JPH10125504A - Organic positive characteristic thermistor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To bond an electrode and a resistor firmly and reduce and uniformize a surface resistance between both thereof by applying anchor conductive grain to front and rear surfaces of a resistor by burying a part thereof in organic polymer and by forming a metallic layer in front and rear of the resistor. SOLUTION: A resistor 3 is formed by mixing conductive grain 2 to organic polymer 1. Anchor conductive grain 4 is partially buried and applied to front and rear surfaces of the resistor 3. An electrode 5 is mounted thereon. In the process, an average grain diameter of the anchor conductive grain 4 is made larger than that of the conductive grain 2 dispersed in the organic polymer 1, and an average grain diameter of the anchor conductive grain 4 is set about 1 to about 50μm. Thereby, a highly reliable organic positive characteristic thermistor is manufactured in which a face resistance between the electrode 5 and the resistor 3 is small and uniform, a resistance value is small and on-off repetition characteristic is excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a positive organic material comprising a resistor formed by forming a composition obtained by dispersing conductive particles in an organic polymer into a sheet, and forming electrodes on the front and back surfaces of the resistor. The present invention relates to a thermistor and a method of manufacturing the thermistor, and more particularly, to a structure of an electrode and a method of forming the electrode.

[0002]

2. Description of the Related Art In an organic positive temperature coefficient thermistor, in order to form electrodes on the front and back surfaces of a sheet-shaped resistor, a metal foil is heat-pressed on the front and back surfaces of a sheet-shaped resistor (US Pat. No. 4,426,633). A sheet-shaped resistor in which conductive particles are dispersed in a polymer is etched on the front and back surfaces to expose the conductive particles on the front and back surfaces, and an electrode layer is formed by electroplating or chemical plating (Japanese Patent Publication No. 4-44401). No.).

[0003]

However, US Pat.
As described in Japanese Patent No. 426633, a thermistor in which a metal foil is heated and pressed on the front and back surfaces of a sheet-shaped resistor has a large contact resistance at an interface between the surface of the resistor and an electrode made of the metal foil, and has a high contact resistance. Because it is non-uniform, a high resistance layer is formed,
There is a problem in that the interface generates heat due to the repetition of on-off, and the resistance value increases due to a difference in thermal expansion between the electrode and the interface, and there is a problem in reliability.

Further, as described in Japanese Patent Publication No. 4-44001, an electrode is plated by exposing conductive particles on the front and back surfaces of a resistor by etching, and the conductive particles on the front and back surfaces of the resistor and the electrode are etched by etching. However, in order to secure the characteristics of the thermistor, the content of the conductive particles in the resistor is limited to a low density of about 20% to 30% by volume. There was a problem that adhesion strength could not be obtained.

[0005] In view of the above problems, the present invention makes it possible to make the electrode and the resistor firmly adhere to each other, reduce the interface resistance between them, and make the interface resistance uniform over the entire electrode surface.
Accordingly, it is an object of the present invention to provide an organic positive temperature coefficient thermistor having a low resistance value and excellent on-off repetition properties, and a method for manufacturing the same.

[0006]

In order to achieve the above object, an organic positive temperature coefficient thermistor of the present invention is formed into a sheet by forming a composition obtained by dispersing conductive particles in an organic polymer into a sheet, and the resistor is formed. In an organic positive temperature coefficient thermistor having electrodes formed on both surfaces of a body, the conductive particles for anchoring an electrode are partially embedded in an organic polymer on the front and back surfaces of the resistor, and the conductive particles for anchor of the electrode are adhered. Wherein a metal layer is formed on the front and back surfaces of the resistor on which an electrode is formed to form an electrode (claim 1).

As the organic polymer, any crystalline polymer can be used without any particular limitation. For example, polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, ionomer resin or a copolymer thereof is generally used. Is used, but other organic polymers may be used as long as similar properties can be obtained. Also,
As the conductive particles dispersed in these organic polymers,
Metal powder such as carbon black, graphite or nickel, or conductive ceramic powder such as titanium carbide or tungsten carbide can be used, but any other powder that satisfies the required conductivity and heat resistance can be used. May be used.

