JPH0374474B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for stably regulating the steady heat generation temperature of a self-temperature regulating heating element, and more particularly to a method for stably regulating the steady heat generation temperature of a self-temperature regulating heating element composition based on polyethylene glycol and carbon fine particles. . It was developed for the purpose of freely adjusting the steady exothermic temperature by adding a third substance, and the purpose is to expand the uses of heating elements in a wide range of fields simply by adding a regulating agent. <Prior art> Polyalkylene oxide, which is the basis of the present invention
For details of the carbon fine particle-based self-temperature-regulating heating element composition, the present inventor has already published JP-A-59-110101;
This was proposed in JP-A No. 60-140692, and these compositions are heated when energized, and when the temperature exceeds a certain value, the electrical resistance value rapidly increases and the current value decreases. When the temperature of the heating element is lowered by cooling, the electrical resistance value decreases and the current increases, resulting in a heating element that maintains the composition at a constant temperature. In other words, such an electrical resistor is called PCTR (Positive Temperature).
Conventionally, barium titanate was known as an inorganic substance, and a polyethylene-carbon fine particle mixed system was known as an organic substance. <Problems to be solved by the invention> However, the barium titanate heating element cannot have a steady heat generation temperature of 70°C or less, and since it is a sintered body, it is difficult to manufacture a planar heating element with a large area. It has the drawback that it is unsuitable for use in other systems, is expensive, and has a PTC effect that is not as great as that of the polyalkylene oxide-carbon fine particle mixture system described above. In addition, the polyethylene (paraffin)-carbon fines system has compatibility problems,
It is still only at the research stage. The above-mentioned polyalkylene oxide-carbon fine particle self-temperature-regulating heating element composition is a novel heating element that is extremely stable and can be expected to have a large PTC effect.
The steady-state exothermic temperature also remains almost constant as long as the concentration of carbon particles is within a certain range, regardless of slight fluctuations in the concentration. When the concentration of carbon fine particles falls below this range, the exothermic temperature becomes proportional to the concentration.
However, from a practical point of view, this is an unfavorable method from the viewpoint of quality control, since a slight variation in the amount of fine carbon particles (for example, graphite) results in a large change in the electrical characteristics of the product. <Means for Solving the Problems> The present invention is based on numerous academic considerations and experiments regarding the PTC effect of polyalkylene oxide-carbon fines-based self-temperature-regulating heating element compositions, and the effectiveness of polyalkylene oxide. At present, it is currently believed that the positively charged part of the π electrons present in the graphite carbon structure interacts with the unpaired electron pair of the ether-bonded oxygen present in these molecules and coordinates. It is believed that this occurs. Therefore, as a result of developing this idea, we developed a carbon fiber that is made of a mixture of polyethylene glycol and fine carbon particles in the form of powder, fibers, whiskers, etc., and has a mixing ratio that allows the electrical resistance to change rapidly in response to temperature changes. Water, alcohol, carboxylic acid, or polyalkylene glycol having side chains as a substance compatible with these compositions and participating in the interaction between the polyethylene glycol and the carbon fine particles, for thermosensitive electrical resistance compositions having the characteristics A method for steadily controlling the heat generation temperature of a self-temperature-regulating heating element has been discovered, which is characterized by adding one or more of the following. As already proposed, an organic compound consisting of a plurality of alkylene oxides connected in a linear or cyclic manner as a unit structure is polyalkylene oxide, and polyethylene glycol is particularly suitable, and polypropylene glycol is also preferred. , block copolymers of polyethylene oxide and polypropylene oxide (Pluronic or Tetronic), and crown ethers are useful. Furthermore, it has already been proposed that these exhibit a unique constant exothermic temperature as a composition with fine carbon particles, and that they can be used individually or in combination (for example, JP-A-60-140692). However, when polyethylene glycol is used in a self-temperature-regulating heating element, the most effective and stable way to adjust its constant exothermic temperature is to add other polyalkylene oxides that have different degrees of interaction with carbon particles. It can be implemented. Furthermore, water is noteworthy because it has an extremely large effect as a regulator, but its use is limited to closed systems due to its high volatility. Alcohols and carboxylic acids are similar to water, and alcohols range from ethyl alcohol and propyl alcohol to higher alcohols such as cetyl alcohol, and polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, and pentitol are also effective. be. As for carboxylic acids, various carboxylic acids can be used, in addition to fatty acids ranging from lower to higher grades similar to alcohols. EXAMPLES Hereinafter, the method for controlling the steady heat generation temperature of the self-temperature-regulating heating element of the present invention will be specifically explained with reference to Examples. Example 1 Graphite carbon (Yoneyama Pharmaceutical Co., Ltd., hereinafter referred to as
Six types of compositions A to F were prepared as shown in Table 1 by adding various amounts of water to polyethylene glycol (Daiichi Kogyo Seiyaku #6000, hereinafter referred to as PG-6000). .

