JPH0310203B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a novel heat-sensitive electrical resistance composition that is made of a mixture of polyalkylene glycols and carbonic acid powder, generates heat when energized, and has a Curie point at a predetermined temperature.

[Prior art and problems to be solved by the invention]

A heat-sensitive resistance element is generally used as an element having a temperature characteristic in which internal heat generation occurs upon application of a voltage, and the resistance value rapidly increases at a certain temperature. Barium titanate with a trace amount of rare earth elements added thereto is used as a positive temperature coefficient thermistor (a heat-sensitive resistance element with positive resistance-temperature characteristics). There are also heat-sensitive resistance compositions made by mixing thermoplastic polymer materials, especially crystalline polyethylene, with carbonate powder, which is also widely used (for example, Japanese Patent Publication No. 36-16338,
Special Publication No. 50-33707, Special Publication No. 55-12683, etc.)
However, polymer compounds have a wider range of melting points than low-molecular organic compounds, making it difficult to use them as sharp thermistors. On the other hand, many of the organic compounds known as heat storage media, such as paraffins and polyalkylene glycols, are themselves poor conductors of electricity and cannot be heated directly with electricity, so heating using an electric heater is necessary. is common. Therefore, the use of a thermistor is essential for temperature control and safety. This has the undeniable drawback of increasing equipment costs.

[Means to solve the problem]

The present invention was obtained in the process of various studies and studies in order to improve the above-mentioned drawbacks of the conventional technology, and consists of mixing 15-40% carbonate powder with polyalkylene glycol, which is solid at almost room temperature and has a melting point of 18-75℃. This is a heat-sensitive electrical resistance composition. Here, polyalkylene glycols are polyethylene glycol, polypropylene glycol, alkyl esters and alkyl esters of polyalkylene glycol, and have a melting point of 18 to 75°C.
It is a solid at almost room temperature.

[Effect]

The mixing ratio of polyalkylene glycols and carbonic acid powder is one of the important factors in the present invention. ，
Figure 1 shows the temperature rise curve of the heat storage medium versus time when an electrode was inserted into the mixture to which 80g was added and electricity was applied. As is clear from this result, the product containing 20g of graphite powder, or 14.3%, hardly conducts electricity, even after 120 minutes.
There is no temperature increase in PEG. 40g or 25%
When mixed, the temperature rises to about 40℃, and 60g or
Melting point 49 within almost 30 minutes by 33.3% contamination
When the temperature approaches ℃, PEG melts. As it melts, the electrical resistance increases from 500Ω to 1900Ω, and the current value increases to 1.5A.
It drops from 0.1A to less than 0.1A. The situation is shown in Figure 2. As is clear from FIGS. 1 and 2, energization causes a rise in temperature, and after a certain point (the Curie point), no rise in temperature is observed and the temperature remains constant. This is because the POSISTOR self-heats when a voltage is applied, and when the current reaches a maximum point, the power becomes constant, so the heat-sensitive resistor composition itself performs an automatic temperature control function. It was explained earlier that the Curie point is related to the melting point of PEG, etc., and FIG. 3 specifically shows this. If the mixing ratio of carbonic acid powder is the same, melting point 18℃, melting point 49℃ and melting point 55℃
In PEG, those with lower melting points have lower current values at the same temperature. In other words, it reaches the Curie point quickly and maintains a constant temperature at a low temperature. Fig. 3 also shows paraffin (dashed line), which is almost solid at room temperature and has a melting point of 18~
Polyalkylene glycols at 75°C, especially those containing polyalkylene glycol as the main component, are particularly good because they are flame retardant and have low flammability. Parafine waxes have prominent electrical properties, ie, the Curie point, and are excellent in automatic temperature control, but have the disadvantage of being flammable. Low molecular weight polyethylene (molecular weight 500-4000, softening point 60-130°C) has a softening point around 100°C as a wax-like organic compound that can be used at around 100°C.
This also applies, but it is difficult to use at temperatures below 75℃. However, like traditional crystalline polyethylene,
The carbonate powder to be mixed with polyethylene glycol or the like can be either crystalline carbon such as graphite powder or amorphous carbon such as activated carbon. The mixing ratio has been described above, but as shown in FIG. 1, as the mixing ratio increases, the temperature regulating effect at higher temperatures is achieved, and when the ratio exceeds a certain level, this effect is no longer obtained. In the case of PEG, which has a melting point of 49℃, when 40% (80g) of graphite powder is added, it melts in 5 minutes with a rapid temperature rise, reaches 90℃ in 10 minutes, and reaches 90℃ in 20 minutes.
The temperature rises to 180°C, resulting in a mixed system that no longer has any temperature regulating effect. Therefore, the mixing ratio that can be safely used as a thermal resistance composition is:
In the case of this PEG, graphite powder accounts for up to 35%,
The best value was around 33%. In the case of other polyalkylene glycols, there are likewise suitable mixing ratios within the range of minimum and maximum mixing ratios. The mixing ratio of each of the organic compounds that best exhibits the temperature control function exists. Aggregates range from about 15-40%.

