JP2008123764A - Self-temperature control heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-temperature control type heater for improving an output stability against a heat fluctuation from the outside.
The present invention relates to a self-temperature control type heater in which two or more electrodes are embedded in the resin composition in which carbon black as a conductivity imparting agent is dispersed in the resin composition. And a medium particle size carbon black having an average particle size of 40 to 70 mμ and a DBP absorption of 60 to 160 cc / 100 g, and a large particle size carbon black having an average particle size of more than 70 mμ, and The mixing ratio of the carbon black having a large particle size to the carbon black having a medium particle size is set to 20 to 50% by mass. Thus, the self-temperature control type heater has improved output stability against external thermal fluctuations.
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Description

  The present invention relates to a self-temperature control type heater in which two or more electrodes are embedded adjacent to each other in a resin composition in which carbon black as a conductivity imparting agent is dispersed. This is intended to improve output stability.

  A self-temperature control type heater (PTC heater) in which two or more electrodes are embedded in a resin composition in which carbon black as a conductivity-imparting agent is dispersed is used to generate heat due to energization from the electrodes and increase in temperature due to heat generation. Since the electrical conductivity (electric resistance) of the resin fluctuates due to the expansion of the resin, as a result, the heat generation temperature is automatically controlled. That is, it is a heater using the PTC function of a conductive polymer. For this reason, a control part such as a thermostat is unnecessary, and low-cost and safe heat generation can be obtained. Therefore, although it is not suitable for high temperature heat generation (above the melting point of the resin) due to the characteristics of the resin, it is widely used in various fields. For example, it is used for heat retention, heating, prevention of freezing of water and sewage, various snow melting systems, etc. for liquid transportation pipes (process pipes such as manufacturing equipment).

In such a self-temperature control type heater, since the properties of carbon black as a conductivity imparting agent, such as particle size, have a great influence on the heater performance, two types of conventional average particle size of carbon particles are used. Has been proposed (Patent Document 1).
Japanese Patent Laid-Open No. 10-294021

  In this conventional heater (Patent Document 1), an average particle size of 30 mμ (nm) or less and an average particle size of 70 mμ or more are appropriately mixed and used. The reason is that when the average particle size is 30 mμ or less, the conductivity is good and the desired low resistance is obtained, while when the average particle size is 70 mμ or more, a large rate of resistance change is obtained by temperature change. By appropriately adjusting the mixing ratio between the two, a small, low voltage and high output heater is obtained.

  However, the heater (Patent Document 1) has a problem that the heater output fluctuates with time. With regard to this point, the inventors of the present invention have made extensive studies, and the following has been estimated. When the usage environment of the heater is subject to thermal fluctuation, for example, in process piping for liquid transportation, the heater is attached to the side of the tube for heat insulation and warming, but when cleaning the piping, spray high temperature steam. It was found that so-called steam cleaning was performed.

  Thus, it is considered that when the heater itself together with the piping is exposed to a heat fluctuation from the outside and receives a heat history, the carbon black in the resin composition is aggregated and its resistance characteristic is changed. In particular, carbon black having a small particle size with an average particle size of 30 mμ or less is likely to agglomerate and is considered to greatly affect this output fluctuation.

  Therefore, as will be apparent from the tests described later, the present inventors have a carbon black with a small particle size having an average particle size of 30 mμ or less, a carbon black with a medium particle size of 40 to 70 mμ, and an average particle size. Prepared carbon black with a large particle size exceeding 70 mμ (size exceeding 70 mμ, excluding 70 mμ), and mixing them at several mixing ratios to produce sample heaters. When heat was applied to reproduce the heat history, it was confirmed that the output fluctuation was large as expected when carbon black having a small particle size was used.

On the other hand, when an average particle size of 40 to 70 mμ and a DBP absorption amount of 60 to 160 cc / 100 g of a medium particle size carbon black and a large particle size carbon black with an average particle size of more than 70 mμ are mixed, It was found that the output fluctuation was small. Here, in the medium particle size carbon black, the DBP absorption amount is set to 60 to 160 cc / 100 g for the following reason. In carbon black, factors affecting the conductivity of the resin include the structure and chemical properties of the particle surface in addition to the average particle size. The carbon particles dispersed in the resin usually take a form in which a large number of particles are aggregated (aggregate: for example, a tuft-like shape), and the degree of development of this aggregate is called a structure. What indirectly indicates the size of the structure is the DBP absorption amount.
Therefore, even when the average particle size of carbon black is medium, when the DBP absorption amount increases, the aggregated form of particles increases, and the desired resin conductivity cannot be obtained.

  Carbon black with a medium particle size of 40 to 70 mμ is used because carbon black with a small particle size with an average particle size of 30 mμ or less is excellent in low resistance, but easily aggregates due to thermal history, and the output Since this is a variable factor, it has been replaced. The reason why the DBP absorption amount is made smaller (60 to 160 cc / 100 g) is to obtain desired conductivity. From the test described below, it was possible to find a good result by setting the DBP absorption amount to be small.

  The present invention has been made from the above viewpoint, and by using a mixture of medium particle size carbon black having a specific DBP absorption amount and large particle size carbon black, the output stability is improved against external thermal fluctuations. The present invention provides a self-temperature control type heater that achieves the above.

The present invention according to claim 1 is a self-temperature control type heater in which two or more electrodes are embedded adjacent to each other in a resin composition in which carbon black as a conductivity imparting agent is dispersed.
As the carbon black, medium particle size carbon black having an average particle size of 40 to 70 μm and DBP absorption of 60 to 160 cc / 100 g, and large particle size carbon black having an average particle size of more than 70 μm The mixing ratio of the carbon black having a large particle size to the carbon black having a medium particle size is 20 to 50% by mass, and the carbon black is further added to 15 to 30% with respect to 100 parts by mass of the base resin composition A self-temperature control type heater is characterized in that the output stability against external thermal fluctuation is improved by adding a mass part.

  The present invention according to claim 2 is the self-temperature control type heater according to claim 1, which is used under an external heat fluctuation environment.

  According to the self-temperature control type heater of the present invention, carbon black in the resin can be used even if there is a thermal fluctuation from the outside because the conventional heater does not use the carbon black having a small particle diameter of 30 mμ or less. Aggregation of particles hardly occurs and stable output is ensured. That is, the output stability can be improved. Also, instead of carbon black having a small particle size, carbon black having an average particle size of 40 to 70 mμ is used, but its DBP absorption is 60 to 160 cc / 100 g, which is smaller. Therefore, desired conductivity can be obtained.

1 to 2 show a structural example of a self-temperature control type heater according to the present invention.
In each figure, 1 is a tape-shaped resin composition, 2 is an electrode embedded in the longitudinal direction of the resin composition 1, and 3a, 3b, and 3 are insulating coatings. Here, 3a is an inner layer insulating coating, and 3b is an outer layer insulating coating. In the case of FIG. 1, the resin composition 1 is a low-density polyethylene-based three-electrode type, the distance between these electrodes 2 and 2 is as narrow as about 2 to 3 mm, and the entire heater is also 5 to 10 mm wide. A thickness of 1.5 to 2.5 mm is obtained as an extremely small size. The insulating coating may have a single layer structure. In the case of FIG. 2, the resin composition 1 is a two-electrode type based on a fluororesin (for example, polyvinylidene fluoride: PVDF), and the distance between these electrodes 2 and 2 is also about 2 to 3 mm. In addition, the entire heater can be obtained in a very small size with a width of 3 to 5 mm and a thickness of 1.0 to 2.0 mm. In addition, although the said electrode 2 is a 0.6 mm diameter tin plating copper wire, it is not limited to this. Tin-plated copper stranded wire, nickel-plated copper wire, nickel-plated copper stranded wire, ordinary copper wire, copper stranded wire, etc. can also be used.

In this configuration, when the resistance value of the resin composition was about 300 Ω · cm, a high output heater was obtained at a low voltage (5 to 50 V). That is, the heat generation amount was 0.4 to 5 (W / 10 cm) at this small size and low voltage.

As the resin composition, in addition to low density polyethylene (LDPE), the following can also be used. High, medium density polyethylene (HDPE, MDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polypropylene (PP), ethylene-propylene copolymer, polyvinylidene fluoride, ethylene -4 fluoroethylene copolymer, chlorinated polyethylene, polyethylene-terephthalate, polyamide, polyether-ethyl ketone, polyphenylene sulfide and the like. These resins may be used alone or in a blended form, and can also be used in combination with rubbers such as ethylene-propylene rubber, silicon rubber and fluorine rubber. For example, in the case of a blend, low density polyethylene (MFR0.1-10 g / 10min) 55-95 mass parts and EEA (MFR0.1-10 g / 10min) 5-45 mass parts are mixed, and the whole is 100 mass parts. Can be used.

Further, the carbon black added to the resin is not particularly limited, but funnes carbon, acetylene black, kettin black and the like can be used. Moreover, what improved the chemical property by giving surface treatment to the particle surface suitably as needed can also be used. Further, as the particle size, carbon black having an average particle size of 40 to 70 μm and a DBP absorption amount of 60 to 160 cc / 100 g, and an average particle size of more than 70 μm (a size exceeding 70 μm). , 70 mμ is not included) and both carbon blacks having a large particle diameter are mixed and used.

