JP2005347480A - Overcurrent protection element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcurrent protection element which can sufficeintly increase an adhesive quality with a metal foil such as a rolling foil or the like which has no need of a lead terminal or the like, and a conductive composition, in particular, which indicates an abrupt resistance rise from the end point of a stable region of a low resistance and shows a sufficient resistance rise corresponding to a durability temperature, and in which even if an overcurrent flows, a return resistance value after that can be suppressed in a practical range. <P>SOLUTION: In the overcurrent protection element in which the metal foils are provided on both surfaces of the sheet-shaped conductive composition, the metal foil is a rolling foil and its surface is roughened by a chemical treatment using a chemical solution of at least one or more of phosphoric acid, chromic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, and fluoric acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an overcurrent protection element comprising a conductive composition using a polymer material, and more specifically, a metal foil on both surfaces of a conductive composition whose electrical resistance increases depending on temperature. The present invention relates to an overcurrent protection device provided with

  An overcurrent protection element is an element having a characteristic (hereinafter referred to as a PTC characteristic) in which an electrical resistance increases depending on a temperature particularly when a sudden overcurrent is generated. Broadly divided into systems. The element using the latter polymer material has a form in which a metal foil such as copper or nickel is pasted on the front and back of a sheet-like material having a polymer resin as a constituent component and having a thickness of 100 to 300 μm. And the composition which comprises this sheet-like material is a composition (henceforth an electroconductive composition) which has electroconductivity formed by disperse | distributing electroconductive fine particles in a polymer composition, Comprising: Normal electric current Is supplied with a low resistance, and when a sudden overcurrent occurs, the resistance becomes high and the circuit is protected by interrupting conduction.

  In order to enhance this blocking function, a polymer having a high degree of crystallinity such as high-density polyethylene is used for the conductive composition. The reason why a polymer with a high degree of crystallinity is used is that heat is generated due to overload, and when the melting point of polyethylene is reached, the polymer crystal melts and the volume rapidly expands, and the distance between the individual conductive fine particles The resistance value increases (hereinafter referred to as trip).

  By the way, when an overcurrent occurs, the overcurrent protection element becomes a high resistance and cuts off conduction. However, when a normal current is supplied again, the overcurrent protection element is in a state before the overcurrent occurs. It is required to return to a low resistance state equivalent to However, although the reason is unknown, the return resistance value generally tends to be higher than the original resistance value. When the return resistance value is considerably higher than the state before the overcurrent occurs, the supply current value to the circuit that should be originally reduced becomes small, which may cause problems in the circuit and the like. For this reason, it is desired that the return resistance value be within a practically acceptable range even if the rise of the return resistance value is suppressed as much as possible and becomes higher than the resistance value before the occurrence of overcurrent.

Conventionally, as a method for suppressing such an increase in the return resistance value, it has been considered to improve the adhesion between the conductive composition and the metal foil, to improve the configuration of the conductive composition, or the like.
For example, a composition sheet in which 45 to 60% by volume of a metal carbide conductive powder filler is kneaded with a crystalline polymer component, and a metal conductive powder filler is kneaded with a crystalline polymer component, and one side is plated. Proposed PTC elements have been proposed, which have excellent repeated operation stability and improved adhesion between the PTC composition and the metal (see, for example, Patent Document 1).

  In addition, electrode foils for energization are respectively provided on the upper and lower surfaces of the main body portion of the polymer PTC element composed of a polymer and a conductive material dispersedly mixed in the polymer, and the pair of electrode foils are attached to the element main body. An overcurrent protection element is proposed in which not only the surface facing the element body serving as the attachment surface is a roughened surface but also Au flash plating is applied to the facing surface (for example, Patent Documents). 2). And the electrical resistance of the connection part between an element main body and an electrode is low enough, and it has stable electrical characteristics, without an electrical resistance rising with respect to an environment, a time-dependent change, etc.

Furthermore, with respect to 100 parts by weight of high-density polyethylene whose molecular ends are modified with maleic anhydride, carbon black A having a particle size of 20 to 30 nm, a specific surface area of 100 to 1000 m ² / g, a particle size of 50 to 100 nm, and a specific surface area of 10 An overcurrent device has been proposed in which electrodes are provided on both sides of a film made of a semiconductive mixture obtained by blending 60 to 120 parts by weight of carbon black B of ˜50 m ² / g (for example, Patent Literature 3). Such a PTC element has high adhesiveness between the semiconductive admixture film and the electrode, low contact resistance between them, low resistance at room temperature, and 10 ⁴ resistance change at normal temperature and high temperature. That's it.

  By the way, in order to improve the adhesiveness between the metal foil and the conductive composition, physical and chemical surface roughening of the metal foil may be mentioned in addition to the above-described metal foil plating method and the like. It is also conceivable to use an electrolytic foil having a rough surface as it is. However, physical surface roughening is not preferable because it tends to cause variation in setting of constant conditions in mass production, and roughening under delicate conditions is difficult. In addition, it takes time in the case of metal foil plating or electrolytic foil, and in particular, in the case of electrolytic foil, the surface can be preferably roughened. Cannot exceed 50 μm. For this reason, the element requires a lead terminal or a base terminal for supporting it, which increases the price of the product itself.

  In the overcurrent protection element, when the resistance before the overcurrent occurs in the element is the initial resistance value R0, and the resistance after the recovery is the recovery resistance value Rr, the resistance against the initial resistance value R0 When the recovery rate {(Rr / R0) 100%} is expressed as a percentage of the recovery resistance value Rr, it is practical that the recovery rate of the overcurrent protection element is 500% or less, more preferably 300% or less. .

Further, in order to obtain low resistance using carbon particles, 1. 1. Small particle size (large surface area) 2. porous (having pores); 3. Structure is long, and The element that there are few surface functional groups and residual polymerization condensation hydrocarbon is mentioned. This is because an electrical bypass is formed between the carbons due to the development of the structure, and the percolation limit is reached at a stage where the filling amount is small. As an index for measuring the length of such a structure, there is DBP oil absorption. Generally, the larger the DBP oil absorption, the longer the structure. However, when carbon having a long structure is used for the overcurrent protection element, there is a problem that the structure of carbon black is entangled at the softening point of the resin, causing an electrical bypass and not tripping. For this reason, carbon particles having no developed structure are highly filled to reduce resistance. This increases the hardness of the protection element, deteriorates the impact resistance, and makes resistance adjustment very difficult, making it difficult to manufacture a stable overcurrent protection element.
JP 2001-110603 A JP 2002-313604 A JP 2002-241554 A

  Therefore, in view of the above problems, the present invention presents a sudden increase in resistance from a metal foil such as a rolled foil that does not require a lead terminal and the like, and a conductive composition, in particular, an end point of a stable region of low resistance, to a durable temperature. Provided is an overcurrent protection element that sufficiently enhances the adhesion to a conductive composition exhibiting a sufficient increase in resistance, and can suppress the subsequent return resistance value to a practical range even when an overcurrent flows. There is.

The present inventors paid attention to the adhesion between the conductive composition comprising the polymer composition and the metal foil, and investigated the surface state of the metal foil, that is, the relationship between various rough surface treatments and the return resistance value. It is possible to keep the recovery rate of the overcurrent protection element low by chemically roughing the metal foil, and the surface roughening is similar to the chemical foil, such as chemicals, than the physical method. It has been found that such a preferable rough surface environment is surely formed on the surface of the metal foil, and an overcurrent protection element which does not require a lead terminal which is not affected by the thickness or the like has been achieved.
In addition, the inventors set the amount of carbon powder used in the conductive composition as a predetermined amount, and by setting the DBP oil absorption amount, average particle diameter, nitrogen specific surface area, etc. of the carbon powder within a predetermined value range. The present inventors have found that the overcurrent protection element exhibits a rapid increase in resistance from the end point of the stable region, and exhibits a sufficient increase in resistance commensurate with the endurance temperature, leading to the present invention.
That is, the overcurrent protection element of the present invention is characterized by the following configuration or structure.

