured as described above, the characteristics of the obtained overcurrent protection element were measured.
That is, a resistance measuring instrument was connected to the overcurrent protection element and placed in an atmosphere of 160 ° C., and the state of maintaining the insulation state due to the PTC drop was observed. At this time, if the insulation state of the resistance value could not be maintained, the measurement was stopped at that time, and if safe, the observation was performed until 1000 hours were reached (equivalent to the aging test of UL1434). Thereafter, the overcurrent protection element in which no problem occurred was allowed to stand at room temperature for 1 hour or more, and then the RT characteristic (resistance-temperature characteristic) was measured.

  The RT characteristic was measured as follows. First, the temperature was raised 10 ° C. sequentially from 20 ° C. every 15 minutes, the resistance value was measured each time, and the temperature was raised to 160 ° C. When the temperature reaches 160 ° C., the temperature is successively decreased every 10 ° C. and measurement is continued until 20 ° C., and the resistance value when the temperature returns to 20 ° C. is recorded as a relaxation resistance value. It was. Tables 1, 2 and 3 show the resistance values during the tests of the examples and comparative examples.

In the case of Examples 1-14, a favorable relaxation state was shown, and the relaxation resistivity after 1000 hours also showed a good value. According to this example, a stable relaxation resistance state could be obtained even after a long trip state.
On the other hand, in the case of the comparative example, the relaxation resistivity was as high as 200%.

Claims (5)

An overcurrent protection element comprising a polymer matrix sandwiched between a pair of opposing conductive foils and containing conductive fine particles in the polymer matrix,
An overcurrent protection element comprising a polymer matrix containing at least one of a metal oxide and a metal nitride.   The overcurrent protection element according to claim 1, wherein nickel or copper is used as the conductive foil.   3. The overcurrent protection element according to claim 1, wherein the polymer matrix contains a crystalline resin.   The polymer matrix contains at least one elastomer composed of an ethylene-α olefin-diene copolymer obtained by adding maleic anhydride to an elastomer modified with an anhydride and a styrene-butadiene polymer. Item 4. The overcurrent protection device according to Item 1, 2, or 3.   The overcurrent protection element according to any one of claims 1 to 4, wherein any one of alumina and magnesium oxide is used as the metal oxide.