JP2006024863A - Overcurrent protecting element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcurrent protecting element which reduces the resistance value in a room temperature area and indicates a rapid trip action, and to provide a method of manufacturing the same. <P>SOLUTION: There are provided a conductive polymer matrix 2 formed on a sheet 1 and a pair of metal foils 3 stuck on both front and rear sides of the conductive polymer matrix 2, and the conductive polymer matrix 2 is prepared from a polymer matrix 20, a carbon black 21 that is a conductive particle kneaded into the polymer matrix 20, and an organic material layer 22 coating the surface of the carbon black 21. The organic material layer 22 is formed by using an organic material which is not compatible with the polymer matrix 20 at molecular level and is different from the polymer matrix 20, more specifically, using a pyrrole conductive resin which is not reactive to the polymer matrix 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an overcurrent protection element that is used in electrical and electronic equipment including, for example, a personal computer, a mobile phone, a DC breaker, and the like, and has a characteristic that a resistance value increases as temperature rises, and a method for manufacturing the same.

  Conventionally, fuses are used to protect electrical and electronic equipment and systems from short-circuit currents. However, these fuses can only be used once, are large, and are expensive. There's a problem. Therefore, in recent years, a compact and inexpensive overcurrent protection element that can be used repeatedly has been proposed, and much research and development has been made on this overcurrent protection element (see Patent Documents 1, 2, and 3).

  An overcurrent protection element is also called a PTC (Positive temperature coefficient) element, and is an element having a characteristic (PTC characteristic) in which an electrical resistance increases depending on temperature when an overcurrent occurs. It is roughly divided into systems.

  The latter polymer-based overcurrent protection element is composed of a sheet formed using a conductive polymer matrix and metal foils provided on both the front and back surfaces of the sheet (not shown) (patented) References 4 and 5). The conductive polymer matrix is prepared by mixing and dispersing carbon-based conductive particles such as carbon black and graphite in a polymer matrix made of high-density polyethylene or the like.

  High-density polyethylene is used for the polymer matrix. If high-density polyethylene with high crystallization is used, heat is generated due to overload, and when the melting point is reached, the crystal melts and the volume rapidly expands. This is because the resistance value increases (hereinafter referred to as trip) as the distance between the individual conductive particles forming the path increases.

  Such an overcurrent protection element exhibits a low resistance value (referred to as an initial resistance value) when a normal current is passed, and when an abnormal overcurrent occurs, the electrical resistance increases rapidly depending on the temperature. It functions as an overcurrent / overheat protection element that shuts off, a self-control heating element, or a temperature sensor. After that, when a normal current is supplied again, it returns to a low resistance value equivalent to or substantially equivalent to the state before the occurrence of overcurrent (referred to as a return resistance value).

By the way, when an overcurrent protection element is used as an overcurrent / overheat protection element connected in series to an electric / electronic circuit, (1) the resistance value in a room temperature range (20 ° C. ± 5 ° C.) is sufficient. Low resistance, (2) The rate of change between the resistance value in the room temperature region and the resistance value during operation is sufficiently large, and (3) The resistance value during repeated operation is small. For the purpose, a large amount of conductivity, DBP oil absorption, carbon black having a large structure and the like are blended.
JP 2001-110603 A JP 2002-313604 A JP 2002-241554 A U.S. Pat. No. 3,243,753 U.S. Pat. No. 3,351,882

  When the conventional overcurrent protection element is used as an overcurrent / overheat protection element as described above, a large amount of conductivity, DBP oil absorption, carbon black with a large structure, etc. are blended in order to reduce resistance. Therefore, the rate of change in resistance with increasing temperature decreases, and there is a high possibility that sufficient characteristics as an overcurrent / overheat protection element cannot be obtained. In addition, when trying to obtain a rapid and good trip behavior at the same time, it is necessary to use carbon black or the like having a DBP oil absorption amount or a small structure, and an overcurrent / overheat protection element excellent in resistance value and trip behavior can be obtained. There is a problem that you can not.

  The present invention has been made in view of the above, and an object of the present invention is to provide an overcurrent protection element having a low resistance value in a room temperature region and exhibiting a rapid trip behavior and a method for manufacturing the same.