【Example】

Next, specific examples of the heat-sensitive resistor composition of the present invention and examples of its use will be explained with reference to Examples. Example 1 A heat-sensitive resistor composition containing 33% of PEG graphite powder with a melting point of 49°C was prepared and formed into a transparent acrylic resin plate 1 and urethane rubber 2 as shown in FIGS. 4 and 5. The heat-sensitive resistor composition 3 was sealed in the gap with a thickness of 50 mm. Then, electrodes 4 and 5 were alternately placed in the heat-sensitive resistor composition. In addition, Fig. 4 is a plan view, and Fig. 5 is A in Fig. 4.
-A section sectional view. The thickness of the acrylic plate and urethane rubber is 2 mm for the former and 30 mm for the latter. Both are 260mm long and 350mm wide. A thermocouple for temperature measurement is arranged in the center of this heat generating device. A voltage of 100V AC was applied to the device described above to examine temperature changes. The results are shown in FIG. When a voltage is applied, it completely melts from the vicinity of the electrode within 5 minutes. Looking at the temperature change, the maximum temperature reached 42℃ after about 2 hours of electricity.
After that, the temperature control function works to maintain the same temperature. After 6 hours and 30 minutes in this state, the voltage application was stopped. Here, if a conventional barium titanate-based heat-sensitive resistance element is used, the temperature immediately returns to room temperature.
However, in this example using PEG, the same temperature was maintained for as long as 1 hour and 30 minutes after the electricity was turned off. After that, the temperature gradually decreases and completely returns to room temperature after 7 hours or more have passed after the electricity is turned off. This is caused by the coagulation heat of PEG. Molten PEG dissipates heat as it solidifies. This maintains the high temperature for a long period of time.
Therefore, by mixing PEG and carbonic acid powder and using it in a heat insulator or thermostat, it is possible to maintain heat for a long time even after the electricity is turned off. However, when the above compounds are used as a thermistor, the response may be delayed. In such cases, the use of low-molecular-weight PEG produces almost no coagulation heat, resulting in a faster response. Example 2 Graphite powder was added to 120 g each of PEG (mp 49°C and 55°C), polyethylene glycol nonyl phenyl ether (Noigen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., mp 75°C), and paraffin (mp 57°C and 70°C). Mix 60g, and for PEG (mp49℃), also mix activated carbon powder in the same way, diameter 12cm, depth 2.5
Place it in a 9 cm glass tray, and use two 0.4 mm thick copper plates with a surface area of 10 cm ² as electrodes on both ends.
Separated and immersed. After cooling the above mixture to room temperature and solidifying it, connect it to a 100V AC power source and start applying electricity.
The energization time, temperature changes, current changes, and resistance values at the beginning and end of energization were measured. The results are shown in Table 1.

[Table] PEG and graphite and PEG and activated carbon based examples melt from the vicinity of the electrode as soon as electricity is applied, and completely melt within 5 minutes. In the comparative examples of paraffin and graphite, the melting near the electrode is extremely rapid, a large current flows in the initial stage, and at 100V it completely shoots out and ignites. Therefore, it is necessary to lower the applied voltage. As is clear from Table 1, all examples generate heat when energized, and maintain a constant temperature as a constant temperature heating element above a predetermined temperature. In addition, the initial current begins to decrease as the temperature rises, and at the stage when it maintains equilibrium as a constant temperature heating element, the current value shows a value so small that it cannot be read. On the other hand, when looking at the electrical resistance, it shows an extremely large value when it is functioning as a constant temperature heating element.
As is clear from these results, a composition obtained by mixing polyalkylene glycols with a melting point of 18 to 75° C. with carbonic acid powder can be used as a heat-sensitive electrical resistance composition in the heat retention region. Example 3 60g of PEG1000 (mp approx. 37℃) and PEG600 (mp approx. 18℃)
) and 60 g of graphite powder were heated and mixed at a temperature of 40°C, and this was placed in the container shown in Example 1 using colored galvanized iron instead of the acrylic plate and heated at 3°C.
The mixture was allowed to solidify in the refrigerator. The temperature showed 2°C. When 100V AC voltage was applied in a constant temperature room set at 5℃ in this state, the Curie point was 16℃, the temperature did not rise above that, and the current was 0.05A.
The power consumption was extremely small. Next, artificial snow was made using an ice scraper, and this was deposited on the colored galvanized iron sheet to a thickness of 10 mm. When the artificial snow melted, it completely melted in about 15 minutes. Electric heating efficiency is approx.
It achieved a rate of 85% and was found to be extremely effective as a snow melting board for roofs, etc.

【Effect of the invention】

There are many possible ways to use the heat-sensitive resistive composition of the present invention. The main uses are as positive temperature coefficient thermistors and as constant temperature heating elements. Using resistance temperature characteristics as a thermistor, it can be used for temperature control (hot air heaters, dryers, rice cookers, mosquito traps, etc.), temperature measurement, temperature indication,
It is possible to detect fire alarms, prevent overheating of electrical equipment, etc.
It can be used as a constant-temperature heating element in heat insulators, electric heaters, thermostats, etc., and can also be used as a large-area heating element in snow melting facilities, heat-retaining mats, etc.

[Brief explanation of the drawing]

1 and 2 are graphs showing the relationship between the current application time and the temperature of the heat-sensitive resistor composition, and FIG. 3 is a graph showing the relationship between the temperature of the heat-sensitive resistor composition and the amount of current. FIG. 4 is a plan view of the constant temperature heating device, and FIG. 5 is a sectional view taken along line AA in FIG. FIG. 6 is a graph showing the relationship between elapsed time and temperature when the device shown in FIG. 5 is energized. 1...Acrylic resin plate, 2...Urethane rubber,
3... Heat-sensitive resistance composition, 4, 5... Electrode.

Claims (1)

[Claims] 1. A heat-sensitive electrical resistance composition prepared by mixing 15-40% of carbon powder with a polyalkylene glycol that is solid at approximately room temperature and has a melting point of 18-75°C.