[0008] The organic positive temperature coefficient thermistor composition obtained by dispersing conductive particles in an organic polymer is prepared by heating and kneading with a kneading machine such as a Banbury mixer and a mixing roll. At this time, kneading aids such as antioxidants and dispersants may be added. Further, it is formed into a sheet or film by an extruder or a hot press. In this case, although not necessary, in order to enhance the crosslinking efficiency, irradiation with electron beams, electron beam crosslinking or chemical crosslinking with the addition of a crosslinking aid, or silane compound polymerization in the presence of a free radical generator are performed. After grafting to PTC, the polymer is subjected to water crosslinking in the presence of a silanol condensation catalyst to perform water crosslinking, thereby suppressing the fluidity of the polymer after PTC expression and stabilizing the resistance value. be able to.

The conductive particles for anchoring are stuck and adhered to the surface of the resistor made of the molded body thus obtained. In this case, the conductive particles for anchor attached to the surface of the resistor may be different from the conductive particles dispersed in the organic polymer. As the conductive particles for anchor, preferably, for the purpose of reducing the interface resistance between the resistor and the electrode,
It is preferable to use metal powder, and particularly to use nickel powder excellent in heat resistance (oxidation resistance). Further, conductive ceramics can be used because of their excellent heat resistance.

The shape of the conductive particles for anchor is not particularly limited, and examples thereof include spherical, needle-like, scaly, spike-like having projections on the surface, and filament-like spike-like fine particles. The average particle size of the conductive particles for anchoring is set to 1 μm or more in order to obtain close contact with the resistor (anchor effect) and contact with the conductive particles in the resistor, and 50 μm to reduce the thickness of the thermistor. It is preferable to set the following (claim 3). In the organic positive temperature coefficient thermistor, when metal powder or ceramic powder is used as the conductive particles dispersed in the organic polymer, these conductive particles having an average particle size of less than 5 μm are used. Preferably, the average particle diameter is larger than the conductive particles dispersed in the organic polymer (claim 2). In recent years, in the use of a thermistor for incorporation in a secondary battery or a small motor for automobiles, further reduction in the thickness of the thermistor has been demanded. The average particle size of the conductive particles for anchor cannot be so large, and in order to meet these requirements and to obtain an excellent anchor effect, the average particle size of the conductive particles for anchor is more preferably 5 μm or more,
It is 15 μm or less.

Further, in the thermistor of the present invention, the material of the conductive particles dispersed in the organic polymer and the material of the conductive particles for the anchor need not necessarily be the same, and a structure in which the materials are different (claim) Item 4) is also adopted.

In the thermistor according to the present invention, the electrode is preferably formed by plating, and more preferably, by nickel plating, chromium plating, or solder plating on nickel plating.

[0013] In the method for producing a thermistor of the present invention, a composition formed by dispersing conductive particles in an organic polymer is formed into a sheet to form a resistor, and conductive particles for anchoring an electrode are formed on the front and back surfaces of the resistor. And depositing a part of the conductive particles for anchor into a resistor, and plating the metal layer on the front and back surfaces of the resistor with the conductive particles for anchor attached to form an electrode. Item 6).

When the method of the present invention is carried out, before the conductive particles for anchor are attached to the front and back surfaces of the resistor, the front and back surfaces of the resistor are mechanically etched by sandpaper or sandblasting or chemically etched. The surface may be roughened in advance by performing an etching process. The method of applying the conductive particles for anchoring to the front and back surfaces of the resistor is not particularly limited. For example, heat is applied to the molded body to directly blow the front and back surfaces in a softened state. A method of preparing a highly-filled paste with a content of about 70% by volume, printing it on the front and back surfaces of a resistor by a doctor blade method or the like, and drying the same, fixing toner in a copying machine, and forming an electrostatic capacitor in the same manner as in a sandpaper manufacturing method. Examples of the method include a method in which conductive particles are adsorbed on the front and back surfaces of the resistor by a coating method, and a method in which conductive particles are rubbed into the front and back surfaces of the resistor by vibration using a fusion method in which vibration is applied to the resistor by ultrasonic waves. In addition, as a plating method, a vapor phase plating method such as sputtering or vacuum deposition is used in addition to chemical plating and electroplating.

[0015]

According to the first aspect of the present invention, a part of the conductive particles for anchoring is buried in the front and back surfaces of the resistor, and the metal serving as the electrode is formed as if the front and back surfaces were roughened by the conductive particles. In addition, the adhesion strength of the electrode is increased, and the interface resistance between the electrode and the resistor can be made uniform over the entire surface of the resistor by making the surface density of the resistor of the conductive particles for anchor uniform. In addition, since the conductive particles provided separately from the resistor are used as the anchor instead of using the conductive particles in the resistor as the anchor of the electrode, the density of the conductive particles for the anchor on the front and back surfaces of the resistor is equal to the density in the resistor. Since the density can be set to a suitable higher density without being restricted by the density of the conductive particles, the bonding strength of the electrode is increased, and the interface resistance is further reduced in combination with the roughening effect.