In the present invention, in order to solve the above problems, the electrical resistance value increases depending on the temperature,
Including a polymer matrix, conductive particles contained in the polymer matrix, and an organic material layer covering the surface of the conductive particles,
The organic material layer is formed using an organic material that is not compatible with the polymer matrix at the molecular level and is different from the polymer matrix.

The polymer matrix can be a thermoplastic polymer.
Further, the conductive particles can be carbon particles.
Moreover, electroconductivity can also be provided to an organic material.
Furthermore, the organic material is preferably a pyrrole material that is not reactive with the polymer matrix.

Further, in the present invention, in order to solve the above problem, the overcurrent protection element manufacturing method according to any one of claims 1 to 5,
The surface of the conductive particles is covered with an organic material layer, and the coated conductive particles are mixed and dispersed in a polymer matrix.

  Here, the carbon black as the carbon particles in the claims preferably has an average particle size in the range of 70 to 120 nm, and the DBP oil absorption is in the range of 30 to 60 ml / 100 g under the measurement method of ASTM D2414-93, preferably Is in the range of about 50 ml / 100 g, more preferably 50 ml / 100 g. This is based on the reason that when the DBP oil absorption is less than 30 ml / 100 g, the resistance value becomes extremely high and becomes inappropriate as an overcurrent protection element. Conversely, when the DBP oil absorption exceeds 60 ml / 100 g, this is based on the reason that the trip becomes low and insufficient.

  The overcurrent protection element can be formed using a conductive polymer matrix composed of 60 to 75% by volume of a polymer matrix and 25 to 40% by volume of carbon black. This overcurrent protection element appropriately includes a low molecular organic compound. Furthermore, the overcurrent protection element is at least an overcurrent / overheat protection element, a self-control heating element, or a temperature sensor, such as a personal computer, a mobile phone, a DC breaker, a primary battery, a secondary battery, etc. Used in systems, speakers, and automobile motors.

  According to the present invention, it is possible to achieve a low resistance value in a room temperature region and to obtain an abrupt trip behavior.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the overcurrent protection element in the present embodiment is a conductive material formed on a thin sheet 1 having a flat rectangular shape. A crystalline polymer matrix comprising a polymer matrix 2 and a pair of metal foils 3 adhered to both the front and back surfaces of the conductive polymer matrix 2, and the conductive polymer matrix 2 made of a thermoplastic polymer. 20, carbon black 21 that is conductive particles kneaded in the polymer matrix 20, and an organic material layer 22 coated on the surface of the carbon black 21. It is formed using an organic material that is not compatible with the matrix 20 at the molecular level and is different from the polymer matrix 20.

  The sheet 1 is formed to a thickness of 100 to 300 μm, and the conductive polymer matrix 2 is prepared by mixing carbon black 21 in the polymer matrix 20 having a crystallinity of 40% or more, preferably 50%. The polymer matrix 20 having a crystallinity of 40% or more refers to a composition in which a mass of 40% or more of a component is occupied by polymer crystals at room temperature. The reason why the crystallinity is required to be 40% or more is that the trip characteristic becomes insufficient when the crystallinity is less than 40%.

  The conductive polymer matrix 2 contains 60 to 75% by volume of the polymer matrix 20 and 25 to 40% by volume of carbon black 21. The carbon black 21 is in the range of 25 to 40% by volume when the blending amount is less than 25% by volume, the resistance value of the conductive polymer matrix 2 in the room temperature region (20 ° C. ± 5 ° C.) is too high. This is because it is inappropriate as an overcurrent protection element. Further, when the blending amount exceeds 40% by volume, the resistance value of the conductive polymer matrix 2 in the room temperature region does not become 15 mΩ or more, so that a sufficient trip behavior cannot be expected.

  The conductive polymer matrix 2 is blended with an elastomer having adhesion to metal in order to enhance adhesion to the metal foil 3. Examples of such elastomers include ethylene-α-olefin-diene copolymers such as ethylene-propylene copolymer (EPR) and ethylene-propylene-diene copolymer (EPDM), and styrene-ethylene-butadiene copolymers. 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 an elastomer having a functional group having an affinity for other metals.

  The molecular structural properties such as Mooney viscosity, intramolecular branching, and molecular weight distribution of these elastomers are arbitrary and are not particularly limited. Further, uncrosslinked rubber or non-crosslinked rubber may be obtained by adding a plasticizer such as paraffin oil to improve fluidity, or may be reinforced with other polymers or fillers.

  The most suitable elastomer having adhesiveness to metal is an ethylene-α-olefin copolymer and an ethylene-α-olefin-diene copolymer added with maleic anhydride. As a method for producing this elastomer, peroxide is mainly used, but it may be used in combination with a crosslinking agent or a crosslinking aid.

  In addition, radiation and electron beams are radiated to the overcurrent protection element to impart heat resistance. The radiation (electron beam) radiation improves the adhesiveness (adhesion strength) of the elastomer to about 50 to 500%. To do.

  Examples of the polymer matrix 20 include α-olefins, for example, polymers such as polyethylene having a density of 0.94 or more and homo-type polypropylene, and polyvinylidene fluoride and polyphenylidene ether having a density of 1.95 or more. These polymer matrices 20 are not limited in molecular structure, such as molecular weight, short-chain or long-chain branching state, molecular conformation such as syndiotactic, isotactic, and attack ticks, and are arbitrary. .

  When an overcurrent protection element is used for a prismatic lithium ion battery or the like, it is required that a trip occurs at a temperature around 80 to 90 ° C. Therefore, in this case, a copolymer of vinyl carboxylate and ethylene, typically ethylene-vinyl acetate, ethylene-methyl acrylate, ethylene-ethyl acrylate, ethylene-butyl acrylate and other acrylic esters and ethylene It is preferable to use a mixture of a polymer, an elastomer such as a copolymer of methacrylic acid ester such as ethylene-methyl methacrylate or ethylene-ethyl methacrylate and ethylene, and a polymer matrix 20 such as polyethylene or polypropylene.

  The polymer matrix 20 may be a mixture of polymers having a crystallinity of 40% or more, or a mixture of the polymer and the mixture with other polymers, oligomers, fillers, stabilizers, and / or additives as appropriate.

  Carbon black 21 has a feature that its average particle size is in the range of 70 to 120 nm, preferably about 100 nm, and is high performance and inexpensive. The reason why the average particle size of the carbon black 21, which is the carbon powder, is in the range of 70 to 120 nm is that the trip is insufficient when the average particle size of the carbon black 21 is less than 70 nm. Conversely, when the average particle size of the carbon black 21 exceeds 120 nm, the initial resistance value increases.

The nitrogen specific surface area of the carbon black 21 is preferably 50 m ² / g or less. This is because when the nitrogen specific surface area of the carbon black 21 exceeds 50 m ² / g, the rise of the overcurrent protection element is deteriorated.

  As an organic material for forming the organic material layer 22, various pyrrole-based conductive resins that are not reactive with the overcurrent protection element or the polymer matrix 20 after being covalently bonded to the carbon black 21 are used. Specifically, pyrrole, paratoluenesulfonic acid, or the like is used.

  The metal foil 3 is a rolled foil having a thickness of 50 to 200 μm, preferably 100 to 150 μm, and the surface is chemically roughened to have fine irregularities, and is also used as a lead wire terminal. . Examples of the material of the metal foil 3 include copper, aluminum, zinc, titanium, stainless steel, iron, gold, silver, nickel and the like. Among these, a nonconductive film is difficult to be formed, and is not easily oxidized. Nickel having excellent conductivity is preferable.

  The thickness of the metal foil 3 is in the range of 50 to 200 μm because it is difficult to handle if it is out of the range. It is also difficult to use as a lead terminal.

  The surface of the metal foil 3 is chemically roughened. As this chemical treatment, the metal foil 3 is immersed in a chemical solution, and the surface of the metal foil 3 is utilized by utilizing the chemical dissolution action of the metal. Is a method of roughening the surface. As chemicals, phosphoric acid, chromic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, fluorine and the like are used. These can be used alone or in combination of two or more.

