JP2002208504A - Polymer ptc device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer PTC device which is capable of displaying suitable characteristics by adjusting physical properties such as the resistivity of an interface between the PTC composition and an electrode and PTC characteristics which are inversely changed, depending on the average grain diameter of the conductive particles, wherein the polymer PTC device is obtained by fixing electrodes on both the surfaces of a sheet of PTC composition composed of crystalline high molecules and conductive particles dispersed into the high molecules. SOLUTION: A plurality of PTC composition sheets which contain conductive particles that are different from each other in average grain diameter are so laminated as to indicate the fact that the conductive particles contained in the PTC compositions between the electrodes get larger in average grain diameter at the center than those contained in the PTC compositions close to the electrodes. By this setup, a polymer PTC device can be prevented from increasing in resistivity at room temperatures, and an interface between the electrode and the PTC composition can be prevented from increasing in resistivity due to an increase in the average grain diameter of the conductive particles, and the PTC device is restrained from deteriorating in PTC characteristics due to a decrease in the average grain diameter of the conductive particles at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer PTC (Positive Tes) comprising a crystalline polymer substance and conductive particles dispersed therein.
The present invention relates to a polymer PTC element in which electrodes are arranged on a PTC substrate formed of a mperature coefficient (positive temperature coefficient) composition, and more specifically, an overcurrent for preventing an overcurrent from flowing when an abnormality occurs in a battery or a circuit of an electronic device. The present invention relates to a polymer PTC element used as a current protection element.

[0002]

2. Description of the Related Art Conventionally, a PTC element exhibiting a positive temperature characteristic in which electric resistance rapidly increases in a specific temperature range is frequently used as a heater for automatically controlling the temperature or a self-recovering type overcurrent protection element. Have been. As a composition used for the PTC element, yttrium oxide (Y
Barium titanate (BaTiO) to which a small amount of ₂ O ₃ ) is added
Ceramic PTC compositions such as ₃ ) and polymer PTC compositions in which conductive particles such as carbon black are dispersed in a crystalline polymer are known.

[0003] PT using ceramic PTC composition
In the C element, a rapid rise in resistance at the Curie point is used.
-A relatively large current of about several A cannot flow due to the high cm. This means that it is difficult to use a PTC element using a ceramic PTC composition as an overcurrent protection element. In addition, the ceramic PTC composition requires many steps to form and process into a desired shape, and has a problem of poor impact resistance.

On the other hand, a PTC device using a polymer PTC composition has a low resistivity at room temperature, so that it is suitable for an overcurrent protection device, has excellent impact resistance, and is easy to mold and process. is there.

[0005] The operating principle of the polymer PTC element is based on the fact that conductive particles forming a network at room temperature are separated by utilizing a large thermal expansion at the crystal melting point of a crystalline polymer. For this reason, at a temperature near the crystalline melting point of the crystalline polymer, the resistivity rises sharply and returns to room temperature,
The network of conductive particles is reformed and the resistivity is reduced.

A general method for producing a polymer PTC element is as follows.
Conductive particles are dispersed in a crystalline polymer using a roll or the like to obtain a PTC composition, which is formed into a sheet by a hot press or a roll, and an electrode made of a metal foil or the like is pressed and formed into a desired shape. It is punching. FIG.
FIG. 3 schematically shows a cross section of the polymer PTC element manufactured as described above.
Reference numeral 1 denotes a single layer, and the average particle diameter of the conductive particles 22 included inevitably becomes unitary.

[0007] If the average particle size of the conductive particles 22 is too large, the degree of network formation of the conductive particles 22 decreases, and the resistivity at room temperature increases. The interface resistivity increases. On the other hand, if the average particle size is too small, it is difficult to cut the network near the crystalline melting point of the crystalline polymer, so that suitable PTC characteristics cannot be obtained. As described above, in the polymer PTC element, there is a problem that the contradictory characteristics depend on the average particle diameter of the conductive particles 22 used.

Further, carbon black powder, which is frequently used as conductive particles of polymer PTC, tends to agglomerate as compared with metal carbide and the like, and when used in a polymer PTC element, the resistivity near the crystal melting point is low. Therefore, there is a problem that the withstand voltage decreases accordingly.

[0009]

SUMMARY OF THE INVENTION Accordingly, the technical problem of the present invention is to adjust the characteristics that change contradictoryly depending on the average particle size of the conductive particles as described above, and to obtain excellent characteristics. To provide a polymer PTC element having the same.

[0010]

In order to solve the above-mentioned problems, the present invention provides a PTC composition in a polymer PTC element with an optimal particle size distribution of conductive particles in a direction between electrodes. This is the result of an examination.

That is, the present invention relates to a polymer PTC element comprising electrodes disposed on both sides of a substantially plate-shaped PTC substrate made of a PTC composition in which conductive particles are dispersed in a polymer compound. Is a polymer PTC element obtained by laminating a plurality of sheets of a PTC composition containing conductive particles having different average particle diameters.

