JPH0374473B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel self-temperature regulating sheet heating element (hereinafter abbreviated as sheet heating element), and its purpose is to obtain a sheet heating element that is inexpensive to manufacture, consumes very little power, is highly safe, and has good physical properties. It was developed by. Many organic compounds have melting points around room temperature ±50°C, have good physical properties such as high thermal stability and little toxicity, and are poor electrical conductors. Examples include paraffins, polyalkylene glycols, higher alkyl ethers, higher alkyl esters, higher fatty acids, and higher alcohols. These organic compounds are known as heat storage media because they melt when the temperature exceeds their melting point due to external heating, and the latent heat of fusion is stored in the substance. The present invention aims to develop a method of storing heat generated by an electric heater from a power generation device using irregular natural energy such as wind power, water power, tidal power, solar heat, etc. using these heat storage media, and to create a heat storage type electric heating device. proposed this in Japanese Patent Application Laid-Open No. 12929/1983. The heat storage medium itself is a poor conductor of electricity and cannot be heated directly with electricity, so it requires heating with an electric heater and a thermostat or thermoprotector for temperature control, which reduces equipment costs. The disadvantage of bulking up is undeniable. As a result of further investigation with the aim of improving this point,
When carbon powder with good conductivity is dispersed and mixed in a heat storage medium, it exhibits extremely unique electrical behavior, generates heat when energized, and has a property in which electrical resistance changes rapidly at a constant temperature. was discovered and published in Japanese Patent Application Laid-open No. 59-66093 as a conductive heat storage medium.
They were proposed as heat-sensitive electrical resistance compositions in JP-A-59-110101 and JP-A-60-140692, respectively. The present invention is a planar heating element completed by applying these compositions, which is suitable for base materials such as floor heating equipment of buildings, heating carpets, heating mats for agricultural and livestock production such as raising chicks, raising children, and raising seedlings. It is something. It is characterized by an organic compound containing multiple alkylene oxides as a unit structure in its molecule and fine carbon particles in the form of powder, fibers, whiskers, etc., and its electrical resistance changes rapidly with temperature changes. It is made by sealing a thermosensitive electrical resistance composition with an electrode together with an insulator. Details of the conductive heat storage medium can be found in the aforementioned JP-A-59-
As detailed in No. 66093, preferred are higher hydrocarbons having a melting point within the range of 20 to 70°C, that is, paraffins, polyalkylene glycols, higher alkyl ethers,
It is a mixture of compounds such as higher alkyl esters, higher alcohols, higher fatty acids, etc., and carbon powder in a specific ratio range. Among the above organic compounds, we focused on the fact that those containing polyethylene glycol as the main component are particularly good, and are excellent as heat storage media because they are flame retardant and have low flammability.As a result of intensive research, we found that organic compounds contains multiple alkylene oxides as a unit structure in the molecule,
We have discovered that it exhibits significantly superior properties compared to other organic compounds, and have proposed it as a heat-sensitive electrical resistance composition as described above. Regarding the heat-sensitive electrical resistance composition, the electrical conductivity of a substance is determined by the number of charge carriers in the substance and the mobility of the carriers. In the case of carbon, carriers are conduction band electrons, so the carrier number is the number of electrons in the conduction band, and therefore follows Aexp (-W/kT) from Boltzmann's law. Here, A is a constant, W is the band gap between the valence band and the conduction band, k is Boltzmann's constant, and T is the absolute temperature. On the other hand, the mobility is generally Aexp(-w/kT)
It is expressed as Here, A is a constant and w is the activation energy of hopping. Therefore, the temperature change in conductivity (δ) is generally expressed as δ=δ ₀ exp(−ΔE/
kT). However, there are substances that comply with the above equation below a certain temperature, but exhibit a much larger resistance value than calculated using the above equation above a certain temperature. This property is called a "positive property." Conventionally, as an inorganic material having positive properties, barium titanate with a trace amount of rare earth element added has been used. On the other hand, subsequent research revealed that a carbon-paraffin-polyethylene system is known as an organic material with sufficiently large positive properties, but this composition has poor compatibility and is difficult to mix due to mixing methods and properties. There is a problem with changes over time. In addition, carbon-polymer compositions have been used, but their positive properties are not so great (for example, JP-A-50-150039). The heat-sensitive electrical resistance composition used in the present invention has a large positive property, and carbon is very easily dispersed in an organic compound containing a plurality of alkylene oxides as a unit structure in the molecule, and has a very large positive property. It is characterized by being stably obtained. An organic compound consisting of alkylene oxide as a unit structure in which a plurality of alkylene oxide units are continuous in a linear or cyclic form, if the alkylene oxide units are continuous,
