JP2936057B2 - Organic PTC thermistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic PTC thermistor, and more particularly, to an organic PTC thermistor which can be used as an overcurrent prevention element for a motor for door lock of an automobile, a battery and the like.

[0002]

2. Description of the Related Art It is generally known that a conductive composition obtained by dispersing a conductive fine powder such as carbon black or metal powder in an organic polymer such as polyethylene or polypropylene exhibits a positive resistance temperature characteristic. Such PTC compositions are disclosed, for example, in U.S. Pat. No. 3,591,526 and U.S. Pat. No. 3,673,121. Further, as a method of forming an electrode on these materials, a method of directly applying metal plating to the surface of the PTC composition (Japanese Patent Publication No. 4-44001), a method of embedding a mesh electrode made of metal in the PTC composition (Tokuhei 2-1
No. 6002) and a method by sputtering (Japanese Patent Application Laid-Open No. 62-85401) are known.

[0003]

Generally, a PTC thermistor used for an overcurrent prevention element such as a motor for door lock of an automobile, a battery or the like has a room temperature specific resistance of 1Ω ·
cm or less, and the resistance change rate (= log10 (maximum resistance value / initial resistance value)) is desirably 5 or more. As an advantage of the low resistance, not only the size can be reduced, but also a large current can be used in normal times. Here, the resistance can be reduced by increasing the amount of the conductive substance, but there is a disadvantage that the resistance change rate becomes small, and it becomes difficult to interrupt the current when an abnormality occurs.

A practical organic thermistor using carbon black as a conductive material has a room temperature specific resistance of 2%.
The resistance was as large as about Ω · cm, and it was difficult to lower the resistance further. Also, when metal powder is used as the conductive substance, the room temperature specific resistance can be lowered,
There is a problem that the durability of an actual load such as an on-off test is poor, and it is not practical.

In the conventional example as shown in FIG. 6, in a method of embedding a mesh electrode made of metal in a PTC composition, the resistance value does not decrease or the resistance value does not decrease depending on the size of the PTC composition body shape. There was a problem that the value was unstable. On the other hand, in the same conventional example as shown in FIG. 7, when a method of directly applying metal plating to the surface of the PTC composition or a method of sputtering is used as the electrode forming method, the thermal expansion and contraction of the PTC composition body causes the electrode film to be formed. There has been a problem that the resistance value increases due to wrinkles or cracks, or peeling off from the element body.

[0006]

SUMMARY OF THE INVENTION An organic PT according to the present invention
The C thermistor is for solving the above-mentioned problem, and its electrode is composed of a combination of a metal mesh and a metal layer.

[0007] The metal mesh is formed on the surface of the PTC composition.
Formed by embedding so that part of it is exposed
Is done.

[0008] The metal layer is formed of a buried metal mesh.
Polishing the surface of the PTC composition containing
Formed after increasing the exposed area of conductive material,
Plating, electroplating, vacuum vapor phase plating, or thermal spraying
It is formed from at least one or more selected materials.

Further, the metal mesh preferably has a thickness of 2 mm.
It is a thing of 00-600 mesh.

The metal mesh is preferably one selected from a plain woven mesh, a crushed plain woven mesh, and a mesh having no step at the intersection of the mesh lines.

The organic polymer in the organic PTC thermistor according to the present invention is polyethylene, polypropylene,
The conductive material is selected from the group consisting of polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, ionomer resin, and a copolymer thereof, and the conductive material is carbon black, graphite, carbon fiber, conductive whisker, metal particles, conductive ceramic. It is selected from a group of powders.

Further, the conductive ceramic powder preferably comprises tungsten carbide.

[0013]

As described above, in the organic PTC thermistor according to the present invention, since the electrode has an electrode structure composed of a combination of a metal mesh and a metal layer, a resistance value corresponding to the size of the PTC element body can be obtained. At the same time, the resistance value can be stabilized.

Further, the metal mesh is buried so that a part of the metal mesh is exposed on the surface of the PTC composition, so that the initial resistance value of the PTC element is reduced, and the stress due to thermal stress is reduced. Mechanical reinforcement such as electrode deformation and crack prevention can be achieved.

Further, the metal layer includes a metal mesh.
By forming on the polished surface of the PTC composition
As a result, the resistance value can be stabilized, and
This metal layer can be formed by chemical plating or electroplating.
Selected from vacuum vapor deposition or thermal spraying
By using at least one of them, the initial resistance of the PTC body is improved.
The resistance value drops.

Further , by using a metal mesh of 200 to 600 mesh, punching and cutting of a predetermined shape are easy and can be formed at low cost.