The present invention also provides the above-mentioned polymer PTC element, wherein the PTC substrate comprises conductive particles having an average particle size different from that of the first sheet on both surfaces of the first sheet made of the PTC composition. N (where n is a natural number) sheets of the PTC composition sheet are laminated, and the nth PTC composition sheet counted from the first sheet has the same composition on both sides,
And a polymer PT containing conductive particles having an average particle size smaller than that of the sheet of the (n-1) th PTC composition.
C element.

[0013] Further, according to the present invention, in the above polymer PTC element, the conductive particles include at least one kind of metal carbide, a substance containing at least one kind of carbon, or at least one kind of metal carbide and carbon. A polymer PTC element characterized by comprising a substance containing:

The present invention also provides a PTC comprising a polymer compound and n + 1 types of conductive particles dispersed therein.
The composition is formed into a sheet, and the average particle size of the conductive particles contained in the n-th PTC composition sheet is on both sides of the PTC composition sheet containing the conductive particles having the largest average particle size. It is characterized in that n layers are laminated so as to be the same and smaller than the (n-1) th PTC composition, electrodes are pressed on both surfaces of the laminated PTC composition sheet, and then cut into a required shape. And a method for producing the polymer PTC element.

[0015]

The polymer PTC element of the present invention has a PTC between electrodes.
The conductive particles contained in the substrate have a distribution in which the particle size is large at the center and small at the interface with the electrode. For this reason, the polymer PTC element of the present invention has low resistivity at room temperature, particularly the resistivity at the interface between the electrode and the PTC substrate, and has the same PTC characteristics as the conventional one. Further, by using a mixture of a plurality of conductive particles, the withstand voltage can be improved more than before.

Here, as an example of the conductive particles that can be used in the present invention, titanium carbide (TiC), tungsten carbide (WC, W
₂ C), zirconium carbide (ZrC), vanadium carbide (VC), tantalum carbide (Ta
C) and molybdenum carbide (MoC). Examples of carbon-based particles include carbon blacks such as furnace black, thermal black and acetylene black, graphite, carbon fiber, carbon beads, and carbon nanotubes.

The polymer compound used in the present invention is preferably a crystalline polymer having a crystallinity of 10% or more, such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene, and ethylene. / Polyolefins such as propylene copolymer and polybutadiene, fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, ethylene-
Acrylic acid copolymers, polyesters, various polyamides, various polyethylene oxides, etc.
It is appropriately selected according to the operating temperature of the C element. These crystalline polymer substances can be used alone or as a mixture.

When a polymer PTC element is manufactured using the above-described polymer PTC composition, the surface of the electrode is known to reduce the contact resistance at the interface between the electrode and the PTC substrate. Surface roughness of 5
The surface is roughened to about μm.

When a three-layer PTC substrate is used between the electrodes, for example, the central layer has an average particle size of 10%.
A polymer PTC composition in which μm of TiC is dispersed is used, and a polymer PTC composition in which TiC having an average particle size of 5 μm is dispersed is used for layers to be pressed on both surfaces.

Further, when a PTC substrate composed of five layers of the polymer PTC composition is used, the average particle size of the conductive particles dispersed in each layer is as follows: (first layer = fifth layer) <(second layer) Layer = fourth layer) <third layer (center layer).

The surface roughness of the electrode surface and the average particle size of the conductive particles are more preferable if the relationship of surface roughness of the electrode surface ≧ average particle size of the conductive particles is satisfied. The contact resistance at the interface between the electrode and the PTC substrate can be reduced by setting the relationship between the surface roughness and the average particle size of the conductive particles.

[0022]

Next, the present invention will be described in detail with reference to specific examples.

Example 1 First, a 30 μm thick nickel foil having a surface roughness of 3 μm was prepared as an electrode. Next, the materials weighed so as to have the compositions shown in Table 1 were kneaded with a roll until uniform, and the PTCs of No. 1 and No. 2 were
A composition was obtained. As shown in Table 1, in this example, TiC and carbon black were used as the conductive particles.
Then, a sheet having a thickness of 80 μm was formed using these forming rolls.

[0024]

[Table 1]

Next, a sheet of the polymer PTC composition of No. 1 was placed on both sides of the sheet of the polymer PTC composition of No. 2, and the roughened surface was placed on both sides of the sheet. The electrode was arranged toward the molecular PTC composition side, hot pressed, and the sheet and the electrode were pressed. This sheet is cut into a square having a side of 4 mm, and a polymer PT having a thickness of 300 μm
C element was used. FIG. 1 schematically shows a cross section of the polymer PTC element. In addition, the conditions of heat press
The temperature is 150 ° C., the pressure is 20 MPa, and the time is 15 minutes.