Shows excellent positive properties regardless of whether it is linear or cyclic. The specific compounds are listed below. Examples of linear compounds include polyoxyalkylenes, such as polyethylene glycol and its high molecular weight polyethylene oxide, block copolymers of polyoxyethylene and polyoxypropylene (so-called Pluronics and Tetronics), and polyethylene glycols. Examples include oxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkyl amine, and polyoxyethylene sorbitan fatty acid ester. In addition to trioxane, cyclic compounds include various crown ethers, such as dibenzo-14-
Crown-4, 15-Crown-5, Benzo-15-
Crown-5, 18-Crown-6, Dibenzo-18
-crown-6, dicyclohexyl-18-crown-6, dibenzo-21-crown-7, dibenzo-
Many examples include 24-crown-8, dicyclohexyl-24-crown-8, tetrabenzo-24-crown-8, and dibenzo-60-crown-20. The positive characteristics of the heat-sensitive electrical resistance composition using these will be specifically described later. The carbon to be mixed into the organic compound consisting of alkylene oxide as a unit structure and a plurality of alkylene oxides connected in a linear or cyclic manner as mentioned above is powdered, fibrous or single crystal such as graphite, activated carbon, amorphous carbon, etc. carbon particles in the form of whiskers, etc., which can be mixed into the above-mentioned linear or cyclic polyether. The greatest feature of a mixture of the two is that it is extremely stable and uniformly mixed at any composition ratio, and does not undergo phase separation. There is a region where positive characteristics appear depending on the mixing ratio of carbon fine particles, which is usually in the range of 10 to 80 parts per 100 parts of the organic matter. When it is less than 10, the resistance is high and there is no conductivity, and when it is more than 80, the conductivity becomes large and it does not exhibit positive characteristics due to temperature changes. However, since the range in which positive characteristics appear varies greatly depending on the type of organic compound and the type of carbon fine particles, it is not limited to the above range. As described above, the mixing specific gravity of the organic compound and the carbon fine particles is an important factor, and the optimum range is set by changing the mixing ratio and judging from the current application time, temperature rise, and change in resistance value. For example, 20 parts of graphite powder is added to 120 parts of polyethylene glycol with a melting point of 49°C.
The time and temperature changes when electricity is applied to systems containing 40, 60, and 80 parts are shown in Figure 1. At 20 parts, the temperature does not rise, and at 80 parts, the temperature rises in a short time. And works well at 40-60 parts, about 40℃ at 40 parts
It can be seen that it is stable at about 50℃ at 60 parts. At the beginning of energization, the electrical resistance is less than 500Ω and the current value is about 1.5A, but as the polyethylene glycol softens or melts, the resistance rises to 1900Ω, the current becomes less than 0.1A, and the equilibrium temperature is reached.
The pattern is shown in Figure 2. Therefore, a heat storage medium mixed with 10 to 60 parts of graphite powder becomes a planar heating element that has a self-temperature adjustment function that does not require a heater or a thermostat. In organic compounds, multiple alkylene oxides that exist consecutively in the molecule play an important role in dispersing carbon particles, and this is considered to be a factor in exhibiting extremely stable and large positive characteristics. Alkylene oxide, regardless of whether it is linear or cyclic,
Even in trioxane, which has three groups of alkylene oxides, even if the bonds between the alkylene oxides are interrupted by the benzene nucleus in the crown ether, the six-membered ring of cyclohexane, etc., there are multiple alkylene oxide groups in the molecule. The above-mentioned Japanese Patent Laid-Open No. 140692/1983 has shown that if it exists, it has been proven that it exhibits positive characteristics. Polyethylene glycol shows the most favorable properties, and even if a polyoxypropylene chain is connected to it, or even if the terminal group is substituted with an alkoxy group such as a hydroxyl group or a methoxy group, or an alkyl ester or an alkyl amine, it maintains positive properties. It has also been proven that A positive characteristic is that the electrical resistance value sharply increases when current is applied at a temperature below the melting point of the organic compound medium. This is the first
Shown in the table.

[Table] Furthermore, the relationship between temperature and electrical resistance value of each heat-sensitive electrical resistance composition used in the present invention is shown in FIGS. 5 and 6. Here, FIG. 5 and FIG. 6 will be explained.
Figure 5 is a graph showing the relationship between composition temperature and electrical resistance when cyclic polyethers having alkylene oxide as a unit structure are used, and Figure 6 is a graph showing the composition when linear polyethers are used. It is a graph showing the relationship between object temperature and electrical resistance. The compositions of these heat-sensitive electrical resistance compositions shown in ~ are as follows. graphite carbon
25% (wt% and below are the same) Trioxane 75% Graphite carbon 28% 18-crown-6 72% Graphite carbon 28% Benzo-15-crown-5 72% Graphite carbon 28% Dicyclohexyl-18-crown-6 72 % Graphite carbon 28% Dibenzo-24-crown-8 72% Graphite carbon 28.5% Polyethylene glycol (#6000) 35.7% 〃 (#2000) 35.7% Graphite carbon 28% Pluronic F68 (MW8000) 72% Graphite carbon 28% Pluronik F88 (MW11800) 72% Graphite carbon 28% Polyethylene glycol ethyl ether (MW5000) 72% Carbon fiber fine pieces (15μφ, L130μ) 40% Polyethylene glycol (#2000) 30% 〃 (#6000) 30% Book The present invention is to prepare a heat-sensitive electrical resistance composition sheet by impregnating the above-mentioned heat-sensitive electrical resistance composition as it is or impregnating it on a non-conductive sheet such as a thin woven fabric, non-woven fabric, or sponge sheet. This is a planar heating element that is sealed with a heat-resistant covering sheet and has conductive wires embedded at predetermined intervals inside the heating element to form a thin sheet. Hereinafter, this will be explained in detail using examples. Embodiment 1 FIG. 3a is a plan view showing the first embodiment of the present invention, and FIG. 3b is an enlarged cross-sectional view taken along line A--A in FIG. In this example, when sealing the thermosensitive electrical resistance composition 1 having the characteristics shown in FIG.
is impregnated with the heat-sensitive electrical resistance composition 1, and copper tapes on both edges in the longitudinal direction of the sheet are used for the conductive wires 4, 4. The non-conductive covering sheets 2, 2 are laminate films of a polyester film and an ethylene-vinyl acetate copolymer film, and the surroundings are also heat-sealed. The planar heating element is 100 mm long and 330 mm wide, and its thickness is thin, less than 2 mm at most. Example 3 below shows an example in which various heat-sensitive electrical resistance compositions were sealed. Example 2 The example shown in Figure 4 is a large prototype, with a vertical
A planar heating element of approximately 500 mm, width 850 mm, and thickness 4 mm is made from two non-conductive sheets 2 made of 1 mm thick polycarbonate plates. The inside of this sheet heating element is elongated in the horizontal direction with a width of 5 mm.
Divide into 5 equal parts with 2mm thick butyl tape, approximately 75mm wide.
Five thin spaces each having a length of about 830 mm were provided, conductive wires 4 and 4 each having a capacity of 10 A were arranged on both sides of a partition tape 5 made of butyl tape, and 120 g of the heat-sensitive electrical resistance composition 1 was directly filled into the thin spaces. The composition of heat-sensitive electrical resistance composition 1 was a mixture of 600 g of polyethylene glycol (#6000) and 295 g of graphite powder. Table 2 shows the relationship between the time when a 100 V AC power source is applied to this sheet heating element and the surface temperature at positions A to E in FIG. 4.

