WO2010067965A2

WO2010067965A2 - Electroconductive silver nanoparticle composition, ink and method for preparing the same

Info

Publication number: WO2010067965A2
Application number: PCT/KR2009/006482
Authority: WO
Inventors: Chang-Mo Ko; Ho-Souk Cho
Original assignee: Ls Cable Ltd.
Priority date: 2008-12-10
Filing date: 2009-11-05
Publication date: 2010-06-17
Also published as: KR20100066810A; WO2010067965A3; KR101140270B1

Abstract

Disclosed is an electroconductive silver nanoparticle ink containing an electroconductive silver nanoparticle composition, comprising a dispersion and silver-coated plate-shaped copper flakes and silver nanoparticles put in the dispersion.

Description

ELECTROCONDUCTIVE SILVER NANOPARTICLE COMPOSITION, INK AND METHOD FOR PREPARING THE SAME

The present invention relates to a metal nanoparticle composition, and an ink containing the same and a method for preparing the ink, and in particular, to an electroconductive silver nanoparticle composition suitable for forming a metal pattern or wiring on a printed circuit board, and an ink containing the same and a method for preparing the ink.

An electroconductive ink is printed on a circuit board by screen printing or inkjet printing to form a thin film metal pattern or wiring. Thus, the electroconductive ink is preferably prepared using metal nanoparticles having uniform particle distribution and excellent dispersion.

Generally, metal nanoparticles used in the electroconductive ink are produced by mechanical methods for pulverizing metal materials using a mechanical force, electrical methods using electrolysis, or chemical methods for synthesizing nanoparticles using a reducing agent.

Among metal materials for the metal nanoparticles, silver is the most suitable in aspects of sintering temperature and specific resistivity. However, silver is costly and increases the manufacturing unit cost.

As copper has good specific resistivity next silver, techniques for synthesizing copper nanoparticles by a wet reducing method to prepare an electroconductive ink are disclosed in, for example, Korean Patent No. 790458 titled copper nanoparticles and preparation method thereof and Korean Patent Publication No. 2008-32625 titled method for manufacturing copper nanoparticles and copper nanoparticles manufactured using the method.

The use of copper nanoparticles reduces the manufacturing unit cost, however because copper is susceptible to oxidation in the air, deteriorates the quality of products such as an increase in sintering temperature and a decrease in specific resistivity.

To solve the problems, Korean Patent Publication No. 2007-88086 titled core-shell structure metal nanoparticles and its manufacturing method discloses spherical metal nanoparticles in which a copper core is coated with a metal thin-film layer such as silver. The silver nanoparticles having the inner copper core reduce the manufacturing unit cost, but have limitations in lowering a specific resistivity to a proper level due to the used copper.

It is an object of the present invention to solve the problems, and therefore, the present invention provide an electroconductive silver nanoparticle composition comprising a mixture of silver-coated copper particles and silver nanoparticles that have their improved shapes for cost reduction and a relatively low specific resistivity, and an electroconductive silver nanoparticle ink and a method for preparing the ink.

The present invention provides an electroconductive silver nanoparticle composition comprising a mixture of silver-coated plate-shaped copper flakes and silver nanoparticles.

Preferably, the silver-coated plate-shaped copper flakes have a major axis length of 2 to 12 μm and a thickness of 100 nm or less.

The silver nanoparticles may have an irregular particle shape or a spherical particle shape.

According to another aspect of the present invention, an electroconductive silver nanoparticle ink containing an electroconductive silver nanoparticle composition comprises a dispersion; and silver-coated plate-shaped copper flakes and silver nanoparticles put in the dispersion.

Preferably, the electroconductive silver nanoparticle ink is in a paste phase having a viscosity of 8,000 to 80,000 cP.

The electroconductive silver nanoparticle ink may contain 100 phr of the dispersion, 55 to 75 phr of the silver-coated plate-shaped copper flakes and 15 to 35 phr of the silver nanoparticles.

According to yet another aspect of the present invention, a method for preparing an electroconductive silver nanoparticle ink comprises (a) preparing a dispersion; (b) adding silver-coated plate-shaped copper flakes and silver nanoparticles to the dispersion; and (c) agitating the mixture to form an ink in a paste phase.

In the step (a), the dispersion is preferably prepared by mixing cellulose as a binder resin with terpineol and diacetone alcohol as organic solvents.

