JP2000109615A - Conductive polymer composition having positive temperature coefficient characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a conductive polymer composition having a high strength of a positive temperature coefficient and improved reproducibility of a positive temperature coefficient behavior by incorporating a specified branched polyolefin polymer with particles having an electricity conducting action. SOLUTION: This composition comprises 35-60 wt.%, desirably, 35-55 wt.% branched polyolefin polymer having a density of 0.865-0.935 g/cm3, a melting point of 50-128 deg.C, and a head of fusion of 50 J/g or above, 20-45 wt.%, desirably, 35-40 wt.% particles treated with a low-molecular-weight polar water-soluble carbon black, having a particle diameter of 5-75 nm, and an electricity- conducting action, and, optionally, 5-20 wt.% polymeric material highly adhesive to an electrode made of e.g. aluminum, copper, or nickel, 25-40 wt.% particulate filler having a coefficient of thermal conductivity of 5 W/mK or above, a resistivity of 1015 Ω-cm or above, a particle diameter at least ten times as large as that of the particles having an electricity conducting effect, and having a heat conducting action but not having an electricity conducting action, a flame retardant, an antioxidant, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a positive temperature coefficient (Po
sitive Temperature Coefficient (hereinafter abbreviated as PTC)
The present invention relates to a conductive polymer composition having properties,
Intensity (log (ρ _max/ Ρ_min), Ρ_max
= Maximum resistivity, ρ_min= Minimum resistivity) is large and P
Excellent reproducibility of TC operation, used as PTC thermistor
The present invention relates to a conductive polymer composition suitable for use in the method.

[0002]

2. Description of the Related Art A PTC thermistor is an electronic element whose resistance coefficient reaches hundreds of thousands of times or more at room temperature when the phase transition temperature is exceeded. Among the many "valence control" type semiconductor ceramics, it is only BaTiO ₃ series ceramics show a clear PTC effect. Since the property of a rapid increase in resistivity within a very narrow temperature range can be utilized as a solid-state switching element, it has attracted attention in the field of material science and material engineering since the announcement of the PTC effect by Vervey in 1950. Prevention of overheating of electric appliances, protection of current controller circuit, indication and control of temperature, fuel level gauge, timer and delay element,
Many application fields such as constant temperature heating elements have already been developed.

[0003] PTC thermistors are widely used for overcurrent protection of circuits. PTC thermistors are based on a different operating principle than fuses and circuit breakers, and can be used for overcurrent protection of the above-mentioned application products while at the same time over temperature
-Temperature) It also has protection function. In addition, since the protection function can be automatically restored, there is no need to replace parts or adjust switches.

[0004] With the progress of material technology, if the conductive particles are added to a semi-crystalline thermoplastic polymer and subjected to an appropriate processing, the self-healing properties and PTC characteristics similar to those of a ceramic-based PTC thermistor are obtained. Can be realized.

The polymer-based PTC has the following characteristics. (1) The polymer-based PTC is light and small, and also has excellent moldability. Therefore, it is suitable to be attached to an element or a series circuit which needs to be protected in a narrow and complicated place. (2) The polymer-based PTC achieves the purpose of conductivity by forming passages in the crystalline resin with conductive particles.
Therefore, the NTC (negative temperature coefficient) phenomenon hardly occurs even when the temperature is lower than the switch temperature, and the thermal runaway phenomenon hardly occurs even when the temperature is higher than the switch temperature. (3) The polymer-based PTC has a low ordinary-temperature resistance value. Therefore, on the other hand, the consumption rate of the entire circuit can be reduced. (4) The polymer-based PTC has low voltage sensitivity. (5) The polymer-based PTC is excellent in mechanical shock resistance and thermal shock resistance.

[0006] Because of the above characteristics, polymer PTC is commonly used for protection of current controllers, interface circuits, rechargeable batteries, and the like, and is also used for circuit protection in general telecommunications, communications, and automobile fields. It is possible to expand.

[0007] Among the known techniques, most of the methods for producing a polymer-based PTC composition cross-link a crystalline polymer by a physical or chemical method. For example, P
olym. Eng. Sci 44, 532 (1973)
Disclosed a method of adding carbon black to high-density polyethylene, blending the resultant, and then adding a peroxide to cause cross-reaction. The resulting material exhibits PTC properties, but has the disadvantage of high manufacturing costs and the residual chemicals in the resin corroding the metal electrodes. In addition, the polymer after cross-linking is not excellent in moldability, and the decrease in crystallinity is P
This leads to a drop in TC strength.

In some cases, a thermosetting resin is used as a polymer group. For example, US Pat. No. 5,545,679
Discloses a method of forming a PTC composition by dispersing conductive particles in a thermosetting polyester resin. However, this method using a thermosetting resin as a polymer group also has disadvantages such as poor moldability and reduced PTC strength.

