KR20160044356A - Method of preparation of conductive paste and conductive paste prepared therefrom - Google Patents

Abstract

The present invention relates to a method for producing a conductive paste and a conductive paste prepared therefrom. According to the method for producing a conductive paste of the present invention, a carbon nanotube dispersion is prepared by mixing a carbon nanotube with a solvent and a dispersion to prepare a paste by mixing with a conductive particle in the form of a dispersion to increase the degree of dispersion of the carbon nanotube, Of carbon nanotube-containing paste can be provided. Therefore, it is possible to exhibit equivalent electrical conductivity while reducing the amount of expensive metal used in the conductive paste, and thus it can be usefully used industrially and economically.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a conductive paste and a conductive paste,

The present invention relates to a method for producing a conductive paste and a conductive paste prepared therefrom.

With the recent depletion of existing energy sources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar cells are attracting attention as next-generation batteries using semiconductor devices that convert solar energy directly into electric energy. Solar cells are divided into silicon solar cell, compound semiconductor solar cell and tandem solar cell. Among them, silicon solar cells are mainstream.

Such a solar cell generally includes a semiconductor substrate and a semiconductor emitter layer made of semiconductors having different conductive types such as a p-type and an n-type, a reflective layer formed on a semiconductor emitter layer, A conductive electrode layer formed on the antireflection film, a front electrode formed on the conductive electrode layer, and a rear electrode formed on the semiconductor substrate. Therefore, a p-n junction is formed at the interface between the semiconductor substrate and the semiconductor emitter layer.

In the production of conventional silicon solar cells, in addition to the cost ratio of wafers, the electrode materials consumed for forming the conductive pattern also account for the high cost portion, and it is necessary to increase cost competitiveness by reducing material cost.

On the other hand, a conductive paste containing silver (Ag) powder is used to form a conductive pattern such as a front electrode. Silver has no problem of oxidation and is excellent in electrical conductivity, but it is a main cause of raising the cost of paste with expensive materials. Therefore, development of a new electrode material capable of imparting high conductivity while being a low-cost material is being demanded.

Among them, there is an attempt to replace silver by adding carbon-based materials having conductivity such as carbon black, carbon nanotubes, carbon nanowires, and activated carbon. For example, Korean Patent Registration No. 1099237 discloses a silver nanoparticle-containing conductive paste containing 15 to 50% by weight of silver nanoparticles, 0.1 to 2.5% by weight of carbon nanotubes, 1 to 15% by weight of a binder and a solvent . However, in the above Korean registered patent, the carbon nanotubes are contained in paste in the form of powder, so that the dispersibility is poor, and the silver nanoparticles are still expensive, and the unit price The savings are not enough.

In order to solve the problems of the prior art as described above, the present invention provides a method for producing a conductive paste in which carbon nanotubes are highly dispersed.

The present invention also provides a conductive paste prepared by the above method.

According to an aspect of the present invention, there is provided a method of manufacturing a carbon nanotube dispersion, comprising: preparing a carbon nanotube dispersion by mixing carbon nanotubes, a first solvent, and a dispersant; And mixing the carbon nanotube dispersion, silver (Ag) powder, a second solvent and a binder.

The present invention also provides a conductive paste obtained by the above production method.

According to the method for producing a conductive paste of the present invention, a carbon nanotube dispersion is prepared by mixing a carbon nanotube with a solvent and a dispersion to prepare a paste by mixing with a conductive particle in the form of a dispersion to increase the degree of dispersion of the carbon nanotube, Of carbon nanotube-containing paste can be provided. In addition, since carbon nanotubes as they are produced can be used without removing a specific pretreatment or a reforming step to remove impurities of the carbon nanotubes and increase purity, the process is simple and does not cause an increase in manufacturing cost due to pretreatment There are advantages.

Therefore, it is possible to exhibit equivalent electrical conductivity while reducing the amount of expensive metal used in the conductive paste, and thus it can be usefully used industrially and economically.

1 is a SEM photograph of an entangled type carbon nanotube.
2 is a graph showing the results of measurement of storage elastic modulus and loss elastic modulus according to external energy for the pastes of Example 1 and Comparative Example 2. Fig.

