KR100853229B1 - Heating cable with improved long-term stability - Google Patents

Abstract

A heating cable with improved long-term lifespan is disclosed in connection with a self-regulating heating cable that exhibits a positive temperature coefficient (PTC). The heating cable includes a heating element composed of a polymer resin composition including PTC and a polyolefin-based or fluorine-based crystalline resin exhibiting PTC characteristics, and a copper conductor of a copper conductor in which the conductor surface is nickel-plated by an electroplating method as a conductor bus wire. It includes a copper conductor that is plated with a sufficient amount of nickel to minimize the exposure of copper to the conductor surface, and an electrically insulated sheath to protect it from the outside. This self-regulating heating cable allows long-term lifespan stability to be significantly improved over conventional heating cables.

Description

Heating cable with improved long-term stability {HEATING CABLE}

1 is an equivalent circuit diagram of a heating cable.

2 is a resistance diagram of a heating cable.

3 is a cross-sectional view of the extrusion molded heating cable.

4 is a graph showing On / Off cycling test results (Example 1, Comparative Example 1-1, Comparative Example 1-2).

5 is a graph showing On / Off cycling test results (Example 1, Comparative Example 1-1, Comparative Example 1-2).

6 is a graph showing the output test results (Example 1, Comparative Example 1-1, Comparative Example 1-2) after high temperature exposure.

Figure 7 is a graph showing the output test results (Example 1, Comparative Example 1-1, Comparative Example 1-2) after high temperature exposure.

The present invention relates to the field of heating cable, and more particularly, to a heating cable with improved long-term lifespan stability with respect to a self-regulating heating cable that exhibits a positive temperature coefficient (PTC) characteristic.

Self-regulating heating cable (hereinafter referred to as "heating cable") using PTC characteristics uses the principle that the resistance of the heating element changes depending on the ambient temperature, and automatically controls the output or the heating value of the heater without a separate temperature controller. Cable. The heating cable is generally composed of a heating element that generates heat, a bus wire that supplies electricity to the heating element as a conductor, and an insulating outer shell for protecting and electrically insulating these components from the outside. The bus wire connected to the power source is mainly in contact with the heating element throughout the heating cable to transfer electricity to the heating element, and as a result, generate Joule heat from the heating element.

The physical and electrical properties of the contact surface between the heating element and the bus wire can significantly affect the electrical properties, among other properties of the heating cable. In particular, these properties are one of the main reasons for changing the characteristics of the product in the long term and in use, rather than the short term in relation to the quality of the product. Therefore, manufacturing and maintaining the contact state between the heating element and the conductor in close contact has a great effect on the life of the product.

In a conventional heating cable, in order to supply a PTC characteristic, a conductive composite material in which an appropriate amount of carbon black is added to select a limited carbon black to obtain a desired electrical conductivity (or resistance) is used as a heating element and to supply power thereto. Tin plated copper wire is used as the bus wire.

At this time, in order to realize the desired resistance of the heating element, a large amount of carbon black must be added. In this case, the melt viscosity of the conductive composite material increases, resulting in poor adhesion to the conductor surface during extrusion, that is, surface wettability. The disadvantage arises of poor adhesion to the conductor surface.

In addition, when tin-plated copper wire is used as a bus wire, the electrical properties of the contact surface between the heating element and the conductor can be maintained by preventing oxidation and corrosion from occurring on the surface of the conductor to some extent depending on the surrounding environment during the air or during the manufacturing process. do. However, in the case of tin-plated copper wire, the electrical properties of the contact surface are maintained for a certain period of time after the heating cable is manufactured, but in case of continuous use, even though the physical adhesion to the heating element is good, the chemical reaction of the plated tin (mainly oxidation reaction) Vulnerability to) gradually worsens the properties of the conductor surface. As a result, the electrical properties of the contact surface rapidly deteriorate, which ultimately degrades the product's characteristics, especially its long-term product life.

The present invention has been made to solve the problems of the prior art as described above, the object of the present invention is to provide a heating cable with improved long-term life stability.