[Table] These compositions A to F were heated and melted,
(During this process, some water evaporates) As shown in Figure 1, composition 1 is placed between two 300 x 80 x 0.11 fiber-coated polyester sheets 2, and the entire
It was made into a sheet of 300 μm. At this time, the electrode has a width of 6
mm, 80 μm thick zigzag copper tape electrode 3,
4, and these are made into one polyester sheet 2
It is pre-glued to the inside (the side with fibers). Aluminum foil 5 with a thickness of 50 μm was adhered to one surface of the planar heating element thus produced to form a heat sink. Furthermore, although not shown, this sheet heating element is
A temperature sensor was attached between two sheets of foamed polystyrene insulation material, and the temperature was measured at each time after 100V AC was applied. The results are shown in Figure 2. Moreover, the relationship between the resistance value (room temperature) and the added water concentration is shown in FIG. As shown in FIG. 2, the steady heat generation temperature decreases with the addition of water, and from FIG. 3 it is clearly seen that the resistance value increases with the addition of water. Example 2 Three types of Pluronics (manufactured by Asahi Denka Kogyo Co., Ltd.) F-68, F-88 and F- were added to the PG-6000-GC system.
108 was added to prepare the compositions shown in Table 2.

[Table] Each of these four compositions was heated and melted to form a polyester sheet with fibers (sheet part 50 μm, thickness 300 μm). On both sides of this sheet heating element, the same aluminum as in Example 1 was applied. Glue the foil to make a heat sink, sandwich it between two 50mm polyurethane foam insulation sheets, attach a temperature sensor,
After applying AC100V, measure the temperature at each time,
The results are shown in Figure 4. As can be seen from FIG. 4, the addition of the three types of pluronics lowers the steady exothermic temperature. What should be noted is that the heat generation decreases as the molecular weight of Pluronic's polypropylene glycol increases. The steady exothermic temperature of each composition is shown in the right column of Table 2 as the equilibrium value in FIG. Example 3 As a result of repeated various experiments for the purpose of manufacturing planar heating elements with steady heat generation temperatures of 45° C. and 35° C., the following compositions were found to be appropriate, and the details thereof will be described below. Composition PG-6000 50g (35.72wt%) PG-2000 50g (35.72wt%) Pluronik F-68 5g (3.57wt%) GC 35g (25wt%) Composition PG-4000 50g (35.72wt%) PG-1000 50g (35.72wt%) Pluronik F-68 5g (3.57wt%) GC 35g (25wt%) The above compositions were heated and melted, respectively.
As in Example 1, a sheet heating element of 300 x 80 x 0.3 mm was made, an aluminum foil heat sink was glued on, a temperature sensor was attached, and it was sandwiched between two sheets of 50 mm heat insulating material.
AC100V was applied and the temperature was measured at each time. The results are shown in Figure 5, and the composition is
At 45°C, the composition reached the desired steady exothermic temperature of 35°C. Example 4 In Example 3, a planar heating element with a steady heat generation temperature of 35° C. and 45° C. was described, but it was investigated how much the heat generation temperature was affected by a small change in carbon concentration. Compositions having carbon concentrations shown in Table 3 were prepared.

[Table] After heating and melting each of the above compositions, make a planar heating element, attach a temperature sensor, and sandwich it between 50 mm insulation materials.
The temperature at each time after 100V AC was applied is plotted in Figure 6. From FIG. 6, it was found that even when the GC concentration was changed by 4 wt%, the steady exothermic temperature was approximately 3°C from the highest to the lowest, so this was not a big problem in terms of quality control in mass production. Example 5 A composition of 70 g of Pluronic (Asahi Denka Kogyo F88), which is a copolymer made by reacting polypropylene glycol with polyethylene glycol on both sides of the molecule, and 30 g of Graphite Carbon (Yoneyama Yakuhin Kogyo) was heated and melted. As shown in FIG. 2, a sheet heating element was prepared by sandwiching a silicone spacer net 7 between two fiber-covered polyester sheets 2 (same as in Example 1) with copper foil electrodes 6 adhered to them. Similar to Example 11, aluminum foil 5 is glued to one side of the sheet heating element to serve as a heat sink, a temperature sensor is attached, and several single dry cell batteries are placed in parallel by sandwiching it between two 50 mm insulation sheets. Figure 8 shows the temperature at each time when electricity was applied using a 1.5VDC power supply connected to the 1.5V DC power supply. <Operations and Effects> Based on the results of the above examples, the operations and effects of the steady heat generation temperature control method of the present invention will be summarized. In Example 1, protons coordinate with the oxygen of the ether bond of PG, and as a result, the resistance value increases.
It was revealed that as the H ₂ O concentration increased, the steady exothermic temperature showed a larger value and decreased, which prevented the coordination of the ether-bonded oxygen of graphite to the unpaired electron pair. In Example 2, next to the oxygen of