A method for producing a conductive paste according to the present invention comprises: preparing a carbon nanotube dispersion by mixing a carbon nanotube, a first solvent and a dispersant; And mixing the carbon nanotube dispersion, silver (Ag) powder, a second solvent and a binder.

The manufacturing method of the conductive paste according to the present invention can lower the manufacturing cost while maintaining excellent electrical characteristics of the conventional silver paste.

In addition, according to the method for producing a conductive paste of the present invention, it is possible to uniformly disperse carbon nanotubes in a conductive paste at a high concentration, and to obtain rheology characteristics even when the carbon nanotubes are directly introduced into a conductive paste production process It is possible to maximize the effect of mixing of carbon nanotubes and to inject carbon nanotubes at a higher concentration. As a result, the conductive paste obtained according to the method of producing conductive paste of the present invention exhibits high electrical conductivity, low surface resistance, good printability, and can be usefully used for forming electrode patterns requiring fine line width and high conductivity.

In the present invention, the terms first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

Also in the present invention, when referring to each layer or element being "on" or "on" each layer or element, it is meant that each layer or element is formed directly on each layer or element, Layer or element may be additionally formed between each layer, the object, and the substrate.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Hereinafter, the method for producing a conductive paste according to the present invention and the conductive paste obtained therefrom will be described in more detail.

A method of manufacturing a conductive paste according to an aspect of the present invention includes: preparing a carbon nanotube dispersion by mixing carbon nanotubes, a first solvent, and a dispersant; And mixing the carbon nanotube dispersion, silver (Ag) powder, a second solvent and a binder.

First, carbon nanotubes, a first solvent and a dispersant are mixed to prepare a carbon nanotube dispersion.

Carbon nanotubes have excellent electrical conductivity in themselves. When they are included as a filler in a conductive paste, they can exhibit similar electrical conductivity while reducing the use of expensive metal particles such as silver (Ag). Recently, carbon nanotubes Has attracted attention as a material for conductive pastes. However, in order for the carbon nanotubes to exhibit the above-mentioned effect, the amount of metal particles to be used must be replaced by a certain amount or more while being uniformly dispersed in the paste. However, carbon nanotubes are difficult to be uniformly dispersed in the paste. In addition, generally used carbon nanotubes have poor flowability when they are contained in a paste, resulting in poor printability.

Therefore, in the present invention, carbon nanotubes are mixed with a solvent and a dispersing agent to prepare a carbon nanotube dispersion without directly injecting the carbon nanotubes when the conductive paste is prepared, and the carbon nanotubes are mixed with the conductive particles in the form of a dispersion, To thereby increase the degree of dispersion of the carbon nanotubes and to produce a carbon nanotube-containing paste having a high concentration, thereby completing the present invention.

According to an embodiment of the present invention, the step of preparing the carbon nanotube dispersion may be performed in two stages.

First, a mixed solution is prepared by mixing a carbon nanotube, a first solvent, and a dispersant. Next, a step of uniformly dispersing the carbon nanotubes in the solvent may be performed after or before the mixing of the mixed solution. The dispersion process may be performed using, for example, a bead mill, a planetary mill, or the like, and is not particularly limited. The diameter of the beads used for the bead mill is not particularly limited, and beads having a diameter ranging from about 0.1 to about 1 mm may be used. By performing the dispersion process, the carbon nanotubes can be more uniformly mixed in the dispersion to increase the degree of dispersion.

According to an embodiment of the present invention, the carbon nanotubes may use entangled carbon nanotubes. The entangled carbon nanotubes exhibit lower specific surface area and higher bulk density than self aligned carbon nanotubes and can be contained in the paste at a higher concentration than other carbon nanotubes of the same volume, The effect of adding carbon nanotubes can be maximized.

