JP2002158101A - Overcurrent preventing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent preventing element where a conductive matrix and a variety of metallic foils can be firmly bonded and superior current cut-off function can be obtained as it shows remarkable trip. SOLUTION: In an overcurrent preventing element, a metallic foil is sticked to each of both sides of a sheet-like body consisting of polymer of 100 pts.vol. of crystallization degree of 60% or more and conductive particle of 11 to 1000 pts.vol. An elastomer selected from (A) or a mixture of 10 to 900 pts.vol. constituted of it are mixed in a composition constituting a sheet-like body. (A) Elastomer selected from the following or a mixture of (A-3). (A-1) Elastomer with carboxylic acid or nonhydrate thereof. (A-2) Elastomer with hydroxyl group and epoxy group. (A-3) A mixture whose constituent element is elastomer of (A-1), (A-2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection element having a characteristic of increasing electric resistance depending on temperature (hereinafter referred to as PTC characteristic).

[0002]

2. Description of the Related Art In recent years, with the development of electronics technology, an overcurrent prevention element has been used. When an electric current is applied, this overcurrent prevention element allows a large current to flow at a low resistance at the beginning of energization. However, when the temperature rises, the resistance value increases to lower the power, and finally, an excellent function of stabilizing the current and temperature is exhibited. Such an overcurrent prevention element is roughly classified into a ceramic type and a polymer type. The latter overcurrent prevention element is provided with a sheet-like body constituting a polymer,
Metal foils made of nickel or the like are respectively adhered to the front and back surfaces of the sheet. The conductive composition constituting the sheet-shaped body (hereinafter, referred to as a conductive composition) is a polymer in which conductive particles are dispersed, and when a normal current is applied, a large current flows at a low resistance, When a sudden overcurrent occurs, the resistance becomes high and the conduction is cut off, preventing conduction of the overcurrent and effectively protecting the electronic circuit.

In order to enhance such a blocking function, a polymer having a high degree of crystallinity, such as high-density polyethylene, is used for the conductive composition as a conductive matrix. The reason why the crystalline polymer having high crystallinity is used is as follows.
When the melting point of polyethylene is reached due to heat generated by overload, the polymer crystals melt and the volume expands rapidly, the distance between individual conductive particles increases, and the resistance increases (hereinafter referred to as trip). ,That's what it means.

[0004]

However, a crystalline polymer has a large problem in adhesion to a metal foil because of a large molding shrinkage. In view of this point, Japanese Patent Application Laid-Open No. 60-1969
No. 01 discloses a technique for obtaining an adhesive strength by roughening a metal foil. However, in this case, the adhesive strength is limited to about 1.0 kgf / cm (90 ° peel test). Commercially available foils to be roughened are limited to copper, nickel and the like. Therefore, for low-resistance metals such as gold, silver and palladium, and cheap metals such as stainless steel and iron,
Since it is not roughened in a commercial product, it cannot be selected.

On the other hand, a composition in which conductive particles are mixed with a simple substance of ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate is also used, and according to this, it is possible to obtain an adhesive strength to the extent that the foil is broken. it can. However, there is a problem that the trip does not appear remarkably because the composition has few crystal components.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has been made in consideration of the above circumstances. It is possible to firmly adhere a conductive matrix to various kinds of metal foils, and to obtain an excellent current interrupting function by a remarkable trip. It is intended to provide a current prevention element.

[0007]

Means for Solving the Problems The present inventor has proposed that, in order to impart adhesion between a metal foil and a conductive composition without impairing the trip characteristics of the crystalline polymer, the conductive composition must be
It was presumed that a polymer having a functional group having an affinity for a metal should be blended, and further studies were made. As a result, the fact that the polymer needed to be an elastomer was found, and the present invention was completed. That is, according to the first aspect of the present invention, in order to achieve the above object, a crystallinity of 60
% Polymer 100% by volume, conductive particles 11 to 100
A sheet-like body composed of 0 volume parts, in which metal foils are adhered to the front and back surfaces of the sheet-like body. In the composition constituting the sheet-like body, an elastomer selected from the following (A) or a constituent component thereof 10 to 900 parts by volume of the mixture described above. (A) an elastomer selected from the following or (A-
The mixture of 3). (A-1) An elastomer having a carboxylic acid or an anhydride thereof. (A-2) An elastomer having a hydroxyl group or an epoxy group. (A-3) A mixture containing the elastomer of (A-1) or (A-2) as a constituent.

[0008] The above (A) can be an ethylene-α-oleefin-diene copolymer obtained by adding maleic anhydride. Further, the above (A) may be a styrene-butadiene-based polymer obtained by adding maleic anhydride.

The compounding formulation of the conductive composition of the overcurrent prevention element according to the present invention essentially comprises a crystalline polymer and a polymer having an adhesive property to a metal, and is mixed with conductive particles. . First, the material used for the overcurrent prevention element according to the present invention will be described in detail.

[0010] The crystalline polymer used in the formulation of the conductive composition in the present invention is limited to those having a crystallinity of 60% or more. Examples of such polymers include polyethylene having a density of 0.94 or more, homo-type polypropylene, and crystalline polymers such as polyvinylidene fluoride and polyphenylidene ether having a density of 1.95 or more. In the present invention, these can be freely selected. And, the crystalline polymer in the present invention, if it is the above-mentioned polymer, a molecule having a molecular weight, a short-chain or long-chain branched state, a molecule such as a syndiotactic, isotactic, or atactic stereotacticity of a molecule. There are no restrictions on the structural features, and they are optional.

Incidentally, a general overcurrent prevention element has a temperature of 130 ° C.
Since it is usual to interrupt the current with a certain degree of heat, it is preferable to select polyethylene having a melting point in the range of 120 to 140 ° C. Among these polyethylenes, it is appropriate to select a high-density polyethylene having a density of more than 0.93. Among these high-density polyethylenes, those having a density of more than 0.96 have a crystallinity of more than 90% and have a trip characteristic. Even better because it is excellent.

The (A) metal-adhesive elastomer used in the formulation of the conductive composition according to the present invention may be used in combination with a metal having an acidic functional group such as carboxylic acid or anhydride thereof, a hydroxyl group or an epoxy group. It is limited to a polymer having a functional group having affinity. The mixture of (A-3) in claim 1 means a mixture containing these elastomers as main components. That is, ethylene-propylene copolymer (EP
R), ethylene-propylene-diene copolymer (EPD
M) and other uncrosslinked styrene rubbers such as styrene-ethylene-butadiene copolymers, styrene rubbers, polyester rubbers, acrylic rubbers, butadiene rubbers, isoprene rubbers, natural rubbers, etc. Elastomers obtained by introducing the above-mentioned functional groups into the rubber correspond to the above.

[0013] Elastomers are generally defined as filamentous polymers with active molecular motion at room temperature.
The same definition is applied to the present invention. These elastomers have arbitrary molecular structural characteristics such as Mooney viscosity, intramolecular branching, and molecular weight distribution, and are not particularly limited in the present invention. Also, a mixture of several kinds may be used.

As a method for producing the above elastomer having a functional group, a monomer or polymer of an unsaturated carbon having the above functional group is added to an elastomer having an unsaturated bond (for example, an uncrosslinked rubber) by using peroxide. Mainly the method of production. However, the production method can be freely selected in the present invention, such as by using a crosslinking assistant or a crosslinking agent together. (A) described in claim 1 of the present invention.
May be a single polymer or a mixture of plural types.

The mixture of (A-3) is a mixture containing the above polymer as a main component. For example, it refers to a rubber obtained by adding a plasticizer such as paraffin oil to the uncrosslinked rubber or non-crosslinkable rubber to improve the fluidity, or reinforced with another polymer or filler.

[0016] The inventions of claims 2 and 3 are a preferred formulation comprising selecting an elastomer obtained by adding maleic anhydride to an ethylene-α-olefin-diene copolymer and a styrene-ethylene-butadiene copolymer. . These elastomers can be obtained by subjecting the raw materials ethylene-α-olefin-diene copolymer and styrene-ethylene-butadiene copolymer to an addition reaction with maleic acid.
The production method is generally performed using a peroxide, but can be arbitrarily selected, for example, by using a crosslinking aid or a crosslinking agent together.

The ethylene-α-olefin-diene copolymer according to claim 2 is a type of α-olefin or a diene. For the α-olefin, propylene having 3 carbon atoms is generally used, and for the diene, ethylnorporene is used. And dicyclopentadiene, vinyl norpolene and the like are usually used. However, the present invention is not particularly limited. The molecular structural characteristics such as the ethylene composition ratio, diene content, Mooney viscosity, intramolecular branching, and molecular weight distribution are also arbitrary and are not particularly limited. Therefore, the fluidity may be modified by the addition of paraffin oil, or the polymer may be reinforced with another polymer or filler. The amount of maleic anhydride to be added to the polymer is not particularly limited, but commercially available ones are 0.2 to 5.5% by weight, and the larger the amount, the better.

The amount of the polymer selected from (A) or the matrix comprising the same is less than 10 parts by volume relative to 100 parts by volume of the crystalline polymer. If the content is not more than 100 parts by volume, the crystal component is small and the trip performance is insufficient.

Examples of the conductive particles in the present invention include carbon-based fine powders such as graphite, graphite, and expanded graphite; metal fine particles such as gold and silver; metal oxide fine particles of metal oxide or metal oxide dripped by other atoms; Examples include fine particles of a conductive polymer such as polyaniline and polyacetylene. The average particle size is not particularly limited, but may be 1000
If it is larger than μm, it is difficult to hold the matrix. There is no lower limit for the particle size, and 0.1 μm to 10 nm is desirable. Further, in the present invention, several kinds of conductive particles may be combined.

The compounding amount of the conductive particles depends on that of the crystalline polymer.
When the total amount of the polymer or matrix of (A) is 100 parts by volume, a low resistance cannot be obtained with less than 10 parts by volume,
It is unsuitable as an overcurrent prevention element. Conversely, if the volume is more than 100 parts by volume, processing becomes difficult because of too many particles. Therefore, the amount of the conductive particles is preferably in the range of 10 to 100 parts by volume, preferably 30 to 60 parts by volume. In addition, in this invention, since (A) is 10-900 volume part with respect to crystalline polymer 100 volume part of crystalline polymer, the compounding quantity of an electroconductive particle will be 11-1000 volume part. .

The overcurrent prevention element according to the present invention is formed in such a form that the sheet-shaped conductive composition is sandwiched between metal foils such as nickel and copper. Conventional conductive composition of overcurrent prevention element lacks adhesion to metal foil, so foil obtained by electrodeposition (having dendrite-like irregularities of several μm), roughening treatment such as press molding and slash Foil or the like is used. On the other hand, according to the present invention, since there is no limitation on the surface condition of the foil, it is possible to use a smooth foil which has been conventionally difficult to adhere and has been avoided. For example, in the past, since it was limited to foils subjected to surface roughening treatment, only materials such as nickel and copper could be selected, but according to the present invention, gold, platinum, low-resistance metals such as palladium, Inexpensive materials such as stainless steel and iron can be selected. That is, according to the overcurrent prevention element of the present invention, there is no limitation on the material of the metal foil. Similarly, the thickness is not limited except for practical use and economy.

The overcurrent preventing element according to the present invention is mixed by a kneading device such as a pressure kneader, a banbury, a two-roll, an extruder, and sheeted by an extruder or a calender, and then laminated with a metal foil. After that, it is punched and formed into an arbitrary shape, but a manufacturing method and a manufacturing apparatus can be freely selected. Further, in general, in order to enhance PTC characteristics, post-treatments such as irradiation or irradiation with an electron beam to perform cross-linking, or tripping several tens of times to develop uneven distribution of conductive particles are performed. It is also preferable to perform such post-processing. The irradiation dose at this time is desirably about 30 to 200 kGry for radiation, and about 3 to 20 MRa for electron beams. By such irradiation of radiation or electron beam, the overcurrent prevention element according to the present invention has an adhesive strength (peeling strength) with metal of 50 to 500.
%.

[0023] In some cases, solder is laminated on the entire surface or a part of a commercially available overcurrent prevention element, but it is also necessary to laminate solder on the overcurrent prevention element according to the present invention. Can be. The overcurrent protection element according to the present invention can be formed by a disc shape, a terminal device, or the like by a stamped shape or a method of laminating solder.
e, Strap, SMD, etc., are used for protection of primary and secondary batteries, protection of motors such as automobiles, protection of speakers, protection of rechargeable batteries of mobile phones, protection of computer circuits, etc. You.

[0024]

EXAMPLES Hereinafter, examples of the overcurrent protection device according to the present invention will be described together with comparative examples. However, the overcurrent protection device according to the present invention is not limited to the description of the following examples. Below, the evaluation of the adhesion between the metal foil and the conductive composition
(90 ° peeling) and PTC characteristics are evaluated. Details of the evaluation method are as follows.

Evaluation of Adhesion between Metal Foil and Conductive Composition (90 ° Peeling Test)
After the metal foil was peeled off by 30 mm, the stress required for peeling was measured by a tensile tester (Tensilon, trade name, manufactured by Toyo Seiki Co., Ltd.). The tensile tester was equipped with a chuck which was lowered vertically from above, and was measured by pulling. As a specific method of the measurement, first, a double-sided tape was stuck to the test piece, horizontally and firmly fixed to a 50 × 200 mm metal plate, and the end of the peeled metal foil was sandwiched by a chuck. / Min and peeled off. As the peeling progressed, the metal foil to be peeled was shifted by hand so that the angle between the horizontal plane and the metal foil was 90 °.

PTC Characteristics A metal foil and a conductive composition are integrated and cut into a size of 10 × 10 mm, electric wires are joined to both metal foils by soldering, and each electric wire is connected to a resistance measuring instrument. The resistance of the overcurrent prevention element was measured. As a specific method of measurement,
First, the measurement environment was set to 30, 80, 100, 110, 12
The temperature was set to 0, 130, and 140 ° C., and the overcurrent prevention element was set in an oven to start measurement. Then, the temperature was gradually raised from 30 ° C., and when the temperature reached the measurement temperature, the temperature was maintained for 5 minutes. At that time (when the temperature was maintained for 5 minutes), the resistance value was plotted.
After plotting, the temperature was raised to the next measurement temperature and measured.

EXAMPLES / COMPARATIVE EXAMPLE 1 Kneading was performed for 20 minutes using a pressure kneader adjusted to a temperature of 230 ° C.
Four kinds of kneaded products having the composition shown in Table 1, that is, a conductive composition were obtained. In Table 1, 1-1, 1-2, and 1-3 are conductive compositions of the overcurrent protection device according to the present invention, 1-4 are conventional compositions, and 1-5 is a comparison with the present invention and conventional examples. It is an example.

[0028]

[Table 1]

Next, before cooling the conductive composition, the temperature was set to 180 ° C.
Into two rolls temperature-controlled to a thickness of 0.50 mm
And a metal foil shown in Table 2 was superimposed on the front and back surfaces of the sheet. The sheet was set in a press molding machine adjusted to a temperature of 230 ° C. and pressurized. The mixture was cooled until the temperature reached ℃ and removed. At this point, samples were obtained from the conventional compounding formulas 1-4 and 1-5 because of the roughened nickel foil (foil A in Table 2).
Only did not adhere to the other foils, so no sample could be obtained.

[0030]

[Table 2]

About 14 points obtained as samples,
Irradiate 15 MPa electron beam with an electron beam
The resultant was cut into a size of 0 × 10 mm to obtain an overcurrent prevention element. When the PTC characteristics of these overcurrent prevention elements were evaluated, the results shown in Table 3 were obtained. Also, 10 × 10
The peel strength (90 ° peeling) required for peeling the metal foil by cutting it to a size of 0 mm was measured.

[0032]

[Table 3]

As shown in Table 3, the conductive composition according to the present invention adhered to any metal foil. On the other hand, the composition of the conventional formulation was able to adhere only to the roughened metal foil. Also, 1-5 containing polyethylene to which maleic anhydride, which is a kind of carboxylic acid, was added, could be adhered only to the roughened metal foil. On the other hand, it was confirmed that the conductive composition according to the present invention adhered to all metal foils and had PTC characteristics suitable for practical use as an overcurrent prevention element.

EXAMPLE / COMPARATIVE EXAMPLE 2 Kneading was performed for 20 minutes using a pressure kneader adjusted to a temperature of 230 ° C.
Ten kinds of kneaded products having the composition shown in Table 4, that is, conductive compositions were obtained. 2-2, 2-4, 2-5, 2 in Table 1
Reference numerals -6, 2-7, and 2-8 are conductive compositions of the overcurrent prevention element according to the present invention, and 2-1 to 2-3, 2-9, and 2-10 are comparative examples to the present invention.

[0035]

[Table 4]

Next, before cooling the conductive composition, the temperature was set to 180 ° C.
Into two rolls temperature-controlled to a thickness of 0.50 mm
And a nickel foil having a smooth surface (B in Table 1) is superimposed on both the front and back surfaces of the sheet.
It was set in a press molding machine adjusted to a temperature of 30 ° C., pressurized, cooled with cooling water until the temperature reached 50 ° C., and taken out. Since the conductive composition 2-1 did not adhere to the metal foil, a sample could not be obtained. Further, the conductive composition 2-10 was not able to obtain a sheet-like body due to too much carbon.

Eight points obtained as samples were irradiated with an electron beam of 15 MPa by an electron beam
The resultant was cut into a size of × 10 mm to obtain an overcurrent prevention element.
When the PTC characteristics of these overcurrent prevention elements were evaluated, the results shown in Table 5 were obtained. Also, 10 × 100m
The peel strength (90 ° peeling) required for peeling the metal foil by cutting into a size of m was measured.

[0038]

[Table 5]

As shown in Table 5, 2-2 according to the present invention,
The PTC characteristics of the overcurrent protection elements in 2-4, 2-5, 2-6, 2-7, and 2-8 were found to be practical. In particular, the trip characteristics of 2-5 and 2-6 were remarkable and excellent. On the other hand, in Comparative Example 2-3, the resistance was too high and did not satisfy the characteristics as PTC. Also, 2-9 had no trip and could not be expected to have the function of cutting off overcurrent.

[0040]

As described above, according to the present invention, the degree of freedom in selecting the material of the metal foil in the overcurrent prevention element is increased,
Low-resistance metals such as platinum and palladium, and inexpensive materials such as stainless steel and iron can be selected. Therefore, there is an effect that the conductive matrix and various kinds of metal foils can be firmly bonded. In addition, since the trip appears remarkably, an excellent current interruption function can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 101/00 C08L 101/00 101/06 101/06

Claims (3)

[Claims] 1. An overcurrent prevention element comprising a sheet-like body comprising 100 parts by volume of a polymer having a crystallinity of 60% or more and 11 to 1000 parts by volume of conductive particles and metal foils attached to both front and back surfaces thereof, An overcurrent prevention element, comprising an elastomer selected from the following (A) or 10 to 900 parts by volume of a mixture containing the same as a component, in a composition constituting the sheet-like body. (A) an elastomer selected from the following or (A-
The mixture of 3). (A-1) An elastomer having a carboxylic acid or an anhydride thereof. (A-2) An elastomer having a hydroxyl group or an epoxy group. (A-3) A mixture containing the elastomer of (A-1) or (A-2) as a constituent. 2. The overcurrent protection device according to claim 1, wherein (A) is an ethylene-α olefin-diene copolymer obtained by adding maleic anhydride. 3. The overcurrent protection device according to claim 1, wherein (A) is a styrene-butadiene polymer to which maleic anhydride is added.