US Pat. No. 4,591,700 disclosed a method of blending two types of crystalline polymers having different melting points with conductive particles to form a PTC composition.
Here, the melting point of the crystalline polymer having a high melting point is 160 ° C. or more, and there is an opening of 25 ° C. or more between the crystalline polymer having a low melting point. However, this type of composition has a problem in that the conductive particles segregate in a molten state, so that NTC (Negative T
emperature Coefficient) phenomenon. In addition, at the time of solidification of the crystal, the conductive particles precipitate at the boundary between the crystal particles, which deteriorates the reproducibility of the PTC characteristics.

Also, a PT manufactured based on a known technique is used.
In the C polymer composition, neither the adhesion to the electrode nor the percolation to carbon black was effectively improved. For this reason, carbon black and non-conductive inorganic particles cannot be percolated in large quantities, and a delamination phenomenon is likely to occur.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned disadvantages of the prior art, and has a low manufacturing cost.
"Conductivity with PTC properties" that excels in moldability, does not leave any chemical substances, has high PTC strength, has excellent reproducibility of PTC properties, and can percolate carbon black and non-conductive inorganic particles in large quantities. Polymer composition "
The purpose is to provide.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above-mentioned object, and as a result, a polymer obtained by blending a specific polyolefin polymer with conductive particles such as carbon black. The composition is low in production cost, excellent in moldability, does not leave any chemical substance, has high PTC strength, has excellent reproducibility of PTC characteristics, and percolates a large amount of carbon black and non-conductive inorganic particles. And found that the present invention was completed.

That is, the “conductive polymer composition having PTC characteristics” according to the present invention is (a) 35 to 60 wt%, preferably 35 to 5 wt% based on the conductive polymer composition.
A polyolefin polymer having a polydispersity (molecular weight distribution) smaller than 2.5 and occupying 5 wt%, and a branched polyolefin polymer;
It is characterized by containing particles having a conductive action so as to account for ４５45 wt%, preferably 35-45 wt%.

The conductive polymer composition of the present invention further comprises:
It is desirable to contain (c) a polymer material that strongly adheres to an aluminum, copper, or nickel electrode, and (d) a particulate filler that has a heat conducting action but is non-conductive.

[0015] The branched polyolefin polymer is
0.865 to 0.935 g / cm² Density of 50 to 12
Have a melting point of 8 ° C and a heat of fusion of 50 J / g or more.
Is preferred.

The polyolefin polymers of this type include:
For example, polyethylene (PE), polypropylene (P
P), EPDM, and PP / PE copolymer.

The dose of this type of polyolefin polymer is:
35 based on the finally obtained conductive polymer composition
It is desirable to account for ６０60 wt%, preferably 35-55 wt%. If the dose exceeds 60 wt%, the electrical resistance at room temperature is too large, while if it is less than 35 wt%, the PTC strength is too low and the PTC characteristics disappear.

The conductive particles are not particularly limited. For example, metal particles may be used, but carbon black is preferable if possible.

The carbon black may be either graphitized carbon black or non-graphitized carbon black, and preferably has a particle size of 5 to 75 nm. The degree of graphitization is appropriately determined depending on the purpose of use. When carbon black is graphitized, various properties of carbon, such as electrical properties, magnetic properties, and mechanical properties, change.

The carbon black may be polyvinyl alcohol (PVA), polyethylene glycol (PE)
G), a polyethylene oxide (PEO), an ethylene vinyl alcohol copolymer (EVOH), or a low molecular weight and polar water-soluble carbon black treating agent such as EVOH or a mixture thereof.

The treatment of carbon black with the treating agent can be carried out by mixing the carbon black and the carbon black treating agent at a constant ratio. That is, the conductive polymer composition of the present invention preferably contains carbon black and the carbon black treating agent in addition to the branched polyolefin polymer.

[0022] The dose of the particles having a conductive effect is 20 to 20 based on the weight of the finally obtained conductive polymer composition.
It is desirable to account for 45 wt%, preferably 35 to 40 wt%. If the dose exceeds 45 wt%, the PTC strength is too low and the PTC characteristics disappear, and if it is less than 20 wt%, the electrical resistance at room temperature is too high.

The dose of the carbon black treating agent is 1 to 10 watts based on the weight of the finally obtained polymer composition.
It is desirable to account for t%.

It is preferable that the conductive polymer composition of the present invention further contains (c) a polymer material which strongly adheres to an aluminum, copper or nickel electrode. By containing such a polymer material, the adhesiveness to the electrode can be increased.