The entangled carbon nanotubes may have a bulk density of about 0.07 to about 0.4 g / cc, or about 0.1 to about 0.3 g / cc. Generally, the bulk density of self-aligned carbon nanotubes is about 0.01 to about 0.05 g / cc, while the bulk density of carbon nanotubes having a tangled structure is at least 0.07 g / cc. When such a carbon nanotube having a large bulk density is used, the dispersion degree of carbon nanotubes in the conductive paste can be high and can be contained at a high concentration, so that the substitution effect of the silver powder without deteriorating the electrical characteristics and rheology of the conductive paste It can be expressed to the maximum extent. Accordingly, the cost reduction effect is very high because expensive silver powder, in particular silver nano powder, is not used and the electroconductivity and printability are equivalent to those of a paste containing silver nanopowder.

Further, in the carbon nanotubes having the entangled structure, the ratio of the length to diameter (L / D ratio) may be about 200 to about 6000, or about 500 to about 4000, or about 500 to about 2500.

The carbon nanotubes have an average diameter of about 5 to about 20 nm, or about 5 to about 15 nm, and an average length of about 5 to about 30 nm, within a range that satisfies the above-described ratio of length to diameter (L / D ratio) Mu] m, or from about 10 to about 25 [mu] m.

In the conductive paste manufacturing method of the present invention, by using the carbon nanotubes having an intertwined structure having a relatively short length and a high bulk density in the above-mentioned range, rheological characteristics are improved compared with the case of using carbon nanotubes having the same content ratio And can contribute to the improvement of conductivity.

The content of the carbon nanotubes in the carbon nanotube dispersion may be about 5 to about 30 parts by weight, or about 5 to about 20 parts by weight based on 100 parts by weight of the carbon nanotube dispersion. If the content of the carbon nanotubes is too small, the effect of the carbon nanotubes is insignificant in the conductive paste to be produced. If the carbon nanotubes are included too much, dispersion of the carbon nanotubes is not effective. .

The carbon nanotube dispersion includes a first solvent as a dispersion medium of the carbon nanotubes. The first solvent may be selected from the group consisting of alpha-terpinol, ethyl cabitol acetate, butyl cabitol acetate, methyl isobutyl ketone, ethyl cellosolve ethyl cellosolve, butyl cellosolve, texanol, or butyl citalol may be used.

The content of the first solvent is not particularly limited as long as it can act as a medium of the carbon nanotubes. For example, about 60 to about 90 parts by weight, or about 100 parts by weight of the carbon nanotube dispersion, 70 to about 90 parts by weight.

Also, in order to increase the degree of dispersion of the carbon nanotubes, the carbon nanotube dispersion includes a dispersant. As the dispersing agent, an acrylate-based polymer, a urethane-based polymer, an acrylate-urethane-based polymer, or a mixture thereof may be used. Further, it may be preferable to use a polymer compound having a weight average molecular weight of 30,000 g / mol or more.

The content of the dispersant is not particularly limited and may be, for example, about 0.1 to about 10 parts by weight, or about 1 to about 10 parts by weight based on 100 parts by weight of the carbon nanotube dispersion.

The carbon nanotube dispersion thus prepared is mixed with a silver (Ag) powder, a second solvent, and a binder to prepare a conductive paste.

The carbon nanotube dispersion may be included in an amount of about 5 to about 30 parts by weight, or about 5 to about 20 parts by weight based on 100 parts by weight of the paste. If the carbon nanotube dispersion is too small, the effect due to the addition of the carbon nanotubes in the conductive paste is insignificant. When the carbon nanotube dispersion is included too much, the viscoelasticity increases due to the characteristics of the linear carbon nanotubes, It may be difficult to implement, and from this point of view, it is preferable that the weight range is included.

In the conductive paste of the present invention, silver (Ag) powder is contained as a conductive powder which imparts electrical characteristics. The silver powder includes not only pure silver (Ag) powder but also silver oxide, silver alloy, silver compound or other material capable of precipitating silver powder by firing. These may be used alone or in combination of two or more.

The silver powder may be a commercially available spherical powder or a powder of a flake type. Alternatively, a silver powder may be used according to a known method using a flake type.