Further, the metal mesh is a plain weave mesh,
By using one selected from a flat woven mesh subjected to crushing processing and a mesh having no step at the intersection of the mesh lines, the thickness of the metal mesh can be reduced, and the metal mesh exposed area on the surface of the PTC element body increases, Since a thinner element is obtained and the polishing operation is facilitated, the manufacturing process is simplified.

The organic polymer in the organic PTC thermistor according to the present invention is selected from the group consisting of, for example, polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, ionomer resin, and copolymers thereof. Is selected from the group consisting of carbon black, graphite, carbon fiber, conductive whiskers, metal particles, and conductive ceramic powder to obtain resistance, resistance change rate, breakdown voltage, and resistance-temperature characteristics (RT characteristics). Excellent in repetition stability and reliability.

By using tungsten carbide as the conductive ceramic powder, a PTC element having low resistance and excellent repetition stability of resistance-temperature characteristics (RT characteristics) can be obtained, and the size of the PTC element can be reduced. Becomes possible.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a perspective view showing a state in which a metal mesh is embedded in an organic PTC thermistor element formed in a sheet shape in an embodiment of the present invention, and FIG. And its AA 'sectional view. 2 to 5
FIG. 4 is a diagram illustrating resistance-temperature characteristics (RT characteristics) according to an example of the present invention.

The organic PTC thermistor composition is produced by kneading an organic polymer and a conductive substance at an appropriate ratio.
Examples of the organic polymer include polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, an ionomer resin, and a copolymer thereof. Examples of the conductive substance include carbon black such as furnace black and acetylene black, graphite, carbon fiber, conductive whiskers, conductive ceramic powder such as tungsten carbide, Ni, Cu, and the like.
Examples include metal particles such as Ag, Fe, and Cr, or a mixture of several of these.

The organic polymer and the conductive material adjusted at an appropriate ratio by a kneader such as a Banbury mixer or a mixing roll are mixed at a temperature of 120 to 250 ° C. for 15 to 15 minutes.
Knead for about 60 minutes. At this time, an antioxidant, a surfactant or the like may be added as a kneading aid. Also, electron beam crosslinking, electron beam crosslinking (US Pat. No. 3,269,862) performed by adding a crosslinking aid to enhance the effect, chemical crosslinking, and silane compound in the presence of a free radical generator. After the grafting onto the organic polymer, the polymer is exposed to water or an aqueous catalyst in the presence of a silanol condensation catalyst, and then subjected to a method such as water crosslinking (Japanese Patent Publication No. 4-11575) to determine the fluidity of the polymer after the development of the positive resistance temperature characteristic. In some cases, the resistance is suppressed and the resistance value is stabilized. Then, it is formed into a sheet or film by a heating roll, a hot press or the like.

A metal mesh is embedded in both main surfaces of the thus obtained molded body by, for example, heat compression.

The metal mesh is better as the mesh is finer. However, when the mesh is extremely fine, the cost of manufacturing the mesh increases, which is not practical. Further, when the mesh is coarse, the diameter of a commonly used metal wire becomes large, so that not only the workability when punching and cutting a molded body after forming an electrode into a predetermined shape is deteriorated, but also the end part is deteriorated. In the above, burrs are generated on the metal wire. For this reason, it is desirable that the mesh size be 200 to 600 mesh. Here, the unit mesh representing the size of the mesh is represented by the number of meshes formed in one side (1 inch) of the unit area (1 inch square).

The material and weave of the mesh are made of stainless steel, metal such as Cu, Fe, Ni, brass, etc., and are subjected to plain weave, twill weave, irregular weave, or crushing, or to these. A plated coating is used, but the smaller the step of the wire, the better. Furthermore, a line having no step at the intersection of lines formed by etching, punching, or the like can be used.

At this time, the mesh is not completely buried inside the molded body, but is uniformly exposed on the surface of the molded body as shown in FIG. 1B. After embedding, the surface is roughened by mechanical polishing such as sandblasting or sandpaper or chemical polishing with an acid to expose the mesh.

Next, a metal layer is formed by chemical plating, electroplating, vacuum vapor phase plating (evaporation, sputtering), thermal spraying, or the like. The metal material used for plating is N
i, Cu, Ag, Sn, Cr, etc., and are not particularly limited.

Finally, it is processed to a desired size by punching, cutting or the like. Further, if necessary, the metal lead wires may be soldered and then molded with an insulating resin, or the external metal terminals may be bonded by a conductive adhesive or soldering.

[0029]

EXAMPLES Specific examples of the present invention will be described.