As such a polymer material, for example,
Examples include a polyolefin polymer grafted with maleic anhydride or acrylic acid, an epoxy resin, or a glycidyl methacrylate / polyolefin copolymer.

The amount of this kind of polymer material (adhesive polymer) preferably accounts for 5 to 20% by weight based on the finally obtained conductive polymer composition.

Further, the conductive polymer composition of the present invention includes:
In addition to the composition described above, (d) a filler, a flame retardant,
And materials such as antioxidants.

As the filler, a non-conductive particulate filler having a heat-conducting effect is preferable, and 5 W / m. It is more preferable that the inorganic particles have a thermal conductivity coefficient of ゜ K or more, a resistance value of 10 ¹⁵ Ω-cm or more, and a particle size of 10 times or more of the particles having a conductive action.

As this type of filler, for example, Al
N, SiC, SiO ₂ and mixtures thereof.

The amount of the filler is desirably 25 to 40% by weight based on the finally obtained conductive polymer composition.

To prepare the conductive polymer composition of the present invention, first, a polyolefin polymer having a specific weight ratio is added to a kneading machine together with particles having a conductive action (for example, carbon black that has been treated with a treating agent). And blending in an extruder. When the above-mentioned adhesive polymer material or filler is added, the mixture thus obtained is further added to an adhesive polymer, high heat conductive and high resistance inorganic particles, an antioxidant, a flame retardant, etc. Is added at a time and blended with a kneader or extruder to adjust.

As described above, since the present invention does not use the cross-linking method, it is possible to avoid an increase in cost and the retention of chemical substances, and at the same time, maintain the PTC strength corresponding to high crystallinity and excellent moldability. You can also.

Further, in the present invention, by using a branched crystalline polymer having a high nucleation density, an adsorption effect on the conductive particles is generated at the branch point, and the conductive particles are segregated in a molten state. Precipitation on the boundaries of crystal grains during solidification can be prevented.

Furthermore, in the present invention, by adding a polymer which adheres well to the metal electrode to the polymer composition, electrode peeling caused by thermal expansion or condensation can be prevented.

Furthermore, since a branched crystalline polymer having a high nucleation density is used as a substrate, carbon black or a non-conductive inorganic material is formed between the steps and on the boundaries of the fine crystal particles. Large amounts of particles can be kept. Therefore, a large amount of carbon black and non-conductive inorganic particles can be percolated. Further, since the nucleation density is high, the melting peak and the crystal peak are very close, and the heat of fusion is smaller. Therefore, the reaction time of the PTC thermistor can be short.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples, but these Examples are only for describing preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Is not limited.

Example 1 "Branched polyethylene" shown in Table 1 was blended with "carbon black" which had been treated with a water-soluble polymer having a low molecular weight and polarity in an extruder and blended. Into an extruder together with "metal adhesive polymer", "high heat conductive and high resistance inorganic particles", "antioxidant" and "flame retardant".
After extruding into an m-shaped film and adjusting it to an appropriate shape, an electrode was attached, and the electric resistance value and PTC strength were measured.
The dose of each composition described above is as shown in the right part of Table 1, and was measured twice in total. The measurement results are shown in Tables 2 and 3.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

Example 2 The "branched polyethylene" shown in Table 4 was blended in an extruder together with "carbon black" which had been treated with a low molecular weight and polar water-soluble polymer, and the resulting mixture was blended. Into an extruder together with "metal adhesive polymer", "high heat conductive and high resistance inorganic particles", "antioxidant" and "flame retardant".
After extruding into an m-shaped film and adjusting it to an appropriate shape, an electrode was attached, and the electric resistance value and PTC strength were measured.
The dose of each composition described above is as shown in the right part of Table 4, and was measured twice in total. The measurement results are shown in Tables 5 and 6.

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

Example 3 The "branched polymer" shown in Table 7 was put in a kneader together with "carbon black" and sufficiently stirred, and then pelletized with a pelletizer. Further, the obtained pellets are put into an extruder together with the “metal adhesive polymer”, extruded into a 0.5 mm film shape using a T-shaped extrusion die, adjusted to an appropriate shape, and an electrode is attached. And P
The TC intensity was measured.

The dose of each composition described above is as shown in the right part of Table 7, and was measured twice in total. The measurement results are shown in Tables 8 and 9.

[0047]

[Table 7]

[0048]

[Table 8]

[0049]

[Table 9]

Comparative Example The "low density polyethylene polymer" shown in Table 10 was mixed with "carbon black" in a kneader and blended, and then pelletized with a pelletizer. Next, the obtained pellets are blended with an extruder together with a “metal adhesive polymer”, “antioxidant” and “flame retardant”, and pellets are again produced. I made it. Lastly, the electrode was attached after adjusting to an appropriate shape, and the electric resistance value and the PTC strength were measured. Also,
Mechanical properties such as elongation, tensile strength, bending resistance, and percolation of the film manufactured in this comparative example and the films manufactured in Examples 1 to 3 were also measured. The dose of each composition described above is as shown in the right part of Table 10, and was measured twice in total. Comparative Example and Examples 1 to 3
Table 11 shows the measurement results of the electrical and mechanical properties of each of the films manufactured in Step 1.