As the mixing ratio, the mixing ratio of carbon black having a large particle diameter to carbon black having a medium particle diameter is set to 20 to 50% by mass. The reason is that if the mixing ratio of the carbon black having a large particle diameter is less than 20% by mass, it is too small to obtain a desired rate of change in resistance value. On the other hand, if it exceeds 50% by mass, the amount of carbon black having a medium particle size decreases, and a desired resistance value cannot be obtained.

Moreover, the reason why the DBP absorption amount of the carbon black having a medium particle diameter is set to 60 to 160 cc / 100 g is that the desired conductivity cannot be obtained if it is less than 60 cc / 100 g, and when it exceeds 160 cc / 100 g, This is because the resistance becomes too low.

The amount of both carbon blacks added to the resin composition is 15 to 30 parts by mass with respect to 100 parts by mass of the resin composition. If the amount is less than 15 parts by mass, the resistance value of the resin composition is too large. It is because it will become too much, and when it will exceed 30 mass parts, on the contrary, the resistance value of a resin composition will become small too much.

In addition to carbon black, other additives can be appropriately added to such a resin composition as necessary. For example, in the case of a fluororesin, particularly a stabilizer, an acid acceptor such as calcium carbonate may be contained. The resin composition may be cross-linked by electron beam cross-linking, chemical cross-linking with an organic peroxide, or the like, either alone or in combination.

In the production of this heater, the resin composition is extruded by embedding an electrode with an extruder or the like, for example, irradiated and cross-linked with an electron beam (for example, dose = 15 Mrad), and obtained by applying a desired insulating coating.

<Examples and comparative examples>
A sample self-temperature control type heater having the same structure as that of FIG. 1 was manufactured using the base resin of the resin composition and carbon black having the composition shown in Tables 1 to 5. The major axis (width) of the heater was 9.0 mm, the minor axis (thickness) was 1.8 mm, and was crosslinked by electron beam irradiation. In the sample evaluation, each heater was cut to 1.0 m. Base resin is fluororesin PVDF (manufactured by Solvay Solexis: Heiler 460), carbon black is manufactured by Columbia (CD705uB), Asahi Carbon (Asahi Thermal FT), CABOT (BLACK-PEARLS 3500, Vulcan XC72), COLUMBIAN (RAVEN460) was used. In addition, the numerical value of base resin and carbon black in each table | surface shows a mass part. Moreover, the particle diameter of carbon black shows an average particle diameter.

Each sample heater was tested for physical property evaluation (output, output change).
<Output test> energized the heater electrode to determine its output (W / m). And if it was the output of the range of 30-60 W / m, it was set as the pass and others were made unsuccessful.
In the <output change test>, the heater was placed in an environment of 230 ° C. × 5 hours, and then the heater electrode was energized, and the output change was obtained by comparison with the output before the test. And when the output change (fluctuation: increase) was within 25%, it was considered as acceptable, and when it was more than that, it was rejected.

As apparent from Tables 1 to 3 above, in the case of the self-temperature control heater of the present invention (Examples 1 to 15), it can be seen that all the physical properties are good.

On the other hand, as is apparent from Table 4, in the case of the self-temperature control type heater lacking the conditions of the present invention (Comparative Examples 1 to 7), it can be seen that there is a problem in any point.
In other words, it can be seen that in Comparative Example 1, the total amount of carbon black added is too small (12 parts by mass), a desired output cannot be obtained, and the output change is large. In Comparative Example 2, it can be seen that the total amount of carbon black added is too large (36 parts by mass) and the output becomes too large.
In Comparative Columns 3 to 7, when the average particle size of carbon black is small (30 mμ), the total addition amount with carbon black having a large particle size is within an appropriate range (15 to 30 parts by mass). It can be seen that the change is large. It can be seen that the output in the comparison column 7 becomes too large.

It is the vertical end view which showed an example of the self-temperature control type heater which concerns on this invention. It is the vertical end view which showed the other example of the self-temperature control type heater which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Resin composition, 2 ... Electrode, 3, 3a, 3b ... Insulation coating

Claims (2)

In a self-temperature control type heater in which two or more electrodes are embedded adjacent to each other in a resin composition in which carbon black as a conductivity imparting agent is dispersed,
As the carbon black, medium particle size carbon black having an average particle size of 40 to 70 μm and DBP absorption of 60 to 160 cc / 100 g, and large particle size carbon black having an average particle size of more than 70 μm The mixing ratio of the carbon black having a large particle size to the carbon black having a medium particle size is 20 to 50% by mass, and the carbon black is further added to 15 to 30% with respect to 100 parts by mass of the base resin composition A self-temperature-controlling heater characterized by adding mass parts to improve output stability against external thermal fluctuations. 2. The self-temperature control type heater according to claim 1, wherein the heater is used in a heat fluctuation environment from the outside.