(1) In an overcurrent protection element in which metal foil is provided on both surfaces of a sheet-like conductive composition, the metal foil is a rolled foil, and the surface is roughened by chemical treatment. Current protection element.
(2) The overcurrent protection element according to (1) above, wherein the chemical treatment is treatment with at least one chemical solution of phosphoric acid, chromic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, and hydrofluoric acid.
(3) The overcurrent protection element according to the above (1) or (2), wherein the surface roughness Ra (centerline average roughness) by the roughening is 0.5 μm or more.
(4) The overcurrent protection element according to any one of (1) to (3), wherein the metal foil can be used as a lead terminal.
(5) The conductive composition is composed of a polymer composition contained in a range of 60 to 75% by volume and a carbon powder contained in a range of 25 to 40% by volume. ) To (4).
(6) carbon powder used in the above conductive composition is in the range DBP oil absorption amount of 120 cm ^3/100 g, in the range of average particle size of 50 to 200 nm, said nitrogen specific surface area is less than 50 m ² / g The overcurrent protection element according to any one of (5).

According to the overcurrent protection element of the present invention, the surface of the metal foil is roughened by a chemical, and optimal adhesion is exhibited between the metal foil and the conductive composition in terms of the return resistance value. It will be a thing.
Usually, a relatively flat metal foil having a small surface roughness is in a close contact state with a weak adhesive force with the conductive composition. At room temperature, since the conductive composition is hardened, it is weakly bonded to the metal foil surface. However, when an overcurrent flows and is exposed to a temperature higher than the melting point, the conductive composition melts and expands in volume. It will not adhere or adhere to the foil. For this reason, it is predicted that innumerable microscopic shifts and peeling occur at the interface between the conductive composition and the metal foil. If the cooling and solidification occurs in such a state where such deviation or peeling occurs, the resistance value at the time of recovery is about the same as the initial resistance value before the occurrence of overcurrent, or even to a practical state. Cannot return.

  When the metal foil is chemically treated to roughen the surface as in the present invention, when the metal foil and the conductive composition are bonded by heating and pressing, the metal foil surface has a high degree of unevenness. The molecular composition enters and an anchor effect is generated, and both are firmly bonded. In such a state, even if an overcurrent flows into the conductive composition and reaches a temperature equal to or higher than the melting point, and the conductive composition melts, the anchor effect works and the movement is restricted. The interface between the conductive composition and the metal foil can be prevented from shifting and peeling in a microscopic state. Therefore, even if it is cooled and then restored, the resistance value before and after the overcurrent protection element does not change greatly.

Hereinafter, embodiments of an overcurrent protection element according to the present invention will be described in detail with reference to the drawings. The overcurrent protection element according to the present invention is not limited to the following embodiment.
FIG. 1 is a graph showing a change in resistance value with respect to the temperature of the overcurrent protection current element. FIG. 2 is a graph showing the change in resistance value with respect to temperature near the inflection point of the overcurrent protection element.
The overcurrent protection element of the present invention is formed by providing metal foil on both surfaces of a sheet-like conductive composition.
The metal foil of the overcurrent protection element is a rolled foil. That is, the rolled foil can be freely set without being restricted in manufacturing by thickness processing like the electrolytic foil. In particular, in the overcurrent protection element, when the metal foil is also used as a lead wire terminal, the thickness of the metal foil is preferably in the range of 50 to 200 μm, particularly in the range of 100 to 150 μm. Easy to process. If the thickness is less than 50 μm, it becomes difficult to handle and it is difficult to use as a lead terminal.

  The electrolytic foil is preferably used for the metal foil of the overcurrent protection element in that the surface of the electrolytic foil itself is roughened. The electrolytic foil has a lot of very fine irregularities on the metal surface, and can be expected to be extremely effective in suppressing the above-described change in the return resistance value. However, since the electrolytic foil is formed by applying electricity to the electrolytic solution to deposit the metal, only a thin product can be practically manufactured and the cost is high. It is difficult to manufacture an electrolytic foil having a thickness of 50 μm or more.

  The metal foil of the overcurrent protection element of the present invention has its surface roughened by chemical treatment. In the chemical treatment, a metal foil is immersed in a chemical solution, and the foil surface is roughened by utilizing the chemical dissolution action of the metal. Examples of the chemical solution include phosphoric acid, chromic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, and hydrofluoric acid. The chemical solution can be used by combining one or more chemical solutions. The time for immersing the metal foil in the chemical solution can be appropriately set according to the metal material, and the roughening treatment is usually completed in 5 to 60 minutes. Also, the immersion temperature may be room temperature, and the treatment may be performed by heating if necessary.

For example, when the metal foil is a nickel rolled foil, nitric acid, hydrochloric acid, hydrogen peroxide solution or the like is used alone or as a mixed chemical solution as the chemical solution to be processed, and in the range of 10 to 90% by mass and temperature of 20 to 60 ° C. Surface roughening is achieved by immersing in a controlled chemical for about 5 to 30 minutes. Further, when the metal foil is immersed in a chemical solution as it is, both surfaces are roughened, and when the double-sided roughening is disliked, a masking film can be attached to one side of the foil to roughen only one side.
The roughening of the metal foil can be performed by physical treatment, but the hardness and size of the beads that collide with the metal foil are likely to vary, and the variation in mass production is severely undesirable. In addition, when the beads are # 400 or more, roughening is not sufficiently achieved, and when the metal foil is processed only on one side, the metal foil tends to curl and the physical treatment is applied to the metal foil. Adversely affected.

The surface roughness due to the roughening of the metal foil of the overcurrent element of the present invention is determined by Ra (center line average roughness), Ry (maximum height), and Rz (measured by a method in accordance with JIS B0601. The ten-point average roughness) is preferably used as an index, and these are correlated with the above-described relationship of the return rate. In particular, the correlation between the Ra value and the return rate is often observed.
The surface roughness Ra of the roughened metal foil is preferably 0.5 μm or more, and particularly preferably in the range of 0.9 to 2.0. The surface roughness Ry of the metal foil is preferably 5.0 μm or more, and particularly preferably in the range of 10-20. The surface roughness Rz of the metal foil is preferably 1.5 μm or more, and particularly preferably in the range of 3.5 to 7.5.
If the surface roughness Ra is less than the above range, a good return rate is not seen as seen in FIG. When the above range is exceeded, the surface roughness of the entire treated surface of the metal foil varies.

Examples of the metal foil material include, but are not limited to, copper, aluminum, zinc, titanium, stainless steel, iron, silver, gold, and nickel.
However, aluminum, zinc, titanium, etc. tend to form a non-conductive film, which is robust and difficult to remove, whereas gold, silver, copper, nickel, and iron do not form a strong non-conductive film. Therefore, it is suitable as this element. However, copper and iron are apt to be oxidized, and accordingly the resistance value changes with time and is not suitable. Stainless steel has low conductivity as a material. Gold and silver are expensive, and their use as this element tends to be avoided. Therefore, nickel is suitable as a material for the overcurrent protection element.

  The conductive composition in the overcurrent protection element of the present invention comprises a polymer composition and conductive particles. In particular, the conductive particles are preferably carbon powder. Conductive particles include carbon-based fine powders such as carbon, graphite and expanded graphite, metal fine particles such as gold and silver, metal oxide or metal oxide fine particles doped with other atoms, and conductive such as polyaniline and polyacetylene. Polymer fine particles may be mentioned. The average particle size is not particularly limited, but if it is larger than 1000 nm, it is difficult to hold the polymer in the polymer as a binder. There is no lower limit of the particle size, and a range of 10 to 200 nm is desirable. In the present invention, several kinds of conductive particles may be combined.