Example 2 The same nickel foil as in Example 1 was prepared as an electrode. Then, the materials weighed so as to have the composition shown in Table 2 were kneaded and formed into a sheet in the same manner as in Example 1. As shown in Table 2, in this example, only TiC was used as the conductive particles. Next, in the same manner as in Example 1, the sheet of the polymer PTC composition of No. 3 and the electrode were placed in this order on both surfaces of the sheet of the polymer PTC composition of No. 4, and pressed and cut. Do,
A polymer PTC element was obtained.

[0027]

[Table 2]

Example 3 The same nickel foil as in Example 1 was prepared as an electrode. The materials weighed so as to have the compositions shown in Table 3 were kneaded and sheet-formed in the same manner as in Example 1. As shown in Table 3, in this example, only carbon black was used as the conductive particles. Next, in the same manner as in Example 1, the sheet of the polymer PTC composition of No. 5 and the electrode were arranged in this order on both surfaces of the sheet of the polymer PTC composition of No. 6, and pressed and cut. This was performed to obtain a polymer PTC element.

[0029]

[Table 3]

(Comparative Example) Next, a PTC element comprising a single-layer PTC substrate and electrodes was prepared for comparison with the above-mentioned embodiment. First, the same nickel foil as that used in Example 1 was prepared as an electrode. The materials weighed so as to have the composition shown in Table 4 were obtained in the same manner as in Example 1.
The mixture was kneaded and formed into a sheet to obtain a 240 μm thick sheet of the PTC composition.

[0031]

[Table 4]

Nickel foil was placed on both sides of the sheet with the roughened surface facing the sheet side, and pressed and cut in the same manner as in Example 1 to have a thickness of 300 μm and a side of 4 m.
m square polymer PTC element was obtained.

Next, with respect to the polymer PTC elements manufactured in the examples and comparative examples, the temperature: 25 ° C., the relative humidity: 40%
, The resistivity: R ₁ , the resistivity at the operating temperature or higher: R ₂ , and the withstand voltage: V were measured. Table 5 shows the results. Note that, here, the embodiment,
In the comparative example, the same chlorinated polyethylene was used as the binder, but the operating temperature was 98 ° C.

[0034]

[Table 5]

As is clear from Table 5, Example 1 and Example
In Example 2, when compared with the comparative example, R ₁Is low and R₂
Is high, and the characteristics as a polymer PTC element
Is excellent. In the third embodiment,
Also, R₁Low between the PTC composition and the electrode
It is clear that the contact resistance has been improved. Furthermore,
Withstand voltage: at V, the polymers of Examples 1 and 2
The PTC element has a voltage of 110 V, which is about three times that of the comparative example.
Numerical values were obtained, and excellent characteristics were obtained.

[0036]

As described above, according to the present invention, in the polymer PTC element, the resistivity increases at room temperature due to the increase in the average particle size of the conductive particles, and the electrode and the PTC composition By increasing the resistivity of the interface between the electrodes and the characteristic that contradicts the decrease in the PTC characteristic due to the decrease in the average particle size of the conductive particles, the PTC substrate between the electrodes is formed into a multilayer structure. Adjustment is possible, and a polymer PTC element having excellent characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a cross section of a polymer PTC element of the present invention.

FIG. 2 is a diagram schematically showing a cross section of a conventional polymer PTC element.

[Explanation of symbols]

 10,20 Polymer PTC element 11,12 PTC composition sheet 13,21 PTC substrate 14,15,22 Conductive particle 16,23 Binding material 17,24 Electrode

Claims (4)

[Claims] 1. A polymer PTC element comprising electrodes disposed on both sides of a substantially plate-shaped PTC substrate comprising a PTC composition in which conductive particles are dispersed in a polymer compound.
A polymer PTC element, wherein the TC substrate is formed by laminating a plurality of sheets of a PTC composition containing conductive particles having different average particle sizes. 2. The polymer PTC element according to claim 1, wherein the PTC substrate has conductive particles having an average particle size different from that of the first sheet on both surfaces of a first sheet made of a PTC composition. N (n is a natural number) layers of PTC composition sheets containing the PTC composition, the nth PTC composition sheet counted from the first sheet has the same composition on both sides, and the (n-1) th PTC composition PTC comprising conductive particles having an average particle size smaller than that of a material sheet
element. 3. The polymer PTC element according to claim 1, wherein the conductive particles are:
A polymer PTC element comprising at least one metal carbide, a substance containing at least one carbon, or a substance containing at least one metal carbide and carbon. 4. A PTC composition in which n + 1 types of conductive particles each having an average particle size dispersed in a polymer compound is formed into a sheet, and the PTC composition containing the conductive particles having the largest average particle size is formed.
N layers on both sides of the TC composition sheet so that the average particle size of the conductive particles contained in the nth PTC composition sheet is the same on both sides and smaller than the (n-1) th PTC composition The polymer PTC element according to any one of claims 1 to 3, wherein the laminated PTC composition sheet is pressed into electrodes on both sides of the laminated PTC composition sheet, and then cut into a required shape. Method.