In the step (b), the silver-coated plate-shaped copper flakes preferably have a major axis length of 2 to 12 μm and a thickness of 100 nm or less.

The silver-coated plate-shaped copper flakes may be produced by performing a milling or chemical process on silver-coated spherical copper particles.

Preferably, the spherical copper particles have a diameter of 500 nm to 3 μm.

Preferably, in the step (b), 55 to 75 phr of the silver-coated plate-shaped copper flakes and 15 to 35 phr of the silver nanoparticles are added to 100 phr of the dispersion.

These and other features, aspects and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

FIG. 1 is a flow chart of a method for preparing an electroconductive silver nanoparticle ink according to a preferred embodiment of the present invention.

Hereinafter, an anode active material for a lithium secondary battery of the present invention will be described in detail according to its preparation method. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

Referring to FIG. 1, first a dispersion is prepared. Silver-coated plate-shaped copper flakes and silver nanoparticles are put in the dispersion. The mixed composition is agitated. In this way, an ink in a paste phase is prepared.

Specifically, in S100, a dispersion used to prepare an ink in a paste phase is prepared by mixing cellulose as a binder resin with terpineol and diacetone alcohol as organic solvents.

Next, silver-coated plate-shaped copper flakes and silver nanoparticles are put into the dispersion S110 and agitated S120 to prepare an ink in a paste phase. When a mixture of plate-shaped copper flakes and silver nanoparticles is heated at low temperature, the silver nanoparticles are sintered to weld and bond adjacent copper flakes to each other. Preferably, the silver nanoparticles have a spherical particle shape. More preferably, the silver nanoparticles have irregular particle shapes for further reducing the sintering temperature.

The silver-coated plate-shaped copper flakes have an anisotropic structure, and thus, have more contact points per unit volume than spherical copper particles. Accordingly, the silver-coated plate-shaped copper flakes have high conductivity and improved specific resistivity. Preferably, the silver-coated plate-shaped copper flakes have a major axis length of 2 to 12 μm and a thickness of 100 nm or less. These values properly increase the contact points per unit volume of the silver-coated plate-shaped copper flakes and maintain the sintering temperature to a proper low temperature.

Hereinafter, description is made about processes for synthesizing silver-coated copper particles and silver nanoparticles according to the prior art and the present invention, and the effects of particle structure on the characteristics of an electroconductive silver nanoparticle ink.

A: silver-coated spherical copper particles

50g of oleyl amine, 50g of 1-hexadecene, 20g of copper nitrate and 15g of ascorbic acid were put in a round-bottom flask with a condenser, and heated at 70 ^OC for 1 hour. Subsequently, after the temperature is increased up to 200 ^OC with a temperature ramp rate of 10 ^OC/min, reaction took place in the solution for 30 minutes. Next, the solution was air-cooled down to 100 ^OC. 7g of silver dodecanate was added to the solution, and after the temperature is increased up to 200 ^OC with a temperature ramp rate of 10 ^OC/min, reaction took place in the solution at 200 ^OC for 1 hour.

After the reaction was completed, 300ml of methanol was added to the solution, so that the synthesized spherical copper particles having a particle size of 500 nm to 3 μm were precipitated. The precipitate was washed with methanol 3 times or more, and dried in an oven of 45 ^OC.

B: silver-coated plate-shaped copper flakes

A milling process or a chemical process was performed to produce silver-coated plate-shaped copper flakes having a substantially rectangular shape. Specifically, a milling process was performed on spherical copper particles having a particle size of 500 nm to 3 μm to obtain silver-coated plate-shaped copper flakes having a length of 2 to 10 μm and a width of 100 nm or less of the rectangular solid. Here, milling time of the milling process varies from 1 to 5 hours. The longer the milling time, the smaller the particle size. A chemical process was performed on a reaction solution containing silver-coated spherical copper particles having a particle size of 500 nm to 3 μm. The maturation time of the reaction solution varies. That is, a reaction solution containing silver-coated copper particles was not added with methanol to terminate the reaction, but maturated at 60 ^OC for 1 to 5 hours, distilled under reduced pressure at 50 ^OC and dried at 60 ^OC for 10 hours to obtain silver-coated plate-shaped copper flakes having a length of 2 to 10 μm and a width of 100 nm or less of the rectangular solid. At this time, the longer the maturation time, the larger the particle size.

