KR20170097340A - A planar heating film using carbon nanotube - Google Patents

Abstract

[0001] The present invention relates to a surface heating element film using carbon nanotubes, in which carbon nanotubes are dispersed in a polyurethane resin and formed in a plane, a connection electrode for connection to an external power source is formed on the surface, And the content of the nanotubes is 6 to 8% by weight.
Such a heating body film is produced by mixing a carbon nanotube powder with a volatile dispersant and stirring the mixture to form a primary mixture liquid in which carbon nanotubes are dispersed in a volatile dispersant, mixing the primary mixture liquid and the urethane resin solution and stirring them to form a secondary mixture liquid A step of casting the secondary mixture liquid into a film form in a plane; Drying the volatile dispersant in a cured product of the secondary mixture cured in the form of an area film to volatilize the cured product and curing the conductive film; and applying a conductive material to the planar film of the cured secondary mixture to form a connection electrode to form a planar heating element film . ≪ / RTI >

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a planar heating element film using carbon nanotubes,

TECHNICAL FIELD [0001] The present invention relates to a planar heating element film, and more specifically, to a planar heating element film using carbon nanotubes as a conductor and a heating element.

Among the heat generating elements formed by the surface heat, the heat generating elements using the heat rays flow through the electric wires. Therefore, if the wires are broken, the heat generating element does not generate uniform heat as a whole, and there is a risk of fire due to interruption of heat generation due to disconnection and overheating. Further, when a linear heating element is applied to a planar structure, the heat loss is large when the heat is transferred from the line to the surface, so that not only the heat efficiency is lowered but also the temperature distribution is uneven due to the localized heat.

Recently, a planar heating element having improved electrical stability and uniformity of temperature distribution has been developed by distributing carbon black, graphite or the like to a heating element, as compared with the case of using a linear heating element.

As one example of this type, the planar heating element disclosed in Patent Publication No. 10-0860258 (Document 1) includes a first synthetic resin film used as the first sheathing, a second synthetic resin film disposed on the upper side of the first synthetic resin film, The first carbon layer, the first carbon layer, the first carbon layer, the lower carbon layer, the first carbon layer, and the first carbon layer. And a second synthetic resin film disposed on the nonwoven fabric covering the upper side and the upper portion of the second carbonaceous conductive layer, which is located on the upper portion of the nonwoven fabric, and contains the carbonaceous substance.

However, since the planar heating element of Document 1 of this structure uses a carbon-based heat generating ink such as carbon black or graphite having a relatively large carbon particle, fine voids are generated between the carbon layer and the copper wire to deteriorate the electrical conductivity, There is an electrical instability such as a minute spark in the pores, and there is a problem in that the durability is deteriorated due to the physical properties between the stacked elements, which may cause delamination during long-term use.

As an invention for solving such a problem, there has been proposed a planar heating element disclosed in Patent Publication No. 10-1128335 (Document 2).

1 showing the planar heating element according to the invention of Document 2, the planar heating element of Document 2 is formed in order to increase the adhesive force between the respective layers and to prevent overheat due to electrical resistance between the heating layer and the electrodes A first film 10 in the form of a synthetic resin thin film, a first adhesive layer 20 laminated on the first film, a copper wire 30 attached to the surface of the first adhesive layer 20 at a predetermined distance, A silver layer 40 laminated on the surface of the copper wire 30 at a width greater than the width of the copper wire, a heating layer 50 laminated on the first adhesive layer and the silver layer, a second adhesive layer 60 laminated on the heating layer, And a second film (70) in the form of a thin film of synthetic resin laminated on the second adhesive layer.

The heat generating layer 50 includes a carbon nano tube (CNT) heat generating ink and a TDI (toluene diisocyanate) curing agent. The adhesive layer includes a modified urethane adhesive containing an ester compound and a TDI And a hardening agent.

However, according to the structure of the planar heating element of Document 2, since the CNTs constituting the heat generating layer, the copper wires supplying power thereto, and the synthetic resin thin film protecting the heat generating layer form a separate layer from each other, There is a possibility of peeling between them. Particularly, since the connecting electrode layer and the covering layer such as the heating element layer, the adhesive layer and the copper wire are formed separately and laminated and adhered, the increase of the manufacturing cost and the decrease of the heat generation and the heat transfer efficiency are inevitable to be.

Patent Publication No. 10-0860258 (Document 1) Patent Publication No. 10-1128335 (Document 2)

The present invention provides a planar heating element using a carbon nanotube as a heating element, which is superior in heat generation and conduction efficiency to a linear heating element, in consideration of the problems of the conventional planar heating elements including the planar heating elements of Documents 1 and 2, The present invention aims at solving the problem that the heat generation efficiency and the manufacturing cost are increased by stacking and bonding a large number of layers like the surface heating element of the present invention.

The present invention is intended to provide a planar heating element having a structure in which a separate sheath or connection electrode layers for power supply can be integrally formed with each other so as to function as a planar heating element.

The above-described object of the present invention is achieved by a planar heating element film and a manufacturing method thereof according to the present invention.

In the present invention, a carbon nanotube is used as a heating element, and these heating elements are considered to be capable of functioning as a surface heating element as a single layer without forming a separate layer. As a result of such consideration, It has been concluded that the film can be used independently as a surface heating element without a separate protective layer or adhesive layer when the film is formed with polyurethane.

The surface heating film according to the present invention is characterized in that carbon nanotubes are dispersed in a polyurethane resin and formed in a plane, and connection electrodes for connection to an external power source are formed on the surface, The content of the carbon nanotubes is 6 to 8% by weight.

The surface heating film of the present invention can be produced by dispersing carbon nanotubes in a flexible polyurethane resin having appropriate elasticity to form a film so that the polyurethane resin covers the carbon nanotubes dispersed in the polyurethane resin, Thereby functioning as the planar heating element.

In particular, in the present invention, the connection electrode can be formed by applying a conductive ink to the surface of the surface heating film. Therefore, compared to the conventional surface heating element in which a copper wire or the like must be buried in order to supply power to the carbon nanotubes, power can be efficiently supplied in a very simple configuration.

Further, the planar heating element film having such a configuration can be formed by the manufacturing method according to the present invention.

The manufacturing method of the present invention comprises: mixing a carbon nanotube powder with a volatile dispersant and stirring the carbon nanotube powder to form a primary mixture liquid in which carbon nanotubes are dispersed in a volatile dispersant; Mixing the primary mixture liquid and the urethane resin solution and stirring to form a secondary mixture liquid; Casting the secondary mixed liquid into a film form in a plane; Drying and curing the volatile dispersant in the cured product of the secondary mixture cured in the form of an on-film film to volatilize; And applying a conductive material to the planar film of the cured secondary mixture to form a connection electrode to form a planar heating element film.

The carbon nano powders in the raw state exist in a state where they are tangled with each other like a thread. The carbon nano powder raw material is mixed and dispersed in a volatile dispersant. When the carbon nano powder is uniformly dispersed, the electric conductivity is rapidly increased even by a small amount of carbon nano powder alone.

In one embodiment, carbon nanotube powder can be uniformly dispersed in a methyl ethyl ketone solution by mixing powder of carbon nano powder with a methyl ethyl ketone solution as a volatile dispersant and applying ultrasonic wave to the mixture.

The carbon nanotube powder is mixed with the polyurethane solution while being uniformly dispersed in the dispersant, and the mixed solution is stirred again to uniformly disperse the carbon nanotube powder in the polyurethane solution.

As one embodiment of the present invention, in the above-mentioned dispersion, uniform dispersion of carbon nanotubes is promoted by stirring a magnetic bar in a mixed solution obtained by mixing a primary mixture of a carbon nanotube powder and a volatile dispersant and a polyurethane resin solution.

The secondary mixed liquid thus dispersed is poured into a frame having a flat shape to form a film form, and the volatile dispersant is evaporated to form a planar heating film.

A conductive ink may be applied to a part of the surface of the thus-formed surface heating element film and cured to form a connection electrode.

According to the surface heating film and the method for manufacturing the same according to the present invention described above, it is possible to provide a multilayered film of carbon nanofilm, a layer for power supply including a copper wire, a coating layer for protection, and an adhesive layer It is possible to form a film in which the carbon nanotubes are uniformly dispersed in the polyurethane resin which also functions as a coating for the carbon nanotubes.

The surface heating film of the present invention has not only a simple structure but also the carbon nanotubes are uniformly dispersed to improve electrical conductivity and thermal conductivity and electric conductivity are improved because there is no gap or the like between dispersed polyurethane resins Heat generation efficiency and heat transfer efficiency become high.

In particular, since a plurality of layers are not separately formed and adhered, the manufacturing cost is lowered and the reliability and durability of the product are improved.

1 is a cross-sectional view showing a configuration of a conventional surface heating element according to Document 2.
2 is a table showing the content of the material used in the production of the planar heating element according to the present invention.
Fig. 3 is a photograph showing a surface heating element film produced with the material content shown in Fig.
4A and 4B are graphs showing electric resistance values according to the content of carbon nanotubes and the distance between electrodes in the planar heating film of FIG.
5A and 5B are graphs showing exothermic behavior of a planar heating element film according to an embodiment of the present invention.

Hereinafter, an embodiment of a planar heating element according to the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.

Carbon nanotubes, which are heating elements, were produced by chemical vapor deposition and had a diameter of 9.5 nm, an average length of 1.5, and a carbon purity of 90%.

When the carbon nanotubes are uniformly dispersed in a three-dimensional manner due to a large aspect ratio, an electrical conduction path is formed and a 'Percolation threshold' occurs in which electrical conductivity is rapidly increased only with a small amount of the carbon nanotubes. The electrical conductivity of carbon nanotubes is 10 ¹¹ A / m ^{2, which} is similar to that of copper, and the thermal conductivity is 3000 ~ 6000 W / m higher than that of diamond. It is also a good material as a material for surface heating elements because it has heat dissipation and exothermic characteristics.

A dispersing agent for forming a planar heating element film, a filler, and a polyurethane resin, which is one of polymer resins, as a coating agent. This is because the polyurethane resin has excellent stretchability and exhibits high flexibility when formed into a film.

The composition of each material for producing the planar heating element is shown in Fig. First, carbon nanotubes were added in a composition range of 0 to 8 wt%. Into a 250 ml beaker, add carbon nanotube powder and methyl ethyl ketone solution as volatile dispersing agent according to the composition.

The carbon nanotubes are entangled like a thread in their structure, but when uniformly dispersed, a conduction path is formed between the carbon nanotubes, and a 'Percolation threshold' occurs in which the electrical conductivity increases rapidly only with a small amount of carbon nanotubes.

The primary mixture of carbon nanotubes and methyl ethyl ketone was placed in an ultrasonic dispersion apparatus for 5 minutes while applying ultrasonic waves to uniformly disperse the carbon nanotubes in the mixture.

The primary mixture solution in which the carbon nanotubes were uniformly dispersed was mixed with the polyurethane resin solution in accordance with the composition ratio shown in FIG. 2 to prepare a secondary mixture solution, and the magnetic bar was added to the secondary mixture solution, and the mixture was stirred for 8 hours.

The secondary mixture of the carbon nanotube-methyl ethyl ketone-polyurethane solution, which had been stirred, was poured onto a 30 cm x 30 cm glass plate to form a film.

The secondary mixed solution in the form of a film was placed in a vacuum drier and dried at a temperature of 60 ° C for 2 hours to evaporate methyl ethyl ketone as a volatile dispersant to be cured in a film form to prepare a film of a planar heating element.

A photograph of the thus produced film is shown in Fig. 3, a polyurethane film (PU film) containing no carbon nanotubes, a film containing 2 wt% (PU-CNT2), and 4 wt% of carbon nanotubes (PU-CNT4), a film containing 6 wt% (PU-CNT6), and a film containing 8 wt% (PU-CNT8).

In order to increase the power supply efficiency, silver paste is applied as conductive ink to the surface of the film in an electrode form and cured to connect to the surface of the surface heating film Electrodes were formed.

Resistance measurement and heat generation test were carried out to confirm the performance of the surface heating film.

The resistance measurement is a digital multimeter with a range of 3 kΩ to 250 kΩ available from GWINSTEK under the model name 'GDM-8245'. Each film (PU-CNT2, 4, 6, 8 wt%) was repeatedly measured 10 times. Infrared thermometer supplied from 'BENETECH' to model 'MG550' with electricity supplied from DIGITAL to LP303-TP (operating range: serial mode, 0 ~ 30V / 0 ~ 0.15A) (Range of use: 0 ~ 200) and a thermal camera.