In order to achieve the above object, one aspect of the present invention, a heating element composed of a polymer resin composition having a positive temperature coefficient (Positive Temperature Coefficient, PTC) characteristics including carbon black in a polyolefin-based or fluorine-based crystalline resin, and a conductor In-bus wire is a copper conductor that is plated with a sufficient amount of nickel among copper conductors of a copper-plated copper conductor in which the conductor surface is electroplated to minimize the exposure of copper to the conductor surface, and electrically to protect it from the outside. It provides heating cable with improved long-term stability with insulated sheath.

In the present invention, the metal conductor used as the bus wire has an aggregate or concentric strand structure in which single wires or a plurality of element wires are combined.

As a preferred embodiment of the present invention, the amount of nickel plated in the metal conductor used as the bus wire is preferably 1.0 to 12 by weight ratio.

In addition, as a preferred embodiment of the present invention, the thickness of the plating with nickel in the metal conductor used as the bus wire is preferably 1 µm to 20 µm.

In addition, as a preferred embodiment of the present invention, it is preferable that all the copper in the metal conductor used as the bus wire is plated with nickel. At this time, it will be more preferable to use a conductor free of contaminants such as cracks in the plating or debris.

As one preferred embodiment of the present invention, when the amount of nickel plated in the metal conductor used as the bus wire is 2 by weight, the plating thickness by nickel is preferably 1.0 μm to 4.0 μm.

As another preferred embodiment of the present invention, when the amount of nickel plated in the metal conductor used as the bus wire is 4 by weight, the plating thickness by nickel is preferably 2.0 µm to 7.5 µm.

As another preferred embodiment of the present invention, when the amount of nickel plated in the metal conductor used as the bus wire is 7 by weight, the plating thickness by nickel is preferably 3.5 µm to 13.0 µm.

As still another preferred embodiment of the present invention, when the amount of nickel plated in the metal conductor used as the bus wire is 10 by weight, the plating thickness by nickel is preferably 5.0 µm to 19.0 µm.

In the present invention, as a bus wire for applying power to both sides of the heating cable in the longitudinal direction, two or three strands of nickel plated copper conductors may be inserted.

In the present invention, non-limiting examples of the polyolefin-based crystalline resin may be mentioned polyethylene, polypropylene, ethylene vinyl acetate and ethylene acrylic acid copolymer.

In the present invention, non-limiting examples of the fluorine-based crystalline resins include polyvinylidene fluoride, ethylene-tetra fluoroethylene copolymer, fluorinated ethylene-propylene copolymer and tetra fluoro ethylene-perfluoro alkyl vinyl Ether copolymers may be mentioned.

In another aspect of the present invention, there is provided a conductive polymer resin composition in which a carbon black satisfying a value of 48 to 51 of the critical carbon black content (CCBC) of the following formula is added to the polyolefin-based crystalline resin to show the constant temperature coefficient characteristics. The constructed heating element, and the copper conductor which is continuously plated with a sufficient amount of nickel among the copper conductors of the copper-coated copper conductor in which the conductor surface is nickel-plated by the electroplating method as a conductor bus wire, and minimizes the exposure of copper to the conductor surface, and this is from outside For protection, we provide heating cables with improved long-term stability including electrically insulated sheaths:

In another aspect of the invention, non-limiting examples of the polyolefinic crystalline resin may be mentioned polyethylene, polypropylene, ethylene vinyl acetate and ethylene acrylic acid copolymer.

Furthermore, another aspect of the present invention is a heating element composed of a conductive polymer resin composition exhibiting a constant temperature coefficient characteristic by adding carbon black satisfying a value of 43 to 46.5 of the critical carbon black content of the following formula to a fluorine-based crystalline resin: And a copper conductor with a sufficient amount of nickel in the copper conductors of the copper-plated copper conductors of which the conductor surface is nickel-plated by the electroplating method as a conductor bus wire to minimize the exposure of copper to the conductor surface, and to protect it from the outside. To provide heating cables with improved long-term stability, including electrically insulated sheaths:

In another aspect of the invention, non-limiting examples of the fluorine-based crystalline resins include polyvinylidene fluoride, ethylene-tetra fluoro ethylene copolymer, fluorinated ethylene-propylene copolymer and tetra fluoro ethylene-perfluoro Alkyl vinyl ether copolymers may be mentioned.

In the present invention, a specially designed nickel plated copper wire is used as a bus wire, and the carbon black added to the heating element is selected to suit a particular condition. It features a cable.