  Although the time which immerses the metal foil 3 in a chemical | medical solution can be set according to the metal material, it is 5 to 60 minutes normally. The temperature at which the metal foil 3 is immersed in the chemical solution may be a room temperature range or may be heated. The metal foil 3 can be roughened on one side or both sides, but when only one side is roughened, a masking film may be attached to one side.

  An example of the chemical surface roughening treatment of the metal foil 3 is as follows. For example, when the metal foil 3 is a nickel rolled foil, nitric acid, hydrochloric acid, hydrogen peroxide, etc. are used as the chemical solution. Is set to conditions of 10 to 90% by mass and a temperature of 30 to 60 ° C., and the metal foil 3 is immersed in the chemical solution for about 5 to 30 minutes to be roughened.

  The surface roughness of the metal foil 3 is determined by using Ra (centerline average roughness), Ry (maximum height), and Rz (ten-point average roughness) measured by a method in accordance with JIS B0601. Is preferred. Ra is 0.5 μm or more, preferably 0.9 to 2.0 μm. The range related to Ra is that, if it is out of this range, the surface roughness of the metal foil 3 varies. Ry is 5.0 μm or more, preferably 10 to 20 μm. Rz is 1.5 μm or more, preferably 3.5 to 7.5 μm.

  In the above, when manufacturing an overcurrent protection element, first, the surface of the carbon black 21 having a DBP oil absorption of 30 to 60 ml / 100 g is deposited by the organic material layer 22 made of a water-soluble pyrrole conductive resin. The polymer matrix 20 and the coated carbon black 21 are put into a pressure kneader that is coated by the above method and adjusted to a temperature of 180 ° C. (not shown), and these are kneaded for 30 minutes to conduct the conductive polymer matrix. 2 is prepared, and the conductive polymer matrix 2 is sheeted with a calender roll to form a sheet 1.

  Next, the metal foils 3 that have already been roughened are laminated on both the front and back surfaces of the sheet 1 and heated and pressed to form an intermediate, and this intermediate is irradiated with an electron beam so that its conductive polymer matrix After cross-linking 2, the overcurrent protection element can be manufactured by cutting into a predetermined size.

  According to the above-described configuration, the organic material layer 22 covering the surface of the carbon black 21 is not compatible with the polymer matrix 20 at the molecular level, and a pyrrole conductive resin different from the polymer matrix 20 is used. Therefore, it is possible to effectively suppress and prevent a decrease in the rate of change in resistance accompanying a temperature rise, and to obtain sufficient characteristics as an overcurrent / overheat protection element.

  In addition, when a good trip behavior is obtained at the same time, it is not necessary to use carbon black 21 having a small DBP oil absorption amount or a structure, so that an overcurrent / overheat protection element excellent in resistance value and trip behavior can be obtained. . Moreover, since the average particle diameter of the carbon black 21 is in the range of 70 to 120 nm and the DBP oil absorption is in the range of 30 to 60 ml / 100 g, the dispersion state of the carbon black 21 is very good. Therefore, it is possible to ensure a good trip characteristic and obtain a sufficient interruption effect when an abnormal overcurrent occurs.

  In addition, since the kneading time of the polymer matrix 20 and the carbon black 21 during the production can be greatly shortened and the kneading energy can be reduced, the production method can be made smooth, efficient and easy. Become. Further, since the metal foil 3 can be used as a lead wire terminal, it is not necessary to newly connect a lead wire, and the number of parts can be greatly reduced.

  Furthermore, since the surface of the metal foil 3 is chemically roughened to form fine irregularities, and the polymer matrix 20 is intruded into the irregularities, strong adhesion between the metal foil 3 and the polymer matrix 20 is expected due to the anchor effect. it can.

Embodiments of an overcurrent protection element and a method for manufacturing the same according to the present invention will be described below together with comparative examples.
The overcurrent protection elements of Examples and Comparative Examples were manufactured, and the PTC characteristics of each overcurrent protection element were summarized in the graph of FIG.