C: silver-coated plate-shaped copper flakes

A milling process or a chemical process was performed on spherical copper particles having a particle size of 500 nm to 3 μm to produce plate-shaped copper flakes having a substantially rectangular shape. The milling time or maturation time was controlled such that silver-coated plate-shaped copper flakes have a length of 20 μm of the rectangular solid.

D: silver nanoparticles having irregular particle shapes

4g of nitric acid was dissolved in 500ml of low molecular weight polyethylene glycol, and temperature of a reactor was increased up to 90^OC with a temperature ramp rate of 1 ^OC /min.

After agitation for about 3 hours, a polar solvent such as acetone was added to the resultant reaction solution, and silver nanoparticles were selectively separated by centrifugal separation. The silver nanoparticles have a particle size of 20 to 50 nm and spherical and triangular shapes. Here, if the temperature of the reactor is increased up to 120 ^OC or more, the particle size is modified to a micro level.

E: spherical silver nanoparticles

4g of nitric acid was dissolved in 500ml of low molecular weight polyethylene glycol, and temperature of a reactor was increased up to 30^OC with a temperature ramp rate of 1 ^OC /min. After agitation for about 3 hours, a polar solvent such as acetone was added to the resultant reaction solution, and silver nanoparticles were selectively separated by centrifugal separation. The silver nanoparticles have a particle diameter of 5 to 20 nm.

<Example 1: silver-coated plate-shaped copper flakes (B) + irregular silver nanoparticles (D)>

A dispersion was prepared by mixing 10 parts by weight of cellulose as a binder resin with 45 parts by weight of terpineol and 45 parts by weight of diacetone alcohol as organic solvents.

100 phr (parts per hundred resin) of the dispersion was added with 75 phr of silver-coated plate-shaped copper flakes and 15 phr of silver nanoparticles having irregular particle sizes to obtain an electroconductive silver nanoparticle ink. The electroconductive silver nanoparticle ink has a metal content of 50 to 60 weight% and a viscosity of 8,000 to 80,000 cP that are suitable for screen printing.

The electroconductive silver nanoparticle ink in a paste phase was printed on a polyimide substrate by screen printing, and placed in an oven of 150^OC for about 15 minutes to form a metal wiring. At this time, the metal wiring had a specific resistivity of 1.60×10^-5ohm.cm.

<Example 2: silver-coated plate-shaped copper flakes (B) + spherical silver nanoparticles (E)>

The dispersion was added with 15 phr of plate-shaped copper flakes having a particle size of 2 to 10 μm and 75 phr of spherical silver nanoparticles and agitated to obtain an electroconductive silver nanoparticle ink.

The electroconductive silver nanoparticle ink in a paste phase was printed on a polyimide substrate by screen printing, and sintered at 160^OC to form a metal wiring. At this time, the metal wiring had a specific resistivity of 1.7×10^-5ohm.cm.

<Comparative example 1: silver-coated spherical copper particles (A) + irregular silver nanoparticles (D)>

The dispersion was added with 75 phr of silver-coated copper particles having a particle size of 500 nm to 3 μm and 15 phr of silver nanoparticles having irregular particle shapes, and agitated to obtain an electroconductive silver nanoparticle ink in a paste phase.

The electroconductive silver nanoparticle ink in a paste phase was printed on a polyimide substrate, and kept at 158^OC for about 15 minutes to form a metal wiring. At this time, the metal wiring had a specific resistivity of 9.5×10^-5ohm.cm.

<Comparative example 2: silver-coated plate-shaped copper particles (C) + irregular silver nanoparticles (D)>

The dispersion was added with 75 phr of plate-shaped copper flakes having a particle size of 20 μm and 15 phr of silver nanoparticles having irregular particle shapes, and agitated to obtain an electroconductive silver nanoparticle ink in a paste phase.

The electroconductive silver nanoparticle ink in a paste phase was printed on a polyimide substrate, and sintered at high temperature more than 300^OC to form a metal wiring. At this time, the metal wiring had a specific resistivity of 6.8×10^-4ohm.cm.