In the present invention, in the case of the carbon black added to impart conductivity, the conductivity which appeared to be a disadvantage by selecting the type and content of the carbon black according to the conditions using the condition of the critical carbon black content, which is a relationship between the specially designed carbon black basic properties The surface adhesiveness of a composite material can be improved. As a result, the adhesion between the heating element and the conductor is improved, resulting in a drop in contact resistance. In addition, the specially designed nickel plated copper wire instead of the existing tin plated copper wire is used as a bus wire to prevent oxidation and damage on the conductor surface that may occur during the manufacturing process, thereby improving and maintaining the electrical properties of the contact surface between the heating element and the bus wire. In addition, it features a heating cable that greatly improves the service life of the product by preventing the deterioration of the contact surface for a long time during use after manufacture.

The heating cable with improved long-term stability consists of a heating element having PTC characteristics, a bus wire for supplying electricity to the heating element, and an insulating sheath that electrically insulates these structures and protects them from the outside. In the case of the heating element, it is composed of a compound type in which carbon black and various additives are mixed in an appropriate ratio in a single species or several kinds of polymer matrices. Carbon black distributed in the polymer matrix creates an electrically conductive path to form a micro-electric circuit between bus wires. This is illustrated by a simple equivalent circuit in FIG.

Joule heat is generated as electricity flows through a myriad of fine electric circuits inside the heating element between the bus wires, which causes the heating cable to emit heat. The change in temperature due to the heat generated from the heating cable or the ambient environment results in a change in the volume of the polymer matrix constituting the heating element, which affects the conductive path formed by the carbon black inside the heating element. The electric resistance of the heating element changes with the change of the conductive path, and this principle forms the basic mechanism of PTC phenomenon.

  The characteristics of autonomous heating cable using PTC phenomenon are greatly influenced by various factors. Short-term product characteristics inherent to heating cables, such as output changes due to temperature changes and switching effects that shut off the output above the critical temperature, are directly affected by the PTC phenomenon of the heating element. In general, the PTC phenomenon can be controlled by changing the type, content, blending method and polymer matrix of the carbon black used. On the other hand, long-term characteristics, such as product life, which continuously occur while using the output under the designed condition, are greatly influenced not only by the material properties of the heating element constituting the heating cable but also by the structural properties of the cable. In particular, the electrical characteristics of the heating cable are changed according to the interface condition of the contact surface where the heating element and the conductor bus wire meet each other, which may significantly affect the cable life. This can be explained as follows.

The item indicating the degree of flow of electricity is generally referred to as electrical resistance, and the resistance can be measured with a simple measuring device. The resistance measured in the heating cable can be considered to generally represent the resistance of the heating element, but more precisely, it can be divided into the sum of various resistance components present in the heating cable in addition to the heating element resistance. To illustrate this, an equivalent circuit composed of a resistance in the heating cable is illustrated as shown in FIG. 2.

As shown in FIG. 2, in addition to the self-resistance of the heating element, there is a contact resistance generated in the conductor resistance of the bus wire and the contact interface of the heating element / bus wire. Therefore, the resistance of the heating cable may be represented by Equation 1 below including the conductor resistance and the electrical resistance of the contact surface, that is, the contact resistance.

Rt = Rh + Rw + Rc

Where

Rt represents the resistance of the heating cable;

Rh represents the resistance of the heating element;

Rw represents the resistance of the conductor;

Rc represents contact resistance.

As described above, the resistance of the heating element is determined according to the type and content of the carbon black used and can be said to be a major component of the heating cable resistance. The bus wire resistance is inversely proportional to the cross-sectional area of the conductors used, and as a result, the bus wire resistance is insignificant compared to other components constituting the resistance of the heating cable. However, the contact resistance can change according to the state of the interface where two phases (heating element / bus wire) contact, and in some cases, a large change in contact resistance affects the heating cable resistance.

