JPH06124803A - Conductive composite body - Google Patents

Abstract

PURPOSE:To stabilize the resistance value when the temperature is restored to a normal temperature and recover it to the initial value even if a PTC phenomenon would be generated repeatedly by using two kinds of superfine glassy carbons having different mean grain size together with an ultrahigh molecular weight polyolefin. CONSTITUTION:A composition containing 20-90wt.% ultrahigh molecular weight polyolefin, 0-40wt.% superfine glassy carbon of 1-20mum in average grain size, and 10-70wt.% superfine glassy carbon of 40-400mum in average grain size is formed by heating. As for the superfine glassy carbon, a thermosetting resin such as furfuryl alcohol resin, phenol resin, etc., is used as material and the result obtained through carbonization or graphitization can be used for its use, but globular phenol resin particles carbonized at 1000-3000 deg.C is most suitable. Thus, even if a PTC phenomenon would be generated repeatedly, the resistance value when the temperature is restored to a normal temperature can be stabilized and recovered to the initial value.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive composite having a stable positive temperature coefficient (hereinafter referred to as PTC).

[0002]

2. Description of the Related Art PTC is a specific temperature range
The electric resistance value thereof is a property of rapidly increasing with an increase in temperature. As a conventional conductive composition having the property of PTC, carbon black or metal powder is added to crystalline polymer such as polyethylene, polypropylene or nylon. Filled conductive compositions are known. For example, JP-A-6
In JP-A 1-218117, a polyethylene having a molecular weight of 200,000 to 400,000 and carbon black are mixed and pelletized, and a molded product obtained by an injection molding method is irradiated with an electron beam to obtain a conductive material having a PTC property. A method of obtaining the composition is disclosed.

Further, in JP-A-62-167358, an organic polymer such as polyethylene and carbon black are melt-mixed, finely pulverized, irradiated with an electron beam, blended with a matrix polymer and molded. After that, a method of further irradiating with an electron beam to obtain a conductive polymer composition having the property of PTC is disclosed. In addition, Japanese Patent Application No. 3-58
Japanese Patent No. 327 discloses a PTC composite composed of ultra-high molecular weight polyolefin and fine granular glassy carbon and a method for producing the same.

However, in any case, the obtained composition has the property of PTC, but when an abnormality such as overcurrent or overvoltage occurs in the circuit, the resistance value is initially set even when the circuit is turned off. It had a drawback that it did not return to the value of 10 times and sometimes became 10 times or more.

[0005]

The object of the present invention is to provide a PT
It is an object of the present invention to provide a conductive composite having excellent properties such that the resistance value is stabilized and returned to the initial value when the temperature is returned to room temperature even if the C phenomenon is repeatedly expressed.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have found that the use of two types of fine-grained glassy carbons having different average particle sizes together with ultra-high molecular weight polyolefin has the purpose. The inventors have found what can be achieved and have reached the present invention. That is, the present invention has an ultrahigh molecular weight polyolefin of 20 to 90% by weight and an average particle size of 1 to 2.
A conductive composite having a positive temperature coefficient obtained by heat-molding a composition containing 0 to 40 wt% of fine glassy carbon having a particle size of 40 to 400 μm and 0 to 40 wt% of fine glassy carbon having a mean particle size of 40 to 400 μm. It is what

The conductive composite of the present invention comprises an ultra-high molecular weight polyolefin and two kinds of finely divided glassy carbons having different average particle diameters, and the total content of the finely divided glassy carbon is 10 to 80% by weight, preferably 20. Is about 70% by weight. If it is less than 10% by weight, it is difficult to obtain sufficient conductivity, and if it exceeds 80% by weight, the strength of the composite tends to be weak, which is not preferable.

The ultra-high molecular weight polyolefin used in the present invention is not particularly limited, and examples thereof include ethylene, propylene and 1
-Butene, 1-hexene, 1-octene, 1-decene,
Examples thereof include homopolymers or copolymers of α-olefins such as 1-dodecene and 4-methyl-1-pentene. In particular, a homopolymer of ethylene is preferable. The intrinsic viscosity of ultra-high molecular weight polyolefin measured in a decalin solvent at 135 ° C. is 400 ml / g or more and 5000 ml / g or less, preferably 500 ml / g or more and 4000 ml / g or less. When the intrinsic viscosity is less than 400 ml / g, the strength of the obtained composite is insufficient, and when it exceeds 5000 ml / g, molding tends to be difficult.

As the ultra high molecular weight polyolefin,
Particle size of 5-800μm is used, 10-100μm
Are preferred. If the particle size is less than 5 μm, secondary aggregation is likely to occur, and if the particle size exceeds 800 μm, it becomes difficult to obtain a composite having sufficient strength.

As the fine granular glassy carbon used in the present invention, those produced through a process of carbonization or graphitization from a thermosetting resin such as furfuryl alcohol resin or phenol resin can be used. Most preferably, the resin particles are carbonized at 1000 to 3000 ° C. In the present invention, the average particle size is 1 to 20 μ.
m fine-grained glassy carbon and average particle size 40-400
It is preferable to use a combination of fine granular glassy carbon having a particle size of μm. However, if a particle size other than that is used, it becomes difficult to return to the initial resistance value when the temperature returns to room temperature after exhibiting the properties of PTC.