<Comparative example 3: silver-coated spherical copper particles (A) + spherical silver nanoparticles (E)>

The dispersion was added with 75 phr of silver-coated spherical copper particles having a particle size of 500 nm to 3 μm and 15 phr of spherical silver nanoparticles, and agitated to obtain an electroconductive silver nanoparticle ink in a paste phase.

The electroconductive silver nanoparticle ink in a paste phase was printed on a polyimide substrate, and placed in an oven of 180^OC for about 15 minutes to form a metal wiring. At this time, the metal wiring had a specific resistivity of 4.7×10^-4ohm.cm.

The following Table 1 shows the sintering temperature and specific resistivity of the electroconductive silver nanoparticle inks according to examples 1 and 2 and comparative examples 1 to 3.

Table 1

Classification	Composition	Sintering temperature (^OC)	Specific resistivity(ohm.cm)
Example 1	B+D	150	1.60×10^-5
Example 2	B+E	160	1.7×10^-5
Comparative example 1	A+D	158	9.5×10^-5
Comparative example 2	C+D	>300	6.8×10^-4
Comparative example 3	A+E	180	4.7×10^-4

Referring to Table 1, the electroconductive silver nanoparticle ink of example 1, containing silver-coated plate-shaped copper flakes and silver nanoparticles having irregular particle shapes, has the lowest sintering temperature and excellent specific resistivity. And, it is found from the results of comparative example 2 that silver-coated plate-shaped copper flakes should have a major axis length of 2 to 12 μm. If the major axis length exceeds the maxim limit, it results in an excessively high sintering temperature.

Typically, an electroconductive silver nanoparticle ink has the sintering temperature requirement of 200 ^OC or less and specific resistivity requirement of 1.7×10^-5ohm.cm or less. Thus, the examples 1 and 2 have more advantageous effects than the comparative examples 1 to 3. Regarding the specific resistivity over the sintering temperature range, the example 1 exhibits a relatively low specific resistivity in the temperature range of 200 ^OC or lower (See Table 2), while the comparative example 1 exhibits a relatively high specific resistivity in the temperature range of 200 ^OC or lower (See Table 3) and the comparative example 2 exhibits a very high sintering temperature and a relatively high specific resistivity in the entire temperature range (See Table 4).

Table 2

Temperature (^OC)	Specific resistivity (ohm.cm)
120	1.5×10^-3
130	7.3×10^-4
140	2.6×10^-4
150	1.6×10^-5
160	2.0×10^-5
170	1.5×10^-5
180	1.1×10^-5

Table 3

Temperature (^OC)	Specific resistivity (ohm.cm)
120	2.3×10^-3
130	7.8×10^-4
140	3.5×10^-4
150	1.1×10^-4
158	9.5×10^-5
165	9.4×10^-4
170	9.6×10^-4

Table 4

Temperature (^OC)	Specific resistivity (ohm.cm)
280	9.0×10^-3
290	5.6×10^-3
300	2.5×10^-3
310	1.0×10^-3
320	6.8×10^-4
330	6.2×10^-4
340	6.5×10^-4

The following Table 5 shows the sintering temperature and specific resistivity according to the content of the silver-coated plate-shaped copper flakes (B) and silver nanoparticles (D) having irregular particle shapes in 100 phr of the dispersion. Here, the electroconductive silver nanoparticle ink in a paste phase was prepared by adding a dispersion with silver-coated plate-shaped copper flakes and silver nanoparticles having irregular particle shapes and agitating them. And, the prepared ink in a paste phase was printed on a polyimide substrate and placed in an oven of 150^OC for about 15 minutes to form a metal wiring. Then, a specific resistivity of the metal wiring was measured.

Table 5

No.	Content (phr)	Sintering temperature(^OC)	Specific resistivity (ohm.cm)
1	B: 75D: 15	150	1.60×10^-5
2	B: 45D: 45	150	1.20×10^-5
3	B: 65D: 25	150	1.23×10^-5
4	B: 55D: 35	150	1.21×10^-5
5	B: 80D: 10	150	6.15×10^-4
6	B: 40D: 50	150	1.20×10^-5