If the contact resistance is small, the effect on the heating cable resistance is small, so the electrical characteristics such as the output of the heating cable depend on the resistance of the heating element. On the other hand, if the contact resistance increases greatly, the high contact resistance affects the resistance of the heating cable, thereby changing the electrical characteristics of the heating cable. In particular, when the contact states of two phases are poor or uneven, micro-cavities are distributed at the interface, or when the conductor surface is oxidized or damaged, a large change in contact resistance occurs. When electricity flows through, a phenomenon such as a partial discharge occurs at this point, damaging the contact surface and the heating element. When the heating cable is used, the damage of the locally generated heating element is easy to propagate along the interface of two phases, which are relatively weaker than the inside of the heating element in terms of physical properties, which means that the contact state of the interface becomes worse. When the contact state of the two phases worsens, as described above, an increase in contact resistance occurs, which causes an increase in resistance of the heating cable. This phenomenon is not limited to a temporary and limited area, but it occurs continuously during use and propagates through the heating cable, and after a certain time, the heating cable resistance increases significantly, resulting in a decrease in the output of the heating cable and a cable life. This results in shortening. Therefore, it is very important for the life of the cable to minimize the contact resistance by contacting the interface between the heating element / conductor to minimize the contact resistance, and to smoothly maintain the normal contact interface in the interface during use.

The interface state between the heating element / bus wire can be influenced by various factors. In order to achieve a normal interface between the two phases, the heating element must be in close contact with the bus wire surface (physical side) and the conductor surface must not be oxidized or damaged (chemical side). In order for the heating element to be in close contact with the bus wire physically, the surface adhesiveness of the conductive material constituting the heating element should be good, which is greatly affected by the melt viscosity of the material. The melt viscosity of the heating element is influenced by the constituents of the conductive material. In particular, since the carbon black is the main constituent, the melt viscosity of the heating element changes depending on the type and content of the added carbon black. In the case of the heating element constituting the self-regulating heating cable, in most cases, a large amount of carbon black is added to realize a desired heating element resistance. In this case, the melt viscosity of the heating element is increased so that the surface adhesion is poor. As a result, the physical adhesion between the heating element and the bus wire is weakened, resulting in an increase in contact resistance.

In addition, since most tin-plated copper wires are made by hot-dip plating, local oxidation or surface damage may occur on the surface of the conductor during the heating element extrusion process. In this case, although the adhesion between the heating elements / conductors is good, local defects on the conductor surface act as a factor to increase the contact resistance and eventually reduce the life of the product.

In the present invention, in order to control the melt viscosity of the composite material constituting the heating element having a significant influence on the surface adhesion, the carbon black added by using the critical carbon black content (Critical Carbon Black Concentration) which is a relationship between the specially designed carbon black properties Select the type and content.

The relationship of the critical carbon black content applied in the present invention is based on the study of the relationship between the dye particles and the binder in the paint field, based on the critical pigment volume concentration established in relation to the adsorption of the binder and the surface of the dye particles. This relation can be expressed as Equation 2 below.

In the above formula, Oil Absorption: ml oil / ml pigment

Another study by several researchers suggests that the relationship between critical dye volume concentrations can be extended to polymer composites including carbon black, in which case the adhesion of the oil used in the relationship is determined by the DBP ( Dibutyl phthalate) oil can be replaced by adhesion. In particular, it was found that the melt viscosity and electrical conductivity of the composite material were greatly influenced by the carbon black mixed in the polymer composite material, and the carbon black mixed in the polymer composite material had a deep correlation with each other. That is, when the carbon black contains a certain content or more, the material exhibits high electrical conductivity, but from this point, the melt viscosity of the material rises rapidly and becomes very high. And the content of carbon black where this change of properties occurs is consistent with each other in a certain region. This may mean that there is a constant correlation between the electrical conductivity and the melt viscosity of the material at selected contents of certain carbon blacks.

In the present invention, the applicability of such a relationship was examined, and when the value of the relationship having a constant constant found through experiments entered a specific range, the electrical conductivity of the material meeting the object of the present invention and a suitable melt viscosity could be obtained. In the present invention, this relationship is referred to as the critical carbon black content, and has shown a critical carbon black content relationship with certain constants determined by the polymer material and some basic physical properties. Carbon black has some basic properties that show its own characteristics, including N ₂ surface area, DBP oil adhesion, particle size, and apparent density. In the present invention, as shown in Equation 3 below, the relationship between the DBP oil adhesion and the apparent density in the basic physical properties of the carbon black is derived using a constant constant determined according to the polymer material, and the value of this relation falls within the range defined in the present invention. It is characterized by determining the type and content of carbon black.

Where

K is a constant determined by the polymer material, and K = 1.6, 48 ≦ CCBC ≦ 51 for polyolefinic crystalline resins, and K = 1.8, 43 ≦ CCBC ≦ 46.5 for fluorine-based crystalline resins.

When the critical carbon black content falls within the defined range according to this relationship, it is possible not only to obtain an appropriate electrical conductivity according to the addition of carbon black, but also to minimize the increase in the melt viscosity of the conductive composite material by the added carbon black. The surface adhesiveness of the heating element can be improved. As a result, the physical adhesion between the heating element and the conductor can be increased, resulting in a drop in contact resistance. In addition, in the present invention, in order to improve the disadvantage of the tin-plated copper conductor used in the heating cable, the interface between the heating element and the bus wire is good by using a nickel-plated copper conductor specially designed for the conditions such as plating method, plating thickness, and plating adhesion. It keeps the contact resistance as low as possible to alleviate the power drop phenomenon during long-term use, improving the life of heating cable.

The heating cable with improved long-term life stability mentioned in the present invention is manufactured through the following process.

1) Inorganic fillers such as calcium carbonate and the like are selected from polyolefin resins or fluorine crystalline resins by selecting one or two or three kinds of inorganic filler mixtures, antioxidants and carbon blacks suitable for the critical carbon black content of Equation 2. After the basis weight to the weight ratio of the carbon black and the inorganic filler is first mixed in a super mixer, and then the mixture is mixed with a polymer resin and a half-barrier mixer, twin screw mixer, booth kneader and the like kneading to prepare a compound. .

2) The conductors for the bus wires are mounted on the dual pay-off of the extrusion line, and the prepared compound is extruded in the form of dumbbell type (heating element + bus wire) as shown in FIG. 3 using an extruder.

3) The molded heating element is completed through the post-treatment process through crosslinking and insulation extrusion process.

Hereinafter, the present invention is illustrated by the following non-limiting examples. In the following examples, the parts by weight are described in parts by weight so as to more clearly understand the ratio by weight of each component. Those skilled in the art having the benefit of this specification will be able to directly perform the experiments described in the examples with reference to the parts specified below. In addition, in the following examples, only the heating cable using the nickel plated copper conductor prepared through the heating cable manufacturing process described above was used as an example.

Example 1

36 parts by weight of carbon black having a critical carbon black content of 50.6, 15 parts by weight of calcium carbonate and 1.5 parts by weight of antioxidant are mixed, mixed for 7 minutes using a super mixer, and 100 parts by weight of the mixture and high density polyethylene are added to a twin screw mixer. Kneaded and nickel plated stranded conductor (Conductor specification: Concentric stranded wire structure (small wire diameter 0.45㎜ nominal, small 7), plating material nickel, plating degree 2wt% or more) to produce a heating element in the extrusion line, and then through the post-treatment process Specimens were prepared by irradiation crosslinking and insulation extrusion.

Example 2

12 parts by weight of carbon black having a critical carbon black content of 44.5, 10 parts by weight of calcium carbonate and 5 parts by weight of zinc oxide were mixed and mixed for 9 minutes using a supermixer, followed by 100 parts by weight of these mixtures and polyvinylidene fluoride. After input and kneading in the mixer, nickel-plated stranded conductor (Conductor specification: Concentric stranded wire structure (small wire diameter 0.574㎜ nominal, small 7), plating material nickel, plating degree more than 4wt%) to produce a heating element in the extrusion line After the treatment process, the specimen was manufactured by cross-linking and insulation extrusion.

Comparative Example 1-1

Specimens of the same output stage were prepared in the same manner as in Example 1 using tin-plated stranded conductors of the same standard together with the compound applied in Example 1.

Comparative Example 1-2

45 parts by weight of carbon black having a critical carbon black content of 51.9, 15 parts by weight of calcium carbonate, and 1.5 parts by weight of antioxidant were prepared to prepare a compound in the same manner as in Example 1, and the same output using a tin-plated stranded conductor of the same specification Specimen was prepared.

Comparative Example 2-1

Specimens of the same output were prepared in the same manner as in Example 2 using a tin-plated stranded conductor of the same specification with the compound applied in Example 2.