Example First, the material shown in Table 1 containing carbon black was added to 500 ml of pure water in a 1 liter beaker, stirred at room temperature for about 1 hour, and filtered under reduced pressure to separate pure water and carbon black at 70 ° C. Was dried under reduced pressure for 8 hours to produce carbon black coated with an organic material layer composed of pyrrole.

  Next, the polymer matrix shown in Table 2 and the coated carbon black were kneaded by a pressure kneader adjusted to a temperature of 180 ° C. to prepare a conductive polymer matrix, and this conductive polymer matrix was calendered Sheeting with a machine formed a sheet having a thickness of 200 μm.

Next, the sheet is sandwiched between a pair of roughened metal foils, set in a press molding machine, heated (250 ° C.) and pressurized (5 kgf / cm ² ), and the sheet, the pair of metal foils, Formed an intermediate having a thickness of 400 μm. When the intermediate is formed in this manner, the intermediate is irradiated with an electron beam of 30 Mrad by an electron beam crosslinking apparatus to crosslink the conductive polymer matrix, and then cut into a size of 5 mm × 12 mm to obtain an overcurrent protection element. Manufactured.

Comparative Example A pressure kneader adjusted to a temperature of 180 ° C. was charged with the polymer matrix shown in Table 3 and ordinary carbon black not coated, and kneaded to prepare a conductive polymer matrix. This conductive polymer matrix was sheeted with a calendering machine to form a sheet having a thickness of 200 μm. Others were the same as in the example.

Measurement of PTC characteristics Connect a wire to each manufactured overcurrent protection element, connect the end of the other wire to a resistance measuring instrument, set the overcurrent protection element in the oven, measure its resistance value, The initial resistance value (resistance value at 20 ° C. before temperature rise), the return resistance value, and the return rate of each overcurrent protection element are summarized in Table 4, and the PTC characteristics are summarized in FIG.

  Specifically, the temperature was increased from 20 ° C. every 10 ° C. to 160 ° C., and the resistance value was measured by holding the temperature for 10 minutes at each measurement temperature. When the temperature reached 160 ° C., this time, on the contrary, the temperature was sequentially cooled every 10 ° C. to 20 ° C., and the resistance value was measured while maintaining the temperature for 10 minutes at each measurement temperature. When the resistance value at 20 ° C. was measured, the resistance value after 1 hour was measured by keeping at 20 ° C. for 1 hour, and this resistance value was defined as the final return resistance value.

  As a result of the measurement, as shown in FIG. 3, in the case of the overcurrent protection element of the example, a rapid and good PTC characteristic was obtained. On the other hand, in the case of the overcurrent protection element of the comparative example, only insufficient PTC characteristics could be obtained.

It is a section explanatory view showing an embodiment of an overcurrent protection element concerning the present invention. It is principal part expansion explanatory drawing which shows the conductive polymer matrix in embodiment of the overcurrent protection element which concerns on this invention. It is a graph which shows the PTC characteristic of the Example of the overcurrent protection element which concerns on this invention, and a comparative example.

Explanation of symbols

1 Sheet 2 Conductive Polymer Matrix 3 Metal Foil 20 Polymer Matrix 21 Carbon Black (Carbon Particles)
22 Organic material layer

Claims (6)

An overcurrent protection element whose electric resistance value increases depending on temperature, comprising a polymer matrix, conductive particles contained in the polymer matrix, and an organic material layer covering the surface of the conductive particles. Including
An overcurrent protection element, wherein an organic material layer is formed using an organic material that is not compatible with a polymer matrix at a molecular level and is different from the polymer matrix.   The overcurrent protection element according to claim 1, wherein the polymer matrix is a thermoplastic polymer.   The overcurrent protection element according to claim 1, wherein the conductive particles are carbon particles.   The overcurrent protection element according to claim 1, 2, or 3, wherein conductivity is imparted to the organic material.   The overcurrent protection element according to any one of claims 1 to 4, wherein the organic material is a pyrrole-based material having no reactivity with the polymer matrix.   6. The method of manufacturing an overcurrent protection element according to claim 1, wherein the surface of the conductive particles is coated with an organic material layer, and the coated conductive particles are mixed and dispersed in a polymer matrix. A method for manufacturing an overcurrent protection element.

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