JPS6243464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive element made of a specific polyamide composition, particularly a heat-sensitive element whose impedance characteristics change significantly depending on temperature.

The use of organic polymeric materials whose electrical properties change rapidly with temperature, such as polyvinyl chloride and polyamide, as heat-sensitive elements has been known for some time, as seen in electric blankets, electric carpets, etc. . Control factors for the thermosensitive element include direct current volume resistivity, specific inductivity, and volume specific impedance, and a combination of one or more of these can operate the control circuit.

Therefore, the characteristics required of a heat-sensitive element are: (1) A large rate of change in electrical properties due to temperature.

(2) Changes in electrical properties due to moisture absorption are small.

(3) It must be stable, with no change in electrical properties over time due to heat cycles.

(4) Excellent mechanical properties such as flexibility and heat resistance, and moldability.

Examples include.

Among the above-mentioned polymeric materials, polyamide in particular has excellent electrical properties, mechanical properties, moldability, etc., and is therefore widely used as heat-sensitive elements such as electric blankets and electric carpets. Various methods have been studied to further improve the relative dielectric constant behavior of these polyamide resins with respect to temperature. Method of adding ionic surfactant
10978), but the former method does not necessarily provide sufficient sensitivity and requires a large amount of additives to achieve high sensitivity, making it difficult to mix the additives uniformly and making it difficult to obtain uniform characteristics. In addition, the latter method has problems such as insufficient sensitivity and migration and precipitation of the surfactant while the heat-sensitive element is energized, resulting in unsatisfactory stability of heat sensitivity. be.

Also, attempts were made to improve the heat-sensitive characteristics by adding halides to polyamides, for example, in JP-A-52-
27594, the potassium iodide exemplified here essentially has poor compatibility with polyamide, so when polyamide containing potassium iodide is molded into a sheet or linear shape, potassium iodide is Other examples include stannous chloride, which has the problem that undissolved crystals tend to precipitate as foreign matter.
Ferric chloride has the disadvantage of significantly corroding copper and aluminum used in signal conductors, and it is difficult to obtain a thermofunctional element material that satisfies all of the various practical properties by simply adding a halide. I can't.

Therefore, the present inventors conducted intensive studies to solve some of the above-mentioned practical problems, and as a result, they discovered that the above object could be achieved by a combination of a specific polyamide resin and a specific metal halide, and arrived at the present invention. did.

That is, the present invention provides a heat-sensitive element comprising a polyamide composition containing 100 to 6000 ppm of lithium chloride as lithium to a polyamide resin having 14 or less amide groups per 100 carbon atoms.

According to the heat-sensitive element of the present invention, the rate of change in electrical properties with respect to temperature is extremely large, and unlike plasticizers and surfactants, the amount does not change over time due to bleed-out. It has excellent stability in properties, does not corrode metals (wires or foils) such as aluminum and copper used for signal conductors, has excellent heat resistance, and is easy to mix with polyamide resin and lithium chloride. Benefits such as:

The polyamide resin used in the present invention is polyaminoundecamide (nylon 11) or polyω
- A polyamide with a low concentration of amide groups such as laurolactam (nylon 12), more specifically, the number of amide groups is 14 per 100 carbon atoms.
homopolyamide or copolyamide.

Furthermore, the amount of lithium chloride added, which is an additive component of the polyamide composition for heat-sensitive elements in the present invention, is 100% as lithium to the polyamide resin.
~6000 ppm, preferably 300 to 3000 ppm is appropriate; if it is less than 100 ppm, the electrical properties cannot be sufficiently improved, and if it is more than 6000 ppm, the mechanical properties of the polyamide resin will deteriorate, which is not preferred.

Further, even if lithium compounds other than lithium chloride, such as lithium fluoride, lithium carbonate, and lithium hydroxide, are used as additives, a satisfactory effect of improving electrical properties cannot be obtained.

The method of adding lithium chloride to the polyamide resin is not particularly limited, and includes a method of adding it during the polymerization stage of the polyamide, a method of mechanically mixing polyamide powder and lithium chloride, or a method of melting and kneading it with an extruder after mixing it with polyamide chips. Any method such as this can be implemented.

The polyamide composition containing lithium chloride is usually further formed into a wire or sheet shape using an extruder or the like to form a heat-sensitive element.

The effects of the present invention will be explained below using examples.

Example 1 Nylon 12/6 copolymer obtained by polymerizing 85 parts by weight of ω-laurolactam and 15 parts by weight of ε-caprolactam (relative viscosity η _r =2.2 when 1 g/98% sulfuric acid solution was measured at 25°C) Add 1000 ppm of lithium each of A lithium chloride, B lithium fluoride, C lithium carbonate, and D lithium hydroxide to the mixture, mix using a Henschel mixer, melt blend using an extruder, and extrude into a gut shape. It was cooled in a water bath and cut into chips using a cutter. Using this pellet, a compression molding machine set at 250℃ produces approximately 1 mm
A thick sheet was formed. About this sheet
The temperature dependence of the relative permittivity and specific volume impedance at 1000 c/s was measured. The results are shown in Figures 1 and 2. The results for nylon alone are shown as E in the same figure.

As can be seen from the above results, the electrical properties of nylon are significantly improved by adding lithium chloride. Lithium fluoride, lithium carbonate, and lithium hydroxide have no effect on improving the electrical properties of nylon.

In addition, the above press sheet and copper foil were heated at 210℃.
When we bonded with heat and pressure at a pressure of 1Kg/cm ² G and left it in a humidity control tank at a temperature of 40℃ and a relative humidity of 90%, no corrosion of the copper foil occurred at all even after 60 days had passed. It was found to be extremely stable.

Comparative Example 1 The nylon 12/6 copolymer used in Example 1 was
1000 ppm of potassium iodide was added, and then mixing/melt blending was carried out in exactly the same manner as in Example 1 to obtain pellets. When this pellet was formed into a sheet approximately 1 mm thick in the same manner as in Example 1, a large number of undissolved potassium iodide crystals were present in the sheet, resulting in unstable electrical properties and poor reliability. found.

Comparative Example 2 1000 ppm of ferric chloride as iron was added to the nylon 12/6 copolymer used in Example 1, and the mixture was mixed/melt extruded and pelletized in exactly the same manner as in Example 1. When this pellet was made into a sheet, no undissolved foreign matter was found, but when the sheet and copper foil were adhered in the same manner as in Example 1 and left in a humidity control tank, the copper foil corroded within one day. It was found that this problem could not be put into practical use.

[Brief explanation of the drawing]

Figure 1 shows the relationship between relative dielectric constant and temperature of a heat-sensitive element made of a mixed composition of nylon 12/6 copolymer and lithium compound according to Example 1, and Figure 2 shows the relationship between the relative permittivity and temperature of a heat-sensitive element made of a mixed composition of nylon 12/6 copolymer and lithium compound according to Example 1. The relationship between the specific volume impedance and temperature of a heat-sensitive element made of a mixed composition of a polymer and a lithium compound is shown.

Claims (1)

[Claims] 1. A heat-sensitive element made of a polyamide composition containing 100 to 6000 ppm of lithium chloride mixed into a polyamide resin having 14 or less amide groups per 100 carbon atoms.