The grain size of the silver powder can be adjusted to a suitable range in consideration of a desired sintering speed and influence in a process of forming an electrode. According to one embodiment of the present invention, the silver powder is expressed in micrometers, For example, having an average particle diameter of from about 1 to about 10 mu m, preferably from about 3 to about 5 mu m.

When particles having a micrometer-unit particle diameter (hereinafter referred to as microparticle) are used, the cost of producing a paste can be reduced compared with particles of nanometer-scale unit (hereinafter referred to as nanoparticle) It is necessary to incorporate a certain percentage of nanoparticles or to use other additives for improvement of physical properties. However, according to the manufacturing method of the present invention, the carbon nanotube dispersion can be produced by incorporating the dispersion in a conductive paste, thereby exhibiting high conductivity and low-temperature sinterability even with microparticles alone without using silver nanoparticles. Further, by replacing a certain amount of the silver powder of the microparticles with the less expensive carbon nanotube without using the silver nanoparticles, the cost can be greatly reduced as compared with the case of using the conventional silver nanoparticles.

The silver powder contained in the conductive paste of the present invention may be contained in an amount of about 35 to about 60 parts by weight, or about 40 to about 50 parts by weight based on 100 parts by weight of the paste. If the amount of the silver powder is too small, the electrical conductivity of the paste deteriorates, the phase separation occurs, or the viscosity becomes low, thereby causing a problem of printing property. If too much silver powder is contained, printing may become difficult and the price may increase.

The conductive paste includes a second solvent as a dispersion medium. The second solvent may include at least one selected from the group consisting of alpha-terpinol, ethyl cabitol acetate, butyl cabitol acetate, methyl isobutyl ketone, ethyl cellosolve ethyl cellosolve, butyl cellosolve, texanol, or butyl citalol may be used. The second solvent may be the same or different from the first solvent and may be used independently.

The content of the second solvent is not particularly limited as long as it can act as a medium of the conductive paste. For example, about 10 to about 50 parts by weight, or about 20 to about 50 parts by weight, relative to 100 parts by weight of the conductive paste 50 parts by weight.

The conductive paste of the present invention includes a binder, and the binder can be used without particular limitation as long as it functions as a binder of each component before firing. As the binder, for example, an epoxy-based binder, a polyester-based binder, an acryl-based binder, an ethyl cellulose-based binder, a nitrocellulose- But is not limited thereto.

The content of the binder is not particularly limited and may be, for example, about 0.1 to about 20 parts by weight, or about 1 to about 15 parts by weight based on 100 parts by weight of the conductive paste.

The conductive paste of the present invention may further contain additives such as a dispersing agent, a thickening agent, a thixotropic agent and a leveling agent, if necessary, in addition to the above components. The amount of such an additive to be added is not particularly limited as long as it does not impair the physical properties of the conductive paste. For example, it may be about 1 to about 10 parts by weight based on 100 parts by weight of the paste.

According to another aspect of the present invention, there is provided a conductive paste obtained by the above-described production method.

The conductive paste obtained by the above-described production method has advantages of excellent sheet resistance property, high conductivity and low cost, and thus can be used as various materials for electronic / electric devices. For example, the electrode pattern formed using the conductive paste of the present invention may be applied to a solar cell, a printed circuit or printed circuit board (PCB), an electrode of a flexible printed circuit board, The formation of a gate and a source electrode of a display such as an electrode of a panel (TSP), a plasma display panel (PDP) and a thin-film transistor liquid crystal display (TFT-LCD) Frequency identification) electrodes and the like, which are required to have high conductivity and reliability.

The conductive paste of the present invention can be applied to a substrate through various processes such as spin coating, dip coating, drop-casting, inkjet printing, screen printing, gravure printing, and offset printing. And the like.

The conductive paste of the present invention contains about 1 to about 10 parts by weight, preferably about 2 to about 5 parts by weight, of carbon nanotubes with respect to 100 parts by weight of the paste, and the carbon nanotubes preferably have an intertwined structure entangled type carbon nanotubes.

The conductive paste of the present invention may contain silver powder in an amount of about 35 to about 60 parts by weight based on 100 parts by weight of the paste, and the silver powder may have a particle diameter in the micrometer range. A more detailed description of the carbon nanotubes and the silver powder is as described in the conductive paste manufacturing method.