As shown in the tables of FIGS. 4A, 4B, 4C, and 4D, the average resistance value of the plane heating element film containing 2 wt% of carbon nanotubes as a result of resistance measurement of the plane heating element film was 149 to 225 kΩ (Fig. 4A). The average resistance value of the 4 wt% surface heating element film was 47.1 to 103.1 k? According to the electrode interval (Fig. 4B). The average resistance value of the 6 wt% area heating film was 13.5 ~ 34.4 k? Depending on the electrode interval (Fig. 4C). The average resistance value of the 8 wt% surface heating element film was 6.4 to 34.4 k? According to the electrode interval (Fig. 4D). As the carbon nanotubes content increased, the resistance value decreased. As the distance between the electrodes increased, the resistance increased.

The 'Percolation' according to the carbon nanotube content and the distance between the electrodes is 10 ¹² Ω for the polyurethane resin without the carbon nanotubes, and the resistance value is decreased to 10 ³ ~ 10 ⁶ Ω when the carbon nanotubes are added. Respectively. That is, 10 ⁶ to 10 ⁹ Ω.

The exothermic behavior was measured according to the carbon nanotube content by supplying electric power to the surface heating film. 2 to 4 wt% The surface heating film had a high resistance value of 10 ⁹ to 47.1 k?, So that no exothermic behavior was observed. However, the 6 to 8 wt% surface heating film had an average resistance value of 13.5 kΩ when it was 6 wt% and an average resistance value of 6.4 kΩ when it was 8 wt%. The exothermic behavior at 6 wt% and 8 wt% is shown in Figs. 5A and 5B, respectively.

In conclusion, the surface heating film was fabricated by using carbon nanotubes and polyurethane, and electric resistance and heat generation according to the contents of carbon nanotubes were measured. As a result, the resistance decreased as the carbon nanotube content increased, and the resistance value increased as the electrode gap increased. That is, the content is high and the resistance value is low as the gap is narrowed.

Also, in the exothermic test, when the content of carbon nanotubes was 2 to 4 wt%, the average resistance value was in the range of 47.1 to 225 kΩ, and the exothermic behavior was not observed, and thus it was confirmed that it could not be used as a heating element. However, when the content of the carbon nanotubes is 6 to 8% by weight, when the voltage of 3 to 24 V is applied, the carbon nanotube generates heat in a temperature range of 50 to 200 ° C, and thus it can be used for various purposes as an area heating element.

The carbon nanotubes manufactured according to the present invention and the method of manufacturing the carbon nanotubes have been described above, and the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the claims.

Claims (5)

As a planar heating element film,
Wherein the carbon nanotubes are dispersed in a polyurethane resin and formed in a plane, a connection electrode for connection to an external power source is formed, and a content of carbon nanotubes relative to the total weight is 6 to 8 wt%. The method according to claim 1,
Wherein the connection electrode is formed of a conductive ink applied to a surface of the planar heating element film. A method for producing a planar heating element film according to claim 1 or 2,
Mixing a carbon nanotube powder with a volatile dispersant and stirring the carbon nanotube powder to form a primary mixture liquid in which carbon nanotubes are dispersed in a volatile dispersant;
Mixing the primary mixture liquid and the urethane resin solution and stirring to form a secondary mixture liquid;
Casting the secondary mixed liquid into a film form in a plane;
Drying and volatilizing the volatile dispersant in the cured product of the secondary mixture cured in the form of a film in the form of a film
Applying a conductive material to the planar film of the cured secondary mixture to form a connection electrode to form a planar heating element film
Wherein the film has a thickness of 100 mu m or less. The method of claim 3,
Wherein the carbon nanotube powder is dispersed in a methyl ethyl ketone solution by mixing the carbon nanotube powder with a methyl ethyl ketone solution and applying ultrasound to the carbon nanotube powder to form the primary mixed solution. The method of claim 3,
Wherein a polyurethane resin solution is added to the primary mixture solution and the magnetic bar is added to the secondary mixture solution to form the secondary mixture solution.

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