Polyvinylidene fluoride (hereinafter referred to as PVDF) [Kyner 711 manufactured by Elf Atochem North America, USA] was used as an organic polymer, and a silane coupling agent [Shin-Etsu Chemical Co., Ltd.] was used based on the weight of the polymer. 10% by weight of KBC1003 manufactured by K.K., and 1 part by weight of organic peroxide 2,5-dimethyl-2,5-di (t-butylperoxin) hexyne-3 at 200 ° C.
The grafted resin was produced with a twin-screw extruder while heating the mixture.

Further, tungsten carbide (hereinafter referred to as WC) [WC-F manufactured by Nippon Shinkin Co., Ltd.] is used as the grafted resin.
Was mixed at 30% by volume and heated to 200 ° C. while rotating at 2 rpm.
The mixture was kneaded at 5 rpm for 1 hour to obtain a PTC composition.

Next, the PTC composition was added at 200 ° C.-30 k
The sheet was hot-pressed at gf / cm 2 to obtain a sheet molded product having a thickness (t) of about 1 mm.

Example 1 A 200-mesh plain-woven stainless steel mesh was embedded on both main surfaces of the sheet molded product thus obtained at 200 ° C.-30 kgf / cm 2, cooled slowly at room temperature, and then electrolessly formed. , Ni plating was applied to a thickness of 1 to 2 µm to obtain a sample.

(Example 2) The surface of the sheet was polished with sandpaper before plating to increase the exposed area.
A sample was obtained under the same conditions as in Example 1.

(Embodiment 3) Instead of plating, an ambient temperature of 16
A sample was obtained under the same conditions as in Example 1 except that Cu was applied at 0 ° C. by vacuum evaporation to a thickness of 1 to 2 μm.

Example 4 A sample was obtained under the same conditions as in Example 3 except that the surface of the sheet was polished with sandpaper to increase the exposed area before vacuum deposition.

Example 5 A sample was obtained under the same conditions as in Example 3 except that a 400-mesh plain-woven stainless steel mesh was used instead of the 200-mesh plain-woven stainless steel mesh.

Example 6 A sample was obtained under the same conditions as in Example 3 except that a stainless steel mesh having no steps at the intersections of 400-mesh lines was used instead of the 200-mesh plain-woven stainless steel mesh.

Comparative Example 1 An electrode was formed only by plating without using a mesh to obtain a sample. (Plating conditions are the same as in Example 1.)

Comparative Example 2 A sample was obtained under the same conditions as in Example 1 except that no plating was performed.

Comparative Example 3 An electrode was formed only by vacuum evaporation without using a mesh, to obtain a sample. (The conditions for vacuum deposition are the same as those in Example 3.)

Each sheet-like sample obtained as described above was punched into a size of 10φ to produce a PTC element. The initial resistance value of each element was measured by a four-terminal method.

A peeling test was performed using an adhesive tape [T4000 manufactured by Sony Chemical Co., Ltd.] to check the adhesion strength of the electrodes. Here, the peeling test is a method in which the adhesive tape is adhered to the entire electrode portion of the element, and the adhesive strength of the electrode is determined by whether or not the electrode is adhered to the adhesive tape when the adhesive tape is instantaneously peeled off. It is a test.

The resistance-temperature characteristics (RT characteristics) of each element from room temperature (25 ° C.) to 200 ° C. were measured.

The above results are summarized in Table 1 and FIGS.

◎

[Table 1]

Only plating or vacuum deposition (Comparative Example 1,
In the case of 3), the adhesion between the electrode and the PTC body was weak, and the initial resistance was high. Only mesh (Comparative Example 2)
In the case of, the mechanical strength of the element was increased, but the initial resistance was high and unstable as shown in FIG.

On the other hand, according to the method of embedding the mesh before plating or vacuum deposition, the initial resistance value is reduced, the stress due to thermal stress is reduced, and the PT is reduced.
It has been found that there is a mechanical reinforcing effect such as deformation and crack prevention of the C element and the electrode. (Examples 1, 3, and 5)

After using a mesh having no step at the intersection of the mesh lines (Example 6) or embedding a plain weave mesh,
By polishing the surface together with the TC element and increasing the surface exposed area of the mesh and the conductive particles in the PTC composition (Examples 2 and 4), the effect can be obtained even more. Figure 2
As shown in FIG. 4, the initial resistance was low.

In the conventional example as shown in FIG. 6 (b), when the mesh 2 is simply thermocompression-bonded to the PTC element 1 due to the structure of the plain woven mesh, intersections 2a of the mesh lines are scattered. And the contact area with the metal layer 3 by plating or vacuum deposition is small, and as a result, the initial resistance value increases. On the other hand, in the embodiment of the present invention as shown in FIG. 1 (b), after the mesh 2 is buried, the surface is polished, so that the surface exposed portion of the intersection 2a of the mesh expands linearly. It is considered that the contact area with the metal layer 3 by plating or vacuum deposition increases, and as a result, the initial resistance value decreases.

In the case of only the metal layer 3 of plating or vacuum deposition as shown in FIG. 7B (Comparative Examples 1 and 3), PT
Due to the difference in the coefficient of linear expansion between the C element body 1 and the metal layer 3, deformation, wrinkles, cracks, and the like of the PTC element body 1 and the metal layer 3 may occur due to stress due to thermal expansion and contraction. On the other hand, by embedding the mesh 2 as in each embodiment, it is considered that the stress at the opening of the mesh 2 is alleviated and the metal layer 3 plays a role as a base (anchor effect). It turned out that the problem in was improved.

[0052]

As described above, according to the present invention, the short circuit of the charging circuit of the secondary battery, the locking of the small motor typified by the motor for the door lock of the automobile, the short circuit of the telephone communication circuit and the information equipment, etc. Organic P useful for current prevention
A TC thermistor can be obtained.

According to the first aspect of the present invention, the PTC element
Stabilizes the resistance value and resistance value according to the body size
At the same time, the initial resistance value decreases. In addition, due to heat stress
Reduces force, prevents deformation of PTC body, wrinkles and cracks in electrodes
And other mechanical reinforcement.

According to the second aspect of the present invention, punching and cutting of a predetermined shape are easy and can be formed at low cost.

According to the third aspect of the present invention, a thinner PTC element can be obtained, the polishing operation is facilitated, and the manufacturing process is simplified.

According to the fourth aspect of the present invention, the resistance value,
Resistance change rate, breakdown voltage, resistance-temperature characteristics (RT characteristics)
With excellent repetition stability and reliability.

According to the fifth aspect of the present invention,
Further, a PTC element having low resistance and excellent in repetition stability of resistance-temperature characteristics (RT characteristics) can be obtained.
The size of the C element can be reduced.

[0058]

[Brief description of the drawings]

FIG. 1 is a diagram showing a state in which a metal mesh is embedded in an organic PTC thermistor element formed in a sheet shape in an example of the present invention.

FIG. 2 is a diagram showing resistance-temperature characteristics (RT characteristics) of Example 1 and Example 2 of the present invention.

FIG. 3 is a diagram showing resistance-temperature characteristics (RT characteristics) of Examples 3 and 4 of the present invention.

FIG. 4 is a graph showing resistance-temperature characteristics (RT characteristics) of Examples 5 and 6 of the present invention.

FIG. 5 is a diagram showing resistance-temperature characteristics (RT characteristics) of Example 3 of the present invention and Comparative Example 2.

FIG. 6 is a diagram showing a conventional example according to the present invention.

FIG. 7 is an explanatory diagram showing a state of thermal stress when measuring resistance-temperature characteristics (RT characteristics) in a conventional example according to the present invention.

[Explanation of symbols]

 1 PTC body 2 Metal mesh 2a Mesh intersection 3 Metal layer

Claims (5)

(57) [Claims] 1. An organic PTC thermistor having a positive temperature coefficient PTC composition in which a conductive substance is dispersed in an organic polymer and at least one pair of electrodes, wherein the electrodes are a combination of a metal mesh and a metal layer. and have a electrode structure composed of the metal mesh, is a part on the surface of the PTC composition
The metal layer is embedded so as to be exposed, and the metal layer is formed of a PTC composition including the metal mesh.
Formed on polished surface, chemical plating, electromechanical
, Vacuum vapor plating, or thermal spraying
An organic PTC thermistor characterized by being formed from at least one kind . 2. The organic P according to claim 1 , wherein the metal mesh is 200 to 600 mesh.
TC thermistor. 3. The metal mesh is one selected from the group consisting of a plain woven mesh, a crushed plain woven mesh, and a mesh having no step at the intersection of mesh lines. Item 3. The organic PTC thermistor according to Item 1 or 2 . Wherein said organic polymer is polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl chloride,
The conductive material is selected from the group consisting of polyvinyl acetate, ionomer resin, or a copolymer thereof, and the conductive material is selected from the group consisting of carbon black, graphite, carbon fiber, conductive whiskers, metal particles, and conductive ceramic powder. The organic PTC thermistor according to any one of claims 1 to 3 , wherein Wherein said conductive ceramic powder, organic PTC thermistor according to any one of claims 1 to 4, characterized in that it consists of tungsten carbide.