As said electroconductive particle, it is preferable to select the carbon powder which is high performance and cheap in this invention. Hereinafter, an aggregate of carbon particles suitable as conductive particles, that is, carbon powder will be described.
The above carbon powder is in the range of an average particle diameter of 50 to 200 nm, with a DBP oil absorption 120 cm ^3/100 g or more, and a nitrogen specific surface area is less than 50 m ² / g.
The carbon powder is an aggregate of carbon particles (primary particles) having an average particle size of about 10 to 200 nm, and the average particle size of primary particles and the particle size of aggregated particles (secondary particles), PH There are many different grades with different chemical properties on the particle surface. Usually, the carbon powder in the application of the overcurrent protection element uses an aggregate of carbon particles (primary particles) having an average particle diameter of about 10 to 200 nm. The average particle size of the carbon powder is preferably 50 nm or more. Further, in the present invention, there is no particular limitation such as PH on the surface of the particle and it can be arbitrarily selected, but the nitrogen specific surface area is preferably 50 m ² / g or less.
When the average particle diameter in the carbon powder is less than 50 nm, the rise after the inflection point of the resistance value increase with respect to the temperature of the protective element becomes worse. If the nitrogen specific surface area also exceeds the above range, the overcurrent protection element will not rise properly.

DBP oil absorption of the carbon powder is provided for in the measurement method of ASTM D2414-93 is preferably at least 120 cm ^3/100 g, in particular, 135~145cm ³ / 100g is preferred. When DBP oil absorption amount of the carbon powder is 120 cm ^3/100 g or more, it is possible to suppress the base value of the resistance value at 20 to 60 ° C. in the overcurrent protection device low.

  In the conductive composition, it is preferable that the polymer composition is contained in a range of 60 to 75% by volume and the carbon powder is contained in a range of 25 to 40% by volume. When the carbon powder exceeds 40% by volume, the resistance value of the conductive composition in the room temperature region (temperature 20 ° C. ± 5 ° C.) does not become 15 mΩ or more, so that the trip behavior cannot be expected sufficiently. On the other hand, when the blending amount of the carbon powder is less than 25% by volume, the resistance value of the conductive composition in the room temperature region is too high to be used as an overcurrent protection element.

Next, the polymer composition used for the overcurrent protection device of the present invention will be described.
The conductive composition is preferably composed of a polymer composition having a crystallinity of 40% or more and the carbon powder. The polymer composition having a crystallinity of 40% or more refers to a composition in which a mass of 40% or more of the components is occupied by polymer crystals at room temperature.
When the crystallinity in the polymer composition is less than 40%, the trip characteristics are insufficient as an overcurrent protection element, and there is no upper limit on the crystallinity, but a higher one is desirable. Considering practicality, if the crystallinity exceeds 50%, the resistance value increases by 1,000 to 10,000 times at the time of trip, so that the crystallinity is particularly preferably 50% or more.
The polymer composition includes a single polymer having a crystallinity of 40% or more, a mixture of a plurality of polymers having a crystallinity of 40% or more, the polymer and the mixture, other polymers, oligomers, fillers, The composition may be a mixture with a stabilizer or other additive substance.

  Examples of the crystalline polymer used in the polymer composition include α-olefins such as polyethylene having a density of 0.94 or more, homotype polypropylene, and polyvinylidene fluoride having a density of 1.95 or more. Examples thereof include liquid crystalline polymers such as phenylidene ether, and can be arbitrarily selected in the present invention. If the crystalline polymer in the present invention is the above-mentioned polymer, the molecular weight, the state of branching of short chains and long chains, molecules such as the conformation of molecules such as syndiotactic, isotactic or attack tic The structural features are not limited and are arbitrary.

  In addition, in an overcurrent protection element used for a prismatic lithium ion battery or the like, it is required to exhibit a trip near a temperature of 80 to 90 ° C. In this case, a carboxylic acid typified by ethylene-vinyl acetate is used. Copolymers of vinyl and ethylene, copolymers of acrylic esters and ethylene such as ethylene-methyl acrylate, ethylene-ethyl acrylate and ethylene-butyl acrylate, methacrylic acid such as ethylene-methyl methacrylate and ethylene-ethyl methacrylate A mixture of an elastomer such as a copolymer of ester and ethylene and a crystalline polymer such as polyethylene or polypropylene is preferable.

