JPS61181859A - Conductive polymer compositions with positive temperature coefficient properties - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive polymer composition, particularly a property that its electrical resistance rapidly increases when it reaches a certain temperature range (hereinafter referred to as r).
It is abbreviated as "PTC characteristics". ).

[Industrial application field]

The present invention provides a conductive polymer composition suitable for heating heaters and the like as energy-saving heating elements.

[Conventional technology]

Conventionally, conductive polymer compositions having PTC properties, which are obtained by dispersing, for example, fine metal powder or carbon black in a crystalline polymer such as polyethylene or polypropylene, are known in this technical field, and are disclosed in, for example, U.S. Pat. 3
, No. 591,526, No. 3.243, No. 753, etc.

This PTC characteristic is due to the rapid increase in volume that occurs when a crystalline polymer transitions from crystalline to amorphous near its melting start temperature. It is thought that this occurs because the electrical resistance of the polymer rapidly increases as the polymer is expanded.

When a polymer composition having PTC characteristics is used as a top heating element, it becomes a heater that has extremely low energy loss and significantly reduces electric power consumption compared to conventional nichrome wires or inorganic insulated wires.

The surface temperature of the heating element with this PTC characteristic is 40 to 70
℃ range &l) can be used as an energy-saving heating element for space heaters, etc.

Conventionally, as a conductive polymer composition having PTC characteristics in this temperature range, a combination of polyethylene oxide and carbon powder is known (Japanese Patent Laid-Open No. 59-6609).
Publication No. 3).

However, in the above conductive polymer composition, PTC
Although the characteristics show a rapid change in resistance value at the transition point,
Stability under the environmental conditions of practical use;
In terms of moisture resistance, the above polyalkylene oxide generally has an affinity for water, and when it absorbs moisture in the air, it swells significantly, causing shape changes and mechanical damage. This not only causes a decline in physical performance, but also causes irreversible changes in electrical performance, making it impossible to obtain stable PTC characteristics.

[Problems to be Solved by the Invention] The present inventors have conducted extensive research in order to improve these drawbacks and develop a crystalline polyalkylene oxide-based conductive polymer composition that has practically stable PTC properties. I did it.

[Ninth way to solve the problem]

As a result, by adding to the conductive polymer composition a modified polyolefin containing a carboxyl group or a carboxylic acid anhydride group in the side chain or the main chain, 5. It has been found that the above drawbacks are significantly improved without substantially impairing the PTC characteristics, and the present invention has been achieved based on this finding.

That is, the present invention provides (al component: crystalline polyalkylene oxide, (b) component: side chain or/and main chain,
A conductive polymer composition having a positive temperature coefficient characteristic, characterized by comprising a modified polyolefin containing a carboxyl group or/and a carboxylic acid anhydride group, and a tc) component: conductive carbon black or/and graphite. .

Next, to explain the present invention in detail, the crystalline polyalkylene oxide of component (a) used in the present invention includes polyethylene oxide, polypropylene oxide, poly-
Examples include 1-butene oxide and poly-2-butene oxide, with polyethylene oxide being particularly preferred.

Its molecular weight is usually 10,000 or more and 500,000 or less, preferably 50,000 to □□□.

Polyolefins used in the production of the modified polyolefin of component (b) of the present invention include polyethylene (low, medium, high density, linear low density), polypropylene, ethylene-
Vinyl acetate copolymer, propylene-ethylene block t
7? :t:t random comonomers and other poly-α-olefins.

In order to produce the above-mentioned modified polyolefin, that is, to introduce a carboxyl group and/or a carboxylic acid anhydride group into the side chain and/or main chain of the above-mentioned polyolefin, unsaturated carboxylic acid (such as acrylic acid, methacrylic acid, etc.) is introduced into the polyolefin. A method of t-graft polymerization of unsaturated carboxylic acid anhydrides (e.g. maleic anhydride, hymic anhydride, etc.), and a method of t-graft polymerization of polyolefins and unsaturated carboxylic acids/and their anhydrides. Alternatively, there are a method of block copolymerization and a method of oxidizing polyolefin.

Among these, those obtained by graft polymerization are particularly preferable, and maleic acid and maleic anhydride are preferable as monomers. Note that a blend of the above-mentioned modified polyolefin and unmodified polyolefin can also be used.

In addition, in the above-mentioned modified polyolefin, the content of carboxyl groups and/or carboxylic acid anhydride groups is suitably 0.01 to 15 times based on the polyolefin,
Preferably it is 0.05 to 10% by weight.