Comparative Example 2-2

45 parts by weight of carbon black having a critical carbon black content of 47.0, 10 parts by weight of calcium carbonate, and 5 parts by weight of zinc oxide were prepared to prepare a compound in the same manner as in Example 2, using a tin-plated stranded conductor of the same specification Specimen was prepared.

Long-term Life Stability Evaluation of Heating Cables

Long-term lifespan stability of the heating cable was evaluated by measuring the change in output over time by performing the on / off cycling test and the output test after the high temperature exposure with the heating cable specimens mentioned in the above examples and comparative examples. This test method is one of the methods used for predicting and evaluating the life of self-regulating heating cable. [Reference: IEEE 515-1997 Standard]. The on / off cycling test and the output test after high temperature exposure are measured by the following method.

One) On / Off Cycling Test

① Prepare a 30cm specimen as a finished product, and terminate one end with insulation and install the other end to supply power. Prepare three specimens for each sample.

② Before the test input, measure the pre-test output of each sample by applying 220Vac of rated voltage at the temperature of 10 ℃.

③ Install the prepared specimens in a specially designed terminal block for power supply and heat them in the oven.

④ Thermally stabilized at a predetermined temperature for 12 hours or more, and then subjected the On / Off cycling test to cut off the power for 3 minutes after applying a rated voltage of 220Vac for 12 minutes (Example 1, Comparative Example 1-1, 1-2: 65 ° C / Example 2, Comparative Example 2-1, 2-2: 100 ° C).

⑤ Turn off the power at a certain time, stabilize the specimen for 24 hours, measure the output of each sample by the same method as ②, and compare the measured result with the measured value before the test. Cycle number).

⑥ Check if there are over 4,800 cycles recorded for each specimen.

2) Output test after high temperature exposure

① Prepare a 30cm specimen as a finished product, and terminate one end with insulation and install the other end to supply power. Prepare three specimens for each sample.

② Before the test input, apply the power of 220Vac rated voltage at 10 ℃ and measure the output power of each sample.

③ Put prepared specimens into oven to stabilize them thermally.

④ After exposing the specimen for 1000 hours at a predetermined temperature, it is thermally stabilized at room temperature for at least 24 hours (Example 1, Comparative Example 1-1, 1-2: 85 ° C./Example 2, Comparative Example 2-1, 2- 2: 110 ° C.).

⑤ Measure the output of each specimen in the same way as ② and compare the result with the measured value before the test and check if the rate of change exceeds 80%.

On / Off cycling test results and output test results after high temperature exposure are shown in Tables 1 to 4 and FIGS. 4 to 7 of the accompanying drawings.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention described in the claims below. It will be appreciated.

As described above, the heating cable with improved long-term lifespan stability according to the present invention is to ensure longer life and stability than the conventional heating cable.

Claims (16)

delete delete delete delete delete delete delete delete delete delete delete delete A heating wire composed of a conductive polymer resin composition in which a carbon black having a critical carbon black content (CCBC) value of 48 to 51 in the following formula is added to the polyolefin-based crystalline resin and exhibiting constant temperature coefficient characteristics, and a conductor wire It is characterized by a long life stability, characterized in that it comprises a metal conductor that is nickel plated continuously and consistently without copper exposure to the copper conductor by the electroplating method, and an electrically insulating insulation sheath to protect it from the outside. Enhanced heating cable:

14. The heating cable of claim 13, wherein the polyolefin-based crystalline resin is selected from the group consisting of polyethylene, polypropylene, ethylene vinyl acetate, and ethylene acrylic acid copolymer. A heating element composed of a conductive polymer resin composition exhibiting a constant temperature coefficient characteristic by adding carbon black satisfying a value of 43 to 46.5 of the critical carbon black content of the following formula to the fluorine-based crystalline resin, and an electroplating method as a conductor bus wire. Long life stability heating cable characterized by consisting of a metal conductor in which nickel is continuously and uniformly plated on the copper conductor without exposing the copper conductor, and an electrically insulated sheath to protect it from the outside:

16. The fluorine-based crystalline resin of claim 15, wherein the fluorine-based crystalline resin is selected from polyvinylidene fluoride, ethylene-tetra fluoro ethylene copolymer, fluorinated ethylene-propylene copolymer and tetra Heating cable with improved long-term stability, characterized in that selected from the group consisting of.

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