In the present invention, the average particle size of the conductive particles for the anchor is larger than that of the conductive particles dispersed in the organic polymer, that is, the conductive particles generally dispersed in the resistor and the conductive particles for the anchor. By making the average particle size of the particles different and increasing the average particle size of the conductive particles for anchor, an excellent anchor effect can be obtained.

According to the third aspect, since the average particle diameter of the conductive particles for anchor is 1 μm or more, the object of embedding the conductive particles in the resistor and roughening the surface of the resistor can be achieved. Further, the average particle diameter of the conductive particles for anchor is 50 μm.
By the following, it is possible to meet the demand for a thin thermistor.

According to the present invention, the conductive particles in the resistor and the conductive particles for anchoring on the surface of the resistor are made of different materials, so that the conductive particles having characteristics suitable for the intended use can be used. Become.

According to the fifth aspect of the present invention, since the electrode is formed of a metal layer formed by nickel plating, chromium plating, or solder plating on nickel plating, an electrode having relatively excellent heat resistance (oxidation resistance) can be obtained. Also, lead soldering is possible.

In the method of manufacturing a thermistor according to the present invention, the conductive particles for anchor are deposited on the surface of the resistor, and then a part of the conductive particles for anchor is embedded in the resistor, so that the conductive particles for anchor become resistant. In addition to being firmly fixed to the body, the conductive particles for the anchor also come into contact with the conductive particles in the resistor to establish electrical continuity, and further, an electrode such as a metal is provided on the surface of the resistor roughened by the conductive particles for the anchor. By forming the electrode by plating, the electrode layer is firmly fixed to the resistor.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example) Tungsten carbide powder as conductive particles was mixed with polyvinylidene fluoride at a ratio of 30% by volume and kneaded by a mill at 200 ° C. for 30 minutes.
As shown in (1), a sheet-shaped formed body (resistor) 3 having a thickness of 0.3 mm was obtained by hot pressing. This sheet-like molded body 3
It was placed on a hot plate at 0 ° C., and while heated, nickel particles having an average particle size of 12 μm were sprayed on the surface of the sheet-like molded body with an air gun. Similarly, nickel particles were sprayed on the back surface of the sheet-like molded body. In this state, as shown in FIG. 2 (B), the nickel particles 4 serving as the conductive particles for the anchor are:
Since most of the conductive particles are merely attached to the front and back surfaces of the sheet-like molded body 3, a part of the conductive particles is embedded in the sheet-like molded body again by hot pressing as shown in FIG. Was.

Thereafter, an electrode 5 shown in FIG. 2D was formed by nickel plating having a thickness of about 20 μm. This nickel plating is performed by performing electroless plating of about 1 μm with a nickel-phosphorus (Ni-P) -based electroless plating solution (phosphorus concentration: about 10%) and then using a Watt bath (nickel sulfate, nickel chloride, boric acid). ), And nickel plating with a total thickness of 20 μm was performed.

(Comparative Example) After the front and back surfaces of the same sheet-shaped molded body as in the example were etched with sandpaper # 320, nickel plating was applied to a thickness of 20 μm by the same process as described above.
m.

The sheet-like molded articles of the above Examples and Comparative Examples were
It was punched into a circle having a diameter of 0 mm to obtain an organic positive temperature coefficient thermistor sample. 1A is a sectional view of an embodiment of the present invention, FIG. 1B is a partially enlarged view thereof, and FIG.
FIG. As can be seen from FIG. 1B, the conductive particles (tungsten carbide powder) 2 are mixed with the organic polymer (polyvinylidene fluoride) 1 to form the resistor 3, and the conductive particles for anchor are provided on the front and back surfaces of the resistor 3. (Nickel particles) 4 are partially embedded and applied, and an electrode (nickel plating layer) 5 is formed thereon.

For these samples, an initial resistance (Ω) and an on-off cycle test (DC 16 V, 15
A, a resistance after 15 seconds on and 165 seconds off for 100 times) and a resistance change rate (resistance after the cycle test / initial resistance) were determined. The results are as shown in Table 1.

[0026]

[Table 1]

As is clear from Table 1, in the case of the embodiment of the present invention, the initial resistance is smaller than that of the comparative example.
In addition, the rate of resistance change by the cycle test is significantly reduced.

