JPH0367322B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field of the invention] The present invention is characterized in that its resistivity increases rapidly when it reaches a certain temperature range, and has a positive temperature coefficient (hereinafter referred to as
The present invention relates to an improvement in an electrical device having a structure in which an organic conductive composition having PTC properties (also referred to as PTC) is sandwiched between metal plate electrodes. [Technical Background and Problems of the Invention] Conventionally, PTC is made by dispersing, for example, metal fine powder, carbon black, or metal fibers in a crystalline polymer such as polyethylene or polypropylene.
Organic conductive compositions (hereinafter referred to as PTC compositions) having characteristics are known. An electrical device made of this PTC composition and a flat metal electrode has good PTC characteristics such as low initial resistance and large resistance change in PTC characteristics, and also has good adhesive properties with the flat metal electrode. Improvement is desired. Therefore, in order to improve the adhesion with metal plate electrodes, we added ethylene/vinyl acetate copolymer (referred to as EVA) or ethylene/ethyl acrylate (referred to as EEA) to crystalline polyolefin as the base polymer of the PTC composition. Attempts have also been made to incorporate copolymers, but EVA or EEA
If the content of VA or EA is 30% or more, it will be as shown in Figure 1, and if the content of VA or EA is less than 30%, it will be as shown in Figure 2.
There was a problem in that a satisfactory PTC composition could not be obtained and an electrical device with sufficient characteristics could not be obtained. However, in the figure, A is a region with high initial resistance, B, C
is the region where the rate of change in resistance of PTC characteristics is extremely small,
D indicates a region where the adhesion between the PTC composition and the metal plate electrode is poor. [Object of the Invention] The present invention has been made to address these conventional drawbacks, and provides an electrical device comprising a sheet-like organic conductive composition having positive temperature coefficient characteristics between two metal plate electrodes. In this method, the organic conductive composition is defined as having a certain blending range of polyethylene or polypropylene with a crystallinity of 20% or more, an ethylene-acrylic acid copolymer, and carbon black, and an acrylic acid content within a certain range. The present invention aims to provide an electrical device that prevents poor adhesion between the PTC polymer and the metal plate electrode without degrading the PTC characteristics by using the ethylene/acrylic acid copolymer of the present invention. [Summary of the invention] That is, the present invention provides a
In an electrical device provided with a sheet-like organic conductive composition having PTC characteristics, the organic conductive composition comprises 15 to 55% by weight of polyethylene or polypropylene with a crystallinity of 20% or more, and 5 to 15 acrylic acid units. Ethylene-acrylic acid copolymer 15-40% by weight, and carbon black 30-50% by weight
% by weight. Crystallinity of organic conductive composition in the present invention: 20
% or more, low-density polyethylene, medium-density polyethylene, and high-density polyethylene can be used, such as Showa Rex (trade name, high-density polyethylene with a crystallinity of 90%, manufactured by Showa Denko) and NUC-8001 ( Manufactured by Nippon Unicar Co., Ltd. (trade name: low-density polyethylene with a degree of crystallinity of 60%). Further, in the present invention, the crystallinity of polyethylene or polypropylene is set to 20% or more because if the crystallinity is lower than this, good PTC characteristics cannot be obtained. The reason why the acrylic acid unit of the ethylene-acrylic acid copolymer (referred to as EAA) used in the present invention is 5 to 15% by weight is that if the acrylic acid unit is less than 5% by weight, as shown in Figure 3, , and when it exceeds 15% by weight, as shown in Figure 4, it is not good.
This is because PTC characteristics cannot be obtained. In the organic conductive composition of the present invention, crystalline polyethylene or polypropylene;
The reason for setting the blending ratio of EAA and carbon black to 15 to 55% by weight: 15 to 40% by weight: 30 to 50% by weight is that good PTC is achieved within this range as shown in Figure 5.
This is because the characteristics can be obtained. The shaded area in Figure 5 has a low initial resistance and an extremely high resistivity of the PTC characteristic.
It also shows a region with good adhesion to the metal flat electrode. The organic conductive composition in the present invention is manufactured, for example, as follows. i.e. 15-55% by weight of crystalline polyethylene or polypropylene
EAA15~40wt% and carbon black 30~
50% by weight is kneaded using an open roll or Banbury mixer at 140 to 180°C, formed into a sheet, and then press-molded into a sheet with a thickness of 0.15 to 2 mm. The electronic device of the present invention is produced by sandwiching the organic conductive composition obtained in this manner between, for example, 20 to 50 μm nickel flat plate electrodes, press-bonding them, and then irradiating and crosslinking them at a dose of 1 to 7 megarads. Manufactured. [Embodiments of the Invention] Next, embodiments of the present invention and conventional examples will be described. Examples 1 to 4, Conventional Examples 1 to 4 The compositions shown in the table were kneaded using a Banbury mixer at 150°C, formed into a sheet, and then sandwiched between 50 μm thick nickel plate electrodes and press-molded into a 0.6 mm thick sheet. Thereafter, both sides were irradiated with 5 megarads for cross-linking to obtain a test piece. Initial resistivity of these specimens, adhesive strength at room temperature and after heat cycling, resistivity at 20℃ and 140℃ and its switching ratio (20℃ and 140℃
The ratio of resistivity of The results are shown in the table. In the heat cycle test, the temperature was raised from room temperature to 40°C at a heating rate of 20°C/15 minutes, held at 40°C for 15 minutes, and then held at the same heating rate for 15 minutes every 20°C. The temperature was finally raised to 140°C and held at this temperature for 1 hour. Next, the temperature was returned to room temperature once for 3 hours, and this operation was repeated 10 times. Furthermore, Fig. 6 shows the PTC characteristics.

[Table] [Effects of the Invention] As detailed above, the electrical device having the PTC characteristics of the present invention has excellent adhesion between the metal flat electrode and the organic conductive composition even after heat cycling, and has a low initial resistance. It has sufficient PTC characteristics such that the change in resistivity is low and large.

[Brief explanation of drawings]

Figures 1 to 4 are explanatory diagrams showing the relationship between the composition and various properties of the organic conductive composition in a conventional electric device, and Figure 5 is the relationship between the composition and various properties of the organic conductive composition in the electric device of the present invention. FIG. 6 is a graph showing an example of the relationship between temperature and specific resistance of the electrical device of the present invention and the conventional electrical device.

Claims (1)

[Claims] 1. In an electrical device comprising a sheet-like organic conductive composition having positive temperature coefficient characteristics between two metal plate electrodes, the organic conductive composition is made of polyethylene or polypropylene 15 with a crystallinity of 20% or more. ~55% by weight, 5-15% by weight of acrylic acid units
An electrical device comprising 15 to 40% by weight of an ethylene-acrylic acid copolymer and 30 to 50% by weight of carbon black.