[0051]

[Table 10]

[0052]

[Table 11]

[0053]

As described above, since the present invention does not use the cross-linking method, it is possible to avoid an increase in cost and the retention of chemical substances, and at the same time, to obtain PTC strength equivalent to high crystallinity and excellent moldability. Can also be maintained.

Further, in the present invention, the use of a branched crystalline polymer having a high nucleation density causes an adsorption effect on the conductive particles at the branch point, and the conductive particles segregate in a molten state. Precipitation on the boundaries of crystal grains during solidification can be prevented.

Furthermore, in the present invention, by adding a polymer which adheres well to the metal electrode to the polymer composition, electrode peeling caused by thermal expansion or condensation can be prevented.

Furthermore, since a branched crystalline polymer having a high nucleation density is used as a substrate, carbon black or a non-conductive inorganic material is formed between steps and on the boundaries of fine crystal grains. Large amounts of particles can be kept. Therefore, a large amount of carbon black and non-conductive inorganic particles can be percolated. Further, since the nucleation density is high, the melting peak and the crystal peak are very close, and the heat of fusion is smaller. Therefore, the reaction time of the PTC thermistor can be short.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J002 BB031 BB121 BB141 BB151 BB213 BB252 BE022 BE032 BN053 CD003 CD193 CH022 DA036 DF017 DJ007 DJ017 FB266 FD017 FD116

Claims (18)

[Claims] (1) 3% based on (a) a conductive polymer composition
A polyolefin polymer having a polydispersity of less than 2.5 and being branched and occupying 5 to 60 wt%, and (b) 20 to 45 wt% based on the conductive polymer composition.
% Of a conductive polymer composition having a positive temperature coefficient characteristic. 2. The branched polyolefin polymer according to claim 1, wherein
0.865 to 0.935 g / cm ² density, 50 to 1
The conductive polymer composition having a positive temperature coefficient characteristic according to claim 1, having a melting point of 28 ° C and a heat of fusion of 50 J / g or more. 3. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 1, wherein the particles having a conductive action are carbon black. 4. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 3, wherein the carbon black is graphitized carbon black. 5. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 3, wherein the carbon black is non-graphitized carbon black. 6. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 1, further comprising a water-soluble carbon black treating agent having a low molecular weight and a polarity. 7. The method according to claim 6, wherein said carbon black treating agent is selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyethylene oxide, and ethylene / vinyl alcohol copolymer. A conductive polymer composition having temperature coefficient characteristics. 8. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 6, wherein the carbon black treating agent accounts for 1 to 10% by weight based on the conductive polymer composition. object. 9. The conductive polymer composition having a positive temperature coefficient according to claim 1, wherein the polyolefin polymer accounts for 35 to 55% by weight based on the conductive polymer composition. . 10. The conductive polymer having a positive temperature coefficient characteristic according to claim 1, wherein the particles having a conductive action occupy 35 to 45 wt% based on the conductive polymer composition. Composition. (C) a polymer material which is strongly bonded to an aluminum, copper or nickel electrode;
The conductive polymer composition having a positive temperature coefficient characteristic according to claim 1, comprising: 12. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 11, wherein the polymer material is a polyolefin polymer grafted with maleic anhydride or acrylic acid. . 13. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 11, wherein the polymer material is an epoxy resin or a glycidyl methacrylate / polyolefin copolymer. 14. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 11, wherein the polymer material accounts for 5 to 20 wt% based on the conductive polymer composition. . 15. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 11, further comprising (d) a particulate filler having a heat conducting function but being non-conductive. object. 16. The method according to claim 16, wherein the particulate filler is 5 W / m. The inorganic particle according to claim 15, wherein the inorganic particle has a thermal conductivity coefficient of ゜ K or more, a resistance value of 10 ¹⁵ Ω-cm or more, and a particle size of 10 times or more of a particle having a conductive action. A conductive polymer composition having a temperature coefficient characteristic of: 17. The conductive polymer composition having a positive temperature coefficient characteristic according to claim 16, wherein the inorganic particles are selected from the group consisting of AlN, SiC, and SiO ₂ . 18. The conductive polymer composition having a positive temperature coefficient according to claim 16, wherein the particulate filler accounts for 25 to 40% by weight based on the conductive polymer composition. object.