Hanging from [formula]

All phenomena can be explained by considering that [Formula] acts as a steric hindrance to the coordination of carbon. It is thought that the more propylene oxide structures there are, the greater the coordination interference, and therefore the steady exothermic temperature is thought to decrease in the order of F-68, F-88, and F-108. Therefore, it was found that it is possible to control the steady exothermic temperature by attaching a side chain to the alkylene group of polyalkylene oxide. What should be noted here is that the exothermic temperature can be controlled simply by adding alkylene groups with side chains, without having to attach side chains to (some or all) of the alkylene groups in the entire matrix. It is a point. The side chain is not limited to the methyl group shown in the examples, but since the purpose is simply to cause steric hindrance, any side chain may be used as long as the electrical resistance is not impaired. Based on this idea, Example 3 has a steady exothermic temperature of 35
This shows that we have succeeded in fabricating a planar heating element at ℃. The value of steady exothermic temperature of 35°C is sufficiently significant. Since the temperature in the composition without Pluronic F-68 is approximately 55°C, a decrease of 10°C occurs with the addition of Pluronic F-68. In the case of the composition, the temperature was approximately 50°C without the addition of Pluronic, so the addition of Pluronic made it possible to reduce the steady exothermic temperature by 15°C. As mentioned above, barium titanate is widely used and has a function similar to that of the present invention. However, this barium titanate has the following two weaknesses. The first is that the Curie point cannot fall below 70°C, and therefore the steady exothermic temperature cannot fall below 70°C. Second, the heat generating surface of barium titanate cannot be made too large. In the present invention, as already shown, it was possible to lower the temperature of a planar heating element that can be mass-produced to 35°C. The lower the steady heat generation temperature can be, the more energy consumption can be saved. The heating element according to the invention comprises:
If used for freezing prevention, snow melting, etc., it becomes an extremely economically efficient heater. Use in cold regions to melt snow on steps for boarding and disembarking buses, to prevent ice from forming on destination display boards, and in other situations where a slight warmth is required (keeps handles warm, grips of motorcycles and bicycles warm)
It can greatly contribute to In Example 4, it was revealed that the invention of Example 3 causes no problems in terms of quality control in mass production. Example 5 shows a slightly different application of Pluronic. As mentioned above, Pluronic has steric hindrance due to the methyl group in the side chain of the propylene group, so a heating element made of a combination of graphite carbon and Pluronic has a considerably high resistance value.
If a conventional type of heating element is used, it would be necessary to make it practically thick. The inventor took advantage of this point as described below. In Examples 1 to 4, the distance between the electrodes of the heating element was 7.6 cm. I have already mentioned in JP-A-61-22591 a planar heating element that uses a battery as a power source by lowering the applied voltage, but it is difficult to make a planar heating element that is sufficiently thin when using a 1.5V dry cell battery as a power source. It was difficult. However, as shown in Example 5, we succeeded in producing a sheet heating element for batteries (1.5V) with a thickness of 1 mm. This is due to the fact that the high electrical resistance of the Pluronic graphite system is utilized to increase the electrode area and to make the distance between the electrodes extremely short. This planar heating element is extremely useful, for example, as a hand warmer.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway plan view of the planar heating element, Fig. 2 is a graph showing the temperature-current application time curve of the composition when water is used as a constant heat generation temperature control agent, and Fig. 3 is a graph showing the temperature-current application time curve of the composition. It is a graph showing the relationship between the moisture content inside and the resistance value. FIGS. 4 to 6 and 8 are graphs showing the relationship between temperature and current application time, showing the effect of adding Pluronic. FIG. 7 is a partially cutaway plan view showing another example of the sheet heating element. DESCRIPTION OF SYMBOLS 1... Composition, 2... Polyester sheet with fibers, 3, 4... Copper tape electrode, 5... Aluminum foil, 6... Copper foil electrode, 7... Silicon spacer net.

Claims (1)

[Claims] 1. A heat-sensitive electrical resistance composition having positive characteristics, consisting of a mixture of polyethylene glycol and fine carbon particles in the form of powder, fibers, whiskers, etc., adjusted to a mixing ratio that has the property of rapidly changing electrical resistance in response to temperature changes. In contrast, one or more of water, alcohol, carboxylic acid, or polyalkylene glycol having a side chain is added as a substance that is compatible with the composition and participates in the interaction between the polyethylene glycol and the carbon fine particles. A method for regulating the steady heat generation temperature of a self-temperature regulating heating element, characterized in that: