JPS6245675B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a self-temperature control heater. Heaters made of nichrome wire or inorganic insulated wire maintain a constant output as long as the voltage remains constant, and they have the disadvantage of consuming a large amount of energy. Therefore, there is an increasing demand for self-temperature control heaters whose output changes with temperature. This utilizes the phenomenon that the resistance value increases as the temperature rises, that is, the PTC characteristic (positive temperature coefficient characteristic). Plastic-based PTC is ceramic PTC
It is being put into practical use because it is cheaper. However, it is not easy to maintain stability during processing and stability when electricity is repeatedly applied. For example, the structure of conductive carbon black is destroyed by shearing during processing, so the resistance value tends to change significantly depending on processing conditions. On the other hand, since graphite does not have a structured structure, it is less affected by processing. However, normal graphite has a maximum particle size of 10
Many of them were larger than μ, and there was a risk of electrical breakdown or ignition occurring during energization. Furthermore, since graphite does not form structures, it has the disadvantage that it requires a larger amount to be added in order to obtain a certain resistance value than the commonly used conductive carbon black. As the amount added increases, the difference in thermal expansion between the polymer and graphite increases, so the gradient of the resistance value-temperature characteristic tends to become smaller. Therefore, the self-temperature adjustment function becomes relatively slow. therefore excellent
In order to exhibit PTC properties, it is important to obtain a composition with a small amount of addition and good processing stability. For the above reasons, if a PTC composition that is made of graphite but requires a small amount of addition can be obtained, it would have an extremely large industrial contribution. The purpose of the present invention is to eliminate the drawbacks of the prior art described above, to provide a novel self-temperature control property using a PTC composition that can greatly reduce the amount of additives that impart conductivity, and has excellent processing stability. The purpose is to provide a heater. That is, the gist of the present invention is that graphite having a maximum particle diameter of 10 μm or less is used as the conductivity imparting material. Crystalline plastics are plastics that have crystals, such as polyethylene, ethylene copolymers such as ethylene-vinyl acetate copolymers, and ethylene-vinyl acetate copolymers.
Examples include propylene copolymer, polyvinylidene fluoride, chlorinated polyethylene, poly-butene-1, polymethylpentyl-1, ethylene-tetrafluoroethylene copolymer, but are not limited thereto. These may be used alone or in combination. Further, for the purpose of imparting flexibility, rubbers such as ethylene-propylene rubber, chlorosulfonated polyethylene, and amorphous chlorinated polyethylene may be used in combination. Graphite with a maximum particle size of 10μ or less refers to a particle whose particle size, which corresponds to a cumulative percentage of 95% in the particle size distribution curve, is 10μ or less. Graphite that meets these conditions is commercially available. For example, KR2.5 (Lonza), AT-30,
Examples include, but are not limited to, AT-40 (Oriental Sangyo), GP-60 (Hitachi Powder Metallurgy), CSSP, CSPE, AUP, HAG-150 (Nippon Graphite Industries), etc. These graphites may be used alone or in combination. Here, the reason why the maximum particle size is limited to 10 μm or less is that if the maximum particle size exceeds this range, it is necessary to add a large amount to obtain a certain resistance value. In that case, the volume fraction of graphite becomes large and the volume fraction of polymer becomes small.
Since the PTC characteristics reflect the specific volume-temperature characteristics of the polymer to some extent, it is not preferable from the viewpoint of the PTC characteristics to add a large amount of graphite, which does not change the specific volume due to temperature. In addition to graphite, metal powder or carbon black may also be used in combination. Other antioxidants, stabilizers, scorch inhibitors,
There is no problem in adding crosslinking aids, lubricants, and flame retardants. Next, examples of the present invention will be described together with comparative examples. Example 1 Polyethylene (density = 0.92, MI = 2) 100 parts by weight Graphite GP-60 (maximum particle size 4μ)
40 parts by weight 4,4-thiobis(6-tertiarybutyl-m-
Cresol) 0.2 parts by weight Trimethylolpropane trimethacrylate
2 parts by weight As shown in the attached drawings, the heating element composition 2 having the above composition was extruded to cover two parallel electrode conductors 1 and 1', and then irradiated with a 20 Mrad electron beam to cross-link the sample. was manufactured. The conductors are 18AWG concentrically twisted, and the distance between the conductors is 7mm. Example 2 Polyvinylidene fluoride 100 parts by weight Graphite KR2.5 (maximum particle size 5μ) 20 parts by weight triallyl trimellitate 5 parts by weight A sample was produced in the same manner as in Example 1. Example 3 Instead of 100 parts by weight of polyethylene in Example 1,
80 parts by weight of polyethylene (density = 0.92, MI = 2) and ethylene-propylene rubber (Mouni viscosity
A sample was manufactured by extrusion coating a heating element composition using 20 parts by weight of the mixture as a base (ML ₁₊₄ = 40) in the shape shown in the attached drawing, and then crosslinking it by irradiating with electrons at 20 Mrad. Comparative Example 1 T-15 (maximum particle size 15μ; Lonza) was used instead of graphite in Example 2. The amount added is the same. Other conditions are the same as in Example 2. Comparative Example 2 The amount of graphite T-15 added in Comparative Example 1 was 30 parts by weight. Other conditions are the same as in Example 2. Comparative Example 3 In place of the graphite used in Example 2, coarse graphite (with a maximum particle size of 200 μm or more) was used. The amount added is
It is 40 parts by weight. Next, Table 1 shows the characteristics of each of the above examples.

【table】

[Table] The test method is as follows. Resistance value: Measure the resistance value at room temperature using a Wheatstone bridge. Power cycle: Apply 200V AC between conductors for 60 minutes. Next, power charging will be suspended for 10 minutes. This is considered one cycle, and is repeated 100 cycles. The operating temperature was measured with a thermocouple when 200V AC was applied. Note that the heater of the present invention may have a structure in which a sheath is wrapped around the structure of the illustrated embodiment, if necessary. In the present invention, the reason why the conductivity imparting effect is significantly improved by using graphite with a maximum particle size of 10μ or less is that the contact between the polymer and graphite is reduced due to the smaller particle shape. This is thought to be because the so-called tunnel effect is promoted by increasing the number of opportunities for

[Brief explanation of the drawing]

The figure is a sectional view showing an embodiment of the self-temperature control heater of the present invention. 1,1': electrode conductor, 2: composition for heating element.

Claims (1)

[Claims] 1 Crystalline plastics or mixtures of crystalline plastics and rubber that can be crosslinked by irradiation with ionizing radiation such as electron beams have a maximum particle size.
A composition having a positive temperature coefficient characteristic formed by adding graphite of 10μ or less, and an electrode integrated with this composition, the composition being crosslinked by ionizing radiation. A self-temperature control heater characterized by: