KR102719076B1 - Method for manufacturing carbon heating paste for manufacturing stretchable heating film - Google Patents

Abstract

The present invention uniformly disperses nanocarbon materials such as graphite, carbon nanotubes, and graphene nanoplates, which are prone to clumping and agglomerating with each other due to self-agglomeration, and polyurethane resin by applying a mixing process (homogenizer, 3-roll mill, resonant mixer) according to the characteristics of the materials. As a result, the dispersion process is optimized, thereby improving the dispersing ability and the uniformity of the paste for manufacturing an elastic heating film, which are reduced due to the addition of the nanocarbon material and the high content of the nanocarbon material, thereby improving the heating performance of an elastic heating film made with the paste for manufacturing an elastic heating film according to the present invention.

Description

{Method for manufacturing carbon heating paste for manufacturing stretchable heating film}

The present invention relates to a method for producing a paste for producing an elastic heating film.

In general, a surface heating element is a heating element that heats the entire surface by connecting a metal electrode on a two-dimensional plane conductive heating film.

Conventionally, planar heaters are manufactured by uniformly spraying or printing metal powder with high thermal conductivity onto a film-shaped resin. However, recently, planar heaters are manufactured using nanocarbon materials such as graphite, carbon black, graphene, and carbon nanotubes, which are conductive nanomaterials, instead of metal powder. Nanocarbon materials not only have excellent electrical and physical properties such as high electrical conductivity, thermal conductivity, heat resistance, corrosion resistance, wear resistance, and lubricity, but also have an electromagnetic wave blocking effect, so planar heaters made of nanocarbon materials can be utilized in various fields.

In order for a planar heater made of nano-carbon materials to exhibit excellent heating characteristics, continuous contact between materials must be achieved to ensure high electrical conductivity, and in the case of an elastic planar heater, the heating performance must be maintained consistently without performance degradation when physically deformed.

However, conventional planar heating elements made of nano-carbon materials have poor dispersibility, making it difficult to maintain heating performance consistently across the entire surface, and there is a problem in that the heating performance changes or deteriorates due to the connection between materials being broken due to deformation of the nano-carbon material during stretching.

In addition, Korean registered patent (10-1294596) proposes a planar heating composition containing bundles of carbon nanotubes aligned in one direction, but it is difficult to apply such a planar heating composition to a curvature area that is bent or folded in all directions.

Korean registered patent (10-1294596)

The purpose of the present invention is to provide a method for producing a paste for producing an elastic heating film that can solve the problems described above.

A method for manufacturing a paste for manufacturing a flexible heating film to achieve the above purpose is provided.

A first step of preparing a first mixed solution in which carbon nanotubes (CNT), graphite, and graphene nanoplatelets (GnP) are uniformly dispersed in a solvent;

A second step of preparing a second mixed solution by adding a portion of polyurethane resin to the first mixed solution and uniformly dispersing it; and

It is characterized by including a third step of adding the remainder of the polyurethane resin to the second mixed solution and uniformly dispersing it.

The present invention uniformly disperses nanocarbon materials such as graphite, carbon nanotubes, and graphene nanoplates, which are prone to clumping and agglomerating with each other due to self-agglomeration, and polyurethane resin by applying a mixing process (homogenizer, 3-roll mill, resonant mixer) according to the characteristics of the materials. As a result, the dispersion process is optimized, thereby improving the dispersing ability and the uniformity of the paste for manufacturing an elastic heating film, which are reduced due to the addition of the nanocarbon material and the high content of the nanocarbon material, thereby improving the heating performance of an elastic heating film made with the paste for manufacturing an elastic heating film according to the present invention.

The present invention induces physical exfoliation of graphene nanoplates by utilizing the high shear force of a homogenizer, forms a network between graphite through the exfoliated graphene, and increases the connection path of a conductive material to improve electrical and thermal conductivity properties.

The present invention is a stretchable heating film in which graphite and graphene nanoplates are mixed with carbon nanotubes of a predetermined length and come into contact with each other, and graphite and graphene nanoplates are uniformly filled between carbon nanotubes that are randomly dispersed in a bent shape. Accordingly, when the stretchable heating film is bent or folded in all directions, when the polyurethane resin, which is a substrate, stretches, the carbon nanotubes in the polyurethane resin only straighten out their bent shapes and do not change their positions or become disconnected from each other, so that not only can heat be evenly generated over the entire surface, but even when the stretchable heating film is bent or folded, the heat generation performance of the stretchable heating film is not reduced and can be maintained constant. In addition, since the graphite and graphene nanoplates fill the empty spaces where the carbon nanotubes are entangled with each other, the carbon content can be increased, thereby increasing the heat generation amount.

Figure 1 is a flow chart showing a method for manufacturing a paste for manufacturing a flexible heating film according to one embodiment of the present invention.
Figure 2 is a schematic diagram illustrating a method for manufacturing a paste for manufacturing an elastic heating film according to one embodiment of the present invention.
Figure 3 is a table showing electrical resistance values according to acid treatment.
Figure 4 is an electron microscope photograph showing the effect of carbon nanotube dispersion according to acid treatment. (a) shows no acid treatment, (b) shows acid treatment with a single acid, and (c) shows acid treatment with a mixed acid.
Figure 5 is a drawing showing carbon nanotubes and graphene nanoplates mixed in a first mixed solution, where (a) shows a case where the first mixed solution is dispersed without using a homogenizer, and (b) shows a case where the first mixed solution is dispersed using a homogenizer.
Figure 6 is a drawing showing the process of stirring the second mixed solution with a 3-roll mill.
Figure 7 is a drawing showing the process of stirring a paste for manufacturing an elastic heating film using a rotary mixer.
Figure 8 is a SEM photograph of a paste for manufacturing a flexible heating film.
FIG. 9 is a photograph of a heating film printed and coated with a paste for manufacturing an elastic heating film manufactured by a method for manufacturing a paste for manufacturing an elastic heating film according to one embodiment of the present invention.
FIG. 10 is a graph comparing the surface resistance of a heating film printed or coated with a paste including graphite/carbon nanotubes/exfoliated graphene nanoplates according to the present invention, the surface resistance of a heating film printed or coated with a paste including graphite/carbon nanotubes according to a comparative example, and the surface resistance of a heating film printed or coated with a paste including graphite/carbon nanotubes/graphene nanoplates according to a comparative example.

Hereinafter, a method for manufacturing a paste for manufacturing an elastic heating film according to one embodiment of the present invention will be described in detail.

As shown in Fig. 1, a method for manufacturing a paste for manufacturing a flexible heating film according to one embodiment of the present invention is as follows.

Step 1 (S11) of preparing a first mixed solution in which carbon nanotubes (CNT), graphite, and graphene nanoplatelets (GnP) are uniformly dispersed in a solvent;

A second step (S12) of preparing a second mixed solution by adding a portion of polyurethane resin to the first mixed solution and dispersing it uniformly; and

It consists of a third step (S13) of adding the remainder of the polyurethane resin to the second mixed solution and dispersing it evenly. Refer to Fig. 2 as a basic reference.

Below, Step 1 (S11) is described.

Nanocarbon materials are uniformly dispersed in a solvent. Nanocarbon materials include carbon nanotubes (CNT), graphene, graphite, and graphene nanoplatelets (GnP).

Carbon nanotubes (CNTs) have a certain length. For example, carbon nanotubes are formed with a diameter of tens of nanometers and a length of tens of micrometers. In other words, carbon nanotubes are carbon nanotubes that are more than a thousand times longer than their diameters, and long carbon nanotubes are entangled with each other. Individual carbon nanotube strands are structurally flexible and can be bent and then straightened. These individual carbon nanotube strands come into contact with each other and become entangled.

Carbon nanotubes may be selected and used by selecting one or more of a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (SWCNT), and a multi-walled carbon nanotube (MWCNT).

Graphite is a plate-like multilayer structure, and graphene is a thin plate-like structure that separates one layer of graphite. Structurally, graphene nanoplates, which are located between graphene and graphite, are composed of small plates in which graphene sheets with a two-dimensional honeycomb lattice structure are stacked in short sections, with a thickness of 5–100 nm and a size of up to 50 μm. In particular, graphene nanoplates have excellent mechanical strength, electrical conductivity, and thermal conductivity, and are applied to various fields such as nanocomposites, electrodes, fuel cells, and solar cells, including conductive inks and coatings.

Nanocarbon materials are centered around carbon nanotubes of a certain length that are randomly arranged and entangled with each other, and graphite, graphene nanoplates, etc. fill the empty space. This increases the carbon content and the heat generation. Graphite and graphene nanoplates do not have the same flexibility as carbon nanotubes, so the elasticity of the stretchable heat-generating film cannot be expected. Therefore, graphite and graphene nanoplates must be added as auxiliary materials to carbon nanotubes.

In this embodiment, the nanocarbon material uses carbon nanotubes (CNT), graphite, and graphene nanoplatelets (GnP). Artificial graphite is used as the graphite. Graphene is formed by exfoliation from graphene nanoplatelets in the dispersion process described below. It is preferable that the content of the nanocarbon material relative to the matrix is 50 wt% or less.

The above first step (S11) is

Step 1-1 of acid treatment of carbon nanotubes;

Step 1 and 2 of dispersing acid-treated carbon nanotubes and graphene nanoplates in a solvent, respectively;

Step 1-3: mixing and dispersing a solution in which acid-treated carbon nanotubes are dispersed and a solution in which graphene nanoplates are dispersed; and

It consists of steps 1 to 4 of preparing a first mixed solution by adding and dispersing graphite into a solution in which acid-treated carbon nanotubes and graphene nanoplates are dispersed.

Below, Step 1-1 is explained.

Carbon nanotubes are acid-treated with an acid solution to improve their dispersibility. When carbon nanotubes are acid-treated, functional groups such as carboxyl groups (-COOH) or hydroxyl groups (-OH) increase in the carbon nanotubes. As a result, when carbon nanotubes are mixed with a solvent, the degree of dispersion increases and they can be mixed more evenly.

Carbon nanotubes are treated with aqua regia using a solution of concentrated hydrochloric acid and concentrated nitric acid in a 3:1 ratio as an acidic solution.

Taking carbon nanotubes as an example, as shown in Fig. 3, carbon nanotubes that have not been acid-treated have poor dispersibility and thus exhibit high electrical resistance, but carbon nanotubes that have been acid-treated with a mixed acid have good dispersibility and thus exhibit low electrical resistance. Acid treatment is performed by placing carbon nanotubes in an acid solution and then applying ultrasonic waves for 1 to 24 hours.

As shown in Fig. 4(a), it can be seen that the dispersibility of carbon nanotubes and graphite is poor in the case of carbon nanotubes that have not been acid-treated. However, as shown in Fig. 4(b), it can be seen that the dispersibility of carbon nanotubes and graphite is improved in carbon nanotubes that have been acid-treated with a single acid, such as sulfuric acid or nitric acid, compared to carbon nanotubes that have not been acid-treated. As shown in Fig. 4(c), it can be seen that the dispersibility of carbon nanotubes and graphite is improved more in carbon nanotubes that have been acid-treated with a mixed acid of sulfuric acid and nitric acid compared to carbon nanotubes that have been acid-treated with a single acid.

Therefore, if the dispersion of nanocarbon materials is improved by aqua regia treatment, uniformity is improved, and this allows the input amount of nanocarbon materials to be increased.

Below, steps 1 and 2 are explained.

Each carbon nanotube and graphene nanoplate treated with aqua regia is dispersed in a solvent. The solvent used is a polar organic solvent, CH7:DMF3. CH7:DMF3 has good solubility in polyurethane resin.

Each solvent containing carbon nanotubes and graphene nanoplates is stirred with a homogenizer for uniform dispersion. The homogenizer disperses the carbon nanotubes and graphene nanoplates in each solvent using a high-shear force dispersion method.

Below, steps 1-3 are explained.

A solvent in which carbon nanotubes are uniformly dispersed and a solvent in which graphene nanoplates are uniformly dispersed are mixed and stirred with a homogenizer for 30 minutes.

Referring to Figure 5, graphite with a size of 2 to 5 μm and graphene nanoplates with a size of 6 to 7 μm exist in a mixed form.

When dispersed without using a homogenizer, as shown in Fig. 5(a), the thickness of the graphene nanoplates is thick and the carbon nanotubes and the graphene nanoplates are each clumped separately. However, when dispersed using a homogenizer, as shown in Fig. 5(b), the thickness of the graphene nanoplates is reduced and graphene nanoplates exfoliated by shear force are formed. As a result, a three-dimensional planar network is formed between the carbon nanotubes and the graphite, which increases the number of connection points between the conductive materials and the contact area, thereby improving the heating performance of the stretchable heating film.

Below, steps 1-4 are explained.

A first mixed solution is prepared by adding graphite to a solvent in which carbon nanotubes and graphene nanoplates are dispersed. The first mixed solution is stirred with an impeller for 20 minutes to uniformly mix the nanocarbon materials (graphite, carbon nanotubes, graphene nanoplates) into the solvent.

Below, the second step (S12) is described.

[write]

In order to ensure that the nanocarbon material contained in the paste (1) for manufacturing an elastic heating film can adhere well to the elastic substrate of the elastic heating film, a substrate of the paste (1) for manufacturing an elastic heating film is required.

The base material of the paste (1) for manufacturing a flexible heating film uses polyurethane (PU) resin.

A portion of the set amount of polyurethane resin is added to the first mixed solution and mixed. The polyurethane resin is dissolved by the solvent contained in the first mixed solution. The viscosity of the solution is generated by the dissolved polyurethane resin.

Polyurethane resin is not a thermosetting resin, but it has a similar three-dimensional structure and has excellent tensile strength and tear strength. It also has flexibility and shape memory ability, so it has a wide range of applications and excellent bonding strength with metals.