By blending these components, room temperature (10 to 10
It has a resistance value of about 10 Ω · cm or less at 30 ℃, 0-20
In the operating temperature range of 0 ° C., the R15 value is 10 or more, or the R100 value is 100 or more, preferably the R15 value is 10 or more.
A conductive composite having the above and R100 of 100 or more is obtained. Here, the R15 value represents the ratio of the first and last resistivities in the temperature range of 15 ° C. in which the increase in resistivity is largest in the operating temperature range of 0 to 200 ° C., and R100
The value represents the ratio of the first and last resistivities in the temperature range of 100 ° C. in which the resistivity increase is largest in the operating temperature range of 0 to 200 ° C.

The electroconductive composite of the present invention can be produced by mixing a predetermined amount of ultra-high molecular weight polyolefin and two kinds of finely divided glassy carbon, and then compression-molding the mixture under heating. At this time, a release agent, an antioxidant, and a filler such as calcium carbonate may be added, if necessary.

The heating temperature is not less than the melting point of the ultrahigh molecular weight polyolefin and not more than (melting point + 30 ° C.), preferably,
Above the melting point of ultra high molecular weight polyolefin, (melting point +20
℃) or less. At a temperature lower than the melting point of the ultra high molecular weight polyolefin, sufficient strength cannot be obtained, and (melting point +30
At a temperature higher than (.degree. C.), the ultra-high molecular weight polyolefin covers the surface of the fine glassy carbon and it becomes difficult to obtain sufficient conductivity.

The molding pressure is 10 to 1500 kg / cm.
² is suitable, preferably 40 to 700 kg / cm ² . The pressing time is suitably 10 to 360 seconds, preferably 20 to 300 seconds. Press pressure is 10
If it is less than kg / cm ² or if the pressing time is less than 10 seconds, it becomes difficult to obtain sufficient strength. If the pressing pressure exceeds 1500 kg / cm ² or the pressing time exceeds 360 seconds, it is uneconomical and not preferable.

Next, the present invention will be described more specifically with reference to examples. Example 1 Ultra high molecular weight polyethylene fine powder (PE-COMP-14
07, manufactured by Toyo Ink Co., Ltd.) 50% by weight, 30% by weight of fine granular glassy carbon (GCP-10H, manufactured by Unitika Ltd.) having an average particle size of 8 μm, and 90% by weight of fine granular glassy carbon (GCP-100H, manufactured by Unitika Ltd.) ) 2
0 wt% was dry blended to obtain a mixture. This mixture is filled in a mold and the mold temperature is 160 ° C and the pressing pressure is 60 kg.
/ Cm ² in do 180 seconds press, and cooled under pressure, the volume resistivity at room temperature to obtain a conductive composite is 3.7 × 10 ⁰ Ω · cm. Next, in order to investigate the stability of the electric resistance value, a temperature cycle test (holding at 140 ° C. for 10 minutes, holding at 25 ° C. for 10 minutes was set as one cycle, and the volume resistance at room temperature after 10 cycles was measured, and The rate of change of the volume resistance value with respect to the initial value was 4.0%, which was stable. The physical property values are shown in Table 1.

Example 2 Ultra high molecular weight polyethylene fine powder (PE-COMP-14
07, manufactured by Toyo Ink Co., Ltd.) 70% by weight, fine granular glassy carbon (GCP-100H, manufactured by Unitika Ltd.) 10% by weight, and fine granular glassy carbon (GCP-10H,
Unitika 20% by weight was dry blended to obtain a mixture. This mixture is filled in a mold and the mold temperature is set to 160
Press for 180 seconds at ℃ and press pressure of 60kg / cm ² ,
Cooled under pressure, the volume resistance at room temperature is 4.0 × 10 ⁰ Ω ・
A conductive composite that is cm is obtained. Table 1 shows the results of the temperature cycle test and the physical properties thereof.

Example 3 Ultra high molecular weight polyethylene fine powder (PE-COMP-14
07, manufactured by Toyo Ink Co., Ltd.) 45% by weight and fine-grained glassy carbon (GCP-100H, manufactured by Unitika) 55
The mixture was obtained by dry blending wt%. This mixture is filled in a mold, the mold temperature is 160 ° C., the pressing pressure is 60 kg /
It was pressed at cm ² for 180 seconds and cooled under pressure to obtain a conductive composite having a volume resistance at room temperature of 1.6 × 10 ⁰ Ω · cm. Table 1 shows the results of the temperature cycle test and the physical properties thereof.

Comparative Example 1 Ultra high molecular weight polyethylene fine powder (PE-COMP-14
07, manufactured by Toyo Ink Co., Ltd.) 50% by weight and average 25 μm
50% by weight of fine granular glassy carbon (GCP-30, manufactured by Unitika Ltd.) was dry blended to obtain a mixture.
This mixture was filled in a mold, and pressed at a mold temperature of 145 ° C. and a pressing pressure of 150 kg / cm ² for 10 seconds, cooled under pressure, and had a volume resistance at room temperature of 1.4 × 10 ⁻¹ Ω · cm. To obtain a conductive composite. Table 1 shows the results of the temperature cycle test and the physical properties thereof.

[0019]

[Table 1]

[0020]

EFFECTS OF THE INVENTION According to the present invention, a conductive composite having excellent characteristics that the resistance value when the temperature is returned to room temperature is stably recovered to the initial value even if the PTC phenomenon is repeatedly expressed is obtained. To be

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Echigo 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd. Central Research Laboratory

Claims (1)

[Claims] 1. Ultra-high molecular weight polyolefin 20 to 90% by weight, finely divided glassy carbon having an average particle size of 1 to 20 μm 0 to 40% by weight, and finely divided glassy carbon having an average particle size of 40 to 400 μm 10 to 70% by weight A conductive composite having a positive temperature coefficient obtained by heat-molding the composition.