In the conductive composition of the present invention, in order to further improve the adhesiveness to the metal foil, it is preferable to blend an elastomer having an adhesiveness to the metal into the polymer composition. Examples of such elastomers include ethylene-propylene copolymers (EPR), ethylene-propylene-diene copolymers (EPDM) and other ethylene-α-olefin-diene copolymers, styrene-ethylene-butadiene copolymers, etc. Styrene rubber, polyester rubber, acrylic rubber, butadiene rubber, isoprene rubber, uncrosslinked rubber such as natural rubber, acid functional group such as carboxylic acid or anhydride, hydroxyl group, epoxy group, etc. And elastomers having a functional group having an affinity for other metals. These elastomers have arbitrary molecular structural properties such as Mooney viscosity, intramolecular branching, and molecular weight distribution, and are not particularly limited in the present invention. Also, several kinds of mixtures may be used.
The above-mentioned uncrosslinked rubber or non-crosslinkable rubber may be modified by adding a plasticizer such as paraffin oil or reinforced with other polymer or filler.
As the elastomer having adhesiveness to the roughened metal foil, the most preferable one is an addition of maleic anhydride to an ethylene-α-olefin copolymer and an ethylene-α-olefin-diene copolymer. . The production method is mainly performed using peroxide, but can be arbitrarily selected such as using a crosslinking agent or a crosslinking aid in combination.

  The overcurrent element is cross-linked by irradiation with radiation or an electron beam in order to impart heat resistance. However, the adhesive component described above has an adhesive strength (peeling strength) with a metal by irradiation with the radiation or electron beam. It can be improved to about 50 to 500%.

Next, a method for manufacturing the overcurrent protection element of the present invention will be briefly described.
The conductive composition is mixed in a kneader such as a pressure kneader, a banbury and a two-roll or an extruder, seated by an extruder or a calendar device, laminated with a metal foil, and then in an arbitrary shape. However, also in the present invention, the selection of the manufacturing method and the apparatus is arbitrary. In general, in order to improve the PTC characteristics, post-treatment such as crosslinking by radiation or electron beam irradiation or development of uneven distribution of conductive particles by tripping several to several tens of times is performed. In the present invention, it is preferable to perform the above-described processing.

In the present invention, the radiation dose is preferably about 30 to 200 KGry. In addition, when the adhesive component mentioned above is mix | blended according to Japanese Patent Application No. 2000-351288, there exists observation that radiation and an electron beam improve to about 50-500% of adhesive strength (peeling strength) with a metal.
In addition, a commercially available overcurrent protection element may have solder laminated on the entire surface or a part thereof, but in the present invention, it can be processed in the same manner.

  The overcurrent protection element of the present invention takes a form such as Disc, Terminal device, Strap, SMD, etc., depending on the punched shape or solder lamination method, and protects primary batteries and secondary batteries, motors such as automobiles. It is used in applications such as protection of speakers, protection of speakers, protection of rechargeable batteries in mobile phones, and protection of computer circuits.

The overcurrent protection device according to the present invention will be described more specifically with reference to examples. The overcurrent protection device according to the present invention is not limited to the following examples.
(Examples 1 to 3 and Comparative Examples 1 and 2)
A roughening treatment was applied to a Ni rolled foil (100 mm × 100 mm) having a thickness of 125 μm. As a chemical treatment, a 40 mass% nitric acid solution, a 20 mass% mixed solution A of hydrogen peroxide: hydrochloric acid = 1: 1, and a 40 mass% mixed solution A are dipped to roughen the surface (both sides). As a physical treatment, sandblasting was performed with glass beads # 400 to roughen the surface (both sides).