In addition, the heat treatment temperature for firing the conductive paste of the present invention may be in the range of about 120 to about 200 캜, or about 120 to about 140 캜.

Also, the sheet resistance of the conductive paste of the present invention may range from about 0.01 to about 20 m? / Sq.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, but the scope of the present invention is not limited thereto.

<Examples>

Example  One

10 g of entangled type CNT (average diameter: 10 nm, average length: 20 탆, bulk density: 0.18 g / cc), 85 g of butyl cellosolve and 5 g of a modified polyacrylic polymer as a dispersant were mixed Next, this was dispersed in bead mill (bead size: 0.8 mm) at room temperature for 8 hours to prepare a carbon nanotube dispersion.

20 g of the carbon nanotube dispersion prepared above, 47 g of silver (Ag) powder (average diameter: 3 to 5 탆, manufacturer: ANP), 13 g of ethylcellulose and 20 g of ethyl citalol acetate were mixed at room temperature And mixed to prepare a paste.

FIG. 1 is a SEM photograph of the entangled type CNTs used in Example 1 enlarged to 250 times (left) and 10,000 times (right), respectively.

Example  2

15 g of butyl cellosolve and 5 g of a modified polyacrylic polymer as a dispersant were mixed with an entangled type CNT (average diameter: 10 nm, average length: 20 탆, bulk density: 0.18 g / cc) This was dispersed in a bead mill (bead size: 0.8 mm) at room temperature for 8 hours to prepare a carbon nanotube dispersion.

20 g of the carbon nanotube dispersion prepared above, 45 g of silver (Ag) powder (average diameter: 3 to 5 탆, manufacturer: ANP), 10 g of ethylcellulose, and 25 g of ethyl citalol acetate were mixed at room temperature And mixed to prepare a paste.

Comparative Example  One

45 g of silver (Ag) powder (average diameter: 3 to 5 탆, manufacturer: ANP), 20 g of ethylcellulose and 35 g of ethyl cabitol acetate were mixed at room temperature to prepare a paste.

Comparative Example  2

2 g of self aligned CNT (average diameter: 10 nm, average length: 80 탆, bulk density: 0.03 g / cc), 92 g of butyl cellosolve and 4 g of a modified polyacrylic polymer were mixed, This was dispersed in a bead mill (bead size: 0.8 mm) at room temperature for 8 hours to prepare a carbon nanotube dispersion.

10 g of the carbon nanotube dispersion prepared above, 47 g of silver (Ag) powder (average diameter: 3 to 5 탆, manufacturer: ANP), 13 g of ethylcellulose and 20 g of ethyl citalol acetate were mixed at room temperature And mixed to prepare a paste.

Comparative Example  3

2 g of self aligned CNT (average diameter: 10 nm, average length: 200 μm, bulk density: 0.01 g / cc), 92 g of butyl cellosolve and 4 g of modified polyacrylic polymer were mixed, This was dispersed in a bead mill (bead size: 0.8 mm) at room temperature for 8 hours to prepare a carbon nanotube dispersion.

10 g of the carbon nanotube dispersion prepared above, 47 g of silver (Ag) powder (average diameter: 3 to 5 탆, manufacturer: ANP), 13 g of ethylcellulose and 20 g of ethyl citalol acetate were mixed at room temperature And mixed to prepare a paste.

The compositions of the pastes according to the examples and the comparative examples are summarized in Table 1 below.

Carbon nanotube content
(Parts by weight) Of carbon nanotubes
Type and Aspect Ratio Silver content
(Parts by weight) Example 1 2 entangled, 2000 47 Example 2 3 entangled, 2000 45 Comparative Example 1 0 Not added 45 Comparative Example 2 0.2 self aligned, 8000 47 Comparative Example 3 0.2 self aligned, 20000 45

* In Table 1, the content of carbon nanotubes and silver means parts by weight based on 100 parts by weight of paste.

* The aspect ratio of the carbon nanotubes means the ratio of the average length (nm) to the average diameter (nm).

<Experimental Example>

The paste prepared in Examples and Comparative Examples was printed on a PET film substrate in a thickness of 10 μm by a screen printing method and then sintered at a temperature of 130 ° C. for 30 minutes to obtain sheet resistance and rheology The results are shown in Table 2. &lt; tb &gt; &lt; TABLE &gt;

(1) sheet resistance

The sheet resistance was measured using Loresta-GP (Mitsubishi Chemical).

(2) rheology

The rheological properties were evaluated by measuring the storage modulus and loss modulus according to external energy using a BROOKFIELD R / S Plus rheometer.

The sheet resistance (m Ω / sq) Example 1 10 to 11 Example 2 15-19 Comparative Example 1 14-16 Comparative Example 2 55 ~ 60 Comparative Example 3 55 ~ 60

The storage modulus and loss modulus according to external energy of the pastes of Example 1 and Comparative Example 2 were measured and the results are shown in FIG. In FIG. 2, G 'represents a storage modulus according to external energy, and G "represents a loss modulus according to external energy.

The storage modulus, denoted G ', refers to the state of storing and releasing energy for a moment, and the loss modulus, denoted G', has the property of releasing energy immediately. The larger the tan δ is, the larger the viscosity of the substance is, and the larger the tan δ is, the smaller the tan δ is.

The paste should change from larger to smaller Tan δ values as the external stress increases, which is related to printability.

Referring to the graph of FIG. 2, it can be seen that the values of G 'and G "of the paste of Example 1 vary greatly depending on the external stress, The paste includes a carbon nanotube having a long length and a low bulk density, so that even when external stress is applied, the change of the G 'and G "values is not large, and the viscoelasticity of the paste is increased to show poor printability.

Claims (15)

Mixing a carbon nanotube, a first solvent and a dispersant to prepare a carbon nanotube dispersion; And
Mixing the carbon nanotube dispersion, silver (Ag) powder, a second solvent and a binder,
A method for producing a conductive paste.
The conductive paste of claim 1, wherein the carbon nanotubes are entangled carbon nanotubes.
The method of claim 1, wherein the carbon nanotubes have a length to diameter ratio (L / D ratio) of 200 to 6000.
The conductive paste according to claim 1, wherein the carbon nanotubes have a bulk density of 0.07 to 0.4 g / cc.
The method of producing a conductive paste according to claim 1, wherein the content of the carbon nanotubes in the carbon nanotube dispersion is 5 to 30 parts by weight based on 100 parts by weight of the carbon nanotube dispersion.
The conductive paste according to claim 1, wherein the content of the carbon nanotube dispersion in the conductive paste is 5 to 30 parts by weight based on 100 parts by weight of the conductive paste.
The method of producing a conductive paste according to claim 1, wherein the silver powder has an average particle diameter of 1 to 10 mu m.
The conductive paste according to claim 1, wherein the content of the silver powder in the conductive paste is 35 to 60 parts by weight based on 100 parts by weight of the conductive paste.
The method of claim 1, wherein the first and second solvents are the same or different from each other and each independently selected from the group consisting of alpha-terpinol, ethyl cabitol acetate, butyl cabitol acetate, methyl isobutyl ketone, ethyl cellosolve, butyl cellosolve, texanol, and butyl cabitol. Or more of the conductive paste.
The method of producing a conductive paste according to claim 1, wherein the dispersant is at least one selected from the group consisting of an acrylate-based polymer, a urethane-based polymer, an acrylate-urethane-based polymer, and a mixture thereof.
A conductive paste obtained by the production method of claim 1.
12. The conductive paste according to claim 11, wherein the conductive paste contains 1 to 10 parts by weight of carbon nanotubes per 100 parts by weight of the conductive paste.
12. The conductive paste according to claim 11, wherein the conductive paste contains 35 to 60 parts by weight of silver powder per 100 parts by weight of the conductive paste.
The conductive paste according to claim 11, wherein the sintering temperature is 120 to 200 占 폚.
12. The conductive paste according to claim 11, wherein the sheet resistance is 0.01 to 20 m? / Sq.

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