[Table] As is clear from Table 2, a current of 7A flows immediately after energization, but after 1 minute it becomes 2A, and after 5 to 10 minutes it reaches the almost equilibrium value of 0.6A. The temperature is also 21℃
The temperature reaches 34℃, and it becomes a heating element that acts as a thermostat that does not rise above 37℃.As the temperature decreases, the resistance value decreases, so the current increases, and the temperature returns to a constant level, so it can be used as a heat insulating mat. (In this example, the surface temperature was measured by placing a thick cloth on the surface of the planar heating element and measuring it from above the covering.) Hereinafter, the structure of the planar heating element of the first example will be explained in more detail by examples using other heat-sensitive electrical resistance compositions. Example 3 Polyethylene glycol (hereinafter referred to as PEG)
Daiichi Kogyo Seiyaku Co., Ltd., #2000) and PEG
#6000 (manufactured by the company) and graphite carbon (below)
It is called GC. (Manufactured by Yoneyama Pharmaceutical Co., Ltd.) 5:
The composition with a weight ratio of 5:4 is melted by heating, stirred, mixed, and placed between two polyester sheets with fibers (thickness: 110μ) as shown in Figure 3a to form a sheet with a thickness of 250μ. (L500mm, W80mm),
The electrodes are made by adhering a zigzag-shaped copper tape to the inside of a polyester sheet in advance, as shown in the figure. A current of 100 VAC was applied to this planar heating element, and the temperature and power consumption measured at each time after the current was applied are shown in FIG. After energization, the temperature gradually rises and approaches the temperature saturation value. On the other hand, power consumption also decreases rapidly over time and reaches a constant value. Example 4 Polyoxypropylene glycol ethylene oxide (hereinafter referred to as Pluronic) (average molecular weight
8000, manufactured by Asahi Denka Kogyo Co., Ltd., Pluronik
A 10:4 weight ratio composition of F68) and GC, and a 10:4 weight ratio composition of Pluronik F88 (average molecular weight 11800) and GC were respectively melted to form the same planar heating element as in Example 1. Temperature and current values were measured. The results are shown in FIG. Even in Pluronic F68 and Pluronic F88, which have a structure in which PEG is bonded to both ends of a polypropylene glycol chain, the temperature rises after electricity is applied and eventually maintains a constant temperature, and correspondingly, the current decreases and eventually reaches a constant value. Therefore, a planar heating element is also possible in this case. Example 5 4 parts of GC was added to 10 parts (by weight) of PEG #5000 with the terminal methoxylated, and the mixture was melted and stirred to form a sheet heating element in the same manner as in Example 1.
The temperature and resistance value were measured at each time after AC100V was applied. The results are shown in FIG. In this case as well, the temperature rises after energization and eventually maintains a constant temperature.
Correspondingly, the current decreases and eventually reaches a constant value. Example 6 PEG #2000, PEG #6000, the carbon fiber fine pieces (manufactured by Kureha Chemical Industry Co., Ltd., M-201S)
After melting the 3:3:4 weight ratio composition, the composition is stirred and mixed,
The same planar heating element as in Example 1 was used, and the temperature and resistance value were measured at each time after AC 100V was applied. The results are shown in FIG. In this case as well, as in Examples 1 to 3 above, the temperature rises after energization and eventually maintains a constant temperature, and the current value also maintains a constant balance.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between energization time and temperature when the mixing ratio of polyethylene glycol and graphite powder is changed, and Figure 2 is a graph showing the relationship between energization time and temperature when the graphite powder in Figure 1 is 60 parts. It is a graph showing the relationship between the current value and the current value. FIG. 3a is a plan view of the first embodiment of the planar heating element, and FIG. 3b is an enlarged sectional view taken along line A-A. FIG. 4 is a plan view showing the planar heating element of the second embodiment. Figure 5 is a graph showing the relationship between temperature and electrical resistance when cyclic polyethers are used, and Figure 6 is a graph showing the relationship between temperature and electrical resistance when linear polyethers are used. be. FIGS. 7 to 10 are graphs showing the relationship between current application time and temperature, and between current application time and current (or power consumption) of the planar heating element of the example. DESCRIPTION OF SYMBOLS 1... Heat-sensitive electrical resistance composition, 2... Non-conductive covering sheet, 3... Cotton gauze, 4... Conductive wire, 5...
...Partition tape.

Claims (1)

[Claims] 1 Consists of a mixture of an organic compound consisting of alkylene oxide as a unit structure and a plurality of alkylene oxide units connected in a linear or cyclic manner and fine carbon particles in the form of powder, fibers, whiskers, etc., and has electrical resistance against temperature changes. 1. A self-temperature-adjusting planar heating element comprising a heat-sensitive electrical resistance composition having positive characteristics adjusted to a composition ratio that causes sudden changes in temperature, and sealed with an insulator together with electrodes.