  The surface roughness of the obtained foil was measured. The surface roughness was measured with a surface roughness measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., SURFCOM 480A). As measurement items, three items of Ra (center line average roughness), Ry (maximum height), and Rz (ten-point average roughness) were measured. The measurement conditions were cut-off value: 0.8 mm and evaluation length: 4 mm. The results of the untreated foil and treated foils 1, 2, and 3 are shown in Table 1.

  Next, the conductive composition having the composition shown in Table 2 below was kneaded with a pressure kneader whose temperature was adjusted at 180 ° C. to obtain a kneaded product. This kneaded product was subjected to sheeting by a calendering machine to obtain a sheet having a thickness of 200 μm.

The treated metal foil shown in Table 1 was overlapped on both surfaces of the obtained sheet and heated and pressed (temperature 250 ° C., 5 kgf / cm ² ) by applying a press molding machine to the conductive composition and the roughened metal foil. Melt bonding was performed to obtain a laminate (total thickness: 400 μm). The obtained laminate was irradiated with an electron beam of 30 Mrad with an electron beam cross-linking apparatus, the polymer compound was cross-linked, and cut into a size of 5 mm × 12 mm and cut into Examples 1 to 3 and Comparative Examples 1 and 2. The overcurrent protection element was obtained.

  The PTC characteristic of the obtained overcurrent protection element was measured. A wire is joined to the overcurrent protection element, and the other end of the wire is connected to a resistance measuring device to measure the measured value. Put the connected overcurrent protection element in the oven and raise the measurement. The temperature was increased from 10 ° C. every 10 ° C. and measured until reaching 160 ° C. When the element reached 160 ° C., it was cooled every 10 ° C., and the resistance value was measured. When the measurement temperature at each stage was reached, the temperature was held for 10 minutes, and the resistance value at that time was measured. After measuring the resistance at a temperature of 20 ° C., the sample was further left at 20 ° C. for 1 hour, and the resistance value after 1 hour was measured. This resistance value is taken as the final return resistance value. Table 3 shows the initial resistance value (resistance value at a temperature of 20 ° C. before temperature rise), the return resistance value (resistance value at a temperature of 20 ° C. after temperature rise), and the recovery rate (before overcurrent occurs) of each element. The initial resistance value R0 is the initial resistance value R0, and the resistance after the recovery is the recovery resistance value Rr. It is shown in Table 3. FIG. 1 shows the initial behavior and return behavior of the resistance value of each overcurrent protection element with respect to temperature.

(Examples 4 to 8)
A conductive composition comprising five kinds of blending compositions shown in Table 4 below was kneaded for 15 minutes with a pressure kneader adjusted at a temperature of 160 ° C. and taken out when the temperature of the kneaded product reached 220 ° C. Immediately after the kneaded material was put into a two roll (roll interval is 3 mm) adjusted to a temperature of 100 ° C., it was made into a sheet shape, cooled and then cut into a dice shape, and 5 types of conductive compositions of 4 mm × 4 mm × 3 mm. A product pellet was obtained. The pellets were put into an extruder adjusted to a temperature of 180 ° C. (single screw extruder with L / D of 15 and the shaft thickness was 40 mm) and operated at a rotational speed of 40 rpm. A fixed molten conductive composition was extruded. This molten composition was supplied to a calender device to obtain a long sheet having a thickness of 75 ± 10 μm, a width of 1250 mm, and a length of 150 mm.

The materials in Table 4 are as follows.
・ High-density polyethylene (crystallinity 95%): Mitsui Chemicals Co., Ltd.
・ Ethylene-acrylate: Nippon Unicar Co., Ltd. NUC-6220
-Maleic acid-modified EPDM: Nippon Synthetic Rubber Co., Ltd. product T7761P
-Carbon powder A: Columbia Carbon Co., Ltd. product 760
(DBP oil absorption of 48cm ^3/100 g, average particle size 30 nm, specific surface area 64m ^2/100 g)
Carbon powder B: Columbia Carbon Co., Ltd. product 420
(DBP oil absorption of 75 cm ^3/100 g, average particle size 86 nm, specific surface area 28 m ^2/100 g)
Carbon powder C: Tokai Carbon Co., Ltd.
(DBP oil absorption 140cm ³ / 100g, an average particle diameter of 60 nm, a specific surface area of 32m ^2/100 g)
-Carbon powder D: Tokai Carbon Co., Ltd. Seast SO
(DBP oil absorption 121cm ³ / 100g, an average particle diameter of 43 nm, a specific surface area of 32m ^2/100 g)
Carbon powder E: Columbia Carbon Co., Ltd. product 420
(DBP oil absorption 136cm ³ / 100g, an average particle diameter of 31 nm, a specific surface area of 67m ^2/100 g)

A nickel rolled foil similar to that in Example 1 was cut into a metal part of 5 mm × 25 mm by wire cutting. Then, the metal parts are stacked on the front and back of each of the above-mentioned sheets, and 100 sets are fixed to the fixing jig, and are inserted into a press apparatus adjusted to a temperature of 180 ° C. as it is, and 100 kgf / cm ^2. The cooling water was circulated through the press apparatus while being pressurized after 5 minutes. After 10 minutes, the temperature reached 50 ° C. and was removed. The obtained overcurrent elements of Examples 4 to 8 were put in one bag for each type, and irradiated with an electron beam irradiation device under a condition of a dose of 32 MRad.

  About the obtained five types of overcurrent elements, the thickness of the element, the average thickness of the conductive composition, and the resistance value at a temperature of 20 ° C. were measured (Table 5). Table 6 shows each resistance value at a temperature of 10 ° C. from a temperature of 20 ° C. to a temperature of 140 ° C. In FIG. 2, the trip behavior of each element near the inflection point at a temperature of 60 to 80 ° C. was examined.

As shown in FIG. 2, for Examples 4 and 5, DBP oil absorption of 120 cm ^3/100 g or more embodiments 6-8, the resistance value of up to 60 ° C. from room temperature inflection temae is suppressed low You can see that In contrast to Examples 7 and 8, Example 6 in which the average particle diameter of the carbon powder is 50 nm or more and the nitrogen specific surface area is 50 m ² / g or less is the rise after the inflection point of the resistance value increase with respect to temperature. Was good.

  The overcurrent protection element of the present invention exhibited a sudden increase in resistance from a metal foil such as a rolled foil that does not require a lead terminal and the like, and a conductive composition, in particular, the end point of a stable region of low resistance, and met the endurance temperature. Adhesiveness with a conductive composition exhibiting a sufficient increase in resistance is sufficiently enhanced, and even if an overcurrent flows, the subsequent resistance value becomes practical, and the industrial applicability is high.

FIG. 1 is a graph showing a change in resistance value with respect to the temperature of the overcurrent protection current element. FIG. 2 is a grab diagram showing a change in resistance value with respect to temperature near the inflection point of the overcurrent protective current element.

Claims (6)

  An overcurrent protection element comprising metal foils on both sides of a sheet-like conductive composition, wherein the metal foil is a rolled foil, and the surface is roughened by chemical treatment .   The overcurrent protection element according to claim 1, wherein the chemical treatment is treatment with at least one chemical solution of phosphoric acid, chromic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, and hydrofluoric acid.   The overcurrent protection element according to claim 1 or 2, wherein the surface roughness Ra (centerline average roughness) by the roughening is 0.5 µm or more.   The overcurrent protection element according to claim 1, wherein the metal foil can also be used as a lead terminal.   The conductive composition is composed of a polymer composition contained in a range of 60 to 75% by volume and a carbon powder contained in a range of 25 to 40% by volume. An overcurrent protection device according to claim 1. Carbon powder used in the above conductive composition is a DBP oil absorption 120 cm ^3/100 g or more, a range of average particle size of 50 to 200 nm, in claim 5 nitrogen specific surface area is less than 50 m ² / g The overcurrent protection element as described.

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