Referring to Table 5, when the content of the silver-coated plate-shaped copper flakes (B) was 45 phr and the content of the silver nanoparticles (D) having irregular particle shapes was 45 phr, the ink exhibited a sintering temperature of 150 ^OC and an excellent specific resistivity of 1.20×10^-5ohm.cm. On the contrary, when the content of the silver-coated plate-shaped copper flakes (B) was 80 phr and the content of the silver nanoparticles (D) having irregular particle shape was 10 phr, the ink exhibited a sintering temperature of 150 ^OC and an inferior specific resistivity of 6.15×10^-4ohm.cm. And, when the content of the silver-coated plate-shaped copper flakes (B) was 40 phr and the content of the silver nanoparticles (D) having irregular particle shapes was 50 phr, the ink exhibited a good specific resistivity but a low economical efficiency due to an excessive silver content. In consideration of the above, preferably 55 to 75 phr of silver-coated plate-shaped copper flakes (B) and 15 to 35 phr of silver nanoparticles (D) having irregular particle shapes are put into 100 phr of a dispersion.

As mentioned above, the electroconductive silver nanoparticle ink of the present invention contains silver-coated plate-shaped copper flakes and silver nanoparticles, and can be used to form, on a circuit board, a metal pattern or wiring having a low sintering temperature of 200 ^OC or less and a low specific resistivity of 1.7×10^-5ohm.cm or less.

As such, the preferred embodiments of the present invention were described hereinabove. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention contains silver-coated plate-shaped copper flakes and silver nanoparticles, thereby preventing oxidation of copper and reducing the manufacturing cost. And, the present invention has the improved specific resistivity and can be sintered at low temperature when compared with the conventional spherical silver-coated copper particles.

Claims

An electroconductive silver nanoparticle composition, comprising:

silver-coated plate-shaped copper flakes; and

silver nanoparticles.
The electroconductive silver nanoparticle composition according to claim 1,

wherein the silver-coated plate-shaped copper flakes have a major axis length of 2 to 12 μm and a thickness of 100 nm or less.
The electroconductive silver nanoparticle composition according to claim 1,

wherein the silver nanoparticles have irregular particle shapes.
The electroconductive silver nanoparticle composition according to claim 1,

wherein the silver nanoparticles have a spherical particle shape.
An electroconductive silver nanoparticle ink containing an electroconductive silver nanoparticle composition, comprising:

a dispersion; and

silver-coated plate-shaped copper flakes and silver nanoparticles added to the dispersion.
The electroconductive silver nanoparticle ink according to claim 5,

wherein the silver-coated plate-shaped copper flakes have a major axis length of 2 to 12 μm and a thickness of 100 nm or less.
The electroconductive silver nanoparticle ink according to claim 5,

wherein the silver nanoparticles have irregular particle shapes.
The electroconductive silver nanoparticle ink according to claim 5,

wherein the silver nanoparticles have a spherical particle shape.
The electroconductive silver nanoparticle ink according to claim 5,

wherein the electroconductive silver nanoparticle ink is in a paste phase having a viscosity of 8,000 to 80,000 cP.
The electroconductive silver nanoparticle ink according to claim 5,

wherein the content of the dispersion is 100 phr, the content of the silver-coated plate-shaped copper flakes is 55 to 75 phr and the content of the silver nanoparticles is 15 to 35 phr.
A method for preparing an electroconductive silver nanoparticle ink, comprising:

(a) preparing a dispersion;

(b) adding silver-coated plate-shaped copper flakes and silver nanoparticles to the dispersion; and

(c) agitating the mixture to form an ink in a paste phase.
The method for preparing an electroconductive silver nanoparticle ink according to claim 11,

wherein, in the step (a), the dispersion is prepared by mixing cellulose as a binder resin with terpineol and diacetone alcohol as organic solvents.
The method for preparing an electroconductive silver nanoparticle ink according to claim 11,

wherein, in the step (b), the silver-coated plate-shaped copper flakes have a major axis length of 2 to 12 μm and a thickness of 100 nm or less.
The method for preparing an electroconductive silver nanoparticle ink according to claim 13,

wherein the silver-coated plate-shaped copper flakes are produced by performing a milling or chemical process on silver-coated spherical copper particles.
The method for preparing an electroconductive silver nanoparticle ink according to claim 14,

wherein the spherical copper particles have a diameter of 500 nm to 3 μm.
The method for preparing an electroconductive silver nanoparticle ink according to claim 11,

wherein, in the step (b), 55 to 75 phr of the silver-coated plate-shaped copper flakes and 15 to 35 phr of the silver nanoparticles are added to 100 phr of the dispersion.