Next, as the conductive carbon black of component (c) used in the present invention, there are, for example, fine powders such as furnace black, thermal black, channel black, and acetylene black. Further, as the graphite, both natural graphite and artificial graphite can be used. Among these, it is preferable to use acetylene black and graphite in combination.

The present invention uses the above-mentioned (a) crystalline polyalkylene oxide, (b) modified polyolefin, and (cl conductive fine powder), and the blending ratio thereof is ta
l is in the range of 30 to 80% by weight, (b) is in the range of 30 to 5% by weight, and [cl is in the range of 45 to 15% by weight, preferably t
a) is in the range of 40 to 70 weight percent [bl] is in the range of 20 to 10 weight percent, and (c) is in the range of 40 to 20 weight percent.

In addition, in the composition of the present invention, an inorganic or organic filler is added as an additional component in addition to the above-mentioned (al +
It can be blended in an amount of not more than 40% by weight, preferably not more than (9)% by weight, based on (b) + tel. As the inorganic filler, calcium carbonate, talc, mica, glass fiber, magnesium hydroxide, etc. can be used, and as the organic filler, charcoal, aromatic polyamide fiber, etc. can be used.

The combination of these fillers can be expected to improve mechanical properties and appearance as well as control conductivity.

The composition of the present invention can be used in batch-type mixers such as Banbury mixers, rolls, and Brabender plastographs, as well as
- It can be obtained using a continuous extruder such as a screw extruder or a twin screw extruder. The order of blending is not particularly limited,
In addition to the method of mixing and kneading the mixture at once, it is also possible to first knead a part in a batch-type or continuous-type mixer, and then knead the mixture and the remaining part.

[Effect]

As mentioned above, the present invention provides a polyalkylene oxide-based conductive polymer composition that has improved stability under the environmental conditions of use, particularly moisture resistance.

The expression of such effects of the present invention is beyond speculation at this stage, but it is possible that the carboxyl group or carboxylic acid anhydride group of the modified polyolefin, the ethereal oxygen of the polyalkylene oxide, and the functionality present on the surface of carbon black or graphite. It is presumed that this is caused by complex bonds with groups.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples.

Example 1 Polyethylene oxide (Alcox R-1000 manufactured by Meisei Chemical Industry Co., Ltd., with a molecular weight distribution of weighted to (9) million), 45 weight tS, maleic anhydride graft-modified ethylene-vinyl acetate copolymer (maleic anhydride) Acid content 1.0
Weight 1) 20% by weight, % weighted graphite, and 5 layers of acetylene diluted with 9 fufu lids were uniformly mixed in a Suhar mixer,
The mixture was then kneaded into pellets using a twin-screw extruder with a diameter of 301111. All of this pellet is press-molded, 100X100X
Two sheets were obtained.

Humidity test specimen (40ccx 90% R)
After 240 hours of Hx, the temperature dependence of the electrical resistance was measured. The results are shown in FIG.

As a comparative example, a similar test was conducted on the above-mentioned composition of 65% by weight of polyethylene oxide, 30% by weight of graphite, and 5% by weight of acetylene black, but after the humidity test, the electrical resistance increased significantly and the temperature dependence was also weak. Unfortunately, it had become impractical. The results are shown in FIG.

Example 2 Concerned about the maleic anhydride graft-modified ethylene-vinyl acetate copolymer of Example 1, the maleic anhydride content was 1.2% by weight.
! A similar test was conducted using maleic anhydride graft modified polyethylene of K.S., and the results are shown in FIG.

〔Effect of the invention〕

As mentioned above, polyalkylene oxide-based conductive polymer compositions lack stability and are impractical because polyalkylene oxide has strong hygroscopicity.
In the composition of the present invention, by blending the modified polyolefin of component fb), it has been possible to significantly improve moisture resistance and create a conductive polymer composition having stable and excellent PTC properties.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are curves showing the relationship between temperature and volume resistivity of the polymer compositions of Example 1, Example 2, and Comparative Example, respectively. Figure 2 Temperature ('C)

Claims (1)

[Scope of Claims] A conductive polymer composition having positive temperature coefficient characteristics, characterized by comprising the following components (a) to (c). (a) Crystalline polyalkylene oxide (b) Modified polyolefin containing a carboxyl group or/and carboxylic acid anhydride group in the side chain or/and main chain (c) Conductive carbon black or/and graphite