[Stirring using a 3-roll mill]

A second mixed solution is prepared by adding a portion of the set amount of polyurethane resin to the first mixed solution. It is preferable to add 70% of the set amount of polyurethane resin.

The second mixed solution is first mixed with nanocarbon material and polyurethane resin dissolved in the solvent by impeller stirring for 20 minutes.

As shown in Fig. 6, the nanocarbon material and polyurethane resin are dispersed secondarily using a 3-roll mill to ensure uniform dispersion. The 3-roll mill is performed 1 to 3 times.

A 3-roll mill homogeneously disperses a second mixed solution by passing the second mixed solution through a fine gap between horizontally placed rollers. Using a 3-roll mill, three adjacent rollers rotate to apply pressure and shear force to the second mixed solution, thereby achieving the effects of mixing, milling, and dispersion. In particular, a homogenized second mixed solution can be obtained along with the mixing and crushing effects of high-viscosity polyurethane resin and nano-carbon material.

Below, the third step (S13) is described.

The remainder of the polyurethane resin, i.e. 30%, set in the second mixed solution is added and primary impeller stirring is performed for 1 hour.

As shown in Fig. 7, the paste for manufacturing a flexible heating film is stirred using a planetary mixer to uniformly disperse the nanocarbon material and polyurethane resin in the second mixed solution. For example, the planetary mixer is operated at Mix: 5 minutes/2000 RPM, Defoam: 5 minutes/2200 RPM.

The planetary mixer is a propellerless stirring method that does not contact the materials, and can evenly stir materials with different viscosities or specific gravity, disperse high-gravity materials without sedimentation, disperse nano-carbon material powder without agglomeration, and homogeneously stir nano-carbon material powder several times the volume of polyurethane resin.

In this way, a paste (1) for manufacturing an elastic heating film is manufactured through the first step (S11), the second step (S12), and the third step (S13). As illustrated in Fig. 8, the carbon nanotubes included in the paste (1) for manufacturing an elastic heating film manufactured in this way further reduce the electrical resistance by effectively connecting the graphite and the carbon nanoplates.

As shown in Fig. 9, the heating film manufactured by the above process is printed and coated on a substrate with a paste for manufacturing a flexible heating film, and the nanocarbon layer is formed uniformly and consistently with a uniform thickness without cracking.

Referring to FIG. 10, it can be seen that the surface resistance of the heating film printed or coated with the paste including graphite/carbon nanotubes/exfoliated graphene nanoplates according to the present invention is lower than the surface resistance of the heating film printed or coated with the paste including graphite/carbon nanotubes according to the comparative example and the surface resistance of the heating film printed or coated with the paste including graphite/carbon nanotubes/graphene nanoplates according to the comparative example. For example, the formation of a network structure between conductive materials shows low surface resistance results of 80Ω and 30Ω in the heating film manufactured using 150mesh screen printing (thickness 0.012 mm) and a doctor blade coater (thickness 0.1 mm).

1: Paste for manufacturing flexible heating film

Claims (5)

A first step of preparing a first mixed solution in which carbon nanotubes (CNT), graphite, and graphene nanoplatelets (GnP) are uniformly dispersed in a solvent;
A second step of preparing a second mixed solution by adding a portion of polyurethane resin to the first mixed solution and uniformly dispersing it; and
A method for producing a paste for manufacturing an elastic heating film, characterized by including a third step of adding the remainder of the polyurethane resin to the second mixed solution and uniformly dispersing it. In the first paragraph, the first step,
Step 1-1 of acid treatment of carbon nanotubes;
Step 1 and 2 of dispersing acid-treated carbon nanotubes and graphene nanoplates in a solvent, respectively;
Step 1-3 of mixing and dispersing the solution in which the acid-treated carbon nanotubes are dispersed and the solution in which the graphene nanoplates are dispersed; and
A method for producing a paste for producing an elastic heating film, characterized in that it includes steps 1 to 4 of producing a first mixed solution by adding and dispersing graphite in a solution in which the acid-treated carbon nanotubes and the graphene nanoplates are dispersed. In the second paragraph,
A method for manufacturing a paste for manufacturing an elastic heating film, characterized in that in steps 1-2 and 1-3, a homogenizer is used to uniformly disperse the paste. In the first paragraph,
A method for manufacturing a paste for manufacturing an elastic heating film, characterized in that in the second step described above, the paste is uniformly dispersed using a 3-roll mill. In the first paragraph,
A method for manufacturing a paste for manufacturing an elastic heating film, characterized in that in the third step, a planetary mixer is used to uniformly disperse the paste.