[0028]

According to the first aspect of the present invention, the conductive particles for anchoring the electrode are applied to the surface of the resistor by partially burying the organic polymer in the organic polymer, and the conductive particles for anchor are applied to the resistor. Since the electrodes are formed by forming a metal layer on the front and back surfaces, the interface resistance between the electrodes and the resistor can be reduced and made uniform, so that the resistance value is small, the on-off repetition is excellent, and A highly reliable organic positive temperature coefficient thermistor having strong contact between the electrode and the resistor can be obtained.

According to the second aspect, since the average particle diameter of the conductive particles for anchor is larger than the conductive particles dispersed in the organic polymer, a superior anchor effect can be obtained. This facilitates the process and increases the degree of freedom in selecting the average particle size.

According to the third aspect, the average particle diameter of the conductive particles for anchor is 1 μm or more and 50 μm or less.
The object of embedding the conductive particles in the resistor and roughening the resistor can be achieved, and the demand for a thin thermistor can be met.

According to the fourth aspect, the conductive particles dispersed in the organic polymer and the conductive particles for the anchor are made of different materials. Therefore, these conductive particles having characteristics suitable for the intended use are used. And the degree of freedom in selecting the material of the conductive particles can be obtained.

According to the fifth aspect, since the electrode is made of nickel-plated, chrome-plated or nickel-plated solder, an electrode having relatively excellent heat resistance (oxidation resistance) can be obtained. In addition, lead soldering is also possible.

According to the sixth aspect, a composition formed by dispersing conductive particles in an organic polymer is formed into a sheet to form a resistor, and the conductive particles for anchoring an electrode are attached to the front and back surfaces of the resistor. Then, a part of the conductive particles for anchor is embedded in a resistor, and a metal layer is plated on the front and back surfaces of the resistor on which the conductive particles for anchor are applied to form an electrode, thereby manufacturing an organic positive temperature coefficient thermistor. Therefore, the conductive particles for anchoring are firmly fixed to the resistor, the conductive particles for anchoring come into contact with the conductive particles in the resistor for electrical conduction, and the resistance is further roughened by the conductive particles for anchoring. By plating electrodes such as metal on the front and back of the body to form electrodes, the electrode layer is firmly fixed to the resistor, and an organic positive temperature coefficient thermistor with low resistance and excellent on / off repetition characteristics can be obtained. .

[Brief description of the drawings]

1A is a cross-sectional view showing one embodiment of a thermistor according to the present invention, FIG. 1B is a partially enlarged view of FIG. 1A, and FIG. 1C is a reduced plan view of FIG.

FIGS. 2A to 2D are diagrams showing manufacturing steps of the present embodiment.

[Explanation of symbols]

1: organic polymer, 2: conductive particles, 3: resistor, 4: conductive particles for anchor, 5: electrode

Claims (6)

[Claims] An organic positive temperature coefficient thermistor obtained by forming a composition obtained by dispersing conductive particles in an organic polymer into a sheet to form a resistor, and forming electrodes on the front and back surfaces of said resistor. An electrode is formed by depositing a part of the organic polymer on the front and back surfaces of the resistor, and applying conductive particles for anchoring the electrode, and forming a metal film on the front and back surfaces of the resistor on which the conductive particles for anchoring are applied. An organic positive temperature coefficient thermistor characterized by comprising: 2. The organic positive temperature coefficient thermistor according to claim 1, wherein an average particle diameter of the conductive particles for anchor is larger than that of the conductive particles dispersed in the organic polymer. 3. The method according to claim 1, wherein the conductive particles for anchor have an average particle size of 1 μm or more and 50 μm or more.
An organic positive temperature coefficient thermistor characterized in that the thickness is not more than μm. 4. The organic positive temperature coefficient thermistor according to claim 1, wherein the conductive particles dispersed in the organic polymer and the conductive particles for the anchor are made of different materials. 5. The organic positive temperature coefficient thermistor according to claim 1, wherein said electrode is made of nickel plating, chromium plating, or nickel plating. 6. A resistor formed by forming a composition obtained by dispersing conductive particles in an organic polymer into a sheet, and applying conductive particles for anchoring an electrode to the front and back surfaces of the resistor. A method for producing an organic positive temperature coefficient thermistor, comprising: embedding a part of conductive particles in a resistor; and forming electrodes by plating metal layers on the front and back surfaces of the resistor having the anchor conductive particles applied thereto.